soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah kenneth carpenter geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover lizard preserved as a carbon film from the parachute creek member of the green river formation (eocene), uinta basin, utah. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 263 abstract a rare specimen of soft tissue preservation of a lizard from the parachute creek member of the eocene green river formation, uinta basin, utah, is described. the preservation is unusual in that it is a mineralized body lacking the skeleton. this, and other small boneless vertebrate specimens also from the parachute creek, indicate occasional demineralizing conditions in lake uinta, but not apparently in the other two lakes of the green river formation—fossil lake and lake gosuite. soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah kenneth carpenter prehistoric museum, utah state university eastern, 155 main st., price, ut 84501; and museum of natural history, university of colorado, boulder, co 80302; ken.carpenter@usu.edu citation for this article. carpenter, k., 2018, soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah: geology of the intermountain west, v. 5, p. 263–269. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction fossil lizards are a rare in the eocene green river formation. grande (2013) reported three taxa, including two specimens of the varanid saniwa ensidens (described by rieppel and grande, 2007), three specimens of the shinisaur (crocodile lizard) bahndwivici ammoskius (described by conrad, 2006), and a single specimen of the iguanian afairiguana avius (described in conrad and others, 2007). to this list are several specimens of lizards represented by two-dimensional, mineralized bodies lacking the skeletons, which had dissolved away. although some of these specimens have been known for decades (e.g., grande, 1984), only recently has one been described (conrad and others, 2014). the specimen consists of the anterior half in dorsal view on part and counterpart slab and is remarkable for the dark mineral film preservation of the eyeballs and brain, in addition to the mineralized scales. edwards and others (2011, 2012) presented fourier transform infrared and synchrotron rapid scanning x-ray fluorescence elemental maps of two other specimens (but no morphological description). these show that the mineralized scales preserved relicts of the amide and sulfur compounds that they inferred were derived from the original keratinous skin. these specimens had previously been illustrated in grande (1984). recently, a nearly complete soft-bodied lizard specimen was found in the collections at the colorado school of mines, golden, colorado. the specimen was collected during a school fieldtrip by w.r. keller “approximately 21 miles south-southwest of vernal, utah” (figure 1), which would place the site near what is now the ouray national wildlife refuge. the specimen was figured as a salamander by johnson (1954) probably because of the rounded head. minute scales, however, clearly establish its lacertilian nature. the locality information is suspect because strata 21 miles south-southwest of vernal is predominately holocene alluvium and eolian deposits (sprinkel, 2007), the lower part of the brennan basin member of the duschesne river formation, and member c of the uinta formation both eocene in age. the matrix of the specimen, 264 soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah carpenter, k. geology of the intermountain west 2018 volume 5 however, is more like the greenish-gray shales of unweathered parachute creek member of the green river formation. the nearest exposures of that member is along willow and hill creeks, more than 39 miles south-southwest of vernal and south of fort duschesne, uintah county. these two creeks border the east and west side of big pack mountain. alternatively, there are other exposures of the parachute creek member along the green river about 40 miles southwest vernal. it is unfortunate that no additional information is available to narrow the location. measurements were determined using imagej 1.50e on an image captured using a high-resolution flatbed scanner (1200 dpi) to minimize parallax. all measurements were rounded to nearest millimeter owing to a certain level of uncertainty about the edges of certain morphological points. abbreviations ceum–college of eastern utah prehistoric museum (now prehistoric museum, utah state university); csmgm–colorado school of mines geological museum. systematic paleontology squamata oppel, 1811 ?iguania cope, 1864 gen et sp. indet. specimen csmgm 14156 skin impression and mineralized film of nearly the entire body (figure 2). locality south-southwest of vernal, utah, presumably near big pack mountain or along the green river, uintah county, utah. probably from the parachute creek member, green river formation. description the specimen is the mineralized body of a lizard preserved in ventral view (figure 2). both forelimbs are appressed against the body making it look armless. the hind legs are parallel with the left leg folded across the abdomen. the short, rounded head is an artifact due to a thin layer of matrix covering the tip of the snout; no trace of a gular dewlap is seen. matrix also covers the distal end of the tail. the covering matrix will probably not come off easily or cleanly as attested by previous attempts in the 1970s to remove matrix over the lower limbs with a needle. most likely an attempt to mechanically expose the snout will result in considerable damage. the specimen has a midline length of 242 mm as exposed; it has an estimated snout-vent length of 141 mm assuming the snout is 3 mm longer and that the vent was approximately in the vicinity of the left knee (+ figure 1. map showing the distribution of the green river formation that identify lake uinta, lake gosuite, and fossil lake. all of the boneless vertebrate skeletons are from the parachute creek member of the lake uinta strata. (1) southwest of vernal csmgm 14156 (this report); (2) nine mile canyon (stokes, 1978, assumed to be shed skin, but in context of this report may be a demineralized lizard); (3) bonanza (grande, 1984; edwards and others, 2011; also boneless fish ceum 81827); (4) douglass pass (langston and rose, 1978; grande, 1984; edwards and others, 2012); (5) anvil points (conrad and others, 2014). green river formation map based on kml files from mineral resources online spatial data (undated) and imagery from google earth. 265 soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah carpenter, k. geology of the intermountain west 2018 volume 5 5 mm). the maximum width of the head is 22 mm, and the midline length of the visible portion is 25 mm measured perpendicular to the maximum width. the neck is approximately 14 mm wide and midline length of 13 mm. the maximum width of the body is 32 mm. the right arm is 23 mm assuming the dark spot at the proximal end is the location of the humeral head. the elbow cannot be identified with certainty, so the separate arm segments are not measured; the manus is either hidden by matrix or in the missing counter slab. the left thigh is approximately 20 mm, the left lower leg 21 mm, and the incomplete left foot 23+ mm. the maximum width of the complete right thigh is 12 mm. all of the width measurements are undoubtedly increased due to compaction of the three-dimensional (3d) body; lengths generally do not change as much. traces of bone are seen as irregular, very dark structures in the tail but lack detail (figures 2 and 3c). the vertebrae in a short segment in the middle of the tail are displaced. a small blob of pyritic mass in the lower abdominal region probably formed due to localized reducing environment from decomposition of gastric residue (yellow box in figure 2). scales are seen all over the body, and the most prominent are those on the neck, chest, and thigh (figure 3). they are tiny, granular, nonoverlapping, and those on the neck and thigh are arranged in rows. those on the neck become progressively larger towards the midline (figure 3a). the scales along the anterior edge of the thigh appear to be a little larger and closely packed, whereas those on the posterior side are smaller and granular. the scales on the tail are square to rectangular, lacking any evidence of having osteoderms, and arranged in longitudinal rows (figure 3c). these scales figure 2. ventral view of csmgm 14156. boxes a to c are shown in figure 3. small yellow box is small pyritic mass probably of gastric residue. white box shows possible degassing rupture; note displaced skin along bottom edge. scale in cm. 266 soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah carpenter, k. geology of the intermountain west 2018 volume 5 often have a small, darker spot along the posterior edge. none of the lateral scales of the tail show evidence of having had osteoderms as in bahndwivici, which would predictably be seen as giving the margin of the tail an irregular, slightly jagged appearance. the squamation of csmgm 14156 is similar to that of bhi-102b figured by edwards and others (2011, figure 1a), suggesting the two specimens probably belong to the same taxon. discussion the measurements given above in conjunction with figure 2 strongly suggest that csmgm 14156 is a medium-sized lizard, having a relatively short, wide head on a distinct neck, wide body, short-limbs, and with tiny granular scales on the belly and transverse rows of small, square or rectangular scales on the underside of the tail. from these characters, csmgm 14156 is questionably referred to as either a gecko or iguanid. the referral relies heavily on what csmgm 14156 is not. for example, the apparent absence of osteoderms eliminates anguids, scincids, helodermids, etc., the presence of a distinct neck is another factor eliminating scincids, and the well-developed, although short limbs, eliminates the anniellids, etc. the small size of the granular scales covering the body supports the interpretation that the local environment in the vicinity of the green river lakes was warm and humid (e.g., wegener and others, 2014). numerous matrix-filled fissures cut across the body and tail dividing it into segments. these fractures are clean and suggest that the skin was subjected to tension force pulling it apart as if brittle. this can best be seen where the skin is broken into smaller pieces that are slightly displaced (figure 3c). there is also some evidence for shearing forces causing a slight offset of the skin, such as the front half of the body relative to the back half (figure 2). the fissures are post-depositional because there must have been sediment holding everything in place as the fissures formed, possibly as a result of sediment compaction. the postmortem subaquatic decay of a lizard carcass (collared iguana oplurus cuvieri) over a two-month period was described by richter and wuttke (2012). as in other studies of decomposition, decay began within the abdomen, which would have led to typical postmortem bloat and float phase (e.g., minshall and others, 1991; rodriguez, 1997). this phase terminates with degassing from rupture of the skin. it is possible that the gap in the skin in the abdominal region of csmgm 14156 represents the site of the rupture, especially given that the skin along the lower margin does appear to be displaced outwards from the body (white box in figure 2). these features are suggestive of rupture but are not definitive. as in other decomposition studies, richter and wuttke (2012) noted that the skin was resilient and long lasting (cf. minshall and others, 1991; rodriguez, 1997). in fact, next to bone, skin is one of the most resilient tissues in the dead vertebrate body in the absence of scavengers (gill-king, 1997). the fossilization of the skin probably involved microbial authigenic mineralization (briggs and mcmalon, figure 3. closeups of squamation: (a) neck region; (b) right inner thigh; (c) mid-tail. scales in mm. 267 soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah carpenter, k. geology of the intermountain west 2018 volume 5 2016). such fossilization can replicate extremely fine detail. edwards and others (2011) presented a taphonomic model to explain the elemental and mineralogical signature of a fossilized lizard skin from the green river formation. this model neglects the ubiquitous microbes associated with dead organic material and does not explain the demineralization of the skeleton. i therefore consider their model as incomplete. as mentioned previously, bone is typically the most resilient tissue in the vertebrate skeleton and can survive little changed for thousands of years in wet environments (von endt and otner, 1984; turner-walker and peacock, 2008). consequently, the fossilization of the skin in csmgm 14156 at the expense of bone must result from unusual environmental conditions. low ph is known to demineralize bone hydroxyapatite (christensen and myers, 2011). such an environment can be created within the carcass during autolysis (gill-king, 1997). subsequent anaerobic bacterial decomposition also leads to a drop in ph, which can initiate bone demineralization (child, 1995). but demineralization of bone is not always a simple matter of low environmental ph (turner-walker and peacock, 2008). bone mineral is also susceptible to dissolution in an environment undersaturated with respect to calcium and phosphate (turner-walker and peacock, 2008). a gentle bottom current would prevent the saturation of calcium and phosphate ions in the local microenvironment around and in the lizard carcass. added to this is the increase porosity of bone by bacterial collagenase, which can increase the surface to volume ratio and facilitate dissolution (hedges and millard, 1995). experimental work has shown that the collagenase-producing bacterial already reside in the gut of most vertebrates at the time of death, thus bacterial bioerosion can begin soon after death (child, 1995; white and booth, 2014). to narrow the probable cause for the demineralization of csmgm 14156, it is necessary to consider the specimen in the context of the other boneless specimens. these additional specimens include the lizards cited in grande (1984), edwards and others (2011, 2012), and conrad and others (2014), the hatchling crocodile described by langston and rose (1978), and a small clupeoid (ceum 81827). plotting these specimens on a distribution map of the green river formation revealed that they are restricted to the lake uinta basin (figure 1), and more specifically to the parachute creek member. the question then arises, what is different about the parachute creek strata as compared to the other members deposited in lake uinta, lake gosuite, and fossil lake that might reflect a difference in bottom-water chemistry? the paleolimnology of the green river formation is most thoroughly treated in smith and carroll (2015), and the parachute creek member in particular by boak and poole (2015), jagniecki and lowenstein (2015), rosenberg and others (2015), and tänavsuu-milkeviciene and sarg (2015). differences in water chemistry between lake uinta on the one hand, and lake gosuite + fossil lake (buchheim and others, 2015) on the other, are seen in their saline enrichment phases whereby the chemicals already in the water are concentrated. nahcolite (nahco3) was deposited in lake uinta, and trona (nahco3 ∙ na2co3 ∙ 2h2o) deposited in lake gosuite and fossil lake. during their high stand phases, the lakes were characterized by stratified dysoxic to anoxic bottom waters (tänavsuu-milkeviciene and sarg, 2012). what made lake uinta different during deposition of the parachute creek member is that it was apparently deeper than the other two lakes (jagniecki and lowenstein, 2015), which may have resulted in a thicker zone of dysoxic or anoxic bottom water. the decomposition of organic matter in this zone, in the upper sediments and within the lizard carcass by sulfate-reducing bacteria, would create hydrogen sulfide, which in water can create a weak acid. over time, even a weak acid can be corrosive to bone if it is not removed by weak bottom currents. a weak acid would most likely persist if the carcass was sealed by a thin layer of anoxic mud. conclusion the discovery of a boneless fossilized lizard from lake uinta strata is not merely a curiosity but provides insight into the condition of the lake bottom at the time of burial. there are several different ways in which bone can be naturally demineralized. the small size of the bones made them more susceptible to dissolution (von endt and ortner, 1984) regardless of which demineralization pathway the skeleton of csmgm 14156 fol268 soft-bodied fossil of a lizard from the parachute creek member, green river formation (eocene), utah carpenter, k. geology of the intermountain west 2018 volume 5 lowed. at least six other boneless specimens of fish, alligator, and lizards are known, all from the parachute creek member. these specimens, all small, suggest a commonality in their demineralization. and that leads to the hypothesis that the anoxic conditions at the bottom of lake uinta were at times slightly acidic. acknowledgments i thank beth simons, colorado school of mines geological museum, who invited me to describe csmgm 14156. thanks also to doug sprinkel for discussions about the green river formation in the vicinity of cowboy canyon, and for review comments and corrections. also to lance grande, field museum of natural history (chicago), for review comments and corrections. references boak, j., and poole, s., 2015, mineralogy of the green river formation in the piceance creek basin, colorado, in smith, m.e., and carroll, a.r., editors, stratigraphy and paleolimnology of the green river formation, western usa: dordrecht, springer, p. 183–209. buchheim, h.p., biaggi, r.e., and cushman, r.a., 2015, stratigraphy and interbasinal correlations between fossil and the green river basin, wyoming, in smith, m.e., and carroll, a.r., editors, stratigraphy and paleolimnology of the green river formation, western usa: dordrecht, springer, p. 127–151. briggs, d.e., and mcmahon, s., 2016, the role of experiments in investigating the taphonomy of exceptional preservation: palaeontology, v. 59, no. 1, p. 1–11. child, a.m., 1995, microbial taphonomy of archaeological bone: studies in conservation, v. 40, no. 1, p. 19–30. christensen, a.m., and myers, s.w., 2011, macroscopic observations of the effects of varying fresh water ph on bone: journal of forensic sciences, v. 56, no. 2, p. 475– 479. conrad, j.l., 2006, an eocene shinisaurid (reptilia, squamata) from wyoming, usa: journal of vertebrate paleontology, v. 26, no. 1, p.113–126. conrad, j.l., head, j.j., and carrano, m.t., 2014, unusual 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m.h., editors, forensic taphonomy—the postmortem fate of human remains: boca raton, florida, crc press, p. 93–108. grande, l., 1984, paleontology of the green river formation, with a review of the fish fauna (2nd edition): wyoming state geological survey bulletin 63, 333 p. grande, l., 2013, the lost world of fossil lake—snapshots from deep time: chicago, university of chicago press, 425 p. hedges, r.e., and millard, a.r., 1995, bones and groundwater—towards the modelling of diagenetic processes: journal of archaeological science, v. 22, no. 2, p. 155– 164. jagniecki, e.a., and lowenstein, t.k., 2015, evaporites of the green river formation, bridger and piceance creek basins—deposition, diagenesis, paleobrine chemistry, and eocene atmospheric co2, in smith, m.e., and carroll, a.r., editors, stratigraphy and paleolimnology of the green river formation, western usa: dordrecht, springer, p. 277–312. johnson, j.h., 1954, the geological museum at “mines:” the mines magazine, v. 44, no. 12, 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dordrecht, springer, 355 p. sprinkel, d.a., 2007, interim geologic map of the vernal 30' x 60' quadrangle, uintah and duchesne counties, utah, and moffat and rio blanco counties, colorado: utah geological survey open file report 506dm, 3 plates, scale 1:100,000. stokes, w.l., 1978, impressions of lizard scales from the green river formation (eocene), uinta basin, utah: journal of paleontology, v. 25, no. 4, p. 407–410. tänavsuu-milkeviciene, k., and sarg, j.f., 2012, evolution of an organic-rich lake basin—stratigraphy, climate and tectonics—piceance creek basin, eocene green river formation: sedimentology, v. 59, no. 6, p. 1735–1768. tänavsuu-milkeviciene, k., and sarg, j.f., 2015, sedimentology of the world class organic-rich lacustrine system, piceance basin, colorado, in smith, m.e., and carroll, a.r., editors, stratigraphy and paleolimnology of the green river formation, western usa: dordrecht, springer, p. 153-181. turner-walker, g., and peacock, e.e., 2008, preliminary results of bone diagenesis in scandinavian bogs: palaeogeography, palaeoclimatology, palaeoecology, v. 266, no. 3–4, p. 151–159. von endt, d.w., and ortner, d.j., 1984, experimental effects of bone size and temperature on bone diagenesis: journal of archaeological science, v. 11, no. 3, p. 247–253. wegener, j.e., gartner, g.e., and losos, j.b., 2014, lizard scales in an adaptive radiation—variation in scale number follows climatic and structural habitat diversity in anolis lizards: biological journal of the linnean society, v. 113, no. 2, p. 570–579. white, l., and booth, t.j., 2014, the origin of bacteria responsible for bioerosion to the internal bone microstructure—results from experimentally-deposited pig carcasses: forensic science international, v. 239, p. 92–102. taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 6 2019 © 2019 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype kenneth carpenter and wayne m. itano geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover two views of a cast of the long-lost holotype of petalodus ohioensis safford, 1853 and hypothetic restoration of the shark. the cast resolves the long historical debate about the validity of this ancient shark tooth species. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 6 2019 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association volume 6 2019 55 abstract only a crude line drawing of the holotype tooth of the shark petalodus ohioensis safford, 1853 has ever been published, and the location of that specimen has long been unknown. the discovery of a cast of the holotype in the collections of the yale peabody museum of natural history demonstrates that p. alleghaniensis leidy, 1856, is a junior subjective synonym of p. ohioensis, thus resolving a long-standing dispute. taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype kenneth carpenter1 and wayne m. itano2 1prehistoric museum, utah state university eastern, 155 main st., price, ut 84501; and museum of natural history, university of colorado, boulder, co 80309; ken.carpenter@usu.edu 2museum of natural history, university of colorado, boulder, co 80309; wayne.itano@aya.yale.edu citation for this article. carpenter, k., and itano, w.m., 2019, taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype: geology of the intermountain west, v. 6, p. 55–60. © 2019 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the discovery of teeth from the late paleozoic shark, petalodus, from the near the top of the permian “lower cutler beds” of the cutler group in southeastern utah, led to a brief description and illustration of many important holotypes and referred specimens in order to determine the taxon to which the lower cutler teeth belonged (carpenter and ottinger, 2018). several important and key specimens were illustrated by photographs for the first time, including the holotypes of p. hastingsii owen, 1840, p. acuminatus (agassiz, 1838), p. rhombus (m’coy, 1854), and p. alleghaniensis leidy, 1856. one crucial specimen that could not be located for photographic inclusion was the holotype of p. ohioensis safford, 1853 from the cambridge limestone of the conemaugh formation in ohio. specimens have been referred to this species (e.g., hay, 1895; lucas and others, 2011; carpenter and ottinger, 2018) based on the crude illustration by safford (1853) (see figures 1a and 1b). this specimen is crucial for resolving the issue of whether p. alleghaniensis (figures 1e and 1f) is a separate taxon from p. ohioensis or a junior subjective synonym of p. ohioensis (e.g., hay, 1895; zidek and kietzke, 1993, 1996; brusatte, 2007; ivanov and others, 2009; ginter and others, 2010; carpenter and ottinger, 2018). the discovery of a cast (figures 1c and 1d) of the holotype of p. ohioensis finally resolves the issue. institutional abbreviations ansp–academy of natural sciences of philadelphia, philadelphia, pennsylvania; mcz–museum of comparative zoology, harvard university, cambridge, massachusetts; nhmuk–natural history museum, united kingdom, london, england; usnm–united states national museum (national museum of natural history), washington, d.c.; ypm–yale peabody museum of natural history, new haven, connecticut. history of the problem the morphological tooth genus petalodus was named by richard owen (1840–1845), as petalodus 56 taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype carpenter, k., and itano, w.m. geology of the intermountain west 2019 volume 6 hastingsii, for a fragment of a tooth from the ticknall limestone (upper viséan = upper middle mississippian) in south derbyshire, england (the fragment, figures 1g and 1h, is not diagnostic and a proposal has been submitted by us to the international commission on zoological nomenclature to make the more complete nhmuk pv p.75414, figures 1i and 1j, from the same locality, the neotype for the taxon; carpenter and itano, 2018). in 1850, professor james safford, geologist at cumberland university in lebanon, tennessee, collected a tooth having a triangular crown from the cambridge limestone of the conemaugh formation (middle to upper missourian = lower upper pennsylvanian) near the town of cambridge in guernsey county, southeastern ohio. fortuitously for him, louis agassiz had emigrated to the united states in 1847 and was at the 1851 american association for the advancement of science meeting, where safford showed him the tooth. before emigrating, agassiz had published his multi-year (1833–1845a, 1833–1845b), ten volume “recherches sur les poissons fossiles” [“research on fossil fish”] and was quite familiar with the kind of tooth safford showed him. agassiz, who was then at harvard university, “pronounced it at once a new species of getalodus” (safford, 1853, p. 142). shortly thereafter, safford was successful in removing the specimen from the matrix and published a brief paragraph (safford, 1853) naming the taxon getalodus ohioensis and provided two views of the tooth (reproduced here as figures 1a and 1b), which hay (1895) reports were woodcuts. safford’s publication was overlooked in subsequent descriptions figure 1. petalodus ohioensis (as getalodus ohioensis) as illustrated by safford (1853, p. 142) in (a) labial and (b) lingual views, compared to a cast (ypm 2861) purported to be of the specimen in (c) labial and (d) lingual views. holotype of petalodus alleghaniensis (ansp 14541) in (e) labial and (f) lingual views. holotype of petalodus hastingsii (nhmuk pv p.613) in (g) labial and (h) lingual views. proposed neotype (nhmuk pv p.75414, formerly part of p.5342; carpenter and itano, 2018) in (i) labial and (j) lingual views. the origin of the green dot on specimen h is uncertain but may have been the code used by woodward (1889) or owen (1840–1845) to denote it was a holotype. the red dot on specimen j is a blob of wax used by woodward (1889) to denote that he included the specimen in his catalog of fossil fishes. the blue star on specimen e is the old symbol used to denote a holotype. scale in mm. 57 taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype carpenter, k., and itano, w.m. geology of the intermountain west 2019 volume 6 of specimens of petalodus from the united states (leidy, 1855, 1856, 1873; newberry and worthen, 1866; st. john, 1870; newberry, 1875), until its “rediscovery” by hay (1895). hay (1895, 1902) commented that the generic name “getalodus” was a typographical error for petalodus, either due to misinterpretation of safford’s handwritten manuscript by the typesetter, or safford’s misunderstanding of louis agassiz’ heavy swiss french accent during their conversations. two years after safford named petalodus ohioensis, leidy (1855) named sicarius extinctus for a tooth that was loaned to him, and noted, that it resembled a pangolin scale. leidy (1855) thought it was fish but did not rule out reptile. the specimen was found in the glenshaw formation (missourian = lower upper pennsylvanian) at bens creek station in what is now the allegheny portage railroad national historic site near cresson, pennsylvania (koch and santucci, 2004). the following year, leidy (1856) renamed the tooth petalodus alleghaniensis (note original spelling, sometimes subsequently misspelled allegheniensis [goto and okura, 2004; monson, 2010]), described it in detail and illustrated it. the specimen is currently in the collections of the academy of natural sciences of philadelphia (ansp 14541, figures 1e and 1f). the name change from sicarius to petalodus is understandable once leidy learned what petalodus teeth were like. what is not clear is why he also changed the species name; no reason was given. hay (1895) raised the possibility that p. ohioensis had priority over p. alleghaniensis, as well as p. destructor named by newberry and worthen (1866) and his own p. securiger. however, because he did not think safford’s drawings were wholly accurate and because the whereabouts of safford’s specimen was unknown for comparison, he only synonymized p. destructor with p. ohioensis based on similarities of the crowns and sizes. eastman (1896) considered p. ohioensis a nomen dubium because safford’s description was insufficient and the drawing probably inaccurate. this position, however, has not been followed (e.g., hay, 1902; hansen, 1985, 1996; dalla vecchia, 1988; zidek and kietzke, 1993; brusatte, 2007; ginter and others, 2010; carpenter and ottinger, 2018). a final resolution recently, one of us (wmi) discovered a cast identified as of the holotype p. ohioensis in the collections of the ypm (ypm 2861) (figures 1c and 1d). notes associated with the cast refer to it as the “plastotype” and that it was obtained from the mcz. the cast was catalogued at the ypm on september 18, 1930 (don brinkman, ypm, written communication, june 15, 2018). however, there are no records at the mcz of the cast or original specimen from which the cast was made (jessica cundiff, mcz, written communication, june 15, 2018). this absence may explain why eastman (1896), who was at the mcz at the time of his article, made no mention of the specimen. although the quality of the cast is low, it does show that the tooth was more than just the crown. of the crown, the cingulum of imbricated ridges at the base of the crown on both the labial and lingual sides as shown by safford (1853) are not very distinct. nor does the cast display the striated occlusal margin as shown by safford. nevertheless, the cast does confirm that the specimen has the distinctive crown of petalodus, which is triangular, vertically short, broad-based, labio-lingually compressed, convex labially, and concave lingually. the root is complete and has the characteristic tongue-shape of petalodus. in addition, it is d-shaped in horizontal cross section, with the lingual side flat. measurements are given in table 1. although larger, the tooth strongly resembles that of p. alleghaniensis in crown profile and presence of a notch in the lower corner of the root, which may help determine tooth position. we can find no reason for recognizing two taxa and here formally synonymize p. alleghaniensis leidy, 1856 with p. ohioensis safford, 1853 as first suggested by hay (1895). systematic paleontology class chondrichthyes huxley, 1880 order petalodontiformes patterson, 1965 petalodontida zangerl, 1981 family petalodontidae newberry and worthen, 1866 genus petalodus owen, 1840 58 taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype carpenter, k., and itano, w.m. geology of the intermountain west 2019 volume 6 synonymies chomatodus agassiz, 1838 (in part) getalodus safford, 1853 err typo ctenopetalus davis, 1881 sicarius leidy, 1855 species petalodus ohioensis safford, 1853 synonymies sicarius extinctus leidy, 1855 petalodus alleghaniensis leidy, 1856 petalodus allegheniensis leidy, 1856 err typo petalodus destructor newberry and worthen, 1866 petalodus securiger hay, 1895 conclusions it has been 165 years since james safford named and illustrated petalodus ohioensis for a tooth from the upper pennsylvanian of ohio. the taxonomic validity of the name has been problematic because the holotype is missing, and the original description and illustrations are insufficient. the discovery of a cast purported to be of the holotype has resolved a decades-long debate as to the validity of the taxon and the seniority of the species name over that of p. alleghaniensis leidy, 1856. pending discovery of the original specimen of p. ohioensis, the cast (ypm 2861) may act as a representative of that specimen, but the cast itself as a three-dimensional illustration of the specimen, is not the holotype (iczn art. 72.5.3 with 73.1.4). the term “plastotype,” which is written on a label with the cast, is a term not regulated by the international code of zoological nomenclature (iczn) and is not used here. this cast also negates the need for a neotype (as defined by iczn article 75) of p. ohioensis, which fortunately has never been published, despite appearing on a label accompanying a cast at the nhmuk in london. that label accompanies a cast, nhmuk pv p.58463, which is a cast of usnm pal 244454. however, iczn article 9 is clear that a notation written on a label is not a valid designation. furthermore, the discovery of the cast of the holotype would set aside the neotype designation (iczn article 75.8). acknowledgments don brinkman (yale peabody museum of natural history, new haven, connecticut) gave w. itano access to collections, which led to the discovery of the cast ypm 2861 and provided collection data. jessica cundiff (museum of comparative zoology, harvard university, cambridge, massachusetts) searched for the original of petalodus ohioensis and provided information on the petalodus specimens under her care. ned gilmore (academy of natural sciences, drexel university, philadelphia, pennsylvania) provided images of the holotype of petalodus alleghaniensis. emma bernard (natural history museum, london, england) provided w. itano access to collections and assigned a new specimen number for a specimen selected as the neotype of petalodus hastingsii. we thank mike hansen (retired, ohio geological survey, the ohio state university, columbus, ohio), jim kirkland (utah geological survey), and spencer lucas (new mexico museum of natural history and science) for their reviews. taxon (catalog number) crown side maximum tooth height (mm) maximum crown width (mm) maximum mid-crown height to top of cingulum (mm) maximum cingulum midheight (mm) p. ohioensis (ypm 2861) (h) labial 39.3 35.3 15.5 3.4 lingual 25.8 3.1 p. alleghaniensis (ansp 14541) (h) labial 34.5 (35.3 e) 30.2 (30.6 e) 15.6 3.7 lingual 20 5.5 p. acuminatus (mhnn-fos 171) (h) lingual na 34.6 (e) 16.6 3.3 table 1. measurements for specimens of petalodus used in this study. abbreviations: (e) – estimate; (h) – holotype; mm – millimeter; na – not available. 59 taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype carpenter, k., and itano, w.m. geology of the intermountain west 2019 volume 6 references agassiz, l., 1833–1845a, recherches sur les poissons fossiles, v. 3, contenant l’histoire de l’ordre des placoïdes: petitpierre, neuchâtel, suisse, 422 p. agassiz, l., 1833–1845b, recherches sur les poissons fossiles. atlas, v. 3: petitpierre, neuchâtel, suisse, 83 plates. brusatte, s.l., 2007, pennsylvanian (late carboniferous) chondrichthyans from the lasalle limestone member (bond formation) of illinois, usa: neues jahrbuch für geologie und paläontologie-abhandlungen, v. 244, no. 1, p. 1–8. carpenter, k., and ottinger, l., 2018, permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah: geology of the intermountain west, v. 5, p. 105–116. carpenter, k., and itano, w., 2018, case 3779 – petalodus owen, 1840 (chondrichthyes, petalodontiformes, petalodontidae)— proposed conservation of usage by designation of a neotype for its type species petalodus hastingsii owen, 1840: bulletin of zoological nomenclature, v. 75, p. 241–246. dalla vecchia, f.m., 1988, first record of a petalodont (petalodus ohioensis safford, 1853) from the alps: gortania-atti del museo friulano di storia naturale, v. 9, p. 47–56. davis, j.w., 1881, on the genera ctenoptychius, agassiz; ctenopetalus, agassiz; and harpacodus, agassiz: annals and magazine of natural history series 5, v. 8, p. 424–427. eastman, c.r., 1896, remark on petalodus alleghaniensis leidy: the journal of geology, v. 4, no. 2, p. 174–176. ginter, m., hampe, o., and duffin, c.j., 2010, chondrichthyes paleozoic elasmobranchii teeth, in schultze, h-p., editor, handbook of paleoichthyology, 3d: munich, verlag dr. friedrich pfeil, 168 p. goto, m., and okura, m., 2004, the chondrichthyan tooth remains from the carboniferous and permian of fukuji, gifu prefecture, central japan: earth science (chikyu kagaku), v. 58, p. 215–228. hansen, m.c., 1985, systematic relationships of petalodontiform chondrichthyans, in dutro, j.t., jr., and pfefferkorn, h.w., editors, ninth international congress on carboniferous stratigraphy and geology: compte rendus, v. 5, p. 523–541. hansen, m.c., 1996, phylum chordata—vertebrate fossils: fossils of ohio, ohio division of geological survey bulletin, v. 70, p. 288–369. hay, o.p., 1895, description of a new species of petalodus (p. securiger) from the carboniferous of illinois: the journal of geology, v. 3, no. 5, p. 561–564. hay, o.p., 1902, bibliography and catalogue of the fossil vertebrata of north america: u.s. geological survey bulletin 179, 868 p. huxley, t.h., 1880, on the application of the laws of evolution to the arrangement of the vertebrata, and more particularly of the mammalia: proceedings of the zoological society, london, v. 43, p. 649–662. ivanov, a., lucas, s.g., and krainer, k., 2009, pennsylvanian fishes from the sandia formation, socorro county, new mexico, in lueth, v., lucas, s.g., and chamberlin, r.m., editors, geology of the chupadera mesa: new mexico geological society 60th field conference, p. 243–248. koch, a.l., and santucci, v.l., 2004, paleontological resource inventory and monitoring, eastern rivers and mountains network: national park service, tic #d-265, 54 p. leidy, j., 1855, indications of five species, with two new genera, of extinct fishes: proceedings of the academy of natural sciences of philadelphia, v. 7, p. 414. leidy, j., 1856, descriptions of some remains of fishes from the carboniferous and devonian formations of the united states: journal of the academy of natural science of philadelphia, 2nd series, v. 3, p. 159–165. leidy, j., 1873, notice of some remains of fishes from the carboniferous formations of kansas—part i, contributions to the extinct vertebrate fauna of the western territories: report of the united states geological survey of the territories—fossil vertebrates, v. 1, p. 311–314. lucas, s.g., spielmann j.a., ivanov, a.o., rinehart, l.f., and krainer, k., 2011, petalodont chondrichthyan teeth from the pennsylvanian-permian horquilla formation, big hatchet mountains, new mexico, in sullivan, r.m., lucas, s.g., and spielmann, j.a., editors, fossil record 3: new mexico museum of natural history and science bulletin 53, p. 110–114. m’coy, f., 1854, contributions to british palaeontology—or, first descriptions of three hundred and sixty species and several genera of fossil radiata, articulata, mollusca, and pisces from the tertiary, cretaceous, oolitic, and palæozoic strata of great britain: cambridge, england, macmillan press, 272 p. monson, c.c., 2010, paleontology and paleoecology of the pennsylvanian in south-central iowa, in marshall, t., and fields, c., editors, the pennsylvanian geology of south-central iowa: geological survey of iowa guidebook 6, p. 27–35. newberry, j.s., 1875, descriptions of fossil fishes—part ii paleontology: report of the geological survey of ohio, v. 2, p. 1–64. newberry, j.s., and worthen, a.h., 1866, descriptions of vertebrates: geological survey of illinois, v. 2, p. 11–141. owen, r., 1840–1845, odontography; or a treatise on the comparative anatomy of the teeth; their physiological relations, mode of development, and microscopic structure in the vertebrate animal, 2 vols: london, england, hippolyte bailliere, 655 p. patterson, c., 1965, the phylogeny of the chimaeroids: philosophical transactions of the royal society of london, series b, biological sciences v. 249, p. 101–219. 60 taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype carpenter, k., and itano, w.m. geology of the intermountain west 2019 volume 6 safford, j.m., 1853, tooth of getalodus ohioensis: american journal of science and arts (second series), v. 16, no. 46, p. 142 st. john, o., 1870, descriptions of fossil fishes, from the upper coal measures of nebraska: proceedings of the american philosophical society, v. 11, p. 431–437. woodward, a.s., 1889, catalogue of the fossil fishes in the british museum (natural history), part i containing the elasmobranchii: london, england, taylor and francis, 567 p. zangerl, r., 1981, chondrichthyes i—paleozoic elasmobranchii, in schultze, h.p., editor, handbook of paleoichthyology 3a: stuttgart, germany, gustav fischer verlag, 115p. zidek, j., and kietzke, k.e., 1993, pre-permian vertebrates of new mexico, with remarks on some early permian specimens, in lucas, s.g., and zidek, j., editors, vertebrate paleontology in new mexico: new mexico museum of natural history and science bulletin 2, p. 1–10. a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa john r. foster theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover the little houston quarry (mammal pit), in the lower middle right of the photograph, is in the morrison formation of the northwestern black hills, crook county, wyoming, which yielded the crocodyliform jaw described here. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 287 abstract a left mandible of a small crocodyliform found in the upper jurassic morrsion formation of northeastern wyoming represents the first occurrence of the atoposaurid theriosuchus in north america. the specimen demonstrates lower jaw morphology, including heterodonty (as indicated by alveolus shape), similar to theriosuchus and knoetschkesuchus, but autapomorphies and a unique combination of characters among these taxa indicate that it is a distinct, new species of theriosuchus. a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa john r. foster utah field house of natural history state park museum, 496 east main st., vernal, ut 84078; eutretauranosuchus@gmail.com citation for this article. foster, j.r., 2018, a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa: geology of the intermountain west, v. 5, p. 287–295. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction fossil crocodylomorphs are diverse in the upper jurassic morrison formation of western north america, with seven species of terrestrial and semi-aquatic forms occurring, with collective widespread distribution and high abundance (e.g., clark, 2011; pritchard and others, 2013; foster and mcmullen, 2017). in 2004, the left mandible of a small crocodyliform was collected from the little houston quarry in the morrison formation of the black hills, northeastern wyoming (figure 1). this specimen was found along with a diverse assemblage of dinosaurs and microvertebrates, the latter including mammals, fish, amphibians, a lizard, sphenodontians, the choristodere cteniogenys, and turtles, among others (foster, 2001). the dinosaurs included particularly abundant basal neornithischians, theropods, and diplodocine and camarasaurid sauropods. the crocodyliform specimen was initially described as a juvenile goniopholidid that would have demonstrated strong allometric growth in the relative elongation of the lower i-25 i-90 w yo m in g lhq site 50 km wyoming so u th d a ko ta jackson laramie sheridan casper sundancegillette devils tower nm newcastle i-90 figure 1. location of little houston quarry (lhq) in crook county, northeastern wyoming, usa. 288 a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa foster, j.r. geology of the intermountain west 2018 volume 5 jaw through ontogeny (foster, 2006). re-examination of the specimen (mwc 5625) indicates heterodonty in the lower jaw and strong similarities to theriosuchus, and a redescription is provided here. institutional abbreviations mwc – museums of western colorado, dinosaur journey museum, fruita, colorado; bmnh – the natural history museum, london, england. systematic paleontology crocodylomorpha crocodyliformes neosuchia mesoeucrocoylia atoposauridae theriosuchus owen, 1879 type species – t. pusillus theriosuchus morrisonensis sp. nov. figures 2 and 3 lsid. urn:lsid:zoobank.org:act:dab8542a-7444-40269460-7735f0143c82 type specimen mwc 5625, left mandible, nearly complete but missing teeth. type locality little houston quarry (mammal pit), crook county, wyoming (foster and martin, 1994; foster, 2001). type horizon morrison formation undifferentiated; thin local morrison section of only ~23 m (mapel and pillmore, 1963); exact stratigraphic level and intraformational correlation with other localities in wyoming unknown. etymology for its occurrence in the morrison formation. diagnosis theriosuchus species with the following unique combination of characters (*denote autapomorphic for species relative to theriosuchus and knoetschkesuchus): greatly enlarged d2 and d3 alveoli*; dramatic reduction in mesiodistal diameter of alveoli from d3 to d4*; overall structure of mandible similar to t. pusillus in depth:length ratio, lack of external mandibular fenestra, retroarticular process angle, and dentary dorsal profile in two “waves” in lateral view; however, dentary nutrient foramina row and symphysis orientation relative to tooth row both more similar to k. guimarotae. revised description (modified from foster, 2006) specimen mwc 5625 is 141 mm long, with a pitted to rugose lateral surface and a relatively deep dorsoventral dimension (figure 2). the lingual side of the jaw (particularly along the ventral margin) is not well preserved in the central area, but the articular region and the rostral third are in good condition. the tooth row is relatively short. there are alveoli for 16 teeth, although all teeth are missing, and the lateromedial widths of the alveoli for the caudal seven of those teeth have been reduced somewhat by postmortem crushing. there is no external mandibular fenestra. in lateral view, the retroarticular process is short, and its dorsal surface is steeply inclined in a caudoventral direction. although sutures of the bones of the lower jaw are difficult to distinguish in many areas, the splenial is involved in the caudal part of the oval symphysis. a deep foramen intermandibularis oralis occurs just caudal to the symphysis. a row of foramina extends along the occlusal surface of the dentary just lingual to the alveoli of d2 to d9 (figure 3). the edges of the alveoli are vertically festooned around d2 through d5 and are flat posterior to that. there is slight damage to the anterior end of the dentary so the nature of the alveolus for d1 is obscured to some degree. diameters of alveoli d2 and d3 are greatly enlarged relative to surrounding tooth positions; diameters of d4 through d9 alveoli are significantly reduced; and mesial-distal diameters of d10 through d16 are somewhat enlarged, some as large as d2 and d3 (table 1; figure 3). despite some mediolateral crush289 a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa foster, j.r. geology of the intermountain west 2018 volume 5 ing of the jaw posterior (caudal) to d8, the mesial-distal diameters of the alveoli do not appear to have been significantly altered, and the crushing appears to have been relatively minor at the caudal end of the tooth row. alveoli for d10 through d16 are so significantly elongate mesial-distally, compared to their labiolingual diameter, that even prior to crushing, the alveoli for these posterior tooth positions appear to have been very different in shape compared with more anterior (rostral) ones. given that the preserved widths of d10 through d16 are about 1 mm each, with a mesiodistal length of ~3 to 4 mm for each, and about 1 mm of labiolingual crushing, these alveoli still appear to have been nearly twice as long mesiodistally as wide labiolingually. thus, from the moderate-sized d1 alveolus posteriorly: d2 and d3 are very large and nearly circular, d4 through d9 are very small and circular, and d10 through d16 are seemingly large and elongate-oval figure 2. theriosuchus morrisonensis (n. sp.), specimen mwc 5625, left mandible. (a) lateral (labial) view. (b) medial (lingual) view. (c) occlusal view; note enlarged dentary teeth d2 and d3, small circular d4 through d9, and slightly crushed but large and elongate d10 through d16. scale bars = 5 cm. abbreviations: d1, dentary alveolus 1; dedw, “waves” in dorsal edge of dentary; nfr, nutrient foramina row; rap, retroarticular process; sd, external sculpturing of dentary; sym, symphysis. 290 a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa foster, j.r. geology of the intermountain west 2018 volume 5 shaped (figure 3; table 1). the interalveolar spaces between positions d10 through d16 appear to have extremely thin septae (at least three positions) or to lack them entirely (confluent), a feature still apparent despite some crushing. the preserved septae are oriented diagonally between alveoli due to crushing (originally perpendicular to the tooth row), but they are generally only about 1 mm in length, again suggesting that teeth d10 through d16 were laterally compressed. these great size differences and apparent change in shape suggest that the tooth row exhibited significant heterodonty and that the dentary possessed at least three tooth types with conical teeth anteriorly and possibly laterally compressed teeth posteriorly. d1? d2-d3 d4-d9 d10-d16 a b figure 3. close-up of anterior third of mandible, specimen mwc 5625, showing diversity of tooth alveoli; dentary tooth alveolus d1 difficult to distinguish; dentary alveoli d2 and d3 greatly enlarged and roughly circular, d4 through d9 roughly circular but greatly reduced in diameter, and d10 through d16 mesiodistally elongate in occlusal view. (a) photo with some key alveoli labeled; nf = nutrient foramina at anterior and posterior end of row; scale bar (red) = 1 cm. (b) tracing of jaw and alveoli with color coded zones of similar alveolar shapes below. note that spaces between positions d13 through d14 and d15 through d16 have very thin septae, indicating minimal labial-lingual crushing; remaining alveoli in positions d10 through d16 may have been confluent. 291 a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa foster, j.r. geology of the intermountain west 2018 volume 5 discussion and conclusions the specimen was found in an abandoned channel-fill pond deposit in interbedded laminated siltstone and green claystone (foster and martin, 1994; foster, 2001). this is a dense bone bed preserving microvertebrate bones (e.g., jaws of mammals) and macrovertebrate bones (e.g., articulated sauropods) in the same layer and just centimeters away from each other. the abandoned channel deposit occurs as an elongate, laterally restricted deposit that lies stratigraphically just above a convex-bottomed channel sand, and it consists of two 1to 10-cm-thick laminated siltstone beds with many aquatic, semi-aquatic, and terrestrial taxa mixed in the same layers. charophytes, horsetails, bivalves, and other non-vertebrate taxa recovered from the deposit are also indicative of a relatively wet environment. teeth of possible goniopholidids as well as unidentified crocodylomorph osteoderms are also found in the deposit. specimen mwc 5625 was originally described as a juvenile goniopholidid that would have undergone dramatic allometric growth in its lower jaw through ontogeny (foster, 2006). i proposed that morrison goniopholidids would have greatly increased the relative length of their tooth row and greatly reduced the relative depth of their lower jaw (greatest mandible depth/ overall mandible length) as they grew to adult size. in both these ratios, however, specimen mwc 5625 is well off the trend lines set by a sample of morrison goniopholidids (amphicotylus and eutretauranosuchus) and a growth series of the modern alligator (figure 4). the apparent growth pattern collectively shown by those three taxa was in fact the reverse of what would have been required to turn the individual represented by specimen mwc 5625 into an adult (foster, 2006). and in shape of the symphysis of the lower jaws, specimen mwc 5625 in fact plotted among the alligators and nowhere near the region of goniopholidids of having a more anteroposteriorly elongate symphysis (foster, 2006). my own graphs in that paper (foster, 2006) suggested, however, that alligator at least did not undergo such dramatic allometric growth from the same small size up to that of the largest morrison specimen, and even the trend among the known morrison goniopholidids (though all are significantly larger than specimen mwc 5625) did not suggest dramatic changes. in re-examining the specimen and data in that paper, it is clear that specimen mwc 5625 shares characters with the atoposaurid crocodyliform theriosuchus, which was first named from the purbeck (lower cretaceous) of england (owen, 1879; salisbury, 2002) and has since had members of its genus or close relatives show up in asia, portugal, spain, romania, and possibly (from teeth) in a few other places, usually in the late jurassic to early cretaceous (martin and others, 2010; young and others, 2016) but also ranging into the late cretaceous. theriosuchus was a small neosuchian with a short and triangular-shaped skull (top view) with large eyes and a short, narrow snout (salisbury, 2002; martin and others, 2014). specimen mwc 5625 is relatively large and differs from the dentary of knoetschkesuchus from portugal in lacking an external mandibular fenestra and in having a mandible less elongate relative to its maximum depth (figure 4; schwarz and salisbury, 2005; schwarz and dentary alveoli mesiodistal diameters d1 2.1 d2 3.2 d3 4.0 d4 1.5 d5 1.4 d6 1.4 d7 1.2 d8 1.5 d9 1.2 d10 2.7 d11 4.2 d12 4.2 d13 2.9 d14 3.3 d15 2.6 d16 3.3 table 1. mesiodistal diameters of dentary alveoli in mwc 5625 (in mm). 292 a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa foster, j.r. geology of the intermountain west 2018 volume 5 others, 2017). based on alveolar diameters, specimen mwc 5625 also appears to have had more pronounced heterodont dentition anteriorly than knoetschkesuchus. it differs from atoposaurus, alligatorium, and alligatorellus in lacking homodont dentition and from alligatorium and alligatorellus specifically in lacking the external mandibular fenestra and smooth external surface of the mandible, respectively (tennant and mannion, 2014; tennant and others, 2016). specimen mwc 5625 also differs from species of sabresuchus in lacking a lateral dentary concavity for reception of an enlarged 5th maxillary tooth, in lacking a diastema between d7 and d8, in lacking as short a symphysis, in not having all dentary teeth in a continuous groove, and in not having the occlusal surface of the dentary entirely lacking nutrient foramina (tennant and others, 2016). turner (2015) found species of theriosuchus and alligatorium to form an atoposaurid clade, although another recent analysis has suggested that atoposauridae may be restricted to atoposaurus, alligatorium, and alligatorellus, and that traditional species of theriosuchus formed a polyphyletic group (tennent and others, 2016). the same latter analysis found, however, that theriosuchus pusillus and knoetschkesuchus at least were sister taxa. specimen mwc 5625 is most similar overall to a referred lower jaw of theriosuchus pusillus (specimen bmnh 48328; figure 5) illustrated by salisbury (2002). although the anterior tip of that specimen is missing, an estimation of the full jaw length suggests that the depth:length ratio of the mandible is very similar to mwc 5625 (figures 4 and 5). additionally, the apparent tooth row length, external sculpturing, and retroarticular process of mwc 5625 are all most similar to t. pusillus; the symphysis length and orientation and the dentary dorsal profile with two “waves” also are similar to theriosuchus (figure 5). specimen mwc 5625 possesses the following characters from the generic diagnosis of theriosuchus in young and others (2016). the folloing numbered list refers to the corresponding character numbers in young and others (2016), and the missing character numbers relate to characters not preserved in the mandible: (1) heterodont dentition with pseudocaniniform and likely labiolingually compressed teeth (judging from alveoli); (5) some of the dentary alveoli form a confluent chain from dentary alveolus d4 through d8 (d10 through d16 in mwc 5625); (7) dentary alveolar size strongly heterogeneous; and (8) external surface of dentary is ornamented with heterogeneously spaced pits, ventrolaterally rugose. specimen mwc 5625 appears to differ in lacking a notch in the dentary for the enlarged 5th maxillary tooth (character 6 in young and others, 2016) and in seeming to lack a progressive reduction in alveolus size from d4 through d6 (character 3; instead figure 4. comparison of mandible greatest depth to total length, by size, for: the atoposaurids theriosuchus pusillus, t. morrisonensis (specimen mwc 5625, labeled), and knoetschkesuchus (stars), several goniopholidids (squares), and a growth series of alligator (circles), showing greater mandible depth:length of theriosuchus. green trendline is for alligator series. length of t. pusillus mandible estimated due to missing tip in bmnh 48328. modified and updated from foster (2006). 293 a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa foster, j.r. geology of the intermountain west 2018 volume 5 mwc 5625 demonstrates dramatic reduction in diameter from d3 through d4). the external sculpting of the mandible and heterodonty were also characters listed in the revised diagnosis of theriosuchus in tennant and others (2016). the revised diagnosis of t. pusillus includes three mandibular characters that mwc 5625 matches: heterodont dentition (apparent indirectly in mwc 5625), absence of a mandibular fenestra, and dorsal edge of dentary with two dorsally projecting “waves” in lateral view. specimen mwc 5625 lacks all mandibular characters listed by tennant and others (2016) for a single speciment assigned to theriosuchus sp. (young and others, 2016) from the middle jurassic of the isle of skye, scotland. the mandibular configuration and combination of characters of mwc 5625 distinctly separate the specimen from goniopholidids, shartegosuchids, and protosuchids/sphenosuchians and suggest that mwc 5625 is within the genus theriosuchus, closest to t. pusillus (also illustrated by salisbury, 2002, and schwarz and others, 2017); however, it differs from that genotype species in having greatly enlarged d2 and d3 alveoli and having the splenial more evenly distributed dorsoventrally along the symphysis (not restricted to dorsal part). specimen mwc 5625 also differs from t. pusillus, and is similar to knoetschkesuchus guimarotae, in havfigure 5. theriosuchus mandibles compared. (a) referred left mandible of theriosuchus pusillus (specimen bmnh 48328) from the purbeck formation, england, showing depth:length ratio, short tooth row, and steep dorsal edge of retroarticular process. also note heterodont dentition and "waves" of dorsal edge of dentary. scale numbered in cm. photo courtesy of d. schwarz (museum für naturkunde, berlin, germany). (b) left mandible holotype of t. morrisonensis (mwc 5625), morrison formation, wyoming, showing similar morphology. scale bar = 5 cm. 294 a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa foster, j.r. geology of the intermountain west 2018 volume 5 ing a line of foramina lingual to the tooth row on the occlusal surface of the dentary from d2 through d9 and in having a symphysis parallel in line to the tooth row. characters that make mwc 5625 unique among theriosuchus and knoetschkesuchus specimens include: (1) very large d2 and d3, relative to d4 through d9, and (2) dramatic reduction in diameter from alveoli d3 through d4. specimen mwc 5625 is too incomplete to run a meaningful phylogenetic analysis (only 35 of 329 characters known from tennant and others [2016]; table 2), and preliminary assessments in tnt software and using the datasets of turner (2015) and tennant and others (2016) show it to be rather unstable within neosuchia. however, its unique features and combination of numerous characters shared with the closely related theriosuchus pusillus and knoetschkesuchus guimarotae (turner, 2015; tennant and others, 2016) suggest that, if more complete, theriosuchus morrisonensis (mwc 5625) would likely be found to lie within this clade, possibly as the sister taxon to t. pusillus. this is the first occurrence of theriosuchus in the late jurassic of north america and is a new crocodyliform species for the morrison formation. although isolated teeth from the early cretaceous cedar mountain formation have been referred to atoposaurids (cifelli and others, 1999), until now no confirmation of theriosuchus or close relatives has been found on this continent. the discovery thus strengthens biotic ties once again between the morrison formation and the late jurassic–early cretaceous of europe (e.g., mateus, 2006). this new occurrence also increases the diversity of crocodylomorphs in the morrison formation to eight taxa, with now at least two goniopholidids (amphicotylus, eutretauranosuchus), two shartegosuchids (fruitachampsa and an unnamed form), two hallopodid sphenosuchians (hallopus, macelognathus), this new species of theriosuchus, and a possible protosuchian (hoplosuchus). the diversity of crocodylomorphs in the late jurassic–early cretaceous of europe may have been even higher. atoposaurids appear to have been terrestrial or semiaquatic, depending on the species (tennant and mannion, 2014). with little of the postcranial skeleton known, the specific ecology of theriosuchus is not clear, but the environmental setting of knoetschkesuchus guimarotae in estuarine lagoons and swamps (schwarz and others, 2017) suggests that that species at least was semi-aquatic. the occurrence of t. morrisonensis in an abandoned channel pond deposit in the apparently wetter northern region of the morrison formation (turner and peterson, 2004; foster and mcmullen, 2017) aligns with the wet paleoenvironmental settings of k. guimarotae and t. pusillus and may indicate that t. morrisonensis too was semi-aquatic in its habits. acknowledgments thanks to the field crews of 2004 that helped on the excavations when we collected this specimen. thanks to kay fredette (museums of western colorado), who prepared mwc 5625, and to julia mchugh (museums of western colorado) for loan of the specimen. suggestions for improvement of the manuscript are greatly appreciated and were offered by daniela schwarz (museum für naturkunde), thomas adams (witte museum), and kelli trujillo (laramie county community college), though none of them necessarily endorses my interpretations. references cifelli, r.l., nydam, r.l., gardner, j.d., weil, a., eaton, j.g., kirkland, j.i., and madsen, s.k., 1999, medial cretaceous vertebrates from the cedar mountain formation, emery county, utah—the mussentuchit local fauna, in gillette, d.d., editor, vertebrate paleontology in utah: utah geological survey miscellaneous publication 99, p. 219–242. theriosuchus morrisonensis (scored here) 201 211 221 231 1012210??? ?00?011111 [0,1][0,1]12111000 11100100?0 ?1 theriosuchus pusillus (from tennant and others, 2016) 201 211 221 231 1112110??? ?12?101111 2111010 11110200?? 01 knoetschkesuchus guimarotae (from tennant and others, 2016) 201 211 221 231 1111111101 120101111 2111010 101002000? 01 table 2. matrix for mandible characters (201 through 242) from tennant and others (2016) for theriosuchus morrisonensis (specimen mwc 5625), compared with two closely related taxa. 295 a new atoposaurid crocodylomorph from the morrison formation (upper jurassic) of wyoming, usa foster, j.r. geology of the intermountain west 2018 volume 5 clark, j.m., 2011, a new shartegosuchid crocodyliform from the upper jurassic morrison formation of western colorado: zoological journal of the linnean society, v. 163, p. s152–s172. foster, j.r., 2001, taphonomy and paleoecology of a microvertebrate assemblage from the morrison formation (upper jurassic) of the black hills, crook county, wyoming: brigham young university geology studies, v. 46, p. 13–33. foster, j.r., 2006, the mandible of a juvenile goniopholidid (crocodyliformes) from the morrison formation (upper jurassic) of wyoming, in foster, j.r., and lucas, s.g., editors, paleontology and geology of the upper jurassic morrison formation: new mexico museum of natural history and science bulletin 36, p. 101–105. foster, j.r., and martin, j.e., 1994, late jurassic dinosaur localities in the morrison formation of northeastern wyoming, in nelson, g.e., editor, the dinosaurs of wyoming: wyoming geological association, 44th annual field conference guidebook, p. 115–126. foster, j.r., and mcmullen, s.k., 2017, paleobiogeographic distribution of testudinata and neosuchian crocodyliformes in the morrison formation (upper jurassic) of north america—evidence of habitat zonation?: palaeogeography, palaeoclimatology, palaeoecology, v. 468, p. 208–215. mapel, w.j., and pillmore, c.l., 1963, geology of the inyan kara mountain quadrangle, crook and weston counties, wyoming: u.s. geological survey bulletin 1121, p. m1–m56. martin, j.e., rabi, m., and csiki, z., 2010, survival of theriosuchus (mesoeucrocodylia: atoposauridae) in a late cretaceous archipelago—a new species from the maastrichtian of romania: naturwissenschaften, v. 97, p. 845–854. martin, j.e., rabi, m., csiki-sava, z., and vasile, s., 2014, cranial morphology of theriosuchus sympiestodon (mesoeucrocodylia, atoposauridae) and the widespread occurrence of theriosuchus in the late cretaceous of europe: journal of paleontology, v. 88, p. 444–456. mateus, o., 2006, late jurassic dinosaurs from the morrison formation, the lourinhã and alcobaça formations (portugal), and the tendaguru beds (tanzania)—a comparison, in foster, j.r., and lucas, s.g., editors, paleontology and geology of the upper jurassic morrison formation: new mexico museum of natural history and science bulletin 36, p. 223–231. owen, r., 1879, on the association of dwarf crocodiles (nannosuchus and theriosuchus pusillus, e.g.) with the diminutive mammals of the purbeck shales: quarterly journal of the geological society, v. 35, p. 148–155. pritchard, a.c., turner, a.h., allen, e.r., and norell, m.a., 2013, osteology of a north american goniopholidid (eutretauranosuchus delfsi) and palate evolution in neosuchia: american museum novitates, no. 3783, 56 p. salisbury, s.w., 2002, crocodilians from the lower cretaceous (berriasian) purbeck limestone group of dorset, southern england: special papers in palaeontology, no. 68, p. 121–144. schwarz, d., raddatz, m., and wings, o., 2017, knoetschkesuchus langenbergensis gen. nov. sp. nov., a new atoposaurid crocodyliform from the upper jurassic langenberg quarry (lower saxony, northwestern germany), and its relationships to theriosuchus: plos one, v. 12, no. 2, e0160617. schwarz, d., and salisbury, s.w., 2005, a new species of theriosuchus (atoposauridae, crocodylomorpha) from the late jurassic (kimmeridgian) of guimarota, portugal: geobios, v. 38, p. 779–802. tennant, j.p., and mannion, p.d., 2014, revision of the late jurassic crocodyliform alligatorellus, and evidence for allopatric speciation driving high diversity in western european atoposaurids: peerj 2:e599, doi 10.7717/peerj.599. tennant, j.p., mannion, p.d., and upchurch, p., 2016, evolutionary relationships and systematics of atoposauridae (crocodylomorpha: neosuchia)—implications for the rise of eusuchia: zoological journal of the linnean society, v. 177, p. 854–936. turner, a.h., 2015, a review of shamosuchus and paralligator (crocodyliformes, neosuchia) from the cretaceous of asia: plos one, v. 10, no. 2, e0118116. https://doi.org/10.1371/ journal.pone.0118116. turner, c.e., and peterson, f., 2004, reconstruction of the upper jurassic morrison formation extinct ecosystem—a synthesis: sedimentary geology, v. 167, p. 309–355. young, m.t., tennant, j.p., brusatte, s.l., challands, t.j., fraser, n.c., clark, n.d.l., and ross, d.a., 2016, the first definitive middle jurassic atoposaurid (crocodylomorpha, neosuchia), and a discussion on the genus theriosuchus: zoological journal of the linnean society, v. 176, p. 443–462. a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah brian m. davis, richard l. cifelli, and guillermo w. rougier theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover small vertebrate fossils wrapped for transport, cisco mammal quarry, upper jurassic morrison formation, grand county, utah. i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott ekeller@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — museum of moab cary woodruff — university of toronto octavio mateus — universidade nova de lisboa editors geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 1 abstract the first mesozoic mammals in north america were discovered in the morrison formation during the closing decades of the 19th century, as by-products of dinosaurs quarried by teams led by o.c. marsh. these tiny fossils served as foundational specimens for our understanding of mesozoic mammal evolution. there are now nearly 25 mammal-bearing localities known from the morrison formation, distributed across the western interior from the black hills to southern colorado and west into utah; the most historically important of these are in wyoming (e.g., como quarry 9). most morrison mammals are known by jaws or jaw fragments, and several important mesozoic groups (e.g., docodonts, dryolestoids, and to a large extent triconodonts and symmetrodonts) were established based on morrison material, shaping the perception of mammalian diversity on a global scale. despite heavy sampling of coeval sites elsewhere, the morrison remains the most systematically diverse (at high taxonomic levels) assemblage of jurassic mammals in the world. here, we describe two mammalian specimens and highlight other remains yet to be fully identified from a new microvertebrate locality in the morrison formation of eastern grand county, utah. the site is positioned low in the brushy basin member and is similar in lithology and stratigraphic level to the famous small vertebrate localities of the fruita paleontological area, located less than 50 km to the northeast. in addition to small archosaurs and squamates, limited excavation to date has yielded at least 20 mammalian specimens representing a minimum of six taxa, several of which are new and quite different from typical morrison taxa. preservation is generally excellent and includes partially articulated cranial and postcranial elements of small vertebrates. this new site has great potential to contribute new taxa and more complete morphological data than typical morrison localities, underscoring the importance of continued field work in the morrison. a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah brian m. davis1,2, richard l. cifelli2, and guillermo w. rougier1 1department of anatomical sciences and neurobiology, university of louisville school of medicine, louisville, ky, 40202; bm.davis@louisville.edu, grougier@louisville.edu 2department of vertebrate paleontology, sam noble museum, university of oklahoma, 2401 chautauqua ave., norman, ok, 73072; rlc@ou.edu citation for this article. davis, b.m., cifelli, r.l., and rougier, g.w., 2018, a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah: geology of the intermountain west, v. 5, p. 1–8. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the upper jurassic morrison formation has yielded one of the most influential mammal assemblages worldwide. at least 40 taxa are currently described from 20+ localities (foster, 2003; kielan-jaworowska and others, 2004), making it the most diverse jurassic assemblage in the world and among the most diverse in the mesozoic. several factors were likely at play in generating this impressive record: (1) intense study of the morrison formation began in the 1870s (marsh, 1878; osborn, 1888; see summary in simpson, 1929), and (2) the unit has www.utahgeology.org 2 a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah davis, b.m., cifelli, r.l., and rougier, g.w. geology of the intermountain west 2018 volume 5 a vast latitudinal range, with exposures across much of the western interior. this geographic expanse, coupled with as much as 7 ma of depositional time (trujillo and kowallis, 2015), suggest that localities in the morrison possibly represent a wide range of paleoenvironments of slightly different ages. typical morrison mammal localities (e.g., como quarry 9 at como bluff, wyoming) are characterized by variations of a standard assemblage of taxa, known mainly by jaws and jaw fragments: the mammaliaform docodon, plagiaulacidan-grade multituberculate mammals, triconodontids, tinodontid “symmetrodonts,” and various dryolestoids (see kielan-jaworowska and others, 2004). mammal assemblages vary across the extent of the morrison formation; this has been studied in detail (foster, 2001, 2003; foster and others, 2006) using taphonomy and the distribution of docodon, which is abundant in sites in the eastern half of the outcrop area but absent from sites to the west. these patterns have been explained in part by variations in paleoenvironment across morrison localities (discussed in foster 2001, 2003), and this is exemplified by the unique and well-preserved fauna from the fruita paleontological area (fpa) (callison, 1987; kirkland, 2006). occasional small skeletons have been found in articulation at sites in the fpa. among mammals, the presence of the highly specialized fruitafossor (luo and wible, 2005) suggests that uncaptured taxonomic diversity awaits future work in the fpa and more broadly in the morrison. as a result of a 2015 survey of jurassic units in southern and eastern utah, a joint field party from the university of louisville and the oklahoma museum of natural history (omnh) discovered a new microvertebrate locality in the morrison formation of eastern grand county, which we named the cisco mammal quarry (cmq) after the nearby ghost town of cisco, utah (figure 1; exact coordinates are on file at the omnh and are available to qualified investigators upon request). limited excavation to date has yielded a large diversity of small taxa, including squamates, archosaurs, and mammals (table 1). several specimens are relatively complete and well preserved, and preliminary study suggests that some represent previously unknown mammal taxa. the sample from cmq also includes the second occurrence of fruitafossor, otherwise known only from the fpa, highlighting unrecognized diversity and rich potential of continued exploration in the morrison formation. our ongoing work at the cmq is certain to increase the already high mammalian diversity, provide evidence on intraformational geographical and temporal faunal variation, and produce further refinement of our understanding of the morrison jurassic ecosystem, the standard against which any other jurassic fauna is to be compared. institutional abbreviations dino = dinosaur national monument, jensen, utah; omnh = oklahoma museum of natural history, norman, oklahoma ypm = yale peabody museum, new haven, connecticut. geologic setting rock units in the cmq (omnh locality v1728) area range from the middle jurassic entrada sandstone, forming the cliffs above the river, to the upper cretafigure 1. location of new mammal-bearing small vertebrate locality, the cisco mammal quarry (cmq, omnh v1728), in grand county, utah. enlarged area is indicated by gray portion of inset map. cmq and fpa (fruita paleontological area) are indicated by open stars. 3 a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah davis, b.m., cifelli, r.l., and rougier, g.w. geology of the intermountain west 2018 volume 5 ceous mancos shale, exposed on the flats along interstate 70. exposures of the morrison formation in the immediate vicinity of the locality are discontinuous, tilted, and terraced to some degree as the landscape descends to the colorado river; consequently, specific beds can be difficult to follow laterally and precise placement of the locality in the section is uncertain. to the southwest of the locality, the colorfully-banded smectitic mudstones typical of the brushy basin member rise to a steep cliff capped by the lower yellow cat member of the lower cretaceous cedar mountain formation (kirkland and others, 2017). large sandstone channels become much more common in outcrops down section to the east and northeast, as is typical of the salt wash member (turner and peterson, 2004). consequently, coarse stratigraphic placement of the cmq is likely low in the brushy basin member. the sequence of pale-colored mudstone and fine-grained sandstone beds that is exposed at the locality is laterally equivalent to the interval at the fpa, which contains the productive microvertebrate localities (s. maidment, imperial college, london, personal communication, 2016). these sites have also been placed low in the brushy basin member (kirkland, 2006). the locality is at the top of a rounded, pale-gray knob in the center of a somewhat isolated series of outcrops, the surface of which has weathered to the popcorn texture and convex slopes characteristic of smectitic clays. the hill preserves an irregular sequence of mudstone and thinner sandstone beds, mostly of uniform pale color. the sandstone beds are more resistant to weathering and appear rounded in profile when exposed. detailed study of the sedimentology at and around the cmq has yet to be completed, but the beds seem to lack sedimentary structures and are strongly indurated. the mudstone beds are smectitic and calcareous, containing a substantial proportion of fineto very fine grained sand. small flecks of biotite are present, and barite nodules are common with some as large as 10 cm. bone has been found at low density throughout much of the worked section, and does not appear to be concentrated at a particular horizon or horizons. it is tempting to draw some comparisons with the well-studied sections at the fpa, which is located less than 50 km to the northeast, just across the colorado border. in the thorough lithofacies analysis by kirkland (2006), the general characteristics of the drab floodplain facies, which yielded the main callison quarry and several other sites, seem most congruent with features of the cmq. mudstone beds are dominant over table 1. preliminary taxonomic list from the cisco mammal quarry (omnh locality v1728, upper jurassic morrison formation), a new mammal-bearing small vertebrate locality in grand county, utah. osteichthyes osteichthyes indet. squamata serpentes parviraptoridae parviraptoridae indet. serpentes indet. squamata indet. archosauria dinosauria heterodontosauridae ?fruitadens sp. archosauria indet. mammaliaformes morganucodonta morganucodonta indet. mammalia order and family incertae sedis fruitafossor windscheffeli multituberculata “plagiaulacida” glirodon grandis multituberculata indet. eutriconodonta eutriconodonta indet. trechnotheria dryolestidae dryolestes priscus paurodontidae paurodontidae indet. trechnotheria indet. 4 a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah davis, b.m., cifelli, r.l., and rougier, g.w. geology of the intermountain west 2018 volume 5 sandstone beds, and primary sedimentary structures are lacking. barite nodules are present, and the beds are calcareous. in a few aspects, the cmq also resembles alkaline pond facies of kirkland (2006), which yielded the important tom’s place microvertebrate site, where the presence of biotite and the relative abundance of barite nodules are similar, but kirkland (2006) described the mudstones of this facies as laminated and non-calcareous. only one thin, ill-defined laminated mudstone lens has been found at the cmq so far; it is calcareous but differs from the typical mudstone at the site in being distinctively darker in color, waxier, and less smectitic, and is far less sandier. this lens yielded a mammalian maxilla, but the lens pinches out quickly where the main quarry face is exposed. methods the initial discovery at the site was a portion of a small limb element weathering from just below the top of the knob. other small bones were discovered as surface float 2 or 3 m below a different face of the knob. surface exploration of the knob yielded an additional small limb element in situ 2 m below the first, suggesting a potentially thick productive zone. work at the cmq in 2016 used mainly hand tools; picks, chisels, and sledge hammers. rock near the surface is fractured to some degree, but is very hard and does not break easily or predictably. a generator-powered jackhammer was used in the 2017 field season to more efficiently fracture the quarry surface. the general approach has been to opportunistically explore various faces of the top of the knob, quarrying out blocks ~0.5 m in diameter, and carefully reducing them with small hand sledges. bone is not concentrated at horizons or along any discernible planes, occurring seemingly at random and in three dimensions. therefore, each broken surface must be carefully examined for tiny fossils, often with a hand lens, as specimens are typically discovered when sectioned. fortunately, most bone is jet back and stands out in strong contrast to the pale-colored rock (though bone ranges in color to pale brown). specimens needing stronger magnification or preparation were wrapped for transport back to the omnh. two mammalian specimens were discovered in situ; these were given small plaster caps for protection, and a gas-powered rock saw was used to cut them free in small blocks of rock. however, the nature of the smectitic clays at the site was not appreciated at the time, and the water from the uncured plaster caused the rock to swell and disturb the specimens. care must be taken to keep specimens and their surrounding rock dry, and liberal application of glue is possibly preferable for stability in the field, even if it must be removed from the specimen later during preparation. the specimens described in this paper, as well as others currently under study, were mechanically prepared under magnification using carbide needles and, occasionally, a pneumatic micro-jack. while the rock at the cmq is very hard and difficult to fracture, it responds very favorably to traditional preparation techniques. partial embedding of the specimens in carbowax mounted in a plaster holder was used to facilitate preparation and provide support; butvar® b76 in different concentrations was used as the main adhesive and consolidant, which occasionally was mixed with sediment to provide a semi-permanent support to fragile portions of the specimens. here, we follow the general practice of abbreviating molars with the letter “m;” teeth belonging to the upper dentition are indicated with an uppercase letter. right and left are abbreviated “r” and “l”, respectively. systematic paleontology mammalia linnaeus, 1758 multituberculata cope, 1884 “plagiaulacida” ameghino, 1889 family incertae sedis glirodon engelmann and callison, 1999 glirodon grandis engelmann and callison, 1999 figures 2a and 2b holotype: dino 10822, a partial skull. type locality: dinosaur national monument, uintah county, utah. referred material: omnh 78595, an isolated lm1. locality: omnh v1728 (cisco mammal quarry), morrison formation (kimmeridgian-tithonian), grand county, utah. 5 a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah davis, b.m., cifelli, r.l., and rougier, g.w. geology of the intermountain west 2018 volume 5 description omnh 78595 is a rectangular tooth with two rows of cusps, lacking ornamentation. though the lingual cusp row is heavily worn, it is clear that the buccal cusps would have been noticeably taller on an unworn tooth. the three cusps in the buccal row are evenly spaced, pyramidal, and subequal in size, with some wear on their lingual faces. steep, vertical valleys separate the cusps from one another. there is a weak, short cingulum limited to the space immediately mesial to the first buccal cusp, connected by a straight, weak crest to the apex of the cusp. there are four cusps in the lingual row, all with rounded bases. there is breakage through the second cusp of the row, but it appears that the mesial two cusps are relatively smaller and are positioned closer to one another, with the remaining cusps larger than the first two (but roughly equal in size to one another). the central valley is broadest mesially and narrows distally, as the lingual cusp row transcribes an arc directed towards the distal midline of the tooth. the central valley is walled mesially by a low crest, but is open distally. the lingual cusps are flattened by wear, which is present buccal, apically, and lingually. the buccal shift of the distal cusps of this row creates a faint bulge at the distolingual corner of the crown, but there is no evidence of a lingual cingulum or additional row of cusps. remarks omnh 78595 agrees with described morphology of glirodon grandis (engelmann and callison, 1999). the specimen differs from the similar plagiaulacidan ctenacodon laticeps (marsh, 1881), the only other morrison multituberculate in which the m1 has been described, based on several features. ctenacodon has a small anterior cuspule in addition to the three main cusps in the buccal row (simpson, 1929); there are only three buccal cusps in omnh 78595. additionally, in ctenacodon the cusps of the lingual row are mostly subequal with one another and are better aligned buccolingually with the buccal cusps than in omnh 78595. the holotype of c. laticeps, ypm 11761, bears a faint cingulum basal and adjacent to the valley separating lingual cusps 3 and 4, suggesting the possibility of incipient cusp development; given that variability cannot be assessed, the significance of this difference with respect to m1 of glirodon cannot be established. dryolestoidea butler, 1939 dryolestidae marsh, 1879 dryolestes marsh, 1878 dryolestes priscus marsh, 1878 figure 3a and 3b holotype: ypm 11820, a right dentary fragment. type locality: como quarry 9, morrison formation (kimmeridgian-tithonian), albany county, wyoming. referred material: omnh 78594, an isolated lm4. locality: omnh v1728 (cisco mammal quarry), morrison formation (kimmeridgian-tithonian), grand county, utah. description omnh 78594 is an isolated upper molar with three roots, the lingual of which is much larger than either buccal root. the crown is mesiodistally compressed (trigon angle of 45°) but bears a shallow ectoflexus and figure 2. omnh 78595, isolated lm1 of glirodon grandis in occlusal (a) stereopair and (b) lingual views, from the cisco mammal quarry (omnh locality v1728, upper jurassic morrison formation, grand county, utah). 6 a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah davis, b.m., cifelli, r.l., and rougier, g.w. geology of the intermountain west 2018 volume 5 a comparatively wide metastylar lobe, suggesting that the tooth is from the middle of the molar series (likely m4, see remarks below). the paracone is tall and erect, with sharp preand postparacristae. the base of the crown is somewhat constricted buccal to the paracone, making the crown slightly waisted in occlusal view. a weak median ridge (martin, 1999) descends buccally from the apex of the paracone (which is damaged), but fades into the trigon basin without contacting any other structures. no median or central cusp is present. the metacone is distinct and broad but much lower than the paracone; the cusp bulges slightly beyond the distal edge of the crown, though this would likely be flattened by wear (the crown bears very little wear). a deep notch separates the metacone from the paracone, but the crest distal to the metacone is uninterrupted and courses around the distobuccal edge of the crown to join the ectocingulum. the stylocone is roughly half the height of the paracone and is positioned somewhat mesially relative to typical dryolestes upper molars. the stylocone anchors the buccal end of the preparacrista, which curves slightly distally to climb to the apex of the cusp but is otherwise straight. a weak distobuccally-directed crest joins the apex of the stylocone with the ectocingulum, but the internal face of the cusp is smooth and weakly convex. the parastyle is positioned low on the crown and directly mesial to the stylocone. though slightly displaced by breakage, the parastyle has a broad, oblique lingual face; no crest connects the parastyle with the stylocone. the metastyle is a low cusp positioned just distal to the deepest point of the ectoflexus. the ectoflexus, which is continuous but for a notch between stylocone to metastyle, bears a sharp ectocingulum which joins the postmetacrista to rim the metastylar lobe of the crown. remarks omnh 78594 compares very favorably with the m4 of amnh 101130, a specimen originally referred to herpetairus humilis (prothero, 1981, figure 3d). martin (1999) revised many dryolestid taxa and synonymized herpetairus with dryolestes; we follow his taxonomy here and assign this specimen to d. priscus. omnh 78594 differs from amnh 101130 only in lacking the weak, internally directed crest on the stylocone, and in a more mesial position of the metastylar cusp, closer to the ectoflexus. discussion although exploration of the cmq is certainly still in early phases, the number and quality of specimens recovered, and the diversity of taxa they record, thus far suggest that this locality has tremendous potential to improve our understanding of jurassic terrestrial vertebrate evolution. among high-level taxa, mammals seem to be surprisingly abundant (though fossils in general are sparse at the site). the sample thus far includes approximately 25 specimens, ranging from isolated teeth or postcranial elements to partial skulls and skeletons (examples illustrated in figure 4). these specimens are awaiting final preparation and study, but preliminary results indicate that several of the mammalian taxa in our small sample are new, suggesting that the cmq fauna figure 3. omnh 78594, isolated lm4 of dryolestes priscus in occlusal (a) stereopair and (b) buccal views, from the cisco mammal quarry (omnh locality v1728, upper jurassic morrison formation, grand county, utah). 7 a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah davis, b.m., cifelli, r.l., and rougier, g.w. geology of the intermountain west 2018 volume 5 may be quite different from traditional morrison faunas and even from the geographically proximate fpa. however, the presence of glirodon and fruitafossor suggests at least some degree of regional homogeneity, as both taxa are present at the fpa and the former also in rainbow park at dinosaur national monument (engelmann and callison, 1999). the cmq specimens of the burrowing mammal fruitafossor include a well-preserved skull and partial skeleton, still undergoing preparation, as well as other isolated material (in addition to the tentatively referred braincase in figure 4). dryolestes is a rather common faunal element in sites around como bluff in southeastern wyoming (kielan-jaworowska and others, 2004), with a much broader distribution extending to the guimarota coal mine in portugal (martin, 1999). however, the specimen described here represents the first reported occurrence of this taxon in the western portion of the morrison formation. foster and others (2006) proposed east-west paleoenvironmental partitioning of morrison mammal localities based on facies analysis and the distribution of the possibly burrowing mammaliaform docodon; a similar trend has been found for semiaquatic turtles and crocodyliforms (foster and mcmullen, 2017). the occurrence of dryolestes at como bluff in the east and the cmq in the west suggests at least some mammal taxa were broadly distributed during the depositional interval of the morrison formation, while others were local, reflecting heterogeneous depositional environments or small temporal differences between localities. acknowledgments we would like to thank j. cohen (california state university, northridge, ca), j. frederickson (sam noble museum, norman, ok), s. madsen (salt lake city, ut), r. nydam (midwestern university, glendale, az), and g. wilbert (sam noble museum, norman, ok) for their help with field work. r. hunt-foster (blm, moab, ut) has been an invaluable resource for logistics. s. madsen mechanically prepared the braincase in figure 4, and j. cohen took the sem images. j. foster (museum of moab, moab, ut), n. kusuhashi (ehime university, matsuyama, japan), j. wible (carnegie museum of natural history, pittsburgh, pa), and an anonymous reviewer provided helpful comfigure 4. examples of high-quality preservation of small mammalian fossils from the cisco mammal quarry (omnh locality v1728, upper jurassic morrison formation, grand county, utah). (a, b) omnh 78599, undescribed partial skull of ?fruitafossor, preserving braincase and mesocranium in dorsal view, with interpretive illustration. (c) omnh 69352, undescribed morganucodontan left maxilla in lateral view (matrix on posterior portion digitally darkened). abbreviations: eo = exoccipital; fadm = foramen for arteria diploëtica magna; fm = foramen magnum; fns = frontonasal suture; fr = frontal; frt = foramen for ramus temporalis; lc = lambdoidal crest; naf = facet for nasal (missing); oc = occipital condyle; pa = parietal; pe = petrosal; ?so = supraoccipital; ?ip = interparietal. scale bar applies to both specimens. 8 a preliminary report of the fossil mammals from a new microvertebrate locality in the upper jurassic morrison formation, grand county, utah davis, b.m., cifelli, r.l., and rougier, g.w. geology of the intermountain west 2018 volume 5 ments on the manuscript. partial support for this project was provided by canyonlands natural history association discovery pool grants (#16-03-blm and #17-03-blm). fieldwork was conducted under permits issued by the utah geological survey and with permission from the utah school and institutional trust lands administration. references ameghino, f., 1889, contribución al conocimiento de los mamíferos fósiles de la república argentina: actas de la academía nacional de ciencias de córdoba, v. 6, p. 1–1027. butler, p.m., 1939, the teeth of the jurassic mammals: proceedings of the zoological society of london, v. 109, p. 329–356. callison, g., 1987, fruita—a place for wee fossils, in averett, w.r., editor, paleontology and geology of the dinosaur triangle: grand junction, colorado, museum of western colorado guidebook, p. 91–96. cope, e.d., 1884, the tertiary marsupialia: american naturalist, v. 18, p. 686–697. engelmann, g.f., and callison, g., 1999, glirodon grandis, a new multituberculate mammal from the upper jurassic morrison formation, in gillette, d.d., editor, vertebrate paleontology in utah: utah geological survey miscellaneous publication 99-1, p. 161–177. foster, j.r., 2001, taphonomy and paleoecology of a microvertebrate assemblage from the morrison formation (upper jurassic) of the black hills, crook county, wyoming: brigham young university geology studies, v. 46, p. 13–33. foster, j.r., 2003, paleoecological analysis of the vertebrate fauna of the morrison formation (upper jurassic), rocky mountain region, u.s.a.: new mexico museum of natural history and science bulletin, v. 23, p. 1–95. foster, j.r., and mcmullen, s.k., 2017, paleobiogeographic distribution of testudinata and neosuchian crocodyliformes in the morrison formation (upper jurassic) of north america—evidence of habitat zonation?: palaeogeography, palaeoclimatology, palaeoecology, v. 468, p. 208–215. foster, j.r., trujillo, k.c., madsen, s.k., and martin, j.e., 2006, the late jurassic mammal docodon, from the morrison formation of the black hills, wyoming—implications for abundance and biogeography of the genus: new mexcio museum of natural history and science bulletin, v. 36, p. 165–169. kielan-jaworowska, z., cifelli, r.l., and luo, z-x., 2004, mammals from the age of dinosaurs—origins, evolution, and structure: new york, columbia university press, 630 p. kirkland, j.i., 2006, fruita palaeontological area (upper jurassic, morrison formation), western colorado—an example of terrestrial taphofacies analysis: new mexico museum of natural history and science bulletin, v. 36, p. 67–95. kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r., 2017, the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata: geology of the intermountain west, v. 3, p. 101–228. linnaeus, c., 1758, systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. vol. 1—regnum animale. editio decima, reformata: stockholm, laurentii salvii, 824 p. luo, z.x., and wible, j.r., 2005, a late jurassic digging mammal and early mammalian diversification: science, v. 308, p. 103– 107. marsh, o.c., 1878, fossil mammal from the jurassic of the rocky mountains: american journal of science, v. 15, p. 459. marsh, o.c., 1879, notice of new jurassic mammals: american journal of science, v. 20, p. 396–398. marsh, o.c., 1881, notice of new jurassic mammals: american journal of science, v. 21, p. 511–513. martin, t., 1999, dryolestidae (dryolestoidea, mammalia) aus dem oberen jura von portugal: abhandlungen der senckenbergischen naturforschenden gesellschaft, v. 550, p. 1–119. osborn, h.f., 1888, on the structure and classification of the mesozoic mammalia: journal of the academy of natural sciences philadelphia, v. 9, p. 186–265. prothero, d.r., 1981, new jurassic mammals from como bluff, wyoming, and the interrelationships of non-tribosphenic theria: bulletin of the american museum of natural history, v. 167, p. 277–326. simpson, g.g., 1929, american mesozoic mammalia: memoirs of the peabody museum, v. 3, p. 1–235. trujillo, k.c., and kowallis, b., 2015, recalibrated 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a: geology of the intermountain west, v. 2, p. 1–8. turner, c.e., and peterson, f., 2004, reconstruction of the upper jurassic morrison formation extinct ecosystem—a synthesis: sedimentary geology, v. 167, p. 309–355. recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. geology of the intermountain west an open-access journal of the utah geological association volume 2 2015 recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. kelli c. trujillo1, and bart j. kowallis2 1uinta paleontological associates, inc., laramie, wy 82070; kellitrujillo@icloud.com 2department of geological sciences, brigham young university, provo, ut 84602; bkowallis@byu.edu © 2015 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. www.utahgeology.org editors douglas a. sprinkel utah geological survey 801.391.1977 dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net production cover design and desktop publishing douglas a. sprinkel cover photograph morrison formation near notom looking towards the east with the henry mountains in the far background. the upper salt wash and colorful brushy basin members of the morrison can be seen in the foreground with the cedar mountain formation and mancos shale above. the tidwell and lower salt wash members are not seen in the photo. photograph by bart j. kowallis. i 2015 president april abate aprilabate@utah.gov 801.538.5214 2015 president-elect jason blake blake-j@comcast.net 435.658.3423 2015 program chair mark milligan markmilligan@utah.gov 801.537.3326 2015 treasurer rebekah stimpson rwood@gmail.com 801.537.3378 2015 secretary jan morse janmorse@utah.gov 801.538.5327 2015 past-president grant willis grantwillis@utah.gov 801.537.3355 uga board uga committees education/scholarship matt affolter gfl247@yahoo.com 801.633.9396 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 sandy eldredge sandyeldredge@utah.gov 801.537.3325 publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 recruitment/outreach greg nielsen gnielsen@weber.edu 801.626.6394 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2014-2016 term tom morris tom_morris@byu.edu 801.422.3761 state mapping advisory committe uga representative terry massoth twmassoth@hotmail.com 801.422.3761 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 geology of the intermountain west an open-access journal of the utah geological association volume 2 2015 1 abstract as a result of recent updating of decay constants and standard ages used for 40ar/39ar dating, it is necessary to recalibrate legacy ages obtained with older methods. these recalibrations bring legacy 40ar/39ar ages into better agreement with ages obtained using 238u/206pb dating methods. we present nine recalibrated 40ar/39ar ages for the upper jurassic morrison formation of the western interior, u.s.a., along with the individual geographic and stratigraphic locations for each sample. these recalibrated ages will be useful for researchers looking to place better age constraints on the flora and fauna of the morrison formation, as well as for those working to understand stratigraphic relationships across the formation. the recalibrated ages also can now be used reliably for comparisons with newer 238u/206pb ages obtained for the morrison formation. recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. kelli c. trujillo1 and bart j. kowallis2 1uinta paleontological associates, inc., laramie, wy 82070; kellitrujillo@icloud.com 2department of geological sciences, brigham young university, provo, ut 84602; bkowallis@byu.edu trujillo, k.c, and kowallis, b.j., 2015, recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a.: geology of the intermountain west, v. 2, p. 1-8. © 2015 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the upper jurassic morrison formation is one of the most-studied rock units in north america. its vertebrate fauna includes fish, amphibians, reptiles, and mammals. dinosaurs from the morrison formation are exhibited in many museums worldwide and are among the best-known and loved dinosaurs in the public imagination. the morrison formation was deposited under terrestrial conditions, mainly on floodplains, in river channels, and in small lakes as well as small dune fields in some areas. the formation is exposed across the western interior of north america, and it is generally recognizable across this depositional area. in the areas of the northern colorado plateau where this study is focused, three formal members are recognized: the lower tidwell member, the middle salt wash member, and the upper brushy basin member. on the southern part of the colorado plateau other members are recognized in the lower parts of the formation, whereas in the northern and eastern parts of the depositional area no formal members are recognized (turner and peterson, 1999). correlations across this large area can be problematic due to discontinuous outcrops and the variable nature of the strata. as a result, radiometric ages are the best method for comparing the ages of disparate fossil localities (trujillo, 2006). as part of a long-term, multi-faceted study of the morrison formation, kowallis and others (1998) published nine 40ar/39ar ages from the morrison formation, as well as listing older 40ar/39ar and 40k/40ar ages previously obtained from these rocks. the ages reported geology of the intermountain west an open-access journal of the utah geological association volume 2 2015 www.utahgeology.org 2 recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. trujillo, k.c., and kowallis, b.j. geology of the intermountain west 2015 volume 2 in kowallis and others (1998) were obtained from sanidine crystals collected from presumed ashfall beds. all but one age was obtained from localities on the colorado plateau in eastern utah; the other age was obtained from a sample collected from south-central colorado, near cañon city. as these ages were the only existing radiometric ages with good resolution from the morrison formation, they have been used extensively in many different papers about various aspects of the formation (e.g., turner and peterson, 1999; foster, 2003). over the last decade, researchers have been working to bring the 40ar/39ar and 238u/206pb dating systems into better agreement with one another, with inter-calibration projects adding new data to our understanding of critical times in earth history (e.g., sageman and others, 2014). in addition, the 40ar/39ar system has undergone revisions to some of its major components. the age of the fish canyon tuff sanidine (fcs), one of the main fluence monitors (standards) used in 40ar/39ar dating, has been modified several times and discussions of its age are ongoing (e.g., renne, 2014; sageman and others, 2014). initially, the fcs was proposed as a standard with an age of 27.79 ma (millions of years before present) (cebula and others, 1986). this age was determined relative to the age of another standard, the mcclure mountain hornblende (mmhb-1). later, when the mmhb-1 age was revised upward, the fcs age was increased to 27.84 ma (samson and alexander, 1987). this age for the fcs was used until renne and others (1998) published an age of 28.02 ma for this standard, which they determined by comparison with another standard known as the ga1550 biotite. kuiper and others (2008) published a new fcs age based on inter-calibration with the astronomical time scale. this new, more precise age of 28.201 ± 0.046 ma also utilized a new decay constant (i.e., min and others, 2000), and researchers with the earthtime project (an international scientific initiative supported by the national science foundation; www. earth-time.org) voted to adopt this value for the fcs in future publications. renne and others (2010) then published new 40k decay constants that used an approach that was independent of astronomical dating and included data from both 40ar/39ar and 238u/206pb dating. these new constants resulted in an age for the fcs of 28.305 ± 0.036 ma (renne and others, 2010). not all workers agreed with these methods and results, however, and schwartz and others (2011) published a comment that questioned some of the methods used by renne and others (2010). as a result, renne and others (2011) published a reply in which they agreed with questions raised by schwartz and others (2011) about one aspect of their methods (the use of data from liquid scintillation counting techniques), and they removed this data from their calculations. this changed their age for the fcs to 28.294 ± 0.036 ma. even with this change, however, some workers (e.g., alexandre, 2011; meyers and others, 2012) have questioned aspects of renne and others (2010, 2011). most recently, sageman and others (2014) looked at three proposed sets of 40k total decay constants and associated ages for the fcs: from renne and others (1998), from kuiper and others (2008), and from renne and others (2010, 2011). they took seven cretaceous samples dated with both 238u/206pb and 40ar/39ar methods, and calculated new 40ar/39ar ages using the three different sets of decay constants and fcs ages. they concluded that in all seven pairs, using the fcs age of 28.201 ± 0.046 ma of kuiper and others (2008) gave the best agreement with the 238u/206pb ages. currently, the majority of 40ar/39ar researchers have adopted the astronomically calibrated age of the fcs of 28.201 ± 0.046 ma from kuiper and others (2008), as well as min and others (2000) 40k decay constant of 5.463 ± 0.107 x 10-10 (sageman and others, 2014). these new developments in 40ar/39ar dating methodology have led to the need to recalibrate the older, “legacy” ages for various samples dated by 40ar/39ar methods. recalibrated ages for samples from the morrison formation are reported here (figure 1; table 1), and it is our hope that researchers will use these ages in lieu of the previously published ages when referring to the age of the morrison formation. methods data from the original 40ar/39ar dating process (kowallis and others, 1998) was entered into a recalibration calculation spreadsheet created by n. mclean (university of kansas) and available on the earthtime website (www.earth-time.org). the decay constants, fluence monitor ages, and uncertainties used in the cal3 recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. trujillo, k.c., and kowallis, b.j. geology of the intermountain west 2015 volume 2 ? ? ? ? ~1 51 m a s c a le m et er s fe et 010203040 05 50 1015 c on gl om er at e s an ds to ne s ilt st on e n od ul ar c ar bo na te m ud dy c ar bo na te a lte re d vo lc an ic a sh m ud st on e li th ol og ie s s w el lin g cl ay s li ttl e c ed ar m tn (l c m ) brushy basin member c ed ar m ou nt ai n fo rm at io n 39 ° 12 " 0 2' n , 1 10 ° 29 ' 4 5" w e m er y c ou nt y, u t salt wash member lc m -1 15 2. 14 ±0 .5 1 m a lc m -3 9 15 0. 00 ±0 .5 2 m a r ai nb ow d ra w (r a in ) u in ta h c ou nt y, u t 40 ° 33 ' 3 0' ' n , 1 09 ° 11 ' 3 6" w ti dw el l m br .salt wash member r a in -1 32 54+ 4 15 6. 84 ±0 .5 9 m a brushy basin member c ed ar m ou nt ai n fo rm at io n n ot om (n tm ) brushy basin member salt wash member ti dw el l m br . c ed ar m ou nt ai n fo rm at io n 38 ° 16 ' 4 4" n ,1 11 ° 07 ' 3 5" w w ay ne c ou nt y, u t n tm -1 31 91 15 6. 77 ±0 .5 5 m a n tm -1 7 15 1. 23 ±0 .5 4 m a s um m er vi lle f or m at io n j5 un co nf or m ity b ur ro c an yo n fo rm at io n m on te zu m a c re ek (m c ) s an j ua n c ou nt y, u t 37 ° 19 ' 1 5" n , 1 09 ° 26 ' 2 6" w salt wash member m c -5 2 15 1. 34 ±0 .5 4 m a m c -3 9 14 9. 74 ±0 .6 4 m a brushy basin member d in os au r q ua rr y w es t ( d q w ) r ed w at er m em be r s tu m p fo rm at io n w in dy h ill m em be r of s un da nc e fo rm at io n j5 un co nf or m ity u in ta h c ou nt y, u t 40 ° 26 ' 2 0" n 1 09 ° 17 ' 4 0" w ti dw el l m br .salt wash member d q w -2 1 15 0. 91 ±0 .4 3 m a brushy basin member c ed ar m ou nt ai n fo rm at io n morrison formation ly tle f m . g ar de n pa rk (g p) fr em on t c ou nt y, c o 3 8° 3 2' 3 9" n ,1 05 ° 11 ' 5 2" w b el l r an ch fm . morrison fm., undifferentiaed g p13 46 -2 8+ 23 15 2. 29 ±0 .2 7 m a id u t w y n e k s n m a z o k d q w & r a in lc m n t m m c g p c o t x fi gu re 1 . r ec al ib ra te d 40 ar /39 ar a ge s f ro m th e m or ri so n fo rm at io n, p la ce d on to lo ca l s tra tig ra ph ic se ct io ns w he re sa m pl es w er e co lle ct ed . st ra tig ra ph ic se ct io ns lo os ely co rr ela te d ba se d on 40 ar /39 ar a ge s t ha t a re w ith in a na ly tic al er ro r o f e ac h ot he r ( bl ue d as he d lin es ). o ra ng e d as he d lin e s ho w s a n es tim at e of th e pl ac em en t o f 1 51 m a tim eli ne b as ed o n str at ig ra ph ic po sit io ns o f 40 ar /39 ar a ge s. s am pl e ar ea s s ho w n on in se t m ap . n ot om se ct io n fro m k ow al lis an d h ea to n (1 98 7) ; l itt le ce da r m tn ., d in os au r q ua rr y w es t, an d m on te zu m a cr ee k se ct io ns m ea su re d by c .e . t ur ne r a nd f . p et er so n, u .s . g eo lo gi ca l su rv ey , w rit te n co m m un ica tio n (1 98 8) ; r ai nb ow d ra w se ct io n fro m t ur ne r a nd p et er so n (1 99 9) ; g ar de n pa rk se ct io n m ea su re d by f . p et er so n, u .s . g eo lo gi ca l s ur ve y, w rit te n co m m un ica tio n (1 99 1) . 4 recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. trujillo, k.c., and kowallis, b.j. geology of the intermountain west 2015 volume 2 sample name published age (1 error with error in j) recalibrated age internal 1 internal + std internal + std + strat. level of sample sample area county state lat. lcm-39 148.07±0.51 150.00 ±0.52 ± 0.53 ± 2.99 104.5 m above base of brushy basin mbr. little cedar mtn emery ut dqw-21 148.97±0.42 150.91 ±0.43 ± 0.44 ± 2.99 55.4 m above base of brushy basin mbr. dinosaur quarry west/douglass draw uintah ut mc-52 149.39±0.53 151.34 ±0.54 ± 0.55 ± 3.01 63.5 m above base of brushy basin mbr. montezuma creek san juan ut ntm-17 149.29±0.52 151.23 ±0.54 ± 0.54 ± 3.01 48.5 m above base of brushy basin mbr. notom wayne ut mc-39 147.82±0.63 149.74 ±0.64 ± 0.65 ± 3.00 51 m above base of brushy basin mbr. montezuma creek san juan ut lcm-1 150.18±0.5 152.14 ±0.51 ± 0.52 ± 3.02 3.8 m above base of brushy basin mbr. little cedar mtn emery ut gp-1346-28+23 150.33±0.27 152.29 ±0.27 ± 0.30 ± 3.00 56 m above base of fm. garden park fremont co ntm-1319-1 154.75±0.54 156.77 ±0.55 ± 0.56 ± 3.12 2.4 m above base of tidwell mbr. notom wayne ut rain-1325-4+4 154.82±0.58 156.84 ±0.59 ± 0.60 ± 3.13 2.7 m above base of fm. rainbow draw uintah ut converted age uncertainties location of top of section long. location of top of section table 1. recalibrated ages in ma for samples from the upper jurassic morrison formation, dated by single-crystal 40ar/39ar laser fusion methods. geographic and stratigraphic information from kowallis and others (1998). see table 2 for details on recalibrations. all samples processed at the berkeley geochronological center. culations are listed in table 2, as are the legacy age data used such as the j value (a parameter associated with the irradiation of 39k to create 39ar) for each sample and their uncertainties. it should be noted that although we chose the age for the fcs of 28.201 ± 0.046 ma from kuiper and others (2008) and the 40k decay constant of 5.463 ± 0.107 x 10-10 from min and others (2000) as discussed above, because of ongoing discussions and research on these topics other workers may chose to use different values (e.g., irmis and others, 2013). the practical differences in the recalibrated ages are small (0.03% in the case of irmis and others, 2013), however, regardless of which values are used. discussion the recalibrated 40ar/39ar ages for nine samples from the morrison formation reported here (figure 1; table 1) are useful for researchers looking to place better age constraints on the flora and fauna of the morrison formation, as well as for those working to understand the stratigraphic relationships across the formation. they are also now more useful for comparisons with newer 238u/206pb ages that have recently been published (kowallis and others, 2007; bradshaw and kowallis, 2009; trujillo and others, 2006, 2008, 2014; trujillo and chamberlain, 2013). it should be noted, however, that comparing ages obtained by 40ar/39ar and 238u/206pb methods is not simply a case of looking at the numbers. two potential issues regarding the uncertainties in ages must be addressed. first, there are differences in the ways that uncertainties are reported between the 40ar/39ar and 238u/206pb systems. with 40ar/39ar ages, the convention is to report the uncertainty in the ages as 1-sigma, while 238u/206pb ages are almost always reported with 2-sigma uncertainties. workers should be aware of this difference, as it may result in misunderstood comparisons between ages obtained with the two different systems. second, although recalibrated 40ar/39ar ages are 5 recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. trujillo, k.c., and kowallis, b.j. geology of the intermountain west 2015 volume 2 now in much better agreement with 238u/206pb ages overall, attention needs to be paid to the uncertainties propagated by recalibration when comparing ages obtained by the different methods. for this study, in tables 1 and 2 the first uncertainty given (converted age uncertainties, internal 1σ column) is the uncertainty involved in the analysis itself. this is the uncertainty that should be used when comparing recalibrated 40ar/39ar ages obtained by the same lab (berkeley geochronological center) using the same methods, standards, and decay constants. in the data reported here, this is the uncertainty that should be used when only these reported recalibrated ages are of interest. the second uncertainty given in tables 1 and 2 (converted age uncertainties, internal + standard column) includes the analytical uncertainty as well as the uncertainty in the age of the fluence monitor (standard, the fish canyon tuff sanidine in this case). this is the uncertainty that should be used when comparing recalibrated 40ar/39ar ages from different labs or when different fluence monitors are used. the final, largest uncertainty given in tables 1 and 2 (converted age uncertainties, internal + standard + λ column) includes the analytical uncertainty, the uncertainty in the age of the fluence monitor, and the uncertainty in the decay constant. this is the uncertainty that should be used when comparing ages obtained by 40ar/39ar methods with those obtained by 238u/206pb methods. the size of this largest uncertainty is disconcerting, as with a range of approximately 6 million years it spans much of the understood depositional time of the entire morrison formation. as a result, it would seem that using the new recalibrated legacy 40ar/39ar ages along with new 238u/206pb ages obtained for the morrison formation could be fraught with error. the importance of this uncertainty to the practical use of these ages is unclear at present. without more data, it is difficult to make this determination; however, two of the localities where legacy 40ar/39ar ages were obtained from the morrison formation at notom, utah, have also been dated using 238u/206pb methods (kowallis and others, 2007; bradshaw and kowallis, 2010). if we look at the recalibrated 40ar/39ar ages without taking the uncertainties into account, they are in very close agreement with the 238u/206pb ages for these same localities (figure 2). these preliminary data suggest that although the uncertainties are large when comparing ages obtained by the two different dating systems, the data themselves may still be useful. old 5.543e-10 ( age of standard, old 27.84 (age of fish canyon tuff sanidine standard from renne and others, 1998) new 5.463e-10 ± 1.07e-11 /yr, 1 ( = decay constant, from min and others, 2000) age of standard, new 28.201 ± 0.023 ma, 1 (age of fish canyon tuff sanidine standard from kuiper and others, 2008) input legacy data age: legacy data age sample age, old (ma) sample age, new (ma) relative change 1 internal j value j 1 unct. internal internal + standard internal + standard + lcm-39 148.07 150.00 1.29% ± 0.51 0.03801 ± 0.00013 ± 0.52 ± 0.53 ± 2.99 dqw-21 148.97 150.91 1.29% ± 0.42 0.01067 ± 0.00003 ± 0.43 ± 0.44 ± 2.99 mc-52 149.39 151.34 1.29% ± 0.53 0.03832 ± 0.00013 ± 0.54 ± 0.55 ± 3.01 ntm-17 149.29 151.23 1.29% ± 0.52 0.03824 ± 0.00013 ± 0.53 ± 0.54 ± 3.01 mc-39 147.82 149.74 1.29% ± 0.63 0.03823 ± 0.00013 ± 0.64 ± 0.65 ± 3.00 lcm-1 150.18 152.14 1.29% ± 0.5 0.03816 ± 0.00013 ± 0.51 ± 0.52 ± 3.02 gp-1346-28+23 150.33 152.29 1.29% ± 0.27 0.01674 ± 0.00001 ± 0.27 ± 0.30 ± 3.00 ntm-1319-1 154.75 156.77 1.29% ± 0.54 0.03793 ± 0.00013 ± 0.55 ± 0.56 ± 3.12 rain-1325-4+4 154.82 156.84 1.29% ± 0.58 0.03811 ± 0.00013 ± 0.59 ± 0.60 ± 3.13 decay constant and standard age used for conversion: /yr ma sample name (in stratigraphic order) output input for error propagation: legacy data j decay constant and standard age used for legacy data: input for all samples output (all 1 absolute) converted age uncertainties:converted age: table 2. data and calculations used for recalibrations of legacy 40ar/39ar data from the upper jurassic morrison formation. sample data from kowallis and others (1995, 1998). results calculated using spreadsheet developed by n. mclean (university of kansas), available at www.earth-time.org. 6 recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. trujillo, k.c., and kowallis, b.j. geology of the intermountain west 2015 volume 2 summary the recalibration of these legacy 40ar/39ar ages from the upper jurassic morrison formation adds new useful data for researchers interested in this widespread rock unit. along with these ages, additional radiometric ages from other geographic areas across the depositional area of the formation will help in decoding the temntm-17 151.2 ± 1.8 ma u/ pb la-icp age 157.2 ± 1.9 ma 151.23 ± 3.01 ma ar/ ar age 156.77 ± 3.12 ma notom (ntm) b ru sh y b as in m em be r s al t w as h m em be r tidwell member cedar mountain formation 38° 16' 44" n,111° 07' 35" w wayne county, ut 40 39 206238 u/ pb la-icp agear/ ar age40 39 206238 ntm-1319-1 ntm_2 ntm_17 m o r r is o n f o r m a ti o n summerville formation j-5 unconformity conglomerate sandstone siltstone nodular carbonate muddy carbonate altered volcanic ash mudstone lithologies scale meters feet0 10 20 30 40 0 5 50 10 15 figure 2. comparison of 40ar/39ar and 238u/206pb ages on samples from the same localities at notom, utah. 40ar/39ar ages shown with analytical uncertainty, uncertainty in fluence monitor, and uncertainty in decay constant included. see figure 1 for location of section. section from kowallis and heaton (1987). 7 recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. trujillo, k.c., and kowallis, b.j. geology of the intermountain west 2015 volume 2 poral relationships among the floras and faunas. techniques for isolating and analyzing very small crystals continue to improve, and more radiometric ages from the morrison formation are forthcoming. in addition, dating of more samples by both 40ar/39ar and 238u/206pb methods would help in determining how much emphasis to place on the high uncertainties when comparing ages obtained by the two dating methods. acknowledgments we thank noah mclean (university of kansas) and john foster (museum of moab) for helpful discussions. reviews from d. sprinkel and t. chidsey (utah geological survey) and m. heizler (new mexico tech) improved the manuscript. references alexandre, p., 2011, comparison between grain size and multi-mineral 40ar/39ar thermochronology: geochimica et cosmochimica acta, v. 75, p. 4260–4272. bradshaw, r.w., and kowallis, b.j., 2010, u-pb dating of zircons from the salt wash member of the morrison formation from near capital reef national park, utah [abs.]: geological society of america abstracts with programs, v. 42, no. 3, p. 11. cebula, g.t., kunk, m.j., mehnert, h.h., naeser, c.w., obradovich, j.d., and sutter, j.f., 1986, the fish canyon tuff, a potential standard for the 40ar/39ar and fission-track dating methods [abs.], in sixth international conference on geochronology, cosmochronology and isotope geology: cambridge, united kingdom, european union of geosciences, terra cognita, v. 6, p. 139–140. foster, j.r., 2003, paleoecological analysis of the vertebrate fauna of the morrison formation (upper jurassic), rocky mountain region, u.s.a: new mexico museum of natural history and science bulletin, v. 23, 95 p. irmis, r.b., nesbitt, s.j, and sues, h., 2013, early crocodylomorpha, in nesbitt, s.j., desojo, j.b., and irmis, r.b., editors, anatomy, phylogeny and palaeobiology of early archosaurs and their kin: geological society of london special publications 379, p. 275–302. kowallis, b.j., britt, b.b., greenhalgh, b.w., and sprinkel, d.a., 2007, new u-pb zircon ages from an ash bed in the brushy basin member of the morrison formation near hanksville, utah, in willis, g.c., hylland, m.d., clark, d.l., and chidsey, t.c., jr., editors, central utah—diverse geology of a dynamic landscape: utah geological association publication 36, p. 75–80. kowallis, b.j., and heaton, j.s., 1987, fission-track dating of bentonitic mudstones from the morrison formation in central utah: geology, v. 15, no. 12, p. 1138–1142. kowallis, b.j., christiansen, e.h., deino, a.l., kunk, m.j., and heaman, l.m., 1995, age of the cenomanian-turonian boundary in the western interior of the united states: cretaceous research, v. 16, p. 109–129. kowallis, b.j., christiansen, e.h., deino, a.l., peterson, f., turner, c.e., kunk, m.j., and obradovich, j.d., 1998, the age of the morrison formation: modern geology, v. 22, p. 235–260. kuiper, k.f., deino, a.l., hilgen, f.j., krijgsman, w., renne, p.r., and wijbrans, j.r., 2008, synchronizing the rock clocks of earth history: science, v. 320, p. 500–504. meyers, s.r., siewert, s.e., singer, b.s., sageman, b.b., condon, d.j., obradovich, j.d., jicha, b.r., and sawyer, d.a., 2012, intercalibration of radioisotopic and astrochronologic time scales for the cenomanian–turonian boundary interval, western interior basin, usa: geology, v. 40, p. 7–10. min, k., mundil, r., renne, p.r., and ludwig, k.r., 2000, a test for systematic errors in 40ar/39ar geochronology through comparison with u-pb analysis of a 1.1 ga rhyolite: geochimica et cosmochimica acta, v. 64, p. 73–98. renne, p.r., 2014, some footnotes on the optimization-based calibration of the 40ar/39ar system, in jourdan, f., mark, d.f., and verati, c., editors, advances in 40ar/39ar dating—from archaeology to planetary sciences: geological society of london special publications, v. 398, p. 21–31. renne, p.r., balco, g., mundil, r., and min, k., 2011, 8 recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a. trujillo, k.c., and kowallis, b.j. geology of the intermountain west 2015 volume 2 response to the comments by w.h. schwarz and others, on “joint determination of 40k decay constants and 40ar*/40k for the fish canyon sanidine standard, and improved accuracy for 40ar/39ar geochronology” by p.r. renne and others (2010): geochimica et cosmochimica acta, v. 75, p. 5097–5100. renne, p.r., mundil, r., balco, g., min, k., and ludwig, k.r., 2010, joint determination of 40k decay constants and 40ar*/40k for the fish canyon sanidine standard, and improved accuracy for 40ar/39ar geochronology: geochimica et cosmochimica acta, v. 74, p. 5349–5367. renne, p.r., swisher, c.c., deino, a.l., karner, d.b., owens, t.l., and depaolo, d.j., 1998, intercalibration of standards, absolute ages and uncertainties in 40ar/39ar dating: chemical geology, v. 145, p. 117–152. sageman, b.b., singer, b.s., meyers, s.r., siewert, s.e., walaszczyk, i., condon, d.j., jicha, b.r., obradovich, j.d., and sawyer, d.a., 2014, integrating 40ar/39ar, u-pb, and astronomical clocks in the cretaceous niobrara formation, western interior basin, usa: geological society of america bulletin, v. 126, p. 956–973. samson, s.d., and alexander, e.c., 1987, calibration of the interlaboratory 40ar/39ar dating standard, mmhb1: chemical geology, v. 66, p. 27–34. schwarz, w.h., kossert, k., trieloff, m., and hopp, j., 2011, comment on the “joint determination of 40k decay constants and 40ar*/40k for the fish canyon sanidine standard, and improved accuracy for 40ar/39ar geochronology” by paul r. renne and others (2010): geochimica et cosmochimica acta, v. 75, p. 5094–5096. steiger, r.h., and jäger, e., 1977, subcommission on geochronology—convention on the use of decay constants in geoand cosmochronology: earth and planetary science letters, v. 36, p. 359–362. trujillo, k.c., 2006, clay mineralogy of the morrison formation and its use in long-distance correlation and paleoenvironmental analyses, in foster, j.r., and lucas, s.g., editors, paleontology and geology of the upper jurassic morrison formation: new mexico museum of natural history and science bulletin 36, p. 17–24. trujillo, k.c., and chamberlain, k.r., 2013, the morrison formation u/pb dating project—using high precision, chemical abrasion (ca-tims), single-zircon, ashfall dates for chronostratigraphic correlations [abs.]: journal of vertebrate paleontology, program and abstracts, p. 227. trujillo, k.c., foster, j.r., hunt-foster, r.k., and chamberlain, k.r., 2014, a u/pb age for the mygattmoore quarry, upper jurassic morrison formation, mesa county, colorado: volumina jurassica, v. 12, p. 107–114. trujillo, k.c., chamberlain, k.r., and bilbey, s.a., 2008, u/pb age for a pipeline dinosaur site—new techniques and stratigraphic challenges [abs.]: geological society of america abstracts with programs, v. 40, p. 42. trujillo, k.c., chamberlain, k.r., and strickland, a., 2006, oxfordian u/pb ages from shrimp analysis for the upper jurassic morrison formation of southeastern wyoming with implications for biostratigraphic correlations [abs.]: geological society of america abstracts with programs, v. 38, p. 7. turner, c.e., and peterson, f., 1999, biostratigraphy of dinosaurs in the upper jurassic morrison formation of the western interior, u.s.a., in gillette, d.d., editor, vertebrate paleontology of utah: utah geological survey miscellaneous publication 99-1, p. 77–114. the upper jurassic morrison formation in north-central new mexico–linking colorado plateau geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. the upper jurassic morrison formation in north-central new mexico—linking colorado plateau stratigraphy to the stratigraphy of the high plains spencer g. lucas theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view of upper part of morrison formation at hub canyon near lamy in santa fe county, new mexico. pale green sandstone ledge in the foreground is salt wash member overlain by greenish slopes of mudrock-dominated brushy basin member capped by white-colored jackpile member at top of morrison formation. the cretaceous dakota sandstone rests disconformably on the jackpile member and is seen as a brown sandstone at the top of the outcrop. photograph by spencer g. lucas. i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott ekeller@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — museum of moab cary woodruff — university of toronto octavio mateus — universidade nova de lisboa editors geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 117 abstract most study of the upper jurassic morrison formation has focused on its spectacular and extensive outcrops on the southern colorado plateau. nevertheless, outcrops of the morrison formation extend far off the colorado plateau, onto the southern high plains as far east as western oklahoma. outcrops of the morrison formation east of and along the eastern flank of the rio grande rift in north-central new mexico (sandoval, bernalillo, and santa fe counties) are geographically intermediate between the morrison formation outcrops on the southeastern colorado plateau in northwestern new mexico and on the southern high plains of eastern new mexico. previous lithostratigraphic correlations between the colorado plateau and high plains morrison formation outcrops using the north-central new mexico sections encompassed a geographic gap in outcrop data of about 100 km. new data on previously unstudied morrison formation outcrops at placitas in sandoval county and south of lamy in santa fe county reduce that gap and significantly add to stratigraphic coverage. at placitas, the morrison formation is about 141 m thick, in the lamy area it is about 232 m thick, and, at both locations, it consists of the (ascending) sandstone-dominated salt wash member, mudstone-dominated brushy basin member, and sandstone-dominated jackpile member. correlation of morrison strata across northern new mexico documents the continuity of the morrison depositional systems from the colorado plateau eastward onto the southern high plains. along this transect, there is significant stratigraphic relief on the base of the salt wash member (j-5 unconformity), the base of the jackpile member, and the base of the cretaceous strata that overlie the morrison formation (k unconformity). salt wash member deposition was generally by easterly-flowing rivers, and this river system continued well east of the colorado plateau. the continuity of the brushy basin member, and its characteristic zeolite-rich clay facies, onto the high plains suggests that localized depositional models (e.g., “lake t’oo’dichi’) need to be re-evaluated. instead, envisioning brushy basin member deposition on a vast muddy floodplain, with some localized lacustrine and palustrine depocenters, better interprets its distribution and facies. the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains spencer g. lucas new mexico museum of natural history, 1801 mountain road n. w., albuquerque, nm 87104, usa; spencer. lucas@state.nm.us citation for this article. lucas, s.g., 2018, the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains: geology of the intermountain west, v. 5, p. 117–129. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction jurassic strata of the morrison formation exposed in north-central new mexico provide an important link between two extensive morrison outcrop belts. to the west, morrison strata of the southern colorado plateau have been studied intensively, particularly because of the uranium resources they contain (e.g., kirk and condon, 1986; turner-peterson and others, 1986; anderson and lucas, 1997). to the east, on the southern high plains, the morrison strata have not received such intensive study, but are clearly genetically related to morrison strata on the southern colorado plateau (e.g., lucas and others, 1985; lucas and woodward, 2001). 118 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 here, i review the morrison formation stratigraphy along a transect from the southern colorado plateau to the southern high plains in north-central new mexico (figure 1). my goal is to correlate the morrison formation strata between san ysidro on the eastern colorado plateau edge, and at romeroville on the western edge of the southern high plains. this correlation has important implications for the extent and nature of morrison unconformities, lithofacies and depositional systems. lucas and anderson (1998) reviewed jurassic stratigraphy in new mexico; the stratigraphic nomenclature they advocated is on the current geologic map of new mexico (nmbgmr, 2003) and is employed here. lucas and others (1999) and lucas and woodward (2001) presented recent reviews of jurassic stratigraphy along parts of the transect from the colorado plateau to the high plains. the oldest cretaceous strata above the jurassic section are referred to the dakota sandstone/formation in north-central new mexico, though alternative names have been proposed elsewhere that may provide more appropriate nomenclature for this lithostratigraphic unit (e.g., mateer, 1987; carpenter, 2014). i can add new data here in the form of morrison formation stratigraphy at placitas in sandoval county (figure 2) and on the san cristobal ranch near lamy in santa fe county (figures 3 to 6) that fill important gaps in earlier coverage of the regional morrison formation lithostratigraphy (figures 1 and 7). stratigraphic sections introduction the correlation presented here is of six surface stratigraphic sections and one well log across an about 141 km transect of northern new mexico (figures 1 and 7). four of these morrison sections and the well log have already been described in detail (see lucas and others, 1999 and references cited therein and below), so they are only briefly reviewed here. two of the surface sections of the morrison formation (placitas, san cristobal ranch) have not been described previously, so they are new data presented here. san ysidro section anderson and lucas (1996; also see woodward, 1987) reviewed jurassic stratigraphy along the southeastern edge of the colorado plateau in the vicinity of san ysidro. the jurassic section there is approxifigure 1. map of part of north-central new mexico, showing locations of the jurassic sections discussed in this article. all sections are in shown in figure 7; the detailed section at placitas is in figure 2; and the detailed sections on the san cristobal ranch are in figures 4 and 5. 119 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 figure 2. stratigraphic sections of jurassic strata measured at placitas, sandoval county, new mexico. a, b, c and d are four overlapping sections measured on different fault blocks, and the column on the right is the composite jurassic section. locations of sections (gps coordinates are utm meters, zone 13, datum nad 27). (a) base of section is located at 367734e, 3906520n, top at 367750e, 3906646n; (b) base of section is located at 366918e, 3906929n, top at 367034e, 3907157n; (c) base of section is located at 369914e, 3907759n, top at 369933e, 3907813n; and (d) section is located at 366307e, 3907103n. member-level stratigraphic nomenclature of the entrada sandstone is based on lucas and heckert (2003). 120 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 mately 300 m thick and is assigned to the (ascending) entrada, todilto, summerville, and morrison formations (figure 7). the morrison formation consists of the salt wash, brushy basin, and jackpile members. the salt wash member is up to 36 m thick and consists mostly of pale yellow, trough cross-bedded, fine to coarse-grained sandstone with chert-pebble conglomeratic zones (mainly in the basal part) interbedded with thinner units of siltstone and mudstone. the overlying brushy basin member is as much as 80 m thick and mostly variegated, smectitic mudstone, and contains a few beds of lenticular, fineand medium-grained sandstone. the jackpile member (owen and others, 1984) is as much as 60 m thick and is mostly pale yellow to white, kaolinitic sandstone with some green mudstone interbeds. the encinal canyon member of the dakota formation rests disconformably on the jackpile member at san ysidro (lucas and others, 1998). shell oil santa fe no. 1 from the jurassic outcrops on the eastern edge of the colorado plateau near san ysidro to jurassic outcrops on the eastern margins of the rio grande rift--at placitas, in the hagan basin and at galisteo dam—a distance of more than 50 km is covered by younger strata (figure 1). to aid in correlation across this gap, a subsurface section about midway between the colorado plateau edge and the sandia uplift along figure 3. overview photographs of morrison formation sections at hub canyon (a) and hub mesa (b). 121 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 the eastern boundary of the rio grande rift is the geophysical log of the shell oil santa fe #1 well in section 18, t. l3 n., r. 3 e. (figure 7). interpretation of this log by black and hiss (1974) and by lucas and others (1999) indicates that the well penetrated the entrada, todilto, summerville, and morrison formations in the subsurface. black and hiss (1974) assigned the 145 m (642 ft) of jurassic strata drilled by the well from 2210 to 2076 m (7252–6810 ft) to the morrison formation and atfigure 4. stratigraphic section of jurassic strata exposed at hub mesa on the san cristobal ranch, santa fe county, new mexico. location of section (gps coordinates are utm meters, zone 13, datum nad 83): base of section is located at 420858e, 3908188n, top at 420426e, 3908577n. 122 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 tempted no further subdivisions. however, lucas and others (1999) concluded that the 79-m-thick (260-ftthick) mudstone-dominated interval from 2106 to 2185 m (6910–7170 ft) is the brushy basin member. if the underlying 33 m (110 ft) of strata belong to the salt wash member (a thickness comparable to the outcrops at san ysidro), then the base of the salt wash corresponds to the base of a prominent sandstone at 2220 m (7280 ft) (figure 7). all of the sandstone strata from 2106 to 2075 m (6910 to 6810 ft), about 31 m (about 102 ft), are assigned to the jackpile member of the morrison formation, though it is possible that a few meters of sandstone at the base of the cretaceous dakota sandstone is included in this sandstone interval (figure 7). placitas placitas is located at the northern end of the sandia mountains in sandoval county (figure 1). here, jurassic strata are exposed on fault blocks at the northern end of the sandia uplift. most of the published information on the jurassic section at placitas is on geologic maps (kelley and northrop, 1975; menne, 1999; connell and others, 1995). in 2000, a complete jurassic section was measured as four overlapping sections on different fault blocks (figure 2). anderson and lucas (2000), in an abfigure 5. stratigraphic section of the morrison formation at hub canyon on the san cristobal ranch, santa fe county, new mexico. location of section (gps coordinates are utm meters, zone 13, datum nad 83). base of section is located at 419981e, 3910395n, top at 419527e, 3911025n. 123 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 stract, briefly reported on this section, which consists of the (ascending) entrada, todilto, summerville, and morrison formations. at placitas, the basal member of the morrison formation, the salt wash member, is as much as 71 m thick and consists of fineto coarse-grained, feldspathic sandstone, with pebbly (conglomeratic) zones as much as several meters thick. in addition to the pebbly beds, other distinguishing features are trough cross-bedding, presence of clay clasts (rip-ups) and nonmarine bioturbation. the overlying brushy basin member is as much as 49 m thick and consists of greenish, mostly smectitic claystone with thin interbeds of dark-weathering, finegrained sandstone and nodular limestone. the uppermost member of the morrison formation, the jackpile member, is as much as 21 m thick locally and consists of trough and planar cross-bedded kaolinitic sandstone. the cretaceous oak canyon member of the dakota sandstone (cretaceous) unconformably overlies the jackpile member at placitas. hagan basin lucas and others (1995a) described in detail the figure 6. photographs of selected outcrops of the morrison formation in the hub canyon section. (a) cross-bedded sandstone in the salt wash member (figure 5, unit 13). (b) dinosaur limb-bone fragment in conglomeratic sandstone of the salt wash member (figure 5, unit 23). (c) silica-pebble conglomerate of the jackpile member (figure 5, unit 51). (d) contact of jackpile member with overlying basal sandstone of the oak canyon member of the dakota sandstone (figure 5, units 63 and 64). 124 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 jurassic section exposed in the hagan basin (figure 1). the entire jurassic section here is as much as 440 m thick and consists of the entrada, todilto, summerville, and morrison formations. in the hagan basin, the salt wash member of the morrison formation disconformably overlies the summerville and is as much as 75 m of mostly grayish-yellow sheets of fluvial sandstone and conglomerate with some interbeds of olive and brown mudstone. the salt wash member grades upward into and intertongues with the brushy basin member of the morrison formation, as much as 128 m of mostly variegated olive, gray, and brown bentonitic mudstone/siltstone. the jackpile member of the morrison formation disconformably overlies the brushy basin member and figure 7. lithostratigraphic correlation of jurassic sections from san ysidro on the southeastern edge of the colorado plateau to romeroville, on the western edge of the southern high plains, a transect of about 141 km. for location of sections see figure 1. 125 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 is as much as 62 m of mostly light gray and pale orange, trough-cross bedded kaolinitic sandstone. cretaceous strata of the dakota sandstone (encinal or oak canyon members) disconformably overlie the jackpile member in the hagan basin (lucas and others, 1998). galisteo dam the jurassic section at galisteo dam (figure 1) is assigned to the (ascending) entrada, todilto, summerville, and morrison formations (lucas and others, 1999). at galisteo dam, the salt wash member is 113 m thick and mostly consists of laterally extensive beds of yellow, gray, and brown arkosic sandstone and conglomerate. green bentonitic mudstone lenses and beds appear in the upper half of the member and support the idea that the salt wash member grades upward into the brushy basin member. at galisteo dam, the first laterally extensive, thick (9 to 10 m) bed of variegated green and brown smectitic mudstone is the base of the brushy basin member, which is nearly 82 m thick. this type of mudstone is the dominant lithology of the brushy basin member locally, which forms a gentle slope between the cliffor cuesta-forming salt wash and jackpile members. brushy basin sandstone beds form thin ledges in that slope and are mostly dark brown, massive, lithic subarkoses. these sandstone beds are less extensive laterally than are sandstone intervals in the salt wash member. the jackpile member is 77 m thick at galisteo dam. it is mostly yellowish-gray and very pale orange, trough cross-bedded, kaolinitic, subarkosic sandstone with some interbeds of greenish-colored sandy mudstone. the base of the dakota sandstone (oak canyon member; no encinal canyon member is present at galisteo dam: lucas and others, 1998) is a prominent disconformity at which clayey, carbonaceous litharenite of the dakota sandstone rests directly on kaolinitic subarkose of the jackpile member. san cristobal ranch south of lamy, the san cristobal ranch is a large holding of patented land that encompasses most of the old san cristobal land grant (figure 1). this land was largely inaccessible to geologists until the current owner of the ranch purchased it in 1985. thus, the only information on the jurassic stratigraphy of the san cristobal ranch previously published was geological mapping by read and others (1944). i measured two sections of jurassic strata on the san cristobal ranch, at hub mesa and at hub canyon (figures 3 to 6). the outcrops at hub mesa expose the entire local jurassic section below the morrison formation (entrada, todilto, and summerville formations; lucas and cather, 2004) overlain by a nearly complete section of the salt wash member of the morrison formation (figure 4). at hub canyon, a complete section of the morrison formation is exposed, between the underlying jurassic summerville formation and below the overlying cretaceous dakota sandstone (figure 5). at hub mesa, the salt wash member of the morrison formation is about 90 m thick, but this is an incomplete section of the unit (figure 4). however, the top of the salt wash member should be a laterally persistent unit overlain by easily eroded brushy basin member mudstone. thus, the fact that the top of the hub canyon section is a mesa defended by salt wash sandstone beds (figure 3b) suggests that it may be very close to the top of the salt wash member. the salt wash member at hub mesa (figure 5) is about two-thirds sandstone (68% of the section) and almost one third mudstone (31%). conglomerate (1%) is a minor constituent of the measured section. most sandstone beds are subarkosic and have trough crossbeds, but laminar beds are also present. colors are mostly light gray, grayish yellow and yellowish brown. mudstone beds that are mostly reddish and less often greenish in color form slopes between sandstone benches. these mudstone beds are not the swelling, smectite-rich clays found higher in the section (see below). conglomerate beds are lenses in sandstone intervals of intraformational (mudstone, calcrete) rip-up clasts. at hub canyon (figure 5), the salt wash member is about 46 m thick. it is almost equally sandstone (46% of the section) and mudstone (49% of the section) with minor conglomerate (5%). most of the sandstone beds have trough cross-beds, and some are bioturbated. mudstone is mostly reddish colored with some greenish-colored bands. conglomerate beds are pebbly lenses of intraformational (mudstone) pebbles, except for 126 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 bed 15, which has extraformational siliceous pebbles. mudstone in the salt wash member does not swell on outcrop when wet. the brushy basin member at hub canyon is about 108 m thick. it is mostly mudstone (89% of the measured section) with a minor amount of sandstone (11%). mudstone colors are those characteristic of the brushy basin member regionally—pale green, grayish red, reddish, and salmon. the stratigraphically lowest clay that swells on outcrop with the addition of water is bed 39 (figure 5), and this apparently is what has been called the “clay line” in the morrison formation section, at which the mineralogy changes from dominantly illitic to smectitic clay. however, i note that trujillo (2006) pointed out that such outcrop observations can be misleading because smectitic clays with a high silt content may not swell when wet on outcrop. at hub canyon, the jackpile member is about 35 m thick. it is mostly sandstone (63% of the measured section), about one-quarter mudstone (27%), and about 10% conglomerate. sandstone is subarkosic and kaolinitic, and yellowish gray and white, as is characteristic of the jackpile member farther west. romeroville the jurassic section exposed at romeroville gap in san miguel county (figure 1) was most recently described by lucas and others (1995b, 1999). here, the jurassic section is approximately 85 m thick and is assigned to the entrada, todilto, summerville, and morrison formations (figure 7). lucas and others (1999) placed the base of the morrison formation at romeroville at a change from siltstone of the summerville formation to coarser, pebbly, trough cross-bedded sandstone that characterizes a 5-m-thick interval assigned to the salt wash member (figure 7). coarse grain size, the presence of clay clasts, and yellowish-brown color characterize the salt wash sandstone interval at romeroville. bentonitic mudstone beds that are variegated brownish, greenish, and grayish dominate the overlying brushy basin member, which is 80 m thick. the lower cretaceous (upper albian) mesa rica sandstone of the dakota group rests disconformably on the brushy basin member at romeroville (lucas and others, 1998). lithostratigraphic correlation correlation of jurassic strata across the northern rio grande rift (figure 7) is a straightforward one based on lithostratigraphy. thickness variation of the units in part reflects unconformities or facies changes and is discussed below. no paleontological control of the correlation is available, there are no radioisotopic ages from the sections, and magnetostratigraphy is only available for the romeroville section (steiner and others, 1994). thus, the correlation presented here is purely lithostratigraphic, matching the member-level lithosomes across the transect (figures 7 and 8). some implications the correlation presented here of morrison strata across northern new mexico improves our understanding of the nature and extent of regional jurassic unconformities, and of deposition in the jurassic paleobasin. it documents the continuity of the morrison depositional systems from the colorado plateau eastward onto the southern high plains. the base of the salt wash member of the morrison formation is here considered to be the regional j-5 unconformity (anderson and lucas, 1995, 1998; lucas and anderson, 1998). the varied thickness changes in the salt wash member evident across northern new mexico (figures 7 and 8) likely reflect paleotopography that developed during the hiatus preceding morrison deposition. indeed, the thickness trends of the salt wash member across northern new mexico may identify a large paleovalley in the hagan basin-galisteo dam-san cristobal ranch area that was filled during early salt wash member deposition (figure 8). jurassic strata in northern new mexico are overlain by cretaceous strata at what pipiringos and o’sullivan (1978) termed the k unconformity. these are strata of the dakota group (formation, sandstone) of late albian or middle cenomanian age (lucas and others, 1998). this unconformity (which represents as much as a 50 million-year-long hiatus) has substantial stratigraphic relief on top of the morrison formation, and the disappearance of the jackpile member between the san cris127 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 tobal ranch and romeroville may in large part be due to erosion at this unconformity (figure 8). the base of the jackpile member also has substantial stratigraphic relief on top of the brushy basin member (figure 8). this suggests that the regional (confined to northern new mexico) low sinuosity river system that deposited the jackpile member (e.g., schlee and moench, 1961; moench and schlee, 1967; flesch, 1974; owen and others, 1984) was either (1) incised into the extensive muddy floodplain deposits of the brushy basin member, or (2) there is a hiatus between the brushy basin and jackpile members during which an incised topography developed through erosion, to be later filled during jackpile deposition. unfortunately, there is insufficient age control on the jackpile member with which to evaluate these alternatives. reconstructions of morrison depositional systems in the southern western interior have largely been confined to the colorado plateau (e.g., peterson, 1994). these studies do not include the morrison strata on the southern high plains, and therefore do not encompass the southern or the eastern portion of the morrison paleobasin. thus, it is clear that salt wash member deposition was generally by easterly-flowing rivers (craig and others, 1955; peterson, 1994; anderson and lucas, 1997), but this river system continued well east of the colorado plateau, and did not simply end in mudflats and dunes on the colorado plateau as depicted by peterson (1994, figure 20). salt wash rivers flowed generally from west to east across the morrison depositional basin, and clastic input to and subsidence of the basin was highly asymmetrical, with the greatest accumulations of salt wash member in the western part of the basin (e.g., craig and others, 1955; anderson and lucas, 1997). continuity of the brushy basin member off the colorado plateau onto the high plains also has particular significance for interpretation of depositional systems. turner and fishman (1991) argued that brushy basin member deposition took place in a large, semi-arid lake centered in the four corners area with a maximum northwest-southeast dimension of 500 km. however, brushy basin member outcrops off the colorado plateau were not included in this lake system, which was termed “lake t’oo’dichi’” by turner and fishman (1991). dunagan and turner (2004) later revised this interpretation to recognize an extensive wetland (palustrine depositional system) instead of a lake centered in the four corners area. however, the continuity of the brushy basin member, and its characteristic zeolite-rich clay facies, onto the high plains suggests that these localized depositional models need to be re-evaluated. instead, brushy basin member deposition on a vast muddy floodplain, with some localized lacustrine and palustrine depocenters, better encompasses the distribution and facies of the brushy basin member (e.g., anderson and lucas, 1997; galli, 2003, 2014; tanner and others, 2014). morrison depositional systems encompassed a significant area east of the colorado plateau and need to be interpreted across their entire outcrop area. figure 8. restored cross section of morrison formation from san ysidro on the southeastern edge of the colorado plateau to romeroville, on the western edge of the southern high plains, a transect of about 141 km. for location of sections see figure 1. datum is base of brushy basin member. j-5 and k unconformities are indicated on the right side of the diagram. 128 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 acknowledgments orin anderson was instrumental in the fieldwork to obtain the stratigraphic data presented here. john estep, jess hunley and clarence pigman assisted in the field. will singleton granted access to the san cristobal ranch, and wesley layman facilitated fieldwork there. john foster, ken galli, and kelli trujillo provided helpful reviews of the manuscript. references anderson, o.j., and lucas, s.g., 1995, base of the morrison formation, upper jurassic, of northwestern new mexico and adjacent areas: new mexico geology, v. 17, p. 44–53. anderson, o.j., and lucas, s.g., 1996, stratigraphy and depositional environments of middle and upper jurassic rocks, southeastern san juan basin, new mexico: new mexico geological society guidebook 47, p. 205–210. anderson, o.j., and lucas, s.g., 1997, the upper jurassic morrison formation in the four corners region: new mexico geological society guidebook 48, p. 139–155. anderson, o.j., and lucas, s.g., 1998, redefinition of morrison formation (upper jurassic) and related san rafael group strata, southwestern u.s.: modern geology, v. 22, p. 39–69. anderson, o.j., and lucas, s.g., 2000, jurassic stratigraphy at placitas, new mexico and its regional significance [abs.]: geological society of america abstracts with programs, v. 32, no. 7, p. a-458. black, b.a., and hiss, w.l., 1974, structure and stratigraphy in the vicinity of the shell oil co. santa fe pacific no. 1 test well, southern sandoval county, new mexico: new mexico geological society guidebook 25, p. 365–370. carpenter, k., 2014, where the sea meets the land—the unresolved dakota problem in utah: utah geological association publication 43, p. 357–372. connell, s.d., cather, s.m., ilg, b., karlstrom, k.e., menne, b., picha, m., andronicus, c., read, a.s., bauer, p.w., and johnson, p.s., 1995, geology of the bernalillo and placitas quadrangles, sandoval county, new mexico: new mexico bureau of mines and mineral resources digital open-file of-gm-2 and ofgm-16, 1 plate, scale 1:24,000. craig, l.c., holmes, c.n., cadigan, r.a., freeman, v.l., mullens, t.e., and weir, g.w., 1955, stratigraphy of the morrison formation and related formations, colorado plateau region, a preliminary report: u.s. geological survey bulletin 1009-e, p. 125–168. dunagan, s.p., and turner, c. e., 2004, regional paleohydrologic and paleoclimatic settings of wetland/lacustrine depositional systems in the morrison formation (upper jurassic), western interior, usa: sedimentary geology, v. 167, p. 269–296. flesch, g.a., 1974, stratigraphy and sedimentology of the morrison formation (jurassic), ojito spring quadrangle, sandoval county, new mexico—a preliminary discussion: new mexico geological society guidebook 25, p.185–195. galli, k.g., 2003, sedimentology and petrology of the brushy basin member, morrison formation (late jurassic), western colorado: amherst, university of massachusetts, ph.d. dissertation, 402 p. galli, k.g., 2014, fluvial architecture analysis of the brushy basin member, morrison formation, western colorado: volumina jurassica, v. 12, p. 69–106. kelley, v.c., and northrop, s.a., 1975, geology of the sandia mountains and vicinity: new mexico bureau of mines and mineral resources memoir 29, 136 p. kirk, a.r. and condon, s.m., 1986, structurally controlled sediment distribution patterns in the jurassic morrison formation of northwestern new mexico and their relationship to uranium deposits, in peterson, j.a., editor, paleotectonics and sedimentation in the rocky mountain region, united states: american association of petroleum geologists memoir 41, p. 597–622. lucas, s.g., and anderson, o.j., 1998, jurassic stratigraphy and correlation in new mexico: new mexico geology, v. 20, p. 97–104. lucas, s.g., and cather, s.m., 2004, stratigraphy of the jurassic san rafael group along the picuris-pecos fault system, santa fe county, new mexico: new mexico geology, v. 26, p. 71. lucas, s.g., and heckert, a.b., 2003, jurassic stratigraphy in west-central new mexico: new mexico geological society guidebook 54, p. 289–301. lucas, s.g., and woodward, l.a., 2001, jurassic strata in east-central new mexico and their regional significance: new mexico geological society guidebook 52, p. 203–212 lucas, s.g., anderson, o.j., and estep, j.w., 1998, stratigraphy and correlation of middle cretaceous rocks (albian-cenomanian) from the colorado plateau to the southern high plains, north-central new mexico: new mexico museum of natural history and science bulletin 14, p. 57–66. lucas, s.g., anderson, o.j., and pigman, c., 1995a, jurassic stratigraphy in the hagan basin, north-central new mexico: new mexico geological society guidebook 46, p. 247–255. lucas, s.g., anderson, o.j., and steiner, m.b., 1995b, the jurassic section at romeroville, san miguel county, new mexico: new mexico geological society guidebook 46, p. 51–53. lucas, s.g., estep, j.w., and anderson, o.j., 1999, correlation of 129 the upper jurassic morrison formation in north-central new mexico–linking colorado plateau stratigraphy to the stratigraphy of the high plains lucas, s.g. geology of the intermountain west 2018 volume 5 jurassic strata from the colorado plateau to the high plains, across the rio grande rift, north-central new mexico: new mexico geological society guidebook 50, p. 317–326. lucas, s.g., kietzke, k.k., and hunt, a.p., 1985, the jurassic system in east -central new mexico: new mexico geological society guidebook 36, p. 213–242. mateer, n.j., 1987, the dakota group of northeastern new mexico and southern colorado: new mexico geological society guidebook 38, p. 223–236. menne, b., 1989, structure of the placitas area, northern sandia uplift, sandoval county, new mexico: albuquerque, university of new mexico, m.s. thesis, 163 p. moench, r.h., and schlee, j.s., 1967, geology and uranium deposits of the laguna district, new mexico: u.s. geological survey professional paper 519, 117 p. nmbgmr (new mexico bureau of geology and mineral resources), 2003, geologic map of new mexico: socorro, new mexico bureau of geology and mineral resources, 2 plates, scale 1:500,000. owen, d.e., watters, l.j., jr., and beck, r.g, 1984, the jackpile sandstone member of the morrison formation in west-central new mexico–a formal definition: new mexico geology, v. 6, p. 44–52. peterson, f., 1994, sand dunes, sabkhas, streams, and shallow seas—jurassic paleogeography in the southern part of the western interior basin, in caputo, m.v., peterson, j.a., and franczyk, k.j., editors, mesozoic systems of the rocky mountain region, usa: denver, rocky mountain section, sepm (society for sedimentary geology), p. 233–272. pipiringos, g.n., and o’sullivan, r.b., 1978, principal unconformities in triassic and jurassic rocks, western interior, u.s.—a preliminary survey: u.s. geological survey professional paper 1035a, 29 p. read, c.b., wilpolt, r.h., andrews, d.a., summerson, c.h., and wood, g.h., 1944, geologic map and stratigraphic sections of permian and pennsylvanian rocks of parts of san miguel, santa fe, sandoval, bernalillo, torrance, and valencia counties, north central new mexico: u.s. geological survey oil and gas investigations preliminary map om-21, 1 plate, scale 1:190,080. schlee, j.s., and moench, r.h., 1961, properties and genesis of “jackpile” sandstone, laguna, new mexico, in peterson, j.a., and osmond, j.c., editors, geometry of sandstone bodies: american association of petroleum geologists special publications 22, p. 134-150. steiner, m.b., lucas, s.g., and shoemaker, e.m., 1994, correlation and age of the upper jurassic morrison formation from magnetostratigraphic analysis, in caputo, m.v., peterson, j.a., and franczyk, k.j., editors, mesozoic systems of the rocky mountain region, usa: rocky mountain section, sepm (society for sedimentary geology, p. 315–330. tanner, l.h., galli, k.g., and lucas, s.g., 2014, pedogenic and lacustrine features of the brushy basin member of the upper jurassic morrison formation in western colorado—reassessing the paleoclimatic interpretations: volumina jurassica, v. 12, p. 115–130. trujillo, k.c., 2006, clay mineralogy of the morrison formation (upper jurassic-?lower cretaceous), and its use in long distance correlation and paleoenvironmental analyses: new mexico museum of natural history and science bulletin 36, p. 17–24. turner, c.e., and fishman, n.s., 1991, jurassic lake t’oo’dichi’—a large saline lake, morrison formation, eastern colorado plateau: geological society of america bulletin, v. 103, p. 538– 558. turner-peterson, c.e., santos, e.s., and fishman, n.s., editors, 1986, a basin analysis case study—the morrison formation grants uranium region new mexico: american association of petroleum geologists studies in geology 22, 391 p. woodward, l.a., 1987, geology and mineral resources of sierra nacimiento and vicinity, new mexico: new mexico bureau of mines and mineral resources memoir 42, 84 p. first unambiguous dinosaur specimen from the upper triassic chinle formation in utah geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 4 2017 © 2017 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. first unambiguous dinosaur specimen from the upper triassic chinle formation in utah xavier a. jenkins, john r. foster, and robert j. gay geology of the intermountain west an open-access journal of the utah geological association 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organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. a�liated with the american association of petroleum geologists. volume 4 2017 �is is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and �gures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com �omas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net editors geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 231 abstract triassic dinosaurs represent relatively rare but important components of terrestrial faunas across pangea. whereas this record has been well studied at various locales across the american west, there has been no previous systematic review of triassic material assigned to dinosauria from utah. here, we critically examine the published body fossil and footprint record of triassic dinosaurs from utah and revise their record from the state. in addition, we describe a sacrum from a locality within the upper triassic chinle formation of southeastern utah. �is specimen represents the only unambiguous triassic dinosaur body fossil from utah. mwc 5627 falls within the range of variation known for sacrum morphology from coelophysis bauri. based on a literature review and examination of specimens available to us, we restrict the triassic utah dinosaurian record to �eropoda from the chinle formation. preliminary reports of triassic dinosaurs from other clades and formations in utah are unsubstantiated. first unambiguous dinosaur specimen from the upper triassic chinle formation in utah xavier a. jenkins1, john r. foster2, and robert j. gay3 1college of liberal arts and sciences, arizona state university, tempe, az 85281; xavier.jenkins@asu.edu 2museum of moab, moab, ut 84532; director@moabmuseum.org 3colorado canyons association, grand junction, co 81501; rob@canyonsassociation.org citation for this article. jenkins, x.a., foster, j.r., and gay, r.j., 2017, first unambiguous dinosaur specimen from the upper triassic chinle formation in utah: geology of the intermountain west, v. 4, p. 231–242. © 2017 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction �eropod dinosaurs are an important but rare component in terrestrial faunas from the triassic of western north america (nesbitt and others, 2007). although several taxa have been identi�ed from new mexico, including coelophysis bauri (colbert, 1989; rinehart and others, 2009), gojirasaurus quayi (carpenter, 1997), chindesaurus bryansmalli (irmis and others, 2007), tawa hallae (nesbitt and others, 2009), and daemonosaurus chauliodus (sues and others, 2011), the surrounding continental deposits have produced little in the way of dinosaurian body fossils. in contrast, an apomorphy-based study by nesbitt and others (2007) examined all referred dinosaurs from the triassic of western north america and found only caseosaurus crosbyensis (long and murry, 1995) present in texas. �e same study found only two theropods, c. bryansmalli (long and murry, 1995) and a coelophysoid (padian, 1986) from arizona. nesbitt and others (2007) did not �nd references to triassic theropods in colorado and utah. unfortunately, that review did not assess reported dinosaurian remains from the four aces mine locality near the glen canyon national recreation area in southeastern utah (parrish, 1999) (�gure 1). in a related study, irmis and others (2007) found reports that described ornithischian dinosaurs from the triassic of north america had been misinterpreted, although this study also overlooked the parrish (1999) report from southeastern utah. various methods have been proposed to explain the distribution of dinosaurs in north america. �e www.utahgeology.org 232 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 current consensus is that the radiation of dinosauria across the globe was diachronous (nesbitt and others, 2009; irmis and others, 2011; kent and others, 2014; see ramezani and others, 2011, for a dissenting view). �e earliest records of all major dinosaurian clades came from southern pangaea in the carnian stage of the late triassic epoch, followed by later appearances in the norian and rhaetian stages in the north of the supercontinent (rauhut and hungerbühler, 2000; parker and martz, 2011). dinosaur body fossil remains from utah may help test some of these timelines and hypotheses by providing additional data on dinosaur distribution and the timing of this distribution. utah and western colorado have a rich record of vertebrate trace fossils from their triassic rocks, including many localities preserving grallator, an ichnotaxon traditionally identi�ed as pertaining to theropod dinosaurs (riggs, 1904; bunker, 1957; parrish and lockley, 1984; hamblin and foster, 2000; foster and others, 2001; gaston and others, 2003; santucci and others, 2006; hunt and lucas, 2007; martz and others, 2014), and some preserving the purported prosauropod track pseudotetrasauropus (lockley and hunt, 1995; foster and others, 2001). recent work by other authors has raised questions about the reliability of identifying dinosaurs from ichnological evidence alone (olsen and others, 1998; marsicano and others, 2007; brusatte and others, 2011; niedźwiedzki, and others, 2013; farlow and others, 2014). although a poposauroid footprint reconstruction based on an articulated specimen of poposaurus gracilis from the circle cli�s of southern utah (farlow and others, 2014) is somewhat similar to grallator, it is only so if the �rst digit never impressed. �ere are a number of grallator specimens from the chinle formation in utah and western colorado that look rather di�erent at least from hypothetical tracks of poposauroids, and the fact that the ichnogenus continues upward through the wingate, kayenta, and navajo formations (by which time poposauroids and other convergent non-dinosaurs were extinct) suggests that many tracks assigned to grallator (though not necessarily all) were likely made by theropods. �e dinosaurian a�nity of pseudotetrasauropus is perhaps a bit more tenuous, as the morphology of these tracks can overlap to some degree with those of several other tetradactyl ichnogenera attributed to non-dinosaurian archosaurs known from the late triassic (lucas and heckert, 2000). �us, the ichnological evidence for the presence of dinosaurs in what is now the state of utah during the triassic period is to some degree ambiguous. �ere may likely be many dinosaurian tracks among the specimens assigned to grallator and pseudotetrasauropus, but it is possible that some non-dinosaurian archosaurs made at least some of the tracks historically assigned to these ichnogenera from various localities, and distinguishing these will require more studies of non-dinosaurian taxa (e.g., farlow and others, 2014). since 2005, several discoveries have taken place in early mesozoic strata across the western united states that require us to revisit the triassic record of dinosauria from the state of utah. other workers have reported on the presence of well-preserved coelophysoid skeletons (chambers and others, 2011; britt and others, 2016) from the nugget sandstone in dinosaur nationfigure 1. map of utah's triassic dinosaur occurrences. cc = corral canyon, fa = four aces. 233 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 al monument. traditionally described as being early jurassic in age, the nugget has been attributed in later reports as being from the late triassic (sprinkel and others, 2011; engelmann and others, 2012; britt and others, 2015, 2016; irmis and others, 2015). although these specimens have not been formally described yet, we think the initial evidence, which remains unpublished but as been presented in poster and talk format previously, matches with a triassic age (shumway and others, 2016). additionally, a site near moab, utah, has yielded new remains that we refer here to theropod dinosaurs. �e specimen described here has come from the chinle formation and is thus unequivocally late triassic (norian-rhaetian) in age (martz and others, 2014 and references therein). �e purpose of the paper is to critically examine the published record of utah’s triassic dinosaur fossils and to determine whether previously described body fossils can con�dently be assigned to dinosauria based upon an apomorphic evaluation. additionally, we describe the �rst unambiguous dinosaur body fossil from the triassic of utah using an apomorphic framework. institutional abbreviations amnh – american museum of natural history, new york (usa); clmnh – cleveland museum of natural history, cleveland, ohio (usa); gr – ghost ranch ruth hall museum of paleontology, ghost ranch, new mexico (usa); mna – museum of northern arizona, flagsta�, arizona (usa); mwc – museums of western colorado, fruita, colorado (usa); nmmnh – new mexico museum of natural history and science, albuquerque, new mexico (usa); nmw – amgueddfa cymru-national museum wales; pvsj – instituto y museo de ciencias naturales, san juan (argentina); tmp – royal tyrrell museum, drumheller, alberta (canada); ucm – university of colorado museum, boulder, colorado (usa). study methods john foster and ray bley collected the sacrum (mwc 5627) in 2005, with locality data being on �le at the mwc’s dinosaur journey repository under bureau of land management (blm) permit ut-s-05-014. �e sacrum (mwc 5627) was collected from a boulder-size block of conglomerate that had fallen o� the outcrop from a bed at the base of the church rock member. �e sacrum was found in a small piece (less than than 25 cm) of conglomerate chiseled from the larger, fallen block as part of the standard �eld procedure for prospecting at this locality. specimen mwc 5627 was prepared over the years by various volunteers at mwc, where it had been damaged as the surrounding matrix was being removed. john foster and robert gay studied mwc 5627 in person. measurements were taken on the specimens using cra�sman model 40257 sliding metal calipers (precision = 0.05 mm). standard paleontological tools (dental tools, ice picks, and natural-bristle brushes) were used to collect all specimens. some of the comparisons between the specimens described here and other taxa were made using in-person examination of original specimens and casts; speci�cally for coelophysis bauri. for other taxa, relevant measurements were taken from the published scientific record. photographs for �gures were taken using a nikon d5100. computer tomography (ct) images of mwc 5627 were obtained at the family health west hospital in fruita, colorado, on february 11, 2016, using an optima ct scanner. speci�c kv values are reported in �gures obtained from ct imaging. ct data were digitally prepared using invesalius 3.0 (64-bit) to create the three-dimensional (3d) digital model of mwc 5627 using a 2186-3071 mask to initially isolate the bones in the digital matrix, then using �ne selection and deletion tools to remove high-density matrix returns from the ct data. sedlog was used to make the stratigraphic column and u.s. geological survey lithological patterns were used. all �gures were created in gimp 2.8.16. localities and geological setting �e corral canyon locality is north of moab, utah (�gure 1). �ere, the chinle formation consists of the lower kane springs beds of blakey and gubitosa (1983, 1984; martz and others, 2014, 2017) and the upper church rock member (stewart and others, 1972; matrtz and others, 2014, 2017) (�gure 2). �e bed, from where 234 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 block containing the sacrum (mwc 5627) broke o�, is at the base of the church rock member in the lower half of the 106-m-thick chinle section; approximately 43 m above the moenkopi-chinle contact and 63 m below the wingate sandstone (�gure 2). �ere are three conglomerate beds in the chinle formation at corral canyon (from ~3 m above the base of the formation to ~18 m below the top), at least two of which were observed to contain numerous teeth and bone fragments of mostly phytosaurs. �e chinle in the corral canyon area also contains abundant permineralized wood; archosaur tracks are found in relative abundance near the top of the formation near the contact with the wingate sandstone (personal observations of john foster and robert gay). to protect the locality of the sacrum, a stratigraphic section of the chinle formation from the general area is used here to illustrate the stratigraphy of the chinle in corral canyon (�gure 3), although this section is thinned in comparison to the specimen's section. systematic paleontology dinosauria owen, 1842; sensu baron and other, 2017 ornithoscelida baron and others, 2017 �eropoda marsh, 1881 neotheropoda bakker, 1986; sensu hendrickx and others, 2015 referred specimen: mwc 5627, sacrum consisting of two primordial sacrals, one inserted sacral, a dorsosacral, and a caudosacral as well as fragmentary neural arches. specimen mwc 5627 is a partial sacrum preserved in a 30-cm-size block of conglomerate (�gure 4). �e pebble to cobble conglomerate is comprised of well-cemented, sandstone matrix with chert and clay clasts. clast size ranges from 1 to 5 cm. �e sacrum consists of three well-preserved complete and two partial, lesswell-preserved, sacral vertebrae, exposed on their ventral and right lateral side. �ey contain impressions of some of the vertebrae, along with some minor bone fragments that do not provide any additional information about the sacrum itself. utilizing the ct data obtained, we digitally prepared mwc 5627 to attempt to better visualize the portion of the sacrum still within the matrix, although the dense nature of the matrix and the low power of the medical scanner, the resolution of the ct images were not high. �ese data were informative and are included as supplementary online materials. sacral vertebra 1 (sv1) is poorly preserved, although when �rst discovered it was much more complete. collection damage, along with some preparation damage, have made interpretation of this element di�cult. partial fusion between sacral vertebra 2 (sv2) and sv1 can be seen at two locations where sv1 remain; along the le� dorsolateral surface and again at the dorsal surface figure 2. partial stratigraphic column of the corral canyon locality, showing the location of mwc 5627 in relation to stratigraphic position. see key for sedimentological symbol details. scale in meters. �e complete stratigraphic column is attached and can be view by clicking here. 235 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 at the neural canal. �e neural spine is likewise mostly gone, possibly due to preparation damage. despite the damage, the centrum of sv1 is clearly hollow (�gure 4). sv2 is the �rst completely preserved vertebra in the sacral series. it is fused to the sacral vertebra posterior to it. it is incompletely fused to the sacral vertebra 3 (sv3). �e anterodorsal gap is 8 mm antero-posteriorly and 5 mm dorsoventrally, making it roughly ovoid in shape. of the four gaps found in mwc 5627 this is the best preserved. its relationship to the sheet of bone forming the lateral surface of the sv2/sv3 neural spines and sacral ribs is clear. it lies 4.5 mm posterior to the attachment of the sv2 sacral rib and 6 mm of fused neural spine are above its dorsal-most point. its posterior-most point is 1 cm anterior to the attachment of the sv3 sacral rib. sv2 itself is cracked and repaired, hollow, and has an overall broader appearance than the preceding sacral vertebrae. sv3 is completely fused on the exterior of its articular surfaces to both sv2 and sacral vertebra 4 (sv4). �e posterior gap above the centrum is 7.5 mm in length antero-posteriorly. a clear portion of bone is visible dorsal to the centrum, representing part of the neural spine, though it is not well de�ned in the ct data (online supplementary data). sv3 is broken along the right lateral surface, showing some of the hollow interior of the centrum. �e centrum being hollow is further supported by the ct data. sv4 is the largest and best preserved of the sacral vertebrae. it is 2.6 cm in length antero-posteriorly, as measured between the points of fusion along the articular surface on the right lateral surface. on the exposed figure 3. section of the chinle formation near corral canyon, grand county, utah, looking west. formation contacts are solid yellow lines; chinle members contact dashed. two lower arrows mark two of three conglomeratic beds in chinle; upper arrow with question mark shows approximate laterally equivalent level of top conglomeratic bed in corral canyon. although this is not the section from where the sacrum was collected, the red circle marks approximate stratigraphic position of mwc 5627 near base of middle conglomerate. scale bar = 12 m. 236 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 lateral surface, 5 mm posterior from the anterior articular surface and just ventral to the dorsal margin, there is a slight depression on the centrum. �is depression is 9 mm in length and 1 mm in depth at its deepest point. between the posterior articular surface and the attachment of the sacral rib, dorsal to the centrum, there is an 8.5-mm-long break or gap allowing access to the neural canal. �is has also been in�lled with matrix, but can be clearly seen with both visual (�gure 4) and ct imaging. �e tallest portion of the neural spine does not show up in the ct data. �e posterior articular surface is well fused around the rim, though ct data shows there to be some unfused portion within the center of the articulation, as between sv1/sv2 (�gure 4). �e anterior articular surface is 1.4 cm mediolaterally, as measured at the dorsoventral midpoint, and 1.3 cm dorsoventrally, as measured at the center of fusion between sv4 and sv3. sacral vertebra 5 (sv5) is the worst preserved vertebra in the sacrum. sv5 is present as an anterior articular surface in articulation with the adjoining sacral figure 4. mwc 5627 in le� lateral and ventral views. ld = lateral depression; ns = neural spine; pdg = posterior dorsal gap; sr = sacral ribs; sv = sacral vertebrae. scale bar = 1 cm. 237 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 vertebrae. �e articular surface is fused to sv4 around the rim of the articular surface, but exhibits incomplete fusion within the midpoint of this same surface. �is is visible in both examinations of the specimen itself as well as in ct images of mwc 5627 (�gure 4, online supplementary data). �e preserved portion of the centrum is broken in several places, with the hollows in�lled with a sand/clay matrix. �e remains of the sacral rib and neural spine are fused to those of sv4. overall the centra of mwc 5627 tend to be shallow ventrally with progressively narrowing midcentra posteriorly. �e neural arches are broad and become complex towards the caudal portion of the sacrum (though this may be a product of preservation). �e sacral rib attachments arise from the anterior portion of the centrum and posterior-most section of the preceding sacrum, almost obscuring the articular surface, especially moving posteriorly. �e preserved sacral ribs are antero-posteriorly elongate and laterally signi�cant (1.2 cm across for the sacral rib on sv4). as mentioned above, some of the anatomical features on the surface of the fossil, speci�cally the thin bony struts of the neural spines and sacral ribs, are not well resolved in the ct data. whereas the ct data do indicate that sv2–sv4 are relatively complete within the matrix, the adjoining neural spines and ribs are not likewise present. because of the fact that portions of these elements have been damaged during past physical preparation and that these elements are not visible in ct image; we have refrained from further physical preparation of mwc 5627 to avoid additional damage or loss of data. taxonomic affinities possessing �ve sacral vertebrae is generally considered a synapomorphy for neotheropoda (padian and others, 1999; sereno, 1999a, 1999b), though it is known that some basal ornithischians possess at least four and possibly �ve sacral vertebrae, as in the case of eocursor parvus (butler and others, 2007), and with heterodontosaurus having six (sereno, 2012). additionally, other archosaurs occasionally have four sacrals and a dorsosacral (nesbitt and others, 2007; nesbitt 2011). considering this, we restrict our comparisons to taxa with similar sacral vertebrae counts, but o�er some brief commentary on some taxa that still warrant consideration. coelophysis bauri is the most common late triassic dinosaur from north america. it has been described from new mexico (colbert, 1989; schwartz and gillette, 1994; rinehart and others, 2009). having one of the largest sample sizes of all theropod dinosaurs from the mesozoic era allows us to use a broad morphological dataset to compare against mwc 5627. coelophysis bauri specimens amnh 7228, amnh 7229, amnh 7245, clmnh 10971-d2, nmmnh p-42351, p-42353, and p-42580 (rinehart and others, 2009) all exhibit a morphology similar to mwc 5627 in that their sv4 and sv5 are not fused, and amnh 7233 exhibits only partial fusion of sv4 and sv 5. specimens amnh 7235, amnh 7243, amnh 7249, clmnh 10971-d10, nmmnh p-44802, tmp 84-63-34, and tmp 84-63-49, again from rinehart and others (2009), show sv4 and sv5 fully fused. �is suggests that fusion in the sacrum of coelophysoid theropods is variable and that an unfused or partially fused sv4/sv5, as seen in mwc 5627, does not preclude it from pertaining to a coelophysoid. coelophysoid sacral vertebrae are also ossi�ed into a ‘rod,’ with the centrum being obliterated, as present in mwc 5627. an additional coelophysoid sacrum (nmmnh p-31661) sheds light onto the a�nities of mwc 5627. illustrated by nesbitt (2011, �gure 29, p. 114), this sacrum shows the same broad, complex neural arches, shallow vertebral centra becoming dorsoventrally deep along the vertebral column, and high anteriorly situated attachments for the sacral ribs. mwc 5627 also shares with nmmnh 31661 several character states listed by nesbitt (2011) which di�erentiate the two from more primitive archosauriforms, including the absence of sacral centra articular rims. although not autapomorphic for the genus, these states are at least present in coelophysis, for example. �is contrasts with the other archosauriform sacra illustrated and described alongside nmmnh p-31661. specimen mwc 5627 is also visibly identical to nmmnh 31661. although most triassic archosaurs possess at least two sacral vertebrae, some members of the poposauridae have four or more (weinbaum and hungerbuhler, 238 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 2007; gauthier and others, 2011; gri�n and others, 2017). although the published descriptions of poposaurus sacra are severely limited, some comparisons are possible. in poposaurus, the �rst sacral vertebra is roughly half the antero-posterior length of the third and fourth sacrals. �e second sacral is roughly a third longer antero-posteriorally than the third or fourth sacral. in addition, only sv1-sv3 fuse, leaving sv4 unfused at the posterior end of the sacrum. �is di�ers from the condition seen in mwc 5627, where at least four sacral vertebrae are fused with the ��h, the posterior-most being partially fused. even if poposaurids exhibit di�ering levels of sacral fusion as does c. bauri, the comparative dimensions of the preserved vertebrae, seen most signi�cantly in sv2 of mwc 5627 and poposaurus specimen tmm-43683-1, rule out mwc 5627 as pertaining to poposaurids. furthermore, the poposaurus sacrum �gured in weinbaum and hungerbuhler (2007), shows additional di�erences in sacral vertebra morphology, with poposaurus sacral vertebrae being much more robust and with less mediolateral constriction in ventral view. shuvosaurus and e�gia have four sacral vertebrae plus a dorsosacral (nesbitt and others, 2007). in shuvosaurus, e�gia, and in many theropods, the centrum has been obliterated, leaving the sacral vertebrae fused into a ‘rod’ (nesbitt and others, 2007). �is ossi�cation is present in mwc 5627 and does not appear present in poposaurus specimen ypm vp.057100. herrerasaurids are known from the chinle formation in arizona and new mexico, speci�cally the taxon chindesaurus bryansmalli (long and murry, 1995; nesbitt and others, 2007, 2009). we have ruled out herrerasaurids in our comparative analysis as herrerasaurids possess only two sacral vertebrae (nesbitt and others, 2007). similarly, eoraptor lunensis, a triassic sauropodomorph from south america (sereno, 1999a), shows a reduced number of sacral vertebrae (3) and nesbitt and others (2009) reported that tawa hallae only possesses two sacrals. like e. lunensis, eodromaeus murphi only possessed three sacral vertebrae (martinez and others, 2011). although an actual number is not given for dracoraptor hanigani, the published record shows a minimum of two and possibly up to three sacrals were present (martill and others, 2016), with possibly more being unpreserved or described. silesaurus, a dinosauriform (dzik, 2003) has four sacral vertebrae. we, therefore, exclude all of these previously described basal theropods and dinosauriforms as pertaining to mwc 5627. although ornithischian dinosaurs are not currently recognized from the triassic of north america (irmis and others, 2007), it is possible that the sacrum of mwc 5627 could represent the �rst possible occurrence of this clade. �e ornithischian dinosaur eocursor parvus (butler and others, 2007) is described as having at least four, and possibly �ve, sacral vertebrae; a character shared with mwc 5627. �e sacral vertebrae are not preserved themselves, but instead are interpreted by the presence of neural arches lacking centra and sacral rib attachment scars. �is makes direct comparisons between mwc 5627 and e. parvus impossible at this time. out of all the possible taxa that preserve sacral vertebrae from the triassic of the western hemisphere, the only one that shares any number of signi�cant morphological features (such as the number of sacral vertebrae, roughly equal antero-posterior centra lengths, and fusion of the sacral vertebrae) with mwc 5627 are neotheropods. we hesitate to diagnose this sacrum to the speci�c level, as speci�c autapomorphies for coelophysis or other theropods are not present within the sacrum. nevertheless, the characteristics described above show that mwc 5627 is a neotheropod sacrum that shows signi�cant similarity in comparative dimensions and overall morphology to that of coelophysis, and we diagnosis it as a neotheropod. four aces mine specimens a study by parrish (1999) found the presence of possible theropod and ornithischian dinosaurs based on the presence of several incomplete ungual phalanges (ucm 76197), several caudal vertebrae (ucm 76198), and a fragmentary right mandible (ucm 76501) from the four aces mine locality near the mouth of white canyon (�gure 1). �e caudal vertebrae described by parrish (1999) were diagnostic based on the subhexagonal cross section in the vertebrae, which parrish (1999) claimed are diagnostic of c. bauri without supporting evidence. from examination of c. bauri specimens at 239 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 mna, grmp, and nmmnhs we do not agree that c. bauri can be diagnosed from a subhexagonal cross section of the caudal vertebrae (personal observation of robert gay) as the morphology exhibited in undisputed c. bauri specimens tends to be more box-like, a plesiomorphic condition within archosauria. based on this, we disagree that the vertebrae are truly diagnostic to �eropoda, or even of archosauria. as for the phalanges (ucm 76197) and the mandible (ucm 76501), both are too incomplete to be diagnostic. parrish (1999) indicates that most specimens are only possibly referable to �eropoda, and cannot be con�dently placed within this clade. considering the lack of synapomorphies present in the specimens described by parrish (1999), we disagree with the placement of the published four aces mine specimens in dinosauria. instead, these specimens are best considered archosauriformes incertae sedis until further work is conducted. in particular, ucm 76501 is of interest considering that since 1999, the ornithischian dinosaur record from the triassic has been substantially revised (irmis and others, 2007). results a critical review of the published literature on dinosaur remains from the state of utah has revealed that all previously described dinosaurian body fossils cannot con�dently be assigned to dinosauria. �e ichnofossil record of dinosauria is likely better but because of substrate variation, convergence in the foot, and lack of precise discriminate methods to di�erentiate between theropods and non-dinosaurian archosaurs we urge caution in interpreting footprints as unambiguously dinosaurian. a sacrum from the upper triassic chinle formation near moab possesses characters indicating a neotheropod origin and is referred to neotheropoda based on structural similarities and the morphology of the sacral vertebrae. �is specimen comprises the entirety of the body fossil record of dinosaurs from the triassic period in the state of utah currently. discussion �e triassic period, as preserved in the american west, has o�ered some of the most complete specimens of early dinosaurs ever found (colbert, 1989). despite this, dinosaur remains have proven to be rare outside of special preservational environments, like those found at ghost ranch, new mexico. �at so few specimens of con�rmed dinosaurs have been reported from the extensive outcrops of utah and arizona is surprising, but given the diversity of large carnivorous and herbivorous non-dinosaurian archosaurs during the late triassic, it may be that dinosaurs were indeed rare in most chinle environments. as utah sits today (as it would have during chinle depositional times) at a higher latitude than the extensive dinosaur-producing quarries of new mexico, these specimens further support previous hypotheses that dinosaur radiation was limited by many factors including increasing paleolatitude (irmis and others, 2011; whiteside and others, 2015). additional, more complete dinosaur specimens from utah’s triassic will help further support or disprove this idea. our con�rmation of late triassic dinosaurs in utah is based on rather fragmentary material, compared with known specimens from new mexico and arizona. �is may not be surprising, as few specimens of any identity are known from mudstone deposits in utah. only the comb ridge sites, indian creek, and some in the red canyon, that we are aware of, regularly produce vertebrate material from mudstone; very few identi�able archosaurian specimens from the moab or lisbon valley areas come from mudstones, and most originate in conglomeratic beds, though this is likely due to a sampling issue. �us, the sacrum described here from moab and numerous phytosaur skulls found in lisbon valley occur as isolated elements in conglomerates. �e fragmentary nature of the specimens from conglomerates at more northern sites probably relates to an overall sandier section comprising the chinle in those areas; comb ridge is more similar to sites in red canyon and arizona in having a higher percentage of mudstone (petri�ed forest member). as demonstrated by mwc 5627, a sacrum found in an area otherwise known for only very fragmentary vertebrate remains in the chinle, more complete material may eventually be found near moab or in lisbon valley or many other areas in the state. it is hoped that additional �eldwork in these areas will add to our understanding of early dinosaur radiation into the american southwest. 240 first unambiguous dinosaur specimen from the upper triassic chinle formation in utah jenkins, x.a., foster, j.r., and gay, r.j. geology of the intermountain west 2017 volume 4 acknowledgments fieldwork at comb ridge was supported by a grant from the canyonlands natural history association. we would like to thank rebecca hunt-foster (blm canyon country district, utah) for assisting with the permitting process. �anks to dinosaur journey volunteer ray bley (museums of western colorado), who found mwc 5627. for discussions about mwc 5627 we thank william parker (division of resource management, petri�ed forest national park, arizona). julia mchugh (museums of western colorado) provided access to specimens under her care. we would like to thank andrew r. c. milner (st. george dinosaur discovery site at johnson farm, city of st. george, utah) for his thoughts on the ichnological evidence presented in this paper. xj would like to thank madison dunbar (unaf�liated), cheyenne jenkins (una�liated), and alessandra jenkins (una�liated) for their assistance in proo�ng the manuscript. rg would like to extend his thanks to jen mccollough (el paso museum of archeology) and jessica uglesich (university of texas, san antonio) for their assistance on this project. special thanks to jim kirkland and doug 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plates, scale 1:2,500,000. sues, h.d., nesbitt, s.j., berman, d.s., and henrici, a.c., 2011, a late-surviving basal theropod dinosaur from the latest triassic of north america: proceedings of the royal society of london b: biological sciences, p.rspb20110410. weinbaum, j.c., and hungerbuhler, a., 2007, a revision of poposaurus gracilis (archosauria: suchia) based on two new specimens from the late triassic of the southwestern usa: paläontologische zeitschri�, v. 81, no. 2, p. 131–145. whiteside, j.h., lindström, s., irmis, r.b., glasspool, i.j., schaller, m.f., dunlavey, m., and turner, a.h., 2015, extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years: proceedings of the national academy of science, v. 112, p. 7909–7913, doi:10.1073/ pnas.1505252112. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. a photo documentation of bipedal ornithischian dinosaurs from the upper jurassic morrison formation, usa kenneth carpenter and peter m. galton theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 emanuel tschopp, daniel brinkman, jaime henderson, mary ann turner, and octávio mateus theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover caudal vertebral elements of the type specimen of diplodocus longus (ypm vp.001920). the letters indicate the vertebrae shown on figures 1 to 5. courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by jamie henderson. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net editors president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 245 abstract the sauropod dinosaur genus diplodocus marsh, 1878, is currently typified by a morphologically undiagnosable type species, d. longus marsh, 1878. only two caudal vertebrae and an associated partial chevron of its holotype (yale peabody museum [ypm] vp.001920) remain reasonably complete, but more, fragmentary caudal vertebrae are available, and provide additional morphological information. ypm vp.001920 can be referred to diplodocus generally, but cannot be distinguished from other diplodocus species based on autapomorphies. thus, the genus diplodocus would have to be considered a nomen dubium. in order to resolve this unsatisfactory taxonomic issue, tschopp and mateus (2016) proposed to designate a new type species for the genus diplodocus: namely, the well-known d. carnegii hatcher, 1901. herein, we expand upon historical and taxonomic issues concerning the holotype of d. longus, in order to: (1) provide additional imagery and information on the specimen and (2) to address comments against the replacement of d. longus by d. carnegii as the type species of diplodocus as proposed by tschopp and mateus (2016). considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 emanuel tschopp1, 2, 3, daniel brinkman4, jaime henderson4, mary ann turner4, and octávio mateus2,3 1american museum of natural history, division of paleontology, central park west at 79th street, new york, ny 10024, usa; tschopp.e@gmail.com 2museu da lourinhã, rua joão luís de moura 95, 2530-157 lourinhã, portugal 3geobiotec, faculdade de ciencias e tecnologia (fct), universidade nova de lisboa, caparica, portugal 4division of vertebrate paleontology, yale peabody museum of natural history, yale university, 170 whitney avenue, new haven, ct, 06511 usa citation for this article. tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o., 2018, considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878: geology of the intermountain west, v. 5, p. 245–262. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the sauropod diplodocus marsh, 1878, is one of the most famous dinosaurs from the upper jurassic morrison formation, and probably the most viewed dinosaur skeleton worldwide thanks, in part, to the widely-distributed sets of casts of the holotype of d. carnegii provided to museums around the globe by american steel magnate andrew carnegie (rea, 2004; otero and gasparini, 2014). however, its taxonomic history is problematic, being based on a very fragmentary and incomplete specimen (ypm vp.001920) from a multi-taxa bonebed near garden park, colorado (the marsh-felch quarry), which cannot be reasonably distinguished from any other specimen referred to the genus diplodocus (gilmore, 1932; tschopp and others, 2015; tschopp and mateus, 2016). other sauropod genera and species reported from the type locality include the diplodocids apatosaurus and galeamopus pabsti, the putative diplodocoids “morosaurus agilis” and haplocanthosau246 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 rus priscus, and the macronarians camarasaurus and brachiosaurus (evanoff and carpenter, 1998; mcintosh and carpenter, 1998; foster, 2003; tschopp and mateus, 2017). ypm vp.001920, the holotype of the type species of diplodocus, d. longus marsh, 1878, was briefly described by marsh (1878) and reassessed by mcintosh and carpenter (1998). doubts about its validity have previously been put forward by gilmore (1932) and tschopp and others (2015). based on these studies, tschopp and mateus (2016) formally proposed a case to the international commission on zoological nomenclature (iczn) to replace the type species d. longus with the much more complete and better known d. carnegii. to date, published comments on this case, iczn case 3700, have been mixed, with the case receiving three positive (lucas, 2017; taylor, 2017; woodruff, 2017), and three negative comments (carpenter, 2017; demirjian, 2017; mortimer, 2017). herein, we provide additional information and photographs of the most complete caudal vertebrae (figures 1 to 8) and of the associated partial chevron (figure 9) of the holotype specimen ypm vp.001920. these photographs were not published in the original case (tschopp and mateus, 2016) due to limited space and restrictions on the use of color. they show that the chevron has the anterior and posterior projections for which the genus was named (figure 9; diplodocus means “double beam”), whereas the fragmentary caudal vertebrae have strongly excavated ventral hollows (figures 1 and 3) and well-developed pneumatic foramina typical for diplodocus (figure 4). however, the photographs also further illustrate the very fragmentary nature of the specimen (figure 8), and, thus, the need for a new type species in diplodocus. we also expand upon the complicated curatorial history of the cataloged ypm sauropod specimens from garden park and we correct an error found in the initial proposal to the iczn by tschopp and mateus (2016). over the years, additional material from the type locality, either currently or previously stored in the ypm vp collections, was thought by one person or another to be attributable to d. longus, perhaps even to the type specimen itself (see mcintosh and carpenter, 1998; carpenter, 2017 for reviews). this additional material consists of two skulls (one of which had an associated atlas), a midto posterior cervical vertebra, part of a pelvis, and several foreand hindlimb elements (mcintosh and carpenter, 1998; carpenter, 2017). in many cases, it is unclear who attributed this material to d. longus or when, but, in some cases, the attributions go all the way back to othniel c. marsh, who appears to have relied heavily on the letters and diagrams of his collectors at garden park: benjamin f. mudge, samuel w. williston, and marshal p. felch (see mcintosh and carpenter, 1998; carpenter, 2017). however, mcintosh and carpenter (1998), in their revision of ypm vp.001920, restricted the holotype to the series of caudal vertebrae (figures 1 to 8) and an associated partial chevron (figure 9) because these were the bones on which the species d. longus was established by marsh (1878). in fact, much of the other ypm material attributed to this species (and, perhaps, even to the type specimen itself) has since been attributed to different taxa (see mcintosh and carpenter, 1998) and given different catalog numbers (i.e., ypm vp.001906, .001921x, .001922x, .004688, .004689, .059136, and .059137). some of these specimens have since been deaccessioned at the ypm and transferred to the smithsonian institution where they now bear united states national museum (usnm v) catalog numbers (e.g., the two skulls usnm v 2672 and 2673). however, those cataloged sauropod specimens from garden park that remain in the ypm vp collections are still stored, regardless of their current taxonomic identifications, near the restricted type so that the ypm can maintain the historic connections between these specimens. recently, carpenter (2017) backed away from his earlier attribution of many of these specimens to different taxa (mcintosh and carpenter, 1998), but did not provide any information on shared morphological features or otherwise unequivocal evidence to support an attribution to the same species, or even individual, as the type tail. below, we briefly discuss these additional referred specimens and we address the critiques of iczn case 3700 by carpenter (2017), demirjian (2017), and mortimer (2017). institutional abbreviations amnh farb, fossil amphibian, reptile, and bird collection, american museum of natural history, new york city, new york, usa; sma, sauriermuseum aath247 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 al, switzerland; usnm v, vertebrate paleobiology collection, united states national museum, washington d.c., usa; and ypm vp, vertebrate paleontology collection, yale peabody museum of natural history, new haven, connecticut, usa. previously cataloged ypm vp material attributed to diplodocus longus from the type locality below is a compilation of previously cataloged ypm material from the type locality that has been attributed to diplodocus longus in the past, and perhaps even to the type specimen itself. specimen ypm vp.001906 this specimen was mentioned by tschopp and mateus (2016), who erroneously stated that it includes a pes. as demonstrated by mcintosh and carpenter (1998), and correctly cited in tschopp and others (2015), ypm vp.001906 consists of a left ulna, radius, metacarpals i-v, and a single atrophied phalanx that is attached to metacarpal v. the metacarpals were figured as d. longus by marsh (1896) and all of the elements were illustrated by mcintosh and carpenter (1998, figure 3). the elements making up ypm vp.001906 were initially referred to “morosaurus,” but later assigned to d. longus by marsh himself (marsh, 1896; mcintosh figure 1. anterior to mid-caudal vertebra of the holotype specimen of diplodocus longus (ypm vp.001920, vertebra “f ” on figure 8), in dorsal (a), anterior (b), left lateral (c), posterior (d), right lateral (e), and ventral view (f). note the deep ventral hollow in the centrum (1). this is the most complete preserved element of the holotype. courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by jamie henderson. 248 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 and carpenter, 1998). mcintosh and carpenter (1998) excluded ypm vp.001906 from the holotype specimen based on its size relative to that of the femur (recently cataloged as part of ypm vp.059136) that was found in association with the type tail, though they did note that the two specimens (ypm vp.001906 and .001920) would have been from a similarly sized, if not the same individual of sauropod. however, sauropod forelimb material is difficult to identify to species, and only a few specimens clearly referable to diplodocus preserve an ulna or a radius, whereas none of them has a manus (bedell and trexler, 2005; e. tschopp, personal observations). based on morphology alone, it is therefore questionable if these bones can be attributed to d. longus, and because of the lack of comparative material in other species, it is unlikely that they would provide reliable autapomorphic features. although ypm vp.001906 is currently identified as diplodocus sp. in the ypm vp database, it could, according to mcintosh and carpenter (1998), possibly either belong with the type tail or be the partial forelimb of an immature apatosaurus (which included brontosaurus at the time; see tschopp and others, 2015) or, even, haplocanthosaurus. ypm vp.001906 differs from most apatosaurine specimens with a manus, which generally have a metacarpal i that is longer than the metacarpal iv (e.g., cm 3018, tate-001, uw 15556, but see nsmt-pv 20375; tschopp and others, 2015). on the other hand, it differs from diplodocines in the less developed distal expansion of the ulna. thus, while we can exclude an attribution to a macronarian saurofigure 2. anterior to mid-caudal vertebra of the holotype specimen of diplodocus longus (ypm vp.001920, vertebra “b1” on figure 8), in dorsal (a), anterior (b), left lateral (c), posterior (d), right lateral (e), and ventral view (f). note the transverse lamina connecting the two prezygapophyses (1). this is the second most complete preserved element of the holotype. courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by jamie henderson. 249 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 pod based on the relatively short metacarpals compared to the radius, it is currently impossible to provide any more detailed identification within diplodocoidea. specimen ypm vp.001921x (= usnm v 2672 + v 5368) this specimen consists of a skull with articulated lower jaws, and an associated atlas. these two specimens, together with a second, less well-preserved skull that was collected in 1884 (ypm vp.001922x), and accessioned together with a midto posterior cervical vertebra in january 1885 (i.e., a specimen received as part of ypm accession number 1738 but never cataloged by the ypm) were eventually transferred to the smithsonian institution where they now bear the catalog numbers usnm v 2672, 5368, 2673, and 4712, respectively (mcintosh and carpenter, 1998). usnm v 2672 was attributed to d. longus by marsh (1884), one year before usnm v 2673 was received at the ypm and referred to the same species without detailed description or illustration (mcintosh and carpenter, 1998). usnm v 2672, 4712, and 5368 were subsequently figured as d. longus by marsh (1896) and later by mcintosh and carpenter (1998), though the latter authors attributed usnm v 4712 to apatosaurus sp. although usnm v 2672 can most probably be referred to the genus diplodocus (evanoff and carpenter, 1998; mcintosh and carpenter, 1998; tschopp and others, 2015; carpenter, 2017), a definitive attribution figure 3. anterior to mid-caudal vertebra of the holotype specimen of diplodocus longus (ypm vp.001920, vertebra “b2” on figure 8), in dorsal (a), anterior (b), left lateral (c), posterior (d), right lateral (e), and ventral view (f). note the deep ventral hollow in the centrum (1). courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by jamie henderson. 250 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 to the holotype specimen of d. longus, or even the species, as purported by carpenter (2017) remains doubtful, and cannot be scientifically justified due to lack of a direct association with the type tail (which was some 15 m away and separated from it by a jumble of bones from multiple individuals; mcintosh and carpenter, 1998). according to evanoff and carpenter (1998), mcintosh and carpenter (1998), and carpenter (2017), usnm v 2673 also likely belongs to d. longus, whereas tschopp and mateus (2017) referred it to galeamopus pabsti, based on shared autapomorphic features with the holotype sma 0011. diplodocid skulls are generally very similar and are rarely found in articulation with the postcranial skeleton (whitlock and others, 2010; whitlock, 2011b), so that referrals to a species or even genus is very difficult and are tentative at best (tschopp and others, 2015). the atlas usnm v 5368 cannot be assigned to a specific genus of sauropod, but it clearly does not exhibit the specific features found in the atlases of g. hayi and g. pabsti (tschopp and others, 2015; tschopp and mateus, 2017), so an attribution to that genus is unlikely. the single, midto posterior cervical vertebra usnm v 4712 was assigned to brontosaurus by hatcher (1903) and to apatosaurus (then including brontosaurus) by mcintosh and carpenter (1998). several features including the strongly ventrolaterally projecting cervical ribs with a reduced anterior process, the absence of pneumatic foramina on the ventral surface, and the extended postzygapophyseal centrodiapophyseal fossa onto the posterior surface of the transverse figure 4. anterior to mid-caudal vertebra of the holotype specimen of diplodocus longus (ypm vp.001920, vertebra “d” on figure 8), in dorsal (a), anterior (b), left lateral (c), posterior (d), right lateral (e), and ventral view (f). note the deep pneumatic foramen on the lateral surface of the centrum, below the transverse process (1). courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by jamie henderson. 251 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 process, support a referral to apatosaurinae (tschopp and others, 2015). a referral to either apatosaurus or brontosaurus would require a more detailed study, which is not in the scope of this paper. specimen ypm vp.004688 this specimen consists of a right scapula, humerus, ulna, and radius. as with the other appendicular material and the beforementioned skulls, the lack of a direct association with the type tail and chevron precludes any unambiguous referral of the material to the holotype individual of d. longus. ypm vp.004688 is currently tentatively cataloged as ?haplocanthosaurus sp. in the ypm vp database. however, according to john (“jack”) s. mcintosh’s unpublished notebook (mcintosh, undated), it was thought at some point that an identification as haplocanthosaurus was likely for at least the humerus and radius, but that the scapula and ulna might be ?brachiosaurus. we add to this reassessment that the radius has a distinct medial projection on the proximal articular surface, resembling the condition in the brachiosaurids giraffatitan (janensch, 1961) and lusotitan (mannion and others, 2013). it is therefore possible that the entire foreleg belonged to a brachiosaurid. specimen ypm vp.004689 this specimen consists of a sacrum and right ilium. it has been figured by both marsh (1896) and mcintosh figure 5. anterior to mid-caudal vertebra of the type specimen of diplodocus longus (ypm vp.001920, vertebra “e” on figure 8), in dorsal (a), anterior (b), left lateral (c), posterior (d), right lateral (e), and ventral view (f). courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by jamie henderson. 252 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 and carpenter (1998). marsh (1896) referred these pelvic elements to d. longus, but they were reidentified by mcintosh and carpenter (1998) as apatosaurus sp. (or possibly brontosaurus, see above). there is some doubt as to whether or not these pelvic elements belong to the left hindlimb (recently cataloged as ypm vp.059136) that was mentioned by marsh (1878) in his original description of d. longus and by both mcintosh and carpenter (1998) and carpenter (2017). both specimens were thought to be apatosaurine by mcintosh and carpenter (1998) and, following mcintosh and carpenter (1998), they are currently identified as apatosaurus sp. in the ypm vp database. however, according to carpenter (2017) he and the late jack mcintosh now think that these pelvic and hindlimb elements are part of the holotype of d. longus as originally thought by marsh’s collectors at garden park: mudge, williston, and felch. until this new article by carpenter and mcintosh is published, it remains unclear based on what evidence they changed their opinion, and, consequently, ypm vp will refrain from changing the current taxonomic identifications of these pelvic and hindlimb elements in its database. recently cataloged ypm vp material attributed to diplodocus longus from the type locality below is a compilation of recently cataloged material from the type locality that has been attributed to d. longus in the past, perhaps even to the type specimen itself. as mentioned above, the caudal series (figures figure 6. anterior to mid-caudal vertebra of the type specimen of diplodocus longus (ypm vp.001920), in dorsal (a), left lateral (b), posterior (c), right lateral (d), and ventral view (e). the vertebra lacks the neural arch and parts of the centrum. courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by emanuel tschopp. 253 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 1 to 8) and associated partial chevron (figure 9) were the elements used by marsh (1878) to erect the new genus and species d. longus (see also mcintosh and carpenter, 1998). however, the section of the ypm vp collections containing ypm vp.001920 (and the other ypm specimens mentioned above) not only includes the caudal series and chevron of the restricted holotype (mcintosh and carpenter, 1998), but also includes a partial right pes that was recently cataloged as ypm vp.059137, the partial left hindlimb mentioned above (ypm vp.059136), and a partial right femur recently cataloged as ypm vp.060256. specimen ypm vp.059136 this specimen, which consists of a partial left hindlimb, is figured in mcintosh and carpenter (1998: figure 5). the long bones of ypm vp.059136 are badly crushed and consist of a left femur, fibula, tibia, and an attached astragalus, as well as some associated left pedal elements, including metatarsals that are shorter and more robust than the right metatarsals in ypm vp.059137 (see hatcher, 1901; mcintosh and carpenter, 1998; carpenter, 2017). unfortunately, the left pes elements, along with two unguals from a right pes and five other phalanges that were mentioned by mcintosh and carpenter (1998), were not seen during a recent reorganization/conservation project on the marsh dinosaur collection at the ypm and are presently considered to be missing. the left hindlimb of the specimen now cataloged as ypm vp.059136 was mentioned as being part of the holotype in the initial description by marsh (1878), but mcintosh and carpenter (1998) excluded the limb from the holotype, following an earlier suggestion by hatcher (1901: p. 55). no features diagnostic of the genus diplodocus were recognized in this hindlimb material by these authors or by us, though carpenter and mcintosh appear to have had second thoughts on this (see carpenter, 2017). to us, however, the robustness of these hindlimb elements (presumably including the currently unaccounted for left metatarsals mentioned by mcintosh and carpenter [1998]) indicate a referral to an apatosaurine (see mcintosh and carpenter, 1998), or possibly galeamopus, a diplodocine genus figure 7. anterior to mid-caudal vertebra of the type specimen of diplodocus longus (ypm vp.001920), in left lateral (a), posterior (b), and ventral view (c). we interpret this as the posterior end of the centrum, because of the presence of relatively well-developed eminences for the articulation with chevrons. courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by emanuel tschopp. 254 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 with similarly stout limbs as apatosaurines (tschopp and others, 2015; tschopp and mateus, 2017). therefore, following mcintosh and carpenter (1998), ypm vp.059136 is currently identified as apatosaurus sp. in the ypm vp database. specimen ypm vp.059137 this specimen, which consists of the right metatarsals i-v, was figured by mcintosh and carpenter (1998: figure 5) and was identified by them as possibly belonging to either haplocanthosaurus sp. or brachiosaurus, both of which are also known from other elements from the marsh-felch quarry no. 1 (foster, 2003). thus, ypm vp.059137 is currently recorded as an indeterminate sauropod in the ypm vp database. the close spatial proximity of these pes elements in the ypm vp collections to both the elements of the restricted holotype and to the elements constituting ypm vp.001906 was the reason for the erroneous statement by tschopp and mateus (2016) that specimen ypm vp.001906 included a pes. brachiosaurid pedes are identifiable, because the distal articular surface of the metatarsal iv is beveled compared to the long axis (d’emic, 2012; mannion and others, 2013; maltese and others, 2018). such a beveling is present in the metatarsal iv of ypm vp.059137, but no pedal material has ever been found articulated with a specimen clearly referable to brachiosaurus (maltese and others, in 2018), so that we herein refer ypm vp.059137 to brachiosauridae indet. specimen ypm vp.060256 three additional fragments present in the ypm colfigure 8. caudal vertebral elements of the type specimen of diplodocus longus (ypm vp.001920). the letters indicate the vertebrae shown on figures 1 to 5. courtesy of the division of vertebrate paleontology; ypm vp.001920, yale peabody museum of natural history, yale university, new haven, connecticut, usa; peabody.yale.edu. photography by jamie henderson. 255 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 lections are of a crushed right femur. these have never been mentioned or figured in any publication and have only recently been cataloged as apatosaurus sp. in the ypm vp database. only the distal portion provides some morphological information, and an indication of its robustness, which appears to be comparable to the robustness of the left femur of ypm vp.059136 mentioned above. we therefore tentatively attribute ypm vp.060256 to apatosaurinae indet. doubts raised on the iczn case autapomorphies mortimer (2017) correctly pointed out that the case of tschopp and mateus (2016) was mainly based on a single phylogenetic analysis (tschopp and others, 2015), which he argued did not include characters representing “every potential aspect of morphological variability” (mortimer, 2017: p. 129). therefore, according to mortimer (2017), the fact that the analysis of tschopp and others (2015) was not able to find autapomorphic features could not be taken as evidence for the type specimen ypm vp.001920 being morphologically undiagnosable. whereas we agree that a phylogenetic analysis based on morphological characters always only captures an incomplete picture of osteological features and their shapes, which is necessarily influenced by the researcher creating the matrix, we also note that the matrix used by tschopp and others (2015) was based on several previous analyses tailored to diplodocoid sauropods (e.g., whitlock, 2011a; carballido and others, 2012; mannion and others, 2012), and added many more characters based on the personal observations of e. tschopp in numerous collections, including the ypm’s. the final matrix analyzed in tschopp and others (2015) included 477 characters, of which 67 (14%) coded for features in the tail (i.e., caudal vertebrae and chevrons). due to the incompleteness of ypm vp.001920, this type specimen could only be scored for 19 of these characters. such an extensive matrix based on the work of a number of figure 9. right half of middle chevron of the holotype specimen of diplodocus longus (ypm vp.001920), in dorsal (a), anterior (b), left lateral (c), posterior (d), right lateral (e), and ventral view (f). courtesy of the division of vertebrate paleontology; ypm vp.001920, peabody museum of natural history, yale university, new haven, connecticut, usa; peabody. yale.edu. photography by jamie henderson. 256 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 researchers can be expected to cover the most significant morphological variability (especially taxonomically informative variation). moreover, the fact that ypm vp.001920 could only be scored for 4% of the characters highlights the very fragmentary state of this specimen, and the improbability of finding new, unique features to accurately diagnose the species. because the matrix of tschopp and others (2015) was designed to study the relations between specimens, and to assess intraspecific variation, it was specifically constructed to capture as much morphological variability as could be recognized, and also included potentially autapomorphic features, which is usually not the case in morphological phylogenetic analyses at species level. in fact, the transverse lamina behind the prezygapophyses found in both ypm vp.001920 (figure 2) and amnh farb 223 (tschopp and others, 2015; tschopp and mateus, 2016) was added as a character to the phylogenetic analysis after e. tschopp’s personal observations at the ypm. by including potentially autapomorphic features as phylogenetic characters, a specimen level analysis can serve as an objective test if they are found to be homologous (and thus of taxonomic importance; longrich, 2015; tschopp and others, 2015; tschopp and upchurch, in press), in particular when using a maximum parsimony criterion, which minimizes the amount of homoplasies during the tree search (farris, 1983). however, as pointed out by tschopp and mateus (2016), the analysis of tschopp and others (2015) could not confirm the lamina to be a phylogenetically informative, and, thus, a potentially diagnostic character for the species d. longus. therefore, we would strongly disagree with carpenter (2017) that an interpretation of this lamina as an autapomorphy of d. longus would be “more conservative” than the result of an extensive phylogenetic analysis (carpenter 2017: p. 48). mortimer (2017) also mentioned two features suggested by mcintosh and carpenter (1998) to be autapomorphic in ypm vp.001920: relatively short caudal centra, and pneumatic foramina that do not extend as far back in the tail as in other specimens of diplodocus. contrary to what mortimer (2017) implies in his comment, characters describing these features were included in the analysis of tschopp and others (2015; see characters 308, 309, 332). however, even if this would not have been the case, these proposed autapomorphies are questionable. the correct interpretation of both of these features depends on the position of the vertebrae in the caudal column. the elongation of the centrum increases considerably from anterior to mid-caudal centra in diplodocine sauropods, and characters describing this elongation have already been included in earlier phylogenetic analyses of sauropod dinosaurs (e.g., yu, 1993; upchurch, 1998). as noted by tschopp and others (2015: p. 130), the relatively low mean elongation ratio of the caudal vertebrae of ypm vp.001920 compared to other specimens of diplodocus is probably just a result of the fact that the specimen only preserves the less elongate anterior mid-caudal elements. difficulties in correctly identifying the position of the series of preserved vertebrae of ypm vp.001920 are highlighted by mcintosh and carpenter (1998), who dedicated more than a page to this issue. they concluded that the caudal series could range from positions 6-23 to 12-29, with the most probable positions being 9-26 (mcintosh and carpenter, 1998: p. 96). these variable positions obviously also impact the interpretation of how far back in the tail the vertebrae still bear pneumatic foramina, which appears to be individually variable within specimens referred to diplodocus hallorum as well as the non-diplodocine sauropods apatosaurus and giraffatitan (wedel, 2005; wedel and taylor, 2013). consequently, and given that erroneous positional interpretations have already led to taxonomic confusion in diplodocines (see the case of “seismosaurus;” gillette, 1991; lucas and others, 2006; lovelace and others, 2007; tschopp and others, 2015), we would argue that the two potentially autapomorphic features proposed by mcintosh and carpenter (1998) and cited by mortimer (2017) are not suitable for diagnosing a species of diplodocine sauropod. stratigraphic age the presumably older stratigraphic age of ypm vp.001920 compared to other specimens and species of diplodocus has been put forward as an argument against a replacement of the type species, d. longus, by demirjian (2017) and mortimer (2017), because it would indicate that d. longus is actually a distinct species and therefore available as the type species of diplodocus. the 257 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 geologically older age is most probably true (tschopp and others, 2016), even though long-distance correlation of quarries across the morrison formation is still difficult (trujillo, 2006; maidment and others, 2017). however, it would be questionable to diagnose a paleontological species solely based on the fact that it occurs in a layer of minimally different geological age than another species. evolutionary rates have been shown to be variable, with certain species evolving very slowly, while others experience fast radiations (e.g., adams, 2013; herrera-flores and others, 2017), so that time alone is an unreliable feature for a species diagnosis. the use of apomorphy-based species concepts instead of chronospecies in paleontology is therefore crucial and indeed widespread in paleontology (allmon and yacobucci, 2016). the mention of d. longus as a potential ancestral species in the abstract of tschopp and others (2016) that was cited by demirjian (2017) was not meant to imply that ypm vp.001920 is diagnosable at the species level, but rather to show that the methodology employed by tschopp and others (2016) might be capable of recognizing ancestral species in a phylogenetic analysis (though we admit that the wording of tschopp and others [2016] did not properly reflect this). ypm vp.001920 is undiagnosable at the species level, thus making the species d. longus a nomen dubium. even in the unlikely case that additional, more complete specimens would be found in strata of an equivalent age as ypm vp.001920, and that these new specimens would also share unique, diagnostic features with ypm vp.001920, a future revalidation of the species d. longus would have no effect on the use and validity of the proposed new type species d. carnegii. the two species would simply both be considered valid, as ypm vp.001920 will always remain the holotype for d. longus, it would just not be considered to be the type species and thus reference for the genus diplodocus, a fact that is effectively already the case now (taylor, 2017). taxonomic instability one of the main arguments of tschopp and mateus (2016) was the fact that having a species declared to be a nomen dubium as the type species would create taxonomic confusion, a fact that mortimer (2017) challenged. whereas it is true that tschopp and others (2015) found ypm vp.001920 to belong to the genus diplodocus, it is also true that highly incomplete specimens like ypm vp.001920 are more prone to phylogenetic instability (wilkinson, 1995; wiens, 2006; butler and upchurch, 2007). indeed, ypm vp.001920 was identified by tschopp and others (2015) as one of the most unstable operational taxonomic units in their analysis (see also taylor, 2017). it also has already been the cause for some taxonomic confusion in the past because of the incorrect identification of the reasonably complete specimen amnh farb 223 as d. longus by osborn (1899), and the subsequent morphological comparisons of newly found specimens with the referred specimen, amnh farb 223, instead of the holotype specimen, ypm vp.001920 (see a summary in tschopp and mateus, 2016). a similar case was the genus titanosaurus, which also was typified by a type species represented by a highly incomplete holotype specimen (wilson and upchurch, 2003). as in diplodocus, the features originally proposed to be diagnostic for the type species t. indicus were later found to be more widespread among sauropods, resulting in t. indicus being a nomen dubium. therefore, wilson and upchurch (2003) suggested to abandon the use of the genus and its co-ordinated higher-ranked taxa, which has since been followed by all sauropod workers. in order to avoid the same fate for diplodocus, tschopp and mateus (2016) proposed to substitute the type species. although the iczn code does not directly have an article discussing the replacement of a type species, and the necessity to have a diagnosable type species for a genus (see article 70, and mortimer, 2017), we argue that similar principles should be applied at the level of genera as the ones that apply at the level of species. as article 61.1 of the code states: “the name-bearing type of a nominal taxon provides the objective standard of reference for the application of the name it bears.” it goes on in article 61.1.1, stating: “no matter how the boundaries of a taxonomic taxon may vary in the opinion of zoologists the valid name of such a taxon is determined (article 23.3) from the name-bearing type(s) considered to belong within those boundaries.” given the instability of ypm vp.001920, and thus the 258 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 species d. longus in phylogenetic analyses, it is not entirely improbable that future discoveries or changes to the matrix or methodology will find ypm vp.001920 in a slightly more basal position, potentially in a polytomy with the well known, and widely accepted genus barosaurus marsh, 1890, which is often found to be the sister genus of diplodocus (whitlock, 2011a; gallina and others, 2014; tschopp and mateus, 2017). in case the relatively robust hindlimb (ypm vp.059136) from the type locality would indeed belong to the type tail, as suggested by carpenter (2017), this might even result in a recovery of ypm vp.001920 within the genus galeamopus, which occurs in the type locality and has more robust limbs than other diplodocine genera (tschopp and mateus, 2017). in these cases, retaining d. longus as the type species of diplodocus, and a strict application of nomenclatural rules would result in the synonymization of the genera diplodocus, barosaurus, galeamopus, and possibly kaatedocus (depending on the phylogenetic analysis used), consequently resulting in the loss of the latter three genera as valid taxa because of the principle of priority. thus, although the non-diagnostic nature of ypm vp.001920 and the invalidity of d. longus might not be an imminent threat to the genus diplodocus (mortimer, 2017), because it was one of the first named sauropod dinosaurs, it could be a threat to other genera erected after diplodocus and considered to be its sister taxa. whereas kaatedocus and galeamopus have only been recently named, and still need to be studied in more detail to be considered to be well-established genera, barosaurus has been studied widely since its erection in the late 1800s, and its validity has never really been questioned (see mcintosh, 2005 for the latest review), so that a synonymization with diplodocus because of the instability of a single, incomplete operational taxonomic unit would be unreasonable. through a replacement of d. longus as the type species of diplodocus by the phylogenetically stable, and well-studied d. carnegii, potential future problems like the one outlined above could be avoided (see also taylor, 2017). at the level of species, the type concept is described in chapter 16 of the code. the designation of a neotype at species level can be the equivalent to the proposal of replacement of the type species at the genus level. article 75.5 states the following: “when an author considers that the taxonomic identity of a nominal species-group taxon cannot be determined from its existing name-bearing type (i.e., its name is a nomen dubium), and stability or universality are threatened thereby, the author may request the commission to set aside under its plenary power (article 81) the existing name-bearing type and designate a neotype.” and further: “when an author discovers that the existing name-bearing type of a nominal species-group taxon is not in taxonomic accord with the prevailing usage of names and stability or universality is threatened thereby, he or she should maintain prevailing usage (article 82) and request the commission to set aside under its plenary power (article 81) the existing name-bearing type and designate a neotype.” (article 75.6). d. longus is both a nomen dubium, and its holotype ypm vp.001920 has generally been substituted by amnh farb 223 as the reference specimen for comparisons with this species (tschopp and mateus, 2016). therefore, both articles 75.5 and 75.6 apply to this case, but with the peculiar difficulty that the incompleteness of ypm vp.001920 also prevents the identification of another specimen suitable to serve as a neotype (tschopp and mateus, 2016). consequently, tschopp and mateus (2016) proposed the replacement of the type species instead of proposing a neotype. there is strong precedent for this among other equally undiagnosable marsh-named taxa, the most similar recent case being the one concerning the wellknown marsh dinosaur genus, stegosaurus marsh, 1877, in which the commission preserved the taxonomic stability by choosing to replace the unidentifiable type species of the genus, i.e., stegosaurus armatus marsh, 1877 (whose holotype specimen is ypm vp.001850), with the very well represented nominal species stegosaurus stenops marsh, 1887 (whose holotype specimen is usnm v 4934) (iczn 2013). possible synonymization the possibility that future finds might lead to the conclusion that d. longus is synonymous to the newly proposed type species d. carnegii has already been discussed by tschopp and mateus (2016), but was put forward again by mortimer (2017) as a potential future threat to the validity of d. carnegii. however, just as 259 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 it is highly improbable that future studies would find unique features diagnosing d. longus (see above), the same applies for the finding of unique, shared features with d. carnegii, but not with the other valid species in the genus d. hallorum. precedent iczn cases tschopp and mateus (2016) mentioned several cases with similar issues of undiagnostic holotypes of the type species, where a replacement of the type species was accepted by the commission in the past, including the one discussed above (iczn 2013). whereas we agree with carpenter (2017) and mortimer (2017) that details may differ among these cases, the main issues of the undiagnosability of the holotype, and the unavailability of a neotype remain the same. we acknowledge that there is no “case law” (principle 8 in the introduction of the code), but given that the nomenclatural rules in the code are intended to serve as “tools that are designed to provide the maximum stability compatible with taxonomic freedom” (principle 4 in the introduction of the code), we should not apply them strictly and equally in all groups of animals with various taxonomic histories. citing precedents outside of dinosauria (mortimer, 2017) is arguable, and the fact that most of the sauropod specialists who expressed an opinion on the case were favorable (lucas, 2017; taylor, 2017; woodruff, 2017) supports the rationale for the tschopp and mateus (2016) proposal. conclusion the famous dinosaur genus diplodocus is currently typified by d. longus, a species with an incomplete and undiagnostic holotype (ypm vp.001920). no bones other than some caudal vertebrae (figures 1 to 8) and an associated partial chevron (figure 9) can be confidently referred to the individual comprising ypm vp.001920 (per mcintosh and carpenter, 1998; and contra carpenter, 2017). even though there is still a lot of sauropod material from the garden park area that remains unprepared and uncatalogued, including several robust phalanges at the ypm, it appears improbable that additional diagnostic material from the same individual will be identified in future. a designation of a new type species for diplodocus, as proposed by tschopp and mateus (2016) is the most reasonable solution to this taxonomic quagmire and the negative comments from others against the case are debatable, further supporting the proposed replacement of d. longus with d. carnegii as the type species for the genus diplodocus. acknowledgments we would like to thank john foster (museum of moab), kelli trujillo (uinta paleontological associates, inc.), and cary woodruff (university of toronto), who organized the poster symposium on the morrison formation at svp 2016 together with one of us (o. mateus), and for their invitation to contribute to this volume. we also thank dan chure (dinosaur national monument, retired) and brooks britt (brigham young university) for providing ypm vp with digital copies of the late, great john (“jack”) s. mcintosh’s notebooks on the dinosaurs from garden park. although jack might not have agreed with all of the arguments made herein, we humbly dedicate this paper to his memory nevertheless.  jack’s encyclopedic knowledge of the ypm dinosaur collection and of the world’s sauropods are greatly missed, as is he. cary woodruff (university of toronto) and mathew wedel (western university of health sciences) provided valuable reviews that helped to strengthen our points. alyson heimer (ypm) shot additional photographs of non-diplodocid material from the marsh-felch quarry. marilyn fox (ypm) and enrica sarotto (new york, usa) helped during a collection visit of e. tschopp to the ypm. most data on which this work is based have been collected during the ph.d. of e. tschopp, which was supported by a doctoral fellowship from the fundação para a ciência e a tecnologia of the ministério de educação e ciência, portugal (sfrh/bd/66209/2009). additional data was collected during the current postdoc of e. tschopp, which is supported by the theodore roosevelt memorial fund and the division of paleontology at the american museum of natural history, new york. references adams, d.c., 2013, comparing evolutionary rates for different phenotypic traits on a phylogeny using likelihood: 260 considerations on the replacement of a type species in the case of the sauropod dinosaur diplodocus marsh, 1878 tschopp, e., brinkman, d., henderson, j., turner, m., and mateus, o. geology of the intermountain west 2018 volume 5 systematic biology, v. 62, p. 181–192. allmon, w.d., and yacobucci, m.m., editors, 2016, species + speciation in the fossil record: chicago, the university of 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partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america julia b. mchugh theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover excavations of the brushy basin member of the morrison formation (upper jurassic) at the mygatt-moore quarry in western colorado with a specimen of diplodocid premaxilla fragment (mwc 8430) superimposed. cover photograph by julia b. mchugh (museums of western colorado). i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott ekeller@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public 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board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — museum of moab cary woodruff — university of toronto octavio mateus — universidade nova de lisboa editors geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 95 abstract two tooth-bearing snout fragments from a diplodocid sauropod from the brushy basin member of the morrison formation (upper jurassic) excavated from the mygatt-moore quarry in rabbit valley, colorado are described. the mygatt-moore quarry has produced thousands of vertebrate fossils from the brushy basin member, with the diplodocid apatosaurus cf. louisae and the tetanuran allosaurus fragilis dominating the assemblage. additionally, remains of another diplodocid, diplodocus sp., have been found near the quarry within rabbit valley. both specimens in this study preserve eight teeth per alveolar position, as observed through broken surfaces at the gross anatomical level and also through computed tomography (ct) scans. this is inconsistent with the genus diplodocus sp., which has been previously shown to have a maximum of six teeth per alveolus. the presence of eight replacement teeth per alveolus has previously only been reported in the cretaceous rebbachisaurid nigersaurus taqueti, which has been interpreted to have occupied a similar ground-height browsing feeding strategy to both diplodocus and apatosaurus. this is the first report of this type of high-count replacement teeth in a diplodocid sauropod from the morrison formation. the high number of replacement teeth in a close relative to the contemporaneous diplodocus provides evidence for niche partitioning among the contemporary ground-height browsing diplodocid sauropods of the late jurassic period in north america. evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america julia b. mchugh1 1museums of western colorado, p.o. box 20000, grand junction, co 81502; jmchugh@westcomuseum.org citation for this article. mchugh, j.b., 2018, evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america: geology of the intermountain west, v. 5, p. 95–103. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction apatosaurus and diplodocus are contemporary sauropod genera found within the upper jurassic morrison formation (tschopp and others, 2015). these genera share a close phylogenetic history, as well as head and neck morphologies that allow for similar biomechanical adaptions to available vegetation zones (stevens and parrish, 1999, 2005; upchurch, 2000; wilson, 2005; whitlock, 2010; stevens, 2013; woodruff, 2017). the presence of such similar, large-bodied herbivores would have had a substantial impact on the available biomass in order to support populations of these two genera. ecological niche partitioning in the upper jurassic morrison formation’s landscape has traditionally been proposed to circumvent this problem (turner and peterson, 2004). however, empirical evidence supporting this partitioning among coeval genera, particularly between adult apatosaurus and diplodocus, has been limited (fiorillo, 1998; whitlock, 2011: d’emic and others, 2013). here, i describe new specimens that shed light on this ecological problem: two diplodocid 96 evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america mchugh, j.b. geology of the intermountain west 2018 volume 5 snout fragments containing numerous teeth (museums of western colorado specimens mwc 6002 and mwc 8430) from the brushy basin member of the morrison formation excavated from mygatt-moore quarry (mmq) in rabbit valley, western colorado (figure 1). the mmq is located within the mcinnis canyons national conservation area and is co-managed by the museums of western colorado (mwc) and the bureau of land management (blm). excavations at the mmq for over thirty years by crews from the mwc, as well as the dinamation international society, have facilitated the recovery of over 5000 vertebrate fossils, including holotype specimens of the bony fish “hulettia” hawesi (kirkland, 1998) and morrolepis schaefferi (kirkland, 1998), and the ankylosaur mymoorapelta maysi (kirkland and carpenter, 1994). however, fossil material from the tetanuran allosaurus fragilis and the diplodocid apatosaurus cf. louisae dominate the assemblage (foster and others, 2007, 2018). two diplodocid taxa are positively identified from the rabbit valley area: diplodocus sp. and apatosaurus cf. louisae. of these two, only apatosaurus cf. louisae has been recovered within the mmq. other sauropods recovered from the quarry include the macronarian, camarasaurus sp., as well as several taxonomically ambiguous caudal vertebrae, which are identified as diplodocinae indet. (foster and others, 2018). sauropod dinosaurs include the largest terrestrial herbivores that the earth has ever known. understanding their biology and interactions with plant biomass and other sauropods within mesozoic ecosystems has been the subject of much research (barrett and upchurch, 1995; stevens and parrish, 1999, 2005; upchurch, 2000; upchurch and barrett, 2000; hummel and others, 2008; yates and others, 2010; gee, 2011; tütken, 2011). sauropods have been broadly divided into “high browsing” and “ground height” browsing ecological types based upon snout shape and neck position (whitlock, 2011), but estimations of neck biomechanics indicate considerable overlap in the range of feeding between disparate types of sauropods (stevens and parrish, 1999, 2005). additionally, co-occurring genera within these broad categories, such as apatosaurus and diplodocus, are known from the morrison formation (tschopp and others, 2015). the refining of these broad ecological groups was attempted using snout shape morphometrics (whitlock, 2011). snout shapes were quantified for six diplodocoid genera (apatosaurus sp., dicraeosaurus sp., diplodocus sp., nigersaurus taqueti, suuwassea emilieae, and tornieria africana) using the ratio of the depth to and breadth in the upper jaw, the premaxillary-maxillary index, and the divergence angle of the premaxillae (whitlock, 2011). whereas some taxa were found to be mathematically distinct from each other; unfortunately, these metrics were unable to separate the broad snouted apatosaurus and diplodocus into disparate ecological groups (whitlock, 2011). tooth microwear has also been used to distinguish among ecological resource use in sauropod dinosaurs (fiorillo, 1998; whitlock, 2011). however, while tooth wear and microwear have been useful in differentiating feeding strategies between co-occurring taxa like camarasaurus sp. and diplodocus sp. (fiorillo, 1998; whitlock, 2011), suitable teeth from apatosaurus sp. for this type of analysis have been lacking (whitlock, 2011). although shed teeth are relatively common for predators like allosaurus fragilis, especially at the mmq, shed teeth from species of apatosaurus are less common and are often difficult to differentiate from those of diplodocus. additional dental material is required to assess the microwear in the genus apatosaurus, and for this type of analysis to be useful in partitioning the ecological niches of apatosaurus and diplodocus. observations of modern herbivores show that ecological niche partitioning is common among similar taxa within an environmental landscape (i.e., bovidae), and that their dental and jaw morphologies are also correlated to this partitioning (spencer, 1995). however, with considerable morphological and biomechanical overlap in sauropod dinosaurs between established ecological types, estimation of niche partitioning at lower taxonomic levels has proven difficult (fiorillo, 1998; whitlock, 2011). tooth replacement may be an illuminating piece of evidence in fully assessing the niche partitioning among sauropods. since variable hardness within food sources can tend to create inconsistent wear on herbivore teeth, a higher level of tooth replacement is often associated with tougher vegetation. tooth replacement rates among diplodocoidea 97 evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america mchugh, j.b. geology of the intermountain west 2018 volume 5 have previously been described in camarasaurus sp., diplodocus sp., dicraeosaurus hansemanni, and nigersaurus taqueti (sereno and others, 2005; d’emic and others, 2013; schwarz and others, 2015). the number of teeth per alveolus within the premaxillae (including both replacement and erupted tooth positions) vary among taxa, with four reported in camarasaurus sp., six in diplodocus sp., five to six in dicraeosaurus hansemanni, and eight in nigersaurus taqueti (sereno and others, 2005; d’emic and others, 2013; schwarz and others, 2015). d’emic and others (2013) suggest the lower number of teeth in camarasaurus sp. is correlated to the relative increase in tooth volume, and thus a physiological investment in individual teeth rather than a biological investment in a lot of teeth. i present here the first description of tooth replacement in a non-diplodocus diplodocid from the morrison formation that provides empirical evidence for an ecological partition between this taxon and diplodocus sp. geological setting the fossil-bearing horizon at the mmq is a 1to 2-m-thick unit exposed within laminated to medium-bedded gray silty mudstone of the brushy basin figure 1. map of mesa county in western colorado showing the location of the mygatt-moore quarry. insert shows excavations at the quarry during 2014. 98 evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america mchugh, j.b. geology of the intermountain west 2018 volume 5 member of the morrison formation (kirkland and carpenter, 1994; foster, 2003; foster and others, 2007, 2018; foster and hunt-foster, 2011). radiometric analysis of ash-fall zircons from the quarry have returned an age of 152.18 ±0.29 ma, which places the quarry on kimmeridgian–tithonian boundary during the late jurassic period (trujillo and others, 2014). the mmq is interpreted to preserve an ecosystem with abundant vegetation and a high water table, but with standing water at the surface occurring only seasonally (foster, 2003; trujillo and others, 2014; foster and others, 2018). the site preserves a dinosaur-dominated assemblage with abundant plant material, with crocodylomorph, turtle, and invertebrate remains being rare (foster 2007; foster and others, 2018). previous taphonomic work has shown the site represents an autochthonous assemblage within an attritional deposit in an overbank setting with few articulated specimens and no preferred orientation of skeletal elements (foster and others, 2018). despite the lack of transport evident in the assemblage, fossils often preserve bone surface modifications (e.g., breakage, abrasion, and feeding traces) that suggest a reworked death assemblage by subsequent living individuals, possibly through feeding and trampling (foster and others, 2018). description both specimens in this study were excavated from the gray mudstone of the brushy basin member of the morrison formation at the mmq using hand-quarrying techniques. both specimens were collected as isolated elements with no additional associated cranial or postcranial material. these specimens were mechanically prepared at the mwc fossil preparation lab, repaired, and stabilized using polyvinyl acetate dissolved in acetone, as well as cyanoacrylate (paleobondtm 750) adhesives, and then imaged using two-dimensional (2d) photography and a 64-slice computed tomography (ct) scanner at colorado canyons hospital in fruita, colorado. mwc 6002—diplodocid maxilla specimen mwc 6002 is a partial maxilla that preserves eight sets of teeth, with each set representing a single alveolus. the mesial suture between the premaxilla and maxilla is poorly preserved and the ventrodistal margin is incomplete. therefore, it is doubtful that all maxillary alveoli are present in the specimen, and alveolar positions are instead referred to as mx1-mx8 and not to their exact maxillary placement (figure 2). the number of replacement teeth per alveolus decreases from medial to distal. the mesial-most four alveolar positions (mx1-mx4) each preserve seven to eight replacement teeth, similar to the numbers preserved in specimen mwc 8430. the next two alveoli (mx5-mx6) preserve six and five replacement teeth, respectively, whereas the distal-most positions preserve only four and three replacement teeth (mx7, mx8). this reduction in the number of replacement teeth reflects the decreasing volume in maxillary space distally. tooth replacement positions vi-viii are labial-linugally compressed. erupted crown morphology and the lingual inflection at the separation of root and crown are both distinguishable by position v and become more pronounced towards the erupted tooth position (i) (figures 3 and 4). mwc 8430—diplodocid premaxilla fragment specimen mwc 8430 is a well-preserved, isolated premaxilla fragment that preserves four sets of replacement teeth, each representing a single alveolus in the upper jaw. however, lack of preservation on the exterior surface has not preserved the alveoli themselves. the lingual face of the premaxilla is preserved as a thin, trapezoidal fragment with a smooth surface morphology. the fragmental nature of specimen mwc 8430 allows for determination of lingual/labial and superior/ inferior orientations, but not mesial/distal and it prohibits assignment to precise tooth row placement. the alveolar positions are therefore referred to as px1-px4 (figure 5). the maximum number of replacement teeth (eight) in an individual set are found within px1, with px2 and px3 each preserving seven teeth, and px4 with four teeth. teeth in the replacement rows incrementally increase in length towards the erupted tooth position. tooth replacement positions vi-viii are labial-lingually compressed. erupted crown morphology is distin99 evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america mchugh, j.b. geology of the intermountain west 2018 volume 5 guishable by position v and becomes more pronounced towards the erupted tooth position (i). also visible at position v is the lingual inflection at the separation of root and crown (figures 5 and 6). discussion despite the lack of association with more diagnostic material, some taxonomic assessments for specimens mwc 6002 and mwc 8430 are possible. these specimens both bear the characteristic peg-like teeth of diplodocoidea. however, they are not consistent with the known pattern of tooth replacement in diplodocus sp. or the african taxon dicraeosaurus hansemanni which have been shown to support no more than five to six tooth positions per alveolus in the premaxilla, including the erupted tooth (d’emic and others, 2013; schwarz, 2015). the newly described specimens mwc 6002 and mwc 8430, although incomplete, preserve a maximum of eight teeth (both replacement teeth and erupted tooth) per alveolus. the premaxilla exhibits the maximum number of replacement teeth, as supported by the mesial increase in the number of tooth replacement position seen in the maxilla, specimen mwc 6002. however, this mesial increase in tooth replacement positions may not be characteristic of all sauropods, for example in the titanosaur euhelopus zdanskyi, the maximum number of tooth replacement positions is located within the maxilla and not the premaxilla (poropat and figure 2. diplodocid maxilla (specimen mwc 6002). (a) dorsal view. (b) ventral view. scale bar equal 10 cm. 100 evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america mchugh, j.b. geology of the intermountain west 2018 volume 5 kear, 2013). minimally, specimens mwc 6002 and mwc 8430 can be assigned as a non-diplodocus diplodocid. the only other known diplodocid taxa from the rabbit valley consists of the very abundant apatosaurus cf. louisae and the ambiguous vertebrae not positively identified beyond diplodocinae indet. the mmq in rabbit valley has been explored in scientific earnest for more than three decades, producing thousands of fossils, none of which were positively assigned to any diplodocid taxon other than apatosaurus cf. louisae. and although the possibility of future diplodocoid discoveries at the site cannot be discounted, given the present data available, it is most parsimonious for specimens mwc 6002 and mwc 8430 to be tentatively referred to apatosaurus sp., pending the recovery of more diagnosable cranial material. despite a closer phylogenetic, geographic, and stratigraphic relationship with diplodocus sp., the specimens in this study that are referred to apatosaurus sp. are more similar to the tooth replacement counts seen in the cretaceous african form nigersaurus taqueti. a higher number of replacement teeth than the coeval diplodocus sp. indicates that these large-bodied, “ground height” browsing herbivores were orally processing different types of vegetation, with apatosaurus sp. potentially adapted for tougher, more abrasive vegetation than diplodocus sp. the morrison formation is interpreted as representing a predominantly riparian landscape with limited botanical biomass (foster, 2003; engelmann and others, 2004; rees and others, 2004; turner and peterson, 2004; hummel and others, 2008; gee, 2011). this partitioning of resources between large herbivores would have been critical for survival in this limiting environment, and may have been the key to the success and diversity of the sauropods in the late jurassic period. conclusions populations of co-occurring herbivores in modern landscapes often partition plant biomass resources to facilitate survival in competitive environments. using modern analogs, paleontologists have long hypothefigure 3. ct scan of specimen mwc 6002 in and superior view. alveolar positions are indicated with mx1-mx8 labels. figure 4. ct scan of specimen mwc 6002 in and mesial view. roman numerals indicate tooth positions for the mx2 alveolus. 101 evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america mchugh, j.b. geology of the intermountain west 2018 volume 5 figure 5. specimen mwc 8430 in (a) ?mesial, (b) ?distal, (c) labial, (d) lingual, (e) superior, and (f) inferior views. roman numerals indicate tooth positions for an individual alveolus. all scale bars equal 1 cm. figure 6. ct scan of specimen mwc 8430 in and inferior view. roman numerals indicate tooth positions for individual alveoli. alveolar positions are indicated with px1-px4 labels. 102 evidence for niche partitioning among ground-height browsing sauropods from the upper jurassic morrison formation of north america mchugh, j.b. geology of the intermountain west 2018 volume 5 sized similar niche partitioning among large sauropod dinosaurs in the mesozoic. new specimens from the mmq in rabbit valley, colorado, reveal higher counts of tooth replacement in apatosaurus sp. than in diplodocus sp. this indicates that species of apatosaurus may have been selectively feeding on tougher vegetation (e.g., cycads and conifers) than species of diplodocus and provides the strong empirical evidence for niche partitioning among these coeval and morphologically similar taxa. acknowledgments thank you to rob gay (colorado canyons association), chris racay (museums of western colorado), john foster (museum of moab), rebecca hunt-foster (bureau of land management, canyon country district), and michael d’emic (adelphi university) for their helpful discussions on this project. i thank dorothy stewart and the volunteer corps at dinosaur journey museum, as well as dinosaur journey field coordinator chris racay and field assistant mitchell lukens for assistance in recovery and preparation of specimens. i sincerely thank the bureau of land management grand junction field office for support and site access, as well as dr. michael neste, m.d. (family health west) and the colorado canyons hospital in fruita for the use of ct imaging facilities. thank you to stephen k. poropat (swinburne university of technology) and femke holwerda (bayerische staatssammlung für paläontologie und geologie) for their thoughtful comments on an earlier version of this manuscript, and i also thank cary woodruff (great plains dinosaur museum), john foster (museum of moab), and daniela schwarz (museum für naturkunde) for their time and comments on this manuscript. references barrett, p., and upchurch, p., 1995, sauropod feeding mechanisms—their bearing on palaeoecology, in sun, a., and wang, y., editors, proceeding 6th symposium, mesozoic terrestrial ecosystems and biotas: beijing, china ocean press, p. 107–110. d’emic, m.d., whitlock, j.a., smith, k.m., fisher, d.c., and wilson, j.a., 2013, evolution of high tooth replacement rates in sauropod dinosaurs: plos one, v. 8, no. 7, p. e69235. engelmann, g.f., chure, d.j., and fiorillo, a.r., 2004, the 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dentition and tooth replacement of dicraeosaurus hansemanni (dinosauria, sauropoda, diplodocoidea) from the tendaguru formation of tanzania: journal of vertebrate paleontology, v. 35, no. 6, p. e1008134. trujillo, k.c., foster, j.r., hunt-foster, r.k., and chamberlain, k.r., 2014, a u/pb age for the mygatt-moore quarry, upper jurassic morrison formation, mesa county, colorado: volumina jurassica, v. 12, no. 2, p. 107–114. tschopp, e., mateus, o., and benson, r.b.j., 2015, a specimen-level phylogenetic analysis and taxonomic revision of diplodocidae (dinosauria, sauropoda): peerj, v. 3, p. e857. turner, c.e., and peterson, f., 2004, reconstruction of the upper jurassic morrison formation extinct ecosystem—a synthesis: sedimentary geology, v. 167, no. 3-4, p. 309–355. tütken, t., 2011, the diet of sauropod dinosaurs—implications from carbon isotope analysis of teeth, bones, and plants, in klein, n., remes, r., gee, c.t., and sander, p.m., editors, biology of the sauropod dinosaurs—understanding the life of giants: bloomington, indiana university press, p. 57–79. upchurch, p., 2000, neck posture of sauropod dinosaurs: science, v. 287, no. 5453, p. 547–547. upchurch, p., and barrett, p.m., 2000, the evolution of sauropod feeding mechanisms, in sues, h-d., editor, evolution of herbivory in terrestrial vertebrates—perspectives from the fossil record: cambridge, england, cambridge university press, p. 79–122. whitlock, j.a., 2010, paleoecology and systematics of the diplodocoid sauropods: ann harbor, the university of michigan, ph.d. dissertation, 369 p. wilson, j.a., 2005, overview of sauropod phylogeny and evolution, in curry rogers, k.a., and wilson, j.a., editors, the sauropods—evolution and paleobiology: berkeley, university of california press, p. 15–49. whitlock, j.a., 2011, inferences of diplodocoid (sauropoda: dinosauria) feeding behavior from snout shape and microwear analyses: plos one, v. 6, no. 4, p. e18304. woodruff, d.c., 2017, nuchal ligament reconstructions in diplodocid sauropods support horizontal neck feeding postures: historical biology, v. 29, no. 3, p. 308–319. yates, a.m., bonnan, m.f., neveling, j., chinsamy, a., and blackbeard, m.g., 2010, a new transitional sauropodomorph dinosaur from the early jurassic of south africa and the evolution of sauropod feeding and quadrupedalism: proceedings of the royal society of london b: biological sciences, v. 277, no. 1682, p. 787–794. silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 6 2019 © 2019 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation carole t. gee, douglas a. sprinkel, mary beth bennis, and dale e. gray theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover fossil wood thin sections of agathoxylon hoodii showing fine anatomical details. all micrographs were taken of radial sections of thin section rdw-004. two photographs of the fossil logs found in rainbow draw, uintah county, utah. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 6 2019 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association volume 6 2019 77 abstract a new local flora of silicified logs and wood has been discovered in the upper jurassic morrison formation in the rainbow draw area near dinosaur national monument, northeastern utah, usa. fossil logs and wood were found in the salt wash member at nine sites at rainbow draw and at one site near miners draw, south of blue mountain. the fossil logs are large and relatively intact, the longest measuring 11 m. the wood is well preserved, coniferous, and can be identified to the species level. diagnostic anatomical features include resin plugs in the ray cells and axial tracheids, araucarioid tracheary pitting and crossfield pitting, and the lack of resin canals and true, regularly occurring growth rings. this taxon of fossil wood, originally described as araucarioxylon hoodii tidwell et medlyn, is recognized here as a new combination, agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis et gray, which pertains to the conifer family araucariaceae. based on the preserved girth of the logs, the minimum height of the trees could be reconstructed. the largest fossil logs measured at least 127 cm in diameter and hence reached a minimum height of 28 m. judging from the growth habit of all naturally occurring araucariaceous trees today, the fossil plants likely formed forests of moderately tall trees and were well over 100 years old. the lack of true growth rings shows that there was no seasonality in the local paleoclimate, neither variations in summer–winter temperatures, nor wet–dry cycles. thus, during the late jurassic, tall conifer forests with agathoxylon hoodii grew in at least two areas in what is now utah: east of the city of vernal and near mt. ellen in the henry mountains. coupled with the fossil evidence of conifer seed cones and pollen found in the morrison formation throughout eastern utah, the newly discovered fossil logs and wood argue for the reconstruction of upper jurassic habitats in this region as mesic and wooded, and the climate as equable, not seasonal, nor semi-arid or arid. silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation carole t. gee1, douglas a. sprinkel2, mary beth bennis3, and dale e. gray3 1institute of geosciences, division of paleontology, university of bonn, nussallee 8, 53115 bonn, germany; cgee@uni-bonn.de 2utah geological survey, po box 146100, salt lake city, ut 84114, usa; douglassprinkel@utah.gov 3utah field house of natural history state park museum, 496 e. main, vernal, ut 84078, usa; marybethbennis@utah.gov, daleegr@aim.com citation for this article. gee, c.t., sprinkel, d.a., bennis, m.b., and gray, d.e., 2019, silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation: geology of the intermountain west, v. 6, p. 77–92. © 2019 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. editor’s note: the current citation format used in the geology of the intermountain west for published works by two authors is to list both authors separated by the word “and” with the date of publication and for published works by more than two authors, only the first author is listed followed by “and others” with the date of publication. however, for published works that name taxon by two authors, both authors are listed separated by the word “et” and for published works that name taxon by more than two authors, the lead author is listed followed by the abbreviation “et al.” following the recommendations of the international code of nomenclature for algae, fungi, and plants, chapter vi, section 1, recommendation 46c. 78 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 introduction as in many ancient terrestrial ecosystems, fossil logs and wood are locally abundant in the upper jurassic morrison formation. in the older reports on the morrison fossil flora, fossil logs and larger pieces of fossil wood were described from 11 localities (tidwell, 1990; ash and tidwell, 1998; peterson, undated). these localities are sites at castle dale, ferron, fremont junction, caineville wash, mount ellen, hansen creek, and clay point in utah; at mygatt-moore quarry and east mcelmo creek in colorado; in the freezeout hills in wyoming; and in the black hills in south dakota. if the narrow, woody axes of the enigmatic hermatophyton and the short shoots of behuninia spp. and steinerocaulis spp. are included, the number of localities increases by seven to include dinosaur national monument, another two sites at clay point, mussentuchit wash, and montezuma creek in utah; and scott’s site and steiner’s site in wyoming (ash and tidwell, 1998; peterson, undated). more recently, silicified wood floras have been reported from the howe-stephens quarry near greybull in north-central wyoming (gee and tidwell, 2010), the escalante petrified forest state park in southern utah (morgan and others, 2010; gee, unpublished data), and a new site west of blanding in southern utah (kirkland, utah geological survey, verbal communication to gee, 2018), as well as a single piece of fossil wood from dinosaur ridge in morrison, colorado (gee, unpublished data), making a total of at least 22 localities with fossil wood remains. yet, the number of fossil conifer woods formally described from the morrison formation is limited to only eight: araucarioxylon hoodii tidwell et medlyn (1993), cupressinoxylon jurassicum lutz (1930), mesembrioxylon carterii tidwell and others (1998), mesembrioxylon obscurum (knowlton) medlyn et tidwell (2002), protocupressinoxylon medlynii tidwell and others (1998), protopiceoxylon resiniferous medlyn et tidwell (1979), xenoxylon moorei tidwell and others (1998), and x. morrisonense medlyn et tidwell (1975) (but see philippe and others, 2013, regarding x. moorei and x. morrisonense). this relatively low number of taxa compared to the number of localities where fossil wood has been found does not necessarily reflect low species diversity in the morrison conifer flora, but is more likely due to the poor preservation of most fossil wood specimens in the morrison formation. for example, the fossil wood at the caineville wash locality, called “black and white wood” by local collectors, is aesthetically pleasing and plentiful, but not worth paleobotanical study owing to the lack of the fine anatomical detail necessary for taxonomic determination (gee, personal observation). however, because of the widespread terrestrial facies and locally abundant occurrence of fossil wood, the potential for finding fossil wood in the morrison formation that is suitable for paleobotanical investigation is high. the discovery of a new local fossil flora with relatively intact logs and good wood preservation in the morrison formation near dinosaur national monument, northeastern utah, has led to this paleobotanical investigation, as well as a concurrent in-depth stratigraphical and sedimentological study of the geological setting (sprinkel and others, 2019). in the paleobotanical study here, we determine the taxonomic affinity of the fossil logs, interpret the paleoenvironmental signals inherent in the wood structure, and reconstruct the minimum heights of the trees based on the measurement of preserved log girth. the results of our study have implications for the floral composition and ecological structure of the late jurassic forests, and hence for dinosaur habitats in the morrison formation. geological setting the fossil logs and wood were discovered by mary beth bennis and dale gray in utah (figure 1), on the southeastern flank of the uinta mountains, east of the city of vernal, in two general areas: rainbow draw to the north and miners draw to the south (figure 2). rainbow draw is located about 36 km (22.4 highway miles) northeast of vernal, and about 30 km northwest of the miners draw site. nine sites with fossil logs and wood have been found at the rainbow draw locality (table 1). all logs occur in the same stratigraphic interval in the salt wash member of the morrison formation (figure 3; sprinkel and others, 2019). the unit containing the logs is 11 79 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 m thick and is composed of fineto very fine grained sandstone and siltstone. the sandstone is well sorted and friable with indistinct bedding and sedimentary features. the logs are mostly silicified, although some may have a coaly exterior. the exposed length of the fossil logs varies from 1 to 11 m. at the miners draw locality, only one site yielding a fossil log has been found so far (table 1). the log at this site in the miners draw area occurs in a silty sandstone unit which is 4 m thick. although this log is stratigraphically higher in the lower salt wash member than those at rainbow draw, the unit is lithologically similar and correlates to the log-bearing unit at rainbow draw (figure 3; sprinkel and others, 2019). like the fossil logs at rainbow draw, this log is silicified and measures 6 m in exposed length. the morrison formation is a laterally widespread formation in the western interior of north america (dodson and others, 1980). at its greatest extent, the morrison formation covered an area from new mexico in the south to alberta and british columbia, canada, in the north. most strata represent terrestrial environments, but some marginal marine beds also occur at the base of the formation in northern utah and colorado northwards (turner and peterson, 2004). in regard to age, the chronostratigraphic age of the morrison formation is accepted to be late jurassic (litwin and others, 1998; schudack and others, 1998; turner and peterson, 2004). recent studies based on single-crystal 40ar/39ar laser fusion methods have yielded recalibrated ages that suggest the lower morrison formation may begin at the end of the oxfordian, but the majority of the formation is kimmeridgian and the upper parts of the formation can reach into the lower tithonian (trujillo and kowallis, 2015). the stratigraphy of the morrison formation is best known on the colorado plateau, where it has been divided into several formally described members (turner and peterson, 2004). at rainbow draw, the members that crop out are the windy hill and tidwell members at the base of the section, which are overlain by the salt wash and brushy basin members. the fossil log and wood horizons are ca. 17 to 27 m above the tidwell member/salt wash member contact and ca. 20 to 50 m below the salt wash member/brushy basin contact (figure 3). recalibrated 40ar/39ar laser fusion dating of single crystals on samples from rainbow draw has yielded a kimmeridgian age bracketed between 152 and 156 ma (trujillo and kowallis, 2015) for the fossil log and wood horizons in the salt wash member at rainbow draw and blue mountain. " " " red fleet reservoir steinaker reservoir vernal naples jensen dry fork a shley creek jones hole cree k big brush creek li t t le b ru s h c re ek clif f c reek gr een river b r ush c r eek gree n river d eep c reek min ers draw morrison fm outcrop dinosaur national monument ´ split mountain yampa plateau blue mountain rainbow draw area m iners dra w area carnegie quarry 0 4 8 12 16 20 km 0 2 4 6 8 10 12 mi u i n ta m o u n t ains u i n t a b asin £¤40 £¤40 £¤191 £¤191 æ·45 æ·88 æ·121 £¤40 figure 2. map showing the morrison formation outcrop belt in and around dinosaur national monument and the location of the renowned carnegie quarry. the miners draw area is south of the blue mountain plateau and rainbow draw is due north of dinosaur national monument. both areas are east of the city of vernal, utah. morrison outcrop locations from hintze and others (2000). figure 1. location of utah (solid gray) and the city of vernal (star) in the western interior of the united states. map modified from http://www.nationsonline.org/oneworld/ usa__blank_map.htm. 80 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 materials and methods fieldwork the location of the fossil logs and wood was mapped in the field (figure 4). exact locality information on all collecting sites is on file at the utah field house of natural history state park museum (fhnhm) in vernal, utah. altogether, there were 10 fossil sites—nine at rainbow draw and one at miners draw, south of blue mountain. a fist-size sample of fossil wood was collected for identification from each log or piece of wood. six fossil logs were found at four of the 10 sites (sites 1, 2, 4, 10). the preserved or exposed length of each fossil log (figure 5a), as well as the maximum diameters at both ends of each log, were measured. if the cross section of the log was not symmetrical, the longest diameter and the so-called short diameter oriented 90˚ to the long diameter was measured. inventory numbers for the specimens were assigned by the fhnhm. laboratory work the ten fossil wood specimens were logged into the inventory system for fossil woods at the university of bonn with the prefix rdw in consecutive order of receipt from rdw-001 to rdw-013. thin sections of all specimens were made at the university of bonn using conventional techniques for petrographic sections. five specimens (rdw-001 to rdw-005) were made in the standard three planes of section—cross, radial, and tangential. thin sections of the other five specimens were cut in only radial section (rdw-006 to rdw-013). all thin sections were studied with a leica dm2500 compound photomicroscope. digital images were taken and processed using the integrated measurement software imageaccess easylab 7. fossil wood thin sections are archived at the division of paleontology, university of bonn, germany, whereas fossil wood samples and duplicate thin sections are deposited at the fhnhm. log length and tree height following the methodology of mosbrugger and others (1994), the minimum height of the trees was reconstructed based on the preserved girth of the logs. the equation l = 0.32 (e/w)1/3 r2/3 was applied, where l is the estimated minimum height of the tree, e is young’s modulus of the wood, w is the specific weight of the wood, and r is the preserved radius area, site, log fossil type length of log (m) max. long diameter (cm) max. short diameter (cm) comments rd, site 1, log 1 log 11.0 127.0 22.9 rd, site 2, log 1 log 2.29 71.1 38.1 rd, site 2, log 2 log 1.27 91.4 30.5 rd, site 3a wood pieces not sampled rd, site 3b wood piece not sampled rd, site 3c wood pieces rd, site 4, log 1 log 1.74 101.6 63.5 rd, site 4, log 2 log 1.27 105.4 110.5 continuation of log 1 at site 4 rd, site 5 wood pieces rd, site 6 log buried, eroding out of hillside rd, site 7 wood piece wood convoluted rd, site 8 wood pieces rd, site 9 log fragmented md, site 10, log 1 log 6.1 buried; full size could not be measured table 1. data collected on morrison formation logs and wood in the field. abbreviations: rd = rainbow draw, md = miners draw. 81 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 fi gu re 3 . s tr at ig ra ph ic se ct io ns m ea su re d in th e m in er s d ra w a nd r ai nb ow d ra w a re as sh ow in g th e fo ss il lo gbe ar in g in te rv al s.m ud st on e si lts to ne si lty s an ds to ne sa nd st on e co ng lo m er at ic s an ds to ne cr os sbe dd ed s an ds to ne co ng lo m er at e ca lc re te pi nk a m yg da lo id al c he rt si lts to ne a nd s an ds to ne sa nd y lim es to ne fo ss il lo g si te fo ss il lo g si te 1 fo ss il lo g si te 1 w oo dbo ne fr ag m en ts up pe r g ra y pa rt no t m ea su re d he re co ve re d co ve re d co ve re d an d no t m ea su re d m ud si lt sa nd gr av el f m c m ud si lt sa nd gr av el f m c m ud si lt sa nd gr av el f m c 10 0 18 0 15 0 50 10 0 18 0 15 0 50 10 0 18 0 15 0 50 m ud si lt sa nd gr av el f m c m et er m ud si lt sa nd gr av el f m c m et er m ud si lt sa nd gr av el f m c m et er br us hy b as in m em be r bu ck ho rn c on gl om er at e m em be r o f ce da r m ou nt ai n fo rm at io n ce da r m ou nt ai n fo rm at io n sa lt w as h m em be r st um p fo rm at io n morrison formation m in er s d ra w s ec tio n (n or th ea st -m id dl e o �s et ) n w 1/ 4 n e1 /4 s ec tio n 3, t . 6 s ., r. 2 5 e. m in er s d ra w s ec tio n (s ou th w es t o �s et ) se 1/ 4 sw 1/ 4 se ct io n 3, t . 6 s ., r. 2 5 e. ra in bo w d ra w s ec tio n n w 1/ 4 n w 1/ 4 se ct io n 24 , t . 3 s ., r. 2 4 e. bu ck ho rn c on gl om er at e m em be r is n ot p re se nt a t r ai nb ow d ra w estimated thickness of unmeasured salt wash and brushy basin members from turner and peterson (1999) j5 un co nf or m ity (? ) so u th n o rt h co lo rs in s ec tio ns a pp ro xi m at es ou tc ro p co lo rs ti dw el l m em be r w in dy h ill m em be r ex pl an at io n 82 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 ´ e e e e! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! e e ! ! ! ! ! ! ! e! ! ! ! ! ! ! ! ! ! ! ! ! e e e " o o o o p p p o p p p #* #* #*#*#* #*#* #* #* #* #* site 1 site 2 sites 3a–3c site 4 site 5 site 6 site 7 site 8 site 9 5 11 10 7 14 19 7 10 8 14 9 qc qc jms jmb qc jms jms qms qac jms jmb kcu qap qc qc jmtw qc jms js qc jmtw jms jms qc jmb jmb jms jms qac jms qc qc jms qc js qc qap r. 24 e. 2423 a a' explanation #* fossil log site o bedding, inclined, field measured p bedding, inclined, calculated cross section a-a' measured section map boundary contact enormal fault, well located normal fault, approximately located ! ! ! ! ! normal fault, concealed syncline marker bed formations qap piedmont gravel qac mixed alluvium and colluvium qc colluvium qms landslide kcu upper member of cedar mountain formation jmb brushy basin member of morrison formation jms salt wash member of morrison formation jmtw tidwell-windy hill members of morrison formation js stump formation 3 t. s. 1 cm = 55.5 m1:5550scale contour interval = 40 feet a 0 1,000 2,000 feet 0 125 250 375 500 meters figure 4. (a) geologic map and (b) cross section of the rainbow draw area wood sites. the morrison formation overlies the stump formation and underlies the cedar mountain formation in rainbow draw. in the mapped area, the morrison includes the windy hill, tidwell, salt wash, and brushy basin members. the fossil log sites are concentrated in two groups on separate ridges. both groups of logs occur in light-colored, fine-grained sandstone and siltstone below a mostly reddish-colored siltstone that was used as a marker bed (blue dashed line). 83 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 figure 5. outcrop photo (a) and micrographs of fossil wood thin sections (b–e) of agathoxylon hoodii comb. nov. gee, sprinkel, bennis et gray. (a) fossil log at rainbow draw (site 2, log 2) that has broken up naturally into pieces. the anatomical structure of this log’s wood is featured in figures 5b, 5c, and 5d. (b) cross section showing an abundance of axial tracheids, but no axial parenchyma nor resin canals. thin section number rdw-002. (c) radial section showing axial tracheids and rays with ray parenchyma cells, some of which bear resin plugs (dark-colored bars). thin section rdw-002. (d) tangential section showing low, uniseriate rays. in this plane, the plugs in the ray cells appear circular in cross section. thin section rdw-002. (e) cross section showing an irregular, discontinuous, partial zone of tracheids with lumina smaller than those of their neighbors. in this case, development of these narrower tracheids was clearly asynchronous relative to tracheids in the same concentric position around the tree trunk. thin section rdw-004. 84 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 of the tree trunk. the exact values for e and w are unknown for these ancient trees, but the ratio e/w is fairly constant (mcmahon and kronauer, 1976; mosbrugger, 1990). in this case, e/w = 1.7 x 106 m was used, which corresponds to a typical conifer such as taxodium or sequoia (wagenführ and schreiber, 1985; cf. mosbrugger and others, 1994). results systematic paleobotany division coniferophyta class coniferospida order coniferales family araucariaceae genus agathoxylon hartig 1848, sensu philippe 1995 agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis et gray comb. nov. figures 5 and 6 synonymy araucarioxylon hoodii tidwell et medlyn — tidwell and medlyn (1993), conifer wood from the upper jurassic of utah, usa—part ii: araucarioxylon hoodii sp. nov.: the palaeobotanist, v. 42, p. 70–77; diagnosis on p. 71; plate 1, figures 1 to 6; plate 2, figures 1 to 6; text figure 2. description: secondary xylem of a fossil trunk (figure 5a); true growth rings absent (figures 5b, 5c, and 5d). in cross section, there are some areas of slower growth that appear as irregular, discontinuous concentric bands of tracheids with narrower lumina (figure 5e). these irregular bands range from 1 to 4 cells thick and did not develop synchronously during the growth of the tree. tracheids subround to elliptical to subangular in cross section; lumen diameters ranging from 11 to 45 µm, those of normal-size cells about 25 µm (figure 5b). tracheid cell walls more uniform in thickness, from 4 to 7 µm thick. radial tracheary pitting consisting of circular bordered pits, most commonly uniseriate (figures 6a, 6b, 6c, and 6d left), or occasionally mixed biseriate and uniseriate (figures 6f, 6g, and 6h). spacing between circular bordered pits along the same tracheid usually contiguous (figures 6a, 6b, and 6d), but also found distant from one another, or so tightly packed that the circular bordered pits begin to take on an angular appearance (figure 6c). when biseriate, pits irregularly arranged (not always in straight lines), varying from alternate to subalternate to subopposite to opposite (figures 6f, 6g, and 6h), even within a single tracheid (figure 6f). pits 10 to 14 µm in diameter, apertures circular, ca. 5 µm in diameter. axial parenchyma not observed. resin plugs common and distinctive in ray cells (figures 5c and 6i), but also clearly observable in cross, radial, and tangential sections (figures 5b, 5c, and 5d). resin plugs also occur in tracheids in the axial system (figure 6d), but less frequently; the tracheids can be identified by the circular bordered pits on their radial walls (figure 6e, arrows). resinous remains also coalesce along the periphery in ray cells, as well as in the cell corners (figures 6a and 6b). rays uniseriate, from 1 to 18 cells high, homocellular, parenchymatous, 20 to 30 µm wide at widest point in tangential section (figures 5c and 6i). horizontal and end walls of ray cells smooth, 1.5 to 3 µm thick, unpitted (figure 6i). crossfield pits numerous and crowded, up to 24 pits per crossfield, contiguous but unordered, with little or no border, bearing a slanted, narrowed aperture (figures 6j and 6k). material studied: the set of fossil wood specimens logged into the university of bonn as rdw-001 to rdw-013 were studied in thin section. repositories: figured thin sections: institute of geosciences, division of paleontology, university of bonn, bonn, germany. fhnm-inventoried specimens of fossil wood and duplicate thin sections: utah field house of natural history state park museum in vernal, utah. collecting sites: sites 1 to 9 in the rainbow draw area (figures 2, 4) and site 10 in the blue mountain area (figure 2), uintah county, utah. the geographic coordinates for all localities are on file at the fhnhm. stratigraphic occurrence: salt wash member of the 85 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 figure 6. caption on the following page. 86 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 morrison formation, late jurassic (figure 3; sprinkel and others, 2019). basionym and type locality: araucarioxylon hoodii tidwell et medlyn from the brushy basin member of the upper jurassic morrison formation on the eastern flank of mt. ellen, henry mountains, utah (tidwell and medlyn, 1993). the holotype was not examined directly during the course of this study. preservation of logs and wood the thin sections made from the wood samples show only secondary xylem. no pith or primary xylem of phloem is present. in the field, the fossil logs are not preserved with bark, and their outer surface appears abraded (figure 5a). even the fossil logs that are relatively intact have weathered surfaces and are worn off unevenly in regard to girth, resulting in logs with different long and short diameters (table 1). these differential girth measurements cannot be attributed to lateral compression of the tree trunks, for the anatomy of the wood cells do not show compression. thus, along with the lack of bark, it can be concluded that the tree trunks are not preserved in their full, original size. taxonomic considerations after over a century of confusion concerning the application of generic names to araucariaceous woods in the fossil record, attempts are being made now to bring the paleoxylological community into agreement regarding the taxonomic priority and validity of agathoxylon, araucarioxylon, dadoxylon, dammaroxylon, and other fossil genera (e.g., philippe and bamford, 2008; philippe, 2011; rößler and others, 2014). most recently, it has been suggested that araucarioxylon be synonymized into agathoxylon (philippe, 2011; rößler and others, 2014), as emended by philippe (1995). thus, following the general consensus of the paleobotanical community for this synonymy (e.g., pujama and others, 2014; rößler and others, 2014), a new nomenclatural combination of agathoxylon hoodii is formally carried out here in our study. until now, this species of fossil wood has only been reported from the upper jurassic morrison formation. comparisons the anatomy of the fossil wood (figures 5b, 5c, 5d, and 5e) shows that all wood studied thus far represents conifer trees and pertains to the same taxon, agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis et gray comb. nov. characteristic of this species are the dominance of axial tracheids (figures 5b, 5c, 5d, and 5e) and the absence of axial parenchyma (figures 5b and 5e) or of any resin canals (figures 5b, 5c, 5d, and 5e); the presence of abundant resin plugs (figures 5b, 5c, 5d, 6d, 6e, and 6i) and other resinous figure 6 is on the previous page. fossil wood thin sections of agathoxylon hoodii showing fine anatomical details. all micrographs were taken of radial sections of thin section rdw-004. (a) axial tracheids with uniseriate, contiguous circular bordered pits. top right, resin remains in the corners of some ray cells. (b) detail of ray cells with resin concentrated along the periphery of the cell walls. (c) radial tracheary pitting so closely spaced that the normally round tracheary pits begin to take on a more angular appearance. (d) two neighboring tracheids: left, one with uniseriate pitting and right, one containing a thick resin plug. (e) close-up of the tracheid with the resin plug in 6d. the focal plane has been shifted to show the outlines of circular bordered pits (arrows), which signify that this is indeed a tracheid and not an axial parenchyma cell. (f) radial tracheary pitting of a single tracheid, showing mixed biseriate and uniseriate pitting. when biseriate, pit arrangement varies from alternate (a), subalternate (sa), subopposite (so), to opposite (o). white lines connect the pit centers of adjacent cells to illustrate the variation in pit arrangement. (g) another example of mixed biseriate and uniseriate tracheary pitting, here in a subalternate arrangement. (h) close-up of the tracheid in 6g to more clearly show the subalternate pit arrangement when biseriate. (i) several cells of a ray showing its homocellular nature and the smooth walls of the ray cells. note the thick, dark-colored resin plug. (j) araucarioid crossfield pitting in ray cells, numerous and crowded, contiguous but unordered, with little or no border, and a slanted, narrowed aperture. (k) another example of araucarioid crossfield pitting in ray cells, showing more clearly the slanted, narrow apertures of the pits. 87 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 remains (figures 6a and 6b); the alternate arrangement of the circular bordered pits in the tracheids, when biseriate (figures 6f, 6g, and 6h); the smooth, unpitted sidewalls and endwalls of the ray cells (figure 6i); and the numerous, small, crowded pits in the crossfields (figures 6j and 6k). true growth rings are absent (figure 5b). however, some wood samples show irregularly occurring, shortterm, slowdowns in growth (figure 5e). these bands or zones of smaller cells with thicker cell walls do not necessarily reach around the entire trunk (figure 5e). furthermore, the cells in the same band of slower growth were not synchronous in their development. reconstruction of minimum tree height the preserved maximum diameters of the four logs at the rainbow draw area vary between 71.1 cm and 127.0 cm (table 1), which results in a minimum reconstructed height of the trees between 19.3 and 28.4 m (table 2), respectively. discussion the form genus, or now more correctly fossil-taxon (cf. turland and others, 2018), of agathoxylon was proposed 20 years ago to apply to fossil woods similar to that of the living araucariaceae, following a review of the systematic history and type material of agathoxylon, araucarioxylon, and dadoxylon (philippe, 2011). in the case of the fossil wood taxon agathoxylon hoodii, its affinity to the araucariaceae is supported by the common occurrence of fossil araucariaceous remains from throughout the morrison formation. in fact, araucaria is known from this formation in the form of seed cones, detached cone scales, seeds, pollen cones, and pollen (litwin and others, 1998; gee and tidwell, 2010; hotton and baghai-riding, 2010; gee, 2013; gee and others, 2014), as well as leaved twigs and branches (gee and tidwell, 2010). agathoxylon hoodii was originally described as araucarioxylon hoodii from the eastern flank of mt. ellen in the henry mountains, south of hanksville in southern utah, which is situated over 300 km southwest of rainbow draw. there are a few minor differences in anatomy between the fossil wood from mt. ellen and the many specimens from the rainbow draw and blue mountain sites. the first difference is that the type material from mt. ellen, a small block of fossil wood roughly 4 cm by 3 cm, appears to contain more resin plugs, especially in the axial tracheids. however, a wide variation in the abundance or scantiness of resin plugs area, site, log fhnhm inventory no. max. radius (cm) reconstructed min. tree height (m) univ. bonn thin section no. taxonomic identification rd, site 1, log 1 fhpr 13360 63.5 28.4 rdw-001, rdw004 agathoxylon hoodii comb. nov. rd, site 2, log 1 fhpr 11749 35.6 19.3 rdw-006 agathoxylon hoodii comb. nov. rd, site 2, log 2 fhpr 11361 45.7 22.8 rdw-002 agathoxylon hoodii comb. nov. rd, site 3a n.a. n.a. agathoxylon hoodii comb. nov. rd, site 3b n.a. n.a. agathoxylon hoodii comb. nov. rd, site 3c fhpr 11751 rdw-007 agathoxylon hoodii comb. nov. rd, site 4, log 1 fhpr 11753 50.8 22.4 rdw-008 agathoxylon hoodii comb. nov. rd, site 4, log 2 fhpr 13362 52.7 25.0 rdw-003 agathoxylon hoodii comb. nov. rd, site 5 fhpr 11755 rdw-009 agathoxylon hoodii comb. nov. rd, site 6 fhpr 11557 rdw-010 agathoxylon hoodii comb. nov. rd, site 7 fhpr 13363 rdw-005 agathoxylon hoodii comb. nov. rd, site 8 fhpr 11759 rdw-011 agathoxylon hoodii comb. nov. rd, site 9 fhpr 11761 rdw-012 agathoxylon hoodii comb. nov. md, site 10, log 1 fhpr 11747 rdw-013 agathoxylon hoodii comb. nov. table 2. utah field house of natural history state park museum inventory numbers, calculated data, university of bonn thin section numbers, and taxonomic identification of morrison formation logs and wood. 88 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 is evident among the wood specimens from rainbow draw. in rdw-002, for example, the resin plugs are only moderately abundant and usually occur in the ray cells, not in the axial tracheids (figures 5b and 5c). in living araucariaceae, the quantity of resin plugs in the wood of individual trees of araucaria bidwillii hook. and a. cunninghamii ait. ex d. don is widely variable, ranging from absent to present (ilic, 1995). in the single specimen of agathoxylon hoodii wood from its type locality on mt. ellen (tidwell and medlyn, 1993), the resin plugs are so plentiful in the rays that it is difficult to observe the crossfield pitting in the ray cells; many axial tracheids in the holotype also contain resin plugs. the abundance and placement of resin plugs in individual wood samples are thus not reliable characters to be used in separating species because they may be subject to individual variations between trees, due to fluctuations in endogenous factors or differences in the paleoenvironment. other minor differences concern the shape of the circular bordered pits and the crossfield pitting. most circular bordered pits on the radial walls of the tracheids are contiguous and round in outline (figures 6a, 6b, and 6d); when more closely arranged, the circular bordered pits take on the more angular appearance (figure 6c) that is characteristic of most other araucarioid wood (e.g., richter and others, 2004). for example, circular bordered pits with a round outline can also be observed in other species of agathoxylon, such as a. desnoyersii (lemoigne) philippe from the middle jurassic of france (philippe, 2011), especially when the circular bordered pits are not crowded and pressing against one another. in the rainbow draw wood specimens, the circular bordered pits are almost always uniseriate. in the rare examples in which the tracheary pitting is biseriate, the circular bordered pits are round in outline (figures 6f, 6g, and 6h), unlike the more angular or hexagonal pits in the single sample of a. hoodii from mt. ellen. in these cases, the round outline of the circular bordered pits in the rainbow draw wood may be attributed to the lack of crowding of the pits in the radial tracheary pitting. the outline of the circular bordered pits can, however, take on a more angular shape approaching hexagonal, for example, when the pits are more closely spaced (figure 6c). in the rainbow draw wood, the pits in the crossfields are narrowly elliptical in shape, with no border or a very narrow border, whereas those in the mt. ellen wood are reported as round to subround and bordered (tidwell and medlyn, 1993). the lack of a round outline in the crossfield pitting of the rainbow draw wood specimens may be attributed to crowding of the pits in the crossfields. similar, elliptical, unbordered crossfield pits can also be observed in agathoxylon pseudoparenchymatosum (gothan) pujana, santillana et marenssi from the eocene of western antarctica (pujana and others, 2014). the fossil wood from the rainbow draw and blue mountain sites does not have true growth rings with well-developed earlywood and latewood, but shows zones of slower and non-synchronous growth. as to be expected in individual trees living under slightly different environmental conditions, the wood specimens have differences regarding the extent and frequency of zones of slower growth. these slowdowns in growth show up as tracheid size in cross section; these tracheids have relatively smaller lumina and relatively thicker cell walls than neighboring, normal-size cells. however, these zones of slower growth are not seasonally induced growth rings, which normally occur in temperate trees, because there is no gradual deceleration in the growth of the secondary xylem (the latewood of one season) followed by a sharp acceleration in growth (the earlywood of the new growing season). furthermore, because the cells within the same zone do not appear to have developed synchronously during the growth of the tree, the slowdowns in growth were possibly induced by endogenous fluxes in growth hormones, such as auxins, in individual trees. such irregular-occurring zones and bands, false rings, and generally uneven growth (e.g., dunwiddie, 1979; oliveira and others, 2010) are common in agathis and araucaria, two of the three living genera in the araucariaceae. in the wood of agathis australia, for example, there may be “areas of locally suppressed or accelerated growth [that] may ‘migrate’ around the tree as it grows,” incomplete sets of growth rings that suddenly appear and ‘wedge out’ on one side of the tree, 89 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 as well as irregular growth-ring thickness within the same ring (dunwiddie, 1979). the wood of wollemia, while very similar to that of agathis and araucaria in many characteristics, appears to be more regular in the pattern of its growth rings (cf. heady and others, 2002). paleoclimatic signal from the lack of growth rings the lack of true growth rings in agathoxylon hoodii suggests that conditions were equable during the entire year and that seasonality was absent, either in temperature or in precipitation, or both. specifically, this means a lack of summer–winter temperature cycles and the associated optimal–nonoptimal growing seasons in temperate woods, or the lack of the wet–dry cyclicity found in monsoonal climates. the climatic equability evident in the wood of agathoxylon hoodii was already pointed out in its original description by tidwell and medlyn (1993), who also remarked on the similarity of the wood to those of living araucarians growing in a warm, humid climate with little or no seasonal fluctuation. other fossil woods from the morrison formation show more seasonality. xenoxylon morrisonense, for example, has either indistinct growth rings, or growth rings with a very wide band of earlywood and a very narrow band of latewood, indicating a long growing season (medlyn and tidwell, 1975). on the other hand, protopiceoxylon resiniferous has well-developed growth rings with a gradual transition from the earlywood to the latewood, which is the pattern commonly in trees undergoing seasonal cyclicity (medlyn and tidwell, 1979). for this reason, tidwell and medlyn (1993) suggested that these tree species grew in different environments; a. hoodii and x. morrisonense likely represent trees in the lowland flora that grew in more equable climates during the late jurassic, whereas the wood of p. resiniferous may have been transported longer distances to lowland facies from environments with more seasonal climate. paleoenvironmental implications the sedimentological occurrence of agathoxylon hoodii in northeastern utah (sprinkel and others, 2019) also supports the hypothesis that a. hoodii was part of the lowland flora. the fossil logs and wood occur in a low-energy fluvial facies, such as found on a floodplain, and they were not transported far from the original growth site of the parent tree (sprinkel and others, 2019). in general, fossil logs and wood in the salt wash member of the morrison formation in utah are found in channel sandstone and conglomeratic sandstone beds. however, the fossil logs in rainbow draw and miners draw occur in very fine to fine-grained sandstone and siltstone beds lacking any sedimentary structures. these beds have been interpreted as overbank deposits on the floodplain (sprinkel and others, 2019), not as a high-energy facies in the river channel. the parautochthonous nature of the logs is reflected in the fine-grained and structureless strata in which they are found. these jurassic trees may have toppled and then been preserved near their original place of growth. alternatively, they may have fallen and then were shifted slightly by low-energy currents during a period of flooding. height, age of morrison trees, and extent of forests the preserved lengths and diameters of the logs at rainbow draw indicate that they represent large trees. the longest fossil tree trunk is log 1 at site 1, which measured 11 m. when the fossil log’s preserved diameter of 127.0 cm is used to reconstruct the height of the living tree (table 1), a minimum height of 28.4 m is attained (table 2); in this case, about 40% of the length of the fossil tree is still intact today. height calculations for the rest of the fossil logs result in minimum reconstructed heights of 25, 22.4, and 19.3 m. these four logs thus yield a canopy height of at least 19 to 28 m for the morrison trees. a height of at least 25 m corresponds to the size of many conifer species native to north america today (burns and honkala, 1990). for example, mature trees of pinus contorta (lodgepole pine), which is a very common species in the rocky mountain and pacific coast regions of north america, reach an average height 90 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 of 25 m at 140 years of age (burns and honkala, 1990). in the subtropical forests of northern queensland in northeastern australia, the native species of a. bidwillii and the plantation trees of a. cunninghamii, a. heterophylla, and a. hunsteinii that were planted about a century ago generally attained heights of about 20 to 30 m (gee, personal observation). in the case of araucaria angustifolia in subtropical brazil, the average height of trees out of 60 trees studied by oliviera and others (2010) was 18 m at one site (average age of trees was 122 years) and 14 m (average age of trees was 90 years) at another site. the minimum tree heights between 19 and 28 m, as calculated for the morrison trees, indicate that the fossil trees were likely as tall, if not taller, than the trees of many extant araucaria species. thus, extrapolating from the height and ages of tall forest conifer trees, specifically those of living araucaria and pinus (burns and honkala, 1990; oliviera and others, 2010), these trees of agathoxylon hoodii most likely were well over 100 years old before they died. some extant species of araucaria, such as a. angustifolia, form large, monospecific forests in brazil, south america (oliviera and others, 2010). other species, such as a. bidwillii in northern queensland, australia, or a. angustifolia in brazil, grow in dense, species-diverse forests and are often the oldest and tallest trees in the forest (gee, personal observation), the so-called canopy emergents (bittencourt, 2007). in any case, extant araucaria spp. are trees that commonly form or grow in forests. if the morrison trees with agathoxylon hoodii wood were similar in habit to living araucaria spp., they would have also formed forests, especially given the optimal growth conditions in the warm, humid, climatically equable, water-unlimited environment. the numerous finds of araucarioxylon hoodii logs and wood in the same stratigraphic horizon at the rainbow draw and miners draw localities—all of which occur in the salt wash member—suggest that the trees were part of a common forest biome in this area, although it is unknown if the individual trees actually lived at the same time. considering the occurrence of a. hoodii in the overlying brushy basin member on what is now mt. ellen in southern utah, a strong case could be made for the widespread presence of a. hoodii conifer forests in northeastern and southeastern utah during the late jurassic. conclusions in summary, newly discovered fossil logs and wood in the rainbow draw and miners draw areas in northeastern utah were found to pertain to agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis et gray comb. nov., a new taxonomic combination proposed in this paper. they were trees that attained at least 127 cm in diameter and 28 m in height, and formed forests of large conifer trees that reached individual ages of over 100 years. their growth rings indicate that the climate was equable; there was no seasonality in the local paleoclimate, neither annual summer–winter temperature cycles, nor wet–dry periods. during the late jurassic, tall conifer forests with agathoxylon hoodii wood grew in at least two areas of what is now utah: east of the city of vernal and near mt. ellen in the henry mountains, south-central utah. acknowledgments we are grateful to olaf dülfer, maren maruhn, and dr. dorota konietzko-meier, all at the university of bonn, for making thin sections, as well as to steven d. sroka, utah field house of natural history state park museum, and p. martin sander, university of bonn, for their support of this research, as well as the utah geological survey. thanks also go to reviewers marc philippe, claude bernard university lyon 1, and john foster, utah field house of natural history state park museum, as well as to grant willis, stephanie carney, and michael hylland, utah geological survey, for their helpful comments. this is contribution no. 174 of the deutsche forschungsgemeinschaft research unit 533, “biology of the sauropod dinosaurs and the evolution of gigantism,” which generously provided funding. references ash, s.r., and tidwell, w.d., 1998, plant megafossils from the brushy basin member of the morrison formation near montezuma creek trading post, southeastern utah: modern geology, v. 22, p. 321–339. 91 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 bittencourt, j.v.m., 2007, araucaria angustifolia—its geography and ecology: the university of reading geography, geographical paper no. 180, p. 1–15, https://www.reading.ac.uk/ web/files/geographyandenvironmentalscience/gp180_araucariajvmb_24jan07_b.pdf. burns, r.m., and honkala, b.h., technical coordinators, 1990, silvics of north america: 1. conifers, agriculture handbook 654., u.s. department of agriculture, forest service, washington, dc., v. 2, p. 877, online, http://www.na.fs.fed.us/spfo/ pubs/silvics_manual/table_of_contents.htm. dodson, p., behrensmeyer, a.k., bakker, r.t., and mcintosh, j.s., 1980, taphonomy and paleoecology of the dinosaur beds of the jurassic morrison formation: paleobiology, v. 6, p. 208– 232. dunwiddie, p.w., 1979, dendrochronological studies of indigenous new zealand trees: new zealand journal of botany, v. 17, p. 251–266. gee, c.t., 2013, applying micro ct and 3d visualization to jurassic silicified conifer seed cones—a virtual advantage over thin-sectioning: applications in plant sciences, v. 1(11). doi: 10.3732/apps.1300039. gee, c.t., dayvault, r.d., stockey, r.a., and tidwell, w.d., 2014, greater paleobiodiversity in conifer seed cones in the upper jurassic morrison formation of utah, usa: palaeobiodiversity and palaeoenvironments, v. 94, p. 363–365. gee, c.t., and tidwell, w.d., 2010, a mosaic of characters in a new whole-plant araucaria, a. delevoryasii gee sp. nov., from the late jurassic morrison formation of wyoming, u.s.a., in gee, c.t., editor, plants in mesozoic time—morphological innovations, phylogeny, ecosystems: bloomington, indiana university press, p. 67–94. hartig, t., 1848, beiträge zur geschichte der pflanzen und zur kenntnis der norddeutschen braunkohlen-flora: botanische zeitung (berlin), v. 6, p. 122–128, 137–141, 166–172, 185–190. heady, r.d., banks, j.g., and evans, p.d., 2002, wood anatomy of wollemi pine (wollemia nobilis, araucariaceae): iawa journal, v. 23, p. 339–357. hintze, l.f., willis, g.c., laes, d.y.m., sprinkel, d.a., and brown, k.d., 2000, digital geologic map of utah: utah geological survey map 179dm, compact disc, 17 p., scale 1:500,000. hotton, c.l., and baghai-riding, n.l., 2010, palynological evidence for conifer dominance within a heterogeneous landscape in the late jurassic morrison formation, u.s.a., in gee, c.t., editor, plants in mesozoic time—morphological innovations, phylogeny, ecosystems: bloomington, indiana university press, p. 294–328. ilic, j., 1995, distinguishing the woods of araucaria cunninghamii (hoop pine) and araucaria bidwillii (bunya pine): iawa journal, v. 16, p. 255–260. litwin, r.j., turner, c.e., and peterson, f., 1998, palynological evidence on the age of the morrison formation, western interior u.s.: modern geology, v. 22, p. 297–319. lutz, h.j., 1930, a new species of cupressinoxylon (goeppert) gothan from the jurassic of south dakota: botanical gazette, v. 90, p. 92–107. mcmahon, t.a., and kronauer, r., 1976, tree structure—deducing the principle of mechanical design: journal of theoretical biology, v. 59, p. 443–466. medlyn, d.a., and tidwell , w.d., 1975, conifer wood from the upper jurassic of utah, part i—xenoxylon morrisonense sp. nov.: american journal of botany, v. 62, p. 303–309. medlyn, d.a., and tidwell, w.d., 1979, a review of the genus protopiceoxylon with emphasis on north american species: canadian journal of botany, v. 57, p. 1451–1463. medlyn, d.a., and tidwell, w.d., 2002, mesembrioxylon obscurum, a new combination for araucarioxylon? obscurum, from the upper jurassic morrison formation: western north american naturalist, v. 62, p. 210–217. morgan, s.k., lindsay, b.w., and williams, a.p., 2010, geology of escalante state park, utah, in sprinkel, d.a., chidsey, t.c., jr., and anderson, p.b., editors, geology of utah’s parks and monuments: utah geological association publication 28 (third edition), p. 429-438. mosbrugger, v., 1990, the tree habit in land plants—a functional comparison of trunk constructions with a brief introduction in the biomechanics of trees: berlin, springer, 161 p. mosbrugger, v., gee, c.t., belz, g., and ashraf, a.r., 1994, three-dimensional reconstruction of an in situ miocene peat forest from the lower rhine embayment, nw germany— new methods in palaeovegetation analysis: palaegeography, palaeoclimatology, palaeoecology, v. 110, p. 295–317. oliveira, j.m., roig, f.a., and pillari, v.d., 2010, climatic signals in tree-rings of araucaria angustifolia in the southern brazilian highland: austral ecology, v. 35, p. 134–147. peterson, f., undated, summary list of late jurassic plants, western interior u.s. & sw canada: online, http://www.webpages. uidaho.edu/~jparrish/morrison_plants.pdf. philippe, m., 1995, bois fossiles du jurassique de franche-comté (ne-france): palaeontographica, abt. b, v. 236: 45–103. philippe, m., 2011, how many species of araucarioxylon?: comptes rendus palevol, v. 10, p. 201–208. philippe, m., and bamford, m., 2008, a key to morphogenera used for mesozoic conifer-like woods: review of palaeobotany and palynology, v. 148, p. 148–207. philippe, m., thévenard, f., nosova, n., kim, k., and naugolnykh, s., 2013, systematics of a palaeoecologically significant boreal 92 silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation gee, c,t., sprinkel, d.a., bennis, m., and gray, d.e. geology of the intermountain west 2019 volume 6 mesozoic fossil wood genus, xenoxylon gothan: review of palaeobotany and palynology, v. 193, p. 128–140. pujama, r.p., santillana, s.n., and marenssi, s.a., 2014, conifer fossil woods from the la meseta formation (eocene of western antarctica)—evidence of podocarpaceae-dominated forests: review of palaeobotany and palynology, v. 200, p. 122–137. richter, h.g., grosser, d., heinz, i., and gasson, p.e., 2004 [second printing 2011], iawa list of microscopic features for softwood identification: iawa journal, v. 25, p. 1–70. rößler, r., philippe, m., van konijnenburg-van cittert, j.h.a., mcloughlin, s., sakala, j., and zijlstra, g., coordinating editors, 2014, which name(s) should be used for araucaria-like fossil wood?—results of a poll: taxon, v. 63, p. 177–184. schudack, m.e., turner, c.e., and peterson, f., 1998, biostratigraphy, paleoecology, and biogeography of charophytes and ostracodes from the upper jurassic morrison formation, western interior, usa: modern geology, v. 22, p. 379–414. sprinkel, d.a, bennis, m.b., gray, d.e., and gee, c.t., 2019, stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah: geology of intermountain west, v. 6, p. 61–76, a1–a5. tidwell, w.d., 1990, preliminary report on the megafossil flora of the upper jurassic morrison formation: hunteria, v. 2, no. 8, p. 1–11. tidwell, w.d., britt, b.b., and ash, s.r., 1998, preliminary floral analysis of the mygatt–moore quarry in the jurassic morrison formation, west-central colorado: modern geology, v. 22, p. 341–378. tidwell, w.d., and medlyn, d.a., 1993, conifer wood from the upper jurassic of utah, part ii—araucarioxylon hoodii sp. nov.: the palaeobotanist, v. 42, p. 1–7. trujillo, k.c., and kowallis, b.j., 2015, recalibrated legacy 40ar/39ar ages for the upper jurassic morrison formation, western interior, u.s.a.: geology of intermountain west, v. 2, p. 1–8. turland, n.j., wiersema, j.h., barrie, f.r., greuter, w., hawksworth, d.l., herendeen, p.s., knapp, s., kusber, w.-h., li, d.-z., marhold, k., may, t.w., mcneill, j., monro, a.m., prado, j., price, m.j., and smith, g.f., editors, 2018, international code of nomenclature for algae, fungi, and plants (shenzhen code), adopted by the nineteenth international botanical congress shenzhen, china, july 2017: regnum vegetabile, v. 159, glashütten, koeltz botanical books, doi: https://doi. org/10.12705/code.2018. turner, c.e., and peterson, f., 2004, reconstruction of the upper jurassic morrison formation extinct ecosystem—a synthesis: sedimentary geology, v. 167, p. 309–355. wagenführ, r., and schreiber, c., 1985, holzatlas: leipzig, fachbuchverlag, 2nd edition, 720 p. a guide to the bedrock geology of range creek canyon, book cliffs, utah geology of the intermountain west an open-access journal of the utah geological association volume 1 2014 a guide to the bedrock geology of range creek canyon, book cliffs, utah nora m. nieminski1 and cari l. johnson2 1department of geological and environmental sciences, stanford university, stanford, california; norski87@gmail.com (formerly department of geology and geophysics, university of utah, salt lake city, utah) 2department of geology and geophysics, university of utah, salt lake city, utah © 2014 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org www.utahgeology.org geology of the intermountain west an open-access journal of the utah geological association editors douglas a. sprinkel utah geological survey 801.391.1977 dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net production cover design and desktop publishing douglas a. sprinkel cover photograph range creek canyon. photograph by nora nieminski. i 2014 president grant willis grantwillis@utah.gov 801.537.3355 2014 president-elect april abate aprilabate@utah.gov 801.538.5214 2014 program chair wayne western waynewestern@utah.gov 801.538.5263 2014 treasurer scott clark clark.scotth@gmail.com 2014 secretary mike hylland mikehylland@utah.gov 801.537.3382 2014 past-president craig morgan craigmorgan@utah.gov 801.537.3370 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 sandy eldredge sandyeldredge@utah.gov 801.537.3325 publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2014-2016 term tom morris tom_morris@byu.edu 801.422.3761 state mapping advisory committe uga representative terry massoth twmassoth@hotmail.com 801.422.3761 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists volume 1 2014 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 6 geology of the intermountain west an open-access journal of the utah geological association volume 1 2014 a guide to the bedrock geology of range creek canyon, book cliffs, utah nora m. nieminski1 and cari l. johnson2 1department of geological and environmental sciences, stanford university, stanford, california; norski87@gmail.com (formerly department of geology and geophysics, university of utah, salt lake city, utah) 2department of geology and geophysics, university of utah, salt lake city, utah nieminski, n.m., and johnson, c.l., 2014, a guide to the bedrock geology of range creek canyon, book cliffs, utah: geology of the intermountain west, v. 1, p. 6-31. © 2014 utah geological association. all rights reserved. for permission to copy and distribute, see the preceeding page or visit the uga website, www.utahgeology.org , for information email inquiries to giw@utahgeology.org introduction range creek canyon is an isolated canyon located southeast of price, utah, within the book cliffs (west of desolation canyon between the book and roan cliffs) in emery county (figure 1). the entire canyon is cut by the serenely flowing range creek, which is guarded on either side by walls of beautifully exposed rock; a physical record of the canyon’s geologic past and a gallery of hundreds of fremont indian sites that recount its archaeological history. range creek canyon was discovered by white settlers in 1884 and was used primarily for cattle ranching until recently. after the wilcox family purchased the property in 1951, two generations of wilcoxes succeeded in making a living in this remote area. the wilcox family held the ranch until 2001, when it was sold to the u.s. bureau of land management. ownership was abstract range creek canyon, located within the book cliffs of eastern utah, contains some of the most abundant and well-preserved archaeological sites in north america. its cliffs and landscapes provide a canvas for rock art panels and a foundation for granaries, ruins, and artifacts of the prehistoric fremont indians. in order to place these range creek sites within a geologic context, an illustrated geologic field guide was created for the general public. the guide focuses on the major bedrock formations that crop out in the canyon, as well as many indicators that facilitate geologic interpretation of these rocks. outcrops of the paleogene flagstaff and colton formations (~58 to 48 million years old) in range creek canyon were investigated in order to interpret their depositional environments. the lacustrine flagstaff limestone contains limestone beds and fossils of freshwater gastropods, oysters, and turtles indicative of lake environments. the unit coarsens upward with an increase of interbedded sandstone, which was deposited in and near ancient river channels. this trend suggests dynamic levels of the ancient lake, with overall encroachment of river systems near the contact with the colton formation. the fluvial colton formation is characterized by discontinuous, stacked beds of sandstone, representing a succession of migrating river channels and floodplain deposits. the colton formation exhibits a general upward trend of increased grain size and increased channel belt (continuous sandstone beds) frequency and lateral extent, implying a transition to higher energy river systems through time. these dynamic, ancient rivers may have been flowing generally northward into eocene lake uinta, recorded in deposits of the green river formation north of range creek canyon. www.utahgeology.org 7 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 later transferred to the state of utah (gerber and aton, 2011). in 2009, the former ranch came under the management of the natural history museum of the university of utah as a field station to train students and serve as a catalyst for the study of the natural history of the area. there are numerous markers throughout the canyon that recount the relatively recent history of range creek. near the top of the switchbacks of the horse canyon road, leading into range creek from the north, historic graffiti strictly warn visitors that there is “no pickin’ flowers” and “no beer drinkin’ ” within the canyon. coal cars used as dams in the creek are still visible. a few stone houses and remains of homesteads can be found near the creek, and abandoned exploratory gas wells document exploration drilling that was abandoned in the 1970s. just as the canyon offers reminiscent remains of “early” settlers of the nineteenth and twentieth centuries, range creek is also filled with evidence of the much more ancient inhabitance by the fremont indians, who occupied the canyon a thousand years ago, before mysteriously disappearing (kloor, 2006). as of 2013 archaeologists have found and recorded 465 archaeological sites, with only about 10 percent of the canyon explored (duncan metcalfe, university of utah, written communication, november 27, 2013). archaeologist kevin jones explains that what makes range creek such a “national treasure” is that “there are few 2 north gate 1 horse canyon pass geneva coal mine 4 locomotive rock 6 5 3 gas well dry-hole marker nelson canyon mud plug granary 7 cherry meadow dilly canyon 8 9wilcox ranch qal stream alluvium qaf alluvial-fan deposits qtpm pediment mantle tg green river formation tc colton formation tfn flagsta�-north horn formations kpru price river formation kc castlegate sandstone kbm bluecastle sandstone kbh blackhawk formation kmu mancos shale qaf qaf quaternary tertiary cretaceous to e as t c ar bo n ci ty w110.15°w110.31° n 39 .4 75 ° n 39 .3 75 ° 2 miles10 price moab green river st. george salt lake city range creek n range creek area figure 1. geologic map of the range creek area showing the route and stops described in this article (geologic map after witkind, 2004). 8 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 places left in the continental u.s. where the sites haven’t been picked over and vandalized to a great extent” (potterfield, 2004; kloor, 2006, p. 70). the relatively pristine condition of many of the sites in range creek offers more dependable insight into their original purpose and use. the fremont indians were foragers and farmers who lived in most of what is now the state of utah between a.d. 200 and a.d. 1300. evidence of their occupation of range creek includes dwellings, granaries, petroglyphs, and pictographs. the specific locations of sites are of particular interest to archaeologists. dwellings are usually found along the lower slopes of the canyon, above the valley bottom and farm plots, where the flat terrain is easily accessible and proximal to the creek. many of the granaries for storage of food, however, are located on heart-stoppingly steep cliff faces hundreds of feet high. clearly, the fremont had something to fear, something from which to keep their food protected (metcalfe, 2008; barlow and phillips, 2010). some archaeologists speculate this threat led to their subsequent, sudden disappearance (madsen and simms, 1998). the dangerous location of granaries is one direct connection that has inspired archaeologists’ interest in the geologic history of range creek—a fascinating story millions of years older than the prehistoric fremont sites. the rocks within range creek offer an excellent opportunity to learn about the region’s geologic history. in particular, the canyon provides abundant clues as to the processes by which the rocks were deposited, millions of years before the fremont came to inhabit them. regional geology the geologic origin of the rocks within range creek canyon is associated with the ancient uinta basin, which encompasses most of northeast utah (johnson, 1985; morgan and others, 2003). the uinta basin is a sedimentary basin, which is a relatively low topographic area that was filled with different layers of sediments deposited during successive time periods (figure 2). at periods when there is high accommodation (space for sediment to be deposited and preserved) relative to sediment supply, lake environments are most common. however, when available accommodation becomes much smaller relative to sediment supply, rivers commonly occupy and migrate over one another across the floodplain. these successive changes of environments are recorded in the stratigraphy of the ancient uinta basin. the uinta basin and co-existing piceance basin (separated by the douglas creek arch in colorado) are generally bound by the uinta mountains to the north, the san rafael swell to the south, the white river uplift and elk mountain (in colorado) to the east, and the wasatch range and wasatch plateau to the west (figure 3; johnson, 1985; morris and others, 1991; dubiel, 2003). the uinta basin formed as a result of active thickening and loading of the earth’s crust due to a regional mountain-building event known as the laramide orogeny, 75 to 35 million years ago, during late cretaceous to late eocene time (johnson, 1985; carroll and others, 2006; lawton, 2008). this tectonic event helped form the uinta basin by loading the crust, which resulted in a depression adjacent to the loading in the same way that a diving board will bend behind the person (load) applying stress to it. structurally, the uplifted surrounding highland produced a basin with internal drainage, which was filled by ancestral lake uinta and lake flagstaff, and was fed by several rivers. this ancestral lake deposited both fluvial (river) and lacustrine (lake) sediments (johnson, 1985; morgan and others, 2003; dubiel, 2003; keighley and others, 2003). rocks and depositional environments of range creek canyon exposed rocks within range creek canyon are roughly late paleocene to early eocene in age, and thus range from approximately 58 to 48 million years old (ryder and others, 1976; franczyk and pitman, 1991). the age ranges for rock units is variable depending on location (figure 2). the major rock units exposed in range creek include the flagstaff and colton formations, both lying below the green river formation (figure 1). each of these rock units is described at various stops in the field guide. flagstaff limestone the flagstaff limestone, partially equivalent to the north horn formation, is late paleocene to early 9 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 eocene in age (beginning ~58 million years ago) and is exposed north of range creek, along the drive up horse canyon and at the southern end of range creek canyon (figure 2; stanley and collinson, 1979; wells, 1983; franczyk and pitman, 1991). in the road guide that follows, the flagstaff limestone is distinguished from the north horn formation, and is first described 11.2 miles from the north gate. in range creek, the flagstaff limestone is comprised primarily of limestone beds. limestone is a sedimentary rock largely composed of calcium carbonate (caco3), which has chemical properties that make it highly soluble in water and weak hydrochloric acid solution (hcl). limestone is formed by organic and inorganic processes that precipitate the mineral calcite in marine, lacustrine, or evaporite environments. within the limestone beds of the flagstaff limestone, there is a relatively high concentration of fossils including gastropods, oyster shells, and even turtle shell fragments, all of which have been documented to inhabit freshwater lakes during the late paleocene and early eocene geological epochs. there are also burrows in the rocks, which can be created by a variety of water-living organisms as they scrounge for food or escape predators in an environment of relatively low energy, such as a lake (stop #8 and corresponding figures). thus, the flagstaff limestone reflects lake and lake-margin depositional environments. the flagstaff limestone, though mostly limestone, coarsens upward and has increased interbedded sandstone layers up-section. sandstone is usually deposited in higher energy environments, such as fluvial depositional environments. the interbedded sandstone within the limestone suggests dynamic levels and hydrology of the ancient lake flagstaff with an overall increase in proximity to fluvial sediment input at the contact of the flagstaff with the colton formation. these dynamic price canyon sunnyside east wasatch canyon green river sego canyon price river formation blackhawk formation blue gate shale member (mancos) green river formation neslen fm.sego ss. buck tongue erosion age in m.y. age lutetian (partial) ypresian selandian thanetian danian maastrichtian campanian c en ez o ic (p ar tia l) m es o zo ic (p ar tia l) c r et a c eo u s (p ar t.) la te (p ar tia l) pa le o g en e (p ar tia l) eo c en e( pa rt .) pa le o c en e 80 70 60 50 colton formation wasatch formation flagstaff limestone north horn formation blue gate shale member of mancos shale castlegate sandstone erosion or non-deposition erosion or non-deposition figure 2. simplified stratigraphic cross section of late cretaceous and early paleogene sedimentary units deposited in the uinta basin near range creek canyon (scaled to time axis). approximate location of range creek canyon is near sunnyside. general stratigraphy exposed near range creek canyon (from oldest to youngest) is: blackhawk, castlegate, price river, north horn, flagstaff, colton, and green river formations. gray, diagonally marked units represent missing time in section (unconformities) from non-deposition or erosion. vertical lines that break up units mark changes in nomenclature, depending on region (modified from franczyk and pitman, 1991). 10 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 lake levels were most probably a response to tectonic and climactic changes at the time, similar to contemporary lakes that vary in size and depth due to the same causes (stanley and collinson, 1979). colton formation exposed in the northern part of range creek canyon, and stratigraphically above the flagstaff limestone, lies the younger colton formation, partially equivalent to the wasatch formation (figure 2; franczyk and pitman, 1991; morgan and others, 2003). the colton formation is early eocene in age, or roughly 55 to 48 million years old (ryder and others, 1976; pitman and others, 1986; franczyk and pitman, 1991). it is composed of sandstone and mudstone and is the rock unit where most of the fremont granaries are located. because sandstone is deposited under higher energy and has a larger grain size, it tends to resist erosion and form large cliff faces, whereas mudstone and shale wear away and appear receded within the walls of rock (stop #4 and corresponding figures), depending on degrees of cementation. fremont granaries were meant to be protected from weather and foe, and that is most likely the reason the fremont indians in range creek chose to build their granaries in more resistive, cliff-forming sandstone rock layers of the colton formation. sandstone beds of the colton formation were deposited by rivers that flowed throughout the area that is now range creek canyon. these rivers flowed northward and fed into ancient lake uinta (dickinson and others, 1986; morris and others, 1991; dickinson and others, 2012). this can most easily be tested with more research within the canyon, specifically by taking measurements of structures within the sandstone bedding to statistically determine the direction of water flow (paleocurrents) as sediments were deposited. it is clear that rivers occupied what is now range creek canyon for millions of years, as indicated by the discontinuous, stacked beds of sandstone and interbedded mudstone layers, representing a succession of migrating river channels and inter-channel (floodplain) deposits. outcrops of discontinuous sandstone beds are indicative of fluvial systems because of the river system’s dynamic energy levels (as opposed to a constant, more stagnant, lower energy lake environment that can be recognized by continuous limestone beds). relatively continuous sandstone cliffs such as those visible throughout range creek indicate migrating river channels. as rivers migrate across a floodplain, they continually stack layers of sand that are deposited out of the water column as high-energy events (like floods) wane to lower-energy flow (figure 4). finer-grained sediments, like mud and silt, in contrast, are more easily transported by low-energy systems. thus, mudstone is usually deposited during lower-energy events, or during sudden (and often complete) waning of high-energy systems. if a river suddenly abandons its channel and moves to another position on the floodplain or if its water level decreases rapidly, the energy dramatically drops from figure 3. location of range creek canyon with respect to bounding structural features that contributed to the formation of the uinta basin. the co-existing piceance basin in colorado (not shown) was separated by the douglas creek arch, also in colorado. the paleogene extent of the uinta-piceance basins is bounded by the uinta mountains to the north, by the san rafael swell to the south, by the white river uplift and elk mountains on its eastern edge in colorado (not shown), and by the wasatch range and wasatch plateau on its western edge (modified after stanley and collinson, 1979; dubiel, 2003). uinta basin uinta mountains san rafael swell w a s a tc h r a n g e salt lake city n range creek wasatch plateau 25 mi 11 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 the high energy of a flowing river to much lower energy. the mud that the river was carrying at higher energy is deposited during such a low-energy event, and eventually becomes mudstone that can often be seen deposited in the shape of its ancient channel (stop #6 and corresponding figure). when a mudstone layer appears to be deposited in the shape of a smile (which, with some imagination, reflects the shape of the cross section of a river channel), it is indicative of an abandoned channel that was filled in by lower-energy mud after the river avulsed from its previous location on the floodplain. smaller-scale features within the colton formation that characterize the fluvial depositional system include cross-bedding within the sandstone, which indicates direction of water flow; channel scours, which are indicative of erosion at the base of river channels; and other sedimentary features such as channel lags, which contain larger-grained pebbles, indicating higher energy of a river channel (stop #5 and corresponding figures). all of these features, both large and small scale, in range creek describe the ancient river regime. the colton formation as a whole exhibits a general upward trend of increased grain size, channel belt (sandstone bed) frequency, and lateral extent. the lower part of the colton formation is distinguished by a darker red lithology (rock composition) that is much finer grained and has more abundant interbedded mudstone compared to the upper, lighter-colored, coarser-grained, sandstone-dominated unit of the colton (figure 5). this coarsening-upward sequence of the colton formation implies a transition from lower energy river environments, deposited just after the deposition of lacustrine sediments of the flagstaff limestone, to higher energy river systems that evolved with time. green river formation even though the green river formation is not exposed in the bottom of range creek canyon, it can be seen in the distance on top of many of the peaks bordering the canyon, capping both the flagstaff and colton formations. the green river formation ties together the depositional history of the flagstaff and colton formations, as the rivers of the colton formation are interpreted to have flowed into lake uinta, which is recorded in the deposits of the middle eocene green river formation (marcantel and weiss, 1968; blakey and ranney, 2008; smith and others, 2008). the green river formation has been extensively described north of range creek canyon, in nine mile canyon. the rock unit is characterized by finer-grained sandstone that has fewer fossils than the flagstaff and colton formations and is interbedded with abundant green shale (marcantel and weiss, 1968; remy, 1992; keighley and others, 2003). the shale beds of the green river formation have proven to be a reliable source for oil and gas in the uinta basin, having been buried to sufficient depths and temperatures to convert ancient biomass to valuable hydrocarbons (cashion, 1967; pitman and others, 1986). deposition at point bar erosion at cutbank previous channel deposit channel migration figure 4. a meandering river channel migrates laterally by cutting away at its cutbank and by depositing sediment at its point bar. the process of erosion and deposition is related to the vortex water flow of the water around each bend of the channel. the arrows in the figure represent the flow path that hits the cutbank with the highest energy, after which a secondary, lower-energy flow carries the eroded material from the cutbank across the floor of the channel where it is deposited at the point bar, at the other side of the channel, and only a small distance downstream. as the channel migrates, the point bar deposits end up stacked on top of one another and can then be preserved in the rock record if ever buried below the surface. the previous channel deposits of a migrating channel represent what comprises the sandstone cliffs in range creek. 12 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 geologic evolution of paleogene strata of range creek just as the fremont history reveals conditions of prehistoric human life in range creek canyon, the geologic layers indicate changing environmental conditions of the area before the canyon cut by range creek ever existed. a working hypothesis is that the paleogene rocks exposed in range creek record a major climatic shift, in addition to changing tectonic conditions (bowen and others, 2008). more detailed study of these rocks, particularly of the contact between the flagstaff and colton formations, might offer information concerning environmental conditions roughly 56 million years ago. the limestone of the flagstaff preserves significant organic content. not only is the limestone abundant in fossils, but it also contains wood fragments and coal seams, both indicative of high organic matter preservation favored particularly in wet, oxygen-reducing conditions (figure 6). the lower unit of the colton formation immediately above the flagstaff, however, is much poorer in organic content and is distinctly red, indicating more oxidized and high-energy environments. organic content does increase near the top of the colton formation and into the green river formation at the top of the plateau. thus, moving upward in the section, or moving up into younger layers, organic content decreases for a certain interval in time before increasing again much higher in the section (later in time). this dramatic change could signify a warming and drying within the periods of deposition of these two layers. on the geologic time scale, the flagstaff and colton formations encompass the paleocene-eocene boundary, which is well known for the paleocene-eocene lower colton formation upper colton formation figure 5. view facing southeast from the mouth of dilly canyon, showing exposed rock formations in range creek. the flagstaff limestone is easily distinguishable by its gray color and laterally continuous thin limestone beds. recall that the flagstaff limestone is exposed along the drive up horse canyon, but is not exposed within range creek canyon until 11.2 miles from the north gate. above the flagstaff limestone in range creek canyon is the lower unit of the colton formation, which is distinguished from the upper unit by its redder color and more abundant interbedded mudstone within the sandstone. the upper colton formation exhibits a higher channel belt frequency (has more abundant laterally continuous cliffs of sandstone). 13 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 thermal maximum (petm). this major climatic shift is documented worldwide as a time when the global mean temperatures increased by 6 to 8°c (11-14°f) within 10,000 to 30,000 years (higgins and schrag, 2006; roehl and others, 2007). regionally, temperatures may have increased by 4 to 5°c (7-9°f) or even by as much as 12°c (22°f) over the subsequent 6 million years following the early deposition of the flagstaff limestone (wilf, 2000; zachos and others, 2001). although the causes of this drastic event are still debated, the warming was clearly triggered by an incredible and sudden influx of carbon into the atmosphere (torfstein and others, 2010). pending further research, it is postulated here that the rocks of range creek canyon could record this remarkable event. road guide to geologic points of interest range creek canyon, although most well known for its beautifully preserved fremont indian sites, is also filled with interesting geologic sites that display features in the rocks that are indicative of ancient depositional processes and geologic history of the area. several select sites are described in this road guide starting at the mouth of horse canyon, 9.5 miles southeast from east carbon city, entering range creek canyon on the east side of horse canyon pass, and ending at the wilcox ranch, roughly 7 miles west of where range creek feeds into the green river. visitor permits (obtained from the national history museum of utah) are required to enter range creek canyon. permitted access to the canyon is available from approximately mid-may to late november. visitors should consult the natural history museum of utah website (www.nhmu.utah.edu) for updated specifications concerning permits. disruption and/or collection of any rocks, fossils, or artifacts from the canyon are strictly prohibited. once within range creek canyon (starting at the second gate, described in the guide), this road guide follows the same 13-mile route through range creek canyon that is covered by guided tours that are available through various tour providers. the guided tours stop at several locations to view rock art and granaries within the canyon. this road guide is best used to supplement a guided tour by adding information about geologic features at many of the stops highlighting fantastic fremont indian sites. figure 1 shows the locations of the nine sites covered in the 23-mile guided route road guide. each of these numbered sites corresponds to the following numbered stops along the route. 1. geneva coal mine at horse canyon to reach the geneva coal mine (stop #1) at the mouth of horse canyon, turn right on ut-124 s and continue 9.4 miles from east carbon city. stay left where ut-124 s becomes horse canyon road. just after the paved horse canyon road that leads to the mouth of horse canyon becomes a dirt road, it passes alongside the remains of the abandoned geneva coal mine figure 6. two indicators of organic content in rocks are wood fragments and coal seams. wood fragments that are preserved in rocks are usually red in color from being oxidized over time. coal is usually thinly bedded and can be poorly consolidated. both wood and coal are often associated with very low-energy, organic-rich depositional environments such as lagoons or backswamps on the other side of river channel levees. 14 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 (figure 7). the mine, originally run by geneva coal and steel, was developed in 1942 to support the world war ii war effort (butler, 1961; also see utah coal program website). the geneva steel mill was built in orem, utah, during the same year to process the mine’s metallurgical grade coal from the book cliffs reserves. after the war, the united states steel corporation purchased both the mine and the mill and continued operation under the name of horse canyon coal mine until the facilities were closed in 1982. the rock layers directly above the mine consist of the upper cretaceous blackhawk formation, castlegate sandstone, and price river formation, ranging from roughly 80 to 70 million years in age (figures 1 and 2). these rock formations, though nicely exposed along the drive up horse canyon road, are not exposed in range creek canyon. the blackhawk formation is characterized as a fineto medium-grained sandstone with siltstone and interbedded coal and has been interpreted as the westernmost edge of the western interior seaway: an ancient sea that divided north america during the late cretaceous (~100 to 66 million years ago). the ancient seaway’s shoreline gradually migrated eastward during the late cretaceous time period, as shown in figure 8 (johnson and others, 2005). this eastward regression of the western interior seaway deposited sediment that resulted from the marine and shoreline depositional environments, and that are represented in the blackhawk formation throughout the book cliffs. by comparison, the flagstaff (north horn), colton (wasatch), and green river formations were deposited beginning ~20 million years later, after this seaway had receded and was replaced by large river and lake systems. the coal that was mined in horse canyon (and the seam of coal that can be seen capping a white layer of shoreface sandstone here at the bottom of horse canyon) was most likely deposited in the coastal mires near the shoreline of the western interior seaway. here organic plant material was deposited as peat and eventually converted to coal during burial. the uppermost part of the drive up horse canyon offers an ample introduction to the rock units that are exposed in range creek canyon; the flagstaff and the colton formations, composed of rocks that were deposited from the lakes and rivers that existed in the area roughly 58 to 48 million years ago (figure 1; franczyk figure 8. north america split in two by the western interior seaway, roughly 100 million years ago. highlight of utah shows the approximate paleoshore during the deposition of the blackhawk formation (modified after johnson, 1985). figure 7. view of geneva coal mine, at the mouth of horse canyon, on the right side of the road looking up the canyon. 15 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 and pitman, 1991; witkind, 2004). above the blackhawk, castlegate, and price river formations there is a transition into the gray limestone of the flagstaff limestone, which is exposed again in the southern end of range creek canyon. along the climb up horse canyon, watch for yet another transition and contact between this gray limestone of the flagstaff limestone and a reddish sandstone that makes up the colton formation (figure 9). 2. horse canyon pass horse canyon pass (elevation 8577 feet) is 5.5 miles farther along the main dirt, horse canyon road, from the horse canyon mine. stop #2 offers an ideal opportunity to step outside the car, take in the beauty of the surrounding book cliffs, and peer down (looking east) into the mystifying range creek canyon. roughly 50 feet from the pullout at the pass, in the direction of horse canyon, there is a road cut that illustrates the transition from lacustrine to fluvial deposits (figure 10). the distinct tabular bedding of sand is indicative of lacustrine deposits, which often include tabular, continuous beds of limestone or other sediments such as siltstone and/or mudstone (figure 10a). alternating layers of red and green siltstone indicate changing conditions of lake levels from more oxidizing to more reducing conditions, respectively, as the lake expanded and contracted over time (figure 10b). overall, these sediments may have been deposited in an interdistributary floodplain (a boggy, low energy environment). north gate is a gate located 4.1 miles past the horse canyon pass along little horse canyon road, which is a continuation of the horse canyon road from the pass. after passing through this first gate, make a right turn (on range creek road) after the creek crossing to reach the second gate (0.3 miles south of first gate) and begin the journey to range creek field station, or wilcox ranch (the road that veers left after crossing the creek leads to private property). 3. gas well dry-hole marker one of the most important applications of geoscience involves the interpretation and mapping of geology in the subsurface for oil and gas exploration. stop #3 is a dry-hole marker on the west side of the road that marks an abandoned exploratory gas well drilled by chevron oil company 1.4 miles past the second gate and at the mouth of dry canyon (figure 11). this well, nelson unit #1 (api# 43-015-30022), is located at an elevation of 6633 feet above sea level and reached flagsta� formation limestone & mudstone colton formation sandstone figure 9. view of flagstaff and colton formations (the two predominant rock units that are exposed within range creek canyon) along the drive up horse canyon. photo taken in horse canyon, facing northwest, approximately 3 miles east of the geneva coal mine. 16 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 a total measured depth of 8773 feet (all inscribed on the marker itself). the drilling of the well commenced in 1974, and the well was plugged and abandoned just over a year later in 1975 (see utah oil and gas program website for well information). schlumberger, an oilfield service company, was hired to run gamma-ray, resistivity, neutron density, and sonic wireline logs (measurements with depth) in the well; no core was taken. these measurements are used by geologists and petroleum engineers to interpret rock types and determine the rock properties of the penetrated subsurface formations. chevron drilled two additional wells within range creek canyon (dilly unit #1 [api# 43-015-30023] and lighthouse unit #1 [api# 43-015-30024]) with the purpose of exploring or testing the lower cretaceous cedar mountain and upper cretaceous dakota formations (roughly ranging from 125 to 94 million years in age) at depths of approximately 7000 feet for potential gas reservoirs. all wells proved non-commercial with respect to gas, producing a significant amount of water but very little gas. perhaps because of successful oil and gas wells north of range creek in the highly productive areas of nine mile canyon, other companies (including bow valley petroleum inc.) also drilled exploration gas wells throughout range creek. however, all wells failed to produce a significant amount of gas and have been plugged and abandoned. figure 11. dry well marker at the mouth of dry canyon, capping an abandoned exploratory gas well drilled by chevron oil company in 1974. a b 1 m figure 10. stratigraphy exposed on the south side of the road at the summit of horse canyon showing red, oxidized siltstone interbedded with tabular beds of sandstone (a) and a green, reduced horizon of siltstone (b). these alternating layers of red and green siltstone indicate fluctuating lake levels from more oxidizing to more reducing conditions, respectively, as the lake expanded and contracted over time. 17 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 4. locomotive rock stop #4 is a pullout on the east side of the road, 0.4 miles past the gas well dry-hole marker. locomotive rock, composed of colton formation, is a stunning geological feature because of the interesting manner in which it eroded into the shape of a steam engine (figure 12). this phenomenon is a result of the contrasting lithologies (rock types) and the role that grain size plays on the erosion of the rocks. grain size is a fundamental property of sedimentary rocks, as it relates to porosity and permeability of a unit (important for petroleum geologists and hydrologists) and is indicative of depositional conditions of sedimentary rocks. coursegrained sediment (sandstone) is usually deposited in relatively high-energy environments such as rivers or beach shorelines, whereas finer-grained deposits (mudstone, siltstone, shale) are deposited in calmer environments such as lakes or river floodplains. just as coarser-grained sediments are deposited by higher-energy events, they also require more energy to erode because they are more resistant to weathering and erosion than are finer-grained sedimentary rocks. cementation may also play a role in differential weathering in some cases. thus, the cliff-forming, rounded rocks that create the shape of the “locomotive” are composed of sandstone, and we can assume that the more receded (eroded), darker red lithologies of the locomotive are mudstone or siltstone. another attraction at locomotive rock is its archaeological sites. to the northeast of locomotive rock, on the opposite (east) side of the canyon, there is a pictograph commonly referred to as “the tv” because of its shape (figure 13a); there are colored pictographs inside the cave in the rock face (figure 13b), and there is a small granary slightly farther to the south on the same rock face (figure 13c). 5. nelson canyon drive 3.2 miles farther along range creek road from the locomotive rock site to the west of the pulloff just past nelson canyon. at stop #5, there is a wall of figure 12. locomotive rock illustrates the role that grain size and cementation exert on the differential erosion of rocks. the “steam engine” is shaped by a combination of cliff-forming sandstone and more erosive and receded mudstone or shale. 18 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 figure 13. highlighted fremont indian sites hidden within the sandstone cliffs of the colton formation on the east side of the road at the locomotive rock stop including rock art (a and b) and a granary (c). 19 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 colton sandstone (figure 14) that is almost entirely covered with petroglyphs (figure 14e). this rock wall not only offers the opportunity to see an incredible number of fremont rock inscriptions, but also to view many geologic sedimentary structures indicative of past depositional environments (figures 14a to 14d). in addition, note that roughly 200 feet north from the pullout, there is a triple-chambered granary nestled in the sandstone cliff face (figure 15a). from this point, there is also a view of budge’s arch, named after the nickname of waldo wilcox’s father, high on the eastern ridgeline of the canyon (figure 15b). channel scour/incision the clearly-cut edge of the sandstone on the bottom left of the petroglyph wall is a channel scour, which is indicative of erosion at the base of a river channel (figure 14a). the erosive nature of fluvial channels can often be recognized by the truncation of sedimentary strata (layers) below the scour surface. trough cross-bedding cross-beds are sedimentary structures that are characterized by inclined layering within a bed of rock. cross-bedding, also known as cross-stratification, is usually indicative of a depositional environment that had a significant flowing force or energy, such as flowing water or wind. trough cross-bedding consists of trough-shaped sets that merge tangentially with their lower surface (figure 14b). these scoop-shaped lineations, or laminae, often originate from the migration of current ripples, commonly at the base of a river channel (boggs, 2006). trough cross-beds are often helpful not only as an indicator of depositional environment, but also as an indicator of direction of current flow at the time of deposition. silty mudstone the mudstone and siltstone that is interbedded within the sandstone is often red in color (figure 14c). the red siltstone beds found near nelson canyon are a b c d e burrow channel incision cross-bedding petroglyphs figure 14. rock wall south of nelson canyon (view west of road) displaying many fremont rock inscriptions (e) in addition to several geologic sedimentary structures that are indicative of past depositional environments. sedimentary features include a channel scour (a), trough cross-bedding (b), and interbedded mudstone/siltstone with a fossilized burrow (c and d). 20 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 similar to those seen at horse canyon pass (stop #2) before entering range creek, and are similarly indicative of an oxidation process. the red color results from iron oxide from a heavily oxidized environment or period of time. the mudstone/siltstone shows some evidence of animal life as well, with a few burrows within the sediment (figure 14d). a burrow is a trace fossil that is the remaining evidence of the movement, or path, of a small worm or snail. stratigraphic column geologists use stratigraphic columns as a representation of the vertical arrangement of different rock units and their relationship to one another. the bottom of a stratigraphic column includes a scale of grain size of sedimentary rocks ranging from very fine grained sediments such as coal and clay to very coarse sand. this small-scale stratigraphic column of the petroglyph wall near nelson canyon (figure 16 ) shows how the sediments that were deposited as part of the colton formation vary in grain size. recall that finer-grained sediments are deposited by lower-energy events, in which these lighter grains settle out from the water column, and coarser-grained sediments result from waning of higher-energy flows. given this distinction in depositional energy, fluvial deposits are generally characterized by a fining upward succession. this occurs because the high-energy (coarse-grained) deposits are initialfigure 15. the stop at nelson canyon also offers this view of a spectacular three-chambered granary (a) and of budge’s arch (b), named in honor of budge wilcox. figure 16. stratigraphic column showing the section that was measured at the nelson canyon rock art panel and representing the vertical arrangement of rock units and their relationship to one another. the column records the vertical variance in grain size and bed thickness, subsequently marking a whole range of depths or energies at which sediments were deposited within a fluvial channel. 21 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 ly deposited in the deeper portion of a river, and are successively overlain by finer-grained sediments as the point bar of the river migrates laterally and water depth decreases (decreasing velocity of flow further). thus, this stratigraphic column records the vertical variance in grain size and bed thickness, subsequently marking a whole range of depths or energies at which sediments were deposited within a fluvial channel system. also note that red coloring of rocks (such as the red mud layer at roughly 11 meters [36 feet]) is associated with oxidizing conditions, whereas green in rocks is associated with reducing conditions. the green color of the rock layer at 9.5 meters (31.2 feet) implies that it was deposited in a reducing environment where oxygen was not available. thus, it could have been deposited in a wet boggy area, possibly on the backside (back-swamp) of a channel levee. mud rip-ups a large boulder (figure 17) that fell from up above now lies just to the left (east) of the foot trail that leads from the road to the petroglyph wall. this boulder is filled with mud rip-up clasts, which are finer-grained, tan-colored clasts in a coarser-grained matrix of sandstone. the partially consolidated mud was most likely torn up in some high-energy water flow, such as the initiation of an erosive river channel. the sharp distinction between the medium-grained sandstone on the bottom part of the boulder and the coarser-grained sandstone that is dominated by pebbles, limestone clasts, and mud rip-up clasts could be interpreted to indicate a river channel’s dramatic change from lower to higher energy. the contact between different grain sizes could be the bottom of a channel that came tearing through muddy sediment with current velocities strong enough to erode and pick up bits of mud along the way. another interesting feature in this boulder is the clasts of limestone that are intermingled in the lag deposit. when hydrochloric acid is applied to the limestone, the calcium carbonate reacts with the acid and causes it to fizz. geologists often carry bottles of dilute hydrochloric acid to perform this test in the field to confirm the presence of limestone in a rock. figure 17. boulder (along the path leading to the nelson canyon rock art panel) with preserved mud rip-up clasts, which are finer-grained, tan-colored clasts in a coarser-grained matrix of sandstone. this partially consolidated mud was most likely torn up in some high-energy water flow, such as the initiation of an erosive river channel that must have had current velocities strong enough to erode and pick up pieces of mud along its path. 22 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 6. mud plug granary another 1.5 miles from the nelson canyon (stop 5), on the east canyon wall 0.5 miles south of calf canyon, a fremont granary is perched at the edge of an outstanding example of a “mud plug” formed by the abandonment of an ancient river channel (figure 18). river channels are very dynamic systems because they constantly migrate within their respective floodplains. when a channel migrates, it deposits continuous beds of sediment, such as the many continuous and stacked beds of sandstone within range creek canyon. a channel is also capable of abandoning (or avulsing from) its path more suddenly. avulsion occurs when a river or stream abandons its channel entirely and moves to another position on the floodplain. this event can result in an oxbow lake. a “mud plug” is geologic evidence of a channel that avulsed, or abandoned its route as it moved across its floodplain, often by cutting off its own path and leaving behind an oxbow lake. note that the highlighted “mud plug” resembles the shape of a smile, or that of the cross section of a river channel (figure 18). channel and levee sandstone shale and shale interbeds and mudstone channel sediment accretion older sediments older sediments older sediments older sediments x x’ x’x x’x x’x x’ x accretion mud plug oxbow lake 1 2 3 4 channel sediment accretion channel sediment accretion point bar active channel backswamplevee point bar point bar point bar (abandoned) active channel active channel oxbow lake backswamplevee figure 18. photo showing the east wall of range creek canyon about 0.5 miles south of calf canyon. left: mud plug highlighted (red/brown) within sandstone (yellow) with a fremont platform granary at the edge of the “smile” of the mud plug. right: an explanation of sequential channel deposits and the formation of mud plugs that are commonly deposited in oxbow lakes (modified after davies and others, 1991). 1: initial point bar deposition during migration of the active channel (migrating left in figure). 2: lateral accretion, or buildup, of point bar deposits and cutbank erosion results in a larger channel meander. 3: continued channel migration leads to an unstable degree of sinuosity (tighter meanders). 4: the main river channel bypasses the meander by cutting it off and begins the process over. the abandoned channel is immediately filled with sediment held in the water column and then filled with future floodplain deposits. water left in this abandoned channel forms an oxbow lake. the sediment that is suddenly deposited in the oxbow lake is left in the sedimentary rock record as a mud plug. 23 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 7. cherry meadow stop #7 is roughly 2.3 miles farther along the road from stop #6. as the name suggests, cherry meadow is the first true opening, or meadow, in range creek canyon. this widening in the canyon relates directly to a change in lithology, or rock composition, in the sedimentary layers in range creek. just as locomotive rock is shaped as it is because of harder, more resilient sediments resisting erosion and softer, finer-grained sediment being weathered away, cherry meadow is evidence of the presence of a finer-grained, softer rock layer that has eroded more easily, leading to a significant opening in an otherwise tight, narrow canyon. this softer sediment layer was not encountered stratigraphically higher in the northern part of the canyon, but is still classified as part of the colton formation. this different rock layer is a lower member of the colton formation and can be distinguished by its redder, mahogany-colored, and finer-grained fluvial sandstone beds, which are less frequent and much less laterally extensive (figure 19). this darker red, finer-grained unit is absent in the exposed section along the drive up horse canyon. recall that in horse canyon, the upper unit of the colton lies directly on top of the gray limestone. this lower colton unit that contains more mudstone interbedded within the sandstone pinches out between here, in cherry meadow, and horse canyon. mud plug recall that a “mud plug” is geologic evidence of a channel that avulsed, or abandoned its route as it moved across its floodplain. the “smile” shape of the mud plug in cherry meadow is filled with a darker, finer-grained layer that was deposited by a channel as its energy decreased when it abandoned its path (figure 19a). thus, the shape of the half smile here outlines the shape of the ancient abandoned channel that was eventually filled by fine sediment. boulder recording migration of a river channel one particular boulder of sandstone nicely illustrates several features that represent directional water flow (figure 19b). in the cross section of a river channel the cutbank is where the erosive process of a channel occurs, while the channel deposits sediment at the point bar (figure 4). thus, a river channel (shown in figure 4 as a meandering river) migrates or expands in the direction of its cutbank. the features outlined near the bottom of this boulder are representative of point bars in a channel migrating to the left (in this orientation). the thick white, drawn-in boundary, topping these migrating bar forms, represents the deposition of much coarser-grained sediment (figure 19b). this coarser-grained sediment even includes small pebbles, and can thus be interpreted as a higher-energy event that occurred after the point bar migration or as the base of a separate channel that formed during a flood stage of the river. mud cracks both contemporary and ancient mud cracks are an indicator of desiccation, or drying up, of sediment. mud cracks usually occur in environments that are alternately wet and dry, where muddy sediment is subjected to intermittent drying. mud cracks are often representative of lagoonal or fluvial floodplain depositional environments (boggs, 2006). they often form in a hexagonal shape and can be preserved either as v-shaped cracks on the top of a muddy sediment bed (appearing just like contemporary mud cracks), or as casts on the base of an overlying bed (figure 19c). the boulder in cherry meadow contains ancient mud cracks preserved as casts, or positive-relief fillings, on the bottom of a younger, overlying sedimentary bed. these casts are the result of ancient mud cracks that formed, then completely dried, were covered with younger wet sediment, and were then buried and preserved. looking at this boulder, we see the underside of a layer of mud cracks that were filled in with overlying sediment. 8. dilly canyon a great location to pull over and explore limestone rock at dilly canyon is 2.4 miles from the cher24 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 ry meadow stop (stop #7). recall that the limestone of the flagstaff limestone was exposed along the drive up horse canyon (figure 5). yet in range creek canyon, the drive from the north gate southward through the canyon has been stratigraphically too high for the flagstaff limestone outcrops. stop #8 is one of the first locations within range creek canyon where the creek cuts low enough in the section to reach limestone beds of the flagstaff limestone, below the colton formation. this stop not only offers an opportunity to walk up to the rocks to see the differences between the flagstaff limestone limestone and the colton formation sandstone, but also to find various fossils within the flagstaff. along the gentle slope of the hill on the east side of the road are loose blocks, or “float,” of limestone that are filled with both body and trace fossils (figures 20 and 21). roughly 500 feet farther down the road and on the east side of the canyon, there is a petroglyph carved into a layer of sandstone interbedded within the flagstaff limestone (figure 22). body fossils body fossils are skeletal and shelly remains of anfigure 19. the view (main panorama) looking east from the road into cherry meadow and opposite lighthouse canyon, offers a view of two units (upper and lower) of the colton formation marking a general upward trend of increased grain size, channel belt (sandstone bed) frequency, and channel belt lateral extent. the coarsening-upward succession of the colton formation (from the darker red, lower unit with numerous interbedded mudstone and little lateral extent, to the lighter-colored, sandstone-dominated upper unit) implies a transition from lower-energy river environments to higher-energy river systems with time. highlighted within the colton is a mud plug (a), which is geologic evidence of a fluvial channel that avulsed, or abandoned its route as it moved across its floodplain. the “smile” shape of the mud plug is filled with a darker, finer-grained layer that was deposited by a channel as its energy decreased when it abandoned its path. thus, the shape of the half smile outlines the cross section of the ancient channel where fine sediment settled out. also highlighted in the foreground is a boulder that has beautifully preserved evidence of channel/stream flow (b) and another boulder with preserved world-class mud cracks (c). 25 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 cient plants or other organisms. although there are many ways that organisms can become fossils, many require the presence of muddy sediment and water, making fossilized marine organisms more common. the flagstaff limestone, as previously mentioned, is representative of an ancient lacustrine, or lake, environment, and preserves evidence of many freshwater organisms that inhabited the region and are now left behind as fossils. some of the abundant fossils that can be found within the flagstaff limestone are gastropods, oysters, and freshwater turtles (figures 20a to 20f). figure 20. body fossils found in the lacustrine limestone of the flagstaff limestone include fossils of gastropods, oysters, and freshwater turtles (a-f). fossils can be found in bedrock exposures, on the talus slope just south of dilly canyon, or wherever there is limestone exposed. 26 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 figure 21. trace fossils are also abundant and easy to find along the road in the fossiliferous limestone of the flagstaff limestone. these fossils do not consist of animal remains as do body fossils, but rather of animal tracks and burrows, indicating evidence of animal behavior. though trace fossils are named after their appearance, they are often qualified by the behaviors that they are interpreted to record as well. planolites is described as cylindrical to subcylindrical infilled burrows that are straight, gently curved, and nonbranching. planolites is considered a grazing trace of a wandering deposit feeder (uchman, 1995). ophiomorpha is a 3d burrow system of cylindrical tunnels that are larger and often dichotomously branch at acute angles. the tunnels can be vertically (shafts) or horizontally oriented and have local swelling at the branching. the walls are internally smooth, but lined with pellets (uchman and gazdzicki, 2006). 27 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 trace fossils trace fossils are preserved trails, depressions, borings, or any kind of trace left by an organism (figure 21). these fossils do not consist of animal remains as do body fossils, but rather of animal tracks and burrows, indicating evidence of animal behavior (seilacher, 1967; prothero, 2004). the image in figure 21 exemplifies, as do many rocks within the flagstaff limestone, the burrowing action of organisms, called bioturbation. 9. wilcox ranch the ranch, which is the final stop of this geologic tour (2.1 miles from dilly canyon, and 23 cumulative miles from stop #1 at geneva coal mine at the mouth of horse canyon), originally served as a line station for cattle operations within range creek canyon. nearly a century later, the original, single-room cabin is still standing. what eventually became known as the wilcox ranch, was a working ranch until the end of the twentieth century. it is currently managed by the natural history museum of utah at the university of utah as a field station (metcalfe, 2008). the mission of the field station is to protect, preserve, and study the remarkable archaeological record within range creek canyon, while providing professional training to students in all aspects of natural history (figure 23). figure 22. view looking east from the road, roughly 300 feet south of dilly canyon, showing a petroglyph of an anthropomorphic figure. sometimes referred to as a shield figure, the petroglyph is pecked into a layer of sandstone that is interbedded in the tabular limestone beds of the flagstaff limestone (top) with a close up (bottom). figure 23. wilcox ranch (top) and its view looking north up range creek canyon (bottom). 28 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 acknowledgments this work was part of an undergraduate thesis sponsored by the university of utah undergraduate research opportunities program. special thanks are extended to corinne springer for her selfless hospitality at the project site and her wealth of knowledge of the field area. thanks are also due duncan metcalfe for permitting entry into range creek canyon, and special thanks to david dinter, jared gooley, and ian semple for indispensible help and knowledgeable input with fieldwork. thanks to sharon hamre for her help with formatting and editing of a previous version of this guide. the authors thank steven schamel for his management of the peer review process and marc eckels, thomas morris, and grant willis for their comments and assistance with manuscript review. this publication is provided free to the public. please consider donations to support range creek research at the natural history museum of utah: www.nhmu.utah.edu. references barlow, r., and phillips, k.l., 2010, simple financial economic models of fremont maize storage and an assessment of external threat: university library of munich, germany, munich personal repec archive, paper 23502, 18 p. blakey, r.c., and ranney, w., 2008, ancient landscapes of the colorado plateau: grand canyon association, 156 p. boggs, s., jr., 2006, principles of sedimentology and stratigraphy, 3rd edition, upper saddle river, new jersey: pearson education, inc., p. 112-462. bowen, g.j., daniels, a.l., and bowen, b.b., 2008, paleoenvironmental isotope geochemistry and paragenesis of lacustrine and palustrine carbonates, flagstaff formation, central utah, u.s.a.: journal of sedimentary research, v. 78, p. 162-174. butler, d.p., 1961, the geneva coal mine at horse canyon, utah: utgenweb project, carbon county <http://www.carbon-utgenweb.com/geneva.html>, accessed april 14, 2011. carroll, a.r, chetel, l.m, and smith, m.e., 2006, feast to famine—sediment supply control on laramide basin fill: geology, v. 34, no. 3, p. 197-200. cashion, w.b., 1967, geology and fuel resources of the green river formation, southeastern uinta basin, utah and colorado: u.s. geological survey professional paper 548, 48 p. old work shed at wilcox ranch. photograph by nora nieminski. 29 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 davies, d.k., williams, b.p.j., and vessell, r.k., 1991, reservoir models for meandering and straight fluvial channels; examples from the travis peak formation, east texas: gulf coast association of geological societies, v. 41, p. 152-174. dickinson, w.r., lawton, t.f., and inman, k.f., 1986, sandstone detrital modes, central utah foreland region—stratigraphic record of cretaceous-paleogene tectonic evolution: journal of sedimentary research, v. 56, no. 2, p. 276-293. dickinson, w.r., lawton, t.f., pecha, m., davis, s.j., gehrels, g.e., and young, r.a., 2012, provenance of the paleogene colton formation (uinta basin) and cretaceous–paleogene provenance evolution in the utah foreland—evidence from u-pb ages of detrital zircons, paleocurrent trends, and sandstone petrofacies: geosphere, v. 8, no. 4, p. 854-880. dubiel, r.f., 2003, geology, depositional models, and oil and gas assessment of the green river total petroleum system, uinta-piceance province, eastern utah and western colorado, in petroleum systems and geologic assessment of oil and gas in the uinta-piceance province, utah and colorado: u.s. geological survey digital data series dds-69-b, chapter 5, 41 p. franczyk, k.j., and pitman, j.k., 1991, latest cretaceous nonmarine depositional systems in the wasatch plateau area—reflections of foreland to intermontane basin transition, in chidsey, t.c., jr., editor, geology of east-central utah: utah geological association publication 19, p. 77-93. gerber, s.l., and aton, j.m., 2011, empires and homesteads—making a living in range creek: utah historical quarterly, v. 79, no. 1, p. 20-41. higgins, j.a., and schrag, d.p., 2006, beyond methane—towards a theory for the paleocene-eocene thermal maximum: earth and planetary science letters, v. 245, p. 523-537. johnson, k.a., culver, s.j., and kamola, d.l., 2005, marginal marine foraminifera of the blackhawk formation (late cretaceous, utah): journal of foraminiferal research, v. 35, no. 1, p. 50-64. johnson, r.c., 1985, early cenozoic history of the uinta and piceance creek basins, utah and colorado, with special reference to the development of eocene lake uinta, in flores, r.m., and kaplan, s., editors, cenozoic paleogeography of the west-central united states: special publication of the rocky mountain section, society of economic paleontologists and mineralogists, symposium 3, p. 247-277. one of many fremont petrolyphs in range creek canyon. photograph by nora nieminski. 30 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 keighley, d., flint, s., howell, j., and moscariello, a., 2003, sequence stratigraphy in lacustrine basins—a model for part of the green river formation (eocene), southwest uinta basin, utah, usa: journal of sedimentary research, v. 73, no. 6, p. 987-1006. kloor, k., 2006, secrets of the range creek ranch: smithsonian magazine, march 2006 <http://www. smithsonianmag.com/history-archaeology/range_ creek_ranch.html>, accessed on december 1, 2010. lawton, t.f., 2008, laramide sedimentary basins: sedimentary basins of the world, v. 5, p. 429-450. madsen, d.b., and simms, s.r., 1998, the fremont complex—a behavioral perspective: journal of world prehistory, v. 12, p. 255-336. marcantel, e.l., and weiss, m.p., 1968, colton formation (eocene: fluviatile) and associated lacustrine beds, gunnison plateau, central utah: the ohio journal of science, v. 68, no. 1, p. 40-49. metcalfe, d., 2008, range creek canyon, in fowler, c.s., and fowler, d.d., editors, the great basin—people and place in ancient times: santa fe, new mexico, school for advanced research press, p. 117-123. morgan, c.d., chidsey, t.c., jr., mcclure, k.p., bereskin, s.r., and deo, m.d., 2003, reservoir characterization of the lower green river formation, uinta basin, utah: utah geological survey open-file report 411, 140 p. morris, t.h., richmond, d.r., and marino, j.e., 1991, the paleocene/eocene colton formation—a fluvial-dominated lacustrine deltaic system, roan cliffs, utah, in chidsey, t.c., jr., editor, geology of eastern-central utah: utah geological association publication 19, p. 129-139. pitman, j.k., anders, d.e., fouch, t.d., and nichols, d.j., 1986, hydrocarbon potential of nonmarine upper cretaceous and lower tertiary rocks, eastern uinta basin, utah, in spencer, c.w., and mast, r.f., editors, geology of tight gas reservoirs: american association of petroleum geologists studies in geology, v. 24, p. 235-251. potterfield, p., 2004, the lost world of range creek: the great outdoors, july 16, 2004, <http://www. greatoutdoors.com/published/the-lost-world-ofrange-creek>, accessed on april 13, 2011. prothero, d.r., 2004, bringing fossils to life—an introduction to paleobiology, 2nd edition: new york, mcgraw-hill companies, inc., 472 p. remy, r.r., 1992, stratigraphy of the eocene part of the green river formation in the south-central part of the uinta basin, utah: u.s. geological survey bulletin 1787-bb, 79 p. roehl, u., westerhold, t., bralower, t.j., and zachos, j.c., 2007, on the duration of the paleocene-eocene thermal maximum (petm): geochemistry, geophysics, geosystems, v. 8, no. 12, p. 1-13. ryder r.t., fouch, t.d., and elison, j.h., 1976, early tertiary sedimentation in the western uinta basin, utah: geological society of america bulletin, v. 87, no. 4, p. 496-512. seilacher, a., 1967, fossil behavior: scientific american, v. 217, p. 72-80. smith, m.e., carroll, a.r., and singer, b.s., 2008, synoptic reconstruction of a major ancient lake system—eocene green river formation, western united states: geological society of america bulletin, v. 120, no. 1-2, p. 54-84. stanley, k.o., and collinson, j.w., 1979, depositional history of paleocene—lower eocene flagstaff limestone and coeval rocks, central utah: american association of petroleum geologists bulletin, v. 63, no. 3, p. 311-323. torfstein, a., winckler, g., and tripati, a., 2010, productivity feedback did not terminate the paleocene-eocene thermal maximum (petm): climate of the past, v. 6, no. 2, p. 265-272. uchman, a., 1995, tiering patterns of trace fossils in the paleogene flysch deposits of the carpathians, poland: geobios, v. 18, p. 389-394. uchman, a., and gazdzicki, a., 2006, new trace fossils from the la mesata formation (eocene) of seymour island, antarctica: polish polar research, v. 27, no. 2, p. 153-170. utah oil and gas program website, undated: utah division of oil, gas and mining, <http://oilgas.ogm. utah.gov>. wells, n.a., 1983, carbonate deposition, physical lim31 a guide to the bedrock geology of range creek canyon, book cliffs, utah nieminski, n.m., and johnson, c.l. geology of the intermountain west 2014 volume 1 nology and environmentally controlled chert formation in paleocene-eocene lake flagstaff, central utah: sedimentary geology, v. 35, no. 4, p. 263-296. wilf, p., 2000, late paleocene-early eocene climate changes in southwestern wyoming: paleobotanical analysis: geological society of america bulletin, v. 112, p. 292-307. witkind, i.j., 2004, geologic map of the huntington 30’ x 60’ quadrangle, carbon, emery, grand, and uintah counties, utah: utah geological survey openfile report 440dm, compact disc, 1 plate, scale 1:100,000, gis data (originally published in 1988 as u.s. geological survey miscellaneous investigations series map i-1764., 1 plate, scale 1:100,000). zachos, j.c., pagani, m., sloan, l., thomas, e., and billups, k., 2001, trends, rhythms, and aberrations in global climate 65 ma to present: science, v. 292, p. 686-693. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. new social insect nests from the upper jurassic morrison formation of utah elliott armour smith, mark a. loewen, and james i. kirkland theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover overturned boulder composed of a floodplain paleosol, revealing the underside of a fossil social insect nest. the boulder is from a locality in the brushy basin member of the upper jurassic morrison formation, near green river, utah. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors society of vertebrate paleontology editors kelli c. trujillo — university of wyoming cary woodruff — university of toronto octavio mateus — universidade nova de lisboa douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees education/scholarship zack anderson zanderson@utah.gov 801.538.4779 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 281 abstract this paper reports a new assemblage of social insect ichnofossils from the brushy basin member of the upper jurassic morrison formation near green river, utah. at least seven distinct nests are visible in the locality horizon, identifiable at the outcrop scale by loci of anastomosing, and orthogonally connected horizontal burrows and vertical shafts. a boulder-sized block from the in situ horizon has eroded and rolled downhill, revealing the ventral aspect of the nest, showing a view of the overall nest architecture. burrow and shaft clusters are organized into mega-galleries which have branching arms and ovate, bulbous chambers. the organization of distinct trace morphologies is consistent with ethological complexity of the social insects. a small sample was collected and analyzed by serial sectioning and petrographic thin sectioning to observe small-scale morphological features. centimeter-scale analysis shows chamber, gallery, and burrow walls have complex topography. pebble-sized, hollow, ellipsoid features are distributed throughout the uppermost facies of the nest and have undergone complete silicification of their outer surfaces. the ellipsoids share similarity with pellet structures made of mud or carton produced by modern termites. this trace fossil assemblage suggests it is possible that termites had acquired subterranean nesting behavior, and mud or carton utilization in nest construction in seasonally arid habitats by the late jurassic. new social insect nests from the upper jurassic morrison formation of utah elliott armour smith1, mark a. loewen2, and james i. kirkland3 1university of washington, department of biology, 24 kincaid hall, seattle, wa 98105; eas37@uw.edu 2university of utah, department of geology and geophysics, 115 s 1460 e #383, salt lake city, ut 84112; mloewen@nhmu.utah.edu 3utah geological survey, po box 146100, salt lake city, ut 84114-6100; jameskirkland@utah.gov citation for this article. armour smith, e., loewen, m.a., and kirkland, j.i., 2020, new social insect nests from the upper jurassic morrison formation of utah: geology of the intermountain west, v. 7, p. 281–299, https://doi.org/10.31711/giw.v7.pp281-299. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction despite their individual cognitive simplicity, eusocial insects (termites, ants, bees, and wasps) are responsible for building some of the most complex structures in the animal kingdom (theraulaz and others, 1998). eusociality, the highest degree of animal sociality, is a remarkable biological phenomenon where members of a species are differentiated into reproductive castes and provide alloparental care (crespi and yanega, 1995). eusocial insects that create the most complex structures are ants and termites, which are some of the most ecologically successful groups of organisms on earth. ants and termites are found on all continents except antarctica and include over 12,000 living species and 3000 fossil species (ward, 2007; krishna and others, 2013). social insects can create structures that are spectacularly more complex than other solitary and subsocial arthropods because of stigmergy and self-organization (theraulaz and others, 1998). stigmergy is the transmission of information via the environment, rather than direct organismal communication (theraulaz and bonabeau, 1999). the nest itself serves as a template for 282 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 the individuals in the colony to respond to stimuli, and their cumulative responses create a complex product in absence of individuals with cognitive complexity (perna and theraulaz, 2017). the nests of social termites are constructed to regulate temperature, moisture, and gas exchange (ocko and others, 2019). the nests of ants have readily observable effects on the chemistry and physical properties of the soil they inhabit (nkem and others, 2000). aside from their ecological dominance and taxonomic diversity, the eusocial insects serve as complex and nuanced models for how selection operates at the group level (fewell, 2003). since wilson’s (1971) groundbreaking book the insect societies was published, social insects were brought to the center of an extensive debate amongst evolutionary scholars on the nature of natural selection, with opinions representing a multi-level selection, and gene selection views (van veleen, 2009). genomic evidence and body fossil continues to shed light on the once obscure origins of these ecologically important and evolutionarily successful groups of animal life. brady and others (2006) estimated the common ancestor of extant ants evolved between 115 to 135 ma, with a fossil-calibrated, molecular phylogenetic analysis. the authors concluded that a jurassic origin of eusocial ants is unlikely. cretaceous amber deposits from burma (99 ma) have yielded a morphologically specialized, stem-group ant taxon that appears to be eusocial (barden and grimaldi, 2016). fossil distribution analysis and molecular phylogenetics have supported the hypothesis that the evolutionary radiation of crown-group ants coincided with the rise of angiosperms (moreau and others, 2006; perrichot and others, 2008). termites (isoptera) are a monophyletic clade of eusocial insects that are now understood to be derived from cockroaches (blattodea) (inward and others, 2007), with the most recent common ancestor of termites and cockroaches likely evolving in the permian (legendre and others, 2015). termites are the sister group to cryptocerus roaches, with an estimated divergence time in the early jurassic (~195 ma), and crown-group diversification occurring in the late jurassic (~150 ma) (bourguignon and others, 2014). in the mesozoic, termites were not speciose, and represent a small fraction of insect diversity in fossil deposits (engel and others, 2009). the first definitive termite fossils date back to the early cretaceous, with the oldest winged, stem-group termite fossils from siberia dated to 135 ma (krishna and others, 2013). despite their rarity, the body fossil record of termites indicates they were cosmopolitan and relatively diverse by the late cretaceous (engel and delcòs, 2010). early cretaceous (99 ma) amber deposits from myanmar reveal a speciose termite fauna with morphs belonging to reproductive castes, a diagnostic feature of eusociality (engel and others, 2016). the most basal living termite species, mastotermes darwiniensis is the only member of the mastotermitidae, and is only found on the continent of australia (krishna and others, 2013). the fossil history of this group has a cosmopolitan distribution, with fossil mastotermitids reported from the lower cretaceous wealden clay of england and eocene amber deposits from the baltic region (engel, 2008; krishna and others, 2013). the fossil history of termite species and their modern distribution indicate that their evolution predated gondwanan rifting and thus did not initially coincide with the rise of angiosperms (engel and others, 2009). genomic and fossil evidence suggest that the the late jurassic was likely a key time in the radiation of crown isoptera (legendre and others, 2015). genomic and body fossils provide only a partial picture of the evolution of social insects. ichnofossils are the only direct evidence of the evolution of nest architecture and nesting behavior. many reported social insect ichnofossils have been controversial (genise, 2016). however, some reported ichnotaxa have been referred to living clades of ants and termites (smith and others, 2011; roberts and others, 2016), but these ichnotaxa are almost exclusively cenozoic (genise and others, 2000). ichnofossils record notable events in termite evolution including the development of fungal agriculture dating back to the miocene (25 ma) of africa (duringer and others, 2006; roberts and others, 2016). ant and termite nests have many similar elements, and nest architecture has been suggested to be of limited phylogenetic utility (hasiotis, 2003; genise, 2016). however, ant and termite nests have both homoplastic and autapomorphic characteristics. in modern ant nests, cylindrical galleries connect oblate to elliptical, 283 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 expanded chambers, connected by vertical descending, cylindrical shafts (tschinkel, 2004). extant ant nest morphologies display diagonal central shafts, and variation in the clustering of chambers either near the top or the bottom of the nest (tschinkel, 2015). the ichnologic record of social insects from the mesozoic is sparse and more taxonomically ambiguous than the cenozoic record; however, it contains localities that inform science about the early evolution of social insects. xing and others (2013) reported insect traces on a dinosaur skeleton from the lower jurassic lufeng formation of china. xing and others (2013) noted the morphological similarity between these traces and the foraging galleries of modern termites, which are constructed with mud or carton (fecal matter mixed with saliva). the authors could not rule out a coleopteran as the trace-maker, they suggest the possibility that traces may be attributed to either a stem or crown-group termite. roberts and tapanila (2006) reported social insect nests housed in the sand infilled casts of tree stumps from the late cretaceous kaiparowits formation of southern utah. however, the kaiparowits social insect nests were not definitively concluded to belong to either ants or termites. termite ichnofossils have been reported from the early jurassic clarens formation of south africa (bordy and others, 2004). the hypothesis of a social insect tracemaker in both reported ichnofossil localities was supported by the occurrence of multiple bioturbation centers. however, the south african early jurassic termite mounds reported by bordy and others (2004) were disputed, with a countering opinion citing a lack of clear morphology overlap between extant termites and failing to eliminate root traces as an origin (genise and others, 2005). the north american ichnofossil record of the terrestrial jurassic has been reported by hasiotis (2004) in a survey of the upper jurassic morrison formation ichnofacies. the author reports a diverse ichnofauna with a variety of ethologies adapted to conditions of channel, floodplain, lacustrine, and marginal-marine environments. in this survey, ichnofossils with ants and termites as interpreted tracemakers are reported. these termite and ant ichnofossils have been contested by bromley and others (2007), who regard these reports as lacking ichnotaxonomic treatment, modern comparative morphology, and a nonsynchronous body fossil record. the new ichnofossil assemblage presented in this paper will add to the diversity of the morrison ichnofauna, and provide previously reported morrison social insect ichnofossils with additional context. geologic setting the trace fossil assemblage in the morrison formation lies 12.4 km southeast of green river, utah, near the crystal geyser area (figure 1) and occurs within the upper brushy basin member of the morrison formation (bell, 1986). deposition of the morrison formation occurred concurrently with the commencement of cordilleran highlands uplift, which provided a source of northeast-travelling clastic sediment (dickinson and gehrels, 2008). the brushy basin member is an approximately 100 ± 30 m succession of mostly fine-grained, smectitic mudstones (dickinson and gehrels, 2008). the upper brushy basin member is characterized by smectitic mudstones attributed to volcanic ash sourced from calderas to the southwest of the depositional basin (turner and peterson, 2004). the depositional environments of the brushy basin are low-gradient stream channels, floodplains, and playa lakes (dickinson and gehrels, 2008). the upper brushy basin member of the morrison was deposited in the continental interior, bordered by a subduction zone to the west, and more proximal to a transcontinental rift zone. this zone was the setting for igneous complexes that provided the source for the volcanic ash seen in the “clay change” between the upper and lower brushy basin member (turner and peterson, 2004). the locality is 8 m below the uppermost jurassic unconformity (figure 2) and lies above the “clay change,” which is described as the presence of extensive bentonitic volcanic ash that contain altered zeolites giving the upper brushy basin member its array of color (turner and peterson, 2004). radiometric dates for the brushy basin member are reported by several groups of authors and are largely in congruence. the top of the brushy basin has been reported by two u-pb dates from near hanksville, utah, at 149.0 + 2.5/-2.2 ma and 149.3 ± 0.5 ma (kowallis and 284 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 others, 2007). trujillo and others (2014) reported an age for the mygatt-moore quarry of mesa county, colorado. the mygatt-moore quarry is reported to be 64 m above the base of the brushy basin member, and these authors report a u-pb age date from a zircon sample, collected from a smectitic mudstone from the quarry, at 152.18 ± 0.29 ma. a recalibrated 40ar/39ar radiometric date from little cedar mountain, emery county, utah, dates the top of the brushy basin member to 150.00 ± 0.52 ma (trujillo and kowallis, 2015). these authors also suggest a congruence between dates occurring in the middle to upper brushy basin across known stratigraphic sections that is approximately 151 ma. galli and others (2018) report u-pb dates ranging from 150.208 ± 0.094 ma in the middle of the brushy basin member, and 149.43 ± 0.059 ma, 2 m from the top of the member. however, the date from the middle of the member may not be as low stratigraphically as these authors report (j. foster, utah field house of natural history state park museum, personal communication, 2019). the new trace fossil locality, which is 8 m below the top of the brushy basin member is stratigraphically higher than the mygatt-moore dinosaur quarry, so the radiometric age date of 152.18 ± 0.29 ma can be confidently placed as a maximum age for the new locality (trujillo and others, 2014). the recalibrated 40ar/39ar radiometric date from little cedar mountain serves as figure 1. geologic map of the crystal geyser area (a), near green river, utah (modified from sable, 1955). a profile satellite image of the locality (b), with yellow dots indicating nest sites. an overhead satellite image of the locality (c), showing the exposure of the nest horizon. satellite images from google earth, full citation in references. 285 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 an appropriate upper age limit for the new morrison trace fossil locality, at 150.00 ± 0.52 ma (trujillo and kowallis, 2015). the paleoenvironment of the morrison formation has been characterized as dry, with high evaporation and transpiration relative to precipitation (turner and peterson, 2004). the flora is most accurately characterized as herbaceous-dominant, with a relative lack of woody plant fossils (parrish, 2004). the upper brushy basin member was deposited as a low gradient alluvial plain with wetlands and inwardly draining alkaline lakes. the water supply to the morrison basin was likely fed by meteoric water in the highlands that fed losing streams that intercepted the surface down gradient (turner and peterson, 2004). the locality horizon can be considered a paleosol due to several lithologic observations (figure 2). the locality horizon lacks clear horizontal bedding features and contains rhizoliths. mudstones and siltstones are mottled and contain discolorations consistent with oxifigure 2. stratigraphy of the type locality of eopolis ekdalei (umnh ip 5233), note the jurassic-cretaceous boundary (a). elaborated detail at the nest horizon shows lateral variation in grain size and color (b). an annotated photograph shows the stratigraphic horizon where umnh ip 5233, the type specimen of eopolis ekdalei, was extracted (c). 286 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 dization. paleosol formation at the uppermost morrison formation unconformity reflects decreasing deposition and/or accommodation and consequently greater longevity of sediments on the depositional surface (demko and others, 2004). methods the ichnofossils in this report were named using a morphology based approach outlined by bertling and others (2006). analysis of these ichnofossils was conducted at a range of visual scales from outcrop to millimeter-scale. eight centers of intense bioturbation eroding in relief were photographed and observed (figure 1). the spatial distribution and elevation of the mounds were recorded with universal transverse mercator (utm) coordinates, and plotted on a 1:24,000 scale u.s. geological survey map (figure 1). a geologic map of tidwell-1 quadrangle was used to construct the locality map (sable, 1955) (figure 1). the stratigraphy of the ichnofossil assemblage was described by utilizing a drainage that eroded through the stratigraphic horizon of the ichnofossil assemblage (figure 2). the lithology and mineralogy of the ichnofossils were described with transmitted light photographs of petrographic thin sections. the photographs were supplemented with a quantitative evaluation of materials by scanning electron microscopy (qemscan) analysis, which produces a quantitatively descriptive image of mineral fabrics by assigning a mineral identity to each pixel based on spectral data. the qemscan analysis was performed at the advanced rock characterization laboratory at the university of utah, which consists of a carl zeiss evo 50 scanning electron microscope running the qemscan proprietary software. a 27 mm2 area of a petrographic thin section was imaged with a 20-micrometer spot for 11 minutes. individual mounds were preserved with pervasive cracks and weathering surfaces. this preservation made approaches to collecting the specimen difficult. ultimately, we decided that leaving the nests at the locality in situ would be the best immediate approach for preserving them, and smaller samples for serial sectioning would be most ideal for describing interior burrow morphology. to assess the internal stratinomy of the uppermost facies in each mound, a ~30 cm in diameter sample was cut into nine serial sections and photographed with consistent parameters. sharp contrast in burrow lining (contact between pale purple and white silt/clay) was accentuated using adobe illustrator (figure 3). the thin sections and serial sections of the ichnofossil sample are reposited at the natural history museum of utah in salt lake city (umnh). systematic ichnology eopolis – new ichnogenus etymology eo(greek), dawn, origin. polis(greek), city. the name refers to the interpreted nature of the trace as a structure built by a social insect, animals that are renowned for the complexity of the structures they build. the name also refers to the early occurrence of the trace, near the evolutionary origin of the earliest social insects. type specimen holotype, umnh ip 5233. material sample is composed of nine serial sections, and two petrographic thin sections. horizon, age, locality holotype specimen collected near the top of the brushy basin member of the upper jurassic morrison formation. the locality is approximately 12.4 km southeast of green river, utah. the nest horizon is approximately 20 m below the unconformable contact with the yellow cat member of the cretaceous cedar mountain formation. diagnosis this trace is defined as a densely clustered burrow network, composed of cylindrical horizontal galleries and vertical shafts, punctuated by expanded, ovate to spherical chambers. clusters of orthogonally and obliquely intersecting cylindrical burrows are contained 287 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 figure 3. serial slice tomography of eopolis ekdalei (umnh ip 5233). (a) annotated photograph of in-situ nest horizon. (b) a diagram illustrating dimensions of macrosample and slice numbers. (c) small scale burrow morphology interpreted from serial section photographs. pale-purple clayey silt is the matrix and white clayey silt is the infill. slice numbers indicate sequence, as shown in (b). ellipsoids are marked in blue for contrast. 288 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 within a larger, also unlined network with anastomosing morphology. chamber walls are unlined, but have a cellular or honeycomb-like morphology. horizontally oriented, or obliquely oriented galleries have cylindrical morphology, with an average diameter of 0.49 cm (n = 13), ranging from 0.32 to 0.79 cm. vertically oriented shafts have similar dimensions, with an average diameter of 0.49 cm (n = 16), ranging from 0.30 to 0.79 cm. chambers are sub-spherical or sub-ovate to amorphous, with undulating, rugose margins. chamber diameter ranges from 5 to 20 cm at their greatest width. the mounds are approximately 0.5 m in vertical relief, and 0.75 to 1 m in horizontal diameter, and possess a cylindrical shape with the vertical axis being the shortest. eopolis ekdalei – new ichnospecies etymology specific epithet for tony ekdale, ph.d., paleontologist and professor in the department of geology and geophysics at the university of utah, for his outstanding contributions to the field of ichnology. diagnosis as the genus. differential diagnosis at this locality, the ichnospecies is represented by at least seven nests that are flat and cylindrical in gross morphology. eopolis has clustered, anastomosing burrow networks like termitichnus (bown, 1982) and socialites (roberts and tapanila, 2006). the highest density of burrows does occur in a central location, however, there is no indication that a spherical pericicie exists as in termitichnus (bown, 1982). there is also no indication that chambers are stacks of oblate discs as in krausichnus (genise and bown, 1994) or daimoniobarax (smith and others, 2011). the small-scale (hand sample) morphology of the trace has roughly horizontal burrow orientation, but there does not appear to be tightly clustered connections of passages by ramps, and distinct partition walls as in coatonichnus (duringer and others, 2007). results lithology and stratigraphy of nest horizon the nest horizon can be described as an approximately 0.5-m-thick layer of tuffaceous, bentonitic siltstone, lying immediately above mudstone-claystone layers with diffuse bioturbation (figure 2). approximately 2 m of outcrop at the horizon of the trace fossil assemblage reveal mostly bioturbated red siltstone with green-gray mottles. the bioturbated siltstones are punctuated by non-bioturbated, red-purple siltstone and mudstone. additionally, green mudstone and sandstone are observed punctuating the red-purple mudstone beds. all eight mounds are topped by a purple and white, bioturbated clay-rich siltstone with pebble-sized, hollow, purple ellipsoid structures. eight mounds of silicified mudstone and siltstone crop out in approximately 0.5 to 1 m of relief (figure 1). burrow concentration and complexity increases generally towards the center of each mound, so each mound is a center of bioturbation. the core of each mound displays a silicified texture with an orange hue, and the surrounding mudstone and sandstone beds appear to deform in a concave-up fashion in relation to the peak of each mound. the deformation of the beds adjacent to the mounds is likely the result of soft-sediment deformation. description anastomosing masses of purple sediment are punctuated with gaps of white sediment approximately 2 to 3 cm in length (figure 4). purple and white sediments in uppermost facies reveal boundary of burrows (figure 3). typically, the white appears as infill, and purple appears as matrix. however, the white sediment is much more abundant, and the purple coloration revealing the matrix is limited through these layers. it is likely much of the matrix is composed of white sediment as well, which obscures the differentiation between burrow and matrix in some places (figure 4a). the matrix-burrow boundaries are gradational, but occasionally display sharp contrast. ovate, columnar structures occasionally transect purple sediment, both directly and obliquely. smaller circular features, white sediment within purple 289 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 figure 4. photographs (left) and interpretations (right) of the type locality of eopolis ekdalei (umnh ip 5233). (a) this view shows an in situ nest with burrows in cross section from lateral view. (b) this view shows a nest block fallen out of place, exposing a transverse planar view underneath a nest. (c) this view shows a close-up photo and interpretation of an extended branch of the mega-gallery. 290 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 sediment, are 2 to 5 mm in diameter. an approximately 25-cm-thick deposit of white siltstone with purple mottles lies directly on top of an unbioturbated gray mudstone (figure 4a). the mound contains a network of vertically and horizontally oriented tunnels, with an average diameter of 0.49 cm (n = 13). the burrows appear in vertical and horizontal relief, with semicircular portions of the cylindrical tunnels exposed in cross section, vertically and horizontally. the vertical and horizontal tunnel join in an approximately orthogonal fashion. the tunnels are unlined but have a rugose texture. the second distinct morphology that can be seen on figure 4a are vertical shafts. shafts are exposed vertically and have an average diameter of 0.49 cm (n = 16). some of the shafts are adjacent to more open galleries with are undulating margins. these are more difficult to see as the sediment lacks the pale purple color. a large boulder-sized block that has fallen from the outcrop above revealed the ventral surface of a nest (figure 4b). an anastomosing gallery is visible on a distinctly larger scale than the tunnel lattice and vertical, undulating galleries seen on figure 4a. this feature is a mega-gallery. the arms or branches of the mega gallery are approximately 25 to 30 cm thick and are composed of the tunnel lattice and smaller vertical galleries. a 1.5-cm-wide, 25-cm-long horizontal tunnel is exposed on the underside of the block (figure 4c). the lining to the tunnel, and adjacent small galleries, is not composed of a distinct substrate, but has an anastomosing, or undulating lining. three to five sinuous waves in the lining occur on a 5 cm horizontal line. vertical and horizontal tunnels 0.5 to 2 cm in diameter, with unlined walls, are visible in the arm of the mega-gallery. vertical galleries with an undulating or sinuous lining are visible from the periphery of a nest location (figure 3). a series of horizontally oriented, ribbon-like striations are visible between tunnel and gallery openings. an open gallery shows a bulb hanging down into the gallery; the bulb is approximately 1.5 cm in diameter. figure 3 shows the tunnel lattice, and how smallscale galleries change in three-dimensional space. slices are approximately 10 to 15 cm in the longest direction, and 2 cm thick. gaps between slices are approximately 1 cm (width of rock saw blade). anastomosing or sinuous vertical gallery walls are crossed by a lattice of vertical and horizontal tunnels. ellipsoid features (figures 5 and 6) are pervasive throughout this horizon, with a mean diameter of 0.31 cm (n = 128) through the short axis. these ellipsoid features can be ruled out as continuous burrows in cross section (figure 3). cross sections of ellipsoids are seen on either side of cuts, (cross sections 3 and 4), but are not horizontally continuous through multiple slices (figure 3). for instance, on figure 3, the cross sections on either side of a cut, numbers 5 and 6, go through a group of ellipsoids. the next pair of cross sections (7 and 8) also cut through a group of ellipsoids that are below the group on cross sections 5 and 6. if these were horizontally continuous burrows, the ellipsoids higher on cross sections 5 and 6 would persist through cross sections 7 and 8 (figure 3). the lining of these ellipsoid features is pale-purple, with white sediment internally. these ellipsoids generally occur at the contact between the pale-purple and white sediment, but are also found isolated within white sediment. qemscan analysis ellipsoid features are ubiquitous through the white and pale-purple siltstone facies (figure 5). the ellipsoids are hollow and vertically compressed. the lining of ellipsoids is approximately 10 to 20 microns thick. the outermost layer these of ellipsoid features is silica. the rock fabric of the purple and white siltstone facies is a groundmass of quartz and clay minerals, along with and barite and feldspar crystals that are larger than the groundmass (figure 5c). ellipsoid structures are composed entirely of silica. feldspar crystals seen in petrographic thin section (figure 5c) are white and elongate (~100 μm length). clay mineral and silt-size quartz grains are likely too small to see in petrographic thin section at the magnification displayed in figure 5. barite crystals appear opaque and dark (figure 5c). the qemscan analysis is unable to differentiate the composition of the clay minerals (figures 5d and 5e) versus the plagioclase crystals, and are all identified as gray pixels. interpretation of locality our study has observed this trace fossil assemblage at outcrop scale (figures 1 to 3), centimeter scale (figure 291 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 figure 5. a close-up photograph of the type locality nest horizon of eopolis ekdalei, where umnh ip 5233 was extracted. some matrix is gray-purple and silica rich, with infill composed of bentonitic clay (a). the field photograph of nest horizon with interpreted burrow linings (b). a petrographic thin section photograph of a silicified ellipsoid feature (c) with an overlain qemscan analysis (d). a visual representation of the qemscan analysis with surface area of mineral content reported as a percentage (e). 292 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 figure 6. an interpretation of the new morrison formation trace fossil site at outcrop scale (a). trace fossil interpretation at close-up scale (slice 5, umnh 5233, figure 4), noting embedding of ellipsoids (blue for contrast) (b). a schematic drawing of a single ellipsoid, with appearance in cross section (c). 293 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 3), and microscopic scale (figure 5). we can use these observations to support an overall interpretation of its reconstruction. large chambers, anastomosing galleries, and single, unbranching galleries are visible in the ventral view of the displaced block (figures 3b and 6a). at the hand-sample scale, purple silt matrix can be differentiated from the white silt infill. silicified ellipsoids occur with an apparently random distribution at the hand-sample scale (figure 6b). burrows are roughly horizontally oriented, but also intersect cross sections vertically, and at oblique angles. walls of the burrows have intensely folded and complex surfaces (figure 6c). individual ellipsoids appear as circles in cross section (figure 6c). discussion these findings demonstrate a new occurrence of social insect nest ichnofossils from the morrison formation, morphologically distinct from reported social insect ichnofossils both within and outside of the morrison. these traces show a high degree of ethologic complexity, consistent with the architecture of modern and fossil social insect nests. features that indicate multiple, synchronous behaviors are reported in these nests including burrow excavation, gallery/chamber construction, and ellipsoid producing behavior. these ichnofossils predate the first body fossil occurrences of social insects by 15 million years (krishna and others, 2013). several alternative hypotheses will be addressed here. ichnofossils created by the activity of plant roots are known as rhizoliths, and they are cited as an alternative tracemaker to reported fossil social insect nests (genise, 2016). rhizolith horizons have a superficial resemblance to social insect burrow networks. rhizolith horizons have cylindrical infillings that are densely clustered and may cross each other in a woven appearance (badawy, 2018). in general, rhizolith horizons are defined by vertically oriented casts, with horizontally extending mats that may appear anastomosing in planar view (owen and others, 2008). often, plant root traces and social insect nests are reported in association with insect burrow networks woven into rhizolith fabrics (roberts and tapanila, 2006; genise and others, 2010). discrete rhizolith horizons can be identified immediately below and above the nest horizon (figure 2), but they are either not as dominant, or are completely obscured by the nest horizon. another alternative hypothesis to explain the origin of these traces is that the nests are a composite product of other solitary to subsocial soil infauna that create a structure that appears complex from their individual burrowing activities. a diversity of modern animal life has soil habitat, creating traces that are the result of resting, breeding, and locomotion behaviors (hasiotis, 2007). neoichnological experiments have demonstrated that individual beetle larvae produce backfilled, meniscate burrows (counts and hasiotis, 2009). cicada larvae have been demonstrated to create similar this type of burrow as well (smith and hasiotis, 2008). a diversity of arthropods create trace fossils with both unique and similar features (hasiotis, 2002). ratcliffe and fagerstrom (1980) demonstrated that beetles (coeloptera) were responsible for creating both single-chambered, branching, and anastomosing burrows in holocene sediments. the brood traces of dung beetles, bee cells, and wasp cocoons are common ichnofossils in the cenozoic record of south america, grouped together as the coprinisphaera ichnofacies (genise and others, 2000). although hasiotis (2004) has reported a diversity of trace fossils attributed to the behaviors of insects in the morrison formation, several lines of evidence do not support a soil insect infauna origin for this assemblage. eopolis, with its anastomosing mega-galleries, appears to be much larger and more complex than nests attributed to termites from the late triassic chinle formation, archaeoentomichnus (hasiostis and dubiel, 1995). however, unlike archeoentomichnus, eopolis lacks a distinct periecie and spiral-shaped ramp (hasiostis and dubiel, 1995). first, the isolated occurrence of any of these trace features (including horizontal shafts, vertical shafts, sinuous walls, ellipsoidal features) can be reasonably attributed to other, non-social taxonomic groups of insects. second, the anastomosing burrows that are contained within a larger gallery apparatus suggest a distinct hierarchy and ethological complexity (figure 4). the similar morphology amongst each mound or locus in this ichnofossil assemblage suggests that the trace-maker is monospecific (figure 2). 294 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 despite their size and complexity of their nests, ants can effectively be ruled out as a trace-maker for these new morrison ichnofossils. there is a clear morphological discrepancy between this trace fossil assemblage and the traces of modern and fossil ant nests. in modern ant nests it has been observed that a positive correlation between colony size and nest size exists, in addition to decreasing nest volume with depth (mikheyev and tschinkel, 2004). ant nests have been described as having a single entrance (tschinkel, 2004) or multiple entrances (guimaraes and others, 2018). despite variation in shaft or gallery density and orientation, fossil ant nests and modern ant nests possess distinctively oblate, disk-like chambers (smith and others, 2011). the genomic and body fossils evidence for the evolution of ants is also incongruent with a late jurassic origin (brady and others, 2006; lapolla and others, 2013). moreau and others (2006) suggest a divergence date for the node of extant ants (formicidae) between the middle jurassic (168 ma) and early cretaceous (140 ma). however, tschinkel (2015) suggested that the earliest ant nests likely resembled ground-nesting wasps and bees, with simple descending shafts and single to few expanded brooding chambers. the first unanimously accepted ant nest ichnogenus, parowanichnus, was described by bown and others (1997) from the eocene claron formation of utah. parowanichnus is consistent with the modern ant nest morphology and other cenozoic ant traces (smith, 2011). despite reported ichnofossils with ants as suggested tracemakers from the early cretaceous (genise and others, 2010), the morphology of these new ichnofossils does bear resemblance to those created by ants. another hypothesis for the origin of these ichnofossils is that they were created by a non-formicid, hymenopteran architect. wasps and bees have a trace fossil record extending back to approximately 85 ma to the late cretaceous, at the terrestrial conacian-santonian boundary of argentina (genise and others, 2007). despite the similarity in the ellipsoid features from the brushy basin nests to reported hymenopteran pupal chambers, these features are too far removed from the hypothesized origin of wasps and bees to be considered of wasp or bee origin. the most recent genetic phylogeny of hymenoptera places their initial major radiation in the paleozoic (281 ma), the first appearance of eusocial bees (apidae) in the cenozoic (approximately 60 ma), and eusocial wasp (vespidae) families (approximately 100 ma) (peters and others, 2017). although additional phylogenetic work does place the major radiation of aculeata (the clade containing ants, bees, and wasps) in the middle jurassic (170 ma) (brady and others, 2009), the first clear evidence of wasp and bee eusocial behavior in the trace fossil record is from the cretaceous (genise and others, 2007). vespid wasps are one of the only eusocial, non-formicid hymenopteran clades that excavate nests in the soil. vespid wasps likely evolved eusociality twice independently (johnson and others, 2013), and the earliest claimed fossil vespid is from the early cretaceous (barremian) of spain (rasnitsyn and martínez-delclòs, 2000). the trace morphology of wasp and bee traces are also not consistent with the eopolis ekdali. the morphology and dimensions of celliforma (hymenopteryan pupation chamber) are consistent in shape, size, and dimension with the ellipsoids in eopolis. however, in celliforma, the cells are clustered around a vertical descending shaft (hasiostis, 2002). in eopolis, the ellipsoidal features are generally found at matrix-infill boundaries but are otherwise random within the burrow complex (figure 3). the ichnofossils presented in this paper support the hypothesis that termites evolved eusocial behavior by the late jurassic, preceding not only the rise of angiosperms, but the rifting of gondwana. termite nests exhibit a significant amount of intraspecific, interspecific, and ontogenetic variation (hasiotis, 2003). termite nests can be characterized as diffuse, or concentrated, depending on the arrangement and geometry of galleries and chambers (genise, 2016). concentrated nests have a central arrangement of cavities referred to as the endocie, and a peripheral boxwork of galleries referred to as the perecie (genise, 2016). the concentrated endocie-perecie morphology is generally restricted the termitidae (korb, 2010), the most derived family of isoptera (engel and others, 2009). the nest morphology displayed in these ichnofossils is more characteristic of the diffuse arrangement, which is best seen in the ventral view of the block (figure 4c). termite mounds exhibit a hierarchy of organization, with the smallest components centrally located underground (korb, 2010). although the nests presented in this paper are 295 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 not consistent with the morphology the higher termitidae, they are likely representative of a termite tracemaker that creates nests in association with a detrital or high-cellulose food source (genise, 2016). these trace fossils occur in a key evolutionary interval for termites, as genomic and fossil studies have highlighted the late jurassic as a period of radiation for crown isoptera (engel and others, 2009; legendre and others, 2015). the fossil record of insects from the late jurassic is poorly sampled, and roaches (blattodea) are a relatively uncommon component of known faunas (grimaldi and engel, 2005). phylogenetic analyses placed the split between termites and their sister group, the wood-feeding cryptocerid roaches, in the triassic, with estimates of 241 ma (ware and others, 2010) and 228 ma (brandl and others, 2007). the understanding of the evolutionary transition of wood-feeding, sub-social cryptocerid roaches (blattodea) to the eusocial termites (isoptera) is highly speculative. these trace fossils suggest it is possible that termites had undergone an initial radiation, and lineages representative of the range of life habit, including wood-restricted lineages (lower termites) and ground-nesting lineages (higher termites), had occurred at a minimum by the late jurassic. the presence of the ellipsoid features (figure 5) have intriguing ethological implications. the qemscan results indicate that the ellipsoid features have a silica rind, or outer layer, that are completely silicified (figure 5). it can be ruled out with near certainty that these ellipsoid features (figure 5) were transported to the depositional site, given that there is a paleosol (figure 2) and the rock is dominated by silt-sized grains or smaller. these purple-rind features do not appear to be continuous burrows, as they would be observed continuing through the sequence of slices of umnh ip 5233 (figure 3). rather, these features appear to have discrete boundaries (figure 6c). it is possible that these pellets vary in porosity to the groundmass and have thus been preferentially silicified. modern termites are observed to incorporate organic matter into their nests in the form of pellets, which can be fecal material mixed with saliva (sarcinelli and others, 2009). there is an extensive record of fossilized termite coprolites in the published literature beginning in the early cretaceous (colin and others, 2011). these ellipsoid structures (figure 6c) share a resemblance in shape to the pellet structures of modern and fossil termites (colin and others, 2011), but are notably larger. average diameter of the ellipsoids reported here is 3.1 mm, whereas termite pellets are in the range of 0.5 to 1 mm in diameter (colin and others, 2011). cosarinsky and others (2005) did not identify pellets in fossil nests in their comparison of modern and fossil termite nest micromorphology. however, these authors did attribute the lack of pellets in reported termite ichnofossils as the result of unfavorable preservation conditions. some of the silicified particles observed in the petrographic thin sections of umnh ip 5233 are not fully enclosed ellipsoids, but rather crescent-shaped fragments of ellipsoids (fig. 5). cosarinsky and others (2005) attributed similarly shaped structures in modern termite nests as possible cuticle fragments. the current consensus regarding the evolution of termites places the expansion of their ecology from obligate wood feeding to ground nesting in the late cretaceous (engel and others, 2009). termites were already quite diverse by the mid-cretaceous (engel and others, 2009). though these nests may not be directly attributable to the higher termites (neoisoptera), they call into question the reported emergence of neoisoptera in the late cretaceous as postulated by molecular phylogenies (bourguignon and others, 2014). these ichnofossils are within the chronologic range of emergence of neoisoptera as suggested by fossil-calibrated phylogenies (ware and others, 2010). despite their low abundance as indicated by the body fossil record, termites may have expanded into ground-feeding niches by the late jurassic. the findings in this paper illustrate the opportunity for palaeoentomology and ichnology to expand its knowledge of the timing and details of social insect evolution. future areas of research include investigating the phylogenetic signal in social insect nest morphology and linking body fossil deposits to contemporaneous nest horizons. a promising avenue of future research with social insects is using three-dimensional digital imaging, which can produce quantitative structure models (varoudis and others, 2018). three-dimensional imaging has great potential for neoichnological experiments because development of burrow morphology 296 new social insect nests from the upper jurassic morrison formation of utah armour smith, e., loewen, m.a., and kirkland, j.i. geology of the intermountain west 2020 volume 7 can be visualized and measured in real time, enhancing the understanding of ethology and trace geometry (himmi and others, 2018). conclusions in this paper we present new social insect nest ichnogenus and ichnospecies, eopolis ekdalei, from the brushy basin member of the upper jurassic morrison formation of utah. at least seven nests are observed at the locality horizon, and they display complex ethology at multiple scales. the organization of anastomosing burrow networks in a diffuse, bulbous arrangement, is consistent with social insect architecture having hierarchical organization. the morphology of these traces does not resemble an ant (formicidae) trace maker. also, the body fossil and molecular evidence does not support a late jurassic origin for ants. the nests are more morphologically consistent with termites, which have a body fossils record indicating a jurassic, gondwanan origin. the large, subterranean nests presented here, if in fact created by termites, suggest it is possible that termites had undergone a transition into soil habitats in seasonally arid climates by the late jurassic. identification and description of contemporaneous social insect trace fossils will shed greater light on the origin of social insects, one of the most ecologically successful groups of organisms on the planet. acknowledgments special thanks are owed to matt joeckel of the university of nebraska who was the first person to recognize in the field the biological origin of the ellipsoid features of this new ichnogenus. this paper was improved by with the advice of several current and former faculty members of the department of geology and geophysics at the university of utah including randall irmis, kathleen ritterbush, erich petersen, marjorie chan, tony ekdale, and the late frank brown. department of geology and geophysics curator quintin sarahtian, and paleontology collections manager carrie levitt-bussian of the natural history museum of utah helped with preparing thin sections and serial sections of the type specimen. don deblieux of the utah geological survey co-wrote the locality report. the specimen was collected on bureau of land management land supervised by the moab field office. thanks to stephen hasiotis and jorge genise for discussions and providing relevant literature. thanks to my master’s advisor, robin o'keefe, for helping me improve this manuscript, and to our reviewers: matthew stimson, spencer lucas, and eric roberts. their comments on this paper were invaluable. also thanks to the utah geological survey reviewers: grant willis, stephanie carney, mike hylland, and bill keach. lastly, thanks to the handling editor john foster for his diligence and patience with this paper, and to the other editors at the geology of the 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fossil placement and calibration on divergence times and rates— an example from the termites (insecta: isoptera): arthropod structure and development, v. 39, no. 2–3, p. 204–219. wilson, e.o., 1971, the insect societies: cambridge, massachusetts, harvard university press, 548 p. xing, l., roberts, e.m., harris, j.d., gingras, m.k., ran, h., zhang, j., xu, x., burns, m.e., and dong, z., 2013, novel insect traces on a dinosaur skeleton from the lower jurassic lufeng formation of china: palaeogeography, palaeoclimatology, palaeoecology. v. 388, p. 58–68. close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah jonathan p. warnock, joseph e. peterson, steven r. clawson, neffra a. matthews, and brent h. breithaupt theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover orthomosaic map of the 2015–2017 excavations of the south butler building at the cleveland-lloyd dinosaur quarry produced from photogrammetry and standard grid mapping. the cleveland-lloyd dinosaur quarry is located on the san rafael swell, emery county, utah. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net editors president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 271 abstract bone distribution data are essential for taphonomic assessments of bonebeds. the cleveland-lloyd dinosaur quarry (cldq), an allosaurus-dominated bonebed within the upper jurassic morrison formation, has been researched for nearly 100 years, but published maps are scarce considering the importance and density of the assemblage. additionally, few detailed maps of bones from the cldq have been published in two dimensions, whereas the third, the stratigraphic/vertical, dimension has never been recorded. utilizing standard field mapping techniques as well as photogrammetry, the three-dimensional orientations of bones currently exposed in the quarry have been analyzed for potential dispersal patterns. additionally, a “living” or continuously updatable, photogrammetric map which allows for researchers to view the bones in three dimensions throughout the course of excavation has been created. continued photogrammetry in future field seasons will allow visualization of bones in three dimensions even after the currently exposed bones have been removed. utilizing these newly available data, two distinct clusters of bone within the south butler building at the quarry are identified. based on statistically significant average orientations and depths of these bones, early-stage post-mortem transport of carcasses prior to disarticulation (i.e., bloat and float) is supported as an important transport and depositional process within the quarry assemblage. furthermore, possible evidence of multiple depositional events is discussed. close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah jonathan p. warnock1*, joseph e. peterson2, steven r. clawson3, neffra a. matthews4, and brent h. breithaupt5 1indiana university of pennsylvania, department of geoscience, 302 east walk, indiana, pa 15705; jwarnock@iup.edu 2university of wisconsin-oshkosh, department of geology, 800 algoma blvd, oshkosh, wi 54901; petersoj@uwosh.edu 33315 cascade ln., new lenox, il 60451; srclawson@comcast.net 4bureau of land management national operations center, geospatial section, denver federal center, bldg. 50, p.o. box 25047, oc-534, denver, co 80225-0047; n1matthe@blm.gov 5bureau of land management, wyoming state office, 5353 yellowstone road, cheyenne, wy 82009; bbreitha@blm.gov *corresponding author citation for this article. warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h., 2018, close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah: geology of the intermountain west, v. 5, p. 271–285. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction upper jurassic bonebeds of the morrison formation are typically sauropod-dominated, with theropods being comparatively rare (engelmann and others, 2004). whereas the dominance of sauropods is possibly a reflection of late jurassic ecosystems (dodson and others, 1980), low predator:prey ratios may also represent taphonomic bias resulting from pre-burial depositional winnowing and weathering of the more easily-transportable and easily weathered theropod bone elements (voorhies, 1969; behrensmeyer, 1975; gates, 2005). 272 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 one notable exception, with a predator:prey ratio of 3:1, is the cleveland-lloyd dinosaur quarry (cldq) on the north end of the san rafael swell, emery county, east-central utah (figure 1), a macrofossil bonebed comprised primarily of the predatory theropod, allosaurus fragilis (miller and others, 1996). the bonebed is also unusual in that the large number of allosaurus preserved at the quarry (n = 46) are dominated by subadult individuals (madsen, 1976). as a result of the distinctly high predator:prey ratio, the cldq has frequently been treated as an anomaly and mystery in the literature (e.g., madsen, 1976; bilbey, 1999; gates, 2005; hunt and others, 2006). a robust taphonomic interpretation of the bonebed is needed in order to understand the cldq in relation to jurassic paleoecology of the region. additionally, the subadult:adult ratio at the cldq cannot be fully interpreted further without development of the quarry’s taphonomic model. understanding whether subadults were more common than adults within the paleogeographic region, or preferentially deposited at the cldq for another reason, requires a detailed understanding of the processes which lead to the deposition of the bonebed. many competing taphonomic hypotheses have been put forth regarding the cldq. early hypotheses focused on a predator trap, where a few dying herbivores attracted large numbers of carnivores (dodson and others, 1980; stokes, 1985; richmond and morris, 1996), even though expected taphonomic evidence (i.e., gnaw marks and trampling of bone) to support these conclusions is not present at the site (gates, 2005). bilbey (1999) suggested the deposit represents a lethal spring or seep; however, no source of toxin is suggested. furthermore, it is unlikely that dinosaurs would have been poisoned to the extent that they would have died at the site of the seep upon drinking. other authors (e.g., gates, 2005) have evoked a drought-induced assemblage. while the surface textures of most of the recovered bones do not suggest post-mortem subaerial exposure in a dry environment, the presence of abundant, small parautochthonous bone fragments dispersed throughout the quarry matrix suggests that subaerial exposure and intense weathering of some bones was occurring (gates, 2005; peterson and others, 2017). peterson and others (2017) utilized novel intramatrix bone fragment (ibf) data and geochemical profiling of bones and sediment in an attempt to synthesize and understand these competing hypotheses. their data suggest that the deposit represents periods of aridity, leading to the generation of ibf’s, followed by one or more flood periods in which the ibf’s were incorporated with sediment and dinosaur carcasses, creating a hypereutrophic ephemeral pond. this hypothesis incorporates components of drought and ‘bloat and float’ deposition as well as flooding (peterson and others, 2017). a key piece of taphonomic data is missing from all these studies and hypotheses however: three-dimensional (3d) bone distribution. despite a great diversity of studies that use the cldq as the primary site of study (e.g., stokes, 1945; figure 1. the cleveland-lloyd dinosaur quarry (cldq) is located in east-central utah about 185 km (115 mi) southeast of salt lake city, utah. 273 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 bilbey; 1999, hanna, 2002; suarez, 2003; gates, 2005; hunt and others, 2006; carpenter, 2010; peterson and others, 2017), maps representing previously excavated bones contain some anomalous gaps (stokes, 1985), and a lack of 3d distribution of bones. the scope of many studies conducted throughout the 20th century (e.g., gilmore, 1920; stokes, 1945; madsen, 1976) focused on the collection of impressive museum specimens and placed little emphasis on mapping, leaving modern studies at risk of falling prey to cartographic artifacts (stokes, 1985). notably, the cldq was unprotected and worked by amateur collectors over the period of time spanning the professional collection of bones by princeton university in 1939 and the university of utah in 1960 (madsen, 1976). due to a lack of cooperation in compiling data, composite maps of the bonebed, including a popularly cited map drafted by the university of utah cooperative dinosaur project in 1967, offer only general two-dimensional (2d) estimations of the original spatial distribution of bone, and lack any description of stratigraphic position or plunge of bones. additionally, the available composite map of the quarry contains many numerous artifacts, including artificial right angles at the edges of the bonebed and gaps within bone deposition. in order to understand the depositional history of the quarry, as well as being able to determine whether or not the allosaurus bones were deposited during a single or multiple events, 3d bone orientation data is needed. in order to address these issues, grid maps composed of previously and recently exposed bones have been drafted over the 2015–2017 field seasons. these maps include depth data relative to a fixed arbitrary datum within the south butler building at the quarry as well as depth relative to the undulatory surface of the freshwater limestone cap, which overlies the productive siltstone bonebed for which the site is famous. finally, we present a “living” photogrammetric map of the quarry which contains 3d bone orientation data. the map is referred to as living because new data, in the form of photographs from future excavations as well as positions of newly exposed bones, can be added to the current file. digital photogrammetry, or the process of three-dimensionally reconstructing the surface texture and topography of objects using oriented digital photographs, offers a modern, precise means of resolving the relative positions of bone (matthews, 2008), and has already seen some applications in the field of vertebrate paleontology (see breithaupt and others, 2004; falkingham, 2012; matthews and others, 2016; and references therein). in the present study, a high-fidelity 3d photogrammetric data file produced for the cldq over the course of three field seasons provides a more accurate representation of the quarry assemblage than previously published maps. geological setting, taphonomy, and history of the clevelandlloyd dinosaur quarry the cldq is located approximately 38 m above the basal contact of the brushy basin member of the morrison formation (bilbey, 1992; peterson and others, 2017). the numerous dinosaur fossils in the quarry are encased in a structureless calcareous mudstone composed primarily of montmorillonite with various silicate minerals (e.g., quartz, feldspar, and biotite). the bonebed ranges in thickness from centimeters to approximately 1 meter. the silty calcareous mudstone is overlain by a bone-bearing micritic limestone unit that varies in thickness from 0.3 to 1.0 m (bilbey, 1992; gates, 2005). the limestone contains notably fewer bones than the silty mudstone. based on limited exposures, the silty mudstone unit is laterally continuous for 50 to 75 m before pinching out to the south (gates, 2005). a total of ten dinosaur genre are present at the quarry including two ornithischian taxa (stegosaurus and camptosaurus), three sauropod taxa (camarasaurus, barosaurus, and apatosaurus), and five theropod taxa (allosaurus, ceratosaurus, stokesosaurus, marshosaurus, and torvosaurus) (gates, 2005; foster and peterson, 2016). of all the present taxa, allosaurus fragilis is the most abundant (46 skeletons) composing 66% of the total skeletons (gates, 2005). due to its abnormal abundance of large theropod dinosaur skeletons, the cldq has received unrivaled attention in regards to taphonomic investigations and depositional interpretations over the last 85 years. the quarry was first formally excavated in 1926 (miller and 274 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 others, 1996), though the first extensive work at the quarry did not begin until 1939, led by w.l. stokes and a field crew from princeton university (stokes, 1945). from the 1960s through 2005 the quarry was worked intermittently by various field crews, most of which were based in utah (e.g., madsen 1976; miller and others, 1996; gates, 2005; hunt and others, 2006). in 1968, the cldq was recognized as a u.s. natural landmark and is currently managed by the u.s. bureau of land management (blm), followed by the installation of two metal butler buildings in the late 1970s (miller and others, 1996). while the site receives frequent visitors and is a positive tourism spot for the state of utah, the enigmatic nature of the fossil assemblage has produced numerous theories by the equally numerous taphonomic studies; this fact was noted by madsen (1976, p. 8), who stated, “theories of the demise of the cleveland-lloyd dinosaurs are but slightly fewer in numbers than the visitors to the quarry.” since its discovery in 1926, the cldq has yielded over 10,000 dinosaur bones (gates, 2005). however, the various field expeditions that have excavated the quarry during that time have each established a different mapping method, many of which are not compatible with previous quarry maps. whereas various depositional models have been proposed for the cldq, the lithologies, abundant vertebrate macrofossils, and rare microvertebrate and invertebrate remains suggest an ephemeral pond or similar overbank deposit with a fluctuating water table (calcareous mudstone facies) that became more permanently hydrated in the form of a shallow lacustrine setting (limestone facies) (bilbey, 1999; gates, 2005; peterson and others, 2017). the presence of freshwater ostracods, gastropods, and charophytes in the limestone cap over the bone-bearing mudstone suggests that the environment supported a freshwater ecosystem during the last stages of sediment filling the pond (bilbey, 1992). an ash bed approximately 1 m above the limestone cap has been dated to 147.2 ± 1 ma to 146.8 ± 1 ma via k/ar dating (bilbey, 1998). methodology field excavation and stabilization fieldwork was performed at the cldq between 2015 to 2017 by field crews from the university of wisconsin–oshkosh and indiana university of pennsylvania. a total of 55 bones were mapped and photographed within the south butler building, representing bones exposed by previous expeditions and left exposed in the south butler building as well as newly exposed elements. grid mapping a grid map of the quarry was constructed using u.s. customary units, as this matches the data generated by the blm previously (figure 2). standard grid mapping of the south butler building was completed using a yard-by-yard pvc grid, containing 15 x 15 cm minor grid squares. only data from the south butler building was used for this study, as the sample set available in the north butler building is skewed to bones at the base of the deposit. a 1-yard square grid frame constructed from pvc tubing and nylon cord on adjustable legs was aligned to a master grid line strung across the entire area of the quarry from fixed datums. this square was used to measure the position of bones within the larger master grid. subsequently, the depth from an arbitrary fixed datum, the upper surface of the concrete foundation of the buildings, was measured via plumb bob at the ends of each bone, allowing for the calculation of dip and precise stratigraphic placement of each element. field specimen numbers, including element field identifications and notes, were recorded according to the format established by prior crews; for example, cldq-001-17 was the first recorded specimen of 2017. furthermore, the thickness of the undulating overlying limestone cap was measured in relation to the building foundation and bone position. the resulting map presents the distribution of bones, with accompanying 3d orientation data (figures 2 and s1, table 1). cardinal orientation was measured outside of the magnetic influence of the steel butler buildings (a likely reason for the cardinal inaccuracy of many maps drafted of the quarry after to the construction of the buildings in 1969) using a standard azimuthal compass-clinometer, adjusted for magnetic declination (11° 5' e). subsequently, each bone element was plotted as a point in two cross sections along the long axis of the 275 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 south butler building (35° west of north), utilizing depth and position data collected in the field. in addition to the bone position, the limestone thickness was plotted (figure 3). two such cross sections were created in order to accommodate the lateral variability in limestone thickness, one through row b and one through row c of the master grid (figures 2 and 3). rows a and d have not been plotted to date due to the small number of bones exposed in those grid rows. photogrammetry photographs were taken using a nikon d3000 single-lens reflex (slr) camera, maintaining an 18 mm focal length. excluding a few skylights on the ceiling, quarry windows were covered with shades to minimize lighting effects. for the purposes of this photogrammetric map, three rounds of photography were necessary: 90° (vertical, facing the quarry floor), 45° (intermediate, at an oblique angle with the quarry floor), and 0° (horizontal, facing the quarry wall), performed in a circular pattern around the inside of the building in two series: facing inward and facing outward. four sets of photographic documentation took place; one in 2015 (547 photos), two collected in 2016 (436 and 446 photos), and one 2017 (404 photos). calibrated photogrammetric targets were used during each photography session. two methods were utilized when placing the targets. first, a series of targets were placed along the building’s foundation at the location of the master grid lines. these targets served to align the grid map to the photogrammetric map. a second set of movable photogrammetric targets were placed within the excavation area and were repositioned between each photogramfigure 2. standard grid map of the 2015–2017 excavations of the south butler building at the cldq. 276 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 field # field id length (cm) width (cm) grid square depth from foundation (cm) limestone thickness (cm) depth below limestone (cm) orientation with respect to north (°) cldq-s-17-001 rib 33 5 b1 121 31.75 74.25 175 cldq-s-17-002 scap 128 48 b2-b3 122 29.21 77.79 14 cldq-s-17-003 rib 13 2.5 b2 140.5 29.21 96.29 173 cldq-s-17-004 toe 4 3 b2 119 29.21 74.79 20 cldq-s-17-005 indet. 11 6 b2 111 29.21 66.79 20 cldq-s-17-006 vertebra 11 10 b2 113 29.21 68.79 41 cldq-s-17-007 toe 3.5 3 b2 113 29.21 68.79 6 cldq-s-17-008 vertebra 15 14 b3 129 43.18 70.82 10 cldq-s-17-009 vertebra 38 8 b3 123 43.18 64.82 x cldq-s-17-010 jacket 126 38 b4 94.5 49.53 29.97 x cldq-s-17-011 vertebra 56 32 b5 97.5 49.53 32.97 105 cldq-s-17-012 rib 6.5 1.5 b4 102 49.53 37.47 35 cldq-s-17-013 rib 24 3.5 b4 107.5 49.53 42.97 110 cldq-s-17-014 centrum 9 8 b5 99.5 49.53 34.97 x cldq-s-17-015 rib 54 5.5 b5 100 38.35 46.65 160 cldq-s-17-016 limb 18.5 5 b5 99 38.35 45.65 155 cldq-s-17-017 rib 6.5 2.5 b5 100 38.35 46.65 35 cldq-s-17-018 limb 14 6 b5 103 38.35 49.65 165 cldq-s-17-019 limb 19 4 b5 98 38.35 44.65 90 cldq-s-17-020 pelvic 37 20 b6 92 29.21 47.79 33 cldq-s-17-021 femur 20 12 c6 98 58.42 24.58 155 cldq-s-17-022 limb 26 17 c6 91 58.42 17.58 x cldq-s-17-023 indet. 24 18 c6 94 58.42 20.58 x cldq-s-17-024 rib 10 10 c6 92 58.42 18.58 73 cldq-s-17-025 toe 5 2.5 c5 96 76.7 4.3 20 cldq-s-17-026 meta 8 3 c5 106 76.7 14.3 43 cldq-s-17-027 vertebra 12 12 c5 98 76.7 6.3 x cldq-s-17-028 illium 50 24 c5 99 76.7 7.3 85 cldq-s-17-029 rib 17 3 c5 96 76.7 4.3 155 cldq-s-17-030 limb x x c5 103 76.7 11.3 35 cldq-s-17-031 cervical rib 10 3 c4 110 90 5 155 cldq-s-17-032 quadrate 13 7 c4 112 90 7 155 cldq-s-17-033 rib 9 5 c4 105 90 0 155 cldq-s-17-034 indet. 12 8 c4 113 90 8 x cldq-s-17-035 centrum 10 7 c4 103 90 -2 x cldq-s-17-036 zygopophysis 10 2 c4 109 90 4 100 cldq-s-17-037 vertebra 8 6 c4 107 90 2 x cldq-s-17-038 limb 11 3 c4 115 90 1 5 cldq-s-17-039 femur (l) 36 10.5 c3 103 86.36 1.64 105 cldq-s-17-040 surangular 27 8 c3 130 86.36 28.64 150 cldq-s-17-041 vertebra 9.5 5.5 c2 115 58.42 41.58 85 cldq-s-17-042 vertebra 6 3 c2 116 58.42 42.58 20 cldq-s-17-043 dentary 12 7 c2 114 58.42 40.58 75 cldq-s-17-044 atlas 10 2.5 c2 115 58.42 41.58 x cldq-s-17-045 limb 49 5 c2 99 58.42 25.58 15 cldq-s-17-046 indet. 3 2 c2 115.5 58.42 42.08 160 cldq-s-17-047 vertebra 30 8 c2 119 58.42 45.58 165 cldq-s-17-048 superior process 9 5 c2 119 58.42 45.58 20 cldq-s-17-049 trans process 20 2.5 c2 120 58.42 46.58 38 cldq-s-17-050 humerus 23.5 7 c1 100 63.5 21.5 35 cldq-s-17-051 limb x x d3 102 86.36 0.64 180 cldq-s-17-052 vertebra 19 17 c5 100 76.7 8.3 x cldq-s-17-053 gastralia 50 10 c6 135 0 120 180 cldq-s-17-054 caudal vert 5 2 c6 98 58.42 24.58 75 cldq-s-17-055 rib 100 60 c4 146 90 41 x table 1. field specimen numbers and tentative field identifications are given for each bone in the south butler building. in addition, bone dimensions and positions are given. x = no data. 277 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 figure 3. cross sections through the bonebed. cross sections are presented through the b and c rows of the grid map (figure 1). black dots represent the centers of bones found in each row. each cross section represents a two-dimensional compression of all of the bones found in each row. the thickness and undulatory lower surface of the limestone cap is shown. following the convention of mapping previously done by the blm the horizontal axis is measured in feet rather than meters. 278 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 metric session as new stratigraphic levels were exposed. all targets served to provide real world units to the photogrammetric processing. all 1833 digital photographs taken of the quarry were imported into agisoft photoscan professional edition, version 1.3.2 build 4205 (64 bit), an image-based 3d modeling/photogrammetric software package. processing was conducted on a dell precision 7710 laptop with intel core 17 vpro processor, 32 gb of ram, and an nvidia quadro m5000m graphics card running windows 10. software procedure to ensure uniformity among the episodes of photography all 1833 images were processed together in the same “chunk.” agisoft photoscan utilizes the term “chunk” to denote a grouping of images upon which the same structure from motion and alignment algorithms, as well as other processing functions, may be applied. the alignment was conducted with an accuracy setting of “high,” generic preselection was disabled so that all images were evaluated with each other for matches, key point limit was set to “80,000,” and tie-point limit was set to “0.” the time associated with this processing phase took 2 days and 21 hours for matching and 3 hours 23 minutes for alignment. the majority (97%) of images aligned successfully on high resulting in a sparse point cloud of over 7 million points. an error reduction and camera optimization workflow was followed (matthews and others, 2016). markers were placed along the upper surface of the concrete building foundation and cross beam at the master grid locations. the automatic coded target detection algorithm within photoscan was used to mark the calibrated photogrammetric targets and for assignment of scale bars of appropriate length. the units of the photoscan project were set to meters. at the conclusion of the error reduction and optimization phase a reprojection error of 0.343 pixels was reached. factoring in an average image resolution of 0.494 mm per pixel and a grid marker error of 0.495 mm a total photogrammetric project error of 1 mm was achieved. the “rotate object” tools was used within photoscan to effectively level the upper surface of the building foundation without skewing or warping the aligned point cloud. the local dip of the cldq, estimated under 2° northwest in the huntington 30' x 60' quadrangle (witkind, 1988), was considered negligible for leveling. a user-defined coordinate system was chosen and an arbitrary elevation of 10 m set for the foundation to avoid negative elevations. the chunk comprised of all episodes was duplicated multiple times to correspond to the four episodes of photographic documentation. within each duplicate chunk one episode was chosen and the images from other episodes were disabled. dense point clouds, meshes, a digital elevation model (dem), and digital orthorectified image mosaics (orthomoasics) were generated for each episode chunk (table 2). the above procedure resulted in all of the photogrammetric products for each episode to be in a uniform coordinate system related to the quarry map grid system. the orthomoasics and dem for each episode were brought into arcmap 10.4.1 and polygons were drawn for each bone element and labeled according to the quarry map (figure 4). all statistics gathered during the excavation were recorded in a spreadsheet that was episode number of points in dense point cloud number of faces in mesh may 2017 66,967,408 (high quality) 49,848,948 june 27, 2016 54,458,463 (high quality) 49,866,034 june 23, 2016 63,239,516 (high quality) 49,922,374 june 2015 66,241,247 (high quality) 49,999,022 table 2. statistics for four photogrammetry episodes from 2015–2017, including number of points in each dense point cloud, number of faces in each mesh after decimation, resolution of each dem, and resolution or each orthomosaic image. note: decimation of the meshes to 50 million (50,000,000) was necessary to ensure response computer processing. 279 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 fi gu re 4 . o rt ho m os ai c m ap o f t he 2 01 5– 20 17 ex ca va tio ns o f t he s ou th b ut le r b ui ld in g at th e c le ve la nd -l lo yd d in os au r q ua rr y pr od uc ed fr om p ho to gr am m et ry an d st an da rd g rid m ap pi ng (fi gu re 1 ). fi el d nu m be rs co rr es po nd to b on es d es ig na tio ns li st ed in ta bl e 1 . a n in te ra ct iv e p d f (fi gu re s 1) is lo ca te d in th e at ta ch m en t p an el . 280 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 joined to the digital quarry map. this allows for visualization of the quarry, in 3d space, based on multiple combination of factors (supplemental figure s1). figure s1 is an interactive photogrammetric model of the excavation in the south butler building at end of the 2017 field season that can be launched by clicking on figure s1 in the attachment panel. activation of the object data tool (adobe) launches the interactive content, permitting selection of individual elements and browsing of element within the map, field number, measurements, depth data, and orientation. for bone designations refer to table 1. statistical analysis circular means and raleigh’s r test for two data subsets were calculated using past (hammer and others, 2001). the data was separated into two bins to calculate circular means based on a gap in bone deposition along a north/south transect. the first mean is calculated for bones found between 0 and 2.13 m (0 and 7 ft) from the north edge of the foundation of the south butler building (n = 19 bones) and the second mean represents bones found between 3.05 and 5.49 m (10 and 18 ft) from the north edge of the foundation (n = 29 bones). as above, feet were used rather than meters to insure continuity with the original grid set up by the utah blm. three bones found between 2.13 and 3.05 m (7 and 10 ft) from the foundation were not included in the statistical analysis. raleigh’s r test was used to determine the the significance of the two circular means (p < 0.05). finally, past was used to test for a significant (p < 0.05) difference in mean depth between the two bone clusters described above. results bone depth and orientation data are provided in table 1. bone orientations ranged from 0 to 175° from north. the limestone thickness varied from 29 to 90 cm and was found to vary in both the north-south and eastwest directions. bones were found from the limestone/ siltstone contact to the base of current excavation. photogrammetry produced a 3d model of the quarry (figure 3) which can also act as a realistic true to scale map view of the quarry. in addition, photogrammetric models produced throughout the course of excavation allow for the display of progressive excavation through the quarry (supplemental figure s2). figure s2 is a “living map” of excavations. animation showing the progression of excavation over the course of the 2015–2017 field seasons. subsequent rounds of photogrammetry can be added as field work continues, providing a visual means to assess the distribution and relative positions of bones even after they are removed from the quarry. the animation can be activated by clicking on figure s2 in the attachment panel. all photogrammetric products are to scale and provide a detailed view of the excavation. two distinct clusters of bone were observed during excavation. the northernmost bone cluster was found to have an average orientation of 60.3° whereas the southernmost bone cluster has an average orientation of 101°. both of these means were found to be significant. in addition, the north bone cluster has an average depth of 119 cm beneath the foundation of the south butler building, whereas the south bone cluster has an average depth of 102 cm. these means were found to be significantly different. discussion a robust orientation analysis is necessary to interpret the paleoenvironment of a bonebed (e.g., voorhies, 1969; behrensmeyer, 1975; rogers and kidwell, 2007; mathews and others, 2009; keenan and scannella, 2014). the photogrammetric scalar field mesh produced by this study offers a 3d alternative to 2d projections for interpreting orientations. by collecting photogrammetric data over the course of many field seasons, a “living” map can be generated (figure s2). this map allows for researchers to view individual bone horizons in three dimensions at multiple excavation levels and can be updated as frequently as new pictures are taken during excavation. by viewing subsequent years of photogrammetry, the placement of bones which have been removed can be compared to those still in place, allowing for detailed previously impossible visualization of the quarry assemblage in a stratigraphic context. furthermore, photogrammetric maps can ground-truth field maps and orientation data collected during exca281 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 vation. the currently produced photogrammetric map includes embedded data for depth, size, orientation, and field identification of each bone element. the creation of a ‘living’ map, in which multiple stratigraphic horizons may be viewed by accessing data across multiple years of photogrammetry, is a novel feature in vertebrate paleontology. combining the aforementioned mapping techniques with photogrammetry reveals multiple depositional bone-bearing layers separated by bone-free horizons. this new technique suggests the genesis of the assemblage could be owed to multiple overlapping depositional events. additionally, abiotic taphonomic signals apparent in the photogrammetric map, e.g., clustering of bone, preferred orientations and preferred depths, support the hypothesis that the cldq represents an ephemeral pond system periodically flooded with overbank sediments (sensu peterson and others, 2017). this new technique, one that can be continually updated by subsequent expeditions and hopefully any subsequent research groups, will help institute a system for the collection of more precise bone orientation data at the cldq. the data presented here represent the first 3d bone distribution data published on the cldq since excavation began in 1926. based on 3d analysis of bone position and orientation via field maps, photogrammetric maps and cross sections, the bones currently exposed in the south butler building can be separated into two main clusters and several isolated elements. the clusters are distinct in that they are physically separated into a northern and southern group. furthermore, each cluster has a distinct and statistically significant orientation. additionally, whereas there is some stratigraphic overlap, the northern bone group has a deeper average depth than the southern bone group relative to a fixed datum and the mean depths of each cluster are significantly different. it is worth noting that only a small area of the quarry has been mapped in such a way to provide this detailed 3d analysis. the results found here may or may not reflect conditions within the entire bonebed. future excavation will provide the opportunity to check these results against other sections of the bonebed. also striking is that the lateral extent of each cluster of bones is constrained by a single large bone and each cluster is composed of associated skeletal remains, although it is currently impossible to be certain the associated elements are from a single individual. the northern cluster of bones is primarily composed of associated allosaurus skull elements as well as small vertebrae and associated pedal elements. these bones are clustered against the medial surface of a large (146 cm length) sauropod left scapula. the southern cluster is comprised mainly of disarticulated and associated vertebrae and disarticulated ribs which are clustered against two articulated sauropod cervical vertebrae (63 cm total length). in both cases the large bone elements (scapula, articulated vertebrae) create a surface against which the smaller bone elements came to rest. furthermore, in both cases the smaller bones resting against the larger elements are associated skeletal elements. this data very strongly supports a bloat and float taphonomic scenario in those areas of the quarry studied and described herein. it is compelling to think about the scenario being present for the entire quarry, but because 3d data is not available for most the quarry area, this interpretation can only be speculated upon for the remainder of the bonebed. however, further work may provide additional evidence in this regard. this evidence suggests that bloat and float processes were important to the formation of the cldq deposits. bloat and float is a process which distributes bones from decaying corpses (e.g., syme and salisbury, 2014). during the early stages of decomposition, corpses bloat. this makes them buoyant and causes them to float. as the bodies continue to decay, segments of the body (i.e., a limb, head, or section of the vertebral column) fall off and rot further. as such, bloat and float processes should result in an accumulation of randomly scattered groupings of associated and articulated bone. if a strong current is present during the bloat and float process, these bones may accumulate against the surface of the depositional basin or fall and settle with a preferred orientation. it is worth noting, however, that bloat and float processes can lead to the deposition of whole skeletons as well (e.g., mallon and others, 2018). bloat and float within the pond setting represented by the cldq deposit would result in bones being associated as they distribute. this setting is influenced by both fluvial (e.g., deposition of sediments escaping the riverbed during high flow periods) and paludal (e.g., 282 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 settling and weak wind-induced wave action) processes. we hypothesize that a weak current within the pond (e.g., short-term flow induced by wind blowing across the pond surface) would have moved rotting carcasses as they fell through the water column, occasionally resting against larger previously deposited skeletal remains which had already sunk to the pond floor. for example, a partially decomposing allosaurus skull may float into pond during a flood stage. during further decomposition, the skull would disarticulate and begin falling through the water column. while falling, elongated elements would orient parallel to any weak current, and settle against a large sauropod scapula and previously deposited vertebrae and pedal elements. these bones are then buried together, maintaining the orientation at depth. those bones which did not come to rest against a larger element are represented by the isolated elements found within the quarry. it is also possible that desiccated remains could have been washed into the cldq pond and rapidly buried to produce the pattern of bone deposition seen here. however, this would require the remains to have been exposed for only a short amount of time, as no evidence of flaking from exposure to the sun is evident on the bones. furthermore, an increased number of scavenging traces would be expected on remains sitting at the surface. past research at the cldq has suggested that the deposit may represent multiple depositional events (peterson and others, 2017). the data presented here provide further evidence that multiple depositional events may have occurred to create the cldq bonebed. the two identified clusters of bone both have distinct, significant orientations. this implies at least two flow directions were involved in the depositional history of this section of the quarry. additionally, the two bone clusters have distinct mean depths. whereas there is some overlap in the depths represented by these clusters, this could be due to the uneven surface of the bottom of the pond at the time of each depositional event. multiple depositional events controlled primarily by bloat and float processes would lead to the formation of an undulatory surface at the bottom of the pond, as isolated clusters of bones draped with mud would create local topographic highs. the undulation of the limestone layer provides evidence of an uneven surface to the bottom of the pond, at least during the final phase of deposition. burial after each depositional event must have been rapid, given that the bones are unabraided, nearly all lack vertebrate and insect scavenging marks, and lack evidence of physical weathering (behrensmeyer, 1975; gates, 2005). the spatial distribution of bone at the cldq is at odds with other morrison formation vertebrate localities. bones at the mygatt-moore quarry are found disarticulated and rarely associated (kirkland and others, 2005) in an environment interpreted as a vernal pool on a poorly drained muddy floodplain, with abundant plant life, possibly from a surrounding woodland (kirkland and others, 2005; foster and hunt-foster, 2011; foster and others, 2018). hence, bone distribution data don’t currently support bloat and float processes at mygattmoore. four additional sauropod-dominated bonebeds from the brushy basin member of the morrison formation (the howe quarry near shell, wyoming, the bs and si quarries near thermopolis, wyoming, and the carnegie museum diplodocus quarry near sheep creek, wyoming) have similar lithologies to the cldq (i.e., calcareous mudstone) and also display considerable disarticulation of skeletal remains (michelis, 2004; ikejiri and others, 2006; jennings and hasiotis, 2006; brezinski and kollar, 2008). all four sites are interpreted as low-energy, poorly drained floodplains associated with seasonal palustrine or lacustrine depositional environments similar to that observed in the cldq. however, the high frequency of shed theropod teeth in close proximity to sauropod remains at the si quarry suggest active feeding took place, disarticulating the skeletal elements by biostratinomic processes (jennings and hasiotis, 2006). both the si and bs sites are interpreted to represent single depositional events (ikejiri and others, 2006; jennings and hasiotis, 2006) rather than cyclic processes (peterson and others, 2017). despite differences with other morrison formation localities, similarities are evident between the cldq and smaller bonebeds that have been described from other formations. fiorillo and others (2000) described a placerias bonebed from the upper triassic chinle formation that is interpreted as a low-energy environment that also possesses numerous carbonate nodules that are pedogenic in origin. bones also pos283 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 sess minimal evidence of fluvial transport, trampling, or predation (fiorillo and others, 2000). keenan and scannella (2014) described a triceratops bonebed from the upper cretaceous hell creek formation (garfield county, montana). whereas the bones of multiple triceratops individuals were recovered in association (mni = 3), differences among the abrasion and orientations of bones belonging to each individual suggest that aggregation of each carcass occurred through the force of multiple independent flooding events (keenan and scannella, 2014). the majority of bones at this bonebed are well preserved, showing little weathering and abrasion or biostratinomic alteration providing further similarity to those of the cldq. additionally, many of these bones are “stacked,” as observed in the clustered bones at the cldq. unlike the cldq, the triceratops bones are positioned in layers of clay-rich siltstone associated with some microvertebrate remains (e.g., gar scales) (keenan and scannella, 2014) implying differences in the freshwater environments represented by each site. regardless, the similarity of orientation and stacking imply similar depositional processes, i.e., multiple depositional events. a similar mode of genesis is evident in a second triceratops bonebed recovered from the upper hell creek formation in carter county, montana (the “homer” locality) (matthews and others, 2009). the bone-bearing layer is roughly 0.5 m thick, and comprises bones that show little to no abrasion, with some small, heavily abraded elements likely representing a background accumulation as a function of its position in a floodplain (matthews and others, 2009). furthermore, these remains exhibit the same stacking pattern and are in some cases clustered against 2-m-long fossilized logs. this deposit represents only a single depositional event; however, bloat and float processes are likely given the association of elements. similarities in the 3d clustering of bones at the cldq and the “homer” locality support similar attritional processes, bloat and float, were significant at both sites. conclusion the maps and data presented here are significant in that they represent the first 3d data published on the distribution of bones from the cldq. adding the vertical perspective to analysis of bone deposition allows for refined understanding of depositional processes. based on bone orientation and clustering patterns, we hypothesize that bloat and float processes have led to the distribution of bones found within the quarry. this can be seen in the common association, but rare articulation, of elements at the cldq. additionally, bloat and float mechanisms would explain the clustering of numerous small associated bones against larger bones. intriguingly, the spatial distribution of bones seen here suggests the possibility of multiple depositional events. if confirmed, the presence of multiple depositional layers may have profound impacts on the understanding of allosaurus ecology. regardless, 3d mapping techniques have added to the understanding of taphonomic processes controlling the cldq. acknowledgments we thank michael leschin, rebecca hunt-foster, and greg mcdonald of the utah office of the blm for facilitating fieldwork and processing permits. all fieldwork was conducted under permit number ut12003e. financial support was provided by the university of wisconsin–oshkosh faculty development fund (grant #fdm250) and by the utah office of the blm. thanks to formal reviewers stuart pond (stuart pond design ltd.) and matteo belvedere (section d’archéologie et paléontologie, porrentruy, switzerland), as well as james i. kirkland (utah geological survey) and peter l. falkingham (liverpool john moores university), for reviewing the manuscript and offering constructive feedback. we also thank richard g. clawson for field and laboratory support during the 2012–2017 field seasons. finally, we offer special thanks to the numerous volunteer field crews from the 2013 and 2017 field seasons. references behrensmeyer, a.k., 1975, the taphonomy and paleoecology of plio-pleistocene vertebrate assemblages east of lake rudolf, kenya: bulletin of the museum of comparative zoology, v. 145, no. 10, p. 473–574. bilbey, s.a., 1992, stratigraphy and sedimentary petrology of the 284 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 upper jurassic-lower cretaceous rocks at cleveland-lloyd dinosaur quarry with a comparison to the dinosaur national monument quarry: salt lake city, university of utah, ph.d. dissertation, 295 p. bilbey, s.a., 1998, cleveland-lloyd dinosaur quarry age, stratigraphy and depositional environments, in carpenter k., chure d., and kirkland j.i., editors, the morrison formation—an interdisciplinary study: modern geology, v. 23, p. 87–120. bilbey, s.a., 1999, taphonomy of the cleveland-lloyd dinosaur quarry in the morrison formation, central utah—a lethal spring-fed pond, in gillette, d.d., editor, vertebrate paleontology in utah: utah geological survey miscellaneous publication 99-1, p. 121–134. breithaupt, b.h., matthews, n.a., and noble, t.a., 2004, an integrated approach to three-dimensional data collection at dinosaur tracksites in the rocky mountain west: ichnos, v. 11, no. 1–2, p. 11–26. brezinski, d.k., and kollar, a.d., 2008, geology of the carnegie museum dinosaur quarry site of diplodocus carnegii, sheep creek, wyoming: annals of carnegie museum, v. 77, no. 2, p. 243–252. carpenter, k., 2010, variation in a population of theropoda (dinosauria)—allosaurus from the cleveland-lloyd quarry (upper jurassic), utah, usa: paleontological research, v. 14, no. 4, p. 250–259. dodson, p., behrensmeyer, a.k., bakker, r.t., and mcintosh, s.j., 1980, taphonomy and paleoecology of the dinosaur beds of the jurassic morrison formation: paleobiology, v. 6, p. 208– 232. engelmann, g.f., chure, d.j., and fiorillo, a.r., 2004, the implications of a dry climate for the paleoecology of the fauna of the upper jurassic morrison formation: sedimentary geology, v. 167, p. 297–308. falkingham, p.l., 2012, acquisition of high-resolution three-dimensional models using free, open-source, photogrammetric software: palaeontologica electronica, v. 15, no. 1, p. 1–15. fiorillo, a.r., padian, k., and musikasinthorn, c., 2000, taphonomy and depositional setting of the placerias quarry (chinle 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society of america special paper 503, p. 349–364. kirkland, j.i., scheetz, r.d., and foster, j.r., 2005, jurassic and lower cretaceous dinosaur quarries of western colorado and eastern utah, in rishard, g., compiler, rocky mountain section of the geological society of america field trip guidebook: grand junction geological society field trip 402, p. 1–26. 285 close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah warnock, j.p., peterson, j.e., clawson, s.r., matthews, n.a., and breithaupt, b.h. geology of the intermountain west 2018 volume 5 madsen, j.h., jr., 1976, allosaurus fragilis—a revised osteology: utah geological survey bulletin 109, p. 1–163. mallon, j.c., henderson, d.m., mcdonough, c.m., and loughry, w.j., 2018, a “bloat-and-float” taphonomic model best explains the upside-down preservation of ankylosaurs: palaeogeography, palaeoclimatology, and palaeoecology, v. 497, p. 117–127. matthews, n.a., 2008, aerial and close-range photogrammetric technology—providing resource documentation, interpretation, and preservation: technical note, u.s. department of the interior, bureau of land management, national operations center, denver, colorado, v. 428, p. 1–42. mathews, j.c., brusatte, s.l., williams, s.a., and henderson, m.d., 2009, the first triceratops bonebed and its implications for gregarious behavior: journal of vertebrate paleontology, v. 29, no. 1, p. 286–290. matthews, n.a., noble, t.a, and breithaupt, b.h., 2016, closerange photogrammetry for 3d ichnology—the basics of photogrammetric ichnology, in falkingham, p.l., marty, d. and richter, a., editors, dinosaur tracks—next steps: bloomington, indiana university press, 520 p. michelis, i., 2004, taphonomie des howe quarry’s (morrison-formation, oberer jura), bighorn county, wyoming, usa: bonn, germany, university of bonn, ph.d. dissertation, 82 p. miller, w.e., horrocks, r.d., and madsen, j.h., jr., 1996, the cleveland-lloyd dinosaur quarry, emery county, utah—a u.s. national landmark (including history and quarry map): brigham young university geology studies, v. 41, p. 3–24. peterson, j.e., warnock, j.p., eberhart, s.l., clawson, s.r., and noto, c.r., 2017, new data towards the development of a comprehensive taphonomic framework for the late jurassic cleveland-lloyd dinosaur quarry, central utah: peerj, doi: 10.7717/peerj.3368 richmond, d.r., and morris, r.k., 1996, the dinosaur death-trap of the cleveland-lloyd quarry, emery county, utah, in moralis, m., editor, the continental jurassic: museum of northern arizona bulletin 60, p. 533–545. rogers, r.r., and kidwell, s.m., 2007, a conceptual framework for the genesis and analysis of vertebrate skeletal concentrations, in rogers, r.r., eberth, d.a., and fiorillo, a.r., editors, bonebeds—genesis, analysis, and paleobiological significance: chicago, illinois, university of chicago press, p. 1–64. syme, c.e., and salisbury, s.w., 2014, patterns of aquatic decay and disarticulation in juvenile indo-pacific crocodiles (crocodylus porosus), and implications for the taphonomic interpretation of fossil crocodyliform material: palaeogeography, palaeoclimatology, palaeoecology, v. 412, p. 108–123. stokes, w.l., 1945, a new quarry for jurassic dinosaurs: science, v. 101, p. 115–117. stokes, w.l., 1985, the cleveland-lloyd dinosaur quarry—window to the past: u.s. department of the interior, bureau of land management, u.s. government printing office, 61 p. suarez, m.b., 2003, analysis of freshwater limestones at the cleveland-lloyd dinosaur quarry, emery county, utah: san antonio, texas, trinity university department of geosciences, senior thesis, 63 p. voorhies, m.r., 1969, taphonomy and population dynamics of an early pliocene vertebrate fauna, knox county, nebraska: contributions to geology, university of wyoming, special paper v. 1, p. 1–69. witkind, i.j., compiler, 1988, geologic map of the huntington 30' x 60' quadrangle, carbon, emery, grand, and uintah counties, utah: u.s. geological survey miscellaneous investigations series map i-1764, 1 plate, scale 1:100,000. 2 10 11 23 22 9 2839 20151 45 40 21 50 5 8 16 46 6 19 27 34 14 32 38 30 43 41 13 54 18 48 52 47 35 33 31 24 55 26 29 3 51 4 3742 44 7 17 25 12 3649 53 cleveland-lloyd dinosaur quarry south butler building mapped features: steven clawson photogrammetric image processing: neffra matthews statistcs: jonathan warnock concept design: joseph peterson color commentator: brent breithaupt ± 1 2 3 4 5 6 0 1 2 3 feet 0 1 meters a b c d legend atlas caudal vert centrum cervical rib dentary femur femur (l) gastralia humerus illium indet. jacket limb meta pelvic quadrate rib scap superior process surangular toe trans process vertebra zygopophysis trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah takashi sato, marjorie a. chan, and allan a. ekdale geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover stacked microbial carbonate mounds in the lacustrine uinta formation just below the sequence boundary at the base of the duchesne river formation. (location: ms24 red cap in the northern part of the uinta basin) i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott emcdermott@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 editors douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 209 abstract trace fossil assemblages in a fluvial-lacustrine sequence stratigraphic context hold significant potential for expanding our understanding of environmental controls and continental basin-fill history. the succession of the eocene uinta formation and four members of the duchesne river formation is extremely well-exposed in the uinta basin of northeastern utah, revealing a robust stratigraphic framework to document broad-scale fluvial-lacustrine facies architectures and associated trace fossil assemblages. greenishand gray-colored mudstone beds with interbedded tabular sandstone representing lacustrine environments contain the trace fossils arenicolites and gordia (= haplotichnus). in contrast, red mudstone beds with interbedded channelized sandstone representing upstream fluvial and alluvial environments contain a variety of insect trace fossils, including scoyenia, ancorichnus, and nest structures. transitional, interfingering lithologies of wetland or shallow, short-lived lacustrine environments on the alluvial plain contain the trace fossil steinichnus. although there are many small-scale (bed-scale) physical sedimentary structures and trace fossils from continental subenvironments, this study focuses on the large-scale (member-scale) change in trace fossil assemblages, with results indicating that the ichnofacies corroborate continental sequence stratigraphic interpretations in a fluvial-lacustrine setting. trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah takashi sato1, 2, marjorie a. chan3, and allan a. ekdale4 1 university of utah, department of geology and geophysics, 115 south 1460 east, room 383 fasb, salt lake city, ut 84112; takashi.sato@inpex.co.jp 2 present address: inpex corporation, domestic exploration and production division, 5th floor, teiseki building, 1-3-1 higashi odori, chuo-ku, niigata city, niigata prefecture 950-8512, japan 3 university of utah, department of geology and geophysics, salt lake city, ut 84112; marjorie.chan@utah.edu 4 university of utah, department of geology and geophysics, salt lake city, ut 84112; a.ekdale@utah.edu citation for this article. sato, t., chan, m.a., and ekdale, a.a., 2018, trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah: geology of the intermountain west, v. 5, p. 209–226. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the concept of ichnofacies, which was originally proposed by seilacher (1967), has been expanded by many subsequent workers (e.g., frey and pemberton, 1984; bromley and asgaard, 1993; smith and others, 1993; buatois and mángano, 1995; genise and others, 2000; ekdale and others, 2007; genise and others, 2010). initially seilacher (1967) proposed a single continental ichnofacies that now has been developed into six continental ichnofacies: scoyenia, mermia, corprinisphaera, entradichnus, termitichnus, and celliforma ichnofacies (buatois and mángano, 2011) (figure 1). additionally, the mostly shallow marine skolithos ichnofacies has been documented in coastal lacustrine environments (e.g., buatois and mángano, 1995, 2007). marine ich210 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 nofacies models are used widely for deciphering and reconstructing paleoenvironments through integrating sedimentological and paleontological data. however, there are far fewer studies of continental ichnofacies integrated within a fluvial-lacustrine sedimentologic and sequence stratigraphic context (buatois and mángano, 2004, 2009). additional works of hasiotis (2002, 2003) contribute insights on paleoecologic interpretations for understanding continental communities. this study documents the ichnology of a well-exposed fluvial-lacustrine depositional system of the uppermost eocene uinta and duchesne river formations of the northern uinta basin. well-exposed trace fossils are: (1) identified to ichnogenus level, (2) placed in a sequence stratigraphic context, and (3) evaluated as trace fossil assemblages or ichnofacies in vertical stratigraphic successions. geological context geologic setting the uinta basin is a prolific oil-producing basin in northeastern utah. it is a part of a laramide lake basin system, straddling the states of wyoming, colorado, and utah (figure 2), which emerged during the latest cretaceous to early paleogene (dickinson and others, 1988). the uinta basin is surrounded by several hinterlands, such as the uinta mountains to the north, sevier figure 1. six continental ichnofacies (a to f) and marginal lacustrine skolithos ichnofacies in a non-marine depositional setting (modified from buatois and mángano, 2007). trace fossil (ichnongenus) compositions of continental ichnofacies models: (a) scoyenia ichnofacies, (b) mermia ichnofacies, and (c) coprinisphaera ichnofacies are from buatois and mángano (2007). the composition of (d) entradichnus ichnofacies is from ekdale and others (2007). (e) termitichnus ichnofacies (e.g., genise and others, 2000) and (f) celliforma ichnofacies (genise and others, 2010) are both paleosol-related ichnofacies, and have convoluted histories (see the detailed historical contexts in buatois and mángano, 2011). 211 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 fold-thrust belt (ftb) to the west, douglas creek arch to the east, and the uncompahgre uplift and san rafael swell to the south. this asymmetric basin is bounded on the north by a high-angle reverse fault in the foothills of the uinta mountains (e.g., fouch, 1975; bruhn and others, 1983, 1986). paleocene-eocene strata of the uinta basin consist of the wasatch and related formations (fluvial), green river (lacustrine), uinta (fluvial-lacustrine transition), and duchesne river (fluvial) formations (figure 2). this study focuses on late-stage basin-fills of the uppermost uinta and duchesne river formations, which generally comprise coarser-grained deposits than the underlying, renowned petroleum source rock of the green river formation. the duchesne river formation is subdivided into four lithologically distinct units: brennan basin (db), dry gulch creek (dd), lapoint (dl), and starr flat (ds) members in ascending order (andersen and figure 2. (a) geological map of the uinta basin. regional dip is to the north and formations get progressively younger toward the uinta mountains. the basin is surrounded by high mountain ranges of the uinta mountains and sevier fold-thrust belt (ftb). the map of laramide lake basin system is from dickinson and others (1988). the geological map is modified from andersen and picard (1974), bryant and others (1989), bryant (1992), hintze and others (2000), and sprinkel (2006 and 2007). (b) schematic geologic column showing the paleogene sequence of the uinta basin (modified from hintze and others, 2000). t2 to t4 exhibits a typical upward-coarsening/shallowing lacustrine basin-fill succession. abbreviations: cgl–conglomerate, ss–sandstone, ms–mudstone, ls–limestone. figure modified after sato and chan (2015). 212 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 picard, 1972) (figure 3). a regional study detailed in sato and chan (2015) depicts the sequence stratigraphic framework and basin-scale facies architectures of the duchesne river formation (figures 3 and 4). previous studies a small number of sedimentological studies focus on the uinta and duchesne river formations, despite their excellent exposures. in contrast, the green river formation including that in wyoming has received much attention documenting sequence stratigraphy and ichnology (e.g., bohacs and others, 2000; keighley and others, 2003; bohacs and others, 2007). andersen and picard (1972) presented a comprehensive regional stratigraphy and proposed the four member subdivisions of the duchesne river formation used here. d’alessandro and others (1987) is so far the only published ichnological study of the duchesne river formation. it should be noted that the study area of d’alessandro and others (1987) is situated in the western part of the uinta basin, where the “undivided duchesne river formation” was proposed by bryant and others (1989), and it includes proximal fluvial deposits time-equivalent to distal lacustrine deposits of the uinta and green river formations. the formation studied by d’alessandro and others (1987) is probably time-equivalent to the uinta or green river formation, and thus is not covered by this study. there is no comprehensive ichnology study on the uinta formation, although some continental trace fossils from this formation were reported by hasiotis (2002). figure 3. geological map of the duchesne river formation in the uinta basin. regional dip is to the north and the duchesne river members (db: brennan basin, dd: dry gulch creek, dl: lapoint, and ds: starr flat) get progressively younger toward the uinta mountains. the locations of 35 measured sections (ms), composite sections a to g (black lines), and the location of the cross section in figure 4 (dashed red polygon) are shown on the map. the map is modified after andersen and picard (1974), rowley and others (1985), bryant and others (1989), and sprinkel (2006, 2007). figure modified after sato and chan (2015). 213 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 methods basin-wide field work was conducted throughout the east-west and north-south exposure of the uppermost uinta and duchesne river formations. the acquired measured geological sections at 35 locations (a total of 2970 m in length, described at resolution of 10 to 20 cm) were regionally correlated (figures 3 and 4). in this paper, trace fossils and their assemblages are described in relation to depositional environments on the basis of their presence or absence. although trace fossils are abundant at some locations, identifications of ichnogenera are sometimes challenging due to poor preservation conditions, including modern weathering. trace fossil descriptions and paleoenvironmental interpretations the succession of the uppermost uinta and duchesne river formations exhibits distinct fluvial-lacustrine facies changes in response to primarily tectonic uplift and subsidence of the uinta mountains and the adjacent basin (figure 4). correspondingly, there are figure 4. east-west regional correlations of composite sections a to g (see figure 3 for locations) showing the stratigraphic framework and detailed basin-scale facies architectures of the uppermost uinta and duchesne river formations (modified from sato and chan, 2015). the stratigraphic datum is set at the base (basal tuffs) of dl, which can be regarded as a nearly isochronous boundary (k-ar ages of ~40 ma reported by several researchers (mcdowell and others, 1973; andersen and picard, 1974; prothero and swisher, 1992; kelly and others, 2012). the succession of the uppermost uinta and the duchesne river formations is characterized by upward-fining continental cycles. 214 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 significant changes in observed trace fossils and their assemblages. in this section of the paper, lithofacies, biofacies (e.g., body fossil occurrence), and observed trace fossils of each unit are first described. subsequently, depositional environments are interpreted in relation to the trace fossil assemblages, compared with continental ichnofacies models and their components. the starr flat member (ds), the uppermost unit of the duchesne river formation, is excluded from this ichnological study due to the insufficient amount of trace fossil data. uppermost uinta formation description the lithofacies of the uppermost uinta formation is characterized by alternating beds of sandstone, mudstone, and limestone, typically comprised of upward-coarsening progradational parasequences. the formation is greenishand gray-colored mudstone-dominated strata at the basin center (e.g., ms13, ms24) (figure 5), and gradually becomes sandy to the west (e.g., ms28) (figure 4). between composite sections a and d, the formation occasionally contains conspicuous stromatolitic limestone mounds (figure 5) and thin-layered fossiliferous limestone containing garfish scales, gastropods, bivalves, and ostracods. trace fossils in the uppermost uinta formation are generally less abundant than in the overlying brennan basin member (db) of the duchesne river formation. most of the traces are observed in epirelief on the top surfaces of tabular sandstones. they include arenicolites isp. (u-shaped burrow with no wall), taenidium isp. (horizontal burrow with meniscate backfill), and gordia (= haplotichnus) isp. (horizontal, small, simple trail with self-overcrossing), which are observed within the same sandstone bed with symmetrical wave ripples at ms24 (figures 6a and 6b). buatois and others (1998) suggested that gordia emmons 1844 is synonymous with haplotichnus miller 1889, and we agree with that interpretation and therefore refer all such traces to gordia in this paper. additionally, planolites isp. (horizontal, simple, straight to gently curved burrow), unidentified trace fossil a (horizontal to oblique, a series of ball-shaped burrows with distinct thick walls) (figure 6c), and unidentified b (slightly u-shaped, clustered, horizontal tubes) are preserved in this uppermost uinta formation unit. figure 5. (a) location ms24 (red cap) showing the distinct contact (i.e., sequence boundary [sb]) between the greenishand gray-colored mudstone-dominated uinta formation (lacustrine) and overlying channelized sandstone-dominated db (fluvial). (b) close-up photo of stacked microbial carbonate mounds with stromatolitic structures in the uppermost uinta formation. abbreviations: ss–sandstone, ms–mudstone. 215 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 interpretation the lithofacies of dominant greenishand gray-colored mudstone with wave-rippled sandstone and conspicuous stromatolitic limestone mounds, clearly indicate an extensive lacustrine environment in the basin center. gradual increase in sandstone to the western part of the basin indicates a transition into a marginal deltaic and fluvial system to the west. a lake environment of the uinta formation was also documented by several previous workers (bruhn and others, 1986; bryant and others, 1989; davis and others, 2009). the uinta formation trace fossil assemblage shows dominantly horizontal grazing traces. the trace fossil composition in this unit indicates a mixture of mermia (e.g., gordia isp.), scoyenia (e.g., taenidium isp.), and skolithos (e.g., arenicolites isp.) ichnofacies (figure 7). all these ichnofacies can occur in lake environments; mermia ichnofacies represents low energy permanent subaqueous conditions, scoyenia ichnofacies represents low to moderate energy fluvial-lacustrine transitions, and skolithos ichnofacies represents moderate to high energy shoreline and delta environments (buatois and mángano, 2007). occurrence of these ichnofacies is consistent with the stated lacustrine paleoenvironment interpretation based on lithofacies and biofacies. brennan basin member (db) description the lithofacies of the basal brennan basin member (db) of the duchesne river formation is dominated by trough cross-stratified, channelized sandstone, thin-layered sandstone and siltstone, and commonly mottled red mudstones, typically arranged in upward-fining parasequences (figure 8a). db exhibits a significant contrast of lithofacies; a high net-sand-to-gross-thickfigure 6. trace fossils observed in the uppermost uinta formation. (a) arenicolites isp. (u-shaped burrow with no wall) and gordia isp. (horizontal, small, simple trail with self-overcrossing) appear on the top surface of asymmetric wave-rippled sandstone at ms24. (b) arenicolites isp. and taenidium isp. (horizontal burrow with meniscate backfill) on the bedding plane of tabular sandstone at ms24. (c) unidentified trace fossil a (horizontal to oblique, a series of ball-shaped burrows with distinct thick walls) on the bedding plane of tabular sandstone near ms28. 216 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 ness ratio (ntg) facies in the western and a lower ntg facies in the eastern part of the basin (figure 4). body fossils are scarce in this unit, although some mammal teeth (e.g., rodent) and bones (e.g., rhinocerotoid) were previously reported (e.g., rasmussen and others, 1999; kelly and others, 2012). a large but unidentified mammal bone was found in channelized sandstone at ms33 during the field work of this study (figure 3). trace fossils are very abundant, especially in the eastern part of the basin. most of the traces are observed both in hyporelief and epirelief, and sometimes in full relief. meniscate trace fossils, such as scoyenia isp. (meniscate backfill with ornamented wall), ancorichnus isp. (meniscate backfill with smoothly lined wall), beaconites isp. (distinct, texturally heterogeneous meniscate backfill), and naktodemasis isp. (thin and tightly spaced meniscate backfill) occur commonly and intensively in this unit (figures 8b to 8e). also, celliforma isp. (trunk burrow with oval-shaped chambers) (figure 9a), termitichnus isp. (large trunk burrow with spherical-shaped holes) (figure 9b), and parawanichnus isp. (large interconnected burrow system with galleries and chambers), which indicate social insect nest structures (e.g., bown and others, 1997; hasiotis, 2003), and unidentified ant nest or plant root structures (network or branching burrows with 2 to 3 mm diameters) are common in sandstone or siltstone beds. additionally, skolithos isp., planolites isp., and palaeophycus isp. are ubiquitous. interpretation lithofacies (channelized sandstone with red mudstone beds) and biofacies (mammal teeth and bones) indicate an extensive alluvial plain environment developed throughout the deposition of this unit. it indicates the progradation of the fluvial deposits of db and the cessation of lake deposition of the uinta formation. db exhibits a significant contrast of fluvial styles between the west (an amalgamated braided fluvial system with high ntg) and east (a relatively sinuous fluvial system with low ntg) (figure 4). this contrast is greatly influenced by the difference in climate and the number of source terrains (i.e., discharge control) (sato and chan, 2015). the trace fossil composition in this unit indicates a mixture of scoyenia (e.g., several types of meniscate backfill traces) and coprinisphaera (e.g., insect nesting structures) ichnofacies (figure 10). most of the intensively burrowed structures occur in contact with red mudstone beds indicating well-drained paleosols (e.g., figure 7. paleoenvironmental reconstruction and trace fossil assemblage of the uppermost uinta formation. a lake environment developed during the deposition of the uppermost uinta formation. trace fossil composition in this unit indicates a mixture of the mermia, scoyenia, and skolithos ichnofacies. arenicolites isp. and gordia isp. are diagnostic trace fossils representing the uppermost uinta environment. 217 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 kraus, 2002; atchley and others, 2004; kraus and hasiotis, 2006) or within silty sandstone beds indicating pedogenically altered overbank deposits. therefore, we interpret this assemblage as coprinisphaera ichnofacies (i.e., paleosol trace fossil suites), because meniscate burrows can also be a part of this ichnofacies (e.g., buatois and mangano, 2007). the db trace fossil assemblage shows a distinct difference from the underlying uinta formation (lake) assemblage. dry gulch creek member (dd) description the dry gulch creek member (dd) of the duchesne river formation is a transitional lithofacies between the underlying sandstone-dominated db and overlying mudstone-dominated lapoint member (dl). dd typically shows alternating beds of channelized and tabular sandstone and greenishand reddish-colored mudstone beds (commonly mottled) including intensive gypsum figure 8. lithofacies and meniscate trace fossils in the basal brennan basin member (db) of the duchesne river formation. (a) typical lithofacies of db at ms33 showing upward-fining parasequences of basal channelized sandstones (highlighted by yellow) and capped red mudstone beds. (b) scoyenia isp. (meniscate backfill with ornamented wall) at the base of sandstone (hyporelief). (c) naktodemasis isp. (thin, tightly spaced meniscate backfill with no wall) in a sectional view of sandstone (within termitichnus isp.). (d) beaconites isp. (distinct, texturally heterogenus meniscate backfill) and skolithos isp. (simple, vertical cylindrical burrow) in a sectional view of sandstone. (e) ancorichnus isp. (meniscate backfill with smoothly lined wall) at the base of sandstone. abbreviations: ss–sandstone, ms–mudstone. 218 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 figure 9. insect nest traces in db. (a) celliforma isp. (trunk burrow with oval-shaped cells or chambers) in a sectional view of trough cross-stratified sandstone. (b) termitichnus isp. in root (large trunk burrow with spherical holes) in a sectional view of trough cross-stratified sandstone. figure 10. paleoenvironmental reconstruction and trace fossil assemblage of db. lake uinta has disappeared and fluvial systems developed on a widespread alluvial plain during the deposition of db. trace fossil composition in this unit indicates a mixture of coprinisphaera and scoyenia ichnofacies. insect nests (e.g., celliforma isp., termitichnus isp., parawanichnus isp.) are diagnostic trace fossils representing the db environment. 219 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 veins and fragmented fossil plant/coaly layers (figure 11a). dd exhibits contrasting mudstone colors across the basin; mixed greenishand reddish-colored mudstone beds in the west and dominant reddish-colored mudstone beds in the eastern part of the basin (figure 4). body fossils are scarce except for fossil plants found in the western part of this unit. trace fossils (in the western part of the basin) are abundant and recognized both in hyporelief and epirelief, and even in full relief. meniscate trace fossils, such as scoyenia isp., ancorichnus isp., beaconites isp., and naktodemasis isp. commonly occur in this unit. steinichnus isp. (large-diameter horizontal burrows with crossing scratch patterns) was observed at the base figure 11. lithofacies and trace fossils in the dry gulch creek member (dd) of the duchesne river formation. (a) upward-coarsening succession of basal greenishand gray-colored mudstone beds with intensive gypsum veins and fragmented fossil plant/coaly layers, alternating beds of thin-layered sandstone and reddish-colored mudstone beds, and a capping channelized sandstone bed at ms15 (wetland to shallow lacustrine fill succession). (b) steinichnus isp. (large-diameter horizontal burrows with crossing scratch patterns) observed at the base of cross-stratified sandstone at ms15. (c) unidentified trace fossil a (horizontal to oblique, a series of ball-shaped burrow with distinct thick wall). abbreviations: ss–sandstone, ms–mudstone. 220 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 of a cross-stratified sandstone at ms15 (figure 11b). additionally, skolithos isp., planolites isp., palaeophycus isp., unidentified trace fossil a (figure 11c) (see the description in the section of the uppermost uinta formation), unidentified trace fossil c (vertical and horizontal branching network burrow with no wall), and unidentified nest or root structures (network/branching burrows with 2 to 3 mm diameters, small ant nest?) are recognized in the western part of this unit. interpretation lithofacies (mixed greenishand reddish-colored mudstone with interbedded channelized and tabular sandstone beds) and biofacies (layered fossil plants/ woods) indicate frequent incursions of shallow and short-lived lacustrine or wetland environments on an extensive alluvial plain in the western part of the basin (i.e., to the west of ms15 ne roosevelt). trace fossil composition in this unit indicates a transitional ichnofacies (i.e., a mixture of scoyenia, coprinisphaera, and skolithos ichnofacies) between those in the underlying db and overlying dl (figure 12). although most of the ichnogenera in this unit are also recognized in db, occurrences of unidentified trace fossil a (observed in the lacustrine uinta formation as described above) and steinichnus isp. indicate some interventions of shortlived lake or wetland environments in dd. steinichnus possibly was made by insects, such as beetles or mole crickets (bromley and asgaard, 1979; bohacs and others, 2007), and it is reported to be distributed in a higher water table environment (bohacs and others, 2007). lapoint member (dl) description the lapoint member (dl) of the duchesne river formation is characterized by fine-grained deposits (i.e., mudstone and tuffaceous fine-grained rocks). it exhibits dominant greenishand gray-colored mudstone interbedded with tabular sandstone beds (occasionally figure 12. paleoenvironmental reconstruction and trace fossil assemblage of dd. short-lived lake or wetland environments developed in the western part of the basin during the deposition of dd. trace fossil composition in this unit indicates a transitional ichnofacies (i.e., a mixture of scoyenia, coprinisphaera, and skolithos ichnofacies) between those in db and dl. steinichnus isp. appears to be a diagnostic trace fossil for this unit as it is reported to be distributed in a higher water table environment than the insect nesting traces (bohacs and others, 2007). 221 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 wave-rippled), tuff, and limestone beds in the western part of the basin (figure 13a), and dominant reddish-colored mudstone beds in the eastern part of the basin (figure 4). body fossils are generally scarce, although shellrich (gastropods and bivalves) limestones and coaly, carbonaceous mudstone layers are observed in some locations (e.g., ms06) in the western part of the basin. trace fossils in the western part of this unit are sparse and tend to occur in epirelief on the top surface of tabular sandstones. trace fossils observed in this unit are arenicolites isp., gordia isp., taenidium isp., and planolites isp. (figure 13), which is an assemblage similar to that of the uppermost uinta formation. interpretation lithofacies (dominant greenishand gray-colored mudstone beds with wave-rippled tabular sandstone beds) and biofacies (gastropods and bivalves in fossiliferous limestones) indicate a widespread lacustrine environment in the western half of the basin. this extensive lake environment developed due to differential subsidence of the basin (sato and chan, 2015). the trace fossil assemblage figure 13. lithofacies and trace fossils in the lapoint member (dl) of the duchesne river formation. (a) overlook of greenishand gray-colored mudstone-dominated dl (white tuffaceous and fine-grained rocks are also abundant) at ms06. lithofacies (dominant greenishand gray-colored mudstone beds and minor occurrences of wave-rippled tabular sandstone and thin fossiliferous limestone) indicates a widespread lacustrine environment. (b) arenicolites isp. (u-shape burrow) on the top surface of tuffaceous silty sandstone. (c) taenidium isp. (horizontal burrow with meniscate backfill) on the top surface of rippled silty sandstone. abbreviations: ss–sandstone, slts–siltstone, ms–mudstone, ls–limestone. 222 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 in this unit indicates a mixture of the mermia, scoyenia, and skolithos ichnofacies (figure 14), which is very similar to ichnofacies of the uppermost uinta formation. this evidence demonstrates the recurrence of lacustrine communities and a distinct difference from the fluvial-floodplain trace fossil assemblage observed in the underlying db. discussion the stratigraphic sequence of the duchesne river formation was primarily controlled by tectonics (sato and chan, 2015). the uplift(s) in the uinta mountains and possibly the sevier ftb created distinct sequence boundaries at the base of db and ds, and led to the development of an upward-fining fluvial sequence from db (lst: lowstand systems tract) to dd and dl (tst/ hst: transgressive/highstand systems tract) (figure 15). the trace fossil assemblages examined in this paper show distinct changes according to these systems tracts, corresponding to water-table-level changes (figure 15). mermia, scoyenia, and skolithos ichnofacies of the uppermost uinta formation indicate relative high water-table conditions consistent with the tst/hst of the lacustrine environment, where the trace fossil assemblage typically represents subaqueous tracemaker communities. the dominant coprinisphaera ichnofacies of db suggests a change to lower water-table and pedogenic conditions typical of a lst. the lacustrine environment of the uinta formation was completely replaced with a relatively dry alluvial plain environment of db over the basin, where the trace fossil assemblage typically represents terrestrial tracemaker communities such as insects. scoyenia, coprinisphaera, and skolithos ichnofacies of dd (tst/hst) indicate a transition into relative high water-table conditions, with the gradual incursion of wetland or subaqueous tracemaker communities. mermia, scoyenia, and skolithos ichnofacies of dl (tst/hst) indicate the recurrence of relative high water-table conditions with subaqueous tracemaker communities. these changes correspond to the large-scale (i.e., member-scale) changes in depositional environment. thus this study cannot offer rigorous bed-by-bed analyses or interpretations on specific small-scale continental environments, such as channel, bar, and levee. in future studies, such detailed bed-scale analysis may lead to decoding a high resolution sequence and to the extraction of more specific trace fossil assemblages (ichnofacies). an ichnofabric approach might be useful for figure 14. paleoenvironmental reconstruction and trace fossil assemblage of dl. an extensive lake environment developed during the deposition of dl. the trace fossil association in this unit indicates a mixture of the mermia, scoyenia, and skolithos ichnofacies, demonstrating the recurrence of lacustrine communities. 223 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 this high-resolution analysis, because there are possibly multiple communities recorded within a sandstone bed. for example, traces in fluvial channels could be overwritten by the later paleosol communities after these channels are abandoned. conclusion a regional outcrop-based study reveals the sequence stratigraphic framework and detailed basin-scale facies architectures of the uppermost uinta and duchesne river formations. this paper documents remarkable changes in continental trace fossil assemblages according to fluctuations in the relative water-table level (i.e., member-scale sedimentary facies changes). specifically, the uppermost uinta formation and lapoint member (dl) of the duchesne river formation indicate extensive lacustrine environments and the corresponding trace fossil assemblage including arenicolites and gordia. by contrast, the basal brennan basin member (db) of the duchesne river formation exhibits a widespread fluvial environment and the corresponding trace fossil assemblage is characterized by a variety of insect trace fossils (e.g., scoyenia, ancorichnus, nest structures). the dry gulch creek member (dd) of the duchesne river formation shows a transitional (i.e., wetland) environfigure 15. synthesis of sequence stratigraphic framework and trace fossil occurrences of the uppermost uinta and duchesne river formations. the uplift(s) in the uinta mountains and possibly in the sevier ftb caused distinct sequence boundaries at the base of db and ds, and led to the development of an upward-fining sequence from db (lst) to dl (tst/hst). the internal basin-scale facies changes reflect laterally variable allogenic controls of discharge (high in the west and low in the east) and tectonic subsidence (higher subsidence rate in the west during the dl deposition) (sato and chan, 2015). trace fossil assemblages show distinct changes according to the water-table level. abbreviations: cgl–conglomerate, ss–sandstone, gn m–green mudstone, rd ms–red mudstone, ls–limestone. figure modified after sato and chan (2015). 224 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 ment where the intermediate trace fossil assemblages including steinichnus are present. the large-scale (member-scale) change in trace fossil assemblages shows that the ichnofacies corroborate continental sequence stratigraphic interpretations and serve as a valuable indicator of paleoenvironmental change in a fluvial-lacustrine setting. the uppermost uinta and duchesne river formations offer a valuable example of dramatic changes in communities of trace-making organisms in response to the tectonic control of the dynamic intermontane basin. acknowledgements we thank cari johnson, lisa stright, and lauren birgenheier at the university of utah for their useful comments on this project. douglas sprinkel at the utah geological survey was a great supporter and provided valuable insight on the uinta basin geology. stephen hasiotis, university of kansas, and luis buatois, university of saskatchewan, provided helpful input on the identification of continental trace fossils. we acknowledge the ute indian tribe and the bureau of land management in vernal and ouray national wildlife refuge who generously provided essential permissions for the field work. references andersen, d.w., and picard, m.d., 1972, stratigraphy of the duchesne river formation (eocene-oligocene?), northern uinta basin, northeastern utah: utah 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and hasiotis, s.t., 2006, significance of different modes of rhizolith preservation to interpreting paleoenvironmental and paleohydrologic settings—example from paleogene paleosols, bighorn basin, wyoming, u.s.a.: journal of sedimentary research, v. 76, p. 633–646. mcdowell, f.w., wilson, j.a., and clark, j., 1973, k-ar dates for biotite from two paleontologically significant localities—duchesne river formation, utah, and chadron formation, south dakota: isochron/west, v. 7, p. 11–12. miller, s.a., 1889, north american geology and paleontology for the use of amateurs, students and scientists: cincinnati, ohio, western methodist book concern, 664 p. prothero, d.r., and swisher, c.c., 1992, magnetostratigraphy and geochronology of the terrestrial eocene-oligocene transition in north america, in prothero, d.r., and berggren, w.a., editors, eocene-oligocene climatic and biotic evolution: princeton, new jersey, princeton university press, p. 46–74. rasmussen, d.t., hamblin, a.h., and tabrum, a.r., 1999, the mammals of the eocene duchesne river formation, in gillette, d.d., editor, vertebrate paleontology in utah: utah geological survey miscellaneous publication 99-1, p. 421–427. rowley, p.d., hansen, w.r., tweto, o., and carrara, p.e., 1985, geologic map of the vernal 1° x 2° quadrangle, colorado, utah, and wyoming: u.s. geological survey miscellaneous investigations series map i-1526, 1 plate, scale 1:25,000. 226 trace fossils and fluvial-lacustrine ichnofacies of the eocene uinta and duchesne river formations, northern uinta basin, utah sato, t., chan, m.a., and ekdale, a.a. geology of the intermountain west 2018 volume 5 sato, t., and chan, m.a., 2015, fluvial facies architecture and sequence stratigraphy of the tertiary duchesne river formation, uinta basin, utah, u.s.a.: journal of sedimentary research, v. 85, p. 1438–1454. seilacher, a., 1967, bathymetry of trace fossils: marine geology, v. 5, p. 413–428. smith, r.m.h., mason, t.r., and ward, j.d., 1993, flash-flood sediments and ichnofacies of the late pleistocene homeb silts, kuiseb river, namibia: sedimentary geology, v. 85, p. 579–599. sprinkel, d.a., 2006, interim geologic map of the dutch john 30' x 60' quadrangle, daggett and uintah counties utah, moffat county, colorado, and sweetwater county, wyoming: utah geological survey open-file report 491dm, compact disc, gis data, 3 plates, scale 1:100,000. sprinkel, d.a., 2007, interim geologic map of the vernal 30' x 60' quadrangle, uintah and duchesne counties, utah, and moffat and rio blanco counties, colorado: utah geological survey open-file report 506dm, compact disc, gis data, 3 plates, scale 1:100,000. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 9 2022 © 2022 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah peter d. rowley, robert f. biek, and david b. hacker geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view south from forshea mountain showing phonolite hill. phonolite hill, a rhyolite dome, erupted 5 million years ago at the bottom of kingston canyon. the photographer is standing on the 8 ma rhyolite of forshea mountain. the top of the gently east-dipping canyon wall across the canyon would have been a valley floor 8 million years ago. the sevier fault is to the right of the hills at the far right of the view, west of which is a glimpse of sevier valley. the base of the 5 ma rhyolite dome of phonolite hill is at the current canyon floor, showing here a minimum of 4000 feet (1200 m) of uplift (it would show as more if the south wall were projected out to the sevier fault) on the sevier fault between 8 and 5 ma. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 9 2022 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2021–2022 uga board president john south john.south@dominionenergy.com 385.266.2113 president-elect rick ford rford@weber.edu 801.915.3188 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 co-program chair ben gilder dgilder@gmail.com 337.962.8383 treasurer kellen gunderson kellen@zanskar.us 801.634.9737 secretary eugene syzmanski eugenes@utah.gov 801.537.3364 past president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 9 2022 1 abstract the sevier plateau is a gently east-tilted, block-faulted range in the high plateaus transition zone of southwestern utah. part of this range underwent basin-range deformation, including at least 6000 feet (1800 m) of uplift, in a 3-million-year time span. the north-south range, whose southern end is just north of bryce canyon national park, was uplifted and tilted by the sevier fault zone along the western side. kingston canyon is a deep, east-west antecedent canyon that cut through the range and maintained itself during uplift. the deformation took place between 8 and 5 ma, constrained by isotopic dating of pre-uplift rhyolite flows (8 ma), now exposed on the crest of the range, and a post-canyon-cutting rhyolite dome (5 ma), now in the bottom of kingston canyon. this episode of uplift and canyon cutting represents the most closely constrained example known in the great basin and adjacent transition zone of main-phase uplift by basin-range faults. basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah peter d. rowley1, robert f. biek2, and david b. hacker3 1geologic mapping inc., p.o. box 651, new harmony, ut 84757; pdrowley@rushisp.com; www.geologicmappinginc.com 2utah geological survey, p.o. box 146100, salt lake city, ut 84114-6100; bobbiek@utah.gov 3department of geology, kent state university trumbull campus, 4314 mahoning ave., warren, oh 44483-1998; dhacker@kent.edu citation for this article. rowley, p.d., biek, r.f., and hacker, d.b., 2022, basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah: geology of the intermountain west, v. 9, p. 1–11, https://doi.org/10.31711/giw.v9.pp1-11. © 2022 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction kingston canyon is a 4000-foot-deep (1200 m), east-west canyon that cuts entirely through the southern sevier plateau, piute county, utah (figure 1). the plateau is bounded on the west by the large, active, down-to-the-west sevier fault zone and on the east by small, discontinuous, down-to-the-east faults, creating a gently east-tilted fault block characteristic of utah’s southern high plateaus. kingston canyon was formed by the ancestral east fork of the sevier river, which now continues flowing west through the canyon; it is an antecedent canyon, which means that the east fork of the sevier river maintained itself as the sevier plateau was uplifted slowly along its bounding faults. the canyon is interesting and unusual for this reason alone (rivers are more commonly diverted by rising mountain blocks), but it is exceptional in that phonolite hill, a rhyolite dome, erupted 5 million years ago in the bottom of the canyon. this shows that the canyon existed 5 million years ago and has been little changed since then, with implications for the development of utah’s southern high plateaus as described below. the sevier plateau is a range that is about 75 miles (120 km) in north-south length and as much as 18 miles (29 km) in east-west width, from just south of richfield on the north to just north of bryce canyon national park on the south. it has relief of about 5000 feet (1500 2 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 m), with its high points of mount dutton south-southeast of circleville and of monroe peak northeast of marysvale, both on the western fault scarp and just over 11,000 feet (3350 m) in elevation. sevier valley separates the plateau from, on the west, the pahvant range, tushar mountains, and markagunt plateau from north to south. on the east, grass valley separates the northern part of the plateau from the fish lake plateau and awapa plateau, and johns valley separates the southern part from the aquarius and table cliffs plateaus. the headwaters of the east fork sevier river are in northern bryce canyon national park, from where the river flows north through johns valley, then past antimony in southern grass valley, where it swings west across the sevier plateau to join the main fork of the river, which continues northward through sevier valley past richfield. the sevier plateau, along with the mountains, plateaus, and valleys mentioned above, belongs to the high plateaus subprovince of the colorado plateau, a transition zone between the great basin to the west and the main part of the colorado plateau to the east. the great basin extends from central utah westward to easternmost california, whereas the main part of the colorado plateau extends from central utah to the grand junction area of western colorado. the great basin formed by basin-range deformation, whereby innumerable faults created alternating north-trending ranges and basins. basin-range faults are generally normal faults that dip steeply, about 60o, and have mostly vertical, extensional motion that is down in the dip direction. the transition zone was affected by basin-range deformation but the faults are less abundant and have less throw than in the great basin, and their number and size decrease eastward before passing into the stable, little deformed, mostly horizontal rocks of the colorado plateau. therefore, the high plateaus subprovince also consists of north-trending ranges (horsts, commonly gently east tilted) and basins (grabens) that are bounded on both sides by faults. the age of basin-range deformation is generally known to postdate about 20 million years old (ma) and to be continuing today. but most of the deformation, including that which formed the present topography, appears to postdate 10 ma (rowley and others, 1981, 2005). the geosite described here provides the best evidence we know in the entire great basin and transition zone that tightly constrains, for at least part of a range, this later main phase of deformation. the geosite is in kingston canyon, at a mountain shown on the topographic map as phonolite hill. basin-range deformation is accompanied by eruption of relatively small volumes of “bimodal” volcanic rocks of either rhyolite or basalt composition. the geosite, 5 ma volcanic dome of phonolite hill, erupted in the bottom of kingston canyon after it was cut (rowley and others, 1981). a volcanic dome is a relatively small edifice of rock that accumulates as short, stubby rhyolite lava flows around its vent, resulting in an upper domical surface that resembles a muffin. we contrast its age with that of a rhyolite lava flow at the top of the northern wall of the canyon that has an isotopic age of about 8 ma. the difference between the two, about 3 million years between 8 and 5 ma, is the interval in time during which this part of the range formed! 112°15' 112° 38° 38°15' 0 1 2 3 4 5 0 2 4 6 kilometers miles n utah map location piute reservoir otter creek reservoir junction kingston antimony circleville 89 89 153 62 22 62 sev ier river e a s t f o r k s e v i e r r i v e r pole canyon tu sh ar m ou nt ai ns g r a s s v a l l e y s e v i e r p l a t e a u kingston canyon phonolite hill fo rs he a m ou nt ai n x mount dutton x figure 1. location map of the kingston canyon area, piute and garfield counties, utah, with the phonolite hill geosite identified. 3 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 location the geosite is midway through kingston canyon, near the central part of the phonolite hill 7.5-minute quadrangle, piute county, utah. the coordinates are: 38o11'19" n., 112o05'30" w., 8.2 miles (13.1 km) east of u.s. highway 89 and 4.2 miles (6.7 km) west of the intersection with state route 22. pull off state highway 62 adjacent to and east of a light-gray outcrop on the north side of the road, near the edge of a volcanic crater that forms the western base of phonolite hill. figure 2 is a simplified geologic map and cross section of the area. geologic setting the sevier plateau lies near the eastern side of the marysvale volcanic field, one of the largest cenozoic volcanic fields in the west. the field is named for the small, former mining town of marysvale, 15 miles (24 km) north of junction (figure 1) and near the center of the 75-mile-diameter (120 km) field. the mapping study of the southern half of the sevier plateau, including kingston canyon, began with a dissertation study by the senior author (rowley, 1968). the study showed that the sevier plateau is a tilt block dipping about 3º to the east and uplifted along the major sevier fault zone on its western side. vertical displacement on the fault zone is at least 6000 feet (1800 m), which includes not only the topographic relief of the range itself but also the amount that the bedrock beneath sevier valley, a graben, was downthrown (at least 1000 feet [300 m]) and filled with sediments resulting from erosion of the range. later mapping showed that, north of the dissertation study area, relatively small down-to-the-east faults separate the eastern side of the sevier plateau from the graben of grass valley (e.g., rowley and others, 1986a, 1986b; biek and others, 2015a, 2015b). therefore, the sevier plateau is an east-tilted horst. many reports and geologic maps have been published about the geology of kingston canyon and surrounding areas, among them those by anderson and rowley (1975), steven and others (1979), and rowley and others (1981, 2005), from which the discussions below come from. the oldest rocks in the sevier plateau belong to the brian head formation, a light-gray, white, and lightgreen sedimentary sequence deposited in streams, on floodplains, and in lakes during the late eocene and earliest oligocene. only the top of this unit, which is locally sheared, is exposed in the central part of kingston canyon (figure 2, labeled tc on the map), although the formation is widely exposed along the flanks of the southern sevier plateau, where it is about 1000 feet (300 m) thick and locally on the western flank of the awapa plateau (biek and others, 2015a, 2015b). the brian head underlies the thick volcanic rocks that make up the marysvale volcanic field; it is rich in volcanic ash, for it represents the start of volcanism at marysvale and in the great basin. this ash has weathered to smectitic clay, which is known for swelling soils and susceptibility to landsliding. importantly, the brian head contains— presumably in weak clay layers—the shear planes for the markagunt and sevier gravity slides (hacker and others, 2014; biek and others, 2019). on the cross section (figure 2), the brian head is shown to be horizontal for simplicity, but in pole canyon east of antimony (see the pole canyon geosite), brian head and many of the overlying volcanic rocks involved in the sevier slide are deformed and are overlain unconformably by post-slide volcanic rocks, notably the osiris tuff, that dip east at the typical 3° (see rowley and others, 2022). the brian head formation is overlain by the wah wah springs formation (30.5 ma, oligocene), one of the largest ash-flow sheets in the world (e.g., best and others, 2013). it was derived from the indian peak caldera complex that spans the utah-nevada border more than 100 miles (160 km) to the west, so it rarely is thicker than about 50 feet (15 m) in the area. above it, the three creeks tuff member (27 ma) of the bullion canyon volcanics is probably the largest ash-flow tuff derived from the marysvale field. it erupted from the three creeks caldera in the southern pahvant range just north of interstate 70 and 35 miles (55 km) northwest of kingston canyon, so it is commonly several hundred feet thick in the area (rowley and others, 1994). these two tuffs, plus an overlying thin tuff, the kingston tuff member of the mount dutton formation, are shown on figure 2 as unit tkcn. stratovolcano deposits of mostly andesitic composition overlie this unit and are more than 1000 feet (300 m) thick in the kingston canyon area. most of the deposits consist of volcanic mudflow 4 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 38° 15’ n. 112° 15’ w.112° 10’ w. 38° 10’ n. geosite forshea mountain phonolite hill kingston 62 62 22 kingston phonolite hill forshea mountain geosite a' a qts try trf tb to tkcn tbh tc tda tdan toa trd quaternary-tertiary alluvium rhyolite of phonolite hill basalt osiris tuff brian head formation claron formation antimony tuff member of mt. dutton formation mt. dutton formation three creeks member of bullion canyon volcanics; wah wah springs fm; mt dutton fm. rhyolite of forshea mountain, rhyolite of dry lake units within sevier gravity slide (sgs) contact normal fault, bar and ball on down side gravity-slide shear plane line of cross section strike and dip of rocks e a a' b3 ma 4.7 7.9 23.0 27, 30 8000 6000 4000 2000 0 fe et 2000 1000 m et er s 0 a southwest a'north tb totda ttw ttw tbhtbh trf to tctdatdoch tda try k i n g s t o n c a n y o n bend in section phonolite hill forshea mountain pre-volcanic sedimentary strata 0 0 1 2 3 4 5 1 2 3 miles kilometers n figure 2. geologic map and cross section of the kingston canyon area, piute and garfield counties, utah, showing phonolite hill. cross section shows phonolite hill erupted at the base of kingston canyon. geologic map modified from rowley and others (2005). 5 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 breccia but interbedded lava flows are also present. most of the volume of the marysvale volcanic field is made up of such locally derived volcanic rocks. they are named the mount dutton formation (tda) and are as much as several thousand feet thick (1000 m); some of these mudflow deposits near mount dutton are older and underlie the wah wah springs formation. near the top of the stratovolcano deposits is a thin (about 40 feet [12 m]), densely welded, crystal-poor ash-flow tuff, the antimony tuff member of the mount dutton formation (tdan). its source is unknown, but its age is about 25.1 ma and is important for it overlies (postdates) and rests in angular unconformity on the sevier gravity slide, showing that the slide must be older than 25.1 ma. the sevier gravity slide consists of all rocks that lie between the upper brian head formation and the antimony tuff member. above the antimony tuff member is another densely welded, crystal-poor ash-flow tuff, the osiris tuff (23.1 ma, unit to), which is commonly light gray and about 50 feet (15 m) thick. the osiris is derived from the monroe peak caldera, the largest in the marysvale field, whose southern margin is about 20 miles (32 m) north of the bottom of kingston canyon. the osiris locally sits directly on the antimony, as at the eastern end of kingston canyon. the youngest rocks in the kingston canyon area are basaltic lava flows and the overlying rhyolite of forshea mountain. the basaltic flows are on both walls of the canyon, whereas the younger rhyolite is only on the north wall. these rocks dip east at about 3o, as with all underlying rocks. rowley’s 1968 dissertation study identified and mapped, at a scale of 1 inch to the mile, the rhyolite of phonolite hill (try), and the rhyolite of forshea mountain (trf) that caps the northern side of kingston canyon (figure 3). in the summer of 1970, rowley joined the u.s. geological survey (usgs) to do reconaissance geologic mapping in antarctica. from about 1975 to 1986, in between five trips to antarctica and later in a maryvale project, he joined two other usgs geologists, thomas a. steven and charles g. (skip) cunningham, in detailed mapping and related studies of the marysvale volcanic field for its mineral-resource potential. on the fourth of july, 1978, when others had returned to their families in denver, tom suggested we take a break from our mapping and give phonolite hill a second look. they has a delightful day in which they circumnavigated the mountain, about a mile (1.6 km) in diameter and rising 1600 feet (500 m). the detailed mapping from this re-examination of phonolite hill showed that the rhyolite dome was sitting in a low crater of tuff and rocks ejected from the vent prior to the main eruption of the dome. eroded pieces of the crater are exposed all around the circumference of the mountain, and the crater contains garage-size rocks of basalt that had been spit out of the vent and into the crater. because they sit in the bottom of a canyon cut across the plateau, the crater and dome must postdate uplift of the sevier plateau and canyon cutting. the team collected samples for isotopic dating by potassium-argon methods, which harald mehnert of the usgs in denver would do for us. a few days later rowley collected a sample of the rhyolite of forshea mountain. they interpreted that the rhyolite on forshea mountain and its underlying rocks were deposited horizontally and predated uplift and eastern tilting of the plateau along the sevier fault zone. canyon cutting began as this uplift and tilting started, and the cutting continued as uplift and tilting continued. in other words, the canyon could not have been present when the rhyolite of forshea mountain erupted, otherwise the rhyolite would have flowed into the canyon. the results of this study were published, including a geologic map and cross section that are more detailed than those in figure 2 (rowley and others, 1981). the k-ar ages determined by harald of the rhyolite of phonolite hill were 4.79 ± 0.23 ma on obsidian and 5.42 ± 0.27 ma on sanidine. of these, k-ar ages on the phenocryst mineral sanidine are considered more accurate. the k-ar ages on the rhyolite of forshea mountain are 7.55 ± 0.44 ma on obsidian and 7.63 ± 0.63 ma on sanidine. the difference in sanidine ages between the two rhyolites is 2.2 million years. the team thus interpreted that the uplift of the sevier plateau along the sevier fault zone had taken place during that interval. this interval, to our knowledge, is the tightest constraint in the entire great basin on the age of basin-range deformation of part of a major range. this conclusion is summarized in rowley and others (1994, p. 24) and in the expanded text on the geologic framework of the panguitch 30' x 60' quadrangle (biek and others, 2015a, p. 131). 6 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 rowley and others’ (1981) conclusion on the age of basin-range deformation of the sevier plateau, however, seems to have been ignored, perhaps because other geologists doubted that such a rapid history of faulting, uplift, and canyon cutting was possible, or perhaps they doubted the isotopic ages. much later, bob biek of the utah geological survey (ugs), dave hacker of kent state university, other colleagues, and i (pete rowley) were again remapping much the same area, namely the panguitch (biek and others, 2015a), loa (biek and others, 2015b), and beaver 30' x 60' quadrangles (rowley and others, 2005), to determine the extent of the markagunt and sevier gravity slides. because the ages of the two rhyolite masses were critical in determining the geomorphology and basin-range history of the area, and now a modern and more accurate method of dating (40ar/39ar) had been developed, the ugs ran samples from the two rhyolites again. the numbers are close, 4.7 ± 0.4 ma on sanidine/plagioclase phenocrysts from the rhyolite of phonolite hill, and 7.89 ± 0.12 ma on sanidine phenocrysts from the rhyolite of forshea mountain (ugs and nmgrl, 2019), for an interval of 3.2 million years during which time this part of the sevier plateau was uplifted and tilted. so the 1981 isotopic ages were essentially verified! corroborating evidence for this story came from the work of skip, tom, and colleagues at big rock candy mountain, adjacent to the sevier river north of marysvale. this work was done after the report by rowley and others (1981) was published, and it was only briefly noted by biek and others (2015a). to understand the significance of this evidence, we need to summarize the erosional history of the high plateaus. during basin-range deformation, the ranges were uplifted along faults and the valleys (basins) were dropped down. the main drainage, the sevier river, maintained itself as this faulting was going on. at times, especially during pleistocene glaciations, the sevier river and its many tributaries were large, and they eroded vigorously downward, acting like buzz saws as the underlying figure 3. view north to the southern side of forshea mountain, showing a thin basalt ledge (tb) overlain by a cliff of the rhyolite of forshea mountain (trf). 7 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 rocks were being uplifted. after the sevier river exits kingston canyon and flows northward past junction and piute reservoir, it goes through two rock obstructions, each about 5 miles (8 km) long, in the middle of sevier valley before it reaches richfield. one of these is south of circleville, and the other is north of marysvale (including big rock candy mountain). yet, the sevier river did not stop at these obstructions but, as with the sevier plateau obstruction, it maintained itself and cut deep canyons (circleville and marysvale canyons) through the obstructions. that indicates these canyons are also antecedent canyons, so the obstructions were uplifted as the river continued to flow through them. big rock candy mountain, at the eastern edge of the tushar mountains in marysvale canyon, is a jagged, colorful, and picturesque mountain, mostly yellow with lesser tinges of orange, red, and white. it is a classic example of hydrothermally altered volcanic rock, formerly deposits of a stratovolcano. at its base is a motel, a former resort of some fame, with a café and gift shop. the café has its walls festooned with publicity photos of movie stars of the 1930s and 1940s, including john wayne if we remember correctly, all of whom came to the resort to hunt elk and mountain lions. the mountain name came from a popular song “big rock candy mountain” first recorded in 1928 by harry “haywire mac” mcclintock and made famous for a second time in a 1950s sanitized children’s recording by burl ives. (buskers sang bawdy versions of the song, which described a child being recruited into hobo life by tales of a “big rock candy mountain,” as early as the 1890s.) soon after the song became popular the first time (in the 1930s), locals erected a sign “big rock candy mountain” at the base of the yellow mountain, and a nearby spring that issued from the yellow mountain became “lemonade springs.” the names stuck. as part of their hunt for mineral resources in the mining districts near marysvale, cunningham and others (2005) studied big rock candy mountain, which is a deposit of alunite, a mineral of aluminum oxide that during world war i was mined for aluminum ore at the ghost town of alunite, about halfway between junction and marysvale. the alunite at big rock candy mountain formed deep (more than a mile [>1.6 km]) below the surface about 21 million years ago when hot water from an underlying pluton altered the andesitic flows and mudflows (cunningham and others, 2005). but much later, after deep erosion into the altered volcanic sequence by streams and the ancestral sevier river, the alunite was exposed to the air and oxidized, weathered, and altered (in a process called supergene destruction) into natrojarosite, gypsum, and other minerals. 40ar/39ar ages on these minerals indicate that the start of this supergene alteration took place at about 6.6 ma. this age is in the same timeframe as the cutting of kingston canyon, and because the sevier river currently is only a couple hundred yards from the base of big rock candy mountain, it is reasonable to conclude that much of the dissection to create marysvale canyon was by the ancestral sevier river, as the tushar mountains and the rock obstruction to sevier valley (beneath marysvale canyon) were rising along their own faults. how widespread was the kingston canyon 3-million-year episode of rapid fault uplift, tilting, and canyon cutting? and how is it possible that uplift along an active fault zone such as the sevier largely ceased at about 5 ma, such that the east fork sevier river cut no further downward? to answer this question, let us look at the geology of red canyon, about 30 miles (50 km) south of kingston canyon. here the sevier fault zone is well exposed as a sharp, youthful (partly pleistocene) structure, as described in the red canyon geosite (biek, 2019). the sevier fault at the western mouth of the canyon is mostly a single north-trending structure that uplifts the southern end of the sevier plateau and, farther south, the paunsaugunt plateau (rowley, 1968; lund and others, 2008). total throw on the sevier fault here is about 3000 feet (900 m), about half what it is at kingston canyon. but a basalt flow, with an 40ar/39ar age of 0.51 ± 0.02 ma, that is exposed on both sides of the fault, is offset about 650 feet (200 m) (lund and others, 2008). so some of the uplift is pleistocene, unlike at kingston canyon. the timing and amounts of the deformation, therefore, are much different from the same fault zone at kingston canyon. the probable reason is segmentation of the sevier fault zone, as described by lund and others (2008). in other words, major faults rupture in independent seismogenic segments rather than their entire length. these segments can be identified by several methods, including map differences in the trace of 8 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 the fault. accordingly, about 4 miles (6 km) north of red canyon, the sevier fault swings north-northeast and dies out into the sevier plateau (lund and others, 2008, figure 2). farther north along the north-trending range front, most bounding faults trend largely north-northeast, making an en echelon pattern of parallel faults, few of which form sharp, well-defined, youthful scarps (rowley, 1968; biek and others, 2015a). this pattern continues northward to kingston canyon, where the canyon mouth has another en echelon pattern of faults, this one trending north-northwest, that intersects the north-northeast faults (rowley, 1968; rowley and others, 2005). clearly the sevier fault at red canyon is a different segment than the one at kingston canyon, and the two segments behaved differently. the site itself as you pull off highway 22 at the light-gray outcrop at the southwestern side of the geosite of phonolite hill, you will see the view shown in figure 4. the lightgray rocks closest to you are moderately consolidated sediments whose bedding planes indicate that they are dipping northward or northeastward. these sediments make up the inner part of the shallow volcanic crater, consisting of tuffaceous debris that was tossed out of a vent as rhyolite lava (magma) was moving upward in a pipelike column. the crater had an outer wall, consisting of similar sediments that dipped south and southwest here, and away from phonolite hill elsewhere, but this part of the crater has been removed by erosion by the sevier river (it is preserved on the northern flank of phonolite hill). the debris is mostly of sand and pebble size, but some larger angular clasts (cobbleand boulder size), at least 3 feet (1 m) in diameter, are also present. most of the clasts are white rhyolite but the larger clasts are black, consisting of basalt torn from the vent’s walls. at other locations, clasts of basalt in the crater are several dozen feet in diameter, as recorded in photos given by rowley and others (1981). if you examine the larger basaltic clasts in the crater deposits at this outcrop, you will see that the clasts sit in their own small craters. clearly these black clasts were tossed hundreds of feet in the air during eruption, and when they fell back into wet crater sediments, they made impact craters as much as several inches deep. the lower part of the rhyolite rock (dome) itself is a vertical feeder pipe that cuts the crater deposits about 600 feet (200 m) to the northeast (figure 4). the rhyolite at the contact is black glass (obsidian) about 3 feet (1 m) thick, a chilled margin that cooled fast and did not devitrify like the white rock. the rhyolite was warped into small flow folds as it oozed past the contact. presumably the upper part of the dome flared outward, but this part has been removed by erosion. rhyolite magma is viscous and flows like bread dough, quite unlike runny basalt flows. some domes, therefore, are intruded as subvertical spines called tholoids, and this tall mountain that towers above may have been such a feature. if you look south, you will see the caprock of basalt and osiris tuff that defines the top of the southern wall of kingston canyon (figure 5). the northern wall of the canyon, however, is difficult to see because it is blocked by rocks lower on the wall, including phonolite hill, but the northern canyon rim is capped by the rhyolite of figure 4. view northeast at the volcanic dome of phonolite hill from the geosite parking lot. the white, left(north-) dipping beds in the foreground are the inner part of a tuffaceous crater that surrounds the dome. light-tan rocks just above the white, snow-covered rocks are the vertical plug (vent) of rhyolite dome rock that intrudes the crater. this rock includes a black-glass chilled margin at the intrusive contact, from where the sample was collected for k-ar dating. rhyolite dome rock, with generally vertical cooling joints, makes up most of the mountain. 9 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 forshea mountain. the rhyolite of forshea mountain was interpreted to have been deposited horizontally, like the beds below it, and only later was the sevier plateau uplifted along the sevier fault zone and tilted east. figure 5 shows the view from forshea mountain; figure 6 gives a glimpse of the northern wall, along with phonolite hill itself. the significance of the kingston canyon geosite is it constrains the main phase of basin-range deformation in this part of a range in the great basin–colorado plateau transition zone to between 8 and 5 ma. this 3-million-year span is the tightest constraint we know of, across the entire great basin and its transition zone, for uplift of a range by basin-range faults. it might be argued that this short span of time for the uplift by basin-range faulting may pertain to only a single range, the sevier plateau. yet this time span fits with what we know about the main period of basin-range deformation across much of these provinces. although basin-range deformation began more than 20 million years ago, the post-10 ma interval produced the greatest deformation and thus most of the present topography. and kingston canyon shows that along some segments of major fault zones, uplift and deformation was more rapid than has been documented before. figure 5. view south from forshea mountain showing phonolite hill. phonolite hill, a rhyolite dome, erupted 5 million years ago at the bottom of kingston canyon. the photographer is standing on the 8 ma rhyolite of forshea mountain. the top of the gently east-dipping canyon wall across the canyon would have been a valley floor 8 million years ago. the sevier fault is to the right of the hills at the far right of the view, west of which is a glimpse of sevier valley. the base of the 5 ma rhyolite dome of phonolite hill is at the current canyon floor, showing here a minimum of 4000 feet (1200 m) of uplift (it would show as more if the south wall were projected out to the sevier fault) on the sevier fault between 8 and 5 ma. 10 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 acknowledgments this short report has an unusual amount of history behind it, and great indebtedness. the late professor j. hoover mackin of the university of texas supervised rowley’s dissertation. the late professor john j. anderson of kent state university participated with rowley in working on the volcanic stratigraphy of the southern marysvale field. the late paul l. williams of the usgs first found and named the osiris tuff and served on rowley’s dissertation committee. the late thomas a. steven of the usgs is partly responsible for the study of the marysvale field and suggested that the rhyolite of phonolite hill was worth mapping in detail. the late charles g. cunningham of the usgs was another close colleague who was key to unraveling the marysvale field. harald h. mehnert of the usgs, probably the best k-ar geochronologist in the business, determined many of the ages of volcanic rocks in the marysvale field, including the initial ages in kingston canyon. lisa peters of the new mexico institute of mining and technology did the argon ages. we thank grant willis, stephanie carney, and mike hylland (ugs) for technical review of the manuscript, and lori steadman for drafting the figures. references anderson, j.j., and rowley, p.d., 1975, cenozoic stratigraphy of southwestern high plateaus of utah, in anderson, j.j., rowley, p.d., fleck, r.j., and nairn, a.e.m., editors, cenozoic geology of southwestern high plateaus of utah: geological society of america special paper 160, p. 1–52. best, m.g., christiansen, e.h., deino, a.l., gromme, c.s., hart, g.l., and tingey, d.g., 2013, the 16-18 ma indian peak–caliente ignimbrite field and calderas, southeastern great basin, u.s.a.—multicyclic super-eruptions: geosphere, v. 9, no. 4, p. 1–87. biek, r.f., 2019, sevier fault at red canyon, in milligan, m., biek, r.f., inkenbrandt, p., and nielsen, p., editors, utah geosites: utah geological association publication 48, 6 p., https://doi. org/10.31711/geosites.v1i1.53. biek, r.f., eaton, j.g., rowley, p.d., and mattox, s.r., 2015b, interim geologic map of the western loa 30' x 60' quadrangle, garfield, piute, and wayne counties, utah (year 2): utah geological survey open-file report 648, scale 1:100,000. biek, r.f., rowley, p.d., anderson, j.j., maldonado, f., moore, d.w., hacker, d.b., eaton, j.g., hereford, r., sable, e.g., filkorn, h.f., and matyjasik, b., 2015a, geologic map of the panguitch 30' x 60' quadrangle, garfield, iron, and kane counties, utah: utah geological survey map 270dm, 162 p., scale 1:65,000. biek, r.f., rowley, p.d., and hacker, d.b., 2019, the gigantic markagunt and sevier gravity slides resulting from mid-cenozoic catastrophic mega-scale failure of the marysvale volcanic field, figure 6. view west-northwest at phonolite hill. the top of forshea mountain in the northern wall of kingston canyon is capped by the 8-million-year-old rhyolite of forshea mountain, barely visible as the farthest hill on the right. the mesa at the left skyline consists of the 27-million-year-old three creeks tuff member of the bullion canyon volcanics. 11 basin-range uplift and canyon cutting in 3 million years, kingston canyon, piute county, southwestern utah rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 utah, usa: geological society of america field guide 56, 121 p., https://lccn.loc.gov/2019045272. cunningham, c.g., rye, r.o., rockwell, b.w., kunk, m.j., and councell, t.b., 2005, supergene destruction of a hydrothermal replacement alunite deposit at big rock candy mountain, utah—mineralogy, spectroscopic remote sensing, stable-isotope, and argon-age evidences: chemical geology, v. 215, p. 317–337. hacker, d.b., biek, r.f., and rowley, p.d., 2014, catastrophic emplacement of the gigantic markagunt gravity slide, southwest utah (usa)—implications for hazards associated with sector collapse of volcanic fields: geology, v. 42, no. 11, p. 943–946. lund, w.r., knudsen, t.r., and vice, g.s., 2008, paleoseismic reconnaissance of the sevier fault, kane and garfield counties, utah, paleoseismicity of utah, v. 16: utah geological survey special study 122, 31 p. rowley, p.d., 1968, geology of the southern sevier plateau, utah: austin, university of texas, ph.d. dissertation, 385 p. rowley, p.d., mehnert, h.h., naeser, c.w., snee, l.w., cunningham, c.g., steven, t.a., anderson, j.j., sable, e.g., and anderson, r.e., 1994, isotopic ages and stratigraphy of cenozoic rocks of the marysvale volcanic field and adjacent areas, west-central utah: u.s. geological survey bulletin 2071, 35 p. rowley, p.d., steven, t.a., and mehnert, h.h., 1981, origin and structural implications of upper miocene rhyolites in kingston canyon, piute county, utah: geological society of america bulletin, v. 92, pt. 1, p. 590–602. rowley, p.d., vice, g.s., mcdonald, r.e., anderson, j.j., machette, m.n., maxwell, d.j., ekren, e.b., cunningham, c.g., steven, t.a., and wardlaw, b.r., 2005, interim geologic map of the beaver 30' x 60' quadrangle, beaver, piute, iron, and garfield counties, utah: utah geological survey open-file report 454, 32 p., scale 1:100,000. rowley, p.d., williams, p.l., and kaplan, a.m., 1986a, geologic map of the greenwich quadrangle, piute county, utah: u.s. geological survey geologic quadrangle map gq-1589, scale 1:24,000. rowley, p.d., williams, p.l., and kaplan, a.m., 1986b, geologic map of the koosharem quadrangle, sevier and piute counties, utah: u.s. geological survey geologic quadrangle map gq1590, scale 1:24,000. steven, t.a., cunningham, c.g., naeser, c.w., and mehnert, h.h., 1979, revised stratigraphy and radiometric ages of volcanic rocks in the marysvale area, west-central utah: u.s. geological survey bulletin 1469, 40 p. utah geological survey and new mexico geochronology research laboratory, 2019, 40ar/39ar geochronology results for the burnt peak and phonolite hill quadrangles, utah: utah geological survey open-file report 707, variously paginated, https:// doi.org/10.34191/ofr-707. maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado kenneth carpenter theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover the controversial vertebra of maraapunisaurus fragillimus (formerly amphicoelias fragillimus) and edward d. cope who described the specimen in 1878. i president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa editors geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 227 abstract in 1878, oramel lucas shipped to e.d. cope of the academy of natural sciences of philadelphia, a huge 1.5-m-tall neural spine from the dorsal vertebra of a sauropod (from the upper jurassic morrison formation) that cope named and illustrated as amphicoelis fragillimus. the holotype was lost and all that is known of the specimen is from cope’s original publication. reanalysis of cope’s publication in light of other sauropods discovered since 1878 indicates that amphicoelias fragillimus is a basal rebbachisaurid characterized by pneumatic neural spine and arch, and the unambiguous rebbachisaurid character of a festooned spinodiapophyseal lamina. because the specimen can no longer be referred to the basal diplodocoid amphicoelias, the genus name is replaced with maraapunisaurus n.g. as a rebbachisaurid, revised dimensions indicate a dorsal vertebra 2.4 m tall and a head–to–tail length for the animal of 30.3 to 32 m, significantly less than previous estimates. maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado kenneth carpenter prehistoric museum, utah state university eastern, 155 east main st., price, ut 84501; ken.carpenter@usu.edu; university of colorado museum of natural history, henderson building, 15th and broadway, boulder, co 80309 citation for this article. carpenter, k., 2018, maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado: geology of the intermountain west, v. 5, p. 227–244. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction between 1877 and 1884, school teacher oramel lucas and his brother ira discovered and excavated numerous dinosaur specimens from the vicinity of a prominent conical hill (a.k.a. “cope’s nipple,” “the nipple,” “saurian hill”) of upper jurassic morrison formation in garden park north of cañon city, colorado (for historical review see carpenter, in press). among the specimens shipped by oramel lucas to edward d. cope, loosely affiliated with the academy of natural sciences of philadelphia, in 1878 was a huge neural spine. the specimen was described and illustrated as amphicoelias fragillimus by cope (1878f: 564) who wrote that “the total elevation of this vertebra, when complete, was not less than six feet, and probably more” (figure 1a). this estimation was never challenged by cope’s contemporaries, nor later by henry osborn and charles mook of the american museum of natural history in their monograph of the cope sauropod collection (osborn and mook, 1921). only more recently have questions been raised about this specimen in the debate about the maximum possible size of terrestrial vertebrates (paul, 1998; mazzetta and others, 2004; carpenter, 2006a; perry and others, 2009; woodruff and foster, 2014). osborn and mook’s access to cope’s sauropods was made possible by the purchase of the cope zoological and paleontological specimens by the american museum of natural history, much to the consternation of the academy of natural sciences of philadelphia, which had hoped to acquire the collections (anonymous, 1899). 228 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 because of financial reasons, cope began negotiating with the american museum in april 1894 to purchase parts of his collections with his friend henry osborn acting as a middleman (osborn, 1931). although this would be considered a conflict of interest today, cope counted on his friend’s honesty to help him leverage the best possible prices and to recoup the estimated $50,000 (~ $1.5 million in 2018) of personal money spent. the cañon city dinosaurs were part of the final sale negotiated with the cope estate in 1897 a few months after his death at age 54. in the end, the american museum spent $60,550 (~ $1.8 million in 2018) for just the four vertebrate fossil collections alone (osborn, 1931). the process of examining, packing and shipping the collections was not rushed, but took several years, with the last of the collections not arriving at the american museum until 1903, six years after cope’s death (jesup, 1896, 1898, 1899, 1900, 1901, 1903). osborn, who was head of vertebrate paleontology, put william d. matthew, curator at the museum, in charge of the vertebrate fossil collection transfers (mathew, 1915, p. 38; osborn and mook, 1921; osborn, 1931; colbert, 1992, p. 51– 53). matthew was aided by albert thompson and jim young, also of the american museum (osborn, 1931). some of cope’s collections were at his house on pine street in philadelphia, but a larger portion was in storage a few miles away in the lower level of the memorial hall building in fairmont park (matthew, 1915). once figure 1. illustrations of different sauropod dorsals made by cope to show why he thought that the neural spine of "amphicoelias" fragillimus (a) was most similar to that of amphicoelias altus (b) than to camarasaurus supremus (c, mid-dorsal; d, more posterior mid-dorsal). scale = 1 m. b to d from cope 1878b; a from cope 1878f. 229 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 the collections arrived at the american museum, the cataloguing of the specimens was handled by walter granger, albert thompson, and william matthew (see jessup, 1901, p. 23; osborn and mook, 1921, p. 251, 258, and 260). while cope was still alive, osborn did write cope about various specimens that could not be accounted for by matthew: “i write to ask whether you can fix your memory upon the type of symborodon torvus and of s. ophryas. we cannot locate definitely the type of either specimen, although one is the type of the genus and the other is described as a nearly complete skull. i hope you will look this up, and if you can, refresh your memory and let me know. dr. matthew also reports that the types of marsupials from the white river are apparently missing. have you seen anything of them?” osborn to cope, may 19, 1896, in osborn (1931, p. 449–450). despite these letters, some of these specimens were never found, e.g., mesohippus cuneatus, amnh 6293, “these types could not be identified when cope’s colorado collection was catalogued by w.d. matthew.” (osborn, 1918, p. 47). the situation was worse when the dinosaur collection was finally dealt with six years after cope’s death. by then it was no longer possible for osborn to inquire of cope where the missing specimens might be, or which sets of bones belonged together because cope never numbered them (see discussion on the comingled specimens in osborn and mook, 1921, p. 259–261). osborn even wrote to oramel lucas: “i find that the records which came to use with the collection from professor cope are very inadequate and do not enable us to determine where the various fossils were found. i write to ask whether you have any records of the number and kind of bones taken out of the different quarries which would enable us to clear up this very import question.” (osborn to lucas, april 30, 1904, gpps docs). among the cañon city dinosaurs, the type of amphicoelias fragillimus was missing, as were the type mandible of laelaps trihedrodon, and parts of the types of camarasaurus leptodirus and amphicoelias latus (osborn and mook, 1921; chure, 2001). mcintosh (1998) also reports that some bones mentioned in the shipping lists of lucas were missing, an oversight that osborn knew nothing about because the documents were assumed to be lost (osborn and mook, 1921; mcintosh, 1998). nevertheless, all of the missing specimens (mammalian, as well as dinosaurian) were assigned catalog numbers in the event that they were eventually found. abbreviation amnh fr – american museum of natural history, fossil reptile collection, new york city, newyork. gpps docs – archives of the garden park paleontological society housed at the royal gorge regional museum and history center, cañon city, colorado. cope’s giant neural spine in his description of amphicoelias fargillimus, cope wrote that he thought the neural spine compared favorably to that of a. altus (figure 1b), a taxon he named the previous year (cope, 1877d): “it [the neural spine] exhibits the general characteristics of the genus amphicoelias, in the hyposphen [sic], antero-posteriorly placed neural spine, and elevated diapophysis for the rib articulation. the diapophyses are compressed and supported by a superior and inferior, and anterior and posterior, thin buttress, separated by deep cavities.” (cope, 1878f, p. 563). at the time of this writing, sauropods had just been discovered in the united states the year before and were very imperfectly known. from cope’s limited point of view, the two neural spines did indeed resemble one another more than to those of camarasaurus supremus, the only other sauropod known to him that included dorsal vertebrae (compare figures 1a and 1b with 1c and 1d). only now with many hundreds more sauropod specimens do we know that many of the cited characters are more widely spread. in differentiating between the two species of am230 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 phicoelias, cope wrote (1878f, p. 563): “as compared with the amphicoelias altus, this reptile differs in the greater elevation and attenuation of the neural spine, as well as its different form; also in the generally more laminar character of its buttresses and walls. the double rib of the anterior border of the spine of a. altus is here [a. fragillimus] represented by two laminae which extend on each side, so as to give a horizontal section of the spine a t shape. the posterior zygapophyses have less lateral expanse than in a. altus, but they continue as horizontal laminae with a deep cavity above and below: their superior surfaces contract into two ridges, which are separated by a deep groove. these ridges, unlike the anterior ones, approximate to each other closely on the border of the spine. the summit of the spine is wanting.” despite these differences, osborn and mook (1921, p. 279), synonymized the two taxa, arguing that “cope’s description indicates an animal with the general characters and proportions of amphicoelias altus. it is doubtful, however, if the characters described by cope warrant the placing of the type in another species different from a. altus. the form is therefore provisionally referred to a. altus.” this position was accepted by mcintosh (1998). in contrast, as will be shown below, i consider the characters listed by cope as valid distinctions and will add to them based on his illustration. the reliability of cope’s illustrations was never questioned by osborn and mook (1921) who were able to match cope’s illustrated bones to specific bones (see captions for their figures 7 to 14 and 17 to 20). cope showed an artistic capability as a child (osborn, 1931) and making his own drawings gave him an eye for detail that is missing in many of o.c. marsh’s publications. although cope’s illustration of the bones from cañon city lacked the refinement of staff artist rudolf weber who did the line drawings for the osborn and mook monograph (figure 2), there is no reason not to accept the reliability of the amphicoelias fragillimus illustration. there is also no reason not to accept the measurements given by cope contrary to woodruff and foster (2014), who suggest “a typographical error” is likely in the vertebra’s height measurement because they perceive another such error in the use of the abbreviation “m” alone for millimeter, rather than the commonly used “mm” today. in point of fact, both meter and millimeter used the same abbreviation at that time (anonymous, 1878, p. 316), and is understood by context. cope also used “m” (upper case) for meter (e.g., cope, 1877b, measurements for camarasaurus supremus) and “m” (lower case) for millimeter (e.g., cope, 1878f, for amphicoelias fragillimus). woodruff and foster (2014, p. 217) also seek to cast doubt as to the reliability of cope’s measurements by focusing on what they contend to be contradictory measurements given by cope for the femur of a. altus (note: cope, 1878b, printed january 12, 1878, as given at bottom of p. 233, not cope, 1877, as stated by woodruff and foster, 2014). cope does write figure 2. the reliability of the drawings made by cope is seen in this example with the femur of amphicoelias altus. (a) femur as displayed in cope's office, circa 1895, slightly rotated with head towards the viewer (from osborn, 1931). (b) femur illustrated by cope (1878b). (c) femur as illustrated by rudolf weber (from osborn and mook, 1921). 231 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 on page 244, “the length of the femur is six feet four inches” (= 1.930 meters) and on page 245 “length of femur 1.524 m.” the illustration by cope (1878b, 1877c; figure 2b) of the femur shows that the distal condyles were missing, therefore cope’s measurement of 1.524 meters is reasonable as a minimum length, whereas osborn and mook (1921) gave a maximum preserved measurement of 1.77 meters. osborn and mook (1921) also note and illustrate the distal half of the left femur, which cope undoubtedly used to estimate the femur length of a. altus as being “six feet four inches.” today, we would qualify this as a “reconstructed” length, but such terminology was not in use at the time. despite this possible alternative explanation, we really have no way of knowing cope’s thinking and might find his explanation logical if we could ask him. amnh fr 5777 as a basal rebbachisaurid traditionally, amnh fr 5777, amphicoelias fragillimus, was considered a diplodocid beginning with osborn and mook (1921) and continuing to this day (woodruff and foster, 2014). even i had previously considered the specimen a diplodocid (carpenter, 2006a), but reanalysis of cope’s description and figure suggests otherwise, and that it is a basal rebbachisaurid. i begin with some points of observation by cope (1878f, p. 563). he stresses the fragility of the bone in several ways, “in the extreme tenuity [i.e., lack of solidity or substance] of all its parts, this vertebra exceeds those of this type already described [i.e., a. altus], so that much care was requisite to secure its preservation.” he also noted the “… attenuation of the neural spine.” compared to the neural spine of a. altus, and all diplodocids for that matter, the neural spine is indeed “attenuated,” meaning it had a “simplified” structure in that there are few laminae and fossa. he notes, for example, that “the double rib [i.e., ridges or laminae] of the anterior border of the spine [i.e., paired spinoprezygapophyseal laminae] of a. altus is here [a. fragillimus] represented by two laminae which extend on each side [i.e., spinoprezygapophyseal + spinodiapophyseal laminae, see figure 3] so as to give a horizontal section of the spine a t shape…” he says nothing about a prespinal lamina, but neither does he of the postspinal lamina, which is seen in figure 1a. thus, it is not clear whether he means the “t-cross section” lacked a prespinal process, or whether he means “t-cross section” with a prespinal lamina. either interpretation is possible (figure 4a). the tetraradiate cross section (a.k.a. “t-cross section”) was considered by carvalho and santucci (2018) as a distinctly rebbachisaurid character, but in fact also occurs in dicraeosaurids (figure 4c). cope also notes the many laminae of the neural arch (“generally more laminar character of its buttresses and walls”) that in the figure define various pneumatic cavities (figure 3). other rebbachisaurid features of the neural spine given by whitlock (2011) can be gleaned from cope’s illustration (figure 3). (1) the festooned spinodiapophyseal lamina, which is the sheet of bone between the neural spine and transverse process, is an unambiguously rebbachisaurid character (figures 4d to 4l; sereno and others, 2007; whitlock, 2011). (2) pneumatic chambers dorsolateral to neural canal are implied by the paired foramina on each side of the postspinal lamina. this character occurs in comahuesaurus (carbadillo and others, 2012), demandasaurus (torcida fernández-baldor and others, 2011), and rebbachisaurus (wilson and allain, 2015). other pneumatic chambers appear to have been widespread throughout the neural arch as revealed by the damaged area below the postzygapophyses. there is a large pneumatic cavity (camera) that probably extended dorsally from the pneumatic cavity of the centrum. this feature is also seen in the damaged d4 of cm 94 (diplodocus carnegii) and in barosaurus (j. foster, utah field house of natural history state park museum, written communication, 2018). pneumatized neural arches also occur in the rebbachisaurids comahuesaurus (carbadillo and others, 2012), demandasaurus (torcida fernández-baldor and others, 2011), katepensaurus (ibiricu and others, 2017) and rebbachisaurus (wilson and allain, 2015). (3) the height of the neural arch below the postzygapophyses is very high among rebbachisaurids, but this character is also shared with haplocanthosaurus, dicraeosaurus, and the last dorsals of apatosaurus (figure 4b, 4c, and 4q). one character that occurs in rebbachisaurids, as 232 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 well as dicraeosaurids and haplocanthosaurus, that is equivocal in amnh fr 5777 is the rather steep angle of the transverse process. much of this process is missing and cope implies that it was nearly horizontal with dashes (figure 1a), but i believe he was influenced by a. altus to which he thought the giant spine was most similar. there appears to be a slight upwards curvature of the distal portion of the spinodiapophyseal lamina best seen on the more complete left side which suggests that the transverse process could have been angled upwards, perhaps as much as 30° (figure 5a). this possibility is also supported by the angle of the lower edge of the centrodiapophyseal laminae and by the angle of the postzygodiapophyseal lamina. as a general rule, the angle of the postzygapophysis also mirrors the angle of the transverse process among diplodocoids, with some noticeable exceptions: dorsal 7 of diplodocus carnegii (hatcher, 1901, plate 8) and dorsals 11–14 in haplocanthosaurus where the postzygapophyses are nearly horizontal, but the transverse processes are steeply angled (hatcher, 1903, plate 1). however, in the latter, the postzygodiapophyseal laminae do reflect the upward angle. the postzygapophyses are proportionally smaller than they are in a. altus where they are very large as notfigure 3. drawing made by e.d. cope of the holotype of maraapunisaurus fragillimus (cope, 1878f) with parts labeled. "pneumatic chambers*" indicate the pneumatic cavities dorsolateral of the neural canal, a feature also seen in several rebbachisaurids. terminology from wilson (1999, 2011) and wilson and others (2011). 233 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 figure 4. caption is on the following page. 234 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 ed by osborn and mook (1921; figure 1c). the articular surfaces in amnh fr 5777 are angled approximately 30°, noticeably steeper than in a. altus. the postzygodiapophyseal lamina connects the postzygapophyses with the spinodiapophyseal lamina just below its dorsal rim. the spinopostzygapophyseal laminae extend dorsomedially from the postzygopophyses to join and form the postspinal lamina as they typically do in rebfigure 4 (figure is on previous page). comparison of various sauropod dorsal vertebrae in posterior view: (a) maraapunisaurus as a rebbachisaurid, (b) haplocanthosaurus (modified from hatcher, 1903), and (c) dicraeosaurus (modified from janensch, 1929). rebbachisaurids: (d) histriasaurus (reconstructed from dalla vecchi, 1999), (e) unnamed (modified from apesteguía, 2007), (f) rebbachisaurus (reconstructed from wilson and allain, 2015), (g) limaysaurus (modified from calvo and salgado, 1995), (h) nopcsaspondylus (reconstructed from nopcsa, 1902), (i) unnamed (modified from carvalho and santucci, 2018), (j) comahuesaurus (reconstructed from carballido and others, 2012), (k) demandasaurus (reconstructed from torcida fernandez-baldor and others, 2011) with neural spine of first caudal, and (l) katepensaurus (reconstructed from ibiricu and others, 2013). basal diplodocoid: (m) amphicoelias (modified from osborn and mook, 1921). diplodocids: (n) apatosaurus (modified from gilmore, 1936), (o) barosaurus (reconstructed from photographs), (p) supersaurus (reconstructed from photographs), (q) diplodocus (reconstructed from photographs; cross section modified from osborn, 1899). cross sections of neural spines also shown for a, c, e, f, m, and q. all scaled to same height, except for b. small red boxes in a, f, i, and l show divergence of the lateral spinopostzygapophyseal laminae from the postspinal lamina. images are not to equal scale. figure 5. comparison of the neural spine of maraapunisaurus fargillimus restored as a rebbachisaurid (a), and the dorsal vertebrae of rebbachisaurus garasbae (b), and histriasaurus boscarollii (c). increments on scale bars = 10 cm. 235 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 bachisaurids, such as rebbachisaurus and histriasaurus (figure 5b and 5c), but also in the dicraeosaurids amargasaurus and dicraeosaurus. the postspinal lamina extends the entire preserved length of the neural spine. the spinopostzygapophyseal laminae form a triangular or lachrymiform spinopostzygapophyseal fossa between them. laterally adjacent to where the postspinal lamina is formed, two short laminae diverge and extend dorsolaterally to combine with the spinodiapophyseal laminae along the sides of the neural spine. the identity of these laminae is problematic because they do not extend to the postzygapophyses. nevertheless, a similar divergence involving the lateral spinopostzygapophyseal laminae occurs in several rebbachisaurids (red boxes in figures 4a, 4f, 4i, and 4l). in diplodocids, the lateral spinopostzygapophyseal laminae of the posterior dorsal vertebrae do not contact the postspinal lamina but are separate. the evidences above show that amnh fr 5777 cannot be referred to the genus amphicoelias as cope (1878f) had originally suggested based on the very limited information available to him. therefore, a new generic name is warranted, but first i need to defend naming the missing type. the fact that the specimen is missing does not invalidate giving it a new generic name (iczn 1999; article 72.5.6). “in the case of a nominal species-group taxon based on an illustration or description, or on a bibliographic reference to an illustration or description, the name-bearing type is the specimen or specimens illustrated or described (and not the illustration or description itself).” this is reiterated in article 73.1.4 (iczn, 1999). some researchers have objected to this provision in the code, but as krell and marshall (2017, p. 4) have noted, “it is important to understand that a change in the code to disallow the use of photographs [or illustrations] as proxies for lost types would not change the underlying taxonomy. the processes of discovery and description of species, which are matters of taxonomic judgment rather than rules, would remain the same.” it must also be remembered that the code is meant for all branches of zoology, not just vertebrate paleontology. a binding rule that physical type specimens must exist would exclude some branches of zoology from the code as listed in krell and marshall (2017). finally, lest it be thought that the code gives free reign to naming taxa from illustrations of existing specimens, it also states “preference for specimens studied by author. an author should designate as holotype a specimen actually studied by him or her, not a specimen known to the author only from descriptions or illustrations in the literature.” (iczn 1999, recommendation 73b). this nonbinding guideline is given as a recommendation because there are instances where the material is missing or destroyed, as was the case for the rebbachisaurid nopcsaspondylus alarconensis named by apesteguía (2007) for a vertebra described and figured (but not named) by nopcsa (1902), for the stegosaur alcovasaurus longispinus by galton and carpenter (2016), and for amnh fr 5777. the recently issued nonbinding declaration 45 (iczn 2017) seeks to promote good taxonomic practice regarding an unpreserved specimen as the name-bearing type. as krell and marshall (2017) commented, “the code cannot dictate what quality or quantity of evidence is enough; that is a matter of taxonomic judgment.” systematic paleontology sauropoda marsh, 1878 diplodocoidae marsh, 1884 (upchurch, 1998) rebbachisauridae bonaparte, 1997 maraapunisaurus fragillimus (cope, 1878f) n.g. figures 1a, 3, 4a amphicoelias fragillimus cope, 1878f amphicoelias altus osborn and mook, 1921 in part amphicoelias altus mcintosh, 1998 in part amphicoelias fragillimus cope, 1878f (carpenter, 2006a) etymology ma-ra-pu-ni (pronounced mah-rah-poo-nee) — southern ute for “huge” used here in reference to the huge size of the animal, and saurus, greek for reptile. the garden park area was traditionally ute tribal territory before they were displaced by settlers in the mid1800s. the name was recommended by the southern ute cultural department, ignacio, colorado. 236 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 holotype amnh fr 5777 (missing) consisting of a posterior dorsal neural arch, including neural spine (minus the distal apex), the proximal parts of the transverse processes, and both postzygapophyses. woodruff and foster (2014, p. 211 and 214) also claim “a distal end of a femur” as part of the type, despite no mention of that by cope (1878f) nor osborn and mook (1921). the only mention of a distal end of a femur occurs in cope’s field notes for 1879. it is here not considered part of the holotype because it could just as easily belong to a large specimen of c. supremus or a. altus which also occurred nearby. diagnosis combination of characters, including extremely tall neural arch to the base of the postzygapophyses (estimated approximately 1/3 total height of the specimen); unbifurcated, simply structured neural spine with spinopostzygapophyseal laminae joined dorsally to form the postspinal lamina; pneumatic camerae in neural arch and paired pneumatic foramina pierce the neural spine on each side of the postspinal lamina just above where spinopostzygapophyseal laminae join; hyposphene present; the postspinal lamina extends dorsally the entire preserved length of neural spine and with the spinodiapophyseal + spinopostzygapophyseal(?) laminae give the neural spine a simple t-shaped cross section. description and discussion the general assumption for amnh fr 5777 is that it is from a posterior dorsal, possibly d-9 or d-10 (osborn and mook, 1921), d-10 (carpenter, 2006a). cope, however, simply referred to the specimen as a “posterior dorsal vertebrae” and could not have identified it as a d-10 contrary to woodruff and foster (2014, p. 213) because the sauropod dorsal counts were unknown at this time. the neural arch below the postzygapophyses is damaged, but exceptionally tall. it has a very prominent intrapostzygapophyseal lamina that slightly widens ventrally towards the missing neural canal (figure 3). dorsally, it merges into a broad surface below the hyposphene. this region appears to be undamaged and what may be the right centropostzygapophyseal lamina indicates that the laminae ended well below the hyposphene, rather than uniting with that structure. the hyposphene is proportionally small for the size of the neural arch and a simple, rectangular structure (figure 3). the hyposphene is plesiomorphic for sauropods (apesteguía, 2005), commonly occurring in flagellicaudata, and only in basal rebbachisaurids (e.g., histriasaurus, comahuesaurus, and demandasaurus). the damaged area of the neural arch reveals several pneumatic chambers (camerae and subcamerae), including a large one (figure 3) that probably extended dorsally from the pneumatic cavity of the centrum. this latter feature is also seen in the damaged d-4 of cm-94 (diplodocus carnegii) and barosaurus (j. foster, utah field house of natural history state park museum, written communication, 2018). pneumatized neural arches also occur in the rebbachisaurids demandasaurus (torcida fernández-baldor and others, 2011), comahuesaurus (carbadillo and others, 2012), rebbachisaurus (wilson and allain, 2015), and katepensaurus (ibiricu and others, 2017). there also appears to be a pair of pneumatic chambers in the neural arch dorsolateral to where the neural canal is assumed to have been (figure 3 “pneumatic chambers*”). this character is shared with demandasaurus (torcida fernández-baldor and others, 2011), comahuesaurus (carbadillo and others, 2012), and rebbachisaurus (wilson and allain, 2015). the postzygapophyses are proportionally smaller than they are in a. altus where they are very large as noted by osborn and mook (1921; figure 1b). the articular surfaces in amnh fr 5777 are angled approximately 30 degrees, noticeably steeper than in a. altus. size of maraapunisaurus it is impossible to discuss amnh fr 5777 without delving into the issue of its size and that of the animal to whom it belonged. in his description of “amphicoelias fragillimus,” cope (1878f, p. 564) wrote: 237 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 “these figures [the measurements] show that the total elevation of this vertebra, when complete, was not less than six feet, and probably more.” woodruff and foster (2014, p. 219) make it plain they do not believe cope, writing: “...that it is highly unlikely that a terrestrial quadruped of such a purported body size could have existed.” it is unfortunate that they seek to disprove cope’s claim by casting aspersions about the quality of his work and go so far as to alter cope’s measurements, claiming that “proportionally these new values fit much better…” there is, however, corroborative evidence for the existence of the big neural spine as stated by cope. in late 1877, when word began to circulate of the large bones being uncovered in garden park, u.s. geological survey geologist hayden visited lucas as reported by pangborn (1878, p. 51). lucas maintained contact with hayden and wrote to him on november 18, 1878 (gpps docs): “you have doubtless seen prof cope’s report on the amphicoelias fragillimus, the vertebra of which is six feet in elevation, requiring a femur twelve feet long, almost fabulous dimensions.” we know from the gpps docs archives that cope sent lucas copies of his publications. lucas would certainly have noticed if the measurements of the neural spine were in error. instead, he corroborates cope’s estimate of a six-foot vertebra in the letter. we also know from copies of the letters he sent to cope that he did measure many of the bones before shipment. for example: “33 caudal vt of all sizes from 2 inches to 14 inches in diameter.” (lucas letter to cope, february 10, 1879, gpps docs). even more detailed measurements were given in annotated drawings he sent with letters to cope, which included various thicknesses as well (e.g., figure 6). thus, it is doubtful that lucas was merely parroting cope when he wrote to hayden. in addition, such a large and impressive fossil is not easily forgotten, as lucas was to recount in an autobiography written for the 50th reunion of the oberlin class of 1880: “i found a single bone a vertebra of another animal. this vertebra was six feet in elevation, i.e., the width of the back bone up and down. what a monster this animal must have been.” (lucas 50th, gpps docs.) given the corroborative evidence, what is the estimated restored size of the vertebra amnh fr 5777? cope modeled the missing centrum after a. altus, as did i initially (carpenter, 2006a). woodruff and foster (2014) preferred a proportionally larger and rounder centrum modeled on supersaurus vivianae on the basis that the figure 6. copy by oramel lucas of one of his illustrations that accompanied one of his letters to cope. the illustrations show the location of various measurements. this and other drawings were apparently made in the field before crating (gpps docs). 238 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 centrum becomes larger and rounder in diplodocids with increased size. as a rebbachisaurid, cope was correct in giving his reconstruction a proportionally small centrum (figure 1a). using rebbachisaurid vertebrae (figure 5) as a guide does imply a small centrum that was wider than deep. in the new reconstruction (figure 5a), it is difficult to know how much of the neural spine and diapophyses are missing, or the actual height of the centrum. the reconstructed proportions are based on rebbachisaurus because of the best fit of two easily identified landmarks when the neural spine is scaled down and overlain other vertebrae. these include the base of the neural pedicle (must be at least slightly above the top of the neural canal) and the upper curved edge of the spinodiapophyseal lamina. using other rebbachisaurid vertebrae, including the basal histriasaurus, was less successful because they have proportionally shorter neural arches. the reconstruction gives a vertebrae 2.4 m tall and less than the previous 2.7 m by me (carpenter, 2006a) and 2.8 m by woodruff and foster (2014). to better understand the possible size of maraapunisaurus, knowing the femur length would be ideal. to give perspective of the huge size of the animal for his readers, cope (1878f, p. 564) estimated the femur length as 3.66 m based on his observation that the femur was twice the height of the dorsal vertebra in a. altus and camarasaurus supremus. the ratio may be significantly different in rebbachisaurids, although few specimens have useable elements. one example is limaysaurus, where the incomplete dorsal is restored as 120 cm tall, whereas the complete femur is 144 cm (calvo and salgado, 1995, as rebbachisaurus tessonei). in this case, the vertebra is 83% the femur length, rather than 50%. if this pattern is representative of most rebbachisaurids, then the femur of maraapunisaurus was approximately 2.9 m tall, which is smaller than estimated by cope and significantly less than my previous estimate of 4.3 to 4.6 m (carpenter, 2006a) assuming skeletal proportions similar to diplodocus. paul (1994) estimated the femur as 3.1 to 4 m, and woodruff and foster (2014) estimated 4.76 m. in comparison, the currently largest known sauropod femur is 2.31 m belonging to cf. antarctosaurus giganteus (huene, 1929). revised as a rebbachisaurid modeled after limaysaurus, one of the few specimens complete enough to for a skeletal reconstruction, maraapunisaurus is only 30.3 m long, and 7.95 m at the hips (figure 7). this is significantly less than my previous estimate length of 58 m (carpenter, 2006a) and paul’s (1994) estimate of 40 to 60 m. woodruff and foster (2014) did not give an estimated length based on their revised size of the vertebra. however, parrish (2006) found that neck length in sauropods scales to torso length to the power of 1.35. that would mean that the neck of maraapunisaurus was 7.6 m long rather than the 6 m long, which it would have if limaysaurus were simply scaled larger. the result is that maraapunisaurus might have been 32 m long, which puts it within the range estimates for supersaurus and diplodocus hallorum (lovelace and others, 2008). finally, the speculative reconstructed hindfoot length of maraapunisaurus, 1.36 m, is in the size range for some of the type a sauropod tracks from broome, figure 7. body comparisons of maraapunisaurus as a 30.3-m-long rebbachisaurid (green) compared with previous version as a 58-m-long diplodocid (black). lines within the silhouettes approximate the distal end of the diapophyses (i.e., top of the ribcage). rebbachisaurid version based on limaysaurus by paul (2016), with outline of dorsal based on rebbachisaurus; diplodocid version modified from carpenter (2006). 239 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 australia (salisbury and others, 2016). i would note, however, that the largest pes track (salisbury and others, 2016, figure 29) is most likely closely set manus and pes prints (compare their figures 27c and 28c; note manus track behind pes). regardless, some of the other tracks in the 1.35 to 1.40 m range contradict woodruff and foster (2014, p. 219) that such huge sauropods were impossible. salisbury and others (2016) rightly note that the broome tracks have major ramifications on the upper size-limits of terrestrial vertebrates. loss of the neural spine as noted above, the holotype of maraapunisaurus fragillimus is one of several specimens that were missing when the american museum of natural history took procession of the cope collection. i have previously hypothesized that the specimen crumbled and was disposed of by cope years before the collection was sold (carpenter, 2006a, p. 134). i still believe that to be the strongest hypothesis, although i now consider that the destruction may have occurred by mishandling or rough handling of the crate with the specimen during its move 8 km to the memorial hall basement storage where cope kept most of the lucas specimens (osborn, 1931). we do know that hay was often used to pack the fossils in crates as cope wrote regarding the shipping of elasmosaurus: “it is very desirable that the specimens should be packed in such a way as to avoid friction or breakage in case of sudden jars. to accomplish this each single piece or mass, should be so surrounded in the hay or other packing as to allow of some elasticity of contact with the next. it is also important that any box should not be too large to bear the rough handling of so much weight: otherwise it may be broken, even much lost.” (cope to theophilus turner, february 13, 1868, given in almy, 1987, p. 188). that the use of hay to pack fossils was widespread at this time is seen by the instructions marsh gave his collectors: “pack fossils in boxes of moderate size, and made of inch boards. plenty of hay or straw should be put on the bottom, and closely around sacks of fossils, so that they cannot move when the box is turned over.” (schuchert and levene, 1940, p. 173; see also davidson and everhart, 2017). the major problem with hay is its compaction under heavy weight, a serious problem as cope noted in a letter regarding the shipment of the elasmosaurus: “each mass should have had a thicker wrapping of hay (still more when paper is used) & the box should be so packed as to prevent the rubbing and moving of the pieces. the largest box had 1/3 to 1/4 vacant space when it arrived & it as well as others, suffered some injury on that account.” (cope to turner, february 13, 1868, given in almy, 1987, p. 189). the large and heavy neural spine of maraapunisaurus would have been difficult to crate and ship safely from colorado to philadelphia where it was described and illustrated by cope, as well as from cope’s home to his memorial hall storage. given that preservatives were not yet in use, it is amazing that the specimen arrived in philadelphia in the first place. lucas does mention that he solved the problem of keeping the fractured bones he was excavating together: “they [the fossil bones] were taken out with great care, each piece for the most part, especially in all the more fragile bones, being secured in its proper position relative to those about it, by pasting paper on the surface of the bones.” (lucas to marsh, march 11, 1879). this precursor to the use of plaster of paris jackets was independently arrived at by different people (see schuchert and levene, 1940). ultimately, however, we will never know what happened to this and other cope specimens that went missing. paleobiogeographical implications maraapunisaurus fragillimus as a rebbachisaurid has profound paleobiogeographical and temporal implications. previously, rebbachisaurids were only known from the cretaceous and have not been report240 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 ed from north america. however, the phylogenetic study by wilson and allain (2015) estimated a 20-million-year ghost lineage for rebbachisaurids extending back to the late jurassic, and thus to the age of maraapunisaurus. this 20-million-year ghost lineage has been shortened recently to 10 million years by xenoposeidon (taylor, 2018). the previous absence of rebbachisaurids from north america does not exclude maraapunisaurus from being the first reported. suuwassea, for example, has only recently been identified as a dicraeosaurid from the morrison formation, making it the first (whitlock, 2011). although maraapunisaurus is a basal rebbachisaurid because of the presence of a hyposphene (shared with histriasaurus, comahuesaurus, and demandasaurus), it also has pneumatic chambers dorsolateral to neural canal as in comahuesaurus, demandasaurus, and rebbachisaurus, but which is apparently lacking in histriasaurus. the neural arch is also very tall and is proportional to that of rebbachisaurus. thus, in some ways maraapunisaurus is more derived than other basal rebbachisaurids, especially histriasaurus in a few of its features (figure 5). the coeval presence of maraapunisaurus and diplodocids in the morrison formation raises interesting issues about the paleobiogeographical origins of rebbachisaurids. the late jurassic age for maraapunisaurus does support the hypothesis for a middle jurassic split of the diplodocoids into the diplodocids and rebbachisaurids (sereno and others, 2007; wilson and allain, 2015). given that there is greater similarities between late jurassic and pre-aptian faunas of north america and europe (galton, 1980; kirkland and others, 1997, 2016; carpenter and others, 2002; carpenter, 2006b; mateus, 2006) than there is between north and south america for the same time interval, it seems more probable that the migration of rebbachisaurids was from north america to europe during the latest late jurassic and earliest early cretaceous, with a later arrival in south america via europe and africa (figure 8). this direction of migration is the reverse to that previously hypothesized (torcida fernandez-baldor and others, 2011; fanti and others, 2013). nevertheless, temporal distribution does seem to support this possibility (figure 8c) and that the presence of post-berriasian–pre-aptian rebbachisaurids in africa are predicted. discussion and conclusion it has been over 140 years since oramel lucas discovered the giant neural spine that was named amphicoelias fragillimus by edward cope in 1878. this specimen was lost prior to 1902, the year the cope reptile collection was transferred to the american museum of natural history. the specimen has long been referred to amphicoelias altus, which is now considered a basal diplodocoid (whitlock, 2011). reanalysis of cope’s description and figure demonstrate at least two unambiguous rebbachisaurid characters: the festooned spinodiapophyseal lamina and pneumatic neural spine. because the specimen cannot be referred to the genus amphicoelias, a new name is proposed, maraapunisaurus fragillimus (cope, 1878f). as a rebbachisaurid, maraapunisaurus from the late jurassic of north america is both the oldest rebacchisaurid and the first from north america and it may be the center of the group's origin. acknowledgments special thanks to pat monaco and the late donna engard for sharing various documents pertaining to oramel lucas. these are now housed at the royal gorge regional museum and history center, cañon city, colorado. andrew smith and melissa smeins (bureau of land management, royal gorge field office, cañon city, colorado), and dan grenard (unafilliated, cañon city, colorado) made additional documents from the garden park paleontology society available. thanks to fabio m. dalla vecchia (institut català de paleontologia miquel crusafont, sabadell, spain) for sharing his unpublished illustration of histriasaurus boscarollii. thanks to ursula göhlich and andreas kroh (natural history museum vienna and jürgen kriwet, university of vienna), for searching their collections for the holotype of nopcsaspondylus alarconensis; the specimen remains lost. the name maraapunisaurus was suggested by hanley frost, sr., edward box iii, and garrett briggs of the southern ute cultural department, ignacio, colorado. i am pleased to acknowledge that zachary taylor ward armstrong (independent 241 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 figure 8. paleogeographic maps showing the distribution of rebbachisaurids during the late jurassic (a) and early cretaceous (b). abbreviations: m–maraapunisaurus (kimmeridgian-tithonian), a–amazonsaurus (aptian-albian), c–comahuesaurus (aptian-albian), d–demandasaurus (upper barremian-lower aptian), h–histriasaurus (upper hauterivian-lower barremian), n–nigersaurus (aptian-albian), t–tataouinea (albian), x–xenoposeidon (berriasian-valanginian), and z–zapalasaurus (barremian-lower aptian). (c) temporal and paleogeographic distribution of late jurassic and early cretaceous rebbachisaurids. paleogeographic maps from the commercial version of ron blakey’s “paleogeography of western north america” that is licensed to the prehistoric museum. 242 maraapunisaurus fragillimus, n.g. (formerly amphicoelias fragillimus), a basal rebbachisaurid from the morrison formation (upper jurassic) of colorado carpenter, k. geology of the intermountain west 2018 volume 5 dinosaur blogger) who independently considered the possibility that amnh fr 5777 was a rebbachisaurid four years before me in his blog: https://palaeozoologist. deviantart.com/journal/was-amphicoelias-a-rebbachisaur-440611550. i came to a similar conclusion based on carvalho and santucci (2018) and apesteguía and others (2010). finally, review comments by greg paul (independent dinosausr artist), john whitlock (mount aloysius college), mike taylor (university of bristol), and john foster (museum of moab) are gratefully acknowledged. references almy, k.j., 1987, thof ’s dragon and the letters of capt. theophilus turner, m.d., u.s. army: kansas history, v. 10, no. 3, p. 170–200. anonymous, 1878, international measures: bulletin of the american metric bureau, v. 20, p. 316–317. anonymous, 1899, cope collection lost: the philadelphia record, december 30, no. 10,166, p. 10, https://news.google.com/ newspapers?nid=qdewnzbrhwac&dat=18991230&printsec=frontpage&hl=en (accessed august 29, 2018). apesteguía, s., 2005, evolution of the hyposphene–hypantrum complex within sauropoda, in tidwell, v., and carpenter, k, editors, thunder-lizards—the sauropodomorph dinosaurs: bloomington, indiana press university, p. 248–267. apesteguía, s., 2007, the sauropod diversity of the la amarga formation (barremian), neuquén (argentina): gondwana research, v. 12, p. 533–546. apesteguía, s., gallina, p.a., and haluza, a., 2010, not just a pretty face—anatomical peculiarities in the postcranium of rebbachisaurids (sauropoda: diplodocoidea): historical biology, v. 22, no. 1–3, p. 165–174, doi: 10.1080/08912960903411580. bonaparte, j.f., 1997, rayososaurus grioensis bonaparte 1995: ameghiniana, v. 34, no. 1, p. 116. calvo, j.o., and salgado, l., 1995, rebbachisaurus tessonei sp. nov. a new sauropoda from the albian-cenomanian of argentina; 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dinosaur: peerj 6:e5212, doi: 10.7717/peerj.5212. torcida fernández-baldor, f., canudo, j.l., huerta, p., montero, d., pereda suberbiola, x., and salgado, l., 2011, demandasaurus darwini, a new rebbachisaurid sauropod from the early cretaceous of the iberian peninsula: acta palaeontologica polonica, v. 56, no. 3, p. 535–552. upchurch, p., 1998, the phylogenetic relationships of sauropod dinosaurs: zoological journal of the linnean society, v. 124, p. 43–103. whitlock, j.a., 2011, a phylogenetic analysis of diplodocoidea (saurischia: sauropoda): zoological journal of the linnean society, v. 161, p. 872–915, doi: 10.1111/j.10963642.2010.00665.x. wilson, j.a., 1999, a nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs: journal of vertebrate paleontology, v. 19, no. 4, p. 639-653, doi:10.1080/02724634 .1999.10011178. wilson, j.a., 2002, sauropod dinosaur phylogeny—critique and cladistic analysis: zoological journal of the linnean society, v. 136, p. 217-276. wilson, j.a., and allain, r., 2015, osteology of rebbachisaurus garasbae lavocat, 1954, a diplodocoid (dinosauria, sauropoda) from the early late cretaceous–aged kem kem beds of southeastern morocco: journal of vertebrate paleontology, v. 35, no. 4, unpaginated, e1000701, doi: 10.1080/02724634.2014.1000701. wilson, j.a., d’emic, m.d., ikejiri, t., moacdieh, e.m., and whitlock, j.a., 2011, a nomenclature for vertebral fossae in sauropods and other saurischian dinosaurs: plos one 6(2): e17114. doi:10.1371/journal.pone.0017114 (accessed february 9, 2018). woodruff, c., and foster, j.r., 2014, the fragile legacy of amphicoelias fragillimus (dinosauria: sauropoda; morrison formation—latest jurassic): volumina jurassica, v. 12, no. 2, p. 211–220. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming john r. foster, darrin c. pagnac, and rebecca k. hunt-foster theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover a few of the elements from the little houston quarry biota represented by individual fossils. left to right and by approximate row top to bottom: nanosaurus femur; seed; dromaeosaurid tooth; unionid bivalve shell imprint; salamander vertebra; nanosaurus tooth; docodon jaw; theriosuchus jaw; abelisauroid(?) tooth; and cteniogenys jaw. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors society of vertebrate paleontology editors kelli c. trujillo — university of wyoming cary woodruff — university of toronto octavio mateus — universidade nova de lisboa douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees education/scholarship zack anderson zanderson@utah.gov 801.538.4779 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 29 abstract the little houston quarry in the black hills of wyoming contains the most diverse vertebrate fauna in the morrison formation (upper jurassic) north of como bluff and the second-most diverse in the entire formation, after reed’s quarry 9. the deposit was an occasionally reactivated abandoned river channel, in interbedded green mudstone and laminated green-gray siltstone above a channel sandstone. the dinosaur material is densely distributed and is disarticulated to articulated, with several associated skeletons. the biota contains charophytes, horsetails, a possible seed fern, possible conifers, gastropods, two types of unionoid bivalves, diplostracans (“conchostracans”), a malacostracan, ray-finned fish, lungfish, a frog, salamanders, two types of turtles, rhynchocephalians, a lizard, choristoderes, two types of crocodyliforms, a pterosaur, allosaurus and several types of small theropods including tanycolagreus? and probable dromaeosaurids, numerous camarasaurus and a diplodocine sauropod, a stegosaur, the neornithischian nanosaurus, and the mammals docodon, amblotherium, and a multituberculate. among these taxa, one of the unionoid bivalves, an atoposaurid crocodyliform, and the species of amblotherium, which appear to be new and unique to the locality so far. the docodon material may represent the first occurrence of d. apoxys outside of its type area in colorado. additionally, small, unusual theropod tooth types reported here may represent the first late jurassic occurrence of cf. richardoestesia in north america and a possible abelisauroid, respectively. an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming john r. foster1, darrin c. pagnac2, and rebecca k. hunt-foster3 1utah field house of natural history state park museum, 496 east main st., vernal, ut 84078; johnfoster@utah.gov 2museum of geology, south dakota school of mines and technology, 501 east st. joseph, rapid city, sd 57701 3dinosaur national monument, p.o. box 128, jensen, ut 84035 citation for this article. foster, j.r., pagnac, d.c., and hunt-foster, r.k., 2020, an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming: geology of the intermountain west, v. 7, p. 29–67, https://doi.org/10.31711/giw.v7.pp29–67. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the morrison formation (upper jurassic) has been known as a massively productive unit for large dinosaurs since the second half of the nineteenth century (dodson and others, 1980; ostrom and mcintosh, 1999). microvertebrate taxa were identified in the formation relatively early on (marsh, 1879; gilmore, 1910, 1928) but large samples of such taxa were restricted to only a handful of sites until relatively recently. work from the past few years has suggested that microvertebrate taxa, and specifically aquatic and semi-aquatic taxa, may be more abundant in the formation than commonly appreciated (foster and trujillo, 2004; foster and heckert, 2011; foster and mcmullen, 2017) and that the morrison may show some paleobiogeographic zonation based on these small taxa and their preferred environments for habitat and preservation (chure and evans, 1998; foster and trujillo, 2000; foster and others, 2006; foster and mcmullen, 2017). paleobiogeo30 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 graphic zonation is also becoming apparent for some groups of dinosaurs within the morrison. the black hills have yielded morrison formation taxa since o.c. marsh (1890a) described the first specimen of barosaurus, which had been partially collected by marsh with j.b. hatcher in 1889 (marsh sent g.r. wieland to collect more of the specimen in 1898). smithsonian (usnm) and american museum (amnh) crews collected diplodocid and camarasaurid specimens from the sturgis, south dakota, area around 1900–1901, and the south dakota school of mines and technology (sdsm) collected mostly sauropod material from sites near spearfish and blackhawk, south dakota, and adjacent to inyan kara creek in wyoming, although theropods, turtles, and crocodyliforms were found at some sites (foster, 1996a, 1996b; foster and chure, 2000). more than a dozen vertebrate localities are now known from the black hills (foster, 1992, 1996a, 1996b, 2003; maltese and others, 2018), and the most productive of these so far is the little houston quarry, west of sundance in crook county, wyoming (figure 1; foster, 1993, 2001; foster and martin, 1994). the little houston quarry was first developed in june 1991 and was worked annually through 2000 by the sdsm and from 2004–2011 by sdsm and the museums of western colorado. the most diverse fauna of vertebrates known from the northern part of the morrison formation is found in the little houston quarry. this paper describes the richness of that fauna and several unique taxa from it that may be endemic to northern parts of the formation minimally and possibly to the black hills specifically. institutional abbreviations amnh–american museum of natural history, new york, new york; fmnh–field museum of natural history, chicago, illinois; mwc–museums of western colorado, dinosaur journey, fruita, colorado; sdsm– south dakota school of mines and technology, museum of geology, rapid city, south dakota; usnm– national museum of natural history, smithsonian institution, washington, d.c.; ebg–field numbers of darrin pagnac for 1996–2000 field seasons, uncatalogued material at sdsm; jrf–field numbers of john foster for 1991–2000 field seasons, uncatalogued material at sdsm. geologic setting and locality the morrison formation in the northwestern black hills is unusually thin (~24 m; mapel and pillmore, 1963) compared to most outcrops of the unit farther south and west, and it consists of red, gray, and green, non-smectitic mudstones (tank, 1956) with only a few thin, lenticular and laterally restricted sandstone beds (foster, 1992; turner and peterson, 1999). in the eastern and southeastern black hills the lower member of the formation consists of an eolian sandstone (the unkpapa sandstone member; szigeti and fox, 1981) that is overi-25 i-90 w yo m in g lhq site 50 km wyoming so u th d a ko ta jackson laramie sheridan casper sundancegillette devils tower nm newcastle i-90 figure 1. location of the little houston quarry (red star) on the northwestern edge of the black hills in crook county, northeastern wyoming, and within the united states. 31 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 lain by an unnamed light gray to green silty mudstone facies that probably represents wet environments bordering the unkpapa dune field to the south. most of the fossil sites in the morrison of the eastern and southeastern black hills occur in this latter facies (foster, 1996b). in the northwestern black hills, the red, gray, and green mudstones have a more “traditional” appearance for the morrison formation, aside from the overall thinness, the lack of smectitic mudstones, and the very thin and restricted channel sandstones (foster, 1992; foster and martin, 1994). the little houston quarry consists of two pits, the main and mammal (figures 2a, 3a, and 3b), in the same abandoned channel deposit, separated laterally by approximately 70 m but easily correlated visually, as the channel cut down into variegated mudstones exposed on either side (foster and martin, 1994). the matrix of the quarry is an interbedded interval of green claystone and thinly laminated siltstone with abundant bone fragments and clayballs (figure 2b), which rests immediately above a thin, convex-bottomed channel sandstone. laterally, the deposit matrix and the bone material are figure 2. (a) the south (main) pit of the little houston quarry in the morrison formation of the black hills. the north (mammal) pit was illustrated as a cover photo in foster (2018). (b) interbedded green mudstone and lighter green-gray laminated siltstone (with lens cap for scale) of the little houston quarry above a thicker siltstone interval containing a sauropod humerus. (c) ilium and metatarsal of an associated juvenile allosaurus jimmadseni skeleton (see foster and chure, 2006) at the little houston quarry. u.s. quarter for scale. (d) left humerus of camarasaurus and femur of diplodocine(?) at the little houston quarry, brunton indicating north. 32 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 restricted to the layers above the channel, which is up to 20 m wide. dinosaur material at the site is largely associated to articulated (figures 2c and 2d), with a significant number of isolated elements as well. microvertebrate material is mixed in with the same layers as the articulated dinosaur elements, often concentrated in two 1to 10-cm-thick layers separated vertically by 15 to 30 cm within the interbedded mudstone and laminated siltstone above the channel sandstone. dinosaur material in the quarry is abundant and densely concentrated, with up to 25% of material in articulation (figures 3a and 3b; for articulation percent comparison with other localities see foster and others, 2018). camarasaurus elements are particularly abundant, with sections of at least four adult individuals in articulation. material and methods fossil material was collected from the little housa n b little houston quarry maps main pit grid squares = 1 m pit black lines: excavation walls mamma pit approximately 70 m north of main pit red: allosaurus green: camarasuarus light purple: diplodocinae light blue: sauropoda indet. mammal pit dark blue: dinosauria indet. orange: nanosaurus tan: tanycolagreus? figure 3. quarry maps of the little houston quarry. (a) map of main pit. (b) map of mammal pit. each map grid square = 1 m. 33 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 ton quarry each summer continuously from 1991 to 2000 and again from 2004 to 2011, principally by the sdsm’s museum of geology but also by the mwc (foster, 1992, 1993, 1996a, 1996b, 2001, 2018; foster and martin, 1994; martin and foster, 1998; pagnac, 1998; foster and trujillo, 2000, 2018; foster and others, 2018). the biota consists of at least 35 taxa, including four plants, five invertebrates, and 26 vertebrates (table 1). foster (2001) assessed the relative abundances and taphonomy of taxa found through the 2000 field season, but the full biota has never been described or illustrated in detail. specimens were compared to existing museum collections and published illustrations of other material. theropod tooth terminology used in tooth descriptions incorporates terms of hendrickx and others (2015) whereas that for mammals utilizes those of kielan-jaworowska and others (2004). cladistic analysis utilized mesquite 3.0 and tnt 1.5. systematic paleontology plantae chlorophyta charophyta indet. three charophyte oogonia have been found in the little houston quarry over the years, but all were lost in the course of study due to unfortunate laboratory mishaps before they could be photographed. there are at least six genera of charophytes known from the morrison formation, and they have been reported at least from the piedmont area of the black hills (south dakota), in addition to the unidentified taxa reported from little houston here (schudack and others, 1998). polypodiopsida equisetales equisetum sp. one plant specimen (jrf 95153) has been identified as a stem of a relatively large horsetail, probably equisetum (figure 4a). horsetail fossils are relatively common in the morrison formation, both in wyoming and the colorado plateau (tidwell and others, 1998, 2006; ash table 1. biota list of taxa known from the little houston quarry, morrison formation, crook county, wyoming. plantae chlorophyta charophyta indet. polypodiopsida equisetales equisetum sp. polysporangiophytes tracheophytes pteridospermatophyta? gymnosperma? indet. metazoa mollusca gastropoda amplovalvata sp. bivalvia unionidae indet. (“unio” stewardi?) unionida indet., new genus? arthropoda malacostraca? crayfish? diplostraca “conchostracans” chordata osteichthyes actinopterygii actinopterygii indet. scale type a actinopterygii indet. scale type b actinopterygii indet. scale type c sarcopterygii dipnoi ceratodus fossanovum amphibia anura indet. caudata indet. reptilia testudinata dinochelys whitei glyptops plicatulus testudinata indet. rhynchocephalia opisthias? squamata cf. paramacellodus archosauria choristodera cteniogenys antiquus crocodylomorpha crocodyliformes atoposauridae theriosuchus morrisonensis goniopholididae? indet. crocodyliformes indet. archosauria indet. pterosauria pterosauria indet. dinosauria saurischia theropoda tetanurae allosauroidea allosaurus jimmadseni coelurosauria tanycolagreus? dromaeosauridae indet. theropoda indet. tooth type a (cf. richardoestesia?) tooth type b tooth type c tooth type d (abelisauroid?) tooth type e sauropoda diplodocidae diplodocinae indet. macronaria camarasauridae camarasaurus sp. ornithischia thyreophora stegosauridae indet. neornithischia nanosaurus agilis mammalia docodonta docodon cf. apoxys multituberculata allodontidae indet. dryolestida dryolestidae amblotherium megistodon n. sp. 34 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 and tidwell, 1998), and this fossil represents one of the larger specimens reported from the unit. polysporangiophytes tracheophytes pteridospermatophyta? one specimen (jrf 9411) represents a small, well preserved seed less than 2 mm in diameter (figure 4b). it appears to consist of a complete seed with ribbed integument, possibly from an indeterminate seed fern (c. gee, university of bonn, written communication, 2018). gymnospermae? indet. carbonized, roughly rectangular (and sometimes relatively thick) plant fragments (represented by sdsm 25305, figure 4c) are the most abundant plant material in the deposit. it is unclear what element or taxon these represent, although one hypothesis is that they are partial cone or seed scales of conifers (e.g., tidwell, 1998; eckenwalder, 2009) or, alternatively, cycad leaf-scales such as those of cycadolepis (e.g., tidwell and others, 1998). metazoa mollusca gastropoda amplovalvata sp. several gastropods have been found in the little houston quarry, and at least one of these (jrf 9359; figure 5a) appears to belong to the genus amplovalvata (yen, 1952; evanoff and others, 1998), although it is not well preserved enough to identify to species. bivalvia unionida unionidae indet. specimens of unionids are relatively abundant in the deposit, and most are preserved as impressions in the siltstone matrix; however, one specimen from the underlying sandstone preserves the shell nearly intact. none of these specimens is well preserved enough to be certain of their identifications within unionidae, but one large (~8 cm) specimen (figure 5b) and the one preserving shell material (figures 5c and 5d) may represent “unio” stewardi or “u.” felchi, and either “unio” sp. or possibly vetulonaia, respectively (branson, 1935; evanoff and others, 1998). unionida indet., new genus? most abundant in the little houston quarry, however, is an unusual unionoid consisting of very elongate shell valves and often preserved as impressions of articulated but open shells (figures 5e and 5f). unionids with this degree of relative elongation (up to 4.6:1) have figure 4. representative plant material from the little houston quarry. (a) horsetail stem equisetum sp., jrf 95153, scale bar = 1 cm. (b) seed of possible pteridospermatophyte (seed fern), jrf 9411, scale bar = 1 mm. (c) carbonized impression of possible cone scale or cycadophyte leaf-scale, sdsm 25305, scale bar = 1 cm. 35 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 not previously been reported from the morrison formation (branson, 1935; yen, 1952; evanoff and others, 1998; good, 2004). among modern unionoids such elongate shell dimensions are known in several genera of the families unionidae and mycetopodidae (anderson, 2014), and these taxa live in a range of freshwater environmental settings, including in muds and sands or firm grounds of rivers or oxygenated to dysoxic lake beds. further identification of this taxon in the little houston quarry will require additional material. arthropoda malacostraca? one small specimen (mwc 5640) appears to be the incomplete posterior walking leg of a small crayfish or other malacostracan (figure 6). the specimen is less than 1 cm long and appears to consist of three to five figure 5. representative little houston quarry mollusca. (a) impression of gastropod amplovalvata sp., jrf 9359, scale bar = 1 cm. (b) impression of indeterminate unionoid, scale bar = 5 cm. (c and d) indeterminate unionoid shell, scale bars = 1 cm. (e) impressions of indeterminate elongate unionoids, scale bar = 5 cm. (f) overview of same slab as in (e), showing additional specimens, scale bar in cm. (b to f) all sdsm unnumbered. 36 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 podomeres, including a spinose dactylus, the propodus, and carpus, but the nature of the more proximal elements is unclear. the leg is similar in size to an isolated, more anterior walking appendage from the fruita paleontological area in western colorado illustrated by hasiotis and others (1998); the limbs of a nearly complete crayfish from the mygatt-moore quarry in western colorado, illustrated by foster and others (2018), are too poorly preserved to compare. diplostraca several diplostracans (previously referred to as “conchostracans;” martin and davis, 2001) have been found in the quarry (e.g., jrf 9521, not figured), but they are very rare. previous studies of morrison diplostracans indicate that there are at least four taxa, mostly in colorado and utah (lucas and kirkland, 1998). chordata osteichthyes actinopterygii indet. actinopterygian fish are represented by many elements from the little houston quarry, including numerous upper and lower jaw fragments (figure 7), and three types of scales similar to those illustrated from other sites by kirkland (1998) and foster and heckert (2011). the scales include abundant, tiny ganoid scales (figures 7a and 7b), whereas the jaw elements include a diverse sample of upper and lower elements, with almost no two the same (figures 7c to 7i). one fish specimen appeared in the field to be an operculum and pectoral fin of a large amioid, but this specimen has not yet been prepared. dipnoi ceratodus fossanovum there are a number of species of lungfish known from the morrison formation, including ceratodus fossanovum, ceratodus robustus, and potamoceratodus guentheri (kirkland, 1987, 1998; pardo and others, 2010), each best distinguished on tooth plate morphology. lungfish are known from several specimens at the little houston quarry, including a left dentary and tooth plate (figure 7j), along with several isolated tooth plates. the tooth plates of most of these specimens, including that of the left lower jaw (mwc 6505), are most similar to ceratodus fossanovum in having a more obtuse inner angle, lower ridges, and a lingual crushing surface; c. fossanovum is also known from quarry 9 at como bluff and from ninemile hill, wyoming (kirkland, 1998; trujillo, 1999). amphibia anura indet. frogs are represented by a single distal half of a humerus with the preserved shaft and trochlea (figure 8a); this specimen is just over 6 mm long and is the only evidence of frogs from the morrison formation north of como bluff, wyoming. the morrison contains a pelobatid frog and the discoglossid enneabatrachus at quarry 9 and the pipoid rhadinosteus at dinosaur national monument (evans and milner, 1993; henrici, 1998), although this partial humerus cannot be identified more precisely. caudata indet. salamanders are known from just a handful of figure 6. crayfish walking leg from little houston quarry, mwc 5640, scale bar = 1 cm. 37 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 figure 7. representative little houston quarry osteichthyan fish fossils. (a) ganoid scale, jrf 9470. (b) ganoid scale, jrf 9588. (c) maxilla(?) fragment with teeth, jrf 95232. (d) maxilla(?) fragment with teeth, jrf 9529. (e) maxilla(?) fragment, jrf 9572. (f) dentary(?) fragment with teeth, jrf 95138. (g) maxilla(?) fragment, sdsm specimen. (h) dentary(?) fragment with teeth, mwc 5762. (i) jaw fragment with two teeth, mwc 5779. (j) lungfish ceratodus fossanovum, left dentary and tooth plate, mwc 6505. scale bars a and b = 2 mm; all other scale bars = 1 cm. 38 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 strongly amphicoelous vertebrae with dorsoventrally elongate diapophyses (figures 8b to 8g). most morrison salamander vertebrae are fairly small, but a few are somewhat larger (evans and milner, 1993), suggesting at least two different-sized groups. the specimen illustrated here is of the larger size class (centra ~5 mm length). some morrison salamanders such as iridotriton (evans and others, 2005) are significantly smaller than the taxon illustrated here from the little houston quarry. reptilia testudinata dinochelys whitei the relatively smooth-shelled turtle dinochelys (gaffney, 1979) is the most abundant turtle in the deposit, outnumbering glyptops significantly. many preserved pleural elements are small and preserved intact and unbroken with unfused sutures, suggesting many of the individuals preserved were juveniles (figures 9a to 9c). at least one shell fragment was found with the laterally radiating dorsal ridges typical of young juveniles (gaffney, 1979). glyptops ornatus the turtle glyptops is known from a number of shell fragments exhibiting strong sculpturing (marsh, 1890b; hay, 1908; figures 9d to 9e); it is far less abundant in the little houston quarry than dinochelys. testudinata indet. many limb and some axial elements of indeterminate turtles are known from the quarry, including humeri, femora, a tibia, and sacral vertebrae (figures 9f to 9i). these cannot be identified to genus but indicate the abundance of turtles generally in the deposit. rhynchocephalia opisthias? the sphenodontian opisthias? is represented by several small dentary fragments, a palatine, and an indeterminate jaw fragment (figures 10a to 10f). the two apparent dentary fragments illustrated here (figures 10c to 10f) are approximately the same size and the first of these (figures 10c and 10d) may be more fragmentary or may represent a morphotype with relatively larger teeth. rhynchocephalians are numerous in the morrison formation (foster, 2003) though not, as far as we currently recognize, particularly diverse, with three genera currently represented: opisthias, theretairus, and the large, herbivorous eilenodon (gilmore, 1910; simpson, 1926; rasmussen and callison, 1981; jones and others, 2018). recent analyses suggest there may be a previously hidden diversity of rhynchocephalians in the morrison formation (demar and others, 2018), although the material from the little houston quarry is not complete enough to identify further. figure 8. little houston quarry amphibia. (a) frog humerus, distal half in anterior view, jrf 9545. (b to g) caudata (salamander) vertebra in (b) anterior, (c) posterior, (d) left lateral, (e) right lateral, (f) dorsal, and (g) ventral views. all scale bars = 5 mm. 39 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 squamata cf. paramacellodus lizards are represented by a single tiny dentary just 6 mm long. it preserves 11 short, blunt teeth suggestive of a scincomorph and is likely a paramacellodid (figure 10g). the scincomorphs of the morrison formation include paramacellodus, saurillodon, and schillerosaurus (prothero and estes, 1980; evans and chure, 1998, 1999). the little houston quarry jaw is not as short and deep as the dentary in saurillodon (broschinski, 2000) nor apparently as slender (dorsoventrally shallow) as schillerosaurus, but it is similar to several specimens of paramacellodus from dinosaur national monument figure 9. representative little houston quarry turtles. (a) dinochelys pleural, mwc 5780. (b) dinochelys pleural, sdsm specimen. (c) dinochelys pleural, sdsm specimen. (d) glyptops pleural fragment, sdsm specimen. (e) glyptops pleural fragment, sdsm 25343. (f) testudinata indet., right humerus, mwc 5783. (g) testudinata indet., left femur, sdsm 25246. (h) testudinata indet., tibia(?), jrf 9528. (i) testudinata indet., sacral vertebra, mwc 5865. all scale bars = 1 cm. 40 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 figure 10. representative little houston quarry lepidosauria. (a to f) opisthias?, rhyncocephalia. (a) left palatine in lateral view, mwc specimen. (b) indeterminate jaw fragment in lateral view, mwc specimen. (c and d) dentary(?) fragment in (c) labial and (d) lingual views, ebg 9833. (e and f) right dentary fragment (mwc specimen) in (e) labial and (f) lingual views. (g) small cf. paramacellodus (scincomorpha, squamata) right dentary in labial view, jrf 95102. scale bars = 5 mm. 41 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 (evans and chure, 1998) in its proportions and overall structure. choristodera cteniogenys antiquus choristoderes are relatively abundant in the deposit, being represented by numerous isolated vertebrae, and several upper and lower jaw fragments (figure 11). cteniogenys was a small (~25 cm long) semiaquatic choristodere common in the late jurassic of north america and europe (gilmore, 1928; evans, 1990). it appears to have been significantly more abundant in the eastern and northern parts of the morrison formation than it was in what is now the colorado plateau region (chure and evans, 1998; foster and trujillo, 2000). crocodylomorpha crocodyliformes atoposauridae theriosuchus morrisonensis this newly named species of atoposaurid crocodyliform (foster, 2018) was based on a lower mandible found in the little houston quarry in 2004 (figures 12a to 12c). the jaw indicates an atoposaurid similar to theriosuchus pusillus and knoetschkesuchus was present in at least the northern region of the morrison formation. goniopholididae? indet. several isolated teeth at the site appear to belong to relatively large crocodyliforms, probably goniopholidids (figure 12d). the form and size of the teeth is essentially indistinguishable from goniopholidids from the morrison formation, such as eutretauranosuchus and amphicotylus (mook, 1967; smith and others, 2010; allen, 2012). crocodyliformes indet. relatively abundant and not particularly large crocodyliform osteoderms from the quarry could be those of goniopholidids, although these are not dorsal armor with the rectangular plates and anterior projections typical of that family. these are squarish to almost oval in shape (figures 12e to 12f) and could conceivably belong to any of several families of crocodyliforms. archosauria indet. one tiny premaxilla appears to belong to an indeterminate small archosauromorph (figure 12g). this small specimen has 5 to 6 conical teeth, a tall nasal process, a thick maxillary process, and is anteroposteriorly relatively short. pterosauria pterosauria indet. pterosaurs are represented by a single, elongate tooth with a tall conical and slightly recurved crown, a long root, and an oval to slightly laterally compressed cross section (mwc 5809; figures 12h to 12i). this is a general form typical of some pterosaurs (wellnhofer, 1991; witton, 2013), and it is rather similar in overall appearance to an anterior dentary tooth from the breakfast bench facies at como bluff described by mclain and bakker (2017). isolated pterosaur teeth are also preserved at quarry 9 at como bluff (carrano and velez-juarbe, 2006). dinosauria saurischia theropoda tetanurae allosauroidea allosaurus jimmadseni a juvenile allosaurus partial skeleton from little houston quarry (figure 2c) was described and illustrated by foster and chure (2006) and was referred to a. jimmadseni by chure and loewen (2020). this specimen (sdsm 30510) demonstrated the extreme elongation of the hindlimb relative to ilium length in juveniles of the genus compared with adults. it is also one of the more complete associated skeletons of a very young individual of the genus yet reported, consisting of cervicals, a dorsal, a sacral, both ilia, caudals, an ischium, 42 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 figure 11. representative little houston quarry cteniogenys (choristodera). (a) left maxilla in labial view, sdsm specimen. (b and c) right dentary fragment, mwc 6504, in (b) lingual view and fragment with well-preserved teeth (missing from (b) in (c) labial view. (d) dentary fragment, jrf 95216. (e) vertebra in dorsal view, sdsm specimen. (f) dentary with teeth, small individual, jrf 95100. scale bars = 1 cm, except e = 5 mm. 43 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 figure 12. representative little houston quarry crocodyliformes, pterosauria, and archosauromorpha indet. (a to c) left mandible of theriosuchus morrisonensis, mwc 5625, in (a) labial, (b) lingual, and (c) occlusal views. (d) tooth of goniopholididae(?), sdsm 25337. (e) osteoderm of crocodyliformes indet., jrf 9571. (f) osteoderm of crocodyliformes indet., jrf 95211. (g) archosauromorpha indet., premaxilla with teeth in lingual(?) view, jrf 95208. (h and i) tooth of pterosauria indet., mwc 5809; tooth tip in h) and base of crown plus root in i). scale bars: a to c = 5 cm; d to f and h to i = 1 cm; g = 5 mm. 44 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 femur, tibia, metatarsals, and manual and pedal phalanges and unguals (foster and chure, 2006). a partial skeleton of an adult allosaurus was also collected from the main pit (figure 3a), consisting of posterior dorsal vertebrae, a sacrum and both ilia, anterior caudal vertebrae, and a femur; preparation of this specimen is still being completed. several teeth assigned to allosaurus are also known from the quarry (figures 13k and 13l). these are relatively large teeth (~19 to 27 mm crown height) with denticles that are neither as coarse as in torvosaurus nor as fine as in ceratosaurus and with a distinctive cross-sectional shape similar to allosaurus (madsen, 1976; madsen and welles, 2000; bakker and bir, 2004). other elements representing the adult allosaurus from the quarry include a quadrate, premaxilla (foster and martin, 1994), dentary fragment, and dorsal and caudal vertebrae. coelurosauria maniraptora tanycolagreus? a single right metatarsal ii, collected from the mammal pit at the little houston quarry, appears to belong to a small theropod (figures 13a and 13b). the metatarsal is too elongate to belong to allosaurus (even a juvenile), ceratosaurus, or torvosaurus and is too robust to be coelurus (madsen, 1976; britt, 1991; madsen and welles, 2000; carpenter and others, 2005a) and too large to be ornitholestes or koparion (assuming the latter was as small as its lone tooth suggests). however, this specimen is essentially indistinguishable in proportions and articular end shapes from the metatarsals of tanycolagreus (carpenter and others, 2005b). the pes of stokesosaurus and marshosaurus is unknown in both. the little houston metatarsal is here tentatively identified as tanycolagreus?, possibly the first occurrence of the taxon north of bone cabin quarry in southern wyoming. dromaeosauridae indet. a single isolated tooth from the quarry (figures 13e to 13g) is small, short, recurved, and laterally compressed (10.8 mm crown height), with strong serrations on the distal carina (4/mm) and only small indistinct serrations on the mesial carina. the distal serrations are slightly hooked apically, and in most of these characters the tooth is similar to those of dromaeosaurus, saurornitholestes, and sinornithosaurus among dromaeosaurids (currie and others, 1990; farlow and others, 1991; fiorillo and currie, 1994; xu and wu, 2001; larson and currie, 2013). it is a relatively large tooth at nearly 11 mm, with fine serrations on the distal carina. the tooth dimensions and denticle characteristics are similar to those of possible dromaeosaurid tooth morphotypes 5 and 6 reported from the middle-late jurassic shishugou formation of china (han and others, 2011). overall tooth shape is also similar to teeth from guimarota (late jurassic of portugal) referred to compsognathus (zinke, 1998), although overall size and the distal denticles are both larger in the little houston specimen. hendrickx and mateus (2014) referred a similar tooth from the late jurassic of lourinhã, portugal, to richardoestesia, although the little houston tooth is approximately twice as large and has much larger denticles on the distal carina. the tooth is less strongly recurved than the morrison troodontid hesperornithoides (hartman and others, 2019) and less labiolingually bulbous than the troodontid koparion (chure, 1994). reports of dromaeosaurid-like teeth from the morrison formation have been rare, with only two teeth illustrated, from the dry mesa quarry in western colorado and the warm springs ranch site in northern wyoming (britt, 1991; ikejiri and others, 2006). the occurrence of dromaeosaurid (or at least dromaeosaurid-like) teeth in at least three deposits in the morrison formation, plus a number of dromaeosaurid teeth in the late jurassic of portugal, spain, germany, ethiopia, and china (zinke, 1998; rauhut, 2000; van der lubbe and others, 2009; han and others, 2011; hall and goodwin, 2011), suggests that this family was rare but certainly present in many areas of the globe during the late jurassic. in the morrison formation, isolated, partial bones of possible dromaeosaurs were reported by jensen and padian (1989), but those are the only nontooth evidence of the family in the formation. that no well-preserved skeletons of dromaeosaurids have been reported yet from the late jurassic may be indicative of their rareness at the time but may more likely be a result of taphonomic bias against smaller, more delicate material. 45 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 figure 13. representative little houston quarry theropoda (dinosauria). (a and b) right metatarsal ii of tanycolagreus?, jrf 95215, in (a) medial and (b) anterior views. (c) tooth of theropod tooth type a (cf. richardoestesia?), jrf 95222, and (d) in close-up showing serrations. (e to g) tooth of dromaeosauridae indet., jrf 95188, in (e) lingual(?), (f) labial(?), and (g) in close-up view of serrations. (h) tooth of theropod tooth type b, mwc specimen. (i and j) tooth of theropod tooth type c in (i) labial and (j) lingual views, jrf 9739. (k and l) teeth of allosaurus, sdsm specimen and jrf 9337. scale bars: a and b = 10 cm; c, e, f, and h to j = 5 mm; d = 2 mm; g = 1 mm; k and l = 1 cm. 46 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 despite the fragmentary evidence so far, it appears reasonable to conclude that dromaeosaurids were present in the morrison formation and that we might expect to find more complete elements in the future. theropoda indet. tooth type a (cf. richardoestesia?) a small (4.1 mm crown height) and laterally compressed tooth (figures 13c to 13d) differs from the dromaeosaurid tooth type described above in having a relatively taller crown, in being less recurved, and in having finer serrations on the distal carina (8/mm) that are shorter with more rectangular and blunt apical profiles. in these characteristics, the tooth type is roughly similar to many teeth assigned to richardoestesia (currie and others, 1990), a taxon which has been identified from the late jurassic of portugal (rauhut, 2000; mateus, 2006; malafaia and others, 2017). although the little houston quarry tooth is similar to some illustrated teeth of cretaceous richardoestesia in being somewhat recurved (currie and others, 1990), a few cretaceous and jurassic specimens are relatively tall and less recurved (see figure 6 in zinke, 1998; see figure 11.9 in rauhut, 2000; longrich, 2008). larson and currie (2013) demonstrated the difficulties, in many cases, of distinguishing species of richardoestesia and other small cretaceous theropod taxa, based on teeth, and this indirectly implies there may be difficulty in referring isolated teeth from other times or geographical areas to the genus. whatever taxon these possible cf. richardoestesia teeth from the morrison and elsewhere in the late jurassic represent, it is clear that the morrison and guimarota faunas, for example, were more diverse in small theropod taxa that was previously apparent and that they likely shared closely related or congeneric taxa with richardoestesia-like teeth. tooth type b another isolated small theropod tooth (figure 13h) from the quarry is roughly similar to tooth type a above but is less laterally compressed and the nature of the serrations is unclear. crown height for the specimen is 5.0 mm. in some general ways this tooth appears similar to those of coelurus (marsh, 1896) and ornitholestes (carpenter and others, 2005a) and especially to an unidentified theropod tooth type from guimarota, portugal (see figures 8a to 8d in zinke, 1998). tooth type c another tooth from the quarry appears to be a small anterior theropod tooth (figures 13i to 13j) with a wear facet and the serrated mesial carina curving distal-lingually; this tooth type may belong to a young allosaurus. it is 5.7 mm in crown height with 3.5 denticles per millimeter. tooth type d (abelisauroid?) a somewhat larger theropod tooth type (11 to 30 mm crown height, as preserved) from the quarry is the most unusual and consists of labiolingually thin, unrecurved teeth with slightly constricted crown bases and relatively distally tall serrations with very elongate, basally oriented interdenticular sulci. the first representative of these teeth (figures 14a to 14e) is approximately 11 mm in crown height; in labial or lingual view the mesial and distal carinae both curve symmetrically toward the apex so that the tooth is unrecurved, except for a very slight posterior(?) curvature at the tip. the tooth is labiolingually thin compared to its mesiodistal length and curves slightly lingually toward the apex. the tooth is serrated from apex to crown base along both mesial and distal carinae, and the lower portion of the mesial carina has approximately 5 denticles per millimeter. each denticle curves slightly apically at its distal end (figure 14e). the second representative of tooth type d is similar in overall shape but the apex is not preserved (figure 14f). it is larger than the first and was probably about 30 mm long when complete. the root of this tooth is missing, suggesting it is a shed tooth, and in lingual view the crown appears to have been very slightly constricted at its base, as in the first tooth described above. also in lingual view, the mesial and distal carinae both curve symmetrically toward the apex so that the tooth is unrecurved. despite being partially in matrix, the tooth can be seen in mesial or distal view to be strongly labiolingually compressed relative to its basal length. the serrations are more elongate proximodistally than 47 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 in most other theropod teeth from the morrison formation and the interdenticular sulci are long and distinct. on this larger tooth there are approximately two serration denticles per millimeter; each denticle curves slightly apically at its distal end. the enamel on the lingual surface is relatively smooth and neither concave figure 14. unusual little houston quarry theropoda (dinosauria) teeth. (a to e) jrf 94130. tooth of theropod tooth type d in (a) labial view, (b) distal view, (c) lingual view, and (d) mesial view. jrf 94130 is approximately 11 mm in height. (e) close-up of denticles of distal carina near base of crown, jrf 94130. (f) second specimen of theropod tooth type d, scale bar = 1 cm. (g) tooth of theropod tooth type e, ebg 9830, in lingual view and (h) with close-up of denticles as marked by white box in g. scale bars: g = 1 cm; h = 5 mm. (photos a to e courtesy of national park service.) 48 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 nor convex, but rather appears to be flat from a subtle central ridge out to the carinae. these teeth (figures 14a to 14f) share some distinct similarities to the procumbent anterior dentary or premaxillary teeth of the noasaurid abelisauroid masiakasaurus from the cretaceous of madagascar (carrano and others, 2002, figures 5a to 5c of fmnh pr 2180) in being thin, not distally recurved, and in having pinched crown bases in labial or lingual view. the little houston quarry teeth are not as thick nor as lingually curved toward the apex as in fmnh pr 2180, however, and are also similar to fmnh pr 2182 (carrano and others, 2002, figure 5e), although they are not recurved as in that masiakasaurus specimen. these similarities suggest that the type d morrison specimens (figures 14a to 14f) may represent the anterior teeth of an unknown smallto medium-sized abelisauroid or ceratosaurian. in the general characteristics of the serrations and overall shape, type d teeth are similar to other late jurassic teeth referred to abelisaurids from lourinhã, portugal (hendrickx and mateus, 2014) and to a possible carcharodontosaurid from the tendaguru formation of tanzania (rauhut, 2011). in overall shape the little houston specimens are also similar to lateral dentary teeth from a very small theropod jaw from guimarota in portugal (zinke and rauhut, 1994). no teeth of this morphology have previously been reported from the morrison formation, and it is unclear if the teeth represent a previously unknown taxon or a currently known taxon for which there is no tooth material. among the morrison theropods for which known teeth do not match tooth type d are: allosaurus, torvosaurus, ceratosaurus, marshosaurus, ornitholestes, coelurus, koparion, hesperornithoides, and tanycolagreus. taxa without teeth or with poorly known teeth include saurophaganax, an unidentified abelisauroid(?) (formerly “elaphrosaurus”), fosterovenator, and stokesosaurus. if the similarities of the type d teeth to those of anterior teeth of masiakasaurus are significant, and if the teeth belong to a known taxon with no or poor tooth representation, the best candidates might be the unidentified abelisauroid or possibly fosterovenator. finding this tooth type with associated skull material will be key to determining its affinities. tooth type e a lone tooth somewhat similar to type d is also known; it is thicker, shorter, and lingually more convex (figures 14g and 14h), though it possesses similarly elongate serration denticles (figure 14c). these serrations are coarser than in type d, too, however (1.75/ mm); the denticles appear to be angled apically and to have slightly enlarged rather than apically curved distal ends, both unlike type d. the crown height is 25 mm. this tooth type appears to be that of an anterior tooth, and the apparently distally enlarged denticles are similar to some referred teeth of abelisaurids (hendrickx and mateus, 2014), but beyond that it is difficult to identify. sauropoda diplodocidae diplodocinae indet. diplodocine sauropods are represented at the little houston quarry by only rare elements including a pubis and at least one complete, slender femur (figures 2d and 3a). the pubis is slender and has an enlarged ambiens process as with diplodocines such as diplodocus and barosaurus (hatcher, 1901; mcintosh, 1990; ostrom and mcintosh, 1999). macronaria camarasauridae camarasaurus sp. camarasaurus is represented by at least six or possibly seven individuals, including four articulated vertebral series: a set of anterior to mid caudals and a set of posterior dorsals and most of a tail from the mammal pit (both in figure 3b); and a partial mid-tail and a nearly complete vertebral column from anterior cervicals to the tip of the tail from the main pit (both in figure 3a). in addition to these four individuals, there is a partial hind foot of a juvenile, a partial skull of a large individual found near (but probably not belonging to) the nearly complete vertebral column (figure 3a), and a hatchling to very young juvenile represented by a tiny tooth. the camarasaurus material from the little houston quarry cannot be assigned to one species (pagnac, 1998), in part because the dorsal vertebrae of the most complete 49 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 specimen do not clearly exhibit diagnostic features due to post-depositional crushing. most anterior caudal vertebrae, however, appear to have only mildly expanded neural spines, suggesting possible affinity to c. lentus (ikejiri, 2005). the skull (sdsm 114501) is relatively large and is flattened to some degree with a number of teeth displaced from their alveoli and the premaxillae, for example, displaced dorsoventrally relative to each other (figure 15a). the skull was found underneath two sauropod ribs and near several camarasaurid metacarpals, several meters away from the end of the neck of the most complete camarasaurus vertebral column in the quarry (figures 15b and 3a). the skull appears to have been too large to go with the neck and skeleton, however. the associated juvenile hind foot consists of the left metatarsals i, iv, and v, plus two unguals, and a phalanx (figure 15c; foster, 1996a). a 5 mm-long tooth crown with partial root (jrf 9584) appears to belong to a very young camarasaurid and has an apical wear facet suggesting some use (figures 15d and 15e). this tooth has the general shape of most adult camarasaurid teeth (ostrom and mcintosh, 1999), although the enamel surface appears to be smoother. ornithischia thyreophora stegosauridae indet. a thin, plate-like bone with surficial grooves appears to be the dermal plate of a stegosaur (sdsm 25300; figure 16). the plates of stegosaurus and hesperosaurus are generally similar in structure, although their shapes differ somewhat, with those of the latter often lower and more oval-shaped (carpenter and others, 2001; maidment and others, 2015). the little houston quarry specimen here is too incomplete to identify with one or the other genus, but its overall morphology appears to be that of some type of stegosaurian plate. hesperosaurus has recently been reported at a number of northern localities in the morrison formation, appearing to be relatively more abundant there compared with the possibly more southern stegosaurus (maidment and others, 2018), and raising the possibility that sdsm 25300 may be hesperosaurus, although there is no way to confirm this yet. neornithischia nanosaurus agilis small neornithischians are represented by relatively abundant material including a dentary with 13 teeth (peirce, 2006; carpenter and galton, 2018; figure 16a), isolated anterior and lateral teeth (figures 17b and 17c), some vertebrate (figure 17d), a humerus (figure 17e), a pubis (figure 17k), a tibia of an adult (figure 17j), and a number of femora ranging in length from just a few centimeters to approximately 20 cm (figures 17f to 17i). the teeth are entirely of the “othnielosaurus” type (galton, 2007), and no “drinker” type teeth (bakker and others, 1990) have been found. carpenter and galton (2018) pointed out that both types of teeth have been found in the same jaw in some instances and synonymized both taxa with nanosaurus agilis (marsh, 1877; galton, 1983). one unusual anterior tooth with root is preserved (figures 17l and 17m), though it has not been fully prepared yet. mammalia multituberculata allodontidae indet. sdsm 26912 is a relatively large, partial right multituberculate dentary with p4 and m1 from the main pit of the little houston quarry (figure 18a). the specimen was probably about 23 mm long when complete, with a p4 length of 2.6 mm. the coronoid process is intact, and the posterior part of the jaw consists of bone and an impression in matrix. the m1 is worn labially but appears to have had two rows of three cusps. the dentary anterior to the p4 is missing but is represented by an impression in the matrix for part of its length. the specimen was identified as psalodon? marshi in its first description by martin and foster (1998); that species is also known from quarry 9 at como bluff (simpson, 1929). this specimen was the first mammal found at the little houston quarry. sdsm 26912 differs from ctenacodon serratus and c. scindens in the larger size of the p4, the larger overall size of the jaw, the relatively smaller m1 (compared with p4), and the slightly greater ratio of the depth of the dentary below p4 to the dentary length (table 2; 50 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 simpson, 1929). the specimen is similar to zofiabaatar (bakker and others, 1990) in the dentary length, the length of p4, and the dentary depth to length ratio, but it differs from that taxon in having: (1) an m1 relatively not as small (compared with p4), (2) an m1 with two rows of three cusps (as opposed to two of two in zofiabaatar), and (3) a condyle not facing as much dorsally as that taxon (table 2; carpenter, 1998). sdsm 26912 differs from glirodon grandis in larger overall size and larger p4, in having a smaller m1 compared to p4, and figure 15. representative little houston quarry camarasaurus (dinosauria, sauropoda). (a) skull in right lateral view, sdsm 114501, showing displaced teeth and offset of premaxilla. (b) left lateral view of caudal vertebra, sdsm 35943, from mammal pit specimen. (c) partial foot of juvenile individual including metatarsals i, iv, and v, phalanx, and two unguals, sdsm specimen. (d and e) tooth of hatchling(?) individual in (d) labial view and (e) distal(?) view showing wear facet. scale bars in a to c in cm; scale bars in d and e = 5 mm. 51 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 in having a less robust ramus (table 2; engelmann and callison, 1999). as in ctenacodon, the post-coronoid portion of the ramus of sdsm 26912 is also relatively longer than in glirodon. the specimen is similar to psalodon? marshi in the structure of m1 and in having a large p4, but it differs from that taxon in having an m1 smaller relative to p4 and has a seemingly longer, lower dentary with a less convex ventral border in lateral view and apparently with a smaller incisor. sdsm 26912 appears not to fit well with p.? marshi, ctenacodon, glirodon, or zofiabaatar and may in fact represent a separate as yet unidentified multituberculate taxon in the morrison formation. p.? marshi itself (e.g., usnm 2684) in fact may represent a taxon closer to plagiaulax becklesii and may not be closely related to ctenacodon. docodonta docodontidae docodon cf. apoxys several jaw fragments and isolated teeth of docodon have been found since 1993 (martin and foster, 1998; foster and others, 2006), when the first mammal specimens were uncovered. these specimens include at least three dentary fragments (foster and others, 2006; figure 18b), a maxilla fragment (figure 18f), a large canine (figure 18d), and some isolated molars. the molars of at least one of the specimens are of the type described for d. apoxys from garden park (rougier and others, 2015) in having reduced molar size near the posterior end of the dentary, especially in the last molar (as indicated by alveolus size in the case of the little houston quarry specimen). this specimen (sdsm 60480; figures 18b figure 16. dorsal(?) plate fragment of stegosauridae indet. from the little houston quarry, sdsm 25300. scale bar = 5 cm. 52 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 figure 17. representative little houston quarry nanosaurus (dinosauria, neornithischia). (a) right dentary with 13 teeth in labial view, mwc 5822. (b) anterior tooth in lingual view, jrf 95220. (c) lateral tooth in labial view, jrf 95148. (d) caudal vertebra in posterior view, sdsm 30496. (e) right humerus in medial view, sdsm 30502. (f) tiny femur mid-shaft with partial fourth trochanter, jrf 9822. (g) left femur in anterior view, sdsm 26913. (h) complete left femur in medial view, sdsm 30494. (i) complete left femur of adult in medial view, sdsm 30490. (j) complete tibia in posterior view, mwc 5630. (k) right pubis, sdsm 30503. (l and m) anterior tooth in lingual view and close-up, jrf 95126. scale bars: a, d, f, and l = 1 cm; b, c, and m = 5 mm; e and g to k = 5 cm. 53 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 figure 18. little houston quarry multituberculate and docodont mammals. (a) partial right dentary with p4 and m1, in labial view, assigned to allodontidae indet., sdsm 26912. scale bar = 1 cm. (b to f) docodon. (b) partial left dentary of docodon cf. apoxys, sdsm 60480, in lingual view, with m2–5(?) and alveoli for m6 and m7. scale bar = 5 mm. (c) close-up labial view of molars m2–m5(?) of jaw in b (sdsm 60480). scale bar = 1 mm. (d) canine tooth in lingual(?) view, sdsm specimen. scale bar = 1 mm. (e) jaw fragment with lower molar, incoming more distal molar(?), and some dentary bone, sdsm specimen. molar length ~2 mm. (f) left maxilla fragment with canine, mwc specimen, in lingual view. scale bar = 5 mm. 54 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 and 18c) consists of a partial left dentary with m2–5(?) and alveoli for m6 and m7 of reduced size (especially m7). this specimen would be the first occurrence of d. apoxys outside of its type area in garden park, colorado. docodon is well known from a number of sites in wyoming (quarry 9 and others) and eastern colorado (small and marsh-felch quarries, garden park) (simpson, 1928; kielan-jaworowska and others, 2004), although it is absent from the morrison of the colorado plateau (foster and others, 2006). cladotheria dryolestida dryolestidae amblotherium amblotherium megistodon, sp. nov. figure 19 lsid. urn:lsid:zoobank.org:pub:a69fb058-c18b4aaf-bc4b-ee68e3682561. type specimen sdsm 148545, left dentary preserved in labial view with p2–p4 and m1–m3 in place. type locality little houston quarry (mammal pit), crook county, wyoming (foster and martin, 1994; foster, 2001). type horizon morrison formation undifferentiated; thin local morrison section of only ~23 m (mapel and pillmore, 1963); thickness and intraformational correlation with other localities in wyoming unknown. etymology from greek μεγíστ (megist) meaning “largest” + όδόυ (odon) meaning “tooth,” in reference to the much larger overall size compared with other species of amblotherium (a. gracile and a. pusillum), especially as reflected in the teeth. diagnosis amblotherium species with isometrically larger dentary and teeth than other species of the genus (m3 up to 87% longer than in other species; 1.5 mm mesiodistal length compared with average of 0.80 mm in a. pusillum and a. gracile) and differing from other species of the genus in having roots of unequal size in m1 and m2 as well as more distal molars; other characters match generic diagnosis of amblotherium. description and identification sdsm 148545 is a mostly complete left dentary with p2–p4 and m1–m3 (figure 19) and is a dryolestid, as indicated by the enlarged and bean-shaped mesial alveolus and reduced, oval-shaped distal alveolus of m4. the dentary is 21.97 mm long as preserved and is missing only the anterior end (incisors and full canine alveoli not preserved), posterior tip, and upper coronoid process. the jaw is in a piece of matrix with the labial and occlusal surfaces exposed, and preparation has exposed the lingual sides of the preserved teeth. the six table 2. comparison of features of various species and specimens of jaws of multituberculate mammals from the morrison formation. ctenacodon psalodon? marshi zofiabaatar pulcher glirodon grandis sdsm 26912 dentary length 17.5 incomplete 23 17.3 ~23.3 length p4 1.65 3 2.6 1.9 2.6 length p4:m1 1.4 1.43 1.98 1.5 1.72 dentary depth at p4: dentary length 0.192 incomplete 0.257 0.297 0.235 m1 cusps 2 rows of 3 2 rows of 3 2 rows of 2 2 rows of 3 2 rows of 3 dentary ramus deeper under coronoid no no yes no no dentary condyle facing posteriorly posteriorly posterodorsally posterodorsally posteriorly references simpson, 1928, 1929 simpson, 1929 bakker and others, 1990; carpenter, 1998; kielan-jaworowska and others, 2004 engelmann and callison, 1999 this report 55 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 preserved teeth include p2–p4 and m1–m3, and the alveolus for p1 is exposed too (figure 19). the alveoli for m5 and m6 are poorly preserved due to partial crushing and are positioned partly lingual to the base of the coronoid process, suggesting the individual is a juvenile (martin, 1999, 2000). the cusps of the molars are sharp and slender (figure 19c). the molars differ from those of laolestes in figure 19. dryolestid mammal amblotherium megistodon n. sp., sdsm 148545, holotype, left dentary, little houston quarry. (a) labial view showing p2–p4 and m1–m3. total length of specimen as preserved is 21.97 mm. (b) occlusal view showing teeth and alveoli (as labelled) from partial canine(?) alveolus to m6(?). (c) close-up view of p3–m3 in labial view with cusps labelled. length of m3 = 1.5 mm. protoconid cusp heights (m1 and m2) reconstructed from field photos. (d) tracing of photo of m3 in occlusal view showing features and proportions. abbreviations for c and d: med = metaconid, pad = paraconid, prd = protoconid, p4 = premolar 4, tc = talonid cusp, tad = talonid, trd = trigonid. 56 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 not having a bifid metaconid, in not having the paraconid and talonid cusp positioned internal to the metaconid (figures 19b and 19d), and in having an essentially erect (not slightly procumbent) paraconid. the premolars lack the anterior accessory cusp characteristic of dryolestes (other than d. leirensis), and the molars differ from those of dryolestes in having a more erect rather than procumbent paraconid (m3 cusp reconstruction in figure 19c based on pre-damage preliminary images). the jaw matches amblotherium in having: (1) a slender ramus, (2) molars with an erect paraconid close to the height of the metaconid, (3) molars with a weak external cingulum, and (4) a coronoid with a low-sloping anterior edge (simpson, 1928, 1929; kielan-jaworowska and others, 2004). the slenderness of the ramus in sdsm 148545 is indicated by the ratio of the maximum jaw depth to the reconstructed jaw length, and the ratio is similar to amblotherium (sdsm 148545 only 4.5% lower than other species of amblotherium; see table 3). this dentary slenderness ratio also differentiates the little houston dentary from dryolestes and laolestes (ratio 19.7% lower than in dryolestes; ratio 24.3% lower than in laolestes). molar size differs relative to jaw depth in sdsm 148545 and amblotherium versus dryolestes and laolestes, with the latter genera having relatively lower crowned molars. the ratio of the crown height of m3 to the depth of the dentary below m3 ranges from means of 0.366 and 0.362 for dryolestes and laolestes, respectively, to 0.707 and 0.657 for amblotherium and sdsm 148545 (table 3). amblotherium (including sdsm 148545) demonstrates a more dramatic increase in molar crown height from position m1 to m3 compared to dryolestes and laolestes, as indicated by the ratio of m3 crown height to that of m1 (table 3). sdsm 148545 differs from other species of amblotherium in having a dentary length and molar mesial-distal length more similar to dryolestes (table 3). the lengths of m3 in dryolestes and sdsm 148545 are approximately 1.5 mm in each case, whereas the mean of four specimens of a. pusillum and a. gracile is 0.80 mm (simpson, 1928, 1929), a size increase of approximately 87.5% from other species of amblotherium to a. megistodon (sdsm 148545). the little houston quarry jaw also differs from other species of amblotherium in having the roots of m1 and m2 being unequal in size, as in the positions from m3 back; in some specimens of other species the first two molars have “normal” roots of equal size. phylogenetic analysis, incorporating the matrix of rougier and others (2012) and adding two characters (appendix), places sdsm 148585 among dryolestids in a polytomy with amblotherium (based on a. pusillum and a. gracile), comotherium, and laolestes+groebertherium, with dryolestes as a sister taxon to the clade (figure 20). the unresolved nature of the comotherium-amblotherium-sdsm 148545 polytomy is likely caused by missing data in sdsm 148545, particularly in the less well preserved posterior dentary region and in the lack of upper jaws. in rougier and others (2012) this relationship (minus sdsm 148545) was resolved as dryolestes+(comotherium+([amblotherium+(laolestes+groebertherium)]). comotherium was described as a dryolestid (prothero, 1981) but has since been classified as a paurodontid by others (martin, 1999; kielan-jaworowska and others, 2004). discussion the jaw length as preserved (~22 mm) suggests a mass estimate for amblotherium megistodon of 33.2 g, compared with estimates of 25.9 g for other species of amblotherium, 71.3 g for laolestes, and 103.7 g for dryolestes (foster, 2009). however, the facts that sdsm 148545 appears to be a juvenile and that the length of m3 is essentially the same as in adult dryolestes suggest that the adult animal likely would have approached laolestes and dryolestes in mass. at the very least, the complete dentary of sdsm 148545, with the missing anterior and posterior ends restored, was likely close to 26 mm long, a length indicating a possible mass of 54.5 g (formula of foster, 2009), a size making a. megistodon the ninth largest mammal in the morrison mammal fauna (of 22). amblotherium gracile, in contrast, is the sixth smallest in the group. amblotherium comprises the species a. gracile from the upper jurassic morrison formation and a. pusillum from the upper jurassic-lower cretaceous purbeck group of england (simpson, 1928, 1929; martin, 1999, 2000; kielan-jaworowska and others, 2004; ave57 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 rianov and others, 2013, 2014). amblotherium gracile includes a. debile and miccylotyrans (averianov and others, 2013) and is known from como bluff (quarry 9 and chuck’s prospect), dinosaur national monument (rainbow park), and garden park (marsh-felch) in the morrison formation. amblotherium megistodon is then a second species within the morrison formation. in addition to partial jaws of amblotherium gracile from quarry 9 at como bluff (simpson, 1929), several referred lower molars from the rainbow park microvertebrate sites at dinosaur national monument were described by engelmann and callison (1998). these latter teeth were small and of an “a. debile” size of 0.62 to 0.72 mm length, in contrast to a. megistodon’s molar length of ~1.5 mm the presence of a species of amblotherium in the morrison formation that is more than 87% larger than a. gracile suggests that either there were two co-existing and niche-partitioned species present in the region during the late jurassic or that the genus underwent body-size evolution over the course of morrison times. because of the inability to correlate the very thin morrison formation of the black hills to other, thicker sections in wyoming or elsewhere, it is unclear if a. megistodon represents a larger contemporary of a. gracile or if it represents an anagenetic change in body size within amblotherium through some part of the ~7 million years of the formation. if the latter, it is even unclear whether the change in body size would have been an increase or decrease. on the other hand, a larger but contemporaneous species in the northern part of the morrison formation could indicate some degree of paleobiogeographic segregation within the genus, but this is not yet conclusive. bone modifications many of the sauropod bones from the little houston quarry (but far fewer of the bones of smaller taxa such as neornithischians) possess a few to near-comtable 3. comparison of features of various dryolestid mammal jaws from the morrison formation. all measurements in mm. morganucodonta docodontids triconodontids symmetrodontids monotremes henkelotherium dryolestes comotherium amblotherium sdsm 148545 laolestes groebertherium paurodontids meridiolestids eutherians metatherians a. megistodon figure 20. simplified phylogenetic tree based on strict consensus of 12 mtps from analysis of 60 taxa and 319 characters (length = 1226), showing relationships of sdsm 148545 (amblotherium megistodon) and other dryolestids. red text indicates taxa with representatives in the morrison formation; yellow box indicates traditional dryolestida. dryolestes laolestes amblotherium sdsm 148545 dentary length 30.5 27.5 18.2 ~22.0 (gui mam 130/75) (ypm 13719) (bmnh 47752) length m3 1.5 1.25 0.8 1.5 dentary depth: length 0.132 0.14 0.111 ~0.106 height m3: dentary depth (mean) 0.366 0.362 0.707 0.657 (n=3) (n=2) (n=4) height m3:m1 (mean) 1.29 1.14 1.65 1.38 (n=4) (n=1) (n=3) 58 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 plete covering of surficial pits, especially along the shafts of long bones (figure 21). these pits are similar to those described as being caused by low ph soil conditions or alternatively by boring dermestid beetles or their larvae (fiorillo, 1998; britt and others, 2008; bader and others, 2009). most sauropod limb elements from the little houston quarry have at least some of these pits, and a number of elements are almost completely covered in them. these modifications suggest at least some subaerial exposure or burial in acidic soils for many of the sauropod elements from the site. theropod(?) tracks several small, tridactyl dinosaur tracks of a grallator-like morphology were found in a sandstone block displaced from just below the quarry level (figure 22), and these were described by foster and lockley (1995). these tracks probably represent small theropod dinosaurs, though some may possibly have been made by small neornithischians. discussion paleoenvironmental setting the little houston quarry contains a very dense deposit of vertebrate material ranging in size from large sauropod dinosaurs to microvertebrates in thin and laterally restricted layers of an elongate, ribbon-shaped deposit above a channel sandstone (figure 23). the deposit is laterally restricted to the space between visible edges incised into variegated floodplain mudstones and is much longer than wide (“ribbon” geometry). the transition from a thin and laterally restricted channel sandstone (with mud clasts) into the quarry interval of interbedded green claystone and sometimes laminated, clay-ball bearing siltstone (figure 2b), similarly laterally restricted, and then into pure floodplain mudstone, all suggests a gradually in-filling abandoned channel that was occasionally reactivated during floods (foster, 2001; e.g., miall, 2010). the quarry layer itself probably represents the laminated fill unit of a fully disconnected channel (e.g., toonen and others, 2012), and most well-preserved microvertebrate bone elements within the deposit are probably parautochthonous to autochthonous (behrensmeyer, 1988; foster, 2001; rogers and brady, 2010). taphonomy the little houston quarry contains microvertebrate material in great abundance and in relatively highly defined layers but with a high degree of disarticulation (~100%) and fragmentation, and its lithology consists of siltstone with heterogeneous clasts of clay balls and small bone fragments (foster, 2001). it thus represents a broad type 1 pond deposit taphofacies for microvertebrate remains in the morrison formation, along with figure 21. modifications of sauropod dinosaur bones from the little houston quarry. (a) pitting on shaft of sauropod ulna sdsm 35952. (b and c) near-total coverage by pitting on a sauropod metapodial mwc 5784. scale bars in cm. 59 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 the small quarry at garden park, colorado, and quarry 9 at como bluff, wyoming (foster, 2001, 2003). this taphofacies contrasts markedly with broad type 2 pond deposits typical of the morrison formation of the colorado plateau, the latter consisting of usually “clean” grayish mudstone with a very low-density deposit of sometimes articulated or associated material, including whole or partial skeletons of microvertebrates such as mammals and sphenodontians (foster 2001, 2003); localities of this type include the callison and tom’s place sites at the fruita paleontological area, colorado (callison, 1987; kirkland, 2006), rainbow park 94 and 96, dinosaur national monument (evans and chure, 1998, 1999; evans and others, 2005), wolf creek, colorado (wood, 1986), and cisco mammal quarry, utah (davis and others, 2018). matrix samples from little houston, small quarry, and quarry 9 placed side by side can be almost indistinguishable from each other and would presumably represent somewhat similar pond settings, although the details of their respective settings differ. the little houston quarry, situated on top of a channel sand, appears to represent the in-filling of an abandoned channel pond (foster, 2001), whereas quarry 9, the main fossiliferous lens of which was under a sandstone (carrano and velez-juarbe, 2006), probably represents a floodplain pond followed by avulsion of a main river channel. the small quarry microvertebrate layer is just below a crevasse-splay sandstone series (rougier and others, 2015) and was probably in a floodplain pond and apparently near a river channel as well. so far, type 1 pond deposits (little houston, small quarry, quarry 9) are restricted to the northern and eastern parts of the morrison formation, and type 2 deposits (fpa, rainbow park, wolf creek, and cisco mammal) are only known from the colorado plateau region in the morrison. this taphofacies segregation may reflect the relative abundance differences in the occurrences of turtles and semi-aquatic crocodyliforms between the colorado plateau and areas north and east (foster and mcmullen, 2017), the northand east-restricted distributions of possibly semi-aquatic mammalian and archosauromorph taxa in docodon and cteniogenys (chure and evans, 1998; foster and trujillo, 2000; foster and others, 2006), and geologic evidence suggesting a higher water table and wetter surface conditions during morrison times in areas that are now parts of wyoming and eastern colorado (turner and peterson, 2004). the little houston quarry therefore helps characterize the faunas of the northern and eastern “wet” setting of the morrison formation. in contrast to the microvertebrate material, up to 25% of dinosaur material in the quarry is in articulation, although the dinosaur material is part of the same dense accumulation as the small taxa. almost uniquely, microvertebrate remains occur in among the articulated and disarticulated dinosaur remains as well, with some mammal jaws from the mammal pit being found centimeters away from an articulated series of camarasaurus caudals. paleobiodiversity with at least 26 vertebrate taxa preserved (and 35 figure 22. tridactyl (theropod?) dinosaur track on sandstone slab from channel just below little houston quarry (see foster and lockley, 1995). scale bar numbered in inches. 60 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 taxa total), the biota from the little houston quarry is the second-most diverse single locality in the morrison formation after reed’s quarry 9 (foster, 2003), the latter at 76 species (72 vertebrates; carrano and velez-juarbe, 2006). the little houston quarry represents the most diverse morrison formation locality north of como bluff, wyoming, and it is important for studying what seems to be a newly recognized “northern fauna” of the unit (e.g., maidment and others, 2018). the little houston quarry is followed closely in vertebrate diversity by the dry mesa quarry of colorado, and then several others. beyond the shared taphonomic characteristics, the biota of the little houston quarry shares with quarry 9 and the small quarry several faunal similarities: (1) a relative abundance of docodon specimens among the mammalian genera (little houston and small appear to specifically share the species d. apoxys); (2) a relative abundance of cteniogenys (so far absent at small); (3) actinopterygian fish represented by vertebrae, teeth, and jaw fragments; (4) the lungfish ceratodus fossanovum (little houston and quarry 9 at least); and (5) relatively abundant turtles and semi-aquatic crocodyliforms. these are taxa and patterns that are absent or rare in type 2 deposits on the colorado plateau. most of the diversity at the little houston quarry is among microvertebrate taxa, and several of the species are particularly rare in other parts of the morrison formation. among these latter taxa are the potentially new, elongate unionid bivalves (figures 5e and 5f), the first occurrence of the atoposaurid crocodyliform theriosuchus in the morrison formation (figures 12a to 12c), several unusual small theropod tooth types (figures 13 and 14), a new species of amblotherium (figure 19), and the first occurrence of the mammal docodon apoxys outside its type locality (figure 18). the abundance of aquatic and semi-aquatic taxa in the deposit reflects the abandoned channel pond setting. the diversity of the biota is probably not unusual for the paleoenvironment of the northern morrison formation but more likely is a product of preservation in a highly concentrated deposit. the morrison formation of the black hills of wyoming and south dakota may preserve even more taxa than are currently known, including possibly new species, but it has been difficult to fully compare the biota from the area to other parts of wyoming and the colorado plateau due to the thinness of the unit in the black hills and the apparent lack of smectitic mudstones, both preventing lithostratigraphic correlations or radiometric age comparisons (e.g., turner and peterson, 1999; trujillo and kowallis, 2015). the diverse biota present at the little houston quarry, and the unusual taxa preserved there, suggest that the region may yet hold even more information about the apparent “northern fauna” of the morrison formation. quarry unit: light greenish-gray (5gy 8/1) to light olive gray (5y 6/1) laminated siltstone and very �ne grained sandstone interbedded with dark greenish-gray (5gy 4/1) to grayish-olive (10y 4/2) claystone; siltstone layers approximately 3-20 cm thick; claystone layers approximately 1-4 cm thick; abundant greenish-gray clay clasts in some siltstone layers; laminations in siltstone are planar to wavy; abundant carbonized plant remains in some siltstone layers; two microvertebrate layers (*) up to approximately 10 cm thick in lower part of unit, containing abundant disarticulated but well-preserved bones light tan, �neto very �ne grained sandstone; moderately well sorted and rounded grains; 1-5 cm planar tabular and trough cross-beds; rounded clasts of calcium carbonate and clay common near base and center of channel; some wellrounded bone fragments near base; minor amount of recognizable turtle shell and crocodyliform teeth light gray limestone light gray limestone gray and maroon claystone dark greenish gray, gray-olive, and maroon claystone; rootcast light tan �neto very �ne grained sandstone; some cross-beds; present above main pit only dark greenish-gray claystone 1 m * * figure 23. stratigraphic section of morrison formation exposure at the little houston quarry showing position of main bone layers (*) above thin channel sandstone. 61 an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming foster, j.r., pagnac, d.c., and hunt-foster, r.k. geology of the intermountain west 2020 volume 7 acknowledgments special thanks for discussions, information, technological assistance, help with figures, and help tracking down publications to (in no particular order): susie maidment (the natural history museum, london), carole gee (university of bonn), peter galton (university of bridgeport, retired), nick fraser (national museums scotland), susan evans (university college london), ken carpenter (prehistoric museum, utah state university–eastern), scott madsen (utah geological survey, retired), tom holtz (university of maryland), bryan small (museum of texas tech university), jim martin (university of louisiana at lafayette), guillermo rougier (university of louisville), lisa baldwin (national park service), tracy ford (independent), dale malinzak (black hills state university), dan chure (national park service, retired), kelli trujillo (laramie county community college), robin beck (university of salford), and brian davis (university of louisville). thanks to crews from the sdms museum of geology and the mwc for their work at the site over the years and to the landowners for access. microphotography facilitated by the south dakota school of mines and technology museum of geology and ben burger (utah state university, uintah basin). finally, thanks to chris noto (university of wisconsin, parkside), jim kirkland (utah geological survey), and kelli trujillo (laramie county community college) for review comments on the manuscript. references allen, e.r., 2012, analysis of north american goniopholidid crocodyliforms in a phylogenetic context: iowa city, university of iowa, m.s. thesis, 89 p. anderson, l.c., 2014, ultra-elongate freshwater 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and mcintosh, j.s., 1980, taphonomy and paleoecology of the dinosaur beds of the jurassic morrison formation: paleobiology, v. 6, p. 208–232. eckenwalder, j.e., 2009, conifers of the world: portland, oregon, timber press, 720 p. engelmann, g.f., and callison, g., 1998, mammalian faunas of the morrison formation: modern geology, v. 23, p. 343– 379. engelmann, g.f., and callison, g., 1999, glirodon grandis, a new multituberculate mammal from the upper jurassic morrison formation, in gillette, d.d., editor, vertebrate paleontology in utah: utah geological survey miscellaneous publication 99-1, p. 161–177. evanoff, e., good, s.c., and hanley, j.h., 1998, an overview of the freshwater mollusks from the morrison formation (upper jurassic, western interior, usa): modern geology, v. 22, p. 423–450. evans, s.e., 1990, the skull of cteniogenys, a choristodere (reptilia: archosauromorpha) from the middle jurassic of oxfordshire: zoological journal of the linnean society, v. 99, p. 205–237. evans, 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hunt-foster, r.k. geology of the intermountain west 2020 volume 7 farlow, j.o., brinkman, d.l., abler, w.l., and currie, p.j., 1991, size, shape, and serration density of theropod dinosaur lateral teeth: modern geology, v. 16, p. 161–198. fiorillo, a.r., 1998, bone modification features on sauropod remains (dinosauria) from the freezeout hills quarry n (morrison formation) of southeastern wyoming and their contribution to fine-scale paleoenvironmental interpretation: modern geology, v. 23, p. 111–126. fiorillo, a.r., and currie, p.j., 1994, theropod teeth from the judith river formation (upper cretaceous) of south-central montana: journal of vertebrate paleontology, v. 14, p. 74–80. foster, j.r., 1992, fossil vertebrates of the morrison formation (upper jurassic) of the black hills, south dakota and wyoming: rapid city, south dakota school of mines and technology, m.s. thesis, 178 p. foster, j.r., 1993, sedimentology and taphonomy of the little houston quarry, morrison formation (upper 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v. 72, p. 179–189. zinke, j., and rauhut, o., 1994, small theropods (dinosauria, saurischia) from the upper jurassic and lower cretaceous of the iberian peninsula: berliner geowissenschaftliche abhandlungen, v. 13, p. 163–177. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 6 2019 © 2019 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado kenneth carpenter and eugene lindsey theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover jurassic morrison formation as exposed at cope’s nipple lying between the orange pennyslvanian fountain formation and overlying cretaceous lytle formation capping the butte to the left. photo courtesy of dan grenard (retired, bureau of land management, cañon city, colorado). i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 6 2019 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees 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gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association volume 6 2019 1 abstract the garden park national natural landmark (gpnnl) is north of cañon city, colorado, and encompasses all of the major historical dinosaur quarries of the upper jurassic morrison formation in this area. the formation there can be divided into the lower redefined ralston creek member and an upper unnamed member. the morrison formation is bracketed below by the j-5 unconformity and above by the k-1 unconformity. the ralston creek member is composed of up to 55 m of arkosic conglomerate, sandstone, siltstone, and gypsum conformably underlying the unnamed member. fossil fishes previously used to infer a middle jurassic age are non-diagnostic. a diplodocid skeleton 4 m above the j-5 unconformity from the west-adjacent shaws park, and a radiometric date of 152.99 + 0.10 ma from the purgatoire river area demonstrate that the ralston creek rightly belongs in the morrison formation and correlates with the tidwell and salt wash members on the colorado plateau. the ralston creek was deposited in a broad playa complex analogous to those of central australia and here called the ralston creek boinka. groundwater flux played an important role in gypsum deposition in gypsisols and playa lakes. the overlying unnamed member in the gpnnl can be subdivided on the west side of fourmile creek into a lower part composed largely of mudstone with many thin, discontinuous channel sandstone beds, and a thicker upper part containing more persistent tabular sandstone beds; this subdivision does not occur east of fourmile creek. several thin limestone beds occur in the ralston creek member and in the lower part of the unnamed upper member. the limestone contains fresh water ostracods and aquatic mollusks indicating a lacustrine origin. however, these fauna are apparently stunted and the ostracod valves closed indicating periodic hypersaline conditions. all detrital rocks in the morrison formation at garden park are composed of varying amounts of quartz, potassic feldspar, and the clay minerals illite, smectite, and kaolinite. mapping of the clay minerals in the unnamed member reflect various paleosols throughout the mudstone interval, including protosols and argillisols. at the top of the formation, a sandstone previously assigned to the morrison is reassigned to the overlying cretaceous lytle formation based on similar weathering characteristics, mineral content, and fabric. thus, the k-1 unconformity between the morrison and overlying lytle rests on the uppermost occurrence of the morrison formation mudstone-sandstone-limestone complex and beneath the blocky, cliff-forming lytle formation. redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado ken carpenter1,2 and eugene lindsey3 1prehistoric museum, utah state university eastern, price, ut 84501; ken.carpenter@usu.edu 2 museum of natural history, university of colorado, boulder, co 80309 3department of earth sciences, denver museum of nature and science, denver, co 80205 (deceased) citation for this article. carpenter, k., and lindsey, e., 2019, redefining the upper jurassic morrison formation in garden park national natural landmark and vicinity, eastern colorado: geology of the intermountain west, v. 6, p. 1–30. © 2019 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 2 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 introduction the garden park national natural landmark (gpnnl)—formely named the garden park geological resources area—is managed by the bureau of land management and encompasses all of the classic dinosaur sites in the upper jurassic morrison formation north of cañon city, colorado (figures 1, 2a, and 2b; monaco, 1998; carpenter, 1999; foster, 2003). the morrison formation can be widely traced throughout the western united states (mook 1916; craig and others, 1955). it was named by whitman cross (1894), with the stratotype given for exposures immediately east of the town of morrison, colorado (figure 3a). the formation was defined as “…prevailingly greenish, pinkish or gray shales and marls. sandstone occurs at the base and is also intercalated at numerous horizons in the upper part of the section with varying development” (cross, 1894, p. 2). the age was assumed to be jurassic based on the dinosaurs collected in the vicinity of the type locality. ethridge (1896, p. 60–62) described the formation in greater detail, but it was lee (1920) who refined the boundaries of the stratotype and published a measured section. more than two decades later, waldschmidt and leroy (1944) designated the west alameda parkway roadcut 2.5 km north of morrison, colorado, as a new stratotype for the morrison formation (figure 3b) and this is still widely followed (e.g., lockley and others, 2015). their justification for moving the stratotype was based on the entire morrison formation being exposed along the road cut, which had been only completed a few years before, and because the exposure was readily accessible. such a relocation of the stratotype was not addressed by the stratigraphic code operating at the time (committee on stratigraphic nomenclature, 1933), but the current north american stratigraphic code forbids it: “once a unit or boundary stratotype section is designated, it is never abandoned or changed; however, if a stratotype proves inadequate, it may be supplemented by a principal reference section …” (north american commission on stratigraphic nomenclature, 2005, article 8(e)). therefore, the stratotype for the morrison formation remains on the western face of the hogback on the east edge of the town of morrison as was originally designated by cross (1894), and the west alameda parkway road cut along the same hogback (now called dinosaur ridge) is the principle reference section for the morrison formation and is attributed to waldschmidt and leroy (1944). previous studies in the gpnnl the morrison formation can be traced almost without interruption for about 200 km from its stratotype near the town of morrison to garden park in south-central colorado. there, it is exposed along the canyon and tributaries of fourmile creek. the first, albeit brief, description of the morrison formation in garden park was by cross (1894) as part of his description of the geology of the pikes peak area. this was followed by a more detailed description by hatcher (1902), who attempted to place stratigraphically the historic dinosaur quarries of o.c. marsh (yale university) and e.d. cope (academy of natural sciences of philadelphia). the first stratigraphic section was presented by mook (1916), who noted a thickness of 97.2 m (originally reported in feet as 319 ft). this contrasted with about 106.7 m (originally reported in feet as 350 ft) given by cross (1894) and 137.2 m (originally reported in feet as 450 ft) by hatcher (1902). the disparity in thickness is due to lack of agreement for the upper contact with the cretaceous beds. subsequent studies on the morrison of garden park prior to the start of our work were mostly theses or dissertations, with a few exceptions (giltner, 1953; schulze, 1954; de lay, 1955; saylor, 1955; frederiksen and others, 1956; hassinger, 1959; sackett, 1961; crammer, 1962; brady, 1967; enciso, 1981; sweet, 1984a; johnson, 1991). beginning in the early 1990s, the denver museum of natural history (now the denver museum of nature and science) began detailed paleontological and geological studies there. the result of these studies are presented in ague and others (1995), harris and carpenter (1996), small and carpenter (1997), alf (1998), bray and hirsch (1998), carpenter (1998a, 1998b, 2019), carpenter and tidwell (1998), evanoff and carpenter (1998), harris (1998), kirkland and others (1998), mcintosh and carpenter (1998), tidwell and carpenter (1998), brill and carpenter (2001), chure (2001), 3 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 figure 1. simplified geological map of the garden park national natural landmark, which is about 9 km north of cañon city, colorado. map courtesy of e. evanoff (university of northern colorado). 4 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 mcwhinney and others (2001), and rougier and others (2015). ancillary work on the stratigraphy of morrison formation in garden park are presented in peterson and turner (1998) and turner and peterson (1999). methods as part of our work on the geology of the morrison formation in the garden park area, one of us (lindsey) prepared a geological map for a 1.25 km2 area west of fourmile creek where most of the classical dinosaur quarries are located (e.g., figure 2). thin sections of sandstone samples from the upper unnamed member were examined with a petrographic microscope, and clay minerals in mudstone samples were analyzed with x-ray diffraction. the results of these analyses were used to help reconstruct paleoenvironments at the time of deposition. morrison formation of gpnnl we divide the morrison formation throughout gpnnl into two members; the lower ralston creek member (new ranking) and an unnamed upper member (figures 4a and 4b). the ralston creek member unconformably overlies the conglomeratic, brick-red to orange pennsylvanian fountain formation (figure 4a, 4b, and 4d). this unconformity, the j-5, represents a time gap of approximately 159 million years. the unnamed upper member (the “traditional” morrison of previous usage in eastern colorado) is overlain by massive sandstone beds of cretaceous age originally called the dakota formation by cross (1894). scott and others (1978) and wobus and others (1985) placed these sandstones in the lower cretaceous purgatoire formation in their mapping around cañon city and garden park, following the terminology of finlay (1916) for southern front range northeast of cañon city. they further subdivide the purgatoire into the basal lytle member, a sandstone, and the overlying glencairn member, a sandstone and shale unit. kues and lucas (1987) and mateer (1987) proposed abandoning the term purgatoire formation and elevating the lytle and glencairn to formation status, a proposal accepted by us. combined, these two cretaceous formations are about 91 m thick in the garden park area. the placement of the k-1 unconformity between the morrison and lytle formations is controversial. two massive cliff-forming sandstone beds cap the mesas throughout garden park (figures 4a and 5). peterson (u.s. geological survey, verbal communication to lindsey, 1995; see also peterson and turner, 1998, figure 5) described a maroon-colored paleosol marking figure 2. (a) felch quarry 1 is in the lower part of the unnamed member of the morrison formation. a marked change occurs from the alternating thin beds of greenish-gray mudstone and sandstone underlying the channel sandstone beds, which lie immediately below the quarry floor, to mixed red and gray bentonitic mudstones above. (b) cope’s nipple quarry in the upper part of the unnamed member. the illitic mudstone beds are predominately red to maroon with some green lenses. the sandstone beds in this interval are mostly tabular. 5 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 the k-1 unconformity at the top the lower sandstone identified as morrison. this is seen, for example, on the southeast side of cottage rock (figure 5b) and on the unnamed butte immediately west of cope’s nipple. both sandstone beds 1 and 2 (figure 5b) are composed of 95% rounded quartz grains, 0.2 to 0.8 mm, and an interstitial mosaic of subangular quartz grains measuring 0.02 to 0.04 mm. both are cemented with a mixture of clay and iron oxide comprising 5% of the rock. feldspar and calcite are absent in both. petrographic examination shows paleosol of peterson and turner (1998) to be composed of 75% to 85% subrounded quartz grains measuring 0.2 to 0.5 mm, 10% to 15% potassic feldspar, with scarce microcline, and 1% to 5% maroon iron oxide. in contrast, sandstones in the unnamed member are heterolithic, coarser grained, have larger quantities of cement that range from calcite to clay and oxide mixtures, and all have potassic feldspars. in light of these observations, we conclude that paleosol of peterson and turner (1998) is a local diagenetic feature and we place the k-1 unconformity 15 m lower (figure 5b) at the base of the lower sandstone (no. 1) of the lytle formation. we also note that there is a local intra-lytle erosion surface at the top of lower sandstone (no. 1; figure 5b). overlying the lytle formation is the glencairn formation. it is the uppermost rock on most of the larger figure 3. morrison formation west of denver. (a) type locality of the morrison formation on the west facing slope of the dakota hogback immediately behind the town of morrison (foreground). this 1899 photograph was taken five years after the naming of the morrison formation by cross (1894). quarry 10 of arthur lakes from which apatosaurus ajax was excavated is circled. (b) the "type" locality of walschmidt and leroy (1944) along the alameda parkway at what is now dinosaur ridge. photograph in (a) is from denver public library, western history collection x-11159. index map by doug sprinkel (utah geological survey).miles kilometers0 1 2 3 4 5 0 1 2 3 n golden denver morrison a 6th ave alameda ave alam ed a p kw y colfax ave w ad sw or th b lv d 6 40 40 6 h og back rd colorado enlarged area b 121 121 470 93 74 93 58 26 8 8 6 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 figure 4. (a) view west across fourmile creek from county road 9 towards cope’s nipple and the “valley of death” (see figure 1). the j-5 unconformity is visible as the abrupt contact between the pennsylvanian fountain formation and the ralston creek member of the morrison formation. this is about 16 m lower than placed by peterson and turner (1998) noted on the right side (j-5 of p&t). the lithological and color change marking the lighter colored lower and pinkish upper portions (generally more vegetated reflecting a change in soil clay minerals) of the unnamed member is visible below cope’s nipple and in the valley of death. the cretaceous lytle formation has a lower (1) and upper (2) sandstone. the k-1 unconformity is at the base of sandstone 1. (b) ralston creek member in shaws park, showing the location of the diplodocid quarry 4 m above the fountain formation. downslope wash of weathered ralston creek hides most of the abrupt contact of the j-5 unconformity. (c) angular quartz pebbles of the conglomeratic sandstone in the diplodocid quarry. camera lens cap ~7.5 cm across. (d) channel sandstone about 2 m above the j-5 unconformity at the top of the orange-colored fountain formation, west side of fourmile creek. photograph in a, courtesy of dan grenard (retired, bureau of land management, ) and d. vicki garrisi (true west properties). 7 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 mesas in garden park (figures 4a, 5a, and 5b). it is a tan to olive, thin-bedded sandstone with some shale layers. sand grains range from medium to coarse and are rounded. calcite is absent. quartz comprises 85% to 90% of the rock and iron oxide and clay cement is about 5%. the ralston creek member we reassign the strata previously called the ralston creek formation as the lowest member of the morrison formation in garden park, along the front range, and in the denver basin. doing so eliminates lithostratigraphic correlation inconsistencies, conflicting ages, and contradictory depositional histories. nomenclature history in the cañon city embayment (which includes garden park at the north), the morrison formation rests upon strata that have been called the ralston formation (de lay, 1955; frederickson and others, 1956; hassinger, 1959; sackett, 1961; cramer, 1962), the ralston creek formation (brady, 1967, 1969; enciso, 1981; sweet, 1984a; carter, 1984; gong, 1986; richardson, 1987; johnson, 1991; anderson and lucas, 1994), the “ralston creek formation” (in quotes, schultze and enciso, 1983), the todilto formation (de ford, 1929; figure 5. (a) west side of shaws park showing the entire morrison formation below an unnamed butte. the reddish colors characteristic of the upper part of the formation along felch creek are absent here. (b) cretaceous lytle formation sandstone beds 1 and 2 below the capping glencairn formation on cottage rock. purple paleosol a and red paleosol b were considered the k-1 unconformity by peterson and turner (1998). we place the k-1 below sandstone 1. photograph courtesy of vicki garrisi (true west proerties). 8 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 heaton, 1950), the wanakah formation (schaeffer and patterson, 1984), and the bell ranch formation (peterson, 1994; peterson and turner, 1998; turner and peterson, 1999). other names that have been applied to the strata in the northern part of the front range, which marks the western edge of the denver basin, include the windy hill sandstone member of the sundance formation (pipiringos and o’sullivan, 1976; imlay, 1980) and canyon springs member of the sundance formation (pipiringos and o’sullivan, 1978). the same strata in southeast colorado have been referred to as the part of the morrison (lee, 1902), an unnamed “middle unit of jurassic age” (oriel and mudge, 1956), bell ranch (prince, 1988), and ralston creek (hager, 2015). in kansas, the gypsum-rich strata are included in the base of the morrison formation (merriam, 1955). the ralston formation [sic] was proposed in leroy's (1944) dissertation and officially published two years later (leroy, 1946). the strata lay between the lykins and morrison formations on the west side of the dakota hogback west of denver, colorado. van horn (1957) amended the name to the ralston creek formation because two other formations were already named ralston (principle of homonymy, north american commission on stratigraphic nomenclature, 2005, article 7(b)). leroy (1946) designated the stratotype at the southwest end of ralston reservoir for 25.3 m (originally reported in feet as 83 ft) of thin beds of predominately gray shale and marlstone, and yellow sandstone and siltstone. the selection of this stratotype is unfortunate because the strata there are not typical of the gypsiferous ralston creek that underlies most of the denver basin. leroy (1946) noted that the gypsiferous facies in the ralston occurred about 19.5 km south near the town of morrison. it is unfortunate that leroy did not continue to trace the ralston creek farther south along the front range because the gypsum-free shale-marlstone (i.e., mudstone and calcareous mudstone) facies of the stratotype was atypical. throughout eastern colorado, the ralston creek mostly consists of variegated mudstone (mostly shades of gray and green with some red) interbedded with gypsum (including some anhydrite) beds, and sandstone (heaton, 1939; saylor, 1955; fredrickson and others, 1956; johnson, 1962; prince, 1988; johnson, 1991; hager, 2015). in the western part of the cañon city embayment and south along the east side of the wet and sangre de cristo mountains, the ralston creek includes arkosic conglomerate, sandstone, and mudstone that probably represent alluvial fans coming off the remnants of the ancestral rocky mountains (de ford, 1929; de lay, 1955; fredrickson and others, 1956; metz, 1959; hassinger, 1959; sackett, 1961; cramer, 1962; johnson, 1991). calcite and dolomite are common carbonate minerals in the non-gypsum facies as either cement, limestone, or calcrete (carter, 1984; gong, 1986; richardson, 1987). ralston creek member contact the contact between the ralston creek (member) and morrison (unnamed member of the morrison formation [our usage]) was placed by leroy (1946, p. 53) at a disconformity below the “basal sandstone of the morrison.” this criterion assumed that the lowest sandstone cropping out intermittently from the talus, soil, and vegetation was the same all along the dakota hogback. later work demonstrated that this was not the case. instead, the basal morrison sandstone was actually lenticular sandstone bodies that were laterally discontinuous and were at slightly different stratigraphic positions relative to one another (scott, 1963; johnson, 1991). elsewhere in eastern colorado, various conflicting criteria have been used to mark the contact: (1) the combination of loss of gypsum, presence of limestone, welded cherts, and ledge-forming, massive sandstone beds (de lay, 1955; saylor, 1955; frederickson and others, 1956; carter, 1984), (2) the top of the highest chert bed (oriel and craig, 1960), (3) the base of the lowest sandstone (sackett, 1961), (4) the top of the highest conglomerate and gypsum bed or color change to gray and green mudstones (cramer, 1962; brady, 1967), (5) the first laterally extensive limestone bed (enciso, 1981), (6) at the base of the lowest welded chert (sweet, 1984a; peterson and turner, 1998), (7) the change from sand-sized grains to clay-sized grains and loss of gypsum (prince, 1988), and (8) at the top of a blue chert bed (hager, 2015). giltner (1953), merriam (1955), johnson (1959), and johnson (1991) concluded that no solution was possible and included the lithofacies in the morrison formation. in doing so, they reverted back to the 9 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 definition of the morrison formation given by cross (1894) and mook (1916), which included gypsum beds. the use of the welded chert boundary is strongly advocated by peterson and turner (1998) as a nearly isochronous boundary in the lower part of the morrison formation. king and merriam (1969) contend that the source of the silica forming the welded chert is from the devitrification of glassy volcanic ash fall. this hypothesis is supported by the discovery of partially devitrified glass shards in the morrison of the front range by keller (1962; see also johnson, 1991). using the welded chert in the morrison, however, is at odds with how it was first described by ogden (1954, p. 914), who identified the welded chert as “near the top of the ralston formation” and used that to correlate with occurrences in the sundance formation of northern colorado and wyoming. in garden park, both hassinger (1959) and sweet (1984a) noted that welded chert beds occurred in facies identified as the lower morrison formation; welded chert is seen, for example, in sandstone beds near the bridge across fourmile creek. prince (1988) on the other hand, noted a change in the stratigraphic position of the welded chert from near the top of the ralston creek lithofacies to near the bottom of the morrison lithofacies along the purgatoire river. cramer (1962) noted that the chert is common in a 18.3-m-thick (originally reported in feet as 60 ft) zone of calcareous sediments that span ralston creek and morrison lithofacies. enciso (1981) concluded that the cherts represented silicified evaporites and discounted the importance of the welded cherts as a reliable marker. joeckel and others (2007) also noted that chert replaced evaporites in the morrison of kansas. at best, we conclude that the welded chert zone is a broad band that straddles the upper ralston creek and lower morrison lithofacies and is not a reliable isochronous surface; it may define a broad zone affected by changing groundwater chemistry during the late jurassic (see further below). whether this holds true for the welded cherts in other formations, such as the sundance, we cannot say. ralston creek member in garden park west of fourmile creek, the ralston creek member is predominately composed of 21 to 24 m of gray, greenish-gray to light-brown sandstone, siltstone, and mudstone, and lesser amounts conglomerate. the conglomerate beds, mostly confined to the lower part, are composed of subroundedto rounded, pebbleto peasized fragments of quartz (figure 4c) and metaintrusives derived from the reddish pikes peak granite of late mesoproterozoic age (1.1 ga, anderson and cullers, 1999). the sandstone beds consist of subrounded to well-rounded, coarseto fine-grained sand, and the siltstone beds are composed of quartz and potassic feldspar grains with calcite cement. the quartz:feldspar ratios range between 70:30 and 90:10. together, quartz and feldspar comprise 40% of the rock at the base of the formation and 75% near the top. clay content ranges from 50% at the base of the formation to 10% to 15% near the top. east of fourmile creek, along the north facing scarp of felch creek (figure 6a), the ralston creek is composed of sandstone, siltstone, mudstone, and some thin gypsum beds. the gypsum content increases eastwards across the cañon city embayment (figures 6b and 6c) as noted by de lay (1955), fredrickson and others (1956), cramer (1962), and carter (1984). poorly preserved fossil fish have been recovered from sandstone beds near the base along felch creek (dunkle, 1942; schultze and enciso, 1983; schaeffer and patterson, 1984), and are discussed further below. composition of the conglomerate and mineral content of the sandstone and siltstone beds suggest that the ralston creek member received sediments from the same source as the underlying fountain formation, and/or that the ralston creek is derived, at least in part, from reworking the fountain; this is elaborated further below. a partial diplodocid sauropod skeleton was collected in this conglomeratic facies 4 m above the fountain formation near the shaws park-garden park divide (figures 4b and 5a); it is under study by virginia tidwell (volunteer, denver museum of nature and science). age of the ralston creek member the correlation of the ralston creek member along all or part of the front range to the cañon city embayment has been demonstrated by de lay (1955), saylor (1955), frederickson and others (1956), and especial10 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 ly johnson (1991). their results contrast with peterson and turner (1998) who are of the opinion that the strata in garden park cannot be assigned to the ralston creek because “some of these beds are middle jurassic in age and therefore older than the type ralston creek west of denver” (peterson and turner, 1998, p. 26). the middle jurassic age was inferred from the fish taxa hulettia americana and todiltia schoewei that were reported figure 6. lateral changes in the ralston creek member. (a) exposure along felch creek, east of fourmile creek with prominent sandstone lenses in the lower part and thinner calcic sandstone, siltstone, and mudstone beds in the upper; some gypsisol horizons also occur in this upper part. (b) alternating petrogypsic horizons, mudstone and sandstone at cramer’s (1962) measured section 12 in eightmile park. this site is about 12.2 km southeast of (a). (c) repetitious alternating gray-weathering gypsisols, and gypsiferous fine-grain sandstone and grayish-green mudstone of a playa margin facies in a road cut of colorado state highway 115, 21.5 km east of (a). (d) alternating thin, laterally discontinuous gypsum beds, reddishto greenish-gray mudstone with nodular gypsum along the purgatoire river, prc site of hager (2015); 173.75 km southeast of (a). rock hammer for scale. photograph (d) courtesy of paul myrow (colorado college). 11 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 from near the base of the strata along felch creek (enciso, 1981; schultze and enciso, 1983; schaeffer and patterson, 1984). these taxa are also present in the todilto formation of new mexico and in the hulett sandstone member of the sundance formation in the big horn basin, wyoming (schultze and enciso, 1983; schaeffer and patterson, 1984). lucas and others (1985) using regional correlation concluded that the todilto formation of new mexico is middle callovian, and imlay (1982) concluded the hulett sandstone of wyoming is lower callovian. two crucial, but overlooked, comments regarding the specimens from garden park are that the specimens are poorly preserved (dunkle, 1942) and are of juveniles in which the diagnostic characteristic features of the adults are not yet developed (schultz and enciso, 1983). the descriptions of todiltia by schultz and enciso (1983) are not of the garden park specimens, but on the better-preserved specimens from the todilto formation of new mexico. furthermore, kirkland (1998) described a second species of hulettia—h. hawesi— from the morrison formation suggesting that, at least at the generic level, jurassic freshwater fishes may be long lived. however, schultz (retired, university of kansas, verbal communications to carpenter, 2017) is not convinced that h. hawesi is diagnostic because the crucial skull is unknown. at best, the specimens from the ralston creek strata indicate the presence of primitive actinopterygians. finally, if as we show below, the ralston creek is nonmarine, then the fish from garden park were probably freshwater and are doubtfully the same taxa as from the marine sundance and todilto formations. we therefore contend that the middle jurassic age for the ralston creek member has not been established based on the fossil fishes. there is now evidence for a kimmeridgian age for the ralston creek strata making it 10 ma younger than previously considered. this evidence includes the diplodocid skeleton collected 4 m above the pennsylvanian-age fountain formation in strata previously identified as ralston creek (de lay, 1955; fredrickson and others, 1956; enciso, 1981; schultze and enciso, 1983; gong, 1986; richardson, 1987 ), and a zircon 206pb/238u weighted mean date of 152.99 ± 0.10 ma reported by hager (2015, appendix c) from near the top of the ralston creek along the purgatoire river (figure 6d). schumacher (reported in hager, 2015) obtained a u-pb date of 151.46 ± 3.1 ma in the same general area from an ash just above the upper-most gypsum bed in traditional morrison lithofacies. these dates straddle the kimmeridgian-tithonian boundary at 152.1 ± 0.9 ma (cohen and others, 2013) and show that the ralston creek strata are coeval with the salt wash member of the morrison formation of the colorado plateau (trujillo and kowallis, 2015) and possibly the tidwell member as well. the younger age (late jurassic) for the ralston creek strata does much to resolve the alleged 10 ma-old disconformity that is supposed to separate the ralston creek and morrison (unnamed member of our usage) formations (schultze and enciso, 1983; schaeffer and patterson 1984; de albuquerque, 1988; anderson and lucas, 1994, and others). we agree with de ford (1929, p. 78), schulze (1954), fredrickson and others (1956), hassinger (1959), brady (1967, 1969), enciso (1981), schultze and enciso (1983), sweet (1984a), richardson (1987), and johnson (1991) that the contact is conformable, except locally beneath the lowest sandstone of the typical morrison (unnamed member of our usage). peterson and turner (1998, p. 27) acknowledged the difficulty in identifying an unconformity (contrary to their figure 5); “the upper contact of a ‘ralston creek formation’ would have to be determined by the presence of a thick or moderately thick sandstone bed at the base of a restricted morrison formation. but where a reasonably thick sandstone bed is absent, the similarity of limestone-bearing red and green mudstone in both formations would make it difficult if not impossible to establish a contact between the two formations.” in addition, it seems inconceivable for there not to be paleosol development in the mudstone marking the alleged 10 ma disconformity or unconformity such as that seen separating the upper jurassic morrison formation from the lower cretaceous cedar mountain formation in eastern utah (e.g., kirkland and madsen, 2007; kirkland and others, 2016). schulze (1954) and hassinger (1959) made a similar observation, noting that the gypsum at the top of the ralston creek does not show erosion or weathering that would be expected for long subareal exposure. 12 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 finally, excluding the dubious identification of the fishes, other fossil evidence suggests a greater affinity of the ralston creek with the morrison formation as acknowledged by leroy (1946) and by curtis (1963). cramer (1962) reported palynomorphs from low in the ralston creek strata in garden park, including the cheirolepidiacean conifer classopollis minor (abundant), the araucariacean callialasporites dampieri (as zonalapollenites dampieri, common), monosulcites sp. (common), and the caytoniaceous seed ferns caytonipollenites sp. and vitreisporites sp. (rare). baghai-riding and others (2014) and dangles and others (2014) report a small assemblage of palynomorphs from near colorado springs, which paul myrow (colorado college, verbal communications to carpenter, 2017) states is high in the ralston creek. taxa include the ferns ischyosporites marburgensis (abundant) and cyathidites minor (abundant), the cheirolepidiacean conifer classopollis (abundant), araucariacean conifer araucariacites spp. (rare), possible taxodiacean conifer exesipollenites tumulus (rare), and bisaccates (pine, voltziales, or podocarp – rare), as well as the probable freshwater dinoflagellates spiniferites and cf. odontochitina (rare). other plants reported from the ralston creek include leaves of the cupressacean elatides williamsoni and the cone palissya sp. (this identity is doubtful because palissya is rhaetian–lower jurassic, pattemore and others, 2014), and the kimmeridgian charophytes aclistochara sp. and echinochara spinosa (leroy, 1946; van horn, 1957; peck, 1957; scott, 1962, 1963). microbialites (mats, stromatolites, biolaminates) also have been reported (cramer, 1962; enciso, 1981; de alburquerque, 1988). invertebrates include freshwater gastropods lymnaea morrisonensis and gyraulus veternus, the unionid cf. vetulonaia faberi, and ostracods indent. (leroy, 1946; van horn, 1957; scott, 1962, 1963). yen (1952) noted that g. veternus is widely distributed in the morrison formation. vertebrate fossils include the diplodocid skeleton in shaws park mentioned above, unidentified dinosaur bones (richardson, 1987), and large ornithopod tracks reported by prince (1988). another dinosaur skeleton was reported in a letter by william utterback from the carnegie museum who was digging at cope’s nipple (see carpenter, 2019); “have portions of a small skeleton found in the jurassic near the trias or red beds. it shows several vert. and what looks to be the sacrum” (letter to john hatcher, december 1, 1901, carnegie museum archives). unfortunately, the skeleton cannot be found in the carnegie museum collections. the “red beds” were assume by hatcher (1902) to be triassic but are now known as the pennsylvanian fountain formation. ralston creek as a member our proposal to include the ralston creek strata in the morrison formation is not without precedence as other authors have included ralston creek in the morrison along the front range (heaton, 1950; imlay, 1952; boos and boos, 1957; grose, 1960; pipiringos and o’sullivan, 1976, in part; and johnson, 1991). o’sullivan (1992) even recommended designation of the ralston creek as a member; “the gypsum-bearing beds in the front range embayment probably should be assigned to the morrison formation as a lower member,” a conclusion we had independently reached as well. we therefore formally reassign (north american commission on stratigraphic nomenclature, 2005, article 19(b)) the ralston creek as a basal member of the morrison formation, with the stratotype at ralston reservoir as originally designated by leroy (1946) for the “ralston formation” (north american commission on stratigraphic nomenclature, 2005, article 8(e)). the ralston creek has four lithofacies as first noted by frederickson and others (1956) that grade into one another west-to-east: (1) a conglomerate facies (figure 4b and 4c), (2) a sandstone facies (figure 4d), (3) a gypsum-mudstone facies (figure 6b and 6c), and (4) a sandstone-mudstone-gypsum facies (figure 6d). owing to the contentious nature of the upper contact in the gypsum-mudstone facies (see above), we place the contact with the overlying unnamed member at the highest readily traceable gypsum or gypsiferous bed (north american commission on stratigraphic nomenclature, 2005, article 23(a)). so defined, the contact is not isochronous, nor does it need to be (north american commission on stratigraphic nomenclature, 2005, article 22 (e)). the bottom contact is the j-5 unconformity, which is well expressed where: (1) the con13 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 glomerate beds of the ralston creek member lap onto precambrian granites west of cañon city, (2) it overlies the pennsylvanian fountain formation in the gpnnl, (3) it overlies the triassic-age lykins formation east of cañon city (figure 6b), and (4) it laps onto older rocks subsurface in eastern colorado and western kansas (de ford, 1929; heaton, 1939; de lay, 1955; merriam, 1955; saylor, 1955; fredrickson and others, 1956; oriel and mudge, 1956; hassinger, 1959; sackett, 1961; cramer, 1962; schultz and enciso, 1986; richardson, 1987; de albuquerque, 1988; prince, 1988; johnson, 1991; hager, 2015). gypsum of the ralston creek member the gypsum facies of the ralston creek member have greatly influenced previous interpretations of the depositional environment. these hypotheses range from marine, including hypersaline embayment, lagoon, or tidal flat (heaton, 1939, 1950; de lay, 1955; frederickson and others, 1956; hassinger, 1959; cramer, 1962; curtis, 1963; scott, 1963; martin, 1965; schaeffer and patterson, 1984; de albuquerque, 1988; anderson and lucas, 1994; peterson and turner, 1998), sabkha (carter, 1984; gong, 1986; see al-youssef, 2014 for discussion of gypsum production in a classic sabkha), fluvial (johnson, 1991), lacustrine (leroy, 1946; sackett, 1961; hager, 2015), or playa (giltner, 1953; merriam, 1955; oriel and mudge, 1956; sweet, 1984b; richardson, 1987; prince, 1988; peterson and turner, 1998). a marine influence is seemingly strengthened by the report of glauconite in sandstones in the ralston creek along the southern margin of the cañon city embayment (de albuquerque, 1988). keller (1958, 1962), however, reported glauconite in the brushy basin member elsewhere in colorado. the presence of glauconite in sediments associated with alkaline-saline lakes has been reported by furquim and others (2010), which supports the hypothesis of keller (1958) that playa lakes might have been responsible. furquim and others (2010) note that transformation of smectites into nonmarine glauconite requires groundwater high in dissolved potassium but low in silica, a moderately alkaline ph, seasonal wet-dry cycles, a high availability of ferric oxide, and a reducing redox potential. presumably, these conditions were present at the time of glauconite production in the ralston creek member, with a potassium source from the weathering of potassium feldspars in the precambrian pikes peak granite. finally, j. ridgely (in prince, 1988) noted that the geochemical signature of the ralston creek gypsum is nonmarine in origin, which we look at next. groundwater, not subaquatic precipitation, is the major source for nonmarine evaporites because groundwater leaches minerals from the surrounding sediments and bedrock, and then precipitates evaporite minerals in arid and semiarid climates (rosen, 1994; warren, 2016). rosen and warren (1990a, 1990b) present five criteria to distinguish between groundwater-formed gypsum and subaquatic-formed (playa lake and marine evaporite basin) gypsum, which we apply to the ralston creek gypsum: (1) individual gypsum layers are typically <30 cm thick (figure 6a and 6b), versus meters thick beds of subaqueous settings (figure 7d). (2) crystals grow displacively below the ground surface (figure 7a), versus subaqueous crystals that are deposited on or grow upwards from a nucleation surface, i.e., the sediment-water interface, thus have a distinct bedding plane (figure 7d; see warren, 2016, figure 1.28). (3) crystals are typically lenticular due to elevated ground temperature and the presence of terrestrial humic compounds (cody and cody, 1988), and the crystals are arranged vertically, with matrix seen as inclusions following the crystal twin planes and surrounding the crystals (figures 7a to 7c), versus subaqueous crystals that are usually prismatic, forming irregular “chicken-wire” texture in laminated beds, and nucleated on a common bedding plane (figures 7d to 7f). (4) crystals form in a zone parallel to the playa lake strandline and rarely co-occurs with halite, versus subaqueous crystals formed in the basin center or inland of the coastline and interlayered with subaqueous halite facies. (5) hydrology is dominated by capillary evaporation (evaporative pumping) from groundwater versus hydrology of evaporite brines formed in a playa lake. however, al-youssef (2014) notes that ground surface evaporation causes recharge of the groundwater from the adjacent arabian gulf in the coastal umm said sabkha, eastern qatar. separating thick gypsum beds formed subaqueously in large playa lakes or marine evaporite basins is difficult (chi14 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 vas, 2007; warren, 2016), although context helps (e.g., marine invertebrates in associated shale or limestone). on a regional scale, playa lake gypsum beds are interspersed with gypsiferous paleosols (e.g., figures 6c and 6d) that formed in a zone marginal to the strandline. for clarification, we use “playa” in the restricted sense of rosen (1994) and briere (2000) with one slight modification; a playa is a discharging intracontinental basin with a negative water balance, remaining dry most of the year. rosen (1994) and briere (2000) set an annual minimum for being dry at 50% and 75%, respectively. in the geological record, we can only make assumptions about how long a playa is dry annually. we assume from studies of modern playas that those in the geologic past were dry for a significant part of the year, thus our vague qualifier “most of the year.” a playa complex is an intracontinental depositional basin that features multiple playas (see jacobson and jankowski, figure 7. comparison of playa and marine gypsum. (a) playa gypsum has vertically oriented crystals that formed within soils of the playa margin. (b) these crystals grow by displacing the substrate silt and clay, which is crowded to edges, thus outlining the crystals. (c) slabbed section showing the internal crystal fabric and displaced substrate outlining the crystals. dark speckles in the center are tiny gypsum or selenite crystals; sample taken from just right of (b). images (a) and (b) from road cut in figure 6c. (d) bed of weathered marine gypsum (center band) at the base of the piper formation (equivalent to sundance formation) south of big pryor mountain, montana. (e) marine gypsum is not dominated by vertically oriented crystals as seen in a close-up of the weathered gypsum (black box in d). displaced substrate outlines the crystals, which are better seen in (f), a polished slabbed section (sample nh.101.11) on display at the draper museum of natural history in cody, wyoming (bright flares are reflections of display lights). this sample shows the characteristic “chicken wire” texture of marine gypsum. scales in cm. 15 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 1989, figure 13; warren, 2016, figure 2.22) and is the concept we envision for the depositional environment of the ralston creek. geologic setting and depositional environment of the ralston creek member the ralston creek was deposited in a broad, 575-km-wide basin that was bounded on the west by the low remnants of the ancestral rocky mountains and on the east by the cambridge arch-central kansas uplift (merriam, 1955) (figure 8). the basin was also bounded on the south by the sierra grande (apishpa) and cimarron arches (prince, 1988), but was mostly open to the north towards the sundance sea, which was located at this time in central or northern wyoming. the base of the ralston was deposited on an irregular terrain with up to 33 m of relief (de lay, 1955; merriam, 1955; frederickson and others, 1956; richardson, 1987). the ancestral rockies at this time were very low, and probably measured in tens to hundreds of meters, not thousands of meters, because they were eroded and buried in the short time represented by ralston creek member. if start of ralston creek deposition was about the same time as the start of the gypsiferous tidwell member on the colorado plateau, then deposition of the ralston creek member took about 4 million years (see trujillo and kowallis, 2015). the inferred low profile of the ancestral rockies was insufficient to produce an effective rain shadow in the manner analogous to the basin and range-created playas today (rosen, 1994). because groundwater apparently could flow northwards down the potentiometric gradient towards the sundance sea, the ralston creek depositional basin is a through-flow or open playa complex as defined by rosen (1994) and chivas (2007). this through-flow groundwater system with local surface discharge (playa lakes) being surrounded by topographically low relief is similar to a system called a boinka in australia (macumber, 1991; rosen, 1994). the formation of gypsisols (as defined by mack and others, 1993) is a “bottom up” phenomenon due to evaporative pumping at the surface, whereas most soils form from the top down. the predominance of gypsum over other evaporites in the ralston creek member is probably due to two equally important phenomena. the first phenomenon is the attainment of a steady state flux ratio, whereby groundwater outflow (evaporation, through-flow, etc.) to inflow is such that only one or two evaporite minerals precipitate rather than a spectrum (wood and sanford, 1990, in contrast to the brine evolution concept of eugster and hardie, 1978). as a result, more soluble minerals such as halite, may never form. or if they do form when the flux ratio changes due to increase groundwater outflow (e.g., during drought), they will quickly dissolve when the system returns to figure 8. reconstruction of the ralston creek boinka, a huge complex of playa lakes and gypsisols. view towards the north from what is now southeastern colorado. the basin is bounded to the west by low remnants of the ancestral rocky mountains, to the east by the cambridge arch-central kansas uplift, and along the south by the sierra grande (apishpa) and cimarron arches. the open northern end of the basin is marked by vegetation. thick beds of gypsum east of the present front range suggests long-lived playa lakes were present near the ancestral rocky mountains. although the landscape may look barren, it was probably covered with gypsophilic and other xeric plants (see discussion by czaja and others, 2014). 16 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 the steady state position with seasonal rain. richardson (1987) reported salt pseudomorphs at the top of limestone beds in the ralston creek near cañon city, and hager (2015) reported salt casts in the ralston creek along the purgatoire river. presumably these are halite pseudomorphs or casts. the second phenomenon was that inflow groundwater along the basin margins was already saturated with dissolved gypsum from older, gypsum-rich bedrock present along the margins of the basin (e.g., triassic lykins formation along the west side, and permian flower-pot, blaine, and dog creek formations along the east side). a strong correlation between gyspic soils and underlying gypsum-rich parent rock has been noted before (e.g., bockheim, 2014; casby-horton and others, 2015). gypsic soils also contain gypsum nodules that may be up to several centimeters in diameter (carter, 1984). in the ralston creek, these nodules occur in mudstone, siltstone, and fine-grained sandstone, and may coalesce into discontinuous irregular beds (e.g., figure 6c and 6d). based on the 152 ma radiometric dates high in the salt wash and ralston creek members (see above), the ancestral rocky mountains must have acted as a topographic barrier between the two depositional systems (see craig and others, 1977). as described above, conglomerates in the western outcrops of the ralston creek indicate low gradient alluvial fans on the eastern side of the remnant mountains, and the isopleth map of grainsize distribution given by craig and others (1955, figure 27) shows a decrease in sorting in the eastern-most portions of the salt wash. a similar decrease in sorting was cited by them as evidence for proximity of the salt wash in south-central utah and northeastern arizona to a source area. thus, the eastern-most salt wash must have been deposited near a source area, which would have been the western side of the ancestral rockies. termination of ralston creek deposition was marked by overtopping of the ancestral rockies as evidenced by the sandstone-mudstone facies of the typical morrison in unconformable contact with precambrian granites along the wet mountains (brady, 1967), in the present day intermountain basins (e.g., north and middle park, wellborn, 1977; south park, fisher, 1977; fraser basin, shroba and others, 2010; webster park, de ford, 1929), and in the conformable contact of the unnamed member with the underlying ralston creek member across eastern colorado and western kansas. the termination of gypsum deposition was gradual as the overtopping morrison facies was deposited progressively farther eastward through time as evidence by the stratigraphic position of the gypsum facies relative to a tuff marker bed (cramer, 1962). this sedimentary change was undoubtedly accompanied by a change in groundwater chemistry, which probably resulted in formation of a welded chert zone. the progressive eastward shift in facies explains the observation by frederickson and others (1956) and prince (1988) that the welded cherts are time transgressive. the change in groundwater chemistry at this time may explain the abundant lacustrine carbonates in the lower part of the morrison formation in eastern colorado (giltner, 1953; prince, 1988; dunagan, 1998). what would have been playa lakes depositing gypsum, were now freshwater lakes maintained by groundwater (dunagan, 1998). a shift in the outflow/inflow ratios during droughts may explain the presence of the occasional evaporites and temporary playa lakes (giltner, 1953; sweet, 1984a, 1984b; dunagan, 1998). as is typical for modern playa areas, eolian sand grains (frosted, unimodal, and usually rounded) occur in the ralston creek member, with the thickest eolian deposits downwind on the east side of the basin (merriam, 1955; frederickson and others, 1956). some of the grains are probably recycled from the older eolian entrada sandstone. de lay (1955) reported chert ventifacts near the base of the ralston creek in the western part of the cañon city embayment. the presence of microbial mats, stromatolites, etc. (de albuquerque, 1988) indicates the presence of more permanent brine lakes. these microbialites form in the strandline (warren, 2016). the unnamed member the unnamed member of the morrison formation in the gpnnl is what has traditionally been referred to as the morrison formation since the introduction of the term “ralston formation” into the cañon city embayment by delay (1955) and saylor (1955) for the gypsiferous facies. the unnamed member is predom17 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 inantly gray-green to rusty red mudstone, with many sandstone lenses, mostly discontinuous, but with a few thicker, more persistent beds (figure 4a; evanoff and carpenter, 1998). color variations of the mudstone beds are in part stratigraphic and in part reflect the oxidation state of the contained iron. in the vicinity of fourmile creek, gray-green is the dominant color of the lower part of the member, and various shades of reddish color in the upper part (figure 2). this allows the member to be subdivided informally here into lower and upper parts. this two-part color separation is absent in the eastern portion of gpnnl (“green acres” area, figure 9) and to the west in the shaws park area (figure 5a). a cyclical sandstone-mudstone unit lies at the base of the unnamed member along fourmile creek (figure 9b), which can be traced to below felch quarry 1 (figure 2a). all detrital rocks in the unnamed member are predominately clay, quartz, and potassic feldspar in varying quantities, and with, or without, calcite cement. thin limestone beds are also present in the lower part, with one prominent bed in “egg gulch” (figure 1). the different lithologies are discussed further below. trujillo and kowallis (2015) report a single-crystal 40ar/39ar laser probe date of 152.29 ± 0.27 ma from a bentonite mine in “green acres.” this mine is about 56 m above the ralston creek member (peterson and turner, 1998, figure 5 place the mine at 8 m above the ralston creek, which is well below the bentonitic mudstone beds that occur above the local clay change). all of the historic dinosaur quarries in garden park occur in the unnamed member of the morrison formation (see carpenter, 1998b; monaco, 1998). therefore, we discuss its sedimentology further. as noted above, the unnamed member west of fourmile creek can be informally subdivided based on color. the lower part consists predominantly of pastel gray-green mudstone and light grayish-white to pastel green sandstone, which make up to 13% to 14% in the measured sections. gray or green mudstone clasts from bank collapse are common in some sandstone beds, such as felch quarry 1, showing that the gray and green colors of the mudstone are primary in origin. the upper part of the unnamed member consists of predominately reddish to maroon mudstone, with lenses of green to greenish-gray paleosols (figure 2b; carpenter, 2019). the mudstones are predominately smectitic, but with an illite-kaolinite assemblage (see below). tabular reddish-white to yellowish-colored sandstone also occurs (figures 2b and 4a). correlations within the morrison throughout garden park are difficult due to the discontinuous, lensy nature of the sandstone and limestone beds, and to quaternary cover and landslide deposits that are mostly developed on the smectitic clays. a stratigraphic map and cross section that features the entire stratigraphic section of the morrison formation west of fourmile creek is shown on figure 10. figure 9. (a) bentonitic green-gray mudstone beds of the middle and upper part of the unnamed member as exposed in “green acres.” a bentonite mine 250 m to the left out of frame produced an 40ar/39ar date of 152.29 ± 0.27 ma (trujillo and kowallis, 2015). two quarries in the area produced partial skeletons of diplodocus longus and camarasaurus grandis. (b) alternating beds of thin sandstone and mudstone of the lower part of the unnamed member as exposed near the fourmile creek bridge. felch quarry 1 is on the other side of the hill (see figure 2a). photograph courtesy of dan grenard (retired, bureau of land management). 18 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 description of lithofacies thin-bedded unit (jmtb) this basal unit of crevasse splay deposits onto a floodplain is composed of thin alternating beds of gray mudstone to siltstone and sandstone exposed below felch quarry 1 (figure 2a) and near fourmile creek bridge (figure 9b). individual beds are rarely more than 2 m thick and most are less than 0.75 m thick. all beds are calcareous. the mudstone-siltstone beds are 50% clay, 50% quartz plus feldspar, with quartz and feldspar content about equal. feldspars are potassic and most show incipient clay alteration. the sandstone beds have identical mineralogy, but clay content is only about 20%. grain size ranges from clay to fine sand and individual grains are angular to subrounded. this unit is about 16.5 m thick. sandstone unit (jmss) the geometry of the sandstone bodies in the sandstone unit is predominately shoestring channels and sheet sands of crevasse splays in the lower portion, esfigure 10. geologic map and cross section showing stratigraphy and distribution of lithofacies in the area around cope’s nipple. line labeled a-b is location of cross section. geologic map by e. lindsey. 19 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 pecially near felch quarry 1 (evanoff and carpenter, 1998), and tabular sheets of sandstone in the upper portion, especially in the vicinity of cope’s nipple. twelve samples of sandstone were collected and examined. the mineralogy is the same as the mudstone except that clay content is only about 10% to 15% of the rock, whereas quartz plus feldspar comprises 85% to 90% of the total. quartz dominates in all samples and quartz:feldspar ratios vary between 75:25 and 90:10. all feldspar fragments are potassic and all display some degree of clay alteration. brady (1967, 1969) reported about 1% plagioclase feldspars in sandstone north of cope’s nipple. as in the mudstone beds, calcite cements the sandstone beds in the lower 73 m of the unnamed member. many sand grains are subrounded and frosted, a point also noted by hassinger (1959). the frosting was attributed to etching by the carbonate cement. alternatively, is the reworking of older, eolian sedimentary rocks. a thin section was made from the sandstone capping the 1830-m bench near cope’s nipple. grain size is about 0.2 mm in diameter, subangular to subrounded, and cemented by a clay and iron oxide mixture. there are very scarce patches of calcite cement. this sandstone was shown lithologically to have produced the holotype of the crocodylomorph hallopus victor (ague and others, 1995). calcareous sandstone occurs on the east side of garden park, in the green acres area. it also occurs sporadically to the west in “stegosaurus gulch,” a west-trending gully containing the small stegosaurus quarry (carpenter, 1998a). the rock is a grayto brown-weathering coarse-grained sandstone. in thin section, it appears to contain about 30% calcite cement whereas quartz grains comprise about 60% of the rock, and potassic feldspar grains are 5% or less. a small amount of clay and opaque minerals are also present. grain sizes range from 0.1 mm to 0.2 mm and they are subangular to subrounded. mudstone unit (jmms) mudstone comprises about 70% to 80% of the unnamed member in the garden park area. the mudstone is typically massive and variegated, and along fourmile creek, consist of alternating bands of greenish-gray, olive-gray, purple, and grayish-red beds in the lower part, and grayish-red, pale-red, reddish-brown, and yellowish-gray beds in the upper part. some of these colors appear differently in the unweathered profile. for example, purple weathered mudstone beds are usually blackish red (munsell color 5r2/2) when excavated, whereas gray weathered mudstone is often a dusky brown (5yr2/2). many colored bands have diffuse contacts with other bands, but some have an abrupt upper or lower contact (e.g., figure 2b). mottling is common in the mudstone, usually as various shades of green in the upper part, and greens and reds in the lower part. pedotubules and carbonate nodules are common, and small (5 mm) ferruginous nodules in the upper red beds. fifteen samples of mudstone in garden park were collected and analyzed (see figure 11 for sample locations). clay content ranges from 60% to 95%, decreasing upward. the quartz:feldspar ratios vary between 60:40 and 90:10. feldspars are potassic and most show some clay alteration. some quartz and feldspar grains are extremely small and are angular to subangular. calcite cement is present in the lower 73 m of the unnamed member. in “green acres” east of fourmile creek, calcite cement is present in the lower 82 m. above these measured levels calcite is absent. the distribution and vertical succession of clay minerals is depicted in figure 11. sample density is sparse in the garden park area, but the vertical distribution of clay minerals in the unnamed member duplicates that found by brady (1967) in a measured section 3.2 km north of cope’s nipple involving 14 samples. in the mudstone beds of the unnamed member, clay minerals form unique assemblages with smectite generally dominant throughout, but with significant illite in the lowermost assemblage. kaolinite, with illite, appears near the top of the section. in the lower middle part of the section brady (1967) reported an 8-m interval is exclusively smectite, whereas near cope’s nipple two samples in the upper middle part of the section are exclusively smectite. detailed clay mineral analyses are given in table 1. paleoenvironmental interpretation of the mudstone is discussed below. limestone unit (not mapped on figure 10) thin, discontinuous limestone beds comprise 5% of the morrison formation in garden park, especially in 20 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 the lower part above the ralston creek member. however, limestone beds also occur in the unnamed member as noted below. these limestone beds are dense, brown to gray, and microcrystalline. they are probably chemical precipitates rather than organic accumulations, and invertebrate fossils, especially ostracods and aquatic mollusks, are present (evanoff and others, 1998; schudack and others, 1998). these invertebrate fossils are fresh water forms indicating a lacustrine environment. ostracods in the limestone beds often have both shells in a closed position, suggesting the animals had enclosed themselves to exclude unfavorable water conditions, such as increased salinity due to seasonal evaporation of the lacustrine waters. this stress may also explain the generally small, stunted size of the gastropods as well. most of these fossils are silicified bright orange. figure 11. map showing distribution of clay mineral zones in the study area west of fourmile creek. mudstone (clay) sample sites labeled 1 to 13. the zone is stratigraphically arranged as shown in the legend. 21 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 the thickest, most laterally extensive limestone in garden park occurs near egg gulch (near sample site 10, figure 11). it is about 1 m thick and extends northsouth about 450 m. stratigraphically, it is near the middle of the unnamed member, in the smectite-dominant clay assemblage. this rock, informally the “egg gulch limestone,” has many hallmarks of a calcrete; it is extensively brecciated, has calcite and chalcedony lined cavities, red chert, and a rhizoliths. however, the presence of silicified, bright orange aquatic gastropods shows that the limestone was initially lacustrine in origin, and that it was later altered by pedogenesis. most of the gastropods are very small, being less than 5 mm in diameter. one exceptionally rich concentration of gastropods was seen within a branching burrow. the large diameter of the burrow, about 3 cm, suggests that it might have been that of a crayfish. another limestone, about 2 m thick, occurs near the bridge crossing at fourmile creek below felch quarry 1 (se¼ne¼se¼ section 28, t. 17 s., r. 70 w.). most of it is a stage iii calcrete (retallack, 1988) consisting of a continuous layer formed by coalescing nodules. the nodules are light-gray (n7) micrite, with splotches of brownish-gray (5yr4/1) color. bright red diagenetic chalcedony occurs as small globular masses or splotches of welded chert (king and merriam, 1969) and as linings in cavities between the nodules. these cherts have been used to correlate lower part of the unnamed member with the tidwell member on the colorado plateau by turner and peterson (1992). however, these welded cherts are not confined to the base of the unnamed member at garden park and depending on the definition of the contact (see section on the ralston creek member contact), they occur in the ralston creek member and as high as 1 m below the upper part of the unnamed member near cope’s nipple. most often, these cherts are associated carbonate beds and are secondary replacement of calcite (hassinger, 1959; cramer, 1962; enciso, 1981; sweet, 1984a). in a few places, the upper calcrete is a stage iv carbonate showing weakly developed lamellar structure. downwards in the bed, the nodules become more distinct and are blocky, calcareous siltstone. the nodules are mottled greenish-gray (10gy5/2) and moderate-red (5r5/4) to grayish-red (5r4/2) in color. a limonitic yellowish-orange stain occurs on the surfaces of the nodules. paleosols in the unnamed member the existence of paleosols in the morrison formation is now well established (e.g., mantzios, 1986; retallack, 1990; demko and others, 2004; tanner and others, 2014). laterally extensive colored banding of mudstones is an important (but not exclusive) feature in the field recognition of paleosols (retallack, 1983; bown and kraus, 1986; tabor and myers, 2015) and this is true of the morrison formation at garden park as well. color bands tend to lighten toward channel bodies reflecting less mature paleosols, the protosols of mack and others (1993). these lighter sediments are also typically coarser grained, being silty or sandy, and probably represent levee and splay deposits. cementation is usually better in the sandier facies resulting in irregular sandstone sheets up to 1 m thick. most sandstone sheets, however, are much thinner, being 10 to 20 cm thick. a basal conglomerate of matrix-supported angular to subangular carbonate nodules and clay balls is also present in many of the channel sandstone beds. the conglomerates originate from fluvial entrainment of bank collapse and table 1. clay breakdown stratigraphically given in percentages. sample locations shown on figure 7. 22 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 show that the formation of soil nodules in the floodplain sediments occurred early in pedogenesis (karcz, 1969, 1972; mather and others, 2008; carpenter, 2013). remnants of termite nests are also present in the sandstone beds showing infestation of tree roots (figure 12; hasiotis and demko, 1998). most of the paleosols in garden park are calcic argillisols based on the calcareous nature of the mudstones b horizons enriched with argillans, or clay skins; calcareous nodules are present and widely scattered throughout the lower portion. the a horizon is typically a blackish-red (5r2/2) color and often shows an extensive network of grayish-green (5g3/2) root casts. at the small stegosaurus quarry located in a former pond, there is an abundance of organic carbon, including fusain (rougier and others, 2015). elsewhere, the in-situ presence of dinosaur eggs provides additional clues to identifying the a horizon. at egg gulch, the eggs occur in a nonswelling, gray-weathering mudstone that, when fresh, is a mottled blackish-red (5r2/2) and grayish-green (5g3/2), blocky, calcareous mudstone with slickensides. medium gray (n5) micritic nodules are present and these have a very light ferruginous coating or dusting. the stratigraphically higher eggs at tim’s site near egg gulch occur in a swelling, grayish-weathering mudstone that was partially in a blackish-red (5r2/2) mudstone, with tiny (1 mm) grayish-orange pink spots (5yr7/2), and partially in a yellowish-gray (5y7/2) mudstone. the c horizon is best developed in the temple canyon area, 17 km southwest of garden park, where the morrison discordantly overlies precambrian granite and metamorphic rocks. here, the precambrian rocks are deeply weathered, with feldspars altered to clays. the basal part of the morrison is frequently a calcite-cemented, conglomeratic sandstone, with boulders up to 1 m in diameter. locally, however, a light-green mudstone is present. brady (1967, 1969), in his work north of cope’s nipple, found the lower 15.6 m of the mudstone beds in the unnamed member to be illitic, the middle 31.1 m to be smectitic, and the upper 55.8 m to be mixed illitic-kaolinitic. a similar succession occurs near cope’s nipple, although the thicknesses of the three assemblages differ. a three-fold division also occurs at the reference section of the morrison formation, but with a kaolinite and illite-dominated lower and middle sections, and a smectitic-dominated (as montmorillonite) upper section (keller 1953). a three-fold division is also present in the morrison of the colorado plateau (keller, 1962); it is present, although not as well developed near dillon, colorado (wahlstrom, 1966) where secondary illite has been identified (bell, 1986). turner and fishman (1991) have hypothesized that some illite may form at low syndepositional temperatures, but most illite is believed to be detrital (keller, 1962). whether the illite at garden park is primary or secondary is not known at this time. the percentage of illite in the samples is shown in table 1. smectitic clays are most likely the product of devitrification of volcanic ash because glass shards are identified throughout the section (keller, 1962; brady, 1969). figure 12. the vertical orientation of a fossil termite nest indicates a formerly infested tree root. sandstone is in the unnamed member of the morrison formation from the west side of felch quarry 1. height is about 50 cm. 23 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 the source of this ash was most likely along the southern california, nevada, and arizona border (rogers and others, 1974; kowallis and others, 2001; christiansen and others, 1994, 2015). the percentage of smectite in garden park is shown in table 1. much of the clay in the unnamed member is a illite-smectite mixed layer (table 1). this clay is widespread through the morrison formation in the western interior (turner and peterson, 1999; trujillo, 2006). this mixed layer clay may form by smectite illitization through the input of potassium ions (rask and others, 1997; cuadros, 2006). the potassium may derive from feldspars, which are ubiquitous in the morrison (keller, 1962). kaolinite appears in the upper part of the upper unnamed member at elevation 1830 m, and on the east side near green acres at elevation 1975 m. tabbutt and others (1989) suggest that kaolinite in the morrison is detrital in origin, whereas tank (1956) and mantzois (1986) believe the kaolinite is produced by weathering potassic feldspar in low ph (acidic) environments. the absence of calcium carbonate cement in the upper member of the morrison supports the possibility that low ph environments did exist and that kaolinite was produced there. kaolinite is also present low in the salt wash member of the colorado plateau, in the lower portions at the type section of the morrison, near golden, colorado, in the lower part of the morrison at blue mesa reservoir, colorado, in the upper portions of the morrison near dillon, colorado, and the black hills of wyoming and south dakota (keller, 1953, 1962; tank, 1956; wahlstrom, 1966; fiorillo and mccarty, 1996). the upward succession of clay mineral assemblages and the distribution of vertebrate fossils leads to contradictory conclusions regarding paleoclimate, a point also noted by tanner and others (2014) in western colorado (but not addressed by demko and others, 2004). based upon clay mineral stability at low pressures and temperatures described by singer (1980), the predominance of illite and smectite in the lower portion of the unnamed member at garden park suggests that waters in the environment were alkaline, with a relatively high cation concentration and a relatively low eh. such conditions would occur on a mature surface with low to moderate rainfall, which would result in slow moving rivers, large and numerous paludal areas, and with devitrifying volcanic ash supplying large amounts of cations to the waters. the appearance of kaolinite in the upper portion implies altered conditions, including a slightly acid ph, increased eh, and dilution of the cation concentration. such conditions could arise from increased rainfall, consequent increased river flow velocities, and flushing and diluting the paludal areas. however, as reported elsewhere (carpenter, 1998b), the aquatic vertebrates and invertebrates are comparatively scarcer in the upper part of the morrison at garden park as compared with the lower part. this scarcity does not appear to be due to taphonomic loss in an acidic environment because of the lack of dissolution features on the abundant dinosaur specimens and the few rare turtle bones found by us. conclusions the morrison formation along fourmile creek in garden park, colorado, is subdivided into the reassigned ralston creek member and overlying unnamed member. the morrison rests on the j-5 unconformity at the base of the ralston creek that can be traced along the front range and the rest of the denver basin. the ralston creek member has several facies. the most widespread facies is characterized by gypsum that was predominantly deposited as gypsisols and in a lesser amounts subaquatically in playa lakes. the non-gypsum facies preserved on the west side of the ralston creek depositional basin represent alluvial fans from the remnants of the ancestral rocky mountains. these mountains were only tens to hundreds of meters high, but formed a topographical barrier that separated the ralston creek and the salt wash depositional basins for about 4 million years. eventually erosion and deposition buried the mountains allowing the unnamed member to be deposited over the ralston creek sediments. the change in groundwater chemistry halted gypsum deposition and gave rise to the welded chert zone. the upper unnamed member of the morrison formation on the west side of fourmile creek can be subdivided into a lower part composed predominantly of green and gray smectite, dominated by smectite-illite mudstone and sandstone, and lesser amounts of la24 redefining the upper jurassic morrison formation in the garden park national natural landmark and vicinity, eastern colorado carpenter, k., and lindsey, e. geology of the intermountain west 2019 volume 6 custrine limestone. paleosols are well developed in the lower part as shown by pedogenic features (brecciated calcrete, welded cherts, a carbonaceous a horizon with rhizoliths, clay skins, and calcareous nodules in the b horizon). the upper part of the unnamed member is composed predominantly of purple and red smectite-dominant mudstone with little or no illite content. sandstone and limestone beds are less abundant here than in the lower part. at the top of the formation, illite is again present and kaolinite occurs for the first time in the clay mineral assemblage. sandstone beds in this upper part, while less abundant, are more continuous. paleosol development in this upper part are not as well defined, although clay skins and ferruginous nodules occur in the b horizon. the paleosols in garden park are mostly calcic argillisols and gypsisols. acknowledgments field photographs to replace those lost by carpenter were made available to us by dan grenard (retired, bureau of land management, cañon city, colorado) and vicki garrisi (true west properties, woodland park, colorado). paul myrow (colorado college, colorado springs, colorado) shared images taken along the purgatoire river, colorado. we thank dan, vicki, and paul for their use. william benzel (marathon oil company) analyzed the clay samples and his assistance is greatly appreciated. thin sections were prepared at the u.s. geological survey facility, denver federal center. air photos, used in the geologic mapping project, were supplied gratis by the bureau of land management. thanks to fred peterson (u.s. geological survey, denver, colorado) and emmett evanoff (university of northern colorado, greeley, colorado) for discussions in the field. thanks to bruce schumacher (u.s. forest service, la junta, colorado) for sharing the report on radiometric dates for the jurassic strata in the purgatoire river valley. review comments of earlier drafts by emmett evanoff, john foster (utah field house of natural history state park museum), kelli trujillo (laramie county community college), and my wife, yvonne wilson are appreciated. finally, field work in the garden park national natural landmark was conducted under bureau of land management permit c-49819(c). references ague, j., carpenter, k., and ostrom, j., 1995, solution to the hallopus enigma?: american journal of science, v. 295, p. 1–17. alf, k., 1998, preliminary study of an eggshell site in the morrison formation of colorado, in carpenter, k., chure, d., and kirkland, j.i., editors, the upper jurassic morrison formation— an interdisciplinary study, part ii: modern geology, v. 23, p. 241–248. al-youssef, m., 2014, gypsum crystals formation and habits, umm said sabkha, qatar, in khan, m.a., böer, b., öztürk, m., al abdessalaam, t.z., clüsener-godt, m., and gul, 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geologie und paläontologie monatshefte, v. 9, p. 565–576. cody, r.d., and cody, a.m., 1988, gypsum nucleation and crystal morphology in analog saline terrestrial environments: journal of sedimentary petrology, v. 58, p. 247–255. cohen, k.m., finney, s.c., gibbard, p.l., and fan, j., 2013, the ics international chronostratigraphic chart: episodes, v. 36, no. 3, p. 199–204, url:http://www.stratigraphy.org/icschart/chronostratchart2018-08.pdf. committee on stratigraphic nomenclature, 1933, classification and nomenclature of rock units: american association of petroleum geologists bulletin, v. 17, no. 7, p. 843–868. craig, l.c., holmes, c.n., cadlgan, r.a., freeman, v.l., mullens, t.b., and weir, g.w., 1955, stratigraphy of the morrison and related formations, colorado plateau region—a preliminary report: u.s. geological survey bulletin 1009-e, p. 125–168. craig, l.c., holmes, c.n., cadlgan, r.a., freeman, v.l., mullens, t.b., and weir, g.w., 1977, sheet 1 – isopach and facies map of salt 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1990, ground-water control of evaporite deposition: economic geology, v. 85, no. 6, p. 1226– 1235. yen, t.c., 1952, molluscan fauna of the morrison formation: u.s. geological survey professional paper 233-b, p. 21–51. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 6 2019 © 2019 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation kenneth carpenter theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover bones of camarasaurus supremus as found and excavated by oramel lucas in 1877. photograph was taken by c.w. talbot (cañon city, colorado). see figure 4 caption for more details. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 6 2019 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association volume 6 2019 31 abstract the discovery in 1877 of what proved to be an extensive multi-taxa bonebed from the upper jurassic morrison formation helped kick-start the first jurassic “dinosaur rush.” located north of cañon city, colorado, the site, known today as cope’s nipple within the garden park national natural landmark, was worked by oramel and ira lucas from 1877 to 1884, again by the carnegie museum in 1901, and sporadically by the denver museum of natural history from 1991 to 1996. the history of this work is presented in depth for the first time using extensive archival records. the quarries occur in a single horizon around the base of cope’s nipple and represents a widespread bonebed in distal overbank silty mudstone that was subsequently modified by pedogenesis. limited taphonomic data indicate the bonebed was a mix of allochthonous and autochthonous bone. history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation ken carpenter prehistoric museum, utah state university eastern, price, ut 84501; ken.carpenter@usu.edu; museum of natural history, university of colorado, boulder, co 80309 citation for this article. carpenter, k., 2019, history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation: geology of the intermountain west, v. 6, p. 31–53. © 2019 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the first jurassic “dinosaur rush” began with the near simultaneous discovery of dinosaur bones close to the towns of morrison and cañon city, colorado, in 1877 (figure 1). the discoveries and their role in the “bone wars” between prominent u.s. paleontologists othniel c. marsh and edward d. cope has been told numerous times by a variety of authors, most recently by jaffe (2000) and thompson (2008), among others. more detailed accounts of the discoveries near morrison by arthur lakes, who taught geology courses at jarvis hall, colorado territory’s first college, and his friend henry beckwith is told in lakes’ journals (kohl and mcintosh, 1997) and by honda and simmons (2009). farther south, two prominent sites were found north of cañon city in the area known as garden park. the account of homesteader marshal felch’s discovery was told in detail by evanoff and carpenter (1998). the other discovery, by school teacher oramel lucas has been briefly discussed by osborn (1931), monaco (1998), and mcintosh (1998). of these, the contribution by mcintosh was the most important because he sought to apportion the e.d. cope dinosaur collection, which had been briefly described in a series of articles (cope 1877a–d; 1878a–g) and later described in greater detail by osborn and mook (1921), to various quarries. the detailed history of the main lucas quarries at the base of a distinctive, conical hill locally known today as cope’s nipple (a.k.a. “the hill,” “saurian hill,” “the nipple,” “talbot’s hill;” figure 1a) from where most of the cope specimens came (figure 1b), is recounted below, along with a discussion of the sedimentology and taphonomy. both the felch and lucas quarries lie within 32 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 the bureau of land management’s garden park national natural landmark—formerly known as the garden park paleontological resource area. materials and methods beginning in the early 1990s, pat monaco and donna engard of wetmore, colorado, amassed a huge amount of e.d. cope and o.c. marsh archival documents for the garden park paleontological society in cañon city, colorado, referred to below as “gpps docs.” these documents are now housed at the royal gorge regional museum and history center, cañon city, colorado. copies of these documents have been made available to me and i draw upon them to recount the history of the excavations around cope’s nipple. other correspondence by oramel lucas to individuals at his alma mater oberlin college reside in the oberlin college archives. among these is a letter addressed to 0 25 mi 0 40 km n colorado enlarged area 470 50 24 24 40 285 93 74 denver morrison pueblo cañon city colorado springs r o c k y m o u n t a i n s dinosaur sites dinosaur sites (garden park) figure 1. (a) distant view of cope's nipple (aka, "the hill," "saurian hill," "the nipple") viewed west showing the location of the lucas quarries. fourmile creek (oil creek) marked by the trees at the base of photograph (image courtesy of vicki garrisi, true west properties). abbreviations: ff – fountain formation (pennsylvanian); rm – ralston creek member of the morrison formation (see carpenter and lindsey, 2019); um – unnamed member of the morrison formation (see carpenter and lindsey, 2019); l – lytle sandstone (cretaceous), (b) illustrations of sauropod dorsals made by cope: camarasaurus supremus (1) mid-dorsal (d-5), (2) a more posterior mid-dorsal (d-8), and amphicoelias altus (3) probably d-10. (4) the neural arch of amphicoelias fragillimus (now maarapunisaurus fragillimus, carpenter, 2018a). (c) example of the use of paper strips glued to the surface to hold fragments together. haplocanthosaurus scapula (ypm 4688) collected by mudge, felch, and williston, november, 1877, from felch quarry. scale in (b) = 1 m; scale in (c) = 10 cm. 1 to 3 from cope 1878b; 4 from cope 1878f. the green dashed line on the index map is the approximate location of the mountain front. index map by doug sprinkel (utah geological survey). 33 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 “will,” presumably one of four classmates named “william” (annonymous, 1876, p. 10–11). copies of these correspondence were made available to me by dan grenard, formerly of the bureau of land management, cañon city, colorado, and are referred to as “oberlin archives.” much of the unpublished information sheds light on the collecting by oramel william lucas (1849–1935) and to a lesser extent by his brother ira hiram lucas (1838–1920). among the documents is a transcription of an oral account, “discovering dinosaurs bones in colorado,” made by oramel lucas to his daughter ethel lucas prior to 1935; this is referred to as “lucas discovery ggps docs.” other gpps documents include an open letter from lucas to the class of 1880 on their 50th reunion (cited below as “lucas 50th, gpps docs”), letters from e.d. cope, as well as copies of drawings of bones made by oramel. published accounts appeared in the local press and in popular books written at the time of discovery. much of joseph pangborn’s (1878) eyewitness account of the lucas excavation was repeated verbatim by binckley and hartwell (1879) and rockafellow (1881). correspondence of oramel lucas, david baldwin, and benjamin mudge to o.c. marsh of the yale peabody museum are available at https:// peabody.yale.edu/collections/vertebrate-paleontology/ correspondence-o-c-marsh. the carnegie museum of natural history reopened some of the lucas quarries in august through september 1901. correspondence quoted from this time between john hatcher, william utterback, george axtell, and william holland is preserved at the carnegie museum of natural history (pittsburgh, pennsylvania) and is referred to as “cm archives.” minor typographic errors in quotes from all of these correspondences have been corrected except where noted by “[sic].” all of this archival information is pulled together below for the first detailed history of the excavations at cope’s nipple. sedimentological and taphonomic data is gleaned in part from various documents and from the denver museum of natural history excavations. dollar conversions to 2018 values are based on www.in2013dollars.com. institutional abbreviations amnh–american museum of natural history, new york, new york; cmnh–carnegie museum of natural history, pittsburgh, pennsylvania; dmnh– denver museum of natural history, denver, colorado; ypm–yale peabody museum of natural history, new haven, connecticut. lucas brothers dig dinosaurs (1877–1884) oramel william lucas, the discoverer of many of the jurassic dinosaur specimens described by edward cope in 1877 and 1878, moved to garden park north of cañon city, colorado, in june 1876. he relocated there from ohio where he had been a junior at oberlin college (anonymous, 1876, p. 10). he left college because he could not afford the costs (~$48/quarter, anonymous, 1876, p. 59; $1,131 in 2018) and took a teaching position in the garden park one-room school arranged by his sister, lucy ripley, who had settled in garden park with her husband (lucas discovery ggps docs). lucas is also sometimes referred to as the superintendent of schools for fremont county (e.g., cope, 1877b), a position he briefly held from april to october, 1877 (binckley and hartwell, 1879). when he left oberlin, he was advised by albert wright, professor of geology and natural history, to study geology out west. he later wrote to wright that he would occasionally wander the hills and mountains looking for geological specimens or deer (lucas to wright, april 6, 1877, oberlin archives; lucas was not an amateur botanist looking for plants as claimed by jaffe, 2000). on one of these jaunts in late march 1877, he made his discovery (the month is given as april by pangborn, 1878). as lucas tells the story, “i wended my way back over the ridge to my sister’s where i spent my holidays. passing over the ridge of hills homeward i picked up a piece of rock, about three inches long and as wide as my hand, the shape of a cross section of a fish. upon examining it closely i found there were fine white streaks running lengthwise. i at once decided that it must be petrified bone instead of a fish [probably a sauropod rib fragment]. looking around in the vicinity i noticed a litt1e hump of dirt, 3 or 4 inches above the level of 34 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 the ground. taking a stick, i poked the dirt away and found a petrified bone 5 or 6 inches in diameter at the smallest place and 3 feet long. greatly surprised, as i had never seen a petrified bone, i covered it up very carefully waiting an opportunity to take it out. my first opportunity, i dug it out and carried it down to my boarding place. i had to make two trips as it was more than i could carry in one load. the next saturday i investigated the neighborhood, looking around in the vicinity, and came upon a bed of petrified bones with numerous pieces scattered around. from this bed i eventually took out a femur bone 6 feet long and about 10 inches in diameter in the smallest place and a shoulder blade 5 1/2 feet long and 3 feet wide at the widest place and quite a number of vertebrae, joints of the back and the tail and pieces of ribs.” quote from lucas discovery ggps docs. lucas collected more specimens and hauled them into cañon city where they attracted local attention (anonymous, cañon city avalanche newspaper, june 14, 1877, gpps docs): “mr. o. w. lucas, superintendent of the county schools, recently discovered about nine miles north of cañon city, the fossil remains of a carnivorous and herbivorous giant which he thinks is that of the iguanodon, a reptile of the cretaceous period, that had somewhat the habits of the hippopotamus. in shape, the iguanodon, resembles a kangaroo in the body, having a serpent-like head with flat serrated teeth, the tail being very long. it is estimated that this fossil is that of an animal at least sixty feet in length, and eighteen feet high. the short leg bone, now in possession of mr. lucas, is six feet in length; the hip bone is three feet three inches long, two feet wide, and twenty-one inches in diameter at the joint: the shoulder-blade is five feet six inches in length, and the vertebrae at the back and tail of corresponding size. the remains now gathered make five wagon loads. next week we will devote more space to this mammoth fossil, and try and describe it more fully, in the meantime it will be on exhibition at the museum of mr. eugene weston, on main street.” weston was a bit of a con-man, who featured himself as an auctioneer, as a middleman for the sale of mines, lands, stock, etc., outfitter for prospectors and tourists, and had a small museum that displayed and sold curiosities (advertisement in the cañon city times, april 19, 1877). lucas would come to regret his involvement with weston as is discussed below. the following week, lucas wrote a letter to the editor in response to the article that announced his discovery. he listed some of the characters of the dinosaurs given in one of his college textbooks, dana’s manual of geology, and noted that: “several of these conditions are found in the bones already taken out, sufficiently so to prove that they belong to that species of the dinosaurs called the ‘iguanodon’ as stated last week – the long bones being hollow, the pelvic arch resembling that in birds, and the sacrum consisting of four vertebrae united in one.” he notes that iguanodon “was estimated to have been twenty-eight to thirty feet long. comparing the dimensions of those bones with what i have would make the latter animal from sixty-three to sixty-five feet long upon the supposition that it is an iguanodon. that my surmise is possibly correct, i would state that a dissection of an ordinary swift, or lizard five inches in length shows many features in common with the fossil.” he goes on to note: “i am still prosecuting the work and think that with proper care and perseverance i shall be able to secure the larger portion, if not nearly the whole skeleton. some of the bones, especially the thin ones, are badly broken and hence require much time and patient labor to properly arrange. another difficulty in the way of successfully prosecuting the work is that many of the bones are removed a hundred yards or more 35 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 distant, evidently soon after the animal died, it was preyed upon by some huge carnivorous animal. i have already obtained the following bones, viz: tibia, three feet one inch long; femur, six feet; hip bone, three feet three inches; sacrum, three feet one inch; shoulder blade, five feet five inches; thirteen caudal vertebrae, several dorsal vertebrae, and several ribs; a small part of the jaw bone containing six teeth, and other bones which i am at present unable to identify. i propose soon to send portions east to someone thoroughly versed in paleontologic science, that if possible, positive knowledge of species and name may be had.” quote from lucas, cañon city avalanche newspaper, june 21, 1877, gpps docs. all of this attention led to a stream of visitors (figure 2) as he wrote: “a great many have been up from town nine miles to see the fossils.” quote from lucas to “will,” november 22, 1878, oberlin archives. this interest by the public to see dinosaur bones in the ground would be repeated years later in utah when earl douglass, cmnh, announced the discovery of a dinosaur skeleton at a site that would eventually become dinosaur national monument (carpenter, 2018b). knowing the scientific importance of the material he was finding, lucas wrote to wright at oberlin college: “i have thought that it would be not only a valuable best as interesting specimen to have in the cabinet at oberlin, but the college is poor and so am i and i cannot afford to take it out, glue it together and transport it to oberlin for nothing. do you care to have this specimen in your cabinet if so what allowance could you guarantee to me for getting it out? if you can, will you give me the name of the geological professors of some of the eastern colleges, also the proprietors of the largest museums in the country? perhaps some of them would like it and allow me something for it.” quote from lucas to wright, april 6, 1877, oberlin archives. wright confirmed that the college lacked funds to buy the specimens and referred him to o.c. marsh at yale university and e.d. cope of philadelphia (lucas discovery ggps docs). alerted by the discovery, marsh ordered one of his collectors who was excavating at morrison, colorado, to investigate. the collector, benjamin mudge, arrived in cañon city at sunset and quickly made his way to weston’s shop to examine the fossils. the next day he sent marsh his hurried observations: “they are not titanosaurus [a sauropod named by marsh for bones sent to him by arthur lakes from morrison, colorado], but the most anomalous in structure of anything i ever saw. very few of the bones have any familiar shape or resemblance though a few of the vertebra refigure 2. the earliest known photograph of visitors to a dinosaur excavation. oramel lucas (center, foreground) and visitors sometime during late summer 1877. these bones are also seen in figure 5b. the photograph is believed to have been taken by c.w. talbot (image courtesy of dan grenard, retired, bureau of land mangement, cañon city, colorado). 36 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 semble the dinosaurs – others are deeply biconcave and some concave–convex. others* are extremely unique, in having a partial frame of the centrum, with most extra-ordinary spinous processes in complex structure, ending in a kind of rounded knob, is if supporting an exoskeleton. no heavy scales or plates have been found. this knob is seen even in the chevron bone (the only one found) of the caudal vertebra. this chevron, in other respects much resembled the one i sent you in the last shipment from morrison only, one fourth larger. the caudal vertebrae and of the cervicals(?) had a strong resemblance to titanosaurus, and it is possible that these bones are from two animals of different genera. only a small portion of the head, a portion of a jaw with four teeth was found, and from the count (sent to cope, & so i did not see it), i think it belonged to a smaller animal than the larger bones. some other portions were sent to cope, and others are now packed and being packed, for sending. excepting the head, the skeleton as well represented by bones of all parts, legs, pelvis, shoulder, & etc. all are on a larger scale that t[itanosaurus] m[ontanus], from 10 to 30 percent. i have the promise of the measurements. i only saw the bones by lamplight – poor at that… [note in margin] *lumber [sic] – possibly dorsal. the sacrum has five vertebrae furnished with spinous process with knob!!!” quote from mudge letter to marsh, august 12, 1877. a few days later mudge wrote: “in looking over mr. lucas’s bones by daylight i find the sacrum is composed of four vert. – not five. it is three feet 1½ inches long one 10/12 feet high(!). the femur six feet long, largest vertebra (centrum) fourteen inches in diameter. length of the scapula five 5/12 feet – width three 2/12. the spinous processes appear to be hollow.” quote from mudge to marsh, august 15, 1877. upon receiving the letter, marsh fired off a telegram to mudge on august 18 to purchase the specimen, and reiterated this in a second telegram, “purchase specimens if possible. jones has violated all agreements.” (marsh to mudge, august 21, 1877). the reference to “jones” is supposed to be a code word for cope (schuchert and levene, 1940). the reference to an agreement with cope is mystery because no evidence for such an agreement is known and may have only resided in marsh’s mind. the two were already deeply involved in their feud by this time and neither had any scruples about “invading” one another’s collecting grounds (osborn, 1931; schuchert and levene. 1940; jaffe, 2000; thompson 2008). unfortunately, by the time marsh telegraphed mudge, it was too late. unlike the cautious and surreptitious approach of marsh, cope had quickly responded to lucas having learned his lesson from his slow response to arthur lake and having lost out on the discoveries near morrison (kohl and mcintosh, 1997; jaffe 2000). cope wrote that he wanted the specimens and would pay lucas to excavate for him. marsh had actually been alerted to large bones in the cañon city area months earlier by one of his collectors, david baldwin, who lived there, “there are bones of large animals in the jura near here” (baldwin to marsh, february 10, 1877). he later wrote marsh about the very same bones that lucas was excavating when baldwin visited the site of an alleged bird fossil (the specimen became the holotype of hallopus victor, ague and others, 1995): “i explored the place farely [sic] thoroughly but found nothing but some very large bones all reptilian i guess. in all the vertebrae that i saw the centrum was biconcave. there are the bones of one tremendous big animal laying on a flat about 15 feet higher than the strata where this [hallopus specimen] was found. one that i saw is imbedded in the red clay or in shale surrounding it measured 20 inches in across and broken off two feet long. some parties here are digging it up and sending it to colorado springs to the curiosity shop over there where it will be sold at so much a chunk to visitors.” quote from baldwin to marsh, april 30, 1877. after learning he lost out to cope, marsh castigated baldwin in a letter sent august 2, 1877, for not securing the fossils. baldwin did not get the letter until the 37 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 following month and wrote back in his defense: “as for those largest bones at cañon 1st another had presented[?] and had commenced digging on them before i saw them and another thing i did not suppose that your cared anything about them as i had written to you along in the winter telling you that there were large bones in the jura near cañon and received no notice whatever from you. i spent two or three weeks in looking around spotting localities hoping that you would write and let me know that you wanted some from there but hearing nothing from you i quit and went to prospecting.” quote from baldwin to marsh, september 4, 1877. unknowingly, mudge rubbed salt in marsh’s wound by reiterating the lost opportunity of securing the fossils before cope, “i exceedingly regret that baldwin did not secure them for you, as he might when they were first discovered.” quote from mudge to marsh, august 12, 1877. the full magnitude of what marsh lost out on became very clear by the series of publications on the specimens by cope (1877a–d; 1878a–g). a year later, marsh still faulted baldwin, who wrote in his defense again: “i infer from what lt. carpenter [who had recommended baldwin to marsh as a collector] writes me that you suppose that i found the large bones that lucas is digging for cope before he (lucas) did. such is not the case. i never saw those bones until after lucas had commensed digging on them. i had found bones in the jurassic in several places two or three months before lucas found those but i did not dig on them on account of not hearing from you that you wanted them. no one except myself has ever dug on any of them. i have shown several places to mr. beckwith [another collector of marsh’s] but he says that you do not want more large bones unless they should be new and what would be new i have no means of finding as mail communications with you are very uncertain.” quote from baldwin to marsh, june 29, 1878. marsh was notorious for not communicating well with his collectors, a common complaint in the various correspondence. the first specimen lucas shipped to cope was not the first fossil he found. instead, he sent a lower jaw that cope (1877a; see also chure, 2001) described in august as the theropod laelaps trihedrodon [=allosaurus sp.] (lucas letter to wright, october 1, 1877). other shipments to cope would eventually follow (summarized by mcintosh, 1998). shipping large, fragile fossils was not easy at this time because the use of burlap and plaster of paris to encase the fossils had not yet been developed. instead, hay was used to pack the fossils in crates as cope wrote regarding the shipping of elasmosaurus bones: “it is very desirable that the specimens should be packed in such a way as to avoid friction or breakage in case of sudden jars. to accomplish this each single piece or mass, should be so surrounded in the hay or other packing as to allow of some elasticity of contact with the next. it is also important that any box should not be too large to bear the rough handling of so much weight: otherwise it may be broken. even much lost.” quote from cope to theophilus turner, february 13, 1868, in almy (1987, p. 188). that the use of hay to pack fossils was widespread at this time is seen by the instructions marsh gave his collectors: “pack fossils in boxes of moderate size, and made of inch boards. plenty of hay or straw should be put on the bottom, and closely around sacks of fossils, so that they cannot move when the box is turned over.” quote from schuchert and levene (1940, p. 173); see also davidson and everhart (2017). the compaction of hay during transport was a serious problem as cope noted in a letter: “each mass should have had a thicker wrapping of hay (still more when paper is used) & the box should be so packed as to prevent the rubbing and moving of the pieces. the largest box had 38 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 1/3 to 1/4 vacant space when it arrived & it as well as others, suffered some injury on that account.” quote from cope to turner, february 13, 1868, given in almy, 1987, p. 189. the large, heavy, and fragile bones lucas excavated would have been difficult to crate and ship safely from cope’s nipple. the crates would have been hauled down an impromptu horse and wagon trail to the main unimproved dirt road along fourmile creek (a.k.a. oil creek) to the railroad station in cañon city. from there the travel was smoother by railroad to philadelphia, where the crates were offloaded and hauled to cope’s house. given that chemical preservatives were not yet in use, it is amazing that the specimens arrived in philadelphia relatively intact. lucas did write about the difficulties he faced with the bones: “these fossils are broken into pieces, but the pieces are in their proper places and as i take them out i glue them together but it is a great deal of work.” quote from lucas to wright, april 6, 1877, oberlin archives. this method was time consuming and he notes in a letter that it took seven days to extract a single cervical vertebra (lucas to “will,” november 22, 1877, oberlin archives). another technique described: “there are numerous thin bones bracing the diapophyses, zigapophises [=zygapophyses] and other processes, some as thin as 1/8 of an inch, and all broken into very small pieces. i can save them only by pasting very strong paper on all the surfaces as soon as he rock is removed.” quote from lucas letter to “will,” november 22, 1877, oberlin archives. he reiterated this technique in a letter to o.c. marsh when he sought to sell the specimens to him, rather than to cope (lucas to marsh, march 11, 1879; lucas had come to feel that he sold his bones to cope too cheaply as mudge wrote to marsh, august 15, 1877). this precursor to the use of plaster of paris jackets to hold fractured bone in place was independently arrived at by different people (figure 1c; see schuchert and levene, 1940). eugene weston, who was displaying the fossil bones found by lucas, saw a money-making opportunity when there seemed to be great interest in the fossil bones lucas was excavating. mudge wrote that: “mr. weston…is well acquainted with this region…he is in search of vertebrates, and has promised me the refusal of all he may find. if he strikes a good spot i shall buy him out…” quote from mudge to marsh, august 26, 1877. searching for fossils was probably more work than weston had anticipated, so he filed a mining claim with the fremont county clerk for the land lucas was excavating (lucas discovery ggps docs). he then offered to sell the claim to lucas, essentially to force lucas to buy his own fossils. lucas consulted a lawyer, who pointed out that by failing to first develop his claim before trying to sell it, weston had forfeited ownership (lucas discovery ggps docs). weston conceded because he had no desire to expend the required labor. lucas immediately filed his own claim for 20 acres (figure 3) under the general mining act of 1872 (30 u.s. code section 35), which stated: “claims usually called ‘placers,’ including all forms of deposit, excepting veins of quartz, or other rock in place…” at first, lucas lived at the site in a tent (figures 2 and 4a, right side) with his brother clarence (lucas to “will,” november 22, 1877, oberlin archives), then later built a small cabin near where the bones were located (lucas discovery ggps docs). the charred foundation for that building still exists (figure 4b), with many burnt fragments of dinosaur bones laying around. these may have been bone fragments left in the cabin when it later burned. lucas had clarence and their father help with the excavation (figure 4a background), and he shipped the specimens to cope in philadelphia (lucas to “will,” november 22, 1877, oberlin archives). the newspaper articles and bones on display drew the attention of c.w. talbor, a photographer in cañon city as lucas wrote: “my diggings and a number of these large vertebrae with other bones were photographed a few days ago.” quote from lucas 39 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 figure 3. map showing the location of the oramel lucas 1877 mining claim near cottage rock, as well as the marshall felch 1885 mining claim (q). text on top margin: “township no. 17 range no. 70 west.” text right margin: “tt in b light shaded showing all the tillable land on the claim of 40 acres – some 7 acres in all – about equally divided by the creek.” bottom text: “a-a&c original pre-emption of m. p. felch sec’s – 21–22–27. b – claim by preemption, of e.l. weld – no title acquired. forty (40) acrers [sic] n.e. qt. of n.e. qt. sec. 28. q. quarry – placer claim by m. p. felch 1884. h–hxxx&c. vacant ground; proposed homestead claim of m. p. felch – to be taken in connection with weld’s claim and the “fossil” claim to make 160 acres.” map is from a letter that was sent from felch to marsh, march 16, 1885. 40 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 to “will,” november 22, 1877, oberlin archives. talbot later sold stereograph cards of the bones as they lay in the ground (figure 5a and 5c, compare with 5b), and writer joseph pangborn presented an illustration of the entire excavation (figure 4a). lucas met cope in late july 1879, when cope made a collecting trip to colorado and wyoming that year (osborn, 1931). lucas took cope to the various fossil sites on july 26, which cope dutifully recorded in a small pocket notebook now preserved at the american museum of natural history (mcintosh 1998; monaco 1998; gpps docs). cope wrote to his wife, “seventh day [i.e., saturday] i made a complete survey of the saurian beds and excavations which commenced 7 miles from town, north, and extended 7 miles further. there are signs of many others [i.e., dinosaurs] in the rocks.” quote from cope letter, july 28, 1879, in osborn (1931, p. 259). fortunately for us, cope made a crude, systematic sketch of the quarry locations in his notebook (figure 6a), which has been instrumental in relocating the main quarries in the vicinity of cope’s nipple (figures 5b and 5c). oramel eventually turned operations over to his older brother, ira, later that summer. he used the money he had been paid by cope to complete his education at oberlin, graduating with the class of 1880 (lucas 50th, gpps docs.). ira, meanwhile, continued to ship specimens to cope through 1884 (ira lucas to cope, january 17, 1884, gpps docs), at which point all work for cope ceased because no other sites in garden park were found as was later recounted: “have met the two men [lucas brothers] that first figure 4. (a) drawing by y.a. snyder (from pangborn, 1878) of the first camarasaurus supremus quarry, with the wagon-cover tent (right) that oramel lucas lived in to guard the site before building a cabin. persons in the background may represent men hired to help lucas excavate or lucas and one of his men. the hill in the background is unnamed and appears in cope's notebook as the "ridge" (see figure 6a). bones in blue box are those in figure 5a and those in yellow box are those in figure 5c. these two clusters show artistic license in and were probably drawn from photographs. (b) foundation of the small cabin lucas built in 1877 to protect his interests in the nearby dinosaur sites. the dark stain is charred remains of the structure and includes burnt dinosaur bone fragments. 41 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 discovered bones in that locality and worked the quarry for cope for a number of years… they tell me that they worked the ground so long as there was any indications of bones.” quote from utterback to hatcher, october 31, 1901, cm archives. further excavations—the carnegie museum of natural history (1901) in 1898, the cmnh undertook a quest to locate a large dinosaur skeleton for display as recounted in detail by brinkman (2010). a major quarry was opened the following year at sheep creek, albany county, wyoming, and worked for two years. the quarry produced the holotype and paratype of diplodocus carnegii (see brezinski and kollar, 2008, for discussion of the geology). other, smaller quarries were also excavated nearby. well before work was completed at sheep creek, john hatcher of the cmnh began considering other sites. unlike andrew carnegie who only wanted a big dinosaur skeleton for his museum, hatcher was thinking in terms of research as he noted in a letter to holland: “…i feel sure we have here [garden park] the key to the development of the sauropoda & i propose to corral everything in sight… there are represented here fully 500 ft. of freshwater jura & dinosaur remains we have found here at many horizons. now i want to pound away here for several years & secure good series from every horizon possible, determining accurately the relative positions of the various horizons, which can be done with ease, & then work out the phylogeny of the different genera of dinosaurs just as i have done the species of titanotheres. it is a great undertaking but we are in a position to do it & must not let the opportunity escape us.” quote from hatcher to holland, august 12, 1901, cm archives. the reference to phylogeny of titanotheres was the article written in 1893, in which hatcher noted stratigraphic, hence chronological, changes in titanotheres of the “titanothere beds” (a.k.a. chadron formation) of wyoming and south dakota (hatcher, 1893). in early may 1900, months before completion of the work at sheep creek, hatcher visited marshall felch in garden park to find out if anything remained at the quarry felch work for marsh. an agreement for figure 5. (a) one of the earliest photographs of a dinosaur quarry, it shows the first camarasaurus supremus specimen discovered by lucas. the photograph was taken in mid-november, 1877 (lucas to “will,” november 22, 1877, oberlin archives). (b) the hill in the background (cottage rock) can be matched with that in the background of (a). (c) another view of the quarry. tree in background can be match with tree in (b), but note the tree is now leaning. bone in red box is in unstable position. the historical photographs are each half of two different stereopticon photographs taken and sold by c.w. talbot (1878) of cañon city. caption on the back of the photographs includes: “the measurements were as follows: thigh bones, upward, 6 feet long, 16 inches in diameter; leg bones, 5 feet long, measuring 22 inches across the toes; vertebrae, 18 inches across, with spinous process 40 inches long; ribs from 6 to 15 feet long, and 23 inches wide at intersection. all other bones in proportion.” photo in b by andrew smith (bureau of land management, cañon city, colorado). 42 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 figure 6. (a) map of sites from e.d. cope’s notebook of 1879. (b) overhead view (google earth) of the lucas quarries (i-vii, xiv) in the vicinity of cope’s nipple as determined from cope’s map and the areal extent of the cmnh excavations outlined in yellow. (c) panorama (90°) from cope’s nipple viewed south to west showing the location of the lucas quarries (i-vii). abbreviations: cs1 and cs2 – camarasaurus supremus partial skeletons; i–vii and xiv various quarries worked by the lucas brothers for cope. photo in c by andrew smith (bureau of land management, cañon city, colorado). 43 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 three years was signed between felch and the cmnh by which felch would be paid $25 ($750 in 2018) per month for the rights to excavate, with payment only if specimens were found (hatcher letters to holland, may 9, 1900, may 31, 1900). in november, hatcher sent william utterback, who he hired to help with the excavations in the miocene of western nebraska to cañon city to reopen the old felch quarry. utterback started work there on november 3, 1900 (hatcher to holland, november 30, 1900, cm archives), and by april 1901, hatcher thought about expanding work to the lucas quarries at the nipple on the off-chance there were still specimens left (hatcher to utterback, april 15, 1901, cm archives). hatcher filed a placer mining claim (no. 59076) under his name and museum director, holland, with the fremont county clerk for 40 acres around the lucas quarries on august 10, 1901 (hatcher to holland, august 12, 1901, cm archives). the 1872 mining act allowed a maximum of 20 acres per person per claim, hence the use of both names on the claim. the claim was to prevent anyone from filing their own claim and forcing the cmnh off the land (he also filed for the felch quarry, placer claim no. 59075, after discovering that felch did not own the land despite convincing hatcher to a sign a lease for the right to excavate. (hatcher letters to holland, may 9, 1900; may 31, 1900, cm archives). previously, both lucas (1877) and felch (1884) had filed placer mining claims with the county clerk for their respective quarries (figure 3). however, neither filed the mandatory annual affidavits with the county clerk attesting that they did at least $100 worth of work in order to maintain the claims after the last bones were excavated. nor did either apply for a patent, which would have given them legal ownership of their claims. thus, by the time the cmnh arrived, the claims were considered abandoned. hatcher was furious with felch for misleading him about ownership of the quarry, accusing him of trying to play the cmnh false (hatcher to holland, august 12, 1901, cm archives). hatcher transferred george axtell, who was with charles gilmore, also from the cmnh, excavating in the freezeout hills, wyoming, to cañon city to help utterback (hatcher to holland, august 12, 1901, cm archives). axtell arrived on august 21 and initially helped utterback with the felch quarry (axtell to hatcher, august 24, 1901, cm archives). two weeks later, utterback sent him to work the lucas quarries at the nipple (axtell to hatcher, september 3, 1901, cm archives; figure 7a). axtell used a horse and plow to break up the mudstone overburden and a horse drawn drag scraper (a.k.a. ‘horse and scraper’) to haul away the broken-up mudstone (axtell to hatcher, september 20, 1901, cm archives). the scraper was a metal scoop pulled by horses to move earth (figure 8). axtell reported to hatcher that: “the work in cope quarries has so far been more of a prospecting nature. the locality where i first started in, yielded nothing more than what you saw viz the vertebra. undoubtedly the most promising place is around and under the ‘nipple’ as it is locally called. i have opened another place just south of the vertebra or as i have dubbed that place ‘cope a’ and think i will find some good things there. have a large rib running into the bank now. a little plow and scrapper work will accomplish wonder, i think.” quote from axtell to hatcher september 3, 1901, cm archives. despite this optimistic start, axtell became increasing disappointed as time went on: “the cope quarries are not yielding the bone that i had hoped for. so far what bone i have found has been very fragmentary -not worth taking up in my judgement. you will perhaps remember that when i last wrote i mentioned having found some ribs running into the bank. when uncovered i found that the proximal ends were missing. since then i have found numerous other fragmentary ribs, pieces of process from vertebrae, the shaft of a radius (both ends gone) and a part of a large bront[osaurus] scapula -about two feet of the proximal end with all the thin and delicate parts gone. that’s all i have to show for two weeks work…i have opened five prospects, three of them being simply excavations of the old cope working, the other two being on opposite sides of the ‘ant-hill’ [i.e., 44 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 figure 7. (a) view west towards cope’s nipple before the cmnh excavation in 1900 (courtesy of a. henrici, cmnh). the excavation in the center foreground is camarasaurus supremus # 1 quarry 23 years after the photographs in figure 5a and 5c. arrow shows the tailing pile seen at the far right in figure 5c. (b) view along the cmnh excavation as it is today. the excavation extended to the base of cope’s nipple and to the edge of the buff to the left (out of view). (c) view west along a trench for quarries i–iii. several small test excavation were dug in 1991. (d) 1991 test excavation at the base of cope’s nipple, west end of the carnegie trench looking east. the main bone-bearing strata of lucas is the greenish mudstone. (e) southeast side of cope’s nipple showing hallopus-bearing sandstone in foreground and the nanosaurus agilis flagstones littering the surface of the slope. the bone-bearing layer of lucas is the light band. 45 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 cope’s nipple].” quote from axtell to hatcher, septemberer 13, 1901, cm archives. a week later this was followed by another letter in which axtell again sounds more optimistic, “since i last wrote i have made something of a ‘strike’ – at least i feel a bit encouraged and hope i may be opening up what will eventually prove to be a fair quarry. i am now working out a fine cervical vertebra and also a rib. i hope these may lead to something better but of course there is a possibility that they will not. as soon as they are up and out of the way i shall begin to strip with plow and scrapper.” quote from axtell to hatcher, septemberer 20, 1901, cm archives. the whereabouts of these bones, especially the cervical vertebra mentioned by axtell, are unknown. there is an apatosaurus dorsal (cm 2044) in the cmnh collections, but none of the other bones (a. henrici, collections manager, cmnh, personal communication, january 18, 2018). to get a better understanding about the lucas excavations at the nipple, utterback met with the two lucas brothers as he reported to hatcher: “have met the two men that first discovered bones in that locality and worked the quarry for cope for a number of years. they gave me considerable information regarding their find around the nipple…they tell me that they worked the ground so long as there was any indications of bones... these men, the lucas bros, tell me all of those fragments were on the surface when they worked the place.” quote from utterback to hatcher, october 31, 1901, cm archives. despite the optimism previously expressed by axtell, utterback own assessment was bleak as he later reported to hatcher: “mr. hatcher i regret very much to have to report to you that our work upon the cope quarries have resulted in a dismal failure. it has not been for the want of hard work or energy on our part, but simply because the bones are not there. i made a stripping of 20 x 100 ft on the south side of the nipple one of about the same dimension on the north side and failed to get even a fragment [which is at odds with axtell’s and my own experiences, see below]. at the old workings near cottage rock we made a cut of 200 feet in length and from 10 to 20 feet in width to bed rock and found nothing but water worn fragments. i think that were you here in person and see the amount of work done and no returns you would think it a waste of time and money to continue it. in all have uncovered over 5000 square feet of surface with no returns.” quote from utterback to hatcher, november 25, 1901, cm archives. utterback stopped work at the nipple soon after but remained in the area a few more weeks prospecting. he found nothing substantial of the sauropods that hatcher wanted and departed for the cmnh that december. one more time—the denver museum of natural history (1991-1996) the nipple quarries had sat idle for ninety years when i started the garden park morrison project (see carpenter and lindsey, 2019, for list of published results). the goal was to locate new sites in a systematic manner by prospecting with a team of volunteers figure 8. cmnh crew using a horse and scraper to remove overburden. agate springs fossil quarry, nebraska. from peterson (1906). 46 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 one section of public land survey at a time. a test pit was excavated at the base of the nipple on the north side (figure 7d). fragments of bone were encountered, which were surprisingly heavily abraded and match utterback’s “water worn fragments” (see further below). the test pit proved to be crucial to understanding the geology of the original bone-bearing horizon bed (see next section). additional material of camarasaurus supremus was excavated in late june 1994, south of cope’s nipple (figure 9a). the material was found in may by students from the university of kansas who thought they were excavating on private property. the bureau of land management requested that the dmnh take over and recover the specimens. during the excavation, i noticed that slabs of local yellow sandstone, 15 to 20 cm thick, had been laid over many of the bones (figure 9b). in addition, infilled trenches of reddish dirt surrounded many of the bones showing that they had been partially excavated previously (figures 8c and 8d). the location of the site and specimen best matched cope’s “lot v” in his field notes. it is surprising that the carnegie crew did not find the bones, nor that the lucas brothers told utterback of their existence. the material excavated included dorsal vertebrae, caudal vertebrae, a pubis, an ischium, and rib fragments (figure 9e). ground-penetrating radar was used in the hunt for any material that might remain in the area of the nipple (figure 9f). the technology uses high frequency electromagnetic energy (radio waves in the microwave spectrum) rather than acoustic energy. the radio waves are reflected from boundaries between materials having different permittivities, i.e., where the electrical properties change. unfortunately, the results were negative, partially because the permittivity of permineralized bone was similar to that of the encasing rock, and partly due to the stripping of so much rock by the cmnh. sedimentology and taphonomy of cope’s nipple cope’s nipple is a prominent erosional remnant that overlooks garden park on the west side of fourmile creek (figure 1a), also known as oil creek because of an oil well drilled in 1863 near the mouth of fourmile canyon. the bone-bearing horizon from which lucas collected most of his specimens was first reported by cope (1877a) as being dakota formation, but he did not give his reasons until later (cope, 1878a, p. 234) when he revealed that “dr. [ferdinand] hayden visited the locality of mr. lucas’ excavations, and informs me that the formation from which the camarasaurus was obtained, is the dakota.” no reason was given why hayden, of the united states geological and geographical survey, referred to the red mudstones as “dakota.” typically, hayden referred strata to the dakota, which he also called “#1 cretaceous,” as the hogback and ridge-forming sandstones below the “#2 cretaceous” (i.e., benton shales) (e.g., hayden, 1869). strata immediately below, he referred to as jurassic. these dinosaur-bearing strata in the garden park area were first identified as morrison formation by whitman cross (1898) and were described in greater detail by hatcher (1901) and mook (1916, largely repeated in osborn and mook, 1921). more recently, the stratigraphy and petrology of the morrison formation in garden park has been described by hassinger (1959), brady (1967, 1969), enciso (1981), sweet (1984), and carpenter and lindsey (2019). a stratigraphic section is presented in figure 10 (see carpenter and lindsey, 2019, for discussion of the morrison members in the garden park area). the lucas quarries occur very high in the morrison formation. unfortunately, no radiometric date is available to ascertain whether the quarry is late kimmeridgian or early tithonian. the uniqueness of the fauna suggests early tithonian based on a kimmeridgian date obtained at a lower level in garden park (trujillo and kowallis, 2015). the bone-bearing strata were described by lucas (cañon city avalanche newspaper, june 21, 1877, gpps docs) as “a thin stratum of fragile shale of bluish color” (see figure 7d). in my analysis, when freshly exposed, the matrix is a blocky, dusky yellow-green (munsell color 5y5/2), slightly calcareous, sandy, illitic mudstone, with mottles of dusky yellow (5y6/4) and dark yellowish-orange (10yr6/6); root casts and limonitic nodules 2 to 3 mm in diameter occur. this light, bone-bearing mudstone overlies a blocky to angular breaking, very dusky red (10r2/2), slightly calcareous claystone with grayish-green non-calcareous 47 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 mottles (10g4/2); small, 2 to 3 mm limonitic nodules occur throughout. the light, bone-bearing mudstone is overlain by a pale-red (5r6/2) weathering calcareous claystone—mottled dusky green (5gy5/2) and dusky brown (5yr2/2) when fresh—with thin pale-olive (10y6/2) sandstone lenses and with grayish-purple (5gy6/1) nodules (see carpenter and lindsey, 2019, for discussion of clay minerals). pangborn (1878) noted, “the fossils are found in rock long upheaved, its character now a sort of shale or figure 9. (a) distant view from south side of site v excavation. cope’s nipple in the background. some stone slabs removed from covering bones are seen in the foreground. (b) view from south side of excavation; arrows point to sandstone slabs still overlaying bone. (c) close-up of excavation. white arrow shows undisturbed gray mudstone and red arrow shows brown infilled trench. rib to left of white arrow is oblique to strata. (d) overview of excavation viewed from north side. arrow points to infilled trench between bones. (e) schematic quarry map showing ribs (r), vertebrae centra (c), pubis (p; midline length 107 cm), and ischium (i; midline length 116 cm). all of the bones were concentrated in a small area less than 3 m across. note that the bones are randomly oriented, although smaller bones are in the fluvial flow shadow of the larger bones. (f) ground-penetrating radar being used in the hunt for other bone in the vicinity of site v. 48 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 marlite [= marlstone] which upon being dug out and exposed to the air crumbles to pieces. in most instances, it is free from bone decay [i.e., the bones are not weathered and crumbly], the parts of animals taken out being remarkable for their clean and perfect solidity.” the mudstone does indeed crumble to pieces and does easily separate from the bones, leaving them remarkably clean (figures 5a and 5c), but unfortunately also reducing the protection the matrix provided the fragile bones. in marked contrast with bones excavated for o.c. marsh at the nearby felch quarry, the bones there occurred in a hard channel sandstone (evanoff and carpenter, 1998). in that excavation, felch removed bone by following along joints, resulting in a considerable amount of extraneous rock that added to the shipping costs and which had to be removed in marsh’s lab. the bone-bearing mudstone of the lucas sites is a paleosol that is widespread around the base of cope’s nipple and southwards towards cottage rock (figures 6c and 7b to 7d). it is bracketed between two maroon mudstones, one of which is underlain by the fine-grained, tabular, maroon, hallopus-sandstone (figures 7e and 10; ague and others, 1995; carpenter and lindsey, 2019), and the other, higher, is a fineto medium-grained sandstone, which produced the holotype of the ornithischian dinosaur nanosaurus agilis (carpenter and galton, 2018). thus, all of the specimens collected by lucas in the vicinity of cope’s nipple came from a single depositional unit about 1.5 m thick. considering the limited area these bones were collected (figure 6b), they constitute a bonebed. regrettably, cope never required lucas to make quarry maps, unlike the directive that marsh gave his collectors (evanoff and carpenter, 1998). all we have are two photographs and a drawing (figures 4a, 5a, and 5c). these, in conjunction with cope’s notes, data in osborn and mook (1921) and mcintosh (1998), and the 1994 dmnh excavation, indicate scattered bone and clusters of disarticulated partial skeletons (figure 6b) covering an area of around 175 m2 (expanded to around 310 m2 by the cmnh). at least two strings of articulated vertebrae were discovered (figure 4a) and these appear to be roughly at right angles to each other and several meters away. these two clusters are cataloged as amnh 5760, which mcintosh (1998) had noted consists of two individuals based on six extra dorsals, at least five extra left ribs, mismatched pubes, two extra ischia, and mismatched femur and tibia. mcintosh (1998) also noted that some of the ribs were articulated with their respective dorsal vertebrae. the occurrence of taxa represented by single bones, as well as partial skeletons, indicate an allochthonous and autochthonous origin for the bonebed. in addition, these sections of vertebrae are ventral side up. most of the large dorsal vertebrae, which are wider than anteroposteriorly long, lay on their articular faces, although some lie oblique to the horizontal (figure 5c, foreground). several rib fragments were also found to lie oblique during the dmnh excavation. one smaller vertebra, possibly a cervical, also stands vertifigure 10. stratigraphic section from the summit of cope’s nipple to the base of the “valley of death” located on the north side of cope’s nipple (see also carpenter and lindsey, 2019). 49 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 cally on its posterior face (figures 4a and 5c, red box), but because it is elongate it is in a fluvially unstable position than the larger vertebrae. bone shapes from osborn and mook (1921, referred to as o&m) range from cylindrical teeth with roots (o&m, plates 60 and 61), cylindrical centra (o&m, figure 22), and cylindrical metacarpals (o&m, figure 85); subspherical vertebral centra (o&m, figure 24); concave, disc-shaped coracoids (o&m, figures 27 and 82); and elongate, flat (low profile) ribs (o&m, plate 79). thus, there is a mixture of fluvially easily transportable shapes (cylindrical and subspherical) and fluvially stable shapes (ribs, coracoid). bone size ranges from easily transportable 1-cm-long centrum of tichosteus aquifacies (= genus and species indeterminant; o&m, figure 16), to the huge, difficult to transport 1.8 m femur of camarasaurus supremus (o&m, figure 107; amnh 5760, not 5761 per mcintosh, 1998). finally, bone preservation includes both slightly distorted vertebrae (o&m, plate 70, figure 4), as well as extremely distorted vertebrae (figure 10; o&m, figure 89; plate 74). a 24 m3 test excavation at base of cope’s nipple (figure 7d) in 1991 revealed an abraded allosaurus tooth fragment, an abraded sauropod(?) rib fragment, and a few small (few cm in diameter), rounded bone fragments dispersed in both the red and lower maroon mudstones. this excavation is immediately adjacent to the cmnh excavation and the fragments are similar to those mentioned by axtell and utterback in their letters to hatcher. these abraded bones in such finegrained sediments suggests that they were entrained into the overbank flow during flooding of a nearby river. the abraded rib was found standing vertically, possibly due to trampling when the mud was still soft. pangborn (1878) also reported evidence of scavenging as evidenced by the co-mingling of theropod teeth (as “laelaps trihedrodon”) and camarasaurus bones. despite the gray-green sediment color, bones excavated this unit are of the “red series” of osborn and mook (1921, p. 256). this is in contradiction to their suggestion that the grayish matrix probably produced the “yellow series.” my conclusion is based on the statement by lucas (lucas, cañon city avalanche newspaper, june 21, 1877, gpps docs) of the sediment color at his first camarasaurus site, the color of the bones as noted by osborn and mook (1921), and the specimen excavated by the dmnh, which were similar to the red series. discussion and conclusion it has been over 140 years since a school teacher discovered a vast treasure trove of dinosaur bones in central colorado. these and other discoveries seized the public’s fascination because of their huge size as reported by holder (1880) (figure 11a). e.d. cope named no fewer than 14 dinosaur species (and two non-dinosaurian reptiles) over a span of two years from the specimens collected by the lucas brothers at the nipple and other quarries in garden park (osborn and mook, 1921). as result of this, and similar naming of taxa by o.c. marsh, there has been what i feel to be unfair criticism of marsh and cope’s naming practices. it is too easy to apply today’s standards in vertebrate paleontology to the fledgling field of the 1800s. given the dearth of specimens at the time, when confronted with morphological differences it made sense to assign a “handle” by which the specimen would be known. only as more specimens were collected was it possible to demonstrate that the variation could be explained for a variety of reasons, including different stages of ontogeny, gender, and individual (carpenter and currie, 1990). the result was a reduction of the cope’s nipple species to four or five taxa in more recent years. it must be remembered that biological entities are not stamped out mechanically and differences are expected among specimens. unfortunately, there has been a return to the mechanistic over-splitting previously done by marsh and cope in recent years, but for different reasons through the use of large data sets for specimens to tackle biological questions (e.g., tschopp and others, 2015). given the short duration of the morrison formation (~5 m.y., trujillo and kowallis, 2015) and one–to–two million years for the brushy basin member from which many sauropod specimens have been collected (trujillo and kowallis, 2015; galli and others, 2018), the great amount of sauropod (diplodocoid) evolution implied by tschopp and others (2015), is highly improbable for such a short time. such large specimen-level data set analyses have their place, but the results should not be assumed to reflect biological entities. as biologist soltis noted, “things can 50 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 be statistically possible without being biologically possible.” (quoted in leford, 2018, p. 153). the camarasaurus supremus material collected by lucas from the cope nipple and surrounding quarries do appear to represent the last appearance datum for the genus and for the species (table 1; figure 11). two other staggered, partially overlapping range zones of c. lentus and c. grandis occur stratigraphically lower (ikejiri, 2005), and these specimens demonstrate variation as expected of biological entities (ikejiri 2004, 2008; ikejiri and others, 2005). the discovery of several clusters of dinosaur bones in the vicinity of cope’s nipple at the south end of garden park was monumental in the history of dinosaur paleontology. among the specimens were several partial skeletons of camarasaurus supremus and these allowed for the first restoration of a sauropod dinosaur skeleton. it is unfortunate that the documents associated with the collecting of the specimens are spotty. nevertheless, what remains indicates that the quarries are part of a large bonebed in which bones occurred figure 11. (a) sketch that appeared in the semi-popular scientific american supplement (holder, 1880) based on illustrations by cope. these are not to scale and were simply illustrative of the bone shapes: 1 – femur of amphicoelias altus from cope 1878c, 2 – femur of “amphicoelias” latus (actually camarasaurus) from cope (1878c), inverted, missing portion restored. 3 – “amphicoelias” fragillimus from cope (1878f) reversed left to right; small bone marked “a” is a crocodilian femur. (b) first skeletal reconstruction of a sauropod made by john ryder under the direction of e.d. cope. the original drawing was life size and was displayed by cope at the december 21, 1877, meeting of the american philosophical society in philadelphia, pennsylvania (modified from osborn and mook, 1921, plate 82). taxa reference (date of publication) current status amphicoelias altus cope, 1878 field notes sauropod amphicoelias fragillimus (h) cope, 1878f maraapunisaurus fragillimus amphicoelias latus cope, 1878f camarasaurus supremus (subadult) amphicotylus lucasii (h) cope, 1878d (see also cope, 1888) amphicotylus lucasii camarasaurus leptodirus cope, 1878 field notes camarasaurus supremus camarasaurus supremus cope, 1877b camarasaurus supremus & apatosaurus sp. epanterias amplexus cope, 1878d epanterias amplexus hypsirhophus trihedrodon cope, 1878 field notes allosaurus sp. (epanterias?) laelaps trihedrodon cope, 1877a allosaurus sp. (epanterias?) morosaurus laticollis cope, 1878 field notes apatosaurus sp. table 1. taxa from the nipple quarries. not all of cope’s holotypes (h-holotype) are from these quarries. other taxa described by cope (e.g., symphyrophus musculosus) may be from one of the nipple quarries, but is not demonstratable. this table should be view with figure 6. 51 history and geology of the cope’s nipple quarries in garden park, colorado—type locality of giant sauropods in the upper jurassic morrison formation carpenter, k. geology of the intermountain west 2019 volume 6 as clusters. the occurrence of single bones and partial skeletons suggest an allochthonous and autochthonous origin for the bonebed. acknowledgments a large volume of archival material pertaining to the history of the excavations around cope’s nipple was gathered by pat monaco and the late donna engard. this material is now at the royal gorge regional museum and history center, cañon city, colorado. andrew smith and melissa smeins (bureau of land management, royal gorge field office, cañon city, colorado), dan grenard (retired, bureaus of land management, cañon city, colorado) and dan brinkman (yale peabody museum, yale university, new haven, connecticut) made additional documents available. andrew smith tracked down copies of the carnegie museum of natural history placer claims. i was aided at excavating at cope’s nipple and of the abandoned camasaurus specimen (#5) by paula canner, kiyo carpenter, lora freudberg, patricia and bill george, mel grantham, suzanne meyer, robert mccarroll, rocco romero, david saitta, john shinton, bryan small, jeff stephenson, virginia tidwell, mike williams, and bruce young. field work was conducted under bureau of land management permit c-49819(c). photographs were generously provided by vicki garrisi (true west properties, woodland park, colorado), andrew smith (bureau of land management, cañon city, colorado), and amy henrici (carnegie museum of natural history, pittsburgh, pennsylvania). amy henrici also made available the correspondence of the vertebrate paleontology department of the carnegie museum of natural history. letters of oramel lucas to o.c. marsh are in the yale peabody museum of natural history archives: http://peabody.yale.edu/collections/ vertebrate-paleontology/correspondence-o-c-marsh. finally, review comments by greg paul (independent dinosaur artist), john whitlock (mount aloysius college, cresson, pennsylvania), mike taylor (university of bristol), and john foster (utah field house of natural history state park museum, vernal, utah) are gratefully acknowledged. references author note: e.d. cope published variants of the same article repeatedly. to set the record of their order straight, publication dates are given in parenthesis. ague, j., carpenter, k., and ostrom, j., 1995, solution to the hallopus enigma: american journal of science, v. 295, p. 1–17. almy, k.j., 1987, thof’s dragon and the letters of capt. theophilus turner, m.d., u.s. army: kansas history, v. 10, no. 3, p. 170–200, https://www.kshs.org/publicat/history/1987autumn_almy.pdf, accessed april 23, 2018. anonymous, 1876, catalogue of the officers and students of oberlin college for the college year 1876–77: toledo, ohio, blade printing & paper company, 61 p. binckley, g.m., and hartwell, f., 1879, southern colorado, historical and descriptive of fremont and custer counties with their principal towns: cañon city, colorado, binckley and hartwell publishers, 136 p. brady, l.l., 1967, stratigraphy and petrology of the morrison formation (jurassic) in the vicinity of cañon city, colorado area: lawrence, university of kansas, m.s. thesis, 111 p. brady, l.l., 1969, stratigraphy and petrology of the morrison formation (jurassic) of the cañon city, colorado area: journal of sedimentary petrology, v. 39, p. 632–648. brinkman, p.d., 2010, the second jurassic dinosaur rush—museums and paleontology in america at the turn of the twentieth century: chicago, illinois, university of chicago press, 312 p. brezinski, d.k., and kollar, a.d., 2008, geology of the carnegie museum dinosaur quarry site of diplodocus carnegii, sheep creek, wyoming: annals of carnegie museum, v. 77, no. 2, p. 243–252. carpenter, k., 1998, vertebrate biostratigraphy of the morrison formation near cañon city, colorado, in carpenter, k., chure, d., and kirkland, j.i., editors, the morrison formation—an interdisciplinary study: modern geology, v. 23, p. 407–426. carpenter, k., 2018a, maraapunisaurus fragillimus, n.g. 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specimen-level phylogenetic analysis and taxonomic revision of diplodocidae (dinosauria, sauropoda): peerj, v. 3, p. e857, https:// peerj.com/articles/857/. vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada (usa) geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 © 2017 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada (usa) kathleen b. springer, jeffrey s. pigati, and eric scott a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover buff-colored deposits sit against the backdrop of the las vegas range just outside the city limits of las vegas. once thought to be remnants of a large pluvial lake called lake las vegas, these deposits actually record the presence of extensive desert wetlands that acted as watering holes to an array of pleistocene megafauna, including mammoth, sloth, camel, horse, bison, american lion, dire wolf, and sabre-toothed cat. i 2016 president bill loughlin bill@loughlinwater.com 435.649.4005 2016 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2016 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2016 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2016 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2016 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 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association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 4 2017 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 55 abstract tule springs fossil beds national monument (tusk) preserves 22,650 acres of the upper las vegas wash in the northern las vegas valley (nevada, usa). tusk is home to extensive and stratigraphically complex groundwater discharge (gwd) deposits, called the las vegas formation, which represent springs and desert wetlands that covered much of the valley during the late quaternary. the gwd deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). the deposits also entomb the tule springs local fauna (tslf), one of the most significant late pleistocene (rancholabrean) vertebrate assemblages in the american southwest. the tslf is both prolific and diverse, and includes a large mammal assemblage dominated by mammuthus columbi and camelops hesternus. two (and possibly three) distinct species of equus, two species of bison, panthera atrox, smilodon fatalis, canis dirus, megalonyx jeffersonii, and nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. this field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the las vegas formation within tusk, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem. vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada (usa) kathleen b. springer1, jeffrey s. pigati1, and eric scott2 1u.s. geological survey, denver federal center, box 25046, ms-980, denver, co 80225 usa; kspringer@usgs.gov; jpigati@usgs.gov 2 dr. john d. cooper archaeological and paleontological center, california state university, fullerton, ca 92834; escott@csusb.edu citation for this article. springer, k.b., pigati, j.s., and scott, e., 2017, vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada (usa): geology of the intermountain west, v. 4, p. 55–98. © 2017 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction tule springs fossil beds national monument tule springs fossil beds national monument (tusk) is located in the upper las vegas wash, in the northern reaches of the las vegas valley, clark county, southern nevada. tusk was established as the 405th unit of the national park service on december 19, 2014, and was created to “conserve, protect, interpret and enhance for the benefit of present and future generations the unique and nationally important paleontological, scientific, educational and recreational resources and values of the land.” paleontological and paleoecological resources, such as fossilized plants, animals, and their traces, including both organic and mineralized remains in body and trace form, are all protected here. www.utahgeology.org 56 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 the nearly 23,000-acre national monument also preserves the last vestiges of extensive middle to late quaternary desert wetland ecosystems, which are represented in the geologic record by stratigraphically complex groundwater discharge (gwd) deposits that contain the vertebrate fossils (cover photo). this field guide provides global positioning sysytem (gps) coordinates, annotated photographs, and descriptions of key sites of geologic and paleontologic interest within the monument (figure 1). as of the publication date of this guide, tusk has no designated trails, roads, or infrastructure. therefore, these sites may be accessed by off-trail hiking only. the monument is fenced at the urban interface with the cities of las vegas and north las vegas, with entry to the park provided at a few select ingress points, most notably the northern termini of durango drive and decatur boulevard (figure 1c). collecting or disturbing fossils, rocks, or plants within a national park unit is illegal. please be mindful. history of geologic and paleontologic research at tule springs vertebrate fossils have been recognized from the upper las vegas wash, clark county, nevada, for more than a century, beginning when josiah spurr of the u.s. geological survey (usgs) reported “mastodon teeth and bones … situated in a clay bank some 10 or 15 feet high” in the wash between corn creek springs and tule springs (spurr, 1903). given the preponderance of mammoth fossils and the extreme paucity of mastodon remains known from pleistocene deposits of the southern great basin and mojave deserts, these specimens were likely mammoth (jefferson, 1991; scott and cox, 2008; springer and others, 2011). regardless, the fossils were apparently collected, but their present whereabouts are unknown. the earliest formal scientific investigations occurred in 1919, when chester stock and his student, richard russell, both from the university of california, berkeley, spent a field season in southern nevada in search of neogene and quaternary vertebrate fossils. while in the las vegas valley, they discovered and collected fossils of horse (equus), bison (bison), and a partial phalanx of the extinct north american lion (panthera atrox). although their findings were never formally published, these specimens are highly significant in that they are the earliest recovered pleistocene vertebrate fossils from the las vegas region that can be located in a museum collection. they are presently housed at the university of california’s museum of paleontology (ucmp) on the berkeley, california campus. tule springs gained notoriety as a potential archaeologic and paleontologic hotbed beginning in 1932–33 with the arrival of a team from the american museum of natural history (amnh) led by archaeologist fenley hunter. working with albert c. silberling, a noted and prolific fossil collector from montana, hunter and his team collected a small but diverse assemblage of pleistocene fossils. they also found charcoal and a single flake of obsidian, the latter of which does not occur naturally in the region, potentially signaling the presence of early humans in the valley. a young vertebrate paleontology curator from the amnh, george gaylord simpson, learned of the tule springs site and was able to study the fossils upon their arrival in new york. he published a “brief and preliminary” account of hunter’s discoveries in october 1933 (simpson, 1933). although simpson himself never visited the nevada site, he recognized—and his 1933 paper emphasized—the significance of the potential association of early humans with the pleistocene fauna. simpson’s (1933) note established the tule springs area as a promising site for further research on the question of whether humans had arrived in north america prior to the extinction of the megafauna, and, if so, the nature of their interaction with the animals. the vertebrate fauna from the hunter’s amnh expedition includes the remains of ground sloth (“nothrotherium” [= nothrotheriops sp. cf. n. shastensis]), columbian mammoth (“parelephas columbi” [= mammuthus columbi]), horse (“equus pacificus” [= e. scotti]), a second, smaller species of horse, camel (camelops hesternus), and probable long-horned bison (“bison aff. occidentalis” [likely = b. latifrons]) (simpson, 1933) (see figure 2). jackrabbit (lepus) and pocket gopher (thomomys) are the only small mammals represented in the fauna. the fossils collected by hunter and silberling, along with associated maps, notes, and photographs, are archived in the vertebrate paleontology 57 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 120°w 110°w 38°n 32°n 0 5 km n las vegas range sheep range upper las vegas wash corn creek flat spring mountains las vegas springer et al, figure 1 tusk boundary(a) (b) 0 2 km corn creek springs 16 15 13 1112 17 14 9 10 4 3 1 2 8 7 5 6 20 18 19 dd db n kyle canyon fan gass peakbajada las vegas range upper las vegas wash “the narrows” hwy 95 eglington fault las vegas valley shear zone (c) tule springs figure 1. (a) site location map for the las vegas valley of southern nevada (red star); (b) aerial photograph of light-colored paleowetland deposits that are exposed in large parts of the valley, including much of tule springs fossil beds national monument (tusk); (c) aerial photograph of the upper las vegas wash showing major physiographic features. numbers adjacent to filled red circles correspond to sites of geologic and paleontologic interest discussed herein. blue stars show the locations of key entry points into tusk; db = decatur blvd., dd = durango drive. all photographs, unless otherwise noted, are from the authors. 58 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 collections of the amnh. news of hunter’s discovery spread quickly and in october 1933, the same month that simpson’s paper was published, archaeologist mark harrington of the southwest museum was in the field at tule springs. harrington’s focus at tule springs was to demonstrate the association of human cultural artifacts and pleistocene megafauna as had been documented at folsom and clovis, new mexico, in the late 1920s and early 1930s. these latter sites had yielded projectile points in association with remains of extinct bison antiquus (folsom) and mammuthus columbi (clovis). at tule springs, harrington collected some bone fragments, stone choppers, and charcoal, but left the upper las vegas wash disappointed by the general lack of artifacts (harrington and simpson, 1961). “this was 1933,” he reported, “and already several western american localities had been found in which man-made implements were associated with the bones of extinct pleistocene animals … since tule springs was yielding so few artifacts, further excavation here did not seem worthwhile” (harrington and simpson, 1961, p. 58). figure 2. (a) american museum of natural history (amnh) expeditions in 1932–33 resulted in the recovery of a skull of bison latifrons (simpson, 1933); (b) the same skull after museum preparation (amnh 30052), oblique right view. anterior is to the right. note the pronounced length of the horn core. this specimen now resides in the amnh. 59 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 as a result, tule springs failed to garner further attention for two decades, but spurred on by the advent of radiocarbon dating as a research tool, harrington and ruth deette “dee” simpson of the southwest museum (and later of the san bernardino county museum [sbcm]) rekindled their interest in the artifacts and fossils from tule springs. unable to acquire satisfactory samples of charcoal from the site during a brief visit in 1952, simpson hunted up the original samples of charcoal collected by harrington and his team in 1933. these samples and additional charcoal from fenley hunter were provided to willard libby, who had recently pioneered the new radiocarbon dating technique, to determine the age of one of the fossil-bearing units. the sample turned out to be older than libby was able to date at that time, yielding results in excess of 23.8 14c ka (thousands of years) (harrington, 1955; simpson, 1955; harrington and simpson, 1961). tule springs was suddenly back on the archeological map, as the putative >23.8 14c ka date, if confirmed, would more than double the age of the arrival of humans in the new world as understood at the time. armed with this new information, harrington and simpson were eager to return to las vegas because “[w]ith that age just one unmistakable flaked stone implement found in place in the charcoal would be tremendously significant” (harrington and simpson, 1961, p. 59). with renewed enthusiasm, a field party from the southwest museum excavated at tule springs in 1955– 56 (figure 3). they uncovered several large deposits of charcoal with minor amounts of associated faunal material, which they interpreted to be the remains of human cooking fires where pleistocene animals were roasted and eaten. charcoal from one such site yielded a finite age of 28.0 14c ka (olson and broecker, 1961), an incredible result assuming that the charcoal was indeed related to human activity. as with earlier studies conducted in the upper las vegas wash by the southwest museum, the perceived significance of the vertebrate fossils discovered at that time was based largely upon whether or not they were associated with artifacts, and as a result collection of vertebrate fossils was not systematic. in 1959, willard libby aspired to apply his nobel prize winning work on radiocarbon dating on a large scale. libby had a strong interest in questions about the presence of early humans in the western hemisphere, and wanted the new radiocarbon lab at ucla to make an impact in this field. after considering several archaeological sites for this research effort, libby chose tule springs as the most promising test case to demonstrate the potential of the new technique. a team of scientists was organized with the primary objective of determining whether or not humans and pleistocene animals were contemporaneous at tule springs, and if so, during what period of geological figure 3. (a) stuart peck (left) and mark harrington (right), excavating fossils in the las vegas valley during the southwest museum expeditions at tule springs; (b) southwest museum survey site 4 being cleared in 1955 by charles rozaire (left) and dee simpson (right). sbcm archival images. 60 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 time. in contrast to earlier expeditions, this study was truly interdisciplinary, combining archaeology and paleontology with geology, biology, and palynology. in what later came to be known as the “big dig,” the 1962–63 excavations at tule springs coupled traditional archaeological and paleontological field techniques with unprecedented and massive earth-moving activities (figure 4). bulldozers and scrapers carved enormous trenches deep into the geologic sediments at tule springs, exposing vertical sections up to ~12 to 13 m high, in order to map the complex stratigraphic relationships without the interference of naturally eroded topography. ten trenches totaling more than 2.13 km in length were excavated, including trench k, which itself figure 4. (a) aerial photograph of the tule springs archaeological site showing trenches (a–k) that were part of the big dig of 1962–63 (after wormington and ellis, 1967; their figure 11b); (b) c. vance haynes, jr. unearthing a pair of mammoth tusks at the tule springs archaeological site; (c) photograph of the inside of one of the trenches as it appeared shortly after excavation; archaeologist dee simpson for scale. sbcm archival image; (d) the bison sp. “bone pile” at locality 2, tule springs site, in 1963. sbcm archival image; (e) metacarpals (v-6243/64646, to left; v6243/64645, to right) of bison antiquus from the “bone pile” at locality 2, tule springs site; specimen access courtesy ucmp. 61 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 was more than a kilometer long (figures 4a and c). c. vance haynes, jr. directed the geological investigation (figure 4b), and subdivided the tule springs sediments into discrete, informally designated stratigraphic units (haynes, 1967), referring to them collectively as the las vegas formation after longwell and others (1965). to establish a temporal framework for this new stratigraphy, more than 80 radiocarbon dates were obtained from libby’s lab at ucla (shutler, 1967a, 1967b), an incredible number for the time and with results produced within a week of collection—a rate that is rarely matched even today. in addition to establishing baseline stratigraphic and chronologic frameworks, the big dig investigations revealed several new vertebrate taxa, including a second type of ground sloth (megalonyx), north american lion (panthera atrox), and pronghorn (?tetrameryx) (mawby, 1967). [note: this was the first report of p. atrox from the las vegas valley published in the scientific literature.] other vertebrates, including rabbits (sylvilagus and possibly brachylagus), rodents (dipodomys, microtus, ondatra), and coyote (canis latrans), were also added to the fauna. birds were documented from the assemblage for the first time, albeit on the basis of fragmentary material; the giant teratorn teratornis merriami was present, as was an owl (bubo), an indeterminate soaring hawk (buteoninae), and a host of waterfowl (fulica, mareca, aythya, mergus, and anseriformes). importantly, the fossils were tied directly into the stratigraphy established by haynes, allowing the scientists to begin tracking patterns of change in the vertebrate faunas through time. for example, they observed that fossils of bison were present in the older members of the las vegas formation (figure 4d and e), but not higher in the section, whereas ?tetrameryx was reported from the younger units, but not the older. small equus was also interpreted to be more common in the younger units of the formation than the older (mawby, 1967). in the end, haynes’ careful excavation, stratigraphy, and chronology demonstrated that human cultural artifacts only occurred in the youngest levels of the formation—those units lacking pleistocene megafaunal remains. the hypothesis of early humans coexisting with pleistocene megafauna in the upper las vegas wash was falsified (wormington and ellis, 1967) and, once again, tule springs fell off the map of important sites for scientific study in north america. paleontologic and geologic studies in the las vegas valley remained essentially dormant for more than three decades until the early 1990s, when scientists from the sbcm began work in the upper las vegas wash (figure 5). these efforts, which continued into the early 2000s, were initially related to paleontologic mitigation associated with bureau of land management (blm) land transfers and construction activities, and were relatively limited in scope. nevertheless, they were productive. in 2001 and 2002, for example, the sbcm discovered nearly 10,000 vertebrate and invertebrate fossils from 36 previously unrecorded fossil localities along the proposed route of a new transmission line running through the upper las vegas wash. these discoveries added to the overall fauna and demonstrated the continued paleontologic richness of the region. to put these findings in context, mawby’s (1967) report on the fossils from the region listed just 12 localities. in 2003 and 2004, the entire tule springs area was designated by public law as a “disposal area” to be sold to accommodate the burgeoning growth of the cities of las vegas and north las vegas. the blm was required to conduct an environmental impact assessment of all protected resources in these lands, including paleontology, and to evaluate potential losses of these resources. the blm authorized the sbcm to conduct an extensive survey of the upper las vegas wash and surrounding areas, and in light of earlier reports, the results were astonishing. the survey discovered and documented 438 previously unrecognized paleontologic localities— nearly ten times the number of all previous investigations combined—firmly establishing the paleontologic wealth of the region. in addition, sbcm scientists demonstrated that understanding the geologic context of the fossils was critical for determining the significance of the resources and showed that the wetland deposits were the last to exist within the las vegas valley (springer and others, 2006). in consideration of these factors, as well as the presence of other sensitive natural and cultural resources, the blm withheld 13,622 acres as the “upper las vegas wash conservation transfer area” to protect the area from development and to allow further scientific studies to occur. 62 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 subsequent field investigations between 2008 and 2014 by the sbcm and usgs combined new geologic mapping and detailed stratigraphic analyses (ramelli and others, 2011, 2012) with expanded and improved geologic interpretations and a more refined geochronology (springer and others, 2015). these efforts led to the ongoing formal designations of the las vegas formation (springer and others, 2017) and tule springs local fauna (tslf) (scott and springer, 2017). over 500 fossil localities and more than 20,000 fossils were collected and curated as a result of these efforts. these detailed studies led to the recognition that extensive wetland ecosystems expanded and contracted many times during the late quaternary in the las vegas valley, tracking hemispheric and global climatic oscillations in near lock step. ultimately, the combination of the initial protection of these lands by the blm, the excitement by the general public and political powers over the fossil discoveries and ongoing scientific studies, and an enthusiastic and steadfast advocacy group, called the protectors of tule springs, led to the designation of tule springs fossil beds national monument in 2014. notable taxa of the tule springs local fauna the vertebrate fauna of tusk occurs throughout most of the temporal and spatial extent of the las vegas formation. the fauna extends from ~100 ka to 13 ka at multiple localities throughout the upper las vefigure 5. (a) paleontologist eric scott of the dr. john d. cooper archaeological and paleontological center (formerly of the sbcm) excavating a mammoth jaw (sbcm l3160-586a) in the upper las vegas wash; (b) mammoth tusk (sbcm l3160-597), one of many recovered from the extensive gwd deposits in tusk (c) sbcm technician conrad salinas iii recovering camel fossils from a spring-fed channel; (d) horse tooth, recovered in situ from gwd deposits in tusk (uncataloged specimen from sbcm locality 2.6.603); (e) geologist kathleen springer of the usgs (formerly of the sbcm) unearthing fossils in the upper las vegas wash in 2002. 63 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 gas wash. the nature of the assemblage matches published definitions for local faunas; it is “local in both time and space” (taylor, 1960), and consists of “samples derived from localities, sites, quarries, pits, prospects, etc.” that can be “organized into aggregates of species … which have a distribution in time and space, based on the record from a restricted geographic area” (tedford, 1970). based upon these definitions, and because of the importance of these remains, the late pleistocene assemblage is being designated as the tule springs local fauna (tslf; table 1) (scott and springer, 2017). all voucher specimens and catalog numbers are included in scott and springer (2017). unless otherwise noted, all specimens discussed are curated in the collections of the san bernardino county museum. a brief discussion of some of the more significant members of the fauna is presented below. columbian mammoth: mammuthus columbi the relative abundance of fossil remains of mammuthus from the upper las vegas wash is noteworthy. seemingly every geologic, paleontologic, and/ or archaeologic report from the region makes some mention of proboscidean bones and teeth in the wash (figure 6), whereas other pleistocene megafauna from the region receive less consistent mention. this phenomenon likely owes its prevalence not only to the actual abundance of mammoth remains in the las vegas formation, but also to the distinctive and readily identifiable nature of mammoth teeth, tusks, and bones— whether whole or fragmentary—as compared to other large mammal bones and bone portions. both simpson (1933) and mawby (1967) observed that remains of mammoths were among the most common in the assemblages they studied from the upper las vegas wash, and current findings (scott and springer, 2017) are consistent with these observations. mammoths were plant eaters, and given their massive bulk they would have consumed enormous amounts of food, an ecological requirement that is inconsistent with the current habitat of the area. the abundance of mammuthus remains in the las vegas formation demonstrates that the extensive desert wetlands provided ample forage during the late pleistocene. juvenile and subadult fossils of mammuthus are not uncommon in the assemblage, indicating that family groups lived in the region. giant camel: camelops hesternus camelops hesternus was widespread across western north america during the late pleistocene, where it is thought to have lived in relatively large herds (kurtén and anderson, 1980). in coastal sites in southern california (rancho la brea), camels are less represented with respect to other large herbivores (horse, bison) (stock and harris, 1930; scott, 2010), whereas they are more plentiful farther inland (diamond valley lake) (springer and others, 2009, 2010). their abundance in the tslf continues this trend, as camel is second only to mammoth in terms of the raw number of fossils, similar to other late pleistocene megafaunal assemblages at other localities in the mojave desert (e.g., jefferson, 1991). north american llama: hemiauchenia sp. prior to 2010, the tslf lacked evidence of the extinct north american llama, hemiauchenia macrocephala, which contrasts sharply with the relative dominance of this taxon at other late pleistocene localities in the mojave desert (jefferson, 1991). however, a locality discovered that same year by the sbcm yielded a proximal right radio-ulna of a small adult camelid. although incomplete and lacking reliable points of measurement, the specimen is sufficiently small that estimated dimensions fell well within the published size range of hemiauchenia (meachen, 2005). given the small size and apparent adult age of the fossil, it was assigned to that genus, and thus represents the first and currently only record of this taxon from the las vegas formation. bison: bison spp. bison are relatively common in the assemblage from the upper las vegas wash (simpson, 1933; mawby, 1967; de narvaez, 1995; scott and cox, 2008; scott, 2010). two species of bison are present in the tslf, including a long-horned species (bison sp. cf. b. latifrons) and the smaller bison antiquus, the latter based on the 64 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 a ni m al ia c ho rd at a o st ei ch th ye s te le os te i bo ny fi sh a m ph ib ia a nu ra b uf on id ae bu fo sp . to ad h yl id ae h yl a sp . 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( sm al l) sm al l f ro g r an id ae ra na sp . po nd fr og r ep til ia c he lo ni a te st ud in id ae g op he ru s s p. to rto is e la ce rti lia ig ua ni da e sc el op or us sp . c f. s. o cc id en ta lis sa ge br us h liz ar d c al lis au ru s s p. c f. c . d ra co ni de s ze br ata ile d liz ar d ph ry no so m a sp . ho rn ed li za rd sq ua m at a a nn ie lli da e an ni el la sp . le gl es s l iz ar d se rp en te s c ol ub rid ae m as tic op hi s s p. co ac hw hi p sn ak e cf . a ri zo na sp . gl os sy sn ak e a ve s a ns er ifo rm es a na tid ae m ar ec a am er ic an a w id ge on ay th ya c ol la ri s rin gne ck ed d uc k ay th ya a ffi ni s le ss er sc au p m er gu s m er ga ns er co m m on m er ga ns er c ic on iif or m es te ra to rn ith id ae te ra to rn is m er ri am i te ra to rn a cc ip itr ifo rm es a cc ip itr id ae bu te on in ae in de te rm in at e so ar in g ha w k g ru ifo rm es r al lid ae fu lic a am er ic an a co ot fu lic a am er ic an a m in or sm al l c oo t st rig ifo rm es st rig id ae bu bo sp . ow l m am m al ia x en ar th ra m eg al on yc hi da e m eg al on yx je ffe rs on ii je ff er so n’ s g ro un d slo th (c on tin ue d on n ex t c ol um n) ta bl e 1. c om po sit e ve rt eb ra te fa un a, l as v eg as f or m at io n. m eg at he rii da e n ot hr ot he rio ps sh as te ns is sh as ta g ro un d sl ot h la go m or ph a le po rid ae sy lv ila gu s s p. co tto nt ai l r ab bi t le pu s s p. ja ck ra bb it ?b ra ch yl ag us id ah oe ns is po ss ib le p yg m y ra bb it r od en tia sc iu rid ae am m os pe rm op hi lu s l eu cu ru s an te lo pe g ro un d sq ui rr el m ar m ot a fla vi ve nt ri s ye llo w -b el lie d m ar m ot g eo m yi da e th om om ys b ot ta e b ot ta ’s p oc ke t g op he r h et er om yi da e d ip od om ys sp . ( la rg e) la rg e ka ng ar oo ra t d ip od om ys sp . ( sm al l) sm al l k an ga ro o ra t pe ro gn at hu s s p. po ck et m ou se c ric et id ae pe ro m ys cu s s p. c f. p. m an ic ul at is de er m ou se re ith ro do nt om ys sp . ha rv es t m ou se o ny ch om ys sp . gr as sh op pe r m ou se n eo to m a sp . c f. n . l ep id a de se rt w oo d ra t m ic ro tu s s p. c f. m . c al ifo rn ic us m ea do w vo le o nd at ra zi be th ic us m us kr at c ar ni vo ra m us te lid ae ta xi de a ta xu s ba dg er c an id ae c an is d iru s di re w ol f c an is la tr an s co yo te fe lid ae pu m a sp . c f. p. c on co lo r pr ob ab le pu m a ly nx ru fu s bo bc at pa nt he ra a tr ox n or th a m er ic an li on sm ilo do n fa ta lis sa br eto ot he d ca t pr ob os ci de a el ep ha nt id ae m am m ut hu s c ol um bi c ol um bi an m am m ot h pe ris so da ct yl a eq ui da e eq uu s s co tti s co tt’ s h or se eq uu s s pp . ( sm al l) sm al l h or se a rti od ac ty la c am el id ae h em ia uc he ni a sp . lla m a c am el op s h es te rn us gi an t c am el c er vi da e o do co ile us sp . de er a nt ilo ca pr id ae pr on gh or n b ov id ae bi so n sp . c f. b. la tif ro ns pr ob ab le lo ng -h or ne d bi so n bi so n an tiq uu s bi so n ? eu ce ra th er iu m po ss ib le sh ru box (c on tin ue d fr om p re vi ou s c ol um n) 65 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 sbcm’s recovery of a partial skull with an intact horn core, as well as less complete crania and measureable postcrania from multiple localities. mawby (1967) reported fossils of extinct bison from unit b2 (= bed b2; see the las vegas formation section below for geologic and chronologic details) but not from any of the younger fossil-bearing strata. however, the sbcm investigations confirmed the presence of bison in both older and younger units of the las vegas formation. bison was recovered in beds b1, b2, d1 and e0 of the las vegas formation; its occurrence in beds b1 and e0 extends the temporal range of this taxon in the tslf. horse: equus spp. horses are also common in the large mammal assemblage from the upper las vegas wash. both simpson (1933) and mawby (1967) found at least two species of horse, one large and one small. simpson (1933) also suggested the possible presence of a third species. current efforts (scott and springer, 2017) support the latter contention; analysis of available elements suggest the large horse species equus scotti, a small stout-limbed horse, and possibly a small stilt-legged species all lived in and around the las vegas valley during the late pleistocene (scott and springer, 2017). the proposed presence of a small stilt-legged horse in the region is strengthened by the documentation of small stiltlegged horses at the nearby gypsum cave locality, ~25 km east of the las vegas valley (scott and lutz, 2014). if all three species of horses at tule springs are confirmed, it would contradict results of recent molecular studies that contend only two species of equus were present in north america during the late pleistocene (e.g., weinstock and others, 2005; orlando and others, 2008). the fossils of equus scotti from the upper las vegas wash were recovered from a spring outflow stream in bed e1d and are directly associated with a calibrated 14c age of 13.69 ± 0.14 ka. these remains are the youngest and most southerly record of this species in nevada, figure 6. bones of a juvenile columbian mammoth eroding out of bed e0 (23.04–18.16 ka) in the upper las vegas wash. this locality was partially excavated as part of the “big dig” in 1962–63. 66 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 and among the youngest anywhere in north america. the presence of e. scotti in the tslf demonstrates its close geographic and temporal proximity to other late pleistocene mojave desert localities that reportedly contain equus “occidentalis.” thus, the range extension documented of e. scotti here may force reevaluation of these prior records. dire wolf: canis dirus until recently, the only large predator known from the las vegas formation was the extinct north american lion panthera atrox (mawby, 1967). fossil remains of this species are rare in the tslf, even though a phalanx of p. atrox was among the earliest fossils discovered in the valley. nevertheless, the paucity of fossils of large carnivorans is consistent with the interpretation that the fossils from the area represent a “normal” population distribution, in contrast to an entrapment setting (e.g., rancho la brea), where herbivores are far more numerous than predators. the first confirmed record of canis dirus from the las vegas formation consists of a right patella discovered in association with other pleistocene taxa (scott and springer, 2016). this specimen was recovered from bed e1b, which places c. dirus in southern nevada towards the end of the pleistocene, between 14.59 and 14.27 ka. this is the first confirmed record of dire wolf in the upper las vegas wash, and the first in the entire pleistocene fossil record of nevada. sabre-toothed cat: smilodon fatalis in 2003, fossils of smilodon fatalis were discovered in the upper las vegas wash by the sbcm, but were not recognized until they were prepared and stabilized in 2012 (scott and springer, 2016). remains of s. fatalis include a proximal left humerus and a distal left radius, as well as a partial sacrum. these fossils were recovered from bed e1a, which dates to between 16.10 and 14.96 ka (springer and others, 2017), thereby establishing the presence of s. fatalis in southern nevada towards the end of the pleistocene. this new record adds to the sparse record of pleistocene sabre-toothed cats from nevada, as the only previous records from the state are from sites located north of the mojave desert (e.g., kurtén and anderson, 1980; dansie and others, 1988; livingston, 1991; jefferson and others, 2004). bobcat: lynx rufus a single right humerus represents the first pleistocene record of bobcat (lynx rufus) from the upper las vegas wash. the specimen was recovered from the floodplain deposits of bed e0 of the las vegas formation and is associated with a calibrated 14c age of 21.04 ± 0.52 ka. present-day bobcats are remarkably eurytopic carnivorans, inhabiting most kinds of environments from dense forest to desert, although they generally prefer broken country with cliffs and rock outcrops interspersed with open grasslands, woods, or deserts (hoffmeister, 1986). the mosaic of ecologic settings in the las vegas valley during the late pleistocene would have offered an ideal habitat for l. rufus. new additions to the tule springs local fauna the lower vertebrate microfauna from the tslf includes fossils of true frog, rana sp., as well as legless lizard (anniella sp.), whipsnake (masticophis sp.), and probable glossy snake (cf. arizona elegans). none of these taxa have been reported previously from the las vegas formation or from the fossil record of the las vegas valley. the mammalian microfauna includes specimens of marmot (marmota flaviventris), probable desert wood rat (neotoma sp. cf. n. lepida), harvest mouse (reithrodontomys sp.), and probable grasshopper mouse (cf. onychomys sp.), which represent additional taxa not previously known from the las vegas formation. finally, the large mammal fauna also includes evidence of a large bovid, smaller than bison but larger than a sheep (ovis), that might represent extinct shrub ox (euceratherium sp.) (scott and springer, 2017). geology, stratigraphy, and paleohydrology of tusk the broad sedimentary basin of the las vegas valley was formed during the neogene by extensional forces associated with the making of the basin and range province of western north america (fleck, 1970; page and others, 2005). the extension resulted in a series of 67 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 normal and strike-slip faults that cut across the region, including the las vegas valley shear zone (lvvsz), a northwest striking, right lateral strike-slip fault system (langenheim and others, 1997, 1998; page and others, 2005). within the monument, the fault system is mostly buried by thick basin-fill deposits, although surface expression occurs at corn creek springs, located just outside of tusk (figure 1). the lvvsz also marks the limit of headward erosion of the upper las vegas wash, and includes discontinuities and subsurface barriers that likely influence local and regional groundwater flow patterns. inset within the basin-fill deposits, the quaternary-age las vegas formation was initially described by longwell and others (1965) from a series of light-colored clay and silt deposits exposed along the upper las vegas wash. through successive periods of erosion and deposition, units within the formation are laterally discontinuous, exhibit complex stratigraphic relations, and combine to form a highly dissected, undulating badland topography. prior to extensive urbanization of the cities of las vegas and north las vegas, sediments of the las vegas formation were exposed throughout the entire valley (longwell and others, 1965; haynes, 1967; matti and others, 1993; donovan, 1996; bell and others, 1998, 1999; page and others, 2005; ramelli and others, 2011, 2012). today, exposures are restricted primarily to the upper las vegas wash and corn creek flat areas (figure 1). haynes (1967) recognized and described five pleistocene and two holocene informal stratigraphic units (a to g, in ascending stratigraphic order) and six intervening soils from exposures at the original tule springs site, which were then extrapolated throughout the upper las vegas valley (quade, 1986). initially, these sediments were thought to be strictly lacustrine in origin (hubbs and miller, 1948; maxey and jamesson, 1948; snyder and others, 1964; longwell and others, 1965), but haynes (1967) determined that at least some of the sediments were deposited in ciénegas, or desert wetlands, although he also postulated the existence of “pluvial lake las vegas” based on the spatial abundance of full-glacial age deposits in the las vegas valley. following suit, other studies have documented the presence of past episodes of groundwater discharge in the southern great basin and mojave deserts in areas formerly reported as lacustrine (mifflin and wheat, 1979; hay and others, 1986; quade, 1986; quade and pratt, 1989; quade and others, 1995, 1998, 2003; pigati and others, 2011; springer and others, 2015, 2017). during the late pleistocene, a climate wetter than today supported a variety of groundwater discharge settings throughout the southwestern u.s., including seeps, springs, marshes, wet meadows, ponds, and spring pools. alluvial, fluvial, and eolian sediment became trapped by wet ground conditions and dense plant cover around these discharge points, and combined with organic material and chemical precipitates (carbonates, silicates) to form gwd deposits (pigati and others, 2014). we are able to distinguish these deposits from lake sediments using sedimentologic and stratigraphic properties, as well as microfaunal assemblages, and are now able to recognize specific hydrologic regimes within the deposits comparable to modern spring ecosystems, including limnocrene (ponding), helocrene (marshes or wet meadows), and rheocrene (stream) flow (springer and stevens, 2008) (figure 7). the types of spring discharge and their spatial distribution throughout the upper las vegas wash are directly related to subsurface structure (faults), aquifer complexity, and local and regional water table levels. such recognition allows us to further constrain our understanding of past environmental and hydrologic conditions. our highly resolved chronologic and paleohydrologic records of the gwd deposits in the upper las vegas wash show that wetlands in the valley were extremely sensitive to climate change in the recent geologic past. multiple cycles of deposition, erosion, and soil formation demonstrate that wetland ecosystems in the valley expanded and contracted many times during the late pleistocene, often collapsing entirely, before disappearing altogether as the last glacial period came to a close. these events exhibit temporal congruence with episodes of abrupt climate change, including dansgaard-oeschger (d-o) cycles and other millennialand submillenial-scale climatic perturbations (springer and others, 2015) (figure 8). drought-like conditions, as recorded by widespread erosion and soil formation, typically lasted for a few centuries, which would have severely impacted the flora and fauna that depended on 68 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 figure 7. examples of groundwater discharge regimes in extant wetlands (panels a, c, e) and their counterparts in the geologic record in tusk (panels b, d, f). rheocrene discharge is characterized by spring-fed streams and outflow channels, limnocrene discharge is characterized by discrete spring-fed pools and ponds, and helocrene discharge is characterized by extensive wet meadows and marshes. 69 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 pb 8.2 ka b a 5 10 15 20 25 30 35 d-o 2 d-o 3 d-o 4 d-o 5 d-o 6 d-o 7 “big wet” yd lithologic breaks and/or erosion erosion/ aridisol aridisol ox. seds aridisol aridisol “big dry”ox. seds erosion widespread erosion aridisol ag e (c al k a) od -45 -35 -30-40 gicc05 δ18o (‰) d1 d2 d3 e0 e2a e2b e2c e1a e1b e1d e1c tu fa fo rm at io n las vegas formation composite stratigraphy axial deposits marginal deposits clay carbonate cap silt / platy carbonate silt marl rheocrene discharge (streams) black mat interbedded silt and sand sand reworked carbonate nodules / sand limnocrene discharge (ponds) crossbedded sand limestone gravel soil helocrene discharge (marshes) unconformity molluskscrossbedded sand / tufa clasts figure 8. caption on following page. 70 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 the springs and wetlands for water in an otherwise arid landscape (springer and others, 2015). it is therefore critical to investigate and understand the geologic and hydrologic context of vertebrate fossil localities in detail if we are to determine how animals (and humans) survived in the ever-changing deserts of the american southwest. the las vegas formation the las vegas formation was designated initially by longwell and others (1965) and haynes (1967), and is being elevated to formal status by springer and others (2017). the nomenclature presented herein largely follows that of haynes (1967) but has been modified to include additional subunits that were not recognized previously. in addition, haynes’ unit c has been dissolved, as detailed stratigraphic analysis and a suite of 14c and luminescence ages have shown that it consisted of sediments that are attributable to members b and d (springer and others, 2017). we describe the las vegas formation, and limit the discussion below to units (now members) a through e because they consist of lithologies that represent various groundwater discharge regimes. units f and g of haynes (1967) represent dry conditions that prevailed during the holocene. additionally, all radiocarbon and luminescence ages discussed in this field guide are documented in springer and others (2015, 2017). ages are presented in ka (thousands of years) and associated uncertainties are given at the 2σ (95%) confidence interval. each of the identified subunits (e.g., members, beds) described below represents a discrete “bin of time” that can be utilized to quantify changes in local faunal assemblages, reconstruct past ecosystems and environments on millennial and submillennial timescales, and evaluate the response of these systems to past episodes of abrupt climate change. in essence, we view the stratigraphic and chronologic frameworks that we have created for the las vegas valley gwd deposits as “scaffolding” for future scientific studies. below, we describe the primary physical characteristics and age ranges for each subunit within the las vegas formation as a composite stratigraphy (figure 9), and note that additional stratigraphic and chronologic details for all subunits described herein are provided in springer and others (2015, 2017). member a (~300 to 155 ka) the stratigraphically lowest member of the las vegas formation, member a, crops out along the length of the upper las vegas wash. it is not as widely exposed as the other members and consequently has been investigated less thoroughly. in general, member a is complex and is characterized by abundant secondary carbonate (nodules, mottling), soil overprinting, and redoxymorphic features (figure 9). along the valley axis, member a consists of greenish to light-gray silts and sands that are present in spring cauldron bedforms (limnocrene discharge), deposits associated with spring outflow streams (rheocrene discharge), and numerous well-developed carbonate horizons, benches, and a massive carbonate cap formed in marshes and wet meadows (helocrene discharge). away from the valley axis, the sediments transition to brown and gray clays and silts deposited in a drier, more marginal facies. member a contains a number of wetland soils, indicative of fluctuating water tables, and aridisols, which represent drier conditions. redoxymorphic features are abundant in member a, an indication that fluctuating water-table levels were common during its formation. overall, member a spans multiple glacial–interglacial cycles (marine oxygen isotope stages [mis] 6–8), displays a wide range of spring discharge types and soils, figure 8 (figure on previous page). stratigraphic and chronologic records of gwd deposits in the las vegas valley of southern nevada (after springer and others, 2015) compared to δ18o data from greenland ice core records using the gicc05 chronology (svensson and others, 2008). filled circles are calibrated radiocarbon ages of the gwd deposits with uncertainties (bars) presented at the 95% (2σ) confidence level. wetland discharge (by type) is shown in graduated shades of green. tan horizontal bars indicate periods of aridity as evidenced by surface stability and/or erosion. d-o = dansgaard-oeschger cycles; “big wet/big dry” after broecker and others (2009); b = bølling; od = older dryas; a = allerød, yd = younger dryas; pb = preboreal; 8.2 ka = 8.2 ka cold event. 71 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 and represents a long-lived and diverse desert wetland ecosystem. vertebrate fossils have yet to be discovered from member a in the las vegas valley itself, but are anticipated based on the lithologies present. they are also known from member a elsewhere in the mojave desert, most notably in the nearly complete member a sequence in the nearby pahrump valley, southern nevada-california. member b (~100 to 40 ka) member b is another long-lived sequence that exhibits a complex stratigraphy consisting of three distinct beds (b1–3) that represent alluvial cut and fill sequences, flood-plain sediments, and discrete groundwater discharge deposits (figure 9). member b, bed b1 (100 to 55 ka) the oldest subunit of member b, bed b1, was deposited between ~100 and 55 ka, and reflects variable hydrologic conditions that occurred during this time. in general, this bed consists of massive to bedded (thin to medium), tan to reddish-brown alluvial silts and sands deposited in relatively dry environments, punctuated by wetland soils and multiple carbonate-rich horizons, representing wetter times. the basal portion of member b is a thick (>1 m) fluvial sequence deposited under (dry) conditions similar to today and contains subangular to subrounded limestone clasts as bedload at the contact with member a. bed b1 also includes a rare, pale-green, silty subunit (b1-wet) representing limnocrene ponding that occurred at ~72 ka. a single locality in bed b1 has yielded the oldest dated fossils from the las vegas valley, including mammuthus and equus, microvertebrates, and a variety of bivalves and gastropods. other b1 sites contain the remains of mammuthus, bison, equus, and camelops. member b, bed b2 (55 to 45 ka) bed b2 was deposited between ~55 and 45 ka, and consists of greenish-gray silt, sand, and clay in laterally discontinuous, cauldron-shaped lenticular beds and associated fluvial channels, characteristic of limnocrene and rheocrene discharge, respectively. pointsource emergence of groundwater from confined or unconfined aquifers in the las vegas valley scoured the cauldron-shaped pools. haynes (1967) describes the internal workings of these ponds, and noted fantastic accumulations of fossils preserved in spring feeder conduits (figure 4d). bed b2 often contains organic material (charcoal and carbonized wood fragments), limestone gravels at the base of the bed, and aquatic gastropod shells of the genera helisoma, pisidium, physa, and gyraulus. the presence of helisoma, in particular, is indicative of the limnocrene ponding that prevailed at this time. vertebrate fossils are especially abundant in bed b2, and are commonly found in the green silts and clays of the limnocrene ponding units. multiple b2 localities have yielded the remains of mammuthus, bison, equus, camelops, aves, and abundant microvertebrates. based on palynological data acquired during the 1962–63 excavation, mehringer (1967) determined that the upper las vegas wash shifted from a sagebrush-dominated desert to moister and possibly cooler environment, and back during member b2 time. member b, bed b3 (45 to 40 ka) bed b3 is composed of tan silt and sand that form channel and overbank deposits, similar to bed b1, and dates to between ~45 and 40 ka. sediments within bed b3 include cross-bedded sand, silt, and localized clay. as in bed b1, groundwater-derived carbonate horizons are present in bed b3, reflecting the presence of groundwater near the surface during short-lived wet phases within this time period. rare vertebrate fossils are known from this unit, most occurring on deflated surfaces as float localities. member d (36.07 to 24.45 ka) member d represents the highest groundwater levels attained in the las vegas valley during the late quaternary. widespread marshes and wet meadows formed during a period of pervasive spring discharge that left behind characteristic gwd deposits, most notably distinct and topographically extensive carbonate benches and caps. member d consists of three distinct beds (d1–3) that contain multiple black mats and exhibit lithologies that vary laterally from the valley axis (wetter) 72 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 marginal deposits (inset) m 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 member d (36.07 to 24.45 ka) member d consists of three distinct discharge episodes, including bed d1 (36.07–34.18 ka), bed d2 (31.68–27.58 ka), and bed d3 (25.85–24.45 ka). sediments include carbonate-rich silts and clays that contain multiple black mats. notably, beds d2 and d3 are capped by widespread carbonate horizons that represent the highest groundwater levels achieved during the late quaternary. within member d, discharge episodes are punctuated by periods of surface stability and/or erosion. member e, bed e2 (12.90 to 8.53 ka) bed e2 of member e consists of three subunits that each exhibit a unique appearance. bed e2a consists of green clays, silts, and sands in cauldron-like bedforms; bed e2b is composed of reddish-tan silts and sands; and bed e2c consists of light tan silts and sands. all three beds contain black mats and bed e2b contains abundant tufa. notably, bed e2b is often armored by gravelly alluvium forming characteristic sinuous inverted topography. member e, bed e1 (16.10 to 13.37 ka) bed e1 of member e is composed of several discrete subunits that each exhibit a unique appearance. bed e1a consists of rhythmically bedded (10–30 cm) tan silts and sands that are capped by carbonate rubble. bed e1b consists of massive gray silts and sands capped by gravels. bed e1c is similar to e1a, and is represented by massive bu�-colored silts and sands, but is also capped by gravels. finally, bed e1d is composed of massive to weakly bedded gray silts and sands that appear to have been deposited near localized discharge points. member e, bed e0 (23.04 to 18.16 ka) the basal portion of bed e0 includes two layers of reworked, rounded carbonate gravels separated by green sands. these strata are overlain by light-green silts and sands that grade into gray silt and sand. the upper portion of bed e0 typically consists of bu�-colored silts and sands capped by thin platy carbonate or carbonate rubble. bed e0 marks the �rst appearance of microbially mediated, ambient-temperature tufa that is common throughout member e. member b (~100 to 40 ka) member b exhibits a complex stratigraphy and contains multiple subunits consisting of alluvial cut and �ll sequences, �ood-plain sediments, wetland soils and aridisols, and groundwater discharge deposits. bed b1 (oldest) consists of bedded, tan, alluvial silts and sands with carbonate horizons, and includes a pale-green, silty sand subunit (b1-wet). bed b2 is composed of greenish-gray silt and sand in cauldron-shaped bedforms. bed b3 (youngest) consists of tan silt and sand as channel and overbank deposits, and is similar in appearance to the dry phase of bed b1. member a (~300 to 155 ka) along the valley axis, beds within member a consist of greenish to light-gray sands, silts, and clays that transition to brown and gray silts and clays with increased carbonate toward the valley margin. sediments in member a exhibit strong soil development, multiple carbonate horizons, and abundant redoxymorphic features. soils in member a include wetland soils, which re�ect �uctuating water-table levels and relatively wet conditions, and aridisols, which re�ect drier conditions. axial deposits bed e1a bed e1c bed e1d bed e1b bed e0 bed e2a bed e2b bed e2cbed d3 bed d3 bed e0 bed d2 bed d1 bed d2 bed b3 bed b2 bed b1 member a qso ? ? bed b1-wet figure 9. composite stratigraphy and brief unit descriptions of the members and beds of the las vegas formation. note that colors shown in the stratigraphic profile are intentionally oversaturated to differentiate between members and/or beds. age control is based on a combination of radiocarbon (14c) and luminescence (irsl) dating (see springer and others, 2017). 73 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 into more marginal facies (drier) upslope (figure 9). all of the beds within member d contain vertebrate fossils. member d, bed d1 (36.07 to 34.18 ka) along the valley axis, bed d1 (36.07 to 34.18 ka) consists of light greenish-gray silts, sands, and clays that represent multiple discharge regimes. the basal portion of the bed includes reworked subangular to subrounded carbonate nodules forming a fluvial bedload up to 15 cm thick, representing rheocrene discharge. the middle and upper portions of bed d1 consist of olive-green silts and clays with helisoma and pisidium shells present in cauldron-shaped pools (limnocrene discharge) and clay-rich sediment with succineidae shells representing a reducing marshy environment (helocrene discharge). away from the valley axis, the marginal facies of bed d1 is more grayish-brown and mottled in appearance with rare gastropod shells. member d, beds d2 and d3 (31.68 to 24.45 ka) beds d2 (31.68 to 27.58 ka) and d3 (25.85 to 24.45 ka) represent similar discharge regimes, consisting primarily of whitish gray silts deposited in extensive marshes and wet meadows. bed d2 contains interbedded black mats and both beds exhibit abundant secondary carbonate. notably, both beds are capped by widespread carbonate benches and caps that represent the highest groundwater levels achieved in the las vegas valley during the late quaternary. these features represent a sequence of relatively wet conditions, during which the sediments were deposited, followed by dry conditions, during which the carbonates became case hardened via evapotranspiration at or near the ground surface. both beds exhibit strong facies changes from wet meadows along the valley axis to phreatophyte flats in more marginal areas. (note the phrase “phreatophyte flats” refers to areas where the water table is shallow enough that plants can tap into it but groundwater has not breached the surface. the plants essentially act as dust traps for eolian sediment, and thus “phreatophyte flats” are represented in the gwd record by tan to light brown silts and fine sands [after quade and others, 1995]). within beds d2 and d3, discharge episodes are separated by periods of surface stability (i.e., soil formation) and/or erosion that formed in response to abrupt climatic perturbations (d-o 4-3 and d-o 2). member e (23.04 to 8.53 ka) member e contains eight beds (e0, e1a, e1b, e1c, e1d, e2a, e2b, e2c) that are temporally distinct and mappable at the outcrop scale (figure 9). overall, the multiple cycles of deposition, erosion, and surface stability represented by member e reflect the extreme hydrologic variability that characterized the las vegas valley following the collapse of the entire wetland ecosystem just after the last glacial maximum. the spring hydrographic environments represented by member e consist of multiple point-source discharge and outflow streams, in contrast to the pervasive marshes that existed during member d time. member e also marks the appearance of a series of braided fluvial channels containing microbially mediated, ambient-temperature tufas that are often intercalated with black mats. colder temperatures inhibit the formation of this type of tufa and therefore its presence within member e constitutes an important climatic and paleoenvironmental signal marking warmer times. member e, bed e0 (23.04 to 18.16 ka) bed e0 is a newly recognized unit of the las vegas formation (ramelli and others, 2011; springer and others, 2015); its distinctive lithologies were assigned to member d in previous mapping efforts by bell and others (1998). bed e0 represents a series of spring outflow streams and associated floodplains. the basal portion of bed e0 contains two medium (10 to 30 cm) beds of rounded carbonate gravels derived from the underlying carbonate cap of bed d2 (and possibly d3) mixed with rounded limestone gravels, as well the first appearance of microbially mediated tufa in the las vegas formation. these gravel layers are often separated by 10 to 20 cm of olive-green sands containing abundant aquatic mollusk shells, dominated by pisidium and physa. overlying the basal strata are massive light-green sands and silts that exhibit numerous feeder conduits, spring chalk, and limonite staining (all indicative of vigorous spring activity), which grade upward into gray silts and sands. in turn, these gray fluvial sediments are overlain by buff-colored fine sands and silts indicative of a drier 74 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 environment and are capped by platy carbonate and/or carbonate rubble. in general, the e0 capping carbonate is thinner and darker in color than the thick whitish caps of member d, likely due to an increased input of dust at the end of e0 time. an extraordinary number of vertebrate fossils localities occur within e0 deposits. member e, bed e1 (16.10 to 13.37 ka) bed e1 of member e consists of several discrete subunits that each exhibit a unique appearance and represent distinct episodes of rheocrene flow. as with bed e0, bed e1 contains a large number of fossil localities. bed e1a (16.10 to 14.96 ka) consists of rhythmically bedded (10 to 30 cm), buff-colored silts and sands that weather to a distinct yellowish-brown hue. the sediments are well sorted, often exhibit a hummocky and honeycombed weathering pattern in section, and are capped by carbonate rubble that is platy in some places. bed e1a often contains charcoal and incipient black mats at the base of exposed sections, as well as interbedded rounded limestone gravels. tufa occurs within the e1a deposits locally, appearing as bedload crusts, phytoclasts, and cyanoliths. bed e1b (14.59 to 14.27 ka) exhibits massive, whitish to light gray silts and sands, and is the most easily recognized subunit within bed e1. the basal portion of the bed is composed of lightto medium-gray channelized cross-bedded silt and sand. the basal channelized portion of the bed typically grades upward into the characteristic whitish silts and sands that represent wet meadow facies, and often contain black mats, feeder conduits, and multiple thin carbonate horizons. toward the narrows (figure 1c), aquatic snail shells (helisoma, physa, pisidium) are common within e1b sediments. importantly, bed e1b is mantled by limestone gravels as opposed to carbonate, which contributes to its distinct appearance on the landscape. bed e1c (14.12 to 13.95 ka) is similar in appearance to bed e1a, consisting of massive buff-colored sands and silts that exhibit a honeycombed weathering pattern, also with a yellowish-brown weathered hue. in contrast, however, bed e1c is mantled by limestone gravels, similar to bed e1b. this bed is not very widespread, but where present, it often contains shells of the aquatic bivalve pisidium, indicative of shallow flowing water. bed e1d (13.69 to 13.37 ka) contains massive to weakly bedded gray silts and sands with reworked carbonate nodules. it is also limited geographically and includes localized light greenish-gray silts and sands deposited near spring orifices, which exhibit inclined bedding. this bed also contains aquatic shells (pisidium, physa) that indicate shallow flowing water. member e, bed e2 (12.90 to 8.53 ka) bed e2 of member e is represented by three subunits that each exhibit a unique appearance, all of which contain black mats. bed e2a (12.90 to 11.60 ka) consists of massive olive-green silts and sands that are present in cauldron-shaped bedforms indicative of limnocrene ponding. this facies of bed e2a is found only rarely in the upper las vegas wash, likely because of the lack of a capping carbonate or gravel layer, which left it especially vulnerable to erosion. bed e2b (11.22 to 10.63 ka) consists of massive reddish-brown to buff-colored sand and silt that are armored by gravelly alluvium forming characteristic sinuous inverted topography. bed2b contains abundant tufa. finally, bed e2c (9.62 to 8.53 ka) consists of light-tan silts and sands that contain aquatic snail shells (physa, pisidium, hydrobiidae) indicative of flowing water. this bed is only found outside the tusk boundaries and represents the last period of intermittent groundwater discharge that occurred during the early holocene. geologic points of interest site 1: 36.31161° n, 115.16706° w (figure 10a) the many bluffs along the edge of the active upper las vegas wash provide excellent exposures of the las vegas formation. this site features a classic example of member a of the las vegas formation. several characteristics are used to differentiate member a from other members and beds within the formation, including strong soil development (both wetland soils and aridisols), abundant secondary carbonate, and striking redoxymorphic features (soil mottling). around the corner to the southeast, the lower part of member a 75 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 was dated to 251 ± 18 ka by luminescence techniques and includes grayish-brown clays and silts with root traces that are filled or lined with iron/manganese oxides, indicative of repeated fluctuating water-table levels and relatively wet conditions. up section, note the reddish-tan silts and sands with numerous carbonate stringers that transition laterally to greenish-gray silts and sands with cauldron-shaped bedforms and outflow channels. near the top of member a at this site, a date of 155 ± 12 ka was obtained from a horizon that consists of grayish-brown to brown clays and silts with angular blocky soil structures and root traces filled or lined with iron/manganese oxides. multiple carbonate horizons/ benches in this section and elsewhere within member a reflect periods of surface stability that punctuated alluvial and wetland deposition. the contact with the fine– medium sands of bed b1 is a distinct lithologic break. sidebar — from site 1, a short hike (~0.35 km) across the wash to the northwest will lead you to locality 5, one of the paleontologic and archaeologic sites dis(a) (b) 155 ± 12 ka bed d2 member a bed d2 member a (ponding) member b bed b1 figure 10. member a at localities in the upper las vegas wash. (a) site 1: 36.31161° n, 115.16706° w; (b) site 2: 36.31168° n, 115.16525° w. overall, member a ranges in age from ~300 to 155 ka and is characterized by complex lithologies, abundant redoxymorphic features, and extensive carbonate-rich benches and caps representing variable hydrologic conditions. 76 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 covered and studied in 1962–63 as part of the “big dig.” this locality boasts one of the many trenches excavated by heavy earth-moving equipment at that time. the deposits here include stream channels of beds e0 and e1b, which yielded abundant vertebrate fossil material; a skull, mandible, and post-cranial elements of mammoth are notable in addition to horse, camel, antelope, teratorn, and small mammals. additionally, human cultural artifacts were discovered at this site, but no temporal association with the vertebrate fossils could be made. note the rounded carbonate gravels at the base of the bed e0 and abundant tufa in the stream channel sediments. excavation of this locality revealed that many of the mammoth remains were encrusted by tufa. from locality 5, follow the stream channels of beds e0 and e1b along the base of the bluffs due east for ~0.20 km. bed e1b is inset into bed e0, and both are dramatically buttressed against the older deposits of members b and d. the importance of understanding the complex stratigraphy resonates here, as multiple fossil localities occurred within both of these spring channel deposits, including the large accumulation of mammoth bones seen in figure 6. this site, within bed e0 (23.04 to 18.16 ka), was presumably excavated and collected (based on historic trash and photographs) during the 1962–63 excavations of the “big dig,” but was abandoned and left with multiple bones still exposed in situ. this site was rediscovered by the sbcm during their original survey for the blm in 2004, but was not collected. instead it served an important purpose for the next decade—it was used as an interpretative site that the local advocacy group showed visitors as they sought to garner support for the new national monument. site 2: 36.31168° n, 115.16525° w (figure 10b) dramatic limnocrene ponding commonly occurs within member a. the greenish-gray silts and cross-bedded sands in this cauldron-shaped bedform are overlain by bed b1 and the prominent carbonate cap of bed d2. traced laterally to the west, the member a ponding unit shown in figure 10b is overlain by a soil that dates to 183 ± 15 ka. sidebar — at the base of the transmission tower, immediately west of site 2, an important locality yielded a diverse faunal assemblage from an inset bed b2 limnocrene pond deposit. taxa included mammuthus, camelops, equus, bison, frog, fish, and multiple varieties of mollusks. the fish, amphibians, and endemic aquatic gastropods are noteworthy, as all are indicative of localized ponding. large mammal fossils recovered from tule springs are frequently fragmentary, in some cases exhibiting evidence of trampling and/or subaerial weathering prior to burial. because of these taphonomic factors, it is often a challenge to recover large mammal fossils that are sufficiently complete to be identifiable to species. at this locality, a left magnum of bison was complete enough to allow proper measurement. the specimen fell within the range of similar elements of bison antiquus from rancho la brea as well as bison previously identified from tule springs. site 3: 36.31258° n, 115.16968° w (figures 11a and 12) sediments at this locality are typical of member b, exhibiting distinct “dry, wet, dry” sequences. throughout the upper las vegas wash, bed b1 overlies the eroded topography of member a unconformably. here, bed b1 dates to 61 ± 10 ka and consists of tan alluvial sand and silt, and a carbonate-rich, wetland soil. bed b2 is inset into bed b1 and consists of distinctive greenish sands and silts in a cauldron-shaped limnocrene pond with endemic molluscan taxa (e.g., helisoma sp.) and abundant vertebrate fossils. at this site, bed b2 dates to 47 ± 4 ka. the member b sequence is completed by oxidized tan silts and sands of bed b3, which dates to 44 ± 6 ka at this locality. sidebar — as one visits the sites in this guide, notice the spectacular inverted paleo-stream channel topography, as it is a distinctive component of the landscape. during member e time (23.04 to 8.53 ka), limestone gravels and cobbles were deposited as alluvial pulses in pre-existing sinuous outflow stream channels. this happened multiple times as discharge ceased, resulting in mantling gravels in beds e1b, e1c, and e2b. the gravel is more resistant to erosion than the fine-grained sediments it mantles, protecting the former stream channels. following erosion, the channels were left high and 77 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 (b) (a) bed d2 member b sequence 47 ± 4 ka 44 ± 6 ka bed b2 bed b1 bed b3 61 ± 10 ka figure 11. member b at localities in the upper las vegas wash. (a) site 3: 36.31258° n, 115.16968° w; (b) site 4: 36.32895° n, 115.21835° w. overall, member b ranges in age from ~100 to 40 ka and is characterized by tan to light-brown fluvial and alluvial sediments interbedded with discrete carbonate horizons (beds b1 and b3) that collectively represent relatively dry conditions punctuated by brief wet episodes, as well as pale olive-green silts and clays in cauldron-like bedforms (beds b1-wet and b2) that are consistent with limnocrene discharge. 78 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 figure 12. vertebrate fossils from member b. (a) bed b1 with typical limestone gravels at base of unit and fossil with plaster jacket ready to be collected; (b) the locality in (a) yielded a tooth and partial skull of camelops hesternus. figured tooth is sbcm l3160-657; (c) horse tooth from bed b1, sbcm l3160-632; (d) a pair of dentaries of bison sp. from a bed b2 pond, sbcm l3160-818.1, l3160-818.2; (e) magnum of bison antiquus, sbcm l3088-1, as noted in sidebar for site 2. 79 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 dry, and are now exposed above the surrounding landscape. the inverted paleo-stream channel topography provides a glimpse of the distribution of late quaternary stream channel flow patterns in tusk, and also protects the fine-grained deposits that contain abundant fossil resources. site 4: 36.32895° n, 115.21835° w (figures 11b and 12) this sedimentary sequence demonstrates the complex stratigraphy of member b and includes at least eight subunits that are visible in the vertical exposures, each separated by varying degrees of soil formation. carbonate horizons derived from evapotranspiration of shallow groundwater during short-lived wet phases often accompany the soils. as at many locations, the b sequence is capped by the ubiquitous carbonate cap of bed d2. site 5: 36.30865° n, 115.14988° w (figures 13a and 14) member d represents the highest groundwater levels achieved in the las vegas valley during the late quaternary. widespread marshes and wet meadows were present between ~36 and 24 ka and left behind a series of distinctive gwd deposits. bed d1 was first defined and characterized at this site with a date of 35.04 ± 0.50 ka (ramelli and others, 2011). overlying member b sediments, the base of bed d1 consists of reworked carbonate clasts, representing rheocrene stream discharge, which transition to greenish-gray silts and sands with the typical cauldron bedform of limnocrene ponding, similar to bed b2. mollusks typical of these ponds (helisoma sp.) are abundant in the sediments, which also contain a “smear” of black mat organics, from which the date shown in figure 13a was obtained. the upper part of bed d1 exhibits strongly oxidized lithologies and an aridisol, which we interpret as representing widespread drying events that correspond in time to d-o 6-5 (figure 8). at this site, bed d1 is overlain by an incipient bed d2 carbonate cap. site 6: 36.30857° n, 115.14934° w (figures 13b and 14) the sedimentary sequence exposed here is nearly identical to site 5, but with the carbonate cap of bed d2 more prominently formed. the base of the section is in contact with member a, where bed d1 exhibits two distinct packages of reworked carbonate clasts deposited in rheocrene streams. these sediments are overlain by light greenish-gray sands, silts, and muds of bed d1 ponds, and a carbonate bench and intervening greengray silt and clay of the marshes that epitomize bed d2 helocrene discharge. radiocarbon dates on terrestrial gastropods within the d2 cap allow us to constrain the age of the full-glacial marshes in this axial portion of the valley. prominent carbonate caps and benches that are resistant to erosion are important marker beds in the full-glacial sequence and form broad, topographically extensive flats throughout the las vegas valley. the caps/benches form at the ground surface or very shallow subsurface via capillary migration of groundwater through the vadose zone. we attribute their formation to abrupt warming that intensified evaporative effects and depressed the water table leading to desiccation of the wetlands. the prominent d2 carbonate cap found here and throughout the valley corresponds in time to d-o 4-3 (figure 8), reflecting the dynamic response of these wetlands to abrupt climatic fluctuations. site 7: 36.30945° n, 115.15371° w (figures 15a, b, and 16) geologic mapping and detailed stratigraphic studies in tusk (ramelli and others, 2011; springer and others, 2015, 2017) led to the documentation of a previously unrecognized lithologic and stratigraphic unit that postdates member d and predates beds e1 and e2. the newly named bed e0 contains prolific vertebrate fossils (figure 16) and dates to between 23.04 and 18.16 ka. it was previously mapped as either “unit d” or “unit e” (haynes, 1967; page and others, 2005). quade (2003) noted a significant hiatus between the collapse and desiccation of the full glacial marshes and the deposition of the younger sediments of bed e1 at ~16 ka. we documented that wetland development was reestablished by 80 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 (a) (b) bed d2 bed d1 bed d2 bed d1 35.04 ± 0.50 ka 31.01 ± 0.44 ka 31.05 ± 0.43 ka contact figure 13. member d at localities in the upper las vegas wash. (a) site 5: 36.30865° n, 115.14988° w; (b) site 6: 36.30857° n, 115.14934° w. member d ranges in age from 36.07 to 24.45 ka and consists of three distinct beds. bed d1 (36.07–34.18 ka) is composed largely of olive-green silts and clays representing limnocrene and helocrene discharge. this bed also contains evidence of episodic rheocrene discharge toward the base, whereas beds d2 (31.68–27.58 ka) and d3 (25.85–24.45 ka) exhibit extensive thick carbonate benches and caps representing helocrene discharge that spanned much of the valley floor during full glacial times. 81 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 figure 14. (a) dramatic outcrop of member d capping older deposits in tusk. member d represents pervasive spring discharge the accompanied the highest water table levels during the full glacial period, and the resultant gwd deposits are topographically high with prominent carbonate caps and benches; (b) camelops hesternus, dentary with tooth, sbcm l3160479; (c) geologist kathleen springer inspecting a juvenile mandible with teeth discovered in bed d2. 82 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 ~23 ka, allowing a more precise chronologic constraint on the discharge hiatus following the collapse of the full-glacial marshes (based on our chronology, the hiatus is ~1.4 ka in duration). in opposition to the extensive full-glacial marshes and wet meadows of member d, bed e0 represents point source rheocrene discharge and outflow streams, marking a dramatic change in the type of discharge that continued throughout the late glacial period. at this outcrop, bed e0 exhibits an angled contact with the underlying deposits of bed d2 as it is inset into d2 and represents the thalweg of a channel. it also includes stromatolitic tufa on the opposite side of the drainage at this site, as well as remnant walls of an excavation that uncovered a large mammoth tusk and tooth (figure 15b). note that the radiocarbon dates shown in figure 15a were obtained from charcoal in organic-rich black mats intercalated with detrital tufa fragments. sidebar — in the general area around sites 6, 7, and 8, it is useful to walk the surface of the gwd deposits to gain familiarity with the characteristics of, and the contact between, the d2 surface and the inset e0 spring channels. carbonate is a constant in this system due to bed e0 tufa 19.80 ± 0.22 ka bed e0 19.71 ± 0.22 ka 20.28 ± 0.22 ka (a) (c) (b) (d) figure 15. bed e0 at localities in the upper las vegas wash. (a) site 7: 36.30945° n, 115.15371° w. (b) within the e0 beds that yielded the radiocarbon dates, an adjacent locality produced a tusk and tooth of mammuthus columbi. figured tooth is sbcm l3160-758; (c) site 8: 36.30916° n, 115.15371° w. (d) this locality produced multiple bones, including this heavily weathered and shattered tusk of mammuthus sp. (sbcm l3160-722) encrusted in tufa as well as abundant charcoal and mollusks. this newly recognized unit ranges in age from 23.04 to 18.16 ka and represents the first major episode of rheocrene discharge (spring-fed streams) in the upper las vegas wash. it also contains the first record of microbially mediated, ambient temperature tufa in the valley. 83 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 figure 16. vertebrate fossils from bed e0. (a) tusk of mammuthus sp., sbcm 3160-586e; (b) partial skull and teeth of bison sp., sbcm l3088-390; (c) maxilla with tooth of mammuthus sp., sbcm l3160-586a; (d) sbcm l3160-460, metacarpal of camelops hesternus. 84 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 recharge from the surrounding mountain ranges that are mostly composed of proterozoic/paleozoic limestone and dolomite. in vertical section, bed d2 forms prominent carbonate caps or benches, but when walking across an eroded surface, discerning the difference between it and other the units can be challenging. for example, bed e0 is capped by platy and/or rubbly carbonate that can be mistaken for the d2 cap. in this area, the contact between the two carbonate units is subtle, and is best seen by color and textural changes between the white carbonate rubble of bed d2 and the darker, tan colored platy and/or rubbly carbonate of bed e0. site 8: 36.30916° n, 115.15371° w (figures 15c, d, and 16) this site is noteworthy with respect to assessing the types of organic material used to date most of the gwd deposits in tusk. charcoal (charred vascular plants) is spilling out of bed e0 sediments at this locality (figure 15c). here and throughout the upper las vegas wash, charcoal is readily available in the deposits and was used to establish much of the chronologic framework of the las vegas formation in tusk. small terrestrial gastropods are also present and contributed to a lesser extent to that effort. tufa is also prolific in the outflow stream here; note the morphology of encrusting tufa on former plant remains (phytoclast tufa). tufa also precipitated on the vertebrate fossil material that was excavated at this locality, resulting in a tufa-encrusted mammoth tusk (figure 15d). this bed e0 outflow stream is very near the point source of the discharge and the date here (19.80 ± 0.22 ka) is similar to those obtained at site 7 (19.71 ± 0.22 ka and 20.28 ± 0.22 ka). it is likely that multiple point sources were discharging in this area during e0 time. site 9: 36.33307° n, 115.22535° w (figure 17a) there are at least 16 distinct and mappable discharge intervals identified within the las vegas formation in tusk that collectively span aproximately 300 ka and reflect varied spring ecosystems. due to multiple phases of erosion and deflation of the gwd sediments, the spatial relationships of these deposits are complex and include multiple permutations of inset and buttressed geometries of spring discharge through time. at this site, the sedimentary sequence includes member b sediments (beds b1 and b2) that are overlain by member d. an axial facies remnant of the bed d3 marsh deposits is attached to the sequence as a buttressed unconformity—this sliver of an outcrop contained mammoth fossils and yielded critical radiometric dates that allowed the full temporal breath of member d to be determined. an outflow stream of bed e0 is also buttressed on members b and d as well as occurring as a capping layer on top of the entire sequence as floodplain deposits. this capping e0 bed proved to be a critical locality for a new record in the tslf lynx rufus (bobcat). this locality is a reminder that the geologic context of fossil localities in the upper las vegas wash must be examined in detail so that the fossils can be placed in time accurately. site 10: 36.33305° n, 115.22484° w (figure 17b) this is another example of the myriad of inset relationships that occur in the gwd deposits in tusk. here, bed e0 is present as an outflow stream channel, inset and draped onto older member b deposits, and consists of green silt that grades upward to tan silt. the geometry of the channel-fill deposits is characteristic of the late quaternary rheocrene spring discharge within the upper las vegas wash in that the outflow streams preserved in the geologic record are roughly parallel to the flow direction of the active wash. this locality yielded an age of 22.05 ± 0.23 ka obtained from shells of terrestrial gastropods (succineidae), and also contains shells from a variety of other terrestrial and aquatic gastropods. site 11: 36.34938° n, 115.28642° w (figure 18a) in the upper las vegas wash, bed d2 grades from gray silts of the axial wet meadow facies into tan silts and sands of the drier phreatophyte flat facies as one moves away from the valley axis. bed d3 is best exposed on the spring 85 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 mountains side of the upper las vegas wash drainage where the marginal facies of bed d2 is topped by d3 sediments and the prominent d3 carbonate cap. at this site, marginal wetland deposits of beds d2 and d3 illustrate the lateral expansion and contraction of the wetlands in response to climate fluctuation. evidence of a brief discharge event in bed d2 dating to 27.58 ± 0.23 ka is positioned between two prominent soils (aridisols). these aridisols represent dry conditions that correlate in time to d-o 4 and 3, respectively, and equate to the widespread and prominent bed d2 carbonate cap discussed at site 6. discharge resumed here with the deposition of bed d3, which was followed by formation of the carbonate cap. the d3 cap correlates temporally with d-o 2 and represents a pervasive desiccation event that ultimately led to the collapse of the vast full-glacial wetland system in the las vegas valley. springer et al, figure 13 bed e0 �oodplain bed e0 channel �ll beds d1/d2 bed d3 buttress unconformity bed b1 (b) bed e0 (channel �ll) member b (a) bed b2 22.05 ± 0.23 ka figure 17. photographs illustrating the multifaceted stratigraphic sequences in the upper las vegas wash. (a) site 9: 36.33307° n, 115.22535° w. complex section showing beds d3 and e0 buttressed against beds b1 and b2, member d, and bed e0. (b) site 10: 36.33305° n, 115.22484° w. a channel of bed e0 inset into member b sediments. 86 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 site 12: 36.34869° n, 115.28997° w (figure 18b) this site offers another excellent opportunity to examine the marginal facies of the wetland system during member d time. here, the d2-d3 contact and conspicuous soils seen at site 11 (representing d-o 4-3) are very clear. the stable surface following d2 time was populated by literally thousands of burrows (possibly from cicada nymphs), the casts of which are weathering out of this contact, a phenomena that can be seen throughout the northern area of tusk (quade, 1986). (b) (a) bed d3 bed d2 27.58 ± 0.23 ka bw bw bed d3 bed d2 contact figure 18. (a) site 11: 36.34938° n, 115.28642° w. marginal facies of beds d2 and d3 with a thin discharge horizon dating to 27.58 ± 0.23 ka that is positioned between aridisols (bw); (b) site 12: 36.34869° n, 115.28997° w. contact between the marginal facies of beds d2 and d3. casts of possible cicada burrows are common along this contact (inset), indicating a period of surface stability prevailed at the end of d2 time. 87 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 site 13: 36.35620° n, 115.28994° w (figure 19) following wetland development represented in the record by bed e0, there was a hiatus in discharge and significant erosion during the time period between 18.16 and 16.10 ka, which includes the “big dry” of broecker and others (2009) (figure 8). discharge resumed at 16.10 ka, represented by bed e1, and was dominated by point-source discharge resulting in emanating flowing streams (rheocrene discharge) with localized tufa formation. subunits within e1 represent distinct discharge intervals and exhibit inset relationships into the dissected topography of bed d2, as well as with each other. bed e1a typically consists of rhythmically bedded, buff-colored silt and sand containing abundant tufa, and is capped by carbonate rubble. it is mappable over a large area of the northern reaches of tusk and has yielded dates ranging from 16.10 to 14.96 ka (figure 19a). bed e1a represents a major discharge period that corresponds temporally to the “big wet” (broecker and others, 2009), a widespread, high-precipitation event that also corresponds temporally to the oldest dryas. bed e1a discharge ended abruptly at 14.96 ka, as evidenced by intense erosion of the deposits in response to the bølling warm period (d-o 1). the first and only confirmed specimen of smilodon fatalis from the tslf and southern nevada was found at a locality near here in bed e1a deposits dating to 15.46 ± 0.25 ka (scott and springer, 2017) (figures 19d to 19g). other vertebrate fossils in bed e1a include the camel metacarpal shown in figures 19b and 19c. site 14: 36.34691° n, 115.27749° w (figure 20) following intense erosion associated with the abrupt warming of d-o 1, rheocrene discharge resumed between 14.59 and 14.27 ka as recorded by bed e1b. the basal channelized portion of bed e1b grades upward to distinctive whitish silts and sands that contain numerous black mats. bed e1b is often mantled in limestone gravels and cobbles, contributing to its distinct appearance. this site is the location of the “super quarry” where the sbcm extracted 500+ vertebrate fossils, including a mammoth skull and jaw, numerous mammoth tusks, bison, horse, and other large vertebrates (figures 20a to 20d). a date of 14.59 ± 0.50 ka was obtained from charcoal within the channel deposits, establishing the site firmly within e1b time. throughout tusk, bed e1b contains an unusual number of vertebrate fossils, including the first definitive record of canis dirus from the tslf and the state of nevada (scott and springer, 2016) (figure 20e). in addition to the spectacular paleontology, this site demonstrates once again the complexity of the gwd sedimentary sequences. nearby exposures show beds e1a and e1b commingling as they drape and fill the older dissected topography of bed d2, whereas at the super quarry, the base of the e1b channel sits directly on top of member a. site 15: 36.36917° n, 115.31560° w (figure 21) bed e1c consists of yellowish to light gray silt and sand, and when not mantled in its characteristic limestone gravel clasts, is difficult to distinguish from bed e1a. however, stratigraphic and chronologic control has established that they are, in fact, separate and mappable stratigraphic units. charcoal in black mats within bed e1c has yielded dates ranging from 14.12 to 13.95 ka. bed e1c typically overlies and is inset unconformably within the earlier discharge intervals of beds e1a and e1b. the sharp lithologic transition from the conspicuously white deposits of bed e1b to the tan sediments of bed e1c marks the onset of older dryas cooling, yet another example of how wetland ecosystems in the las vegas valley responded dynamically to abrupt climate change in the recent geologic past. this site yielded multiple elements of mammoth from beds e1b and sparse bone fragments from bed e1c. bed e1c is newly recognized and vertebrate fossils are, so far, rare in this bed. site 16: 36.37807° n, 115.32807° w (figure 22) exposures of bed e1d are not very common in the upper las vegas wash, but where present, represent a discrete discharge interval that includes rheocrene dis88 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 15.46 ± 0.25 ka bed e 1a (a) (d) (c) (b) 1 cm teres major tuberosity deltoid crest 1 cm (g)(e) (f ) 10 cm figure 19. (a) bed e1a at site 13: 36.35620° n, 115.28994° w; a date of 15.46 ± 0.25 ka was obtained from charcoal at this locality; (b) metacarpal of camelops hesternus eroding out of the deposits, and (c) same specimen, prepared. sbcm l3160645.1; (d) sbcm l3160-1019, distal left radius of smilodon fatalis, dorsal view; (e) in situ radius and humerus of smilodon fatalis; (f) smilodon fatalis; art by adrienne picchi; (g) sbcm l3160-1018, proximal left humerus of smilodon fatalis, lateral (left) and anterior (right) views. photographs shown in panels d and g are after scott and springer (2016). 89 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 (a) (c) (e) (b) (d) bed e1b 14.59 ± 0.50 ka figure 20. (a-d) bed e1b at site 14: 36.34691° n, 115.27749° w, referred to as the “super quarry;” (a, b) the excavation of the quarry took nearly a year to complete; seen at various stages; (c) one of five mammuthus sp. tusks recovered; (d) partial skull and teeth of mammuthus sp.; (e) sbcm l3160-1257, right patella of canis dirus, dorsal view. 90 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 charge and minor ponding. the deposits of bed e1d date to between 13.69 and 13.37 ka, and consist of medium gray silt and cross-bedded sand with reworked carbonate, abundant mollusks, and interbedded black mats that are typically exposed in low relief along ‘the narrows’ (figures 1c and 22a). bedding planes within bed e1d tend to be inclined near spring orifices. vertebrate fossils are rare (figure 22b), but significant—of the three potential horses from tusk, the only one distinguishable to species (equus scotti) was discovered in bed e1d (scott and springer, 2017) (figures 22c and 22d). site 17: 36.34842° n, 115.28834° w (figure 23) the final phase of wetland development in the las vegas valley occurred during the latest pleistocene and early holocene and is represented by beds e2a–c (collectively 12.90 to 8.53 ka). at this site, called “the islands,” we observe one of the few places in tusk that exhibits a complete sedimentary sequence depicting the dramatic lithologic differentiation that occurred at this time as a result of climatic fluctuations. the base of the section consists of silts and sands of beds e1b and e1d, which 14.12 ± 0.21 ka bed e 1b bed e 1c contact figure 21. (a) bed e1c at site 15: 36.36917° n, 115.31560° w. the discharge interval represented by bed e1c is spatially restricted within tusk and, so far, is rarely fossiliferous. 91 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 represent rheocrene discharge that occurred during and after the bølling-allerod warm period. these beds transition abruptly to olive-green silts and clays in cauldron-like bedforms, representing limnocrene ponding of bed e2a during the younger dryas cold event. in turn, these sediments are overlain by the oxidized tan to brown silts of bed e2b that represent drier conditions and intermittent rheocrene discharge that occurred during the pre-boreal climate oscillations (figure 8). vertebrate fossils are known from this area and likely represent the last gasp of the pleistocene fauna in tusk before the terminal pleistocene extinction (~13 ka). site 18: 36.30489° n, 115.15128° w (figure 24a) this “carbonate river frozen in time” represents e2 rheocrene discharge that dominated the las vegas valley during the late glacial period. this extensive groundwater-fed, braided fluvial tufa system consists of microbially mediated, ambient temperature tufas that exhibit a distinctive morphology resembling an anastomosing fluvial network dating to bed e2b time (11.22–10.63 ka) (figure 25). to our knowledge, this braided fluvial tufa system is unique in north america, and is characterized by flowing streams emanating from numerous (a) (c) (b) (d) bed e1d 13.69 ± 0.14 ka 1 cm 1 cm figure 22. (a) bed e1d at site 16: 36.37807° n, 115.32807° w showing the limited relief typical of bed e1d; (b) in situ mammuthus sp. tooth; (c) equus scotti, occlusal view, sbcm l3160-1015; (d) equus scotti, left dentary, lateral view, sbcm l31601016a. 92 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 (a) (b) bed e2a bed e1b bed e1d bed e2b 14.42 ± 0.28 ka 13.50 ± 0.07 ka 12.90 ± 0.12 ka 11.10 ± 0.07 ka 12.85 ± 0.12 ka bed d3 aridisols within bed d2 bed e2b bed e2a bed e1 figure 23. (a, b) bed e2 in the upper las vegas wash at site 17: 36.34842° n, 115.28834° w. overall, this bed ranges in age from 12.90 to 8.53 ka and consists of three distinct subunits, beds e2a, e2b, and e2c. 93 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 figure 24. examples of inset relationships in the las vegas formation. (a) site 18: 36.30489° n, 115.15128° w. bed e2b with carbonate tufa channel lag mantling the highly dissected bed d2 topography. (b) site 19: 36.30491° n, 115.15159° w. stream channel of bed e1a inset into the eroded topography of bed d2. 94 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 point sources. tufa associated with bed e2b is preserved at this site as surficial lag deposits that mantle the resistant carbonate topography of bed d2 (figure 24a). the stromatolitic tufa exposed at the surface here also occurs in situ within the host fluvial channel sediments of bed e2b and is intercalated with black mats. site 19: 36.30491° n, 115.15159° w (figure 24b) this site provides another example of a river frozen in time. this stream channel of bed e1a is clearly inset into the eroded topography of bed d2. here and at many other locations in the northern portion of tusk, the eroded surface of bed d2 is all that remains of extensive marsh deposits that once spanned most of the valley axis during full glacial times. site 20: 36.30252° n, 115.14020° w (figure 26) tufa that occurs in the context of the braided fluvial system exhibit many external morphologies, including phytoclasts, oncoids, cyanoliths, stromatolites, as well as resurgence features (also seen at site 18). although braided fluvial tufas predominate, paludal and lacus115.142 °w115.150 °w115.158 °w115.166 °w 36.316 °n 36.308 °n 36.300 °n 36.292 °n 0 250 500 m n 18 20 figure 25. aerial photograph of the mapped extent of the braided fluvial tufa system (in blue) in the upper las vegas wash. to our knowledge, this is the only occurrence of this type of system in north america. locations of tufa at sites 18 and 20 are shown in red. 95 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 figure 26. site 20: 36.30252° n, 115.14020° w. photographs of (a) barrage tufa and (b) phytoclast tufa that formed in springfed channels. 96 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 trine tufas associated with pooling water behind tufa are also noted, as we observe at this site. this is a spectacular example of a barrage tufa (springer and stevens, 2008), with phytoclasts encasing branches, logs, and other stream-edge plants. parting thoughts this field guide touches on some of the highlights of the vertebrate paleontology, stratigraphy, age control, and the response of desert wetland ecosystems to abrupt climate change that we have established for the las vegas formation within tule springs fossil beds national monument. the new monument is a treasure trove of geologic and paleontologic information and, with the aid of this interpretive guide, one can easily imagine a water-filled past, teeming with wildlife and flora on this valley floor. tusk protects the ancient desert wetland deposits and their attendant flora and fauna for posterity. future studies here will reveal much more about the ever-changing desert ecosystem and the animals that once called it home. acknowledgments we thank the bureau of land management (blm) and the national park service (nps) for protecting these lands. we are especially grateful to scott foss and gayle marrs-smith (blm) for their long-term support of our studies and with funding through federal assistance agreement l08ac13098 (to kbs). we also thank interim superintendent of tusk, vincent santucci (nps), who got the ball rolling, as well as the first permanent superintendent, jon burpee, as he moves tusk from its infancy to fruition as a full-fledged national park unit. special thanks to both vince and jon for allowing our work to continue in tusk with the first research permit issued (tusk-2015-sci-001)! we thank gene ellis, harland goldstein, janet slate, greg mcdonald, and doug sprinkel for constructive reviews of earlier versions of the field guide. we also thank paco van sistine and jeremy havens for assistance with some of the figures. this project was supported by the u.s. geological survey’s climate and land use change research and development program. references bell, j.w., ramelli, a.r., and caskey, s.j., 1998, geologic map of the tule springs park quadrangle, nevada: nevada bureau of mines and geology map 113, 1 plate, scale 1:24,000. bell, j.w., ramelli, a.r., depolo, c.m., maldonado, f., and schmidt, d.l., 1999, geologic map of the corn creek springs quadrangle, nevada: nevada bureau of mines and geology map 121, 1 plate, scale 1:24,000. broecker, w.s., mcgee, d., adams, k.d., cheng, h., edwards, r.l., oviatt, c.g., and quade, j., 2009, a great basin-wide dry episode during the first half of the mystery interval?: quaternary science reviews, v. 28, no. 25/26, p. 2557–2563. dansie, 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bureau of mines and geology map 175, 8 p., 1 plate, scale 1:24,000. ramelli, a.r., page, w.r., manker, c.r., and springer, k.b., 2012, preliminary geologic map of the corn creek springs nw quadrangle, clark county, nevada: nevada bureau of mines and geology open-file report 2012-07, 1 plate, scale 1:24,000. scott, e., 2010, extinctions, scenarios, and assumptions—changes in latest pleistocene large herbivore abundance and distribution in western north america: quaternary international, v. 217, p. 225–239. scott, e., and cox, s.m., 2008, late pleistocene distribution of bi98 vertebrate paleontology, stratigraphy, and paleohydrology of tule springs fossil beds national monument, nevada springer, k.b., pigati, j.s., and scott, e. geology of the intermountain west 2017 volume 4 son (mammalia; artiodactyla) in the mojave desert of southern california and nevada, in wang, x., and barnes, l.g., editors, geology and vertebrate paleontology of western and southern north america—contributions in honor of david p. whistler: california, natural history museum of los angeles county, v. 41, p. 359–382. scott, e., and lutz, c.m., 2014, gypsum cave, nevada—a treasure trove of fossils of late pleistocene equus from the mojave desert, in proceedings of the 10th conference on fossil resources, rapid city, south dakota: dakoterra, v. 6, p. 67–68. scott, e., and springer, k.b., 2016, first records of canis dirus and smilodon fatalis from the late pleistocene tule springs local fauna, southern nevada: peerj 4:e2151; doi 10.7717/ peerj.2151. scott, e., and springer, k.b., 2017, the tule springs local fauna: quaternary international, accepted for publication. shutler, r., jr., 1967a, archaeology of tule springs, in wormington, h.m., editor, pleistocene studies in southern nevada: carson city, nevada state museum anthropological papers no. 13, p. 208–303. shutler, r., jr., 1967b, cultural chronology in southern nevada, in wormington, h.m., editor, pleistocene studies in southern nevada: carson city, nevada state museum anthropological papers no. 13, p. 304–308. simpson, g.g., 1933, a nevada fauna of pleistocene type and its probable association with man: american museum novitates, v. 667, p. 1–10. simpson, r.d., 1955, hunting elephants in nevada: the masterkey, v. 29, no. 4, p. 114–116. snyder, c.t., hardman, g., and zdenek, f.f., 1964, pleistocene lakes in the great basin: u.s. geological survey miscellaneous geological investigations map i-416, 1 plate, scale 1:1,000,000. springer, a.e., and stevens, l.e., 2008, spheres of discharge of springs: hydrogeology journal, v. 17, no. 1, p. 83–93. springer, k.b., manker, c.r., and pigati, j.s., 2015, dynamic response of desert wetlands to abrupt climate change: proceedings of the national academy of sciences usa, v. 112, no. 47, p. 14522–14526. springer, k.b., pigati, j.s., manker, c.r., and mahan, s.a., 2017, the las vegas formation: u.s. geological survey professional paper, accepted for publication. springer, k.b., sagebiel, j.c., manker, c.r., and scott, e., 2006, preserving the past—geologic mapping and paleontologic investigation, las vegas formation, north las vegas, in lucas, s.g., speilmann, j.a., hester, p.m., kenworthy, j.p., and santucci, v.l., editors, fossils from federal lands: new mexico museum of natural history and science bulletin 34, p. 38–39. springer, k.b., scott, e., manker, c.r., and rowland, s.m., 2011, vertebrate paleontology of pleistocene ice age lakes and groundwater discharge deposits of the mojave desert and southern great basin: nevada state museum paleontological papers number 1, p. 156–230. springer, k.b., scott, e., sagebiel, j.c., and murray, l.k., 2009, the diamond valley lake local fauna—late pleistocene vertebrates from inland southern california, in albright, l.b.i., editor, papers on geology, vertebrate paleontology, and biostratigraphy in honor of michael o. woodburne: flagstaff, museum of northern arizona, p. 217–235. springer, k.b., scott, e., sagebiel, j.c., and murray, l.k., 2010, late pleistocene large mammal faunal dynamics from inland southern california—the diamond valley lake local fauna: quaternary international, v. 217, p. 256–265. spurr, j.e., 1903, descriptive geology of nevada south of the fortieth parallel and adjacent portions of california: u.s. geological survey bulletin 208, 229 p., 1 plate, scale 1:~6600. stock, c., and harris, j.m., 1930, rancho la brea—a record of pleistocene life in california: natural history museum of los angeles county, science series no. 37, 7th edition, 113 p. svensson, a., andersen, k.k., bigler, m., clausen, h.b., dahl-jensen, d., davies, s.m., johnsen, s.j., muscheler, r., parrenin, f., rasmussen, s.o., röthlisberger, r., seierstad, i., steffensen, j.p., and vinther, b.m., 2008, a 60,000 year greenland stratigraphic ice core chronology: climates of the past, v. 4, p. 47– 57. taylor, d.w., 1960, late cenozoic molluscan faunas from the high plains: u.s. geological survey professional paper 337, 94 p. tedford, r.h., 1970, principal and practices in mammalian geochronology in north america: proceedings of the north american paleontological convention, part f, p. 666–703. weinstock, j., willerslve, e., sher, a.v., tong, w., ho, s.y.w., rubenstein, d., storer, j., burns, j., martin, l., bravi, c., prieto, a., froese, d., scott, e., xulong, l., and cooper, a., 2005, evolution, systematics, and phylogeography of pleistocene horses in the new world—a molecular perspective: plos biol 3(8): e241. doi:10.1371/journal.pbio.0030241. wormington, h.m., and ellis, d., editors, 1967, pleistocene studies in southern nevada: carson city, nevada state museum anthropological papers no. 13, 409 p. stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado geology of the intermountain west an open-access journal of the utah geological association volume 2 2015 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado kendall r. grazul1, jacqueline e. huntoon2, and jennifer m.k. o’keefe3 1department of cognitive and learning sciences, michigan technological university, houghton, mi 49931; kgrazul@mtu.edu 2department of geological and mining engineering and sciences, michigan technological university, houghton, mi 49931; jeh@mtu.edu 3department of earth and space sciences, morehead state university, morehead, ky 40351; j.okeefe@moreheadstate.edu © 2015 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. geology of the intermountain west an open-access journal of the utah geological association editors douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net production cover design and desktop publishing douglas a. sprinkel cover photograph the palisade is a narrow ribbon-like mesa that rises abruptly from the surrounding area. a layer-cake succession of late paleozoic to jurassic-aged strata is exposed in the cliff faces that comprise the margins of the palisade. photograph by kendall r. grazul. i 2015 president april abate aprilabate@utah.gov 801.538.5214 2015 president-elect jason blake blake-j@comcast.net 435.658.3423 2015 program chair mark milligan markmilligan@utah.gov 801.537.3326 2015 treasurer rebekah wood rwood@gmail.com 801.537.3378 2015 secretary jan morse janmorse@utah.gov 801.538.5327 2015 past-president grant willis grantwillis@utah.gov 801.537.3355 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 sandy eldredge sandyeldredge@utah.gov 801.537.3325 publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2014-2016 term tom morris tom_morris@byu.edu 801.422.3761 state mapping advisory committe uga representative terry massoth twmassoth@hotmail.com 801.422.3761 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 2 2015 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 9 abstract exposures of the late paleozoic cutler formation, near the town of gateway, colorado, have traditionally been interpreted as the product of alluvial-fan deposition along the western flank of the uncompahgre uplift and within the easternmost portion of the paradox basin. the paradox basin formed between the western margin of the uncompahgre uplift, a segment of the ancestral rocky mountains, and the western paleoshoreline of the north american portion of pangea. this part of pangea is commonly thought to have experienced semi-arid to arid conditions and warm temperatures during the pennsylvanian and permian. we present stratigraphic and fossil plant evidence in this paper to support prior interpretations that the cutler near gateway, colorado, was deposited by alluvial fans that hosted localized wetland areas. our findings are consistent with the results of prior studies that have suggested the climate in the area was warm, semi-arid, and ice-free at the time the plants described in this paper were living. plant fossils collected from the cutler formation came from two sites in the palisade wilderness study area (managed by the u.s. department of the interior, bureau of land management) of western colorado. the stratigraphic sections at the sites were composed mostly of pebble to cobble conglomerate and sandstone, but the fossil plants were mainly preserved in fine-grained intervals (fine-grained sandstone to siltstone). the preservation of plant fossils in the proximal cutler formation is remarkable because the surrounding sections consist mostly of conglomerate and sandstone interpreted as fluvial and debris-flow deposits. the fine-grained strata containing the plant horizons must have been deposited in a wet and protected setting, possibly a spring-fed abandoned channel on the alluvial fan. the plants and their surrounding sediment must have been rapidly buried in order to allow for long-term preservation of the fossils. it seems likely that vegetation was abundant in and adjacent to low-lying wet areas on the fan’s surface, based on the abundance of plant fossils found at the two sites. the fossil plant assemblage includes calamites, walchia, and pecopteris. the flora are interpreted to have lived near the apex of the alluvial-fan system. these fossils suggest that warm and at least seasonally and locally wet conditions existed in the area during the time that the plants were growing. more arid conditions during the late paleozoic are suggested by the characteristics of some of the time-equivalent and near time-equivalent rocks exposed to the west of the study area in the central paradox basin. stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado kendall r. grazul1, jacqueline e. huntoon2, and jennifer m.k. o’keefe3 1department of cognitive and learning sciences, michigan technological university, houghton, mi 49931; kgrazul@mtu.edu 2department of geological and mining engineering and sciences, michigan technological university, houghton, mi 49931; jeh@mtu.edu 3department of earth and space sciences, morehead state university, morehead, ky 40351; j.okeefe@moreheadstate.edu grazul, k.r., huntoon, j.e., and o’keefe, j.m.k., 2015, stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado: geology of the intermountain west, v. 2, p. 9-27. © 2015 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. geology of the intermountain west an open-access journal of the utah geological association volume 2 2015 10 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 introduction this study focuses on the stratigraphy and paleobotany of a portion of the cutler formation (late paleozoic) and their paleoclimatic implications for an area located near the modern-day town of gateway, colorado. for this study, samples were collected from sites located within the palisade wilderness study area (wsa) / outstanding natural area (ona) / area of critical environmental concern (acec), which is managed by the grand junction field office of the u.s. department of interior, bureau of land management. the palisade wsa is located in western colorado, approximately 30 miles southwest of grand junction (figure 1). the palisade wsa is named for a towering, ribbon-like mesa known as the palisade. in contrast to the the palisade itself, the majority of the palisade wsa consists of relatively subdued topography formed on the cutler formation. the cutler was deposited along the western flank of the uncompahgre uplift, a segment of the ancestral rocky mountains, within the easternmost part of the paradox basin during the pennsylvanian and permian (baker and reeside, 1929; turnbow, 1955). exposures of the cutler in the palisade wsa include some of the most proximal deposits contained within the formation (mack and rasmussen, 1984). canyons and gullies carved by modern ephemeral streams provide outstanding three-dimensional exposures, making the area an ideal location for study of the proximal cutler formation. exposures of the cutler formation near gateway have traditionally been interpreted as the products of deposition in an alluvial fan (walker, 1967; werner, 1974; campbell, 1979; mack and rasmussen, 1984; campbell, 2003). the cutler near gateway is commonly referred to as “the gateway fan.” despite the conventional thought regarding the formation’s depositional environment, attempts to characterize the climate at the time of deposition have resulted in considerable debate. evidence has been presented to support interpreted climate conditions ranging from ever-wet (campbell, 1979), through seasonally wet and semi-arid to sub-humid (mack and rasmussen, 1984; campbell, 2003), to semi-arid to arid (walker, 1967; werner, 1974). interpretations of semi-arid to arid conditions during the late paleozoic are supported by the presence of halite, anhydrite, and gypsum in the paradox formation, which was deposited in the central portion of the paradox basin during the pennsylvanian (hite and buckner, 1981). the paradox formation may be, in part, a lateral equivalent to the oldest parts of the cutler formation (condon, 1997). younger lateral equivalents in the central and western paradox basin region include permian sandstones deposited in eolian environments (e.g., cedar mesa and white rim sandstones). these eolian sandstones, like the paradox formation, indicate arid conditions were dominant in the central paradox basin for extended periods during the time of deposition of the cutler formation (nuccio and condon, 1996). in contrast to the traditional understanding of the cutler formation as the product of alluvial-fan deposition, soreghan and others (2009) interpreted the cutler in the palisade wsa as a low-latitude, proglacial, fluvial-lacustrine deposit. this hypothesis suggested that tropical glaciers existed at low elevations and low latitudes in western pangea during the late paleozoic. more recently however, an analysis of plant fossils collected from the proximal cutler formation (huntoon and others, 2014) led to the conclusion that interpretations of an alluvial fan origin for the formation near gateway are justified. figure 1. location of the palisade wsa in western colorado. colorado river, dolores river, and unaweep canyon all shown on map. inset map shows location of main map area in utah and colorado. 11 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 in addition to huntoon and others (2014), other studies have investigated plant fossils and palynomorphs obtained from the proximal cutler formation (e.g., werner, 1974; mack and rasmussen, 1984; soreghan and others, 2007). the results of previous analyses provide a rich source of data that can be used to constrain interpretations regarding environmental conditions in the local area at the time of deposition of the cutler. the additional plant fossils described in this paper support the interpretation of the cutler as an alluvial-fan deposit. the plants and lithofacies also suggest that the climate in the palisade wsa during the late paleozoic was warm and that water was locally present on the upper reaches of the alluvial fan at the time of deposition. it seems that there must have been abundant vegetation in and adjacent to low-lying wet areas at the time the cutler formation was deposited based on the amount of fossilized plant material found. geologic setting during the late paleozoic, the area that now makes up the palisade wsa was located near the western margin of proto-north america at near-equatorial paleolatitudes (figure 2). the palisade wsa was at that time bounded on the east by the southwestern faulted margin of the uncompahgre uplift. this uplift was the westernmost outlier of the ancestral rocky mountains. segments of the ancestral rocky mountains extended across late paleozoic north america (ye and others, 1996). the uncompahgre highlands rose and continuously eroded during the late paleozoic. they contributed sediments that were deposited in and adjacent to the paradox basin, which was located to the west of the uplift. the cutler formation in the palisade wsa consists of mostly coarse-grained sediment eroded from the uncompahgre uplift (werner, 1974) and deposited directly adjacent to its western margin in the easternmost part of the paradox basin. the cutler reaches a maximum thickness of approximately 5 kilometers (barbeau, 2003) proximal and medial to the uncompahgre highland; the palisade wsa is located along the flank of the uplift. the formation thins to about 500 meters (barbeau, 2003) to the west and southwest across the paradox basin and undergoes lithofacies changes so that it is referred to as the cutler group (condon, 1997) in the western part of the paradox basin. the lowermost part of the cutler formation and group in areas more distal to the uncompahgre uplift record cycles of marine flooding and evaporation in the paradox bain that resulted from long-term cycles of sea-level change during the late paleozoic (rankey, 1997). reconstructions of the original thickness of the cutler formation, as well as precise determination of its current thickness in different areas, are subjects of much debate. deformation of the pennsylvanian paradox formation that occurred during deposition of the cutler formation resulted in the development of numerous salt-related structures (e.g., mini-basins, saltwalls) in the subsurface of the paradox basin (trudgill, 2011). these features influenced deposition of the cutler formation and its lateral equivalents, including figure 2. simplified geologic map of the study area (modified from huntoon and others, 2014). geology modified from cater (1955): pє = precambrian rocks (dark gray); pz = paleozoic cutler formation (medium gray); mz = mesozoic strata (light gray); q = quaternary alluvium (white). locations of fossil plant sites are indicated with the red box. latitude and longitude shown for the northwest, northeast, and southwest corners of the map. (inset a) location of study area and late paleozoic paleoequator (calculated by smirnov, michigan technological university, personal communication, 2011). (inset b) location of study area; small rectangle enclosing gateway is shown expanded as the main map in this figure. 12 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 the cutler group (trudgill, 2011). the proximal portions of the cutler formation are currently exposed near gateway due in part to laramide uplift (white and jacobsen, 1983; bump and davis, 2003) that resulted in reactivation of one or more paleozoic faults and development of additional faults along the southwest margin of the modern uncompahgre plateau (white and jacobsen, 1983; mankowski, 2003). cenozoic uplift of the colorado plateau (sahagian and others, 2002) and subsequent incision by the colorado river and its tributaries produced the exposures examined in this study. in the palisade wsa, the cutler formation typically consists of pastel-colored (reddish, pinkish, purplish, and light grayish hues) proximal clastic rocks that are dominated by conglomerate and sandstone (huntoon and others, 2014). quartz and feldspar are the most abundant minerals within the cutler, although biotite, hematite, epidote, muscovite, and opaque minerals are also common (campbell, 2003). although coarse sandstone and conglomerate beds are common in the cutler formation in the study area, the fossils described in this paper were primarily collected from fine-grained beds. the proximal cutler formation was vegetated during the late paleozoic. recently, huntoon and others (2014) described plants fossils from the cutler, including pecopteris, calamites, archaeocalamites, and neuropteris. all of these plants are thought to have lived in environments with a high water table for a large portion of the year (tidwell, 1998). additionally, mack and rasmussen (1984) documented the presence of rhizocretions in the proximal cutler formation and soreghan and others (2007) identified late paleozoic palynomorphs (densosporites, lycospora, vesicaspora, and florinites) in samples they collected in and near the palisade wsa. methods the goal of this study was to document and describe plant fossils and fossil-bearing strata in the cutler formation within the palisade wsa. in order to achieve this goal, fieldwork was conducted in the summer of 2014. field investigations focused on two areas located to the west of the mouth of unaweep canyon, to the north of west creek and to the south and east of the topographic promontory known as the palisade (see figure 3 and cover photograph). the area was mapped and samples were collected and transported to michigan technological university for further analysis. the field study covered areas located on the gateway and two v basin u.s. geological survey 7.5-minute topographic quadrangle maps. locations were determined using hand-held garmin global positioning system (gps) units and the 1:24,000-scale topographic maps (gateway and two v basin). draws, side canyons, and ridges were explored in search of plant fossils. at the same time, the contact between the cutler formation and the precambrian rocks that formed the core of the uncompahgre uplift was traced and mapped. when fossil-bearing rocks were encountered, their locations were indicated on the field map. the occurrences of rocks with a lithology similar to the fossil-bearing strata were also mapped. fossil plants and plant fragments were collected figure 3. aerial view of a portion of the study area. approximate location of sample collection sites labeled. more precise location information withheld in compliance with bureau of land management permitting requirements. faulted contact between precambrian granite and gneiss (labeled pє) and late paleozoic sedimentary cutler formation (labeled lppc) shown with dotted line. locations of plant fossil localities are outlined with red boxes and are situated adjacent to the contact. locations of sites containing relatively fine-grained material, similar in lithology to the fossil-bearing layers, are shown with black filled circles. image from google earth and u.s. department of agriculture farm service agency. 13 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 from two sites; usnm 43857 (site 1) and usnm 43856 (site 2). it is important to note that these sites are subdivisions of a prior collection site (usnm 43705) described in huntoon and others (2014). the fossils were photographed in place, collected, and transported from the field for detailed description and identification in the laboratory. measured sections were prepared for the two fossil-bearing sites. hand samples were collected from the two fossil-bearing sites and from one non-productive site (usnm 43858, site 3) that was similar in lithology to the fossil-bearing rock. these hand samples were later processed in the laboratory in an attempt to retrieve late paleozoic palynomorphs. despite careful searching, no other plant fossil localities were identified. although lithofacies similar in color and grain size to the fossil-bearing units were encountered at several other sites, material exposed at the surface at the majority of those other sites was too unconsolidated to allow for successful collection of plant material, even if it was present. extensive excavations were not undertaken however, so it is possible that better lithified material is present below the surface at some of those sites. in the laboratory, the samples containing plant fossils were organized by type, renumbered, and re-photographed. each fossil was described, and fine details were examined and sketched. photographs and sketches were used to compare to plant fossils described in the literature in order to identify each specimen. all of the fossils are now housed in the type/illustrated collections of the national museum of natural history, smithsonian institution, washington, d.c. hand samples were taken to morehead state university for palynological processing and analysis. the hand samples were crushed to pass through a 1-mm mesh sieve, and 2 gram sub-samples were split from each crushed hand sample using a microriffler. the material was demineralized and deflocculated in preparation for the extraction of organic material. the o’keefe method was used to process the samples (o’keefe and others, 2011; o’keefe and eble, 2012). permanent slides were prepared and inventoried for palynomorphs. unfortunately, no identifiable late paleozoic palynomorphs were obtained. description of plant fossil sites the plant fossils were described and collected from two sites (figure 3) located near the faulted contact between the cutler formation and the precambrian granite and gneiss that formed the core of the uncompahgre uplift of the ancestral rocky mountains (figure 4). in the vicinity of the plant fossil sites, the cutler formation is cut by reverse faults (possibly reactivated during the laramide orogeny) that place precambrian rock above the cutler formation and older cutler on top of younger cutler (mankowski, 2003). these structural complications make it difficult to trace individual stratigraphic horizons across the study area. the intervals containing the plant fossils at the two sites are 2 to 3 meters thick, a small fraction of the total modern-day thickness of the cutler formation near gateway, which has been estimated at 150 to 300 meters (condon, 1997). below is a detailed description of the fossil-plant horizons and the fossil plants collected at each site. figure 4. faulted contact between late paleozoic cutler formation (left of hammer) and precambrian granite (right of hammer). the precambrian granite is up on the east-northeast relative to the cutler formation on the west-southwest. view is to the northwest. fault trace strikes n. 20° w., and dips 60° ne. both plant fossil sites are located near the faulted contact between the cutler formation and the precambrian rocks. 14 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 site 1 stratigraphic description the fossil-plant horizon at site 1 (usnm 43857) is at the top of an approximately 3-meter thick section that consists of three units (figures 5 and 6). unit 1, the lowest unit in the measured section, is a dark gray, poorly sorted, matrix-supported boulder conglomerate (figure 5). it contains subangular to subrounded randomly oriented clasts composed of granite and gneiss. the lower unit also contains approximately 50% clasts with a maximum size of 35 centimeters and an average size of 5 centimeters. the matrix is very coarse to finegrained sandstone consisting of angular to subangular grains of quartz and feldspar. the base is not exposed. unit 1 is interpreted as a debris-flow deposit. unit 2 is an olive-black, poorly sorted, sandy, pebble to cobble conglomerate with angular clasts of feldspar and quartz. it contains approximately 40% clasts with a maximum size of 4 centimeters and an average size of 0.5 centimeters. the matrix is mudstone to very coarse sandstone. this unit contains alternating layers of coarseand fine-grained strata interrupted by scattered lenses of sandstone and sandy siltstone on the order of 1 to 5 centimeters thick. unit 2 is interpreted as the product of fluvial deposition. unit 3 contains the fossil-bearing horizon. it has a maximum thickness of 10 centimeters and consists of moderate yellowish-brown, thinly laminated, micaceous siltstone to fine-grained sandstone. this unit is interpreted as the product of deposition under slack-water conditions in a fluvial system due to the abundance of fine-grained material, including flakes of mica. fossil content four distinct specimens of identifiable plant fossils were collected from site 1. the first group of identifiable specimens are all members of the genus calamites. many small and incomplete calamitean fragments were found at this location. the best preserved specimen (figure 7) is 13.5 centimeters long and 3 centimeters wide. this sample appears to be an incomplete external stem cast (dimichele and falcon-lang, 2012). the external surface of the cast is longitudinally ribbed with grooved indentations. the ribs are 0.1 centimeters wide. there are three nodes visible on the specimen and the ribs alternate at the nodes, as is typical of calamites (tidwell, 1998). the fossil is light brown in color and is present in a moderate yellowish-brown siltstone. the second specimen collected is walchia. it is 2.6 centimeters long and 0.3 to 0.5 centimeters wide (figure 8). the scale-like leaves are oval and come to a point where they join the stem. each leaf is approximately 0.2 centimeters long and 0.1 centimeters wide and is oriented at an acute angle to the center stem. walchia is characterized by narrow branches with small, upright leaves that taper to a point (arnold, 1941), as is evident in this specimen. no veins are visible on the impressions of individual leaves. the specimen is moderate yellowish-brown and is present in a pale yellowish-brown siltstone. the third specimen collected is a pecopteris fossil (figure 9). it has a rachis that is 15 centimeters long, 0.3 centimeters wide, and is straight and heavy as is common for pecopteris (wittry, 2006). the pinnae alternate along the stem. some impressions of the pinnae are very faint, but those that are recognizable measure between 5 and 6 centimeters long and 0.5 to 1 centimeter wide. the pinnae come to a point at their figure 5. measured section of site 1. plant fossil horizon is in fine-grained strata of unit 3. see main text for description. 15 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 distal ends. as is typical of pecopteris, the pinnae consist of small pinnules with a broad basal attachment to the costa and slight confluence between adjacent pinnules (dimichele and others, 2010). the stem is moderate brown. both the fronds and surrounding siltstone are moderate yellowish-brown in color. figure 6. photographs of site 1 (jacob’s staff marked in 10 centimeter increments). (a) surface view of top of fossil-bearing unit 3 as it is exposed along the crest of a ridge. (b) conglomerate and sandstone beds typical of unit 2. (c) conglomeratic beds of unit 1 near base of the measured section. 16 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 the last identifiable specimen found at site 1 is another pecopteris specimen (figure 10). the specimen is 5 centimeters long and 3 centimeters wide at the base. the pinnules, which are about 0.4 centimeters wide, get progressively smaller away from the base of the pinna. pecopteris tends to have alternate, closely spaced, and straight-sided pinnules (wittry, 2006). each pinnule is rounded and has a well-defined rib in the center. the pinnules have flat bases where attached to the stem. the pecopterid is moderate yellowish-brown in a pale yellowish-brown siltstone. site 2 stratigraphic description site 2 (usnm 43856) is located very close to, but stratigraphically below, site 1 in the cutler formation and within 100 meters of the faulted contact with precambrian rocks of the uncompahgre uplift (figures 3 and 4). the section at site 2 is approximately 2 meters thick and consists of three units (figures 11 through 13). the basal unit 1 and the capping unit 3 are very similar to unit 2 described at site 1. units 1 and 3 at site 2 are interpreted as the product of fluvial deposition. the middle unit at site 2, which contains the majority of the plant fossils, is approximately 70 centimeters thick and consists of interbedded coarseand fine-grained strata. the coarse-grained strata of unit 2 are mediumto very coarse grained, reddish-orange sandstone less than 5 centimeters in thickness. the relatively fine-grained figure 7. specimen of calamites (specimen dimensions = 13.5 cm x 3 cm) at site 1 (usnm 43857). usnm specimen 611005. figure 8. specimen of walchia (specimen dimensions = 2.6 cm x 0.4 cm) at site 1 (usnm 43857). usnm specimen 611006. figure 9. specimen of pecopteris (specimen dimensions = 15 cm x 8 cm) at site 1 (usnm 43857). usnm specimen 611007. figure 10. specimen of pecopteris (specimen dimensions = 5 cm x 3 cm) at site 1 (usnm 43857). usnm specimen 611008. 17 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 strata consist of thinly laminated light olive-gray, very fine grained sandstone to micaceous sandy siltstone. unit 2 at site 2 has a scoured basal boundary and fines upward overall. the best preserved plant fossils at site 2 were found within the fine-grained strata of unit 2, although the coarser strata within unit 2 also contained fossil fragments. some of the thinly laminated micaceous beds within unit 2 show small-scale wavy deformation that is possibly due to compression. unit 2 is interpreted as the product of deposition under standing-water conditions in a fluvial system. unit 3 at site 2 also contained some plant material including a calamitean fragment that appears to have been preserved in place in an upright orientation (figure 13). fossil content four identifiable plant fossils were collected from site 2. the first pecopteris specimen (figure 14) collected at site 2 is 3.5 centimeters in length and 4.5 centimeters at its widest point. a partial stem is visible with fragments of pinnae attached in a v-shaped pattern. the pinnae are alternately arranged and 2.2 to 3 centimeters figure 11. measured section of site 2. fine-grained strata of unit 2 contain the majority of the plant fossils at site 2. see main text for description. figure 12. photographs of measured section at site 2 (jacob’s staff marked in 10 centimeter increments). (a) view of full measured section. the location of the contact between units 1 and 2 is obscured by float in the photo; the approximate position of the contact is as shown. location of a scoured channel within unit 3 is shown in red near the top of the measured section and outcrop. (b) close-up view of unit 2 and base of unit 3 at site 2. 18 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 long and 0.1 to 0.5 centimeters wide. pinnae become thinner away from the site of attachment to the stem and come to a point at the distal tips. similar to the pecopteris specimen from site 1, there are small pinnules with a broad basal attachment to the costa and slight confluence between adjacent pinnules (dimichele and others, 2010). the specimen is olive-gray within a dark greenish-gray micaceous siltstone. a second pecopteris specimen (figure 15) was collected from site 2. it is 3 centimeters long and 1 centimeter wide. the pinnules in this specimen are 0.5 centimeters long, 0.4 centimeters wide, rounded, and adhered to the stem along the entire base. the pinnules are alternately arranged, closely spaced, and generally attached nearly perpendicular to the mid-rib (wittry, 2006). sparse venation is present and appears to be widely forked and one-time divided, as is characteristic of pecopterids (w.a. dimichele, smithsonian museum of natural history, personal communication, 2015). the fossil is grayish brown within a moderate yellowish-brown siltstone. site 2 also yielded walchia specimens. the best preserved walchia fossil (figure 16) from site 2 is 2.8 centimeters long and 0.3 centimeters wide. the specimen is characterized by narrow branches with small, upright leaves that taper to a point (arnold, 1941). the leaves are seed shaped and also come to a point where they are attached to the stem. each leaf is 0.3 centimeters long and the average width is on the order of 0.1 centimeters. the fossil is brownish-gray within a dark greenish-gray micaceous siltstone. a small fossil calamitean cone (figure 17), possibly figure 13. calamitean fragment in place in unit 3 at site 2. (a) outcrop-scale view of part of the measured section with person pointing to calamitean fragment. (b) close-up view of calamitean fragment. 19 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 from the genus palaeostachya, is 1.8 centimeters long and 0.4 centimeters wide. the different kinds of calamitean cones cannot always be recognized without clear preservation of the spore-bearing organs (arnold, 1958). these organs are not distinguishable in this specimen. the cone is incomplete because the base and stem are not preserved. the central axis has regularly spaced discs with whorls of bracts extending from the sides (arnold, 1958). the fossil is preserved as an olive-gray impression in a dark greenish-gray micaceous siltstone. site 3 site 3 (figure 18, usnm 43858) contained no plant fossils, but was sampled for pollen, spores, and other organic material. site 3 is a massive to cross-stratified, grayish-purple pebble conglomerate that contains lenses of micaceous, platy siltstone. siltstone lenses average 3 centimeters thick with the largest lens reaching 5 centimeters in thickness. we sampled a lens that extended for several meters horizontally. the unit as a whole is exposed for several tens of meters along the west side of bull draw (figure 3). the coarsegrained components of the unit contained angular clasts, averaging 1 centimeter in diameter, of feldspar and granite supported by matrix consisting of siltto clay-sized particles. the fine-grained (siltstone) lenses at site 3 are similar to the fossil-bearing horizons at sites 1 and 2 in terms of grain size and platy texture, but contained lesser amounts of mica. organic material obtained from the sample collected at site 3 contained only modern palynomorphs and charcoal. the cross-stratified conglomerate at site 3 reflects deposition by fluvial processes. the lenses of micaceous, platy siltstone were deposited under low-flow or standing-water conditions. figure 14. specimen of pecopteris (specimen dimensions = 3.5 cm x 4 cm) at site 2 (usnm 43856). usnm specimen 611009. figure 15. specimen of pecopteris (specimen dimensions = 3 cm x 1 cm) at site 2 (usnm 43856). usnm specimen 611010. 20 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 discussion the stratigraphic successions at the three sites described for this study included pebble conglomerate that was deposited by fluvial processes. all three sites contained evidence of variations in depositional energy through time. at sites 1 and 2, fluctuations in flow strength were indicated by the presence of alternating layers of relatively coarse and fine material. the finest layers at all three sites consisted of platy, micaceous fine-grained sandstone to siltstone that was deposited under standing-water or low-flow conditions. only site 1 included matrix-supported boulder conglomerate containing subrounded randomly oriented clasts up to 35 centimeters in diameter that is interpreted as a debris-flow deposit. in aggregate, the stratigraphfigure 16. specimen of walchia (specimen dimensions = 2.8 cm x 0.3 cm) at site 2 (usnm 43856). usnm specimen 611011. figure 17. specimen of a calamitean cone (specimen dimensions = 1.8 cm x 0.4 cm) at site 2 (usnm 43856). usnm specimen 611012. 21 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 ic successions at the three sites reflect subaerial deposition in an environment that experienced variability in discharge and sediment supply through time. the coarsest materials, within the debris-flow deposits, required substantial energy for transport (and probably steep slopes) whereas the finest materials would have only been deposited and preserved in protected settings under low-energy flow conditions. taken together, the lithologic characteristics documented at the three sites suggest that deposition occurred near the apex of an alluvial fan (huntoon and others, 2014). debris flows would have been active during high-discharge events that flushed accumulated debris from the uncompahgre highland toward the west where it could be deposited in the easternmost part of the paradox basin. although fluvial deposition was the dominant depositional process at each of the three sites, moderate to high energy down-fan flows were temporarily interrupted at each site for an extended period of time. the interruption of down-fan fluvial transport probably resulted from channel abandonment. large floods in arid and semi-arid climates can cause avulsion of the main fan channel, shifting the locus of deposition to previously inactive parts of the fan (chawner, 1935). abandoned or blocked fluvial channels are generally recognized as good sites for the potential preservation of plant material in continental environments (gastaldo and demko, 2011). if the downstream end of an abandoned channel is blocked by vegetation or debris, the abandoned channel may experience standing-water conditions. the occurrence of low-flow or standing-water conditions in small, localized sites during deposition of the cutler formation is suggested by the presence of the fine-grained layers, including micaceous siltstone, at each of the three sites. extremely small shear stresses are required to move platy mica grains and these grains would have been transported far downstream by flows of any appreciable strength. deposition of micaceous siltstone must have occurred in protected areas under standing-water or very low-energy flow conditions. although ultimately short-lived, the protected, quiet-water sites existed for a sufficient amount time for finegrained sediment and plant material to be deposited. overall, the characteristics of the strata at sites 1 and 2 (including debris-flow, fluvial, and slack-water deposits) indicate that the area was at least seasonally and locally wet during deposition of the fossil-bearing strata. preservation of both the fine-grained sediment and the fossil plants required rapid burial and subsidence. rapid burial was required to protect the finegrained sediment and plant material from post-depositional erosion. subsidence was required to ensure that the plant material was maintained at depths below the water table so that it could be preserved (gastaldo and demko, 2011). unusual conditions were required for both the deposition and preservation of the finegrained plant-bearing layers as well as the plant fossils themselves. although many protected, vegetated wetland sites may have existed at the time of deposition of the proximal cutler formation, micaceous siltstone layers are now uncommon. this is not surprising, given that the majority of the cutler in the palisade wsa was deposited under conditions that would have easily transported silt and sand-sized materials downstream. where present, the majority of the remaining preserved occurrences of micaceous siltstone in the cutler formation in the study area are devoid of even small fragfigure 18. photograph of site 3 (jacob’s staff marked in 10 centimeter increments) showing the sampled dark-gray micaceous siltstone. surrounding material, and the majority of the outcrop consists of grayish-purple pebble conglomerate. 22 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 ments of plant material. again, this is not unexpected because fragile plant material would not have survived any appreciable downstream transport, and would have been rapidly degraded if it remained at or near the surface for any length of time. the fossil flora found near gateway are a mixture of species typical of seasonally dry environments as well as wetland settings. most of the plant fossils collected from the cutler formation are, however, known to have inhabited environments dominated by wet conditions (tidwell, 1998). for example, calamites has been found in both coal swamps and flood basins (gastaldo, 1986, 1987), and is tolerant of excessive flooding and sediment burial (gastaldo and others, 1995; dimichele and others, 2001). pecopteris has been found in carboniferous coal swamps, but is also known from relatively dry permian environments (dimichele and others, 2001). although most of the plants are interpreted to have lived in a wide variety of wetland settings, walchian conifers were stress-tolerant plants that lived in relatively dry habitats (rothwell and others, 1997). coniferous genera such as walchia have long been considered a common constituent of the permian flora, but walchia also occurs in association with typical pennsylvanian genera (arnold, 1941). the appearance of walchia in the mid-continent region is thought to reflect increasing aridity (arnold, 1941). the presence of walchia in the cutler formation may be a good indication of the regional or background climate in the area at the time of deposition. arid to semi-arid climate conditions in upland settings would have confined the wetland species described above to parts of the landscape with high water tables (dimichele and others, 2014). whereas the wet-tolerant plants may have grown in low-lying and wet abandoned channels, the walchia probably grew in drier settings surrounding the geographically isolated wetlands. the wet areas were more favorable for fossil preservation than the drier areas, potentially making the wetland plants appear more abundant than they actually were (dimichele and others, 2014). preliminary analysis of the paleomagnetic signature of the rocks in the collection area suggested that the cutler formation near sites 1 and 2 was deposited near the equator during the late pennsylvanian (mankowski, 2003). a late pennsylvanian age was also suggested by the presence of archaeocalamites in the proximal cutler formation (huntoon and others, 2014). archaeocalamites was more common during the pennsylvanian but tended to be increasingly rare in the permian (mamay and bateman, 1991; w.a. dimichele, smithsonian museum of natural history, personal communication, 2015). therefore, a late pennsylvanian age for the deposits at sites 1 and 2 seems likely but is not fully confirmed. intraformational faults (mankowski, 2003) in the cutler formation in the the palisade wsa place relatively older cutler above relatively younger cutler, making stratigraphic relations difficult to determine with certainty. nevertheless, it seems likely that although the fossil-bearing rocks are now exposed at the surface, they are part of the older portions of the cutler formation. the fossil-bearing rocks are almost certainly older than the cutler formation strata exposed around the gateway town site, where they are likely permian in age and are unconformably overlain by the triassic moenkopi formation. whether the deposits at sites 1 and 2 are late pennsylvanian or permian in age, deposition occurred at near-equatorial paleolatitudes (blakey and ranney, 2008). warm temperatures and humid conditions at the time of deposition might be expected for such a location, particularly a site along the margin of a highland such as the uncompahgre uplift. pennsylvanian evaporites and permian eolian rocks deposited in the central paradox basin to the west of the palisade wsa indicate that extended episodes of aridity affected western equatorial pangea however. despite the common interpretation that warm and wet conditions persisted across large portions of midcontinent north america during the pennsylvanian (scotese and mckerrow, 1990), the western equatorial margin of pangea appears to have experienced warm and dry conditions, at least intermittently, throughout the late paleozoic. the fossils and their encasing strata appear to indicate climate conditions more similar to those experienced in the central paradox basin than in the midcontinent. a semi-arid background climate with seasonally concentrated precipitation is inferred based on the lithologic characteristics and fossil content at sites 1 and 2. semi-arid 23 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 conditions would have allowed for the establishment of walchia. seasonally concentrated precipitation would have produced the debris flow and fluvial deposits documented at the two sites. wetter conditions in abandoned channels would have provided ideal conditions for the growth of wet-tolerant plants such as calamites and pecopteris. it must be noted that the two sites described in this study represent only a small part of the total time interval represented by the cutler formation and that the climate in the region experienced substantial variability at multiple temporal scales during the late paleozoic (langford and chan, 1988; dubiel and others, 1996; rankey, 1997; stanesco and others, 2000; mountney, 2006; cain and mountney, 2009; jordan and mountney, 2010, 2012; huntoon and others, 2014). huntoon and others (2014) proposed a detailed model for the deposition of the proximal cutler formation and associated formations deposited in the central paradox basin. in their model, climate and sea-level change are the primary processes controlling deposition. during the late paleozoic, sediment was eroded from the uncompahgre uplift and deposited along the margins of the adjacent paradox basin. subsidence of the paradox basin foreland was an ongoing process resulting from faulting along the western margin of the uncompahgre uplift and compaction of previously deposited sediment (huntoon and others, 2014). deposition in the rapidly subsiding basin would have been conducive to fossil preservation even under seasonal semi-arid conditions (looy and others, 2014). as stated earlier, rapid subsidence would have kept the fossil-bearing strata at depths below the water table, as is required for the preservation of plant material (gastaldo and demko, 2011). it is notable that both of the fossil-bearing sites were located directly to the west of a faulted contact between the cutler formation and the precambrian rocks of the uncompahgre uplift (figure 3). it is possible that the proximity of the fault to the fossil-bearing horizons was important in the preservation of the plant material. if the fault was active at the time the fossil-bearing layers were deposited, freshwater springs may have reached the surface along the fault providing an abundant source of water for any plants living nearby in abandoned channels. upon burial, proximity to the fault may have resulted in preferential cementation of the cutler adjacent to the contact. conclusions the observations made of the cutler formation in the palisade wsa near gateway (colorado) indicate that the rocks were deposited in a proximal alluvial-fan environment. the fossils preserved at two sites in the proximal cutler are probably late pennsylvanian in age. they suggest deposition occurred under warm and locally wet conditions under a semi-arid background climate. although most of the plants collected at the two sites are known from wet environments, the presence of walchia indicates drier conditions. the inference that warm temperatures and dry conditions were experienced in the paradox basin region during deposition of the cutler formation is consistent with the occurrence of evaporite and eolian deposits in late paleozoic rocks deposited to the west of the study area. alluvial fans are sites of transport of large volumes of sediment and do not provide an ideal setting for fossil preservation. in order to be preserved, plants grew and died in a protected setting and must have been rapidly buried. based on the characteristics of the fossils and their encasing strata, it seems that the fossils were deposited in small, isolated wetland areas that formed in abandoned channels in the proximal reaches of the alluvial fan. these abandoned channels may have been fed by springs emerging from the faulted western margin of the uncompahgre uplift. although preserved plant material is rare in the proximal cutler formation, the two occurrences documented here provide new information about climate conditions during deposition of some of the older portions of the late paleozoic cutler. based on these results it appears that vegetation was common in and adjacent to low-lying wet areas at the time some of the older portions of the cutler formation were being deposited. acknowledgments we thank the bureau of land management for its assistance with this project; it would not have been 24 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 possible without the help and advice provided by harley armstrong, madeline grant-hoffman, and david (scott) gerwe. the work was conducted under u.s. department of the interior, bureau of land management colorado state office paleontological resources use permits coc76491 and coc76492. we thank dr. bill dimichele, smithsonian museum of natural history, for his assistance and patience in helping us to identify and interpret plant material collected for this and other studies of the cutler formation. we also thank dr. dimichele for agreeing to allow us to use the national museum of natural history as the repository for our samples. we thank dan chaney, smithsonian museum of natural history, for his guidance in preparing the samples for shipment to the smithsonian. we thank jack stanesco, red rocks community college, for his assistance in the field. we thank the reviewers of this manuscript (doug sprinkel and tom chidsey, utah geological survey; steve schamel, geox consulting; brooks britt, brigham young university; and jerry waanders, consulting palynologist) for their helpful comments. finally, we thank the michigan space grant consortium for its financial support, which made it possible for the first author to first visit the study area during a field-based course for pre-college teachers that was taught by the second author and offered as a graduate course by michigan technological university. references arnold, c.a., 1941, some paleozoic plants from central colorado and their stratigraphic s i g n i f i c a n c e : contributions from the museum of 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survey bulletin 2000-p, 46 p. dimichele, w.a., cecil, c.b., chaney, d.s., elrick, s.d., and nelson, w.j., 2014, fossil floras from the pennsylvanian-permian cutler group of southeastern utah, in maclean, j.s., biek, r.f., and huntoon, j.e., editors, geology of utah’s far south: utah geological association publication 43, p. 491–504. dimichele, w.a., chaney, d.s., kerp, h., and lucas, s.g., 2010, late pennsylvanian floras in western 25 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 equatorial pangea, cañon del cobre, new mexico: new mexico museum of natural history and science bulletin, v. 49, p. 75–113. dimichele, w.a., and falcon-lang, h.j., 2012, calamitalean “pith casts” reconsidered: review of palaeobotany and palynology, v. 173, p. 1–14. dimichele, w.a., pfefferkorn, h.w., and gastaldo, 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and bias through time: topics in geobiology, v. 32, p. 249–285. gastaldo, r.a., pfefferkorn, h.w., and dimichele, w.a., 1995, taphonomic and sedimentologic characterization of roof-shale floras, in darrah, w.c., and lyons, p.c., editors, historical perspective of early twentieth century carboniferous paleobotany: geological society of america memoir 185, p. 341–352. hite, r.j., and buckner, d.h., 1981, stratigraphic correlations, facies concepts, and cyclicity in pennsylvanian rocks of the paradox basin, in weigand, d.l., editor, geology of the paradox basin: rocky mountain association of geologists, p. 147–159. huntoon, j.e., boks, k., mankowski, l., campbellwyrembelski, t.l., dubiel, r.f., and stanesco, j.d., 2014, fossil plants from a proximal alluvial-fan complex: implications for late paleozoic sedimentary processes in western tropical pangea, in maclean, j.s., biek, r.f., and huntoon, j.e., editors, geology of utah’s far south: utah geological association publication 43, p. 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cutler formation (permopennsylvanian) near gateway, colorado: geological society of america bulletin, v. 95, p. 109–116. mamay, s.h., and bateman, r.m., 1991, archaeocalamites lazarii, sp. nov.—the range of archaeocalamitaceae extended from the lowermost pennsylvanian to the mid-lower permian: american journal of botany, v. 78, no. 4, p. 489–496. mankowski, l.c., 2003, structural mapping of the uncompahgre front near gateway, colorado—field evidence of an ancestral rocky mountain decollement: houghton, michigan technological university, m.s. thesis, 88 p. 26 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 mountney, n.p., 2006, periodic accumulation and destruction of aeolian erg sequences in the permian cedar mesa sandstone, white canyon, southern utah, usa: sedimentology, v. 53, p. 789-823. nuccio, v.f., and condon, s.m., 1996, burial and thermal history of the paradox basin, utah and colorado, and petroleum potential of the middle pennsylvanian paradox formation, in huffman, a.c., jr., lund, w.r., and godwin, l.h., editors, geology and resources of the paradox basin: utah geological association publication 25, p. 57-76. o’keefe, j.m.k., hower, j.c., hatch, r., and bartley, s., 2011, fungal forms in miocene eel river coals—extraction across a rank suite [abs.]: the palynological society, southampton, united kingdom, 44th annual meeting of american association of stratigraphic palynologist program with abstracts, p. 30. o’keefe, j.m.k., and eble, c.f., 2012, a comparison of hf-based and non hf-based palynology processing techniques in clay-rich lignites from the claiborne group, upper mississippi embayment, united states: palynology, v. 36, p. 116–130. rankey, e.c., 1997, relations between relative changes in sea level and climate shifts—pennsylvanianpermian mixed 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the upper paleozoic cutler formation, western tropical pangea: journal of sedimentary research, v. 79, p. 495–522. stanesco, j.d., dubiel, r.f., and huntoon, j.e., 2000, depositional environments and paleotectonics of the organ rock formation of the permian cutler group, southeastern utah, in sprinkel, d.a., chidsey, t.c., jr., and anderson, p.b., editors, geology of utah’s national parks and monuments: utah geological association publication 28, p. 591605. tidwell, w.d., 1998, common fossil plants of western north america, 2nd edition: washington, smithsonian institution press, p. 38–39, 70–71, 87–88, and 90. trudgill, b.d., 2011, evolution of salt structures in the northern paradox basin—controls on evaporite deposition, salt wall growth and super-salt stratigraphic architecture: basin research, v. 23, no. 6, p. 208-238. turnbow, d.r., 1955, permian and pennsylvanian rocks of the four corners area—geology of parts of paradox, black mesa and san juan basins: four corners geological society guidebook, four corners field conference, p. 66-69. walker, t.r., 1967, formation of redbeds in modern and ancient deserts: geological society of america bulletin, v. 78, p. 353–368. werner, w.g., 1974, petrology of the cutler formation (pennsylvanian–permian) near gateway, colorado, and fisher towers, utah: journal of sedimentary petrology, v. 44, p. 292–298. white, m.a., and jacobsen, j.i., 1983, structures associated with the southwest margin of the ancestral uncompahgre uplift, in averett, w.r., editor, northern paradox basin—uncompahgre uplift: grand junction geological society, field guidebook, p. 33-39. wittry, j., 2006, the mazon creek fossil flora: downers 27 stratigraphy and fossil plants from the cutler formation (late paleozoic) and their paleoclimatic implications, eastern paradox basin, colorado grazul, k.r., huntoon, j.e., and o’keefe, j.m.k. geology of the intermountain west 2015 volume 2 grove, esconi associates, 154 p. ye, h., royden, l., burchfiel, c., and schuepbach, m., 1996, late paleozoic deformation of interior north america—the greater ancestral rocky mountains: american association of petroleum geologists bulletin, v. 80, no. 9, p. 1397–1432. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel kenneth carpenter theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover a partial camarasaurus skeleton about to be buried by an advancing subaquatic dune. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors society of vertebrate paleontology editors kelli c. trujillo — university of wyoming cary woodruff — university of toronto octavio mateus — universidade nova de lisboa douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees education/scholarship zack anderson zanderson@utah.gov 801.538.4779 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 97 abstract an oval recycling flume with live-beds (moveable) of medium and very coarse grained sands were used to explore the process of bone burial as a precursor to fossilization. two-dimentional computation fluid dynamics was used to visualize and interpret the flow turbulence around bones. results show that a water mass approaching and passing a static bone (obstruction) is subjected to flow modification by flow separation, flow constriction, and flow acceleration producing complex flow patterns (turbulence). these complex patterns include an upstream high-pressure zone, down flows, and vortices (with flow reversal near the bed) causing bed shear stress that produce bed erosion. downstream of the bone, the water mass undergoes flow deceleration, water recirculation (turbulence eddies), flow reattachment, low-pressure zone (drag), and sediment deposition. scour plays a crucial role by undercutting bone on the upstream side and may cause the bone to settle into the bed by rotation or sliding. scour geometry is determined by bone size and shape, approaching flow velocity and angle to flow, flow depth, bed topography, and bed friction. drag on the downstream side of the bone causes scoured sediment deposition, but burial by migrating bed forms is the most important method of large bone burial. bone may be repeatedly buried and exposed with renewed scour. however, each episode of scour may lower the bone deeper into the bed so that it essentially buries itself. no difference in these effects were noted between experiments using fine or coarse grain sizes. this experimental work is then used to interpret the possible history of bone burial in the upper jurassic morrison formation on the bone wall inside the quarry exhibit hall at dinosaur national monument, utah. hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel kenneth carpenter museum of natural history, university of colorado, boulder, co 80302 usa; kenneth.carpenter-1@colorado.edu citation for this article. carpenter, k., 2020, hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel: geology of the intermountain west, v. 7, p. 97–120, https://doi.org/10.31711/giw.v7.pp97–120. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the interaction of bone and moving water has been explored using laboratory flumes to investigate taphonomic bias caused by bone dispersal from sliding, rolling, and floating in moving water, and also abrasion to bone by impact with sand in suspension or on the bed (voorhies, 1969; dodson, 1973, boaz and behrensmeyer, 1976; hanson, 1980; boaz, 1982; frison and todd, 1986; coard and dennell, 1995; blob, 1997; morris, 1997; trapani, 1998; coard, 1999; fernandez-jalvo and andrews, 2003, 2016; pante and blumenschine, 2010; kaufmann and others, 2011; thompson and others, 2011; griffith and others, 2016). the flumes used in these studies are a form of physical hydraulic modeling, which may be predictive to obtain a specific answer to a specific problem or may be investigative to further the understanding of hydrological processes (grayson and others, 1992; blöschl and sivapalan, 1995). for example, flumes have been used to analyze design and operation issues in hydrauling engineering, including bed-load sediment transportation, debris transport, flow and lo98 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 cal scour around hydraulic structures, or obstructions (e.g., bridge abutments, dikes, low walls, coastal piers), and flow around deflectors in stream rehabilitation (summarized in hoffmans and verheij, 1997; ettema and others, 2000). these process models are often used in conjunction with numerical modeling (e.g., computational fluid dynamics) to understand what is observed in the physical models. additionally, numerical modeling is used as a predictive tool for fluvial systems when certain parameters change (e.g., 100to 500-year flood, horritt and bates, 2002). predictive numerical modeling has greatly improved with the integration of remote sensing data of the real world (e.g., matgen and others, 2007; schumann and others, 2009). the reliability of flume modeling is dependent on geometric similitudes, which are important prerequisites for dynamic similitudes (franco, 1978; ettema and others, 2000). similitude refers to how close the flume conditions simulates or matches real-world conditions. perfect similitude is not practical and not necessary given that specific problems are typically being investigated. by limiting similitude to specific conditions, complex real-world situations become manageable through restricting variables and allowing for experiment repeatability. for example, studies of bed erosion (local scour) around bridge abutments do not simulate specific river types (braided, meandering, or anastomosing) because the investigation is only concerned with the interaction of flowing water, the bed material, and the obstacle (i.e., the abutment) (ettema and others, 2000). likewise, differential bone transport studies have not included river type because the problem investigated is the interaction of flowing water and bone. such limited modeling gives generalized results that can then help to understand or interpret real world events, past or present (e.g., voorhies, 1969; boaz, 1982; morris, 1997; carpenter, 2013, 2016). many of these flume bone transport studies are similitudes of sheet-wash conditions because water depths are only a few centimeters and the bones are not always completely submerged; deeper water modeling is rarely done. water depth is a known major factor in hydraulic modeling as discussed below in the section on the basics of flow dynamics. the error between the real-world example (called the “prototype” in hydraulic modeling) and the similitudes increases with scaling due to the unscalable properties of water, such as flow inertia, viscosity, and surface tension. other properties are also fixed, such as gravity and the lower limit of grain size. down scaling of grain size to silt and clay size is difficult because of how differently these smaller particles behave in water (e.g., settling velocities). this scaling problem of grain size complicates the scaling of bed forms. despite these limitations, a broad range of flow and dynamic situations can be analyzed with flumes either by minimizing down scaling, down scaling some but not all components, using particles other than sand, or using fluids other than water (franco, 1978; ettema and others, 2000; ettema and muste, 2004). the bone transport experiments are a form of actualistic taphonomic investigation. what has not been studied in detail is what happens after bone transportation stops. how do bones become buried in order to become fossilized? uncontrolled “wild” field studies are of limited value because the burial of bones are rare, unpredictable events, and when they do occur, visibility of the processes is negligible because of water depth, suspended sediment, and water turbulence. at best, studies of such examples are post-process interpretation (figure 1; e.g., boaz, 1982). very little controlled experimental work has examined the burial process in a fluvial environment. one exception was the preliminary work presented previously as part of a larger work on the bone accumulation in the upper jurassic morrison formation at the carnegie quarry in dinosaur national monument (carpenter, 2013). that study used casts of bones in a creek to better understand the effects of bone obstruction (not transport) to water flow and how that may influence burial. this present study delves further into the processes of bone burial in a fluvial environment by using flume experiments and computational fluid dynamics to interpret the flow dynamics (carpenter, 2016). in some ways this study was preceded by johnson (1957) who used a flume to study the scour burial of shells. the advantages of flume experimentation are multiple: (1) to make real world problems manageable, (2) to control variables for a particular issue, and (3) replicability (ettema and others, 2000). in the example of the cow carcass (figure 1), the events leading up to the car99 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 cass being deposited where it was found are unknown. this includes the origin, timing, and actions leading to carcass entrainment in the water, how far transport occurred, and the effects on fluvial flow patterns once the carcass became stationary; these effects can only be inferred, not observed (figure 1a). it is also not known if the carcass remained at this spot and decayed in place. more importantly for this study is if in situ burial eventually took place and if so, how? a major question of the flume experiments is: can the generalized results be used to interpret a fossil bone site in a manner analogous to how flume bone dispersal studies are used to understand taphonomic bias and bone orientation? the bone wall inside the quarry exhibit hall at dinosaur national monument is used as a case study. materials and methods to study bone burial, a prerequisite for fossilization, a variety of casts and real bones were used (table 1) in an elliptical (“racetrack”) flume with a moveable bed of sand. the fiberglass covered plywood and stud-framed flume has an axial length of 362 cm and a width of 213 cm. the functional part of the flume, the trough, has a width of 75 cm, a floor of 49,314 cm2, and walls 50 cm tall. the interior of the trough was coated with multiple layers of fiberglass cloth and polyester resin. water dimensions for various depths used in the experiment are given in table 2 (water slope = 0). a paddle wheel rather than pump was used to move the water unidirectionally so as to pulse the water. pulsing caused minor fluctuations in velocity and water depth mimicking the unsteady, nonuniform flow of rivers. the paddle wheel had a radius of 42.7 cm and a circumference of 268.25 cm; figure 1. limitations of non-flume studies to interpret prefossilization burial. (a) cow carcass in a river channel as an example of real-world observation to understand bone burial is limited and mostly a post-process interpretation. inset (b) shows the carcass highlighted as a guide to (a). table 1. bones used in the flume experiments. abbreviations: r = real bone; c = cast bone. table 2. physical parameters of the water in the flume. alligator mississippiensis skull (r) allosaurus fragilis skull (c) bos taurus skeletal elements (r) camarasaurus lentus vertebra (c) canis familiaris skull (r) castor canadensis skull (r) dryosaurus skull (c) felis domesticus skull (r) odocoileus hemionus skeletal elements (r) varanus salvator vertebral column (r) depth (cm) hydraulic area (cm2) hydraulic radius (cm) volume (cm3) 30 2250 16.6 1,479,420 35 2625 18.1 1,725,990 40 3000 19.4 1,972,560 100 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 each of the eight paddles had an area of 800 cm2. the paddle wheel was belt driven using a 230-volt, threephase motor, with an auxiliary external fan to prevent overheating. speed was controlled with a teco inverter motor speed regulator and water velocities recorded with a vernier flow rate sensor connected to a lenovo yoga 700 convertible laptop. as with many flume studies, water temperature was not considered significant and not recorded. two types of commercial sand were used to determine if grain size had any effect on bone burial. one was a fine white quartz sand with a d60 of 0.35 mm, and another of poorly sorted, coarse quartz-feldspar playsand with a d60 of 0.9 mm (range 0.6–1.0 mm). the sands were dry screened to remove the smaller fractions (<0.35 mm and <0.6 mm, respectively), then washed to remove any dust, which would cloud the water reducing visibility. an exterior swimming pool filter pump was used to filter any remaining particles from the flume water. an acrylic deflector at one end of the race track diverted the water and sand towards the middle of the study section of the trough; otherwise flow would be confined centripetally against the outer side. bones were placed on a smooth bed that was at least 2 cm deep at the start of each run and in long duration runs, bed structures were allowed to develop naturally (figure 2). the effects of various flow speeds (0.25 to 2 m/s) on bone burial were investigated, but most with a mean horizontal velocity (u) between 0.5 and 1 m/s, which lies within the dune stability field (figure 3). lower velocities were used in clear water scour studies (scour developed but no bed forms developed upstream), which were of short duration (minutes) and repeated to understand various events, such as the initiation of local scour (i.e., scour at the bones). higher velocities were used in live bed studies in which bed forms developed and passed over the bones. an acrylic window in the side of the flume provided an underwater view of the objects resting on the bed. photographs were taken through the window, as well as underwater with a nikon coolpix waterproof digital camera. flow was occasionally stopped to allow plan-view photography without turbulence distortion of water surface. flowsquare 4.0 (minamoto, 2013) computational fluid dynamics (cfd) software on a lenovo thinkcentre desktop computer was used to understand the complex flow field developed when a bone obstruction is encountered. flowsquare can simulate incompressible non-reacting flows, such as flowing water in a two-dimensional channel. to simplify analyses of flow obstruction in an open channel, the approaching flow was set as laminar, with steady uniform mean velocity (u; these are given below with the experiments), uniform figure 2. sedimentary structures in the flume. (a) 20-cmtall dune with crest-shedding fine grains into the water column, water velocity about 1 m/s. (b) turbulent flow around a dune, water velocity about 2 m/s. because of the extreme turbulence, few experiments were conducted at this velocity; most were between 0.5 and 1 m/s. figure 3. stability field for various bed form states relative to grain size and flow velocity. vertical axis are grain sizes (median d60) used in this study (green = 0.35 mm; purple = 0.9 mm). horizontal axes bracket the average velocities for most studies (light blue = 0.5 m/s; blue = 1 m/s). note that the intercept of the grain size axes and velocity axes lie with the dune stability field. the critical velocity for grain movement is variable and is denoted by the dotted line. modified from southard and boguchwal (1990). 101 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 flow depth (also given below with examples), and an immobile lower (bed) wall boundary layer. data input is in the form of a bitmap of the obstacle and boundaries, and a control text file containing modeling parameters (fluid density, fluid velocity, etc.; grid size, duration of the run, etc.). the number of grid points were usually set as x = 574, y = 187, occasionally higher for greater detail. visualization as a gradient of colors (blue = lowest values, yellow = intermediate values, red = highest values; peak values are given in the captions) and flow vectors are displayed in real time and the results saved at specified intervals as bitmap files for post-analysis and for use in figures. when the program is executed, the continuity equation and the equation for momentum is solved for each grid cell (mesh) as the “flow” moves with each time step from the inflow boundary (left margin of the grid) towards the outflow boundary (right margin). to maximize similitude in the flume, real bone and casts of full-size dinosaur bones were used. because the intent of the flume studies was not bone transportation, which has been investigated by others listed above, weights were tied or inserted within skulls to keep the plastic resin casts on the sediment surface so that they acted as stable obstacles to flow. skulls were used to determine how an open structure affected events leading to burial, and incidentally provided information about the burial of the isolated skulls. terminology used below is given in figure 4. except where noted, flow is left to right in all figures. basics of flow dynamics around an obstruction the hydraulic literature is rich with studies about the impact a hydraulic structure (a.k.a., obstruction) resting on the bed has on unidirectional flow (e.g., lefeuvre, 1965; dargahi, 1990; olsen and melaaen, 1993; brørs, 1999; ettema and others, 2000; istiarto, 2001; biron and others, 2005; smith and foster, 2005; tritico and hotchkiss, 2005; cataño-lopera and garcía, 2006; carré and others, 2007; bocchiola, and others, 2008; dey and others, 2008; kirkil and constantinescu, 2010; bocchiola, 2011; mazumder and others, 2011; euler and herget, 2011, 2012; termini, 2011; dixen and others, 2013; menzel and others, 2013; maity and mazumder, 2014), and most importantly for this study—the resulting burial of low obstructions (e.g., dill, 1958; inman and jenkins, 1996, 2005; jenkins and others, 2007; cataño-lopera, and others, 2011; friedrichs and others, 2016). these studies corroborate one another about figure 4. illustration of terminology used. (a) water velocity; color gradient from slowest (blue), intermediate (yellow), and fastest (red). (b) water pressure; color gradient from lowest (blue), intermediate (yellow), and highest (red). (c) water vortices in plan view (red and blue denote different vortices; intensity of color indicates relative speed of vortices). (d) water vortices in three-dimensional (3-d) view. (e) scour detail in cross section (length of arrows corresponds to relative velocities). 102 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 underlying principles of the flow regime around an obstacle, as well as the important effects of obstacle shape, water depth, and water velocity. an obstacle causes flow resistance, creating complex three-dimensional (3-d) flow separation, or turbulence. these flow separations produce areas of acceleration and deceleration (figure 4a, vector arrows). because water is a non-compressible fluid, differential pressure gradients, which is drag, develop around the obstacle (figure 4b). the pressure gradients form because the same mass of water on the upstream side of the obstacle is squeezing past the obstacle (figures 4c and 4d), the so-called “thumb on the garden hose” effect. near and at the bed, changes in flow dynamics produce turbulence and bed shear stress along the x-, y and z-axes (figure 4e). the highest values of near-bed turbulence occur in front of and immediately adjacent to the obstacle thereby causing scour, i.e., bed erosion (figure 4d). this turbulence is manifested as a horizontal helical or horseshoe vortex (figures 4c and 4e), which forms as approaching water is forced down due to overlying hydrostatic pressure and continued inflow of water from upstream (figure 4d). if the water is shallow, velocity high, and hydrostatic pressure low, part of the water deflects upwards producing a dome or crest of water above the obstacle as a standing wave. the downward flow is deflected upstream by the bed because of the presence of a low-pressure gradient due to drag of the bed effect (note the narrow lower pressure zone above the bed in figure 4b and narrow deceleration zone delineated by arrow length in figures 4a and 4d). the upstream recirculation flow then reincorporates into the downstream flow producing a localized spiral motion of the water (figure 4d). however, the constant inflow of water coming from upstream produces a high-pressure zone and the water spirals laterally in both directions as a helix towards the regions of lower pressure. once past the obstacle, water coming from upstream deflects the helix in the downstream direction so that the helix has a horseshoe shape, hence is known as a horseshoe vortex (figure 4c). the energy of helical motion erodes the bed producing a horseshoe-shaped scour when the ratio between the approaching water velocity and critical velocity (minimum water velocity to initiate grain movement) is about 0.45 m/s (dou and jones, 2000). as the helix extends downstream past the obstacle, the energy dissipates and sediment that was transported from the scour settles out when the velocity falls below transport threshold. for obstructions that do not extend above the water surface, flow above the hydraulic pressure threshold for down welling deflects up and over or around (figure 4a and 4d). flow separation results in an arch-shaped vortex on the downstream side of the obstruction, as well as shedding wake vortices. this trailing system of wake vortices diffuses as the energy dissipates (figure 4c). backflow in the recirculation zone deposits sediment eroded by the horseshoe vortex (compare figure 4c with 4a). this region is also marked by a low-pressure zone (figure 4b). the low pressure zone also plays a role in generating lift; this was discussed elsewhere (carpenter, 2013). testing similitude of bone in flowing water the most basic question is whether bone as an obstacle affects water flow in the same manner as other obstacles used in hydraulic studies. to test this, a cow femur was immersed in shallow water (10 cm) and subjected to unidirectional flowing water (u = 0.25 m/s) (figure 5). the femur was initially supported on the bed by the distal condyles, which sank into the substrate a few millimeters until it reached the competency of the sand. shortly after flow initiated, clear water scour developed on the upstream side as a horizontal helical flow at the base of the femur and progressed rapidly until the femoral shaft rested on the bed (figures 5a to 5c). thus, support shifted from the distal condyles to the shaft. sediment scoured on the upstream side (figures 5d and 5e) produced the characteristic horseshoe-shaped scour (figure 5f), with the eroded sediment deposited downstream adjacent to the femoral shaft (figure 5d). analysis of the distal end of the femur with cfd (figure 5g) showed that there was an increase in pressure as the water piled up in front of the condyles. the region of maximum pressure is also where the horseshoe scour developed (compare figure 5g with figure 5f). the results of this first study revealed the similitude of bone as an obstacle to uniform flow hydraulics. 103 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 flume experiment results the process leading to burial for all bones can be divided into two phases: clear water phase, in which most bed events occur in the vicinity of the bone and no bed forms develop upstream, and live bed phase which involves migrating bed forms. each of these in turn can be further divided into events and are listed numerically to keep each distinct. the behavior of the bones as obstacles in unidirectional flow were similar reflecting basic underlying principles and therefore are treated together to minimize repetitiveness; skulls, however, are treated separately from postcrania. clear water phase skulls the skulls used include casts of allosaurus (figures 6 and 7) and dryosaurus (figure 8) and real skulls of alligator (figure 9), canis (figure 10), and castor (figure 11). no large skulls (e.g., bos) were included owing to limitations imposed by flume width. 1. for skulls aligned perpendicular to flow, the skulls initially pivoted horizontally on the bed from the increased water pressure until reaching equilibrium with bed friction (compare figures 6a and 6b to figures 8a and 8c). the exceptions were the beaver skull (discussed further below) and the alligator skull, palate side down, in which the teeth acted as anchors in the bed. 2. immediately upon initiation of clear water phase, bed erosion is evidenced by a depression, the scour hole, forming directly on the upstream side of the skull (frontal scour) and by sand grains entrained into the helical vortex (e.g., figures 6b and 8c). this scour forms in the high-pressure zone at the skull-bed interface, which does not necessarily correspond to highest velocities (compare figure 6m with 6n; figure 9j with 9k; figure 10g with 10h). 3. this initial scour began as a short segment on the bed near mid-skull as the pressure gradient grew very rapidly (figure 6n) and the velocity of the helical vortex exceeded the critical velocity threshold of the sand grains (see figure 3, black lines and dashes). figure 5. distal end of a cow femur as an obstruction. conditions: sand d60 = 0.35 mm, water depth = 30 cm, u = 0.25 m/s. (a) at start, the femur is supported by the distal condyles leaving a gap below the shaft. (b) initial scour begins at the condyles causing them to sink into the bed and reducing the gap below the shaft. (c) continued scour eventually eliminates the gap and the shaft rests on the bed. (d) sediment removed by the scour is deposited posterolaterally adjacent to the condyles. (e) close-up view along the axis of the helical vortex; sand is spirally towards viewer. (f) horseshoe scour seen in plan view. (g) cfd analysis showing water pressure gradient. the region of maximum pressure (red, peak at 1125 pascals [pa]) explains why the horseshoe scour develops immediately in front of the femur. 104 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 4. the helical vortex rapidly grew in width (z axis) until the lateral by-pass flow (x axis) forced the vortex to curve downstream producing the horseshoe-shaped vortex (figure 6m), which was manifested on the bed by development of the characteristic horseshoe scour (figures 6b and 8c). 5. eroded sediment moved to the lee side of the skull by the wake vortex system where it is defigure 6. the effects of flow on an allosaurus skull cast resting on a live-bed of medium sand. conditions: sand d60 = 0.35 mm, water depth = 30 cm, u = 0.5 m/s. (a) skull placement at start. (b) pivot of skull (about 35°) before scouring began. scour and deposition co-occur. red line is approximate location of figures 6m and 6n. (c) burial of skull by advancing dunes. detail upstream side of skull. (d) start position of skull. (e) initial scour and undercutting of skull on upstream side. white specks and streaks are sand particles in suspension. (f) extended under-scouring, just before skull slumped into scour hole. detail downstream side of skull. (g) start position of skull. (h) initial deposition from through-flow (arrow) and recirculation. (i) more advanced stage of deposition from through-flow (arrow) and recirculation. burial by dune. (j) advancing dune. scour still occurring. (k) infill of scour by cascading sand on lee side of dune. (l) burial of skull by dune. (m) cfd of horizontal velocity (u = 0.5 m/s) around the skull in map view. note a near doubling of the flow velocity, from 0.5 m/s to 1 m/s as it passes around the ends of the skull. (n) cfd pressure fields peak at 4922 pa on the upstream side of the skull and drop to 210 pa on the downstream side. (o) cfd showing complex flow dynamics through open skull (cross section through antorbital fenestrae approximately at red line in 6b); peak u = 1.9251 m/s. (p) vectors showing simple flow dynamics over flesh covered skull (without lower jaws); peak u = 1.9251 m/s. 105 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 posited by subcritical recirculation flow, which is a low-pressure zone (figures 6m to 6o). other sediment is carried through the skull and deposited in the low-pressure zone on the downstream side (figures 6b, 6h, 6i, 6o, and 8c). 6. propagation of the frontal scour depth (y axis) and length (x axis, mostly in the downstream direction), ultimately undercut the skull (figures 6e, 6f, and 8d). the dual frontal scour zones reported by euler and herget (2012) were not seen, but may be due to the higher flow velocity. 7. when the frontal scour undercut beyond the center of gravity, the mass of the unsupported portion of the skull underwent rotational motion in an upstream direction (x axis) causing it to tilt into the scour (y axis). renewed undercutting by the horseshoe vortex caused the upstream side of the skull to settle deeper into the substrate (compare slope of quadrates in figures 8b and 8d). this is the same principle that makes stone imbrication in river channels, even of several hundred-kilogram boulders (see euler and others, 2017, figure 1c). 8. frontal scour growth stops once a state of dynamic equilibrium is reached whereby sediment removal equals live-bed sediment inflowing. the maximum depth for this dynamic equilibrium is dependent on obstruction area facing the flow, median grain size, mean water velocity, and hydraulic pressure of water depth (euler and others, 2017). 9. the open framework of the skulls used in the experiments allowed through-flow creating a more complex flow dynamics than flow around and over a bone (figures 6o, 9j, 9l, and 10g). in the experiments with the beaver skull aligned perpendicular to flow, it immediately flipped onto its dorsal surface when flow was initiated (compare figure 11a with 11b). the reason for this is seen by the differential pressure fields on the upstream and downstream sides of the skull and the absence of through-flow (figure 11h). although similar fields are developed with the other skulls, the small size of the skull made it particularly susceptible to the effects of the pressure gradient. the higher pressure on the upstream side sought to push the skull downstream, whereas the low-pressure zone on the downstream side sought to pull the skull figure 7. the effects of flow on an allosaurus skull cast resting on a live-bed of coarse sand. conditions: sand d60 = 0.9 mm, water depth = 20 cm, u = 1 m/s. overall behavior of the sand is similar to finer grained sand. (a) scour on upstream side. (b) burial by advancing dune (streaks in lower right are sand grains in brief suspension). (c) view downstream showing stoss side of advancing dune, skull palate side this time facing upstream; flow stopped for photography. (d) burial of skull by advancing dune; flow stopped for photography. (e) profile of advancing dune, skull on right; flow stopped for photography. 106 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 in that direction. the net result of the push-pull forces on the skull was to flip it because tooth-bed resistance prevented the skull from merely sliding downstream. postcrania bones used included a cast cervical vertebra of camarasaurus (figure 12), articulated dorsal and caudal vertebrae of varanus salvator (figure 13), and femur of bos (figures 5 and 14). many of the same events with the skulls also occurred with the postcrania, such as the development of horseshoe scour on the upstream side, undercutting and sinking into the bed (figure 5f), and recirculation with deposition on the downstream side. the exception is the varanus caudals as discussed separately below. with the rest of the postcrania, there were some notable differences from the skulls: 1. the deepest and largest scour occurred on the downstream side of vertebrae and femur aligned perpendicular to flow due to piping and lee side vortices (figures 12b, 13b, 13d, and 14b to 14f). piping is due to the narrowness of bone-bed contact which allows higher seepage flow through porous sand, coupled with differential pressure on the upstream and downstream sides. this piping is similar to that seen with underwater pipes and horizontal cylinders, which leads to their self-burial (chiew, 1990; cataño-lopera and garcía, 2006). piping scour by its nature undercuts the bone on the downstream side because of fluidization of the bed, whereby water pressure forces the sediment upwards off the bed (figure 14g). the effects of piping is predicted to decrease the greater the mud content figure 8. the effects of flow on a dryosaurus skull cast resting on a live-bed. conditions: sand (d60 = 0.35 mm, water depth = 30 cm, u= 0.5 m/s. skull at start in (a) plan view and (b) underwater view of rear of skull. (c) pivot of skull (about 42°) before scouring began. scour and deposition co-occur; flow stopped for photography. (d) upstream skull rotation into the horseshoe scour; compare with 8a and 8b; flow stopped for photography. (e) burial by advancing dunes. (f) side view showing burial by due to multiple dunes; flow stopped for photography. (g) large dune about to bury protruding quadrate. white streaks and speckles are sand in suspension. (h) start of exhumation of skull as sand dune passes; flow stopped for photography. (i) skull about to be reburied (dune 3) after partial exhumation; flow stopped for photography. 107 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 of the substrate due to reduction in pore space. 2. non-piping, lee side scouring occurs if the approaching velocity is high enough to cause flow over the bone to reach supercritical velocity due to hydrostatic pressure of the water column (“thumb on the garden hose” effect). it then swoops down behind the bone in a jet-like motion to scour the bed (figure 14g). this effect is similar to the stratified flow hydraulic jump described by dorrell and others (2016). 3. once the scour hole is formed, the bone rotates downstream into the scour hole (figures 12b and 14c to 14f). this movement is assisted by high flow pressure on the upstream side and low-pressure wake vortex on the downstream side (figure 14h). piping and scour can also cause a bone to sink into the bed with minimal downstream rotation, especially if the bone is relatively narrow and with a low profile (figures 14j and 14k). the varanus caudal section behaved different from figure 9. effects of flow on an alligator skull. conditions: sand d60 = 0.35 mm, water depth = 30 cm, u = 0.5 m/s. (a) skull at start in plan and side view. (b) initiation of scour (white streaks are sand grains in suspension). (c) burial by advancing dune; flow stopped for photography. (d) sand grains being deposited within the skull. (e) skull being infilled with sand cascading through the suborbital fenestra. (f) skull nearly buried. skull perpendicular to flow. (g) skull at start from rear. (h) view upstream showing the burial by dunes. (i) cfd showing flow velocity fields (u = 0.5 m/s) through skull aligned with flow. the low velocity through-flow explains deposition of sand grains within the skull seen in 9d. blue = 0.026 m/s, red = 1.087 m/s. (j) cfd of pressure showing high-pressure at the tip of the snout where scour is seen in 9b. peak pressure 3203 pa. note lower pressure within most of the skull. (k) cfd showing complex flow velocity fields (u = 0.5 m/s) though the rear portion of the skull set perpendicular to flow. blue 0.00297 m/s; yellow = 0.495 m/s; red 1.287 m/s. (l) cfd pressure gradients of 9k with peak at 1125 pa. 108 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 the other postcranial elements and is discussed separately. when the caudal ribs were pressed into the bed, they acted as anchors and scour developed as with the skulls. in contrast, when the caudal vertebrae were supported by the chevrons and caudal ribs (figures 13g and 13h), through flow beneath the centra prevented the buildup of pressure on the upstream size and no scour developed. burial was strictly by bed migration. live bed phase in these experiments, scour alone was insufficient for bone burial because scour-hole depth never exceeded bone height. tilting of the bone into the scour hole reduces its profile in the flow, thereby reducing both the downwelling and effective scour energy. eventually, a point of dynamic equilibrium is reached at which no further deepening of the scour occurred, generally between half to three-quarter bone height and is dependent on the approaching mean flow velocity. this phenomenon of equilibrium has been noted in other scour studies (euler and herget, 2012; friedrichs and others, 2016; euler and others, 2017). complete burial of skulls and postcrania is due to migrating bed forms (figures 6j to 6l, 7d, 7e, 8e to 8g, 9c, 9f, 9i, 10e, 10f, and 11c), with several events occurring: 1. downstream deposition of turbulent sand suspension from the crest of an approaching dune due to vortex shedding in the separation zone where peak velocity occurs (figures 2b, 4b, 4c, and 8g; kostaschuk and villard, 1999; best, 2005). entrained sand grains in the recirculation zone then settled on the bone once flow velocity dropped below the transport threshold (figures 6h and 6i). although a minor cause of burial by sand compared to burial by the dune itself, this downstream deposition was found to increase as the dune approached and the dune flow shadow enveloped the bone. 2. because flow deceleration occurs on the lee side of dunes (best, 2005), bed erosion in the vicinity of the bone gradually slows and eventually halts, then infills from cascading sand from the dune slip-face (compare figure 6f with 6j, and 6k). figure 10. effects of flow on a modern dog skull aligned with flow presenting a minimal profile. conditions: sand d60 = 0.35 mm, water depth = 30 cm, u = 0.5 m/s. (a) skull in plan view. (b) skull in side view. note the canines hold the palate off the bed. (c) under scour causes the rear part of the skull to sink into the bed; flow stopped for photography. (d) maximum self-burial of skull prior to burial by advancing dune. (e) recirculating flow along lee side of advancing dune (u = 1 m/s). (f) near burial by dune (u = 1 m/s); flow stopped for photography. (g) cfd flow velocity fields (u = 0.5 m/s). blue = 0.00394 m/s; yellow = 0.497 m/s; red = 1.274 m/s. (h) cfd of pressure gradients; note higher pressure beneath the skull, exactly where scour occurs in 10c causing the skull to sink. pressure beneath the skull about 1563 pa. 109 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 3. once the dune begins to envelope the bone, cascading sand infills open voids within bone and skulls, except for dead end pockets that face upwards (figures 9d and 9e). currents flowing down the lee side of the dune may also push sand grains into voids. 4. further advancement of the dune completely covers the bone (figures 8f, 8g, 9f, and 11b to 11d), unless the bone height exceeds dune height (figure 10f). 5. continued downstream migration of the dune may exhume the bone (figures 8g, 8h, and 11c to 11f), then it may be reburied by the next advancing dune. this cycle can occur repeatedly subjecting the bone to abrasion by approaching saltating grains (thompson and others, 2011; griffith and others, 2016) that may mimic bone transport abrasion (shipman and rose, 1988; andrews, 1995; fernández-jalvo and andrews, 2003), but this abrasion is not uniform over the bone. permanent burial occurs in aggrading channels, but even so, the rate of aggradation will be less than the rate of dune migration. this implies that a cycle of burial and exhumation is part of the normal process of bone burial. conclusion of flume studies bone burial in an aggrading fluvial channel is not a simple process of sand being transported and deposited over the bone. rather, the bone sets up the initial condition for its burial. this point was also noted by johnson’s (1957) study of shells in a flume; however, the study did not explain the hydraulic effects that took place. bones disrupting flow causing a u or horseshoe vortex that scours the bed along the entire upstream side. the scour may extend beneath the bone as well and if this undercutting extends to more than half the bone width (as measured in the x axis, the direction of flow), the bone may tilt into the scour hole. this event in unidirectional flow is seldom sufficient to completely lower the bone below the bed surface. in contrast, scour may be the primary method for burial when the object is subjected to oscillatory flow because of under scour on both side of figure 11. effects of flow on modern beaver skull perpendicular to flow, with repeated burial and exhumation. conditions: sand d60 = 0.35 mm, water depth = 30 cm, u = 0.5 m/s. (a) skull at start. (b) skull was immediately flipped over. advancing dunes of live bed start burying the skull; flow stopped for photography. (c) skull nearly completely buried. (d) skull completely buried; flow stopped for photograph. (e) start of exhumation as dune moves. (f) maximum exhumation; flow stopped for photography. (g) cdf of flow velocity around skull. blue = 0.00565 m/s; yellow = 0.3983 m/s; red = 1.332 m/s. (h) cdf of pressure gradients showing high pressure (red to yellow) on the upstream side of the skull and large area of low pressure (blue) on the downstream side. this differential pressure explains why the skull flipped over. peak pressure = 1406 pa. 110 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 the obstruction (dill, 1958; cataño-lopera and garcía, 2006). the process of burial occurs when flow velocity drops below the critical threshold for grain transport. this generally occurs first in the localized recirculation zones of flow shadows of complex bone shapes due to form drag and flow separation. these localized recirculation zones may also develop where through-flow passes into the unconstrained downstream side of various skull openings. cascading sand on the lee side of approaching dunes infills bone voids, but this may be hampered by soft tissue. once decay has removed the tissue, then sand, if not lithified, is predicted to infill much of the void from fluidized sand injection by overpressure. primary voids in fossil skulls (daniel, 2012) demonstrate that infilling is not always complete. advancement of the dune eventually envelops the bone and if the bone is less than the dune height, it will be completely buried. continued migration of the dune may exhume the bone as the sand moves downstream. however, subsequent dune migration cyclically buries and exposes the bone. we may predict that only in aggrading river channels is burial eventually permanent. using flume modeling to interpret a bone bed the different flume bone burial experiments described above show repeated patterns regardless of bone size and shape suggesting underlying principles at work summarized in the previous section. this raises the question whether the results can elucidate events that led to the burial of bones in an actual fossil bone deposit. this hypothesis is explored using the bone bed in the morrison formation at the quarry visitor center at dinosaur national monument, utah. the bones at the quarry occur in fluvial channel sandstones (holland, 1915; gilmore, 1936; bilbey, 1973; bilbey and others, 1974; lawton, 1976, 1977; turner and peterson, 1992; fiorillo, 1994; foster, 2003; carpenter, 2013), and most probably represent a braided river complex (lawton, 1976, 1977; carpenter, 2013). the recent crevasse splay hypothesis of brezinski and kollar (2018) is doubtful because: (1) the conglomeratic quarry sandstone (larger clast sizes 2–10 cm) is in contrast to the generally coarse sandto finesand of crevasses splays (millard and others, 2017), (2) the healing of the crevasse that would result from the abrupt decrease in competence, and specifically the conglomeratic-coarse sand carrying capacity as part of the river flow was diverted out of channel (nienhuis and others, 2018), (3) the difficulty in transporting large clasts with masses in the high tens of kilogram (e.g., sauropod bones) by rapidly decelerating water of a splay (these should also accumulate at figure 12. effects of under scouring piping on a vertebra. (a) cervical vertebra (camarasaurus) cast at start of experiment, dune to the left. (b) downstream rotation after scour from piping and force of flow deflected over the dune at the far left. 111 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 the mouth of the crevasse channel causing blockage and healing; see #2), (4) dinosaur bones are known to act as sediment traps because of frictional flow resistance (form drag) and turbulent eddies from flow separation causing a velocity drop and an loss of sediment transport competence (figure 15), (5) related to #4 are that the bone jams are analogous to boulder arrays, which are known to bear a significant component of bed shear stress, thereby reducing the available shear stress available for sediment transport (papanicolaou and others, 2012), and (6) the difficulty of accounting for the enormous volume of water at supercritical flow needed to move large dinosaur bones of the 1.8-km-wide conglomeratic splay hypothesized by brezinski and kollar (2018) in a semiarid environment. these and other issues are dealt with elsewhere (carpenter, in preparation). bed forms responsible for bone burial are well displayed either in historical photographs (see figure 13 in carpenter, 2013) or currently on the bone wall. these bed forms include channel bars (figure 16a), dunes and planar cross-beds of dunes (see figure 26 in carpenter, 2013). these planar cross-beds show the coarsening upwards and fining towards the toe that is characteristic of high sediment transport rate (bridge, 2003). these bed forms can be shown to have buried the bones as discussed below. some of the features generated by the bone obstacles in the flume experiments are observed on the quarry. scour is perhaps the most obvious paleo-event observed, especially the downward displacement of the ends of articulated vertebrae strings explained as due to the horseshoe scour extending around the edge of the obstacle and pliable ligaments (figure 16b). scour evidence is also seen by bones angled in the upstream direction of the paleoflow, with the downstream side higher than the upstream side (figure 16c). this angling is similar to that seen by the upstream helical undercutting and tilting of bone. the effects of flow on one moderate-sized scapula-coracoid was even more extreme because the bone stands almost vertical in the sediments (figure 16d). this is interpreted to have been caused by undercutting along the anatomical dorsal margin, which faced upstream, and subsequent tilting and renewed under cutting. no large scapula-coracoids show such extreme tilting probably because their large (relative to stream flow) size prevented renewed under scour after the tilting. not all bones show evidence of figure 13. the effects of flow on an articulated string of varanus vertebrae. conditions: sand d60 = 0.35 mm, water depth = 30 cm, u = 0.5 m/s. (a) oblique view of vertebrae perpendicular to flow at start. (b) scour upstream side and deposition on downstream side from underflow. (c) scour along the entire upstream side. (d) scour from piping and advancing dune, which shut off and then buried the scour. (e) after the advance of the dune, there is renewed scour. (f) front (end) view of e showing the under scour. (g) articulated caudal vertebrae supported by the chevrons and transverse processes at start. (h) upstream view showing advancing dune. little scour occurred because flow could pass under the vertebrae. 112 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 undercutting and these are typically elongate and parallel with paleoflow. because undercutting scour must extend more than 50% for the bone to tilt into the scour hole, these elongated bones never experienced that amount of scour before burial so remained horizontal on the substrate (figure 16e). however, elongate bones not parallel to flow or which were subjected to more than 50% under cutting do slope upstream (figure 16f). evidence for wake scour and fill is best seen where finer grain sand infilled the scour around the sides and downstream of the bone (figure 17a). a helical scour hole near the front edge of a vertebra may have infilled with fine-grained sand when the force of the flow decreased with the proximity of an approaching bed form (figure 17b). through or underflow and scour are seen with the coosified stegosaurus sacrum and ilia (presumably without the pubes and ischia). the infilling is with fine-grained sand (figures 17c and 17d). a pocket of gravel (figure 17d) may be lag from winnowing of the bed by the underflow. overflow of a low-profile bone results in the formation of a low-pressure recirculation zone on the lee side of the bone (e.g., figure 17 g) resulting in the deposition of fine-grained sediment (figure 17e), as well as smaller bones (figure 17f). one peculiar burial is an immature diplodocus pelvis oriented perpendicular to the sediments, anterior side down (figures 18a to 18c). the most parsimonious explanation in light of this study, is that the pelvis somehow got into a stable vertical position where it was soon enveloped by a migrating bar or megadune, which figure 14. effects of flow on a domestic cow femur. conditions: sand d60 = 0.35 mm, water depth = 30 cm, u = 0.5 m/s. (a) femur at start aligned perpendicular to flow. (b) distal end showing condyles only half underwater. (c) scour beginning at distal condyle (cloudiness due to sand particles in suspension). (d) femur begins to sink into bed scour; note more of the condyles submerged. (e) being more submerged increased surface area subjected to flow resulting in femur rotating downstream. (f) continued scouring lead to partial burial of femur. (g) cfd showing flow velocity fields (u = 0.5 m/s). blue = 0.0060 m/s; yellow = 0.413 m/s; red= 1.432 m/s. (h) cfd showing differential pressure gradients of (g) to explain why the femur rotated in (e); red is high pressure zone; blue is lowest pressure. (i) femur inverted to a more stable position seen in plan view aligned perpendicular to flow. (j) proximal end seen underwater. arrow draws attention to the bone just contacting the surface. (k) scour has resulted in the bone sinking into the bed. arrow denotes gap between bone and surface. 113 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 is represented today by “the hump” on the quarry face (figure 16a; carpenter, 2013). there is a large portion of what may be the rest of the skeleton exposed on the west side of “the hump” but these bones are lying horizontally. one skull remaining on the bone wall (“cliff face” skull) shows the effects of paleoflow, which resulted in its slight displacement from the articulated cervical vertebrae (figures 18d and 18e). sauropods are notorious for the rarity of their skulls being found with the skeleton and this specimen suggests that the muscles and ligaments attaching the vertebral column to the skull decompose rapidly. the cervical vertebrae are ventral-side up, whereas the skull lies on its left side, implying that originally there must have been considerable torsion stress at the skull-neck junction. eventually, the stress on the decay-weakened joint separated the skull, possibly aided by the force of the water. the skull was then pushed along the bed several centimeters. decay also affected the connective tissue of the joints on the upside (right side) of the skull. the liberated right quadrate, quadratojugal, and some of the palatal elements were gravitationally displaced towards the downside of the skull. the articulated dentary, surangular, and angular, and the disarticulated prearticular, splenial, and many of the teeth of the right mandible were displaced downstream a little from the skull (madsen and others, 1995). this evidence for the decay of almost all of the soft tissue allowed sand to cascade into and fill the inside of the skull (compare with figure 9e). because clay-poor (<10%) siliciclastic sediment with grain-to-grain contact has long been known to resist mechanical compaction from postdepositional overpressure (e.g., athy, 1930; weller, 1959), the lack of crushing of the skull indicates that all the major cranial voids (e.g., brain cavity and snout) were supported by sand grains. this contrasts with skulls from clay-rich sandstone or skulls still encased in soft tissue at the time of burial; these skulls show compaction crushing (carpenter, 2013). conclusions laboratory water flumes have played an important role in our understanding of fluvial systems using controlled and repeatable experiments to understand hydrological processes. laboratory flumes have also been used to understand bone sorting and transport, which has been important in understanding taphonomic bias observed in fossil deposits. this study used a laboratory flume to study the next phase, bone burial under controlled conditions. the bones used, real and cast, replicate many of the features documented for bed obstacles (e.g., martinuzzi and tropea, 1993; istiarto, 2001; smith and foster, 2007; dey and others, 2008; euler and herget, 2011; mazumder and others, 2011), including turbulent flow features also seen around obstacles (e.g., figure 15. example of a bone bed that acted as a sediment trap to crevasse splay sands. splay sandstone in the foreground rapidly thins towards the back and ends approximately at red line. beyond that bones lie in sandy mudstone. note femur in foreground that cuts obliquely through sandstone due to original scouring of upstream end (nearest viewer). children's museum of indianapolis excavation, morrison formation, big horn basin, wyoming. 114 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 euler and herget, 2012; euler and others, 2017). therefore, bones are governed by the same hydraulic principles (i.e., similitude) and can be reliably modeled in a flume and by computational fluid dynamics. the bones in the flume showed the following generalities, with no marked difference between the fine (d60 0.35 mm) and coarse (d60 of 0.9 mm) grain bed loads: 1. along the upstream side, the constant approach of water causes down flow and development of a horseshoe-shaped helical vortex as the water seeks to escape around the bone margins into regions of lower pressure. 2. depending on how deep into the bed substrate the bone rests, under scour can develop along the upstream edge. if this scour extends to greater than half the bone length, the bone can tip upstream into the scour hole and lay at an angle to the strata. this suggests caution for interpreting low angled (30°) fossil bones in sand-rich sedimentary rock as indicative of trampling. 3. underflow can also cause scour beneath the bone where the water is constricted beneath any irregularly shaped bone in which a part maybe slightly elevated above the bed. 4. t he erosive strength of the down flow along the upstream side is reduced when the bone has a streamlined frontal area because the flow is more easily deflected around the bone. 5. under scour can develop from piping due to hydrostatic pressure on the upstream side forcing sand up off the bed on the downstream side, but this seems to be confined to vertebrae laying perpendicular to flow. presumably, pipping can figure 16. bone wall inside the quarry exhibit hall at dinosaur national monument. (a) inclined strata of a channel bar preserved on “the hump” at the west end of the carnegie quarry. flow was left to right. scale approximately 1 m; the pelvis in figure 18 is immediately to the right of the scale. (b) evidence of scour at the end of the diplodocid cervical vertebrae (white arrow), and possible pipping erosion + underflow scour (yellow arrow). (c) arrows point to the lower end of bones at an oblique angle through the strata due to scour; diplodocus anterior caudal (white arrow), diplodocid humerus (yellow arrow). (d) sauropod scapula (arrow) dipping upstream due to scour. (e) lack of apparent under scour seen with two long sauropod femora (lower diplodocus; upper apatosaurus) lying flat on bedding surface. (f) two long bones (arrow; humerus, left; femur, right) oblique to strata due to under scour. unless stated otherwise, average flow direction was from the top of image. 115 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 also occur with ribs or other slender bones presenting a narrow cross section to flow. 6. as the water passes over or around the bone, flow deceleration and separation occurs forming recirculation eddies on the downstream side. recirculation is in a lower pressure gradient causing deposition of sediment, part of which is derived from the frontal scour. this lower pressure is the result of a rapid change from constricted to unconstricted flow. the drop in velocity causes a loss in the transport capacity, with a net gain in sedimentation. despite some bones partially setting up the conditions for their own burial through settling into a scour hole or acting as sediment traps, the main cause of burial is by migrating bed forms. the results of the flume experiments do explain some of what is seen on the bone wall at dinosaur national monument, and suggests the generalized results have a broader applicability with other fossil bone deposits as well. however, this study only investigated the processes of burial for bones resting on a sandy, claypoor substrate. the effects of interstitial binding agents (clay or microbial mats) to resist bed erosion were not considered. these agents are known to hinder scouring until the critical velocity of the sediment is surpassed (paterson, 1994; droppo and others, 2015; the so-called “stick ‘n’ peel” of orr and others, 2016, may not hold for sandy beds). future investigation should examine flow around single bones using 3-d computation fluid dynamic figure 17. bone wall inside the quarry exhibit hall at dinosaur national monument. (a) downstream scour from wake vortices and later infill (darts) around bone obstacle. note bone was at slight angle relative to flow resulting in more pronounced scour on right side. clam (c) valves came to rest in stable position in flow shadow. (b) fine-grained fill of the scour formed by the helical vortex along the front edge of the obstacle (diplodocid vertebra). inset shows detail. (c) partial stegosaurus pelvis oriented parallel with current with scour and fill structures downstream (lighter lenses). white box is landmark in (d). white streaks caused by excavation tools. (d) detail of scour from underflow of stegosaurus sacrum and ilia and with lag and later infill. white box is landmark in (c). white streaks caused by excavation tools. (e) fine-grained sand deposited in the flow shadow side of a diplodocid sauropod humerus; note coarser sand farther downstream (lower right). (f) small bone (ulna) and other small bones in the flow shadow side of a sauropod (diplodocus) ischium (note also the finer grained sandstone). 116 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 software with a variety of grain sizes in a moveable bed. this should provide a refined understanding of bones as obstacles and an understanding of bone burial. in addition, scour hole geometry is known to be influenced by the angle of the obstruction to the flow (johnson, 1957; haltigin and others, 2007), but this was only partially examined in this set of experiments (e.g., alligator and dog skulls). scour is also known to occur at the confluence on the downstream side of bars (ashmore and parker, 1983; szupiany and others, 2019) and this is predicted to influence bone burial. finally, modeling of carcasses and partial carcasses also remain an important area for future exploration. acknowledgments henry galliano (maxilla and mandibles) provided the alligator skull used in the study. access to the carnegie quarry was made possible most recently by rebecca hunt-foster (national park service), and previously by russell king, tobe wilkins, dan chure, ann elder, and scott madsen (all of the national park service), refigure 18. bone wall inside the quarry exhibit hall at dinosaur national monument. (a) end view of posterior side of sauropod pelvis (diplodocus) standing vertically through bar deposit. (b) side view of sauropod pelvis at "the hump." darts indicate a lithological boundary that may represent a bed surface. (c) interpretative sketch. (d) anterior cervical vertebrae and slightly displaced skull of camarasaurus. (e) palatal view showing that the skull is not crushed and infilled with sandstone. white arrows indicate separation of skull from cervical vertebrae. 117 hydraulic modeling and computational fluid dynamics of bone burial in a sandy river channel carpenter, k. geology of the intermountain west 2020 volume 7 view comments to earlier versions by three anonymous reviewers, susannah maidment (natural history museum, london), patrick orr (department of geology, national university of ireland), and kathleen huber (paleontological society) are gratefully acknowledged. this article is the seventh in a series on dinosaur national monument. references andrews, p., 1995, experiments in taphonomy: journal of archaeological science, v. 22, no. 2, p. 147–153. ashmore, p., and parker, g., 1983, confluence scour in coarse braided streams: water resources research, v. 19, p. 392– 402. athy, l.f., 1930, density, porosity, and compaction of sedimentary rocks: american association of petroleum geologists 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petroleum geologists bulletin, v. 43, p. 273–310. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. methane emissions from muds during low water-level stages of lake powell, southern utah, usa margariete malenda, thomas a. betts, wendy s. simpson, michael c. wizevich, edward simpson, and laura sherrod geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover examples of the fluid-escape features related to lower water levels in the lake powell near hite, utah. the mud volcanoes range from being extensive (left, with 1.7-m-tall individual) to relatively small in size, such as the bubbling volcano on the right (frog is approximately 5 cm). i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter 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house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 121 abstract the glen canyon dam, along the colorado river in page, arizona, was completed in 1963, creating the lake powell reservoir which spans the arizona-utah border. the water levels of lake powell peaked in 1983 and have declined since, releasing overlying pressure on the underlying sediment. in general, water levels experience seasonal highs and lows, with punctuated periods of considerable and steady decreases (1987 to 1993, 1999 to 2005, and 2011 to 2014) and less dramatic recoveries (1993 to 1999 and 2005 to 2011). this release of overpressure coupled with increasing pore pressures due to biological methane production has created mud volcanoes, structures along the shoreline made of cavities that allow fluid and gas to rise to the surface and escape. although these sedimentary structures have been assessed using geophysical techniques and excavation to characterize their morphologies and fracture propagation, limited chemical data has been reported on the inputs and products of these gasand fluid-escape features. this research investigates the relative proportions of methane (ch4), carbon dioxide (co2), and air (unseparated nitrogen [n2] and oxygen [o2]) gas released, the variability of these proportions through time, and how these gases formed in the subsurface. the field site is along the lake powell near hite, utah. three gas samples were collected from mud volcanoes along the delta in july 2014, whereas 21 samples were collected in july 2015 and were analyzed via gas chromatography (gc). the gc analyses from 2014 and 2015 have a mean ch4 concentration of 81.47 ± 9.29 percent of volume (% v/v) and 32.40 ± 15.31% v/v, respectively. in may 2016, 50 samples from 25 vents were collected and analyzed via gc for bulk composition, and 11 of which were analyzed by isotope ratio mass spectrometry (irms) for carbon and hydrogen isotope content of ch4. the 2016 gc analysis detected average relative concentrations for ch4, co2, and air of 74.51 ± 14.08% v/v, 2.82 ± 3.76% v/v, and 22.67 ± 14.28% v/v, respectively. gas compositions from individual vents varied over the three-day sampling timeframe in the summer of 2016 including ch4 decreases of up to 66% v/v and increases of up to 38% v/v. irms signatures of samples collected in 2016 indicate the gasses are in part generated during microbial respiration through hydrogenotrophic and acetoclastic methane production. methane emissions from muds during low water-level stages of lake powell, southern utah, usa margariete malenda1, thomas a. betts2, wendy s. simpson3, michael c. wizevich4, edward simpson2, and laura sherrod2 1department of geophysics, stanford university, 397 panama mall, mitchell building, stanford, ca 94305; malenda@stanford.edu 2department of physical sciences, kutztown university of pennsylvania, 15200 kutztown road, kutztown, pa 19530 3parkland high school, 2700 north cedar crest blvd., allentown, pa 18104 4department of geological sciences, central connecticut state university, copernicus hall, 1615 stanley st., new britain, ct 06050 citation for this article. malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l., 2020, methane emissions from muds during low water-level stages of lake powell, southern utah, usa: geology of the intermountain west, v. 7, p. 121–136, 4 appendices, https://doi.org/10.31711/giw.v7.pp121-136. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 122 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 introduction methane generation in lacustrine settings mud volcanoes, pockmarks, water-filled craters (salses), and sedimentary deformation features in lacustrine settings can serve as natural gas seeps and can provide insight on mechanisms behind hydrocarbon and greenhouse gas generation and expulsion (dlugokencky and others, 1995; judd, 2005; forster and others, 2007; etiope and others, 2009; bussmann and others, 2011). for example, up to 40 to 60 million tons (40–60 teragrams) of methane (ch4) are released annually via geological sources including mud volcanoes (etiope, 2004), and 70 l/min of ch4 has been estimated to vent from the dashgil mud volcano along the coast of azerbaijan alone (kopf and others, 2010). more specifically, terrestrial and marine mud volcanoes are recognized as significant sources of ch4 that may be of either biogenic, thermogenic, or a combination of both origins (hovland and others, 1997; tinivella and giustiniani, 2012). one primary source of ch4 is the respiration of microorganisms such as those prevalent in lacustrine settings, wetlands, rice paddies, and landfills among other natural and anthropogenic sources (chanton and others, 2005). large reservoir systems created by dams are also sites of significant biogenic ch4 (st. louis and others, 2000; joyce and jewell, 2003; maeck and others, 2014; deemer and others, 2016; harrison and others, 2017), and water level declines in such systems have been linked to increased rates in ch4 release (maeck and others, 2014; beaulieu and others, 2017; harrison and others, 2017). similarly, prior studies explain that the gas seeps of utah’s lake powell reservoir delta (figure 1) are the result of increasing pore-water pressures from biogenic ch4 production and decreasing overlying pressure from the lowering water table (netoff and others, 2010; livingston and others, 2014, 2015; sherrod and others, 2016; miller and others, 2018). these studies identify algal blooms and the organic-rich clays as substrates to sustain methanogens (ch4-producing microorganisms). for example, the organic-rich clay layer described in miller and others (2018) contained mm thick zones of fine, macerated plant materials and stem fragments decomposed, in part by microorganisms. this layer underlies heterolithic layers containing gas-filled cavities and ranges in depths from 0 to 6 m due to fluid migration and subsequent sediment mobilization. these prior studies have discussed the origins and evolution of the lake powell gas seeps from primarily physical observations. for the first time, here we document the chemical signature of these gases through relative hydrocarbon compositions, then relate isotopic composition to the biogenic mechanisms for methanogenesis, and finally consider potential biological, hydrological, and chemical controls on ch4 production in discussing future field measurements. geologic setting of the lake powell delta lake powell is a reservoir located on the utah-arizona border and results from the 1963 completion of the glen canyon dam near page, arizona (figure 1). water levels experience seasonal highs and lows, with punctuated periods of considerable and steady decreases (1987 to 1993, 1999 to 2005, and 2011 to 2014) and less dramatic recoveries (1993 to 1999 and 2005 to 2011) (figure 2; u.s. bureau of reclamation, 2017). such drastic water level fluctuations trigger undercutting erosion of canyon walls, subaqueous gravity flows, and up to one-hundred-fold increases in sediment accumulation (pratson and others, 2008; anderson and others, 2010). over the three-year sampling period presented here (july 2014, july 2015, and may 2016), water levels were approximately 1100 m above sea level in 2014 and 2015, and 1097 m high during the 2016 period (figure 2). overall, the reservoir has been gradually decreasing since the 1127 m full pool high in 1983. lake powell, in the study area, is underlain by the cedar mesa sandstone, a confined aquifer sealed by lake powell muds. the uppermost 2 m of the delta consists of clays, silts, and fine sands (willis, 2012). notable soft-sediment deformation, gasand fluid-escape features including domes, pockmarks, craters, salses, sediment-filled craters, mud and sand volcanoes, dike systems, and sub-centimeter gas bubble cavities are recognized at hite (netoff and others, 2010; livingston and others, 2014, 2015; sherrod and others, 2016; miller and others, 2018). these soft-sediment deformation 123 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 structures (ssds) are non-seismic in origin as the region has only experienced two earthquakes since 1850, both under 3.5 magnitude, and are well below the 5.5 magnitude threshold for liquefaction and fluidization (allen, 1986; obermeier, 1996; galli, 2000; anderson and others, 2010; university of utah seismograph stations, 2020). decreasing overlying water pressure and increasing underlying pore water and gas pressures are the primary triggers for the lake powell ssds (netoff and others, 2010; livingston and others, 2014, 2015; sherrod and others, 2016; miller and others, 2018). these prior studies have attributed ch4 production to decaying organic matter in the subsurface and from algal blooms. in particular, macerated plant material in a mm-thick clay-rich, laterally extensive layer has been identified and is a likely source of organics on which methanogens can feed (sherrod and others, 2016; miller and others, 2018). methanogenic pathways lacustrine greenhouse gases can be produced through various mechanisms. the following processes, salt lake city lake powell field work location near hite marina. utah escalante river g re en r iv er colo ra do r ive r san juan river dirty devil river boat ramp (270 m e to w) volcanoes sampled colorado river n figure 1. sample locations along the lake powell delta, near hite, utah, during low lake level in may 2016. sampled mud volcanoes are denoted with white x’s. lake powell reservoir is located in southeast utah along the colorado river and was created by the construction of glen canyon dam near page, arizona (not shown here). source of aerial photograph is from u.s. department of agriculure (usda)-farm service agency (fsa)-aerial photography field office (apfo)-national agriculture imagery program (naip). 124 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 hydrogenotrophic production and acetoclastic production, are the focus of this study as they are most relevant to the lake powell delta system. these two mechanisms are mediated by the amount of substrates and hydrogen available to the methanogens as well as the amount of sulfate-reducing bacteria present. in this study, we use the ratios of carbon (12c versus 13c) and hydrogen (1h versus 2h—also known as deuterium, d) measured in mud volcano ch4 to interpret the methanogenic processes responsible for the gas ebullition. further details regarding the isotopic characterization can be found in appendix a, but provided here are general descriptions of methanogenic and thermogenic processes sourced from whiticar and others (1986) and whiticar (1999). the first process described here, hydrogenotrophic production, is characterized by the following reaction: co2 + 8 h+ + 8e→ ch4 + 2h2o it is the most predominant process of biogenic gas production and the main source of ch4 in marine/saline settings. however, it may occur in freshwater settings when acetate sources are exhausted, and methanogens require a new substrate. hydrogenotrophic production is often the secondary means of microbial ch4 generation in freshwater environments, but will predominate when acetate pools, such as those necessary for certain acetoclastic formation, are exhausted. at this point, the microorganisms switch to reducing the bicarbonate with hydrogen. the second process described is acetoclastic production. upon the breakdown of organic matter, acetate (ch3cooh) is generated and subsequently converted to ch4 in the respiration processes of microorganisms (whiticar and others, 1986): ch3cooh → ch4 + co2 this is the dominant means of biogenic gas production in freshwater environments (whiticar and others, 1986). the carbon dioxide (co2) produced through this fermentation can subsequently serve as a reactant in hydrogenotrophic production (above) when the acetate source is depleted (whiticar, 1999). sulfate-reducing bacteria will (chemically) reduce the acetate otherwise used in fermentation with a greater energy yield, and therefore can limit the amount of fermentation and subsequently the amount of hydrogenotrophic production. in sulfate-rich marine settings, sulfate-reducing bacteria out-compete methanogens for acetate, mitigating acetate fermentation (chanton and others, 2005). therefore, acetate fermentation tends to be more characteristic of the freshwater rhizosphere than marine. finally, thermogenic ch4 occurs when organic matter is broken down by elevated temperatures (> 100°c) and pressures. although lake powell is located within the kaiparowits basin, which has been assessed to contain gas (national assessment of oil and gas, 2012), we will 2014 2015 2016 sampling 1100 1105 1095 1090 1085 lake powell hydrograph: daily measurements lake powell hydrograph: all time water levels 2014-2016 1963 until jan. 2017 1100 1090 1120 1110 1080 1070 1060 1050 1040 1130 e le va ti o n ( m e te rs a b o ve s e a l e ve l) e le va tio n ( m e te rs a b o ve s e a l e ve l) month measured date measured oct. nov. dec. jan. feb. mar. apr. may. jun. jul. aug. sep. 19 65 19 70 19 75 19 80 19 85 19 90 19 95 20 00 20 05 20 10 20 15 figure 2. lake powell historical water levels from 1963 (inception) to 2017 along with daily water level data during the three years of sampling. sampling events are noted with circular symbols (u.s. bureau of reclamation, 2017). 125 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 discuss why this is an unlikely mechanism for gas generation along the delta. materials and methods gas collection samples were collected during the field seasons of july 2014 and 2015, and in may 2016. the 2014 and 2015 samples were collected during lake level highs for each season (between 1100 and 1102 m above sea level) whereas the 2016 samples were collected during lake level lows (about 1095 m above sea level, figure 2). the majority of samples reported here were collected in 2016 from 25 vents (figure 3). fifty of the samples collected in 2016 were analyzed via gas chromatography (gc) for bulk composition, and 11 samples with elevated percent volumes of ch4 were selected for isotope ratio mass spectrometry (irms) of carbon and hydrogen isotope content of the ch4. gas samples were collected by filling a 20-ml headspace vial (restek) with liquid from within a mud volcano or the colorado river (depending on the sampling site) then inverted for sampling. a small plastic funnel was immersed in the sampling site with the stem inserted into the mouth of the headspace vial. gas bubbles were directed into the headspace vial using the funnel until the vial was approximately 4/5 full of gas (1/5 lake water). the vial was capped under water with a ptfe/ silicone septum lined cap (restek), sealed with parafilm and maintained in an upside-down position until analysis with the 1/5 water content preventing gas escape. at least 20 volcanoes were sampled once on a single day, whereas three volcanoes were sampled over a two-day period, and six volcanoes were sampled over a three-day period. samples for the 2016 season were refrigerated until september, when chromatography tests were completed. remaining gas from the 2016 season continued to be refrigerated until april of 2017 when isotopic analyses were completed. the authors did not conduct tests to determine whether biological activity altered relative gas compositions during storage. gas chromatography gas standards and samples collected in 2014 and 2015 were analyzed using a hewlett-packard 5890 gas chromatograph equipped with a packed, 2.4-m-long by 0.3 cm (8-ft-long by 1/8 in) o.d., 80/100 mesh poropak q column and a thermal conductivity detector. gas mixtures were prepared in 20-ml headspace vials over water to mimic the conditions of the samples. a gas-tight syringe was used to transfer aliquots of gas to water-filled, inverted 20-ml headspace vials leaving 4 ml of water remaining in the vials. vials were capped underwater and remained upside-down until analysis. gas standards and samples from 2016 were analyzed using an agilent 7890 gas chromatograph equipped with g1888 automated headspace sampler (agilent technologies). a 200°c injector operating at a 20:1 split ratio was connected to a 30 mm by 0.53 mm carboxen 1006 plot column (supelco) to separate the gas components. thermal conductivity and flame ionization detectors were used in series to quantify and confirm chromatographic peak identities (see appendix b for headspace sampler and chromatograph operating conditions). isotope ratio mass spectrometry isotopic compositions of carbon and hydrogen in ch4 can be used to identify the processes behind the ch4 generation (whiticar and others, 1986). details on the theory behind carbon to hydrogen isotopic ratios can be found in appendix a. eleven samples from 2016 were favorably selected for irms analyses if they had relatively higher quantities of ch4 (as detected with the gas chromatography) and if the samples were in a set of multiples taken from the same volcano (appendix c). for irms, samples were separated and analyzed using an agilent gc combustion unit (either hp 6890 or hp 6890/7890 gas chromatography) joined with a mass spectrometer (either to thermofinnigan delta plus advantage or thermo scientific delta v plus) in continuous flow mode. peak detection and quantification were completed in finnigan’s isodat software. hydrocarbon components were isolated in the gc unit and were introduced into a combustion furnace to produce co2 which was sent to the mass spectrometer for isotopic analyses of 13c. liquid nitrogen was used to remove air and enrich concentrations of hydrocarbons. for the 126 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 deuterium analysis, gas was channeled through a pyrolysis furnace to permute ch4 to h2 and carbon, upon which the h2 entered the mass spectrometer. each sequence began with reference gases, and 10% of the analyses were check standards. analytical results gas chromatography all gc values are noted in percent of volume of specific gas to total sample volume when denoted with “v/v” unless otherwise specified. the average percent volume of ch4 for each of the three years, 2014, 2015, and 2016, is 81.47% v/v with a ± 9.29% v/v standard deviation, 32.40 ± 15.31% v/v, and 74.51 ± 14.08% v/v, respectively (figure 4, tables c1 to c3 in appendix c). the average ch4 composition of the 50 gas samples collected in 2016 is approximately 7% v/v lower than the average concentration of ch4 in gas samples previously collected from the marina during the 2014 field season (livingston and others, 2014) and is about 42% a b dc figure 3. field photographs during may 2016. (a) salse near the edge of lake powell with high effusive rates disrupting the water surface. individual is 1.7 m tall. (b) mud volcano with gas effusion. the individual is 1.7 m tall. (c) salse with slow effusing gas emission. the card (bottom left) is 15 cm long. (d) field scientist (1.75 m tall in prone position) sampling a salse. note the shore of the lake powell in the background. 127 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 v/v greater than the average ch4 collected in 2015. although sample sizes (n) vary from year to year, the following data sets convey the variation in gas content between samples between and from the same field seasons. for example, although at 81.47% v/v, the 2014 sampling year had the greatest ch4 on average, the 2016 sampling year includes ch4 compositions ranging from 25.31% v/v to 93.34% v/v. overall, the 2015 sampling year had the least amount of ch4 on average, and also yielded the lowest minimum and maximum concentrations of ch4 (0.00% v/v minimum and 45.50% v/v maximum). for each sampling year, of the three gases tested, co2 yields the lowest percent content on average, and for each year, when compared to ch4 and air (unseparated nitrogen [n2] and oxygen [o2]), co2 also yields the lowest minimum and maximum percent content (tables c2 and c3 in appendix c; figure 4). of the 2016 data, chromatographic analyses yielded an average concentration of 74.51 ± 14.08% v/v ch4, 2.82 ± 3.76% v/v co2, and 22.67 ± 14.28% v/v air (tables c1 and c3 in appendix c). the ch4, co2, and air concentrations ranged from 25.31 to 93.34% v/v, 0.00 to 23.58% v/v, and 5.28 to 74.69% v/v, respectively. four volcanoes (16-1, 16-3, 16-5, 16-10) were sampled over the course of two days, whereas six volcanoes (16-7, 16-12, 16-17, 16-20, 16-25, 16-27) were sampled over a three-day timespan (figure 5). for the following fluctuation calculations, duplicates taken from the same volcano in the same day were averaged to a single measurement for that day (tables c3 and c4 in appendix c; figure 5). for example, all four ch4 measurements collected at volcano 16-20 on the third day (samples 1620c1 to 16-20c3, and 16-20c5) were averaged to represent a single measurement at volcano 16-20 on day three. daily fluctuations were calculated using the averaged measurements. in 2016, there was a mean increase of 6.08% v/v in ch4 from the first to second day and a 24.68% v/v decrease from the second to third day while the co2 content showed a 0.89% v/v increase between the first two days of sampling and a 0.5 %v/v decrease from the second to third day. the average variation from day to day was a 5.46% v/v decrease in ch4 and a 0.37% v/v increase in co2 (table c4 in appendix c). geographically, there is a cluster of eight volcanoes, a single volcano to the north (16-1), and a single volcano to the south (16-10). changes in relative ch4 concentration range from extremely low variation of only 2% v/v increases (volcano 16-17), to great variations of up to 38% v/v increases (volcano 16-5) and 66% v/v decreases (volcano 16-7) across multiple days. several volcanoes within the southern end of the cluster (volcanoes 16-3, 16-5, 16-7, 16-20, 16-27) exhibited increases 2014 n=3 2015 n=21 2016 n=50 23% 3% 75% 67%<1% 32% 16% 3% ch4 co 2 air (n + o )2 2 82% all values are in % v/v figure 4. average relative gas concentrations and sample sizes during the 2014–2016 sampling seasons. in general, the relative ch4 content is high in july 2014 at 82% v/v and in may 2016 at 75% v/v and is lower at 32% v/v in july 2015. relative carbon dioxide content remains minimal ranging between less than 1% v/v to 3% v/v between the three years, and the resulting relative concentration of air ranges from 16% v/v in july 2014 to 67% v/v in july 2015. 128 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 in ch4 from day one to day two while 16-12 and 16-7 had steady ch4 fluxes, and only 16-25 observed a decrease. two volcanoes, 16-7 and 16-12, are proximal to one another and both exhibited decreases in ch4 from 80% v/v or more down to less than 40% v/v between the second and third day. volcano 16-20 also shows a decrease from day two to three, but not as severe (about a 35% v/v fall). vent 16-10 to the south exhibits a slight increase from day one to day two while vent 16-1 in the north shows the opposite trend. isotope ratio mass spectrometry all irms results are detailed in table d1 in appendix d. when plotted on a carbon-deuterium (cd) ch4 source discrimination diagram (figure 6; whiticar, 1999), δ13c and δd ch4 signatures of all but two samples lie within the ranges characteristic of bacterially produced ch4 (regions 1 and 2 in figure 6) (>-100 to about -45 δ13c‰ pdb, and about -400 to -150 δ13d‰ smow). this excludes the possibilities of geothermal or hydrothermal (region 5), abiogenic or mantle (region 6), or artificial (region 7), production of these gases. discussion gas chromatography compositions flux measurements are commonly used to assess ch4 and co2 emissions with production mechanisms. although gas fluxes were not collected from the lake powell gas seeps, relative magnitudes of ch4, co2, and air should be considered during future flux measurements from vents along the delta near hite. for this study, temporal changes in relative lacustrine ch4 content are discussed across a short-term (within a threeday time frame) and long-term period (beyond a threeday time frame) below. sampling of the following would be useful in understanding controls on temporal correlations with methanogenesis in the lake powell delta: (1) seasonal flux sampling throughout the year and over a longer period of time, (2) soil and water temperatures, (3) soil and root redox potentials, and (4) identification 1166--2255 1166--2277 1166--2200 1166--1177 1166--1122 1166--77 1166--551166--33 1166--1100 400 m 16-1 ch4 co 2 air (n + o )2 2sampling days in white (1,2,3) 16-1 16-25 16-271166--220016-171166--11221166--771166--551166--33 1166--1100 1 1 1 1 11 1 1 1 12 2 2 2 3 3 3 3 3 322 2 2 2 2 vent sampled c o m p o s iti o n ( % v /v ) composition variation during 2–3 day sampling period, 2016 colorado river figure 5. (left) graph of relative gas concentrations of mud volcanoes sampled over multiple days in may 2016. concentrations are in percent volume gas to volume of sample (% v/v), assuming 100% v/v of the gas was detected during gc analyses. (right) locations of the vent sources sampled in may 2016. aerial photograph was taken june 2014. source of the aerial photograph is from the usda-fsa-afpo-naip. 129 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 -450 -400 -350 -300 -250 -200 -150 -100 -50 -100 -80 -60 -40 -20 0 δd methane (‰, smow) 1 3 δ c m e th a n e ( ‰ , p d b ) predicted methane oxidation shift as applied to irms samples samples reported in this study shift due to substrate depletion shifts in isotopic variation due to secondary effects 1 2 3 4 5 atmospheric 6 7 1) bacterial: hydrogenotrophic (carbonate reduction) 6) abiogenic or mantle 7) artificial 3) bacterial: mixed 4) thermogenic 5) geothermal or hydrothermal crystalline 2) bacterial: acetoclastic (methyl type fermentation) figure 6. δ13c versus δd diagram used for classification of natural gas (adapted from whiticar, 1999). higher values of δ13c and δd will plot closer to zero than lower values. the isotopic signatures follow more closely the oxidation trend as emphasized with the single-headed arrow and the region outlined with a dashed border. 130 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 and quantification of vegetation and organic sources among the sampled vents. short-term changes in relative methane content short-term, specifically diurnal fluxes in ch4 ebullition have been attributed to acute water depth fluctuations and water circulation, soil redox potentials, and vegetation. these variables are explored in context of the ten mud volcanoes sampled for relative ch4 content over multiple days in 2016. in the instance of water depth fluctuation, sebacher and others (1986) found an increase in methanogenic ch4 fluxes of about 300 mg m-2 d-1 with increasing water depth of about 45 cm in alaskan bogs, fens, and marshes. among other variables including water temperature and permafrost depth, water level held the strongest correlation to fluxes in their study. moore and roulet (1993) synthesized aerobic and anaerobic peat columns in the laboratory using bog, fen, and swamp soils. they observed that ch4 fluxes increased with initially falling water levels (0 to 20 cm depth) and then a decrease in fluxes upon further falling water levels (20 to 50 cm depth). the authors concluded that there is a strong but complex relationship between water table fluctuations and ch4 outgassing. similarly to moore and roulet (1993), if there is a relationship between the lake powell delta water table level and relative ch4 content variations from day to day, then it may be complex and vary to some degree from volcano to volcano. during the most recent sampling period (2016), water levels increased daily between 17 and 19 cm (u.s. bureau of reclamation, 2017). yet upon steady water level increase, relative ch4 content experienced an average 6.08% v/v increase from sampling day one to day two, and on average a 24.68% v/v decrease from day two to three (table c4 in appendix c). variations in water levels could impact certain gas fluxes in volcanoes more than others. changes in water levels will impact a greater volume of pores in spatially larger volcanoes and impart a more extensive impact on gas fluxes. additionally, volcanoes that experience more extreme or frequent episodes of wetting and drying may exhibit different patterns of gas production. therefore in order to better understand how water levels are affecting day-to-day ch4 release from volcanoes along lake powell, it would be beneficial to measure not only the ch4 flux, but also overall water levels and water levels local to each gas seep. water circulation has also been shown to impact short-term ch4 production in settings similar to the lake powell delta. effects of water circulation were observed when podgrajsek and others (2014) found that the greatest ch4 generation of a freshwater lake (38 km2 area and 1.3 average depth) occurred in the morning (average of about 10 nmol m-2s-1 and outliers of over 100 nmol m-2s-1) and lowest in the evenings (average of about 5 nmol m-2s-1 and outliers of less than 30 nmol m-2s-1). they consider that water-side convection is one mechanism of transporting ch4 from various depths in the water column to the surface. in measuring convection, they installed a 6-m-high monitoring tower, which may not be feasible along the clay and mud-rich lake powell delta. to investigate the impact of water circulation on short-term changes in relative ch4 concentrations, an alternative approach to measuring water circulation measurements might be necessary. duan and others (2005) found pronounced variations in ch4 ebullition fluxes correlated with the predominant vegetation (phragmites australis and potamogeton pectinatus) but no direct correlation with mean water level (about 46 cm depth versus about 83 cm depth) in wuliangsu lake of inner mongolia. however, they noted that water level will determine the type of vegetation which thrives and indirectly ch4 generation as well. their study also showed that increased diurnal ch4 fluxes were correlated with increasing photosynthetically active radiation (par) in reeds and more so than in pondweeds. coupling par measurements with surrounding vegetation and daily flux measurements of the lake powell volcanoes would be useful in understanding the effects of low versus high photosynthetic activity along the delta on ch4 generation. prior studies show that redox potentials of plant roots and soils have also been correlated with daily changes in ch4 production. chen and others (2010) found ch4 fluxes in a ponded system of up to 15 mg ch4 m-2 hr-1 with flux increases of about 10 mg ch4 m-2 hr-1 in a six-hour period. these diurnal variations were significantly correlated with paralleled soil redox 131 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 potentials taken at 5 and 10 cm depth. fluxes did not correlate well with changes in water and soil temperatures at these depths however, and similar trends (strong correlation with redox potential but not soil temperatures) were also identified in bansal and others (2018). flux and redox potential measurements at each volcano could also be useful in determining to what extent these influence short term ch4 generation. long-term fluctuations in methane content from 2014 to 2016 the influencing factors on long-term changes in methanogenic production discussed here are temperature and precipitation as previous studies show these factors vary between seasons and impact methanogenesis in similar freshwater systems. for example, pugh and others (2018) showed that average monthly ch4 fluxes were strongly correlated with air temperatures. in their study, ch4 fluxes increased from near-zero fluxes in winter and up to 39 mg c m-2 day-1 in summer months. schulz and conrad (1996) demonstrated that after including a chloroform inhibitor, a temperature increase of 16°c resulted in ten times more methanogenesis over a six-day-long incubation period. with a 25 to 32 day incubation and a sampling time frame of less than two weeks, schulz and others (1997) showed that ch4 production rates peaked around 35°c (in a comparison to temperatures ranging from 0 to 50°c). chanton and others (2005) showed that elevated temperatures in the summer result in sulfate depletion and more availability of acetate to methanogens. alternatively, rask and others (2002) demonstrated with 300 days’ worth of data, that temperature had variable influence on ch4 fluctuations depending on the location (flark, string, deep bay or shallow bay) in their freshwater system. although we did not sample for temperature or precipitation variables, we relate relative ch4 concentrations to regional temperature and precipitation and discuss below how these would impact gas ebullition along the lake powell delta. the average temperatures of july 2014 and 2015 were similar (23.27°c and 21.69°c, respectively), while the average temperature of may 2016 was lower at 12.5°c (u.s. climate data, 2020). if temperature is a predominant predictor of ch4 ebullition along the lake powell delta, one might suspect the july 2014 and 2015 ch4 relative concentrations to be more similar and deviate from the 2016 data; however, this trend is not observed in the data. future work measuring gas fluxes, air temperature, and temperature of water pooled in each volcano throughout longer term sampling could allow us to constrain the correlation between heat energy and ch4 production in this system. precipitation and wetting may be one explanation for the variation in ch4 between sampling seasons. estop-aragones and others (2016) conducted a year-long study on 15 bogs in europe focusing on an initial wet period, a prolonged dry period (when the water table decreased over 35 cm), and a rewetting episode (when the water table increased 30 cm). they observed a peak in ch4 fluxes during the early dry period (520.7 mg c-ch4 m-2d-1) yet continued drying decreased fluxes through time (down to 14.5 mg c-ch4 m-2d-1). upon rewetting, ch4 fluxes increased once more, but not to the point of early dry period fluxes. similar trends (sharp peaks at the beginning of drought conditions and slow recovery of ch4 emissions) were found in gully-mires over a sixyear period (hughes and others, 1999) and a 10-week period (dowrick and others, 2006). drought conditions (lasting two weeks) in the auchencorth moss peatland of scotland also resulted in delayed increase in ch4 flux and subsequent dramatic decrease without rebounding to original fluxes (dinsmore and others, 2009). the lake powell delta experienced slightly less precipitation (on average 3.48 and 2.16 cm precipitation, respectively) and elevated ch4 concentrations (greater than 70% v/v) in both the july 2014 and may 2016 sampling months while the month of july 2015 experienced slightly greater precipitation (5.23 cm) and experienced the lowest average ch4 concentrations (less than 35% v/v). lake powell temperature and precipitation data were sourced from usclimate.data.com. isotope ratio mass spectrometry compositions in this study, we use the ratios of carbon (12c versus 13c) and hydrogen (1h versus 2h—also known as deuterium, d) measured in mud volcano ch4 to interpret the methanogenic processes responsible for the gas ebullition. upon plotting ‰ δ13c and ‰ δd against one 132 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 another, nine of the eleven ch4 samples lie within the “mixed” methanogenic region (region 3 of figure 6). region 1 is denoted with signatures of bacterial hydrogenotrophic production (carbonate reduction) and region 2 is denoted with bacterial acetoclastic production (methyl-type fermentation) signatures (whiticar and others, 1986; whiticar, 1999). the isotopic signatures of this study fall relatively well within the freshwater sediment range (-65 to -50‰ δ13c and -400 to -250‰ δd) described in whiticar and others [1986]). the δ δd/δ δ13c value (the slope of the line when plotting δd versus δ13c) of our samples is 4.81, r = 0.8344, which lies within the range (2.5 to 13.5 δ δd/δ δ13c) associated with methanotrophic activity in chanton and others (2005). in addition to the physical water datum discussed above, water chemistry such as sulfate, acetate, and organic content measurements would offer additional insight into gas generation within the lake powell delta mud volcanoes. the impacts of these chemical variables are discussed in more detail below in context of specific methanogenic pathways. isotopic signatures within the “mixed” region of the δ13c and δd plot may result from one or both of two scenarios. scenario one is that separate pools of gas (some derived from acetoclastic production and others from hydrogenotrophic production) are initially generated in isolation and are later transported and converge during migration. scenario two is that the ch4 source itself is shifting either spatially or temporally. for example, ch4 of isolated sources may have been mixed due to migration or diffusion of gas (whiticar, 1999). decreasing surface water levels of lake powell contribute to depressurizing of pore fluids and gases, allowing trapped ch4 from separate subsurface sources (with varying initial substrates and isotopic signatures) to migrate upwards through the sediment as gas bubbles. this proposed mechanism would parallel previously reported evidence of gas release and upward migration by pressurization (netoff and others, 2010; livingston and others, 2014, 2015; sherrod and others, 2016; miller and others, 2018). in this instance, the isotopic composition of the original substrate may shift the signatures of the produced ch4. for example, if a precursor substrate had both 13ch3ooh and 12ch3ooh acetate, the substrate will more easily diffuse the lighter compound with lesser mass, than the former acetic acid molecule. this will result in a greater amount of bacterial 12ch4 generated and very little bacterial 13ch4 created. as 13c is left behind in the original substrate, the next generation of bacterial ch4 will be more enriched in 13c than the first, and so on (whiticar, 1999; chanton and others, 2005). this transition would result in differences in the amount of δ13c generated (whiticar, 1999). additionally, a change in substrate composition and methanogenesis is often observed with increasing depth. for example, hornibrook and others (1997) showed that acetate fermentation processes predominated in shallow organic-rich soils, while in deeper (greater than 45 cm depth), older, less reactive peat, co2 reduction predominated. similar observations have been previously reported in the literature (hornibrook and others, 1997, 2000a, 2000b; chasar and others, 2000a, 2000b). this transition will result in decreasing δ13c (of ch4) signatures with depth similar to the decrease in the 11 samples presented here. quality of the substrate throughout the delta could impact the scarcity of nutrients and mechanism of methanogenesis. however, should these be the only processes taking place, the carbon isotopic signatures alone would exhibit a wide range and result in a linear shift (figure 6: “shift due to substrate depletion”) (whiticar, 1999). these two processes alone do not account for the wider range in δd. increasing δ13c and δd of isotopic signatures, which results in a “sympathetic” trend (linear and trending from lesser to greater signatures of both isotopes), is often the result of oxidizing methanotroph bacteria (chanton and others, 2005). this aerobic oxidation often occurs during bacterial ch4 consumption in freshwater settings at the anoxic/oxic interface (whiticar, 1999) which lies in the top several centimeters of lake sediments. similar oxidation and subsequent δd/δ13c trends have been observed in landfill soils, wetlands, and laboratories incubation studies (chanton and others, 2005). thermogenic sources tend to have greater δ13c signatures than biogenic sources, and will have further increased δ13c signatures with greater maturity (whiticar, 1999), supporting the conclusion that the lake powell delta gas seeps are not related to thermogenic activity. 133 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 conclusions • this is the first reporting of ch4, co2, and air (n2+ o2) compositions as well as ch4 isotope signatures of samples collected over a multiple day and multiple year period at lake powell, hite, utah. average relative concentrations of ch4, co2, and air released from the lake powell gas volcanoes in the spring of 2016 ranged from 74.51 ± 14.08% v/v, 2.82 ± 3.76% v/v, and 22.67 ± 14.28% v/v, and ranged from 25.36 to 93.34% v/v, 0.00 to 23.58% v/v, and 5.28 to 74.69% v/v. • gas chromatography data show changes in relative ch4 concentrations ranging from extremely low variations of only 2% v/v increases, to greater variations of up to 38% v/v increases and 66% v/v decreases across multiple days. acute water depth fluctuations and water circulation, soil redox potentials, and vegetation have been shown to result in short-term changes in ch4 ebullition rates in the literature, but more work must be done to understand the extent to which these factors influence ch4 production along the lake powell delta. • carbon and hydrogen isotopes from 11 samples with the greatest concentrations of ch4 were analyzed using irms. the δ13c and δd signatures of these samples support that the ch4 ebullition along the lake powell delta is biogenic and may source from a mixture of acetoclastic production and hydrogenotrophic production. this mixture may be the result of two possible mixing mechanisms. first, there may exist isolated ch4 generation (of either predominantly acetoclastic production or predominantly hydrogenotrophic production), subsequent upward migration during pore depressurization, and finally mixing. alternatively, original ch4 sources are shifting from fermentation to reduction, resulting in a mixed isotopic signature. isotopic signatures may potentially result from original substrates becoming depleted in lighter isotopes (12c ), and heavier isotopes (13c) are subsequently used in bacterial respiration as well as ch4 oxidation. additionally, if methanogenesis occurs in an organic-rich zone and shifts to a depleted zone, the process may shift from fermentation to reduction. • future field work should include measuring ch4 concentrations through time to calculate and relate fluxes to literature values. additional biological, hydrological, and chemical measurements within and around gas-producing volcanoes are necessary to further constrain impacts on biological ch4 production along the delta. additional data must be gleaned to constrain long-term (seasonal and annual) changes in ch4 ebullition and potential influences. two possible controls on ch4 production are temperature and wetting of the delta subsurface. measurements of soil and water temperature, observations of water table fluctuations, and monitoring of wetting within and surrounding the mud volcanoes are necessary to better understand controls on ch4 production. acknowledgments the authors greatly appreciate the aid of john spence, “chief scientist” of the national park service at the glen canyon and the encouragement and guidance of utah state paleontologist, jim kirkland. we would also like to thank william parry for his helpful review and doug sprinkel for his thorough and timely editing. this work was supported by the kutztown university undergraduate research committee and the pennsylvania state system of higher education professional development committee. all field work was completed by kutztown university affiliates. there exist no conflicts of interest among any author related to this research, and all reported data can be found in the appendices and has been submitted to the mendeley data repository (https://data.mendeley.com/datasets/ yv9s92r5rh/1). references allen, j.r.l., 1986, earthquake magnitude-frequency, epicentral distance and soft-sediment deformation in sedimentary basins: sedimentary geology, v. 46, p. 67–75, 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chen, z., marquis, m., averyt, k.b., tignor, m., and miller, h.l., editors, climate change 2007— the physical science basis: contribution of working group i to the fourth assessment report of the intergovernmental panel on climate change, p. 129–234, doi:10.1103/physrevb.77.220407. galli, p., 2000, new empirical relationships between magnitude and distance for liquefaction: tectonophysics, v. 324, p. 169– 187, doi:10.1016/s0040-1951(00)00118-9. harrison, j.a., deemer, b.r., birchfield, m.k., and o’malley, m.t., 2017, reservoir water-level drawdowns accelerate and amplify methane emission: environmental science and technology, v. 51, no. 3, p. 1267–1277, doi:10.1021/acs.est.6b03185. hornibrook, e.r.c., longstaffe, f.j., and fyfe, w.s., 1997, spatial distribution wetland of microbial methane production pathways in temperate soils—stable carbon and hydrogen isotope evidence zone: geochimica et cosmochimica acta, v. 61, no. 4, p. 745–753, doi: 0.1016/s0016-7037(96)00368-7. hornibrook, e.r.c., longstaffe, f.j., and fyfe, w.s., 2000a, factors 135 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 influencing stable isotope ratios in ch4 and co2 within subenvironments of freshwater wetlands—implications for δ-signatures of emissions: isotopes in environmental and health studies, v. 36, no. 2., p. 151–176, doi:10.1080/10256010008032940. hornibrook, e.r.c., longstaffe, j.j., and fyfe, w.s., 2000b, evolution of stable carbon isotope compositions for methane and carbon dioxide in freshwater wetlands and other anaerobic environments: geochimica et cosmochimica acta, v. 64, no. 6, p. 1013–1027, doi: 10.1016/s0016-7037(99)00321-x. hovland, m., hill, a., and stokes, d., 1997, the structure and geomorphology of the dashgil mud volcano, azerbaijan: geomorphology, v. 21, p. 1–15, 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international journal of earth sciences, v. 99 (supplemental 1), p. 227–240, doi:10.1007/ s00531-009-0487-4. livingston, k., bogner, e., ireland, s., simpson, e., betts, t., and laub, e., 2014, the geomorphic evolution of shallow-sourced methane produced mud volcanoes—lake powell, hite utah [abs.]: geological society of america abstracts with programs, v. 46, no. 6, p. 766–767. livingston, k., bogner, e., simpson, e.l., malenda, m., sherrod, l.a., betts, t.a., and laub, e., 2015, the proposed evolution of shallow-sourced methane mud volcano geomorphology lake powell, hite utah [abs.]: geological society of america abstracts with programs, v. 47, no. 7, p. 588. maeck, a., hofmann, h., and lorke, a., 2014, pumping methane out of aquatic sediments—ebullition forcing mechanisms in an impounded river: biogeosciences, v. 11, no. 11, p. 2925– 2938, doi:10.5194/bg-11-2925-2014. miller, k., simpson, e.l., sherrod, l., wizevich, m.c., malenda, m., morgano, k., richardson, a., livingston, k., and bogner, e., 2018, gas bubble cavities in deltaic muds, lake powell delta, glen canyon national recreation area, hite, utah: marine and petroleum geology, v. 92, no. 4, p. 904–912, doi:10.1016/j. marpetgeo.2018.03.032. moore, t.r., and roulet, n.t., 1993, methane flux—water table relations in northern wetlands: geophysical research letters, v. 20, no. 7, p. 587–590, https://doi.org/10.1029/93gl00208. national assessment of oil and gas, 2012, assessment of undiscovered oil and gas resources in the paradox basin province, utah, colorado, new mexico, and arizona, 2011: u.s. geological survey fact sheet 2012–3031, 1–4 p. netoff, d., baldwin, c.t., and dohrenwend, j., 2010, non-seismogenic origin of fluid/gas escape structures and lateral spreads on the recently exposed hite delta, lake powell, utah, in carney, s.m., tabet, d.e., and johnson, c.l., editors, geology of south-central utah: utah geological association publication 39, p. 61–92. obermeier, s.f., 1996, use of liquefaction-induced features for paleoseismic analysis—an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo-earthquakes: engineering geology, v. 44, no. 1–4, p. 1–76, doi:10.1016/s0013-7952(96)00040-3. podgrajsek, e., sahlee, e., and tugersson, a., 2014, diurnal cycle of lake methane flux: journal of geophysical research biogeosciences, v. 119, no. 3, p. 236–248, doi:10.1002/2013jg002327. pratson, l., hughes-clarke, j., anderson, m., gerber, t., twichell, d., ferrari, r., nittrouer, c., beaudoin, j., granet, j., and crockett, j., 2008, timing and patterns of basin infilling as documented in lake powell during a drought: geology, v. 36, no. 11, p. 843–846, doi:10.1130/g24733a.1. pugh, c.a., reed, d.e., desai, a.r., and sulman, b.n., 2018, wetland flux controls—how does interacting water table levels and temperature influence carbon dioxide and methane fluxes in northern wisconsin?: biogeochemistry, v. 137, no. 1, p. 15–25, doi:10.1007/s10533-017-0414-x. rask, h., schoenau, j., and anderson, d., 2002, factors influencing methane flux from a boreal forest wetland in saskatchewan, canada: soil biology and biochemistry, v. 34, no. 4, p. 435– 443, https://doi.org/10.1016/s0038-0717(01)00197-3. schulz, s., and conrad, r., 1996, influence of temperature on pathways to methane production in the permanently cold profundal sediment of lake constance: fems microbiology ecology, v. 20, no. 1, p. 1–14, https://doi.org/10.1111/j.1574-6941.1996. tb00299.x. schulz, s., matsuyama, h., and conrad, r., 1997, temperature dependence of methane production from different precursors in a profundal sediment (lake constance): fems microbiology ecology, v. 22, no. 3, p. 207–213, doi:10.1016/s01686496(96)00091-8. 136 methane emissions from muds during low water-level stages of lake powell, southern utah, usa malenda, m., betts, t.a., simpson, w.s., wizevich, m.c., simpson, e., and sherrod, l. geology of the intermountain west 2020 volume 7 sebacher, d.i., harriss, r.c., bartlett, k.b., sebacher, s.m., and grice, s.s., 1986, atmospheric methane sources—alaskan tundra bogs, and alpine fen, and a subarctic boreal marsh: chemical and physical meteorology, v. 38, p. 1–10, doi:10.3402/tellusb.v38i1.15059. sherrod, l., simpson, e.l., higgins, r., miller, k., morgano, k., snyder, e., and vales, d., 2016, subsurface structure of water–gas escape features revealed by ground-penetrating radar and electrical resistivity tomography, glen canyon national recreation area, lake powell delta, utah, usa: sedimentary geology, v. 344, p. 160–174, doi:10.1016/j.sedgeo.2016.02.005. st. louis, v., kelly, c., duchemin, é., rudd, j., and rosenberg, d., 2000, reservoir surfaces as sources of greenhouse gases to the atmosphere—a global estimate: bioscience, v. 50, no. 9, p. 766–775, doi:10.1641/0006-3568(2000)050[0766:rsasog]2.0. co;2. tinivella, u., and giustiniani, m., 2012, an overview of mud volcanoes associated to gas hydrate system, in nemeth, k., editor, updates in volcanology—new advances in understanding volcanic systems: rijeka, croatia, intech open, p. 225–267, doi:10.5772/3390. u.s. climate data, 2020: https://www.usclimatedata.com/climate/ lake-powell/utah/united-states/usut0284. u.s. bureau of reclamation, 2017, lake powell—daily data: https:// www.usbr.gov/rsvrwater/historicalapp.html. university of utah seismograph stations, 2020, utah’s earthquake threat: https://quake.utah.edu/outreach-education/utahsearthquake-threat. whiticar, m.j., 1999, carbon and hydrogen isotope systematics of bacterial formation of methane: chemical geology, v. 161, p. 291–314. whiticar, m.j., faber, e., and schoell, m., 1986, biogenic methane formation in marine and freshwater environments— co2 reduction vs. acetate fermentation—isotopic evidence: geochimica et cosmochimica acta, v. 50, no. 5, p. 693–709, doi:10.1016/0016-7037(86)90346-7. willis, g.c., 2012, geologic map of the hite crossing–lower dirty devil river area, glen canyon national recreation area, garfield and san juan counties, utah: utah geological survey map 254dm, 12 p., 1 plate, scale 1:62,500, gis data. a-1 appendix a carbon to hydrogen isotope theory isotope ratio mass spectrometry (irms) was used to determine the quantity of 13c and 2h, or deuterium (d), in samples containing the greatest amount of ch4. isotopic measurements as reported in parts per million (‰), are described by the following: 𝛿 = ( 𝑅𝑠𝑎𝑚𝑝𝑙𝑒 𝑅𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 − 1) ∗ 103 where r is the 13c/12c or the 2h/1h ratios relative to the pee dee belemnite (pdb) and the standard mean ocean water (smow) standards, respectively. via plotting 𝛿13c vs 𝛿d of the gaseous samples and comparing these signatures to those of gas samples with known origins, the sources of ch4 can be inferred (figure 6; whiticar, 1999). it is worth mentioning the following: carbon from both bacterial and thermogenic gases has or is involved in biological processes of near-surface carbon cycles (whiticar, 1999). because irms was conducted on only ch4 in the 11 samples, analyses and conclusions regarding fractionation factors (carbon dioxide-methane [co2-ch4], in this case) could not be made. b-1 appendix b gas chromatography sample conditions table b. the sampling and operating conditions used in the agilent-based gas chromatography are listed below. agilent g1888 headspace sample conditions headspace oven temperature: 42oc loop temperature: 110oc transfer line temperature: 110oc gc cycle time: 35 min vial equilibration time: 0 min pressurization time: 0.2 min loop fill time: 0.2 min loop equilibration time: 0.2 min injection time: 0.1 min agilent 7890 operating conditions inlet temperature: 200oc split ratio: 20:1 he carrier gas flow: 3 ml/min column: carboxen plot 30 m x 0.53 mm oven temperature: 35oc for 5 min, 20oc/min to 200oc, hold for 10 min tcd temperature: 230oc tcd ref gas flow: 20 ml/min tcd makeup gas flow: 2 ml/min fid temperature: 230oc fid h2 flow: 30 ml/min fid air flow: 400 ml/min fid makeup gas flow: 3 ml/min tcd = thermal conductivity detector fid = flame ionization detector c-1 appendix c gas chromatography results average gas compositions from all three years; individual compositions of samples collected during each year and compositions from volcanoes sampled over a multiple day period in 2016 are provided. table c1. summary of averaged gas chromatography results from all three years of sampling. all gas contents are reported in percent by volume (% v/v). sampling period sample size known sample locations ch4 standard deviation co2 standard deviation air (n2 + o2) standard deviation july 2014 3 no 81.47 9.29 2.67 0.47 15.60 9.70 july 2015 21 no 32.40 15.31 0.19 0.21 67.37 15.29 may 2016 50 yes 74.51 14.08 2.82 3.76 22.67 14.28 tables c2a and c2b. chromatography results from 2014 and 2015, respectively. all data are reported in percent by volume (% v/v). table c2a: 2014 gas chromatography data (% v/v) table c2b: 2015 gas chromatography data (% v/v) sample # ch4 co2 air (n2 + o2) sample # ch4 co2 air (n2 + o2) 1 91.40 3.20 5.40 1 0.00 0.13 99.90 2 80.00 2.50 16.70 2 13.20 0.65 86.10 3 73.00 2.30 24.70 4 37.80 0.21 62.00 average 81.47 2.67 15.60 5 43.50 0.14 56.40 standard deviation 9.29 0.47 9.70 6 33.10 0.21 66.70 maximum 91.40 3.20 24.70 7 23.10 0.11 76.80 minimum 73.00 2.30 5.40 8 43.50 0.14 56.40 9 25.30 0.98 73.70 c-2 sample # ch4 co2 air (n2 + o2) 10 37.10 0.30 62.60 11 44.60 0.18 55.20 12 45.50 0.12 54.30 13 41.10 0.18 58.70 14 45.10 0.13 54.70 15 45.20 0.20 54.60 16 3.00 0.07 97.00 17 41.40 0.07 58.50 18 32.70 0.18 67.10 19 2.00 0.05 97.90 20 44.20 0.24 55.50 21 39.10 0.10 60.80 22 40.00 0.23 59.80 average 32.40 0.19 67.37 standard deviation 15.31 0.21 15.29 maximum 45.50 0.98 99.90 minimum 0.00 0.05 54.30 c-3 table c3. gas chromatography data from 2016 field season. the “x” in “16-x” corresponds to the volcano of interest, “a to c” indicates which day of the sampling period the gas was collected (with a being day 1, b is day 2, and c is day 3). subsequent values following these letters distinguish duplicate samples from one another. for example, 16-20b1 and 16-20b2 were both taken from vent 16-20 on the second sampling day, while 16-7 was taken from a volcano on the first sampling day, 16-7b was taken from that same volcano on the second day, and 16-7c was taken on the third day. 2016 gas chromatography data (% v/v) volcano sample name ch4 co2 air (n2 + o2) 16-1a 89.68 2.09 8.23 16-1b 73.01 1.63 25.36 16-1 75.76 0.28 23.96 16-3a 74.60 1.50 23.89 16-3b 84.11 1.28 14.60 16-l3 80.45 0.77 18.78 16-4 76.08 1.04 22.88 16-5 54.30 1.99 43.71 16-5b 91.58 2.86 5.56 16-6 74.94 0.72 24.34 16-7 80.46 3.04 16.50 16-7b 90.52 4.20 5.28 16-7c 25.31 0.00 74.69 16-8b 78.98 1.42 19.59 16-9 77.61 0.70 21.70 16-10 84.25 0.00 15.75 16-10b 93.34 0.64 6.02 c-4 volcano sample name ch4 co2 air (n2 + o2) 16-11 78.09 1.17 20.74 16-12 79.54 0.55 19.91 16-12b 79.05 2.16 18.78 16-12c 38.85 0.00 61.15 16-14 79.25 0.88 19.86 16-15 86.06 3.04 10.90 16-16 71.77 0.40 27.83 16-17 82.16 1.52 16.32 16-17b 80.00 2.55 17.44 16-17c 79.69 2.08 18.23 16-18 63.77 1.86 34.38 16-20 73.74 2.04 24.22 16-20b1 83.03 5.27 11.70 16-20b2 90.34 4.04 5.62 16-20b3 89.66 5.04 5.29 16-20c1 42.84 4.07 53.10 16-20c2 65.04 5.17 29.79 16-20c3 46.86 3.95 49.19 16-20c5 58.97 5.40 35.63 16-21 75.02 4.80 20.18 16-22 89.01 5.41 5.58 16-23 66.25 5.17 28.58 c-5 volcano sample name ch4 co2 air (n2 + o2) 16-24 63.55 0.54 35.91 16-25a 91.09 2.37 6.54 16-25b 83.49 3.57 12.93 16-25b-1 75.40 2.71 21.89 16-25c 63.60 13.10 23.30 16-25c1 76.73 2.27 21.00 16-26 76.06 1.31 22.63 16-27 67.23 0.00 32.77 16-27b 79.08 0.77 20.15 16-27c 80.25 0.17 19.58 16-28 64.86 23.58 11.56 average 74.51 2.82 22.67 standard deviation 14.08 3.76 14.28 maximum 93.34 23.58 74.69 minimum 25.31 0.00 5.28 c-6 table c4. temporal fluctuations over the three-day sampling period. duplicate samples were averaged in this calculation. for example, 16-20b1 through 16-20b3 were averaged and considered as one sample of gas from vent 16-20 on day 2. ch4 co2 ch4 co2 ch4 co2 day 1 2 3 max % (v/v) 91.09 3.04 93.34 4.79 80.25 7.68 min % (v/v) 67.23 0.00 73.01 0.64 25.31 0.00 average % (v/v) 77.71 1.51 76.17 2.40 57.95 2.43 average change from prior day % (v/v) 6.08 0.89 -24.68 -0.50 average day to day percent change % (v/v) -5.46 0.37 d-2 appendix d table d1. isotope ratio mass spectrometry (irms) results of eleven 2016 field-season samples with elevated methane. gas chromatography compositions presented below were analyzed in spring 2017 prior to irms characterization. gas chromatography compositions (% v/v) irms volcano sample name ch4 co2 air (n2 + o2) 𝛿13c‰ 𝛿d‰ 16-7b 74 6 20 -71.7 -306.2 16-10 61 4 35 -71.7 -298.8 16-17 60 2 38 -65.5 -281.5 16-12 59 1 40 -66.0 -284.7 16-10b 59 1 40 -68.5 -302.4 16-20b2 57 8 35 -60.7 -254.1 16-22 55 4 40 -67.0 -270.2 16-17b 54 3 43 -64.7 -277.9 16-20b1 53 9 39 -59.3 -247.0 16-3b 53 2 46 -63.1 -261.1 16-7 44 4 52 -63.7 -251.2 average 57.18 4.00 38.91 -65.63 -275.92 standard deviation 7.32 2.68 7.94 3.99 21.05 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 © 2016 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah alan l. titus, jeffrey g. eaton, and joseph sertich a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa post-meeting field trip october 30–november 1, 2016 geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover view looking west over the blues from the upper view point along utah sr 12. the lower 400 m of the upper cretaceous kaiparowits formation is seen from this view as well as the pink and and white cliffs of the paleocene–eocene claron formation. i 2016 president bill loughlin bill@loughlinwater.com 435.649.4005 2016 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2016 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2016 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2016 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2016 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2016-2018 term craig morgan craigmorgan@utah.gov 801.422.3761 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 3 2016 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 229 abstract the late cretaceous succession of southern utah was deposited in an active foreland basin circa 100 to 70 million years ago. thick siliciclastic units represent a variety of marine, coastal, and alluvial plain environments, but are dominantly terrestrial, and also highly fossiliferous. conditions for vertebrate fossil preservation appear to have optimized in alluvial plain settings more distant from the coast, and so in general the locus of good preservation of diverse assemblages shifts eastward through the late cretaceous. the middle and late campanian record of the paunsaugunt and kaiparowits plateau regions is especially good, exhibiting common soft tissue preservation, and comparable with that of the contemporaneous judith river and belly river groups to the north. collectively the cenomanian through campanian strata of southern utah hold one of the most complete single region terrestrial vertebrate fossil records in the world. late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah alan l. titus1, jeffrey g. eaton2, and joseph sertich3 1 bureau of land management, grand staircase-esclanate national monument, kanab, ut 84741; atitus@blm.gov 2 natural history museum of utah, salt lake city, ut 84108; jeaton@weber.edu 3 denver museum of nature & science, denver, co 80205; joe.sertich@dmns.org citation for this article. titus, a.l., eaton, j.g., and sertich, j., 2016, late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah: geology of the intermountain west, v. 3, p. 229–291. © 2016 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the primary purpose of this field trip is to highlight the late cretaceous vertebrate paleontology and stratigraphy of southern utah. this is a daunting task in three days and at best this can only be an overview of what is easily accessible along the road from cedar city to escalante (figure 1). the emphasis of this trip is on the terrestrial faunas and facies (figure 2), although the marine tropic shale and its fauna will also be examined. there are many other road logs available that highlight broader aspects of the geology of the region and these include eaton and others (2001), biek (2014), knudsen and biek (2014), and we have borrowed richly from these. this region has also been recently mapped by biek and others (2015) and we make constant reference to that exhaustive study. vertebrate faunal lists for cretaceous formations and members, organized by plateau, are presented in the appendix. overview of cretaceous stratigraphy and vertebrate paleontology, southwestern utah upper cretaceous strata crop out (figure 2) across an almost continuous 210-km-wide band between the hurricane fault system (west) and the southeast edge of the kaiparowits plateau. scattered outcrops of late cretaceous strata also occur west of the hurricane fault system around the pine valley mountains, gunlock reservoir, and parowan gap. all of the rock units in these exposures were deposited within the western interior www.utahgeology.org 230 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 basin (figure 3) between late albian and maastrichtian time, during the sevier and early laramide phases of the north american cordilleran orogeny (figure 3). as a generalization, the southern utah cretaceous section is mostly terrestrial in the western half, and to the east, mixed marine-terrestrial in the lower half and dominantly terrestrial in the upper half (figure 4). the cretaceous stratigraphy of the kaiparowits plateau, which has become the framework for most of the region, was established by gregory and moore (1931), lawrence (1965), peterson (1969), and eaton (1991). the general stratigraphic section is similar throughout the region, but there are some marked facies changes in formations, mostly trending east-west (figure 4). paleontological investigations of these outcrops were initiated by the powell survey starting in the 1870s. however, during the subsequent 100 years, the region lay largely unnoticed by vertebrate paleontologists, who were content to work in other, more immediately gratifying, and easily accessed regions. this started to change in the 1970s when crews from the university of utah and brigham young university began prospecting the fossil-rich badlands of the late campanian kaiparowits formation for vertebrates with good results (weishampel and jensen, 1979; decourten and russell, 1985). soon after, j. eaton and r. cifelli began long term collaborative investigations on the microvertebrate faunas of the kaiparowits basin (e.g., cifelli and eaton, 1987; cifelli, 1990a, 1990b, 1990c, 1990d; eaton, 1993a, 1993b, 1995), emphasizing mammalian evolution and biostratigraphy. eaton and cifelli were the first researchers to intensively sample the entire late cretaceous terrestrial record for vertebrates, and it was their work that led to recognition of the exceptional continuity and quality of the kaiparowits’ vertebrate fossil record. among other things, the region can claim to yield figure 1. google earth image of area covered by this road log. numbers refer to stops in the road log. mp=markagunt plateau, pp=paunsaugunt plateau. 231 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 diverse terrestrial vertebrate faunas from every stage of the late cretaceous except the maastrichtian. when supplemented by the emerging understanding of the adjacent paunsaugunt and markagunt plateaus, this record becomes truly exceptional, with nearly continuous sampling possible for a 26-million-year time span (ca 100–74 ma) in facies ranging from shallow marine and coastal plain to alluvial fan (figure 4). the establishment of grand staircase-escalante national monument (gsenm) by presidential proclamation on september 18, 1996, led to the need for assessment of condition and significance of all known fossil sites so that a management framework could be built with the latest and most accurate data. toward this end, the monument formed a partnership with the utah geological survey, who initiated field studies in early 1998. one of the results of this work (foster and others, 2001) was the realization that many areas within gsenm with high potential for fossils had never been adequately surveyed. as a direct result, a key management plan decision was formed that required ongoing annual inventory of geological formations with potential to produce significant fossils (gsenm management plan, 2000: pal-1). after the monument management plan was put into practice, the monument-utah geological survey figure 2. map showing cretaceous outcrops in southern utah. also shown are major structural features, landforms, location of measured sections, and type sections for the tropic (t), straight cliffs (sc), wahweap (w), and kaiparowits (k) formations and the type sections for the tibbet canyon (tc), smoky hollow (sh), john henry (jh), and drip tank (dt) members of the straight cliffs formation. abbreviations as follows: gr – gunlock reservoir; pvm – pine valley mountains; hf – hurricane fault; sf – sevier fault; pp – paunsaugunt plateau; pf – paunsaugunt fault; ekm – east kaibab monocline; ecm – echo cliffs monocline; wf – waterpocket fold. modified from titus and others (2013). 232 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 partnership was expanded to include the natural history museum of utah (nhmu; formerly named the utah museum of natural history [umnh]) and the museum of northern arizona (mna) with the intention to intensively survey the late cretaceous section of the kaiparowits basin region, emphasizing macrovertebrates. a number of articulated or associated specimens of dinosaurs or other macrovertebrates were documented the first year of this effort in 2000. the first new dinosaur taxon named from the kaiparowits basin, hagryphus giganteus (zanno and sampson, 2005), was based on a partial articulated skeleton of a large oviraptorid collected by the nhmu. subsequently, 11 other new dinosaur taxa have been named from the kaiparowits basin. intensive recent efforts by the denver museum of nature & science begun in 2011 have focused largely on the wahweap and kaiparowits formations underscoring a rare modern model of collaboration between major u.s. institutions (e.g., nhmu, mna, and others) and gsenm land managers. the marine macrovertebrate record continues to expand as well, with at least five taxa of plesiosaur and a mosasaur (the region’s first) discovered and/or published since 1996. perhaps most importantly, synthesis of the area’s outstanding macrofloral record is also underway, which will provide an extremely robust ecological framework within which to place the various vertebrate species. also occurring in the last 20 years was the expansion of eaton’s original kaiparowits plateau work into the markagunt and paunsaugunt plateaus, and the western peripheral outcrops of the iron springs formation (e.g., eaton, 1999b). the most recent summary of available faunal data for the region’s late cretaceous succession is found in the 2013 dated indiana university press volume “at the top of the grand staircase—the late cretaceous of southern utah,” edited by titus and loewen (2013) and much of the appendix is derived from that work. day 1: cretaceous stratigraphy and paleontology of cedar canyon, western markagunt plateau 0.0 miles – set trip odometer to 0 at intersection of state road (sr) 130 (main street) and sr 14 (center street), cedar city. 0.4 miles – cross the hurricane fault system. this marks the boundary between the colorado plateau to the east and basin and range province to the west. the lower triassic moenkopi formation is evident here. 0.9 miles – prominent hogback of the resistant shinarump member of the triassic chinle formation. 1.0 miles – normal fault and lower chinle strata (purple and gray mudstones) exposed. 1.2 miles – the sequence visible to the north includes the petrified forest member of the chinle (upper triassic), the dinosaur canyon member of the moenave formation (upper triassic and lower jurassic), the springdale sandstone member and main body figure 3. map showing relationship of the cordilleran thrust belt (i.e., sevier fold and thrust belt) with the adjacent sevier foreland basin or cretaceous western interior basin. from titus and others (2013). 233 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 of the kayenta formation (lower jurassic), and the base of the navajo sandstone (lower jurassic). 1.8 miles – contact of the navajo sandstone and the overlying co-op creek limestone member of the carmel formation (middle jurassic). 2.0 miles – folded and deformed gypsiferous part of carmel formation. 3.4 miles – stop 1. cedar mountain, naturita (dakota), and tropic formations: in cedar canyon, basal cretaceous beds rest unconformably (figure 5) on the middle jurassic winsor member of the carmel formation (biek and others, 2015). previously, the entire cretaceous section below the tropic shale in cedar canyon was referred to the dakota formation (e.g., eaton and others, 1999a). however, recent mapping has referred the basal conglomerate and lower 15 to 20 m of variegated, pastel colored smectitic figure 4. generalized cross section of cretaceous rocks covered in this road log showing relative chronostratigraphic relationships and stratigraphic position of field trip stops (numbered). no vertical thickness implied. blue color indicates marine facies. abbreviations as follows: per – period; paleog – paleogene; sta – stage; m – maastrichtian; sa – santonian; co – coniacian; tur – turonian; cen – cenomanian; berrias – berriasian; bajoc-tith – bajocian to tithonian; t.m. ss – tarantula mesa sandstone; upp – upper; mid-middle; mp – markagunt plateau; pp – paunsaugunt plateau; kp – kaiparowits plateau; hb – henry mountains basin. 234 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 mudstone (these units are not clearly evident in figure 6), which rests unconformably on the bleached sandstones of the middle jurassic winsor member of the carmel formation, to the cedar mountain formation. the overlying more tan, brown, and gray colored succession is now referred (kirkland and others, 2016) to the naturita formation (figure 6). dating of the cedar mountain beds in the markagunt plateau region has been somewhat problematic; no radiometric ages older than early cenomanian have been obtained, yet palynomorph data suggests a late albian age (biek, 2015). regardless, this interval largely correlates with the mussentuchit member of the cedar mountain formation in its type area (kirkland and others, 2016). the cedar mountain is overlain by the middle and upper cenomanian naturita formation (formerly dakota, [young, 1960; carpenter, 2014; kirkland and others, 2016]) (figures 5 and 6), the lower portion of which is non-marine. the upper portion of the naturita is paralic and age equivalent to the lower portion of the tropic shale in the kaiparowits basin. overall, the naturita is much thicker in the markagunt region probably because of higher subsidence rates nearer to the fold and thrust belt. the non-marine part of the naturita has produced an extensive microvertebrate fauna simply by washing a single road cut (eaton, 2009, see appendix). extensive research on the paleontology of the naturita in this area remains to be done. the marine part of the naturita formation in cedar canyon has been critical to studies of milankovitch cycles in the western interior seaway (laurin and sageman, 2001, 2007; tibert and others, 2003) and the cretaceous anoxic event, oae 2 (barclay and others, 2010). in cedar canyon, the tropic shale ranges from 0 to 10 m thick. the ammonites fagesia catinus and watinoceras sp. have been found in the formation indicating it is entirely turonian in age, with the cenomanian–turonian boundary occurring essentially just below its base (eaton and others, 1999a; tibert and others, 2003). the tropic fauna by volume consists mostly of inoceramid bivalves and other mollusks. shark teeth or other vertebrate remains are rather rare and no reptilian fauna has been reported, although turtle remains are found in the underlying paralic portion of the upper naturita formation associated with oysters and other brackish water mollusks (joyce and others, 2016). 5.4 miles – maple canyon to the north. detailed studies of the brackish to marine history of the upper naturita formation, the very thin tropic shale, and the tibbet canyon member of the straight cliffs formation figure 5. stratigraphic column for cretaceous rocks in cedar canyon. numbers correspond with field trip stops in the road log. abbreviations as follows in ascending order: ca – carmel; w – winsor member; cm – cedar mountain; t – tropic; smoky hol – smoky hollow; dt – drip tank; c – capping sandstone; g – grand castle; km – cretaceous beds on markagunt (= lowermost kaiparowits formation); cl – claron; l – lower; m – middle; u – upper. 235 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 has been undertaken here by eaton and others (2001), laurin and sagemen (2001, 2007), and tibert and others (2003). 5.8 miles – stop 2. umnh vp locality 162: outcrops in this road cut have yielded microvertebrates, including mammals (faunal list in appendix; figure 7), through blind washing methods (eaton, 2009). the mammalian fauna here includes a multituberculate (dakotamys malcolmi) that is identical to the taxon recovered from late cenomanian umnh vp locality 27 on bulldog bench along the eastern margin of the paunsaugunt plateau. however, eoalphadon woodburnei (figure 8) appears distinctly more primitive than species of eoalphadon recovered from umnh vp locality 27 and may suggest that the naturita formation here could be slightly older than the fauna from bulldog bench, possibly middle cenomanian. 6.3 miles – normal fault brings the tibbet canyon member to the road level. 6.9 miles – after crossing bridge to the right, outcrop exposes tibbet canyon member against coal and mudstone beds of the naturita formation. 8.1 miles – contact between tropic shale and vertical outcrops of the tibbet canyon member of the straight cliffs formation (figure 9) in road cut. the tropic shale is overlain by a very thick (190 m) section of late early to middle turonian tibbet canyon. this marine to marginal marine section and contains abundant brackish and marine mollusks (eaton and others, 2001). 10.2 miles – contact between the tibbet canyon member and the basal coal beds of what we have identified as smoky hollow member. see discussion in stop 3 about identification, correlation, and nomenclature of the members of the straight cliffs formation. 10.6 miles (just past milepost 11) – stop 3. straight cliffs formation: in general, recognizing the standard four members of the straight cliffs formation in the markagunt region is difficult, as compared to the type sections in the kaiparowits plateau (figure 2). as biek and others (2015) have done the most recent and extensive fieldwork in the region, figure 6. looking north at naturita (dakota) – tibbet canyon member section. annotated by jiri laurin (institute for geophysics at the czech academy of sciences). 236 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 we are following their terminology. in general, here the tibbet canyon member, the lower portion of which is age equivalent to the upper portion of the tropic shale in the kaiparowits region, is much thicker, and the john henry member in the markagunt has almost none of the paralic character seen at its type section; more closely resembling the iron springs formation. at this stop, the base of the smoky hollow member contains common brackish water gastropods described by hoffman (2005; locality “jeff ’s snail slope”). many of these gastropods are identical to those found in the lower smoky hollow member along sr 12 at the east side of the paunsaugunt plateau in bryce canyon national park (the glory cove fauna). the brackish water invertebrate fauna here is mostly mollusks, but foraminifera and ostracods have been recovered from just above the tibbet canyon member (umnh vp locality 66) just west of the southern utah university (suu) center. hoffman (2005) considered the gastropod fauna to be late middle turonian. at umnh vp locality 66, very low in the smoky hollow member, abundant rhinobatoid teeth and other fish teeth have been recovered (eaton and others, 1999). the smoky hollow brackish section here is 54 m thick, much thicker than on the kaiparowits plateau indicating that subsidence rates are still higher in the markagunt plateau area (eaton and others, 1999). the remaining upper part of the smoky hollow member (53 m) consists of fluvial channel and floodplain deposits. no fossils have yet been recovered from the upper fluvial sequence. the john henry member here consists of variegated floodplain deposits and meandering river sandstones. in its type area, the smoky hollow member is usually capped by a distinctive thick and laterally continuous conglomerate referred to as the calico bed. overlying the calico is the base of the john henry. in the markagunt plateau, locally there is a sandy discontinuous conglomeratic unit 107 m above the base of the smoky hollow that may be an equivalent to the calico bed. unfortunately, since it is discontinuous in the cedar figure 7. looking across sr 14 at lower naturita (dakota) formation (umnh vp locality 162). 237 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 figure 8. stereo pair photo of a specimen of the metatherian eoalphadon woodburnei recovered from umnh vp locality 162. specimen is approximately 3 mm in horizontal length. figure 9. contact of tropic shale and the tibbet canyon member on south side of road in landslide area along sr 14. 238 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 canyon area, the boundary between the two members can be difficult to recognize. the road on suu property across from the center leads to ridges that have much better exposures of the straight cliffs formation than is seen in cedar canyon. there, localities provide important age controls on the section, including umnh vp localities 8 and 9 (vertebrate faunal list in appendix). well above the base (115 m and 150 m, respectively) of the john henry member are two localities, umnh vp 9 and umnh vp 8 (eaton and others, 1999, 2001; eaton, 2006a). both of these lie well below a horizon with an 40ar/39ar date, taken on euhedral biotite, of 86.72 ± 0.58 ma (eaton and others, 1999) corrected to 87.28 ma in albright and titus (2016), suggesting a coniacian (or older) age for these localities (see faunal lists in appendix). umnh vp locality 8 contains abundant freshwater sharks which may represent the coniacian transgression. these are the only freshwater sharks or rays found in the entire section in cedar canyon. no age-diagnostic fossils have yet been recovered above the horizon with the radiometric date and below the drip tank member in which the age of the john henry member would presumably be santonian. umnh vp locality 9, the stratigraphically lowest vertebrate locality has produced a small fauna that includes marsupial and multituberculate teeth, but the producing horizon has never been located (eaton, 2006a). umnh vp locality 8 contains abundant freshwater shark teeth and rare mammalian specimens including the multituberculate cedaromys and fragments of eutherian molars (eaton, 2006a). much more work needs to be done on these localities as well as prospecting for additional localities. the uppermost member of the straight cliffs formation is the drip tank member (santonian, see albright and titus, 2016) on the kaiparowits plateau (peterson, 1969). moore and straub (2001) suggested that a conglomerate found 457 m above the top of the tibbet canyon member is the drip tank member. along sr 14 in cedar canyon, this conglomerate is only a few meters thick and eaton (in eaton and others, 2001, figure 5) placed a question mark next to the drip tank in the stratigraphic column. biek and others (2015) indicate the same conglomerate is 30 m thick just to the south. edward sable (u.s. geological survey, written communication, 1994), moore and straub (2001), and biek (2015) claimed to have traced the unit around the southern margin of the plateau to long valley where they correlate it with what was previously referred to as the lower member of the grand castle formation. 10.9 miles – a conglomerate that crops out on the north side of the road (as much as 12 m thick) is thought to possibly represent the calico bed, but identification/ correlation is uncertain because it is not laterally continuous. 12.6 miles – typical outcrops of john henry member equivalent rocks are in the road cuts. notes these include variegated mudstone and thin sandstone; however, in this area, the section is dominated by mudstone. macrovertebrate remains are known from the john henry on the markagunt plateau, and a partial, small articulated coelurosaur-grade theropod was recovered from north of cedar canyon many years ago. this specimen remains undescribed. if the outcrops were more extensive, it is likely that macrovertebrate remains would be found much more frequently. 12.8 miles – outcrop of a thin pebbly conglomerate considered to represent the drip tank member (see discussion under stop 3 above). this conglomerate does appear to be laterally continuous and is thicker elsewhere. biek and others (2015) consider this sandstone to be equivalent to the lower conglomeratic member of the grand castle formation in parowan canyon. 13.0 miles – stop 4. lower wahweap formation-umnh vp locality 10: drive a short distance and walk down to umnh vp locality 10 (figure 10). umnh vp locality 10 (see faunal list in appendix) is located 21 m above the drip tank conglomerate. the site contains some taxa (see appendix) similar to those previously recovered from the santonian part of the john henry member (cimolomys sp.) or the santonian milk river formation of canada (picopsis sp.) (eaton, 2006a). one taxon (cimolodon similis) has been recovered both from the milk river and the wahweap formations and two taxa (symmetrodontoides sp. cf. s. foxi and cimolodon sp. cf. c. nitidus) are almost iden239 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 tical to those recovered from the wahweap formation (eaton, 2006a). this suggests a fauna transitional between that of the john henry member and the wahweap formation. however, based on stratigraphic correlation this locality is most likely late early campanian. the wahweap in the type area has thick laterally accreted sandstone bodies and drab organic-rich floodplain mudstone beds (eaton, 1991). the sequence above the drip tank member in cedar canyon is 290 m thick and is dominated by variegated light-colored mudstone and isolated sandstone bodies representing meandering rivers (eaton and others, 2001); as is much of the section beneath the drip tank member in cedar canyon. for this reason (and others discussed below) eaton and others (2001, figure 5) placed a question mark next to wahweap in the stratigraphic column. to emphasize the uncertain identification, eaton has sometimes applied the term “formation of cedar canyon” (e.g., roček and others, 2013, figure 12.3) for this part of the stratigraphic section. titus and others (2013, figure 2.7) considered this part of the section to represent the john henry member of the straight cliffs formation. the interpretation of biek and others (2015) for the upper portion of the cretaceous sections is followed here. 40ar/39ar dates of 80.6 and 79.9 ma (jinnah and others, 2009; jinnah, 2013) from low in the wahweap formation on the kaiparowits plateau and paleomagnetic sections from the formation (albright and titus, 2016) indicate that in the kaiparowits plateau region there is a significant unconformity between the drip tank member and the overlying wahweap formation such that strata of the lower campanian are missing. if the unit in cedar canyon is actually a western equivalent of the wahweap, perhaps the lower campanian strata are present in this area. future research involving radiometric dating and paleomagnetic studies would be most helpful in resolving this issue. 0.0 miles (restart mileage). 1.0 miles – note fine-grained variegated mudstone beds of the wahweap formation, which are essentially indistinguishable from those of the john henry member in cedar canyon. 1.3 miles – turnoff to webster flats. here the white sandstone (figure 11) is considered to represent the capping sandstone member (as defined by eaton, 1991) of the wahweap formation used by pollock (1999) and lawton and others (2003), but this interpretation is not universal (see discussion below under stop 5). the sandstone consists largely of reworked navajo sandstone. it has not yielded any identifiable vertebrate fossils but does contain the molds of plant material in iron concretions and on bedding planes. 1.4 miles – stop 5. umnh vp locality 11: this locality lies at the very top of the wahweap formation in cedar canyon (267 m above umnh vp locality 10, eaton, 2006a). it has a very enigmatic fauna with “pediomyids” similar to those of the santonian milk river formation but also with a taxon (meniscoessus sp. cf. m. intermedius) closer to known taxa of the wahweap formation or even judithian faunas. the locality also contains an anuran (nezpercius dodsoni) that has only been recovered in southwestern utah from the wahweap (gardner and demar, 2013). high in the cretaceous section above the wahweap, nichols (1977) reported the recovery of no palynomorphs younger than santonian, which supports the interpretation of titus and others (2013); however, lawton and others (2003) reported a distinctly middle campanian palyfigure 10. josep san juan girbau (american university, beirut) at umnh vp locality 10. 240 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 nomorph (dyadonapites reticulatus) from the capping sandstone member at the webster flat exposures (see below) and this is the probable age for these beds. the about 60-m-thick quartz arenite sandstone, exposed at the webster flat turnoff from sr 14 (mile 1.3), lies immediately above the variegated floodplain deposits of the wahweap formation containing umnh vp locality 11. this unit has been variously referred to the kaiparowits(?) formation (moore and straub, 2001), the middle member of the grand castle formation (goldstrand, 1991, 1992) and the capping sandstone member of the wahweap formation (pollock, 1999; lawton and others, 2003). eaton and others (2001) used the noncommittal term “white sandstone” for this sandstone body. we are in agreement with biek and others (2015) that this unit is indeed the capping sandstone member of the wahweap formation. the complexity of this area of been recently examined during mapping of the region by biek and others (2015). this mapping necessarily involved trying to resolve the complex relationship between outcrops in cedar canyon and those in parowan canyon, which is the next major canyon 20 to 30 km to the north. parowan canyon is floored by a cretaceous sequence of tabular sandstone beds separated by thin mudstone beds previously mapped as iron springs formation (mapping that eaton still thinks was correct) that has now been mapped as john henry member of the straight cliffs formation in biek and others (2015). two localities, umnh vp 6 and vp 64 (eaton and others, 2001, figure 5) are known from the iron springs/john henry member of parowan canyon, and although umnh vp 64 was relatively rich in non-mammalian vertebrates none of those specimens have yet been described. overlying the iron springs/john henry member in parowan canyon is the grand castle formation of figure 11. capping sandstone member of the wahweap formation, websters flat turnoff. 241 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 goldstrand (1991, 1992) and goldstrand and mullett (1997). it rest on a deeply weathered surface on top of the iron springs/john henry member, enough of an unconformity that goldstrand (1991, 1992) and goldstrand and mullett (1997) suggested a paleogene age for the grand castle. the grand castle formation was originally divided into three members. the middle sandstone member of the grand castle was shown to be cretaceous by the discovery of dinosaur tracks by hunt and others (2011) and palynomorphs reported by biek and others (2015). the underlying lower conglomeratic member of the grand castle has been correlated in biek and others (2015) to the drip tank member in cedar canyon and assigned to that member. biek and others (2015) correlated the few tens of meters of the lower middle sandstone member of the grand castle formation in parowan canyon 20 km away to the 290 m of the wahweap formation underlying the capping sandstone member (figure 12) and the rest of the middle member directly to the capping sandstone member. this represents a remarkable thickening of capping sandstone member (formerly, the middle member of the grand castle formation) from parowan canyon to cedar canyon, whereas the lower unit thins from 30 to 41 m or less. this geometric problem has not been resolved and much more work needs to be done on the relationships of the cretaceous sequence in parowan and cedar canyons. 0.0 miles – restart mileage. 0.7 to 0.8 miles – still traveling in the capping sandstone. upper portion of this mapped unit here contains poorly exposed pebble and cobble conglomerates that are similar to those observed at the top of the capping sandstone member of the wahweap formation in the western paunsaugunt plateau (hillsdale canyon) and represent distal equivalents of the grand castle formation. the grand castle as now defined is about 55 m thick in parowan canyon and thins into cedar canyon where it is variable in thickness from 0 to 8 m. 1.1 to 1.3 miles – road cuts are in a unit (as much as 60 m thick) that biek and others (2015) mapped as “km” (cretaceous strata on the markagunt plateau). this series of sandstone, mudstone, and siltstone beds overlie the coarse conglomeratic facies at the top of the capping sandstone member of the wahweap formation and underlies the base of the claron formation (paleogene). importantly, this interval contains abundant black chert lithics and minor feldspar, which are virtually absent in the underlying capping sandstone member. biek and others (2015) state (p. 151) that “the stratigraphic position of the km unit precludes it being santonian in age.” we agree even though nichols (1977) reported santonian palynomorphs from this same interval. biek and others (2015) reassessed the palynomorphs from the km beds and reported late campanian to maastrichtian taxa, which agrees better with the current lithostratigraphic correlations. a very similar interval was mapped by biek and others (2015) above the capping sandstone member of the wahweap formation in hillsdale canyon on the west side of the paunsaugunt plateau as kwcg (pebbly sandstone unit of the wahweap above the capping sandstone) and kkl (lower unit of the kaiparowits formation—see biek and others, 2015; figure 28, in which kwu = kkl). these are mostly likely facies variations within the lower kaiparowits depositional system that arise where approaching the thrust belt and expanding the section. 1.4 miles – basal claron formation (eocene) in road cut. figure 12. umnh vp locality 11, upper wahweap formation below the capping sandstone member. 242 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 3.5 miles – intersection with sr 148 to cedar breaks. 5.7 miles – cinder cone and basalts of the markagunt plateau volcanic field which erupted from latest pliocene through the pleistocene and possibly into the holocene (johnson and others, 2010). 9.0 miles – claron formation to left and navajo lake to the right which formed as a result of basalts damming the drainage. 19.2 miles – claron formation outcrops which contain abundant trace fossils described in bown and others (1997). 21.7 miles – short canyon turnoff. 22.3 miles – mile 38 sign post. 22.7 miles – outcrop to right is the basal brian head formation (late eocene). this blind wash locality (umnh vp locality 1085, ip locality 186) has produced rodent teeth, ostracods, ray teeth, and miscellaneous fragments of fish. initially, this locality was thought to be part of the claron formation by eaton and others (2011) and they reported the mammals and ostracods from this locality to be from the claron formation. subsequent location of a thin pebble conglomerate (the boat mesa conglomerate) below this white unit demonstrates that it is instead part of the brian head formation and not the claron. 23.0 miles – claron outcrop in road cut. 23.3 miles – outcrops of brian head formation (figure 13). 23.4 miles – claron formation. the lithology of the claron in this area is unusual with abundant finegrained, soft, pastel-colored beds of brown quartzose sandstone, and white carbonate beds. these lithologies are exposed for the next 16 km northward on u.s. highway 89. the only bone fragments recovered from the claron formation anywhere are from these outcrops of brown sandstone. 25.1 miles – junction sr 14 and us 89, long valley junction. driving north from the junction, the upper part of the claron formation is exposed in the road cuts. 34.5 miles – driving on top of the claron formation, hills above the white carbonate are made of the lower brian head formation. 35.5 miles – stop 6. overview of the paunsaugunt plateau: to the east is the western margin of the paunsaugunt plateau. the sevier normal fault exposes the cretaceous section consisting of the upper straight cliffs and wahweap formations. here, the john henry member consists dominantly of fluvial sandstone with almost no mudstone. this cretaceous block is separated from the claron formation to the east by another fault, the sand pass fault. these faults merge just south of hillsdale canyon (major canyon to the north) where overlying the capping sandstone member (figure 14) of the wahweap formation, biek and others (2015) delineated the following succession: kwcg (pebbly sandstone unit in the wahweap formation), kkl (lower unit of the kaiparowits formation), and kk (typical kaiparowits formation). the hillsdale section is critical for understanding correlations of the upper portion of the cretaceous section between figure 13. outcrop of the late eocene brian head formation showing the quarry horizon in 2011. 243 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 fi gu re 1 4. u pp er c re ta ce ou s s tr at ig ra ph ic co lu m ns fo r t he p au ns au gu nt an d k ai pa ro w its p la te au s. a bb re vi at io ns as fo llo w s: c l – c la ro n; g c – g ra nd c as tle ; c a – c ar m el ; c -n – c ed ar m ou nt ai n an d n at ur ita ; l – l ow er ; m – m id dl e; c w g – pe bb ly sa nd st on e u ni t o f t he w ah w ea p; k kl – lo w er u ni t o f th e k ai pa ro w its ; k k – ty pi ca l k ai pa ro w its ; d t – d rip t an k; s h – s m ok y h ol lo w ; t c – t ib be t c an yo n; u – u pp er ; w – w in so r; c p – c an aa n pe ak ; en – e nt ra da ; c s – ca pp in g sa nd st on e; h s – h en rie vi lle s an ds to ne . s ee fi gu re 2 fo r g en er al lo ca tio n of se ct io ns . 244 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 the markagunt and kaiparowits plateaus. the capping sandstone member is overlain there by a conglomerate identical in character to that of the upper grand castle formation, which is in turn overlain by sandstones that increase upsection in black chert lithic content, more typical of the kaiparowits formation. the overall coarser grain content of what are mapped as kaiparowits formation equivalents is largely due to its proximity to the fold and thrust belt. the lower portion of the section, including the cedar mountain, naturita, tropic shale, and lower straight cliffs formations, are well exposed around glendale and orderville, farther south. in general, because of the higher altitude and associated plant cover, the outcrops on the paunsaugunt are not as extensive as they are on the kaiparowits, but are generally more fossiliferous with vertebrates than their eastern counterparts. unfortunately, the kaiparowits formation was largely removed from the paunsaugunt (and markagunt) areas by pre-claron aged laramide uplift (figure 14). the cedar mountain and naturita formations are exposed only around the southern and eastern margins of the paunsaugunt plateau. exposures of naturita formation along the southwest side of the plateau have produced significant microvertebrate material near the town of alton (mna 939/umnh vp 123). the tibbet canyon member of the straight cliff formation is quite thin (20 m) along the southern margin of the plateau (mill creek section of eaton, 1993b). the overlying john henry member is 190 m thick (figure 5). along the south side of the plateau a few vertebrate localities have been found (mna 1201, 1204); but abundant private land has restricted access to the john henry member there. along the eastern margin of the paunsaugunt plateau within bryce canyon national park (bcnp), and just east of the park, the john henry member is relatively rich in vertebrate fossils. this includes localities in the basal coniacian part of the member, which range from fish-rich microvertebrate localities (umnh vp 823-826, 860-866, 1084, 1276) and macrovertebrate localities containing turtles to dinosaurs. unfortunately, little work has yet been done on this area, the richest known for coniacian macrovertebrate and microvertebrate fossils in the entire region. santonian localities are also abundant (umnh vp 419, 420, 424, 781, 799, 826, 1144) and particular umnh vp locality 424 (a “blind wash locality”) in the uppermost part of the john henry member in bcnp produced a remarkably rich microvertebrate assemblage described in eaton (2009), roček and others (2010), brinkman and others (2013), and gardner and demar (2013). the overlying drip tank member is 50 m thick in the mill creek section, but is highly variable in thickness around the plateau and is very thin in tropic canyon at the northeast corner of the plateau. the wahweap formation on the paunsaugunt plateau has been problematic. gregory (1951) and doelling and davis (1989) thought the youngest cretaceous strata on the plateau belonged to the kaiparowits formation. bowers (1990) and tilton (1991) considered the uppermost cretaceous rocks to represent the wahweap formation. eaton (1993) and eaton and others (1993) favored the kaiparowits formation interpretation based on petrology and comparative faunas. unquestionable wahweap is found in the campbell creek area along the eastern margin of the plateau south of the town of tropic. here, the wahweap formation mudstones are drab colored and umnh vp localities 77 and 82 contain abundant shark and ray teeth; both characteristics are common to the wahweap formation on the kaiparowits plateau. however, in an erosional window through the claron formation on top of the plateau (south of tropic reservoir), are exposures of colorful variegated mudstone, which contained no shark or ray teeth, but contains the turtles compsemys, neurankylus, as well as kinosternids, taxa that are more common in the kaiparowits formation than in the wahweap (eaton, 1993b, 1999a). although initially favored a kaiparowits formation equivalency based on the vertebrate faunas, eaton ultimately accepted the more parsimonious interpretation of wahweap formation (eaton, 1999a) but suggested marked paleoecologic controls on the vertebrate fauna that reflect the shift from relatively poorly drained coastal floodplains (preserving organics, having abundant sharks and rays) to the east to better drained more upland settings (variegated mudstone, no sharks and rays) to the west. biek and others (2015) described a “lower unit” of the kaiparowits formation (kkl) present on the western side of the paunsaugunt plateau that thins eastward 245 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 and completely disappears by the east fork of the sevier river. they considered this unit to represent the kaiparowits formation, even though it is unlike the typical lithologies of that formation. it is also lithologically unlike the underlying capping sandstone of the wahweap formation but is somewhat like the basal kaiparowits formation found along henrieville creek. the only kaiparowits formation with lithologies typical of the strata in its type area is a remnant along the west margin of the paunsaugunt plateau in hillsdale canyon (biek and others, 2015; see figure 28). along the eastern margin of the paunsaugunt plateau, the wahweap formation has been eroded from the tops of laramide folds such that in places the claron formation rests directly on the straight cliffs formation and the entire wahweap has been removed (bowers, 1990; biek and others, 2015). the type section of the limerock canyon formation is east of this stop (kurlich and anderson, 1997). work by kevin rafferty (2015; a student formerly at weber state university and now at univeristy of nevada, las vegas) has shown that much of the limerock canyon (miocene) is actually brian head formation. brian head localities in this area have produced rodent teeth, ostracods, and charophytes. 39.0 miles – road cut is in the upper tertiary fan alluvium (taf) and includes an exposure of the 5.0 ma rock canyon lava flow (biek and others, 2015). 45.2 miles – intersection of us 89 and sr 12, turn right onto sr 12. white outcrops at this intersection have been blind washed and produced latest miocene rodents (william korth, rochester institute of paleontology, written communication to eaton, 2016), as well as unaltered gastropods and bivalves (umnh vp locality vp 1999, ip locality 89). 47.8 miles – sevier fault. 48.0 miles – red canyon; note conglomerate on the left side of the road in the claron formation. conglomerate becomes more common to the northwest. 53.5 miles – town of tropic, utah, and the type section for the cretaceous marine tropic shale. end of day 1. day 2: cretaceous stratigraphy and paleontology of the paunsaugunt and kaiparowits plateaus 0.0 miles – tropic, utah, at the intersection of 200 north and sr 12. proceed west on sr 12. 3.5 miles – paunsaugunt fault. gray beds of the john henry member of the straight cliffs formation faulted against the lower red member of the claron formation. this normal fault has the same general orientation as the sevier fault on the west side of the paunsaugunt plateau. 7.4 miles – intersection with sr 63 to bryce canyon nation park. on the eastern flank of the park there are extensive exposures of the john henry member of the straight cliffs formation and the wahweap formation. eaton conducted a five year (2006-2010) inventory of fossil resources within the park. both the john henry member and the wahweap formation are more fossiliferous there than on the kaiparowits plateau and hundreds of localities were identified. only a few localities were intensively worked because of the lack of access. bulk mudstone samples taken to process for microvertebrates had to be back-packed out of the park, often requiring 3 hours of hiking per sack of matrix in the middle of summer. one of the most significant localities is umnh vp locality 424 (figure 15) which is almost at the top of the john henry member and is the richest microvertebrate site yet known from that member (see appendix for a complete listing of taxa). 10.3 miles – turnoff to tropic reservoir. make a left turn and proceed south. 17.3 miles – tropic reservoir. continue south. from about this point south, outcrops in the lower portions of the valley are of the middle campanian wahweap formation overlain unconformably by the claron formation. 246 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 21.6 miles – stop 7. wahweap formation on the paunsaugunt plateau – mill creek area (umnh vp locality 83/mna locality 1073): the wahweap formation on the paunsaugunt plateau is exposed in a window eroded through the claron formation by the east fork of the sevier river and its tributaries. this stop, umnh vp locality 83/mna locality 1073, in the mill creek area, is one of the most easily accessed of all the highly fossiliferous localities (figure 16). the obvious interpretation of these strata, based on their stratigraphic position, would be the wahweap formation, but aspects of the lithology and fossil content were questioned (eaton, 1993b; eaton and others, 1993). the wahweap formation on the kaiparowits plateau (type area) consists of rather drab organic-rich floodplain mudstones and siltstones and laterally aggrading channel sandstone. eaton and others (1993) noted that the sandstone high in the wahweap section on the paunsaugunt plateau were petrologically more similar to the kaiparowits formation than to sandstone of the wahweap formation. biek and others (2015) have now mapped these sandstone beds as the lower kaiparowits formation (kkl). the wahweap mudstone exposed here also differ markedly from those of the type area as they are variegated and very fossiliferous. sampling the wahweap formation on the kaiparowits plateau for microvertebrate fossils commonly figure 15. umnh vp locality 424 (santonian), near the top of the john henry member of the straight cliffs formation. note the drip tank member just above the locality. here the claron formation rests unconformably on the drip tank member due to erosion across the laramide aged bryce canyon anticline. 247 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 produces shark and ray teeth as well as crab claws, with other taxa much less common. on the paunsaugunt plateau recovered fossils (see appendix) include taxa that are common in the kaiparowits formation but rare or unknown from the wahweap formation of the kaiparowits plateau. the paunsaugunt wahweap strata also lack ray and shark teeth or crab claws indicating a fundamental environmental shift between the two regions, most likely a more upland, better drained environment with less coastal influence. the mammalian fauna (eaton, 1993b) also initially did not compare well to that of the wahweap formation on the kaiparowits plateau. for these reasons eaton (1993b) and eaton and others (1993) kept open the possibility that these strata might represent the kaiparowits formation or possibly another unit. however, subsequent study of the fauna (eaton, 2013), aided by systematic revisions by other workers, showed a reasonably good correlation with the fauna of the wahweap formation to the east. the difference in the overall vertebrate fauna seems to reflect a shift from relatively poorly drained coastal floodplains to better drained more upland floodplains. return to tropic and reset trip meter. 0.0 miles – intersection of 200 n with sr 12. proceed east. 1.6 miles – road cut exposes upper marine portion of the naturita formation and lowermost beds of the tropic shale. 4.7 miles – entering cannonville. 4.8 miles – turn right (south) onto the cottonwood canyon road to kodachrome basin state park. 4.9 miles – stop 8. overview of naturita formation, paunsaugunt-kaiparowits transition: to the west of the cannonville town park and grand staircase-escalante national monument visitor center parking lots, the redand white-banded cannonville member of the entrada is in view and overlain by the naturita formation cutting out much of figure 16. typical variegated fossiliferous mudstone of the wahweap formation along mill creek at umnh vp locality 83/mna locality 1073. 248 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 the intervening bleached looking henrieville sandstone (figure 17). the henrieville sandstone as described by thompson and stokes (1970) is somewhat controversial as a map unit and has been synonymized with the upper portion of the entrada sandstone by some workers (bowers, 1983; biek and others, 2015). resolution of this issue awaits more detailed lithologic study of all the potentially correlative units. for this guide, we retain these beds in the henrieville sandstone. the cedar mountain formation is locally absent, being discontinuous over much of the kaiparowits plateau. thin, gravelly facies at the bottom of the naturita in this region are probably reworked cedar mountain sediments. here, on bulldog bench, the nonmarine lower unit of the naturita formation is unusually fossiliferous with vertebrates, including mesovertebrate remains such as turtles and crocodylians. although many localities have been discovered, only one has been extensively screen washed (figure 18) – mna 1067/umnh vp locality 27. this remarkable locality has produced mammalian jaws, including early marsupials, but also large lungfish plates, and material of frogs and lizards (see appendix). the mesovertebrate fossil content of the naturita appears to be highest trending between bulldog bench and the southwestern margin of the kaiparowits plateau, where turtle and crocodylian remains are similarly abundant. the naturita in the kaiparowits region contains abundant coal and carbonaceous beds. macrovertebrate skeletal remains are virtually unknown although dinosaur trackways and teeth recovered from microsites indicate the region was inhabited by larger animals. return to sr 12. 5.0 miles – turn right (east) onto sr 12. 9.7 miles – outcrops of the middle jurassic henrieville sandstone (overlying entrada sandstone) overlain by the lower and upper members of the naturita formation visible to the west of sr 12 (figure 19). 11.2 miles – stop 9. overview of kaiparowits plateau stratigraphy, the naturita formation, and the tropic shale: from sr 12, hike approximately 0.16 km) due south to the naturita-tropic contact. the basic cretaceous stratigraphy of the kaiparowits plateau (figure 20) was established by gregory and moore (1931), lawrence (1965), peterfigure 17. henrieville sandstone (jurassic)– naturita (cretaceous) formation contact on bulldog bench. the lower nonmarine naturita formation is much thicker here than anywhere else in the kaiparowits-paunsaugunt plateaus region. 249 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 son (1969), and eaton (1991). the upper cretaceous section is approximately 2600 m thick and fairly similar throughout the region, but there are some marked facies changes in formations, mostly trending east-west. as a rule, exposures are much better for all of the units in this region than they are in either the paunsaugunt or markagunt plateaus. the oldest unit mapped is the cedar mountain formation, which in the kaiparowits region is mostly limited to the pebbly conglomerate facies. the smectitic gray mudstone facies is absent. in the kaiparowits basin, the overlying naturita formation is relatively thin, averaging only 30 to 35 m in thickness. as it overlies the basal cretaceous unconformity and in turn is overlain by the marine tropic shale, it represents a variety of terrestrial and nearshore marine environments, in a generally retrogradational sequence. with the exception of shark and fish remains, vertebrate fossils are largely confined to the lower member, occurring in floodplain, channel, and crevasse splay facies. large mesovertebrate and macrovertebrate remains are generally uncommon and usually occur as isolated elements, but 0.3-m-diameter turtle shells can be locally abundant in lacustrine and channel facies, particularly in the southwestern portion of the kaiparowits basin. the bulldog bench area near tropic (stop 8) is one of the only places where larger vertebrates besides turtles have been found in any quantity. dinosaur trackways also occur sparingly in the middle unit (titus and others, 2013). the overlying tropic shale is as much as 300 m thick (doelling and davis, 1989), entirely marine in origin, and spans late cenomanian to middle turonian time. the formation is dominantly gray-weathering mudstone, but calcisiltites and calcarenites also occur throughout the formation. the lower half of the tropic is more carbonate rich, whereas the upper half is more siliciclastic. fossils, mostly invertebrates are common throughout, but vertebrate remains are only locally common. non-fish vertebrates are uncommon to rare, but long-term collecting has revealed a highly diverse assemblage that will be discussed in more detail below. the overlying straight cliffs formation is a highly heterogeneous unit that probably exhibits the most lateral variation of any formation in the kaiparowits basin. spanning much of the later turonian, as well as the entire coniacian and santonian, it also represents the longest time span (~ 10 ma) of any cretaceous formation in the region except for the related iron springs formation. in general, marine and marginal-marine facies dominate the eastern outcrops, with shoreface, beach complex, estuarine, and deltaic beds interleaved with coastal mire and distributary fluvial units (allen and johnson, 2010), whereas western outcrops are composed mostly of meandering fluvial and floodplain deposits. the unit was deposited during the end of the greenhorn and throughout the entire niobrara cyclothems (middle turonian to late santonian age). in the kaiparowits basin the straight cliffs locally produces abundant microvertebrate remains. however, macro and mesovertebrate sites are actually somewhat rare. the highest densities of such sites occur in the southwest portion of the kaiparowits plateau where alluvial-plain facies dominate. there multiple sites yielding dinosaur material, including a multi-individual ornithopod bonebed have been found, but not in the same quantities as observed on the paunsaugunt plateau. dinosaur trackways are locally known, particularly in coal seems, but bone is quite rare in the eastern half of the figure 18. mna 1067/umnh vp locality 27 quarry in the naturita (dakota) formation on bulldog bench. this appears to be an overbank deposit immediately adjacent to a meandering river levee. large material is found along the levee and fines rapidly away from the levee. there are clearly several flood events separated by organic mats. 250 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 figure 19. henrieville sandstone (je) in contact with the naturita (knl, knu) formation. there is very little lower nonmarine naturita even though this outcrop is only about 16 km from bulldog bench. figure 20. kaiparowits plateau stratigraphy visible from stop 9. the kaiparowits formation is not visible, but widely exposed behind the ridge formed in the wahweap formation. the highest outcrops of white-colored eocene age claron formation are at powell point, at the very south end of the table cliffs plateau. see figure 23 for wide view. 251 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 plateau, leading to the conclusion that either the depositional rates or soil conditions were unfavorable to preservation of large bone. the seaway withdrew at the end of the niobrara cycle never to inundate southern utah again. as a result, the overlying wahweap and kaiparowits formations are entirely terrestrial in origin and fairly homogeneous, although not without marine influence on their deposition and occasional brackish water incursions (e.g., roberts and others, 2008). the marine portion of the upper naturita at this stop consists of alternating (cyclic) mudstone and sandstone deposited in a shallow, near-shore muddy shelf setting during the early greenhorn cyclothem event. mollusk assemblages alternate between oyster epiboles and more diverse assemblages reflecting fluctuating sea levels. a thin coal bed just below the top of the formation marks a lowstand associated with the top of the metoicoceras mosbyense biozone. the biostratigraphically useful inocermid bivalve inoceramus fragilis occurs near the base of the member, whereas ammonites of the dunveganoceras problematicum and metoicoceras mosbyense biozones occur in the middle and top of the unit, respectively. collectively, the marine invertebrate record indicates the upper member is entirely late cenomanian, spanning much of that substage. vertebrates are not common, and consist mostly of isolated elements of brackish and marine chondrichthyans and osteoichthyans. the overlying tropic shale (figure 21) was deposited in an open water, offshore muddy shelf setting. at peak transgression, the shoreline was over 115 km to the west. the tropic shale is mostly gray mudstone and contains abundant invertebrate and vertebrate fossil fauna. ammonites in the formation indicate it spans the vascoceras diartianum through prionocyclus hyatti ammonite biozones (middle late cenomanian to middle middle turonian). the nearshore position of the tropic shale depocenter in a regime of relatively high accommodation space make the cenomanian-turonian stratigraphic record in the region especially thick and complete (elder and others, 1994). in particular, the events surrounding ocean anoxic event ii (oae ii) and the associated extinction are recorded in great detail (elder, 1991). most of the large vertebrate fossils are found in the early turonian, although rare specimens are known from the underlying cenomanian (gillette and others, 1999). an overview of the vertebrate fauna was given by albright and others (2013) and the described fauna is summarized in the appendix. chondrichthyan and osteichthyan remains including fully articulated specimens occur commonly in the tropic, but no detailed studies have ever been published. over the last 16 years a diverse and significant marine reptile fauna has been recovered from the unit. plesiosaur remains are most common, but turtles, early mosasaurs, and rare dinosaur remains have also been found. five taxa of plesiosaurs (one pliosaurid and four polycotylids) are now documented from the formation (figure 22), making the assemblage one of the most diverse known from any greenhorn age deposits. three significant trends/ events in vertebrate evolution appear to be recorded in the tropic: (1) the extinction of the archaic pliosaurid plesiosaurs, (2) the diversification of the polycotylid plesiosaurs, and (3) the rise of true mosasaurs in north america. 11.6 miles – view north towards jimmy canyon is of the open marine tropic shale and the shoreface facies of the tibbet canyon member forming the cliff, which holds up the benches. resting on the benches is the paludal smoky hollow member (turonian). on the bench directly to the north (figure 23) is the richest smoky hollow member micro-site known, mna 995/umnh vp locality 129. this very productive site is difficult to recover large quantities of matrix from (figure 24). in 1991, a small helicopter made several trips to move 86 moderately sized sacks of matrix from the bench to the valley floor. this locality has provided much of the basis for the faunal list presented in the appendix. 13.0 miles – turnoff to henderson canyon (figure 25). the lower john henry member contains coals (figure 26), is very organic rich, and produces a brackish-water fauna of both vertebrates and invertebrates (e.g., mna 706-2/umnh vp locality 98). the upper part of the john henry member in henderson canyon is less organic rich (figure 27) and includes umnh vp locality 99 (santonian), a very productive microvertebrate locality from which much of the vertebrate faunal 252 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 figure 21. overview of the tropic shale at stop 9. lettered bentonites are key marker beds (of elder, 1991) that can be traced throughout the southern western interior, including the cenomanian-turonian boundary global stratotype section and point near pueblo, colorado. figure 22. mna v9433, (a) dorsal view of nearly complete cranium, and (b) dorsal view of complete mandible of the pliosaurid plesiosaur brachauchenius lucasi. from albright and others (2013). 253 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 list in the appendix is derived. 14.2 miles – stop 10. smoky hollow and john henry members of the straight cliffs formation: the tibbet canyon member is overlain by the early late turonian smoky hollow member, which has coal and lignite low in the member (figure 28). it also contains brackish-water faunas. the upper part of the member consists of beds of fluvial deposition. the smoky hollow member is capped by fluvial sandstone and conglomerate termed the calico bed by peterson (1969). the john henry member is upper coniacian-santonian and rests disconformably upon the calico bed (figure 29). as with the underlying smoky hollow member, the lower part of the john henry member is very carbonaceous and contains brackish-water faunas (listed in appendix). the upper part of the formation here is largely nonmarine; howfigure 23. looking northeast at bench with mna 995/umnh vp locality 129 in the smoky hollow member of the straight cliffs formation. figure 24. the late jared morrow at mna 995/umnh vp locality 129 quarry, smoky hollow member of the straight cliffs formation, turonian. 254 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 ever, thin sandstone tongues containing marine taxa are present in the unit. along the eastern margin of the plateau (type section for the straight cliffs formation) the john henry member is mostly nearshore to marine. 14.8 miles –stop 11. upper john henry and drip tank members, straight cliffs–wahweap formations: on the north side of the canyon, the prominent cliff-forming drip tank member of the straight cliffs formation (santonian) is unconformably overlain by the less resistant ledge-forming sandstone and mudstone of the lower member of the wahweap formation (figure 30). the drip tank member in the kaiparowits basin is locally fossiliferous with vertebrate material, including dinosaur bone, but owing to the high-energy nature of its depositional system, most of the material is fragmentary and non-diagnostic. the overlying alternating sandstones and mudstones of the wahweap formation are well exposed in this area (figure 30), but the formation generally forms steep slopes making it difficult to prospect for fossils. in the kaiparowits region, most of the identifiable macrovertebrate remains have been collected from along the smoky mountain road and the southern margin of the plateau. the unit is also more paralic in character here than in the paunsaugunt region, commonly containing carbonaceous beds indicative of paludal environments. the majority of the macrofauna of the wahweap formation is now well constrained as older than the oldest described assemblages of the judith river and foremost formations (albright and titus, 2016), and it includes the oldest named north american representatives of the tyrannosauridae (lythronax), lambeosaurinae (adelolophus), centrosaurinae (diabloceratops), and pachycephalosauridae dinosaur clades. at least two different species of large alligatofigure 25. view of the looking north up henderson canyon from the sr 12 turnoff of the tropic shale and overlying members of the straight cliffs fomration. figure 26. typical coal and sandstone interbeds in the lower john henry member in henderson canyon. 255 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 roids and a pholidosaur-like crocodylian have also been recovered, but await description. cranial material of a nodosaurid ankylosaur was also recovered recently but is also awaiting description. based on the hadrosaurs (gates and others, 2014) and ceratopsids, the early middle campanian wahweap dinosaur assemblage has some similarity to the slightly younger foremost and oldman assemblages found in alberta, canada. 16.4 miles – stop 12. capping sandstone member and lower kaiparowits formation: in this vertical cliff face exposed along henrievfigure 27. upper part of the john henry member in henderson canyon. note channel complex at the top of the member. umnh vp locality 99 is in the underlying fine-grained part of the section. figure 28. the smoky hollow member (kscsh) overlies the nearshore deposits of the tibbet canyon member (ksctc); note the carbonaceous horizons low in the smoky hollow member. the smoky hollow is capped by the sandstones and conglomerates of the calico bed. 256 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 figure 29. the calico bed of the smoky hollow member (kscsh) is overlain disconformably by the john henry member (kscjh). the lower john henry is locally very carbonaceous and produces a brackish-water fauna. figure 30. contact between the upper part of the john henry member and the drip tank member along henrieville creek. the drip tank member is a quartz arenite to pebbly conglomerate as opposed to the non-conglomeratic feldspathic sandstones of the upper john henry member. kw = wahweap formation. 257 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 ille creek (figure 31) is the contact between the capping sandstone member of the wahweap (kwcs) and the base of the kaiparowits formation (kk). lawton and others (2014) noted a 26-m interval at the base of the kaiparowits formation, which they considered transitional between the sandstone lithology of the wahweap formation and the more feldspar-rich lithology of kaiparowits formation. several fossil localities were found in the lowest part of the kaiparowits, which produced ostracods and miscellaneous vertebrate materials including ray teeth (lawton and others, 2014). 18.2 miles – turn on small dirt road and proceed about 100 m to the north and park. stop 13. kaiparowits formation overview: from this view you can see most of the gray-colored middle and upper members of the kaiparowits formation below the prominent cliff-forming outcrops of the claron formation. the intervening slope between the kaiparowits and claron formations is formed in the canaan peak and pine hollow formations and other coarse clastic units referred to the grand castle formation, but which cannot belong to that formation because they post-dates the kaiparowits formation. these formations are not visible from this vantage point because they are covered with slumps and vegetation. outcrops to the east (figure 32) form the type section of the kaiparowits formation, which here is approximately 860 m thick. the immediate foreground is in the middle member, about 200 m above the base of the formation (eaton, 1991, figure 15). although the section appears dominantly composed of mudstone, it is close to an even mix of sandstone and mudstone. however, the sandstone beds are generally friable and weather into rounded shapes that resemble more mud-rich outcrops. dated ash-fall tuffs in the kaiparowits formation have yielded an age range of 76.6 to 74.5 ma, which spans most of the lower half of the late campanian (roberts and others, 2013); however, given its thickness the kaiparowits was deposited at a remarkably fast rate (roberts and others, 2013). what is possibly even more remarkable is that the entire formation was removed from portions of the paunsaugunt and markagunt plateaus area in the early to middle paleocene during the laramide uplift. the kaiparowits is by far the richest macrovertebrate-producing unit in the entire region. 18.7 miles – stop 14. middle kaiparowits sedimentology and taphonomy: park on south side of highway, east of culvert. hike down into creek and north into the culvert. emerge on other side in small canyon carved into middle member of the kaiparowits formation. many features of kaiparowits depositional systems can be observed in the canyon walls in good detail. exposed are overbank, fine-grained sequences that have carbonate pedogenic features, which are incised, scoured, and overlain by fluvial channel sandstones bearing large carbonized logs and fossil-rich lags. whereas the overall vertebrate diversity of the kaiparowits has mostly been assessed from mudstone-rich pond and floodplain lake facies, many of the articulated macrovertebrate specimens, some displaying soft tissue impressions, are found at the bases of these channel systems, above the scours. many associated macrovertebrate specimens actually bear mudstone or pedogenic carbonate in their interstices, indicating that they were reworked into the channels from finer grained facies. the preservation of individual kaiparowits vertebrate specimens is sometimes spectacular (figure 33). complete or partial articulation and preservation of softer elements such as epidermis and the keratinous portions of beaks and claws is not rare, particularly in fluvial channel facies. the turtles adocus (knell and others, 2011) and basilemys have both been found preserved with clutches of eggs (figure 34). unusual paleobiological information has also been gained from rare specimens showing predatory or behavioral traits (e.g., boyd and others, 2013). the distribution of fossils is irregular throughout the formation although the lower and middle portions of the middle member are by far the most fossiliferous. fossil content largely is inversely proportional to the maturation of calcic paleosol features that are pervasive in overbank sequences. reworking of vertebrate materials of all size classes, including associated dinosaurs, out of finer grained overbank facies into fluvial channel bottom lags is a very common perservational mode. soft tissue preservation is most often observed as primary burials in fluvial channels, although rarely hadrosaurs have been observed with soft 258 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 figure 31. contact between the capping sandstone member of the wahweap formation (kwcs) and the kaiparowits formation (kk) along henrieville creek. figure 32. outcrops of the lower kaiparowits formation (above 200 m) in the blues, the type section of the kaiparowits. 259 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 tissue preserved in calcite concretionary overgrowths in floodplain lake facies. strong correlation between suites of invertebrate fossils and depositional facies (tapanila and roberts, 2013) shows promise for vertebrate assemblages. indeed, anecdotal observations seem to support gross separation of fluvial and overbank assemblages of both microvertebrates and macrovertebrates. a 0.8-km-long hike to the northeast towards the very first utahceratops quarry will afford a look at a typical associated hadrosaur site that includes skin impressions. 20.7 miles – stop 15. kaiparowits formation diversitythe blues overlook: the kaiparowits formation flora (miller and others, 2013), invertebrate fauna (tapanila and roberts, 2013), and vertebrate fauna are exceptionally diverse (see appendix). although these are the most accessible outcrops of the formation, most of the type localities for new dinosaurs and other macro and mesovertebrate taxa are actually out of view and to the south of canaan peak. two exceptions to this are the type specimens for the oviraptor hagryphus giganteus and the troodontid talos sampsoni, both of which were collected in the lower elevation hills due west of the overlook (figure 35). the most common large dinosaur remains are lambeosaurine and saurolophine dinosaurs. ceratopsids are found in lesser numbers, but are still clearly a significant part of the ecosystem, displaying exceptionally high diversity. most other dinosaur taxa are uncommon to rare, some being represented by a single specimen (e.g., hagryphus). the only larger elements of the fauna besides dinosaurs are two taxa of crocodylians, a pholidosaur very similar to denazinasuchus and deinosuchus. ongoing reconnaissance efforts in the kaiparowits formation continue to add to its diverse vertebrate fauna and have rapidly enhanced the figure 33. ram 14000, an exceptionally well preserved juvenile specimen of the dinosaur parasaurolophus sp. individual is fully articulated and exhibits soft tissue preservation. the black scale bar is 10 cm. photograph by raymond alf (museum of paleontology). 260 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 macrovertebrate assemblages documented in previous published summaries (see appendix). as of now, the kaiparowits holds the record for most diverse late campanian assemblages of turtles, mammals, squamates, and crocodylians in north america and is rapidly closing the gap with the diverse dinosaur assemblages known from the dinosaur park formation (dinosaur provincial park, alberta, canada). new discoveries continue to add fossil materials to previously documented macrovertebrate taxa, permitting more thorough comparison and phylogenetic evaluation, and add new forms to the overall assemblage. this includes many new, exquisitely preserved crocodyliform specimens that expand the documented diversity and completeness of the group: (1) several associated pterosaur specimens that radically enhance the non-marine record of pterosaurs; and (2) new dinosaur materials that include several specimens of a new chasmosaurine ceratopsian, two new genera of ankylosaur (wiersma, 2016), and a possible small lambeosaurine hadrosaurid. these new finds, coupled with ongoing efforts to document the microverterate record, the plant macrofossil record, the invertebrate fossil record, and the geological record of the kaiparowits formation, promise to make it among the best-documented and understood terrestrial ecosystems in the mesozoic. comparison of the kaiparowits vertebrate assemblage to contemporaneous faunas from dinosaur park formation have documented significant differences in vertebrate taxa. differences are attributed to possible physiographic barriers (e.g., sampson and others, 2010; gates and others, 2012) or climatic/floral differences (e.g., miller and others, 2013; nydam and others, 2013). end of day 2, return to tropic, utah. figure 34. umnh vp 16868, adocus with skeleton and eggs, the latter are visible in the bottom center of the photo (yellow arrows). scale = 10 cm. 261 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 day 3: cretaceous-paleogene boundary in southern utah 0.0 miles – start in tropic at 200 north and sr 12. proceed west on sr 12. 7.2 miles – junction of sr 12 and sr 22 (johns valley road). turn right (north) on sr 22 and proceed north. 20.6 miles – junction with sr 17 (old escalante road). turn right (east) and proceed east. 23.3 miles – stop 16. k-pg boundary and the canaan peak formation: the more resistant beds of the canaan peak formation (figure 36) are well exposed on this general stretch of sr17. the observable lithosomes are completely typical for the formation, and consist of trough cross-bedded pebble and cobble conglomerate with distinctive black chert clasts and other rocks derived from the lower paleozoic siliceous strata of the sevier fold and thrust belt as well as the earlier antler foreland detritus. jurassic and early cretaceous age volcanic clasts ranging in composition from rhyolite to andesite can locally make up as much as 30% of the total rock (schmitt and others, 1991). the type section is located 30 km to the south (bowers, 1972), on the south side of canaan peak, where it rests with slight angular unconformity on the kaiparowits formation and contains an identical clast composition (schmitt and others, 1991). goldstrand (1992) subsefigure 35. view looking west over the blues from the upper view point along sr 12. mostly the lower 400 m of the kaiparowits formation is seen from this view. 262 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 quently recognized an upper unit in the canaan peak which completely lacks volcanic clasts and is instead dominated by more proximally derived paleozoic and mesozoic sedimentary clasts from the wah wah thrust system. given the similar composition of this upper canaan peak unit with the grand castle formation in its type section (western markagunt plateau), these units were correlated and the term grand castle was extended into the table cliffs area by goldstrand (1992). all of this pre-supposed that the grand castle in its type section was actually paleogene (post-kaiparowits formation) in age. now that the entire type grand castle formation as originally conceived by goldstrand can be demonstrated to be both cretaceous and pre-kaiparowits formation in age (lower and middle campanian [biek and others, 2015]), use of the term grand castle in the table cliffs area should be abandoned. based on gross clast composition, this locally occurring volcanic clast-free lithosome in the table cliffs area may be genetically related to the overlying pine hollow formation, but this needs further work. surprisingly, the areal extent of the canaan peak formation is fairly limited, given its resistant nature and substantial thickness. over most of the region the cretaceous-paleogene boundary represents a much more substantial hiatus (figure 14). unequivocal canaan peak is known with certainty only east of the paunsaugunt fault, around the table cliffs and canaan peak. however, it was obviously once much more widespread as current directions indicate a source area to the west and southwest (schmitt and others, 1991). the precise age of the canaan peak formation proper is unknown as it has not yielded any age diagnostic faunal data or datable ash beds. paleocene palynological assemblages (goldstrand, 1990) have been reported from the upper volcanic-clast-free unit (grand castle of figure 36. conglomerate and cross-stratified sandstone of the canaan peak formation exposed in horse canyon, north of sr 17. 263 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 goldstrand, 1992). if these palynology data are correct, then the canaan peak, as we define it here (excluding the non-volcanic clast-bearing part), can only be constrained as post middle upper campanian to paleocene. eric roberts (james cook university, oral communication, 2013) has observed dinosaur bone in the lower portion of the canaan peak near the type section. however, it is unknown at this time whether this represents contemporaneous bone or elements reworked from the underlying kaiparowits formation. the volcanic clast content of the canaan peak formation ties it genetically to the underlying kaiparowits formation and strongly differentiates it from all overlying units (larsen and others, 2010). from a strictly event-oriented view, since laramide uplift completely removed the canaan peak and kaiparowits formations from the paunsaugunt plateau region, mostly likely in the late paleocene or early eocene (i.e., pre-claron), it seems reasonable to assume that the volcanic lithic-rich kaiparowits and canaan peak formations occupy a space in time closer to each other than the canaan peak would with the pine hollow formation because the pine hollow is compositionally very close to the claron formation (larsen, 2007). as such, the canaan peak formation, which could be campanian-maastrichtian in age, could also locally span the cretaceous-paleogene boundary. end of field trip acknowledgements we would like to thank the reviewers for making substantial improvements to the manuscript and the geology of intermountain west editors for assistance with the editing. we would also like to thank the bureau of land management—grand staircase-escalante national monument for support during the writing of this paper, and also supporting much of the paleontological research in the kaiparowits basin that has been undertaken since 1996. references albright, l.b., iii, gillette, d.d., and titus, a.l., 2007a, plesiosaurs from the upper cretaceous (cenomanian-turonian) tropic shale of southern utah, part 1—new records of the pliosaur brachauchenius lucasi: journal of vertebrate paleontology, v. 27, p. 31–40. albright, l.b., iii, gillette, d.d., and titus, a.l., 2007b, plesiosaurs from the upper cretaceous (cenomanian-turonian) tropic shale of southern utah, part 2—polycotylidae: journal of vertebrate paleontology, v. 27, p. 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270 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 appendix late cretaceous vertebrate faunal lists for southern utah background although the total number of taxa is known to be higher in every single cretaceous formation of southern utah, these faunal lists were generated only from published papers that documented specific specimens from specific localities with certain taxonomic assignments. taxa listed in undocumented faunal lists (e.g., eaton, 1999; eaton and others, 1999a, 1999b) or overly broad taxonomic assignments are not included. as such, we only list the published turtle fauna from hutchison and others (2013, kaiparowits formation) and holroyd and hutchison (2016, wahweap formation) even though turtle remains are common in nearly every formation. similarly, a large number of additional dinosaur taxa are known from the wahweap and kaiparowits formations, but either the specimens have never been described or the material is not specifically diagnostic. irmis and others (2013) described the crocodyliform fauna at the order-suborder level and generally did not provide locality information for specimens; however, two taxa at lower levels were described from the kaiparowits formation, and since fossils are only known from that formation on the kaiparowits plateau, those are included below. the fish described by brinkman and others (2013) are from a limited number of localities and are only recorded in the faunal lists from the specific plateau from which the specimens are documented. as such, there is a large list of fish represented from the wahweap formation of the paunsaugunt plateau, but these were not extended to the wahweap formation of the kaiparowits plateau as there is no documentation for that presented in brinkman and others (2013). in the faunal lists, names, and years in parentheses cite the original publication naming that taxon, whereas those citations preceded by “in” merely refer to a source that documents the taxon in southern utah. for nearly all macrovertebrates, the reference is the same as the original paper naming the taxon. cretaceous vertebrate faunas of cedar canyon – markagunt plateau naturita formation, cenomanian (localities: umnh vp 161, 162) allocaudata albanerpetontidae gen. and sp. indet. (in gardner and demar, 2013) anura family incertae sedis gen. and sp. indet. (in roček and others, 2010) squamata boreoteiioidea bicuspidon smikros (in nydam, 2013) scincomorpha contogenidae utahgenys antongai (in nydam, 2013) paramacellodid/cordylid grade morphotype a (in nydam, 2013) morphotype b (in nydam, 2013) anguimorpha family incertae sedis gen. and sp. indet. (in nydam, 2013) multituberculata family incertae sedis – paracimexomys group gen. and sp. indet. (in eaton, 2009) cf. paracimexomys sp. (in eaton, 2009) cedaromys minimus (in eaton, 2009) dakotamys malcolmi (in eaton, 2009) cimolodontidae gen. and sp. indet. (in eaton, 2009) ?cimolodontidae gen. and sp. indet. (in eaton, 2009) symmetrodonta spalacotheriidae gen. and sp. indet. (in eaton, 2009) boreosphenida family incertae sedis gen. and sp. indet. (in eaton, 2009) marsupialia “alphadontidae” eoalphadon woodburnei (in eaton, 2009) ?eoalphadon sp. (in eaton, 2009) 271 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 john henry member (coniacian?), straight cliffs formation (localities: mna 1260/umnh vp 8, 9) elasmobranchii lonchidiidae lonchidion sp. (in kirkland and others, 2013) neoselachii ginglymostomatidae cantioscyllium markaguntensis (kirkland and others, 2013) neopterygii semionotidae lepidotes sp. indet. (in brinkman and others, 2013) pycnodontidae coelodus sp. (in brinkman and others, 2013) teleostii otophysi order and family indet. gen. and sp. indet. (in brinkman and others, 2013) acanthomorpha order and family indet. gen. and sp. indet. (in brinkman and others, 2013) urodela scapherpetontidae gen. and sp. indet. (in gardner and demar, 2013) family incertae sedis gen. and sp. indet. (in gardner and demar, 2013) anura family incertae sedis gen. and sp. indet. (in roček and others, 2010) multituberculata family incertae sedis – paracimexomys group cedaromys sp. (in eaton, 2006a) marsupialia family “alphadontidae” ?varalphadon sp. (in eaton, 2006a) eutheria order and family incertae sedis gen. and sp. indet. (in eaton, 2006a) “wahweap” formation (basal, lower? campanian) (locality: umnh vp 10/mna 1417) allocaudata albanerpetontidae gen. and sp. indet. (in gardner and demar, 2013) anura family incertae sedis gen. and sp. indet. (in roček and others, 2010) multituberculata family incertae sedis – paracimexomys group cf. paracimexomys sp. (in eaton, 2006a) 272 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 bryceomys sp. (in eaton, 2006a) cedaromys sp. cf. c. hutchisoni (in eaton, 2006a) cedaromys sp. (in eaton, 2006a) ?cimoxomys sp. (in eaton, 2006a) cimolomyidae cimolomys sp. (in eaton, 2006a) ?cimolomys sp. (in eaton, 2006a) cimolodontidae cimolodon wardi (in eaton, 2006a) cimolodon similis (in eaton, 2006a) cimolodon sp. cf. c. nitidus (in eaton, 2006a) neoplagiaulacidae mesodma sp. cf. m. minor (in eaton, 2006a) trechnotheria spalacotheriidae symmetrodontoides sp. cf. s. foxi (eaton, 2006a) marsupialia order and family incertae sedis cf. anchistodelphys sp. (in eaton, 2006a) “alphadontidae” cf. varalphadon sp. (in eaton, 2006a) cf. protalphadon sp. (in eaton, 2006a) eoalphadon sp. cf. e. clemensi (in eaton, 2006a, see eaton, 2009) eoalphadon sp. (in eaton, 2006a, see eaton, 2009) cf. turgidodon sp. (in eaton, 2006a) ?pediomyidae ?”pediomys” sp. (in eaton, 2006a) boreosphenida picopsidae picopsis sp. (in eaton, 2006a) cf. picopsis sp. a (in eaton, 2006a) cf. picopsis sp. b (in eaton, 2006a) “wahweap” formation (high, campanian?) (locality: umnh vp 11) urodela family incertae sedis nezpercius dodsoni (in gardner and demar, 2013) anura family incertae sedis scotiophryne pustulosa (in roček and others, 2010; gardner and demar, 2013) gen. and sp. indet. (in roček and others, 2010) multituberculata family incertae sedis – paracimexomys group cedaromys sp. (in eaton, 2006a) cimolomyidae 273 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 meniscoessus sp. cf. m. intermedius (in eaton, 2006a) cimolomys sp. (in eaton, 2006a) ?cimolomys sp. (in eaton, 2006a) cimolodontidae cimolodon sp. cf. c. similis (in eaton, 2006a) marsupialia “alphadontidae” gen. and sp. indet. (in eaton, 2006a) protalphadon sp. (in eaton, 2006a) ?protalphadon sp. (in eaton, 2006a) eoalphadon sp. cf. e. clemensi (in eaton, 2006a, see eaton, 2009) “pediomyidae” gen. and sp. indet. (in eaton, 2006a) “pediomys” sp. near “p.” exiguous (in eaton, 2006a) ?aquiladelphis laurae (in eaton, 2006a) cretaceous vertebrate faunas of the paunsaugunt plateau naturita formation, cenomanian (locality: umnh vp 123/mna 939) anura family, gen. and sp. indet. (in roček and others, 2010) multituberculata cimolodontidae gen. and sp. indet. (in eaton, 1995) family incertae sedis – paracimexomys group paracimexomys sp. cf. p. robisoni (in eaton, 1995) paracimexomys sp. (in eaton, 1995) cf. paracimexomys sp. (in eaton, 1995) dakotamys malcolmi (in eaton, 1995) theria family, gen. and sp. indet. (in eaton, 1993b) marsupialia “alphadontidae” eoalphadon lillegraveni (in eaton, 1993b as “alphadon” lillegraveni) eoalphadon sp. (in eaton, 1993b as “alpahdon” sp.) family incertae sedis pariadens kirklandi (in eaton, 1993b) john henry member (basal, coniacian), straight cliffs formation (localities: umnh vp 417, 823, 856, 1064) elasmobranchii hybodontidae hybodus sp. (in kirkland and others, 2013) lonchidiidae lonchidion sp. (in kirkland and others, 2013) 274 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 anura family incertae sedis gen. and sp. indet. (in roček and others, 2010) dinosauria ornithopoda iguanodontia gen. and sp. indet. (in gates and others, 2013) multituberculata cimolodontidae mesodma sp. cf. m. minor (in eaton, 2013) john henry member (santonian), straight cliffs formation (localities: umnh vp 419, 420, 424, 426, 427, 569, 781, 799, 821, 843, 1144, 1156) elasmobranchii hybodontidae hybodus sp. (in kirkland and others, 2013) neopterygii lepisostidae lepisosteus sp. indet. (in brinkman and others, 2013) neopterygii semionotidae lepidotes sp. indet. (in brinkman and others, 2013) pycnodontidae micropycnodon sp. (in brinkman and others, 2013) amiidae gen. and sp. indet. (in brinkman and others, 2013) teleostii hiodontidae gen. and sp. indet. (in brinkman and others, 2013) elopiformes family indet. gen. and sp. indet. (in brinkman and others, 2013) sorbinichthyidae diplomystus sp. (in brinkman and others, 2013) otophysi order and family indet. gen. and sp. indet. (in brinkman and others, 2013) euteleostei order and family indet. gen. and sp. indet. u-4 (in brinkman and others, 2013) acanthomorpha order and family indet. gen. and sp. indet. (in brinkman and others, 2013) allocaudata albanerpetontidae gen. and sp. indet. (in gardner and demar, 2013) cf. albanerpeton nexuosum (gardner and demar, 2013) urodela scapherpetontidae scapherpeton sp. (in gardner and demar, 2013) 275 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 batracosauroididae opistotriton sp. (in gardner and demar, 2013) gen. and sp. indet. (in gardner and demar, 2013) sirenidae habrosaurus sp. (in gardner and demar, 2013) family incertae sedis gen. and sp. nov. (in gardner and demar, 2013) anura family incertae sedis scotiophryne pustulosa (in roček and others, 2010, gardner and demar, 2013) gen. and sp. indet. (in roček and others, 2010) scincomorpha paramacellodid/cordylid grade monocnemodon syphakos (in nydam, 2013) anguimorpha family incertae sedis cf. colpodontosaurus sp. (in nydam, 2013) platynota family incertae sedis morphotype b (in nydam, 2013) morphotype c (in nydam, 2013) autarchoglossa family incertae sedis morphotype d (in nydam, 2013) scincomorpha family incertae sedis gen. and sp. indet. (in nydam, 2013) serpentes family incertae sedis coniophis sp. (in nydam, 2013) dinosauria nodosauridae gen and sp. indet. (in loewen and others, 2013a) triconodonta triconodontidae gen. and sp. indet. (in eaton, 2013) cf. alticonodon sp. (in eaton, 2013) multituberculata family incertae sedis – paracimexomys group dakotamys shakespeari (in eaton, 2013) cedaromys sp. cf. c. hutchisoni (in eaton, 2013) neoplagiaulacidae mesodma sp. cf. m. minor (in eaton, 2013) mesodma sp. (in eaton, 2013) ?mesodma sp. (in eaton, 2013) 276 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 cimolodontidae cimolodon sp. cf. c. foxi (in eaton, 2013) cimolodon similis (in eaton, 2013) cimolodon sp. cf. c. similis (in eaton, 2013) ?cimolodon sp. (in eaton, 2013) cimolomyidae cimolomys sp. a (in eaton, 2013) cimolomys sp. b (in eaton, 2013) ?cimolomys sp. a (in eaton, 2013) ?cimolomys sp. b (in eaton, 2013) trechnotheria spalacotheriidae ?spalacotheridium sp. (in eaton, 2013) symmetrodontoides sp. (in eaton, 2013) marsupialia “didelphomorpha” family incertae sedis gen. and sp. indet. (in eaton, 2013) apistodon sp. cf. a. exiguous (in eaton, 2013) cf. “anchistodelphys” sp. (in eaton, 2013) “alphadontidae” ?varalphadon sp. (in eaton, 2013) stagodontidae eodelphis sp. (in eaton, 2013) pediomyidae gen. and sp. indet. (in eaton, 2013) ?leptalestes sp. (in eaton, 2013) wahweap formation, campanian (localities: umnh vp 61, 77, 78, 80, 83, 807, 792, 1073, 1074; mna 1073, 1074) neoselachii hemiscyllidae chiloscyllium missouriense (in kirkland and others, 2013) batomorphii rhinobatoidea family incertae sedis cristomylus cifellii (kirkland and others, 2013) sclerorhynchiformes sclerorhynchiidae columbusia deblieuxi (kirkland and others, 2013) neopterygii lepisostidae lepisosteus sp. indet. (in brinkman and others, 2013) semionotidae lepidotes sp. indet. (in brinkman and others, 2013) pycnodontidae micropycnodon sp. (in brinkman and others, 2013) 277 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 actinopterygii albulidae parabula sp. (in brinkman and others, 2013) otophysi order and family indet. gen. and sp. indet. (in brinkman and others, 2013) acanthomorpha order and family indet. gen. and sp. indet. (in brinkman and others, 2013) allocaudata albanerpetontidae gen. and sp. indet. (in gardner and demar, 2013) urodela scapherpetontidae scapherpeton tectum in gardner and demar, 2013) batracosauroididae opistotriton kayi (in gardner and demar, 2013) family incertae sedis nezpercius dodsoni (in gardner and demar, 2013) gen. and sp. nov. (in gardner and demar, 2013) anura family incertae sedis scotiophryne pustolosa (in roček and others, 2010) gen. and sp. indet. (in roček and others, 2010) multituberculata family incertae sedis – paracimexomys group paracimexomys sp. (in eaton, 1993b) ?paracimexomys sp. (in eaton, 2013) cedaromys sp. cf. c. hutchisoni (in eaton, 2013) ?cimexomys gregoryi (in eaton, 1993b) gen. and sp. indet. (in eaton, 2002) neoplagiaulacidae mesodma sp. cf. m. minor (in eaton, 2013) mesodma sp. cf. m. archibaldi (in eaton, 2002, 2013) mesodma sp. cf. m. formosa (in eaton, 1993b, 2013) mesodma sp. cf. m. hensleighi (in eaton, 1993b) mesodma sp. (in eaton, 1993b) cimolodontidae cimolodon similis (in eaton, 2002) cimolodon sp. cf. c. nitidus (in eaton, 1993b) cimolodon sp. cf. c. foxi (in eaton, 2013) ?cimolodon sp. (eaton, 1993b) cimolomyidae cimolomys milliensis (in eaton, 1993b) cimolomys sp. (in eaton, 2013) ?cimolomys sp. (in eaton, 2013) ?cimolomys sp. b (in eaton, 2002) 278 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 meniscoessus sp. (in eaton, 2013) trechnotheria spalacotheriidae symmetrodontoides foxi (in eaton, 1993b) marsupialia order and family incertae sedis cf. iugomortiferum sp. (in eaton, 2013) gen. and sp. indet. a (in eaton, 2013) gen. and sp. indet. b (in eaton, 2013) cf. apistodon sp. (in eaton, 2013) “alphadontidae” alphadon sp. cf. a. wilsoni (in eaton, 1993b) alphadon sp. cf. a. attaragos (in eaton, 1993b) turgidodon sp. cf. t. russelli (alphadon sp. cf. a. russelli in eaton, 1993b) turgidodon sp. (in eaton, 1993b) varalphadon sp. cf. v. creber (in eaton, 2013) cf. varalphadon sp. (in eaton, 2013) pediomyidae gen. and sp. indet. (in eaton, 2013) cretaceous vertebrate faunas of the kaiparowits plateau naturita formation, cenomanian (localities: umnh vp 27/mna 1067/omnh v808; umnh vp 804) batomorphii rhinobatoidea family incertae sedis cristomylus bulldogensis (kirkland and others, 2013) pseudomyledaphus sp. (in kirkland and others, 2013) elasmobranchii hybonontidae hybodus sp. (in kirkland and others, 2013) lonchidiidae lonchidion sp. (in kirkland and others, 2013) neopterygii semionotidae lepidotes sp. (in brinkman and others, 2013) pycnodontidae coelodus sp. (in brinkman and others, 2013) amiidae gen. and sp. indet. (in brinkman and others, 2013) teleostei osteoglossomorpha family indet. coriops sp. (in brinkman and others, 2013) hiodontidae gen. and sp. indet. (in brinkman and others, 2013) elopiformes family indet. 279 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 gen. and sp. indet. (in brinkman and others, 2013) ellimmichthyiformes family indet. gen. and sp. indet. type lvd (in brinkman and others, 2013) gen. and sp. indet. type u-7 (in brinkman and others, 2013) sorbinichthyidae diplomystus sp. (in brinkman and others, 2013) euteleostei order and family indet. gen. and sp. indet. u-4 (in brinkman and others, 2013) sarcopterygii ceratodontiformes ceratodus gustasoni (kirkland, 1987) allocaudata albanerpetontidae cf. albanerpeton nexuosa (in gardner and demar, 2013) urodela scapherpetontidae gen and sp. indet. (in gardner and demar, 2013) batracosauroididae gen. and sp. nov. (in gardner and demar, 2013) anura family incertae sedis gen. and sp. indet. (in roček and others, 2010) squamata boreoteiioidea bicuspidon smikros (in nydam, 2013) scincomorpha paramacellodid/cordylid grade dakotasaurus gillettorum (in nydam, 2013) morphotype c (in nydam, 2013) webbsaurus lofgreni (in nydam, 2013) family indet. morphotype d (in nydam, 2013) ?scincomorpha family incertae sedis gen. and sp. indet. (in nydam, 2013) anguimorpha aff. xenosauridae cnodontosaurus suchockii (in nydam, 2013) platynota family indet. morphotype e (in nydam, 2013) anguimorpha family incertae sedis gen. and sp. indet. (in nydam, 2013) serpentes 280 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 family incertae sedis coniophis sp. (in nydam, 2013) multituberculata family incertae sedis – paracimexomys group paracimexomys sp. cf. p. robisoni (in eaton, 1995) paracimexomys sp. (in eaton, 1995) cf. paracimexomys sp. (in eaton, 1995) dakotamys malcolmi (in eaton, 1995) ?dakotamys sp. (in eaton, 1995) gen. and sp. indet. a (in eaton, 1995) gen. and sp. indet. b (in eaton, 1995) cimolodontidae cimolodon sp. cf. c. similis (in eaton, 1995) gen. and sp. indet. (in eaton, 1995) ?boreosphenida order and family incertae sedis gen. and sp. indet. (in eaton, 1993a) dakotadens morrowi (in eaton, 1993a) dakotadens sp. (in eaton, 1993a) marsupialia family “alphadontidae” eoalphadon clemensi (in eaton, 1993a as “alphadon” clemensi) eoalphadon lillegraveni (in eaton, 1993a as “alphadon” lillegraveni) eoalphadon sp. (in eaton, 1993a as “alphadon” sp.) protalphadon sp. (in eaton, 1993a) gen. and sp. indet. (in eaton, 1993a) family indet. pariadens kirklandi (cifelli and eaton, 1987) tropic shale (late cenomanian-middle turonian) elasmobranchii mitsukurinidae scapanorhyncus raphiodon (in albright and others, 2013) anacoracidae squalicorax curvatus (in albright and others, 2013) cretoxyrhinidae cretoxyrhina mantelli (in albright and others, 2013) cretolamna appendiculata (in albright and others, 2013) sclerorhynocoidei cf. ptychotrygon sp. (in albright and others, 2013) ptychodontidae ptychodus decurrens (in albright and others, 2013) ptychodus cf. p. mammillaris (in albright and others, 2013) ptychodus whipplei (in albright and others, 2013) ptychodus occidentalis (in albright and others, 2013) 281 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 ptychodus anonymus (in albright and others, 2013) ptychodus sp. indet. (in albright and others, 2013) neopterygii pycnodontidae gen. and sp. indet. (in albright and others, 2013) actinopterygii ichthyodectidae gillicus arcuatus (in albright and others, 2013) ichthyodectes ctenodon (in albright and others, 2013) ichthyodectes cf. i. ctenodon (in albright and others, 2013) xiphactinus cf. x. audax (in albright and others, 2013) testudinata protostegidae desmatochelys lowi (in albright and others, 2013) gen. and sp. indet. (in albright and others, 2013) family incertae sedis naomichelys sp. (in albright and others, 2013) sauropterygia pliosauridae brachauchenius lucasi (albright and others, 2007a) polycotylidae eopolycotylus rankini (albright and others, 2007b) dolichorhyncops tropicensis schmeisser mckean, 2012) palmulasaurus quadratus (albright and others, 2007b) trinacromerum cf. t. bentonianum (in albright and others, 2013) dinosauria therizinosauridae nothronychus graffami (zanno and others, 2009) smoky hollow member (turonian), straight cliffs formation (localities: umnh vp 129/mna 995/omnh v843; omnh v4, 60, 1404) batomorphii rhinobatoidea (family incertae sedis) cristomylus sp. cf. c. bulldogensis (in kirkland and others, 2013) osteichthyes-neopterygii lepisostidae lepisosteus sp. (in brinkman and others, 2013) semionotidae lepidotes sp. (in brinkman and others, 2013) pycnodontidae coelodus sp. (in brinkman and others, 2013) amiidae gen. and sp. indet. (in brinkman and others, 2013) ?melvius sp. (in brinkman and others, 2013) teleostii 282 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 hiodontidae gen. and sp. indet. (in brinkman and others, 2013) elopiformes family incertae sedis gen. and sp. indet. (in brinkman and others, 2013) ellimmichthyiformes family incertae sedis. gen. and sp. indet. type u-7 (in brinkman and others, 2013) otophysi order and family incertae sedis gen. and sp. indet. (in brinkman and others, 2013) euteleostei order and family incertae sedis gen. and sp. indet. u-4 (in brinkman and others, 2013) order and family incertae sedis gen. and sp. indet. type hvb (in brinkman and others, 2013) allocaudata albanerpetontidae albanerpeton cifellii (in gardner, 1999) cf. albanerpeton nexuosum (in gardner and demar, 2013) gen. and sp. indet. (in gardner and demar, 2013) urodela batracosauroididae gen. and sp. nov. (in gardner and demar, 2013) family incertae sedis gen. and sp. nov. (in gardner and demar, 2013) gen. and sp. indet. (in gardner and demar, 2013) anura family incertae sedis gen. and sp. indet. (in roček and others, 2010) scinocomorpha polyglyphanodontini dicothodon cifellii (in nydam and others, 2007) chamops sp. cf. c. signus (in nydam, 2013) contogeniidae utahgenys evansi (in nydam, 2013) paramacellodid/cordylid grade morphotype a-h (in nydam, 2013) anguimorpha anguidae aff. odaxosaurus sp. (in nydam, 2013) aff. xenosaurida cnodontosaurus sp. (in nydam, 2013) platynota family incertae sedis morphotype i-j (in nydam, 2013) anguimorpha family incertae sedis gen. and sp. indet. (in nydam, 2013) 283 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 serpentes family incertae sedis coniophis sp. (in nydam, 2013) dinosauria ornithopoda iguanodontia gen. and sp. indet. (in gates and others, 2013) multituberculata ?taeniolabidoidea family incertae sedis gen. and sp. indet. (in eaton, 1995) suborder and family incertae sedis paracimexomys group paracimexomys sp. cf. p. robisoni (in eaton, 1995) bryceomys fumosus (in eaton, 1995) ` bryceomys sp. cf. b. fumosus (in eaton, 1995) bryceomys hadrosus (in eaton, 1995) bryceomys sp. (in eaton, 1995) symmetrodonta family incertae sedis gen. and sp. indet. (in cifelli and gordon, 1999) spalacotheriidae symmetrodontoides oligodontos (in cifelli and gordon, 1999) spalacotheridium mckennai (in cifelli and gordon, 1999) aegialodontia deltatheridiidae gen. and sp. indet. (in cifelli, 1990a) family incertae sedis gen. and sp. indet. (in cifelli, 1990a) marsupialia family incertae sedis ?varalphadon delicates (in cifelli, 1990a) ?stagodontidae gen. and sp. indet. (in cifelli, 1990a) john henry member (basal coniacian), straight cliffs formation (localities: omnh v856; umnh vp 663) batomorphii rhinobatoidea family incertae sedis pseudomyledaphus madseni (kirkland and others, 2013) allocaudata albanerpetontidae gen. and sp. indet. (in gardner and demar, 2013) urodela scapherpetontidae scapherpeton tectum (in gardner and demar, 2013) gen. and sp. indet. (in gardner and demar, 2013) john henry member (santonian), straight cliffs formation (localities: umnh vp 98, 99, 567; omnh v27; mna 706) 284 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 neoselachii ginglymostomatidae cantioscyllium markaguntensis (kirkland and others, 2013) batomorphii rhinobatoidea family incertae sedis pseudomyledaphus madseni (kirkland and others, 2013) allocaudata albanerpetontidae gen. and sp. indet. (in gardner and demar, 2013) urodela batracosauroididae opistotriton kayi (in gardner and demar, 2013) gen. and sp. indet. (in gardner and demar, 2013) anura family incertae sedis gen. and sp. indet. (in roček and others, 2010) scincomorpha paramacellodid/cordylid grade monocnemodon syphakos (in nydam, 2013) morphotype a (in nydam, 2013) multituberculata family incertae sedis – paracimexomys group cedaromys sp. cf. c. hutchisoni (in eaton, 2006b) cedaromys sp. (in eaton, 2006b) family incertae sedis gen. and sp. indet. (in eaton, 2006b) neoplagiaulacidae mesodma sp. cf. m. minor (in eaton, 2006b) cimolodontidae cimolodon foxi (in eaton, 2006b) cimolodon sp. (in eaton, 2006b) ?cimolodon sp. (in eaton, 2006b) cimolomyidae ?cimolomys sp. (in eaton, 2006b) theria spalacotheriidae spalacotherium sp. (in eaton, 2006b) symmetrodontoides sp. cf. s. oligodontos (in cifelli and gordon, 1999) family incertae sedis potamotelses sp. (in eaton, 2006b) picopsis sp. (in eaton, 2006b) marsupialia “alphadontidae” alphadon sp. cf. a. halleyi (in eaton, 2006b) varalphadon sp. (in eaton, 2006b) 285 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 ?stagodontidae gen. and sp. indet. (in eaton, 2006b) family incertae sedis ?anchistodelphys sp. (in eaton, 2006b) gen. and sp. indet. (in eaton, 2006b) wahweap formation, middle campanian (localities: omnh v2, 8, 11, 16; umnh vp 82, 130; mna 455, 456, 702, 705, 707, 1015, 1294) elasmobranchii hybodontidae hybodus sp. (in kirkland and others, 2013) lonchidiidae lonchidion sp. (in kirkland and others, 2013) neoselachii ginglymostomatidae cantioscyllium estesi (in kirkland and others, 2013) hemiscyllidae chiloscyllium missouriense (in kirkland and others, 2013) batomorphii rhinobatoidea family incertae sedis cristomylus cifellii (kirkland and others, 2013) sclerorhynchiformes sclerorhynchiidae columbusia deblieuxi (kirkland and others, 2013) texatrygon brycensis (kirkland and others, 2013) osteichthyes-neopterygii amiidae melvius cf. m. chauliodous (in holroyd and hutchison, 2016) lepisostidae gen. and sp. indet. (in holroyd and hutchison, 2016) actinopterygii polydontidae gen. and sp. indet. (in brinkman and others, 2013) urodela batracosauroididae opistotriton kayi (in gardner and demar, 2013) family incertae sedis nezpercius dodsoni (in gardner and demar, 2013) anura family incertae sedis scotiophryne pustulosa (in roček and others, 2010) gen. and sp. indet. (in roček and others, 2010) testudines baenidae arvinochelys sp. (in holroyd and hutchison, 2016) 286 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 denazinamys nodosa (in holroyd and hutchison, 2016) neurankylus sp. (in holroyd and hutchison, 2016) nanhsiungchelyidae basilemys sp. (in holroyd and hutchison, 2016) trionychidae gen. and sp. indet. (in holroyd and hutchison, 2016) squamata cf. anguimorpha indet. (in nydam, 2013) serpentes family incertae sedis coniophis sp. (in nydam, 2013) cf. scincomorpha – family incertae sedis morphotype a (in nydam, 2013) gen, and sp. indet. (in nydam, 2013) dinosauria-saurischia theropoda-tyrannosauridae lythronax argestes (lowen and others, 2013c). dinosauria-ornithischia ornithopoda-hadrosauridae saurolophinae acristavus sp. (in gates and others, 2013) c.f. brachylophosaurus sp. (in gates and others, 2013) lambeosaurinae (crested hadrosaurs) adelolophus hutchisoni (gates and others, 2014) ceratopsidae centrosaurinae diabloceratops eatoni (kirkland and deblieux, 2010) machairoceratops cronusi (lund and others, 2016) “wahweap centrosaurine c” (in loewen and others, 2013b) pachcephalosauridae gen. and sp. indet. (in evans and others, 2013) multituberculata family incertae sedis – paracimexomys group gen. and sp. indet. (in eaton, 2002) ?paracimexomys sp. (in eaton, 2002) cf. paracimexomys sp. a (in eaton, 2002) cf. paracimexomys sp. b (in eaton, 2002) bryceomys sp. cf. b. fumosus (in eaton, 2002) cedaromys sp. (in eaton, 2002) cf. cedaromys sp. (in eaton, 2002) ?cimexomys sp. cf. c. antiguus (in eaton, 2002) neoplagiaulacidae mesodma sp. cf. m. formosa (in eaton, 2002) mesodma sp. cf. m. minor (in eaton, 2002) mesodma sp. cf. m. archibaldi (in eaton, 2002) 287 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 cimolodontidae cimolodon electus (in eaton, 2002) cimolodon similis (in eaton, 2002) cimolodon sp. cf. c. nitidus (in eaton, 2002) cimolodon sp. cf. c. foxi (in eaton, 2002) cimolodon sp. (small) (in eaton, 2002) cimolomyidae cimolomys sp. cf. c. trochuus (in eaton, 2002) ?cimolomys sp. a (in eaton, 2002) ?cimolomys sp. b (in eaton, 2002) ?cimolomys sp. c (large) (in eaton, 2002) meniscoessus sp. cf. m. intermedius (in eaton, 2002) symmetrodonta family incertae sedis gen. and sp. indet. (in cifelli and gordon, 1999) spalacotheriidae symmetrodontoides foxi (in cifelli and madsen, 1986; cifelli and gordon, 1999) order and family incertae sedis zygiocuspis goldingi (in cifelli, 1990c) marsupialia “alphadontidae” varalphadon crebreforme (in cifelli, 1990b) varalphadon wahweapensis (in cifelli, 1990b) gen. and sp. indet. (in cifelli, 1990b) ?marsupialia family incertae sedis iugomortiferum thoringtoni (in cifelli, 1990b) cf. iugomortiferum sp. (in cifelli, 1990b) insectivora ?nyctitheriidae paranyctoides sp. (in cifelli, 1990e) kaiparowits formation, upper campanian (localities: omnh v5, 6, 9, 61; umnh vp 24, 25, 51, 54, 56, 108, 1078, 1268; mna 453, 454, 458, 697, 704, 1004, 1310; ucm 83240; 83258; for turtle bearing localities see hutchison and others, 2013) neoselachii hemiscyllidae chiloscyllium missouriense (in kirkland and others, 2013) batomorphii rhinobatoidea family incertae sedis myledaphus bipartitus (kirkland and others, 2013) sclerorhynchiformes sclerorhynchiidae columbusia deblieuxi (kirkland and others, 2013) osteichthyes-neopterygii 288 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 semionotidae lepidotes sp. indet. (in brinkman and others, 2013) amiidae gen. and sp. indet. (in brinkman and others, 2013) lepisostidae lepisosteus sp. indet. (in brinkman and others, 2013) teleostei osteoglossomorpha family incertae sedis coriops sp. (in brinkman and others, 2013) hiodontidae gen. and sp. indet. (in brinkman, 2013) albulidae parabula sp. (in brinkman and others, 2013) clupeiformes family incertae sedis gen. and sp. indet. type g (in brinkman and others, 2013) otophysi order and family incertae sedis gen. and sp. indet. (in brinkman and others, 2013) characiformes family incertae sedis gen. and sp. indet. (in brinkman and others, 2013) euteleostei order and family incertae sedis gen. and sp. indet. u-4 (in brinkman and others, 2013) esocoidea family incertae sedis estesesox foxi (in brinkman and others, 2013) estesesox sp. (in brinkman and others, 2013) order and family incertae sedis gen. and sp. indet. type bve (in brinkman and others, 2013) acanthomorpha order and family incertae sedis gen. and sp. indet. (in brinkman and others, 2013) allocaudata albanerpetontidae albanerpeton galaktion (in gardner and demar, 2013) albanerpeton gracile (in gardner and demar, 2013) albanerpeton nexuosum (in gardner and demar, 2013) urodela scapherpetontidae scapherpeton tectum (in gardner and demar, 2013) lisserpeton bairdi (in gardner and demar, 2013) batracosauroididae opistotriton kayi (in gardner and demar, 2013) prodesmondon copei (in gardner and demar, 2013) sirenidae habrosaurus sp. (in gardner and demar, 2013) anura family incertae sedis scotiophryne pustulosa (in gardner and demar, 2013) 289 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 theatonius sp. (in gardner and demar, 2013) cf. eopelobates sp. (in gardner and demar, 2013) gen. and sp. indet. (in roček and others, 2010; roček and others, 2013) scincomorpha borioteiioidea peneteius saueri (in nydam, 2013) meniscognathus molybrochorus (nydam and voci, 2007) chamops sp. cf. c. segnis (in nydam, 2013) cf. leptochamops sp. (in nydam and voci, 2007) tripennaculus eatoni (in nydam and voci, 2007) contogeniidae palaeoscincosaurus pharkidodon (nydam and fitzpatrick, 2009) paramacellodid/cordylid grade morphotype a-g (in nydam, 2013) anguimorpha anguidae odaxosaurus roosevelti (in nydam, 2013) xenosauridae ?exostinus sp. (in nydam, 2013) platynota family incertae sedis parasaniwa cynochoros (nydam, 2013) morphotypes h-j (in nydam, 2013) serpentes family incertae sedis coniophis sp. (in nydam, 2013) testudines pleurosternidae compsemys victa (in hutchison and others, 2013) baenidae neurankylus hutchisoni (lively, 2015b; new sp. a in hutchison and others, 2013) neurankylus utahensis (lively, 2015b; new sp. b in hutchison and others, 2013) arvinachelys goldeni (lively, 2015a) denazinemys nodosa (in hutchison and others, 2013; lively, 2015b) boremys grandis (in hutchison and others, 2013; lively, 2015b) plesiobaena sp. (in hutchison and others, 2013) thescelus sp. (lively, 2015b) chelydridae gen. and sp. indet. (in hutchison and others, 2013) kinosternidae gen. and sp. indet. (in hutchison and others, 2013) adocidae adocus sp. (in hutchison and others, 2013) nanhsiungchelyidae basilemys nobilis (in hutchison and others, 2013) 290 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 trionychidae helopanoplia sp. (in hutchison and others, 2013) aspideretoides sp. (in hutchison and others, 2013) derrisemys sp. (in hutchison and others, 2013) plastomenoides sp. (in hutchison and others, 2013) gen. and sp. indet. (in hutchison and others, 2013) crocodylia neosuchia cf. denazinasuchus sp. alligatoroidea family incertae sedis cf. leidyosuchus sp. (in farke and others, 2014) deinosuchus hatcheri (in irmis and others, 2013) brachychampsa sp. (in irmis and others, 2013) ?pterosauria gen. and sp. indet (in farke and others, 2013) dinosauria-saurischia theropoda-ornithomimidae ornithomimus sp. indet. (in claessens and loewen, 2015) oviraptoridae hagryphus giganteus (zanno and sampson, 2005) dromaeosauridae morphotype a (cf. dromaeosaurus) (in zanno and others, 2013) morphotype b (cf. saurornitholestes) (in zanno and others, 2013) troodontidae talos sampsoni (zanno and others, 2011) aviales avisaurus sp. (in zanno and others, 2013) tyrannosauridae teratophoneus curriei (carr and others, 2011) dinosauria-ornithischia hypsilophodontidae gen and sp. nov. (in boyd, 2015, “hypsilophodontid” in gates and others, 2013) hadrosauridae-saurolophinae gryposaurus cf. g. notabilis (in gates and others, 2013) gryposaurus monumentensis (gates and sampson, 2007) hadrosauridae-lambeosaurinae parasaurolophus sp. (in gates and others, 2013) ceratopsidae-chasmosaurinae utahceratops gettyi (sampson and others, 2010) kosmoceratops richardsoni (sampson and others, 2010) ceratopsidae-centrosaurinae nasutoceratops titusi (sampson and others, 2013) “centrosaurine b” (in loewen and others, 2013b) pachycephalosauridae (dome-headed dinosaurs) gen. and sp. indet. (in evans and others, 2013) 291 late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, and kaiparowits plateaus, southern utah titus, a.l., eaton, j.g., and sertich, j. geology of the intermountain west 2016 volume 3 nodosauridae (spike-tailed armored dinosaurs) gen. and sp. indet. (in loewen and others, 2013a) ankylosauridae new genus and species a (in viersma, 2015) new genus and species b (in viersma, 2015) mammalia-multituberculata family incertae sedis cimexomys sp. cf. c. judithae (in eaton, 2002) cimexomys or mesodma sp. (in eaton, 2002) family incertae sedis – paracimexomys group cedaromys hutchisoni (in eaton, 2002) cedaromys sp. (in eaton, 2002) dakotamys magnus (in eaton, 2002) neoplagiaulacidae mesodma archibaldi (in eaton, 2002) mesodma sp. cf. m. archibaldi (in eaton, 2002) mesodma minor (in eaton, 2002) mesodma sp. (large) (in eaton, 2002) cimolodontidae cimolodon foxi (in eaton 2002) cimolodon sp. cf. c. nitidus (in eaton, 2002) cimolodon sp. cf. c. similis (in eaton, 2002) ?cimolodontidae kaiparomys cifellii (in eaton, 2002) cimolomyidae meniscoessus sp. cf. m. intermedius (in eaton, 2002) meniscoessus sp. cf. m. major (in eaton, 2002) cimolomys sp. a cf. c. clarki (in eaton, 2002) cimolomys sp. b cf. c. clarki (in eaton, 2002) ?cimolomyidae ?cimolomys butleria (in eaton, 2002) marsupialia family incertae sedis aenigmadelphys archeri (in cifelli, 1990d; cifelli and johanson, 1994) “alphadontidae” varalphadon wahweapensis (in cifelli, 1990d) turgidodon lillegraveni (in cifelli, 1990d) turgidodon sp. cf. t. lillegraveni (in cifelli, 1990d) turgidodon madseni (in cifelli, 1990d) turgidodon sp. (in cifelli, 1990d) alphadon halleyi (in cifelli, 1990d) “alphadon attaragos” (in cifelli, 1990d) insectivora leptictidae gypsonictops sp. (in cifelli, 1990e) ?nyctitheriidae paranyctoides sp. (in cifelli, 1990e) order and family incertae sedis avitotherium utahensis (in cifelli, 1990e) major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 © 2016 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado john r. foster, julia b. mchugh, joseph e. peterson, and michael f. leschin a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa pre-meeting field trip october 24–25, 2016 geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover a morrison formation scene from 152 million years ago. sauropods, theropods, stegosaurs, ankylosaurs, and crocodyliforms feed, rest, or stroll near a small river while pterosaurs fly low. artwork by brian engh, dontmesswithdinosaurs.com. i 2016 president bill loughlin bill@loughlinwater.com 435.649.4005 2016 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2016 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2016 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2016 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2016 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2016-2018 term craig morgan craigmorgan@utah.gov 801.422.3761 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 3 2016 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 33 introduction the morrison formation is a mostly freshwater-terrestrial unit of late jurassic age exposed in eight states in the rocky mountain region of western north america (dodson and others, 1980). the formation is famous for dinosaur discoveries but contains a diverse fossil biota, including more than 90 species of fossil vertebrates from fish to mammals (foster, 2003; chure and others, 2006). in a formation with numerous large bonebeds in channel sandstone deposits (e.g., carnegie quarry at dinosaur national monument, hanksville-burpee quarry, bone cabin quarry, and dry mesa quarry), the northern part of the colorado plateau stands out for being home to several large quarries and some important, highly productive microvertebrate sites, all in fine-grained mudstones. whereas the large sites in sandstones appear to be longer term attritional deposits sampling a broad range of dinosaurian taxa from surrounding areas, the major mudstone quarries of the morrison formation demonstrate taphonomic and preservational characteristics suggesting individually unique sampling of aspects local populations not typically seen at sites in coarser-grained sediments representing higher-energy environments. here, we profile four important sites in the morrison formation: the cleveland-lloyd dinosaur quarry near price, utah; the fruita paleontological area, near major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado john r. foster1, julia b. mchugh2, joseph e. peterson3, and michael f. leschin4 1museum of moab, 118 east center st., moab, ut 84532; director@moabmuseum.org 2museums of western colorado, p.o. box 20,000, grand junction, co 81502; jmchugh@westcomuseum.org 3university of wisconsin-oshkosh, department of geology, 800 algoma boulevard, oshkosh, wi 54901; petersoj@uwosh.edu 4bureau of land management, price field office, 125 south 600 west, price, ut 84501; mleschin@blm.gov citation for this article. foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f., 2016, major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado: geology of the intermountain west, v. 3, p. 33–66. © 2016 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. abstract the morrison formation contains a number of large quarries that have yielded dinosaurs and other vertebrates, and many of these occur in sandstone beds representing ancient river channels. however, a number of very productive sites occur in mudstone beds representing other environments such as ephemeral ponds, and some of these yield both large dinosaurs and microvertebrates; these localities in mudstone beds represent different taphonomic modes of preservation and often preserve vertebrate taxa in different relative abundances from the channel sandstone sites. among these important and very productive mudstone localities are the cleveland-lloyd quarry, the mygatt-moore quarry, and the microvertebrate sites of the fruita paleontological area, and each of these preserves distinct vertebrate paleofaunas, different from sandstone sites and from each other, suggesting that mudstone localities had a very different mode of sampling the local biotas than did sites in sandstone. www.utahgeology.org 34 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 fruita, colorado; the riggs quarry 13 locality in grand junction, colorado; and the mygatt-moore quarry near the utah-colorado border. cleveland-lloyd quarry history of site and research the cleveland-lloyd dinosaur quarry (cldq) of central utah is located in the brushy basin member of the upper jurassic morrison formation at the northern end of the san rafael swell (figure 1). the quarry is world-famous for its unusually high concentration of dinosaur bones, including at least 70 individuals representing a minimum of nine genera (madsen, 1976a; gates, 2005). of these, 66% (mni: 46, based on a count of left femora) are attributable to a single taxon— allosaurus fragilis. six more dinosaurs from four different species yield a predator-prey ratio of 3:1 (madsen, 1976a; gates, 2005) (figure 2). since the initial discovery of the site in 1927, more than 10,000 bones have been collected by at least seven institutions. in 1929, the first formal excavations were carried out by the university of utah, collecting nearly 1000 bones from 1929 to 1931 (miller and others, 1996). excavations resumed again in 1939 through 1941 by w.l. stokes and princeton university, which excavated and collected approximately 450 bones during the three-year period. during the early 1960s, the university of utah resumed excavations and collected nearly 7000 bones from 1960–1964 (miller and others, 1996) (figure 3). excavations resumed again in the late 1970s by the utah division of state history, and continued intermittently through the 1980s by brigham young university, collecting nearly 1100 bones (miller and others, 1996). the quarry was once again worked from 2001– 2002 through the natural history museum of utah (umnh), yielding 400 bones (gates, 2005). in 2008, the university of utah briefly worked the quarry and collected approximately 20 bones. in 2012, the university of wisconsin-oshkosh began surveying the quarry and started excavations in the south butler building, collecting nearly 50 bones and focusing efforts on researching the 3d distribution of bones, microfossils, and geochemistry of the quarry. figure 1. location of the cleveland-lloyd dinosaur quarry in emery county, utah. figure 2. vertebrate faunal composition of the cldq. modified from gates, 2005. 35 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 fi gu re 3 . c om po sit e m ap o f t he c ld q ex ca va tio ns fr om 1 96 019 90 , c ol or -c od ed b as ed o n ge ne ra . a llo sa ur us fr ag ili s r em ai ns ar e r ep re se nt ed in g re en . m od ifi ed il lu st ra tio n co ur te sy o f m ar k lo ew en (n at ur al h ist or y m us eu m o f u ta h) . 36 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 stratigraphy and paleoenvironmental interpretations the brushy basin member is composed of floodplain-deposited mudstone and limestone, with some channel sandstone, and is the youngest of three laterally extensive members of the morrison formation (gates, 2005). in the immediate vicinity of the cldq, other extensive members are present, including the basal evaporites and playa/sabkha limestones of the tidwell member and the distal alluvial fan complex of the salt wash member, which underlies the brushy basin member (peterson and turner-peterson, 1987; gates, 2005). previous reconstructions of late jurassic climate patterns in utah indicate strong seasonality, subject to variably arid to monsoonal conditions (e.g., dodson and others, 1980; hallam, 1993; rees and others, 2000; parrish and others, 2004; sellwood and valdes, 2008; tanner and others, 2014). furthermore, scarce plant material and coal deposits (dodson and others, 1980) and the distribution of authigenic minerals associated with periodic aridity throughout the morrison formation strongly support this climatic interpretation (turner and fishman, 1991). the cldq is located approximately 38 m above the basal contact of the brushy basin member (bilbey, 1992). the bone-bearing unit is composed of a calcareous mudstone that varies in thickness from a few cm to 1 m, and also includes abundant diagenetic limestone nodules and clay clasts. the mudstone underlies a micritic limestone unit that varies in thickness from 0.3 to 1.0 m, and overlies a massive silty mudstone approximately 20 m in thickness (bilbey, 1992; suarez, 2003; gates, 2005) (figure 4). based on limited exposures, the bone-bearing mudstone unit is laterally continuous for 50 to 75 m before pinching out to the south (gates, 2005). whereas various depositional models have been proposed for the cldq, the lithologies, abundant vertebrate macrofossils, and rare microvertebrate and invertebrate remains suggest an ephemeral pond or similar overbank deposit with a fluctuating water table (calcareous mudstone facies) that became a more permanent basin in the form of a shallow lacustrine setting (limestone facies) (bilbey, 1999; gates, 2005). taxonomy/biota/major discoveries invertebrate and micropaleontology the cldq has produced few identifiable microvertebrate remains other than shed dinosaur teeth, two shed neosuchian crocodyliform teeth, a crocodyliform osteoderm, and partial vertebra possibly attributable to the choristodere cteniogenys. however, the quarry also contains microfossils such as charophytes and ostracodes (madsen, 1976b) and three taxa of gastropods (stokes, 1985), which contribute to the freshwater depositional model (table 1). vertebrate paleontology the vertebrate fauna of the cldq has received figure 4. stratigraphic column of the brushy basin member of morrison formation, cleveland-lloyd dinosaur quarry. 37 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 considerably more attention than the invertebrate or microfossil faunas and floras due to the sheer abundance of dinosaur taxa present at the quarry (table 1). stokes (1945) first reported on remains of stegosaurus, camptosaurus, ceratosaurus, and allosaurus at the quarry, followed by two new theropod taxa, including the holotypes of stokesosaurus clevelandi (madsen, 1974) and marshosaurus bicentesimus (madsen, 1976b). later excavations produced skeletal material attributable to the sauropods barosaurus, camarasaurus, and possibly haplocanthosaurus (stokes, 1985), and remains assigned to the large megalosaurid torvosaurus tanneri (richmond and morris, 1996). recently, a large cervical vertebra attributable to apatosaurus was described, and still remains in the quarry (foster and peterson, 2016). other notable discoveries include a single dinosaur egg, which is relatively uncommon in the morrison formation (hirsch and others, 1989), and shell fragments from the turtle glyptops and the aforementioned shed teeth and scute attributable to a goniopholidid (stokes, 1985). however, the most striking aspect of the quarry assemblage is the unusual predator to prey ratio, which is dominated by theropods (75%, gates, 2005); of the 52 theropods present at the quarry, 46 are attributable to allosaurus fragilis, representing 66% of the total dinosaur assemblage (gates, 2005). taphonomy and models of skeletal accumulation typically the sedimentology of the bonebed would provide data which would help to highlight a most likely hypothesis to explain the strange assemblage represented within the cldq. however, the unique sedimentology of the quarry, (a hard mudstone containing abundant calcite nodules, often associated with bone, and capped with ~1 m of limestone) makes further environmental and taphonomic interpretations difficult (suarez, 2003; gates, 2005). additionally, the taphonomy of the vertebrate remains is unusual. unlike the majority of the bones found within the morrison formation, 30% of the bones in the cldq possess some form of syndepositional fracturing, and less than 1% are crushed (gates, 2005). furthermore, very few bones in the cldq show signs of surface traces such as tooth marks and insect borings (gates, 2005). this implies a very rapid deposition and/or an environment largely devoid of scavengers. whereas this specific quarry has received wide research attention focusing on the taphonomic signatures of dinosaur bones, there is little agreement among the numerous interpretations and hypotheses for the development of the accumulation (table 2); as madsen once table 1. list of fossil genera from the cleveland-lloyd dinosaur quarry. numerals indicate estimated number of individuals (modified from bilbey, 1999). 38 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 stated, “theories on the demise of the cleveland-lloyd dinosaurs are but slightly fewer in numbers than visitors to the quarry” (madsen, 1976a). the first technical record of the quarry interpreted the assemblage as an evaporating pond on which dinosaurs died and skeletons became disarticulated by scavenging and trampling (stokes, 1945). whereas this conclusion was based on very preliminary stratigraphic and petrologic data, it failed to take the distribution of skeletal elements into consideration. furthermore, this hypothesis would also require a high frequency of crushed and trampled bones (weigelt, 1989); a condition that is relatively rare in the remains at the cldq. a broader analysis of lithofacies and taphonomic properties of the cldq elements later interpreted the quarry as a predator trap, in which allosaurus became mired in a bog formed by an oxbow lake as they approached previously mired herbivore carcasses (dodson and others, 1980). this hypothesis has been prevalent in the literature in one form or another for the last 30 years; stokes (1985) interpreted the site as a bog in which dinosaurs sank over a long period of time. hunt and others (2006) concluded that the site had evidence of both attritional miring and catastrophic scenarios based on sedimentologic data. using x-ray defraction and sedimentary petrology, bilbey (1999) proposed that dinosaurs were mired in a spring-fed pond or seep. despite the popularity of the general miring hypothesis, animals mired in a viscous medium, such as mud or a bog, are commonly found articulated and (in some cases) still standing (weigelt, 1989). the lack of articulation at the cldq makes this general hypothesis—and the many versions of it—problematic. while some hypotheses have attempted to explain the disarticulation of elements, such as struggling animals churning previously deposited bones or groundwater disarticulating skeletons, these types of movements are unlikely to be sufficient in disarticulating remains to the degree observed in the quarry (weigelt, 1989). gates (2005) proposed that the quarry represents a drought-induced death assemblage, based on a review of diverse sedimentologic and taphonomic data. while this hypothesis addresses the problems normally overlooked by the “miring” or “predator trap” hypotheses, it does not specifically address the large number of predator fossils in the quarry. furthermore, this hypothesis predicts that individual skeletons should be found articulated or associated, which is uncommon in the cldq. current research whereas sedimentological and microfossil analyses suggest that the cldq represents a small ephemeral pond, new information is required to form a robust taphonomic framework supported by all available data. current research efforts by the university of wisconsin at oshkosh and indiana university of pennsylvania are being coordinated to produce a comprehensive taphonomic framework for the cldq. first, small bone fragments (< 5 mm) recovered from quarry sediment were analyzed for relative degree of abrasion and hydraulic equivalency. the fragments have a hydraulic equivalence equal to grains larger than the encasing matrix, suggesting an autochthonous or parautochthonous origin. furthermore, fragments possess a wide range of relative abrasion stages, suggesting multiple depositional events (peterson and others, 2016a) (figure 5). second, 3d photogrammetric mapping of the deposit within the north quarry building reveals distinct orientations of bones in at least three layers, providing further evidence of multiple depositional events in table 2. selected interpretations for the cleveland-lloyd dinosaur quarry (modified from hunt and others, 2006). 39 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 addition to bone fragment data (clawson and others, 2015) (figure 6). finally, x-ray diffraction (xrd) and x-ray fluorescence (xrf) comparisons of the sediments of the cldq and sedimentary beds above and below the quarry indicate enrichment in heavy metals relative to other sediments from the morrison formation (peterson and others, 2016b). whereas some metals, such as uranium, may be diagenetic in origin, other metals present in elevated concentrations, such as as, pb, sr, and cr may have bioaccumulated in the shallow depression from the decay of a large quantity of predator carcasses, promoting reducing conditions that further explain the lack of expected freshwater fauna, the rarity of feeding traces on remains recovered from the quarry, and the presence of sulfide minerals in the quarry cement (figure 7). in order to further understand the taphonomy of cldq, and thereby use it to gain insights into jurassic paleoecology, future research will include 3d mapping of bones as they are exposed in the deposit, geochemical comparisons to other morrison bonebeds, and geochemical and isotopic analysis of the bones preserved at the quarry. fruita paleontological area history of the site vertebrate fossils from the badlands southwest of fruita, colorado (figure 8), have been known since their first reports in 1891 (armstrong and perry, 1985). these early reports drew paleontologist elmer riggs from the columbian field museum in chicago, illinois (now the field museum of natural history), to the grand valley in 1900 and 1901. though he apparently did not visit what is now known as the fruita paleontological area (fpa), riggs’ discoveries in nearby grand junction and the redlands north of colorado national monument included the discovery of brachiosaurus, as well as the recovery of remains of camarasaurus, apatosaurus, and others. amateur geologist, al look, was instrumental in the early promotion of the geological and paleontological resources in the area, but it was not until the 1970s that the gray badlands southwest of fruita (now figure 5. relative abrasion stages of bone fragments collected from the matrix of the cldq. stage 0 represents angular fragments and stage 3 represents rounded fragments. scale bar equals 5 mm. figure 6. (a) photogrammetric model of the north cldq building; (b) model with false-coloration based on depth. 40 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 figure 7. regional stratigraphy and geochemistry of the cleveland-lloyd dinosaur quarry (cldq) vicinity (modified from peterson and others, 2016b). (a) stratigraphic column of the morrison formation in the area around the cldq shown in meters above the basal contact of the salt wash member of the morrison formation with the upper summerville formation. standard usgs symbols of rock units are used in the diagram. (b) map showing the stratigraphic section line and regional stratrigraphy in the context of the san rafael swell (from witkind, 1988). abbreviations are as follows: qsw – quaternary slope wash; kdc – dakota-cedar mtn fms; morrison formation – jmbb (brushy basin mbr), jms (salt wash mbr), jmt (tidwell mbr); js – summerville fm; jcu – curtis fm; je – entrada ss. (c) x-ray fluorescence results of concentrations of selected metals dectected in sediment and bone samples collected from the cldq and compared with sediments from the stratigraphic column through the morrison formation (labeled “strat”). all values are given in ppm, and abbreviations are as follows: min – minimum; ave – average; max – maximum. 41 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 the fruita paleontological area [fpa]) became the subject of detailed scientific research (armstrong and perry, 1985). prior to the protection of the paleontological resources in the fpa, vandalism and theft of fossils was increasing. in 1975, in direct response to this illegal collection and vandalism, presumably by commercial fossil collectors, curator of paleontology, lance eriksen, of the historical museum institute of western colorado (changed to museum of western colorado but in 2015 became the museums of western colorado) applied for a permit to excavate vertebrate fossils from the fpa. he recovered the skull and partial skeleton of ceratosaurus in 1976, as well as stegosaurus and allosaurus material from a separate quarry (eriksen, 1976; blm, unpublished transcript, 1977; madsen and welles, 2000). these became the first catalogued vertebrate paleontological specimens at the museum. in the summer of 1975, george callison first brought his students from california state university at long beach to fruita, colorado. during a tour of the colorado national monument, the group spied the gray, low hills of the fpa from the “historic trail overlook” and decided to prospect in that area (armstrong and perry, 1985). callison’s expeditions, with the help of volunteers from earthwatch, continued for the next decade, recovering the small vertebrate fossils from multiple sites in the fpa (figure 9) (callison, 1987). they had prospected other sites in the grand valley, but only the fpa produced good quarries for small vertebrate remains (armstrong and perry, 1985; blm, unpublished transcript, 1977). due to the abundance of swelling clays in the horizon, fossils were excavated through hand quarrying and not through the more traditional method of screen washing, which tends to disassociate remains. through this practice, not only were numerfigure 8. map of the fruita, colorado (approximately 19 km west of grand junction, co) area showing the location of the fpa. figure 9. field work under the callison expeditions c. 1979. crew clockwise from the left are jim clark, steve may, and mark norell. photo courtesy of george callison, california state university. 42 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 ous small vertebrates recovered, including several new taxa (see discussion below), but whole and partial skeletons were recovered, offering a more complete picture of mesozoic small vertebrate biology. due to the conservation and scientific efforts of george callison, lance eriksen, and their colleagues, a workshop was held with the u.s. bureau of land management (blm) to discuss the paleontological resources of the fpa and how to ensure their protection and availability for scientific research (blm, unpublished transcript, 1977). from this workshop protection measures were moved forward and the fpa was established as a protected research area by the blm in 1977. in 1998, the fpa was incorporated into the interpretive sites of the dinosaur diamond national scenic byway. by 2000, the fpa and surrounding areas were designated as a national conservation area by the u.s. department of interior’s blm, creating the colorado canyons national conservation area and black ridge canyons wilderness (public law 106-535), but in 2004 the area was renamed to its current designation: the mcinnis canyons national conservation area and black ridge wilderness. this designation has allowed for the longterm preservation of the cultural and natural, including paleontological, resources of the area. stratigraphy the fossil sites of the fpa are located within the upper jurassic morrison formation. two members of the formation are exposed within the fpa, the older salt wash member and the younger brushy basin member (figure 10). all vertebrate fossil localities in the fpa are found within the lower part of the brushy basin (kirkland, 2006). the lower brushy basin in the fpa contains a localized change in clay lithology that has been proposed to be laterally extensive across the morrison formation (owen and others, 1989; turner and peterson, 1999, 2004); however, trujillo (2006, 2014) has shown this regional clay change to be questionable. this change, from predominately illitic, non-swelling clays to smectitic, swelling clays, is likely the result of an increase in the amount of volcanic ash that was deposited in the area from sources to the south and west of the morrison basin. after ash was incorporated into the mud, it may have been altered by specific chemical conditions after burial to smectitic clay that swells when exposed to water. if no other alterations occur, this swelling clay can often be observed in outcrop as mudstone with a distinctive “popcorn” texture (moore and reynolds, 1997). in the fpa region, a change in clay mineralogy low in the brushy basin member has been documented in xrd studies, and it is often visible in outcrop (kirkland 2006; trujillo, 2006). in other areas, however, several changes in clay mineralogy at varying stratigraphic levels occur throughout the brushy basin member as a result of a variety of chemical conditions. the contact between the underlying salt wash member and the brushy basin member is defined as the top of the uppermost thick and laterally extensive sandstone unit (turner and peterson, 1999; kirkland, 2006). previously, the contact between these units was placed higher in the section, near the local “clay change,” but its placement has been restored lower in the section, atop the highest occurring sandstone unit (rasmussen and callison, 1981a, 1981b; callison, 1987; kirkland 1994, 2006). deposition and taphonomy more than 20 quarries have been excavated for vertebrate remains in the fpa since 1975. an exhaustive summary of each of these quarries’ depositional and taphonomic origins is beyond the scope of this paper; therefore, we chose to focus the following selected quarries which exemplify three disparate depositional and taphonomic regimes: kirkland egg site, eriksen ceratosaurus, and tom’s place. the kirkland egg site is the lowest in the fpa section of the three exemplar quarries discussed here. this site lies 3.6 m below the local “clay change” in the lower brushy basin member, in the illitic clays of overbank deposits. this low-energy depositional environment is characterized in the fpa by interbedded sandstone and mudstone, with occasional intervals of sandstone and siltstone interbeds. vertebrate fossil sites are less common below the local “clay change,” making the preservation of this nesting site, preserving egg shell fragments along with vertebrate remains of fruitachampsa and young dryosaurus, even more remarkable (kirkland, 43 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 1994, 2006). the eriksen ceratosaurus occurs above the local “clay change” at the intersection of a sandstone unit, representing a channel facies, and a levee facies within the fpa at the edge of a crevasse splay (kirkland, 2006). vertebrate fossils are generally rare in the levee facies, with the exception of the ceratosaurus, though trace fossils (burrows, tracks, etc.) can be more common (hasiotis and others, 1998a, 1998b). dinosaurian remains are most abundant within the sandstone facies, particularly in high sinuosity channels (e.g., the eriksen ceratosaurus channel) compared to the other ten channels in the brushy basin member of the fpa; the sandstone facies and high sinuosity channels may have created more optimal conditions for trapping large carcasses than other facies (kirkland, 2006). the channel is a well-cemented, coarse-grained to conglomeratic lithic arenite, with most of the lithics representing volcanics sourced from the southwest of the morrison basin (turner and peterson, 2004; kirkland, 2006). other sites located in channel facies include the eriksen stegosaur and the traildust theropod quarry. vertebrate taxa recovered from the sandstone facies in the fpa include allosaurus, apatosaurus, camarasaurus, ceratosaurus, figure 10. stratigraphic column for the fruita paleontological area (modified from kirkland, 2006). 44 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 dryosaurus, and stegosaurus (kirkland, 2006). tom’s place lies above the local “clay change” in the lower brushy basin member (turner and peterson, 1999) in similar overbank/floodplain deposits to the kirkland egg site (figures 10 and 11). deposition would have been similar to the kirkland egg site, with a low-energy environment allowing fine particle sedimentation and deposition of clays. however, unlike at levels at and below the kirkland egg site, above the local “clay change,” vertebrate fossil sites are much more abundant, suggesting more rapid burial than floodplain facies below the “clay change” with little to no transport, protecting small vertebrates from scavenging and damage due to surface exposure, as well as promoting the preservation of articulated remains (kirkland, 2006). preserved vertebrate fossils include egg shell fragments, actinopterygian scales and teeth, mammals, lizards, turtles, sphenodontians, sphenosuchians, and small dinosaurs (rasmussen and callison 1981a, 1981b; callison, 1987; engelmann and callison, 1998, 1999; evans and chure, 1999; göhlich and others, 2005; arcucci and others, 2013). the preservation of articulated and associated nearly complete skeletons of microvertebrates at tom’s place is similar to other sites such as rainbow park at dinosaur national monument and the wolf creek quarry in northwestern colorado, and it differs significantly from the taphonomic preservation of microvertebrates at other productive localities such as quarry 9 at como bluff, the small quarry at garden park, and the little houston quarry in the black hills (foster, 2001a, 2003). palynomorphs are also found in the tom’s place sediments. early cementation coupled with increasing alkalinity of sediments may have isolated the palynomorphs and favored their preservation (litwin and others, 1998). figure 11. view of tom’s place (tp). black arrow indicates level of the “clay change.” 45 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 major discoveries and preserved biota most recovered taxa represent small vertebrates (lepidosaurs, mammals, etc.), but larger crocodylomorphs and dinosaurs are also present in the assemblage (foster, 2003). small vertebrate faunas are rare in the morrison formation, making their abundance and diversity in the fpa of great scientific interest. the fpa may more closely represent original ecosystem diversity than most other sites in the morrison formation (foster, 2003). vertebrate fossils collected from the fpa have been reposited in collections at the natural history museum of los angeles county (lacm), carnegie museum of natural history (cm), the american museum of natural history (amnh), and the museums of western colorado (mwc). seven specimens recovered from the fpa have been designated as holotype material. these type specimens include the mammals priacodon fruitaensis (rasmussen and callison, 1981a) and fruitafossor windscheffeli (luo and wible, 2005), the sphenodontian eilenodon robustus (rasmussen and callison, 1981b), the snake diablophis gilmorei (caldwell and others, 2015), the crocodylomorph fruitachampsa callisoni (clark, 1985, 2011), and the dinosaurs fruitadens haagarorum (butler and others, 2010) and ceratosaurus magnicornis (madsen and welles, 2000). paratype material of the multituberculate mammal glirodon grandis is from the fpa, the holotype being from dinosaur national monument (engelmann and callison, 1999). a full list of vertebrate taxa recovered from quarries in the fpa is given in table 3. the fpa has produced at least three small, cursorial crocodylomorphs: the shartegosuchid fruitachampsa (clark, 2011), the sphenosuchian macelognathus (göhlich and others, 2005), and an unnamed new sphenosuchian (arcucci and others, 2013). the diversity and abundance of small, terrestrial crocodylomorphs at the fpa are higher than in any other area of the morrison formation. among dinosaurian taxa, the discovery of ceratosaurus in 1975 by lance eriksen was the second known skeleton of the genus (kirkland, 2006) and was thought to represent a new species, c. magnicornis (madsen and welles, 2000). however, recent analtable 3. alpha taxonomy of sites within the fruita paleontological area. * indicates that the type locality of that taxon occurs within the fpa. 46 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 yses by rauhut (2003), carrano and sampson (2008), and carrano and others (2012) have cast doubt on the number of species of ceratosaurus represented in the morrison formation, favoring only one: c. nasicornis (figure 12). the discovery of fruitadens haagarorum from the fpa (originally in 1976) marked the first occurrence of the ornithischian clade heterodontosauridae in north america (figures 13 and 14) (galton, 2007; butler and others, 2010). the smallest known ornithischian, f. haagarorum was one of the last surviving members of this enigmatic clade, shedding light on a rare evolutionary trend in the group. early members are interpreted to be rather specialized herbivores, but later members like f. haagarorum have a more generalized omnivorous dentition (butler and others, 2010). multiple sites preserving egg shell fragments have been reported from the morrison formation (hirsch, 1994; kirkland, 1994; foster, 2003). however, the kirkland egg site in the fpa is the only one of these sites that preserves both egg shell and hatchling bones, identifying the egg layer as dryosaurus sp. (kirkland, 1994). this site produces a bimodal assemblage of dryosaurus material, including both hatchling size and juvenile size individuals—adults have not yet been recovered from the site. also recovered from the site are egg shell, belonging to the oospecies preprismatoolithus coloradonesis (hirsch, 1994; carpenter, 1999), and postcranial remains of the shartegosuchid crocodylomorph fruitachampsa callisoni, hypothesized to have been figure 12. cranial and postcranial elements of the holotype specimen of ceratosaurus magnicornis (mwc 1) on exhibit. scale bar equals 1 cm. 47 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 raiding the dinosaur nests (kirkland, 1994). discoveries from the fpa have not only shed light on taxonomic and ecosystem-level questions (foster, 2003; kirkland, 2006), but have revealed early evolutionary pathways in several higher taxonomic groups. the discovery of fruitafossor windscheffeli by wally windscheffel generated a rare jurassic mammal known not just from isolated teeth and bones, but with rare articulated cranial and postcranial remains (figure 15) (luo and wible, 2005). examination of the specimen revealed a basal mammal with a combination of many primitive characteristics and numerous derived skeletal adaptations for a fossorial lifestyle that are convergent with modern xenarthans, suggesting a more complicated early radiation of basal mammals than previously thought, driven by ecological selection (luo and wible, 2005). the evolutionary origin of serpentes, once hypothesized to have occurred during the jurassic period, lacked support of fossil evidence to solidify the clade’s diversification and origin in that time period. callison’s crews collected the partial remains of a peculiar lepidosaur from the fpa, which were first described by evans (1996) as an anguimorph lizard: parviraptor gilmorei. however, caldwell and others (2015) re-examined the material in the light of new fossil discoveries from europe and reassigned the taxon to diablophis gilmorei, an early snake, corroborating an early idea by callison (1987) almost 30 years prior. together with the new european discoveries, caldwell and others (2015) pushed the origin of the clade back nearly 70 million years into the middle jurassic period. current research excavations continue today at several sites in the fpa. a team led by gabe bever from the new york institute of technology and the american museum of figure 14. holotype and referred jaw and limb specimens of fruitadens, lacm 128258, lacm 115747, lacm 115727, and lacm 120478 (figure 2 from butler and others, 2010). figure 13. cast of fruitadens jaws, lacm 128258, in dorsal (left) and oblique (right) views. scale bar equals 1 cm. 48 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 natural history in new york continues excavations for small vertebrates at tom’s place, investigating the early evolution of mammals, as well as rhynchocephalians, snakes, and other lepidosaurs. the mwc also continues to excavate sites in the fpa each summer. currently, excavations are focused on the small vertebrates of the original callison quarry, the allosaurus bonebed at the traildust theropod quarry, the kirkland egg site, as well as surface collection throughout the fpa, which in 2015 yielded the first conifer cone from the fpa. riggs hill (quarry 13) in the winter and spring of 1900, elmer riggs of the field columbian museum (now named the field museum of natural history) in chicago was planning a paleontological field expedition to western colorado. riggs was a former student of s.w. williston and classmate of barnum brown at the university of kansas. originally from indiana, riggs had been at the field for several years working as its assistant curator of geology. he had been working in wyoming previously and had spent the season of 1899 in the freezeout hills working in the morrison formation. riggs recognized the utility of working near rail lines and had written letters to the scientific societies of several small towns along rail routes in the western united states, in hope of learning the outcrops from which to collect dinosaurs for the museum. he had received a letter back from a dentist in charge of the scientific society in grand junction, colorado (a town that was less than 20 years old at the time), saying that dinosaur bones had been being collected from area badlands since the town was first settled in the early 1880s (armstrong and perry, 1985). riggs initially planned to return to the freezeout hills and investigate the western colorado lead on his 1900 expedition but eventually settled on just the grand junction area. in a series of letters to the department head, who was the advocate with the museum’s director, riggs argued in favor of the grand junction destination and justified a submitted budget, at one point explaining that the request for funds for a new field tent was justified because the anthropology department at the museum had borrowed the geology tent and never returned it! by may, riggs’s expedition was approved and figure 15. reconstruction of fruitafossor by mark klingler, carnegie museum of natural history, (figure 2 from luo and wible, 2005). 49 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 a $700 budget was provided for the summer, mostly for field equipment, shipping, train tickets for the crew, and a team of horses and a wagon in colorado. riggs brought a young man named harold menke as his field assistant, and menke was also the photographer for the expedition, much to the benefit of later paleontologists. riggs also hired a relative named victor barnett as the camp cook. the three arrived in grand junction early in the summer and began prospecting morrison formation outcrops south and west of the city. as riggs noted, they had very little luck for about six weeks and only found one site worth excavating, quarry 12, which was located near today’s east entrance to colorado national monument. this site produced a number of bones of the sauropod camarasaurus, but nothing of major significance. on july 4, the crew took a break from digging and went prospecting along the outcrops west of the quarry. menke found the end of a limb element sticking out of the south slope of a hillside about 4 km north and west of the area of quarry 12, in the brushy basin member of the morrison formation (figure 16). riggs was curious, but at the time the site did not look promising enough to move from the quarry on which they were already working. so, for several more weeks riggs and the crew worked on quarry 12. on july 26, 1900, riggs and the crew began digging in to menke’s find from the fourth of july. they uncovered a humerus just over 2 m long, and riggs recognized immediately that the material was significant and unusually large. this became riggs’s quarry 13 (figure 17). in a letter written to the director from camp that night, riggs told the director of the find and asked that it be kept quiet; riggs knew that the carnegie museum and american museum of natural history were also working in the morrison formation at the time and that they would certainly pay the grand junction area a visit if they knew of riggs’s success there. riggs told the director that time was needed to collect “the cream of it” from the area (not just the current sauropod) before figure 16. view of riggs hill from the south in 1900. quarry 13 in its early stages is visible to the lower right of the center of the photo, with a light patch of debris rock below it (arrow). courtesy of field museum of natural history. 50 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 other museums moved in. on the evening of july 27, riggs presented a lantern-slide lecture in downtown grand junction, detailing their work in the area and the history of dinosaurs in the western states. a grand junction newspaper article reporting on the talk mentioned riggs’s low-key manner and the strong round of applause afterwards, but consistently misspelled the paleontologist’s name as “prof briggs,” not the last time riggs would be the victim of spelling mistakes related to his work in the area. from the last week in july, when they started the dig, until the second week of september, when they shipped the material by train to chicago, riggs and the crew uncovered and removed a humerus, femur, articulated dorsal series, sacrum, two caudals, and several ribs of a large sauropod (figure 18). menke took a number of photographs of the quarry and their work as it progressed. riggs suspected from the first day, based on the large size, that it was a new taxon. many residents of grand junction came out to tour the quarry, to the point that it became disruptive to the crew’s work. riggs, about 31 at the time, wrote letters to his girlfriend back in chicago (they would marry after the 1901 field season) describing camp life and how comfortably he’d set things up, and he mentioned the younger menke’s letter writing to multiple women back in chicago. riggs’s future bride told him in a return letter that she suspected that he missed her, although she knew he would likely deny that (brinkman, 2010). after shipping their material out on september 11, riggs, menke, and barnett returned to the midwest, and then the work of uncovering the material began. within several years, riggs had named the new sauropod (fmnh 25107) brachiosaurus altithorax, more figure 17. quarry 13 looking west in 1900, as the excavation was underway. courtesy of field museum of natural history. 51 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 or less the “deep-chest arm-lizard” (riggs, 1903a). brachiosaurus is one of the largest and rarest sauropods in the morrison formation, and it has still only been found at a handful of localities in the unit (foster, 2001b), but closely related late jurassic brachiosaurids have been found as far away as portugal and tanzania (paul, 1988; mateus, 2006; taylor, 2009). assuming it was similar in the cervical region to giraffatitan, brachiosaurus was adapted for browsing relatively high in trees, above most other sauropod species, with a long neck, a raised shoulder region, and a relatively short tail. in 1901, riggs and his crew returned to colorado, this time to the fruita area, to collect a partial apatosaurine skeleton from the brushy basin member just across the colorado river from town at quarry 15. the study of this specimen (fmnh 25112) led riggs to propose the synonymy of apatosaurus and brontosaurus (riggs, 1903b), and this assessment stood largely uncontested until tschopp and others (2015) suggested that the individual was an as yet undetermined apatosaurine within a clade including both apatosaurus and brontosaurus as valid genera. ironically, as riggs likely worked quarry 15 one day in may of 1901, and unbeknownst to either party, henry f. osborn and john b. hatcher rode past on the train less than a mile north of the site, on their way out figure 18. view of quarry 13 showing vertebrae, ribs, femur, and sacrum of brachiosaurus during excavation. courtesy of field museum of natural history. 52 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 to the green river, utah, area to investigate morrison outcrops (and for osborn, of the amnh, to work on luring hatcher away from the carnegie museum; brinkman, 2010). riggs may never have known how close he came to having his rival institutions find out about his grand junction-fruita finds before even publishing the brachiosaurus work. riggs returned to grand junction years later, in 1938, for the dedication of a plaque and monument to brachiosaurus at quarry 13 produced by a local service group (figure 19). a similar monument for the apatosaurus was installed at quarry 15 near fruita in a second ceremony on that same trip. unfortunately, the names of the dinosaurs on each plaque were misspelled. harley armstrong and dave wolny of the mwc returned to quarry 13 in 1989 and installed the replica vertebrae seen at the site today (figure 19). wolny found a partial caudal centrum and a few other fragments from the pit, which are now on display at the mwc’s dinosaur journey museum in fruita (mwc 435). the properties on which both riggs quarries (13 and 15) are located were donated to and are now managed by the mwc (in cooperation with the blm, which manages adjacent public land access, in the case of quarry 15). very small bone fragments are still abundant in quarry 13, and many of these may well derive from eroded elements of the brachiosaurus skeleton. please leave these in place for future visitors to discover also. note – most of the information for this section is taken from copies of letters between riggs and other figure 19. view of riggs’s quarry 13 c. 2010 showing the stone monument plaque installed in 1938 and the concrete vertebrae marking the site of the find (installed 1989). 53 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 field columbian museum employees, receipts for tickets and shipments during the trip, harold menke’s field photos, and contemporary grand junction newspaper articles, from the field museum of natural history and the loyd files research library at the mwc. another key source has been paul brinkman’s the second jurassic dinosaur rush: museums and paleontology in america at the turn of the twentieth century (university of chicago press, 2010). black and white photos included here are all by harold menke and are courtesy of the field museum of natural history by way of the loyd files research library at the mwc. mygatt-moore quarry the mygatt-moore quarry is a deposit of several thousand dinosaur bones in the brushy basin member of the morrison formation in western colorado. the quarry appears to be an attritional deposit of a relatively restricted diversity of dinosaurs, with few other non-dinosaurian taxa, that accumulated in an ephemeral pond deposit in an overbank setting. history of site and research the mygatt-moore quarry is located in the middle of the brushy basin member of the morrison formation in mesa county, colorado, just 2.5 km from the utah-colorado state line (figures 20 and 21). the quarry is one of several large bonebed deposits in mudstone in the morrison and is well-known for having produced several type specimens as well as an abundance of dinosaur material. the site was found in march 1981 by j.d. and vanetta moore and pete and marilyn mygatt (figure 22), who happened across the first exposed bones while out hiking (armstrong and perry, 1985; armstrong and others, 1987; mygatt, 1991; kirkland and armstrong, 1992). the site was worked by lance eriksen and the mwc briefly around 1984 and has been excavated by the same institution every summer since 1987, with harley armstrong, then brooks britt, and then rod scheetz leading the efforts through the 2000 season (figure 23). the dinamation international society worked the site simultaneously with the mwc until 1998, with jim kirkland responsible for that organization’s work. in this time, more than 4000 bones have been cataloged from the site (figures 24 and 25), and more than 20 individual dinosaurs are represented. stratigraphy and paleoenvironmental interpretations the top of the salt wash member of the morrison formation in rabbit valley is formed by the top of one or several tan, laterally continuous channel sandstones that can be traced across the valley (armstrong and mcreynolds, 1987). the brushy basin member consists of approximately 100 to 140 m of gray, maroon, and greenish-gray claystone with numerous channel sandstones and thin splay sandstones and only a few, thin limestone beds; it lies above the salt wash member of the morrison and below the cedar mountain formation (burro canyon formation south of the colorado river) in western colorado (peterson, 1988). the mygatt-moore quarry occurs approximately 64 m above the base of the brushy basin, in a section in which the member is a total of 135 m thick. this puts the quarry near the top of the lower half of the brushy basin (47% of the way up in the section). the “fish layer” above the quarry serves as a useful marker bed that can be traced more than 500 m to the east of the quarry. the main quarry layer itself is a gray claystone and contains a significant percentage of silt-sized grains but also demonstrates a high abundance of carbonized plant debris, clayballs (some containing silt clasts themselves), and wood fragments. the bone layer can be traced in outcrop for approximately 100 m east-west. drilling uphill from the quarry to the northwest and west in june 2013 (figure 26) found the bone layer tens of meters away from the current edge of the quarry and indicates that the quarry probably measures at least 130 by 140 m. like the cleveland-lloyd quarry, the deposit appears to represent an ephemeral overbank pond that developed over time into a permanent lake (foster and others, 2007; hunt-foster and foster, 2014). ash fall zircons from the bone layer gave a u/pb age for the quarry of 152.3 ±0.2 ma (trujillo and others, 2014), placing the site near the kimmeridgian-tithonian boundary. 54 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 figure 21. the mygatt-moore quarry during excavations in the 1990s. photo by françois gohier (freelance photographer). photograph courtesy of mwc. figure 20. location of the mygatt-moore quarry in western colorado, west of fruita and grand junction. 55 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 biota, taxonomy, and major discoveries paleobotany the quarry bone layer, so rich in unidentifiable plant fragments, has also produced more than 14 identifiable species of fossil plants, including quillwort relatives, horsetails, ferns, tree ferns, ginkgoes, czekanowskia, and a number of conifers (table 4; figure 27). these are preserved as abundant carbonized fragments in the quarry mudstone, but fossilized wood and pollen and spores are also common in the quarry (tidwell and others, 1998; hotton and baghai-riding, 2010). invertebrate paleontology the mygatt-moore quarry has produced gastropods and conchostracans, though most of these have been found either just below or a bit above the quarry stratigraphically; very few of these invertebrate fossils were found in the bone layer itself. two crayfish have been found stratigraphically above the main quarry, just above the greatest abundance of conchostracans (see table 4). vertebrate paleontology the vertebrate fauna of the mygatt-moore quarry is relatively limited considering the number of bones the main layer has produced. several small, indeterminate reptiles have been reported (king and foster, 2014), one represented by a very small tooth (figure 28), and a single neosuchian crocodyliform bone has been found. beyond this, the fauna consists of seven dinosaur genera: ceratosaurus, allosaurus, apatosaurus, camarasaurus, an indeterminate diplodocine, othnielosaurus, and the type material of the polacanthid ankylosaur mymoorapelta (kirkland and carpenter, 1994; foster and others, 2007; table 4 and figure 29). among this dinosaur material is a reasonable percentage of juvenile elements (figure 30). in addition, the “fish layer” approximately 2 m above the main bone layer has yielded the fish “hulettia” hawesi, morrolepis, and cf. leptolepis (kirkland, 1998; figure 31). among the vertebrate material, by individual bone count and by mni, allosaurus and apatosaurus are by far the most abundant taxa (foster and others, 2007). the otherwise common morrison formation sauropod camarasaurus is rare. other notable vertebrate discoveries include two small, fragmentary dinosaur eggs (bray and hirsch, 1998) and possible coprolites of herbivorous dinosaurs (chin and kirkland, 1998). several examples of dinosaur skin have been preserved in the quarry also (foster and hunt-foster, 2011; figure 32). taphonomy and models of skeletal accumulation a sample inventoried in the mwc, including taxonomically unidentifiable material, consisted of nearly 1900 specimens. although fragmentary bones were most abundant, teeth, vertebrae, and ribs were well represented, particularly those of allosaurus and sauropods. the 2300+ mapped bones out of the mygattmoore quarry show a pattern of disarticulation and figure 22. j.d. moore (left) and pete mygatt (right) at the quarry that bears their families’ names. 56 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 only slight association. of the entire mapped sample only eight bones are in articulation with at least one other one. the main bone layer is approximately 1 m thick, and the occurrence of bones within this interval is concentrated near the basal 33 cm or so. the quarry appears to show a random orientation of the bones at mygattmoore. azimuth orientations of bones from the quarry, measured off the map and categorized as either bidirectional or unidirectional, suggest that indeed the orientation is random. bones out of the mygatt-moore quarry, as noted above, are often broken and fragmenfigure 23. previous mygatt-moore quarry principal investigators. (a) harley armstrong (dark blue shirt) and volunteers wrestle a field jacket into a truck at mygatt-moore in 1987; armstrong worked at the site for mwc from the mid-1980s until 1993. (b) jim kirkland led the dinamation international society work at mygatt-moore until 1998. (c) brooks britt and volunteer bonnie carter working under an apatosaur sacrum in 1993; britt worked the site for mwc from 1993 to 1998. (d) rod scheetz (left) overlapped with britt and led work at the quarry from 1998 to 2000. pete mygatt is on the right in the photograph. 57 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 tary, but a large number are fairly well preserved and complete. breakage, abrasion, and corrosion of bones is fairly common. evidence of trampling and scavenging are common as well, including bones broken in place, material on edge in the mudstone, shed teeth of carnivores (figure 33), and carnivore tooth marks on bones. characteristics of the quarry sediment and the bones contained in it suggest that the site was a topographic low near a fluvial system into which calcium carbonate nodules, clayballs, silt, and skeletal material were washed; both lithologic and skeletal material appear to have had both local and more distant sources. figure 24. field work at the mygatt-moore quarry mostly involved mediumto large-sized jackets. (a) an apatosaurus scapula ready to remove in 2001. (b) lowering a sauropod dorsal vertebra in its jacket onto a transport trailer in 2001 are (left to right): don kerven, don chaffin, and joshua a. smith (museum of western colorado). (c) city of fruita backhoe lifts out an apatosaur scapulocoracoid in 2012. (d) mwc volunteers ready a sauropod pubis in field jacket for lowering onto a flatbed trailer, 2013. 58 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 although there is a component of allochthonous and very worn bone fragments, well-preserved elements were probably derived from animals that died in or very close to the quarry setting. it appears that carcasses were being scavenged at the site, but it is unclear if any of the animals were killed by predators there; direct evidence of miring is lacking. current research ongoing work at the mygatt-moore quarry every season continues to produce interesting material (figure 34), including large diplodocid elements such as a scapulocoracoid and a femur, the latter measuring 1876 mm in length. a small jaw of othnielsosaurus was identified at the site less than 10 years ago, and a 2 mm tooth (figure 28) and other small reptile remains have been found in the same recent time period. the site continues to produce new and important data, especially regarding the taphonomy of the deposit. an extensive taphonomic study of the quarry, started in 2010, is nearing completion. acknowledgments thanks to the bureau of land management and the museums of western colorado, which manage the cleveland-lloyd, mygatt-moore, and fruita paleontological area, and riggs hill sites, respectively. thanks to kelli trujillo and spencer lucas for helpful review comments. randy irmis, carrie levitt-bussian, and janaki krishna of the natural history museum of utah assisted with cleveland-lloyd dinosaur quarry curation. thanks to harley armstrong and paul brinkman for filling in some of the information details on riggs hill. figure 25. uncovering a juvenile sauropod pubis in the main bone layer at mygatt-moore quarry in 2001. figure 26. core drilling nearly 100 m southwest of the mygatt-moore quarry in 2013 confirmed that dinosaur bone and the mudstone with plant debris characteristic of the quarry bone layer extend at least that far under the hill. 59 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 table 4. biota of the mygatt-moore quarry in western colorado, morrison formation. plant listing based on tidwell and others (1998) and hotton and baghai-riding (2010). * indicates a type specimen from the mygatt-moore quarry. 60 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 figure 29. reconstruction of the polacanthid ankylosaur mymoorapelta by thomas adams (witte museum). courtesy of mwc. figure 27. although plant fragments are abundant in every piece of matrix from the bone layer at mygatt-moore quarry, identifiable plant remains are rare. figure 28. small tooth of an unidentified reptile from the mygatt-moore quarry, found by mwc volunteer richard peirce during screenwashing of matrix from a field jacket containing a femur of a juvenile sauropod. 61 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 figure 32. section of sauropod skin with roughly hexagonal scale pattern found in mygatt-moore quarry. scale in cm (from foster and hunt-foster, 2011). figure 30. juvenile and ankylosaur material from the mygatt-moore quarry. (a) left scapula of juvenile apatosaur. (b) left femur of juvenile diplodocid. (c) dorsal of juvenile sauropod in left lateral view. (d) three cervical vertebrae of juvenile sauropods in dorsal view. (e) cervical vertebra of juvenile sauropod in left lateral view. (f) lateral spine of mymoorapelta. (g) lingual view of left dentary (top) and right dentary fragment (bottom) of juvenile allosaurus found in 2002. all scale bars = 10 cm. figure 31. fish from the mygatt-moore “fish layer.” (a) indeterminate fish skeleton, possibly cf. leptolepis. (b) posterior section and caudal fin of probable morrolepis. scales = 1 cm 62 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 figure 34. the mygatt-moore quarry c. 2010, closing in on 30 field seasons of operation. figure 33. some of the more than 300 mostly shed theropod teeth found at the mygatt-moore quarry, in the collections of mwc. 63 major bonebeds in mudrocks of the morrison formation (upper jurassic), northern colorado plateau of utah and colorado foster, j.r., mchugh, j.b., peterson, j.e., and leschin, m.f. geology of the intermountain west 2016 volume 3 references arcuccui, a., ortega, f., pol, d., and chiappe, l., 2013, a new crocodylomorph from the morrison formation (late jurassic: kimmeridgian-early tithonian?) from the fruita paleontological area, western colorado, usa [abs.]: journal of 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(for more information see chan and others, 2003; chan and godsey, 2016). background image is gilbert’s (1890; plate xx) map of the stockton bar. see figure 6 for more description. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2020–2021 uga board president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 president-elect john south john.south@dominionenergy.com 385.266.2113 program chair maria slack petromns18@gmail.com 801.810.9154 treasurer brent greenhalgh brent.greenhalgh@dominionenergy.com 385.626.8972 secretary ryan gall rgall@utah.gov 801.537.3312 past president leslie heppler lheppler@utah.gov 801.538.5257 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 301 abstract the bonneville shoreline, the highest, and second-most prominent shoreline of pleistocene lake bonneville in utah, nevada, and idaho, has been thought for many years to have formed during a period of prolonged overflow (500 to 1000+ years) and lake-level stability prior to the bonneville flood. that traditional idea was initially promoted by g.k. gilbert during the 1870s before he spent over a decade on field work related to lake bonneville. during gilbert’s field work, his observations led him to a different interpretation of how the bonneville shoreline developed, and by the time his final report on lake bonneville was published in 1890, he was no longer promoting the idea of prolonged overflow. instead he thought of the bonneville shoreline as a geomorphic record of the highest level attained by the transgressing lake in the closed basin; the shoreline marks the boundary between lacustrine-dominated landforms below and fluvial-dominated landforms above. for over 120 years after gilbert’s (1890) monograph was published, researchers ignored his interpretation, and assumed (but did not present supporting evidence), that lake bonneville had overflowed for a prolonged period prior to the bonneville flood while the bonneville shoreline developed. re-examination of the geomorphology of the bonneville shoreline, the stratigraphy of lake bonneville deposits, the geomorphology of the overflow area, and the history of lake bonneville, shows that gilbert’s 1890 interpretation is consistent with observations. considering this, to accurately interpret the history of lake bonneville the bonneville shoreline should be viewed as the level the lake had reached in the closed basin when its transgression ceased and it began to spill into the snake river drainage basin. g.k. gilbert and the bonneville shoreline charles g. oviatt department of geology, kansas state university. manhattan, ks 66506: joviatt@k-state.edu citation for this article. oviatt, c.g, 2020, g.k. gilbert and the bonneville shoreline: geology of the intermountain west, v. 7, p. 301–320, https://doi.org/10.31711/giw. v7.pp301-320. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the bonneville shoreline, the highest, and second-most prominent shoreline of pleistocene lake bonneville in utah, nevada, and idaho (figures 1 and 2), for many years has been interpreted as having formed during a period of prolonged overflow prior to the bonneville flood. the period of overflow was thought to be hundreds of years to 1000+ years in duration (see scott and others, 1983, p. 277). in this interpretation lake-level stability for this prolonged period of overflow allowed the bonneville shoreline to become strongly developed. this idea was first presented in print by g.k. gilbert in the 1870s (gilbert, 1875; it is possible gilbert published something regarding this prior to 1875, but this is the earliest publication i have found) as he was beginning his field studies in the bonneville basin as a member of the wheeler survey. apparently the idea gained momentum when w.m. davis published his interpretation of the bonneville shoreline, probably influenced by gilbert because davis, himself, did 302 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 not work in the field in the bonneville basin: “the highest or bonneville terrace . . . marks a stand at the level of overflow northward to snake river” (davis, 1883, p. 570). apparently davis (1892) persisted with the interpretation of prolonged overflow and lake-level stability after gilbert (1890) had published a different interpretation. the idea of prolonged overflow and lake-level stability was stated over and over by all researchers who studied the lake after gilbert, through the 20th century into the early 21st century, as if it were simply a fact that everyone knew. but no evidence was ever presented to support it. the purposes of this paper are to describe the bonneville shoreline, including its geomorphology and geochronology, and its history of development, and to describe a process of shoreline development that is consistent with gilbert’s (1890) interpretation. field observations are consistent with the interpretation that prolonged overflow did not occur. geomorphology and stratigraphy of the bonneville shoreline the bonneville shoreline (figure 3) is prominent in many places in the basin (figure 4), but in some areas it is poorly developed and difficult to identify (figure 5). a typical location where no shoreline is developed figure 1. map showing lake bonneville at its maximum level, the outline of which is the bonneville shoreline. based on the mapping of currey (1982). figure 2. hydrograph of lake bonneville (generalized from data in oviatt, 2015). elevations are adjusted for differential isostatic rebound in the basin (currey and oviatt, 1985; oviatt, 2015). the red dashed line and the estimated long-term rates of transgression (about 13 m/1000 years, and about 50 m/1000 years) are based on approximate ages and elevations read from the diagram. 303 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 may have near-vertical exposures of resistant bedrock, and in such a situation incoming waves bounced off the bedrock and accomplished no geomorphic work. the character of the shoreline changes along its length, ranging from being constructional or depositional in some places (expressed as barrier beaches, spits, and bars; figure 6), to erosional in other places (expressed as scarps, “sea” cliffs in bedrock, or “sea” bluffs in unconsolidated alluvium; gilbert, 1885; 1890; currey, 1982; chen and maloof, 2017). in some places it is possible to trace the shoreline from an erosional reach into a depositional reach (figure 7). in areas where waves eroded directly into unconsolidated alluvium or easily eroded bedrock, erosional shorelines are well formed (figures 3 and 8). where abundant sediment was available and the geomorphology was conducive to producing constructional landforms (figure 6), tremendous constructional landforms were produced. the elevation of the bonneville shoreline (and of the provo shoreline) varies from place to place in the basin because of the effects of isostasy. as recognized by gilbert (1886; 1890), the weight of the water in lake bonneville caused earth’s crust to be bowed downward, and when the water evaporated from the basin the crust bowed back up or rebounded (gilbert, 1890; crittenden, 1963; currey, 1982; bills and others, 2002). shorelines that had formed on horizontal planes while the basin was isostatically depressed became warped as they rebounded. as a result the bonneville shoreline is now 74 m higher in the lakeside mountains, just west of great salt lake (figure 1), where the water load was greatest, than it is at red rock pass, at the edge of the lake far from the center of load. the isostatic gradient is very low (about 0.0005), so that from one viewpoint within the basin the shoreline appears to be horizontal, but at a basinwide scale the deformation is readily apparent (see maps in gilbert, 1890; bills and others, 2002). a particular kind of barrier that gilbert (1890) called a “v-bar” is commonly found at the bonneville shoreline and at lower levels in the bonneville basin. v-bars are barriers that have a v shape in map view (figures 9 and 10), so they appear distinctly different than barriers that are linear in form. the exact mechanism of formation of v-bars has not been discussed in the literature, but gilbert’s description (1890, p. 57–59) is excellent: “they are triangular in ground plan, and would claim the title of delta were it not appropriated, for they simulate the greek letter more strikingly than do the river-mouth structures. they are built against coasts of even outline, and usually, but not always, upon slight salients, and they occur most frequently in the long, narrow arms of old lakes.” gilbert further stated: “the v-bar, while a conspicuous feature of the bonneville shores, is not believed to be a normal feature of lakes maintaining a constant level.” v-bars resemble “cuspate forelands” in plan form figure 3. oblique aerial view, looking toward the southwest, of the bonneville shoreline on steep mountain, at the south end of salt lake valley on the traverse mountains (permission to reproduce this photograph was obtained from university of washington libraries, special collections, john shelton collection, kc3275). the large spit and barrier complex is called “point of the mountain” (figure 1). for many years the prominent snow-covered bench visible in the photograph was considered one of the best-developed erosional platforms at the bonneville shoreline in the lake basin. however, careful investigations of the geomorphology at the steep mountain site indicate that the bench is a constructional platform, not an erosional platform — it was produced by deposition of sand and gravel rather than by erosion of the underlying material (oviatt and jewell, 2016). 304 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 (e.g., semeniuk and others, 1988), but the genetic relationship between v-bars and cuspate forelands has not been thoroughly investigated. field observations (unpublished) suggest that v-bars, which may be 10s of meters high, were built by vertical accretion in a generally rising lake, in contrast to cuspate forelands, which were built by lateral accretion of sediment (semeniuk and others, 1988). it is common in the bonneville basin to find places where “stacks” of v-bars rise from the basin floor (most commonly at elevations above the provo shoreline) up to the bonneville shoreline (figure 9). at such places the v-bar at the top of the stack, the one at the bonneville shoreline, is pristine – that is, except for any post-bonneville erosion and alluvial or eolian deposition that might be present on the v-bar, the lacustrine character is well preserved and easily visible. however, the surface expressions of the lower v-bars in the same stack are subdued, as would be expected if the lake had continued to rise to higher levels after each v-bar was formed at the lake margin during the transgressive phase (figure 9). figure 4. google earth image of part of the eastern piedmont of the pilot range, far western utah and eastern nevada (41.1° n. latitude, 114.0° w. longitude). in this area the bonneville shoreline has an elevation of about 1590 m; the elevation of pilot valley playa is about 1296 m. note how the bonneville shoreline is very conspicuous in this area, primarily because it marks the boundary between the lacustrine landforms below and the fluvial-dominated landforms above. map data ©2020 google. figure 5. photo of the east face of the silver island range, northeast of wendover, utah, near 40.8° n. latitude, 113.9° w. longitude), showing the stansbury, provo, and bonneville shorelines. note that the stansbury and provo shorelines are obvious from a distance, primarily because of the accumulations of shoreline tufa, but that the bonneville shoreline is not well defined on the steep bedrock exposures where tufa is uncommon. photograph credit: ken krahulec. 305 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 lake bonneville was dammed by an alluvial fan at the north end of cache valley in southeastern idaho (figure 1; gilbert, 1890; o’connor, 1993; o’connor, 2016; shroder and others, 2016). the alluvial fan was built by marsh creek, which flowed out of the portneuf mountains into the pass between the portneuf mountains on the east and the northern end of oxford mountain (commonly referred to as the bannock range) on the west (gilbert, 1890; janecke and oaks, 2011; shroder and others, 2016). as the lake rose during its transgressive phase and reached an elevation where it intersected the fan alluvium, water began to leak through the permeable fan deposits and to discharge in springs on the north flank of the alluvial fan (o’connor, 1993; o’connor, 2016; shroder and others, 2016). at an elevation about 50 m below the bonneville shoreline (1550 m), at about 22,000 years b.p. (before present), the long-term rate of transgression of the lake slowed from about 50 m/1000 years to about 13 m/1000 years (figure 2), and this may mark the elevation and time when significant groundwater discharge from the lake slowed the transgression (a thorough investigation of the possible causes of the change in the long-term transgressive rate has not been conducted; one possible cause of the change in rate [change in the rate of groundwater outflow] is mentioned here; another possible cause — a possible change in the shape of the basin, that is, a flattening of the hypsometric curve at an elevation of about 1550 m—is not supported by evidence… the hypsometric curve in this elevation range is straight and does not flatten [currey, 1990; wambeam, 2001]). traditionally it has been thought that lake bonneville overflowed at the low point on the marsh creek alluvial fan (many references could be cited here, but some important ones are gilbert [1890], o’connor [1993], and shroder and others [2016]). an exception to that interpretation was by malde (1968), who thought that lake bonneville first rose higher than the marsh creek figure 6. plate xx from gilbert (1890). this is gilbert’s map of the stockton bar, a depositional complex that includes the bonneville shoreline at the top of the sequence. north is to the left on the map. the stockton bar is one of the places in the basin where the bonneville shoreline is depositional or constructional. the coarse gravel in the stockton bar was transported by longshore currents from erosional sites in alluvium and bedrock to the northeast; the southwestern-most erosional sites are shown on the map, and more of the eroded alluvial fan complex is visible in the cover image. the rate of longshore transport of gravel that was deposited in the stockton bar was between 9600 and 16,000 m3/yr (volume estimates by oviatt [unpublished] and d.t. nelson [utah valley university], personal communication, 2013; these estimates are for gravel accumulated at stockton bar in about 2000 years). published estimated rates of longshore transport in modern systems range between about 6000 and 3,800,000 m3/yr (johnson, 1956; galvin, 1973; schoones, 2000), with a mean near 300,000 m3/yr. the estimate of longshore transport rate for stockton bar is near the low end of that range. in other words, although the stockton bar is an impressive feature, it is not nearly as big as it might have been if the longshore transport rate were close to average. a period of prolonged overflow and stillstand at the bonneville shoreline (which has been proposed by burr and currey, 1988) is not required for gravel to accumulate in stockton bar. 306 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 fan to a level he did not identify, then dropped during the bonneville flood to the level of the bonneville shoreline, which in his interpretation was determined by overflow across a bedrock threshold (this interpretation has not been reproduced by subsequent researchers). the interpretation that lake bonneville overflowed at the low point on the alluvial fan cannot be directly supported by evidence because the low point of the fan was eroded away during the bonneville flood. the geomorphology and stratigraphy of the fan have not been studied in detail, but no evidence or arguments have been presented that conflict with the interpretation that the lake overflowed across the low point of the alluvial fan, and that interpretation is used here. groundwater seepage would have caused sapping and the formation of rounded firstand second-order valleys on the fan slope away from the lake (i.e., the north flank of the fan; o’connor, 1993; shroder and others, 2016). those firstand second-order valleys would have migrated headwardly upslope toward the fan crest as long as seepage continued, in a direction generally opposite that of the groundwater flow direction. in this interpretation, as lake level continued to rise, the difference in hydraulic head between lake bonneville in cache valley and the water table on the north flank of the fan would have increased, thus leading to a greater rate of groundwater discharge and sapping. in this scenario, by the time the lake had transgressed to the elevation of the low point on the fan crest, sapping would have facilitated the rapid erosion of the fan deposits by weakening the fan dam, and the bonneville flood was initiated as soon as the lake began to overflow. the alluvial-fan dam would have collapsed just as modern earthen dams collapse when they are subjected to similar processes of sapping and overflow (shroder and others, 2016). gilbert (1890) may or may not have been aware of groundwater sapping as a geomorphic process. however, he did recognize fluvial erosion of unconsolidated fan materials as being important: “uncemented alluvium is easily and rapidly torn up and removed, and as soon as a current began to flow across the divide, it must have commenced the excavation of a channel”(gilbert, 1890, p. 175). most gravel in barriers at the bonneville shoreline is horizontally bedded. ground-penetrating radar (gpr) results (smith and others, 2003; schide and others, 2018) and observations in gravel pits (unpublished observations by c.g. oviatt) are consistent with this conclusion. for barrier gravel to be dominated by a thick sequence of horizontal beds rather than dipping foresets, the gravel must have been deposited in a vertically accreting sequence in a rising lake rather than in a constant-level lake, where lateral accretion and foreset bedding would dominate (figure 11). dipping beds of gravel will be present even in features dominated by vertical accretion, because dipping beds of gravel would have figure 7. plate x from gilbert (1890) showing the bonneville shoreline at a locality on the east side of snake valley in western utah (near 39.46° n. latitude, 113.86° w. longitude). north is toward the right. note that the topographic feature labeled “bonneville sea cliff ” in the lower part of the map area is an erosional shoreline that grades into a depositional complex in the bonneville shoreline zone in the central and upper parts of the map area. 307 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 been deposited on the flanks and fronts of barriers and spits, or any place where depositional surfaces were not level. in addition, foreset bedding would have been associated with progradation during each of the frequent fluctuations and oscillations that occurred during the transgressive phase. bedding observed in barriers and spits at the bonneville shoreline is similar to that in transgressive-phase barriers throughout the basin (schide and others, 2018). gilbert (1890) called many of the large barriers “intermediate” because they are found at elevations between those of the bonneville and provo shorelines (numerous transgressive-phase barriers are also found at elevations lower than the provo shoreline). the intermediate barriers were formed during the transgressive phase, which was the approximate 12,000-year period during which the long-term trend was for lake bonneville to rise to its highest level from levels near those of modern great salt lake. short-term fluctuations and oscillations during the transgressive phase were frequent, and some are documented based on stratigraphic relationships (oviatt, 1997; nelson and jewell, 2015). the causal relationships between intermediate barriers and short-term oscillations and fluctuations of lake level, in addition figure 8. the bonneville shoreline in tooele valley, on the west side of the oquirrh mountains, west of salt lake valley. the photographs show two expressions of the bonneville shoreline at locations adjacent to each other. (a) photograph taken from interstate highway 80 toward the southeast of the high scarp at the bonneville shoreline at the upper end of a long erosional slope formed on pre-bonneville alluvium. (b) prominent bonneville shoreline where it has been cut into sandstone and limestone bedrock of the pennsylvanian-permian oquirrh group, view looking east. (c) schematic cross section of the relationships shown in photograph a; note that no platform is present at a and that the scarp (or “sea” bluff) indicates a tremendous amount of wave erosion during the transgressive phase; the bonneville shoreline at this locality is erosional. (d) schematic cross section of the relationships shown in photograph b; note that a prominent constructional platform marks the upper limit of wave erosion, deposition of coarse-grained gravel eroded from the bedrock, and the bonneville shoreline. 308 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 to other potential factors in the development of transgressive-phase barriers, is an ongoing, but in-complete, field of investigation. study of those causes began with gilbert (1890, p. 135–153), who proposed the hypothesis that the intermediate shorelines formed as lake level generally rose but was punctuated by oscillations. geochronology of lake bonneville the general history of lake bonneville is well known (see gilbert, 1890; oviatt, 2015; and oviatt and shroder, 2016; and numerous references cited therein), but details of the chronology are still under investigation (laabs and others, 2019). the bonneville lake cycle consisted of three main phases: the transgressive phase, the overflowing phase, and the regressive phase (figure 2). the transgressive phase lasted about 12,000 years from 30,000 years b.p. until 18,000 to 17,500 years b.p., during which the lake rose by over 270 m in a hydrographically closed basin with no river outflow. the stansbury shoreline, one of three regionally mappable shorelines in the bonneville basin (bonneville and provo are the other two), formed during at least two of the many oscillations of lake level that occurred during the transgressive phase (gilbert, 1890; oviatt and others, 1990; nelson and jewell, 2015; oviatt, 2015). at the end of the transgressive phase the bonneville flood (o’connor, 1993; 2016) dropped lake level by over 100 m (miller and others, 2013) in less than a year, an event that marked the beginning of the overflowing phase of provo shoreline development in the hydrographically open basin. the overflowing phase lasted until about 15,000 years b.p. (figure 2), or possibly until about 16,500 years b.p. (laabs and others, 2019). the regressive phase in the once-again closed basin lasted until about 13,000 years b.p. (figure 2) when the lake dropped to elevations similar to those of modern great salt lake. of primary interest for this paper is the chronology at the end of the transgressive phase. the bonneville flood occurred at the end of the transgressive phase. the age of the flood is not known with high precision (figures 12 and 13), but some ages figure 9. stack of transgressive-phase v-bars in snake valley (39.47° n. latitude, 114.00° w. longitude)—the general slope of the land surface is upward from right to left. the highest, best-preserved v-bar is at the bonneville shoreline; the lower v-bars, which are not as well preserved, were deposited earlier during the transgressive phase. map data ©2020 google. 309 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 help to narrow the possibilities. the age is limited by three radiocarbon dates for samples collected from basal stratigraphic positions at elevations close to the bonneville shoreline (figure 13). two of the samples consist of charcoal from a soil buried by bonneville gravel 7 m below the bonneville shoreline (oviatt, 1991, 2015), and one sample consists of wood in lagoon deposits near the base of bonneville gravel 15 m below the bonneville shoreline (scott, 1988; oviatt, 2015). the wood and charcoal ages are limiting ages — the bonneville flood cannot be older than those ages. if simple assumptions about a steady rise of lake level are used (figure 13), the three ages suggest that the lake had reached the elevation of the bonneville shoreline by approximately 18,000 years b.p. (oviatt, 2015), although the actual time of the initiation of overflow and of the bonneville flood could have been as young as about 17,000 cal yr b.p. (calibrated years before present) (figure 13). amidon and farley (2011) used an age of 17,500 cal yr b.p. for the bonneville flood for calibrating cosmogenic 3he production rates in western north america. until more information becomes available the figure 10. v-bars in closed pleistocene lake basins in nevada. (a) stack of v-bars in railroad valley (38.52° n. latitude, 115.54° w. longitude). (b) stack of v-bars near walker lake, lake lahontan basin (38.67° n. latitude, 118.65° w. longitude). map data ©2020 google. 310 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 precise age of the end of the transgressive phase and of the bonneville flood cannot be determined, but 17,500 ± 500 years b.p. is an acceptable estimate. at tabernacle hill in the southern sevier basin (figure 1), a basalt flow and tuff ring were erupted into lake bonneville after the bonneville flood had dropped the lake to the level of the provo shoreline (gilbert, 1890; oviatt and nash, 1989; oviatt, 1991). eight radiocarbon ages for tufa (lifton and others, 2015) cemented to the outer edges of the basalt flow provide age estimates for the lake at that level. the maximum range of all the calibrated tufa ages from tabernacle hill is about 1500 yr, and that range overlaps by about 630 yr with the limiting age range for the wood and charcoal ages from just below the bonneville shoreline. a proposed age for the beginning of the provo overflowing phase (18,300 years b.p.; lifton and others, 2015) is based on the assumption that there was no radiocarbon reservoir at tabernacle hill at that time, an assumption that may not be correct considering the local hydrogeology and the history of the lake. the area near tabernacle hill is characterized by a high modern water table and flowing wells (holmes and thiros, 1990). a gigantic hot-springs tufa mound was deposited nearby in late quaternary time (meadow hot springs tufa mound; nelson and fuchs, 1987; oviatt, 1991), and hot springs are still active at the tufa mound (https:// utah.com/meadow-hot-springs; website accessed on october 5, 2020). these observations suggest that modern groundwater is actively discharging in the tabernacle hill area. it is reasonable to think that groundwater discharge was enhanced in that area in late pleistocene times when the climate was cooler and wetter than today (ibarra and others, 2018). groundwater discharge would have abruptly increased in many places within the lake at the provo level, including near tabernacle hill, after the bonnefigure 11. schematic diagrams showing the expected differences in bedding between lateral and vertical accretion. figure 12. geochronology of the latter part of the transgressive phase at elevations higher than the provo shoreline. the approximate long-term trend of the transgressive phase for this part of the chronology (about 13 m/1000 yr; figure 2) is shown by the dashed gray line, and the bonneville flood is shown by the vertical gray line. the approximate elevations of the bonneville and provo shorelines, adjusted for the effects of isostatic rebound, are shown with the yellow lines (data from currey, 1982, and oviatt, 2015). the calibrated, two-sigma age ranges for radiocarbon ages of samples of three different categories of material, plotted relative to their isostatically adjusted collection elevations, are shown with the blue, black, and red lines. note that the age of the bonneville flood is not precisely constrained by the available calibrated radiocarbon ages; a likely age is 17,500 ± 500 years b.p., although it could easily be younger than that (figure 13) if the rate of transgression were less than the estimated value of about 13 m/1000 yr (figure 2). 311 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 ville flood had increased the difference in hydraulic head by over 100 m from recharge areas to discharge areas (with the drop in lake level from bonneville to provo). groundwater that discharges in springs or in diffuse discharge areas has been travelling through the groundwater system for some amount of time since it was recharged to the groundwater system (freeze and cherry, 1979). therefore, groundwater is usually older than the surface water (i.e., precipitation or runoff) in the same area. lerback and others (2019) have shown that modern groundwater in the great salt lake desert (figure 1), in the western bonneville basin, has ages that range from 0 (zero) to over 21,000 years b.p although the possibility of a radiocarbon reservoir in lake bonneville in the area of tabernacle hill when the lake was at the provo shoreline has not been tested, it is a reasonable expectation and could be an important factor in accounting for the overlap in tufa ages from the provo shoreline with the wood and charcoal ages near the bonneville shoreline. radiocarbon ages for gastropod shells from provo-aged deposits (miller and others, 2013) have potential for helping with the chronology of the provo shoreline, but are difficult to interpret because they are older than expected. the age ranges overlap with the tufa age ranges from tabernacle hill. some “old” gastropod ages reported by miller and others (2013) are for samples collected from gravel that forms the two prominent barrier beaches at the provo shoreline, which formed relatively late in the overflowing phase (miller, 2016). more work is needed to be certain, but it is reasonable to conclude that the gastropod ages have been influenced by radiocarbon reservoirs in the lake water (possibly different magnitudes of the reservoirs at different locations in the basin) — this would be consistent with the input of groundwater into the provo lake. previously i and most authors have assumed that lake bonneville overflowed during a prolonged period of 500 to 1000 14c years, or more, at its highest level prior to the bonneville flood (oviatt and jewell, 2016). for this to have happened, however, several events would have occurred during the apparent about 630 year period of overlap between the wood and charcoal ages near the bonneville shoreline and the tufa ages at the provo level — these events are: the completion of the transgressive phase in its uppermost 7 to 15 m, the proposed prolonged period of overflow, the bonneville flood, the eruption and cooling of the basalt flow and tuff ring at tabernacle hill, and the precipitation of tufa on the basalt at tabernacle hill. it is likely that provo-shoreline tufa (including the tufa at tabernacle hill) was precipitated during the latter part of the overflowing phase rather than at the beginning of that phase. considering the uncertainty of the numerical ages and their collective age ranges (individual ages are not points in time, but rather are age ranges), and the limited availability of appropriate ages for the bonneville and provo shorelines, it may be possible, if prolonged overflow did actually occur, to add in a period of prolonged overflow into figure 13. an enlargement of the chronology of the end of the transgressive phase, as determined by the limits placed on the transgression by radiocarbon ages (calibrated) of two charcoal samples from a buried soil 7 m below the bonneville shoreline near kanosh, utah (dates 2 and 3 and thick black line representing 2-sigma age range), and a sample of wood from basal lagoon deposits 15 m below the bonneville shoreline (date 1 and thick black line) (data from scott, 1988; oviatt, 1991, 2015), compared to the approximate long-term average rate of transgression (about 13 m/1000 yr; figures 2 and 12), which is shown by the two black dashed lines, one that intersects the young end of the 2-sigma range for date # 1, and one that intersects the old end of the 2-sigma range for data # 1. the age of the bonneville flood (the end of the transgressive phase) falls between those two lines, marked by the red, double-pointed line. based on this analysis, an age between about 17,600 and 17,000 years b.p. is reasonable. 312 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 the lake bonneville chronology. but if that were to be done, independent observations should be available to clearly support the conclusion of prolonged overflow. it turns out that no such evidence has been described and apparently does not exist (oviatt and jewell, 2016). following the publication of gilbert’s monograph on lake bonneville in 1890, all publications on the history of the lake that were published during the 20th century include statements or assumptions that lake bonneville had reached its highest level and overflowed for a prolonged period so that the prominent bonneville shoreline could develop at a stabilized lake level. importantly, this presumed overflow was presented as not causing rapid downcutting of the marsh creek alluvial fan (the speculation was that it took time for the overflowing river to cut headwardly up the north flank of the alluvial fan to the overflow point [i.e., scott and others, 1983, p. 276–277]). gilbert’s initial ideas gilbert expressed in print in 1875 (p. 90–91) the idea of prolonged overflow at the elevation of the bonneville shoreline. “the level of great salt lake, like that of other lakes without overflow, is notoriously inconstant, for the obvious reason that it depends on the ratio between precipitation and evaporation over a limited area — factors which diverge, and change their conditions of equilibrium, with every fluctuation of annual mean temperature or humidity. it is difficult to imagine that so unstable a climatal equilibrium was maintained for the time that was consumed in the production of either the bonneville or the provo beach, and, before we accept such explanation of their origin, we are led to inquire whether at these levels the stage of water was not regulated by an overflow. the coincidence of one of the constant levels with the highest water stage of all, renders the presumption of an outflow at that stage especially strong.” in 1875, gilbert had not thoroughly studied the geomorphology of red rock pass or the bonneville shoreline. it is important to realize that gilbert recognized that lakes in closed basins do not maintain a constant level for a prolonged period — if evidence were to be found that a lake had maintained a constant level for a extended period, some causal mechanism would be required, and such a mechanism is likely to be surface-water overflow. even in a hydrographically open-basin lake, the level does vary to some extent, depending on the geometry of the overflow channel and changes in the rates of inflow and outflow. but that variation is likely to be limited to a narrow vertical range, measured in meters or tens of meters in extreme cases (street-perrott and harrison, 1985). lake bonneville, on the other hand occupied a hydrographically closed basin for most of its history, in which the total range of lake-level variation was hundreds of meters. the largest oscillations of lake level during the transgressive phase, which are likely to have been caused by millennial-scale changes in climate, were probably on the order of 40 to 50 m in amplitude (oviatt, 1997; nelson and jewell, 2015). the idea of prolonged overflow at the bonneville shoreline was probably part of gilbert’s interpretations of the bonneville shoreline prior to 1875, but it is hard to know exactly when the idea originally arose. in 1874, in a brief description of the lake for the report of the wheeler survey (gilbert, 1874), he said nothing about the length of time the lake might have lingered at either the bonneville or provo shorelines. perhaps the idea of prolonged overflow and lake-level stability while the bonneville shoreline formed was just a natural conclusion that anyone might have arrived at after first seeing the shorelines. gilbert’s field notes from the period from about july 1876 to november 1880 as transcribed by hunt (1982), give hints that during that period when he was investigating the geology of the bonneville basin on the ground, he was thinking that both the bonneville and provo shorelines had formed during periods of prolonged overflow and stable lake levels. however, during that period his ideas may have begun to shift. a drawing from gilbert’s field notes for september 24, 1877 (figure 14a), shows a description and interpretation of the shoreline that is consistent with his 1890 statement. the accompanying drawing (figure 14b) and comments in gilbert’s field notes from the same day are more am313 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 biguous. perhaps at that point he was not aware of the rapid regression from the bonneville shoreline caused by the bonneville flood. gilbert’s ideas in 1890 during the 1880s, gilbert published a few papers related to his work on lake bonneville (e.g., gilbert, 1885; 1886), but he said little about the formation of the bonneville shoreline in those publications. much of the material from the 1880s was revised and republished as part of monograph 1 in 1890. the following quote from gilbert’s 1890 monograph on lake bonneville summarizes his thinking at that time (gilbert, 1890, p. 171). “thirteen years ago i had the temerity to predict, first, that the position of the bonneville shore-line would eventually be shown to have been determined by an overflow of the lake, and second, that the provo shore-line would be found to have been similarly determined. the first of these predictions has been verified in its letter, but not in its spirit; the second has proved to have full warrant. my anticipation was based on the following consideration: a lake without overflow has its extent determined by the ratio of precipitation to evaporation within its basin; and since this ratio is inconstant, fluctuating from year to year and from decade to decade, it is highly improbable that the water level will remain constant long enough to permit its waves to carve a deep record. i failed to take account of the fact that the highest shore-mark of the series is conspicuous by reason of the contrast there exhibited between land sculpture and littoral sculpture. we now know that the height of the bonneville shore-line was determined in a certain sense by overflow, since a discharge limited the rise of the water; but the carving of the shore was essentially completed before the discharge; and as soon as that began, the water level fell. at the provo horizon, on the contrary, a constant or nearly constant water-level was maintained by discharge for a very long time.” it is not exactly clear what he meant by “13 years ago.” he said in monograph 1 (gilbert, 1890, p. 17) that, “the field work that afforded this information [that is, the information published in monograph 1] was performed chiefly in the years 1867–70, but publication was delayed until 1877–78.” presumably, “1877–78” referred to reports of the wheeler and powell surveys of the american west, in which he was employed. thirteen years prior to 1890 is 1877. the publication of monograph 1 took many years to complete (hunt, 1980; pyne, 1980), but regardless of the precise year, “13 figure 14. drawing from gilbert’s field notes (hunt, 1982, figure 8.2). (a) gilbert showed relationships similar to those in figure 5d of this paper—assuming lake level was rising, in gilbert’s drawing the constructional platform grew in height as the waves cut into the underlying materials (alluvium or bedrock); the abrupt angle between the platform and the scarp or cliff is the shoreline. gilbert said in his field notes, as related to this drawing: “as the water rose on a salient point its waves carried a cliff before them and at any time of the progressive advance the profile might be a continuous advance leaving a somewhat continuous surface behind it.” (b) gilbert showed field relationships of depositional features near the bonneville shoreline. apparently at this point gilbert thought the beginning of the regression from the bonneville shoreline was slow and he had not realized at that time that lake level dropped very rapidly from the bonneville shoreline during the bonneville flood. that realization would come later after he had spent more time at red rock pass and assembled all the pieces of the puzzle. 314 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 years ago” would have been sometime during the decade of the 1870s. in the 1890, p. 171, quote, gilbert eloquently described his interpretation of how the bonneville shoreline developed. as is discussed below, however, i have found no case in the published literature (or in unpublished sources) where anyone paid attention to his 1890 interpretation. i include myself in this. post-gilbert interpretations during the last decade of the 1800s, and for all of the 20th century into the early 21st century, everyone assumed that the bonneville shoreline had formed during a period of stable lake level caused by prolonged overflow (oviatt and jewell, 2016). the assumption was made with apparent certainty. my own experience is not different from that of others. when i first began learning about lake bonneville in the field in the late 1970s, the assumption of prolonged overflow was part of the “lore” of lake bonneville — no one thought to question the idea and it was part of the well-known history of the lake that everyone accepted. for decades as i continued to learn about the lake and to publish papers, i inserted, without the slightest hesitation, a period of prolonged overflow into diagrams and summaries of lake history. i never heard anyone question the idea of prolonged overflow, and authoritative statements, such as “the 10to 20-m-wide wave-cut benches that were locally cut in bedrock at the bonneville shoreline require a stand of some duration at the highest level” (scott and others, 1983, p. 277), left no doubt that prolonged overflow was real. this spell was broken for me, however, sometime early in the decade of 2011–2020, when i realized that i didn’t know what the evidence was for prolonged overflow or for its duration. for all those years i had been blindly repeating the word of others without checking for myself. i have been unable to find any published or unpublished interpretations of the bonneville shoreline that are consistent with or that cite gilbert’s (1890) interpretations. in the literature i discovered that no evidence for prolonged overflow has ever been presented, and that the presumed period of overflow has never been dated (scott and others, 1983, did not give the locations of “the 10to 20-m-wide wave-cut benches that were locally cut in bedrock at the bonneville shoreline”— all benches i have seen at the bonneville shoreline are constructional [depositional]). since gilbert (1890), depictions of the end of the transgressive phase and the initiation of the bonneville flood have varied. here are a few published accounts from the literature (see oviatt and jewell, 2016, for additional examples): “the bonneville shore line . . . was formed while the lake stood at the level of overflow . . .” (boutwell, 1933, p. 36). “here [at the bonneville shoreline] it [lake bonneville] came to a halt and remained stationary for a very long time, long enough, indeed, to construct a terrace much larger than it had done at any of the lower levels” (pack, 1939, p. 31). “the well-developed shore features throughout the bonneville basin at the highest level of the lake seem to require that the highest lake was maintained at constant level by outflow” (williams, 1952). “. . . a level later controlled by the height of resistant bedrock in red rock pass . . . the true height of overflow is not determinable, but it could have been 100 feet above the bonneville shoreline . . .” (malde, 1968, p. 11). “the lake briefly overflowed (probably less than 500 yr) near red rock pass, id, as the bonneville shoreline formed . . .” (oviatt and miller, 1997, p. 349). processes of formation at the cronus-earth project site (cosmic-ray produced nuclide systematics on earth) in the promontory mountains (figure 1; lifton and others, 2015), a tremendous amount of quartzite bedrock was eroded during the late transgressive phase of lake bonneville. many sites in the basin have similar geomorphology, but i discuss this one here because it has been well described in the literature (figure 15; lifton and others, 2015). at this site the ground surface below the “sea” cliff, along line a-a' but not necessarily in the adjacent valleys, is a wave-cut erosional surface on quartzite bedrock. an abrasion platform with a very low lake-ward gradient, which would have been produced by wave erosion if the lake had remained at a nearly constant level for a prolonged period, is not present. the erosional surface was produced by waves eroding the quartzite as the lake 315 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 figure 15. information about the cronus site in the promontory mountains (near 41.264° n. latitude, 112.473° w. longitude), where a tremendous volume of quartzite bedrock (cambrian tintic quartzite) was eroded during the late transgressive phase of lake bonneville (lifton and others, 2015). (a) google earth image of the site area (map data ©2020 google). the elevation of the barrier at currey (1982) site 164 is 1614 m (5295 ft). (b) same area shown on u.s.g.s. 7.5-minute pokes point topographic map (for scale, the red lines mark u.s. land-survey sections of 1 mi2; contour interval = 20 ft). (c) topographic profile along line a-a', drawn using contours in map b. (d) topographic profile along line b-b', drawn using contours in map b. the two profiles cross at the location marked by the arrows. at that location water depth would have been about 17 m at the time the lake occupied the bonneville shoreline. the eroded surface along profile a-a' appears, from an appropriate vantage point, to be a wave-cut platform, but its slope is too great to have formed while the lake maintained a constant level during a prolonged period of overflow. 316 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 generally rose over time to multiple contiguous levels. topographic profiles at the cronus site (figure 15, a-a', b-b') intersect on the erosional surface at an elevation of about 1597 m (about 5240 ft). the bonneville shoreline has an elevation of about 1614 m near the cronus site (currey, 1982, site number 164; lifton and others, 2015) (this elevation estimate ignores the difference between still-water level and the level of the geomorphic expression of that level; the geomorphic [“paleo-shoreline”] evidence could be 2 to 3 m higher than the still-water level, but that difference is rarely obvious or measurable in late-pleistocene cases [atwood and others, 2016]). so, the water depth on the erosional surface where the two profile lines intersect was about 17 m, which is too great for significant (if any) wave-caused abrasion of the quartzite bedrock. it took approximately 1300 years for lake bonneville to transgress the last 17 m to its highest level — this estimate is based on a long-term transgressive rate of 13 m/1000 years (figure 2), but if the transgressive rate slowed during this time interval the amount of time it took the lake to transgress the last 17 m would have been longer than about 1300 years. the observations at the promontory cronus site, plus other observations of the geomorphology of the bonneville and transgressive-phase shorelines, indicate that lake bonneville did not maintain a near-constant level for a prolonged period of time during the formation of any shoreline (except for the provo shoreline, which is not discussed in this paper). instead, all field observations are consistent with the interpretation that the bonneville shoreline formed as part of an evolutionary sequence (i.e., as part of a sequence of incremental changes over a long period) — the bonneville shoreline marks the highest level attained by the transgressing lake (figures 2, 12, and 16). if the overflow threshold, which was the low point on the basin divide (i.e., the low point on the crest of the marsh creek alluvial fan), had been higher, the bonneville shoreline would have been higher. if the threshold had been lower, the bonneville shoreline would have been lower. as gilbert stated in 1890 (p. 171): “. . . the height of the bonneville shore-line was determined in a certain sense by overflow, since a discharge limited the rise of the water; but the carving of the shore was essentially completed before the discharge; and as soon as that began, the water level fell.” observations described above are consistent with the interpretation that the bonneville shoreline represents the highest level attained by lake bonneville, and that the shoreline is conspicuous because it marks the boundary between lacustrine-dominated landforms below and fluvial-dominated landforms above (as noted by gilbert in 1890). some important observations that are consistent with the idea that the lake continued to transgress while the bonneville shoreline formed are the dominance of horizontal bedding in barriers and the presence of depositional platforms that from a distance look like erosional platforms. the interpretation that lake bonneville overflowed for a prolonged period prior to the bonneville flood apparently originated with gilbert himself as an unsupported assumption and then persisted for over 120 years. however, observations are consistent with the interpretation that the bonneville shoreline represents only a moment in time at the end of the transgressive phase of the bonneville lake cycle, consistent with gilbert’s 1890 interpretation. i have not found a publication of gilbert’s in which he defended his 1890 view. he passed away in 1918 and published many insightful papers and books on geology in the 28 years after the monograph on lake bonneville was released (yochelson, 1980). if gilbert did publish something related to his understanding of how the bonneville shoreline developed, other than the 1890 monograph, it has not been recognized by the researchers who came after him. conclusions g.k. gilbert was an amazing observer and scientist. although he made a few mistakes in his career as a geologist, his 1890 interpretation of the history of the bonneville shoreline was not one of them. we should recognize that gilbert’s (1890) interpretation of the bonneville shoreline was correct and abandon the idea of prolonged overflow prior to the bonneville flood. 317 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 figure 16. schematic diagrams showing the evolution of the highest shoreline of lake bonneville, from time 1 through time 8. blue arrows and blue lines show the long-term rise of the lake during the transgressive phase (probable multiple fluctuations and oscillations of lake level in the hydrographically closed basin are not shown). 318 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 acknowledgments i am grateful to the late don currey (university of utah) for many years of stimulating discussions about lake bonneville and to stephen pyne for valuable discussions during the past few years. don clark, utah geological survey, has endured some of my field discussions and examinations of bonneville shoreline localities, and he has provided valuable insights. thanks to ken krahulec (utah geological survey, retired), who took the photograph used in figure 5. i am grateful to ben laabs (north dakota state university) and dave miller (u.s. geolgical survey) for helpful review comments and to doug sprinkel for help and support. references amidon, w.h., and farley, k.a., 2011, cosmogenic 3he production rates in apatite, zircon and pyroxene inferred from bonneville flood erosional surfaces: quaternary geochronology, v. 6, p. 10–21. atwood, g., wambeam, t.j., and anderson, n.j., 2016, the present as key to the past—paleoshoreline correlation insights from great salt lake, in oviatt, c.g., and shroder, j.f., jr., editors, lake bonneville—a scientific update: developments in earth surface processes 20, elsevier, p. 1–27. bills, b.g., wambeam, t.j., and currey, d.r., 2002, geodynamics of lake bonneville, in gwynn, j.w, editor, great salt lake—an overview of change: utah geological survey, utah department of natural resources special publication, p. 7–32. boutwell, j.m., 1933, excursion 1 — wasatch front, in 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netherlands, elsevier, p. 127–144. miller, d.m., oviatt, c.g., and mcgeehin, j.p., 2013, stratigraphy and chronology of provo shoreline deposits and lake-level implications, late pleistocene lake bonneville, eastern great basin, usa: boreas, v. 42, p. 342–361. nelson, d.t., and jewell, p.w., 2015, transgressive stratigraphic record and possible oscillations of late pleistocene lake bonneville, northern hogup mountains, utah, u.s.a.: palaeogeography, palaeoclimatology, palaeoecology, v. 432, p. 58–76. nelson, m.e., and fuchs, w.e., 1987, geology of a quaternary travertine deposit, central utah, in kopp, r.s., and cohenour, r.e., editors, cenozoic geology of western utah—sites for precious metal and hydrocarbon accumulations: utah geological association publication 16, p. 351–365. o’connor, j., 1993, hydrology, hydraulics, and geomorphology of the bonneville flood: geological society of america special paper 274, 83 p. o’connor, j., 2016, chapter 6, the bonneville flood—a veritable débâcle, in oviatt, c.g., and shroder, j.f., jr., editors, lake bonneville—a scientific update: developments in earth surface processes 20, amsterdam, netherlands, elsevier, p. 105– 126. oviatt, c.g., 1991, quaternary geology of the black rock desert, millard county, utah: utah geological and mineral survey special studies 73, 23 p. oviatt, c.g., 1997, lake bonneville fluctuations and global climate change: geology, v. 25, p. 155–158. oviatt, c.g., 2015, chronology of lake bonneville, 30,000 to 10,000 yr b.p.: quaternary science reviews, v. 110, p. 166–171. oviatt, c.g., and jewell, p.w., 2016, the bonneville shoreline— reconsidering gilbert’s interpretation, in oviatt, c.g., and shroder, j.f., jr., editors, lake bonneville—a scientific update: developments in earth surface processes 20: amsterdam, netherlands, elsevier, p. 88–104. oviatt, c.g., currey, d.r., and miller, d.m., 1990, age and paleoclimatic significance of the stansbury shoreline of lake bonneville, northeastern great basin: quaternary research, v. 33, p. 291–305. oviatt, c.g., and miller, d.m., 1997, new explorations along the northern shores of lake bonneville, in link, p.k., and kowallis, b.j., editors, mesozoic to recent geology of utah: brigham young geology studies, v. 42, pt. 2, p. 345–371. oviatt, c.g., and nash, w.p., 1989, basaltic volcanic ash and volcanic eruptions in the bonneville basin, utah: geological society of america bulletin, v. 101, p. 292–303. oviatt, c.g., and shroder, j.f., jr., editors, 2016, lake bonneville—a scientific update: developments in earth surface processes 20, amsterdam, netherlands, elsevier, 659 p. pack, f.j., 1939, lake bonneville—a popular treatise dealing with the history and physical aspects of lake bonneville: bulletin of the university of utah, v. 30, no. 4, 112 p. pyne, s.j., 1980, grove karl gilbert—a great engine of research: austin and london, university of texas press, 306 p. schide, k.h., jewell, p.w., oviatt, c.g., jol, h.m., and larsen, c.f., 2018, transgressive-phase barriers as indicators of basin-wide lake-level changes in late pleistocene lake bonneville, utah, 320 g.k. gilbert and the bonneville shoreline oviatt, c.g. geology of the intermountain west 2020 volume 7 usa: geomorphology, v. 318, p. 390–403. schoonees, j.s., 2000, annual variation in the net longshore sediment transport rate: coastal engineering, v. 40, p. 141–160. scott, w.e., 1988, transgressive and high-shore deposits of the bonneville lake cycle near north salt lake, utah: utah geological and mineral survey miscellaneous publication 88-1, p. 38–42. scott, w.e., mccoy, w.d., shroba, r.r., and rubin, m., 1983, reinterpretation of the exposed record of the last two cycles of lake bonneville, western united states: quaternary research, v. 20, p. 261–285. semeniuk, v., searle, d.j., and woods, p.j., 1988, the sedimentology and stratigraphy of a cuspate foreland, southwestern australia: journal of coastal research, v. 4, no. 4, p. 551–564. shroder, j.f., cornwell, k., oviatt, c.g., and lowndes, t.c., 2016, landslides, alluvial fans, and dam failure at red rock pass— the outlet of lake bonneville, in oviatt, c.g., and shroder, j.f., jr., editors, lake bonneville—a scientific update: developments in earth surface processes 20, amsterdam, netherlands, elsevier, p. 75–87. smith, d.g., simpson, c.j., jol, h.m., meyers, r.a., and currey, d.r., 2003, gpr stratigraphy used to infer transgressive deposition of spits and a barrier, lake bonneville, stockton, utah, usa, in bristow, c.s., and jol, h.m., editors, ground penetrating radar in sediments: london, geological society special publication 211, p. 79–86. street-perrott, e.a., and harrison, s.p., 1985, lake levels and climate reconstruction, in hecht, a.d., editor, paleoclimate analysis and modeling: new york, wiley, p. 291–340. wambeam, t.j., 2001, modeling lake bonneville basin morphometry using digital elevation models: salt lake city, university of utah, m.s. thesis, 75 p. williams, j.s., 1952, red rock pass, outlet of lake bonneville: geological society of america bulletin, v. 63, no. 12, p. 1375. yochelson, e.l., editor, 1980, the scientific ideas of g.k. gilbert— an assessment on the occasion of the centennial of the united states geological survey (1879–1979): geological society of america special paper 183, 148 p. rise of the erg—paleontology and paleoenvironments of the triassic-jurassic transition in northeastern utah geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 © 2016 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. rise of the erg—paleontology and paleoenvironments of the triassic-jurassic transition in northeastern utah brooks b. britt, daniel j. chure, george f. engelmann, and jesse dean shumway a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa pre-meeting field trip october 23–25, 2016 geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover three articulated sphenosuchians from the saints & sinners quarry, which is stop 5 of this field trip. the voids of various colors are weathered concretion sites. i 2016 president bill loughlin bill@loughlinwater.com 435.649.4005 2016 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2016 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2016 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2016 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2016 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2016-2018 term craig morgan craigmorgan@utah.gov 801.422.3761 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 3 2016 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 1 abstract this field trip focuses on the late triassic-early jurassic transition in northeastern utah. this transition records one of the most striking terrestrial environmental transformations in the history of north america, wherein the fluvio-lacustrine chinle formation is transgressed by the vast erg system of the nugget (wingate+navajo)/navajo/aztec sandstones. exposures in northeastern utah are ideal for studying this transition as they are closely spaced and accessible. the uppermost chinle formation beds are lacustrine/fluvial fine-grained sediments which are overlain by increasingly drier, sandy, transitional beds. the non-eolian basal beds of the nugget sandstone preserve a late triassic ichnofauna, with some sites including brachychirotherium tracks. large-scale dune deposits comprise most of the nugget sandstone and contain vertebrate (brasilichnium) tracks and a diverse invertebrate ichnofauna. interdunal, carbonate, spring mounds, as much as 3 m tall, fed carbonate freshwater lake deposits containing gastropod body fossils and invertebrate ichnofossils. another lacustrine deposit, located at the saints & sinners quarry, is on the shoreline of a non-carbonate interdunal lake/oasis. over 11,500 bones have been collected from the site and represent two theropod dinosaur taxa, sphenodonts, sphenosuchians, a pterosaur, and drepanosaurs (with many complete, three-dimensional, articulated skeletons). in addition to bones, dinosaur trackways are also preserved in shoreline and other interdunal beds. the fauna shows that this interdunal area of the nugget sandstone was the site of intense biological activity. the drepanosaurs are chronologically significant in that they are restricted globally to the late triassic, indicating that at least the lower one-fourth to one-third of the formation is late triassic in age. rise of the erg—paleontology and paleoenvironments of the triassic-jurassic transition in northeastern utah brooks b. britt1, daniel j. chure2, george f. engelmann3, and jesse dean shumway1 1museum of paleontology and department of geological sciences, brigham young university, provo, ut, 84602; brooks_britt@byu.edu, jdshumway@byu.edu 2dinosaur national monument, jensen, ut 84035; dan_chure@nps.gov 3department of geography and geology, university of nebraska at omaha, omaha, ne 68182; gengelmann@unomaha.edu citation for this article. britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d., 2016, rise of the erg—paleontology and paleoenvironments of the triassicjurassic transition in northeastern utah: geology of the intermountain west, v. 3, p. 1–32. © 2016 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the chinle-nugget formational transition records one of the most dramatic continental environmental changes in the phanerozoic of north america, where a fluvial and lacustrine environment is gradually replaced by an eolian-dominated environment represented by a vast erg that covered much of the western u.s. for mil2 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 lions of years (blakey and ranney, 2008). these formations along the south flank of the uinta mountains have received less attention than equivalent exposures farther south on the colorado plateau. over the last decade, however, intensive work in the chinle formation by randall irmis (utah museum of natural history), and at the nugget sandstone area of dinosaur national monument (dino) by dan chure (national park service), george engelmann (university of nebraska), and brooks britt (brigham young university) has shed new light on the chinle-nugget transition (irmis and others, 2015) and the paleontology and paleoenvironments of the nugget sandstone (chure and others, 2014a and 2014b). this field trip focuses on recent paleontological discoveries in the nugget sandstone that provide insights into the rise of the erg, its biota, and paleoenvironments. we have selected sites for their significance and to minimize travel time so that more time can be spent on the outcrop and less time driving between stops. several different names and ranks, as summarized by irmis and others (2015), have been applied to the stratigraphic unit referred to here as the nugget sandstone. recently, this issue was addressed by sprinkel and others (2011) and irmis and others (2015), and both studies recommend the use of the nugget sandstone. the nugget sandstone correlates with the glen canyon group, the wingate/moenave, kayenta, and navajo strata (see references in doelger, 1987, and analyses in sprinkel and others, 2011). sprinkel and others (2011) propose using the term nugget sandstone in areas where the kayenta formation, a fluvial unit present between the wingate and navajo sandstones farther south, is absent. the nugget sandstone spans the triassic-jurassic boundary, but the position of this boundary is uncertain (see references and discussions in sprinkel and others, 2011; irmis and others, 2015). with a dearth of body fossils and the absence of volcanic units, including ash, that could be radiometrically dated, there are no calibrated ages for the nugget. consequently, dating is limited to stratigraphic bracketing and correlation using vertebrate trace fossils. the nugget sandstone rests conformably on the late triassic chinle formation (irmis and others, 2015) whereas the marine middle jurassic carmel formation rests unconformably on top of the nugget sandstone. in the absence of age-specific invertebrate fossils, dating of the nugget is based on vertebrate tracks, with a brachychirotherium suite in the lower portions of the formation indicating a late triassic age (lockley and others, 1992) and the early jurassic grallator, otozoum, eubrontes assemblage near the top (lockley and others, 1992; lockley, 2011). these traces, however, do not help resolve the position of the triassic-jurassic boundary within the formation. the saints & sinners quarry fauna sheds additional light on these issues by corroborating the ichnofossil-derived early triassic age for the lower portion of the formation with body fossils because the quarry contains a drepanosaur and a sphenosuchian with a rod-like posterior expansion of the coracoid. drepanosaurs are known only from the carnian to norian (renesto and binelli, 2006; renesto and others, 2010) and sphenosuchians with such expansions are known only from the late triassic (james clark, george washington university, personal communication, 2016). the saints & sinners quarry horizon is 55 m above the base of the lowest contiguous eolian sandstone of the formation (figure 1a), indicating that at least the lower 25% of the formation locally is no younger than late triassic in age. it should be noted that molina-garza and others (2003) conducted a paleomagnetic study of the underlying chinle formation in our study area and concluded that the gartra member at the base of the chinle was approximately 207–205 ma (rhaetian)—ages that are younger than indicated by vertebrate fossils from the lower one quarter of the nugget sandstone. recent summaries of studies of the chinle formation in, and adjacent to dino can be found in erickson (2007) and irmis and others (2015). in the study area, the nugget sandstone has received less attention than the chinle formation. much of the work on the nugget in this area has focused on nomenclature and correlation (peterson, 1988, 1994; sprinkel and others, 2011). previously, little detailed work had been done on the paleontology and paleoenvironments throughout the nugget, in part because it consists predominantly of eolian dunes, with a sparse fossil record composed primarily of dinosaur track sites (e.g., lockley and others, 1992; lockley and hunt, 1995; lockley, 2011). in 2006, 3 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 chure and engelmann began a systematic inventory of the paleontology and paleoenvironments of the nugget sandstone in dino. this intensive study was designed to provide basic information that could be used to establish baselines for resource protection, management, and research activities in the monument (chure and others, 2014a). this study yielded an unexpectedly rich fossil and paleoenvironmental record, including the discovery of the saints & sinners lagerstatten, providing an unprecedented view into the erg’s biota. study areas there are two major study areas for the chinle and nugget formations reported in the present work (figure 2). the first is in the western end of dino around the nose of the split mountain anticline and adjacent lands managed by the bureau of land management. the second is around steinaker reservoir north of vernal, utah, about 28 km northwest of the quarry visitor center in dino. localities to protect the resources visited in the course of this field trip, we will not provide exact locality data for the sites in this publication, with the exception of field trip stop 1 (the cub creek petroglyph site) which is a designated stop (no. 14) on dino’s “guide to the tilted rocks.” this visitor stop is for viewing fremont culture petroglyphs which feature a large lizard and kokopelli (figure 3a), along with less defined rock art. carmel lo w er ju ra ss ic chinle u pp er t ria ss ic formation ? m . j . < 20 0 m 5 5 m dominant environment n ug ge t s an ds to ne 2 1 3 6 5 m marine eolian �uvial-eolian �uvial in te rd un e interdune �at st ru ct ur el es s fo rm er d un es w ith c ro ss -b ed re lic s dunes 1 m a b 25 m sw of quarry bonebeds la cu st rin e eolian interdune figure 1. nugget sandstone stratigraphy and depositional environments in the vicinity of saints & sinners quarry. (a) section from the upper chinle through the carmel formations showing the stratigraphic position of the interdune complex within the nugget sandstone and depositional environments. (b) strata within the interdunal portion of the nugget sandstone. the lacustrine units, which contain the three bonebed layers of the quarry are located near the bottom of the interdune unit (see figure 18a). 4 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 safety issues the stops on this trip are fairly safe to visit. those acclimated to lower elevations may find hiking difficult and breathing labored due to the relatively high elevation (~1.5 km/5000 ft). temperatures in late october are comfortable, and heat should not be a problem. characteristics of the stops are described briefly below. stop 1. cub creek petroglyphs: elevation gain of ~50 m over 0.2 km (one way) hike, following, from road to exposure, the established trail at stop 14 of the tour of the tilted rocks route in dino. the steepest parts of the trail have rock steps. stop 2. cub creek chirothere site: negligible elevation change. 0.7 km hike (one way) following a drainage floor. stop 3. josie’s cabin: lunch stop. stop 4. big mounds: negligible elevation change. hike approximately 0.7 km one-way across several drainages. some mounds are near the sloping rim of a deep canyon and caution should be exercised. stop 5. saints & sinners quarry: short easy hike with approximately 30 m of elevation loss from parking stop to quarry. the quarry is situated at the edge of a canyon and some drops are quite long. observe caution and do not go to the edge of quarry as the sandstone is often slippery due to loose sand grains and especially lichens that are extremely slick when wet. stop 6. the museum of paleontology at brigham young university (byu), provo, utah. stop 1. cub creek petroglyph site: the chinle formation – nugget sandstone transition stop 1 (figure 3) offers a close look at the base of the nugget sandstone, the contact with the underlying chinle formation, and transitional environments that here form the lower few meters of the nugget. the chinle is characterized by mudstone, siltstone, and sandstone deposited in fluvial-lacustrine environments (e.g., irmis and others, 2015). elsewhere in the western u.s., the chinle is often fossiliferous, but body fossils are rare in northeastern utah and most are fragmentary (irmis and others, 2015). the overlying nugget is dominated by approximately 200 m of eolian sandstone but includes an interval of a few meters of non-eolian sandstone and mudstone, and occasional, small eolian dunes at its base (figure 1). the thickness and lithologic characteristics of this interval vary from one location to another, even within the study area, so no single site can be considered as typical (irmis and others, 2015). at the cub creek petroglyph site these non-eolian beds are visible and easily accessible. the petroglyphs (figure 3a) were pecked into desert varnish on sandstone cliff faces low in the eolian portion of the nugget sandstone. following the trail northward along the base of the cliff leads to the fluvial unit of the basal nugget, which consists of alternating tan sandstone and brown-red mudstone beds (figure 3b and c). the slope at this locality is the purple interval at the top of the chinle formation (figure 3c, bottom right), which here is largely covered by colluvium. the uppermost chinle is marked by an informally named “purple interval” that includes a distinctive, striped sandstone and grayish-red siltstone/mudstone layers that are exutah cou t 5 km vernal jensen dino us 40 gree n r ive r figure 2. nugget sandstone exposures in the vicinity of dinosaur national monument. mapped area indicated by the shaded area in the inset map of the state of utah. orange = nugget sandstone exposures. green = utah portion of dinosaur national monument. modified from irmis and others (2015). 5 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 posed at its top at stop 1; irmis and others (2015) place the boundary between the chinle and nugget at the top of these beds (figure 3b and c), just above the colluvium. the formation boundary is at the base of a channel sandstone that overlies the grayish-red mudstone, just above irmis and others’ (2015) “red stripe sandstone” (figures 3c and 4). branching, horizontally oriented, hemicylindrical features (downward-protruding ridges approximately 10 cm wide) stand out on the sole of the sandstone. these may be burrows or large, rounded, desiccation cracks. close inspection of the sole of the sandstone, especially of the branching features, reveals many cylindrical burrows 5 to 8 mm in diameter that groove, or penetrate the surface (figure 5). these small traces can also be seen penetrating the sandstone in cross section. this lowest sandstone in the nugget sandstone varies in thickness over the extent of its outcrop at stop 1, from as much as 0.5 m to as little as 10 cm. a thin to almost absent mudstone separates the basal sandstone from a thicker sandstone above. the mudstone has well-developed mudcracks, and the overlying sandstone contains rip-up clasts of this mudstone. above the mudstone in the nugget is an interval of fluvial sandstones and red mudstones/siltstones approximately 2 m thick. at the southern end of the outcrop, this interval consists of massive to cross-bedded sandstone beds 0.5 m or less in thickness, alternating with red, laminated mudstones and siltstones. tracing figure 3. nugget sandstone exposures at stop 1, cub creek petroglyph site. (a) petroglyphs chipped into desert varnish on the nugget sandstone cliff face. (b) exposures as seen from the road at the petroglyph site. the lower slope is the upper chinle formation. the cliff is the lower part of the nugget sandstone. (c) cliff base. this is the location of a measured section described in detail in irmis and others (2015). the white dashed line marks the boundary between the chinle and nugget formations as interpreted by irmis and others (2015). 6 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 this interval along the outcrop to the north, the sandstones and mudstones of the upper part thin and pinch out, whereas the basal sandstone of the interval thickens. at the northernmost end of the outcrop, this interval consists almost entirely of sandstone with only thin partings of mudstone. above the fluvial interval just described, the cliff continues upward as uninterrupted sandstone. the lower 1 to 2 m thick interval of the sandstone is fluvial, as indicated by small, low-angle cross-beds. this interval is overlain by the large-scale, high angle cross-beds of eolian sandstone that are typical of most of the overlying portions of the nugget sandstone. the contact between these two facies is not pronounced, although the lowest 1 to 2 m of the eolian sandstone is marked by soft-sediment-deformation features. based on sorting and grain size, it is likely that the fluvial sandstone beds were reworked from eolian dunes. figure 4. full section at stop 1, cub creek petroglyph site. (a) measured section including the top of the chinle formation and the base of the nugget sandstone (modified from irmis and others, 2015). (b) exposure where the section in (a) was measured. the white dashed line marks the formation boundary. the scale is 18 cm long. 7 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 nowhere in the chinle-nugget section exposed at stop 1, or elsewhere in the study area, is there evidence for an unconformity (irmis and others, 2015). the transition from the fluvial-lacustrine environments of the chinle to the dominantly eolian environments of the nugget is gradual. in accord with walther’s law, stacked, conformable facies were also coeval within the depositional basin. thus, the purple interval of the top of the chinle formation, the interbedded sandstones and mudstones of the basal nugget sandstone, and the eolianites of the balance of the formation represent different depositional facies that were laterally adjacent and graded into one another on a regional scale. the relatively wetter fluvial-lacustrine facies of the chinle formation graded laterally into the semi-arid fluvial system with intermittent, small dunes (not preserved at this stop) of the basal nugget sandstone which in turn graded downslope into the dune fields of the nugget (may, 2014). stop 2. cub creek chirothere site: non-eolian environments in the basal nugget sandstone although generally thought of as an eolian unit, the basal part of the nugget sandstone was deposited primarily in fluvial environments (sprinkel and others, 2011; may, 2014; irmis and others, 2015). we have not measured a section at stop 2, but here the fluvial base of the nugget is approximately 10 m thick (figure 6), consisting of fineto medium-grained, moderately well-sorted sandstone with small-scale cross-beds (figure 7). elsewhere, this same interval includes small eofigure 5. partially bioturbated, large-scale desiccation crack, or possible burrow, at the base of the nugget sandstone, extending into the underlying mudstone. the feature contains numerous small burrow traces in various orientations. small divisions on left side of the scale equal 1 cm. 8 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 lian dunes (may, 2014). at cub creek, vertebrate tracks occur on two bedding planes separated vertically by about 10 cm (anderson and others, 2011; anderson, 2013). the tracks occur over a total of 123 m2 of exposed bedding surface, with track density as high as 4.4 tracks/m2. tracks occur as manus-pes pairs (hand-foot), but because of the density of the tracks and their poor preservation, few trackways can be identified. most or all tracks are undertracks, often poorly preserved with little morphological detail. pes impressions are longer (as much as 30 cm) than wide and manus impressions wider than long (figure 8). asymmetrical push-up rims are rare. only one type of track is present at stop 2, and poor preservation of the tracks makes assignment to an ichnotaxon problematic. the fact that all tracks are manus-pes pairs indicates that the track-maker was a likely obligate quadruped. lockley and hunt (1995) identified well-preserved brachychirotherium isp. from the base of the nugget at the nearby bourdette draw tracksite (figure 9). this occurrence is significant because brachychirotherium is regarded as diagnostic of triassic age (lucas and others, 2006). the pedal claw impressions in the tracks at stop 2 show five digits of unequal length (figure 10). this is unlike the tridactyl pedal impressions of ornithopods and theropods. these cannot be prosauropod pedal impressions, which consist of four, elongate digits as opposed to five (lockley and other, 1992). we feel confident that the stop 2 tracks are chirothere tracks, but a more specific ichnotaxon assignment is not warranted. in addition to stop 2, there are two other chirothere sites within the monument with similarly figure 6. horizontally bedded, non-eolian basal beds of the nugget sandstone at stop 2. the overlying cliff faces are composed of thick, large-scale cross-bedded eolianites. 9 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 preserved tracks. both sites are within the fluvial beds in the lower, non-eolian portions of the nugget sandstone. stop 3: lunch at historic josie morris settler cabin, dinosaur national monument josie morris was born in the latter part of the 19th century and raised in remote browns park, utah, north of present-day dino. this rugged upbringing gave her a strong sense of independence and resourcefulness. in 1913, josie decided to homestead in the cub creek area where she built her own cabin and lived until she died of complications from a broken hip in 1963. she married five husbands and divorced four. she was a colorful character, a friend of outlaws such as butch cassidy, and was tried and acquitted for cattle rustling when she was in her 60s (mcclure, 1985). we will lunch at josie’s homestead, which includes her cabin, chicken coop, cattle pond, fences, orchards, and shade trees. her cabin is open to the public, so wander in and step back for a few moments into the life of a pioneer and colorful character. stop 4. large carbonate mounds: interdunal lakes of the erg system stop 4 shows some of the features of the interdunal carbonates that occur within the nugget sandstone in the study area. nugget carbonate beds carbonate beds make up part of interdunal facies at figure 7. small-scale cross-beds in the basal non-eolian section of the nugget sandstone. scale bar in cm. 10 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 three different areas (figure 11) in the overall study area. these carbonate localities include exposures at stop 4, as well as other nearby outcrops (figure 11, area 1), a larger occurrence consisting of a layer along the rim of a mesa west of steinaker reservoir north of vernal (figure 11, area 2), and exposures in a nugget sandstone hogback on the south flank of the blue mountain anticline cut by cocklebur draw (figure 11, area 3). all the carbonate beds in the study area are of limited lateral extent (<0.5 km along strike). some of the beds include mound structures. all are dolomitic and incorporate sand-sized quartz grains. there are calcite infills within post-lithification fractures and cavities. carbonate layers are exposed south of cub creek (figure 11, area 1), along the rims and walls of canyons cut by a small drainage that flows into the green river near where the cub creek road (state route 149) crosses the drainage. the carbonate layers are exposed along the rim on the north and south sides of the main, west-draining canyon, in the east and west walls of the westernmost tributary canyon that drains northward into the main canyon, and high on the divide between the tributary canyon just mentioned and the next canyon to the east. the carbonate beds are not vertically stacked, that is, we have not observed carbonates repeated through a significant vertical thickness of section. figure 8. (a) overview of chirothere trackway site at stop 2. (b) chirothere manus-pes pair showing proportions of impressions. scale bar in cm. 11 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 the single exception consists of two carbonate horizons separated by < 2 m of sandstone. in the absence of horizontal marker beds and the laterally discontinuous nature of interdune horizons in the nugget sandstone, we cannot tell whether carbonates occur within a preferential horizon within the nugget or are distributed through a greater portion of the section. this is true between and even within the carbonate exposure areas noted above. carbonate beds exposed in the canyons south of cub creek occur as horizontal layers and as several mound structures. the carbonate layers vary in thickness from 10 to almost 100 cm. beds within the carbonate horizons range in thickness from 1 to 10 cm and are usually massive, but some contain fine, wavy laminae. at stop 4, the carbonate mounds occur on both the north and south rims of the main canyon directly opposite each other. large mounds carbonate beds are exposed along the north rim of the main canyon. the most prominent features of these carbonate units are mound structures, which are preserved and dissected to varying degrees (figure 12). there are at least five mounds. these mounds are relatively large, the largest being at least 10 m across figure 9. brachychirotherium pes print from basal beds of nugget sandstone in bourdette draw. scale bar in cm. figure 10. deep chirothere pes impression at stop 2 showing differing lengths of toes. scale bar in cm. 12 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 at its greatest preserved extent. they are approximately aligned, with a nearly west-northwest trend. these mounds and intervening horizontal layers extend more than 110 m along the canyon rim. the mounds are hemispherical in shape, and their peripheries merge contiguously with a horizontal carbonate layer that continues to the next mound (figure 13). where erosion has exposed the core of a mound, laminae are inclined away from the center. the core can also be seen as an area where the carbonate laminae are brecciated and separated by intruded sand and the underlying sand units rise up in the center of the mound (figure13b and c). also visible in the area of the large mounds is the sandstone underlying the mound structures. the easternmost and largest of the mounds is perched on the canyon rim in such a way that it and the underlying sandstone are exposed in cross section through the mound core (figure 13b). this reveals soft-sediment deformation in the sandstone below the mound, in which reddish sandstone has intruded upward through light-colored, partly-consolidated sandstone into the base of the mound core. soft-sediment deformation in the sandstone beneath the carbonate layer is also visible to a depth of 10 m or more in the wall of a small, south-draining canyon that cuts across the trend of the mounds. the deformation consists of contorted beds and fractured and offset, partly consolidated sandstone layers. parrish and falcon-lang (2007), parrish and dorney (2009), parrish and others (2016) have described similar mound structures in the navajo sandstone near moab, utah. they interpret them as the result of upwelling of groundwater beneath the mounds, and this hypothesis fits the characteristics of mounds in cub creek canyon equally well. associated with the large mounds at cub creek are abundant taenidium isp. invertebrate traces in the sandstone immediately beneath the carbonate layer (good, 2013, 2014). they are particularly well represented in exposures on the eastern periphery of the largest mound (figure 14). here they consist of numerous, randomly area 3 area 1 area 2 vernal cub creek rd us 40 steinaker reservoir u s 19 1 g re en r iv er 10 km northu t a h figure 11. interdune carbonate occurrences in the study area. the small polygons labeled areas 1, 2, and 3 indicate where carbonates are exposed. area 1 includes stop 4 on this field trip. 13 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 oriented, tubular traces typically 1 to 2 mm in diameter. there are several larger meandering burrows, 10 to 12 mm in diameter, with meniscoid backfills. carbonate beds extend 200 m eastward along the north rim. at the level of the mound structures, erosion has stripped away any in situ carbonate, but there are some large (~0.5 m), loose carbonate blocks and several smaller pieces that indicate it was present; at least as a layer and possibly including additional mound structures. over part of this same interval, a thin (10 to 20 cm) layer of horizontally bedded carbonate is present perhaps 2 to 3 m stratigraphically lower than the level of the mounds. these horizontal beds often exhibit fine, wavy laminae and there is a single, small mound structure about 30 cm across and about 20 cm thick. crinkled laminae in this small mound suggest that it is stromatolitic in origin. small mounds south and west across the main canyon from the large mounds there are carbonate beds at what is probably the same stratigraphic level, including four mound structures (figure 15). these mounds are similar in morphology to those to the north, but are significantly smaller, the largest being about 2 m across. as with the mounds across the canyon to the north, these mounds are in line, oriented northwest-southeast, and about equally spaced, spanning a distance of about 8 m. the carbonate mounds pinch out or are lost to erosion to the east, but a horizontally bedded carbonate layer connects figure 12. carbonate exposures at stop 4. (a) view is to the south of carbonate mounds exposed along the north rim of a canyon beyond (not visible). arrows indicate carbonate mounds. (b) view to the east of the same area showing the same mounds. 14 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 to the mound structures along a persistent outcrop to the north and west where it is usually 10 to 25 cm thick. gastropods occur as external molds within the horizontally bedded carbonate layer, along exposures 20 to 40 m north and west of the mound structures (figure 16). these fossils occur at a wide range of angles to bedding. patchy exposures and float show that the carbonate layer extended farther north and west to, and a short distance along, the south rim of the main canyon (figure 17). these last exposures along the rim are nearly 1 m thick in places, and show evidence of disturbance and brecciation. carbonates are also exposed in the walls of the westernmost canyon that empties northward into the main canyon of this small drainage system. they occur as horizontal layers 10 to 20 cm thick within associated interdunal facies that are as much as 2 m thick. stop 5. the saints & sinners quarry—a lagerstatten in the erg the saints & sinners locality (figures 1 and 18) preserves a wealth of bones, tridactyl theropod tracks, and an isolated vertebrate burrow, all about 55 m above the base of the eolian portion of the nugget sandstone. this site is byu locality 1442, and coordinates are in the files of the byu museum of paleontology. this is the most figure 13. large carbonate mound structures at stop 4. (a) gray-weathering carbonates of mound draped over white and red sandstone that is higher at the center of the mound. the inclination and thinning of the carbonates away from the center is also apparent. (b) mound dissected by erosion, viewed from below. the cross section exposes apparent soft-sediment deformation in the underlying red and white sandstones. (c) carbonate in the core of a dissected mound structure separated and surrounded by sandstone. divisions on left of scale equal 1 cm. 15 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 figure 14. trace fossils in sandstone immediately beneath a carbonate layer peripheral to one of the large mound structures at stop 4. traces of varying size and orientation include burrows that exhibit meniscoid backfill structure and other possible burrows or root traces. divisions on the scale equal 1 cm. figure 15. small mounds (arrows) in carbonate bed exposed along the rim on the south side of a canyon at stop 4. although smaller in scale, these features are similar in all respects to the large mounds on the north side of the canyon. 16 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 prolific body-fossil-producing site of any of the late triassic to early jurassic sand ergs in terms of number of bones, number of individuals, and taxonomic diversity. the site was first excavated in 2009 and continues to be actively worked. to date, over 11,500 specimens (articulated skeletons, bones, and partial bones) have figure 16. gastropods preserved as external molds in carbonates on the south rim of the canyon a short distance from the small carbonate mounds at stop 4. (a) carbonate slab with numerous gastropod molds of varied size and orientation. (b) silicone rubber cast of a gastropod (mold of a natural external mold) from carbonates along the south rim of the canyon. most of the gastropods have this high-spired morphology. figure 17. carbonate exposures along the south rim of the canyon as seen from stop 4. the small carbonate mounds and the location of gastropod fossils are indicated by arrows. 17 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 been prepared with thousands more awaiting preparation. all preparation is done by byu students at the university’s museum of paleontology, which will be the last stop of our trip.  the vertebrate fauna (table 1) consists of two sphenosuchian genera, a drepanosaur, two theropod genera (a coelophysoid and a medium-sized taxon of unknown affinity), and a dimorphodontid pterosaur. an informal tally (many specimens are not yet in the database) indicates there are at least 76 individuals, 41 of the smaller sphenosuchian and 20 of the coelophysoid. the saints & sinners quarry, byu locality 1442 (figures 1 and 18a), is located along a flank of the section ridge anticline, a laramide structure that strikes southwest to northeast in northeastern utah, along the south flank of the uinta mountains uplift. the anticline deforms and exposes paleozoic to cretaceous strata. the resistant nugget sandstone forms a marked cuesta above the strike valley of the chinle and moenkopi formations. a series of small canyons, developed in fault zones, breach the cliff-forming nugget cuesta, which locally dips about 20° to the southwest. the saints & sinners quarry is on about a 4 by 10 m shelf at the top of the cliff wall of one of these canyons (figure 18a). all of the shelf is bone bearing, but only 19 m2 have been excavated (figure 19a). this stratigraphic interval is traceable to the southwest of the quarry into a small alcove bounded by small cliffs (figure 18a). although no bones are present in those cliffs, they provide exposures crucial to understanding the depositional environment of the quarry and our detailed stratigraphic section (figure 1) was measured in the alcove (figure 18a). from our vehicles we will walk to the rim of the cuesta to look down at the chinle formation and the lower nugget sandstone at the base of the cliff that conformably overlies the chinle formation. from the overlook we will walk into the quarry to observe its various units, then down into the alcove to put the bone-bearing unit into context with underand overlying strata. the quarry discovery the site of what is now known as the saints & sinners quarry was first seen by two of us (dan and george) on july 8, 2007. we were wrapping up a long, hot day of prospecting for fossils and interdunal deposits in the nugget sandstone. looking north across a canyon, we spied a vertical outcrop on the opposing canyon wall containing well-defined interdunal deposits (figure 18a, alcove). as it was the last day of the field season, we decided to visit the outcrop the following year. in taxon, high taxon, mid taxon, low size, approx. common name notes # in di vi du al s body fossils plantae gymnospermophyta cycadeoidophyta cycadeoid bennettitalian "cycad" isolated frond, rhachi, petioles animalia sauroposida "reptilia" incerta sedis drepanosaurid 40-cm-long bird-like head, digging arms articulated/associated/disarticulated >5 lepidosauromorpha sphenodontian a, normal-jawed 30-cm-long tuatara-like "lizard" isolated jaw elements 7 lepidosauromorpha sphenodontian b, slender-jawed 30-cm-long tuatara-like "lizard" isolated jaw elements crocodylomorpha sphenosuchian a, primitive 20 to 50-cm-long crocodylomorph, terrestrial articulated/associated/disarticulated >41 crocodylomorpha sphenosuchian b, large 1.5-m-long crocodylomorph, terrestrial braincase, dermal ossicles 1 pterosauria dimorphodontid 1.5-m-wingspan pterosaur single individual, partial skull + phalanx 1 dinosauria, theropoda, coelophysoid 1.5 to 3-m-long predatory dinosaur disarticulated 20 dinosauria, theropoda, medium-sized 7-m-long predatory dinosaur teeth, partial vertebrae 1 trace fossils invertebrata skolithos < 8 mm diameter invertebrate burrows in dune facies planolites < 8 mm diameter invertebrate burrows in dune facies vertebrata grallator ~15-cm-long small tridactyle tracks only in/on crinkly beds? burrow at toe of dune to beach 15 cm diameter x 1.5 m vertebrate burrow single occurrence table 1. faunal and floral list from the saints & sinners quarry (mm = millimeters, cm = centimeters, and m = meters). 18 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 june 2008, we, along with intern, josh finkelstein, hiked back to the location and worked our way around the upper canyon to get to the interdunal facies in the vertical wall of the alcove. as we crossed what is now the western part of the saints & sinners quarry, george spied grooves in the sandstone and called out to dan, who was farther ahead, that it looked like there were tool marks similar to those we had seen at the cub creek petroglyph site. at cub creek, grooves in the sandstone at the base of the cliff had been made by native amerfigure 18 caption on following page. 19 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 icans sharpening tools on the sandstone. in the alcove we examined the interdunal layers, and dan found a tridactyl track. on our way out of the alcove, we checked out the groove and noticed it didn’t look right. dan recognized it as the external mold of a small tibia. looking around, we found more external molds of bones, some with traces of bone still in them, and saw short strings of small vertebrae nearby. we followed that surface to the east, continuing to see scattered bone. when we got to the main surface where the quarry is, there was abundant and identifiable bone everywhere (figure 19b). we were elated with the discovery, and our excitement was obvious as we tried to assess what we had found. josh, not being familiar with paleontologists, thought we were putting him on, on his first day in the field. in fact, it turned out to be the find of our (djc and gfe) lives.   collecting following the discovery of bones in 2008, chure and engelmann contacted the byu museum of paleontology to see if it was interested in collaborating with collecting and researching the site. after a visit to the site by rodney scheetz, byu agreed. a permit was applied for and obtained for the 2009 season. the site is unusual compared to other areas we have worked, with numerous, small, fragile bones on the surface embedded in structureless sandstone, largely lacking fractures. the bones are three-dimensional, with no crushing, which we attribute to burial in clean sands (now sandstone) that does not compress because of grain-to-grain contact. the sandstone matrix is generally poorly cemented. the bones are not permineralized, and many can be scratched or pulverized with a fingernail. the softness of the bones is evident from the many external molds on the tops of the bonebed; the bone is usually more easily eroded than the sandstone. fragile bones were stabilized with vinac b-17 (polyvinyl acetate) in a low-viscosity acetone solution. because the bone-bearing layers are low in relief, we created a grid of 1-m squares with spray paint (figure 19a). painted lines are short-lived, however, so the intersections of the easting and northing lines were marked with large washers engraved with grid coordinates and affixed with concrete nails (figure 19b to f).  initially, not knowing how abundant the bones were, we made silicone rubber casts in the external molds. our first season of collecting involved recovery of cobble-to-small-boulder-sized fragments of the bone-bearing units that had fallen downslope, and loose blocks of in situ sandstone. we also used air scribes to remove individual bones (figure 20a). working in the field with air scribes is painfully slow, expensive to employ, and figure 18 (on previous page). saints & sinners area overview, depositional environments, and facies. (a) overview of quarry area with interdune strata bounded by solid arrowheads, sandwiched between prominently cross-bedded sandstones representing dunes. bars with “l” = lacustrine bed, which pinch out to the right (east) at the shoreline arrow and to the north, but the latter terminus is covered. the lacustrine beds are underlain by interdune flat deposits, indicated with a ball and bar, consisting primarily of cm-scale dune and ripple sandstone (b, e). the position of the measured section (figure 1) is indicated by elongate rectangle in the upper left. (b) site-typical interdunal flat, lacustrine, and bioturbated dune facies sequence. the lacustrine facies consists of stacks of couplets of structureless sandstones overlain by green silty clays. tracks are common on the top of the lacustrine facies. individual digits (toe infillings) are sometimes visible when the undersurface of the tracks are exposed, confirming these are tracks. (c) oblique view of grallator isp. tracks on the upper surface of a lacustrine couplet. the mm-thick clay at the top of the couplet has been eroded, but the clay provided the parting plane between the two bounding sandy beds. the 3-cm-thick bed overlying the tracks is a typical wrinkly facies bed, interpreted as a silty sand interdune flat layer that was once covered by a biofilm. (d) several interdune flat wrinkly units exposed in plan view showing a grallator track in the upper left and ridges in bottom right. the ridges are interpreted as pressure ridges developed as evaporites accumulated just below the surface in the triassic interdune. (e) detail of microdune playa flat deposit in cross section. the thin trough cross-bed sets are interpreted as microdunes (large sand ripples) migrating across the interdune. the teepee structure (upper right) may be related to curled biofilm edges and/or evaporite-related pressure ridges (pakzad and kulke, 2007). (f) possible vertebrate burrow, 15 cm in diameter in the toe of a dune along the shoreline of the lake. moderate bioturbation has destroyed all trough cross-bedding in the dune except the larger, cm-scale trough cross-bed sets. 20 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 figure 19 caption on following page. 21 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 too dependent on weather. this quickly necessitated a shift to creating moderate-sized blocks that could be prepared in the lab.  the bones occur in three massive sandstone beds separated from each other by parting planes developed along mm-thick silty clay layers (figure 20e). at first we and the crew leader, jeff higgerson, worked slowly to enhance the few natural cracks to break out individual blocks from each bonebed stratum. however, cracks were few and some blocks defined by natural cracks were very large. later, a demolition saw (figure 20c) was employed to cut out blocks, but the bonebeds are 25 cm thick, which was too thick to cut through with the diamond blade. we experimented with a standard pressure washer (figure 20b) and succeeded in cutting through 30 cm of sandstone, but the process was messy and the cut relatively thick and uneven. the most effective cutting tool has proven to be a concrete-cutting chain saw, which can penetrate up to 60 cm in a single cut (figure 20d). the extraction system we have settled on is as follows. a block is outlined with a timber crayon, the initial guide cut made with a demolition saw (figure 20c), and the ultimate cut made with a concrete-cutting chainsaw (figure 20d). we have honed this method to the degree that several workers can cut, extract, and load 544 kg of sandstone blocks in a few hours by either winching the blocks upslope to a lift-gate truck (figure 20g) or driving a truck with a bed-mounted crane into the quarry. quarry geology stratigraphy in the vicinity of the quarry, the true thickness of the nugget sandstone is difficult to measure because of the dip of the beds and the fact that it is an incomplete section. we estimate the thickness in the area to be no more, and probably substantially less, than 200 m, with the quarry being about 55 m from the base of the upper, eolian part of the formation (figure 1a). the quarry is positioned near the bottom of a large wedge-shaped unit (figure 18a, with the upper and lower boundaries indicated by solid arrowheads) dominated by structureless sandstone along with a stratum consisting of cm-scale sandstone layers separated by mm-scale mud drapes, all related to the interdunal environment (figure 18b). the maximum area within which the wedge is exposed is 320 m north-to-south and 50 m east-to-west. the wedge becomes untraceable at its north and south ends in canyons developed along faults. to the west it is obscured where it dips into the subsurface and the eastern boundary has been lost to erosion. the maximum thickness of this wedge is 10 m at its south end and it gradually thins to less than 1 m figure 19 (on previous page). saints & sinners quarry map and fossils. (a) most of the quarry map as of mid-2016 showing the positions of over 11,500 bones. for numerical perspective, the upper right block (b84 outlined by a red rectangle) alone yielded 827 bones from the uppermost horizon, bonebed 3. horizontal bone distribution is non-uniform, as exemplified by b84. blocks with no bone have not been prepared. although there are three superimposed bone layers, each approximately 25 cm thick, at the time this map was made only one layer had been prepared for most areas of the quarry. (b) coelophysoid theropod dorsal vertebra in transverse section exemplifying how bones look as exposed by erosion. (c) coelophysoid left maxilla in medial view after preparation showing the excellent, uncrushed nature of bones from the locality. (d) naturally eroding bones (white) of a small, articulated sphenosuchian near the bottom of bonebed 2 horizon. weathering reveals submm-thick, irregular laminae not apparent in fresh exposures. (e) associated and somewhat broken pelvis and hind limbs of one of the smaller coelophysoids from the top of bonebed 2. these were the only bones preserved in this area of the quarry, making it clear that they pertain to a single individual. in other areas bones of multiple individuals are mixed together, making it difficult to discern individuals. (f) three articulated sphenosuchians from middle to top of bonebed 2. this cluster suggests they died in a burrow during estivation but at least five other specimens of the same size were found in the same area in different orientations and there was no evidence of a burrow. the voids of various colors are weathered concretion sites. (g) plant debris covered with efflorescent, puffy evaporites on modern playa flat bordered by, and overlain by dunes in utah’s west desert. (h) top of bonebed 2 with what appear to be sandstone casts of plant debris based on their straightness and bundled morphology. compare with g, to the left. 22 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 thick over some 200 m to the north. the wedge continues another 120 m in that direction before being terminated by a fault. the wedge also thins eastward. above and below this wedge-shaped stratum is sandstone with figure 20. collecting methods. (a) air scribes were used for the first season before we realized the bones were abundant and often closely spaced. (b) a high pressure washer with a stream nozzle was used successfully to cut to depths of over 30 cm but the cut was wide (15 mm) and rough. (c) a demolition saw is used to make the guide cuts after block locations are demarcated with timber crayons and the block numbers marked on the sandstone. we often followed pre-existing joints for the cuts. (d) a concrete chain saw with a potential cut depth of 60 cm is used to cut through up to two bonebeds simultaneously. water to cool the chain is sourced from standard barrel equipped with a gas-powered pump. (e) cut blocks ready to collect showing the three discreet bonebeds separated by mm-thick silty clay beds. quarry grid lines marked in orange spray paint. (f) grid coordinates are engraved on washers at grid intersections held in place by concrete nails. (g) a truck-mounted crane is used to lift and load larger blocks. 23 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 high-angle cross-beds, a facies that overwhelmingly dominates the nugget sandstone and represents dune fields (figure 18a). interdune strata the three bone-bearing strata (figure 20e) constitute only part of a complex of strata deposited in an interdunal flat that at times included a lake (shumway and britt, 2015, 2016). the base of the interdunal wedge is marked by a planar deflation surface on which there are centimeter-scale, cross-bedded and convolute sandstone beds, whose contacts are accentuated by post-depositional hematite laminae (figure 18e). these sandstones represent alternately dry to damp (kocurek and fielder, 1982) interdunal flats, sometimes with biofilm-covered surfaces (hagadorn and bottjer, 1993; eisenberg, 2003). the small-scale, trough cross-bedding represents small dunes (ahlbrandt and fryberger, 1981). this interdunal flat stratum extends across the entire base of the interdunal wedge, and to the north, it is the only facies of the wedge preserved. largely structureless sandstone beds cm to dm thick and overlain by green, silty mudstones (figure 18b) are indicative of a flooded interdune (ryang and chough, 1997), and were deposited in a small lake. the lacustrine units pinch out only 30 m north of the southern end of the wedge. it is on the northeastern shoreline of this lake that the bones are preserved. at the north end of the lake, cm-scale beds exhibiting wavy textures in cross section, a wrinkly surface, and pressure ridges in plan view (figure 18d) sometimes overlie lacustrine, clay-sand couplets. some of these wrinkly beds preserve grallator tracks. often, these beds exhibit pressure ridges, and alternate with the finer lacustrine beds (figure 18). these beds represent short-lived interdune flats sometimes blanketed with biofilms or biomats that developed as the lake level dropped (hagadorn and bottjer, 1993; eisenberg, 2003). these organic-rich beds are thought to play a role in the preservation of vertebrate tracks (carvalho and others, 2013). the pressure ridges formed as the surface dried and growth of evaporite crystals increased the surface area of the bed surface (pakzad and kulke, 2007). overlying the uppermost lacustrine unit are structureless sandstone beds with some relict cross-bedding and sporadic deflation surfaces (figure 18a, 18b, and 18c) that are now accentuated by post-depositional hematite. this unit is as much as 7 m thick and represents eolian dunes that migrated across the flats, covering the shoreline and what was left of the lake. these dune sands were often wetted by a high water table. the moist sands encouraged vegetation and burrowing invertebrates, ultimately resulting in the structureless texture (thomas, 1984; loope and rowe, 2003). the intense burrowing all but destroyed the trough cross-bedding. on top of these structureless sandstone beds rest thick, high-angle, trough cross-bedded sandstone representing structurally intact (not bioturbated) dunes, marking the end of the local interdunal phase (figure 18a). the interdune story is summed up as follows: (1) deflation and development of an interdunal flat with deflation being controlled by the water table – specifically by the capillary zone above the water table, (2) deposition of ~1 m of sand and silt on the interdunal flat in the form of thin layers of sand via microdunes/sand ripples (some trapped by moist ground) with minor development of biofilms, (3) flooding of the southern part of the interdunal flat, and development of a lake, with fluctuating lake and shoreline levels, (4) development of cm-scale sand/biofilm layers along the lake shoreline resulting in the preservation of theropod tracks, (5) partial drying of the lake and dune migration across the interdunal flat (these dunes are bioturbated by invertebrates during damp phases), and (6) complete burial of the interdunal flat by large dunes. the bonebeds are part of the lacustrine phase and are described and interpreted below. the quarry bonebeds description the quarry is small, with only 19 m2 (figure 19a) excavated to date, and in most areas only one of the three bone-bearing layers has been collected. the quarry is located in the lacustrine facies, along the paleoshoreline, which consists of generally structureless sandstones separated by green silty clays as described above. in the main area of the quarry, there are three superposed bone-bearing strata (figures 1b and 20e). the 24 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 sediments are often mottled, with light, off-white blebs among a more pervasive tan matrix. this mottling may be a function of invertebrate bioturbation. all three layers are sandstone that appear to be essentially devoid of sedimentary structure, except for sub-mm-thick green clay layers. deep weathering, however, reveals thin, irregular sandstone laminae that may represent relict ripple laminae, near the bases of bonebeds 2 and 3 (figure 19d). it is the thicker or closely spaced mud drapes that on weathering separate the three layers and permit their extraction (figure 20e). bones in the quarry are not evenly distributed, neither vertically nor horizontally (figure 19a). vertically, there is a high predictive value from the level of occurrence to both the size of bones and degree of articulation. the articulated small skeletons are found on the very top of bonebed 1 (the lowest bone layer) and the bottom to middle of bonebed 2. bones of larger taxa are common upward from the middle of bonebed 2 and abundant in bonebed 3 (figure 19a). the orientation of bones/skeletons ranges from roughly random, from the bottom of bonebed 1 to bonebed 2 (figure 20e), to substantially oriented in bonebed 3 (britt and others, 2011; chambers and others, 2011). interpretation the three nearly structureless sandstone beds that contain bone are interpreted to represent sand blown into standing water during haboobs or local wind storms. the capping green clay laminae on top of each sandstone bed marks a quiescence that allowed silt and clays to settle. the large number of animals and the taxonomic diversity of the fauna suggest a mass dieoff, likely during drought. the animals may have gathered from across the interdunal flat to the last oasis and died because the waters were not potable, or the oasis completely dried up. in the drought, the carcasses may have dried and littered the landscape. then when the lake level rose, the small carcasses of the drepanosaurs and sphenosuchians were buried by wave action or by sands blown in during a haboob. larger carcasses were not immediately buried, and macerated in the shallows, where wave action reworked them, oriented them, and finally largely buried them. the increased orientation of bones in the uppermost bonebed, which consists of the disarticulated bones of the coelophysoid, suggests substantial reworking but only very minor transport by wave action. the quarry flora and fauna flora the only plant fossils identifiable to a reasonable degree are extremely faint external molds of compressed cycadeoid fronds (william tidwell, byu, personal communication, 2012). usually only the rachis or petiole is found but one specimen preserves pinnae (leaflets) that extend at right angles from the rachis.  we attribute the dearth of plants to postdepositional oxidizing groundwaters and/or alkaline waters. the latter is common in desert environments and can break down plant tissues before or soon after burial (retallack, 2001). despite the rarity of plant fossils, it is likely that the interdune supported a substantial floral mass and that growing conditions were favorable for relatively long periods. the same conditions that destroyed the plants could have destroyed organic components of the bones, resulting in their “bleached” white color. the absence of relic organics explains, in part, the friable condition of the bones.   fauna invertebrate: no invertebrate body fossils have been observed within the quarry nor in the vicinity of the quarry. whereas this could be a preservational bias, the absence of invertebrate trace fossils in the lacustrine deposits suggests that no complex invertebrates of any size resided in sediments at the bottom of the lake. the abundance of small vertebrates that were probably at least partly insectivorous, along with the occurrence of skolithos and planolites traces throughout the dune sands where slipface surfaces are well exposed, indicate that invertebrates were common. the near complete disruption of sedimentary structure by bioturbation of dunes above and lateral to the lake indicates that invertebrates thrived in such environments in the interdune area. the mottled sediments in the bonebeds is best interpreted as evidence of moderate bioturbation by invertebrates. 25 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3  vertebrate: aside from the sheer number of individuals (>76), the most surprising aspect of the site is the faunal diversity. the minimum number of individuals (mni) presented here is a conservative estimate because of a backlog of about 9000 specimens that have yet to be entered into the database. the estimates for mni are most accurate for the larger taxa, the bones of which were the first recovered and entered into the database. we recognize eight vertebrate taxa at saints & sinners, which are enumerated in table 1 and briefly described here. this diversity is far greater than at any other site in the triassic to jurassic ergs of the american southwest. most, if not all, of these taxa are new and most are now in various stages of study, preparatory to their formal descriptions. sphenosuchians – the most common taxon in the quarry is a crocodylomorph, sphenosuchian a. over 41 individuals are present based on articulated and associated skeletons. the taxon is represented by a range of sizes, with skulls ranging from 25 to >50 mm and body lengths to >500 mm. many, if not all, are juveniles. articulated, complete and partial skeletons are apparently randomly distributed between bonebeds 1 and 2, and about halfway up into bonebed 2 (figure 20e). some skeletons occur in discrete clusters, with one cluster consisting of three overlapping skeletons all facing the same direction (figure 19f), suggesting they may have died in an estivation burrow. the armor is simple, limited to the parasagittal region, and dermal plates are unornamented save for a single ridge. the greatly elongated legs (figure 19f), a common feature in sphenosuchians, indicate it was fleet of foot, an advantage in the open spaces of the desert environs.   a second crocodylomorph, sphenosuchian b, is represented solely by a partial braincase and a couple of scutes of a 1.5-m-long individual(s). this may simply be an adult of sphenosuchian a but the morphology of the skull differs more than we expect for a single taxon.   sphenodonts – based solely on mandibular rami, there are two sphenodontian genera, one form with a mandible more typical for the group, and one other with a more gracile mandible, both similar in size. unlike the other small taxa in the fauna, no articulated specimens have been recovered. counting both forms, only six individuals have been recovered.   drepanosaur – numerous individuals are present including at least six articulated individuals of varying degrees of completeness plus numerous other partial skeletons (engelmann and others, 2012, 2013; chure and others, 2013, 2015). all portions of the skeletons save for the last half of the tail are known. the head is bird-like with large orbits and an expanded braincase; the arms and shoulder are adapted to scratch digging with a hypertrophied ungual on digit ii (chure and others, 2015); the chest is barrel-like; and proximal caudal vertebrae have bifid chevrons. there appear to be two morphs, distinguished primarily by differences of the pes, which we attribute to sexual dimorphism. the teeth are rectangular in cross section and high-crowned. the saints & sinners taxon differs from drepanosaurus in a number of characters, including elongate straight unguals on digits iii, iv, v of the manus; slender and thin digit i; an opposable hallux on the male morph; unexpanded distal end of the scapula; and more. theropods – there are two distinct theropods, a coelophysoid and much larger taxon. the larger taxon is represented only by few shed, robust, tooth crowns up to 40 mm long, suggesting a body length of approximately 7 m. the coelophysoid mni is 20, with skulls ranging from 100 to 350 mm long and an estimated maximum body length of 3 m. overall the taxon is similar to coelophysis in build and morphology (britt and others, 2010). a diagnostic difference is seen in that the shaft of metatarsal ii is reduced to a splint, but with a functional distal articulation. no specimen is articulated, aside from short strings of vertebrae and partial limbs, but the skulls are typically closely associated and the skeletons of several individuals can be discerned based on related elements of bone pertaining to exceptionally large or small individuals. the large number of bones of intermediate sizes are not easily differentiated into individuals because the bones are so common and closely spaced.   pterosaur – a dimorphodontid pterosaur is represented by a single individual consisting of a partially articulated and closely associated skull and a single 26 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 postcranial element, the distalmost wing phalanx (britt and other, 2015a, 2015b). most of the skull is known, and it shares a number of diagnostic characters with dimorphodon (e.g., supernumerary small teeth in the mandible along with two rostral fangs, needle-like nasal process in lateral view), but there are substantial differences in the saints & sinners taxon (e.g., large and bladiform maxillary teeth and a small orbit). triassic pterosaurs are extraordinarily rare, with only 27 reported finds worldwide, and the majority of the finds consist of isolated elements, all of which are from marine or lacustrine deposits. the discovery of a desert-dwelling, triassic pterosaur was quite unexpected.   vertebrate trace fossils: the quarry horizon is bordered by a ledge that protrudes from a ledge/cliff along one side and sandstone hills or ledges on the other three sides. on one of these sides, erosion has been sufficient to show the toe of a dune interfingered with the shoreline lacustrine facies of the bonebeds. thus, at least on one side of the lake, dunes migrated into the lake. the toe of this dune preserves several relics of larger slip-face laminae, but is otherwise nearly structureless. a gently curved, cylindrical trace (figure 18f), about 15 cm in diameter and about 1.5 m long, follows the slope of the slipface down toward the lake margin. there are no positively discernable scratch or other marks nor branches on the surface of the trace, and it does not branch. similar burrows in other parts of the erg have been interpreted to have been made by reptiles or synapsids (odier and others, 2004, 2007; hasiotis and others, 2007). such burrows indicate the sand was moist when burrowed (loope, 2006). wilkens (2008), however, argued that the branching traces described by those authors were made by plant roots, not vertebrates. the 15-cm-diameter trace at saints & sinners does not branch, and we attribute it to a relatively small, unknown vertebrate. interpretation of fossils the diversity of fossils at saints & sinners quarry is unexpectedly diverse for a desert-dwelling biota. elsewhere in the nugget sandstone, and at most fossil localities in the balance of the late triassic to early jurassic sand erg, ichnofossils are the only fossils, with body fossils being extraordinarily rare, and those occurring as isolated specimens (engelmann and others, 2016). happily, the saints & sinners, where bones are abundant and well preserved, representing eight taxa, is an exception to this general characterization. little can be said about the flora as it contains only poorly preserved compressions, molds, and casts. however, the presence of a cycadeoid and the sizes of the molds and casts of unknown plant parts indicate the area provided adequate growing conditions for at least years to decades. in addition to vascular plants, the biofilm covering wet to damp interdune surfaces likely consisted of photosynthesizing and non-photosynthesizing microbes, and played a role in vertebrate track preservation. invertebrates are represented only by trace fossils assignable to skolithos and planolites, and these are only discernible immediately below and in the lightly bioturbated dune sands east of the lake, overlying the interdune wedge. intense bioturbation by invertebrates, however, is responsible for the structureless sandstones, indicating favorable conditions for a number of invertebrates. the diversity of the vertebrate fauna indicates habitable conditions (abundant food in the form of arthropods/plants and fresh water) were stable for some time, allowing the area to become populated with a number of taxa, ranging from small, lizard-sized reptiles up to a medium-sized theropod. the presence of vertebrates with low vagility, such as drepanosaurs and sphenodontids, supports the idea of the lake/oasis being a permanent feature of long duration. the taxonomic diversity and large number of individuals seems too large for the size of the preserved portion of the interdune, suggesting either that the interdune area was much more expansive or that animals from other interdunes migrated to this area in response to drought or other conditions. one of the great mysteries of the saints & sinners fauna is that is it composed entirely or almost entirely of carnivorous and insectivorous taxa. were insects the dominant primary consumers? through continuing research, we will be able to paint a better picture of this rare desert biota as we determine the taxonomy/phylogeny and taphonomy of this spectacular site in the near future. 27 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3  summary the saints & sinners quarry, including sphenosuchians, drepanosaurs, theropods, and a pterosaur, represents the most diverse vertebrate assemblage known from the late triassic-early jurassic erg of north america. it provides insights into the diversity and adaptations of vertebrates early in the age of dinosaurs. the bones are uncrushed and reveal previously unknown osteological details of pterosaurs and drepanosaurs that have been obscured by crushing at other triassic localities. the drepanosaur and basal sphenosuchian indicate that much more of the nugget sandstone is triassic than previously suspected.  the bones preserved at the saint & sinners quarry represent part of a biocoenosis inhabiting an interdune flat and perhaps the surrounding dunes during a climatic wet phase, when the interdune hosted a longlived playa lake abutted by sand dunes. there was likely a moderately developed plant community that included cycadeoids. the plants and the diversity of the small vertebrates indicate that, although no body fossils are preserved, invertebrates were common. the diversity of the vertebrate thanatocoenosis suggests that the death assemblage is the result of a single drought, perhaps as the lake dried out and animals gathered at the last standing water. carcasses accumulated in the lowest portion of the interdune. as the lake rose, the smaller carcasses were buried by wind-blown sands settling into the shallow margins of the lake. larger carcasses were later entombed as the waters continued to rise, macerating the carcasses and facilitating disarticulation. the remainder of the bones were buried after slight-to-moderate reworking by wave action along the shoreline combined with silt and sand blown into the waters from nearby dunes. ultimately, the interdune was buried by continued or renewed migration of the dunes.  unlike the other interdune sites visited on this field trip, there are no carbonates at the saints & sinners locality. even though the dominant cement in the sandstones is calcite, cementation is weak. it is clear that the lakes in the carbonate mound area and the lake at saints & sinners differed substantially. this implies a different source of water, or different positions of the interdunes relative to the water source as a result of geographic or temporal variation. stop 6. the museum of paleontology, brigham young university specimens from the saints & sinners quarry are housed at the byu museum of paleontology. byu is a private research university owned and operated by the church of jesus christ of latter-day saints. with about 30,000 students, the campus is located in provo, utah, along the eastern boundary of the basin and range province. it is nestled against the wasatch range, which is part of the cordilleran thrust belt west of the colorado plateau. on the edge of campus, we will visit the byu museum of paleontology. this museum began as a small geology department museum that housed a collection primarily of minerals and invertebrates. it started to thrive in 1960 when james a. jensen was hired as the new curator. prior to coming to byu, jensen worked as one of al romer’s preparators at harvard’s museum of comparative of zoology. jensen’s lack of academic degrees was made up for by his uncanny artistic and tradesman skills. his earlier careers as a card-carrying machinist, welder, and longshoreman came in handy when collecting giant sauropods, where hands-on knowledge was more valuable than academic experience. his ability to gain the trust of rockhounds, however, was his skill that paid the highest dividends. with the added input of rockhounds combing the upper jurassic morrison formation of the intermountain region, many significant finds were discovered that were passed on to jensen. jensen then often used heavy equipment, such as bulldozers, to open large quarries, many of which produced thousands of bones (e.g., dry mesa, dalton wells, cactus park). some of these specimens represented new taxa, ranging from the diminutive, a pterosaur, mesadactylus, or two small ornithopods such as othneliasaurus, to giant sauropods including supersaurus and the massive theropod torvosaurus. in the 1960s and most of the 1970s, there were very few dinosaur workers. but in a little more than a decade after jensen’s arrival at byu, the museum began growing exponentially. in 1972, with his opening (by bulldozer) 28 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 of the dry mesa quarry, byu’s dinosaur program received world-wide coverage in the media and the collections grew rapidly. largely because of the dry mesa collection and its giant sauropods, the university spun the museum off from the geology department and a new museum was built specifically for vertebrate paleontology. the museum was completed in 1976. jensen was awarded an honorary doctorate (perhaps his greatest source of pride), and became known world-wide as “dinosaur jim.” the collections now consist of over 20,000 cataloged specimens, primarily dinosaurs. the collections are housed in three buildings: (1) one for fossil mammals (primarily amassed by wade e. miller (retired byu vertebrate paleontologist) between the 1970s and the end of the millennium), (2) one for unprepared specimens (with pallet racking and a forklift), and (3) the main museum with exhibit halls, an 167-m2 preparation lab with a 5-ton ceiling crane, and two collections areas, one with two forklifts. the crane, forklifts, and 6-m-high pallet racking are crucial in the handling and storage of the many sauropod bones. the field trip will begin with a quick tour of the museum’s main buildings and dinosaur collections. the focus, however, is the saints & sinners quarry collection, which currently consists of over 11,500 mapped specimens. these specimens range from broken bones, to isolated and associated bones, to dozens of articulated skeletons of drepanosaurs and sphenosuchians. we will lay out some of the most spectacular specimens for examination by participants. in the lab, we will watch as students use a combination of several sizes of pneumatic scribes to conduct the gross preparation. moderate-level preparation is done with sharpened carbide rods and the preparation of small bones is conducted with a needle under a microscope. we will demonstrate how specimens are mapped in the lab. this begins with marking blocks with a 10 or 20-cm grid system using permanent markers. then each bone is labeled with the block and field number and photographed. the bones in the photographs are traced using wacom pen-on-screen monitors and digitally mapped using avenza system’s map publisher, a geographic information system (gis) package that runs in adobe illustrator. with so many bones in a single quarry (one sandstone block 0.75 m2 and 25 cm thick yielded 834 bones), a link between field and specimen databases is crucial. using the special database analysis features of gis we have been able to discover an associated skeleton in what appears to the eye to be an incoherent mass of bones. the wide size range of the bones, from a few mm to about 400 mm, requires different storage methods. few bones are fully extracted from the matrix; most are prepared in bas-relief. both are stored in standard specimen drawers. some bones are left in blocks of sandstone to preserved taphonomic and geologic information and are stored on pallets such that the blocks can be reassembled on the floor. the bone is soft, sometimes not much harder than graham crackers, and only rarely can bones be completely extracted from the matrix. important bones prepared only in bas relief have been scanned using a micro ct (micro computed tomography), segmented, and printed on high resolution 3d printers. all the bones of the saints & sinners dimorphodontid pterosaur have been printed. holding the printed bones to the light allows one to peer inside and discern, for example, how the bones of the mandible articulate and how they are pneumatized. this can be done on a computer using 3d images, but it is infinitely more satisfying to hold in your hand printed bones of bizarre late triassic creatures. following the visit to the byu museum of paleontology, we head 45 minutes north to the host hotel where the field trip ends. the dune deposits not unexpectedly, an erg deposit such as the nugget sandstone is dominated by dune sediments. these beds can contain significant fossils, all in the form of trace fossils. although ichnofossils are generally rare, they can be locally abundant. the only vertebrate trace fossils found in the dune deposits themselves are assignable to brasilichnium, which is a track believed to have been made by an advanced non-mammalian synapsid such as a tritylodont (engelmann and chure, in press). engelmann and others (2010) reported a site with approximately 400 brasilichnium footprints on a 10 m2 surface (figure 21). 29 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 figure 21. ichnofossils in the dune deposits of the nugget sandstone in and around dinosaur national monument. (a) dune slip surface with hundreds of brasilichnium isp. tracks traveling upslope. (b) close up of single brasilichnium isp. pes track from (a). (c) paleohelcura isp. trackway. (d) octopodichnus isp. trackway. (e) dune slip surface with abundant planolites beverleyensis. (f) possible small vertebrate burrow. scale bar in cm. 30 rise of the erg—paleontology and paleoenvironments of the triassic–jurassic transition in northeastern utah britt, b.b., chure, d.j., engelmann, g.f., and shumway, j.d. geology of the intermountain west 2016 volume 3 invertebrate traces are more widespread and diverse than vertebrate ichnofossils in the dune sediments. paleohelcura and octopodichnus are trackways made by scorpions and spiders (figure 21c and d). entradichnus, planolites, and taenidium are invertebrate burrows and trails both parallel and perpendicular to the bedding surfaces of the dune slip face (figure 21e). in modern dune environments, such traces are made by larval dipterans and coleopterans. in addition, there are a number of unnamed forms that are of uncertain affinities and/or behavior (good, 2013, 2014). large burrows far out on the toe of the dune face (figure 21f) may have been made by large scorpions or small vertebrates (engelmann and others, 2014). acknowledgments work in the chinle formation by irmis (university of utah) was funded by the national park service (nps) co-operative ecosystem studies unit ta j8r07100009. work in the nugget sandstone by engelmann (university of nebraska at omaha) was funded by the nps co-operative ecosystem studies unit ta j1404094676. dan chure is supported by dino. we thank robin l. hansen (bureau of land management vernal, utah) for supporting our work at the saints & sinners quarry which is operated under permit ut08-025e. we are grateful to reviewers douglas sprinkel (utah geological survey) and judith parrish (university of idaho) whose comments and suggestions improved this paper. we thank melissa morgan for her input and douglas sprinkel for formatting the document. we also thank the geology of the intermountain west editors for their work to help bring this paper to publication. references ahlbrandt, t.s., and fryberger, s.g., 1981, sedimentary features and significance of interdune 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groups, jurassic-triassic of northern arizona and northeast utah: journal of geophysical research b, v. 108, no. b4, 2181, p. 1–23. odier, g., lucas, s. g., mccormick, t., and egan, c., 2004, therapsid burrows in the lower jurassic navajo sandstone, southeastern utah [abs.]: geological society of america abstracts with programs, v. 36, no. 5, p. 67. odier, g., mccormick, t., and egan, c., 2007, preliminary report on new vertebrate burrow localities in the lower jurassic navajo sandstone, moab area, southeastern utah—architectural and surficial burrow morphologies indicative of mammals or therapsids, and social behavior [abs.]: geological society of america abstracts with programs, v. 39, no. 3, p. 74. pakzad, h.r., and kulke, h., 2007, geomorphological features in the gavkhoni playa lake, se esfahan, iran: carbonates and evaporites, v. 22, no. 1, p. 1–15. parrish, j.t., and dorney, l.j., 2009, carbonate spring mounds and interdune lakes in the navajo sandstone (jurassic, western 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paleogeography in the southern part of the western interior basin, in caputo, m.v., peterson, j.a., and franczyk, k.j., editors, mesozoic systems of the rocky mountain region: society for sedimentary geology (sepm), rocky mountain section, p. 233–272. renesto, s., and binelli, g., 2006. vallesaurus cenensis wild, 1991, a drepanosaurid (reptilia, diapsida) from the late triassic of northern italy: revista italian di paleontologiia e stratigraphia, v. 112, no. 1, p. 77–94. renesto, s., spielmann, j.a., lucas, s.g., and spagnoli, g.t., 2010, the taxonomy and paleogiology of the late triassic (carnian– norian—adamanian–apachean) drepanosaurs (diapsida— archosauromorpha—drepanosauromorpha): new mexico museum of natural history and science bulletin 46, p. 1–81. retallack, g.j., 2001, soils of the past—an introduction to paleopedology: oxford, u.k., blackwell science, ltd., 404 p. ryang, r.h., and chough, s.k., 1997, sequential development of alluvial/lacustrine system—southeastern eumsung basin (cretaceous), korea: journal of sedimentary research, v. 67, p. 274–285. shumway, j.d., and britt, b.b., 2015, facies analysis, depositional environments, and micro sequence stratigraphy of saints and sinners dinosaur quarry strata, nugget sandstone, northeastern utah [abs.]: geological society of america abstracts with programs, paper 229-21. shumway, j., britt, b.b., chure, d.j., engelmann, g.f., scheetz, r.d., hood, s., and chambers, m., 2016, facies analysis and depositional environments of the saints & sinners quarry (ssq) in the lower nugget sandstone (late triassic) of northeastern utah show that the diverse vertebrate assemblage was preserved in a lacustrine interdunal environment [abs.]: society of vertebrate paleontology, program with abstracts, p. 224. sprinkel, d.a., kowallis, b.j., and jensen, p.h., 2011, correlation and age of the nugget sandstone and glen canyon group, utah, in sprinkel, d.a., yonkee, w.a., and chidsey, t.c., jr., editors, sevier thrust belt—northern and central utah and adjacent areas: utah geological association publication 40, p. 131–149. thomas, d.s.g., 1984, ancient ergs of the former arid zones of zimbabwe, zambia and angola: institute of british geographers, transactions, new series, 9, p. 75-88. wilkens, n.d., 2008, paleoecology of early jurassic navajo sandstone interdune deposits: phoenix, arizona state university, ph.d. dissertation, 417 p. the major pre-mississippian unconformity in rock canyon, central wasatch range, utah geology of the intermountain west an open-access journal of the utah geological association volume 1 2014 the major pre-mississippian unconformity in rock canyon, central wasatch range, utah david l. clark1,, drew derenthal2, bart j. kowallis2, and scott m. ritter2 1department of geosciences, university of wisconsin, madison, wi; dlclark15@gmail.com 2department of geological sciences, brigham young university, provo, ut © 2014 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org www.utahgeology.org geology of the intermountain west an open-access journal of the utah geological association editors douglas a. sprinkel utah geological survey 801.391.1977 dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net production cover design and desktop publishing douglas a. sprinkel cover photograph cambrian and devonian section and possible location of the pre-mississippian unconformity in rock canyon, utah; figure 2 from article. photograph by bart j. kowallis. i 2014 president grant willis grantwillis@utah.gov 801.537.3355 2014 president-elect april abate aprilabate@utah.gov 801.538.5214 2014 program chair wayne western waynewestern@utah.gov 801.538.5263 2014 treasurer scott clark clark.scotth@gmail.com 2014 secretary mike hylland mikehylland@utah.gov 801.537.3382 2014 past-president craig morgan craigmorgan@utah.gov 801.537.3370 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 sandy eldredge sandyeldredge@utah.gov 801.537.3325 publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2014-2016 term tom morris tom_morris@byu.edu 801.422.3761 state mapping advisory committe uga representative terry massoth twmassoth@hotmail.com 801.422.3761 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists volume 1 2014 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 1 geology of the intermountain west an open-access journal of the utah geological association abstract in central utah, the major pre-mississippian unconformity is fairly well understood at most of the localities where it is recognized. however, the unconformity is more enigmatic in rock canyon of the central wasatch range. at this locality, dolomitization of most pre-mississippian rocks obscures stratigraphic identification of devonian and older units. the absence of any identifiable angular relationship further complicates resolution. because of this, both identification of the stratigraphic level of the unconformity and, consequently, its magnitude remain controversial. large-size dolomite samples taken in rock canyon at closely spaced intervals for the 3.6-m directly below definite upper devonian rocks yield microfossils, including conodonts, in the uppermost 1.6-m of that interval that indicate no unconformity exists between the cambrian maxfield limestone and the upper devonian-lower mississippian fitchville dolomite at the horizon previously identified as unconformable. rather, an unknown thickness of dolomitized upper devonian pinyon peak formation and probable older rock (possibly bluebell dolomite and victoria formation) occurs between the top of definite maxfield and base of the fitchville. the identification of the unconformity horizon remains unknown. our preliminary work outlines a promising procedure for future understanding of the magnitude and stratigraphic level of the unconformity. volume 1 2014 the major pre-mississippian unconformity in rock canyon, central wasatch range, utah david l. clark1, drew derenthal2, bart j. kowallis2, and scott m. ritter2 1department of geosciences, university of wisconsin, madison, wi; dlclark15@gmail.com 2department of geological sciences, brigham young university, provo, ut clark, d.l., derenthal, d., kowallis, b.j. and ritter, s.m., 2014, the major pre-mississippian unconformity in rock canyon, central wasatch range, utah: geology of the intermountain west, v. 1, p. 1-5. © 2014 utah geological association. all rights reserved. for permission to copy and distribute, see the preceeding page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org the problem earliest documentation of the widespread upper devonian unconformity in central and eastern utah included the conclusion that in rock canyon (figure 1), upper middle cambrian dolomite beds are overlain by lower mississippian carbonates (baker, 1947; rigby, 1959). however, additional work on the mississippian section in this part of utah demonstrated that the lower part of the carbonates assigned to the mississippian contained late devonian conodonts (beach, 1961), and the rocks earlier interpreted to be lower mississippian were differentiated into the fitchville formation of late devonian-early mississippian age and the overlying gardison formation of younger mississippian age (morris and lovering, 1961). since this early work, the major pre-mississippian unconformity in rock canyon has been interpreted to occur between the base of the www.utahgeology.org 2 the major pre-mississippian unconformity in rock canyon, central wasatch range, utah clark, d.l., derenthal, d., kowallis, b.j., and ritter, s.m. geology of the intermountain west 2014 volume 1 devonian-mississippian fitchville formation, marked by a sandstone unit, and what was assumed to be the underlying late middle cambrian maxfield limestone (sandberg and gutschick, 1979; derenthal and others, 2008; hintze and kowallis, 2009), an unconformity perhaps representing almost 150 my. a similar unconformable relationship exists at other localities in central and eastern utah, but the fitchville rests on paleozoic strata of different ages in some of these areas (rigby, 1959). in several areas of central utah, the fitchville formation consists of several hundred meters of carbonate with the base of the formation marked by a 30to 50-cm-thick bed of sandstone and sandy dolomite. in the fitchville type area of the east tintic mountains, the basal sandstone is referred to as the “sand grain marker bed” (morris and lovering, 1961, p. 82). a similar stratigraphy is recognized in rock canyon. in rock canyon, all of the dolomites below the sand grain marker bed of the fitchville formation have previously been assigned to the cambrian maxfield limestone. the maxfield is widespread in central utah, but it is not as easily understood in the wasatch range where exact stratigraphic interpretations are difficult because the limestone beds of the maxfield and overlying formations have been dolomitized. in addition, there are few diagnostic fossils in any part of the maxfield, especially in the wasatch range. as a consequence of these observations, we have questioned whether the stratigraphic level of the major pre-mississippian unconformity in rock canyon has been accurately determined. we have considered the possibility that the dolomite beds traditionally assigned to the upper part of the maxfield limestone and below the fitchville might be older devonian, silurian, or even ordovician in age because strata of all of these ages underlie the upper devonian unconformity at different localities elsewhere in central utah (rigby, 1959). this appears reasonable because rocks of these early paleozoic ages are much thicker only a few kilometers west of the wasatch due to a general eastward thinning onto the shelf and because this locality was on the south flank of a west-trending crustal arch that affected paleozoic deposition (morris and lovering, 1961). during the early paleozoic, the area of the present wasatch range was the eastern margin of the same depositional basin. at least some of the dolomite beds assigned to the upper part of the cambrian maxfield limestone in rock canyon could be older devonian and possibly as old as ordovician (figure 2). in order to address this problem, we decided to use the same method that was successfully used in resolving a similar problem involving the cambrian-ordovician unconformity in southern wisconsin. there, the dolomites and dolomitic sandstones of the cambrian-ordovician interval are conformable and contain few megafossils, but large size samples treated with formic acid yielded definitive conodonts and other microfossils that were adequate for a high level of stratigraphic resolution (parsons and clark, 1999). therefore, in order to figure 1. location of section studied in rock canyon, adjacent to provo. figure 2. photograph of rock canyon section showing contact of fitchville and pinyon peak, formerly considered to be the pre-mississippian unconformity. precise age of lower strata unknown. 3 the major pre-mississippian unconformity in rock canyon, central wasatch range, utah clark, d.l., derenthal, d., kowallis, b.j., and ritter, s.m. geology of the intermountain west 2014 volume 1 better understand the nature of the unconformity in rock canyon, we sampled the dolomites immediately below the base of the fitchville clastic unit at 10to 40cm increments over an interval of 3.6 meters. a total of 96, two to four kg samples were processed for conodonts and other phosphatic or siliceous fossils. results of lab work the conodont terminology used here is the same as that documented in the conodont treatise on invertebrate paleontology (clark and others, 1981). for purposes of description, the 3.6-m section has been divided into six units as shown on figure 3. unit 1 – the 30-cm interval of dolomite immediately beneath the upper devonian clastic unit of the fitchville formation yielded 23 conodonts, all fragmentary, in 12 samples, including: polylophodonta ?, polygnathus sp. aff. costatus, polygnathus fragments, various probable conodont fragments including p. semicostatus, icriodus pa, two fragments of basal part of coniform elements of icriodus, one partial and one complete pa element (spathognathodid) of ozarkodina sp., one unidentified ramiform, and unidentified fragments. a single shark dermal denticle and a broken sponge spicule were also recovered. unit 2 – the next lower 75-cm interval (16 samples) yielded fragments of probable ramiform specimens and a fragmentary piece of an icriodus pa element plus a broken sponge spicule. unit 3 – the next 30-cm interval below (14 samples) yielded a single fragment of the pa element of icriodus and several unidentifiable fragments. unit 4 – the next lower 30-cm interval (16 samples) yielded possible conodont fragments plus the partial internal mold of a gastropod. unit 5 – the next lower 60-cm interval (9 samples) yielded no conodonts or fragments, but at the base of the interval several specimens of tasmanites, a phosphatic green algae with an extremely long stratigraphic range in the paleozoic. unit 6 – the lower 135-cm interval of the sampled interval (29 samples) yielded part of an internal mold of a gastropod, plus a single possible fragment of a coniform conodont. interpretations the uppermost 1.3-m of what has been assigned to the cambrian maxfield limestone yielded 25 poorly preserved devonian conodont fragments (cai 5+), a single sponge spicule, and one shark dermal denticle (figure 3). in addition, a number of unidentifiable fragments, possible pieces of conodonts, occur in this upm ax fi el d l im es to n e ?? p in y o n p ea k f o rm at io n f it ch v il le f m . u pp e r d e v o n ia n ?? ? c a m b r ia n ? 6 29 samples 5 9 samples 4 16 samples 3 14 samples 2 16 samples 1 12 samples 0 cm 50 100 150 200 250 300 350 400 cm polylophodonta ? polygnathus sp. a�. costatus polygnathus semicostatus icriodus ozarkodina sp. shark dermal denticle sponge spicule icriodus sponge spicule gastropod conodont fragments icriodus tasmanites bryozoan fragment, possible coniform conodont gastropod figure 3. details of stratigraphic section with fossils and numbered sequences of samples referred to in text. 4 the major pre-mississippian unconformity in rock canyon, central wasatch range, utah clark, d.l., derenthal, d., kowallis, b.j., and ritter, s.m. geology of the intermountain west 2014 volume 1 permost interval as well as in the next 30-cm lower unit (4) in the section that also yielded a single gastropod mold. together, the conodont fragments suggest that at least the uppermost 1.6-m interval of the rocks (units 1 to 4) assigned to the cambrian maxfield limestone in rock canyon are late devonian in age and are more realistically considered to be part of a dolomitized pinyon peak formation. the conodonts of the upper part of the pinyon peak are the same age and are representative of the same fauna as that described from the overlying basal fitchville formation (sandberg and gutschick, 1979), a condition that has been noted in other parts of north-central utah (gosney, 1982). while the conodont faunas are separated by a clastic layer that marks the base of the fitchville formation, both faunas (i.e., that from the upper part of the dolomite beds previously assigned to the cambrian maxfield and that from the dolomites and limestone beds of the overlying fitchville), represent a late devonian (probably expansa) interval, slightly older than the youngest late devonian conodont zone recognized. whether there exist additional beds of the pinyon peak limestone or other rocks younger than the cambrian maxfield (i.e., the bluebell dolomite and victoria formation) below our lowest sampled interval was not determined. however, approximately 60-cm lower, the phosphatic green algae tasmanites occurs along with another partial internal mold of a gastropod. tasmanites has been reported from strata ranging through rocks of the entire phanerozoic era. a possible bryozoan fragment occurs just above the 3-m base of our sampled section. although this tiny fragment is not definitive, most likely it is not cambrian. summary the poorly preserved conodont fauna of the 1.6-m interval underlying the basal fitchville formation clastic unit in rock canyon firmly identifies the interval as late devonian (figure 3). clearly, the clastic unit of the basal fitchville does not mark the unconformity as previously assumed. the devonian dolomite beds of what have previously been assigned to the cambrian maxfield limestone are not distinctive from the beds of definite maxfield found lower in the rock canyon section. thus, position of the major pre-mississippian unconformity is somewhere below the 1.6-m interval of conodont-bearing dolomite beds (below the basal clastic unit of the fitchville). the dolomite lithologies as well as the absence of an angular relationship in the underlying strata are problems that will continue to trouble those attempting to identify the location and age of the unconformity. clearly, the major pre-mississippian unconformity in utah is not well understood. additional field work is needed in rock canyon and elsewhere in central and eastern utah in order to retrieve large size samples taken at closely spaced stratigraphic intervals below the established devonian strata. microfuana from such samples will be the most helpful tool for understanding the location and magnitude of utah’s major pre-mississippian unconformity. acknowledgments charlie sandberg, u.s. geological survey, provided details of his earlier work in rock canyon as well as suggestions that were important for our interpretations. ray ethington, university of missouri, reviewed conodont identifications. funding for the field and lab work was provided from the weeks bequest of the university of wisconsin geoscience department and from the department of geological sciences, brigham young university. 5 the major pre-mississippian unconformity in rock canyon, central wasatch range, utah clark, d.l., derenthal, d., kowallis, b.j., and ritter, s.m. geology of the intermountain west 2014 volume 1 references baker, a.a., 1947, stratigraphy of the wasatch mountains in the vicinity of provo, utah: u.s. geological survey oil and gas investigations preliminary chart 30, 1 plate. beach, g.a., 1961, late devonian and early mississippian biostratigraphy of central utah: brigham young university geology studies, v. 8, pt. 2, p. 37-54. clark, d.l., sweet, w.c., bergström, s.m., klapper, g., austin, r.l., rhodes, f.h.t., müller, k.j., ziegler, w., lindström, m., miller, j.f., and harris, a.g., 1981, miscellanea, supplement 2, conodonta, in robison, r.a., ashlock, v., keim, j., and williams, r.b., editors, treatise on invertebrate paleontology, part w: geological society of america and university of kansas, 202 p. derenthal, d., pahnke, p., and ritter, s.m., 2008, stratigraphy and geochemistry of the cambro-devonian unconformity, rock canyon, utah: power point presentation, department of geological sciences, brigham young university, spring research conference. gosney, t.c., 1982, conodont biostratigraphy of the pinyon peak limestone and the fitchville formation, late devonian-early mississippian, north salt lake city, utah: brigham young university geology studies, v. 29, pt. 2, p. 27-39. hintze, l.f., and kowallis, b.j., 2009, geologic history of utah: brigham young university geology studies special publication 9, 225 p. morris, h.t., and lovering, t.s., 1961, stratigraphy of the east tintic mountains, utah: u.s. geologic survey professional paper 361, 145 p., 5 plates, various scales. parsons, b.p., and clark, d.l., 1999, conodonts and the cambrian-ordovician boundary in wisconsin: geoscience wisconsin, v. 17, p. 1-10. rigby, j.k., 1959, upper devonian unconformity in central utah: geological society of america bulletin, v. 70, p. 207-218. sandberg, c.a., and gutschick, r.c., 1979, guide to conodont biostratigraphy of upper devonian and mississippian rocks along the wasatch front and cordilleran hingeline, utah, in sandberg, c.a., and clark, d.l., editors, conodont biostratigraphy of the great basin and rocky mountains: brigham young university geology studies, v. 26, pt. 3, p. 107-133. new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa valentin zuchuat, arve r.n. sleveland, douglas a. sprinkel, algirdas rimkus, alvar braathen, and ivar midtkandal geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view from the lower south desert overlook, capitol reef national park, displaying the earthy facies of the callovian entrada sandstone (reddish-colored sandstone), overlain by the oxfordian, tidally influenced curtis formation (light-colored sandstone). the two units are separated by the j-3 unconformity, which coincides here with the major transgressive surface (mts) at the base of the informal middle curtis. note the evidences of tidal ravinement at the base of the middle curtis. the middle curtis consists mainly very fine to fine-grained sandstone, and corresponds to a subto intertidal channel-dune-flat complex depositional setting. the middle curtis gradually grades into the thinner-bedded, very fine-grained, subto intertidal heterolithic flat deposits of the upper curtis, which is conformably overlain by the summerville formation. note the geologist in the lower right quadrant of the photograph for scale. i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott emcdermott@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net editors geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 131 abstract based on a methodic sedimentological analysis, the late jurassic (oxfordian) curtis formation unravels the intricate facies variability which occurs in a tide-dominated, fluvially starved, low-gradient, semi-enclosed epicontinental basin. this unit crops out in east-central utah, between the eolian deposits of the underlying middle jurassic (callovian) entrada sandstone, from which it is separated by the j-3 unconformity, and the conformable overlying supratidal summerville formation of oxfordian age. a high-resolution sedimentary analysis of the succession led to the recognition of eight facies associations (fa) with six sub-facies associations. based on the specific three-dimensional arrangement of these eight facies associations, it is proposed to separate the curtis formation into three sub-units: the lower, middle and upper curtis. the j-3 unconformity defines the base of the lower curtis, which consists of upper shoreface to beach deposits (fa 2), mud-dominated (fa 3a) and sand-dominated heterolithic subtidal flat (fa 3b), sand-rich subto supratidal flat (fa 4a) and correlative tidal channel infill (fa 4c). it is capped by the middle curtis, which coincides with the subto intertidal channel-dune-flat complex of fa 5, and its lower boundary corresponds to a transgressive surface of regional extent, identified as the major transgressive surface (mts). this surface suggests a potential correlation between the middle and the upper curtis and the neighboring todilto member of the wanakah formation or todilto formation. the upper curtis consists of the heterolithic upper subto intertidal flat (fa 6) and coastal dry eolian dunes belonging to the moab member of the curtis formation (fa 7), and it conformably overlies the middle curtis. the spatial distribution of these sub-units supports the distinction of three different sectors across the study area: sector 1 in the north, sector 2 in the south-southwest, and sector 3 in the east. in sector 1, the curtis formation is represented by its three sub-units, whereas sector 2 is dominated by the middle and upper curtis, and sector 3 encompasses the extent of the moab member of the curtis formation. this study also highlights the composite nature of the j-3 unconformity, which was impacted by various processes occurring before the curtis formation was deposited, as well as during the development of the lower and middle curtis. local collapse features within the lower and middle curtis are linked to sand fluid overpressure within a remobilized sandy substratum, potentially triggered by seismic activity. furthermore, the occurrence of a sub-regional angular relationship between the middle curtis and substratum implies that the area of study was impacted by a regional deformational event during the late jurassic, before the deposition of the middle curtis. new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa valentin zuchuat1, arve r.n. sleveland1, douglas a. sprinkel2, algirdas rimkus1, alvar braathen1, ivar midtkandal1 1 university of oslo, department of geosciences, sem sælands vei 1, 0371, oslo, norway; valentin.zuchuat@geo.uio.no 2 utah geological survey, po box 146100, salt lake city, utah 84114; douglassprinkel@utah.gov citation for this article. zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i., 2018, new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa: geology of the intermountain west, v. 5, p. 131–165. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 132 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 introduction the complex aspect of tide-dominated environments was reported as early as first century ad, when pliny the elder, in his historia naturalis, wondered whether such areas “invaded twice each day and night by the overflowing waves of the ocean…are to be looked upon as belonging to the land, or whether as forming portion of the sea?” (translation from bostock and riley, 1855). since then, it has been shown that the essence of tidal deposits resides within their typical three-dimensional intricate assemblage of heterolithic facies, which distribution is dictated by a fine equilibrium of sediment input, basinal hydrodynamic forces, as well as avulsing and migrating channels (davis and dalrymple, 2012; references therein). this complexity is further enhanced by temporal and cyclical variations of tidal currents in a basin, which unevenly impact the erosion-transport-deposition mechanisms of the different grain classes within the system (kvale, 2012; wang, 2012; references therein). adding to the intrinsically dynamic system, the effects of fluctuating rates in relative sea-level variation are amplified by a low-gradient shelf through shifting facies belts over great distances (midtkandal and nystuen, 2009). poor time constraints, limited but changing accommodation, and pre-existing basin floor relief further complicate the accurate interpretation and correlation of such deposits. despite highly complex depositional scenarios, these conditions may produce substantial volumes of reservoir-grade sandstone, and represent potentially viable aquifers, co2-injection targets, or petroleum reservoirs (martinius and others, 2005; halland and others, 2014). research focusing on siliciclastic tide-dominated environments recognizes four main categories: (1) the upward fining, transgressive estuarine, (2) the (semi-)protected lagoonal systems, (3) the prograding tide-dominated deltas, as well as (4) the open-coast tidal flats (e.g., boyd and others, 1992; dalrymple and others, 1992; fan, 2012). whereas modern analogs can help scientists identifying such depositional systems in the rock record, tape and others (2003) highlighted the fact that some tidally influenced sedimentary units do not belong to any of the above-mentioned classes and cannot be illustrated by modern equivalent environments either, as they were deposited on broad and shallow epicontinental shelves. the outstanding outcrop quality and the significant internal variability of the middle jurassic entrada sandstone and late jurassic curtis-summerville formations of east-central utah allow a detailed investigation of gradual, subtle, and intricate interactions within such a low-gradient, continental to subtidal epeiric system, characterized by a starvation of major fluvial input (kreisa and moiola, 1986; caputo and pryor, 1991; wilcox and currie, 2008). the main objective of this study is to develop a detailed data-driven classification of heterolithic facies and facies associations present on a tidally influenced siliciclastic-dominated shelf of regional extent, represented by the curtis formation of early oxfordian age (about 161–159 ma) (kreisa and moiola, 1986; caputo and pryor, 1991; wilcox and currie, 2008; ogg and others, 2016). this work establishes the sedimentary basis for deconstructing the growth and infill dynamic of such a tide-dominated basin, which will be analyzed in a separate study. the overarching goal of this venture is to generate a multi-disciplinary predictive protocol to assess the combined seal-reservoir properties of such heterolithic deposits, notably for carbon capture and storage purposes. geological setting basinal setting since the mesozoic, utah’s geological history has been profoundly influenced by several tectonic events, markedly by the development of the north american cordillera and its cascade of orogenies; key orogenies, partly overlapping in time and space (bump and davis, 2003; hintze and kowallis, 2009; thorman, 2011; anderson, 2015; yonkee and weil, 2015; and references therein), are (1) the middle jurassic-early cretaceous nevadan orogeny, whose remains notably consist of small granitic batholiths at today’s utah-nevada border, (2) the middle jurassic elko orogeny, which differs from the other orogenies by alternating extensional and contractional tectonic events, (3) the early cretaceous to paleogene sevier orogeny, with its resultant thinskinned contractional structures associated with a fore133 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 land basin development, and (4) the late cretaceous to paleogene laramide orogeny seen as basement-rooted monoclines, from which the san rafael swell and other large uplifts emerged. additionally, rocks from east-central to southeastern utah were also affected by movements of the paradox basin salt deposits (trudgill, 2011), regional uplifts of the colorado plateau, and related extensional events (levander and others, 2011; murray and others, 2016). there were also intrusive and extrusive magmatic episodes during the middle to late oligocene; the latter are expressed by the henry, la sal, and abajo mountains igneous complexes (sullivan and others, 1991; nelson, 1997). burial history data compiled by nuccio and condon (1996) and petrie and others (2017) suggest that the curtis formation was buried to depths of 2.45 km and 2.86 km near the san rafael swell. stratigraphy the westward-thickening sedimentary succession of the san rafael group was deposited in neighboring areas of the utah-idaho trough, a north-northeast to south-southwest-trending distal retroarc foreland basin parallel to the elko highlands (figure 1) (anderson and lucas, 1994; brenner and peterson, 1994; peterson, 1994; bjerrum and dorsey, 1995; thorman, 2011). this basin recorded multiple transgressive-regressive marine cycles (anderson and lucas, 1994). the marine and intertonguing eolian sediments of the coastal paleo-erg of the middle jurassic (aalenian to bajocian) temple cap formation in southwestern and central utah unconformably overlies the eolian navajo sandstone of early jurassic age on the j-1 unconformity (pipiringos and o’sullivan, 1978; peterson and pipiringos, 1979; sprinkel and others, 2011). paleowind indicators for the navajo sandstone suggest a north-northwest to south-southeast wind direction, whereas paleowind indicators for the temple cap formation suggest a northeast to southwest wind direction (parrish and peterson, 1988; peterson, 1988; hartwick, 2010). to the east in south-central utah, the former basal harris wash member of the page sandstone unconformably overlies the navajo sandstone, above the j-2 unconformity of pipiringos and o’sullivan (1978) and peterson and pipiringos (1979). isotopic ages obtained from ash beds in the harris wash member indicated they were time equivalent to the temple cap formation and hence pre-dated the basal carmel formation (kowallis and others, 2001; dickinson and others, 2010; sprinkel and others, 2011). this stratigraphic relationship brought into question the validity of the j-2 unconformity and led to the recommendation to re-assign the beds representing the harris wash member of the page sandstone to the temple cap formation (sprinkel and others, 2011; doelling and others, 2013). the shallow marine middle jurassic carmel formation (gilluly and reeside, 1928) conformably overlies the temple cap formation, reflecting marine incursions from the northern sundance seaway from bajocian to early callovian time (anderson and lucas, 1994; brenner and peterson, 1994; peterson, 1994; hintze and kowallis, 2009; sprinkel and others, 2011). however, the carmel formation does unconformably overlie the navajo sandstone in places where the temple cap formation is missing because of irregular deposition of the temple cap on a pre-existing paleotopography and its depositional pinch-out in eastern utah (sprinkel and others, 2011; doelling and others, 2013). continental conditions returned with the deposition of the middle jurassic (callovian) entrada sandstone (peterson, 1994: hintze and kowallis, 2009), formally defined by gilluly and reeside (1928). this sedimentary formation is divided into two units: (1) the basal slick rock member, which consists of alternating eolian dune and interdune intervals, and (2) the overlying informal, intermittently vegetated, earthy facies, which was deposited in a marginal marine setting (witkind, 1988; crabaugh and kocurek, 1993; carr-crabaugh and kocurek, 1998; mountney, 2012; doelling and others, 2015). the entrada sandstone and correlative formations (twist gulch and preuss formations) thicken westward towards the utah-idaho trough and northwards towards the sundance seaway (imlay, 1980; kocurek and dott, 1983). dickinson and gehrels (2009, 2010) showed that the siliciclastic grains of the entrada sandstone were mostly recycled from river systems sourced from the appalachian mountains, on the eastern side of the continent. the entrada sandstone recorded four erg con134 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 struction-destruction cycles (sensu mountney, 2006), dictated by regional variations of the paleo-water table, themselves related to relative sea level fluctuations (carr-crabaugh and kocurek, 1998; mountney, 2012). the entire system is truncated along its top by the regional j-3 unconformity (pipiringos and o’sullivan, 1978; hintze and kowallis, 2009), with local relief of up to about 23 m. in areas of south-central utah, the j-3 unconformity truncates subtle, large-amplitude folds developed in the entrada sandstone and underlying formations, exhibiting distinctive angular relationships along the unconformity (see figure 7 of wheatley and price moab hanksville salt lake city uinta mountains utah green river san rafael swell 109°0'0"w111°0'0"w113°0'0"w 38 °0 '0" n 40 °0 '0" n 42 °0 '0" n 100 km b 1000 kma n b 24 191 24 191 95 25km n lacustrine in te rc on ne ct ed se co nd ar y re se rv oi rs re gi on al re se rv oi r re gi on al re se rv oi r se co nd ar y re se rv oi rs lacustrine mixed tidal mixed aeolian marginal marine aeolian fluvial re gi on al ca pr oc k age formation lithology cr et ac eo u s ju ra ss ic m an co s sh al e m o rr is o n summerville curtis mt carmel page sst navajo sandstone blue gate ferron sst tunuk shale dakota shale mbr buckhornce da r m t brushy basin salt wash tidwell central utahc in te rc on ne ct ed entrada slick rock earthy facies 10 11 1 2 3 4 5 6 7 8 9 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 grid eas�ng northing 1 sulphur canyon 27.06.2015 12 s 538598 4354691 2 stove gulch east 23.06.2015 12 s 541150 4354677 3 humbug flats east 30.06.2015 12 s 545496 4349054 4 neversweat wash 01.07.2015 12 s 546582 4345984 5 middle canyon 21.09.2015 12 s 545582 4340631 6 dry mesa 02.07.2015 12 s 546370 4336290 7 cur�s point 03.05.2016 12 s 549241 4328385 8 wet gulch 04.05.2016 12 s 550874 4325353 9 sven's gulch 22.09.2015 12 s 552531 4323706 10 smith's cabin 03.07.2015 12 s 553584 4319583 11 rabbit gulch 19.05.2016 12 s 553369 4314960 12 interstate 70 06.05.2016 12 s 550457 4308362 13 uneva mine canyon 12.05.2016 12 s 547594 4304403 14 crystal geyser 15.09.2015 12 s 575060 4310623 15 lower san rafael rd 20.05.2016 12 s 570049 4295643 16 ruby ranch meandre 04.06.2016 12 s 576420 4298161 17 ruby ranch road 03.06.2016 12 s 583113 4296930 18 duma point 01.06.2016 12 s 588894 4293333 19 horse flies gulch 31.05.2016 12 s 590606 4293184 20 dune mesa 30.05.2016 12 s 590620 4290953 utm coordinates log n° log name date grid eas�ng northing 21 ten mile rd 28.05.2016 12 s 594368 4291828 22 petrified tree gulch 29.05.2016 12 s 596564 4287509 23 dubinky well rd 27.05.2016 12 s 595351 4284912 24 safari road 26.05.2016 12 s 601764 4282137 25 bartle� wash 16.06.2015 12 s 605257 4286436 26 salt valley 21.05.2016 12 s 608768 4302663 27 lost spring canyon 23.05.2016 12 s 624118 4294979 28 dewey bridge 10.05.2016 12 s 647467 4298329 29 big pinto mesa 22.05.2016 12 s 654182 4294917 30 goblin valley 29.04.2017 12 s 522572 4269001 31 li�le flat top 08.05.2016 12 s 544488 4266008 32 hanksville 05.05.2017 12 s 525317 4248736 33 notom ranch 09.05.2017 12 s 492291 4226559 34 cainville airstrip 11.05.2017 12 s 495813 4244029 35 l. south desert ov. 12.05.2017 12 s 481839 4250657 36 lcd the two towers 27.04.2017 12 s 477493 4275207 37 lcd road cut 25.04.2017 12 s 472428 4279105 38 salt wash view area 16.05.2017 12 s 490555 4298727 39 sid and charley 15.05.2017 12 s 500015 4311719 40 lower cedar mt rd 14.05.2017 12 s 518557 4340815 log name date utm coordinates log n° figure 1. (a) maps of the study area. (b) green dots represent visited localities where the curtis formation crops out, whereas red dots (not numbered) illustrate its absence. each dot number on the map refers to a specific locality in the attached table (geological units after hintze, 1980; witkind, 1988; doelling, 2001; and doelling and others, 2015). (c) schematic stratigraphic column of the area (modified from ogata and others, 2014). 135 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 others, 2016). depending on location, this boundary can be characterized as a conformable contact, a paraconformity, a disconformity, or an angular unconformity. it is important to note that the precise time encapsulated in the composite j-3 unconformity remains unknown. since the definition of an unconformity implies a “lacuna of substantial duration” (sensu holbrook and bhattacharya, 2012), the nature of the j-3 unconformity remains a point of discussion. peterson (1994) argued that a regional tectonic uplift in the west played the major role in the development of this unconformity, whereas caputo and pryor (1991) as well as eschner and kocurek (1988), respectively, advocated that (unidentified) marine or tidal currents during the earliest stage of the curtis transgression reworked the substratum. the overlying tidally influenced curtis formation of early oxfordian age (kreisa and moiola, 1986; caputo and pryor, 1991; wilcox and currie, 2008; ogg and others, 2016) was first formally defined by gilluly and reeside (1928), and its type section of curtis point is located about 5.3 km south of dry mesa, along the northeastern margin of the san rafael swell (utm coordinates: 12s 547430/4331169). the formation is characterized by its greenish-whitish color due to the presence of glauconite or chlorite (gilluly and reeside, 1928; caputo and pryor, 1991; peterson, 1994). its striking color contrast to the underlying earthy red entrada sandstone is readily identifiable in outcrops. the typical thickness ranges between 30 and 80 m around the san rafael swell (caputo and pryor, 1991). nevertheless, as it was deposited in the foredeep basin of the elko orogeny (thorman, 2011; anderson, 2015), the formation pinches out southwards towards tergeson flats, about 38 km southwest of hanksville, as well as eastwards in the vicinity of duma point, about 28 km south-southeast of green river (figure 1) (gilluly and reeside, 1928; caputo and pryor, 1991; peterson, 1994). as a note, the coastal paleo-erg of the moab member of the curtis formation is the lateral equivalent to the marine beds of the curtis towards the east of the study area (wright and others, 1962; caputo and pryor, 1991; peterson, 1994; doelling, 2001). the summerville formation conformably overlies the curtis formation in the san rafael swell and henry mountains basin and is characterized by dark-red and chocolate-brown hypersaline sabkha deposits, including evaporative ponds, which resulted in precipitation of gypsum and anhydrite (gilluly and reeside, 1928; caputo and pryor, 1991; peterson, 1994; lucas, 2014). peterson (1994) described the marine curtis formation and the conformably overlying supra-tidal and sabkha deposits of the summerville formation as representing the fifth transgressive-regressive cycle within the jurassic system of the western interior basin. this cycle potentially corresponds to haq and others (1987) lza-2.3 third-order transgressive-regressive interval, after calibrating their curve onto wilcox and currie (2008) age and ogg and others (2016) time scale. the curtis-summerville interval correlates to the redwater shale member of the sundance formation (imlay 1947, 1980) in wyoming, the stump formation around the wyoming-idaho border (mansfield and roundy, 1916; pipiringos and imlay, 1979; imlay, 1980), and the stump formation in the uinta mountains of northeastern utah (pipiringos and imlay, 1979; imlay, 1980; wilcox and currie, 2008), reflecting the same transgressive-regressive period of the sundance sea (pipiringos and o’sullivan, 1978; mcmullen and others, 2014). in the four corners area, the curtis formation has been correlated to the todilto member of the wanakah formation, whereas the summerville formation is replaced by the beclabito member of the wanakah formation (condon and huffman, 1988). note that anderson and lucas (1994) used a different nomenclature for the same interval; they regarded the todilto as a formation rather than a member, whereas the summerville formation extends into the four corners area. the summerville formation is capped by the j-5 unconformity (pipiringos and o’sullivan, 1978), which resulted from the fall of the regional base level (caputo and pryor, 1991; peterson, 1994), generating a relief of at least 20 m, before being overlain by the fluvial sediments of the tidwell member, the lowermost unit of the continental morrison formation south of the uinta mountains (waldschmidt and leroy, 1944; peterson, 1988; turner and peterson, 1999). figure 1c displays a summary stratigraphic column of the study area. 136 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 methods and data in order to understand the genesis of the curtis formation in the study area, fieldwork campaigns were conducted in 2015, 2016, and 2017. the data included in this paper comprise (1) 40 detailed sedimentary logs (figure 1), which locations were chosen based on outcrop exposure quality, accessibility, and regular distance between each measured section; (2) pictures taken at and between log-sites by all members of the research group involved in the project, as well as unmanned aerial vehicles (uavs), aerial photographs, satellite images, and open-source imagery available from google and microsoft bing databases; and (3) recordings of paleocurrent directions and other structural data. three-dimensional (3d) virtual outcrops were generated for selected localities following westoby and others (2012) structure-from-motion photogrammetry principles, in order to assess the architecture of the sedimentary succession. uav data were processed using photoscan pro by agisoft (agisoft llc, st. petersburg, russia), whereas the 3d-generated models were subsequently analyzed and interpreted in lime (developed by the virtual outcrop geology (vog) group from the universities of bergen and aberdeen). traditional sedimentologic methods were applied, such as identification of depositional sub-environments and correlation across short and long distances in order to reconstruct the spatial and temporal distribution of sub-units of the target strata. the resultant assimilation of data allows the construction of an improved depositional model for the curtis formation, and sheds light on how sediments are dispersed across a shallow shelf in general. results twenty-four sedimentary facies were recognized and summarized in table 1. rock fabric, composition, and structure(s) are the key to interpreting the processes and conditions under which these sediments were deposited. as a result, these facies have been organized in eight main facies associations (fa 1 to fa 8) with six sub-facies associations (fa 1a, fa 1b, fa 3a, fa 3b, fa 4a, and fa 4b), which are summarized in table 2 and carefully described below. these facies associations are not homogeneously distributed across the study area (figures 2 and 3). it is important to mention that the datum on which the measured sections are aligned on figure 3 corresponds to the j-3 unconformity. to increase the visibility of the correlation, 19 out of 41 visited localities were selected based on spatial distribution and completeness of the sedimentary succession. pie charts reflect the ratio between the different facies associations present in the curtis formation, whereas the entrada sandstone and the summerville formation are neglected. based on the spatial distribution of these various facies associations, it is possible to divide the study area into sectors 1, 2 and 3 (figure 3), which are discussed further below. fa 1 – coastal wet eolian deposits description this unit corresponds to the cross-stratified eolian dunes and sandy interdunes (facies a in table 1) of the slick rock member (entrada sandstone, fa 1a), which crops out in the eastern and southeastern part of the study area (figure 1). towards the west, fa 1 coincides with the parallel-laminated to mottled deposits (facies b) dominating the earthy facies (fa 1b) of the entrada sandstone, with interfingering trough cross-stratified sandstone (facies c), rippled cross-stratified sandstone (facies u), and isolated coastal eolian dunes (facies a). the hoodoos of goblin valley state park mainly consist of structureless sandstone (facies d). this sedimentary package thickens westward. only at safari road (figure 1), fa 1 is capped by a rusty-red, calcite-cemented, thoroughly bioturbated, fine-grained sandstone (facies e). facies c (trough cross-stratified sandstone) occurs sporadically within fa 1, reaching a maximum thickness of about 1 m and is located 13 m below the base of the curtis formation at the crystal geyser section (figure 1). here, the well-sorted foresets alternate between coarse and fine-grained sand with potential double mud drapes. facies a, facies b, facies c, and facies t are characterized by a sharp contact at their base, which can also be erosive, especially for facies a, c, and t. facies t usually appears both at the base and at the top of eolian dune packages (facies a) but can also crop out 137 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 fa cie s de sc rip tio n st ru ct ur es gr ai n  si ze * in te rp re ta tio n fo rm at io n a cr os s‐s tra tif ie d  sa nd st on e un id ire ct io na l ta ng en tia l cr os s‐b ed de d ve ry fin e to fin e‐ gr ai ne d sa nd st on e, al te rn at in g gr ai n flo w an d gr ai n fa ll de po sit s, sh ar p ba se ,r us ty re d or w hi te ,l oc al ly bl ea ch ed , lo ca l oc cu rre nc e of rh izo lit hs , va ry in g be df or m /b ed fo rm se ts siz e, m ax im um in di vid ua ld un e th ick ne ss 15 m .p ot en tia lo cc ur re nc e of co un te r‐r ip pl es at  th e  to e  of  th e  fo re se ts vf  ‐  f eo lia n  du ne  d ep os its , l oc al ly  in flu en ce d  by  a   dy na m ic  an d  m ig ra tin g  w at er  ta bl e/ sa tu ra te d  le ve l en tra da  ss . m oa b  m br . b pl an e  pa ra lle l‐l am in at ed  to  m ot tle d  m ud st on e  w ith  lo ca liz ed  e va po rit es da rk re d sil ty m ud st on e w ith pa le ye llo w to w hi te ve ry fin e to fin e‐ gr ai ne d sa nd le ns es , pl an e pa ra lle l‐l am in at ed to ‐st ra tif ie d or m ot tle d, po te nt ia l bl ea ch ed pa tc he s ar ou nd rh izo lit hs ,l oc al ize d ev ap or ite ‐ri ch ho riz on s, m ax im um in di vid ua l ho riz on  1  cm si  ‐ c l eo lia n  in te rd un e  de po sit s s ho w in g  oc ca sio na l  flo od in g  w ith  d ev el op m en t o f s ab kh a‐ ty pe  d ep os its   an d/ or   s up er fic ia l v eg et at io n en tra da  ss . su m m er vil le  fm . c tr ou gh  cr os s‐s tra tif ie d  sa nd st on e tr ou gh cr os s‐s tra tif ie d ve ry fin e to m ed iu m ‐g ra in ed sa nd st on e, po te nt ia l m ud dr ap es an d rip ‐u p m ud cla st s, ev en tu al de sic ca tio n cr ac ks an d/ or ev ap or ite ‐ri ch ho riz on s.  th ick ne ss  ra ng in g  be tw ee n  dm ‐ t o  m  va lu es vf  ‐  m ti da lly  in flu en ce d  m ig ra tin g  3d ‐d un es en tra da  fm . cu rti s f m . su m m er vil le  fm . d st ru ct ur el es s f lu id ize d  sa nd st on e de fo rm ed to st ru ct ur el es sf lu id ize d of gr ee n to pi nk sil tt o fin e‐ gr ai ne d sa nd st on e, lo ca lf lu id ‐e sc ap e an d lo ad in g st ru ct ur es st ill vis ib le ,s om et im es vis ua lly ex pr es se d as w el lr ou nd ed sa nd st on e bo ul de rs w ith in je ct ed m ud st on e, m ax im um bo ul de r di am et er  (ø ) 2 5  cm ,   m ax im um  b ed  th ick ne ss  2  m si‐ f de st ru ct io n  of  o rig in al  se di m en ta ry  st ru ct ur es  d ue   to  fl ui ds  fl ow in g  th ro ug h  th e  sa nd st on e  be d  or   th ro ug h  liq ue fa ct io n  of  w at er ‐sa tu ra te d  ho riz on s en tra da  ss . cu rti s f m . e th or ou gh ly  bi ot ur ba te d  co nd en se d  sa nd st on e ru st y‐ re d co nd en se d, ce m en te d, fin e‐ gr ai ne d sa nd st on e, th or ou gh ly bi ot ur ba te d. , m ax im um  th ick ne ss  2 5  cm f se di m en t s ta rv at io n  in  a  se m i‐a rid  co as ta l p la in   se tti ng en tra da  ss . f m at rix ‐su pp or te d  ba sa l c on gl om er at e ro un de d to w el l‐r ou nd ed ,m at rix ‐su pp or te d ba sa lc on gl om er at e, no pr ef er re d cla st or ie nt at io n bu t th ei r lo ng ax is te nd to be pa ra lle lt o th e be dd in g pl an e, m at rix co ns ist s of fin e‐ to m ed iu m ‐g ra in ed sa nd st on e, m ax im um cla st ø 8 cm ,m ax im um be d  th ick ne ss  2 0  cm f‐ pb fla sh  fl oo d  de po sit s cu rti s f m . ? g pl an ar ‐ t o  lo w  a ng le  cr os s‐s tra tif ie d  sa nd st on e pl an e‐ pa ra lle lt o lo w ‐a ng le cr os s‐s tra tif ie d, ve ry fin e to fin e‐ gr ai ne d, gr ay to gr ee n to w hi te sa nd st on e, po te nt ia lh er rin gb on e cr os s‐l am in at io n, cu rre nt an d os cil la tio n rip pl e‐ la m in at io n, as w el l as dm ‐sc al e so ft‐ se di m en t de fo rm at io n, m ax im um in di vid ua l b ed  th ick ne ss  6 0  cm vf  ‐  f up pe r s ho re fa ce  to  b ea ch  d ep os its  w ith  ti da l  in flu en ce cu rti s f m . h ta ng en tia l c ro ss ‐st ra tif ie d  gr av el ly  sa nd st on e m at rix ‐su pp or te d co ng lo m er at ic du ne , hm ‐sc al e la te ra l ex te nt , su b‐ ho riz on ta l er os ive ba se ,r ip ‐u p m ud cla st s, ex tra ‐b as in al su b‐ to ro un de d cla st s, m ax im um cla st ø 2. 5 cm , un id ire ct io na lc ur re nt tro ug h cr os s‐s tra tif ica tio n, m ax im um in di vid ua l du ne  th ick ne ss  2 .5  m m  ‐  gr hi gh  e ne rg y,  a sy m m et ric  ti da l f lo w  p at te rn  w ith in  a   la te ra lly  re st ric te d  em ba ym en t  cu rti s f m . i ti da lly  in flu en ce d  cr os s‐s tra tif ie d  co ng lo m er at ic  sa nd st on e m at rix ‐ to cla st ‐su pp or te d le ns e‐ sh ap ed in tra fo rm at io na l co ng lo m er at e of re st ric te d la te ra le xt en t, lo ca lly de ve lo pe d an d am al ga m at ed in tid al bu nd le s, rip ‐u p m ud cla st s, ex tra ‐b as in al su b‐ to ro un de d cla st s, m ax im um cla st ø 2. 5 cm , bi di re ct io na lc ro ss ‐st ra tif ica tio n w ith su pe rim po se d cu rre nt rip pl es ,m ax im um be d th ick ne ss  6 0  cm f ‐  g r hi gh ‐e ne rg y t id al  ch an ne ls– in le ts cu rti s f m . j pl an ar  cr os s‐s tra tif ie d  sa nd y  co ng lo m er at e cl as t‐ to m at rix ‐su pp or te d co ng lo m er at e, hm ‐sc al e la te ra l ex te nt , co nv ex ‐d ow n er os ive ba se ,f la tt op ,e xt ra ‐b as in al su b‐ to ro un de d cla st s, m ax im um cla st ø 2. 5 cm , pl an ar  cr os s‐s tra tif ica tio n,  m ax im um  in di vid ua l t hi ck ne ss  3 .0  m m  ‐  gr po in t b ar  la te ra l a cc re tio n  w ith in  a  m ig ra tin g  tid al   ch an ne l cu rti s f m . k pl an e  pa ra lle l‐l am in at ed  m ud ‐ t o  sil ts to ne pl an e pa ra lle l‐l am in at ed m ud to sil ts to ne , sc at te re d bi di re ct io na l cu rr en t rip pl e cr os s‐s tra tif ica tio ns , gr ay to gr ee n, oc ca sio na l de sic ca tio n cr ac ks , sp or ad ic bi ot ur ba tio ns  b ot h  pa ra lle l a nd  n or m al  to  th e  be dd in g  pl an es si  ‐ c l ge nt le  fl ow  a ct ivi ty  w ith  ti da lly  re la te d  cu rre nt   re ve rs al s cu rti s f m .              * cl =c la y,  si =s ilt , v f= ve ry  fi ne , f =f in e,  m =m ed iu m , g r= gr av el , p b= pe bb le ; g ra in  si ze  in  p ar en th es e  de no te s r ar el y   pr es en t a nd  b ra ck et ed  d en ot es  a t t he  b ou nd ar y b et w en  v f a nd  f t ab le 1 . f ac ie s d es cr ip tio n fo r t he e nt ra da s an ds to ne , c ur tis f or m at io n, a nd s um m er vi lle f or m at io n (c on tin ue d on fo llo w in g pa ge ). 138 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 fa cie s de sc rip tio n st ru ct ur es gr ai n  si ze * in te rp re ta tio n fo rm at io n l he te ro lit hi c s ilt ‐ a nd  sa nd st on e  w ith   le nt icu la r b ed di ng ri pp le d ve ry fin e to fin e‐ gr ai ne d sa nd st on e, gr ay ish le ns es co nt ai ni ng he rr in gb on e an d cu rr en t rip pl e cr os s‐ st ra tif ica tio ns w ith in a m at rix of la m in at ed gr ay to gr ee n m ud ‐ to sil ts to ne s, oc ca sio na l de sic ca tio n cr ac ks , sp or ad ic bi ot ur ba tio ns bo th pa ra lle l a nd  n or m al  to  th e  be dd in g  pl an es si  ‐  f cu rr en t r ev er sa ls  in  lo w er  su bt id al  zo ne cu rti s f m . m he te ro lit hi c s ilt ‐ a nd  sa nd st on e  w ith   w av y  be dd in g ri pp le cr os s‐ st ra tif ie d ve ry fin e to fin e‐ gr ai ne d gr ay ish sa nd la ye rs , w ith bi ‐ di re ct io na l cu rr en t in di ca to rs an d in te rb ed de d w ith la m in at ed gr ay to gr ee n sil ts to ne ,o cc as io na ld es icc at io n cr ac ks ,s po ra di c bi ot ur ba tio ns bo th pa ra lle la nd no rm al  to  th e  be dd in g  pl an es , v ar yi ng  a m ou nt  o f o rg an ic  m at te r si  ‐  f cu rr en t r ev er sa ls  in  su bt id al  zo ne  (s ha llo w er  th an   fa cie s l ) cu rti s f m . m oa b  m br . n he te ro lit hi c s an ds to ne  w ith  fl as er   be dd in g ri pp le an d he rr in gb on e cr os s‐ st ra tif ie d ve ry fin e to fin e‐ gr ai ne d gr ay to gr ee n to w hi te sa nd st on e, sc at te re d m ud le ns es ,a s w el la s sin gl e an d do ub le m ud dr ap es , va ry in g  am ou nt  o f o rg an ic  m at te r vf  ‐  f up pe r s ub ‐ t o  lo w er  in te rti da l s an dy  fl at cu rti s f m . o sa nd st on e  w ith  cl im bi ng  ri pp le s cl im bi ng  ri pp le  cr os s‐ st ra tif ie d  ve ry  fi ne  to  fi ne ‐g ra in ed  sa nd st on e,  g ra y  to  g re en vf  ‐  f ti da l c ha nn el  o ve rb an k  sp ill  o n  tid al  fl at , u pp er  su b‐   to  lo w er  in te rti da l s an dy  fl at cu rti s f m . p cr os s‐ st ra tif ie d  sa nd st on e  ar ra ng ed  in   w el l‐d ef in ed  rh yt hm ic  tid al  b un dl es ve ry fin e to fin e‐ gr ai ne d (m ed iu m ‐g ra in ed ra re ly pr es en t) gr ay to gr ee n to w hi te sa nd st on e, ar ra ng ed in tid al bu nd le s, w ith oc ca sio na la nt i‐r ip pl es do cu m en te d fro m th ei rt oe se ts ,v ar yi ng am ou nt of or ga ni cm at te r vf  ‐  f  (‐m ) ti da l i nl et s,  lo w er  e ne rg y  th an  f ac ie s i cu rti s f m . q st ru ct ur el es s s an ds to ne ve ry fin e to fin e‐ gr ai ne d gr ai ne d gr ay to gr ee n to w hi te sa nd st on e, m as siv e, w ith po te nt ia l sc at te re d sin gl e an d‐ or do ub le m ud dr ap es . us ua lly ro un de d an d sm oo th ly  w ea th er ed vf  ‐  f th e  na tu re  o f t he  la ck  o f s tru ct ur e  m ig ht  o nl y  be   du e  to  in te ns iv e  su rfa ce  w ea th er in g.  p re se nc e  of   m ud  d ra pe s i nd ica te  su b‐  o r i nt er tid al  e nv iro nm en t cu rti s f m . r th or ou gh ly  b i‐d ire ct io na l r ip pl ed   cr os s‐ st ra tif ie d  sa nd st on e th or ou gh ly rip pl ed sil tt o ve ry fin e gr ai ne d sa nd st on e, do m in at ed by he rr in gb on e cr os s‐ st ra tif ica tio ns s  ‐ v f de ep  su bt id al  e nv iro nm en t w ith  n ea r e qu al  fl oo d  an d  eb b  tid al  cu rr en t c on di tio ns . n ot e  th at  th e  w ea th er in g  ca n  in  so m e  ca se s e ra se  m os t o f t he   se di m en ta ry  st ru ct ur es cu rti s f m . m oa b  m br . s pl an e  pa ra lle l‐s tra tif ie d  sa nd st on e pl an e pa ra lle l‐s tra tif ie d ve ry fin e to fin e‐ gr ai ne d sa nd st on e w ith sc at te re d cu rr en t rip pl e la m in at io n, w hi te ,p in k or gr ee n. no te th at th e w ea th er in g ex pr es sio n of th is fa cie sv ar ie sb et w ee n th e di ffe re nt un its of th e cu rti sf m .p ot en tia lm ud cr ac ks an d so ft‐ se di m en t d ef or m at io n (s i‐)  v f  ‐ f sa nd y  tid al  fl at , u pp er  fl ow  re gi m e  (to  lo w er   an tid un e‐ re gi m e? ).  do cu m en te d  m ud  cr ac ks   in di ca te  sh or t‐l iv ed  su ba er ia l e xp os ur e cu rti s f m . m oa b  m br . t co nd en se d  sa nd st on e  th in , ye llo w st ru ct ur el es s sa nd st on e, oc ca sio na lly di sp la yi ng lo w ‐a m pl itu de un du la tio ns , ex clu siv el y ob se rv ed ca pp in g th e m oa b m em be r of th e cu rti s fm . m ax im um  b ed  th ick ne ss  1 0  cm [v f‐ f]  f co nd en se d  ho riz on m oa b  m br . u ri pp le d  cr os s‐ st ra tif ie d  sa nd st on e un du la te d to rip pl ed cr os s‐ st ra tif ie d, ve ry fin e to fin e‐ gr ai ne d, gr ay to br ow n sa nd st on e, w ith 3d cu rr en t rip pl es , po ss ib le in te rfe re nc e rip pl es , po te nt ia lm ud cr ac ks  a nd  so ft‐ se di m en t d ef or m at io n vf  ‐  f 3d  m ig ra tin g  rip pl es  u nd er  u ni di re ct io na l c ur re nt   co nd iti on s en tra da  s s. cu rti s f m . m oa b  m br . su m m er vi lle  f m . v pl an e  pa ra lle l‐l am in at ed  si lts to ne da rk re d so ft slo pe ‐fo rm in g sil ts to ne , m os t pr ob ab ly pl an e pa ra lle l‐l am in at ed , sc at te re d pa le w hi te bl ea ch ed le ns es an d ev ap or ite s si su pr at id al  p la in su m m er vi lle  f m . w iro n  ric h  rip pl e‐  a nd  p ar al le l‐ la m in at ed  sa nd st on e da rk re d to br ow n ce m en te d ve ry fin e to fin e‐ gr ai ne d sa nd st on e, ge nt le rip pl e cr os s ‐ st ra tif ica tio n,  p ot en tia l d es icc at io n  cr ac ks vf  ‐  f fl uv ia l o ve rb an k  flo od in g  de po sit s su m m er vi lle  f m . x pa le os ol da rk  p ur pl e  m ud  o r s ilt cl ‐s i su b‐ ae ria lly  e xp os ed  su rfa ce  w ith  su pe rfi cia l s oi l  de ve lo pm en t en tra da  s s. cu rti s f m . m oa b  m br . su m m er vi lle  f m .              * cl =c la y,  si =s ilt , v f= ve ry  fi ne , f =f in e,  m =m ed iu m , g r= gr av el , p b= pe bb le ; g ra in  si ze  in  p ar en th es e  de no te s r ar el y   pr es en t a nd  b ra ck et ed  d en ot es  a t t he  b ou nd ar y b et w en  v f a nd  f t ab le 1 (c on tin ue d fr om p re vi ou s p ag e) . f ac ie s d es cr ip tio n fo r t he e nt ra da s an ds to ne , c ur tis f or m at io n, a nd s um m er vi lle f or m at io n. 139 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 as individual beds within a mottled interval (facies b). note that facies b can locally grade up-section into paleosols (facies x). bleached patches of rock commonly underlie and overlie paleosols or are found in the direct vicinity of such horizons, contributing to the mottled expression (blodgett, 1988). the top of fa 1 is capped by regional j-3 unconformity of pipiringos and o’sullivan (1978). facies  association depositional environment facies included formation fa 1a coastal wet eolian dune system (kocurek and havholm, 1993;  mountney, 2012), with episodic (marine) partial flooding of  interdunes deposits and superficial development of soil‐ and  vegetated horizons a, c, x entrada ss. slick rock mbr. fa 1b coastal wet eolian interdune system (kocurek and havholm,  1993; mountney, 2012), with episodic (marine) partial  flooding of interdune deposits and superficial development of  soil and vegetated horizons b, c, d, x entrada ss. earthy facies fa 2 beach deposits to upper shoreface deposits, with potential  associated tidal channel cut‐and‐fill c, g, s, u curtis fm. fa 3a subtidal heterolithic mud, silt,  and very fine grained  sandstone, generally coarsening up from laminated  mudstone, wavy bedding, scarsely bioturbated h, i, j, k, l, m curtis fm. fa 3b subtidal heterolithic vf‐ to f‐grained sandstone generally  coarsening up from wavy bedding to flaser bedding, scarsely  bioturbated h, i, m, n curtis fm. fa 4a sandy tidal flat with correlative major tidal channels, having  potential subaerial exposures s, u, x curtis fm. fa 4b tidal channel infills and splays, distal correlative of fa 4a in  the northern areas c, h, i, l, m, n, s,  u curtis fm. fa 5 high energy, sub‐ to intertidal sand ‐dominated  environments, encompassing tidal flats, tidal channels, and  beaches c, g, (k, l, m,) n,  o, p, q, r, s(, x) curtis fm. fa 6 upper intertidal heterolithic channels and flats complex,  fining up, with intermittent prolonged subaerial exposures  and rare bioturbation, indicator of a more stressed  environment than fa 3 k, l, m, n, q, s, u,  x curtis fm. fa 7 coastal dry eolian dune field (mountney, 2012), arranged in  four to five sequences separated by supersurfaces, upon  which transgressive water‐carried sediments and/or paleosol  can be observed a, n, q, s, t, u, x curtis fm. moab mbr. fa 8 supratidal lower coastal plain, with episodic marine flooding u, v, w, x summerville fm. table 2. facies associations for the entrada sandstone, curtis formation, and summerville formation. 140 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 v v v v v v v v v v v v v v v v v v v 35 30 2545 40 20 15 10 5 c la y si v f f m sa n d 35 30 25 20 15 10 5 c la y si v f f m sa n d 45 40 35 30 25 20 15 10 5 c la y si v f f m c v c g sa n d c la y si v f f m c sa n d 80 75 70 6595 90 85 60 55 50 45 40 35 30 25 20 15 10 5 c la y si v f f m c sa n d 80 75 70 6595 90 85 60 55 50 45 40 35 30 25 20 15 10 5 c la y si v f f m 45 40 35 30 25 20 15 10 5 35 30 254550 40 20 15 10 5 c la y si v f f m sa n d v v v v v v v v v v v v v v v v v v v 65 60 55 50 45 40 35 30 25 20 15 10 5 c la y si v f f m sa n d 24 19 1 24 19 1 95 25 km n u ta h 10 0 km n cl ay si vf f m c vc g pe b. su pr at id al m ud � at su pr at id al sa nd � at sc he m at ic lo g ar ch ite ct ur al e le m en ts sa nd -ri ch su b to su pr at id al � at a nd co rre la tiv e tid al ch an ne l i n� l ti da l b un dl es su bt id al sa nd -d om in at ed h et er ol ith ic � at up pe r s ub t o in te rt id al sa nd -d om in at ed he te ro lit hi c c ha nn el -� at co m pl ex up pe r s ub t o in te rt id al m ud -d om in at ed he te ro lit hi c � at su bt id al co ng lo m er at ic d un es su bt id al m ud -d om in at ed h et er ol ith ic � at su b to in te rt id al ch an ne l-d un e�a t c om pl ex co as ta l i nt er du ne s co as ta l d un es up pe r s ho re fa ce to b ea ch d ep os its co as ta l d un es , b le ac he d fa 1 a fa 1 b fa 2 fa 3 a fa 3 b fa 4 b fa 4 a fa 5 fa 6 fa 8 pr ox im al d is ta l fa 7 cl ay si vf f upper c. lower c.middle c. j3 m ts su lp hu r c an yo n m id dl e c ur tis lo w er c ur tis up pe r c ur tis lo w er c ur tis su m m er vi lle fo rm at io n en tra da sa nd st on e ea rth y fa ci es en tra da sa nd st on e sl ic k r oc k m b. n ev er sw ea t w as h sv en ’s g ul ch in te rs ta te 7 0 h an ks vi lle n ot om r an ch bi g pi nt o m es a g ob lin v al le y 11 .5 k m n or th so ut hw es t ea st 24 k m 15 .5 k m 48 k m 20 .5 k m 40 k m 17 5 km j3 un co n. m ts fa ci es a ss oc ia tio ns fa 8 s up ra tid al � at fa 7 c oa st al d ry e ol ia n du ne s i m oa b m em be r fa 4 s an dric h su b to su pr at id al � at a nd co rre la tiv e tid al ch an ne l i n� ll fa 3 b su bt id al sa nd -d om in at ed he te ro lit hi c � at fa 6 u pp er su b to in te rt id al h et er ol ith ic � at fa 3 a su bt id al m ud -d om in at ed he te ro lit hi c � at fa 5 s ub t o in te rt id al ch an ne l-d un e � at co m pl ex fa 1 b ea rt hy fa ci es fa 1 a co as ta l d un es a nd s lic k ro ck m em be r fa 2 u pp er sh or ef ac e to b ea ch de po sit s �g ur e 4c , d facies associations height [m] paleocurrent fi gu re 2 . n or th -s ou th w es tea st c ro ss se ct io n ac ro ss th e st ud y ar ea sh ow in g th e sp at ia l d ist rib ut io n of th e m ai n fa ci es a ss oc ia tio ns id en tifi ed w ith in th e up pe rm os t s tr at a of th e en tr ad a sa nd st on e, th e cu rt is fo rm at io n an d th e lo w er m os t s tr at a of th e su m m er vi lle f or m at io n al on g th e w es te rn m ar gi n of th e sa n ra fa el s w el l a nd s ou th to th e h en ry m ou nt ai ns . th e bi g pi nt o m es a m ea su re d se ct io n re pr es en ts th e ty pi ca l e xp re ss io n of th e m oa b m em be r o f t he c ur tis f or m at io n. d et ai le d se di m en ta ry in fo rm at io n on th e va rio us a rc hi te ct ur al e le m en ts p re se nt a t t he se le ct ed lo ca lit ie s i s di sp la ye d on th e m ea su re d se ct io ns , w he re as fa ci es as so ci at io ns ar e c ol or -c od ed in ea ch su m m ar y co lu m n ne xt to th ei r r es pe ct iv e m ea su re d se ct io n. 141 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 10 m 24 19 1 24 19 1 95 25 km n u ta h 10 0 km n 0. 1 % f a 6 sc n sw sg i7 0 g v h k n r ls d lc m r s& c sw va lc d lf tls rr d p tm r n o d at a n o d at a n o d at a n o d at a n o d at a sr bp m ls c sc n sw sg i7 0 g v h k n r lc d lc m r s& c sw va ls d lf t ls rr d ptm r sr bp m ls c scn sw sgi7 0 g v h k n r ls d lc m r s& c sw va lc d lf t ls rr d p tm r srbp m ls c su lp hu r c an yo n n ev er sw ea t w as h sv en ’s g ul ch in te rs ta te 7 0 g ob lin v al le y h an ks vi lle n ot om r an ch lo w er s ou th d es er t o ve rlo ok lo w er c ed ar m ou nt ai n ro ad si d & c ha rle y sa lt w as h vi ew a re a la st c ha nc e d es er t li tt le f la t t op lo w er s an r af ae l r oa d d um a po in t te n m ile r oa d sa fa ri ro ad bi g pi nt o m es a lo st s pr in g ca ny on 38 .2 3 m 62 .0 0 m 80 .5 0 m 38 .7 5 m 26 .0 0 m 41 .5 5 m 33 .6 5 m 29 .0 0 m 63 .2 5 m 34 .4 0 m 56 .4 0 m 67 .0 5 m 35 .8 0 m 13 .6 0 m 01 .3 0 m 14 .2 5 m 28 .6 0 m 65 .0 5 m co de se ct io n n am e cu rt is f m . le ng th 40 .1 0 m fa 8 s up ra tid al fl at fa 7 c oa st al d ry e ol ia n du ne s i m m oa b m em be r fa ci es a ss oc ia ti on s: fa 4 s an dric h su b to s up ra tid al fl at a nd iiic or re la tiv e tid al c ha nn el in fill fa 3 b su bt id al s an ddo m in at ed h et er ol ith ic fla t fa 6 u pp er s ub t o in te rti da l h et er ol ith ic fla t fa 3 a su bt id al m ud -d om in at ed h et er ol ith ic fla t fa 5 s ub t o in te rti da l c ha nn el -d un efla t c om pl ex fa 2 u pp er s ho re fa ce to b ea ch d ep os its fa 1 b ea rth y fa cie s fa 1 a co as ta l d un es a nd s lic k ro ck m em be r cu rti s fo rm at io n upper c. lower c.middle c. en tra da sa nd st on e j3 un co nf or m ity lo we r o xf or di an upper jurassic middle up pe r ca llo via n a b se ct or 1 lo w er , m id dl e an d u pp er c ur tis se ct or 2 m id dl e an d u pp er c ur tis se ct or 3 m oa b m em be r fa 2 -3 -4 d at a: 1 32 n fa 5 d at a: 1 69 n fa 6 -7 d at a: 2 2 n fi gu re 3 . ( a ) 3 d c or re la tio n be tw ee n se le ct ed lo ca lit ie s. a s th e se di m en ta ry s ec tio ns a re a lig ne d on th e j3 un co nf or m ity (r ed li ne ), th e en tr ad a sa nd st on e ap pe ar s b el ow th e m ap , w he re as th e cu rt is fo rm at io n re m ai ns a bo ve it . p al eo cu rr en t m ea su re m en ts a re a rr an ge d st ra tig ra ph ic al ly fr om bo tto m to to p. (b ) p ie ch ar ts re pr es en tin g th e r at io b et w ee n th e d iff er en t f ac ie s a ss oc ia tio ns b el on gi ng to th e c ur tis f or m at io n at ea ch lo ca lit ie s. se e te xt fo r d isc us sio n of u nu su al p at te rn in l itt le f la t t op (l ft ). 142 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 on a structural geology note, numerous conjugated extensional faults, associated fractures, and remobilized, injected and disintegrated sand (facies d), as well as hydroplastic deformation occur in the upper entrada sandstone in the humbug flats area, at smith’s cabin in the north, farther south between interstate 70 and uneva mine canyon, and north of hanksville airport (figure 1). fractures typically feature a bleached front in their direct vicinity (figure 4a). fault planes are mostly planar; however, growth-fault geometry on south-facing faults is found near smith’s cabin. faults show meter-scale offset in the earthy facies of the entrada sandstone, whereas most of them are concealed by the base of the curtis formation, which remains undisturbed. faults strike east-west around the humbug flats-smith’s cabin area in the north; whereas south of interstate 70 they strike north-south. note that bleaching is common along fractures and faults within fa 1 (figure 4a). however, 2.1 km north of hanksville airport, the earthy facies (fa 1b), was impacted by synto post-depositional localized extensional and contractional faults, as well as synchronous erosion, generating a 2 to 3 m relief at the top of the entrada sandstone (figure 4f). these fault clusters display a semi-circular surface expression. the heterolithic deposits of lower curtis (fa 3-4) passively filled the preexisting topography, before being rapidly overlain by the middle curtis sediments (fa 5), which abruptly collapsed by faulting while or shortly after being deposited. it remains unclear how precisely and when these processes jolted the deposits of the middle curtis. interpretation interbedding of eolian dune, interdune, sabkha, and tidal deposits are typical features for coastal wet eolian desert environments, as interpreted and described by several authors (crabaugh and kocurek, 1993; kocurek and havholm, 1993; mountney, 2012). occurrence of marginal marine sandstones, gypsum-rich beds, and paleosols horizons within an interval dominated by facies b are related to partial marine flooding and/or relative water table rises within the sediments (carr-crabaugh and kocurek, 1998; mountney, 2006). on the contrary, intervals dominated by eolian dunes reflect short-lived relative base level falls (mountney, 2006, 2012). mottling is ascribed to forced disturbance from roots and has been enhanced by circulation of organic acids through the tight mudstones (blodgett, 1988), most probably flowing along root burrows. also, the development of the condensed and bioturbated sandstone bed (facies e) at the top of fa 1 indicates an extended period of sediment starvation (urash and savrda, 2017) around the area known today as safari road (figure 1). consequently, fa 1 is considered to represent a coastal eolian system, where marine processes and water table variations jointly and increasingly influenced the sedimentary development of the entrada sandstone. bleached fronts observed along fractures in the earthy facies occurred as a consequence of post-depositional reducing fluid circulation within a naturally co2-charged system (kampman and others, 2013; ogata and others, 2014; skurtveit and others, 2017; sundal and others, 2017). as conjugated fault sets mostly offset the strata of the earthy facies, consequent extensional faulting appears to have occurred post-earthy facies deposition, but pre-curtis sea transgression. the occurrence of disturbed earthy facies layers, as well as lower and middle curtis strata 2.1 km north of hanksville airport implies that the lowermost late jurassic strata responded to episodes of sand mobility which impacted the surface morphology. fa 2 – beach to upper shoreface deposits description fa 2 is recorded at curtis point, sven’s gulch, interstate 70, and uneva mine canyon measured sections (figure 1). it reaches a maximum thickness of about 1.70 m at sven’s gulch. fa 2 shows a clear upward-fining trend, where the lowermost plane parallel-stratified sandstone of facies s and planar to low-angle cross-stratified sandstone of facies g are overlain by the trough cross-stratified sandstone of facies c and/or ripple-laminated sandstone of facies u. mud drapes and rip-up clasts are also documented at interstate 70 and uneva mine canyon. fa 2 overlies fa 1, from which it is separated by the j-3 unconformity, locally displaying load structures (figure 5). the transition between fa 2 and the overlying fa 3 occurs either as a gradual and 143 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 figure 4. caption on the following page. 144 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 fining-upward changeover or corresponds to a sharp and erosive contact (figures 4a and 5). note that the lateral extent of fa 2 reaches 200 to 500 m, and at the measured section interstate 70, fa 2 is arranged in laterally accreting sandstone bodies, interbedded with fa 3 finer heterolithic material. interpretation the high sand content of these rocks combined with the extremely low mud content indicate a high-energy marine environment. the deformation of the j-3 unconformity and the underlying fa 1b by loading suggests a poorly lithified entrada sandstone at the time of deposition (owen and others, 2011). the occurrence of oscillation ripple lamination, as well as planar to low-angle cross-stratified sedimentary structures are clear indicators of upper shoreface to beach deposits. the occurrence of rip-up clasts and mud drapes testifies of secondary tidal action over the system. the overall fining-upward trend from fa 2 into fa 3 indicates a gradual transgression of the curtis sea over the j-3 unconformity, whereas the restricted character of fa 2 suggests a direct influence of the pre-existing erosional relief over the distribution of these marginal marine deposits. they represent the onset of marine deposition into an erosional topography, and thus initially filled the available accommodation in the dips and furrows. fa 2 also displays the same deepening-upward development at sven’s gulch. however, its base is characterized by a short-lived shallowing-upward event, as recorded by the basal oscillation ripple-laminated sandstone of facies u (ripple-laminated sandstone). it is then overlain by the 3d migrating dunes of facies c before grading into the high-energy deposits of facies s (plane-parallel stratified sandstone) and g (planar to low-angle cross-stratified sandstone). it subsequently follows the same deepening-upward pattern as mentioned above. the fact that these marginal marine-beach deposits are only documented from the measured sections south of curtis point (figure 1) suggests a flooding of the southern areas from the northeast, before expanding towards the northern higher grounds. fa 3 – heterolithic subtidal flat and fa 4 – sand-rich subto supratidal flat and correlative tidal channel infill description fa 3 (figure 4) displays the lowermost sedimentary package, which represents the gilluly and reeside (1928) type section of the curtis formation and crops out mostly in sector 1, as well as little flat top and hanksville (figure 3). it is separated into a lower mud-dominated interval (fa 3a), which grades into an figure 4 (figure on the previous page). overview of the lower curtis in sector 1. see figure 3 for sectors, and figure 1 for photograph locations. (a) the beach to upper shoreface deposits of fa 2 overlie the earthy facies of entrada sandstone (fa 1b) at sven’s gulch. fa 2 is truncated at its top by a regressive surface a marine erosion (rsme), corresponding to the base of fa 3b (sand-dominated subtidal heterolithic flat). note the plume geometry of the bleached zones below the j-3 unconformity, suggesting a trapping of the reducing fluids below the sand of fa 2 as they circulate along fractures within the entrada sandstone (white arrows; skurtveit and others, 2017, sundal and others, 2017). (b) the three parasequences occurring in the lower curtis, as observed at the sid and charley sections on the western margin of the san rafael swell. note the occurrence of two small tidal channels (white surfaces) at the base of rsme 1 (fs: flooding surface). the lower curtis is capped the a major transgressive surface (mts), which can be traced across the study area. (c and d). major tidal incision observed at sven’s gulch, carved during a short-lived regressive phase within parasequence 2. the red arrow points at a boulder of entrada sandstone within a matrix of curtis formation, indicating that the entrada was poorly lithified when incised. the presence of this boulder, as well as fa 3 cannibalising its substratum, show that this depression was actually carved into the entrada sandstone by tidal currents, rather than being a pre-existing relief subsequently filled by the curtis formation. note also the bi-truncation of parasequence 2 during the early transgression of parasequence 3, followed by the cannibalisation by fa 4b of its substratum during a short-lived regressive phase within parasequence 3. (e) display of two incision phases within the fa 4b deposits of parasequence 3. (f) collapse structure complex linked to sand mobility in the lower and middle curtis cropping out 2.1 km north of hanksville airport. white lines indicate normal faults, whereas the black lines highlight contractional structures. 145 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 upper sand-dominated association (fa 3b) (table 2). fa 3a and fa 3b dark-green to gray color makes it readily identifiable in the field, where their combined thickness can vary significantly over a few hundred meters, ranging from less than a meter to about 30 m. fa 3 (dis)conformably overlies or onlaps the j-3 unconformity which caps fa 1 notably in the northern part of the study area (figure 1). it can also overlie fa 2 from which it fines upward or erodes into (figures 4 and 5). fa 3 displays at least two major coarsening-upward parasequences (parasequence 2 and parasequence 3) (sensu catuneanu and others, 2009). a third parasequence (parasequence 1) has been observed at sven’s gulch and the sid and charley section (figure 1). both parasequence 2 and parasequence 3 comprise a suite of sedimentary facies commonly associated with tidal deposits: fa 3a includes laminated mudstone (facies k), lenticular (facies l), and wavy bedding (facies m), whereas fa 3b comprises wavy bedding (facies m) and flaser bedding (facies n), with the presence of straight, sinuous-crested, and linguoid current ripples, as well as herringbone cross-lamination. sub-vertical and sub-horizontal bioturbations are recorded in fa 3a and fa 3b; the degree of disturbance varies, but remains limited, and corresponds to droser and bottjer’s (1986) ichnofabric index n°3. furthermore, their diversity is circumscribed to only a few types, such as thalassinoides, cruziana, or gyrochorte comosa ichnofossils, similarly reported from the carmel formation (de gibert and ekdale, 1999). fa 3 increases in grain size towards the south, with a generally higher sand-to-mud ratio on the western margin of the study area. its upper boundary is truncated by fa 5, which can, however, be locally conformable. a significant tidal incision can be observed at sven’s gulch, carving about 15 m into its substratum (fa 1b and fa 2) and reaching a width of about 60 m (figures 4c and 4d). the infill of that incision shows an intricate architecture, which mostly consists of fa 3b material, as well as one boulder of earthy facies (fa 1b). meter-scale, runnel-shaped gravelly bodies (facies i) are also documented at all locations north of sven’s gulch, displaying evidence of tidal reworking within a heterolithic environment. the area north of middle canyon (figure 1) is marked by the occurrence of laterally extensive gravel-rich compound dunes, displaying basinward-dipping, meter-thick tangential cross-stratification, with a non-erosive bedding-parallel base and a concave-up top surface (facies h) (figure 6), and are usually found in the lowermost meters of the curtis formation. conglomeratic dunes are not to be mistaken with the laterally accreting conglomeratic tidal channels, which are characterized by planar to tangential cross-stratification and a concave-down erosive base (facies i and j). also, at the measured section just south of interstate 70, fa 2 is overlain by a 1-m-thick greenish-colored sandstone, figure 5. transition from the entrada sandstone into the lower curtis as observed at sven’s gulch. fa 2 (beach to upper shoreface deposits) overlies the earthy facies of the entrada sandstone (fa 1b), from which it is separated by the j-3 unconformity. note the presence of load casts at the base of fa 2 at some localities. fa 2 rapidly grades into fa 3a (mud-dominated heterolithic subtidal flat), which can be cannibalised by the sand-dominated subtidal deposits of fa 3b (rsme: regressive surface of marine erosion). 146 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 figure 6. (a) outline of a westward laterally migrating tidal channel observed in the cliffs of cedar mountain, filled by the conglomeratic sandstone of facies i. the transition from a cross-stratified conglomerate into a more parallel-bedded conglomerate reflects a change in the channel orientation, as the cross-stratified deposits correspond to a transversal cross section of the channel, whereas the parallel-bedded part of the channel represents a longitudinal cross section through the same channel. (b) transversal section across a north-westward migrating conglomeratic dune (facies h, table 1) in the cliffs of last chance desert. this dune was influenced by tidal processes, as illustrated by the bundle-like regular and rhythmic thickness variations observed between the foresets. the biggest discrepancy between the tidal channel and the tidal dune resides within their respective base. the tidal channel displays a concave-down erosive base and a flat upper surface, whereas the dune is characterised by a non-erosive and bedding-parallel base and a convex upper boundary. 147 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 completely disturbed by processes related to liquefaction and water escape (facies d), which has not been observed anywhere else in the study area. the road cut section measured at last chance desert (figure 1) also displays a unique feature which has not been documented anywhere else: a 20-cm-thick, matrix-supported basal conglomerate, with randomly oriented, rounded to well-rounded extra-basinal clasts that are about 8 cm in diameter (facies f). the outcrop exposure of this conglomeratic bed limits the exact measurement of its lateral extent, but reaches a minimum of 70 m. fa 4a conformably lies within and must interfinger with fa 3a and fa 3b within parasequence 2. it represents 30% to 50% of the curtis formation in hanksville and little flat top, but it has not been observed at the locations north of smith’s cabin nor on the western margin of the san rafael swell (figures 1, 2, 3, and 7). it is characterized by its dominant light-pink, plane parallel-stratified or structureless, very fine to fine-grained sandstone (facies s) and subordinate unidirectional straight-crested 2d and 3d current ripple-dominated intervals (facies u), as well as centimeter-thick marine mudstone. episodes of subaerial exposure are recorded as dark-purple paleosol horizons (facies x, figure 7) or desiccation cracks. each individual bed measures as much as 1.50 m thick and can be laterally traced over several kilometers. although appearing isopachous at outcrop scale, its thickness ranges from about 15 m at rabbit gulch to 2 m at uneva mine canyon (figure 1), and it reaches a maximum of about 20 m thick at little flat top (figure 1). about 250 m south of the interstate 70 measured section, fa 4a forms a convex-down, flattopped feature with sand-dominated heterolithic beds that thicken towards the center. it measures 6.25 m thick and about 45 m wide. at first glance, the architecture and shape resemble a channel infill succession, but it lacks any erosional scour at its base or internally. it only thickens in its central part due to differential loading (figure 7d). fa 4b has exclusively been documented in the parasequence 3 interval at sven’s gulch (figure 1), where the measured section traces a 15 m thick succession between two tidal channels that incise their fa 3 substratum by as much as about 10 m (figures 4c, 4d, and 4e). note that at least two episodes of incision might have occurred during the deposition of fa 4b, as visible in sven’s gulch. the first incision carves the deepest into the fa 3a-3b deposits, whereas the second incision is shallower. the channel infills are dominated by facies h, i, n, c, s, and u, with a very high sandto-mud ratio. no evidence of subaerial exposure is recorded in fa 4b. the channel margins contain facies h and facies i, which interfinger with facies e, f, m, p, and q. individual beds are >1 m thick. fa 2, fa 3, and fa 4 are dominated by a north to north-northeast paleocurrent direction, with some northeast flows and with a subordinate and opposing south-southwest component (figure 3). note the strong underrepresentation of west-southwest to southwest flow indicators (figure 3). interpretation the heterolithic nature of fa 3 indicates a fluctuating energy level within the system (kvale, 2012). straight-crested to linguoid ripple marks suggest different durations of flow events, as equilibrium linguoid morphology requires more time to form (baas, 1999). the presence of parasequence 0 exclusively at sven’s gulch suggests that this area was the first part of the system to be flooded. the base of each parasequence is marked by a flooding surface and the development of fa 3a, followed by the coarsening-upward tidally influenced sediments of fa 3b. this is envisioned as a result of increased energy within the system due to shallower water and an increasingly proximal subtidal to tidal flat setting. the same increased energy trend is also indicated by the coarsening southward of fa 3, which suggests shallower water depth towards the present-day location of hanksville. whereas several flooding surfaces may be identified in outcrops, their exact correlation between the different measured sections is impossible due to the extreme dynamic nature of tidal environments, and because these flooding surfaces might stem from local variations in relative sea level such as avulsions, rather than regional signals. when traced laterally, the infill of the steep and deep incision observed at sven’s gulch (figures 4c and 4d) belongs to parasequence 2. the occurrence of an entrada sandstone boulder within a matrix of curtis formation indicates that the entrada sandstone was 148 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 poorly lithified as the tidal currents funneled into it, highlighting the poly-nature of the j-3 unconformity. both the presence of this boulder and a fa 3 cannibalizing its substratum show that this depression was actually carved into the entrada sandstone by tidal currents during a short-lived regressive phase within parasequence 2, rather being a pre-existing negative relief subsequently and passively filled by the curtis formation. the limited bioturbation degree and diversity indicate stressed environmental conditions within a restricted, tidally influenced marginal-marine tidal flat setting, potentially indicating hypoxic conditions as well as salinity values superior to normal marine standards (middleton, 1991; nio and yang, 1991; de gibert and figure 7. overview of fa 4a. (a) picture of little flat top, where the light pink, isopachous sand-rich subto supratidal flat deposits of fa 4a overlie the earthy facies of the entrada sandstone (fa 1b). the exact location of the j-3 unconformity at that location remains uncertain due to the lack of an erosive, or flooding surface between these two facies associations, uncertainty reinforced by an unusual gradual color change between fa 1b and fa 4a. the black arrows indicate paleosol horizons which could potentially represent the lithostratigraphical boundary between the two formations. fa 4a is capped by the major transgressive surface (mts), and subsequently overlain by the subto intertidal deposits of fa 6, whereas the fa 5 is absent. (b) double mud drape indicated by the white arrows, suggesting occasional subtidal depositional conditions. (c) scattered unidirectional current ripple within a fine-grained sandstone dominated by upper-flow regime plane parallel-stratifications, which, together with the near-lack of clay material, suggest higher energy conditions in fa 4a with respect to fa 3. (d) mini sag basin formed by the collapse of fa 3b deposits while being filled by the sandstone of fa 4a, just south of interstate 70, near where the highway cuts through the eastern flank of the san rafael swell. 149 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 ekdale, 1999; fan, 2012; hughes, 2012; daidu, 2013). the laterally extensive compound conglomeratic dunes of facies h in the northern area require high energy within the system at time of deposition. this succession shows strong similarities with the modern submarine dune field in laterally restricted san francisco bay, especially regarding the protracted extent of these features and their unidirectional, basinward development, suggesting a dominant ebb tide and subordinate flood tide as advocated by barnard and others (2006). these conglomeratic dunes coexist with laterally migrating tidal channels (facies j). the occurrence of cross-stratified conglomeratic lenses with interfingered greenish-colored silt and mud implies significant variation and asymmetry in current velocities, at least locally. the dominant current will mobilize gravel and coarse sand, forming lens-shaped dunes, locally amalgamated within a tidal channel, whereas the subordinate current will cut the bedform, generating reactivation surfaces, and potentially develop counter ripples and small dunes. the replacement of the greenish-colored tidally influenced deposits of fa 3 by the pinkish-colored relatively well-sorted plane parallel-stratified sediments of fa 4a suggests (1) higher energy and more stable current conditions within the system compared to fa 3, (2) a more oxygenated water column, oxidizing the iron present in the sediments, (3) a potential change in sediment sourcing, now originating from more homogeneous very fine to fine-grained sand-rich continental strata with a potential higher k-feldspar content, and (4) a short-lived relative sea-level drop with subaerial exposure. the channels of fa 4b are regarded as distal subtidal channels, due to the lack of intertidal indicators and the absence of any evidence of subaerial exposure, as well as the interfingering with the subtidal deposits of fa 3a and fa 3b. they are also regarded as the distal time correlative unit of the more proximal fa 4a. also, the two incision events of fa 4b documented at sven’s gulch (figure 4) might relate to the short lived relative sea-level fall and subsequent subaerial exposure episodes of fa 4a. the fact that the first incision carves deeper into the deposits of fa 3 implies a more important relative sea-level fall during the first episode of incision than during the second incision. fa 4 architecture and paleocurrent directions suggest a dominant basinward ebb-flow direction and a subordinate flood-tide in the lower part of the curtis formation. interestingly, the basal conglomerate documented at last chance desert (figure 1, facies f) is interpreted as flash-flood deposits resting directly on pipiringos and o’sullivan’s (1978) j-3 unconformity, which implies that these deposits are older than the curtis formation as defined by gilluly and reeside (1928), yet younger than the entrada sandstone. fa 5 – subto intertidal channel-dune-flat complex description fa 5 is present in every locality in this study, with the notable exception of little flat top (figures 1 and 3). in comparison with the underlying fa 3 and 4 deposits, the sand-dominated interval corresponding to fa 5 is relatively homogeneous (figure 8). fa 5 is easily identifiable in the field by its light green-white color, as well as its polished weathering appearance. it generally overlies fa 3 or fa 4, but between the measured sections interstate 70 and uneva mine canyon (figure 1), fa 5 caps fa 2 and fa 1 at a noticeable angle (figures 8f and 8g). fa 5 rests directly on fa 1 in sectors 2 and 3, with the exception of the hanksville section, and is absent from little flat top (figures 1, 2, and 3). the thickness and, to a lesser extent, the stacking architecture of this sedimentary unit strongly vary between studied sections, nevertheless displaying a southward-thinning trend, reaching more than 45 m thick at stove gulch, about 15 m thick at interstate 70, and only 4.60 m thick at hanksville (figures 1, 2, and 3). it also thins towards the east, measuring only about 1.30 m thick at duma point and about 0.8 cm thick at crystal geyser, but never exceeding 3.80 m thick in sector 3 (figures 1 and 3). its lower sharp contact is either conformable with the underlying strata, onlapping its substratum, or erosive in nature, and corresponds to the mts. fa 5 is dominated by sand-rich facies, featuring sedimentary structures such as flaser bedding (facies n), climbing ripples (facies o), or thoroughly rippled intervals, dominated by herringbone cross-stratification (facies r). some bedding surfaces display interference ripple marks that are arranged in a nearly orthogonal pattern. fine-grained 150 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 figure 8. caption on the following page. 151 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 material arranged in laminated mudstone to lenticular to wavy bedding is recorded at smith’s cabin (facies k, l, m, figure 1). other sedimentary structures and type of architecture can be observed, such as (1) locally amalgamated cmto m-scale tidal bundles with varying amount of organic matter captured within their toesets (facies p), (2) 3d dunes cut by several reactivation surfaces on top of which counter ripples can sometimes be seen (facies c), and (3) plane parallel-stratified intervals (facies s). these facies interfinger with one another over about 5 to 40 m. both single and double mud drapes as well as desiccation cracks occur within several horizons included in fa 5. the fact that three shallow core-drilling attempts through these sandstone beds failed at providing any usable cored plugs suggests the unit is poorly consolidated, at least through its first 20 cm, but the degree of consolidation varies significantly over tens of meters. weathering can obscure sedimentary structures, which results in a structureless appearance (facies q). the stacking pattern of these different facies is extremely intricate, and each locality has subtly unique architecture. therefore, the internal complexities of fa 5, coupled with distance between each location, render the detailed correlation between the measured sections very challenging and incompletely constrained. note that the thickness, size, and wavelength of tidal structures diminish up-section, whereas the lower half of fa 5 displays a relatively constant scale of sedimentary architecture. towards the east, in sector 3, fa 5 is dominated by rippled cross-laminated to undulated beds, with scattered structureless intervals. current data are shifted in comparison with the underlying units, from a north-dominated to a more symmetrical northwest to southeast trend (figure 3). however, fa 5 shows similarities with the underlying facies associations, as recordings of a west-southwest to southwest flow direction are rare. interpretation the overall high sand-to-mud ratio within fa 5 indicates an elevated energy level within the depositional environment, in comparison with the underlying units. however, this energy level fluctuated through space and time, as testified by the nature and the varying scale of the documented sedimentary structures, as well as by the intricate lateral and vertical interfingering and stacking pattern of the different facies. all of these features display the effect of individual and multiple tide cycles over a tidal flat (facies c, l, m, n, o, and r), as well as neap-spring tidal cyclicity within a tidal channel (facies p) (kreisa and moiola, 1986; middleton, 1991; nio and yang, 1991; fan, 2012; hughes, 2012; daidu, 2013). ephemeral episodes of subaerial exposure occurred, as evident by desiccation cracks and, to a lesser extent, single intertidal mud drapes, typical for intertidal zones. tidal channels are present, but never quite reach the size of the tidal channels observed in the underlying fa 3 as their lateral extent remains on the order of the decameter (dkm) with well-developed laterally accreting architecture (facies i, figure 8e). the occurrence of other tidal channels is indicated by the presence of herringbone cross-stratification and sigmoidal tidal bundles (kreisa and moiola, 1986; hughes, 2012). considering this coastal setting, a highly various and undulating coastline is suggested, which caputo and figure 8 (figure on the previous page). overview of fa 5 (middle curtis). (a) bidirectional tidal inlets (red and blue contours), and a third south-westward laterally accreting tidal channel (green contour) within a subto intertidal flat surrounding environment. the respective migration direction of these three bedforms is color-coded on the rose-diagram, whereas the black line on the diagram illustrates the outcrop orientation. (b) heterolithic sandstone with an alternation of flaser bedding (fb, facies n) and wavy bedding (wb, facies m). lenses cap: 67 mm. (c) enrichment of organic matter (om) in the toesets of certain rhythmic tidal bundles (facies p). (d) weathered surface of a structureless sandstone. (e) south-westward laterally accreting tidal channel, incising into subtidal sandstone with flaser bedding (fb). the channel was subsequently overlain by 3d tidally influenced dunes (td) migrating towards the northeast. (f and g) the two pictures are respectively taken 1.3 and 2.2 km south of the interstate 70 measured section. they show the erosive and angular relationship between fa 5 and its substratum, as the curtis sea was transgressing its poorly consolidated and uplifted substratum. the mts at the base of fa 5 can be traced over the entire study area. 152 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 pryor (1991) and wilcox and currie (2008) bring forth and visualize by their paleoenvironment reconstruction models. as depositional energy conditions increase basinward, the clear change in grain size in comparison with the underlying finer grained deposits of fa 2, fa 3, and fa 4 and the extended erosive tidal ravinement surface at the base of fa 5 suggest an overall transgression within a context of limited available accommodation space, with the emplacement of high energy tidal channels and bars system, shielding the back barrier intertidal mix-flat in the southeast (fa 6) (see dalrymple and others, 2012). the overall fa 5 interval corresponds to flemming’s (2012) bare tidal flat depositional system. the diminishing thickness, size, and wavelength of tidal structures up-section, as well as towards the east and the south, is interpreted to represent a decrease of tidal amplitude and influence over the study area as a result of the early stage of a prograding coastline within an asymmetrical, eastward-pinching foreland basin, which followed a period of architectural aggradation. fa 6 – upper heterolithic subto intertidal flat description fa 6 (figure 9) represents the topmost overall finning-upward heterolithic interval of the curtis formation documented throughout the whole study area, but its occurrence is limited in sector 3 in comparison with the neighboring sectors 1 and 2. it conformably overlies the sand-dominated fa 5, whereas, at little flat top, it directly overlies fa 3. its thickness is fairly constant, gently varying between about 7 and 17 m. internal structures include asymmetrical currentand wave-ripple lamination of facies l, m, and n, interbedded with laminated mudstone, and structureless or planar parallel-stratified sandstone (facies c, k, s). fa 6 is also marked by an increase of unidirectional current ripple lamination (facies u), whereas bidirectional herringbone cross-laminations become increasingly sparse. individual beds are as much as 10 to 40 cm thick. darkred paleosol horizons and scattered desiccation cracks, as well as scattered evaporite-rich levels are recorded throughout the successions. reddish to orange-colored chert nodules often arranged along well-defined horizons are also common within fa 6. paleocurrent data must be regarded with caution due to the low number of measurements (figure 3). further, fa 6 sees the return of bioturbation, exclusively consisting of root burrows. fa 6 is characterized by an extreme scarcity, and a dramatically reduced bioturbation size, which would correspond to droser and bottjer (1986) ichnofabric index n°2. note that once again the crystal geyser section remains an outcast, as the 2 to 5 m of interpreted curtis formation displays only facies s, u, and x. interpretation the alternation of heterolithic deposits such as in fa 6 is closely related to systematic and periodic energy level fluctuations, typical of a tide-influenced environment (kvale, 2012). in comparison with the underlying units, the amplitude of flow velocity change, as well as the available accommodation is reduced, as suggested by the limited thickness of each bed and the size of the bedforms populating them. the disappearance of relatively deep tidal channel-related herringbone cross-lamination and its gradual replacement by an increased frequency of unidirectional landward-oriented washover deposits directly reflects a reduced rate of relative sea level rise, which marks the onset of a normal regression (highstand system tract [hsst]). the development of fa 6 is accompanied by a weaker tidal and overall marine influence over the intertidal flat, which generates extremely stressed habitability conditions within the system (jaglarz and uchman, 2010) coupled with episodes of subaerial exposure, as supported by precipitation of gypsum, the desiccation cracks, and the development of superficially vegetated paleosol horizons. fa 6 represents a more restricted and more proximal depositional environment than its fa 5 basinward equivalent. fa 7 – coastal dry eolian dune field description fa 7 corresponds to the eolian deposits of the moab member of the curtis formation, which crop out in the vicinity of moab and arches national park, utah (figure 1). the overall thickness of fa 7 is as much as 50 m 153 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 in the easternmost visited localities and pinches out a few 100 m east of duma point (figures 1 and 3). it rests directly on the slick rock member of the entrada sandstone in the east and on the earthy facies towards duma point (figure 1). it is characterized at its base by a sedimentary package that mainly consists of light-green to white, structureless to ripple to trough cross-stratified, very fine to fine-grained sandstone (facies q and u), with greenish-colored silty sandstone intervals (facies l), and superficial paleosols (facies x). facies q and u are over-represented with respect to facies x in the west, whereas this ratio inverts itself towards the east. note that this facies has not been observed at dewey bridge section (figure 10). soft-sediment deformation is common. this basal unit is overlain by a 1to 3-m-thick, planar parallel-stratified, white fine-grained sandstone (facies s), with locally occurring 0.3to 0.5-m-thick tangential cross-stratified sandstone (facies a) sets. the rest of the succession consists of four to five packages of amalgamated, large-scale (>2 m) tangential cross-stratified, fine-grained white sandstone (facies a). the maximum height of individual foreset reaches about 15 m. each of these sedimentary packages is truncated at their top by a supersurface, upon which paleosols (facies x) and/or fine-grained, undulating to rippled cross-stratified white sandstone (facies u) that is as much as 1 m thick can be observed. note that rhizoliths can be visible up to 2 m below these supersurfaces (figures 10c and 10d). fa 7 can be capped by a thin 10to 20-cm-thick, fine-grained, structureless yellow sandstone (facies t). interpretation the thick, tangential cross-stratified sandstone beds are interpreted as migrating compound eolian dunes (facies a), with alternating grain-fall and grainfigure 9. (a) photo illustrating the conformable contact between the middle curtis (fa 5), the upper curtis (fa 6), and the summerville formation (fa 8), accompanied their upward-thinning and upward-finning of the beds. (b) close up of the conformable contact between the upper curtis and the summerville formation. the lithostratigraphic boundary lies at the top the hammer handle. 154 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 figure 10. (a) picture of the moab member (mtmb; fa 5 and fa 7) at big pinto mesa, where a 50-m-thick section was measured through the eolian deposits of fa 7. it can be divided in five sequences (a-e). the mtmb crops out in sector 3 (see figure 3), and it overlies the earthy facies (fa 1b) in the western part of sector 3, whereas it rests directly on the slick rock member (fa 1a) towards the east. (b, c, d, and e) close-up photographs of the lowermost meters of fa 7, which conformably overlies water-carried sediments of fa 5. each eolian sequence is capped by a supersurface (ss). rhizoliths and their precipitation fronts (white arrows, and close-up d) can be present up to several decimeters below such a supersurface. they indicate that vegetation developed prior to the deposition of the following sequence. 155 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 flow deposits on the foresets of each dune. the westward-pinching geometry of fa 7 indicates that the main eolian depocenter was, at the time, located in the vicinity of big pinto mesa (figure 1). the extent of the moab member (fa 7) suggests that the paleo-erg covered an area of at least 1800 km2. however, this surface is certainly underestimated, due to the low preservation potential of eolian deposits (rodríguez‐lópez and others, 2014), as well as the limited area where the moab member has not yet been eroded. the vertical stacking architecture of fa 7 makes it no stranger to the kocurek (1988, 1999), kocurek and lancaster (1999), and mountney (2006) cyclic depositional pattern: (1) construction, (2) accumulation, and (3) preservation phases of eolian deposits. the occurrence of the basal facies q, u, and l implies a marine incursion within a coastal plain domain, during a period of optimal climatic conditions allowing the development of (superficial) paleosols. note that, when traced basinward, this basal tidally influenced marginal marine interval corresponds to the transgressive deposits of fa 5, which highlights the spatial extent of this major transgressive event, whereas the intervals characterized by facies u represent short-lived marine transgression as fa 6 was being deposited farther to the west. the transition from a “wet” environment to a dry phase of eolian accumulation is accompanied by the deposition of sand sheets (facies s) and small-scale eolian dunes (facies a). the onset of this shift results from an increased amount of loose sediment available for wind transport, as a consequence of a lowering of the saturated level within the sedimentary column (kocurek, 1988, 1999; kocurek and lancaster, 1999; mountney, 2012). the replacement of small-scale bedforms by large-scale eolian dunes represents the major phase of accumulation, also indicative of peak aridity and highest loose sediment budget. each eolian dune package (facies a) is capped by laterally extensive deflation surfaces, which are referred to as supersurfaces (brookfield, 1977; talbot, 1985; kocurek, 1988; havholm and kocurek, 1994), resulting from the cannibalization of the system down to the water saturated level, as the sand supply became exhausted. similar to mountney’s (2006) models from the permian cedar mesa sandstone, the observed supersurfaces are also characterized, at least locally, by “abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode” (mountney, 2006), and the potential development of superficial vegetation. the stacking of four to five of these eolian sequences suggests cyclic climatic alternations between humid and arid episodes (mountney 2006, 2012). the near absence of interdune deposits, and the wedge-symmetry of the succession, assign fa 7 to a dry temporally and spatially dynamic eolian system (kocurek and havholm, 1993; mountney, 2012). fa 8 – supratidal flat description fa 8 marks the stratigraphic top of this study and corresponds to the lowermost strata of the summerville formation, which is observed at each measured section (figure 9). fa 8 is characterized by a gradual yet shortlived transition from mostly greenish-colored tide-influenced strata (fa 6) into a succession dominated by dark-red laminated mudstone (facies v), paleosols (facies x), and evaporite-rich horizons. in the eastern part of the study area, fa 8 overlies fa 7, and the transition between the two units is abrupt, with no evidence of erosion. centimeterto decimeter-scale (cmto dm-scale), lightto dark-green-colored, ripple-laminated strata (facies u) and multi-dm-thick, trough cross-stratified sandstone beds (facies i) occur repeatedly in fa 8. facies u occurs ubiquitously within fa 8, whereas facies i has been documented only in the eastern part of the study area. both their number and thickness diminish up-section. episodic but rare interbedded, fluvial-dominated strata (facies w) occur within the succession. note that both facies u and facies w locally display desiccation cracks. interpretation fine-dominated grain size, fairly well-sorted, small sedimentary structures, architecture, dark-red colors and evaporites suggest a quiet and arid coastal environment, with episodic seasonal fluvial floods as well as periodic short-lived marine incursions, marked by the thin greenish-colored ripple-laminated and thicker 156 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 trough cross-stratified beds. the fact that marine floods diminish up-section indicates a basinward-prograding coastline during a phase of normal regression (hsst). discussion sector 1, sector 2, and sector 3 the study of these facies associations shows that the curtis formation, as defined by gilluly and reeside (1928) at their type section at curtis point (figure 1), can be divided in three lithostratigraphic sub-units easily identifiable in the field. these units are herein referred to as the lower, middle, and upper curtis (informal nomenclature). the lateral equivalent moab member was originally defined by wright and others (1962) as a member or a tongue of the entrada sandstone at the time. doelling (2001) officially reassigned these eolian deposits as a member of the curtis formation. the spatial distribution of these three sub-units shows that the curtis formation displays three different expressions of itself over the study area, which are herein delimitated as sectors 1, 2, and 3. the complete sub-unit trilogy of the curtis formation are only found in sector 1 (figure 3), which extends north of uneva mine canyon on the eastern limb of the san rafael swell monocline; however, the triptych character of the formation disappears south of last chance desert on the western margin of the san rafael swell (figures 1 and 3). sector 2 (figure 3) is dominated by the middle and upper curtis, with the notable following exceptions: (1) duma point, where only the middle curtis is exposed, (2) little flat top, where the middle curtis is absent, and (3) hanksville, where the three sedimentary sub-units crops out again (figure 1). on figure 3b, little flat top’s pie chart displays a particular pattern in the sense that it reflects the uncertain location of the formation boundary between the entrada sandstone and the fa 4a of the curtis formation. at that specific locality, three lithological candidate boundaries remain, hence influencing the resulting ratio between the different facies associations present in the curtis formation. sector 3 delineates the extent of the moab member of the curtis formation (figure 3). lower, middle, and upper curtis the lower curtis crops out in sector 1, as well as at little flat top and at hanksville in sector 2 (figures 1, 2, and 3). its base corresponds to the j-3 unconformity as defined by pipiringos and o’sullivan (1978). as shown in figures 4c and 4d, figures 5 and 6, as well as figures 8f and 8g, the unconformity is characterized by various types of relief formed by different processes, such as eolian deflation, and fluvial or tidal currents, which impacted the unconformity at various times. however, defining the base of the lower curtis by this polygenetic and composite surface notably implies that the basal flash-flood conglomerates at last chance desert (figure 1, facies f) also belong to the curtis formation, despite predating and being genetically unrelated to the formation. instead, if it is decided to define the base of the formation using the multi-faceted transgressive surface while regrouping genetically related shallow marine deposits only, then this basal conglomerate at last chance desert would become a-formational, as it would neither belong to the entrada sandstone nor the curtis formation. for lithostratigraphic convenience, it is suggested to use the highly diachronous j-3 unconformity of pipiringos and o’sullivan (1978) as the boundary for the lower curtis, and thus keep these basal conglomerate within this sub-unit. the lower curtis is dominated by fa 3a-b darkgreen to gray subtidal heterolithic strata, whereas fa 2 and fa 4 are present locally in the eastern part of sector 1, notably at neversweat wash, sven’s gulch, rabbit gulch, and interstate 70 (figures 1, 2, and 3). the ratio between the mud-dominated (fa 3a) and the sand-dominated heterolithic succession (fa 3b) varies spatially. the highest concentration of coarser-grained material, including conglomeratic beds, occurs in the western part of sector 1 at lower cedar mountain road and last chance desert, whereas, on the eastern margin of sector 1, sven’s gulch and rabbit gulch show similar enriched sand-to-mud ratios (figures 1, 2, and 3). the exact provenance of the different conglomeratic facies occurring in the curtis formation remains indeterminate. it is certain, however, that these extra-basinal lithoclasts are sourced from terrane(s?) exposed beyond the extent of the underlying strata of the entrada sand157 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 stone, due to the presence of metamorphosed polycrystalline quartz within these gravels and pebbles. skeletal carbonate fragments of unidentified bryozoan also exclude the entrada sandstone as a potential source for these conglomeratic beds, as opposed to the bulk of the curtis formation, which has a modal composition similar to the underlying entrada sandstone (dickinson and gehrels, 2009, 2010). despite the lack of provenance data, we suggest that these conglomerate beds represent reworked material, potentially from flash flood deposits, sourced from the uplifted highlands west of the study area (thorman, 2011; anderson, 2015) or from the nearby uncompahgre highlands to the east of moab (otto and picard, 1976; scott and others, 2001). the fact that most dune-forming and channel-filling conglomeratic facies are in the lowermost meters of the lower curtis suggests that, as the overall curtis transgression proceeded, their sediment supply was exhausted. it seems that another sediment entry point emerged in the south to southeast parts of the study area, draining a different basin, from which reworked material from the entrada sandstone could have been assimilated into the curtis formation. indeed, towards the south to southeast, fa 4a consists of relatively similar texture with respect to the underlying earthy facies of the entrada sandstone; it becomes increasingly dominant within the lower curtis, as the heterogeneity and complex architecture of fa 3 is replaced by the laterally extensive, light-pink beds of fa 4a. the fact that no bleached front along fractures has been observed in this unit suggests that, unlike bleached fractures and corridors in the carmel formation and in the entrada sandstone (ogata and others, 2014), no reducing fluids have circulated within these rocks (skurtveit and others, 2017; sundal and others, 2017; figures 4a and 7). the middle curtis consists exclusively of fa 5 deposits (figure 3), and its lower boundary corresponds to the mts, which can sometimes display an erosional relief of about 50 to 90 cm and is hence locally identified as a tidal ravinement surface. in sector 1, the middle curtis overlies the lower curtis in a possibly conformable to disconformable to angular way, whereas in sector 2 and 3, the mts merges with and partially reworks the j-3 unconformity (figure 8g). the angular unconformity between the lower and middle curtis, visible south of interstate 70 (figures 8f and 8g), suggests a sub-regional pre-middle curtis uplift in the area which may signal regional yet unidentified tectonic activity over the area during the late jurassic, prior to the deposition of the middle curtis. further, local to sub-regional dome features, ascribed to sandy substratum mobility related to fluid overpressure and seismic activity (jolly and lonergan, 2002; wheatley and others, 2016), are for instance visible 2.1 km north of hanksville airport, where the lower and middle curtis display a fault system driven by an underlying, circular sand pillow (figure 4f). just as for the j-3 unconformity, the terms unconformity and disconformity are to be taken with caution, as they imply, by definition, a significant time gap between the adjacent units (van wagoner and others, 1988; holbrook and bhattacharya, 2012), a temporal dimension, which, in the case of the curtis formation, cannot be assessed with great precision. the middle curtis pinches out southward in sector 2 whereas it thins towards the east in sector 3. due to the extreme low gradient present over the study area during the jurassic (and through the cretaceous) times (heller and others, 1986; fillmore, 1991; lockley, 1991; jones and blakey, 1993), it is suggested that the time encapsulated in this transgression was short. this major and rapid transgression potentially reached far beyond the study area. indeed, it may be linked to the deposition of the todilto formation and its calcareous saline sediments in southwestern colorado and northwestern new mexico (lucas and anderson, 1997), which were deposited after a blitz-flooding of the entrada sandstone by a marine incursion (benan and others, 2000). it is important to note that other regional marine embayments co-existed with the curtis sea in similar low-gradient conditions, such as the ralston creek lobe of anderson and lucas (1994) in southeastern colorado. thus, the todilto formation is likely related to the mts and to the base of the middle curtis, which implies that the paleo-erg of the entrada sandstone existed in new mexico until “instantaneous” transgression of benan and others (2000), whereas it was cannibalized by the lower curtis transgression in utah. the upper curtis mainly consists of fa 6 deposits, with mudand sand-dominated channel and tital-flat complexes. it has been recorded at each visited locality 158 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 in sectors 1 and 2, with the notable exception of duma point (figure 3). its lower boundary is gradational, as it conformably overlies the middle curtis. the main differences between the middle and upper curtis reside in the up-section’s increased heterogeneity, as well as a more pronounced green color, and the gradual replacement of the multi-m-thick bedforms by smaller scale sedimentary structures and thinner strata. it implies that the rate of accommodation decreased in the basin, whereas the sediment supply remained either constant, or potentially increased. the upper curtis corresponds to the laterally equivalent moab member, which crops out in sector 3. the moab member is characterized by the dominance of the eolian dunes of fa 7 arranged in four to five distinct sequences, representing at least 78% of the curtis formation in the eastern part of the study area. the remaining percentages are recorded as a thin basal middle curtis interval, whereas marine incursions (fa 6) or superficial paleosols and supratidal deposits (fa 7) separate the different eolian sequences (figure 10). note that the base of the summerville formation (fa 7), which stratigraphically overlies the curtis formation conformably in the study area despite their obvious lateral stratigraphic relationship on a more regional scale, suffers from the same gradual transition, from which no evident lithological boundary rises. it is therefore proposed to define the base of the summerville formation as the line where, over a meter of succession, more than 50% of the deposits belong to the supratidal fa 8. spatial distribution of the various facies associations: illustration by modern analogs no modern analogs exist to fully illustrate the overall curtis formation depositional evolution. nevertheless, as shown in figure 11, the inner gulf of california and the wadden sea are suggested to represent similarities to the aforementioned curtis formation subdivisions. such comparisons have limitations, and mainly regard spatial extent of modern environments in comparison with the size of their respective curtis formation counterparts, as well as basinal geometry approximations. the modern analogs are not meant to represent a similar tectonic setting to the curtis formation foreland basin conditions. the lower curtis is compared the fluvially starved, arid and unprotected tide-dominated bay of las lisas, mexico (figure 11) (utm coordinates: 12r 221191/3504767), on the northeastern margin of the gulf of california. the bay offers a window on a probable convoluted facies belt arrangement which occurred during one of the lower curtis short-lived regressive episodes. in the case of las lisas, such a regression is linked to rift flank uplift in the neogene (mark and others, 2014). as displayed on figure 11, the area close to the shoreline features sand-rich deposits similar to fa 4a interfingering with finer-grained, supratidal sediments of fa 8 and possibly conformably overlying pre-existing substratum (equivalent of fa 1a). farther into the basin, the heterolithic subtidal flat deposits of fa 3 are interfingering with gravel-bearing tidal channels (fa 4b) and migrating dunes (facies h). the middle curtis is paralleled with the dutch part of the shielded and tide-dominated shallow wadden sea (figure 11; utm coordinates: 31u 650032/5902807), where intricate and dynamic interplay of subto intertidal channels, tidal flats, and migrating tidal dunes and shoals (fa 5) has developed over an extensive and gently sloping area, behind barrier islands, as a result of a major and quick transgression (linked to holocene glacio-eustatic sea-level rise in the wadden sea (oost and de boer, 1994)). it is important to point out that similar well-defined barrier islands are not recognized in the middle curtis deposits (fa 5), although evidences for subaerial exposure episodes have been documented. the selected paragon for the upper curtis is the fluvially starved and arid, back-barrier bay of la pinta, located 75 km to the southeast of las lisas (figure 11) (utm coordinates: 12r 286227/3460602). here, the subto intertidal sediments (fa 6) deposited in this protected environment are being progressively overlain by supratidal deposits (fa 8), as the underfilled depocenter morphs into an overfilled basin. it is accompanied by a seaward migration of the coastline, leading to the potential development of an eolian dune system (fa 7) in the neighboring area as sediments become subsequently available for transport (carr-crabaugh and kocurek, 1998; mountney, 2012). 159 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 utm coordinates: 12r 221191/3504767 utm coordinates: 12r 286227/3460602 utm coordinates: 31u 650032/5902807 25 km 25 km n n lower curtis tr cycles middle curtis major transgression upper curtis normal regression a. modern analogs of the curtis formation las lisas, mexico b. modern analogs transposed to the curtis formation basinal setting wadden sea, the netherlands la pinta, mexico n 3 km si o s n 4 km si o s n 1km si o ssios satellite image orientation and scale n 25 km moab green river hanksville 100 km coloradoutah wyoming gr hk mb gj slc elko orogeny uncompahgre study area fa 8 supratidal �at fa 7 coastal dry eolian dunes, moab member fa 4a sand-rich subto supratidal �at fa 3b subtidal sand-dominated heterolithic �at fa 6 upper subto intertidal heterolithic �at fa 3a subtidal mud-dominated heterolithic �at fa 5 subto intertidal channel-dune �at complex fa 1b earthy facies fa 1a coastal dunes and slick rock member fa 2 upper shoreface to beach deposits fa 4b correlative tidal channel in�ll legend facies associations tectonic setting oxfordian slc salt lake city. gr green river. hk hanksville. mb moab. gj grand junction moab green river hanksville moab green river hanksville figure 11. (a) modern analogs of the lower, middle, and upper curtis formation, respectively. note that these pictures are not aligned to the true north, but are rotated in a way that allows them to fit the orientation of the curtis basin (satellite images from microsoft bing maps). (b) modern analogs draped with the corresponding facies associations from the curtis formation. the change of scale between a and b illustrates how much bigger the curtis basin setting is with respect to the three modern analogs. tr cycles – transgressive-regressive cycles. tectonic setting after heyman (1983) and thorman (2011). 160 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 conclusions 1. eight main facies associations (fa), including six sub-facies associations, were identified based on lithology, internal sedimentary structures, architectural arrangements, and spatial relationships. these facies associations are regarded as diagnostic expressions resulting from tidal processes in a fluvially starved, low-gradient, semi-enclosed epicontinental basin. 2. it is proposed to divide the curtis formation into three sub-units: the lower, middle, and upper curtis. the specific spatial distribution of these sub-units allows the distinction of three different sectors across the study area: sector 1 in the north, sector 2 in the south-southwest, and sector 3 in the east. 3. the lower curtis consists of laterally restricted upper shoreface to beach deposits (fa 2) overlain by a subtidal mud-dominated heterolithic succession (fa 3a), which grades into a sand-dominated subtidal flat (fa 3b). fa 3a and fa 3b interfinger with the more proximal and shallower fa 4a sand-rich subto supratidal flat, as well as with its more distal fa 4b correlative tidal channel infill. 4. fa 5, which corresponds to the middle curtis, is mainly composed of a characteristic light green to white, very fine to fine-grained sandstone, appearing as an intricate arrangement of tidal channels, dunes, and tidal flats. the base of the middle curtis coincides with the mts, which can be traced throughout the entire study area. 5. the upper curtis conformably overlies the middle curtis and is characterized by heterolithic subtidal to intertidal deposits of fa 6, as well as their lateral and contemporaneous continental eolian dunes of the moab member (fa 7). the transition from the upper curtis into the summerville formation is also gradual, with a progressively increasing occurrence of supra-tidal deposits (fa 8) within the succession. 6. the lower, middle, and upper curtis occur in sector 1, whereas only the middle and the upper curtis crop out in sector 2 (with local exceptions). sector 3 corresponds to the area where the moab member of the curtis formation was deposited. 7. it is possible to compare the lower curtis to the bay of las lisas in the gulf of california, the middle curtis to the wadden sea in the netherlands, and the upper curtis to the bay of la pinta in the gulf of california. 8. the todilto formation or todilto member of the wanakah formation, which crops out in southwestern colorado and northwestern new mexico, is likely related to the major transgression that defines the base of the middle curtis and is considered its lateral contemporaneous equivalent. hence, the upper wanakah formation is regarded as the lateral equivalent of the summerville formation. 9. the middle curtis overlies its substratum with an angular relationship on a sub-regional scale, suggesting an underlying and more regional deformational event during the late jurassic. further, with the occurrence of localto sub-regional collapse features within the lower and middle curtis, the late jurassic must been impacted by episode(s) of sand mobility, which influenced the local surface morphology. 10. the j-3 unconformity exposed a composite nature, as it was impacted by various processes occurring before the curtis formation was deposited, as well as during the development of the lower and middle curtis. acknowledgments the norwegian research council is to be sincerely acknowledged, with their awarded grant copass 244049, which funded the first author and allowed the ad hoc conduct of the required field campaigns for this research. the authors would like to extend their gratitude to dr. anja sundal, anna van yperen, nathan “the legend” cote, dr. miquel poyatos-moré, dr. mark mulrooney, ole rabbel, and kristine halvorsen for their assistance and helpful comments which elevated the standard of this work. acknowledgments are to be extended to grant c. willis of the utah geological survey (ugs) for his fruitful comments and review of an 161 new insights on the impact of tidal currents on a low-gradient, semi-enclosed, epicontinental basin—the curtis formation, east-central utah, usa zuchuat, v., sleveland, a.r.n., sprinkel, d.a., rimkus, a., braathen, a., and midtkandal, i. geology of the intermountain west 2018 volume 5 early version of this manuscript. the authors also thank kimm harty (ugs) for her careful review and editing. 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sevier and laramide belts within the north american cordillera orogenic system: earth-science reviews, v. 150, p. 531–593. source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 4 2017 © 2017 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah samuel m. hudson, trevor tuttle, and matthew wood geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover extensive folding of fractured carbonate and deformed shale beds in the onion creek diapir in the northern paradox basin near moab, utah. i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott ekeller@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017-2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committee uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 4 2017 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net editors geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 215 abstract the onion creek diapir is one of the best exposures of a dissected salt diapir in the world, offering a unique opportunity to better understand the internal character of heterolithic diapirs that are common in sedimentary basins worldwide. large amounts of interbedded shale, carbonate, and evaporites are incorporated into the diapir as stringers or boudins, and excellent three-dimensional exposure allows us to document the nature, size, deformation, and distribution of these stringers. blocks range in size from single, disaggregated layers of dolomite to several meters of coherent stringers that contain multiple cycles of dolomite-shale-evaporite and are upwards of 20 m thick and more than 100 m in observed length. the largest blocks are most commonly located along the margins of the exposed diapir, though stringers are common throughout the exposed caprock. in areas devoid of large stringers, there is more extensive deformation of the gypsum caprock, suggesting that the presence of stringers leads to a more heterolithic distribution of stress within the salt as it diapirically rises. these observations can help to better characterize similar diapirs elsewhere that are not well exposed at the surface. black shale is present in all observed large stringers of the onion creek diapir. these shale beds are interpreted to have been deposited in a shallow, restricted marginal marine environment along with the interbedded carbonate and evaporite strata. pyrolysis analysis of 13 samples from within the stringers shows a range of 2.56 to 60.22% total organic carbon (toc), with an average value of 16.93%. these strata contain type i/type ii hydrocarbon source facies, consistent with a restricted shallow marine environment. tmax data suggest that these source rock facies have been exposed to sufficient thermal energy to generate hydrocarbons (average = 437o c), as evidenced by common hydrocarbon staining of intra-stringer carbonate strata and evaporite beds surrounding the stringers. twelve additional samples were collected from these stained strata and pyrolysis analysis shows that all are enriched in free oil, as shown by elevated s1 peaks, high production index ratios, and toc values of 0.64 to 1.66%. this hydrocarbon staining is found around stringers near the center of the exposed caprock, as well as stringers along the margins. near the margins in particular, extensive alteration can be seen across tens of meters of evaporitic strata, showing that hydrocarbons are effectively generating within and migrating away from stringers fully encased in the anhydrite caprock of the onion creek diapir. this has important implications for potential seal integrity of diapiric caprocks, as well as providing a potential mechanism for caprock carbonate formation suggested by other researchers. source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah samuel m. hudson1, trevor tuttle1, and matthew wood2 1department of geological sciences, brigham young university, provo, ut 84602, usa; sam.hudson@byu.edu, trevortuttle15@icloud.com 2school of geology and geophysics, university of oklahoma, norman, ok 73019, usa; woodmatt52@gmail.com citation for this article. hudson, s.m., tuttle, t., and wood, m., 2017, source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah: geology of the intermountain west, v. 4, p. 215–229. © 2017 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. www.utahgeology.org 216 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 introduction salt diapirism is an important process in many of the world’s sedimentary basins, leading to complex syntectonic sedimentation patterns in surrounding salt withdrawal mini-basins. whereas much work has focused on the effects of salt on surrounding strata, less has been done to better understand the internal dynamics of diapiric bodies themselves. important exceptions to this are dominantly from studies of the zechstein salts of the netherlands and diapirs in the gulf of mexico, both of which commonly have large stringers, rafted blocks, or layered evaporites (williamson and others, 1997; callot and others, 2006; van gent and others, 2011; fiduk and rowan, 2012; li and others, 2012; strozyk and others, 2012; reiche and others, 2014; strozyk and others, 2014). the onion creek diapir, located near moab, utah (figure 1), offers a rare opportunity to study the detailed internal dynamics of a complex salt diapir in surface exposures. it is part of a series of northwest-southeast trending diapiric salt walls originating in the pennsylvanian paradox formation within the paradox basin. the onion creek diapir is part of the larger fisher valley salt wall, and is the only part exposed at the surface. the fisher valley salt wall is the most proximal salt wall to the uncompahgre uplift to the northeast (figure 1, trudgill and arbuckle, 2009), and diapirism was initiated by the deposition of the overlying permian cutler paradox basin uncompahgre uplift paradox salt walls la sal intrusives ut co az nm salt structures a cc cane creek cv castle valley da dolores fv fisher valley gv gypsum valley hc hamilton creek lv lisbon valley mv moab valley pv paradox valley sr sinbad sv salt valley moabcc sv cv da fv gv hclv mv pv sr onion creek diapir n 40 km200 ut co nmaz fi gu re 2 figure 1. regional map showing trends of major salt structures associated with the paradox basin and uncompahgre uplift, utah and colorado. the onion creek diapir (marked with a star) is associated with the fisher valley salt wall, located on the northern margin of the paradox basin. the location of figure 2 is shown by the black line running from fisher towers in the northeast to the needles district of canyonlands national park in the southwest. modified from rasmussen and rasmussen (2009). 217 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 formation, which was shed off from the nearby uplift (ohlen and mcintyre, 1965; doelling, 1988; barbeau, 2003; trudgill and others, 2004; kluth and duchene, 2009; trudgill, 2011; venus and others, 2015). the diapir exposes approximately 5 km2 of highly deformed paradox formation (mccalla, 2008). the paradox formation of the hermosa group was deposited in the paradox basin; a broad, shallow marine basin nearly surrounded by highlands (ohlen and mcintyre, 1965). open marine conditions were common, as evidenced by preserved limestone and shale beds (hite and buckner, 1981; handschy and dyer, 1987; blakey and knepp, 1989; dickinson and lawton, 2003). however, frequent eustatic sea level changes resulted in complex and cyclic depositional patterns (hite and buckner, 1981). this, combined with the semi-arid to arid climate (guthrie and bohacs, 2009), led to frequent basin restriction and deposition of appreciable amounts of evaporitic strata (baker and others, 1933; rasmussen and rasmussen, 2009). originally, there were 29 evaporite-carbonate cycles of interbedded shale, carbonate, and evaporites (halite, gypsum, anhydrite, and potash) identified within the paradox formation (figure 2) (hite 1960; hite and buckner, 1981; trudgill and arbuckle, 2009); however, as many as 80 stratigraphic sequences (cycles) are now identified (rasmussen and rasmussen, 2009). the exposed paradox formation at onion creek is dominated by gypsum with minor amounts of anhydrite, but interbedded shales and carbonates of the paradox are common within the caprock as well. these more competent layers of strata within the diapir (shale and carbonate) are from within the paradox formation and thus are identified as stringers. they are differentiated from rafted blocks, which are from older or younger formations that have been entrained into the salt during diapirism (talbot and jackson, 1987; reuning and others, 2009; fiduk and others, 2014). stringers within the onion creek diapir formed by the rupture and displacement of carbonateand shale-rich beds as the paradox formation was diapirically deformed by sub-regional sediment loading. these stringers are preserved as boudins within the caprock ranging in size and expression from large, competent blocks of strata greater than 100 m in observed length (and possibly longer – exposure is two-dimensional and may be oblique to the longest axis of these bodies), to concentrated layers of cobble-sized clasts of carbonate. stringers have been observed elsewhere in both outcrop (jackson and others, 1990) and the subsurface (talbot and jackson, 1987; warren, 2006; van gent and others, 2011; strozyk and others, 2012), and are a common phenomenon in salt bodies worldwide (fiduk and rowan, 2012; reiche and others, 2014). the excellent exposure of the onion creek diapir enables detailed description of the character, deformation, and distribution of these stringers within the exposed caprock. black shale beds of the paradox formation are enriched in preserved organic carbon, with previous studies reporting total organic carbon (toc) values as high as 20% from nearby wells (tischler, 1995; nuccio and condon, 1996; van buchem and others, 2000; guthrie and others, 2004; rasmussen and rasmussen, 2009). association of evaporites and black shale is common in both shelfal and intracratonic settings such as the paradox basin, the williston basin (north dakota), the eagle-gypsum basin (colorado), and the cretaceous strata along the gulf coast (krumbein, 1951; sloss, 1953; zharkov, 1983). the organic-rich shales of the paradox formation are incorporated into the stringers of the onion creek diapir, and hydrocarbon staining due to the migration of free oil is common within both the stringers and the evaporitic strata surrounding them. this observation has potentially important implications for seal integrity of caprock facies, as well as local implications for hydrocarbon generation and migration on a limited scale, and perhaps on the formation of caprock dolomite. methods five transects were described throughout the diapir, and thirteen sections were measured along these transects where stringers were identified (figure 3a). observations made along these transects include presence or absence of stringers, stringer size, lithologic composition, relative levels of deformation, and their location relative to the edge of the diapir. the location of each observation was recorded using a trimble differential gps unit, with sub-meter accuracy for all gathered 218 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 points. a basic geospatial model of surface observations was built using petrel software. two paradox formation carbonate samples were collected from within the largest two stringers and analyzed for mineralogical content using the bruker d2 phasor x-ray diffraction (xrd) instrument. samples were run for 25 minutes using a lynxeye silicon strip detector from 5 to 65° 2-theta at a step increment of 0.02°. a copper-sealed tube was used, and samples were front-loaded for analysis. quantification was done by rietveld analysis using the diffrac. topas software package. thirteen black shale samples were collected from within the stringers of the onion creek diapir, and 12 samples were taken from hypothesized hydrocarbon-stained strata from both the stringers and the gypsum caprock surrounding these stringers. in order to obtain total organic and carbonate carbon, as well as source type and relative maturity, these samples were analyzed by whole-rock pyrolysis and total organic carbon/carbonate carbon (toc+cc) techniques at brigham young university using the wildcat technologies hawk workstation. a standard pyrolysis+toc method was used, where the sample was heated from 300⁰ c to 850⁰ c at a rate of 25⁰ c/minute during the pyrolysis stage, and from 300⁰ c to 850⁰ c at a rate of 25 ⁰c/minute during the oxidation stage (espitalie and white rim sandstone u n in d if fe re n ti at ed c u tl er g ro u p paradox formationhermosa group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . moenkopi formation _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ shafer limestone honaker trail formation ismay zone desert creek zone akah zone barker creek zone alkali gulch zone honaker trail formation honaker trail formation honaker trail formation + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + paradox salt honaker trail formation organ rock formation cedar mesa sandstone lower cutler beds 289.9 ma 308 ma 270-280 ma pe rm ia n pe n n sy lv a n ia n tr ia ss ic pa ra do x f m he rm os a g ro up fisher towersneedles district northeastsouthwest figure 2. composite stratigraphic column of pennsylvanian and permian strata of the study area, near moab, utah. see figure 1 for column location. modified from hintze and kowallis (2009) and venus and others (2015). 219 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 others, 1977; peters and cassa, 1994). observations stringers were identified throughout the onion creek diapir from the margins to the center and high in the exposed caprock to the lowest observable point. the stringers observed in the diapir range from concentrated exposures of disarticulated cobble-sized clasts to relatively undeformed interbedded stringers with continuous bedding that are as much as 100 m long and greater than 20 m thick. six large, intact stringers were identified (figure 3b), with many smaller stringers of interbedded carbonate and black shale throughout the exposed caprock. stringers with intact bedding planes average between 2 to 3 m thick and 2 to 10 m long parallel to bedding. some of the stringers are highly folded (figure 4a) whereas others are relatively undeformed, with well-preserved parallel bedding planes (figure 4b). throughout the diapir and across the spectrum of stringer sizes, there is common preservation of cyclic packages of shale, carbonate, and gypsum. carbonate strata are the dominant facies represented in the stringers. the carbonate observed in outcrop is not limestone, as has been reported at depth (rasmussen and rasmussen, 2009), but is dolomitic limestone and dolomite (figsalt carbonate shale 1 2 3 4 5 6 transects edge of salt a b figure 3. aerial view of the onion creek diapir. (a) black lines show transects of the onion creek diapir that are a part of this study, and the approximate edge of salt is marked (pink dashed line) where it is in contact with younger strata of the dominantly the permian cutler formation. (b) pie charts represent locations of measured sections along transects, with the relative abundance of evaporite, carbonate, and shale shown. the six large stringers discussed later are marked 1 through 6, with stringer 6 being more interior to the diapir whereas 1 through 5 are at or near the margins of the diapir. 220 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 ure 5a). xrd analysis of two carbonate samples from different stringers show high dolomite content of 63% and 98%, respectively (figure 5b). the sample containing lower dolomite content (63%) also contains clastic material, with 26% orthoclase, 8% muscovite, and 3% quartz. these carbonates are often fractured, but primary bedding is discernable and sedimentary structures can be observed. in multiple stringers, microbial textures are observed, as shown in figure 5c. thirteen large stringers (greater than 10 m in length) were measured as part of this study (figure 3b). of these, six are larger than 50 m in length (figure 3b). five of the six largest stringers are located along the margins of the diapir, either at the edge of salt or very close to the contact. the only other stringer larger than 50 m in length is located in the southwestern interior of the diapir (figure 3b, section 6). stringers at or near the edge of the diapir show coherent bedding, and beds are steeply dipping and roughly aligned with the edge of the diapir, though internal folding is often prevalent in these stringers. the very large stringer in the interior of the diapir, in contrast, shows less deformation of beds and is near-horizontal in orientation. composition varies within the largest six stringers, with four being dominated by carbonate strata and two being dominated by black shale. in general, shale is better preserved in the largest stringers with smaller stringers being dominated by dolomite. though stringers of various sizes are common throughout the diapir, there are large sections of the ba gypsum deformed stringer vertical stringer figure 4. examples of stringers within the onion creek diapir showing: (a) extensive folding of fractured carbonates and deformed shales, and (b) a large carbonate-dominated stringer near the southwest margin of the diapir. gps antenna shown in the images is 2 m in height. 221 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 exposed caprock that are devoid of significant stringer material. in these areas, it is common to find highly banded and deformed gypsum (figure 6). these sections of gypsum can form resistant outcrops near the margins and within the interior of the exposed caprock. proximal to the stringers, in contrast, caprock gypsum is commonly more massive to weakly bedded. it is common to find hydrocarbon staining associated with the preserved paradox formation black shales in the onion creek diapir. staining is typically rusty brown to yellow to black and is found both within the stringers and surrounding gypsum caprock. in all large stringers observed, staining and the associated live oil is focused along fractures within dolomite beds, as well as within the surrounding deformed gypsum caprock (figure 7). in smaller stringers, staining of dolomite is common as well, though to a lesser extent. in contrast to the large stringers, staining in small stringers is commonly restricted to fractured dolomite, and does not stain the surrounding gypsum. whole-rock pyrolysis analysis was performed on the 12 samples collected from black shale within the large stringers of the onion creek diapir. pyrolysis was also performed on the 13 samples collected from stained carbonates within the stringers and stained caprock gypsum proximal to the stringers. all samples showed appreciable toc values, ranging from 0.64% to 60.22% (table 1). samples collected from paradox black shale within in the large stringers had consistently higher toc values, ranging from 2.56% to 60.22%, with a mean of 16.93%. samples collected from the stained beds are easily distinguished based on much lower toc values, with a range of 0.64% to 1.71% and a mean of 1.06%. additionally, the two sample sets can be differentiated by the proportionately higher s1 (free oil) signal in the stained beds (table 1). though the level of preserved organic carbon is lower within the samples of migrated material, the ratio of s1/(s1+ s2), otherwise known as the production index (pi), is much higher for these samples (figure 8). discussion stringer character and distribution we interpret the observed stringers within the onion creek diapir to be intact blocks of paradox formaa c b figure 5. carbonates within the onion creek diapir. (a) intensely folded bedding of paradox formation dolomite. although diagenetically altered, microbial textures are still preserved. (b) xrd analysis of paradox formation carbonate samples within the stringers show dolomitic composition, whereas the paradox carbonates are limestone at depth nearby, suggesting diagenetic alteration (rasmussen and rasmussen, 2009). (c) a thin section from within one of the large stringers shows preserved microbial texture of the dolomite. 222 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 tion strata that have moved as coherent bodies into the diapir. the interbedded nature of strata is interpreted to be the original depositional bedding of the paradox. cyclic packages of carbonate, shale, and gypsum are best observed in fresh washes cut into the side of the exposed caprock. in more weathered outcrops, carbonate facies are most easily observed, whereas the interbedded shale and gypsum can be less obvious due to their less resistant nature. although the carbonate strata observed within the exposed diapir are dominantly dolomite rather than the limestone observed at depth (rasmussen and rasmussen, 2009), the interbedded nature and preserved sedimentary structures within these carbonate rocks (figure 5) leads us to conclude that they are altered original paradox strata. the cause of this alteration to dolomite within the stringers is likely infusuion of meteoric waters due to uplift and exposure of the onion creek caprock. these interbedded stringer dolomites are different than the brecciated, structureless lateral caprock dolomite exposed infrequently around the margins of the diapir (figure 9). lateral caprock dolomite forms at depth in response to hydrocarbon presence and the associated sulfate-reducing bacteria (giles and others, 2012; jackson and lewis, 2012), and has been described along the flanks of the nearby castle valley salt wall (figure 1) by giles and others (2012). a 15-m-long, 1-m-thick lateral caprock dolomite is present along the northern margin of the onion creek diapir in direct contact with both the adjacent permian cutler strata and the diapiric salt. the absence of primary sedimentary structures or bedding, the high degree of brecciation, and the position along the edge of the diapir are all consistent with what is seen at the castle valley salt wall to the south, leading to clear differentiation between primary stringer dolomite and lateral caprock dolomite at the onion creek diapir. whereas large stringers were identified throughout the diapir, the largest and most continuous stringers are generally located near the margins. some of these stringers are as much as tens of meters of cohesive, relatively undeformed strata, and can be least 100 m long. the concentration of larger stringers along the margins of the diapir suggest that this part of the diapir may have experienced less extensive deformation as compared to the more highly deformed stringers observed in the interior parts of the diapir. additionally, the highly deformed, interior stringers appear to be aligned roughly with the edge of salt in many places. though many of the largest stringers are located at or near the margins of the diapir, one of the larger stringers observed was found approximately 500 m from the edge of the diapir along the southern transect (figure 3b, section 6). this stringer is a large (~95 m in observed length), laterally continuous stringer containing several cyclic packages. this exception points to the fact that stringers of significant size can be present within the interior of a diapir as well. future work at other diapirs is important to validate these trends. as previously mentioned, all stringers exhibit deformation; however, there is a wide range in the degree figure 6. large exposure of highly banded and deformed gypsum. this locality is far from any sizable stringers and is typical of the high level of deformation seen in areas devoid of stringers. gps pole in image is 2 m tall. 223 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 of deformation. the deformation correlates well with stringer size. the smallest identified stringers are discrete clusters of aligned, fist-sized fragments of dolomite. these are common and present throughout the diapir. in contrast, only modest amounts of brittle deformation are seen in the core of larger stringers, with deformation becoming more evident towards the edges. there is a spectrum of intermediate deformation between these two end members, and smaller coherent stringers transitioning laterally into shattered stringers are common in the more central parts of the diapir. regardless of stringer size, fracturing and destruction of bedding increases towards the edges of all observed stringers. this is consistent with the interpretation that these are boudins of strata that have been stretched and deformed as entrained blocks during diapiric deformation of paradox strata (jackson and others, 1990; warren, 2006; strozyk and others, 2012). lastly, although stringers were identified throughout the diapir, there are large areas within the diapir where stringers are absent. these areas are dominated by banded, highly deformed gypsum that is very different than the often massive, structureless gypsum seen in proximity to the stringers (figure 6). the increased deformation in gypsum-dominated sections suggests that there is heterogeneity of strain within the diapir, driven by the heterogeneity of the lithologies moving upwards during diapirism. this may indicate that the stringers provide added rigidity to the diapir as it rises and may even, to a degree, reduce internal deformation during diapiric rise. further work, both observational and experimental, can be done to test this hypothesis, which may add to our understanding of the more detailed processes that occur within deforming salt bodies. a b figure 7. (a) black to yellow staining associated with migrated hydrocarbons within fractured carbonates of a large stringer near the margin of the onion creek diapir (stringer 3), and (b) black to rusty staining resulting from migrated hydrocarbons within the evaporites surrounding a boudin block of dolomite near stringer 2. see figure 3b for stringer locations. 224 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 hydrocarbon generation and migration within the diapir and implications the black shale beds of the paradox formation are extremely enriched in organic carbon, as evidenced by high toc values from samples within the stringers that average nearly 17%. high hydrogen index (hi) values are consistent with the restricted marine depositional environment invoked for the paradox formation, with marine microbial preserved organic types (type i and type ii kerogens) seen in the sample suite (figure 8). tmax data, while not as accurate as vitrinite reflectance or other thermal indicators, suggest that samples taken from the diapir are within the early oil window, with most values between 435 and 460 o c (tissot and others, 1987). all samples collected from black shale beds within the stringers are interpreted to be from the akah or barker creek zones of the paradox formation (rasmussen and rasmussen, 2009), emplaced as part of the onion creek diapir during initial diapiric rise. this is consistent with data from subsurface wells and outcrop from within the paradox formation. toc values of type ii marine source rock facies that are consistently above 1%, and occasionally as much as 20%, have been reported at multiple levels and multiple locations at depth within the basin (tischler, 1995; nuccio and condon, 1996; van buchem and others, 2000; guthrie and bohacs, 2009; rasmussen and rasmussen, 2009). based on the similarity of organofacies, the characteristics of these strata have not significantly changed as the result of stringer emplacement; the black shale within the stringers of the onion creek diapir are classified as excellent marine source rock facies capable of generating hydrocarbons in the past. within the fractures of all large and many smaller stringers, hydrocarbon staining is interpreted to be evsample id toc-total organic carbon (weight %) s1 free oil (mghc/g rock) s2 kerogen yield (mghc/g rock) s3 (mgco2/g) tmax-maturity (°c) cc-carbonate carbon (weight %) goc-generative organic carbon (weight %) ngoc-nongenerative organic carbon (weight %) pi-production index (s1/s1+s2) hi-hydrogen index (mghc/gtoc) oi-oxygen index (mgco2/gtoc) primary shale samples t 4.13 20.26 7.78 125.83 0.45 439 0.63 11.38 8.88 0.06 621 2 t4 s13 c 20.23 6.36 94.90 2.37 435 0.70 8.75 11.48 0.06 469 11 t4 s13 b 19.44 6.92 103.85 1.48 435 0.31 9.48 9.95 0.06 534 7 t4 s13 a 20.32 7.67 122.10 0.71 440 0.19 11.07 9.25 0.06 600 3 t 4.12 10.92 2.81 50.70 0.77 433 0.15 4.58 6.34 0.05 464 7 t 4.7 60.22 17.99 356.31 4.56 437 0.37 32.00 28.22 0.05 591 7 t4.11 2.56 0.33 10.47 0.28 435 12.04 0.93 1.63 0.03 409 11 t 1.2 16.99 2.75 107.39 0.79 438 0.22 9.41 7.59 0.03 632 4 t 4.3 7.25 0.73 45.25 0.25 431 5.64 3.92 3.33 0.02 624 3 t 4.14 18.01 2.80 127.40 0.73 439 0.45 11.09 6.92 0.02 707 4 t 1.1 8.00 0.31 28.09 1.25 439 0.33 2.46 5.53 0.01 351 15 t 4.5 6.14 0.25 20.51 0.61 437 1.80 1.79 4.36 0.01 333 9 t 4.6 9.80 0.38 55.49 0.37 437 2.83 4.77 5.03 0.00 566 3 secondary hydrocarbon stained samples 03 sc 15 1.23 0.12 0.40 0.17 374 17.85 0.05 1.17 0.24 32 14 t 1.7 0.64 0.17 0.55 0.20 446 0.20 0.07 0.57 0.23 85 31 t 1.9 1.71 0.10 0.37 0.30 428 2.45 0.05 1.66 0.21 21 17 t 2.1 0.66 0.08 0.34 0.19 439 0.23 0.04 0.62 0.19 51 28 t 1.8 1.12 0.10 0.43 0.13 426 0.36 0.06 1.06 0.19 38 11 t 4.2 1.66 0.09 0.42 0.37 449 0.67 0.06 1.60 0.17 25 22 t 4.1 1.15 0.07 0.35 0.29 442 7.35 0.05 1.10 0.17 30 25 t 1.5 0.65 0.14 0.77 0.25 441 0.26 0.09 0.56 0.16 118 38 t 1.6 0.65 0.11 0.60 0.24 441 0.44 0.07 0.57 0.15 93 37 t 1.10 0.72 0.08 0.50 0.26 453 18.30 0.06 0.66 0.13 70 36 t 1.3 1.59 0.17 1.58 0.30 438 3.47 0.16 1.43 0.10 99 18 t 1.12 0.94 0.08 1.21 0.33 460 0.75 0.13 0.82 0.06 128 35 table 1. whole-rock pyrolysis data for 25 samples collected from the onion creek diapir. thirteen samples were taken from shales within the stringers (primary shale samples), whereas 12 samples were taken from altered carbonates and evaporites (secondary hydrocarbon-stained samples). 225 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 idence of migrated hydrocarbons. this staining is also prevalent in the gypsum caprock surrounding many stringers, including all large stringers. staining is black to rusty colored to yellow colored along the fractures of dolomite stringers and within the groundmass of the gypsum caprock (figure 7). hydrocarbon staining of strata within the onion creek diapir is similar in appearance to other instances of hydrocarbon migration associated with salt diapirs, such as documented within and proximal to the la popa diapir in mexico (hudson and hanson, 2010). toc values from these stained samples are much lower than values reported from primary black shale within the stringers (table 1), but values are above 0.5%, which is still considered significant source rock potential (peters and cassa, 1994), confirming that there are hydrocarbons present. production index (pi) values (ratio of free oil to total hydrocarbons) in the stained samples are elevated in comparison with the primary black shales. this can be the result of two things: (1) higher relative thermal maturation (the most common use of this indicator), or (2) the presence of migrated hydrocarbons (tissot and welte, 1984; peters and cassa, 1994). both interpretations are based on the assumption that primary kerogens have cracked and organic carbon is increasingly being stored in pore space. tmax results from both the primary shale samples and the stained samples suggest that all samples have experienced a similar thermal history and are within the ear0 100 200 300 400 500 600 700 800 900 1000 0 50 100 150 200 h yd r o g en i n d ex (h i, m g h c /g t o c ) oxygen index (oi, mg co2/g toc) type i oil prone type ii (usu. marine) oil prone m ixed type ii / iii oil / gas prone type iii gas prone type iv gas prone figure 8. modified van krevelen diagram (van krevelen, 1950), showing a clear division between primary black shale samples collected from within the stringers of the onion creek diapir (green squares) and samples collected from the fractured dolomite stringers and the surrounding evaporite caprock (red diamonds). samples from stringers of paradox black shale are classified as type i/type ii source rock facies, whereas migrated hydrocarbon samples are classified as a type iii/type iv source rock facies. the low hydrogen index (hi) values for the migrated hydrocarbon samples are not indicative of a terrestrial-rich organic source, as might be the case for a primary source rock, but rather the lean hi is the result of thermal cracking of kerogens, as shown by the high production index (pi) ratio (table 1). figure 9. one of several examples of lateral cap rock dolomite observed on the northern side of the onion creek diapir. it is characterized by a highly brecciated texture that is in contrast with dolomitic textures that are common within the stringers, such as shown in figure 5. 226 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 ly oil window. given the observed field relationships of these samples and the primary paradox shale they are associated with, we believe that local migration of hydrocarbons from within the black shale beds of large stringers is occurring within the onion creek diapir. this is further supported by depletion of hi within secondary stained samples in comparison to primary black shale samples (figure 8). evidence that hydrocarbons can be generated locally in quantities sufficient for expulsion and migration has several important implications for exploration around salt bodies. around other similar salt diapirs, which incorporate organic-rich strata as stringers or rafted blocks, there is a possibility for false indicators of significant hydrocarbon accumulations. this could be as simple as hydrocarbon shows within a juxtaposed reservoir; while these stringers are generating enough free oil for migration to occur, there is insufficient material within even the largest stringers to form an economic accumulation. less obviously, we propose that local generation of hydrocarbons from stringers within the caprock of a diapir could lead to local precipitation of caprock dolomite. work by giles and others (2012) suggests that the presence of anaerobic sulfate-reducing bacteria, commonly associated with hydrocarbons, is necessary for the precipitation of a carbonate caprock, thus implying that the presence carbonates is an indicator of a working petroleum system. if local generation and migration of hydrocarbons occurred in association with stringers along the margin of a diapir, it is possible that this could lead to the precipitation of a carbonate caprock in the absence of a large-scale working petroleum system. thus, the presence of a carbonate caprock alone could lead to a false characterization of the basin source rock potential or the migration pathways of hydrocarbons within a productive basin if the carbonate caprock formed from local generation and migration rather than regional thermal maturation of a source rock interval. lastly, the observation that hydrocarbons are freely migrating through gypsum caprock, similar to what was documented at the la popa diapir, mexico, (hudson and hanson, 2010), has important implications for the sealing capacity of diapiric caprock, regardless of the inclusion of stringers. salt is commonly considered to be a near-perfect seal, but evidence is increasingly showing that within the altered caprock of a diapir, the more brittle nature of the salt can lead to banding, fracturing, and potential migration pathways, as seen in the onion creek diapir. we interpret hydrocarbon migration within the onion creek caprock to happen only at a local scale, but these observations show that vertical migration within diapiric caprock should be considered as a risk in other basins where large quantities of hydrocarbon are being generated at depth, and salt is often called upon to be a lateral and/or vertical seal. conclusions cyclic packages of carbonate, shale, and salt are commonly found throughout the onion creek diapir. these packages preserve, even after deformation and emplacement into a salt diapir, the original interbedded nature of the paradox formation. this suggests that although diapirism is an intense deformational process, more coherent stratal packages can maintain structural integrity in the form of boudins. banded, highly-deformed gypsum in areas without notable stringers may help to explain the relatively undeformed nature of the large stringers, suggesting that strain is differentially partitioned into less competent evaporite-rich layers. these observations suggest that the internal mechanics of diapirs are perhaps less chaotic than is often assumed, in particular, where interbedded non-evaporitic strata are present. spatially, there are trends within the onion creek diapir that are significant. larger, less deformed stringers are more common near the margin of the diapir. this implies that either: (1) there was more interbedded material originally in this part of the strata, which is assumed to be the youngest, stratigraphically highest paradox strata exposed, or (2) that rigid, interbedded strata was concentrated near the margins during the process of diapiric rise and caprock formation. both hypotheses have different implications for diapiric mechanics, with the latter suggesting a more chaotic diapiric process and the former suggesting a more layered, organized model. the onion creek diapir presents an excellent, accessible exposure of a heterolithic diapiric salt body that can serve as an analog for subsurface heterolithic salt bodies elsewhere. whereas seismic 227 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 data is capable of imaging large stringers in the subsurface, outcrop observations offer important details at the sub-seismic scale. the frequency of both large and small stringers observed throughout the onion creek diapir suggests that stringers should be expected to be present throughout similar salt bodies, even when not detected by geophysical methods. whereas larger stringers may be more commonly encountered along the margins, significant intervals of non-evaporitic strata are common regardless of relative location within the diapir. in addition to adding to our understanding of the distribution and character of stringers in diapirs, the inclusion of organic-rich strata in the stringers of the onion creek diapir gives us important insight into hydrocarbon resource evaluation. diapiric salt is considered a near-perfect, impermeable seal; however, within the caprock strata of the onion creek diapir, migration of hydrocarbons is associated with every large and many of the smaller stringers of organic-rich shale studied, as evidenced by the presence of hydrocarbon-stained strata within and surrounding the stringers. this has important implications for similar, “dirty salt” diapirs in the gulf of mexico and elsewhere. beyond this, the prevalence of hydrocarbons within the caprock of the onion creek diapir suggests that fluid migration through caprock should be a consideration in all diapiric systems, whether stringers are present or not. acknowledgments the authors would like to acknowledge kate giles (university of texas el paso), mark rowan (rowan consulting), richard langford (university of texas el paso), thomas hearon (eog resources), and carl fiduk (fiduk consulting) for discussion that helped to improve this manuscript. involvement with the institute of tectonic studies at university of texas el paso and the opportunity to discuss this work with both the researchers and sponsors of this consortium was invaluable. comments and suggestions from frank strozyk (aachen university) on an earlier draft of this work were very much appreciated as well. additional 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and implications for salt tectonic evolution: interpretation, v. 2, no. 4, p. 1–17. strozyk f., van gent, h., urai, j.l., and kukla, p.a., 2012, 3d seismic study of complex intrasalt deformation—an example from the upper permian zechstein 3 stringer, western dutch offshore: london, geological society special publications 363, p. 489–501. talbot, c.j., and jackson, m.p.a., 1987, internal kinematics of salt diapirs: american association of petroleum geologists bulletin, v. 71, no. 9, p.1068–1093. tischler, k.l., 1995, paradox basin source rock, southeastern utah—organic geochemical characterization of gothic and chimney rock units, ismay and desert creek zones, within a sequence stratigraphic framework: austin, university of tex229 source within the seal—distribution and implications of organic shale-bearing stringers within the onion creek diapir, northern paradox basin, utah hudson, s.m., tuttle, t., and wood, m. geology of the intermountain west 2017 volume 4 as, m.s. thesis, 123 p., 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usa, in post, p.j., editor, salt–sediment interactions and hydrocarbon prospectivity— concepts, applications and case studies for the 21st century: gulf coast society of economic paleontologists and mineralogists foundation, 24th bob f. perkins research conference proceedings, p. 669–700. van buchem, f.s.p., houzay, j., and peniguel, g., 2000, variation in distribution and quality of organic matter in pennsylvanian source rock levels of the paradox basin (utah, usa), in homewood, p.w., and eberli, g.p., editors, genetic stratigraphy on the exploration and production scales—case studies from the pennsylvanian of the paradox basin and the upper devonian of alberta: elf aquitaine memoir 24, p. 29–69. van gent, h., urai, j.l., and keijzer, m., 2011, the internal geometry of salt structures—a first look using 3d seismic data from the zechstein of the netherlands: journal of structural geology, v. 33, p. 292–311. van krevelen, d.w., 1950, graphical-statistical method for the study of structure and reaction processes of coal: fuel, v. 29, p. 269-284. venus, j.h., mountney, n.p., and mccaffrey, w.d., 2015, syn-sedimentary salt diapirism as a control on fluvial-system evolution—an example from the proximal permian cutler group, se utah, usa: basin research, v. 27, no. 2, p. 152–182, doi: 10.1111/bre.12066. warren, j.k., 2006, evaporites—sediments, resources, and hydrocarbons, 2nd edition: berlin, springer verlag, 1035 p. williamson, m.d., murray, s.j., hamilton, t.a.p., and copland, m.a., 1997, a review of zechstein drilling issues: society of petroleum engineers onepetro, spe-38483-ms, 8 p., doi:10.2118/38483-ms. zharkov, m.a., 1983, classification of salt-bearing associations according to material composition and patterns of spatial position: international geology review, v. 25, no. 2, p. 151–164. paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 © 2017 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah paul c. murphey, k.e. beth townsend, anthony r. friscia, james westgate, emmett evanoff, and gregg f. gunnell a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa post-meeting field trip october 30–november 1, 2016 geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover view of the bridger d and e on “old hat mountain,” a prominent butte on the southeast flank of hickey mountain, in the bridger basin sector of the green river basin, uinta county, wyoming. photo taken looking southwest. i 2016 president bill loughlin bill@loughlinwater.com 435.649.4005 2016 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2016 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2016 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2016 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2016 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2016-2018 term craig morgan craigmorgan@utah.gov 801.422.3761 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 4 2017 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 1 “a large part of the collection in this region was of the remains of small animals. the fossils were generally found in the buttes, and on account of their minuteness, their discovery was attended with much difficulty. instead of riding along on the sure-footed mule and looking for a gigantic tell-tale vertebra or ribs, it was necessary to literally crawl over the country on hands and knees…often a quarter of a mile of the most inviting country would be carefully gone over with no result, and then again someone would chance upon a butte which seemed almost made of fossils.” a description of fossil collecting in the bridger formation written by an unnamed member of the 1871 yale college expedition, led by paleontologist o.c. marsh. abstract the bridger formation is restricted to the green river basin in southwest wyoming, and the uinta and duchesne river formations are located in the uinta basin in utah. these three rock units and their diverse fossil assemblages are of great scientific importance and historic interest to vertebrate paleontologists. notably, they are also the stratotypes from oldest to youngest for the three middle eocene north american land mammal ages—the bridgerian, uintan, and duchesnean. the fossils and sediments of these formations provide a critically important record of biotic, environmental, and climatic history spanning approximately 10 million years (49 to 39 ma). this article provides a detailed field excursion through portions of the green river and uinta basins that focuses on locations of geologic, paleontologic, and historical interest. in support of the field excursion, we also provide a review of current knowledge of these formations with emphasis on lithostratigraphy, biochronology, depositional, and paleoenvironmental history, and the history of scientific exploration. paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah* paul c. murphey1, k.e. beth townsend2, anthony r. friscia3, james westgate4, emmett evanoff5, and gregg f. gunnell6 1department of paleontology, san diego natural history museum, 1788 el prado, balboa park, san diego, ca 92101, usa; pmurphey@sdnhm.org 2arizona college of osteopathic medicine, midwestern university, 19555 n. 59th avenue, glendale, az, 85308, usa; btowns@midwestern.edu 3department of integrative biology and physiology, university of california, los angeles, 621 charles e. young dr. so., los angeles, ca 90095-1606, usa; tonyf@ucla.edu 4department of earth & space sciences, lamar university, beaumont, tx 77710, usa; james.westgate@lamar.edu 5department of earth sciences, university of northern colorado, greeley, co 80639, usa; emmett.evanoff@unco.edu 6division of fossil primates, duke lemur center, durham, nc 27705, usa; gregg.gunnell@duke.edu *this field guide is an updated version from murphey and others (2011). we thank the geological society of america for its kind use. murphey, p.c., townsend, k.e.b., friscia, a.r., and evanoff, e., 2011, paleontology and stratigraphy of middle eocene rock units in the bridger and uinta basins, wyoming and utah, in lee, j., and evans, j.p., editors, geologic field trips to the basin and range, rocky mountains, snake river plain, and terranes of the u.s. cordillera: geological society of america field guide 21, p. 125–166. citation for this article. murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f., 2017, paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah: geology of the intermountain west, v. 3, p. 1–53. © 2017 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. www.utahgeology.org 2 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 introduction and structural setting situated to the north and south of the uinta mountains in wyoming and utah, respectively, the green river and uinta basins have great scientific importance and are of historic interest to vertebrate paleontologists. the rock units and fossils of the bridger basin (an informal subarea of the southern green river basin) and the uinta basin have been the focus of paleontological investigations for the last 140 years. perhaps the most familiar of the rock units within the green river and uinta basins is the green river formation because of its economic importance and exquisitely preserved vertebrate, invertebrate, and plant fossils. however, despite the geological and paleontological importance of this world renowned lacustrine rock unit, this field excursion focuses on three closely related, stratigraphically adjacent and overlying fluvial rock units that are best known for their assemblages of middle eocene vertebrate fossils. the bridger, uinta, and duchesne river formations are the stratotypes for the bridgerian, uintan, and duchesnean north american land mammal ages (nalma) (wood and others, 1941; gunnell and others, 2009). the fossils and sediments of these formations provide a critically important record of biotic, environmental, and climatic history spanning approximately 10 million years (49 to 39 ma). the greater green river basin occupies 32,187 km2 (12,430 mi2) of southwestern wyoming and northwestern colorado (roehler, 1992a). structurally, it is a large asymmetrical syncline with an approximately northsouth axis and with mostly gently dipping flanks (3° to 5°) having steeper dips along the southern margin of the basin (koenig, 1960; roehler, 1992a). the greater green river basin is divided into four smaller basins by three intrabasin arches (figure 1). the largest of these arches, the north-south trending rock springs uplift, divides the basin into roughly equal halves, with the green river basin to the west, and the great divide, sand wash, and washakie basins to the east. the term bridger basin used and shown by hayden (1871), matthew (1909), osborn (1929), and bradley (1961) generally refers to the outcrop extent of the bridger formation in the western part of the greater green river basin, which nearly coincides with the green river basin on figure 1. the uinta basin occupies 10,943 km2 (4225 mi2) of northeastern utah. structurally, it is an asymmetrical, elongate, east-west trending synclinal basin bounded by the uinta mountains to the north, the douglas creek arch and roan plateau to the east, the book cliffs/tavaputs plateau to the south, and the wasatch range to the west (figure 2). it was formed in the latest cretaceous and paleocene during the laramide uplift of the uinta mountains. the uinta basin is closely related structurally and sedimentologically to the piceance creek basin in northwestern colorado. the uinta and piceance creek basins are separated by the douglas creek arch, a broad north-south trending anticline that separated the two sedimentary basins until the early-middle eocene, when the two basins coalesced across the top of the arch to form one large sedimentary basin (moncure and surdam, 1980; johnson, 1985, 1989). like the uinta basin, the piceance creek basin is highly asymmetrical (johnson, 1985). early cenozoic strata in the uinta basin dip gently from all directions to the northern margin of the basin, where the strata are sharply upturned and faulted along the southern flank of the uinta mountains uplift (johnson, 1985). the greater green river, uinta, and piceance creek basins began forming during the laramide orogeny, a period of tectonism in western north america that was initiated during the late cretaceous and continued for approximately 30 million years until the latest eocene. in addition to the uplifting of surrounding mountain ranges, laramide tectonism resulted in rapid subsidence in basin depositional centers, and lacustrine and fluvial deposition in these intermontane basins was mostly continuous. lacustrine deposition was characterized by a complex history of expansions and contractions in response to basin subsidence, climatic conditions, and volcanic activity (roehler, 1992b; murphey, 2001; murphey and evanoff, 2007). part i. southern green river basin field trip with its abundant and diverse vertebrate fossils and extensive exposures, the bridger formation provides 3 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 an excellent opportunity to study middle eocene continental environments of north america. the dramatic and picturesque bridger badlands are an 842 m (2763 ft) thick sequence dominated by green-brown and red mudstone and claystone, with interbedded scattered ribbon and sheet sandstone, widespread beds of micritic, sparry, and silicified limestone, and thin but widespread beds of ash-fall tuff (evanoff and others, 1998; murphey and evanoff, 2007). this field trip offers participants the opportunity to examine paleontologically significant strata of the bridger formation in the southern green river basin. the following sections of the field trip guide provide a summary of the cenozoic geologic history of the green river basin, as well as the history of investigations, stratigraphy, depositional and paleoenvironmental history, and fossils of the bridger formation. this is followed by a detailed road log. paleogene geologic history of the green river basin, wyoming the greater green river basin was filled with paleocene and eocene fluvial and lacustrine sediments, and, during the eocene, sedimentation appears to have been continuous in most of the basin. the oldest cefigure 1. index map of the greater green river basin showing major structural features and surrounding uplifts. numbered yellow stars are the approximate location of the field trip stops in the type area of the bridger formation (modified from murphey and evanoff, 2007). 4 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 nozoic rock units in the greater green river basin, the paleocene fort union formation and the early eocene wasatch formation, are exposed mostly along its eastern and western flanks. during the paleocene and earliest eocene, deposition in the greater green river basin was predominantly fluvial, with epiclastic sediments accumulating in river drainages and on adjacent floodplains. the onset of lacustrine deposition associated with the green river lake system may have commenced as early as the late paleocene (grande and buchheim, 1994). lake sediments accumulated on broad floodplains of low topographic relief, and the lake waters expanded and contracted numerous times over the next approximately 5 million years in response to climatic changes, tectonic influences, and episodic volcanic activity. occupying the center of the basin in the shape of a large, irregular lens (bradley, 1964; roehler, 1992b, 1993), the green river formation is the result of at least 5 million years of lacustrine deposition lasting from about 53.5 to 48.5 ma (smith, 2003), although lacustrine deposition may have persisted later in the southernmost part of the basin along the uinta mountain front (murphey and evanoff, 2007). the green river formation was deposited in a vast ancient lake system that existed from the late paleocene to the middle eocene in what is figure 2. index map on right showing adjacent structural and physiographic features. the gray region represents the areal extent of tertiary deposits in both the uinta basin, utah, and piceance creek basin (not labeled), western colorado. the douglas creek arch separates the two basins. map on left (location indicated by red box on map to the right) showing approximatel location of the field trip stops (numbered green stars); u-numbered stars are uinta formation stops and d-numbered stars are duchesne river formation stops. 5 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 now colorado, utah, and wyoming. the smallest and oldest of these lakes, fossil lake, was deposited in fossil basin, which is located in the wyoming thrust belt just to the west of the green river basin in southwestern wyoming. lake gosiute was deposited in the greater green river basin, which includes the green river and washakie basins in southwestern wyoming, and the sand wash basin in northwestern colorado. fossil lake and lake gosiute may never have been physically connected (surdam and stanley, 1980). lake uinta was deposited in the uinta basin in northeastern utah and the piceance creek basin in northwestern colorado. lithologically, the green river formation in the greater green river basin is a complex sequence of limestone, shale, and sandstone beds with a maximum thickness of approximately 838 m (2750 ft) (roehler, 1993). it was deposited lateral to and above the predominantly fluvial wasatch formation, and lateral to and below the fluvial and lacustrine bridger and washakie formations. the laney member is the uppermost member of the green river formation in wyoming and represents the final expansion of lake gosiute. most volcaniclastic sediments deposited in the green river basin during the middle eocene were apparently transported from the absaroka volcanic field in what is now northwestern wyoming. these sediments were washed into the basin in rivers and streams. some volcaniclastic sediments were transported into the basin via eolian processes and deposited as ash fall in lakes and on floodplains. a large influx of fluvially transported volcaniclastic sediment is believed to have led to the final middle eocene filling of lake gosiute (mauger, 1977; surdam and stanley, 1979; murphey, 2001; murphey and evanoff, 2007). mauger (1977) and surdam and stanley (1979) estimated that lake gosiute was ultimately extinguished by about 44 ma. the bridger, green river, and washakie formations are locally and unconformably overlain by the oligocene bishop conglomerate and the middle-to-late– miocene browns park formation. since the eocene, the greater green river basin has been modified by erosion, regional uplift, and normal faulting, but the basic structure of the basin remains the same as it was during deposition of the wasatch, green river, washakie, and bridger formations. middle eocene paleoenvironments of the green river basin numerous studies based on paleontological and geological evidence have concluded that the eocene-age rock units in the greater green river basin were deposited in warm temperate, subtropical, and tropical climatic conditions (roehler, 1993). perhaps the most reliable information concerning paleoclimates comes from analysis of plant megaand micro-fossils. according to leopold and macginitie (1972), early eocene floras (based on palynology of samples collected from the niland tongue of the wasatch formation and the luman and tipton tongues of the green river formation) suggest a humid subtropical to warm temperate climate having summer rainfall and only mild frost and with a mean annual temperature of 55°f. nichols (1987) concluded that the climate of the basin floor during deposition of the niland tongue was subtropical, without freezing temperatures. the earliest middle eocene climates pertaining to the cathedral bluffs tongue of the wasatch formation and the wilkins peak member of the green river formation were interpreted as generally hot and dry (leopold and macginitie, 1972). climatic conditions in the early-middle eocene during deposition of the lower part of the laney member of the green river formation were characterized as warm and humid with tropical affinities. floras of the upper part of the laney member indicate a change to cooler, subhumid conditions (leopold and macginitie, 1972). both pollen and leaf data from the washakie formation indicate a dry but temperate climate (leopold and macginitie, 1972). roehler (1993) reported in a written communication that macginitie reinterpreted temperature and precipitation ranges on the basis of palynology of samples collected from the washakie basin by roehler (1992a). this reinterpretation estimated mean annual temperatures of 18°c (65°f) during the early eocene, 17°c (63°f) during the earliest middle eocene, and 16°c (62°f) during the middle eocene. average annual precipitation was estimated at more than 100 cm (40 in) during the early eocene, 65 to 90 cm (25–35 in) during the earliest middle eocene, and 38 to 50 cm (15–20 in) in the middle eocene. sedimentological evidence of a 6 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 more arid climate during the middle eocene (transitional uintan nalma) includes massive beds of gypsum capping the turtle bluff member of the bridger formation (murphey, 2001; murphey and evanoff, 2007). the shift from dominantly tropical forest environments to more open, savanna-like conditions in the eocene intermontane basins during late bridgerian (early-middle eocene) and uintan (middle eocene) times has also been studied by using ecological diversity analysis applied to mammalian faunas (townsend, 2004; murphey and townsend, 2005). as indicated by fossil distribution and diversity, the green river lakes and their forested margins provided highly favorable habitats and preservational environments for both aquatic and terrestrial organisms. lake margin habitats, riparian corridors, and adjacent floodplains were apparently vegetated during much of the time of green river formation deposition, as indicated by a paleoflora that includes a variety of trees and bushes such as palm, cinnamon, oak, maple, lilac, and hazel, as well as cattails and rushes. insects of many varieties lived in the lakes and forests and are locally well preserved in lake sediments. a variety of terrestrial and aquatic mollusks (clams and snails) are also known to have inhabited the green river lakes (hanley, 1974). crayfish, prawn, and ostracods inhabited the warm lake waters, as did a diversity of fish species, including relatives of the herring, perch, paddlefish, bowfin, gar, catfish, and stingray (mcgrew and casilliano, 1975; grande, 1984; grande and buchheim, 1994). frogs, crocodiles, and turtles were common residents of shallower proximal shoreline waters. a diversity of reptile species, including tortoise, lizards, and snakes, inhabited the forests surrounding eocene lakes and ponds. flamingos, hawks, rails, stone curlews, and other bird species frequented the forests, wetlands, and lakes (murphey and others, 2001). the forests teemed with the primitive ancestors of many modern mammalian groups, including rodents, insectivores, bats, primates, perissodactyls (horse, rhinoceros, and tapir), and carnivores, as well as more bizarre archaic forms such as creodonts, brontotheres, and massive six-horned uintatheres (mcgrew and casilliano, 1975; gazin, 1976; grande and buchheim, 1994; gunnell and bartels, 1994; murphey and others, 2001). bridger formation history of paleontological investigations in the bridger formation john colter, who traveled to the headwaters of the green river in 1807, was probably among the first non-native americans to visit the green river basin (chadey, 1973). hundreds of subsequent trappers and explorers traversed the basin during the first half of the nineteenth century, and a number of records of these early explorations make reference to fossils and coal (roehler, 1992a). the earliest scientific observations on the geology of the green river basin were made by army lt. john c. fremont. after entering the basin through south pass at the southern end of the wind river mountain, fremont (1845) described varicolored rocks (now known as eocene-age wasatch formation) along the big sandy and new fork rivers. femont also collected fossil shells from near cumberland gap (veatch, 1907). the earliest vertebrate fossils reported from the green river basin were fishes discovered in the green river formation. in 1856, dr. john evans collected a specimen of a fossil fish from an unknown green river formation locality west of green river city. evans sent this specimen to paleontologist joseph leidy in philadelphia for study, and leidy named it clupea humilis (later renamed knightia humilis) (west, 1990). hayden (1871) described the discovery of a locality he referred to as the “petrified fish cut” along the main line of the union pacific railroad about 3.2 km (2 mi) west of green river. employees of the railroad had initially discovered the locality and later turned many specimens over to hayden. paleontologist edward drinker cope described the fish fossils from the “petrified fish cut” in hayden’s (1871) expedition report. the initial discovery of mammalian fossils in the green river basin was probably made by a long-time local resident, trapper jack robinson (also called robertson) who found what he described as a “petrified grizzly bear” sometime in the late 1860s. the specimen came from what is now called the bridger formation but had initially been named the “bridger group” by hayden (1869). this story was related to joseph leidy by judge william carter of fort bridger as an explana7 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 tion for the name “grizzly buttes,” an area 16 to 24 km (10–15 mi) southeast of fort bridger where fossils were particularly common (the name grizzly buttes has since disappeared from the local geographic vocabulary). several government geological and topographical surveys with specific but overlapping territories were operating in the southern green river basin between 1867 and 1879. hayden and his party collected along the henrys fork valley and farther north in the vicinity of church buttes in 1870 as part of the 1867 to 1878 u.s. geological and geographical survey of the territories (hayden, 1873). fossils collected by hayden’s group were sent to leidy for study and were described in a monograph on fossil vertebrates (leidy, 1873). later paleontological studies for the hayden survey were carried out by cope. under the direction of john wesley powell, the u.s. geological and geographical survey of the territories, second division (1875–1876), worked along the henrys fork river in 1869, and in a corridor 16 to 32 km (10–20 mi) wide on either side of the green river in 1871 (powell, 1876). the u.s. geological survey of the fortieth parallel (1867–1872), directed by clarence king, worked in the green river basin in 1871 and 1872. the fossils collected by the king survey were sent to othniel charles marsh for description. most of the fossils collected during these surveys were discovered in the bridger formation. many of the early scientific expeditions to the green river basin were based out of fort bridger, a trading post originally set up in 1843 by trapper and guide jim bridger and his partner louis vasquez. the fort became an army post after the 1857 mormon war. judge carter and dr. j. van a. carter, later residents of fort bridger, maintained an active correspondence leidy during the late 1860s and early 1870s. this correspondence included mailing fossils to leidy, which were described in subsequent publications (leidy, 1869, 1871, 1872a, 1872b, 1873). leidy, who is often regarded as the father of north american vertebrate paleontology (lanham, 1973), named the first bridger formation fossil to be formally described, the omomyid primate omomys carteri, after dr. carter (leidy, 1869). omomys carteri was also the first described fossil primate from north america. early reports of fossils from the green river basin did not go unnoticed by rival paleontologists marsh and cope. the incidents that set the stage for the long and bitter conflict between these two men began in the green river basin while they were prospecting in the bridger formation in 1872. sometimes referred to as the “bone wars,” the dispute between marsh and cope lasted for more than 30 years and included efforts by each man to destroy the scientific reputation and integrity of the other (lanham, 1973). this conflict soured leidy’s interest in paleontology and led to his eventual abandonment of the discipline after 1872. professor marsh was the first professional paleontologist to collect fossils from the bridger formation and for four consecutive summers from 1870 to 1873 brought crews with him from yale college. leidy’s only excursion to the west took place in 1872, when he visited the bridger badlands guided by the carter brothers of fort bridger. cope’s only visit to the bridger badlands occurred in 1872, while cope was attached to the hayden survey as the paleontologist. this visit infuriated marsh, who, at the time, considered the green river basin and bridger formation his exclusive fossil-collecting territory. by the late 1870s, cope and marsh had left the green river basin for good, although both men independently and at different times retained the services of paid fossil collector sam smith (west, 1990). other early fossil collectors who visited the green river basin in 1877 and 1878 included henry fairfield osborn, william berryman scott, and francis speir for princeton university. scott returned to the area with speir in 1886. jacob wortman and james w. gidley collected for the american museum of natural history (amnh) in 1893. the early fossil-collecting expeditions to the green river basin resulted in large collections of fossils primarily from the bridger formation at the philadelphia academy of natural sciences (leidy), yale university (marsh), the amnh (which purchased cope’s collection just before the turn of the century), and princeton university (osborn, scott, and speir). unfortunately, these early collectors paid little attention to the stratigraphic provenance of the fossils they collected. their collections do, nevertheless, contain the holotypes of most presently recognized bridgerian mammal taxa. in 1902, h.f. osborn, who was then the u.s. geo8 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 logical survey (usgs) paleontologist, initiated the first program of stratigraphic fossil collection to take place in the green river basin and one of the first in north america. osborn charged walter granger and william diller matthew of the amnh with the task of carrying out the study. matthew was also directed to find a uintathere to display at the amnh. the amnh party, led by granger, worked in the bridger basin from 1902 to 1906 (matthew, 1909). the second halves of the 1903 and 1905 field seasons were devoted to mapping and describing the stratigraphy of the bridger formation, while the remainder of the time was spent searching the badlands for fossils. the efforts of the amnh parties over these four years resulted in an excellent fossil collection that was, for its time, very well documented stratigraphically. these amnh expeditions also resulted in the first paper to be published on the geology of the bridger formation by william j. sinclair (1906), who had joined the amnh field party for the summer of 1905. the geology of the bridger formation was described briefly, and a system of stratigraphic subdivisions for the formation was introduced in matthew’s classic 1909 monograph, the carnivora and insectivora of the bridger basin, middle eocene. matthew’s subdivisions, bridger a–e, were based on areally extensive limestone beds, which he called “white layers.” following the early fossil-collecting expeditions of the nineteenth century and initial scientific field studies conducted by amnh crews in the early twentieth century, the bridger formation in the green river basin has remained the focus of almost continuous paleontologic inquiry because of its abundant and diverse vertebrate fossils, although matthew’s (1909) original stratigraphy was only recently refined by murphey and evanoff (2007). west (1990) wrote an excellent historical summary of vertebrate paleontological work in the green river basin from 1840 to 1910. osborn devoted considerable discussion to the bridger formation and its fossils in a monograph, the titanotheres of ancient wyoming, dakota, and nebraska (osborn, 1929). horace elmer wood (1934) divided the bridger formation into two members. the blacks fork member corresponds to matthew’s bridger a and b, and the twin buttes member corresponds to matthew’s bridger c and d, with the sage creek white layer marking their boundary. contrary to rules of stratigraphic nomenclature, these members were defined on perceived faunal differences rather than lithologic differences. the informal usage of the terms “blacksforkian” and “twinbuttean” as land mammal subages derives from the names of the two bridger members. under the direction of j.w. gidley, followed by c. lewis gazin, the smithsonian institution began an active collecting program in the bridger formation beginning in 1930. gazin was active in the green river basin from 1941 to 1968. this period of activity resulted in a relatively large and well-documented collection that was the subject of numerous publications by gazin (e.g., 1934, 1946, 1949, 1957, 1958, 1965, 1968, and 1976) focused primarily on the systematic paleontology of bridgerian mammal fossils. paul o. mcgrew and raymond sullivan worked on the stratigraphy and paleontology of the bridger a in the late 1960s and published the results of their work in 1970. robert m. west began an active collecting program for the milwaukee public museum in 1970 and worked in the basin until the late 1970s. west’s work, which also resulted in a large number of paleontological publications, included the use of screenwashing techniques to collect microvertebrates, a portion of the fauna that had not been previously well sampled. like wood (1934) and koenig (1960), west (1976) noted difficulties with the correlation of matthew’s white layers across the basin and suggested that a bipartite division of the bridger into upper (twin buttes) and lower (blacks fork) members was most appropriate. west and hutchison (1981) named matthew’s bridger e the cedar mountain member, adding a third member to the bridger formation. paleontological and geological studies of tabernacle butte, an isolated remnant of the bridger formation of late bridgerian age with an important fossil fauna, were published by mcgrew (1959), mckenna and others (1962), and west and atkins (1970). evanoff and others (1998), murphey (2001), and murphey and evanoff (2007) significantly refined matthew’s (1909) bridger formation stratigraphic scheme. their work included the addition of newly described marker units; the establishment of new stratigraph9 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 ic subdivisions and correlation of marker units across the southern part of the basin where the most complete stratigraphic sequence is exposed; descriptions of detailed stratigraphic sections measured through the bridger b, c, d, and e; renaming of the cedar mountain member to the turtle bluff member in order to conform with the rules of stratigraphic nomenclature; stratigraphic positioning of more than 500 fossil localities; isotopic dating of four ash-fall tuffs; and geologic mapping of more than 1600 km2 (600 mi2) of the southern green river basin at the scale of 1:24,000. geologic maps and publications relating to the bridger formation are available at http://www.rockymountainpaleontology.com/bridger. stratigraphy and depositional environments of the bridger formation the bridger formation was named the “bridger group” by hayden (1869). the first stratigraphic framework for the bridger formation was established by w.d. matthew (1909) of the amnh in the southern green river basin where the formation is thickest and best exposed. matthew’s (1909) stratigraphic subdivisions of the bridger formation were based primarily on five areally extensive limestone beds. these he named the cottonwood, sage creek, burnt fork, lonetree, and upper white layers, and some were used to subdivide the formation into five units, from lowest to highest: bridger a, b, c, d, and e. matthew’s intent was to make it possible to stratigraphically locate the numerous known fossil localities in the formation. because they are the most fossiliferous, the bridger b, c, and d were further divided into five subunits corresponding to basal, lower, middle, upper, and top levels (e.g., b1, b2, b3, b4, b5). because matthew (1909) did not define the upper and lower boundaries of these subunits with stratigraphic markers or measured sections, correlations between them and the later subdivisions proposed by evanoff and others (1998), murphey (2001), and murphey and evanoff (2007) are uncertain. the history of stratigraphic nomenclature for the bridger formation is provided in figure 3. in 1909 monograph, matthew (1909:296) gave a brief description of five proposed members and white layers. “horizon a” was 60 m (200 ft) thick, composed primarily of calcareous shales alternating with tuffs, and with rare fossils. “horizon b” was 140 m (450 ft) thick, consisting of two benches separated by the cottonwood white layer and containing abundant and varied fossils. matthew went on to note that the largest number of complete skeletons from the entire formation was found in the lower part of horizon b (b2). “horizon c” was 90 m (300 ft) thick, “defined inferiorly” by the sage creek white layer, with the burntfork white layer occurring at about its middle, and with abundant and varied fossils. matthew also noted that the sage creek white layer was the “heavy and persistent calcareous stratum” at sage creek spring, thus designating a type locality where this unit had been previously described and illustrated, but not named, by sinclair (1906). “horizon d” was 107 m (350 ft) thick, composed of harder gray and greenish-gray sandy and clayey tuffs, “defined inferiorly” by the lonetree white layer, containing the upper white layer about 23 m (75 ft) from the top, and with abundant and varied fossils. “horizon e” was 150 m (500 ft) thick, composed of soft banded tuffs having heavy volcanic ash layers, with a high gypsum content and nearly barren of fossils. the total thickness of the bridger reported by matthew was 550 m (1800 ft). despite the lithologic descriptions of the five horizons made by matthew (1909), subsequent workers have not been able to subdivide the bridger formation on the basis of lithologic differences (bradley, 1964; roehler, 1992a; evanoff and others, 1998; murphey, 2001; murphey and evanoff, 2007). furthermore, with the exception of the bridger b–c and d–e boundaries, matthew’s subdivisions do not correspond to major faunal changes (simpson, 1933; wood, 1934; murphey, 2001; murphey and evanoff, 2007). the bridger formation has been subdivided into three members. the blacks fork member, or lower bridger, is equivalent to matthew’s bridger a and b; the twin buttes member, or upper bridger, is equivalent to matthew’s c and d; and the turtle bluff member, also considered part of the upper bridger, is equivalent to matthew’s bridger e. a detailed history of geologic and paleontologic investigations focusing on the bridger formation, and the history of stratigraphic nomenclature for this unit, are provided by murphey and evanoff (2007). 10 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 evanoff and others (1998), murphey (2001), and murphey and evanoff (2007) published the first major stratigraphic revision of the bridger formation since matthew (1909). the most recent stratigraphic subdivisions are based on widespread limestone beds, tuffs, and tuffaceous sheet sandstone which are used as marker units. fifteen such units were described, and seven of these were considered major markers. these were used to subdivide the bridger c and d (twin buttes member) into lower, middle, and upper informal subdivisions (figures 3 and 4). two additional markers were used to redefine the base and define the top of the bridger e (turtle bluff member). four of matthew’s original “white layers” were included in the stratigraphy of the bridger c and d, and these were mapped and redescribed in detail. in conjunction with the latest stratigraphic revision, geologic mapping of ten 7.5-minute quadrangles which cover the area encompassed by the upper bridger formation was completed, and these maps are available from the wyoming state geological survey. because many marker units are not continuously exposed or traceable across the entire basin (from hickey mountain, sage creek mountain, and cedar mountain east to twin buttes and black mountain), a distance of approximately 64 km (40 mi), accurate correlation was made possible by using the mineralogically diagnostic henrys fork tuff as a datum. rock accumulation rates, isotopic ages of ash-fall tuffs (murphey and others, 1999), and fossils indicate that the 842-m-thick (2763 ft) bridger formation was figure 3. history of bridger formation stratigraphic nomenclature from 1869 until present. the correlation between mathew’s (1909) subdivisions (1–5) and the lower, middle, and upper subdivisions of murphey and evanoff (2007) are uncertain. 11 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 deposited over an approximately 3.5-million-year interval from about 49.09 to 45.57 ma, and that the faunal transition from the bridgerian to the uintan land mammal age was underway by about 46 ma as indicated by fossils collected from the turtle bluff member (evanoff and others, 1994; murphey, 2001; robinson and others 2004; murphey and evanoff, 2007; gunnell and others, 2009). recognized depositional environments of the bridger formation include fluvial, lacustrine, playa lacustrine, paludal, marginal mudflat, basin margin, and volcanic. murphey and evanoff (2007) concluded that an influx of fluvially transported volcaniclastic sedifigure 4. generalized stratigraphic section of the bridger formation in the southern green river basin, southwestern wyoming. isotopic ages reported by murphey and others (1999) have been recalculated using the 28.201 ma sanidine standard for the fish canyon tuff (renne and others, 1998). 12 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 ment to the green river basin during middle eocene time led to the filling of lake gosiute and the development of muddy floodplains of low topographic relief, which persisted for up to 85% of the time during which the upper bridger was deposited. occasional lapses in the flow of sediment to the basin permitted the development of shallow, mostly groundwater-fed lakes and ponds, which accumulated up to four times as slowly as floodplain deposits. these lapses decreased in frequency throughout deposition of the upper bridger formation. as indicated by fossil distribution and diversity, lakes and their margins provided favorable habitats for both aquatic and terrestrial organisms during deposition of the bridger formation. fossils and biochronology of the bridger formation one of the world’s most abundant and diverse middle eocene vertebrate faunas is preserved in the bridger formation. preserved in a variety of sedimentary environments, preservational states, associations, and in locally varying abundances, these fossils include primarily vertebrates and mollusks, with less common plants and ichnofossils. plant fossils include leaves, seeds, and wood, which is sometimes algal covered (see murphey and others, 2001). ichnofossils include solitary bee cases, earthworm pellets, caddis fly larvae, and fish pellets. vertebrate fossils include fish, amphibians, reptiles (lizards, snakes, turtles, and crocodilians), a diversity of birds (see murphey and others, 2001), and mammals. mammalian fossils include apatotheres, artiodactyls, chiropterans, carnivores, condylarths, dermopterans, dinoceratans (uintatheres), edentates, insectivores, leptictids, marsupials, pantolestids, perissodactyls, primates, rodents, taeniodonts, and tillodonts (gazin, 1976; gunnell and others, 2009; woodburne and others, 2009a, 2009b; unpublished paleontological data, university of colorado museum, compiled in 2002). combined for all biochrons in the bridger formation more than 125 species representing 77 genera, 35 families, and 18 orders of fossil mammals are recognized (gazin, 1976; gunnell and others, 2009). leidy’s 1869 description of omomys carteri was the first scientific description of a fossil from the bridger formation. subsequently, bridger fossils have been the subject of numerous publications, including many classic papers by pioneers of american vertebrate paleontology (leidy, 1869, 1871, 1872a; marsh, 1871, 1886; cope 1872, 1873; granger, 1908; matthew, 1909; osborn, 1929). like many other highly fossiliferous formations, the bridger contains an abundance and diversity of fossils that make it well suited for paleontological research, most of which has focused on the phylogenetics, systematic paleontology, and biostratigraphy of the vertebrate fauna (gazin, 1957, 1958, 1965, 1968, 1976; mcgrew and sullivan, 1970; west and hutchison, 1981; krishtalka and others, 1987; evanoff and others, 1994; covert and others, 1998; robinson and others, 2004; gunnell and others, 2009). despite the relative ease with which diverse and statistically significant fossil samples can be collected, and the large historical collections of bridger vertebrates available in many museums, taphonomic and paleoecologic studies of bridger vertebrate faunas are relatively few (gunnell and bartels, 1994; gunnell, 1997; murphey and others, 1999; brand and others, 2000; alexander and burger, 2001; townsend, 2004; murphey and townsend, 2005; townsend and others, 2010). over the last twenty years, stratigraphically documented fossil collections made by workers from the university of colorado museum, denver museum of nature and science, university of michigan museum of paleontology, and more recently by the san diego natural history museum, have added significantly to existing biostratigraphic knowledge of the bridger formation. these collections, together with precise provenance data, have made it possible to define formal biochronologic units for the bridgerian nalma, most of which are based upon stratotype sections that are located in the bridger formation. gunnell and others (2009) divided the bridgerian into four “biochrons.” formerly referred to as gardnerbuttean land mammal sub-age, or br0, biochron br1a is the only bridgerian biochron not found in the bridger formation. its stratotype section is the eotitanops borealis interval zone of the davis ranch section of the wind river formation. biochron br1b is equivalent to the lower blacksforkian, and its stratotype spans the bridger a (lower part of the blacks fork member). biochron br2 is equivalent to the upper blacksforkian, and its stratotype section spans the 13 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 bridger b (upper part of the blacks fork member). biochron br3 is equivalent to the twinbuttean, and its stratotype section spans the entire bridger c and d (twin buttes member). the uppermost member of the bridger formation, the turtle bluff member or bridger e, is the stratotype section for the earliest uintan biochron, ui1a (walsh and murphey, 2007; gunnell and others, 2009; kelly and murphey, in press; murphey and kelly, in review; murphey and others, in preparation). in summary, the mammalian fauna of the bridger formation has been used to formally define biochrons br1b, br2, br3, and ui1a. appendix a in murphey and others (2011; modified from gunnel and others, 2009) is a biochronologic range chart for bridgerian, uintan, and duchesnean mammalian taxa based on the most up to date information at that time. it is important to note that the ui1a fauna listed in appendix a is inaccurate because it lacks faunal revisions and additions that have recently been made (kelly and murphey, in press; murphey and kelly, in review; murphey and others, in preparation). the fossil assemblages of the bridger formation and other eocene rock units in the greater green river basin provide an unprecedented opportunity to study ancient communities and environments. studies of these fossils and the rocks in which they are preserved are the source of much of our knowledge of the eocene epoch of north america. the vertebrate faunas are of particular scientific importance because they represent an exceptional record of early tertiary mammalian evolution and diversification spanning the wasatchian, bridgerian, and earliest uintan nalma. bridger formation field trip stops the field trip route travels through the southern green river basin (bridger basin sector) making 11 stops in an approximately stratigraphic manner (figure 1). after leaving historic fort bridger, the staging area for many of the early fossil collecting expeditions to the bridger formation, the route travels east along interstate 80 (i-80) crossing through badland outcrops of the bridger b that are stratigraphically close to the bridger a-b boundary (blacks fork member). we travel west along i-80 to lyman and then head south along wyoming highway 414 to the historic grizzly buttes badlands in the bridger b (br2). we continue south along wyoming 414, climbing stratigraphically through the bridger c and d (twin buttes member, br3), and examine exposures of this interval in the vicinity of sage creek and hickey mountains, and at the “lonetree divide” (base of bridger d). weather permitting, we will then make our way to the southwest rim of cedar mountain and visit exposures of the bridger e (turtle bluff member). finally, we will head east along wyoming highway 414 along the south side of cedar mountain with excellent vistas of the bridger c, d, and e that are overlain by the oligocene bishop conglomerate. the field trip concludes after visiting exposures of the bridger c at the base of black mountain. note that all field trip distances are provided in statute (miles), whereas stratigraphic thicknesses are provided in both metric and statute. all distances were measured using a handheld gps device calibrated to the nad27 datum. stop 1. fort bridger state historic site parking lot (0.0 km/miles, cumulative 0.0 km/miles): fort bridger was originally established as a trading post in 1843 by trapper jim bridger and his guide louis vasquez. the u.s. army acquired the trading post in 1857 during the mormon war. it was located along the emigrant trail to oregon, california, and utah, and more than twenty years after the establishment of the trading post, the route of the newly constructed union pacific railroad passed not far to the north. as discussed in greater detail above, many of the early scientific expeditions to the bridger formation were based out of fort bridger. yale university paleontologist o.c. marsh and his field classes stayed at fort bridger before heading out to the bridger badlands in 1870, 1871, and 1873. rival paleontologist e.d. cope stayed at the fort in 1872 during his only fossil collecting expedition to the bridger. joseph leidy, often regarded as the father of north american vertebrate paleontology and the first paleontologist to formally describe a bridger formation fossil, made his only fossil collecting trip to the west in 1872, and also stayed at fort bridger. today, fort bridger is a state historical site and has been partially reconstructed. the low butte just to the west of fort bridger is bridger butte, and is composed of bridger b strata and capped 14 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 with quaternary gravels. turn west out of the fort parking lot along the i-80 business loop and then turn east onto i-80 (towards green river). drive for approximately 32 miles and take the granger junction exit (exit 66) heading north along u.s. highway 30. follow u.s. highway 30 for 1.8 miles after exiting the interstate. then turn east and cross the cattle guard onto a dirt road for 0.2 miles at which point you will arrive at the route of old u.s. highway 30 (unmarked gravel road that is still paved in places). park immediately after turning right (southeast) onto old u.s. highway 30. outcrops of the lyman limestone are located just to the east. stop 2. the lyman limestone at granger junction (58.4 km [36.3 mi] from stop 1, cumulative 58.4 [36.3 mi]): this stop provides a close up look at the lyman limestone, which marks the boundary between the bridger a and the lower bridger b within the blacks fork member (figures 3 and 4). here, the lyman is a gray limestone with locally abundant shells of the gastropod goniobasis. the presence of this high-spired snail is a useful diagnostic indicator for this marker unit at many localities in the bridger basin. the lyman limestone is widespread in its distribution. it is exposed to the west where it forms the bench that is visible to the south of i-80 upon which its namesake the town of lyman is situated, almost as far east as the rock springs uplift, at least 24 km (15 mi) north of granger, and almost as far south as the town of manila, utah. stratigraphically below the lyman limestone are strata of the bridger a. this interval has been problematic for paleontologists because it is sparsely fossiliferous. p.o. mcgrew and r. sullivan worked on the stratigraphy and paleontology of the bridger a in the late 1960s and published the results of their work in 1970 (mcgrew and sullvian, 1970). more recently, parties from the university of michigan, museum of paleontology have greatly expanded the known diversity of the bridger a (gunnell, 1998; gunnell and bartels, 2001). this has made possible the recent formalization of new biochronologic units (gunnell and others, 2009). as discussed above in “fossils and biochrononlogy,” the bridger a contains a mammalian fauna (biochron br1b) that is biostratigraphically distinct from the fauna of the bridger b (br2). optional stop: approximately 18 m (59 ft) stratigraphically above the lyman limestone 2.7 km (1.7 mi) to the southeast along old u.s. highway 30 is an unusual type of deposit for the bridger formation. approximately one third of the way up the hill, look for abundant dark brown rock fragments littering the slopes underlain by a thick green mudstone interval. the thin dark brown bed contains abundant fossil caddis-fly larval cases and other more enigmatic fossils preserved in what appear to be algal covered logs (sdsnh loc. 5783). the taphonomy and paleoecology of this unit has yet to be adequately studied. the fossil-bearing bed is overlain by a 2.8 m (9 ft) thick sequence of green to tan, well-indurated, platy, fine-grained, silty sandstone. it is underlain by a 1.5 m (5 ft) thick, platy, grayish-brown, non-fossiliferous, mudstone with a distinct top contact. insect and plant fossils are sparse in the bridger formation, and this bed contains the most abundant insect trace fossils known from the formation. return to i-80 and head west (note that throughout this field trip guide the mileages given refer to the prior stop unless specified otherwise). heading west along i-80, the first prominent butte you come to south of the interstate is jagged butte, which is capped by the jagged butte limestone. the second prominent butte you come to (approximate highway milepost 56.5) is wildcat butte, which is capped by the sage creek limestone (sage creek white layer of matthew, 1909), and which forms the base of the twin buttes member. exit i-80 at the church butte exit (exit 53) and turn north onto church butte road (no sign). at 30 km (19.2 mi) from stop 2, with church butte just to the east of your location, turn left (southwest) onto granger road, uinta county road (cr) 233. at kilometer 33.8 (mile 21.0), turn southeast off of county road (cr) 233 onto a two track road heading towards the westernmost point of jackson ridge. park where the two track road crosses the pipeline right-of-way at 34 km (21.2 mi) from stop 2. stop 3. church butte and jackson ridge (34.1km [21.2 mi] from stop 2, cumulative 92.5 km [57.5 mi]): church butte is a large linear badland knob formed by the erosion of rocks of the middle bridger formation 15 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 (lower bridger b beds, figures 4, 5, 6, and 7a). the butte was a landmark along the old oregon-california-mormon trail, now uinta cr 233. just to the west of the butte is a north-south trending rim separating porter hollow on the east with the valley of the blacks fork river on the west. the trail dropped off the rim just to the southwest of church butte, and the outcrops of bridger formation below the rim were easily accessed by early geologists and paleontologists who travelled along the trail. church butte and the rim exposures are all within the middle part of the blacks fork member of the bridger formation of wood (1934), or the lower bridger b of matthew (1909). the rocks in the area are primarily interbedded brown to green mudstone sheets and brown to gray sandstone ribbons and sheets. the sequence includes two sandstone-dominated intervals and three mudstone-dominated intervals (figure 5). four thin but regionally widespread marker units occur in the sequence that is 120 m (394 ft) thick. the following descriptions are of the bridger exposures along the west side of the rim, over an area approximately 8 km2 (3 mi2) south of where the county road crosses the rim. the two sandstone-dominated intervals are characterized by a series of thick ribbons to broadly lenticular sheet sandstone beds within a sequence of stacked, thin, muddy sandstone and mudstone sheets. sandstones can comprise 100% of the total thickness within the sandstone-dominated interval, but the lower interval averages 58% sandstone and the upper interval averages 84% sandstone within a minor amount of mudstone. the thick sandstone beds within these sandstone-dominated sequences are highly connected both laterally and vertically. the thick beds have a reticulate pattern, with some beds oriented toward the south-southeast (vector mean of 173°) and others oriented toward the east-southeast (vector mean 118°). the sinuosities of the individual sandstone beds are low (mean 1.02). these sandstone-dominated intervals represent a river system with numerous splays and local avulsions. the two intervals outcrop as cliffs in the badland exposures. the mudstone-dominated intervals are characterized by thick ribbon sandstone beds that are typically separated from adjacent sandstones by extensive mudstone beds. mudstone-dominated intervals have sandstone contents that range from 10% to 35% of total interval thickness. the sandstone ribbons represent large channels carrying mostly medium sand within a mud-dominated system. the paleocurrent indicators in these ribbons (mostly medium to thick trough crossbed sets) and bed orientations indicate an original flow toward the east-southeast (vector mean of 120°). the sinuosities of the sandstone beds are low (mean 1.03) and their geometry is in a “broken stick” pattern with long straight reaches and short sharp bends. sandstone bed widths and thicknesses are relatively small in straight reaches, but at bends the sandstone beds are thicker and wider and contain well-developed lateral accretion sets. fossil bones typically accumulate near the bases of these bends. thin sandstone sheets representing overbank splay deposits are rare and are limited to near their source channels. the mudstone-dominated intervals outcrop as benches and slopes in the badland exposures. the eocene streams which deposited the lower bridger b channel sandstones in this area were perennial and flooded every year. this is indicated by the abundance of freshwater turtles, gar-pike scales, fish bones, and a large freshwater snail fauna in the overbank deposits. the channel-belt deposits also contain the shells of numerous freshwater mussels (unionid clams), which indicate perennial, well-oxygenated waters in streams and rivers. fossil plants of this time (macginitie and leopold, 1972) indicate subtropical temperatures and mesic moisture with seasonal precipitation. there are four regionally widespread marker beds in the bridger exposures in this area. two widespread thin limestone sheets occur at the base and top of the section in the church butte area. the lower limestone is the lyman limestone at the base of the bridger b (along the blacks fork), and in this area it is a brown to gray ostracodal limestone with scattered catfish bones. the upper limestone occurs on the flat-surface on top of the rim, just south of the county road. this upper limestone is a brown micrite with brown to black banded chert masses and scattered large planorbid snail shells (biomphalaria sp.). both limestone beds can be mapped over much of the bridger basin in lower bridger b exposures. the predominantly fluvial sequence preserved in the church butte area was bracketed by these wide16 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 figure 5. geologic map of the church butte – jackson ridge area showing major marker beds in the lower bridger b interval, laterally extensive sandstone sheet intervals, and trends of major sandstone channel-belt deposits. also shown are important sites of the hayden 1870 expedition, including known sites where w.h. jackson took photos. see the text for details. 17 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 figure 6. index map of the western bridger basin, uinta and sweetwater counties, wyoming. 18 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 spread lacustrine deposits. two lithified volcanic ash beds (tuffs) occur in the section. the lower tuff is represented by a red clayey mudstone that ranges from 0.2 to 0.6 m (0.6–2 ft) thick, 33 m (108 ft) above the lyman limestone. the bed does not contain euhedral biotite crystals in this area, but in other parts of the bridger basin this bed thickens and is white with euhedral biotite crystals. this bed has not been radiometrically dated. this red tuff has been mapped over much of the western bridger basin. a second tuff bed occurs between 10.1 and 11.7 m (33 and 39 ft) below the upper limestone and ranges in thickness from 0.5 to 0.7 m (1.6–2.3 ft) thick. it is a tan to olive clayey mudstone bed that weathers gray and contains abundant euhedral crystals of biotite and hornblende. sanidine in this tuff has produced a 40ar/39ar age of 49.05 ± 0.16 ma (smith and others, 2008). this upper tuff is called the church butte tuff, with the type locality located at the north side of the point on the east end of the long ridge called jackson ridge (utm coordinates of zone 12t, 572123me, 4592105mn, wgs 84). the church butte tuff occurs throughout the bridger basin wherever lower bridger b rocks are exposed. many of the first fossils collected from the bridger formation came from the church butte area. the first geologist known to have collected fossils from the area was f.v. hayden. in 1868 hayden collected fragments of a fossil turtle that were later described as trionyx guttatus by leidy (1869). hayden returned to the area as part of the geological and geographical survey of the territories of 1870. the survey camped just to the west of the area along the blacks fork river and collected fossils in the church butte area on september 10 and 11 of 1870 (figure 7; hayden, 1872, p. 41). the 1870 survey figure 7. (a) william h. jackson photo of church butte taken on september 10 or 11, 1870. the view is to the east northeast. the utm location of the photo site is zone 12t, 571955me, 4595101mn, wgs84 datum (usgs photo jwh00462). (b) william h. jackson photo of the west end of jackson ridge, taken mid-day either on september 10 or 11, 1870. the view is toward the northwest. the hayden survey campsite was along the blacks fork river near here but is not in view of this photo. notice the crack that was in the original glass-plate negative. the utm location of the photo site is zone 12t, 571318me, 4592360mn, wgs84 datum (usgs photo jwh00309). 19 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 was the first time the pioneer photographer w.h. jackson accompanied hayden. years later, jackson recalled these two days: “twelve miles farther on we came to church buttes, a remarkable formation in the bad lands and a famous landmark along the old trail. while gifford [an artist of the 1870 expedition who assisted jackson] and i were making pictures of the interesting scenes, the geologists under the lead of dr. hayden were digging for fossils. they collected a wagon load of ancient turtles, shell fish, and other creatures... for my part, i made seventeen negatives during the day, something of a record for wet plate work, considering the many changes of location i had to make in getting the different views.” (jackson and driggs, 1929, p. 89, 91) the best known of jackson’s photos from the area (figure 7b) was taken near the end of a long badlands ridge that is herein named jackson ridge in honor of the photographer. the upper limestone bed marker in the area is named the jackson ridge limestone. jackson’s photos of the area document the type area of such fossil mammals as notharctus tenebrosus, palaeosyops paludosus, hyrachyus agrestis, and microsus cuspidatus, all described by leidy (1870, 1872b) and illustrated in 1873 (leidy, 1873). the mollusk type specimens collected at church butte by the hayden survey include physa bridgerensis, “viviparus” wyomingensis (a land snail that is similar in form to the aquatic viviparus), and “unio” leanus described by meek (1870, 1871, 1872). seven other species of fossil mammals have their type area in or near the church butte area, and these were collected by such paleontologists as e.d. cope, o.c. marsh, and j. wortman. type species of fossil mammals collected from the church butte area are listed in table 1. drive back onto cr 233, and turn left (southwest) towards lyman. turn left at mile 5.5 onto cr 247 which then crosses the blacks fork river, winding south to i-80. turn westbound (towards evanston) onto i-80 at kilometer 12 (mile 7.4). pass the lyman exit and drive to the mountain view-fort bridger (exit 39, 25 km [15.5 mi] from stop 3). turn south onto wyoming highway (sh) 414, crossing the blacks fork river and climbing up onto the lyman limestone at the top of the hill. continue through urie and mountain view, where the highway will bend to the east near the center of town. refer to figure 8 for a map that shows the major geographic features of the remainder of the field trip route. as you drive east from the center of mountain view along wyoming highway 414, the badlands to the south that are visible beginning at wyominh highway 414 milepost 105 were known to the early residents and explorers as “grizzly buttes” (lower and middle bridger b). the north end of the badlands to the northeast constitute the type area of the blacks fork member. continue southeast on wyoming highway 414 and the table 1. type species of fossils from the church butte – blacks fork area. 20 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 highway rises onto the cottonwood bench. immediately after reaching the top of this bench, at 47.8 km (29.7 mi) from stop 3, turn east and then immediately north. at 0.3 km (0.2 mi) from the turn off, do not turn east on cedar mountain road (blm 4315) and instead continue traveling north. at 50 km (30.4 mi) from stop 3, turn west onto the two track road and follow it for 1 km (0.6 mi) to the grizzly buttes overlook. stop 4. grizzly buttes (49.9 km [31.0 mi] from stop 3, cumulative 142.4 km [88.5 mi]): heading southeast from mountain view, wyoming highway 414 rises through a panel of badland exposures and climbs onto a high flat called the cottonwood bench. the bench is capped by gravels derived from the bishop conglomerate and transported to the area by cottonwood and sage creeks. below the gravel-flat is a series of badlands cut by leavitt creek, little dry creek, and their tributaries. the badland hills directly west of the overlook comprise the traditional “grizzly buttes” of the early explorers, but the name is not known to the modern population of the smith’s fork valley (see history of paleontological investigations in the bridger formation). matthew (1909, p. 297) stated about the buttes: “this is the richest collecting ground in the basin; thousands of specimens have been taken from it, and many skulls and skeletons more or less complete.” type species of fossil mammals collected from the grizzly buttes area are listed in table 2. the lower half of the bridger b is exposed in the grizzly buttes and along the cottonwood bench escarpment. not far below the quaternary gravels at this overlook is a widespread limestone that was named by matthew (1909), the cottonwood white layer (now known as the cottonwood limestone). it is a white micritic limestone that is very widespread but is locally absent in the church butte area. the cottonwood limestone is typically 5 m (16 ft) above the church butte tuff, but in this area it is 10.4 m (34 ft) above the tuff. the thickness of intervals between the widespread figure 8. map of a part of the southern green river basin encompassing most of the area of outcrop of the upper bridger formation. map shows both modern and historic geographic terminology (from murphey and evanoff, 2007). 21 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 marker beds increases from the church butte area toward the southwest. the jackson ridge limestone has been eroded by cottonwood creek on the bench, but in this area it is typically 6 m (20 ft) above the cottonwood white layer. the church butte tuff is a prominent gray band about half way down the escarpment. notice that channel sandstone beds are not as abundant in the lower bridger b rocks below you as they are in the church butte area. to the east is a prominent escarpment rising far above the cottonwood bench. this escarpment is capped by the sage creek white layer, the boundary between the blacks fork and twin buttes members of the bridger formation (the boundary between matthew’s bridger b and c). almost all the upper half of the bridger b is exposed in the west face of the escarpment. return to wyoming highway 414 and travel south for 9.2 km (5.7 mi). then turn east and drive for 0.3 km (0.2 mi) and park on the north side of the road. a short walk to the northeast will lead you to sage creek limestone and the type locality of the sage creek white layer. stop 5. sage creek white layer type locality (9.5 km [5.9 mi] from stop 4, cumulative 151.9 km [94.4 mi]): this outcrop of the sage creek white layer is located next to the site of the old sage creek stage station and sage creek spring along the old lonetree stage road. it was first described and photographed by sinclair in 1906 (figure 9), and then named and mapped by matthew (1909). the sage creek white layer is the base of matthew’s bridger c, the base of the twin buttes member, and the base of the upper bridger formation as presently defined. since matthew’s (1909) work, this unit has been renamed the sage creek limestone, and is the base of the lower bridger c of evanoff and others (1998), murphey (2001), and murphey and evanoff (2007). the general stratigraphy of the upper bridger formation in the sage creek mountain area is illustrated in figure 10. at its type locality, the sage creek limestone is 4.1 m (13.5 ft) thick. it consists of a lower massive tan micritic limestone, a middle shaly limestone with dark gray to black chert bands, and an upper platy to shaly limestone. elsewhere, it includes massive to blocky marly and micritic limestone, ledgy marlstone, and platy calcareous shale, and is locally interbedded with green to brown mudstone and claystone and thin carbonaceous shale. fossils of this unit consist of scattered gastropods, bone fragments (mostly fish), and turtle shell fragments; the limestone within it is locally stromatolitic. the sage creek limestone supports a very widespread bench, and it is the thickest and most widespread lacustrine deposit table 2. type species of fossil mammals from grizzly buttes. 22 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 in the upper bridger formation. stratigraphically overlying the sage creek limestone within the lower bridger c are two other limestone beds that are much thinner but are also widespread— the whisky reservoir and the butcher knife limestones (see figure 10). the lower bridger c is the least fossiliferous subunit of the upper bridger formation (twin buttes and turtle bluff members), despite the fact that it is by far the most geographically widespread. continue south along wyoming highway 414 for 5.1 km (3.2 mi). travelling south, the highway route travels up section through the lower bridger c and into the middle bridger c. sage creek mountain is the highest point on the west side of the highway and hickey mountain is the highest point on the east side of the highway. both of these mountains are capped by the oligocene bishop conglomerate. at 5.1 km (3.2 mi) from stop 5, pull into the henry #1 gas well pad on the east side of the road. stop 6. soap holes and hickey mountain limestones (5.1 km [3.2 mi] from stop 5, cumulative 157 km [97.6 mi]): the soap holes limestone, the lower of the two thin, rusty brown limestone beds visible at this cliffy exposure, is a widespread marker unit that forms the base of the middle bridger c (evanoff and others, 1998; murphey, 2001; murphey and evanoff, 2007). we believe that matthew (1909) considered this bed to be equivalent to the burnt fork limestone, which is a lithologically similar unit that is exposed to the southeast in the henrys fork valley but is actually not present in the section in this part of the basin. in the henrys fork valley, however, it is in fact is 33 m (108 ft) higher than the soap holes limestone. the soap holes limestone contains few fossils, but it is noteworthy that it is stratigraphically closely associated with fossil logs at several localities. fossils of the soap holes limestone include isolated, disarticulated and poorly preserved bones of fish, reptiles (especially turtles), and mammals within and on top of the unit. in the black mountain area, it is locally underlain by thin carbonaceous shale beds which preserve plant fragments. the sage creek and soap holes limestones have in fact yielded the fewest vertebrate fossils of any upper bridger lacustrine deposits. situated within the middle bridger c at 10.5 m (34 ft) above the base of the soap holes limestone (in the upper bridger formation reference section, murphey and evanoff, 2007), the hickey mountain limestone is a well studied and very important unit paleontologically. figure 9. photograph of the sage creek white layer taken by w.h. sinclair in 1906 (sinclair, 1906, plate 38). note the unit numbers penned in near the left edge of the photo. 23 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 it has a relatively limited areal distribution, occurring over a distance of approximately 9.0 km (5.6 mi) north of hickey mountain and west of sage creek mountain, and is the upper limestone bed exposed on the cliff at this stop. this unit provides an excellent example of one of the most paleontologically prolific depositional settings in the upper bridger formation. the early fossil collectors were the first to notice the close association between vertebrate fossils and the “white layers,” which are typically limestone and marlstone beds that were deposited in shallow lakes and ponds. more recently, paleontologists observed that it is not the marlstone beds that contain the majority of vertebrate fossils, but the immediately overlying and underlying mudstone beds. these mudstone beds, which are occasionally carbonaceous, are inferred figure 10. generalized stratigraphic section of the upper bridger formation in the sage creek mountain area, uinta county, wyoming. the diagram shows widespread and more localized markers, as well as informal submembers of matthew (1909). thicknesses taken from the reference section of the twin buttes member and the type section of the turtle bluff member (from murphey and evanoff, 2007). 24 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 to have been deposited along lake margins during lake transgressions and regressions (murphey, 1995; murphey and others, 2001). typically, the limestone and marlstone beds contain the remains of mostly aquatic organisms such as snails, clams, fish, amphibians, pond turtles, and crocodilians. the lake margin mudstones contain a mixed aquatic and terrestrial assemblage, and the terrestrial elements include locally abundant reptiles such as lizards, as well as bird bones and mammal bones and teeth. one particularly prolific fossil locality, the omomys quarry, is located approximately 0.8 km (0.5 mi) west of this stop in the hickey mountain limestone and overlying mudstone. this unusual fossil accumulation has produced over 2300 specimens of vertebrates, gastropods, and plants from an 8to 10-cm-thick (3 to 4-in-thick) deposit in a 4 m2 (43 ft2) area (murphey and others, 2001). what makes the assemblage so unusual is that it contains a high concentration of dental and post-cranial remains of the primate omomys, avian skeletal remains, and eggshell fragments. the unusual components of the fauna are superimposed on a more typical bridger fauna that occurs at the quarry and lateral to it in the same stratigraphic interval. four taphonomic agents have been postulated for the formation of the omomys quarry fossil accumulation: (1) an attritional accumulation of aquatic taxa in lacustrine sediments, (2) an attritional accumulation of both aquatic and terrestrial taxa in shoreline sediments, (3) an attritional accumulation consisting primarily of bird bones and eggshell formed in close proximity to a nesting area, and (4) a predator accumulation dominated by omomys but probably including other vertebrates formed by owls in close proximity to a nest, day roost, or night feeding station. the fauna and flora of the omomys quarry is listed in table 3. the same pattern of fossil distribution observed in the hickey mountain limestone occurs throughout the upper bridger formation as illustrated in figure 11. most fossils are found in association with lacustrine deposits, although stream channels are also productive. least productive are the volcaniclastic mudstone and claystone beds that were deposited on low-relief floodplains, and, together with stream-channel deposits, comprise 95% of the total thickness of the upper bridger. examples of the floodplain deposits, here consisting of green and gray mudstone and claystone beds, are well exposed at this stop above and below the soap holes and hickey mountain limestones. both the soap holes and hickey mountain limestones are better exposed, with some minor faulting, on the east side of the highway just to the north of this location. continue south on wyoming highway 414 for 1.8 km (1.1 mi) and turn east onto the gas well road. follow this road to the east and it will bend to the north for a total distance of 2.5 km (1.6 mi) from stop 6. park on the north side of the henry #10 well pad. the henrys fork limestone (type locality of this unit) and the underlying henrys fork tuff are exposed above the well pad on the badland hill just to the north. look for the gray-weathered bed near the top of the badland slope and an overlying thin light gray marlstone, and bring a shovel to examine the tuff. stop 7. type locality of the henrys fork limestone (2.6 km [1.6 mi] from stop 6, cumulative 159.6 km 99.2 mi]): the henrys fork limestone (and associated shore margin deposits) is another highly fossiliferous unit, and has produced hundreds of fossil mollusks and vertebrates across its distribution. it is quite widespread, covering an area of approximately 402 km2 (155 mi2), and was deposited in an elongate east-west trending basin which formed in the downwarp along the uinta mountain front. at this location, which is near the western edge of ancient henrys fork lake, the deposit is only 3 cm (1.2 in) thick, but it attains a maximum thickness of 1.65 m (5.4 ft) on the south side of cedar mountain near the center of its depositional basin. it is of taphonomic interest that the upper bridger formation with its abundant vertebrate fossils preserved in lacustrine and associated shore margin deposits contains few articulated skeletons or even partially articulated vertebrate remains, most of which have been collected in the bridger b (see alexander and burger, 2001). immediately underlying the henrys fork limestone is the henrys fork tuff, a unit that was first discovered by emmett evanoff while conducting field work in the sage creek mountain area in 1991. this ash-fall tuff is the most analyzed tuff in the bridger formation, and it is beyond the scope of this paper to report the various ages that have been published. most recently, smith and 25 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 others (2008) have reported a 40ar/39ar age of 48.44 ± 0.15 ma based on sanidine. ash-fall tuff deposits comprise less than 1% of the total thickness of the upper bridger formation, and based on their mineralogy, are believed not to have originated in the absaroka volcanic field to the north like other volcaniclastic bridger formation sediments, but rather in the challis volcanic field located in central idaho. at its type locality on the south side of cedar mountain, the tuff is 0.95 m (3.1 ft) thick (murphey and evanoff, 2007). the tuff is a blocky, non-calcareous, gray to white biotitic claystone with a distinct bottom contact and a diffuse top contact. it contains biotite, zircon, allanite, and apatite crystals. plagioclase is the most abundant feldspar. it typically consists of a structureless lower unweathered portion with coarse euhedral biotite (up to 1.3 mm [0.05 in] in diameter) which grades upward into a reworked portion with less coarse and less abundant biotite. the base of the henrys fork tuff forms the base of the upper bridger c, and is 121 m (397 ft) above the base of the sage creek limestone in upper bridger formation reference section (murphey and evanoff, 2007). table 3. fauna and flora of the omomys quarry with number of identifiable specimens for vertebrates shown in right column. eggshell is not included. from murphey and others, 2001. 26 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 weathered badland exposures of the henrys fork tuff form a distinctive dark gray weathering bed that is readily discernable from other bridger lithologies, especially when wet. return to wyoming highway 414 and drive south for 3.0 miles (note the exposures of henrys fork tuff which is visible as a subtle gray bed on both sides of the highway just above road level after turning back onto the highway). then turn west onto the access road for conoco fed 20-2 gas well pad. proceed to the well pad and park (5 km [3.2 mi] from stop 7). the route you just drove continued up section through the upper bridger c to the level of the lonetree limestone (base of lower briger d) which is at the approximate level of the highway at the lonetree divide. this is the stratigraphically highest point that wyoming highway 414 attains in the bridger formation. stop 8. the lonetree divide (5.1 km [3.2 mi] from stop 7, cumulative 164.7 km [102.4 mi]): this area provides some excellent vistas of the upper bridger formation and its marker units, especially from the top of the ridge just to the north. the base of the lower bridger d, the lonetree limestone (lonetree white layer of matthew, 1909), is well exposed at the base of the badland slopes at road level. the base of the middle bridger d, the basal blue sheet sandstone, is exposed on the slopes of the prominent conical butte to your west as well as on parts of the ridges to the north and south. the prominent butte, called “old hat mountain” by the locals, is an erosional remnant of hickey mountain (figure 12a) to which it is still attached. the ‘rim of the hat’ is the upper white limestone (upper white layer of matthew, 1909). the butte is capped by a thin interval of red mudstone of the turtle bluff member (bridger e of matthew, 1909). to the northeast is sage creek mountain, with a thick sequence of bridger e (red beds overlying gray beds of bridger d) visible near its summit. the basal bridger e tuff (40ar/39ar age of 46.16±0.44 ma, murphey and evanoff, 2007) occurs just below the base of the bridger e on sage creek mountain. o.c. marsh called sage creek mountain “big bone butte” because of the abundance of uintathere bones found in the area. visible to the east is cedar mountain, with the thickest and best exposed sequence of turtle bluff member. all three of the mountains in this area (hickey, sage creek, and cedar) are capped by oligocene bishop conglomerate. numerous fossil localities have been documented in the lonetree divide area. these include the classic lonetree localities of matthew (amnh expeditions of 1903–1906) and gazin (usnm expeditions between 1941 and 1969). this area was also worked by robert m. west of the milwaukee public museum during the 1970s, and by crews from the university of colorado museum during the 1990s. channel sandstone beds in this area indicate paleocurrent directions to the southeast. turn south on wyoming highway 414 for 3 km (1.9 mi) and turn east onto cedar mountain rim road (blm figure 11. stratigraphic distribution of catalogued mammalian specimens from the upper bridger formation (university of colorado museum collections) (scls, sage creek limestone; shls, soap holes limestone; hmls, hickey mountain limestone; hfls, henrys fork limestone; ltls, lonetree limestone; hrls, hickey reservoir limestone; uls, upper white limestone; bels, basal bridger e limestone). 27 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 road 4314). at 4.5 km (2.8 mi) from stop 8, the road bends to the north and cuts stratigraphically through the upper bridger c, crossing the lonetree limestone, and continuing up through the lower and middle bridger d. at the junction of cedar mountain rim road and sage creek mountain road (8.4 km [5.2 mi] from stop 8), turn south onto a two track road. drive south on the two track, keeping straight at 9.9 and 10.1 km (6.2 and 6.3 mi) where other tracks diverge, until reaching the turtle bluff member overlook (10.3 km [6.4 mi] from stop 8). note that if the ground is wet, it is not advisable to leave the paved highway (wyoming highway 414). stop 9. the turtle bluff member on cedar mountain (10.3 km [6.4 mi] from stop 8, cumulative 175 km [108.8 mi]): looking east from this location affords an excellent view of the upper bridger d, the highest subunit in the twin buttes member, overlain by the turtle bluff member of the bridger formation (matthew’s bridger e). the contact between the two members is shown on figure 12b, and is defined on the basis of a limestone that occurs at the approximate level of the lowest red bed (note that some of the strata observed are slumped). the limestone that supports the bench that you are standing on is the upper white limestone. consisting primarily of banded red, gray, and tan beds of gypsiferous claystone and mudstone, rocks of the turtle bluff member are the least volcaniclastic in the bridger formation. lithologically, the turtle bluff member is somewhat distinct from the rest of the formation, being similar in appearance to the red and brown sandstone, mudstone, and claystone beds of parts of the washakie and uinta formations of similar age. the turtle bluff member occurs only on hickey mountain, sage creek mountain, the south end of black mountain, and twin buttes, but by far the most extensive and thickest exposures occur here on the southwest side of cedar mountain. the type section for the turtle bluff member on cedar mountain is a 131.5 m (431 ft) thick sequence of reddish-brown and gray claystone beds with a high gypsum content. this gypsum is both primary and secondary. secondary gypsum consists of selenite and satin spar crystals which are abundant on the upper slopes of cedar mountain. primary gypsum occurs in thin beds, but the turtle bluff member on cedar mountain is capped by a thick and laterally extensive gypsum bed. the mostly fine-grained reddish turtle bluff sediments were probably derived from the adjacent uinta mountains based on their color, unlike those of the bridger a-d, which were largely derived from more distal volcanic sources. the turtle bluff member contains two markers: (1) the basal bridger e limestone, which marks the base of figure 12. (a) view of the bridger d and e on “old hat mountain,” a prominent butte on the southeast flank of hickey mountain, uinta county, wyoming. photo taken looking southwest (bbs, basal blue sheet sandstone; uls, upper white limestone; bels, basal bridger e limestone); (b) view of the bridger d and bridger e on the southwest flank of cedar mountain, uinta county, wyoming. photo taken looking east (uls, upper white limestone; bels, basal bridger e limestone; brgb, behunin reservoir gypsum bed; tbdm, middle bridger d; tbdu, upper bridger d, tbe, bridger e; tbi, bishop conglomerate. 28 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 the member (base of matthew’s bridger e), and (2) the behunin reservoir gypsum bed, which is the youngest and stratigraphically highest well exposed rock unit in the bridger formation (note that behunin is pronounced “buhannan” by locals). here on southwest cedar mountain, the turtle bluff member contains four additional unnamed limestone beds, and on twin buttes there are three. a 2.3-m-thick (7.5 ft) laterally extensive, quartz arenite bed that lies 75 m (246 ft) above the base of the member on cedar mountain is the only sandstone bed. similar sandstone beds in the turtle bluff member also occur on the northwest flank of hickey mountain and the south flank of sage creek mountain, and may be roughly stratigraphically equivalent. the behunin reservoir gypsum bed is lithologically unique for the bridger formation. although other gypsum beds occur in the turtle bluff member, they are much thinner. restricted to just below the southwest rim of cedar mountain (below the bishop conglomerate), this unit consists of a 7 m (23 ft) thick sequence of gray and tan unfossiliferous bedded gypsum beds interbedded with gypsiferous mudstones and marlstones. it is visible from a great distance as a prominent white bed high on cedar mountain. this bed is interpreted as an evaporitic playa lacustrine deposit, and may indicate changing climatic conditions near the end of bridger formation deposition. because of its sparse fossils and steep, limited exposures, the biochronologic affinity of the turtle bluff member has been difficult to determine. matthew was the first worker to comment on the age of the member, saying that its few mammal fossils prove sufficiently that it “belongs to the bridger age” (matthew, 1909, p. 296). osborn (1929) correlated the bridger e with the washakie b and uinta b, although he cited no evidence to support this correlation. simpson (1933), wood and others (1941), and gazin (1976) also regarded the bridger e as uintan, although this was apparently not based on fossil evidence. based on eight isolated rodent teeth identified as paramys cf. p. delicatior, and “several” bone fragments identified as brontothere, west and hutchison (1981) concluded that the bridger e (their cedar mountain member) was bridgerian. subsequent work during the 1990s by crews from the university of colorado museum (evanoff and others, 1994; murphey and evanoff, 2007) and in the 2000s by crews from the san diego natural history museum (walsh and murphey, 2007) resulted in the collection of a much more diverse faunal assemblage from multiple stratigraphic levels within the turtle bluff member. donna’s locality (ucm loc. 92189) is near the base of the member, and is the only locality thus far to produce specimens of the newly described species of the omomyid primate hemiacodon engardae (murphey and dunn, 2009). located 105 m (344 ft) above the base of the member, roll the bones (sdsnh loc. 5844) and red lenses (sdsnh loc. 5844) are the stratigraphically highest localities to yield identifiable fossils in the member. hundreds of fossils have now been collected from these and other localities mostly via screenwashing of sedimentary matrix. non-bridgerian taxa include epihippus, metanoiamys, pareumys, triplopus, sespedectinae indet., and oromerycidae gen. and sp. nov. the faunal assemblage of the turtle bluff member is now considered to be earliest uintan in age (biochron ui1a of gunnell and others, 2009), although efforts to obtain additional fossils from this biochronologically important interval member on cedar mountain and other locations within the bridger basin are ongoing. these efforts have produced a much more diverse and abundant mammalian fauna including additional new taxa for the member, both bridgerian and uintan. the mammalian fauna of the turtle bluff member has been intensively studied and is formally described in a series of three forthcoming publications (kelly and murphey, in press; murphey and kelly, in review; murphey and others, in preparation). because of its earliest uintan biochronologic age, the geochronologic age and magnetic polarity of the turtle bluff member are particularly important for achieving a robust correlation with the geomagnetic polarity time scale.  there are currently two published radiometric ages that pertain to the turtle bluff member.  murphey and others (1999) reported an age of 46.14 ± 0.44 ma (sanidine, plagioclase, biotite) for the basal bridger e tuff, which is located stratigraphically 8 m (26 ft) below the base of the turtle bluff member within the upper bridger d on sage creek mountain.  this date was recalculated by smith and others (2003) using the fish canyon sanidine standard of renne and others (1998) 29 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 at 46.83 ± 0.90 ma.  smith and others (2008) reported an age of 47.45 ± 0.15 ma (sanidine, corrected, see smith and others, 2010; tsukui and clyde, 2014) for the sage creek mountain pumice, which is located stratigraphically 44 m (144 ft) above the base of the turtle bluff member on sage creek mountain.  two other samples have recently been dated using the u-pb zircon technique from the turtle bluff member in the thicker stratotype section on cedar mountain (murphey and others, in preparation). these samples, yet to be named, will provide ages for localities that are 74 m and 105 m (243 ft and 345 ft) above the base of the turtle bluff member, respectively.  according to tsukui and clyde (2014), the sage creek mountain pumice lies within chron c21n, and suggests that the entire earliest uintan turtle bluff member sequence and its fauna also lies within chron c21n.  the bridger formation is unconformably overlain by the bishop conglomerate, which is visible from this stop capping cedar mountain. to the east of this location it forms massive cliffs and spectacular columns. this unit is a very coarse conglomerate composed primarily of arkosic cobbles and boulders derived from the proterozoic uinta mountain group, with locally common cobbles and boulders of paleozoic limestone (bradley, 1964). it is as much as 40 m (131 ft) thick. the bishop conglomerate is unfossiliferous, but is oligocene in age based on isotopic ages of 29.50 ± 1.08 ma, k/ar biotite (hansen, 1986) and 34.03 ± 0.04 to 30.54 ± 0.22 ma, 40ar/39ar sanidine (kowallis and others, 2005) obtained from tuffs that are preserved within it on the south side of the uinta mountains. return to wyoming highway 414, and continue south. the highway crosses the henrys fork of the green river, passes by the hamlet of lonetree, and bends to the east. there is an excellent view of the henrys fork tuff and henrys fork limestone on the north side of the highway at wyoming highway 414 milepost 128. the henrys fork tuff is the prominent gray bed exposed low on the slopes of cedar mountain not far above road level, and the henrys fork limestone is a prominent white bed immediately overlying the tuff. continuing east, the highway passes through the hamlet of burntfork. at highway milepost 130.6 there is a point of historic interest on the south side of the highway. this location is near the site of the first (1825) mountain man fur trading “rendezvous” led by general william ashley and attended by a then “green” jim bridger and jedediah smith. at the mckinnon junction (16.6 miles from stop 9), turn north onto sweetwater county highway 1. proceed to 18.8 miles from stop 9 and pull over on the east shoulder next to the road cut. stop 10. the mckinnon road cut (30.3 km [18.8 mi] from stop 9, cumulative 205.3 km [127.6 mi]): this road cut features the thickest lacustrine sequence in the upper bridger formation. the sage creek limestone is the thick blocky limestone near the top of the cut. underlying it are at least 30 m (98 ft) of lacustrine shale, mudstone, marlstone, and limestone, but the total thickness of the lacustrine sequence is unknown. it has been postulated that this sequence and underlying lacustrine strata of unknown thickness represents a final transgressive phase of lake gosiute (laney shale member of green river formation) (brand, 2007), although there is little supporting evidence. whatever the case, this sequence, combined with evidence provided by other upper bridger lacustrine deposits (thicknesses and areal distribution), suggests that lacustrine deposition during upper bridger deposition was most prevalent just to the north of the uinta mountain front. continue north on sweetwater cr 1. here, the road is built on rocks of the lower bridger c and descends into upper bridger b strata at approximate sweetwater cr 1 milepost 16.7 before climbing stratigraphically again to the lower bridger c strata at highway milepost 15.8. at 18.5 km (11.5 mi) from stop 10, turn east onto a two track road towards the north end of black mountain. twin buttes is the conical peak to the south of black mountain. bear right at 19.5 km (12.1 mi). take the left fork at 21 km (13.0 mi) and look for the blm wilderness study area sign. park at the base of black mountain at 22.2 km (13.8 mi). note that if the ground is wet, it is advisable to stay on the paved highway. stop 11. twin buttes and black mountain (22.2 km [13.8 mi] from stop 10, cumulative 227.5 km [141.4 mi]): although the classic bridger badlands and collecting areas we have already visited are located far to 30 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 the west, the twin buttes member and the twinbuttean land mammal subage was named for twin buttes. because of this, murphey and evanoff (2007) designated their type section of the twin buttes member for the upper bridger sequence on the south side of twin buttes, and established their twin buttes member reference section of the upper bridger for the sequence in the sage creek and hickey mountain area. however, the reference section is thicker and contains more marker units. the major stratigraphic features of the upper bridger in the twin buttes and black mountain area are shown in figure 13. in front of this position is another upper bridger marker bed. the horse ranch red bed occurs only in the eastern part of the basin (east side of cedar mountain [mass mountain], black mountain, and twin buttes). it is an approximately 4-m-thick (13 ft) sequence of non-calcareous brick red, greenish-gray, and light brown claystone, blocky mudstone, and blocky fine-grained muddy sandstone (murphey and evanoff, figure 13. generalized stratigraphic section of the upper bridger formation in the twin buttes area, sweetwater county, wyoming. the diagram shows widespread and more localized markers, as well as informal submembers of matthew (1909). thicknesses taken from the type section of the twin buttes member, which includes the turtle bluff member on twin buttes (from murphey and evanoff, 2007). 31 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 2007). it is locally fossiliferous. for many years, paleontologists were vexed by the difficulty of correlating between twin buttes and cedar mountain to the west, especially considering the classic “layer cake geology” of the bridger with very low dips and laterally persistent marker units. this was because the stratigraphic positions of the “white layers” did not align as expected when using the sage creek limestone as a datum. this problem was finally solved by locating the mineralogically diagnostic henrys fork tuff not far from here on black mountain, and using it as a stratigraphic datum. the reason that earlier workers had difficulties establishing a correlation between the twin buttes and black mountain area with exposures to the west using the “white layers” is that the lower bridger c thins dramatically from the west to the east as seen at twin buttes, where the thickness between the sage creek limestone and soap holes limestone is 21 m (69 ft) less than in the nearest correlative sequence to the west. one is stratigraphically located within the middle bridger c, and the henrys fork tuff is located 42 m (138 ft) above this level. in fact, all of the major marker units present in the twin buttes reference section are present in the twin buttes type section except for the basal blue sheet sandstone (base of middle bridger d). the lonetree limestone is very well exposed in the saddle between black mountain and twin buttes, and the upper white limestone is exposed near the top of twin buttes. only 21 m (69 ft) of turtle bluffs member occurs at twin buttes, which is capped by a thin remnant of bishop conglomerate. the hike from this stop to the saddle between twin buttes and black mountain is well worth the effort if you have the time. this is the end of the green river basin (bridger basin) portion of the field trip. from here we will head south to manila, utah, via sweetwater cr 1 and wyoming highway 414, and then continue south over the uinta mountains to vernal and the uinta basin. part ii. uinta basin field trip this portion of the field trip will examine rocks of the uinta and duchesne river formations in the uinta basin. the following sections of the field trip guide provide a summary of the early cenozoic geologic history of the uinta basin, as well as the history of investigations, stratigraphy, depositional and paleoenvironmental history, and fossils of the uinta and duchesne river formations. this is followed by a detailed field trip road log. early cenozoic geologic history by the late paleocene (clarkforkian nalma), large shallow lakes and ponds occupied a large portion of both the uinta and piceance creek basins. during the latest paleocene and early eocene (late clarkforkian and early wasatchian nalma), there was a return to fluvial sedimentation in both basins, which is represented by rocks of the wasatch formation (also called debeque formation by some paleontologists). this was followed by a return to dominantly lacustrine conditions in the early eocene with the establishment of two large freshwater lakes (one in each basin). bradley (1931) named the tongue of the freshwater lacustrine unit which was deposited during this brief time of maximum transgression the “basal tongue” of the green river formation where it crops out in indian canyon in the western part of the uinta basin. the two early freshwater lakes in the uinta and piceance creek basins appear to have been similar to the approximately contemporaneous lake luman, the early freshwater stage of lake gosiute, which existed in the greater green river basin in wyoming. the sediments deposited during lacustrine maximums in both the uinta and piceance creek basins almost connect over the top of the douglas creek arch, suggesting that during at least in part of the freshwater period the two basins were hydrologically connected (johnson, 1985). during this period, the two basins are believed to have drained externally since the lake waters in both basins remained fresh enough to support abundant freshwater mollusks (johnson, 1985). at the end of the early eocene (wasatchian-bridgerian boundary), a major transgression associated with expansion and deepening of lake water marked the beginning of lake uinta as an unbroken body of water across the douglas creek arch in both the piceance creek and uinta basins (moncure and surdam, 1980; johnson, 1985). johnson 32 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 (1984) named this the long point transgression. after the maximum transgression, lake uinta extended close to the margins of the combined uinta and piceance creek structural and sedimentary basins; it covered a much larger area than that of the maximum transgression during the earlier freshwater stage of the lake. five stages in the developmental history of the larger saline lake uinta have been identified based on changes in water chemistry and depositional events (johnson, 1985). throughout most of these five stages, the salinity of lake uinta increased steadily. ultimately, salinity increased to the point at which nahcolite and halite were precipitated. the gradual filling of lake uinta during the middle eocene was due to an influx of volcaniclastics from the absaroka volcanic field in wyoming to the north and from volcanic centers farther to the west, and then later by an increase in sediment resulting from rejuvenated local laramide uplifts. there is no direct geologic evidence that lakes uinta and gosiute were ever physically connected. however, fluvially deposited volcaniclastics in lake uinta, demonstrably derived from the absaroka volcanic field in northwestern wyoming, would be a persuasive line of evidence. this would not rule out the possibility of transport of volcaniclastic material from lake gosiute south to lake uinta via streams over the lowest drainage divides after the greater green river basin had been filled (surdam and stanley, 1980). as lacustrine deposition in lake uinta diminished because of basin filling, fluvial sedimentation resulted in deposition of the uinta formation in the piceance creek and uinta basins (stokes, 1986). at this time, fluvial deposition began to dominate in the basin as streams flowed into it from the north and east (stokes, 1986). the east-west flow resulted in the formation of limey siltstone beds and fine-grained uinta formation shale in the eastern part of the uinta basin, contrasting with the red sandstone, shale, siltstone, conglomerate, and limestone beds in the west (stokes, 1986). today, fluvial rocks of the middle eocene uinta formation (uintan nalma) are preserved above green river formation strata only in the northern part of the uinta basin. the late middle eocene (duchesnean nalma) duchesne river formation overlies rocks of the uinta formation in the north-central and western parts of the uinta basin, and the cretaceous-age mesaverde group on asphalt ridge. both the uinta and duchesne river formations were deposited in river channels and on adjacent floodplains (stokes, 1986) and in river deltas (townsend, 2004). riparian environments were forested, and the rivers and streams flowed through a savanna-type environment with some swampy and marshy areas and forested highlands (hamblin, 1987; townsend and others, 2010). uinta formation the uinta formation is exposed south of the uinta mountains as a discontinuous outcrop belt that can be traced approximately 145 km (90 mi) from near the west edge of the uinta basin to as far east as the utah-colorado state line (peterson and kay, 1931; bryant and others, 1989; hamblin and others, 1999; sprinkel, 2007, 2009, 2015). it overlies the lacustrine green river formation, with an interfingering contact between the two formations that reflects their closely related depositional history (ryder and others, 1976; hintze, 2005). the uinta formation is approximately 1298 m (4257 ft) thick (including subsurface and exposed rock) and contains bitumen in the form of gilsonite veins (cashion, 1986; hintze, 2005; sprinkel, 2007). the uinta formation was deposited under fluvial conditions as the lake depositing the green river formation was receding (ryder and others, 1976). history of paleontological investigations o.c. marsh led the first paleontological expedition to the uinta basin in 1870 as part of a yale college scientific expedition (betts, 1871; marsh, 1875a, 1875b). in an unexplored area between the green and white rivers, marsh's party collected numerous fossil mammals, the beginnings of an assemblage that would later define the uintan nalma, a time period that spans approximately 46.5 to 40 ma (wood and others, 1941; prothero, 1996; murphey and evanoff, 2007). in the 1880s, francis speir of princeton university collected in this same area and the mammalian fossils he collected were studied by w. b. scott and h.f. osborn, whose efforts produced the first comprehensive publications on mammals from the uinta formation (scott and os33 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 born, 1887, 1890; rasmussen and others, 1999a). at the turn of the century, the carnegie museum sent expeditions to the uinta basin at different times led by o.a. peterson and then earl douglass (douglass, 1914; peterson, 1919). peterson (1919) initially described many of the medium and smaller-sized mammals from the uinta formation, many now recognized as index taxa for the uintan nalma and therefore crucial for understanding uintan biochronology on both the regional and continental scales (walsh, 1996). after these initial expeditions, museums across north america sent parties to collect small samples of uintan mammals, the most notable of these being the smithsonian institution. in 1993, an expedition from washington university in st. louis began what would be a 15+ year project (still ongoing) in the uinta and duchesne river formations, with the goal of collecting small mammals (rasmussen and others, 1999a, 1999b; townsend and others, 2006). these latest expeditions have amassed one of the largest assemblages of uintan mammals from the rocky mountain region (townsend, 2004). stratigraphy of the uinta formation whereas the uinta formation has been formally divided into a lower wagonhound member and an upper myton member, many geologists and paleontologists continue to utilize the informal tripartite scheme in which the formation was initially subdivided from lowest to highest: uinta a, b, and c, (wood and others, 1941; prothero, 1996; sprinkel, 2007). the tripartite division of the formation is a modification of osborn’s (1929) stratigraphic nomenclature: uinta a, uinta b1, uinta b2, and uinta c (peterson and kay, 1931; prothero, 1996; walsh, 1996; townsend and others, 2006; sprinkel, 2007). the lowermost unit, uinta a, intertongues with the underlying parachute creek member of the green river formation and is comprised of resistant fine-grained sandstones that are yellowish-brown and yellowish-gray (sprinkel, 2007). these beds are medium to massive sandstone beds that weather to cliffs, ledges, and softer gray slopes and have been measured to be about 226 m (740 ft) in thickness (cashion, 1974). within in uinta a, there is a 1.8 m (6 feet) thick tuffaceous bed (“a” tuff), and the base of this bed occurs 56 m (185 ft) below the top of the uinta a (cashion, 1974). uinta b is composed of light-gray, light greenish-gray, light-brown, light-purple mudstone and claystone forming non-resistant slopes (sprinkel, 2007). these are interbedded with green-gray, yellow, and brown fine-grained sandstone beds that form thin resistant ledges (townsend and others, 2006; sprinkel, 2007). there are prominent gilsonite veins in this unit (cashion, 1986). in the eastern part of the basin, the uinta b is capped by a massive fineto coarse-grained gray and brown sandstone bed that weathers to dark brown, and was named the amynodon sandstone (riggs, 1912). this massive sandstone unit is over 1.6 km (1 mi) in length, and was originally defined as the boundary between the uinta b and uinta c horizons (riggs, 1912), but is now known to be local in extent. uinta c is distinctive in that the lower intervals and upper intervals are strikingly different in terms of rock type and coloration (townsend and others, 2006). the lower part of uinta c is comprised of light-gray, lightgreenish-gray, and light-brown mudstone and claystone that interbed with fine-grained sandstone beds, which are also greenish gray or commonly yellow or brown (townsend and others, 2006; sprinkel, 2007). the upper part is composed of mainly deep red-orange, red, dark-brown, grayish-purple, and yellow mudstone and claystone with thin gray and green fine-grained sandstone beds that form thin ledges (townsend and others, 2006; sprinkel, 2007). the stratigraphy of the uinta formation has been less well studied than that of the green river formation, and most of the stratigraphic work has been undertaken by paleontologists. the early publications that produced the initial description of the formation has been confused by changes in terminology describing the lithologic horizons and by shifting boundaries of the units that divide these horizons (riggs, 1912; osborn, 1929; stagner, 1941; cashion, 1986; prothero, 1996; townsend, and others, 2006). osborn (1895) cited peterson as first dividing the formation into informal units uinta a, b, and c, and all units were reported to be fossiliferous. all early fossil collections have these horizon designations assigned as stratigraphic data (prothero, 1996). osborn (1929) removed the top 120 m (400 ft) of peterson’s uinta a, and called it uinta b1, leaving the remaining sandstones of 34 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 uinta a without any known record of fossil vertebrates. additionally, osborn designated the amynodon sandstone of riggs (1912) as the boundary unit between uinta b (now b2) and uinta c, further altering peterson’s initial scheme. osborn’s (1929) uinta b1 had an upper limit bound by another massive unit, the “metarhinus” sandstone. the massive sandstone units of uinta b1 are not laterally extensive, and a red shale and siltstone unit described by cashion (1974) might be a more appropriate boundary unit. the various changes in terminology and marker units have caused significant confusion in museum locality data, and has adversely affected the accuracy of the stratigraphic ranges of numerous uintan taxa. prothero (1996) constructed a magnetostratigraphic section correlating the various historical uinta formation localities. with the local ranges of various mammalian taxa in disorder due to earlier stratigraphic nomenclatural changes, prothero’s (1996) work was an essential first step in clarifying and correlating localities across the exposed formation in the uinta basin. townsend and others (2006) described a series of stratigraphic sections through the upper intervals of osborn’s (1929) uinta b2 and uinta c, up to the contact with the overlying duchesne river formation (figure 14a). these authors suggested a new boundary between the uinta b and uinta c based on a significant lithologic and color change. the suggested boundary is approximately 73 m (240 ft) higher than the amynodon sandstone of osborn (1929). sprinkel (2007) mapped the boundary between the uinta c and the duchesne river formation higher in the section, and because it is associated with such a gradual lithology change in the eastern part of the basin, but noted there was an intertonguing transition zone between the formations. sprinkel mapped the uinta b-c boundary using a distinctive and reportedly more laterally persistent greenish-mudstone bed that occurs just below the amynodon sandstone. stratigraphic work continues in conjunction with the current paleontological work. paleoenvironmental history, paleontology, and biochronology of the uinta formation the eocene epoch is the time when many modern orders of mammals first appear in the fossil record (e.g., primates, bats, artiodactyls, perissodactyls, rabbits). prior to the eocene, mammalian faunas were comprised of archaic forms that had diversified just after the demise of the dinosaurs at the cretaceous-paleogene boundary. during the early eocene, global climates were exceedingly warm and produced an almost pole-to-pole tropical greenhouse (zachos and others, 2001). the uintan nalma and the final intervals of the preceding bridgerian, mark the beginning of the end of this global greenhouse, and this is reflected in the ecological diversity of the mammals that lived during this time (woodburne and others, 2009a, 2009b; townsend and others, 2010). tropical arboreal forms, typical of the early eocene greenhouse began to drop off, and mammals that were more adapted to subtropical, even temperate conditions and habitats began to appear (townsend and others, 2010). the uintan nalma also marks a key transition in the evolutionary history of north american mammalian faunas as approximately 31% of modern mammalian taxonomic families (ancestors of canids, camelids, felids, and some modern rodents) appeared in the fossil record (black and dawson, 1966). the uinta formation fossils that form the basis of the uintan nalma are from uinta b1, b2, and c units. the fauna from uinta b1 comes mainly from the wagonhound-bonanza area, an early locality (well no. 2), and the willow creek-ouray area. the assemblage from this unit is small and includes achaenodon uintensis, protoreodon parvus, oromeryx plicatus, harpagolestes, eomoropus amarorum, hyrachyus eximius, a species of triplopus, and a diverse group of brontotheres and uintatheres (prothero, 1996; gunnell and others, 2009). these taxa are considered an early uintan assemblage corresponding to biochron ui2 of gunnell and others (2009). the uinta b2 fauna is incredibly diverse (see appendix) constitutes the bulk of the assemblage that is considered early uintan, and corresponds to biochron ui2 of gunnell and others (2009). strata that have yielded faunas from the uinta b2 unit include white river pocket and areas around kennedy’s hole. recent fossil collecting efforts have made it possible to formally define biochronologic units and stratotype sections for the uinta formation (gunnell and others, 2009). the beginning of ui2 is defined by 26 index taxa (outlined 35 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 in gunnell and others, 2009). numerous taxa range through ui2, but only a few are unique to ui2 and these are from uinta b2 beds: amynodon reedi, eobasileus cornutus; eomoropus amororum, hyrachyus eximius, limnocyon potens, mesonyx obtusidens, metarhinus fluviatalis, metarhinus sp., pantolestes longicaudus, paramys sp., sciuravus popi, uintatherium anceps (gunnell and others, 2009). fossil mammals found in uinta c sediments are typically considered to be late uintan and correlate to biochron ui3 of gunnell and others (2009). strata that have yielded late uintan faunas include myton pocket (southeast of myton, utah), kennedy’s hole, leota ranch, devil’s playground, leland bench draw, and antelope draw. the uinta c fauna is equally as diverse as the uinta b2 fauna. twenty-four taxa define the beginning of ui3 including auxontodon, colodon, duchesneodus, eosictis, janimus, mytonius, mytonomeryx, pentacemylus, procyonodictis, protadjiduamo, protitanotherium, and metatelmatherium. one of the striking differences between ui2 and ui3 faunas is that the younger assemblages is dominated by artiodactyls. therefore, this biochron was designated the “pentacemylus progressus interval zone” reflecting the abundance of this particular taxon (gunnell and others, 2009). whereas the taxonomic composition of ui3 is quite different than ui2, only a few genera make their first appearance during this interval (gunnell and others, 2009). current fieldwork is focused on collecting the upper intervals of the uinta c unit via excavation and screenwashing in order to increase the sample of small mammals (westgate and others, 2013, 2014; townsend and murphey, 2015). uinta formation field trip stops travelling south across the uinta basin via state route (sr) 45, we will cross both the green and white rivers and make our way to the base of the uinta formation just south of wagon hound canyon. note that the driving distance from the utah field house museum in vernal to the first field trip stop is 68.5 km (42.6 mi). examination of the uinta formation begins at the base of the formation where it overlies strata of the parachute creek member of the green river formation along the white river. from there travel north across wagon hound canyon to examine rocks of the uinta a and interbedded green river formation. continuing north are the green siltstone and brown sandstone beds that are typical of uinta b1. from there, the typical reddish and grayish beds defining uinta b2 and the orange-red beds that typify the brennan basin member of the duchesne river formation are seen in the distance. most of the day will be spent exploring the typical uinta b2 localities in the coyote wash area with a drive to the red wash area where the transition to uinta c rocks is well exposed. from red wash, drive northwest up section to a fossil locality that is stratigraphically high in uinta c and near the contact with the overlying brennan basin member of the duchesne river formation. the final uinta formation stop is located to the southwest of this location at a classic uinta formation fossil locality, white river pocket. stop 1. uinta formation – green river formation contact along the white river at wagon hound canyon (0.0 km/mi; cumulative 0.0 km/mi; sr 45 highway milepost 0.8): peterson in osborn (1895) described the contact between the uinta formation and the green river formation as a series of “hard brown sandstones” that conformably overlie the green river shales. looking north across the white river, the parachute creek member of the green river formation is exposed as sloping yellow-brown, tan, and green-gray mudstone and claystone directly underlying the massive sandstone cliffs of uinta a (figure 14b). looking to the east along the white river, the green river shale beds are exposed as dark brown bands within the member. the “hard brown sandstones” of the uinta formation are markedly different from the underlying green river formation in that they form massive resistant cliffs of yellow-brown sandstone. there are few reported identifiable vertebrate fossils from the uinta a with stratigraphically reliable locality data, and none collected thus far are biostratigraphically diagnostic. the uinta a may be earliest uintan (ui1a) in part (or possibly even br3 in part), and therefore could be partially equivalent with the turtle bluff member of the bridger formation (see murphey and daitch, 2007). drive north on sr 45 and turn left (west) at 2.7 km (1.7 mi; at milepost 2.4) onto a graded dirt road. bear right at the bottom of the hill 0.16 km (0.1 mi) ahead 36 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 figure 14. caption on following page. 37 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 (cumulative 2.9 km [1.8 mi] from stop 1), and turn onto a less well-maintained road. pull off after 0.16 km (0.1 mi), cumulative 3 km (1.9 mi) from stop 1. stop 2. uinta a and cashion’s “a” tuff (3 km [1.9 mi] from stop 1; cumulative 3 km [1.9 mi]): driving north on sr 45 through wagon hound canyon, turn west onto a graded dirt road. here the sloping yellow-gray siltstone and cliff-forming sandstone of uinta a are well exposed. cashion’s (1974) “a” tuff is exposed on the slope and is most visible just below the cliffs to the north. this tuff has not yet been dated because it is so crystal poor. the boundary between the uinta a and uinta b is mapped as occurring half way up the cliff above the tuff. beds of lacustrine shale are interbedded with the lower part of the uinta a sequence in this general area, reflecting the complex transition from lacustrine to fluvially dominated depositional environments. fragments of fossilized bone and wood have been found in some of the side canyons in this area. optional stop: peterson’s 1924 dolichorhinus quarry. continue southwest from stop 2. after passing a small gilsonite mine the road will bend to the northwest. after another 0.24 km (0.15 mi), there is a fork in the road. take the right fork to the top of the hill to the north. at approximately 2.9 km (1.8 mi) from stop 2, the spoils pile from peterson’s 1924 dolichorhinus quarry will be visible 0.32 km (0.2 mi) to the east of the road. this historic quarry site was re-located by vernal paleontologists evan hall and sue ann bilbey. return to stop 2, then get back on sr 45 and drive north and northeast past the bonanza gilsonite mining operation. park on the east shoulder of the highway (5.5 km [3.4 mi] from stop 2). stop 3. uinta b1 and metarhinus sandstone (5.5 km [3.4 mi] from stop 2, cumulative 8.5 km [5.3 mi]; sr 45 highway milepost 5.6): this unit is composed of a massive yellow-gray sandstone bed underlain by greenish-gray siltstone (figure 14c). the metarhinus sandstone is not a widespread unit. it is the boundary between osborn’s (1929) uinta b1 and b2. to the west, both the bonanza and independent gilsonite veins are visible. the most common vertebrate remains found here are turtle and crocodile. mammals that have been recovered include mostly brontotheres and other large uintan mammals. continue northwest on sr 45. at 6.3 km (3.9 mi) from stop 3 (sr 45 highway milepost 9.3), turn northeast at the intersection with uinta cr 3150. the dark brown, bench-supporting, sandstone bed to your east and west is the amynodon sandstone, which has traditionally formed the boundary between the uinta b and uinta c. continue down uinta cr 3150 for 6.4 km (4 mi) to an intersection with a dirt road (the railroad will be to the south). turn right onto the dirt road and cross over the railroad tracks. after crossing the railroad tracks, veer to the right and then turn left heading south as the dirt road continues. after turning south on the dirt road travel for 1.3 km (0.82 mi) until reaching a two-track road veering to the right. this twotrack road goes across quaternary sediments with uinta formation outcrops to the north. the two-track road will veer to the right, towards the outcrops. this is the region of the wu-18 locality. stop 4 is located 9 km (5.6 mi) from the junction of sr 45 and uinta cr 3150 (old bonanza highway), and 15.3 km (9.5 mi) from stop 3. figure 14 (figure on previous page). (a) stratigraphic sections from townsend and others (2006) indicating the level of the amynodon sandstone of osborn (1929) at the top of b section—considered the traditional boundary between uinta b2 and uinta c—and the uinta b2 and uinta c boundary at devil’s playground as suggested by townsend and others (2006) indicated by the arrow at devil's playground 1; (b) view of massive cliff-forming uinta a sandstone beds overlying and interfingering with parachute creek member of the green river formation; (c) measuring one of the massive sandstone units in uinta b; (d) collecting at wu-18, a typical uinta b2 locality; (e) sandstone channels associated with the wu-110 locality complex. 38 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 stop 4. uinta b2 and wu-18 (15.3 km [9.5 mi], cumulative 23.8 km [14.8 mi]): driving into coyote wash, strata characteristic of uinta b2 lithologies can be observed; greenish-gray, yellow, and light-pink to red mudstone and claystone. the wu-18 locality or “gnatout-of-hell,” is a typical uinta b2 locality in terms of the lithology (figure 14d). wu-18 is the single most productive uinta b2 locality currently known. the main productive level is a dark-brown, sandy mudstone that has produced numerous mammals, including the early primate chipetaia and large bodied amynodont rhinocerotoids and brontotheres (rasmussen, 1996; rasmussen and others, 1999a). coprolites with small mammal bones from wu-18 indicate that this locality may have been partially accumulated by a diurnal raptor (thornton and rasmussen, 2001). stratigraphically above and to the northeast of wu-18 is the amynodon sandstone, the classic boundary between uinta b2 and uinta c (osborn, 1929). this massive sandstone unit sometimes yields large-bodied ungulates, such as its rhinocerotoid namesake, amynodon, and brontotheres. screenwashing at wu-18 has resulted in the recovery of multiple bird bones, increased samples of primates and small rodents. return to sr 45 and drive north for 1.9 km (1.2 mi), to the left will be a graded turn off just east of a small overpass. turn off onto this road and follow the road for 4.2 km (2.6 mi). park on the south shoulder of the road. notice an expansive gas well pad to the east. stop 5. uinta c wu-117 locality complex (6.3 km [3.9 mi] from turn turnoff of cr 3150 to sr 45, cumulative 30.1 km [18.7 mi]): looking south from the shoulder of the road is an expanse of thick, gray mudstone capped by a golden sheet sandstone. to the east are massive golden sandstone channels are present. the wu-117 locality complex spans the uinta b2-uinta c boundary as defined by townsend and others (2006). the primary lithology in the area consists of gray-green, tan, and yellow-brown mudstone. a distinctive feature of this complex include large dark-brown, fineto coarsegrained channel sandstone beds (figure 14e). numerous fossils have been discovered in a dark-brown siltstone layer that weathers pink at wu-110. these fossils include the primate ourayia, the artiodactyls protoreodon and leptotragulus, as well as numerous rodents. the remaining localities in the area wu-110, 115, 116, have also been quite productive. in addition to more small mammal dentaries, large bodied perissodactyls, carnivore postcrania, and a specimen of simidectes have been recovered. return to sr 45 and head north for 0.62 miles and pull off to a graded turnout on the west side of sr 45. stop 6. devil’s playground red beds (1 km [0.62 mi] from turnoff to sr 45, cumulative 31.1 [19.3 mi]): to the southwest, there is an expansive section of mudstone; at the top there are two distinctive red beds. townsend and others (2006) consider these beds to be at the top of the uinta c and transition to the brennan basin member of the duchesne river formation in this eastern region of the basin. head north on sr 45 for 4.8 km (3 mi) and turn northeast onto a short graded road at sr 45 highway milepost 14.0. there is an old information kiosk and small wind turbine located approximately 100 m (300 ft) east of the highway at this location. stop 7. uinta formation-duchesne river formation lower transition zone contact (5.8 km [3.6 miles from stop 6; cumulative 36.9 km [22.9 mi]; sr 45 highway milepost 14.0): this is the approximate stratigraphic location of the base of the transition zone between the uinta c (myton member) and the brennan basin member of the duchesne river formation as mapped by sprinkel (2007). drive northwest along sr 45 for 1.1 km (0.7 mi) until coming to an intersection with the paved road, which leads to the deseret power plant. turn southwest on the power plant road and stop. stop 8. uinta formation – duchesne river formation upper transition zone contact (1 km [0.62 mi] from stop 7; cumulative 37.9 km [23.5] mi]; sr 45 highway milepost 14.7): looking east is a view of the approximate stratigraphic location of the top of the transition zone between the uinta c (myton member) and the brennan basin member of the duchesne river formation as mapped by sprinkel (2007). continue north on sr 45 for about 8 km (5 mi), 39 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 turn left at the intersection leading to the glen bench road and deadman bench road. glen bench road is paved and intersects on the right with wonsits valley road (cr 3250) which is a graded dirt road. take the right onto wonsits valley road and continue across deadman bench for 11.1 km (6.9 mi) and then make a left turn to travel south along wonsits valley road going down section through the lower part of the brennan basin member and transitional contact with underlying uinta formation. drive 1.6 km (1 mi) and turn left onto a graded road. then drive 1.2 km (0.75 mi), still veering left, and pull onto the shoulder of the road. stop 9. uinta c, wu-50, wu-49, lower transition zone contact with the brennan basin member of the duchesne river formation (21.9 km [13.6] miles from stop 8; cumulative 59.8 km [37.2 mi]): nearing the top of the uinta formation, the strata are brightly pigmented and weather deep brown, bright orange, and various shades of red. in the wu-50 area, sloping dark-red, gray, and tan mudstone beds are interbedded with large, ledge-forming, blocky yellow-brown sandstone beds. at this stratigraphic level in the formation, the duchesne river and uinta formations are locally interbedded. conglomeratic resistant sandstone channels typical of the brennan basin member of the duchesene river formation can be viewed above the darkred mudstone of wu-49. these localities and others surrounding it are highly productive and have yielded numerous perissodactyls including early tapiroids, such as isectolophus, and almost complete skeletons of large rodents like pseudotomus. from the wu-50 locality complex, return to wonsits valley road and head south for approximately 1 mile and turn right. continue to drive west for 1 mile and pull off the road. stop 10. uinta c, wu-26 locality micromammal screenwash site (3.2 km [2.0 mi] from stop 9; cumulative 63 km [39.2 mi]): the wu-26 fossil locality has yielded the first micro-mammal fauna from the late uintan (late middle eocene) from uinta c of the uinta formation in the uinta basin. the formation outcrops comprise the type locality for species, which define the uintan nalma. our field crews have processed more than 25 tons of bulk sample from wu-26 and recovered more than 600 micro-mammal specimens identifiable to at least the genus level (figure 15). the fossil-bearing horizon is a 15-cm-thick (6 in), green claystone interepted as pond or oxbow lake deposits, and lies 40 m (130 ft) below thick channel sandstone beds at the base of the brennan basin member of the duchesne river formation (figure 16). wu-26 provides a unique glimpse into the micro-mammal community which inhabited the uinta basin near the end of deposition of the uinta formation. the virtual absence of paleobotanical specimens in the uinta formation makes paleoclimatic reconstructions problematic. a tiny palynologic flora recovered from wu-26 is currently under study. more than 1000 micro-mammal specimens were collected at texas memorial museum locality 42486 from the parallic, late middle eocene, laredo formation, at laredo, texas. microand macro-floral remains along with fish and reptilian species indicate the casa blanca community lived in a lowland tropical rain forest and coastal mangrove setting. the wu-26 sample size is now large enough to make meaningful comparisons with the ui3-age casa blanca micro-mammal community (table 4). protoreodon parvus is present in both faunas. several other genera are present in both faunas including herpetotherium, mytonius, epihippus, ?amynodon, microparamys, mytonomys, and pauromys; indicating that both environments shared habitats compatible for these taxa. that fact and the presence of crocodilians including “allognathosuchus,” the carettochelyid turtle pseudanosteira pulchra, along with the tortoise hadrianus, and at least four species of omomyid primates, suggest that the paleoclimatic regime at wu-26 was subtropical or warmer. it is significant that the earliest known north american lagomorph, mytonolagus petersoni, as well as janimus, pareumys, sciuravis, and talpavus are present at wu-26, but absent from tmm 42486, indicating that paleoecological differences also existed. small mammals in the casa blanca fauna not yet discovered at wu-26, include mahgarita, laredomys, and microeutypomys. return to sr 45 via wonsits valley road (8.92 miles) and turn left onto sr 45 traveling north. drive 11.68 miles and pull over at sr 45 highway milepost 31.5, 20.60 miles from stop 10. 40 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 stop 11. view of asphalt ridge (32.2 km [20.6 mi] from stop 10; cumulative 96.2 km [59.8 mi]; sr 45 highway milepost 31.5): driving the last 18.8 km (11.7 mi), has been through rocks of the brennan basin member of the duchesne river formation. this stop affords an excellent view of asphalt ridge, a geologically interesting structure composed of uplifted and tilted strata of the brennan basin member of the duchesne river formation unconformably overlying more steeply tilted strata of the late cretaceous mesaverde group. the structural geology of asphalt ridge documents multiple episodes of uplift and erosion related to uinta mountain tectonics. asphalt ridge contains significant tar sand deposits that mostly saturate sandstone beds of the mesaverde group and lowermost part of the eocene duchesne river formation (ritzma, 1979; blackett, 1996). the final uinta formation field trip stop is a visit to the classic fossil locality white river pocket. detailed directions to this field trip stop are not included in this field trip guide because there are numerous ways to get there. as a result, the mileage to this field trip stop is not connected to the preceding field trip stops. to get to white river pocket, travel to the point at which sr 88 crosses the white river bridge south of the hamlet of ouray. stop 12: white river pocket: head south on sr 88 for 0.2 miles. pull over onto the shoulder. the badland hill and surrounding area to the east is a classic fossil locality called white river pocket. the fossil assemblage from white river pocket provided the basis for early uintan faunas, and are significant because a large number of genus wu-26 42486 common name amia x bowfin lepisosteus x x gar psuedanosteira x carettochelyid allaeochelys x carettochelyid apalone x x softshell turtle hadrianus x x tortoise chelonia undet. x x misc. turtle frags. “allognathosuchus” x x alligator crocodylid undet. x x crocodilian glyptosaurus x x lizard herpetotherium x x mouse opposum talpavus x insectivore centetodon x insectivore pantolestid x pantolestid cf. omomys x primate mytonius x x primate ourayia x primate trogolemur ? primate mahgarita x primate miacid x x carnivore harpagolestes x mesonychid sirenian x sea cow epihippus x x 4-toed horse colodon x tapir amynodon ? x rhino notiotitanops x titanothere protoreodon x x artiodactyl leptoredon x artiodactyl leptotragulus x artiodactyl toromeryx x artiodactyl mytonomys x x rodent microparamys x x mouse janimus x mouse microeutypomys x mouse pauromys x x mouse pareumys x mouse sciuravis x mouse laredomys x mouse mytonolagus x rabbit x = genus is present ? = insufficient material for firm generic identification figure 15. jeffrey westgate and dana cope bulk sampling the 15-cm-thick micro-mammal-bearing green claystone at wu-26. between 2007-2015, 25 tons of bulk sample were collected from this horizon. table 4. presence of genera at wu-26 and tmm 42486. 41 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 small mammal taxa were found there. drive north on sr 88 for 18.8 km (11.7 mi). just past the pelican lake café, turn left onto uinta cr 2762. drive west for 7.5 km (4.7 mi) and park on the north shoulder. to the right are spectacular cliffs that are historically known to paleontologists as “randlett point,” with excellent exposures of the sequence that contains the conformable boundary between the uppermost uinta c (myton member) and the brennan basin member of the duchesne river formation, type sequence of the “randlett horizon.” for further explanation, see stop 1 of the duchesne river formation field trip below. duchesne river formation the duchesne river formation is widely exposed in the northern and western parts of the uinta basin. its definition and stratigraphic history are related to the underlying and apparently conformable uinta formation. in the northern part of its distribution along the uinta mountain front, it unconformably overlies rocks of triassic and jurassic age. the lower part of the duchesne river formation also contains tar sand in the asphalt ridge area (ritzma, 1979; usgs, 1980; blackett, 1996). the duchesne river formation was deposited under mostly fluvial conditions but includes some minor lacustrine deposits. andersen and picard (1972) proposed the presently accepted stratigraphy and described the following members in ascending stratigraphic sequence: brennan basin, dry gulch creek, lapoint, and starr flat. the brennan basin member is composed of soft to figure 16. stratigraphic section from wu26 quarry in the upper uinta c member of the uinta formation, up to the base of the brennan basin member of the duchesne river formation which lies 40 m above the wu-26 quarry horizon. 42 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 moderately resistant, light-to-medium red, light-gray, light-brown, yellow, and tan ledgy sandstone, mudstone, conglomerate, shale, and siltstone with a maximum thickness of about 600 m (1970 ft) south of vernal. this member thins significantly to the east and west. the dry gulch creek member consists of soft to moderately resistant, light-to-medium gray, medium-red, purplish-gray, and yellow sandstone, mudstone, shale, and conglomerate. it is approximately 149 m (490 ft) thick. the lapoint member consists of mostly soft, light-red, tan, and yellow sandstone, siltstone, and mudstone with minor amounts of conglomerate. it contains diagnostic beds of light-gray to medium-gray or bluish-gray bentonite, and ranges in thickness from approximately 119 to 299 m (390–980 ft). the lapoint ash, which forms the base of the lapoint member (where most of the vertebrate fossils have been discovered), has been dated at 39.74 ma ± 0.07 ma (prothero and swisher, 1992). the starr flat member consists of moderately resistant, lightto medium-red and tan sandstone, mudstone, with a significant amount of red and gray conglomerate. the starr flat ranges from 38 to 235 m (124–770 ft) thick (anderson and picard, 1972; rowley and others, 1985). it sporadically crops out along the southern flank of the uinta mountains. the history of stratigraphic nomenclature for the duchesne river formation is somewhat confusing (table 5). clarence king (1878) named the uinta group for what we now call the uinta and duchesne river formations. peterson, in osborn (1895), proposed that the uinta group be subdivided into a, b, c horizons, with the c horizon being equivalent in part to what we now know as duchesne river formation and equivalent in part to the upper uinta group. douglas (1914) suggested that the name uinta group be replaced by the name uinta tertiary to avoid confusion with the precambrian uinta mountain group. scott in peterson (1931) named the duchesne formation, and it was renamed duchesne river formation by kay (1934) because the name duchesne formation was preoccupied. kay (1934) defined the duchesne river formation by removing the red beds of osborn’s (1895) upper uinta group, recognizing they have a younger mammalian fossil fauna. he also recognized three biostratigraphic “horizons:” randlett, halfway, and lapoint. gazin (1955) removed the randlett horizon from the duchesne river formation, recognizing that it contains a fauna that is almost identical to that of the uinta c. warner (1963) recognized two members, the minor bentonite member, equivalent to the brennan basin and dry gulch creek members, and the major bentonite member, equivalent to the lapoint member. andersen and picard (1972) named the currently recognized members: brennan basin, dry gulch creek, lapoint, and starr flat. with regard to andersen and picard’s (1972) stratigraphic terminology, the brennan basin member is equivalent to the randlett horizon of kay (1934) and the lower part of halfway horizon, the dry gulch creek member is equivalent with the upper part of the halfway horizon, and the lapoint member is equivalent to the lapoint horizon. fossils and biochronology of the duchesne river formation in comparison with the underlying uinta formation and correlative strata of duchesnean age in coastal southern california, the vertebrate fossil fauna of the type duchesne river formation is sparse. however, it is a critically important period in mammalian evolutable 5. history of duchesne river formation stratigraphic nomenclature. 43 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 tion (lucas 1992; rasmussen and others, 1999b; robinson and others, 2004). although it is the nominal stratotype for the duchesnean nalma (wood and others,1941), its validity has been the subject of some controversy among paleontologists (see wilson, 1978; lucas, 1992). nevertheless, the duchesnean nalma has now been widely accepted by paleontologists (rasmussen and others, 1999b; robinson and others, 2004). lucas (1992, p. 88) made the observation that the duchesne river formation “has either been questioned, abandoned, subdivided, or defended.” scott (1945) regarded the duchesne river formation as oligocene in age. simpson (1946) and gazin (1955) considered it eocene. faunally, the importance of the duchesne river formation and the duchesnean nalma is based on the fact that it records a major faunal replacement in north america, as demonstrated by its large number of first and last occurrences, as well as the small number of genera that are restricted to it (black and dawson, 1966; robinson and others, 2004). robinson and others (2004) tentatively assigned duchesnean first appearances to include hyaenodon, duchesneodus, duchesnehippus intermedius, amynodontopsis, and eotylopus. the fauna of the brennan basin member, which was previously assigned to the randlett horizon and lower part of the halfway horizon of kay (1934), includes a faunal assemblage that is generally considered to be intermediate between the uinta c (biochron ui3, gunnell and others, 2009) and the lapoint member of the duschesne river formation, although most workers regard it as late uintan. the brennan basin member outcrops over a fairly large area, and several somewhat productive localities are known. it contains a reasonably diverse assemblage of uintan artiodactyls including protoreodon, pentacemylus, diplobunops, and leptotragulus. perissodactyls include a mix of uintan and duchesnean brontotheres, as well as tapirs and rhinos. specimens of the uintan lagomorph mytonolagus and the rodents pareumys and mytonomys have also been collected (rasmussen and others, 1999b). until recently, only two published specimens had ever been reported from the dry gulch creek member, and these represented the “halfway fauna” (rasmussen and others, 1999b). the specimens include the holotype of duchesnehippus intermedius, a genus of horse that is purportedly intermediate between the uintan horse epihippus and the chadronian horse mesohippus, and a femur and astragalus tentatively identified as (?) hyracodontid rhinoceros. walsh and murphey (2007) discovered a locality that produced a diversity of small mammals in the dry gulch creek member (67 identifiable specimens). sdsnh loc. 5939 (“halfway hollow one”) is situated roughly in the stratigraphic middle of the dry gulch creek member (tdr-dgc), at about the same level as the type locality of d. intermedius. the fauna of this locality and other newly documented localities from the duchesne river formation was described by kelly and others (2012). new records form the dry gulch creek member include copedelphys sp.; lipotyphla (genera and species indeterminate); mytonolagus sp.; pareumys guensburgi; griphomys sp.; heliscomys sp.; passaliscomys sp.; metanoiamys lacus; metanoiamys sp., cf. m. korthi; protadjidaumo typus; protadjidaumo sp., cf. p. typus; paradjidaumo sp.; adjidaumo sp., cf. a. craigi; simiacritomys sp.; microeutypomys sp.; eutypomys sp.; and poabromylus kayi. importantly, pareumys guensbergi, protadjidaumo typus, and passaliscomys sp. suggest a duchesnean age for most or all of the dry gulch creek member, and that the uintan-duchesnean boundary occurs somewhere within the upper part of the brennan basin member or the lower part of the dry gulch creek member. the mammalian fauna of the lapoint member is considered the type duchesnean fauna, although misidentifications, data loss, and mistakes made by earlier workers have resulted in considerable confusion regarding what was actually collected at this horizon. most of these problems seem to have been resolved by the efforts of rasmussen and others (1999b). the lapoint fauna contains diverse assemblages of artiodactyls such as protereodon, agriochoerus, simimeryx, and brachyops, and perissodactyls such as colodon, hyracodon, duchesnehippus, and duchesneodus. also present are carnivores, the mesonychid hessolestes, the hyaenodont hyaenodon, the lipotyphlan centetodon, and the rodents pareumys and protadjidaumo. no published accounts of fossils have been reported from the stratigraphically highest starr flat member. however, paul murphey and mark roeder of the 44 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 san diego natural history museum discovered a highly fragmented mammal tooth that was tentatively identified as a partial upper molar of a large artiodactyl from near the base of the member. this specimen was described by kelly and others (2012). although the lapoint and brennan basin members of the duchesne river formation are the most fossiliferous, fossils are generally scarce throughout the formation. any new discoveries would be highly significant, especially from the dry gulch creek and starr flat members. it is also noteworthy that reptiles in general are poorly represented from the duchesne river formation. much work remains to be done in order to document the faunal changes within the duchesne river and ascertain the position of the uintan-duchesnean boundary. as concluded by kelly and others (2012), the mammalian assemblages from the dry gulch creek and lapoint members of the duchesne river formation are combined as the halfway/lapoint fauna and regarded as the “type fauna” of the duchesnean nalma. new correlations of the uintan and duchesnean faunas from the sespe formation of california to the global polarity time scale are based on taxonomic comparisons of the sespe faunas to those from the uinta basin and radioisotopic data. based these new correlations, the uintan-duchesnean boundary occurs within chron c19n of the gpts, or about 41.4 ma. duchesne river formation field trip stops our exploration of the duchesne river formation begins at randlett point where the contact between the uinta c of the uinta formation (myton member) and the overlying brennan basin member of the duchesne river formation is well exposed and relatively easy to discern. from there we travel north through strata of the brennan basin member in halfway hollow, and then examine exposures of the dry gulch creek member and discuss the paleontology of this sparsely fossiliferous unit that appears to contain the boundary between the uintan and duchesnean nalma although the precise stratigraphic position of the boundary has not yet been determined. from a distance, we then view the lapoint member and overlying starr flat member in halfway hollow. heading east along the lapoint highway to twelvemile wash, our last stop is at the site of the famous carnegie museum titanothere quarry just above the base of the lapoint member, as well as the lapoint ash at quarry level. stop 1. randlett point (0.0 km/mi, cumulative 0.0 km/mi): peterson and kay (1931) defined the base of the duchesne river formation at this location. the boundary between the uinta c (myton member) and overlying brennan basin member in this part of the uinta basin is easier to discern than farther to the east in the type area of the uinta formation in the coyote basin. here the contact is marked by the change from slope-forming pink, purple, light-gray, and red (variegated) mudstone and siltstone beds of the uinta formation to ledge-forming orange, reddish-brown, and gray siltstone and sandstone beds of the overlying brennan basin member (figure 17a). the carnegie museum’s randlett quarry is approximately 1.6 km (1 mi) to the north of this location. with the exception of the large duchesnean brontothere duchesneodus, the fauna of the brennan basin member resembles that of the uinta c, and the fauna of the lower part of the brennan basin member is regarded by most workers to be uintan in age. drive east on the ouray-randlett road (uinta county road 2762) for 4.7 miles to the junction of state route (sr 88). turn left (north) on sr 88 and drive to u.s. 40. turn right (east) on u.s. 40 and drive for about 2.2 miles to the intersection of the halfway hollow road and then turn north on th dirt road. stop 2. brennan basin member-dry gulch creek member boundary (30.6 km [19 mi] from stop 1, cumulative 30.6 km [19 mi]: andersen and picard (1972) defined this boundary as the base of the lowest bed of fine-grained rock overlying the highest resistant sandstone of the brennan basin member (figure 17b). this contact was mapped by rowley (unpublished field maps), rowley and others (1985), and sprinkel (2007) as the sandstone bed visible at this stop. this tan sandstone and conglomerate is highly variable in thickness, and crosses halfway hollow road at utm zone 12, 609901 me, 4470184 mn (nad 27). a widespread 45 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 but thin 0.5-m-thick (1.6 ft) dark-red, indurated, finegrained sandstone, interpreted by andersen and picard (1972) as a paleosol, can be seen approximately 18 m (60 ft) above the top of the sandstone. fossil snails and bone fragments have been receovered from screenwashing sediments collected from between the boundary sandstone bed and red paleosol approximately 0.4 km (0.25 mi) to the southwest of this location. however, no identifiable mammal fossils have been found to date in these samples. continue driving north on halfway hollow road for 3.7 km (2.4 mi). stop east of a large evaporation pond with five tank batteries located along its southern edge. stop 3. dry gulch creek member fauna (3.8 km [2.4 mi] from stop 2, cumulative 34.4 km [21.4 mi]): this part of halfway hollow has produced the only known mammal fossils from the dry gulch creek member. a relatively fossil-rich micromammal quarry was discovered just to the east of the road (halfway hollow one, sdsnh loc. 5939) in 2006, and is discussed above. these fossils are currently being formally described, and it is likely that additional screenwashing of sedifigure 17. (a) the contact between the uinta c (tu-c) and brennan basin member of the duchesne river formation (tdr-bb) at randlett point, uintah county, utah; (b) view looking northeast at the sandstone bed (base dgc) that divides the brennan basin member of the duchesne river formation (tdr-bb) from the overlying dry gulch creek member (tdr-dgc) in halfway hollow, uintah county, utah; (c) view looking west at the carnegie museum teleodus quarry (tq), the lower bentonite bed (lb) that marks the boundary between the dry gulch creek member (tdr-dgc) of the duchesne river formation and the overlying lapoint member (tdr-lp), and the lapoint tuff (lpt), uintah county, utah. 46 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 ments from this locality will yield additional mammal fossils. peterson (1931c, p. 70–71) described the type specimen of epihippus (duchesnehippus) intermedius (along with specimens tentatively identified as a partial femur and astragalus of a hyracodontid rhinoceros) as coming from “the west side of halfway hollow, from a red clay about 8 feet thick, overlain by a massive brown sandstone and underlain by a reddish nodular clay associated with astragalus and horse jaw.” the specimens were collected by john clark on july 21, 1931 (alan tabrum, carnegie museum of natural history, written communication, 2006). continue driving north to northeast on halfway hollow road for 1.5 km (0.9 mi) until reaching sr 121 (lapoint highway). stop just beyond the cattle guard. stop 4. view of lapoint and starr flat members (1.5 km [0.9 mi] from stop 3, cumulative 35.9 km [22.3 mi]): looking north from this spot is an excellent view of the lapoint member, the starr flat member, and the distant uinta mountains with marsh peak at 3668 m (12,198 ft) on the skyline. the base of the lapoint member is defined as the lowest widespread bentonite bed. thick, laterally persistent bentonite beds are characteristic of this member. several additional american museum of natural history and carnegie museum fossil localities are located in this part of halfway hollow to the north of the lapoint highway, although recent efforts to relocate them have proven unsuccessful. the contact between the lapoint and overlying starr flat members is located at the approximate level of the tops of the red cliffs seen in the distance at the north end of halfway hollow. however, the top of the duchesne river formation is not visible from this location. as discussed above, the starr flat member has yielded tooth fragments from one locality, but no other fossils have been reported. that said, it has yet to be thoroughly prospected. it is possible that the fauna of the starr flatt member is younger than the duchesnean nalma. turn east onto the lapoint highway (sr 121) and drive for 4 km (2.5 mi). just past the sr 121 milepost 31, turn north onto a two-track road and drive for 1.1 km (0.7 mi) for a total of 5.1 km (3.2 mi) from stop 4. the carnegie teleodus quarry pit is located near the summit of the large hill to the northwest of this location. stop 5. carnegie titanothere quarry and lapoint ash (5.1 km [3.2 mi] from stop 4, cumulative 41 km [25.5 mi]): this is the site of the famous carnegie titanothere quarry (also known as the teleodus quarry and the duchesneodus quarry; figure 17c). for many years prior to the discovery of this quarry, there remained a recognized hiatus between the earlier mammalian faunas of the rocky mountain intermontane basins and the younger mammalian faunas of the white river badlands of south dakota and nebraska. in discovering and working this quarry, j.l. kay of the carnegie museum made the first important paleontological discovery to begin to fill this knowledge gap. peterson (1931a, 1931b, 1931c) and peterson and kay (1931) described the fossils from this locality and from other localities in the then lapoint horizon. these workers regarded the fauna as “perfectly transitional” (peterson, 1931c, p. 62). in addition to the brontothere fossils collected from the quarry, bunodont and selenodont artiodactyls, a rodent, an insectivore, hyracodontid rhinos, and a creodont and mesonychid were discovered and described. note that a recent thorough re-inspection of the quarry and surrounding area has failed to yield any additional fossils. the thin bentonite bed visible on the slope below the quarry is considered to be the base of the lapoint member by andersen and picard (1972). however, the lapoint ash (39.74 ± 0.07 ma, prothero and swisher, 1992) is actually the thicker, higher bentonite bed that is cut by the red sandstone channel in which the carnegie quarry fossils were preserved (figure 15c). therefore, the carnegie titanothere quarry is located stratigraphically just above the base of the lapoint member and is slightly younger than the lapoint tuff that was cut by the red sandstone channel. acknowledgments the authors wish to express their deepest gratitude to the many colleagues, students, and volunteers that have assisted with our field work in the bridger and uinta basins over the years. in particular, we are grateful for the participation of faculty, staff, and students from the university of colorado museum, washington university in st. louis, san diego natural his47 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 tory museum, college of charleston, the university of michigan, albion college, the university of alberta, midwestern university, and lamar university. we also thank the wyoming and utah state offices of the usdi bureau of land management, and the kemmerer, rock springs, and vernal field offices. without the support of the blm, our field work would not have been possible. we would like to thank the donors of the american chemical society petroleum research fund for partial support of this research. we are indebted to dr. robert anemone of the university of north carolina and dr. gregg gunnell of duke university for reviewing the original version of this field trip guide published by the geologial society of america in 2011. finally, we thank justin strauss and margaret madsen for their assistance with the compilation of the field trip mileage log. references alexander, j.p., and burger, b.j., 2001, stratigraphy and taphonomy of grizzly buttes, bridger formation, and the middle eocene of wyoming, in gunnell, g.f., editor, eocene biodiversity— unusual occurrences and poorly sampled habitats: new york, kluwer academic/plenum publishers, p. 165–196. andersen, d.w., and picard, m.d., 1972, stratigraphy of the duchesne river formation 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273–280. smith, m.e., singer, b., and carroll, a.r., 2003, 40ar/39ar geochronology of the eocene green river formation, wyoming: geological society of america bulletin, v. 115, no. 5, p. 545–565. smith, m.e., carroll, a.r., and singer, b.s., 2008, synoptic reconstruction of a major ancient lake system—eocene green river formation, western united states: geological society of america bulletin, v. 120, no. 1-2, p. 54–84. 52 paleontology and stratigraphy of middle eocene rock units in the southern green river and uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 smith, m.e., chamberlain, k.r., singer, b.s., and carroll, a.r., 2010, eocene clocks agree—coeval 40ar/39ar, u-pb, and astronomical ages from the green river formation: geology, v. 38, no. 6, p. 527–530. sprinkel, d.a., 2007, interim geologic map of the of the vernal 30' x 60' quadrangle, uintah and duchesne 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with comments on uintan biostratigraphy: the mountan geologist, v. 43, no. 2, p. 115–134. townsend, k.e.b., and murphey, p.c., 2015, fossil collection practices and their effect on museum collections composition, in vanden berg, m.d., ressetar, r., and birgenheier, l.p., editors, geology of utah’s uinta basin and uinta mountains: utah geological association publication 44, p. 439–453. townsend, k.e.b., rasmussen, d.t., murphey, p.c., and evanoff, e., 2010, middle eocene habitat shifts in the north american western interior—a case study: palaeogeography, palaeclimatology, palaeoecology, v. 297, no. 1, p. 144–158. tsukui, k., and clyde, w.c., 2014, fine-tuning the calibration of the early to middle eocene geomagnetic polarity time scale—paleomagnetism of radioisotopically dated tuffs from laramide foreland basins: geological society of america bulletin, v. 124, no. 5/6, p. 870–885. u.s. geological survey, 1980, asphalt ridge, white rocks, and vicinity, utah tar sands leasing minutes no. 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uinta basins, wyoming and utah murphey, p.c., townsend, k.e.b., friscia, a.r., westgate, j., evanoff, e., and gunnell, g.f. geology of the intermountain west 2017 volume 4 westgate, j., townsend, b., cope, d., and gartner, c., 2013, progress report on the first uinta c micro-mammal fauna from the uinta basin and its comparison with the casa blanca mammal community from laredo, texas [abs.]: geological society of america abstracts with programs, v. 45, no. 7, p. 325. wilson, j.a., 1978, stratigraphic occurrence and correlation of early tertiary vertebrate faunas, trans-pecos, texas, part 1— vieja area: texas memorial museum bulletin, v. 25, p. 1–42. wood, h.e., 1934, revision of the hyrachyidae: bulletin of the american museum of natural history, v. 67, article 5, p. 182–295. wood, h.e., chaney, r.w., clark, j., colbert, e.h., jepsen, g.l., reeside, j.b., and stock, c., 1941, nomenclature and correlation of the north american continental tertiary: geological society of america bulletin, v. 52, p. 1–48. woodburne, m.o., gunnell, g.f., and stucky, r.k., 2009a, land mammal faunas of north america rise and fall during the early eocene: denver museum of nature and science annals, no. 1, 78 p. woodburne, m.o., gunnell, g.f., and stucky, r.k., 2009b, climate directly influences eocene mammal faunal dynamics in north america: proceedings of the national academy of sciences, v. 106, p. 13399–13403. zachos, j., pagani, m., sloan, l., thomas, e., and billups, k., 2001, trends, rhythms, and aberrations in global climate 65 ma to present: science, v. 292, p. 686–693. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 8 2021 © 2021 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop stephen p. phillips and samuel m. hudson geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover drone photograph of the north side of vermillion creek. the upper cretaceous rock springs formation is centered in the photograph. the top of the rock springs formation is just right of center within a prominent valley. above the rock springs formation is the gray-colored trail member of the ericson sandstone, followed by the brown colored rusty zone of the ericson sandstone. the rusty member also forms a prominent valley. the canyon creek member of the ericson sandstone is in the upper right-hand corner of the photograph. the horizontal distance across the center of the photograph is approximately 500 m. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 8 2021 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are 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volume 8 2021 45 abstract the upper cretaceous rock springs formation of the mesaverde group in northwestern colorado, southwestern wyoming, and northeastern utah is composed of fluvial, deltaic, and marine sediments that record the regression of the western interior seaway during the early to middle campanian. contemporaneous deposits are present along the eastern and southeastern margins of the greater green river basin in wyoming, but correlation across the basin is challenging. analysis of a small (1-km-long), understudied outcrop in northwestern colorado assists in bridging that gap. the outcrop consists of distal and proximal deltaic deposits, overlain by distributary-channel complexes within delta-plain deposits. correlation panels based on subsurface wireline logs and outcrop gamma-ray profiles show that the deposits are younger than lithostratigraphically equivalent strata of the rock springs formation in utah and wyoming. regional nomenclature is introduced for the area, and it is shown that these deposits differ from better-documented, older rock springs formation deposits in utah and wyoming by having a higher net sandstone percentage due to the presence of substantial distributary-channel complexes. this study benefits subsurface exploration efforts in the greater green river basin by providing outcrop analogs of reservoir distribution and quality. the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop stephen p. phillips1 and samuel m. hudson1 1department of geological sciences, brigham young university, s389 eyring science center, provo ut, usa 84602; the.geologsist@outlook.com; sam.hudson@byu.edu citation for this article. phillips, s.p., and hudson, s.m., 2021, the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop: geology of the intermountain west, v. 8, p. 45–71, https://doi.org/10.31711/giw.v8.pp45-71. © 2021 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the upper cretaceous rock springs formation of the mesaverde group in northwestern colorado, southwestern wyoming, and northeastern utah records an overall regression of the cretaceous western interior seaway during the early to middle campanian (e.g., roehler, 1993; plink-björklund, 2008, 2019; rudolph and others, 2015). it represents an early-stage sedimentary wedge sourced from the sevier orogenic fold and thrust belt (armstrong and oriel, 1986) and is composed of fluvial, deltaic, shallow marine, and deep marine deposits (e.g., roehler, 1993; plinkbjörklund, 2008, 2019; rudolph and others, 2015). the rock springs formation has been studied in detail via outcrops around the rock springs uplift and along the northern flank of the uinta mountains (e.g., roehler, 1993; plink-björklund, 2008, 2019; rudolph and others, 2015). outcrop of the rock springs formation is also present in a small, tectonically complex exposure in northwest colorado along vermillion creek (sears, 1924, 1925; hale, 1950) (figure 1). this outcrop has never been studied in detail and its relationship to other outcrops has not been well-established. it is commonly 46 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 figure 1. caption is on the following page. 47 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 bypassed via subsurface correlation panels that tie the rock springs uplift to outcrops on the edge of the sand wash basin, colorado, even though it represents a strategic tie-point along that transect (hale, 1955; douglass and blazzard, 1961; keith, 1965; miller, 1977; kiteley, 1983; roehler, 1987; luo and nummedal, 2010). the aims of this paper are to present a detailed description of the sedimentology and architecture of the outcrop, interpret depositional settings based on that description, and utilize this information to facilitate a comparison to subsurface geophysical data. additionally, this paper aims to utilize this information to enable comparisons between outcrops on the north flank of the uinta mountains and the east flank of the rock springs uplift (figure 1). a better understanding of the depositional history of this outcrop can inform future studies that utilize subsurface correlation and sequence stratigraphic interpretation. future paleogeographic reconstructions will also benefit from a better understanding of shoreline position of the rock springs formation deposits through time. additionally, the rock springs formation has a rich history of economic significance, mainly through the mining of coal in the rock springs uplift (e.g., andrew, 1965; roehler, 1986; scott and others, 1995). however, oil and gas accumulation within the rock springs formation is potentially significant, yet unknown, largely because of sparse testing in much of the greater green river basin (finn and johnson, 2005; johnson and others, 2005). this work can inform future exploration efforts through detailed description of facies distribution and reservoir geometry/connectivity in the subsurface of the washakie and sand wash basins. geologic setting study area the rock springs formation is present in a small tectonically complex exposure on the southern edge of the vermillion basin in northwestern colorado (e.g., sears, 1924; hale, 1950; burger, 1965; ritzma, 1965, 1971) and is divided into two key outcrop areas by vermillion creek—the nw outcrop area and the se outcrop area (figure 1c). in total, the outcrop stretches for less than 5 km in a northwest-southeast direction with about 1 km of high-quality outcrop (figure 1). the vermillion basin is a modern-day basin or topographic low drained by vermillion creek and its tributaries (e.g., nightingale, 1930; gras, 1955) and is located within the greater green river basin (rigatti and others, 2007) (figure 1). the greater green river basin is further divided into several sub-basins and uplifts (figure 1). the outcrop area is located along a northern bounding fault of the uinta mountains called the sparks fault (figures 1 and 2). the sparks fault is a thrust fault with a sinistral component (weber, 1971; johnson and andersen, 2009) and a history of movement during the late paleocene to early eocene (ritzma, 1965, 1971; weber, 1971; bradley, 1995). faulting and associated folding was followed by erosion and the unconformable deposition of younger eocene deposits above older rocks (ritzma, 1965; bradley, 1995). this is highlighted in the vermillion creek area by an angular unconformity that juxtaposes shallowly dipping (2°to 10°) deposits of the wasatch and green river formations against vertical to nearly vertical cretaceous rocks (sears, 1924; ritzma, 1965) (figure 2). figure 1 (figure is on the previous page). location maps of various scales. (a) map of the greater green river basin showing the location of the rock springs formation and equivalent rocks. red dashed box indicates the extent of map shown in b. basemap attribution: esri, usgs, and noaa. abbreviations: wftb = wyoming fold and thrust belt, hb = hanna basin, wrm = wind river mountains, sba = sandy bend arch, gm = granite mountains, ma = moxa arch, rsu = rock springs uplift, vb = vermillion basin, grb = green river basin, um = uinta mountains, gdb = great divide basin, wa = wamsutter arch, wb = washakie basin, cr = cherokee ridge, swb = sand wash basin, ru = rawlins uplift, sm = sierra madre, pr = park range. outcrop pattern in wyoming is from love and christainsen (1985). (b) map of the study area showing the extent of the rock springs formation outcrop, available well data, and surface to subsurface correlation lines for figure 8. the location of c is also indicated. (c) satellite image of the vermillion creek area showing the location of the rock springs formation outcrop examined in the study. satellite imagery attribution: esri, maxar, geoeye, earthstar geographics, cnes/ airbus ds, usda, usgs, aerogrid, ign, and the gis user community. cross section is shown on figure 9. 48 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 additional outcrops of the rock springs formation are located in three distinct areas from the vermillion creek area in the vermillion basin: clay basin is 45 km to the northwest, the glades is 60 km to the northwest, and the rock springs uplift is 50 km to the north (figure 1). rocks of a similar age, but different lithostratigraphic nomenclature, are also present 105 km east of the vermillion creek area on the east edge of the washakie basin (lynds and slattery, 2017) (figure 1). the laramide-age rock springs uplift began to form around 79 ma (lynds and xie, 2019). the center of the uplift is cored by the older baxter and blair formations (schultz, 1920) and the rock springs formation is present around this anticlinal structure in beds that dip away from the center of the uplift (yourston, 1955) (figure 1). the glades and clay basin outcrops figure 2. overview photo of the southeast outcrop (vantage point is from the northwest outcrop). the nearly vertical cretaceous rocks are annotated as well as the sparks fault and the nearly horizontal tertiary green river and wasatch formations. 49 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 are located on the north flank of the uinta mountains and dip northward into the subsurface (roehler, 1986) (figure 1). additional data for the rock springs formation is available in the subsurface between these outcrop areas via borehole geophysical logs from oil and gas wells (figure 1). stratigraphy the name “rock springs formation” has its origins in a report by schultz (1920) where coal-rich continental deposits of the rock springs uplift were termed the “rock springs coal group.” sears (1925) first used the name “rock springs formation” and burger (1965) established the eastern flank of the rock springs uplift as the type locality for the formation. the rock springs formation has since been subdivided into a series of members or tongues named after various ranches and physiographic features in the rock springs uplift. in ascending order, these members are: the chimney rock tongue (hale, 1950), black butte tongue (hale, 1950), brooks sandstone tongue (smith, 1961), coulson shale tongue (smith, 1961), mccourt sandstone tongue (smith, 1961), and gottsche tongue (roehler, 1965; smith, 1965) (figure 3). we propose a new member, the vermillion creek tongue, for the rock springs formation. the vermillion creek tongue overlies the gottsche tongue and unconformably underlies the trail member of the ericson sandstone. the mccourt sandstone and gottsche tongues are also present in the vermillion creek area. the rock springs formation is underlain by the blair formation and unconformably overlain by the trail member of the ericson sandstone (sears, 1925; roehler, 1965; miller, 1977) (figure 3). together, the blair formation, rock springs formation, ericson sandstone, and younger almond formation make up the mesaverde group in the rock springs uplift area (yourston, 1955) (figure 3). chimney rock tongue the basal member of the rock springs formation is called the chimney rock tongue and consists of an upward coarsening, sandy marine wedge that pinches out into marine mudstone to the southeast of the rock springs uplift. it also transitions into continental deposits to the northwest. the chimney rock tongue has been interpreted as a wave-dominated deltaic system by many workers (hale, 1955; roehler, 1978; hendricks, 1983; levey, 1985; løseth and others, 2006; plinkbjörklund, 2008). the main sandstone wedge consists of proximal and distal delta-front deposits that grade into prodeltaic deposits in a basinward direction (hale, 1955; roehler, 1978; hendricks, 1983; levey, 1985; løseth and others, 2006; plink-björklund, 2008). landward of the main sandstone wedge, delta-plain deposits are composed of various depositional environments such as fluvial, lagoonal, bay, estuarine, lacustrine, and swamp (hale, 1950, 1955; douglass and blazzard, 1961; jacka, 1970). other workers have favored a shoreface figure 3. stratigraphic columns for the eastern rock springs uplift, vermillion creek area in the vermillion basin, and the eastern washakie basin. the study interval is highlighted with a red box. columns and age data are modified from lynds and slattery (2017) except for the vermillion creek column. absolute ages for the vermillion creek tongue are not known, therefore, this column is simply placed in its relative position based on stratigraphic relationships. 50 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 centric terminology (roehler, 1990; purwanto, 2002; vanholland, 2005; rudolph and others, 2015). black butte tongue the chimney rock tongue is overlain by, and transitional with, marine mudstone deposits of the black butte tongue (hale, 1950). the black butte tongue weathers recessively forming distinct valleys between the chimney rock tongue and overlying sandy tongues of the upper rock springs formation. it is generally interpreted as a marine prodeltaic deposit (roehler, 1965, 1978; kirschbaum, 1985, 1986) or lower shoreface to offshore deposits (rudolph and others, 2015). these sediments are thought to have been deposited within an embayment bordered by swampy deltaic plains (hale, 1955). the tongue forms an important subsurface marker that can be correlated over great distances (more than 100 km) and is used to subdivide the lower sandy parts (chimney rock tongue) from the upper sandy parts (brooks and mccourt sandstone tongues) of the rock springs formation (hale, 1955; douglass and blazzard, 1961; weichman, 1961; miller, 1977; hendricks, 1983; kiteley, 1983; roehler, 1985, 1987; luo and nummedal, 2010; rudolph and others, 2015). brooks sandstone tongue the brooks sandstone tongue is one of two major upward-coarsening marine sandstone units of the upper rock springs formation that pinch out into marine mudstone in a southeastward direction. deposits of the brooks sandstone tongue transition into continental deposits in a northwestward direction, and the member is not recognized in the far north of the rock springs uplift. equivalent rocks in the north remain undivided. it has not been studied individually, but has been considered in larger scale studies of the rock springs formation and mesaverde group (e.g., roehler, 1965; hendricks, 1983; rudolph and others, 2015). it is interpreted as a wave-dominated deltaic system by some authors (hale, 1955; douglass and blazzard, 1961; roehler, 1978; hendricks, 1983; kirschbaum, 1985; levey, 1985; uroza, 2008) and as a shoreface system by others (e.g., rudolph and others, 2015). coulson shale tongue the brooks sandstone tongue is overlain by, and transitional with, marine mudstone deposits of the coulson shale tongue. the coulson shale tongue weathers recessively despite having thin sandstone beds, including a regional sandstone marker bed that lies just above the brooks sandstone tongue on the east flank of the rock springs uplift, southern green river basin, and clay basin (rudolph and others, 2015). the coulson shale tongue has been interpreted as offshore marine (roehler, 1978; rudolph and others, 2015) or prodeltaic (roehler, 1983, 1985, 1986). similar to the black butte tongue, it forms an important subsurface marker that can be correlated over great distances (more than 100 km). the coulson shale tongue is used to separate sandy deposits of the brooks and mccourt sandstone tongues in the subsurface (hale, 1955; douglass and blazzard, 1961; weichman, 1961; miller, 1977; hendricks, 1983; kiteley, 1983; roehler, 1985, 1987; luo and nummedal, 2010; rudolph and others, 2015). mccourt sandstone tongue the mccourt sandstone tongue is the second (upper) of two major upward-coarsening marine sandstone units of the upper rock springs formation that pinch out into marine mudstone in a southeastward direction. deposits of the mccourt sandstone tongue transition into continental deposits in a northwestward direction, and the member is not recognized in the far north of the rock springs uplift. equivalent rocks in the north remain undivided. the mccourt sandstone tongue has been studied in detail (roehler, 1986; uroza, 2008) as well as in larger-scale studies of the rock springs formation and mesaverde group (e.g., roehler, 1965; hendricks, 1983; kirschbaum, 1986, 1989; rudolph and others, 2015). it has been interpreted as both a deltaic system (roehler, 1983, 1986; uroza, 2008) and a shoreface system (roehler, 1986; rudolph and others, 2015) on the east flank of the rock springs uplift and in the glades area. in the vicinity of the city of rock springs, wyoming, it has been interpreted as a mixture of wave-dominated deltaic and shoreface deposits (kirschbaum, 1986, 1989). 51 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 gottsche tongue the uppermost member of the rock springs formation on the rock springs uplift is the gottsche tongue because the upper part of the rock springs formation has been cut out by an unconformity (see figure 3). it is chiefly composed of mudstone with varying amounts of lenticular sandstones and isolated coal beds (roehler, 1983, 1990). though early workers commonly combined the gottsche tongue with the ericson sandstone (e.g., hale, 1955; douglass and blazzard, 1961), they are easily differentiated because the ericson sandstone has nearly 100% sandstone and conglomerate, and is generally coarser in grain size than the gottsche tongue. the gottsche tongue is interpreted as being deposited in freshwater marshes and swamps developed on coastal plains (roehler, 1983, 1990). small distributary-channel and splay deposits are locally present and soils are generally poorly drained due to permanent saturation (roehler, 1990). between the rock springs uplift, clay basin, and vermillion creek area, the deposits of the gottsche tongue transition into fully marine delta-front deposits. nomenclatural issues due to lithologic and environmental changes in a northwestward direction, the nomenclature as outlined becomes problematic. moving landward, sandstone tongues (chimney rock, brooks, and mccourt sandstone tongues) transition into rocks of continental origin that lack significant marker beds, and mudstone tongues (black butte and coulson shale tongues) pinch out completely. in this northernmost area, workers commonly refer to these rocks as “the main body of the rock springs formation,” as “continental deposits,” as “the coal bearing facies,” or something similar (hale, 1950; douglass and blazzard, 1961; roehler, 1965). some workers have interpreted the outcrops in the vermillion creek area as part of the rock springs formation (burger, 1965; kiteley, 1983). however, the nomenclature from the rock springs uplift has not been introduced to the vermillion creek area, possibly due to correlation issues. historically, most workers have tended to focus on outcrop to the west, north, and east of vermilion basin and neglect to include outcrop information from this locality (hale, 1955; douglass and blazzard, 1961; keith, 1965; weichman, 1961; miller, 1977; kiteley, 1983; roehler, 1987; luo and nummedal, 2010). we introduce a new nomenclatural scheme for the vermillion creek area in the vermillion basin based on correlation and facies analysis. vermillion creek tongue the vermillion creek tongue (a new member and stratotype) is named for vermillion creek, which flows through the outcrop area on the southern edge of vermillion basin. the type section begins at 40°50'5.84" n., 108°40'34.94" w., and ends at 40°50'7.22" n., 108°40'29.43" w. however, the entire outcrop area, which stretches from approximately 40°50'13.58" n., 108°40'44.04" w. to 40°49'47.13" n., 108°40'1.76" w., can be considered as a type locality. due to the limited surface exposures of the outcrop belt, a type log (shell creek unit 6, api no. 0508106438) is presented alongside the type measured section for subsurface reference (figure 4). additionally, the landward extent of the unit is shown on figure 1. the eastward extent of the unit beyond the outcrop is unknown due to sparse welllog data, and uncertain correlation in that direction. the rock springs formation in the vermillion creek area consists of only two tongues: the gottsche tongue and the newly named vermillion creek tongue. the gottsche tongue can be readily distinguished from the vermillion creek tongue by color and bioturbation. the gottsche tongue has a distinct brown color and contains iron-stained burrows and concretions. the vermillion creek tongue is colored various shades of gray to white at its base. the specific sedimentological characteristics of this new tongue are presented in following sections of this paper, and a type section is located to the northwest of vermillion creek (figure 4). in short, the vermillion creek tongue differs from the gottsche tongue by being composed of a single sandrich progradational package of deltaic and nearshore delta-plain deposits, whereas the gottsche tongue is composed of more landward mud-dominated deltaplain deposits. it is also clearly a younger progradational package separated from the gottsche tongue by a flooding surface in the vermillion creek area (figure 52 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 figure 4. comparison between the vermillion basin nw measured type section from the nw outcrop area and outcrop gamma-ray curve (measurements every 0.5 m) with the nearest along-strike (northeast) subsurface well log. both coarsening-upwards successions that are present at the outcrop are also present in the subsurface. additionally, a typical (incorrect) gamma-ray/lithostratigraphic pick for the base of the ericson sandstone is shown in blue. the true base of ericson pick should be made much higher in the well log based on comparison with the outcrop gamma-ray curve. this highlights the usefulness of surface to subsurface ties in the vicinity of the vermillion creek area. 53 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 4). the vermillion creek tongue’s westward extent is limited by erosion prior to deposition of the ericson sandstone as well as the transition from nearshore deposits to more landward facies, characteristic of the gottsche tongue. age constraints the rock springs formation was deposited during the campanian (roehler, 1986) from 81.71 ma (scaphites hippocrepis ii zone) at its base to approximately 80 ma (baculites maclearni zone) at the upper erosional unconformity (luo and nummedal, 2010) (figure 3). parts of the haystack mountains formation at the eastern edge of the washakie basin are time-equivalent to the rock springs formation, including parts of the rock springs formation that were eroded prior to deposition of the ericson sandstone (luo and nummedal, 2010) (figure 3). lynds and slattery (2017) published a helpful correlation of upper cretaceous strata from wyoming that summarizes radiometric ages and ammonite biozones. the entire marine part of the rock springs formation in the rock springs uplift is younger than the hatfield sandstone member of the haystack mountains formation (lynds and slattery, 2017); howerver, some older sandstone units of the haystack mountains formation (cow creek sandstone, o’brien spring sandstone, bolten ranch, and tapers ranch sandstone members) are equivalent to the marine tongues of the upper rock springs formation (lynds and slattery, 2017) (figure 3). no age data is available for the vermillion creek area. surface to subsurface correlation several workers have attempted subsurface correlation to try and tie outcrops of the rock springs uplift with outcrop on the edges of the greater green river basin (hale, 1955; hallock, 1960; douglass and blazzard, 1961; weichman, 1961; keith, 1965; miller, 1977; hendricks, 1983; kiteley, 1983; roehler, 1985, 1987; irwin, 1986; vanholland, 2005; luo and nummedal, 2010; rudolph and others, 2015). several of these correlations pass very near outcrops of the rocks springs formation in the vermillion creek area (miller, 1977; kiteley, 1983; irwin, 1986; roehler, 1987; luo and nummedal, 2010). in spite of the close proximity, these correlations did not incorporate the outcrop data. tectonic setting the rock springs formation was deposited in a foreland basin (wiltschko and dorr, 1983; decelles, 1994; liu and nummedal, 2004; luo, 2005). the thrust belt was active in the campanian causing rapid subsidence in the foreland basin and the creation of significant accommodation (wiltschko and dorr, 1983). however, subsidence was not only controlled by flexure near the thrust front, but must also have had a dynamic mantle flow component (liu and nummedal, 2004; liu and others, 2005) as evidenced by rapid and widespread subsidence all across wyoming, not just in the foredeep depozone (liu and others, 2005). the boundary between the rock springs formation and the overlying ericson sandstone is a widespread angular unconformity (smith, 1961; roehler, 1965; miller, 1977). the length of time represented by the unconformity is approximately 1.5 million years (miller, 1977; kiteley, 1983) (figure 3). during a cessation of thrusting, isostatic rebound and associated erosion took place prior to deposition of the ericson sandstone (liu and nummedal, 2004; liu and others, 2005). deformation progressed eastward through time resulting in the incorporation of foredeep sediments within the thrust belt and erosion of older foredeep sediments, including part of the rock springs formation (decelles, 1994; liu and nummedal, 2004; liu and others, 2005). while it is clear that a foreland basin was present, the basin was likely subdivided or broken by laramide deformation, which complicates the standard foreland basin model (decelles, 2004; rudolph and others, 2015). laramide deformation probably began after deposition of the rock springs formation (as early as 79 ma; gosar and hopkins, 1969; lynds and xie, 2019), but a pre-laramide deformational history may have had a local positive effect on subsidence (hagen and others, 1985). the overall highly progradational nature of the rock springs formation is generally controlled by high sediment supply derived from the growth and erosion of the thrust belt, coupled with lower accommodation due to 54 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 slowing subsidence rates (gill and cobban, 1973; hendricks, 1983; kiteley, 1983; decelles, 1994; hudson and others, 2019). generally, sedimentation rates were equal to or higher than rates of subsidence (hendricks, 1983; kirschbaum, 1986; devlin and others, 1993; rudolph and others, 2015). however, during deposition of the transgressive black butte and coulson shale tongues, subsidence either increased briefly, or eustatic sea level rose, causing widespread flooding and the deposition of significant marine mudstone over more proximal facies (hendricks, 1983; kiteley, 1983; roehler, 1990; rudolph and others, 2015). methods to better understand the variability of deposits in the field area, field data were collected from outcrops on both sides of vermillion creek (nw outcrop area and se outcrop area; figure 1), including photographs and two measured sections. measured sections include a graphic log with observations of texture, sedimentary structure, bedding, bioturbation, and geomorphic expression. sections were located based on accessibility. facies were then defined by grain size, sedimentary structure, and/or bioturbation (table 1; figure 5) and subsequently grouped into associations. additionally, one scintillometer (radiation solutions inc. rs-230 bgo super-spec handheld gamma-ray spectrometer) survey was undertaken to measure the natural radioactivity of the rock along the same path as the measured section in the nw outcrop area (figures 1 and 4) . measurements were taken every half meter. the resulting gamma-ray profile was then used to correlate units from the outcrop with subsurface gamma-ray curves from boreholes north of the outcrop. additional outcrop gamma-ray profiles and measured sections were obtained for the east flank of the rock springs uplift and for clay basin to facilitate correlations between major outcrop areas (figure 1). a gamma-ray cutoff of 65 api units was used for net sandstone calculations on well-log data using ihs petra. to map the vertical and lateral architectural element organization within the outcrop, additional photographs were taken using a dji phantom 4 pro drone and used to create a photogrammetric model of the main part of the outcrop (figure 6). agisoft metashape professional was used to develop the photogrammetric model, and interpretations were made using lime software (buckley and others, 2019). finally, to aid environmental interpretations, samples were collected from mudstone beds throughout the section for pyrolysis. fresh samples were obtained by digging holes beyond the surface exposure. whole rock pyrolysis was performed using the hawk workstation (wildcat technologies). samples were crushed with a mortar and pestle to 40 mesh size, then combusted to measure evolved hydrocarbons, co, co2, and total carbon (table 2). a standard total organic carbon/ carbonate carbon (toc+cc) method was used where the sample was heated from 300°c to 850°c at a rate of 25°c per minute during the pyrolysis stage, and from 300°c to 850°c at a rate of 25°c per minute during the oxidation stage (espitalié and others, 1977; peters and cassa, 1994). facies analysis facies association 1 (fa1) – delta front fa1a distal delta front – description fa1a deposits are composed of heterolithic very fine grained sandstone and silty shale (10% to 60% sandstone) (figure 5a). sandstone beds increase in thickness from laminated (< 1 cm) to thick bedded (30 to100 cm) upsection. they are structureless, low to high-angle cross-stratified, planar cross-stratified, hummocky cross-stratified, or wave-rippled (figure 5b) and contain ubiquitous terrestrial organic matter. laminated parts (both sandstone and mudstone) of the association have no discernible burrowing. when beds reach cm-scale, chondrites (figure 7a), planolites, schaubcylindrichnus freyi, and cylindrichnus (figure 7b) burrows are present with a maximum bioturbation index (bi) of 3 (reineck 1963; taylor and goldring, 1993). bioturbation intensity is highly variable on the bed scale. thicker sandstone beds may contain palaeophycus (figures 7c and 7d), thalassinoides, chondrites, planolites, rosselia rotatus (figure 7e), cylindrichnus, neonereites multiserialis (figure 7f), intrites (cf., menon and others, 2017) (figure 7c), and tool marks (figure 7c), especially along both basal and 55 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 upper bedding planes (figure 7b; bi up to 3). minor (cmscale) load features are common on the base of sandstone beds. the shale beds are laminated and fissile to chippy. the association is recessive, but locally, exceptionally well exposed due to the vertical attitude of the bedding. where exposed, beds appear to maintain thickness laterally. table 1. facies in the rock springs formation. facies code facies name sedimentary structures, textures, and additional notes bedding facies association ss1 trough cross-stratified sandstone very fine to medium grained; variable cementation; commonly contains carbonaceous debris; ophiomorpha, thalassinoides; high and low-angle foresets thin to medium fa1 fa2 fa3 ss2 asymmetric ripple cross-stratified sandstone fine to medium grained; variable cementation; skolithos very thin to thin fa2 ss3 symmetric ripple cross-stratified sandstone very fine to fine grained; variable cementation; commonly contains carbonaceous debris; skolithos very thin to thin fa2 ss4 planar cross-stratified sandstone very fine to fine grained; variable cementation; indistinct horizontal burrows thin to medium fa1a ss5 hummocky to swaley cross-stratified sandstone fine grained; variable cementation; contains carbonaceous debris; ophiomorpha medium fa1a ss6 bioturbated or rooted sandstone very fine to medium grained; variable cementation; bioturbation has nearly to completely destroyed original bedding and sedimentary structures; ophiomorpha, thalassinoides, planolites, chondrites, chondrites, schaubcylindrichnus freyi, cylindrichnus, paleophycus, rosselia rotatus, neonereites multiserialis medium or obscured fa2 ss7 soft-sediment deformed sandstone medium grained; variable cementation; commonly contains carbonaceous debris very thin to thick fa1 fa2 ss8 structureless sandstone very fine to medium grained; variable cementation; ophiomorpha medium or obscured fa1 fa2 fa3 m silty mudstone structureless to laminated; nodular or chippy to fissile; chondrites laminated fa1 fa3 l pebble lag pebbles are composed of mud clasts that typically weather leaving voids along basal surfaces; apectoichnus longissimus in woody debris na fa2 c coal and carbonaceous mudstone contains carbonaceous debris; true coal exhibits well-developed cleats laminated to medium fa3 56 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 fa1b proximal delta front – description fa1b deposits are composed of very fine to medium grained, medium bedded (10 to 30 cm), low to high-angle trough cross-stratified, structureless, or soft-sediment deformed sandstone. bioturbation is composed of locally abundant, but typically sparse, ophiomorpha (figure 7g) or palaeophycus burrows (bi = 1 to 2). both basal and upper contacts are sharp. the unit is laterally continuous across the entire outcrop. interpretation and depositional setting we interpret the deposits of fa1 as marine-deltaic. several key criteria for a deltaic deposit are outlined in the literature: (1) a direct link to feeding rivers can be identified, (2) significant progradation occurred indicating a fluvial sediment source, (3) deposits are upward-shallowing, (4) seaward-dipping clinoforms are present, and (5) the deposit is lobate or elongate as a shoreline protuberance (e.g., kirschbaum, 1989; roehler, 1990; bhattacharya, 2006, 2010). no direct link to feeding rivers could be established for the lowermost deposits exposed in the vermillion creek area possibly due to wave reworking of the delta front, and also possibly due to limited spatial outcrop exposure. however, these deposits are overlain by delta-plain and distributary-channel deposits (figure 6), which do indicate a direct link to a fluvial source, at least for younger deposits (e.g., bhattacharya, 2006, 2010). the abundance of terrestrial organic matter is also likely derived from a fluvial source on or near a delta. additionally, the presence of intrites structures and soft-sediment deformation indicate high sedimentation rates potentially associated with fluvio-deltaic sedimentation (e.g., bhattacharya, 2006, 2010; menon and others, 2017). progradation can be established to be at least 15 km downdip figure 5. selected facies from the vermillion creek area. (a) interbedded sandstone and silty mudstone which includes facies m, ss1, ss3, ss4, and ss7. (b) symmetrical rippled sandstone (ss3). (c) trough cross-stratified sandstone (ss1). (d) asymmetrical rippled sandstone (ss2). (e) small-scale soft-sediment deformed sandstone (ss6). (f) large-scale softsediment deformed sandstone (ss6) within distributary channel deposits. note that f has been rotated to horizontal (top is to the right) to highlight that this slump feature occurred at the base of the sandstone. 57 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 figure 6, part 1. virtual outcrop interpretations for the nw outcrop area northwest of vermillion creek. (a) aerial view of the nw outcrop looking straight down from above. solid yellow line represents measured section segments and dashed yellow line represents section offsets. (b) line drawings of the nw outcrop indicating important surfaces and channel complexes (1 through 3). (c) facies map of the nw outcrop indicating various depositional environments. refer to figure 1 for location of outcrop area. 58 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 figure 6, part 2. virtual outcrop interpretations for the se outcrop area southeast of vermillion creek. (d) oblique aerial view of the se outcrop. solid yellow line represents measures section segments and dashed yellow line represents section offsets. (e) line drawings of the se outcrop indicating important surfaces and channel complexes (4 through 6). (f) facies map of the se outcrop indicating various depositional environments. refer to figure 1 for location of outcrop area. 59 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 (southeast) via subsurface correlation, but to the east and southeast of the outcrop, well data is too sparse for confident correlation. progradation may be up to 27 km based on available well data. for comparison, the mccourt sandstone tongue can be correlated at least 70 km in the subsurface with outcrop control over much of that distance. the mccourt sandstone tongue has been interpreted as deltaic by many authors, and meets all of the aforementioned criteria for deltaic deposits (roehler, 1983, 1986; uroza, 2008). the deposits of fa1 do meet the criteria that the deposits be upward-shallowing. this is evidenced by the increase in more proximal facies over more distal facies. however, other systems also exhibit upward shallowing of facies such as shoretable 2. pyrolysis data in stratigraphic order with sample dp-l near the top of the rock springs formation and sample ps1-1 near the base. see figure 8 for sample locations. sample id s1 (mg/g) s2 (mg/g) s3 (mg/g) pi toc (%) tmax (°c) hi oi kerogen type facies association dp-l 3.33 51.04 11.24 0.06 10.26 424 497 109 ii fa3 dp-k 1.1 16.17 4.59 0.06 5.96 425 271 77 ii/iii fa3 dp-j 0.77 14.95 5.93 0.05 5.89 423 253 100 ii/iii fa3 dp-i 0.38 1.01 0.69 0.28 0.87 412 115 79 iii fa3 dp-h 0.73 1.1 0.75 0.4 1.06 409 103 71 iii fa3 dp-g 0.24 0.43 0.75 0.36 0.72 409 59 103 iii fa3 dp-f 7.84 110.72 19.02 0.07 17.02 423 650 111 i fa3 dp-e 3.52 27.77 8.51 0.11 10.1 418 274 84 ii/iii fa3 dp-d 1.84 45.93 23.35 0.04 15.28 425 300 152 ii fa3 dp-c 2.06 10.89 1.93 0.16 3.58 425 303 53 ii fa3 dp-b 0.3 1.26 0.6 0.19 0.74 429 169 80 iii fa3 dp-a 2.99 17.2 2.77 0.15 4.41 426 390 62 ii fa3 dp-a-eq 1.37 19.61 4.45 0.07 6.1 430 321 72 ii fa3 dp-7 0.44 0.43 0.56 0.51 0.59 363 71 94 iii fa3 dp-6 0.46 0.45 0.55 0.51 0.58 394 78 95 iii fa3 dp-5 0.36 0.45 0.58 0.45 0.71 417 62 81 iii fa3 dp-4 0.33 0.36 0.34 0.48 0.35 316 102 97 iii fa3 dp-3 0.65 1.01 0.96 0.39 1.32 418 76 72 iii fa3 dp-2 0.35 0.39 0.5 0.47 0.49 369 79 102 iii fa3 dp-1 0.36 0.77 0.62 0.32 0.94 412 81 65 iii fa3 ps2-7 0.28 1.62 0.94 0.15 1.49 427 108 62 iii fa1a ps2-6 1.18 1.92 1.31 0.38 1.65 415 116 79 iii fa1a ps2-5 0.33 0.98 0.92 0.25 1.16 415 84 79 iii fa1a ps2-4 0.52 1.49 1.24 0.26 1.49 417 99 82 iii fa1a ps2-3 0.46 1.32 0.98 0.26 1.38 416 95 70 iii fa1a ps2-2 0.44 1.19 0.82 0.27 1.28 423 92 64 iii fa1a ps2-1 0.21 1.35 1.05 0.14 1.15 428 116 91 iii fa1a ps1-4 0.15 0.27 0.32 0.35 0.33 428 80 97 iii fa1a ps1-3 0.25 0.49 0.44 0.33 0.45 427 109 97 iii fa1a ps1-2 0.09 0.19 0.29 0.32 0.27 434 71 105 iii fa1a ps1-1 0.19 0.77 1.02 0.2 0.84 428 92 121 iii fa1a 60 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 face systems and bayhead deltas. the outcrop is not extensive enough to identify any clinoformal surfaces, and we cannot prove deltaic geometry with available data. deltaic environments are commonly stressed due to high turbidity and lowered salinity (e.g., howard and frey, 1973; wightman and others, 1988; pemberton and wightman, 1992; bhattacharya, 2006, 2010). the relatively low bi in the vermillion creek area more closely matches the expectations for deltaic shorelines rather than shoreface systems that are distant from active deltaic processes. furthermore, the trace fossil assemblage for deposits of fa1 (rosselia rotatus, planolites, schaubcylindrichnus freyi, cylindrichnus, thalassinoides, and chondrites) are referable to the rosselia ichnofacies of sandy delta-front deposits (maceachern and bann, 2020). the variable, and generally low, bi are characteristic features of this ichnofacies (maceachern and bann, 2020). the variable bioturbation intensity at the bed scale is another feature common to the rosselia ichnofacies, and may indicate variable physico-chemical stresses common in deltaic environments (maceachern and bann, 2020). the presence of neonereites multiserialis is a noteworthy departure from expectations for deltaic sediments. examples from the literature suggest figure 7. selected photographs of trace fossils. (a) chondrites burrows (ch). (b) cylindrichnus burrow (cy). (c) palaeophycus burrows (p), tool marks (t), and intrites (i). (d) palaeophycus burrows (p) and ophiomorpha burrows (o). (e) rosselia rotatus burrow (r). (f) neonereites multiserialis traces (n). (g) ophiomorpha burrows (o) within the proximal delta-front sandstone. (h) apectoichnus longissimus borings (a). (i) heavily bioturbated distributary channel sandstone. all traces are ophiomorpha (o). 61 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 that these traces are confined to deep water flysch (e.g., pickerill, 1991; cherif and naimi, 2021) or lower shoreface to offshore transition deposits (e.g., bouchemla et al., 2021). the noted presence of neonereites multiserialis may be the first instance of that trace in delta-front sediments. architecture fa1a deposits are overlain by fa1b deposits, and there are two repeated successions of this stacking pattern (figure 6). the lowermost succession is obscured at its base by quaternary sediments (figure 6), so its association with underlying sediments cannot be ascertained at the outcrop. however, correlations to subsurface boreholes via wireline logs indicate relatively high gamma-ray readings suggestive of shale deposits (figure 4). the second succession is overlain by deposits of fa3 (delta plain; figure 6). facies association 2 (fa2) – distributary channel description fa2 deposits are dominantly composed of fine to medium grained sandstone with minor interbeds of mudstone. beds range from thin to thick bedded. the dominant sedimentary structure is unidirectional trough cross-stratification (figure 5c), but asymmetrical rippled (including climbing ripples; figure 5d) and soft-sediment deformed sandstone (figures 5e and 5f) is common. sandstone can sometimes appear structureless. symmetrical ripples are present at the tops of some units. internal mud-clast lags are also present and carbonaceous debris is common throughout. apectoichnus longissimus (figure 7h) and skolithos burrows are present as well as locally abundant ophiomorpha (figure 7i). the bi is highly variable from 0 up to 4. basal contacts are sharp and scoured. master bedding surfaces extend from the top to the base of each unit (figure 6). individual sandstone bodies pinch out laterally and have a lensoidal geometry except in cases where the edges of the bodies are obscured. the association can be underlain or overlain by additional fa2 (distributary channel) deposits or by fa3 (delta plain) deposits (figure 6). interpretation and depositional setting these deposits are interpreted as distributary-channel deposits near and behind the delta front. master bedding surfaces that extend from the top to the base of individual channel bodies are interpreted as accretion surfaces and may include lateral and/or downstream components (figure 6). the lensoidal geometry of these deposits coupled with the presence of distinct accretion surfaces suggests a fluvial origin (e.g., miall, 2010). however, the presence of ophiomorpha and brackish-water apectoichnus (previously teredolites) burrows suggests close proximity to marine conditions in distributary channels (e.g., bromley and others, 1984; gingras and others, 2004, 2005; donovan, 2018; king and others, 2020). architecture fa2 deposits (distributary channel) are arranged in multistory and multilateral channel complexes with intervening fa3 deposits (delta plain). there are a total of six complexes, and no attempt has been made to correlate complexes between the northwest and southeast outcrops. complexes 1, 2, 3, and 5 exhibit both multistory and multilateral architectures (figure 6). individual complexes range from 2 to 6 stories. complex 4 and 6 suffer from poor exposure making identification of story surfaces difficult (figure 6). however, for complex 4, variable dip directions for interpreted master bedding surfaces indicates higher complexity than what is apparent from the virtual outcrop data (figure 6). it is likely that all six complexes are multistory and multilateral. facies association 3 (fa3) – delta plain description fa3 deposits are composed of silty mudstone, silty carbonaceous mudstone (figure 5f), coal (figure 5f), and isolated, very thin (1 to 3 cm) to medium (10 to 30 cm) beds of very fine to fine-grained carbonaceous sandstone. sandstone beds can be trough cross-stratified or structureless. carbonaceous debris and wood fragments are common throughout. the association is usually overlain and underlain by fa2–distributary channel deposits (figure 6). however, it also overlies deposits of fa1b–proximal delta front (figure 6). 62 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 interpretation and depositional setting these deposits are interpreted collectively as deposits of the delta-plain environment. the abundance of carbonaceous material, coal beds, and lack of marine bioturbation suggests a continental origin. thin sandstone deposits are likely crevasse splays (e.g., allen, 1964; miall, 2010) and coal beds indicate the presence of swampy conditions on the delta plain (roehler, 1983, 1990). pyrolysis thirty-one samples were collected from mudstone beds along the measured section in the nw outcrop area in order to better understand kerogen types within various units (figure 8). pyrolysis data shows variability in organic matter type and richness throughout the section. data from samples representing delta-front strata (fa1) indicate a relatively low hydrogen index (hi; 50 to 200) typical of type iii, terrestrially sourced kerogen (table 2; figure 8). all samples contain coal flecks that are sometimes visible with the naked eye, and always visible with the aid of a hand lens (10x). low hi values in delta-front deposits are likely due to significant terrestrial input from fluvial point sources on a delta (e.g., meilijson and others, 2020). samples taken from delta-plain strata (fa3) exhibit a wider range of hi (59 to 650; table 2; figure 8). samples with the highest hi values correspond with the highest toc (table 2). these samples contain significant carbonaceous material, that is visible to the naked eye, yet have hi values that indicate a mixed type ii/ iii kerogen. this suggests that fa3 deposits consist of a mix of humic and algal kerogens. while not common, coal-bearing strata can contain mixed kerogen types (e.g., fleet and scott, 1994). peat swamps can contain algal matter via marine flooding (bagge and keeley, 1994) or non-marine lacustrine facies variation (parnell, 1988; powell and boreham, 1994; thompson and others, 1994). both scenarios are possible for the fa3 deposits in the vermillion creek area. with hi values as high as 650 (sample dp-f), there is also the possibility that some samples contain some type i kerogen. type i kerogens are algal and distinctly lacustrine in origin, suggesting lacustrine influence. coal and lacustrine deposition often take place in close proximity to each other, with ponded waters commonly occurring in a poorly drained delta-plain environment, and can be gradational through time forming two separate end members of a depositional continuum (fleet and scott, 1994). correlation two correlation panels have been created to tie the sections in the vermillion creek area to the rock springs uplift and clay basin (figure 9). in attempting to correlate between these outcrops, it was first necessary to determine how the section in the vermillion creek area compared to the closest available borehole wireline data along depositional strike (figure 4). of interest is the interpretation of the basal contact of the trail member of the ericson sandstone. this contact has historically been located at the base of a significant increase in net sandstone and grain size, as determined by the abundance of low gamma-ray response in wireline logs (e.g., kiteley, 1983; roehler, 1987) (figure 4); a purely lithostratigraphic interpretation. our outcrop gamma-ray measurements indicate that the uppermost rock springs formation deposits also have this same log response, and we have interpreted the basal erosional unconformity of the ericson sandstone as much higher in the section than previous workers (kiteley, 1983; roehler, 1987) (figure 4). correlation between major outcrops was aided by the use of high-confidence picks that could be matched to outcrop gamma-ray curves (figure 9). these high-confidence picks include the rock springs formation/ericson sandstone contact, the flooding surface of the coulson shale tongue, and minor flooding surfaces within and above the mccourt sandstone tongue (figure 9). we also make the assumption that the ericson sandstone members are relatively isopachous over short distances (about 10 km or less). over larger distances (many tens of km), the ericson sandstone thickens gradually eastward (figure 9). thicknesses of the ericson sandstone in the vermillion creek area were measured from satellite imagery with the assumption that the deposits are nearly vertical, similar to the rock springs formation in the area. 63 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 figure 8. hydrogen index (hi) shown with the vermillion basin nw section from the nw outcrop area. hi values are typically indicative of type iii, terrestrial kerogen or type ii/iii mixed terrestrial/marine or possibly lacustrine kerogen*. the abundance of type iii kerogen suggests a heavy fluvial source common in deltaic settings. note that measured section data does not extend as low as gamma-ray data due to outcrop quality. holes were dug through cover to obtain the lowermost gamma-ray measurements. refer to figure 4 for explanation of symbols. 64 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 our correlation panels indicate that almost the entire section preserved at the vermillion creek area is younger than the rock springs formation at both the rock springs uplift and clay basin (figure 9). another notable feature is the apparent thinning of the gottsche tongue between the vermillion creek area and clay basin (figure 9), indicating that the basal ericson sandstone erosional unconformity removed more figure 9. surface to subsurface correlations. (a) correlation from the east flank of the rock springs uplift (pretty water creek pipeline) to the vermillion creek type section. prominent sandstones of the mccourt sandstone tongue pinch out in a southeastward direction. upward-coarsening marine sandstones of the vermillion creek area are partly equivalent to the gottsche tongue of the rock springs uplift. note the presence of a second coarsening-upward marine sandstone, labeled as “marine marker,” which is the lower part of the vermillion creek tongue. the basal ericson sandstone unconformity removes progressively more of the rock springs formation to the west. also note that the outcrop gamma ray for the pretty water creek pipeline location is shifted away from the neighboring well log (s.p. fed. 14-20 well) for ease of viewing. the original position is still shown behind the s.p. fed. 14-20 well. (b) correlation from the clay basin area to the vermillion creek outcrop. prominent sandstones of the mccourt sandstone tongue pinch out in a southeastward direction. upwardcoarsening marine sandstones of the vermillion creek area are partly equivalent to the gottsche tongue of the clay basin area. again, note the presence of a second coarsening-upward marine sandstone, labeled as “marine marker,” which is the lower part of the vermillion creek tongue. the basal ericson sandstone unconformity removes progressively more of the rock springs formation to the west. vct = vermillion creek tongue. see figure 1 for location of cross sections. 65 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 of the rock springs formation in the clay basin area, possibly due to increased uplift (e.g., smith, 1961; roehler, 1965; miller, 1977; uroza, 2008). the correlation panels also indicate that the gottsche tongue of the rock springs uplift and clay basin transitions into laterally continuous marine deposits approximately 16 km southeastward from the southernmost rock springs uplift outcrop (figure 9). overlying this basal marine gottsche tongue is a progradational package of deltaic, delta plain, and distributary-channel complexes herein defined as the vermillion creek tongue. a type section for this new tongue is presented in figure 4. discussion comparison with nearby areas deposits of the sandy marine tongues of the rock springs formation at the rock springs uplift and clay basin meet the established criteria for deltaic deposits, namely: (1) a direct link to feeding rivers can be identified, (2) significant progradation occurred indicating a fluvial sediment source, (3) deposits are upward-shallowing, (4) seaward-dipping clinoforms are present, and (5) the deposit is lobate or elongate as a shoreline protuberance (e.g., kirschbaum, 1989; roehler, 1990; bhattacharya, 2006, 2010). marine shoreline deposits exposed at the base of the rock springs formation in the vermillion creek area are also interpreted as deltaic deposits. however, there are a few key differences. outcrops in the vermillion creek area contain a significantly higher biodiversity (eight or more ichnogenera) than deltaic deposits of the other areas (an average of three different ichnogenera per location). additionally, the total thickness of each of the fa1 sequences in the vermillion creek area is just over 20 m whereas similar deposits elsewhere are 40 m or more thick. the delta-plain deposits of the gottsche tongue at the rock springs uplift and clay basin and the deltaplain interval in the vermillion creek tongue are not time-equivalent (figure 9). however, both intervals record the final preserved marine influence of each area until flooding events associated with the upper campanian almond formation occurred. there are some similarities between locations. thin, discontinuous coal beds are common in all areas, as well as thin sandy splay deposits. teredolites or apectoichnus bored logs in channel lag deposits were found in the rock springs uplift and in the vermillion creek area. brackish-water burrows such as these, suggest close proximity to the sea in distributary channels (e.g., bromley and others, 1984; gingras and others, 2004, 2005; king and others, 2020). the differences between the outcrops in the vermillion creek area and other areas are readily apparent. the gottsche tongue has a significantly lower net sandstone percentage (29% average near the rock springs uplift, n = 28) than the upper deposits of the vermillion creek tongue (62% average near vermillion creek, n = 16). however, in spite of a low net sandstone percentage, multistory and multilateral deposits do exist in the gottsche tongue, though single story channel deposits are more common. stacking patterns and implications for subsurface exploration the vermillion creek area exhibits an overall progression from fully marine deltaics to marine-influenced distributary-channels and delta-plain deposits. this progression is consistent with the progradation of a deltaic system having more proximal facies associations systematically overlying more distal facies associations (e.g., coleman and prior, 1982; bhattacharya, 2006, 2010). the stacked distributary-channel complexes are separated by laterally continuous delta-plain deposits suggesting periodic abandonment and reoccupation of the vermillion creek area by distributary channels. periods of abandonment correlate with incidences of higher hi, suggesting marine or lacustrine influence. the fact that marine influence (marine trace fossils) is present in at least three of the six distributary-channel complexes, including the uppermost complexes, suggests aggradation of the shoreline. contemporaneous shoreline deposits were likely near the vermillion creek area for the entirety of the deposition of the distributary-channel complexes. wireline data is sparse and correlation is difficult east of the vermillion creek area. while difficult to prove time-equivalency, coarsening upward successions are present east of the ver66 the upper cretaceous rock springs formation of northwest colorado—a previously undescribed key deltaic outcrop phillips, s., and hudson, s.m. geology of the intermountain west 2021 volume 8 million creek area that may be time-equivalent to the delta-plain and distributary-channel deposits. the interpretation that contemporaneous shoreline deposits are likely present to the east of the vermillion creek area has implications for oil and gas exploration activities in the nearby sand wash and washakie basins. marine sandstone reservoirs may have greater prospectivity than channelized facies due to larger lateral extents. oil and gas accumulation within reservoirs of this type, east of the vermillion basin, are sparsely tested, and may be significant (finn and johnson, 2005; johnson and others, 2005). the type of delta has an influence on the geometry of subsurface reservoirs (e.g., slatt, 2006). it is unknown what type of delta deposits are present east of vermillion creek. however, wave-dominated deltas typically have fewer distributary channels than their fluvial-dominated counterparts, and can become entrenched (e.g., bhattacharya, 2006, 2010). the fact that the percentage of distributary-channel deposits in the rock springs formation is significantly higher in the vermillion creek area than the rock springs formation elsewhere may suggest a slight shift toward fluvial dominance, but also may be due to fluctuating accommodation. distributary channels display high-sedimentation rates as indicated by significant soft-sediment deformation in channelized deposits and high sedimentation rates can be an indicator of fluvial dominance (e.g., bhattacharya, 2006, 2010). conclusions the rock springs formation of the vermillion creek area in northwestern colorado is composed of marine-deltaic, distributary-channel, and delta-plain sediments representing progradation to aggradation of the shoreline. the rock springs formation outcrops in the vermillion creek area differs from rock springs formation outcrops elsewhere in utah and wyoming by having thinner delta-front successions and having a higher net sandstone (distributary channels) within delta-plain deposits. the rock springs formation in the vermillion creek area is younger than rock springs formation elsewhere in utah and wyoming. it also preserves the youngest available outcrop of the rock springs formation described in literature and is an important data point between outcrops of the rock springs uplift or clay basin and contemporaneous deposits on the east and southeast edges of the greater green river basin. additionally, a new member of the rock springs formation has been defined and has been named the vermillion creek tongue. future subsurface exploration for hydrocarbons east of the vermillion basin is likely to encounter shoreline deposits that are time-equivalent to the distributary-channel complexes of the vermillion creek tongue. this geographic area is not well tested, and may be significant. acknowledgments this work was funded by conocophillips. we are grateful to joe phillips (occidental petroleum corporation), jonathon sevy (brigham young university), chelsea jolley (marathon oil), riley brinkerhoff (wasatch energy management), and peter pahnke (wexpro) for their help in the field. we also thank ryan king (western colorado university) and peter pahnke for reviews of this manuscript. finally, we thank the giw editors for their for their attention to details. references allen, j.r.l., 1964, studies in fluviatile sedimentation—six cyclothems from the lower old red sandstone, anglowelsh basin: sedimentology, v. 3, p. 163–198. andrew, s.g., 1965, the rock springs uplift, a history of mineral exploration and exploitation, in bitter, 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editors, green river basin: wyoming geological association 10th annual field conference guidebook, p. 197–202. stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 6 2019 © 2019 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa douglas a. sprinkel, mary beth bennis, dale e. gray, and carole t. gee theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover west view of the morrison formation at rainbow draw. the fossil log horizon is in the greenish-colored siltstone beds near the center of the photograph. the cretaceous cedar mountain through the frontier formations are exposed on the distant ridge. see figure 7 for details. inset photo of a fossil log typically found in rainbow draw. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 6 2019 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors president peter nielsen peternielsen@utah.gov 801.537.3359 president-elect leslie heppler lheppler@utah.gov 801.538.5257 program chair gregory schlenker gcsgeoscience@gmail.com 801.745.0262 treasurer dave garbrecht garbrechtd@yahoo.com 801.916.1911 secretary george condrat gcondrat@loughlinwater.com 435.649.4005 past president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 uga board october 2018 – september 2019 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association volume 6 2019 61 abstract the outcrop belt of the upper jurassic morrison formation in the northeastern uinta basin and southeastern flank of the uinta mountains is particularly rich in dinosaurian and non-dinosaurian faunas, as well as in fossil plants. the discovery of several well-preserved, relatively intact, fossil logs at several locations in rainbow draw and one location in miners draw, both near dinosaur national monument (utah), has provided an opportunity to study the local paleobotany, stratigraphy, and sedimentology of the morrison formation in northeastern utah. the morrison formation in northeastern utah consists of four members. in ascending chronostratigraphic order, they are the windy hill, tidwell, salt wash, and brushy basin members. the lithology (including the presence of glauconite grains) and fossil assemblage of the lower two members (windy hill and tidwell) indicate a marine to marginal marine (coastal plain) depositional environment, whereas the lithology, fossil flora and fauna assemblage of the upper two members (salt wash and brushy basin) indicate a fluvial–lacustrine depositional environment. at least 10 fossil log sites in rainbow draw have been documented so far, and geologic mapping indicates that the logs and wood all occur in the same stratigraphic interval within the salt wash member, approximately 17 to 27 m above the base of the member. the unit containing the logs and wood is about 11 m thick and consists of very fine to fine-grained sandstone and siltstone with indistinct bedding and no discernible sedimentary features. the logs are siliceous, some have a coaly exterior, and they range in exposed length from 0.5 to 11 m and reach diameters up to 1.1 m. in the miners draw area, a single siliceous log is documented in the upper part of the salt wash member within a silty sandstone unit that is 4 m thick; its exposed length is about 6 m. although the correlation of the miners draw log-bearing interval to the interval in rainbow draw is uncertain, both units are lithologically similar and both occur in the upper part of the salt wash member. the logs have been identified as araucariaceous conifers that pertain to the same taxon originally described as araucarioxylon hoodii tidwell et medlyn 1993 from mt. ellen in the henry mountains of southern utah. concurrent systematic work will prompt a nomenclatural transfer of this species to the genus agathoxylon. based on the abundance of large fossil logs and wood in the same stratigraphic interval in rainbow draw, we hypothesize that the area was covered by stands of moderately large trees of araucariaceous conifers. the sedimentological evidence suggests that the trees were not transported far from their original site of growth before they were deposited in a low-energy floodplain environment. stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa douglas a. sprinkel1, mary beth bennis2, dale e. gray2, and carole t. gee3 1utah geological survey, po box 146100, salt lake city, ut 84114, usa; douglassprinkel@utah.gov 2utah field house of natural history state park museum, 496 e. main, vernal, ut 84078, usa; marybethbennis@utah.gov, daleegr@aim.com 3institute of geosciences, division of paleontology, university of bonn, nussallee 8, 53115 bonn, germany; cgee@uni-bonn.de citation for this article. sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t., 2019, stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa: geology of the intermountain west, v. 6, p. 61–76. © 2019 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 62 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 introduction the upper jurassic morrison formation is a spectacular and easily recognizable formation across the colorado plateau, and is distinctive because of its array of rainbow-colored mudstone, siltstone, and sandstone beds that typically form a “badlands” landscape. in northeastern utah, it is well-exposed along the south flank of the uinta mountains (figure 1) and around split mountain and the yampa and blue mountain plateaus in and around dinosaur national monument (figure 2). the morrison gained its fame from the discovery of well-preserved dinosaur bones on the south flank of split mountain in august 1909 by earl douglass, a paleontologist with the carnegie museum of pittsburgh (douglass, 2009). subsequent development of the carnegie quarry (figure 2) produced a rich and diverse dinosaur assemblage (elder, 1999; engelmann, 1999; turner and peterson, 1999; chure and others, 2006; carpenter, 2013). in addition to dinosaurs, the morrison has produced other vertebrate fossils (e.g., pterosaurs, crocodylomorphs, and mammals), invertebrate fossils, and fossil insects (engelmann, 1999; evans and chure, 1999; hasiotis, 2004; chure and others, 2006). fossil wood is also commonly found in the morrison formation, but it is mostly scrappy pieces preserved in channel sandstone castle dale coalville duchesne green river gunnison heber city kamas manila manti nephi salt lake city tabiona vernal price provo jensen morrison fm outcrop belt uinta basin boundary dinosaur national monument wyoming c o lo r ad o utah u tah 109° 41° 40.5° 40° 39.5° 39° 112° 111° 110° 109° 112° 111° 110° 40° 39.5° 41° 40.5° 39° ´ study area uinta basin ui nta mo untai ns w a s a t c h r a n g e utah lake great salt lake flaming gorge reservoir 0 10 20 30 40 50 60 70 80 90 100 mi 0 30 60 90 120 150 km gr ee n ri ve r green river yampa river w hite river duchesne river strawberry river " " " " " " " " " " " " " " " " figure 1 figure 1. regional map showing the morrison formation study area in the eastern uinta mountains of northeastern utah, usa. morrison outcrop locations from hintze and others (2000). 63 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 and conglomeratic depositional units in the salt wash and brushy basin members (engelmann, 1999; gee and others, 2014). in some places, the morrison contains fossil logs of varying sizes, which occur as solitary logs or in clusters (gee, unpublished data). engelmann (1999) surveyed several national park service units in utah and surrounding states and documented 34 sites where log segments a few meters in length were found in the morrison formation. he described one site at dinosaur national monument as “…a large area covered by silicified logs of considerable diameter, possibly a log jam”(engelmann, 1993). escalante petrified forest state park, near the town of escalante in south-central utah, is another location with a concentration of fossil logs in the morrison formation. these silicified (agatized) logs occur in a conglomerate bed in the upper part of the brushy basin member (morgan and others, 2012). many other unpublished sites in utah had concentrations of fossil logs in the morrison, but many of these sites have been picked clean over the years by collectors (james kirkland, utah geological survey, verbal communication, march 2018). a reconnaissance paleontological survey of the morrison formation by mary beth bennis and dale gray (utah field house of natural history state park museum) on bureau of land management lands east of vernal, utah, and outside dinosaur national monument, identified two areas that have large, relatively intact, and well-preserved fossil logs. one area is located south of blue mountain plateau near miners draw, and the other area is north of dinosaur national monument in rainbow draw (figure 2). the rainbow draw area is of particular importance because it contains a concentration of as many as 11 logs in a relatively small area (240,000 m2 or about 60 acres). the miners draw site is located in an unnamed tributary of miners draw (figure 2) where a single log was found at the base of a morrison formation slope (figure 3). the rainbow draw area is located northeast of vernal and north of dinosaur national monument (figure 2). there, 10 fossil logs were discovered in beds in the area. the logs are concentrated into two groups within the 60-acre surveyed area. in each group, the fossil logs were somewhat dispersed, except for one site in the western group with a cluster of three large logs (site 3). it is unclear if this cluster of logs represents three individual trees or if it represents only one tree trunk that has broken into segments that have moved downslope. all fossil logs in the miners draw and rainbow draw areas were found in the salt wash member of the morrison formation, but it was not clear at the time of the survey if the logs were at the same stratigraphic horizon " " " red fleet reservoir steinaker reservoir vernal naples jensen dry fork a shley creek jones hole cree k big brush creek li t t le b ru s h c re ek clif f c reek gr een river b r ush c r eek gree n river d eep c reek min ers draw morrison fm outcrop dinosaur national monument ´ split mountain yampa plateau blue mountain rainbow draw area m iners dra w area carnegie quarry 0 4 8 12 16 20 km 0 2 4 6 8 10 12 mi u i n ta m o u n t ains u i n t a b asin £¤40 £¤40 £¤191 £¤191 æ·45 æ·88 æ·121 £¤40 figure 2. map showing the morrison formation outcrop belt (marked in green) in and around dinosaur national monument and the location of the renowned carnegie quarry. the miners draw area is south of the blue mountain plateau and rainbow draw is due north of dinosaur national monument. both areas are east of the city of vernal, utah. morrison outcrop locations from hintze and others (2000). 64 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 or if they were merely preserved in strata of similar depositional environments. subsequent visits to both areas were made to measure the logs, collect hand samples for paleobotanical analysis, and describe and measure morrison formation sections. geologic mapping was conducted in the field on aerial photographs and imagery to help trace member contacts and key beds. the purpose of this study is to describe the morrison formation strata, especially those related to the fossil logs, and to place the logs within a stratigraphic framework for the interpretation of the depositional environment of the log-bearing intervals at both locations. geologic setting of the fossil log sites the miners draw and rainbow draw areas are situated along the flanks of highlands—blue mountain plateau, yampa plateau, and split mountain—that formed during the laramide uplift of the uinta mountains (figure 2) (stone, 1993; gregson and others, 2010). the highlands rose mostly along high-angle reverse faults, miners draw fault to the south and island park fault to the north. the formations within the highlands were folded into a series of monoclines and asymmetrical anticlines (hansen and others, 1983; hansen, 1986; sprinkel, 2006, 2007). the bedrock stratigraphy in the miners draw and rainbow draw areas include (in ascending chronostratigraphic order) the upper jurassic stump and morrison formations, the lower cretaceous cedar mountain and dakota formations, and the upper cretaceous mowry and frontier formations. in the miners draw area, the formations wrap around a gently plunging anticlinal nose that is faulted on the north limb (figure 4). three partial stratigraphic sections were measured to produce a composite section from the top of the stump formation to the base of the cedar mountain formation because of the distance between the exposed base and top of the morrison formation and stratigraphic position of the fossil logs. key marker beds were used to offset between the section segments. in rainbow draw, the formations generally dip less than 20° southwest, although the morrison formation is very gently folded into a broad, low-amplitude syncline (figure 5). jms fossil log site jmbu jmbl kcb figure 3. fossil log site in the miners draw area in the upper salt wash member of the morrison formation (jms). the brushy basin member of the morrison formation is divided into a lower banded unit (jmbl) and an upper gray unit (jmbu). the buckhorn conglomerate of the cedar mountain formation (kcb) caps the morrison formation. the yellow dashed line represents the upper part of the trail creek measured section. blue mountain plateau is the highland in the distance. view to the northwest. 65 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 morrison formation stratigraphy the morrison formation in northeastern utah consists of four members. in ascending chronostratigraphic order, they are the windy hill, tidwell, salt wash, and brushy basin members. the windy hill member is composed of siltstone, mudstone, and thin-bedded rippled limestone that ranges from 4 to 20 m thick (figures 6a and 6b), and the invertebrate fossil assemblage and glauconite grains indicate marine deposition (turner and peterson, 1999). the tidwell member is composed of cross-bedded and rippled siltstone and sandstone, and thin shale beds (figure 6c). marine e ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! e ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! j ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! je e ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! e j j #* qae kcu kmr kd qac kcu kcuqaf qac kcb kd qafqac kcb qac jms kf qmt kmr jmb qms qackd qac kcu jmb kcb qmt qc jms jms jmtw js qc qms (jmb) qc js qac kcu qac kd qc qc jms js qc qac jmtw js qms qac kcu kcb jmb jms jmtw js qac js r. 25 e. ´ explanation #* fossil log site o p measured sections bedding, inclined, field measured bedding, inclined, calculated map area contact ! ! ! ! ! !enormal fault, concealed enormal fault, approximately located ! ! ! ! ! ! ! ! fold, anticline, upright, concealed fold, anticline, upright, well located qac mixed alluvium and collovium qae mixed alluvium amd eolian qaf alluvial fan qc colluvium qmt talus qms landslide qms (jmb) landslide (brushy basin member) qms (jms) landslide (salt wash member) kf frontier formation kmr mowry shale kd dakota formation kcu upper member of cedar mountain formation kcb buckhorn conglomerate member of cedar mountain formation jmb brushy basin member of morrison formation jms salt wash member of morrison formation jmtw tidwell-windy hill members of morrison formation js stump formation 3 6 s. t. 1:10,000 1 cm = 100 mscale contour interval = 20 feet qms (jmb) o o o p o o p p p 7 17 25 15 7 6 14 12 13 9 p 0 1,000 2,000500 feet 0 140 280 420 560 meters figure 4. geologic map of the miners draw area fossil log site. the morrison formation overlies the stump formation and underlies the buckhorn conglomerate member of the cedar mountain formation. the morrison includes the windy hill, tidwell, salt wash, and brushy basin members. we further divided the brushy basin member into a lower banded unit and an upper gray unit. we measured the members of the morrison in three sections at blue mountain; the windy hill to the lower banded member is in the northeast part of the map area, whereas the top of the salt wash member, the lower banded and upper gray unit of the brushy basin are in an offset section in the southwest part of the map area because of folding, faulting, and landslides. the fossil log site occurs in the upper part of the salt wash member, about 17 m below the brushy basin member, along the southwest offset measured section. 66 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 figure 5. (a) geologic map and (b) cross section of the rainbow draw area fossil log sites. the morrison formation overlies the stump formation and underlies the cedar mountain formation in rainbow draw. in the mapped area, the morrison includes the windy hill, tidwell, salt wash, and brushy basin members. the fossil log sites are concentrated in two groups on separate ridges. both groups of logs occur in light-colored, fine-grained sandstone and siltstone below a mostly reddish-colored siltstone that was used as a marker bed (blue dashed line). ´ e e e e! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! e e ! ! ! ! ! ! ! e! ! ! ! ! ! ! ! ! ! ! ! ! e e e " o o o o p p p o p p p #* #* #*#*#* #*#* #* #* #* #* site 1 site 2 sites 3a–3c site 4 site 5 site 6 site 7 site 8 site 9 5 11 10 7 14 19 7 10 8 14 9 qc qc jms jmb qc jms jms qms qac jms jmb kcu qap qc qc jmtw qc jms js qc jmtw jms jms qc jmb jmb jms jms qac jms qc qc jms qc js qc qap r. 24 e. 2423 a a' explanation #* fossil log site o bedding, inclined, field measured p bedding, inclined, calculated cross section a-a' measured section map boundary contact enormal fault, well located normal fault, approximately located ! ! ! ! ! normal fault, concealed syncline marker bed formations qap piedmont gravel qac mixed alluvium and colluvium qc colluvium qms landslide kcu upper member of cedar mountain formation jmb brushy basin member of morrison formation jms salt wash member of morrison formation jmtw tidwell-windy hill members of morrison formation js stump formation 3 t. s. 1 cm = 55.5 m1:5550scale contour interval = 40 feet a 0 1,000 2,000 feet 0 125 250 375 500 meters 67 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 fossil dinoflagellate tests were recovered from the tidwell member near dinosaur national monument, and some glauconitic sandstone occurs as well (turner and peterson, 1999). the tidwell also contains abundant pinkish-colored botryoidal chert (figure 6d) (also referred to as “welded chert”) near or at the base of the member, which has been recognized throughout the region (king and merriam, 1969; peterson, 1980). a marginal marine to coastal plain (supralittoral) depositional environment is indicated for the tidwell member in northeastern utah (turner and peterson, 1999), but it may be somewhat fluvial near the top as indicated by the bioturbated and mottled beds (appendix). the tidwell member in northeastern utah ranges from 9 to 17 m thick. the salt wash member is composed of interbedded sandstone, siltstone, and mudstone with some beds of channel-form pebble sandstone, as well as conglomerate that ranges from 75 to 80 m thick (figure 7a). the salt wash was deposited in a fluvial system (peterson, 1980; turner and peterson, 1999, 2004). the capping brushy basin member is composed of a lower banded unit of siltstone, silty sandstone, and clay-rich mudstone (about 12 to 16 m thick) as well as an upper gray unit of predominately popcorn-weathering mudstone (about 70 to 88 m thick) and ranges from 82 to 104 m thick (figures 3 and 7b). the brushy basin memjmw js jmt jmt jms a b c d figure 6. photographs of lower members of the morrison formation and contacts within the study area. (a) the windy hill member of the morrison formation (jmw) overlies the stump formation (js) and underlies the tidwell member on the north flank of split mountain. the windy hill is composed of siltstone, mudstone, and thin-bedded rippled limestone. (b) rippled limestone in the windy hill member on the north flank of split mountain. (c) contact between the tidwell and salt wash members of the morrison formation near the measured section in rainbow draw. (d) example of the botryoidal chert commonly found near the base of the tidwell member. specimen collected south of the green river between split mountain and blue mountain plateau. 68 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 ber was deposited in a fluvial–lacustrine environment (turner and peterson, 1999, 2004) with significant input of volcanic ash (turner and fishman, 1991; christiansen and others, 2015). the morrison formation overlies the stump formation throughout northeastern utah. the nature of the contact between the stump and morrison is complex, however. conventional thinking is that the contact in northeastern utah is unconformable (the j-5 unconformity of pipiringos and o’sullivan [1978]), similar to exa b jms jmbu jmbl figure 7. photographs of the salt wash and brushy basin members of the morrison formation. (a) salt wash member near the measured section at miners draw showing varicolored siltstone beds and the brownish-gray channel sandstone beds; view to the northeast. (b) view of the salt wash and brushy basin members from near the top of the measured section at rainbow draw; view to the west. the yellow arrow points to the fossil log-bearing interval, which is overlain by the reddish-colored marker bed. the brushy basin is divided into a lower banded unit and an upper gray unit. the cretaceous cedar mountain through the frontier formations are exposed on the distant ridge. 69 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 posures in east-central utah where the tidwell member of the morrison unconformably overlies the summerville and older formations (peterson, 1988). however, turner and peterson (1999) noted that the j-5 surface is unconformable in some areas and conformable in others. other workers in northeastern utah showed the boundary as conformable in the eastern uinta mountains and uinta basin (e.g., currie, 1998; bilbey and others, 2005). our examination of the contact in the miners draw and rainbow draw areas indicates that it appears to be gradational and conformable. the upper jurassic morrison formation is unconformably overlain by the lower cretaceous cedar mountain formation. picking the contact between the two formations can be difficult, despite being an unconformity (k-1), because their similar lithologies are easily weathered to clay flats or clay-covered slopes. lithostratigraphic, biostratigraphic, and chemostratigraphic criteria are emerging that will help identify the contact (see cifelli and others, 1997; kirkland and others, 1999, 2003, 2011, 2016; ludvigson and others, 2003, 2015; greenhalgh and britt, 2007; kirkland, 2007; kirkland and madsen, 2007; sprinkel and others, 2012). for example, the basal unit of the cedar mountain formation can include the buckhorn conglomerate member, a cobble and boulder conglomerate that varies in thickness and typically forms a resistant cliff above the morrison formation (stokes, 1952; kirkland and others, 2016), as it does in the miners draw area (figure 8a). where the buckhorn conglomerate is missing, the basal bed of the cedar mountain formation is typically mottled, yellowish-orange, chert-pebble-bearing mudstone that underlies the first cedar mountain calcrete bed (sprinkel and others, 2012; kirkland and others, 2016), as it is in the rainbow draw area (figure 8b). stratigraphy of the fossil log sites sections of the morrison formation were measured at the miners draw and rainbow draw areas to describe beds and place the fossil log sites in stratigraphic and sedimentological context. at the miners draw area, several sections were measured to capture the entire morrison formation (windy hill, tidwell, salt wash, and brushy basin members) and the stratigraphic horizon of the fossil log site because distance between base and top of the morrison is large and complicated by being exposed on the nose of a southwest-plunging anticline (figure 4). the contact between the lower banded and upper gray units of the brushy basin member was used to trace around the miners draw area to the fossil log site. the section measured at rainbow draw included the windy hill, tidwell, and part of the salt wash members; the salt wash member was measured only through the fossil log-bearing unit to a light greenishto reddish-colored siltstone marker unit, which was overlain by a light-gray sandstone unit that capped the ridge. this distinctive marker unit was mapped and used to correlate between the two groups of fossil logs sites within the rainbow draw area. salt wash member at the miners draw area the salt wash member at miners draw consists of fineto coarse-grained, cross-bedded sandstone with some conglomeratic sandstone and conglomerate beds, silty sandstone, and siltstone (figure 9). the coarse-grained sandstone, conglomeratic sandstone, and conglomerate beds are mostly shades of brownish gray. the fine-grained and silty sandstone beds are light brownish-gray to greenish gray and medium reddish-brown. the siltstone beds are greenish gray to dark reddish-brown, somewhat clayey, and have a pseudo popcorn-weathering appearance. black and orange-colored accessory grains are common in the sandstone beds. the coarser grained beds typically form resistant ledges and may include fossil wood and bone fragments, whereas the finer grained beds tend to be slope forming (appendix). the fossil log-bearing interval at miners draw is light greenish-gray to brownish-gray, silty to very fine grained sandstone that is slightly clay rich with indistinct bedding and no discernable sedimentary features. the interval is weakly cemented and poorly exposed but the log weathers out in relief. the interval is 4.3 m thick and the fossil log occurs 3.0 m above the base of the unit and 7.8 m below the top of the salt wash member (figure 3). the fossil log is about 6 m long and its long axis is oriented east–west (see gee and others, 2019, for additional log dimensions). 70 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 salt wash member in the rainbow draw area the salt wash member in rainbow draw consists of very fine to fine-grained sandstone, some medium to coarse-grained sandstone, siltstone, and mudstone (figure 9; appendix). the sandstone beds are very light gray and light to medium greenish-gray and are medium to thin bedded and tabular with small-scale planar figure 8. the lower cretaceous cedar mountain formation unconformably overlies the brushy basin member of the morrison formation. (a) in the miners draw area, the buckhorn conglomerate member of the cedar mountain (conglomerate boulder in the foreground) makes it easy to locate the contact between the two formations; view to the northeast. (b) in many places, the contact between the morrison and cedar mountain formations is difficult to locate where the buckhorn conglomerate member is missing. here the contact (white line) is placed at a chert-pebble, mottled, yellowish-orange mudstone that underlies the first cedar mountain calcrete bed. photograph taken south of u.s. highway 40 between steinaker and red fleet reservoirs; view to the northeast. 71 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 m ud st on e si lts to ne si lty s an ds to ne sa nd st on e co ng lo m er at ic s an ds to ne cr os sbe dd ed s an ds to ne co ng lo m er at e ca lc re te pi nk a m yg da lo id al c he rt si lts to ne a nd s an ds to ne sa nd y lim es to ne fo ss il lo g si te fo ss il lo g si te 1 fo ss il lo g si te 1 w oo dbo ne fr ag m en ts m ud si lt sa nd gr av el f m c m ud si lt sa nd gr av el f m c m ud si lt sa nd gr av el f m c 10 0 18 0 15 0 50 10 0 18 0 15 0 50 10 0 18 0 15 0 50 m ud si lt sa nd gr av el f m c m et er m ud si lt sa nd gr av el f m c m et er m ud si lt sa nd gr av el f m c m et er 1 12 34 67 811 5 23456789101112 13 15 17 up pe r g ra y pa rt no t m ea su re d he re 14 16 123456789 345 2 167891011 co ve re d co ve re d co ve re d an d no t m ea su re d br us hy b as in m em be r bu ck ho rn c on gl om er at e m em be r o f ce da r m ou nt ai n fo rm at io n ce da r m ou nt ai n fo rm at io n sa lt w as h m em be r st um p fo rm at io n morrison formation m in er s d ra w s ec tio n (n or th ea st -m id dl e o �s et ) n w 1/ 4 n e1 /4 s ec tio n 3, t . 6 s ., r. 2 5 e. m in er s d ra w s ec tio n (s ou th w es t o �s et ) se 1/ 4 sw 1/ 4 se ct io n 3, t . 6 s ., r. 2 5 e. ra in bo w d ra w s ec tio n n w 1/ 4 n w 1/ 4 se ct io n 24 , t . 3 s ., r. 2 4 e. bu ck ho rn c on gl om er at e m em be r is n ot p re se nt a t r ai nb ow d ra w estimated thickness of unmeasured salt wash and brushy basin members from turner and peterson (1999) j5 un co nf or m ity (? ) so u th n o rt h co lo rs in s ec tio ns a pp ro xi m at es ou tc ro p co lo rs ti dw el l m em be r w in dy h ill m em be r ex pl an at io n fi gu re 9 fi gu re 9 . s tr at ig ra ph ic se ct io ns m ea su re d in th e m in er s d ra w an d ra in bo w d ra w ar ea s s ho w in g th e f os sil lo gbe ar in g in te rv al s. la be l n um be rs r ef er to m ea su re d se ct io n un its in ap pe nd ix . 72 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 cross-beds and some ripple laminations. the siltstone beds are light to medium greenish-gray and mottled reddish-brown, whereas the mudstone beds are dark greenish-gray, somewhat clayey, slightly micaceous, and fissile. the fossil logs are concentrated in two groups. the measured section of the salt wash member began at the eastern group of logs along a small drainage that contains the top of the stump formation to the top of a ridge where the fossil log-bearing interval and the overlying marker bed are exposed (figure 5a). the fossil log-bearing interval along the measured section is light to medium greenish-gray, very fine to fine-grained, friable sandstone and siltstone with indistinct bedding and no discernable sedimentary structures. the interval is generally slope forming and has fossil wood fragments scattered on the slope. the fossil log along the measured section at site 1 is 11 m in length, moderately well exposed, and fairly intact (figure 10). the log-bearing interval is 10.8 m thick, and the fossil log occurs 1.9 m below the base of the overlying marker bed and 29.7 m above the base of the salt wash member (figure 9). a short fossil log is located a short distance along strike of the measured section. that log occurs about 2 m above the base of the salt wash member. other fossil log sites of the eastern group are along the ridge within the log-bearing interval. these sites were also in the light to medium greenish-gray, very fine to fine-grained, friable sandstone and siltstone at slightly varying stratigraphic levels within the interval, except the logs at site 9 (see figure 5a). the log at site 9 is about 10 to 12 m lower than the other logs on the ridge. the only other fossil log measured in the eastern group is at site 7 (see figure 5a) where it is partially exposed in the hillside, is slightly more than 0.5 m in length, and has a convoluted wood grain on its surface. the western group of logs is located along a low ridge about 500 m northwest of the eastern group. no sections were measured through the western group, but detailed geologic mapping and comparison of the stratigraphy indicates that the log-bearing interval in the western group occurs in the same stratigraphic interval as the eastern group (figure 5). as in the eastern group, the log-bearing interval in the western group is light to medium greenish-gray, very fine to fine-grained, friable sandstone and siltstone with indistinct bedding and no discernable sedimentary structures. the measured lengths of the fossil logs range from about 1.3 to 2.3 m, with diameters ranging from 0.5 to 1.1 m. all sites within each group contain a single log, with the exception of site 1 (eastern group), which has two closely spaced logs, and site 3 (western group), which has multiple closely spaced log segments. the log segments at site 3 may represent multiple logs or a single log that has moved downslope because of erosion and broken apart. the measured azimuths of the long axis of the fossil logs in rainbow draw area indicate that they are randomly oriented. general description of the fossil wood only a basic description of the fossil logs is presented here because a detailed description is being made by gee and others (2019). the fossil logs in both the miners draw and rainbow draw areas are shades of light to medium brown in color and siliceous, and some have a figure 10. fossil log at site 1 in rainbow draw (see figure 5a). this fossil log occurs along the measured section in the salt wash member of the morrison formation. the fossil log-bearing interval is a light to medium greenish-gray, very fine to fine-grained, friable sandstone and siltstone with indistinct bedding and no discernable sedimentary structures. the log is 11 m in length and is oriented east–west; view is to the east. 73 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 coaly exterior (figure 11). the logs are large, mostly intact and have exposed lengths that range from 0.5 to 11 m and diameters up to 1.1 m. the fossil logs have been compressed somewhat due to compaction or have been unevenly abraded so that they have a long and short diameter (figure 12). the logs are well preserved and can be identified to species level from thin sections made from hand samples collected from both areas. the fossil logs have been identified as conifers that pertain to the same taxon originally described as araucarioxylon hoodii tidwell et medlyn 1993 in the family araucariaceae from mt. ellen in the henry mountains of southern utah (gee and others, 2019). concurrent systematic work will prompt a nomenclatural transfer of this species to the genus agathoxylon (gee and others, 2019). discussion the fossil logs in both the miners draw and rainbow draw areas occur in the salt wash member of the morrison formation. the single fossil log at miners draw is found in a silty to very fine grained, slightly clay-rich sandstone, which is 4.3 m thick and located 17 m below the base of the brushy basin member. unfortunately, the base of the salt wash member is not exposed at the fossil log site, but the salt wash is 78 m thick in the section measured to the northeast. similarly, we have mapped all the fossil log sites in the rainbow draw area to a single log-bearing interval, a very fine to fine-grained sandstone and siltstone having indistinct bedding and no discernable sedimentary features (lithologically like the miners draw interval) that is 10.8 m thick. most fossil logs are found in the upper part of the log-bearing interval, but logs are near the base of the interval as well, indicating that the entire interval may contain logs. we did not measure the entire salt wash member at rainbow draw, but turner and peterson (1999) indicated that this member in rainbow draw is about 80 m thick. our measured thickness to the top of the log-bearing interval is 31.5 m, and we calculate the thickness of the remaining salt wash, from the top of the log-bearing interval to the base of the brushy basin, to be about 40 m thick. thus, the measured and calculated thickness of the salt wash is about 72 m, which would place the log-bearing interval just below the middle of the salt wash member. though we may be inclined to correlate the log-bearing intervals at miners draw and rainbow draw as the same stratigraphic horizon because the strata of all sites are lithologically very similar, the log-bearing interval at miners draw seems to be stratigraphically higher in the section and probably does not correlate to the interval at rainbow draw. the salt wash member was deposited in a large flufigure 11. the fossil logs in both the miners draw and rainbow draw areas are shades of light to medium brown and mostly siliceous; some have a coaly preservation. (a) typical log in the rainbow draw area; view to the north. (b) example of wood with a coaly material; note the black organic matter. 74 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 vial floodplain system of mostly meandering and braided channels, migrating bar sand, and fine-grained overbank deposits (peterson and roylance, 1982; turner and peterson, 2004; kjemperud and others, 2008). both highand low-energy deposition is indicated by the range in grain sizes. much of the fossil wood found in the salt wash member occurs in channel sandstone and conglomeratic sandstone beds, but the fossil logs in the miners draw and rainbow draw areas are in an interval of very fine to fine-grained sandstone and siltstone beds that lack any discernable sedimentary structures. we interpret the log-bearing intervals as overbank deposits in the floodplain depositional environment. in addition, we speculate that the fossils logs may not have been transported far from their growth locations because of the fine-grained and structureless strata in which they are preserved. we are uncertain if the logs were transported by low-energy currents during a period of flooding or if the trees were toppled by a highwind event. the concentration of fossil logs into two groups in rainbow draw suggests that there may have been at least two stands of conifers in this area, if not a larger forest of moderately tall trees. summary although scraps of fossil wood are commonly found in the morrison formation, large fossil logs occur in both the salt wash and brushy basin members in northeastern utah near dinosaur national monument. in rainbow draw, the fossil logs occur in the middle of the salt wash member based on its measured and calculated thickness. the log-bearing interval is a very fine to fine-grained sandstone and siltstone that lacks sedimentary features, suggesting the logs are preserved in floodplain overbank deposits. the fossil log at miners draw is preserved in similar strata in the upper part of the salt wash member and is thought to be deposited in the same depositional environment as the logs in rainbow draw. the log-bearing intervals at miners draw and rainbow draw seem to be at two different stratigraphic horizons and do not correlate with one another. the nature of the sediments in which they are encased suggests that the logs did not travel far from their growth locations, but we are uncertain if the fossil logs were transported by low-energy currents or by some other mechanism. paleobotanical study of samples collected from both sites indicate the logs pertain to conifers of the family araucariaceae. acknowledgments we would like to thank the utah geological survey for their support during this project. we also thank steve sroka (utah field house of natural history state park museum) for his assistance in measuring the fossil logs in rainbow draw. thanks also go to the reviewers, john foster (museum of moab), grant willis and stephanie carney (both utah geological survey), for their constructive comments and suggestions to improve the manuscript and figures. finally, we are grateful to rebecca hunt-foster (utah bureau of land management, canyonlands district) for permission to collect the hand samples of fossil wood for analysis, and lisa baldwin (dinosaur national monument) for providing the internal paleontological resources report. figure 12. the fossil logs are large and mostly intact, range in exposed length from 0.5 to 11 m, and reach diameters of as much as 1.1 m. the fossil logs have been abraded so that they have a longer and a shorter diameter. the logs are well preserved and can be identified to the species level from thin sections made from hand samples (see gee and others, 2019) collected from the rainbow draw and miners draw areas (under permit from bureau of land management). 75 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 references bilbey, s.a., mickelson, d.l., hall, e.j., kirkland, j.i., madsen, s.k., blackshear, b., and todd, c., 2005, vertebrate ichnofossils from the upper jurassic stump to morrison transition— flaming gorge reservoir, utah, in dehler, c.m., pederson, j.l., sprinkel, d.a., and kowallis, b.j., editors, uinta mountain geology: utah geological association publication 33, p. 111–123. carpenter, k., 2013, history, sedimentology, and taphonomy of the carnegie quarry, dinosaur national monument, utah: annals of carnegie museum, v. 81, no. 3, p. 153–232. chure, d.j., litwins, r., hasiotis, s.t., evanoff, e., and carpenter, k., 2006, the fauna and flora of the morrison formation—2006, in foster, j.r., and lucas, s.g., editors, 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region, usa—paleoenvironmental, stratigraphic, and paleoclimate significance of terrestrial and freshwater ichnocoenoses: sedimentary geology, v. 167, p. 177–268. hintze, l.f., willis, g.c., laes, d.y.m., sprinkel, d.a., and brown, k.d., 2000, digital geologic map of utah: utah geological survey map 179dm, compact disc, 17 p., scale 1:500,000. king, r.j., and merriam, d.f., 1969, origin of the “welded chert,” morrison formation (jurassic), colorado: geological society of america bulletin, v. 80, no. 6, p. 1141–1148. kirkland, j.i., 2007, redefining the jurassic-cretaceous contact in east-central utah [abs.]: geological society of america abstracts with programs, v. 39, no. 5, p. 16. kirkland, j.i., cifelli, r.l., britt, b.b., burge, d.l., decourten, f., eaton, j.g., and parrish, j.m., 1999, distribution of vertebrate faunas in the cedar mountain formation, east-central utah, in gillette, d.d., editor, vertebrate paleontology in utah: utah 76 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 geological survey miscellaneous publication 99-1, p. 201– 218. kirkland, j.i., ludvigson, g.a., gonzalez, l., joeckel, r.m., and madsen, s.k., 2003, correlating early cretaceous dinosaur sites using stratigraphic trends in 13c from pedogenic carbonates—an example from the cedar mountain formation [abs.]: journal of vertebrate paleontology, v. 23, no. 3, p. 67a. kirkland, j.i., and madsen, s.k., 2007, the lower cretaceous cedar mountain formation, eastern utah—the view up an always interesting learning curve, in lund, w.r., editor, field guide to excursions in southern utah: utah geological association publication 35, p. 1–108. kirkland, j.i., madsen, s.k., hunt, g., j., waanders, g., and sprinkel, d.a., 2011, contact, ages, and correlation of lower cretaceous strata on the north side of the uinta basin, northeastern utah [abs.]: geological society of america abstracts with programs, v. 43, no. 4, p. 2. kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r.k., 2016, the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata: geology of the intermountain west, v. 3, p. 101–228. kjemperud, a.v., schomacker, e.r., and cross, t.a., 2008, architecture and stratigraphy of alluvial deposits, morrison formation (upper jurassic), utah: american association of petroleum geologists bulletin, v. 92, no. 8, p. 1055–1076. ludvigson, g.a., gonzalez, l.a., kirkland, j.i., and joeckel, r.m., 2003, a mid-cretaceous record of carbon isotope excursions in palustrine carbonates of the cedar mountain formation of utah—marine-terrestrial correlation of aptian-albian oceanic anoxic events 1a, 1b, and 1d 9 [abs.]: the 3rd international limnogeology congress abstract volume, p. 169. ludvigson, g.a., joeckel, r.m., murphy, l.r., stockli, d.f., gonzález, l.a., suarez, c.a., kirkland, j.i., and al-suwaidi, a., 2015, the emerging terrestrial record of aptian-albain global change: cretaceous research, v. 56, p. 1–24. morgan, s.k., lindsay, b.w., and hoffman, a.p., 2012, geologic trail guide for escalante state park, utah, in anderson, p.b., and sprinkel, d.a., editors, geologic road, trail, and lake guides of utah’s parks and monuments: utah geological association publication 29 (third edition), p. 8. peterson, f., 1980, sedimentology of the uranium-bearing salt wash member and tidwell unit of the morrison formation in the henry and kaiparowits basins, utah, in picard, m.d., editor, henry mountains symposium: utah geological association publication 8, p. 305–322. peterson, f., 1988, stratigraphy and nomenclature of middle and upper jurassic rocks, western colorado plateau, utah and arizona: u.s. geological survey bulletin 1633-b, p. b17–b56. peterson, l.m., and roylance, m.m., 1982, stratigraphy and depositional history of the upper jurassic morrison formation near capitol reef national park: brigham young university geology studies, v. 29, no. 2, p. 1–12. pipiringos, g.n., and o’sullivan, r.b., 1978, principal unconformities in triassic and jurassic rocks, western interior united states—a preliminary survey: u.s. geological survey professional paper 1035-a, 29 p., 1 plate. sprinkel, d.a., 2006, interim geologic map of the dutch john 30' x 60' quadrangle, daggett and uintah counties, utah, moffat county, colorado, and sweetwater county, wyoming: utah geological survey open-file report 491dm, compact disc, gis data, 3 plates, scale 1:100,000. sprinkel, d.a., 2007, interim geologic map of the vernal 30' x 60' quadrangle, uintah and duchesne counties, utah, moffat and rio blanco counties, colorado: utah geological survey open-file report 506dm, compact disc, gis data, 3 plates, scale 1:100,000. sprinkel, d.a., madsen, s.k., kirkland, j.i., waanders, g., and hunt, g.j., 2012, cedar mountain and dakota formations around dinosaur national monument—evidence of the first incursion of the cretaceous western interior seaway into utah: utah geological survey special study 143, 20 p., 7 appendices. stokes, w.l., 1952, lower cretaceous in colorado plateau: american association of petroleum geologists bulletin, v. 36, no. 9, p. 1766–1776. stone, d.s., 1993, tectonic evolution of the uinta mountains—palinspastic restoration of a structural cross section along longitude 109o15', utah: utah geological survey miscellaneous publication 93-8, 19 p. tidwell, w.d., and medlyn, d.a., 1993, conifer wood from the upper jurassic of utah, usa-part ii—araucarioxylon hoodii sp. nov.: the palaeobotanist, v. 42, no. 1, p. 70–77. turner, c.e., and fishman, n.s., 1991, jurassic lake t'oo'dichi-a large alkaline, saline lake, morrison formation, colorado plateau: geological society of america bulletin, v. 103, no. 4, p. 538–558. turner, c.e., and peterson, f., 1999, biostratigraphy of dinosaurs in the upper jurassic morrison formation of the western interior, u.s.a., in gillette, d.d., editor, vertebrate paleontology in utah: utah geological survey miscellaneous publication 99-1, p. 77–114. turner, c.e., and peterson, f., 2004, reconstruction of upper jurassic morrison formation extinct ecosystem—a synthesis: sedimentary geology, v. 167, p. 309–355. a-1 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 appendix miners draw section (southwest offset) general area of the camptosaurus site along the k ranch road along an unnamed tributary of miners draw, south of blue mountain plateau se1/4 sw1/4 section 3, t. 6 s., r 25 e., uintah county, utah vernal 1:100,000, snake john reef 1:24,000 section measured by douglas a. sprinkel, mary beth bennis, and dale e. gray; october 22, 2013 n40°19.603', w109°5.350' (nad83/wgs84, utm 12: 662333 easting, 4465775 northing); offset southward along top of lower banded subunit (unit 17 of north section); elevation 1718 m; dip direction 328°, dip 7° description thickness (meters) interval total buckhorn conglomerate member of cedar mountain formation 10. conglomerate, light brownish-gray, poorly sorted, planar bedding, black chert pebbles to cobbles, massive weathering, forms a resistant cap on morrison formation .......................................................... nm morrison formation brushy basin member upper gray part 9. covered with abundant buckhorn conglomerate debris, measured to base of first conglomerate bed.............................................................................................................................................. 14.9 86.6 8. sandstone, light-gray (unweathered) that weathers to light brownish-gray, fine-grained with coarse-grained beds, moderately well sorted, calcareous, mud rip-ups at the base of coarsegrained beds, slightly cross-bedded .................................................................................................................. 2.9 71.7 7. claystone, mudstone, and siltstone interval, medium-gray (unweathered) and weathers lightgray, popcorn weathering, calcite veins weathering out on slope ............................................................. 52.3 68.8 total upper gray unit ....................................................................................................................................... 70.1 lower banded unit 6. siltstone to silty sandstone, alternating greenish-gray and reddish-brown, contains thin resistant fine-grained sandstone, resistant sandstone 5 to 10 cm thick, unit is slope-forming, scattered manganese and carbonate nodules on slope .................................................................................. 9.0 16.5 5. silty sandstone, light brownish-gray, very fine grained, forms slope, poorly exposed ............................. 7.5 7.5 total lower banded unit ................................................................................................................................... 16.5 total brushy basin member ............................................................................................................................ 86.6 salt wash member (incomplete; base of member is covered); dip direction 190°, dip 17° 4. sandstone, brownish-gray, coarse-grained, poorly to moderately sorted, subangular to subrounded, 1% accessory grains of orange and black, highly cross-bedded ............................................ 7.5 22.3 3. covered ................................................................................................................................................................ 9.0 14.8 2. silty sandstone, light greenish-gray to brownish-gray, very fine grained and slightly clay rich, no discernable sedimentary features, weakly cemented, mostly slope covered, and poorly exposed, contains large fossil log that weathers out in relief, azimuth of log direction is 255°, log is 3.0 m above the base of unit 2 ................................................................................................................. 4.3 5.8 1. sandstone, light-gray, fineto medium-grained, subrounded, moderately well sorted, planar cross-bedding, forms low ledge; paleocurrent measurement 220°, 130°, 170°, 230°, 240°, 220°, and 290° ................................................................................................................................................................ 1.5 1.5 base of salt wash member is covered total salt wash member (incomplete) ........................................................................................................... 22.3 a-2 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 appendix miners draw creek section (middle offset) along the k ranch road along an unnamed tributary of miners draw, south of blue mountain plateau nw1/4 ne1/4 section 3, t. 6 s., r 25 e., uintah county, utah vernal 1:100,000, snake john reef 1:24,000 section measured by douglas a. sprinkel, mary beth bennis, and dale e. gray; october 22, 2013 n 40°20.086', w109°5.034' (nad83/wgs84, utm 12: 662761 easting, 4466677 northing) with offset southwest along top of lower banded part (unit 17) that underlies upper gray part of brushy basin member; see section and coordinates below; elevation 1755 ft; dip direction 328°, dip 7° description thickness (meters) interval total morrison formation brushy basin member (incomplete) upper gray unit 18. claystone, mudstone, and siltstone interval, medium-gray (unweathered) and weathers lightgray, popcorn weathering, calcite veins weathering out on slope ..................................................................... nm lower banded part 17. siltstone, reddish-gray, interbedded thin resistant (but subdued) sandstone beds, approximately 5 to 10 cm thick ...................................................................................................................... 14.1 17.0 16. mudstone, claystone, and silty mudstone, dark greenish-gray with alternating reddish-gray, forms slope, popcorn weathering, intervals of calcium carbonated nodules weathering out on slope, iron manganese zone............................................................................................................................... 0.3 2.9 15. iron manganese zone ......................................................................................................................................... 0.3 2.6 14. siltstone to silty mudstone, medium greenish-gray, slightly fissile, calcareous, forms slope .................. 2.0 2.3 13. calcrete, calcium carbonate densely cemented with rounded coarse sand grains .................................... 0.3 0.3 total brushy basin member (lower banded unit) .......................................................................................... 17.0 salt wash member 12. siltstone, greenish-gray to dark reddish-gray, mottled, slightly clayey, slightly slope-forming, pseudo popcorn weathering .............................................................................................................................. 2.6 78.3 11. sandstone, light-gray (unweathered) and weathers medium-brown, very fine grained, subangular to subrounded, scattered dark grains, well-sorted, laminated (bedding parallel laminations), cross-bedded, calcareous, forms subdued resistant ledge..................................................... 0.7 75.7 10. sandstone, brownish-gray (like unit 8), fine-grained, slope covered, contains a 0.8 m thick iron manganese limonitic zone that is about 2.3 m from base of unit ...................................................... 10.0 75.0 9. sandstone, similar to unit 4, resistant and ledge-forming, scrappy wood, slopes below bare scrappy bone and wood ..................................................................................................................................... 3.6 65.0 8. sandstone, brownish-gray, coarse-grained, moderately to poorly sorted, crosslaminated, calcareous, resistant ledge-forming .................................................................................................................. 9.4 61.4 7. sandstone, same as unit 4, but forms slope ..................................................................................................... 4.5 52.0 6. sandstone, brownish-gray, poorly sorted, coarse-grained, graded, fining up, cross-bedded like unit 4, resistant ledge-forming .................................................................................................................. 0.9 47.5 5. sandstone, same as unit 4 but more slope forming ....................................................................................... 5.2 46.6 4. sandstone, light brownish-gray, coarse-grained, poorly sorted, clasts are subangular to subrounded, graded, fining up, cross-bedded, calcareous, abundant reddish-colored chert, limestone clasts, resistant ledge-forming ........................................................................................................ 2.6 41.4 3. sandstone, greenish-gray, very fine grained, subrounded, well-sorted, calcareous, slopeforming, more resistant in the top 0.8 m ......................................................................................................... 2.3 38.8 2. silty sandstone, medium reddish-gray, very fine grained, subrounded, some clay, calcareous, weathers to smooth slopes ................................................................................................................................. 9.6 36.5 a-3 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 appendix 1. sandstone, light-gray, fine-grained, well-sorted, subrounded, scattered blackand orangecolored accessory grains (~1% total; dark grains are more abundant) calcareous, moderatescale planar cross-bedding, massive weathering, ......................................................................................... 26.9 26.9 total salt wash member .................................................................................................................................. 78.3 miners draw section (northeast offset) — tidwell and windy hill members along the k ranch road along an unnamed tributary of miners draw, south of blue mountain plateau nw1/4 ne1/4 section 3, t. 6 s., r 25 e., uintah county, utah vernal 1:100,000, snake john reef 1:24,000 section measured by douglas a. sprinkel, mary beth bennis, and dale e. gray; june 12, 2017 n 40°20.07342', w109°05.00.312' (nad83/wgs84, utm 12: 662894.01 easting, 4466657.27 northing); elevation 1755 m; dip direction 325°, dip 6° description thickness (meter) interval total morrison formation salt wash member (measured in middle offset section) 12. sandstone, light brownish-gray to very light gray, fine-grained, abundant large-scale planar and trough cross-beds, very thickly bedded ................................................................................................................. nm tidwell member 11. siltstone as in unit 9; lumpy siltstone and sandstone as unit 10 but bioturbated ...................................... 0.5 0.5 10. sandstone, light brownish-gray to light greenish-gray, fine-grained, well-sorted, parallel bedded .................................................................................................................................................................. 0.4 0.9 9. siltstone, reddish-brown with light greenish-gray mottling, ripple laminated with some softsediment deformation, some mud rip-up clasts ............................................................................................. 0.6 1.5 8. sandstone, light greenish-gray, fine-grained, lumpy, bioturbated .............................................................. 0.5 2.0 7. sandstone as unit 6 but forms ledges; interbedded shale as in unit 5 ......................................................... 7.4 9.4 6. sandstone, very light yellowish-brown, fine-grained, friable, forms slope ................................................ 2.0 11.4 5. shale, dark-gray, fissile, forms slope ................................................................................................................ 1.9 13.3 4. sandstone, light yellowish-brown, very fine grained, forms slope .............................................................. 1.4 14.7 3. siltstone, light-gray, thinly bedded, forms slope ............................................................................................ 0.8 15.5 2. chert, pink, botryoidal, replaced calcite or gypsum forms base of tidwell member ............................... 1.1 16.6 total tidwell member ...................................................................................................................................... 16.6 windy hill member 1. siltstone and sandstone–interbedded; siltstone, light-gray, thin-bedded, small-scale ripples; sandstone, light-gray to light greenish-gray, fine-grained, well-sorted, abundant glauconite with some black accessory grains, thin-bedded, rippled ............................................................................. 16.1 16.1 total windy hill member ................................................................................................................................ 16.1 stump formation (redwater member) limestone, light-gray to greenish-gray, finely crystalline (sparite), sandy, glauconitic, rippled........................... nm nm = not measured total brushy basin member (south offset section) ........................................................................................ 86.6 total salt wash member (north section) ........................................................................................................ 78.3 total tidwell member ...................................................................................................................................... 16.6 total windy hill member ................................................................................................................................ 16.1 total morrison formation (composite section) .................................................................. 197.6 a-4 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 appendix rainbow draw section measured west of wagon bench road along east side of rainbow draw nw1/4nw1/4 section 24, t. 3 s., r 24 e., uintah county, utah dutch john 1:100,000, island park 1:24,000 salt wash member section measured by douglas a. sprinkel, mary beth bennis, dale gray, and larry r. edwards; october 23, 2013 n 40°33.065, w109°10.850 (nad83/wgs84, utm 12: 654032 easting, 4490515 northing); elevation 1707 m tidwell and windy hill members section measured by douglas a. sprinkel, mary beth bennis, and dale gray; november 20, 2014 n 40°33.136, w109°10.813 (nad83/wgs84, utm 12: 654081 easting, 4490648 northing); elevation 1724 m; dip direction 263°, dip 5° description thickness (meter) interval total morrison formation (incomplete) salt wash member (incomplete) 11. sandstone, light-gray, mediumto coarse-grained, subangular to subrounded, moderately well sorted, approximately 30% accessory grains (equal black, orange and yellow), forms resistant ledges through slope, thickto medium-bedded, cross-bedded ................................................ nm 10. siltstone, light-gray to light greenish-gray becoming mostly reddish-brown at top, forms slope, channel sandstone within unit not along the line of section; channel sandstone is 9 m long and maximum 1.5 m thick, channel sandstone, light-gray, very fine to fine-grained, subrounded to subangular, well sorted, contains 5% accessory grains, mostly black with some orange ................................................................................................................................................................. 10.5 42.06 9. sandstone and siltstone, light to medium greenish-gray, fineto very fine grained, wellsorted, subrounded, less than 1% orange and dark accessory grains, poorly cemented, friable, forms slope, scattered fossil wood weathering out on slope; fossil log segment possibly in place along section at 8.8 m from base of unit 10 (2 m above base of unit 9 and 22.76 m above the base of the salt wash member); fossil log site 1 is 1.9 m below base of unit 10 (8.9 m above base of unit 9 and 29.66 m above base of the salt wash member) ............................................................ 10.8 31.56 8. siltstone, mottled reddish-gray to greenish-gray, fine-grained, well-sorted, bedding indistinct, forms slope ........................................................................................................................................ 1.5 20.76 7. sandstone, same as unit 4 but well cemented ............................................................................................... 0.06 19.26 6. sandstone, medium greenish-gray, well-sorted, fine-grained, subrounded, calcareous .......................... 2.7 19.2 5. mudstone, dark greenish-gray, silty, slightly clayey, slightly micaceous, fissile, calcareous .................... 1.3 16.5 4. sandstone, same as unit 1 but poorly exposed, forms slope ...................................................................... 13.7 15.2 3. sandstone, very light gray, very fine grained, well-sorted, less than 1% dark accessory grains, calcareous, mediumto thin-bedded, tabular-bedded, small planar cross-bedding, some ripple laminations ............................................................................................................................................... 1.5 1.5 total salt wash member .................................................................................................................................. 42.06 tidwell member; dip direction 233°, dip 6° 2. siltstone and sandstone (poorly exposed); siltstone light brownish-gray, forms slope; sandstone, light-gray, fine-grained, well-sorted, abundant pink botryoidal chert and sparsely glauconitic, calcareous, medium to thin bedded, tabular-bedded, small-scale cross-bedding, symmetrical ripples; forms resistant ledges .................................................................................................. 17.1 17.1 total tidwell member ...................................................................................................................................... 17.1 a-5 stratigraphic setting of fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa sprinkel, d.a., bennis, m., gray, d.e., and gee, c.t. geology of the intermountain west 2019 volume 6 appendix windy hill member; dip direction 233°, dip 6° 1. siltstone, mudstone, and limestone (calcarenite) mostly covered; siltstone and mudstone, greenish-gray, forms slope; limestone, sandy, light greenish-gray, fine-grained, well-sorted, sparsely glauconitic, calcareous, thin-bedded, tabular-bedded, small-scale cross-bedding, ripples; forms resistant ledges ......................................................................................................................... 20.4 20.4 total windy hill member ................................................................................................................................ 20.4 total morrison formation (incomplete) .................................................................................. 79.56 redwater shale member of stump formation: limestone (calcarenite), light brownish-gray to greenish-gray, fine-grained, scattered ooids to oolitic, pelecypod shell hash .................. nm nm=not measured total brushy basin member (south offset section) ........................................................................................ nm total salt wash member (incomplete) ........................................................................................................... 42.06 total tidwell member ...................................................................................................................................... 17.1 total windy hill member ................................................................................................................................ 20.4 total morrison formation (incomplete section) ................................................................ 79.56 geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source michael s. jensen, bart j. kowallis, eric h christiansen, casey webb, michael j. dorais, douglas a. sprinkel, and brian jicha geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover east view of the prominent 5.5-m-thick tuff bed at the base of the lapoint member of the duchesne river formation. the base of the light-colored tuff bed is used as the contact with the underlying dry gulch creek member of the duchesne river formation. this outcrop of the tuff is located about 13 km west of vernal, utah, just off utah sr-121 at 40.416519 n. latitude and 109.746494 w. longitude. see figure 3 and appendix 1 in this article for details. i uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 1 abstract thin fallout tuffs are common in the terrestrial deposits of the eocene duchesne river formation on the flanks of the uinta mountains of eastern utah. their ages and compositions provide new insight into the tectonic events and magmatic history of the western cordillera and provide important constraints on the cenozoic land mammal chronology. whole-rock compositions of the volcanic ash show that they underwent post-emplacement argillic alteration, typical of a wetland/floodplain depositional setting. however, immobile element ratios and abundances, such as zr/ti, la/nb, and y are typical of rhyolites formed in a subduction-related setting. glass shards preserved in one sample all had sio2 values >75%, typical of high-silica rhyolite. preserved phenocrysts in the ash beds include quartz, sanidine, plagioclase, and biotite with variable amounts of accessory zircon, apatite, titanite, and allanite. biotite compositions have fe/(fe+mg) ratios typical of calc-alkaline igneous rocks and clusters of chemical compositions suggest a genetic relationship to three or four separate eruptions. sanidine compositions from five samples range from or73 and or79. only one sample had preserved plagioclase with compositions ranging between an22 – an49. allanite from the ash beds has lower total rare earth elements (ree) concentrations than allanite from other well-studied rhyolites. titanite in one sample has lower concentrations of ree, fe, and al than expected of rhyolites and is probably detrital. plagioclase and sanidine from two different tuff beds near the middle of the duchesne river formation yielded analytically indistinguishable 40ar/39ar ages of 39.47 ± 0.16 ma and 39.36 ± 0.15 ma, respectively. these dates, along with the compositional data seem to limit the eruptive source for these fallout tuffs to the northeast nevada volcanic field, one of the few volcanically active regions of western north america at the time. these new radiometric ages, along with stratigraphic relations and previously published ages for tuffs in the bishop conglomerate (which unconformably overlies the duchesne river formation), constrain the timing of late laramide uplift in the region from 39 to about 37 ma and post-laramide epeirogenic uplift from 34 ma to 30 ma. finally, the ages also provide additional evidence that the duchesnean north american land mammal age ended in the eocene, which was originally named and defined from the duchesne river formation. fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source michael s. jensen1, bart j. kowallis1, eric h christiansen1, casey webb1, michael j. dorais1, douglas a. sprinkel2, and brian jicha3 1 department of geological sciences, brigham young university, provo, ut, 84602; wasabae@gmail.com 2 azteca geosolutions, pleasant view, ut 84414; utah geological survey, salt lake city, ut 84114; dsprinkel@gmail.com 3 university of wisconsin, department of geoscience, madison, wi, 53706; bjicha@geology.wisc.edu citation for this article. jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b., 2020, fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source: geology of the intermountain west, v. 7, p. 1–27, 2 appendices, supplemental data, https://doi.org/10.31711/giw.v7.pp1–27. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 2 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 introduction preserved volcanic ash in sedimentary rock sections can provide insights into the geologic history of a region through radioisotopic dating and geochemical analysis, leading to better interpretations of tectonic events and settings (kowallis and others, 2001; hildreth and wilson, 2007; smith and others, 2014; christiansen and others, 2015; hong and others, 2019). radiometric dating of tuffs also provides better age constraints on sedimentary rocks and fossils (kowallis and others, 1991, 1998, 2001; riggs and others, 2003; smith and carrol, 2015). additionally, accurate dates of volcanic ash in sedimentary succession can be used as important markers for stratigraphic correlation (huff, 2016). we have employed high-precision, single-crystal, 40ar/39ar laser-fusion dating along with whole-rock and mineral geochemical analyses on the fallout tuffs in the duchesne river formation located in the uinta basin of eastern utah. previous work on the duchesne river formation tuff beds has provided some information on their age (andersen and picard, 1974; bryant and others, 1989; sprinkel, 2007) but the dates were imprecise and geochemical data was essentially nonexistent. in the overlying bishop conglomerate, which also contains altered fallout tuffs, previous work has shown that more accurate and precise 40ar/39ar dating techniques and detailed chemical compositions can be used to constrain the timing, tectonic setting, and sources of altered middle cenozoic tuffs, as well as inferences about the original composition (kowallis and others, 2005). in this study, we attempt to answer the following questions: 1. what are the ages of the fallout tuffs within the duchesne river formation? 2. what phenoclasts are preserved within these tuffs and what are their compositions? 3. how has alteration affected the chemistry of the duchesne river formation tuffs and can inferences be made about their original composition? 4. where is/are the eruptive source or sources of the tuffs? 5. do more precise ages help to better constrain the age of fauna within the duchesne river formation, which serves as the type formation for the duchesnean north american land mammal age (nalma)? 6. do the ages obtained from the ash beds help constrain periods of uplift of the uinta mountains? geologic setting laramide orogeny the laramide orogeny was characterized by basement block uplift along high-angle reverse faults apparently due to shallow subduction of the farallon plate from 70-34 ma (dickinson and others, 1988; liu and others, 2010; jones and others, 2011; fan and carrapa, 2014; yonkee and weil, 2015). the east-west-trending uinta mountain range is one such basement block and has experienced multiple periods of uplift and erosion (hamilton, 1978; hansen, 1986; dickinson and others, 1988) as recorded by the sediments in the adjacent uinta basin (figure 1), including the green river, uinta, and the duchesne river formations. ponded basins, such as the uinta basin, were common during the laramide and were often filled with fresh or saline lakes that acted as efficient sediment traps (carroll and bohacs, 1999; tanavsuu-milkeviciene and others, 2017). the lakes and fluvial environments were also efficient traps for erupted volcanic material, and fallout tuffs have been found in many of the formations throughout the strata within the uinta basin and have been used to date the timing of volcanic, tectonic, and sedimentary events (bryant and others, 1989; remy, 1992; smith and others, 2003; kowallis and others, 2005; smith and carroll, 2015). during the early stages of the laramide orogeny, volcanism was uncommon due to shallow subduction of the farallon plate (decelles, 1994; dickinson, 2004; schellart and others, 2007). however, as the farallon plate steepened, subduction-related volcanism resumed about 54 ma beginning in present-day montana and idaho (norman and mertzman, 1991) and then migrated south into the nevada-utah region around 40 ma, finally reaching the southern great basin about 36 ma (lipman and others, 1972; humphreys, 1995; castor and others, 2000, 2003; best and others, 2013a). volca3 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 tds tdl tdd tdb drf-b drf-c through drf-i drf-j tb k drf-a 1 2 9 24 54 3 3 0 1 0 1 kilometers miles tuff bed (tb) bishop conglomerate duchesne river forma�on (tds) starr flat mbr (tdl) lapoint mbr (tdd) dry gulch creek mbr (tdb) brennan basin mbr (k) cretaceous units undivided tuff sample loca�ons volcanic field strike and dip symbol vnw vernal nw quadrangle b 40°30' 40°22'30'' 109°45' 109°37'30'' drf-k utah state route sr-121 a challis 51-45 ma absaroka 55-45 ma ne nevada 43-39 ma southern rocky mountains 36.5-30 ma 100 mi keetley 35-32 ma oregon nevada idaho w yo m in g arizona new mexico utah colorado california tuscarora 40-39 ma 114°116°118°120° 112° 110° 108° 36° 38° 40° 42° vnw uinta mountains 100 km tin�c 35-30 ma central nevada 36-18 ma indian peakcaliente 36-18 ma thomas-keg-desert mtn 42-30 ma marysvale 30-22 ma figure 1. (a) regional map of western united states with boundaries and ages of middle cenozoic volcanic fields that formed as a result of slab rollback. (b) a simplified geologic map of the vernal nw quadrangle showing locations of tuff samples, the principal geologic units, and contacts of the different members of the duchesne river formation. the cretaceous units are undivided. 4 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 nic activity during this time period was so intense it has been called the middle cenozoic ignimbrite flare-up. the challis, absaroka, northern nevada-utah, and the central and southern great basin volcanic fields document this time of intense volcanic activity (brooks, 1995a; chandler, 2006; henry, 2008; best and others, 2016). these repeated volcanic episodes have been proposed as a contributor to the global cooling at the eocene-oligocene boundary (zanazzi and others, 2007; jicha and others, 2009). silicic volcanic rocks from this time period typically range from dacite to rhyolite in composition and are commonly preserved as fallout tuffs, ash-flow tuffs, flow breccias, and silicic domes (lipman and others, 1972; brooks and others, 1995c). like other distal fallout tuffs, the duchesne river formation tuffs were likely sourced from large plinian or coignimbrite eruptions (blaylock, 1998; kowallis and others, 2005; chandler, 2006; christiansen and others, 2015). duchesne river formation stratigraphy sedimentary rocks, which record the uplift and erosion history of the uinta mountains and contain fallout tuffs that can be used to study and date that record, are well exposed on the southern flanks of the uinta mountains in the vernal nw quadrangle just west of vernal, utah (figure 1). along with cretaceous units, the predominant formation within the quadrangle is the duchesne river formation where all four members (in ascending stratigraphic order: brennan basin, dry gulch creek, lapoint, and starr flat) are exposed (figure 2). tuffaceous beds were not found in the basal brennan basin member and the capping starr flat member in the study area; however, tuff beds have been reported within these members elsewhere in the uinta basin region (sprinkel, 2007, 2018a). the dry gulch creek and lapoint members contain numerous tuffaceous beds. these members are predominantly composed of siltstone and mudstone that intertongue with fineto medium-grained sandstone and conglomerate with both members becoming progressively coarser towards the uplifted uinta mountain front (warner, 1966; andersen and picard, 1972, 1974; sato and chan, 2015; webb, 2017). tuff beds in the dry gulch creek and lapoint members have been mostly altered to clay minerals (andersen and picard, 1974). they are light to medium gray and stand out against the moderate-red to reddish-brown siltstone and mudstone (figure 3). several tuff beds are laterally extensive throughout much of the quadrangle and the lowermost tuff bed is used as the contact between the lapoint and dry gulch creek members (webb, 2017) (figure 3a). the oldest and youngest members of the duchesne river formation, the basal brennan basin member and the capping starr flat member, respectively, are predominantly pebble to boulder conglomerates with minor sandstone and siltstone, indicating they either were deposited in closer proximity to the uplifting uinta mountain front to the north or were deposited when streams flowing off the uplift were transporting coarse material farther out into the basin as a result of increased gradient (sato and chan, 2015). the starr flat member is capped by the gilbert peak erosion surface, a widespread oligocene surface of erosion and non-deposition found on both the south and north flanks of the uinta uplift (hansen, 1986; sprinkel, 2007; webb, 2017). the gilbert peak erosion surface is considered to mark the end of the laramide orogeny in the uinta basin region (hansen, 1986; aslan and others, 2017). the stratigraphy and distribution of the duchesne river formation members within the study area are reported in greater detail in webb (2017). in addition to the tuff beds, the duchesne river formation also contains key mammal fossils and has been used as the type section of the duchesnean nalma (wood and others, 1941; clark and others, 1967; prothero, 1995). the duchesnean nalma is used throughout north america and the fauna within that time period are used to better understand the evolution of animals and climate in north america during the middle eocene (emry, 1981; rassmussen and others, 1999; alroy, 2000). sampling and analytical methods stratigraphic relations and structural evolution of the area were established by geological mapping (webb, 2017). during the course of the mapping, four samples were collected from three tuff beds within the upper and 5 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 drf-k (25 cm thick) drf-b (1 m thick) drf-c (30 cm thick) drf-a (50 cm thick), 39.47± 0.16 ma drf-d, e, f, g (5.5 m thick) drfh, i (25 cm thick), 39.36 ± 0.15 ma drf-j (27 cm thick) la te e oc en e d uc he sn e r iv er la po in t d ry g ul ch c re ek ep oc h fo rm at io n m em be r stratigraphy a b (approximately 30 m) (approximately 25 m) (approximately 35 m) formation symbol thickness meters not to scale lithology notes bishop conglomerate starr flat member lapoint member dry gulch creek member brennan basin member tb tds tdl tdd tdb 315 102 243 0 111 0 150 437 564 eo ce ne unconsolidated deposits q less than 50quaternary d uc he sn e r iv er f or m at io n gilbert peak erosion surface massive conglomerate interbedded conglomerate/ sandstone and siltstone prominent ash beds throughout duchesneodus uintensis fossils distinct sandstone tongues of tds fan conglomerates grade southwestward to sandstone diplacodon elatus fossils 40ar/39ar age 34.03 ± 0.04 ma angular unconformity local angular unconformity group 1 group 2 group 3 group 4 geochemical groups 40ar/39ar age 39.47 ± 0.16 ma 40ar/39ar age 39.36 ± 0.15 ma epoch oligocene 40ar/39ar age 30.54 ± 0.22 ma moderate-red to redish-brown mudstone, siltstone, and sandstone redish-brown to red-purple siltstone, sandstone, and minor pebble conglomerate halfway hollow quarry un0117 (agriochoerus maximus) carnegie titanothere quarry un0012 (duchesneodus uintensis) stratigraphic interval of fossil mammal quarries figure 2. (a) stratigraphic column of paleogene units in the vernal nw quadrangle from webb (2017). 40ar/39ar ages from the bishop conglomerate are from kowallis and others (2005) and fossils are from burger and tacket (2014). red box indicates area of stratigraphic column shown in part b. (b) stratigraphic column of the dry gulch creek and lapoint members of the duchesne river formation showing the relative locations and thicknesses of the tuff beds (gray). note that samples drf-d, drf-e, and drf-f are from the same 5.5-m-thick tuffaceous bed which serves as the contact between the dry gulch creek and lapoint members. samples drf-h and drf-i are also from the same tuffaceous bed but collected from different locations about 2 km apart. geochemical groups based on the chemical composition of the samples within each tuff. note that the tuffs are grouped stratigraphically. 6 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 middle dry gulch creek member and seven samples were collected from four tuff beds within the lapoint member and within the vernal nw quadrangle (table 1). roughly 5 to 8 kg of sample was collected at each site (site descriptions and photographs can be found in appendix 1). a split of each sample was processed to liberate the mineral phenoclasts, which were extracted by standard washing and heavy liquid techniques. phenocrysts were mounted in epoxy and then polished for microprobe analysis at brigham young university (byu). table 2 summarizes the analytical parameters used for each mineral. a portion of each sample was also prepared for x-ray fluorescence (xrf) analyses of major and trace elements also at byu. two hundred sanidine grains from sample drf-h and two hundred plagioclase grains from drf-a were hand-picked from the clean concentrates at byu. they were dated using single crystal 40ar/39ar laser fusion methods at the university of wisconsin-madison wiscar geochronology lab. the 40ar/39ar ages were calculated relative to the fc-201 sanidine standard age of 28.201 ma and a total 40k decay constant of 5.643 e-10/a (kuiper and others, 2008). methodology for laser fusion dating of single crystals of sanidine are outlined on the wiscar lab website (http://geochronology.geoscience.wisc. edu/analytical-approaches/). a summary of all the ages and the analytical parameters is given in appendix 2. one of the benefits of the single crystal method is that anomalously old or young grains can be identified and removed from a weighted average and a more accurate lapoint member dry gulch creek member a b figure 3. (a) view to the east of the basal 5.5-m-thick tuff bed at the contact (underlined in yellow) between with dry gulch creek and the lapoint members. the gray color of the ash stands out against the reddish-orange colors of the siltstone. samples drf-d, drf-e, drf-f, and drf-g were collected from this key layer which shows evidence of detrital mixing and has likely been thickened by post-sedimentary processes. (b) collection site of sample drf-c shown between the red lines is 18 m above the basal ash bed in a, which is covered by quaternary unconsolidated gravel. 7 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 eruption age can be determined. this method is particularly critical for tuff beds collected from sedimentary sections where even slight reworking of the ash can contaminate it. both samples contained detrital feldspar much older than the duchesne river formation. one of the drawbacks of single crystal analysis, however, is that because the crystals and argon signal sizes are small, the analytical uncertainties are higher than they would be using the multi-crystal fusion method; consequently, the analytical errors are on the order of 100,000 years rather than 10,000 years. isotopic ages several isotopic ages have previously been reported from the prominent tuff bed near the base of the lapoint member of the duchesne river formation (table 3). fairly consistent k-ar and 40ar/39ar biotite ages of approximately 41 ± 0.5 ma from this bed have been reported by mcdowell and others (1973), andersen and picard (1974), and prothero and swisher (1992) whereas fission track ages from the same bed in the lapoint member averaged 34 ± 1–3 ma (bryant and others, 1989). additionally, a biotite k-ar age of 37.6 ± 1.4 ma and a zircon fission track age of 36.7 ma ± 3.9 ma were obtained from a tuff within the younger starr flat member from the neola nw quadrangle (table 3). the previous k-ar and fission track ages from the duchesne river formation all have relatively large uncertainties. the biotite ages may also suffer from alteration, typical of biotite in this type of environment, giving erroneous ages (smith and others, 2008). we chose to date feldspar because it is more resistant than biotite to alteration and table 1. characteristics of tuffs from the duchesne river formation. table 2. parameters for electron-microprobe analyses. member sample latitude longitude phenocryst assemblage age (ma) temperature (°c) rock type (zr/ti -nb/y) tectonic settting (nb-y)feld bt lapoint drf-a 40.491478 -109.746676 qz-bt-sa-pl-aln-gls-zrn 39.47 +/0.16 630 711 dacite volcanic arc lapoint drf-b 40.449856 -109.720892 qz-bt-sa-mc 704 dacite volcanic arc lapoint drf-c 40.417679 -109.749658 qz-bt-aln 658 dacite volcanic arc lapoint drf-d 40.416545 -109.746362 qz-bt-ap-zrn 697 dacite volcanic arc lapoint drf-e 40.416564 -109.746445 qz-bt dacite volcanic arc lapoint drf-f 40.416583 -109.746469 qz-bt 645 dacite volcanic arc lapoint drf-g 40.416519 -109.746494 qz-bt-mc 650 dacite volcanic arc dry gulch creek drf-h 40.418116 -109.747051 qz-bt-sa-mc-aln 638 trachyte volcanic arc dry gulch creek drf-i 40.418127 -109.747087 qz-bt-sa-mc-aln-ttn-zrn 39.36 +/0.15 645 trachyte volcanic arc dry gulch creek drf-j 40.409754 -109.699966 qz-bt-sa 698 rhyolite volcanic arc dry gulch creek drf-k 40.397333 -109.726184 qz-bt-mc 696 rhyolite volcanic arc note: feldspar temperature calculated using the thermodynamic parameters of elkins and grove (1990) at a pressure of 5 kb. biotite temperatures are an average of multiple grains, calculated using the thermometer of luhr and others (1984). mineral abbreviations from whitney and evans (2010). aln is allanite, ap is apatite, bt is biotite, gls is glass, mc is microcline, pl is plagioclase, sa is sanidine, ttn is titanite, qz, is quartz, zrn is zircon. mineral standard analytical conditions for unknown biotite lemhi biotite 20 na current, 15kv acceleration voltage, 5µ beam size sanidine orthoclase 20 na current, 15kv acceleration voltage, 5µ beam size plagioclase anorthosite 20 na current, 15kv acceleration voltage, 5µ beam size allanite none 20 na current, 15kv acceleration voltage, 5µ beam size titanite sphene-t 30 na current, 15kv acceleration voltage, 10µ beam size apatite apa-durango 10 na current, 15kv acceleration voltage, 5µ beam size glass rhyo-gls 10 na current, 15kv acceleration voltage, 5µ beam size note: names of standards are from the list of standards used by the byu department of geological science. 8 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 typically provides more accurate ages (kowallis and others, 1998, 2001, 2005). sanidine extracted from our sample drf-h gave a 40ar/39ar age of 39.36 ± 0.15 ma and plagioclase from drf-a gave an age of 39.47 ± 0.16 ma (figure 4). drf-h was taken from a tuff bed at the top of the dry gulch creek member, only 2 to 3 m from the contact with the lapoint member. drf-a was taken from a tuff bed within the overlying lapoint member several kilometers northeast of drf-h near where the lapoint member pinches out between the starr flat member and brennan basin member (figure 1). the ages are stratigraphically inverted but are not analytically distinguishable from one another. despite being very close in age, drf-a and drf-h are not from the same ash bed based on field mapping and chemical and mineralogical differences outlined below. this is significant because sample drf-a represents a tuff bed that was mapped as part of the starr flat member (sprinkel, 2007). our recent mapping at 1:24,000 scale (webb, 2017) and the new age suggest that the tuff bed is from the upper part of the lapoint member where the lapoint and starr flat members intertongue. the analytical uncertainties for these new ages are much smaller than previous ones and constrain the boundary between the lapoint and dry gulch creek members to about 39.4 ma. these ages are significantly younger than the previously reported ~41 ma ages from the same series of tuff beds (mcdowell and others, 1973; andersen and picard, 1974; prothero and swisher, 1992). table 3. compilation of selected isotopic ages of the duchesne river formation. 35 40 45 50 55 drf-h (sanidine) 39.36 0.15 ma± n = 13 of 25 a age (ma) 35 40 45 50 55 drf-a (plagioclase) 39.47 0.16 ma± n = 11 of 16 b figure 4. rank order plots with probability density curves for feldspar ages from samples drf-h (a) and drf-a (b) from the dry gulch creek and lapoint members of the duchesne river formation, respectively. individual 40ar/39ar dates, as well as weighted mean ages, are shown with 2σ analytical uncertainties. filled circles are the ages that were used in the age calculation. reference/report sample id age ±2sd (ma) method member 7.5' quadrangle latitude (n) longitude (w) this study drf-h 39.36 ± 0.15 40ar/39ar, plagioclase lapoint vernal nw 40° 24'59.4" 109° 44'47.6" this study drf-a 39.47 ± 0.16 40ar/39ar, sanidine dry gulch creek vernal nw 40° 29'28.9" 109° 41'28.94" bryant and others (1989) n-83-2 36.7 ± 3.9 fission track, zircon starr flat neola 40° 28'43" 110° 05'54' bryant and others (1989) icp-1a 30.5 ± 1.4 fission track, zircon starr flat ice cave peak 40° 35'49" 109° 59'52" constenius and others (2011) knc070109-1 38.90 ± 0.80 u-pb, zircon starr flat wolf creek summit 40° 23'240" 111° 00'908" bryant and others (1989) vnw-1 36.9 ± 1.8 fission track, zircon lapoint vernal nw 40° 24'33" 109° 42'01" bryant and others (1989) la-1 35.2 ± 1.6 fission track, zircon lapoint lapoint 40° 24'52" 109° 45'43" prothero and swisher (1992) lp1 39.47 ± 0.17 40ar/39ar biotite lapoint vernal nw not reported not reported bryant and others (1989) blu-83-1 33.0 ± 3.4 fission track, zircon dry gulch creek bluebell 40° 19'41" 110° 09'17" bryant and others (1989) blu-83-2 34.5 ± 4.4 fission track, zircon dry gulch creek bluebell 40° 19'40" 110° 09'21" ugs apatite to zircon (2014) hc08122012-1 40.66 ± 1.88 u-pb, zircon brennan basin hancock cove 40° 18'02.89" 110° 04'58.03" 9 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 mineral assemblages and compositions in addition to providing ages, magmatic phenocrysts in tuff beds can provide information that can help in determining the composition of the source magma, in correlating ash beds across a broader area, and provide insights into the tectonic setting. table 1 summarizes the mineral assemblage of each of the samples collected from the duchesne river formation. the presence of quartz, biotite, and sanidine and absence of pyroxene and hornblende is a common subduction-related rhyolitic mineral assemblage and typical of other volcanic ash beds from the late eocene of western north america (lipman and others, 1972). allanite was found in four samples. titanite and apatite were the least abundant minerals and were only found in one sample each. because these ashes were deposited in a dominantly fluvial environment, there is an inherent risk of contamination by detrital grains and all samples contained sedimentary grains of quartz, carbonate, and diagenetic clay. quartz quartz grains were present in all the duchesne river formation samples. igneous quartz grains were identified by their prismatic, euhedral shape, and presence of glassy melt inclusions. detrital quartz grains were rounded, frosted, lacked melt inclusions, and tended to be larger than the volcanic quartz grains. biotite biotite phenocrysts were present in all the duchesne river formation tuffs and are the main mafic phase present. in several samples, abundant biotite was visible in the field without the aid of a hand lens. in general, biotite is less resistant to the effects of weathering than sanidine, quartz, and allanite. the biotite phenocrysts collected showed signs of alteration with many grains being rounded and light brown in color; however, no evidence of chloritic alteration was found in the polished grain mounts. chloritic alteration is a concern because k can be replaced with h2o and cl during diagenesis (bisdom and others, 1982; smith and others, 2008). these chemical changes lead to low analytical totals and the resulting isotopic ages cannot be considered accurate (smith and others, 2008). to avoid alteration, only black, euhedral grains were picked for electron microprobe analysis and from those, only analyses with totals (not including water) of 90% or above were considered. al, fe, and mg in biotite are typically fairly immobile and may help in understanding the original composition of the tuff beds (christiansen and others, 2015). molar fe/(fe+mg) and total al (atoms per formula unit – apfu) plot within or near the calc-alkaline rhyolite field (figure 5) and are similar to biotites from the subduction-related oligocene fish canyon tuff and jurassic tuffs from the temple cap, carmel, and morrison formations (kowallis and others, 2001; christiansen and others, 2015). total al plots between 1.2 and 1.5 apfu for biotite in seven of the samples, but biotite in drf-c, drf-d, drf-f, and drf-g have total al greater than 1.5 apfu. samples drf-d, drf-f, and drf-g are from different horizons within the same prominent ash bed at 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 fe /(f e+ m g) al total (apfu) two-mica granites a-type calc-alkaline bishop tuff fish canyon tuff and middle jurassic ash beds biotite morrison fm tuffs group 1 group 2 group 3group 4 drf-a drf-b group 1 drf-c drf-d drf-f drf-g group 2 drf-h drf-i group 3 drf-j drf-k group 4 figure 5. compositions of biotite from the tuffs of the duchesne river formation compared to the bishop tuff, fish canyon tuff, morrison formation tuffs, and middle jurassic tuffs from the carmel and temple cap formations, which are all subduction-related pyroclastic deposits. fields for different types of granite are from christiansen and others (1986). the four clusters formed by the duchense river formation samples are grouped stratigraphically. compositions are presented in atoms per formula unit (apfu). 10 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 the same geographic location at the base of the lapoint member (figures 1 and 2, appendix 1) and form the high al group. an enrichment of al is sometimes the result of alteration as the more mobile elements like k and na are removed and al becomes relatively enriched (christiansen and others, 2015). however, the grains with high al also have k levels of at least 8 wt.% (jensen, 2017), an indication that the biotite has undergone little alteration. sericitic alteration could explain the elevated al paired with normal levels of k but sericitic alteration occurs at higher temperatures and also decreases mg below a 3/2 mg/fe ratio, which is not the case for the duchesne river formation tuffs (figure 6). additionally, these samples have relatively high analytical totals (93 > wt.%) compared to other duchesne river formation biotite phenocrysts. drf-d, drf-f, and drf-g were collected from the top, middle, and bottom of the same thick ash bed at the same locality at the base of the lapoint member and they all have the fe/mg ratios, al values, and high analytical totals described above; this consistency would not be expected if the biotite was altered by secondary processes. consequently, we consider these biotites to have magmatic compositions. the total al vs fe/(mg+fe) diagram also reveals distinct clusters of biotite from the duchesne river formation tuffs (figure 5). the clustering follows stratigraphic order with the oldest middle dry gulch creek samples, drf-k and drf-j, plotting together. the upper dry gulch creek samples drf-h and drf-i were taken from the same ash bed at two different localities about 2 km apart and form an isolated cluster. these two groups have fe/(mg+fe) ratios slightly higher than typical biotite in calc-alkaline rhyolite, which could be an indication of a more evolved and differentiated melt or that crystallization occurred at a lower ƒo2 than typical calc-alkaline rhyolites. also seen on figure 5, five biotite grains from drf-d (yellow) have lower total al and fe/(fe+mg) ratios than the rest of drf-d grains. these grains have analytical totals above 96 wt.% so their anomalous compositions could be an indication of a detrital component or of the secondary mixing of ash from two separate eruptions rather than alteration. drf-d was collected at the top of the prominent, basal ash bed of the lapoint member (figure 2 and appendix 1) and could have experienced reworking in the floodplain depositional environment. drf-c represents a tuff bed about 10 m above the basal lapoint member ash bed and also lies in the high al group. finally, the middle lapoint samples, drf-b and drf-a, form a loose cluster with similar fe/(fe+mg) ratios within the range of typical calc-alkaline rhyolites to see if the groups selected on figure 5 are statistically significant, a hierarchical cluster analysis was run using all the elements analyzed in biotite according to ward’s minimum variance method (ward, 1963) using the jmp software. a constellation plot (figure 7) shows that the samples in the total al diagram cluster in the same way when tio2, al2o3, feot, mgo, na2o, k2o, f, and cl are all considered. these four clusters of biotite analyses are grouped stratigraphically which suggests that the composition of the magmatic source of the duchesne river formation tuffs became less evolved over time. for example, fe drops from 1.8 to 1.0 apfu, while mg increases from 1.0 to 1.7 apfu (figure 6) from the lower dry gulch creek member tuffs to the mid lapoint member tuffs. biotite compositions are also useful in geothermometry (luhr and others, 1984). titanium is a temperature-sensitive element in biotite and increases with increasing temperature (figure 8). temperature calculations from the biotite minerals from the duchesne river figure 6. mg and fe abundances for biotite phenocrysts from the tuffs of the duchesne river formation plot near or above a ratio of 3 to 2. a 3/2 ratio eliminates sericite alteration as a cause for the high amounts of al and k in these tuffs. the mg/fe ratio gradually increases over time. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 m g (a pf u) fe (apfu) group 1 group 2 group 4 group 3 drf-a drf-b group 1 drf-c drf-d drf-f drf-g group 2 drf-h drf-i group 3 drf-j drf-k group 4 11 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 formation tuffs range between 625 and 725°c. the low end of the range is suspect because typical biotite temperatures in fresh rhyolite are close to 700°c but samples drf-c through drf-i all plot at 650°c or lower. these low-temperature biotite minerals also show enrichment of al but maintain k abundances greater than 0.9 apfu. speculatively, the low temperatures and the high al and k content could be the result of metasediments being incorporated into the magma prior to eruption. comparison of log(xmg/xfe) and log(xf/xoh) from the duchesne river formation biotites (figure 9) plot in the oxidized, moderately contaminated (i-mc) field (ague and brimhall, 1988). the biotites have lower log(xf/xoh) than that in the oligocene fish canyon tuff and only overlap the lower log(xf/xoh) of biotite from the late jurassic morrison formation tuffs from eastern utah (christiansen and others, 2015). based on lower mg/fe ratios, they are also more reduced than most of the middle jurassic ash beds of the temple cap and carmel formations collected in southwestern utah (kowallis and others, 2001). nonetheless, they are similar to sierran granites (ague and brimhall, 1988) and thus are similar to other subduction-related, typically oxidized silicic suites. feldspar alkali feldspar was the most common feldspar found in the duchesne river formation tuffs and was present in six samples whereas phenocrysts of plagioclase were found in only one sample (drf-a from the middle part of the lapoint member). plagioclase phenocrysts were commonly zoned and compositions ranged from an50 to an17 (figure 10). since plagioclase has a low tolerance to weathering, it is unlikely to be a detrital component and is considered volcanic. of the six samples with alkali feldspar, only four contained volcanic sanidine with or72-or81. the other alkali feldspar grains in drf-b, drf-g, drf-i, and drf-k are detrital with or values >or89; in drf-h these are likely the grains that give older eocene to jurassic ages and usually have higher k/ca ratios. using plagioclase and sanidine from drf-a, a two-feldspar eruption temperature was calculated using drf-a drf-b drf-c drf-d(a) drf-f drf-g drf-h drf-i drf-j drf-k drf-d(b) group 4group 1 group 2 group 3 figure 7. constellation plot showing how individual biotite analyses compare to each other on the basis of oxide wt.% of tio2, al2o3, feot, mgo, na2o, k2o, f, and cl. note that drf-d was separated into different clusters (a) and (b). this mixing is likely due to post-deposition detrital mixing. drf-f, drf-c, drf-g, and drf-d are somewhat mixed but become more distinctive when all elements are considered, especially sio2, feot, and mgo. figure 8. temperatures calculated from biotite compositions using the thermometer of luhr and others (1984) which depends on the ti/fe ratio. the groups in this diagram are the same as in figure 5. 0.100 0.150 0.200 0.250 0.300 500 550 600 650 700 750 800 ti (a pf u) t (°c) luhr drf-a drf-b group 1 drf-c drf-d drf-f drf-g group 2 drf-h drf-i group 3 drf-j drf-k group 4 12 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 solvcalc (wen and nakvasil, 1994) and the thermodynamic parameters of elkins and grove (1990). average temperatures of 643°c, 630°c, and 608°c were calculated at 5, 3, and 2 kilobars, respectively, using the average composition of the five most sodic plagioclase grains ranging from an20 to an27 and one or79 sanidine grain. the temperatures are low compared to other volcanic rhyolite feldspars and since only one sanidine grain was used in the calculations these temperatures are not likely to be reliable. allanite allanite, a common accessory mineral in silicic igneous rocks, is a complex, rare earth element-rich mineral of the epidote group with a general formula of a2m3si3o11(o, f)(oh), in which a is commonly ca2+, th4+, ree3+, or u4+, and m typically includes al3+, fe3+, or fe2+ (deer and others, 1997). rare earth elements (rre) are essential constituents in allanite through the coupled substitution of ca2++ fe3+ = ree3+ + fe2+ (giere and sorensen, 2004). euhedral grains of allanite were found in three different tuff beds in the duchesne river formation, represented by four samples—drf-a, drf-c, drf-h, and drf-i. the grains are relatively unaltered with analytical totals between 98% and 100%. duchesne river formation allanite minerals have cao concentrations ranging from 11 to 13 wt.%, which is several percent higher than in allanite from the toba and bishop tuffs of sumatra and california, respectively (figure 11). they also have about 0.65 apfu total light rare earth elements (lree), which is about 0.3 apfu less than the allanites in the toba or the highly-evolved bishop tuff as shown on figure 12. high ca and low ree could be an indication that the melt in which the allanite formed was slightly depleted in ree and so ca remained high in the a site. chesner and ettlinger (1989), however, found that ree abundance in allanite may not be a good indicator of ree concentrations in the magmatic melt. for example, allanite from the bishop tuff (hildreth, 1979) has higher ree concentrations than allanite in the toba tuff but lower whole-rock ree abundances. chesner and ettlinger (1989) concludlo g (x f/x o h ) log (xmg/xfe) 0.0 -0.5 -1 -1.5 -2 -2.5 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 i-scr i-sc i-mc i-wc fish canyon tuff middle jurassic ash beds morrison formation tuffs drf-a drf-b group 1 drf-c drf-d drf-f drf-g group 2 drf-h drf-i group 3 drf-j drf-k group 4 figure 9. compositions of duchesne river formation biotite phenocrysts compared to the fish canyon tuff, morrison formation tuffs of christiansen and others (2015), and to ash beds in the middle jurassic of southern utah (kowallis and others, 2001) in terms of log(xmg/xfe) vs. log(xf/xoh), where x is mole fraction. granite fields are for sierra nevada granitoids from ague and brimhall (1988): i-scr—i-type, strongly contaminated and reduced; i-sc—i-type, strongly contaminated; i-mc—i-type, moderately contaminated; i-wc—i-type, weakly contaminated. these biotites are most like those in the moderately contaminated granites. figure 10. ternary diagram of feldspar compositions. drf-a is the only sample with two feldspars. sanidine phenocrysts from drf-i and -j have relatively high or levels. potassium feldspars with >or90 were interpreted to be detrital grains from plutonic rocks. these high or grains are late jurassic to early cretaceous in age based on 40ar/39ar ages (jensen, 2017). 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00ab or an drf-a drf-b drf-h drf-i drf-j drf-a plagioclase detrital k feldspar 13 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 ed that physical parameters such as temperature exert a greater control on ree substitution in allanite than composition of the coexisting melt and suggested that higher temperatures correlate with higher ree abundances in allanite. the allanite-bearing tuffs from the duchesne river formation apparently had low eruptive temperatures around 650 to 710°c based on biotite compositions. the lower ree content of allanite thus seems to agree with this notion. low eruption temperatures could explain other chemical differences between the duchesne river formation allanite and other well-studied tuffs, if ti in the octahedral site is a function of temperature as it is in biotite and hornblende. allanite in duchesne river formation tuffs has ti concentrations between 0.0 to 0.06 apfu compared with 0.06 to 0.12 for allanite in the toba tuff and 0.16 and 0.19 for the bishop tuff. petrik and others (1995) argued that the ree and al content of allanite is a function of fe3+/fetotal and is thus an indicator of magmatic fo2. in this regard, allanite from duchesne river formation tuffs contains more al than the other silicic tuffs used for comparison (>1.8 vs. 1.2–1.6 apfu). as a consequence, allanite has relatively low calculated fe3+/fetotal of 0.3–0.4 (figure 11b), even lower than in the bishop tuff (0.5–0.6), which crystallized near the qfm oxygen buffer (hildreth, 1979). thus, given the control of fe3+ vs al3+ by fo 2, it is possible that the low ree contents are also related to relatively low fo 2. moreover, fe3+/fetotal in allanite from drf-h and drf-i indicates more reducing conditions than to drf-a and drf-c. based on fe/(fe+mg) ratios (figure 5), biotite in these same samples show similar relationships and substantiates the control by oxygen fugacity. figure 12. lree-y pattern for allanite in tuffs from the duchesne river formation compared to the average lree abundances of allanite in the bishop and toba tuffs; all are quite similar. the lree-y pattern for average titanite in sample drf-i is plotted for comparison. allanites are strongly enriched in lrees, including y, compared to titanites. the compositional field for titanite in other cenozoic tuffs of the great basin is shown for comparison. figure 11. (a) allanite phenocryst compositions from the duchesne river formation tuffs compared to allanite in the bishop tuff (california) and toba tuff (sumatra), which are relatively more enriched in rees and other a-site substitutions. (b) duchesne river formation allanites have lower inferred fe3+/fetotal ratios (0.3–0.4) than both the bishop and toba tuffs, implying lower fo2 in the parent magmas. 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 0.60 0.80 1.00 1.20 1.40 1.60 1.80 r ee +y +t h+ u +n a (p fu ) ca (pfu) bishop tuff c&e toba drf-a drf-c drf-h drf-i a b 0.00 0.25 0.50 0.75 1.00 1.0 1.5 2.0 2.5 3.0 r e e +y +t h+ u ( ap fu ) al (apfu) bishop tuff c&e toba fe3+/fetot tie lines drf h drf i drf-a drf-c ferriallanite allanite epidote 0.20.4 0.6 0.8 clinozoisite la ce nd sm 100 1000 10,000 100,000 1,000,000 10,000,000 c ho nd rit e n or m al iz ed v al ue s y drf-i titanitebishop tuff toba drf-i drf-a drf-h drf-c allanite titanite representative cenozoic titanite composition 14 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 titanite titanite was only found in one sample of one ash bed, drf-i from the upper dry gulch creek member. it occurs as isolated, euhedral grains that lack clear evidence of a detrital origin but is also distinct from other volcanic titanites. titanite in drf-i has an average composition of ca0.99ti0.91si0.98o0.96f0.04 with only minor substitutions for ca, ti, and si. its major element composition is similar to other volcanic titanites in the database of kowallis and others (2019). however, fe and al are lower than most other volcanic titanites with average fe+al at 0.078 apfu compared with 0.11 apfu for titanite in other silicic tuffs (figure 13). it also has distinctively low y and mn and a high nb/y ratio, a characteristic shared by the whole-rock composition. these titanite grains have lree + y patterns similar to these other tuffs but with lower ree values and somewhat steeper slopes from la to y (figure 12). the lree/y ratio of about 9.6 from titanite in drf-i is higher than cenozoic great basin tuffs, which typically have lree/y of about 3.6. the presence of titanite contradicts the evidence from biotite and allanite that the source magma was a reduced, low-temperature, rhyolitic magma, with low lrees. elevated fe/(mg+fe) ratios in biotite and low calculated fe3+/fetotal ratios in allanite indicate fairly reducing conditions but this is unusual for titanite-bearing magmas that typically indicate oxidizing conditions. for example, christiansen and others (2015) noted that the tuffs from the morrison formation containing titanite were more oxidized than tuffs without titanite, as indicated by high mg/fe ratios in biotite. the opposite relationship is seen in the duchesne river formation biotites associated with titanite, which have log(xmg/xfe) ratios around -0.2 as opposed to 0.1–0.43 for duchesne river tuffs that lack titanite (figure 9). these contradictions of oxidizing vs. reducing conditions, along with the atypical compositions discussed above and shown on figure 13, and the fact that titanite was only found in drf-i but not drf-h (same tuff bed) probably indicate that the titanite grains are detrital rather than a magmatic component of the tuff. apatite apatite was only found in one tuff, drf-d, and proved to be significantly weathered despite a euhedral and prismatic appearance. the average analytical total was 93.56% and p2o5 and cao were several weight percent lower on average than is typical for apatite. f was very high, making up as much as 4.35 wt.% of the apatite grains, a strong indication of alteration (deer and others, 1997). drf-d has a strong detrital component and these apatite grains may be further evidence of detrital mixing. whole-rock composition whole-rock data was gathered using xrf techniques as well as microprobe analysis of glass shards from sample drf-a. whole-rock compositions provide insights about the altered and original composition of the tuffs. analytical totals from the whole-rock xrf analyses are good (>99.74 wt.%), but loss on ignition (loi) ranges from 4.8 wt.% all the way up to 18 wt.% for drf-c and drf-j. however, most samples had loi measurements less than 9% as shown in table 4. samples with high lois also show abnormally high cao concentrations and the samples may have been contaminated with detrital carbonate despite soaking the samples in an acid bath during preparation. some glass shards managed to survive diagenesis 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.00 0.02 0.04 0.06 0.08 0.10 fe a pf u al pfu drf-i titanite volcanic figure 13. compositions of titanite from the duchesne river formation. drf-i titanites are depleted in both al and fe compared to volcanic titanite from the cenozoic tuffs compiled by kowallis and others (personal communication) and are probably detrital. 15 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 in sample drf-a from the middle part of the lapoint member. drf-a is the least altered of the all the duchesne river formation tuffs based on sio2 levels in the glass and immobile elements such as nb, zr, and ti. the electron microprobe analyses indicate these shards are high-silica rhyolite with sio2 >75% with low concentrations of tio2, fe2o3, and mgo when normalized to 100% on a volatile free basis (see the supplemental data file). immobile elements given the altered condition of the duchesne river formation tuffs and likely contamination from detrital material, whole-rock compositions do not represent the original composition of the volcanic ash. however, by comparing immobile elements such as nb, zr, ti, and ree, some information about the initial composition can be determined. even though immobile element concentrations will typically be changed by alteration, they are similarly enriched or depleted so that ratios of table 4. x-ray fluorescence analyses of altered tuffs from the duchesne river formation. sample drf-a drf-b drf-c drf-d drf-e drf-f drf-g drf-h drf-i drf-j drf-k member tdl tdl tdl tdl tdl tdl tdl tdd tdd tdd tdd major oxides sio2 71.81 59.62 52.7 68.84 73.86 70.11 65.58 67.37 66.66 54.16 73.62 tio2 0.44 0.38 0.4 0.51 0.53 0.31 0.38 0.24 0.18 0.21 0.3 al2o3 14.91 17.57 16.74 17.6 13.29 15.41 16.45 21.29 21.34 14.64 7.55 fe2o3 3.08 3.14 3.64 2.99 3.46 2.67 3.24 2.33 2.51 1.99 1.72 mno 0.04 0.08 0.27 0.01 0.02 0.02 0.07 0.01 0.01 0.27 0.06 mgo 1.6 5.69 5.78 5.2 3.08 4.6 4.91 5.35 5.83 4.8 2.32 cao 2.97 10.74 19.79 2.54 2.4 3.41 6.84 1.76 1.74 21.42 12.23 na2o 2.06 1.71 0.09 0.91 0.66 1.47 0.91 0.61 1.08 1.29 0.17 k2o 2.98 0.93 0.45 1.25 2.39 1.88 1.51 0.99 0.61 1.14 1.81 p2o5 0.11 0.13 0.13 0.16 0.32 0.12 0.11 0.07 0.04 0.07 0.24 loi 4.83 12.06 18.97 7.37 5.44 7.28 9.94 8.69 8.55 18.21 11.09 analysis total 99.99 99.74 100.3 99.93 99.97 99.92 100.01 99.91 99.94 99.94 100.16 trace elements sc 8 7 6 6 9 5 8 4 3 1 9 v 37 53 48 45 55 39 46 14 12 21 38 cr 22 10 22 22 40 18 20 9 4 11 27 ni 9 10 17 11 15 12 17 17 12 9 12 cu 10 10 13 13 16 7 9 10 6 8 17 zn 60 60 74 58 55 64 82 60 59 47 44 ga 18 15 20 18 16 19 21 19 19 14 9 rb 126 39 39 42 81 45 44 41 23 34 52 sr 352 217 225 276 205 222 255 239 268 252 127 y 18 17 21 21 41 18 16 6 5 30 16 zr 174 135 140 150 153 135 122 103 88 104 182 nb 13 12 13 14 12 9 10 18 18 11 7 ba 750 421 179 184 280 432 363 68 48 193 189 la 28 22 22 33 44 23 27 12 11 26 25 ce 56 52 43 64 83 44 52 23 27 47 40 nd 25 16 7 30 43 24 25 15 16 4 9 sm 6 4 3 7 8 6 5 5 5 2 2 pb 22 27 21 23 19 21 24 33 35 24 12 th 13 16 13 14 11 9 11 17 16 12 9 u 4 7 2 4 3 3 5 2 2 5 3 note: major oxides are in wt% and trace elements are reported in ppm. tdl-lapoint member, tdd-dry gulch creek member, loi-loss on ignition. normalized to 100% on a volatile free basis. 16 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 these elements can still be used to make general inferences about the original composition and volcanic setting (kowallis and others, 2001; christiansen and others, 2015). tio2/al2o3 ratios in altered ash beds from terrestrial settings can also be used to determine the extent of physical reworking and chemical alteration and tio2/al2o3 values <0.055 are indicative of primary ash composition (hong and others, 2019). despite extensive argillic alteration seen in most of the duchesne river formation tuffs (discussed below) all the tuffs appear to have maintained a tio2/al2o3 ratio <0.055. on the discrimination diagrams of winchester and floyd (1977), the duchesne river formation tuffs plot in the dacite and rhyolite fields based on nb/y vs. zr/ ti (figure 14a). samples drf-h and drf-i have anonymously low y resulting in high nb/y ratios so they plot in the trachyte field, but their zr/ti ratios are rhyolitic. the distinctive low y content could be the result of pre-eruptive fractionation of titanite and allanite which are both present in the tuff and have high partition coefficients for y. (as noted earlier, the titanite in this sample also has an anomalously high nb/y ratio.) when zr/ti is plotted against ce ppm, all of the duchesne river samples plot in the rhyolite field (figure 14b) which agrees with the fresh glass analysis and the mineral assemblages and compositions (e.g., sodic sanidine, quartz, low ti biotite). tectonic setting can also be inferred from immobile elements and careful use of some mobile trace elements. figure 15 shows discrimination plots by pearce (1984) that compare nb, y, and rb concentrations. both diagrams show that the duchesne river formation tuffs have compositions characteristic of a volcanic arc setting, assuming the elements plotted have not been significantly changed by alteration. a volcanic arc setting also agrees with trace element patterns of the duchesne river formation tuffs (figure 16) which are typical of subduction-related calc-alkaline magmas including large negative nb anomalies, strong positive pb anomalies, and a generally decreasing trend from left to right. average abundances of trace elements from volcanic arc tuffs that also experienced argillic alteration (described below) from the jurassic morrison formation (christiansen and others, 2015) are plotted as a comparison to the duchesne river tuffs. argillic alteration the extensive secondary alteration exhibited by the duchesne river formation tuffs can provide insight into the depositional environment (christiansen and others, 2015). all the tuffs exhibit signs of argillic alteration to swelling clays as is typical of the alteration of volcanic glass. sio2 values range from 68% in drf-a all the way to 42% in drf-c, all low for rhyolite magmas figure 14. (a) immobile element diagram modified from winchester and floyd (1977). duchesne river formation tuffs all plot in the rhyolite field. ce has not been reported for the northeast nevada volcanic field. (b) most of the tuffs plot in the dacite and rhyolite field. drf-h and drf-i have anomalously low nb/y ratios. unaltered ignimbrite compositions from the northeast nevada volcanic field (nenvf) are shown for comparison (brooks, 1995a). 0.00 0.01 0.10 1.00 0.1 1.0 10.0 zr /t i p pm nb/y rhyolite foidite phonolite trachyte comendite basalt basaltic andesite trachyandesite alkali basalt dacite andesite nenvf 0.00 0.05 0.10 0.15 0.20 0.25 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 zr /t i p pm ce ppm drf-a drf-b drf-c drf-d drf-e drf-f drf-g drf-h drf-i drf-j drf-k comendite rhyolite dacite-andesite trachyandesite a b 17 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 which typically have sio2 values in the low to mid 70s. al2o3 tends to increase as sio2 decreases in the altered morrison formation tuffs and a similar trend occurs in the duchesne river formation samples (figure 17). argillic alteration also causes an increase in mgo as sio2 is removed, but the opposite relationship is seen in feldspathically altered tuffs, which have relatively low mgo and high sio2. another important effect of the diagenesis of the tuffs was the deposition of carbonate minerals. the high cao content (table 4) in the tuffs is as high as 20 wt.%; a normal rhyolite would have about 1 wt.%. carbonate precipitation significantly diluted the less mobile elements like al2o3 and sio2. the presence of argillic alteration of the tuffs, an indication of a freshwater setting (christiansen and others, 2015), agrees with sedimentologic evidence on the depositional environment of the duchesne river formation in a freshwater fluvial/wetland setting (andersen and picard, 1972, 1974; sato and chan, 2015; webb, 2017). carbonates also formed and filled the pore spaces during diagenesis. discussion eruptive source of the duchesne river formation tuffs age, inferred original composition, eruption type, figure 15. trace element discrimination diagrams from pearce and others (1984). (a) nb vs. y. duchesne river formation and northeast nevada volcanic field (nenvf) tuffs plot in the volcanic arc field and are almost identical except for two anomalously low y samples. (b) rb vs. y+nb duchesne river formation tuffs and nenvf tuffs plot in the volcanic arc field. rb is probably low in most samples because of secondary alteration. figure 16. trace element patterns normalized to primitive mantle (mcdonough and sun, 1994) for bentonitic tuffs from the duchesne river formation and the average argillically altered tuff from the morrison formation. the duchesne river tuffs and morrison tuff average are similar and have general patterns typical of a continental subduction zone setting. the irregularity of some of the patterns is probably the result of secondary alteration, e.g., ba, rb, la, nd, and p are quite variable. 1 10 100 1 10 100 1000 n b (p pm ) y (ppm) within plate volcanic arc ocean ridge 1 10 100 1000 1 10 100 1000 r b (p pm ) y + nb (ppm) syn collisional within plate volcanic arc ocean ridge nenvf nenvf drf-a drf-b drf-c drf-d drf-e drf-f drf-g drf-h drf-i drf-j drf-k a b 0.1 1.0 10.0 100.0 1000.0 r oc k/ p rim iti ve m an tle drf tuffs morrison formation mean ba rb th u k nb la pb ce sr nd p sm zr ti y 18 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 and geographic location are the main criteria we have used to try to identify eruptive sources for the ash beds within the duchesne river formation. any potential source would need to have erupted within a narrow age range around 39.4 ma, have a high-silica, calc-alkaline composition, be capable of producing large plinian eruptions, and lie to the west of the uinta basin where prevailing winds could transport the ash east to eventually be deposited. several large volcanic fields in western north america (figure 1) might have been eruptive sources for the duchesne river formation tuff beds. these include the northeast nevada (brooks and others, 1995a, 1995b; 1995c; rahl and others, 2002), tuscarora (henry and others, 1998; smith and others, 2017), absaroka (chandler, 2006), challis (chandler, 2006), central nevada (best and others, 2009; 2013b), indian peak (best and others, 2013c), and robinson mountain (lund-snee and others, 2016; smith and others, 2017). these volcanic fields either pre-date or post-date the duchesne river formation tuffs except for the northeast nevada and tuscarora fields. ages of volcanic, volcaniclastic, and plutonic rocks of the tuscarora volcanic field range from about 41 to 39 ma (coats and mckee, 1972; berger and others, 1991; henry and others, 1999; castor and others, 2003; henry, 2008). however, the only known large ash-flow tuff from this field, the tuff of big cottonwood canyon, has a well-established age of 39.92 to 40.15 ± 0.10 ma (henry, 2008), recalculated for a fish canyon age of 28.201 ma. comparing these ages to our new ages on the duchesne river formation tuffs (40ar/39ar ages of 39.47 ± 0.16 ma and 39.36 ± 0.15 ma) shows that the tuff of big cottonwood canyon is older. the keetley volcanics (crittenden and others, 1973; bromfield and others, 1977; constenius and others, 2011), tintic mountain volcanic group (moore, 1973; keith and others, 1989), marysvale volcanic field (rowley and others, 2002), and volcanic rocks of the thomas caldera in north and central utah are hundreds of kilometers closer to the uinta basin than those in nevada but are several million years too young to be considered correlative as illustrated on figure 18 and summarized in table 5. figure 18 also lists possible intrusive complexes that could be considered as the source for the duchesne river formation tuffs. however, the ages we have obtained on the tuffs do not match any of these regional intrusive complexes except the bingham intrusive complex in northern utah which was active from 39.18 to 37.2 ma (warnaars and others, 1978; deino and keith, 1997). the composition of the bingham stock is more primitive and mafic and includes monzonite, quartz monzonite, and quartz latite with hornblende and py0.0 1.0 2.0 3.0 4.0 5.0 6.0 40 50 60 70 80 m go (w t.% ) 1.0 6.0 11.0 16.0 21.0 26.0 31.0 36.0 40 45 50 55 60 65 70 75 80 85 90 al 2o 3 ( w t.% ) sio2 (wt.%) morrison argillic morrison feldspathicmorrison zeolitic morrison feldspathic morrison zeolitic morrison argillic drf glass drf glass drf-a drf-b drf-c drf-d drf-e drf-f drf-g drf-h drf-i drf-j drf-k figure 17. two element diagrams of the duchesne river formation tuffs and fields for morrison formation tuffs showing the different effects of alteration type on major elements. the composition of the glass from drf-a is plotted as representative of the original unaltered composition of the tuffs. the duchesne river formation and morrison formation argillic samples show similar patterns of sio2 depletion and mgo and al2o3 enrichment. morrison formation feldspathic samples show the opposite relationship of argillic and zeolitic samples which show little change in al2o3 but significant additions of mgo—neither of which apply to the altered tuffs of the duchesne river formation. 19 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 figure 18. timeline illustrating the sequence of major regional magmatic and tectonic events in utah and nevada, as well as local events in the uinta basin area. the ages of the volcanic and plutonic events (orange and red lines) indicate that the northeast nevada volcanic field is the most likely volcanic source of the duchesne river formation tuffs. references for the ages of volcanic fields and plutonic complexes are listed in table 5. u-pb ages and k-ar ages are included to show the large errors in the previously used ages. other 40ar/39ar ages from various tuffs from the northeast nevada volcanic field are plotted to demonstrate the volcanic activity of the northeastern nevada region at this time. folding of the duchesne river formation took place over a short span of time and was likely coeval with the deposition of the starr flat member. d ee p c re ek fa ul t z on e pe rio d ep oc h m em be r stra tig rap hy f or m at io n pa le og en e o lig oc en e eo ce ne b is ho p c on gl om er at e s ta rr f la t g ilb er t p ea k e ro si on s ur fa ce la po in t d ry g ul ch c re ek b re na n b as in d uc he sn e r iv er f or m at io n k/arfission track 40ar/39ar bc-1 la-1 vnw-1 bc-2 u nc on fo rm ity n or th ea st n ev ad a p os t-l ar am id e ep iro ge ni c up lif t u in ta m ou nt ai n up lif t tu sc ar or a drf-a, h ghss c en tra l n ev ad a m ar ys va le k ee tle y ti nt ic m or on i/g ol de ns r an ch w hi tn ey an o re lla n c ha nd ro ni an d uc he sn ea n lm a fo ld in g of d uc he sn e r iv er f or m at io n an gu la r u nc on fo rm ity b in gh am c an yo n ib ap ah p ilo t p ea k c en tra l w as at ch r an ge m cg in ty 30 31 32 33 34 35 36 37 38 39 40 41 30 31 32 33 34 35 36 37 38 39 40 41 42 29 selected magmatic and tectonic events b in gh amr ob in so n m t th om as /k eg /d ru m g ro us e c re ek g ro us e c re ek g ro us e c re ek e m ig ra nt p as s s ul ph ur s pr in gs r an ge h ar ris on p as s major volcanic fields in utah and nevada major plutonic complexes in utah syncline in duchesne river formation uinta mountain uplift ages from tuffs within the northeast nevada volcanic field timing of deep creek fault zone ages from tuffs within the duchesne river formation and bishop conglomerate eh cb pr age column key legacy and new isotopic ages (ma) cmc tc cb 40ar/39ar ages from smith and others, 2017 eh = elko hills cmc = coal mine canyon cb = copper basin pr = pinon range tc = taylor canyon 40ar/39ar ages from brooks and others, 1995 ss = southern snake mountains gh = gold hill pr drf-a drf-h 40ar/39ar ages from kowallis and others, 2005 bc = bishop conglomerate 1, 2 la-1 and vnw-1 are fission track, zircon ages from bryant and others, 1989 new sanidine and plagioclase 40ar/39ar ages from this work drf = duchesne river formation a, h l oc al n on -d ep os iti on c en tra l w as at ch r an ge 20 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 roxene (moore, 1973; waite and others, 1997), minerals that are entirely absent in the duchesne river formation tuffs. this suggests that the bingham stock is an unlikely intrusive counterpart to the duchesne river formation tuffs. the volcanic rocks associated with the bingham intrusion also have a more mafic composition except for some rhyolitic lava flows which erupted near the end of volcanic activity around 33 ma. another potential source is the volcanism in northeast nevada. coats (1964) mapped several tuffs in the jarbidge quadrangle along the nevada-idaho border. the oldest of these, the dead horse formation (smith and others, 2017), is a composite unit composed of several ash-flow tuffs including rhyolitic tuffs with a phenocryst assemblage (quartz, biotite, sanidine, plagioclase, apatite, zircon, and allanite) similar to the duchesne river formation tuffs. the recalibrated ages of the tuffs in the dead horse formation range from 47.61 ± 0.4 to 34.97 ± 0.25 ma (smith and others, 2017), overlapping the range of the duchesne river formation. brooks and others (1995a, 1995b, 1995c) determined the compositions and ages of a number of ash-flow tuffs in the northeast nevada volcanic field. 40ar/39ar ages from sanidine show that, of the multiple ash-flow tuffs in this volcanic field, several have ages with errors that overlap the 39.47 and 39.36 ma ages reported in this paper for duchesne river formation tuffs. based on age and compositional constraints, the most likely place to look for a source of the duchesne river formation tuffs is in the northeast nevada volcanic field. the northeast nevada field tuffs are silicic to intermediate composition, calc-alkaline tuffs, and have similar mineral assemblages including quartz, biotite, and feldspar. whole-rock comparisons between the duchesne river formation and northeastern nevada tuffs also show similar abundances of major and trace elements. for example, nb/y and zr/ti ratios of altered duchesne river formation tuffs are similar to those from the northeast nevada volcanic field (brooks and others, 1995a, 1995c) (figure 14a). a plot of nb vs. y table 5. list of magmatic events, ages, and references used on figure 18. plutonic complex age (ma) reference central wasatch range 29.45, 32.2–35.38 john and others, 1997; biek and others, 2005; smyk and others, 2018 sulphur springs range 31.5–36.9 ryskamp and others, 2008 grouse creek 34.3, 36.3, 41.3 egger, 2003; strickland and others, 2011 harrison pass 36 barnes and others, 2001 bingham canyon 37.0–38.6 warnaars, 1978; deino and keith, 1997; vogel and others, 2001 mcginty 37 hintze and kowallis, 2009 pilot peak 37.7–38.2 wooden and others, 1999; woodburne, 2004 ibapah 39 hintze and kowallis, 2009 volcanic field age (ma) reference central nevada 18–36 best and others, 2013; christiansen and others, 2015 tintic 30.3–35 keith and others, 1989 marysvale 31–35 rowley and others, 2002 keetley 32–35 constenius and others, 2011; smyk and others, 2018 bingham 34.2–39 moore, 1973; biek and others, 2005 thomas/keg/drum 34.92–36.77 shubat and snee, 1992 goldens ranch/moroni 35.9–39.9 hintze and kowallis, 2009 emigrant pass 36.4–38.2 egger, 2003; johnson, 2015 robinson mountain 37.5–38.5 lund-snee and others, 2015 ne nevada 39–42.6 brooks, 1995b; smith and others, 2017 tuscarora 39.8–40.5 henry and others, 1995; henry, 2008 note: the central wasatch range plutonic complex includes the clayton peak, alta, little cottonwood, flagstaff, mayflower, ontario, glencoe, valeo, pine creek, and park premier stocks. 21 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 (figure 15a) also shows that the duchesne river formation tuffs have compositions similar to the northeast nevada volcanic field. however, rb (ppm) levels in duchesne river formation tuffs are lower than in the northeast nevada volcanic field (figure 15b), probably due to leaching of rb during alteration. the least altered tuff which retains glass shards (drf-a) seems to have retained its initial rb concentrations, however, and plots near the volcanic rocks from the northeast nevada volcanic field. similar compositional data on the tuff beds in the nearby dead horse formation of northern nevada are lacking. aside from correlating with other igneous units to determine the eruptive source of the tuffs, compositional data can be used to make interpretations about the tectonic setting and eruptive conditions. the mineral assemblage, mineral compositions, eruption temperatures, and whole-rock compositions of the duchesne river formation tuffs indicate a rhyolite-dacite composition and the immobile trace element plots provide evidence for a typical continental subduction-zone tectonic setting. there is no evidence of intraplate, a-type or extension-related magmatism in these tuffs. the rhyolitic magmas from which these fall-out tuffs originated were likely generated as the subducting farallon slab foundered and rolled back at the close of the laramide orogeny (best and others, 2016). timing of uinta mountain uplift the high-precision ages of the tuffs in the duchesne river formation also place important constraints on the tectonic history of the region. we propose that after a time of relative tectonic quiescence when the brennan basin, dry gulch creek, and lapoint members were deposited, a renewed laramide uplift began in the uinta mountains about 39 ma, as illustrated on figure 18. the cessation of the uplift event is loosely constrained by a u-pb zircon age of 37 ± 1.5 ma from a tuff in the starr flat member (bryant and others, 1989). this uplift event created a syncline in the duchesne river formation, which dips to the south 1 to 9°, proximal to the uinta mountains to the north, and then dips to the north 1 to 3° farther south in the uinta basin (figure 1b). uplift was followed by the development of an unconformity called the gilbert peak erosion surface that formed over a period of approximately 4 million years during which uplift and deposition apparently slowed and erosion dominated (webb, 2017). the bishop conglomerate was deposited around 34 to 30 ma (kowallis and others, 2005) atop the gilbert peak erosion surface with some angular discordance between it and the underlying duchesne river formation members (figure 2). hansen (1986), dickinson and others (1988), aslan and others (2017), and sprinkel (2018a) all interpreted the gilbert peak erosion surface as the end of the laramide in the uinta basin. although evidence of post-laramide but pre-extensional tectonic activity is seen throughout the uinta mountains, it is likely caused by epeirogenic regional uplift of the uinta mountains and nearby rocky mountains (sprinkel, 2014, 2018a; aslan and others, 2017). hansen (1986) also considered changing climate conditions from warm and humid to cool and dry to explain the existence and composition of the bishop conglomerate. duchesnean north american land mammal age the duchesne river formation, near the town of lapoint, utah, is the type section of the duchesnean nalma (emry, 1981), which extends from 42 to 38 ma (alroy, 2000). some disagreement has arisen over the numerical age of the fauna that define the age, and whether the fauna is entirely late eocene or part eocene and part oligocene (emry, 1981; prothero, 1995; rasmussen and others, 1999). the majority of fossils collected from the duchesne river formation come from the brennan basin and lapoint members (rasmussen and others, 1999; burger and tacket, 2014). the carnegie titanothere quarry (un0012) is stratigraphically located in the lower lapoint member and the halfway hollow quarry (un0117) is stratigraphically located in the uppermost dry gulch creek member (figure 2). however, the halfway hollow quarry was originally reported to be in the lower lapoint member (emry, 1981). workers have relied on old isotopic ages taken from tuffs within these members to constrain the age of the fauna (lucas and emry, 2004). these old and imprecise radiometric dates have been the main reason for 22 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 the confusion about the age of the fauna. an 40ar/39ar age of 41.10 ± 0.32 ma and a u-pb zircon age of 40.66 ± 1.88 ma were reported from the brennan basin member (sprinkel, 2018a). more importantly, two 40ar/39ar ages of 39.47 ± 0.16 and 39.36 ± 0.15 ma from the lapoint (sample drf-a) and dry gulch creek (sample drf-h) members are reported in this study. the 34.03 ± 0.04 ma age of the tuff in the lower part of the overlying non-duchesnean bishop conglomerate (kowallis and others, 2005) is conclusive evidence that the faunas found within the duchesne river formation are entirely late eocene which, according to the official time scale of the international commission on stratigraphy, ended about 33.9 ma. conclusions the duchesne river formation is an important fluvial-lacustrine deposit that records the uplift and development of the uinta mountains, a laramide-age uplift in eastern utah. two key fallout tuff beds in the duchesne river formation give 40ar/39ar ages on feldspars of 39.47 ± 0.16 ma and 39.36 ± 0.15 ma. the tuffaceous layers in the lapoint member are concentrated in the lower and middle part of that member, and the tuffs from the dry gulch creek member lie in the upper and middle parts. these new ages from the duchesne river formation constrain a period of laramide uplift of the uinta mountains from about 39 to 37 ma. the compositions of the phenocrysts in the thin (0.25–5.5 m) tuffs are typical of rhyolitic subduction-related magmas. the mineral assemblage of quartz, biotite, feldspar, with accessory zircon, and allanite is typical for calc-alkaline magmas. however, calculated temperatures from biotite and feldspar along with relatively low ti and ree concentrations in allanite suggest that the magmas were cooler and less oxidized than typical arc rhyolites. biotite compositions suggest that the parent magmas evolved compositionally over time (figure 7). the tuffs fell into fresh-water environments and the glass altered to clay, but most of the phenoclasts survived. whole-rock compositions of the tuffs are typical of argillically altered rhyolite, indicated by an enrichment of al and mg, depletion of si and k, stable levels of nb, y, ti, zr, and ree, and formation of smectitic and illitic clays as a result of the diagenesis of the volcanic glass. the immobile trace element patterns are typical of rhyolites produced in a subduction zone. based on age, composition, eruption style, and geographic location, the northeast nevada volcanic field is the most likely source of the duchesne river formation tuffs. other potential sources are too old or too young or have different eruptive compositions. these tuffs are distal equivalents of slab rollback-related volcanism as it flared up in northern nevada in the late eocene. the faunas of the duchesne river formation, which define the duchesnean nalma, are about 39.4 ma. this is younger than the previously published age of 41.0 ma (rasmussen and others, 1999). based upon our new ages and ages reported earlier from the overlying bishop conglomerate, the duchesnean nalma is middle eocene. ackowledgments funding for the project was provided by the department of geological sciences and college of physical and mathematical sciences at brigham young university. additional support was given by the utah geological survey (ugs). assistance with sample preparation and xrf analyses was provided by david tomlinson (rio tinto kennecott). martha hayden (ugs) provided us with quarry locations so we could compare the stratigraphic position of the quarry to our sample locations. we thank the following for their reviews and technical editing: grant willis, stephanie carney, and michael hylland (ugs) and paul murphey (san diego natural history museum). references ague, j.j., and brimhall, g.h., 1988, regional variations in bulk chemistry, mineralogy, and the compositions of mafic and accessory minerals in the batholiths of 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earth-science reviews, v. 150, p. 531–593. zanazzi a., kohn, m.j., macfadden b.j., and terry, d.o., jr., 2007, large temperature drop across the eocene-oligocene transition in central north america: nature, v. 445, p. 639–642. 1–1 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 appendix 1 descriptions of volcanic ash bed samples drf-a (latitude 40.491478, longitude -109.746676). light grayish-tan tuffaceous sandstone, 1 to 2 m thick with visible biotite grains when examined with a hand lens. this ash is distinct from all the other ashes in the field and is a moderately sorted, subrounded, poorly lithified sandstone with little clay. contains biotite, sanidine, plagioclase, allanite, glass shards, zircon, magnetite, and detrital quartz grains. this is the only ash bed with coexisting plagioclase and sanidine. laterally continuous where exposed. 40ar/39ar age from plagioclase of 39.5 ma. drf-b (latitude 40.449856, longitude -109.720892). light-gray clay matrix, 2 m thick with some visible biotite grains. collected from middle lapoint member. contains biotite, sanidine, and detrital grains including microcline. laterally continuous where exposed. drf-c (latitude 40.417679, longitude -109.749658). lightto medium-dark-gray clay matrix, 0.4 to 1 m thick, with abundant visible biotite grains. highest tuff collected from bobcat ridge. contains biotite, allanite, and detrital grains. laterally continuous where exposed. pictured to the right. drf-d (latitude 40.416545, longitude -109.746362). mediumto dark-gray clay matrix, uppermost part of 5.5-m-thick tuff bed with some visible biotite grains. collected from bobcat ridge. poorly exposed due to erosion so lateral distribution is unknown. contains biotite, apatite, zircon, and detrital grains. drf-e (latitude 40.416564, longitude -109.746445). lightto medium-gray clay matrix, upper-middle part of 5.5-m-thick tuff bed with some visible biotite grains. laterally continuous and used as contact between lapoint and dry gulch creek members. contains biotite and detrital grains. drf-f (latitude 40.416583, longitude -109.746469). lightto medium-gray clay matrix, middle part of 5.5-m-thick tuff bed with some visible biotite grains. laterally continuous and used as contact between lapoint and dry gulch creek members. contains biotite and detrital grains. drf-g (latitude 40.416519, longitude -109.746494). lightto medium-gray clay matrix, lowermost part of 5.5-m-thick tuff bed with some visible biotite grains. laterally continuous and used as contact between lapoint and dry gulch creek members. contains biotite and detrital grains including microcline. pictured to the right. drf-h (latitude 40.418116, longitude -109.747051). lightto medium-gray clay matrix, 25 cm thick with abundant visible biotite drf-c ash drf-g ash 1–2 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 appendix 1 (continued) descriptions of volcanic ash bed samples grains. lowest tuff bed from bobcat ridge and directly beneath lapoint and dry gulch creek contact. poorly exposed so lateral distribution is unknown. sampled from same tuff bed as drf-i. contains biotite, sanidine, allanite, titanite, and detrital grains including microcline. drf-i (latitude 40.418127, longitude -109.747087). lightto medium-gray clay matrix, 25 cm thick with abundant visible biotite grains. lowest tuff bed from bobcat ridge and directly below lapoint and dry gulch creek contact. poorly exposed so lateral distribution is unknown. sampled from same tuff bed as drf-h. contains biotite, sanidine, allanite, titanite, and detrital grains including microcline. 40ar/39ar age from sanidine of 39.36 ± 0.15 ma. drf-j (latitude 40.409754, longitude -109.699966). lightto medium-gray clay matrix, 27 cm thick, and some visible biotite grains. collected from the upper dry gulch creek member. poorly exposed so lateral distribution is unknown. contains biotite, sanidine, and detrital grains. pictured to the right. drf-k (latitude 40.397333, longitude -109.726184). lightto medium-gray clay matrix, 25 cm thick with some biotite grains visible with a hand lens. collected from the upper dry gulch creek. poorly exposed so lateral distribution is unknown. contains biotite and detrital grains including microcline. pictured below. drf-j ash drf-k ash 2–1 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 jva lu e: 0. 00 78 19 9 ± 0. 00 00 05 5 (2 σ) in st ru m en t: m a p 21 550 sa m pl e: d r fh st an da rd : fi sh c an yo n sa ni di ne m at er ia l: sa ni di ne a ge (m a) : 28 .2 01 ± 0. 04 60 k ui pe r a nd o th er s ( 20 08 ) in cl ud ed in 40 a r ± 1 σ 4 0 39 a r ± \1 σ 3 9 38 a r ± 1 σ 3 8 37 a r ± 1 σ 3 7 36 a r ± 1 σ 3 6 % 40 a r* 40 a r* /39 a r k ± 2σ k /c a a ge ± 2σ w td . m ea n 0. 25 44 87 ± 0. 00 02 37 0. 08 75 18 ± 0. 00 01 52 0. 00 10 32 ± 0. 00 00 31 0. 00 03 39 ± 0. 00 02 76 0. 00 00 26 ± 0. 00 00 03 96 .8 9 2. 81 74 35 ± 0. 01 22 05 11 1. 17 1 39 .1 3 ± 0. 34  0. 11 41 78 ± 0. 00 02 04 0. 03 97 90 ± 0. 00 00 88 0. 00 04 46 ± 0. 00 00 19 0. 00 06 52 ± 0. 00 02 84 0. 00 00 05 ± 0. 00 00 03 98 .7 4 2. 83 33 94 ± 0. 02 58 37 26 .2 61 39 .3 5 ± 0. 71  0. 21 44 51 ± 0. 00 02 20 0. 07 50 33 ± 0. 00 01 39 0. 00 09 24 ± 0. 00 00 10 0. 00 07 43 ± 0. 00 02 80 0. 00 00 07 ± 0. 00 00 03 99 .0 1 2. 82 97 45 ± 0. 01 34 13 43 .4 17 39 .3 0 ± 0. 37  0. 09 50 63 ± 0. 00 02 19 0. 03 22 91 ± 0. 00 00 76 0. 00 03 52 ± 0. 00 00 20 0. 00 03 45 ± 0. 00 03 43 0. 00 00 17 ± 0. 00 00 03 94 .5 7 2. 78 41 28 ± 0. 02 89 60 40 .2 98 38 .6 7 ± 0. 80  0. 17 76 20 ± 0. 00 02 26 0. 06 24 24 ± 0. 00 01 15 0. 00 07 55 ± 0. 00 00 25 0. 00 05 62 ± 0. 00 02 95 0. 00 00 02 ± 0. 00 00 03 99 .5 9 2. 83 37 95 ± 0. 01 55 28 47 .7 38 39 .3 6 ± 0. 43  0. 72 27 95 ± 0. 00 03 70 0. 08 99 63 ± 0. 00 01 32 0. 00 10 42 ± 0. 00 00 20 0. 00 01 35 ± 0. 00 03 25 0. 00 00 13 ± 0. 00 00 03 99 .4 7 7. 99 15 50 ± 0. 01 62 65 28 6. 23 5 10 8. 89 ± 0. 43 0. 06 39 18 ± 0. 00 01 85 0. 01 99 79 ± 0. 00 00 64 0. 00 02 33 ± 0. 00 00 15 0. 00 00 50 ± 0. 00 03 28 0. 00 00 23 ± 0. 00 00 03 89 .1 4 2. 85 18 91 ± 0. 04 63 69 17 0. 88 7 39 .6 0 ± 1. 27  0. 28 86 60 ± 0. 00 02 59 0. 06 21 07 ± 0. 00 01 08 0. 00 07 10 ± 0. 00 00 30 0. 00 01 31 ± 0. 00 03 21 0. 00 00 29 ± 0. 00 00 03 96 .9 8 4. 50 73 15 ± 0. 01 76 78 20 3. 15 7 62 .2 1 ± 0. 48 0. 30 87 59 ± 0. 00 02 59 0. 03 16 51 ± 0. 00 00 73 0. 00 04 01 ± 0. 00 00 12 0. 00 03 06 ± 0. 00 02 47 0. 00 00 96 ± 0. 00 00 03 90 .6 9 8. 84 69 25 ± 0. 03 90 76 44 .4 74 12 0. 17 ± 1. 03 0. 13 75 80 ± 0. 00 02 03 0. 04 24 47 ± 0. 00 00 79 0. 00 05 09 ± 0. 00 00 14 0. 00 09 09 ± 0. 00 02 83 0. 00 00 36 ± 0. 00 00 03 92 .1 4 2. 98 64 86 ± 0. 02 30 81 20 .0 86 41 .4 5 ± 0. 63 0. 18 77 62 ± 0. 00 02 51 0. 06 52 40 ± 0. 00 01 01 0. 00 07 41 ± 0. 00 00 15 0. 00 04 36 ± 0. 00 03 24 0. 00 00 06 ± 0. 00 00 03 99 .0 8 2. 85 14 81 ± 0. 01 48 64 64 .4 12 39 .6 0 ± 0. 41  0. 08 98 66 ± 0. 00 02 03 0. 03 13 58 ± 0. 00 00 61 0. 00 03 80 ± 0. 00 00 18 0. 00 00 47 ± 0. 00 02 98 0. 00 00 00 ± 0. 00 00 03 99 .8 4 2. 86 10 80 ± 0. 03 12 99 28 5. 50 8 39 .7 3 ± 0. 86  0. 18 04 30 ± 0. 00 02 11 0. 04 87 43 ± 0. 00 00 94 0. 00 06 05 ± 0. 00 00 28 0. 00 00 43 ± 0. 00 03 98 0. 00 00 13 ± 0. 00 00 03 97 .8 3 3. 62 11 63 ± 0. 02 03 18 48 6. 11 5 50 .1 4 ± 0. 56 0. 74 22 68 ± 0. 00 03 77 0. 07 24 27 ± 0. 00 01 02 0. 00 08 79 ± 0. 00 00 27 0. 00 01 97 ± 0. 00 03 08 0. 00 00 12 ± 0. 00 00 03 99 .5 1 10 .1 98 21 2 ± 0. 02 00 30 15 8. 00 1 13 7. 84 ± 0. 52 0. 16 26 17 ± 0. 00 02 18 0. 05 69 21 ± 0. 00 01 02 0. 00 07 67 ± 0. 00 00 17 0. 00 02 88 ± 0. 00 03 13 0. 00 00 03 ± 0. 00 00 03 99 .4 1 2. 84 00 99 ± 0. 01 80 32 84 .8 74 39 .4 4 ± 0. 50  0. 07 29 44 ± 0. 00 02 19 0. 02 56 67 ± 0. 00 00 60 0. 00 03 09 ± 0. 00 00 23 0. 00 02 43 ± 0. 00 02 66 0. 00 00 06 ± 0. 00 00 03 97 .6 3 2. 77 45 01 ± 0. 03 82 66 45 .3 98 38 .5 4 ± 1. 05  0. 13 75 31 ± 0. 00 02 24 0. 04 79 40 ± 0. 00 00 95 0. 00 05 65 ± 0. 00 00 15 0. 00 00 57 ± 0. 00 03 15 0. 00 00 02 ± 0. 00 00 04 99 .5 9 2. 85 70 33 ± 0. 02 69 16 36 1. 56 1 39 .6 8 ± 0. 74  0. 14 47 88 ± 0. 00 02 19 0. 05 05 72 ± 0. 00 00 91 0. 00 05 87 ± 0. 00 00 15 0. 00 02 60 ± 0. 00 03 16 0. 00 00 01 ± 0. 00 00 03 99 .8 0 2. 85 72 33 ± 0. 02 02 01 83 .4 96 39 .6 8 ± 0. 56  0. 07 96 38 ± 0. 00 02 00 0. 02 79 15 ± 0. 00 00 65 0. 00 03 58 ± 0. 00 00 19 0. 00 03 56 ± 0. 00 02 52 0. 00 00 01 ± 0. 00 00 03 99 .7 9 2. 84 69 74 ± 0. 03 40 61 33 .6 91 39 .5 4 ± 0. 94  0. 90 46 83 ± 0. 00 05 34 0. 08 26 78 ± 0. 00 01 51 0. 00 10 34 ± 0. 00 00 20 0. 00 04 48 ± 0. 00 03 57 0. 00 00 16 ± 0. 00 00 03 99 .4 8 10 .8 85 44 0 ± 0. 02 38 03 79 .3 75 14 6. 77 ± 0. 62 0. 48 68 29 ± 0. 00 03 23 0. 04 23 81 ± 0. 00 00 82 0. 00 05 16 ± 0. 00 00 22 0. 00 01 06 ± 0. 00 02 57 0. 00 00 03 ± 0. 00 00 03 99 .8 3 11 .4 67 43 3 ± 0. 03 28 55 17 1. 63 8 15 4. 30 ± 0. 85 0. 79 73 24 ± 0. 00 04 64 0. 07 53 22 ± 0. 00 01 14 0. 00 09 14 ± 0. 00 00 21 0. 00 06 88 ± 0. 00 02 84 0. 00 00 47 ± 0. 00 00 04 98 .2 3 10 .3 98 01 8 ± 0. 02 18 81 47 .0 51 14 0. 44 ± 0. 57 0. 16 81 51 ± 0. 00 02 41 0. 05 22 16 ± 0. 00 00 90 0. 00 06 26 ± 0. 00 00 39 0. 00 02 19 ± 0. 00 03 08 0. 00 00 01 ± 0. 00 00 03 99 .9 0 3. 21 69 94 ± 0. 01 81 93 10 2. 74 2 44 .6 1 ± 0. 50 0. 30 32 05 ± 0. 00 03 06 0. 03 37 15 ± 0. 00 00 65 0. 00 04 00 ± 0. 00 00 22 0. 00 03 47 ± 0. 00 02 65 0. 00 00 12 ± 0. 00 00 03 98 .8 1 8. 88 66 06 ± 0. 03 26 98 41 .8 30 12 0. 69 ± 0. 86 0. 08 49 88 ± 0. 00 01 77 0. 01 96 70 ± 0. 00 00 53 0. 00 02 36 ± 0. 00 00 12 0. 00 01 18 ± 0. 00 03 60 0. 00 00 01 ± 0. 00 00 03 99 .5 3 4. 30 05 74 ± 0. 04 94 91 71 .7 25 59 .4 0 ± 1. 35 w ei gh te d m ea n ag e (1 3 of 2 5) : 39 .3 6 ± 0. 15 λ 4 0a r (0 .5 80 ± 0 .0 14 ) x 1 0-1 0 a -1 m in a nd o th er s ( 20 00 ) (40 a r/39 a r) k 0. 00 05 4 ± 0. 00 01 4 ji ch a & b ro w n (2 01 4) 40 a r/36 a r 29 8. 56 ± 0. 31 le e an d ot he rs (2 00 6) λ b (4 .8 84 ± 0 .0 99 ) x 1 0-1 0 a -1 m in a nd o th er s ( 20 00 ) (38 a r/39 a r) k 0. 01 21 0 ± 0. 00 00 2 ji ch a & b ro w n (2 01 4) 38 a r/36 a r 0. 18 85 ± 0. 00 03 le e an d ot he rs (2 00 6) 39 a r (2 .5 8 ± 0. 03 ) x 1 0-3 a -1 st oe nn er a nd o th er s ( 19 65 ) (39 a r/37 a r) c a 0. 00 06 95 ± 0. 00 00 1 r en ne a nd o th er s ( 20 13 ) 37 a r (8 .2 3 ± 0. 04 2) x 1 0-4 h -1 st oe nn er a nd o th er s ( 19 65 ) (38 a r/37 a r) c a 0. 00 00 19 6 ± 0. 00 00 01 r en ne a nd o th er s ( 20 13 ) 36 c l (2 .3 03 ± 0 .0 46 ) x 1 0-6 a -1 (36 a r/37 a r) c a 0. 00 02 65 ± 0. 00 00 2 r en ne a nd o th er s ( 20 13 ) c om pl et e 40 a r/39 a r r es ul ts d ec ay c on st an ts in te rfe rin g is ot op e pr od uc tio n ra tio s a tm os ph er ic a rg on ra tio s appendix 2 summary of ages and analytical parameters 2–2 fallout tuffs in the eocene duchesne river formation, northeastern utah—ages, compositions, and likely source jensen, m.s., kowallis, b.j., christiansen, e.h, webb, c., dorais, m.j., sprinkel, d.a., and jicha, b. geology of the intermountain west 2020 volume 7 appendix 2 (continued) summary of ages and analytical parameters jva lu e: 0. 00 78 19 9 ± 0. 00 00 05 5 (2 σ) in st ru m en t: m a p 21 550 sa m pl e: d r fh st an da rd : fi sh c an yo n sa ni di ne m at er ia l: sa ni di ne a ge (m a) : 28 .2 01 ± 0. 04 60 k ui pe r a nd o th er s ( 20 08 ) in cl ud ed in 40 a r ± 1 σ 4 0 39 a r ± \1 σ 3 9 38 a r ± 1 σ 3 8 37 a r ± 1 σ 3 7 36 a r ± 1 σ 3 6 % 40 a r* 40 a r* /39 a r k ± 2σ k /c a a ge ± 2σ w td . m ea n 0. 25 44 87 ± 0. 00 02 37 0. 08 75 18 ± 0. 00 01 52 0. 00 10 32 ± 0. 00 00 31 0. 00 03 39 ± 0. 00 02 76 0. 00 00 26 ± 0. 00 00 03 96 .8 9 2. 81 74 35 ± 0. 01 22 05 11 1. 17 1 39 .1 3 ± 0. 34  0. 11 41 78 ± 0. 00 02 04 0. 03 97 90 ± 0. 00 00 88 0. 00 04 46 ± 0. 00 00 19 0. 00 06 52 ± 0. 00 02 84 0. 00 00 05 ± 0. 00 00 03 98 .7 4 2. 83 33 94 ± 0. 02 58 37 26 .2 61 39 .3 5 ± 0. 71  0. 21 44 51 ± 0. 00 02 20 0. 07 50 33 ± 0. 00 01 39 0. 00 09 24 ± 0. 00 00 10 0. 00 07 43 ± 0. 00 02 80 0. 00 00 07 ± 0. 00 00 03 99 .0 1 2. 82 97 45 ± 0. 01 34 13 43 .4 17 39 .3 0 ± 0. 37  0. 09 50 63 ± 0. 00 02 19 0. 03 22 91 ± 0. 00 00 76 0. 00 03 52 ± 0. 00 00 20 0. 00 03 45 ± 0. 00 03 43 0. 00 00 17 ± 0. 00 00 03 94 .5 7 2. 78 41 28 ± 0. 02 89 60 40 .2 98 38 .6 7 ± 0. 80  0. 17 76 20 ± 0. 00 02 26 0. 06 24 24 ± 0. 00 01 15 0. 00 07 55 ± 0. 00 00 25 0. 00 05 62 ± 0. 00 02 95 0. 00 00 02 ± 0. 00 00 03 99 .5 9 2. 83 37 95 ± 0. 01 55 28 47 .7 38 39 .3 6 ± 0. 43  0. 72 27 95 ± 0. 00 03 70 0. 08 99 63 ± 0. 00 01 32 0. 00 10 42 ± 0. 00 00 20 0. 00 01 35 ± 0. 00 03 25 0. 00 00 13 ± 0. 00 00 03 99 .4 7 7. 99 15 50 ± 0. 01 62 65 28 6. 23 5 10 8. 89 ± 0. 43 0. 06 39 18 ± 0. 00 01 85 0. 01 99 79 ± 0. 00 00 64 0. 00 02 33 ± 0. 00 00 15 0. 00 00 50 ± 0. 00 03 28 0. 00 00 23 ± 0. 00 00 03 89 .1 4 2. 85 18 91 ± 0. 04 63 69 17 0. 88 7 39 .6 0 ± 1. 27  0. 28 86 60 ± 0. 00 02 59 0. 06 21 07 ± 0. 00 01 08 0. 00 07 10 ± 0. 00 00 30 0. 00 01 31 ± 0. 00 03 21 0. 00 00 29 ± 0. 00 00 03 96 .9 8 4. 50 73 15 ± 0. 01 76 78 20 3. 15 7 62 .2 1 ± 0. 48 0. 30 87 59 ± 0. 00 02 59 0. 03 16 51 ± 0. 00 00 73 0. 00 04 01 ± 0. 00 00 12 0. 00 03 06 ± 0. 00 02 47 0. 00 00 96 ± 0. 00 00 03 90 .6 9 8. 84 69 25 ± 0. 03 90 76 44 .4 74 12 0. 17 ± 1. 03 0. 13 75 80 ± 0. 00 02 03 0. 04 24 47 ± 0. 00 00 79 0. 00 05 09 ± 0. 00 00 14 0. 00 09 09 ± 0. 00 02 83 0. 00 00 36 ± 0. 00 00 03 92 .1 4 2. 98 64 86 ± 0. 02 30 81 20 .0 86 41 .4 5 ± 0. 63 0. 18 77 62 ± 0. 00 02 51 0. 06 52 40 ± 0. 00 01 01 0. 00 07 41 ± 0. 00 00 15 0. 00 04 36 ± 0. 00 03 24 0. 00 00 06 ± 0. 00 00 03 99 .0 8 2. 85 14 81 ± 0. 01 48 64 64 .4 12 39 .6 0 ± 0. 41  0. 08 98 66 ± 0. 00 02 03 0. 03 13 58 ± 0. 00 00 61 0. 00 03 80 ± 0. 00 00 18 0. 00 00 47 ± 0. 00 02 98 0. 00 00 00 ± 0. 00 00 03 99 .8 4 2. 86 10 80 ± 0. 03 12 99 28 5. 50 8 39 .7 3 ± 0. 86  0. 18 04 30 ± 0. 00 02 11 0. 04 87 43 ± 0. 00 00 94 0. 00 06 05 ± 0. 00 00 28 0. 00 00 43 ± 0. 00 03 98 0. 00 00 13 ± 0. 00 00 03 97 .8 3 3. 62 11 63 ± 0. 02 03 18 48 6. 11 5 50 .1 4 ± 0. 56 0. 74 22 68 ± 0. 00 03 77 0. 07 24 27 ± 0. 00 01 02 0. 00 08 79 ± 0. 00 00 27 0. 00 01 97 ± 0. 00 03 08 0. 00 00 12 ± 0. 00 00 03 99 .5 1 10 .1 98 21 2 ± 0. 02 00 30 15 8. 00 1 13 7. 84 ± 0. 52 0. 16 26 17 ± 0. 00 02 18 0. 05 69 21 ± 0. 00 01 02 0. 00 07 67 ± 0. 00 00 17 0. 00 02 88 ± 0. 00 03 13 0. 00 00 03 ± 0. 00 00 03 99 .4 1 2. 84 00 99 ± 0. 01 80 32 84 .8 74 39 .4 4 ± 0. 50  0. 07 29 44 ± 0. 00 02 19 0. 02 56 67 ± 0. 00 00 60 0. 00 03 09 ± 0. 00 00 23 0. 00 02 43 ± 0. 00 02 66 0. 00 00 06 ± 0. 00 00 03 97 .6 3 2. 77 45 01 ± 0. 03 82 66 45 .3 98 38 .5 4 ± 1. 05  0. 13 75 31 ± 0. 00 02 24 0. 04 79 40 ± 0. 00 00 95 0. 00 05 65 ± 0. 00 00 15 0. 00 00 57 ± 0. 00 03 15 0. 00 00 02 ± 0. 00 00 04 99 .5 9 2. 85 70 33 ± 0. 02 69 16 36 1. 56 1 39 .6 8 ± 0. 74  0. 14 47 88 ± 0. 00 02 19 0. 05 05 72 ± 0. 00 00 91 0. 00 05 87 ± 0. 00 00 15 0. 00 02 60 ± 0. 00 03 16 0. 00 00 01 ± 0. 00 00 03 99 .8 0 2. 85 72 33 ± 0. 02 02 01 83 .4 96 39 .6 8 ± 0. 56  0. 07 96 38 ± 0. 00 02 00 0. 02 79 15 ± 0. 00 00 65 0. 00 03 58 ± 0. 00 00 19 0. 00 03 56 ± 0. 00 02 52 0. 00 00 01 ± 0. 00 00 03 99 .7 9 2. 84 69 74 ± 0. 03 40 61 33 .6 91 39 .5 4 ± 0. 94  0. 90 46 83 ± 0. 00 05 34 0. 08 26 78 ± 0. 00 01 51 0. 00 10 34 ± 0. 00 00 20 0. 00 04 48 ± 0. 00 03 57 0. 00 00 16 ± 0. 00 00 03 99 .4 8 10 .8 85 44 0 ± 0. 02 38 03 79 .3 75 14 6. 77 ± 0. 62 0. 48 68 29 ± 0. 00 03 23 0. 04 23 81 ± 0. 00 00 82 0. 00 05 16 ± 0. 00 00 22 0. 00 01 06 ± 0. 00 02 57 0. 00 00 03 ± 0. 00 00 03 99 .8 3 11 .4 67 43 3 ± 0. 03 28 55 17 1. 63 8 15 4. 30 ± 0. 85 0. 79 73 24 ± 0. 00 04 64 0. 07 53 22 ± 0. 00 01 14 0. 00 09 14 ± 0. 00 00 21 0. 00 06 88 ± 0. 00 02 84 0. 00 00 47 ± 0. 00 00 04 98 .2 3 10 .3 98 01 8 ± 0. 02 18 81 47 .0 51 14 0. 44 ± 0. 57 0. 16 81 51 ± 0. 00 02 41 0. 05 22 16 ± 0. 00 00 90 0. 00 06 26 ± 0. 00 00 39 0. 00 02 19 ± 0. 00 03 08 0. 00 00 01 ± 0. 00 00 03 99 .9 0 3. 21 69 94 ± 0. 01 81 93 10 2. 74 2 44 .6 1 ± 0. 50 0. 30 32 05 ± 0. 00 03 06 0. 03 37 15 ± 0. 00 00 65 0. 00 04 00 ± 0. 00 00 22 0. 00 03 47 ± 0. 00 02 65 0. 00 00 12 ± 0. 00 00 03 98 .8 1 8. 88 66 06 ± 0. 03 26 98 41 .8 30 12 0. 69 ± 0. 86 0. 08 49 88 ± 0. 00 01 77 0. 01 96 70 ± 0. 00 00 53 0. 00 02 36 ± 0. 00 00 12 0. 00 01 18 ± 0. 00 03 60 0. 00 00 01 ± 0. 00 00 03 99 .5 3 4. 30 05 74 ± 0. 04 94 91 71 .7 25 59 .4 0 ± 1. 35 w ei gh te d m ea n ag e (1 3 of 2 5) : 39 .3 6 ± 0. 15 λ 4 0a r (0 .5 80 ± 0 .0 14 ) x 1 0-1 0 a -1 m in a nd o th er s ( 20 00 ) (40 a r/39 a r) k 0. 00 05 4 ± 0. 00 01 4 ji ch a & b ro w n (2 01 4) 40 a r/36 a r 29 8. 56 ± 0. 31 le e an d ot he rs (2 00 6) λ b (4 .8 84 ± 0 .0 99 ) x 1 0-1 0 a -1 m in a nd o th er s ( 20 00 ) (38 a r/39 a r) k 0. 01 21 0 ± 0. 00 00 2 ji ch a & b ro w n (2 01 4) 38 a r/36 a r 0. 18 85 ± 0. 00 03 le e an d ot he rs (2 00 6) 39 a r (2 .5 8 ± 0. 03 ) x 1 0-3 a -1 st oe nn er a nd o th er s ( 19 65 ) (39 a r/37 a r) c a 0. 00 06 95 ± 0. 00 00 1 r en ne a nd o th er s ( 20 13 ) 37 a r (8 .2 3 ± 0. 04 2) x 1 0-4 h -1 st oe nn er a nd o th er s ( 19 65 ) (38 a r/37 a r) c a 0. 00 00 19 6 ± 0. 00 00 01 r en ne a nd o th er s ( 20 13 ) 36 c l (2 .3 03 ± 0 .0 46 ) x 1 0-6 a -1 (36 a r/37 a r) c a 0. 00 02 65 ± 0. 00 00 2 r en ne a nd o th er s ( 20 13 ) c om pl et e 40 a r/39 a r r es ul ts d ec ay c on st an ts in te rfe rin g is ot op e pr od uc tio n ra tio s a tm os ph er ic a rg on ra tio s supplemental data — compositions of duchesne river formation biotite phenocrysts page 1 sample drf-c sio2 36.68 38.06 37.06 35.99 39.79 36.84 36.25 35.55 36.62 28.85 28.74 29.02 28.97 29.49 28.68 29.45 31.55 tio2 3.39 3.10 3.46 3.53 3.21 3.34 3.40 3.49 3.33 3.40 3.60 3.42 3.45 3.59 3.52 3.43 3.23 al2o3 13.40 12.62 13.76 13.61 11.99 13.87 14.23 13.63 12.62 14.46 14.58 14.37 14.45 14.76 14.37 14.23 16.38 feo t 16.96 15.84 16.70 16.90 15.18 16.87 17.27 17.19 15.82 18.78 18.04 17.83 16.03 18.93 18.13 16.87 21.00 mno 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.27 0.25 0.21 0.18 0.29 0.26 0.25 0.21 mgo 11.59 10.77 12.20 11.90 11.66 12.31 12.27 11.51 11.53 12.74 13.06 12.71 14.37 12.13 12.98 13.68 10.06 cao 0.30 0.49 0.23 0.26 0.39 0.21 0.13 0.21 0.30 0.04 0.01 0.00 0.01 0.08 0.09 0.01 0.08 na2o 0.21 0.34 0.37 0.32 0.21 0.34 0.33 0.34 0.25 0.47 0.52 0.47 0.52 0.51 0.46 0.43 0.36 k2o 7.72 7.32 7.95 7.92 7.47 8.13 8.35 8.19 7.56 8.49 8.52 8.45 8.23 8.29 8.42 8.31 9.04 bao 0.87 1.06 0.85 0.92 1.08 0.85 0.83 0.75 f 0.37 0.40 0.50 0.48 0.33 0.34 0.42 0.43 0.35 0.37 0.28 0.31 0.34 0.37 0.30 0.28 0.41 cl 0.09 0.09 0.09 0.09 0.13 0.09 0.10 0.07 0.05 0.14 0.10 0.11 0.11 0.15 0.15 0.13 0.09 h2o* 3.50 3.40 3.51 3.45 3.51 3.59 3.56 3.45 3.43 3.36 3.41 3.36 3.39 3.37 3.37 3.41 3.47 total 94.04 92.24 95.60 94.23 93.70 95.75 96.11 93.86 91.71 92.05 92.04 90.96 90.80 92.85 91.42 91.15 96.42 drf-a drf-b supplemental data — compositions of duchesne river formation biotite phenocrysts page 2 sample sio2 tio2 al2o3 feo t mno mgo cao na2o k2o bao f cl h2o* total 30.62 33.22 32.54 34.49 32.90 31.86 32.10 31.55 31.10 30.41 29.86 29.53 30.38 29.30 30.19 31.15 28.94 3.19 2.86 2.85 2.55 2.79 2.91 2.99 2.71 2.81 2.95 2.54 2.90 2.78 2.73 2.97 2.63 3.16 15.48 16.52 16.85 17.41 17.59 17.05 17.58 18.04 18.18 16.87 16.52 16.32 17.04 16.64 17.73 17.41 16.44 20.80 20.81 20.62 17.65 20.13 21.04 21.37 19.85 20.36 20.97 19.47 20.15 20.48 20.34 20.68 18.60 20.66 0.18 0.21 0.19 0.17 0.18 0.19 0.23 0.19 0.16 0.20 0.16 0.20 0.20 0.19 0.19 0.18 0.17 9.88 9.70 9.66 9.61 9.22 9.07 9.37 9.14 8.99 9.43 11.06 10.25 9.90 9.71 9.01 8.24 10.67 0.14 0.05 0.01 0.43 0.01 0.07 0.01 0.07 0.02 0.01 0.05 0.13 0.06 0.04 0.02 0.88 0.21 0.36 0.28 0.42 0.32 0.27 0.27 0.27 0.39 0.41 0.38 0.41 0.26 0.39 0.34 0.40 0.39 0.26 8.80 9.07 9.35 4.16 9.13 8.97 9.01 8.30 8.47 9.12 8.73 7.91 8.74 9.00 9.15 7.64 6.64 0.25 0.33 0.42 0.32 0.24 0.38 0.57 0.36 0.40 0.46 0.36 0.63 0.33 0.26 0.56 0.43 0.32 0.36 0.41 0.39 0.34 0.35 0.35 0.35 0.31 0.34 0.48 0.41 0.42 0.40 0.37 0.36 0.52 0.33 0.05 0.07 0.06 0.12 0.07 0.06 0.07 0.10 0.12 0.07 0.08 0.07 0.07 0.09 0.08 0.10 0.06 3.39 3.51 3.50 3.50 3.52 3.47 3.54 3.48 3.46 3.37 3.39 3.34 3.41 3.34 3.41 3.22 3.43 93.33 96.85 96.67 90.88 96.22 95.51 97.28 94.34 94.63 94.49 92.85 91.90 93.99 92.19 94.56 91.14 91.14 drf-c supplemental data — compositions of duchesne river formation biotite phenocrysts page 3 sample sio2 tio2 al2o3 feo t mno mgo cao na2o k2o bao f cl h2o* total drf-f 28.53 29.48 28.95 29.62 28.32 35.79 36.16 36.28 34.87 35.50 36.61 35.33 35.26 36.28 35.56 31.03 3.21 3.12 2.97 3.00 2.91 3.04 3.15 3.38 2.93 2.94 4.32 3.05 3.19 4.47 2.95 3.10 16.79 16.05 15.55 16.19 15.92 16.04 15.86 15.44 17.02 17.40 13.67 15.94 16.29 14.11 16.89 15.97 20.88 19.91 14.15 14.23 20.63 15.93 16.18 15.89 19.58 19.69 17.32 20.00 18.15 18.17 19.56 18.94 0.23 0.17 0.13 0.07 0.21 0.01 0.00 0.01 0.01 0.00 0.03 0.01 0.00 0.02 0.02 0.13 10.12 10.81 15.78 16.60 9.83 13.39 13.38 13.34 8.99 9.23 12.64 10.00 9.97 11.73 9.19 10.61 0.12 0.30 0.05 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.00 0.00 0.01 0.01 0.00 0.27 0.29 0.88 0.71 0.30 0.50 0.49 0.50 0.32 0.26 0.48 0.30 0.36 0.44 0.31 0.33 7.68 6.69 9.12 9.18 9.16 9.11 9.08 8.97 9.29 9.26 8.65 9.27 9.09 8.85 9.27 8.85 0.42 0.29 0.18 0.06 0.33 0.60 0.29 0.37 1.75 1.92 0.27 0.44 0.41 0.49 0.37 0.42 0.44 0.37 0.46 0.39 0.37 0.39 0.07 0.03 0.19 0.06 0.05 0.05 0.05 0.06 0.05 0.04 0.13 0.05 0.05 0.15 0.04 0.06 3.42 3.40 2.76 2.83 3.34 3.64 3.68 3.62 3.53 3.57 3.58 3.58 3.49 3.59 3.57 3.39 91.90 90.74 91.68 93.66 91.15 97.75 98.24 97.75 96.80 98.11 97.65 97.73 96.10 98.01 97.57 93.21 drf-c drf-d supplemental data — compositions of duchesne river formation biotite phenocrysts page 4 sample sio2 tio2 al2o3 feo t mno mgo cao na2o k2o bao f cl h2o* total 32.30 35.43 32.28 35.09 32.39 32.71 35.51 35.61 35.18 35.60 35.61 35.88 35.10 35.16 31.80 31.55 30.68 2.23 2.56 2.52 2.70 2.67 2.74 2.70 2.63 2.78 2.73 2.58 2.62 2.58 2.74 3.10 2.97 3.05 17.92 17.23 18.45 17.22 16.74 15.86 17.12 17.46 16.96 17.27 17.37 17.04 17.67 17.64 15.28 15.68 14.92 19.06 20.08 20.03 20.26 20.04 19.62 18.43 19.15 19.23 18.98 18.29 18.66 20.39 20.00 24.54 22.70 24.41 0.19 0.16 0.19 0.18 0.17 0.15 0.00 0.00 0.00 0.01 0.00 0.02 0.21 0.17 0.22 0.17 0.20 9.48 9.84 8.46 8.99 9.42 9.13 10.02 10.42 10.53 10.59 9.63 9.47 9.84 10.33 8.31 9.26 8.14 0.03 0.00 0.00 0.00 0.04 0.07 0.02 0.00 0.03 0.03 0.07 0.00 0.00 0.02 0.03 0.02 0.13 0.24 0.31 0.30 0.31 0.37 0.40 0.35 0.32 0.33 0.32 0.40 0.32 0.34 0.30 0.35 0.41 0.42 8.61 9.31 9.46 9.20 9.01 8.56 9.20 9.30 9.19 9.36 8.92 9.16 8.74 9.13 8.67 8.56 8.14 0.11 0.58 0.40 0.33 0.15 0.34 0.57 0.30 0.62 0.53 0.32 0.28 0.33 0.35 0.44 0.44 0.56 0.41 0.30 0.42 0.38 0.44 0.41 0.47 0.42 0.25 0.22 0.27 0.16 0.05 0.02 0.07 0.07 0.10 0.04 0.04 0.05 0.04 0.06 0.05 0.03 0.06 0.11 0.09 0.00 3.48 3.65 3.48 3.54 3.42 3.29 3.57 3.69 3.60 3.65 3.53 3.54 3.61 3.65 3.50 3.52 3.44 93.94 99.38 95.79 98.11 94.72 93.26 97.19 98.79 98.12 98.80 96.70 96.99 99.33 99.73 96.64 95.56 93.99 drf-gdrf-f drf-h supplemental data — compositions of duchesne river formation biotite phenocrysts page 5 sample sio2 tio2 al2o3 feo t mno mgo cao na2o k2o bao f cl h2o* total 30.72 29.96 30.86 31.32 32.16 32.08 31.80 34.42 34.04 34.53 33.99 34.13 34.15 35.43 35.35 34.90 3.16 2.82 3.14 2.87 3.13 3.09 3.48 2.97 2.92 3.10 3.04 3.15 3.11 3.14 3.09 3.06 15.40 15.23 15.68 15.89 15.25 15.45 15.88 15.40 14.88 15.28 14.41 15.68 15.13 15.39 15.10 15.23 24.97 24.71 25.18 24.11 24.40 23.60 24.59 23.43 22.43 22.15 21.43 23.86 23.45 22.90 23.66 22.28 0.25 0.24 0.26 0.23 0.20 0.18 0.19 0.02 0.01 0.01 0.01 0.00 0.00 0.01 0.00 0.00 8.16 8.10 8.28 8.68 8.63 8.80 8.49 8.07 8.04 8.06 7.81 7.81 7.72 8.55 8.35 8.08 0.00 0.10 0.03 0.02 0.01 0.04 0.02 0.00 0.04 0.07 0.00 0.01 0.01 0.01 0.00 0.00 0.36 0.38 0.37 0.37 0.37 0.35 0.35 0.46 0.46 0.40 0.37 0.38 0.39 0.38 0.42 0.35 8.90 8.67 8.91 8.77 8.51 8.17 8.95 8.75 8.21 8.68 8.29 8.89 8.87 8.83 8.79 8.81 0.50 0.54 0.52 0.50 0.58 0.52 0.69 0.23 0.23 0.27 0.31 0.30 0.29 0.24 0.28 0.21 0.28 0.26 0.24 0.28 0.23 0.24 0.24 0.09 0.09 0.10 0.07 0.07 0.09 0.09 0.10 0.12 0.08 0.13 0.08 0.08 0.06 0.08 0.11 3.49 3.42 3.50 3.49 3.52 3.51 3.56 3.54 3.49 3.50 3.39 3.57 3.50 3.63 3.62 3.53 96.10 94.36 96.96 96.49 96.98 96.02 98.19 97.30 94.74 96.00 92.99 97.68 96.54 98.44 98.59 96.45 drf-idrf-h supplemental data — compositions of duchesne river formation biotite phenocrysts page 6 sample sio2 tio2 al2o3 feo t mno mgo cao na2o k2o bao f cl h2o* total 35.13 34.52 31.69 32.58 34.78 35.42 34.87 34.29 35.77 36.13 34.13 35.78 34.59 34.62 31.80 34.70 35.12 4.50 4.19 2.86 4.30 4.45 4.40 4.17 4.26 3.42 4.33 4.46 4.35 4.40 4.22 3.19 4.16 4.34 13.91 13.82 14.00 14.05 14.09 14.75 12.85 14.12 14.64 14.35 14.20 14.18 14.20 13.63 15.12 13.41 14.05 23.25 22.51 21.23 22.52 23.64 23.42 21.72 22.85 15.38 22.65 23.03 23.58 23.16 22.51 23.79 22.23 22.62 0.21 0.27 0.23 0.27 0.21 0.20 0.18 0.21 0.17 0.25 0.21 0.23 0.25 0.26 0.24 0.19 0.21 8.99 9.04 10.25 9.36 9.25 9.80 8.84 10.01 13.75 9.80 9.47 9.56 9.63 9.20 8.53 9.54 9.54 0.11 0.01 0.29 0.12 0.02 0.03 0.20 0.05 0.16 0.01 0.05 0.04 0.08 0.09 1.72 0.12 0.09 0.36 0.35 0.03 0.36 0.39 0.35 0.24 0.45 0.54 0.37 0.39 0.45 0.46 0.14 0.18 0.14 0.37 8.36 8.48 6.09 8.13 8.59 8.55 7.64 8.11 7.83 8.47 8.32 8.52 8.21 7.89 3.70 7.11 8.10 0.79 0.94 0.04 0.66 0.83 1.11 0.35 0.98 0.71 0.89 0.86 0.67 1.20 0.23 0.40 0.25 0.93 0.33 0.45 0.30 0.37 0.49 0.37 0.44 0.45 0.40 0.34 0.39 0.40 0.47 0.41 0.28 0.45 0.45 0.19 0.22 0.08 0.17 0.20 0.18 0.26 0.22 0.06 0.22 0.21 0.20 0.19 0.27 0.08 0.24 0.21 3.56 3.43 3.42 3.43 3.50 3.65 3.35 3.51 3.61 3.64 3.52 3.61 3.52 3.45 3.48 3.43 3.51 99.50 97.99 90.37 96.12 100.20 102.03 94.87 99.27 96.25 101.24 99.01 101.35 100.11 96.68 92.35 95.73 99.31 drf-j drf-k biotite sample drf-a drf-b drf-c drf-c drf-c drf-d drf-f drf-f drf-g drf-h drf-h drf-i drf-j drf-k sio2 36.68 38.06 37.06 35.99 39.79 36.84 36.25 35.55 36.62 28.85 28.74 29.02 28.97 29.49 28.68 29.45 31.55 30.62 33.22 32.54 34.49 32.90 31.86 32.10 31.55 31.10 30.41 29.86 29.53 30.38 29.30 30.19 31.15 28.94 28.53 29.48 28.95 29.62 28.32 35.79 36.16 36.28 34.87 35.50 36.61 35.33 35.26 36.28 35.56 31.03 32.30 35.43 32.28 35.09 32.39 32.71 35.51 35.61 35.18 35.60 35.61 35.88 35.10 35.16 31.80 31.55 30.68 30.72 29.96 30.86 31.32 32.16 32.08 31.80 34.42 34.04 34.53 33.99 34.13 34.15 35.43 35.35 34.90 35.13 34.52 31.69 32.58 34.78 35.42 34.87 34.29 35.77 36.13 34.13 35.78 34.59 34.62 31.80 34.70 35.12 tio2 3.39 3.10 3.46 3.53 3.21 3.34 3.40 3.49 3.33 3.40 3.60 3.42 3.45 3.59 3.52 3.43 3.23 3.19 2.86 2.85 2.55 2.79 2.91 2.99 2.71 2.81 2.95 2.54 2.90 2.78 2.73 2.97 2.63 3.16 3.21 3.12 2.97 3.00 2.91 3.04 3.15 3.38 2.93 2.94 4.32 3.05 3.19 4.47 2.95 3.10 2.23 2.56 2.52 2.70 2.67 2.74 2.70 2.63 2.78 2.73 2.58 2.62 2.58 2.74 3.10 2.97 3.05 3.16 2.82 3.14 2.87 3.13 3.09 3.48 2.97 2.92 3.10 3.04 3.15 3.11 3.14 3.09 3.06 4.50 4.19 2.86 4.30 4.45 4.40 4.17 4.26 3.42 4.33 4.46 4.35 4.40 4.22 3.19 4.16 4.34 al2o3 13.40 12.62 13.76 13.61 11.99 13.87 14.23 13.63 12.62 14.46 14.58 14.37 14.45 14.76 14.37 14.23 16.38 15.48 16.52 16.85 17.41 17.59 17.05 17.58 18.04 18.18 16.87 16.52 16.32 17.04 16.64 17.73 17.41 16.44 16.79 16.05 15.55 16.19 15.92 16.04 15.86 15.44 17.02 17.40 13.67 15.94 16.29 14.11 16.89 15.97 17.92 17.23 18.45 17.22 16.74 15.86 17.12 17.46 16.96 17.27 17.37 17.04 17.67 17.64 15.28 15.68 14.92 15.40 15.23 15.68 15.89 15.25 15.45 15.88 15.40 14.88 15.28 14.41 15.68 15.13 15.39 15.10 15.23 13.91 13.82 14.00 14.05 14.09 14.75 12.85 14.12 14.64 14.35 14.20 14.18 14.20 13.63 15.12 13.41 14.05 feo t 16.96 15.84 16.70 16.90 15.18 16.87 17.27 17.19 15.82 18.78 18.04 17.83 16.03 18.93 18.13 16.87 21.00 20.80 20.81 20.62 17.65 20.13 21.04 21.37 19.85 20.36 20.97 19.47 20.15 20.48 20.34 20.68 18.60 20.66 20.88 19.91 14.15 14.23 20.63 15.93 16.18 15.89 19.58 19.69 17.32 20.00 18.15 18.17 19.56 18.94 19.06 20.08 20.03 20.26 20.04 19.62 18.43 19.15 19.23 18.98 18.29 18.66 20.39 20.00 24.54 22.70 24.41 24.97 24.71 25.18 24.11 24.40 23.60 24.59 23.43 22.43 22.15 21.43 23.86 23.45 22.90 23.66 22.28 23.25 22.51 21.23 22.52 23.64 23.42 21.72 22.85 15.38 22.65 23.03 23.58 23.16 22.51 23.79 22.23 22.62 mno 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.27 0.25 0.21 0.18 0.29 0.26 0.25 0.21 0.18 0.21 0.19 0.17 0.18 0.19 0.23 0.19 0.16 0.20 0.16 0.20 0.20 0.19 0.19 0.18 0.17 0.23 0.17 0.13 0.07 0.21 0.01 0.00 0.01 0.01 0.00 0.03 0.01 0.00 0.02 0.02 0.13 0.19 0.16 0.19 0.18 0.17 0.15 0.00 0.00 0.00 0.01 0.00 0.02 0.21 0.17 0.22 0.17 0.20 0.25 0.24 0.26 0.23 0.20 0.18 0.19 0.02 0.01 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.21 0.27 0.23 0.27 0.21 0.20 0.18 0.21 0.17 0.25 0.21 0.23 0.25 0.26 0.24 0.19 0.21 mgo 11.59 10.77 12.20 11.90 11.66 12.31 12.27 11.51 11.53 12.74 13.06 12.71 14.37 12.13 12.98 13.68 10.06 9.88 9.70 9.66 9.61 9.22 9.07 9.37 9.14 8.99 9.43 11.06 10.25 9.90 9.71 9.01 8.24 10.67 10.12 10.81 15.78 16.60 9.83 13.39 13.38 13.34 8.99 9.23 12.64 10.00 9.97 11.73 9.19 10.61 9.48 9.84 8.46 8.99 9.42 9.13 10.02 10.42 10.53 10.59 9.63 9.47 9.84 10.33 8.31 9.26 8.14 8.16 8.10 8.28 8.68 8.63 8.80 8.49 8.07 8.04 8.06 7.81 7.81 7.72 8.55 8.35 8.08 8.99 9.04 10.25 9.36 9.25 9.80 8.84 10.01 13.75 9.80 9.47 9.56 9.63 9.20 8.53 9.54 9.54 cao 0.30 0.49 0.23 0.26 0.39 0.21 0.13 0.21 0.30 0.04 0.01 0.00 0.01 0.08 0.09 0.01 0.08 0.14 0.05 0.01 0.43 0.01 0.07 0.01 0.07 0.02 0.01 0.05 0.13 0.06 0.04 0.02 0.88 0.21 0.12 0.30 0.05 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.00 0.00 0.01 0.01 0.00 0.03 0.00 0.00 0.00 0.04 0.07 0.02 0.00 0.03 0.03 0.07 0.00 0.00 0.02 0.03 0.02 0.13 0.00 0.10 0.03 0.02 0.01 0.04 0.02 0.00 0.04 0.07 0.00 0.01 0.01 0.01 0.00 0.00 0.11 0.01 0.29 0.12 0.02 0.03 0.20 0.05 0.16 0.01 0.05 0.04 0.08 0.09 1.72 0.12 0.09 na2o 0.21 0.34 0.37 0.32 0.21 0.34 0.33 0.34 0.25 0.47 0.52 0.47 0.52 0.51 0.46 0.43 0.36 0.36 0.28 0.42 0.32 0.27 0.27 0.27 0.39 0.41 0.38 0.41 0.26 0.39 0.34 0.40 0.39 0.26 0.27 0.29 0.88 0.71 0.30 0.50 0.49 0.50 0.32 0.26 0.48 0.30 0.36 0.44 0.31 0.33 0.24 0.31 0.30 0.31 0.37 0.40 0.35 0.32 0.33 0.32 0.40 0.32 0.34 0.30 0.35 0.41 0.42 0.36 0.38 0.37 0.37 0.37 0.35 0.35 0.46 0.46 0.40 0.37 0.38 0.39 0.38 0.42 0.35 0.36 0.35 0.03 0.36 0.39 0.35 0.24 0.45 0.54 0.37 0.39 0.45 0.46 0.14 0.18 0.14 0.37 k2o 7.72 7.32 7.95 7.92 7.47 8.13 8.35 8.19 7.56 8.49 8.52 8.45 8.23 8.29 8.42 8.31 9.04 8.80 9.07 9.35 4.16 9.13 8.97 9.01 8.30 8.47 9.12 8.73 7.91 8.74 9.00 9.15 7.64 6.64 7.68 6.69 9.12 9.18 9.16 9.11 9.08 8.97 9.29 9.26 8.65 9.27 9.09 8.85 9.27 8.85 8.61 9.31 9.46 9.20 9.01 8.56 9.20 9.30 9.19 9.36 8.92 9.16 8.74 9.13 8.67 8.56 8.14 8.90 8.67 8.91 8.77 8.51 8.17 8.95 8.75 8.21 8.68 8.29 8.89 8.87 8.83 8.79 8.81 8.36 8.48 6.09 8.13 8.59 8.55 7.64 8.11 7.83 8.47 8.32 8.52 8.21 7.89 3.70 7.11 8.10 bao 0.87 1.06 0.85 0.92 1.08 0.85 0.83 0.75 0.25 0.33 0.42 0.32 0.24 0.38 0.57 0.36 0.40 0.46 0.36 0.63 0.33 0.26 0.56 0.43 0.32 0.42 0.29 0.18 0.06 0.33 0.60 0.11 0.58 0.40 0.33 0.15 0.34 0.57 0.30 0.62 0.53 0.32 0.50 0.54 0.52 0.50 0.58 0.52 0.69 0.79 0.94 0.04 0.66 0.83 1.11 0.35 0.98 0.71 0.89 0.86 0.67 1.20 0.23 0.40 0.25 0.93 f 0.37 0.40 0.50 0.48 0.33 0.34 0.42 0.43 0.35 0.37 0.28 0.31 0.34 0.37 0.30 0.28 0.41 0.36 0.41 0.39 0.34 0.35 0.35 0.35 0.31 0.34 0.48 0.41 0.42 0.40 0.37 0.36 0.52 0.33 0.29 0.37 1.75 1.92 0.27 0.44 0.41 0.49 0.37 0.42 0.44 0.37 0.46 0.39 0.37 0.39 0.28 0.33 0.35 0.44 0.44 0.56 0.41 0.30 0.42 0.38 0.44 0.41 0.47 0.42 0.25 0.22 0.27 0.23 0.23 0.27 0.31 0.30 0.29 0.24 0.28 0.21 0.28 0.26 0.24 0.28 0.23 0.24 0.24 0.33 0.45 0.30 0.37 0.49 0.37 0.44 0.45 0.40 0.34 0.39 0.40 0.47 0.41 0.28 0.45 0.45 cl 0.09 0.09 0.09 0.09 0.13 0.09 0.10 0.07 0.05 0.14 0.10 0.11 0.11 0.15 0.15 0.13 0.09 0.05 0.07 0.06 0.12 0.07 0.06 0.07 0.10 0.12 0.07 0.08 0.07 0.07 0.09 0.08 0.10 0.06 0.07 0.03 0.19 0.06 0.05 0.05 0.05 0.06 0.05 0.04 0.13 0.05 0.05 0.15 0.04 0.06 0.16 0.05 0.02 0.07 0.07 0.10 0.04 0.04 0.05 0.04 0.06 0.05 0.03 0.06 0.11 0.09 0.00 0.09 0.09 0.10 0.07 0.07 0.09 0.09 0.10 0.12 0.08 0.13 0.08 0.08 0.06 0.08 0.11 0.19 0.22 0.08 0.17 0.20 0.18 0.26 0.22 0.06 0.22 0.21 0.20 0.19 0.27 0.08 0.24 0.21 h2o* 3.50 3.40 3.51 3.45 3.51 3.59 3.56 3.45 3.43 3.36 3.41 3.36 3.39 3.37 3.37 3.41 3.47 3.39 3.51 3.50 3.50 3.52 3.47 3.54 3.48 3.46 3.37 3.39 3.34 3.41 3.34 3.41 3.22 3.43 3.42 3.40 2.76 2.83 3.34 3.64 3.68 3.62 3.53 3.57 3.58 3.58 3.49 3.59 3.57 3.39 3.48 3.65 3.48 3.54 3.42 3.29 3.57 3.69 3.60 3.65 3.53 3.54 3.61 3.65 3.50 3.52 3.44 3.49 3.42 3.50 3.49 3.52 3.51 3.56 3.54 3.49 3.50 3.39 3.57 3.50 3.63 3.62 3.53 3.56 3.43 3.42 3.43 3.50 3.65 3.35 3.51 3.61 3.64 3.52 3.61 3.52 3.45 3.48 3.43 3.51 total 94.04 92.24 95.60 94.23 93.70 95.75 96.11 93.86 91.71 92.05 92.04 90.96 90.80 92.85 91.42 91.15 96.42 93.33 96.85 96.67 90.88 96.22 95.51 97.28 94.34 94.63 94.49 92.85 91.90 93.99 92.19 94.56 91.14 91.14 91.90 90.74 91.68 93.66 91.15 97.75 98.24 97.75 96.80 98.11 97.65 97.73 96.10 98.01 97.57 93.21 93.94 99.38 95.79 98.11 94.72 93.26 97.19 98.79 98.12 98.80 96.70 96.99 99.33 99.73 96.64 95.56 93.99 96.10 94.36 96.96 96.49 96.98 96.02 98.19 97.30 94.74 96.00 92.99 97.68 96.54 98.44 98.59 96.45 99.50 97.99 90.37 96.12 100.20 102.03 94.87 99.27 96.25 101.24 99.01 101.35 100.11 96.68 92.35 95.73 99.31 supplemental data — compositions of duchesne river formation biotite phenocrysts page &p sanidine composition of duchesne river formation sanidine phenocrysts sample drf-a drf-b drf-h drf-i drf-j drf-j sio2 64.68 64.83 61.31 60.82 65.73 64.31 65.17 88.63 66.50 66.03 65.79 64.63 64.72 65.89 64.86 65.19 65.31 64.57 62.59 62.74 64.80 63.08 65.00 62.90 64.49 65.19 65.31 64.57 62.59 62.74 64.80 63.08 65.00 62.90 64.49 al2o3 18.72 19.00 19.57 19.71 18.60 18.25 18.55 6.70 19.23 18.83 19.01 18.59 18.64 18.89 19.26 18.35 18.30 18.46 19.33 18.96 18.67 19.00 18.53 19.03 18.50 18.35 18.30 18.46 19.33 18.96 18.67 19.00 18.53 19.03 18.50 fe2o3 0.02 0.01 0.05 0.05 0.10 0.07 0.00 0.13 0.02 0.01 0.02 0.04 0.04 0.02 0.06 0.05 0.04 0.03 0.03 0.05 0.03 0.06 0.00 0.04 0.01 0.05 0.04 0.03 0.03 0.05 0.03 0.06 0.00 0.04 0.01 cao 0.14 0.11 0.13 0.15 0.11 0.09 0.10 0.18 0.12 0.11 0.09 0.11 0.11 0.09 0.10 0.07 0.12 0.15 0.19 0.17 0.10 0.19 0.15 0.15 0.15 0.07 0.12 0.15 0.19 0.17 0.10 0.19 0.15 0.15 0.15 bao 3.17 3.08 0.65 0.47 0.96 0.10 0.06 0.06 1.35 1.40 1.29 1.52 1.53 1.05 0.80 0.88 3.16 3.34 0.56 3.52 0.76 3.21 0.81 1.05 0.80 0.88 3.16 3.34 0.56 3.52 0.76 3.21 0.81 na2o 2.12 2.13 2.79 2.79 1.95 2.03 2.80 0.94 2.71 2.72 1.97 1.92 2.10 2.02 2.02 2.82 2.87 2.91 2.69 2.65 2.85 2.54 2.82 2.69 2.83 2.82 2.87 2.91 2.69 2.65 2.85 2.54 2.82 2.69 2.83 k2o 13.31 13.11 11.78 11.97 13.60 13.77 12.26 4.00 13.04 13.09 13.60 13.53 13.28 13.35 13.38 12.43 12.38 12.49 11.84 11.72 12.59 11.52 12.35 11.71 12.49 12.43 12.38 12.49 11.84 11.72 12.59 11.52 12.35 11.71 12.49 total 98.98 99.19 98.81 98.57 100.73 98.99 99.84 100.69 101.66 100.84 101.82 100.21 100.17 101.77 101.20 99.96 99.82 99.49 99.83 99.63 99.59 99.90 99.61 99.72 99.27 99.96 99.82 99.49 99.83 99.63 99.59 99.90 99.61 99.72 99.27 plagioclase compositions of duchesne river formation plagioclase phenocrysts sample drf-a drf-a drf-a drf-a drf-a drf-a drf-a drf-a drf-a sio2 60.53 61.41 61.01 62.69 62.91 59.70 59.69 55.78 58.17 60.89 61.06 62.13 62.32 58.65 58.87 61.95 62.08 58.62 58.87 59.40 60.34 57.55 59.18 60.55 62.22 60.14 60.70 62.27 61.78 61.76 60.25 59.77 60.60 61.00 61.73 62.05 58.06 58.65 57.74 61.38 60.53 60.47 60.82 60.18 58.76 62.22 59.39 60.79 59.95 58.98 61.59 62.24 63.82 64.04 64.93 64.09 60.30 63.28 61.18 59.48 59.24 60.78 61.53 60.32 62.05 61.79 60.80 62.27 62.83 57.31 58.99 57.74 58.95 58.76 59.19 58.94 57.79 58.63 59.02 61.50 al2o3 26.06 25.12 24.84 24.50 24.84 25.25 25.27 27.47 26.56 24.50 24.37 24.65 24.48 26.24 26.16 24.43 24.51 25.99 26.51 25.89 25.62 27.45 25.96 25.66 24.50 25.50 24.67 24.66 24.78 24.66 25.67 26.26 25.48 25.64 24.48 24.38 27.20 26.77 26.92 26.12 26.52 25.49 25.06 25.20 25.68 23.95 25.69 25.80 24.19 25.77 24.52 24.00 22.68 23.10 21.96 22.32 25.85 24.10 24.81 26.19 26.22 25.19 25.03 24.86 24.36 24.52 24.89 23.60 23.91 26.12 27.02 26.31 26.99 27.08 26.48 27.26 27.35 25.40 25.97 24.83 fe2o3 0.15 0.17 0.15 0.06 0.04 0.04 0.04 0.28 0.24 0.07 0.05 0.04 0.06 0.26 0.25 0.13 0.14 0.13 0.21 0.18 0.20 0.15 0.12 0.12 0.12 0.17 0.12 0.13 0.09 0.07 0.14 0.17 0.17 0.15 0.10 0.07 0.34 0.27 0.29 0.25 0.25 0.11 0.10 0.15 0.16 0.19 0.17 0.16 0.08 0.04 0.04 0.06 0.03 0.07 0.05 0.07 0.15 0.12 0.17 0.18 0.19 0.17 0.19 0.21 0.15 0.18 0.07 0.07 0.06 0.20 0.15 0.13 0.23 0.16 0.16 0.17 0.21 0.20 0.11 0.12 cao 7.60 6.86 6.53 5.73 6.10 7.05 7.01 9.94 8.61 6.06 6.02 5.93 5.83 8.47 8.02 6.07 6.04 8.15 8.54 7.92 7.48 9.65 7.96 7.19 6.13 7.34 6.74 6.32 6.37 6.53 7.29 7.99 7.20 6.79 6.07 5.96 9.31 8.76 9.32 7.47 7.96 7.17 6.83 7.25 7.73 5.56 7.90 7.35 6.45 7.67 6.06 5.48 4.39 4.57 3.52 4.12 7.48 5.65 6.55 8.03 8.24 7.03 6.76 7.15 6.17 6.00 6.72 5.32 5.21 8.56 8.72 8.63 8.59 8.76 8.30 8.98 9.33 7.69 7.78 6.56 na2o 6.91 7.13 7.30 7.74 7.46 6.98 7.03 5.45 6.26 7.58 7.67 7.72 7.70 6.35 6.82 7.55 7.50 6.59 6.32 6.68 6.94 5.91 6.68 6.99 7.55 6.81 7.35 7.48 7.58 7.46 6.93 6.68 6.94 6.91 7.40 7.65 5.77 5.76 5.63 6.41 6.05 7.02 7.30 7.06 6.65 7.73 6.92 6.89 7.71 6.94 7.65 7.97 8.39 8.11 8.72 8.65 6.80 7.70 7.21 6.70 6.32 6.52 7.08 7.12 7.47 7.55 7.39 8.14 8.03 6.62 6.30 6.32 6.31 6.29 6.36 6.04 6.02 6.97 6.83 7.28 k2o 0.50 0.54 0.64 0.78 0.68 0.55 0.56 0.31 0.40 0.62 0.59 0.68 0.73 0.40 0.45 0.64 0.72 0.42 0.40 0.45 0.49 0.35 0.44 0.53 0.67 0.50 0.57 0.62 0.64 0.58 0.52 0.45 0.55 0.53 0.68 0.67 0.62 0.65 0.59 0.52 0.46 0.50 0.51 0.47 0.48 0.77 0.48 0.48 0.62 0.50 0.66 0.74 0.98 1.01 1.25 1.03 0.48 0.71 0.59 0.44 0.42 0.54 0.56 0.54 0.61 0.67 0.55 0.69 0.74 0.42 0.39 0.41 0.42 0.42 0.42 0.37 0.36 0.47 0.49 0.60 total 101.75 101.23 100.47 101.50 102.03 99.57 99.59 99.23 100.23 99.72 99.75 101.15 101.13 100.36 100.58 100.77 100.99 99.89 100.86 100.52 101.07 101.06 100.35 101.04 101.18 100.47 100.14 101.48 101.24 101.06 100.80 101.32 100.94 101.02 100.46 100.77 101.30 100.85 100.48 102.14 101.77 100.75 100.60 100.31 99.46 100.41 100.56 101.46 98.99 99.89 100.51 100.47 100.29 100.90 100.44 100.28 101.06 101.56 100.50 101.02 100.63 100.24 101.14 100.20 100.80 100.71 100.42 100.09 100.78 99.22 101.55 99.53 101.49 101.45 100.91 101.76 101.05 99.36 100.19 100.89 allanite compositions of duchesne river formation allanite phenocrysts sample drf-i drf-i drf-i drf-a drf-a drf-h drf-h drf-h drf-c drf-c sio2 31.81 31.93 30.89 31.75 31.99 31.34 31.79 31.77 32.76 31.30 30.88 31.80 32.36 30.69 30.79 31.07 31.40 30.96 31.59 31.84 31.02 31.48 30.01 31.57 30.56 31.82 31.71 30.93 31.59 30.69 31.25 30.58 30.58 31.18 30.77 31.37 30.49 30.33 31.24 31.66 31.84 32.56 30.87 31.32 31.46 31.56 31.27 31.87 31.80 31.78 31.23 31.38 30.91 31.39 31.66 30.60 31.31 31.18 30.85 30.68 30.72 31.05 31.27 30.71 30.88 31.16 tio2 0.34 0.41 0.32 0.29 0.30 0.28 0.33 0.32 0.29 0.43 0.26 0.31 0.51 0.40 0.28 0.30 0.28 0.38 0.38 0.29 0.52 0.56 0.69 0.47 0.69 0.39 0.43 0.55 0.37 0.61 0.77 0.59 0.44 0.61 0.32 0.56 0.32 0.35 0.50 0.42 0.55 0.34 0.19 0.54 0.58 0.32 0.33 0.56 0.32 0.46 0.24 0.31 0.22 0.32 0.52 0.41 0.40 0.46 0.41 0.67 0.40 0.20 0.48 0.29 0.37 0.49 al2o3 17.40 17.34 16.64 17.44 17.70 17.28 17.75 17.15 17.14 16.52 16.39 16.60 17.39 16.21 16.52 16.95 17.04 17.19 16.94 17.27 15.34 15.94 16.01 15.73 15.79 16.99 15.74 15.60 15.77 15.48 15.69 15.60 15.44 15.46 15.87 15.53 15.77 15.56 16.16 17.39 16.57 17.81 16.68 16.61 16.89 17.19 16.91 17.34 17.02 17.41 16.63 17.07 16.57 17.02 16.79 15.65 15.83 16.11 15.93 16.16 15.87 16.17 15.92 15.57 15.86 15.98 feo 12.27 12.56 12.41 12.40 12.32 12.31 12.39 12.15 12.36 11.90 12.29 12.38 12.15 12.51 12.18 12.21 12.10 12.57 12.37 12.17 13.03 12.60 12.28 13.10 12.41 12.57 12.72 12.55 12.88 13.01 11.55 12.55 12.91 11.89 12.88 12.68 12.64 12.82 12.60 12.36 12.26 12.07 12.53 12.38 12.45 12.27 12.15 12.04 12.42 11.91 12.58 12.52 12.64 12.33 12.46 12.82 12.66 12.50 12.60 12.13 12.59 12.65 12.72 12.70 12.46 12.89 mno 0.34 0.20 0.34 0.49 0.27 0.37 0.27 0.31 0.46 0.40 0.36 0.35 0.25 0.35 0.27 0.27 0.19 0.19 0.42 0.32 0.17 0.14 0.15 0.19 0.19 0.34 0.33 0.27 0.29 0.20 0.10 0.14 0.23 0.06 0.41 0.21 0.28 0.29 0.24 0.22 0.19 0.24 0.43 0.22 0.24 0.26 0.37 0.16 0.39 0.14 0.50 0.17 0.41 0.32 0.19 0.31 0.22 0.26 0.36 0.18 0.35 0.52 0.21 0.48 0.32 0.29 mgo 0.58 0.62 0.60 0.51 0.49 0.57 0.57 0.58 0.60 0.59 0.62 0.57 0.68 0.56 0.60 0.57 0.57 0.56 0.66 0.62 0.94 0.90 1.05 0.95 1.24 0.55 0.94 1.09 1.00 1.01 1.68 1.01 0.89 1.72 0.99 1.02 0.91 0.95 1.05 0.73 0.80 0.72 0.55 0.75 0.69 0.67 0.72 0.80 0.70 0.70 0.58 0.55 0.57 0.70 0.67 0.96 0.97 1.05 1.01 1.13 1.02 0.83 0.96 1.00 0.95 0.87 cao 12.73 12.26 12.20 12.45 12.77 11.80 11.82 12.92 12.04 11.84 12.38 12.50 12.57 12.13 12.42 12.69 12.47 11.57 12.76 12.73 13.46 13.50 13.43 13.12 12.80 12.66 11.79 12.21 11.99 12.62 12.24 13.40 12.81 12.11 11.40 13.26 11.83 11.24 13.37 12.94 12.50 14.48 11.76 12.27 12.94 12.75 12.19 14.30 12.23 13.16 11.53 11.71 11.46 12.47 12.98 12.16 12.95 13.33 12.58 13.38 12.35 11.18 13.48 11.23 12.41 13.57 u2o3 0.25 0.16 0.00 0.49 1.07 0.00 0.66 0.00 0.33 0.00 0.00 0.00 1.64 0.00 1.47 3.34 0.00 0.00 0.00 0.41 1.07 3.83 4.71 0.00 0.00 0.00 0.00 3.09 0.00 0.00 4.30 1.55 0.74 1.95 0.00 0.00 0.82 0.00 0.00 0.00 0.00 0.00 1.15 0.00 1.88 0.99 1.96 3.44 0.00 2.54 0.00 1.31 2.20 0.00 0.00 0.00 0.90 0.00 1.55 0.00 0.00 2.03 0.00 1.63 0.00 0.00 tho2 1.77 1.59 1.53 1.80 1.92 1.51 1.20 1.66 1.49 1.35 1.86 1.79 1.62 1.46 1.42 1.12 1.76 1.73 1.71 1.34 1.34 0.67 0.62 1.31 0.67 1.70 1.16 0.74 0.88 0.54 0.86 0.90 1.43 0.59 0.82 1.10 1.22 0.89 0.82 1.27 1.39 0.97 1.66 1.33 1.46 1.51 1.07 1.38 1.08 0.87 1.50 0.67 1.69 1.39 1.47 1.11 1.17 0.91 0.89 0.96 0.88 1.26 1.01 1.07 0.51 1.07 y2o3 0.15 0.11 0.13 0.13 0.06 0.12 0.06 0.09 0.10 0.09 0.11 0.13 0.08 0.16 0.19 0.16 0.12 0.04 0.07 0.13 0.16 0.11 0.12 0.18 0.05 0.10 0.11 0.11 0.08 0.18 0.03 0.11 0.10 0.03 0.12 0.14 0.19 0.17 0.09 0.05 0.09 0.12 0.18 0.14 0.12 0.08 0.19 0.14 0.21 0.09 0.18 0.06 0.20 0.08 0.09 0.15 0.15 0.15 0.17 0.16 0.09 0.15 0.15 0.19 0.11 0.17 la2o3 5.65 6.26 6.11 5.63 5.73 5.89 6.14 5.68 5.83 5.84 5.44 5.64 5.92 5.76 5.85 5.99 5.85 6.21 5.63 5.50 4.82 5.26 5.92 5.27 6.27 5.68 6.36 6.63 6.33 5.93 7.01 5.39 5.28 7.57 5.95 5.44 5.88 6.09 5.11 5.64 6.58 4.79 5.66 6.53 5.85 5.55 6.15 4.95 6.08 5.64 5.85 6.99 6.15 5.76 5.90 6.00 5.15 5.40 5.34 5.64 5.46 5.78 5.06 5.88 6.24 4.51 ce2o3 9.75 10.85 10.75 9.98 9.59 10.69 10.67 9.55 10.59 10.04 10.52 9.87 9.84 10.59 10.26 10.13 10.13 10.47 10.22 10.27 9.74 10.09 9.90 10.28 11.08 10.29 11.07 11.23 11.27 10.78 11.39 9.86 10.10 12.22 11.27 10.44 11.10 11.82 9.96 10.14 10.49 9.08 10.82 10.78 9.80 9.87 10.51 8.67 10.86 10.33 11.01 11.95 10.74 10.26 9.94 10.85 10.13 10.11 10.48 10.47 10.96 11.55 9.60 11.60 11.52 9.29 nd2o3 3.13 3.25 3.28 3.10 3.03 3.38 2.93 3.30 3.51 3.31 3.39 3.36 2.83 3.17 3.57 3.42 3.12 2.90 3.26 3.24 3.64 3.48 2.85 3.34 3.45 3.20 3.92 3.53 3.61 3.36 2.90 3.37 3.89 2.87 3.93 3.60 3.81 3.82 3.75 3.17 3.04 3.12 3.67 3.12 2.80 3.00 3.31 2.63 3.31 2.94 3.63 2.99 3.72 3.36 3.10 3.64 3.78 3.52 3.91 3.27 3.77 3.97 3.71 3.99 3.55 3.67 sm2o3 0.41 0.38 0.46 0.47 0.39 0.55 0.31 0.42 0.31 0.33 0.57 0.50 0.29 0.49 0.44 0.39 0.46 0.37 0.31 0.45 0.61 0.49 0.43 0.50 0.44 0.44 0.51 0.46 0.57 0.53 0.31 0.45 0.60 0.16 0.54 0.54 0.63 0.57 0.70 0.33 0.33 0.39 0.42 0.40 0.33 0.37 0.36 0.37 0.49 0.41 0.52 0.41 0.53 0.38 0.42 0.65 0.57 0.55 0.54 0.33 0.51 0.62 0.57 0.49 0.38 0.66 h2o+ 1.60 1.60 1.56 1.60 1.61 1.58 1.61 1.59 1.62 1.55 1.55 1.58 1.61 1.54 1.54 1.56 1.57 1.57 1.59 1.59 1.55 1.56 1.53 1.57 1.55 1.59 1.57 1.55 1.57 1.55 1.56 1.54 1.53 1.56 1.56 1.56 1.53 1.53 1.57 1.60 1.58 1.63 1.56 1.57 1.58 1.59 1.57 1.60 1.59 1.59 1.57 1.58 1.56 1.58 1.58 1.54 1.56 1.57 1.55 1.55 1.55 1.56 1.56 1.54 1.55 1.56 total 98.16 99.52 97.22 98.51 99.23 97.67 98.48 97.48 99.42 95.49 96.60 97.39 99.75 96.03 97.81 100.18 97.08 96.70 97.88 98.18 97.40 100.60 99.71 97.59 97.19 98.32 98.33 100.54 98.18 96.48 101.61 97.04 96.98 99.97 96.81 97.45 97.39 96.44 97.17 97.92 98.21 98.31 98.11 97.94 99.08 97.95 99.06 100.24 98.49 99.96 97.54 99.67 99.54 97.35 97.76 96.85 97.74 97.09 98.14 96.71 96.52 99.52 96.69 98.36 97.10 96.18 gg titanite compositions of duchesne river formation titanite phenocrysts sample drf-i drf-i drf-i drf-i drf-i drf-i sio2 28.64 29.14 28.92 29.25 29.61 28.68 28.21 29.06 29.39 27.88 29.12 29.11 28.69 29.04 28.02 28.18 28.98 28.13 28.72 28.00 27.07 28.28 27.90 26.89 27.49 28.18 28.08 27.62 28.47 28.31 27.82 27.89 28.97 27.37 27.33 27.48 28.55 28.66 28.19 28.17 28.22 29.03 29.18 27.45 28.25 28.49 27.25 28.44 28.30 27.87 29.15 al2o3 0.70 1.56 0.82 0.73 0.63 0.92 0.79 0.85 0.91 0.86 0.77 0.65 0.83 0.75 0.97 0.84 0.86 0.78 0.62 0.77 0.86 0.83 0.89 0.65 0.61 0.67 0.86 0.92 0.84 0.92 0.75 0.80 0.64 0.86 0.80 0.81 1.01 0.97 0.69 0.65 0.67 0.95 1.06 0.98 0.81 1.03 0.64 0.86 0.71 0.74 0.68 tio2 35.39 35.15 34.68 36.32 36.00 34.62 34.85 35.37 34.90 34.65 35.68 35.84 35.74 35.02 34.23 34.90 35.31 33.73 34.93 35.18 34.01 0.00 33.55 33.39 34.86 35.58 35.06 34.69 35.56 35.17 34.97 35.25 35.61 35.25 35.21 35.23 34.58 34.96 35.40 34.79 35.24 34.97 35.81 32.68 35.31 34.17 35.47 35.11 35.18 35.23 35.77 mgo 0.02 0.02 0.01 0.00 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.00 0.01 0.01 0.01 0.00 0.00 0.02 0.01 0.02 0.00 0.00 0.01 0.00 0.01 0.00 0.01 0.01 0.01 0.00 0.01 0.02 0.01 0.01 0.01 0.00 0.02 0.03 0.01 0.00 0.01 0.02 0.03 0.00 0.00 fe2o3 1.37 0.94 1.41 1.15 1.39 1.59 1.67 1.46 1.53 1.40 1.41 1.28 1.34 1.49 1.68 1.42 1.54 1.82 1.19 1.48 1.72 1.33 1.80 4.54 1.43 1.32 1.55 1.73 1.45 1.50 1.27 1.44 1.25 1.67 1.46 1.54 1.67 1.56 1.26 1.34 1.32 1.56 1.16 2.03 1.52 1.87 1.29 1.50 1.69 1.41 1.32 k2o 26.77 27.94 26.31 27.66 27.58 26.54 27.06 27.34 27.51 27.15 27.03 27.32 27.25 26.31 26.05 26.58 26.87 26.27 27.02 26.45 25.79 29.40 25.89 25.67 26.00 26.76 26.09 26.54 27.36 27.36 26.32 26.74 27.05 27.21 26.87 27.06 26.54 26.83 26.79 26.88 26.81 27.22 27.73 24.66 27.03 26.29 26.58 27.22 27.27 27.15 27.27 sno2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.01 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 v2o5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 ta2o5 0.00 0.00 0.04 0.00 0.00 0.18 0.00 0.09 0.13 0.08 0.00 0.09 0.03 0.10 0.11 0.00 0.00 0.01 0.03 0.00 0.15 0.08 0.09 0.00 0.02 0.09 0.14 0.18 0.00 0.10 0.00 0.00 0.01 0.08 0.06 0.00 0.03 0.00 0.00 0.06 0.00 0.00 0.00 0.14 0.00 0.02 0.00 0.05 0.00 0.07 0.11 mno 0.03 0.00 0.05 0.06 0.02 0.07 0.00 0.08 0.09 0.10 0.07 0.07 0.06 0.08 0.03 0.06 0.06 0.07 0.06 0.05 0.01 0.07 0.01 0.05 0.03 0.07 0.06 0.05 0.10 0.10 0.05 0.11 0.08 0.05 0.07 0.06 0.07 0.06 0.07 0.10 0.08 0.10 0.00 0.00 0.07 0.06 0.05 0.09 0.01 0.07 0.07 nb2o5 0.98 0.24 0.87 0.23 0.20 0.62 0.13 0.46 0.49 0.65 0.64 0.80 0.53 0.68 0.51 0.48 0.45 0.59 0.65 0.57 0.00 0.58 1.32 0.68 0.91 0.80 0.56 0.53 0.54 0.30 0.77 0.44 0.61 0.40 0.45 0.59 0.54 0.52 0.87 0.55 0.66 0.65 0.75 1.30 0.51 0.47 0.72 0.77 0.20 0.87 0.41 y2o3 0.12 0.05 0.13 0.10 0.07 0.15 0.17 0.21 0.11 0.29 0.12 0.11 0.14 0.30 0.30 0.11 0.13 0.29 0.12 0.14 0.30 0.18 0.45 0.08 0.14 0.11 0.60 0.34 0.15 0.08 0.14 0.19 0.16 0.11 0.18 0.09 0.25 0.38 0.09 0.11 0.11 0.20 0.06 0.70 0.11 0.26 0.12 0.08 0.03 0.13 0.12 la2o3 0.38 0.24 0.64 0.17 0.22 0.39 0.47 0.23 0.18 0.16 0.40 0.29 0.28 0.31 0.52 0.29 0.37 0.40 0.12 0.36 0.43 0.13 0.46 0.41 0.72 0.36 0.28 0.20 0.29 0.15 0.54 0.22 0.18 0.24 0.43 0.23 0.39 0.20 0.25 0.41 0.43 0.08 0.14 0.44 0.20 0.53 0.31 0.28 0.50 0.26 0.29 pr2o3 1.21 0.61 1.57 0.51 0.56 1.15 1.22 0.61 0.82 0.64 1.15 0.96 1.11 1.22 1.54 0.99 1.03 1.50 0.70 1.19 1.53 0.55 1.67 1.00 1.49 1.02 1.25 0.82 0.79 0.85 1.49 0.68 0.79 0.92 1.18 0.73 1.54 0.94 1.04 1.14 1.19 0.44 0.51 1.93 0.95 1.68 1.20 0.74 0.90 0.85 0.87 nd2o3 0.50 0.21 0.56 0.12 0.21 0.40 0.43 0.31 0.25 0.45 0.41 0.32 0.49 0.61 0.76 0.39 0.41 0.64 0.29 0.38 0.70 0.26 0.86 0.46 0.53 0.33 0.87 0.44 0.34 0.25 0.54 0.35 0.38 0.23 0.31 0.27 0.68 0.49 0.32 0.24 0.40 0.22 0.26 1.25 0.44 0.74 0.40 0.22 0.30 0.31 0.28 sm2o3 0.13 0.08 0.09 0.03 0.15 0.11 0.09 0.07 0.13 0.01 0.10 0.17 0.10 0.20 0.10 0.13 0.01 0.17 0.07 0.05 0.06 0.04 0.00 0.07 0.00 0.11 0.03 0.15 0.06 0.10 0.11 0.03 0.05 0.00 0.31 0.13 0.13 0.12 0.12 0.02 0.05 0.06 f 0.26 0.69 0.25 0.32 0.26 0.31 0.55 0.38 0.41 0.28 0.34 0.26 0.35 0.27 0.26 0.41 0.31 0.33 0.28 0.31 0.32 0.34 0.24 0.30 0.19 0.26 0.22 0.36 0.40 0.46 0.25 0.39 0.28 0.45 0.35 0.43 0.35 0.30 0.27 0.28 0.24 0.28 0.57 0.17 0.43 0.37 0.26 0.41 0.37 0.27 0.34 o=f 0.11 0.29 0.11 0.13 0.11 0.13 0.23 0.16 0.17 0.12 0.14 0.11 0.15 0.11 0.11 0.17 0.13 0.14 0.12 0.13 0.14 0.14 0.10 0.13 0.08 0.11 0.09 0.15 0.17 0.19 0.11 0.16 0.12 0.19 0.15 0.18 0.15 0.13 0.11 0.12 0.10 0.12 0.24 0.07 0.18 0.16 0.11 0.17 0.16 0.12 0.14 total 96.37 96.52 96.19 96.50 96.64 95.57 95.43 96.36 96.60 94.60 97.08 97.08 96.71 96.21 94.99 94.56 96.27 94.55 94.63 94.85 92.94 61.98 95.23 94.10 94.46 95.47 95.70 94.35 96.17 95.42 94.85 94.32 95.97 94.65 94.66 94.36 96.20 95.81 95.23 94.72 95.32 95.63 97.03 94.00 95.58 95.95 94.31 95.72 95.35 95.17 96.60 apatite compositions of apatite phenocrsysts from the duchesne river formation sample drf-d sio2 0.16 0.01 4.71 2.27 3.99 0.02 0.66 3.72 2.16 1.66 fe2o3 0.17 0.08 0.34 0.39 0.18 0.04 0.05 0.14 0.22 0.03 mno 0.02 0.00 0.00 0.01 0.02 0.08 0.02 0.00 0.02 0.01 cao 54.03 51.85 49.29 51.66 50.69 53.86 54.13 51.29 51.94 53.62 na2o 0.59 1.29 0.49 0.62 0.42 0.62 0.40 0.52 0.58 0.39 la2o3 0.13 0.00 0.08 0.00 0.08 0.05 0.07 0.17 0.07 0.04 ce2o3 0.23 0.00 0.00 0.10 0.20 0.07 0.11 0.01 0.00 0.02 p2o5 36.75 35.56 34.97 36.23 35.44 37.17 37.60 35.71 36.45 37.59 f 4.20 3.93 4.03 4.17 3.85 4.21 4.36 3.91 4.17 4.39 cl 0.02 0.03 0.02 0.02 0.03 0.01 0.01 0.01 0.00 0.00 sum 95.94 92.65 88.87 92.79 90.71 95.99 96.69 91.62 93.21 96.05 -o=f,cl 1.77 1.66 1.70 1.76 1.63 1.78 1.84 1.65 1.76 1.85 subtotal 94.17 90.99 87.17 91.03 89.08 94.21 94.85 89.97 91.45 94.20 h2o* -0.30 -0.22 -0.26 -0.30 -0.16 -0.30 -0.36 -0.17 -0.29 -0.36 total 93.87 90.77 86.91 90.73 88.92 93.91 94.49 89.80 91.16 93.84 glass shard table 10: compositions of glass shards from drf-a of the duchesne river formation *normalized average sio2 76.55 68.82 69.39 68.29 68.67 69.39 69.59 70.68 69.67 68.74 68.33 70.11 68.56 70.03 68.70 66.64 70.56 tio2 0.08 0.15 0.08 0.02 0.07 0.14 0.08 0.03 0.06 0.11 0.04 0.05 0.09 0.07 0.04 0.05 0.03 al2o3 13.82 12.43 11.91 11.87 12.44 12.57 11.61 13.29 12.78 12.91 12.93 12.70 12.50 12.26 12.49 12.78 12.25 feo 0.78 0.78 0.81 0.69 0.54 0.88 0.59 0.49 0.78 0.64 0.62 0.63 0.55 0.58 0.59 0.69 0.34 mno 0.05 0.04 0.03 0.05 0.11 0.00 0.00 0.00 0.05 0.07 0.03 0.01 0.05 0.10 0.07 0.10 0.08 mgo 0.12 0.16 0.10 0.08 0.09 0.18 0.08 0.04 0.11 0.16 0.11 0.10 0.11 0.07 0.10 0.10 0.09 na2o 2.90 2.65 2.73 2.83 2.69 2.38 2.54 2.70 2.86 2.64 2.51 2.64 1.99 2.84 2.69 2.39 2.89 cao 0.66 0.58 0.41 0.45 0.48 0.79 0.37 0.81 0.71 0.85 0.87 0.71 0.48 0.45 0.43 0.83 0.41 k2o 5.11 4.52 4.92 4.86 4.70 4.18 5.01 5.04 4.24 4.19 4.23 4.41 4.78 4.58 4.75 4.49 4.97 total 100.07 90.13 90.37 89.14 89.77 90.50 89.86 93.07 91.25 90.30 89.68 91.35 89.13 90.97 89.86 88.08 91.62 xrf drf x-tay fluorescence analyses of duchesne river formation tuffs sample drf-a drf-b drf-c drf-d drf-e drf-f drf-g drf-h drf-i drf-j drf-k sio2 71.81 59.62 52.70 68.84 73.86 70.11 65.58 67.37 66.66 54.16 73.62 tio2 0.44 0.38 0.40 0.51 0.53 0.31 0.38 0.24 0.18 0.21 0.30 al2o3 14.91 17.57 16.74 17.60 13.29 15.41 16.45 21.29 21.34 14.64 7.55 fe2o3 3.08 3.14 3.64 2.99 3.46 2.67 3.24 2.33 2.51 1.99 1.72 mno 0.04 0.08 0.27 0.01 0.02 0.02 0.07 0.01 0.01 0.27 0.06 normalized to 100% on a volatile-free basis mgo 1.60 5.69 5.78 5.20 3.08 4.60 4.91 5.35 5.83 4.80 2.32 cao 2.97 10.74 19.79 2.54 2.40 3.41 6.84 1.76 1.74 21.42 12.23 na2o 2.06 1.71 0.09 0.91 0.66 1.47 0.91 0.61 1.08 1.29 0.17 k2o 2.98 0.93 0.45 1.25 2.39 1.88 1.51 0.99 0.61 1.14 1.81 p2o5 0.11 0.13 0.13 0.16 0.32 0.12 0.11 0.07 0.04 0.07 0.24 loi 4.83 12.06 18.97 7.37 5.44 7.28 9.94 8.69 8.55 18.21 11.09 anal total 99.99 99.74 100.30 99.93 99.97 99.92 100.01 99.91 99.94 99.94 100.16 sc 8.1 7 6 6 9 5 8 4 3 1 9 v 36.8 53 48 45 55 39 46 14 12 21 38 cr 21.6 10 22 22 40 18 20 9 4 11 27 56 25.5 6.2 21.8 13.3 4.2 ni 8.7 10 17 11 15 12 17 17 12 9 12 52 16 4 27 16 7 cu 10 10 13 13 16 7 9 10 6 8 17 43 7 3 21 13 2 zn 59.5 60 74 58 55 64 82 60 59 47 44 64 30 7 23 14 4 ga 18.4 15 20 18 16 19 21 19 19 14 9 83 43 8 19 11 3 rb 126.4 39 39 42 81 45 44 41 23 34 52 44 24 6 21 9 3 sr 352.2 217 225 276 205 222 255 239 268 252 127 52 25 5 24 11 5 y 18.3 17 21 21 41 18 16 6 5 30 16 23 15 5 33 17 2 zr 174.4 135 140 150 153 135 122 103 88 104 182 27 16 5 35 16 2 nb 12.9 12 13 14 12 9 10 18 18 11 7 47 4 2 24 12 5 ba 750.3 421 179 184 280 432 363 68 48 193 189 40 9 2 12 9 3 la 28.4 22 22 33 44 23 27 12 11 26 25 ce 56 52 43 64 83 44 52 23 27 47 40 nd 25.5 16 7 30 43 24 25 15 16 4 9 sm 6.2 4 3 7 8 6 5 5 5 2 2 pb 21.8 27 21 23 19 21 24 33 35 24 12 th 13.3 16 13 14 11 9 11 17 16 12 9 u 4.2 7 2 4 3 3 5 2 2 5 3 xrf nenvf x-tay fluorescence analyses of northeast nevada voclanic field tuffs sample 88t 56 90 b6 90 b11 88t 55 90 b3 90 b7a 90 b7b 90 b12 90 b13 90 b5 90 b19a 90 b19b 90 b24a 90 b24b 91 t10 90 b9a sio2 72.84 69.01 69.59 78.85 76.30 78.11 77.30 80.00 76.36 77.89 78.01 80.42 77.75 73.64 71.63 71.78 tio2 0.38 0.46 0.40 0.10 0.10 0.09 0.09 0.11 0.10 0.16 0.11 0.08 0.13 0.11 0.31 0.33 al2o3 14.49 16.95 16.13 11.73 13.02 11.84 11.72 10.81 12.76 11.93 12.11 10.38 11.40 14.32 14.59 14.56 fe2o3 1.82 1.84 2.66 0.45 0.95 0.76 1.79 1.06 1.38 1.22 0.69 0.35 1.15 2.23 2.77 2.74 mno 0.02 0.02 0.02 0.02 0.04 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.04 0.03 0.03 mgo 0.54 0.67 0.62 0.12 0.30 0.25 0.22 0.19 0.23 0.54 0.17 0.10 0.23 0.85 0.91 0.62 cao 2.34 2.81 2.63 0.77 0.90 0.89 0.80 0.88 0.91 1.46 0.99 0.12 0.76 1.94 3.06 3.11 na2o 3.24 3.89 3.58 2.49 3.13 2.57 2.46 2.28 2.92 1.52 2.69 1.23 1.68 2.43 3.53 3.54 k2o 4.22 4.22 4.23 5.42 5.21 5.40 5.55 4.61 5.27 5.20 5.15 7.25 6.73 4.36 3.05 3.13 p2o5 0.11 0.14 0.14 0.05 0.05 0.07 0.05 0.05 0.05 0.06 0.05 0.05 0.14 0.09 0.13 0.16 loi 0.96 1.48 2.41 0.67 1.25 1.01 1.65 1.96 1.65 4.69 1.69 1.27 1.74 6.90 1.35 0.99 anal total 98.98 99.44 99.12 99.59 99.54 98.95 98.93 99.09 99.61 99.44 99.11 99.51 99.10 99.79 99.36 99.20 rb 144 157 152 201 203 251 154 205 115 177 183 200 146 110 111 sr 598 573 109 163 154 130 138 143 480 176 79 153 246 450 441 y 20 24 18 22 25 23 21 22 18 18 14 21 16 17 13 zr 276 252 99 141 120 114 112 128 149 143 121 146 110 133 136 nb 15 12 12 15 14 11 12 12 14 17 11 11 13 9 9 ba 2110 2550 605 1043 915 711 967 773 1941 1146 895 1499 1658 1468 1535 xrf mor x-tay fluorescence analyses of morrison formation tuffs sample mc-9 nh-18 nh-52 bd-5 bd-8 nor-10 nor-11 sio2 76.66 83.94 87.66 82.21 81.59 tio2 0.22 0.27 0.25 0.24 0.30 al2o3 9.11 9.60 6.17 9.77 9.78 fe2o3 3.96 1.15 2.20 1.82 2.42 mno 0.18 0.02 0.04 0.05 0.05 mgo 1.93 0.42 0.66 0.71 0.90 cao 5.07 1.20 1.21 1.19 0.40 na2o 1.87 2.08 0.78 2.73 2.68 k2o 0.93 1.26 0.87 1.24 1.85 p2o5 0.07 0.06 0.16 0.04 0.03 loi 6.31 2.25 2.21 2.63 2.43 total 106.31 102.25 102.22 102.63 102.43 sc 4 2 8 4 9 17 14 v 44 34 39 23 39 87 86 cr 4 20 21 3 5 49 53 ni na na na na na 11 13 cu 1 14 12 9 11 21 14 zn 35 25 39 29 40 69 51 ga 9 13 7 11 11 32 22 rb 28 57 45 54 65 234 206 sr 437 158 78 178 143 292 204 y 31 21 22 18 18 51 53 zr 211 113 160 146 145 320 286 nb 9 13 7 11 9 32 23 ba 599 432 169 214 1405 126 156 la 15 23 24 14 12 67 61 ce na na na na na 132 119 nd 31 21 18 29 23 53 50 sm na na na na na 10.6 9.5 pb na na na na na 39 24 th 3 10 6 7 7 29 22 u na na na na na 4 3 geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 11 2024 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. the wasatch monocline, central utah—a pre-basin and range extensional structure shelley a. judge, david h. elliot, terry j. wilson, and kenneth a. foland geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view to the northeast of the wasatch monocline as expressed along manti canyon near manti, utah. significant east-west drainage transects are perpendicular to the monocline axial trace, exposing strata folded into the limb of the monocline. in manti canyon, the variegated beds of the cretaceous-paleocene north horn formation are capped by cliff-forming strata of the paleocene flagstaff formation. monocline flexure is punctuated by east-dipping antithetic normal faulting that displaces strata by tens to hundreds of meters. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 11 2024 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2023–2024 uga board president eugene syzmanski eugenes@utah.gov 801.537.3364 president-elect keilee higgs keileeann@utah.gov 801.537.3304 program chair chris stallard cstallard@utah.gov 801.386.0976 treasurer aubry dereuil aubry@zanskar.us 850.572.2543 secretary trae boman tboman@teanues.com 801.648.5206 past president rick ford rford@weber.edu 801.915.3188 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2023–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor william lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 11 2024 1 abstract the wasatch monocline is a major structure in the transition zone between the basin and range and colorado plateau physiographic provinces. the timing of formation of the monocline and its tectonic significance has been the subject of debate because it is an anomalous structural style for central utah. constraining the age for flexure and outlining the tectonic regime responsible for wasatch monocline formation are principal objectives of this research. field mapping near the southern end of the monocline revealed an unconformity between the older, middle eocene crazy hollow formation, included in monocline folding, and the younger, middle eocene (bartonian) formation of aurora deposited against the monocline. we report an incremental step-heating and direct single-grain laser fusion age of 38.0 ± 0.2 ma for biotite from an ash-flow tuff within the formation of aurora, which constrains monocline formation to no younger than the mid-eocene. structural data from the wasatch monocline, in the context of regional structural and tectonic analysis, indicate the monocline formed in an extensional regime as a forced fold or a rollover fold of the east-facing sanpete half-graben, formed during pre-basin and range extension, also recorded in the paleogene-neogene basins of utah valley and salt lake valley regions. the wasatch monocline, central utah—a pre-basin and range extensional structure shelley a. judge1, david h. elliot2, 3,terry j. wilson2, 4, and kenneth a. foland2, 5 1department of earth sciences, the college of wooster, wooster, oh 44691 usa; sjudge@wooster.edu 2 school of earth sciences, the ohio state university, columbus, oh 43210 usa; 3elliot.1@osu.edu; 4wilson.43@osu.edu; 5kfoland@ geology.ohio-state.edu citation for this article. judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a., 2024, the wasatch monocline, central utah—a pre-basin and range extensional structure: geology of the intermountain west, v. 11, p. 1–19, https://doi.org/10.31711/giw.v11.pp1-19. introduction importance of study most monoclines within the colorado plateau are prominent laramide structures, formed as drag folds above reactivated, high-angle, reverse faults due to contractional tectonics (e.g., kelley and clinton, 1960; davis, 1978, 1999; anderson and barnhard, 1986; erslev and rogers, 1993; bump, 2003). central utah is the physiographic transition zone along the boundary between the colorado plateau province to the east and the basin and range province to the west. the wasatch monocline is a broad and open fold with the form of typical regional monoclines; it extends for about 110 km (68 mi) through central utah and is the structural backbone of the transition zone (figure 1). the west-facing monocline also forms the western front of the wasatch plateau, a notable geomorphic feature of the region (figure 2). the wasatch monocline is in an area that has been subject to both contractional and extensional tectonics since the early cretaceous. the development of the monocline by either tectonic regime is of specific interest, because it is an anomalous structural style for central utah. no indisputable laramide-style deformation has been documented in the wasatch plateau region of central utah, and this research confirms that the wasatch monocline is not a laramide-style feature, characterized by monocline flexure due to high-angle, 2 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 reverse dip-slip motion of basement blocks (davis, 1978). new information on the wasatch monocline is invaluable for improving knowledge on the timing and extent of contraction or extension in the region, including correlating the timing of tectonic regimes to known events to the north and west. although workers have reported on wasatch monocline development for over 140 years (e.g., dutton, 1880; spieker, 1946; erb, 1971; willis, 1986; anderson et al., 2001; schelling et al., 2007), the timing and formation of the wasatch monocline has remained uncertain and controversial. previous workers have suggested a wide range of possible ages for monocline formation from the middle eocene through the early miocene (ca. 40 to 20 ma; e.g., spieker, 1949; erb, 1971; willis, 1986; witkind, 1994; anderson et al., 2001). spieker (1949) and his students generally accepted the monocline as late eocene to miocene in age using only stratigraphic and structural relationships. more recent age constraints have been based on radiometric age dates from several different formations (willis, 1986), but these radiometric dates have not extended the inferred age range significantly. the exceptions are anderson et al. (2001) and frank royse, jr. (chevron, written communication, 2020) who proposed that the monocline is miocene or younger, essentially making it a basin and range structure. purpose of research here we report new data to constrain the timing of monocline flexure and its relationship to contractional and/or extensional tectonics. new field-based information obtained to determine the timing of flexure includes studies on stress regimes, paleocurrents, stratigraphic field relationships, and 40ar/39ar dating. focused mapping near the southern end of the structure reveals an angular unconformity between older strata included in monocline folding and younger strata deposited unconformably against the monocline. these stratigraphic data bracket the timing of flexure by providing maximum and minimum ages of monocline formation. wasatch monocline age constraints can be combined with established tectonic information to provide a more comprehensive picture of changing stress regimes in a regional context. geologic setting regional tectonic setting the wasatch monocline resides in a key location in the complex mesozoic-cenozoic tectonic framework of central utah. the monocline lies in the transition zone, which separates the western margin of the colorado plateau province and the eastern margin of the basin and range province. it also lies along the late precambrian to paleozoic cordilleran sedimentary hingeline of central utah and with the eastern limit of the figure 1. regional dem map of central utah displaying the topographic highs and adjacent valleys. important geographic or geologic localities from the text are mapped for reference, including: the wasatch plateau, san pitch mountains, cedar hills, and valley mountains (black), sanpete, sevier, and juab valleys (black), the axial trace of the wasatch monocline (blue), and the wasatch and gunnison faults (red). the locations of rock and dry canyons and gulley south of black cap mountain (yellow) are also mapped. 3 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 figure 2. (a) photograph of the wasatch monocline in profile, as seen in manti canyon on the wasatch plateau. manti canyon is within the central part of the fold, signifying its highest structural relief. a series of east-dipping antithetic normal faults displace strata of the flagstaff formation and the north horn formation along the monocline limb, which dips west toward sanpete valley. view to the northeast. (b) schematic cross section across sanpete valley. modified from schelling et al. (2007). the red box indicates the placement of the photograph along the cross-section profile. the locations of the gunnison fault and ephraim faults bound sanpete valley to the west and east, respectively. ja = jurassic arapien formation; jt+kcm = jurassic twist gulch formation and cretaceous cedar mountain formation; kil = cretaceous indianola group, lower; kiu = cretaceous indianola group, upper; pc = precambrian strata; pgkn+pgf = cretaceous-paleogene north horn formation and paleogene flagstaff formation; pz = paleozoic strata; tr+j = triassic and jurassic strata. 4 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 cretaceous sevier fold-thrust belt. the utah hingeline, which geographically is oriented approximately northsouth along the center of the state, has long been recognized as a zone of crustal weakness and tectonic activity during many periods of utah’s geologic history (baer, 1976; ritzma, 1981; stokes, 1988; hintze and kowallis, 2021). central utah has undergone changes from one stress regime to another through time. structural overprinting shows both contractional features associated with sevier orogenesis and extensional features associated with oligocene-miocene and then basin and range extension. several studies have outlined the regional tectonic evolution. decelles and coogan (2006) proposed a regional thrusting chronology associated with the sevier fold-and-thrust belt of central utah (c.a. 145 to 65 ma; latest jurassic-early cretaceous to early paleocene). their chronology rewrote the previous tectonic interpretation for synorogenic deposits (see villien and kligfield, 1986). constenius (1996) and constenius et al. (2003) were instrumental in outlining the timing of pre-basin and range extension (ca. 49 to 20 ma; middle eocene to early miocene) throughout the western u.s. cordillera. they noted that the change from compressional to tensional stress regime was not synchronous everywhere, with northern segments of the sevier foldand-thrust belt showing extensional overprinting earlier in time. other studies conducted near the southern and northern extent of the monocline have focused on issues of structural overprinting. toward the southern end, cline and bartley (2007) tested five competing hypotheses on observed relationships of the cenozoic-jurassic geology of sevier valley. they determined that the principal process responsible for a unique contact in sevier valley was regional extension and called the fault the salina detachment. anderson et al. (2001) noted many neogene extensional features in the region near the town of salina, and therefore suggested a miocene or younger age for the wasatch monocline. they based their results on structural concordance and the absence of deposition against paleotopography of the monocline. north of the monocline, in the charleston-nebo segment of the sevier thrust belt, constenius et al. (2003) provided evidence for crustal extension (ca. late eocene to middle miocene) evidenced by reactivation of thrust structures to form half grabens. monocline expression the wasatch monocline is a north-northeast-trending, west-verging monocline in sanpete-sevier valleys of central utah exposed between millburn and salina canyon for approximately 110 km (68 mi) (figure 1; willis, 1986). its northern segment trends 020° to 030°; however, there is a noticeable change in the anticlinal axial trace to 000° to 005° near its southern end. the wasatch monocline, a major geomorphic feature, is a doubly plunging fold, with its highest topographic expression and structural relief (1710 m; 5600 ft) in the central part of the fold (figure 2). topographic relief in the northern and southern ends is approximately 850 m (2790 ft) and 700 m (2297 ft), respectively. mcgookey (1958) attributed this reduced relief at the southern end to less displacement, to less resistant strata exposed at the surface, and to the overlap of folded units by younger strata. access to monocline exposures is excellent not only along the trend of the monocline, but also across the monocline flexure due to several cross-strike structural transects formed by large drainage basins. in profile, nearly flat-lying paleogene sedimentary strata that dip less than 10° west form the plateau summit; these strata are displaced by several northeast-southwest-striking en echelon grabens. the plateau grabens are large-scale features that dominate the landscape of the summit. smaller shoulder grabens and east-dipping antithetic normal faults break the continuity of the folded strata within the anticlinal hinge zone of the wasatch monocline. along the limb of the monocline, strata dip 15° to 40° west—steepest within the central part of the monocline limb—and are cut by a series of antithetic normal faults that divide the limb into distinct structural domains (figure 2). in each structural domain, smaller-scale mesoscopic normal faults, joints, and veins are prominent. eventually, limb strata plunge beneath the adjacent sanpete valley; a broad, synclinal hinge has been interpreted at depth in several balanced structural cross sections of the region (schelling et al., 2007). 5 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 regional stratigraphy geologic units are well exposed along the length and width of the wasatch monocline due to the several east-west-drainage transects. units exposed in the central part of the monocline include the cretaceous to paleogene north horn formation and the paleogene flagstaff, colton, green river, and crazy hollow formations (figure 3). the north horn formation represents shallowing of the foredeep during gunnison thrust emplacement during the sevier orogeny (decelles and coogan, 2006). flagstaff through crazy hollow strata were deposited during times of laramide uplift, which produced areas of high topographic relief separated by numerous basins (dickinson et al., 1988). in central utah, intermontane ponded basins dominated, and the flagstaff and green river formations represent lacustrine intervals that interfingered with siliciclastic-rich colton and crazy hollow fluvial units (stanley and collinson, 1979; weiss and warner, 2001; davis et al., 2009; dickinson et al., 2012). additional units with significant volcanic/volcaniclastic components are exposed along the monocline at its extreme northern and southern ends. at the northern end, the moroni formation laps onto the green river formation in several places, and in all probability, also laps onto the crazy hollow formation along the eastern flanks of the cedar hills (fograscher, 1956; albrecht, 2001; weiss and warner, 2001). moroni k/ar dating from cedar hills samples, conducted by albrecht (2001), provided a 34.3 ± 0.3 ma age for the formation. at the southern end, beds assigned to the formation of aurora by willis (1986) lap onto the monocline; we show here that aurora strata figure significantly in the geologic history of monocline flexure. the formation of aurora was proposed by willis (1986; replaced bald knoll formation) but not formally defined. willis (1986) described it as a sequence of “interbedded mudstone, bentonitic shale, limestone and sandstone.” he further mentions that the formation becomes increasingly volcanic toward the south (away from salina) and includes rhyolitic ash-flow tuff. for purposes of this research, we follow the stratigraphic definition of the formation of aurora set by willis (1986) but acknowledge that aurora formation was used in a stratigraphic column by hintze and kowallis (2021). competing hypotheses for monocline development there are several competing hypotheses to explain the origin and timing of wasatch monocline development: (1) contractional folding associated with the final stages of the sevier orogeny (e.g., spieker, 1946; standlee 1982; lawton, 1985; villien and kligfield, 1986); (2) differential subsidence due to salt tectonics (e.g., witkind, 1992, 1994); (3) laramide-style contractional deformation above a reactivated, high-angle reverse fault, modeling many other monoclines in the colorado plateau (for research on verified laramide monocline examples, see davis, 1978; reches and johnson, 1978; yin, 1994; davis and bump, 2009; keating et al., 2012); and figure 3. generalized stratigraphic column of principal units affected by flexure of the wasatch monocline in the southern portion of the study area. thickness data taken from the mouth of salina canyon. modified from hintze and kowallis, 2021). k = cretaceous; m = maastrichtian. 6 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 (4) extensional deformation associated with a younger tensional regime (anderson et al., 2001; schelling et al., 2007; frank royse, jr., chevron, written communication, 2020). these several competing hypotheses coincide with three different orogenic events affecting the region (i.e., sevier, laramide, and basin and range tectonism) and with the wide range of proposed ages for development of the monocline (middle eocene through the early miocene or even younger; e.g., spieker, 1949; erb, 1971; willis, 1986; witkind, 1994; anderson et al., 2001; frank royse, jr., chevron, written communication, 2020). methods this research tests the hypotheses for monocline origin through an integrated, primarily field-based study of the development and timing of flexure. we obtained a series of data sets (i.e., field mapping, stereonet analysis on stratal bedding, and ash-flow tuff geochronology) and combined data about the geologic structures of the region and the age, lateral extent, and sedimentary characteristics of regional formations. field mapping the most important locality with respect to monocline timing is in a gulley southwest of the summit of black cap mountain and west of twist canyon (utm 12 s. 0423792 e., 4310373 n.; figures 4 and 5). here, aurora beds are in contact with the crazy hollow formation, and the nature of this contact has been uncertain for decades in the literature. willis (1986) indicated the importance of finding a depositional relationship between the two units in this region; however, it was erb (1971) who first provided clues as to where this depositional relationship might be located, even though he did not definitively identify the crazy hollow formation. in his thesis, erb (1971) stated, “unless some future worker can determine, without doubt, the identity of the crazy hollow(?) wedge, this particular angular unconformity will be of little use in determining the validity of…flexing of the wasatch monocline.” the suggestion of an angular unconformity in this area provided incentive to include black cap mountain as a figure 4. geologic map of the area south of black cap mountain. the red star in the center of the map marks the viewpoint for figure 5 (photograph of the gulley transect). 7 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 field mapping site in this study. this research clarifies the nature of the spatial relationships and the contact between the crazy hollow formation and the formation of aurora. the goal of field mapping near black cap mountain was (1) to identify definitively each unit in the field, and (2) to locate and to interpret either a conformable or unconformable contact between the two units (figure 4). although we had scoured the trend of the monocline for exposures that provided concrete spatial relationships, only the southern end of the monocline was suitable for detailed mapping. using unit descriptions for crazy hollow and for aurora strata (willis, 1986; weiss and warner, 2001), we identified both units. a northeast-southwest transect through one gulley was used to measure and to document the numerous bedding attitudes of both units near the contact (crazy hollow, n = 22; aurora, n = 38) (figure 5). we constructed a detailed stratigraphic column (figure 6) that starts above the characteristic red beds of the crazy hollow formation but includes its typical ‘salt-and-pepper’ sandstone and terminates at the unconformably overlying ash-flow tuff within aurora strata. careful field mapping in the area documented bedding patterns, small-scale faulting, and contacts between exposed units (figure 4). finally, we gathered stratigraphic thickness data between two selected beds—one bed in the crazy hollow and the other in the aurora—to test for stratigraphic consistency along three separate transects, each progressively closer to the monocline fold axial trace. this was done to discount any other structural explanation responsible for bedding attitude disparities. stereonet analysis we undertook data analysis of bedding attitudes in both the crazy hollow formation and the formation of aurora (figure 7). because of the impact of multiple deformation events in the area and small-scale faulting east of the gulley, only measurements from the northeast-southwest-gulley transect were used for final analysis to prevent any chance of comparing attitudes from figure 5. photograph of the gulley south of black cap mountain that shows the spatial relationships between the crazy hollow formation (pgch) and the overlying and onlapping formation of aurora (pgau). the ash-flow tuff is apparent in the bottom right of the photograph, and an arrow designates where samples were collected for 40ar/39ar age dating. the thickness associated with each resistant bed correlate to the stratigraphic placement within the graphic column in figure 6. 8 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 different fault blocks. bedding measurements from a single formation within a single fault block were plotted, and the average bedding orientation was determined from the contoured maxima of poles to bedding planes. both the crazy hollow and aurora average bedding planes were rotated to restore bedding in aurora strata back to horizontal to simulate its attitude at the time of its deposition. the resultant stereonet shows the attitude of the crazy hollow formation at the time of deposition of aurora strata (figure 7), documenting their angular discordance. ash-flow tuff exposures field observations at black cap mountain focused on white to gray ash-flow tuff beds in the lower part of aurora strata. for this study, samples for analysis were taken from the least weathered interval near the base of the ash-flow tuff and again at about 7.6 m (25 ft) above the base of the unit (figure 7). biotites within the ash-flow tuff were dated using two different 40ar/39ar techniques, incremental step-heating and direct, single-grain laser fusion, following the methods described in mcdougall and harrison (1988, 1999) and foland et al. (1993). our goal was to compare these 40ar/39ar dates to previous age dating of the aurora. willis (1986) described three k/ar radiometric dates from nearby localities: 40.5 ± 1.7 ma from the lower part of the unit in the southernmost salina 7.5-minute quadrangle, about 5.5 km (3.4 mi) to the south-southeast, and 39.6 ± 1.5 ma and 38.4 ± 1.5 ma from near the top of the unit in the adjacent aurora 7.5-minute quadrangle, about 9.3 km (5.8 mi) to the west. field results and analysis angular discordance near black cap mountain constraining the timing of wasatch monocline flexure is a primary aim of this research. black cap mountain is the only known place where a depositional contact between the beds involved in wasatch monocline flexure and overlapping beds are exposed. due to subsequent erosion and deformation along the trend of the monocline, no other localities provide this critical field relationship. at this locality, red beds assignable to the crazy hollow formation are overlain by 43.3 m (142 figure 6. stratigraphic column of part of the crazy hollow formation and the formation of aurora. the column was measured in a prominent gulley south of black cap mountain and shown in figure 5. 9 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 ft) of strata comprising mudstone, siltstone, sandstone, and thin micrite beds (figures 5 and 6). this sequence includes thin sandstones with black chert grains characteristic of the crazy hollow formation, but otherwise it is atypical of that formation and somewhat similar to aurora strata as described by willis (1986, 1988). this 43.3 m-thick (142 ft) interval is overlain by a white ashflow tuff, which itself is overlain by a sequence of volcaniclastic sandstones and tuffaceous beds that share similarities with both aurora strata and the “unnamed sandstone, mudstone and conglomerate beds” of willis (1986). field mapping supports a difference in the attitudes between the crazy hollow formation and aurora strata (figure 4). bedding analysis along our northeast-southwest transect demonstrates an angular discordance of about 15° between the aurora ash-flow tuff and the underlying beds (figure 7). the average bedding attitude for the crazy hollow beds beneath the unconformity is 316°, dip 29° ne. (n. 44° w., dip 29° ne.), whereas that figure 7. (a) stereonet plots showing the average bedding attitude from measurements taken from the crazy hollow formation and the formation of aurora in the vicinity of the mapped area shown in figures 4 and 5. field data from the crazy hollow show an average orientation of 316°, dip 29° ne. (n. 44° w., dip 29° ne.), whereas field data from the aurora show an average orientation of 319°, dip 45° ne. (n. 41° w., dip 45° ne.). (b) raw field data of aurora strata were rotated back to horizontal (a fold test) to determine the orientation of the crazy hollow formation at the time the aurora was being deposited. when the aurora was horizontal (0° dip), the crazy hollow was oriented 144°, dip 16° sw. (s. 36 e., dip 16° sw.). an idealized cross section (without antithetic normal faults) shows the discordant relationship between crazy hollow and aurora strata. 10 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 for the aurora ash-flow tuff and overlying strata is 319°, dip 45° ne. (n 41° w., dip 45° ne.). when the ash-flow tuff is rotated back to horizontal during the fold test, the underlying fine-grained strata and the definitive crazy hollow beds assume an average attitude of 144°, dip 16° sw. (s 36° e., dip 16° sw.) (figure 7). thus, at the time of deposition of the ash-flow tuff, the underlying eroded and truncated beds were dipping about 15° southwest and therefore were part of the west-dipping limb of the wasatch monocline. these transect bedding results replicated in all bedding data produced from field mapping of both units in the area. our stratigraphic column (figure 6) starts above the characteristic red beds of the crazy hollow formation, includes its typical salt-and-pepper sandstone, and terminates at the unconformably overlying the ashflow tuff. thin micrite beds in that interval are a key to demonstrating the angular discordance. thickness transects of stratigraphic intervals between selected crazy hollow micrite marker beds and the ash-flow tuff demonstrate increasing thickness between the markers from east to west up the gulley wall. these differences in stratigraphic thickness show that the ash-flow tuff unit is progressively thinning to the east toward the mapped axial trace of the wasatch monocline. these data demonstrate the presence of a westward-thickening wedge that onlaps the monocline limb and can be dated to give an upper age limit for monocline flexure. the angular relationship just described raises several stratigraphic issues. if the 43.3-m (142 ft) section of beds above the typical red crazy hollow strata and below the unconformity are assigned to the crazy hollow formation, then it represents a depositional environment unlike any other in that formation. if they should be assigned to the formation of aurora, then the ash-flow tuff above the unconformity could be assigned to the “unnamed sandstone, mudstone and conglomerate beds” of willis (1986). alternatively, if the 43.3-m (142 ft) section and the overlying ash-flow tuff belong to aurora strata, the angular relations could be evidence for a progressive unconformity developed by temporal coincidence of monocline deformation and deposition of aurora strata. for the purposes of this discussion, the ash-flow tuff is assigned to the aurora. geochronology dating the ash-flow tuff is critical to this study because of its relationship to older crazy hollow beds near black cap mountain. the ash-flow tuff is easily identified in the field. the white to pale-gray tuff is rhyolitic in composition and contains abundant pumice fragments and hexagonal to pseudo-hexagonal biotite. the two different 40ar/39ar techniques of incremental step-heating and direct, single-grain laser fusion yielded consistent radiometric dates for the biotites (figure 8). two step-heating runs gave well-defined plateaus with remarkably similar plateau ages (tp) of 37.9 ± 0.2 ma and 38.0 ± 0.2 ma. for each run, the isotope correlation ages (tic) are identical to the plateau ages. one run by the single-grain laser fusion technique on 24 grains was conducted. several grains had large uncertainties, and these were rejected, leaving 17 grains in the final estimated date of 38.2 ± 0.2 ma (weighted by age uncertainties), which does not differ from the date derived from all 24 grains. the date obtained from weighting each analysis by the amount of 39ar released is 38.5 ± 0.3 ma. the isotope correlation age for the single grain analyses (n = 17) is 38.1 ± 0.2 ma, although it is not a particularly well-constrained correlation. dates obtained in this study range from 37.9 ± 0.2 ma to 38.5 ± 0.3 ma. most dates cluster around 38.0 ma. therefore, a best estimate age of 38.0 ± 0.2 ma is accepted for the aurora ash-flow tuff. because initiation of flexure is older than the base of the ash-flow tuff that onlaps the limb of the wasatch monocline, the accepted 40ar/39ar date provides a minimum age for flexure of the monocline: namely, pre-late eocene (pre-priabonian). discussion critical age relationships the wasatch monocline did not have significant topographic relief during eocene crazy hollow deposition. paleocurrent directions, collected from the crazy hollow in the sanpete-sevier valley, indicate a general flow pattern from south-southeast to north-northwest through the area where the wasatch monocline presently stands (judge, 2007). these patterns suggest that the wasatch monocline did not affect paleoflow during 11 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 fi gu re 8 . a ge d at in g re su lts fr om th e as hflo w tu ff in th e fo rm at io n of a ur or a. (a a nd b ) 40 a r/ 39 a r i nc re m en ta l-h ea tin g re le as e pa tte rn fo r b io tit e; t in t = in te gr at ed a ge ; t p = p la te au a ge . th e a cc ep te d ag e f or th e a irf al l t uff n ea r t he b as e o f t he fo rm at io n of a ur or a is 38 .0 ± 0 .2 m a. (c ) 40 a r/ 39 a r s in gl e gr ai n fu sio n pa tte rn fo r b io tit e; t av g = a ve ra ge a ge ; t ic = is ot op eco rr el at io n ag e. si ng le g ra in fu sio n ag es c om pa re fa vo ra bl y w ith th e in cr em en ta l st ep -h ea tin g re su lts . 12 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 deposition of the unit. unfortunately, the age of the crazy hollow formation is poorly constrained. previous age dating includes three stratigraphically disparate airfall tuffs from the underlying green river formation in sanpete valley that yielded biotite ages of about 46.4 to 43.1 ma by 40ar/39ar analysis (sheliga, 1980). the aurora ash-flow tuff gives a minimum age for monocline flexure of 38.0 ± 0.2 ma (figure 8), with fold initiation preceding ash-flow deposition. this aurora ash-flow tuff age is slightly older than ages for the volcanic/volcaniclastic moroni formation of the cedar hills and south of thistle farther to the north, both near the northern end of the wasatch monocline. k/ar ages between 30.6 ± 1.1 ma to 37.8 ± 2.2 ma on biotite, plagioclase, and hornblende separates, were obtained by witkind and marvin (1989), whereas 40ar/39ar dates of 34.3 ± 0.3 ma on biotite from an ash-flow tuff and 37.5 ± 0.1 ma on amphibole from a sandstone were obtained by albrecht (2001). the hornblende analyzed by witkind and marvin (1989) came from an ash-flow tuff south of thistle, but its stratigraphic position is not recorded. the detrital amphibole (albrecht, 2001) only gives a maximum age of deposition of the moroni formation. constenius et al. (2003) reported two sanidine dates from pumice clasts at the base of the moroni formation south of thistle. these are 34.4 ± 0.1 ma and 34.6 ± 0.1 ma and are similar to the biotite date obtained by albrecht (2001) for an ashflow tuff. end of sevier contraction sevier orogenesis impacted the sanpete valley region, from the san pitch mountains in the west to the wasatch plateau in the east. contractional events, in the form of a north-northeast-trending, west-vergent monocline (the rock and dry monocline) and several thrust faults, are exposed along the eastern margin of the san pitch mountains (kilmer, 1988; judge et al., 2011). many previous workers attributed formation of the rock and dry monocline to contractional events associated with the final stages of the sevier orogeny (e.g., spieker, 1946; standlee, 1982; lawton, 1985; villien and kligfield, 1986; kilmer, 1988). lawton and weiss (1999) and weiss and sprinkel (2002) mapped the area in 7.5-minute quadrangles and suggested that the rock and dry monocline was a fault-propagation fold that formed during the late eocene to oligocene or post-early eocene, respectively. two authors herein (judge et al., 2011) undertook a modern structural analysis of the rock and dry monocline, following initial work done by kilmer (1988). structural work on the rock and dry monocline focused on the near-continuous exposures of units involved in monocline flexure, with a focus on dip domain stations along cross-strike transects in the paleogene flagstaff limestone (figure 3). kinematic data and analyses of these mesoscopic structural features (stylolites and teeth, calcite veins, and thrust faults) of the rock and dry monocline indicated that an east-west compression (trend 278° to 098° [n. 82° w. to s. 82° e.]) preceded flexure and continued as the monocline developed. this maximum compression direction is sub-perpendicular to the trend of the monocline. west-vergent thrust faults with an average orientation of 020°, dip 42° se. (n. 20° e., dip 42° se.) along east-dipping bedding planes in the jurassic twist gulch formation place the twist gulch over the campanian-paleocene north horn formation. the back thrusts caused localized flexure and uplift of paleogene strata in the area into a fault-propagation fold. these thrust-fold spatial associations and the evidence for layer-parallel compression clearly link rock and dry monocline formation with forced-folding associated with west-vergent thrusting and regional compression of the sevier thrust belt. the rock and dry monocline, therefore, was developed in the latest stage of back thrusting associated with the gunnison thrust system in the easternmost sevier thrust belt (kilmer, 1988; judge et al., 2011). the timing of the rock and dry monocline has regional tectonic implications. because the paleocene to lower eocene colton formation (figure 3) is the youngest unit visibly affected by rock and dry monocline folding, flexure and amplification of the monocline occurred after deposition of at least the lower approximate 60 m (197 ft) of the colton. if the overlying green river formation, exposed only to the west of the rock and dry monocline at higher elevations, is also involved in that flexure, then the green river ash beds dated at about 46 to 43 ma (sheliga, 1980) provide a maximum 13 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 age of post-early eocene for the contractional rock and dry monocline. considering a younger age limit for the green river formation of about 42 ma, then this back thrusting likely occurred prior to about 41 ma. it was the youngest phase of sevier orogenesis in this region. pre-monocline extension the limb of the wasatch monocline is dominated by normal faults, both large-scale antithetic faults and hundreds of small-scale mesoscopic faults (judge, 2007). these faults, some of which are accommodation features resulting from flexure, document multiple slip events and divide the limb into several distinctive north-south-trending structural domains. although strike-slip faults occur locally, normal faults are by far the most abundant and pervasive structures. reverse or thrust faults are nearly absent along the monocline summit and limb, as are tectonic stylolites (judge, 2007). in addition to the abundant normal faults, each structural domain exposes prominent smaller-scale, mesoscopic joints and calcite veins within paleogene units. data from the systematic joints and veins (i.e., attitude, spacing, density, morphologic, and mineralogic characteristics) were collected along several cross-strike transects for a kinematic analysis across the monocline. simple fold test analyses of the joints and veins show that these fractures formed prior to the limb rotation of the wasatch monocline (judge, 2007). therefore, a tensional stress regime in the sanpete valley region pre-dated monocline flexure. this tensional regime suggests that the wasatch monocline formed in a different and younger tectonic regime than the sevier-influenced rock and dry monocline, just west across the valley (judge, 2007). based on the dated unconformable relations discussed previously, the change to a tensional regime occurred in the eocene prior to monocline flexure. evidence of pre-basin and range extension in central utah, there is no evidence of laramide-style, basement-cored uplifts distinct to other regions influenced by contractional tectonics. the longlived compressional sevier stress regime that produced localized rock and dry monocline back thrusting was replaced by a tensional stress regime in the eocene. cordilleran pre-middle miocene extension is well documented, with some evidence for extension as early as the eocene (e.g., burchfiel et al., 1992; axen et al., 1993; murphy et al., 1998; rowley et al., 1998). there is ample evidence of mid-cenozoic extension in utah. to the north of our study area, constenius (1996) and constenius et al. (2003) have documented extension in the uinta arch region and northward along the wyoming border. this period of extension has been attributed to gravitational collapse following cessation of sevier contractional tectonism (constenius, 1996; vogel et al., 2001; constenius et al., 2003). to the west and south of our study area, geologic contacts in sevier valley show evidence for regional tectonic extension (cline and bartley, 2007). on a broader scale, constenius et al. (2003) pointed out that this mid-cenozoic extension is recorded regionally by the metamorphic core complexes in northeastern nevada and adjacent idaho. in particular, the snake range detachment has been dated as no older than ca. 35 ma, the age of the regionally extensive kalamazoo ash-flow tuff deposited on a subdued landscape (e.g., gans et al., 1989; miller et al., 1999). during the mid-cenozoic, there was extensive volcanism in utah, linked with the transition from regional contraction to extension (e.g., constenius 1996; constenius et al., 2003). the volcaniclastic aurora strata and our new age at black cap mountain likely reflect this regional framework. we establish a 38 ma age for the aurora ash-flow tuff. this age is slightly older than the ages of 33.5 to 36.6 ma given for emplacement of the keetley volcanics, which are a part of the wasatch intrusive belt and located in the central wasatch range, east-southeast from salt lake city (vogel et al., 2001; constenius et al., 2003). the age for the aurora ash-flow tuff also is slightly older than the age assigned to tephras in the tibble half graben on the south flank of the uinta arch (constenius et al., 2003). the oldest tephra from basin-fill in the tibble half graben has been dated at 36.4 ± 0.2 ma using a biotite 40ar/39ar plateau age (vogel et al., 2001). finally, the marysvale volcanic field lies 65 km (40 mi) to the south-southwest of our study area; however, there is no indication that its initial volcanism, which is accepted at 32 ma (steven et al., 1978; cunningham et al., 2007), was active at the time of aurora 14 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 ash-flow tuff deposition. for central utah, constenius (1996) and constenius et al. (2003) proposed that, south of 40° n. latitude, extension began at about 39 ma; they bracketed extension regionally based on the relationships between the ages of the youngest foreland basin deposits, paleogene volcanic/volcaniclastic deposits, and synextensional basin-fill. constenius et al. (2003) showed a series half grabens bounded by normal faults in their work on the charleston-nebo salient of the utah thrust belt to the north of this study. in these half grabens, pre-extension strata have rollover fold geometries and underlie basin deposits characterized by symmetrical stratal growth. one of the obvious extensional structural features of sanpete valley is the gunnison fault (also called the valley fault and the wales fault; see fong, 1995; lawton and weiss, 1999; weiss and sprinkel, 2002; main, 2015), which forms the structural boundary between sanpete valley and the san pitch mountains (figure 1). the fault is an east-dipping normal fault with several thousand meters of offset. from well data, sprinkel (1994) shows paleogene units with 945 m (3100 ft) of stratigraphic offset between the san pitch mountains and the underlying sanpete valley. the gunnison fault’s 60° east dip at the surface becomes listric at depth below sanpete valley and is responsible for the formation of a half graben beneath the valley; the san pitch mountains are its horst block to the west (e.g., fong, 1995; lawton and weiss, 1999; schelling et al., 2007; main, 2015). weiss and sprinkel (2002) suggested that early movement along the fault might have occurred during the miocene. here we suggest that the formation of the sanpete half graben, a result of movement along the gunnison fault, could have been initiated at the same time (ca. 39 ma) as proposed by constenius et al. (2003) for the region immediately to the north. the gunnison fault remains in a tensional stress regime, as recent alluvium north of the rock and dry monocline is cut by the fault, and fault scarps are evident in outcrop (e.g., fong, 1995; lawton and weiss, 1999; weiss and sprinkel, 2002). formation of the wasatch monocline during extension we document a narrow time window between contractional deformation and extensional deformation between about 41 to 38 ma, which agrees with the proposed timing of early extension for central utah (constenius, 1996; constenius et al., 2003). therefore, we argue that the wasatch monocline formed in an extensional setting. there is a spatial proximity between the wasatch monocline and the subsurface west-dipping ephraim fault interpreted from seismic data (moulton, 1976; schelling et al., 2007). the ephraim fault has typically been interpreted as a normal fault that formed as part of the eastern boundary of the middle jurassic sanpete-sevier rift. some recent interpretations, however, suggest post-jurassic reactivation of the ephraim fault during neogene basin and range extension (e.g., schelling et al., 2007; frank royse, jr., chevron, written communication, 2020). this suggests a model of the monocline as a forced fold above a west-dipping subsurface normal fault, analogous to folds modeled by withjack et al. (1995). the age data reported here, however, indicates monocline formation in the eocene, associated with pre-basin and range extension. an alternative model is development of the monocline as a rollover fold associated with a half graben bound to the west by the listric, east-dipping gunnison fault that forms the sanpete half graben (schelling et al., 2007). analogous rollover folds in extensional settings (see models of groshong, 1989; schlische, 1995; poblet and bulnes, 2005; withjack and schlische, 2006; uzkeda et al., 2014) have many of the same general features as those of the wasatch monocline: (1) a lower limb that is either horizontal or dips slightly toward the major fault; (2) synthetic and antithetic faults displacing the fold limb; and (3) the presence of a shoulder graben near the anticlinal hinge of the monocline (withjack et al., 1995). rollover folds exhibit axial traces parallel to subparallel to the strike of major listric normal faults (schlische, 1995). in the case of the wasatch monocline, its axial trace (020° to 030° in the northern segment, 000° to 005° in the southern segment) is subparallel to the trace of the gunnison fault, which is segmented and varies from 005° to 030°. we prefer the rollover model given the newly documented timing of monocline development during the regional development of extensional half grabens during 15 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 sevier orogenic collapse, as documented by constenius et al. (2003). future modeling work is planned to test compatibility of these extensional folding mechanisms with the architecture of the wasatch monocline. conclusions the purpose of this research is to better constrain the age of wasatch monocline flexure and to improve our understanding of the geologic history of central utah regarding the change from the sevier compressional stress regime to the pre-basin and range tensional stress regime. three lines of evidence provide information about the timing and affiliated stress regime of monocline flexure: (1) the transition from contraction in the rock and dry monocline to extension and development of the wasatch monocline in a short time window in the eocene, (2) paleoflow patterns of paleogene fluvial systems that crossed central utah without deflection by topography at the site of the monocline, and (3) the age of a volcaniclastic unit in the formation of aurora deposited as a wedge onlapping the wasatch monocline during flexure. biotite from an ash-flow tuff at the base of the onlapping formation of aurora at the southern end of the wasatch monocline yielded a best estimate 40ar/39ar age of 38.0 ± 0.2 ma. thus, the wasatch monocline flexure was initiated after the middle eocene (using sanpete valley green river formation biotite dates) but before the upper eocene ash-flow tuff at the base of the aurora. in contrast to both sevier deformation and classical laramide monocline formation, the wasatch monocline is interpreted here to have most likely formed as a rollover fold associated with a half graben in an extensional setting. because the wasatch monocline documents early extensional tectonics in the region, the development of the monocline must post-date sevier orogenesis. this interpretation of the wasatch monocline supports weiss and sprinkel (2002) and more recent work in sanpete and sevier valleys by cline and bartley (2007), schelling et al. (2007), and main (2015). if wasatch monocline development occurred during this tensional stress regime, then it is one of the first documented occurrences of pre-basin and range extension affecting sanpete-sevier valley and extends the region of extension related to gravitational collapse of the sevier thrust belt defined by constenius (1996) and constenius et al. (2003) in northern utah. acknowledgments this research was supported by funds from the american association of petroleum geologists, the colorado scientific society, the geological society of america, the college of wooster, the ohio state university graduate school, the society for sedimentary geology, and sigma xi. special thanks to field and lab assistance from j. olney (hillsborough community college), d. caccamise (noaa national geodetic survey), f. hubacher (the ohio state univerity), k. lewandowski (eastern illlinois university), and to t. brunner (college of wooster) and j. robison (college of wooster) for graphical design assistance. the authors enjoyed conversations on the geology of central utah with w. ausich (the ohio state university), j. collinson (the ohio state university), l. krissek (the ohio state university), d. sprinkel (utah geological survey), c. summerson (the ohio state university), and g. willis (utah geological survey). thanks to r. allmendinger (cornell 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sedimentation in central utah, in petersen, j.a., editor, paleotectonics and sedimentation in the rocky mountain region, united states: american association of petroleum geologists memoir 41, p. 281–307. vogel, t.a., cambray, f.w., and constenius, k.n., 2001, origin and emplacement of igneous rocks in the central wasatch mountains, utah: rocky mountain geology, v. 36, no. 2, p. 119–162. weiss, m.p., and sprinkel, d.a., 2002, geologic map of the manti 7.5-minute quadrangle, sanpete county, utah: utah geological survey map 188, 22 p., 2 plates, scale 1:24,000. weiss, m.p., and warner, k.n., 2001, the crazy hollow formation (eocene) of central utah: brigham young university geology studies, no. 46, p. 143–161. weiss, m.p., mcdermott, j.g., sprinkel, d.a., banks, r.l., and biek, r., 2003, geologic map of the chriss canyon quadrangle, juab and sanpete counties, utah: utah geological survey map 185, 26 p., 2 plates, scale 1:24,000. willis, g.c., 1986, geologic map of the salina quadrangle, sevier county, utah: utah geological and mineral survey map 83, 20 p., 2 plates, scale 1:24,000. willis, g.c., 1988, geologic map of the aurora quadrangle, sevier county, utah: utah geological and mineral survey map 112, 21 p., 2 plates, scale 1:24,000. withjack, m.o., and schlische, r.w., 2006, models of extensional fault-bend folds, in buiter s.j.h., and schreurs g., editors, analogue and numerical modelling of crustal-scale processes: geological society of london special 19 the wasatch monocline, central utah—a pre-basin and range extensional structure judge, s.a., elliot, d.h., wilson, t.j., and foland, k.a. geology of the intermountain west 2024 volume 11 publication 253, p. 285–305. withjack, m.o., islam, q.t., and la pointe, p.r., 1995, normal faults and their hanging-wall deformation—an experimental study: american association of petroleum geologists bulletin, v. 79, no. 1, p. 1–18. witkind, i.j., 1992, paired, facing monoclines in the sanpete-sevier valley area, central utah: the mountain geologist, v. 29, no. 1, p. 5–17. witkind, i.j., 1994, the role of salt in the structural development of central utah: u.s. geological survey professional paper 1528, p. 1–145. witkind, i.j., and marvin, r.f., 1989, significance of new potassium-argon ages from the goldens ranch and moroni formations, sanpete-sevier valley area, central utah: geological society of america bulletin, v. 101, p. 534–548. yin, a., 1994, mechanics of monoclinal systems in the colorado plateau during the laramide orogeny: journal of geophysical research, v. 99, no. b11, p. 22,043–22,058. what factors influence our reconstructions of morrison formation sauropod diversity? geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 6 2019 © 2019 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover based on morphology alone, differing attributes (including body size, cranial, vertebral, and limb morphologies) between two specimens could result in the interpretation that they are distinct. conversely, from just histology, only age is assessed from a growth perspective. however, by increasing the lines of evidence, by incorporating both morphology and histology, we can more accurately account for a growth series. growth is gradational, so we should expect to see not just the extremes, but transitional forms as well. human scale bar is augustus saint-gaudens’ diana of the tower, depicting diana as 1.83 m. diplodocus sp. silhouettes originally based on art by s. hartman available via phylopic (creative commons attribution-sharealike 3.0 unported). i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 6 2019 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors president leslie heppler lheppler@utah.gov 801.538.5257 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 treasurer greg gavin greg@loughlinwater.com 503.509.1509 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 past-president peter nielsen peternielsen@utah.gov 801.537.3359 uga board october 2019 – september 2020 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielson gnielson@weber.edu 801.626.6394 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — utah field house of natural history state park museum cary woodruff — university of toronto octavio mateus — universidade nova de lisboa geology of the intermountain west an open-access journal of the utah geological association volume 6 2019 93 abstract the upper jurassic morrison formation classically represents the “golden age” of sauropods, and the morrison formation is reported to have yielded 13 genera and 24 species of sauropods. this incredible diversity has produced numerous theories attempting to reconcile the co-occurrence of such large, and similar taxa. previously, a comparably high diversity has been proposed for the late cretaceous hell creek formation of north america – possibly comprising nearly three dozen species from over 20 genera of ankylosaura, caenagnathids, ceratopsians, dromaeosaurids, hadrosaurs, ornithomimids, pachycephalosaurs, thescelosaurs, and tyrannosaurs. however, much of the morphologic variation previously ascribed to taxonomic differences has recently been shown to be a result of stratigraphy and/or ontogeny – resulting in this rich assemblage being downsized to 13 genera and 16 species. whereas still rich in diversity, such factors have an immediate effect towards our reconstruction of true richness. following the example of the hell creek formation, we can investigate the ontogenetic and stratigraphic origin of possible diversity inflation in other formations, and within this study, apply it to the morrison formation. new dating techniques are resulting in finer temporal resolution, and are changing the temporal position of well-known quarries. differences in body size and ontogenetic stages can also affect diversity estimates. plotting body size stratigraphically, it initially appears that larger specimens (interpreted as different species) occur higher in the section. an increase in average body size may be a legitimate trend, but there are several specimens that counter this “rule” for many genera. likewise, dramatic allometric ontogenetic trajectories have led to the erection of at least three diplodocid genera – amphicoelias, seismosaurus, and suuwassea – and it is suspected that many more morrison formation “species” could alternatively be explained as ontogimorphs. we have a long way to go towards revealing the true nature of morrison formation sauropod diversity. although dietary partitioning undoubtedly occurred at the level of both the species (e.g., brachiosaurus vs. diplodocus) and between ontogenetic stages, a base of 24 levels of co-occurring divisions seems unlikely. the morrison formation may have exhibited a sauropod-rich assemblage unlike any other in north america, and the implications of stratigraphy, ontogeny, and variation may be minor, yet these factors alter perceived “diversity.” true diversity will not be fully understood unless these factors are considered. what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff1,2,3 1royal ontario museum, 2department of ecology and evolutionary biology, university of toronto, toronto, ontario, canada, 3great plains dinosaur museum & field station, malta, mt, usa; sauropod4@gmail.com citation for this article. woodruff, d.c., 2019, what factors influence our reconstructions of morrison formation sauropod diversity?: geology of the intermountain west, v. 6, p. 93–112. © 2019 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 94 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 introduction the upper jurassic morrison formation of the western united states of america was home to some of the most classic of dinosaur species. though the morrison formation is well known for theropods (e.g., allosaurus), thyreophorans (e.g., stegosaurus), and ornithopods (e.g., camptosaurus), the sauropods are the quintessential morrison dinosaurs. species such as apatosaurus, brachiosaurus, camarasaurus, and diplodocus—discovered well over a century ago—are still famed, highly regarded, and important taxa. it is not just the species of sauropods found in the morrison formation that are unique, however, but also their apparent diversity. if interpretations are correct, the morrison formation was home to 13 to 14 genera and 24 species of sauropods—amphicoelias altus, a. fragillimus (a.k.a., “maraapunisaurus” of carpenter, 2018), apatosaurus ajax, a. louisae, a. excelsus, a. parvus, a. yahnahpin (the last three may alternatively belong to brontosaurus [tschopp and others, 2015]), barosaurus lentus, brachiosaurus altithorax, camarasaurus grandis, c. lentus, c. lewisi, c. supremus, diplodocus carnegii, d. hallorum, d. longus, dystrophaeus viaemalae, galeamopus hayi, g. pabsti, haplocanthosaurus delfsi, h. priscus, kaatedocus siberi, supersaurus vivianae, and suuwassea emilieae (figure 1). although the morrison formation was geographically expansive—representing an area of 1.5 million square km (dodson and others, 1980; foster, 2007)—how could 24 of some of the largest terrestrial herbivores ever co-exist? niche and dietary partitioning could account for some of this species richness, but we can also examine the realities of such seemingly high species co-occurrence. the late cretaceous hell creek formation represents a dinosaur-bearing formation that is historically well known and extensively studied, with similarly high dinosaur diversity to that of the morrison formation. however, over the past decade, ontogenetic and stratigraphic assessments (horner and goodwin, 2006, 2008, 2009; scannella and fowler, 2009; scannella and horner, 2010, 2011; campione and evans, 2011; horner and others, 2011; scannella and fowler, 2014; scannella and others, 2014; goodwin and evans, 2016; fowler 2017; wosik and others, 2017, 2018) have reassessed the diversity, life development, and evolution of the hell creek formation dinosaurs. these analyses alternatively suggest lower species richness. using the hell creek formation diversity analysis as a guide, we can re-examine the morrison formation sauropod diversity, assessing the effect considering ontogeny and stratigraphy. institutional abbreviations ans: academy of natural sciences, philadelphia, pennsylvania; dnm: dinosaur national monument, jensen, utah; gmnh: gunma museum of natural history, japan; nmmnh: new mexico museum of natural history, albuquerque, new mexico; omnh: sam noble oklahoma museum of natural history, norman, oklahoma. factors influencing our view of diversity ontogeny compared to many other dinosaur groups, sauropod ontogeny has received relatively less attention, and has been mostly restricted to histologic analysis of relative bone maturity (including curry, 1999; sander, 2000; sander and tückmantel, 2003; klein and sander, 2008; lehman and woodward, 2008; woodward and lehman, 2009; sander and others, 2011; waskow and sander, 2014; rogers and others, 2016). although no sauropod nesting sites are yet known from the morrison formation, based on those from south america, such as auca mahuevo (chiappe and others, 1998), the potential difference in body mass between a hatchling and an adult morrison formation sauropod is at least four orders of magnitude. descriptions of immature morrison formation sauropods (gilmore, 1925; carpenter and mcintosh, 1994; foster, 1995; britt and naylor, 1996; curtice and wilhite, 1996; curry, 1999; foster, 2005a; schwarz and others, 2007; myers and storrs, 2007; myers and fiorillo, 2009; whitlock and others, 2010; carballido and others, 2012; storrs and others, 2012; tschopp and mateus, 2013; hedrick and others, 2014; tschopp and others, 2015; woodruff and others, 2015, 2017; melstrom and others, 2016; hanik and others, 2017, show that sauropods did not grow iso95 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 metrically (though some appendicular elements generally appear more isometric than allometric; woodruff and others, 2017). sauropod ontogenetic development is still the subject of much discussion (whitlock and harris, 2010; whitlock and others, 2010; woodruff and fowler, 2012; wedel and taylor, 2013; hedrick and others, 2014; tschopp and others, 2015; melstrom and others, 2016; woodruff and others, 2017), and continuing investigations and conversations are invaluable. this review adheres to the hypothesis that sauropods underwent radical ontogenetic development, but i strongly encourage readers to examine all sides of this discussion. the implications of ontogeny could complicate our understanding of the species richness within morrison formation sauropods. if these sauropods did undergo radical size and ontogenetic changes, how do we recognize these growth stages, and how do we assign ontogimorphs to genera? several studies have examined sauropod maturational states. some of these studies rely on morphology (whitlock and others, 2010; woodruff and fowler, 2012; wedel and taylor, 2013; carballido and sander, 2014), whereas others rely on histology (curry, 1999; sander, 1999, 2000; klein and sander, 2008; lehman and woodward, 2008; griebeler and others, 2013; mitchell and others, 2017). whereas histology is the demonstrably proven way to assess and verify maturity in dinosaurs (see padian and lamm [2013] and the sources therein), given the extreme changes throughout growth, understanding the development and life history of a sauropod represents a complex association with both morphology and histology. contrary to previous speculation, sauropods did not take centuries to mature (sensu curry, 1999; sander, 1999, 2000; erickson and others, 2001; sander and tückmantel, 2003; sander and others, 2004; rogers and erickson, 2005; lehman and woodward, 2008; woodward and lehman, 2009; griebeler and others, 2013; waskow and sander, 2014; woodruff and others, 2017). figure 1. the entirety of possible sauropod species within the morrison formation. amphicoelias: a. altus (or diplodocus altus [woodruff and foster, 2014]), a. fragillimus (a.k.a., “maraapunisaurus” of carpenter, 2018); apatosaurus: a. ajax, a. louisae, a. excelsus, a. parvus, a. yahnahpin (the last three may alternatively belong to brontosaurus [tschopp and others, 2015]); barosaurus lentus; brachiosaurus altithorax; camarasaurus: c. grandis, c. lentus, c. lewisi, c. supremus; diplodocus: d. carnegii, d. hallorum, d. longus; dystrophaeus viaemalae; galeamopus: g. hayi, g. pabsti; haplocanthosaurus: h. delfsi, h. priscus; kaatedocus siberi; supersaurus vivianae; suuwassea emilieae. as historically portrayed in other dinosaur-bearing formations, the sauropods of the morrison formation are largely depicted as homogenized – an inaccurate portrayal for numerous reasons outlined in this review. species to supposed scale. silhouettes by s. hartman available via phylopic (creative commons attribution-sharealike 3.0 unported). 96 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 recent histologic analyses have recorded an estimated maximum age-of-death in the thirties to forties in specimens of camarasaurus and diplodocus (waskow and sander, 2014; woodruff and foster, 2017; woodruff and others, 2017). although maximum longevity is unattainable, the majority of sauropods likely fell within the half century interval, although some exceedingly rare specimens may have extended this envelope (wings and others, 2007; d.c. woodruff, personal observations). thanks to the pioneering work of waskow and sander (2014), sauropod dorsal rib histology allows for numerical age estimates as opposed to maturational rankings (histological ontogenetic stage; klein and sander, 2008). as paleontology relies on morphology in part to distinguish different species, these growth differences/ changes are quantifiable with radical ontogenetic trajectories. if we had several specimens that unbeknownst to us represented a growth series, given their “unique” and “defining” characters/combinations, one could identify each specimen as a separate taxon. how then are we to separate taxa from ontogimorphs? the case for triceratops ontogeny and synonymy, although still debated, (scannella and horner, 2010, 2011; longrich and field, 2012; mairoino and others, 2013) represents a good case study. this species-rich genus was previously thought to consist of over a dozen species, all co-existing. however, analyses by horner and goodwin (2006, 2008) demonstrated that this high degree of morphologic variability was largely caused by ontogenetic development within two species. thus, the hell creek formation chasmosaurines were reduced to t. horridus, t. prorsus, and torosaurus latus. scannella and horner (2010) later “reduced” this diversity even more by identifying that torosaurus was an extremely mature individual of triceratops. from the studies of horner and goodwin (2006, 2008) and scannella and horner (2010), the hell creek formation “lost” over 90% of its chasmosaurine diversity. the conclusions of horner and goodwin (2006; 2008) were reached based on morphology that was ultimately corroborated via histology (scannella and horner, 2010; horner and lamm, 2011); thus, histology proved to be the test. combining morphology and histology allowed for the recognition of ontogenetic change, and how these changes occurred (echoed by hone and others, 2016). as done for triceratops, we should be taking a similar approach towards the morrison formation sauropods. once several specimens have been morphologically and histologically studied, then comparisons can be made regarding (1) changes through ontogeny and (2) differences among taxa. in doing so, groupings or patterns may start to occur, such as different growth stages grouping together (“juveniles” will group separately from “adults”), and similarities and/or differences among taxa will become more evident (i.e., immature diplodocus and apatosaurus are more alike, but both are more distinct from immature camarasaurus; woodruff and others, 2017; figure 2). given the incompleteness of the fossil record, many purportedly new genera may represent immature specimens of known taxa. the morrison formation sauropod suuwassea emilieae may be one such example. recognized from a single individual (specimen ans 21122), the taxonomy of suuwassea has been debated (harris and dodson, 2004; lovelace and others, 2008; whitlock and harris, 2010; whitlock, 2011a; woodruff and fowler, 2012; wedel and taylor, 2013; hedrick and others, 2014; tschopp and others, 2015; woodruff and others, 2017). histology shows that specimen ans 21122 lacks an external fundamental system (efs) (hedrick and others, 2014; woodruff and others, 2017; efs, the skeletal indicator of osteogenesis—padian and lamm, 2013). yet the morphologies have been interpreted to be valid, distinguishable characters (harris and dodson, 2004; wedel and taylor, 2013; hedrick and others, 2014), or alternatively ontogenetic (woodruff and fowler, 2012; woodruff and others, 2017). aside from the differing taxonomic interpretations, the holotype of suuwassea represents a relatively small-statured immature animal with intriguing morphologies (see a list of these features in woodruff and fowler, 2012). currently the holotypic material of suuwassea could equally represent an immature individual from a known taxon, a distinct taxon, a maturationally varied individual or taxon with pedomorphic attributes, and possibly a combination of these conditions. at this time the holotype does not unanimously support one distinct interpretation. another example from the morrison formation is the sauropod diplodocus hallorum. originally known 97 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 figure 2. caption is on the following page. 98 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 as “seismosaurus” (specimen nmmnh p-3690; gillette, 1991), this specimen likely represents one of the largest morrison formation sauropods (woodruff and foster, 2014). whereas this taxon was originally diagnosed mainly on postcranial proportional differences, in a reassessment of the genus, lucas and others (2006) proposed that these differences were simply due to its extreme body size (and the “hook-like” ischium was found to be inaccurate; lucas and others, 2006). now indistinguishable from diplodocus, lucas and others (2006) synonymized “seismosaurus” into a species of diplodocus. in their taxonomic revision of diplodocidea, tschopp and others (2015) phylogenetically recognized several specimens now referable to d. hallorum; however, the question remains whether the holotype of d. hallorum represents a distinct species, or an incredibly elderly diplodocus. (histologic analysis of specimen nmmnh p-3690 is currently underway by dcw and k. waskow). similar to the case of d. hallorum is that of amphicoelias. the holotype material of a. fragillimus hints at a posterior dorsal vertebra in excess of 2.8 m – making it unquestionably the largest vertebrate ever (carpenter, 2006; woodruff and foster, 2014; see also carpenter, 2018). serious doubt should be raised to the validity of this taxon (as all of the holotype material vanished; woodruff and foster, 2014), whereas we now have revised autamorphies for this species (tschopp and others, 2015), as some of the first autamorphies for d. hallorum were size related (such as a more robust pubis; lucas and others, 2006), does “big” necessarily equal distinct? ontogeny should not just be considered when examining small-bodied individuals; large-bodied specimens can be just as guilty (trujillo and others, 2011). the rarity of torosaurus compared to the prolific triceratops was proposed by scannella and horner (2010) to be the result of “torosaurus” being a senescent triceratops. nature is unkind to the young and old, and attritional mortality shows that samples of specimens in these age ranges should be underrepresented (lyman, 1994). whereas immature sauropods are known from the morrison formation (gilmore, 1925; carpenter and mcintosh, 1994; foster, 1995; britt and naylor, 1996; curtice and wilhite, 1996; curry, 1999; foster, 2005a; myers and storrs, 2007; schwarz and others, 2007; myers and fiorillo, 2009; whitlock and others, 2010; carballido and others, 2012; storrs and others, 2012; tschopp and mateus, 2013; hedrick and others, 2014; tschopp and others, 2015; woodruff and others, 2015, 2017; melstrom and others, 2016; hanik and others, 2017), it might be possible that a few of these specimens, though identified as different species, may alternatively represent differing ontogenetic stages of known taxa. and while not yet histologically demonstrated, the case of “elosaurus” parvus (peterson and gilmore, 1902) representing an immature apatosaurus (mcintosh, 1995; or brontosaurus by tschopp and others, 2015), or diplodocus “lacustris” (marsh, 1884) being an immature diplodocus (upchurch and others, 2004; although see tschopp and others, 2015), demonstrate that even previously, morrison formation sauropod diversity reconstructions have been altered by ontogeny. figure 2 is on the previous page. the interpretations that could result from single lines of evidence. morphology: not only differing body sizes, but the differing cranial, vertebral, and limb morphologies between two specimens could result in the two being interpreted as separate taxa. histology: from just the histology, only the individual ages of these specimens could be assessed from a growth perspective. however, by increasing the lines of evidence (here with histology and morphology), and additionally by incorporating more specimens, we see a growth series. growth is gradational, so we should expect to see not just the extremes, but transitional forms (so “unique” character combinations may instead represent hallmarks of ontogeny). human scale bar is augustus saint-gaudens’ diana of the tower, depicting diana as 1.83 m. femora and histologic images modified from woodruff and others (2017). diplodocus sp. silhouettes modified from woodruff and others (2017) and originally based on art by s. hartman available via phylopic (creative commons attribution-sharealike 3.0 unported). immature diplodocus sp. skull drawing in histology and histo. morph. by k. scannella, adult diplodocus sp. and suuwassea emilieae skulls in histology and histo. morph. from whitlock (2011b). 99 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 biostratigraphy the morrison formation represents a time interval of approximately 7 million years and spanning a geographical range of about 14° latitude and to 12° longitude (kowallis and others, 1998; turner and peterson, 1999; foster, 2007; trujillo and kowallis, 2015). thus, the morrison formation represents a significant geographic region and temporal interval. historically, the biota appeared to be homogeneously distributed within the formation with little if any recording of stratigraphic occurrence (especially during the “bone wars” of o.c. marsh and e.d. cope; foster, 2007). in a pioneering attempt to correlate localities and compile the stratigraphic distribution of dinosaurs, turner and peterson (1999) correlated 230 morrison formation localities to the dnm section. from such correlations, turner and peterson (1999) claimed the formation could be better understood as a single functional unit. not only did turner and peterson (1999) claim to correlate sections over vast areas with the aid of the so-called “clay change” (the sudden shift between the lower and upper brushy basin member from non-smectitic to smectitic clays, which denotes increased volcanism), but they also claimed to see diversity and species patterns change. camarasaurus lasted longer than apatosaurus, diplodocus survived longer than its sister taxon barosaurus, and the perhaps distinct amphicoelias appeared to be the last surviving sauropod within the formation (turner and peterson, 1999). the incredibly detailed and thorough work of turner and peterson (1999) has served as a platform for subsequent morrison formation studies. as demonstrated within the hell creek formation, stratigraphy is an important consideration for diversity estimates (horner and others, 2011; scannella and others, 2014; fowler, 2017). while horner and goodwin (2006) were able to show that triceratops species diversity was a false artifact from ontogimorphs of two species, scannella and others (2014) was able to refine this image by incorporating stratigraphic information. by plotting the stratigraphic position of over 50 specimens of triceratops and noting their ontogenetic states, scannella and others (2014) were able to plot evolutionary patterns. not only did they document morphological details (such as the nasal horn increasing in size through time), but more importantly, they were able to plot the evolution of t. horridus to t. prorsus through anagenesis (scannella and others, 2014). from the change in triceratops within only ~1 million years (scannella and others, 2014), one might expect to see evolutionary changes in sauropods over the course of ~7 million years (kowallis and others, 1998; turner and peterson, 1999; trujillo and kowallis, 2015) in the morrison formation. by correlating species occurrence within the formation, a body size trend may exist: apatosaurus yahnahpin (or brontosaurus yahnahpin; tschopp and others, 2015) occurs prior to a. louisae, camarasaurus lentus occurs before c. supremus, and diplodocus carnegii occurs prior to d. hallorum (turner and peterson, 1999; figure 3). it would seem that all of the smaller species occur before the larger; therefore, one could say that morrison formation sauropods increased in size through time. however, when plotting additional species and specimens, it becomes apparent that this is not a strict rule. an apatosaurus sp. (museum of the rockies [mor] 857) from the stratigraphically lower salt wash member of the morrison formation equivalent may be comparable in size to the largest specimen ever collected (specimen omnh 1670) from the higher brushy basin member equivalent levels of the morrison formation in western oklahoma. the smallest species of camarasaurus, c. lewisi, occurs stratigraphically between the larger c. lentus and c. supremus, and diplodocus carnegii occurs before the larger d. hallorum. however, we should not think of this as a strict trend, as the stratigraphically highest occurrence of apatosaurus (within the upper meters of the brushy basin member in arches national park, utah), is of a size typical for the average adult lower in the formation (foster, 2005b). tentatively, whereas body size increase is not a strict rule throughout the formation, average body size increases may be a legitimate trend (sensu foster, 2007). plotting sauropod genera stratigraphically may even have the potential to highlight major evolutionary processes. in 2013, the diplodocid kaatedocus siberi (tschopp and mateus, 2013) was named from the howe-stevens quarry in north-central wyoming. whereas there has been some informal discussion as to whether this taxon is distinct or not, 100 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 fi gu re 3 . th e la rg es t s pe ci es o f a pa to sa ur us , c am ar as au ru s, an d d ip lo do cu s a pp ea r st ra tig ra ph ic al ly h ig he r co m pa re d to th ei r sm al le r co un te rp ar ts . th us , o ne m ig ht in fe r t ha t m or ris on f or m at io n sa ur op od g en er a i nc re as e i n bo dy si ze th ro ug h tim e ( a ). h ow ev er , b y pl ot tin g m or e sp ec im en s/ sp ec ie s ( b) , w e se e th at th e pr ev io us a ss um pt io n is no t a ru le n or a st ric t p at te rn . w he re as a n in cr ea se in a ve ra ge bo dy si ze a m on gs t s au ro po d ta xa m ay b e a le gi tim at e tr en d ob se rv ed w ith in th e m or ris on f or m at io n, w e ar e no t a dv oc at in g or su gg es tin g c op e’s l aw (t ha t l in ea ge s m us t i nc re as e in si ze th ro ug h tim e) . s ilh ou et te s b y s. h ar tm an a va ila bl e vi a ph yl op ic (c re at iv e c om m on s at tr ib ut io nsh ar ea lik e 3. 0 u np or te d) . a fu llsiz e ve rs io n of fi gu re 3 is in th e at ta ch em en ts p an e. 101 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 based on cranial and vertebral morphologies the holotype of kaatedocus may represent an immature individual (d.c. woodruff, personal observations; and note not a synonymous ontogimorph). what has not been discussed in-depth is the stratigraphic occurrence. correlated to the dnm stratigraphic section (turner and peterson, 1999), kaatedocus appears to be stratigraphically lower than any reported diplodocus. according to turner and peterson (1999), all diplodocus and barosaurus specimens occur within the upper part of the salt wash or brushy basin members or their equivalents, whereas kaatedocus may occur equivalently in the lower regions of the salt wash member. more work and better resolution is needed—both ontogenetic and stratigraphic—but the apparent stratigraphic distinctness could be used as evidence in favor for the validity of kaatedocus. furthermore, given that kaatedocus is geologically one of oldest morrison formation diplodocids known, it could represent part of a diplodocine cladogenic or anagenetic lineage (figure 4). as the morrison formation temporally represents an increasing terrestrial space (foster, 2007), and as fauna migrate into this newly acquired space through time, could we expect to document evolutionary changes? anagenesis (potentially with kaatedocus and the co-occurring diplodocid galeamopus) and cladogenesis (apatosaurus vs. brontosaurus?) are evolutionary processes that should be considered. fortunately, due to the wealth of time spent exploring the morrison formation and the vast number of specimens collected (foster, 2007; brinkman, 2010), these kinds of questions have the potential to be examined. finally, the assumptions and inferences regarding morrison formation stratigraphy could be derived from a false signal. as presented herein, stratigraphic distribution of sauropods within the morrison has been based around the framework created by turner and peterson (1999). within the past decade, the reliability of turner and peterson (1999) has been questioned. starting with trujillo (2006), it was demonstrated that the “clay change” was not supported by clay mineralogy nor x-ray diffraction (xrd) data. according to trujillo (2006), this marker unit was not a consistently developed horizon, and within a given section numerous clay-type alterations could occur. these findings meant that correlating sections in this manner, particularly over such long distances, was not reliable (trujillo, 2006). after the trujillo (2006) “clay change” study, there were a series of seminal papers reporting on u-pb dates and recalibrated 40ar/39ar dates for several morrison formation localities (trujillo and chamberlain, 2013; trujillo and others, 2014; trujillo and kowallis, 2015). radiometric dating (such as k/ar or 40ar/39ar) can rely on silicate (or potassium feldspar) minerals from overlying or underlying volcaniclastic deposits to determine a relative temporal interval (olsson, 1986). however, by using non-detrital zircon crystals from smectitic mudstones, some of these newer studies were able to determine dates for localities previously dated with detrital material, in addition to new, and geographically distant localities (trujillo and chamberlain, 2013; trujillo and others, 2014; trujillo and kowallis, 2015). as the standard used for 40ar/39ar dating and decay constants became over time more refined, these necessitated recalibration; and these recalibrated dates now correspond more favorably to the same derived from u-pb (trujillo and kowallis, 2015). with these refined dates, while relative stratigraphic position of many localities remains the same, their position within a chronostratigraphic context has changed. from 40ar/39ar dating, turner and peterson (1999) had the mygatt-moore quarry in western colorado correlated within the upper portion of the upper brushy basin member between 147.8 ± 0.6 and 150.3 ± 0.3 ma. however, new studies conducted using zircon u-pb chemical abrasion (ca-tims), still place this locality within the lower portion of the upper brushy basin member, but with a date of 152.18 ± 0.29 ma (trujillo and others, 2014; figure 4). in fact, based on recalibrated 40ar/39ar dates, the entire temporal positioning has likewise changed. from 40ar/39ar dating, turner and peterson (1999) chronostratigraphically placed the correlated dinosaur quarries between 148.1 ± 0.5 and 154.8 ± 0.6 ma, yet 40ar/39ar recalibration by trujillo and kowallis (2015) refined this range to 150.00 ± 1.03 and 156.84 ± 1.18 ma, respectively. newer magnetostratigraphic and sequence stratigraphic studies are also changing the interpretation of the northern extent of the formation. following the correlated section of turner and peterson (1999), lo102 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 figure 4. (a) the stratigraphic section of the morrison formation (from turner and peterson, 1999) with the recalibrated dates of trujillo and kowallis (2015). note the locations of the mygatt-moore quarry (co-21; red) and the o’hair quarries (mt-2; blue). in turner and peterson (1999) the mygatt-moore quarry was correlated within the upper portion of the upper brushy basin member between 147.8 ± 0.6 and 150.3 ± 0.3 ma. with the recalibrated 40ar/39ar dates of trujillo and others (2014), this locality still remains within the upper portion of the upper brushy basin member, but now at 152.18 ± 0.29 ma. the outlined blue box represents the correlated position of o’hair quarries (mt-2) from turner and peterson (1999). the solid blue box represents this locality’s new correlated position based on new magnetostratigraphic (maidment and muxworthy, 2016) and sequence stratigraphic studies (mcmullen and others, 2014; mcmullen, 2016). the undulating gray line is to cross out the “clay change” of turner and peterson (1999). portions of this image – particularly those pertaining to the palynomorph zones and the recalibrated 40ar/39ar dates – are modified from trujillo (2016). (b) possible trends in camarasaurus body size throughout the formation. (c) possible explanation of kaatedocus within the evolutionary trajectory of diplodocus. silhouettes by s. hartman available via phylopic (creative commons attribution-sharealike 3.0 unported). 103 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 calities from montana were placed equivalently within the upper portion of the salt wash member (specifically the o’hair quarries; cooley and schmitt, 1998; schimelfening and others, 2014). in addition to correlation with the dnm section, association with the underlying marine swift formation and the predominance of sandstone to mudstone beds, all supported a salt wash member-equivalent position (cooley and schmitt, 1998; turner and peterson, 1999; schimelfening and others, 2014). however, new magnetostratigraphic (maidment and muxworthy, 2016) and sequence stratigraphic analyses (mcmullen and others, 2014; mcmullen, 2016) are changing the position of these localities. the magnetostratigraphic analyses of maidment and muxworthy (2016) proposes that the o’hair quarries are temporally equivalent to the upper brushy basin member in dinosaur national monument (figure 4). how then can stratigraphic correlation and magnetostratigraphy produce such different results? in the beginning of the deposition of the morrison formation, the terrestrial area in the southwest was adjacent to the sundance sea. later this same region was seasonally arid, or savanna-like (foster, 2007). but as the sundance sea kept retreating northwards, the contiguous terrestrial deposits would continue to have a coastal composition. systems and environments do vary latitudinally, but the lower stratigraphic placement of the montana localities could be due to an inaccurate stratigraphic signal. a time-transgressive morrison formation has been previously proposed by harris and dodson (2004) and harris (2005), and perhaps the geographical extremes of the formation are the better locations to study this phenomenon. if this is correct, then due to the regression of the sundance sea, by the time montana had become terrestrial, it would have been temporally equivalent to dinosaur national monument. but the coastal environment in montana would result in depositional systems similar to those recognized in the lower and earlier portions of the formation. in light of these newer and ongoing studies, the work of turner and peterson (1999) should still be commended. prior to turner and peterson (1999), morrison formation stratigraphic research had little, if any, cohesion or unity. workers outside of the colorado plateau region were unable to place and understand their localities within the context of the entire formation. the correlatable “clay change” of turner and peterson (1999) at the time seemed to change that. even in consideration of these studies incorporating new techniques/recalibration (trujillo and chamberlain, 2013; trujillo and others, 2014; trujillo and kowallis, 2015), the morrison formation may be too large to correlate, and perhaps geographical regions are not a part of the same depositional system (s. mcmullen, hess corporation, written communication, 2018). certainly, regional correlation may still possible, but the aforementioned radiometric, magnetostratigraphic, and sequence stratigraphic studies collectively suggest that incorporating all of this new information should result in a better and more accurate reconstruction of these localities. an initial blend of this new information is already being performed by tschopp and others (2016). by taking morrison formation diplodocid occurrences and incorporating them into the magnetostratigraphy of maidment and muxworthy (2016), tschopp and others (2016) may be able to reanalyze these basic morrison formation sauropod questions, and i greatly await these results and future works. furthermore, while we continue to relocate, recalibrate, and reanalyze specimens within a stratigraphic context, we can thus far identify—even at coarse resolution—some levels of biozones (sensu foster, 2003, 2007; figure 5). due to the inherent inaccuracies in assuming formational homogeneity, foster (2003, 2007) suggested that differing paleoenvironments throughout the formation would consist of differing groups of dinosaurs. the benefits of biozone demarcations are that they reflect environmental groupings throughout the course of the formation (i.e., environments + time versus strictly time). until we have a better understanding of the time component, which admittedly could significantly alter the biozone signals, grouping via biozones may be a more neutral way to group or demarcate morrison formation sauropod taxa. there are four tentative biozone signals that we may see within the morrison formation. (1) the lowermost occurrence of barosaurus, dystrophaeus, and haplocanthosaurus in zone 1 may indicate that these forms could represent or be relics of pre-morrison formation sauropod genera. (2) the low sauropod diversity of zones 1, 3, and 6 could indicate 104 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 fi gu re 5 . b io zo ne d em ar ca tio ns o f s au ro po ds w ith in th e m or ris on f or m at io n. b io zo ne s a re fr om f os te r ( 20 03 ) w ith ad di tio na l s pe ci m en s pl ot te d ac co rd in g to st ra tig ra ph ic p la ce m en t v ia t ur ne r a nd p et er so n (1 99 9) . s tr at ig ra ph ic se ct io n is fr om f os te r ( 20 03 ). c lo se d sil ho uet te s r ep re se nt g en er a w ith id en tifi ed sp ec ie s, op en si lh ou et te s r ep re se nt o nl y ge ne ric le ve l r ef er ra l. si lh ou et te s b y s. h ar tm an a va ila bl e vi a ph yl op ic (c re at iv e c om m on s a ttr ib ut io nsh ar ea lik e 3. 0 u np or te d) . s ilh ou et te s t o re la tiv e sc al e. a fu llsiz e ve rs io n of fi gu re 5 is in th e at ta ch em en ts p an e. 105 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 negative events/environments, or this signal could indicate poor sampling. (3) the ecology of zones 5 and 6 may have been more conducive to speciation—these zones exhibit the most genera and the greatest number of species. (4) out of all of the sauropod genera that appear in at least two zones, only barosaurus and brachiosaurus have a single species—such could indicate something special about their biology (being longer occurring species), or their diversity (number of species) may be incorrect (note that woodruff and others, 2017 suggest that based on possible morphologic differences seen stratigraphically, barosaurus may represent more than a single species). ecological capacity in addition to ontogeny and stratigraphy, there are several other factors at play that could equally be interfering with our signal of morrison formation sauropod diversity. as previously mentioned, 24 different kinds of multi-ton herbivores across a single landscape would theoretically be ecologically taxing. many studies have proposed ecological segregation among the morrison formation sauropods including feeding height (bakker, 1971; dodson and others, 1980; bakker, 1986; martin, 1987; stevens and parrish, 1999, 2005; upchurch and barrett, 2000; christian, 2002; foster, 2003, 2007; dzemski and christian, 2007; christian, 2010; hummel and clauss, 2011), dietary niche partitioning (galton, 1986; fiorillo, 1998; upchurch and barrett, 2000; christian, 2002; foster, 2003, 2007; engelmann and others, 2004; stevens and parrish, 2005; carpenter, 2006; whitlock and others, 2010; hummel and clauss, 2011; young and others, 2012; d’emic and others, 2013; button and others, 2014; woodruff and others, 2015), or ontogenetic segregation (dodson and others, 1980; foster, 2003; myers and storrs, 2007; myers and fiorillo, 2009; woodruff and others, 2015). such ecological segregation undoubtedly had to occur, and likely several of these forms co-occurred—such as young sauropods feeding on different plant material than their adult forms (sensu whitlock and others, 2010 and woodruff and others, 2015). not only are feeding-related factors important, but so too is their respect to body size. the african savanna today is made up a multitude of co-occurring herbivores ranging from the dik-dik (up to 6 kg; grubb, 2005) to the african elephant (up to 10,400 kg; larramendi, 2016). several exemplary studies have examined the relationship between body size and foraging height to explain the extreme prevalence of herbivores in this ecosystem (du toit, 1990, 2003; woolnough and du toit, 2001; fritz and others, 2003; cameron and du toit, 2006; anderson and others, 2016), and possibly a similar body size to feeding height/vegetation type stratification occurred within the sauropods of the morrison formation. perhaps the predominance of smaller body sized morrison formation sauropods, such as camarasaurus (approximately 12,530 kg for c. grandis; specimen gmnh 101 – this analysis) versus the rarity of larger body sized taxa, such as supersaurus (36,287 kg; lovelace and others, 2008) may be analogous to the pattern seen in the african savanna. individual morphological variation within species another possible confounding factor is individual variation. unlike the degree of variation observed within hadrosaurs (campione and evans, 2011; fowler and horner, 2015; woodward and others, 2015; mcfeeters and others, 2018; takasaki and others, 2018) and ceratopsians (scannella and horner, 2010; frederickson and tumarkin-deratzian, 2014; scannella and others, 2014; campbell and others, 2016, 2018), the exacting degrees of morphologic variation in morrison formation sauropods have not been precisely quantified. morrison sauropod workers have colloquially referred to observed variation, but as morphologic variation in sauropods can derive from taxonomy or body size (among others), denoting whether a character is taxonomically distinct or within the range of variation can become more nebulous (foster, 2015). also, treating what may be continuous variation as discrete characters from low sample sizes is likely to be problematic (j. foster, utah field house of natural history state park museum, written communication, 2018). as an example, let us examine cranial openings. one could presume that the number of cranial openings would be a significant taxonomic signal. therefore, said number or presence/absence of specific openings would seemingly be a strong phyloge106 what factors influence our reconstructions of morrison formation sauropod diversity? d. cary woodruff geology of the intermountain west 2019 volume 6 netic indicator. and yet, this is absolutely not the case in camarasaurus. the frontal aperture (woodruff and foster, 2017) is variably present among camarasaurus specimens of various species and body sizes (echoed in madsen and others, 1995). if the presence of an extra cranial opening is demonstrably not a taxonomically viable character in a morrison formation sauropod, then what characters are significant, and how do we begin to measure and quantify such variability? conclusions the information presented herein and throughout this themed set of morrison formation papers, beginning in 2016 in the geology of the intermountain west, will hopefully contribute to a shift in our understanding of the true nature and complexities within the morrison. in regard to the sauropod diversity, the morrison formation may have legitimately exhibited unparalleled sauropod diversity. however, stratigraphy and ontogeny, among others, have been demonstrated to have repercussions on diversity estimates. previously, the hell creek formation was thought to harbor nearly three dozen dinosaurian species. however, subsequent analyses examining the critical variables of ontogeny, stratigraphy, and variation have shown that while still highly diverse, this diversity is in actuality constructed by less than half of the perceived species (carr and williamson, 2004; horner and goodwin, 2009; scannella and horner, 2010; campione and evans, 2011). certainly, there are unique attributes of the morrison formation, one such is clade representation. within the hell creek formation, species richness seems fairly evenly distributed across the different clades. yet, in the morrison formation, the dominating clade constitutes almost an equal number of species to all the other clades combined (26 versus 24, respectively). as in the hell creek formation, the morrison formation was likely very species rich. this review is not meant to admonish against richness, merely to contemplate the multifaceted factors that could affect said richness. in consideration of the expanse that is the morrison formation, approximately 7 million years, and a geographical range of 14 degrees of latitude and 12 degrees of longitude (kowallis and others, 1998; turner and peterson, 1999; foster, 2007; trujillo and kowallis, 2015), stratigraphy, ontogeny, variation, evolutionary patterns, and environments should have some effect on sauropod diversity. currently the degree or significance of these factors towards morrison formation sauropod diversity is unresolved; yet in another formation it has been demonstrated that these factors do alter diversity reconstructions. therefore, until these factors are accounted for, we may not be accurately reconstructing the true diversity of sauropods within the morrison formation. acknowledgments thanks to the society of vertebrate paleontology for hosting the “an ecosystem we thought we knew: the emerging complexities of the morrison formation” symposium during the 76th annual meeting, and to all of the presenters for such an informative, engaging, and thought-provoking symposium. my presentation co-author denver fowler (dickinson museum center) provided numerous encouraging and lively discussions that culminated in this work. finally, thanks to v. díez díaz (universidad del pais/euskal herriko unibertsitatea), f. holwerda (bayerische staatssammlung für paläontologie und geologie), and j. richard (delgado community college) for review comments on the manuscript; j. foster (utah field house of natural history state park museum), and k. trujillo (laramie county community college) for editorial assistance and comments on an earlier version of the manuscript; and k. nordén (princeton university) and d. fowler (dickinson museum center) for fruitful discussions and encouragement. references anderson, t.m., white, s., davis, b., erhardt, r., palmer, m., swanson, a., kosmala, m., and packer, c., 2016, the spatial distribution of african savannah herbivores—species associations and habitat occupancy in a landscape context: philosophical transactions of the royal society b, v. 371, 20150314, p. 1–14, http://dx.doi.org/10.1098/rstb.2015.0314. bakker, r.t., 1971, ecology of the brontosaurs: nature, v. 229 (5281), p. 172–174. bakker, r.t., 1986, the dinosaur heresies: new york, william 107 what factors influence our reconstructions of morrison formation sauropod diversity? 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behaviour in an extinct megaherbivore: naturwissenschaften, v. 99, p. 637–643. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 11 2024 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah adam d. marsh, donald d. de blieux, and james i. kirkland geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover a theropod dinosaur scans the horizon as sauropodmorphs walk to the river, which flows across the early jurassic landscape. the sediments deposited by the river systems will eventually 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801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 11 2024 45 abstract the vertebrate assemblage of the lower jurassic kayenta formation is known for its preservation of post-end triassic mass extinction lineages, including lissamphibians, lepidosaurs, turtles, mammaliamorphs, crocodylomorphs, pterosaurs, and ornithischian, theropod, and sauropodomorph dinosaurs. most of the body fossils from the formation are known from its ‘silty facies’ in north-central arizona and southwestern utah, whereas the sandier ‘typical facies’ of northeastern arizona preserves few body fossils, and until recently they were completely absent in the typical facies of southeastern utah. a 2011 team conducting a paleontological survey of arches national park discovered the first body fossils from the typical facies of the kayenta formation in utah, here identified as belonging to a single individual of a saurischian dinosaur, likely a theropod. the fossil elements include a partial centrum articular face, a prezygapophysis, part of a caudal vertebra, the distal end of a left radius, part of the distal end of a left femur, a shaft fragment from the left fibula, the distal end of right metatarsal i, and the proximal portion of left metatarsals iii and iv. this specimen from arches national park underscores the importance of federally protected land in fossil resource management and suggests that the typical facies of the kayenta formation may be undersampled and could preserve more vertebrate bones than previously thought. the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah adam d. marsh1, donald d. de blieux2, and james i. kirkland2 1department of science and resource management, petrified forest national park, az 86028 usa; adam_marsh@nps.gov 2utah geological survey, salt lake city, ut 84114 usa; dondeblieux@utah.gov, jameskirkland@utah.gov citation for this article. marsh, a.d., de blieux, d.d., and kirkland, j.i., 2024, the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah: geology of the intermountain west, v. 11, p. 45–57, https://doi.org/10.31711/giw.v11.pp45-57. introduction the lower jurassic kayenta formation unconformably overlies the upper triassic-lower jurassic moenave formation or wingate sandstone, depending on the location (the j-sub-k unconformity; riggs and blakey, 1993; blakey, 1994). it interfingers with the higher navajo sandstone (figure 1a), forming a sequence of strata that records erg sands blowing over fluviolacustrine deposits as the north american plate moved north into an arid climate belt (harshbarger et al., 1957; riggs et al., 1993; blakey, 1994; priddy and clarke, 2020). the kayenta formation preserves an important vertebrate assemblage that represents the terrestrial biotic recovery following the end-triassic mass extinction in western north america. fossils discovered in the formation include lissamphibians, lepidosaurs, turtles, mammaliamorphs, pterosaurs, crocodylomorphs, and dinosaurs (clark and fastovsky, 1986; sues et al., 1994; lucas et al., 2005; tykoski, 2005). this assemblage is best known from the ‘silty facies’ of parts of northern arizona and southwestern utah (figure 1b), but its sandier ‘typical facies’ like what is present at its type section at comb ridge, arizona, also preserves vertebrate fossils, primarily as tracks (lockley and hunt, 1994, 1995; hunt and lucas, 2006). as harshbarger et al. (1957, p. 17) observed, “the typical and silty facies of the kayenta 46 the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah marsh, a.d., de blieux, d.d., and kirkland, j.i. geology of the intermountain west 2024 volume 11 formation represent a lateral variation of deposition within a single basin.” this perceived disparity of the presence of body fossils in the two facies of the kayenta formation may be the result of different depositional processes, the fact that the typical facies tends to form cliffs rather than more accessible slopes, or geographic sampling bias. if the latter is true, then increased inventory of the typical facies of the kayenta formation should result in the discovery of more body fossils. this hypothesis was tested by a paleontological inventory that was undertaken within arches national park (arch) in 2011, resulting in the discovery of fragmentary fossil bones from the kayenta formation (figure 2). here, we describe that specimen (arch 4012) as the first dinosaur bones from the typical facies of the kayenta formation in utah. this specimen highlights the importance of fossil resources on federally protected land and suggests that more vertebrate bones may be present elsewhere in the typical facies of the kayenta formation. materials and methods a two-week paleontological field survey of the phanerozoic strata of arch was led by the utah geological survey (ugs) in 2011 under cooperative agreement #h230097080 with the u.s. national park service (nps; geologic resources division). a previous nps arch survey was accomplished in 2000 (swanson et al., 2005) but it focused on the chinle formation (upper triassic), curtis formation (middle jurassic), morrison formation (upper jurassic), and cedar mountain formation (lower cretaceous). paleontological localities identified or monitored during the 2011 survey were photographed and documented in the nps and ugs databases (madsen et al., 2012), and scientifically significant fossils were collected, including arch 4012. the arch collection, formerly at a regional nps facility in moab, utah, was rehoused with archival materials in 2020 and is reposited at petrified forest national park (pefo) with other fossil collections from the nps 0-1300 200-500 250-450 200-300 250-550navajo sandstone kayenta formation wingate sandstone chinle formation moenkopi formation tr ia ss ic ju r as si c g le n c an yo n g ro up thickness near arch (ft)a 100 miles arch z 5 miles gb mf tc wt w cr b flagstaff moab st. georgest. george moab flagstaff sf tf sf tf n figure 1. selected fossil localities in the kayenta formation of arizona and utah. (a) map of northern arizona and southern utah showing localities and arches national park, the extent of kayenta formation facies is shown as brown and tan; (b) stratigraphic context of the glen canyon group near arches national park. locality specimen arch 71v shown as a green star. abbreviations: arch, arches national park; cr, comb ridge; gb, goblin valley; mf, many farms; sf, silty facies; tc, tsegi canyon; tf, typical facies; w, warner valley; wt, ward terrace, including the echo and adeii eechi cliffs; z, zion national park. approximate extent of the silty facies and typical facies of the kayenta formation modified from priddy and clarke (2020). 47 the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah marsh, a.d., de blieux, d.d., and kirkland, j.i. geology of the intermountain west 2024 volume 11 southeastern utah group. photographs of arch 4012 were taken with a nikon d90 digital camera equipped with a nikon af-s nikkor 24–85 mm lens. arch 4012 was laser scanned at pefo using an artec space spider on artec studio 16 professional (16.0.5.114). the resulting surface files can be accessed at https://www. morphosource.org/projects/000572397. institutional abbreviations arch, arches national park, utah, usa.; mna, museum of northern arizona, flagstaff, arizona, usa.; pefo, petrified forest national park, arizona, usa.; tmm, texas vertebrate paleontology collections, the university of texas at austin, austin, texas, usa.; ucmp, university of california museum of paleontology, berkeley, california, usa. systematic paleontology avemetatarsalia benton, 1999 sensu nesbitt et al., 2017 dinosauria owen, 1842 sensu padian and may, 1993 saurischia seeley, 1887 sensu gauthier, 1986 theropoda marsh, 1881 sensu gauthier, 1986 (figures 2 and 3) referred specimen specimen arch 4012, fragmentary skeletal elements likely belonging to a single individual (figures 2 and 3), including part of a presacral centrum and prezygapophysis, a caudal centrum, the distal end of a left radius, the distal end of a left femur, a shaft fragment from the proximal half of a left fibula, the distal end of right metatarsal i, and the proximal ends of left metatarsals iii and iv. justification for identification the specimen can be attributed to the saurischia because of the presence of a hypantrum on the presacral vertebra, as well as the presence of a groove separating the lateral condyle and tibiofibular crest on the distal end of the femur (figures 2p and 2r), both of which are present in early-diverging saurischian dinosaurs (nesbitt, 2011; stefanic and nesbitt, 2019) and absent in the ornithischian scutellosaurus lawleri found in the kayenta formation (colbert, 1981; breeden and rowe, 2020; breeden et al., 2021). if our identifications of the proximal ends of metatarsal iii and metatarsal iv of arch 4012 are correct, the proximal shapes more closely resemble those of the neotheropod dilophosaurus wetherilli than those of the sauropodomorph sarahsaurus aurifontanalis (figure 3), which are the two saurischians present in the kayenta formation in the same size range as arch 4012, suggesting a neotheropod affinity rather than that of a sauropodomorph. locality, horizon, and age locality arch 71v, near the garden of eden, about 2.5 km northwest of the windows area of arch (figure 1b); typical facies of the kayenta formation; “bone was found eroding from red mudstone next to exposed area of white sandstone” (madsen et al., 2012, p. 16–17). the kayenta formation is early jurassic in age (figure 1a), likely pliensbachian-sinemurian, and the middle of the silty facies of the kayenta formation in northeastern arizona may be as young as about 183 ma (padian, 1989; marsh et al., 2014; suarez et al., 2017; marsh, 2018). description axial skeleton presacral vertebrae the partial centrum preserves less than half of what we hypothesize to be the posterior articular facet in posterior view (figure 2a). we identify it as belonging to the posterior cervical or trunk series because the angle formed by the posterior and ventral margins in lateral view is rather acute; this angle is larger in anterior cervical centra that tend to be more parallelogram in shape in dilophosaurus wetherilli (e.g., specimen ucmp 37302) 48 the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah marsh, a.d., de blieux, d.d., and kirkland, j.i. geology of the intermountain west 2024 volume 11 a c b d e f g h i j k l m n o p q r s t u v xw y abaa ac afae ag z ad as 2 cm ashy prz as ncj tfc tfc lc lc lc tfc tfc lc lf lf as g g g g figure 2. caption is on the following page. 49 the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah marsh, a.d., de blieux, d.d., and kirkland, j.i. geology of the intermountain west 2024 volume 11 and sarahsaurus aurifontanalis (e.g., specimen tmm 43646-2). the prezygapophysis preserves the relatively flat dorsal articular surface for the preceding postzygapophysis and the concave medial margin that would have formed the hypantrum (figure 2f), which is present on the trunk vertebrae in dilophosaurus wetherilli (e.g., ucmp 37302) and sarahsaurus aurifontanalis (e.g., tmm 43646-2). caudal vertebra less than half of the element is preserved as seen in lateral view (figure 2i). the articular face is concave rather than flat, and the dorsal ridges that form the junction with the neural arch are present. the ventral margin of the articular face lacks the sloped surface that would have articulated with a haemal arch, indicating that this caudal vertebra was likely far enough back in the tail to be posterior to the last haemal arch. forelimb and radius the distal end of the ?left radius is identical to that of dilophosaurus wetherilli (e.g., ucmp 77270) and sarahsaurus aurifontanalis (e.g., tmm 43646-2). in lateral/medial view (figures 2l and 2n), the posterior margin is relatively straight, and the anterior margin is concave. the distal outline is subelliptical (figure 2m). hindlimb femur only the lateral sides of the lateral condyle and tibiofibular crests are preserved. a concavity is present on the lateral side of the tibiofibular crest that continued distally to form a groove between the tibiofibular crest and the lateral condyle (figure 2p). in distal view the lateral margin of the lateral condyle is subcircular (figure 2r). figure 2 (figure is on the previous page). preserved fragments of arch 4012 compared with elements of dilophosaurus wetherilli, ucmp 37302. arch 4012, centrum face (a, b) in ?posterior (a) and ?right lateral view (c); ucmp 37302, vertebra 15 (c, d) in right lateral (c) and dorsal view (b); arch 4012, trunk prezygapophysis (e, f) in medial (e) and dorsal view (f); ucmp 37302, vertebra 54 in left lateral view (g); arch 4012, partial caudal centrum (h through j) in ?posterior (h), ?left lateral (i), and dorsal view (j); ucmp 37302, left radius in lateral view (k); arch 4012, distal end of ?left radius (l–n) in ?lateral (l), distal (m), and ?medial view (n); ucmp 37302, distal end of right femur, reversed (o, q) in lateral (o) and distal view (q); arch 4012, distal end of left femur (p, r) in lateral (p) and distal view (r); ucmp 37302, proximal end of left fibula (s, u) in proximal (s) and lateral view (u); arch 4012, fragment of ?left fibula shaft (t, v) in proximal (t) and lateral (v) view; ucmp 37302, proximal end of left metatarsal iv (w, y) in lateral (w) and proximal view (y); arch 4012, proximal end of ?left metatarsal iv (x, z) in lateral (x) and proximal view (z); ucmp 37302, proximal end of left metatarsal iii (aa, ac) in ventral (aa) and proximal view (ac); arch 4012, proximal end of ?left metatarsal iii (ab, ad) in ventral (ab) and proximal view (ad); ucmp 37302, right metatarsal i in lateral view (ae); arch 4012, distal end of ?right metatarsal i (af, ag) in lateral (af) and dorsal view (ag). abbreviations: as, articular surface; hy, hypantrum; lc, lateral conyle; lf, ligament fossa; g, groove; ncj, neurocentral junction; prz, prezygapophysis; tfc, tibiofibular crest. elements of ucmp 37302 are not to scale. dashed lines indicate broken margins. iii iv iii iv b c a iiiiiiv v iiiii�� i v iiiiiiv v iiiii�� i v figure 3. left metatarsi of larger-bodied saurischians in the kayenta formation in proximal view. (a) dilophosaurus wetherilli, ucmp 37302 (modified from marsh and rowe, 2020); (b) theropoda, arch 4012; (c) sarahsaurus aurifontanalis, tmm 43646-3 (reversed, modified from marsh and rowe, 2018). elements are not to scale. roman numerals identify each digit. 50 the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah marsh, a.d., de blieux, d.d., and kirkland, j.i. geology of the intermountain west 2024 volume 11 fibula a portion of the proximal end of the shaft is present, identified by the cross-sectional shape in proximal view (figure 2t). this is likely the shaft of a fibula and not a fragment of the shaft of the femur because what would be the medial side has a small patch of cortical bone that would not be present inside a femur. the fibula fragment would have been too proximal to preserve the ridge present in dilophosaurus wetherilli (e.g., ucmp 37302) and sarahsaurus aurifontanalis (e.g., tmm 43646-2) that represents the insertion site for the m. iliofibularis (parrish, 1993; nesbitt, 2011). metapodials half of the distal articular surface of metatarsal i is present (figures 2af and 2ag). it preserves a ligament fossa as well as the ventral expansion found in dilophosaurus wetherilli (e.g., ucmp 37302) but not sarahsaurus aurifontanalis (e.g., tmm 43646-3). the identifications of metatarsals iii and iv are based on the shape of the partial proximal ends of each element (figure 3b). metatarsal iii is broken ventrally but the dorsal margin is roughly parallelogram-shaped in proximal view (figure 2ad), similar to that of dilophosaurus wetherilli (e.g., ucmp 37302; figure 3a). the shape of the proximal end is also consistent with that of d. wetherilli in ventral view. the dorsal and medial margins of the proximal end of metatarsal iv are complete, but the ventral portion is broken. in proximal view (figure 2z), the remaining bone is roughly subtriangular in shape, consistent with metatarsal iv of dilophosaurus wetherilli (e.g., ucmp 37302). discussion vertebrate body fossils and age of the kayenta formation two major lithologic regimes are represented in the kayenta formation, described as the sandier ‘typical facies’ (i.e., what is present at the type section; baker et al., 1936) and the finer-grained ‘silty facies’ (averitt et al., 1955; harshbarger et al., 1957). the delineation of these regimes bisects northern arizona and southern utah (figure 1b) such that the typical facies is present northeast of tuba city, arizona, including southeastern utah, and the silty facies occurs at the adeii eechi cliffs southeast of tuba city and in southwestern utah. these two facies have a dramatic difference in vertebrate body fossil occurrence, which drove differing age interpretations for the formation and the location of the triassic-jurassic boundary within the glen canyon group since the early part of the 20th century. arizona the kayenta formation was recognized as a different unit from the todilto formation of the middle jurassic san rafael group and ultimately named for its type section at comb ridge near kayenta, arizona (baker et al., 1936). at that time, the formation was thought to be triassic in age and its only reported fossils were plant “stems” (baker et al., 1936, p. 5), unionid bivalves (baker, 1933), and dinosaur footprints (eubrontes and anchisauripus according to r. lull, yale peabody museum, written communication, 1917; gregory, 1917, p. 56). age interpretations for the kayenta formation oscillated between the late triassic and early jurassic in subsequent decades, justified primarily by two major fossil discoveries within the formation published in the same year of 1954. the first was the discovery of two skeletons of a relatively large hypothesized megalosaurus-like theropod dinosaur from near the base of the silty facies near moenave, arizona (welles, 1954); this taxon was later named dilophosaurus wetherilli (welles, 1970). welles (1984) used the size and proportions of limb elements to argue early jurassic affinities for this new dinosaur, now hypothesized to be only distantly related to european middle jurassic tetanuran theropods (marsh and rowe, 2020). the type locality of dilophosaurus wetherilli is across the road from a famous megatracksite at the base of the kayenta formation (welles, 1971; morales and colbert, 1986; lucas et al., 2005; marsh, 2018). the second major discovery was of a tritylodontid cynodont skeleton associated with a protosuchid crocodyliform (lewis, 1958) near the top of the typical facies near comb ridge in kayenta, arizona (figure 1b; averitt et al., 1955; harshbarger et al., 1957). the trity51 the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah marsh, a.d., de blieux, d.d., and kirkland, j.i. geology of the intermountain west 2024 volume 11 lodontid represented the first of its kind in the western hemisphere at the time and was first thought to more closely resemble ‘old world’ taxa from the triassic of china and south africa (averitt et al., 1955). thus, during the late 1950s the silty facies of the kayenta formation seemed to provide a younger age estimate for the formation than the typical facies. subsequent work helped to clarify this chronological uncertainty, including extensive revisions of the stratigraphic relationships and major unconformities of the kayenta formation and stratigraphically adjacent units (e.g., lewis et al., 1961; pipiringos and o’sullivan, 1978; peterson and pipiringos, 1979; clark and fastovsky, 1986), more refined understanding of triassic/jurassic strata and vertebrate assemblages around the world (e.g., olsen and sues, 1986; luo and wu, 1994; fang et al., 2000; huang, et al., 2005; bordy et al., 2020), revisions in the anatomy and taxonomy of theropods and tritylodontids (e.g., kermack, 1982; welles, 1984; sues, 1986a, 1986b, 1986c), and the eventual use of u-pb detrital zircon geochronology within the glen canyon group (dickinson and gehrels, 2003, 2010; marsh et al., 2014). the entire kayenta formation is now accepted to be early jurassic in age (sinemurian-pliensbachian) and the end-triassic mass extinction and triassic-jurassic boundary (now chronologically decoupled; blackburn et al., 2013) occur within the underlying dinosaur canyon member of the moenave formation and the lateral equivalent of the wingate sandstone (figure 1a; lucas et al., 1997; donohoo-hurley et al., 2010; martz et al., 2017; suarez et al., 2017). other than the tritylodontid (and others later found at the same site) and protosuchid mentioned above (lewis, 1958), the only other vertebrate fossils from the typical facies of arizona occur near tsegi canyon and include hybodont shark teeth and a potential batoid tooth (curtis and padian, 1999); however, it has been suggested that the latter is likely the result of screen wash contamination from a concurrent cretaceous microvertebrate sampling effort at mna (milner et al., 2006). the tritylodontid kayentatherium wellesi was named from the silty facies near many farms, arizona (figure 1b; kermack, 1982), and is considered the senior synonym of the only named tritylodontid from the typical facies of far northeastern arizona (lewis, 1956). most of the vertebrate assemblage of the kayenta formation is known from sites in the silty facies spanning the echo and adeii eechii cliffs along ward terrace (figure 1b). this area includes the type localities of dilophosaurus wetherilli (welles, 1954), ‘syntarsus’ kayentakatae (rowe, 1989), sarahsaurus aurifontanalis (rowe et al., 2010), scutellosaurus lawleri (colbert, 1981), rhamphinion jenkinsi (padian, 1984), kayentasuchus walkeri (clark and sues, 2002), eopneumatosuchus colberti (crompton and smith, 1980), calsoyasuchus valliceps (tykoski et al., 2002), kayentachelys aprix (gaffney et al., 1987), navajosphenodon sani (simões et al., 2022), prosalirus bitis (shubin and jenkins, 1995), eocaecilia macropodia (jenkins and walsh, 1993), dinnebitodon amarali (sues, 1986b), and dinnetherium nezorum (jenkins et al., 1983). in addition to these taxa, the silty facies in that area also produced a larger-bodied thyreophoran (padian, 1989), unnamed protosuchid crocodyliforms (clark and sues, 2002), an oligokyphus-like tritylodontid (sues, 1985), a lungfish (kirkland, 1987; milner and kirkland, 2006), and microvertebrates including actinopterygians (clark and fastovsky, 1986; curtis and padian, 1999; milner et al., 2006), hybodontoid sharks, potential salamanders, and a haramiyid mammaliaform (curtis and padian, 1999). utah the kayenta formation in utah includes the typical facies in the eastern region near moab and the silty facies in the western region around st. george (figure 1b; harshbarger et al., 1957; priddy and clarke, 2020), the latter being underlain by the springdale sandstone as a second lower unit in the formation (lucas and tanner, 2006). the springdale sandstone, the silty facies, and the typical facies of the kayenta formation frequently preserve trace fossils of various dinosaurs and other archosaurs, including megatracksites in the st. george area (deblieux et al., 2004, 2006; hamblin et al., 2006; milner et al., 2012 and references therein; lockley et al., 2018). the silty facies of utah preserves semionotid fish scales at zion national park (lockley, 1984; deblieux et al., 2004, 2006; milner and kirkland, 2006), coelacanths, semionotid and paleoniscoid fish, and poten52 the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah marsh, a.d., de blieux, d.d., and kirkland, j.i. geology of the intermountain west 2024 volume 11 tial crocodylomorph bones at warner valley (milner et al., 2012), as well as unpublished articulated semionotids and teeth belonging to actinopterygians, crocodylomorphs, ornithischians, theropods, and a possible pterosaur from a more recent roadcut near st. george (figure 1b; milner et al., 2017). the typical facies also preserves other fish in utah, including a semionotid fish skeleton from near moab (milner et al., 2006) on exhibit at the moab museum, and a lungfish tooth plate west of goblin valley (frederickson and cifelli, 2017). despite occurring within what would otherwise be mapped as the typical facies of the kayenta formation (figure 1b), the arch dinosaur described here occurs in interbedded red mudstone and white sandstone in the northern part of the paradox basin (madsen et al., 2012), which may have been providing more syndepositional accommodation owing to salt dissolution in the underlying pennsylvanian paradox formation and thus deposit more silt than would otherwise be expected in the typical facies in the broader region (bromley, 1991). other dinosaur fossils from arches national park dinosaur fossils are relatively common in the mesozoic units within the boundaries of arch and are mostly represented by tracks. the church rock member of the upper triassic chinle formation preserves the ichnogenus grallator, likely made by a small-bodied coelophysoid theropod (lockley and gierliński, 2009; martz et al., 2017). grallator is also known from the base of the overlying wingate sandstone (swanson et al., 2005; madsen et al., 2012). at least the lower part of the wingate sandstone is late triassic in age owing to the presence of a phytosaur in the nearby lisbon valley south of moab (morales and ash, 1993; martz et al., 2017). a single zygapophysis was found as float during a survey of the wingate sandstone (madsen et al., 2012), but it is rather large for contemporaneous dinosaurs and because the source stratum was not found it is more parsimonious to consider it to have come down from the overlying kayenta given the rarity of body fossils from the wingate sandstone (tweet and santucci, 2018). in addition to the arch dinosaur body fossils described here, the kayenta formation also preserves indeterminate theropod tracks (swanson et al., 2005), and the overlying lower jurassic navajo sandstone includes grallator (madsen et al., 2012) and tracks of sauropodomorph dinosaurs (navahopus or otozoum; tweet et al., 2018). in the lower upper jurassic units there are tridactyl tracks within the moab tongue member of the curtis formation (swanson et al., 2005). the famous moab megatracksite (including arch) at the contact of the moab tongue member and the overlying summerville formation preserves innumerous tracks and trackways referred to the larger ichnogenera megalosauripus and therangospodus (lockley, 1991, 2022). higher in the section, the upper jurassic morrison formation preserves sauropod postcranial bones including a partial apatosaurine skeleton (doelling, 1985; swanson, et al. 2005). the ruby ranch member of the lower cretaceous cedar mountain formation preserves numerous dinosaurian ichnotaxa, including those belonging to iguanodontid ornithischians, sauropods, and theropods including dromaeosaurids (swanson et al., 2005; madsen et al., 2012; lockley et al., 2014). conclusions the arch specimen described here is important because (1) it represents the first body fossils of a dinosaur from the kayenta formation of utah outside of teeth from a roadcut locality near st. george, and (2) it represents the only unambiguous dinosaur body fossil from the kayenta formation within arches national park. the u.s. national park service has 286 units known to contain fossils (67% of all units as of march 2023; https://www.nps.gov/subjects/fossils/fossilparks-list.htm) and not all have been surveyed, but only 16 were established explicitly to protect paleontological resources (tweet and santucci, 2021). arch was founded to protect geologic resources, and though paleontological resources are considered important resources, they are not considered fundamental resources to the park (https://www.nps.gov/arch/learn/management/ foundation-document.htm#cp_jump_5740030). this discovery shows the potential for more vertebrate body fossils from the typical facies of the kayenta in arizona and utah, highlighting the importance of inventory 53 the first dinosaur postcranial body fossils from the lower jurassic kayenta formation of utah marsh, a.d., de blieux, d.d., and kirkland, j.i. geology of the intermountain west 2024 volume 11 and monitoring of fossil resources in federally protected areas. acknowledgments thanks to scott madsen (ugs) and vince santucci (nps) for their work in the field and reporting on the 2011 arch paleontological survey. we thank kevin padian, pat holroyd, and mark goodwin (ucmp), chris sagebiel and matt brown (tmm), peekay briggs (arch), and matt smith and debbie wagner (pefo) for access to collections and archives in their care. this is petrified forest national park paleontological contribution no. 90. the conclusions presented here are those of the authors and do not represent the views of the united states government. funding was provided by the utah geological survey and the national park 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information. email inquiries to giw@utahgeology.org. an unconformity in the the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide peter d. rowley, robert f. biek, and david b. hacker geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view south of unconformity on hoodle creek. the vertical light-colored beds of the brian head strata are truncated under gently east-dipping, well-bedded brownish-colored gravels likely of the sevier river formation. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 9 2022 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2021–2022 uga board president john south john.south@dominionenergy.com 385.266.2113 president-elect rick ford rford@weber.edu 801.915.3188 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 co-program chair ben gilder dgilder@gmail.com 337.962.8383 treasurer kellen gunderson kellen@zanskar.us 801.634.9737 secretary eugene syzmanski eugenes@utah.gov 801.537.3364 past president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 9 2022 13 abstract pole canyon is cut into the western backslope of the sevier plateau of southwestern utah, a gently-tilted, block-faulted range that extends north from bryce canyon national park through the eastern part of the marysvale volcanic field. the canyon exposes a spectacular angular unconformity that separates brecciated, intensely deformed, and steeply dipping eocene to oligocene sedimentary and volcanic rocks below, from gently east-dipping miocene volcanic rocks above. although identified in 1968 by the senior author, it took renewed geologic mapping in 2015 by all three authors to discover that the rocks below the unconformity were deformed by gravity sliding. we named it the sevier gravity slide, one of the largest terrestrial landslides on earth. the ages of the volcanic rocks above and below the unconformity constrain the age of sliding at between 25.8 and 23.1 ma; later dating elsewhere put the slide movement at between 25.2 and 25.1 ma. an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide peter d. rowley1, robert f. biek2, and david b. hacker3 1geologic mapping inc., p.o. box 651, new harmony, ut 84757; pdrowley@rushisp.com; www.geologicmappinginc.com 2utah geological survey, p.o. box 146100, salt lake city, ut 84114-6100; bobbiek@utah.gov 3department of geology, kent state university trumbull campus, 4314 mahoning ave., warren, oh 44483-1998; dhacker@kent.edu citation for this article. rowley, p.d., biek, r.f., and hacker, d.b., 2022, an unconformity in the pole creek area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide: geology of the intermountain west, v. 9, p. 13–24, https://doi.org/10.31711/giw.v9.pp13-24. © 2022 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the sevier plateau is a 75-mile (120-km) long, north-trending range in the high plateaus of utah that was uplifted on its western side at least 6000 feet (1800 m) by the sevier fault zone and tilted about 3 degrees to the east. pole canyon, whose mouth is just west of antimony in southern grass valley, is cut in the eastern backslope of the sevier plateau (figure 1). pole canyon affords a visit to a spectacular angular unconformity that separates brecciated, intensely deformed, and steeply east-, north-, and west-dipping eocene to oligocene sedimentary and volcanic rocks below from undeformed, gently (3 degrees) east-dipping miocene volcanic rocks above (figure 2). the unconformity is exposed for more than a mile (1.6 km) about 50 feet (15 m) above a dirt road in the bottom of the canyon. the deformed rocks below the unconformity are part of the sevier gravity slide, perhaps the third largest terrestrial landslide on earth. the unconformity provides information on the age of the gravity slide. location the geosite is a series of rock exposures extending along the northern side of east-draining pole canyon, which is between 400 and 800 feet (120-240 m) deep and whose mouth is about a half mile (0.8 km) west of antimony. pole canyon is in the northern part of the deep creek 7.5-minute quadrangle, garfield coun14 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 ty, utah. a dirt road goes 3 miles (5 km) up the bottom of the canyon to a spring whose water is piped to antimony. the eastern end of the geosite (coordinates 38º05'52''n., 112º02'03'' w., circled location #1 on figure 3) is where hoodle creek joins the canyon from the south, a point that is about 2 miles (3 km) up the canyon. the western end of the geosite (38º06'03'' n., 112º03'12'' w., circled location #2 on figure 3), a little more than a mile (1.6 km) farther west, is where the dirt road ends at the spring. two words of caution about this geosite: (1) it requires fording the east fork of the sevier river and (2) the pole canyon road is tricky to find. fording the river requires a high-clearance 4-wheel-drive vehicle—the river bottom has a cobble floor that may be potholed and the banks may be oversteepened by erosion—and the crossing should not be attempted in winter, spring, or when the river is high. to deal with point number two, take utah highway 22 to the antimony mercantile and trailer park in antimony. go south for 0.1 mile (0.15 km), where the highway bends sharply left to head east. at that point a good gravel road to mt. dutton enters the highway from the south. turn right off the highway onto the mt. dutton road and go 0.4 miles (0.6 km) to a bridge across an irrigation canal, just beyond which a lesser dirt road comes in on the right (north) just before the mt. dutton road bends left to a bridge across the sevier river. take the lesser dirt road (an unnumbered road that leads to forest road 1073) north for a little more than 0.1 mile (0.15 km), where it will bear left at a gate in a north-south fence; open the gate and drive through (then close the gate). go north-northwest for about 0.3 miles (0.5 km) to where you can see the road cross the river, just north of where the gulch in pole canyon joins the river. cross the river and head up the northern side of the gulch in pole canyon. if the river crossing is impassable, an overlook into nearby hoodle creek, where the unconformity is also well exposed, is 4.0 miles up the well-graded gravel road to mt. dutton (forest road 125). there, a small pullout on the right affords a view down into hoodle creek (figure 3a). 112°15' 112° 38° 38°15' 0 1 2 3 4 5 0 2 4 6 kilometers miles n utah map location piute reservoir otter creek reservoir junction kingston antimony circleville 89 89 153 62 22 62 sev ier river e a s t f o r k s e v i e r r i v e r pole canyon tu sh er m ou nt ai ns g r a s s v a l l e y s e v i e r p l a t e a u kingston canyon phonolite hill fo rs he a m ou nt ai n x mount dutton x hoodle creek geosite figure 1. location map of the kingston canyon and pole canyon areas, piute and garfield counties, utah. the geosite is a mile-long (1.6 km) span in pole canyon. figure 2. view east down pole canyon showing gently east-dipping, undeformed osiris tuff (to) and underlying volcanic mudflows of the mount dutton formation (td) that unconformably overlie variously dipping and deformed white brian head (tbh) strata in the lower half of the slope. 15 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 antimony willow s pring c reek fores t creek b 3 50 64 15 23 b b b b b b b 3 3 26 a a' qta qta qtb qtb qtb qtb qta qta qta tbh tda tbh qtb ttw ttw tdk tda tda tdatda tdk ttw qtb qtb to to to to to to qtb tda tda tda tda s e v i e r p l a t e a u hoodle creek pole canyon east fork sev ier river mt. dutton road 22 0 1 2 1 2 3 miles kilometers 112°05' w 112° w 38°05' n 38°07'30" n 2 1 8000 7000 6000 5000 2400 2100 1800 1500 4000 fe et m et er s a west a' east unconformity to to tbh tda tda tda tda ttw tdktda sevier gravity slide gravity slide shear plane t a t a vertical exaggeration = 2x qta qtb ttw tbh to tdk tda tda units within sevier gravity slide quaternary-tertiary alluvium quaternary-tertiary basalt osiris tuff mount dutton formation kingston canyon tuff member of mount dutton formation three creeks member of bullion canyon volcanics, wah wah springs fm brian head formation river or stream road unconformity above sgs contact normal fault, bar and ball on downthrown side line of cross section gravity-slide shear plane (cross section) t, toward; a, away strike and dip of rocks b 3 t a a a' figure 3. geologic map and cross section of the pole canyon area, garfield county, utah, showing location of the mile-long (1.6 km) geosite area between areas labeled 1 and 2. geologic map after rowley (1968) and rowley and others (2005). vertical exaggeration (vertical scale) on the cross section is two times (the horizontal scale). the sevier gravity slide moved south, toward the viewer, then during later basin-range deformation all rocks including the slide were tilted east. 16 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 geologic setting the geosite described here provides a glimpse of the geologic history before the present topography formed. the present topography consists of a range within the high plateaus, a subprovince of the colorado plateau. but in fact the high plateaus is a transition zone between the great basin to the west and the main part of the colorado plateau to the east. the great basin has been undergoing basin-range deformation, which is characterized by east-west crustal extension (pulling apart of the crust in an east-west direction) for the last 20 million years. the result of the deformation is north-trending ranges that alternate with north-trending basins, all created by north-trending normal faults. normal faults are those in which the sense of displacement between one side of the fault with respect to the other is largely vertical, and the faults are high-angle, with an average dip of 60o in the downthrown direction. although this deformation started at about 20 ma, its main phase that produced the present topography dates only to about 10 ma (rowley and others, 1981, 2005). in contrast to such deformation, the main part of the colorado plateau is largely undeformed, being made figure 3a. view north to unconformity on hoodle creek from overlook on forest road 125. here, west-dipping, severely fractured three creeks tuff (tbtc) and mount dutton formation volcanic mudflow deposits (td) in the bottom of the canyon are unconformably overlain by gently east-tilted gravels of the sevier river formation (tsr) and a remnant of a pliocene basaltic lava flow (tb). 17 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 up of plateaus and mesas of flat-lying rocks. however, the high plateaus is more closely allied with the great basin, differing only by having fewer and smaller faults. the ranges and plateaus of the high plateaus were uplifted along the normal faults, and adjacent valleys were downthrown along the normal faults. the rocks making up the northern high plateaus are largely volcanic rocks that have an age of early oligocene to pleistocene (about 33 ma to several tens of thousands of years), if not younger, formed as part of the huge (75 miles [120 km] in diameter) marysvale volcanic field. in the southern high plateaus, the volcanic rocks sit on a light-gray sedimentary sequence deposited by streams in channels and floodplains and by lakes, known as the brian head formation of late eocene to early oligocene age (figure 2) (biek and others, 2015a). the brian head contains beds of airfall tuff that represent the start of volcanism in the great basin and marysvale field; these beds have weathered (altered) to smectite clays that are weak and prone to landsliding. south of pole canyon in the southern sevier plateau, the brian head in turn rests on the claron formation, a late paleocene(?) and eocene sequence of stream and lesser lake strata, mostly altered to paleosols (ancient soils) and all predating middle tertiary volcanism. the claron is famous for its erosion into pink hoodoos at bryce canyon national park and cedar breaks national monument (biek and others, 2015a). claron strata underwent rapid facies changes northward from bryce canyon such that, near antimony, equivalent strata are yellow-brown sandstone, siltstone, mudstone, and conglomerate that lack the bright colors and fossil soils of typical claron. the geologic setting of the pole canyon area is identical to that of nearby kingston canyon to the north (see the kingston canyon geosite by rowley and others). the kingston canyon geosite describes evidence that documents the age of the basin-range deformation that resulted in the uplift of the sevier plateau. the pole canyon geosite, in contrast, bears on an entirely different topic, much older than the story told by kingston canyon. this story is the sevier gravity slide. as with the geologic story of kingston canyon, pole canyon was mapped as part of a dissertation study of the southern sevier plateau by the senior author (rowley, 1968). the unconformity was recognized at this time, for it is well exposed along the northern wall of pole canyon. it was also mapped to the south, where it extends for more than a mile (1.6 km) along both walls of the canyon of hoodle creek, a tributary to pole canyon. and it was mapped along forest creek, the next east-draining canyon south of hoodle creek; there its outcrops extend for about 1.5 miles (2.5 km) along the canyon walls near the confluence of forest creek and willow spring creek. only pole canyon is accessible by a maintained dirt road. rowley (1968) interpreted that the rocks beneath the unconformity represent the result of an old fault that offset and tilted older rocks, which were then eroded to form the unconformity, after which additional volcanic rocks were deposited on the unconformity. the sevier plateau was remapped by rowley during the late 1970s as part of a major study by the u.s. geological survey (usgs) of mineral resources of the marysvale volcanic field. the remapping found that the unconformity of pole canyon was also exposed at the western crest (mt. dutton) of the sevier plateau. extreme southern parts of the dissertation area were also published (rowley and others, 1987). the marysvale study, with t.a. steven, c.g. cunningham, and rowley as principals but with many colleagues, lasted almost a decade and resulted in more than 200 publications. one final publication was the richfield 1º x 2º quadrangle (1:250,000 scale), which included the geosite area and most of the marysvale field and extended west almost to the nevada border (steven and others, 1990). most of the marysvale effort, however, was concentrated in the heart of the marysvale field north of kingston canyon, where most of the intrusive, caldera, and vent sources (the most likely sites for mineral resources) of the volcanic rocks were exposed, and this area was mapped as 1:24,000-scale quadrangles. summary geologic maps were published by cunningham and others (1983), steven and others (1990), and rowley and others (2002). later, under contract with the utah geological survey (ugs), the beaver 1:100,000-scale quadrangle (rowley and others, 2005), which covered most of the volcanic field, was compiled. none of these studies recognized the real significance of the angular unconformity. the significance, of course, is that the rocks below 18 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 the unconformity had been deformed by movement of a huge gravity slide. that realization, however, first required the recognition of another, even larger gravity slide that mantled high points of the markagunt plateau, the next range west of the southern sevier plateau. initial recognition, yet never realizing its great size, was by professor john j. anderson and his graduate students at kent state university, who did extensive mapping in the late 1970s, the 1980s, and the early 1990s, resulting in theses, published maps, and a final report that named it the markagunt megabreccia (anderson, 1993). florian maldonado of the usgs found more outcrops of gravity slides in the western markagunt plateau and the next range to the west, the red hills (e.g., maldonado, 1995). putting these pieces of old gravity slides together, then totaling about 200 mi2 (500 km2), then expanding the mapping was the work of bob biek of the ugs, who had been assigned in 2006 to geologically map the panguitch 1:100,000-scale quadrangle, south of the beaver quadrangle. over multiple years, as he compiled areas in the panguitch sheet mapped by anderson, students, and maldonado, then mapped those quadrangles in-between that had not been studied, he found that the individual pieces of slides correlated with each other and interpreted that many intervening areas were underlain by the same slide plane, thus first recognizing that he was seeing a slide of truly monumental proportions. realizing that he needed more expertise to study the features of gravity slides, he enlisted the help of professor dave hacker of kent state university, whose areas of research included gravity slides, notably in the iron springs and bull valley mining districts southwest of cedar city (e.g., hacker, 1998; hacker and others, 2002, 2007). then dave discovered, on the markagunt plateau, the first veins of pseudotachylyte! pseudotachylyte (frictionite) is a friction-generated melt rock typically produced on deeply buried (>6 miles [10 km]) fault zones and in meteorite impacts; rarely is it associated with gigantic landslides that formed near the earth’s surface. pseudotachylyte is important to demonstrate high temperatures on slip surfaces, hot enough to melt rock and thus implying high slip rates to generate enough heat so near the earth’s surface. this and other evidence shows that the markagunt slide moved catastrophically, probably over the span of minutes, south from highlands in the active center of the volcanic field. together we realized that the markagunt slide was enormous, rivaling the one other known great slide, the famous heart mountain gravity slide, of eocene age, in the absaroka mountains of northwestern wyoming (see, for example, hauge, 1993; malone and craddock, 2008; beutner and hauge, 2009). the first writeups of the story of this large slide, and the name markagunt gravity slide (mgs), came from hacker and others (2014), then biek and others (2014). at this time, the mgs was estimated to have a size of 1300 mi2 (3400 km2), larger than rhode island and the same size as the heart mountain slide. but the outer boundaries of the markagunt slide had not all been found, and additional tracing of these into adjacent mapped areas continued over the next several years. the panguitch sheet, which contained the southern part of the slide, was published in final form by biek and others (2015a), at which time the mgs size was estimated to be 1600 mi2 (4160 km2). much of the slide by then was found to be in adjoining 1:100,000-scale sheets, notably the tushar mountains of the beaver sheet where the breakaway area was. in the field season after publication of the panguitch sheet, biek and hacker gave a second look at canyons cutting the eastern sevier plateau south of forest creek, an area within the panguitch sheet and within the areas mapped by rowley (1968) and rowley and others (1987). although some of the same rock units that were exposed beneath the pole canyon unconformity had been mapped in these southern canyons by rowley (1968) and rowley and others (1987), no unconformity had been recognized. biek and hacker, however, noticed that these same units (those beneath the pole canyon unconformity) were significantly deformed, with features that resembled deformed rocks within the mgs. all of a sudden, it became clear that another huge landslide caused not only these southern deformed rocks, but those beneath the unconformity as well. this overall feature was named the sevier gravity slide (sgs). again, boundaries were sought in outlying areas by the authors, including in the breakaway area in the beaver sheet and in the loa sheet (biek and others, 2015b) east of the beaver map. a week-long international field conference, the thompson field forum sponsored by the geological society of america, utah 19 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 geological association, and ugs was held september 2017. it allowed landslide experts to visit and help interpret the mgs and sgs (biek and others, 2017), which we then interpreted to be 2000 mi2 (5000 km2, about the size of delaware) and 600 mi2 (1500 km2), respectively, in size. interestingly, new field work by malone and others (2014) had by then suggested that the heart mountain slide was also about 2000 mi2 (5000 km2) in size. a large summary report on the field stops of the field forum and their meaning, distributed in draft form to forum participants, was prepared for publication (biek and others, 2019). the beaver sheet is being revised, one quarter at a time (rowley and others, 2019, 2020), and parts of the loa and panguitch sheets will also be remapped, showing the extent of the slides. the site itself after crossing the sevier river, most of the outcrops you will see in pole canyon, until hoodle creek enters on the south, consist of undeformed volcanic mudflow breccia, overlain by a ledge about 20 to 50 feet (6-15 m) thick of similarly undeformed osiris tuff, all dipping east at about 3o (figure 2). the osiris tuff is a distinctive, tan and gray, densely welded ash-flow tuff with k-ar ages (anderson and rowley, 1975) and 40ar/39ar ages (cunningham and others, 2007; ball and others, 2009; ugs unpublished data) of about 23.1 ma. it is widely exposed throughout the marysvale volcanic field and was derived from the monroe peak caldera, the largest in the field and almost 30 miles (50 km) north of pole canyon (rowley and others, 2002). all these rocks are above the unconformity and postdate the sgs. furthermore, they put an upper age limit on the sgs. (in contrast, the osiris was deformed by the mgs, and the age of overlying undeformed rocks indicate that the mgs slid sometime between 23.1 and 22.75 ma). based on the rocks exposed at the geosite and elsewhere, we can closely constrain the age of movement of the sgs, demonstrating that it is about 2 million years older than the mgs. incidentally, the view south towards hoodle creek reveals a second, younger angular unconformity. although we have not yet studied this area in detail, it appears that osiris tuff and mount dutton strata are eroded away so that volcaniclastic gravels, likely of the sevier river formation, rest directly on vertical brian head strata (figure 4). upon reaching the easternmost point of the geosite, which is just before where hoodle creek joins the canyon, white cross-bedded sandstone and mudstone of the brian head formation are exposed low on the northern wall of the canyon, beneath the gently east-dipping mudflows. although these rocks do not look badly deformed, they are dipping 28º toward the northeast and underlie the unconformity. as one goes westward up the canyon, where the stream has cut a little more deeply into the rocks, the steeply dipping rocks that underlie the unconformity are better exposed. the unconformity, dipping eastward at about 3o, is obvious about 50 feet (15 m) above the bottom of the canyon. it is overlain by mudflow beds and locally the osiris tuff, all dipping east the same amount. brian head rocks below the unconformity are mostly tan and light-gray, pebbly to bouldery, tuffaceous sandstone, with some debris flows, mudstone, and conglomerate. most of the pebbles, cobbles, and boulders are volcanic, but perhaps 10 percent are white limestone and quartzite. in most places these rocks are clearly deformed by shears of mostly low-angle, and beds are locally broken and churned within overlying or underlying beds (figure 5). these beds are in places weathered into hoodoos. some of the larger clasts (as much as 3 feet [1 m] in diameter) in the sandstone are shattered, and many quartzite clasts (which seem to be the most brittle clasts) are broken into pieces that have moved with respect to each other, a feature called jigsaw deformation that is considered characteristic of large landslides (and also of debris avalanches) (e.g., pierson and others, 2018; biek and others, 2019). dips as steep as 64º were measured, but most of the section may be overturned, for dips are in different directions, although most are northerly. at the western end of the geosite, where the dirt road ends at the spring, are massive, tan and lightto medium-gray, crystal-rich ash-flow tuffs of the 30.5 ma wah wah springs formation (rowley, 1968; anderson and rowley, 1975) and the overlying 27 ma three creeks member (steven and others, 1979) of the bullion canyon volcanics (the section is at least 100 feet [30 m] thick), locally sheared and brecciated (figure 20 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 6), and dips westerly at about 15º, and is locally cut by clastic dikes (figure 7). these two tuff units are exposed in both the northern and southern walls of the canyon, with the spring developed in joints and shears in these tuffs. the base of the wah wah is brecciated but crumbly and poorly exposed and not photogenic. some of the sandstone below this contact has deformation bands, a strange hardening of beds at various angles that is distinctive in some sandstones that have been compressed (davis, 1999). farther west up the canyon, beyond the road and spring, a deformed 30-foot-thick (9 m), red, crystal-poor, densely welded ash-flow tuff known as the kingston canyon tuff member of the mount dutton formation, which also overlies the three creeks member in other places too, is exposed dipping westward beneath the unconformity, which is visible on the canyon walls above. the tuff has a k-ar age of 25.8 ma (anderson and rowley, 1975; fleck and others, 1975), which makes it one of the youngest rocks involved in the sgs. the significance of the pole canyon geosite is that its unconformity provides clear evidence of deformation of rocks below it. and with the evidence of similar deformed rocks as far north as the undeformed margin of the monroe peak caldera, and as far south as the southernmost sevier plateau, it is easy to interpret this as another huge gravity slide. the slide mass broke away from a highland of erupting stratovolcanoes to the north, which were being uplifted by a rising underlying batholith (large plutonic mass) that was the source for the volcanoes in the volcanic field. at the time the figure 4. view south to unconformity on hoodle creek; inset photograph shows vertical brian head strata (tbh) truncated under gently east-dipping, well-bedded gravels likely of the sevier river formation (tsr?). 21 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 southern sevier plateau, including the kingston and pole canyon areas, were southern lowlands, and that is where the slide headed. it was only later, during basin-range deformation, that the sevier plateau assumed its present topography. pole canyon constrains the age of sgs landslide failure at a catastrophic instant in miocene time, somewhere between 25.8 and 23.1 ma, the ages of the kingston canyon member and the osiris tuff. another red, crystal-poor, densely welded ash-flow tuff, the 25.1 ma antimony tuff member of the mount dutton formation, underlies the osiris tuff in kingston canyon and is similarly not deformed. and along the west flank of the sevier plateau north of kingston canyon, still another slightly older, densely welded ash-flow tuff, the tuff of tibadore, is deformed. it recently yielded an age of about 25.2 ma, so that we now know that the sgs was emplaced between about 25.2 and 25.1 ma. emplacement is thus constrained to a short interval of time between the eruptions of two similar densely welded ash-flow tuffs. it is tempting to talk about such eruptions as a trigger for the sgs, and that mystery is one we continue to ponder. acknowledgments we thank grant willis and mike hylland (ugs) and kimm harty (ugs retired) for technical review of the manuscript, and lori douglas (ugs) for drafting the figures. figure 5. steeply northeast-dipping brian head formation exposed in the northern wall of pole canyon. tan ledge in upper right is undeformed osiris tuff (to) above the unconformity, dipping gently east (right). hammer for scale. 22 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 a b figure 6. brecciated and sheared wah wah springs formation on the northern wall of pole canyon (north of the spring). (a) two large fractured clasts can be seen below the pick of the rock hammer, and small breccia clasts can be seen between them and left of the pick of the hammer. (b) fractured blocks commonly exhibit puzzle-like patterns with small offsets between pieces, a fabric we call jigsaw fractures. figure 7. clastic dike (injectite) in wah wah springs formation. clastic dikes are evidence of overpressured fluids at the base of the slide that serve to facilitate sliding. the dike rock is a breccia of mostly ground up wah wah springs injected under pressure into cracks in upper-plate rocks. 23 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 references cited anderson, j.j., 1993, the markagunt megabreccia—large miocene gravity slides mantling the northern markagunt plateau, southwestern utah: utah geological survey miscellaneous publication 93-2, 37 p. anderson, j.j., and rowley, p.d., 1975, cenozoic stratigraphy of southwestern high plateaus of utah, in anderson, j.j., rowley, p.d., fleck, r.j., and nairn, a.e.m., editors, cenozoic geology of southwestern high plateaus of utah: geological society of america special paper 160, p. 1–52. ball, j.l., bailey, c., and kunk, m.j., 2009, volcanism on the fish lake plateau, central utah [abs.]: geological society of america abstracts with programs, v. 41, no. 6, p. 17. beutner, e.c., and hauge, t.a., 2009, heart mountain and south fork fault systems—architecture and evolution of the collapse of an eocene volcanic system, northwest wyoming: rocky mountain geology, v. 44, no. 2, p. 147–164. biek, r.f., eaton, j.g., rowley, p.d., and mattox, s.r., 2015b, interim geologic map of the western loa 30' x 60' quadrangle, garfield, piute, and wayne counties, utah (year 2): utah geological survey open-file report 648, scale 1:100,000. biek, r.f., hacker, d.b., and rowley, p.d., 2014, new constraints on the extent, age, and emplacement history of the early miocene markagunt megabreccia, southwest utah—the deposit of one of the world’s largest subaerial gravity slides, in maclean, j.s., biek, r.f., and huntoon, j.e., editors, geology of utah’s far south: utah geological association publication 43, 565–598 biek, r.f., hacker, d.b., and rowley, p.d., 2017, catastrophic mega-scale landslide failure of large volcanic fields (thompson field forums report): gsa today, v. 27, no. 12, p. 30–31. biek, r.f., rowley, p.d., anderson, j.j., maldonado, f., moore, d.w., hacker, d.b., eaton, j.g., hereford, r., sable, e.g., filkorn, h.f., and matyjasik, b., 2015a, geologic map of the panguitch 30' x 60' quadrangle, garfield, iron, and kane counties, utah: utah geological survey map 270dm, 162 p., scale 1:65,000. biek, r.f., rowley, p.d., and hacker, d.b., 2019, the gigantic markagunt and sevier gravity slides resulting from mid-cenozoic catastrophic mega-scale failure of the marysvale volcanic field, utah, usa: geological society of america field guide 56, 121 p., https://lccn.loc.gov/2019045272. cunningham, c.g., rowley, p.d., steven, t.a., and rye, r.o., 2007, geologic evolution and mineral resources of the marysvale volcanic field, west-central utah, in willis, g.c., hylland, m.d., clark, d.l., and chidsey, t.c., jr., editors, central utah—diverse geology of a dynamic landscape: utah geological association publication 36, p. 143–162. cunningham, c.g., steven, t.a., rowley, p.d., glassgold, l.b., and anderson, j.j., 1983, geologic map of the tushar mountains and adjoining areas, marysvale volcanic field: u.s. geological survey miscellaneous investigations series map i-1430-a, scale 1:50,000. davis, g.h., 1999, structural geology of the colorado plateau region of southern utah, with special emphasis on deformation bands: geological society of america special paper 342, 157 p. fleck, r.j., anderson, j.j., and rowley, p.d., 1975, chronology of mid-tertiary volcanism in high plateaus region of utah, in anderson, j.j., rowley, p.d., fleck, r.j., and nairn, a.e.m., editors, cenozoic geology of southwestern high plateaus of utah: geological society of america special paper 160, p. 53–61. hacker, d.b., 1998, catastrophic gravity sliding and volcanism associated with the growth of laccoliths—examples from early miocene hypabyssal intrusions of the iron axis magmatic province, pine valley mountains, southwest utah: kent, ohio, kent state university, ph.d. dissertation, 258 p., scale 1:24,000. hacker, d.b., biek, r.f., and rowley, p.d., 2014, catastrophic emplacement of the gigantic markagunt gravity slide, southwest utah (usa)—implications for hazards associated with sector collapse of volcanic fields: geology, v. 42, no. 11, p. 943–946. hacker, d.b., holm, d.k., rowley, p.d., and blank, h.r., 2002, associated miocene laccoliths, gravity slides, and volcanic rocks, pine valley mountains and iron axis region, southwestern utah, in lund, w.r., editor, field guide to geologic excursions in southwestern utah and adjacent areas of arizona and nevada, geological society of america, rocky mountain section meeting, cedar city, utah: u.s. geological survey open-file report 02-172, p. 236–283. hacker, d.b., petronis, m.s., holm, d.k., and geissman, j.w., 2007, shallow emplacement mechanisms of the miocene iron axis laccolith group, southwest utah, in lund, w.r., editor, field guide to geologic excursions in southern utah: utah geological association publication 35, 49 p. hauge, t.a., 1993, the heart mountain detachment, northwestern wyoming—100 years of controversy, in snoke, a.w., steidtman, j.r., and roberts, s.m., editors, geology of wyoming: wyoming geological survey memoir 5, p. 530–571. maldonado, f., 1995, decoupling of mid-tertiary rocks, red hills-western markagunt plateau, southwestern utah, in scott, r.b., and swadley, w.c., editors, geologic studies in the basin and range—colorado plateau transition in southeastern nevada, southwestern utah, and northwestern arizona: u.s. geological survey bulletin 2056, p. 233–254. malone, d.h., and craddock, j.p., 2008, recent contributions to the understanding of the heart mountain detachment, wyoming: northwest geology, v. 37, p. 21–40. malone, d.h., craddock, j.p., and mathesin, m.g., 2014, origin of allochthonous volcanic rocks at squaw peaks, wyoming—a distal remnant of the heart mountain slide?: northwest geology, v. 51, p. 321–336. 24 an unconformity in the pole canyon area (sevier plateau) west of antimony, western garfield county, utah, and its bearing on the sevier gravity slide rowley, p.d., biek, r.f., and hacker, d.b. geology of the intermountain west 2022 volume 9 pierson, t.c., siebert, l., harpel, c.j., and scott, k.m., 2018, geologic field-trip guide of volcaniclastic sediments from snow and ice-capped volcanoes—mount st. helens, washington, and mount hood, oregon: u.s. geological survey scientific investigations report 2017–5022–f, 97 p., https://doi. org/10.3133/sir20175022f. rowley, p.d., 1968, geology of the southern sevier plateau, utah: austin, university of texas, ph.d. dissertation, 385 p. rowley, p.d., biek, r.f., hacker, d.b., vice, g.s., mcdonald, r.e., maxwell, d.j., smith, z.d., cunningham, c.g., steven, t.a., anderson, j.j., ekren, e.b., machette, m.n., and wardlaw, b.r., 2019, interim geologic map of the southwestern quarter of the beaver 30' x 60' quadrangle, beaver, iron, and garfield counties, utah: utah geological survey open-file report 686dm, 18 p., scale 1:100,000. rowley, p.d., biek, r.f., hacker, d.b., vice, g.s., mcdonald, r.e., maxwell, d.j., smith, z.d., cunningham, c.g., steven, t.a., anderson, j.j., ekren, e.b., machette, m.n., and wardlaw, b.r., 2020, interim geologic map of the northwestern quarter of the beaver 30' x 60' quadrangle, beaver, iron, and garfield counties, utah: utah geological survey open-file report 729dm, 25 p.,1 plate, scale 1:62,500. rowley, p.d., cunningham, c.g., steven, t.a., workman, j.b., anderson, j.j., and theissen, k.m., 2002, geologic map of the central marysvale volcanic field, southwestern utah: u.s. geological survey geologic investigation series map i-2645-a, scale 1:100,000. rowley, p.d., hereford, r., and williams, v.s., 1987, geologic map of the adams head—johns valley area, southern sevier plateau, garfield county, utah: u.s. geological survey miscellaneous investigations series map i-1798, scale 1:50,000. rowley, p.d., mehnert, h.h., naeser, c.w., snee, l.w., cunningham, c.g., steven, t.a., anderson, j.j., sable, e.g., and anderson, r.e., 1994, isotopic ages and stratigraphy of cenozoic rocks of the marysvale volcanic field and adjacent areas, west-central utah: u.s. geological survey bulletin 2071, 35 p. rowley, p.d., steven, t.a., and mehnert, h.h., 1981, origin and structural implications of upper miocene rhyolites in kingston canyon, piute county, utah: geological society of america bulletin, v. 92, pt. 1, p. 590–602. rowley, p.d., vice, g.s., mcdonald, r.e., anderson, j.j., machette, m.n., maxwell, d.j., ekren, e.b., cunningham, c.g., steven, t.a., and wardlaw, b.r., 2005, interim geologic map of the beaver 30' x 60' quadrangle, beaver, piute, iron, and garfield counties, utah: utah geological survey open-file report 454, 32 p., scale 1:100,000. steven, t.a., cunningham, c.g., naeser, c.w., and mehnert, h.h., 1979, revised stratigraphy and radiometric ages of volcanic rocks in the marysvale area, west-central utah: u.s. geological survey bulletin 1469, 40 p. steven, t.a., morris, h.t., and rowley, p.d., 1990, geologic map of the richfield 1o x 2o quadrangle, west-central utah: u.s. geological survey miscellaneous investigations series map i-1901, scale 1:250,000. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting bart j. kowallis, douglas a. sprinkel, eric h christiansen, skylor steed, and david f. wheatley geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover large, rounded igneous, boulder-sized clast from near where sample wh-1 was collected in the white house area, kane county, utah. the boulder has broken into several large pieces having maximum diameters of 1.3, 1.0, and 0.8 m with several other 0.5 m blocks and is compositionally similar to other igneous clasts in the area. these igneous clasts are weathered out from deris-flow beds within the paria river member of the carmel formation. david wheatley for scale. photograph by mark hansford. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 69 abstract a stratigraphic layer containing rhyolite cobbles and boulders in the middle jurassic carmel formation of southern utah represents a singular, unusual event in the otherwise low-energy sedimentation of this formation. a laser-fusion, single-crystal 40ar/39ar age of 171.73 ± 0.19 ma obtained from sanidine in one of the clasts is about 8 m.y. older than a zircon u-pb age obtained on a fallout tuff from the sediments surrounding the clasts (163.9 ± ~3.3 ma). the volcanic clasts are poorly-welded rhyolite ignimbrites that may have been deposited as much as 200 km from the eruptive center, perhaps along pre-existing valleys. the tuff deposits then remained in place for several million years during which time they were subjected to weathering, alteration, and perhaps topographic inversion, creating mesas capped with tuff underlain by soft middle jurassic silt and mud. triggered by unusual rainfall or earthquakes, debris flows carried the clasts a few 10s of kilometers from their outcrops to the depositional site. earlier work proposed that the middle jurassic arc was a low-standing, arc-graben. if this was the case, then the tectonic setting was likely similar to the modern central american arc in the vicinity of nicaragua where tuffs erupted from a low-standing arc deposited onto an adjacent highland and were then eroded by streams flowing to the east onto a fluvial plain that is near the sea. rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting bart j. kowallis1, douglas a. sprinkel2, eric h christiansen1, skylor steed1, and david f. wheatley3 1department of geological sciences, brigham young university, provo, ut 84604 (bkowallis@byu.edu) 2azteca geosolutions, pleasant view, ut 84414 and utah geological survey, salt lake city, ut 84114; dsprinkel@gmail.com 3department of geology and geophysics, university of utah, salt lake city, ut 84112; davidfwheatley@gmail.com citation for this article. kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley d.f., 2020, rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting: geology of the intermountain west, v. 7, p. 69–96, appendix, https://doi.org/10.31711/giw.v7.pp69-96. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the middle jurassic (163–174 ma) of the western cordillera was a time of active arc magmatism, leaving behind volcanic and plutonic rocks within the arc that have been widely studied (dunne, 1986; karish and others, 1987; busby-spera, 1988; busby-spera and others, 1990; dunne and walker, 1993; riggs and others, 1993; schermer and busby, 1994; fackler-adams and others, 1997; sorensen and others, 1998; fohey-breting and others, 2010; tosdal and wooden, 2015; barth and others, 2017). in addition, ash beds preserved in more distal sedimentary environments have provided further insights into the character and frequency of eruptions along the jurassic arc (wright and dickey, 1963; marvin and others, 1965; nielson, 1988; everett and others, 1989; christiansen and others, 1994, 2015; blakey and parnell, 1995; zhang, 1996; kowallis and others, 2001; dickinson and others, 2010; sprinkel and others, 2011; doelling and others, 2013. chapman (1987, 1989, 1993), marzolf (1990), and 70 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 blakey and parnell (1995) reported on volcanic pebbles, cobbles, and boulders ranging in size from 2.5 cm to 2.6 m in the upper member of the carmel formation (equivalent to the thousand pockets and paria river members; see doelling and others, 2013) in southern utah and northern arizona (figure 1). chapman (1987, 1989) described the clasts as rhyolitic, welded tuffs (ignimbrites) with quartz, sanidine, biotite, plagioclase, hornblende, and magnetite, but having almost all the plagioclase replaced by calcite and the hornblende replaced by iron oxides. based upon directional transport indicators in the enclosing sedimentary rocks, the clasts were transported north and northeast into the carmel formation depositional basin (chapman, 1989; blakey and parnell, 1995). but how did cobbleand boulder-sized clasts travel from somewhere near the western continental margin jurassic volcanic arc to their current depositional location? chapman (1993) proposed that debris flows generated by huge floods carried the cobbles and boulders as much as 250 to 300 km from their source in the arc to their present depositional site (palinspastically corrected for later extension), but acknowledged the unresolved problem of how large boulders could move over such large distances. blakey and parnell (1995) suggested that now-eroded outcrops of these volcanic rocks may have only been several kilometers from the sites of boulder and cobble deposition. but blakey and parnell (1995) did not explain why outcrops of ignimbrite might have been so close to the depositional sites when eruptive centers must have been 250 to 300 km away as chapman (1993; luscombe, 2018) recognized. a similar problem of source for coarse volcanic detritus (up to 25 cm+ diameter) occurs in the triassic chinle formation (stewart and others, 1972; dodge, 1973). stewart and others (1986) suggested that one possible solution to the problem was tectonic removal of the source by strike-slip offset along a major shear system cutting between the source area and the deposits. however, this does not seem to be a reasonable solution for the middle jurassic deposits. chapman (1987) examined several possibilities including: (1) the magmatic source was closer to the colorado plateau at the time of clast deposition than the palinspastic reconstruction estimate of 250 to 300 km; (2) a broad, now eroded, volcanic apron existed around the arc region bringing source material closer to the depositional sites of the clasts; (3) transport might have been enhanced by paleovalleys that helped to extend ash-flow and debris-flow runout distances; and (4) an undiscovered jurassic volcanic complex existed much closer to the colorado plateau with deposits that lapped up onto the plateau (similar to the proposal of blakey and parnell, 1995). in this paper we review the stratigraphic setting of the volcanic clasts, re-examine their composition, texture, and age, then, using these data, re-examine possible solutions to the problem of transport distance between the volcanic arc and depositional basin. middle jurassic stratigraphy of the southern kaiparowits basin the kaiparowits basin of south-central utah is one of several laramide basins on the colorado plateau (figure 1). middle jurassic formations exposed in the basin and surrounding region include (in ascending stratigraphic order) the temple cap formation, carmel formation, and entrada sandstone (figure 2). the temple cap formation unconformably overlies the lower jurassic navajo sandstone. it was deposited on the eroded navajo in what was identified as the j-2 unconformity by pipiringos and o’sullivan (1978) but is now considered to be the j-1 unconformity because of regional stratigraphic work of sprinkel and others (2011) and doelling and others (2013). the temple cap formation is well exposed in southwestern and south-central utah. the formation irregularly thins eastward from about 120 m in the st. george area (about 150 km west of the study area) to about 8 m in the lake powell area (about 50 km east of the study area), but is locally missing across the paleotopographic high of the kaibab uplift (peterson and pipiringos, 1979; wright and others, 1979; doelling and others, 2013). the temple cap formation is seemingly missing within the study area but is present about 7 km to the southeast at judd hollow (sprinkel and others, 2011; doelling and others, 2013), suggesting the easternmost flank of the kaibab uplift extends into this area. thin fallout tuffs in the temple cap formation in the region provided 40ar/39ar (sanidine and biotite) and u-pb (zircon) ages that range from 172.93 ± 0.56 to 71 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 area of paleohigh 0 20 40 60 80 100 miles 0 20 40 60 80 100 kilometers ¹ san rafael swell monument upwarp kaiparowits basin henry mtns basin uinta basin blanding basin markaguntpaunsaugunt basins eroded middle jurassic total thickness (arapien-carmel-twin creek) in meters 0-30 30-60 60-120 120-180 180-240 240-300 300-600 > 600 area of igneous clasts basin boundary eroded eroded a r a p i e n b a s i n twin creek limestone twin creek limestone carmel formationcarmel formation ar ap ie n fo rm at io n ar ap ie n fo rm at io n u i n t a a r c h st. george kanab x johnson canyon moab extent of sand influxextent of sand influx zone of pipes and deformation panguitch page escalante salt lake city vernal colo ra do r ive r dirty devil r. gr ee n ri ve r san juan river waterpocket fold teasdale anticline circle cliffs-escalante uplift figure 1. paleogeologic map of utah showing relationships for the middle jurassic along with the location of the igneous clasts in the paria river member of the carmel formation, southwestern part of the kaiparowits basin (modified from doelling and others, 2013). the map also depicts the area of sand influx that formed the thousand pockets member and is responsible for the sandy nature of the other carmel members. the middle jurassic carmel formation (and equivalent strata) generally thins from west to east; however, note that the carmel thins across a paleohigh that stretches from the western margin of the kaiparowits basin northeastward to the western flank of the san rafael swell. the paleotopography developed on the lower jurassic navajo sandstone on which the middle jurassic temple cap formation was irregularly deposited; in some areas along the paleohigh, the temple cap is missing. the red box shows the area enlarged in figure 3. also shown is a zone of pipes and deformed beds in permian to cretaceous strata (between dashed lines), the width approximately shown by the purple arrows (wheatley and chan, 2013, 2018; wheatley and others, 2016; wheatley, 2018. 72 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 170.5 ± 0.95 ma, which indicate the temple cap is aalenian (kowallis and others, 2001; dickinson and others, 2010; sprinkel and others, 2011; doelling and others, 2013; sprinkel and others, in preparation) (figure 3 and table 1). the carmel formation conformably overlies the temple cap formation and contains the igneous clasts; thus, it is described in detail below. conformably overlying the carmel formation is the entrada sandstone. the entrada is exposed about 8 km northwest of the study area and consists mostly of reddish-brown, mediumto large-scale, cross-bedded sandstone that weathers to form rounded bare rock (slickrock) and cliffs (doelling and others, 1989; doelling and others, 2010). the entrada ranges from 90 to 180 m thick in the southern kaiparowits basin (doelling and others, 1989). carmel formation the carmel formation was described and mapped by pioneering geologists investigating the geology of the kaiparowits area (gregory and moore, 1931), the nearby san rafael swell (gilluly and reeside, 1928), and elsewhere in southern and eastern utah (baker and others, 1936). the carmel is formally subdivided into four members throughout southern utah with varying names for the lowest two members, which reflect significant lithofacies changes across the region (figure 2). the four members of the carmel formation in the kaiparowits basin include (in stratigraphic ascending order) the judd hollow, thousand pockets-crystal creek, paria river, and winsor members (figure 2; phoenix, 1963; thompson and stokes, 1970; blakey and others, 1983; doelling and others, 1989, 2013). the carmel 0 20 4010 30 miles n enterprise cedar city gunlock leeds hurricane st. george kanab big water cannonville henrieville escalante boulder alton utah arizona 1 2 3 4 5 166.1 163.5 166.3 170.3 174.1 winsor member paria river member crystal creek member judd hollow mbr paria river member winsor member thousand pocket member co-op creek limestone member sinawava, white throne, esplin point members manganese wash member j-1 unconformity 1-johnson wash 2-lick wash 3-cockscomb 4-study area 5-hole-in-rock road west east winsor = 165–164 ma crystal creek-thousand pockets-paria river = 166–165 ma co-op creek limestone-judd hollow = 169–167 ma temple cap formation = 173–170 ma carmel formation navajo sandstone temple cap formation entrada sandstone entrada sandstone carmel formation temple cap formation navajo sandstone callovian bathonian bajocian aalenian toarcian lo w er ju ra ss ic m id dl e ju ra ss ic formationtime mastagesystem igneous clasts gypsum figure 2. southwest-to-northeast diagram of formation and member names recommended across the middle jurassic embayment in south-central utah. the co-op creek limestone member should only be used in southwestern utah where the member is greater than 25 m thick and where it is mostly limestone in composition. the carmel formation east of the green and colorado rivers (not shown on figure) consists of a lower, mostly planar-bedded sandstone unit (for which we will propose the name rone bailey member in a future publication) and an upper, mostly siltstone and mudstone of the established dewey bridge member. an influx of sand from the south is responsible for the sandy nature of the carmel formation in the kaiparowits basin and the deposition of the thousand pockets member. 73 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 formation in this area was deposited near the southern end of a jurassic western interior seaway that occupied nearly all of utah (blakey and others, 1983; brenner, 1983; kocurek and dott, 1983). the depositional setting ranges from shallow marine to marginal marine, eolian, and fluvial environments. these members are identifiable by their lithology throughout southwestern and eastern utah. the basal member, the judd hollow, is dominated by dark to medium reddish-brown sandstone and siltstone beds of marine to marginal marine origin deposited on a tidal flat. the clastic beds of the judd hollow member grade laterally westward to mostly thick marine limestone strata, interbedded with thin marginal marine sandstone and mudstone beds of the correlative co-op creek limestone member (doelling and others, 1989; doelling and others, 2013). palynomorphs recovered from the mudstone beds and isotopic ages of 169.0 ± 0.62 to 168.2 ± 1.3 ma (concordant u-pb zircon) from ash beds indicate the judd hollow is bajocian in age (sprinkel and others, 2011; doelling and others, 2013; sprinkel and others, in preparation) (figure 3 and table 1). these ages are consistent with the palynologic and isotopic ages obtained from the co-op creek limestone member (kowallis and others, 2001; sprinkel and others, 2011; sprinkel and others, in preparation). the ### ## # # # # ## " " " " " " " " " " alton big water cannonville escalante henrieville kanab panguitch page fredonia glendale fbe eb fow tw-1 tw-2 wr-1 wr-6 jh-1 wh-1 wh-21-1 s ev i e r r ive r escalante river ea st fo rk vir g in r iv er paria river paria river 111°0'0"w 111°0'0"w 111°30'0"w 111°30'0"w 112°0'0"w 112°0'0"w 112°30'0"w 112°30'0"w 37°30'0"n 37°30'0"n 37°0'0"n 37°0'0"n 0 5 10 15 20 miles 0 10 20 30 kilometers¹ jc jc jc 0 500 1,000 feet 0 100 200 300 meters wh-2 1-1 # # jcw jcw jcp jcp jcw u t a h lake powell figure 3. locations and sample numbers of fallout tuffs with isotopic ages from the temple cap (yellow triangles) and carmel (red triangles) formations. the carmel formation outcrop belt is shown in green (jc). the inset map shows the locations of the igneous clast collected from the paria river member of the carmel formation. jcp – paria river member and jcw – winsor member of the carmel formation. results of isotopic age analyses are in table 1. 74 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 judd hollow member thins eastward from 17 m in the study area to 8 m near lake powell (peterson and pipiringos, 1979; wright and others, 1979; doelling and others, 1989). the overlying thousand pockets member of the carmel formation (doelling and others, 2013) is dominated by eolian sand. the unit generally intertongues with fine-grained, marginal marine (tidal flat) red beds of the crystal creek member (peterson and pipiringos, 1979; doelling and others, 2013). fallout tuff beds are preserved in several sections of the crystal creek member within and outside of the study area. outside of the study area ages of 166.0 ± 0.7 to 165.0 ± 1.2 ma (u-pb zircon; sprinkel and others, 2011; doelling and others, 2013; sprinkel and others, in preparation) have been reported (figure 3 and table 1). an age of 167.1 ± 0.7 ma (2σ, sanidine 40ar/39ar) comes from a sample collected at the top of the thousand pockets or the base of the overlying paria river member. in the study area, the thousand pockets and intertonguing crystal creek members are about 60 to 85 m thick and thin eastward near lake powell to about 38 m thick (peterson and pipiringos, 1979; wright and others, 1979; doelling and others, 1989). the paria river member overlies the thousand pockets-crystal creek members and consists generally of dark reddish-brown to light-gray sandstone of marginal marine to fluvial origin deposited mostly on a tidal flat. some sandstone beds are mottled or banded with shades of lightto dark-brown, light-gray, and purplish-gray hues. the paria river includes interbedded dark reddish-brown siltstone and thin beds of dark reddish-brown mudstone and thin beds of calcarenite to limestone. the unit also contains several conglomerate beds, which are of interest because they contain the ignimbrite clasts. the description, chemistry, and age sample number field number type of sample latitude longitude (± 2σ) mineral dated 1-1 ph-2015-05-15-1-1 cobble-sized clast 37.041537 -111.824346 171.73 ± 0.19 ar/ar sanidine 1-2 ph-2015-05-15-1-2 cobble-sized clast 37.041550 -111.824321 1-3 ph-2015-05-15-1-3 cobble-sized clast 37.041687 -111.824493 1-4 ph-2015-05-15-1-4 cobble-sized clast 37.041687 -111.824493 1-5 ph-2015-05-15-1-5 cobble-sized clast 37.041687 -111.824493 2-1 ph-2015-05-15-2-1 boulder-sized clast 37.041687 -111.824493 wh-1 wh-07-20-2013-1 fallout tuff 37.087886 -111.882425 163.6 ± 3.3 u-pb zircon wh-2 wh-07-20-2013-2 cobble-sized clast 37.041766 -111.824458 174 ± 5 u-pb zircon wr-1 wr-111808-1 fallout tuff 36.950250 -111.492433 164.40 ±4.50 ar/ar sanidine wr-6 wr-111808-6 fallout tuff 36.962217 -111.490983 167.10 ±0.70 ar/ar sanidine jh-1 jh-111708-1 sandstone 37.004900 -111.808200 170.5 ±0.95 u-pb zircon eb east bay fallout tuff 37.015167 -111.249817 171.02 ±0.92 ar/ar biotite fbe face bay east fallout tuff 37.009567 -111.245800 169.52 ±0.99 ar/ar biotite fow face one west fallout tuff 37.014333 -111.268450 171.90 ±1.9 u-pb zircon tw-1 tw-111908-1 sandstone 37.645417 -111.464393 168.20 ± 1.30 u-pb zircon tw-2 tw-111908-2 fallout tuff 37.645958 -111.465062 165.30 ± 1.20 u-pb zircon nom gr-051809-1a fallout tuff 38.680934 -110.154717 167.68 ± 0.82 u-pb zircon nom rc-051909-2 fallout tuff 38.752650 -110.038550 166.70 ± 0.52 u-pb zircon note: locations are also shown on figure 3 except 2 sample marked as nom = locations not on map. samples 1-1, 1-2, 1-3, 1-4, and 2-1 all come from the locality and are labeled as 1-1 on figure 3. table 1. sample locations and radiometric ages. 75 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 of the igneous clasts are discussed in a separate section as they are the focus of this study. regionally, the paria river member ranges from about 80 to 180 m thick and thins eastward to 15 m near lake powell (peterson and pipiringos, 1979; wright and others, 1979; doelling and others, 1989). within the study area, the paria river member is 20 to 23 m thick (wheatley, 2018) (figure 4). the capping winsor member of the carmel formation consists of interbedded sandstone, siltstone, and silty mudstone of marginal marine to fluvial origin deposited on a tidal flat. the winsor strata are varicolored forming a colorful banded unit that ranges from dark reddish-brown, reddish-orange, pale-orange, and lightbrown to grayish purple, greenish-gray, and light-gray beds. gypsum beds are typically found in the winsor member but are notably absent in the study area. also atypical in the study area is the amount of sandy material that has infiltrated the member. the sandy nature of the winsor is likely related to the same source of sand that is responsible for deposition of the thousand pockets member (doelling and others, 2013). a volcanic ash bed sampled from near the base of the winsor member (figure 3 and table 1) in the study area provided a u-pb zircon age of 163.6 ± 3.3 ma (u-pb zircon) and indicates a callovian age. palynomorphs recovered from mudstone beds outside the study area indicate that the winsor member is bathonian to callovian (sprinkel and others, 2011; sprinkel and others, in preparation). the winsor member ranges from about 95 to 110 m in the general study area but thins eastward to about 78 m near lake powell. methods samples of volcanic cobbles and of possible volcanic ash were collected in 2013 and 2015 from the carmel formation east of kanab (table 1 and figure 3). the outcrop consists of a layer that contains mostly volcanic pebbles and cobbles in various stages of preservation (figure 5). we collected several of the best-preserved clasts (clasts 1-1, 1-2, 1-3, 1-4, and 1-5), in addition to a sample of a large, highly-weathered volcanic boulder (2-1) that was at least 0.5 m across (we could not determine its full size because it was partially buried). two of us (sprinkel and wheatley) earlier collected material from a purplish-gray, weathered clast (wh-2) out of the same conglomeratic layer from which we collected the other clasts. in addition, we collected a biotite-rich, purple, altered, and likely reworked, fallout tuff (wh-1) from near the white house campground on the paria river approximately 1 m above the base of the winsor member. the cobbles were cut to a billet from which polished thin sections were produced for petrographic and electron microprobe analysis (table 2). a split of each sample was first washed in acid to remove carbonate cement and areas where carbonate has replaced the original tuff. after drying, the split was then pulverized in a tungsten carbide shatter box or agate ball mill for whole-rock chemical analysis. x-ray fluorescence (xrf) analyses were done at brigham young university using a siemens srs-303 spectrometer. major elements (si, al, ti, fe, mn, mg, ca, na, k, and p) were determined on glass disks formed by fusing rock powder with lithium metaborate and are reported as oxides. trace elements (ba, ce, cr, cu, ga, la, nb, nd, ni, pb, rb, sc, sm, sr, th, u, v, y, zn, and zr) were determined on pressed powder pellets with a cellulose backing (table 3). in both cases, natural rocks were used as calibration standards. analytical precision and accuracy were assessed from repeat analyses of international geochemical reference materials. clast 1-1 contained an abundance of clear, apparently unaltered sanidine crystals and a piece of this clast was sent to the wiscar geochronology laboratory at the university of wisconsin-madison for mineral separation 40ar/39ar dating. the 40ar/39ar ages were calculated relative to the fc-201 sanidine standard age of 28.201 ma and a total 40k decay constant of 5.643 e-10/a (kuiper and others, 2008). methodology for laser fusion dating of single crystals of sanidine is outlined on the wiscar lab website (https://geochronology.geoscience. wisc.edu/analytical-approaches/), and values used in calculations are given in table 4 along with data on individual grains. zircons were extracted by heavy-liquid separation methods from the possible fallout tuff (wh1) and from a cobble-sized clast (wh-2). laser ablation icp-ms spot analyses were collected in zircon grains by apatite to zircon, inc. their analytical methodology is available upon request to the authors. 76 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 q u at er n a ry q a st re am a llu vi um q ag a llu vi al g ra ve l q ea m ix ed e ol ia nal lu vi um ju ra ss ic je en tr ad a sa nd st on e jc u ca rm el f m ., w in so rpa ri a m br s. jp t ca rm el f m ., th ou sa nd s po ck et s m br . jc j ca rm el f m ., ju dd h ol lo w m br . jn n av aj o sa nd st on e 1 2 3 4 5 6 2930 m et er s 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 2930 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 8 7 6 5 4 3 2 1 0 8 7 6 5 4 3 2 1 0 clay silt v.f. sand v. sand m. sand c. sand v.c. sand gravel clay silt v.f. sand v. sand m. sand c. sand v.c. sand gravel clay silt v.f. sand v. sand m. sand c. sand v.c. sand gravel clay silt v.f. sand v. sand m. sand c. sand v.c. sand gravel clay silt v.f. sand v. sand m. sand c. sand v.c. sand gravel clay silt v.f. sand v. sand m. sand c. sand v.c. sand gravel en vi ro nm en t o f d ep os iti on sa bk ha fl uv ia l eo lia n d eb ris f lo w co ve re d pl an ar c ro ss -b ed di ng u nd ul at or y/ co nt or te d be dd in g ri pp le s sy nse di m en ta ry f au lti ng u nd i� er en tia te d cr os sbe dd in g ro ot c as ts ri pup c la st s se di m en ta ry s tr uc tu re s pl an ar l am in at io ns tr ou gh c ro ss -b ed di ng m ud c ra ck s ta ng en tia l c ro ss -b ed di ng ig ne ou s cl as t a sh b ed w h -1 ; 1 63 .6 ± 3 .3 m a n w se se ct io n 1 w hi te h ou se n 37 ° 0 5’ 0 9. 75 ” w 11 1° 5 3’ 0 6. 05 ” se ct io n 2 n w p ar ia o ve rlo ok n 37 ° 0 3’ 2 0. 77 ” w 11 1° 5 1’ 1 3. 85 ” se ct io n 3 pa ria o ve rlo ok n 37 ° 0 3’ 1 3. 17 ” w 11 1° 5 1’ 0 8. 79 ” se ct io n 4 pi pe h ol lo w d s n 37 ° 0 2’ 3 8. 37 ” w 11 1° 4 9’ 5 3. 03 ” se ct io n 5 pi pe h ol lo w g al le ry n 37 ° 0 2’ 3 0. 67 ” w 11 1° 4 9’ 2 7. 77 ” se ct io n 6 pi pe h ol lo w n 37 ° 0 2’ 2 4. 52 ” w 11 1° 4 9’ 2 3. 53 ” 4. 34 k m 0. 26 k m 2. 18 k m 0. 67 k m 0. 22 k m vo lc an ic la st ic sa nd st on e 3 cm v ol ca ni c fr ag m en ts vo lc an ic la st ic sa nd st on e tw -2 ; 1 65 .3 0 ± 1. 2 m a w in so r m em be r pa ria ri ve r m em be r cry sta l cre ek th ou sa nd p oc ke ts m em be r m em be r 11; 1 71 .7 3 ± 0. 19 m a w h -2 ; 1 74 ± 5 m a fi gu re 4 . m ea su re d se ct io ns o f t he p ar ia r iv er m em be r o f t he c ar m el f or m at io n in th e p ar ia c an yo n ar ea sh ow in g th e b ed s t ha t c on ta in th e i gn eo us cl as ts . th es e be ds a re in te rp re te d as d eb ris -fl ow d ep os its . sa m pl es w h -1 a nd w h -2 (s ee ta bl e 1) w er e co lle ct ed fr om n ea r m ea su re d se ct io n 4. m od ifi ed fr om w he at le y an d c ha n (2 01 8) . g eo lo gi c m ap fr om d oe lii ng a nd w ill is (2 00 6) . s tr uc tu re c on to ur s ( re d da sh ed li ne s) d ra w n at b as e of th e n at ur ita f or m at io n (fo rm er ly d ak ot a fo rm at io n) . c on to ur in te rv al is 1 00 m . 77 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 character of the clasts petrography: phenocrysts, textures, and welding chapman (1987, 1989, 1993) characterized a large number of clasts from these deposits and concluded that almost all of the large clasts (>1 cm) were welded rhyolite tuffs. in the clasts smaller than about 1 cm, some were of intermediate and mafic composition, as well as intrusive igneous rocks, and a few metamorphic rocks. our focus was not to duplicate chapman’s efforts, but to better characterize the rhyolite tuff clasts that comprise the majority of the clasts within the conglomerates and all of the larger cobbles and boulders. thin section examination of the rhyolite clasts reveals that most of them have nicely preserved relict shard textures (figures 6 and 7). shards are not flattened and only weakly oriented preferentially in most of the samples, preserving round bubble walls and bubble triple junctions (figures 6a, 6b, and 7c). relict pumice fragments are also not significantly flattened (figure 7). figure 7d shows several slightly flattened pumices, but in figure 7c the large relict pumice is fairly equant. our examination of these thin sections shows that the tuffs were not significantly welded, and must have had fairly low rock densities at the time of transportation and deposition. phenocrysts preserved in the clasts include sanidine, quartz, biotite, apatite, and zircon. sanidine grains are preserved with little or no alteration in some of these volcanic clasts. they appear as clear euhedral to subhedral grains in thin section (figures 6a, 6e, 6f, 6h, and 7b,). quartz is frequently embayed (figures 6e and 6f), suggesting that it was being resorbed at the time of eruption. biotite occurs as partially to completely oxidized booklets (figure 6g). dark oxides are concentrated on cleavage planes where fluids could alter them. plagioclase is not preserved, but must have initially been present in the tuffs as noted for other tuffs from the temple cap and carmel formations (kowallis and others, 2001). relict amphibole appears as iron oxides surrounding calcite cores (figures 6c and 6d) and relict pumice fragments as fine-grained aggregates of quartz and feldspar (figure 7b). thin sections from sample wh-2 have less abundant quartz and sanidine, more abundant relict pumice, and fewer relict amphiboles. no primary fe-ti oxides appear to have survived in any of the samples. nonetheless, the mineral assemblage is consistent with a rhyolitic bulk composition. xrf analyses (figure 8 and table 2) also show the rocks were probably rhyolites and trachytes before alteration. however, their k2o contents are anomalously high (6.5 to almost 8% in the fresher clasts and over 10% in the altered boulder), and na2o values are low (0.8 to 1.3% in the fresher clasts and 0% in the altered boulder), when compared to fresh rhyolite, indicating that secondary alteration has significantly modified their chemistry. cao concentrations (0.13 to 0.02 wt%) are figure 5. (top) large, rounded igneous, boulder-sized clast from the white house area (37.089487, -111.885517) near sample wh-1. the boulder has broken into several large pieces having maximum diameters of 1.3, 1.0, and 0.8 m with several other 0.5 m blocks and is compositionally similar to other igneous clasts in the area. (photo credit: mark hansford). (bottom) layer with volcanic cobbles where samples 1-1 through 1-5 were collected (see table 1 for location). 78 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 also lower than the 0.5 wt% typically found in rhyolite. immobile element concentrations can be used to infer the probable original volcanic rock types before alteration (see for example, christiansen and others, 2015). on tectonic discrimination diagrams (figure 9) using nb versus y, most of the samples plot in the volcanic arc field (pearce, 1996) and are similar to analyses from the temple cap and carmel formations published previously (kowallis and others, 2001). we also collected electron microprobe analyses from biotite and feldspar in the clasts (table 3). only sanidine feldspar grains are preserved in the tuff clasts. this preservation is like that found in altered fallout tuff beds from the carmel and temple cap formations (kowallis and others, 2001). the composition of sanidine grains falls into three groups (figure 10). clast 1-5 is distinctive with the highest or content (or72–or76). wh-2 sanidine is also distinctive, but has lower or values (or64–or69). all the other clasts clump between or59 and or64. the same three groups appear on a plot of k versus ba in these sanidines (figure 11). wh-2 grains have the highest ba content and are typically unzoned in ba (one grain out of six that were probed had a rim with lower ba content). clast 1-5 is also distinctive with high k and intermediate ba concentrations. all of the sanidine in the other clasts clump together. biotite occurs in all of the ignimbrite clasts we examined. compositions of biotite in terms of molar fe/ (fe + mg) and total al relative to ideal end members sample number analysis number sio2 tio2 al2o3 feo mno mgo cao bao na2o k2o f cl sum h2o* total sanidine 1-1 6b 66.17 18.94 0.19 0.25 0.07 4.12 11.03 100.76 1-1 6c 66.47 18.94 0.16 0.23 0.21 4.24 11.01 101.26 1-2 10c 66.07 19.03 0.14 0.24 0.62 4.30 10.55 100.95 1-2 10d 65.88 18.97 0.17 0.22 0.52 4.39 10.82 100.97 1-3 2-8 65.72 18.79 0.17 0.27 0.50 4.16 10.88 100.48 1-3 2-9 66.00 18.42 0.18 0.28 0.34 4.05 10.96 100.23 1-4 5d 65.57 19.01 0.08 0.36 0.39 4.29 10.94 100.64 1-4 5e 65.68 19.11 0.18 0.26 0.47 4.05 11.11 100.87 1-5 3-2 65.08 18.92 0.08 0.21 0.80 3.00 12.50 100.59 1-5 3-3 65.28 18.52 0.08 0.17 0.66 3.04 12.60 100.35 wh-2 b-1c 63.41 19.25 0.17 0.26 2.41 3.60 11.47 100.56 wh-2 b-3b 63.90 19.04 0.19 0.29 1.78 3.66 11.60 100.45 biotite 1-1 2a 37.69 4.21 13.35 15.42 0.60 15.41 0.00 0.33 0.60 9.51 1.28 0.18 97.99 3.33 101.32 1-1 2b 37.78 4.37 13.19 15.31 0.61 15.11 0.01 0.22 0.60 9.43 1.31 0.20 97.53 3.28 100.81 1-2 5a 36.81 4.19 12.38 12.74 1.63 18.56 0.03 0.17 0.57 9.35 4.48 0.16 99.14 1.87 101.01 1-2 5b 37.26 4.35 13.03 13.08 1.31 17.53 0.01 0.17 0.68 9.62 4.01 0.17 99.48 2.08 101.56 1-3 3b 36.91 4.28 12.93 15.74 0.55 15.03 0.03 0.36 0.62 9.49 1.70 0.18 97.05 3.06 100.11 1-3 3c 37.73 4.31 12.81 15.68 0.55 15.17 0.02 0.09 0.59 9.67 1.58 0.16 97.66 3.16 100.82 1-4 1c 36.61 4.21 13.11 13.63 1.16 16.93 0.03 0.49 0.57 9.38 4.07 0.18 98.62 2.00 100.62 1-4 2a 35.73 4.13 13.24 13.50 1.45 17.74 0.06 0.60 0.52 9.04 4.16 0.15 98.54 1.99 100.53 1-5 2c 36.22 4.58 13.60 19.52 0.29 12.85 0.00 0.17 0.50 9.47 1.12 0.24 98.02 3.32 101.34 1-5 3a 36.48 4.55 13.49 18.16 0.28 12.98 0.00 0.24 0.28 9.62 2.21 0.26 97.56 2.76 100.32 wh-2 2-a8 35.28 5.19 14.56 15.93 0.45 14.23 0.00 2.39 0.54 9.06 1.00 0.05 98.25 3.42 101.67 wh-2 3-a12 34.36 5.55 14.21 16.13 0.49 13.49 0.00 2.69 0.55 8.55 0.92 0.07 96.60 3.37 99.97 *calculated value for water in biotite table 2. selected electron microprobe analyses of sanidine and biotite. 79 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 fall mostly within the field for calc-alkaline igneous rocks from the western united states (christiansen and others, 1986; figure 12a), with sample 1-5 bordering on the lower end of the field for the rhyolitic bishop tuff, and similar to the composition of the dacitic fish canyon tuff (hildreth, 1979; whitney and stormer, 1985; christiansen and others, 1986). the low fe/mg ratios of the biotite indicate a high oxygen fugacity and are thus consistent with generation in a subduction-related magmatic arc. fluorine content of biotite from these tuffs is also similar to that of the fish canyon tuff but only slightly overlaps into the field for biotite from other middle jurassic tuff beds in the temple cap and carmel formations that we have previously examined (kowallis and others, 2001; figure 12b). a number of grains from samples 1-2 and 1-4 plot at higher f and mg content than the rest of the grains, suggesting that they have been affected by secondary alteration; these anomalous grains also have low altot (figure 12a). based on the biotite and feldspar compositions, it appears that the cobble and boulder deposits in the carmel formation have clasts from a minimum of three different volcanic units. because our sampling of clasts was fairly limited, it is likely that the actual number of different eruptive units is higher. in conclusion, the volcanic clasts in this part of the carmel formation appear to be rhyolite ignimbrites, in agreement with chapman’s (1987, 1989, 1993) original assessment of the clasts. however, we disagree with chapman on the degree of welding. chapman (1987) stated that the clasts are “partly welded to welded rhyolitic tuff ” and that the “boulders of welded tuff could not have been derived from the distal non-welded edges of an ignimbrite sheet” (chapman, 1993). smith (1960) examined welding in ash flow tuffs and stated, “the degree of welding may range from incipient stages marked by the sticking together or cohesion of glassy fragments at their points of contact and within the softening range of the glass to complete welding marked by the cohesion of the surfaces of glassy fragments accompanied by their deformation and the elimination of pore space.” smith (1960) continued by saying that, “deformation of pumiceous fragments and shards is the only positive criterion of welding in the tuffs which have crystallized, particularly in older rocks.” using these criteria, we propose that the clasts were derived from the non-welded to incipiently welded parts of an ignimbrite sheet; none of the clasts we examined showed evidence of strong welding. welded rhyolite tuffs have rock densities of 1.8 to 2.4 g/cm3, whereas poorly to non-welded rhyolite tuffs have densities of 1.0 to 1.8 g/ cm3 (healey, 1970; olsson, sample number 1-1 1-2 1-3 1-4 1-5 2-1 2-2 2-3 major elements (wt%) sio2 74.44 72.83 73.79 77.71 76.50 62.69 63.25 62.60 tio2 0.16 0.16 0.24 0.16 0.32 0.35 0.35 0.35 al2o3 12.80 13.76 12.49 10.90 10.39 18.23 18.55 19.01 fe2o3 1.93 2.04 2.53 1.73 3.05 3.65 3.46 3.42 mno 0.03 0.03 0.03 0.06 0.02 0.02 0.02 0.01 mgo 0.12 0.18 0.20 0.10 0.22 0.42 0.45 0.40 cao 0.12 0.13 0.07 0.11 0.12 0.02 0.01 0.01 na2o 1.25 1.31 0.84 1.14 0.88 0.00 0.00 0.00 k2o 6.45 6.65 7.87 7.21 7.06 10.11 10.31 10.47 p2o5 0.01 0.01 0.02 0.00 0.01 0.02 0.01 0.01 loi 2.08 2.09 1.26 0.64 0.72 4.40 3.73 3.78 total 99.38 99.19 99.33 99.76 99.29 99.90 100.15 100.06 trace elements (ppm) ba 383 364 589 751 591 324 275 297 ce 18 20 141 7 23 75 68 64 cr 0 0 1 1 16 1 1 0 cu 5 4 3 4 7 18 4 6 ga 12 12 10 9 8 18 18 18 la 11 12 40 5 12 29 23 24 nb 13 13 17 12 16 21 20 21 nd 10 12 61 3 7 34 30 29 ni 3 2 2 1 2 2 2 3 pb 9 11 14 9 15 8 8 8 rb 173 175 191 168 208 146 145 151 sc 1 2 1 0 1 4 4 4 sm 4 3 10 2 3 6 6 5 sr 25 23 38 40 47 20 17 15 th 14 17 19 13 24 19 19 17 u 3 4 4 4 5 4 4 4 v 14 15 32 12 37 24 20 24 y 26 25 34 7 21 39 36 33 zn 20 19 10 14 12 32 19 21 zr 131 123 190 139 181 250 244 244 table 3. x-ray fluorescence analyses (major and trace elements) for carmel formation clasts. 80 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 sa m pl e: p h -2 01 505 -1 51 jva lu e: 0 .0 07 66 92 ± 0 .0 00 00 38 (1 σ) d /a m u: 1 .0 08 44 ± 0 .0 00 81 (1 σ) m at er ia l: sa ni di ne fi le la se r po w er (% ) 40 a r (m ol es ) 40 a r (v ol ts ) ± 1σ 40 (v ol ts ) 39 a r (v ol ts ) ±1 σ39 (v ol ts ) 38 a r (v ol ts ) ± 1σ 38 (v ol ts ) 37 a r (v ol ts ) ± 1σ 37 (v ol ts ) 36 a r (v ol ts ) ± 1σ 36 (v ol ts ) % 40 a r* 40 a r* /39 a rk ± 1σ a ge ± 2 σ (m a) ( m a) k /c a in cl ud ed in w td . m ea n m a a 65 59 -0 00 35 4. 96 1e -1 4 8. 40 60 77 0. 00 35 47 0. 65 35 55 0. 00 08 10 0. 00 79 48 0. 00 00 69 0. 00 79 86 0. 00 02 27 0. 00 00 63 0. 00 00 06 99 .7 8 12 .8 34 01 5 0. 01 70 5 17 1. 84 ± 0 .4 4 35 .1 88 ✓ m a a 65 60 -0 00 35 4. 36 6e -1 4 7. 39 72 86 0. 00 24 44 0. 57 44 71 0. 00 05 75 0. 00 68 84 0. 00 00 69 0. 00 67 29 0. 00 02 03 0. 00 01 57 0. 00 00 06 99 .3 7 12 .7 95 57 8 0. 01 38 4 17 1. 35 ± 0 .3 5 36 .7 11 ✓ m a a 65 62 -0 00 35 3. 98 4e -1 4 6. 75 06 25 0. 00 17 03 0. 52 33 07 0. 00 05 49 0. 00 64 43 0. 00 00 83 0. 00 61 44 0. 00 01 63 0. 00 01 38 0. 00 00 06 99 .3 9 12 .8 21 50 1 0. 01 42 6 17 1. 68 ± 0 .3 6 36 .6 23 ✓ m a a 65 63 -0 00 35 2. 55 5e -1 4 4. 32 88 82 0. 00 11 03 0. 33 65 89 0. 00 03 69 0. 00 39 21 0. 00 00 68 0. 00 35 93 0. 00 01 20 0. 00 00 47 0. 00 00 05 99 .6 7 12 .8 19 29 7 0. 01 52 2 17 1. 66 ± 0 .3 9 40 .2 80 ✓ m a a 65 65 -0 00 35 4. 84 2e -1 4 8. 20 44 02 0. 00 32 31 0. 63 91 51 0. 00 06 85 0. 00 76 47 0. 00 00 96 0. 00 71 06 0. 00 02 19 0. 00 00 45 0. 00 00 06 99 .8 4 12 .8 15 71 2 0. 01 48 8 17 1. 61 ± 0 .3 8 38 .6 74 ✓ m a a 65 66 -0 00 35 2. 85 1e -1 4 4. 83 01 54 0. 00 12 00 0. 37 22 99 0. 00 03 99 0. 00 43 46 0. 00 00 58 0. 00 40 61 0. 00 01 38 0. 00 01 78 0. 00 00 06 98 .9 0 12 .8 31 66 7 0. 01 49 3 17 1. 81 ± 0 .3 8 39 .4 21 ✓ m a a 65 68 -0 00 35 3. 57 7e -1 4 6. 06 03 12 0. 00 25 78 0. 46 82 78 0. 00 05 91 0. 00 56 11 0. 00 01 07 0. 00 61 66 0. 00 01 76 0. 00 00 88 0. 00 00 06 99 .5 7 12 .8 86 43 9 0. 01 75 7 17 2. 51 ± 0 .4 5 32 .6 54 m a a 65 69 -0 00 35 4. 38 7e -1 4 7. 43 38 03 0. 00 26 55 0. 57 55 98 0. 00 07 25 0. 00 68 95 0. 00 00 63 0. 00 74 01 0. 00 02 32 0. 00 01 49 0. 00 00 06 99 .4 1 12 .8 38 28 6 0. 01 70 9 17 1. 90 ± 0 .4 4 33 .4 42 ✓ m a a 65 72 -0 00 35 3. 36 6e -1 4 5. 70 30 67 0. 00 25 95 0. 44 39 05 0. 00 05 07 0. 00 52 03 0. 00 00 72 0. 00 50 78 0. 00 01 83 0. 00 00 41 0. 00 00 06 99 .7 9 12 .8 20 24 9 0. 01 62 0 17 1. 67 ± 0 .4 1 37 .5 93 ✓ m a a 65 74 -0 00 35 3. 84 4e -1 4 6. 51 31 83 0. 00 15 94 0. 50 67 06 0. 00 06 41 0. 00 60 28 0. 00 00 47 0. 00 61 52 0. 00 01 70 0. 00 00 75 0. 00 00 06 99 .6 6 12 .8 10 43 4 0. 01 68 6 17 1. 54 ± 0 .4 3 35 .4 17 ✓ m a a 65 75 -0 00 35 2. 98 4e -1 4 5. 05 63 47 0. 00 15 47 0. 39 36 71 0. 00 04 33 0. 00 46 11 0. 00 00 77 0. 00 43 89 0. 00 01 57 0. 00 00 35 0. 00 00 06 99 .7 9 12 .8 17 78 1 0. 01 52 2 17 1. 64 ± 0 .3 9 38 .5 67 ✓ m a a 65 77 -0 00 35 2. 87 0e -1 4 4. 86 33 05 0. 00 15 98 0. 37 77 42 0. 00 03 88 0. 00 45 19 0. 00 00 39 0. 00 44 32 0. 00 01 26 0. 00 00 27 0. 00 00 06 99 .8 4 12 .8 53 86 4 0. 01 45 6 17 2. 10 ± 0 .3 7 36 .6 53 ✓ m a a 65 78 -0 00 35 6. 10 3e -1 4 10 .3 40 82 0 0. 00 33 01 0. 80 37 46 0. 00 08 04 0. 00 95 23 0. 00 00 70 0. 00 97 83 0. 00 03 18 0. 00 00 95 0. 00 00 06 99 .7 3 12 .8 31 06 2 0. 01 36 9 17 1. 81 ± 0 .3 5 35 .3 28 ✓ m a a 65 80 -0 00 35 2. 00 7e -1 4 3. 40 11 86 0. 00 10 73 0. 26 52 14 0. 00 03 18 0. 00 32 21 0. 00 00 59 0. 00 31 87 0. 00 01 32 0. 00 00 36 0. 00 00 06 99 .6 9 12 .7 84 54 5 0. 01 70 8 17 1. 21 ± 0 .4 4 35 .7 80 ✓ m a a 65 81 -0 00 35 3. 00 3e -1 4 5. 08 78 68 0. 00 20 12 0. 39 55 52 0. 00 05 18 0. 00 47 49 0. 00 00 52 0. 00 69 15 0. 00 01 95 0. 00 00 48 0. 00 00 06 99 .7 3 12 .8 27 47 6 0. 01 80 4 17 1. 76 ± 0 .4 6 24 .5 96 ✓ m a a 65 83 -0 00 35 2. 72 2e -1 4 4. 61 13 22 0. 00 13 12 0. 35 85 35 0. 00 03 77 0. 00 42 03 0. 00 00 35 0. 00 40 62 0. 00 01 62 0. 00 00 51 0. 00 00 06 99 .6 7 12 .8 19 62 6 0. 01 47 3 17 1. 66 ± 0 .3 8 37 .9 53 ✓ m a a 65 84 -0 00 35 3. 65 5e -1 4 6. 19 23 23 0. 00 20 86 0. 48 15 34 0. 00 05 52 0. 00 58 03 0. 00 00 89 0. 02 03 70 0. 00 04 78 0. 00 02 29 0. 00 00 06 98 .9 2 12 .7 20 70 2 0. 01 57 2 17 0. 40 ± 0 .4 0 10 .1 65 m a a 65 86 -0 00 35 3. 68 2e -1 4 6. 23 80 65 0. 00 26 62 0. 48 14 07 0. 00 05 42 0. 00 57 40 0. 00 00 80 0. 00 56 66 0. 00 02 28 0. 00 00 69 0. 00 00 06 99 .6 7 12 .9 15 91 6 0. 01 59 7 17 2. 89 ± 0 .4 1 36 .5 32 m a a 65 87 -0 00 35 4. 48 8e -1 4 7. 60 38 98 0. 00 22 30 0. 58 99 59 0. 00 06 52 0. 00 71 06 0. 00 01 10 0. 00 69 37 0. 00 01 85 0. 00 00 97 0. 00 00 06 99 .6 2 12 .8 40 24 3 0. 01 49 6 17 1. 92 ± 0 .3 8 36 .5 71 ✓ m a a 65 89 -0 00 35 3. 32 6e -1 4 5. 63 53 94 0. 00 11 35 0. 43 73 54 0. 00 04 86 0. 00 53 24 0. 00 00 70 0. 00 50 70 0. 00 01 85 0. 00 00 62 0. 00 00 06 99 .6 7 12 .8 43 17 9 0. 01 50 7 17 1. 96 ± 0 .3 9 37 .0 91 ✓ m a a 65 90 -0 00 35 2. 89 9e -1 4 4. 91 13 42 0. 00 28 50 0. 38 19 40 0. 00 04 99 0. 00 45 59 0. 00 00 55 0. 00 40 48 0. 00 01 55 0. 00 00 32 0. 00 00 06 99 .8 1 12 .8 34 45 4 0. 01 88 6 17 1. 85 ± 0 .4 8 40 .5 69 ✓ m a a 65 93 -0 00 35 2. 34 5e -1 4 3. 97 23 90 0. 00 14 41 0. 30 81 18 0. 00 03 65 0. 00 36 41 0. 00 00 33 0. 00 35 28 0. 00 01 37 0. 00 00 55 0. 00 00 06 99 .5 9 12 .8 39 65 1 0. 01 68 4 17 1. 92 ± 0 .4 3 37 .5 58 ✓ m a a 65 95 -0 00 35 2. 86 9e -1 4 4. 86 02 77 0. 00 13 56 0. 37 80 92 0. 00 04 75 0. 00 44 18 0. 00 00 40 0. 00 41 28 0. 00 01 43 0. 00 00 46 0. 00 00 06 99 .7 2 12 .8 18 76 1 0. 01 70 5 17 1. 65 ± 0 .4 4 39 .3 86 ✓ th e va lu es in th is ta bl e re pr es en t b la nk , d isc rim in at io n, a nd d ec ay (37 a r a nd 39 a r) co rr ec te d va lu es . w ei gh te d m ea n ag e (2 0 of 2 3) : 17 1. 73 ± 0 .1 9 at m os ph er ic a rg on ra tio s d ec ay co ns ta nt s in te rf er in g iso to pe p ro du ct io n ra tio s 40 a r/ 36 a r 29 8. 56 ± 0 .3 1 le e an d ot he rs (2 00 6) λ 40 a r (0 .5 80 ± 0 .0 14 ) x 1 010 a -1 m in a nd o th er s ( 20 00 ) (40 a r/ 39 a r) k ( 5. 4 ± 1. 4) x 1 0-4 38 a r/ 36 a r 0. 18 85 ± 0 .0 00 3 le e an d ot he rs (2 00 6) λ b(4 .8 84 ± 0 .0 99 ) x 1 010 a -1 m in a nd o th er s ( 20 00 ) (38 a r/ 39 a r) k (1 .2 10 ± 0 .0 02 ) x 1 0-2 39 a r (2 .5 8 ± 0. 03 ) x 1 03 a1 st oe nn er a nd o th er s ( 19 65 ) (39 a r/ 37 a r) c a (6 .9 5 ± 0. 09 ) x 1 0-4 37 a r (8 .2 3 ± 0. 04 2) x 1 04 h1 st oe nn er a nd o th er s ( 19 65 ) (38 a r/ 37 a r) c a (1 .9 6 ± 0. 08 ) x 1 0-5 36 c l (2 .3 03 ± 0 .0 46 ) x 1 06 a1 (36 a r/ 37 a r) c a (2 .6 5 ± 0. 02 2) x 1 0-4 ta bl e 4. c om pl et e 40 a r/ 39 a r r es ul ts fo r s am pl e 11 re la tiv e to 2 8. 20 1 m a fo r t he f ish c an yo n sa ni di ne st an da rd . 81 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 ap b bb b g s q e s q h f c am c d s a b figure 6. textures and minerals in the clasts. clast 1-1 shown in a, e, f, and g; clast 1-2 in b, c, and d; clast 1-4 in h. the wide dimension on all the photomicrographs is about 1 mm, except for photomicrograph h, which is 5 mm. s = sanidine, q = quartz, c = calcite, b = biotite, am = relict amphibole, ap = apatite. pairs c-d and e-f are plane and cross-polarized images of the same area. all other photomicrographs are in plane-polarized light. 82 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 1991; wohletz and heiken, 1992). moving low-density, non-welded tuff boulders over long distances would be much easier than moving blocks of more densely welded tuff, but they would also be more friable. age chapman (1993) reported a 40ar/39ar age of 169 ± 4 ma for one clast provided only as an oral communication from john obradovich at the u.s. geological survey (this age would be ~171 ma using current decay constants and standards). the age of the carmel formation sediments enclosing the volcanic clast layer can be estimated from the age of fallout tuff sample wh-1, which gave a tuffzirc age of 163.6 +3.3/-1.4 ma for a group of 45 coherent grains and a u-pb weighted mean age of 163.9 ± ~3.3 ma (figure 13; assuming a 2% error, 2-sigma, [see gehrels and others, 2008]). this age fits well with other ages (~162–164 ma) obtained from the upper part of the carmel formation by palynology and radiometric dating of other ash beds (table 1; sprinkel and others, 2011). no zircons older than the middle jurassic were identified. on the other hand, zircons from tuff clast wh-2 gave a spectrum of ages ranging from middle jurassic to archean even though it lacks any evidence of a sedimentary component. a tuffzirc analysis of the youngest grains from wh-2 produced a coherent group of 20 grains with an age of 174 ± ~5 ma (figure 14). this age is significantly older than other ages we have obtained from the volcanic deposits in the upper members sq s s pm pm b pm pm pm pm pm pm pm pm pm pm pma c d b figure 7. textures and minerals in clast wh-2. the wide dimension on all the photomicrographs is about 5 mm, except for photo b, which is 1 mm. s = sanidine, q = quartz, c = calcite, b = biotite, pm = pumice. photomicrographs a, c, and d are plane-polarized light. photomicrograph b is a blow-up of part of a taken in cross-polarized light. 83 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 of the carmel formation (sprinkel and others, 2011) and seems likely to represent the age of the youngest detritus in this sample. the older detrital grains in sample wh-2 match up well with the signal obtained from lower and middle jurassic strata of the colorado plateau by dickinson and gehrels (2010). sanidine grains have been preserved with little or no alteration in some of the volcanic clasts. they appear as clear euhedral to subhedral grains in thin section (figures 6a, 6e, 6h, and 7b). a laser-fusion, single-crystal 40ar/39ar age of 171.73 ± 0.19 ma was obtained on sanidine from clast 1-1 (figure 15 and table 4). this age is similar to ages obtained by kowallis and others (2001) from sanidine from fallout tuffs in the temple cap formation in southwestern utah (ages ranging from 170.24 to 172.93 ± ~0.5 to 0.6 ma; corrected to new fish canyon age standard and decay constants following kuiper and others [2008]). dickinson and others (2010) dated a tuff from an eolianite equivalent to the temple cap formation collected farther east in southernmost utah along the shores of lake powell (see figure 1 in dickinson and others, 2010). their sample gave a u-pb zircon age of 171.5 to 171.9 ± ~2.0 ma and an 40ar/39ar biotite 1 10 100 1000 1 10 100 1000 y (ppm) within-plate granite volcanic-arc & collision granite ocean-ridge granite n b (p pm ) 1-5 1-1 1-2 1-3 2-1 1-4 figure 9. nb and y trace element compositions of volcanic clasts from the carmel formation fall in the volcanic arc field on the discriminant diagram of pearce and others (1984). the green area compares the clast compositions to those of ash beds in the carmel and temple cap formations from kowallis and others (2001). dacite sio2 weight % k 2o + n a 2o w ei gh t % 41 0 8 6 4 2 16 10 12 14 6661565146 7671 1-11-2 2-1 1-5 1-3 1-4 phonotephrite tephriphonolite phonolite trachyandesite basaltic trachyandesitetrachybasalt picrobasalt basalt basanite basaltic andesite rhyolite andesite trachyte figure 8. total alkali versus silica volcanic rock classification diagram (after le bas and others, 1986). sample numbers are shown next to data points. 84 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 age of 171.02 ± 0.92 ma. our new ages, along with the earlier age reported in chapman (1993), provide clear evidence that the clasts in the conglomerates found in the upper carmel formation are derived from outcrops of volcanic rocks of temple cap formation age that are approximately 8 to 10 million years older than the carmel formation deposit in which they are found. moving boulders across a large distance nearest outcrops the nearest current outcrops of middle jurassic volcanic rocks of the right age (~170 ma) are located in the lower colorado river region of southern california and southwestern arizona (tosdal and wooden, 2015). chapman (1987) proposed that the magmatic arc was closer during the jurassic than it is today due to basin and range extension in order to account for transporting coarse volcanic boulders and cobbles ~350 km (straight line, closest current distance) from the jurassic arc to the depositional site in south-central utah (figure 16). however, because a significant portion of the distance between the arc and the deposit falls on the colorado plateau (~180 km), which was not extended, how much shortening can we reasonably propose for the remaining 170 km? estimates of horizontal extension due to basin and range activity vary widely from extremes of 400% to as little as 20% (hintze and kowallis, 2009). extension near the latitude of las vegas, nevada, in an area called the colorado river extensional corridor has been the subject of several papers. wernicke and others (1988) proposed extension in this region of 300 to 400%. faulds and others (1990, 2001) discuss the extension in this region but do not give a percentage, only stating that large amounts of extension occurred. marzolf (1990), in general agreement with wernicke and others (1988), produced a middle jurassic palinspastic reconstruction of the southwestern united states showing a significant reduction (225 km as opposed to 350 km) in the distance the boulders would need to travel from a proposed tuff apron around the arc (figure 16). two-hundred and twenty-five km is still a substantial distance over which to move large boulders. 333 3333 333334444444412 222222222211111 555555555555555511 ab or an 0 10 20 30 40 50 50 60 70 80 90 100 3 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0 0.01 0.02 0.03 0.04 0.05 0.06 k ( a p f u ) ba (apfu) figure 10. compositions of sanidine grains from the clasts collected at sites ph-2015-05-15 (samples 1-1 to 1-5) and wh-07-20-2013-2 (wh-2 stars). figure 11. barium (ba) concentration in sanidine grains (atoms per formula unit) plotted versus k from clasts collected at sites ph-2015-05-15 (samples 1-1 to 1-5) and wh-07-202013-2 (wh-2 stars). 85 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 run-out distances for tuffs chapman (1987) also suggested that a factor to consider was the run-out distance for ash-flow tuffs and compiled a list of 17 eruptions where the run-out was over 30 km; two of them, a member of the bates mountain tuff (now called the nine hill tuff) and the peach springs tuff, perhaps exceeded 200 km of run-out. we have compiled a larger list of 48 ignimbrites from the cenozoic of the western united states with maximum run-outs greater than 40 km (corrected for post-eruption extension, table 5). of these tuffs, 22 have maximum run-outs of over 100 km, and 5 have run-outs of 200 km or more. the nine hill tuff provides an informative comparison. henry and faulds (2009) showed that this tuff was channeled in river valleys that cut across the (then lower) sierra nevada batholith from its eruptive source in western nevada—a distance of over 200 km when corrected for later extension. these paleovalleys are typically 7 to 10 km wide and as much as 1 km deep. if the carmel formation cobbles and boulders were sourced from distal run-out lobes where flow was extended because of focusing in paleovalleys, then the distance from the tuff outcrops to the conglomerate depositional site could be reduced by another 100 to 200 km. as discussed earlier in this paper, our analysis of the clasts shows them to be poorly welded to unwelded, not unusual for distal parts of an ignimbrite. if we use the palinspastically reconstructed distance proposed by marzolf (1990) of about 225 km and the run-out distances from table 5, then distal outflow ignimbrites could have been deposited close to the location of the gravel and boulder beds of the paria river member of the carmel formation. remobilizing the outcrops as debris flows based upon careful analysis of the sedimentology of the clast-bearing outcrops, chapman (1987, 1993) concluded that these deposits were formed from debris flows or lahars that likely occurred shortly after eruption, with the tuffs being laid down on a softer substrate of quartz-rich sedimentary rock (chapman, 1989). we agree that the clast-bearing deposits represent one or more debris flows but disagree that these flows occurred soon after eruption of the tuffs. the ages on the clasts range between 171 and 174 ma, whereas the age of the enclosing paria river member is ~163 to 167 ma (table 1 and figure 4; doelling and others, 2013), 5 to 10 ma younger. regardless of the age of the clasts, they were incorporated into a debris-flow rich in volcanic detritus 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 fe /( fe +m g) al (apfu) (a) two-mica granites a-type granites & topaz rhyolites calc-alkaline rhyolites & granites fish canyon tu� and middle jurassic ash beds bishop tu� 1111 111 1 1 1 12 2 2 2 22 2 2 2 2222 22 2 2 2 2 2 2 3 3 33 3 3 3 333 3 3 4 4 4 4 4 4 44 4 4 5 5 5 5 555 55 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 -1.2 -0.8 -0.4 0.0 0.4 1 111 1 111 1 1 1 2 2 2 2 2 2 2 2 2 2 22 2 2 2 2 2 2 2 2 2 3 3333 3 3 3 3 3 3 4 4 4 4 44 4 4 4 4 5 5 5 5 55 5 5 fish canyon tu� middle jurassic ash beds i-scr i-wc i-mc i-sc lo g (x f / x o h ) log (xmg /xfe) (b) figure 12. (a) compositions of biotite from carmel formation clasts compared to fish canyon and bishop tuffs (hildreth, 1979) in terms of molar fe/(fe + mg) and total al relative to ideal end member. fields for different types of granite are from christiansen and others (1986). (b) compositions of biotite from carmel formation clasts compared to biotite from the fish canyon tuff and middle jurassic ash beds from temple cap and carmel formations (kowallis and others, 2001). granite fields from ague and brimhall (1988): i-scr = i-type, strongly contaminated and reduced; i-sc = i-type, strongly contaminated; i-mc = i-type, moderately contaminated; i-wc = i-type, weakly contaminated. 86 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 that must have been sourced in an area where multiple volcanic tuffs had accumulated on a surface with a significant east or northeast slope. debris flows are capable of transporting very large clasts and may travel distances in excess of 100 km (neall, 1976; siebert and others, 1987; carrasco-núñez and others, 1993; mothes and others, 1998; scott and others, 2001). however, they are typically sourced in fairly steep terrain. as an example, mothes and others (1998) stated that, “the chillos valley lahar (cvl), the largest holocene debris flow in area and volume as yet recognized in the northern andes, formed on cotopaxi volcano’s north and northeast slopes and descended river systems that took it 326 km north–northwest to the pacific ocean and 130+ km east into the amazon basin.” more recently, the eruption of nevado del ruiz volcano in colombia in 1985 produced lahars that traveled 60 to 70 km from their source along the channels of the 90 110 130 150 170 190 210 230 23 8 u – 20 6 pb a ge (m a) tu�zirc age = 163.6 (+3.3, -1.4) ma box heights are ± 2σ u-pb weighted mean age = 163.9 ± 3.3 ma 0 5 10 15 20 25 30 35 re la tiv e ag e fr eq ue nc y (r ed c ur ve ) u-pb age (ma) wh-1 wh-1 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 100 120 140 160 180 200 220 240 u /t h (b lu e po in ts ) (a) (b) figure 13. 238u-206pb ages for zircons from the basal winsor member of the carmel formation ash bed wh-1. (a) a relative age probability diagram of individual u-pb grain ages (red curve) (hurford and others, 1984, and kowallis and others, 1986). also shown are u/th ratios (blue dots) for each analyzed spot. (b) tuffzirc plot (ludwig and mundil, 2002) for zircons from sample wh-1. blue bars and open bars are analyses not included in the overall age. the blue bars do not overlap the error range and the open bars are low resolution ages. 90 110 130 150 170 190 210 23 8 u – 20 6 pb a ge (m a) tu�zirc age = 174.3 (+4.1, -5.7) ma box heights are ± 2σ wh-2 0 5 10 15 20 25 30 35 0 500 1000 1500 2000 2500 re la tiv e ag e fr eq ue nc y (r ed c ur ve ) u-pb age (ma) wh-2 dickinson and gehrels (2010) lower to middle jurassic �uvial and marine detrital zircon, colorado plateau, utah this paper: zircon population from clast wh-2 in paria river member of carmel formation, colorado plateau, utah 169-177 ma peak from volcanic arc (a) (b) figure 14. (a) 238u-206pb zircon ages from sample wh-2 (red line) plotted with the detrital zircon ages reported by dickinson and gehrels (2010) from lower to middle jurassic sedimentary rocks of the colorado plateau. the peaks from both curves correlate quite well neglecting the young population of grains in wh-2. (b) u-pb tuffzirc plot for the subset of young zircons from clast wh-2. 87 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 rio azufrado and rio lagunillas, burying the city of armero and killing more than 25,000 people (naranjo and others, 1986; voight, 1990). to provide the necessary slope for debris flows to form and transport the clasts, we propose that the distal tuff deposits described above were deposited in a highland area northeast of the low-standing middle jurassic arc. they remained in place for several million years after their initial emplacement during which time they were subjected to weathering and alteration. even poorly welded tuffs would likely be more resistant to erosion than the silt and mud of the underlying temple cap-age sediments. as erosion and weathering progressed, it is possible that inverted valley topography formed (cundari and ollier, 1970; hamblin, 1987) with the tuffs rising somewhat above the surrounding country, providing additional gravitational potential and the slope needed for moving the clasts by debris flows over the last few tens of kilometers to reach the depositional site. in southwestern utah, basaltic lavas have produced inverted topography of over 300 m relief in less than 3 million years (hamblin, 1987; biek and others, 2009). discussion the eruptive sources of the large ignimbrite clasts in the jurassic carmel formation of southern utah remain problematic. emplacement of the parental ignimbrites occurred in southern california and across southern nevada and northern arizona with distal lobes extending up to 200 km from their vents (figure 16). these lobes would have reached across the location of the modern-day grand canyon. after remaining in place and weathering for some 5 to 10 million years, they were remobilized as debris flows that carried the clasts the remaining distance (±50 km) into their current depositional setting. this would account for even the large boulder-sized clasts found in the paria river member of the carmel formation. however, the event or events that brought the clasts into the depositional basin were not common, as we do not find the volcanic clasts throughout the carmel formation. their occurrence is restricted to only one or two horizons. chapman (1993) proposed that the boulder beds in the carmel formation required catastrophic floods to carry the boulders over the transport distance of 200 to 300 km to get them from their source to the depositional site. this proposed flooding could have originated in a highland arc terrain due to excessive rainfall or due to the collapse of a crater lake or natural volcanic dam. alexander and cooker (2016) have shown that during flash floods—defined as any overland flow of water within or outside a river channel that arrives suddenly at a fixed point, changes quickly, and lasts a short time—large boulders can be moved farther than would normally be predicted due to the inherently unstable nature of the flow. we agree with chapman that this type of event could be a possible trigger for the deposits. however, as we have discussed above, the distance required for transport was likely much less than 200 to 300 km and more likely in the range of 50 km. this distance is not unreasonable for a debris flow to carry the low-density tuff boulders and cobbles. near an active arc, another possible triggering factor may have been earthquakes. scott and others (2001) give examples of several earthquake-triggered debris flows, with some traveling over 100 km from their sources. for example, a 1994 earthquake in colombia generated a debris flow that “conveyed a catastrophic wave of debris” along the río páez for over 100 km (scott and others, 2001). it is apparent that earthquakes large enough to liquefy and deform the sedimentary deage -ma 170 0 4 3 2 1 175174173172171 relative probabilityn um be r o f a ge s weighted mean age = 171.73 ± 0.19 ma peak age = 171.75 ma 23 grains figure 15. relative probability plot for 40ar/39ar sanidine ages from clast 1-1. bars are individual grain ages. 88 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 42° 34° 36° 46° 44° 40° 38° 32° 124° 120° 116° 112° 108° 0 middle jurassic tectonics 0 0 50 100 150 200 250 mi 200100 300 400 km sl-ms sz great a nc es tr al ro ck ie s valley group klamath mtns m odern shoreline blue mtns ar ap ie nca rm el em ba ym en t sundance sea mogollon highland paria r ive r f luvial s yste m dunes tidal �at dunes 20° n 15° n ua middle jurassic felsic pluton plate motion wind direction volcanic clast deposits stream �ow ancestral uinta arch snow lake-mojavesonora shear zone (sl-ms sz) triassic luning-fencemaker terrane jurassic coast range ophiolite and great valley group jurassic franciscan subduction complex paleozoic-early mesozoic oceanic arcs (klamath, blue mtns, n. sierra nevada) paleozoic oceanic terranes (roberts mountains and golonda allochthons) north america craton possible source area for volcanic clasts ua figure 16. paleogeographic and tectonic map for the middle jurassic during deposition of the paria river member of the carmel formation. information used in compiling this figure comes from blakey and others (1983), kocurek and dott (1983), chapman (1987), busby-spera (1988), thorman and others (1991), dilek and moores (1993), taylor and others (1993), christiansen and others (1994), lawton (1994), marzolf (1994), peterson (1994), blakey and parnell (1995), decelles and currie (1996), lawton and mcmillan (1999), kowallis and others (2001), and dickinson (2006). 89 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 table 5. runout distances for selected ignimbrites from the western united states. stratigraphic unit age (ma) composition location runout (km) corrected correction factor runout (km) today reference fraction tuff 18.6 rhyolite central nevada vf 44 0.714 62 best and others, 2013a pahranagat formation 22.9 rhyolite central nevada vf 114 0.714 160 best and others, 2013a tuff of clipper gap 25.0 rhyolite central nevada vf 214 0.714 300 best and others, 2013a tuff of lunar cuesta 25.7 dacite-rhyolite central nevada vf 130 0.850 153 best and others, 2013a upper tuff member of spf 26.4 rhyolite central nevada vf 200 1.000 200 best and others, 2013a tikaboo tuff member of spf 26.8 rhyolite central nevada vf 114 0.850 134 best and others, 2013a hancock tuff member of spf 26.8 rhyolite central nevada vf 80 0.714 112 best and others, 2013a lower tuff member of spf 27.0 rhyolite central nevada vf 121 1.000 121 best and others, 2013a tuff of orange lichen creek 27.1 rhyolite central nevada vf 61 0.850 72 best and others, 2013a monotony tuff 27.6 dacite-rhyolite central nevada vf 136 0.850 160 best and others, 2013a tuff of hot creek canyon 30.0 rhyolite central nevada vf 43 1.000 43 best and others, 2013a windous butte formation 31.7 dacite-rhyolite central nevada vf 228 0.850 268 best and others, 2013a pancake summit tuff 35.3 rhyolite central nevada vf 78 0.850 92 best and others, 2013a stone cabin upper member 35.8 rhyolite central nevada vf 76 1.000 76 best and others, 2013a stone cabin middle member 35.8 rhyolite central nevada vf 76 0.850 89 best and others, 2013a hiko 22.6 rhyolite caliente caldera complex 65 0.733 89 best and others, 2013a racer canyon 18.6 dacite-rhyolite caliente caldera complex 49 1.000 49 best and others, 2013a harmony hills tuff 22.6 andesite caliente caldera complex 116 0.870 133 best and others, 2013a bauers tuff 23.0 rhyolite caliente caldera complex 120 1.000 120 best and others, 2013a swett tuff 24.2 rhyolite caliente caldera complex 143 0.733 195 best and others, 2013a leach canyon 24.0 rhyolite caliente caldera complex 120 0.870 138 best and others, 2013a hole in the wall member of isom fm 24.6 trachydacite indian peak vf 80 0.666 120 best and others, 2013a bald hills member of isom fm 27.5 trachydacite indian peak vf 107 0.666 160 best and others, 2013a ripgut tuff 29.0 rhyolite indian peak vf 61 0.870 70 best and others, 2013a petroglyph cliff tuff 29.1 dacite-trachydacite indian peak vf 43 0.870 50 best and others, 2013a lund tuff 29.2 dacite indian peak vf 97 0.666 145 best and others, 2013a silver king tuff 29.4 dacite-rhyolite indian peak vf 42 0.666 63 best and others, 2013a mackleprang tuff 30.0 rhyolite indian peak vf 61 0.666 92 best and others, 2013a greens cayon 30.1 rhyolite indian peak vf 19 0.666 29 best and others, 2013a deadman spring 30.0 dacite indian peak vf 50 0.870 58 best and others, 2013a wash wah springs tuff 30.1 dacite indian peak vf 133 0.666 200 best and others, 2013a cottonwood wash tuff 31.1 dacite indian peak vf 104 0.870 120 best and others, 2013a lamerdorf 32.0 rhyolite indian peak vf 64 0.733 87 best and others, 2013a marsden 33.0 rhyolite indian peak vf 48 0.870 55 best and others, 2013a sawtooth 33.5 rhyolite indian peak vf 40 1.000 40 best and others, 2013a tunnel spring tuff 35.3 rhyolite indian peak vf 15 0.666 22 best and others, 2013a the gouge eye 36.0 dacite-rhyolite indian peak vf 25 1.000 25 best and others, 2013a blue sphinx/hu pwi 24.5 rhyolite western nevada vf 76 0.870 88 henry and john, 2013 bates mtn a/rattlesnake canyon 31.2 rhyolite western nevada vf 126 0.666 189 henry and john, 2013 arc dome 25.1 rhyolite western nevada vf 61 0.666 91 henry and john, 2013 campbell creek/bates mtn c 28.9 rhyolite western nevada vf 257 0.733 350 henry and john, 2013 candelaria hills 26.0 rhyolite western nevada vf 47 0.980 48 henry and john, 2013 gabs valley 25.1 rhyolite western nevada vf 123 0.733 168 henry and john, 2013 nine hill tuff 25.4 rhyolite western nevada vf 167 0.666 250 henry and john, 2013 new pass tuff 25.3 rhyolite western nevada vf 97 0.666 146 henry and john, 2013 singatse tuff 26.9 rhyolite western nevada vf 136 0.733 185 henry and john, 2013 toiyabe tuff 23.3 rhyolite western nevada vf 157 0.733 214 henry and john, 2013 mickey pass tuff 27.1 rhyolite western nevada vf 210 0.733 287 henry and john, 2013 notes: corrected for 50% post volcanic east-west extension in western nevada and central nevada volcanic fields (vf); corrected for 40% post volcanic east-west extension in indian peak volcanic field and caliente caldera complex; distances in red are for runouts over 100 km; sfp = shingle pass formation. 90 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 posits of the carmel formation did occur during deposition of this formation. marzolf (1988, 1990) noted that associated with these boulder and cobble beds in the carmel formation are “massive silty sandstones [that] display abundant evidence of liquefaction and fluidization, including remnants of contorted stratification, foundered conglomerate beds, and spectacular elutriation pipes.” more recently, wheatley and others (2016) also concluded that these structures and pipes were likely caused by one or more earthquakes. an earthquake at the right time of year when the source outcrops were saturated with seasonal rainfall or snowmelt could have provided a trigger for the debris flows. whatever the triggering mechanism, a highland area to the southwest of the depositional site was needed. from the time of eruption of the tuff beds at about 172 to 174 ma until the formation of the transporting debris flows, subduction and volcanic activity appear to have been fairly continuous along the jurassic arc as evidenced by the numerous fallout ash beds that were deposited in the carmel-twin creek (sundance) seaway (marvin and others, 1965; everett and others, 1989; zhang, 1996; kowallis and others, 2001; sprinkel and others, 2011). busby-spera (1988) proposed that the arc during this time period was a low-standing, arc-graben. chapman (1993) countered, arguing that by the time the debris flows were carrying boulders over long distances into the carmel basin, there must have been a significant highland to the southwest of the depositional site. we agree that debris flows require a significant gravitational potential in order to travel even a few tens of kilometers and that the source area must have been at a significantly higher elevation than the deposits, but this may not necessitate a change in the model of a low-standing arc-graben at the time these deposits were formed. the modern central american volcanic arc formed along the middle american trench is in part a low-standing arc-graben similar to what busby-spera (1988) proposed for the middle jurassic. figure 17 shows the central american arc with a low-standing, arc-graben formed between northern costa rica and northern nicaragua. to the northeast of this part of the arc is a highland region with rivers flowing off of it toward the caribbean coast. we have superimposed on the figure our modeled source area and location of the clast deposits from figure 16. the scale of the modern arc and distance from the arc to the eastern fluvial plain are remarkably similar to what we propose for the middle jurassic. additionally, studies of landslides and debris flows in the highland areas of guatemala, el salvador, costa rica, and nicaragua have documented run-out distances of up to 50 km (alvarado and others, 2004; siebert and others, 2006; devoli and others, 2007, 2009), similar to what we propose would have been needed to transport the middle jurassic clasts from the outcrop area to the depositional site. triggers for landslides in nicaragua include earthquakes, volcanic eruptions, and rainfall associated with tropical storms or hurricanes (devoli and others, 2007). conclusions the source for coarse volcanic detritus in the middle jurassic carmel formation of southern utah has been problematic. we propose that poorly welded rhyolite tuffs generated during temple cap formation time (~173 ma) from the middle jurassic arc in southern california were likely emplaced in distal run-out lobes focused in fluvial valleys, perhaps as much as 200 km from the source vents extending out across the location of the modern grand canyon. these tuff outcrops were then stable for several million years as the processes of weathering and alteration proceeded perhaps producing an inverted topography with the tuffs capping mesas above weaker sedimentary units. about 164 ma, debris flows sourced in these tuff-capped mesas formed and then flowed perhaps 50 km (but possibly even farther) carrying cobbles and some boulders along channels to the depositional site in fluvial channels on a broad tidal flat. triggers may have been torrential rain, earthquakes, or some combination of these factors. acknowledgments we acknowledge the assistance of michael dorais, david tingey, magnolia serrano-tomlinson, and david tomlinson at brigham young university for their assistance with electron microprobe and geochemical analyses, brian jicha at the wiscar lab at the university of wisconsin for assistance with 40ar/39ar analyses, 91 rhyolite ignimbrite boulders and cobbles in the middle jurassic carmel formation of utah and arizona—age, composition, transport, and stratigraphic setting kowallis, b.j., sprinkel, d.a., christiansen, e.h, steed, s., and wheatley, d.f. geology of the intermountain west 2020 volume 7 and paul o’sullivan at apatite to zircon inc. for u-pb analyses. we also thank the utah geological survey and brigham young university for financial support for isotopic and geochemical analyses, as well as travel to the field area. references ague, j.j., and brimhall, g.h., 1988, regional variations in bulk chemistry, mineralogy, and the compositions of mafic and accessory minerals in the batholiths of california: geological society of america bulletin, v. 100, p. 891–911. alexander, j., and cooker, m.j., 2016, moving boulders in flash floods and estimating flow conditions using boulders in ancient deposits: sedimentology, v. 63, p. 1582–1595. alvarado, g.e., benito, b., staller, a., climent, á., camacho, e., rojas, w., marroquín, g., molina, e., talavera, j.e., martínez-cuevas, s., and lindholm, c., 2017, the new central american seismic hazard zonation—mutual consensus based on up to day seismotectonic framework: tectonophysics, v. 721, p. 462–467. alvarado, g.e., vega, e., chaves, j., and vásquez, m., 2004, los grandes deslizamientos (volcánicos y no volcánicos) de tipo debris avalanche en costa rica: revista geológica de américa central, v. 30, p. 83–99. 15° 20° 10° 85°90° 80° 85°90° 80° 15° 20° 10° mid-american trench central america 0 0 50 100 150 200 250 mi 200100 300 400 km nicaragua honduras guatemala mexico costa rica panama el salvador belize n figure 17. the central american volcanic arc with the mid-american trench to the southwest. the pink shaded area is the western u.s. source area shown on figure 16 superimposed over central america at the same scale; the red star would be the location of the clast deposits. the arc through northern costa rica to northern nicaragua is a low-standing arc-graben. however, highland areas exist to the northeast with rivers flowing off into the atlantic, similar to what we propose for the time the volcanic clasts were 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volcanic ashes in the middle jurassic of southern utah: provo, utah, brigham young university, m.s. thesis, 75 p. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah thomas c. chidsey, jr., david e. eby, and douglas a. sprinkel geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover left: cave breccia consisting of large, poorly sorted, white angular clasts of fractured limestone (or dolomite) surrounded by a yellowish altered matrix of feldspathic and granitic conglomerate and sandstone. note also the greenish clay and black bitumen. leadville limestone, big flat no. 2 well, grand county, utah; slabbed core from 7630.5 feet (2325.8 m). right: “autobreccia” due to probable natural hydrofracturing showing a dolomite in which the “clasts” have moved very little; the black material surrounding the in-place clasts is composed of porous, late replacement dolomite coated with black bitumen. leadville limestone, lisbon nw usa no. b-63 well, san juan county, utah; slabbed core from 9938.3 feet (3029.2 m). i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 243 abstract two types of breccia are found in the mississippian leadville limestone, paradox basin, southeastern utah: (1) breccia associated with karstification and (2) breccia created by natural hydrofracturing, i.e., “autobreccia.” breccia associated with sediment-filled cavities is relatively common throughout the upper one-third of the leadville limestone in lisbon and other paradox basin oil and gas fields. these cavities and/or cracks are related to karstification of exposed leadville during late mississippian time. infilling of cavities by detrital carbonate and siliciclastic sediment occurred before deposition of the pennsylvanian molas formation or hermosa group. transported material consists of poorly sorted detrital quartz and feldspar grains, chert fragments, as well as clasts of carbonate and clay. carbonate muds infilling karst cavities are very finely crystalline non-porous dolomites. post-burial brecciation, caused by natural hydrofracturing, is also quite common within leadville reservoirs at lisbon and other fields. brecciation created an explosive-looking, pulverized rock, an “autobreccia” as opposed to a collapse breccia. clasts within autobreccias remained in place or moved very little. dolomite clasts are commonly surrounded by solution-enlarged fractures partially filled with coarse rhombic and late saddle dolomites. areas between clasts exhibit good intercrystalline porosity and microporosity or are filled by dolomite cements. intense pyrobitumen lining of pores was concurrent with, or took place shortly after, brecciation. the presence of zebra dolomites and zebra vugs attest to high temperatures associated with natural hydrofracturing. rimmed microstructures or stair-step fractures are present, reflecting shear and explosive fluid expulsion from the buildup of pore pressure. abundant pyrobitumen makes porous breccias and dolomites look like black “shales.” post-burial breccias are associated with the best reservoir development at lisbon field. outcrop analogs for both breccia types are present in the stratigraphically equivalent mississippian section along the south flank of the uinta mountains in northeastern utah. based on field observations, a key component for autobrecciation is the presence of an underlying aquifer that serves as a conduit for hydrothermal fluids. large volumes of water throughput are required to produce brecciation and the amount, type, and generations of dolomite present at lisbon field. we propose a model where convection cells bounded by basement-rooted faults transfer heat and fluids possibly from crystalline basement, pennsylvanian evaporites, and oligocene igneous complexes. post-burial brecciation often results in the formation of large, diagenetic hydrocarbon traps. a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah thomas c. chidsey, jr.1, david e. eby2, and douglas a. sprinkel3 1utah geological survey, salt lake city, ut 84114; tomchidsey@utah.gov 2eby petrography & consulting, inc., denver, co 80204; epceby@aol.com 3utah geological survey, salt lake city, ut 84114; azteca geosolutions, pleasant view, ut 84414; sprinkel@aztecageo.com citation for this article. chidsey, t.c., jr., eby, d.e., and sprinkel, d.a., 2020, a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah: geology of the intermountain west, v. 7, p. 243–280, https://doi.org/10.31711/giw.v7.pp243-280. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 244 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 introduction the mississippian leadville limestone is one of two major oil and gas plays in the paradox basin (figure 1), the other being the pennsylvanian paradox formation (chidsey and eby, 2016; chidsey and others, 2016). the paradox basin is within the west-central part of the colorado plateau physiographic province, southeastern utah and southwestern colorado. the leadville is a shallow, open-marine carbonate shelf deposit having a variety of facies. traps for hydrocarbons in the leadville are fault and fault-related anticlines (figure 2), as is the case for lisbon field (morgan, 1993; chidsey and eby, 2016; chidsey, in press). hydrocarbon production and most drilling oil shows are found along the northwest-trending paradox fold and fault belt in the northern part of the basin (figure 1). mississippian rocks in the paradox basin and other areas of the colorado plateau contain localized zones or pipes of breccia due to either collapse associated with paleokarstification or explosive natural hydrofracturing which created shattered-looking, pulverized rock, i.e., “autobreccia.” these characteristics are identified in several leadville cores throughout the northern paradox basin. breccia associated with sediment-filled collapsed cavities is relatively common in several areas and formed during periods of subaerial exposure. autobreccia can be an irregular-shaped or cylindrical mass of brecciated rock that formed when hydrothermal solutions forced their way towards the surface through zones of weakness or fracture zones and naturally break up rocks in the process. the best examples of both breccia types are found in cores from lisbon field, san juan county, utah (figure 1), which accounts for most leadville oil and gas production in the paradox basin (~51.5 million barrels of oil [mmbo] produced as of january 1, 2020 [utah division of oil, gas and mining, 2020]). porosity associated with karst breccias is often poor, whereas porosity in autobreccias and related dolomites can be very high in the lisbon field area. however, saddle dolomite that formed as cement in autobreccia zones can reduce porosity. a key to identifying porous zones is the presence of abundant pyrobitumen, which makes porous breccias and dolomites appear like black “shales.” the mississippian strata along the south flank of the uinta mountains in northeastern utah has similar characteristics to the leadville limestone. these rocks provide production-scale analogs of the facies and diagenetic characteristics, geometry, distribution, and nature of boundaries contributing to the overall heterogeneity of leadville reservoirs. they also contain local zones of breccia due to either natural collapse or hydrofracturing and serve as a model for breccia formation in the leadville limestone. the goal of this paper is to provide new information about two breccia types critical in understanding trapping mechanisms, reservoir quality and history, and figure 1. regional setting of the paradox basin, showing fields (lisbon highlighted) that produce oil and gas including carbon dioxide (co2) from the mississippian leadville limestone, and thickness of the leadville; contour interval is 100 feet (30 m). modified from parker and roberts (1963). the leadville limestone paradox basin play area is colored dark tan. modified from morgan (1993). 245 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 production in leadville limestone reservoirs. the understanding of breccia types can lead to identification of large, untapped diagenetic-type hydrocarbon traps in underexplored parts of the paradox basin and other analogous brecciated carbonate reservoirs. general characteristics of the leadville limestone depositional environments during the late kinderhookian through early meramecian, the colorado plateau was covered by a tropical, warm-water, shallow-shelf, variable energy epicontinental sea that covered a large part of the north american craton, with a shelf break into a deeper starved basin west of the four corners area (figure 3a). this platform was the site of extensive carbonate deposition implying arid, shallow marine conditions south of the paleoequator (blakey and ranney, 2008). little sand or mud was transported into the shallow, clear water, providing favorable sites for growth of lime-secreting marine organisms, grains, and microbialites (blakey and ranney, 2008; eby and others, 2014). mississippian marine fauna are corals, brachiopods, pelecypods, bryozoans, and crinoids; however, these fossil types are relatively rare in some areas. other common biota include ostracods, benthic foraminifera, and gastropods. microbial-dominated rocks are present, but uncommon. depositional environments include mud-rich tidal flats; burrowed peloid mud in subtidal, intertidal, and supratidal settings; restricted marine; high-energy ooid shoals; middle shelf; storm-dominated, outer shelf open-marine, crinoid banks with mudrich interbanks; and offshore low-energy, open-marine settings below wave base (figure 3b). conditions in the interior of the leadville carbonate platform were right for early marine reflux dolomitization derived from magnesium-bearing brines. locally, mud-supported boundstone created buildups or mud mounds (waulsortian facies), involving growth of “algae” (wilson, 1975; fouret, 1982, 1996; ahr, 1989). waulsortian buildups or mud mounds developed exclusively during the mississippian in many parts of the world (wilson, 1975). during late mississippian (chesterian) time, the entire carbonate platform in southeastern utah and southwestern colorado was subjected to subaerial exposure and erosion, resulting in the formation of a lateritic regolith (figure 4) (welsh and bissell, 1979). this regolith and associated carbonate dissolution (karstification) are important factors in leadville reservoir potential. figure 2. schematic block diagram of the paradox basin displaying basement-involved structural trapping mechanisms for the leadville limestone fields. modified from petroleum information (1984; original drawing by j.a. fallin). 246 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 lithology and carbonate fabrics mississippian formations are mostly lightto darkgray, fineto coarse-crystalline, cherty limestone. dolomitic units are gray to tan, sucrosic to crystalline, and medium bedded with occasional silty partings. both limestone and dolomite units are the main reservoir lithologies for the leadville limestone. chert is typically light gray and forms lenses and nodules. the most common carbonate fabrics of the leadville and other mississippian formations include peloid, skeletal, and ooid grainstone, packstone, and wackestone; skeletal and intraclast rudstone and floatstone are also present. cross-bedded grainstone fabrics of crinoid debris are referred to as encrinites. mudstones appear as microcrystalline and cryptocrystalline limestone and dolomite. stratigraphy the leadville limestone is 300 to 600 feet (100–200 m) thick in the paradox basin (hintze and kowallis, 2009, and references therein) (figure 1). the leadville limestone is divided into two informal members (figure 5): (1) a dolomitic limestone lower member and (2) a limestone and dolomite upper member, separated by a regional disconformity within the leadville. according to baars (1966) this disconformity can be correlated figure 3. (a) paleogeography of utah during early late mississippian (early meramecian) time when a warm shallow sea covered much of utah. modified from blakey and ranney (2008). (b) block diagram for the mississippian leadville limestone displaying major depositional facies during early late mississippian time, as determined from lisbon field cores. from chidsey and eby (2016). 247 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 throughout the paradox basin. brecciation and sediment-filled cavities, related to karstification of subaerially exposed leadville in southwestern colorado, are relatively common throughout the upper one-third of the formation (evans and reed, 2006, 2007). average depth to the leadville in paradox basin fields is 8760 feet (2920 m). the mississippian leadville limestone and overlying pennsylvanian molas formation (where present) or hermosa group are separated by a major unconformity in southeastern utah (figure 5). this same unconformity is found at the top of the stratigraphically equivalent mississippian redwall limestone in the grand canyon (mckee, 1969), where subaerial exposure resulted in development of karst topography with carbonate breccia-filled collapse features (paleo-sinkholes) and terra rosa (red earth cave fills) near the top of the formation. similar features are recognized in leadville cores. an unconformity separates the leadville from the underlying devonian ouray limestone (figure 5). lisbon field, san juan county, utah a wealth of core from lisbon field is available at the utah core research center (ucrc) in salt lake city, utah, as well as petrographic and other core-related data. reservoir characteristics (clark, 1978; smith and prather, 1981; fouret, 1982, 1996; chidsey and eby, figure 4. (a) paleogeography during late mississippian (chesterian) time when the entire carbonate platform in southeastern utah and southwestern colorado was subjected to subaerial erosion. modified from blakey and ranney (2008). (b) block diagram for the mississippian leadville limestone displaying co-occurrence of karst-related breccias, cave sediments, and dolomites related to the exposed leadville during late mississippian time with overprint of post-burial, fault-related breccias, fractures, and porous dolomites, as determined from cores in the paradox basin. after chidsey and eby (2016). 248 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 2016), particularly brecciation from karstification and natural hydrofracturing, and leadville facies can be applied regionally to other fields and exploration trends in the paradox basin. therefore, we selected lisbon as the major leadville limestone case-study field. field synopsis lisbon field is trapped within an elongate, asymmetric, northwest-trending anticline beneath the thick, salt-bearing pennsylvanian paradox formation. the anticline has nearly 2000 feet (600 m) of structural closure and is bounded on the northeast flank by a major, basement-involved normal fault that has over 2500 feet (760 m) of displacement (smith and prather, 1981) (figures 6 and 7). several minor, northeast-trending normal faults divide the lisbon leadville reservoir into compartments. producing units in lisbon field contain crinoidal/ skeletal dolograinstone, dolopackstone, and dolowackestone fabrics. diagenesis includes fracturing, autobrecciation, karst development, hydrothermal dolomitization, and bitumen plugging. net reservoir thickness is 225 feet (69 m) over a 5120-acre (2100 ha) area (clark, 1978; smouse, 1993). reservoir quality is improved by natural fracturing associated with the paradox fold and fault belt. porosity averages 6% in fracture-enhanced intercrystalline and moldic networks; permeability averages 22 millidarcies (md). reservoir drive is via an expanding gas cap and gravity drainage; original water saturation was 39% (clark, 1978; smouse, 1993). bottom-hole temperature ranges from 133° to 189°f (56°– 87°c). lisbon field was discovered in 1960 by the pure oil company no. 1 nw lisbon usa well (ne1/4nw1/4 section 10, t. 30 s., r. 24 e., salt lake base line and meridian [slbl&m]), san juan county, utah (figure 6), with an initial flowing potential of 179 barrels of oil per day (bopd) and 4376 thousand cubic feet of gas per day (mcfgpd). the original reservoir field pressure was 2982 pounds per square inch (20,560 kpa) (clark, 1978). currently, 18 producing (or shut in) wells, 13 abandoned producers, 5 injection wells (4 gas injection wells and one water/gas injection well), and 4 dry holes are in the field. cumulative production as of january 1, 2020, was 51,489,472 barrels of oil, 810.2 billion cubic feet of gas (cycled gas), and 50,600,821 barrels of water (utah division of oil, gas and mining, 2020). hydrocarbon gas, re-injected into the crest of the structure to control pressure decline, is now being produced; acid gas is still re-injected. figure 5. devonian through middle pennsylvanian stratigraphic column for the paradox basin showing the major unconformity (defined by paleokarst features) between the mississippian leadville limestone and the overlying pennsylvanian molas formation. note that the leadville is divided into two informal members separated by an unconformity. modified from welsh and bissell (1979) and evans and reed (2007). 249 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 figure 6. top of structure of the leadville limestone, lisbon field. modified from c.f. johnson, union oil company of california files (1970) courtesy of tom brown, inc. cross section a–a' shown on figure 7. also displayed are wells from which cores were described in this study. figure 7. schematic east-west structural cross section, lisbon field. line of section shown on figure 6. note the juxtaposition of the mississippian (m) section against the pennsylvanian (ip) section, which includes evaporites (salt) and organic-rich shale. ogc = oil-gas contact, owc = oil-water contact. modified from clark (1978). 250 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 facies three primary depositional facies were identified in leadville limestone cores in the lisbon case-study field: (1) open marine, (2) ooid and peloid shoals, and (3) middle shelf (figure 3b). open-marine lithofacies are represented by crinoidal banks or shoals and waulsortian-type buildups (figure 3b). crinoidal banks and shoals represent high-energy environments with well-circulated, normal-marine salinity water in a subtidal setting, although they can also be present in restricted marine, middle shelf settings. we estimate that water depths ranged from 5 to 45 feet (1.5–14 m). waulsortian-type buildups were first described in lisbon field by fouret (1982) and are steep-sloped tabular, knoll, or sheet forms composed of several generations of mud deposited in a subtidal setting (fouret, 1982, 1996; lees and miller, 1995) (figure 3b). lime mud was precipitated by cyanobacteria (microbialites) (lees and miller, 1995). we estimate that water depths ranged from 60 to 90 feet (20–30 m). ooid and “hard” peloid shoals developed as a result of agitated, shallow-marine processes on the open-marine or bordering restricted-marine middle shelf (figure 3b). this lithofacies represents moderate to high energy, with moderately well-circulated water in a shoal setting. sediment deposition and modification probably occurred in water depths that we estimate ranged from near sea level to 20 feet (6 m) below sea level within wave base. middle-shelf lithofacies covered extensive areas across the shallow platform and represent a low-energy, often restricted-marine environment (figure 3b). mud and some sand were deposited in a low energy, subtidal (burrowed), inter-buildup/shoal setting. we estimate that water depths ranged from 60 to 90 feet (20–30 m). mississippian outcrop analogs in the uinta mountains the leadville limestone is not exposed in southeastern utah; however, equivalent mississippian rocks outcrop along the flanks of the east-west-trending uinta mountains in northeastern utah (figure 8). uplift of the uinta mountains occurred during the laramide orogeny from latest cretaceous time (maastrichtian, about 70 ma) through the eocene (about 34 ma). the mississippian rock section along the southern flank of the uinta mountains is over 1600 feet (490 m) thick (sprinkel, 2018) (figures 9 and 10). mississippian outcrops along the western end of the uinta mountains consist of the madison, humbug, and doughnut formations (bryant, 1990; figures 9 and 10). however, bryant’s (1990) madison includes the fitchville formation (upper devonian-lower mississippian [385–340 ma]). in addition, the madison includes a phosphatic shale interval identified by sandberg and gutschick (1980) and mapped by sprinkel (2018) as the delle phosphatic member of the deseret limestone. the delle phosphatic member separates lower cliff-forming carbonate (gardison limestone) from upper cliff-forming carbonate (deseret limestone). thus, the terms gardison and deseret limestones are recommended for the western uinta mountains and are overlain by the humbug and doughnut formations (figures 9 and 10). the delle phosphatic member either pinches out or grades to mostly thin-bedded carbonate rocks in the eastern uinta mountains. where the delle is not recognized and the gardison and deseret cannot be easily separated, the term madison limestone is used (sprinkel, 2006, 2007). for simplicity, the interval will be collectively referred to as the mississippian section in this study. contacts between the mississippian formations in the uinta mountains are mostly conformable (sadlick, 1955, 1957; carey, 1973; hintze and kowallis, 2009). three sites were selected for detailed outcrop studies (figure 8): (1) south fork provo river, (2) dry fork canyon, and (3) crouse reservoir/diamond mountain plateau. each study site has a unique set of depositional lithofacies and post-depositional breccia characteristics created by karstification and/or hydrofracturing in mississippian strata that are identical or very similar to those observed in leadville limestone cores from lisbon field in the paradox basin (figure 1), with samples collected for slabbing and thin section analysis. the south fork provo river study site is on the western end of the southern flank of the uinta mountains, wasatch county (figure 8). the site is a series of roadcuts along the eastern side of state highway 35, 11 miles (18 km) east of the town of francis, and 25 miles (42 km) north251 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 figure 8. mississippian outcrop reservoir analogs in utah showing the location of the study sites. (a) location of mississippian rock outcrops in utah equivalent to the leadville limestone. (b) generalized geologic map of the uinta mountains, northeastern utah. modified from hintze and others (2000). 252 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 west of the town of hanna, utah (figure 11). the dry fork canyon study site is in the east-central part of the southern flank of the uinta mountains, uintah county (figure 8), 20 miles (32 km) northwest of the town of vernal, utah. this site includes several noteworthy outcrops along the red cloud loop road where it forks and turns up brownie canyon (figure 12). the crouse reservoir/diamond mountain plateau study site is in the eastern part of the southern flank of the uinta mountains, uintah county (figures 8 and 13), 29 miles (47 km) northeast of vernal. karst breccia, sediments, and other cave deposits breccia created by karstification and cave sediments is found around the world where subaerial exposure of limestones is presently occurring or occurred during the geologic past. excellent examples are found in leadville limestone and mississippian rocks in the uinta mountains, northeastern utah. mississippian karst breccia and cave sediments resulted when much of the western north american craton, including eastern utah, was subaerially exposed (figure 4). subsurface leadville limestone, paradox basin a paleokarst lithofacies classification was developed for leadville limestone outcrops in colorado by evans figure 9. lithologic column of a part of the paleozoic section along the western end of the southern flank of the uinta mountains. modified from hintze and kowallis (2009) and sprinkel (2018). figure 10. lithologic column of a part of the paleozoic section along the eastern end of the southern flank of the uinta mountains. modified from hintze and kowallis (2009). 253 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 and reed (2006, 2007) (table 1). we characterized paleokarst lithofacies, as well as post-burial autobreccia, from regional and lisbon field wells (figure 14). five cave sediment lithofacies were recognized in three cores based on the evans and reed (2006, 2007) classification: (1) speleothem, (2) breccia, (3) fissure-fill sediments, (4) conglomerate, and (5) fine-grained sediment. speleothem a speleothem is defined as any natural secondary mineral deposit formed in a cave by water movement. speleothems take on a variety of forms depending on whether groundwater drips, seeps, condenses, flows, or ponds (hill and forti, 1997). most speleothems are calcareous and composed of calcite or aragonite. in the case of the leadville limestone, they originated in situ essentially where they are found (autochthonous) within vadose paleocave passages and consist of dripstone, flowstone, cave pearls (a small spherical speleothem with concentric layers around a nucleus), a variety of cave crystals, and many other types (evans and reed, 2006, 2007). caves are commonly decorated with dripstone in the form of stalactites, stalagmites, and columns. flowstone is a sheet-like deposit on the cave floors and walls and can also form cave drapery (thin, wavy sheets of calcite or aragonite that hang downward from the roof of the cave) or rimstone dams that appear like stairs and build up in pools of water. figure 11. google earth image (© 2018 google) showing the location of study site 1, south fork of the provo river and possible paleokarst features and the hydrothermal breccia pipe along the western end of the southern flank of the uinta mountains in wasatch county, utah. the mississippian deseret limestone outcrops are best exposed in roadcuts within the elongated yellow oval; the red arrow is the location of possible paleokarst features and the red square is the location of the breccia pipe. figure 12. google earth image (© 2018 google) showing the location of study site 2, dry fork canyon (yellow circle). 254 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 a speleothem was identified in core from the big flat no. 2 well (figures 14 and 15). the speleothem, most likely sheet-like flowstone of calcite, caps a karst breccia. no other speleothems were identified in the cores examined. breccia breccia, formed via karstification, is common in many cores examined in the study. the breccia consists of a chaotic mix of various clast sizes infiltrated with a siliciclastic matrix. cave breccia in the leadville limestone developed in the vadose zone and originated near or not too far from where they are found (parautochthonous) under paleosinkholes (also called paleodolines) or from the creation of breakout domes (large rooms formed when the cave ceiling collapsed) (loucks, 1999; evans and reed, 2006, 2007). an excellent example of cave breccia is shown in core from the big flat no. 2 well (figures 14 and 16). the breccia consists of angular chaotic clasts ranging from pebbles to boulders(?) in a greenish-gray siliciclastic matrix. fissure-fill sediments fissure-fill sediments, often referred to as geopetal, represent infilling of open, solution-enlarged fissures, fractures, or joints (grikes) (evans and reed, 2006, 2007). leadville limestone fissure-fill geopetal sediment developed in the vadose zone and generally originated in a place other than where they are found (allochthonous). they may be horizontally or vertically laminated depending on whether their formation was due to successive events or reopening of closed fissures, respectively (evans and reed, 2006, 2007). other fissure fills can be massive (cave fill). both laminated and massive fissure-fill sediments were identified in core from the big flat no. 2 and no. 3 wells, respectively, and in lisbon field (figure 14). vertically laminated fissure-fill sediments (geopetal) infiltrated into linear and curvilinear, dissolution-enlarged fractures and dissolution cavities (vugs) (figure 17). dissolution features are often funnel-shaped, especially with massive-fissure fills in large, dissolution cavities (figure 18). massive fissure-fill sediment alternates between clay and loessite (lithified paleoloess) deposits. fissure-fill sediments in these cores likely originated from the overlying pennsylvanian molas formation above the regional unconformity (figure 5). conglomerate cave conglomerates are massive to poorly stratified (miall, 1978; evans and reed, 2006, 2007). sorting is poor, clasts are subrounded to subangular, and conglomerate is clast supported. leadville limestone cave conglomerates developed in both vadose and phreatic zones and, like the fissure-fill sediments (geopetal), are allochthonous. conglomerates were identified in core from the big flat no. 2 well (figures 14 and 19). unlike solution rounded limestone and chert described by evans and reed (2006, 2007) in table 1, poorly stratified conglomfigure 13. google earth image (© 2018 google) showing the location of study site 3, crouse reservoir/diamond mountain plateau (key brecciated outcrop indicated with yellow circle). 255 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 lithofacies description interpretation origin speleothem (s) sf flowstone sd: dripstone sc: cave pearls carbonate buildups as mounds or sheets of calcite spar or as radially banded calcite spar (cave pearls), interbedded with red siliciclastics. in situ chemical precipitates in vadose paleocave passages. autochthonous (vadose zone) breccia (b) br: chaotic, mosaic, or crackle breccia clast-supported, limestone-chert boulder-pebble breccia, with infiltrated red siliciclastic matrix. cave collapse breccia formed due to roof collapse in breakout domes or paleodolines. parautochthonous (vadose zone) fissure-fill sediments (j) ji: laminated fissure-fills jm: massive fissure-fills funnel-shaped dissolution features infilled by infiltrated red loessite from the overlying molas formation mixed with locally derived gravel-sized, angular limestone or chert clasts. gravity infilling of open fissures or joints (grikes). horizontal lamination represents successive infilling events. vertical lamination represents the re-opening of closed fissures due to shifting of underlying blocks. allochthonous (vadose zone) diamict (d) dmm: massive diamict dms: stratified diamict pebble-cobble diamicts with siltstone-rich matrix. some vertical clast orientations. debrites (siltstone-rich, subaqueous debris-flow deposits). allochthonous (vadose and phreatic zones) conglomerate (g) gm: massive to poorly stratified conglomerate clast supported, imbricated conglomerate consisting of solution rounded limestone and chert clasts with siltstone intraclasts. coarse-grained fluvial cave sediment. represents bedload transport of locally derived clasts through phreatic tubes. allochthonous (vadose and phreatic zones) sandstone (sn) snr: ripple-laminated and climbingripple laminated sandstone fine-grained, silty sandstone with climbing-ripple lamination. fine-grained fluvial cave sediment. represents rapid sedimentation rates. allochthonous (vadose and phreatic zones) siltstone (ss) ssm: massive siltstone massive, sandy siltstone that can show primary current lineation. fine-grained fluvial cave sediment. the abundant siltstone is a legacy of the loessite source material. primary current lineation indicates upper flow regime conditions. allochthonous (vadose and phreatic zones) fine-grained sediments (f) fi: laminated siltstone-mudstone rhythmite fm: massive silty mudstone fed: claystone drape with mudcracks argillaceous quartz siltstone, siltstone-claystone rhythmites, and mudstone drapes, often with mudcracked upper surfaces. fine-grained fluvial cave sediment. the abundant siltstone is a legacy of the loessite source material. the rhythmites are siltstones with thin mudstone partings. allochthonous (vadose and phreatic zones) table 1. paleokarst lithofacies classification developed for leadville limestone exposures in colorado by evans and reed (2006, 2007). figure 14. location of wells in the paradox fold and fault belt with cores used for examples of (1) karst breccia and cave sediment lithofacies (highlighted in yellow), and (2) post-burial breccia, pyrobitumen, dolomitization, and porosity (highlighted in pink). 256 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 erate in the big flat no. 2 core consists of granitic clasts in a matrix of pink feldspathic sand. this coarse-grained cave sediment fill may have been associated with fluvial sedimentation within the leadville cave system. fine-grained sediment fine-grained sediment in caves consists of quartz siltstone, silt-rich mudstone, siltstone-mudstone rhythmites, or mudstone drapes (miall, 1978; evans and reed, 2006, 2007). in the leadville limestone, finegrained sediments were deposited in both vadose and phreatic zones, are allochthonous, and laminated or massive. source of leadville fine-grained sediments in southwestern colorado is loess where the mississippian paleokarst served as a “dust trap” for identical deposits in the overlying pennsylvanian molas formation (figure 5); the provenance for the loess is unknown because the silt is composed almost entirely of quartz and there are no paleocurrent features (evans and reed, 2006, 2007). fine-grained sediment may also represent fluvial cave figure 15. karst breccia with speleothems (red arrows) capping massive to poorly stratified conglomerate consisting of pink feldspathic sandstone and granitoid clasts between leadville limestone country rock. big flat no. 2 well (section 11, t. 26 s., r. 19 e., slbl&m, grand county, utah, figure 14), slabbed core from 7729 to 7730 feet (2355.8–2356.1 m). figure 16. typical cave breccia infiltrated with a siliciclastic matrix. note the clast-supported early chert (ch). big flat no. 2 well (figure 14), slabbed core from 7744 feet (2360 m). 257 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 sediment (evans and reed, 2006, 2007). both laminated and massive fine-grained sediment were identified in cores from the big flat no. 2 and no. 3 wells, respectively (figures 14 and 20). fine-grained sediment in these cores is silt-rich mudstone. laminated fine-grained sediment infiltrated between solution-modified clasts (figure 20a). massive bedded strata infiltrated into a dissolution cavity (vug) (figure 20b). cave-fill sediments in lisbon field fissure-fill sediments and sediment-filled cavities are common throughout the upper one-third of the figure 17. vertically laminated fissure-fill sediments (between red arrows) infiltrated into (a) a linear dissolution-enlarged fracture or joint (grike) developed within a well-bedded peloidal/skeletal wackestone, and (b) a curvilinear to funnel-shaped dissolution cavity developed within a well-bedded oolitic/peloidal grainstone. big flat no. 2 well (figure 14), slabbed core from 7724.5 feet (2354.4 m) (a) and 7631 feet (2326 m) (b). 258 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 leadville limestone in lisbon field (figures 14 and 21). contacts between transported material and country rock can be sharp, irregular, and corroded with small associated mud-filled fractures (figures 21a and 21b). transported material consists of poorly sorted detrital quartz grains (silt size), chert fragments, carbonate clasts, clay (figure 21c), and occassional clasts of mud balls (desiccated and cracked). infilling sediment displays crude lamination. carbonate mud infiltration of karst cavities is dolomitized (later diagenetic process), consists of very fine crystals, and is non-porous (figures 21 and 22); porosities are less than 2% and permeability is about 11 md. typically, the surrounding limestone matrix is also non-porous. other karst features observed in leadville thin sections include (1) the presence of “root hairs,” i.e., thin, sinuous cracks filled with dolomitized mud, and (2) clasts with a coating of clay. both of these features may be indicative of a soil zone. figure 18. massive fissure-fill sediments consisting of clay and loessite infiltrated into a large dissolution cavity developed within a well-bedded peloidal/oolitic grainstone. big flat no. 3 well (section 23, t. 26 s., r. 19 e., slbl&m, grand county, utah, figure 14), slabbed core from 7677 feet (2340 m). figure 19. cave breccia consisting of large, poorly sorted, white angular clasts of fractured limestone (or dolomite) surrounded by a yellowish altered matrix of feldspathic and granitic conglomerate and sandstone. note also the greenish clay and black bitumen. big flat no. 2 well (figure 14), slabbed core from 7630.5 feet (2325.8 m). 259 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 karstification in uinta mountain mississippian outcrops study site 1 – south fork provo river study site 1, south fork provo river, and the surrounding area was mapped by eskelsen (1953), mcdougald (1953), and bryant (1990). sprinkel (2018) mapped an adjacent area along the southern flank of the uinta mountains and western uinta basin. the primary outcrop containing breccias is in the deseret limestone (osagean through middle meramecian). the contact with the overlying humbug formation is difficult to recognize due to the poor nature of the outcrops and extensive slope cover. eskelsen (1953) and mcdougald (1953) mapped the area as deseret-humbug undifferentiated. bryant (1990) mapped fitchville, gardison, and deseret together in the area of the breccias at study site 1 with humbug mapped separately. elsewhere, bryant (1990) mapped each formation as separate units. although bryant (1990) lumped fitchville, gardison, and deseret together at study site 1, our examination of these outcrops determined that rocks containing breccias are deseret. the deseret limestone at study site 1 is a darkto light-gray limestone consisting of skeletal grainstone to packstone (figure 23) representing a high-energy, open-marine environment. in deseret outcrops at study site 1, possible paleokarst features have similar characteristics found in leadville cores (as well as outcrops of the equivalent mississippian redwall limestone in the grand canyon). stratiform polymictic brecciation figure 20. fine-grained sediment. (a) laminated silty green mudstone infiltrated between solution-modified clasts of leadville peloidal mudstone. big flat no. 2 well (figure 14), slabbed core from 7737 to 7738 feet (2358.2–2358.5 m). (b) massive silty mudstone infiltrated into a dissolution cavity developed within a crinoidal/ skeletal grainstone (with rugose corals). big flat no. 3 well (figure 14), slabbed core from 7723.5 feet (2354.1 m). 260 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 (collapse) is extensive (figures 24a and 24b), but without calcite veins, dolomitization, and explosive characteristic of a breccia pipe. red staining at the top of the deseret limestone, mapped as the madison limestone by bryant (1990), is possible terra rosa (red earth) weathering (i.e., reddish-colored clay-rich layer containing hematite that ranges in thickness from a few inches to several feet and can be found coating limestone in ancient and modern karst areas), but could be coming from the overlying humbug formation (figure 24c). karstification and formation of collapse breccias may have begun shortly after deposition of the deseret, which would argue for an unconformity between the deseret and humbug; however, this has not been figure 21. karst-related processes at lisbon field. (a) core slab of a limey, oolitic, peloidal/skeletal grainstone (brown) and dolomitized silty carbonate sediment (light gray) that filled a solution-enlarged cavity or fissure. the smaller yellow box indicates the approximate position of the thin section photomicrograph shown on b. (b) low-magnification photomicrograph (plane light) showing the contact between the non-porous limestone matrix (stained red for calcite) and the equally non-porous dolomitized and siliciclastic karst cavity filling. the yellow box indicates the approximate position of the closeup photomicrograph shown on c. (c) higher magnification photomicrograph (cross-polarized light) of white detrital quartz grains (q) and small dark gray carbonate clasts (l) within the non-porous, dolomitized mud filling the karst cavity. lisbon no. d-616 well (figure 6), 8308 to 8309 feet (2532.3–2532.6 m), porosity = 1.2%, permeability = 11.1 md. 261 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 identified elsewhere. several sinkholes are mapped in undivided deseret and humbug outcrops, as well as in the gardison limestone and weber sandstone (pennsylvanian-permian), in the area by eskelsen (1953). karst-related features likely postdate the mississippian, beginning as early as late eocene to oligocene (godfrey, 1985; spangler, 2005). mayo and others (2010) suggested the cave system formed relatively recently (pleistocene). study site 2 – dry fork canyon the dry fork canyon stratigraphic section demonstrates heterogeneity as well as cyclicity (two shoaling upward cycles) of madison limestone depositional environments within a 40-foot-thick (12 m) outcrop (figure 25). the base of the section is oolitic/hard pellet grainstone with well-defined, planar to low-angle cross-stratification representing a beach/foreshore depositional environment. the next unit is a wavy to bioturbated, peloidal/skeletal packstone to grainstone with hard pellets, benthic forams, and other microfossils indicative of a stable, shallow, subtidal bay depositional environment. the section coarsens up to oolitic/hard pellet grainstone with smallto medium-scale cross-stratification representing an ooid shoal. tidal-flat mud and deeper, subtidal, burrowed, pellet mud overlies the ooid shoal consisting of soft pellet mudstone with crinkly continuous cryptalgal (microbial) laminates and skeletal microfossils (ostracods and benthic forams). these sediments are overlain by thin-bedded to bioturbated, peloidal/skeletal packstone to grainstone with endothyrid forams and other microfossils indicating return to a stable, shallow, subtidal bay. the cycle continues to coarsen upward with lowto medium-angle cross-stratified oolitic grainstone of an ooid shoal. the top of the section is mudstone with continuous cryptalgal laminates (microbial), pellets, possible desiccation cracks and rip-up clasts, and no fossils, all features indicative of a peritidal tidal-flat mud. the madison at this site is predominately dolomite. several post-depositional features can be found at study site 2. a megabreccia is exposed at the western end of the madison outcrop where the section was described (figure 26a). this breccia is a paleokarst collapse where limestone and dolomite clasts are set in a non-porous mud-rich matrix. in thin section (figure 26b), this breccia appears similar to collapse breccia seen in core from lisbon field (compare to figure 21). figure 22. photomicrograph of another example of a non-porous, dolomitized sediment filling of a karst cavity in this low-magnification view (plane light and stained red for calcite). in addition, there is no visible porosity within the partially dolomitized crinoidal grainstone matrix. lisbon no. d-616 well (figure 6), 8356 to 8357 feet (2546.9–2547.2 m). figure 23. skeletal (crinoid and rugose coral) grainstone and packstone in the deseret limestone at study site 1 (within the yellow oval on figure 11). 262 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 country rock is cross-bedded, oolitic dolograinstone (ooid shoal) capped by low-angle, stratified dolograinstone (foreshore) (figure 26a). post-burial breccia post-burial brecciation can be formed by high-temperature hydrofracturing, creating an explosive looking, pulverized rock referred to as an “autobreccia” as opposed to a collapse breccia. breccia clasts within an autobreccia remain in place or moved very little. similar to brecciation associated with collapse due to karstification, excellent examples of autobreccia are found in the leadville limestone and mississippian rocks of the uinta mountains, northeastern utah. in addition to autobrecciation, late dolomitization, saddle dolomite, and dolomite cement precipitation may have occurred at progressively higher temperatures, i.e., hydrothermal dolomite. hydrothermal events can improve reservoir quality by increasing porosity through dissolution, dolomitization, development of microporosity, and natural fracturing (forming breccia) and kept open with various minerals (smith, 2004, 2006; davies and smith, 2006; smith and davies, 2006). hydrothermal dolomite precipitates under temperature and pressure conditions greater than the ambient temperature and pressure of the host limestone (davies, 2004; davies and smith, 2006; smith, 2006; smith and davies, 2006). the result can be formation of large, diagenetic-type hydrocarbon traps. subsurface leadville limestone, paradox basin cores from leadville limestone wells in the paradox fold and fault belt (figure 14) and lisbon field (figure 6) reveal that autobrecciation due to hydrofracturing was common. associated with autobreccia are pyrobitumen linings, saddle and zebra dolomite, rimmed microstructures or stair-step fractures, and porosity development or reduction. autobreccia, pyrobitumen, and porosity autobrecciation is characterized by massive fracturing and stylolites, which control post-burial leachfigure 24. possible paleokarst features just southeast of the breccia pipe at study site 1 (see red arrow within the yellow oval on figure 11). (a) extensive collapse polymictic breccia. (b) close-up of limestone and chert breccia clasts. note the lack of calcite veins and dolomite. (c) red staining, possibly terra rosa weathering, at the top of the deseret limestone near the contact with the overlying humbug formation(?). 263 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 ing and dolomitization (figures 27, 28, and 29). as these processes go to greater completion, various rock types appear to have an in situ, highly brecciated fabric with apparent “clasts” or autoclasts, which have moved little from where they formed. fractures are solution enlarged, and “clast” sizes are highly variable, chaotic, and generally angular to subangular. there is no detrital sediment infilling between the “clasts” or within solution-enlarged fractures (figure 29). the combination of post-burial fracturing, late dissolution, and saddle dolomite replacement, followed by pyrobitumen lining of pores and fractures, is an important step in the creation of an “autobreccia” or in situ breccia within leadville reservoirs (figure 30). dissolution porosity formed first due to undersaturated water migrating up faults/fractures and through matrix to enhance porosity. later, when recharging water reached saturation with respect to dolomite (under higher temperature and pressure), saddle dolomite formed as cement that reduced porosity and permeability. these processes and resulting fracture breccias are important elements of lisbon field. intense bitumen plugging is concurrent or takes place shortly after brecciation (figures 27 through 31). coarse, late replacement, saddle dolomitization and dissolution results in post-burial porosity that is marked by black pyrobitumen. black areas between “clasts” are an indication of very good intercrystalline porosity as pores are lined with pyrobitumen; low porosity is represented by light gray dolomite “clasts.” these clasts are often surrounded by solution-enlarged fractures partially filled with coarse rhombic and saddle dolomites that are also coated with pyrobitumen. typically, black and gray core slabs show remnants of white to gray limestone that originally contained low porosity (figure 30). processes of fracturing, saddle dofigure 25. madison limestone section at study site 2. figure 26. megabreccia at study site 2. (a) small-scale ooid shoal and collapse breccia (outcrop is approximately 10 feet [3 m] high). (b) photomicrograph (plane light) showing the contact between dolomitic grainstone (light gray, upper left) and the dolomitized karst cavity filling of small carbonate clasts. 264 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 lomitization, leaching, and brecciation, followed by pyrobitumen coating of matrix pore systems often continue unabated leading to very porous fractured dolomite. hence, by these processes former burial breccias appear to superficially resemble black “shales” (figure 30b). the black overprint of the original rock fabric is due to intense pyrobitumen coating of pores and is observed in thin section (figure 32). pyrobitumen rather than detrital sediment line many of the pores. these overprints can stop at healed fracture or stylolitic contacts (figure 32c). this black-rock-appearing lithofacies forms important reservoirs in lisbon field. figure 27. autobrecciation in the leadville limestone from lisbon field. (a) core slab showing a dolomite autobreccia in which the “clasts” have moved very little. the black material surrounding the in-place “clasts” is composed of porous, late replacement dolomite coated with pyrobitumen. the red box indicates the approximate position of the thin section shown on b. (b) entire thin section overview image (plane light) from the brecciated portion of the core shown on a, showing low-porosity, light gray dolomite “clasts” surrounded by solution-enlarged fractures partially filled with coarse rhombic dolomite (rd) and saddle dolomite that is coated with black pyrobitumen (bit). the open fracture segments (in blue) between clasts are bridged by coarse saddle dolomite crystals (sdc). lisbon nw usa no. b-63 well (figure 6), 9938.3 feet (3029.2 m), porosity = 6.4%, permeability = 54 md. 265 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 late dolomite replacement, saddle dolomite, poikilotopic calcite, and quartz crystals petrographic analysis shows that late, coarse dolomitization, rhombic white saddle dolomites, and poikilotopic calcite (also referred to as macrocalcite) are associated with post-burial breccia (figure 33). saddle dolomite characteristically displays curved crystal shapes in thin section and sweeping extinction under cross-polarized lighting. dissolution and fracture porosity can be filled with saddle dolomite, late poikilotopic calcite, and pyrobitumen (figure 33). small fluid inclusions, most of which are less than a figure 28. autobrecciation in the leadville limestone from the northwestern region of the paradox fold and fault belt. (a) core slab showing fractures, coarse dolomitization, leaching, and the formation of breccia due to post-burial processes. black pyrobitumen lines the significant post-burial porosity and fractures that are superimposed on a well-bedded oolitic/ peloidal grainstone. long canyon no. 1 well (section 9, t. 26 s., r. 20 e., slbl&m, grand county, utah, figure 14), 7733 feet (2357 m). (b) core slab showing fractures, and post-burial fracture dissolution and dolomitization that results in porosity that is marked by black pyrobitumen. the fracture and dissolution create the appearance of an in situ brecciated fabric that overprints a well-bedded oolitic/peloidal grainstone. big flat no. 3 well (figure 14), 7790 feet (2374 m). (c) core slab showing solution-enlarged vertical fractures, and post-burial leaching and dolomitization of a very well cemented crinoidal grainstone. the combination of the fracturing, leaching, and dolomitization in the black areas (porous areas lined with pyrobitumen) leads to the appearance of an in situ brecciated fabric. big flat no. 2 well (figure 14), 7784 feet (2373 m). 266 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 few micrometers in length, are common in saddle dolomite. large saddle dolomite crystals frequently contain fluid-rich, cloudy cores and fluid-poor, clear rims (figure 33), suggesting two distinct periods of dolomitization. these inclusions define growth zones and are therefore primary in origin. both aqueous and oil inclusions are found in the saddle dolomite within the lisbon cores (joseph n. moore, energy & geoscience institute, written communication, 2009), indicating sweep through the reservoir with oil-in-place. inclusion-poor rims may have formed after movable hydrocarbons were swept from the reservoir leaving pyrobitumen behind. poikilotopic calcite consists of late, large, slow-growing crystals, and although not extensive in the leadville figure 29. photomicrographs (plane light) from a highly brecciated dolomite in which fracturing and associated dissolution have created apparent “clasts,” lisbon field. (a) much of the porosity in this view is lined or plugged with black pyrobitumen. lisbon no. d-616 well (figure 6), 8579 feet (2615 m). (b) large autoclasts and bitumen in the intensely brecciated dolomite. note that pyrobitumen (and non-detrital sediment) lines many of the pores such that this rock is black when viewed in a core. this image was taken under plane light using the “white card technique” which makes it easier to see some of the small breccia clasts that result from intense fracturing. lisbon no. d-816 well (figure 6), depth = 8423 feet (2567 m), porosity = 10.5%, and permeability = 47 md. figure 30. core slabs showing the combination of fracturing, saddle dolomite replacement, and leaching followed by pyrobitumen lining of pores and fractures creating an in situ breccia or “autobreccia” within leadville reservoirs. (a) an example of brecciation due to intense development of these processes within an oolitic/peloidal grainstone. long canyon no. 1 well (figure 14), 7732 feet (2357 m). (b) core slab showing remnants of white limestone that originally exhibited very low porosity. by the processes listed above, the rock appears to superficially resemble a black “shale.” big flat no. 3 well (figure 14), 7735 feet (2358 m). 267 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 limestone at lisbon field, its presence provides some significant insight into the diagenetic history of these rocks. examples shown in figure 33 display an autobreccia that retains small amounts of early, finely crystalline (low-permeability) dolomite replaced by “mini-saddles” and medium crystalline (euhedral) dolomite. early during the sample’s history, it once had intercrystalline porosity that was enhanced by dissolution to form additional pores. subsequently, the pores were partially filled with coarsely crystalline saddle dolomite and bitumen. finally, the remaining solution-enlarged pores were occluded by poikilotopic calcite. poikilotopic calcite may have formed as oil-field water rose through time, following the gas/condensate cap. scanning electron microscopy (sem) reveals that microporosity, in the form of intercrystalline porosity, is common in the leadville limestone in lisbon field. dissolution has contributed to porosity and enhanced permeability, creating moldic, vuggy, and channel porosity, and enlarged fractures in breccias. there is a significant porosity increase where non-porous (low-permeability) early dolomites have been replaced by late, rhombic and saddle dolomites. euhedral quartz, identified in sem, also fills some voids within late dissolution pores and fractures (figure 34). quartz crystals are referred to as “mini-herkimers” (i.e., doubly terminated) and contain high-temperature fluid inclusions (joseph n. moore, energy & geoscience institute, written communication, 2009). the presence of mini-herkimers suggests that a high-temperature event(s) occurred in the leadville (discussed later). zebra dolomite and rimmed microstructures zebra dolomite is recognized by distinctive dark and light banding (figure 35a). banding is parallel to bedding, with light layers coarser than darker layers. bands range in thickness from millimeters to centimeters. alternating dark and light bands in zebra dolomites form by dolomite replacement of original carbonate host rock and void-filling saddle dolomite (swennen and others, 2003; diehl and others, 2010; wallace and hood, 2018). zebra dolomite is a complex late diagenetic combination of infiltration of high-temperature and pressure brines, recrystallization, dissolution, fracturing and brecciation, and fabric-selective replacement (diehl and others, 2010; wallace and hood, 2018). faulting/ figure 31. brecciation in dolomite from the leadville limestone from lisbon field. (a) core slab of a dolomitized, peloidal/ crinoidal packstone/wackestone with swarms of fractures marked by black, coarse dolomite. the red box indicates the approximate position of the thin section photomicrograph shown on b. (b) representative photomicrograph (plane light) from the core in a, showing highly deformed and brecciated dolomite within a bitumen-lined fracture zone. lisbon no. d-816 well (figure 6), 8438.5 feet (2572.1 m), porosity = 11% and permeability = 5 md. 268 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 fracturing is usually a controlling factor (swennen and others, 2003). zebra dolomite can host economic base metal mineralization and other ore deposits. in the leadville limestone, much of the dolomite associated with zebra structures is white saddle dolomite. incipient zebra dolomite banding occurs through development of layered clusters of coarse, white, almost “pearly” saddle dolomite. late, post-burial porosity created by saddle dolomitization and dissolution of original low-porosity limestone host rock is typically lined with black pyrobitumen producing the darker bands. zebra dolomite can also form layered megascopic open pores or zebra vugs in coarse dolomite (figure 35b). vertical stylolites are a product of a compressional event(s) (i.e., laramide orogeny). these layered pore systems often terminate against and post-date both bed-parallel and bed-normal (vertical) stylolites (figure 35). pyrobitumen lines pore space and fractures. in other intervals, zebra dolomite takes on a breccia-like appearance. rimmed microstructures having distinctive parallel “railroad” or stair-step fractures, are present in leadville cores (figure 36). associated with these fractures are replacement saddle dolomite and matrix porosity lined with pyrobitumen. they reflect shear and explosive fluid expulsion from buildup of pore pressure. areas between clasts can exhibit very good intercrystalline porosity or microporosity or may be filled by low-porosity saddle dolomite cement. most saddle dolomite acts as cement. autobrecciation in uinta mountain mississippian outcrops two of the three sites selected for mississippian outcrop studies in the uinta mountains (figure 8) expose features attributed to autobreccia due to hydrofracturing: (1) study site 1 – south fork provo river (figure 11) and (2) study site 3 – crouse reservoir/diamond mountain plateau (figure 13). both study sites 1 and 3 have autobreccia characteristics analogous to those observed in cores of leadville limestone. in addition, when put into the regional stratigraphic setting, they provide a hydrologic model by which autobreccia in the leadville may have formed. figure 32. photomicrographs (plane light) of a black carbonate breccia from the lisbon no. d-816 well (figure 6), lisbon field. (a) intense fracture system and the brecciated “look” within a coarse dolomite. the rock looks like a black “shale” in core due to pyrobitumen lining fractures and matrix pores. depth = 8423 feet (2567 m), porosity = 10.5%, and permeability = 47 md. (b) intensely fractured and dolomitized matrix. black pyrobitumen lines open fractures and pores. depth = 8435.8 feet (2571.2 m), porosity = 7.5%, and permeability = 0.03 md. (c) black overprint of a peloidal/ oolitic grainstone with a well-preserved early pore system (in blue). this overprint appears to stop at a healed fracture or stylolitic contact. depth = 7897 feet (2407 m), porosity = 6.3%, and permeability = 83 md. 269 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 study site 1 – south fork provo river a large breccia pipe in the deseret limestone is the most striking feature at study site 1 (figure 37). a breccia pipe is a cylindricalor irregular-shaped mass of brecciated rock. hydrothermal breccia pipes form when hydrothermal solutions forced their way towards the surface through zones of weakness or fracture zones and naturally break up the rocks in the process (i.e., hydrofracturing); breccia pipes can also form by collapse. the breccia pipe at study site 1 is subvertical, 17 feet (5 m) wide at the base of the outcrop, and cuts vertically through about 30 feet (9 m) of deseret limestone. the interior of the pipe contains poorly sorted breccia with small to large clasts surrounded by pulverized rock (figure 38a). calcite veins, dolomitized zones, and vugs are widespread (figure 38b). contacts of the pipe with unaltered limestone country rock are sharp. vertical, commonly calcite-filled fractures are prevalent on both sides of the breccia pipe. thin sections reveal the presence of mini-herkimer quartz crystals (figure 38c), which were also found in leadville limestone cores from lisbon field (see figure 34). the presence of mini-herkimer crystals also suggests a high-temperature event occurred at the study site, presumably emplacing the breccia pipe. study site 3 – crouse reservoir/diamond mountain plateau the mississippian section at study site 3, crouse reservoir/diamond mountain plateau, is mapped as madison limestone. it consists of unaltered units of limestone showing cycles of three depositional environments: (1) storm-dominated, outer-shelf, crinoid shoals, (2) low-energy, open-marine, mud-rich intershoal (inner ramp or inner shelf), and (3) low-energy, open-marine, outer-shelf above storm wave base. a unique feature at study site 3 is a ridge with two depressions dominated by intense breccia zones (pipes?), 75 to 100 feet (25–30 m) wide composed of highly brecciated dolomitic matrix (figures 39 and 40). the depressed zones are characterized by coarse calcite vein-like mineralization (figures 41 and 42a). figure 33. photomicrographs (plane light) showing late dolomite, calcite, and pyrobitumen associated with post-burial breccia from the northwest lisbon no. b-63 well (figure 6), lisbon field. (a) coarse, white saddle dolomite crystals and a single, coarse, late calcite cement crystal (stained red) filling part of a large dissolution/fracture pore (blue) in a brecciated dolomite matrix. depth = 9991.8 feet (3045.5 m). (b) coarse rhombic and saddle replacement dolomite that displays cloudy cores and clear rims. the cloudy appearance is due to abundant aqueous and oil fluid inclusions. dissolution pores are filled with pyrobitumen and late calcite (stained red). the pyrobitumen emplacement within this late porosity system gives the rock a black “shale” appearance when viewed in core. depth = 10,005 feet (3050 m), porosity = 14.4%, and permeability = 1.9 md. 270 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 dolomitization and leaching of matrix limestone has occurred throughout these zones (figure 42b). these distinctive elements imply a hydrothermal event rather than a paleokarst collapse origin for the breccia zones. discussion similar depositional environments described from outcrops above are also observed in leadville cores from lisbon field. carbonate buildups containing good porosity/permeability are the best reservoir analog units, whereas low-porosity/permeability, open-marine packstones and wackestones represent less attractive reservoir analog units, unless they have experienced dolomitization in the subsurface that improved reservoir quality. breccia pipes, paleokarst, and fractures also enhance reservoir quality. post-burial breccias associated with hydrothermal events, fracturing, and dissolution in the leadville limestone yield the best reservoirs at lisbon field. model for post-burial brecciation in uinta mountain mississippian outcrops breccia pipes and zones discovered at study sites 1 and 3 are likely the result of hydrothermal activity in the geologic past. the presence of the basal cambrian tintic quartzite in the southern flank of the western uinta mountains (figure 9) and the stratigraphically equivalent lodore formation in the eastern part of the range (figure 10) may serve as hydrothermal recharge aquifers and are important contributors to the hydrothermal story. the tintic quartzite is a very coarse to granular sandstone with moderately sorted, subrounded to spherical, monocrystalline and polycrystalline quartz grains. the tintic has thin to thick cross-bedding, is moderately indurated, and contains a few shale partings, which have small amounts of mica and some biogenic feeding trails (dockal, 1980). the contact of the tintic with overlying mississippian strata is sharp. the lodore is a very fine to medium-grained, well-sorted, very thin bedded to cross-bedded (with undulatofigure 34. scanning electron microscope photomicrograph from brecciated dolomites in lisbon field. (a) euhedral quartz filling voids (q) within late dissolution pores surrounded by a dolomitized and fractured matrix. lisbon no. d-616 well (figure 6), 8356 feet (2547 m). (b) clusters of euhedral, doubly terminated quartz crystals (i.e., “mini-herkimers”) (q) from a black carbonate with intense fracturing and brecciation. the small spiky materials precipitated on many of the surfaces are either pyrobitumen or sulfide minerals (arrows). lisbon no. d-816 well (figure 6), 8486 feet (2587 m). 271 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 figure 35. zebra dolomite structures in the leadville limestone from the northwestern region of the paradox fold and fault belt. (a) core slab of zebra dolomite showing distinctive black and white bands that are the result of coarse white saddle dolomite replacement and vug development in layers as well as dissolution of rock matrix with black pyrobitumen lining pores. the zebra banding stops against and probably post-dates a bed-parallel stylolite at the base of this segment (between arrows). floy no. 1 salt wash well (figure 14), 9647 feet (2940 m). (b) core slab showing the host rock consisting of well-cemented peloidal/oolitic grainstone with extensive development of zebra vugs and layered zebra dolomite in the right-hand portion of the slab that abuts against a vertical (bed normal) stylolite (see arrows). long canyon no. 1 well (figure 14), 7745 feet (2361 m). figure 36. core slab showing a variety of fracture types, including rimmed microstructures with their distinctive parallel “railroad” or stair-step appearance (see examples between arrows). long canyon no. 1 well (figure 14), 7728 feet (2356 m). 272 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 ry surfaces) sandstone marked by argillaceous partings (figure 43); quartz grains are subrounded to spherical. the lodore can be calcareous and slightly ferruginous; the top appears to be eroded (dockal, 1980). both the lodore and tintic contain porous and permeable units. as aquifers, they likely supplied hot water to a former hydrothermal system. three-dimensional numerical models of seafloor hydrothermal convection by coumou and others (2008) demonstrated that convection cells organize themselves into pipe-like upflow zones surrounded by narrow zones of warm downflow. recharge can occur over an extensive area or along faults as water migration pathways. the tintic quartzite is mapped on the western end of the uinta mountains whereas the lodore formation is present on the eastern end. through the central part of the southern flank of the uinta mountains, porous cambrian sandstone is absent and mississippian strata lie unconformably on precambrian (middle neoproterozoic) red pine shale and older formations of the uinta mountain group (as observed in whiterocks canyon [figure 8]). no hydrothermal breccia zones or pipes are found in the central part of the southern flank, lending credence to the concept that aquifers in the tintic and lodore were a required condition for past figure 37. large breccia pipe cross-cutting the deseret limestone at study site 1. note pulverized nature of the material that comprises the pipe, the sharp contact with the country rock, and parallel, calcite-filled vertical fractures. figure 38. characteristics of the explosive hydrothermal breccia pipe at study site 1. (a) brecciated rock in shattered-looking, pulverized groundmass. (b) close-up of sharp contact with unaltered limestone country rock. note vuggy dolomite and white calcite veins. (c) photomicrograph (plane light) of dolomite containing a mini-herkimer quartz crystal (center) suggesting a high-temperature event. 273 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 hydrothermal activity. after pressure builds up to a certain point, the hydrothermal fluids within the aquifer can very rapidly and explosively break through zones of weakness at the intersections of fractures or along faults; this can occur as a single event or over several stages. thus, when targeting the leadville limestone in the paradox basin for potential hydrothermal dolomite and enhanced reservoir quality due to natural hydrofracturing, the presence of an underlying aquifer and fracture zones or faults may be necessary ingredients, supported in part from what can be observed from the breccia zones at study site 1 and 3. strontium isotope geochemistry from post-burial breccias, leadville limestone strontium (sr) isotope analysis is used as a dating tool in marine carbonates. strontium composition of ancient seawater and its variation through geologic time has been determined from common marine carbonate minerals, especially calcite, aragonite, and dolomite (brass, 1976; burke and others, 1982; allan and wiggins, 1993). the ratio of 87sr/86sr is the most useful for tracking the secular changes of seawater sr. these two isotopes come from separate sources in the earth. strontium-87 is radiogenic (from the radioactive decay of rubidium-87 with a half-life of about 50 billion years), whereas strontium-86 is non-radiogenic (faure and powell, 1972; faure, 1977). strontium isotopic ratios for three leadville samples (late calcite, saddle dolomite, and sucrosic matrix dolomite) from lisbon field were plotted on the phanerozoic marine carbonate curve for 87sr/86sr ratios (figure 44). leadville samples are more radiogenic than accepted values for marine carbonate minerals derived from seawater sources in the phanerozoic. the source of these radiogenic sr ratios may have been from fluids that interacted with basement granites. leadville 87sr/86sr ratios are also similar to numerous publications on radiogenic saddle dolomites in diverse paleozoic reservoirs of north america. burial history and temperature profiles for post-burial diagenesis in the leadville limestone burial history and temperature profiles for the leadville limestone at lisbon field provide some guidance as to when tectonic, diagenetic, and porosity-forming events occurred (figure 45). as discussed in previous sections, saddle dolomite, euhedral quartz, pyrobitumen, and late calcite are all components of post-burial breccias, fractured zones, and major porosity intervals within lisbon and other nearby leadville fields. in addition to the calculated temperature profile, figure 39. topographic depressions at the sites of major breccia zones (pipes?) along a ridge of madison limestone (view to the southeast). figure 40. slabbed specimen of highly brecciated rock typical of deposits present at study site 3. 274 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 we have inferred anomalous temperature spikes for: (1) maximum burial, (2) late laramide reactivation along normal faults that extend to basement, and (3) oligocene igneous events, such as emplacement of the nearby la sal and abajo laccolith complexes, 10 miles (16 km) north and 23 miles (37 km) southwest, respectively, of lisbon field (figure 1). temperature spikes may be responsible for quartz precipitation, sulfide mineralization, pyrobitumen formation, late dissolution of carbonates, late saddle dolomite cements, and providing a heat source for hydrothermal solutions that cause autobrecciation. however, vertical (bed-normal) stylolites that pre-date much of the zebra dolomite banding and zebra vug porosity as well as some brecciation were probably the result of laramide compression. proposed model for fault-controlled, postburial brecciation, dolomitization, and porosity development, lisbon field we propose a model with convection cells bounded by basement-rooted faults to transfer heat and flufigure 41. breccia zone at study site 3. (a) coarse calcite vein in a highly brecciated dolomitic matrix. (b) close-up of large, representative calcite crystals within the dolomitic matrix of the breccia zone. figure 42. photomicrographs (plane light) from breccia samples at study site 3. (a) vein of coarse calcite in a low-permeability dolomitic matrix. (b) unusual concentric dolomite cement (high temperature?) overgrowths in a dolomitic breccia matrix. 275 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 ids possibly from crystalline basement, pennsylvanian evaporites, and oligocene igneous complexes. large volumes of water are required to produce the brecciation and amount, type, and generations of dolomite present at lisbon field. there is probably not enough water moving through the regional hydrodynamic system to account for the leadville dolomite. therefore, convection or circulation cells would be much larger from surface feeder systems into the subsurface, most likely sweeping through igneous intrusives and basement to acquire heat, and form circulation systems. fault movement at various scales provided the power to pressure up and move fluids throughout the subsurface. recycling hot, brine-bearing water in convection cells may have driven dolomitization. a diagrammatic south to north cross section of the greater lisbon field area (figure 46) shows possible convection cells of the circulation model for ascending warm fluids responsible for saddle dolomite (also see block diagram on figure 4b), high-temperature quartz, pyrobitumen, aggressive dissolution of limestone and dolomite, and sulfide mineralization. the basal aquifer for inferred fault-controlled cells could be the devonian mccracken sandstone, similar to the lodore formation in the uinta mountains. the mccracken is locally porous enough to produce oil at lisbon field. source of heat may have been precambrian basement rocks and/ or oligocene igneous intrusives. mapped faults cutting lisbon field may have been involved with thermal convection cells circulating fluids during late burial diagenesis (figure 47). wells near faults appear to have better reservoir quality, produce greater volumes of oil, and have higher residual bottom-hole temperatures than wells away from these faults. conclusions two distinctive types of breccias—(1) karst-related, and (2) and post-burial “autobreccias” (created by hydrofracturing)—are encountered within the mississippian leadville limestone in lisbon and nearby fields in the paradox basin fold and fault belt. • karst-related breccias are intimately associated with cave-filling detrital sediments. karst cave-filling sedimentary facies classified by evans and reed (2006, 2007) for the leadville from colorado outcrops were identified in cores within lisbon and other nearby fields. • porosity associated with karst breccias, cave-filling detrital sediments, and dolomitized carbonate cave-filling sediments is low. cave-filling sediments disrupt lateral flow continuity within porous or fractured leadville hydrocarbon reservoirs. • post-burial breccias occur within fracture swarms and singular faults/fractures. their origin is caused by natural hydrofracturing in the subsurface. breccias (or “autobreccias”) form in association with zebra structures, vugs, coarse figure 43. basal cambrian lodore formation. (a) outcrop of thin-bedded lodore formation north of study site 3, southwest of crouse reservoir. (b) lodore formation hand sample of very fine grained, well-sorted, cross-bedded, slightly ferruginous sandstone. 276 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 saddle dolomite, and extensive late dissolution of host rock. breccias and zebra structures in leadville fields post-date vertical (bed normal) stylolites that formed during laramide compression. • porosity associated with post-burial breccias and saddle dolomite in the lisbon field area is high. however, porosity is difficult to appreciate on core slab surfaces because abundant pyrofigure 44. strontium isotope seawater composition curve with leadville limestone late calcite, saddle dolomite, and sucrosic matrix dolomite samples from lisbon field plotted for comparison. modified from burke and others (1982), elderfield (1986), and allan and wiggins (1993). figure 45. burial history and temperature profiles with inferred diagenetic windows at lisbon field. 277 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 bitumen makes porous breccias and dolomites appear like black “shales.” • strontium isotope ratios and associated minerals found within post-burial breccias and saddle dolomite indicate a likely fluid source that interacted with basement rocks in the area. these results show similarities to published studies on radiogenic saddle dolomites in diverse paleozoic reservoirs throughout north america. • the deseret and madison limestones in the uinta mountains contain local zones of breccia due to either collapse or natural hydrofracturing. breccia associated with sediment-filled collapsed cavities is common. these cavities are related to paleokarstification of the deseret/madison when subaerially exposed during late mississippian time. brecciation caused by explosive natural hydrofracturing created similar shattered-looking, pulverized rock identified in lisbon cores. breccia pipes are related to past hydrothermal activity. • the basal cambrian tintic quartzite and lodore formation were important contributors to the hydrothermal story. they served as aquifers to supply hot water to the hydrothermal system. through the central part of the southern flank of the uinta mountains, porous cambrian sandstone units are absent, with mississippian strata lying unconformably on middle neoproterozoic red pine shale. no mississippian hydrothermal breccia zones or pipes are found in the central part of the southern flank, lending credence to the concept that aquifers below in the tintic and lodore may be a required condition for past hydrothermal activity to have occurred. thus, targeting leadville limestone areas for potential hydrothermal dolomite and enhanced reservoir quality due to hydrofracturing may require an aquifer below as a necessary ingredient (i.e., the devonian mccracken sandstone). • large volumes of water were required to produce brecciation and amount, type, and generations of dolomite present at lisbon field. we propose a model where convection cells bounded by basement-rooted faults transferred heat and fluids possibly from crystalline basement, pennsylvanian evaporites, and oligocene igneous complexes. figure 46. possible heat sources and convection cells for late dolomitization and brecciation of the leadville limestone focused along high-angle faults that reach basement in the lisbon field area. figure 47. top of structure of the leadville limestone, lisbon field, showing possible thermal convection cells between small, northeast-southwest-trending normal faults that probably go to basement. modified from c.f. johnson, union oil company of california files (1970) courtesy of tom brown, inc. 278 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 • breccias and associated late porosity and pyrobitumen pore coatings in fields like lisbon may be best found or developed using a structural model involving fault geometry and fracturing rather than attempting to identify major subaerial exposure surfaces such as at the top of the leadville limestone. exploration methodology using seismic attributes focused on identifying high-angle, basement-penetrating fault systems and fracture trends with attendant porosity indicators related to hydrothermal dolomitization should lead to greater success in mississippian exploration of the paradox basin and other analogous brecciated carbonate reservoirs. acknowledgments funding for this research was provided as part of the advanced and key oilfield technologies for independents (area 2 – exploration) program of the u.s. department of energy, national energy technology laboratory, tulsa, oklahoma, contract number defc26-03nt15424. support was also provided by the utah geological survey (ugs) and eby petrography & consulting, inc., denver, colorado. cheryl gustin and james parker of the ugs drafted figures. core photography was conducted by ammon mcdonald of the ugs. michael d. laine and thomas dempster assisted with core preparation and data collection from the utah core research center. this paper was carefully reviewed by robert f. lindsay, lindsay consulting llc and affiliate professor, brigham young university; and david e. tabet, robert ressetar, michael d. vanden berg, stephanie m. carney, michael d. hylland, and bill keach of the ugs, along with the editors of this publication. their suggestions and constructive criticism greatly improved the manuscript. references ahr, w.m., 1989, mississippian reef facies in the southwest—a spectrum of 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(editor and compiler), in press, the mississippian leadville limestone oil and gas play, paradox basin, southeastern utah and southwestern colorado—lisbon field, regional, and analog studies: utah geological survey bulletin. chidsey, t.c., jr., and eby, d.e., 2016, chapter 9—mississippian leadville limestone paradox basin play, in chidsey, t.c., jr., editor, major oil plays in utah and vicinity: utah geological survey bulletin 137, p. 145–157. chidsey, t.c., jr., morgan, c.d., and eby, d.e., 2016, chapter 10—pennsylvanian paradox formation paradox basin play, in chidsey, t.c., jr., editor, major oil plays in utah and vicinity: utah geological survey bulletin 137, p. 159–206. clark, c.r., 1978, lisbon, san juan county, utah, in fassett, j.e., editor, oil and gas fields of the four corners area: four corners geological society, v. ii, p. 662–665. coumou, d., driesner, t., and heinrich, a., 2008, the structure and dynamics of mid-ocean ridge hydrothermal system: science magazine, v. 321, 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vertical profile models in braided river deposits—a summary, in miall, a.d., editor, fluvial sedimentology: canadian society of petroleum geologists memoir 5, p. 597–604. morgan, c.d., 1993, mississippian leadville limestone, in hjellming, c.a., editor, atlas of major rocky mountain gas reservoirs: new mexico bureau of mines and mineral resources, p. 94. parker, j.w., and roberts, j.w., 1963, devonian and mississippian stratigraphy of the central part of the colorado plateau, in bass, r.o., editor, shelf carbonates of the paradox basin: four corners geological society, 4th field conference guidebook, p. 31–60. petroleum information, 1984, paradox basin—unravelling the mystery: petroleum frontiers, v. 1, no. 4, p. 22. sadlick, w., 1955, the mississippian-pennsylvanian boundary in 280 a tale of two breccia types in the mississippian leadville limestone of lisbon and other fields, paradox basin, southeastern utah chidsey, t.c., jr., eby, d.e., and sprinkel, d.a. geology of the intermountain west 2020 volume 7 northeastern utah: salt lake city, university of utah, m.s. thesis, 77 p. sadlick, w., 1957, regional relations of carboniferous rocks of northeastern utah, in seal, o.g., editor, guidebook to the geology of the uinta basin: intermountain association of petroleum geologists 8th annual field conference, p. 57–77. sandberg, c.a., and gutschick, r.c., 1980, sedimentation and biostratigraphy of osagean and meramecian starved basin and foreslope of the western united states, in fouch, t.d., and magathan, e.r., editors, paleozoic paleogeography of the west-central united states-rocky mountain symposium 1: rocky mountain section, society of economic paleontologist and mineralogists (society for sedimentary geology), p. 129–147. smith, l.b., 2004, hydrothermal alteration of carbonate reservoirs—how common is it? [abs.]: american association of petroleum geologists annual convention, official program with abstracts, v. 13, p. a130. smith, l.b. jr., 2006, origin and reservoir characteristics of upper ordovician trenton—black river hydrothermal dolomite reservoirs in new york: american association of petroleum geologists bulletin special issue—hydrothermally altered carbonate reservoirs, v. 90, no. 11, p. 1691–1718. smith, l.b., jr. and davies, g.r., 2006, structurally controlled hydrothermal alteration of carbonate reservoirs—introduction: american association of petroleum geologists bulletin special issue—hydrothermally altered carbonate reservoirs, v. 90, no. 11, p. 1635–1640. smith, k.t., and prather, o.e., 1981, lisbon field—lessons in exploration, in wiegand, d.l., editor, geology of the paradox basin: rocky mountain association of geologists guidebook, p. 55–59. smouse, deforrest, 1993, lisbon, in hill, b.g., and bereskin, s.r., editors, oil and gas fields of utah: utah geological association publication 22, non-paginated. spangler, l.e., 2005, geology and karst hydrology of the eastern uinta mountains—an overview, in dehler, c.m., pederson, j.l., sprinkel, d.a., and kowallis, b.j., editors, uinta mountain geology: utah geological association publication 33, p. 201–214. sprinkel, d.a., 2006, interim geologic map of the dutch john 30' x 60' quadrangle, daggett and uintah counties, utah, moffat county, colorado, and sweetwater county, wyoming: utah geological survey open-file report 491dm, compact disc, gis data, 3 plates, scale 1:100,000. sprinkel, d.a., 2007, interim geologic map of the vernal 30' x 60' quadrangle, uintah and duchesne counties, utah, moffat and rio blanco counties, colorado: utah geological survey open-file report 506dm, compact disc, gis data, 3 plates, scale 1:100,000. sprinkel, d.a., 2018, interim geologic map of the duchesne 30' x 60' quadrangle, duchesne and wasatch counties, utah: utah geological survey open-file report 689, 37 p., 2 plates, scale 1:62,500. swennen, r., vandeginste, v., and ellam, r., 2003, genesis of zebra dolomites (cathedral formation—canadian cordillera fold and thrust belt, british columbia): journal of geochemical exploration, v. 78–79, p. 571–577. utah division of oil, gas and mining, 2020, oil and gas production report by field, december 2019: online, https://oilgas. ogm.utah.gov/oilgasweb/publications/monthly-rpts-by-fld. xhtml?rpttype=fld, accessed may 2020. wallace, m., and hood, a., 2018, zebra textures in carbonate rocks—fractures produced by the force of crystallization during mineral replacement: sedimentary geology, v. 368, no. 3, doi:10.1016/j.sedgeo.2018.03.009. welsh, j.e., and bissell, h.j., 1979, the mississippian and pennsylvanian (carboniferous) systems in the united states—utah: u.s. geological survey professional paper 1110-y, 35 p. wilson, j.l., 1975, carbonate facies in geologic history: new york, springer-verlag, 471 p. permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. permo-pennsylvanian sharks from the lower cutler beds near moab, utah kenneth carpenter and lin ottinger geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott ekeller@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 editors douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net production cover design and desktop publishing douglas a. sprinkel cover shark teeth from the lower cutler beds, shafer basin from near moab, utah newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 105 abstract several shark teeth have been collected from limestones in the marine-nonmarine transitional zone of the lower cutler beds in the shafer basin near moab, utah. the shark teeth include the pennsylvanian petalodontiform petalodus ohioensis, which is the first described from the state, and the permo-carboniferous cladodontomorph cladodus sp. the petalodus specimens are compared with the holotype p. hastingsae owen, p. acuminatus (agassiz), p. ohioensis (shafer), and p. alleghaniensis (leidy). several of these key taxa are illustrated with photographs for the first time. permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah kenneth carpenter1 and lin ottinger2 1prehistoric museum, utah state university eastern, 155 main st., price, ut 84501; and museum of natural history, university of colorado, boulder, colorado 80302; ken.carpenter@usu.edu 21095 jackson st., moab ut 84532; annertel@gmail.com citation for this article. carpenter, k., and ottinger, l., 2018, permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah: geology of the intermountain west, v. 5, p. 105–116. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the late paleozoic shark record from utah is poorly known, but what is known was summarized by sumida and others (1999). they report teeth of the freshwater xenacanth orthacanthus from the lower permian halgaito shale (cutler group) and an unnamed partial chondrichthyean tooth from the nonmarine lower permian organ rock formation (cutler group). in addition, miller (1981) reported on occurrences of the form genus cladodus sp. from the mississippian great blue limestone and the manning canyon shale in north central utah. one of us (ottinger) amassed a small collection of marine shark teeth during the 1970s from the area between the potash mine and evaporation ponds in the shafer basin southwest of moab, utah. this is the same general area that lohman (1974) reported the cochliodont shark deltodus sp. and the petalodont shark petalodus. lohman’s specimens have not been figured or described and their current location are unknown. owing to the importance of documenting the new collection, we describe and illustrate the material below. original specimens or casts of specimens are curated at the prehistoric museum, utah state university eastern, price, utah. exact locality information for each specimen is no longer known. geological setting the specimens were collected in the shafer basin, which is located between cane creek and shafer anticlines, southwest of moab utah (figure 1). here, the permian strata are well exposed along the colorado river below the cliffs of dead horse point state park (figure 2a). matrix adhering to the teeth show that all but one came from the shafer limestone bed, an informal name applied to a prominent limestone in the shafer basin. this limestone caps a 90 m interval (figure 2b) of alternating marine limestones and muddy sandstones containing invertebrate fossils and burrows (fig106 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 ure 2c), and nonmarine arkosic sandstones and aeolian sandstones containing rhizoliths (figure 2d), including a possible lycopod root (figure 2e). these strata have been variously called or mapped in this basin as the rico formation (prommel, 1923; baker and others, 1927; mcknight, 1974; hinrichs and others, 1967; loope, 1984), rico transition facies (wengerd and matheny, 1958), elephant canyon formation (terrell, 1972; campbell, 1987), the lower cutler beds (condon, 1997; doelling and others, 1994; doelling and chidsey, 2009; dubiel and others, 2009), lower cutler group (doelling, 2004), or simply considered as part of the cutler formation undifferentiated (mattox and brand, 1974; huntoon and others, 2002). we refer these marine-continental transition strata as the “lower cutler beds” as used by loope and others (1990), with the shafer limestone as the top of this unit. specimen abbreviations: ceum – college of eastern utah museum (now prehistoric museum, utah state university eastern), price, utah. mhnn – muséum d’histoire naturelle de neuchâtel, neuchâtel, switzerland; nhmuk – natural history museum, united kingdom, london, england. systematic paleontology class chondrichthyes huxley 1880 order petalodontiformes zangerl 1981 family petalodontidae newberry and worthen 1866 genus petalodus owen 1840–1845 species petalodus ohioensis (safford 1853) material ceum 81502, 81503, 81504 teeth ceum 81643 cast, ceum 81644 cast figures 3a to 3g petalodus is a distinctive form genus characterized by a labio-lingually compressed, vertically short, broadbased, triangular crown that is convex anteriorly and concave posteriorly. the base of the crown is bordered by a band or cingulum composed of imbricated ridges that are especially well developed on the lingual side (leidy, 1856, first referred to the structure as a cingulum and is followed here; robb, 2003 refers to it as the “distal crown tongue”). the crown is situated on a long, tapering root (base). the five teeth vary in size and in the height and width of the crowns; their measurements are given in table 1. part of these differences may be ontogenetic; wear and location in the jaws as has long been recognized (e.g., newberry and worthen, 1866; eastman, 1896). the specimens are assigned to the species p. ohioenesis because of the vertically narrow cingulum around the crowns; the cingulum is much wider in p. acuminatus. hansen (1985) notes that p. ohioenesis is the only species in the pennsylvanian and lower permian of the united states. ceum 81502 (figures 3a to 3c) the most complete tooth in the collection, it has a crown that is convex on the labial surface and concave on the lingual side just above the root. the concavity may accommodate the convex surface of the succeeding replacement tooth (figure 4a) in a manner similar to those reported by davis (1883) for the petalodontiforms petalorhynchus and glossodus. lucas and others (2011) suggested that the concavity accommodated the crown apex of the opposing tooth (figure 4b). in profile view, the root and crown are slightly angled relative to one another. the cutting edges of the crown terminate in a figure 1. map showing the location of shafer basin southwest of moab, utah, where the shark teeth were found. adapted from doelling and chidsey (2004). 107 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 figure 2. (a) complete section of the cutler group at pyramid butte, south end of shafer basin; colorado river in foreground and shafer anticline to immediate left out of frame. (b) stratigraphic column based on a measured section of the shafer basin given by terrell (1972, appendix 1) extending northwest from the j.l. eddy boat ramp (38°30'19.97"n, 109°39'33.75"w). (c) burrows in the marine facies of the lower cutler beds, shafer anticline (38°27'57.41"n, 109°43'12.23"w). (d) rhizoliths in an eolian facies (note uniform grain size) of the lower cutler beds, shafer anticline (38°27'53.99"n, 109°43'9.65"w). (e) unusual occurrence of a lepidodendrale(?) root and rootlets in aeolian facies of the lower cutler beds, shafer anticline (approximately 38°27'52.63"n, 109°43'11.44"w). 108 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 slightly acuminate asymmetrical apex. a narrow band on each side of the edges shows tiny parallel dentine tubules. the labial band shows irregular wear, which extends onto the crown and exposes the underlying tangled-fibered enameloid as described and illustrated by lund (1989, figure 16). a broad, slightly developed medial ridge extends from the apex towards the base were it merges. the labial side of the crown base is sigmoid and shows faint traces of ridges where the enameloid is preserved. in profile, the crown overhangs the root, which becomes thicker distally. the root is d-shaped in horizontal cross-section, with the lingual side flat. the acuminate and slight asymmetry of the crown indicate this is an anteromedial tooth (robb, 2003). ceum 81503 (figure 3d) the smallest of the teeth, it is also the most worn. much of the upper part of the crown reveals the enameloid on the surface well below the parallel dentine tubule band on the labial side. the apex is worn to a notch and the medial ridge is absent. the low, elongate crown indicate that it is a lateral tooth (robb, 2003). ceum 81504 (figure 3e) unlike the other teeth, this one was recovered from a white to light grey, arkosic, coarse sandstone, which terrell (1972) states only occurs in the middle of the upper limestone (unit 20) in shafer basin. the tooth is white, rather than gray to reddish colored. the medial crown ridge is absent. the enameloid surface is etched and in places has remnants of pink feldspar and white quartz embedded. the parallel dentine tubules are accentuated from wear. the root is missing, but the low, elongate crown shows that it is a lateral tooth (robb, 2003). ceum 81643 cast (figure 3f) much of the crown is damaged, either lacking enameloid or missing exposing the inner core. the impression shows that the apex was not acuminate, possible due to wear. a trace of the medial ridge is present. the root is incomplete, but enough remains to show that it was expanded distally in profile. the low, elongate crown, with low apex suggests it was lateral to the medial teeth, but not far posterolaterally in the jaw. ceum 81644 cast (figure 3g) the crown is also damaged, with all of the enameloid eroded exposing the inner core. the lingual side of the tooth is exposed. the distal end of the root is damaged, but enough remains to suggest it curved labially much like one of the specimens figured by lucas and others (2011; figure 3d). the high crown suggests this was an anteromedial tooth. superorder cladodontomorphi ginter, hampe and duffin 2010 order ctenacanthiformes glikman 1964 family ctenacanthidae dean 1909 genus cladodus agassiz 1843 species cladodus sp. ceum 81505 tooth (figure 5h) the tooth is heavily damaged, having an incomplete mid-crown and a base of one side crown attached to an incomplete base. it is assigned to the form genus on the basis of the large median cusp that is convex on the lingual side, flat on the labial side, and the broken base of a smaller, rounded in cross section lateral cusp. this specimen is the youngest occurrence of cladodus in utah. the two others reported by miller (1981) are from the mississippian great blue limestone and from the manning canyon shale. adhering matrix is a dull, reddish-brown, fine, micaceous sandstone. table 1. tooth crown measurements (in mm) of petalodus sp., ceum 81644 too damaged to be included. catalog number width height ceum 81502 40.5 22.5 ceum 81503 17.8 11.1 ceum 81504 21.2 13.75 ceum 81643* 50.75 25.2 *measured from impression on matrix 109 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 a review of some key specimens of petalodus the five teeth of petalodus from utah are the first described and illustrated from the state. at least 21 species of petalodus have been named (hansen, 1985), the majority during the 1800s when the range of variation of tooth shape was less well known. the consensus today is that the majority of the species either belong to other genera or are morphological variants based on position within the jaws (e.g., hansen, 1985; lucas and others, 2011; ginter and others, 2015). unfortunately, there is no agreement as to whether there is only a single species (lucas and others, 2011) or two species that are chronostratigraphical distributed (hansen, 1985). as a result, it was necessary for us to look closely at several key species and specimens in order to determine the correct species name for the utah specimens. figure 3. shark teeth from the lower cutler beds, shafer basin. petalodus ohioensis. ceum 81502 in (a) labial, (b) profile, and (c) lingual views. ceum 81503 in (d) labi al view. ceum 81504 in (e) labial view. ceum 81643 cast in (f) labial view. ceum 81644 cast in (g) lingual view. cladodus sp. ceum 81505 in (h) labial view. scale in mm. 110 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 the genus was proposed by richard owen (1840– 1845 as petalodus hastingsii, p. 61; also given as p. hastingsae, figure caption). however, there is a problem regarding this specimen that apparently has not been discussed before in the literature. namely, that the description and figures of type tooth do not remotely look anything like the teeth traditionally referred to petalodus. owen (1840–1845: p. 3) described the tooth as “a thin lamella, slightly concave like a finger-nail …which i have, on that account, named petalodus” (greek petalon leaf, and odus tooth). his more detailed description (p. 61–62) refers to the tooth being “lamelliform,” i.e., thin plate form, plate-like or scale-like. the tooth (nhmuk pv p613) was illustrated as more complete than it actually is (figures 5a to 5c vs 5d to 5g). woodward (1889) referred to the specimen as a fragment, so was probably not more complete when described by owen. it is most likely that the tooth was reconstructed by mirroring the fragment to give the impression of how an entire tooth would look (e. barnard, natural history museum, london, england, written communication, 2017). such a technique was used, for example, by yale paleontologist o.c. marsh (e.g., 1896, pl. 21, brontosaurus excelsus dorsal). despite owen misleading reconstruction, louis agassiz correctly referred a nearly complete tooth from his collection to the genus petalodus, thus establishing the sub-rhomboidal or subtriangular morphology by which it is known. this version of petalodus, rather than the rectangular shape given by owen, was established in agassiz’s multi-year (1833–1845), 10 volume, limited edition “recherches sur les poissons fossiles.” the multi-year publication was due to his constant revisions (18 non-consecutive revised printings of the 10 volumes, jeannet 1928). in text volume 3, he named a new genus, chomatodus, and three species for several fossil fish teeth he states are from the bristol museum, england (but also stated as received from roderick murchison, p. 108). one of these teeth was named (text: agassiz, 1833–1845a, p. 108–109) and figured (atlas: agassiz, 1833-1845b, plate 19, figures 11 to 13) as chomatodus acuminatus (figures 5s and 5t), which woodward (1889) states were published in 1838 and confirmed by brown (1890) and jeannet (1928, p. 120). later (revised text: agassiz, 1833–1845a, p. 159), agassiz writes that the tooth differs too much from the other two species of chomatodus “since it is a tooth with a cutting blade…it is in the new genus petalodus, by mr. owen.” he reiterates this in a footnote (p. 174), which woodward gives as published in 1843 and confirmed by brown (1890) and jeannet (1928, p. 122). the “cutting blade” is apparently the only justification that agassiz gives as his reason for considering chomatodus acuminatus as belonging to the genus petalodus. the specimen was damaged (figure 5u) sometime between 1838 and 1927 as first reported by jeannet (1927, p. 109) “exemplaire mutilé depuis qu’il a été figuré” (“specimen mutilated since it was figured”). agassiz had a second tooth (figure 5v) also acquired from the bristol museum that he never discussed or figured. despite glaring differences between the owen and agassiz illustrations and descriptions, subsequent authors were quick to accept agassiz’s synonymy. the same year that agassiz referred c. acuminatus to petalodus, geologist joseph portlock (1843) described and illustrated a tooth (figure 5w) that he referred to as “petalodus hastingsii (agassiz)” [sic]. his reasons for this identification was never stated. portlock was followed a few years later by frederick m’coy (1848), who named figure 4. possible serial stacking of replacement teeth in lateral view (a) of petalodus to explain the convexo-concave crown (a, lower teeth only), versus the dental occlusion (b, lower and upper teeth) advocated by lucas and others (2011) for the same convexo-concave feature. the serial stacking is more in keeping with the serial replacement of teeth seen in sharks. 111 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 petalodus rhombus for a complete tooth, noting its more rhomboid crown as compared with p. acuminatus (he says nothing of p. hastingsii). however, in 1854, m’coy (1854) synonymized p. rhombus with p. acuminatus and illustrated the specimen (figures 5x to 5z). the synonymy was based on what he thought were a range of variation in several new specimens and marks the first time that morphological variation was taken into account in petalodus taxonomy. although the low profile of the crown is also seen in some petalodus teeth (e.g., figures 5n and 5o), the tooth lacks the ridges along the base of the crown and cingulum that typify petalodus. it is therefore possible that this tooth does not belong to that genus. woodward (1889) later briefly described and illustrated several teeth (nhmuk pv p5342, plate i, figures 4 to 7, here as figures 5h to 5o) that are crucial for showing what owen’s specimen would probably have looked like undamaged (figure 5e). most importantly, these teeth are from the same locality and horizon as owen’s holotype p. hastingsii (woodward, 1889). the teeth share with the holotype, nhmuk pv p613, the unique, wide (deep) ridged band that occupies the lower half or more of the crown on the lingual side (figures 5d and 5e arrow). in all other species of petalodus, this ridged band occupies a narrow zone at the base of the crown, where it is angled ventroposteriorly and protrudes so that a cingulum is formed (e.g., figures 5s and 5t). in addition, the lingual side of p. hastingsii is only slightly concave in side view (figures 5f and 5g) compared to most other petalodus (e.g., figure 5s), and the root is proportionally short compared to crown height. other specimens referred to petalodus share with nhmuk pv p5342 an acuminate apex crown that is convex and subtriangular on the labial side where a well-developed anteroventrally facing, inverted w-shaped ridged cingulum lies at the base of the crown. we therefore conclude that p. hastingsii is a valid species contrary to woodward (1889). in addition, p. hastingsii is known from the flechado formation (desmoinesian, middle pennsylvanian) of new mexico (zidek and kietzke, 1993) (figures 5p to 5r). owing to the importance of the owen and agassiz holotype specimens to the taxon petalodus, their stratigraphic position needs to be established (international code on zoological nomenclature article 76). woodward (1889) reports that the teeth here referred to petalodus hastingsii were collected from the “upper carboniferous limestone” at the village of ticknall in south derbyshire, england. this stratum is now called the ticknall limestone (monteleone, 1973; carney and others, 2001) and was an important source of building stone. the quarries produced numerous fossils (parsons, 1917; monteleone, 1973), which date the strata as brigantian (upper visean, a.k.a. upper middle mississippian) (waters and others, 2009). ginter and others (2015) described non-petalodontiform shark teeth from these beds, which also supported a visean age. agassiz obtained the holotype petalodus acuminatus (agassiz), mhnn-fos 171, from british geologist roderick murchison, who collected the specimen from the carboniferous limestone near the town of whorlton in county durham, england. this stratum is identified by the british geological survey (2017) as the stainmore formation (middle carboniferous or namurian, a.k.a. upper mississippian to lower pennsylvanian). the formation is characterized by numerous limestone beds known to have been historically quarried as building stone (king, 2012). the petalodus teeth from the lower cutler beds better compare with petalodus acuminatus than to p. hastingsii chiefly in lacking the wide ridged band on the lingual side. however, unlike p. acuminatus, the lingual cingulum is very narrow and the crown taller relative to width. they are more similar to the tooth named and illustrated as getalodus ohioensis (figures 5a' and 5b') by james m. safford (1853). the generic name is most certainly a typographical error (hay, 1895), either due to misinterpretation of safford’s handwritten manuscript by the typesetter, or safford’s misunderstanding of louis agassiz’ heavy swiss french accent during conversations safford (1853) states he had with agassiz about the tooth at the 1851 meeting of american association for the advancement of science. the tooth was subsequently referred to as the holotype of petalodus ohioensis (e.g., hay, 1895; lucas and others, 2011; we were unable to locate this specimen to re-illustrate). safford reports that the specimen was collected from near cambridge, ohio, and condit (1912) that it came from the cambridge limestone, which is in the conemaugh forma112 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 figure 5. caption on following page. 113 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 tion (rice and others, 1994), or the glenshaw formation if the conemaugh is raised to group (e.g., rollins and others, 1979; heckel and others, 2011). conodonts demonstrate a middle to upper missourian stage (middle pennsylvanian) for the cambridge (heckel and others, 2011; barrick and others, 2013). oddly, newberry (1875) says nothing about this specimen in his review of fossil fishes from ohio, but does refer all petalodus to p. allegheniensis (see below). p. acuminatus supposedly differs from p. ohioensis in the wide, ridged, lingual cingulum (hansen, 1997). the specimens of newberry are important because they appear to represent additional specimens of p. ohioensis and provide more accurate information about this species (attempts to locate these specimens to re-illustrate were unsuccessful). newberry reports that the specimens are all from the crinoidal limestone, which condit (1912) identifies as the ames limestone of the conemaugh formation (or the glenshaw formation if the conemaugh is raised to group). conodonts place the ames in the lower virgilian (heckel and others, 2011); i.e., lower upper pennsylvanian, and closer in time to the petalodus specimens from utah. two of the teeth were figured by newberry (figures 5c' and 5d'), and one of them (figure 5d’) shows a tall crown and similar crown profile to the illustration by safford (figures 5a' and 5b'). these teeth also confirm the one feature that has been used to diagnose p. ohioensis, namely the vertically narrow cingulum band of ridges (e.g., hansen, 1985; dalla vecchia 1988), which is about one-third to one-half that of p. alleghaniensis (see next). two years after safford named petalodus ohioensis, leidy (1855) named sicarius extinctus for a tooth he described as resembling a pangolin scale. it was renamed and figured (figures 5e' and 5g') as petalodus alleghaniensis the following year (leidy, 1856); the reason for changing the species name was not given by leidy. p. extinctus was used only once, by eastman (1896) and is considered nomen oblitum (iczn art. 23.9). the tooth described by leidy was recovered from the glenshaw formation at bens creek station in what is now the allegheny portage railroad national historic site (koch figure 5 (figure on previous page). petalodus as seen from original illustrations and photographs of the specimens. holotype of petalodus hastingsii as figured by owen (1840–1845) in (a) lingual, (b) edge, and (c) labial views compared with the actual, far less complete specimen (nhmuk pv p613) in (d) lingual, (e) labial (silhouette based on more complete teeth), left broken edge (f), and right broken edge (g) views. the upper edge of the crown is heavily worn and exposes the dentine tubules. arrows point to the distinctive ridges at the base of the enameloid crown on the lingual side. sample of four out of 25 teeth (all nhmuk pv p5342) from the same bed and locality as the holotype and showing a range of variation in tooth form. note the well-developed ridges at the base of the enameloid crown of the lingual side (h, j, l, and n), and on the cingulum of the labial side (i, k, m, o). modified from woodward 1899. petalodus hastingsii (unm 11959 – now missing), flechado formation, taos county, new mexico, in lingual (p), right broken edge view (q) and labial (r) views (adapted from zidek and kietzke, 1993). note that the ridges occur at the base of the crown on the lingual side and on the cingulum of the labial side. holotype of petalodus acuminatus (as chomatodus acuminatus) as illustrated by agassiz (1838, pl. 19, figs. 11, 13) in (s) edge and (t) labial views; and actual tooth (mhnn-fos 171, as preserved today (u) lacking part of the crown and root (note the distinctive chip missing in the cingulum in t and in u). a second tooth of petalodus acuminatus in the agassiz collection, mhnn-fos 174, but not mentioned by him and illustrated for the first time in (v) labial view. petalodus tooth illustrated by portlock (1843, plate 14, figure 10) a few years after agassiz’s descriptions (scale unknown) in (w) labial view. illustrations of a tooth originally described as petalodus rhombus by m’coy (1854, plate 3g, figure 4) in (x) lingual and (y) labial views compared to a photograph of specimen today in (z) labial view (crown is now damaged and a corner missing from the root). holotype of petalodus ohioensis (as getalodus ohioensis) in (a’) labial and (b’) lingual views (from shafford 1853, p. 142); no scale given. the whereabouts of this specimen is unknown. two specimens (c’ and d’) described by newberry (1875, plate 58, figures 13 and 13a). holotype of petalodus allegeniensis as illustrated by leidy (1856, plate 16, figures 4 and 5) compared with recent photographs: (e’ and f’) in labial and (g’ and h’) lingual views. arrows point to the ridged basal band or cingulum. the origin of the green dot on specimen d is uncertain, but may have been the code used by woodward (1889) or owen (1840–1845) to denote it was a holotype. the red dot on specimen f is a blob of wax used by woodward (1889) to denote that he include the specimen in his catalog of fossil fishes. the blue star is probably the old symbol used to denote a holotype. scales in cm. 114 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 and santucci, 2004). conodonts from the glenshaw are missourian stage (middle pennsylvanian) (heckel and others, 2011; barrick and others, 2013) and thus, p. alleghaniensis is contemporaneous with p. ohioensis. hay (1895) raised the possibility that p. alleghaniensis might be synonymous with p. ohioensis, although in the end he did not accept that. the holotype of p. alleghaniensis does differ from the holotype of p. ohioensis as figured by safford (compare figure 5a’ and 5b’ with 5e’ to 5h’) in having a vertically wider cingulum of ridges (about twice or more wider). the narrower cingulum of p. ohioensis was cited by dalla vecchia (1988), hansen (1997) and brusatte (2007) as diagnostic. however, the reliability of this character was questioned by ivanov and others (2009) and lucas and others (2011). ginter and others (2010) and hansen (1985) seem to accept only p. ohioensis as the valid taxon but do not explicitly say so. zidek and kietzke (1993) consider p. alleghaniensis synonymous with p. ohioensis but do not state why. ivanov and others (2009) suggested that the width of the lingual band is so variable in petalodus that it may be unreliable as a diagnostic character and that the differences may be due to position in the jaws. we agree that the utility of this character is questionable given that we can find no functional reason for a rigid dichotomy between narrow and wide bands. in addition, we note that the specimens figured by newberry (figures 5c' and 5d') show variable cingulum width, with one (figure 5c’) approaching that of p. alleghaniensis (figures 5e' to 5h'). we therefore conclude that p. alleghaniensis is synonymous with p. ohioensis to which we refer all of the lower cutler bed specimens. conclusions the lower cutler beds in the shafer basin have produced several teeth of the petalodontiform shark petalodus ohioensis and one of ctenacanthid cladodus. most of the teeth are from the shafer limestone, an informal name applied to the widespread limestone at the top of the lower cutler beds. the petalodus teeth are the first documented occurrence of this taxon in utah, and cladodus the youngest occurrence in the state. among the various petalodus form species, we recognize p. hastingsii as a valid taxon characterized by a crown with a gently concave vertical cross-section, broad band of ridges on the lingual side and a ridged, outward facing cingulum on the labial side. p. acuminatus as having a low crown compared to width, with a more concave vertical cross-section than in p. hastingsii, and imbricated ridges on the ventrally facing cingulum. p. ohioensis is characterized by tall crowns compared to width, having a more concave vertical cross-section than in p. hastingsii, and imbricated ridges on a ventrally facing cingulum. both p. acuminatus and p. ohioensis are larger taxa than p. hastingsii. “petalodus” rhombus is either a petalodus species characterized by the lack of ridges on the crown, or more likely that it represents a distinct genus. acknowledgments we are extremely grateful to the help we had with the search for several key specimens of petalodus, as well as providing photographs of key specimens: emma bernard, natural history museum, london, england; christian klug, paläontologisches institut und museum, zurich, switzerland; andreas müller, eth-bibliothek, zurich, switzerland; thierry malvesy, conservator, muséum d’histoire naturelle de neuchâtel, switzerland who located the long lost tooth of petalodus acuminatus, alain germond, muséum d’histoire naturelle de neuchâtel, switzerland provided the photograph of the long lost type; deborah hutchinson, bristol city museum, bristol, england; matt riley, sedgewick museum, cambridge university, cambridge, england; ned gilmore, academy of natural sciences of drexel university, philadelphia, pa. thanks also to emma bernard for email discussions regarding owen’s holotype, and thierry malvesy for discussions regarding the agassiz specimens at the muséum d’histoire naturelle de neuchâtel. the teeth described from the “lower cutler beds” are from a legacy collection made in the 1970s by ottinger. fianlly, review comments by james kirkland, grant willis, and doug sprinkel are appreciated, especially in discussions on the proper name of the strata the teeth were collected from. references agassiz, l., 1833–1845a, recherches sur les poissons fossiles, v. 3, contenant l’histoire de l’ordre des placoïdes: petitpierre, neuchâtel, suisse, 422 p. 115 permo-pennsylvanian shark teeth from the lower cutler beds near moab, utah carpenter, k., and ottinger, l.. geology of the intermountain west 2018 volume 5 agassiz, l., 1833–1845b, recherches sur les poissons fossiles. atlas, v. 3: petitpierre, neuchâtel, suisse, 83 plates. baker, a.a., dobbin, c.e., mcknight, e.t., and reeside, j.b., jr., 1927, notes on the stratigraphy of the moab region, utah: american association 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g.a., and verville, g.j., 1990, abandonment of the name “elephant canyon formation” in southeastern utah— physical and temporal implications: the mountain geologist, v. 27, p. 119–130. lucas, s.g., spielmann j.a., ivanov, a.o., rinehart, l.f., and krainer, k., 2011, petalodont chondrichthyan teeth from the pennsylvanian-permian horquilla formation, big hatchet mountains, new mexico, in sullivan, r.m., lucas, s.g., and spielmann, j.a., editors, fossil record 3: new mexico museum of natural history and science bulletin 53, p.110–114. lund, r., 1989, new petalodonts (chondrichthyes) from the upper mississippian bear gulch limestone (namurian e2b) of montana: journal of vertebrate paleontology, v. 9, p. 350–368. marsh, o.c., 1896, the dinosaurs of north america: u.s. geological survey 16th annual report for 1894-1895, p. 133–244. mattox, r.b., and brand, j.p., 1974, stratigraphic relationships of the shafer limestone, san juan county, utah: the museum of texas tech university occasional 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of leicester, ph.d. dissertation, 159 p. newberry, j.s., 1875, descriptions of fossil fishes—part ii paleontology: report of the geological survey of ohio, v. 2, p. 1–64. newberry, j.s., and worthen, a.h., 1866, descriptions of vertebrates: geological survey of illinois, v. 2, p. 11–141. owen, r., 1840–1845, odontography; or a treatise on the comparative anatomy of the teeth; their physiological relations, mode of development, and microscopic structure in the vertebrate animal, 2 vols.: hippolyte bailliere, london, 655 p. parsons, l.m., 1917, the carboniferous limestone bordering the leicestershire coalfield: quarterly journal of the geological society of london, v. 73, p. 84–110. portlock, j.e., 1843, report on the geology of the county of londonderry, and of parts of tyrone and fermanagh: dublin, ireland, andrew milliken, 784 p. prommel, h.w.c., 1923, geology and structure of portions of grand and san juan counties, utah: american association of petroleum geologists, bulletin, v. 7, p. 384–399. rice, c.l., hiett, j.k., & koozmin, e.d., 1994, glossary of pennsylvanian stratigraphic names, central appalachian basin, in rice, c.l., editor, elements of pennsylvanian stratigraphy, central appalachian basin: geological society of america special paper, v. 294, p. 115–155. robb, a.j., 2003, notes on the occurrence of some petalodont shark fossils from the upper pennsylvanian rocks of northeastern kansas: transactions of the kansas academy of science, v. 106, p.71–80. rollins, h.b., carothers, m., and donahue, j., 1979, transgression, regression and fossil community succession: lethaia, v. 12, p. 89–104. safford, j.m., 1853, tooth of getalodus ohioensis: american journal of science and arts, (second series), v. 16, 142 p. sumida, s.s., albright, g.m., and rega, e.a., 1999, late paleozoic fishes of utah, in gillette, d.d., editor, vertebrate paleontology of utah: utah geological survey miscellaneous publication 99-1, p. 13–20. terrell, f.m., 1972, lateral facies and paleoecology of permian elephant canyon formation, grand county, utah: brigham young university geology studies, v. 19, part 2, p. 3–44. waters, c.n., waters, r.a., barclay, w.j., and davies, j.r., 2009, a lithostratigraphical framework for the carboniferous successions of southern great britain (onshore): british geological survey research report rr/09/001, 175 p. wengerd, s.a., and matheny, m.l., 1958, pennsylvanian system of four corners region: american association of petroleum geologists, bulletin, v. 42, no. 9, p. 2048–2106. woodward, a.s., 1889, catalogue of the fossil fishes in the british museum (natural history). part i containing the elasmobranchii: london, taylor and francis, 567 p. zangerl, r., 1981, chondrichthyes 1 paleozoic elasmobranchii—handbook of paleoichthyology volume 3a: stuttgart, germany, gustav fischer verlag, 115 p. zidek, j., and kietzke, k.e., 1993, pre-permian vertebrates of new mexico, with remarks on some early permian specimens: new mexico museum of natural history and science bulletin, v. 2, p. 1–10. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 9 2022 © 2022 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat—new 40ar/39ar, geochemical, and paleomagnetic data stacy henderson, tiffany rivera, peter c. lippert, and brian r. jicha geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover the pleistocene basalt of antelope flat dammed the snake river in swan valley, southeast idaho, producing hyaloclastite visible along us highway 26. i become a member of the uga to 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geology of the intermountain west an open-access journal of the utah geological association volume 9 2022 115 abstract swan valley is a graben in eastern idaho that formed by extension along the grand valley and snake river faults and preserves a record of explosive rhyolitic volcanism sourced from the yellowstone plateau and heise volcanic fields, as well as locally sourced basaltic lavas. the pleistocene basalt of antelope flat intersected the south fork of the snake river and generated a temporary hyaloclastite dam. previous workers proposed that the lava dam allowed for the accumulation of water that led to the generation of paleo-swan lake. although lacustrine deposits from paleo-swan lake have not been described or mapped, several-meters thick intercalated hyaloclastites and pillow lavas require the interaction between continued volcanism and standing water. in this work, we present new geochemical, geochronologic, and paleomagnetic data to reinterpret the eruptive history of the basalts within the valley, estimate the volume and duration to fill paleo-swan lake, and calculate incision rates of the snake river through quaternary basalts. using geochemical and paleomagnetic data, we reinterpret deposits previously mapped as the basalt of antelope flat as three temporally distinct units. the duration to fill paleo-swan lake is calculated as 12 to 20 years. an absence of lacustrine deposits, shorelines, or other indicators of a lake environment led us to propose that shallow, marshy, wetland conditions existed locally to produce hydrovolcanic deposits characteristic of the basalt of antelope flat. we report a new 40ar/39ar age of 904 ± 11 ka (2σ) for the basalt of antelope flat, which we use to determine an average incision rate of 0.014 cm/yr for the snake river through quaternary basalts. our multi-method approach provides updated constraints to the eruptive and geomorphological history of southeastern idaho. geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat—new 40ar/39ar, geochemical, and paleomagnetic data stacy henderson1, 2, tiffany rivera1, peter c. lippert3, and brian r. jicha4 1 westminster college, 1840 south 1300 east, salt lake city, ut 84105; trivera@westminstercollege.edu 2 montana state university, culbertson hall, 100, bozeman, mt 59717; stacy.henderson@student.montana.edu 3 department of geology and geophysics, university of utah, 115 s 1460 e, salt lake city, ut 84112; pete.lippert@utah.edu 4 department of geoscience, university of wisconsin-madison, 1215 west dayton street, madison, wi 53706; brian.jicha@wisc.edu citation for this article. henderson, s., rivera, t., lippert, p.c., and jicha, b.r., 2022, geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat—new 40ar/39ar, geochemical, and paleomagnetic data: geology of the intermountain west, v. 9, p. 115–130, https://doi. org/10.31711/giw.v9.pp115-130. © 2022 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the snake river plain-yellowstone (srp-y) volcanic province is known for its time-transgressive caldera-forming super-eruptions, numerous interand intra-caldera rhyolite domes, and voluminous basaltic lava flows that bury most older calderas (christiansen, 2001). srp-y volcanic activity for the past 16 million years spans southern idaho and northwestern wyoming. volcanism and related tectonism are often attributed to the passage of north america over a stationary hotspot (pierce and morgan, 1992; smith and 116 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 braile, 1994; camp, 1995), although small-scale upper mantle convection (humphreys and others, 2000) or mantle return flow around the subducting farallon slab remnant (james and others, 2011; fouch, 2012) have also been proposed. the rhyolitic products of the srp-y province have been intensely studied for their distribution, geochemistry (hamilton, 1965; christiansen and blank, 1972; christiansen, 1982, 2001), geochronology (e.g., obradovich, 1992; rivera and others, 2017), super-eruption cycles (christiansen and blank, 1972; christiansen, 1982, 2001; obradovich, 1992; rivera and others, 2017), and rates of magmatic evolution (rivera and others, 2014, 2016, 2017; matthews and others, 2015; stelten and others, 2015; troch and others, 2017; shamloo and till, 2019, 2021). basaltic eruptions across the srp-y province have provided myriad insights into physical and chemical processes associated with lithospheric structure (e.g., shervais and hanan, 2008), melt generation and differentiation (e.g., leeman, 1976; hughes and others, 2002; putrika and others, 2009; rivera and others, 2021), and eruption characteristics (e.g., greeley, 1982; kunz, 1982; creighton, 1987). the interaction of pleistocene basaltic lavas with water is preserved in areas of the snake river plain. lavas have filled paleo-channels and dammed and diverted rivers, and rivers and flooding have incised deep canyons through these basalts. for example, the south fork of the boise river was dammed multiple times over a 2-million-year period (howard and others, 1982) and basalts erupted from mckinney butte dammed the snake river near bliss, idaho, generating a lava delta with abundant pillow basalts (malde, 1971,1982). at american falls, the 70 ka cedar butte lava flow dammed the snake river; the lava dam led to the filling of american falls lake, which persisted until the bonneville flood (scott and others, 1982). the snake river canyon and the malad gorge, both in the central snake river plain, are two examples of incised canyons that were carved by the downcutting of rivers (lamb and others, 2014). swan valley is a graben in eastern idaho that formed by extension along the grand valley and snake river faults. the graben preserves a record of both explosive and effusive volcanism from the yellowstone plateau (0 to 2 ma) and heise (4.5 to 6.6 ma) volcanic fields (figure 1), as well as locally sourced basaltic lavas. one of these local effusive eruptions is the basalt of antelope flat. originally described by hackett and morgan (1988) as part of the conant valley volcanics, dossett and others (2012) later divided the deposit into multiple facies including rim and canyon-filling subaerial facies, a dam complex facies, and a hyaloclastite facies. these observations led previous workers to propose that the basalt of antelope flat dammed the channelized snake river and impounded water upstream, producing a short-lived lake (hackett and morgan, 1988; moore and embree, 2016). continued eruption of basalt allowed for the development of pillow lavas as flows entered the shallow standing water upstream and fluvial deposition continued downstream of the lava dam. termed swan lake (moore and embree, 2016), this impoundment persisted for some unknown time until the dam was breached, causing the snake river to divert its course and join a second drainage, which now forms the present-day canyon. swan lake is hypothesized to extend nearly 50 km toward the southeast and occupy an area twice the size of the present-day palisades reservoir (moore and embree, 2016). in this contribution, we present a new 40ar/39ar eruption age, as well as geochemistry and paleomagnetic data for the basalt of antelope flat. with these data, we reinterpret the quaternary geology of swan valley to (1) assess the eruptive history of basalts within the valley, (2) estimate the volume and fill rate for swan lake, and (3) calculate incision rates of the diverted snake river through quaternary basalts. materials and methods planarand cross-bedded hyaloclastite consists of juvenile sand-size, angular, dark brown glassy basalt fragments, with a weathered, burnt orange palagonitic cement. accidental clasts include quartz arenite, vesicular basalt, and dense rhyolite cobbles and pebbles (hackett and morgan, 1988). approximately 80 m of subaerial lavas, basal tuff breccias interpreted as mass wasting deposits from failure of water-saturated palagonite tuffs, cross-bedded laminated tuffs interpreted as 117 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 lacustrine deposits, and subaerial flows with pillow bases indicative of flow into shallow standing water, are present within the swan valley graben (hackett and morgan, 1988; dossett and others, 2012; moore and embree, 2016). poor sorting and the absence of bomb sags were interpreted as evidence for deposition as a sheet wash, rather than indicating proximal air-fall deposits (hackett and morgan, 1988). for this work, we sampled the basalt of antelope flat dam complex and hyaloclastite facies (location 1 in figure 2). the dam complex lava (samples 16af-1 and 17af-2) is a dark gray, vesicular basalt (figure 3) with phenocrysts of olivine and plagioclase and minimal secondary mineralization in the vesicles (figure 4). the hyaloclastite sample (17af-3) consists of glassy brown to black sand-size basaltic fragments. paleomagnetic methods eleven 2.5-cm-diameter cores approximately 10 to 15 cm in length were drilled from a single flow in the dam facies of the basalt of antelope flat (sample 17af2) on the northeast side of state highway 26 in idaho (43.4891° n, 111.4494° w). cores were drilled using a gasoline-powered drill over 1 vertical m and several lateral meters of outcrop. cores were oriented in situ figure 1. location map of the heise and yellowstone volcanic fields in the eastern snake river plain (srp), idaho and northwestern wyoming. caldera boundaries are indicated by the dashed lines. swan valley is indicated by the star (detail is provided in figure 2). inset map shows the calderas of the srp resulting from hotspot-related volcanism. base map generated from geomapapp; map modified from bindeman and others (2007) and watts and others (2011). approximate locations (not to scale) of basaltic lavas discussed in text are denoted by m (massacre rocks state park), h (hell’s half acre), and w (idaho national laboratory drill core wo-2). 118 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 using a magnetic compass. the cores were cut into 10 cm3 specimens and the freshest specimens from each sample were used for analysis at the utah paleomagnetic center at the university of utah. the natural remanent magnetism (nrm) of each 10 cm3 core specimen was measured using an agico jr6a spinner magnetometer operating in the fast, six-position automatic mode. the nrm was demagnetized along the x, y, and z axes using alternating fields in steps from 5 mt to 300 mt (as required by specimen) with a minimum of 14 steps using a magnon 300 alternating field demagnetizer. measurement was stopped when the specimens retained <10% of their original magnetic intensity. 40ar/39ar dating methods bulk rock of the basalt of antelope flat (sample 16af-1) was crushed, milled, and sieved to the 180 to 250 μm fraction at the university of wisconsin-madison. this fraction was purified using a combination of magnetic separation and handpicking to ensure a phenocryst-free groundmass. groundmass was irradiated for three hours with the alder creek rhyolite sanidine figure 2. location of swan valley and sampling sites of the basalt of antelope flat and other lavas discussed in this text. lava flow, coordinates, and other data are provided in table 2. the star symbol is the sampling location for original data presented here; ovals are sampling locations of anders and others (1989); hexagons are sampling locations of dossett and others (2012). pine creek bench (pcb) is the area enclosed by the broken line. the downthrown sides of the snake river and grand valley faults are indicated by the ball and stick. fault locations, vent, and distribution of the basalt of antelope flat are approximate. extent of the basalt is interpreted from the geologic map, cross sections, and well logs of dossett and others (2012). base map generated from google earth. 119 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 standard at oregon state university in the cadmium-lined in-core irradiation tube (clicit) facility. upon return, argon isotopic analyses were conducted using a 60w co2 laser and a nu instruments noblesse multi-collector mass spectrometer following the procedures of jicha and others (2016). analyses of the alder creek rhyolite sanidine were conducted as single crystal fusion experiments, whereas the groundmass of the basalt of antelope flat was analyzed by incremental heating. ages are reported relative to an alder creek rhyolite sanidine standard age of 1.1864 ma (rivera and others, 2013; jicha and others, 2016) and decay constants of min and others (2000). uncertainties are reported at 2σ and include the error contribution from the irradiation parameter j, unless otherwise indicated. geochemistry methods geochemical analyses were performed on dense, fresh, crushed whole rock powder made from the dam complex facies sample 17af-2, whereas hand-picked glassy fragments of the hyaloclastite were used for analysis of sample 17af-3. all analyses were conducted at the peter hooper geoanalytical lab at washington state university. major and minor element analyses were conducted by x-ray fluorescence (xrf) whereas trace and rare earth elements were conducted by inductively coupled plasma mass spectrometry (icpms). results paleomagnetic results all 11 basalt of antelope flat core specimens exhibited similar demagnetization behavior. a consistent and well-defined characteristic remanent magnetization (chrm) is evident after a steep downward direction was removed between 5 and 10 mt; the chrm is southfigure 3. outcrop of the basalt of antelope flat (location 1 on figure 2). (a) google earth image of the road cut with the dam complex and hyaloclastite facies indicated. (b) palagonitic to glassy hyaloclastite capped by the dam complex facies. (c) dark gray to black vesicular basalt of antelope flat dam complex facies. 120 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 west and up and decays toward the origin of orthogonal vector plots (table 1; appendix). we interpret the low coercivity downward component as a recent magnetic overprint and the chrm as the primary magnetization acquired at the time of eruption. directions from 8 of the 11 specimens were used to determine the site mean direction. three specimens were excluded due to outlying declination directions (figure 5). the remaining eight specimens cluster tightly and clearly indicate a reverse polarity chrm direction fit by principal component analysis (pca; kirschvink, 1980). the fisher mean direction is an inclination of -36.5° and a declination of 247.3° (α95 = 3.3°, κ = 287.6; figure 5, table 1). the site mean direction differs from the time-averaged dipole direction at this site, but this can be explained by secular variation of the geomagnetic field at the time of eruption. importantly, a single lava flow is not expected to record a time-averaged direction. the magnetic polarity recorded by the basalt of antelope flat is unambiguously reversed. 40ar/39ar dating results two incremental heating experiments of groundmass from the basalt of antelope flat (sample 16af-1) produced plateaus with >75% of the 39ark released. plateau-defining steps are presented in blue (figure 6); steps excluded from the plateau age are presented in white. plateaus were achieved with 9 out of 12 heating steps in the first analysis and 5 out of 11 heating steps in the second analysis. the first experiment yielded a plateau age of 893 ± 18 ka (2σ, including j; figure 6a). the second experiment yielded a plateau age of 910 ± 14 ka (2σ, including j; figure 6b). combining the ages of the two experiments yields a weighted mean age of 904 ± 11 ka (2σ, including j). full analytical data are provided in the appendix. geochemical results the basalt of antelope flat has a sio2 content of about 48 weight percent (wt.%) and total alkali content (na2o + k2o) of about 3 wt.%, thus placing the sample within the field of “basalt” on a total alkali versus silica diagram (le bas and others, 1986). figure 7 shows major element oxides and selected trace element concentrations (parts per million [ppm]) for the basalt of antelope flat dam and hyaloclastite facies in comparison to several other basalts of the eastern snake river plain (esrp) region. the hyaloclastite glass has slightly specimen number demagnetization steps n mad ig dg 17af2.1 40-150 mt 7 2.8 -26.9 229.0 17af2.2 40-175 mt 8 2.9 -35.0 246.9 17af2.3 80-275 mt 9 8.9 -33.4 250.6 17af2.4 40-250 mt 10 3.6 -37.9 254.4 17af2.5 40-250 mt 10 3.2 -34.5 244.6 17af2.6 50-200 mt 8 4.7 -40.3 243.9 17af2.7 50-200 mt 8 4.1 -36.8 243.3 17af2.8 80-175 mt 5 8.9 -37.0 254.5 17af2.9 50-225 mt 9 3.1 -36.6 240.2 17af2.10 50-225 mt 9 4.1 -35.6 271.4 17af2.11 50-175 mt 7 4.0 -31.2 267.5 table 1. site 17af2 – antelope flats (43.489239°n, 111.449723°w). demagnetization steps, mean angular deviation (mad) of the characteristic remanent magnetization (chrm) fit, declination (dg), and inclination (ig) of 11 analyses of the basalt of antelope flat. n: number of consecutive demagnetization steps used to define the chrm. 121 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 lower sio2, al2o3, cao, and total alkali relative to the dam facies. it also had a higher volatile concentration as measured by “loss on ignition,” which may be due to the inclusion of some hydrated palagonitic glass in the sample during handpicking. full analytical data are provided in the appendix. discussion geochemistry we compare the composition of our sample of the basalt of antelope flat to several suites of snake river plain basalts (figures 1 and 7). the idaho national lab (inl) wo-2 drill core sampled basalt lavas at depth with ages that range from about 0.2 to about 2.3 ma (shervais and others, 1994). hell’s half acre is located within the esrp, and is geographically closer to swan valley, but the lavas are substantially younger than the basalt of antelope flat (14c age of 5200 ± 150 years before present as of kuntz and others, 1986). the 6.3 ma (armstrong and others, 1975) basalts of the massacre volcanics erupted along the southern margin of the figure 4. basalt of antelope flat dam complex facies (sample 17af-2) in thin section. all images are in cross-polarized light. (a) vesicular basalt. (b, c, d) glomerocrysts of olivine and plagioclase laths set in a fine-grained groundmass. scale bar in b, c, and d is 500 micrometers; ves: vesicle, glom: glomerocryst, ol: olivine, plag: plagioclase, gm: groundmass. 122 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 fault-bounded esrp. our samples are geochemically most similar to the temporally equivalent lavas encountered at depth within the inl core (figure 7). although srp lavas are notorious for their elevated p2o5 contents (e.g., leeman, 1982), as demonstrated in the young lavas at hell's half acre, the basalt of antelope flat does not show the elevated p2o5 at similar sio2 contents. furthermore, the basalt of antelope flat has elevated tio2, sr, and zr but lower mgo relative to the basalts of the massacre volcanics, thus making them dissimilar to this older suite of basaltic lavas. these geochemical variations may signify derivation from different mantle source regions or may be indicative of processes such as fractional crystallization or assimilation of country rock occurring at shallow depths prior to eruption. the petrogenetic processes governing the chemical variability are beyond the scope of this work. basalt flows of the swan valley graben the swan valley graben has three prominent areas where basaltic lavas are present (figures 2 and 8; dossett and others, 2012). the northwesternmost area is antelope flat, which is dominated by the basalt of antelope flat and is bound by the snake river on its eastern side. at a similar elevation, pine creek bench is dissected by the snake river on the west and by pine creek across the center of the bench. here, the 4.0 ma basalt of swan valley and a paleocanyon-filling facies of the basalt of antelope flat are exposed near the mouth of pine creek canyon, where pine creek joins the snake river (anders and others, 1989; dossett and others, 2012). the paleocanyon facies may contain three to five different flow units (dossett and others, 2012). the dam, rim, and hyaloclastite facies of the basalt of antelope flat are prominent at the confluence between pine creek bench and antelope flat. the rim facies is characterized by columnar jointing and pillow bases. the 4.0-ma basalt of swan valley is also exposed here (dossett and others, 2012). swan valley is the topographically lower area to the southeast of pine creek bench (figures 2 and 9). although previous workers have identified different facies of the basalt of antelope flat (dossett and others, 2012), we use the geochemical and paleomagnetic results to reinterpret some of these facies. our results suggest that the paleocanyon-filling facies and the pillow-bearing rim facies on pine creek bench are distinct lava flows, unrelated to the eruption of the basalt of antelope flat. in figures 7 and 9, we compare our geochemical and paleomagnetic analyses to other basalt samples from antelope flat and pine creek bench (anders and others, 1989; dossett and others, 2012). our sample is geochemically most similar to basalts sampled at locations 2 and 4 (figure 8). our site mean direction of the cored dam complex facies is indistinguishable from site results obtained at locations 3 and 4 (figures 8 and 9). we thus conclude that samples collected from locations 1 through 4 are the basalt of antelope flat. the lavas sampled at locations 5 and 8 (figure 8) are geochemically distinct from the basalt of antelope flat, with lower sio2 and mgo, and elevated feot, p2o5, and figure 5. stereonet of site mean direction, expected dipole direction, and the international geomagnetic reference field (igrf) direction for june 2017 when sample 17af-2 was obtained. 123 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 tio2 (figure 7). these lavas are present at the mouth of pine creek canyon and on the eastern side of the snake river canyon, separated from antelope flat, which is west of the snake river (figure 8). furthermore, their paleomagnetic site mean directions are distinct from the basalt of antelope flat, and each other. these variations lead us to conclude that samples collected from sites 5 through 10 do not represent the basalt of antelope flat. we further conclude from the paleomagnetic results of anders and others (1989) and dossett and others (2012) that basalt samples from locations 5 and 6 represent one lava flow that is geochemically similar to, but temporally distinct from, a second lava flow sampled at sites 7 through 10. a possible, and we argue parsimonious, explanation for the distinct site mean directions at locations 5 and 6 compared to locations 7 through 10 is geomagnetic secular variation during the matuyama reversal, which could be tested with new radioisotopic dates of these lavas. alternatively, slip along an unmapped structure between the two location groups could explain the different site mean directions, but our current knowledge of the local geology does not support this interpretation. well logs presented by dossett and others (2012) provide additional evidence for multiple flows. although they grouped all quaternary basalts into the basalt of antelope flat and assigned different flow facies, the well logs show significantly thicker lava (about 120 m) on pine creek bench, and thinner basalt (15 to 30 m) along the snake river canyon. the thickness of the lavas in pine creek canyon was interpreted as the basalt of antelope flat filling a paleochannel, which allowed for the accumulation of the thick lava (moore and embree, 2016). however, geochemical and paleomagnetic evidence suggest that the lava in pine creek canyon is not the basalt of antelope flat. thus, we conclude that there are at least four distinct basaltic lavas within the swan valley graben (figure 8 and table 2): 1. the basalt of antelope flat, with an eruption age of 900 ka, dammed the snake river and produced the hyaloclastite and associated subaerial lavas. this lava is sampled at locations 1 through 4 and includes samples collected in this work and by dossett and others (2012). 2. pine creek basalt 1 corresponds to locations 5 and 6 sampled by dossett and others (2012). these lavas share similar site mean magnetic directions, which are distinct from the other lavas discussed here. these lavas are undated. 3. pine creek basalt 2 corresponds to locations 7 through 10 sampled by anders and others (1989) and dossett and others (2012). these lavas share similar site mean magnetic directions, which are distinct from pine creek basalt 1 and the basalt of antelope flat. the lava sampled at location 10 was dated by k/ar to 1.5 ± 0.8 ma (anders and others, figure 6. 40ar/39ar incremental heating analyses of groundmass from basalt of antelope flat (sample 16af-1). open boxes are steps excluded from the calculation of the plateau age. mswd: mean square weighted deviate, prob.: probability, n/n: number of steps included/total number of steps. 124 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 1989) and was later assigned to the basalt of antelope flat paleocanyon-filling facies (dossett and others, 2012). here, we interpret pine creek basalt 2 as distinct from the basalt of antelope flat. 4. finally, the sample collected at location 11 is a basalt flow that must be older than 2.08 ma because it underlies the huckleberry ridge tuff. its composition is characterized by elevated sio2 and mgo, and lower total alkalis, p2o5, and tio2. this basalt has been termed the basalt of swan valley (dossett and others, 2012) and was dated by k/ar to 4.0 ± 1.0 ma (anders and others, 1989). figure 7. bivariate plots of selected major element oxides (wt.%) and trace element concentrations (ppm). data for basalt of antelope flat (baf) dam facies and hyaloclastite are from this study. samples from dossett and others (2012) are the same as those featured in figures 2 and 8. other snake river plain basalt chemistry is from massacre rocks (trimble and others, 1976), hell’s half acre (karlo, 1977), an inl drill core (shervais and others, 1994), and downloaded via navdat (www. navdat.org). locations are provided in figure 1. 125 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 paleo-swan lake calculations of area, volume, and the duration to fill the proposed paleo-swan lake occupied the area from the lava dam (sampling site 1 in figure 2) southeast through swan valley and may have included the area occupied by present-day palisades reservoir, thus occupying approximately twice the area of the modern reservoir (moore and embree, 2016). our sample location, which records the transition from a lacustrine to subaerial environment, marks the surface of the paleo-lake at an elevation of about 1707 m. using the google earth measuring tool to define the area of a polygon, we use the 1707-m contour to trace the area of the paleo-lake from the lava dam to the eastern edge of the palisades reservoir. using this method, our estimated area of swan lake is 145 km2. this maximum area (and consequently, the maximum volume calculated below) assumes that the present-day topography is unchanged by erosion or subsidence from the time of eruption of the basalt of antelope flat at about 900 ka. next, we use the surface elevation of the valley to represent the lake floor (1607 m). using our estimated area and elevations, we determined that the volume of swan lake was about 14.5 km3. for comparison, this is approximately the volume of yellowstone lake in yellowstone national park. to calculate the amount of time required to fill swan lake, we used the annual mean of monthly discharge rates of the snake river from u.s. geological survey gauging stations upstream from palisades reservoir in two man-made dam-influenced locations: flagg ranch, wyoming and near moran, wyoming. the calculated mean discharge at the flagg ranch station is 24.8 m3/s, but is 40.5 m3/s near moran (appendix). the duration to fill can be calculated by dividing the volume by the flow rate: we calculate the duration to fill the estimated about 14.5 km3 with an input of 24.8 m3/s and 40.5 m3/s was approximately 12 to 20 years. this conceptual model assumes that the lava dam was built instantaneously, relative to the time of formation, yet field evidence indicates that the dam formed incrementally: subaerial lavas are interbedded with hyaloclastite, and hyaloclastite deposits are about 60 m thick (dossett and others, 2010). our simplified model also assumes that present-day discharge rates along the figure 8. interpreted distribution of the basalt of antelope flat, pine creek basalt 1, and pine creek basalt 2 based on geochemistry, paleomagnetism, and unit thicknesses in well logs. the basalt of antelope flat has a geochemical and paleomagnetic signature that is distinct from the pine creek basalts. the contact between pcb1 and pcb2 is not defined by geologic mapping. 126 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 snake river are similar to those at 0.9 ma, and assumes a constant bottom depth for swan lake, rather than using an integrated bottom depth over the length of the lake to account for the slope of the lakeshore and irregularities in the paleotopography of the valley floor. furthermore, our model assumes that the lava dam was completely sealed and no leakage occurred from the base or sides of the lava dam. if, however, the lava dam leaked, then the input from the snake river into swan lake must have been greater than the leakage from the dam for the water to become deep enough for pillow lavas to form. pillow lavas are characteristic of the ocean floor, but they are also prevalent in lacustrine systems or shallow marine settings, and they have been documented in other lava-dammed temporary lakes in idaho (e.g., malde, 1971; howard and others, 1982) and in the grand canyon, arizona (e.g., crow and others, 2015). hackett and morgan (1989) note that individual flows of the basalt of antelope flat grade from basal pillow lavas upward to subaerial pahoehoe, which led them to conclude that the water body was only a few meters deep. thus, it is feasible that pillow lavas could develop in a relatively shallow swan lake that formed when the snake river backed up within the small canyon around the southwest side of pine creek bench into conant valley; this would produce the depth needed to generate the observed pillow lavas. no lacustrine sediments, shorelines, pleistocene tufa, or fossils have been recognized in swan valley that would indicate longevity of paleo-swan lake. we conclude this suggests that the lake was dammed, filled, and drained relatively quickly. water in shallow ponds may also provide sufficient depth for isolated pillow lavas to develop, such as the pillow lavas at tabernacle hill, in west-central utah (hintz, 2008). there, the existence of pillow lavas interbedded with tufa and the presence of other phreatomagmatic deposits led hintz (2008) away from the hypothesis of the basalts interacting with lake bonneville and figure 2 location latitude (˚n) longitude (˚e) geochemistry paleomagnetism dating basalt of antelope flat 1 43.4892 -111.4497 17af-2, 17af-3 17af-2 16af-1; ar/ar 2 43.4867 -111.4341 sr-post h 3 43.6014 -111.5777 srtr11 4 43.5907 -111.6108 sf-1 sfp1 4 43.5905 -111.6114 sfp2 pine creek basalt 1 5 43.5201 -111.3370 sr-6 10p05 6 43.4489 -111.3795 10p04 pine creek basalt 2 7 43.6025 -111.6439 srwf11 8 43.6057 -111.5086 sr-12 10p03 9 pcb1 10 pcb3 k/ar pre-huckleberry ridge tuff (>2.08 ma) 11 43.4867 -111.4341 sr-pre h table 2. sample location coordinates, corresponding location on figure 2, and sample identifiers for geochemical and paleomagnetic analyses. samples are compiled from this study, anders and others (1989), and dossett and others (2012). no coordinates were provided for locations 9 and 10. sample 16af-1 was dated in this study; sample pcb3 was dated by the k/ ar method (anders and others, 1989). 127 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 instead toward the interpretation of interaction with pluvial waters. we propose that the interaction of the basalt of antelope flat with the snake river produced a hyaloclastite dam, which allowed for marsh-like conditions and subsequent formation of pillow lavas in subaerial (rather than subaqueous) waters. draining swan lake moore and embree (2016) proposed that the lava dam was breached and the water accumulated in swan lake incised the present-day canyon that diverts the snake river to the east of antelope flat (figure 8). if swan lake drained catastrophically through the modern-day canyon, then we expect to find flood deposits such as scoured bedrock, dry waterfalls, or watermelon boulders. the lack of these deposits, and the absence of shorelines, delta deposits, or sediments and fossils observed as remnants of other snake river plain lava-dammed lakes supports our hypothesis of a temporary wetlands or marsh-like environment at the interface between the dam and the snake river. in our interpretation, we predict the geometry of the lava dam as shown in figure 10, where the lava dam blocked the area bounded by the hyaloclastite facies deposits on either side of the modern snake river. as waters rose, the lava dam was breached on the southeastern side, where the snake river is adjacent to the eastern canyon wall. as the hyaloclastite dam failed from river incision, the snake river began to carve a path through the basalt of antelope flat and underlying volcanic and sedimentary units. following dam failure, the snake river diverted its course to the east, joining with pine creek. from this location, the snake river now cuts a canyon through about 120 m of rock and sediment, comprising the basalt of antelope flat, pine creek basalt 2, the huckleberry ridge tuff, cenozoic–quaternary gravels, and is currently incising the 4.0 ma basalt of swan valley (anders and others, 1989; dossett and others, 2012). optically stimulated luminescence (osl) dating of a river terrace 5 to 10 m above the modern river suggests that the terrace is about 60 ka (bufe and others, 2017), and thus that the canyon was largely incised between the eruption of the basalt of antelope flat and 60 ka. using our new age for the basalt of antelope flat, the 60 ka minimum age for canyon completion and the present-day canyon depth of 120 m, we calculate an average incision rate for the snake river of 0.014 cm/yr between 900 and 60 ka. we envision that incision was faster following dam failure (due to higher stream power provided by the impounded water, abundance of bed load from dam failure, and an overall wetter climate) and has slowed over time. our calculated incision rate is consistent with rates previously calculated for this section of the snake river from 60 ka to present (bufe and others, 2017). however, it is lower than rates calculated for sections of the snake river where incision rates may be enhanced by movement along normal faults of the grand valley fault system (tuzlak and others, 2021). conclusions snake river plain volcanism provides geomorphic information about landscape evolution beyond that associated with the migration of north america over the yellowstone hotspot. the work presented here reports geochemical, geochronological, and paleomagnetic data from the basalt of antelope flat in swan valley, idaho. from these data, we evaluated the eruptive history and interaction with the snake river within the swan valley graben. paired geochemical and paleomagnetic signafigure 9. site mean directions for the basalt of antelope flat sampled in this study (location 1) with paleomagnetic results from dossett and others (2012) and anders and others (1989). note the strong correlation between our results and those from locations 3 and 4. two additional distinct flows are identified: one flow sampled at locations 5 and 6; and a second flow sampled at locations 7 through 10. sample identifiers correspond to locations in figure 2 and table 2. 128 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 tures of basalts exposed in swan valley demonstrate that there are four distinct lavas within swan valley: the basalt of swan valley (4.0 ma), pine creek basalt 1 (undated), pine creek basalt 2 (1.5 ma), and the basalt of antelope flat (0.9 ma). the 904 ± 11 ka basalt of antelope flat dammed the south fork of the snake river, evidenced by alternating layers of hyaloclastite and dense, subaerial lava at the dam site. impounded water behind the dam resulted in a temporary marsh-like environment, rather than a long-lived lacustrine environment. when the hyaloclastite dam was breached, the course of the snake river was diverted eastward, joining pine creek and carving the present-day canyon. we calculate an average incision rate through the south fork of the snake river canyon of 0.014 cm/yr for the period between 900 and 60 ka, which is consistent with, albeit slightly higher than, rates calculated from 60 ka to present. this rate is less than those calculated for other sections of the snake river where incision may be influenced by movement along the grand valley fault system. acknowledgments this research was supported by a grant from the national science foundation (ear-1524840). samples for this work were obtained from the traditional lands of the shoshone-bannock people. many thanks to dan moore (brigham young university-idaho) for an introduction to the basalt of antelope flat and swan lake story during the 2016 tobacco root geological society field conference, providing sample 16af-1, and for continued conversations over the last several years. we thank doug sprinkel (azteca geosolutions) for editorial handling and glenn thackray (idaho state university) and joel pederson (utah state university) for their insightful reviews. references anders, m.h., geissman, j.w., piety, l.a., and sullivan, j.t., 1989, parabolic distribution of circumeastern snake river plain seismicity and latest quaternary faulting—migratory pattern and association with the yellowstone hotspot: journal of geophysical research, v. 94, p. 1589, doi: 10.1029/ jb094ib02p01589. armstrong, r. l., leeman, w. p., and malde, h. e., 1975, k-ar dating, quaternary and neogene volcanic rocks of the snake river plain, idaho: american journal of science, v. 275, p. 225–251. bindeman, i.n., watts, k.e., schmitt, a.k., morgan, l.a., and shanks, p.w.c., 2007, voluminous low δ18o magmas in the late miocene heise 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by the dashed lines. well 9 contains an about 75-m-thick deposit of hyaloclastite; well 10 lacks hyaloclastite but has about 120 m of canyon-filling basalt. geology and well information from dossett and others (2012). geologic contacts, unit thicknesses, and well locations are approximate. the age of the basalt of swan valley is from anders and others (1989). imagery from google earth, historical image of 2012. 129 geomorphic and tectonic development of swan valley, southeast idaho, since the eruption of the basalt of antelope flat— new 40ar/39ar, geochemical, and paleomagnetic data henderson, s., rivera, t., lippert, p.c., and jicha, b.r. geology of the intermountain west 2022 volume 9 tana: u.s. geological survey professional paper 729-g, 120 p. christiansen, r.l., blank, j., and richard, h., 1972, volcanic stratigraphy of the quaternary rhyolite plateau in yellowstone national park: u.s. geological survey professional paper 729-b, 17 p. creighton, d.n., 1987, menan buttes, 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intermountain west 2022 volume 9 lava creek supereruption and magma chamber assembly at yellowstone based on 40ar/39ar and u–pb dating of sanidine and zircon crystals: geochemistry, geophysics, geosystem, p. 1–21, doi: 10.1002/2015gc005881. moore, d.k., and embree, g.f., 2016, field guide to the recent volcanic history of the south fork area between swan valley and ririe, id: the journal of the tobacco root society, v. 45, p. 95–100. obradovich, j.d., 1992, geochronology of the late cenozoic volcanism of yellowstone national park and adjoining areas, wyoming and idaho: u.s. geological survey open-file report 92-408, p. 1–45. pierce, k.l., and morgan, l.a., 1992, the track of the yellowstone hot spot—volcanism, faulting, and uplift, in link, p.k., kuntz, m.a., and platt, l.b., editors, regional geology of eastern idaho and western wyoming: geological society of america memoir 179, p. 1–54. rivera, t.a., darata, r., lippert, p.c., jicha, b.r., and schmitz, m.d., 2017, the duration of a yellowstone super-eruption cycle and implications for the age of the olduvai subchron: earth and planetary science letters, v. 479, p. 377–386, doi: 10.1016/j.epsl.2017.08.027. rivera, t.a., schmitz, m.d., crowley, j.l., and storey, m., 2014, rapid magma evolution constrained by zircon petrochronology and 40ar/39ar sanidine ages for the huckleberry ridge tuff, yellowstone, usa: geology, v. 42, p. 643–646, doi: 10.1130/g35808.1. rivera, t.a., schmitz, m.d., jicha, b.r., and crowley, j.l., 2016, zircon petrochronology and 40ar/39ar sanidine dates for the mesa falls tuff—crystal-scale records of magmatic evolution and the short lifespan of a large yellowstone magma chamber: journal of petrology, v. 57, p. 1677–1704, doi: 10.1093/petrology/egw053. rivera, t.a., storey, m., schmitz, m.d., and crowley, j.l., 2013, age intercalibration of 40ar/39ar sanidine and chemically distinct u/pb zircon populations from the alder creek rhyolite quaternary geochronology standard: chemical geology, v. 345, p. 87–98. scott, w.e., pierce, k.l., bradbury, j.p., forester, r.m., 1982, revised quaternary stratigraphy and chronology in the american falls area, southeastern idaho, in bonnichsen, b., and breckenridge, r.m., editors, cenozoic geology of idaho: idaho bureau of mines and geology bulletin 26, p. 581–595. shamloo, h.i., and till, c.b., 2019, decadal transition from quiescence to supereruption—petrologic investigation of the lava creek tuff, yellowstone caldera, wy: contributions to mineralogy and petrology, v. 174, p. 1–18, doi: 10.1007/ s00410-019-1570-x. shamloo, h.i., till, c.b., and hervig, r.l., 2021, multi-mode magnesium diffusion in sanidine—applications for geospeedometry in magmatic systems: geochimica et cosmochimica acta, v. 298, p. 55–69. shervais, j., vetter, s., and hackett, w.r., 1994, chemical stratigraphy of basalt in coreholes nrp-e and wo-2, idaho national engineering laboratory, idaho—implications for plume dynamics in the snake river plain: proceedings of the 7th international symposium on the observation of the continental crust through drilling. shervais, j.w., and hanan, b.b., 2008, lithospheric topography, tilted plumes, and the track of the snake river-yellowstone hot spot: tectonics, v. 27, no. 5, p. 1–17, doi: 10.1029/2007tc002181. smith, r.b., and braile, l.w., 1994, the yellowstone hotspot: journal of volcanology and geothermal research, v. 61, p. 121–187. stelten, m.e., cooper, k.m., vazquez, j.a., calvert, a.t., and glessner, j.j.g., 2015, mechanisms and timescales of generating eruptible rhyolitic magmas at yellowstone caldera from zircon and sanidine geochronology and geochemistry: journal of petrology, v. 56, p. 1607–1642. trimble, d.e., and carr, w.j., 1976, geology of the rockland and arbon quadrangles, power county, idaho: u.s. geological survey bulletin, report b 1399, 104 p. troch, j., ellis, b.s., mark, d.f., bindeman, i.n., kent, a.j.r., guillong, m., and bachmann, o., 2017, rhyolite generation prior to a yellowstone supereruption—insights from the island park–mount jackson rhyolite series: journal of petrology. v. 58, p. 29–52. tuzlak, d., pederson, j.l., bufe, a., and rittenour, t., 2021, patterns of incision and deformation on the southern flank of the yellowstone hotspot from terraces and topography: geological society of america bulletin, v. 134, no. 5-6 p. 1–15, doi: 10.1130/b35923.1. ar results complete 40ar/39ar results for incremental heating analyses of basalt of antelope flat sample: 16af-1 j-value: ?0.0008085 ± 0.0000014 (2σ) material: groundmass laser 40ar ± 2σ40 39ar ±2σ39 37ar ± 2σ37 36ar ± 2σ36 included in file power (%) (cps) (cps) (cps) (cps) (cps) (cps) (cps) (cps) 40ar*/39ark ± 2σ %40ar* age (ka) ± 2σ (ka) k/ca wtd. mean naf4618 3.3 ?63907 ± 44 ?25076 ± 44 ?58819 ± 469 ?178.36 ± 2.65 ??0.611030 ± 0.031815 ??23.94 904 ± 47 0.18 ü naf4621 3.8 ?54563 ± 39 ?21836 ± 39 ?64203 ± 503 ?153.92 ± 2.51 0.627574 ± 0.034550 ??25.06 929 ± 51 0.15 ü naf4624 4.5 ?69565 ± 42 ?26185 ± 45 ?93490 ± 711 ?204.49 ± 2.65 ??0.608574 ± 0.030567 ??22.85 900 ± 45 0.12 ü naf4627 5.2 ?85628 ± 44 ?28797 ± 47 ?125086 ± 934 ?264.60 ± 3.20 ??0.575090 ± 0.033539 ??19.28 851 ± 50 0.10 ü naf4630 6 ?92606 ± 46 ?31734 ± 51 ?145117 ± 1074 ?283.65 ± 3.42 ??0.612773 ± 0.032571 ??20.93 907 ± 48 0.09 ü naf4633 6.8 ?91034 ± 49 ?29957 ± 50 ?151538 ± 1141 ?284.46 ± 3.60 ??0.605599 ± 0.036387 ??19.86 896 ± 54 0.08 ü naf4636 7.8 ?110540 ± 54 ?31802 ± 49 ?188731 ± 1386 ?359.08 ± 4.13 ??0.576215 ± 0.039308 ??16.51 853 ± 58 0.07 ü naf4639 9 ?139536 ± 57 ?30721 ± 47 ?237267 ± 1731 ?466.96 ± 4.73 ??0.617787 ± 0.046746 ??13.53 914 ± 69 0.06 ü naf4642 10.3 ?163519 ± 61 ?28004 ± 42 ?290477 ± 2114 ?571.25 ± 5.59 ??0.573047 ± 0.060613 ??9.74 848 ± 90 0.04 ü naf4645 11.9 ?166113 ± 65 ?24352 ± 37 ?324256 ± 2363 ?605.01 ± 5.93 ??0.461072 ± 0.074026 ??6.70 682 ± 110 0.03 naf4648 13.9 ?164158 ± 65 ?19358 ± 32 ?319506 ± 2358 ?610.69 ± 5.91 ??0.370964 ± 0.092916 ??4.32 549 ± 137 0.03 naf4651 16 ?109989 ± 52 ?13066 ± 24 ?246399 ± 1831 ?418.53 ± 4.27 0.350637 ± 0.099784 ??4.11 519 ± 148 0.02 weighted mean age (9 of 12): 893 ± 18 sample: 16af-1 j-value: ?0.0008085 ± 0.0000014 (2σ) material: groundmass laser 40ar ± 2σ40 39ar ±2σ39 37ar ± 2σ37 36ar ± 2σ36 included in file power (%) (cps) (cps) (cps) (cps) (cps) (cps) (cps) (cps) 40ar*/39ark ± 2σ %40ar* age (ka) ± 2σ (ka) k/ca wtd. mean naf6917 3.5 ?80844 ± 40 ?46694 ± 70 ?92603 ± 885 ?197.94 ± 2.74 ??0.622942 ± 0.017720 ??35.93 922 ± 26 0.18 ü naf6920 4.9 ?146230 ± 55 ?77364 ± 113 ?239608 ± 2172 ?393.68 ± 4.04 0.616706 ± 0.015960 ??32.56 912 ± 24 0.15 ü naf6923 6.3 ?134138 ± 58 ?65023 ± 96 ?286551 ± 2599 ?393.13 ± 3.97 ??0.607803 ± 0.018749 ??29.37 899 ± 28 0.12 ü naf6926 7.7 ?106474 ± 43 ?43088 ± 66 ?254310 ± 2315 ?336.01 ± 3.80 ??0.611806 ± 0.026913 ??24.66 905 ± 40 0.10 ü naf6929 9 ?111642 ± 48 ?28384 ± 44 ?217579 ± 1993 ?374.65 ± 4.02 ??0.601619 ± 0.043109 ??15.21 890 ± 64 0.09 ü naf6932 10.3 ?121259 ± 46 ?20260 ± 33 ?220900 ± 2031 ?434.13 ± 4.50 ??0.453218 ± 0.067521 ??7.52 671 ± 100 0.08 naf6935 11.6 ?128849 ± 55 ?16225 ± 27 ?259088 ± 2383 ?478.10 ± 4.93 ??0.411140 ± 0.092684 ??5.12 608 ± 137 0.07 naf6938 13 ?89770 ± 44 ?10788 ± 20 ?203919 ± 1915 ?347.48 ± 3.57 ??0.202372 ± 0.101423 ??2.40 299 ± 150 0.06 naf6941 15 ?78457 ± 42 ?8862 ± 18 ?186740 ± 1769 ?302.32 ± 3.45 ??0.339848 ± 0.119310 ??3.78 503 ± 177 0.04 naf6944 19 ?88098 ± 49 ?9556 ± 19 ?249529 ± 2320 ?349.30 ± 4.11 ??0.378202 ± 0.131735 ??4.03 560 ± 195 0.03 naf6947 25 ?42017 ± 30 ?5233 ± 13 ?161848 ± 1576 ?179.24 ± 2.65 ??0.255137 ± 0.155143 ??3.11 378 ± 230 0.03 weighted mean age (5 of 11): 910 ± 14 the values in this table have been corrected for instrument background, source mass bias, detector efficiency, and decay of 37ar and 39ar instrument: noblesse 5-collector mass spectrometer standard: alder creek rhyolite sanidine standard age (ma): 1.1864 ± 0.0012 rivera et al. (2013); jicha et al. (2016) atmospheric argon ratios 40ar/36ar 298.56 ± 0.31 lee et al. (2006) 38ar/36ar 0.1885 ± 0.0003 lee et al. (2006) interfering isotope production ratios (40ar/39ar)k 0.00054 ± 0.00014 jicha & brown (2014) (38ar/39ar)k 0.01210 ± 0.00002 jicha & brown (2014) (39ar/37ar)ca 0.000695 ± 0.00001 renne et al. (2013) (38ar/37ar)ca 0.0000196 ± 0.000001 renne et al. (2013) (36ar/37ar)ca 0.000265 ± 0.00002 renne et al. (2013) decay constants l40ar (0.580 ± 0.014) x 10-10 a-1 min et al. (2000) lb(4.884 ± 0.099) x 10-10 a-1 min et al. (2000) 39ar (2.58 ± 0.03) x 10-3 a-1 stoenner et al. (1965) 37ar (8.23 ± 0.042) x 10-4 h-1 stoenner et al. (1965) 36cl (2.303 ± 0.046) x 10-6 a-1 xrf results major elements (wt. %) 17af-2 17af-3 sio2 48.17 47.41 tio2 2.95 2.94 al2o3 15.09 14.53 feo* 13.21 13.17 mno 0.20 0.20 mgo 6.63 5.78 cao 9.72 8.95 na2o 2.57 2.23 k2o 0.70 0.61 p2o5 0.55 0.53 sum 99.81 96.40 loi % 0.00 2.61 trace elements (ppm) ni 81 71.9 cr 207 189.5 sc 32 31 v 291 266 ba 435 447 rb 12 12 sr 313 314 zr 256 259 y 36 38 nb 25 25 ga 20 20 cu 49 51 zn 131 132 pb 7 5 la 30 30 ce 70 65 th 3 1 nd 34 36 u 2 3 icpms results sample id la ppm ce ppm pr ppm nd ppm sm ppm eu ppm gd ppm tb ppm dy ppm ho ppm er ppm tm ppm yb ppm lu ppm ba ppm th ppm nb ppm y ppm hf ppm ta ppm u ppm pb ppm rb ppm cs ppm sr ppm sc ppm zr ppm tri 17af-2 29.10 62.25 8.22 34.62 8.20 2.88 8.36 1.35 7.84 1.54 3.99 0.55 3.29 0.52 428 1.47 24.94 38.39 5.89 1.58 0.39 4.78 10.2 0.17 325 31.5 266 tri 17af-3 29.14 62.39 8.21 34.76 8.30 2.85 8.41 1.33 7.92 1.54 4.05 0.56 3.31 0.52 433 1.51 25.00 38.65 5.95 1.56 0.38 4.98 10.6 0.18 323 31.4 267 zijderveld plots representative stereonet and zijderveld plots for each of the eleven paleomagnetic analyses of the basalt of antelope flat. all zijderveld diagrams depict the demagnetization of natural remanent magnetization (nrm), following 13-15 alternating field demagnetization treatment steps. open (closed) circles represent inclination (declination). lake filling m km elevation sample 1707 1.707 valley floor 1607 1.607 delta elevation 100 0.10 sq km area of swan lake 145 km3 volume of swan lake 14.5 m3/s km3/s discharge (annual) moran, wy 40.50 4.1e-08 sec hours days weeks months years time to fill (annual) 3.58e+08 99,439 4,143.31 591.90 147.98 12.33 m3/s km3/s discharge (annual) flagg ranch, wy 24.76 2.5e-08 sec hours days weeks months years time to fill (annual) 5.86e+08 162,653 6,777.20 968.17 242.04 20.17 filling conant valley canyon m km elevation sample 1707 1.707 elevation bottom of canyon 1585 1.58 delta elevation 122 0.12 sq km area of conant valley cyn 10.4 km3 volume 1.3 m3/s km3/s discharge (annual) moran, wy 40.50 4.1e-08 sec hours days weeks months years time to fill (annual) 3.13e+07 8,704 362.67 51.81 12.95 1.08 https://nwis.waterdata.usgs.gov/nwis/monthly?site_no=13011000&amp;por_13011000_45164=1152892,00060,45164,1903-10,2019-12&amp;format=html_table&amp;date_format=yyyy-mm-dd&amp;rdb_compression=file&amp;submitted_form=parameter_selection_list 1903-2019 moran, wy apr may jun jul aug sep oct nov dec jan feb mar mean of monthly discharge (ft3/s) 762 1,570 3,460 3,760 3,350 2,050 382 308 341 324 377 481 convert to m3/s 21.58 44.46 97.98 106.47 94.86 58.05 10.82 8.72 9.66 9.17 10.68 13.62 0.0283168 m3/s 70.57 average for these months 10.44 average for these months 40.50 average annual teton county, wyoming hydrologic unit code 17040101 latitude  43°51'31", longitude 110°35'09" nad27 drainage area 807  square miles contributing drainage area 807  square miles gage datum 6,727.84 feet above ngvd29 https://nwis.waterdata.usgs.gov/nwis/monthly/?referred_module=sw&amp;site_no=13010065&amp;por_13010065_45154=1152882,00060,45154,1983-10,2021-11&amp;format=html_table&amp;date_format=yyyy-mm-dd&amp;rdb_compression=file&amp;submitted_form=parameter_selection_list 1983-2021 flagg ranch, wy apr may jun jul aug sep oct nov dec jan feb mar mean of monthly discharge (ft3/s) 724 3,060 3,030 866 399 329 346 353 346 346 340 355 convert to m3/s 20.50 86.65 85.80 24.52 11.30 9.32 9.80 10.00 9.80 9.80 9.63 10.05 m3/s 39.68 average for these months 9.84 average for these months 24.76 average annual teton county, wyoming hydrologic unit code 17040101 latitude  44°05'56", longitude 110°40'03" nad83 drainage area 486  square miles contributing drainage area 486  square miles gage datum 6,801.61 feet above ngvd29 about:blankabout:blank image1.png geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 10 2023 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. utah geosite—the salina canyon unconformity, a classic example of missing time shelley judge, emmett werthmann, cristina millan, michael braunagel, and erica maletic geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view of the salina canyon unconformity in the southern part of the wasatch plateau. the jurassic twist gulch formation forms the vertical to subvertical unit under the angular unconformity. salina canyon is an example of a progressive unconformity, with overlying strata including paleogene sandstone beds of the flagstaff and colton formations capped by the variegated cliffs of the paleogene green river formation. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 10 2023 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2022–2023 uga board president rick ford rford@weber.edu 801.915.3188 president-elect eugene syzmanski eugenes@utah.gov 801.537.3364 program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 treasurer aubrey dereuil aubrey@zanskar.us 850.572.2543 secretary tom chidsey tomchidsey@gmail.com 801.824.0738 past president john south johnvsouth@gmail.com 801.367.9292 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 10 2023 169 abstract salina canyon, utah, reveals a spectacular angular unconformity along an east-west transect through the southern part of the wasatch plateau. this region of utah is well known as the eastern extent of sevier orogenesis, but it also includes subsequent extensional overprinting. earliest descriptions of this unconformity were published by dutton (1880) and spieker (1946, 1949), and work continues today. field relationships expose many classic stratigraphic and sedimentologic features of erosional surfaces. due to the geometry of the progressive unconformity onto the topographic high of the sanpete-sevier valley antiform, the angular discordance of strata results in a gap in time of greater than 107 million years in the west, decreasing toward the east to about 39 million years and finally to less than 17 million years. paleosols and small-scale channels/scours with infilled basal conglomerates are also prominent along the unconformity, as are several mine adits. because of its abundant geologic features, the salina canyon unconformity is a superb teaching and learning space for geoscientists and outdoor naturalists. utah geosite—the salina canyon unconformity, a classic example of missing time shelley judge1, emmett werthmann1, 3, cristina millan2, 4, michael braunagel2, 5, erica maletic2, 6 1department of earth sciences, the college of wooster, wooster, oh 44691 usa; sjudge@wooster.edu 2 school of earth sciences, the ohio state university, columbus, oh 43210 usa; 3emmett.werthmann@wri.org; 4millan.2@osu.edu; 5braunagel.2@buckeyemail.osu.edu; 6maletic.2@osu.edu citation for this article. judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e., 2023, utah geosite—the salina canyon unconformity, a classic example of missing time: geology of the intermountain west, v. 10, p. 169–183, https://doi.org/10.31711/giw.v10.pp169-183. introduction unconformities are stratigraphic contacts between rock layers where nondeposition or extensive erosion of the underlying older rock unit occurred before deposition of the overlying younger rock, indicating a gap in time when sedimentation was not continuous. one type of unconformity—an angular unconformity—is easily identified in the field, because the rock layers above and below the unconformity are not parallel. as ancient surfaces of erosion, unconformities are important to geology because they signify a disruption in the typical, uninterrupted deposition of sedimentary layers. unconformities help geoscientists understand geologic time by bracketing the age range of geologic events. salina canyon, utah (figure 1), is home to one of the most striking angular unconformities in the state. many geoscientists travel to see this unconformity just east of the city of salina and the salina city park. the salina canyon unconformity exhibits many of the classic features of unconformities. in addition, the erosional surface itself displays relief, and hence, ensuing depositional onlap. geographically it marks the eastern extent in utah of the sevier orogeny, a mountain building event from about 170 to 40 million years ago. previous work has been instrumental in our understanding of this angular unconformity at salina canyon. dutton (1880) published the earliest description of the salina canyon unconformity. the first detailed fieldwork at salina canyon was conducted by spieker (1946, 1949), first with the u.s. geological survey and later as a faculty member at the ohio state university. spieker described the field relationships between rocks both below and above the unconformity. in 1947, spieker 170 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 moved ohio state’s field camp program from tennessee to snow college in ephraim in sanpete valley (weiss, 1995). for decades, ohio state’s field camp (still based in ephraim) has visited the salina canyon angular unconformity, colloquially known to these geoscientists as the “spieker unconformity.” the salina canyon unconformity has been described by numerous additional workers. gilliland (1963) attributed the large-scale folding in the sanpete-sevier valley region to the sevier orogeny, whereas witkind (1982, 1983, 1994) considered diapiric action to be the cause of younger units pinching out against the regional large-scale fold. the unconformity has been described and interpreted in field guides (e.g., lawton and willis, 1987) and in geologic maps of the area (e.g., willis, 1986). additional research characterizing the unconformity and associated bedrock units (judge and krissek, 2003; werthmann, 2018) has added to the story of the unconformity from a stratigraphic and sedimentologic perspective. this paper aims to (1) provide the physical location and geologic setting for the salina canyon unconformity, (2) outline the geologic characteristics of this unconformity, which illustrates many classic stratigraphic and sedimentologic features of erosional surfaces, and (3) summarize recent research on the unconformity regarding paleosol (ancient soil) formation and the sedimentary characteristics along the boundary. location the salina canyon unconformity is in northern sefigure 1. (a) location of salina canyon in relation to the city of salina, i-70, and major state highways. the area in the yellow box is the primary focus of this field guide. yellow arrows indicate the driving route from downtown salina to the unconformity. the red “p” denotes possible parking. (b) inset map shows the transect where the salina canyon unconformity is well exposed. stations 1, 2, and 3 are described in the text. modified from google earth, utah agrc. 171 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 vier county, central utah (figure 1). outcrops visited in this guide are within the wasatch plateau, which is immediately east of the sanpete-sevier valley. the unconformity is exposed at the southern end of cedar mountain, which lies a few miles east of salina, the northern segment of fishlake national forest. the unconformity is best exposed just north of interstate 70 (i-70) at the entrance to soldier canyon. the dirt access road to the unconformity is 3.8 miles (6.1 km) east of state street (u.s. highway 89 [u.s. 89]) in salina and just 2 miles (3.2 km) east of salina city park. beautiful exposures of the unconformity can be seen along an east-west transect for a minimum of 1 mile (1.6 km), although the surface continues farther to the east (figure 2a). several of the most spectacular locations showing image-worthy angular discordance and other exceptional features are located within 0.25 mile (0.4 km) of each other. these stations are described in detail in the stratigraphy section: • station 1 (well-developed paleosol): 38°56.049'n., 111°48.584'w. (figure 2b). • station 2 (mine adit): 38°56.033'n., 111°48.549'w. (figure 2c). • station 3 (stunning photo opportunity): 38°56.113'n., 111°48.404'w. (figure 2d). suggested driving directions the salina canyon unconformity is easily accessible from any cardinal direction because the nearby city of salina is at the crossroads of several major state highways and i-70 (figure 1). each of the directions below end on e. main street; from there, more detailed directions are provided in the last paragraph of this section. • when driving from the north or south via u.s. 89 or when driving from the west via u.s. route 50, proceed to the intersection of state street and e. main street in downtown salina. the famous mom’s cafe (voted one of the best places to eat in america and featured in national geographic explorer magazine) sits on the southeast corner of this intersection. proceed east on e. main street. (follow directions below.) • when driving from the west or east via i-70, take exit 56 (salina). proceed north on u.s. 50/u.s. 89 (state street) to the intersection of state street and e. main street in salina. (follow directions below.) the pull-off for the salina canyon unconformity is 3.8 miles (6.1 km) from the intersection of state street (u.s. 89) and e. main street. drive east on e. main street and proceed three blocks to s. 300 e. turn south on s. 300 e.; a small, wooden sign at this intersection marks this intersection as the turn-off for salina city park. s. 300 e. (old highway 10) gently curves to the southeast and finally to the east. on the south side of the road, visitors will pass salina city park, which has two entrances/exits. the pull-off for the salina canyon unconformity is 2 miles (3.2 km) ahead. proceed east to a “y” junction at 38°55.964'n., 111°48.673'w. vehicles with high clearance can proceed left at the “y” junction and park along the dirt track once it flattens out. vehicles lacking high clearance should park on s. 300 e. do not park too close to the tunnel, which is just ahead, about 520 feet (160 m). note: visitors have driven too far when the road curves to the south and turns into a one-lane tunnel as it passes under i-70. visitors who wish to observe a large segment of the salina canyon unconformity and stations 1, 2, and 3 simultaneously can do so from the south side of i-70. when on s. 300 e., drive south under the i-70 tunnel toward the entrance to soldier canyon. proceed immediately east on the frontal road before entering soldier canyon, and there will be opportunities for a large-scale perspective and transect photographs. structural geology physiographic provinces salina canyon is in a region that exposes the complex mesozoic and cenozoic geology of central utah (spieker, 1936, 1946, 1949; villien and kligfield, 1986; anderson and others, 2001; schelling and others, 2007). an older compressive phase (145 to 38 ma) was followed by younger extension (post 38 ma), creating exceptional structural overprinting (mattox and weiss, 1987; decelles and others, 1995; constenius, 1996; decelles, 2004; judge and others, 2005; decelles and coo172 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 gan, 2006). the salina canyon unconformity lies in the transition zone between the basin and range province to the west and the colorado plateau to the east (figure 3; stokes, 1977). the transition zone is within the utah hingeline, a zone of structural weakness and repeated tectonic reactivation that runs generally north-south through the state and marks the eastern limit of the sevier fold-thrust belt (stokes, 1976; ritzma, 1981; schelling and others, 2007) as well as the boundary between thin and thick paleozoic limestone successions. contractional tectonics deformation from the sevier orogeny was a result of compressive stress established along the western margin of north america (decelles, 2004). in central utah, the pulses of thrusting spanned about 80 million years (decelles and coogan, 2006). multiple research (i.e., structural geology and tectonics, stratigraphy, geochronology, and geophysics) guides our understanding of the timing of deformation in the region and of the regional paleostress orientations (decelles and coogan, 2006; schelling and others, 2007). the sanpete-sevier valley antiform (ssva), also called the salina anticline (schelling and others, 2007), is one of the dominant geologic features of central utah and is exposed in the sanpete and sevier valleys (figure 3). a north-plunging, upward arching fold, the ssva is figure 2. (a) aerial photograph of the location of stations 1, 2, and 3 in salina canyon. view to the northeast. inset shows a clearer view of the outcrop for stations 1 and 2. note the adit in the center of the photograph. modified from google earth. (b) station 1, where a well-developed paleosol (purplish pink) is present below the unconformity. view to the east. (c) station 2 depicts the vertical beds of the jurassic twist gulch formation (average attitude of 028°, 85° se; n. 28° e., 85° se) under the unconformity and the overlying paleogene fluvial sandstones (average attitude of 320°, 12° sw; n. 40° w., 12° sw). view to the north. (d) station 3, which is the best-known photogenic locality of the salina unconformity. strata here have similar attitudes to station 2. view to the northeast. 173 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 reported as 50 to 70 miles (80-113 km) long with vertical structural relief up to 20,000 feet (6100 m), varying from 2 to 4 miles (3-6 km) wide and opening toward the south (gilliland, 1963; anderson and others, 2001). its location and sheer size play an important role in petroleum resources of central utah. covenant field in sevier county is along the east limb of the ssva (chidsey and others, 2007), and a similar field, providence, lies to the northeast of covenant. in these regions, the subsurface geology includes a series of imbricate thrusts, fault-bend folds (with well-developed hanging-wall anticlines), and backthrusts that create a triangle zone within the core of the ssva (schelling and others, 2007). here, the jurassic navajo sandstone and temple cap formation (white throne member) are the producing reservoirs, and the jurassic arapien formation acts as the reservoir seal (chidsey and others, 2007; schelling and others, 2007; sprinkel and others, 2011). several researchers hypothesized that buckling associated with sevier thrusting was the primary cause of ssva folding and related deformation. lateral compression is likely the mechanism responsible for the deformation (gilliland, 1963; lawton, 1985; willis, 1986; weiss, 1994). extensional tectonics the region also experienced a change in the stress regime from east-west crustal shortening to extension. two distinct episodes of cenozoic extension overprint previous compressive deformation (constenius, 1996; judge and others, 2005). rowley and others (1998) corfigure 3. simplified map on left shows the major physiographic provinces of utah, including the relationship of the transition zone to the basin and range, colorado plateau, and middle rocky mountains provinces. the blue line represents the eastern extent of sevier orogenesis in utah, whereas the red line is the axial trace of the ssva. modified after utah geological survey (2018). map on right illustrates the major geomorphic features of the sanpete-sevier valley area. the red line shows the axial trace of the ssva. 174 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 related these extensional periods with two magmatic episodes: (1) an episode of pre-middle miocene extension (also referred to as pre-basin and range extension), and (2) the more well-known and well-documented basin and range extension that began in late miocene time and continues to this day. regional structures on the wasatch plateau that demonstrate extensional tectonics include normal faults and extensional fractures (opening mode joints and calcite veins) that overprint the unconformity. in addition, the formation of the wasatch monocline in salina canyon is interpreted as a roll-over fold from a half-graben caused by this regional extension (judge and others, 2005, in press; judge, 2007). geologic history of salina canyon the salina canyon uniformity captures millions of years of earth history and tectonic deformation in the transition zone of central utah. below is a summary of the geologic history of the area, incorporating both sedimentation and age dating to create a timeline of events. stratigraphy and sedimentation the middle jurassic and cretaceous stratigraphy of central utah was controlled by mountain building, creating a region of dynamic sedimentation. depositional packages can be divided into four general time intervals: (1) jurassic foreland basin development (perkes and morris, 2011; sprinkel and others, 2011), (2) cretaceous sevier orogenesis (villien and kligfield, 1986; decelles and others, 1995; decelles and coogan, 2006; schelling and others, 2007), (3) paleogene uplifts and basins (dickinson and others, 1988), and (4) miocene to recent regional extension (mattox and weiss, 1987; constenius, 1996; judge and others, 2005). in salina canyon, units representing each of these four intervals are exposed along an east-west transect through the area. our focus is on the jurassic, cretaceous, and paleogene units adjacent to the unconformity (figure 4). strata in the core of the ssva were deposited during the jurassic. the arapien formation is interpreted as an open marine, marginal marine, and restricted marine deposit, deposited in a developing foredeep basin as part of the jurassic carmel-twin creek seaway (sprinkel and others, 2011; hintze and kowallis, 2021; d.a. sprinkel, utah geological survey, written communication, 2023). the age range from palynomorphs for the uppermost member of the arapien, which is exposed in salina canyon, is about 164 to 162 ma (sprinkel and others, 2011). overlying the arapien is the jurassic twist gulch formation, which is interpreted as primarily an alluvial to shallow marine unit in salina canyon, derived from highlands to the west and deposited into the arapien basin (a subbasin within the regional foreland basin system; perkes and morris, 2011). its age range from u-pb geochronology of detrital zircons and supported by palynomorphs is about 165 to 155 ma (perkes and morris, 2011). cretaceous units comprise the limbs of the ssva (spieker, 1946, 1949; gilliland, 1963; schelling and others, 2007). cretaceous units are a thick sequence of clastic sediments, derived from the sevier orogenic highlands to the west, that were deposited in a foredeep basin (villien and kligfield, 1986; decelles and others, 1995; decelles and coogan, 2006; schelling and others, 2007). these cretaceous units are tied directly to multiple east-propagating thrusting events (decelles and coogan, 2006). sedimentation from the orogenic highlands to the west record a terrestrial to marine transition from west to east. in salina canyon, cretaceous units include the cedar mountain formation and the indianola group (san pitch, sanpete, allen valley, and funk valley formations), which range in age from about 145 to 75 ma (spieker, 1949; lawton and willis, 1987; sprinkel and others, 1999; decelles and coogan, 2006). the north horn formation spans the cretaceous/paleogene boundary (figure 4). sanpete-sevier valley antiform and the unconformity the ssva underwent several pulses of deformation and uplift during its evolution (gilliland, 1963). seismic interpretations, along with studies of exposed strata, indicated that the ssva was initiated between about 80 to 70 ma (gilliland, 1963; schelling and others, 2007) after deposition of the funk valley formation (about 80 ma; lawton, 1985; lawton and others, 1997). it may have been actively folding during deposition of the sixmile canyon formation (lawton and others, 1997), but it 175 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 was uplifted prior to deposition of the basal beds of the north horn formation (schelling and others, 2007). after ssva formation and erosion, it was covered by a mile-thick (1.5 km) package of lacustrine, fluvial, and volcanic deposits that created unconformable relationships with the dipping strata of the ssva (spieker, 1946, 1949; gilliland, 1963). in salina canyon, these younger paleogene units include the flagstaff, colton, green river, and crazy hollow formations. volcaniclastics and volcanic units overlie the crazy hollow. due to the presence of unconformities between dipping ssva strata and overlying strata in central utah, researchers hypothesize that ssva uplift was episodic, with each episode marked by an angular unconformity (gilliland, 1963). cenozoic overprinting in salina for central utah, constenius (1996) proposed that south of 40° n. latitude, extensional tectonics (pre-basin and range extension due to the gravitational collapse of the sevier orogenic belt) began between 40 and 35 ma. judge and others (2005) constrained the timing of sanpete-sevier extension to 38.0 ± 0.2 ma from radiometric dates for an ash-flow tuff in the aurora formation, which onlaps the wasatch monocline flexure adjacent to western salina canyon. cline and bartley (2007) noted evidence for extension in sevier valley, south of salina canyon. overall, this extensional regime produced the normal faults that cross-cut the salina canyon unconformity, as mapped by willis (1986). recognition of the unconformity subaerial unconformities, like the one in salina canyon, can be recognized in the field by a suite of characteristics: angular discordance, a gap in the fossil record, karst features (in carbonate settings), paleosol formation, and basal conglomerates (shanmugam, 1988). the salina canyon unconformity is an instructive teaching locality because it contains most of these classic features. angular discordance the angular unconformity is easily observed at the outcrop. at several localities (especially stations 2 and 3), the jurassic twist gulch formation beds are nearly vertical below the unconformity (figures 2c and 2d). at these photogenic stations, the twist gulch is a red, gray, tan/white, and sometimes mottled sequence of interbedded sandstones, mudstones, and siltstones. sandstones vary from fine to coarse grained, subrounded to subangular, and are well sorted. they contain quartz/ rose quartz, feldspar, biotite, red jasper, opaque/black figure 4. generalized stratigraphic column for salina canyon. jurassic, cretaceous, and paleogene strata are exposed along the transect discussed in this manuscript and outlined in figures 1 and 2. modified from lawton and willis (1987). cgl = conglomerate; ls = limestone; mdst = mudstone; sh = shale; slts = siltstone; ss = sandstone. 176 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 lithics, and calcareous cement. the unit contains graded beds and parting lineation. although determining facing (i.e., younging to the east) is sometimes a challenge for the beginning geology student at station 2, students recognize the wonderfully preserved ripples, climbing ripples, cross-laminations, and cross-bedding at station 3. to the east of station 3, progressively younger units are exposed below the unconformity, beginning with the cretaceous cedar mountain formation and ending with the funk valley formation (figures 5a and 5b). there is an obvious change in the bedding dip of these units from west to east as they progressively pass from nearly vertical to subhorizontal, eventually becoming subparallel to those units that overlie the unconformity. the cause of this gradual change in bedding dip is structural. the dipping jurassic and cretaceous units below the unconformity form the eastern limb of the ssva (gilliland, 1963; schelling and others, 2007), and this eastern limb gradually is less steep as you transect west to east through salina canyon. above the unconformity, beds pinch out to the west against the erosional surface, demonstrating onlap. salina canyon is an example of a progressive unconformity since overlying strata onlap onto the regional paleotopographic high of the ssva. these strata have a shallow dip, observed from a distance. we interpret the small ledges of sandstone above the unconformity from station 1 to station 3 as colton formation beds because of their petrographic similarities to known colton localities north of salina (north of stone quarry and near willow creek). the unconformity exhibits slight relief; therefore, in this interpretation the flagstaff formation is missing where beds assigned to the colton rest directly on the unconformity. these basal colton sandstones are gray to tan, but younger colton strata include interbedded mudstone, shale, and limestone. sandstones vary from fine to medium grained, subrounded to subangular, and moderately to well sorted. they contain quartz/rose quartz, feldspar (plagioclase and microcline), biotite, muscovite, amphibole, red jasper, malachite, chert, opaque/ black lithics (in thin section, igneous, sedimentary, and metamorphic grains), and calcareous cement with minor iron oxides. the unit has planar cross-bedding, various sizes of trough cross-bedding, loading, pinch-andswell geometries, and lenticular channel scours. age relationships the salina canyon unconformity does not represent an equal gap in geologic time along its west to east transect. in the west, this gap in geologic time is greater than 107 million years, decreasing toward the east to about 39 million years and finally to less than 17 million years. the age range for the unconformity can be constrained by using the ages of the units both below and above the surface. below the unconformity, the middle jurassic arapien formation is exposed to the west of station 1 in salina canyon, where they have an age range of about 164 to 162 ma based on regional palynology (sprinkel and others, 2011). the arapien shows extreme diapiric deformation (witkind, 1982, 1983, 1994), thus making for challenging field relationships and interpretations. beds of the upper jurassic twist gulch near station 3 have an age range of 159.5±5.1 ma (perkes and morris, 2011). above the unconformity near these stations, colton sandstones are exposed but have not been radiometrically dated. the colton in salina canyon has been assigned a late paleocene to early eocene age based on fossil evidence (fouch and others, 1982; willis, 1986). therefore, at stations 1 and 2, the unconformity spans approximately 107 million years (from ca. 160 to 53 ma). to the east in salina canyon, the age range for the unconformity is less, because younger cretaceous units are below the surface. the cedar mountain formation and indianola group are exposed to the east of the twist gulch formation (figure 5) and have not been radiometrically dated in salina canyon. their approximate age is based on fossil evidence and relative age relationships. east of station 3 the flagstaff formation rests unconformably on the sanpete formation. here, the unconformity spans about 39 million years (from the late cretaceous to the early eocene, about 92 to 53 ma). still farther to the east (beyond the geologic map limit of figure 5) where the angular unconformity becomes a disconformity, beds of the north horn formation rest on the funk valley formation. this disconformity spans 177 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 about 17 million years (within the late cretaceous; ca. 87 to about 70 ma; schelling and others, 2007). paleosols paleosols are ancient soils that leave behind traces of past environments. these deposits can provide information on the climate, depositional environment, and flora/fauna present at the time the soils developed. they are commonly located at unconformities where little information can be inferred about the gap in the rock record (kraus, 1999). a well-developed paleosol at station 1 provides an opportunity to better understand the salina canyon area during formation of the unconformity. at station 1, the strata was divided into five distinct zones based on mottling (after retallack, 1988), color, texture, burrow abundance, carbonate nodule abundance, and stage of paleosol development (figures 6a and 6b; after retallack, 1997). other characteristics, such as the presence or absence of drab-haloed root traces or hematite/goethite (after kraus and hasiotis, 2006), were also noted. table 1 summarizes the characteristics of each zone. werthmann (2018) interpreted the paleosol at salina canyon to be two stacked paleosols that most closely resemble vertisols (figure 6b). the older paleosol 1 comprises zones 1 through 3. it contains an abundance of burrows in zones 2 and 3, implying these portions of the soil were near the surface. prominent mottling, commonly oriented in vertical streaks, is aligned with the bedding in the underlying twist gulch formation and is attributed to organic matter within the vadose zone (smith and others, 2008). there is gradual boundaries between each zones, suggesting high connectivity and internal deformation (retallack, 1997). paleosol 2, the younger paleosol, consists of zones 4 and 5. there are fewer burrows and root traces, as well as a decrease in mottling. there is a clear boundary between zones 3 and 4, which marks a change from red mottling to the bulbous structure characteristic of zone 4. zone 5 is very weakly developed. figure 5. (a) aerial photograph of salina canyon with superimposed geologic units. modified from google earth; willis (1986). yellow stars denote the extent of the cross section in figure 5b. (b) idealized cross section through salina canyon depicting the progressive unconformity, onlap of paleogene strata onto paleotopography, and the folded ssva. the cross section was constructed for the time of flagstaff/colton deposition and prior to deposition of the green river formation and subsequent extensional events. jtg = twist gulch fm; kcm = cedar mountain fm; ks = san pitch fm; ksp = sanpete fm; pgf = flagstaff fm; pgc = colton fm; pggr = green river fm; qms = landslide deposits; qal = alluvial-fan deposits. pg represepents paleogene in the symbol pgf, pgc, and pggr. 178 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 perhaps the most interesting feature of these paleosols is the presence of naktodemasis bowni (figures 6c and 6d), an adhesive meniscate burrow (amb) defined as “burrows composed of distinct, ellipsoid packets that contain indistinct, meniscate backfill” (smith and others, 2008). defined by smith and others (2008), naktodemasis has since been noted as a junior synonym of taenidium (buatois and others, 2017). this is the first report of amb at salina canyon, and these burrows are found without evidence of other organisms in the soil and in the presence of root traces. smith and others (2008) concluded that amb were formed by burrower bugs (hemiptera: cydnidae) and cicada nymphs (hemiptera: cicadae). we conclude that these insects probably produced the burrows in the station 1 paleosol. werthmann (2018) further classified these burrow-filled zones as a or upper b soil horizons using estimations of the soil depth where these insects typically live and the moisture content of the soil (smith and others, 2008). figure 6. (a) generalized stratigraphic column of the paleosol at station 1. the internal features of the strata are depicted in the key: channels/scours, cross-bedding, mottling, burrows, root traces, and carbonate nodules. for mottling, the ellipses within each zone are organized by the abundance of color. the largest ellipse represents the most abundant mottling color, whereas the smallest ellipse represents the least abundant color. (b) station 1 correlated to the stratigraphic column. paleosol development for each zone is labeled (i.e., strongly developed, moderately developed, etc.). two stacked paleosols are shown by respective yellow arrows, separated by the dashed yellow line. the blue dashed line near the top of the photograph marks the salina canyon unconformity, above which is subhorizontal colton strata. view to the east. (c) line drawing of adhesive meniscate burrow (amb) showing the morphology of the burrow. modified after smith and others (2008). (d) amb examples from within zone 3 at station 1. a pencil tip at the bottom of the photograph provides scale. view to the east. 179 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 basal conglomerates on a regional scale, paleotopography on the unconformity has been demonstrated by onlap of strata. at outcrop-scale, the erosional surface at the contact is undulatory. at station 2, small-scale channels and scours are present along the unconformity (figure 7a) and are infilled with basal conglomerates. this reflects erosion and paleoflow on the boundary surface. twist gulch beds contain small-scale paleoflow indicators (figure 7b), whereas the colton fluvial sandstones above the unconformity contain large, planar to slightly festoon cross-bedding, as well as small-scale and broad trough cross-bedding (figure 7c). paleocurrent analysis for the area near station 2 shows a mean vector of 321° (n. 39° w.), indicating local paleoflow to the northwest along the regional paleoslope (figure 7d). this data agrees with all measured flow directions in the colton formation in the sanpete-sevier valley region (judge and krissek, 2003; judge, 2007). for decades, previous workers concluded that the colton formation was sourced primarily from the south-southeast as it onlapped onto the paleotopography of the unconformity (e.g., stanley and collinson, 1979; chapman, 1982; zawiskie and others, 1982; dickinson and others, 1986; judge and krissek, 2003; judge, 2007). more recent work concentrated on detrital zircons in the colton formation of the uinta basin and used u-pb ages to interpret a source area to the south-southwest, suggesting that sediment was transported to central utah from arizona and california by a paleodrainage system named the california paleoriver (davis and others, 2010; dickinson and others, 2012). additional features there are several small mine adits in the area easily viewed along the trace of the unconformity. the geographic area of stations 1 through 3 is part of the salina creek mining district. the lead hill mine is the adit immediately adjacent to station 2 and was the only productive mine in the area (perry and mccarthy, 1976). historically, small amounts of lead ore was produced from 1908-1912 and in 1944. perry and mccarthy (1976) identified both beds below the unconformity and the channel sandstones above the unconformity as the mining targets. minerals identified include: galena, cerussite, sphalerite, pyrite, chalcocite, malachite, azurite, and celestite (perry and mccarthy, 1976; willis, 1986). perry and mccarthy (1976) reported that the mineralized zone of the lead hill mine was 0.5 to 6 feet (0.1-1.8 m) thick and was mined for nearly 600 feet (180 m) underground. geologic uniqueness if you are driving through salina, utah, then the salina canyon unconformity is only a brief stop outside of town. it is well worth the visit for professional geoscientists, rockhound enthusiasts, and outdoor naturalists. below are several reasons why the unconformity is special: 1. outcrops provide spectacular views of classic features characteristic of unconformities. the outcrops near stations 1, 2, and 3 are easily accessible and do not require much climbing, so most friends and family members can enjoy them. zone level of development burrows root traces nodules ped type 5 very weakly none identified none identified absent none 4 moderately present present present blocky 3 very strongly present present present granular 2 strongly present present present granular 1 strongly none identified none identified present granular table 1. basic characteristics of each of the paleosol zones at station 1, following the classification schemes of retallack (1988, 1997). 180 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 2. salina canyon is an example of a progressive unconformity. below the erosional surface, the bedding dips change from vertical in the west to horizontal toward the east. the overlying strata progressively onlap from the east onto the paleohigh of the ssva. when you are at the outcrop on the north side of i-70, it can be difficult to view the “big picture.” however, if you drive south under the i-70 tunnel toward soldier canyon and then proceed immediately east on the frontal road, you will have photo opportunities for the entire transect. 3. salina canyon geology represents the eastern extent of sevier orogenesis in the region. spieker (1949) wrote, “no less than 5,000 and possibly more than 7,000 feet of beds come in and flatten out beneath the unconformity, and the unconformity itself passes eastward into a disconformity that is not easy to discern.” spieker (1949) first noticed this relationship, but since his time, the geosciences have witnessed the advent of plate tectonics and our increased understanding of sevier mountain-building. salina canyon can now be better placed in a comprehensive regional context. in a short transect, visitors can observe the near vertical deformed strata that were folded as part of the ssva, flattening to the east. these near horizontal strata represent undeformed units not impacted by the lateral compression of sevier mountain-building, marking the eastern limit of the sevier orogeny in utah. figure 7. (a) undulatory erosional surface at station 2 showing small channel/scour with basal conglomerate. view to the north. (b) paleoflow and facing indicators in the twist gulch formation are best observed at station 3. view to the north-northeast. (c) colton fluvial sandstones above the unconformity at station 2 show trough cross-bedding. (d) rose diagram of paleocurrent analysis (mean vector = 321°) of paleogene fluvial sandstones above the unconformity at station 2. 181 utah geosite—the salina canyon unconformity, a classic example of missing time judge, s., werthmann, e., millan, c., braunagel, m., and maletic, e. geology of the intermountain west 2023 volume 10 acknowledgments this work was supported by the college of wooster department of earth sciences and the ohio state university school of earth sciences geology field camp. we appreciate wooster students peter hurst, eduardo luna, and mara sheban for their help in the field. thanks to a. lanier (formerly a wooster student; now ohio department of national resources) and n. wiesenburg (wooster) for assistance in the rock prep lab. we are grateful to ohio state field camp colleagues w.i. ausich, d.h. elliot, w.a. griffith, l.a. krissek, and t.j. wilson, and to, utah geological survey geologists d.a. sprinkel and g.c. willis for rich and enjoyable discussions on utah stratigraphy. we welcomed the detailed suggestions from informal reviewers d.h. elliot (ohio state), r. faatz (snow college), and m.a. wilson (college of wooster), and from formal reviewers r.f. biek, m. milligan, and p.j. nielsen (all utah geological survey). their time and effort on the manuscript is much appreciated. this manuscript was originally part of the 2019 utah geological association (uga) publication 48 edited by m. milligan, r.f. biek, and p. inkenbrandt (all of the utah geological survey), but later transferred to the geology of the intermountain west for publication. we would like to thank the editors of uga publication 48 for their work on this manuscript. references anderson, r.e., diehl, s.f., and barnhard, t.p., 2001, age and style of deformation and stratal thinning at the transition, wasatch plateau to great basin, central utah: rocky mountain geology, v. 36, no. 1, p. 49–80. buatois, l., wisshak, m., wilson, m.a., and mángano, g., 2017, categories of 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survey special study 97, 21 p. sprinkel, d.a., doelling, h.h., kowallis, b.j., waanders, g., and kuehne, p.a., 2011, early results of a study of middle jurassic strata in the sevier fold and thrust belt, utah, in sprinkel, d.a., yonkee, w.a., and chidsey, t.c., jr., editors, sevier thrust belt—northern and central utah and adjacent areas: utah geological association publication 40, p. 151–172. stanley, k.o., and collinson, j.w., 1979, depositional history of paleocene-lower eocene flagstaff limestone and coeval rocks, central utah: american association of petroleum geologists bulletin, v. 63, no. 3, p. 311–323. stokes, w.l., 1976, what is the wasatch line?, in hill, j.g., editor, geology of the cordilleran hingeline: rocky mountain association of geologists symposium, p. 11–25. stokes, w.l., 1977, physiographic subdivisions of utah: utah geological and mineral survey map 43, scale 1:2,400,000. utah geological survey, 2018, physiographic provinces: online, 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7.5-minute quadrangle, sevier county, utah: utah geological and mineral survey map 83, scale 1:24,000. witkind, i.j., 1982, salt diapirism in central utah, in nielson, d.l., editor, overthrust belt of utah: utah geological association publication 10, p. 13–30. witkind, i.j., 1983, overthrusts and salt diapirs, central utah: geological society of america memoir 157, p. 45–59. witkind, i.j., 1994, the role of salt in the structural development of central utah: u.s. geological survey professional paper 1528, p. 1–145. zawiskie, j., chapman, d., and alley, r., 1982, depositional history of the paleocene-eocene colton formation, north-central utah, in nielson, d.l., editor, overthrust belt of utah: utah geological association publication 10, p. 273–284. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 10 2023 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. snow drought and monsoon floods: hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah erich r. mueller, garrett p. sudweeks, shadrach a. ashton, and micah c. olson theme issue engineering geology and geohazards of utah utah geological association annual field conference october 22, 2022 salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover flooding of residential areas in cedar city, utah, following an intense thunderstorm on july 26th, 2021. photograph by shawn glover, courtesy of st. george news/stgnews.com. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 10 2023 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2022–2023 uga board president rick ford rford@weber.edu 801.915.3188 president-elect eugene syzmanski eugenes@utah.gov 801.537.3364 program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 treasurer aubrey dereuil aubrey@zanskar.us 850.572.2543 secretary tom chidsey tomchidsey@gmail.com 801.824.0738 past president john south johnvsouth@gmail.com 801.367.9292 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david 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utah geological survey adammckean@utah.gov rick chesnut terracon rick.chesnut@terracon.com geology of the intermountain west an open-access journal of the utah geological association volume 10 2023 93 abstract water year 2021 was a year of extremes in the cedar valley watershed of southern utah, with snow drought resulting in extremely low snowmelt runoff of coal creek and intense monsoon rainfall resulting in several floods in different parts of the valley. winter snow accumulation was depressed throughout southern utah, perhaps due to la nina conditions affecting winter storm trajectories. coal creek, the principal stream providing surface water to cedar valley, typically receives most of its annual flow from snowmelt runoff, but in 2021 had a peak snowmelt discharge 15% to 25% of that recorded in the previous two years and the third lowest snowmelt runoff on record. following this extremely low snowmelt runoff period, more than 10 floods of coal creek occurred following monsoon storms in july and august that exceeded the 2021 snowmelt peak. additionally, several thunderstorms produced rainfall rates in exceedance of the 100-year event and induced flooding within cedar city and the town of enoch. flood inundation modeling using hec-ras and high-resolution topographic data showed good agreement with field and pubic-survey data on the high-water stage during the enoch flooding, and demonstrated that the flooding was likely exacerbated by the low topography and limited drainage potential in flooded areas. whereas the monsoon storms improved soil moisture and helped alleviate drought conditions, they also resulted in urban flooding and did little to replenish the regional water supply. snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah erich r. mueller1,2, garrett p. sudweeks1,3, shadrach a. ashton1,4, and micah c. olson1,5 1department of geosciences, southern utah university, cedar city, ut 84720 usa 2erichmueller@suu.edu, 3garrett@kairosgeodetics.com, 4shadashton@gmail.com 5olsonmicah86@gmail.com citation for this article. mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c., 2023, snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah: geology of the intermountain west, v. 10, p. 93–111, https://doi.org/10.31711/giw.v10.pp93-111. introduction streamflow and flooding in southern utah occur through a combination of snowmelt, rainfall, and rainon-snow (lund, 1992; wilkowske and others, 2006; lund and others, 2010). for perennial or intermittent streams draining higher elevation terrain, groundwater inputs contribute the seasonal baseflow, but floods typically occur from more rapid surface runoff during snowmelt or intense rain storms. from a management perspective, streams and rivers provide a major component of the water supply as both surface runoff and a source of groundwater recharge to downstream basins, but also present a hazard as floods are common throughout the region and often impact developed areas. for larger watersheds with headwaters in higher elevation terrain, snowmelt plays an important role in the regional water supply because most streamflow is derived from direct snowmelt runoff and snowmelt-derived recharge 94 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 of groundwater and stream baseflow (julander and clayton, 2018). on the other hand, the largest floods are typically generated by convective thunderstorms in the late summer and early fall or via winter rain events (wilkowske and others, 2006). for example, the virgin and santa clara rivers that merge near st. george, utah, have experienced large floods due to warm pacific storm systems interacting with terrain to produce sustained rain and rain-on-snow at higher elevations (bardsley and julander, 2005; wilkowske and others, 2006). flash floods from intense convective thunderstorms also cause flooding across basins of many scales, but often have their greatest impact on smaller watersheds due to the often-isolated nature of storm development (woolley, 1946; berwick, 1962; smith and others 2019); these types of “cloudburst” floods have long been recognized as a frequent cause of flooding throughout utah (woolley, 1946). in this study, we explore the hydrological events during water year 2021 in cedar valley, utah, that both exacerbated drought conditions due to a lack of significant snowmelt, and caused extensive flooding during multiple events within different areas of the valley. we use long-term hydrological records from coal creek, the principal stream and primary water source draining into cedar valley, to document the long-term watershed hydrology and evaluate water year 2021 relative to nearly 100 years of streamflow measurements. we also use precipitation data to estimate return frequencies for three flood events that occurred due to convective thunderstorms, and hydraulic modeling to evaluate the flood impacts in an urbanized area during one of those events. cedar city is one of the fastest growing micropolitan areas in utah, and a limited water supply and potential for flooding in developing areas are prominent concerns. within cedar city, numerous flood-control projects have been implemented, such as levees and diversion structures, to alleviate flooding during periods of high streamflow. additionally, several projects have been implemented so that any excess streamflow can be diverted into basins for aquifer recharge. water year 2021 provides a perspective on which to view potential challenges in water management for cedar city and cedar valley in terms of both drought and floods. background hydrology of the cedar valley watershed the cedar valley watershed is a closed basin in eastern iron county, utah. the watershed extends from the harmony hills and markagunt plateau in the south, to the black mountains in the north (brooks and mason, 2005). the valley is a graben bounded by normal faults associated with basin and range extensional faulting, and all streamflow drains internally toward quichapa lake in the southern part of the basin and rush lake in the northern part of the basin (brooks and mason, 2005). the primary surface water source to the valley and largest of the contributing watersheds is coal creek, which debouches from the markagunt plateau at cedar city (figure 1). the headwaters of coal creek occur at the high elevation rim (greater than 10,000 feet) of the plateau in cedar breaks national monument. as a result, significant winter snowfall feeds the perennial flow of coal creek and produces the bulk of the streamflow (julander and clayton, 2018). aside from shirts creek, which is considerably smaller than coal creek, the remaining watersheds emerging from the mountainous areas along the edges of the valley are ephemeral (brooks and mason, 2005). whereas some of these watersheds may experience a minor snowmelt pulse some years, they are most likely to generate significant streamflow and flooding during convective summer thunderstorms. coal creek has a long history of flooding; the first recorded flood occurred on september 3, 1853, and caused extensive damage in cedar city (lund, 1992). most of the development in the valley is focused near cedar city and the nearby town of enoch, and the focus of this study is on the streamflow hydrology of coal creek and the precipitation climatology of flooding during rain events affecting those towns. for the coal creek watershed, the largest volume of water is supplied during the snowmelt period that typically lasts from spring through early summer. alternatively, the largest magnitude floods occur during intense convective rain events in the late summer and early fall as part of the north american monsoon. floods from these storms can cause flooding of coal creek or any number of other watersheds and ephemeral streams in the area. for coal creek, this imparts a somewhat 95 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 unique hydrology with respect to water resources and hazard mitigation: wherein the water supply is dependent on snow during the winter and the resulting snowmelt flood pulse, the primary flood hazards result from short-duration and typically localized intense precipitation during the monsoon season. during the period of record, significant floods of coal creek have not occurred during the winter, unlike in the virgin river system where rain-on-snow events are more common and the mean basin elevation is significantly lower. coal creek has streamflow records dating back to 1916, and provides important context to evaluate the unique hydrology of 2021. effects of el nino southern oscillation on winter precipitation previous studies have shown a correlation between the phases of the el nino southern oscillation (enso) and winter precipitation in the western united states (redmond and koch, 1991; cayan and others, 1999; clark and others, 2001; jin and others, 2006; tamaddun and others, 2017). in particular, areas in the southwestern united states tend to experience increased winter precipitation during el nino years and decreased winter precipitation during la nina years (brown and comrie, 2004). the opposite signal is apparent in the northwestern part of the united states. importantly, enso phases figure 1. map of study area showing the locations of the precipitation and streamflow measurement stations used in this study; mesowest and snotel site names are labeled. the coal creek watershed is outlined upstream from the u.s. geological survey stream gage just upstream from cedar city. 96 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 in june through november can be a predictor of the subsequent winter snowpack and spring runoff (redmond and koch, 1991; oubeidillah and others, 2011). weak la nina conditions preceded the winter snow accumulation season in water year 2021, and we explore the influence of el nino/la nina cycles on snow accumulation and streamflow for the coal creek watershed. north american monsoon and summer precipitation the north american monsoon (hereafter, monsoon) is a seasonal change in the predominant windflow direction and atmospheric circulation associated with summer heating of the interior of the north american continent (adams and comrie, 1997). continental heating causes a low-pressure cell to develop over the high elevation interior of the western united states and induces flow of warm and moist air from the gulf of california and the gulf of mexico (hereford and webb, 1992). as a result, daily convective storms are common in much of northern mexico and the southwestern united states due to diurnal heating, and are responsible for numerous flash floods. as utah is at the periphery of its strongest influence, the year-to-year variability in monsoon intensity can be large. for example, the 2020 monsoon season saw relatively little storm activity and flash flooding in most of southern utah, whereas the 2021 monsoon season caused widespread flash flooding in much of the southwest (national oceanic and atmospheric administration, 2021). meteorologically, the monsoon period begins june 15th, but monsoon thunderstorm activity is greatest from july through september, and three floods caused by intense monsoon rains in water year 2021 are evaluated in this study. methods streamflow and snow hydrology of the coal creek watershed coal creek is the primary surface water source for cedar valley (figure 1), and u.s. geological survey (usgs) stream gage 10242000 is located just upstream from the mouth of the canyon east of cedar city. upstream from the stream gage, the watershed is effectively unregulated, with no major water diversions or reservoirs. as such, the gage provides a useful data source to assess the trends in the long-term natural hydrology of the watershed, with annual flood magnitudes reported back to 1916. for the streamflow, precipitation, and snowpack data described herein, we use english units consistent with those reported by government agencies and commonly used for resource management and hazard assessment. furthermore, in all cases, we use the water year, which extends from october 1st through september 30th, as the hydrologically relevant time scale over which to assess annual patterns. we consider the march 1st through june 30th period as generally associated with snowmelt, and the july 1st through september 30th period as reflecting monsoon floods overprinted on the baseflow. streamflow volumes we use the usgs daily data from the coal creek gage to evaluate the long-term trends of streamflow volume. we report the total annual runoff volume (per water year), the march 1st through june 30th (snowmelt) runoff volume, and the july 1st through september 30th (monsoon plus baseflow) runoff volume. flood frequency analysis a flood frequency analysis using the standard usgs log-pearson iii approach, with a gage specific skew, was used to estimate return periods for floods of different magnitude (e.g., kenney and others, 2007). because the stream is affected by both snowmelt floods and monsoon-induced flash floods, we used multiple approaches to evaluate flood return periods. first, we use the maximum annual flood for each year, regardless of whether it was generated by snowmelt or summer rainfall (kenney and others, 2007). we then evaluated the gage record to find the maximum snowmelt and maximum monsoon rainfall flood for each year to examine the annual flood frequencies for the different flood-generating mechanisms (e.g., yu and others, 2022). for the period since 1988, instantaneous values (every 15 minutes) of discharge are available, and we simply select the highest flows in the snowmelt and monsoon time periods (as defined above) for the different 97 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 flood types (snow versus rain). for the period prior to 1988, we use the maximum daily discharge during the spring period to estimate the peak snowmelt flood to the beginning of the period of record. for monsoon rainfall floods, the daily discharge will underestimate flood peaks because of the rapid rise and fall of the hydrograph. when the monsoon flood was the peak for the year, we use the (instantaneous) peak flow value reported by the usgs. for other years, we extend the gage record of rain-induced floods by using a relation between daily and instantaneous values for the 1988– 2021 period. this provides a conservative estimate of these floods, and allows us to establish a longer record of rain-induced flood frequencies using the standard usgs approach that includes years with smaller monsoon floods. snowpack because snowmelt is the dominant driver of the streamflow (water supply) of coal creek, we evaluate the historical variability in snowpack as a complement to our streamflow analysis. we use data from snow telemetry (snotel) sites operated by the u.s. department of agriculture (usda) natural resources and conservation service (nrcs) that are within or directly adjacent to the headwaters of the coal creek watershed (figure 1). we chose sites with long-term daily records dating back to water year 1981: the webster flat, kolob, midway, and castle valley snotel sites (figure 1). for each site, we found the maximum snow water equivalent (swe) reported for each site for each year, with the expectation that the maximum swe value represents the water available for runoff in the subsequent spring and early summer. soil moisture soil moisture data at snotel sites were assessed for the period 2019–2021. soil moisture is known to have an effect on streamflow generation in snowmelt-dominated watersheds of utah (clayton, 2016; harpold and others, 2017). in this case, we used data from the four long-term snotel sites above, and two additional nearby sites installed in the 2010s: brian head and southern utah university (suu) ranch. soil moisture is reported as volumetric water content at 2-, 8-, and 20-inch depths, and we focus on the 8and 20-inch data as more representative of the long-term and depth-integrated soil moisture likely to affect streamflow. we report values as the percent of the median from the 2019–2021 period of analysis. southern oscillation index (soi) we use the average of the june through november standardized southern oscillation index (soi) to assess the impact of enso cycles on the snow and streamflow hydrology of coal creek (redmond and koch, 1991). the soi is a measure of the difference in sea-level pressure of the equatorial pacific, and is thus a measure of the relative strength of enso. el nino years occur when the soi is less than -0.5; whereas, la nina years occur when the soi is greater than 0.5. other years are considered neutral. since 1951, about half the years have been neutral, and the other half were either el nino or la nina years. we group maximum swe values and annual march–june runoff into el nino, neutral, or la nina categories based on the previous year soi values, and use student’s t-tests to test for statistical differences based on the enso conditions. precipitation hydrology of monsoon flood events in 2021 precipitation data to evaluate the monsoon flooding in cedar valley was derived from a variety of sources. the primary precipitation events evaluated were the july 26th flooding in cedar city, the august 1st flooding in enoch, and the august 18th and 19th flooding of coal creek (figure 2). national oceanic and atmospheric administration (noaa) radar reflectivity data available from the national centers for environmental information were used to document the extent and duration of the precipitation events. additionally, a noaa national weather service station is located near the cedar city regional airport. this weather station recorded significant precipitation on july 26th, but otherwise registered minimal precipitation during the other events. thus, we gathered data from any publicly available precipitation records for those events, as described below. 98 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 figure 2. (a) flooding of residential areas and (b) along cross hollow drive in cedar city on july 26, 2021 (courtesy of st. george news/stgnews.com). (c) residents survey flooding along midvalley road in enoch on august 1, 2021 (courtesy of st. george news/stgnews.com). (d) backyard flooding with a damaged fence in the background in enoch on august 1, 2021 (courtesy of an enoch resident). (e) street flooding in enoch on august 1, 2021 (courtesy of lisa baker). (f) flooding along coal creek east of cedar city near the usgs stream gage and (g) in cedar city near main street on august 18, 2021 (courtesy of st. george news/stgnews.com). all photographs used with permission. 99 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 mesowest data mesowest is a university of utah program that collects weather data from a variety of public sources and provides access to the historical data records. four mesowest sites were used in this study (figure 1), with two of the sites located near the headwaters of coal creek and two sites located near its mouth. these sites were used to evaluate precipitation during the august 18–19 flooding of coal creek, with data typically reported at 15-minute intervals. none of the mesowest sites in the areas of cedar city or enoch reported useable data during the july 26th and august 1st floods. snotel data precipitation data from four snotel sites (suu ranch, brian head, webster flat, and midway flat) were combined with the mesowest data to evaluate rainfall rates during the august 18–19 flooding. snotel data are reported at 1-hour intervals. precipitation rates at snotel sites compared very favorably to precipitation rates measured at nearby mesowest sites. weather underground data because of the dearth of precipitation data available from government agencies or mesowest for the july 26th and august 1st flood events, we utilized publicly available precipitation data from the weather underground website. weather underground has compiled a network of thousands of personal weather stations (pws) and provides real-time data access to the network. further, they provide detailed information on compatible weather stations and station siting to help ensure the accuracy of the data provided. whereas individual weather stations may not have been professionally installed, information on the weather station manufacturer and precision and accuracy specifications are available for each site. in total, nine pws stations from the weather underground site were used to evaluate precipitation rates. typically, these data were reported at 5-minute intervals. precipitation probability data measured precipitation rates for the sites above were compared to point estimates of depth-duration-frequency precipitation probability estimates from noaa (bonnin and others, 2011). probability tables were downloaded from the noaa atlas 14 point precipitation frequency estimates website based on the latest revision of the atlas in 2011 (bonnin and others, 2011). the estimates are based on a partial duration series, meaning that all large events above a threshold are included in the analysis, regardless of the year in which they occurred (as opposed to an annual maximum series). the reported values are then based on the highest n number of events for a period of record of n years (bonnin and others, 2011). hydraulic modeling with hec-ras we used the u.s. army corps of engineers hydraulic engineering center–river analysis system (hec– ras) hydraulic model to evaluate the august 1st flooding in enoch. hec-ras solves the two-dimensional (2d), vertically averaged, shallow-water equations to model unsteady flow across channels and floodplains as defined by a digital terrain model that quantifies the topography in the model domain. the utah geospatial resource center (ugrc) and the utah division of emergency management acquired lidar over enoch, utah from may 2nd through may 25th, 2020. half-meter bare earth digital elevation models (dems) and first return digital surface models (dsms) were produced and published by ugrc. aerial photos and lidar aerial surveys with a real-time kinematic positioning (rtk) enabled airframe and base station, a high-resolution rbg (red-blue-green) sensor, and lidar payload were used to refine the surface model of enoch in the flooded area using agisoft metashape pro. the bare earth surface model was reviewed to validate point cloud classification results aligned with ground-benchmark data. remaining data artifacts were then manually removed. watersheds that flowed into or out of the enoch study area were delineated using the esri (environmental systems research institute, inc.) arcgis pro water resource management hydrologic scripting routines. a hydro-flattened dem was created and mosaiced with existing ugrc dem data. manual dem reconditioning was performed to establish natural surface flow 100 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 through bridges and culverts, including densely vegetated areas. stormwater-infrastructure data provided by the cedar city engineering department included culverts, storm drains, weirs, open channels, and riser pumps, but additional data on culvert dimensions were collected in the field using high resolution global positioning system (gps). pre-processed shapefiles were imported into hecras as feature layers and allocated respectively to a geometry type as 2d flow areas, perimeters, breaklines, and refinement regions. vector data representing structures such as culverts, bridges, weirs, and trapezoidal channels were characterized by their attributes needed to calculate hydraulic flow and dynamically linked to their catchment domain. unsteady flow was modeled throughout the catchment network in hec-ras using a flow hydrograph and rating curve calculated based on peak precipitation rate and expected peak discharge lag time. field measurements of high water using gps and online public surveys were used as benchmarks for model calibration. our voluntary online public survey asked participants to provide a map location, the date and time of when the flooding occurred, and depth of inundation (ashton and others, 2022). unsteady flow was computed iteratively to match benchmark calibration parameters. kairos group, llc. gave instruction and advised on flow-model construction, computation, calibration, and verification. results and discussion water year 2021 and the long-term hydrology of coal creek in a typical year for the coal creek watershed, 69% of the runoff volume occurs during the march-june snowmelt period, and 15% of the runoff volume occurs during the july-september monsoon period. the remainder (16%) occurs during the late fall and winter months primarily as baseflow. furthermore, the bulk of the baseflow that occurs throughout the year likely owes its origin to snowmelt and other cold-season precipitation events (julander and clayton, 2018). as such, the total runoff volume for all periods is well predicted by the maximum swe values at snotel sites surrounding and within the basin; 2021 had the fourth lowest total runoff on record (figure 3). similarly, the maximum swe value is also a good predictor of the maximum snowmelt flood each year (figure 3). the influence of enso on winter snowpack and resultant streamflow is also evident. for both the maximum swe and the march–june streamflow volume, values are greater during el nino years compared to la nina years (student’s t-test, p<0.05) (figure 4). however, la nina years were not significantly different than neutral years in terms of snowpack or runoff volume (figure 4). for el nino years, the maximum swe was significantly greater than during neutral years (student’s t-test, p<0.05), but the march–june streamflow was not. on average, the march–june streamflow volume was about 65% greater than the median value during el nino years, but only 8% less than the median value during la nina years. the wettest, and two driest, years were both during neutral conditions. in 2021, the snowmelt runoff was the lowest ever recorded during a la nina year. thus, overall, enso has a discernable effect on the watershed hydrology, tending to result in greater streamflow and snowpack during el nino years. while the opposite is true for la nina years, la nina is not as strongly distinguished from neutral conditions in terms of hydrologic variability. figure 5 shows the hydrograph of coal creek and corresponding soil moisture conditions for water years 2019 through 2021, contrasting a range of conditions from high (2019) to average (2020) snowmelt with minimal monsoon activity, to that of 2021 with very low snowmelt and frequent monsoon floods. climatologically, 2019 was characterized by neutral enso conditions, whereas 2020 was a weak el nino, and 2021 was a weak la nina. perhaps the weak la nina conditions contributed to low snowpack and snowmelt in 2021, but low soil moisture conditions likely also contributed to the reduced snowmelt runoff (clayton and others, 2021). the exceedance probability for the maximum swe at the snotel sites ranged from 0.79 to 0.9 in 2021, meaning that there is a 79% to 90% chance of those values being exceeded in a given year. yet the snowmelt runoff volume had an exceedance probability of 0.95 to 0.97, indicating an exceptionally low snowmelt runoff—the third lowest on record. figure 5b shows that 101 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 figure 3. (a) runoff volume for total annual runoff, snowmelt period runoff, and monsoon period runoff versus the maximum snow water equivalent (swe) as measured at the midway snotel site. values for 2021 are shown with an x through the symbol. (b) peak snowmelt discharge in cubic feet per second (cfs) of coal creek versus the maximum swe as measured at the midway snotel site. 2021 shown in red. figure 4. (a) box plots showing the variation in maximum snow water equivalent (swe) for four sites bounding the coal creek watershed and (b) box plots showing the variation in march through june total stream flow for coal creek, differentiated by el nino, neutral, and la nina years. boxes represent the median and interquartile range (iqr), mean values are indicated by an x, and outliers are shown as open circles (identified as values more than 1.5 times the interquartile range above the 3rd quartile or less than 1.5 times the interquartile range below the 1st quartile). 102 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 soil moisture at snotel sites never reached the levels attained in 2019 and 2020, suggesting that the soils at depth were not fully saturated. this would reduce the amount of direct surface runoff from snowmelt as water continued to be stored in soils (clayton and others, 2021). figure 5b also shows significant increases in soil moisture following monsoon rain events such that soil moisture at the end of the water year was higher than in 2019 and 2020. more than 10 monsoon floods of coal creek exceeded the snowmelt flood during 2021 (figure 5c), and the proportion of annual runoff that occurred during the monsoon period (july 1 through september 30) was the greatest in the observational record and nearly equivalent to that of the snowmelt period (march 1 through june 30) (figure 6). total annual flow in 2021 was about 10,250 acre-feet, 42% of the long-term average and the fourth lowest recorded. annual floods of coal creek are caused by either snowmelt, as in 2019, or monsoon rainfall, as in 2020 and 2021 (figure 5a). figure 7 shows the average day of year (julian day) for the peak flood of each water year dating back to 1935. for the 86-year record, snowmelt caused the peak flood 35 times (41%), and rainfall caused the peak flood 51 times (59%). the data suggest something of a cyclicity in the dominant mode producing the annual flood, which may reflect longer timescale figure 5. (a) hydrograph of coal creek for water years 2019 through 2021. gray shading indicates snowmelt period, and yellow shading indicates monsoon period. (b) soil moisture at 8 and 20 inches depth using the mean value from six snotel sites bounding the coal creek watershed. soil moisture plot shows mean and standard deviation for the six sites on october 1 and march 1 of each year. (c) hydrograph of coal creek for water year 2021. 103 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 climate controls on either winter snow accumulation or monsoon activity (waite and thomas, 1955; hereford and webb, 1992; nowak and others, 2012). in the last twenty years, 15 of the largest annual floods were produced during monsoon rainfall (figure 7). figure 8 shows the usgs standard log-pearson type iii flood-frequency analysis for the annual snowmelt floods, annual rainfall flood, and the annual flood regardless of when it occurred (combined snowmelt and rainfall flood populations). as expected, the peak magnitude of snowmelt floods is roughly half or less than that of rainfall floods for a given return interval. the largest recorded snowmelt flood with an approximate 100-year recurrence was 1820 cubic feet per second (cfs), which would be approximately a 5-year recurrence for rainfall floods. in 2021, the peak flood during the monsoon season was 2000 cfs. while a relatively common flood with a recurrence of 6 to 7 years, the repeated flooding during this event caused considerable localized flooding as discussed in the next section. it is clear that for the combined record the highest discharges with recurrence intervals greater than about 5 years occur primarily due to rainfall (figure 8). on the other hand, smaller floods with recurrence intervals less than 5 years may be caused by either mechanism in the combined record. treating the flood frequencies separately based on the different flood-generating mechanisms (snowmelt versus rain) demonstrates that published flood probabilities combining flood types may underestimate the magnitude of rare (100-year) monsoon rainfall floods (yu and others, 2022) (figure 8). precipitation extremes and monsoon floods in the context of the above discussion of watershed hydrology for coal creek, water year 2021 can viewed as a year of contrasts – hydrological (snow) drought overprinted by an intense monsoon season that resulted in numerous floods in cedar valley. point precipitation measurements during the three floods analyzed herein all showed locations where precipitation rates exceeded the computed 100-year precipitation rates for durations between 1 and 24 hours. in the following subsections, we describe the precipitation climatology relative to the depth-duration frequencies published by noaa (bonnin and others, 2011), and, where available, streamflow hydrology, for the three major monsoon floods that impacted cedar valley in 2021. cedar city, july 26th, 2021 the storm of july 26th produced intense precipitation over much of cedar city. most of this precipitation fell over an urban area with rapid overland flow along roadways, causing significant flooding of residences and roadways in low areas near the intersection of figure 6. proportion of total annual runoff derived during the snowmelt (march 1 through june 30) versus monsoon (july 1 through september 30) periods plotted versus the annual flow volume for coal creek. figure 7. julian day of annual flood peaks from 1935 to 2021, with the 10-year moving average centered on each point shown as a solid line. peaks prior to june 15 are considered to be derived from snowmelt, and after june 15 from monsoon rainfall. 104 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 interstate 15 (i-15) and west 200 north. precipitation rates exceeded the 200-year event for one of the gauges for durations of 30 minutes to 3 hours (figure 9a). at this gauge, more than 2.5 inches of rain fell in 1 hour. the national weather service gauge recorded more than 2 inches of rain in approximately 1 hour, which is greater than a 100-year event. several other gauges recorded between 1.5 and 2.5 inches of rain in 2 hours (figure 9a). city officials declared a state of emergency following this event due to the extensive damage caused by flooding of homes in the area. enoch, august 1st, 2021 precipitation rates during the august 1st flooding in enoch were somewhat less than measured less than a week earlier in cedar city. one gauge showed precipitation rates that exceeded the 100-year event for durations of 2 and 3 hours, with total accumulations of 2 to 2.5 inches (figure 9b). yet, no precipitation gauges exist just east of and in the vicinity of i-15, where several small and steep drainages provide direct inflow to low-lying urban areas already experiencing heavy rain. radar data during the event shows high precipitation rates across these drainages and directly over the southern part of the city for nearly an hour (figure 10). there is also clear evidence of flooding from these drainages in the form of debris, high water marks, and fresh sediment movement. the water from the drainages passed through culverts beneath or overtopped i-15, temporarily closing the roadway. the floodwaters then inundated low-lying areas and neighborhoods of enoch, causing extensive damage. hec-ras modeling of flood inundation provides a clearer picture of the flood extent on august 1st (figure 11). using a discharge hydrograph calibrated to measured high-water marks in tributary basins and flooded areas, the modeled inundation shows significant flooding of neighborhoods in low-lying areas of enoch. the modeled depths and extents are also consistent with feedback from public surveys on flood damage and extent at individual properties (figure 11d). the extent of flooding on august 1st caught many residents of enoch off guard because there are no major drainages in the area. because cedar valley is a closed basin, floodwaters emanating from steep tributaries along the range front do not necessarily coalesce into a primary channel with a higher conveyance, but instead flood across large areas at relatively shallow depths (figure 11). this highlights the fact that small drainages can produce large floods during convective monsoon storms, and flooding may be exacerbated by rapid runoff from urbanized areas. coal creek, august 18-19, 2021 precipitation rates during the coal creek floods exceeded the 500-year event for one gauge, and the 100year event for four gauges, but over longer durations of 6 to 48 hours compared to the floods described above figure 8. log-pearson type iii fits to annual peak flood flows derived from snowmelt, monsoon rain, and the combined snowmelt and rain periods as measured at the coal creek usgs stream gage from 1935–2021. 105 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 (figure 12). the highest precipitation rates were recorded near the rim of cedar breaks at the headwaters of coal creek, where 5 to 6 inches of rain fell in 12 hours and storm totals exceeded 6 to 7 inches at two gauges in this study. cedar breaks national monument measured over 6 inches of rain according to media reports. these are among the highest 24-hour rainfall totals ever recorded in utah – 6.78 inches at the u.s. highway 14 mesowest site, and 6.1 inches at the midway valley snotel site (figure 12c). according to noaa’s state climate extremes committee, the 24-hour precipitation record in utah is 5.08 inches; but higher values have been reported in media stories at regional weather stations not likely considered by noaa. the initial pulse of intense precipitation began around midnight on august 18th, and caused a rapfigure 9. depth-duration-frequency precipitation plots during (a) the july 26th flooding of cedar city, utah, and (b) the august 1st flooding of enoch, utah. symbols represent data from different weather underground personal weather stations, except for the cedar city national weather service (nws) site shown as a diamond on a. 106 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 id rise in coal creek to a peak discharge of 2000 cfs at around 3 a.m. (figure 13). this was the largest flood peak of the water year. this initial flood pulse was followed by a second, smaller pulse of 1310 cfs. after a period of quiescence, a second storm impacted the watershed near midnight on august 19th with as much of 2 inches of additional precipitation focused more in the center of the watershed. this caused a third flood pulse of approximately 1000 cfs (figure 13). residents reported all three flood pulses, and significant flooding occurred along a channel of coal creek north of the cedar city airport. cedar city has figure 10. noaa radar reflectivity mosaic (in decibels, dbz) showing the august 1, 2021, storm that caused flooding in enoch, utah. top panel shows the 1-hour build up to the peak rainfall rates, middle panel shows 15 minutes during the most intense part of the storm, and lower panel shows the final half hour and initial dissipation of the storm. 107 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 built flood diversion structures, channels, and levees to protect against flooding of coal creek, but some of this infrastructure was overwhelmed by the high debris (wood) and sediment loads of the flood. the intense precipitation during the initial flood event occurred in steep terrain that likely resulted in debris flows and overland flow that picked up woody debris and trees from the forested hillslopes. the debris and sediment clogged diversion structures and channels, resulting in levee overtopping and flooding of some residential areas. whereas, this was not a particularly large flood (recurrence of 6 to 7 years), it demonstrates the important role of sediment and debris loads in exacerbating flood effects – especially in communities at the mouths of steep mountain watersheds where monsoon floods may occur. conclusions water year 2021 in southern utah was characterized by an extremely muted spring and early summer snowmelt period that worsened existing drought conditions, followed by a strong monsoon season that caused figure 11. hec-ras model results showing inundation depth (in meters) from (a) flood initiation to (b) maximum precipitation to (c) maximum flood extent during the august 1st enoch, utah, flooding. (d) results of public survey showing a subset of impacted homes and estimated inundation depth; note that map in d is not at the same scale as a through c, as indicated by the black lines showing common points in each image. 108 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 figure 12. depth-duration-frequency precipitation plots for the august 18th and 19th flooding of coal creek, showing (a) low-elevation sites, (b) a mid-elevation site, and (c) upper-elevation sites. 109 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 numerous floods. the runoff of coal creek is vital to the water supply of cedar city and the groundwater recharge of the cedar valley’s aquifers. here we show that the overall streamflow is predictably related to snow accumulation and different phases of enso. in 2021, low snowpack and soil moisture during a weak la nina contributed to extremely low snowmelt runoff. the dry conditions were followed by an unusually intense monsoon season. measured precipitation rates exceeded the 100-year rainfall rates, and in some cases the 500-year rainfall rates, for multiple storms during the 2021 summer monsoon, resulting in localized flooding throughout cedar valley. the floods in cedar city and enoch were likely exacerbated due to extreme precipitation over urban areas, and hydraulic modeling shows good agreement with measured inundation and public surveys of the impacted area during the august 1st flooding of enoch. for coal creek, there are no long-term trends in discharge volume or flood frequency in the stream gaging record, and no individual event in the gage record during 2021 broke any records. yet the hydrology of water year 2021 was unique in the combined effects of an extremely low snowmelt followed by an intense monsoon season that resulted in widespread flooding of residential areas, an unfortunate but instructive combination from the perspective of water resources and hazard analysis. acknowledgments we would like to thank the southern utah university geosciences department and geoclub for supporting this research. david maxwell provided surveying and gis resources and expertise that greatly facilitated the field research and hydraulic modeling. the community of enoch provided invaluable information on flooding extent and damage via public surveys. jordan clayton (nrcs) and paul grams (usgs) provided helpful reviews that improved the clarity of the manuscript. references adams, d.k., and comrie, a.c., 1997, the north american monsoon: bulletin of the american meteorological sofigure 13. (a) hydrograph of coal creek and (b) accumulated precipitation during the august 18th and 19th flooding of coal creek. in b, blue lines indicate snotel sites and black lines indicate mesowest sites. 110 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 ciety, v. 78, no. 10, p. 2197–2214. ashton, s., sudweeks, g., olson, m., and mueller, e., 2022, precipitation and streamflow hydrology during the summer 2021 monsoon flooding of the cedar valley, utah: geological society of america abstracts with programs, v. 54, no. 2, doi: 10.1130/abs/2022cd-373772. bardsley, t., and julander, r., 2005, the documentation of extreme events—two case studies in utah, water year 2005: proceedings of the western snow conference, v. 73, p. 33–42. berwick, v.k., 1962, floods in utah, magnitude and frequency: u.s. geological survey circular 457, 24 p. bonnin, g.m., martin, d., lin, b., parzybok, t., yekta, m., and riley, d., 2011, precipitation-frequency atlas of the united states: national weather service, silver spring, maryland, noaa atlas 14, v. 1, version 5.0, 65 p. brooks, l.e., and mason, j.s., 2005, hydrology and simulation of ground-water flow in cedar valley, iron county, utah: u.s. geological survey scientific investigations report 2005-5170, 114 p. brown, d.p., and comrie, a.c., 2004, a winter precipitation ‘dipole’ in the western united states associated with multidecadal enso variability: geophysical research letters, v. 31, l09203, 4 p. cayan, d.r., redmond, k.t., and riddle, l.g., 1999, enso and hydrologic extremes in the western united states: journal of climate, v. 12, no. 9, p. 2881–2893. clark, m.p., serreze, m.c., and mccabe, g.j., 2001, historical effects of el nino and la nina events on the seasonal evolution of the montane snowpack in the columbia and colorado river basins: water resources research, v. 37, no. 3, p. 741–757. clayton, j.a., 2016, summer soil moisture loss at utah snotel sites and streamflow recession at nearby gauges— variability in runoff generation and the potential for flow forecasting: hydrological processes, v. 30, no. 1, p. 119–134. clayton, j., brosten, t., sutcliffe, k., eiriksson, d., burly, j, and neff, d., 2021, utah water supply outlook report (5/1/2021): salt lake city, utah, natural resources conservation service, 74 p. harpold, a.a., sutcliffe, k., clayton, j., goodbody, a., and vazquez, s., 2017, does including soil moisture observations improve operational streamflow forecasts in snow‐ dominated watersheds?: journal of the american water resources association, v. 53, no. 1, p. 179–196. hereford, r., and webb, r.h., 1992, historic variation of warm-season rainfall, southern colorado plateau, southwestern usa: climatic change, v. 22, no. 3, p. 239–256. jin, j., miller, n.l., sorooshian, s., and gao, x., 2006, relationship between atmospheric circulation and snowpack in the western usa: hydrological processes, v. 20, no. 4, p. 753–767. julander, r.p., and clayton, j.a., 2018. determining the proportion of streamflow that is generated by cold season processes versus summer rainfall in utah, usa: journal of hydrology, v. 17, p. 36–46. kenney, t.a., wolkowske, c.d., and wright, s.j., 2007, methods for estimating magnitude and frequency of peak flows for natural streams in utah: u.s. geological survey scientific investigations report 2007–5158, 28 p. lund, w.r., 1992, flooding in southwestern utah, in harty, k.m., editor, engineering and environmental geology of southwestern utah: utah geological association publication 21, p. 159–164. lund, w.r., knudsen, t.r., and sharrow, d.l., 2010, geologic hazards of the zion national park geologic-hazard study area, washington and kane counties, utah: utah geological survey special study 133, 97 p. national oceanic and atmospheric administration, 2021, review of the 2021 monsoon across the southwest u.s.: compiled by noaa/nws phoenix, arizona, https:// www.weather.gov/psr/2021monsoonreview. nowak, k., hoerling, m., rajagopalan, b., and zagona, e., 2012, colorado river basin hydroclimatic variability: journal of climate, v. 25, no. 12, p. 4389–4403. oubeidillah, a.a., tootle, g.a., moser, c., piechota, t., and lamb, k., 2011, upper colorado river and great basin streamflow and snowpack forecasting using pacific oceanic–atmospheric variability: journal of hydrology, v. 410, no. 3–4, p. 169–177. redmond, k.t., and koch, r.w., 1991, surface climate and streamflow variability in the western united states and their relationship to large‐scale circulation indices: water resources research, v. 27, no. 9, p. 2381–2399. smith, j.a., baeck, m.l., yang, l., signell, j., morin, e., and goodrich, d.c., 2019, the paroxysmal precipitation of the desert—flash floods in the southwestern united states: water resources research, v. 55, no. 12, p. 10218– 10247. 111 snow drought and monsoon floods—hydrological extremes in the cedar valley watershed during water year 2021, southwestern utah mueller, e.r., sudweeks, g.p., ashston, s.a., and olson, m.c. geology of the intermountain west 2023 volume 10 tamaddun, k.a., kalra, a., bernardez, m., and ahmad, s., 2017, multi-scale correlation between the western us snow water equivalent and enso/pdo using wavelet analyses: water resources management, v. 31, no. 9, p. 2745–2759. waite, h.a., and thomas, h.e., 1955, effect of current drought upon water supplies in cedar city valley, utah: eos, transactions american geophysical union, v. 36, no. 5, p. 805–812. wilkowske, c.d., kenney, t.a., and mckinney, t.s., 2006, flooding and streamflow in utah during water year 2005: u.s. geological survey fact sheet 2006-3085, 6 p. woolley, r.r., 1946, cloudburst floods in utah, 1850–1938: u.s. geological survey water-supply paper 994, 128 p. yu, g., wright, d.b., and davenport, f.v., 2022, diverse physical processes drive upper‐tail flood quantiles in the us mountain west: geophysical research letters, v. 49, 11 p., e2022gl098855, https://doi.org/10.1029/2022gl09885. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 10 2023 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research adam i. hiscock, emily j. kleber, adam p. mckean, ben a. erickson, greg n. mcdonald, richard e. giraud, jessica j. castleton, and steve d. bowman theme issue engineering geology and geohazards of utah utah geological association annual field conference october 22, 2022 salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover subsidence features on the salt flats near the great saltair likely caused by liquefaction from the 2020 m5.7 magna, utah earthquake. photo by adam hiscock. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 10 2023 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2022–2023 uga board president rick ford rford@weber.edu 801.915.3188 president-elect eugene syzmanski eugenes@utah.gov 801.537.3364 program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 treasurer aubrey dereuil aubrey@zanskar.us 850.572.2543 secretary tom chidsey tomchidsey@gmail.com 801.824.0738 past president john south johnvsouth@gmail.com 801.367.9292 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com giw editors uga field conference editors jason kaiser southern utah university jasonkaiser@suu.edu john south geologist johnvsouth@gmail.com adam mckean utah geological survey adammckean@utah.gov rick chesnut terracon rick.chesnut@terracon.com geology of the intermountain west an open-access journal of the utah geological association volume 10 2023 113 abstract the march 18, 2020, mw 5.7 magna earthquake was the largest earthquake in utah since the 1992 ml 5.8 st. george earthquake. the magna earthquake occurred in the northwest corner of the salt lake valley, home to 1.2 million people. immediately following the earthquake, the utah geological survey organized teams to collect perishable field data on the geologic effects of ground shaking near the epicenter, as well as establish a web-based digital clearinghouse to collect, distribute, and archive data related to the earthquake. this earthquake also coincided with the beginning of the covid-19 global pandemic, which added extra challenges to our earthquake response. teams used a small, unmanned aircraft system to obtain aerial photos and videos of geologic effects to supplement ground-based reconnaissance. the observed geologic effects of ground motions from the magna earthquake include liquefaction in the form of sand boils, tension cracks, lateral spreading, and localized subsidence. no primary surface fault rupture was observed. the areas with the highest observed concentration of liquefaction features were close to the shore of great salt lake and near the epicenter, northeast of the town of magna. photos and other documentation of the geologic effects associated with this earthquake are critical in helping to understand the hazards associated with moderate magnitude earthquakes in the wasatch front region. the earthquake sequence and associated geologic effects were well documented, due to the proximity to a major metropolitan area and the mainshock and aftershocks occurring within the densest part of the utah regional seismic network. in the two years since the earthquake, numerous studies have been published documenting and interpreting data to characterize the magna event and discuss how new data add to what is known about seismic hazards along the wasatch front. the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research adam i. hiscock1, 2, emily j. kleber1, 3, adam p. mckean1, 4, ben a. erickson1, 5, greg n. mcdonald1, 6, richard e. giraud1, 7, jessica j. castleton1, 8, and steve d. bowman1, 9 1utah geological survey, salt lake city, ut, 84116 usa 2adamhiscock@utah.gov, 3ekleber@utah.gov, 4adammckean@utah.gov, 5benerickson@utah.gov, 6gregmcdonald@utah.gov, 7rich124swe@gmail.com, 8jessicacastleton@utah.gov, 9stevebowman@utah.gov citation for this article. hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d., 2023,the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research: geology of the intermountain west, v. 10, p. 113–129, https:// doi.org/10.31711/giw.v10.pp113-129. introduction over 80% of utah’s population lives along the 350-km-long wasatch fault zone (wfz), one of the most active faults in the intermountain west. the densely populated salt lake valley is bounded to the east by the wfz, and is also home to the antithetic west valley fault zone (wvfz) in the center of the valley (figure 1). both the wfz and the wvfz are holocene-active normal faults. the march 18, 2020, moment magnitude (mw) 5.7 magna earthquake was the largest earthquake in the salt lake valley since the 1962 local magnitude (ml) 5.2 magna earthquake, and the largest in utah since the 1992 114 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 ml 5.8 st. george event. the mainshock was located approximately 16 km west of downtown salt lake city (40.751°n, 112.078°w) at an approximate depth of 11.9 km (u.s. geological survey [usgs], 2022; figure 2). the mainshock occurred within the densest part of the utah regional seismic network, and additional temporary stations were deployed following the mainshock to monitor the aftershock sequence (pankow and others, 2021). from march 18, 2020, to february 28, 2021, the university of utah seismograph stations (uuss) identified 2590 earthquakes associated with the magna earthquake sequence (figure 2; uuss, 2021). based on the interpretation of geologic and geophysical data, the magna earthquake occurred on a gently dipping part of the wfz (pang and others, 2020; kleber and others, 2021; messimeri and others, 2021). this earthquake was widely felt along the densely populated wasatch front; 26,364 felt reports have been reported to the usgs as of january 18, 2022 (usgs, 2022). the magna earthquake caused approximately $70 million in public infrastrucfigure 1. map of the northern salt lake valley showing figure locations, regional faults, cities, and locations referenced in this report. kti – kennecott tailings impoundment, slc – salt lake city international airport. faults from ugs hazards portal (2022), basemap from ugrc (2019). 115 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 ture damage in salt lake and tooele counties, with additional damage to residential and commercial property (kleber and others, 2021). abundant paleoseismic data on the timing and size of prehistoric earthquakes on the wfz and other faults in the wasatch front region show a history of large (m > 6.75) surface-rupturing earthquakes in the region. at least 22 surface-rupturing earthquakes have occurred on the wfz in the past 6000 years, with a 43% probability of a m ≥ 6.75 earthquake occurring in the wasatch front region over the next 50 years (working group on utah earthquake probabilities [wguep], 2016). despite less data about the timing and recurrence of moderate magnitude earthquakes in the region due to a lack of evidence in the geologic record, the probability of a m ≥ 5.0 occurring in the next 50 years is still 93% (wguep, 2016). immediately following the magna earthquake, the utah geological survey (ugs) geologic hazards program organized field teams to collect perishable data on the geologic effects related to the earthquake. the earthquake occurred less than a week after most ugs staff switched to a telecommuting schedule and the state of utah entered a two-week lockdown due to the covid-19 pandemic. the timing of the magna earthquake, near the beginning of a global pandemic, added an extra challenge to the earthquake response for the ugs and other groups (pankow and others, 2021; mcentire, 2021). early in the covid-19 pandemic, there was a lot of uncertainty with public health safety measures and guidelines. ugs field teams did their best to follow available public health measures while performing fieldwork and interacting with the public while responding to the magna earthquake. a mw 5.7 earthquake does not release enough energy to cause surface fault rupture in the intermountain west region, so field teams focused on identifying ground shaking-related effects. these teams were deployed to figure 2. magna earthquake sequence, from march 18, 2020, to february 28, 2021. figure from university of utah seismograph stations (2021). 116 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 areas thought to be susceptible to ground shaking-related geologic effects (e.g., liquefaction, lateral spreading, sand boils, ground cracking, ground deformation) based on geologic conditions such as seasonally high groundwater levels, recent geologic mapping showing underlying fine-grained silt and sand deposits (mckean, 2019; mckean and hylland, 2019a; mckean and others, 2019; clark and others, 2020), and proximity to great salt lake. teams focused their efforts primarily at areas along the jordan river and the shoreline of great salt lake (figure 1). liquefaction susceptibility mapping for the magna 7.5-minute quadrangle indicates the majority of the area around the epicenter of the magna earthquake has a high susceptibility for liquefaction (castleton and others, 2011). additionally, the ugs received reports of ground deformation from local geologists, governmental agencies, and consultants which helped guide reconnaissance efforts. geologic effects jordan river and goggin drain one of the first areas the field teams performed reconnaissance the morning of the earthquake was along the jordan river. the jordan river runs south to north through the center of the salt lake valley (figure 1), from utah lake in utah valley to great salt lake (figure 1). the river is fed by numerous snowmelt-sourced small streams flowing out of the wasatch range to the east and the oquirrh mountains to the west. in the late holocene, the course of the river has shifted several times in response to changing lake levels and possibly also in response to surface-fault-rupturing earthquakes and tectonic subsidence associated with the wfz and wvfz (keaton, 1987; mckean and hylland, 2019b). we inferred that ground deformation effects associated with ground shaking would be concentrated along the jordan river because the river is a major control on the local groundwater base level in the salt lake valley (wallace and lowe, 2009). we observed small, localized features in several places along the river including at several sites near the salt lake city international airport and the goggin drain (figure 1). east of redwood road along the jordan river, we observed a small (1 to 2 m wide) lateral spread feature along the riverbank (figure 3). west of the airport at the goggin drain, we observed small (5 to 10 cm) wet craters with fresh ground cracking (figure 4), perhaps indicating fluctuating groundwater levels due to earthquake ground shaking (kleber and others, 2021). the great saltair and i-80/sr-202 interchange multiple liquefaction features were observed on foot and by a small, unmanned aircraft system (suas) in the general vicinity of the great saltair event center (figure 1). initially, several sand boils were observed in roadway fill material along the i-80/sr-202 interchange as well as extensional cracking indicating ground failure towards the retaining ponds (figures 5 and 6). upon investigation with a suas, numerous (tens) subaqueous sand boils were observed in several of the ponds around the interchange and were much more numerous than the subaerial sand boils (figure 7a). water levels in these ponds fluctuate seasonally; oftentimes the ponds are wet in the spring months and dry in the summer months (kleber and others, 2021). sand boils ranged from 10 to 50 cm in diameter and were only observed in areas with artificial fill around the interchange and along the margins of the ponds (figure 7b). these observations suggest the presence of the roadway infrastructure on top of the underlying lacustrine deposits may have played a role in the formation of sand boils. a return visit in august 2020, when the ponds around the interchange had dried up, allowed us to examine the previously subaqueous sand boils and dig small trenches across several of them to view them in cross section (figure 7c). lighter colored oolitic sands were observed in the center of the cross section, cutting and depositing on top of dark, organic-rich clays and silts (figure 7b). additional sand boils were observed in the parking lots for the great saltair event center, but unfortunately had been driven over and destroyed by emergency response crews on the day of the earthquake. several days after the mainshock, acting on an informal report of small collapse features from a ugs colleague, we performed reconnaissance of the mud flats along the shore of great salt lake north of the great saltair event center. on foot and using a suas, we docu117 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 mented numerous collapse features in the mud flats near the great salt lake shoreline (figure 8a). these features ranged from 5 to 25 cm in diameter and 5 to 10 cm in depth. they were relatively widespread; in some areas, upwards of 20 features were present in a small area (figure 8b). other spring-related features are often found seasonally around the great salt lake shoreline, but the sudden onset and relative fresh appearance of these features suggest they were created by rapid groundwater withdrawal due to earthquake ground shaking. great salt lake state park several days after the magna earthquake, employees at the great salt lake state park marina reported cracking along the main access road and around several parking lots and park buildings. several tension cracks associated with lateral spreading were observed on foot and with a suas along the access road. these cracks indicated approximately 2 to 20 cm of vertical separation within the road surface, on the road shoulder, and along the roadway base (figure 9). multiple cracks along the roadway base indicated a stepping, en echelon pattern (figure 10a). one of the larger cracks at the roadway base measured approximately 6 m long, up to 30 cm deep, and 10 to 20 cm wide (figure 10b). additionally, suas aerial survey data showed multiple subaqueous sand boils in several ponds near the entrance station to the great salt lake state park marina (figure 11). these appeared similar in color and texture to the subaqueous sand boils documented near the great saltair event center. like the other sand boils, these were only observed near the margins of the ponds close to artificial roadway fill from the marina access road. thick vegetation made follow-up observations later in 2020 to document the sand boils after the water levels in the ponds had dropped, not possible. damage was also observed around a maintenance building on the southwestern side of the marina property. ground shaking causing separation between a concrete sidewalk and the building damaged a vertical natural gas line coming from below ground to the side of the building (figure 12a). tension cracks up to 10 m long with 5 to 10 cm of vertical separation in fill material around the watercraft dry storage area were also documented (figure 12b; kleber and others, 2021). these cracks were expanding towards the retention ponds, away from the buildings and developed area, indicating some near-surface lateral spreading in fill material. figure 3. small, 1 to 2 m lateral spread along the banks of the jordan river. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photo. figure 4. ground cracking in small 5 to 10 cm depressions near the goggin drain, indicating fluctuating groundwater levels due to earthquake ground shaking. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photo. 118 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 epicenter and other reconnaissance areas the epicenter of the magna earthquake occurred directly east of the kennecott tailings impoundment (kti; figures 1 and 2). a previous utah geological association publication details the seismic hazards associated with the kti area (wong and others, 1995). since the 2020 earthquake, the tailings piles have come back into question for their role in the magna and future earthquakes (hu and others, 2021). we did not perform reconnaissance of the kti area due to a lack of access. we assumed that rio tinto performed their own analysis of the performance of their tailing impoundments, but that information is not publicly available at this time. we performed extensive reconnaissance of the epicentral area outside of the kti, looking for additional ground deformation. in several seasonally wet areas, we documented small, fresh ground cracks formed in radial patterns (figure 13; kleber and others, 2021). these features may have formed coseismically and may represent syneresis cracking caused by rapid earthquake-induced dewatering of seasonally wet areas (pratt, 1988). more reconnaissance was performed along the western range front of the wasatch range and the northern end of the oquirrh mountains to look for possible coseismic landslides and rockfalls. we documented one small rockfall deposit north of downtown salt lake city near ensign peak (figure 14) but were unable to determine if it was caused by ground shaking from the earthquake. additionally, a nearby landslide in city creek canyon showed some signs of reactivation after the magna earthquake but has previously shown signs of movement in the spring due to run-off, so we were unable to conclusively determine if landslide activity was earthquake-induced. digital clearinghouse within two hours of the earthquake, the ugs established a digital, web-based clearinghouse to collect, distribute, and archive perishable data related to the earthquake (https://geodata.geology.utah.gov/ pages/search.php?search=!collection609). the clearinghouse provides timely public-facing information that is used by the media, and provides a permanent archive for data related to the magna earthquake (figure 15). various organizations contributed to the figure 5. subaerial sand boils near the i-80/sr-202 interchange and great saltair event center. field notebook (10 cm wide) for scale. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photo. https://geodata.geology.utah.gov/pages/search.php?search=!collection609 119 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 clearinghouse including the ugs, salt lake county, university of utah seismograph stations, u.s. geological survey, utah department of transportation, earthquake engineering research institute, unavco, utah state historic preservation office, utah division of emergency management, university of utah, utah state university, utah valley university, natural history museum of utah, stanford research computing center, utah geological association, granite school district, strongmotions inc., geohazards tep, poll sound, utah division of state history, and salt lake city. the ugs began a public outreach campaign through social media to encourage citizens to share their media from the earthquake. using a google form available through ugs’s various social media pages, 17 people responded, contributing 50 photographs and 15 videos (ugs ghp, 2020), which were added to the magna earthquake clearinghouse. the majority of the media items submitted to the clearinghouse were photographs of documented damage to structures and ground deformation caused by earthquake ground shaking. numerous videos submitted documented the varied intensity of ground shaking experienced throughout the salt lake valley. local, regional, and international researchers also submitted maps and figures to help contextualize the earthquake sequence. as of february 3, 2022, the magna earthquake clearinghouse contained 949 items (figure 15). summary of publications on the 2020 magna earthquake sequence in the nearly two years since the magna earthquake, numerous studies and journal articles have been published documenting multiple scientific aspects of the earthquake (table 1). the march 2020 mw 5.7 magna earthquake was one of four moderate magnitude intermountain west earthquakes that occurred in 2020, including the mw 6.5 stanley, idaho, mw 6.5 monte cristo, nevada, and mw 5.8 lone pine, california earthquakes. in the first paper to be published after the magna earthquake, pang and others (2020) used near-surface geophysical data from the mainshock and ongoing sequence to interpret a listric subsurface geometry for the salt lake city segment of the wfz. a special issue of seismological research letters (srl) on the intermountain west (imw) earthquakes of 2020 was published in march of 2021. an overview of the imw figure 6. subaerial sand boil (center of photo) and extensional ground crack with 2–3 cm of vertical separation (indicated by arrows) near the i-80/sr-202 interchange and great saltair event venue. field notebook (10 cm wide) for scale. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photo. 120 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 figure 7. subaerial and subaqueous sand boils identified along the i-80/sr-202 interchange. (a) june 2017 satellite imagery at a water level somewhat similar to that of march 2020. note lack of lightly colored features interpreted to be subaqueous sand boils. (b) suas image (area of image shown in a) showing subaqueous and subaerial sand boils. (c) inset photo shows cross section of one previously subaqueous sand boil later in the summer, in august 2020. figure modified from kleber and others (2021). resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photos. satellite imagery in a from ugrc (2017). figure 8. (a) collapse feature near the shore of great salt lake. fresh circular cracking suggests these features were caused by earthquake ground shaking and rapid groundwater withdrawal. (b) arrows pointing to numerous collapse features like the one shown in a. view looking southwest, towards the northern end of the oquirrh mountains. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photos. 121 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 figure 9. suas image of the great salt lake state park marina access road showing an approximately 6-meter-long crack in the roadway base material (shown by arrows). resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photo. figure 10. (a) multiple cracks (shown by arrows) in the roadway base material along the great salt lake state park marina access road. primary crack shows approximately 3–4 cm of vertical separation. field notebook (10 cm wide) for scale. (b) close-up view showing approximately 30-cmdeep crack. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photos. figure 11. suas image of subaqueous sand boils (outlined by white line) near the great salt lake state park marina access road. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photo. 122 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 earthquakes (gold and others, 2021) set the stage to present important and timely information associated with these sequences including near-field ground motions, geologic observations, kinematic rupture models, aftershock statistics, and seismic hazard implications. the 2021 imw srl special issue begins with a summary article by wesnousky (2021) contextualizing the seismotectonics of the magna and other imw earthquakes as well as statistically analyzing the aftershock sequences. another summary article discusses a method to use high-rate global positioning system (gps) observations to determine peak ground velocities for the imw earthquakes of 2020 (crowell, 2021). because of the dense regional network of seismometers along the wasatch front and the deployment of temporary seismic stations, several papers were written to analyze the data collected by these instruments for the magna earthquake. mesimeri and others (2021) determined the hypocenter and rupture characteristics of the magna mainshock. holt and others (2021) discussed constraining the magnitudes of smaller aftershocks of the magna sequence using spectral-based methods for calculating moment magnitude. baker and others (2021) doubled the total number of hypocenters in the aftershock catalog of the magna earthquake using machine learning and data from 180 three-component temporary seismometers along with seismic observations from the permanent regional seismic network. integrating seismic data and geodetic observations from gps and interferometric synthetic aperture radar (infigure 12. (a) repaired gas line and sidewalk damage along the great salt lake state park marina maintenance building. (b) cracking in fill material in the dry boat storage area of the great salt lake state park marina. coffee thermos is ~26 cm tall. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photos. 123 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 sar), pollitz and others (2021) determined coseismic slip and afterslip of the mw 5.7 magna earthquake mainshock. they concluded that the mainshock and afterslip were due to normal slip on a gently west-dipping fault plane with some afterslip affected by a steeply northeast-dipping nodal plane, presumably a fault. wong and others (2021) presented a comparison of normal-faulting ground-motion recordings from the 2020 magna earthquake with ground motions predicted by the next generation attenuation-west2 ground-motion models in the salt lake valley (bozorgnia and others, 2014). wong and others (2021) found that the recorded data matched well with the predicted shaking from ground-motion modeling and discussed the seismic hazard implications for a more gently dipping wfz, as proposed by pang and others (2020). finally, kleber and others (2021) used recent geologic mapping as well as seismic and gravity data to add additional geologic context to seismic observations (pang and others, 2020), finding nothing contradicting a listric model for the salt lake city segment of the wfz. additionally, kleber and others (2021) documented some geologic effects of the magna earthquake that are discussed more in depth in this paper. the srl imw special issue was very comprehensive in its scientific reporting on the magna earthquake; however, other publications exist on the magna earthquake. pankow and others (2021), in a srl special issue on scientific response to earthquakes during the covid-19 pandemic, detailed the coordination to deploy uuss figure 13. syneresis cracking near the epicentral area showing a radial pattern characteristic of earthquake ground shaking-induced fluctuations in groundwater. field notebook (10 cm wide) for scale. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photo. 124 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 and usgs seismic instruments, as well as provide timely scientific information to the public during a pandemic. also related to disaster response during a global pandemic, mcentire (2021) reported in the journal of emergency management the benefits and complications from an emergency management perspective and inferred that lockdowns due to the pandemic could have been why there were no reported injuries or fatalities due to the earthquake. two papers from lead author xie hu discussed the hydrologic and stress changes related to fluctuating groundwater levels and the industrial loads of the kti in the salt lake valley (hu and bürgmann, 2021; hu and others, 2021). hu and bürgmann (2021) used sentinel-1 sar (synthetic aperture radar) imagery collected between 2014 and 2019 to observe seasonal, millimeter-scale uplift (springtime) and deflation (winter) in the salt lake valley due to fluctuating groundwater. the hydrologic systems in the salt lake valley are partially modulated by faults and upon investigating poroelastic strain fields, they determined that the mw 5.7 magna earthquake was not triggered by stress changes due to fluctuating groundwater. addressing a similar question on triggering, hu and others (2021) investigated the potential influence of the kti material on triggering the magna earthquake, concluding that the about 60 million tons/year of mill slurry piled on the tailings impoundment since the early 1990s could accelerate or decelerate the occurrence of earthquakes on the order of several hundred years. because of the 2020 magna earthquake, there will likely be additional journal articles, publications, presentations, and discussions for decades to come for those living and working in seismic science and hazards along the wasatch front. conclusions documenting ground effects from the march 18, 2020, mw 5.7 magna, utah earthquake and establishing a digital clearinghouse was critical in the aftermath of the earthquake. collecting perishable data is important for broadening the understanding of seismic hazards along the wasatch front in the wake of a moderate-magnitude earthquake. liquefaction was the most widely observed geologic effect from this earthquake. a combination of seasonally high groundwater levels, figure 14. possible seismically induced rockfall near ensign peak, north of downtown salt lake city. rockfall deposit outlined in white, blue backpack (~0.5 m long) for scale. resource id from the magna earthquake online clearinghouse labeled in bottom right corner of photo. 125 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 fi gu re 1 5. s cr ee ns ho t of t he u g s’s 2 02 0 m 5. 7 m ag na , u ta h ea rt hq ua ke c le ar in gh ou se ( ht tp s:/ /g eo da ta .g eo lo gy .u ta h. go v/ pa ge s/ se ar ch .p hp ?se ar ch =! co lle ct io n6 09 , o r s ca n q r co de a bo ve ). 126 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 the presence of fine-grained great salt lake and lake bonneville sedimentary deposits, and the potential for significant ground shaking from regional earthquakes creates a high liquefaction hazard along much of the wasatch front (castleton and others, 2011). even the moderate magnitude of the 2020 magna earthquake was sufficient to create damaging liquefaction features. recent geologic hazard mapping by the ugs aims to identify areas of high liquefaction susceptibility based on geologic conditions in the subsurface (castleton and others, 2011; castleton and mckean, 2012). based on our observations following the magna earthquake, these maps correctly identified liquefaction hazard areas in the salt lake valley. future hazard mapping should incorporate observations from the magna earthquake to help refine and improve identification and mapping of liquefaction susceptibility along the wasatch front. this earthquake was a timely reminder that the wasatch front is seismically active, despite the lack of large-magnitude earthquakes in historical times. the probabilities of one or more earthquakes occurring in the wasatch front region for various earthquake magnitudes are: 43% for a large (m ≥ 6.75) earthquake, 57% for a m ≥ 6.0 earthquake, and 93% for a m ≥ 5.0 earthquake, such as the magna earthquake (wguep, 2016). despite the 2020 magna earthquake, paleoseismic data indicate that the salt lake city segment of the wfz remains overdue for a major surface-rupturing earthquake, as enough strain was not relieved in this quake to drastically alter the probabilities reported in 2016 (wguep, 2016; pang and others, 2020). despite the lack of fatalities and injuries, the presence of damaging ground-shaking-related geologic effects serves as a reminder for the region’s population of what the effects of a large-magnitude earthquake (m ≥ 6.75) would have on the wasatch front. publication title authors journal link/doi keywords monitoring the 2020 magna, utah, earthquake sequence with nodal seismometers and machine learning baker, b., holt, m. m., pankow, k. l., koper, k. d., and farrell, j. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220200316 seismology near-field strong ground motions from gps-derived velocities for 2020 intermountain western united states earthquakes crowell, b.w. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220200325 seismology, geodetic data preface to the focus section on the 2020 intermountain west earthquakes gold, r. d., bormann, j. m. bormann, and koper, k. d. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220210001 earthquake geology, seismology, geodetic data, seismotectonic setting toward robust and routine determination of mw for small earthquakes: application to the 2020 mw 5.7 magna, utah, seismic sequence holt, j., whidden, k. m., koper, k. d., pankow, k. l., mayeda, k., pechmann, j. c., edwards, b., gök r., and walter, w. r. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220200320 seismology, machine learning aquifer deformation and active faulting in salt lake valley, utah, usa hu, x. and bürgmann, r. earth and planetary science letters, vol. 547 https://doi.org/10.1016/j.epsl.2020.116471 hydrology, active faulting, stress modeling stress perturbations from hydrological and industrial loads and seismicity in the salt lake city region hu, x., xue, l., bürgmann, r., and fu, y. journal of geophysical research: solid earth, vol.126 https://doi.org/10.1029/2021jb022362 hydrology, active faulting, stress modeling geologic setting, ground effects, and proposed structural model for the 18 march 2020 mw 5.7 magna, utah, earthquake kleber, e. j., mckean, a. p., hiscock, a. i., hylland, m. d., hardwick, c. l., mcdonald, g. n., anderson, z. w., bowman, s. d., willis, g. c., and erickson, b. a. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220200331 earthquake geology, seismology, geophysics when emergencies and disasters collide: lessons from the response to the magna, utah earthquake during the covid-19 pandemic mcentire, d. a. journal of emergency management, vol. 19, no. 7 https://doi.org/10.5055/jem.0615 emergency management, pandemic table 1. list of publications on the 2020 magna, utah, earthquake. table 1 continues on next page. 127 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 references baker, b., holt, m.m., pankow, k.l., koper, k.d., and farrell, j., 2021, monitoring the 2020 magna, utah, earthquake sequence with nodal seismometers and machine learning: seismological research letters, v. 92, no. 2a, 787–801, https://doi.org/10.1785/0220200316. bozorgnia, y., abrahamson, n.a., atik, l.a., ancheta, t.d., atkinson, g.m., baker, j.w., baltay, a., boore, d.m., campbell, k.w., chiou, b.s.-j., darragh, r., day, s., donahue, j., graves, r.w., gregor, n., hanks, t., idriss, i.m., hon, m., kamai, r., kishida, t., kottke, a., mahin, s.a., rezaeian, s., rowshandel, b., seyhan, e., shahi, s., shantz, t., silva, w., spudich, p., stewart, j.p., watson-lamprey, j., wooddell, k., and youngs, r., 2014, nga-west2 research project: earthquake spectra v. 30, no. 3, p. 973– 987, https://doi.org/10.1193/072113eqs209m. castleton, j.j., and mckean, a.p., 2012, the utah geological survey geologic hazards mapping initiative, in hylland, m.d. and harty, k.m., editors, selected topics in engineering and environmental geology: utah geological association publication, v. 41, 35 p. castleton, j.j., elliott, a.h., and mcdonald, g.n., 2011, geologic hazards of the magna quadrangle, salt lake county, utah: utah geological survey special study 137, 68 p., 1 plate, scale 1:24,000, https://doi.org/10.34191/ss-137. clark, d.l., oviatt, c.g., and dinter, d.a., 2020, geologic map of the tooele 30' x 60' quadrangle, tooele, salt lake, and davis counties, utah: utah geological survey map 284dm, 48 p., 4 plates, scale 1:62,500, https://doi. org/10.34191/m-284dm. crowell, b.w., 2021, near-field strong ground motions from gps-derived velocities for 2020 intermountain western united states earthquakes: seismological research letters v. 92, p. 840–848, https://doi. org/10.1785/0220200325. publication title authors journal link/doi keywords backprojection imaging of the 2020 mw 5.5 magna, utah, earthquake using a local dense strong-motion network mesimeri, m., zhang, h., and pankow, k. l. seismological research letters, vol. 92, no. 6 https://doi.org/10.1785/0220200326 seismology seismic wave propagation and basin amplification in the wasatch front, utah moschetti, m. p., churchwell, d, thompson, e. m., rekoske, j. m., wolin, e., and boyd, o. s. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220200449 seismology evidence for a listric wasatch fault from the 2020 magna, utah, earthquake sequence pang, g., koper, k.d., mesimeri, m., pankow, k.l., baker, b., farrell, j., holt, j., hale, j.m., roberson, p., burlacu, r., pechmann, j.c., whidden, k., holt., m.m., allam, a., and duross, c. geophysical research letters https://doi.org/10.1002/essoar.10503691.1 seismology, earthquake geology responding to the 2020 magna, utah, earthquake sequence during the covid-19 pandemic shutdown pankow, k. l., rusho, j., pechamnn, j. c., hale, j. m., whidden, k., sumsion, r., holt, j., mesimeri, m., wells, d., and koper, k. d. seismological research letters, vol. 92, no. 1 https://doi.org/10.1785/0220200265 emergency management, seismology coseismic fault slip and afterslip associated with the 18 march 2020 m 5.7 magna, utah, earthquake pollitz, f. f., wicks, c. w., and svarc, j. l. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220200312 seismology seismotectonic snapshots—the 18 march 2020 mw 5.7 magna, 31 march 2020 mw 6.5 stanley, and 15 may 2020 mw 6.5 monte cristo intermountain west earthquakes wesnousky, s. g. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220200314 seismology the 18 march 2020 m 5.7 magna, utah, earthquake: strong-motion data and implications for seismic hazard in the salt lake valley wong, i., wu, q., and pechmann, j. c. seismological research letters, vol. 92, no. 2a https://doi.org/10.1785/0220200323 seismology table 1 (continued). list of publications on the 2020 magna, utah, earthquake. 128 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 gold, r.d., bormann, j.m., and koper, k.d., 2021, preface to the focus section on the 2020 intermountain west earthquakes: seismological research letters, v. 92, no. 2a, p. 636–639, https://doi.org/10.1785/0220210001. holt, j., whidden, k.m., koper, k.d., pankow, k.l., mayeda, k., pechmann, j.c., edwards, b., gök r., and walter, w.r., 2021, toward robust and routine determination of mw for small earthquakes—application to the 2020 mw 5.7 magna, utah, seismic sequence: seismological research letters, v. 92, no. 2a, p. 725–740, https://doi. org/10.1785/0220200320. hu, x. and bürgmann, r., 2020, aquifer deformation and active faulting in salt lake valley, utah, usa: earth and planetary science letters, v. 547, https://doi. org/10.1016/j.epsl.2020.116471. hu, x., xue, l., bürgmann, r., and fu, y., 2021, stress perturbations from hydrological and industrial loads and seismicity in the salt lake city region: journal of geophysical research, solid earth, v. 126, https://doi. org/10.1029/2021jb022362. keaton, j.r., 1987, potential consequences of earthquake-induced regional tectonic deformation along the wasatch front, north-central utah, in mccalpin, j., editor, proceedings of the 23rd symposium on engineering geology and soils engineering: boise, idaho department of transportation, p. 19–34. kleber, e.j., mckean, a.p., hiscock, a.i., hylland, m.d., hardwick, c.l., mcdonald, g.n., anderson, z.w., bowman, s.d., willis, g.c., and erickson, b.a., 2021, geologic setting, ground effects, and proposed structural model for the 18 march 2020 mw 5.7 magna, utah, earthquake: seismological research letters, v. 92, no. 2a, p. 710–724, https://doi.org/10.1785/0220200331. mcentire, d.a., 2021, when emergencies and disasters collide: lessons from the response to the magna, utah, earthquake during the covid-19 pandemic: journal of emergency management 2021 special issue on covid-19, v.19, no.7, p. 19–37, https://doi.org/10.5055/ jem.0615. mckean, a.p., doelling, h.h., willis, g.c., and yonkee, w.a., 2019, geologic map of the antelope island south quadrangle, salt lake, davis, and tooele counties, utah: utah geological survey map 280dm, 28 p., 2 plates, scale 1:24,000, https://doi.org/10.34191/m-280dm. mckean, a.p., and hylland, m.d., 2019a, geologic map of the baileys lake quadrangle, salt lake and davis counties, utah: utah geological survey map 281dm, 28 p., 2 plates, scale 1:24,000, https://doi.org/10.34191/m281dm. mckean, a.p., and hylland, m.d., 2019b, post-lake bonneville migration of the jordan river, salt lake valley, utah [abstract], in lund, w.r., mckean, a.p., and bowman, s.d., editors, proceedings volume—2018 lake bonneville geologic conference and short course, october 3–6, 2018: utah geological survey miscellaneous publication 170, variously paginated, https://doi.org/10.34191/mp170. mckean, a.p., 2019, geologic map of the saltair ne quadrangle, salt lake and davis counties, utah: utah geological survey map 282dm, 28 p., 2 plates, scale 1:24,000, https://doi.org/10.34191/m-282dm. mesimeri, m., zhang, h., and pankow, k.l., 2021, backprojection imaging of the 2020 mw 5.5 magna, utah, earthquake using a local dense strong-motion network: seismological research letters, v. 92, no. 2a, p. 640–646, https://doi.org/10.1785/0220200326. moschetti, m.p., churchwell, d., thompson, e.m., rekoske, j.m., wolin, e., and boyd, o.s., 2021, seismic wave propagation and basin amplification in the wasatch front, utah: seismological research letters, v. 92, no. 6, p. 3626–3641, https://doi.org/10.1785/0220200449. pang, g., koper, k.d., mesimeri, m., pankow, k.l., baker, b., farrell, j., holt, j., hale, j.m., roberson, p., burlacu, r., pechmann, j.c., whidden, k., holt., m.m., allam, a., and duross, c., 2020, evidence for a listric wasatch fault from the 2020 magna, utah, earthquake sequence: geophysical research letters, https://doi.org/10.1002/ essoar.10503691.1. pankow, k.l., rusho, j., pechmann, j.c., hale, j.m., whidden, k., sumsion, r., holt, j., mesimeri, m., wells, d., and koper, k.d., 2021, responding to the 2020 magna, utah, earthquake sequence during the covid-19 pandemic shutdown: seismological research letters, v. 92, no. 1, p. 6–16, https://doi.org/10.1785/0220200265. pollitz, f.f., wicks, c.w., and svarc, j.l., 2021, coseismic fault slip and afterslip associated with the 18 march 2020 m 5.7 magna, utah, earthquake: seismological research letters, v. 92, no. 2a, p. 741–754, https://doi. org/10.1785/0220200312. pratt, b.r., 1998, syneresis cracks—subaqueous shrinkage in argillaceous sediments caused by earthquake-induced dewatering: sedimentary geology, v. 117, p. 1–10. 129 the march 2020, mw 5.7 magna, utah, earthquake—documentation of geologic effects and summary of new research hiscock a.i., kleber, e.j., mckean, a.p., erickson, b.a., mcdonald, g.n., giraud, r., castleton, j.j., and bowman, s.d. geology of the intermountain west 2023 volume 10 utah geographical reference center (ugrc), 2017, 15-cm resolution google imagery, available at https://gis.utah. gov/data/aerial-photography/ (last accessed february 2022). utah geographical reference center (ugrc), 2019, 30cm resolution hexagon imagery, available at https://gis. utah.gov/data/aerial-photography/ (last accessed february 2022). utah geological survey geologic hazards program (ugs ghp), 2020, the ugs response to the march 18, 2020, magnitude 5.7 magna, utah, earthquake and aftershock sequence: utah geological survey, survey notes, v. 52, no. 3, p. 1–5, https://ugspub.nr.utah.gov/publications/ survey_notes/snt52-3.pdf united states geological survey (usgs), 2022, 2020 magna earthquake sequence executive summary page, available at https://earthquake.usgs.gov/earthquakes/eventpage/ uu60363602/executive (last accessed february 2022). university of utah seismograph stations (uuss), 2021, 2020 magna earthquake sequence faq, available at https://quake.utah.edu/special-events/2020-magnaearthquake-sequence-faq (last accessed february 2022). wallace, j., and lowe, m., 2009, ground-water quality classification for the principal basin-fill aquifer, salt lake valley, salt lake county, utah: utah geological survey open-file report 560, 80 p., 3 plates, scale 1:75,000, https://doi.org/10.34191/ofr-560. wesnousky, s.g., 2021, seismotectonic snapshots—the 18 march 2020 mw 5.7 magna, 31 march 2020 mw 6.5 stanley, and 15 may 2020 mw 6.5 monte cristo intermountain west earthquakes: seismological research letters, v. 92, no. 2a, p. 755–772, https://doi.org/10.1785/0220200314. wong, i., olig, s., green r., moriwaki, y., abrahamson, n., barnes, d., silva, w., somerville, p., davidson, d., pilz, j., and dunne, b., 1995, seismic hazard evaluation of the magna tailings impoundment, in lund, w.r., editor, environmental and engineering geology of the wasatch front region: utah geological association publication 24, p. 95–110. wong, i., wu, q., and pechmann, j.c., 2021, the 18 march 2020 m 5.7 magna, utah, earthquake—strong-motion data and implications for seismic hazard in the salt lake valley: seismological research letters, v. 92, no. 2a, 773–786, https://doi.org/10.1785/0220200323. working group on utah earthquake probabilities (wguep), 2016, earthquake probabilities for the wasatch front region in utah, idaho, and wyoming: utah geological survey miscellaneous publication 16-3, 164 p., 5 appendices, https://doi.org/10.34191/mp-16-3. https://gis.utah.gov/data/aerial-photography/ https://gis.utah.gov/data/aerial-photography/ https://ugspub.nr.utah.gov/publications/survey_notes/snt52-3.pdf https://earthquake.usgs.gov/earthquakes/eventpage/uu60363602/executive https://quake.utah.edu/special-events/2020-magna-earthquake-sequence-faq shorelines and vertebrate fauna of pleistocene lake bonneville, utah, idaho, and nevada geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 © 2017 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. shorelines and vertebrate fauna of pleistocene lake bonneville, utah, idaho, and nevada mark milligan and h. gregory mcdonald a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover restored outline of lake bonneville. geological data by g.k. gilbert and e.e. howell. lithography by j. bien. dated 1876. from, “topographical atlas projected to illustrate united states geographical surveys west of �e 100th meridian,” a collection of 135 topographical and geological atlas sheets, 1876 to 1881. downloaded from the david rumsey map collection, www. davidrumsey.com. ancient lake surface in light blue. present (1876) lake surfaces and running water courses in dark blue. ancient land surface in dark drab. �ought to be the oldest published map of lake bonneville, this 1876 map does not show the full extent of the lake as depicted in gilbert’s 1890 monograph. i 2017 president bill loughlin bill@loughlinwater.com 435.649.4005 2017 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2017 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2017 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2017 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2017 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental a�airs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt a�olter g�247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017-2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual �eld conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. �e uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. a�liated with the american association of petroleum geologists. volume 4 2017 �is is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and �gures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com �omas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 181 abstract pleistocene lake bonneville created many classic examples of lacustrine shoreline landforms, which preserve a wide variety of vertebrate fossils. �is �eld guide provides a review of the published literature for a sampling of the lake’s world-class localities. �is guide also provides a brief overview of modern great salt lake and its microbialites recently exposed by near-record low lake levels. stops include g.k. gilbert geologic view park, draper spit, steep mountain beach, point of the mountain spit, american fork delta, stockton bar, and great salt lake state park. shorelines and vertebrate fauna of pleistocene lake bonneville, utah, idaho, and nevada mark milligan1 and h. gregory mcdonald2 1utah geological survey, p.o. box 146100, salt lake city, ut 84116; markmilligan@utah.gov 2bureau of land management, utah state o�ce, 440 w. 200 s., salt lake city, ut 84101; hmcdonald@blm.gov citation for this article. milligan, m., and mcdonald, h.g., 2017, shorelines and vertebrate fauna of pleistocene lake bonneville, utah, idaho, and nevada: geology of the intermountain west, v. 4, p. 181–214. © 2017 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org introduction to lake bonneville and the bonneville basin �e following section is modi�ed from godsey and others, 2005a. lake bonneville was a large pluvial lake that occupied the eastern great basin during latest pleistocene marine oxygen isotope stage (mis) 2, from approximately 30 to 13 cal ka (�gure 1) (gilbert, 1890; oviatt, 2015). �is region is part of the basin and range province that developed in response to east-west crustal extension beginning ca. 20 ma. normal faulting and subsidence caused the formation of basins separated by upli�ed fault blocks. �e most signi�cant subsidence occurred at the eastern margin of the basin and range province, and it is here that the bonneville basin formed. extension continues to modify the landscape in the basin and range today. �e bonneville basin has been a region of internal drainage for the past 15 m.y. and lakes of varying sizes have occupied part of the basin throughout most of this figure 1. simpli�ed hydrograph of lake bonneville. altitudes adjusted for isostatic rebound. bars at top show transgressive (t), over�owing (o), and regressive (r) phases. modern great salt lake (gsl) average altitude is 1280 m. lake gunnison is an isolated lake in the sevier sub-basin that formed with the regression of lake bonneville. figure courtesy of jack oviatt (kansas state univeristy). www.utahgeology.org 182 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 time (currey and others, 1984). researchers have produced evidence that at least four deep-lake cycles have occurred in the bonneville basin over the past 780,000 years, the bonneville lake cycle being the youngest of these (oviatt and others, 1999). lake bonneville began to form ca. 30 ka when colder and/or wetter climate conditions during the last glacial maximum caused it to rise (oviatt, 2015). �e timing and/or the rapidity of the rise may have been in�uenced by diversion of the upper bear river into the bonneville basin ca. 30 ka (reheis and others, 2014), although pederson and others (2016) report evidence that the river diversion occurred about 50 ka. �e transgression continued until ca. 25 ka when changing climate conditions caused the lake to undergo a slight regression (oviatt, 2015). for nearly 3000 yr, the level of the lake oscillated through a vertical range of about 50 m near 1370 m above sea level (masl), forming the stansbury shoreline, and then began to rise again. by ca. 18 ka, the lake had reached the level of the topographic divide near zenda, idaho (�gure 2), and began to over�ow. �is marks the beginning of the open-basin phase of the lake and the formation of the bonneville shoreline (�gure 1). when the lake became very deep and heavy in the center of the basin, transgression was enhanced by hydro-isostatic subsidence. however, the primary driver of transgression was a change in water budget caused by climate change in the basin. water inputs from precipitation, groundwater, and runo� became much greater than outputs by evaporation and groundwater. at 18 ka lake bonneville was over 300 m deep and covered an area of ~51,000 km2 (oviatt and miller, 1997). rivers emanating from the high mountains to the east provided large amounts of clastic material that was deposited in deltas along the mountain fronts (lemons and others, 1996). spits, barriers, bars, and beaches were supplied sediment by alluvium and weathered bedrock in regions with little riverine input. muds and marls were deposited in more distal, o�shore locations (oviatt and miller, 1997). catastrophic failure of the alluvial-fan dam (the alluvial-fan deposits overlie tu�aceous sediments of the neogene salt lake formation) at the zenda (�gure 2) threshold in southern idaho ca. 18 ka caused a massive �ooding of lake waters into the snake river drainage (gilbert, 1890). �ere is insu�cient resolution to determine how long the lake remained at the threshold before failure, although it is likely the over�ow period was figure 2. shaded-relief map showing the extent of lake bonneville and other great basin lakes (blue) and select mountain ranges with valley glaciers (white) during the latest pleistocene. dashed line delineates great salt lake. red boxes indicate the locations, little cottonwood (lc) and american fork (af) canyons, of study areas for 10be cosmogenic surface-exposure dating of erratic boulders atop moraines by laabs and others (2011) and laabs and munroe (2016). modi�ed from laabs and others (2011). 183 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 very short (oviatt, 2015; oviatt and jewell, 2016). �is event, called the bonneville �ood, caused a drop in the lake level of at least 125 m (miller and others, 2013) and is believed to have occurred in less than one year’s time (malde, 1968; o’connor, 1993, 2016). headward erosion by �ood waters shi�ed the drainage divide to the southeast ~3.2 km to near red rock pass, idaho (currey, 1982). �e lake re-stabilized at the new threshold, probably on massive landslide deposits, and the provo shoreline began to form (�gure 1; gilbert, 1890; miller, 2016). �e lake oscillated at or near the level of the red rock pass outlet until a change in climate conditions permanently drove the lake below the threshold, starting ca. 15 ka (godsey and others, 2011; oviatt, 2015). by ca. 13 ka, the lake had reached levels comparable to modern great salt lake (oviatt, 2015). �is marks the end of the bonneville lake cycle and the beginning of its successor, great salt lake. �e lake appears to have risen again brie�y ca. 11.6 ka during the gilbert episode (oviatt and others, 2005; oviatt, 2014), but the existence and extent of a gilbert shoreline is suspect and the subject of ongoing investigations (oviatt, 2014). �e mass of lake bonneville’s water weighed down and isostatically depressed the earth’s crust. with the demise of the lake the crust rebounded to its original elevation, thus elevating and distorting the originally horizontal shorelines (gilbert, 1890; adams and bills, 2016). �e greatest rebound, up to 74 m, was at the deepest part of the basin on the west side of great salt lake (currey, 1990). climate and glaciation �ough permanent diversion of the upper bear river into the bonneville basin may have in�uenced the timing and/or the rapidity of the rise of lake bonneville (reheis and others, 2014), the climatic variables of evaporation and precipitation subsequently controlled lake level and glacial extent in the bonneville basin (laabs and munroe, 2016). �e importance of temperature vs. precipitation in controlling lake and glacier mass balance has been controversial (laabs and others, 2011; reheis and others, 2014). some studies suggest a cold and dry climate in the interior western u.s. during mis 2 (e.g., porter and others, 1983; kaufman, 2003). other studies suggest increased precipitation drove lake and glacier expansions (e.g., benson and �ompson, 1987). �e long-held idea that glacial maxima predated lake-level highstand (e.g., madsen and currey, 1979) favored a wetter and warmer scenario. however, godsey and others (2005b) describe glacial till stratigraphically above and below bonneville shoreline deposits. furthermore, laabs and munroe (2016) used 10be cosmogenic surface-exposure dating of erratic boulders to determine that terminal moraines in the bonneville basin were occupied near the time of the bonneville highstand at 18 ka and subsequently abandoned while the lake continued to over�ow at the provo threshold. �us, the climate favored simultaneous lake transgression and glacial advance until ca. 18 ka. �e apparent start of ice retreat while the lake still over�owed suggests that sometime a�er 18 ka the climate warmed but precipitation remained high enough to sustain a positive water budget for the lake until retreat from the provo shoreline at ca. 15 ka (laabs and munroe, 2016). the pleistocene and holocene vertebrate fauna of lake bonneville in gilbert's 1890 monograph on the geology of lake bonneville, it only brie�y mentions vertebrate remains as some “elephantine bones and ivory” recovered from a “post-bonneville” marsh east of utah lake. however, pleistocene vertebrate remains associated with the lake deposits were being discovered in the area during the earliest studies of the lake (chadbourne, 1871) and the recovery of vertebrate fossils from lake bonneville sediments and sediments in caves in the bonneville basin continues to the present (�gure 3). our knowledge of the pleistocene vertebrate fauna associated with lake bonneville is based on numerous localities in the lake basin. je�erson and others (1994) listed 18 localities in salt lake county, three in davis county, and one each in box elder and weber counties. most of our knowledge of the fauna has occurred recently (stokes and others, 1964; smith and others, 1968; nelson and madsen, 1978, 1980, 1983, 1986, 1987; miller, 1982, 2002; feduccia and oviatt, 1986; gillette and miller, 1999; schmitt and lupo, 2016). based on the 184 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 location, elevations, and the physical stratigraphy of the various sites, the majority of the fauna associated with lake bonneville gravel deposits comes from sediments deposited at or near the bonneville and provo shorelines (nelson and madsen, 1987; mcdonald and others, 2001). a�er dropping from the bonneville to provo level, the lake occupied the provo shoreline for about 3000 years. �e provo shoreline is formed by a complex of several coalescing coastal landforms, many of which form a pattern of distinctive beach ridges that can be identi�ed throughout the basin (burr and currey, 1988; godsey and others, 2005a; miller and others, 2013; miller, 2016). radiocarbon ages of sediments associated with the provo shoreline indicate that lake bonneville dropped rapidly from the provo shoreline at about 12,600 14c yr b.p. (15,000 cal yr b.p.). �e rapid lowering of the lake level from the provo shoreline correlates with the decline of lakes lahontan in nevada and estancia in new mexico, and with the onset of the bølling–allerød warming event (godsey and others, 2011). �e earliest report of pleistocene vertebrates from deposits associated with lake bonneville was by king (1878) who noted that “the latest subaerial gravels [i.e., provo shoreline] yielded a skull of bison latifrons and fragments of bones, supposed to be a “reindeer.” unfortunately the location where the specimens were found is unknown as is the current location, and it is not known if they were even collected. bison antiquus is also present and has been recovered from gravel pits along the eastern shoreline of the lake (�gure 4b). �e deposits associated with the provo shoreline span the time interval when the climate in the great basin was transitioning from the colder, wetter conditions of the last glacial maximum to the warmer, drier conditions of the late pleistocene and early holocene (godsey and others, 2011). �e expansion and contractions of lake levels in the great basin during the late pleistocene to holocene transition have been linked to position of the jet stream as it was de�ected around the north american ice sheets (kutzbach, 1987). in general, pluvial lakes at lower latitudes (ca. 32°–35° n), such as lake estancia in new mexico, reached their highstand when the continental ice sheets had reached their maximum extent about 15,000 14c years ago (garcia and stokes, 2006). in contrast, lakes at higher latitudes (ca. 38°–40° n), such as bonneville and lahontan, experienced their figure 3. �e bonneville basin showing locations of selected paleontological and archaeological sites with vertebrate remains. circles are open air sites and triangles are cave or rock-shelter sites: (1) franklin peccary site, (2) logan cemetery, (3) hogup cave, (4) homestead cave, (5) danger cave, (6) bonneville estates rock shelter, (7) camels back cave, (8) lark, (9) jordan narrows, (10) point of the mountain sloth site, (11) monroc gravel pit, (12) huntsman, (13) sandy mammoth, (14) orem sloth site, (15) spanish fork, (16) tabernacle crater camel site, (17) crystal ball cave, (18) smith creek cave and cathedral cave, and (19) snake creek burial cave. modi�ed from schmitt and lupo (2016). 185 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 figure 4. pleistocene vertebrate fossils from gravel pits on the east side of lake bonneville. (a) camelops hesternus, proximal phalanx, anterior view. (b) bison antiquus metacarpal, anterior view. (c) arctodus simus right tibia, anterior view. (d and e) equus sp. braincase, right lateral, posterior view. (f and g) ovis canadensis braincase, anterior and right lateral view. (h and i) mammuthus columbi right upper molar, occlusal, lateral view. (j and k) bootherium bombifrons (male) braincase, posterior and dorsal view. all specimens in the natural history museum of utah. scale is 5 cm. 186 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 highstands slightly later (ca. 14,500–13,500 14c yr b.p.) following the retreat of the ice sheets northward (adams and wesnousky, 1998; benson and others, 1990; garcia and stokes, 2006). as the ice sheets continued to retreat, storm tracks also shi�ed northward, resulting in reduced annual precipitation and a lowering of water levels in pluvial lakes in the region. �e development of a clear record of changes in the lake-level within the bonneville basin is critical for examining regional climate patterns and the degree of synchronicity in the highstands in the numerous pluvial lakes across the western united states during the last glacial maximum (benson and others, 1990; adams and wesnousky, 1998; benson, 1999; licciardi, 2001; garcia and stokes, 2006; broecker and others, 2009). a better understanding of the climatic conditions that determined lake levels also provides a framework for understanding how the pleistocene fauna of the region was impacted by climatic and environmental change since changes in precipitation not only impacted lake levels but vegetation as well. multiple caves (e.g., homestead cave and cathedral cave in utah, and danger cave and smith creek cave in nevada) are associated with lake bonneville that after becoming exposed with the lowering of lake level accumulated small vertebrate remains. sediments in homestead cave have been dated from 11,270 ± 135 to 1020 ± 40 14c yr b.p. (broughton, 2000). radiocarbon dates for cathedral cave range from 15,310 ± 60 to 740 ± 40 14c yr b.p. (madsen, 2000). whereas the fauna recovered from both caves spanned the pleistocene-holocene transition no extinct species were recovered from either cave. �e composite fauna which is derived from multiple sites spanning thousands of years is highly biased toward larger taxa; 15 mammals, two birds, and six �sh are reported by nelson and madsen (1987). since then the megafauna has been expanded by the discovery of two separate �nds of the je�erson ground sloth, megalonyx je�ersonii (gillette and others, 1999; mcdonald and others, 2001). whereas some specimens can be placed within a chronology based on where they were collected, the vertebrae faunal record is not su�ciently robust or has a tight enough chronology at this time to actually document any faunal change in response to climatic change. few of the older specimens have been radiocarbon dated, and in many cases the quality of preservation of many specimens does not permit a radiocarbon date. schmitt and lupo (2016, table 13.1) provide a list of the extinct pleistocene mammals of the bonneville basin, although some of the taxa were recovered from localities adjacent to the basin and not the basin proper. a composite list of taxa from sites directly associated with lake bonneville appears in table 1. a muskox skull was among the �rst vertebrate fossils to be described from the bonneville basin (chadbourne, 1871). nelson and madsen (1987) recognized two taxa of musk ox, bootherium bombifrons and symbos cavifrons, from the bonneville basin but these two taxa are now considered male (symbos) and female (bootherium) of the same species (mcdonald and ray, 1989), so one extinct species of muskox, bootherium bombifrons, is now recognized from the late pleistocene in north america, along with the extant muskox, ovibos moshatus. nelson and madsen (1987) reported four skulls of the female have been recovered and 21 skulls of the male along with some post-cranial material. gillette and miller (1999) reported a partial skeleton found during construction of the huntsman chemical corporation headquarters in salt lake city, another skull from the staker gravel pit, an ear region and vertebrae from a gravel pit owned by the kennecott copper company in salt lake county, a skull from spanish fork in utah county, and post-cranial bones from the same gravel pit at point of the mountain that produced a ground sloth. �e predominance of male skulls has been noted elsewhere (mcdonald and ray, 1989) and has been explained as re�ecting the more robust build of the male skull which favors its preservation (�gures 4j and 4k). nelson and madsen (1987) observed that skulls are readily noticed by machinery operators in the gravel pits so have a better chance of being collected. �e sample of skulls of bootherium from the bonneville basin is one of the largest samples for the species and one of the few places where both skull morphs have been found. as is common in the western united states, mammoth, as represented by mammuthus columbi (�gures 4h and 4i), is more common than mastodon, mammut americanum, and this is also true for the bonneville ba187 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 table 1. late pleistocene and early holocene vertebrate taxa associated with lake bonneville. compiled from nelson and madsen (1987), gillette and others (1999), broughton (2000), grayson (2000), and broughton and others (2000), livingston (2000), mcdonald and others (2001), schmitt and lupo (2016), and wolfe and broughton and smith (2016). * = extinct taxa. class osteichthyes gila atraria richardsonius balteatus catostomus ardens catostomus discobolus panosteus virescens chasmistes cf. liorus cf. salvelinus con�uentus oncorhynchus clarki (also reported as salmo clarki) prosopium gemmifer prosopium spilonotus prosopium abyssicola cottus bairdi cottus extensus class aves podilymbus podiceps podiceps sp. aechmophorus occidentalis phalacrocorax auritus (reported as p. macropus) branta sp. anas sp. athya sp. bucephala albeola bucephala clangula oxyura jamaicensis cygnus buccinator circus cyanus accipiter striatus buteo sp. falco sparverius falco columbiarius falco cf. mexicanus phasianidae rallus limnicola porzana carolina porphyra/gallinula/fulica recurvirostra americana phalaropus sp. larus sp. zenaida macroura coccyzus americanus tyto alba otus sp. bubo virginianus glaucidium gnoma athene cunicularius asio sp. ageolius acadicus chordeiles cf. acutipennis phalaenontilus nuttallii melanerpes lewis sphyrivicus sp. picoides sp. colantes auratus tyrannus verticalis eremophilia alpestris cf. stelgidopteryx serripennis cyanocetta stelleri aphelocoma coerulescens pica pica troglodytidae myadestes townsendi turdus migratorius oreoscoptes montanus bombycilla garrulous b. cf. cedrorum lanius ludoviciana piranga ludociviana pheuticus cf. melanocephalus piplio cf. chlorurus piplio cf. erythrophthalmus agelaius phoeniceus sturnella neglecta xanthocephalus xanthocephalus fringillidae carpodacus mexicanus carduelis tristis coccothraustes vespertinus class mammalia megalonyx je�ersonii * brachylagus idahoensis lepus californicus lepus townsendii sylvilagus cf. audubonii sylvilagus cf. nuttallii ammospermophilus lecurus tamias minimus marmota �aviventris spermophilus mollis �omomys bottae �omomys talpoides chaetodipus formosus dipodomys microps dipodomys ordii microdipodops megacephalus perognathus longimembris perognathus parvus lemmiscus curtatus microtus sp. neotoma cinerea neotoma lepida ondatra zibethicus onychomys leucogaster peromyscus sp. pitymys sp. reithrodontomys megalotis vulpes vulpes vulpes velox canis latrans canis lupus arctodus simus * ursus americanus lynx rufus mustela erminea mustela frenata mustela vison spilogale putorius taxidea taxus equus sp. platygonus compressus * camelops hesternus * odocoileus hemionus navahoceros cf. fricki * antilocapra americana ovis canadensis bison cf. antiquus * bootherium bombifrons (including symbos cavifrons) * mammut americanum * mammuthus columbi * 188 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 sin with 17 documented records of mammoth and only one record of mastodon (nelson and madsen, 1987; larson, 1999). �is may simply re�ect di�erences in preferred habitat with mastodons more closely associated with coniferous forests that would have been present at higher elevations in the wasatch range outside the lake basin (miller, 1987), while the mammoths would have grazed in the more open grassland habitat at lower elevations. �e recovery of a mammoth from a gravel pit near newcastle in the escalante valley, iron county, is the southernmost record of this taxon associated with lake bonneville (larson, 1999). �e specimen was recovered from an alluvial-fan complex and was radiocarbon dated at 28,670 ± 260 14c yr b.p., which predates the lake’s highstand in that valley 12,000 years later. however, while the southern edge of lake bonneville did extend into the northern part of the escalante valley (currey, 1982) the lake did not extend as far south as the site where the mammoth was found. another taxon associated with lake bonneville that is relatively rare in the western united states is the �at-headed peccary, platygonus compressus (mcdonald, 2002). �e single record, consisting of most of the skeleton of one individual comes from the cache valley. �e specimen was radiocarbon dated at 11,340 + 50 14c yr b.p. and indicates the �oor of the valley was inhabited by terrestrial fauna relatively soon a�er the �ood and drop in lake level. �e extinct camel, camelops, which is uncommon, has been referred to c. hesternus, primarily based on size (�gure 4a). mule deer, odocoileus heminous, is known only from a humerus and femur recovered the same gravel pit. horse, currently not referred to species, is also present but also uncommon (�gures 4d and 4e). among the most common species recovered from sediments associated with lake bonneville is the mountain or bighorn sheep, ovis canadensis (stokes and condie, 1961; stokes, 1966). �is species is represented by a least two dozen individuals but is a highly-biased sample. �e mountain sheep is primarily represented by crania (�gures 4f and 4g) or horn cores of adult males. skulls of females and juveniles have not been recovered and only a very few post-cranial bones have been found. stokes (cited in nelson and madsen, 1987) suggested that the large sinuses in the male skulls and horns allowed them to partially �oat and thus be transported. as noted by nelson and madsen (1987) almost all the specimens show abraded surfaces suggestive of being rolled on the beach prior to burial. unfortunately, the way most vertebrate specimens associated with lake bonneville are recovered during commercial gravel and sand quarrying has precluded the recovery of any good taphonomic data. �e sample is highly biased towards larger specimens that are more easily noticed and no longer in situ. consequently most �nds are of single bones, although a few associated bones of an individual are occasionally found, such as the short-faced bear which includes a partial vertebral column of posterior thoracic to sacral vertebrae, pelvis, and bones of the hind limbs (nelson and madsen, 1983). as expected only a few carnivores have been recovered from the gravel deposits. �ese include two extant canids, vulpes vulpes and canis lupus, and two bears, the extant ursus americanus and extinct arctodus simus (nelson and madsen, 1983, 1986, 1987) (�gure 4c). �e arctodus is one of two records of this taxon in utah; the other is from the huntington dam mammoth site in the wasatch plateau south of the bonneville basin (gillette and madsen, 1992). �e only partial skeletons recovered to date are from the short-faced bear, arctodus, and the sloth, megalonyx. unlike most of the other taxa, which are from deposits associated with the bonneville shoreline, the two sloth records are from the provo level. also, both sloth specimens come from the south end of the basin from point of the mountain and orem, and both were recovered in situ. �e sedimentologic and taphonomic data for the point of the mountain specimen suggest that the sloth carcass may have washed into lake bonneville relatively intact. �e carcass was transported some distance along the wasatch front by longshore dri�. as the carcass was transported toward point of the mountain, it made its way to the edge of the wavebuilt terrace of a large spit. �e spit would have been migrating to the west, but the longshore current and direction of the spit would have produced foreset beds oriented to the northwest. �e carcass eventually fell o� the wave-built terrace of the spit and settled into deeper water (approximately 10 m) that had been receiving only suspended-load, hemipelagic sediments. eventual189 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 ly, foreset lamination from spit progradation buried the carcass, thus preventing scavenging and disassociation of the skeleton (mcdonald and others, 2001). �e sand and gravel in which the orem skeleton was buried are either deltaic deposits of the provo phase of the bonneville lake cycle or stream alluvium related to the provo phase of the bonneville lake cycle (machette, 1992). �e skeleton was in coarse, ungraded and unbedded gravel, but with slight imbrication of the gravel clasts immediately adjacent to the bones that suggested high-energy �uvial sedimentation. virtually all of the small mammal remains associated with lake bonneville have been recovered from cave deposits. most of these accumulations appear to be the result of foraging by owls. �e small mammal remains from homestead cave have been intensively studied (grayson, 2000) based on 183,798 identi�ed bones and teeth. �is documentation of the changing proportions of species pairs and species replacement in succeeding strata indicates major shi�s in the climate and consequently the vegetation (grayson, 2000). two species of dipodomys are present, d. microps and d. ordii. d. microps, the chisel-tooth kangaroo rat, which uses its lower incisors to shave o� the outer hypersaline tissue from the leaves of atriplex sp. in order to access the palatable inner tissue, whereas d. ordii is a granivore that is usually associated with sagebrush habitat, so there is minimal overlap in the distribution of the two species. �e increase in the number of specimens of d. microps and decline of d. ordii in the stratigraphic sequence suggests the progressive replacement of sagebrush-dominated habitat by shadscale-dominated habitat through the holocene. a similar pattern is demonstrated by the changes in abundance of microtis and lemmiscus. microtis utilizes grassland habitat whereas lemmiscus prefers habitat dominated by sagebrush, usually artemisia tridentata. microtis is common in the late pleistocene and early holocene sediments at homestead cave but decreases in number a�er 8.3 ka and is uncommon a�er 7 ka, and is replaced by lemmiscus as the common vole. also, around 8.3 ka, neotoma lepida replaces n. cinerea in the fauna. a similar pattern is seen in the pocket mice, perognathus, with p. parvus common in the late pleistocene and then replaced by p. longimembris. p. parvus in the great basin today is found at higher elevations indicating a preference for cooler temperatures whereas p. longimembris tends to be found at lower elevations with higher temperatures. likewise, the pocket gopher, �omomys talpoides, is found at higher elevations and mountain valleys in utah today while t. bottae lives in the lower valleys. at homestead cave, t. talpoides is present only in the late pleistocene and is replaced by t. bottae, indicating a transition from cooler to warmer temperatures. �e yellow-bellied marmot, marmota �aviventris, lives at higher elevations in the southern part of its range and at lower elevations in the more northern parts of its range, re�ecting its sensitivity to warmer temperatures. at homestead cave, it is more common in the lower late pleistocene strata and appears to have disappeared from the area around 8 ka so its disappearance may be indicative of warming temperatures. most bird remains associated with lake bonneville consist of isolated �nds and the only known avifaunas are from cave deposits, like those of homestead cave. �e avifaunal assemblage from homestead cave consists of 6000 specimens representing 75 species from 26 families (livingston, 2000). �e avifauna includes not only taxa that would be expected to be associated with a lake—divers, specialized �shers, waterfowl, shorebirds and marshbirds—but also upland game birds, woodpeckers, and perching birds. �e diurnal predators like hawks and falcons, and nocturnal predators, owls, are believed to have been the primary contributors to the fauna in the cave. �e three most common families of birds from homestead cave are the podicipedidae (grebes) at 30% of the total assemblage, anatidae (ducks) at 15% of the assemblage, and alaudidae (larks) at 20% of the assemblage. �e presence of the two aquatic families is expected given the cave’s association with the lake. in fact, the two lowest strata in the cave, when the lake level was still relatively high, are dominated by waterfowl in terms of both the number of taxa, and percentage of bones from waterfowl recovered. larks do not become common until the upper stratigraphic levels, re�ecting the lower lake level and presence of more open habitat. missing from the avifauna are larger taxa like loons, pelicans, swans, cranes, and herons that are all larger than the predatory birds in the fauna. cormorants and 190 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 mergansers, which are obligate piscivores, are restricted to the lower levels of homestead cave and disappear early, likely re�ecting the loss of a food source with lower lake levels and increased salinity. while �sh do not live in great salt lake today, fresher water during the bonneville lake cycle supported a variety of �sh (broughton and smith, 2016). broughton and smith (2016) described 10 primary localities in the bonneville basin that produced �sh remains: six are open-air sites and four are caves. broughton and smith (2016) documented 13 species of �sh represented by fossils, out of the 21 species present in the extant fauna (table 1). �e �sh found in lake bonneville sediments account for three of the four endemic and �ve of the nine native species in modern bear lake (�gure 3). homestead cave is in the lakeside mountains (�gure 3). �e opening of the cave at 1406 m is between the provo and stansbury shorelines. �e pleistocene fauna recovered included 11 species of freshwater �sh concentrated in the lowest stratum of the deposits and 11 freshwater species from sediments that accumulated in the cave a�er 11,200 14c yr b.p. eight of the species occur in bear lake. �e �sh remains are thought to have been caught by owls (broughton, 2000; broughton and others, 2000). analysis of the 87sr/86sr values of the �sh bone from the lowest stratum of the cave suggests they grew near the terminal pleistocene gilbert shoreline. a decrease in �sh size and an increase in species tolerant of higher salinities or temperatures in the lowest deposits suggest multiple die-o�s associated with declining lake levels. an initial, catastrophic, post-provo die-o� occurred at 11,300 –11,200 14c yr b.p. (~ 13.2 to 13.1 cal ka) and was followed by at least one rebound or recolonization of �sh populations. around 3.7 cal ka there was a highstand of the lake and this is re�ected in a peak in the frequency of bones of gila atraria (utah chub) in the cave sediments. despite this rebound �sh were gone from lake bonneville sometime before 10,400 14c yr b.p. cathedral cave which is close to homestead cave has a distinctively di�erent �sh fauna that consists exclusively of sculpin. as sculpins prefer cold deep water their presence in the cave sediments is attributed to accumulating during a deep-water phase, ca. 100–200 m of lake bonneville when the lake was at either the bonneville or provo level. strata above the level with the sculpins had a radiocarbon age of 15,310 ± 60 14c yr b.p. (broughton and smith, 2016). road guide �e road guide begins at the grand america hotel in salt lake city (�gure 5). �e route heads south to the g.k. gilbert geologic view park, the draper spit, steep mountain shorelines, the point of the mountain spit, and the american fork delta. �e route then heads west to the stockton bar, north to great salt lake, and east to return to grand america. mileage (mi) description interval / cumulative 0.0 / 0.0 grand america hotel’s porte cochere entrance at approximately 60 east 600 south street, salt lake city (�gure 5). turn le� out of porte cochere and proceed several hundred feet to state street. 0.0 / 0.0 turn right onto state street. 0.6 / 0.6 turn right onto 900 south and proceed west. 0.3 / 0.9 turn le� onto west temple and merge onto the interstate 80 (i-80) east ramp to cheyenne. 2.5 / 3.4 merge onto i-80 east. 4.6 / 8.0 take exit 128 for i-215 south. 6.3 / 14.3 take exit 6 for 6200 south and turn le�, proceeding east. 0.8 / 15.1 6200 south curves right (south) and becomes wasatch boulevard. 3.2 / 18.3 bear right at signal to continue on wasatch boulevard. 1.1 / 19.4 turn right onto little cottonwood road at signal. 0.1 / 19.5 to stop 1. pull into dirt parking area on right at 3345 east little cottonwood road, sandy. stop 1 g.k. gilbert geologic view park located near the mouth of little cottonwood canyon, this geologic park showcases multiple geomorphic and geologic features and has long been a destination for �eld trips. �e park was dedicated in 2008 and in191 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 cludes �ve non-technical interpretive signs with information about bedrock geology, mining and quarrying activity, the wasatch fault, lake bonneville, and glaciation (�gure 6). �ree bedrock formations are visible from the park: (1) early proterozoic little willow formation, (2) late proterozoic big cottonwood formation, and (3) oligocene little cottonwood stock (eldredge, 2008). contorted quartz schist and gneiss primarily comprise the little willow formation. alternating shale and quartzite originally deposited in a tidal/shoreline environment generally comprise the big cottonwood formation. quartz monzonite comprises the bulk of the little cottonwood stock. gold was mined from the little willow formation more than a century ago, and mine dumps are evident near the north side of the canyon mouth (eldredge, 2008). “granite” (quartz monzonite) has been quarried from the temple quarry, located just out of view in the lower canyon. �is stone was used to construct the church of jesus christ of latter-day saints’ salt lake temple and other prominent buildings in salt lake city and has been quarried intermittently since the 1860s. formed by repeated earthquakes and reaching more figure 5. field trip stops. �e blue line is the 5200-foot-elevation contour, which approximates the bonneville shoreline (not adjusted for isostatic rebound). 192 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 than 30 m high, the scarps visible here on the salt lake city segment are some of the largest of the wasatch fault zone (�gure 7). �e wasatch fault zone is an approximately 370-km-long, 10-segmented normal fault system that forms the wasatch front and the eastern boundary of the basin and range province (machette and others, 1992). faulting began approximately 18 ma (parry and bruhn, 1987) and vertical slip rates have apparently varied through time. long-term slip rates are about 0.7 mm/yr since ca. 18 ma (parry and bruhn, 1987), 0.2–0.4 mm/yr since 5 ma (armstrong and others, 2004), and 0.5–1.0 mm/yr since 0.4–0.8 ma (mayo and others, 2009). displaced latest pleistocene shorelines and fans yield vertical slip rates of approximately 0.1–0.3 mm/yr (machette and others, 1992). post-provo level paleoseismic trenching data yield slip rates of approximately 1–2 mm/yr (e.g., machette and others, 1992; lund, 2005; duross and others, 2016). modern geodetic horizontal extension across the fault zone is ~1.6–3.2 mm/yr (chang and others, 2006; kreemer and others, 2010). �e park is located above the elevation of the bonneville shoreline and lake features are not visible. �e park rests on glacial till and would have been covered by glacial ice near the time of the bonneville highstand at 18 ka (laabs and munroe, 2016). glacial features visible from the park include the classic u-shaped valley of little cottonwood canyon, moraines, and scattered glacial boulders. �is is one of only a few localities in the world where mid-latitude alpine glaciers entered lakes during the last glacial maximum. as discussed in the climate and glaciation section above, laabs and munroe (2016) dated erratic boulders found both on the north side of the canyon mouth and on top of the moraine crest visible to the south, which yielded figure 6. annotated view to the northeast from the g.k. gilbert geologic view park. 193 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 a cosmogenic exposure age of ca. 18 ka (�gures 6 and 7). continue road guide. 0.0 / 19.5 turn le� out of parking area onto little cottonwood road. 0.1 / 19.6 turn right onto wasatch boulevard and proceed southwest on wasatch boulevard. 4.4 / 24.0 turn le� onto 1700 east and proceed south. 0.7 / 24.7 1700 east curves right (west) and becomes draper parkway. 0.4 / 25.1 to stop 2 at 1360 east draper parkway, draper. stop 2 walmart neighborhood market �is is intended as a restroom stop, but the parking lot provides distal views to the south of steep mountain (�gure 8) and the entire north �ank of the traverse mountains (see stop 3). �is store and parking lot are on the south �ank of the draper spit. �e bare slope across the road to the north was the headwall of a now reclaimed gravel pit. �e sand and gravel that comprise the spit were presumably sourced from little cottonwood and big cottonwood canyons to the north. �e elevation of the parking lot is below the provo shoreline at approximately 1420 m. continue road guide. 0.0 / 25.1 turn le� out of parking lot onto draper parkway and proceed west. 0.2 / 25.3 turn le� onto 1300 east at signal. 0.2 / 25.5 proceed through tra�c circle and continue on 1300 east. 1.6 / 27.1 turn right onto highland drive and proceed southwest. 2.2 / 29.3 to stop 3. pull o� on the right shoulder south of intersection of highland drive and bangerter parkway-traverse ridge road (approximately 155 east highland drive, draper). stop 3 view of steep mountain �e traverse mountains are an east-west trending range in an area dominated by north-south trending ranges. �ey extend between the wasatch range to the figure 7. view to the southeast from the g.k. gilbert geologic view park. prominent ridge at center is a le� lateral glacial moraine that is o�set by two prominent west-facing wasatch fault scarps (yellow lines). 194 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 east and the oquirrh mountains to the west, and have a gap cut by the jordan river. additionally, the traverse mountains lie at the boundary between two segments of the wasatch fault, the salt lake city segment to the north and the provo segment to the south. �e location and orientation of the traverse mountains is thought to be due to an ancient crustal structure that predates the crustal extension that created the modern landscape. �e east-west orientation of these mountains subjected their north �ank to intense waves generated across a 200-km-long, unimpeded stretch of lake bonneville that once extended to the north (scho�eld and others, 2004). �e north-facing steep mountain part of the traverse mountains is composed of highly fractured quartzite of the pennsylvanian oquirrh group (�gure 9). �is quartzite was readily pulverized by waves, creating an enormous supply of sand and gravel. beneath the steep face of bedrock lies the steep mountain beach complex, a broad bonneville-level depositional platform consisting of sediment deposited o�shore as the lake transgressed to its highstand (oviatt and jewell, 2016). �e sediment-to-bedrock contact below this platform is evidenced by a change in vegetation on the slope above the provo shoreline. �e sand and gravel of the upper half of this slope is dominated by shrubby vegetation, the bedrock of the lower half by grasses (�gure 8). while substantial amounts of sand and gravel remained in the steep mountain beach complex, strong longshore currents traveling west and south through the jordan river narrows transported much of the material, redepositing it in the point of the mountain spit (scho�eld and others, 2004). previous workers (e.g., shelton, 1966) have cited this location as a prominent example of a bonneville shoreline erosional platform, presumably developed during a prolonged period (hundreds of years or more) of open basin over�ow at the bonneville highstand. however, oviatt and jewell’s (2016) recognition of a depositional platform deposited during lake transgression shows that there is no evidence for such a period of prolonged over�ow at this location. �is interpretation coupled with consistent evidence from other locations suggests that the lake transgressed to the bonneville shoreline and then over�owed only brie�y before the bonneville �ood, a return to gilbert’s original 1890 hypothesis. continue road guide. 0.0 / 29.3 continue southwest on highland drive. 0.6 / 29.9 turn le� onto minuteman drive and proceed south. note, minuteman drive becomes frontage road. 2.7 / 32.6 turn le� onto flight park road and proceed east. 0.9 / 33.5 flight park road curves le� and loops around to the west. 0.6 / 34.1 to stop 4. stop at end of flight park road. stop 4 flight park state recreation area, utah county �e point of the mountain spit and adjacent steep mountain beach are two of the largest and most spectacular shoreline features of the bonneville basin. as with all prominent shoreline features in the bonneville basin, g.k. gilbert (1890) was the �rst to document this spit complex (�gure 10). �e gross shape of the spit is that of figure 8. aerial view (toward west) of the prominent bonnevilleand provo-level shorelines at steep mountain on the north side of the traverse mountains. photo courtesy of mark bennett (una�liated). 195 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 a v-shaped embankment anchored laterally to bedrock, but in reality it is a complex feature that formed not only during the bonneville lake cycle but also during known older lake cycles (scho�eld and others, 2004). based on clast lithology and geomorphic analysis of multiple shoreline features at and adjacent to point of the mountain, scho�eld and others (2004) determined that the point of the mountain spit formed as a result of the highly fractured bedrock of steep mountain being exposed to wave trains that approached from the north-northwest causing north-to-south longshore sediment transport (�gure 11). shoreline development and sediment transport on the southern portion of the spit were minimal. a predominant northerly wind direction during the pleistocene matches modern winter storms that tend to come from the northwest, though southern winds from prefrontal lows can also be signi�cant. point of the mountain has been extensively mined for aggregate (�gures 12 and 13). �e total amount of sand, gravel, and rock removed is unknown, but according to utah division of oil, gas and mining documents, roughly 25 million tons was mined just from 2009 to 2014. just east and uphill from this stop a mine is permitted with a 5 to 22 year life expectancy and an estimated 2 million tons of mostly bedrock material removed per year. continue road guide. 0.0 / 34.1 return back down flight park road to frontage road. 1.5 / 35.6 turn le� onto frontage road. note, frontage road becomes digital drive. proceed east and then south. 2.1 / 37.7 turn le� onto timpanogos highway figure 9. prominent bonneville bench and provo-level shoreline at steep mountain, on the north side of the traverse mountains. figure 10. point of the mountain “v-shaped embankment” (spit). north is toward top of page. from gilbert (1890, plate 7). 196 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 figure 11. shaded-relief image of the traverse mountains. image is approximately 5 km across. figure 12. view of the north side of the traverse mountains. photo shows point of the mountain before any signi�cant mining activity; date unknown. figure modi�ed from shelton (2004). 197 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 state road (sr) 92 and proceed east. 6.0 / 43.7 turn le� onto north county boulevard (4800 west) and proceed north. 0.2 / 43.9 turn right onto 11200 north and proceed east to end of road. 0.3 / 44.2 to stop 5, 4560 west 11200 north, highland city. stop 5 american fork delta �e following section is modi�ed from godsey and others, 2005a. �e american fork delta is a classic gilbert-type delta. gilbert’s 1890 study of pleistocene lake bonneville was the �rst detailed geomorphic and stratigraphic study of gravelly deltas. gilbert is reported to have visfigure 13. mining has removed much of the pleistocene sediments and some of the bedrock at point of the mountain. top photos 1993 (le�) and 2015 (right) google earth imagery. bottom photo of gravel pit shows view to the north from flight park state recreation area in utah county. google earth imagery © 2015 google inc.; top le� image—u.s. geological survey and top right image–landsat. 198 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 ited all of the lake’s deltas; however, only two locations were discussed in detail, the bonneville-level delta at american fork and the provo-level logan river delta (located in cache valley, northeastern utah). from these observations of the lake’s coarse-grained deltas, gilbert developed the topset-foreset-bottomset model (�gure 14). however, gravel-pit exposures show that one of gilbert’s original study localities, the bonneville-level delta at american fork, is composed almost entirely of subhorizontal gravel (topsets). taking advantage of such gravel-pit exposures not available to gilbert, this model can be re�ned to show two end member deltas: (1) topset-dominated deltas deposited during the bonneville transgression, and (2) foreset-dominated deltas deposited at the provo shoreline and during the provo regression (�gures 15 and 16) (milligan and chan, 1998). other gravel-pit exposures at the bonneville level of the big cottonwood canyon and american fork deltas displayed a predominance of horizontally strati�ed gravel that comprises the topset-dominated delta system. other gravel-pit exposures at the provo level of the big cottonwood canyon and brigham city deltas displayed a predominance of steeply dipping gravel that comprises the foreset-dominated delta systems. �ree key factors contribute to the development and depositional styles of these wasatch front gilbert deltas: active tectonism, rapid lake-level �uctuation, and drainage basin deglaciation. slip on the wasatch fault zone produced the steep drainage basins responsible for the overall coarse-grained nature of these gilbert deltas. figure 14. gilbert’s classic topset-foreset-bottomset model of coarse-grained deltas (from gilbert, 1890). 199 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 however, slip rates of 0.76–1.5 mm/yr, the average for the last 15 kyr in study areas (machette, 1988; schwartz and lund, 1988; personius and scott, 1992), are overprinted by lake-level change that can exceed 80 mm/yr (long-term post-provo regression rate) or even 125 m/ yr for the nearly instantaneous bonneville �ood event. drainage basin deglaciation and the release of glacial outwash played a role in sediment supply and, thus, the distribution of facies found at some localities. �e e�ects of deglaciation are best seen at big cottonwood canyon (about 5 km north of stop 1), where glaciers neared the bonneville shoreline producing topsets of subaerial glacial outwash. evidence for glaciation (e.g., moraines and striations) is also found in the upper reaches of the american fork drainage basin (laabs and others, 2011). facies distributions were most strongly in�uenced by lake level �uctuation, which largely controls accommodation space and sediment supply. topset-dominated deltas formed with increasing water depth created by climate-driven transgression to the bonneville shoreline. foreset-dominated deltas formed with decreasing water depth. catastrophic lake-level drop due to the bonneville �ood and the subsequent climate-driven provo regression not only greatly reduced accommodation space, but also provided abundant sediment supply by exposing unlithi�ed bonneville-level deltaic sediments for reworking. �e bonneville-level american fork delta seen at this stop exempli�es a topset-dominated system that displays a classic “∆” shape in plan view. �ese gravel topset deposits consist of horizontal clast-supported pebble and cobble gravel with lenses of silty sand deposited during the bonneville transgression and brief highstand. figure 15. top photo shows the horizontal gravel of topset-dominated at the bonneville level (late-transgressive-phase), american fork delta, ca. 1993. bottom photo shows the steeply dipping gravel of a foreset-dominated delta, provo level at brigham city, ca. 1993. 200 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 near the top of the delta (dark band in top photo of �gure 15) is an intervening 9-m section of sandy clay and coarse-grained to very coarse grained sand with granules and oblate pebbles. sedimentary structures include wave ripples and tabular cross-bedding. �e cross-bedding suggests a southerly �ow direction (parallel to the shoreline) and is likely to have been created by littoral currents. �e presence of oblate pebbles and symmetric ripples suggest shallow-water, wave-in�uenced deposition in a delta-front beach environment. �e occurrence of this �ne-grained beach facies amidst coarse-grained delta topsets may be attributed to a downward lake-level oscillation (machette, 1988). �e drop in lake level during this oscillation (�gure 1) probably caused the american fork river to incise a channel through the delta, thus transferring the river deposition westward into the basin (�gure 17). �is river channel (until �lled) would have cut o� the coarsegrained sediment supply (during the oscillation rise and �nal transgression to the bonneville shoreline), allowing the accumulation of the �ner-grained beach and delta-front sands. continue road guide. 0.0 / 44.2 return on 11200 north to 4800 west (north county boulevard). 0.3 / 44.5 turn le� onto 4800 west and proceed south. 0.2 / 44.7 turn right onto sr 92 and proceed west. 5.0 / 49.7 turn le� onto 1200 west and proceed south. 1.4 / 51.1 1200 west curves right and becomes sr 85, proceed west. 2.8 / 53.9 turn le� onto redwood road and proceed south. 1.8 / 55.7 turn right onto sr 73 and proceed west. 0.9 / 56.6 turn right to stay on sr 73 and continue west. 35.7 / 92.3 turn right onto sr 36 towards stockton and tooele and proceed north. 5.2 / 97.5 turn right onto silver avenue (look for sinclair station on the corner) and proceed east. 0.2 / 97.7 silver avenue curves right and becomes copper street. proceed south. 0.2 / 97.9 turn right onto roger street and proceed west. 0.1 / 98.0 to stop 6. figure 16. schematic representation of american fork’s topset-dominated delta (area above “tst/hst” on top �gure) deposited during the bonneville transgression and brief highstand, and brigham city’s foreset-dominated delta (lower �gure) deposited at the provo shoreline and during the provo regression. sequence stratigraphy terms: sb = sequence boundary, lst = lowstand systems tract, tst = transgressive systems tract, hst = highstand systems tract. from milligan and chan (1998). 201 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 stop 6 alex baker baseball park (382 south roger street, stockton) �is was the planned lunch stop. �e south side of the stockton bar and spit complex can be viewed from here. see stop 7 for a complete description. continue guide. 0.5 / 98.6 return to sr 36, turn right, and proceed north. 1.9 / 100.5 turn le� onto entrance road for bauer pit and park. 0.0 / 100.5 to stop 7 at the bauer pit entrance road. stop 7 stockton bar overview, tooele county �e following section is modi�ed from godsey and others, 2005a. general description �e stockton bar is enormous and perhaps the most impressive geomorphic feature found in the bonneville basin. g.k. gilbert �rst documented this area in the 1890 monograph (�gures 18 and 19). stockton bar consists of a series of spits, barriers, and beach ridges in the valley between the stansbury and oquirrh mountains. �e bar and spit complex ultimately isolated lake waters in rush valley to the south from the main body of lake bonneville (gilbert, 1890; gilluly, 1929; burr and currey, 1988). how the barrier bar and spit complex grew and evolved has still not been satisfactorily resolved (c.g. oviatt, kansas state university, written communication, 2016). complex surface geomorphology and internal stratigraphy has led to various interpretations of its development. gilbert (1890) recognized a series of seven sequential “beds” between the oquirrh mountains and south mountain that was correctly interpreted as building during the lake’s rise to the bonneville level and creating the stockton bar (�gure 18). gilbert also recognized that the stockton spit complex and an unnamed spit on the west side of stockton bar superseded this barrier bar series. furthermore, gilbert recognized that buried stratigraphy might further re�ne or reinterpret the simple depositional history. based on detailed study of surface geomorphology, burr and currey (1988) show transgressive-age shorelines (t on �gure 20) to the north and south of the main bar, and a series of shorelines (b1, b3, b5, b6, b8 on �gure 20) formed during a prolonged period of over�ow at the zenda threshold. however, there is no independent evidence of prolonged over�ow at the bonneville highstand (c.g. oviatt, kansas state university, written communication, 2016). based on ground-penetrating radar, smith and others (2003) believed the barrier bar formed �rst by vertical accretion during slow transgression due to climate or basin subsidence, followed by the continued transgression and a reorientation of longshore transport that figure 17. aerial view of the bonneville-level (late-transgressive-phase) american fork delta ca. 1970. note incision by the modern american fork river channel. photo from utah geological survey aerial image collection. 202 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 figure 18. g.k. gilbert recognized a series of seven sequential “beds,” labeled a–g, deposited during the lake’s rise to the bonneville level. gilbert also postulated that the stockton spit complex and an unnamed hook-shaped spit on the west side of stockton bar superseded this barrier bar series. map of stockton bar by h.a. wheeler as illustrated in lake bonneville, u.s. geological survey monograph 1, by g.k. gilbert (1890). 203 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 created stockton spit, and a �nal rise that again reoriented longshore transport and created the smaller upper spit (�gure 21). �ese various interpretations are likely to be re�ned by future work. �e stockton bar as a geoantiquity concerned scientists have been involved in research to document and preserve important landforms, named geoantiquities or geosites, related to lake bonneville and pleistocene earth surface processes (chan and others, 2003; chan and godsey, 2016). sediments that make up lake bonneville landforms are typically well rounded, well sorted, and unconsolidated, making them prime aggregate material and targets for quarrying operations. �e stockton bar tops the list of important geoantiquities, not only because of its scienti�c and educational merit, but also because of its historical, aesthetic, and recreational value. �e bar has been a site of mining activity for at least 60 years, but excavation e�orts have increased steadily with the growing aggregate needs of neighboring urban communities. a�er many public speeches, �eld trips, community education campaigns, and partnerships with various conservation organizations, the struggle for preservation of the stockton bar has met with mixed but generally positive results. a land�ll and a tailings pond exist on the north side of the bar, homes have been developed on the transgressive shorelines to the south, and mining still threatens to remove deposits on the east side of the bar. however, multiple attempts for new mining permits have been stalled. e�orts to protect the bar began in earnest in 1999 with a permit request to remove 400,000 tons of sand and gravel. due to extensive e�orts by local citizens and scientists, the tooele county planning commission did not issue the permit. in 2009, an uprising of local citizens supported by scientists prevented rezoning that would have allowed increased mining. again in 2015, under pressure from local citizens and nationally and internationally renowned scientists, the tooele county planning commission rejected a rezoning request by an aggregate mining company. perhaps most signi�cantly, the tooele county general plan update 2016 includes language that recognizes the stockton bar as “perhaps the most important natural feature in the area,” the mining of which would be “an incalculable loss,” and recommends modifying county code “to ensure the stockton bar and other irreplaceable natural features are preserved and protected in perpetuity.” while encouraging for preservationists, the landownership of stockton bar remains private and thus protection is uncertain. continue north on sr 36. continue road guide. 16.2 / 116.7 take the i-80 eastbound ramp. 5.4 / 122.1 take exit 104 for sr 202. figure 19. top image, “�e great bar at stockton, utah” as illustrated in lake bonneville, u.s. geological survey monograph 1, by g.k. gilbert (1890). �e name has subsequently been shortened to stockton bar. bottom image shows a similar but recent perspective of the stockton bar. photo courtesy of holly godsey (university of utah). 204 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 0.5 / 122.6 turn le� onto sr 202 and proceed northwest. 0.3 / 122.9 turn le� onto frontage road and proceed southwest towards great salt lake state park. 2.0 / 124.9 to stop 8 at the great salt lake marina, 1075 south 13312 west, magna. stop 8 great salt lake state park marina although great salt lake is but a small remnant of lake bonneville, it has the largest surface area of any natural lake west of the mississippi river. as a terminal lake with no outlet, its level is in constant �ux (�gures 22 and 23). in holocene time its level has �uctuated less than 15 m. in the roughly 170-year historic period the lake has �uctuated about 6 m, responding primarily to changes in precipitation and consumptive use of fresh water in the basin. construction of causeways and dikes has divided the lake into four major parts (north arm, south arm, bear river bay, and farmington bay) with figure 20. based on detailed study of surface geomorphology, burr and currey (1988) show transgressive-age shorelines (t) to the north and south of the main bar, and a series of shorelines (b1, b3, b5, b6, b8) that formed during a prolonged period of over�ow at the zenda threshold. however, there is no independent evidence of prolonged over�ow at the bonneville highstand (c.g. oviatt, kansas state university, written communication, 2016). rp and rg demark rush valley provoand gilbert-age shorelines. modi�ed from burr and currey (1988). 205 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 di�erent levels and salinities (�gure 24). �e lake is a major source of mineral resources, supports a multi-million dollar brine shrimp industry, is a globally important migratory bird site, and much more. entire books are dedicated to great salt lake (e.g., gwynn, 2002). �is �eld trip guide will not attempt to touch upon this wealth of information but will give a brief overview of microbialites recently exposed by near-record low lake levels. general characteristics of great salt lake (gywnn, 1996 and modi�ed from vanden berg and others, 2015) • 33rd largest lake in the world (largest fresh or saltwater lake in the united states a�er the great lakes) • averages 121 km long by 56 km wide. • surface elevation: historical average (since 1847) ~1280 m (4200 �) covering 4185 km2, historical high 1283.77 m (4211.85 �) in 1986 and 1987, historical low 1277.52 m (4191.35 �) in 1963. railroad elevation (m) dip angle dirt road paved road highway sediment transport direction st oc kt on s p it rush valley tooele valley up pe r s pi t stockton tooele 5 km f e d c b a 0 km 0.50 36 b arrier bar 4-10 4-10 25 25 25 o ª1583 ª 1546 ª ª 1548 ª 1585 ª 1576 ª 1594 1 2 3 figure 21. smith and others (2003) used ground-penetrating radar to develop a depositional model of the stockton bar complex that suggests the barrier bar portion (1) formed �rst during slow transgression, followed by continued transgression and a reorientation of longshore currents that deposited the stockton spit (2), and a �nal rise that again reoriented currents and deposited the smaller upper spit (3). modi�ed from smith and others (2003). 206 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 figure 22. areal extent, elevation, volume, and maximum depth of great salt lake at historic high, average, and historic low-water levels. from gwynn (1996). 207 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 • lake-level �uctuations: 0.3-0.6 m (1-2 �) annually on average. • maximum depth at average elevation (1280 m [4200 �]): ~10 m (33 �). • volume: 19 km3. • salinity: south arm = 5-22% (highly dependent on lake level and location), north arm = 24–26% (near or at salt-saturation point). • average chemical composition: chloride = 56%, sodium = 32%, sulfate = 7.0%, magnesium = 3.3%, potassium = 2.1%, calcium = 0.2%. • estimated reduction of lake level due to consumptive uses: 3.4 m (11 �) (wurtsbaugh and others, 2016). • estimated south arm lake-level drop due to a 55 m long union paci�c causeway breach: ~0.5 m (1.5 �). breach made on december 1, 2016. • lake levels for october 2016: south arm = ~1277.8 m (4192.3 �), north arm = ~1276.8 m (4189.1 �), maximum water depth ~7.7 m (25 �). fish at its historic high level in 1986 the lake’s south arm salinity dropped below 6%. �is was low enough for a breeding population of brackish-water killi�sh (lucania parva) to enter the lake from a formerly isolated spring located on the south shore (stephens, 1990). with the subsequent lake-level drop the killi�sh were gone by the following spring. microbialites an unforeseen bene�t of the otherwise problematic recent low lake levels is the exposure of incredible expanses of microbialites (�gure 25). microbialites are organic sedimentary deposits formed when microbial communities (cyanobacteria) trap and bind sediment and/or form the locus of mineral precipitation, principally calcium carbonate (burne and moore, 1987). more commonly known stromatolites are a type of mifigure 23. great salt lake hydrograph (from vanden berg and others, 2015). 208 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 crobialite that exhibit internal lamination. �e microbialites of great salt lake do not typically show internal lamination but a thrombolitic (clotted) fabric (�gure 26) (chidsey and others, 2015). microbialites develop in mats, typically composed of bacteria, fungi, protozoans, or algae. lindsay and others (2016) have used dna sequencing to determine the abundance of bacteria, archaea, and eukarya in great salt lake microbialities (�gure 27). �eir results show south arm of great salt lake microbialites contain an abundance of photoautotrophic taxa that may drive carbonate precipitation and thus suggest the microbialites are still actively growing. figure 24. google earth image of great salt lake. image dates range from august 16, 2014 to july, 8, 2016. google earth imagery © 2015 google inc. 209 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 figure 25. microbialites northeast of stansbury island, south arm great salt lake. �e large bioherm (lower le�) has an approximate 3 m diameter. �e green-brown color on the microbialites is due to a covering of cyanobacteria. �e lighter area is dead and bleached due to exposure. photo courtesy of michael vanden berg, utah geological survey. photo date november 4, 2015. figure 26. a sliced microbialite from south arm of great salt lake. photo courtesy of michael vanden berg, utah geological survey. figure 27. relative abundances of archaeal, bacterial, and eukaryl rrna genes in south and north arms of great salt lake. modi�ed from lindsay and others (2016). 210 shorelines and vertebrate fauna pleistocene lake bonneville, utah, idaho, and nevada milligan, m., and mcdonald, h.g. geology of the intermountain west 2017 volume 4 continue road guide. 2.8 / 127.7 return to i-80 eastbound ramp and proceed east towards salt lake city. 14.7 / 142.4 take exit 121 for 600 south and proceed east on 600 south. 1.6 / 144.0 turn le� onto state street and proceed north. 0.2 / 144.2 return to grand america hotel. end of road log. acknowledgments no new work is presented in this geologic road guide. it is merely a compilation of previously published work. as such, we acknowledge the authors of our main sources of information: don currey (university ofutah), holly godsey (university of utah), benjamin laabs (north dakota state uinversity), jack oviatt (kansas state university), marith reheis (u.s. geological survey), ian scho�eld (loughlin water associates), and michael vanden berg (utah geological survey). a new comprehensive book, lake bonneville, a scientific update (edited by oviatt and shroder, 2016) necessitated updates to the original manuscript. we would also like to acknowledge and thank jack oviatt for his extremely helpful review of this manuscript. we thank the vertebrate paleontology department of the natural history museum of utah for permission to photograph the fossil specimens in their collection illustrated in �gure 4. references adams, k.d., and bills, b.g., 2016, isostatic rebound and palinspastic restoration of the bonneville and provo shorelines in the bonneville basin, ut, nv, and id, in oviatt, c.g., and shroder, j.f., jr., editors, lake bonneville—a scienti�c update: cambridge, elsevier, p. 145–164. adams, k.d., and wesnousky, s.g., 1998, shoreline processes and the age of the lake lahontan highstand in the jessup embayment, nevada: geological society of america 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files.geology.utah.gov/emp/microbialite/microbialite_poster_ilc0615.pdf, accessed october, 2016. wolfe, a.l., and broughton, j.m., 2016, bonneville basin avifaunal change at the pleistocene/holocene transition—evidence from homestead cave, in oviatt, c.g., and shroder, j.f., jr., editors, lake bonneville—a scienti�c update: cambridge, elsevier, p. 371–419. wurtsbaugh, w., miller, c., null, s., wilcock, p., hahnenberger, m., and howe, f., 2016, impacts of water development on great salt  lake  and  the  wasatch  front: unpublished white paper from the s.j. & jessie e. quinney college of natural resources, utah state university, 9 p., http://www.qcnr.usu. edu/pdfs/publications/great%20salt%20lake%20water%20 level_feb%2024%202016.pdf, accessed october, 2016. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 10 2023 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. the concrete diplodocus of vernal—a cultural icon of utah michael p. taylor, steven d. sroka, and kenneth carpenter geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel and michael p. taylor cover the concrete diplodocus of vernal through time. top left: field house museum director g. ernest untermann and staff scientist billie untermann preparing concrete dorsal vertebrae (24 january 1957). top right: the untermanns and field house staff assemble the concrete diplodocus outside the museum, starting with the sacrum, pelvis, and hind limbs (later in 1957). bottom left: the completed outdoor mount (undated). bottom right: a second-generation lightweight cast made from molds taken from the concrete diplodocus (may 8, 2016). i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 10 2023 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2022–2023 uga board president rick ford rford@weber.edu 801.915.3188 president-elect eugene syzmanski eugenes@utah.gov 801.537.3364 program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 treasurer aubrey dereuil aubrey@zanskar.us 850.572.2543 secretary tom chidsey tomchidsey@gmail.com 801.824.0738 past president john south johnvsouth@gmail.com 801.367.9292 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 10 2023 65 abstract although many casts have been made of the carnegie museum’s iconic diplodocus, initially in plaster and more recently in various plastics, one stands alone as having been cast in concrete. this skeleton, made from the original carnegie molds starting in 1956–1957, was unveiled at the utah field house of natural history in vernal, utah, in 1957, and stood outside the museum for three decades. the fate of the molds after this casting is uncertain. the concrete diplodocus was the museum’s icon for 32 years until the weather damage became too great. the cast was then taken down and repaired, and fresh molds made from it by dinolab in salt lake city. from these molds, a new replica was cast in water-expanded polyester and mounted inside the field house. this cast was moved to the field house’s new location in 2004 and was remounted in the atrium, but the old concrete cast could not be easily remounted and was instead transferred to the prehistoric museum at price, utah. it has, however, yet to be remounted there, as it awaits a new building for the museum. meanwhile, the new molds have been used to create more diplodocus casts that are mounted in japan and elsewhere, and have also furnished missing parts of the iconic rearing barosaurus skeleton in the atrium of the american museum of natural history in new york city. thus, the concrete diplodocus of vernal has become one of the most influential of all diplodocus specimens, second only to the carnegie original. the concrete diplodocus of vernal—a cultural icon of utah michael p. taylor1, steven d. sroka2 and kenneth carpenter3 1department of earth sciences, university of bristol, bristol bs8 1rj, uk; dino@miketaylor.org.uk 2utah field house of natural history state park museum, vernal, ut 84078 usa; stevesroka@utah.gov 3university of colorado museum, boulder, co 80309 usa; kenneth.carpenter-1@colorado.edu citation for this article. taylor, m.p., sroka, s.d., and carpenter, k., 2023, the concrete diplodocus of vernal—a cultural icon of utah: geology of the intermountain west, v. 10, p. 65–91, https://doi.org/10.31711/giw.v10.pp65-91. introduction diplodocus is a sauropod dinosaur from the late jurassic of north america, found in the extensive morrison formation of the western states. although larger and more complete sauropods are now known, diplodocus was the first giant dinosaur known from a substantially complete skeleton—the carnegie museum’s iconic specimen cm 84 (figure 1). this individual, the holotype of the species diplodocus carnegii, was discovered and excavated in early july 1899 at sheep creek in albany county, wyoming, by a team under the leadership of jacob l. wortman. as described by taylor and others (in preparation a) and expounded in detail by nieuwland (2019), casts of this important specimen were sent all around the globe, and as a result this individual became – and remains – the single best-known dinosaur in the world. among the numerous diplodocus casts that have been mounted, many have been made in plaster, in66 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 cluding all the oldest ones; and many have been made in modern lightweight materials such as water-expanded polyester (wep). however, one stands alone, having been cast in concrete by the utah field house of natural history state park museum in vernal, utah. in this paper, we will briefly summarize the history of the original carnegie diplodocus, discuss how the concrete cast came to be, and consider its legacy. nomenclature a distinction is made between molds and casts. a mold is a negative structure made from an original specimen (or, less commonly, a cast), in which the spaces inside the mold match the shapes of the original specimen. a cast is a positive structure, a copy made of a specimen made by filling a mold, and its shape matches that of the original specimen. institutional abbreviations: • amnh – american museum of natural history, new york, new york, usa, • cm – carnegie museum of natural history, pittsburgh, pennsylvania, usa, • cmnh – cleveland museum of natural history, figure 1. mounted skeleton of diplodocus carnegii: the original fossil material mounted in the public gallery of the carnegie museum in pittsburgh, pennsylvania. this mount consists primarily of the holotype specimen cm 84, augmented by elements from cm 94 and cm 307, plus casts and sculptures based on several other specimens. skeleton in left anterolateral view, with homo sapiens mathew j. wedel for scale. photograph by michael p. taylor. 67 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 cleveland, ohio, usa, • hmns – houston museum of natural science, houston, texas, usa, • lacm – natural history museum of los angeles county, los angeles, california, usa, and • mosi – museum of science and industry, tampa, florida, usa. history of the concrete diplodocus the original carnegie diplodocus as related by taylor and others (in preparation a), the industrialist and philanthropist andrew carnegie was inspired by a newspaper article in the late 1800s to ask the director of the museum that bears his name to obtain a giant dinosaur skeleton for exhibit. in july 1899, an expedition from the museum found a largely complete specimen of the sauropod diplodocus, which when excavated and prepared was given the specimen number cm 84 and described in john bell hatcher’s (1901) monograph as the new species diplodocus carnegii. in 1907, this specimen was mounted in the new dinosaur hall of the carnegie museum, its missing portions filled in with bones from a second diplodocus carnegii specimen cm 94, and casts and sculptures based on other closely related specimens, some of them from other museums. this mounted skeleton quickly became the icon of the carnegie museum, and has remained so up to the present, even after the addition to the dinosaur hall of the even larger apatosaurine mounted skeleton cm 3018, which was designated the holotype of the new species apatosaurus louisae (holland, 1915; gilmore, 1936). the diplodocus skeleton, known by the rather inelegant nickname “dippy,” has been moved and modified several times in the years since its initial mounting, most recently in a major redesign of the carnegie museum in 2005–2007. it presently co-stars with cm 3018 in the new jurassic hall. the first casts of the carnegie diplodocus well before the mounting of the real bones of cm 84, king edward vii of england asked carnegie for a diplodocus skeleton to be displayed in the british museum (natural history) in london. carnegie naively hoped to put an end to war by encouraging arbitration instead (nieuwland, 2019, p. 55), and to this end was always keen to gain influence with heads of state. he therefore enthusiastically agreed to the king’s request and instructed museum director william. j. holland to find another specimen. considering it unlikely that another diplodocus of the same quality would quickly become available without great expense, holland proposed instead to create a replica. carnegie swiftly agreed. holland’s chief fossil preparator arthur coggeshall oversaw the creation of a set of plaster molds by a crew of italian plasterers led by serafino agostini. the molds corresponded to the bones of cm 84 and the other bones that were to be included in the real-bone mount a few years later. some differences exist between the molds and the real skeleton (for details, see taylor and others, in preparation a) but the molds corresponded closely to the original skeleton. these molds were used to create not just the cast skeleton requested by king edward vii, but four additional casts. after the british museum unveiled its mounted cast to great fanfare on may 12, 1905, and after the original bones were mounted at the carnegie museum in 1907, carnegie went on to gift the other four casts to kaiser wilhelm ii of germany, président armand fallières of france, emperor franz joseph of austria and king victor emmanuel iii of italy, in 1908 and 1909. as with the london replica, holland and his chief preparator arthur s. coggeshall travelled to each recipient country to supervise the mounting of the casts. buoyed by the success of his donation program, carnegie authorized the creation of five more casts from the same molds, destined to be donated to other heads of state. between 1910 and 1913, three of these were given to tsar nicholas ii of russia, president roque sáenz peña lahitte of argentina, and king alfonso xiii of spain. but the outbreak of the great war in 1914 (world war i) put an end to carnegie’s dream of arbitration replacing warfare. when he died in 1919, not only had the two remaining skeletons not been donated, but the museum was left relatively impoverished. the continuing funding from carnegie’s trust “certainly did not allow 68 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 the natural history museum to keep up its competition with new york’s amnh” (nieuwland, 2019, p. 250). as noted by gangewere (2011, p. 24), carnegie’s gifts to his institute and library during the last 20 years of his life amounted to $11,729,470 (about $200,000,000 in current dollars); but in the 20 years after his death, only an additional $1.4 million (in the dollars of the time) was provided – and relatively little of this would have gone to the natural history museum. while holland had considered closing the carnegie quarry, near vernal, as early as 1917 (carpenter, 2018, p. 13), the reduction in funding must have played some part in the eventual decision to abandon it in 1922. only years later, with the aid of funds from carnegie’s widow louise, would the last two casts be sent to mexico city (in 1930) and munich (in 1934), the latter never even being mounted. the molds, having last been used in the 1910s, then lay forgotten in the basement of the carnegie museum for more than 40 years (untermann, 1959, p. 364). the utah field house museum in vernal as harvey (1991) and carpenter (2018) explain in detail, the carnegie quarry in northeastern utah (now in dinosaur national monument) was exploited extensively in the early 20th century by teams from the carnegie museum led by earl douglass. although douglass himself was on good terms with utah paleontologists, all the dinosaur material excavated at this quarry was of course shipped to the carnegie in pittsburgh, pennsylvania, leading to growing resentment among utahns that their own state was not benefitting from the discoveries being made there. the inhabitants of vernal, only 20 miles from the quarry, were frequent visitors and supplied douglass’s crew. two of these local crew members would go on to work at museums: golden york at the university of utah, and leroy “pop” kay at the carnegie museum. commercial groups at vernal hoped that a visitor center at the quarry would provide some revenue for the state and the town, but william holland, the director of the carnegie museum, treated these plans with contempt, exacerbating existing tensions between the western state and the eastern museum. as recounted by untermann and untermann (1971), the genesis of the utah field house lay with arthur g. nord, supervisor of the ashley national forest. in the 1930s, he and others became concerned that the fossil wealth of the vernal area was being stripped by museums outside the locality. realizing the importance of tourism to utah, nord recommended that a museum could position vernal as a gateway to the state on u.s. highway 40 (kirby, 1998, p. 2). the creation of a museum in vernal was formally proposed by dr. j.e. broadus of the state museum association at the vernal lions club meeting of september 9, 1934 (anonymous, 1969), and it was reported in the local press only 18 days later (anonymous, 1934). however, the idea languished for nine years until the club returned to it on september 6, 1943 (anonymous, 1969). a museum committee was then formed to advocate for a local museum (anonymous, 1943). a state senate bill approving the museum was passed in 1945, and the next year governor herbert b. maw made $200,000 available to construct the museum building (anonymous, 1969). g. ernest untermann was appointed director of the museum project, and his wife billie, a capable scientist and administrator who became the first female naturalist at dinosaur national monument (kirby, 1998, p. 2), was the staff scientist. based on drawings created by the untermanns, salt lake city architect miles e. miller drew up the plans, and the building was erected by dorland construction company. the work was begun on october 16, 1947, and completed on july 1, 1948, and the building was dedicated on october 29, 1948, by governor maw. the concrete cast in vernal as noted above, vernal native j. leroy kay had gained his entry to paleontology by working with earl douglass at what was then the carnegie quarry. after excavation there ended, douglass had recommended that the carnegie museum hire kay to continue work on removing the collected dinosaur bones from their encasing rock, writing to museum director douglas stewart on september 20, 1922 as follows: “i understand that you are contemplating giving mr. j. leroy kay the opportunity to gain a wider experience by allowing him the opportunity of going to pittsburg [sic] where he can for a time have the 69 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 advantages of the laboratory, museum, and library. while i would not advise any man to take up museum work if he has a family to support an[d] is not wealthy, mr kay is a very capable and resourceful man and can later turn his hand to more remunerative work if he wishes. if the museum is to continue the work of collecting especially in this field it will undoubtedly be the gainer by giving him this opportunity.” working at the carnegie museum for the next 30 years, kay rose to become the head of the museum’s section of fossil vertebrates. he was in this post when, in 1952, museum director graham netting started thinking about purging the collections of dinosaur material (rodeck, 1952; tschopp and others, 2019, p. 10) because the dinosaur bones took up too much storage space (lee, 1955a, 1955b). kay would later announce to the vertebrate paleontology community that the specimens had been “unfrozen” (wright, 1956, p. 26). the initial downsizing plan was soon scaled back to removing only the duplicate specimens. among the materials to be disposed of were the plaster molds that had been used for the d. carnegii casts. the molds were large and heavy, and some were damaged and coated with coal dust from the coal-fired heating system. kay, who was close to retirement and planned to move back to vernal, wanted to find a home for the molds in his own state. he first contacted the utah state museum (now the natural history museum of utah in salt lake city), but the museum was not willing to pay for the molds to be shipped. ernest untermann had been trying to obtain a dinosaur skeleton for the utah field house and stepped in at this point. in 1952 (not 1955 as stated by untermann and untermann, 1971), kay gifted the original plaster molds of the carnegie diplodocus to the field house (untermann, 1952, 1959), on the condition that the field house would arrange transportation. as the molds weighed 5 tons (untermann, 1956) this was no small undertaking. local trucker grant southam used his own equipment to transport the molds at cost, and the utah lions club provided the necessary $1000 payment. the molds arrived on or shortly before august 7 (untermann, 1952) (figure 2). however, having already been used to create ten casts, they were by this time “deteriorating” (gangewere, 1999, p. 17), “almost unusable” (nieuwland, 2019, p. 251), and “in pretty bad shape” (ken carpenter, university of colorado museum, written communication, 2022). curiously, the poor condition of the molds is not discussed in untermann’s (1959) otherwise comprehensive account of the creation of the vernal cast. he recounts that the molds were dirty with pittsburgh soot, requiring a steam bath, and that some repairs were necessary for molds that were actually broken, but the erosion and decay arising from ten prior castings are not mentioned. since the mounted skeleton’s 76-foot length would be too long for the museum’s 50-foot-long exhibit halls, plans were made to situate it outside the museum. wind, rain, and extreme temperatures (the vernal climate typically ranges between –10°f and 89°f, and extremes of –40°f and 100°f have been recorded) required a more robust casting material than the usual plaster. after some experimentation with different materials, the team setfigure 2. the original diplodocus molds created by the carnegie museum, shown in the utah field house some time between 1953 and 1955. in the background to the left is the mold for the sacrum and coalesced ilia, seen in right ventrolateral view with anterior to the top. the molds closely follow the shapes of the bones they were modelled from, but are noticeably bulkier. scanned by eileen carr for the j. willard marriott digital library, image id 1212242. used by permission, uintah county library regional history center. 70 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 tled on a mix of one part cement to three parts aggra-lite (a lightweight aggregate made of volcanic pumice). the complete cast would consist of about 600 pieces, many more than the number of bones, as the complex vertebrae were made from eight or more pieces (anonymous, undated). about a hundred of these pieces had been completed when otto buehner, president of salt lake city’s otto buehner concrete products company, visited the museum, became interested in the casting, and expressed doubts about the use of aggra-lite (untermann, 1959, p. 365). further experimentation, aided by buehner’s experienced workers, resulted in the selection of a new mixture, one part cement to three parts aragonite (the high-pressure polymorph of calcium carbonate). most of the pieces were cast in this material by grant merrell, the museum’s preparator, at the otto buehner facilities, with the more intricate parts completed at the museum. reinforcing wire and rods were used where necessary, and the completed bones were coated in fiberglass to protect them from the elements. the buehner company benefitted from its involvement with the casting, as they discovered in the course of the process that fiberglass, when set with a catalyst, made a better and cheaper adhesive than they had previously been using to repair italian marble when it was broken in transit. the field house also adopted fiberglass as its bonding agent of choice after positive experiences with the concrete cast. the result of all this work was nearly 600 concrete elements, which then had to be put together into a skeleton. first, the individual bones were assembled from their pieces, work done by the untermanns and merrell. identifying numbers on the molds had mostly faded with age, so this had to be done from anatomical principles. pieces were fastened together with steel rods and bonded by fiberglass. the assembled bones were then laid out in the workshop to verify that everything was present and correct (figure 3; untermann, 1959, figures 1 and 2). with this done, the work moved outside. on a concrete base, and surrounded by a chain-link fence, the latter provided by the same vernal lions club that had paid for the molds to be transported, the cast bones were assembled: sacrum and pelvis first (figure 4a), then hind limbs, dorsal vertebrae, caudal and cervical vertebrae, and skull (figure 4b), and then finally the front limbs and ribs. the skull was mounted 21 feet above the ground at the end of a somewhat elevated neck, in a posture that corresponds well with the prediction of taylor and others (2009) that sauropods, like extant tetrapods, habitually held their necks elevated at the base. the whole skeleton was not only supported on a steel scaffolding, but also guyed by thinner rods, enabling it to withstand 70 mile per hour winds that uprooted nearby trees (untermann, 1957, 1959, p. 367–368). the completed concrete skeleton weighed 8 tons (untermann, 1957). the outdoor cast was dedicated on june 8, 1957, during the utah state lions club convention at vernal (anonymous, undated), in a ceremony attended by j. leroy kay, arthur g. nord, and g. ernest untermann (anonymous, 1957), not on june 6 as reported by untermann and untermann (1971). the work had taken about a year and a half, from early 1956, and cost only $10,000 in total (about $105,400 in 2022 dollars), almost all of it in salary. the cast stood for 32 years (figure 5). it was repainted on june 22, 1967 (figure 6), in what was likely a periodic event (anonymous, 1967). the fate of the original molds so far as we have been able to determine, the casting of the concrete diplodocus of vernal was probably the last time the carnegie museum’s original molds were used to create a complete new cast. however, that was not untermann’s intention. as early as june 1956, well before the completion of the vernal cast, he was in negotiation with theodore downs, curator of vertebrate paleontology at the lacm, to have the molds shipped there when the vernal mount had been erected (untermann, 1956). furthermore, tentative plans were already in place for the molds to subsequently be used by “some museum in the state of louisiana” (ogawa, 1957), most likely either mcneese state college (now mcneese state university) or louisiana state university (downs, 1957); michigan state university had also expressed an interest (downs, 1957). downs’s intention was to mount the lacm cast indoors, underneath the recently added hanging skeleton of a 70-foot-long blue whale, in the hall of evolving life 71 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 (downs, 1956). by may of 1957, however, this project was foundering due to “lack of room in the [los angeles] museum, lack of time and money for technological supervision, labor and material, and perhaps lack of interest also” (ogawa, 1957). more specifically, lacm had recently acquired the california institute of technology collection of 55,000 vertebrate fossils, and needed the display space for the dozen or so exhibit specimens that were included (downs, 1957). with the los angeles plan having fallen through, untermann followed up with mcneese state college, but they failed even to reply to three letters (untermann, 1958) and so were removed from consideration. untermann remained anxious to get rid of the molds, which were taking up far too much of the small museum’s limited space. in his 1959 account, he wrote (p. 368–369): “several museums in the united states and from lands as distant as japan and italy have expressed a desire to acquire the molds and cast a diplodocus of their own from either plaster or some of the newer synthetics. to date no museum has apparently been able to make satisfactory arrangement for the acquisition of the molds and the casting of a skeleton. we still have the molds in vernal, and any musefigure 3. field house museum director g. ernest untermann (left), and his wife, staff scientist billie untermann (right), grouting the cast dorsal vertebrae of the field house’s concrete diplodocus. january 24, 1957. scanned by aric hansen for the j. willard marriott digital library, image id 1086940. used by permission, uintah county library regional history center. 72 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 um, anywhere, is welcome to them just for hauling them off. […] the diplodocus on the lawn of the utah field house is the eleventh replica to be cast from the molds […] does anyone wish to cast the twelfth?” from here, though, the story becomes uncertain and accounts are contradictory. sassaman (1988) reported that “the molds finally fell apart because of old age soon after it [the concrete diplodocus] was made.” similarly, ilja nieuwland (written communication, 2022; huygens institute, royal netherlands academy of arts and sciences) says that “the original moulds were thrown away somewhere during the 1960s (nobody at the [carnegie museum] could be more specific than that),” suggesting that the molds may have been returned to their origin. both these accounts seem to be in error, however. as shown by a 1960 report in the vernal express newspaper (anonymous, 1960a; figure 7; see also carr and hansen, 2005), in the middle of july 1960, the molds were collected by the rocky mount children’s museum (now the rocky mount imperial center, children’s museum & science center) in north carolina, with the intention that they would be used to create a twelfth cast, which would be mounted outside the museum building next to the tar river in rocky mount’s sunset park. however, it seems the new cast was never completed. reports in the rocky mount evening telegram from april to july 1960 (anonymous, 1960b; bell, 1960a, 1960b; williams, 1960) enthusiastically announced and discussed the impending arrival, and the later articles say that by july 7, 1960, museum board president harold minges had left for utah to collect the molds. in fact, minges took his whole family on this trip to collect the molds (leigh minges in herring, 2022a). anonymous (1960a) confirmed that the molds were collected on or around july 14, 1960. however, as rea (2001, p. 210) reported, “from vernal the molds kept travelling – first, to the rocky mount children’s museum in rocky mount, north carolina, although a cast was never made there.” similarly, moore (2014, p. 234–235) stated that “from vernal, utah, [cm] molds of diplodocus carnegii are shipped to rocky mount children’s museum in rocky mount, north carolina. because of the age-related damage to the molds, a cast was never prepared.” at first, there was some excitement in rocky mount. mae woods bell, who had been the museum director ever since its creation in 1951 (anonymous, 1962b) made presentations about the dinosaur project to the rotary club (anonymous, 1960c) and the lions club (anonymous, 1960d). on august 26, 1960, bell reportfigure 4. assembly of the outdoor concrete diplodocus at the utah field house in 1957. (a) in right posterolateral view. the sacrum and fused ilia having been mounted on the main support to begin the process, the hind limbs, last four dorsal vertebrae and first caudal vertebra have now been added. (b) in left anterodorsolateral view, probably taken from the roof of the museum. the mount is almost complete, with only the forelimbs, their girdles and the dorsal ribs yet to be attached. note that, contra untermann (1959, p. 367–368), the skull is already in place. both images scanned by aric hansen for the j. willard marriott digital library, image ids 1090660 and 1090647. used by permission, uintah county library regional history center. 73 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 ed that casting “will start soon” (anonymous, 1960d), but evidently that work was significantly delayed as nearly a year later on june 11, 1961, the museum reported that “work will begin here monday on a replica of a pre-historic dinosaur that will eventually tower 21 feet in sunset park […] the project will consume many months before the animal will be erected on a frame in the park” (anonymous, 1961a). already by this point the disorganization and physical state of molds was of concern as “several months will be involved classifying and preparing molds for casting” (anonymous, 1961a). an invitation was now issued to local citizens who wished to volunteer for the work, and they began to work on monday and tuesday evenings (anonymous, 1961a) in a warehouse provided by minges (anonymous, 1962b) on hill street, east of the intersection with washington street behind the old pepsi bottling plant (alan anderson in herring [2022a]). the tuesday sessions were soon halted due to the hot weather (anonymous, 1961b). their suspension may have been intended as a temporary measure but by september 28, “the dinosaur project [was] progressing steadily, with museum personnel, trustees and volunteers working each monday night” (anonymous, 1961c). on october 10, bell told the junior woman’s club that “the work of the dinosaur was progressing nicely” (anonymous, 1961d), and on january 9, 1962, harold minges told the museum’s annual meeting that the dinosaur was “rapidly being brought back to life by museum members” (anonymous, 1962a). from this we must conclude that figure 5. the completed outdoor diplodocus mount in a rare color photograph (undated). scanned by eileen carr for the j. willard marriott digital library, image id 415530. used by permission, uintah county library regional history center. 74 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 some elements had been successfully cast by this point. on february 20, 1962 the rocky mount evening telegram reported, presumably with bell’s authority, that “during the year prospects are bright for the museum’s ‘big’ project to be completed.” this optimism was to prove misplaced, however: nearly two years later on january 8, 1964 new museum president ted p. williamson called for “completion of the dinosaur project […] which they hope to have on display during the year” (anonymous, 1964a); on december 8 that year, bell told trustees that “work is continuing on the dinosaur project” (anonymous, 1964b). still the work lingered on, and as of march 23, 1966, john thompson and harold minges were listed as co-chairmen of the museum’s dinosaur committee (anonymous, 1966). the last mention of the project in the telegram is in response to a question from “e.e.a.” published on march 3, 1968, “what happened to the giant concrete dinosaur project at sunset park?” (anonymous, 1968). “there is no positive answer concerning the future of this project,” runs the reply. minges is quoted as saying “the project was delayed for several years for one reason or another. the molds now are stored in the old avalon airport building on nc 97 east. we expect to resume work on the project in the spring.” avalon airport was a small airstrip on leggett highway in the mid-1940s (at that time known as route 95, later changed to highway 97 to avoid confusion with the new interstate 95.) it was closed after operations were moved to rocky mount municipal airport on north church street (herring, 2022b), and all buildings associated with it are now gone; there is still a local airport on highway 97, but it is a completely different complex on the west side (traci thompson, braswell memorial library, written communication, 2022). it seems likely, but is not certain, that the molds and any elements that had been cast from them, were destroyed or discarded when the old building was demolished. at any rate, by 1985 the molds seem to have been lost. the then curator of the utah field house wrote to the rocky mount children’s museum to ask whether a cast had ever been made and mounted, and what had happened to the molds (laraba, 1985). in his response, the rocky mount museum director wrote that “we do not have the molds nor do i know where they went” (mckinnon, 1985). it seems then, that while some casts were probably made from the molds, the project petered out and the casts as well as the molds were lost or destroyed. hurricane floyd devastated rocky mount in 1999, with flooding from the tar river destroying the original children's museum along with all its exhibits and records (leigh white, rocky mount children’s museum, written communication, 2022), so no records survive figure 6. the outdoor diplodocus mount is repainted on june 22, 1967, in what was likely an periodic event. field house employee ivan hall applies a mixture of linseed oil and brown stain while g. ernest untermann holds the ladder. scanned by eileen carr for the j. willard marriott digital library, image id 1091738. used by permission, uintah county library regional history center. 75 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 that could confirm the eventual outcome, if any, of the diplodocus project. the museum was located next door to a municipal water treatment facility that also flooded and released unknown chemicals, so museum property that might have otherwise been salvageable in that area was deemed contaminated and had to be destroyed. if any molds or casts were in storage at the children’s museum at this time, then this was likely the end of their story. the children’s museum was re-established at the newly built imperial center, where it still resides, but no trace exists there of molds or casts of diplodocus. corroborating the likely conclusion that no cast was ever completed, most staff who worked at the museum in the 1980s at its old location do not recall any such cast (leigh white, rocky mount children’s museum, written communication, 2022). potentially contradicting this, however, jan engle hicks, curator of education at the rocky mount children’s museum from 1971–2002, has a memory of diplodocus casts being on exhibit at the museum when she started work in 1971. she does not recall if they were still part of the museum collection in 1999 when the collection was destroyed. it is possible that the diplodocus specimens that hicks remembers on display were not casts made from the carnegie molds, but other specimens that were given to the children’s museum by leroy kay from the carnegie museum (bell, 1960a). whether or not a cast was made at rocky mount, it is possible that this was not the end for the molds. williams (1960) had written that “the local museum plans to pass the molds on to the next group that makes satisfactory arrangements to acquire them […] already two inquiries have come to the children’s museum asking ‘who has them next?’.” rea (2001, p. 210) claims that “eventually the molds found their way to the houston museum of [natural] science, where they were used to fill in gaps in the diplodocus hayi skeleton that had been swapped from pittsburgh to cleveland before ending up in houston,” citing a personal communication from john s. mcintosh. (the skeleton in question is that of cm 662, which became cmnh 10670 in cleveland, then hmns 175 in houston. having been nominated as the holotype of the new species diplodocus hayi by holland [1924, p. 399], the species was later moved to its own new genus galeamopus by tschopp and others [2015, p. 267].) due to the loss of the rocky mount children’s museum records, we cannot confirm that they ever shipped the molds to houston; and the molds cannot be located at the houston museum (robert bakker, hmns, written communication, 2022). brian curtice (fossil crates, written communication, 2022) also reports that he was in houston in 1995 and did not see the molds in the collection, nor hear of their ever figure 7. the original diplodocus molds being loaded onto a truck for shipment to the rocky mount children’s museum, north carolina, on or shortly before july 14, 1960. from left to right: truck driver william randolph turnage, field house employee dee hall, and field house director g. ernest untermann. scanned by aric hansen for the j. willard marriott digital library, image id 1086142. used by permission, uintah county library regional history center. 76 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 having been there. in the absence of evidence that the molds ever made it to houston, it seems more likely that the missing bones in hmns 175 were cast and supplied by dinolab inc., using the second-generation molds described below, and that rea (2001) misreported this. as recently as 1988, rolfe (1988) wrote to lurae caldwell of the utah field house, on behalf of the royal museum of scotland, “at present i am exploring the possibility of re-using the carnegie museum, pittsburgh moulds, although there is considerable doubt about whether they are up to the job, after so much previous use.” sadly, his letter does not mention their then-current whereabouts, and it must be considered possible that rolfe was working from false or outdated information. rolfe cannot now recall any details of this initiative (written communication via jeff liston, royal tyrrell museum of palaeontology, 2022) and it is considered unlikely that any further relevant correspondence survives or is discoverable (michael a. taylor, university of bristol, written communication, 2022). in an unpublished manuscript, madsen (1990, p. 4) wrote that “the fate of the initial set of molds is somewhat in question, but wann langston (written communication, 1989) suggests that they seem to have been lost, strayed, or stolen during transport from ? to ?. principles [sic] contacted in regard to the disposition of the molds could not provide specific information.” infuriatingly, the question marks are in the original. since both langston and madsen are now deceased, there is no way to discover on which journey langston thought the molds were lost or destroyed. it is unlikely, at least, that langston had in mind their initial journey from vernal to rocky mount. kirby (1998, p. 4) wrote that “somewhere along the line, as the story goes, the molds received from the carnegie had been shipped to a school down south and never arrived. so they were lost.” since rocky mount is about 2000 miles east (not south) of vernal, it might seem that “a school down south” could not have referred, in a utah publication, to a museum in the east. on the same basis, the houston museum would not seem an especially likely candidate for this designation, being 1300 miles southeast of vernal. however, “down south” in the usa does not necessarily refer to strict geographic direction, but to “the south,” a region composed mostly of states that were confederate during the civil war, a designation that includes both north carolina and texas. yet another account of the molds is described by david s. berman (verbal communication, 2022), relating a verbal communication from john s. mcintosh. in this version, a person who had obtained the molds for the use of a public museum, most likely harold minges for the rocky mount children’s museum, became embroiled in a dispute with the museum administrators and sequestered the molds in a barn. there they remained for some time until the rubber straps that held together the molds constituting each element perished, and the 600 pieces that made up the molds became hopelessly jumbled. re-associating the pieces would have been an enormous job, as some of the more complex vertebrae were made from 20 to 30 molds (nieuwland, 2019, p. 63), and it was probably never done. most likely, the dissociated pieces of the molds would have been discarded sometime later. putting it all together, there is no way that all the reports cited here can be accurate. among the more likely scenarios is that the molds were successfully shipped to rocky mount in july 1960 (anonymous, 1960a, 1960b), but some way into the casting project they were found not to be up to the job (rea, 2001, p. 210; moore, 2014, p. 234–235) and left in storage. at some later point it may be that they were shipped to a school in a southern state (kirby, 1998, p. 4) but did not arrive (langston cited in madsen, 1990, p. 4). it is possible that this happened in late 1988 or early 1989, between rolfe’s (1988) letter that expressed an interest in using the molds and langston’s personal communication to madsen in 1989. but since this scenario is assembled from fragments, it is perhaps more parsimonious to assume that mcintosh’s account via berman is correct. at any rate, where the molds are now, if they survive at all, we can only speculate. as madsen (1990, p. 4) concluded, “it is truly a mystery that an estimated 3–6 tons of plaster molds could simply vanish!” the lightweight cast in vernal by the late 1980s, the concrete diplodocus was inevitably deteriorating (madsen, 1990, p. 3). museum staff decided they wanted a new, lightweight cast of diplodo77 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 cus to mount indoors. as noted above, the 50-foot-long galleries could not accommodate a 76-foot-long mount at its full length, but it was decided to curve the tail to enable it to fit. that of course had been an option in 1957 when the concrete cast was created, but perhaps untermann, then the museum director, had wanted the tail laid straight out. untermann had died in 1975, two years after his wife billie (lewis, 1977); a decade after his death, his preference would not have held such weight. on january 26, 1988, alden h. hamblin, then park superintendent of the utah field house, informally discussed with william c. “lucky” murdock, director of the las vegas museum of natural history, the possibility of having the las vegas museum make molds from the concrete cast. murdock’s january 28, 1988, letter of confirmation (murdock, 1988) proposed a deal where the las vegas museum would make a new fiberglass cast for the field house and mount it for them in vernal, and would retain the concrete cast as well as the new molds, with permission to cast additional specimens. james e. king, director of the carnegie museum of natural history, got wind of this plan and wrote on february 23, 1988 to hamblin and murdock requesting that only two casts (for las vegas and the field house) be made from the new molds (king, 1988). negotiations progressed to the point where a draft contract was written up (las vegas museum of natural history, 1988), with the intention of signing it on march 8, 1988. this version of the agreement was more favorable to the field house; the las vegas museum was to disassemble and transport the concrete diplodocus, make molds from it, and cast two fiberglass replicas from them. it would retain one and display it with acknowledgment to the field house; and it would keep the new molds in storage but they would belong to the field house. the las vegas museum was to return the concrete original and the second fiberglass replica to vernal, and mount the new vernal cast in the field house. all of this was to be done at the las vegas museum's expense and under its own insurance. the agreement stated that the work would be completed by june 30, 1988, which seemed highly optimistic. additional casts would be made only with written permission from both the field house and the carnegie museum. these plans were briefly noted by krishtalka (1988, p. 17). however, the arrangement with the las vegas museum fell through. in a letter to james h. (jim) madsen, jr., field house curator, sue ann bilbey said only that “las vegas is no longer interested in obtaining a copy or making new molds” (bilbey, 1989), and a letter from royal museum of scotland’s keeper of geology william d.i. rolfe (1988) to lurae caldwell of the field house makes it clear that the las vegas plans had been abandoned by october 24, 1988. the las vegas museum was to go bankrupt and close in 1990 (michele jones, las vegas natural history museum, written communication, 2022), so it seems likely that its waning interest was due to lack of funds. with the las vegas plans having failed, and with little funding of its own, the field house was in a difficult position. the plan at this stage was to move the existing concrete cast indoors (bilbey, 1989). bilbey again wrote on april 2, 1989 to james h. madsen of dinolab, inc., floating the possibility of a collaboration along the broad lines of those of the failed las vegas deal, but leaving it to madsen to propose the details in a way that would make the project commercially worthwhile for dinolab (bilbey, 1989). at this time, the royal museum of scotland was very interested in obtaining a complete skeleton (bilbey, 1989). madsen replied on may 16, 1989 with some caution (madsen, 1989a), proposing that dinolab might make the project financially viable by creating up to 15 additional diplodocus copies from molds that it would make from the field house’s concrete cast, but expressing concern about the size of the project and worrying that “details and approvals may become too tedious to work with,” most likely a reference to the carnegie museum’s reluctance to allow multiple copies to be made (king, 1988). it does not seem that the carnegie museum had any actual authority to veto the creation of new casts, but all parties would have been reluctant to alienate an important ally. madsen’s reservations were evidently overcome, the project was quickly begun, and by the time he wrote to hamblin on june 12 (madsen, 1989b), he was able to say “we are into the work with gusto.” it became apparent that a great deal of work was necessary to clean, stabilize, and repair the concrete casts, which had suffered badly from three decades of climate extremes, before they could be used to make new molds (madsen, 78 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 1989b). a year later, madsen (1990, p. 3) would write that “it is evident now that the decision at that time to dismantle and repair the skeleton was a wise one, since close examination during preparation and stabilization has revealed incipient fracturing and surface deterioration due to weathering of numerous elements [...] such damage would have been progressively more difficult, if not impossible, to repair after a few more years of precipitation and the temperature extremes typical of the harsh winters and hot summers of the uintah basin.” the arrangement with dinolab was formalized by a contract dated june 30, 1989 (madsen and others, 1989), although work had already begun before this was signed. the work was eventually to take more than two full years. during this time, dinolab repaired the deteriorated concrete cast as detailed above, restoring and sealing the bones. they then made new molds from the repaired concrete diplodocus elements, and used these new molds to create a new lightweight indoor diplodocus for the field house, largely using wep. as madsen’s (1990, p. 1) unpublished manuscript explained, they “used a variety of plastics in different combinations for casting individual bones […] for example the elements of the axial skeleton, manus, pes, and skull are cast in w.e.p. (water extended polyester); while the ribs, ilia, femora, humeri, and scapulae/coracoids are all hollow cast in a gelcoat with fiberglass and resin. other newly developed hollow-cast techniques may be used as well. a tinted gelcoat (resin) is used as a base in producing the fiberglass elements to simulate the natural color of the original, fossil bone. the w.e.p. parts may also be tinted to approximate the color of the original bone.” dinolab intended to improve the field house cast beyond merely duplicating its concrete predecessor: “alterations were also made to improve the scientific accuracy and integrity of the specimen. for example the manus and pes were earmarked for replacement with elements (or casts) provided by (?) [sic], when it was confirmed that those in the original mount were camarasaurid rather than diplodocid (mcintosh, 1981)” (madsen, 1990, p. 3–4). the question mark is unfortunately in the original. madsen is in error here, as mcintosh (1981) says that the right pes of the carnegie mount is taken from cm 94, a referred specimen of diplodocus carnegii, but does not say where the left pes was taken from. the replacement of the forefeet by diplodocid material would definitely be an upgrade. however, it seems that this was not done: the present field house cast has the same old-style forefeet as the original carnegie mount had, with unguals on all of the first three digits. by contrast, the cast in the museum für naturkunde berlin has revised forefeet with fewer phalanges and unguals only on digit i (taylor, personal observation). it may be that the berlin mount still uses the originally supplied camarasaurid pes casts, but has re-posed them and discarded the excess phalanges and unguals. using the new molds, which they retained, dinolab reserved the right to make up to 20 additional casts, with the field house to receive $5000 for each one sold (madsen and others, 1989). this was a significant concession from the carnegie museum, which had previously wanted to limit the number of new casts to two. perhaps it was made possible by a clause saying that “if the carnegie identifies and refers to dinolab a new buyer who ultimately purchases a new replica, dinolab will pay to the carnegie a commission of $3,500.” hamblin obtained from jerry miller (the director of utah division of parks and recreation) a formal statement that royalties obtained from additional casts would be used for exhibits at the field house (hamblin, 1990). dinolab was contracted to deliver the indoor mount to the field house not later than june 30, 1991, and it arrived only a few days before this (anonymous, 1991). the concrete skeleton had been returned to the field house, too, but it “remain[ed] in a back room in the fieldhouse. it [could] not be reassembled because when it was taken apart linking material had to be cut” (anonymous, 1991). the dinolab contract was in one respect inferior to that agreed with the las vegas museum. in the older agreement, las vegas would have been responsible for mounting the field house’s new cast, but dinolab undertook only to provide “technical assistance […] in the design, fabrication and construction of a free-standing exhibit incorporating that skeleton” (madsen and others, 1989). it was intended that the new cast would be assembled that winter (anonymous, 1991), but delays were to prevent the public from seeing it for nearly three further years. by june 23, 1993, only the limbs and tor79 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 so had been erected (anonymous, 1993). in june 1994, the mount of the new cast was finally completed, with its head and neck looming over the admission counter (figure 8). it was unveiled as part of the dinosaur days festival on saturday, june 18 (morrison, 1994), having been “pieced together by maintenance employee, danny anderson, who worked on him over a two year period only as time allowed.” anderson had been working at the museum on and off since 1988, and since 1991 had been full time. one of the questions he had been asked when interviewing for the job in mid-october 1991 was whether he could assemble the diplodocus (kirby, 1998, p. 3). evidently, he had the necessary skills and ingenuity, but other responsibilities meant that very nearly five years were to elapse after the removal of the outdoor concrete diplodocus before the unveiling of its indoor wep successor. the lightweight diplodocus that dominated the original field house exhibit hall was in place for only ten years before the museum moved to a new and much larger purpose-built facility on may 22, 2004. the wep cast was taken down and remounted in a more dynamic pose in the entry hall of the new museum, where it remains to this day (figure 9). new casts made from molds of the concrete diplodocus in subsequent years, further casts were made from the dinolab molds. table 1 summarizes information from madsen’s (1993) report to the carnegie museum and the field house, together with additional infigure 8. the second-generation lightweight diplodocus cast as originally displayed at the old field house building between 1994 and 2004. (a) right anterolateral view, showing the head and neck projecting above the admission counter. (b) left posterolateral view, emphasizing the curvature of the elevated tail necessary to fit the 76-foot-long skeleton into the 50-foot-long exhibit hall. photographs taken in may 1999 by chet gottfried, using a pentax lx camera with a 17 mm rectilinear fisheye lens. used by kind permission. 80 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 formation from dinolab, kindly provided by lisa and chris madsen. of particular interest is that dinolab are claimed to have supplied a cast to odawara in the kanagawa prefecture of japan in january 1990 before delivering to the field house. this must be considered doubtful, as the work, begun with the collection of the concrete cast only in june 1989, could scarcely have progressed far enough to deliver a complete cast only seven months later; a date of january 1992 (nine months after the vernal delivery) is more likely. some reported subsequent casts have proven difficult to track down. for example, nieuwland (2010, p. 68) reported that the new molds “opened up the possibility of a whole slew of further copies of this particular copy, which was immediately exploited by the las vegas natural history museum. one of these has been placed in the las vegas natural history museum.” but this seems to be an error based on misunderstanding krishtalka’s (1988, p. 17) report of an earlier las vegas museum’s intention to make its own molds of the concrete diplodocus as discussed above. the las vegas museum of natural history (note the subtly different name) went bankrupt and closed in 1990, before the new molds were available for casting, so it could not have received a diplodocus cast. the las vegas natural history museum, a completely different institution, which opened in june 1991, has never had a diplodocus (michele jones, las vegas natural history museum, written communication, 2022). the molds taken from the concrete diplodocus were used again in an eighteen-month project in 1996 and 1997, led by david letasi, to create a unique exhibit at the museum of science and industry (mosi) in tampa, florida (david letasi, formerly of mosi, written communication, 2022). when susan swartz of mosi obtained a $500,000 grant from the national science foundation for its “assemble a sauropod” project, the museum board were initially interested in purchasing a cast of a large sauropod skeleton from china. however, based on photographs of this skeleton, letasi was skeptical about its authenticity. on advice from mark norell (american museum of natural history), letasi con# date client city region country royalties paid field house carnegie 1 january 1990 meitetzu odawara kanagawa japan $5000 n/a 2 october 1992 meitetzu shiramine ishikawa japan $5000 n/a 3 may 1992 mitzukoshi (travelling exhibit) japan $5000 $3500 4 june 1992 rci shimizu tokai japan $5000 n/a 5 may 1991 alden hamblin vernal utah usa (towards stegosaurus) n/a 6 february 1998 aurora oval tokyo japan (towards stegosaurus) 7 october 1998 david letasi tampa florida usa (towards stegosaurus) 8 october 1998 david letasi tampa florida usa (towards stegosaurus) 9–12 (not recorded) 13 2006 the dinosaur store cocoa beach florida usa table 1. casts made from the molds taken from the concrete diplodocus of vernal. this table represents a synthesis of three sources of information: (1) a list maintained by dinolab and forwarded by brian d. curtice, (2) james h. madsen’s (1993) memorandum to mary dawson (carnegie museum) and alden h. hamlin (utah field house), and (3) an accounting made by dinolab to steve sroka shortly after he started work at the field house (dinolab, 2001). the first of these sources lists specific cities that the casts were sent to, includes dates, and extends to #13. the second source only applies to the first four casts, which lists clients, gives regions rather than cites, and notes what royalties were paid. the third source notes where payments were made “in kind” as contribution towards the cost of a stegosaurus cast. note that dinolab’s numbering of the casts does not proceed in chronological order, and that casts 9–12 are not recorded in the available documents. n/a = not available. 81 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 sulted paul sereno (university of chicago), who had recently seen the specimen in question, and discovered that it was almost entirely extrapolated from a handful of bones; these were so restored with plaster that it was impossible to determine what was real. sereno therefore wrote to the museum directors, recommending that the project take a different form. jim kirkland (state paleontologist with the utah geological survey) who was lecturing at a mosi event at this time, recommended that a diplodocus skeleton could be used, and that jim madsen was able to produce the casts, using the molds taken from the concrete diplodocus of vernal. the museum directors approached madsen, who recommended that two individuals of diplodocus be created and posed together, creating a unique tableau. letasi conceived the idea of mounting one of them in a rearing position. to better understand what this would entail, he consulted mark norrell, who six years earlier had mounted a cast of barosaurus skeleton in the american museum of natural history atrium (taylor and others, in preparation b). letasi also consulted robert bakker on the active, defensive pose of the quadrupedal skeleton; phil currie on the dynamics of the whiplash tail; and kent stevens on the mechanics of the rearing posture. sauropod specialist john s. mcintosh reviewed the resulting design. the elements of the mounts were cast by jim madsen of dinolab, using hollow core resin casting with figure 9. the second-generation lightweight diplodocus cast as currently displayed at the new field house building since 2006. skeleton in right lateral view, with homo sapiens michael p. taylor for scale. photograph by mathew j. wedel. 82 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 lightweight foam filler to reduce weight. whereas the postcranial skeleton was created from the second-generation vernal molds, the cast skull was based on a separate carnegie museum individual, cm 11161. all these elements were then shipped to ontario to be assembled into their selected postures by peter may of research casting international (rci) with guidance from letasi. aside from biological and mechanical verisimilitude, it was also necessary to consider the space the skeletons were to be mounted in. letasi was concerned that it would be difficult to place the mounts in the main lobby without restricting evening events, as the space was used for public dinner engagements and rotating exhibits. with space in the lobby limited, it was not clear that the skeletons, widely cited in the literature as being 85 feet in length, would fit. at letasi’s request, jim madsen laid out the skull and axial skeleton at his lab, and measured it at 75 feet, so it appears that the 84 feet given by holland (1905, p. 448) for the london cast was an exaggeration. letasi visited rci for the trial mountings of both skeletons. the only problem that became apparent was the position of the tail on the upright mount, which when installed at the museum would have collided with a balcony. the tail posture was changed and the problem avoided. the two mounted skeletons at their true size of 75 feet, and with the tail posture modified, were able to fit perfectly into the mosi lobby. the upright mount was placed on a 10-foot-high pedestal and an existing concrete bunker was used for the quadrupedal mount, so neither encroached greatly on floor space (figure 10). sadly, this impressive exhibit was to last only 20 years in its original form. on august 13, 2017, the museum, in financial difficulties, closed 85% of its space (contorno, 2017; schreiner and ochoa, 2017) and many exhibits had to be discarded. happily, in 2019 the rearing mounted diplodocus was moved to a new position in the kids in charge gallery in the surviving part of the museum. the quadrupedal mount was sold to a company that in turn sold it on to rci who had mounted it in the first place. at present, this cast is on display at the cleveland museum of natural history in cleveland, ohio, as a filler while rci mounts their haplocanthosaurus skeleton, and its intended destination after that is the quinte natural history museum, trenton, ontario (peter may, research casting international, written communication, 2022), only 100 yards or so from rci’s workshop. in addition to providing complete casts of diplodocus carnegii, dinolab negotiated the right to use the vernal molds to create individual elements for various museums (madsen and others, 1989, p. 1). in 1989 or 1990, sauropod expert john s. mcintosh helped to broker a deal between dinolab and rci whereby dinolab created casts of the diplodocus elements needed to make up the missing parts of the amnh barosaurus mount. this was necessary as the material of other known barosaurus specimens would not have filled the gaps, and diplodocus was at that time the most closely related known sauropod to barosaurus. see gordy (1991), norell and others (1991), dingus (1996, p. 20–29), and taylor and others (in preparation b). the fate of the concrete diplodocus the contract that the utah field house negotiated with dinolab (madsen and others, 1989) stipulated that the 1957 concrete cast, having been repaired, would be returned to the field house. but when the cast was returned to them some time before the end of june 1991, it was not a simple matter to remount it outside the museum, as the scaffolding on which the cast was mounted had been cut in order to take it down (anonymous, 1991). as a result, the concrete cast was never remounted at the field house, and was instead stored in the building crawl space. the femora, separated from the rest of the skeleton, were left outside the building in a children’s sandbox “dino dig” area. as noted above, the field house museum moved to a new purpose-built building on may 22, 2004, and the wep cast was remounted in the entry hall. the concrete cast was left behind in the old building. in 2012, however, all field house materials had to be removed from the old building, as uintah county had traded the old building for the new, and the agreement for the museum to continue using the old building had expired. a company was hired to demolish what remained, including built-in exhibit cases, the front counter, etc. one of the demolition company workers, assuming the femora were abandoned, took them home. ken carpenter sug83 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 gested posting a news article requesting the return of the bones, and the workman came forward with them enabling the femora to be reunited with the rest of the concrete skeleton. at this time, the concrete casts were squeezed into collections at the new building, but there was not room for them to be properly stored and they had to sit in the middle of the repository aisle. it was apparent that, despite the concrete cast’s important role in the field house’s history, it was no longer wanted. since the cast was state property, it had to go to a state repository. steve sroka, the museum paleontologist, therefore contacted ken carpenter to ask whether utah state university (usu) could take it. on april 29, 2013, utah division of parks and recreation signed a memorandum of understanding with the usu eastern prehistoric museum in price (carpenter and hayes, 2013), agreeing that the concrete cast would go on an effectively permanent loan (99 years, renewable) to the prehistoric museum. the cast was collected on april 8, 2013 (figure 11a). it then sat in carpenter’s garage for a year (figure 11b), until carrie herbel, a preparator at the prehistoric museum, obtained a $5000 grant from the utah museums association for the repair of the casts. given that the casts had been in storage since dinolab’s 1989–1990 repairs, when they undertook to “stabilize, restore and seal the concrete casts of the individual bones,” it is surprising that the prehistoric museum found every bone to be damaged. it took herbel nine months to sandblast the old paint off (figure 12) and repair the broken and missing pieces using a concrete patch used to repair airport runways. it was never an option to mount the repaired concrete diplodocus outside the prehistoric museum’s current building; there is no space on the south side befigure 10. double diplodocus mount at the museum of science and industry (mosi), tampa, florida. both individuals are identical, having been cast from the molds made by dinolab from the concrete diplodocus of vernal. photograph by anthony pelaez, taken between 1997 and 2017. 84 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 cause that is where the city holds outdoor events, and no room on the north side because of the parking lot and overhead main power line for downtown businesses. the intention was that the cast would be mounted outside a new museum in price, which was then in the planning and fund-raising stage. however, due to funding difficulties this museum was never built and the land that had been donated for the museum was returned to the donor. in light of these developments, carpenter discussed with the usu chancellor the possibility of temporarily mounting the skeleton on campus. however, this idea was not implemented since carpenter feared that mounting and later dismantling the cast to move it to a new museum would damage it. therefore, it currently sits in the basement storage area on the usu eastern campus (figure 13), waiting for a new museum to be built where it can be displayed outdoors. the fate of the new molds dinolab began to wind down after its proprietor jim madsen died in 2009 aged 77 (anonymous, 2007). in 2019, dinolab’s storage building in ogden, utah, was scheduled for demolition, so new homes had to be found for the stored materials. the diplodocus molds that had been taken from the concrete cast were moved to research casting international (rci) in trenton, ontario, canada. here, they were kept in storage for figure 11. the elements of the concrete cast moving from vernal to price, utah, on april 8, 2013. (a) the concrete cast packed onto wooden pallets outside the new field house building, having been prepared for transportation to the utah state university eastern campus in price, about 100 miles southwest of vernal. photograph by steven d. sroka. (b) the same bones having been unpacked into ken carpenter’s garage in price, utah. photograph by ken carpenter. 85 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 dinolab; some of them still in good condition, some in rough shape. at the time of writing, these are probably the only carnegie diplodocus molds in the world. discussion projects like the casting and mounting of the concrete diplodocus, the subsequent remolding from the elements of the mount, and the creation of the second-generation wep cast are historically and scientifically significant, and it is important to document how and when they were done. we are fortunate in the present case to have untermann’s (1959) account of the initial casting in concrete as a basis; but subsequent to that point, as with so many dinosaur-mounting exercises, documentation has been lacking. it has been a lengthy and painstaking process to reconstruct the history, more than six decades after some of the events, largely by reference to contemporary newspaper reports, unpublished letters and memos, and personal recollections—many of them second hand. even with our best efforts, though, frustrating gaps remain, not least the mysterious ultimate fate of the original carnegie diplodocus molds. we urge museums undertaking large-scale projects to ensure that they are formally documented as they are taking place, and to publish an account of their work, as for example the museum für naturkunde berlin did with the 2007 remounting of giraffatitan (remes and others, 2011). working on this project has been a rather melancholy task at times. it is noticeable that projects which begin with excitement often end rather forlornly, or trail away into nothing. the original carnegie molds yielded the diplodocus replicas that were received with such excitement in london, paris, and other great cities. however, they were lost, stolen, or destroyed sometime between 1960 and 1990; more than that, we cannot say. the replica diplodocus that was to have been erected in sunset park by the rocky mount children’s museum was either destroyed by hurricane floyd, or more likely never made at all. the concrete diplodocus that was such a celebrity in vernal for three decades, which was supposed to have been repaired by dinolab and returned to vernal for remounting was never re-erected, but shipped to a garage, thence to another museum’s basement, where it awaits the building of yet a third museum. the new molds that were made from the concrete casts seem to have sat unloved in the dinolab building for some years until it was torn down, and now they lurk in rci’s storage. the double diplodocus display at mosi was taken down as part of a retrenchment program to save the museum money, and one of the skeletons sold back to the company that had mounted it. figure 12. carrie herbel, a preparator at the prehistoric museum in price, sandblasting old paint off the concrete diplodocus casts recently obtained from vernal, on november 1, 2014. by comparison with hatcher (1901, plate v), which shows anterior-view photographs of the cervical vertebrae of diplodocus carnegii holotype cm 84, this appears to be the cast of the 15th and last cervical, based on the wide zygapophyseal facets, the broad diapophyseal wings, the well-developed “v”-shaped intraprezygpophyseal lamina, and the tall, well-separated halves of the bifid neural spine with little dorsal expansion. 86 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 even the diplodocus that started it all, the cast presented by andrew carnegie to the british museum (natural history) on may 12, 1905, seems to be ambling towards an undistinguished fate. having been the centerpiece of the museum’s main hall for nearly four decades, it was removed in 2017 to make more space for corporate events (steerpike, 2015; nieuwland, 2019, p. 260). the cast was sent on a tour of the uk, but now that this has concluded, “in all likelihood the plaster dinosaur will meet an inglorious end in the basement of the museum” (nieuwland, 2019, p. 4). however, while the fate of the london cast stands as a stern warning of what can happen when commercial considerations supersede a museum’s actual mission, there remains hope for the concrete diplodocus of vernal, which may yet become the concrete diplodocus of price. acknowledgments no paper is ever written without the help of other people, and that is especially true of this one. in tracing the multiple intertwining strands of history that make up this story, we have been helped repeatedly by people figure 13. the elements of the concrete cast as they are now, having been cleaned and stored in the basement storage area on the utah state university eastern campus in price, utah. photograph by jason huntzinger (utah state university). 87 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 going far beyond the call of duty to dig out old information for us. in the isolating times in which we live, with political polarization and the ongoing covid pandemic, it is deeply gratifying to feel part of a global network of people working generously together. we thank the following people, with apologies to anyone we have overlooked. elaine carr (uintah county regional history center) furnished high-resolution images from the history center archives and helped us to trace the history associated with some of them. leigh white (rocky mount children’s museum) provided invaluable information about the museum. michele jones (las vegas natural history museum) explained to us the various natural history museums that have existed in las vegas. david letasi (formerly of the museum of science and industry, tampa, florida) provided extensive background on the double diplodocus mount at mosi. chris madsen (dinolab, inc.) identified his father’s unpublished manuscript (madsen, 1990); he and his sister lisa madsen (dinolab, inc.) gave permission to list dinolab’s records of diplodocus casts created from the vernal molds. josh lively (prehistoric museum, price, utah) helped us to recover old photographs taken by ken carpenter. chet gottfried provided photographs of the field house’s wep cast, in its original location, for figure 8. mathew j. wedel provided the photograph of the field house’s current diplodocus mount for figure 9. anthony pelaez (museum of science & industry, tampa, florida) provided the photograph of the double diplodocus mount for figure 10. jason huntzinger (utah state university) supplied the photograph of the concrete elements in collections for figure 13. andy farke (raymond m. alf museum of paleontology) and john foster (utah field house of natural history) went to great lengths attempting to help us track down references. traci thompson (braswell memorial library) helped us to track down newspaper articles on the rocky mount diplodocus project. robert bakker (houston museum of natural science), brian curtice (fossil crates), jeff liston (royal tyrrell museum of palaeontology), peter may (research casting international), ilja nieuwland (huygens institute, royal netherlands academy of arts and sciences), and michael a. taylor (national museums scotland) allowed us to cite written communications. david s. berman (late of the carnegie museum) provided verbal communication. online digital archives were invaluable in preparing this paper. among those we used are the following. (1) the j. willard marriott digital library of the university of utah at https://collections.lib.utah.edu/ provided many photographs of the concrete diplodocus, and the metadata associated with the photographs contained information that was useful to us. (2) utah digital newspapers at https://newspapers.lib.utah.edu/ search contained exhaustive archives of the vernal express, which were crucial in reconstructing the story. (3) newspapers archive at https://newspaperarchive.com/ included coverage of the rocky mount evening telegram. many of the letters and newspaper articles referenced herein can be found in the archive at https:// github.com/miketaylor/palaeo-concrete. we are grateful to doug sprinkel (azteca geosolutions) for his efficient editorial handing of this paper, and to brian d. curtice (fossil crates), and paul d. brinkman (north carolina museum of natural sciences) for detailed, careful, and constructive reviews. our dearest hope for this paper is that it inspires someone to create a dungeons and dragons module in which the concrete diplodocus of vernal is a quest artifact with magical powers. references anonymous, undated, “dippy” the traffic stopper: journal, volume, and pagination not known. anonymous, 1934, construction of museum at vernal urged: vernal express, september 27, 1934, p. 1, https://newspapers.lib.utah.edu/details?id=21512583. anonymous, 1943, committee for museum to make plans for project: vernal express, september 23, 1943, p. 1, https://newspapers.lib.utah.edu/details?id=21493559. anonymous, 1957, dinosaur ceremonies climax 3-year project: vernal express, june 13, 1957, p. 1, https:// newspapers.lib.utah.edu/details?id=21485044. 88 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 anonymous, 1960a, dinosaur molds take long ride to no. carolina children’s home: vernal express, july 14, 1960, p. 15, https://newspapers.lib.utah.edu/ ark:/87278/s6zk6w6s/21338221, drafted by g. ernest untermann as “dippy rides again.” anonymous, 1960b, something ‘big’ for a fact: rocky mount evening telegram, july 8, 1960, p. 4a, https://newspaperarchive.com/rocky-mount-evening-telegram-jul-08-1960-p-4/. anonymous, 1960c, mrs. bell tells rotary about coming dinosaur: rocky mount evening telegram, august 23, 1960, p. 7. anonymous, 1960d, mrs. bell talks to local lions: rocky mount evening telegram, august 26, 1960, p. 9. anonymous, 1961a, work to begin monday on dinosaur project: rocky mount evening telegram, june 11, 1961, p. 5. anonymous, 1961b, dinosaur work: rocky mount evening telegram, july 31, 1961, p. 7. anonymous, 1961c, new officers, trustees named for city museum: rocky mount evening telegram, september 28, 1961, p. 15. anonymous, 1961d, junior women's club program on children's museum: rocky mount evening telegram, october 12, 1961, p. 9. anonymous, 1962a, children's museum has 57,000 visitors during year; observes 10th anniversary: rocky mount evening telegram, january 10, 1962, p. 11. anonymous, 1962b, birthday for the museum: rocky mount evening telegram, february 20, 1962, p. 4. anonymous, 1964a, williamson new head of children's museum: rocky mount evening telegram, january 8, 1964, p. 11. anonymous, 1964b, children's museum trustees study plans for an addition: rocky mount evening telegram, december 9, 1964, p. 13. anonymous, 1966, museum lists its committees: rocky mount evening telegram, march 23, 1966, p. 9. anonymous, 1967, dippy and a friend share a coat of fresh linseed oil mixed with brown stain: vernal express, june 22, 1967, p. 1, https://newspapers.lib. utah.edu/ark:/87278/s6pk1vwz/21595150. anonymous, 1968, what happened to the giant concrete dinosaur project at sunset park?: rocky mount evening telegram, march 3, 1968, p. 6. anonymous, 1969, early plans for utah field house started by vernal lions club in 1934: vernal express, april 24, 1969, p. 1b, https://newspapers.lib. utah.edu/ark:/87278/s6515c19/21656624. anonymous, 1991, dippy returns as beast of new mold: vernal express, 26 june 1991, page 1, https://newspapers.lib.utah.edu/ark:/87278/s6rv4bxq/22646163. anonymous, 1993, “dippy” the diplodocus is being reassembled: vernal express, june 23, 1993, https://newspapers.lib.utah.edu/ark:/87278/s6b88zdc/22648688. anonymous, 2007, james madsen obituary: https:// www.legacy.com/us/obituaries/deseretnews/name/ james-madsen-obituary?id=28417430, archived at https://web.archive.org/web/20220424032554/ https : / /www.legac y.com/us/obituar ies/des e r e t n e w s / n a m e / j a m e s m a d s e n o b i t u ary?id=28417430. bell, m., 1960a, dinosaur’s coming here brings questions galore: rocky mount evening telegram, may 14, 1960, p. 2, https://newspaperarchive.com/rockymount-evening-telegram-may-14-1960-p-2/. bell, m., 1960b, ‘dinosaur’ soon to arrive here: rocky mount evening telegram, july 3, 1960, p. 3a, https://newspaperarchive.com/rocky-mount-evening-telegram-jul-08-1960-p-8/. bilbey, sue ann, 1989, letter to james h. madsen, 2 april 1989. carpenter, k., 2018, rocky start of dinosaur national monument (usa), the world's first dinosaur geoconservation site: geoconservation research, v. 1, no. 1, p. 1–20. carpenter, k., and hayes, f., 2013, memorandum of understanding between the state of utah division of parks and recreation and prehistoric museum— 89 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 utah state university eastern for loan of concrete diplodocus model. carr, e., and hansen, a., 2005, william randolf turnage, dee hall, and ernest untermann [archive photograph with metadata]: university of utah, j. willard marriott digital library, image 1086142. https://collections.lib.utah.edu/details?id=1086142. contorno, s., 2017, mosi to close most of its building, imax to save money before move to downtown tampa: tampa bay times, may 18, 2017, https:// www.tampabay.com/news/business/tourism/mosi-to-close-part-of-its-building-to-save-moneybefore-move-to-downtown/2324358/, archived at https://web.archive.org/web/20211125120642/ https://www.tampabay.com/news/business/tourism/mosi-to-close-part-of-its-building-to-savemoney-before-move-to-downtown/2324358/. dingus, l., 1996, next of kin—great fossils at the american museum of natural history: new york, rizzoli, 160 p. dinolab, inc., 2001, utah field house museum of natural history state park accounting sheet, august 2001. downs, theodore, 1956, letter to g. ernest untermann, july 19, 1956. downs, theodore, 1957, letter to g. ernest untermann, may 23, 1957. gangewere, r.j., 1999, this is huge, really huge: carnegie magazine july/august, p. 12–18. gangewere, r.j., 2011, palace of culture—andrew carnegie's museums and library in pittsburgh: university of pittsburgh press, pennsylvania, 360 p. gilmore, c.w., 1936, osteology of apatosaurus with special reference to specimens in the carnegie museum: memoirs of the carnegie museum, v. 11, p. 175–30, plates xxi–xxxiv. gordy, m., 1991, dinosaur’s last stand?—exhibit’s pose is all wrong, experts assert: new york newsday, v. 52, no. 88 for november 29, 1991, p. 3 and 27. hamblin, alden h., 1990, memorandum to jerry miller, 28 august 1990. harvey, m.w.t., 1991, utah, the national park service, and dinosaur national monument, 1909–56: utah historical quarterly, v. 59, no. 3, p. 243–263. hatcher, j.b, 1901, diplodocus (marsh)—its osteology, taxonomy and probable habits, with a restoration of the skeleton: memoirs of the carnegie museum, v. 1, p. 1–63, plates i–xiii. herring, g., 2022a, rocky mount has a skeleton in its closet...we just don't know where it is: rocky mount...way back when, october 12, 2022, https:// www.facebook.com/groups/34407448334/permalink/10159232557673335/. herring, g., 2022b, it seems that every time i research and post a story about rocky mount, more facts are revealed: rocky mount...way back when, october 14, 2022, https://www. facebook.com/groups/34407448334/permalink/10159236326718335/. holland, w.j., 1905, the presentation of a reproduction of diplodocus carnegiei to the trustees of the british museum: annals of the carnegie museum, v. 3, no. 3, p. 443–452, plates xvii–xviii. holland, w..j., 1915, a new species of apatosaurus: annals of the carnegie museum, v. 10, p. 143–145. holland, w.j., 1924, the skull of diplodocus: memoirs of the carnegie museum, v. 9, no. 3, p. 379–403. king, james e., 1988, letter to alden h. hamblin, copied to william c. “lucky” murdock, february 23, 1988. kirby, r., 1998, danny and the dinosaurs: chamber spirit (newsletter of the vernal area chamber of commerce), v. 3, no. 4, p. 1–6. krishtalka, l., 1988, body double—duplicating dinosaurs: carnegie magazine, v. 59, no. 4, p. 12–20. laraba, peter h., 1985, letter to karl l. mckinnon, august 31, 1985. las vegas museum of natural history, 1988, cooperative agreement between las vegas museum of natural history and utah division of parks and recreation: operations and maintenance, utah field house of natural history. 90 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 lee, ronald f., 1955a, memorandum to howard w. baker, june 16, 1955. lee, ronald f., 1955b, draft letter to m. graham netting, draft date june 16, 1955. lewis, marlene, 1977, g. ernest untermann papers, 1893–1975: archives west for university of utah libraries, special collections, https://archiveswest. orbiscascade.org/ark:/80444/xv38626, archived at https://web.archive.org/web/20220610005257/ https://archiveswest.orbiscascade.org/ark:/80444/ xv38626. madsen, james h., 1989a, letter to sue ann bibey, may 16, 1989. madsen, james h., 1989b, letter to alden h. hamblin, june 12, 1989. madsen, j.h., 1990, diplodocus carnegiei—production and design of replica skeletons: unpublished draft manuscript. (no author is named in the manuscript, but madsen’s son chris believes it is his work.) madsen, james h., 1993, memorandum to mary dawson and alden h. hamblin, january 29, 1993. madsen, james h., king, james e., miller, jerry a., hamblin, alden h., and barker, richard l., 1989, agreement between dinolab, inc., and the utah field house of natural history state park. mcintosh, j.s., 1981, annotated catalogue of the dinosaurs (reptilia, archosauria) in the collections of carnegie museum of natural history: bulletin of the carnegie museum, v. 18, p. 1–67. mckinnon, karl l., 1985, letter to peter h. laraba, november 21, 1985. moore, r., 2014, dinosaurs by the decades—a chronology of the dinosaur in science and popular culture: santa barbara, california, greenwood, an imprint of abc-clio, llc, 473 p. morrison, m., 1994, museum unveils new exhibits during dino-day: vernal express, june 15,1994, https://newspapers.lib.utah.edu/ark:/87278/ s6r53f0k/22649899. murdock, william c. “lucky,” 1988, letter to alden h. hamblin, january 28, 1988. nieuwland, i., 2010, the colossal stranger—andrew carnegie and diplodocus intrude european culture, 1904–1912: endeavour, v. 34, no. 2, p. 61–68. nieuwland, i., 2019, american dinosaur abroad—a cultural history of carnegie’s plaster diplodocus: university of pittsburgh press, 318 p., isbn: 9780822945574, doi:10.2307/j.ctvh4zh5n. norell, m.a., dingus, l.w., and gaffney, e.s., 1991, barosaurus on central park west: natural history, v. 100, no. 12, p. 36–41, http://hdl.handle. net/2246/6497. ogawa, william y., 1957, letter to g. ernest untermann, may 22, 1957. rea, t., 2001, bone wars—the excavation and celebrity of andrew carnegie’s dinosaur: pittsburgh, pennsylvania, university of pittsburgh press, 276 p. remes, k., unwin, d.m., klein, n., heinrich, w., and hampe, o., 2011, skeletal reconstruction of brachiosaurus brancai in the museum für naturkunde, berlin—summarizing 70 years of sauropod research, in klein, n., remes, k., gee, c.t., and sander, m.p., editors, biology of the sauropod dinosaurs—understanding the life of giants, bloomington, indiana university press, p. 305–316. rodeck, hugo g., 1952, letter to david canfied, july 2, 1952. rolfe, william d.i., 1988, letter to lurae caldwell, october 24, 1988. sassaman, r., 1988, carnegie had a dinosaur too: american heritage, v. 39, no. 2, p. 72–73. schreiner, m., and ochoa, j., 2017, mosi to close imax, other exhibits in cost-saving reconfiguration: wusf public media—wusf 89.7, may 18, 2017, https:// wusfnews.wusf.usf.edu/news/2017-05-18/mosi-to-close-imax-other-exhibits-in-cost-saving-reconfiguration, archived at https://web.archive.org/ web/20210507091810/https://wusfnews.wusf.usf. edu/news/2017-05-18/mosi-to-close-imax-other-exhibits-in-cost-saving-reconfiguration. steerpike, 2015, dippygate—natural history museum’s diplodocus sacrificed on the commercial altar: 91 the concrete diplodocus of vernal—a cultural icon of utah taylor, m.p., sroka, s.d., and carpenter, k. geology of the intermountain west 2023 volume 10 spectator, february 18, 2015, https://www.spectator.co.uk/article/dippygate-natural-history-museum-s-diplodocus-sacrificed-on-the-commercial-altar. taylor, m.p., wedel, m.j., and naish, d., 2009, head and neck posture in sauropod dinosaurs inferred from extant animals: acta palaeontologica polonica, v. 54, no. 2, p. 213–230, doi:10.4202/app.2009.0007. taylor, m.p., lamanna, m.c., henrici, a. church, l., and nieuwland, i., in preparation a, the history and composition of the carnegie diplodocus, https:// github.com/miketaylor/palaeo-carnegie. taylor, m.p., may, p., dingus, l., and gaffney, e.s., in preparation b, the skeletal reconstruction of barosaurus lentus in the american museum of natural history, https://github.com/miketaylor/palaeo-baromount. tschopp, e., mateus, o., and benson, r.b.j., 2015, a specimen-level phylogenetic analysis and taxonomic revision of diplodocidae (dinosauria, sauropoda): peerj 2:e857, doi:10.7717/peerj.857. tschopp, e., maidment, s.c.r., lamanna, m.c., and norell, m.a., 2019, reassessment of a historical collection of sauropod dinosaurs from the northern morrison formation of wyoming, with implications for sauropod biogeography: bulletin of the american museum of natural history, v. 437, p. 1–79. untermann, g.e., 1952, moulds for huge dinosaur model arrive from carnegie museum: vernal express, thursday, august 7, 1952, v. 195, p. 1. untermann, g. ernest, 1956, letter to theodore downs, july 27, 1956. untermann, g.e., 1957, dippy draws “dudes” by thousands, boosts tourist travel to museum: vernal express, december 19, 1957, https://newspapers.lib. utah.edu/ark:/87278/s6mw3wpx/21314960. untermann, g. ernest, 1958, letter to theodore downs, copied to william y. ogawa, february 7, 1958. untermann, g.e., 1959, a replica of diplodocus: curator, v. 2, no. 4, p. 364–369, doi:10.1111/j.2151-6952.1959. tb00520.x untermann, b.r., and untermann, g.e., 1971, natural history state museum: journal, volume and pagination not known—perhaps utah parks and recreation newsletter. williams, o., 1960, pre-historic dinosaur to tower over city—giant animal four times taller than man: rocky mount evening telegram, april 24, 1960, p. 3b, https://newspaperarchive.com/rocky-mountevening-telegram-apr-24-1960-p-11/. wright, h.e., 1956, untitled note, in society of vertebrate paleontology news bulletin 46, february 1956. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 9 2022 © 2022 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah edward l. simpson, michael c. wizevich, dakota pittinger, garrett rogers, and kayla lazer geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover photograph of preserved canada goose track preserved in pustular mat. the upper surface is treated with polyurethane (shiny coating on surface) applied in order to facilitate sample extraction. the polyurethane shrank the pustules. note the massive mud below the track. scale bar in mm. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 9 2022 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2021–2022 uga board president john south john.south@dominionenergy.com 385.266.2113 president-elect rick ford rford@weber.edu 801.915.3188 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 co-program chair ben gilder dgilder@gmail.com 337.962.8383 treasurer kellen gunderson kellen@zanskar.us 801.634.9737 secretary eugene syzmanski eugenes@utah.gov 801.537.3364 past president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 9 2022 131 abstract microbially induced sedimentary structures (miss) increase the preservation potential of vertebrate and invertebrate ichnofossils. the colorado river forms a delta in lake powell at hite, utah, and the deltaic shoreline provides a natural laboratory to examine the development of miss and their influence on vertebrate track preservation. two types of miss were identified: pustular and blister. pustular miss occur in proximity to the june 2020 high water line. the pustular morphology is characterized by mm-scale small mounds, or pimple-like shapes. field emission scanning electron microscopy (fesem) examination identified preserved filamentous cyanobacteria intertwined with fine siltand clay-sized sediment and well-preserved freshwater diatoms. branta canadensis (canada goose) tracks are well developed and they vary from single tridactyl tracks to trampled horizons. blister miss, in contrast to pustular miss, are present in lower elevations, forming in deeper water, greater than 0.5 m. blisters are mmto cm-scale irregular mounds that consist of arching mats that are detached from the underlying sediment creating a pore space. through time the blister mat mounds are destroyed by fragmentation due to desiccation combined with wind processes. fesem and energy-dispersive spectroscopy system (eds) analyses indicate the presence of filamentous cyanobacteria on the exterior and palisade bacillus-type bacteria are in the interior of the blister arch, and gypsum crystals within the mat arch. freshwater diatoms are present in both mat types. a single human track and multiple trackways of canis latrans (coyote) were identified on the blister mats. weakly impressed canada goose tracks are present. tracks cross cutting or modifying the pustular miss have preserved miss surface textures except in the heavily trampled areas, whereas tracks linked to the blister mat typically do not have preserved mat texture, and usually contain fragmented mat within the impression. because of fluctuating lake levels and desiccation, these track types had a limited temporal window where they may be produced when moisture conditions permitted miss development, about two months. any vertebrates through the area out of the “track window” were not recorded in sediment and mat modification. tracks imprinted on pustular miss in lacustrine environments will have a high preservation potential if there are annual fluctuations in lake levels. microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah edward l. simpson1, michael c. wizevich2, dakota pittinger1, 3, garrett rogers1, 4, and kayla lazer1, 5 1department of physical sciences, kutztown university, kutztown, pa 19530; simpson@kutztown.edu 2department of geological sciences, central connecticut state university, new britain, ct 06050; wizevichmic@ccsu.edu 3dpitt527@live.kutztown.edu; 4groge296@live.kutztown.edu; 516klazer@gmail.com citation for this article. simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k., 2022, microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah: geology of the intermountain west, v. 9, p. 131–151, https://doi.org/10.31711/giw. v9.pp131-151. © 2022 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 132 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 introduction the preservation potential of vertebrate tracks has been scrutinized for well over seven decades. numerous studies have demonstrated that the preserved morphology of vertebrate tracks is a function of the producer’s anatomy and behavior, coupled with the substrate condition at the time of imprinting, and any modification by post-imprint processes (peabody 1947, 1948; lockley, 1986, 1987, 1991a, 1991b; lockley and conrad, 1991; marchetti and others, 2019a, 2019b, 2020; cuadrado and others, 2021). the fidelity of tracks as a direct function of grain size, moisture variability, and rheology is well documented (allen, 1989; manning, 2004; milań and others, 2004; milań and bromley, 2006; milań and loope, 2007; dalman and weems, 2013; falkingham and gatesy, 2014; belvedere and others, 2017; gatesy and falkingham, 2017; szewcyk and others, 2020; and many more). post imprint processes include weathering, erosion, bioturbation, early cementation, and post-depositional deformation (laporte and behrensmeyer, 1980; nadon, 2001). the presence of microbially induced sedimentary structures (miss) has been invoked as a condition that increases the preservation probability of vertebrate tracks (paik and others, 2001; conti and others, 2005; marty and others, 2009; carmona and others, 2011; carvalho and others, 2013; dai and others, 2015; fillmore and others, 2017; noffke and others, 2019; carvalho and leonardi, 2021; cuadrado and others, 2021). miss both stabilize the initial track structure and may overgrow impressions protecting them from subsequent erosional processes (marty and others, 2009). in addition, early mineral precipitation of calcium carbonate (caco3) induced by microbial metabolic processes (chafetz and buczynski, 1992; dupraz and others, 2009; marty and others, 2009; cuadrado and others, 2011; carvalho and others, 2013; xing and others, 2015a, 2015b, 2015c) and evaporites in arid environments (lockely and rodríguez-de la rosa, 2009) may form during the initial stages of lithification and promote track preservation. the occurrence of vertebrate tracks associated with miss is documented from modern and ancient tidal flats (avanzini and others, 1997; marty and others, 2009; cuadrado and others, 2011; noffke and others, 2019). in continental settings, track preservation associated with miss has been documented from alluvial fan to fluvial systems (carvalho and others, 2013), but rarely lacustrine settings (lockley and rodríguez-de la rosa, 2009; moratalla and others, 2017). tracks and associated miss in modern lacustrine systems have not been scrutinized extensively. delta-top deposits in lake powell, a reservoir within the glen canyon national recreation area, utah and arizona, provide an opportunity to examine the vertical distribution of microbial mats on the shoreline, track generation linked to miss type, and potential destruction of miss and tracks over time (figure 1). geologic setting of lake powell after the 1963 completion of the glen canyon dam (figure 1), lake powell levels rose until reaching a maximum pool height of 1127 m elevation above sea level in 1983. this was followed by a long-term decline caused by superimposed annual drawdowns and diminished recharges from spring snowmelt combined with summer monsoonal precipitation (figures 2 and 3). with the development of lake powell, a delta formed near the confluence of the colorado and dirty devil rivers at hite, utah (pratson and others, 2008; anderson and others, 2010; netoff and others, 2010). lake-level fluctuations over the last several years has led to repeated flooding and exposure of the delta top at hite as well as channel incision by the colorado river. the hite delta has been subject to increased scrutiny because of the focused emission of greenhouse-related biological methane (ch) (malenda and others, 2020; waldo and others, 2021). the release of fluid and gas (ch, carbon dioxide [co], and air) produces soft-sediment deformation escape features including domes, pockmarks, water-filled (salsas) and dry craters, sediment-filled craters, mud and sand volcanoes, clastic dike systems, and small-scale gas fractures (figure 4; netoff and others, 2010; livingston and others, 2015; sherrod and others, 2016; miller and others, 2018; malenda and others, 2020). the uppermost 2 m of the delta consists typically of different proportions of clay, silt, and fine-sand deposits 133 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 that formed from surface runoff and/or lake-rise flooding (willis, 2012; sherrod and others, 2016). at the southern end of the hite delta top, a topographic low is present that was periodically inundated as lake level rose during spring snow melt and spring and summer precipitation (figures 2 and 3). the ephemeral nature of the flooded area permits examination of the surface features on the delta top and enables an understanding of the sequential history of miss and vertebrate track development (figure 3). the study area was inundated sometime in june–july 2020 (figure 3), based on the lake powell hydrograph and the elevation of the study area, with a gradual decline in water level that continued through january 2022. methods the study area is located in the southern part of the exposed delta and was imaged via an unmanned aerial vehicle (drone). using metashapepro™, the photographic images were compiled into a three-dimensional model of the study area (figure 2). the area examined was relatively vegetation free. field observations of the miss were during early june and early august of 2021. samples of pustular mats were stabilized with polyurethane during june 2021 to protect them from damage. samples of surface fragments collected in august 2021were scraped off the top of blister sediment surface miss. both types were later analyzed in the field emission scanning electron microscope (fesem) at kutztown university without additional preparation such as coating. energy-dispersive spectroscopy system (eds) examination determined elemental composition. spectra were taken at 5kv and weight percent (wt.%) are adjusted using 5kv standards in the aztec cambridge software. description of lake powell mats and vertebrate tracks two end-member miss morphologies were distinguished on microbial mat cover surfaces in the study figure 1. location map of lake powell, glen canyon national recreation area, utah and arizona. the study area is near hite. (a) google earth image of the hite delta exposed at low water during september 2013. box denotes study area, and enlarged in (b). dashed-line box in (b) is approximate location of figure 2. 134 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 area, blister and pustular. pustular miss are present in the high elevations along the upper shoreline zone along the eastern margin of the ponded area, abutting vegetated zones (figure 2). the blister miss are located at lower elevations (relatively deeper water) relative to the pustular mat (figure 4), continue to the west, and abut a thickly vegetated zone that does not contain microbial mats. no other variety of miss morphology was recognized. both miss types were dry and the uppermost half meter of deltaic sediment is cut by deep desiccation cracks in the montmorillonite-rich clay (figure 4; netoff and others, 2010). in the pustular miss area, desiccation cracks are about 20 cm significantly shallower than in the blister mat area. description of pustular miss the pustular miss morphology is characterized by mm-scale small mounds, or pimple-like shapes, forming a single head on the surface (figure 5). pustules are randomly distributed with no apparent patterning or size difference across the surface and are symmetrical to nearly symmetrical in plan view (figure 5). an individual pustule surface is rough and irregular textured (figure 6). smaller forms may be superimposed on larger forms resulting in a structure that resembles a small cauliflower curd (figure 5). in cross section, pustular mats are less than 1 mm thick and cored with clayto silt-size sediment (figure 6). white evaporite crusts are restricted to the margins of the cross-cutting desiccation cracks. no morphological differences in the pustular mats were observed between june and august 2021. fesem examination of the pustular miss documents the presence of preserved flattened filaments (figures 7a through 7d) and diatoms (figures 7e through figure 2. orthographic model of the study area generated from aerial drone images taken june 3, 2021. color banding on the left model reflects surface features and probably differences in moisture content. highlighted colors on the right model equate to the distribution of mat types. see scale on left-side model. 135 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 7g). flat filaments are twisted and entangled around siltto clay-size particles (figures 7a and 7b). filaments have lengths of over 100 μm and widths of approximately 2 to 3 mm. clay particles are adhered to the filament surface. structureless organic masses are recognizable on the filament surfaces (figure 7c). complete to nearly complete diatoms are present and have frustule shapes varying from cylindrical, pennate, to fusiform (figures 7e through 7f). canada goose (branta canadensis) tracks are preserved cross cutting the pustular miss (figures 5 and 6). these tridactyl tracks range from single distinct tracks to heavy trampling (sensu richter and böhme, 2016). the pustular texture is reduced in size within the true tracks than the surrounding miss. tracks depress the underlying sediment surface, but under-track deformational structures are not apparent due to the structureless nature of the underlying mudstone and siltstone (figure 6). description of blister miss during the june 2021 observation, the surface expression of the blister miss was represented by mmto cm-scale irregular mounds with maximum length of about 3 cm and widths of about 1.5 cm (figure 8). thickness of crust was less than 1 mm. the blister mounds were randomly distributed with no apparent patterning across the surface (figure 8). these positive structures were slightly asymmetrical with no apparent preferred orientation and arcuate to straight in planform along the crests (figure 8). the surface texture of the blisters was irregular to smooth (figures 8a and 8b). in cross secfigure 3. lake powell pool level over the past five years. blue bar, set at study area elevation of the delta top, denotes time period that the lake level was most recently above the area. note the 2021 reduction in water level, especially the absence of inundation of the study area that typically occurs from june through november. data from lakepowell.water-data.com/ lakepowell/; msl = mean sea level. 136 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 tion, the blisters have a distinct open void beneath the thin mm-thick crusts that corresponds to the overall dimensions of each individual blister. the arch height was up to 5 mm and varies with blister size. in june 2021, numerous crusts were breached with linear and irregular desiccation cracks, illustrating their void-like nature (figures 4, 5, 8, 9, and 10). the brittle, rigid nature of the microbial mat is displayed by crust fragments overhanging the mud cracks (figure 8c). the overhanging blister miss pieces matched across the fractured surfaces of the desiccation cracks. some pieces appeared to show a lineation perpendicular to the desiccation crack, suggesting ductile behavior of the mat in the early stages of desiccation (figure 8c). fesem coupled with eds examination determined the presence of gypsum crystals within the crusts by crystal morphology and elemental composition (figure 11). during the august 2021 observation period, the destruction was ubiquitous when nearly all the blisters overhanging voids were reduced to small fragments figure 4. field photographs of fluid/gas escape structures in the study area. (a) drone photograph of dried salsa in northern edge of study area. yellow arrow shows salsa in e. red arrow marks features that are illustrated in b and d. blue arrow shows position of filled crater/salsa. (b) gas escape crater marked with red arrow. (c) erupting mud volcano. note the various age flows reflected in the different colors. scale bar is 16.5 cm. (d) asymmetrical gas escape crater. yellow scale bar is 2 m. (e) salsa with erupting gas contained in the crater. shovel is 0.7 m (white arrow). 137 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 (compare figure 12 with figure 8). the blister mat fragments that originally overhung the desiccation cracks were absent (figure 12). in blister mat samples, three groupings of microfossils were observed under the fesem: rods capsules, flat fibers, and diatoms (figure 13). capsule dimensions are approximately 300 mm in length with widths of 75 mm. capsules are clustered and commonly tightly packed with long axes nearly perpendicular to the sediment surface forming a palisade-like arrangement. some capsules have up to four, node-like features (figure 13a). rods are encrusted with sediment (figure 13b). flat filaments and diatoms are noticeably less common than in the pustular miss (compare figures 7a and 7b to figure 13g). filaments are twisted and entangled around silt and clay particles (figure 13c). filament lengths vary up 20 mm with widths of approximately 0.5 mm (figure 13c). diatoms are fragmented with long axes of fragments in the 2 to 15 mm range. vertebrate tracks are preserved in the blister miss that include a human shoe print trackway, coyote (canis latrans) tracks and trackways, and canada goose prints (figures 14a and 14b). all trackways are linear and cross-cut the blister mat. within individual tracks, the mat texture is destroyed and in some the track tops are covered with fractured pieces of miss indicating figure 5. field photographs of pustular miss. (a) pustular miss with canada goose track. (b) enlargement and delineation by orange shading of track in a. (c) pustular miss. note the size of the pustules highlighted by arrows. (d) multiple canada goose tracks on pustular mat. (e) pustular miss. note the subcentimeter size of the pustules and white gypsum (arrow). (f) pustular miss cross cut by goose track. (g) enlargement and delineation by green shading of canada goose track in f. use scale bar in f. note the destruction of pustules in the track. 138 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 brittle deformation of the blister miss surface. in august 2021 fragments on the mat surface and in tracks continued to be reduced in size. all tracks on the blister mat are impressed in the underlying sediment, indicating the pliable character of the underlying sediment when tracks were imprinted as opposed to the brittle nature of the mats. interpretation of pustular and blister miss preservation of filamentous bacteria intertwined with sediment is consistent with a miss attribution for both the pustular and blister structures (chafetz and buczynski, 1992; noffke 1999, 2009, 2010; noffke and others, 2001, 2002, 2006; noffke and chafetz, 2012). cyanobacteria, palisade bacillus, and diatoms are a characteristic freshwater assemblage that can be found inhabiting the photic zones of lacustrine settings (cohen, 2003). rods are best interpreted as bacillus-type bacterium that form palisades – large structureless masses identified on fesem images and are best interpreted as extrapolymeric substance (eps) biopolymers secreted by microorganisms. bacterial eps interactions with clay minerals can develop large structureless features that can be on the scale of 10s of mm to mm figure 6. photograph of preserved canada goose track preserved in pustular mat. the upper surface is treated with polyurethane (shiny coating on surface) applied in order to facilitate sample extraction. the polyurethane shrank the pustules. note the massive mud below the track. scale bar in mm. 139 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 figure 7. fesem images of untreated pustular miss specimens. scale bars are at left of the bottom data bar for each image. (a) flat microbial fibers interlaced with siltand clay-sized particles. note the twisting of fibers and attached particles (arrow). (b) twisted flat microbial fibers interlaced with clay agglomerates (arrow). (c) microbial sheath with extrapolymeric substance (eps) highlighted with yellow arrow. note the adhering clay particles highlighted with red arrows. (d) flat twisted microbial fibers with adhering clay particles (arrows). (e) cylindric diatoms (arrows). (f) cylindrical diatom. 140 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 (alimova and others, 2006). greater abundance of cyanobacteria in the pustular mats to that of the blister appears to be primarily ecological and may be related to light penetration of the sediment-rich water (nofke, 2010). diatoms are more abundant in the pustular miss also supports ecological partitioning in the microbial mats based on light penetration. finer pustules in the impressed tracks indicate miss recovery after imprinting. upward arching of the sediment surface of the blisters may be the result of gas generation, probably oxygen or decay products by the bacteria being trapped under the less porous microbial mat. oxygen buildup caused separation of the mat from the sediment surface. this mat-sediment surface separation process is commonplace in modern ephemeral ponds characterized by filamentous bacteria (simpson and simpson, 2014). the upward arching permits bacillus-type bacteria to reproduce and grow in the open space, generating the palisade structure, a morphology associated with reproduction. adhesion structures produced by saltating sand grains sticking to a sediment surface that is water saturated by capillary action are crudely similar to pustular miss and can occupy similar marineor lacustrine-shoreline settings (hunter, 1973; kocurek and fielder, 1982; dott and others, 1986; olsen and others, 1989; koster and others, 1993). however, adhesion ripples are sand deposits. sand-size grains are absent figure 8. field photographs of blister miss. (a) blister miss with a coyote track within circle. scale bar in cm (top) and inches. (b) blister miss with coyote track (circled). scale bar in inches. (c) blister miss. note the crust overhanging the desiccation crack and their adjacent symmetry across the cracks and breaching of crusts over voids highlighted by arrows. scale bar in cm. 141 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 from the mats. in addition, adhesion structures have a distinctive asymmetrical cross section with internal low-angle pseudo-cross laminations and therefore should not be confused with pustular miss (hunter, 1973; kocurek and fielder, 1982; davies and others, 2016). pustular miss has been recognized throughout the rock record (prave, 2002; bottjer and hagadorn, 2007; schieber, 2007; sheldon, 2012; zhong-wu and others, 2013; kumar and ahmad, 2014; wilmeth and others, 2014). simpson and others (2022) named pustular miss as a trace fossil ichnospecies pustularichnus rebeccahuntfosteri with the holotype at the early cretaceous mill canyon dinosaur tracksite north of moab, utah, usa, where 10 distinctive vertebrate track types are recognized (lockley and others, 2014a, 2014b). in contrast to pustular miss, recognition of blister miss may be problematic in the rock record as evidenced by the blister destruction documented on the lake powell surface supporting their low probability of preservation. a possible equivalent example is termed “cyanobacteria-laden salt ridges” in modern interdune deposits in evaporitic settings (fryberger and others, 1983, 1988; simpson, 1983; simpson and loope, 1985). these cm-scale modern salt ridges have efflorescent crusts that are separated from the underlying sediment surface with cyanobacteria rimming the arch, gypsum or other types of evaporites present, and limited breeching of the crestline (fryberger and others, 1983, 1988; figure 9. field photograph of a close-up view of blister surface. breeches of blister arches are highlighted by arrows. 142 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 simpson, 1983; simpson and loope, 1985). differences between the modern salt ridges and the blister miss include (1) linear ridge morphology with evaporitic interdunal areas for salt ridges versus the nonlinearity shape to the blisters on lake powell, and (2) erosion resistance in interdunes versus erosion prone structures on lake powell. simpson (1983) recognized flame-like features in excavated interdune deposits of white sands national park, new mexico. these features were attributed to the burial of salt ridges indicating that longer-term preservation of open structures could mimic flame structures and suggests how the fragile blister miss may look like if buried before destruction. lockley and rodríquez-de la rosa (2009) recognized the role of wetting and drying, dissolution, capillary evapotranspiration, and wind deflation in the preservation of human tracks. the destruction of the blister-mat features at lake powell is interpreted as prolonged desiccation of the microbial mats inducing reduction in thickness by water loss. the thinning and loss of filament flexibility causes the blister structure to undergo tension on the outer surface leading to crest failure. once breeched, wind-induced turbulence rapidly enhances arch breakup. wind destruction of miss in relation to topography has been documented on tidal flats (bouougri and porada, 2012) and ancient tidal flats (noffke and others, 2019). our observations on the delta surface indicate these newly formed fragments are mobilized by wind and gradually infill the desiccation cracks leveling the deflation surface. destruction by wind action of the pustular mat is limited because the interior is filled with sediment as opposed to the voidlike nature of blister mats. discussion tracks in the rock record are more commonly found associated the fine-grained sediments, suggesting that fine-grained sediments provide better footprint preservation. detailed study of tracks developed in coarser-grained sediment is in its infancy (carvalho, 2004; fillmore and others, 2012, 2017; szewcy and others, 2020). miss types and associated tracks along the hite delta shoreline were developed in water-laden fine-grained sediment and indicate a short timeframe where conditions were amenable to track generation and preservation. in recent sediments, footprint morphology can be figure 10. trackways on blister miss. large units on scale bar are in inches. (a) blister mat with human shoe print trackway (arrows). (b) multiple superimposed coyote trackways (arrows) across the blistered miss surface. (c) isolated coyote trackway (arrows). 143 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 figure 11. eds spectral analysis of gypsum found in the blister miss. the six spectral graph locations are shown on the electron image at the top. note the presence of ca and s, indicating gypsum. table results are in weight percent. 144 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 related the microbial mat thickness and water content of the mat and underlying sediment (marty and others, 2009). microbial mats are generally only produced during wet conditions, restricting the timeframe during which footprints are registered/preserved (marty and others, 2009). generally, poorly defined footprints or no footprints at all form on dry mats, whereas imprints are sharp in water-saturated mats, and may have associated well-defined displacement rims (marty and others, 2009). in addition, cuadrado and others (2011) noted that examining recent tidal flats over a period of time, dried mats only have tracks that were poorly preserved or significantly modified to be unrecognizable. microbial mats can form a low-permeability layer, which separates the sediment beneath from the atmosphere insulating against water loss; as a result, the sediment below is wet or moist and not necessarily as dry as the overlying mat (porada and others, 2007). these observations permit the interpretation of mat and sediment conditions at the time of track imprinting at lake powell. pustular miss were imprinted with tracks and enough time passed to allow the mat to recover but the underlying sediment remained plastically deformed and hence did not recover to its original shape. in the blister miss area well-preserved tracks display both a destroyed mat texture and mat fragments resting in the track indicating two different sets of physical conditions for the track generation. coyote tracks and trackways were generated when both the mat and underlying sediment where wet or moist, allowing for plastic deformation of both the mat and sediment. the human tracks were made during a time period when the blister miss was dry enough to fracture under the foot pressure and sediment was moist enough to plasfigure 12. august 2021 field photographs of blister mats after partial destruction. a and b eroded blistered miss. note the sediment “small flakes” of earlier blister structures (arrows) and the absence of crust overhanging the mud cracks. scale bar in cm. 145 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 figure 13. fesem images of microbes in blister mats. scale bars are at the left of the bottom data bar for each image. (a) clustered ovate capsules on the underside of sediment crust. (b) cross section through blister miss. note fine silt and clays attached to the outer surface. upper surface is to the left. (c) close-up of aligned capsules in clusters. note parallel alignment. (d) capsule with four node-like features (arrow). (e) enlargement of capsule. (f) flat fibers (yellow arrow) with gypsum evaporite in the background (red arrow). 146 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 tically deform. since these blister mats are subjected to extensive destruction by desiccation and wind erosion, they may not be recognizable as a mechanism that enhances track preservation in the rock record. these miss and sediment deformation observations and inferred conditions indicate that the lake powell track types had a limited window for the development of the well-preserved tracks centered around the june– august 2020 time period, as water level peaked and dropped enough and dried after in the arid setting. pustular miss tracks formed near the high-water setting, with temporally equivalent blister miss submerged. the blister miss exposure was followed “quickly” by transverse track formation. vertebrates that traversed the depression area out of the “track production window” of approximately two months, were not recorded in sediment or mat modification. in addition, the high-yield strength of the mat and underlying sediment may not have permitted the development of tracks from smaller fauna biasing the record towards larger fauna (lockley and hunt, 1995; noffke and others, 2019) thulborn (1990) showed that footprints are most figure 14. field photographs of tracks in the blister miss. (a) weakly impressed canada goose track (circle). (b) isolated coyote track. note the absence of broken fragments and similar coloration as to the associated mat (circle). (c) human boot print. note the fractured pieces of mat in the track (circle) and the well preserved tread lugs. compare this style of preservation with that of b, brittle versus ductile behavior of mat deformation. (d) human boot print with brittle fragments in the track (circle). scales is in inches and centimeters. 147 microbially induced sedimentary structures and the preservation of vertebrate tracks on the colorado river delta in lake powell, hite, utah simpson, e.l., wizevich, m.c., pittinger, d., rogers, g, and lazer, k. geology of the intermountain west 2022 volume 9 commonly preserved in depositional settings in which cyclic accumulation of sediments takes place. rapid covering of tracks of sediment and overgrowth by microbial mats are significant factors increasing the potential preservation of footprints (marty and others, 2009). lacustrine sediments are sensitive indicators of variations in precipitation and snow pack in the source area on a yearly cycle (barnett and others, 2005; sadro and others, 2018). lake powell shoreline deposits are subjected to these types of annual lake-level fluctuations (figure 3), which would enhance the likelihood of track preservation. summary the lake powell deltaic shoreline at hite is a natural laboratory to unravel the development of miss and their controls on vertebrate track preservation. two types of miss were present, pustular and blister. pustular miss are restricted to the high-water line of the ponded area. fesem examination identified preserved cyanobacteria interleaved with very fine silt and clay-size grains and freshwater diatoms. canada goose tracks are isolated and as trampled zones. lower elevations are characterized by blister miss and are constructed of arching mats that separated from the underlying sediment by an open pore space. ultimately over time, the blister mat arches are razed by desiccation and wind processes. fesem and eds indicate the presence of filamentous cyanobacteria, palisade bacillus, and gypsum crystals on the mat arch of the blister. vertebrate tracks in the blister mats consist of human and coyote trackways that traverse the blister mats area in contrast to the tracks restricted to the pustular mat zone, which circle the edge of the water indicating shoreline hunting or drinking behavior. tracks in pustular miss destroyed the original mat and subsequently the mat recovered with a smaller pustular texture development, implying the mats were moist when impressed. tracks linked to the blister mat consisted of two different impression types: (1) destroyed mat texture with plastically deformed sediment, and (2) fragmented mat on top of the plastically deformed sediment in the true track. these vertebrate track types had a limited development window, centered on the two-month, high-water lake level followed by track formation in the lower elevations. any vertebrates that traversed the area out of the “track preservation window” were not recorded in sediment deformation or mat modification as numerous generations of scat preserved on the sediment surface. even during the optimal time period, smaller fauna cannot exert enough vertical pressure to affect the mat or the underlying sediment. annual variation in precipitation inducing lake-level change will increase the preservation potential of the lake margin track systems. acknowledgments kutztown university (ku) research committee funded participation of ku students and staff. connecticut state university-american association of university professors faculty research grants funded participation of central connecticut state university students and staff. kurt friehauf (kutztown university) aided in the fesem and eds analyses. we thank john foster, utah field house of natural history state park museum, and doug sprinkel, azteca geosolutions, for their helpful reviews. references allen, j.r.l., 1989, fossil vertebrate tracks and indenter mechanics: journal geological society london, v. 146, p. 600–602. alimova, a., roberts, m., katz, a., rudolph, e., steiner, j.c., alfano, r.r., and gottlieb, p., 2006, effects of semectite clay on biofilm formation by microorganisms: biofilm, v. 3, p. 47–54. anderson, 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klein, h., mccrea, r.t., buckley, l.g., belvedere, m., mateus, o., gierlinski, g.d., pinuela, l., persons, w.s., wang, f., ran, h., dai, h., and xie, x., 2015a, an ornithopod-dominated tracksite from the lower cretaceous jiaguan formation (barremian-albian) of qijang, south-central china—new discoveries, ichnotaxonomy, preservation and palaeoecology: plos one, 10, e0141059. xing, l., li, d., lockley, m.g., marty, d., zhang, j., scott persons, w., you, h., peng, c., and kümmell, s.b., 2015b, dinosaur natural track casts from the lower cretaceous hekou group in the lanzhou-minhe basin, gansu, northwest china—ichnology, track formation, and distribution: cretaceous research, v. 52, p. 194–205, doi: 10.1016/j. cretres.2014.10.001. xing, l., peng, g., lockley, m.g., ye, y., klein, h., mccrea, r.t., zhang, j., and scott persons, w., 2015c, saurischian (theropod-sauropod) track assemblages from the jiaguan formation in the sichuan basin, southwest china—ichnology and indications to differential track preservation: historical biology 28, p. 1003–1013, doi: 10.1080/0 8912963.2015.1088845. zhong-wu, l., zhong-qiang, c., xian-hua, l., and kuino, k., 2013, microbially induced sedimentary structures from the mesoproterozoic huangqikou formation, helan mountain region, northern china: precambrian research, v. 233, p. 73–92. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. paleontology of bears ears national monument (utah, usa)— history of exploration, study, and designation robert j. gay, adam k. huttenlocker, randall b. irmis, m. allison stegner, and jessica uglesich geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover jessica uglesich prospects the triassic chinle formation in bears ears national monument, with the bears ears themselves visible on the far horizon. the triassic moenkopi formation and pennsylvanian-permian cutler group are exposed in the canyon in the middle ground. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg 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giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 205 abstract bears ears national monument (benm) is a new landscape-scale national monument in southeastern utah, jointly administered by the bureau of land management and the u.s. forest service as part of the national conservation lands system. as initially designated in 2016, benm encompassed 1.3 million acres of land with exceptionally fossiliferous rock units. subsequently, in december 2017, presidential action reduced benm to two smaller management units (indian creek and shash jáá). although the paleontological resources of benm are extensive and abundant, they have historically been under-studied. herein we summarize prior paleontological work within the original benm boundaries to provide a more comprehensive picture of the known paleontological resources, which are used to support paleontological resource protection. the fossil-bearing units in benm comprise a nearly continuous depositional record from aproximately the middle pennsylvanian period (about 310 ma) through the middle of the cretaceous period (about 115 ma). pleistocene and holocene deposits are known from unconsolidated fluvial terraces and cave deposits. the fossil record from benm provides unique insights into several important paleontological intervals of time including the carboniferous-permian icehouse-greenhouse transition and evolution of fully terrestrial tetrapods, the rise of the dinosaurs following the end-triassic mass extinction, and the response of ecosystems in dry climates to sudden temperature increases at the end of the last glacial maximum. paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation robert j. gay1, adam k. huttenlocker2, randall b. irmis3, m. allison stegner4, and jessica uglesich5 1colorado canyons association, 543 main st. #4, grand junction, co 81501; rob@canyonsassociation.org; paleorob@gmail.com 2department of integrative anatomical sciences, university of southern california, los angeles, ca 90007; huttenlo@usc.edu 3natural history museum of utah and department of geology & geophysics, university of utah, salt lake city, ut 84108-1214; irmis@ umnh.utah.edu 4department of biology and jasper ridge biological preserve, stanford university, stanford, ca 94305-5020; astegner@standford.edu 5friends of cedar mesa+, bluff, ut 84512 and university of texas at san antonio, department of geosciences+, san antonio, tx 78249; jessica.ugelsich@gmail.com; +former affiliation citation for this article. gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j., 2020, paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation: geology of the intermountain west, v. 7, p. 205–241, https://doi.org/10.31711/giw.v7.pp205-241. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction southeastern utah has a diverse and significant paleontological record of the late paleozoic through mid-mesozoic eras. the first published paleontological work in the region dates to the 1870s, based on fieldwork by the 1859 macomb expedition (newberry, 1876), but interest and exploration among local native communities predates the late 19th century and extends to ancestral puebloan communities (mayor 2005; smith and others, 2016; w. greyeyes, navajo nation, verbal communication, 2017). in a remarkable union of archaeol206 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 ogy and paleontology, there is evidence in bears ears national monument that ancestral puebloans intentionally utilizing fossils in pueblo construction (smith and others, 2016). today, paleontological research in the region is advancing our understanding of critical evolutionary events, major extinctions, biogeography and ecology of extinct and extant organisms, and the morphologic and taxonomic diversity of life on earth through time. specific high-priority research objectives in benm include deepening our understanding of the evolution of fully terrestrial ecosystems during the icehouse-hothouse transition preserved in the upper pennsylvanian-lower permian cutler group, generating a comprehensive unified stratigraphy and inventory across the triassic chinle formation, and inventory and study of the quaternary fossil resources of the monument to elucidate post-glacial diversity change. illegal excavations and collections in this region have been problematic for at least the past several decades, and likely longer (r. gay, j. uglesich, r.b. irmis, and m.a., stegner., personal observations; r. hunt-foster, national park service (formerly blm), verbal communication, 2017). despite stronger enforcement and education of paleontological laws over the past several decades (united states v. peter larson, 1997; public law 111-11, title vi, subtitle d; 16 u.s.c. §§ 470aaa – 470aaa-11), looting and vandalization of paleontological resources remains a prevalent problem in southeastern utah. looting hinders resource preservation and past, present, and future geoscience research. in december 2016, president barack obama, in an executive order, proclaimed 1.35 million acres of southeastern utah as benm (obama, 2016), under authority delegated by the antiquities act of 1906 (figure 1). the monument is named for two resistant sandstone-capped buttes, which are sacred to the navajo, hopi, ute, and new mexico pueblo peoples. benm’s natural beauty provides the backdrop to lands incredibly rich in paleontological and cultural resources, both of which are explicitly protected in the monument proclamation (obama, 2016). as noted in the proclamation: “the paleontological resources in the bears ears area are among the richest and most significant in the united states, and protection of this area will provide important opportunities for further archaeological and paleontological study (obama, 2016).” institutional abbreviations benm, bears ears national monument; blm, bureau of land management; gsenm, grand staircase-escalante national monument; sgdds, st. george dinosaur discovery site at johnson farm; ucmp, university of california museum of paleontology; umnh, natural history museum of utah; usgs, united states geological survey; usc, university of southern california. history of monument designation the idea of federal protection for the region now known as benm was conceived as early as 1936. at that time, a proposed “escalante national monument” included what is now grand staircase-escalante national monument, glen canyon national recreation area, natural bridges national monument, and the majority of canyonlands national park (davidson, 1991). as awareness of the conservation value of the region increased, so too did scientific data on the fossils of the region, further supporting preservation. heightened federal protection of this overall region has been piecemeal, with benm the last major unit to receive special designation. by 2016, public support for the idea of a national monument or national conservation area in southeastern utah was gaining momentum. this was due in large part to the immense numbers of archaeological sites documented across the region. at the time, most of support regarding monument designation and conservation was centered on these archaeological resources. however, two alternative proposals both recognized the significance of paleontology within the area. one plan put forward by utah’s congressional delegation, known as “utah’s public lands initiative” (or pli) included a broad-reaching rearrangement of public lands in the state of utah, including the creation of a 1.4-million-acre bears ears national conservation area (bishop, 2016). the second proposal, put forward by a coalition of five native american tribes with historic and prehistoric connections to the region, called for the creation of a 1.9-million-acre bears ears national monument (bears ears intertribal coalition, 2016). in late december of 2016, benm was established by a 207 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 figure 1. the boundaries of bears ears national monument (benm) as established by proclamation 9558 (obama, 2016), as modified by proclamation 9681 (trump, 2017), and its location within the state of utah. the indian creek unit is labeled 1 and the shash jáá unit is labeled 2. 208 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 presidential proclamation which incorporated language that explicitly protected known paleontological resources and the localities in which those resources have potential to be found (obama, 2016). at the recommendation of secretary of the interior zinke, following lengthy public discourse and a formal public comment period, president trump issued a new proclamation in december 2017, greatly reducing benm to two management units—indian creek and shash jáá (trump, 2017) (figure 1). this reduced the size of the national monument by 85%, and thus excluded lands containing paleontology resources from the valley of the gods, cedar mesa, white and fry canyons, the northern portion of indian creek, and black mesa. also excluded were beef and lockhart basins (trump, 2017), which remain largely un-prospected despite notable fossil-bearing potential (see discussion below). this executive order is currently the subject of ongoing litigation. the monument management plan (mmp) for the indian creek and shash jáá units was released in july 2019 but has not yet been implemented. for the purposes of the following discussion, benm refers to the original boundaries of the monument. geographical and geological setting bears ears national monument lies in the heart of what is known as utah’s canyon country (figure 1). it is bounded by canyonlands national park to the north and west, glen canyon national recreation area to the west, the san juan river to the south, and highway 191 to the east. it is part of the large colorado plateau uplift deformed internally by anticlines related to salt tectonics (e.g., doelling and others, 1988) and mid-cenozoic laccolith intrusions (e.g., abajo mountains; witkind, 1964). a prominent structural feature is the monument upwarp, a broad north-south-trending anticline, 177 km long and 64 to 97 km wide, containing secondary anticlines and synclines, expressed most prominently at comb and elk ridges (sears, 1956). uplift events, millions of years of river incision, and erosion have carved the landscape into the visually stunning, desolate terrain we see today (e.g., barnes, 1993; baars, 2000). within the last two millennia this land was the home of the ancestral puebloan people, whose remaining stone structures and artifacts were driving forces behind the creation of benm (obama, 2016). erosion across the benm exposed flat-lying to low-dipping, virtually continuous sedimentary strata spanning over 150 million years of geologic time, from the pennsylvanian paradox formation to the lower cretaceous burro canyon formation (lewis and others, 2011) (figure 2). vertebrate, invertebrate, plant, and trace fossils are found throughout most of the geologic formations within benm. late paleozoic geology and paleontology the oldest rocks exposed in benm are the middle to upper pennsylvanian hermosa group, known for extensive potash and oil deposits in the four corners region (stokes, 1986; hintze and kowallis, 2009). locally, the group includes the paradox and honaker trail formations (baker and others, 1933; wengerd, 1958). during most of pennsylvanian time, present-day utah was close to the paleoequator and covered by a shallow tropical ocean. sediments deposited during that time are primarily marine and highly fossiliferous. during the pennsylvanian and early permian, the uplift of the ancestral rocky mountains was marked in utah by the rising uncompahgre highlands along the northeastern margin of the actively subsiding paradox basin (stokes, 1986; hintze and kowallis, 2009), near what is today the colorado-utah border. this north-northwestto south-southeast-trending uplift was relatively rapid, with high erosion rates of sediment that were subsequently deposited in the paradox basin to the west. in the benm region, the oldest exposed strata of these synorogenic sediments are the paradox formation (mid-pennsylvanian), which comprises cycles of limestone, dolomite, sandstone, shale, and anhydtrite beds capped by halite (stokes, 1986; condon, 1997). though poorly fossiliferous, a borehole in the indian creek area of benm produced important palynomorphs (rueger, 1996). the overlying honaker trail formation (cyclically bedded limestone, sandstone, and shale) is known for its diversity of invertebrate marine fossils (melton, 209 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 1972; condon, 1997; lewis and others, 2011). these include multiple species of fusulinaceans, brachiopods, rugose corals, bryozoans, and conodonts, among other marine invertebrates (williams, 1949; melton, 1972; condon, 1997; ritter and others, 2002). using conodont faunas in the hermosa group outcropping along the san juan river, ritter and others (2002) pioneered conodont biostratigraphy for regional correlation of cycles in the paradox basin with the better-studied cycles in the midcontinent. based on conodonts, the top of the honaker trail formation near the valley of the gods and the glen canyon recreation area correlates to the south bend cycle (lansing group) at the top of the missourian midcontinental cyclothem sequence (ritter and others, 2002). overlying the hermosa group is the cutler group (figure 3), which was originally named by cross and howe (1905) and assigned formation status by sears (1956). these strata preserve a near continuous record of nearshore to nonmarine rocks that provide a window shinarump member monitor butte member moss back member tidwell member 0.126 aso mre h g ro up petrified forest member owl rock member church rock member ~205.5 big indian rock beds upper kane springs beds recapture member alluvium, gravels figure 2. stratigraphic column of rocks exposed within bears ears national monument. 210 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 into early terrestrial life in western pangea and the late paleozoic icehouse-greenhouse transition (e.g., montañez and others, 2007; montañez and poulsen, 2013). most early authors subdivided the cutler into four major subunits (bottom to top)—halgaito tongue, cedar mesa sandstone, organ rock tongue, and de chelly sandstone (baker and reeside, 1929; baker, 1936; orkild, 1955; sears, 1956; baars, 1962; o’sullivan, 1965). orkild (1955) and sears (1956) redefined these units in the vicinity of mexican hat and valley of the gods where the de chelly sandstone is absent. wengerd (1958) further revised the nomenclature, elevating the cutler to group status and subsuming the transitional beds of the pennsylvanian rico formation into the cutler group. farther north, along the eastern and northern margins of canyonlands national park, these lower strata were initially assigned to both the rico (loope, 1984) and elephant canyon formations (baars, 1962, 1975, 1987; terrell, 1972; campbell, 1987), but we follow the recommendation of loope and others (1990) and condon (1997) in using the informal name ‘lower cutler beds.’ in addition to a diverse invertebrate assemblage, rocks of the lower cutler beds (including the halgaito formation) record the rise of amniotes, egg-laying limbed vertebrates with internal fertilization. this clade includes the common ancestor of modern reptiles and mammals, and all of their descendants. also present are some of the first terrestrial vertebrate herbivores. the geology of the cutler group and its fossil assemblages reveal a complex ecosystem of coastal wetlands and estuaries, seasonal and perennial lakes, alluvial fans, and shifting dune fields (e.g., mountney and jagger, 2004; cain and mountney, 2009, 2011; jordan and mountney, 2010, 2012; wakefield and mountney, 2013). during this time, repeated brief marine incursions from the west covered large portions of present-day utah depositing thin marine carbonates, beach sands, and coastal dune strata in benm (jordan and mountney, 2010). though paleosols and fossil plants in the lower cutler beds suggest a cool, dry climate with some seasonal precipitation, the early permian environment became increasingly warm and arid through time (soreghan and others, 2002a, 2002b; dimichele and others, 2014). the cedar mesa ss lower cutler beds arkosic cutler cedar mesa ss cedar mesa ss cedar mesa ss halgaito fm halgaito fm ‘a’ ls ‘mckim’ ls lower cutler beds (“rico fm”) a b c d a b c d figure 3. upper carboniferous-lower permian cutler group lithostratigraphy in bears ears national monument and vicinity. (a and b) indian creek. (c) moqui dugway. (d) valley of the gods. abbreviations: fm, formation; ls, limestone; ss, sandstone.” 211 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 principal cutler dune fields are preserved as the cedar mesa sandstone in benm (figure 3) (e.g., condon, 1997; mountney and jagger, 2004; mountney, 2006). though additional erg deposits exist higher in the cutler group in the northwestern portions of benm and canyonlands national park, such as the white rim sandstone, very little of these units are present within the monument boundaries. resulting from early geological surveys of the monument valley area, collections of cutler vertebrates in the vicinity of benm were known to paleontologists for decades before their first descriptions (baker, 1936). in 1954, the museum of comparative zoology and the usgs made brief collecting trips in the red beds near the utah-arizona border. the university of california, los angeles, added to these collections in the 1960s and 1970s. vaughn (1962, 1973) described many fossils from nonmarine strata of the halgaito formation in the mexican hat and valley of the gods areas, including the first utah records of paleozoic xenacanth sharks, actinopterygians, osteolepiforms, temnospondyl amphibians (such as eryops and the sail-backed dissorophoid platyhystrix), a possible nectridean lepospondyl, stem amniote diadectomorphs, and the non-mammalian synapsids ophiacodon and sphenacodon. additionally, this unit contains plant macrofossils (leaves and stems) of walchian conifers, calamitaleans, cordaitaleans, marattialean ferns, and lycopsids (vaughn, 1962; berman and others, 1981; lockley and madsen, 1993; sumida and others, 1999a, 1999b, 1999c; hasiotis and rasmussen, 2010; dimichele and others, 2014). during the 1990s and 2000s, work was conducted in the vicinity of valley of the gods by california state university at san bernardino and the carnegie museum of natural history. these studies focused on the latest pennsylvanian vertebrates of the halgaito formation, prompting taxonomic revisions and producing additional new records that included dipnoans, the osteolepiform lohsania, limnoscelid diadectomorphs, edaphosaurus, and an araeoscelid reptile (frede and others, 1993; sumida and others, 1999a, 1999b, 1999c, 2005; scott and sumida, 2004; scott, 2005, 2013; huttenlocker and others, 2018). chondrichthyans, actinopterygians, osteolepiforms (lohsania?), and possible aïstopod (phlegethontia?) fossils have also been reported from lateral equivalents of the upper halgaito in the lower cutler beds of the arch canyon area, approximately 27 km northeast of valley of the gods (vaughn, 1967; sumida and others, 1999a, 1999b, 2005). nearshore and marine strata here also preserve abundant marine invertebrates and conodont elements (a.k. huttenlocker, in preparation), making these time-transgressive facies of the lower cutler beds in arch canyon an ideal location to precisely identify the carboniferous-permian (c-p) boundary in utah. in nearby monument valley, vertebrate records from the organ rock formation include numerous large-bodied diadectes, tseajaia, seymouria, and the sphenacodontid ctenospondylus. their presence suggests that multiple assemblages may be distributed stratigraphically throughout the cutler group of utah, some likely correlative to parts of the permian wichita group in north-central texas (vaughn, 1964, 1966a, 1966b, 1967, 1973; sumida and others, 1999a, 1999b, 1999c). vaughn (1962, p. 530) remarked, “it may be possible to build up in the four corners region a broad paleozoogeographic picture of faunas, at the same horizons, spread across several wide belts of different environmental conditions … san juan county would occupy a central part of such a picture.” however, unlike in monument valley, the truncated organ rock formation sequence in comb wash (benm) appears to preserve only some well-developed paleosols and rhizoliths; it is apparently largely devoid of body fossils. farther to the north, in the northeastern part of benm, rare fossil localities have been reported from the cutler group. vaughn (1967, p. 153) first reported, but did not describe, “shark teeth, marine invertebrates, and small vertebrae” from the lower cutler beds of indian creek. subsequently, stanesco and campbell (1989, p. f8–f9) reported the first fossils from the cedar mesa sandstone at indian creek, including plant leaf and stem impressions in fluvial facies, and permineralized logs and associated tetrapod bones in a fluvio-lacustrine interdunal setting. in the early 1990s, the dinosaur museum (blanding, utah) collected vertebrate material and a large permineralized log from the same site. although the log is currently on display in the museum’s exhibits, these specimens were never published. teams from the smithsonian institution’s national museum of natural history collected leaf and stem fossils from a 212 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 dozen different sites in the lower cedar mesa sandstone in indian creek, describing marattialean pteridophytes (pecopteris and asterotheca), sphenophyllaleans, and conifers (walchia) from these assemblages (dimichele and others, 2014). carboniferous-permian strata west-southwest of moab and adjacent to the northern boundary of canyonlands national park are continuous with those in the northernmost tip of the monument. here, where these units are bisected by the colorado river, abundant and diverse marine invertebrates have been reported from the honaker trail formation (melton, 1972). in the overlying transitional lower cutler beds, marine invertebrates, chondrichthyan teeth, and osteichthyan vertebrae have been described or reported (vaughn, 1967; terrell, 1972; carpenter and ottinger, 2018). close to the boundary of the honaker trail formation and lower cutler beds, tidwell (1988) described a diverse latest pennsylvanian floral assemblage containing nearly 20 taxa, including leaf and stem impressions of lycopodiopsids, sphenophyllaleans, equisetaleans, marattialean pteridophytes, medullosalean pteridosperms, and cordaitaleans. although these localities are outside benm, they nevertheless indicate potential paleontological resources that are likely present in lockhart basin at the northernmost portion of the monument. ongoing work relatively few continuous stratigraphic records of this time interval and paleoenvironment exist in other parts of north america, so benm rocks continue to provide a rare and relatively complete picture of ecosystems that developed during the late paleozoic prior to the devastating end-permian mass extinction. the oldest rocks of the paradox formation, though poorly fossiliferous, contain biohermal dolomitic limestone and a diverse assemblage of microfossils important for biostratigraphy (wengerd, 1955). most recently, ritter and others (2016) reported conodont assemblages just north of benm that promise to provide new age controls on the desmoinesian (mid-pennsylvanian) marine assemblages of the paradox formation in southeastern utah. the carboniferous-permian transition and the location of the c-p boundary in utah continues to be of considerable interest in documenting the key evolutionary innovations evident in animals and plants during this time. ongoing field investigations by the university of southern california, california state university at san bernardino, and carnegie museum of natural history are focusing on correlating old and new vertebrate sites in san juan county, including those in the halgaito formation at the valley of the gods, to the lower cutler beds in the north (arch canyon, dark canyon, and canyonlands areas). this work has resulted in discovery of several new localities and specimens that are currently under study by two of us (a.k. huttenlocker and r.b. irmis). along with usc-umnh collaborative fieldwork at latest carboniferous-permian localities exposed in northern san juan county just north of benm, the ongoing studies fill substantial spatial and temporal gaps between the carboniferous and permian vertebrate assemblages of utah. for example, new work at the “birthday bonebed” in the upper halgaito formation in valley of the gods has revealed a diverse vertebrate assemblage preserved in a slackwater deposit of a nonmarine channel tributary, providing critical new data for the latest carboniferous on the colorado plateau (huttenlocker and others, 2018). investigations into the sedimentary environment, flora, and invertebrate fauna by teams from the national museum of natural history and illinois state geological survey reveal the seasonally fluctuating riparian environments. discoveries include lycopsids, walchian conifer branches, calamitalean and cordaitalean foliage, and myriapod invertebrate trackways in the valley of the gods, lime ridge, and indian creek areas, where work is still ongoing (dimichele and others, 2011, 2014; chaney and others, 2013). additional work on trace fossils led by university of kansas has discovered large-diameter burrows of possible vertebrate origin in the cedar mesa sandstone (hasiotis and rasmussen, 2010), research that is ongoing. this and other studies of trace fossils are contributing to a more complete understanding of the record of early terrestrial life and environments in the cutler group (dzenowski and others, 2013), and by extension early tetrapod life globally. in 2009, umnh began long-term excavation of the indian creek bonebed in the cedar mesa sandstone 213 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 that was first mentioned by stanesco and campbell (1989). this interdunal site has revealed in situ permineralized logs and hundreds of tetrapod bones from the interface between pond and fluvial deposits, as well as permineralized logs, conifer foliage, and osteichthyan and small tetrapod bones from the immediately overlying lacustrine limestone. the specimens are currently being studied by a.k. huttenlocker, r.b. irmis, and colleagues. preliminary results show that tetrapod assemblage is dominated by the early synapsid sphenacodon, including a new species of the temnospondyl amphibian eryops (rasmussen and others, 2016). elsewhere in the area, the usc-umnh team has discovered plant and vertebrate material from both marine and nonmarine horizons in the lower cutler beds. this research group is collaborating on several other important sites in northern san juan county relevant to benm, and though this work is in its earliest stages, a faunal assemblage broadly consistent with other late paleozoic localities in north america is emerging, although with some significant taxonomic differences. early-middle triassic geology and paleontology during the triassic period, southwestern north america was located between the equator and approximately 15°n (kent and irving, 2010; torsvik and others, 2012). at this time, western utah was situated on the coast and shallow marine shelf along the eastern margin of the panthalassic ocean. during the early and middle triassic, central and eastern utah comprised the coastal and nonmarine fluvial siliciclastic deposits of the moenkopi formation (mckee, 1954; stewart and others, 1972b; blakey, 1974). outcrops of the moenkopi formation are widespread in benm (figure 4a), including the indian creek area, dark canyon wilderness and farther west, and comb ridge. none of the carbonate-bearing units (e.g., black dragon and sinbad limestone members) of the moenkopi extend far enough east to reach benm (blakey, 1974). consequently, exact correlation of benm moenkopi strata to the marine stages of the geologic time scale is poorly constrained. within benm, the moenkopi formation contains the hoskininni, torrey, and moody canyon members, in ascending order. the base of the hoskininni member is coarse grained, but the rest of the moenkopi in benm comprises reddish deltaic and fluvial mudstone, siltstone, and fine-grained sandstone that are slope and ledge-forming units (mckee, 1954; stewart and others, 1972b; blakey, 1974). to the west and north of benm, the torrey member overlies the marine sinbad member, which preserves an ammonoid assemblage characterized by anasibirites kingianus (stewart and others, 1972b; blakey, 1974; lucas and others, 2007; brayard and others, 2013), suggesting a latest spathian (middle olenekian) age (e.g., balini and others, 2010; ogg, 2012). this implies that the greater part of the moennavajo ss kane springs bds kayenta fm wingate ss church rock mbr owl rock mbr moenkopi fm c hinle fm kayenta fm wingate ss church rock mbr owl rock mbr hite bed c hinle fm navajo ss a b a b cc figure 4. triassic-lower jurassic lithostratigraphy in bears ears national monument and vicinity. (a) indian creek. (b and c) comb ridge. abbreviations: fm, formation; mbr, member; ss, sandstone; bds, beds. 214 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 kopi formation, the torrey and moody canyon members, are spathian (middle-upper olenekian) in age or younger (i.e., anisian). published reports of fossils from the moenkopi formation within the benm are rare. mckee (1954) noted “plant fragments” and “good fish remains” from the upper moenkopi formation (about 40 m below the top of the unit) near bears ears proper; but did not illustrate or describe any specimens. stewart and others (1972b, p. 68) briefly described actinopterygian scales, vertebrae, and teeth from the upper moenkopi formation (8 m below the top of the unit) in fry canyon, but failed to illustrate the specimens or mention repository/ specimen numbers. nearby in white canyon, just outside of the western boundary of benm, mckee (1954, figure 9) noted a bone-bearing conglomerate just above the base of the formation, but again no details were provided. mckee (1954, p. 69) also mentioned “amphibian bones” from bears ears (about 15 m below fish-bearing unit mentioned above) and “vertebrate remains” from the indian creek area. mckee (1954, p. 71) noted reptile tracks in the measured sections from bears ears and the indian creek area, but did not provide any further details. more recently, thomson and lovelace (2014) described archosauriform reptile swim tracks from the torrey member just inside the western boundary of benm along highway 95, as well as a number of similar sites just outside the western boundary of the monument. perhaps the most important fossil locality in the moenkopi formation within benm is a site discovered in 1945 by university of california-berkeley paleontologist samuel p. welles and colleagues in the indian creek area. here, the berkeley team discovered and excavated the complete skull and lower jaws of a capitosaurian temnospondyl amphibian in the upper moenkopi formation. although welles (1967, 1969) failed to describe the specimen, it was twice mentioned and once illustrated (welles, 1967, p. 14), noting its striking similarity to parotosuchus helgolandicus (welles, 1967, p. 13) from the lower middle buntsandstein of northern germany, which is smithian/lower olenekian in age (see szurlies, 2007; hounslow and muttoni, 2010). morales (1987, p. 6) also mentioned the specimen and stated, without further explanation, that it was from the torrey member. despite a lack of detailed description, formal taxonomic assignment, or stratigraphic data, lucas and schoch (2002, p 101) asserted that the specimen was assignable to parotosuchus helgolandicus and repeated morales’ statement that it was from the torrey member. lucas and schoch (2002) also incorrectly described the specimen as being found near hite. these authors then used the specimen to correlate the moenkopi formation with the buntsandstein in germany. ongoing work work on new moenkopi formation track sites from the white canyon region is in its nascent stages but the assemblage of invertebrate burrows and surface tracks indicates a diverse fauna that requires full description. these track sites were discovered in the 2016 and 2017 field seasons by one of us (r.j. gay). additionally, r.b. irmis has recently relocated the site of welles’ parotosuchus-like temnospondyl in the indian creek area, as part of work to describe the specimen and place it in a precise geologic context. although the moenkopi formation in benm has historically been poorly surveyed, these discoveries suggest that systematic prospecting of the unit may reveal significant fossil localities. late triassic stratigraphy and depositional environments during the late triassic, pangaea began to drift northward (kent and tauxe, 2005; kent and irving, 2010). what is now the southwestern united states changed from having a semi-humid to a semi-arid climate (kent and tauxe, 2005; whiteside and others, 2011, 2015). no strata are preserved in this region that record the late middle triassic and early late triassic environment. base-level change near the end of the carnian (about 228 ma) (atchley and others, 2013) initiated deposition of the fluvially dominated sediments of the chinle formation (e.g., blakey and gubitosa, 1983; dubiel, 1994; riggs and others, 1996). as the climate of the region became progressively more arid toward the end of the triassic period, the northwest-flowing rivers and floodplains depositing the chinle formation were increasingly better drained (e.g., dubiel and hasiotis, 215 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 2011; martz and others, 2014). ultimately, during the latest triassic, fluvial deposition became ephemeral and sand dunes gradually encroached upon the eastern half of the state (martz and others, 2014; irmis and others, 2015; britt and others, 2016). by the beginning of the jurassic, dune fields extended across large portions of the colorado plateau. the dunes are preserved as the wingate sandstone (stokes, 1986; peterson, 1988, 1994; blakey, 1994), which directly overlies the chinle formation. no other geologic formation in benm has attracted more paleontological research than the upper triassic chinle formation (e.g., parrish and good, 1987; parrish, 1999; fraser and others, 2005; gay and st. aude, 2015, martz and others, 2014, 2017; figures 4a and 4b). the lithostratigraphy of the chinle is complex with a high degree of lateral facies variability. within the southern benm, the chinle formation can be divided into six members, from oldest to youngest—shinarump, monitor butte, moss back, petrified forest, owl rock, and church rock (stewart, 1957; stewart and others, 1972a; blakey and gubitosa, 1983; dubiel, 1994; lewis and others, 2011) (figure 4b). in the south-central and southeastern parts of benm, near bears ears proper and comb ridge, the monitor butte and moss back members interfinger (stewart and others, 1972a; blakey and gubitosa, 1983; dubiel, 1994), making them difficult to differentiate (lewis and others, 2011). for stratigraphic convenience the interfingered parts of the formation is referred to simply as the monitor butte member (gay and st. aude, 2015). in the abajo mountains and indian creek areas to the north, the lower part of the chinle formation is absent. the base of the formation is equivalent to the petrified forest member (blakey and gubitosa, 1983; martz and others, 2014, 2017). here the chinle subdivisions are, from oldest to youngest—kane springs beds, owl rock member, and church rock member (witkind, 1964; blakey and gubitosa, 1983, 1984; martz and others, 2014, 2017) (figure 4a). the shinarump member fills paleovalleys incised into the underlying moenkopi formation. this member is dominated by coarse-grained braided stream deposits laid down by large river systems flowing to the northwest (blakey and gubitosa, 1983, 1984; dubiel, 1983, 1987, 1994). the coarse-grained sediments pass upward with an interfingering relationship into finer-grained floodplain sediments of the monitor butte member that preserve marsh, pond, and small stream environments having a fluctuating water table (blakey and gubitosa, 1983; dubiel, 1983, 1987, 1994; dubiel and hasiotis, 2011). laterally the monitor butte strata grade into and are overlain by braided stream deposits of the moss back member, which represent the larger trunk streams of the same fluvial system (blakey and gubitosa, 1983, 1984; dubiel, 1983, 1987, 1994). in the southern benm, the moss back is overlain by the welldrained paleosols and meandering stream deposits of the petrified forest member, which record increasingly arid and seasonal conditions during the norian (blakey and gubitosa, 1983; dubiel, 1987, 1994; dubiel and hasiotis, 2011; martz and others, 2017). in the northern benm and vicinity, the kane springs beds are in part correlative to the petrified forest member. these beds are the lowest chinle strata in this area (blakey and gubitosa, 1983, 1984; martz and others, 2014, 2017). this unit represents an assemblage of fine-grained floodplain and meandering stream deposits that locally fill paleovalleys in the underlying moenkopi formation (blakey, 1978; blakey and gubitosa, 1983, 1984; martz and others, 2014; hartley and evenstar, 2018). the owl rock member rests on both the petrified forest member and kane springs strata throughout benm (figure 4a). this member is characterized by fine-grained overbank and minor channel deposits (blakey and gubitosa, 1983; dubiel, 1994; dubiel and hasiotis, 2011). crayfish burrows extending from channel and levee facies down into underlying fine-grained paleosols are common (hasiotis and mitchell, 1989, 1993; hasiotis and others, 1993; hasiotis, 1995). descriptions of widespread lacustine environments in the owl rock member are a consequence of misinterpretation of the carbonate-rich pedogenic horizons and the coarse-grained layers with both diagenetic carbonate cement and intraformational carbonate nodule clasts (tanner, 2000, 2003). the uppermost unit of the chinle formation across all the benm is the church rock member having coarse-grained overbank and ephemeral channel deposits indicating a distinctly seasonal paleoclimate (blakey and gubitosa, 1983; dubiel, 1987, 1994; martz and others, 2014). locally at the 216 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 boundary between the top of the church rock member and the overlying wingate sandstone, there are fluvial sandstone and conglomerate beds named big indian rock beds by martz and others (2014). these beds indicate that the chinle-wingate transition was variable and not correlative strictly with the onset of eolian deposition. as in northeastern utah (cf. irmis and others, 2015), the fossils in these beds indicate that the base of the wingate sandstone is still triassic in age (martz and others, 2014). history of geological and paleontological exploration the earliest publication of vertebrate fossils from the benm region described the first occurrence of a phytosaur from utah. this specimen was collected from the clay hills area, south of fry canyon and east of what is now lake powell (lucas, 1898). phytosaurs are perhaps the most common vertebrate fossil from the chinle formation in benm (martz and others, 2014; mccormack and parker, 2017; authors personal observations). these semi-aquatic, archosauriform reptiles superficially resemble modern crocodylians. they were globally distributed and abundant during the late triassic (stocker and butler, 2013). during the early part of the 20th century geologic exploration in benm focused principally on mineral and oil exploration along the san juan river (e.g., baker, 1933, 1936; wengerd, 1951). as part of this work, a 1926 usgs geological field party collected fragmentary phytosaur bones from moab (camp, 1930, p. 12; baker, 1933, p. 41). charles camp of the university of california, berkeley, conducted additional fieldwork in the chinle formation of southeastern utah in 1927, discovering localities near moab (ucmp a280), indian creek (ucmp a281), and bears ears (ucmp a277). camp (1930, p. 13) briefly mentioned fragmentary phytosaur material, as well as other bone fragments, from these sites. in the 1950s, exploration in the chinle formation shifted away from fossils and toward another resource. the post-world war ii uranium boom resulted in mining claims throughout southeastern utah. the chinle formation became one of the country’s most productive formations for uranium (isachsen and evensen, 1956; ringholz, 1989). this explosion of mineral exploration and extraction also promoted renewed interested in triassic stratigraphy on the colorado plateau. during the 1950s and 1960s, the atomic energy commission funded a large-scale study of nonmarine triassic lithostratigraphy by a usgs team resulting in two comprehensive monographs (stewart and others, 1972a, 1972b). not only did this work provide fundamental insights into the stratigraphy and sedimentology of the chinle formation (stewart, 1956, 1957; stewart and others, 1959, 1972a; stewart and wilson, 1960), but additional paleontological sites were discovered. these include sites from benm and surrounding areas, such as molluscs from fry canyon, white canyon, the clay hills, and lisbon valley (stewart and others, 1972a, p. 78–79); crustaceans from white canyon and lisbon valley (stewart and others, 1972a, p. 79); temnospondyl amphibians from fry canyon (stewart and others, 1972a, p. 80); and phytosaurs from white canyon and deer flat (stewart and others, 1972a, p. 82). a diversity of fossil leaf localities were reported, including sites preserving ferns, bennettitaleans, and conifers in the shinarump and monitor butte members at elk ridge, deer flat, white canyon, and monitor butte (stewart and others, 1972a, p. 85–86). many of these specimens subsequently were described in more detail by ash (1975a, 1975b, 1977, 2001; ash and others, 1982; ash and litwin, 1996). mullens (1960, p. 287– 288) mentioned gastropods, teeth, and bone fragments from the clay hills area and o’sullivan (1965, p. 62) reported fragmentary phytosaur remains from comb ridge. just east of benm, in the lisbon valley area, geologists conducting uranium exploration (isachsen, 1954; isachsen and others, 1955; isachsen and evensen, 1956; weir and puffett, 1960) discovered several sites in the church rock member (see martz and others, 2014) that preserve articulated skeletons of multiple species of actinopterygian fish and the coelacanth chinlea. these specimens were described by schaeffer (1967). though the uranium boom ended in the late 1960s with falling commodity prices, its effects can still be felt in unexpected ways by modern paleontologists who work in benm. for example, old uranium roads provide access to sites that would otherwise be inaccessible, because the chinle formation forms impenetrable 217 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 badlands within benm. uranium readily replaces calcium in bone (neuman and others, 1949) and often precipitates in association with organic material (spirakis, 1996). in areas with high concentrations of uranium minerals, radioactive fossilized bone and wood are common (steen and others, 1953; gross, 1956; isachsen and evensen, 1956; trites and others, 1956; weir and puffett, 1960; johnson and thordarson, 1966; r. gay, personal observation). historical archaeological artifacts of the uranium boom, including mine shafts and assorted machinery, core holes and discarded core, and mining haul roads are common across the region. abandoned camps can be found across benm wherever triassic strata are well exposed. following the seminal work on chinle stratigraphy by stewart and others (1972a), paleontological reconnaissance of the chinle formation across southeastern utah was performed during the mid-1980s by michael parrish, steven good, and russell dubiel. prior to field campaigns by parrish, good, and dubiel, fossil occurrences in the chinle formation within benm had been limited due to the rough terrain and lack of systematic prospecting, and were largely restricted to finds made by the geologic studies cited above. parrish and good (1987) and parrish (1999) had discovered vertebrate fossils in the shinarump, monitor butte, moss back, and petrified forest members of the chinle formation, including metoposaurid temnospondyls, phytosaurs, and aetosaurs. the discovery of the phytosaur ‘rutiodon tenuis’ (= machaeroprosopus pristinus—see long and murry, 1995) and a partial osteoderm of the aetosaur typothorax lead parrish and good (1987) to correlate the petrified forest member in the white canyon region of benm with the petrified forest member in arizona and new mexico. this correlation is consistent with lithostratigraphic correlations by stewart and others (1972a), blakey and gubitosa (1983), and martz and others (2017). parrish and good (1987) also discovered numerous invertebrate fossils, including bivalves, gastropods, ostracods, and conchostracans. in addition, they reported the occurrence of the molluscs triasamnicola assiminoides, diplodon gregori, antediplodon sp., and unio sp. the most significant discoveries from the 1980s surveys were two separate sites that preserve small vertebrates, both of which are adjacent to uranium mines. the first was discovered in the monitor butte member of the red canyon area. from this site parrish (1999) described several vertebrae, limb elements, and armor plates of at least two individual diminutive crocodylomorphs belonging to the same taxon, as well as three additional armor plates from crocodylomorphs assigned to archosauriformes. none of the ‘crocodylomorph’ material is actually assignable to that clade. the osteoderms (parrish, 1999; figure 1) and possibly some of the postcrania (figures 2 and 3 of parrish, 1999) appear to be referable to the early suchian revueltosaurus (cf. parker and others, 2005; r.b. irmis., personal observation). similarly, the indeterminate archosauriform osteoderms are nearly identical to those of the suchian archosaur acaenasuchus from the blue mesa member of the chinle formation of eastern arizona (cf. see figures 117 and 118 of long and murry, 1995; figure 6d of irmis, 2005a; marsh and others, in press). this site, including parrish’s finds, was included in the original monument proposal (bears ears intertribal coalition, 2016) but omitted in the final declaration (obama, 2016). the second site, in the petrified forest member in white canyon, produced vertebrae and claws from a possible theropod dinosaur and a fragmentary right mandible from a possible ornithischian dinosaur (parrish, 1999). for nearly two decades these represented the only published occurrence of dinosaur body fossils from the triassic of utah. although the discovery appeared to be highly significant, recent work has cast doubt on their assignment to dinosauria (jenkins and others, 2017). this site is within the original boundaries of benm (obama, 2016), but it is excluded from the revised monument boundaries (trump, 2017). another notable discovery was a skull of a procolophonid parareptile from the owl rock or church rock members in the abajo mountains area (fraser and others, 2005). this unnamed leptopleuronine is the only described associated skull of a procolophonid from the chinle formation. procolophonid remains of any kind are very rare from the unit (martz and others, 2017). this specimen appears to be taxonomically distinct from hypsognathus and other leptopleuronines known from the late triassic of north america (fraser and others, 2005). 218 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 other paleontological work in the area occurred sporadically throughout the 1980s and 1990s. litwin (1986), litwin and skog (1991), and litwin and others (1991) described diverse palynological assemblages from the shinarump member at kigalia point, north of bears ears buttes, and from the petrified forest member at copper point, east of white canyon. the palynomorphs supported regional biostratigraphic correlation of the chinle formation (litwin and others, 1991). just east of benm, ash (1982, 1987) described specimens of petrified wood, casts of neocalamites, leaves of pelourdea poleoensis, and leaves of sanmiguelia lewisi from the church rock member in lisbon valley. dubiel and others (1987, 1988, 1989) described lungfish burrows from the monitor butte and owl rock members in the white canyon area. however, it was quickly noted by other researchers that these were crayfish burrows identical to those containing rare crayfish body fossils in the owl rock member at indian creek (mcallister, 1988; hasiotis and mitchell, 1989, 1993; hasiotis and others, 1993; hasiotis, 1995). these ichnofossils provide evidence for a fluctuating water table during the norian in this area. also at indian creek is the shay canyon track site described in lockley (1986) and lockley and hunt (1995). this important site preserves over 250 footprints on a single horizon in the church rock member. it is dominated by tracks of brachychirotherium, thought to be made by aetosaurs (refer to heckert and others, 2010; lucas and heckert, 2011). atreipus-like tridactyl prints are also preserved (lockley and hunt 1995; hunt-foster and others, 2016). ongoing work parrish and good (1987) and parrish (1999) were the first researchers to demonstrate the potential for significant chinle sites in the area designated as benm. three decades later the list of institutions engaged in active chinle research in benm has grown significantly to include museums of western colorado, the natural history museum of utah, the st. george dinosaur discovery site, the natural history museum of los angeles county, petrified forest national park, appalachian state university, and the university of california, berkeley. in a large collaborative effort that has become the norm for paleontological research, scientists from these institutions are working to fill gaps in our understanding of the late triassic period (martz and others, 2014; delgado and others, 2017; gay and others, 2017). recent and ongoing efforts by teams have assembled substantial collections from benm and the surrounding region, much of which awaits preparation and research. work in the southern area has recovered a diverse microvertebrate assemblage from the base of the chinle formation at comb ridge (gay and others, 2016). this site has already produced hundreds of specimens from surface collection alone, with screen washing done in 2018. the taxonomic diversity is greater than any published upper triassic microvertebrate site in utah. as of 2017, the recovered diversity (293 specimens comprising 14 clades) is similar to other north american sites of the same age. gay and others (2017) report a bonebed in the chinle formation in red canyon that had previously produced a skull and partial skeleton of the phytosaur pravusuchus (mccormack and parker, 2017). preliminary fieldwork conducted at this site in september of 2017 indicated that the bonebed is a laterally extensive assemblage unlike any previously discovered in benm or elsewhere in the chinle formation of utah. it is apparent that over the past two decades illegal collecting had been done at this site, highlighting the fragility of this extremely significant paleontologic resource and others like it (gay and others, 2018). in the northern part of benm, particularly in the indian creek area, joint fieldwork from 2013 to the present by the sgdds and umnh has identified over 200 new fossil localities in the chinle formation that preserve a record of late triassic plants, molluscs, and vertebrates. these sites occur throughout formation with fossils in the kane springs beds, owl rock member, and church rock member (see figure 12 of martz and others, 2014, p. 426–428). discoveries include multiple taxa of leaves, a quarry containing many articulated actinopterygian fish, metoposaurid temnospondyls, phytosaur skulls and associated skeletons, aetosaurs, “rauisuchians,” skeletal remains of small as-yet unidentified tetrapods, and a diversity of tetrapod footprints (e.g., brachychirotherium, rhynchosauroides, evazoum, and gwyneddichnium; see hunt-foster and others, 2016). to the east, just outside of benm, the same team encountered 219 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 a similar fossil assemblage in the kane springs beds and church rock member in lisbon valley. fossils found include leaves of ferns, bennettitaleans, and sanmiguelia; conchostracans; ostracods; molluscs; multiple taxa of actinopterygian fish; coelacanths; metoposaurid amphibians; the phytosaur redondasaurus, the aetosaur typothorax; paracrocodylomorphs; and footprints from the ichnotaxa grallator, brachychirotherium, apatopus, and rhynchosauroides (milner, 2006; milner and others, 2006, 2011; gibson, 2013a, 2013b, 2015; ash and others, 2014; martz and others, 2014; see figures 6 to 12 and table 1 of hunt-foster and others, 2016). the specimens in the indian creek area and lisbon valley comprise the most abundant fossil assemblages in utah from the chinle formation and are among the richest assemblages from the church rock member anywhere on the colorado plateau. the triassic-jurassic boundary the end of the triassic period is marked by one of the five largest mass extinctions in earth’s history, the end-triassic mass extinction (e.g., raup, 1994; bambach, 2006; alroy and others, 2008). this biotic crisis at 201.6 ma is thought to have been caused by eruption of the central atlantic magmatic province (camp) flood basalts. these were extruded on land as the atlantic margins of north america, south america, europe, and africa began to rift apart (e.g., schoene and others, 2010; whiteside and others, 2010; blackburn and others, 2013; percival and others, 2017). although the extinction event is relatively well characterized in marine ecosystems, its severity and timing in nonmarine environments remains controversial (e.g., pálfy and others, 2000; olsen and others, 2002; tanner and others, 2004; whiteside and others, 2007, 2010; lindström and others, 2017). the difficulty with nonmarine records is that age dating is poorly constrained (e.g., irmis and others, 2010; mundil and others, 2010). in north america the sole exception is the tetrapod footprint record from the newark supergroup along the east coast (olsen and others, 2002), which is tied to the newark-harford astrochronostratigraphic time-scale (kent and others, 2017) and now verified by high-precision u-pb ages from the chinle formation (kent and others, 2018). the uppermost chinle formation and glen canyon group on the colorado plateau has potential to complement the newark supergroup record because it preserves an abundant footprint and body fossil record (e.g., sues and others, 1994; irmis, 2005b; lucas and others, 2005; tykoski, 2005; milner and others, 2012) and contains a much longer post-extinction record (cf. marsh and others, 2014; marsh, 2015). however, the principal limitation of the colorado plateau record is the absence of precise geochronologic age constraints. there is even debate over the stratigraphic placement of the triassic-jurassic boundary (lucas and others, 2005, 2006b, 2006c, 2011; kirkland and milner, 2006; lucas and tanner, 2007; donohoo-hurley and others, 2010; milner and others, 2012; kirkland and others, 2014; suarez and others, 2017). nonetheless, evidence is strong that the triassic-jurassic transition is preserved without significant gaps in deposition across the colorado plateau (lucas and others, 2006c; sprinkel and others, 2011a; martz and others, 2014; irmis and others, 2015; britt and others, 2016; suarez and others, 2017), and specifically in benm (molina-garza and others, 2003; lewis and others, 2011). therefore the glen canyon group within and adjacent to benm can provide important insights into the end-triassic extinction on land, the subsequent ecological recovery of non-marine ecosystems, and the final stages of the emergence of dinosaurs (e.g., brusatte and others, 2010; langer and others, 2010; irmis, 2011). geology and paleontology in benm, the chinle formation is overlain by the upper triassic-lower jurassic wingate sandstone of the glen canyon group, which acts as a resistant cliff-forming “cap” (baker, 1936; sears, 1956; stewart, 1957; witkind and others, 1963; witkind, 1964; o’sullivan and maclachlan, 1975; martz and others, 2014, 2017). although predominantly an eolian sandstone, the base of this unit locally preserves fluvially deposited sands (e.g., martz and others, 2014). the wingate sandstone represents the onset of the early jurassic continental erg (e.g., blakey, 1994; blakey and others, 1988; peterson, 1988, 1994; sprinkel and others, 2011a; irmis and others, 2015; britt and others, 2016), a pro220 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 found and sustained desertification of western north american driven in part by the breakup of pangea and the northward drift of the continent (kent and irving, 2010). paleontologic (lockley and others, 2004; lucas and others, 2006c; martz and others, 2014; hunt-foster and others, 2016), geochronologic (molina-garza and others, 2003), and lithostratigraphically correlative strata (sprinkel and others, 2011a; irmis and others, 2015; britt and others, 2016; suarez and others, 2017) all indicate that the triassic-jurassic boundary is preserved within the wingate sandstone. except for vertebrate body fossils found at the chinle-wingate contact in the aforementioned fluvial sandstones (morales and ash, 1993; martz and others, 2014), the wingate sandstone has yet to produce diagnostic body fossils. no wingate fossil sites within benm have been published. however, numerous wingate track sites have been found north and west of benm, as well as in northeastern arizona (longwell and others, 1925, p. 13; baker, 1936, p. 50; lockley and hunt, 1995; schults-pittman and others, 1996; lockley and others, 2004; smith and foster, 2004; lockley and gierliński, 2006; lucas and others, 2006c; hunt-foster and others, 2016). at these sites the presence of brachychirotherium and absence of eubrontes in the lower wingate sandstone and vice versa in the upper wingate, along with the presence of synapsid, batrachopus, and otozoum tracks, is consistent with the placement of the triassic-jurassic boundary near the middle of the formation (lockley and others, 2004; lucas and others, 2006c). ongoing work a sgdds-umnh investigation in the indian creek area has discovered a number of important wingate sandstone footprints in slump blocks covering the slope-forming chinle formation. these include tracks of brachychirotherium, eubrontes, and a spectacular vertical block covered in dozens of tracks of evazoum and grallator (see figures 16f and 17 of hunt-foster and others, 2016, p. 88–89). although not in original stratigraphic position, the footprint assemblages add credence to the proposition that the wingate sandstone in benm contains a record of the end-triassic extinction and the triassic-jurassic boundary. jurassic geology and paleontology the glen canyon group contains three formations—the eolian wingate sandstone at the base, the fluvial-dominated kayenta formation, and, with an interfingering relationship, the eolian navajo sandstone at the top (middleton and blakey, 1983; herries, 1993; blakey, 1994; peterson, 1994). all three units outcrop prominently throughout the benm (figures 4a and 4b). access to the outcrops is generally difficult because they form steep ledges and cliffs. radioisotopic ages, magnetostratigraphy, and palynomorphs from the underlying moenave formation in southwestern utah and northern arizona provide maximum age constraints for the kayenta formation indicating it is no older than sinemurian (litwin, 1986; cornet and waanders, 2006; downs, 2009; donohoo-hurley and others, 2010; suarez and others, 2017). new u-pb zircon ages from the ‘silty facies’ of the formation in northern arizona suggest at least part of the kayenta is late pliensbachian to early toarcian in age (marsh and others, 2014; marsh, 2015). this is consistent with magnetostratigraphic data from the kayenta formation and interfingering tenny canyon tongue of the navajo sandstone in southwestern utah, which steiner and tanner (2014) correlated with the lower-middle pliensbachian, but would be equally consistent with an upper pliensbachian-lower toarcian age (cf. moreau and others, 2002; ogg and hinnov, 2012). descriptions of fossils from the kayenta formation in benm are few. baker (1933, p. 46) reported unionid bivalves from the northern tip of the original monument. umnh has in its collection a tetrapod rib (umnh vp 29841) and a large bone fragment (umnh vp 29842) from the formation in the comb ridge area. there are no published accounts of footprints in benm, but diverse and abundant track assemblages are known to the north and west (lockley and hunt, 1995; foster and others, 2001; lockley and gierliński, 2006, 2014a; milner and others, 2012). in northeastern arizona, the ‘silty facies’ of the kayenta formation contains a diverse body fossil assemblage, including hybodont and osteichthyan fishes, amphibians, caecilians, turtles, croco221 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 dylomorphs, dinosaurs, cynodonts, dicynodonts, and mammals (sues and others, 1994; lucas and others, 2005; tykoski 2005). a new site in southwestern utah has produced a diverse assemblage of fossil leaves, vertebrate body fossils, and vertebrate ichnotaxa (milner and others, 2017). the hypothesized toarcian age of the navajo sandstone is constrained only by the age of the unit that conformably underlies it, as described above, and the middle jurassic (aalenian) temple cap formation (kowallis and others, 2001; sprinkel and others, 2011b; doelling and others, 2013) that unconformably rests on it. a remarkable discovery in the navajo sandstone at comb ridge in benm is the type specimen of the early sauropodomorph dinosaur seitaad ruessi (sertich and loewen, 2010). this is the oldest dinosaur identified to the species level in utah. the single specimen is an articulated postcranial skeleton missing the neck and tail. it is one of few vertebrate body fossil specimens collected from the entire formation. elsewhere the navajo sandstone contains other sauropodomorphs, the theropod segisaurus, crocodylomorphs, tritylodontid cynodonts, and actinopterygian fish (irmis, 2005b; harward and irmis, 2014; frederickson and davis, 2017). trace fossils in the navajo sandstone are abundant and diverse. rainforth (1997) documented occurrences in benm near comb ridge, indian creek, and kane springs canyon, including footprints of grallator, eubrontes, anomoepus, and otozoum. in southern utah outside of benm, navajo sandstone invertebrate and vertebrate traces are numerous. they include the extensive trackway site at the kayenta-navajo boundary in lisbon valley (stokes, 1978; lockley and others, 1992; lockley and hunt, 1995; rainforth, 1997; loope and rowe, 2003; loope, 2006a; ekdale and others, 2007). particularly important are spring-fed interdunal pond deposits containing fossils of large conifer logs, leaves, ostracods, invertebrate and vertebrate burrows, and dinosaur tracks (eisenberg, 2003; loope and others, 2004; lucas and others, 2006a; parrish and falcon-lang, 2007; riese and others, 2011; parrish and others, 2017). the middle to upper jurassic san rafael group unconformably overlies the glen canyon group. middle jurassic and younger strata are exposed only on the eastern and western margins of benm (figure 5). post-lower jurassic rocks have been eroded from the top of the monument upwarp (e.g., hintze and others, 2000; see figure 1 of doelling and others, 2013). consequently, the oldest unit in the san rafael group is the carmel formation, which is biostratigraphically and radioisotopically dated as bajocian through lower callovian (sprinkel and others, 2011b; doelling and others, 2013). no fossils have been reported from the carmel formation in southeastern utah, but extensive invertebrate fossil assemblages are known from marine facies to the west and north (imlay, 1948, 1964; lowrey, 1976; bagshaw, 1977). dinosaur footprints have been reported from coastal deposits in northeastern utah (lockley and hunt, 1995; lockley and others, 1998a). the carmel formation is conformably overlain by the eolian entrada sandstone, which is thought to be late callovian (sprinkel and others, 2011b; doelling and others, 2013). no fossils have been reported from the entrada in benm, but to the west and north invertebrate burrows (ekdale and picard, 1985), vertebrate burrows (loope, 2006b, 2008), and theropod and sauropod dicarmel fm bluff ss summerville fm entrada ss brushy basin mbr, morrison fm a b a b figure 5. middle-upper jurassic lithostratigraphy in bears ears national monument and vicinity. (a) butler wash. (b) black mesa. abbreviations: fm, formation; mbr, member; ss, sandstone. 222 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 nosaur footprints (foster and others, 2000) occur. the san rafael group includes the moab tongue along the eastern margin of gsenm. this localized stratigraphic unit had been considered part of the entrada sandstone, but it is now assigned to the younger curtis formation (doelling, 2001, 2004; o’sullivan 2010a). the curtis formation is considered to be latest callovian or earliest oxfordian in age, because the base of the overlying morrison formation is dated as middle-late oxfordian (cf. pellenard and others, 2013; trujillo and kowallis, 2015; muttoni and others, 2018). this age assignment is consistent with u-pb dates from detrital zircon in the curtis formation (dickinson and gehrels, 2009). no curtis formation fossils have been reported in benm; however, to the north the top of the moab tongue contains abundant dinosaur tracks, a “mega track site,” as well as tracks of the controversial archosaur ichnotaxon pteraichnus (lockley, 1991; lockley and hunt, 1995; lockley and gierliński, 2014b). in eastern benm the summerville formation (oxfordian) directly overlies the moab tongue. the summerville’s assigned age is constrained only by its stratigraphic position immediately beneath the fossiliferous morrison formation. at butler wash in benm there is an important theropod dinosaur track site in the upper summerville formation. similar footprints, including pteraichnus, are found in an equivalent stratigraphic position north of ticaboo, west of benm (lockley and others, 1996; lockley and mickelson, 1997). towards the close of the jurassic period, a broad network of rivers, floodplains, and ponds developed across the western interior. the deposits of variegated mudstone, siltstone, and sandstone form the morrison formation (upper jurassic). this formation holds one of the richest dinosaur-bearing fossil assemblages in north america (e.g., turner and peterson, 1999, 2004; foster, 2003, 2007; chure and others, 2006). the best exposures of the morrison formation are along the eastern part of benm, from bluff to north of monticello. at the south end of the outcrop belt the formation has four members—bluff sandstone, recapture, westwater canyon, and brushy basin (in ascending order). at the north end just three members crop out—tidwell, salt wash, and brushy basin (peterson, 1994; turner and peterson, 2004, 2010; o’sullivan, 2010b; kirkland and others, 2020). the tidwell member has been radioisotopically dated to approximately 157 ma (middle-late oxfordian)—the top of morrison formation is about 150 ma, slightly younger than the kimmeridgian-tithonian boundary (kowallis and others, 1998, 2007; pellenard and others, 2013; trujillo and others, 2014; trujillo and kowallis, 2015; muttoni and others, 2018). most fossils are found in the salt wash and brushy basin members (turner and peterson, 1999; foster, 2003). however, in 1859, just east of the indian creek unit of benm, the type and only known specimen of the enigmatic sauropod dinosaur dystrophaeus viaemalae was discovered in the tidwell member (gillette, 1996a, 1996b; mcintosh, 1997; bernier and chan, 2006). this specimen comprises the oldest known skeletal remains of a eusauropod dinosaur from north america. the site is currently under renewed excavation by the utah field house of natural history and umnh (foster and others, 2016a). four to five million years later, during salt wash and brushy basin time, iconic dinosaurs such as allosaurus, camarasaurus, brachiosaurus, apatosaurus, and stegosaurus roamed across the 1.1 million-squarekm morrison landscape leaving behind footprints and dozens of multispecies bonebeds (turner and peterson, 1999, 2004; foster and lockley, 2006; foster and others, 2016b). although important salt wash and brushy basin fossil sites are common across utah (turner and peterson, 1999; foster, 2003), few have been documented in benm. this is due to insufficient systematic prospecting, though this is beginning to change (kirkland and others, 2020). an unpublished fragmentary sauropod specimen (umnh vp 29894) in the white mesa area east of benm (umnh vp loc. 2391) was collected in 1979 from the brushy basin member during a survey for the white mesa uranium mill. the blanding dinosaur museum also has morrison formation sauropod material in its collection, including a fragmentary pelvis from near blanding and a camarasaurus humerus. sites near the northern boundary of benm preserved fish; the sphenodontian eilenodon; squamates; ornithischian dinosaurs stegosaurus, camptosaurus, and fruitadens; sauropod dinosaurs camarasaurus, apatosaurus, diplodocus; theropod dinosaur allosaurus; and several mammaliaforms, including fruitafossor, 223 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 glirodon, dryolestes, a morganucodont, a eutricodont, and a paurodontid (foster, 2003, 2005; davis and others, 2018). tetrapod footprints are common in the salt wash and brushy basin members (lockley and others, 1998b; foster and lockley, 2006), but only a single site has been published within benm. milàn and chiappe (2009) described the first north american occurrence of the possible stegosaur ichnotaxon deltapodus from the brushy basin member between blanding and bluff. despite the rarity of documented finds within benm (kirkland and others, 2020), sites in the salt wash member to the south (lockley and others, 1998c) and east (foster and lockley, 2006) of the monument have footprints of crocodyliforms, ornithopod dinosaurs, sauropod dinosaurs, and theropod dinosaurs, including the type localities of dinehichnus socialis (lockley and others, 1998c) and hatcherichnus sanjuanensis (foster and lockley, 1997). among morrison formation plant localities (parrish and others, 2004; deblieux and others, 2017), perhaps the most important in benm region is in the brushy basin member near montezuma creek. at this site fine-grained tuffaceous deposits contain fossil wood, palynomorphs, leaves, conchostracans, fish, and invertebrate traces (ash, 1994; ash and tidwell, 1998; litwin and others, 1998; hasiotis and others, 2004; parrish and others, 2004). the megafloral assemblage includes at least eight different species of bryophytes, ferns, cycadophytes, ginkgophytes, conifers, and problematic taxa, such as hermanophyton (ash, 1994; ash and tidwell, 1998). this site is assigned an age of late kimmeridgian-earliest tithonian (cf. muttoni and others, 2018) and has been 40ar/39ar dated to 149 to 152 ma (kowallis and others, 1998; trujillo and kowallis, 2015). baker (1933, p. 52) refers to petrified wood from the salt wash member in the northern benm, but does not specify the location. ongoing work the morrison formation across utah has suffered greatly from illegal fossil collecting over the last several decades, with several looted sites discovered only by cursory blm surveys (j. uglesich, r.j. gay, personal observations). although much of the morrison formation has been explored in other areas, such as near moab (foster, 2005, 2007; davis and others, 2018), benm outcrops are only now being systematically surveyed by professional paleontologists (deblieux and others, 2017). since late 2016 the utah geological survey (ugs) has been actively surveying benm morrison formation outcrops. given the richness of the morrison formation in other areas and the initial results of limited sampling, it is certain that significant paleontological resources remain to be discovered (deblieux and others, 2017). future exploration within benm will continue to expand the depth and breadth of knowledge of jurassic biodiversity within the region, especially in the largely neglected recapture member and bluff sandstone. this assertion is supported by the presence of a significant sauropod-dominated bonebed located just outside of benm that is currently being excavated by the natural history museum of los angeles county (mocho and others, 2014; mocho and chiappe, 2018). early cretaceous although most benm fossils are found in mid-mesozoic and older rocks, terrestrial cretaceous strata also exist within the monument. the burro canyon formation is a lateral equivalent of the fossil-rich lower cretaceous cedar mountain formation (kirkland and madsen, 2007; kirkland and others, 2016). it outcrops on the eastern side of benm in the vicinity of and capping the black mesa. just beyond the monument boundaries, east of blanding, abundant vertebrate trace fossils are known from the burro canyon formation (milàn and others, 2015), including footprints of theropods, sauropods, and ornithischians. investigation of the formation by the ugs and other groups is just commencing. baker (1933, p. 55) describes unidentified leaf fossils from the “dakota (?) sandstone,” a unit now assigned to the naturita formation (carpenter, 2014; kirkland and others, 2016), but did not provide the location. ash and others (1976, p. 12) described petrified wood specimens of the tree-like fern tempskya from both the burro canyon and naturita formations near moab, north of benm. 224 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 quaternary geology and paleontology beginning in the latest cretaceous-paleogene, laramide tectonics drove the uplift of the colorado plateau (liu and gurnis, 2010). during the oligocene, larger laccolithic intrusions created the abajo and la sal mountains. establishment of the colorado river drainage (pederson, 2008) was the primary driver of the erosion that carved canyon country across the colorado plateau. the la sal mountains were glaciated repeatedly during the quaternary. each glacial cycle brought periods of melting, alluviation, and erosion (richmond, 1962; richmond and fullerton, 1986; stokes, 1986; pierce, 2003). there are no pre-quaternary cenozoic deposits in benm, but quaternary cave and alcove deposits are common across the region. packrat middens in the southwestern united states document past insect, vertebrate, and plant diversity. these sites are critical for understanding desert paleoecology, biogeography, species-environment interactions, demographic and population changes, and diets of extinct and extant mammals (tweet and others 2012). in benm, alcoves large enough to accumulate packrat middens for thousands of years are normally found in eolian formations, including the pennsylvanian-permian cutler group (white rim and cedar mesa sandstones), lower jurassic navajo sandstone, and middle jurassic entrada sandstone. fossil-bearing quaternary gravels have been reported, but little research has been conducted to date (m.a. stegner and r. gay, personal observations). during the last glacial maximum (lgm) and prior to about 14 ka, the colorado plateau was considerably cooler and more mesic than it is today. in benm and surrounding regions, modern plant communities were 700 to 900 m lower in elevation than at present (cole, 1990; anderson and others, 2000). climatically, the early holocene was cooler than today, but more mesic than during the lgm due to stronger summer monsoons (weng and jackson, 1999). the current monsoon boundary was established during the early holocene (betancourt, 1984). from about 8.5 to 6 ka this cool, mesic period gave way to an arid and warm mid-holocene (weng and jackson, 1999; reheis and others, 2005). during the interval about 6 to 3 ka, cool-wet conditions returned (betancourt, 1984; reheis and others, 2005). fossil pollen from the abajo mountains reveals a maize agriculture existing in the vicinity of benm at 3.12 ka (betancourt and davis, 1984). analysis of eolian and alluvial deposition in canyonlands national park suggests that from 2 ka to the present, drier conditions returned, as evidenced by greater mobility of eolian sand (reheis and others, 2005). in the 1980s and 1990s, researchers from northern arizona university and the usgs documented packrat cave deposits throughout the four corners region, mainly in national parks. many sites were studied in the needles district of canyonlands national park northeast of benm (elias and others, 1992; tweet and others, 2012). although these southeastern utah sites contain still unpublished small vertebrate skeletal remains, it was large mammals (e.g., mead and others, 1987; mead and others 1991) and plant macrofossils (e.g., betancourt, 1984; cole, 1990; coats and others 2008) that were the primary research focus. remains of oreamnos harringtoni, an extinct mountain goat, were discovered with packrat middens in a rock shelter in natural bridges national monument, adjacent to benm (mead and others, 1987). plant macrofossils and dung revealed the diet of this extinct species, as well as that early holocene vegetation was dominated by a “no-analog” (williams and jackson 2007) mixture of species. some of the plant varieties are found locally today whereas others are “extra-local,” such as hackberry (celtis reticulata), common juniper (juniperus communis), englemann spruce (picea englemanii), and limber pine (pinus flexilis) (mead and others, 1987). two important plant macrofossil localities, allen canyon cave in the southern abajo mountains and fishmouth cave at comb ridge (betancourt, 1984; coats and others, 2008), reveal that xeric-, as well as mesic-adapted, plants were present in the region at the end of the lgm, and modern dominant species like pinyon pine (pinus edulis) and ponderosa (pinus ponderosa) did not appear until the mid-holocene (betancourt, 1984; coats and others, 2008). these sites are historically important for shaping our understanding of high desert plant communities. additional dendrochronological work in beef basin (pederson and 225 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 others, 2011), white canyon, natural bridges national monument (dean and bowden, 1994; stahle and others, 2016), and near the northernmost extent of comb ridge (dean and robinson, 1994) indicate aridification of benm and surrounding areas during the late holocene. together with extensive archaeological research, dendrochronological studies reveal a series of multidecadal “megadroughts,” beginning around 870 to 820 ybp. these data are crucial to understanding why ancestral puebloans who lived in southeastern utah and western colorado migrated out of the region, a process that concluded around 650 ybp (benson and berry, 2009). ongoing work in the last five years, investigations conducted by university of california museum of paleontology researchers have concentrated on the vertebrate faunas in midand late holocene packrat middens in and near benm (stegner, 2015, 2016; stegner, unpublished data). since 2013, four small cave deposits—two less than 1 km north of benm in dry valley, one in the benm indian creek subunit, and one now excluded from benm, northwest of the abajo mountains—have been excavated and extensively radiocarbon-dated (stegner, 2016; stegner, unpublished data). these sites reveal how small mammals responded to environmental change during the interval of holocene climate warming and aridification (stegner, 2015, 2016). the mammal fauna remained remarkably stable in abundance and composition over the last about 6 ka (stegner, 2015, 2016), though several extant species not found in benm today (e.g., notiosorex crawfordii) are also present in these deposits. the avifauna and herpetofauna of these sites are currently under study (stegner and stidham, 2018). because these deposits are young and the bones are extraordinarily well preserved (m.a. stegner, 2016, personal observation), the specimens could be used for ancient dna studies that would deepen our understanding of colorado plateau biogeography. planned excavations of packrat middens in beef basin, in the northwestern corner of benm, will shed light on floral and faunal change in this understudied and remote grassland. research trajectories research productivity in benm has been increasing since the 1990s and ongoing efforts in the region promise continued progress (figure 6). this is attributable to both increased attention to the region overall, as well as an increase in the number of researchers in the field. the upper triassic chinle formation is the subject of 30% of total paleontology publications from benm. notably, there was a spike in publications from benm during the time of the “uranium boom” on the colorado plateau (1950s to 1960s), with the majority of papers published in those decades focusing on the chinle formation (figure 6). the upper jurassic morrison formation has a high fossil yield potential (pfyc) (bureau of land management and department of energy, 2015) based on work conducted elsewhere in the region. the lower triassic moenkopi formation and pennsylvanian-permian cutler group are considered low pfyc based on work conducted elsewhere in the region, but these designations may well increase as more research is conducted. the cutler, moenkopi, and morrison are widely exposed within benm, lending themselves to future investigation. in contrast, study of the rise of the dinosaurs in the lower jurassic is hampered by difficult access to wingate and navajo sandstones, which typically form very steep slopes. the kayenta formation, which is known to be fossiliferous elsewhere in the region, is typically thin and also difficult to access in benm. paleontological resource protection fossils in southeastern utah have been the target of looting, illegal sale, and private collecting for decades (united states v. jared ehlers, 2014; gay and others, 2018; r. hunt-foster [national park service]; j. kirkland [ugs], verbal communications; j. uglesich, personal observations; and r.b. irmis, personal observations). the blm has used education and outreach as a complementary approach to law enforcement in protection of paleontological resources. in 2016, the blm partnered with the conservation group “tread lightly” to launch the “respect and protect” campaign, a statewide initia226 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 tive designed to eliminate looting and destruction of fossil and cultural sites through education and outreach about the significance and fragility of these resources (uglesich and hunt-foster, 2016). respect and protect also sought to connect local communities with public lands by bringing paleontology outreach programs into neighboring schools and community centers and to instill a sense of stewardship in these communities. blm’s canyon country district, which includes benm, is over 3.6 million acres in size. the region has abundant and diverse paleontological resources that are currently being studied by over a dozen permitted researchers. it is critical that robust staff, as well as financial and support resources continue to be allocated to manage and protect these paleontological resources. regardless of management status, these areas preserve important world-class paleontological resources that require protection, preservation, and study. it is also essential to provide guidance and oversight for the research activities on these public lands. in many cases this means that, as far as possible, specimens must be collected and curated in a publicly accessible repository for scientific study and public enlightenment. conclusions the bears ears national monument region contains a geologic record of many significant events in the development of life and in the history of our planet. these include the dominance of vertebrate life on land during the pennsylvanian-permian transition, the triassic-jurassic transition and accompanying faunal turnover, the upper jurassic dinosaur-dominated terrestrial ecosystem of the morrison formation, and the response of near-modern environments to rapid climate change at the end of the last period of glaciation. the fossil resources in benm are scientifically important and, in many instances, unique. several taxa are known exclusively from benm or their occurrence in benm represents a major range extension. this includes the sauropodomorph seitaad ruessi, the archosauromorph crosbysaurus harrisae, and the phytosaur pravusuchus hortus. additionally, two of the five major biologic transitions, pennsylvanian-permian and triassic-jurassic, are recorded within benm, indicating the potential for additional highly significant scientific discoveries. at benm, research across the geological time scale currently is being conducted by many institutions and individuals. the ongoing projects will, in many cases, take years to decades to bring to fruition. as surveying and sample excavation continue in the future, the number of fossil taxa described from benm will increase, adding to an ever-expanding knowledge of earth’s history and the history of life itself. long-term protection of paleontological resources is vital to advancing these efforts. figure 6. graph showing both the distribution of publication topics from within benm as well as a chronological plot showing number of papers produced per decade on data derived partially or wholly from within the initial boundaries of benm. 227 paleontology of bears ears national monument (utah, usa)—history of exploration, study, and designation gay, r.j., huttenlocker, a.k., irmis, r.b., stegner, m.a., and uglesich, j. geology of the intermountain west 2020 volume 7 acknowledgments we thank j.k. haschenburger (university of texas at san antonio), x. jenkins (formerly arizona state university now idaho state university), a.r.c. milner (st. george dinosaur discovery site), and h.g. mcdonald (bureau of land management) for review of early drafts. the map was generously provided by b. mueller (bureau of land management). all authors are grateful to the bureau of land management (blm) for administration of permits, and r. hunt-foster (national park service, but with blm at the time of the study) in particular for assistance with permitting, facilitation of fieldwork, and valuable insight. thank you to all the field crews who helped with discoveries past and present, as well as everyone who has labored over specimens from benm and brought these discoveries to light. fieldwork and research in benm was conducted under permits from the blm (r.j. gay: ut14-001s, ut17-008e, ut17009e; a.k. huttenlocker: ut12-005s, ut15-019e, ut17-001s, ut18-008e; r.b. irmis: ut07-023s-sw, ut10-005e, ut14-004e; m.a. stegner: ut13-001s, ut13-020e), and was funded by the blm and national conservation lands grants program (l17ac00064 to a.k. huttenlocker, l17ac00057 to r.j. gay), the wilderness society (r.j. gay), national geographic society committee for research and exploration (9071-12 to r.b. irmis), canyonlands natural history association (r.j. gay, r.b. irmis, and m.a. stegner), university of utah (r.b. irmis), national science foundation (dge1106400 to m.a. stegner), the paleontological society (m.a. stegner and j. uglesich), geological society of america (m.a. stegner), sigma xi (m.a.s.), university of california museum of paleontology (m.a. stegner), university of california-berkeley 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v. 20, no. 4, p. 10-15. welles, s.p., 1969, collecting triassic vertebrates in the plateau province: journal of the west, v. 8, no. 2, p. 231–246. weng, c., and jackson, s.t., 1999, late glacial and holocene vegetation history and paleoclimate of the kaibab plateau, arizona: palaeogeography, palaeoclimatology, palaeoecology, v. 153, p. 179–201. wengerd, s.a., 1951, reef limestones of hermosa formation, san juan canyon, utah: american association of petroleum geologists bulletin, v. 35, no. 5, p. 1038–1051. wengerd, s.a., 1955, biohermal trends in pennsylvanian strata of san juan canyon, utah, in cooper, j.c., editor, geology of parts of paradox, black mesa and san juan basins: four corners geological society guidebook 1, p. 70–77. wengerd, s.a., 1958, pennsylvanian stratigraphy, southwest shelf, paradox basin, in sanborn, a.f., editor, guidebook to the geology of the paradox basin: intermountain association of petroleum geologists ninth annual field conference, p. 109–134. whiteside, j.h., grogan, d.s., olsen, p.e., and kent, d.v., 2011, climatically driven biogeographic provinces of late triassic tropical pangea: proceedings of the national academy of sciences, v. 108, p. 8972–8977. whiteside, j.h., lindström, s., irmis, r.b., glasspool, i.j., schaller, m.f., dunlavey, m., nesbitt, s.j., smith, n.d., and turner, a.h., 2015, extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years: proceedings of the national academy of sciences, v. 112, p. 7909–7913. whiteside, j.h., olsen, p.e., eglinton, t., brookfield, m.e., and sambrotto, r.n., 2010, compound-specific carbon isotopes from earth’s largest flood basalt province directly link eruptions to the end-triassic mass extinction: proceedings of the national academy of sciences, v. 107, p. 6721–6725. whiteside, j.h., olsen, p.e., kent, d.v., fowell, s.j., and et-touhami, m., 2007, synchrony between the central atlantic magmatic province and the triassic-jurassic mass-extinction event?: palaeogeography, palaeoclimatology, palaeoecology, v. 244, p. 345–367. williams, j.s., 1949, paleontology of the leadville, hermosa, and rico formations (p. 17–24), in eckel, e.b., editor, geology and ore deposits of the la plata district, colorado: u.s. geological survey professional paper 219, 179 p. williams, j.w., and jackson, s.t., 2007, novel climate, no-analog communities, and ecological surprises: frontiers in ecology and the environment, v. 5, no. 9, p. 475–482. witkind, i.j., 1964, geology of the abajo mountains area, san juan county, utah: u.s. geological survey professional paper 453, 110 p. witkind, i.j., thaden, r.e., malde, h.e., and johnson, d.h., 1963, geology and uranium-vanadium deposits of the monument valley area, apache and navajo counties, arizona, with sections on serpentine at garnet ridge and mineralogy and paragenesis of the ore deposit at the monument no. 2 and cato sells mines: u.s. geological survey bulletin 1103, 171 p. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 9 2022 © 2022 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah peter d. rowley, david b. hacker, and robert f. biek geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view west at the geosite, within the selvage-joint phase of the three peaks intrusion. for scale, a rock hammer is near the base of the cliff, left of center and above the shadows on the left. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 9 2022 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2021–2022 uga board president john south john.south@dominionenergy.com 385.266.2113 president-elect rick ford rford@weber.edu 801.915.3188 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 co-program chair ben gilder dgilder@gmail.com 337.962.8383 treasurer kellen gunderson kellen@zanskar.us 801.634.9737 secretary eugene syzmanski eugenes@utah.gov 801.537.3364 past president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 9 2022 25 abstract the discovery of the origin of iron in the iron springs mining district of southwestern utah is a story of unconventional thinking based on detailed geologic mapping. this district, for many years the largest iron producer in the west, owes its resources to emplacement of three miocene laccoliths of quartz monzonite porphyry. a visit to the geosite, in the outer part of one of them, the three peaks laccolith, reveals evidence of magma emplacement and mineralization of the overlying host rock. this outcrop formed by upward and outward bulging during intrusion of a rapidly congealing, crystal-rich magma. the pluton was emplaced remarkably close to the surface, about 1.2 miles (2 km) depth, and the ferromagnesian phenocrysts became unstable and broke down (deuteric alteration), releasing iron molecules into the hydrothermal solutions. as the magma solidified, subvertical extension joints formed. the radial joints in particular, oriented perpendicular to the intrusive contacts, allowed the iron-rich solutions to escape into the concordant upper contact of a pure limestone about 280 feet (85 m) thick. this limestone is the co-op creek limestone member of the carmel formation (middle jurassic). the joints tapped the solidifying crystal mush adjacent to the joints. the iron in the solutions replaced some or most of the co-op creek limestone member, creating huge ore bodies of hematite. a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah peter d. rowley1, david b. hacker2, and robert f. biek3 1geologic mapping inc., p.o. box 651, new harmony, ut 84757; pdrowley@rushisp.com; www.geologicmappinginc.com 2department of geology, kent state university trumbull campus, 4314 mahoning ave., warren, oh 44483-1998; dhacker@kent.edu 3utah geological survey, p.o. box 146100, salt lake city, ut 84114-6100; bobbiek@utah.gov citation for this article. rowley, p.d., hacker, d.b., and biek, r.f., 2022, a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah: geology of the intermountain west, v. 9, p. 25–37, https://doi.org/10.31711/giw.v9.pp25-37. © 2022 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the iron springs mining district in southwestern utah was for many years the largest iron district in the western u.s.a. mining began with the utah pioneers and in fact was the reason for establishing cedar city, which is about 10 miles east of the district (figure 1), but production then was insignificant. mining began in earnest in 1923, but iron production climbed spectacularly during world war ii (bullock, 1970) and therefore the district was strategically important for the allies. at that time, as part of the war effort that involved most u.s. adults in some form or other, the geology of the district was studied through detailed geologic mapping and aeromagnetic surveys (by magnetometers in aircraft), and ore bodies were identified and mined. ore was shipped by train to blast furnaces that were built at geneva, utah (west of provo) and at pueblo, colorado. mining continued at high production after the war, with a spurt during the korean war, and on through the 1980s (macdonald, 1991), closing in the mid-1990s. during this time, iron mining and businesses that depended upon it were important employers in cedar 26 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 city. mining resumed in 2010 with ore extracted from the comstock/mountain lion ore bodies on northeastern iron mountain and shipped to china, but closed again in 2014 due to a drop in metal prices; the mine has since reopened. this geosite is on the southwestern side of the three peaks intrusion, one of three mineralized plutons in the iron springs district. the site is significant because it illustrates how careful field observation in the course of detailed geologic mapping explained how these huge iron-ore deposits probably formed. as intruding crystal-rich magma solidified, extension joints formed to al0 1 2 3 4 kilometers0 1 2 3 miles c e d a r v a l l e y eightm ile hills granite mountain th e t hre e pea ksiron springs 113°10' 113°05' 37°45' 37°43' 37°41' n 254 253 253 56 56 m ai n st re et cedar city i-15 figure 1. location map of the cedar city to the three peaks area, iron county, utah. the geosite is marked by a star. on the trip to the geosite, just before the turn to the cedar city landfill, you will drive past a low barren hill just east of two former mine buildings (utah construction) that contains a spectacular angular unconformity. an unconformity is a surface of erosion, here beveled by stream erosion. when bedded sedimentary rocks below an unconformity have a steeper dip than the beds above the unconformity, it is an angular unconformity, for those strata were deformed before being eroded to a flat surface, then the beds above them were deposited on the surface. the rocks below this unconformity are steeply west-southwest-dipping tan sandstone of the iron springs formation, deformed during thrusting. the rocks above the unconformity are more gently south-dipping pink conglomerate of the claron formation, concordantly dipping off the three peaks intrusion to the north. the erosion to form the unconformity took place sometime between late cretaceous (about 100to 66-ma) and early eocene (56to 34-ma) time, a span of at least 30 million years. paved utah highway 254, which you will follow through iron springs gap and past the angular unconformity, follows the old spanish trail, partly chosen to go here because it allowed the travelers to stop at iron springs (labeled). later, the springs were a watering hole for herds of cattle driven west during the midto late-1800s to pioche and other mining districts to the west. the springs are a half mile (0.8 km) west of our geosite turnoff, where some buildings may be seen. beyond the springs, and where highway 254 is going, is a complex of white buildings in the distance known as wecco (western electro-chemical co.), a plant that manufactures ammonium perchlorate, a component of solid-rocket fuel. this plant is a renamed version of the pepcon plant in the suburb of henderson, nevada, that blew up in 1988, killing one and injuring 326 persons. for our geosite, turn northeast off the highway and cross the railroad tracks and iron springs wash. 27 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 low upward passage of iron-rich solutions derived from the breaking down (deuteric alteration) of iron-bearing mineral crystals. these solutions passed outward from the intrusive contacts to form replacement iron bodies in adjacent limestone strata. the results of deuteric alteration, explained below, are visible at the geosite. the iron springs mining district occurs along the iron axis, a northeast-trending string of igneous plutons of miocene age. three of these (the three peaks, granite mountain, and iron mountain intrusions) were mineralized, forming the district (mackin, 1947b, 1954, 1960, 1968; blank and mackin, 1967; bullock, 1970; rowley and barker, 1978; barker, 1995; rowley and others, 2006; hacker and others, 2002, 2007). the plutons of the iron axis are concordant (intrusive contacts are parallel to the bedding of sedimentary country rocks), many of them demonstrably laccoliths. laccolithic plutons have upward-convex roofs and flat basal floors. other workers in the district disputed the laccolith idea. instead, while acknowledging that the roof was concordant, they argued that the lower part of the intrusion was a stock or plug whose contacts continued downward vertically. bullock (1970) was particularly adamant in urging such a model. his reason, as with others, was that he could not see how huge hematite ore bodies could result from a laccolith. evidence from later mapping of the plutons of the iron axis (e.g., blank and others, 1992; hacker, 1998; hacker and others, 1996, 2002, 2005, 2007) disclosed more laccolith floors. additionally, a petroleum exploration drill hole was spudded in the iron springs formation west of the exposed part of the three peaks intrusion and passed entirely through the intrusion (a thickness of 2586 feet, or 788 m) and into a floor of the carmel formation and navajo sandstone, demonstrating a laccolith origin (van kooten, 1988). huge stratabound ore bodies of mostly hematite occur sporadically around the intrusive margins of the three plutons. the hematite replaced, volume for volume, limestone of the carmel formation (jurassic) that is essentially adjacent to the intrusive contacts. the ore was mined by steam shovels in open pits, and some of the huge holes that remain now on the eastern side of granite mountain are ignominiously being filled in by cedar city’s garbage, as landfills (figure 2). magnetite, a higher grade of iron ore but more difficult to smelt, also was mined, but a much smaller volume. the magnetite occurs in “veins” or “dikes,” as much as 10 feet wide, within the plutons. most information on the ore deposits of the iron springs district during world war ii came from plane-table mapping (at scales of 1:1200 to 1:4800, including the topography inasmuch as no detailed topographic maps existed at the time) and related field and laboratory studies by j. hoover mackin. mackin was a professor in the department of geology at the university of washington before and after the war, but during the war was employed by the u.s. geological survey (usgs). magnetometer surveys and diamond drilling accompanied the mapping, as he and assistants worked closely with economic geologists, geophysicists, and drillers employed by the u.s. bureau of mines and by the three mining companies in the district, u.s. steel, cf&i steel, and utah construction and mining. after the war, mackin published his scientific conclusions. these included geologic maps, aeromagnetic surveys, and summary reports on the district, as well as reports on more regional aspects that resulted from his discoveries during his war efforts, such as structural geology figure 2. view north into the armstrong pit at granite mountain, now the site of the cedar city landfill. note the warped, near-vertical iron springs strata in the pit wall on right (east); the granite peak intrusion forms the left (west) wall of the pit. the three peaks is visible in the distance. photo courtesy of tyler knudsen. 28 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 and the volcanic rocks. back at the university of washington, and later when he was hired by the university of texas, mackin enlisted the aid of his graduate students in at least a dozen masters and doctorate studies of the geology of areas in and extending outward from the district. rowley was mackin’s last graduate student to finish his studies before mackin died in 1968. best known as a geomorphologist, mackin in fact was a genius and a great field geologist, whose sense of humor and largerthan-life personality helped make him the best teacher rowley and virtually all other students who took his classes ever had. he received many awards and was a member of the national academy of sciences, but tragically he died early (not yet 63 years old) of a bad heart valve (anderson and others, 2001). he was a generalist who did his best thinking in the field, but hardly an expert on mineral deposits. his brain and mapping skills nonetheless led to an innovative hypothesis for the origin of the ore deposits at iron springs. then he reached out to collaborators who were excellent economic geologists and petrologists, and with their counsel he refined his ideas. much of the evidence for his hypothesis on the origin of the iron deposits came from the three peaks intrusion, although it had the fewest ore bodies, and the geosite is here. mackin’s hypothesis was given in abstracts in 1946-1948 (mackin, 1946, 1947a; mackin and switzer, 1948), a remarkably perceptive report in 1947 (mackin, 1947b), the expanded text of his granite mountain map (mackin, 1954), and a short paper in 1960, this last one with a junior author who was an outstanding economic geologist (mackin and ingerson, 1960). mackin called it the deuteric-release hypothesis. harold l. james, a friend and equally renowned (member of the national academy of sciences, a chief geologist of the usgs) economic geologist, stated in his memorial to mackin that this hypothesis was “one of the finest contributions to the science of ore deposits of the past three decades” (james, 1974). it was not until much later (1995) that daniel s. barker, a young professor at the university of texas, was able to put together the geochemistry that made mackin’s hypothesis a likely explanation. barker took such a long time because he feared that he could not be objective, for he not only loved mackin as we did but he married barbara, mackin’s beautiful daughter! location the geosite is in the southwestern part of the three peaks pluton, at the northern edge of the cedar city nw 7.5-minute quadrangle, west of cedar city, iron county, utah. the coordinates are: 37o44’53” n., 113o12’ 01.32” w. a word of warning about the geosite—after a significant rainfall, the dirt road that allows the final access to the site is likely to become a mudhole. a fourwheel drive vehicle may be necessary to reach the site and even such a vehicle might not be good enough!past these mudholes and after the dirt road swings north, you will go past some blocky outcrops, first on the left, then on the right, of the peripheral shell of the three peaks pluton. this fresh, hard, fine-grained igneous rock is the chilled margin of the once intruding, semi-molten pluton. from these outcrops it is 0.7 miles (1.1 km) farther north to the geosite. before you reach it, you will pass mine dumps and two mine roads that head west to the great western mine, a shallow pit that mined a northeast-trending “dike,” about 10 feet (3 m) wide, of magnetite. if you look south just before you reach the geosite, you will have a good view of granite mountain and big pits that were mined for iron at the intrusive contact (figure 3). a geologic map and stratigraphic column of the area is shown by figures 4 and 5. geologic setting the iron springs mining district is in the great basin, a physiographic province west of the stable colorado plateau and making up the western half of utah and all of nevada. the great basin was formed starting about 20 million years ago, when east-west regional extension (pulling apart in an east-west direction) created north-trending basin-range normal faults that broke the earth’s crust into north-trending ranges and alternating north-trending basins. most basin-range deformation, however, has taken place since about 10 million years ago, when the present topography began to be created (anderson and mehnert, 1979; rowley and others, 1979, 1981, 2006; rowley, 1998; hurlow, 2002). the great north-trending hurricane fault, which passes through the eastern edges of cedar city and creates the hurricane cliffs south of cedar city, marks the boundary between the great basin and colorado plateau. it is 29 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 a normal fault with vertical, down-to-the-west displacement of at least 6000 feet (1800 m) (hurlow, 2002). cedar basin west of it is a typical north-trending basin, whereas the hills and mountains of, and south of, the iron springs district can be looked upon in aggregate as a typical north-trending range. a down-to-the-east normal fault zone that forms the western margin of cedar basin chopped off the eastern side of the three peaks pluton and dropped it down so that it is now concealed beneath basin-fill sediments. the oldest rock unit exposed in the iron springs district is the manganese wash member of the temple cap formation of early jurassic age, an olive-colored sandstone and siltstone no more than 50 feet (15 m) thick. it exhibits hornfels-grade contact metamorphism in the district because it is in contact with the intrusions. the unit was originally assigned as the basal siltstone member of the carmel formation (mackin, 1947, 1954), but was reassigned following sprinkel and others (2009, 2011) and doelling and others (2013). regionally, temple cap strata unconformably overlie lower jurassic navajo sandstone, a massive pink eolian (from sand dunes) sandstone about 2000 (600 m) feet thick. the middle jurassic carmel formation, which overlies the temple cap and is marine, consists of a lower co-op creek limestone member about 280 feet (85 m) thick and an upper crystal creek member about 200 feet (60 m) thick; upper members of the carmel are cut out under the cretaceous unconformity (knudsen and biek, 2014). the co-op creek member was mineralized, whereas the crystal creek member, a sandstone, was not. overlying rocks include the enigmatic marshall creek breccia (a possible sedimentary breccia) overlain by the upper cretaceous iron springs formation, about 3000 feet (1000 m) of mostly non-marine tan mudstone and sandstone and subordinate limestone, conglomerate, and coal. iron springs strata are in turn overlain by the eocene claron formation, generally pink in its lower part and white in its upper part, consisting of mostly fluvial but locally lacustrine mudstone, sandstone, limestone, and conglomerate almost 2000 feet (600 m) thick; claron strata are unusual in that they are mostly altered into a stacked sequence of paleosols (fossil soils). a series of volcanic rocks of oligocene and miocene age, virtually all ash-flow tuffs that erupted from calderas in the great basin, are almost 1500 feet (500 m) thick. all these rocks predated emplacement of the laccoliths and represent a total cover of only about 1.2 miles (2 km), so the laccoliths were intruded remarkably close to the surface. figure 3. view south from the geosite toward the granite mountain pluton and the mined pits that surround it. 30 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 the laccoliths of the iron axis rose above a large source batholith at depth, guided by the iron springs gap thrust, one of the main late cretaceous to paleocene sevier thrust faults in southwestern utah. in the district, the thrust places jurassic temple cap and carmel strata over cretaceous iron springs strata and provided a pathway for magma to migrate through the massive navajo sandstone. the laccoliths are 22 to 20 million years old, slightly predating initiation of basin-range tectonism (hacker, 1998; rowley, 1998; hacker and others, 2002, 2007; rowley and others, 2006). as magma rose along the thrust fault it intruded beneath the manganese wash member, then bulged it, the carmel, and overlying rocks upward to form laccoliths (figure 6). the floor of the laccolith is largely the contact with the underlying navajo. each pulse of the laccolith magma (a liquid mush containing solid minerals that had crystallized) pushed up overlying rocks. shallow intrusions such as this are called hypabyssal, and are common in mining districts in the west. emplacement of iron springs intrusions was remarkably rapid, such that the slab of temple cap and younger strata bulged faster than streams could erode them, and the slab grew rapidly into mountains with considerable relief. inasmuch as some of these rocks were unstable mudstones (in the iron springs formation) to begin with, the result of the growth of many of these mountains was gravity slides that resulted from iron spring gap thrust fault n geosite 0 0.5 1 mile 0 0.5 1 kilometer 254 254 37.75 ° n. 113.19 ° w.113.225 ° w. 37.723 ° n. figure 4. geologic map of the southern part of the three peaks intrusion and adjacent places, iron county, utah. the geosite is marked by a star. see figure 5 for map units. gray areas show mined or disturbed ground with underlying geology from mackin and others (1976) and mackin and rowley (1976). modified from knudsen and biek (2014). 31 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 lithologic column 200 iron springs formation 0– 3000 0– 915ki member b 400 120 tca member a 100– 300 30–90 tcc member c 350 105 tib member d 10–60 3–18 conglomerate at boat mesa 300+ 90+ 500 150 tcd tbm tqcs tql tih isom fm. tqh oldest fan alluvium 400+ 120+ surficial depositsq 0–200+ 0–60+ u pp er c r e t a c e o u s t e r t i a r y m io ce ne p lio ce ne q u at . pleist. holocene thickness lithology formation membersy m bo l s e r ie s sy st em feet meters in contact with quartz monzonite unconformity unconformity unconformity c la ro n fo rm at io n pa leo ce ne e oc en e tbh middle volcaniclastic unit of brian head formation 30 10 250 75baldhills tuff hole-in-the-wall tuff 150– 300 45–90 0–50 0–15 qtaf older fan alluvium source of iron ore bodies (tir) white limestone ledge 200+ 60+ temple cap formationjt c ar m el fo rm at io n co-op creek limestone memberjcc km marshall creek breccia crystal creek member 0–8 0–25 jcx 50+ 15+ 280 85 60 m id dl e unconformity unconformity(?) host for iron ore abundant calcedony tcb leach canyon formation bauers tuff m. of condor canyon fm. harmony hills tuff swett tuff member of condor canyon fm. mount dutton formation, alluvial facies 0–75 0–23 150 45 tmd 180– 250 55– 75 tqcb three peaks laccolith granite mountain laccolith tigp taf peripheral-shell phase interior phase with selvage joints interior phase peripheral-shell phase interior phase with selvage joints 1000+ 300+ 1000+ 300+ titpi titps titpp tigs l.ju r as si c ? o lig oc en e unconformity forms gruss-covered slopes forms rounded bluffs forms rounded bluffs highly brecciated near thrust faults soft-sediment deformation 21.5 ma 21.76 ma 22 ma 22.7 ma 23.7 ma 23.8 ma 26–27 ma q ui ch ap a g ro up q ui ch ap a g ro up pleist. figure 5. stratigraphic column showing rock units in the geosite area. from knudsen and biek (2014). 32 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 failure of mudstone beds in the flanks of the laccoliths. the iron mountain intrusion, in fact, shed gravity slides at least 4 miles (6.5 km) to the south and southeast (mackin, 1960; blank and mackin, 1967; hacker, 1998; hacker and others, 1996, 2002, 2007; rowley and others, 2006). the granite mountain laccolith, immediately south of the three peaks, also produced a small gravity slide off its southeastern flank (knudsen and biek, 2014). for some intrusions, although not the three mineralized ones, gravity slides took off part of the cover rocks to breach the upward moving, partly molten intrusion (hacker, 1998; hacker and others, 2002, 2007), like popping the cork on a bottle of champagne and much like the gravity slide (“the bulge”) on the northern flank of mount st. helens, washington, whose failure in 1980 was triggered by an earthquake, resulting in the may 18 eruption. in his detailed mapping of the three peaks pluton, mackin (1947b) paid particular attention to the joints within the intrusive rocks, and their comparison to flow a) lateral sill migration carmel formation and overlying volcanic rocks navajo sandstone< 1km b) vertical growth extension reduces lateral support c) gravity sliding from flanks gravity slide mass future slide figure 6. schematic diagram illustrating growth of a typical laccolith. (a) initial lateral migration of a sill within the carmel formation to its fullest extent at a relatively shallow depth, (b) vertical growth of the laccolith by continued injection of magma, and (c) gravity sliding of oversteepened flanks. modified from willis (2002) and hacker and others (2002). 33 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 foliation in the rock. he realized very quickly that joints were part of the story on how the hematite and magnetite ore bodies formed. the flow foliation, identified by the pattern of the phenocrysts in the rock, told him the directions that the crystal mush moved as it pushed upward and outward against the country rocks. when used in conjunction with careful mapping of the intrusive contacts, he identified not only bulges and folds of semi-solid magma at the contact but also places where the contacts were broken by this outward movement along intrusive faults. the flowage of the magma controlled the development of extension joints, and the tighter the folded magma, the more gaping were the joints. as in most plutons, joints were of three types based on their trend: (1) radial to a central part of the pluton (that is, perpendicular to the intrusive contacts), (2) concentric to the contact, and (3) oblique. these joints were extension joints, subvertical and widest (open) near intrusive contacts and tapered and terminating downward into the pluton. the joints related directly to the flow foliation, indicating that they were extending as the crystal mush was flowing. in other words, the joints developed as the intrusive mass was solidifying but being pushed by younger magma pulses coming up the laccolith feeder. the higher the angle of the flow foliation, the more the magma was pushing outward against the intrusive contact and the more open were the extension joints. of course, as the upper convex surface of the laccolith was growing and moving upward, closer to the surface, the upper parts of the molten mass expanded as the lithostatic pressure decreased. most plutons in the iron axis have three lithologic phases whose mapping suggested the deuteric-release hypothesis to mackin (mackin, 1947b, 1954, 1960, 1968; mackin and ingerson, 1960; mackin and others, 1976; mackin and rowley, 1976; rowley and barker, 1978; barker, 1995; rowley and others, 2006). these phases, from intrusive margin to interior, were the thin (less than 100 yards [30 m]) peripheral-shell phase, the selvage-joint phase, and the interior phase. chemically and petrologically, however, all phases are quartz monzonite porphyry (phenocrysts of plagioclase and quartz and ferromagnesian minerals in a fine-grained crystalline mass), a rock type common in mineralized tertiary plutons. the peripheral shell consists of resistant, fresh, fine-grained rock that represents the chilled margin of the pluton, whereby the semi-molten rock rapidly froze (consolidated) against the cool country rocks of the temple cap and carmel formations. in contrast, the interior phase is altered coarse-grained rock, easily eroded to lowlands. here magmatic water (deuteric solutions) within the crystal mush altered the rock, in other words the mush “stewed in its own juices” and the phenocryst minerals broke down into alteration clays and other secondary minerals. at the shallow level in the crust where they had been emplaced, the rock was unstable because it had originated and partly crystallized under deeper and hotter conditions in the source batholith. the selvage-joint phase is the interesting phase, for its story relates to the joint study. the word selvage comes from a border on a piece of cloth that is finished so as to prevent unraveling. rock selvages are the borders of the extension joints, averaging about 2.5 inches (6 cm) wide on each side, containing rock that is deuterically altered (a reaction between primary magmatic rock and water-rich solutions that separate from the magma during late-stage cooling). farther away from the joints, however, the rock is fresh. selvage rock resembles that of all the interior phase. chemical analyses of the selvages shows that the rocks are depleted in iron by about 30 percent when compared with fresh rock inward from selvages, from peripheral shell rock, and—perhaps unexpectedly—from interior rock. furthermore, the extension joints in the selvage-joint phase contain magnetite crystals or crusts, giving mackin the idea of where the iron-rich solutions or gases went (both liquids and gases are possible)! in places, closer to the intrusive contacts, where the magnetite “veins” were as much as 10 feet (3 m) wide, the extension joint opened progressively wider and wider with time, each time producing a magnetite coating. iron-rich solutions came from the breakdown (deuteric alteration) of ferromagnesian phenocrysts, especially biotite but also hornblende and pyroxene, in the solidifying crystalline mush of the selvage-joint phase. the extension joints, especially the radial joints, provided the avenue for escape upward of the iron solutions. in contrast, joints were poorly developed and much less common in the 34 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 interior phase, and none contained selvages, so here the rocks entirely altered in place, contributing no iron to the ore bodies. intrusive faults formed where the outward and upward pressure broke the rocks above rather than folding them. many of these faults are reverse faults that dip inward into the pluton and provide a way that inward parts of the pluton push upward and flare outward. intrusive faults are important because they tapped the extension joints and provided the main escape for the solutions through the peripheral shell, which congealed rapidly and was largely solid while the rest of the pluton was a crystal mush. in fact, mapping showed that many of the ore bodies are found adjacent to intrusive faults. the largest ore body that was mined in the district was the comstock body within the iron mountain intrusion, where intrusive faults created a graben of limestone that dropped into the crystal mush. once the iron solutions escaped the peripheral shell, they replaced the nearly adjacent carmel limestone. a calculation of volumes of selvage rock indicated that all the huge hematite ore bodies could be accounted for as coming from selvage rock. the three peaks pluton had far fewer mineable hematite bodies because its roof was relatively flat (as indicated by flow foliation), whereas the roof of the granite mountain pluton arched much more and hematite ore bodies surround parts of the intrusive contact. in the same way that a plate of plexiglass has more and larger extension cracks (and failure, the equivalent of intrusive faults) the more it is bent, greater arching of the solidifying magma produced more and larger extension joints. the iron mountain pluton, which has still higher structural relief (uplift and arching), contains the largest ore bodies in the district because its roof was especially peaked and bulged, and large intrusive faults cut pluton margins. furthermore, no interior phase is exposed in these two plutons; nearly the entire exposed volume of the plutons is selvage-joint phase. the site itself as one stands in the dirt road, facing west at the geosite, you will see a cliff of light-gray selvage-joint-phase plutonic rock at least 50 feet (15 m) high (figure 7). it is cut by many vertical joints that trend west, the radial joints. such a high concentration of joints characterizes the selvage-joint phase. close inspection reveals that light-green altered rock lines both sides of each joint. these are the selvages, with the light-green color coming from altered ferromagnesian minerals. yet inward from the selvages, the ferromagnesian minerals are fresh. most of the joints are lined with magnetite crystals. if you walk up into the saddle just north of the cliff face, you will see a magnetite “dike” about a foot wide. it grew incrementally from the edge to the middle as the joint opened up periodically due to new pulses of upwardor outward-pushing crystal mush, and each time iron-bearing solutions moved vertically and laterally toward the intrusive contacts. pale-yellow crystals of apatite, whose long axis is horizontal and normal to the controlling extension joint, are apparent. the top of the dike contains a fuzz of tiny magnetite fragments magnetically attached; the upper part of the dike is a natural magnet, called lodestone, due to lightning strikes (you may know that magnetite is high in iron and is attracted to a magnet, but it does not attract iron by itself; an external energy source, such as lightening, is needed to align its molecules to make it into a magnet). this geosite is significant because it illustrates how careful field observation in the course of detailed geologic mapping resulted in a logical explanation of how huge, economically important iron-ore deposits likely formed. the deuteric-release hypothesis should be an idea that geologists carry around in their heads when they study other ore deposits of iron and other metals adjacent to other hypabyssal intrusions. acknowledgments early visits by the senior author to the outcrops making up the geosite discussed here were done with hoover mackin, paul l. williams, john j. anderson, and dan barker. these mentors used it as a focal point to start a wide-ranging discussion on the origin of the iron deposits, for which we thank them. we later reciprocated when we brought many students and others to the geosite over many years. we are grateful to grant willis and mike hylland (ugs) and kimm harty (ugs retired) for technical review of this manuscript, and lori douglas (ugs) for drafting the figures. 35 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 references anderson, j.j., rowley, p.d., fisher, r.v., dover, j., schultz, p., williams, p.l., threet, r.l., and osmond, j., 2001, j. hoover mackin—a personal tribute, in erskine, m.c., faulds, j.e., bartley, j.m., and rowley, p.d., editors, the geologic transition, high plateaus to great basin—a symposium and field guide (the mackin volume): utah geological association publication 30 and pacific section of the american association of petroleum geologists guidebook gb 78, p. xii–xx. anderson, r.e., and mehnert, h.h., 1979, reinterpretation of the history of the hurricane fault in utah, in newman, g.w., and goode, h.d., editors, basin and range symposium: rocky mountain association of geologists and utah geological association, p. 145–165. barker, d.s., 1995, crystallization and alteration of quartz monzonite, iron springs mining district, utah—relation to associated iron deposits: economic geology, v. 90, p. 2197–2217. blank, h.r., jr., and mackin, j.h., 1967, geologic interpretation of an aeromagnetic survey of the iron springs district, utah: u.s. geological survey professional paper 516-b, 14 p. blank, h.r., rowley, p.d, and hacker, d.b., 1992, miocene monzonite intrusions and associated megabreccias of the iron axis region, southwestern utah, in wilson, j.r., editor, field guide to geologic excursions in utah and adjacent areas of nevada, idaho, and wyoming, geological society of america, rocky mountain section meeting: utah geological survey miscellaneous publication 92-3, p. 399–420. bullock, k.c., 1970, iron deposits of utah: utah geological and figure 7. view west at the geosite, within the selvage-joint phase of the three peaks intrusion. for scale, a rock hammer is near the base of the cliff, left of center and above the shadows on the left. 36 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 mineralogical survey bulletin 88, 101 p. doelling, h.h., sprinkel, d.a., and kuehne, p.a., 2013, temple cap and carmel formations in the henry mountains basin, wayne and garfield counties, utah, in morris, t.h., and ressetar, r., editors, the san rafael swell and henry mountains basin—geologic centerpiece of utah: utah geological association publication 42, p. 279–318, 2 ppendices. hacker, d.b., 1998, catastrophic gravity sliding and volcanism associated with the growth of laccoliths—examples from early miocene hypabyssal intrusions of the iron axis magmatic province, pine valley mountains, southwest utah: kent, ohio, kent state university, ph.d. dissertation, 258 p., scale 1:24,000. hacker, d.b., holm, d.k., petronis, m.s., rowley, p.d., and arnold, b.j., 2005, relation between miocene volcanism and iron-axis laccolith emplacement, southwest utah [abs.]: geological society of america abstracts with programs, v. 37, no. 7, p. 72. hacker, d.b., holm, d.k., rowley, p.d., and blank, h.r., 2002, associated miocene laccoliths, gravity slides, and volcanic rocks, pine valley mountains and iron axis region, southwestern utah, in lund, w.r., editor, field guide to geologic excursions in southwestern utah and adjacent areas of arizona and nevada, geological society of america, rocky mountain section meeting, cedar city, utah: u.s. geological survey open-file report 02-172, p. 236–283. hacker, d.b., petronis, m.s., holm, d.k., and geissman, j.w., 2007, shallow emplacement mechanisms of the miocene iron axis laccolith group, southwest utah, in lund, w.r., editor, field guide to geologic excursions in southern utah: utah geological association publication 35, 49 p. hacker, d.b., rowley, p.d., blank, h.r., and snee, l.w., 1996, early miocene catastrophic gravity sliding and volcanism associated with intrusions of the southern iron axis region, southwest utah [abs.]: geological society of america abstracts with programs, v. 28, no. 7, p. a511. hurlow, h.a., 2002, the geology of cedar valley, iron county, utah, and its relation to ground-water conditions: utah geological survey special study 103, 74 p. james, h.l., 1974, joseph hoover mackin, 1905-1968—biographical memoir: national academy of sciences of the united states of america, v. xlv, p. 249–262. knudsen, t.r., and biek, r.f., 2014, interim geologic map of the cedar city nw quadrangle, iron county, utah: utah geological survey open-file report 627, 18 p., scale 1:24,000. macdonald, g.d., iii, 1991, the magnet—iron ore in iron county, utah: cedar city, utah, g.d. macdonald iii (self published), 63 p. mackin, j.h., 1946, structural control for mineralization in the iron springs district, southwestern utah [abs.]: geological society of america bulletin, v. 57, no. 12, p. 1255. mackin, j.h., 1947a, joint patterns in the three peaks laccolith, iron springs district, utah [abs.]: geological society of america bulletin, v. 58, no. 12, p. 1255. mackin, j.h., 1947b, some structural features of the intrusions in the iron springs district: utah geological society guidebook 2, 62 p. mackin, j.h., 1954, geology and iron deposits of the granite mountain area, iron county, utah: u.s. geological survey mineral investigations field studies map mf-14, scale 1:12,000. mackin, j.h., 1960, structural significance of tertiary volcanic rocks in southwestern utah: american journal of science, v. 258, no. 2, p. 81–131. mackin, j.h., 1968, iron ore deposits of the iron springs district, southwestern utah, in ridge, j.d., editor, ore deposits of the united states, 1933-1967 (graton-sales volume): new york, american institute of mining and metallurgical petroleum engineers, v. 2, p. 992–1019. mackin, j.h., and ingerson, f.e., 1960, an hypothesis for the origin of ore-forming fluid: u.s. geological survey professional paper 400-b, p. b1–b2. mackin, j.h., nelson, w.h., and rowley, p.d., 1976, geologic map of the cedar city nw quadrangle, iron county, utah: u.s. geological survey geologic quadrangle map gq-1295, scale 1:24,000. mackin, j.h., and rowley, p.d., 1976, geologic map of the three peaks quadrangle, iron county, utah: u.s. geological survey geologic quadrangle map gq-1297, scale 1:24,000. mackin, j.h., and switzer, g., 1948, origin of mineralizing emanations in the iron springs district, southwestern utah [abs.]: geological society of america bulletin, v. 59, no. 12, p. 1339. rowley, p.d., 1998, cenozoic transverse zones and igneous belts in the great basin, western united states—their tectonic and economic implications, in faulds, j.e., and stewart, j.h., editors, accommodation zones and transfer zones—the regional segmentation of the basin and range province: geological society of america special paper 323, p. 195–228. rowley, p.d., and barker, d.s., 1978, geology of the iron springs mining district, utah, in shawe, d.r., and rowley, p.d., editors, guidebook to mineral deposits of southwestern utah: utah geological association publication 7, p. 49–58. rowley, p.d., steven, t.a., anderson, j.j., and cunningham, c.g., 1979, cenozoic stratigraphic and structural framework of southwestern utah: u.s. geological survey professional paper 1149, 22 p. rowley, p.d., steven, t.a., and mehnert, h.h., 1981, origin and structural implications of upper miocene rhyolites in kingston canyon, piute county, utah: geological society of america bulletin, v. 92, pt. 1, p. 590–602. rowley, p.d., williams, v.s., vice, g.s., maxwell, d.j., hacker, d.b., 37 a site bearing on the origin of iron deposits in the iron springs mining district, iron county, utah rowley, p.d., hacker, d.b., and biek, r.f. geology of the intermountain west 2022 volume 9 snee, l.w., and mackin, j.h., 2006, interim geologic map of the cedar city 30' x 60' quadrangle, iron and washington counties, utah: utah geological survey open-file report 476dm, scale 1:100,000. sprinkel, d.a., doelling, h.h., kowallis, b.j., waanders, g., and kuehne, p.a., 2011, early results of a study of middle jurassic strata in the sevier fold and thrust belt, utah, in sprinkel, d.a., yonkee, w.a., and chidsey, t.c., jr., editors, sevier thrust belt—northern and central utah and adjacent areas: utah geological association publication 40, p. 151–172. sprinkel, d.a., kowallis, b.j., waanders, g., doelling, h.h., and kuehne, p.a., 2009, the middle jurassic temple cap formation, southern utah—radiometric ages, palynology, and correlation with the gypsum spring member of the twin creek limestone and harris wash member of the page sandstone [abs.]: geological society of america abstracts with programs, v. 41, no. 7, p. 690. van kooten, g.k., 1988, structure and hydrocarbon potential beneath the iron springs laccolith, southwestern utah: geological society of america bulletin, v. 100, p. 1533–1540. willis, g.c., 2002, massive gravity slides show the value of detailed mapping: utah geological survey, survey notes, v. 34, no. 3, p. 1–3. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 9 2022 © 2022 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa joseph e. peterson, jonathan p. warnock, jason j. coenen, charles a. bills, mateo e. denoto geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover photograph of the upper part of the upper jurassic brushy basin member of the morrison formation from about 45 m south of the cleveland-lloyd dinosaur quarry. photograph of morrison formation by jonathan warnock. below photograph is the charophyte aclistochara bransoni from the quarry. left is apical view, center is lateral view, and right is basal view. see figure 3 more information. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 9 2022 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2021–2022 uga board president john south john.south@dominionenergy.com 385.266.2113 president-elect rick ford rford@weber.edu 801.915.3188 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 co-program chair ben gilder dgilder@gmail.com 337.962.8383 treasurer kellen gunderson kellen@zanskar.us 801.634.9737 secretary eugene syzmanski eugenes@utah.gov 801.537.3364 past president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 9 2022 39 abstract the cleveland-lloyd dinosaur quarry at jurassic national monument in central utah has been extensively studied for nearly 80 years. during this time, studies have heavily focused on the taphonomy, depositional setting, and potential behavioral inferences of the most dominant vertebrate taxon at the quarry, allosaurus fragilis. however, despite their importance for paleoecological interpretations, microfossils from the quarry, such as charophytes and ostracods, have been conspicuously absent from any detailed discussion in the literature. here we present a review of the known taxa of charophytes from the cleveland-lloyd dinosaur quarry and test the variability of abundance and taphonomic conditions throughout the quarry deposit. our results indicate that significant differences in charophyte abundances exist in the lower and upper parts of the quarry, and a wide variance of taphonomic conditions is present in charophyte gyrogonites in the uppermost contact with the overlying carbonate bed. these results support prior interpretations of the cleveland-lloyd dinosaur quarry as an ephemeral pond and bring further attention to the importance of microfossils in paleoecological reconstructions. a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa joseph e. peterson1, jonathan p. warnock2, jason j. coenen1, charles a. bills3, mateo e. denoto4 1department of geology, university of wisconsin-oshkosh, oshkosh, wi 54901; petersoj@uwosh.edu; coenenj@uwosh.edu 2department of geography, geology, environment, and planning, indiana university of pennsylvania, indiana, pa 15705; jwarnock@iup.edu 3department of geosciences, mississippi state university, starkville, ms 39762; charlesabills@gmail.com 41530 grandview ct., kansasville, wi 53139; mateo.denoto@yahoo.com citation for this article. peterson, j.e., warnock, j.p., coenen, j.j., bills, c.a., and denoto, m.e., 2022, a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa: geology of the intermountain west, v. 9, p. 39–47, https://doi.org/10.31711/giw.v9.pp39-47. © 2022 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the cleveland-lloyd dinosaur quarry (cldq) at jurassic national monument (jnm) is an upper jurassic morrison formation fossil locality in central utah where over 10,000 dinosaur bones have been discovered since the 1920s, including over 70 individuals of 10 different genera of dinosaur (gates, 2005). more than 70% of the vertebrate fossils discovered are attributed to the late jurassic theropod allosaurus fragilis based on left femora, yielding a predator prey ratio of 3:1 (madsen, 1976; gates, 2005). due to the abundance of allosaurus the quarry has been extensively studied in regard to taphonomy and depositional environment (stokes, 1985; richmond and morris, 1996; bilbey, 1999; gates, 2005; hunt and others, 2006; peterson and others, 2017; warnock and others, 2018). whereas the dinosaur remains have been the focus of much research, microfossils such as charophytes (freshwater algae) that are present in the same deposits as dinosaurs have received relatively little attention. charophyta, fresh-to-brackish water algae, are com40 a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa peterson, j.e., warnock, j.p., coenen, j.j., bills, c.a., and denoto, m.e. geology of the intermountain west 2022 volume 9 mon microfossils in the morrison formation and are regularly found associated with gastropods, ostracods, conchostracans, and dinosaurs. due to their abundance and taxonomic similarities between extant and fossil taxa, they are of considerable interest for biostratigraphy and paleoecological inferences throughout the fossil record (e.g., peck, 1937; wood, 1950; ross, 1960; sohn and peck, 1963; schudack and others, 1998; georgescu and braun, 2006). whereas charophytes have been found throughout the morrison formation, there have been relatively infrequent applications of charophytes in jurassic paleoecologic studies (peck, 1957; bilbey, 1992; schudack and others, 1998; turner and peterson, 2004; martín-closas and others, 2008). here we present a review of charophytes from the cldq at jnm and discuss the taxonomy and taphonomy of charophyte species microstratigraphically throughout the cldq bonebed. two hypotheses are tested in this study: (1) differences exist between the charophyte taxa in the upper and lower parts of the bonebed assemblage, and (2) differences exist between the taphonomic conditions of charophytes within the upper 15 cm of mudstone below the mudstone/limestone contact of the upper cldq. geologic setting the cldq is located 38 m above the base of the brushy basin member of the morrison formation, which was deposited in the late jurassic epoch (tithonian age) (bilbey, 1992) (figures 1a and 1b). the brushy basin member is characterized by fluvial mudstones, limestones, and channel sandstones (kirkland and others, 2020) and measures approximately 100 m thick at jnm (peterson and others, 2017). furthermore, the climate is interpreted as being strongly seasonal, with monsoons alternated with periods of semi-aridity (e.g., dodson and others, 1980; hallam, 1993; rees and others, 1999; parrish and others, 2004; sellwood and valdes, 2008; tanner and others, 2014). the bottom part of the quarry is a silty mudstone of variable thickness from several to tens of centimeters that quickly grades upward into a fossiliferous calcareous mudstone, similarly variable in thickness. above the mudstone is a limestone figure 1. (a) location of the cleveland-lloyd dinosaur quarry in jurassic national monument, emery county, utah, usa, and (b) stratigraphic placement of the cleveland-lloyd dinosaur quarry within the brushy basin member of the morrison formation. 41 a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa peterson, j.e., warnock, j.p., coenen, j.j., bills, c.a., and denoto, m.e. geology of the intermountain west 2022 volume 9 layer, which is capped with a volcanic ash bed (bilbey, 1992; gates, 2005). microfossils such as charophyte gyrogonites preserve well within the smectite-rich mud and within the limestone unit (bilbey, 1992). methods sampling and preparation a total of 110 kg of bulk sediment was collected from the 1-m-thick bonebed. the sediment samples were collected from two sections (upper and lower 50 cm) to explore variation in charophyte floral assemblages throughout the unit. all collected gyrogonites were obtained by a method of submerged disaggregation with gentle air agitation similar to previously utilized methods (e.g., mckenna, 1962; ward, 1981; peterson and others, 2011, 2017). sediment samples were placed in 23 x 43  cm (28  cm deep) plastic basins with 1 m of flexible perforated airline tubing coiled at the bottom. the tubing was connected to a double-output aquarium air pump (3.5 watt, 1200 cc air per minute output) placed outside of the basins. the resulting system produced gentle air-powered agitation in the basins to promote sediment disaggregation. following disaggregation, sediments were rinsed through two 63-micron mesh sieves and left to air dry. following drying, samples were collected under light microscopy and imaged with a hitachi s-3000n environmental scanning electron microscope (sem) under low vacuum pressure. only specimens more than 50% complete were tabulated for taxonomic abundance. after tabulation, the results between the upper and lower quarry assemblages of charophytes were tested for statistical significance via the chi-square test (p >0.05). taphonomic methods charophyte specimens were also analyzed for taphonomic condition in the upper 15 cm transitional zone of the bonebed along the contact of the overlying limestone unit. samples consisted of a total of 3 kg of mudstone (1 kg from each interval) collected from the uppermost 0 to 5 cm below the limestone, 5 to 10 cm, and 10 to 15 cm below the contact, respectively. charophyte gyrogonites were extracted, processed, and imaged through the methods outlined above. specimens were graded based on the completeness of the gyrogonites, degree of fracturing, and degree of abrasion. a complete charophyte gyrogonite showing no discernable fractures or abrasion was scored as a 0, a fractured or weathered charophyte gyrogonite was scored as a 1, and a charophyte gyrogonite displaying both fractures and abrasion was scored as a 2 (figure 2). the taphofigure 2. taphonomic stages of charophyte gyrogonites. stage 0 indicates a gyrongonite with no apparent fracture or abrasion, a stage 1 indicates a gyrogonite displaying fracture or abrasion, and a stage 2 indicates a gyrogonite displaying both fracture and abrasion. 42 a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa peterson, j.e., warnock, j.p., coenen, j.j., bills, c.a., and denoto, m.e. geology of the intermountain west 2022 volume 9 nomic condition of gyrogonites from the lower 45 cm of the bonebed below the limestone contact was also noted for comparisons with the 15 cm transitional zone. results systematic paleontology (charophytes) three distinct charophyte taxa (aclistochara bransoni, latochara concinna, and stellatochara obovata) (figures 3a through 3i) were identified in the cldq mudstone (bilbey, 1999). charophytes specimens are housed in the department of geology at the university of wisconsin oshkosh. phylum charophyta migula, 1897 class charophycaea smith, 1938 order charales lindley and green, 1836 family characeae gray, 1821 subfamily charoidae migula, 1897 genus aclistochara aclistochara bransoni peck, 1937 (figures 3a through 3c) the general shape of the gyrogonite is ovoid to ellipsoid with a truncated apex. the spirals are smooth in form, varying from concave to gently convex. the apical opening is closed by the calcified tips of the spiral cells, which differs from charophytes within porocharaceae where this region is open. the spirals turn on the truncate apex to form its outer rim, then bend down into a central periapical depression, and finally turn sharply into the center of the summit and expand (feist and others, 2005). family porocharaceae (grambast, 1962) subfamily stellatocharoidea (grambast, 1962) latochara concinna (peck, 1957) (figures 3d through 3f) the general shape of latochara varies from subglobular to ovoid. at the rim of the summit, the spiral cells level off, turn inward, and then turn abruptly upward into an almost vertical position to form a small pyramidal projection in the center of the summit (feist and others, 2005). stellatochara obovata (peck, 1957) (figures 3g through 3i) general shape of stellatochara is usually ovoid, though occasionally ellipsoidal or subglobular. the genus is well characterized by its long apical elongated neck. the spiral cells progressively bend at the rim of the apex forming a wide apical neck that is less than one-third of the total gyrogonite length (feist and others, 2005). abundance and taphonomic analysis over 128 specimens were identified in the upper mudstone, and 59 were identified in the lower (figures 4a through 4i, table 1). an additional 16 gyrogonites from the lower mudstone and 12 from the upper mudstone were collected but were unable to be identified taxonomically due to their fragmentary conditions. the difference in the abundances of gyrogonites between the upper and lower parts of the quarry assemblage was found to be statistically significant (p <0.03). comparisons of taphonomic conditions of charophyte gyrogonites in the upper 15 cm of the bonebed along the contact with the overlying limestone revealed a wide variance of taphonomic states (figure 5, table 2). the difference in the variation of taphonomic conditions of gyrogonites in the upper 15 cm of the bonebed was not found to be statistically significant (p <0.5). discussion whereas the three identified taxa are also well known throughout the morrison formation, their variable and dynamic abundances have the potential to yield notable paleoecological interpretations. the three identified charophyte genera found in the cldq indicate still or slow-moving water with a neutral to sub-alkaline ph; aclistochara and porocharaceans such as latochara and stellatochara suggest fresh-to-brackish and alkaline waters (peck, 1957; feist and others, 1991; turner and peterson, 2004; martín-closas and others, 2008; benoit and others, 2017). these taxa fit with the 43 a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa peterson, j.e., warnock, j.p., coenen, j.j., bills, c.a., and denoto, m.e. geology of the intermountain west 2022 volume 9 previous interpretation of fresh-to-brackish, sub-alkaline wetlands for the morrison formation (turner and peterson, 2004; noto and grossman, 2010). the lower mudstone has fewer total charophytes, but a higher proportion are unidentifiable, fragmentary, and abraded gyrogonites relative to the upper mudstone. the relatively higher proportion of abrasion suggests the gyrogonites may represent an allochthonous/parautochthonus assemblage, perhaps introduced during periods of fluctuating water level (gates, 2005; peterson and others, 2017; warnock and others, 2018). alternatively, the upper mudstone has a considerably higher abundance of well-preserved gyrogonites, representing a more authochthonous assemblage and sugfigure 3. charophytes of the cleveland-lloyd dinosaur quarry. aclistochara bransoni (uwo-cldq0121) in (a) apical, (b) lateral, and (c) basal views; latochara concinna (uwo-cldq0122) in (d) apical, (e) lateral, and (f) basal views; stellatochara obovata (uwo-cldq0123) in (g) apical, (h) lateral, and (i) basal views. 44 a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa peterson, j.e., warnock, j.p., coenen, j.j., bills, c.a., and denoto, m.e. geology of the intermountain west 2022 volume 9 gesting that the deposit was becoming a more stable and permanent body of water. the transition to a more permanent body of water is further supported by the freshwater limestone capping the mudstone unit, which also contains charophyte gyrogonites and ostracods. turner and peterson (2004) note that brackish, alkali and often ephemeral ponds and wetlands are not conducive to life beyond algae. this, coupled with presence of brackish-tolerant charophytes and the rarity of fish, turtle, and crocodilian fossils found in the cleveland-lloyd assemblage, supports the interpretation of the depositional setting as an ephemeral pond (gates, 2005; peterson and others, 2017; warnock and others, 2018). furthermore, as with the results of this study, the brackish-tolerant a. bransoni is rarely in high abundance in the morrison formation, and stellatochara and latochara commonly occur together, but with abundances at odds with one another (ross, 1960). relative abundances and associations such as these may be due to taphonomic biases (i.e., transport), sampling biases, or differences in gyrogonites production. however, they may also suggest ecological controls on charophyte distributions, previously suggested by wood (1950) where extant charophytes demonstrate similar relationships due to seasonal shoreline banding and restrictions to the margins of lakes. such restriction of charophytes to the margins of lakes may explain the variable abundances of porocharacean charophytes observed throughout the cleveland-lloyd deposit and strengthens interpretations of the deposit as an ephemeral pond (gates, 2005; peterson and others, 2017) that fluctuated with water level somewhat regularly with slow-moving waters present during a higher-level stage (warnock and others, 2018). furthermore, this result indicates that from a charophyte ecology standpoint, the cldq ephemeral pond did not stand out from most other morrison formation deposits in the colorado plateau. significantly, this indicates that the environmental conditions important for charophyte ecology (i.e., salinity, ph, stillness of water column) were not different in the cldq pond relative to other morrison formation environments in the colorado plateau. the variation in taphonomic condition among charophytes in the upper 15 cm of the bonebed is strongly correlated with intramatrix bone fragments observed throughout the quarry deposit (peterson and others, 2017). the varying degree of abrasions observed in bone fragments has previously been suggested to be the result of fluctuations in water levels during the duration of the deposit accumulation; less-abraded fragments indicate recent breakage of dinosaur bones that had been subaerially exposed before burial in the jurassic, whereas more abraded fragments represent the remains of bones that had gone through numerous reworking cycles (peterson and others, 2017). similarly, the charophyte gyrogonites extracted from the cldq show comparable variation in their degree of abrasion, suggesting that the more fractured and abraded specimens indicate periods of subaerial exposure and reworking prior to burial and incorporation into the more stable lacustrine system that is represented by the overlying limestone. figure 4. percent abundance of charophytes in the upper and lower 50 cm of the cleveland-lloyd dinosaur quarry. upper (0–50 cm) lower (50–100 cm) aclistochara bransoni 3 3 latochara concinna 70 28 stellatochara obovata 55 28 unidentified gryogonites 12 16 table 1. abundance of charophyte gyrogonites from the upper and lower 50 cm of the cleveland-lloyd dinosaur quarry. 45 a review of charophytes of the cleveland-lloyd dinosaur quarry at jurassic national monument in the upper part of the morrison formation (late jurassic), emery county, utah, usa peterson, j.e., warnock, j.p., coenen, j.j., bills, c.a., and denoto, m.e. geology of the intermountain west 2022 volume 9 conclusion microfossils such as charophytes and ostracods play an essential role in extant ecosystems. as such, a more robust understanding of their nature in the morrison formation can yield considerable information regarding this important and dynamic ancient ecosystem. whereas the taxonomic composition of the charophyte assemblages do not significantly change in the upper and lower mudstones, the variability of charophyte abundance and preservation support interpretations of a highly dynamic depositional environment in the latest jurassic of utah, corroborating previous results (peterson and others, 2017; warnock and others, 2018). these observations help to characterize the depositional environment of the cldq, a necessary step for understanding its uniqueness and place in the morrison ecosystem, while providing an ecological metric for comparison to other morrison formation deposits. acknowledgments we thank the reviewers john foster and carles martín-closas for their helpful suggestions and constructive criticisms. dana truman, casey dooms, michael leschin, and everyone from the price field office of the bureau of land management for their continued assistance in providing access and resources for field work in jurassic national monument. their collaboration and support are necessary and appreciated. we also thank the university of wisconsin oshkosh for providing financial assistance for this research through the faculty development fund and the faculty/student collaborative program. furthermore, we thank an anonymous donor who has helped offset transportation costs for students and volunteers. finally we thank dr. todd kostman of the department of biology at the university of wisconsin oshkosh for providing access to the sem facility and david vaccaro for assistance in sem image processing. references benoit, r.-a., néraudeau, d., and martín-closas, c., 2017, a review of the late jurassic–early cretaceous charophytes from the northern aquitaine basin in south-west france: cretaceous research, v. 79, p. 199–213, doi:10.1016/j.cretres.2017.07.009. bilbey, s.a., 1992, stratigraphy and sedimentary petrology of the upper jurassic-lower cretaceous rocks at cleveland-lloyd quarry with a comparison to the dinosaur national monument quarry, utah: salt 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geological survey bulletin 1161-a, p. a1–a10. stokes, w.l., 1985, the cleveland-lloyd dinosaur quarry— window to the past: u.s. government printing office, 27 p. tanner, l.h., and galli, k.g., 2014, pedogenic and lacustrine features of the brushy basin member of the upper jurassic morrison formation in western colorado—reassessing the paleoclimatic interpretations: volumina jurassica, v. 12, p. 115–130. turner, c.e., and peterson, f., 2004, reconstruction of the upper jurassic morrison formation extinct ecosystems—a synthesis: sedimentary geology, v. 167, p. 309– 355. ward, d.j., 1981, a simple machine for bulk processing of clays and silts: tertiary research, p. 121–124. warnock, j., peterson, j., clawson, s., matthews, n., and breithaupt, b., 2018, close-range photogrammetry of the cleveland-lloyd dinosaur quarry, upper jurassic morrison formation, emery county, utah: geology of the intermountain west, v. 5, p. 271–285, doi:10.31711/giw. v5.pp271-285. wood, r.d., 1950, stability and zonation of characeae: ecology, v. 31, p. 642–647, doi:10.2307/1931582. paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western coloradoimplications for upper jurassic dinosaur preservation modes geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado—implications for upper jurassic dinosaur preservation modes john r. foster, rebecca k. hunt-foster, mark a. gorman ii, kelli c. trujillo, celina a. suarez, julia b. mchugh, joseph e. peterson, jonathan p. warnock, and heidi e. schoenstein theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover thin section micrograph of nearly pristinely preserved osteons from a “spongy” and almost rounded dinosaur bone fragment excavated from the morrison formation in the mygatt-moore quarry. micrograph image by jane baer (university of utah) and john foster (museum of moab). i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott ekeller@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 5 2018 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — museum of moab cary woodruff — university of toronto octavio mateus — universidade nova de lisboa editors geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 23 abstract the mygatt-moore quarry is a deposit of several thousand dinosaur bones in the brushy basin member of the morrison formation in western colorado. the site has been worked for more than 30 years and nearly 2400 mapped specimens have been collected. this study gathered data about the quarry from many sources to investigate the origin of the deposit. the mygatt-moore quarry appears to be an attritional deposit of a relatively restricted diversity of dinosaurs, with few other non-dinosaurian taxa, that accumulated in a vernal pool deposit in an overbank setting. bone modification was mostly by corrosion and breakage by trampling; scavenging was abundant. the paleofauna is dominated by allosaurus and apatosaurus (mni and nis), with the polacanthid ankylosaur mymoorapelta less common. the matrix of the main quarry layer includes abundant carbonized fragments of plant material, and the mud during the time of deposition may have been often at least damp and occasionally acidic and dysoxic. the cleveland-lloyd dinosaur quarry is a close correlate of the mygatt-moore quarry in terms of lithology and taphonomy, but demonstrates significant differences upon close inspection of matrix details and bone modification. large quarries of fine-grained facies in the morrison formation possess a very different preservation mode as well as different taxon and relative abundance profiles from those in coarser sediments, which suggests that more may be learned in the future from taphofacies study of large quarries in mudstone beds. paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado—implications for upper jurassic dinosaur preservation modes john r. foster1, rebecca k. hunt-foster2, mark a. gorman ii3, kelli c. trujillo4, celina a. suarez5, julia b. mchugh6, joseph e. peterson7, jonathan p. warnock8, and heidi e. schoenstein9 1museum of moab, 118 east center st., moab, ut 84532; director@moabmuseum.org 2bureau of land management, canyon country district, 82 east dogwood, moab, ut 84532; rhuntfoster@blm.gov 3denver museum of nature and science, 2001 colorado blvd., denver, co 80205; mark.gormanii@gmail.com 4laramie county community college, laramie, wy 82070; kellitrujillo@icloud.com 5university of arkansas, department of geosciences, 226 gearhart hall, fayetteville, ar 72701; casuarez@uark.edu 6museums of western colorado, 550 jurassic ct., fruita, co 81521; jmchugh@westcomuseum.org 7department of geology, university of wisconsin-oshkosh, oshkosh, wi 54901; petersoj@uwosh.edu 8department of geoscience, indiana university of pennsylvania, indiana, pa 15705; jwarnock@iup.edu 9grand junction geological society, p.o. box 4045, grand junction, co 81502; hsthurmon@gmail.com citation for this article. foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e., 2018, paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado—implications for upper jurassic dinosaur preservation modes: geology of the intermountain west, v. 5, p. 23–93. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 24 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 introduction the morrison formation is an upper jurassic alluvial deposit that originally covered at least ~1,000,000 km² of what is now the western united states (dodson and others, 1980; turner and peterson, 2004). the formation is well known for having produced some of the largest and most iconic dinosaurs from the late jurassic, and it has yielded one of the most diverse and abundant mesozoic paleofaunas from anywhere in the world. although forms such as brachiosaurus, stegosaurus, and allosaurus are recognized even by non-paleontologists worldwide, the morrison formation’s real significance lies in its preserved biota, including more than 90 vertebrate forms (more than 60 of which are not dinosaurs), plus plants, bivalves, gastropods, crustaceans, and others (chure and others, 2006). dinosaur quarries in the morrison formation number in the hundreds and include those producing a range from a few bones of one individual up to more than 10,000 bones of multiple individuals and species (dodson and others, 1980; foster, 2003). most quarries are dominated by dinosaurian remains; rare others produce almost exclusively non-dinosaur material. the diversity of preservational modes is great, particularly between those preserving mostly dinosaurs versus mostly non-dinosaurians, but several taphofacies are consistently encountered in widely scattered areas and levels. among sites producing primarily dinosaurs, a number are considered “large,” defined here as having produced multiple individuals and 500 or more mappable bones (i.e., excluding fragments unmappable at approximately 10 cm = 1 m). among these are sites such as the carnegie quarry at dinosaur national monument, howe quarry, dry mesa quarry, and cleveland-lloyd dinosaur quarry (curtice and wilhite, 1996; miller and others, 1996; carpenter, 2013). the greatest number of bones, individuals, and species among these sites appears to be preserved in relatively coarse sand deposits of channel sandstones. these localities also preserve relatively even numbers of each species, often reflective of the relative abundances of the species in the formation as a whole. in contrast, “large” dinosaur quarries (as defined above) preserved in drab mudstone may produce very large numbers of bones, but generally contain fewer species than channel sandstone sites and are often dominated by one or a couple of species (e.g., cleveland-lloyd dinosaur quarry, gates, 2005 and peterson and others, 2017; howe quarry, bird, 1985; mygatt-moore quarry, foster and others, 2016). among the latter mudstone sites, with relatively low diversity and a predominance of just a few species, is the mygatt-moore quarry in western colorado. this site is unusual among morrison localities in preserving a moderate diversity of plant macrofossils and palynomorphs, abundant dinosaur bones but of relatively low taxonomic diversity, and rare microvertebrate fossils, all in the same productive layer. this study examines the general paleontology, vertebrate taphonomy, and sedimentology of the mygattmoore quarry as a large dinosaur bonebed and their implications for the origin of the deposit. locality and previous work the mygatt-moore quarry was discovered on march 14, 1981, by j.d. and vanetta moore and pete and marilyn mygatt (armstrong and perry, 1985; armstrong and others, 1987; mygatt, 1991; p. mygatt, verbal communication, 2001). it is approximately 2.5 km from the utah-colorado state line in far western mesa county, colorado (figure 1), about 27 km west of fruita. the quarry (figure 2a) is in the northwestern part of rabbit valley, a drainage that runs south to the colorado river. the upper rim of the valley is composed of the cretaceous cedar mountain and naturita (formerly dakota) formations (figure 2b), and the floor of most of the northern part of the valley is salt wash member of the morrison formation. most of the hills of the valley all around are composed of partially grass-covered slopes of the brushy basin member of the morrison. the quarry has been worked every summer since 1985 and has produced more than 2300 mapped bones. the quarry has developed into a significant excavation over the years (figures 2c to 2f) but has shown no signs of playing out. in fact, results presented here suggest the bone deposit is much larger than previously suspected. compared to its fossil diversity, abundance, and the number of years it has been worked, relatively little has been published about the mygatt-moore quarry. plant 25 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 macrofossils from the mygatt-moore quarry have been studied by tidwell and others (1998) and the fossil spores and pollen by hotton and baghai-riding (2010). king and foster (2006) reported on the few non-dinosaurian vertebrates found in the quarry, whereas the ankylosaurian dinosaur mymoorapelta—the first jurassic ankylosaur in north america—was described by kirkland and carpenter (1994) and kirkland and others (1998, 2010). surprisingly, these latter two are the only papers that described any element of the dinosaur fauna exclusively. chin and kirkland (1998) reported possible herbivorous dinosaur coprolites from the quarry, and bray and hirsch (1998) described rare eggshell material from the site. the occurrence of dinosaur skin at the site, as carbonization and impressions, was reported by foster and hunt-foster (2011). only two abstracts have been produced dealing with overall site taphonomy (kirkland and armstrong, 1992; foster and others, 2007), and general site characteristics have previously been covered in papers only preliminarily (kirkland and others, 2005; foster and others, 2016). geologic setting rabbit valley (and the mygatt-moore quarry) is on the northwestern edge of the uncompahgre plateau uplift and northwest of the local uplift of ruby canyon along the colorado river; on its western edge the uncompahgre borders the laccolithic uplift of the la sal mountains, which are to the southwest of rabbit valley. this region is on the northeastern edge of the colorado plateau. in rabbit valley, the salt wash member of the morrison formation is about 96 m thick (armstrong and mcreynolds, 1987), and the brushy basin member is about 100 to 140 m thick. the morrison formation in the area is underlain by what is called either the upper jurassic summerville formation (carter and gualtieri, 1965; lohman, 1965; lucas and others, 2006) or the wanakah formation (scott and others, 2001) and the entrada sandstone (both middle jurassic), and is overlain by the lower cretaceous cedar mountain formation and then the naturita formation (stokes, 1952; young, 1960; kirkland and others, 1997; currie and others, 2008; sprinkel and others, 2012; carpenter, 2014). the cedar mountain formation is equivalent to the burro canyon formation of the south and east side of the colorado river in colorado and utah (young, 1960); the formation is traditionally considered cedar mountain in rabbit valley only because of the valley’s position north and west of the colorado river. the mygatt-moore quarry is in the upper part of the grand junction aspen denver colorado springs interstate 70 in te rs ta te 2 5 mygattmoore quarry colorado 100 km n front range san juan mountains elk range sangre de cristo range saw atch range m osquito range g ore range park range figure 1. location of the mygatt-moore quarry in western colorado (red star). major outcrops in colorado of the morrison formation in blue-green. 26 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 2. development and stratigraphy of the mygatt-moore quarry in western colorado. (a) view of the quarry from the southeast in the 1990s. (b) stratigraphy of the uppermost jurassic-lower cretaceous contact above and west of the quarry. jmbb = upper brushy basin member of the morrison formation; kcm = cretaceous cedar mountain formation; kn = cretaceous naturita (formerly dakota) formation. (c) view of the mygatt-moore quarry in september 1987, looking northeast (photo courtesy of kay fredette, museums of western colorado). (d) same view as c in july 2011 showing subsequent development of the quarry. (e) view of the quarry in september 1987, looking east-southeast (photo courtesy of kay fredette, museums of western colorado). (f) same view as e in july 2011. (g) panorama of the mygatt-moore quarry, looking southeast, in july 2011. 27 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 lower half of the brushy basin member of the morrison formation (turner and peterson, 1999, also had the quarry at this approximate level; although armstrong and mcreynolds, 1987, had the quarry low in the upper half). the morrison formation is late jurassic in age, ranging from the kimmeridgian (or possibly the latest oxfordian) up into the early tithonian (turner and peterson, 2004; trujillo and kowallis, 2015). at the time of quarry deposition, the morrison basin consisted of an alluvial plain with rivers flowing generally east out of the western mountains and across the floodplain (turner and peterson, 2004). wetlands and lakes existed to the east of what is now western colorado, and immediately to the south of the mygatt-moore area was “lake t’oo’dichi’” (turner and fishman, 1991), a large, alkaline wetland/lacustrine complex in a hydrologically closed basin that had high evaporation rates and groundwater flow blocked to the east (turner and peterson, 2004). other authors have interpreted the evidence differently and see no indication of such a complex (anderson and lucas, 1997; galli, 2014). methods the mygatt-moore quarry has been excavated for approximately three to four months per year since around 1990. before that time, most seasons were approximately two weeks. mapping of the bones in the quarry has always been from a main datum established near the original point of discovery, consisting of a survey marker-type cap, and a second marker at 40 m due north; these two markers establish the north-south coordinate axis. the grid is measured along meters approximately east-west and north-south of the datum. (it was recognized several years ago that the grid system used year to year is aligned on a bearing of approximately 350o and not true north, though the northern survey marker up slope from the quarry is correctly aligned.) most bones have been found in an arc approximately southwest to northeast of the main quarry datum; the main quarry layer (may also be referred to as quarry layer) has already been eroded away to the south and east, and it is under the hillside to the north and west. each bone removed was also assessed for stratigraphic level within the quarry. the main bone layer is approximately 1 m thick in most areas; this interval is divided into lower, middle, and upper thirds (each approximately 33 cm thick), and as each bone was collected its stratigraphic interval was noted. in areas where the full bone layer is somewhat thinner, each stratigraphic level is correspondingly thinner so that the full layer was still divided visually into thirds. this system was developed a number of years ago after abandonment of a measurement of a z-coordinate in the mapping. the z-coordinate had been mapped off the top of the so-called “pebble layer” (see below). it was eventually discovered, however, that the “pebble layer” was indurated (and thus usable) in some areas of the quarry but not others, that where it was present its upper (and lower) boundaries undulated laterally, and that it is almost non-existent in other parts of the quarry. thus, the simple three-part lower, middle, and upper bone layer subdivision was adopted. stratigraphic sections were measured in ten locations along approximately 1.62 km of strike (southwest-northeast) on the north end of rabbit valley. west to east, these are (1) far west nose, (2) west nose, (3) quarry, (4) cam stop, (5) caudal draw, (6) channel lake traverse 1, (7) channel lake traverse 2, (8) gravel hill, (9) east trail through time, and (10) far east ridge (figures 3 and 4). two sections (quarry and far east ridge; figures 3 and 4) covered the complete brushy basin member from the top of the salt wash member of the morrison formation up through the cedar mountain formation and into the naturita formation. the other stratigraphic sections were connected to at least one laterally adjacent section by traceable beds (generally the “fish layer” or various sandstone beds), so that all ten sections could be correlated. sections were measured with a jacob staff and brunton compass set to the local dip of 5° northwest. five trenches were excavated with a backhoe (figure 5). three sites were within the quarry excavation and two sites were excavated adjacent to the quarry on either side. these sections were also measured with a jacob staff. two drill holes—mm-1, which was about 87 m to the northwest of the quarry, and mm-2, which was about 95 m to the southwest—were bored with a 28 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 track-mounted rig (figure 5). the 2.5-inch-diameter core was logged at the surface. only 3 to 5 m of core below the “fish layer” (see below) was collected and is preserved in the museums of western colorado paleontology collections. positions of the trenches and drill holes were recorded by marking with 40 cm diameter circular orange markers and digitally photographing the whole area with a fixed-wing drone aircraft; the camera had a resolution of approximately 10 cm. five hand samples were collected from standard layers in each trench; the “fish layer” was sampled from all five. two samples from the main quarry layer were collected from each trench; other samples varied between trenches. thin sections were made from these samples. lithologic descriptions of the trenches were recorded in the field and from the hand samples and thin sections. thin sections were studied under a petrographic microscope and digitally photographed. in addition to the trench hand samples, numerous calcareous nodules were collected from the base of the quarry, and the five of these were thin sectioned (pb-1 through pb-5). four bones were also thin sectioned to compare their microstructures; two rounded, pebble-sized bone fragments (with only trabecular bone left) and two fragments containing cortical bone. all thin sections are preserved at the museums of western colorado. in addition to the thin sectioning of the calcium carbonate nodules, two of them plus three other representatives of these nodules (pb-1, pb-2, and pb-7 through pb-9) were analyzed for rare earth element ratios at the department of geosciences, boise state university. samples were crushed in a mortar and pestle to a fine powder and 125 mg of that powder was added into teflon microwave digestion vessels. the samples were then soaked in 30% trace grade h2o2 for an hour to extract any trace elements from any remaining organic matter. after an hour, a 4.5:1.5:5.5 ml solution of concentrated trace grade hno3:hcl:ddi h2o was added to the microwave digestion vessels. samples were digested on a mars microwave digester using the pre-programmed 3052xp-15min xpress method that uses a 15 minute ramp-up time, a 15 minute hold at 190ºc, and figure 3. map showing locations and names of the stratigraphic sections measured for this study near the mygatt-moore quarry in rabbit valley. quarry labeled and marked by arrow. base from google earth. 29 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 st ra ti g ra ph ic s ec ti o ns in r ab bi t va ll ey , m es a co un ty , c o lo ra d o fa r w es i n os e w es t n os e q ua rr y se ot lo n w ith p os iti on s of ve rt eb ra te fo ss il oc cu rr en ce s gr h n d ay si on e 1c... -� red d ay st on e ....._ ....._ w ith p a! eo sl:l l a t t ap ......_ -.. -. ...._ � c lay sto ne � s ilt sto ne � s an ds to ne � l im es to ne igo ld , re d, an d ta n sa nd ,t on e 80 m m yg at tm oo re q ua rr y: 60 m a j/o sa ur us ap ar os au ru s m ym oo ra pe /ta d ip lo do t:::u s ca m ar as au ru s ce ra to sa ur us 40 m o th ni t!l os au ru s 20 m om hy �o ti, es ize d co rre lat io n or � in ch ou t tr ac ea bl e be d co rre lat i0 n f<i n:m at io n or m em h>e r 0 ou nd ar y ,... fo ss il v er te h>r at e oc cu rr en ce gr ay , re d, an d gr ee n cla ys to ne es da ko ta fo rm at io n ce da r m ou nta in fo rm at io n g ra ve l h ill ca m ar as au r s to p ca ud al d ra w ch an ne l-l ak e se ct io n ch an ne l-l ak e tr av er sa 1 m o r r is o n fo r m a t io n b, us l,y b as in m em be r tr av er se 2 ea st t ra il th ro ug h ti m e fa r e as t r id ge 12 0m 10 0m bo m gr ay an d da rk g ra y m ud st on e ta n sa nd st on e t o pe bb ly sa nd st on e w ith • fe w gr ay , w hi te -w ea th er in g, so ft sa nd st on e; fin e to m ed iu m -� ra in ed lig ht g re en cl ay st on e gr ay to re d m ot tle d ca lci um c ar bo na te lig ht g ra y c la ys to ne w ith m in or am ou nt s o f m ar oo nre d cla ys to ne ; pa le os ol at to p gr ay , g re en ,.a nd m in or am ou nt s o f m ar oo n cla ys to ne gr ay to ta n, m ed iu m t o fin egr ain ed sa nd st on e w hi te , t an -w ea th er in g, m os tly m ed iu m to v er y c oa rs e gr ai ne d sa nd st on e; ln te rb ed d1< d m ar oo n, re dbr ow n, ;in d gn1 y cla ys to ne ;s om e m ot tli ng ;o ne lo crn fi ne ­g ril ln ed sa nd st on e ne ar m id dl e w hi te ,ta n to b ro w n cr os sbe dd ed fin e- to m os tly m ed iu m -g ra in ed sa nd st on e gr •y a nd ra d cla ys to ne gr ee ngr .iy c la ys to ne w 11---. 1---. 1-4 -< >---1 � e -l oo m -6 00 m ~l 50 m -1 00 m ~b orn -s om -b orn ~3 00 m ~2 60 m fi gu re 4 . s tr at ig ra ph ic se ct io ns m ea su re d fr om th e to p of th e sa lt w as h m em be r o f t he m or ris on f or m at io n (o r w ith in b ru sh y ba sin m em be r) up to th e ba se o f t he n at ur ita f or m at io n in r ab bi t v al le y ne ar th e m yg at tm oo re q ua rr y, w es te rn c ol or ad o. s ec tio ns a nc ho re d on th e m or ris on -c ed ar m ou nt ai n co nt ac t. sa nd st on es a nd o th er m ar ke r b ed s t en ta tiv el y co rr el at ed . d ak ot a = n at ur ita f or m at io n. q ua rr y an d fiv e ot he r fo ss il oc cu rr en ce le ve ls la be le d an d m ar ke d w ith a rr ow s. 30 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 a 15 minute cool-down. samples were then evaporated on a hot plate at 90ºc and re-hydrated to 2% ddi hno3, filtered, and analyzed using solution inductively coupled plasma mass spectrometer (icp-ms). samples were analyzed on a thermo x series 2 quadrupole icpms for 43ca, 44ca, 66zn, 86sr, 88sr, 89y, 135ba, 137ba, all rare earth elements (ree), 208pb, 232th, and 238u. analysis was monitored via an internal 100 ppb (part per billion) re standard. all ree patterns were plotted relative the nasc (gromet and others, 1984). matrix samples for x-ray flourescence (xrf) analysis were collected from within the quarry’s main bone layer, from the same stratigraphic level (about 2 to 3 m below the “fish layer”) but outside the quarry about 250 m to the east (caudal draw), and a bone sample from within the quarry. xrf of sediment and bone samples carried out at indiana university of pennsylvania using an innov x delta professional handheld xrf analyzer in soil mode. concentrations of selected elements are given in ppm (parts per million). sediment samples were ground prior to analysis in a glass mortar and pestle. bone samples were cleaned of matrix with de-ionized water, but analyzed whole. the u-pb (zircon) radiometric age for the mygattmoore quarry was obtained from an ash-fall bed isolated from the quarry mudstone of the main bone layer, collected from the northern part of the quarry (quarry map coordinates 1021n, 998e) on june 6, 2011. the sample was analyzed by the university of wyoming geochronology lab and reported by trujillo and others (2014). a variety of zircon morphologies were separated from the mudstone sample; of more than 125 zircons, at least 30 demonstrated characteristics (elongate tips, longitudinal bubble trails, transverse channels) consistent with ash grains. selected zircons were annealed at 850°c for 48 hours and then dissolved in two steps, modified from the chemical abrasion method of mattinson (2005). the first step used concentrated hf and hno3 for 12 hours at 180°c. this removed the most metamict domains and surficial pb. after rinsing and discarding the leachate, individual grains were completely dissolved in hf and hno3 at 240°c for 30 hours; the solutions were converted to chlorides and evaporated with 0.05n h3po4 in preparation for thermal ionization mass spectrometry. nearly every piece of matrix from the main bone layer at the mygatt-moore quarry contains carbonized plant fragments. the only plant specimens saved are those that are complete enough to be identified to some taxonomic level. some but not all of the wood was collected as well. plants were identified based on comparisons with publications such as miller (1987), tidwell (1990), tidwell and medlyn (1992), ash (1994), ash and tidwell (1998) and tidwell and others (1998, 2006), as well as by consultation with some paleobotanists. mollusks were identified using yen and reeside (1952) and evanoff and others (1998). identifications of fossil vertebrates were compared to museum collections around the country as well as many references including, but not limited to, the following: hatcher (1901), osborn and mook (1921), gilmore (1925, 1936), madsen (1976), galton (1980, 1981, 1983, 2007), mcintosh (1990, 2005), carpenter and mcintosh (1994), kirkland and carpenter (1994), kirkland (1998), kirkland and others (1998), madsen figure 5. close-up image of the mygatt-moore quarry area showing locations of trenches 1–5 (bars) and drill hole mm-1 and drill hole mm-2 (circles). base is from google earth. 31 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 and welles (2000), upchurch and others (2004), and tschopp and others (2015). taphonomic scoring for bones is based on (1) the 0 to 3 scales of fiorillo (1988) for abrasion, (2) a 0 (none) to 3 (extensive) scale for corrosion (e.g., eberth and others, 2007), (3) behrensmeyer’s (1978) 0 to 3 scale for weathering, and (4) a 0 to 3 scale for breakage (0 = none, 3 = broken on most sides; ryan and others, 2001). abrasion was scored based on rounding of otherwise sharp edges, as well as on any surficial scratching. corrosion relates to chemical or biochemical erosion of bone surfaces and was scored by the rotting of bone ends or edges that was not clearly due to abrasion. that most end and edge loss of bone surface in mygatt-moore material is due to corrosion rather than abrasion is evidenced by the occurrence of outer bone-surface spalling, with sediment preserved between the flaking outer surface and the spongy inner surface that is then so often found (the spalling outer surface would be long eroded away had the material been abraded). weathering relates to degradation and cracking of bone surfaces due to surface exposure to the elements. breakage involves pre-burial breaks in the bone that, in most cases, fragment the element. breakage and weathering are fairly straight forward to assess, but abrasion and corrosion can be difficult to distinguish, as in either case the result is rounding of edges. these taphonomic data were collected on a randomly selected subsample of the mygattmoore quarry collections, representing approximately 23.5% of the censused collection. the randomly selected subsample of the cleveland-lloyd dinosaur quarry collection at the natural history museum of utah consisted of about 289 bones including those excavated by gates (2005). number of identified elements is based on a census of the collections of the museums of western colorado, consisting of material prepared through 2013. minimum number of individuals (mni) is based on the census data sorted for element but is not based on any single element. in the case of apatosaurus, for example, the mni count is based on the presence of a juvenile, a sub-adult and, based on femora, at least two adults. in the case of allosaurus, on the other hand, the number of individuals is based on femora and metatarsals of adults, plus one juvenile represented by dentaries. a significant percentage of the bone material in the mygatt-moore quarry is fragmented and mostly unidentifiable to element or taxon. therefore, most bones used for mni calculations were taken from a relatively small overall sample of more complete elements. a true calculation of the number of identified specimens to minimum number of skeletal elements (ratio nisp:mne, e.g., lyman, 1994) would be difficult, and, if knowable, the ratio would likely be rather high (although we did not attempt calculating either for this study). shed teeth of theropods were censused and measured for maximum basal crown length with a digital caliper. mean and standard deviation were calculated in a spreadsheet. allosaurus and ceratosaurus teeth were distinguished by the more laterally compressed maxillary and dentary teeth, and smaller serrations, in ceratosaurus, plus the lingual ridges of anterior dentary and premaxillary teeth in ceratosaurus, as demonstrated by madsen (1976), madsen and welles (2000), and bakker and bir (2004). two rose diagrams for orientations of bones were constructed, one bidirectional for bones with no clearly more massive end, and a unidirectional rose diagram for those with a clearly more massive end. bidirectional bones were measured toward the orientation between 0° and 180° and made bidirectional in representation in the computer program. unidirectional bones were measured toward the less massive end. the rose diagrams were constructed using 30° intervals in the program rose.net (https://en.freedownloadmanager.org/windows-pc/rose-net-free.html). compass readings for the rose diagram data were taken off the quarry map. voorhies group analysis was based on the group i– iii bone categories in carpenter (2013, table 6), and the work of frison and todd (1986) on transportability of elephant bones. it is recognized that the original sheep material studied (voorhies, 1969) may not be fully comparable to bones of large dinosaurs, as noted by gates (2005) and carpenter (2013); however, the analysis is carried out here to facilitate comparisons with other similar mudstone sites, such as the cleveland-lloyd dinosaur quarry, for which such analyses have also been 32 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 conducted previously. there is currently no other system available, based on flume or river studies of more appropriate (large) analogs, with which to conduct these analyses. a randomly selected, previously unexcavated single grid square (1010 to 1011n, 1009 to 1010e) was selected to be excavated and every bone, regardless of size or preservation, was collected. this was done as a possible representation of what an unbiased square meter of the main quarry layer was like, because in the past, excavation of the quarry had been biased towards larger and/ or scientifically significant specimens. the test square meter was excavated in the 2013 season and each bone, tooth, and bone fragment was collected and mapped on x, y, and z coordinates. the z coordinate was taken off a datum at the top of the bone layer (below the soil layer). the bones were measured for maximum length, width, and height and identified if possible. volume was calculated for each bone incorporating the formula for the volume of an ellipsoid cylinder, using the three dimensions measured. these volumes (as a rough approximation of overall size) were then graphed in a histogram and the mean volume calculated in a spreadsheet. articulation ratios for mygatt-moore, and other quarries used for comparison, were calculated by dividing the number of bones in articulation with at least one other bone by the total number of bones mapped from the site. these ratios were calculated by counting the bones on available quarry maps (published and unpublished). these ratios were calculated for the mygattmoore, cleveland-lloyd, carnegie, howe, howe-stephens, poison creek, little houston, and dry mesa quarries. results geology measured sections the top of the salt wash member of the morrison formation in rabbit valley is at the top of one or several light-brown, laterally continuous channel sandstones that can be traced across the valley. the overlying brushy basin member consists of approximately 100 to 140 m of gray, maroon, and greenish-gray claystone with numerous channel sandstone and thin splay sandstone beds and only a few thin limestone beds (figure 4). the largest laterally traceable channel sandstone beds appear to be at least 250 to 500 m wide. most channel sandstone beds are mediumto very coarse grained, contain many tabular and trough cross-beds, and basal lag deposits. mudstone beds of the brushy basin appear to be smectitic and contain at least some silt-sized grains (trujillo, 2006). the top of the morrison formation was observed in four of the measured sections. in most sections, the top is recognized as a deep maroon-red paleosol overlain by light green, sometimes silty or pebbly claystone of the cedar mountain formation. approximately 6 m up into the cedar mountain is a 0.5to 2.0-m-thick nodular limestone to paleosol carbonate layer similar to one often found low in the formation farther west in eastern utah (figure 2b); this unit is consistently at this level low in the cedar mountain and is overlain by a thicker unit of silty light green mudstone. the top of the cedar mountain is formed by light green claystone or a lightbrown sandstone overlain by a basal conglomerate and/ or a soft white sandstone marking the base of the naturita formation. immediately above this white sandstone are several meters of dark gray to black carbonaceous, and in some places coaly, mudstone characteristic of the naturita as well. above this first dark-gray carbonaceous mudstone is the first of two thick, yellow-brown sandstone beds that cap the ridges of rabbit valley to the west, north, and east. in one measured section (west nose), the top of the morrison formation is at the top of a thick, pebbly and cross-bedded channel sandstone; this unit is overlain by typical light green claystone of the lower cedar mountain, with the caliche/nodular limestone layer approximately 5 to 6 m up section. interestingly, this channel sandstone pinches out to the west within about 100 m from the west nose section, so that the morrison-cedar mountain contact is a red claystone and paleosol directly below the light green claystone of the lower cretaceous at the next section (far west nose) to the west (figure 2b). the mygatt-moore quarry occurs approximately 64 m above the base of the brushy basin member of the 33 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 morrison formation, in the quarry section (figure 4) in which the member is 135 m thick. this puts the quarry near the top of the lower half of the brushy basin member (47% of the way up in the section). galli (2014) measured a composite section of part of the brushy basin member but had the quarry in a slightly lower position; turner and peterson (1999) had mygatt-moore quarry at a slightly lower relative stratigraphic position on their master composite section. in both, however, the quarry was in the upper part of the lower half of the member. other vertebrate bone sites in the northern part of rabbit valley were tied in to the measured sections based on correlations of the channel sandstones in which they occur and were measured and correlated with the network of sections (figure 4). the stratigraphically lowest of these is a thin sandstone that contains a partial skeleton of camptosaurus (averett locality), a partial skeleton of allosaurus (under the cedar tree site), and a goniopholidid crocodylomorph osteoderm. these three sites are on the east end of the trail through time (a blm trail in the rabbit valley research natural area that begins at the mygatt-moore quarry). next higher site in the brushy basin member section is a sandstone that contains a proximal caudal series and several other elements of a diplodocid sauropod (probably diplodocus); this is also a stop on the east end of the trail through time. the stratigraphically youngest site contains a partial diplodocid skull (and elements of a skeleton still in the sandstone) collected several years ago from the far east ridge section east of and above the trail through time. between these sites and the mygatt-moore quarry there is a channel sandstone approximately 340 m wide east to west. this channel is stratigraphically a few meters above the mygatt-moore quarry. it contains the partial skeleton of a camarasaurus (a stop on the trail through time) and a single caudal centrum of a theropod dinosaur at the caudal draw section a little to the east. these latter sites are stratigraphically younger than the partial diplodocus from the eastern trail through time, but whether they are similar in age to the diplodocid skull, or are slightly older, is difficult to determine (see figure 4). the “fish layer” above the quarry is a distinct marker bed that can be traced more than 500 m to the east of the quarry. tracing the relationships of beds stratigraphically immediately adjacent to this marker bed indicates that (1) the camarasaurus channel sandstone pinches out laterally to the west of the sauropod stop along the trail, before it gets to the quarry outcrop, (2) the camarasaurus channel sandstone scours out the “fish layer” at the channel-lake traverse 2 section, (3) the camarasaurus channel sandstone pinches out on its east end, west of the gravel hill section, and (4) from at least the caudal draw section east, the stratigraphic level of the mygatt-moore quarry (about 2 m below the fish layer) no longer consists of medium light-gray claystone with abundant plant debris. the caudal draw and sections east that level are an often dark-red mudstone devoid of any fossil content (see figure 4). detailed quarry sections five trenches excavated by backhoe were dug in the quarry area; three were in the back wall of the quarry itself, and one each was just outside the excavated quarry to the south and east (figures 5 and 6). these trenches were excavated from the “fish layer” down to below the main quarry layer. the base of the main quarry layer to the base of the “fish layer” is 2 to 3 m thick. the main quarry layer unit (defined as a nodule-lag based, medium light gray claystone with abundant carbonized plant debris) was approximately 70 cm (in trench 1 south of the main quarry) to 1.5 m (in trench 3 on the northwest edge of the quarry) thick. in trenches 2 and 4, also in the excavated quarry, the main quarry layer was a more typical 1 to 1.2 m thick. the main quarry layer is directly underlain by a soft, light-green silty claystone that sometimes has some white mottling and is generally devoid of fossil vertebrate material, although some specimens have been found at the very top of this layer at its contact with the overlying bone layer. most notable, the soft, light-green claystone layer contains no carbonized plant material at all, unlike the mudstone immediately above it. the main quarry layer is a greenish-gray (5gy 6/1) to medium light-gray (n6) claystone with silt-sized clasts of quartz and minor plagioclase feldspar (in thin section), abundant carbonized plant fragments, and common greenish-colored or white clay-ball clasts that are rounded and about 2 to 5 mm in diameter (figure 6; 34 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 fi gu re 6 . s tr at ig ra ph ic s ec tio ns o f t re nc he s 1 to 5 in a nd n ea r th e m yg at tm oo re q ua rr y. ita lic iz ed n um be rs to r ig ht o f s ec tio ns in di ca te th in se ct io n nu m be rs a nd th ei r s am pl e le ve ls. 35 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 appendix a). trenches 2 to 4 have dinosaur bone and were in areas from which dinosaur material had been collected nearby in years past. some of the trenches have carbonate nodules near the base of the main quarry layer (trenches 1 to 3). above the main quarry layer is greenish-gray, light-green, and medium-green claystone with no carbonized plant fragments except in trench 2. a thin bed with minor amounts of plant debris is about 1.75 m above the base of the main quarry layer in trench 2. other trenches were devoid of plant material above about 1 m above the base of the main quarry layer. to the east, some reddish-colored claystone was present about 1.5 m from the base of the trench 5, unlike any of the other trenches. this and the fact that the main quarry layers are thinner in trench 5 compared to the other trenches, and that the base of the main layer in trench 5 lacked clay balls, bones, or nodules, and contained fewer plant fragments, all suggest that trench 5 may be closer to the eastern edge of the bone deposit than the other trenches. the indurated, laminated silty claystone at the top of each trench (the “fish layer”) was consistent except in trench 4 where the layer was mottled and laminations were less obvious. thin section micrographs comparison of thin section micrographs from the different layers across the five trenches indicates subtle differences in the claystone content that are not obvious in hand sample (figure 7; appendix a). the soft, lightgreen claystone underlying the main quarry layer appears to contain a higher percentage of larger silt-sized clasts than any of the other layers. the main quarry layer also contains a significant percentage of silt-sized grains but also has a high abundance of carbonized plant debris, clay balls (some containing silt clasts themselves), and wood fragments; these elements are missing from almost all samples from other layers (figure 7). the layer above the main quarry layer is similar in clay and silt content but is devoid of fossils and clay balls (except one sample with a single small wood fragment). the thin sections of the “fish layer” demonstrate the overall finer grained nature of the silt-sized clasts. none of the silt clasts in the “fish layer” from trenches 1 to 3 approach the size of those from underlying units. laminations are apparent in some of the thin section, particularly trench 1. the very different non-laminated texture of the “fish layer” thin section from trench 4 is reflected in the unusual mottled appearance in outcrop. the coarser size of the silt grains in this thin section matches that of many of the underlying layers. the “fish layer” thin section from trench 5 also has slightly coarser maximum silt grain size. the unusual texture for the “fish layer” thin sections of trench 4 (and to a lesser extent, trench 5) is somewhat unexpected because this laminated bed is traceable in outcrop for more than a half kilometer to the east. despite the consistent appearance of the “fish layer” for hundreds of meters in outcrop, the apparent differences in the thin sections may partly explain why, to date, fish skeletons have only been found in the quarry area. in any case, the mottled, non-laminated appearance of the “fish layer” at the top of trench 4 reflected in the thin section micrograph is clearly different from the other “fish layer” thin sections. also important to note from the thin sections (figure 7) is the somewhat different appearance of some of the trench 5 micrographs. this again may suggest that the eastern edge of the quarry deposit was near trench 5. previous exploration excavations in this area turned up little in the way of bone (b. britt, brigham young university, verbal communication, 2014), which is consistent with this interpretation. “pebble bed” nodules a concentration of calcium carbonate nodules commonly found at the base of the main quarry layer is sometimes referred to informally as the “pebble bed.” the “pebble bed” was present in trenches 1 through 3. the nodules are typically smaller and fewer in the southwestern part of the quarry and larger and more numerous in the northern part. the “pebble bed” commonly contains fragmented and heavily abraded dinosaur bone. this layer is well indurated only in some places, especially under larger sauropod bones such as a pubis and scapulae. based on anecdotal evidence from the earlier years of the excavation, this “pebble bed” was more extensively indurated toward the southern part of the current quarry area, but in the past decade or so of excavation, only isolated spots have proved to be 36 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 strongly cemented. in most areas of the northern part of the quarry, the basal layer of the main quarry deposit contains abundant large dinosaur bones and bone fragments in relatively soft, plant fragment-rich claystone with a few to abundant, hard calcium carbonate nodules of irregular shape that range from 1 to 10 cm in greatest dimension. most nodules are approximately 2 to 5 cm across and are devoid of plant material. the southwestern part of the quarry that was opened in 2005 and worked most years since, has no well-indurated areas, and, as mentioned above, has fewer and smaller calcium carbonate nodules; however, the southwest area has a greater number of clay balls than the northern part of the quarry. the exact source of the calcium carbonate nodules is uncertain. the calcium carbonate nodules are mostly composed of claystone with some angular to subrounded, silty to fine-grained sand grains. in hand sample "fish layer" green-gray and light green claystone quarry layer light green claystone gray claystone trench 2 trench 3 trench 4 trench 5 trench 1 figure 7. thin section micrographs of samples from trenches 1–5, showing differentiation of layers and range of silt size within quarry layer. within each trench column, thin sections are numbered in ascending order. note plant fragments parallel to bedding in quarry layer samples; also note organics in laminations in “fish layer” samples. each micrograph view is approximately 2000 µm across. see appendix a for descriptions. 37 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 and when seen in cross section, some of the nodules appear to be laminated and some also have manganese dendrites growing in from their outer edges. several of these nodules were thin sectioned and were found to contain siltand fine-sand-sized clasts in a higher concentration than many of the layers sampled from the quarry (figure 8). the silt and sand clasts are not as large as the largest grains in the underlying light-green claystone. the thin sectioned nodules are perhaps most similar in texture to the main quarry layer level from trench 5 or trench 4 and possibly to the lowermost gray claystone in trench 1. the nodules are least similar in texture to the underlying light-green claystone found in the main quarry layer of trenches 1 through 3, and the “fish layer.” the nodules are similar to those in the mudstone layers below, above, and lateral to the quarry, but differ from the mudstone layers in the main quarry layer. this, along with the clay balls in the main quarry layer, and very rare clasts of finely bedded, fine-grained sandstones (and sometimes a basal lag of abraded bone fragments), suggest that the calcium carbonate nodules were washed into the quarry deposits from elsewhere. taken together, the evidence suggests that the nodules were likely formed in place as incipient soil structures outside of the quarry area but were reworked and redeposited in the mygatt-moore quarry topographic low by hydraulic influence. this reworking of soil-related calcium carbonate nodules was also suggested by kirkland and armstrong (1992). total rare ree concentrations for the nodules in the “pebble bed” layer range from 74.8 to 112.5 ppm. there are two ree patterns when normalized to the north american shale composite (nasc) (gromet and others, 1984). samples pb-1, 7, and 9 exhibit a light ree pattern typical of shale, which concentrates light ree over middle and heavy ree. samples pb-2 and 8 are middle ree depleted. this may be due to scavenging of the middle ree by mn oxides; however, additional analysis needs to be conducted. all samples have a negative europium (eu) anomaly typical of a volcaniclastic source rock, consistent with the volcaniclastic nature of the sediment from the brushy basin member of the morrison formation. the preliminary ree analysis of several of the calcium carbonate nodules also indicates that the nodules may have mixed together from two separate sources based on the two geochemical signatures (figure 9). more data on these ree signatures should be forthcoming as more nodules are analyzed in the future. matrix xrf analysis the brushy basin section in the mygatt-moore quarry represents a mudflat deposit, which was ephemerally wetted (foster and hunt-foster, 2011). the metal profile detected in the mygatt-moore quarry matrix using xrf analysis is likely the result of apatite diagenesis in an ephemerally subaqueous environment. samples analyzed from within mygatt-moore quarry differ from morrison formation samples collected at the same stratigraphic horizon outside the bonebed. specifically, the matrix at mygatt-moore quarry contains figure 8. thin section micrographs of calcium carbonate nodules (“pebbles”) p-1 through p-5 from low in main bone layer, showing variable silty texture. each micrograph view is approximately 2000 µm across. 38 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 elevated k, ti, v, ni, zn, and pb at levels at least twice those detected outside the quarry (table 1). from within this set, ni, zn, and pb have been reported in obsidians, the chemical composition of which were used as proxies for volcanic ash deposited during the jurassic (hubert and others, 1996). ash would have been incorporated into the sediment of mygatt-moore quarry during ashfall events, resulting in these elements being found in elevated levels in the matrix and bone. some elements detected via xrf are enriched within mygatt-moore quarry bone samples relative to mygatt-moore quarry matrix. elevated levels of metals such as as, sr, and pb within apatite are known from other jurassic deposits, such as the lower jurassic kayenta formation, as well as the upper cretaceous prince creek, hell creek, and dinosaur park formations (e.g., goodwin and others, 2007). diand trivalent ions substitute for ca2+ in apatite during early diagenesis within bones in contact with water (trueman and tuross, 2002). this is one likely source of the metals, which are elevated in mygattmoore quarry bone. a second possibility is organic content within the deposit. mygatt-moore quarry contains abundant plant fragments (ref), and organic-rich soil horizons have been shown to be enriched in metals, e.g., cu, pb, mn, zn, and hg (martí and others, 2003). it is possible that decaying dinosaur tissue contributed to the elemental metals found within mygatt-moore quarry, as has been suggested at the cleveland-lloyd dinosaur quarry (peterson and others, 2017). however, the elemental metal profiles detected here contrast with those reported from the cleveland-lloyd dinosaur quarry in regard to the relative concentrations in bone versus matrix from cleveland-lloyd dinosaur quarry (peterson and others, 2017). in contrast, the elemental metal profiles seen here resemble those of other jurassic sites whose elemental metal content was determined to be diagenetic (e.g., hubert and others, 1996; goodwin and others, 2007). whereas abundant sulfide minerals, such as pyrite and chalcopyrite, were detected at cleveland-lloyd dinosaur quarry, the mygatt-moore quarry sediment and bone samples contain considerably lower levels of sulfides, implying a sometimes more oxygen-rich setting at mygatt-moore than cleveland-lloyd. despite evidence from carbonized skin at mygatt-moore quarry, the lower levels of sulfides imply that the levels of decay at mygatt-moore quarry were not high enough to utilize the available oxygen, making it unlikely that enough dinosaur tissue was decaying to provide the observed metals. furthermore, herbivore tissues, which dominate the mygatt-moore quarry assemblage (by number of identified species and minimum number of individuals [mni]), generally contain lower concentrations of elemental metals compared to carnivore tissues due to trophic focusing (vijver and others, 2004). therefore, the large amounts of dinosaur bone apatite are the most likely source of elevated el 0.1 1 la ce pr nd sm eu gd tb dy ho er tm yb lu pb-1 pb-2 pb-7 pb-8 pb-9n or m al iz ed n a sc element figure 9. rare earth element geochemistry plot of five calcium carbonate nodules (e.g., pb-1), showing two apparent signature groups and suggesting multiple sources of these “pebbles.” log-scale y-axis. 39 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 emental metals within the mygatt-moore quarry relative to morrison formation sediment from the same stratigraphic horizon via diagenetic processes. drill hole cores the cores from the two drill holes (figures 5 and 10; appendix b) demonstrated several things. first, the “fish layer,” which is traceable in outcrop for more than 500 m to the east along the trail through time and which is mostly covered beyond trench 1 to the southwest, was present in both drill holes. the drill holes are ~100 m apart indicating that the lake deposit extends a significant distance to the west in general. second, the distinctive main quarry layer is also present in both cores (figures 10a and 10b); in mm-1 at 17.4 to 17.8 m and mm-2 at 15.7 to 16.6 m. more importantly, the core from mm-2 preserves an approximately 4-cmlong fragment of dinosaur bone from the 16.5 m level in the medium light gray claystone with abundant plant fragments (figure 10c). these results indicate that the main quarry layer is geographically much larger than previously believed, especially to the southwest. the original intent of the drilling was to bracket the western and southwestern edges of the quarry in the directions the main quarry layer goes in the subsurface, but the discovery that the quarry claystone continues at least about 87 m to the northwest (drill hole mm-1) and about 95 m to the southwest (drill hole mm-2) suggests that the main quarry layer may be up to eight times larger than the area excavated so far. the area formed by a triangle linking drill holes mm-1 and mm-2 to the quarry and to each other is estimated to be approximately 4130 m2. in contrast, the area of the quarry excavated so far is approximately 500 m2. age the age of the mygatt-moore quarry has been estimated by u-pb dating of ash-fall zircon crystals obtained from smectitic mudstone sampled from near table 1. x-ray flourescence (xrf) analysis results for elements in matrix samples from the mygatt-moore quarry, from the same level as the quarry but about 250 m east of the quarry at the caudal draw stratigraphic section, and for bone from the quarry (ppm). *from main bone layer. bolded values highlight elevated levels compared to values outside the quarry. **from about 2 m below “fish layer." element quarry matrix* (ppm) caudal draw matrix** (ppm) ratio quarry matrix: caudal draw matrix quarry bone (ppm) ratio quarry matrix: quarry bone p 0 0 253,739 0.00 s 9953 0 5112 1.95 k 17,129 7517 2.28 8636 1.98 ca 17,128 95,736 0.18 343,740 0.05 ti 2267 1088 2.08 2539 0.89 v 175 24 7.29 618 0.28 cr 39 23 1.69 841 0.05 mn 1111 1101 1.01 1204 0.92 fe 10,354 8931 1.16 3443 3.01 ni 45 6 7.50 167 0.27 cu 17 12 1.42 48 0.35 zn 107 26 4.11 86 1.24 as 58 0 38 1.53 sr 150 293 0.51 4880 0.03 mo 6 0 16 0.38 pb 61 14 4.34 127 0.48 40 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 several dinosaur bones in the main quarry layer. the calculated radiometric age for the quarry was 152.18 ± 0.29 ma (trujillo and others, 2014; figure 11), a date that puts the quarry at the kimmeridgian-tithonian boundary. this date is very close to that obtained for the famous reed’s quarry 9 at como bluff, wyoming (trujillo and others, 2015), a site that yielded many hundreds of microvertebrates from the morrison formation (carrano and velez-juarbe, 2006). systematic paleontology preserved taxa—main quarry layer the macrofossil record of plants from the mygattmoore quarry is unusual for the morrison formation in that it is found among abundant bones of sauropods and other dinosaurs. unidentifiable plant fragments are abundant in every piece of matrix out of the quarry; in fact, as noted above, this plant-debris layer is one way to identify the quarry level even before bones have been located. among all this preserved plant material, a small percentage is more than fragmentary and can be identified in some cases. the preserved plants from the mygatt-moore quarry include at least 18 species (tidwell and others,1998; this report), including horsetails (equisetum figures 12b, 12e, and 12f) cycadophytes (otozamites, cycadolepsis, jensensispermum ), ginkgoes (ginkgo; figure 12d), czekanowskiales (czekanowskia; figures 12n and 12o), and numerous conifers, based 0.09 0.13 0.17 0.20 pb/ u207 235 0.0228 0.0232 0.0236 0.0240 0.0244 0.0248 148 150 156 152 154 mygatt-moore quarry ca-tims data mean 206/238 date: 152.18+/-0.29 95% conf. mswd = 0.56, probability = 0.64 figure 11. concordia plot single grain, chemical abrasion, isotope dilution, thermal ionization mass spectrometric u-pb analyses of zircon from the mygatt-moore quarry, showing approximate age of ~152.2 ma. figure 10. drill cores from the mygatt-moore quarry area. (a) view of medium light gray claystone with abundant carbonized plant fragments, characteristics of the main quarry layer, from the 17.7 m depth of drill hole mm-1. (b) view of medium light gray mudstone with abundant carbonized plant fragments from the 16.3 m depth of drill hole mm-2. (c) side view of core section showing dark spongy-textured dinosaur bone fragment drilled through at the 16.5 m depth of drill hole mm-2, approximately 95 m southwest of the current edge of the quarry excavation. all scales bars = 5 cm. 41 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 12. plant fossils from the mygatt-moore quarry. (a) isoetaceae?, mwc uncataloged. (b) equisetum sp., mwc uncataloged. (c) indet. fern?, mwc uncataloged. (d) ginkgo?, mwc uncataloged. (e) equisetum?, mwc uncataloged. (f) equisetum sp., isolated tuber, mwc uncataloged. (g) coniopteris sp., mwc 6000. (h) indeterminate plant, mwc uncataloged. (i) indet. conifer, mwc 2190. (j) brachyphyllum sp., mwc field number mm1205. (k) coniopteris sp., mwc 2155. (l) sphenopteris?, mwc field number mm1308. (m) pagiophyllum sp., mwc field number mm1212. (n–o) part and counterpart czekanowskia sp., mwc uncataloged. (p) matrix block showing aligned elongate plant fragments, mwc uncataloged. (q) matrix block showing aligned elongate plant fragments from southwest excavation area, mwc 5683. all scale bars = 1 cm, except p which is in cm and q which is 5 cm. 42 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 mostly on wood, cones, and short shoots (steinerocaulis, behuninia, conites, protocupressinoxylon, mesembrioxylon, xenoxylon), but some based on small branch sections (pagiophyllum, figure 12m; brachyphyllum, figure 12j). macrofossil plants reported here for the first time from the quarry include the ferns coniopteris (figures 12g and 12k) and sphenopteris? (figure 12l), plus a possible indeterminate isoetaceae (figure 12a) and the conifer pagiophyllum (figure 12m). these identifications are tentative, but the specimens are illustrated here to show the specimens found since the tidwell and others (1998) publication; only figure 12i (indet. conifer) was illustrated previously (tidwell and others, 1998). a palynological sample from the mygatt-moore quarry, collected and studied by hotton and baghai-riding (2010) along with seven other samples from the morrison formation from new mexico to wyoming, is unusual in having an abundance of lycopodiophytes (relatives of modern quillworts and clubmosses), ferns, and conifers. the conifers are mostly podocarpaceans, with a number of indeterminate bisaccate forms. it is interesting that at the nearby fruita paleontological area, the conifers identified by pollen are mostly cupressaceae. the abundance of fossilized wood in the mygatt-moore quarry (figure 13) was studied by tidwell and others (1998) and includes podocarpaceous wood species, which parallels the abundance of podocarpaceous pollen found in the palynological sample (hotton and baghai-riding, 2010), suggesting that the wood and pollen are of local origin and that podocarpaceous conifers grew rather close to the quarry deposit. several samples of abundant plant fragments in the mygatt-moore quarry (figures 12p and 12q) show a preferred alignment of long axes of elongate fragments. these have been noted particularly in the southwest part of the excavated quarry. this preferred alignment would seem to suggest orientation by gentle water action, perhaps on the edge of a pond; the plant material is small and light enough that its being aligned in such a way by unidirectional hydraulic transport seems unlikely. more likely, the water action may have been oscillatory. such alignment seems unlikely to result from trampling by large vertebrates, which would seem more likely to produce random orientations. trampling undoubtedly occurred at the site, however, and this plant fragment alignment simply indicates that a possibly hydrological influence was overprinting fragmentation figure 13. some of the fossilized wood from the mygatt-moore quarry. (a) smaller wood fragments, mwc uncataloged. (b) larger wood piece, mwc uncataloged. both scale bars = 10 cm. 43 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 and possible in situ churning of the plant material. taxa marked with an asterisk (*) are those reported from the mygatt-moore quarry for the first time here. brief descriptions of each of the specimens are provided using the terms and architectural characteristics of ellis and others (2009). specimens that were previously described in alternate papers have been appropriately referenced but not formally described here. plantae division lycopodiophyta class lycopodiopsida order isoetales family isoetaceae indet.?* single, partial, lanceolate leaf lamina specimen. greater than 4.5 cm in length, 0.5 cm in width at the base, and less than 0.2 cm approaching the apex. the base of the specimen is lobate with a wide, obtuse angle. one fragmentary plant specimen is believed to represent a quillwort (figure 12a), a group also identified from the site by spores. although rare at the site as macrofossils, if correctly identified, isoetaceaeans appear to be relatively abundant in the palyonologial record (hotton and baghai-riding, 2010). division sphenophyta order equisetales family equisetaceae equisetum sp. cf. laterale* complete specimens are unknown. internodes are long and cylindrical. the stem bulges at each node by approximately a millimeter. leaf organization is free and whorled or occurring in a sheath. leaves overlap nodes; course parallel; apex acute and convex. horsetails are represented by several macrofossil fragments (figures 12b, 12e, and 12f); as with most macrofossil plants at mygatt-moore, they are not particularly complete. the less typical specimens are similar to some assigned to equisetum from montezuma creek and dinosaur national monument and illustrated by ash and tidwell (1998) and foster (2007). division pteridophyta order filicales family dicksoniaceae coniopteris sp.* complete fronds are unknown and specimens at this site are fragmentary and represented by individual pinnae. the pinna is highly dissected into pinnules and appears to be odd-pinnately compound. the pinnules occur opposite along each pinna rachilla with a decurrent attachment and are obovate in shape. this fern is represented by four fragments (figures 12g and 12k). this is the first identification of fern macrofossils from the mygatt-moore quarry, although hotton and baghai-riding (2010) identified fern spores in their sample from the site. why ferns are rare as macrofossils may reflect their rarity in the original flora, but this is more likely a taphonomic artifact. order incertae sedis sphenopteris(?) cf. metzgerioides* complete fronds are unknown. it is unknown whether the frond is imparipinnate or paripinnate. the overall appearance is feathery and delicate with a robust and linear imparipinnate costa. shape and course are elongate, feathery and highly dissected. the costa attachment is decurrent and alternate. the pinnules are asymmetrical and deeply dissected. the apex of the pinnules are rounded. the base of the pinnule is indistinguishable from the costa and has a decurrent attachment. this may be a new fern taxon for the brushy basin member, identified based on this small piece from the mygatt-moore quarry (figure 12l) and a recently discovered, more complete specimen from southeastern utah (s. ash, university of new mexico, verbal communication, 2017). division cycadophyta order cycadales otozamites sp. this cycad is known from a single pinna illustrated and discussed by tidwell and others (1998). 44 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 cycadolepis(?) sp. cycadolepis is represented by a single scale (tidwell and others, 1998), but since then several more possible scale specimens of this cycad have been found. jensensispermum redmondii this cycad was represented by a single seed in tidwell and others (1998), and since then several more have been found at the site. division ginkgophyta order ginkgoales ginkgo(?) sp. a single leaf with similarities to a specimen from the montezuma creek locality, illustrated by ash and tidwell (1998), may represent ginkgo (figure 12d). it is possible that this specimen instead represents the conifer steinerocaulis radiatus (see below) or a single leaflet from the bennettitalean, anomozamites sp. order czekanowskiales czekanowskia turneri(?) the wet-adapted ginkgophyte czekanowskia is represented by a single fragmentary fossil (figures 12n and 12o) from the quarry. division coniferophyta brachyphyllum rechtenii this species was identified at mygatt-moore by tidwell and others (1998) based on individual leaves; the specimen illustrated here (figure 12j) is a partial branch that appears to belong to this species of conifer. unidentified conifer the counterpart of the specimen illustrated here (figure 12i) was also illustrated and discussed by tidwell and others (1998), who also noted the broad base of the leaves. this specimen remains unidentified although it was compared to elatides and geinitzia by tidwell and others (1998). behuninia provoensis this species is represented by a short-shoot from mygatt-moore (tidwell and others, 1998), and is known from several other sites in utah and wyoming. steinerocaulis radiatus already described from mygatt-moore by tidwell and others (1998), this conifer is represented by a number of similar specimens now. conites sp. two seed cones are known from the quarry, and they represent the largest known cones from the morrison formation (tidwell and others, 1998). pagiophyllum sp.* only fragmentary specimens are known. the rachis is very thick and robust. the pinna can be arranged opposite to spirally around the rachis. the pinna is diamond shaped and comes to an acute, needle-like point at the apex. the base attachment is sessile and the pinna show a rounded attachment to the rachis. both the base and the apex are rounded. this new conifer identification for the mygattmoore quarry (figure 12m) was previously known only from the belt area sites in montana (tidwell and others, 1998) and the temple canyon locality (gorman and others, 2008). protocupressinoxylon medlynii mesembrioxylon carterii xenoxylon moorei these three types of fossil wood from the morrison formation were described as new species by tidwell and others (1998). all three types of wood exhibited evidence of wood-rotting fungi that, in modern woods, most commonly function in moderately warm and wet conditions (either humidity or soil); in some cases mygatt-moore wood exhibited evidence of collapse, which happens in some modern woods during drying of previously soaked heartwood – this is most common in modern wetland species (tidwell and others, 1998). 45 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 metazoa phylum mollusca class gastropoda family vividparidae viviparus reesidei gastropods have been found in the “fish layer” and just below it, and well above the main bone layer. however, in 2013, several specimens of viviparus reesidei were identified at the bottom of the main quarry bone layer at its contact with the underlying light green claystone. the sample included approximately eight internal shell casts and fragments of shell casts (figure 14), and all were in nodular green claystone devoid of plant material. phylum chordata subphylum vertebrata class amphibia clade caudata caudata indet. amphibians are uncommon fossils in jurassic sediments and include only two groups: (1) the modern lissamphibians (anurans, caudatans and caecilians), and (2) the larger, brachyopoid temnospondyls. of these groups, only anurans and caudatans are found in the morrison formation. prior to the 2017 season, amphibians were unknown from the mygatt-moore quarry, but a new specimen of a caudatan has since been recovered at the site. the fragile limb bone (mwc 8649) was found isolated, high in the bone-bearing horizon, just a few centimeters below the level where a rhynchocephalian was found the same season (see below). it is complete, densely mineralized (no primary bone tissue remains visible in the specimen) and is preserved as a part (figure 15a) and counterpart. there is no ossification of the epiphyses, as is typical in living caudatans, and the diaphysis is asymmetrical with a deeply concave inflection directed toward the midline of the limb. the element is 8.75 mm in length and is much longer than the 2.2 mm radius of iridotriton from dinosaur national monument, which also has a straighter shaft than this specimen. mwc 8649 thus likely represents a different, potentially undescribed caudatan taxon. this element is strikingly similar to the morphology of the ulna in extant necturus and likely represents either a forelimb (radius or ulna) or hindlimb (tibia or fibula) element in this extinct taxon. unfortunately, as distal limb elements are not diagnostic at lower taxonomic levels, it is impossible to identify the genus to which this limb belongs or to erect a new genus based solely on this element. mwc 8649 is not referable to anura, based on its gross morphology. in anurans, the foreand hindlimb elements are much straighter and there is notable fusion between the radius and ulna, and likewise between the tibia and fibula. no fusion is evident in this specimen. additionally, the elongate tarsals (tibiale and fibulare) also tend to be fairly straight elements, and are inconsistent with the morphology seen in mwc 8649. class reptilia order rhynchocephalia rhynchocephalia indet.* in 2017, the first rhynchocephalian fossil was discovered at the mygatt-moore quarry after more than three figure 14. gastropod viviparus reesidei from the base of the mygatt-moore quarry, mwc field number mm1724. width of specimen approximately 13 mm. 46 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 15 caption on following page. 47 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 decades of excavations (figure 15b). the microfossil was found high in the bone-bearing horizon where the mudstone has a higher sand content than lower in the section. at this level, large complete vertebrate remains are not as abundant as they are lower. the element is a partial right dentary (mwc 8671) that is preserved in lingual view and contains five spade-shaped acrodont teeth, each bearing small denticles along the margins. the dentary measures 6.9 mm in length and is broken on both ends, suggesting that taphonomic factors such as trampling or predation/scavenging were at play prior to burial. although the dentary is too fragmentary to be diagnostic at lower taxonomic levels, mwc 8671 resembles a juvenile eilenodon with unworn teeth or possibly could be referred to the genus opisthias (m. jones, university of adelaide, written communication, 2017). reptilia indet. a small reptilian vertebral centrum from the mygatt-moore quarry (figured 15e to 15g) may belong to either a small ornithopod dinosaur or perhaps a goniopholidid neosuchian crocodylomorph, the latter of which do not have procoelous vertebrae (steel, 1973), making identification of small reptilian vertebral centra from the jurassic particularly difficult. this vertebra also has unfused neurocentral sutures so the neural arch and spine are missing. a fragment of a very hollow limb bone (figure 15j) was found in the quarry but is too incomplete to identify. based on the degree of hollowness, however, king and others (2006) suggested that this specimen may represent a pterosaur limb element. a third, very small, reptilian is represented by a single, tiny conical tooth, approximately 2 mm tall (figure 15h). this specimen was found by screen washing the matrix in a jacket containing a juvenile sauropod femur. the tooth has slightly wrinkled enamel on the lingual surface and is slightly laterally compressed just at the tip, though it is mostly conical. the tooth is larger than those of most lizard specimens from the morrison formation, and it is not of certain crocodylomorph affinity. it is generally similar to some teeth assigned to embryonic sauropods from the lower cretaceous of france (barrett and others, 2016), although even this assignment for the specimen would be tentative. small reptilian elements were found in 2005 in the soft green mudstone immediately below the main bone layer in the southwestern part of the quarry. these associated elements include three vertebrae, a fragmentary limb bone, a girdle bone, and several small fragments (figures 15i and 15k to 15l). the vertebrae measure 7 to 9 mm long and 4 to 7 mm in diameter; the centra have wide neural canals and laterally widely spaced pedicals with detached neural arches and exposed sutures. the girdle bone, possibly a scapula, is 30 mm long and has a somewhat blade-like shaft and a preserved “glenoid.” the limb bone is preserved in several elements, approximately 42 mm long total, and appears hollow to some degree. the material suggests either a relatively large rhynchocephalian or possibly a turtle; in the latter case, the girdle bone would be an ilium, not a scapula. clade crocodyliformes family goniopholididae goniopholididae indet. goniopholidids are represented by a single vertebra at the mygatt-moore quarry (mwc 1902). this vertebra is small but is very slightly procoelous and has the ventrally projecting hypapophysis typical of neosuchian figure 15 (figure on previous page). fossils of amphibian(?) and small reptiles from the mygatt-moore quarry. (a) small limb element of caudata(?) indet., possibly a fibula, mwc 8649. (b) lingual view of partial right dentary(?) of rhynchocephalian, possibly opisthias?, mwc 8671. (c) small vertebra of a goniopholidid neosuchian crocodyliform in anterior view, mwc 1902. (d) same in right lateral view. (e–g) small vertebra (possible neornithischian or goniopholidid) in dorsal, ventral and posterior(?) views, respectively, mwc 5634. (h) tiny reptilian tooth ~2 mm tall in mesial or distal view, mwc 5444 (image courtesy of andy heckert, appalachian state university). (i) partial limb elements of reptile?, part of mwc 5999 (associated with k and l). (j) small hollow limb element (pterosaur?), mwc 5728. (k–l) associated small bones of indeterminate reptile, mwc 5999. (k) three vertebrae in ventral view. (l) pectoral or pelvic girdle element (?). all scale bars = 1 cm, except a, b, and h which are 1 mm. 48 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 posterior cervical to anterior dorsal vertebrae (figures 15c and 15d). at least one small tooth of a goniopholidid crocodylomorph was found at the quarry as well, but no other such material has been found in nearly 30 years of excavations. clade dinosauria order saurischia suborder theropoda family ceratosauridae ceratosaurus nasicornis ceratosaurus is represented in the fauna by nine isolated shed teeth characterized by either ridged lingual enamel surfaces (in the case of mesial teeth of the dentary and premaxilla) or by large strongly laterally compressed, finely serrated distal teeth of the dentary and maxilla (figure 16a; gilmore, 1920; madsen, 1976; madsen and welles, 2000). the holotype of ceratosaurus (usnm 4735) is from the marsh-felch quarry in garden park, near cañon city, colorado (gilmore, 1920). ceratosaurus magnicornis was named from a partial skull and skeleton from the fruita paleontological area, and c. dentisulcatus was named from another partial skull and skeleton from the cleveland-lloyd dinosaur quarry (madsen and welles, 2000; sanders and smith, 2005). rauhut (2003) suggested that the two more recently named species of ceratosaurus from the morrison formation were not sufficiently differentiated from the type species, and carrano and sampson (2008) formally synonymized c. magnicornis and c. dentisulcatus with c. nasicornis. although this taxon is only identified from teeth out of the mygatt-moore quarry they are tentatively referred to ceratosaurus nasicornis, because there are no differences between the mygatt-moore material and the other specimens. ceratosaurus is relatively common in the area figure 16. theropod teeth from the mygatt-moore quarry, just a few of many. (a) anterior tooth of ceratosaurus, showing lingual ridges. (b) anterior tooth of allosaurus, note lack of lingual ridges. (c) laterally compressed and finely serrated maxilla or dentary tooth of ceratosaurus. (d) large but less laterally compressed and more coarsely serrated maxilla or dentary tooth of allosaurus. all scale bars = 1 cm. 49 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 17. skeletal material of allosaurus from the mygatt-moore quarry. (a) left dentary of juvenile in lingual view, mwc 5440. (b) right dentary fragment in labial view, mwc 5441, juvenile and associated with a, probably the same individual. (c) left lacrimal in lateral view, mwc 5309. (d–e) cervical vertebra, mwc 4010, in posterior and left lateral view. (f) dorsal vertebra in anterior view, mwc 2861. (g) right scapula in lateral view. (h) right ilium in lateral view. (i) left femur in anterior view. (j) metatarsals ii–iv. (k) manus claw, mwc 3730. all scale bars = 10 cm. 50 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 around mygatt-moore, as it has been found at three other sites nearby: (1) the twin juniper quarry, just 800 m south of mygatt-moore in rabbit valley, produced a partial skeleton of an articulated apatosaurus and a single, large, shed tooth of ceratosaurus, and (2) two sites in the nearby fruita paleontological area, just 25 km to the east. these fruita paleontological area specimens include the partial skeleton at the eriksen ceratosaur quarry (madsen and welles, 2000; sanders and smith, 2005) and isolated teeth found at the tom’s place quarry (j.r. foster, personal observation). clade tetanurae family allosauridae allosaurus fragilis bones of allosaurus are the most abundant vertebrate fossils at the mygatt-moore quarry (foster and others, 2007). this theropod is represented by more than 240 elements and at least 360 teeth in the quarry (figures 16b and 16d). represented elements include skull, girdle, and limb elements, with dorsal and caudal vertebrae particularly abundant (figure 17). the material is identified as allosaurus based on the presence of (1) a single lateral pneumatic fossa on the cervical centra (versus two in ceratosaurus), (2) absence of prespinal chonos on the dorsal vertebrae (versus presence in ceratosaurus), (3) tapering of neural spines of anteriorto mid-caudal vertebrae so that the distal end is narrower than the base in lateral view (“beveled cranial margin of the spine” in holtz and others, 2004; distal end and base same width in lateral view in ceratosaurus), (4) scapula with a less expanded proximal end than in ceratosaurus, and (5) tibia with the astragalus contact ridge on the antero-distal surface that rises well up the shaft (versus very low in less derived theropods). none of the theropod material out of the mygatt-moore quarry is referable to the megalosauridae or torvosaurus. teeth are identified as allosaurus based on the lack of lingual ridges on the anterior teeth and on the smaller size of the tooth crown, less lateral compression, and moderate-size serrations relative to ceratosaurus and torvosaurus (bakker and bir, 2004). there are several named species of allosaurus, and although few authors agree on which are valid (e.g., a. atrox and a. fragilis in paul, 1988; a. fragilis and a. maximus in smith, 1996, 1998), it is possible that only three species of allosaurids were present during morrison times: the stratigraphically older-ranging allosaurus n. sp. (chure, 2000), the more common (and more robust) a. fragilis (madsen,1976), and the rare and stratigraphically high saurophaganax maximus (chure, 1995; see rauhut, 2003, and holtz and others, 2004). dalman (2014) named a. lucasi based on material from southwestern colorado, although this taxon has not yet been addressed by others. carpenter (2010) documented significant variation in the allosaurus fragilis population from the cleveland-lloyd dinosaur quarry, which suggests that some of the variation used to define species of allosaurus in the morrison formation may be suspect. the material of the mygatt-moore quarry is not large and robust enough to be s. maximus but is more robust than allosaurus n. sp. the complete dorsal vertebrae from mygatt-moore lack the accessory horizontal processes along the bases of the neural spines seen in s. maximus (chure, 1995). although autapomorphies of allosaurus nov. sp. are missing from the mygatt-moore material due simply to lack of elemental overlap, the overall robustness of the vertebrae and girdle elements differentiates this material from that species. additionally, a left lacrimal of allosaurus from the mygatt-moore quarry preserves the pneumatic recesses at the base of the cornual process; the presence of these is one of the autapomorphies of a. fragilis (chure, 2000). the mygatt-moore quarry material is therefore referred to this species. suborder sauropoda family diplodocidae subfamily apatosaurinae genus apatosaurus a large number of the sauropod elements out of the mygatt-moore quarry may be referred to the diplodocid genus apatosaurus, with all regions of the skeleton present and cervical and caudal vertebrae particularly abundant (figure 18). the generic identification is based on the following characters: (1) short and robust cervical ribs, (2) cervical ribs set well below and lateral to the centrum, (3) anterior caudal vertebrae have “wing-like” 51 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 18. skeletal material of the apatosaurus from the mygatt-moore quarry. (a–b) cervical vertebra mwc 1916 in left lateral and ventral views. (c–d) cervical vertebra mwc 3829 in left lateral and anterior views. (e–f) cervical vertebra in left lateral and dorsal views. (g) posterior cervical vertebra in anterior view with associated dorsal rib and chevron, as preserved in quarry. (h) close-up of cervical rib of cervical vertebra. (i–j) caudal vertebra in anterior and right lateral views. (k) large left femur measuring 1876 mm overall length; robusticity index for this element puts it in a range of overlap between slender apatosaurus and robust diplodocus, so identification is tentative. (l) right tibia in posterior view. all scale bars = 10 cm except for k which is 25 cm. 52 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 caudal ribs (similar to diplodocus and barosaurus) but generally lack well-developed lateral pneumatic fossae (pleurocoels) in the centra, (4) coracoids with roughly quadrangular lateral profile, and (5) proximal condyles of the ulna sub-equal in length (upchurch and others, 2004). the material from the mygatt-moore quarry may be referred to apatosaurinae based on the following synapomorphies of tschopp and others (2015; numbers in parentheses refer to their synapomorphy identifiers): (1) cervical ribs project well beneath centrum so that the diapophysis/tuberculum is approximately the same length as the posterior process, (2) no paired pneumatic fossae on the ventral surface of anterior cervical vertebrae, and (4) anterior process of posterior cervical ribs is absent or reduced to a short bump-like process. because we treat the clade apatosaurinae of tschopp and others (2015; apatosaurus + brontosaurus) as consisting of several species but all within apatosaurus (foster and peterson, 2016), we identify the mygatt-moore material as belonging to apatosaurus. apatosaurus cf. louisae by upchurch and others (2004) criteria, the apatosaurus material from the mygatt-moore quarry may best be referred to the species a. cf. louisae, first identified from dinosaur national monument (gilmore, 1936). among the recognized species of morrison apatosaurs, a. ajax and a. parvus may be ruled out as candidate species for the mygatt-moore material due to the cervical vertebrae not having a width:height ratio of 1.5 or greater and to the scapular acromial ridge being at less than a 90-degree angle to the long axis of the scapular blade, respectively. foster (2015), however, noted that the interspecific variation in these characters among apatosaurines was slight and that, regardless, the small sample size left the characters potentially statistically insignificant. the mygatt-moore material is in some respects similar to a. excelsus by upchurch and others’ (2004) criteria but bears greater similarity to material of a. louisae. as in a. excelsus, the cervical ribs terminate anterior to the posterior end of the centrum; as in a. louisae, the proximal ends of the sacral ribs are on the anterior part of their respective centra, the anterior caudal centra are ventrally keeled (a “ventral midline ridge”), and the beveled glenoids of the scapulae face anteriorly, ventrally, and medially (upchurch and others, 2004). the mygatt-moore material is thus tentatively assigned to apatosaurus cf. louisae. identifying the mygatt-moore material to species based on synapomorphies identified by tschopp and others (2015) is more ambiguous. the quarry’s apatosaurine material includes few skull elements, but of four autapomorphies of a. ajax, three are in the skull; the fourth, “elliptical depression between the lateral spinal lamina of caudal neural spines and the postspinal lamina,” is true of most anterior caudal vertebrae from the site. (a possible juvenile apatosaur basioccipital-basal tubera, figures 21a and 21b, does not seem to match autapomorphy 3 for a. ajax.) however, there are 28 autapomorphies for a. louisae (tschopp and others, 2015) and of these the mygatt-moore material is clearly lacking characters 11 and 12 (the rest of them are unclear in the preserved material or cannot be confirmed because the material was found disarticulated). of seven autapomorphies of brontosaurus excelsus listed by tschopp and others (2015), most are ambiguous regarding the disarticulated mygatt-moore material, but character 1 does not match the type and referred material (some mygatt-moore cervical vertebrae do have median tubercles) and character 3 is highly variable within the mygatt-moore material. the mygatt-moore apatosaurine material does not match characters 5, 8, or 9 for b. parvus (tschopp and others, 2015; character 1 is true only of a few anterior cervical vertebrae, but not most cervicals among mygatt-moore material), and it matches character 5 but not character 2 for b. yahnahpin (tschopp and others, 2015). based on these results, it is difficult to assign the mygatt-moore material with confidence to any one apatosaurine species defined in tschopp and others (2015). most elements out of the quarry either lack the right data for most characters or their disarticulated condition prevents certainty when characters depend on skeletal position. most importantly, for many characters for which we can identify their states, the material is contradictory by matching some autapomorphic characters, but not matching others. this would not be 53 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 unexpected if there are multiple species in the sample, but we assume the mygatt-moore apatosaurine material represents a single species because most other large dinosaur quarries in the morrison formation contain a single species of each genus of sauropod (foster, 2003). we therefore are relying, until contradictory evidence is found, on the autapomorphies of upchurch and others (2004) and identify the mygatt-moore apatosaurine material as a. cf. louisae. discussion – some of the material assigned to apatosaurus consists of juvenile elements, including at least one cervical rib, a femur and a scapula (see sauropoda misc. section for figures). juvenile elements have been recognized from the mygatt-moore quarry for some time, and juvenile material in general is not especially rare in the morrison formation (foster, 2005a). a very large, complete femur from the quarry (1876 mm in length) may belong to apatosaurus (figure 18k) and represents the second longest complete femur ever found in the formation (after the type specimen of brachiosaurus fmnh 25107). in 2016, museums of western colorado crews collected the nearly complete skull of an apatosaurine (with cervicals 1–3 nearly in articulation) from mygatt-moore (mchugh and others, 2017); this specimen is still being prepared. subfamily diplodocinae diplodocinae indet. eight elements, all caudal vertebrae, may be referred to non-apatosaurine diplodocids based on the “winglike” caudal ribs, deep pleurocoels, and ventral excavations of the anterior caudal vertebrae. the mid-caudal vertebrae are elongate with small pleurocoels and groove-like ventral excavations (figure 19). these caudals are distinct from those of apatosaurus and are similar to diplodocus and barosaurus (hatcher 1901; mcintosh, 1990; ostrom and mcintosh, 1999). distinguishing caudals of diplodocus and barosaurus is rather difficult, as most of the differences between these two morrison diplodocines are in the cervical vertebrae and the number of dorsals (curtice, 1996; mcintosh, 2005). barosaurus may have mid-caudal centra that are relatively shorter and less deeply excavated ventrally than in diplodocus (mcintosh, 1990; foster, 1996), but quantifying these differences is difficult. the material from the mygatt-moore quarry is therefore identified only as diplodocinae indet. numerous isolated teeth of diplodocids are found in the quarry, and some of them may have belonged to diplodocus or barosaurus individuals, but figure 19. elements of diplodocinae indet. from the mygattmoore quarry. (a) right lateral view of an anterior caudal vertebra collected in 1989, mwc uncataloged. (b–c) mid-caudal vertebra in lateral and ventral view, mwc 3707. all scale bars = 10 cm. 54 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 the teeth cannot be distinguished from apatosaurus. clade macronaria family camarasauridae camarasaurus sp. cf. lentus camarasaurus sp., the most abundant dinosaur in the morrison formation overall (foster, 2003), is rare at the mygatt-moore quarry. it is represented by 23 bones, mostly caudal vertebrae, a braincase, two dorsal vertebrae, a scapula (distally expanded), three pelvic elements, several limb elements, a dentary fragment with teeth of a juvenile, and 35 shed teeth, mostly of adults, but with some juveniles represented. these elements are characteristic of camarasaurus within the morrison formation in having (1) anterior caudals with simple caudal ribs, no pleurocoels, rounded unexcavated ventral outlines, and short transversely expanded dorsal ends of the neural spines, (2) dorsal vertebrae with transversely expanded (“fan-shaped”) neural spines (figure 20), (3) particularly elongated metacarpals, (4) robust, spoon-shaped teeth, and (5) antero-posteriorly narrow, transversely elongate supratemporal fenestra, compared with diplodocids (osborn and mook, 1921; gilmore, 1925; berman and mcintosh, 1978; madsen and others, 1995). the two dorsals do not preserve the neurocentral sutures well enough to determine if they are the high-pedicel-bearing type of camarasaurus grandis or the low morphology of c. lentus (mcintosh, 1990), but all specimens are smaller than those assigned to c. supremus. the caudal neural spines appear to be gradually transversely expanded near the distal ends, in the manner of c. lentus and not like c. grandis or c. supremus (ikejiri, 2005). sauropoda misc. many specimens cannot be assigned to lower taxonomic levels but are clearly sauropod elements. most of these belong to adult sauropods, but a number of juveniles are represented, some of them very young. juvenile sauropod elements represented in the quarry include a diplodocid basioccipital (figures 21a to 21c), a camarasaurus dentary fragment (figure 21d), a possible apatosaurus cervical (figure 21e), a possible camarasaurus dorsal (figure 21g), and several apatosaurus elements (figures 21h to 21j). the sample represents at least three juvenile sauropods (mni). order ornithischia clade ankylosauria family polacanthidae mymoorapelta maysi the polacanthid ankylosaurian mymoorapelta is represented by more than 160 elements from all parts of the skeleton (figure 22; kirkland and hunt-foster, in preparation), making this genus the third most abundant vertebrate in the mygatt-moore quarry. particularly abundant are lateral spines, osteoderms, dorsal and caudal vertebrae. based on comparative size of elements, there are at least two individuals present; occurrence of some ankylosaurs osteoderms stratigraphically high within the quarry suggests that more than two individuals may in fact be represented. mymoorapelta was the first jurassic ankylosaur identified in north america (kirkland and carpenter, 1994). polacanthid ankyfigure 20. posterior dorsal vertebra of camarasaurus from the mygatt-moore quarry. (a) anterior view. (b) posterior view, mwc 2864. scale bars = 10 cm. 55 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 21. juvenile sauropod specimens from the mygatt-moore quarry. (a–c) basioccipital of a juvenile diplodocid in dorsal, ventral, and posterior view, mwc 7224. (d) fragment of right dentary of sub-adult camarasaurus with several teeth in lingual view, mwc 5009. (e–f) two cervical vertebrae of very young indeterminate sauropods in dorsal view, mwc 1917 and mwc 3828. (g) dorsal vertebra of indeterminate juvenile sauropod (possibly camarasaurus) in left lateral view, mwc 3630. (h) left cervical rib of young apatosaurus, mwc 1925. (i) left femur of juvenile apatosaurus in anterior view, mwc 5439. (j) left scapula of juvenile apatosaurus in lateral view, mwc 1848. all scale bars = 5 cm. 56 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 22. mymoorapelta elements from the mygatt-moore quarry. (a–b) braincase fragment in left lateral (internal) and right lateral views, mwc 5435. (c) cervical vertebra in anterior view, mwc 6737. (d) dorsal vertebra in right lateral view, mwc 1801. (e) anterior caudal vertebra in anterior view, mwc 1805. (f) two distal caudal vertebrae. (g) ulna, mwc 5643. (h) lateral spine, mwc 2678. (i) osteoderm. (j) lateral spine. all scale bars = 5 cm. 57 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 losaurs have since been found at a number of other sites in other areas of the morrison formation, including western colorado, utah, and wyoming (e.g., kirkland and others, 1998; tremaine and others, 2015). clade neornithischia othnielosaurus consors othnielosaurus was found in the quarry in 2008, the first new dinosaur taxon for the quarry in 18 years at the time. it is represented by a small maxilla or dentary fragment with three teeth in matrix (figure 23; mwc 5966). the teeth are tiny (0.9–1.4 mm in mesiodistal length), diamond-shaped, and contain two to four denticles each, characteristic of some othnielosaurus from other localities (galton, 1983, 2007) and perhaps distinct from other small neornithischians of the morrison formation such as drinker (bakker and others, 1990), and very distinct from dryosaurus (galton, 1981). the teeth also lack the cingula of stegosaurus and ankylosaurs. carpenter and galton (in press) suggest that othnielosaurus is a junior synonym of drinker nisti. dinosauria? indet. eggshell angustiprismatic morphotype a 43 x 34 mm fragment of what was estimated to have been an originally 10 cm diameter egg was found in the mygatt-moore quarry during the 1990s (figure 24). this calcitic eggshell is of an unnamed type that is considered a dinosauroid-prismatic basic type, and is also unique to the mygatt-moore quarry within the morrison formation (bray and hirsh, 1998). preserved taxa—“fish layer” phylum mollusca class gastropoda several indeterminate gastropods have been identified in the “fish layer” beds. these are not well preserved and are difficult to identify. phylum arthropoda clade crustacea class branchiopoda order diplostraca a number of “conchostracans” have been found in the claystone just below the “fish layer” (kirkland and carpenter, 1994) (figure 25). all are in light gray mudstone devoid of plant material. the term conchostracan has been abandoned after determination that the group was paraphyletic. the taxa formerly within “conchostraca” are now placed within several families within the diplostraca (martin and davis, 2001). figure 23. neornithischian jaw fragment with three teeth, mwc 5966, probably othnielosaurus. scale bar = 1 cm. figure 24. dinosaur egg in the mygatt-moore quarry, photo taken in the field. counterpart in upper left; egg still in situ in lower right below u.s. nickel, mwc 1900 and 1901. photo courtesy of jim kirkland, utah geological survey. 58 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 these bivalve crustaceans are capable of dormancy in dry habitats and are thus able to survive in ephemeral wetlands. class malacostraca order decapoda unnamed crayfish a nearly complete crayfish fossil was found in the “fish layer” during the 1990s, and this specimen has not yet been described or named. a second fragmentary crayfish specimen was discovered at the site in 2005 (figure 26i). phylum chordata superclass osteichthyes clade palaeoniscoidea morrolepis schaefferi several specimens of the coccolepid palaeoniscoid morrolepis have been found since the description of the type specimen by kirkland (1998) (figures 26b to 26d). some of these specimens show details of caudal and dorsal fin morphology better than the type, due to better preservation. another specimen preserves a skull, possibly of morrolepis (figure 26g). class actinopterygii subclass neopterygii order indet. “hulettia” hawesi the type specimen of “hulettia” hawesi is from the fruita paleontological area, but the species was soon after identified from the “fish layer” at the mygatt-moore quarry. there are now at least five specimens known from the “fish layer,” including a scale patch, two scale patches with partial caudal fins, an anterior third of a fish with the skull, and a nearly complete fish except for the skull (figure 26a). the latter two specimens have been found since 2005. this species probably belongs in a separate genus from hulettia, from the marine sundance formation (j. kirkland, utah geological survey, verbal communication, 2003), which is why the generic name is in quotations here. infraclass teleostei order leptolepiformes family leptolepidae cf. leptolepis a partially complete teleost fish was described by figure 25. diplostracan arthropods (“conchostracans”) from the morrison formation, including the upper part of the mygatt-moore quarry just below the “fish layer” in gray claystone matrix without plant material. (a) lioestheria sp., mwc 1854, from the wolny site near grand junction, colorado (lucas and kirkland, 1998). (b) unidentified diplostracan from upper levels of mygatt-moore, mwc 1862. (c) unidentified diplostracan from upper levels of mygatt-moore, mwc 1865. all scale bars = 5 mm. 59 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 26. species from the “fish layer” above the mygatt-moore quarry. (a) the possible semionotid fish “hulettia” hawesi, mwc 5564. (b) the coccolepid fish morrolepis schaefferi, holotype, mwc 440. (c–d) referred specimens of morrolepis, mwc 5306 and mwc 5305. (e) teleost cf. leptolepis, mwc 3722. (f) actinopterygii indet., mwc 5941. (g) skull of possible morrolepis, mwc 5307. (h) undescribed crayfish. (i) partial crayfish, mwc 5566. all scale bars = 1 cm. 60 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 kirkland (1998) out of the “fish layer” (figure 26e). this specimen is missing most of the skull and is the only confirmed teleost from the site. actinopterygii indet. several other specimens are known from the “fish layer,” most consisting of partial or isolated fins, and these generally cannot be identified to a lower taxonomic level. one partial fish skeleton, preserved in the left lateral view in its posterior portion and in oblique right-dorsal view in its anterior portion (figure 26f), is somewhat more complete but still awaits identification. taphonomy sample size over 30 years of work at the mygatt-moore quarry, several thousand bones have been collected and mapped. the quarry map contains nearly 2400 mapped elements, whereas the census of the data in the museums of western colorado collections consists of more than 900 elements. relative abundances of fossil vertebrates the sample of 897 identifiable bones indicates that the mygatt-moore quarry is dominated by sauropod dinosaurs and the theropod allosaurus fragilis (figure 27). by number of elements, the most abundant vertebrate taxa by far are indeterminate sauropods and apatosaurus cf. louisae, followed by allosaurus and then mymoorapelta (figure 27a). all other taxa are rare, including the otherwise common morrison sauropod camarasaurus. by minimum number of individuals, allosaurus is most abundant followed by apatosaurus and then indeterminate sauropods (figure 27b). allosaurus is also particularly abundant based on the tooth sample out of the quarry (figure 28). the tooth sample indicates a normal distribution of basal crown length of allosaurus teeth and a larger sample, contrary to what was found previously with a smaller example from the quarry by foster (2005b). preserved elements the total sample inventoried in the museums of western colorado, including taxonomically unidentifiable material, consisted of nearly 1900 elements (table 2). although fragmentary bones were most abundant, 0 50 100 150 200 250 300 n = 897 n u m b er o f i d en ti fie d e le m en ts apato sa uru s s p. allo sa uru s f ra gilis m ym oora pelta m aysi cam ara sa uru s s p. dip lo docin ae in det. cera to sa uru s n asic orn is oth nielosa uru s c onso rs gonio pholid id ae in det. reptil ia in det. a sauro poda in det. reptil ia in det. b a 0 1 2 3 4 5 6 7 8 adult sub-adult juvenile n = 24 m in im u m n u m b er o f i n d iv id u al s apato sa uru s s p. allo sa uru s f ra gilis m ym oora pelta m aysi cam ara sa uru s s p. dip lo docin ae in det. cera to sa uru s n asic orn is oth nielosa uru s c onso rs gonio pholid id ae in det. reptil ia in det. a sauro poda in det. reptil ia in det. b b figure 27. relative abundances of vertebrate taxa from the main quarry layer at the mygatt-moore quarry. (a) by number of identified elements. (b) by minimum number of individuals and with relative age designated. 61 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 teeth, vertebrae, and ribs were well represented (figure 29). girdle, limb, and dermal bones were about equally represented, and skull elements were comparatively rare. an analysis of the preserved elements by modified voorhies bone distribution groups (voorhies,1969; carpenter, 2013; see methods) for the sauropods and allosaurus subsamples of the inventoried collection (figure 30) indicates that the percentage representation of elements in highly transportable (group 1) to transport resistant (group 3) categories closely matches the representation of the elements in the respective (sauropod and allosaurus) skeletons. this suggests that the better-preserved, identifiable material from the quarry was not likely transported into the quarry area as an assemblage nor winnowed to its current condition with element number of identified specimens cranial braincases 4 dentaries 4 other skull elements 7 teeth 438 axial cervical vertebrae 56 cervical ribs (isolated) 5 dorsal vertebrae 75 dorsal ribs 86 rib fragments 192 sacra 6 caudal vertebrae 190 chevrons 54 appendicular scapulae 10 coracoids 6 humeri 10 radii 4 ulnae 3 carpals 3 metacarpals 15 ilia 5 pubes 7 ischia 9 femora 17 tibiae 14 fibulae 11 astragali 4 metatarsals 38 phalanges 56 unguals 22 other dermal spines 20 osteoderms 70 miscellaneous elements 25 fragments 869 total: 1897 bones 438 teeth table 2. mygatt-moore quarry bone sample by element. all taxa combined. 0 10 20 30 40 50 mygatt-moore quarry theropod teeth allosaurus n = 375 range: 3.0-26.2 st. dev.: 3.96 basal crown length (mm) n u m b er o f t ee th 5 10 15 20 25 mean: 13.6 0 1 2 3 4 5 ceratosaurus n = 9 range: 3.0-26.2 st. dev.: 3.96 theropoda indet. n = 35 range: 4.9-22.2 st. dev.: 5.25 basal crown length (mm) n u m b er o f t ee th 5 10 15 20 25 mean: 14.1 mean: 21.8 a b figure 28. size distributions of theropod dinosaur teeth from the mygatt-moore quarry, measured along the basal crown length. (a) allosaurus. (b) theropoda indet. plus ceratosaurus. 62 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 highly transportable elements washed elsewhere. rather, the voorhies element analysis results seem to indicate that at least the identifiable material was essentially autochthonous to the local quarry area (fragmentary and rounded; i.e., transported allochthonous material, however, is also abundant in the quarry). age distribution the main bone layer sample includes, by minimum number of individuals of dinosaurs and other vertebrates, four juveniles, one sub-adult, and 17 adult-sized animals (figure 31). such a distribution with many adults, fewest number of sub-adults, and moderate representation of juveniles is suggestive of an attritional morality assemblage with delayed burial (eberth and others, 2007, their figure 5.7). this argues against a non-selective catastrophic mortality for the animals preserved and indicates that the skeletal material was teeth 18.7% fragments 38.3% vertebrae 13.7% ribs and rib frags. 12.1%dermal spines/ osteoderms 3.8% phalanges/ unguals 3.3% hindlimb 3.6% pelvic 1.2% forelimb 1.5% scapulae/coracoids 0.7% chevrons 2.3% skull elements 0.6% total mygatt-moore quarry sample by element n = 2335 figure 29. frequency of bones from the mygatt-moore quarry sample by element. 0 10 20 30 40 50 60 0 10 20 30 40 50 60 group 1 group 2 group 3 group 1 group 2 group 3 pe rc en t o f s am p le pe rc en t o f s am p le voorhies groups sauropods voorhies groups allosaurus observed n = 322 observed n = 173 a b o b se rv ed ex p ec te d ex p ec te d ex p ec te d ex p ec te d ex p ec te d ex p ec te d o b se rv ed o b se rv ed o b se rv ed o b se rv ed o b se rv ed figure 30. voorhies group analysis for sauropod and allosaurus bones from the mygatt-moore quarry. group 1 is highly transportable, group 2 less so, and group 3 is least transportable. observed is the percentage of elements within each group actually preserved in the sample; expected is the percentage of elements in the respective skeletons. samples unusually high in group 1 elements would be expected to have been perhaps washed into the area, whereas a group 3-dominated sample suggests a lag deposit in which only the most transport-resistant elements are left in a winnowed assemblage. the fact that in both cases here, the observed distribution of elements is similar to what would be expected out of a skeleton suggests the bones are essentially autochthonous and are neither significantly transported in nor winnowed. 63 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 exposed for some time before burial, which is consistent with other taphonomic factors noted about the site (see below). bone distribution the nearly 2400 mapped bones from the mygattmoore quarry show a pattern of disarticulation and only slight association in rare instances (figure 32). of the entire mapped sample only eight bones are in articulation with at least one other one (three pairs of dorsal vertebrae and one pair of cervical vertebrae, all of apatosaurus; two of the three dorsal pairs appear to be from the same sub-adult individual). this ratio of articulated bones to the total number (0.00337) is lower than for any other major quarries of the morrison formation studied here (table 3). the almost totally disarticulated nature of the sample out of the mygatt-moore quarry has been one of its notable features since it was first worked. from the quarry map (figure 32) it is also apparent that the orientation and distribution of material in the quarry is random (see below); bones are scattered in all parts of the quarry, lightly in some areas but clustered in some others. the main bone layer is approximately 1 m thick and the occurrences of bones within this interval are concentrated near the basal 33 cm or so. more than half of the bones collected from the 2000–2013 seasons were found in that lower third of the deposit (figure 33). elements from the upper third accounted for only a little more than 15% of the sample. the vertical distribution of fossils in the quarry area was also illustrated qualitatively in sections by kirkland and carpenter (1994) and kirkland (2006). based on the number of mapped bones to mapped area, there appear to be approximately 4.9 mapped bones per square meter of the quarry. this density, however, is based on the bones large enough to map and record. because very small and fragmentary bones have been noted as common in the quarry, but have not historically been documented, an unexcavated square meter was selected from the eastern part of the quarry to excavate and collect everything found to record the density of material within this test area. this nearly cubic meter (m3) of matrix contained about 100 randomly distributed bones (figure 34); mostly these are small fragments, but the sample also included four theropod teeth. the results showed a relatively random orientation within the meter but concentrated in the lower portion. the fragments were mostly unidentifiable and small, with a mean volume of 6.78 cm3 and a maximum volume of about 47 cm3 (figure 35). the excavated m3 is thought to be typical of the deposit overall because it is from an area close to where large dinosaur bones have been excavated. it is from neither within the current excavation nor close to what appears to be the edge of the deposit to the east. the material was found within typical medium light-gray claystone containing abundant carbonized plant fragments. if the many small bone fragments randomly distributed within this 1 m3 indicate what is typical of the quarry, there may have been approximately 50,000 individual bone pieces within the about 500 m2 of the quarry excavated so far. extrapolated to the potential area of the quarry demonstrated by the drill coring (see above), the entire deposit may contain as many as 463,000 bones, based on the fully sampled single m3, and as many as 23,150 mappable bones, based on the density demonstrated by the quarry map (figure 0 5 10 15 20 juveniles sub-adults adults m in im u m n u m b er o f i n d iv id u al s n = 22 age profile figure 31. age profile of the vertebrates out of the mygattmoore quarry, discounting indeterminate reptiles. sample is high in adults, lower in juveniles, but is mostly missing mid-sized animals. 64 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 32. quarry map of mygatt-moore quarry main quarry layer, through the 2013 season. scale bars marked in meters. 65 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 32). the abundance of small fragmentary bones, along with larger better preserved bones and more complete dinosaur elements in the same deposit, may suggest two sources for the material. as mentioned above, the quarry map (figure 32) appears to show a random orientation of the bones at mygatt-moore. azimuth orientations of bones from the quarry, measured off the map and categorized as either bidirectional or unidirectional, suggest that indeed the orientation is random. neither bidirectional bones nor those that are unidirectional demonstrate any strongly preferred azimuth orientation (figure 36) such as would be expected if there were current influence on the material (toots, 1965). random orientations of bones as demonstrated by figure 36 suggest scattering by scavenging and other process other than hydraulic current influence. bone preservation and modification a large number of bones in the quarry are fairly well preserved and complete. most of the identifiable elements that have been collected over the years are nearly complete, with only moderate degradation by abrasion, corrosion, weathering, and breakage. among the bone modifications are green fractures that appear to have occurred when the bones were in or on the muddy matrix near the surface, well before lithification. examples of these breaks include splintered, broken sauropod ribs (figures 37a and 37b), a broken and displaced allosaurus metatarsal (figures 37e and 37f), and an allosaurus distal tibia broken off before burial. a random survey of a subsample of the total collections inventory (446 specimens, or about 23.5% of the bone collection) indicates that approximately 61.6% of bones have post-mortem, pre-burial breaks that in many cases probably resulted from trampling. only about 0.46% of the bones have pathologies (table 4). one of these includes a sauropod ulna with a slightly forked, distally-pointing bone spur along the shaft near the distal end of the element (mwc 5044). another common modification on bones is tooth marks left by carnivorous theropod dinosaurs. approximately 4.62% of the bones out of the quarry have some quarry state lithology number of mapped bones bones in articulation articulation ratio map reference mygatt-moore quarry co mudstone 2372 8 0.00337 this paper cleveland-lloyd quarry ut mudstone 6197 123 0.01984 miller and others (1996) carnegie quarry, dnm ut sandstone 2993 1848 0.61744 g. york; carpenter (2013) howe quarry wy siltstone 1668 644 0.38609 bird (1985) howe-stephens quarry wy mudstone 649 217 0.33436 ayer (1999) poison creek quarry wy mudstone 469 127 0.27079 erickson, unpublished (1984) dry mesa quarry co sandstone 416 33 0.07933 miller and others (1991) little houston quarry wy siltstone 255 65 0.25490 pagnac, unpublished (2014) table 3. articulation ratios for several larger quarries in the morrison formation. 0 100 200 300 400 500 600 high medium low 15.6% 26.1% 58.3% stratigraphic level within 1 m-thick bone layer number of bones collected n = 971 figure 33. stratigraphic distribution of vertebrate material within the main quarry layer showing concentration of most elements in the lower and middle thirds of the deposit. each level is approximately 33 cm thick. (there is no correlation between bone size or volume and level at which they occur; large bones have been found high in the deposit, and many small ones are found low.) 66 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 indication of tooth marks (table 4), which is perhaps not surprising given the more than 400 teeth of theropods that have been found in the deposit (98.3% of these teeth appear to be shed and were probably lost during scavenging, as only a few percent of the 419 teeth counted for this study had intact roots). these teeth are so abundant that they are often found in close association with bones of herbivores. one tooth was found in close proximity to the pleurocoel of an apatosaurus cervical vertebra (figure 37g), and in another case nine teeth were excavated in 2005 from around a single sauropod femur. among the distinctly tooth-marked bones from the quarry are an apatosaurus ischium (figure 37d), an apatosaurus pubis, and the type ilium of mymoorapelta (kirkland and carpenter, 1994). abrasion of bones was noted in about 24.5% of the bones surveyed. it was characterized commonly by single, small, shallow, and randomly oriented scratches on the bone surface in some cases, but most often by rounding of originally sharp edges of bones or broken elements of them, a common characteristic of transport modification. in some cases, abrasion was difficult to distinguish from corrosion. if a bone was not significantly broken otherwise, it was assumed that most wearing of edges was more likely due to corrosion than transport abrasion. the corrosion of bone from mygatt-moore was found to be concentrated on the edges of vertebral centra and on the ends of long bones such as limb elements and ribs (figure 37c), where cortical bone is thin and trabecular bone close to the surface. most limb boneshafts, for example, where cortical bone is thick, are unaffected by corrosion. the nature of this bone loss is confirmed as corrosion rather than abrasion by the documentation of thin and delicate spalled outer bone surfaces separated from trabecular bone in cross sections of several mygatt-moore bones collected and thin sectioned in the 1990s (j. kirkland, utah geological survey, verbal communication, 2013). weathering was noted in 25.2% of bones from the figure 34. x-, y-, and z-coordinate plot of 98 bone positions within the square-meter test pit in the mygatt-moore quarry, showing the density of distribution and the material’s concentration lower in the main quarry layer. this may be typical of most of the quarry. 67 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 sample and was generally characterized by cracking and decay of the outer surface of the bone. the degree of weathering (i.e., average weathering stage) of bones from the quarry, however, was generally low. the majority of bones surveyed were either unabraded (0) or only slightly so (1, figure 38a). a number of bones demonstrated an abrasion condition of 1 to 2 and none was at 3. similarly, most surveyed bones were unweathered (0) and none reached class 3. corrosion and breakage were much more common (figures 38b and 38d), and for both of these a number of bones were in classes 2 and 3. in contrast, a surveyed subsample of the collection from the cleveland-lloyd dinosaur quarry (at the natural history museum of utah) indicates much less modification in all four categories (figure 39); none of those elements reached class 3 (in case of weathering, class 1 was the highest recorded for any bone). although the degree of corrosion and breakage within the cleveland-lloyd subsample was higher than it was for abrasion and weathering, all were lower than for the mygatt-moore quarry subsample. the cleveland-lloyd dinosaur quarry sample was, however, museum-based, meaning that there was a collecting 0 10 20 30 40 50 60 mygatt-moore quarry test meter approximate bone volume (cubic centimeters) 10 20 30 40 50 n u m b er o f e le m en ts mean: 6.78 cc figure 35. histogram showing the size distribution of bone pieces collected from the test pit square-meter, measured by calculated bone volume. most pieces are small and fragmentary. figure 36. rose diagrams of bone azimuth orientations in the mygatt-moore quarry. (a) bidirectional plot for long bones with no heavier end. (b) unidirectional plot for long bones with a heavier end. both distributions show no strong preferred orientation. weak lower frequency in west-northwest–east-southeast orientation in both. 68 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 bias in favor of better preserved material from the start. the sample studied from the single test meter in the mygatt-moore quarry, interestingly, showed a different pattern from the collection inventory subsample. the test meter consisted of a full recording of every bone piece within a square meter, regardless of size or identification potential. because of that fact, we perhaps should not be surprised that the results for the test meter (figure 40) are quite different from the quarry collections subsample, and from the cleveland-lloyd dinosaur quarry subsample, for that matter. in fact, recent detailed work at the cleveland-lloyd quarry indicates a similar pattern in that most bones in the matrix (generally uncollected) are small and fragmentary (gates, 2005; peterson and others, 2017), and thus the collections sample surveyed here is skewed in favor of better preservation by collection bias. many bones at mygattmoore are abraded, more are corroded, a number are lightly weathered, and a large majority are broken quite badly, many rounded into a “bone pebble” shape. the test meter results may indicate that numerous allochthonous, fragmentary bones were transported into the site, although these were not necessarily transported long distances, nor out of the home ranges of the animals they belonged to (see behrensmeyer and rogers, 2017). histological slides of two very rounded bone “pebbles” (containing no outer bone surface), and of two bone fragments containing sections of the outer surface of the elements as well, indicate very different states of preservation at a microscopic scale. whereas at fine scale, some bone specimens appear nearly pristine (figure 41c), and others are very well preserved (figure 41b), others have some or a great number of micro-fractures in the bone cell structure (figures 41a and 41d). the range of preservation of these elements suggests that these apparently allochthonous bone fragments may come from several different source areas. especially interesting is that most rounded and abraded bone “pebble” specimens (figures 41c and 41d) are, respectively, the best and worst preserved pieces at a microscopic scale among the four that were thin sectioned; there was no way to predict this prior to sectioning. the nearly perfect preservation of the osteons in one specimen (figure 41c) and the heavily fractured nature of the same in another (figure 41d) suggest very different pre-burial (or possibly digenetic) histories of these elements and perhaps a complex set of origins for the “background” majority of small bone fragments that comprises the bone sample out of the quarry. dinosaur skin at least two patterns of dinosaur skin have been found in the mygatt-moore quarry (foster and hunt-foster, 2011), one identified as that of a sauropod consists of ~30 mm diameter hexagonal scales (figure 42a) and another consisting of much smaller polygonal scales (figures 42b and 42d) that belongs to an indeterminate dinosaur. these skin sections are preserved as either carbonized patches or similarly partially carbonized impressions of scales in matrix. in some cases, the mygatt-moore quarry collections (n=446; ~23.5%) cleveland-lloyd dinosaur quarry collections (n=282; ~4.6%) tooth marks 4.62% 0.73% pathologies 0.46% 1.82% juveniles 1.61% 6.72% sub-adults 1.16% 16.42% table 4. comparison of percentage occurrence of tooth marks, pathologies, juveniles, and subadults among museum collections from mygatt-moore and cleveland-lloyd dinosaur quarries. percentages after n values indicate approximately how much of full museum sample was surveyed for this study. 69 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 figure 37. examples of taphonomic modifications of bones from the mygatt-moore quarry. (a) sauropod rib with splintered fracture, mwc field number mm1260. (b) close up of splintered fracture in a. (c) corrosion of the end of a long bone, mwc 2882. (d) distal end of theropod tibia with fresh break of lower half of shaft; break surface was surrounded by matrix when found. (e) deeply gouged tooth marks on distal end of a sauropod ischium (arrow), mwc 4011. (f–g) fractured allosaurus metatarsal as found, mwc field number mm1398. (h) theropod tooth preserved in matrix almost in a pleurocoel of an apatosaurus cervical vertebra (upside down), showing the often close association of sauropod material and shed theropod teeth, mwc 5046. all scale bars = 10 cm. 70 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 skin pieces are folded over within the matrix and are separated by up to 1 cm of matrix. discussion paleoenvironmental setting the stratigraphic sections around rabbit valley suggest that the quarry area itself was surrounded by an alluvial system of poorly-drained to well-drained floodplains and sandy to very gravelly river channels. these channels may have been meandering to anastomosing (e.g., cooley and schmitt, 1998), as they are only traceable laterally for at most several hundred meters and are noticeably less laterally extensive than the channel sandstones of the underlying salt wash member. the sections also indicate a great degree of lateral variability within the brushy basin member strata as mudstone 0 50 100 150 200 250 300 350 0 1 2 3 classes n u m b er o f e le m en ts n = 441 abrasion mygatt-moore quarry collection 0 50 100 150 200 250 0 1 2 3 classes n u m b er o f e le m en ts n = 441 corrosion 0 50 100 150 200 250 300 350 0 1 2 3 classes n u m b er o f e le m en ts n = 441 weathering 0 50 100 150 200 0 1 2 3 classes n u m b er o f e le m en ts n = 443 breakage a b c d figure 38. bone modification of material from the mygatt-moore quarry collections inventory, by classes and type of modification. generally, the severity of modification goes up from classes 1 to 3; 0 = no modification. modification less than average for whole quarry due to this being a collected museum sample of better material. 71 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 bed, channel sandstone, and the “fish layer” beds were all documented to change or pinch out laterally within tens to hundreds of meters. the lateral variability is matched by almost universal changes in the vertical stacking patterns (figure 4). these vertical components document changing paleoenvironments over time, and within the quarry area itself we can document several changes. a transition from a permanent or ephemeral overbank topographic low into an ephemeral pond and then to a permanent but small (and probably shallow) lake is indicated by the lithologic variability of the quarry interval. later, a return to floodplain deposition with a nearby river represented by the channel sandstone at the camarasaur stop. the main quarry layer demonstrates features of a pond or pool. the lack of bones east of trench 5 and the reddish-colored mudstone at the quarry level at the 0 50 100 150 200 250 300 350 0 1 2 3 classes n u m b er o f e le m en ts n = 281 abrasion cleveland-lloyd quarry collection 0 50 100 150 200 250 0 1 2 3 classes n u m b er o f e le m en ts n = 281 corrosion 0 50 100 150 200 250 300 350 0 1 2 3 classes n u m b er o f e le m en ts n = 282 weathering 0 50 100 150 200 0 1 2 3 classes n u m b er o f e le m en ts n = 282 breakage a b c d figure 39. bone modification of material from the cleveland-lloyd dinosaur quarry collections survey, by classes and type of modification. generally, the severity of modification goes up from classes 1 to 3; 0 = no modification. modification less than average for whole quarry due to this being a collected museum sample of better material. 72 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 caudal draw stratigraphic section, the different character of trench 5 in both trench stratigraphy and thin sections, and the fact that drill holes mm-1 and mm-2 showed that the main quarry layer is thinner and slightly higher stratigraphically, all suggest that the quarry layer is a convex-bottomed, laterally restricted lens. the minimum area of the deposit is approximately 18,200 m2 and may be the deepest near the present northern part of the quarry (dimensions about 130 x 140 m, measured drill hole mm-1 to trench 5 and drill hole mm-2 to trench 4). although this is an approximately rectangular area, the actual deposit is probably roughly oval. paleoenvironment of the main quarry layer the base of the main quarry layer (with abundant plant debris and bone) appears to begin with deposition in a quiet, perennial pond, in that the very base of the 0 10 20 30 40 50 0 1 2 3 classes n u m b er o f e le m en ts n = 94 abrasion mygatt-moore quarry test meter a b 0 10 20 30 40 50 0 1 2 3 classes n u m b er o f e le m en ts n = 91 corrosion 0 5 10 15 20 25 30 35 40 0 1 2 3 classes n u m b er o f e le m en ts n = 71 weathering 0 10 20 30 40 50 60 70 80 0 1 2 3 classes n u m b er o f e le m en ts n = 98 breakagec d figure 40. bone modification of material from the mygatt-moore quarry test pit square-meter. generally, the severity of modification goes up from classes 1 to 3; 0 = no modification. 73 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 quarry (at the contact with the underlying light-green silty claystone) is a layer that contains several viviparid gastropods. the sediments that contain these gastropods, however, do not have any plant fragments. so, these gastropods occur in a basal layer or unit rather different than the actual main bone layer just a few centimeters higher in the section. the main quarry layer has some seemingly contradictory taphonomic characteristics. some characteristics suggest very wet conditions, possibly perennial standing water; others suggest wet or damp conditions but only ephemeral water. some evidence suggests the bones in the quarry are locally autochthonous, whereas other rounded and abraded elements seemingly indicate transport a moderate distance; it is unlikely even heavily modified bones were transported great distances or mixed into areas outside the ranges of the animals they derive from (behrensmeyer and rogers, 2017). although there is no clear evidence of miring of dinosaurs at the mygatt-moore quarry as there is at some other sites (e.g., howe quarry, farlow in bird, 1985), the abundance of theropod material might at first suggest a predator trap. even though the sample is dominated by just two of the present dinosaur taxa, the age profile figure 41. thin section micrographs of samples from bone fragments out of the mygatt-moore quarry. (a) relatively well preserved bone fragment, bg-1, nevertheless showing some micro-fracturing. (b) well preserved bone fragment, bg-2, showing fairly good preservation even at microscopic scales. (c) a “spongy” and almost rounded bone fragment, bp-1, that preserves nearly pristine osteons. (d) another poorly preserved, rounded bone fragment, bp-2, with highly micro-fractured osteons. all thin section micrograph views are approximately 2000 μm across. 74 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 suggests an attritional assemblage (see below). the mygatt-moore quarry “bone layer” may represent an ephemeral pond surrounded by conifers, similar to a wooded vernal pool, although there is a paucity of direct evidence to confirm this. amphibians, often characteristic of modern vernal pools may be very rare at the site due to taphonomic bias. the unit geometry (see above) and the mudstone (with some silt) lithology indicate that it is not a channel and is likely some type of overbank deposit. the presence of many bone fragments (almost a ‘background’ of small, nearly rounded fragments), calcium carbonate “pebbles,” and small clayballs indicates that a significant portion of the material was washed in, probably during flooding of a nearby channel. the range of micro-preservation characteristics in the histological bone samples, the appearance of two figure 42. dinosaur skin specimens from the mygatt-moore quarry. (a) sauropod skin patch with large hexagonal scales, mwc 6718. (b) patch of smaller scales belonging to an indeterminate dinosaur, mwc 1903. (c) pattern of very small tubercles, possibly superimposed on larger hexagonal pattern, mwc 5537. (d) another patch, partly carbonized but also preserved as impression; this specimen is also folded over on itself, discovered during the 2013 season, mwc field number mm1687. 75 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 distinct geochemistry signals in the calcium carbonate nodules, and the different colors and range of the silt and clay content in the clayballs, all in the lower main quarry layer, suggest that there were multiple sources for the allochthonous bones, “pebbles,” and clay clasts in the quarry. in addition, these sources mixed during a single phase of emplacement, though probably not a single episode. variation in clay clast, nodule, and bone characteristic does not appear to stratigraphically correlate. despite the “background” of small fragmentary bones (allochthonous), a significant number of nearly complete, well-preserved, but often rotted (corroded), bones are present in the main quarry layer, which probably represent an autochthonous component. small, elongate plant debris that is often aligned might indicate light (possibly oscillatory) water influence during deposition of the bone layer. the fact that the rose diagrams both show no preferred orientation suggests that whatever current there was, it was not a unidirectional current and not strong enough to align dinosaur skeletal material. the total lack of fish from the main quarry layer, the fact that not a single turtle element has ever been confirmed from the layer, and the extreme paucity of neosuchian material all suggest that permanent water was probably not present at the site at the time of deposition of the main bone layer. the restriction of “prosobranch” gastropods to layers above and below the main bone layer indicates that the quarry area was a locality of perennial water, but there is no direct evidence to indicate this with certainty from the bone layer itself. that “conchostracans” are present just below the “fish layer” suggests that the area may have been an ephemeral water hole at times, but again there is no direct evidence of these ephemeral pond inhabitants in the bone layer. actinopterygian fish are restricted to the overlying “fish layer” and indicate perennial water with certainty, but only well after dinosaur quarry (bone layer) deposition was over. in addition, the fact that other sites such as the small quarry (garden park), quarry 9 (como bluff), and the little houston quarry (black hills) seem to represent ponds, and also preserve abundant turtles, neosuchians, and fish (foster, 2001, 2003), suggests that if these aquatic and semi-aquatic taxa were present at the mygatt-moore quarry at the time, they would have been preserved. their absence may be due to a mechanical taphonomic bias that filtered out smaller animals (behrensmeyer and others, 1979), but this bias seems unlikely for taxa as robust as turtles. if these animals were present in large numbers at the mygatt-moore quarry, it would seem at least a few would be preserved. the abundance of plant material and carbonized plant fragments throughout the main quarry layer at the mygatt-moore quarry suggest that the soil was acidic. the high degree of corrosion (or “rot” along with resulting spalling) in the quarry is also probably indicative of acidic conditions in the quarry mud at the time, as bone preservation can deteriorate in lower-ph conditions (baxter, 2004). the effects of low ph on bones can sometimes be quite variable even between samples in the same soil, however (nicholson, 1996). preservation of dinosaur skin, not just as impressions in matrix, but more often as carbonization, suggests occasional dysoxia in the mud of the deposit, if not necessarily in any standing water that may have been present. dysoxic or anoxic conditions may have enhanced the frequency of plant preservation also (briggs, 1999). the presence of contemporary wood-rotting fungi in a number of the wood specimens from the quarry (tidwell and others, 1998) would also seem to suggest that the environmental setting was wet and possibly humid. like the cleveland-lloyd dinosaur quarry, the mygatt-moore quarry bone layer matrix is elevated in several elements such as pb, as, mn, k, and s (peterson and others, 2017). it is unknown if this phenomenon is due to original conditions in the deposit, diagenetic factors, or perhaps is a result of decomposition of carcasses at the site (peterson and others, 2017). as discussed above (matrix xrf analysis), it seems more likely that the elevation of several elements is the result of diagenetic processes at the mygatt-moore quarry. perhaps perennial water was present at the mygattmoore quarry during deposition of the bone layer, but were there environmental conditions that kept smaller aquatic and semi-aquatic animals out? the acidic soils and dysoxic conditions apparent at the site during deposition of the main quarry layer might have been 76 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 such factors to make the area unappealing to these taxa. however, the fact that turtles, crocodylians, and fish are abundantly preserved in the dark, carbonaceous (presumably somewhat acidic) mudstone and the (sometimes dysoxic; mummifying) sandstone beds of late cretaceous deposits suggest that such conditions were neither always avoided by the animals nor detrimental to their preservation. the paucity of neosuchians and the lack of fish and turtles from the main quarry layer may well be a paleobiological pattern then, and the possibility remains that the mud that now comprises the main quarry layer was only seasonally under water. the presence of trampled bones suggests that living animals frequented the deposit area, stepping on bone already in the mud during times of low (or no) water. this trampling is evidenced by many bones broken clearly after the element was in the mud but still exposed at or near the surface; unhealed, splintered fractures are relatively common and were documented in the field as having occurred prior to collection by matrix adjacent to broken surfaces. documented field evidence, such as vertical changes in mudstone bedding within the quarry and post-depositionally broken bones, also suggests that many bones were churned in the soft mud, again presumably by trampling. among observed elements that seem to have been preserved in soft wet mud were multiple bones preserved at an angle to horizontal, thin bones with fresh unabraded edges preserved in the matrix on edge, and at least one shed theropod tooth found on end (vertically) with the tip down in the matrix (no associated skull material). the frequent presence of carnivores and abundant scavenging in the quarry area are indicated by the abundance of allosaurus bones, the abundance of shed theropod teeth, and the moderate amount of tooth marks on bones. the extremely high rate of disarticulation and significant disassociation compared with other large quarries in the morrison formation may be due to trampling by dinosaurs (as with scatter of modern elephant bones by elephants; haynes and klimowicz, 2015) and scattering by scavenging theropods. some modern bones, however, can also be found scattered by lake waters, surface sheet flow, and possibly wind along lacustrine margins in autochthonous deposits (cobo-sánchez and others, 2014). therefore, a number of factors may have been acting in scattering the material at the mygatt-moore quarry. several of the plant types preserved in the quarry are associated with wet environments, including horsetails, czekanowskia (tidwell and others, 1998), and lycopodiophytes. lycopodiophytes today are common elements of some vernal pools (keeley, 1990) and, in some settings, live in slightly acidic water (wang and others, 2002). ferns and conifers are also particularly abundant, and plenty of ginkgoes and cycadophytes are also present. the fact that podocarpaceous wood and pollen are both found in the quarry (tidwell and others, 1998; hotton and baghai-riding, 2010) indicates that some of the abundant fossil wood at mygatt-moore is almost certainly local and therefore that the surrounding area was probably wooded. among the plants common at the mygatt-moore quarry, equisetum and ginkgoes are two of the better candidates for plant fodder for herbivorous dinosaurs, whereas podocarpaceae were probably less appealing (gee, 2010). vertebrate age profiles in hypothetical standing populations would have many juveniles and fewer adults, and non-selective catastrophic mortality would result in a similar profile (eberth and others, 2007). attritional mortality could result in an age profile with many juveniles and adults and fewer mid-age classes. rapid burial of such a profile would result in a similar distribution, whereas delayed burial would favor preservation of adult-size classes (although myers and storrs, 2007, noted that with sauropod remains, rate of burial may have less influence on preservation effects than with smaller taxa). still, delayed burial of an attritional assemblage may result in an age profile with few mid-sized animals, more juveniles, and an abundance of older animals (eberth and others, 2007) and this is what is observed at the mygatt-moore quarry. the extremely high degree of disarticulation of the material seen at the quarry (lowest measured articulation radio among large morrison sites) is also consistent with delayed burial (myers and fiorillo, 2009). despite the unusual abundance of two taxa (allosaurus and apatosaurus) in the quarry, the age profile seems to indicate an attritional assemblage with non-rapid burial. therefore, 77 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 the deposit does not appear to be the result of a catastrophic mortality of dinosaurs. the slow burial would seem support the existence of an ephemeral overbank pond, but the high abundance of just two taxa is harder to explain. among several scenarios, it is possible that the deposit built up over multiple environmental stresses (e.g., occasional droughts), with the high abundance of apatosaurus resulting from a population frequenting the water source repeatedly during times when the rest of the floodplain was drying out. that apparently-shed sauropod teeth (mostly diplodocidae but with a number of camarasaurids) are relatively abundant at the site suggests that in fact the animals were feeding nearby, and it is estimated that population densities on the morrison landscape would have allowed for a handful of individuals of each sauropod species per km2 (farlow and others, 2010). possibly, a regional apatosaur population tended to frequent the area seasonally, coincidentally when stresses on the herd were highest, while other sauropod taxa migrated through during other, less stressful times (j. kirkland, utah geological survey, verbal communication, 2013). there seems to be some evidence of regional migration among sauropods from the morrison (fricke and others, 2011). at times when the population was in the area it may have had higher densities of animals because the group was absent at other times, and because presumably at times when the apatosaurs were there, the other sauropods were away. an alternative hypothesis is that a local apatosaur population frequented the area yearround, preferring an environmental or dietary aspect of the surrounding area, to the general competitive exclusion of other sauropods. in this scenario, the attritional assemblage would also have been built up over time as the area was populated long-term by a high percentage of apatosaurus. although we were able to discern an attritional versus catastrophic origin for the bone assemblage, distinguishing between the two above scenarios to explain the abundance of apatosaurus relative to camarasaurus and diplodocinae indet., may be difficult. the facts that the macro-plant and pollenspore assemblages are thus far almost unique among plant sites in the morrison (hotton and baghai-riding, 2010), and that the mygatt-moore quarry is one of the only apatosaur-dominated sites in the formation, suggest that perhaps something about the flora of the local habitat was attractive to these particular sauropods. still, determining whether this attraction was seasonal or perennial may be impossible. comparison to other quarries cleveland-lloyd dinosaur quarry the major quarry to which the mygatt-moore quarry compares most closely is the cleveland-lloyd dinosaur quarry in the morrison formation of the san rafael swell of east-central utah (stokes, 1985; miller and others, 1996; bilbey, 1999; gates, 2005; peterson and others, 2017). similarities to the mygatt-moore quarry include mudstone matrix, many disarticulated bones, highly mixed arrangements of the bones, many allosaurus elements (mni = 49), and a relatively thin bone layer (richmond and morris, 1996; gates, 2005; hunt and others, 2006; foster and others, 2016). differences of cleveland-lloyd dinosaur quarry compared to mygatt-moore quarry include (1) lack of carbonized plant material in the mudstone, (2) higher degree of articulation, and (3) greater dominance by allosaurus primarily. additionally, as found in this study, the mygatt-moore quarry has a much higher percentage of shed carnivore teeth (versus rooted), has slightly more tooth marked bones, has more fragmented, weathered, abraded, and corroded bone, and has more allochthonous clasts and bone fragments. mygatt-moore quarry also demonstrates less evidence of hydraulic sorting and more random azimuth orientations of the bones as compared to the cleveland-lloyd dinosaur quarry (see gates, 2005). the cleveland-lloyd dinosaur quarry has only a single apatosaurus element (foster and peterson, 2016), whereas the mygatt-moore quarry has no elements clearly belonging to stegosaurus; the reasons for these taxa being rare or missing are unclear, as they are otherwise very common overall in the morrison formation. the mygatt-moore quarry also has a lower percentage of juveniles and sub-adults than does the cleveland-lloyd dinosaur quarry. 78 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 howe quarries the howe quarry (bird, 1985) and the howe-stephens quarry (ayer, 1999) are large, multi-taxic sites in the morrison formation of northern wyoming. both differ from the mygatt-moore quarry in that the matrix is a silty to slightly sandy mudstone with more direct evidence of fluvial influence (more so at howe-stephens). the howe quarry contains an abundance of diplodocine sauropod material relative to other taxa, and in this sense, it is similar to the mygatt-moore and cleveland-lloyd dinosaur quarries. the howe quarry also preserve a relative abundance of dinosaur skin (czerkas, 1992). little houston quarry the little houston quarry is in the thin morrison formation of the black hills in northeastern wyoming (foster and martin, 1994; foster, 2001). this quarry is in a laterally restricted, ribbon-like abandoned channel deposit with interbedded green claystone and laminated gray-green siltstone. articulation of dinosaur bones is moderate, density of the bone material is high, and microvertebrate material is very abundant, even in among the sauropod bones in some levels. this site preserves a diversity of large dinosaurs and especially small reptiles, mammals, and fish, along with an abundance of turtles and neosuchian crocodyliforms. this preservation mode is common in the northern and eastern parts of the morrison formation (foster and mcmullen, 2017) and is characteristic of the small quarry and quarry 9 as well (foster, 2001, 2003). this mode is taphonomically very different from the mygatt-moore and cleveland-lloyd mode of preservation. carnegie quarry, dinosaur national monument the carnegie quarry at dinosaur national monument in utah is a good representative of the taphonomic mode of preservation so common among large dinosaur quarries in the morrison formation in that it occurs in a thick, pebbly sandstone (lawton, 1977; carpenter, 2013). the site preserves a diversity of dinosaurs, most of the reasonably common ones in the formation, in fact, and in high numbers. there are thousands of bones in this quarry and probably more than 120 individuals represented. the degree of articulation is the highest measured for this study. sedimentologically and taphonomically channel sandstone deposits like the carnegie quarry are very different from large sites in mudstone like mygatt-moore and cleveland-lloyd dinosaur quarries. preserved diversity by site one interesting aspect of the preservation of dinosaur taxa at some of the large quarries in the morrison formation is the variation in the relative abundance of the most common dinosaur taxa. for example, within the morrison overall, the most abundant dinosaurs are, in descending order, camarasaurus, allosaurus, stegosaurus, apatosaurus, and diplodocus. each of these is slightly less abundant than the next highest in rank abundance. if we look at large quarries in mudstone and siltstones (fine-grained sites), we notice that (1) this pattern does not hold up and that the relative abundances among these five taxa are highly uneven, with some quarries missing one genus entirely, (2) one or two taxa often dominate, with the other taxa rare, and (3) the dominant taxon or taxa are variable (figure 43; foster and others, 2016). although the mygatt-moore quarry has a number of allosaurus individuals, it is dominated by apatosaurus by number of identified elements (as opposed to mni). cleveland-lloyd dinosaur quarry is even more dramatically dominated by allosaurus, and the howe quarry is dominated by diplodocines. the pattern demonstrated by large quarries in channel sandstones, however, more closely reflects the pattern in the morrison formation overall (figure 43). all of the “big five” dinosaur genera are present at all sites, relative abundances are much more even, and no site is dominated by one taxon to the degree that the fine-grained sites are. these different relative abundances probably reflect the relative size of the sampled geographic area and the amount of time averaging within each deposit. the geographic area from which large morrison river channels were drawing skeletons could well have been rather extensive, particularly considering the possible areas of the individual drainage basins on a relatively 79 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 05010 0 15 0 20 0 minimum number of individuals cam ara sa uru s allo sa uru s stegosa uru s apato sa uru s diplodocus m o rr is o n f o rm at io n o ve ra ll 012345678 cam ara sa uru s allo sa uru s stegosa uru s apato sa uru s dip lo docin ae m yg at tm o o re q u ar ry 01020304050 cam ara sa uru s allo sa uru s stegosa uru s apato sa uru s dip lo docin ae c le ve la n d -l lo yd q u ar ry 024681012 cam ara sa uru s allo sa uru s stegosa uru s apato sa uru s dip lo docin ae h o w e q u ar ry minimum number of individuals 051015202530 minimum number of individuals cam ara sa uru s allo sa uru s stegosa uru s apato sa uru s diplodocus c ar n eg ie q u ar ry , d in o n at ’l m o n 0. 0 0. 5 1. 0 1. 5 2. 0 2. 5 3. 0 3. 5 4. 0 cam ara sa uru s allo sa uru s stegosa uru s apato sa uru s dip lo docin ae m ar sh -f el ch q u ar ry 024681012 cam ara sa uru s allo sa uru s stegosa uru s apato sa uru s dip lo docin ae b o n e c ab in q u ar ry 012345 cam ara sa uru s allo sa uru s stegosa uru s apato sa uru s dip lo docin ae d ry m es a q u ar ry minimum number of individuals m u d st o n e/ si lt st o n e si te s sa n d st o n e si te s o v er a ll p a t te r n fi gu re 4 3. c om pa ris on o f r el at iv e a bu nd an ce (b y m n i) o f t he fi ve m os t c om m on d in os au rs o f t he m or ris on f or m at io n at ea ch o f t hr ee fi ne -g ra in ed (m ud st on e/ sil ts to ne ) f ac ie s q ua rr ie s a nd e ac h of fo ur sa nd st on e fa ci es q ua rr ie s, w ith c om pa ris on to th e m or ris on f or m at io n ov er al l s am pl e. re pre se nt at io n an d re la tiv e ab un da nc es o f t ax a in sa nd st on e fa ci es a re m or e re pr es en ta tiv e of th e fo rm at io n ov er al l t ha n th e oft en v er y un ev en re pr ese nt at io n an d re la tiv e ab un da nc e in la rg e m ud st on e fa ci es si te s. 80 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 flat floodplain at the time (behrensmeyer, 1982). although sauropod bones and carcasses probably would not have been transported great distances in recognizable form (myers and storrs, 2007), it would not be surprising if the area from which a dinosaur deposit in a channel sandstone was drawn was in fact far broader than that of a local pond or overbank topographic low. there is variation in the amount of time represented by different sites within the fine-grained site subsample, with the mygatt-moore quarry perhaps representing an attritional and possibly more time-averaged sample than cleveland-lloyd dinosaur quarry, for example. the amount of time-averaging in an attritional mudstone site was probably still far less than that of a channel sandstone deposit like the carnegie quarry, which appears to include several lag beds superimposed in a thickness of several meters. both mygatt-moore and cleveland-lloyd dinosaur quarries are much thinner beds of about 1 m thickness. this pattern of uneven relative abundances at mudstone sites and more diverse and evenly represented taxa at sandstone sites (figure 43) suggests that large quarries of dinosaur bones in the morrison formation fall into at least two major taphonomic modes. many sites in the morrison consist of paucispecific deposits of a few individuals and up to a few hundred bones, sometimes also dominated by one or a few taxa, in poorly drained floodplain mudstones (e.g., tucker, 2011). very large deposits of multiple hundreds or thousands of bones are often either (1) diverse sandstone quarries with relatively even abundance distributions among the most common dinosaurs, or (2) less diverse fine-grained (mudstone or siltstone) quarries with sometimes wildly uneven abundance distributions among the most common dinosaurs (some missing entirely). there are undoubtedly a number of the former deposits in the morrison formation channel sandstone beds with many bones and many taxa (e.g., carnegie quarry, dry mesa quarry), and undeveloped examples can be seen in the morrison formation at least in colorado and utah figure 44. reconstruction of the mygatt-moore quarry, 152 million years ago. an allosaurus feeds on the carcass of an apatosaurus. shed teeth and tooth marks of carnivores suggest that theropod dinosaurs regularly concentrated their feeding on the large muscles of the hind limbs and pelvis. ©todd marshall 81 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 (e.g., split rock, mill canyon). perhaps there are yet undiscovered deposits of the latter kind, large potential quarries in mudstone that sampled a camarasaurusor ankylosaur-dominated fauna, for example. these sites have the potential to tell us a little more about the vagaries of preservation and dinosaur paleobiology than do more time-averaged and geographically blended sites. conclusions the mygatt-moore quarry is late jurassic in age (152.18 +/-0.29 ma), very close to the kimmeridgian-tithonian boundary. the mygatt-moore quarry is in a claystone that has slightly higher (and coarser) silt content than the surrounding claystone beds. claystone beds that are lateral to the quarry deposit are different in color and silt content and, in some cases, include sandstone beds near quarry level away from the site. the bones were probably deposited on a topographically low part of the floodplain, possibly within 800 to 1000 m of a river channel to the east (figure 4). the quarry was at least about 130 m by 140 m across, possibly an oval shape. the area may be as much as 18,200 m2 as currently known from excavations, trenches, and drill cores. the thickest part of the quarry is in the northern area of the current excavation; it thins to the east, southwest, and northwest. the base slopes upward in those latter directions as well, so that the bone layer is somewhat lens-shaped (convex down). the quarry preserves both autochthonous and allochthonous bone components. there is a group of mostly fragmented and almost rounded bones that was probably washed in early in the deposit’s history from a significant distance and a second group of more intact bones that were sourced from skeletons of animals that died near or at the point of deposit itself. as a probably perennially damp to seasonally flooded low area of the floodplain, the quarry area was very likely occupied and immediately surrounded by a greater abundance of conifers, horsetails, and, to a lesser degree, ferns than the next most outlying areas. abundant plant material in the quarry bone layer matrix was likely preserved due to acidic soil conditions, which are conductive to plant preservation. relatively low ph during deposition of the bone deposit seems likely, although at the earliest stages when the “pebble layer” was deposited, ph may have been higher. dampness from high moisture content in conifer wood in the quarry area led to rotting of wood by fungi. preservation of carbonized skin of dinosaurs (and plant material) suggests the mud of the deposit may have been dysoxic to anoxic. the calcium carbonate nodules that are abundant near the base of the bone layer appear to be washed in from at least two different source areas, but how far they were transported is difficult to assess. they formed in place as incipient soil nodules but were then reworked and deposited at the quarry after transport. their origin could be from a different area than the rock clasts and clayballs in the matrix of the main bone layer. much of the initial input to the bone layer (basal portion) thus appears to have been from elsewhere. the abundance of allosaurus bones and teeth is almost certainly a result of a combination of environmental stresses on the animal (drought?) causing slightly higher mortality of the population and increase in the number of individuals in the area, probably drawn in to scavenge on carcasses of both herbivorous and carnivorous dinosaurs (figure 44). although the abundance of shed teeth and tooth-marked bone clearly indicates scavenging, there is no direct evidence of predation occurring at the site. the abundance of apatosaurus appears to be from attritional mortality of a resident population of animals that frequented the area either year-round or seasonally. if these animals were around all year, it may have been due to an affinity for the mygatt-moore quarry area’s unique mix of plant types. other sauropods like camarasaurus were probably competitively excluded or simply did not like the fodder in the area and so would be preserved less frequently. although it is possible that acidity or oxygen-poor conditions excluded small aquatic taxa or caused them not to be preserved, this is not the case at other, very wet sites in the morrison formation (e.g., little houston, quarry 9). we believe the near total lack of aquatic and semi-aquatic animals represents their actual rarity during deposition of the deposit due to infrequent (possibly only seasonal) presence of standing water at 82 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 the site. the extremely high degree of disarticulation of bones in the quarry appears to be a result of scavenging of carcasses by predators, trampling and churning of the bones in mud by living animals, and relatively long exposure before the bones were locked in the sediment and fully buried. still, the exposure time was not long enough for there to be significant weathering of the bone material. acknowledgments we first need to thank the mygatt and moore families for their discovery and reporting of the site in 1981 and their early work at the site. the current research project was made possible by a grant from the national landscape conservation system in 2010. past funding for work at the mygatt-moore quarry, and on its collections, came from the david b. jones foundation, chuck safris, dinamation international society, and the museums of western colorado. thanks to ken carpenter and bucky gates for critical reviews of the manuscript. lance eriksen started working on the quarry for the museums of western colorado and was followed by curators (in order) harley armstrong, brooks britt, rod scheetz, john r. foster (lead author), and julia b. mchugh (co-author). harley armstrong in particular has been a continuing encyclopedia of archival information about the quarry. jim kirkland worked the site for dinamation international society for years and has been an invaluable resource about the geology and paleontology of the site, particularly about specimens collected long ago that we eventually relocated in the collections during the inventory. volunteers from the museums of western colorado have been the backbone of field and lab work for the site for 30+ years and are probably too numerous to name, but we will try to cover as many as we can: mike perry, dorothy stewart, kay fredette, bonnie carter, walt williams, ray bley, don boden, darrell bay, tom lawrence, tom schroer, dale jones, dorothy stewart, dick peirce, bob whitehorne, gary spever, ken stadtman, dee hall, nancy colaizzi, ralph nash, larry marshall, lyn farber, norm cyphers, bill and ginger mitchell, john doyle, marty doyle, edie mangano, gary anderson, marge and walt averett, mel moyer, maury jean and gordon peterson, dave wolny, grace brown, gaylord headrick, fred savage, charlie neill, george moorehead, bob smith, carter burnham, and many others. museums of western colorado staff that have worked frequently at the site over the years include don chaffin, mike perry, don kerven, josh smith, vaia barkas, lorin king, alex morrow, zach cooper, krista brundridge, jacob gottlieb, nehali dave, lucia herrero, kelsie abrams, tom temme, rob gay, chris racay, and mitch lukens. dinamation interns from the past years include matt bonnan, jason head, and jonathan weinbaum. thanks also to the thousands of dig participants of the museum of western colorado and dinamation paleontology expedition programs of the past 25 years or so; many of the most interesting discoveries in the quarry were made by these folks. the grand junction field office of the bureau of land management has been critical to the research at the mygatt-moore quarry and museums of western colorado research at the site has been conducted under paleontological resources use permits c-60150a and coc75354; liz mcreynolds, nikki grant-hoffman, scott gerwe, harley armstrong, katie stevens, collin ewing, bruce fowler, greg gnesios, and wade johnson have all been particularly helpful. robert bakker and jack mcintosh provided expertise and advice early in the operation of the quarry. the city of fruita department of public works and john mcbride have been generous in assisting with removal and shifting of overburden and with lifting out large field jackets. rick charlesworth helped assemble much improved shade tents in 2012. special thanks to associated builders and contractors for significant overburden removal in 2006 that has made work at the quarry safer and easier over the past 12 years. harold bollan led preparation on many of the dinamation-collected specimens, with help from staff and volunteers such as dave and marilyn younie, marlies aeberlic, lee campbell, bob marsh, kim clark, bob gabbert, robin prunty, roxie mobley, marilyn sokolosky, duane and pat hogue, rick adleman, sandy and bill hood, pat and lee mitchell, bob waters, judy bay, 83 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 phyllis bollan, chris mays, chris mays, jr., and russell bucher. rex cole (colorado mesa university) and jane baer and randy irmis (university of utah) provided microscope access, micrograph assistance, and image rescue. study of the cleveland-lloyd dinosaur quarry material at the natural history museum of utah (nhmu) was facilitated by randy irmis and carrie levitt-bussian. assistance with data collection at the nhmu courtesy of ruby foster. jonathan cooley (colorado mesa university) has worked at the mygatt-moore quarry for many years in cooperation with museum crews, and two of his young crew members found the (so far) only othnielosaurus specimen. kay fredette loaned the 1987 field photos in figures 2c and 2e. mike perry assisted in measuring the stratigraphic sections. bruce erickson (science museum of minnesota) and darrin pagnac (south dakota school of mines and technology) provided research quarry maps of the poison creek and little houston sites, respectively. san juan drilling did the drill cores. ben miller helped map the quarry area trenches and drill holes with the fixed-wing drone. andy heckert (appalachian state university) shot the 2 mm tooth from the mygatt-moore quarry on an sem. jim kirkland (utah geological survey) provided the photo of the egg in the field. and todd marshall painted the allosaurus feeding scene. references armstrong, h.j., averett, w.r., averett, m.e., mc reynolds, e.s., and wolny, d.g., 1987, mid-mesozoic paleontology of the rabbit valley area, western colorado, in averett, w.r., editor, paleontology and geology of the dinosaur triangle: museums of western colorado guidebook for 1987 field trip, september 18–20, 1987, p. 37–43. armstrong, h.j., and mcreynolds, e.s., 1987, stratigraphic correlation of dinosaur quarries near grand junction, colorado, in averett, w.r., editor, paleontology and geology of the dinosaur triangle: museums of western colorado guidebook for 1987 field trip, september 18–20, 1987, p. 103–106. armstrong, h.j., and perry, m.l., 1985, a century of dinosaurs from the grand 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synthesis: sedimentary geology, v. 167, p. 302–355. upchurch, p., tomida, y., and barrett, p.m., 2004, a new specimen of apatosaurus ajax (sauropoda: diplodocidae) from the morrison formation (upper jurassic) of wyoming, usa: national science museum (tokyo) monographs, no. 26, p. 1–108. vijver, m.g., van gestel, c.a.m., lanno, r.p., van straalen, n.m., and peijnenberg, w.j.g.m., 2004, internal metal sequestration and its ecotoxicological relevance—a review: environmental science and technology, v. 38, (18):47054712 doi 10.1021/ es040354g. voorhies, m.r., 1969, taphonomy and population dynamics of an early pliocene vertebrate fauna, knox county, nebraska: university of wyoming contributions to geology, special paper no. 1, 69 p. wang, q-f., xing, l., taylor, w.c., and he, z-r., 2002, isoetes yunguiensis (isotaceae), a new basic diploid quillwort from china: novon, v. 12, p. 587–591. yen, t-c., and reeside, j.b., 1952, molluscan fauna of the morrison formation: u.s. geological survey professional paper 233-b, p. 21–51. young, r.g., 1960, dakota group of colorado plateau: american association of petroleum geologists bulletin, v. 44, no. 2, p. 156–194. 90 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 appendix a – geologic thin sections descriptions of hand samples and thin sections made from them. specimens numbered within each trench from stratigraphically lowest upward. trench 1 #5 – clay (90–95%) with black mineral or organic carbon laminations; 5–10% angular to subrounded quartz silt; less silt and smaller grains than main quarry layer; “fish layer.” #4 – clay (80%) and silt to fine sand (20%) that is sub-angular to subrounded and mostly quartz; few clayballs and mostly without silt; some carbonized plant fragments. #3 – clay (80–85%) and silt to fine sand (15–20%) that is sub-angular to subrounded and mostly quartz; angular to sub-angular clayball clasts of various colors, some purely clay, some with minor amounts of silt grains within them; many carbonized plant fragments; “main bone layer.” #2 – clay (80–85%) and silt to fine sand (15–20%) angular to subrounded; silt grains mostly quartz but with at least one plagioclase feldspar. #1 – clay and mostly angular to some rounded silt, mostly quartz with a few non-quartz, non-feldspar silt grains; tiny amounts of detrital micas; 85–90% clay and about 10–15% silt. trench 2 #5 – clay (90–95%) with black mineral laminations; 5–10% angular to subrounded quartz silt; less silt and smaller grains than main quarry layer; “fish layer.” #4 – clay (95%) and silt to fine sand (5%) that is sub-angular to subrounded and mostly quartz; few clayballs and mostly without silt; some carbonized plant fragments and at least one small plant stem or woody plant fragment. #3 – clay (95%) and silt to fine sand (5%) that is sub-angular to subrounded and mostly quartz; no clayballs; some carbonized plant fragments. #2 – clay (85–90%) and silt to fine sand (10–15%) sub-angular to subrounded; silt grains mostly quartz but with at least one plagioclase feldspar; rounded to sub-angular clayballs of various colors to 9 mm diameter, some with and some without internal silt grains; many carbonized plant fragments and one small wood fragment; “main bone layer.” #1 – clay and mostly sub-angular to subrounded silt, mostly quartz; 80–90% clay and about 10–20% silt, no clayballs. trench 3 #5 – clay (90–95%) with black mineral laminations; 5–10% angular to subrounded quartz silt; less silt and smaller grains than main quarry layer; “fish layer.” #4 – clay (95%) and silt to fine sand (5%) that is angular to subrounded and mostly quartz with at least one plagioclase feldspar; some light hematite mottling. #3 – clay (90–95%) and silt to fine sand (5–10%) that is sub-angular to subrounded and mostly quartz; no clayballs; some carbonized plant fragments. #2 – clay (90–95%) and silt to fine sand (5–10%) angular to subrounded; silt grains mostly quartz and minor amounts of plagioclase feldspar; carbonized plant fragments; one bone fragment. #1 – clay (90–95%) and silt to fine sand (5–10%), angular to subrounded; silt grains quartz and minor amounts of plagioclase feldspar; abundant carbonized plant fragments; some clayballs; “main bone layer.” 91 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 trench 4 #5 – clay (90–95%) and silt to fine sand (5–10%); angular to subrounded quartz and minor amounts of rock fragments as silt grains; mottled but no laminations; “fish layer.” #4 – clay (95%) and silt to fine sand (5%) that is angular to subrounded and mostly quartz with minor plagioclase feldspar grains; single carbonized plant fragment; mottled; no clayballs. #3 – clay (95%) and silt to fine sand (5%) that is angular to rounded and mostly quartz; no clayballs; very rare carbonized plant fragments. #2 – clay (90–95%) and silt to fine sand (5–10%) angular to rounded; silt grains mostly quartz; some carbonized plant fragments; one clayball; “main bone layer.” #1 – clay (85–90%) and silt to fine sand (10–15%), angular to subrounded; silt grains quartz and minor amounts plagioclase feldspar; no plant material; no clayballs. trench 5 #5 – clay (90–95%) and silt to fine sand (5–10%) with dark laminations; angular to subrounded quartz silt grains; “fish layer.” #4 – clay (95%) and silt (5%) that is angular to subrounded and mostly quartz with minor plagioclase feldspar grains. #3 – clay (95%) and silt to fine sand (5%) that is sub-angular to rounded and mostly quartz. #2 – clay (90–95%) and silt to fine sand (5–10%) sub-angular to subrounded; silt grains mostly quartz with some minor amounts of plagioclase feldspar; some carbonized plant fragments. #1 – clay (95%) and silt to fine and medium-fine sand (5%), sub-angular to subrounded; silt grains quartz and minor amounts plagioclase feldspar and rock fragments; some carbonized plant material; one clayball; “main bone layer.” pebbles (p-1 through p-5) clay (90–95%) and silt (5–10%); silt grains angular to subrounded and mostly quartz; silt grains finer grained but more numerous than some in-place silty claystone; edges of pebbles same as center; dendrites growing in from some edges; p-5 is laminated but otherwise no different from the others. p-1 is somewhat laminated, too. all appear to be calcite cemented nodules, no chert nor rock fragments. 92 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 appendix b – core descriptions mygatt-moore quarry drill hole mm-1 june 25, 2013 logged by j. foster utm: 12s 0670796e, 4340409n 105m ~wnw of 1000, 1000 quarry datum cap top 107 cm soil 274 cm light gray claystone 25 cm darker gray claystone 107 cm light gray claystone 180 cm maroon to brick-red, slightly silty mudstone (some minor light gray mottling) 140 cm light gray to light green claystone 134 cm gray mudstone, becomes silty near base 173 cm deep red silty mudstone 36 cm light gray mudstone 33 cm silty gray and purple mudstone 127 cm light gray silty mudstone 13 cm deep red to purple and green-gray mottled and laminated siltstone 13 cm deep red mudstone 33 cm silty gray mudstone, with black and white (dentritic?) staining in bottom half 228 cm light gray silty mudstone 18 cm purple and light gray laminated siltstone (“fish layer”) 8 cm very dark gray, crumbly mudstone 8 cm light gray and purple mottled mudstone 84 cm light gray and light greenish-gray mudstone 38 cm light gray mudstone with abundant carbonized plant fragments (main quarry layer) 8 cm green mudstone 137 cm light gray to greenish-gray slightly silty mudstone 71 cm gray, silty mudstone 30 cm light gray and greenish-gray very fine grained sandstone bottom mygatt-moore quarry drill hole mm-2 june 25–26, 2013 logged by j. foster and h. schoenstein utm: 12s 0670809e, 4340274n 118m ~sw of 1000, 1000 quarry datum cap top -- loose gravel 23 cm green and red mottled mudstone 61 cm maroon-red mudstone 93 paleontology, taphonomy, and sedimentology of the mygatt-moore quarry, a large dinosaur bonebed in the morrison formation, western colorado–implications for upper jurassic dinosaur preservation modes foster, j.r., hunt-foster, r.k., gorman, m.a., ii, trujillo, k.c., suarez, c.a., mchugh, j.b., peterson, j.e., warnock, j.p., and schoenstein, h.e. geology of the intermountain west 2018 volume 5 20 cm green-gray mudstone 23 cm gray siltstone to very fine grained sandstone 25 cm dark gray mudstone 25 cm green-gray crumbly mudstone with yellow staining of the cracks 97 cm light gray claystone 41 cm dark reddish gray mudstone 145 cm light gray to light greenish-gray mudstone and siltstone 51 cm dark gray mudstone, some reddish mudstone near base 221 cm light greenish-gray mudstone, with golden-tan mineralization in cracks near the base 48 cm red and light greenish-gray mottled mudstone 183 cm dark red mudstone, with some light gray mottling 71 cm light greenish-gray mudstone 51 cm red mudstone mottled with light gray 129 cm light gray to white siltstone and slightly silty mudstone 30 cm green-gray mudstone 165 cm light gray to white, finely laminated silty mudstone with some very fine grained sandstone 8 cm light gray siltstone with thicker, slightly purple laminations (“fish layer”) 13 cm dark gray mudstone 8 cm light green siltstone, slightly laminated purple (“fish layer”) 33 cm light green mudstone 48 cm medium green mudstone 94 cm medium greenish-gray to gray mudstone with moderate to abundant carbonized plant fragments; some layers of light green, rounded clayballs to 5 mm diameter; dinosaur bone fragment in core at 16.5 m down (main quarry layer) 33 cm light green, soft mudstone (“clay layer”) 33 cm light green mudstone 38 cm medium green mudstone 15 cm medium green to reddish mudstone 299 cm medium to light green and maroon-red mottled, silty mudstone bottom geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 10 2023 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado thomas c. chidsey, jr. theme issue engineering geology and geohazards of utah utah geological association annual field conference october 22, 2022 salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover midwest exploration and utah southern no. 1 shafer well, drilled in 1924. left photograph is the view if the rig across the colorado river. the cable-tool rig was floated down the river from the town of moab. right photograph of the well blowing out after encountering gas at 2028 feet (618 m) in the cane creek shale. the rig caught on fire and was destroyed. courtesy of the utah division of state history and the utah state historical society. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 10 2023 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2022–2023 uga board president rick ford rford@weber.edu 801.915.3188 president-elect eugene syzmanski eugenes@utah.gov 801.537.3364 program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 treasurer aubrey dereuil aubrey@zanskar.us 850.572.2543 secretary tom chidsey tomchidsey@gmail.com 801.824.0738 past president john south johnvsouth@gmail.com 801.367.9292 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors uga field conference editors jason kaiser southern utah university jasonkaiser@suu.edu john south geologist johnvsouth@gmail.com adam mckean utah geological survey adammckean@utah.gov rick chesnut terracon rick.chesnut@terracon.com geology of the intermountain west an open-access journal of the utah geological association volume 10 2023 131 abstract the cane creek shale of the pennsylvanian paradox formation represents a major target for oil and gas in the paradox fold and fault belt of the northern paradox basin of southeastern utah and southwestern colorado. early exploration and development attempts resulted in blowouts due to unexpected gas-bearing intervals and casing collapses caused by salt flowage in the paradox formation. these problems represent some of the types of drilling hazards that could be expected when planning cane creek wells. horizontal drilling first used in the early 1990s changed the cane creek shale play from one of mostly drilling failures to a more successful commercial play. depending on the location, exploratory cane creek wells may penetrate a section that ranges in age from cretaceous through pennsylvanian. drilling in the region often encounters a wide variety of lithologies (carbonates, shale, mudstone, sandstone, and evaporites) and associated potential hazards that may include: (1) swelling clays, (2) high porosity-permeability or fractured zones resulting in lost circulation or excessive mudcake buildup, (3) “kicks” due to the influx of reservoir fluid (oil, water, or gas) into the wellbore, (4) uranium-rich zones, (5) washouts, (6) hole deviation, sticking, and other well-integrity problems, (7) chert, and (8) overpressured intervals. in addition, natural carbon dioxide, which flows from the partially human-made crystal geyser near some cane creek wellsites, represents an unusual drilling hazard if encountered in the northernmost part of the fold and fault belt. using the lessons learned from the recently completed research well, state 16-2 (renamed the state 16-2ln-cc, api no. 43-019-50089, after the horizontal leg was drilled), and other wells in the region, drilling engineers and operators can better plan for potential hazards when exploring for hydrocarbons in the cane creek shale or deeper targets (mississippian leadville limestone and devonian elbert formation) in the fairly remote, relatively sparsely explored paradox fold and fault belt. the goal is to de-risk wells, lower expenses, and mitigate problems before they occur. the expected results are safer and more successful drilling of wells to the cane creek shale and deeper reservoirs ultimately leading to additional commercial hydrocarbon discoveries in the region. potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado thomas c. chidsey, jr., emeritus utah geological survey, salt lake city, utah 84114 usa; tomchidsey@gmail.com citation for this article. chidsey, t.c., jr., 2023, potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado: geology of the intermountain west, v. 10, p. 131–167, https://doi.org/10.31711/giw.v10.pp131-167. introduction exploration for oil in the paradox fold and fault belt of the northern paradox basin in southeastern utah and southwestern colorado has been ongoing for over 100 years. early wells mainly targeted surface structures. in 1924, the midwest exploration and utah southern no. 1 shafer well was drilled on the large, northwest-southeast-trending cane creek anticline (figures 1a and 2). the cable-tool rig was floated 20 miles (32 km) down 132 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 a b figure 1. midwest exploration and utah southern no. 1 shafer well, drilled in 1924. (a) view across the colorado river. the cable-tool rig was floated down the river from the town of moab. (b) the well blew out after encountering gas at 2028 feet (618 m) in the cane creek shale and the rig caught on fire and was destroyed. courtesy of the utah division of state history and the utah state historical society. figure 2. panorama of the cane creek anticline (middle ground); view east from dead horse point state park overlook; unannotated (a) and annotated (b). note solar evaporation ponds in front of the fold and the jointed jurassic navajo outcrops of the behind the rocks area in front of the la sal mountains in the distance. the lower jurassic kayenta formation forms the rim of the overlook at the point followed down section by the wingate, chinle, moenkopi, and cutler formations at the base. modified from doelling and others (2010). 133 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 the colorado river from the town of moab, utah. however, after encountering oil and gas in the cane creek shale of the pennsylvanian (desmoinesian) paradox formation, the well blew out at 2028 feet (618 m), and the rig caught fire and was destroyed (figure 1b) (smith, 1978). cumulative production was 1887 barrels of oil (bo) and 25,000 thousand cubic feet of gas (mcfg) before abandonment of what was called the cane creek oil field (stowe, 1972). drilling activity targeted subsidiary structures along the cane creek anticline again from the mid-1950s through the early 1960s leading to the discoveries in 1962 of long canyon and bartlett flat fields, with wells also targeting the cane creek shale (figure 3). bartlett flat produced 26,000 bo before salt flowage in the paradox formation caused the production casing to collapse around the tubing. all subsequent drilling and completion attempts similarly failed and the field was abandoned (smith, 1983). it was not until the advent of horizontal drilling techniques and their application to bartlett flat field area (now called big flat, figure 3) in the early 1990s that the cane creek shale became a commercially viable drilling target and emerging unconventional oil play in the region. total production from the cane creek shale is over 10 million bo from 18 fields in the utah part of the paradox basin, with some wells having initial flowing potentials up to 1500 bo per day (vanden berg, 2021; utah division of oil, gas and mining, 2023a). the problems that occurred during the early drilling and completion attempts described above represented an indication that due diligence would be required if operators were to successfully find and produce oil and gas from the cane creek shale in the paradox fold and fault belt. drilling may encounter both common and unusual hazards that can significantly add to rig time and well costs: swelling clays, high porosity-permeability or fractured zones resulting in lost circulation or excessive mudcake buildup, a wide variety of lithologies (carbonates, shale, sandstone, and evaporites), and overpressured intervals (summarized in table 1). beginning in 2020 and into 2021, the utah geological survey (ugs), energy & geoscience institute of the university of utah, and zephyr petroleum company (formerly rose petroleum) drilled the state 16-2 research well (renamed the state 16-2ln-cc, api no. 43-019-50089, after the horizontal leg was drilled; section 16, t. 22 s., r. 17 e., salt lake base line & meridian [slbl&m]) (figure 3) to take core from the cane creek shale as part of a project to better characterize the petrographic and petrophysical properties of the reservoir, and extend the play farther north (vanden berg, 2021; paronish and others, 2022; vanden berg and others, 2022). the state 16-2 research well, and several dry holes nearby that penetrate the stratigraphic section into the paradox formation, provide a wealth of drilling information about the rocks encountered and any associated hazards common to the region. in addition, drill cuttings and cores from several wells are publicly available at the ugs’s utah core research center in salt lake city, and can be used as a further stratigraphic guide along with mudlogs, and caliper and geophysical logs (figure 4). close-up photographs of representative cuttings of the cretaceous mancos shale through the cane creek are included in the appendix. as with any exploratory well targeting hydrocarbons in the cane creek shale, or deeper potential reservoirs (mississippian leadville limestone and devonian elbert formation), the wellsite geologist and mudlogger need to pay close attention to (1) the rate of penetration (rop), (2) mud weight, (3) bit wear and number of times they have to be replaced, (4) loss of circulation, (5) unexpected and unwanted influx of reservoir fluid (oil, water, or gas) into the wellbore (referred to as a “kick”) due to an underbalanced condition in which pressure inside the wellbore or bottom-hole pressure is less than formation pressure, (6) hole integrity (e.g., washouts, borehole breakouts, rugosity, deviation, excessive mudcake buildup, sticking problems), (7) increases in chloride content, (8) changes in background and trip gas, and (9) characteristics of cuttings (e.g., size and shape, lithology, hydrocarbon shows). the goal of this paper is to de-risk wells, lower expenses, and mitigate problems before they occur by providing drilling engineers and operators the information they need to help plan for potential drilling hazards when exploring for additional commercial hydrocarbons in the cane creek shale and deeper targets in the fairly remote, relatively sparsely explored paradox fold 134 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 figure 3. location of the state 16-2 research well (section 16, t. 22 s., r. 17 e., slbl&m, grand county), as well as oil and gas fields in green and red, respectively (cane creek field names in bold), surrounding parks, towns, and highways, southeastern utah. black dots indicate locations of the wells from which cuttings were obtained and photographed for the appendix. 135 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 formation thickness (ft) dominant lithologies potential drilling hazards mancos shale ±3800 shale sticking & bit balling due to swelling clays, washouts naturita formation 0–200 sandstone possible gas in lenticular sandstone beds, water flow in porous sandstone cedar mountain fm. 80–300 mudstone, conglomerate possible gas in lenticular sandstone beds, water flow in porous sandstone, sticking in mudstones, washouts morrison formation 400–1000 mudstone, sandstone possible gas in lenticular sandstone beds, sticking in mudstones, bit balls, washouts, sloughing, water flow in porous sandstone, radioactive zones summerville fm. 5–400 siltstone, mudstone washouts curtis formation 0–230 sandstone loss of circulation in porous units entrada sandstone 60–500 sandstone well deviation due to jointing & contorted bedding, loss of circulation or water flow in porous units carmel formation 20–300 sandstone, siltstone, mudstone washouts navajo sandstone 0–510 sandstone loss of circulation or water flow in porous units, thin limestone beds, possible carbon dioxide kayenta formation 60–360 sandstone loss of circulation in porous units wingate sandstone 70–450 sandstone loss of circulation or water flow in porous units & jointing & fracture zones chinle formation 150–630 mudstone, shale sticking and bit balling due to swelling clays, washouts, drilling problems due to contorted bedding, radioactive zones moenkopi formation 240–910 sandstone, siltstone, mudstone washouts, well deviation issues black box dolomite 60–160 dolomite, limestone loss of circulation in fractured zones white rim ss. 0–500 sandstone loss of circulation & sticking due to mudcake buildup in porous units, water flow in porous units organ rock fm. 0–300 sandstone, shale washouts elephant canyon fm. 1000–1200 sandstone, limestone loss of circulation in porous & fractured zones, excessive bit wear due to chert cutler formation 900–1200 arkosic sandstone, siltstone, limestone loss of circulation or water flow in porous & fractured zones honaker trail fm. 1600–5000 sandstone, limestone, siltstone loss of circulation or water flow in porous & fractured zones, excessive bit wear due to chert, possible gas-bearing zones paradox formation ±14,000 sandstone, siltstone, limestone & dolomite mudstone, shale, anhydrite, halite washouts, sticking, salt flowage, gas kicks, overpressure, loss of circulation due to hydrofracturing by weighted drilling fluid, difficulties drilling horizontally in complex geology table 1. potential drilling hazards while targeting the cane creek shale in the paradox fold and fault belt. 136 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 and fault belt. using this report, and the lessons learned from drilling the state 16-2 research well, will hopefully result in future wells successfully reaching the objective cane creek shale reservoirs with minimal unexpected cost and downtime while creating the safest work environment possible for the rig crew and other wellsite personnel. overview of the cane creek shale play paradox basin the paradox basin is an elongate, northwest-southeast-trending, evaporite-rich basin that developed predominately during the pennsylvanian, about 323 to 299 million years ago (ma). the dominant structural features in the basin are surface anticlines that extend for miles in the northwesterly trending fold and fault belt (figure 5). during cambrian through mississippian time, this region, as well as most of eastern utah, was the site of typical marine deposition represented by a relatively thin stratigraphic section on a craton with thicker deposits in a miogeocline to the west (hintze and kowallis, 2021). however, major changes began in the pennsylvanian when a pattern of basins and fault-bounded uplifts developed from utah to oklahoma. one result of this tectonism was the uplift of the ancestral rockies in the western united states, including the uncompahgre highlands (uplift) in eastern utah and western colorado. the uncompahgre highlands are bounded along their southwestern flank by a stack of large, basement-involved, high-angle, reverse faults identified from seismic surveys and exploration drilling (frahme and vaughn, 1983; kluth and duchene, 2009). as the highlands rose, an accompanying depression, or foreland basin, formed to the southwest—the paradox basin. rapid basin subsidence, particularly during the pennsylvanian and continuing into the permian, accommodated large volumes of evaporitic and marine sediments that intertongue with non-marine arkosic material shed from the highland area to the northeast (hintze and kowallis, 2021). deposition in the basin produced the thick cyclical sequence of carbonates, evaporites, and organic-rich shale that compose the paradox formation. the paradox basin can generally be divided into three areas: the paradox fold and fault belt in the north, the blanding sub-basin in the south-southwest, and the aneth platform in the southernmost part in utah (figure 5). the area now occupied by the paradox fold and fault belt was also the site of greatest pennsylvanian-permian subsidence and salt deposition. the area was created during the late cretaceous through quaternary by a combination of (1) reactivation of basement normal faults, (2) additional salt flowage followed by dissolution and collapse, and (3) regional uplift (trudgill and paz, 2009; doelling, 2010). figure 4. map of the cane creek shale play area showing locations of wells with drill cuttings and cores from the cane creek publicly available at the utah geological survey’s utah core research center. cumulative cane creek oil production in barrels (bbls) also shown. after vanden berg (2021). 137 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 stratigraphy and thickness the paradox formation is part of the pennsylvanian hermosa group (figures 6 and 7). the 500to 5000-foot-thick (150–1500 m) paradox formation is overlain by the honaker trail formation and underlain by the pinkerton trail formation (hintze and kowallis, 2021). the cane creek shale generally ranges from 0 to about 200 feet (0–60 m) thick in the region. within the main cane creek play “fairway” (figures 4 and 5), the thickness is 60 to 170+ feet (18–52+ m) (figure 8). the depositional strike of the cane creek is north-northwest to east-southeast with a thinner section through the central part of the trend that thickens to the northeast and southwest (figure 8). however, farther to the southwest it thins where it laps onto the lower paradox member or the pinkerton trail formation (carney and others, 2014; morgan and others, 2014). thickness variations are the results of diapiric salt movement, depositional thickening on the downthrown side of faults, or depositional thinning on the upthrown side of faults or over subtle, early structural highs (morgan, 1992). depositional environment throughout the pennsylvanian, the paradox bafigure 5. oil and gas fields in the paradox basin of utah, colorado, arizona, and new mexico. modified from harr (1996) and wood and chidsey (2015). the extent of the pennsylvanian paradox formation is shown in light orange; the cane creek shale play area within is light brown. from chidsey and eby (2017). 138 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 figure 6. stratigraphic column in the northern part of the paradox fold and fault belt of utah. modified from hintze and kowallis (2009). 139 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 figure 7. stratigraphic column in the central part of the paradox fold and fault belt of utah near big flat field, and canyonlands and arches national parks. modified from hintze and kowallis (2009) and doelling and others (2010). 140 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 figure 8. general thickness of the cane creek shale using selected wells with cuttings (black dots) and cores (red dots). other wells not shown are scattered throughout the region or concentrated in the producing oil fields, and if used as data points would likely result in a map showing additional thick and thin areas related to salt flowage, faulting, or depositional thinning over minor early structural highs. after chidsey and eby (2017). 141 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 sin had subtropical, dry climatic conditions (peterson and hite, 1969; heckel, 1977; parrish, 1982; blakey and ranney, 2008). during transgressions, open-marine waters flowed across a shallow cratonic shelf into the basin through up to four postulated marine access ways (fetzner, 1960; ohlen and mcintyre, 1965; hite, 1970). periodic decreased water circulation resulted in deposition of thick salts (halite with sporadic thinner beds of potash and magnesium salts) and anhydrite in the northern and northeastern part of the basin. cyclicity during paradox basin deposition was primarily controlled by glacio-eustatic sea-level fluctuations. these sea-level cycles were also influenced by (1) regional tectonic activity and basin subsidence (baars, 1966; baars and stevenson, 1982), (2) proximity to basin margin (hite, 1960; hite and buckner, 1981), (3) climatic variation and episodic blockage of open marine-water access ways (fetzner, 1960; ohlen and mcintyre, 1965; hite, 1970), and (4) fluctuations in water depth and water energy (peterson and ohlen, 1963; peterson, 1966; hite and buckner, 1981; heckel, 1983). the cane creek shale generally records a low-energy environment varying between aerobic to dysaerobic and occasionally anoxic conditions (for thin, organic-rich black shale intervals). water depths were probably variable, ranging from below fair-weather and storm wave base for organic shales to relatively shallow to near exposure for the siltstones, sandstones, limestones, finely crystalline primary or very early diagenetic dolomites, and nodular anhydrites and other evaporites (chidsey and eby, 2017). petroleum geology structure and trapping mechanisms structurally the cane creek shale is deepest in the northern part of the play area, -2400 to -4000 feet (-730 to -1200 m) below sea level (figure 9). the cane creek shallows near the southwestern edge/shelf of the basin. petroleum is usually trapped in fractured sandstones and dolomites on subtle, seismically defined subsidiary structural noses and fault closures along major southeast-northwest-trending, salt-cored regional anticlines, or on the crests of other smaller, local anticlinal closures (smith, 1978; morgan, 1992; grove and others, 1993; chidsey and others, 2016; chidsey and eby, 2017). salt movement along zones of weakness or areas of low confining pressure formed large folds such as the cane creek and shafer anticlines (figure 2). second-order folds caused by salt flowage are aligned directly over local bulges or pillows of paradox salt and the overlying rocks are fractured (lorenz and cooper, 2009). fracture data from oriented cores in the cane creek show regional, northwest to southeast and northeast to southwest, near-vertical, open, extensional fracture systems that are not significantly affected by orientations of localized folds (morgan and others, 1991, 2014; grove and rawlins, 1997). hydrocarbon production from the cane creek is not limited to the crests of anticlines but also from structurally high positions on upthrown fault blocks and on the downthrown side of faults. plunging noses without apparent four-way closure produce from the cane creek as well as where extensive fracturing exists. hydrocarbon source and seals hydrocarbons in paradox formation reservoirs are thought to be generated from source rocks within the formation itself. organic-rich sapropelic shale in the cane creek and other organic-rich shales are well-established source rocks for hydrocarbon production in the paradox basin (hite and others, 1984; nuccio and condon, 1996). the average total organic content of the black shale in the cane creek is 15% with some samples containing up to 28% (grummon, 1993; morgan and others, 2014). kerogens are oil-prone types i and ii; maturity (based on tmax) and production indices from three cores place the cane creek in mostly the oil window (morgan and others, 2014; chidsey and eby, 2017). the cane creek shale began to generate hydrocarbons within the paradox fold and fault belt from 270 to 239 ma (middle permian–middle triassic) (rasmussen and rasmussen, 2009). expulsed hydrocarbons migrated through dolomite, sandstone, and other porous lithologies along regional northwest-trending folds, faults, and fracture zones. the upper and lower seals for the reservoir units in the cane creek shale are provided by anhydrite and 142 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 figure 9. generalized structural map on top of the cane creek shale. the map was created by combining published oil field reservoir maps (peterson, 1973; quigley, 1983; grove and others, 1993; morgan, 1994) and regional geologic maps and cross sections (gualtier, 1988; doelling, 2002, 2004; doelling and others, 2015) without the benefit of seismic data. major folds and faults projected from surface expressions may die out in paradox salt zones above the cane creek, whereas basement-involved structures may be present at the cane creek level where they can best be detected by seismic. the map also shows selected wells with cuttings (black dots) and cores (red dots). other wells not shown are scattered throughout the region or concentrated in the producing oil fields, and if used as data points would likely result in a map with greater structural complexity. additional faults and folds are present but are not shown given the small scale of the map. after chidsey and eby (2017). 143 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 halite beds. lateral seals are permeability barriers in unfractured rock. thus, the cane creek serves as the source and seal, as well as the oil reservoir rock. reservoir properties the cane creek shale in the big flat field area (figure 3) exhibits a net-pay thickness of 25 to 30 feet (7–9 m). dolomites and sandstones have been the main targets of horizontal drilling. productive zones have porosity (matrix and fractures) up to 15% (grove and others, 1993; morgan and others, 2014). pore types in dolomite beds are predominantly intercrystalline and microbial constructional pores, microporosity, and minor interparticle porosity (chidsey and eby, 2017). sandstones and siltstones exhibit intergranular porosity. these lithologies can also contain significant microporosity and fracture porosity, including microfractures (gathogo and others, 2022). microfractures resulted from internal hydrocarbon generation (fritz, 1991). potential oil-prone areas in the cane creek play were identified based on hydrocarbon shows in porous lithologies recognized using epifluorescence microscope techniques on cuttings, core chips, and uncovered thin sections (chidsey and eby, 2017). matrix permeability in the big flat area (figure 3) from horner plots is less the 0.1 millidarcies (md), but ranges from 39 to 400 md with fractures (grove and others, 1993). the larger tectonic fractures may account for most of the permeability, but the microfractures probably provide most of the fracture porosity in the reservoir. core analysis from the productive interval in the cane creek no. 26-3 well (section 26, t. 25 s., r. 19 e., slbl&m) in big flat field (figure 3), grand county, utah, showed sandstones, argillaceous sandstones, and dolomitic argillaceous siltstones contain 5% to 12% porosity, and permeability ranging from 0.002 to 36 md; porosity and permeability in silty dolomite was 7% and 0.004 md, respectively (core laboratories, inc., 2013; morgan and stimpson, 2017). initial water saturations are estimated at 10% for the fractured cane creek shale. the reservoir temperatures range from 119º to 132ºf (48º–56ºc) and the reservoir drive mechanism is solution gas (grove and others, 1993). the cane creek is highly overpressured in the big flat area (but not everywhere in the cane creek play area), which is probably the result of hydrocarbon generation between very impermeable upper and lower anhydrite and halite seals. the sedimentary sequence above the salt is lower pressure due to exposure along the canyons of the colorado river (morgan and stimpson, 2017). fluid gradients exceed 0.85 to 0.94 pounds per square inch (psi)/foot (19.23–21.27 kpa/m); the initial reservoir pressures average 6650 psi (45,850 kpa) (grove and others, 1993; morgan and stimpson, 2017). horizontal drilling natural fractures and the need to drill through them, organic-rich shale beds, overpressure, low permeability, thin intervals, and the widespread stratigraphic presence of the cane creek shale are characteristics ideal for horizontal drilling, which is required for commercial hydrocarbon production. fracture orientation, critical for determining horizontal drilling directions, are often difficult to predict. once identified, vertical to near-vertical natural fractures in the cane creek can allow economic oil production without the need for hydraulic fracturing unlike the unconventional oil plays in the permian basin of west texas and williston basin of north dakota (vanden berg, 2021). the relatively thin cane creek shale zone, averaging about 100 feet (30 m) thick or less, is bounded by salt. fractures created by hydraulic fracturing in the cane creek would likely penetrate the salt beds above and below, possibly mobilizing the salt that could plug up the existing and new fractures, thus preventing fluid flow from the reservoir into the wellbore (vanden berg, 2021). drilling horizontally greatly increases the probably of intersecting vertical to near-vertical open fractures in the cane creek shale. the direction of the horizontal wellbore is based on the dip of the structure being tested, predicted fracture orientation, the available surface location, and lease and reservoir drainage models (morgan and stimpson, 2017). the orientation and length of each cane creek horizontal well are different and can result in varying amounts of oil production. some short-radius laterals (100 to 800 feet [30–250 m]) parallel to the regional fracture trends have produced more oil than long-reach laterals (greater than 2000 feet 144 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 [600 m]) drilled in a similar direction or perpendicular to the fracture trend (morgan and stimpson, 2017; islam and hossain, 2020). finally, horizontal drilling in the cane creek shale, or other paradox clastic cycles, have presented additional hazards and problems over those occurring in vertical wells. these must be anticipated and overcome to achieve commercial cane creek oil production. regional stratigraphy and drilling hazards wells, such as the state 16-2 research well, targeting the cane creek shale in the paradox fold and fault belt may penetrate a stratigraphic section ranging from the cretaceous mancos shale or older formations to the pennsylvanian paradox formation (figures 6 and 7). drilling hazards may occur before reaching or within the cane creek shale. this region is particularly unique in that all of the formations encountered during drilling, with the exception of the paradox, are exposed at the surface within 50 miles (80 km) of any well (figure 10). this affords the opportunity to visit outcrop sites before and while drilling to better understand the stratigraphic section, the physical characteristics of the rocks, and problems that may occur. many drill sites in the region may have a relatively thin veneer of unconsolidated quaternary deposits overlying the bedrock geology. these deposits typically include alluvium and colluvium, older alluvium, and eolian sands. thick eolian sands could present initial drilling problems due to sloughing and require setting conductor pipe to protect the integrity of the shallow wellbore. the bedrock stratigraphic section, from the mancos shale through the paradox formation, is described below based on geologic maps (hintze, 1980; gualtieri, 1988; hintze and others, 2000; doelling, 2002, 2004; doelling and others, 2015) and research in the region published by various workers and analysis of core and well cuttings (nielsen and others, 2013; chidsey and eby, 2017; morgan and stimpson, 2017; jagniecki and others, 2021). these descriptions include the age, general lithology (with close-up photographs of typical well cuttings in the appendix), thickness ranges, and the nature of the contacts with overlying and underlying formations. the descriptions are followed by potential drilling hazards that may be encountered while drilling through the respective formations. however, it is important to note that there is always the possibility of new unforeseen problems, especially when drilling in the paradox fold and fault belt where wells penetrating the paradox formation are relatively sparse. cretaceous mancos shale lithology, thickness, and contacts the shallow open marine, upper cretaceous mancos shale is the youngest formation exposed in the paradox fold and fault belt and is divided into the upper main body, juana lopez member, and basal tununk member within the region (birgenheier and others, 2015; hintze and kowallis, 2021) (figure 6). for the most part these members are soft and deeply weathered, forming slopes and low, rounded hills devoid of vegetation; the state 16-2 research well spudded in the tununk member of the mancos. the tununk and main body have very similar characteristics in outcrop and drill cuttings consisting of light to dark gray, medium to dark brown or black shale, shaley siltstone, and mudstone (appendix, figure a1). shale is fissile, breaking into platy, angular fragments. some shale beds are bentonitic, providing regional correlation markers. bedding is indistinct or even, thin, and laminated with a few siliceous zones. the juana lopez is a light to dark gray, organic-rich, thinto medium-bedded, heterolithic zone of shale and shaly siltstone. the mancos shale is about 3800 feet (1160 m) thick; the amount of section that would be penetrated by most new wells in the northern part of the paradox fold and fault belt is significantly less. the juana lopez and tununk members range in thickness from 10 to 30 feet (3–9 m) and 350 to 400 feet (107–120 m), respectively (hintze and kowallis, 2021). drilling hazards the mancos shale consists of beds composed of a 145 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 figure 10. geologic map of part of the paradox fold and fault belt and surrounding region of east-central utah. note the locations of the state 16-2 research well and crystal geyser. modified from hintze and others (2000). 146 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 variety of clays and a number of bentonite beds that can swell causing sticking problems and bit balling while drilling. bit balling is a condition that arises when clays stick to the drill bit and form a ball. a balled-up bit can reduce the rop and torque on the bit (mccoremick, 2015). in addition, like all shale beds, washouts can be a major wellbore problem, especially when the hole size is large during the initial phase of drilling. conductor pipe is often set in the underlying naturita formation. cretaceous naturita (dakota) formation lithology, thickness, and contacts the upper cretaceous naturita formation (formerly called the dakota) unlike other formations is not widespread. the naturita represents an alluvial and coastal floodplain environment and consists of light yellow, tan, yellow-brown, orange-gray, light tan-gray, or light brown sandstone (appendix, figure a2), conglomeratic sandstone, conglomerate, shale, and coal, particularly east of the san rafael swell (doelling, 2002; kirschbaum and schenk, 2011; doelling and others, 2015). sandstones are friable, quartzitic, fine to coarse grained, and moderately to well sorted. conglomerates contain rounded to sub-rounded pebbles of chert and quartzite. sandstones and conglomerates are thin to thick bedded and cross-stratified; some ripple and convolute bedding is also present. the upper part of the naturita contains lenticular sandstone beds, 5 to 12 feet (1.5–3.7 m) thick and encased in mudrock (kirschbaum and schenk, 2011). shale beds are often the only rocks that represent the naturita section. the naturita formation is 0 to 200 feet (0–60 m) thick (hintze and kowallis, 2021) (figures 6 and 7). the contact with the conformable overlying mancos shale is defined by the first absence of deeper marine shale (molenaar and cobban, 1991). drilling hazards low-permeability lenticular sandstone beds of the naturita formation produce gas in small combination stratigraphic/structural traps at greater cisco and other fields along the northwest-plunging uncompahgre uplift (figure 3). although gas in similar sandstone beds is not anticipated in wells drilled to the west in the northernmost part of the paradox fold and fault belt, the possibility does exist for a gas kick. water flows from the naturita are unlikely in areas where it outcrops but are possible elsewhere. the water that is present in the formation may potentially be fresh depending on the hydrodynamics of the aquifer system. cretaceous cedar mountain formation lithology, thickness, and contacts the lower cretaceous cedar mountain formation was deposited on alluvial plains, in meandering channels and floodplains. it is divided into two members along the western flank of the san rafael swell and to the east (figure 6): the ruby ranch and the basal buckhorn conglomerate (kirkland and others, 2016). in outcrop and cuttings, the ruby ranch member consists of subtle bands of dark gray to dark purplish-gray mudstone and tan to gray sandstone (appendix, figure a3) (doelling, 2002; doelling and others, 2015; kirkland and others, 2016). mudstone is clayey and silty with local lenticular sandstone beds. sandstone is fine grained to pebbly, poorly sorted, trough cross-stratified, and discontinuous, and usually occurs in the upper half of the section. the ruby ranch is medium to thick bedded. the buckhorn conglomerate is discontinuous and consists of gray to dark brown conglomerate to conglomeratic sandstone having subordinate amounts of sandstone and mudstone. pebbles and cobbles are composed of poorly to moderately sorted, sub-angular to well-rounded clasts of white quartzite, and black, brown, light brown, and light gray chert. conglomerate beds are either clast supported or supported by a matrix of clay or mediumto coarse-grained sandstone. bedding is lenticular, thick to massive, trough cross-stratified, and generally fines upward. regionally, the cedar mountain formation ranges from 80 to 300 feet (24–90 m) thick (hintze and kowallis, 2021); in the northern paradox fold and fault belt, the ruby ranch and buckhorn conglomerate members range in thickness from 60 to 130 feet (18–40 m) and 0 to 80 feet (0–24 m), respectively (kirkland and others, 147 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 2016). the contact between the cedar mountain and the underlying upper jurassic morrison formation is difficult to recognize when the buckhorn conglomerate member is absent and thus the two formations are mapped together in the subsurface. in san rafael swell outcrops, this situation places the ruby ranch member of the cedar mountain over the brushy basin member of the morrison formation—both create colorfully banded steep slopes and badland topography. however, the cedar mountain has (1) a more drab, variegated color, (2) less smectite clay, (3) the presence of polished chert pebbles (gastroliths), (4) abundant carbonate nodules, and (5) a thick paleosol at the base (kirkland and madsen, 2007). the contact with the overlying naturita formation is an unconformity with about 2 feet (0.6 m) of relief in some areas (doelling and others, 2009). drilling hazards like the naturita formation, low-permeability lenticular sandstone beds are present in the cedar mountain formation and also produce gas in small stratigraphic/structural traps in many fields along the uncompahgre uplift (figure 3). the naturita and cedar mountain are also often mapped together in the subsurface and the production is commingled. again, gas in these sandstones is not anticipated in wells drilled in the northern part of the paradox fold and fault belt, but the possibility does exist for a gas kick. in addition, much of the cedar mountain formation consists of mudstone beds that can washout and/or cause sticking problems while drilling. water flows from the cedar mountain formation, like the overlying naturita formation, are unlikely in areas where it outcrops. the water that is present in the cedar mountain may also be fresh. jurassic morrison formation lithology, thickness, and contacts the upper jurassic morrison formation, world famous for its dinosaur fossils, was deposited in meandering rivers, lakes and ponds, and floodplains. it is divided into three members within the region, which in descending order are the brushy basin, salt wash, and tidwell (figures 6 and 7). the brushy basin member consists of purple, green, red, yellow, maroon, bluish-gray, gray, and white-colored bands of mudstone, claystone (often bentonitic/smectitic), and siltstone interbedded with white, gray, and light brown sandstone with subordinate limestone and conglomerate (gualtieri, 1988; doelling, 2002; doelling and others, 2015). the salt wash member consists of red, gray, purple, or brown mudstone and siltstone with a few sandy limestone beds and light yellow-gray, light gray to gray sandstone (appendix, figure a4), conglomeritic sandstone, and conglomerate (doelling and others, 2015). sandstone beds are fine to coarse grained, sub-angular to well rounded, arkosic or quartzose, and contain well-displayed trough cross-stratification. conglomerate is composed of poorly sorted, sub-angular to well-rounded chert and quartzite ranging in size from pebbles to cobbles in a matrix of coarse quartz sand. the tidwell member consists of lavender, maroon, red, red-brown, or light gray interbedded siltstone, shale, limestone (marl), sandstone, and gypsum. the morrison was a major target and producer of uranium during the boom of the 1950s. the morrison formation ranges in thickness from 400 to 1000 feet (120–300 m): the brushy basin member is 240 to 500 feet (73–152 m), the salt wash member is 130 to 400 feet (40–122 m), and the tidwell member is 20 to 100 feet (6–30 m) (hintze and kowallis, 2021). the brushy basin is separated from the overlying lower cretaceous cedar mountain formation by the k-0 unconformity (pipiringos and o’sullivan, 1978; hintze and kowallis, 2021). drilling hazards the morrison formation, again similar to the overlying cedar mountain and naturita formations, contains lenticular sandstone beds. these produce oil in small stratigraphic/structural traps at greater cisco field (figure 3). oil and gas (including helium and carbon dioxide at harley dome [figure 3] within the greater cisco field complex [bon, 1999; wiseman and eckels, 2020]) in similar morrison sandstones is also not anticipated in new wells in the northern part of the paradox fold and fault belt, but like the gas in the formations above the possibility does exist for a kick. 148 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 much of the brushy basin member consists of bentonitic/smectitic claystone beds that can washout and/ or swell causing sticking and bit balling problems while drilling. sloughing while penetrating the morrison has been reported in shallow wells in the greater cisco field and other areas. water flows from the morrison are unlikely in areas where it outcrops like the overlying naturita and cedar mountain formations. the water that is present in the morrison may be fresh. flowing water was encountered in the lower section of the salt wash member in the state 16-2 research well. finally, the morrison may contain intervals rich in uranium-bearing ores that would need to be cased off as required by the utah division of oil, gas and mining. jurassic summerville formation lithology, thickness, and contacts the lower upper jurassic summerville formation, the uppermost unit of the san rafael group, represents a tidal flat/sabkha environment and consists of red-brown, light to medium brown siltstone, mudstone, sandstone, and white gypsum with subordinate claystone/shale and gray limestone (appendix, figure a5) (stanton, 1976; caputo and pryor, 1991; doelling, 2002). the summerville becomes sandstone dominated to the southeast before pinching out. siltstone is the most common lithotype in east-central utah, present both as mottled regular bedded units or small lenses, and is composed of silt with abundant clay. sandstone is very fine to fine grained, and silty; bedding is laminar to medium. the summerville formation is 5 to 400 feet (1.5–120 m) thick (hintze and kowallis, 2021). the summerville is separated from the overlying morrison formation by the regional j-5 unconformity of pipiringos and o’sullivan (1978); the contact is sharp. drilling hazards siltstone, mudstone, and gypsum beds within the summerville formation will likely cause circulation problems, especially washouts. these beds are fairly consistent throughout the formation and the rop will probably be slow. jurassic curtis formation lithology, thickness, and contacts the shallow-shelf and marginal marine, lower upper jurassic curtis formation of the san rafael group consists of light gray-green, light gray, to light brown sandstone (sublitharenite, lithicarenite, and subarkose), siltstone, and claystone/shale (appendix, figure a6) with subordinate conglomerate and limestone (smith, 1976; caputo and pryor, 1991; doelling, 2002; doelling and others, 2015). in the central part of the fold and fault belt, the curtis consists of eolian sandstone of the moab tongue (doelling, 2010). sandstone is very fine to coarse grained, poorly to moderately sorted, sub-rounded to sub-angular, and quartzose. the green color in east-central utah is attributed to the presence of glauconite in the matrix, although it may be iron-chlorite clay instead (written communication to mario v. caputo from richard pollastro, u.s. geological survey, october 1987). bedding is finely laminated to medium. the curtis formation is 0 to 230 feet (0–70 m) thick (hintze and kowallis, 2021). the contact with the overlying summerville formation is gradational and conformable. drilling hazards the relatively thin sandstone beds that comprise the curtis formation should drill relatively problem free. some loss of circulation could occur in the more porous units. jurassic entrada sandstone lithology, thickness, and contacts the middle jurassic entrada sandstone of the san rafael group represents a wide variety of depositional environments: intertidal/subtidal marine, supratidal mudflats and ponds, and coastal dunes. it consists of orange-brown, red-brown, or light brown sandstone (appendix, figure a7), siltstone, mudstone, and subor149 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 dinate oolitic limestone in the northern to northwestern part of the paradox fold and fault belt. red siltstone and silty sandstone are dominant in the basal part of the entrada (gualtieri, 1988). in the central part of the fold and fault belt, the entrada consists almost entirely of eolian sandstone and is the primary arch former in arches national park (doelling, 2010). sandstone beds are friable, porous, silty or very fine to fine grained with scattered coarse grains, poorly to moderately sorted, and cemented with calcite or iron oxide. a variety of sedimentary structures are found in the entrada: ripple marks, mudcracks, rip-up clasts, trough cross-stratification, micro-cross-lamination, and soft-sediment deformation. bedding is thin to massive, sometimes with deformation features in the basal section along the contact with the underlying carmel formation. the entrada sandstone is 60 to 500 feet (18–152 m) thick (hintze and kowallis, 2021). the entrada is separated from the overlying curtis formation by the regional j-3 unconformity of pipiringos and o’sullivan (1978). drilling hazards the entrada sandstone is a thick, relatively homogenous formation that generally presents few drilling problems. however, it is prone to jointing at the surface, as observed in arches national park to the southeast, which may cause possible well deviation issues. porous zones may result in some loss of circulation or water flow whereas thin, impermeable units may slow the rop when they are encountered. contorted beds near the base of the entrada may also cause some well deviation. gas, including carbon dioxide and helium, is produced at harley dome within the greater cisco field complex to the east (bon, 1999; wiseman and eckels, 2020) but is unlikely to be encountered in new wells in the northern part of the paradox fold and fault belt due to lack of a trapping mechanism. jurassic carmel formation lithology, thickness, and contacts the middle jurassic carmel formation, the lowermost unit of the san rafael group, was deposited in a restricted to open/marginal marine environment. it is divided into four members, which in descending order are the: winsor, paria river, crystal creek, and judd hollow (forming the dark flatirons along the steeply dipping east flank of the san rafael swell to the west) in the northern paradox fold and fault belt (figure 6). however, all four members are not always present within the region; in the arches-canyonlands area, the carmel consists only of shale and siltstone beds of the dewey bridge member (doelling, 2010; hintze and kowallis, 2021) (figure 7). the members of the carmel and other middle jurassic formations in the region have been mapped, measured, and described by sprinkel and others (in preparation). in general, the carmel consists of interbedded light-brown to light-gray or yellow sandstone (appendix, figure a8), red to gray siltstone, darkgray to green mudstone, and lightto medium-gray limestone with subordinate amounts of dolosiltite, doloarenite, calcarenite, and calcisiltite. limestone may be laminated, micritic, or finely crystalline, with silty, argillaceous, and dolomitic zones. the paria and winsor members also contain silty or white alabaster gypsum beds. these lithotypes are generally thin to medium bedded. the carmel formation ranges in thickness from 20 to 300 feet (6–91 m) (hintze and kowallis, 2021). the entrada sandstone lies conformably above the carmel formation. however, at the contact with the overlying entrada, bedding in the carmel is irregular, contorted, and “bumpy” caused possibly by loading of thick entrada sand onto non-lithified carmel mudstone related to groundwater activity, gypsum dissolution or flowage, or paleoearthquakes. drilling hazards drilling through siltstone, mudstone, and gypsum beds within the carmel formation may produce washouts. the heterogeneous distribution of these beds may make drilling the carmel difficult as lithologies change rapidly as the formation is penetrated. surface casing is often set in the carmel because there is a potential for higher pressure in the underlying navajo sandstone. 150 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 jurassic navajo sandstone lithology, thickness, and contacts the lower jurassic navajo sandstone, the uppermost unit of the glen canyon group (figures 6 and 7), was deposited in a vast erg (dune) system with interdune playas and oases. the navajo is light brown to light gray, thick-bedded to massive sandstone that is cross-stratified in large trough sets. the sandstone beds are friable and composed of clean, fineto medium-grained, frosted, sub-rounded to sub-angular, moderately to well-sorted quartz sand (appendix, figure a9) with minor amounts of feldspar and scattered heavy mineral grains. the navajo locally contains thin, lenticular, light-gray limestone beds. the navajo sandstone is 0 to 510 feet (0–160 m) thick (hintze and kowallis, 2021). the navajo sandstone is separated from the overlying middle jurassic carmel formation by the j-1 unconformity (pipiringos and o’sullivan, 1978) and the contact is sharp. drilling hazards the thick, porous navajo sandstone is a relatively homogenous formation deposited as great dunes in an erg system that may present a number of drilling problems. dunal sandstone intervals have high porosity and permeability (greater than 20% and up to 700 md based on outcrops in the san rafael swell to the west [dalrymple and morris, 2007]) that could result in significant loss of circulation and mudcake buildup causing drill string sticking problems. as with all high-porosity and -permeability sandstones, there is also the potential for water flow while drilling depending on regional hydrodynamic conditions. in addition, interdune intervals composed of limestone beds 6 to 8 feet (1.8–2.4 m) thick (dalrymple and morris, 2007; doelling and chidsey, 2012) may quickly slow the rop and increase bit wear. the navajo produced 38,775 bo and 4556 mcfg from a small, faulted anticline at the shut-in blaze canyon field about 10 miles (16 km) northeast of the state 16-2 research well (figure 3) (matheny, 1993; utah division of oil, gas and mining, 2023a). similar structural traps could exist but have not been identified in the northern part of the paradox fold and fault belt area. one of the more unusual geologic features in the area is crystal geyser along the green river, 7.5 miles (12 km) northwest of the state 16-2 research well (figures 3, 10, and 11). the geyser is partially human-made; an exploration well drilled in 1936 encountered a pressurized groundwater system in the navajo sandstone (and possibly the entrada sandstone above) that was charged with carbon dioxide gas. the east-west-trending little grand wash fault acted as a barrier to gas migration from depth and served as a conduit for upward flow into the navajo, thus creating a structural trap (baer and rigby, 1978; mayo and others, 1991; shipton and others 2004; heath and others, 2009; weaver, 2018). salt tectonics created the little grand wash fault and the nearby ten mile graben (figures 9 and 10). the timing of the creation of these faults is post-jurassic so the navajo structure will be similar to the paradox structure along these features (figure 9). tufa deposits related to ancient (pleistocene?) geysers and springs (doelling, 2002; doelling and others, 2015) are located on the highest part of the hanging wall near the little grand wash fault cutoff. geologic evaluations of new cane creek wells planned for the area should evaluate the shallower structural geology where carbon dioxide could be trapped and associated drilling hazards. jurassic kayenta formation lithology, thickness, and contacts the lower jurassic kayenta formation, the middle unit of the glen canyon group (figures 2, 6, and 7), was deposited in a sandy braided river system and consists mostly of sandstone lenses, with lesser amounts of eolian sandstone, intraformational conglomerate, siltstone, and shale. the unit is primarily red-brown sandstone (appendix, figure a10), but individual lenses and beds vary considerably in color; some are purple, lavender, tan, orange, or white. sandstone in the kayenta exhibits both high-angle and low-angle cross-bedding. the grain size is more variable than in the underlying wingate and overlying navajo sandstones, ranging mostly from fine to medium. siltstone, shale, and intraformational conglomerate appear as partings or are in151 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 terlayered with the sandstone. these softer constituents are rare in the lower half of the formation and become common in the upper part. the kayenta formation is 60 to 360 feet (18–110 m) thick (hintze and kowallis, 2021). the upper contact is mostly sharp, but intertonguing between the kayenta and the overlying navajo sandstone is common. drilling hazards the relatively thin sandstone lenses that comprise the sand-rich kayenta formation should drill relatively problem free. some loss of circulation could occur in the more porous sandstone beds. there have been oil shows and minor, non-commercial production from the kayenta in the northernmost part of the paradox fold and fault belt, but there is no trapping mechanism to the south. triassic–jurassic wingate sandstone lithology, thickness, and contacts the eolian (dune erg system) upper triassic–lower jurassic wingate sandstone, the lowermost unit of the glen canyon group (figures 2, 6, and 7), consists mostly of light-orange-brown, moderate-orange-pink, or pale-red-brown, fine-grained, well-sorted sandstone (appendix, figure a11). the rock is usually well cemented and well indurated, and cross-bedded in outcrop. the wingate is ordinarily described as one massive unit because partings or bedding planes are rare except near the base of the formation where parallel sandstone beds occur. the wingate sandstone is 70 to 450 feet (90–137 m) thick (hintze and kowallis, 2021). the contact of the wingate with the overlying kayenta formation is generally sharp and conformable. drilling hazards the wingate sandstone, like the eolian navajo sandstone above is also a thick, porous, homogenous formation that may present some potential for drilling problems. high porosity and permeability zones could result in significant loss of circulation. however, there is also the potential for water flow while drilling. in outcrop, jointing is extensive due to the nature of the underlying chinle formation, discussed in the next section. jointing and fractures at depth could be an additional cause of lost circulation. triassic chinle formation lithology, thickness, and contacts the upper triassic chinle formation is famous for its petrified wood, uranium in red-brown lenticular channel sandstone beds, and multicolored mudstone and shale derived from altered volcanic ash. it figure 11. crystal geyser, grand county, utah. photograph by lance weaver, utah geological survey. 152 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 was deposited in a floodplain with river channels, oxbow lakes, ponds, and swamps. the chinle consists of complex interbedding and lensing arrangements of sandstone, pebble conglomerate, siltstone, mudstone, and rare limestone. the red-brown, tan, and gray-red sandstones are very fine to coarse grained, moderately to well sorted, quartzose, and slightly micaceous. pebble and intraformational conglomerates occur as lenses and in scour channels concentrated in the lower parts of sandstone beds. siltstone is interbedded with the sandstones and conglomerates, and displays low-angle cross-stratification and ripple lamination. mudstone is gray-red to gray-green, and bentonitic. the chinle formation was a major target and producer of uranium during the 1950s along with the morrison formation described above. the chinle is divided into as many as five members within the region, the two most widespread of which are the church rock and moss back conglomerate/sandstone members at the top and base, respectively (doelling and chidsey, 2010; hintze and kowallis, 2021) (figures 6 and 7). the church rock member is mostly a red-brown sandstone and siltstone (figure 2; appendix, figure a12), but sandstone beds are more common in the lower part. some beds include distinctive ripple-laminated sandstone, but the bedding in much of this unit is indistinct. red-brown, fine-grained, well-sorted, thick-bedded sandstone is common in the upper 10 to 30 feet (3–9 m) of the section (doelling and chidsey, 2010). the moss back conglomerate/sandstone is dominated by red-brown sandstone (appendix, figure a13) and conglomerate. in outcrop, the sandstones commonly contain scattered logs and branches of petrified wood. lowermost lenses of sandstone are locally mineralized with uranium and copper minerals. the upper contact is gradational into the upper section. the chinle formation ranges in thickness from 150 to 630 feet (45–190 m); church rock member is 150 to 400 feet (45–120 m) and moss back conglomerate is 0 to 100 feet (0–30 m) (hintze and kowallis, 2021). the contact of the chinle formation with the overlying wingate sandstone of the glen canyon group is sharp and conformable, commonly being placed below the massive well-sorted sandstone typical of the wingate. no regional channeling or angular unconformity is apparent, and the lowermost part of the wingate includes thin, bedding-parallel sandstone and siltstone beds that suggest continuous deposition across the chinle–wingate contact. drilling hazards the thick chinle formation presents a number of drilling challenges. it contains volcanic ash composed of bentonite and other clay minerals that can swell causing sticking and bit balling problems. mudstone and shale beds produce major washouts while drilling and wells in the paradox basin have had to case through them to maintain circulation. contorted bedding may also lead to additional hole integrity problems. in addition, wells in the region have drilled straight until encountering the chinle where some then drifted updip. finally, as with the morrison formation up section, the chinle may contain uranium-rich intervals that would also need to be cased off as required by the utah division of oil, gas and mining. triassic moenkopi formation lithology, thickness, and contacts the lower triassic moenkopi formation was deposited in a shallow marine to tidal flat environment. it is divided into four members in the northern part of the paradox fold and fault belt, which in descending order are the moody canyon, torrey, sinbad limestone, and black dragon (hintze and kowallis, 2021) (figure 6); in the dead horse point–arches national park area they are the sewemup, ali baba, tenderfoot, and hoskinnini members (figures 2 and 7) (doelling and others, 2010; doelling and chidsey, 2012). the classic outcrops of the moenkopi in southern utah and northern arizona are chocolate brown, whereas those in the san rafael swell and the northern paradox fold and fault belt have been bleached to various shades of yellow, possibly by migrating hydrocarbons and iron-reducing groundwater. in outcrop and in cuttings, the slope-forming moody canyon/sewemup member consists of red-brown to chocolate-brown, interbedded very fine to fine-grained 153 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 sandstone, siltstone, and mudstone (appendix, figure a14), having subordinate muddy limestone and calcisiltite. the ledgey to slope-forming torrey/ali baba and tenderfoot members consist of sandstone and shaly siltstone with minor limestone, calcarenite, calcisiltite, and pebble conglomerate. these beds display a variety of colors, locally banded: altered green-gray, yellow-gray, red-brown, yellow, yellow-brown, or tan-gray. sandstone beds are very fine to fine grained with some micaceous and calcareous units. the sinbad limestone member represents a mixed carbonate-siliciclastic cyclic sequence consisting of medium gray and yellow-gray to light brown limestone, dolomitic limestone, and calcareous sandstone with a few shaly siltstone intervals in outcrops and cuttings (appendix, figure a15), (doelling, 2002; doelling and kuehne, 2008; doelling and chidsey, 2010). carbonate fabrics include mudstone (crystalline), or grainstone and packstone composed of ooids, peloids, intraclasts, and skeletal grains (goodspeed and lucas, 2007; morris and others, 2007). the basal black dragon/hoskininni member consists of sandstone, siltstone, and mudstone that may be greengray, yellow-gray, light gray, or light yellow-brown in color (appendix, figure a16). sandstone beds are very fine to fine grained and composed of quartz sand. bedding is thin to medium and most units are calcareous; some have argillaceous or gypsiferous beds. a few gray limestone and cherty pebble conglomerate beds are found at the top and base of the black dragon, respectively. some zones appear saturated with hydrocarbons (doelling, 2002; doelling and kuehne, 2008). regionally, the moenkopi formation ranges in thickness from 240 to 910 feet (73–277 m); the moody canyon and torry members are 470 to 650 feet (143– 198 m), the sinbad member is 30 to 50 feet (9–15 m), and the black dragon member is 170 to 210 feet (52–64 m) in the northern part of the paradox fold and fault belt (hintze and kowallis, 2021). the contact with the overlying chinle formation is sharp and unconformable, but commonly poorly exposed. it is placed at the base of a distinctive white to mottled gritstone, or between the gray-red or gray-green mudstone and siltstone of the lower part of the chinle and the orange-red siltstones of the upper part of the moenkopi. drilling hazards the thick, mud-rich moenkopi formation also produces large washouts and openings during drilling like the overlying chinle formation as shown by caliper logs. operators have had to steer back to vertical due to deviation while drilling through the moenkopi and chinle and case through it to maintain circulation. the rop should be typically slow, consistent with a shale-dominated formation. permian black box dolomite lithology, thickness, and contacts the lower permian black box dolomite is equivalent to the kaibab formation (listed as such in many publications and maps covering the region) and was deposited on a shallow carbonate shelf. it generally consists of light gray, light brown, brown, or cream-colored cherty dolomite (appendix, figure a17) and limestone overlying yellow-gray to gray sandstone. in outcrop, a zone of light brown, sandy thin-bedded limestone or calcareous sandstone is locally present at the base of the formation, representing reworking of the underlying permian white rim sandstone (doelling, 2002). some limestone beds consist of oolitic grainstone whereas others are coarsely crystalline; sandstone beds are fine grained. nodules and geodes (up to 6 inches [15 cm] in diameter) composed of chert, quartz, or calcite are diagnostic features within these beds (doelling, 2002; doelling and kuehne, 2008). doelling (2002) reports that some geodes contain oil. carbonates range from thin to thick bedded whereas clastic beds are generally thin bedded. the black box dolomite, where present, ranges in thickness from 60 to 160 feet (18–49 m) (hintze and kowallis, 2021) (figure 6). to the east, the black box has been eroded off the uncompahgre uplift and thins and is missing to the south of the northern part of the paradox fold and fault belt where the moenkopi lies directly on the permian white rim sandstone or cutler formation. the erosional boundary between the permian and triassic is sharp, referred to as the tr-1 unconformity (pipiringos and o’sullivan, 1978). 154 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 drilling hazards the relatively thin black box dolomite should present few drilling problems. possible loss of circulation could occur in any fractured zones encountered and the rop should be typically slow, consistent with a carbonate-dominated formation. permian white rim sandstone lithology, thickness, and contacts the white rim sandstone, the uppermost formation on the lower permian cutler group, was deposited as coastal dunes (figure 6). it is a fineto medium-grained quartzose sandstone (appendix, figure a18), exhibiting both planar and cross-stratified beds. the upper section is a reworked marine unit whereas the lower unit is eolian-dominated having large-scale cross-stratification. the upper contact of the white rim strata with the overlying triassic beds is sharp, marked by local scouring and channeling and is unconformable. the white rim is up to 300 to 500 feet (90–150 m) thick (hintze and kowallis, 2021). it pinches out to the east as observed from the view west from dead horse point (doelling and chidsey, 2010). drilling hazards the chief drilling hazard associated with the white rim sandstone will be loss of circulation, especially when heavier drilling muds are required in the deeper paradox formation (smith, 1983). the white rim can have excellent porosity and permeability as seen in outcrops within the san rafael swell, but cores taken from wells farther to the west show it as almost a quartzite, which if encountered could damage drill bit cones. fractures are common and can lead to greater loss of circulation when encountered. however, while drilling the state 16-42 (section 16, t. 22 s., r. 17 e., slbl&m) in the same section as, but drilled previously to, the state 16-2 research well (figure 3), the drill string became stuck in the white rim resulting in a fishing operation and required a sidetrack hole. possible causes include (1) a decrease in hole size, as indicated by the caliper log due to excessive mudcake buildup in a highly porous and permeable section of the white rim, or (2) differential pressure from an overbalanced mud system (rose petroleum, written communication, 2019). the state 16-2 research well encountered significant water flow in the white rim and thus water flow could also be a major drilling problem when targeting the cane creek shale and deeper potential reservoirs. gas shows in the white rim sandstone have been observed in salt wash field (figure 3). water flows from the white rim in some wells on the hanging wall of the little grand wash fault (figure 9) are charged with carbon dioxide. finally, small amounts of hydrogen sulfide have also been reported in the white rim. permian organ rock formation lithology, thickness, and contacts the organ rock formation of the cutler group (figure 6) was deposited in a marginal to shallow marine environment and consists of reddish-brown, finegrained to silty sandstone, sandy shale, and minor siltstone (appendix, figure a19); it is medium to thick bedded. the upper contact of the organ rock strata with the overlying white rim sandstone is sharp and conformable. the organ rock ranges in thickness from 0 to 300 feet (0–90 m) (hintze and kowallis, 2021). drilling hazards the mud-rich organ rock formation also produces large washouts like the moenkopi and chinle formations. the rop should again be typically slow, consistent with a shale-dominated formation. permian elephant canyon formation lithology, thickness, and contacts the elephant canyon formation, the basal formation of the cutler group in the region (referred to as the pakoon dolomite in a number of past publications) (figure 6), was deposited on a shallow marine shelf and consists of interbedded pink dolomite, light gray to light brown or red sandstone and limestone (appendix, figure a20), locally cherty. sandstone is fine grained and com155 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 monly dolomitic; bedding is thin to thick (doelling, 2002). the elephant canyon formation ranges in thickness from 1000 to 1200 feet (300–370 m) (hintze and kowallis, 2021). regional analyses of fusulinid (welsh and bissell, 1979) and conodont (ritter and others, 2007) zones indicate an unconformity between the lower permian and upper pennsylvanian. drilling hazards the elephant canyon formation, although thick, should present few drilling problems. possible loss of circulation could occur in any fractured zones or sandstone beds encountered. the rop should be typically slow in carbonate-dominated sections and speed up in sandstone beds. the presence of chert within the carbonates can cause rapid and extensive wear on the bit as well as extremely slow drilling. permian cutler formation lithology, thickness, and contacts where the white rim sandstone is missing, as seen at its stratigraphic pinchout from dead horse point, the triassic moenkopi formation overlies the permian cutler formation, which is divided into informal upper and lower members (doelling and others, 2010) (figures 2 and 7). during the permian, the uncompahgre highland to the northeast that began during the pennsylvanian continued to rise, and erosion eventually exposed granitic and mafic (iron-manganese-rich) rocks that were very old (proterozoic, 570 to 2000 ma). the clastic erosional debris shed to the southwest into the dead horse point area and near arches national park was deposited as a series of alluvial fans at the foot of the mountain range; the embayment was filled and the ocean shorelines retreated farther to the southwest. the iron content of the source rocks imparted a red coloration to the rocks deposited in this area. granites, made up of quartz, feldspar, mica, and small percentages of dark iron-bearing minerals, were eroded and provided source material for sandstones rich in feldspar, or arkoses (doelling and others, 2010). the upper and lower members of the cutler formation are similar and were deposited in interfingering back beach, marine, fluvial, and alluvial-fan environments. they consist of interbedded arkosic sandstone, subarkosic sandstone, sandstone, conglomerate, micaceous siltstone, and limestone. in outcrop, many of the arkosic and subarkosic sandstone beds display trough cross-bedding and cut-and-fill structures. in the upper member of the cutler, arkosic and quartzose sandstones are mostly fine grained, well sorted, and micaceous (appendix, figure a21). the fluvially deposited arkoses, subarkoses, and conglomerates are dark red to purple whereas the eolian rocks are mostly orange and red-orange. the lower member of the cutler formation contains numerous gray marine limestone beds (appendix, figure a22), laid down during short intervals when the sea was able to push shorelines northeastward. these beds form the basis for dividing the lower from the upper member; the shafer trail below dead horse point is on a limestone bed representing the contact (doelling and chidsey, 2012). the number of limestone beds decreases northeastward. in outcrop, these are locally fossiliferous, containing brachiopods, bryozoans, gastropods, crinoid debris, and rare cephalopods and trilobites. the cutler formation ranges in thickness from about 900 to 1200 feet (300–370 m); the upper member and lower members are 700 to 1000 feet (200–300 m) and 180 to 220 feet (55–67 m) thick, respectively (doelling and others, 2010). the regional unconformity between the lower permian and upper pennsylvanian is found at the base of the cutler (welsh and bissell, 1979; ritter and others, 2007). drilling hazards the cutler formation, although thick, should present few drilling problems. possible loss of circulation could occur in any units with good intergranular porosity or fractured zones, particularly limestone beds, or sandstone/arkosic beds encountered. again, the rop should be typically slow in carbonate-dominated sections and speed up in sandstone-dominated sections. 156 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 pennsylvanian honaker trail formation lithology, thickness, and contacts the shallow marine honaker trail formation, the uppermost formation of the pennsylvanian hermosa group (figures 6 and 7), consists of interbedded sandstone, limestone, and siltstone in outcrop and cuttings (appendix, figure a23). the sandstone is very fine to fine grained, well to moderately sorted, micaceous, and calcareous; some beds are cross-bedded. bedding is thick to massive. limestone is gray to light gray, variably argillaceous (clayey), and 1 to 10 feet (0.3–3 m) thick. many limestone beds are fossiliferous, containing a marine fauna of crinoid debris, brachiopods, bryozoans, gastropods, foraminifera, and rare trilobites. chert nodules are common and many fossils have been silicified. the siltstone is micaceous, locally bioturbated, and cross-stratified. the honaker trail formation is 1600 to 5000 feet (490–1500 m) thick (doelling and others, 2010; hintze and kowallis, 2021). the contact between the pennsylvanian honaker trail formation and the overlying permian rocks of the cutler formation is a paraconformity, with beds of both formations parallel to one another. drilling hazards the honaker trail formation, although generally thicker than the elephant canyon and cutler formations, should likewise present few drilling problems. similarly, possible loss of circulation could occur in any fractured zones or porous sandstone beds encountered. the rop should also slow in carbonate-dominated sections and speed up in sandstone beds. chert is fairly common within the carbonates causing an extremely slow rop and rapid wear on the bits. some sandstone beds in the honaker trail formation produce gas in the paradox basin. gas shows in the honaker trail occur in drilling mud systems and from drill-stem tests. there is a possibility of gas in sandstones that pinchout updip to the southwest in the region. pennsylvanian paradox formation lithology, thickness, and contacts the targeted cane creek shale zone is within the paradox formation of the hermosa group (figures 6 and 7). the paradox formation was deposited on a shallow carbonate shelf to restricted marine environment in the paradox basin. the paradox formation is divided into (1) an upper member of interbedded dolomite (appendix, figure a24), dolomitic shale, and anhydrite, (2) a middle (saline) member consisting of thick halite interbedded with dolomite, dolomitic siltstone and shale, and anhydrite, and (3) a lower member consisting of interbedded black shale, siltstone, dolomite, and anhydrite. the thickness of the paradox formation is up to 14,000 feet (4270 m) in the interior of the basin where the paradox fold and fault belt is located (hintze and kowallis, 2021). the contact between the paradox formation and the overlying honaker trail formation is conformable and can be difficult to identify. conodonts and other fossils are often used to define the contact in outcrops and cores, but generally the first encounter of evaporites (anhydrite) is used in well logs. hite (1960), hite and cater (1972), and hite and buckner (1981) divided the middle member of the paradox formation in the evaporite basin into 29 salt cycles that onlap onto the basin shelf to the west and southwest (figure 12); rasmussen (2010) identified as many as 35 cycles. each cycle consists of a clastic interval/salt couplet described in detail by massoth and tripp (2011) and massoth (2012). the clastic intervals are typically interbedded dolomite, dolomitic siltstone, and organic-rich shale (appendix, figures a25, a27 through a32, and a36) generally overlain and underlain by anhydrite and halite (figure 13; appendix, figures a26 and a36). these intervals typically range in thickness from 10 to 200 feet (3–60 m) and are generally overlain and underlain by 200 to 400 feet (60–120 m) of halite beds. within the interior of the basin, a typical cycle consists of a black shale lithofacies overlain almost entirely by salt, whereas on the shelf, a cycle consists of a black shale lithofacies overlain primarily by carbonates. the regionally extensive black shale lithofacies allows correlation of salt cycles in the interior of the basin with 157 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 carbonate cycles on the shelf. the paradox formation is divided into informal zones, in descending order: ismay, desert creek, akah, barker creek, and alkali gulch (figure 12) (hite and cater, 1972; reid and berghorn, 1981). this terminology is currently the most common in the literature, as well as in completion and production reports. the cane creek shale zone is the basal part of cycle 21 in the alkali gulch zone (figure 12) and the targeted shale generally ranges from 0 to about 200 feet (0–60 m) thick. the cane creek consists of thin dolomitic sandstones/ siltstone and dolomite interbedded with anhydrite and organic-rich marine shale overlain and underlain by halite (smith, 1983; morgan, 1992; grove and others, 1993). the cane creek is divided into three intervals in descending order: a, b, and c (figure 13). the thickness of the a interval averages 31 feet (10 m), ranging from 10 to 84 feet (3–26 m); it is generally thicker to the north. the average thickness of the b interval is 26 feet (8 m), ranging from 4 to 72 feet (1.2–22 m). it forms a thick band east to west across the region. the average thickness of the c interval is 36 feet (11 m), ranging from 10 to 81 feet (3–25 m); it is generally thicker to the north as more sandstone is included. lithologically, the a interval is composed of alternating thin beds (1 to 4 feet [0.3–1.2 m] thick) of silty and anhydritic dolomitic mudstone (appendix, figure a33), gray to black shale and mudstone of low to high percent toc, and laminated to nodular anhydrite, with minor amounts of burrowed or bioturbated siltstone and fine-grained sandstone (chidsey and others, 2016; chidsey and eby, 2017; morgan and stimpson, 2017; jagniecki and others, 2021, 2022; vanden berg and others, 2022). porosity and permeability are low. the a interval was deposited under anoxic-saline conditions (jagniecki and others, 2021). the b interval, the primary fractured oil reservoir unit, is composed of interbedded, thin-bedded gray and black shale and mudstone of low to high percent toc, silty to sandy laminated dolomite, and abundant finegrained sandstone and siltstone beds (figures 14 and 15; appendix, figure a34) (chidsey and others, 2016; morgan and stimpson, 2017; jagniecki and others, 2021, 2022; vanden berg and others, 2022). bedded anhydrite figure 12. stratigraphic column for the paradox basin; cycles and informal zones with significant production are highlighted with colors. note the position of the cane creek shale, which occurs below the u.s. geological survey’s hovenweep, gothic, and chimney rock shale oil and gas assessment units (2012) in the paradox basin (also see chidsey, 2016). modified from hite (1960), hite and cater (1972), and reid and berghorn (1981). 158 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 is absent although some beds contain minor mottled anhydrite. wave ripples, burrows, and bioturbation are common in siltstone and sandstone. sandstone is thicker in the central and northern parts of the play. fractures and microfractures are commonly sealed with halite, anhydrite, clay, and calcite (chidsey and others, 2016; morgan and stimpson, 2017; jagniecki and others, 2021, 2022; gathogo and others, 2022; paronish and others, 2022). porosity and permeability are low to high. the b interval was deposited under oxic-fresher water conditions (jagniecki and others, 2021). the c interval is composed of interbedded abundant fine-grained sandstone and siltstone, silty dolomite, and laminated anhydrite with shale and mudstone of low percent toc in the lower part (appendix, figure a35) (chidsey and others, 2016; morgan and stimpson, 2017; jagniecki and others, 2021, 2022; vanden berg and others, 2022). wave ripples, burrows, and bioturbation are common in siltstone and sandstone. sandstone is thicker in the northern part of the play. porosity and permeability are medium to high. the b interval was deposited under mixed oxic-anoxic conditions (jagniecki and others, 2021). drilling hazards the targeted paradox formation poses the most drilling hazards and challenges for any well in the refigure 13. typical gamma ray-sonic log of the cane creek shale, long canyon field, grand county, utah, showing the divisions of the cane creek shale into “a,” “b,” and “c” intervals. cumulative production from a vertical wellbore in this well (to january 1, 2023) = 1,134,948 barrels of oil, 1.16 billion cubic feet of gas, and 610,423 barrels of water (utah division of oil, gas and mining, 2023b). see figure 3 for location of long canyon field. 159 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 gion. the loss of drilling fluids from the wellbore into fractured clastic beds is common. weighted drilling fluid could hydrofracture the salt and adjacent clastics, creating possible pathways for fluid circulation into the formation. gas shows or gas kicks can occur while drilling through paradox salt. (in 1964, texas gulf sulfur inc., began underground room-and-pilar mining of potash [sylvite] from the paradox cycle 5 along the cane creek anticline near dead horse point state park [figures 2 and 9]. underground mining operations were difficult due to pockets of natural gas, high temperatures, and contorted beds [phillips, 1975]. before mine figure 14. typical fractured, silty to muddy dolomite with thin siltstone and black organic-rich shale beds (left box) and silty to very fine grained sandstone (right box) deposited in the deep water, open marine environment of unit b in the cane creek shale zone; cane creek unit no. 26-3 well (section 26, t. 25 s., r. 19 e., slbl&m), big flat field, grand county, utah, slabbed core from 7418 to 7432 feet (2261–2265 m). core photography by triple o slabbing, denver, colorado, provided courtesy of fidelity exploration & production company. 160 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 operations began, 18 miners were killed in a gas explosion while constructing later shafts [huntoon, 1986]). to eliminate the potential for large gas kicks in clastic zones, 10,000-pound blowout preventors are required by the utah division of oil, gas and mining. nevertheless in january 2023, zephyr energy reported a major gas kick in their state no. 36-2 lnw-cc well (section 36, t. 22 s., r. 17 e., slbl&m, grand county, utah) when drilling encountered a major fracture network in the cane creek shale at 9598 feet (2925 m). the unexpected influx of gas was safely diverted at the surface and flared until the well was stabilized (press release, zephyr energy, january 19, 2023). washouts due to dissolution of salt beds may also occur but can be prevented by switching to oil-based muds (morgan and stimpson, 2017) and using the natural supersaturated brine available in the area (smith, 1983). the geology can be unpredictable due to salt movement. faults, folds, and vertical beds can be present that might jam drill bits. bedding in salt may be highly contorted and slowly flow into the wellbore. salt flow can result in sticking problems during drilling, coring, and logging operations, and later when setting casing, or completing or working over wells. salt flow can cause the casing to collapse. for example, bartlett flat field (now part of big flat field, figure 3) was originally discovered with a vertical well in 1962; however, after producing 26,000 bo, the production casing collapsed around the tubing and the original completion was abandoned (smith, 1983). drilling rapidly through the salt before it begins to flow and subsequently using high-strength casing cemented completely across the salt section are practices that can be employed to avoid salt-flow problems (e.g., greentown field [figure 3]). conducting three-dimensional seismic surveys over prospective areas will reduce drilling risks and lead to a better understanding of the salt tectonics and structure as well as define drilling targets. as mentioned earlier, the cane creek shale zone and other clastic cycles in the paradox formation are often overpressured and the water salinity is high. in greentown field (figure 3), blowouts occurred related to clastic cycles 18 and 19. overpressure in clastic cycle 1-a was encountered in three wells in the field requiring up to 12.8-pound mud to control; the wells likely penetrated an open fracture system due to salt tectonics. a blowout could result in potential flow of oil or brines into lower pressure zones in or around salts 21 or 22 (figure 13). such a drill hole could be shut-in for days or weeks. as a well penetrates the paradox, a number of overpressure indicators may be observed in the mud system: (1) an increase in background gas, (2) an increase in chlorides, and (3) the cuttings will increase in size and the shape will appear as if spalling has occurred. best practices involve drilling to the top of the salt section and setting casing. the objective of horizontal drilling in the cane creek shale is to penetrate the zone with the drill bit parallel to the bedding plane and perpendicular to open vertical or near-vertical natural fractures. the cane creek is not a flat-lying bed and is often folded due to salt tectonics so the trajectory of the wellbore can be very complex and sinusoidal as shown on figure 16 (morgan and stimpson, 2017). it is generally desirable to drill the bed at low dip (up or down) so the drill string can slide through the horizontal section. the cane creek has structural dip and secondary folding due to salt movement. these folds generally have a wave height of 300 feet (90 m) and distance of 1000 feet (300 m) (grove and others, figure 15. fractured silty to very fine grained sandstone in unit b in the cane creek shale zone. remington no. 21-1h wildcat well (section 21, t. 31 s., r. 23 e., slbl&m), san juan county, utah, photomicrograph (plane light) from 7450 feet (2270 m). from nielsen and others (2013). 161 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 1993). as a result, a horizontal lateral in the cane creek can have a wavy pattern in a structural dip. in addition, drilling horizontally in the a interval is difficult because of the presence of relatively thick anhydrite beds interbedded with soft shales or mudstones (i.e., the bit tends to “bounce” off the anhydrite beds). finally, the cane creek is challenging to core and prone to jamming (e.g., the anhydrite problem in the a interval or vertical/contorted), adding to the cost of the drilling operations through increased rig time and possible loss of the wellbore in the cane creek. summary the cane creek shale represents a major target for oil and gas in the paradox fold and fault belt of the paradox basin. exploratory wells may penetrate a section that ranges in age from cretaceous through pennsylvanian. drilling will encounter a wide variety of lithologies (carbonates, shale, mudstone, sandstone, and evaporites) that may result in both common and unusual hazards that can significantly add to rig time and well costs. these hazards include: (1) swelling clays, (2) high porosity-permeability or fractured zones resulting in lost circulation or excessive mudcake buildup, (3) kicks due to the influx of reservoir fluid, oil, water, or gas into the wellbore, (4) uranium-rich zones, (5) washouts, (6) hole deviation, sticking, and other well-integrity problems, (7) chert, and (8) overpressured intervals. these potential difficulties demonstrate the need for operators to carefully monitor mud systems (cuttings, background and trip gas, chlorides, circulation, etc.), the rate of penetration, and wellbore location to successfully find and produce oil and gas from the cane creek shale, other clastic zones in the paradox formation, and deeper formations. following these recommendations and the lessons learned from past drilling efforts, figure 16. horizontal profile of the lateral drilled in the cane creek unit 26-3h well (ne1/4sw1/4 section 26, t. 25 s., r. 19 e., slbl&m, grand county; bottom-hole location – sw1/4nw1/4 section 25), big flat field. the lateral was drilled in a down-dip direction and encountered secondary salt folding that added to the difficulty of keeping the wellbore in the target zone of the cane creek shale. the well bottomed in the underlying salt after encountering an apparent dip reversal. data from utah division of oil, gas and mining well records. after morgan and stimpson (2017). 162 potential drilling hazards for wells targeting the cane creek shale, pennsylvanian paradox formation, paradox fold and fault belt, southeastern utah and southwestern colorado chidsey, t.c., jr. geology of the intermountain west 2023 volume 10 drilling engineers and operators can plan for potential hazards when exploring for hydrocarbons in the cane creek shale in the fairly remote, relatively sparsely explored paradox fold and fault belt. the result should be de-risking wells by successfully and safely drilling to the cane creek shale reservoir or other targets with minimal unexpected cost and rig downtime, ultimately leading to additional commercial hydrocarbon discoveries in the region. acknowledgments this research was conducted as part of a project titled “improving production in utah's emerging northern paradox unconventional oil play,” funded by the u.s. department of energy, national energy technology laboratory, contract number  de-foa-0001990. support was also provided by the utah geological survey (ugs), the energy & geoscience institute of the university of utah, and zephyr petroleum company (formerly rose petroleum).   cheryl wing, jay hill, jen miller, john good, and jackie dewolfe of the ugs prepared figures. elliot a. jagniecki and michael d. vanden berg of the ugs and dave list and gregor maxwell of zephry energy provided valuable information from the state 16-2 research well and other wells in the region. well cuttings were compiled by thomas dempster at the ugs’s utah core research center and photographed by austin jensen and eugene szymanski of the ugs. this paper was carefully reviewed by michael d. vanden berg, stephanie m. carney, michael d. hylland, bill keach, and adam mckean of the ugs, and the editors of this publication. their suggestions and constructive criticism greatly improved the manuscript. references baars, d.l., 1966, pre-pennsylvanian paleotectonics—key to basin evolution and petroleum occurrences in the paradox basin, utah and colorado: american association of petroleum geologists bulletin, v. 50, no. 10, p. 2082– 2111. baars, d.l., and stevenson, g.m., 1982, subtle 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10–11, https://doi.org/10.34191/snt-50-1. welsh, j.e., and bissell, h.j., 1979, the mississippian and pennsylvanian (carboniferous) systems in the united states—utah: u.s. geological survey professional paper 1110-y, 35 p. wiseman, t.j., and eckels, m.j., 2020, proven and hypothetical helium resources in utah: utah geological survey miscellaneous publication 174, 52 p., 1 plate, scale 1:850,000, https://doi.org/10.34191/mp-174. wood, r.e., and chidsey, t.c., jr., 2015, oil and gas fields map of utah: utah geological survey circular 119, scale 1:700,000, https://doi.org/10.34191/c-119. https://oilgas.ogm.utah.gov/pub/publications/reports/prod/well/wel_dec_2022.pdf https://doi.org/10.34191/snt-53-1 https://pubs.usgs.gov/fs/2012/3031/fs12-3031.pdf chidsey. t.c., jr. appendix photographs of selected drill cuttings a-1 appendix photographs of selected drill cuttings from the cretaceous mancos shale through the pennsylvanian paradox formation, paradox fold and fault belt, paradox basin, utah chidsey. t.c., jr. appendix photographs of selected drill cuttings a-2 introduction this appendix contains close-up photographs of selected drill cuttings from wells in the paradox fold and fault belt in the northern part of the paradox basin, utah. these cuttings cover all formations that may be encountered when drilling a well in the region targeting the cane creek shale and other clastic cycles of the pennsylvanian paradox formation: the cretaceous mancos shale into the pennsylvanian paradox formation (text figures 6 and 7). all cuttings are publicly available at the utah geological survey’s utah core research center in salt lake city. the photographs of the cuttings were taken dry, using a high-resolution digital camera. the scales are the same in all photographs. refer to figure 3 in the text for the locations of the wells from which the cuttings were obtained. each photograph includes the formation and/or member name; well name, location, and api number; and a brief general description from the mudlog or wellsite geologist’s drilling report (well logs and mudlogs are publicly available at the utah division of oil, gas and mining’s website [https://oilgas.ogm.utah.gov/oilgasweb/index.xhtml] under well files and well logs); note, at the time of this paper, the confidentiality period for the state 16-2 research well was still in effect (renamed the state 16-2ln-cc, api no. 43-019-50089, after the horizontal leg was drilled; the operator is listed as rose petroleum). the cuttings are meant to represent the typical characteristics, such as lithology, grain size, and color of the drilled formations. they were generally taken from the middle or well into the individual formations, so the material contains fewer grains sloughed off from formations above. certain formations include members with distinct characteristics that differ from other members. in many of those cases, cuttings from specific members are included. in other instances, the depth ranges of the cuttings in the sample envelopes cover anywhere from 10 to as much as 50 feet (3–15 m) of section. thus, intervals that cross formation/member boundaries were not used. some members are relatively thin and identifying a specific set of cuttings was not always possible. finally, the cuttings photographed were simply what were in the sample envelopes and thus, there was no hand picking of individual rock chips, which would not be representative of the section drilled. the paradox formation consists of cycles of clastic interval/salt couplets, as described in more detail in the main report text. the clastic intervals are typically composed of significant amounts of fine-grained sandstone interbedded with dolomitic siltstone, dolomite, organic-rich shale and mudstone, and anhydrite generally overlain and underlain by halite. because many of these clastic intervals look very similar, only nine examples, which show some variations from each other, are included in this appendix; one example of halite is also included. the cane creek shale is divided into three intervals in descending order: a, b, and c (text figure 13). because the cane creek is the primary drilling objective, it is critical to identify these intervals even if the differences are very subtle. therefore, examples of cuttings from each interval are included in this appendix. (note: the core descriptions, reservoir data, and other information obtained from the cane creek shale in the state 16-2 research well was presented in gathogo and others, 2022; jagniecki and others, 2021, 2022; paronish and others, 2022; szymanski and reiners, 2022; chidsey. t.c., jr. appendix photographs of selected drill cuttings a-3 vanden berg and others, 2022.) the purpose of this appendix in providing photographs of drill cuttings from the formations possibly penetrated by wells targeting the cane creek shale is to serve as an additional guide, along with mudlogs and geophysical logs, for the mudlogger and wellsite geologist during drilling operations. the appendix can also help geologists in their mapping and exploration efforts by using the photographs as templates to evaluate wells where cuttings or cores are not available. it is certainly not all-inclusive because stratigraphic units and facies change throughout the region. finally, the photographs and descriptions of these cuttings will help drilling engineers, and their geologic counterparts, in identifying potential drilling hazards that may be encountered when targeting the cane creek shale, other clastic cycles in the paradox formation, or deeper formations. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-4 mancos shale book cliff 3 section 10, t. 18 s., r. 24 e., slbl&m, grand co., utah api no.: 43-019-31366 330–360 feet figure a1. shale, medium to dark gray to gray-brown, slightly silty in part, soft to medium firm, platy to blocky; relatively small-sized cuttings. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-5 naturita (dakota) formation grand wash fault unit 14-24 section 24, t. 21 s., r. 15 e., slbl&m, emery co., utah api no.: 43-015-11182 610–620 feet figure a2. sandstone, light to dark gray or tan to orange-gray or light purple, very fine to fine grained, friable, sub-angular to rounded, moderate to well sorted, occasional iron staining; shale, light to dark gray, platy, occasionally carbonaceous; distinctively larger and variable sized cuttings than the mancos shale above. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-6 cedar mountain formation, ruby ranch member grand wash fault unit 14-24 section 24, t. 21 s., r. 15 e., slbl&m, emery co., utah api no.: 43-015-11182 630–640 feet figure a3. mudstone/shale, dark red and reddish to purplish orange, soft, clayey to silty, platy; sandstone, tan to gray, very fine to fine grained, sub-angular to sub-rounded, poorly sorted; occasional limestone from limestone nodules; contact with underlying brushy basin member of the morrison formation difficult to recognize with cuttings as well as in outcrop when the basal buckhorn conglomerate member is absent because they have near-identical characteristics. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-7 morrison formation, salt wash member grand wash fault unit 14-24 section 24, t. 21 s., r. 15 e., slbl&m, emery co., utah api no.: 43-015-11182 910–920 feet figure a4. sandstone, buff to white to light red, quartzose, very fine to coarse grained, friable to well cemented, sub-angular to well rounded, moderate to well sorted, calcareous cement. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-8 summerville formation green river unit 1 section 2, t. 22 s., r. 16 e., slbl&m, grand co., utah api no.: 43-019-10030 645–650 feet figure a5. mudstone/shale, light brown-red, sandy to clayey, platy to blocky; siltstone to sandstone, pale red, very fine to fine grained, granular, calcareous; some gray limestone. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-9 curtis formation green river unit 1 section 2, t. 22 s., r. 16 e., slbl&m, grand co., utah api no.: 43-019-10030 790–795 feet figure a6. sandstone, cream to pale red to greenish gray, quartzose, very fine to medium grained, poorly to moderately sorted, sub-rounded to sub-angular, calcite to dolomitic cement; claystone/shale, light gray to greenish gray. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-10 entrada sandstone green river unit 1 section 2, t. 22 s., r. 16 e., slbl&m, grand co., utah api no.: 43-019-10030 1000–1005 feet figure a7. sandstone, pinkish cream, quartzose, friable, silty, very fine to medium grained, poorly to moderately sorted, good porosity, sub-rounded to rounded; cuttings consist of variable sizes. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-11 carmel formation state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 1620–1650 feet figure a8. sandstone (80%), translucent, light orange to pink, friable to firm in part, fine to medium grained, rounded to sub-angular, moderately to poorly sorted, calcareous cement; shale (20%), red-brown, firm, earthy to silty, sandy in part, slightly calcareous, grading to interbedded silts; probably represents the basal judd hollow member of the carmel formation. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-12 navajo sandstone state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 1650–1700 feet figure a9. sandstone, quartzose, translucent, white to light orange, firm to friable in part, fine to medium grained, frosted, rounded to sub-angular, well sorted, good intergranular porosity, calcareous cement. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-13 kayenta formation state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 2050–2100 feet figure a10. sandstone, quartzose, pale orange-brown colored, fine grained, friable, well sorted, moderate to good intergranular porosity, siliceous to slightly calcareous cement, occasional redbrown silty matrix. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-14 wingate sandstone state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 2200–2250 feet figure a11. sandstone, quartzose, light orange-brown to white, very fine to fine grained, subangular to rounded, distinctively smaller sized cuttings than the navajo sandstone or kayenta formation above. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-15 chinle formation, church rock member state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 2650–2700 feet figure a12. shale, silty in part, red-brown, calcareous mottling, blocky, firm to brittle, grading to siltstone, possible rare fossil fragments; distinctively small-sized cuttings. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-16 chinle formation, moss back member state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 2850–2900 feet figure a13. sandstone, red-brown to purplish-brown to off white, fine grained, firm, subangular to sub-rounded, well sorted, argillaceous matrix in part, calcareous, trace of conglomerate; distinctively larger-sized cuttings than the church rock member above. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-17 moenkopi formation, moody canyon member state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 2950–3000 feet figure a14. sandstone, light orange-brown to light brown, firm to slightly hard, fine to very fine grained, sub-angular to sub-rounded, red-brown argillaceous matrix in part, calcareous. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-18 moenkopi formation, sinbad limestone member state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 3450–3500 feet figure a15. shale, brown, blocky to platy, silty in part grading to siltstone; limestone, translucent to white, clean crystalline calcite, occasionally sandy. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-19 moenkopi formation, black dragon member state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 3500–3550 feet figure a16. sandstone, white to reddish-brown, quartzose, clean, medium to fine grained, poorly to moderately sorted, calcite and silica cement; distinctively larger-sized cuttings than the sinbad limestone above. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-20 black box dolomite jakey’s ridge 34-15 section 15, t. 23 s., r. 16 e., slbl&m, emery co., utah api no.: 43-015-10737 2440–2460 feet figure a17. dolomite, gray to light gray, platy, finely crystalline, noncalcareous (dolomite), no visible porosity, some possible chert; distinctively smaller-sized cuttings than the black dragon member of the moenkopi formation above. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-21 white rim sandstone state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 3600–3650 feet figure a18. sandstone, white to translucent, quartzose, fine to medium grained, frosted, hard to firm, sub-angular to sub-rounded, moderately to well sorted, calcareous cement, trace of very fine pyrite. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-22 organ rock formation state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 3900–3950 feet figure a19. sandstone, moderate to abundant orange-brown matrix, very fine to medium grained, rounded to sub-rounded, calcareous cement, occasional sandy limestone in part; siltstone grading to shale, orange brown to brown, slightly to very calcareous, abundant mica; distinctively very small sized cuttings. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-23 elephant canyon formation state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 4600–4650 feet figure a20. limestone, dark gray to light gray to gray-brown, mudstone to wackestone, cryptocrystalline to microcrystalline, massive, calcareous; sandstone, red-brown to gray to light orange, translucent to frosted, firm to hard, fine to medium grained, sub-angular to subrounded, moderately to well sorted, calcareous cement, trace of dark gray shale. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-24 cutler formation, upper member long canyon 1 section 9, t. 26 s., r. 19 e., slbl&m, grand co., utah api no.: 43-019-15925 1362–1393 feet figure a21. arkose, dark red to orange, friable, very fine to medium grained, angular to subangular, moderately to well sorted, occasional small gray lithic fragments, calcareous cement; distinctively very small sized cuttings. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-25 cutler formation, lower member long canyon 1 section 9, t. 26 s., r. 19 e., slbl&m, grand co., utah api no.: 43-019-15925 2127–2158 feet figure a22. limestone, light gray, friable, mudstone to wackestone, slightly argillaceous, calcareous; distinctively very small sized cuttings. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-26 honaker trail formation state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 5300–5350 feet figure a23. siltstone, light brown to brown, slightly sandy in part, brown argillaceous matrix, occasional mica, calcareous; interbedded with limestone and sandstone; limestone, dark gray to brown-gray to gray, wackestone to mudstone, microcrystalline to cryptocrystalline, massive, calcareous; sandstone, light gray to translucent, frosted, firm, very fine to fine grained, subangular to sub-rounded, moderately to well sorted, calcareous cement. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-27 paradox formation state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 6250–6300 feet figure a24. dolomite, limestone in part, light to medium gray, laminated, microgranular to silty, slightly argillaceous, anhydrite blebs; anhydrite, white, soft. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-28 paradox formation, clastic cycle 1a state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 6421–6432 feet figure a25. dolomite, gray-brown, wackestone to packstone, microcrystalline; shale, black to dark gray, firm, blocky, calcareous; anhydrite, white, soft, microcrystalline, amorphous, noncalcareous. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-29 paradox formation, salt cycle 1 state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 6510–6570 feet figure a26. halite (salt), white to off white, translucent to opaque, crystalline, brittle to hard; this description applies to all subsequent halite beds. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-30 paradox formation, clastic cycle 1 state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 7060–7070 feet figure a27. limestone, gray, mudstone, cryptocrystalline, bitumen alteration, rippled appearance; shale (below limestone [not shown]), black, earthy to waxy, occasionally carbonaceous, calcareous. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-31 paradox formation, clastic cycle 7 state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 8020–8040 feet figure a28. dolomite, light to dark gray, laminated, argillaceous to shaly; shale (10% to 15%), medium to dark gray, organic-rich, carbonaceous (sooty); anhydrite (5% to 10%), white, soft to firm, slightly to moderately calcitic. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-32 paradox formation, clastic cycle 8 state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 8220–8250 feet figure a29. dolomite, light to dark gray, laminated, argillaceous to shaly in part; shale (10% to 15%), medium to dark gray to black, organic-rich, carbonaceous (sooty); anhydrite (5% to 10%), white, soft to firm, slightly to moderately calcitic. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-33 paradox formation, clastic cycle 10 state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 8480–8500 feet figure a30. dolomite (40%), gray to light gray, finely laminated in part; halite (30%); shale (15%), black, firm to soft, earthy to waxy in part, calcareous to slightly calcareous, occasionally carbonaceous (sooty) appearance; anhydrite (15%), white, soft to firm, slightly to moderately calcitic; distinctively larger-sized cuttings than clastic intervals above. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-34 paradox formation, clastic cycle 14 state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 8800–8830 feet figure a31. dolomite, light gray, mudstone to wackestone, cryptocrystalline to microcrystalline in part, argillaceous, calcareous; shale, black, firm to soft, blocky to platy, earthy to waxy, occasionally carbonaceous (sooty) appearance, slightly calcareous. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-35 paradox formation, clastic cycle 18 state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 9260–9270 feet figure a32. shale, black to dark gray, soft to firm, organic-rich, carbonaceous (sooty), bitumen, calcareous; dolomite, light to medium gray, chalky to micro sucrosic; anhydrite, light gray to white, soft, chalky; halite. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-36 paradox formation, cane creek shale (cycle 21), a interval state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 9633–9638 feet figure a33. siltstone, dark to medium to light gray, sandy, fine grained; dolomite, dark to medium to light gray, mudstone, anhydritic; shale, black, firm, blocky, carbonaceous (sooty appearance), earthy, very slightly calcareous; anhydrite, white, chalky, occasionally microcrystalline. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-37 paradox formation, cane creek shale, b interval state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 9670–9680 feet figure a34. siltstone, light to medium gray, sandy, fine grained; limestone, light to medium gray, silty, dolomitic, brittle, mudstone; shale, black, firm to hard, blocky, earthy to waxy, organic-rich (sooty appearance), calcareous in part. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-38 paradox formation, cane creek shale, c interval state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 9700–9710 feet figure a35. siltstone, dark to medium to light gray, sandy, fine grained; dolomite, light gray to gray, silty, laminated, mudstone to wackestone, cryptocrystalline to microcrystalline, firm, anhydritic to argillaceous, calcareous in part; shale, black, firm to hard, blocky, earthy to waxy, organic-rich (sooty appearance), calcareous in part. chidsey. t.c., jr. appendix photographs of selected drill cuttings a-39 paradox formation, salt cycle 21 and clastic cycle 22 state 16-2 section 16, t. 22 s., r. 17 e., slbl&m, grand co., utah api no.: 43-019-50089 9730–9740 feet figure a36. halite, white to opaque to light brown, coarse, crystalline, brittle to hard; dolomite, light to medium gray, laminated to massive, calcareous to anhydritic, silty to organic-rich, mudstone; shale, black, dense, organic-rich. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa colin boisvert, gunnar t. bivens, brian curtice, ray wilhite, mathew wedel geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover a skeletal reconstruction and life restoration of the enigmatic late jurassic morrison formation sauropod haplocanthosaurus (scale is 2 m). image of skeletal reconstruction is by gunnar bivens and image of life restoration is by jun-hyeok jang. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 12 2025 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2023–2024 uga board president keilee higgs keileeann@utah.gov 801.678.3683 president-elect rob buehring robbuehring@yahoo.com 713.412.9269 program chair mike arnoff marnoff@utah.gov 385.303.0431 treasurer will hurlbut wdhurlbut@gmail.com 860.733.3190 secretary trae boman tboman@teanues.com 801.648.5206 past president eugene syzmanski eugenes@utah.gov 801.537.3364 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greggavin@gmail.com 513.509.1509 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.580.1331 aapg house of delegates 2023–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor william lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 1 abstract currently known from two valid species, haplocanthosaurus priscus and h. delfsi, the late jurassic sauropod haplocanthosaurus (morrison formation, western united states) has often been described as an enigmatic sauropod taxon due to its unstable phylogenetic position and paucity of specimens. here, we quantify the number of haplocanthosaurus specimens known from the literature and in collections. although most regions of the postcranial skeleton are known, the most commonly found elements of haplocanthosaurus are vertebrae (dorsals and caudals) and tibiae. our investigation identified twelve individuals of haplocanthosaurus from ten localities across four states, colorado, utah, montana (private specimen), and wyoming, making haplocanthosaurus spatially widespread in the central part of the morrison formation. the existence of twelve individuals across four states indicates this genus was widely distributed and more abundant than historically thought. haplocanthosaurus has been characterized as a ‘primitive’ sauropod restricted to the lower half of the morrison formation, but the identification of haplocanthosaurus in the dry mesa dinosaur quarry confirms that the genus was also present within the upper part of the morrison formation. census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa colin boisvert1, gunnar t. bivens2, brian curtice3, ray wilhite4, mathew wedel5 1oklahoma state university center for health sciences, tulsa, ok 74107 usa; cdboisvert1998@gmail.com 2mesa community college, mesa, az usa; gunnarbivens@gmail.com 3arizona museum of natural history, mesa, az 85202 usa; bcurtice@asu.edu 4auburn university, auburn, al 36849 usa; drw0004@auburn.edu 5western university of health sciences, pomona, ca 91766 usa; mathew.wedel@gmail.com citation for this article. boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m., 2025, census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa: geology of the intermountain west, v. 12, p. 1–23, https://doi.org/10.31711/giw.v12.pp1-23. introduction haplocanthosaurus has long been considered among the most enigmatic of late jurassic morrison formation sauropods (mcintosh and williams, 1988; curtice et al., 2023). it has been recovered in several disparate positions, either as a basal macronarian (upchurch, 1995; wilson and sereno, 1998; upchurch et al., 2004b), a brachiosaurid (riggs, 1904), a derived eusauropod outside neosauropoda (harris, 2006), or (the most well-supported position currently) a basal diplodocoid (wilson 2002; whitlock, 2011; mannion et al., 2012; tschopp et al., 2015a). hatcher (1903a) used the name haplocanthus priscus for a partial skeleton recovered from marshfelch quarry 1 in colorado (cañon city quarry 1 and felch quarry 1 are synonymous with marsh-felch quarry 1; we use the latter designation throughout) (figure 1). later hatcher (1903b) incorrectly believed his name was preoccupied by the acanthodian fish haplacanthus (agassiz, 1844), and proposed the replacement name haplocanthosaurus. the two names were not, however, identical in either spelling or pronunciation and so haplocanthus held priority over haplocanthosaurus until the international commission on zoo2 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 logical nomenclature ruled to suppress it (iczn, 1991). a second species, haplocanthosaurus ‘utterbacki’, was also named by hatcher (1903c) for a second, more complete partial skeleton from the same quarry, and a third, haplocanthosaurus delfsi, was named for a specimen that was both larger and stratigraphically older than either h. priscus or h. ‘utterbacki’ (mcintosh and williams, 1988). in addition to some less complete specimens found either at or in the vicinity of marsh-felch quarry 1, new colorado material was found both near the town of snowmass (foster and wedel, 2014) and at the extensive dry mesa dinosaur quarry (boisvert et al., 2024). material has also been recovered from two different sites in wyoming (erickson, 2014; tschopp et al., 2019), two in utah (bilbey et al., 2000; the other new to the literature), and finally a possible new specimen from montana (ronson, 2016). contrary to previous statements, haplocanthosaurus is more common than once thought (wilson and sereno, 1998; foster and wedel, 2014; maidment, 2024). this study provides a short description of eleven publicly held valid haplocanthosaurus specimens from nine locales in three states and currently held in eight public collections with a note on other possible public specimens, as well as specimens that should not be identified as haplocanthosaurus. materials and methods members of our team visited collections to examine as many specimens as possible firsthand. for the figure 1. spatial distribution map showing all confirmed haplocanthosaurus locales, with the area around garden park, colorado, inset zoomed in to show the comparative abundance of specimens found in this area. the states shown here contain surface exposures of the morrison formation. 3 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 remaining specimens, we relied on published sources, unpublished photographs, and assistance from museum staff. measurements were taken, when possible, for comparison. identification to genus and/or species level was made using measurements and known autapomorphies. diagnostic characters of the various haplocanthosaurus specimens are given in table 1, and information on the multiple specimens is provided in table 2. we follow the terminology of wilson (1999, 2012) for vertebral laminae and wilson et al. (2011) for vertebral fossae. furthermore, a map of the known haplocanthosaurus specimens was produced (figure 1). whereas it would be greatly beneficial to place all of the known haplocanthosaurus specimens into a well-calibrated stratigraphic framework, unfortunately, such does not yet exist for the entirety of the morrison formation. on the northern part of the colorado plateau, the morrison formation can be divided into three distinct members (the tidwell, salt wash, and brushy basin members). outside the colorado plateau, some local sections can be correlated to the tidwell, salt wash, and brushy basin (e.g., the oklahoma panhandle, richmond et al., 2020), but others show no clear correlation (e.g., the black hills of wyoming, foster et al., 2020). long-distance correlations based on an inferred “clay change” (turner and peterson 1999) have not been supported by the absolute dates provided by radiometric dating (trujillo 2006, trujillo and kowalis, 2015). in the absence of radiometric dates for most of the haplocanthosaurus localities, we have placed the known specimens into relative correlation where possible (table 3). institutional abbreviations blm – bureau of land management, utah, usa byu – brigham young university, provo, utah, usa cm – carnegie museum of natural history, pittsburgh, pennsylvania, usa cmnh – cleveland museum of natural history, cleveland, ohio, usa dmns – denver museum of nature and science, denver, colorado, usa fhpr – utah field house of natural history state park museum, vernal, utah, usa mwc – dinosaur journey, museums of western colorado, fruita, colorado, usa mmch – museo municipal ‘ernesto bachman’, villa el chocón, neuquén, argentina ncsm – north carolina museum of natural sciences, raleigh, north carolina, usa smm – science museum of minnesota, st. paul, minnesota, usa usnm – united states national museum of natural history, washington, d.c., usa ypm – yale peabody museum of natural history, new haven, connecticut, usa systematic paleontology dinosauria owen, 1842 saurischia seeley, 1888 sauropodomorpha huene, 1932 sauropoda marsh, 1878 neosauropoda bonaparte, 1986 diplodocoidea upchurch, 1995 haplocanthosaurus hatcher, 1903b type species: haplocanthosaurus priscus hatcher, 1903a. revised diagnosis the genus haplocanthosaurus is diagnosed by the following characters (autapomorphies marked with asterisks): (1) presacral centra pneumaticity—procamerate, (2) simple lateral pneumatic fossae in the cervical and dorsal vertebrae, (3) dorsal neural arches with elongate cpols* (unambiguous autapomorphy), (4) dorsal neural arches dorsoventrally heightened relative to total vertebral height, (5) mid-posterior dorsal diapophyses projecting dorsolaterally at 45° and approaching the dorsoventral height of the neural spines* (unambiguous autapomorphy), (6) large articular chevron facets on caudal vertebrae, (7) caudal vertebrae neural canals anteriorly inclined* (ambiguous autapomorphy), (8) scapular acromion process narrow, (9) scapular blade with a dorsally and ventrally expanded distal end, (10) large obturator foramen of pubis, (11) ambiens process absent (within diplodocoidea, this state is only shared 4 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 with limaysaurus tessonei), (12) proximal femur medial to the midshaft meridian (mmm) ratio about 75% (unique within diplodocoidea, see sassani and bivens, 2017, figure 9), and (13) tibia with a flared distal end. additionally, haplocanthosaurus can be assigned to diplodocoidea based on the following shared apomorphies: (1) dorsal neural spine prsl formed by conjoined sprl (seen in all diplodocoids except supersaurus vivianae), (2) cervical rib anteroposterior lengths shorter than respective centra, and (3) posterolaterally facing fibular facet of astragalus. other diagnoses wilson and sereno (1998) considered the proximal end of the tibia subcircular. however, our personal observation suggests this profile is more likely due to diagenetic distortion than a legitimate feature. wilson (2002) also considered the presence of 13 dorsal vertebrae an autapomorphy of haplocanthosaurus by way of reversal. thirteen dorsal vertebrae, however, appear to be the plesiomorphic condition for eusauropoda, with reduced vertebral counts in some mamenchischaracter specimen(s) source cervical ribs shorter than centra cm 572, 879, cmnh 10380 hatcher (1903c), whitlock (2011) procamerate presacral vertebrae byu 11506, 17530, 17689, cm 572, 879, cmnh 10380, mwc 8028 wedel (2003, 2005), foster and wedel (2014), boisvert et al. (2024) 13 dorsal vertebrae cm 879 wilson (2002) long dorsal cpols byu 17530, 17531, cm 572, 879, cmnh 10725, 10380 wilson (2002) dorsal diapophyses at 45° byu 11506, 17530, 17531, cm 572, 879, cmnh 10725, 10380, fhpr 1106 hatcher (1903c), mcintosh and williams (1988), wilson (2002), boisvert et al. (2024) dorsal prsl formed by sprls byu 11506, 17530, cm 572, 879, cmnh 10380 whitlock (2011) caudal vertebrae with large chevron facets cm 572, 879, 36034, 36036, cmnh 10380, mwc 8028, smm p 90.37.10 mcintosh and williams (1988), foster and wedel (2014) scapular acromion narrow cm 879 wilson (2002) proportionally large obturator foramen cm 572, cmnh 10380 hatcher (1903c), personal observation scapular distal end expanded cm 879, cmnh 10380 mcintosh and williams (1988), wilson (2002) tibia distal end flared byu 12865, cm 2043, cmnh 10725, usnm v 4275 mcintosh and williams (1988), boisvert et al. (2024) posterolaterally facing fibular facet of the astragalus smm p 90.37.10, usnm v 4275 whitlock (2011) lack of ambiens process cm 572, cmnh 10380, fhpr 1106 hatcher (1903c), mcintosh and williams (1988) dorsal neural arches dorsoventrally heightened relative to total vertebral height byu 11506, 17530, 17531, 17689, cm 572, 879, cmnh 10380, fhpr 1106, mwc 8028 hatcher (1903c), mcintosh and williams (1988), foster and wedel (2014), boisvert et al. (2024) simple lateral pneumatic fossae in presacral vertebrae byu 11506, 17530, 17531, 17689, cm 572, 879, cmnh 10380, fhpr 1106, mwc 8028 hatcher (1903c), mcintosh and williams (1988), foster and wedel (2014), boisvert et al. (2024) caudal vertebrae neural canals anteriorly inclined cm 572, 879, cmnh 10380, fhpr 1106, mwc 8028, smm p 90.37.10 hatcher (1903c), mcintosh and williams (1988), foster and wedel (2014), erickson (2014) table 1. diagnostic characters of haplocanthosaurus, and the specimens in which they are visible. 5 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 specimen number quarry strat age species year described state known elements usnm v 4275 marsh-felch quarry 1 morrison, age unknown h. priscus 1896 co left femur, right femur, both ischia, left tibia, left fibula, left astragalus cm 572 marsh-felch quarry 1 morrison, age unknown h. priscus 1903 co two posterior cervicals, ten dorsals, five sacrals, both ilia, both ischia, and both pubes, nineteen anterior caudals, two chevrons, a nearly complete series of ribs, and a left femur cm 879 marsh-felch quarry 1 morrison, age unknown h. priscus 1903 co ten cervical, thirteen dorsal, five sacral, and seven caudal vertebrae, several ribs, left scapula, right coracoid cm 2043 marsh-felch quarry 1 morrison, age unknown h. priscus 1981 co right tibia, fibula, and astragalus cm 2046 marsh-felch quarry 1 morrison, age unknown h. priscus 1981 co left tibia and fibula cm 33995 marsh-felch quarry 1 morrison, age unknown h. priscus 1981 co left scapula cmnh 10380 cleveland-delfs quarry morrison, age unknown h. delfsi 1988 co four anterior cervicals, nine posterior dorsals with ribs on left side, five sacrals, fourteen anterior caudals, several chevrons, partial left scapula, possible fragmentary coracoid, right sternal plate, partial left radius and ulna, both ilia, left pubis, left femur, and left ischium smm p 90.37.10 poison creek quarry morrison, age unknown h. sp. 2014 wy left tibia, fibula, astragalus, calcaneum, and foot minus proximal phalanx of digit one, along with 30 articulated caudal vertebrae smm d14-77 poison creek quarry morrison, age unknown h. sp. undescribed wy tibiae, caudal vertebrae p 78.21.20 p 78.21.36 p 84.15.72 p 87.14.6 fhpr 1106 william’s slow eagle quarry salt wash (upper) h. sp. 2000, paper in prep ut cervical, dorsal, sacral, and caudal vertebrae, scapulocoracoid, humerus, radius, ulna, metapodial elements, femur, tibia, fibula, ribs, and pelvic material mwc 8028 gordon-bramsonbrothers quarry morrison, age unknown h. sp. 2014 co four dorsal centra, five partial ribs, sacrum, five caudal vertebrae, three chevrons, five partial neural spines, and bone fragments. cm 312 rfprb morrison, age unknown h. sp. 2019 wy anterior caudal vertebrae, chevrons, partial ischium cm 36034 rfprb morrison, age unknown h. sp. 2019 wy two middle caudal vertebrae cm 36036 rfprb morrison, age unknown h. sp. 2019 wy middle caudal vertebra byu 9194, 11506, 12865, 17530-1, 17689 dry mesa dinosaur quarry brushy basin (middle) h. sp. 2024 co seven dorsal vertebrae (three articulated, four disarticulated), right tibia blm field specimen tal site salt wash (upper) h. sp. undescribed ut dorsal vertebra, ribs cmnh 10725 oil creek quarry morrison, age unknown h. sp. undescribed co two partial dorsal vertebrae, right tibia, and bone pieces table 2. confirmed haplocanthosaurus specimen information including stratigraphic age, location (discovery and curation), paper mention/description, and material available. rfprb = red fork of the powder river quarry b. 6 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 aurids (e.g., “omeisaurus” tianfuensis, he et al., 1988; xinjiangtitan shanshanesis, zhang et al., 2022), all macronarians, and flagellicaudata. within diplodocoidea, 13 dorsal vertebrae are seen in rebbachisauridae (e.g., nigersaurus taqueti, the unnamed specimen mmch-pv 49, see vidal, 2019). haplocanthosaurus priscus hatcher, 1903a =haplocanthus priscus hatcher, 1903a =haplocanthosaurus utterbacki hatcher, 1903c holotype: specimen cm 572. revised diagnosis haplocanthosaurus priscus can be diagnosed by the following characters: (1) middle dorsal vertebrae mildly opisthocoelous, and (2) distal end of ischia fused (see discussion below). referred specimens: cm 2043, cm 2046, cm 879, cm 33995. haplocanthosaurus delfsi mcintosh and williams, 1988 holotype: specimen cmnh 10380. revised diagnosis haplocanthosaurus delfsi can be diagnosed based on the following characters (autapomorphies marked with an asterisk): (1) middle dorsal vertebrae strongly opisthocoelous, (2) v-shaped anterolaterally projecting laminae present on mid-dorsal vertebral neural spines*, (3) posterior dorsal vertebral neural spines with greater development of median laminae compared to h. priscus*, (4) pelvis and femur more robust than h. priscus, and (5) distal end of ischia unfused. other diagnoses mcintosh and williams (1988) considered h. delfsi distinct from h. priscus based on its larger body size (roughly a third again as large, see below). however, size is variable within adult taxa of other dinosaur populatable 3. stratigraphic position of the known haplocanthosaurus specimens within the late jurassic morrison formation. the asterisks refer to a potential haplocanthosaurus specimen. stratigraphic unit quarry name state brushy basin member (youngest strata) dry mesa quarry colorado salt wash member william’s slow eagle quarry tale site utah utah tidwell member (oldest strata) none morrison formation, age unknown cleveland-delfs quarry como bluff* gordon-bramson-brothers quarry marsh-felch 1 quarry oil creek quarry poison creek quarry red fork of the powder river quarry b colorado wyoming colorado colorado colorado wyoming wyoming 7 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 tions (e.g., allosaurus, edmontosaurus, plateosaurus). additionally, at least one other specimen attributable to haplocanthosaurus (smm p 90.37.10) is comparable in size to the h. delfsi holotype cmnh 10380 and does not appear to be referable to this species. haplocanthosaurus sp. referred specimens: byu 9194, byu 11506, byu 12865, byu 17530, byu 17531, byu 17689, cm 312, cm 36034, cm 36036, cmnh 10725, fhpr 1106, mwc 8028, smm p 90.37.10, unnumbered blm specimen, usnm v 4275. issues with diagnosing haplocanthosaurus species whereas various specimens have been attributed to haplocanthosaurus in the past, little has been done in the way of diagnosing the lower-level taxonomy of this genus. when initially described, haplocanthosaurus delfsi was distinguished from h. priscus (mcintosh and williams, 1988); however, little to no effort has been made in distinguishing the latter from the former or from other haplocanthosaurus specimens. at least one character used by mcintosh and williams (1988) to distinguish h. delfsi from h. priscus—the lack of fused ischia in the former—could represent ontogenetic or individual variation. specimen usnm v 4275 was found in close proximity to the specimens of h. priscus and possessed fused ischia as in that taxon, yet the femoral least breadth to length measurements, as currently defined, imply closer affinities to h. delfsi. it is unclear which, if any, of these characters are more taxonomically informative. some characters that have been previously used to distinguish the species of haplocanthosaurus, such as the level of co-ossification of sacral neural spines, are likely a result of individual variation, whereas others may be attributable to ontogeny or other factors (hone et al., 2016). for example, specimen cm 572 exhibits a pneumatic fossa at least in the first caudal vertebra (upchurch and mannion, 2009; wedel, 2009); although at this time it is unclear whether this is a result of individual variation or is more taxonomically significant. other characters, such as a proportionally large obturator foramen for the genus, may be phylogenetically informative but have yet to be extensively discussed (figure 2). ontogeny and individual variation have long plagued sauropod taxonomy and phylogeny (woodruff, 2019) and it is unclear how much these factors affect haplocanthosaurus. additional study and reevaluation, both of the original type specimens and new specimens, such as specimen fhpr 1106, will hopefully further elucidate the interrelationships of this genus. specimen descriptions specimen cm 572 this specimen represents the holotype for the genus haplocanthosaurus and of the species h. priscus (hatcher 1903a, 1903b, 1903c). specimen cm 572 was recovered from the marsh-felch quarry 1 (turner and peterson, 1999) and includes two posterior cervical and figure 2. comparative photographs of the large obturator foramen (of) of haplocanthosaurus based on specimens cm 572 (a) and apatosaurinae indet. byu 681-12915 (b). image of cm 572 (not to scale) is modified from an unpublished image by john s. mcintosh (wesleyan university), courtesy of dan chure (dinosaur national monument). 8 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 ten dorsal vertebrae, the sacrum and ilia, ischia and pubes, nineteen anterior caudal vertebrae, two chevrons, a nearly complete series of dorsal ribs, and a left femur (figure 3). as the genoholotype of this taxon, it forms the basis for the generic diagnosis, including the tall neural arch pedicles, non-bifurcated neural spines, dorsally angled transverse processes, and simple amphicoelous caudal centra with large chevron facets (hatcher, 1903c). a right tibia, fibula, and astragalus cataloged as specimen cm 2043 likely belongs to haplocanthosaurus (mcintosh, 1981) and possibly to the genoholotypic individual of h. priscus (contra mcintosh and williams, 1988) due to the least breadth/length measurement of the tibia, tibial morphology, overall limb proportions, and its proximity to other bones in the quarry assigned to haplocanthosaurus. there is also no overlap in elements with specimen cm 572, which further suggests such an association (figure 3). the limb proportions also do not match specimen cm 879, providing evidence against it being assigned to that haplocanthosaurus specimen. a left scapulocoracoid specimen cm 33995 and left tibia and fibula specimen cm 2046 also match the cross-scaled limb proportions for cm 572 and very likely also belong to this individual. specimen cm 879 specimen cm 879 was originally designated the holotype of haplocanthosaurus ‘utterbacki’ (hatcher, 1903c). also recovered from marsh-felch quarry 1, this specimen consists of ten cervicals (likely representing cervical vertebrae two, three, and five through twelve), thirteen dorsal vertebrae, several dorsal ribs, the sacrum, the anterior seven caudal vertebrae, the left scapula, and right coracoid (hatcher, 1903c). this individual was referred to haplocanthosaurus based on tall neural arch pedicles, the simple non-bifurcated neural spines, and dorsally angled transverse processes (hatcher, 1903c, and figure 4). haplocanthosaurus ‘utterbacki’ was distinguished by hatcher (1903c) solely based on the level of sacral neural spine fusion. however, this character was later recognized as ontogenetically variable, and as a result, this species was synonymized with h. priscus (mcintosh and williams, 1988). figure 3. skeletal reconstruction of composite type individual (a), with specimen cm 572 cervical eleven in right lateral (b), dorsal thirteen in posterior and right lateral views (c), fused ischia in posterior view (d), right tibia specimen cm 2043 in posterior view (d), and fused left scapulocoracoid specimen cm 33995 in left lateral view (f). scale bars equal 2 m (a), 20 cm (b) and 50 cm (c, d, e, f). scale individual for this and all skeletals is co-author gtb at his natural height of 165 cm. photographs of ischia and scapulocoracoid modified from unpublished images by john s. mcintosh (wesleyan university), courtesy of dan chure (dinosaur national momument). 9 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 specimen cm 36034 specimen cm 36034 was collected from the red fork of the powder river quarry b in wyoming (tschopp et al., 2019). cm 36034 consists of two mid-caudal vertebrae (figure 5). tschopp et al. (2019) considered this specimen to belong to an indeterminate neosauropod, as the prezygapophyses of these caudals are shorter proportionally than can be seen in other haplocanthosaurus specimens (e.g., specimens cm 572, cm 879, cmnh 10380, smm p 90.37.10). it is possible, however, that this is an artifact of taphonomic processes rather than a legitimate feature; and besides this morphological discrepancy, the remainder of the vertebral morphologies are consistent with haplocanthosaurus. for example, the large chevron facets exceed those of camarasaurus, but are consistent with those of haplocanthosaurus; therefore, we recognize cm 36034 as haplocanthosaurus sp. additionally, specimens cm 36036 and cm 312, also from the red fork of the powder river quarry b, preserve additional anterior and mid-caudal vertebrae, several chevrons, and a partial ischium. whereas originally being assigned to separate individuals, this material likely belongs to the same individual as specimen cm 36034, based on the comparable size and morphology present in all the vertebrae. there may be additional haplocanthosaurus material from this quarry as well (originally all cataloged as specimen cm 1256), although given the disarticulated nature of this quarry and lack of a quarry map (see tschopp et al., 2019), it requires further study that is outside the scope of this review. specimen cmnh 10380 specimen cmnh 10380 represents the holotype of haplocanthosaurus delfsi (mcintosh and williams, 1988). cmnh 10380 comes from the cleveland-delfs quarry (or “delfs’ quarry” of turner and peterson, 1999). this specimen is represented by cervical vertebrae one through four, nine posterior dorsal vertebrae with left dorsal ribs, five sacral vertebrae, caudal vertebrae one through fourteen, several chevrons, shaft and distal end of left scapula, a possible fragmentary coracoid, right sternal plate, proximal ends of the left radius and ulna, both ilia, left pubis, left femur, and left ischium (mcintosh and williams, 1988, and figure 6). this specimen was referred to haplocanthosaurus based on the tall neural arch pedicles, dorsally angled transverse processes, and a flared distal end of the tibia (mcintosh and williams, 1988). figure 4. skeletal reconstruction of specimen cm 879 (a), with fifth cervical in left lateral view (b), unfused sacral neural spines in right lateral view (c), and first caudal in right lateral view (d). scale bars equal 2 m (a), 20 cm (b, d), and 50 cm (c). images of cervical and sacrals modified from ones by john s. mcintosh (wesleyan university), courtesy of dan chure (dinosaur national monument). 10 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 specimen cmnh 10725 specimen cmnh 10725 comes from the oil creek quarry in colorado. while cmnh 10725 awaits description, the specimen is represented by two dorsal vertebrae, a right tibia, and some unidentified fragments. the specimen was referred to haplocanthosaurus based on the tall neural arch pedicles, dorsally angled transverse processes, and flared distal end of the tibia (hatcher, 1903c, mcintosh and williams, 1988, and figure 7). cmnh 10725 was found in close proximity to the specimens from the cleveland-delfs and marsh-felch quarries in colorado (figure 1), suggesting populations of haplocanthosaurus were more numerous here than in other areas. specimen mwc 8028 specimen mwc 8028 comes from the gordon-bramson-brothers quarry in undifferentiated morrison strata in colorado (foster and wedel, 2014), and includes four dorsal centra, five partial dorsal ribs, sacrum, five caudal vertebrae, three chevrons, and many unidentified fragments (figure 8). mwc 8028 was identified as haplocanthosaurus based on the amphicoelous caudal vertebrae with large chevron facets. further studies have indicated that this individual had caudal vertebrae with unusually large neural canals and deeply amphicoelous centra (wedel et al., 2021), and that these morphologies, in combination with other differences in the centra and neural spines, may indicate enough morphological disparity to warrant a new species within the genus. specimen usnm v 4275 specimen usnm v 4275 comes from marsh-felch quarry 1 in colorado and is represented by a left femur, right femur, both ischia, left tibia, left fibula, and left astragalus. usnm v 4275 was referred to haplocanthosaurus based on the least breadth to length measurement, flared distal end of the tibia, and fused ischia – as in h. priscus (mcintosh and williams, 1988, and figure 9). of historical note, specimen usnm v 4275 was described seven years before specimen cm 572. marsh (1896; pl. xviii) originally figured the ischia of this specimen and assigned them to diplodocus longus. however, gilmore (1907) recognized that they were very different from ischia referred to diplodocus, and reassigned these elements to “morosaurus.” figure 5. skeletal reconstruction of the red fork of the powder river quarry b individual (a), with specimen cm 36034 twelfth caudal in left lateral view (b), and specimen cm 312 fused posterior caudals in left lateral view (c). scale bars equal 2 m (a) and 20 cm (b, c). photograph of fused caudals modified from tschopp et al. (2019) 11 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 specimen fhpr 1106 specimen fhpr 1106 is the most complete haplocanthosaurus known to date, with over 60% of the skeleton recovered (bilbey et al., 2000). while currently under study, fhpr 1106 was recovered from the william’s slow eagle quarry in utah within the upper salt wash member of the morrison formation (turner and peterson, 1999; maidment, 2024; boisvert et al., 2024). fhpr 1106 is represented by a majority of the cervical, dorsal, sacral, and caudal vertebral series, a scapulocoracoid, numerous stylopodial, zeugopodial, and metapodial elements, dorsal ribs, and pelvic material (bilbey et al., 2000, and figure 10). the specimen has been tentatively figure 6. skeletal reconstruction of specimen cmnh 10380 (a), with twelfth dorsal in posterior view (b), and first caudal in right lateral and posterior views (c). scale bars equal 4 m (a) and 50 cm (b, c). figure 7. skeletal reconstruction of specimen cmnh 10725 (a), with middle dorsal in anterior and left posteroventral views (b), and right tibia in medial and posterior views (c). scale bars equal 2 m (a) and 50 cm (b, c). 12 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 identified as haplocanthosaurus based on the tall neural arch pedicles, simple non-bifurcated neural spines in the dorsal vertebrae, and dorsally angled transverse processes (hatcher, 1903c). the caudal vertebrae possess enlarged chevron facets. due to its completeness, this specimen will be important in future phylogenetic and taxonomic analyses of haplocanthosaurus. specimens smm d14-77, p 78.21.20, p 78.21.36; p 84.15.72, p 87.14.6, p 90.37.10 specimen smm p 90.37.10 was discovered in wyoming at the poison creek quarry, and is represented by a lower left hind limb with a tibia, fibula, astragalus, calcaneum, pes (minus the proximal phalanx of digit 1), figure 8. skeletal reconstruction of specimen mwc 8028 (a), with sacrum in right lateral view (b), and third caudal in anterior and right lateral views (c). scale bars equal 2 m (a) and 20 cm (b, c). figure 9. skeletal reconstruction of specimen usnm v 4275 (a), with left femur in anterior view (b), fused ischia in posterior view (c), and left fibula, and fused tibia and astragalus in posterior view (d). scale bars equal 2 m (a) and 50 cm (b, c, d). 13 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 and thirty articulated caudal vertebrae (erickson, 2014). it was referred to haplocanthosaurus based on the flared distal end of the tibia and large posterior chevron facets on the caudal vertebrae (mcintosh and williams, 1988; erickson, 2014; and figure 11). this specimen marks the northernmost occurrence of the genus haplocanthosaurus within a museum collection. additional smm specimens examined by the authors indicate at least three additional individuals of haplocanthosaurus in the quarry, based on tibiae (specimens smm field no. d14-77, smm p 78.21.20, smm p 84.15.72) and caudal vertebrae (specimens smm p78.21.36, smm p87.14.6). figure 11. skeletal reconstruction of specimen smm p 90.37.10 (a), with caudals 5 and 6 in right lateral view (b), and left crus and pes in anterior view (c). scale bars equal 4 m (a), 50 cm (b), and 1 m (c). photograph of left limb modified from erickson (2014). figure 10. skeletal inventory of specimen fhpr 1106. scale bar equals 2 m. 14 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 specimens byu 9194, 11506, 12865, 17530, 17531, and 17689 these specimens, probably representing a single individual, come from the dry mesa dinosaur quarry in the middle brushy basin member of the morrison formation in colorado (turner and peterson, 1999; curtice et al., 2023; boisvert et al., 2024; maidment, 2024; and figure 12). the byu specimens are represented by three anterior dorsal vertebrae, four disarticulated posterior dorsal vertebrae, and a right tibia (curtice et al., 2023; boisvert et al., 2024). the specimens were referred to haplocanthosaurus based on the tall neural arch pedicles, dorsally angle transverse processes, and the flared end of the distal tibia (hatcher, 1903c; mcintosh and williams, 1988). these byu specimens are also the geologically youngest haplocanthosaurus specimens (turner and peterson, 1999), and suggest that haplocanthosaurus may have temporally spanned a much longer part of the morrison formation than has traditionally been thought (boisvert et al., 2024). blm specimen the blm specimen was discovered on blm land, known as the tal site, near the brachiosaur gulch quarry (foster et al., 2021, and figure 1). it is still in the ground at the time of this paper’s publication. the only material found was a single dorsal vertebra and associated partial ribs. it is identified as haplocanthosaurus by the tall neural arch pedicles and dorsally angled transverse processes (hatcher 1903c, and figure 13). the locality is in the upper salt wash member of the morrison formation (foster et al., 2021; boisvert et al., 2024). the specimen is currently under study for possible collection by fhpr. specimens potentially referable to haplocanthosaurus there is a large partial skeleton from spindletop dome quarry 3 in central montana that has been previously suggested to be haplocanthosaurus (woodruff and foster, 2017; richmond, 2023). this specimen is currently in private hands so further information was not gleaned from it (ronson, 2016). figure 12. skeletal reconstruction of the composite byu individual (a), with conjoined anterior dorsals byu 17531 in right lateral (b), dorsal thirteen in posterior and right lateral views (c), and right tibia from specimen byu 12865 in anterior view (d). scale bars equal 2 m (a), and 50 cm (b, c, d). 15 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 specimen ncsm 28359 specimen ncsm 28359 consists of a radius, ulna, manual ungual, left femur, phalanx, metapodial, and a fragmentary element that may belong to either a coracoid or sternal plate. it was found at como bluff in wyoming (no more precise locality information is currently available). much of the material is in poor condition and difficult to identify to a lower phylogenetic level. the femur is not incongruent with other haplocanthosaurus femora but cannot reliably be distinguished from camarasaurus either. further research is needed on this specimen, which should be revisited once specimen fhpr 1106 is described, as more of the skeleton of haplocanthosaurus will be known (including the radius and ulna, which cannot be compared to any confirmed haplocanthosaurus specimens at the moment). if referable to haplocanthosaurus, this would document the first occurrence of this genus within southern wyoming. specimen usnm v 4264 specimen usnm v 4264 consists of a partial left humerus, radius, ulna, and five left metacarpals from marsh-felch quarry 1, which is cataloged in the usnm database as “haplocanthosaurus? sp.” these elements were not found in association with the partial skeletons of haplocanthosaurus from this quarry. to date no associated haplocanthosaurus forelimb has been described, so usnm v 4264 cannot be referred to haplocanthosaurus. specimen usnm v 4267 specimen usmn v 4267, consisting of a right humerus, radius, and ulna, is from marsh-felch quarry 1 and is cataloged in the usnm database as “haplocanthosaurus? sp.” it is quite probable, given the similar ratios and overall size of the elements, that this is the opposite limb of specimen usnm v 4264. specimen ypm vp.001906 specimen ypm vp.001906 consists of the left radius, ulna, metacarpals i-v, and manual phalanx v-1, and was recovered from marsh-felch quarry 1. ypm vp.001906 was originally considered to belong to “morosaurus”, then diplodocus longus (marsh, 1896), before being tentatively excluded by mcintosh and carpenter (1998), who considered it possibly belonging to either apatosaurus or haplocanthosaurus. tschopp et al. (2018) only assigned it as far as diplodocoidea indet., noting it differed from both apatosaurinae and diplodocinae. the first metacarpals of specimen fhpr 1106 (the only confirmed haplocanthosaurus specimen with a manus) are both incomplete, thus precluding comparison here to determine if it was proximodistally longer than metacarpal iv as in most apatosaurines (but see specimen nsmt-pv 20375; upchurch et al., 2004a). we agree with tschopp et al. (2018) in tentatively identifying this specimen diplodocoidea indet. figure 13. mid-posterior dorsal of the unnumbered blm specimen in situ. scale bar equals 10 cm. 16 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 specimens not referable to haplocanthosaurus several additional specimens have been previously referred to the genus haplocanthosaurus. here, we briefly review these specimens and discuss issues with these referrals. specimen dmns epv.2909 specimen dmns epv.2909 was recovered from dmnh locality 582, the “haplocanthosaurus quarry,” in colorado. mcintosh and carpenter (1998) considered dmns epv.2909, which consists of a dorsal vertebra, caudal vertebrae, and two femora, to belong to haplocanthosaurus, and additionally referred specimen usnm v 4273 to this taxon as well (see below). the dorsal vertebral transverse processes are dorsoventrally short compared to the very dorsoventrally tall neural spines, and they do not project dorsally. additionally, the chevron facets are small, and the femoral shafts are also slenderer than seen in other haplocanthosaurus specimens (figure 14). taking all of these characters into account, we consider dmns epv.2909 to represent an indeterminate diplodocid. specimen usnm v 4723 specimen usnm v 4723 consists of a series of mid-posterior caudals from marsh-felch quarry 1, and was originally referred to diplodocus longus by marsh at the advice of marshal felch. mcintosh and carpenter (1998) questioned this assignment based on comparison to the caudal sequence cm 307 from the red fork of the powder river quarry b, and assigned usnm v 4723 to haplocanthosaurus based on favorable comparison to that of specimen dmns epv.2909. as discussed above, the latter specimen is clearly not referable to haplocanthosaurus, and as a result, we exclude usnm v 4723 as well, and consider it to be an indeterminate diplodocid. specimen usnm pal 337859 specimen usnm pal 337859 includes several partial cervical vertebrae from marsh-felch quarry 1. regarding one of the middle cervical vertebrae, mcintosh and carpenter (1998) wrote it “...has an undivided neural spine and probably belongs to haplocanthosaurus.” this specimen is listed as “cf. brachiosaurus sp.” in the usnm collections database. personal observation by mathew j. wedel (western university of health sciences, october 31, 2023) shows an anteroposteriorly long cervical centrum and preand post-zygapophyses that are set forward of their respective centrum ends, consistent with brachiosaurids and unlike those seen in haplocanthosaurus, corroborating the usnm’s database assignment. specimen ypm vp.004688 specimen ypm vp.004688 consists of a right scapula, humerus, radius, and ulna from marsh-felch quarry 1. it is currently cataloged as “?haplocanthosaurus sp.” in the collections database and was identified as such figure 14. diplodocinae indet. specimen dmns epv.2909 mid-posterior dorsal vertebra in posterior (a), right lateral (b), and anterior (c) views. haplocanthosaurus priscus specimen cm 572 dorsal thirteen in posterior (d), right lateral (e), and anterior (f) views. scale bars equal 20 cm. 17 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 by carpenter (2019, figure 1c). however, tschopp et al. (2018) note that the radius possesses a distinct medial projection on the proximal articular surface, a morphology consistent in known brachiosaurid radii (e.g., cedarosaurus, giraffatitan, lusotitan). the radius:humerus ratio of ypm vp.004688 also compares favorably to brachiosauridae, although some diplodocoids possess a similar ratio (table 4). the scapular morphology of ypm vp.004688 is similar to other brachiosaurids in the widely expanded distal end and slender shaft. collectively, we find it most parsimonious that ypm vp.004688 represents brachiosauridae indet. specimen ypm vp.059137 specimen ypm vp.059137 consists of five right metatarsals from marsh-felch quarry 1, was originally cataloged as part of specimen ypm vp.001920 (mcintosh and carpenter, 1998), and was considered by them to belong to either brachiosaurus or haplocanthosaurus. as noted by tschopp et al. (2018), this pes shares the synapomorphic brachiosaurid beveling of the distal end of metatarsal iv relative to its proximodistal long axis (mannion et al., 2013; maltese et al., 2018), and our current analysis agrees with their assignment of the specimen to brachiosauridae. discussion despite the proportionally low number of specimens compared to the coeval sauropods apatosaurus, diplodocus, or camarasaurus, all of which are known from dozens or even hundreds of specimens (foster, 2020), haplocanthosaurus appears to be both geographtable 4. measurements ( in mm) and radius:humerus ratios of various sauropod forelimbs. taxon specimen humerus radius ratio reference brachiosauridae indet. ypm vp.004688 1700 985 0.58 personal observation haplocanthosaurus? sp. usnm v 4264/4267 816/805 537/525 0.66 personal observation brachiosaurus altithorax byu 4744/usnm 21903 2060 1270 0.61 d’emic and carrano (2019) brachiosaurus sp. gyeryongsan museum specimen 1530 940 0.61 personal observation giraffatitan brancai mb.r.2181 2130 1240 0.58 janensch (1961) cedarosaurus weiskopfae dmns 39045 1380 812 0.59 tidwell et al. (1999) camarasaurus lewisi nmz 1000002 705 464 0.66 tschopp et al. (2015b) camarasaurus grandis ypm vp.001901 890 615 0.69 vidal (2019) camarasaurus lentus wdc b 1140 795 0.69 ikejiri (2004) camarasaurus lewisi byu 9047 1018 720 0.71 mcintosh et al. (1996) apatosaurus louisae cm 3018 1150 800 0.69 gilmore (1936) brontosaurus excelsus ypm vp.001980 1101 765 0.69 personal observation diplodocus hallorum usnm v 10865 1010 690 0.68 gilmore (1932) galeamopus pabsti nmz 1000011 870 601 0.69 tschopp and mateus (2017) barosaurus lentus sdsm 25217 735 571 0.77 foster (1996) 18 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 ically and temporally widespread, and potentially ecologically present across a wide expanse of the morrison formation based on latitudinal occurrences. although rare demographically, it is possible that haplocanthosaurus may be a part of the cosmopolitan morrison formation sauropod fauna represented by apatosaurus, diplodocus, and camarasaurus, as these taxa are also found in wyoming, utah, colorado, and montana (dodson et al., 1980; woodruff and foster, 2017; foster, 2020; boisvert et al., 2024). if haplocanthosaurus contributed to this cosmopolitan fauna, it raises further ecological questions of how this basal sauropod survived throughout and across the morrison formation. as one example, co-occurrence with more numerous and derived sauropod taxa highlights a potentially complex series of ecological mechanisms necessary to concurrently sustain a high diversity and abundance of large-bodied terrestrial herbivores (button et al., 2014). the specimens listed above represent a census of known haplocanthosaurus remains. the scarcity of published material and lack of complete skeletons (e.g., no skull material) have impacted nearly every aspect of our understanding of this genus. hopefully as more specimens are identified and described, this will answer many of the questions surrounding this genus. currently, there is support for at least three species within the genus; two are the previously described and valid h. priscus and h. delfsi, in addition to one currently under study (specimen mwc 8028 by mathew j. wedel). this raises other ecological questions regarding the species turnover rate in the morrison formation, as many taxa found in the late jurassic of north america have multiple species to a genus, especially the sauropods (table 5). genus species taxonomic authority amphicoelias a. altus cope (1877c) apatosaurus a. ajax, a. louisae marsh (1877), holland (1915) ardetosaurus a. viator van der linden et al. (2024) barosaurus b. lentus marsh (1890) brachiosaurus b. altithorax riggs (1903) brontosaurus b. excelsus, b. parvus, b. yahnapin marsh (1879), peterson and gilmore (1902), filla and redman (1994) camarasaurus c. grandis, c. lentus, c. lewisi, c. supremus cope (1877b), marsh (1877), marsh (1889), jensen (1988) diplodocus d. carnegii, d. hallorum, d. longus marsh (1878), hatcher (1901), gillette (1994) dystrophaeus d. viaemalae cope (1877a) galeamopus g. hayi, g. pabsti holland (1924), tschopp et al. (2015), tschopp and mateus (2017) haplocanthosaurus h. delfsi, h. priscus hatcher (1903a), hatcher (1903b), mcintosh and williams (1988) kaatedocus k. siberi tschopp and mateus (2013) maraapunisaurus m. fragillimus cope (1878), carpenter (2018) smitanosaurus s. agilis marsh (1889), whitlock and wilson (2020) supersaurus s. vivianae jensen (1985) suuwassea s. emilieae harris and dodson (2004) table 5. valid morrison formation sauropod species as recognized at the time of writing. 19 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 conclusion from the current paleobiological data, the sauropod genus haplocanthosaurus is restricted to the northwestern and central regions of the morrison formation. temporally, haplocanthosaurus is known from the middle and upper parts of the defined morrison formation and potentially, based on undifferentiated strata (i.e., not able to be correlated within the tidwell, salt wash, or brushy basin members), may be found throughout nearly the entirety of the formation stratigraphically. whereas more detailed description and identification of some of the aforementioned specimens are needed, the current evidence illustrates that haplocanthosaurus was more geographically and stratigraphically widespread than previously known, and there is currently support for high species diversity within this genus. acknowledgments we thank rod scheetz and brooks britt (brigham young university) for permitting us to study and photograph the specimens in the byu collections. we thank michael brett-surman and matthew miller (national museum of natural history) and vicki yarborough (yale peabody museum) for collections access. we thank caitlin colleary (cleveland museum of natural history) for photographs of specimens and matt lamanna and amy henrici (carnegie museum of natural history) for access to the carnegie collections. we thank sean moran and vince schneider (north carolina museum of nature and sciences) for helping with specimens from their collection. we thank dan chure (dinosaur national monument) for the use of photographs from the john s. mcintosh archives. we thank emanuel tschopp (freie universität, berlin) and cary woodruff (phillip & patricia frost museum of science) for constructive reviews that greatly improved the quality of this work. references agassiz, l., 1844, monographie des poissons fossiles du vieux grés rouge, ou système dévonien (old red sandstone) des iles britanniques et de russie: neuchatel, xxvi, 171 p. bilbey, s.a., hall, j., and hall, d.a., 2000, preliminary results on a new haplocanthosaurid sauropod dinosaur from the lower morrison formation of northeastern utah [abs.]: journal of vertebrate paleontology, programs with abstracts, v. 2000, p. 30a. boisvert, c., curtice, b., wedel, m., and wilhite, r., 2024, description of a new specimen of haplocanthosaurus from the dry mesa dinosaur quarry: the anatomical record, 19 p., https://doi.10.1002/ar.25520. bonaparte, j.f., 1986, the early radiation and phylogenetic relationships of jurassic sauropod dinosaurs, based on vertebral anatomy, in padian, k., editor, the beginning of the age of dinosaurs—faunal change across the triassic-jurassic boundary: cambridge, cambridge university press, p. 247–258. button, d.j., rayfield, e.j., and barrett, p.m., 2014, cranial biomechanics underpins high sauropod diversity in resource-poor environments: proceedings of the royal society b: biological sciences, v. 281, p. 1–9. carpenter, k., 2018, maraapunisaurus fragillimus, n.g. 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dinosaur quarry and a comment on sauropod diversity, in hunt-foster, r.k., kirkland, j.i., and loewen, m.a., editors, 14th symposium on mesozoic terrestrial ecosystems and biota: the anatomical record, v. 306 (s1), p. 79–81. d'emic, m.d., and carrano, m.t., 2019, redescription of brachiosaurid sauropod dinosaur material from the upper jurassic morrison formation, colorado, usa: the anatomical record, v. 303, no. 4, p. 732–758. 20 census of currently known specimens of the late jurassic sauropod haplocanthosaurus from the morrison formation, usa boisvert, c., bivens, g.t., curtice, b., wilhite, r., and wedel, m. geology of the intermountain west 2025 volume 12 dodson, p., behrensmeyer, a.k., bakker, r.t., and mcintosh, j.s., 1980, taphonomy and paleoecology of the dinosaur beds of the jurassic morrison formation: paleobiology, v. 6, no. 2, p. 208–232, https://doi.org/10.1017/s009483730000676x. erickson, b.r., 2014, history of the poison creek expeditions 1976–1990, with description of haplocanthosaurus post cranials and a subadult diplodocid skull: science museum of minnesota monograph, v. 8, p. 1–34. filla, b.j., and redman, p.d., 1994, apatosaurus yahnahpin—a preliminary description of a new species of diplodocid dinosaur from the late jurassic morrison formation of southern wyoming, the first sauropod dinosaur found with a complete set of “belly ribs,” in nelson, g.e., editor, the dinosaurs of wyoming: wyoming geological association 44th annual field conference guidebook, p. 159–178. foster, j.r., 1996, sauropod dinosaurs of the morrison formation (upper jurassic), black hills, south dakota and wyoming: university of wyoming contributions to geology, v. 31, no. 1, p. 1–25. foster, j.r., 2020, jurassic west: the dinosaurs of the morrison formation and their world (2nd edition): indiana university press, 560 p. foster, j.r., and wedel, m.j., 2014, haplocanthosaurus (saurischia: sauropoda) from the lower morrison formation (upper jurassic) near snowmass, colorado: volumina jurassica, v. 12, no. 2, p. 197–210, https://doi. org/10.5604/17313708.1130144. foster, j., pagnac, d., and hunt-foster, r., 2020, an unusually diverse northern biota from the morrison formation (upper jurassic), black hills, wyoming: geology of the intermountain west, v. 7, p. 29–67, https://doi.org/10.31711/ giw.v7.pp29-67. foster, j., wedel, m.j., engh, b., hunt-foster, r.k., haridy, y., and kirkland, j.i., 2021, geologically oldest specimen of brachiosaurus (sauropoda) from the salt wash member of the morrison formation, southern utah [abs.]: society of vertebrate paleontology, annual meeting conference abstracts with programs, p. 113a. gillette, d.d., 1994, seismosaurus—the earth shaker: new york, columbia university press, 205 p. gilmore, c.w., 1907, the type of the jurassic reptile morosaurus agilis redescribed, with a note on camptosaurus: proceedings of the united states national museum, v. 32, p. 151–165. gilmore, c.w., 1932, on a newly mounted skeleton 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pone.0017114. woodruff, d., 2019, what factors influence our reconstructions of morrison formation sauropod diversity?: geology of the intermountain west, v. 6, p. 93–112., doi: 10.31711/giw. v6.pp93-112. woodruff, d.c., and foster, j.r., 2017, the first specimen of camarasaurus (dinosauria: sauropoda) from montana, the northernmost occurrence of the genus: plos one, v. 12, no. 5, e0177423, https://doi.org/10.1371/journal. pone.0177423. woodruff, d.c., fowler, d.w., and horner, j.r., 2017, a new multi-faceted framework for deciphering diplodocid ontogeny: palaeontologia electronica, 20.3.43a, 53 p., https:// doi.org/10.26879/674. zhang, x-q., li, n., xie, y., li, d-q., and you, h-l., 2022, redescription of the dorsal vertebrae of the mamenchisaurid sauropod xinjiangtitan shanshanesis wu et al. 2013: historical biology, v. 36, no. 1, p. 49–75, https://doi.org/10.1080/0 8912963.2022.2147428. tracking dinosaurs in blm canyon country, utah geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 © 2016 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. tracking dinosaurs in blm canyon country, utah rebecca k. hunt-foster, martin g. lockley, andrew r.c. milner, john r. foster, neffra a. matthews, brent h. breithaupt, and joshua a. smith a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover a navajo sandstone scene from 185 million years ago. a variety of vertebrates stroll and swim near an interdunal lake “oasis” while small animals take refuge in their burrows and pterosaurs fly overhead. artwork by brian engh, dontmesswithdinosaurs.com. i 2016 president bill loughlin bill@loughlinwater.com 435.649.4005 2016 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2016 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2016 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2016 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2016 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2016-2018 term craig morgan craigmorgan@utah.gov 801.422.3761 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 3 2016 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 67 abstract the remarkably extensive and abundant mesozoic-aged exposures on public lands around moab have made this region well known for ichnofossils. the nearly complete record of upper triassic through lower cretaceous rocks exposed in this area is well known for its sheer abundance of tracks and traces. this three-day field trip will visit many important classic and new sites exposed in the bureau of land management’s canyon country district. this field trip guidebook will give one an overview of the major sites we will visit, as well as a brief summary of work previously done in these areas. tracking dinosaurs in blm canyon country, utah rebecca k. hunt-foster1, martin g. lockley2, andrew r.c. milner3, john r. foster4, neffra a. matthews5, brent h. breithaupt6, and joshua a. smith7 1bureau of land management – canyon country district, 82 east dogwood, moab, utah 84532; rhuntfoster@blm.gov 2university of colorado denver, campus box 172, university of colorado denver, po box 173364, denver, colorado 80217; martin.lockley@ ucdenver.edu 3st. george dinosaur discovery site at johnson farm, 2180 east riverside drive, st. george, utah 84790; arcmilner@gmail.com 4museum of moab, 118 east center street, moab, utah 84532; director@moabmuseum.org 5bureau of land management national operations center, geospatial section, denver federal center, bldg. 50, p.o. box 25047, oc-534, denver, colorado 80225-0047; n1matthe@blm.gov 6bureau of land management, 5353 yellowstone road, cheyenne, wyoming 82009; bbreitha@blm.gov 7dominguez anthropological research group (darg), p.o. box 3543, grand junction, colorado 81502; dinotrack@hotmail.com citation for this article. hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a., 2016, tracking dinosaurs in blm canyon country, utah: geology of the intermountain west, v. 3, p. 67–100. © 2016 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. field trip overview on day 1, the field trip will start in salt lake city and travel south on interstate 15 (i-15) exiting at spanish fork, where we will proceed on u.s. highway 6 across soldier summit through price to green river between the san rafael swell to the west and the book cliffs (figure 1). we will continue east on interstate 70 (i-70) continuing along the south side of the book cliffs. this transect represents one of the longest continuous exposures of the regressing late cretaceous coastline anywhere in north america (van wagoner and others,1991; kirkland and others, 2016). our first stop will be the copper ridge dinosaur tracksite, where we will view the tracks of a turning sauropod in the upper jurassic morrison formation, along with the first hispanosauropus tracks identified outside europe (foster, 2015). this trackway has historically been attributed to a limping theropod. immediately following we will visit the mill canyon dinosaur tracksite (cedar mountain formation; ruby ranch member). this newly discovered tracksite preserves one of the most diverse and largest early cretaceous dinosaur tracksites in north america and was the subject of recent interpretive efforts by the bureau of land management (blm). if time allows, we will visit a possible cynodont burrow complex found in the erg deposits of the lower jurassic navajo sandstone west of www.utahgeology.org 68 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 figure 1. (a) field trip route. (b) day one stops: 1 – copper ridge dinosaur tracksite, 2 – mill canyon dinosaur tracks, and 3 – synapsid burrows. (c) day two stops: 4 and 5 – lisbon valley and the last phytosaur, 6 – shay canyon, 7 – track city, and 8 – bridger jack mesa. (d) day three stops: 9 – bull canyon dinosaur tracks, 10 – poison spider dinosaur tracks, 11 – moline reef tracksite, and 12 – utah state university–eastern prehistoric museum. 69 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 moab. we will spend the evening in moab.   day 2 will consist of driving south to the indian creek and lisbon valley areas to view tracks in the chinle, wingate, and navajo formations, along with the last phytosaur—a cast of a phytosaur skull pressed into the basal-most sands of the triassic-jurassic wingate sandstone. we will view a variety of eubrontes and grallator tracksites, including archosauromorph and dicynodont tracks. we will return to moab for the evening.   day 3 we will visit the fisher mesa tracksite on forest service land in the la sal mountains. this middle jurassic entrada sandstone tracksite is part of the moab “megatracksite” that preserves millions of megalosauripus tracks in the moab area. afterwards we will visit our last moab area site, the poison spider tracksite, where we will view eubrontes, grallator, and the type of small bird-sized anomoepus moabensis in an oasis deposit within the navajo sandstone. we will then travel to the new moab giants museum for a tour of the facilities before heading through the san rafael swell where we will visit the moline reef tracksite (also called the moore tracksite) in the turonian ferron sandstone. our last stop will be at the utah state university eastern prehistoric museum in price, where we will view tracks found in the upper cretaceous mesaverde group from the surrounding book cliffs before returning to salt lake city. final schedule will be flexible to accommodate maximum tracking opportunities (figure 1). introduction to tracks of the moab area the prehistoric track record in utah is exceptionally good, particularly in southeastern utah. fossil footprints are found abundantly in most terrestrial deposits from the late paleozoic through cenozoic and are diverse, well-documented and represented at an extraordinarily large number of sites (lockley and hunt, 1995). in the moab area, abundant sites are known from most mesozoic terrestrial formations. the most representative track assemblages and sites from this area represent the main focus of this guide and field trip. early and middle triassic track assemblages are dominated by archosaur tracks. among the most representative are those of the famous chirotherium or “chirothere” (meaning hand animal) group. these have a global distribution and have been well-documented in the western united states by peabody (1948) especially in the moenkopi formation of northern arizona. peabody, however, also described swim tracks from utah, which he attributed to amphibians. the upper triassic chinle formation has proved a rich source of both tracks and body fossils as described in this guide and in martz and others (2014). chinle formation tracks are particularly diverse, and include the ubiquitous tridactyl theropod track grallator, which is arguably the first unequivocally identified dinosaur track, although the rare track atreipus may be as old. a zone with abundant small grallator tracks, also identified in europe, has been interpreted as evidence of the early global radiation of small theropods. associated chinle tracks, found abundantly in the moab area, and elsewhere in utah, include brachychirotherium, probably representing an aetosaur, the lacertiform ichnogenus rhynchosauroides, and the less common apatopus, of probable phytosaur affinity. these assemblages are associated with diverse chinle plant fossils, indicative of humid paleoenvironmental conditions that generated paleosol and fluvio-lacustrine deposits containing fishes, amphibians, phytosaurs, and other aquatic fauna. the transition from the chinle formation to the upper triassic-lower jurassic glen canyon group, consisting, in ascending order of the wingate, kayenta, and navajo formations, marks a very significant change in paleoenvironmental conditions. the upper triassiclower jurassic wingate and lower jurassic navajo sandstones predominantly consist of dune sands with the sandy fluviatile facies of the lower jurassic kayenta in between. all three formations are locally track rich but almost devoid of body fossils. there is a marked change in the track assemblages (ichnofaunas) just above the base of the wingate where the aforementioned chinle ichnofauna is replaced by a fauna containing grallator and eubrontes (both representing theropods), otozoum (prosauropod track), anomoepus (ornithischian), and batrachopus (small, terrestrial crocodylomorph). one small anomoepus morphotype has been named a. moabensis (lockley and gierlinski, 2006; lockley and others, 2014a). this is typical of early 70 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 jurassic assemblages worldwide and has been referred to as the first truly global tetrapod track biochron (lucas, 2007). facies variation is important in these formations, with the moenave formation in southwest utah (partly equivalent to the wingate sandstone in southeastern utah) representing a fluvio-lacustrine system in this region, and has yielded theropod swim tracks around st. george (milner and others, 2006c). likewise, the kayenta formation transitions into a silty facies in northern arizona and southwestern utah. the synapsid track brasilichnium, which is difficult to distinguish from permian chelichnus also occurs in the dune facies with octopodichnus and small grallator tracks, especially in the navajo sandstone, long regarded as a classic dune (erg) deposit. the navajo contains localized playa deposits with algal carbonates and zones with fossil wood; all evidence of pluvial periods. the tetrapod record for the middle jurassic is rather sparse both in utah and globally. the carmel formation has produced carmelopodus, from near vernal, and the dune facies of the entrada sandstone has produced the small terrestrial crocodylian entradasuchus and a few small theropod tracks. by contrast the uppermost surface of the entrada around moab, where it represents the interface with the marine, upper tongue of the summerville formation, has produced abundant theropod tracks assigned to the ichnogenera megalosauripus and therangospodus, and two isolated occurrences of sauropod tracks of which only one site has been described by foster and others (2000) as the oldest recorded in north america. this aggradational flooding surface has produced a regionally extensive track zone known as the moab megatracksite, which covers an area of several hundred square km (lockley, 1997). megatracksites, also popularly known as dinosaur freeways, can be attributed to the dynamics of sea level change associated with coastal plain systems. immediately above the megatracksite surfaces, in thin upper summerville deposits, abundant pterosaur tracks (ichnogenus pteraichnus) occur in marginal marine deposits along with a few theropod tracks. this unit marks the transition into the upper jurassic, which is mainly represented by the morrison formation, containing abundant tetrapod skeletal remains and a somewhat more scattered record of saurischian-dominated (sauropod and theropod) tracksites. a few sites have also yielded ornithischian tracks including the type of stegopodus, from near moab airport (lockley and hunt, 1998). crocodylian and turtle tracks also occur at a few sites, including the type of hatcherichnus, a crocodylian swim track with associated sinuous tail traces (foster and lockley, 1997). the cretaceous track record in southeastern utah is represented by lower cretaceous assemblages from the cedar mountain formation and the naturita formation (formerly known as the dakota formation), with the upper cretaceous assemblages from the broadly defined mesaverde group. recent studies of the cedar mountain have revealed the first dromaeosaurid trackways from north america, and an assemblage of bird tracks (aquatilavipes) that are arguably the oldest evidence of birds from north america (lockley and others, 2014b, 2015). in contrast to the cedar mountain formation, which is rich in bone sites and contains skeletal and track evidence of sauropods, the overlying naturita formation, although very track-rich, is almost completely devoid of tetrapod body fossils and contains no track evidence of sauropods, apparently marking the beginning of the so called “sauropod hiatus.” although containing abundant track evidence of theropods (lockley, 2016), ornithopods, ankylosaurs, pterosaurs, crocodylians, and turtles, most of the better-documented naturita formation tracksites occur in colorado. nevertheless, sites with ornithopods, theropod, and crocodylian tracks have been reported from utah. moreover, given that the colorado sites represent a vast dinosaur freeway associated with coastal plain aggradation along the margins of the western interior seaway, the naturita formation tracksite occurrences in utah must be considered an integral part of the dinosaur freeway complex. the upper cretaceous coal-bearing mesaverde group, the youngest mesozoic-aged rocks in southeastern utah, are also historically famous for dinosaur tracks, including miscellaneous theropod and giant hadrosaur tracks, some of which were excavated early in the 20th century. there have also been scattered reports of a few sites yielding pterosaur, bird, mammal, and frog tracks. recent studies indicate as yet undocumented turtle, ceratopsian, and therizinosaur tracks 71 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 although tetrapod tracks are abundant and diverse in the mesozoic of southeastern utah, the question arises as to their utility in paleobiology. clearly they are important indicators of behavior, helping distinguish walkers from runners, sprawling from erect gaits, obligatory from facultative bipeds and quadrupeds, and solitary from gregarious tendencies. we also find evidence of swimming among theropods, crocodylians, turtles, and pterosaurs (milner and lockley, 2016), or even indications of theropod courtship (lockley and others, 2016b). it is also accepted that because tracks represent in situ evidence of living animals, they have value for paleoecological census purposes. formations have been categorized on the basis of the relative number of sites yielding tetrapod tracks versus skeletal remains (lockley, 1991). regionally, a surprising number of formations yield only tracks (type 1), or are heavily track-dominated (type 2): e.g., wingate, navajo, entrada, summerville, and naturita. in contrast, formations dominated by skeletal remains and relatively few tracks (type 4): e.g., morrison and cedar mountain formations are less common, and there are no bone-bearing formations which lack tracks entirely (type 5). formations with equal number of vertebrate track and vertebrate body fossil sites are classified as type 3. this reinforces the conclusion that tracks are abundant and useful in helping characterize faunas associated with given deposits. it is also well known that track assemblages are often consistent within given sedimentary facies. this gives rise to the ichnofacies concept, the classic example being the dune or chelichnus ichnofacies, which gives insight into permian through jurassic and even some cenozoic dune-dwelling faunas. the most diverse tetrapod ichnofaunas appear to occur in fluvio-lacustrine and floodplain paleoenvironments such as are represented by various chinle, morrison, and cedar mountain deposits. the naturita formation and mesaverde group also yield diverse ichnofaunas associated with what can be broadly defined as well-vegetated, coal-producing coastal plain systems, which in turn generate regionally extensive megatracksite or dinosaur freeway complexes shaped by sea level dynamics. this field trip guide will take one through each site we will visit during the 2016 society of vertebrate paleontology field trip of the same name. these sites are all managed by the blm – canyon country district office, unless otherwise noted. please remember that it is illegal to collect or take vertebrate body fossils, as well as casts or molds of vertebrate trace fossils, including the use of latex, or other surface disturbing activities, without a permit under the paleontological resources preservation act of 2009. any excavations or clearance of the below mentioned sites have been done by permitted paleontologists through the blm, or other appropriate agencies. the blm maintains six publicly interpreted tracksites within the canyon country district, of which we will visit three examples – copper ridge, poison spider, and mill canyon. day 1: middle jurassic – early cretaceous of grand county stop 1 – copper ridge the copper ridge tracksite (sometimes referred to as the valley city site, e.g., lockley and hunt, 1995, or the turning sauropod site, e.g., barnes, 1997) was discovered in the 1980s and was reported by lockley and hunt (1995), who also published a map of the site (figure 2). the tracksite level is in the upper few meters of the salt wash member of the morrison formation, on a current-ripple-marked surface of sandstone likely representing a sand bar lateral to a fluvial channel. it is late jurassic, most likely kimmeridgian in age. trackways at the site include a large sauropod (ichnogenus brontopodus, figure 2) making a nearly 90-degree right turn and a large theropod with an apparent limp. several other smaller, isolated tracks of theropods are preserved around the sauropod trackway. the large, possibly limping theropod trackway has recently been assigned to the ichnogenus hispanosauropus (foster, 2015, figure 2). hispanosauropus, previously known from the upper jurassic of europe, is distinct from megalosauripus and most likely was made by an allosauroid theropod, although it might have been made by a spinosauroid (torvosaurid) or a ceratosauroid. close geographic and stratigraphic association of hispanosauropus with the large theropod body fossil taxa allosaurus, torvosaurus, and ceratosaurus in both north america and the iberian peninsula strength72 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 figure 2. caption on following page. 73 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 ens the case for the tracks having been made by one of these genera. megalosauripus appears to dominate large theropod track samples from the base of the morrison formation (tidwell member); hispanosauropus, and similar tracks are most common in the salt wash member and its equivalents, suggesting taxonomic turnover in the large theropod faunas during the early part of morrison formation deposition. stop 2 – mill canyon dinosaur tracksite the mill canyon dinosaur tracksite (mcdt) in the cedar mountain formation (ruby ranch member) is the largest and most diverse of the eight known cedar mountain tracksites. although well known for its lower cretaceous vertebrate fauna in eastern utah, the cedar mountain has previously yielded relatively few dinosaur tracksites. among these the arches national park site (lockley and others, 2004) and another yielding a large assemblage of bird tracks (lockley and others, 2015) are important locations within a 24 km (15 mi) radius of the mcdt. preliminary results from the mcdt site (lockley and others, 2014b, 2014c) indicate the presence of at least eight diagnostic ichnotaxa including three distinct theropod track morphotypes identified as irenesauripus, a dromaeosauripus-like form, and an un-named ichnite. poorly preserved bird tracks have also been identified. sauropod tracks include brontopodus and manus-only sauropod undertracks. ornithopod tracks resemble caririchnium. the tracks occur in the upper part of the ruby ranch member, which mostly consists of gray, calcareous mudstone with micritic limestone beds and nodules. however, the track bed is complex lithologically, and is best described as a light gray, microcrystalline impure chert, with a hardness of 5.5. the hardness of the track-bearing layer has contributed to its preservation. in fact, in addition to the main tracksite area (figure 3), which reveals at least 175 well-defined tracks and undertracks comprising more than 20 trackways, there are two nearby areas, one to the north, with ~35 tracks in at least eight trackways (lockley and others, 2014c), and one to the east with ~30 tracks. both these areas are within ~100 m of the main site and represent the same surface, which is intermittently exposed over a large area between and around these sites. the mcdt was developed for public visitation and interpretation in 2014, opening to the public fully in april of 2016. partly with such developments in mind the mcdt site has been subject to special study using innovative strategies. first the site was considerably enlarged, from the size of the original natural exposure, using mechanical excavation techniques, which are not often used at tetrapod tracksites. this phase of work was funded through univerity of colorado by the korean national research institute of cultural heritage. second, the site was subject to a thorough photogrammetric survey, which provided images for publications (e.g., lockley and others, 2014b, figure 4) and interpretative signs. third, a boardwalk up to 80 m long and 2 m wide was installed over the site so that visitors can “walk with the dinosaurs” without stepping on or damaging the tracks (figure 3). a shade structure was also installed. utah friends of paleontology (ufop), moab giants, canyonlands natural history association (cnha), and grand county trail mix were community partners in these efforts during most phases of the project. the mcdt has revealed a number of enigmatic traces that can broadly be described as slip and scratch marks. some resemble swim tracks but cannot definitively be placed in this category. likewise the largest of these traces, a pair of elongate grooves, are tentatively inferred to be of possible crocodylian origin (lockley and others, 2014b). an herbivore coprolite was also found in the middle of the main site (lockley and othfigure 2 (figure on previous page). (a) location of copper ridge dinosaur tracksite (after foster, 2015). (b) brontopodus tracks. (c) map of tracksite by lockley and hunt (1995). (d) example of photogrammetric model of the copper ridge hispanosauropus trackway (matthews, unpublished data). (e) hispanosauropus (track 1, after foster, 2015). (f) participants of the mid-mesozoic field conference learning photogrammetry techniques on the hispanosauropus trackway at copper ridge dinosaur tracksite from neffra matthews and brent breithaupt in 2014. (g) new interpretive signage installed at the copper ridge dinosaur tracksite by the blm in 2016. art by brian engh (dontmesswithdinosaurs.com). 74 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 figure 3. caption on following page. 75 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 ers, 2014c). the site has considerable potential for further excavation and future study. stop 3 – synapsid burrows the lower jurassic (pliensbachian-toarcian) navajo sandstone of utah, colorado, new mexico, and arizona, along with the nugget sandstone to the north (idaho, wyoming) and the aztec sandstone to the south (nevada, california), represents the largest erg to have ever existed on earth. located on the western margin of pangaea for almost 10 million years, this erg is estimated to have covered an area of approximately 644,000 km2 (400,000 mi2), now represented by over 322,000 km2 (200,000 mi2) of exposed eolian sandstone outcrop. vertebrate and invertebrate trace fossils have long been known from the navajo, and its equivalents, and are usually associated with relatively small carbonate lenses representing interdunal lakes. at the rocky tops burrow site near moab, utah, figure 3 (figure on previous page). (a) map of the mill canyon dinosaur tracksite (mcdt) modified after lockley and others (2014c). (b) carmelopodus-like track. (c) irenesauripus. (d) caririchnium-like track. (e) hatcherichnus-like trace. the mcdt also contains sauropod tracks that include brontopodus and manus-only sauropod undertracks. (f to h). signage at the mcdt. (i) completed trail, which opened on april 1, 2016. scale = 10 cm (4 in). photographs by blm. figure 4. (a) breithaupt and matthews conducting systematic stereoscopic imagery acquisition of the main track-bearing surface at the mill canyon dinosaur tracksite (mcdt), utah (lower cretaceous cedar mountain formation) in summer 2014. (b) a single didactyl theropod track from mcdt (center image); color depth map with relative depths recorded in cm (left image); and orthorectified image (right image), 1 mm (0.04 in) topographic contour map. (c) orthorectified image mosaics composed of over 1000 images. yellow inset box of area shown in 4d. (d) inset showing detail of a small portion of the surface from 4c as a color depth map. (e) a single theropod track from mcdt (center image); color depth map with relative depths recorded in cm (left image); orthorectified image (right image), 5 mm (0.2 in) topographic contour map. see lockley and others (2014b) and matthews and others (2016). 76 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 “enigmatic” cylindrical and mounded sandstone structures are present in eolian sandstone beds, at times below carbonate beds. two main types of burrows are represented at this site: type i and type ii (figure 5). alternative interpretations proposed for these structures include rhizoliths, termite nests and other invertebrate traces, concretions, fluid escape features, and wind-erosion features (lucas and others, 2006; riese and others, 2011). type i burrow structures have been defined as being comprised of high-density, complex networks of interconnected yand t-branching tunnels, with inclined ramps, horizontal to subhorizontal large-diameter structures preserved as differentially weathered low-relief mounds. the walls are predominantly smooth, with evidence of rhizoliths and small-diameter, passively filled burrows. these are most comparable with large complex burrow systems and mounds produced by social and eusocial mammals that show interconnected, sinuous, and multiple branching tunnels and ramps. whereas no body fossils of mammals have been found within the navajo sandstone (although therapsids have been found in this unit), modern animals that dig similar structures include prairie dogs, voles, and naked mole rats. a few specimens observed by riese and others (2011) exhibit scalloped walls, likely created by the organism’s hand during excavation motions (figure 5). type ii is represented by dorsoventrally flattened structures comprised of horizontal to subhorizontal, helical, curving, and simple branching tunnels that may lead to an enlarged chamber (figure 5, smith, 1987; groenewald and others, 2001; miller and others, 2001; hasiotis and others, 2004; riese and others, 2011). these are thought to have been created by therapsids, based on their simple architecture, burrow diameter, and raised floors. they are typically less complex and less interconnected. parallel longitudinal ridges on the surface of the burrows could possibly represent scratches produced by the organism’s claws, beaks, or incisors. these types of burrows likely represent a permanent dwelling and brooding structure. similar modern tunnels include those of alligators, crocodiles, some monitor lizards (varanus mertensi), and skinks, along with modern mammals such as the platypus, armadillo, and figure 5. type i and ii burrows (from riese and others, 2011). (a, c to e, and g) y-branching structures—(c) with an outward branching structure and (d) with an outward branching element. (f) tand y-branching structures. (i to l) sinuous architecture. (m and n) surficial morphology of type i structures with scallops marks by arrows. (n) represents and extant mole burrow cast with scallops. (h and o) type ii structures and surficial morphology; (h) is the raised floor creating a bioturbated morphology and (o) shows three parallel ridges on the lobes, indicated by arrows. scale bar = 1 cm. 77 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 aardwolf. the type ii burrows were likely excavated by large tritylodontid therapsids, based on size and comparisons to similar burrows from the permian and triassic of antarctica and south africa. a tritylodontid therapsid was recently found in the navajo sandstone in sand flats recreation area east of moab. an additional navajo sandstone tritylodontid from arizona was assigned to kayentatherium (winkler and others, 1991) but was regarded as a mammalian cynodont of the tritylodontidae by sues and others (1994). this specimen was also found in interdunal deposits. day 2: late triassic–early jurassic of san juan county lisbon valley stratigraphy and paleontology the overall history and most recent lithostratigraphic and vertebrate biostratigraphic assessment of lisbon valley were thoroughly covered by martz and others (2014). the upper triassic chinle formation within lisbon valley is estimated to be late norian-rhaetian in age (~208-201 ma) based on body fossils, especially aetosaurs and phytosaurs (martz and others, 2014). the chinle formation is unconformably underlain by the lower permian cutler group and overlain by the upper triassic-lower jurassic wingate sandstone (figure 6). the chinle in lisbon valley is divided into the kane springs beds capped by the church rock member (also called the dolores formation in nearby colorado and the rock point formation in arizona and new mexico; lucas (1993) refers to the chinle as a group rather than formation). salt tectonics in the region during the triassic likely resulted in the complete erosion of the lower part of the chinle formation, the entire moenkopi formation, and the upper part of the cutler group. locally, the lower part of the kane springs beds incised paleovalleys into the cutler group (martz and others, 2014). however, precise stratigraphic correlation of the chinle formation in the lisbon valley outlier is problematic; especially the kane springs beds (martz and others, 2014). the uppermost kane springs beds contain a prominent conglomerate in the region called black ledge (martz and others, 2014; figure 6). another distinct unit toward the top of the church rock member is called red ledge (figure 6); again, mostly composed of conglomerates deposited in a large braided river system. the red ledge beds are very fossiliferous. finally, between the contact of the church rock member and the lukachukai member of the wingate sandstone is a mostly fluvial unit called the big indian rock beds (martz and others, 2014; figure 6). the big indian rock beds contain the last phytosaur skull (see below) and important tracksites located on eagle nest ridge (see discussion below) to the south. lisbon valley research current investigation of lisbon valley began with exhaustive and thorough fieldwork in 2004 through 2015 by andrew r.c. milner and the st. george dinosaur discovery site at johnson farm (sgds). in 2009, the natural history museum of utah (umnh) and other researchers from colorado and arizona joined the team resulting in spectacular findings of plants, invertebrates, vertebrates, and invertebrate and vertebrate trace fossils (figure 7). extensive study of vertebrate body fossils from lisbon valley has been conducted on fishes (schaeffer, 1967; milner and others, 2006a, 2006b; gibson, 2013a, 2013b, 2015), with some work on phytosaurs, especially the last phytosaur (morales and ash, 1993; lucas and others, 1997; martz and others, 2014), and aetosaurs (martz and others, 2014). several publications are presently being written to describe many of the new vertebrate specimens both from lisbon valley and indian creek (see discussion on indian creek), as well as the vertebrate trace fossils and localities summarized below (table 1). stop 4 – lisbon valley camp hill swimtracks (figure 8) a set of large didactyl to tetradactyl swimtracks referable to characichnos isp. occur on a large fallen block of sandstone preserved in concave epirelief (milner and lockley, 2016; figure 8b). swimtracks may represent punting marks left by a large phytosaur swimming or bottom-walking in a channel, although orientation of travel cannot be determined. the best preserved set of 78 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 figure 6. stratigraphy of the chinle formation in the lisbon valley area. (a) generalized stratigraphy of skull ridge showing the positions of black ledge and red ledge beds (modified from ash and others, 2014). (b) detailed stratigraphic section of skull ridge (modified from martz and others, 2014). unit/subunit numbers: 1 – cutler group, 2 – lower kane springs beds, 3 – middle kane springs beds, 4 – upper kane springs beds, 5a–black ledge, 5b to f – lower church rock member, 6–red ledge, 7a to f – upper church rock member, and 8–wingate sandstone. (c) explanation for b (modified from martz and others, 2014). 79 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 swimtracks was replicated (sgds 1196) and measures 30 cm long by 17 cm wide (12 in long by 7 in wide), and the deepest point being 1.7 cm (0.67 in) in the middle of the center digit. sets of circular depressions arranged in arches may represent a trace called “pentasauropus” (figure 8c; lockley and hunt, 1995), although identification as actual trace fossils cannot be determined at this site. the fallen block containing these tracks matches well with the red ledge beds of the church rock member above (martz and others, 2014; figure 8a). the thicker sandstone layer is cross-bedded representing a broad, braided river system (martz and others, 2014). additional in situ examples of smaller characichnos traces occur to the southwest on camp hill with a swim direction toward the northwest. other isolated swim tracks occur on eagle nest ridge to the north and three step hills to the south. robert’s canyon tracksite (figure 9) this is a very informative tracksite set in a sequence of fluvial channel beds containing abundant invertebrate trace fossils throughout. this site is immediately below the wingate sandstone in the uppermost church rock member of the chinle formation situated just above figure 7. examples of vertebrate body fossils from the chinle formation of lisbon valley. (a) hemicalypterus weiri schaeffer, 1967 (usnm v 23425), composite part and counterpart image courtesy sarah z. gibson (modified from gibson, 2015). (b) synorichthys stewarti schaeffer, 1967 (umnh vp 22906). (c) lophionotus sanjuanenesis gibson, 2013a (umnh vp 19420a). (d) tanaocrossus kalliokoskii schaeffer, 1967 (umnh vp 22905). (e) lophionotus chinleana gibson, 2013b (umnh vp 19417 = holotype). (f) partial articulated phytosaur skeleton with osteoderms, dorsal vertebrae, ribs, and pelvis (umnh vp 24650). (g) crocodylomorpha new genus and species partial skull (umnh vp 21212). (h) “redondasaurus” (machaeroprosopus) sp. skull (umnh vp 24304). (i) typothorax coccinarum incomplete lateral osteoderm (umnh vp 24232). scales a-e and i = 1 cm (0.4 in); g = 2 cm (0.8 in); and f, h = 10 cm (4 in). 80 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 the red ledge beds (martz and others, 2014). tracks occur on a high northern ridge in the step-walled “robert’s canyon” named after its co-discoverers, robert baldazzi and robert gay. david slauf, however, found this tracksite along with several other small tracksites located farther to the south and southeast of the robert’s canyon locality. most of these nearby tracksites only have brachychirotherium preserved along with deep mud cracks, and they resemble sites preserved to the north on the northeastern slope of redd ridge. only one of these additional localities preserves a single evazoum gatewayensis track. the robert’s canyon tracksite preserves abundant brachychirotherium (figure 9a to 9d and 9g), although possible evazoum (figure 9e and 9f) and rhynchosauroides tracks are also present. all tracks at this site are preserved in concave epirelief. latex peels were created under permit for the longest brachychirotherium trackway and for two small possible evazoum tracks in a single trackway. abundant smaller tracks were recognized over the entire surface after the latex peels were later examined at the sgds. because of the steep-walled canyon, low-angle light on the tracksite surface makes these smaller tracks invisible. all of the tracks on this surface are small, compared to other sites in lisbon valley. eagle nest tracksites (figure 10) the big indian rock beds (martz and others, 2014) at the contact between the church rock member of the chinle formation and the lukachukai member of the wingate sandstone contain abundant tracks locally with most preserved as natural casts (figures 10a and 10b). brachychirotherium (figure 10c) and small grallator (figure 10d and 10e) are locally abundant, preserved in mediumto coarse-grained sandstone. tracks occur on at least four stratigraphic levels and most surfaces have not been mapped because the ledges are long and narrow with in-situ tracks on the undersides. one surface has poorly preserved grallator in concave epirelief and can be oriented into its in-situ position (figure 10b and 10f). grallator tracks range in size from 15.5 cm (6.1 in) long and 9 cm (4 in) wide to 6 cm (2 in) long and 4.5 cm (1.8 in) wide with several tracks displaying phalangeal pads. these grallator tracks are small in comparison to older and larger grallator found at a site near the base of the red ledge beds on schaeffer ridge to the south (figure 10g). brachychirotherium cf. parvum are mostly incomplete and have an average length/width of 12 cm (5 in) by 14 cm (6 in), respectively. several small, in situ tracksites have also been recorded within the lower part of the lukachukai member of the wingate sandstone on the southeastern side vertebrate species actinopterygii indet. hemicalypterus weiri schaeffer, 1967 (fig. 7a) lophionotus sanjuanenesis gibson, 2013a (fig. 7c) lophonotus chinleana gibson, 2013b (fig. 7e) synorichthys stewarti schaeffer, 1967 (fig. 7b) cionichthys dunklei schaeffer, 1967 lasalichthys hillsi schaeffer, 1967 tanaocrossus kalliokoskii schaeffer, 1967 (fig. 7d) tanaocrossus sp. arganodus dorotheae (case, 1921) chinlea sorenseni schaeffer, 1967 phytosauria indet. (fig. 7f) pseudopalatine indet. “redondasaurus” (machaeroprosopus) sp. (fig. 7h) machaeroprosopus sp. aetosauria indet. typothorax sp. typothorax coccinarum cope, 1875 (fig. 7i) paracrocodylomorpha indet. crocodylomorpha indet. crocodylomorpha n. gen. et sp. (fig. 7g) vertebrate ichnofossils undichna isp. rhynchosauroides isp. gwyneddichnium isp. brachychirotherium parvum (hitchcock, 1889) brachychirotherium sp. evazoum gatewayensis lockley and lucas, 2013 evazoum isp. “pseudotetrasauropus” isp. “pentasauropus”? apatopus isp. grallator isp. grallator? characichnos isp. table 1. species and ichnospecies lists for the chinle formation in the lisbon valley area. 81 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 of eagle nest ridge. all of the tracks on these surfaces are natural cast of theropod footprints, many attributed to grallator (figure 10h and 10i). redd ridge north and south (figure 11) at least two stratigraphic levels of tracks on the north side of redd ridge in the upper church rock member preserve footprints in concave epirelief and convex hyporelief respectively. small and large mudcracks are present on both surfaces. unfortunately, dense foliage on very steep, covered slopes, makes their exact stratigraphic position uncertain. the natural cast surface resembles desiccated horizons to the south near robert’s canyon, north of steen canyon, and farther to the west in the indian creek area. only brachychirotherium are preserved at all of these localities (figure 11a to 11c). on the southeast side of redd ridge, two large fallen blocks covered in current ripple marks have two long and parallel evazoum gatewayensis trackways (figure 11d and 11e) and a shorter brachychirotherium trackway. by looking at the block shapes, both can then be oriented into their correct positions so that trackway directions in relationship to current flow can be determined. these tracks along with a nearby block containing swim tracks (figure 11f) come from the uppermost portion of the red ledge beds of the church rock member. stop 5 – last phytosaur (figure 12) the last phytosaur represents the dorsal impression of a pseudopalatine phytosaur skull probably referable to “redondasaurus” (figure 12a and 12b). the name last phytosaur was coined by morales and ash (1993) because of the skulls stratigraphic position, either in the basal wingate sandstone, or within the uppermost church rock member of the chinle formation (see also lucas and others, 1997). martz and others (2014) named the unit (8a in figure 12c) the big indian rock beds, placing it within the lowermost wingate. morales and ash (1993) mention a second skull found nearby and this may be represented by mna v10650 which was recently prepared at the sgds. in recent years the sgds and umnh crews have collected figure 8. camp hill outcrop and tracks. (a) locality of fallen phytosaur swim track block (red arrow) showing where it originated from in the red ledge beds (yellow arrow), church rock member, chinle formation. photo courtesy of jeff martz (university of houston). (b) best set of large phytosaur swim tracks (i.e., characichnos isp. = sgds 1196 replica). scale = 10 cm. (c) cf. “pentasauropus” on same surface with swim tracks. 82 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 an additional three “redondasaurus” skulls from skull ridge within less than a 0.4 km (0.25 mi) of the last phytosaur skull. however, all of these specimens come from the red ledge beds lower down in the church rock member (martz and others, 2014). finally, vertebrate tracks have been found in the lower part of red ledge on the south side of skull ridge to the east of the last phytosaur skull. this tracksite includes abundant invertebrate burrows and grazing trails, with the only identifiable specimens of apatopus—possibly representing phytosaur tracks (figure 12d and 12e), and poorly-preserved brachychirotherifigure 9. robert’s canyon tracksite in the upper church rock member, chinle formation. (a) tracksite map. (b) brachychirotherium trackway 1 drawing showing track set 4-6 only. (c) brachychirotherium trackway 2 showing entire exposed trackway, inverted photo of latex peel. (d) drawing of brachychirotherium trackway 2. (e) drawing of two tracks in possible evazoum isp. trackway. (f) photo of tracks in e. (g) first track in brachychirotherium trackway 2 showing metatarsal impression. scale in b, d, e = 50 cm (20 in); c = 10 cm (4 in); scale in g = 5 cm (2 in). a and b, d and e are interpretive drawings made by martin g. lockley during 2011 field season. 83 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 um (figure 12f). the red ledge beds represent a thick braided river sequence (martz and others, 2014). stop 6 – shay canyon tracksite (figure 13) upon entering the indian creek valley from the south, we drive down through the kayenta formation, underlain by the wingate sandstone, and the chinle formation. in the uppermost part of the church rock member of the chinle, approximately 15 m below the chinle-wingate contact lies the shay canyon tracksite (lockley and hunt, 1995, p. 77–78, figure 3.8; called rock point formation by hunt and lucas, 2007, p. 223). figure 10. eagle nest ridge tracksites. (a) southeast side of eagle nest ridge showing the position of the track-bearing big indian rock beds and lukachukai member of the wingate sandstone. (b) track-bearing big indian rock beds on eagle nest ridge. the two upper fallen slabs are those mapped in f. (c) in situ natural cast tracks on underside of ledge in big indian rock beds. brachychirotherium (white arrow left center) and grallator (yellow arrow top right). (d) isolated grallator natural cast from big indian rock beds (umnh vp 24637). scale = 2 cm (0.8 in). (e) grallator natural cast (umnh vp 21876). scale = 2 cm (0.8 in). (f) two mapped grallator-dominated slabs in b. scale = 10 cm (4 in). (g) two natural cast grallator tracks from the base of red ledge beds of church rock member from schaeffer ridge. these are the largest grallator from the chinle formation of the region (umnh vp 22885). scale = 5 cm. (h) natural cast tracks preserved in lukachukai member on eagle nest ridge (photo courtesy david slauf, volunteer at sgds). (i) same track surface as in h showing at least 20 theropod tracks on two stratigraphic levels (photo courtesy david slauf). 84 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 although only briefly described by lockley and hunt (1995), very little has been published on this very large tracksite, which is by far the largest chinle tracksite exposed in the region. the site preserves over 250 tracks on a single bedding surface (figure 13a), dominated by brachychirotherium tracks and trackways (figure 13b). less common atreipus-like tracks are also reported, along with possible pentasauropus tracks (lockley and hunt, 1995; figure 3.10). other problematic tracks include several enigmatic scratch and scrape marks, which were first interpreted as phytosaur swim tracks, although this is highly speculative (lockley and hunt, 1995). hunt and lucas (2007) identify tracks at the shay canyon site as brachychirotherium thuringiacum, anchisauripus sillimani, and pentasauropus sp. several patches of fish debris (figure 13c) have been interpreted as coprolites by lockley and hunt (1995). it is possible that these are simply disarticulated and/or figure 11. tracks from redd ridge. (a) brachychirotherium parvum trackway with mudcracks preserved as actual tracks (umnh vp 22334). scale = 10 cm (4 in). (b) close-up of second set manus and pes tracks in a. scale = 5 cm (2 in). (c) partial brachychirotherium trackway with unusual gate. first pes tracks has elongate metatarsal impression (umnh vp 21875). scale = 10 cm (4 in). (d) two large current ripple-covered evazoum track blocks fallen from red ledge beds in background with wingate sandstone behind that. (e) latex peel showing examples of two evazoum gatwayensis tracks in trackway from lower block shown in d. (f) possible swim track set from red ledge beds. scale = 5 cm (2 in). 85 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 associated fish remains since fossil fishes are very abundant locally within the church rock member in both the indian creek and lisbon valley areas. at indian creek, the chinle formation unconformably overlies the lower triassic moenkopi formation which is very thin here compared to other areas. the lower member of the chinle superficially resembles the kane springs beds as seen in lisbon valley, but is identified as the owl rock member (martz and others, 2014). the upper member is the church rock member capped by the wingate sandstone (figure 14). fossils are locally abundant within the chinle formation and wingate sandstone in indian creek. phytosaurs, aetosaurs, crocodylomorphs, theropods, metoposaurs, and a variety of fishes have been collected in the indian creek valley from 2013-2016 by umnh and sgds field crews. several small tracksites have also been recognized in the upper part of the owl rock (see track city below) and church rock members of the chinle, and the lukachukai member of the wingate. stop 7 – track city (figure 15) the “track city” tracksite is the oldest tracksite in the chinle formation known from the indian creek area. it is located in the upper part of the owl rock figure 12. “last phytosaur” and tracks found nearby on skull ridge. (a) in situ pseudopalatine phytosaur skull impression at last phytosaur locality. note white bone to the right in photos and abundance of large associated mudstone clasts. jeff martz pictured for scale. (b) close-up of last phytosaur skull. green clay still remains in replica from first replication of specimen housed at museum of northern arizona (mna). yellowish material is old latex left behind from a failed replica attempt. this has since been removed for umnh and sgds latex peel. finger on right is pointing to end of snout. scale = 10 cm (4 in). (c) stratigraphic section through last phytosaur site (black arrow) situated in big indian rock beds (unit 8a) in basal wingate sandstone (modified from martz and others, 2014). (d) apatopus natural cast tracks (umnh vp 24921). scale = 2 cm (0.8 in). (e) apatopus natural cast tracks (umnh vp 24919). scale = 2 cm (0.8 in). (f) pair of brachychirotherium natural cast tracks with abundant invertebrate burrows (umnh vp 24920). scale = 5 cm (2 in). 86 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 member and holds brachychirotherium (umnh vp 26000 in figure 15a and 15f; umnh vp 25993, figure 15d to 15e), rhynchosauroides (figure 15a and 15g), evazoum gatewayensis (umnh vp 26000, figure 15a to 15c), gwyneddichnium (umnh vp 25992, figure 15i), and several unidentified tracks (figure 15a and 15h). this locality still requires excavation. as mentioned above, several other tracksites have been identified within the upper part of the church rock member within the indian creek region. many of these are small, isolated sites similar to those in the lisbon valley area, only preserving a few tracks. the figure 13. shay canyon tracksite. (a) northern 30 m of tracksite map; each bar = 1 m (3 ft); a = atreipus-like trackways, b = brachychirotherium trackways, c = coprolites. (b) southern 26 m (85 ft) of tracksite map; each bar = 1 m (3 ft). (c) rose diagram of northern map track orientations. (d) rose diagram of southern map track orientations. (e) stratigraphic section of the uppermost chinle formation at shay canyon tracksite showing track horizon (footprint). scale = 5 m (16 ft). (f) part of southern tracksite surface and the upper part of the chinle formation capped by the wingate sandstone. (g) close-up of trampled track surface. (h) sketch of right brachychirotherium manus and pes set. scale = 10 cm (4 in). (i) right brachychirotherium manus and pes set on tracksite surface. (j) sketch of right atreipus-like track. scale = 10 cm (4 in). (k) left atreipus-like track on tracksite surface. (l) in-situ fish debris in possible coprolite. scale = 2 cm (0.8 in). a-e, h, j are all modified from lockley and hunt (1995, figure 3.8). 87 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 figure 14. generalized stratigraphy of the indian creek valley and view of bridger jack mesa showing the owl rock and church rock members making up the chinle formation, capped by the wingate sandstone. figure 15. examples of vertebrate tracks from the “track city” locality situated in the upper part of the owl rock member, chinle formation. (a) discovery block containing actual tracks in fine-grained sandstone (umnh vp 26000). scale = 10 cm (4 in). (b) large, well-preserved evazoum gatewayensis track (umnh vp 26000). scale = 5 cm (2 in). (c) two partial evazoum tracks only displaying digits iii and iv (umnh vp 26000). scale = 2 cm (0.8 in). (d to e) brachychirotherium track through thick sediment, showing the track outline and infill, and the undertrack on opposite side (umnh vp 25993). scale = 5 cm (2 in). (f) brachychirotherium manus and pes set (umnh vp 26000). scale = 5 cm (2 in). (g) rhynchosauroides isp. (umnh vp 26000). scale = 1 cm (0.4 in). (h) unidentified small tracks (umnh vp 26000). scale = 1 cm (0.4 in). (i) actual track that likely represents gwyneddichnium pes with possible metatarsal impression (umnh vp 25992). scale = 2 cm (0.8 in). 88 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 most common tracks are those of brachychirotherium. a single site has surfaces covered with hundreds of very common rhynchosauroides tracks (figure 16a, b, and d), and a single unidentified chirotheriid-like track (figure 16d). brachychirotherium tracks from the wingate sandstone have also been found (figure 16f). stop 8 bridger jack mesa tracksite (figure 17) this giant fallen track block was discovered in 2015 (figure 17a and 17b). it originated from an uncertain stratigraphic level in the wingate sandstone above, but came to rest near the contact of the owl rock and figure 16. examples of isolated track specimens from the chinle and wingate formations in indian creek valley. (a) natural cast rhynchosauroides isp. tracks from red ledge beds (umnh vp 24237). scale = 1 cm (0.4 in). (b) natural cast rhynchosauroides isp. tracks with associated toe drag marks from red ledge beds (umnh vp 24237). scale = 1 cm (0.4 in). (c) unidentified four-toed track from upper owl rock member. scale = 1 cm (0.4 in). (d) natural cast, unidentified chirotheriid-like track (right center) with associated rhynchosauroides isp. track from red ledge beds (umnh vp 24237). scale = 1 cm (0.4 in). (e) grallator-like theropod track from upper owl rock member. scale = 5 cm (2 in). (f) natural cast brachychirotherium-like trackway from wingate sandstone. scale = 10 cm (4 in). photos c, e, and f courtesy david slauf (volunteer at sgds). 89 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 church rock members of the chinle formation (figure 17a). it is covered with grallator-like theropod tracks and evazoum gatwayensis preserved in convex hyporelief (figure 17c). other fallen blocks on this slope include additional grallator associated with brachychirotherium and an isolated eubrontes-like theropod track (figure 17d). several isolated track blocks from the wingate sandstone have been recognized and most preserve brachychirotherium, grallator, or slightly larger theropod tracks in the anchisauripus size-range. day 3: early jurassic – late cretaceous of grand and emery counties stop 9 – bull canyon tracksite: an extension of the moab megatracksite the bull canyon tracksite (also known as the fisher mesa tracksite) is at nearly 2743 m (9000 ft) elevation on the north slope of the la sal mountains, among scrub oak and ponderosa pine, managed by the u.s. forest service. the surface is at the top of the curtis formation (moab figure 17. the “bridger jack mesa tracksite,” wingate sandstone. (a) view of giant fallen block sitting near the contact of the upper triassic owl rock and church rock members of the chinle formation. red arrow points to benn breeden extracting an in-situ phytosaur squamosal in the uppermost conglomerates of the owl rock member. (b) view of the main track-bearing slab containing actual tracks around the border of the block. (c) close-up of grallator (g) and evazoum sp. (e) tracks on the lower right corner of the block. (d) partial eubrontes-like track preserved as a natural cast from a nearby fallen block. 90 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 tongue) and the site is thus part of the moab megatracksite (lockley and hunt, 1995). it is late jurassic (oxfordian) in age. the surface contains approximately 50 tracks of large and medium theropod dinosaurs assigned to the ichnogenera megalosauripus and therangospodus, mostly clearly and deeply preserved. trackways preserve evidence of animals walking between 4 and 5.6 km/hr (2.5 and 3.5 mi/hr), and in at least one track there are visible metatarsal impressions. as part of the moab megatracksite, the bull canyon locality represents the same surface that preserves tracks at sites around arches national park, sites such as the dinosaur stomping grounds and willow springs, both public tracksites managed by the blm. there are also tracksites from this level as far northeast as dewey bridge and near the cisco boat ramp. all of these sites preserve the same types of theropod tracks. the only unequivocal non-theropod trackway described from this interval is a sauropod trackway from the upper entrada sandstone of grand staircase-escalante national monument (foster and others, 2000). the bull canyon tracksite was recently developed as an interpretative trail, with pathways to the two main sites, where easily recognizable tracks are visible (figure 18d). here we designate these as the east site (at the cliff edge) and the west site (figure 18f and 18g). the east site reveals about 17 tracks comprising at least 7 trackway segments (t1-t7). three of these are oriented east-southeast with parallel orientations (figure 18g). there is a high vertical drop off on the east side of the east site, which is dangerous to approach too closely (17d). parts of the southern edge of this site are also collapsing and isolated tracks can be seen on displaced blocks. the west site reveals 29 tracks, which resolve into 7 trackway segments (t8-t14). here the modal trackway orientation is towards the northwest. a single trackway (t15) of 3 footprints has been identified 20 m (66 ft) west-southwest of the western edge of the west site. it is oriented towards the north at 15° azimuth. nearly all recognizable tracks are assigned to megalosauripus, a common large theropod track at other moab megatracksite localities. the outlines of five well-preserved tracks are shown in figure 18. they range in length from ~38 to ~46 cm (~15 to ~18 in) with corresponding widths of ~30 to ~37 cm (~12 to ~14 in). the moab megatracksite the term “megatracksite” which is synonymous with the term “dinosaur freeway” refers to a regionally extensive surface or thin unit of beds which is consistently track-bearing. the original definitions were proposed by lockley and pittman (1989) and the phenomenon has since been discussed extensively elsewhere (lockley, 1991, 1997; lockley and hunt, 1995). as noted in the introduction, megatracksites can be “attributed to the dynamics of sea level change associated with coastal plain systems.” currently there are three well-defined areas in the western usa where megatracksites have been identified and described in some detail. the “moab megatracksite” is the oldest, and is associated with the transgressive flooding surface (transgressive systems tract) at the interface between the curtis formation (moab tongue) and summerville formation where a thin sequence of marginal marine sediments was deposited in the area (lockley and others, 2007). the age of the moab megatracksite is earliest late jurassic (oxfordian). the other two well-documented megatracksite areas in the western usa are associated with two albian age levels (two discrete megatracksites) in the glen rose formation of texas and the albian-cenomanian-aged naturita formation in colorado and adjacent states. it is worth noting that all these megatracksites are associated with transgressive systems tracts (flooding surfaces), and that they all show certain consistent ichnological characteristics. these can be described as follows with specific reference to the moab megatracksite. all known megatracksites or dinosaur freeways have aerial extents on the order of x 1000s to x 100,000s of km2. the moab megatracksite extends over the entire area of arches national park, and as far east and northeast as the bct at the upper end of castle valley, and westwater, near the colorado-utah border. this area is conservatively estimated to be on the order of a minimum of ~1820 km2 (~700 mi2), but may extend to the blanding area about 130 km (80 mi) to the south. the area has been most extensively studied on the southwest flank of the salt valley anticline, which corresponds, approximately to the western boundary of arches national park. here a total of 24 sites (designated as a-x) have been mapped: see lockley (1991) for maps of sites a, b, 91 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 c, w, and x, and two additional sites on the northeast flank of the anticline, lockley and others (2000a, 2000b) for photographs of site e, and tracks from other sites, lockley and hunt (1995) for a map of site q, with more than 2000 footprints. the latter site has been designated as an interpretative site by the blm and has been called the “dinosaur stomping ground.” with the addition of other known sites, the moab megatracksite is based on a total of at least 30 reported sites. the only tracks found at all these sites are largeand medium-sized theropod tracks named megalosauripus and therangospodus, respectively (figure 19b to 19e). thus, the ~3000 tracks reported from ~30 sites represent only two morphotypes. such site-to-site track-type consistency indicates a scientific repeatability of results that strongly suggests that tracksites are reliable indicators or censuses of the faunas that occupied this region at this time in the middle to late jurassic transition. the other aforementioned cretaceous megatracksites also show site-to-site consistency in the track types, based on samples of between ~42 sites in texas and ~120 sites in the colorado area. studies of tracks found just below and just above the moab megatracksite surfaces indicate quite different faunas inhabiting the region just before and after the megatracksite was registered. in the eolian dune deposits, just below, small crow-sized theropod tracks (wildeichnus) occur, whereas just above, in the marginal marine deposits of the upper tongue of the summerville formation, pterosaur tracks (pteraichnus) are regionally distributed. a fourth suite of theropod, sauropod, stegosaur, and crocodylian tracks occur in the overlying salt wash member of the morrison formation (lockley and others, 2007, figure 2 = figure 19 herein). stop 10 – poison spider dinosaur tracksite as mentioned earlier, the navajo sandstone in southeastern utah represents possibly the largest erg ever to develop during the phanerozoic (parrish and falcon-lang, 2007). multiple occurrences of carbonate beds, representing spring-fed lakes that ponded between dunes, are present in the navajo sandstone in the moab area. these carbonate beds, and other siliciclastic water-lain interdune deposits, frequently preserve a variety of dinosaur tracks, most notably eubrontes, grallator, otozoum, and anomoepus. elsewhere in the moab area, large clusters of conifer tree remains occur in association with these interdunal deposits. the presence of these conifers has been inferred to represent long-lived pluvial episodes where the erg was stabilized. alternatively they may reflect erg-margin locations in this area of the colorado plateau (parrish and falcon-lang, 2007). the tracks known from the poison spider dinosaur tracksite represent a variety of theropod dinosaurs, ranging in size from very small to over 1.5 m at the hips. the tracks on the main blocks represent up to 10 different animals. the rocks containing the tracks fell from the navajo sandstone cliffs, split along the bedding planes and now rest on the kayenta formation, which makes up the slopes below the cliff (figure 20a). both true tracks and the corresponding natural casts occur on the main slabs, and mostly represent eubrontes and grallator (figure 20e). the larger, upper track slab, first documented by the blm in 1965, was later mapped by lockley and hunt (1995, figure 20b). the block had tilted outward from the cliff base, revealing eubrontes and grallator, but also the type specimen of anomoepus moabensis, a small threetoed bird-like track produced by ornithischian dinosaurs (figure 20d and 20f). more than 24 theropod tracks of various sizes are preserved here (see figure 20c). whereas tracks are very common and well known from these interdune deposits, body fossils for dinosaurs of this age are very rare, with only one dinosaur, seitaad, having been found in the navajo sandstone in utah (sertich and loewen, 2010), and one small theropod, segisaurus, known from arizona (camp, 1936, figure 20g). thus, most information on early jurassic life at this time is based on trackways, such as these, which are very common in interdune units within the navajo. stop 11– moline reef tracksite the moilne reef tracksite represents an ornithopod tracksite in the upper cretaceous (turonian) ferron sandstone member of the mancos shale (decourten, 1998; jones, 2001; kirkland and madsen, 2007; figure 21). this deltaic/coastal environment represented by the ferron sandstone has only rarely produced tracks with92 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 figure 18. caption on following page. 93 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 in utah. the moilne reef tracksite is located on a fallen sandstone block, which fell out of the escarpment located directly north of the site. the tracks are preserved as natural casts and true tracks. there are nine tridactyl tracks preserved, which are not well-defined, and manus tracks were noted by gierlinski and lockley (2013, figure 24.2a and b). the footfalls in the moilne reef tracksite show a consistent 97 cm (38 in) length in the left and right paces, and the animal is estimated to be roughly 72 cm (0.3 in) tall at the hips (jones, 2001). stop 12 – tracks from the mesaverde group since the 1920s upper cretaceous tetrapod tracks have been reported from the coal-bearing strata of the broadly defined mesaverde group (campanian and maastrichtian) at various sites in utah, colorado, and wyoming, especially around the price coal mining district of utah and grand mesa in western colorado (carpenter, 1992). during the deposition of this unit, swamps were developing in interdeltaic to coastal plain environments (parker and balsley, 1989; carpenter, 1992). some tracks have been extracted as isolated casts from the roofs of coal mines (peterson, 1924) whereas others have been described from surface exposures (robison, 1991; lockley and others, 2011). in the 1930s the tracks were often treated sensationally, as in the case of peterson’s claim of a tyrannosaurus track and barnum brown’s excavation of a slab for the american museum with tracks he attributed to a “mystery dinosaur” with a giant stride (brown, 1938). these latter interpretations figured in 1970s debates about dinosaur speed, as well as by carpenter (1992). only in a few cases have large surfaces with trackway segments been mapped in detail (lockley and others, 1983, 2011; parker and balsley, 1989). tracks occurring in the campanian blackhawk formation of utah, near price, utah, have frequently been discovered in coal mines near the area, and are commonly known to locals. a large collection of trackways from these coal mines can be found at the utah state univerfigure 19. tracks from dinosaur stomping grounds (dsg) in the upper jurassic curtis formation (moab tongue). (a and b) megalosauripus tracks found at dsg. (c and d) therangospodus tracks at other sites around the moab megatracksite area, west of arches national park, on blm lands. photographs by rebecca hunt-foster. figure 18 (figure on previous page). bull canyon dinosaur tracksite (bct) on national forest service land, east of moab, utah. a selection of theropod tracks from the bct (fischer mesa tracksite) were photogrammetrically documented in 2004. above (from left to right columns) are (a) color depth maps, (b) orthographic images, and (c) topographic contour maps (5 mm [0.2 in] contours). all graphics are depicted at a uniform scale. scale bar is 50 cm (20 in) in length. a camera calibration photo set (see matthews and others, 2016) was taken for each track; however, multiview matching software was not yet available and calibrated objects of known length had not been developed. the coded targets, visible in the orthographic image map, were place around the subject to aid in manual image alignment necessary in the software of the day. (d) andrew milner and brent breithaupt at the bct during documentation in 2004. (e) new signage at the bct trail installed by the forest service in july of 2016. (f-h). map of the tracks at the bct by m.g. lockley, with associated upper surface (shaded yellow) of the moab member, which is part of the moab megatracksite. (f) relationship of the east and west sites to the pathways, fence, and vegetation (in green). (g) details of the two sites with main trackway orientations and outlines of best preserved tracks. (h) orientation patterns derived from 13 trackways with reliably measured orientations. (i) location of the bct. 94 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 sity – eastern prehistoric museum (figure 22). tracks found in the vicinity of grand mesa, in western colorado, are known from just above the campanian bowie shale member of the lower williams fork formation (also known as the hunter canyon formation). these tracks preserve a wide variety of taxa including the mammal tracks schadipes (lockley and foster, 2003; figure 23), crocodiles, ceratopsians, hadrosaurs, and a possible therizinosaur. the dominant track types in the mesaverde group figure 20. the poison spider dinosaur tracksite (psdt) west of moab, utah. (a) these tracks are present in the lower navajo sandstone (early jurassic). (b and c) large track block containing multiple different tracks (map after lockley and hunt, 1995). (d) eubrontes track. (e) main track block at psdt displaying eubrontes and grallator tracks. (f) anomoepus moabensis track. (g) new signage installed at psdt in 2016. art (g) and figure layout (a) by brian engh. photographs by rebecca hunt-foster. 95 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 appear to be those of large hadrosaurs, likely related to rhinorex, with large numbers represented, and a variety of size classes present (parker and rowley, 1989; carpenter, 1992; gates and scheetz, 2014, figure 23), along with theropods of various sizes (lockley and others, 1983, 2011). a lesser number of tetradactyl tracks may be attributed to ceratopsians, but these have not been studied in detail. there are scattered reports of pterosaur tracks (lockley, 1999) as well as bird and frog tracks (robison, 1991). ongoing work has revealed the presence of turtle and other tetrapod tracks, as yet undescribed. other reports of tracks from the mesaverde group include peterson (1924), strevell (1932, 1940), look (1951, 1955), wilson (1969), collins (1976), lockley (1984, 1986), parker and balsley (1986, 1989), rowley and parker (1986, 1989), lockley and jennings (1987), lockley and conrad (1989), parker and balsley (1989), and rowley and parker (1989). acknowledgments we acknowledge our sponsors, artists and volunteers, who have helped with these sites, along with the bureau of land management, national forest service, state of utah, and regional museums for permitted access to sites and specimens. all the authors thank their coauthors and respective institutions mentioned and referred to in the relevant citations. we also thank the utah geological association for editorial and production support. references ash, s.r., milner, a.r.c., sharrow, d., and tarailo, d., 2014, first known post-triassic occurrence of the palm-like plant fossil sanmiguelia brown, in maclean, j.s., biek, r.f., and huntoon, j.e., editors, geology of utah’s far south: utah geological association publication 43, p. 511–516. barnes, f.a., 1997, canyon country dinosaur tracks and trackers: moab, utah, canyon country publications, 176 p. brown, b., 1938, the mystery dinosaur: natural history, v. 41, p. 190–202. camp, c., 1936, a new type of small bipedal dinosaur from the navajo sandstone of arizona: berkeley, university of california bulletin 24, p. 39–56. carpenter, k., 1992, behavior of hadrosaurs as interpreted from footprints in the “mesaverde” group (campanian) of colorado, utah, and wyoming: contributions to geology, v. 29, no. 2, p. 81–96. case, e.c., 1921. a new species of ceratodus from the upper triassic of western texas: occasional papers of the museum of zoology, v. 101, p. 1–2. collins, b., 1976, coal deposits of the carbondale, grand hogback and southern danforth hills coal fields, eastern piceance basin, colorado: quarterly of the colorado school of mines, v. 71, no. 1, 138 p. figure 21. (a) moline reef tracksite, an ornithopod tracksite in the upper cretaceous (turonian) ferron sandstone member of the mancos shale. (b-c). gierlinksi and lockley (2013) re-evaluated the trackway described by jones (2001) and illustrated previously-unrecorded manus tracks indicating an unusually wide straddle of fore limbs. 96 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 figure 22. (a) the w. doug wilson dinosaur tracks collection, collected from the royal coal mine in price canyon, blackhawk formation. (b) tracks from the kenilworth mine. (c) tracks from the late cretaceous mesaverde group, carbon county, utah, on exhibit at the utah state university – eastern prehistoric museum in price, utah. (d to h) blackhawk formation tracks. photographs by rebecca hunt-foster. 97 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 cope, e.d., 1875, report on the geology of that part of northwestern new mexico examined during the field season of 1874, in annual report upon the geographical explorations west of the 100th meridian [wheeler survey], appendix ll: annual report chief of engineers for 1875, p. 61–97 of separate issue, p. 981– 1017 of full report. decourten, f.l., 1991, new data on early cretaceous dinosaurs from the long walk quarry and tracksite, emery county, utah, in chidsey, t.c., jr., editor, geology of east-central utah: utah geological association publication 19, p. 311–324. foster, j.r., 2015, theropod dinosaur ichnogenus hispanosauropus identified from the morrison formation (upper jurassic), western north america: ichnos, v. 22, no. 3-4, p. 183–191. foster, j.r., and lockley, m.g., 1997, probable crocodilian tracks and traces from the morrison formation (upper jurassic) of eastern utah: ichnos, v. 5, p. 121–129. foster, j.r., hamblin, a.h., and lockley, m.g., 2000, the oldest evidence of a sauropod dinosaur in the western united states and other important vertebrate trackways from grand staircaseescalante national monument, utah: ichnos, v. 7, p. 169–181. gates, t.a., and scheetz, r., 2014, a new saurolophine hadrosaurid (dinosauria: ornithopoda) from the campanian of utah: north america journal of systematic paleontology, http://dx. doi.org/10.1080/14772019.2014.950614. gierlinski, g., and lockley, m.g., 2013, first report of probable therizinosaur (cf. macropodosaurus) tracks from north america, with notes on the neglected vertebrate ichnofauna of the ferron sandstone, chapter 23, in titus, a.l., and loewen, m.a., editors, at the top of the grand staircase: bloomington, indiana university press, p. 530–535. gibson, s.z., 2013a. a new lump-backed ginglymodian fish (neopterygii, semionotiformes) from the upper triassic chinle formation of southeastern utah: journal of vertebrate figure 23. (a to c). dr. ryan king (independent) and martin lockley at a large block of fluvial/paludal sandstone and mudstone from the campanian hunter canyon formation resting on its side in debeque canyon, colorado. the underside of the bed is exposed showing multiple tracks in multiple trackways preserved as sand-infillings in convex hyporelief; a latex mold (a and b) is being applied to one of the tracks, under a permit from the colorado blm. (d) closeup of c showing a large tetradactyl track, possibly therizinosaur, next to in-situ tree bole. (e) newly discovered footprints in the campanian hunter canyon formation in debeque canyon, colorado, possibly of a ceratopsian. (f) field team of dr. martin lockley, dr. ryan, and eric eckberg (blm) collecting data on fossil footprints in the campanian hunter canyon formation in debeque canyon, colorado. 98 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 paleontology, v. 33, no. 5, p. 1027–1050. gibson, s.z., 2013b, biodiversity and evolutionary history of †lophionotus (neopterygii: †semionotiformes) from the western united states: copeia, v. 2013, no. 4, p. 582–603. gibson, s.z., 2015, evidence of a specialized feeding niche in a late triassic ray-finned fish—evolution of multidenticulate teeth and benthic scraping in †hemicalypterus: the science of nature – naturwissenschaften, v. 102, no. 3-4, p. 10. groenewald, g.h., welman, j., and maceachern, j.a., 2001, vertebrate burrow complexes from the early triassic cynognathus zone (driekoppen formation, 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p. 48–51. kirkland, j.i., and madsen, s.k., 2007, the lower cretaceous cedar mountain formation, eastern utah—the view up an always interesting learning curve, in lund w.r., editor, field guide to geological excursions in southern utah: geological society of america rocky mountain section and utah geological association publication 35, p. 1–108, compact disk. kirkland, j.i., suarez, m., saurez, c., and hunt-foster, r., 2016, the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata: geology of the intermountain west, v. 3, p. 101–228. lockley, m.g., 1984, dinosaur tracking: science teacher, v. 51, p. 18–24. lockley, m.g., 1986, dinosaur tracksites: university of colorado at denver geology department magazine special issue 1, 56 p. lockley, m.g., 1991, tracking dinosaurs—a new look at an ancient world: new york, cambridge university press, 238 p. lockley, m.g., 1997, the paleoecological and paleoenvironmental importance of dinosaur footprints, in 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5–13. lockley, m.g., meyer, c.a., and moratalla, j.j., 2000a, therangospodus—trackway evidence for the widespread distribution of a late jurassic theropod with well-padded feet, gaia: revista de geociencias, museu nacional de historia natural, lisbon, portugal, v. 15, p. 339–353. lockley, m.g., meyer, c.a., and dos santos, v.f., 2000b, megalosauripus, and the problematic concept of megalosaur footprints, gaia: revista de geociencias, museu nacional de historia natural, lisbon, portugal, v. 15, p. 313–337 lockley, m.g., gierlinski, g.d., houck, k., lim, j-d., kim, k.s., kim d.y., kim, t.k.,  kang, s.h., hunt-foster, r., li, r., chesser, c., gay, r., dubicka, z., cart, k., and wright, c., 2014c, new excavations at the mill canyon dinosaur track site (cedar mountain formation, lower cretaceous) of eastern utah, in lockley, m.g., and lucas, s.g., editors, fossil footprints of western north america: new mexico museum of natural history and science bulletin 62, p. 287–300. lockley, m.g., 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birthisel, t.a., 2006a, late triassic-early jurassic freshwater fish faunas of the southwestern united states with emphasis on the lake dixie portion of the moenave formation, southwest utah, in harris, j.d., lucas, s.g., spielmann, j.a., lockley, m.g., milner, a.r.c., and kirkland, j.i., editors, the triassic-jurassic terrestrial transition: new mexico museum of natural history and science bulletin 37, p. 522–529. milner, a.r.c., and lockley, m.g., 2016, dinosaur swimtrack assemblages—characteristics, contexts and ichnofacies implications, in falkingham, p.l., marty, d., and richter, a., editors, dinosaur tracks—next steps: bloomington, indiana university 100 tracking dinosaurs in blm canyon country, utah hunt-foster, r.k., lockley, m.g., milner, a.r.c., foster, j.r., matthews, n.a., breithaupt, b.h., and smith, j.a. geology of the intermountain west 2016 volume 3 press, p. 152–181. milner, a.r.c., lockley, m.g., and kirkland, j.i., 2006c, a large collection of well-preserved theropod 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dinosaur tracks and traces: new york, cambridge university press, p. 353–359. parker, l.r., and rowley, r.l., 1986, dinosaur footprints in coal mine roof surfaces from the cretaceous of utah [abs.], in gillette, d.d., editor, first international symposium on dinosaur tracks and traces: albuquerque, new mexicon museum of natural history abstracts and programs, p. 22. parker, l.r., and rowley, r.l., 1989, dinosaur footprints from a coal mines in east-central utah, in gillette, d.d., and lockley, m.g., editors, dinosaur tracks and traces: new york, cambridge university press, p. 361–366. parrish, j.t., and falcon-lang, h.j., 2007, coniferous trees associated with interdune deposits in the jurassic navajo sandstone formation, utah, usa: paleontology, v. 50, no. 4, p. 829–843. peabody, f.w., 1948, reptile and amphibian trackways from the lower triassic moenkopi formation of arizona and utah: university of california department of geological sciences bulletin 27, p. 295–468. peterson, w., 1924, dinosaur tracks in the roofs of coal mines: natural history, v. 24, p. 388–391. riese, d.j., hasiotis, s.t., and odier, g., 2011, burrows excavated by mammals or therapsids in the navajo sandstone and their association with other organisms represented by trace fossils in a wet desert ecosystem: journal of sedimentary research, v. 81, p. 299–325. robison, s.f., 1991, bird and frog tracks from the late cretaceous blackhawk formation in east-central utah, in chidsey, t.c., jr., editor, geology of east-central utah: utah geological association publication 19, p. 325–334. rowley, r., and parker, l., 1986, demonstration of dinosaur footprints from coal mine roof surfaces from the cretaceous of utah [abs.], in gillette, d., editor, first international symposium on dinosaur tracks and traces—abstracts with programs: albuquerque, new mexico museum of natural history, p. 24. rowley, r., and parker, l. 1989, dinosaur footprints from a coal mine in east-central utah, in gillette, d., and lockley, m.g., editors, dinosaur tracks and traces: new york, cambridge university press, p. 353–359. schaeffer, b., 1967, late triassic fishes from the western united states: bulletin of the american museum of natural history, v. 135, no. 6, p. 285–342. sertich, j.j.w., and loewen, m.a., 2010, a new basal sauropodomorph dinosaur from the lower jurassic navajo sandstone of southern utah: plos one, v. 5, no. 3: e9789, doi:10.1371/journal. pone.0009789. smith, r.m.h., 1987, helical burrow casts of therapsid origin from the beaufort group (permian) of south africa: palaeogeography, palaeoclimatology, palaeoecology, v. 60, p. 155–170. strevell, c., 1932, dinosauropodes: salt lake city, desert news. strevell, c., 1940, story of the strevell museum: salt lake city public schools, 96 p. sues, h-d., clark, j.m., and jenkins, f.a., jr., 1994, a review of the early jurassic tetrapods from the glen canyon group of the american southwest, in fraser, n.c., and sues, h-d., editors, in the shadow of the dinosaurs—early mesozoic tetrapods: new york, cambridge university press, p. 284–294. van wagoner, j.c., nummedal, d., jones c.r., taylor, d.r., jennette, d.c., and riley, g.w., 1991, sequence stratigraphy applications to shelf sandstone reservoirs—outcrop to subsurface examples: american association of petroleum geologists field conference, sept 21–31, 1991, variously paginated. wilson, w., 1969, footprints in the sands of time: gems and minerals, june 1969, 25 p. winkler, d.a., jacobs, l.l., congleton, j.d., and downs, w.r., 1991, life in a sand sea—biota from jurassic interdunes: geology, v. 19, p. 889–892. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. the whole plant of araucaria delevoryasii and agathoxylon hoodii— giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa carole t. gee, aowei xie, and mariah m. howell geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover photograph of the first tree trunk discovered in the howe-stephens quarry in 1998 with hans-jakob siber for scale. image modified from ayer (2000). inset consists of photomicrographs of agathoxylon hoodii. all images were taken of radial and tangential sections of thin sections of specimen number sma 0424-021. see figure 7 for detailed descriptions. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, 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williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 293 abstract reconstructing whole plants based on their detached parts in an assemblage is a major goal in modern paleobotany. plant parts pertaining to an ancient species of conifer, for example, can be found as separate organ fossils such as seed cones, pollen cones, twigs with leaves, pieces of wood, and tree trunks. although fossil conifer remains are widely known from the upper jurassic morrison formation in the western usa, until now, conifer cone compressions and silicified wood have not yet been linked with one another to form a whole plant. here we identify silicified wood as agathoxylon hoodii, based on a detailed description of its anatomy, from a dinosaur bonebed in the howe-stephens quarry in north-central wyoming. in addition to numerous pieces of wood, the fossil flora in the bonebed consists of hundreds of coalified compressions of conifer seed and pollen cones, detached seed scales, abscised seeds, and branches with brachyphyllum-type leaves previously assigned to a single species, araucaria delevoryasii. two giant coalified tree trunks in the quarry also pertain to this upper jurassic conifer, and their preserved diameters reconstruct trees with minimum heights of 74 to 78 m and 64 to 65 m, respectively. the gross morphology of the trunks, especially their taper, is also described and found to be similar to that of living araucaria trees. collectively, the separate fossil plant organs are recognized here as a whole plant called the araucaria delevoryasii tree. this species of tree likely grew directly on the riverbanks of a meandering river. the paleobiogeography of agathoxylon hoodii wood at four localities in the central morrison formation documents the widest extent of all morrison wood species thus far. the compression fossils and silicified wood from the howe-stephens quarry in north-central wyoming, as well as silicified logs in utah, represent an araucaria tree that helped to form the old-growth upper jurassic conifer forests in the central morrison formation. the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa carole t. gee1, 2, aowei xie1,3, and mariah m. howell1 1bonn institute of organismic biology, division of paleontology, university of bonn, 53115 bonn, germany; cgee@uni-bonn.de, mariah. howell@uni-bonn.de 2utah field house of natural history state park museum, vernal, utah 84078 usa 3current address: senckenberg forschungsinstitut und naturmuseum frankfurt, 60325 frankfurt am main, germany; aowei.xie@ senckenberg.de citation for this article. gee, c.t., xie, a., and howell, m.m., 2025, the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa: geology of the intermountain west, v. 12, p. 293–314, https://doi.org/10.31711/giw.v12.pp293-314. 294 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 introduction a major goal in modern paleobotany is reconstructing whole plants based on their separate parts found in an assemblage. in regard to a mesozoic conifer, for example, this would mean the linking of detached reproductive organs, such as seed and pollen cones, with nonreproductive parts, such as the trunk, wood, branches, and leaves, which are commonly not found in organic connection to one another. however, they can be found in abundance co-occurring in close physical association with one another in a deposit. especially if the plant organs are morphologically and anatomically consistent with one another, as well as found in a fossil flora with few or no other species, they are likely to represent the various parts of a single species. in the upper jurassic flora of the howe-stephens quarry in north-central wyoming, hundreds of fossils consisting of conifer seed cones, detached seed scales, isolated seeds, pollen cones, and branches with brachyphyllum-type leaves (gee and tidwell, 2010) have been found intermixed in intimate association with numerous pieces of wood in a productive dinosaur bonebed (ayer, 2000; gee and tidwell, 2010), with little evidence of other fossil plant species. the reproductive material, leaves, and branches pertain to a single species of araucarian conifer, araucaria delevoryasii gee (gee and tidwell, 2010), but until now, the abundant pieces of silicified wood and two giant tree trunks in the quarry had remained undescribed. in recent years, renewed interest in the paleobotany of the upper jurassic morrison formation has encouraged a number of studies on fossil wood and logs (gee, 2023). new occurrences of silicified wood have been correctly described and photographically documented from the state of utah, i.e., agathoxylon hoodii tidwell et medlyn (gee et al., 2019) and xenoxylon utahense xie et gee (xie et al., 2021), and montana1, namely xenoxylon meisteri palibin et jarmolendo (richmond et al., 2019) and circoporoxylon bighornense (hoff, 2022; hoff et al., 2025). the species of xenoxylon morrisonense medlyn et tidwell (1975) has recently been transferred to a newly established genus, morrisonoxylon philippe, richmond, lupia et mclemore (2023), as the species m. morrisonense. the four wood studies published in the last six years supplement the taxonomic list of species already known of the morrison paleoxyloflora: cupressinoxylon jurassicum lutz (1930), mesembrioxylon carterii tidwell, britt et ash (1998), m. obscurum (knowlton) medlyn et tidwell (2002), protocupressionoxylon medlynii tidwell, britt et ash (1998), protopiceoxylon resiniferous medlyn et tidwell (1979), and xenoxylon moorei tidwell, britt et ash (1998)2. silicified logs at several localities in northeastern utah have been studied in regard to their taxonomic determination, wood anatomy, and estimated ancient living-tree height, such as with the logs of agathoxylon hoodii and xenoxylon utahense (gee et al., 2019; xie et al., 2021), as well as in regard to ecological interactions of upper jurassic insects and fungi found within the fossil woods (gee et al., 2022; xie et al., 2023). the petrified forest log assemblage in the morrison formation near the town of escalante in south-central utah (morgan et al., 2024) is also currently under intense study (gee et al., 2023). it should be noted that in general, intact fossil logs offer more biological information than isolated chunks of silicified wood, because ancient tree heights and trunk taper can be calculated using log diameter, which can lead to a deeper understanding of ancient tree sizes, appearance, and the structure of the forest canopy. here we describe the assemblage of silicified wood and coalified tree trunks that occurs in a dinosaur bonebed in the howe-stephens quarry in the morrison formation of north-central wyoming. the wood in this flora is identified here as agathoxylon hoodii of the conifer family araucariaceae, and the two giant fossil trunks cooccurring in the assemblage offer data on ancient tree height and trunk taper. the association of agathoxylon 1other occurrences of fossil wood from montana have been reported in meeting abstracts, but because these reports are not illustrated and/or peer-reviewed, these taxa are not included here. 2it has been suggested that xenoxylon moorei be excluded from the genus xenoxylon based on anatomy (richmond et al., 2019), but a new taxonomic determination has not yet been made. 295 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 hoodii with the seed cones, seed cone scales, seeds, pollen cones, and leaved twigs of araucaria delevoryasii allows for the first whole-plant reconstruction of a conifer species in the morrison consisting of the tree trunk, wood, and reproductive material. it also provides evidence for a widespread distribution of the araucaria delevoryasii tree species some 150 million years ago across what is today wyoming and utah. geological setting the fossil wood specimens and log data under study here were collected from the howe-stephens quarry on howe ranch located near the towns of greybull and shell in the big horn basin in north-central wyoming, usa (figure 1). the howe-stephens quarry is a prolific fossiliferous site that has produced numerous skeletons and isolated bones of dinosaurs (e.g., ayer, 2000; wiersma-weyand et al., 2021) as well as fossil plant remains (gee and tidwell, 2010) that were excavated by hans-jakob siber and his field team from the sauriermuseum aathal (aathal dinosaur museum), in aathal (near zurich), switzerland. excavations in this particular quarry were initiated in 1992 and continued annually until 2002. during this decade, the siber field team collected numerous pieces of silicified wood from this quarry. in the howe-stephens quarry, the dinosaur and plant fossils occur in the morrison formation, a geological unit that is widely distributed in the western united states (foster, 2020, and references therein). on howe ranch, the morrison crops out in a southwest–northeast direction, and consists primarily of sandstone and mudstone with rare layers of limestone having a thickness of ca. 55 m. the fossiliferous layer in the quarry has not been attributed to a specific stratigraphic member by other paleontologists working on this deposit (e.g., michelis, 2004; tschopp and mateus, 2017) because the morrison is considered undifferentiated in northern wyoming (turner and peterson, 1999; foster, 2020). the matrix of the bonebed consists of a light brown, very fine grained, cross-bedded sandstone. carbonaceous plant remains are usually concentrated in lenses in the cross-bedded sandstone, ranging from a few centimeters to several decimeters in thickness (ayer, 2000). the numerous pieces of silicified wood from the howe-stephens quarry were found in close association with the dinosaur bones and skeletons, as well as alongside coalified compressions, which represent the conifer seed cones, detached seed cone scales and seeds, pollen cones, and twigs with leaves of araucaria delevoryasii (gee and tidwell, 2010). unlike the faunal remains, the exact provenance of the specimens of silicified wood and plant compressions gathered from the quarry was not noted, although the quarry map shows the exact location of two fossil tree trunks unearthed in the bonebed (figure 2). geological mapping of the howe-stephens quarry by jacques ayer (university of neuchâtel, switzerland) produced a schematic cross section of the bonebed (figure 3), which shows diagrammatically the co-occurrence of dinosaur bones and fossil plants in the same lens of brownish sandstone. this sandstone lens was interpreted as channel-fill deposits of a point bar sequence in a meandering river depositional system (jacques ayer, university of neuchâtel, switzerland, written communication to ctg, 2006). materials and methods taxonomy and wood anatomy twenty-three specimens of silicified wood, grouped under the specimen number sma 0424, were selected for study from the collections of the sauriermuseum aathal. to track the wood specimens through the thin section-making process at the university of bonn, germany, they were each given an additional specimen number, from 001 to 023. paleoxyological study was initiated by ctg in 2005, concurrent with the study of the compression flora. however, the study of the fossil wood was soon set aside and later offered to two graduate students who, independently of one another, prepared some thin sections but were not able to continue successfully with the next stages of research. conception and design of the fossil wood project (ctg), selection of wood specimens for study on multiple trips to the sau296 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 riermuseum aathal paleobotanical collection (ctg), identification of the wood to the genus and species level (ctg, aowei xie [ax]), description and interpretation of wood (ax, ctg) and cuticle (ctg), photography of the wood (ax) and cuticle (ctg), calculation and interpretation of trunk taper (ctg, ax, mariah m. howell [mmh]), cuticle preparation (mmh), preparation of line drawings (ctg, ax), writing of the manuscript (ctg, ax, mmh), and submission were performed by this core team. for taxonomic identification and anatomical work, standard petrographic thin sections were made using conventional methods. all specimens of silicified wood were cut in the three planes of section necessary for study, namely, transversely, radially, and tangentially. the thin sections were investigated with a leica dm2500 compound photomicroscope. images and measurements were taken with software imageaccess easylab 7 integrated with the photomicroscope. in the wood description, we follow the anatomical terms defined by the iawa committee (iawa committee, 2004), with additional reference to philippe and bamford (2008) and boura et al. (2021). remnants and thin sections of the fossil wood specfigure 1. locality map of the howe-stephens quarry on howe ranch (star), located between greybull and shell in the bighorn basin in north-central wyoming, usa. modified from ayer (2000). inset: the location of the state of wyoming (gray) within the contiguous usa. 297 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 figure 2. detailed, 21 x 30 m quarry map of the howe-stephens quarry, showing dinosaur skeletons, bones, and two giant coalified trunks (labeled here as tree a and tree b), plotted to scale by esther premru, sauriermuseum aathal. colors represent the bones of 14 individual dinosaurs, following color scheme of ayer (2000) and wiersma-weyand et al. (2021). dashed lines show associated bones grouped together on the same horizon. 298 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 imens are stored at the sauriermuseum aathal, grouped under specimen number sma 0424. gross morphology of tree trunks two large, coalified tree trunks were found in the howe-stephens quarry bonebed through the original excavation activity by the siber team. the fossil tree to the south, designated here as tree a, was discovered in 1998 (figure 4), and the fossil tree to the north, called here tree b, was uncovered in 2002 (esther premru, sauriermuseum aathal, verbal communication to ctg, 2004). description of the gross morphology of these tree trunks here is based on the drawing of the trunks in the quarry map made by e. premru during the multi-year excavation of the bonebed by the siber team. given the division of the quarry map into 1 x 0.5 m squares as well as the precise and detailed illustration of the skeletal remains, it is assumed that the fossil trunks, designated here as trees a and b, were also drawn in a similarly accurate manner. estimation of tree height the two fossil tree trunks sketched on the quarry map offered good approximations for trunk diameter. while exact measurements of the tree trunks’ girth were not made during the excavation process, we extrapolated from the quarry map approximate diameter values, such as diameter at breast height (dbh), a standard forestry measurement defined as 130 cm from the tree trunk–soil interface, for the purpose of estimating the height of the ancient trees. based on the height–diameter relationship of living trees of araucaria spp., three height–diameter growth models have been recognized as the most appropriate models for reconstructing the minimum heights of the ancient araucarian trees (xie et al., 2024). they are the median modified mosbrugger model (equation 1), the median 2ppower model (equation 2), and the median curtis model (equation 3), respectively, and can be given as: figure 3. schematic cross section through the howe-stephens quarry interpreted as containing the channel-fill facies of a meandering river. the dinosaur bones and fossil plants (coalified tree trunks, silicified wood, cone and twig compressions and impressions) occur jumbled in the same bonebed. redrawn and modified from a stratigraphic section mapped by jacques ayer (university of neuchâtel, switzerland). 299 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 equation 1 h = 57.22 × d0.67 equation 2 h = 58.03 × d0.72 equation 3 h = 101.78 × d / (1+d)0.80 where: h = estimated tree height in m, and d = maximum preserved diameter of the fossil log in m. we apply all three equations to the two fossil tree trunks in the howe-stephens quarry to obtain a minimum estimated height of the trees when living. calculation of trunk taper in addition to ancient tree height, trunk taper was also reconstructed based on the drawing of the two fossil trunks on the quarry map. in living trees, there is a relationship between diameter and taper that characterize individual taxa (larsen, 2017). any one trunk will exhibit at least two rates of taper: the first rate of taper is trunk diameter from the soil–trunk interface to dbh, and the second rate is from dbh to the diameter at base of the tree crown. the “simple taper” equation developed by larsen (2017) was based on the stem analysis of 11,610 angiosperm and conifer trees encompassing 34 species, including 14 species of pinus, taxodium, and tsuga. the simple taper equation of larsen (2017) is given here as equation 4: equation 4 dh = dbh + p × (h bh) where: dh = trunk diameter d at height h of the tree, dbh = trunk diameter at breast height, p = tree taper rate, h = a second height of the tree serving as starting point or an endpoint for taper, and bh = breast height of the tree. figure 4. photograph of the first tree trunk discovered in the howe-stephens quarry in 1998, called here tree a, with hans-jakob siber for scale. image modified from ayer (2000). 300 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 mathematically, this equation can be rearranged to determine trunk taper (equation 5) and expressed as: equation 5 p = (dh dbh) / (h bh) equation 5 was then used to determine three rates of taper in the fossil trees: in the stump from trunk base to breast height, in the mid trunk from breast height to 4-m height mark, and in the upper trunk from the 4-m height mark to the top of the tree. calculating the taper rates for the fossil trees was based on eight trunk parameters observed in the howe-stephens quarry map (figure 5). these measurements included: stump diameter (dark blue), breast height (130 cm, light green), dbh (light blue), stem length between dbh and 4-m height mark (orange), diameter at 4-m height mark (green), stem length between 4-m height mark and top of tree (yellow), diameter at top of trunk (purple), and stem length of entire trunk (white). for comparison, size data from five living trees of araucaria araucana were measured at the botanical garden of the university of bonn in october 2022, using the same trunk parameters to calculate their stump and mid-trunk stem taper rates. in these cases, measurements were taken of their trunk circumference with a flexible tape measure and later mathematically converted to diameter data. leaf cuticle cuticle was extracted from brachyphyllum-type leaves on fossil twigs collected from the same bonebed and considered as pertaining to araucaria delevoryasii (gee and tidwell, 2010). samples from five specimens were prepared using either standard cuticle preparation with schulze’s reagent (kerp, 1990) or with gentle bleaching with sodium hypochlorite (howell et al., 2022). the prepared cuticle samples were mounted on glass slides with euparal mounting medium and studied using light microscopy, or examined using scanning electron microscopy. results systematic paleobotany of silicified wood division coniferophyta class coniferopsida order coniferales family araucariaceae genus agathoxylon hartig, 1848 sensu philippe, 1995 agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis et gray, 2019; figures 6 and 7 figure 5. trunk parameters of trees a and b measured using the howe-stephens quarry map to determine the stump taper rate and stem taper rates. color key: dark blue = stump diameter, light green = breast height (130 cm), light blue = dbh (diameter at breast height), orange = stem length between dbh and 4-m height mark, green = diameter at 4-m height mark, yellow = stem length between 4-m height mark and top of tree, purple = diameter at top of trunk, white = stem length of entire trunk. 301 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 synonymy araucarioxylon hoodii tidwell et medlyn – tidwell and medlyn (1993), conifer wood from the upper jurassic of utah, usa—part ii: araucarioxylon hoodii sp. nov.: the palaeobotanist, v. 42, p. 70–77; plate 1, figures 1 to 6; plate 2, figures 1 to 6; text-figure 2. fossil logs in rainbow draw – sprinkel et al. (2019), stratigraphic setting of the fossil log sites in the morrison formation (upper jurassic) near dinosaur national monument, uintah county, utah, usa: geology of the intermountain west, v. 6, p. 61–76; figures 10, 11a, and 12. agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis et gray – gee et al. (2019), silicified logs of agathoxylon hoodii (tidwell et medlyn) comb. nov. from rainbow draw, near dinosaur national monument, uintah county, utah, usa, and their implications for araucariaceous conifer forests in the upper jurassic morrison formation: geology of the intermountain west, v. 6, p. 77–92; figures 5 and 6. note: the fossil log in miners draw is excluded here in this synonymy (see instead xenoxylon utahense described by xie et al., 2021). type species: araucarioxylon hoodii tidwell et medlyn, 1993, which was later recognized as a new combination, agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis et gray, 2019. description of wood anatomy: only secondary xylem is described here, because bark, pith, and primary xylem are lacking. in transverse section, true growth rings absent (figures 6a through 6c); irregular, discontinuous concentric bands of tracheids with narrower lumina locally apparent (figures 6b and 6c), ranging from one to four cells thick and developing asynchronously during the growth of the tree. tracheids subround to elliptical to polygonal in transverse section (figures 6b though 6f); lumen ranging from 25 to 66 µm in tangential diameter, those of normal-size cells about 46 µm (figure 6e). axial parenchyma and resin canals absent. in radial section, tracheids on average 61 μm wide (52 to 75 μm). radial tracheid pits usually uniseriate, but also locally biseriate. when uniseriate, arrangement of tracheary pits contiguous and compressed (figures 6g and 6h), occasionally distant (figure 6h); when biseriate, alternate (figures 7a and 7b, arrows), occasionally opposite (figure 7c, arrow). bordered pits generally oblate in outline. crassulae not observed. resinous remains coalesced along the periphery in ray cells and the cell corners (figure 7d, arrow). rays consisting of parenchymatous cells with thin, smooth horizontal and end walls (figure 7d). cross-field pitting araucarioid type sensu iawa committee (2004). each cross-field bearing numerous pits, 7 through 16 cupressoid pits with a circular or oval outline, contiguous, arranged in 3 through 5 alternate vertical rows (figures 7e and 7f). in tangential section, rays are homogenous, parenchymatous, uniseriate (figures 7g through 7j). the rays are variable in height, ranging from very low to high, 2 to 25 cells high, mostly 3 to 8 cells tall. bordered pits on the tangential tracheary walls circular, 15.8 μm in diameter, usually uniseriate distant, but also locally contiguous (figures 7i, arrow, and 7j). resin plugs also evident in tracheids of axial system (figure 7j, arrow). locality: howe-stephens quarry, howe ranch, near greybull, wyoming, usa. specimens studied: sma 0424-001 to 023. horizon and age: morrison formation undifferentiated, upper jurassic (kimmeridgian). this site is considered wy-62 in dinosaur zone 2 of turner and peterson (1999) and systems tract c5 of maidment and muxworthy (2019) and maidment (2024). repository: sauriermuseum aathal, switzerland. taxonomic assignment of wood all pieces of silicified wood from the howe-stephens quarry described here can be assigned to the genus agathoxylon based on a shared suite of distinct characters: araucarian radial tracheid pitting and araucarioid cross302 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 figure 6 caption is on the following page 303 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 field pitting; many radial tracheid pits uniseriate, contiguous, and compressed, but also uniseriate contiguous to distant, or biseriate alternate to opposite; cross-fields bearing 7 to 16 densely arranged cupressoid pits; resin plugs or resin remnants in the ray cells or in the axial parenchyma cells. in particular, two specimens of wood (sma 0424021 and 022) are well-preserved enough to determine the wood to the species agathoxylon hoodii and form the basis of the anatomical description of the wood here. the species-specific characters include the dominance of axial tracheids (figures 6a through 6f), the absence of axial parenchyma (figures 6a through 6f), and the lack of resin canals (figures 6a through 6f); contiguous to distantly arranged, uniseriate circular bordered pits on the radial walls of the tracheids (figures 6g, 6h, and 7a through 7c), the alternate (or occasionally opposite) arrangement of the circular bordered pits in the tracheids, when biseriate (figures 7a through 7c, arrows); the smooth, unpitted sidewalls and endwalls of the ray cells (figure 7d); and the numerous, small, crowded cupressoid pits in the cross-fields (figures 7e and 7f); the presence of resinous remains and resin plugs, particularly in the radial system (figures 7d, arrow, 7g, 7h, and 7j, arrow), but also in the axial system (figure 6j, arrow). what appears in cross section to superficially resemble growth rings are not consistent across the trunk (figures 6b and 6c), and thus represent irregular slow-downs in growth, not true growth rings. all of these features are found in agathoxylon hoodii wood from mt. ellen in southeastern utah (tidwell and medlyn, 1993) and from rainbow draw in northeastern utah (gee et al., 2019), and pinpoint the assignment of the howe-stephens wood species to this species that has only been described up to now from the morrison formation of utah. remarks although numerous pieces of fossil wood were excavated and collected from the howe-stephens quarry, 23 specimens were selected for thin sectioning and study. of these, only seven wood specimens yielded anatomical characters sufficient for unequivocal identification, due to the generally poor preservation of the fossil wood flora from the howe-stephens quarry. the two specimens (sma 4024-021 and 022) that show moderately good preservation also show tangential tracheid pits that are usually uniseriate distant, but occasionally contiguous. because this character was not mentioned in the original description of araucarioxylon hoodii by tidwell and medlyn (1993), nor in the description of the new combination of agathoxylon hoodii by gee et al. (2019), we have added this minor detail here. gross morphology of tree trunks the gross morphology of both coalified trees found in the howe-stephens quarry is similar (figures 2 and 5). both trees consist of long trunks with a very slight and uniform taper in the upper trunks for most of their respective lengths. each tree has a sudden root flare at their trunk base. however, the root flare of tree a is visually much greater than that of tree b (figure 5). there is no obvious evidence of branching, nor large branch scars, along either trunk. in tree a, ca. 7.24 m of the original length is preserved, whereas in tree b, ca. 8.22 m of its length is still evident (table 1). for each fossil trunk, the dbh, i.e., the diameter of the trunk 1.3 m above the base of each fossil tree, is estimated for tree a as 152 cm and for tree b as 117 cm (table 1). figure 6 is on the previous page. agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis, et gray from the upper jurassic morrison formation at the howe-stephens quarry; all photographs were taken of transverse and radial sections of thin sections of specimen number sma 0424-021. (a) transverse section showing growth rings indistinct, true growth rings absent. (b) transverse section showing irregular, discontinuous concentric bands of tracheids with narrower lumina apparent. (c) close-up of b, transverse section showing details of tracheids with narrower lumina. (d) transverse section showing ray cells. (e) transverse section showing details of tracheids, subround to elliptical to polygonal. (f) transverse section showing details of decayed tracheids. (g) radial section showing tracheids with uniseriate, contiguous, and compressed bordered pits. (h) close-up of g, radial section showing details of radial tracheid pits. modified from xie (2022). 304 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 figure 7 caption is on the following page 305 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 reconstruction of ancient tree heights applying the median modified mosbrugger model, the median 2ppower model, and the median curtis model, which were given earlier as equations 1, 2, and 3, respectively, results in the reconstruction of a minimum height of the fossil trees at howe-stephens quarry (table 2). for tree a, the minimum height of the living tree would have ranged between 73.9 and 78.5 m, averaging 76.0 m. for tree b, the minimum height of the living tree would have varied between 63.6 and 65.0 m, averaging 64.2 m. stump and stem taper rates of fossil and living trees the measurements given in table 3 were used to calculate stump taper rate and stem taper rates of the fossil trees in the howe-stephens quarry, as well as the living araucaria trees measured in bonn university botanic garden. these data yielded a stump taper rate (pb), a stem taper rate for the mid trunk (pmid trunk), and a stem taper rate (pupper trunk) for each of the eight trees studied (table 3). the results reveal that fossil tree a has a stump taper rate (pb = -0.28) and a mid-trunk stem taper rate (pmid trunk = -0.23) that is much greater than those of the second fossil tree (tree b), which has a stump taper rate (pb = -0.08) and a mid-trunk stem taper rate (pmid trunk = -0.03). interestingly, the stump and the two stem taper rates of tree b are much closer to those of the living araucaria araucana trees. among living a. araucana trees, stump taper ranges from -0.03 to -0.18, with an average of -0.09. in the upper trunk of the two fossil trees, stem taper rate is relatively low (tree a: pupper trunk = -0.01; tree b: pupper trunk = -0.05). these values are comparable to the variation in stem taper rates found in living a. araucana trees, which range from -0.02 to -0.05, with an average of -0.03. fossil leaf cuticle the leaf cuticle is moderately well-preserved (figure 8a). stomata are arranged in longitudinal files along the length of the leaf, commonly represented by holes in the leaf tissue where the guard cells are not found preserved (figure 8b). the paired guard cells appear lightly sunken. the ring of subsidiary cells adjacent to the guard cells is monocyclic and consists of wide cells (figure 8c); the number of subsidiary cells in each ring was not observable. the oval area occupied by one set of guard cells and the stoma measures roughly between 16 to 19 µm, whereas the stomatal complex has a diameter of approximately 37 µm. on the basis of the long axis of the stomatal apparatuses aligning with longitudinal axis of the leaf, it appears that they are oriented parallel to leaf axis (figure 8b). in the non-stomatal zones, epidermal cells are elongate and rectangular, with their long axis parallel to leaf long axis (figure 8b). average epidermal cell measures roughly 16 x 11 µm. anticlinal walls and periclinal are straight, not sinuous. there are about 10 files of epidermal cells between the stomatal zones. no papillae, protrusions, or trichomes were observed, neither on the guard cells nor on the epidermal cells. figure 7 is on the previous page. agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis, et gray from the morrison formation at the howe-stephens quarry; all photographs were taken of radial and tangential sections of thin sections of specimen number sma 0424-021. (a and b) radial section showing tracheids with biseriate alternate bordered pits (arrow). (c) radial section showing tracheids with biseriate opposite bordered pits (arrow). (d) radial section showing resinous remains coalesced along the periphery in ray cells and the cell corners (arrow). (e and f) radial section showing details of araucarioid cross-field pits in which each cross-field bears 7 to 16 cupressoid pits. (g) tangential section showing uniseriate rays. (h) close-up of g, tangential section showing details of uniseriate rays. (i) tangential section showing uniseriate tangential tracheid pitting (arrow). (j) tangential section showing resin plugs (arrow). modified from xie (2022). 306 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 discussion comparison to other morrison woods all silicified woods from the howe-stephens quarry studied here can be assigned to agathoxylon hoodii, based on a shared suite of characters. as described in detail above, these characters include araucarian radial tracheid pitting and araucarioid cross-field pitting; most radial tracheid pits uniseriate, contiguous, and compressed, but also uniseriate contiguous to distant, or biseriate alternate to opposite; cross-fields each bearing 7 to 16 densely arranged cupressoid pits. previously, this species had only been described from utah (tidwell and medlyn, 1993; gee et al., 2019). prior to our study, only two species of fossil araucariaceous woods from the morrison formation had been reported from wyoming, namely, araucarioxylon? obscurum knowlton from the freezeout hills, south-central wyoming (knowlton, 1900) and araucarioxylon wyomingense andrews et pannell from the gros ventre canyon in western wyoming (andrews and pannell, 1942). when the freezeout hills wood was described in 1900, knowlton was uncertain of its generic position and tentatively assigned the wood to araucarioxylon, because it had obscure growth rings and a relatively low ray height (knowlton, 1900; medlyn and tidwell, 2002). although the freezeout hills wood was transferred to mesembrioxylon obscurum on the basis of its podocarpaceaous anatomy (medlyn and tidwell, 2002), the genus mesembrioxylon seward (1919) is considered invalidly published because this genus name was proposed to replace gothan’s two valid genera podocarpoxylon and phyllocladoxylon (see arguments made by bamford and philippe, 2001; philippe and bamford, 2008). the freezeout hills wood differs from the howe-stephens quarry wood by having mostly uniseriate, distant radial tracheid pits and one to three thin-bordered podocarpaceous pits per cross-field (medlyn and tidwell, 2002), whereas our wood show mostly uniseriate, contiguous, compressed radial tracheid pits, and araucarioid cross-field pitting. the second araucariaceous species from wyoming, araucarioxylon wyomingense, differs from the howe-stephens quarry wood in its very low rays (one to three cells high), locally strongly flattened radial tracheid pits, and a lack of tangential tracheid pits (andrews and pannell, 1942). our wood has mostly uniseriate, distant tangential tracheid pits, higher rays (one to nine cells high), and a lack of strongly flattened radial tracheid pits. beyond wyoming, with the exception of agathoxylon hoodii in utah, the howe-stephens quarry wood differs from all other upper jurassic wood taxa in the morrison formation. major differences are most evident in the cross-field pitting between the ray cells and axial tracheids, as well as in the abundance of resin in a. hoodii. this includes fossil woods previously described from utah, such as mesembrioxylon carterii (tidwell et al., 1998), mesembrioxylon obscurum (medlyn and tidwell, 2002), protocupressinoxylon medlynii (tidwell et al., 1998), protopiceoxylon resiniferous (medlyn and tidwell, 1979), xenoxylon utahense (xie et al., 2021), and  morrisonoxylon morrisonense  (philippe et al., 2023); from montana, such as xenoxylon meisteri table 1. preserved length and diameter at breast height (dbh) for trees a and b, estimated from the howe-stephens quarry map (figure 5). tree preserved length (m) preserved diameter at dbh (cm) a 7.24 152 b 8.22 117 table 2. minimum estimated heights for the two coalified tree trunks at the howe-stephens quarry, based on their respective dbh and calculated using the three most appropriate growth models for ancient araucarian trees, as tested by xie et al. (2024). tree median modified mosbrugger model (m) median power model (m) median curtis model (m) averaged minimum height of living tree (m) a 75.8 78.5 73.9 76 b 63.6 65 64.1 64.2 307 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 (richmond et al., 2019) and circoporoxylon bighornense (hoff, 2022; hoff et al., 2025); and from south dakota, cupressinoxylon jurassicum (lutz, 1930). other wood genera (richmond, 2023) reported as occurring in montana, such as cupressinoxylon, piceoxylon, protocedroxylon, and in western oklahoma, such as xenoxylon, cupressionoxylon, and agathoxylon, are not accepted here, but are still pending acceptance, as they have not yet been identified, fully described, and adequately figured in peer-reviewed publications. there is only one minor difference between the agathoxylon hoodii specimens from the 13 logs in rainbow draw and the 23 wood specimens of a. hoodii from the howe-stephens quarry. the rainbow draw wood appears to contain a greater number of resin plugs or resinous remains, especially in the ray cells. differences in resin abundance were also already noted by gee et al. (2019) when comparing the rainbow draw wood flora with the holotype specimen from mt. ellen (cf. tidwell and medlyn, 1993). however, because a scantiness or absence of organic deposits such as resin plugs is not diagnostic for systematic identification (iawa committee, 2004), all fossil wood specimens from the howe-stephens quarry should be considered as pertaining to a. hoodii. paleobiogeographic extent of agathoxylon hoodii the identification of agathoxylon hoodii wood in the howe-stephens quarry flora expands the paleobiogeographic range of the species to north-central wyoming (figure 9, yellow star). this new occurrence is ca. table 3. trunk data collected from the upper jurassic logs in the howe-stephens quarry and living trees of araucaria araucana cultivated at the bonn university botanic garden and calculated stump taper rate (pb), mid-trunk stem taper rate (pmid trunk), and upper-trunk stem taper rate (pupper trunk). tree location, accession number stump diameter (cm) height from trunk base to breast height (cm) diameter at breast height, dbh (cm) stem length from dbh to 400 (cm), hmid trunk diameter at 4-m height mark (cm) stem length from 4-m height mark to top of tree (cm), hupper trunk diameter at top of tree (cm) maximum preserved length (fossil tree) or total estimated height (living tree) (m) stump taper rate, pb stem taper rate from dbh to 3 or 4 m, pmid trunk stem taper from 4 m to top of tree, pupper trunk tree a howe-stephens quarry 189 130 152 270 89 324 85 7.24 -0.28 -0.23 -0.01 tree b howe-stephens quarry 128 130 117 270 109 422 80 8.22 -0.08 -0.03 -0.05 araucaria araucana magnolia garden, 3980-001979/2 43 130 34 270 24 not measured not measured 14.6 -0.07 -0.04 incalculable araucaria araucana magnolia garden, 09735 56 130 32.5 270 21 not measured not measured 12 -0.18 -0.04 incalculable araucaria araucana magnolia garden, 07163 35.7 130 31.2 270 25 not measured not measured 9.2 -0.03 -0.02 incalculable araucaria araucana mesozoic forest, 11995-91920 60.5 130 48.4 270 41 not measured not measured 17.1 -0.09 -0.03 incalculable araucaria araucana nees institute parking lot, shorter tree 30.2 130 19.4 270 10.5 (at base of crown) not measured not measured 5.05 -0.08 -0.05 incalculable araucaria araucana (tree since cut down) nees institute parking lot, taller tree 38.2 130 23.9 270 19 (at base of crown) not measured not measured 8 -0.11 -0.02 incalculable 308 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 1000 km northeast from where it was last described at rainbow draw in northeastern utah (figure 9, orange star) and ca. 1600 km away from its type locality on mt. ellen (figure 9, green star). recently, another well-preserved specimen of agathoxylon hoodii has been identified (gee, unpublished data) from a new fossil log and dinosaur locality called the tal site log assemblage (figure 9, blue star) in southern utah (john r. foster, utah field house of natural history state park museum, written communication to ctg, 2024). this makes for a current total of four occurrences in the morrison formation, from what is today north-central wyoming to the north, to southeastern utah to the south. among all fossil wood species described from the morrison formation so far, a. hoodii appears to have the widest paleobiogeographic extent known to date and thus may have comprised a sizeable part of the conifer forests in the central morrison formation during the late jurassic. hence, it would not be surprising if the fossil wood species agathoxylon hoodii or the fossil seed cones araucaria delevoryasii were to show up in deposits of the morrison in western colorado sometime in the future. figure 8. in situ cuticle from a twig bearing brachyphyllum-type leaves from the howe-stephens quarry. (a) cuticle from near the leaf apex, showing the general pattern of longitudinal files of stomata. (b) close-up of a, showing the arrangement of stomata in longitudinal files. the actual stomatal apparatuses are not preserved, but are represented by holes in the tissue. note the rectangular epidermal cells between the lines of stomata. (c) one stomatal apparatus complete with a central stoma, a pair of guard cells, and a single ring of subsidiary cells. 309 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 the whole plant of agathoxylon hoodii/araucaria delevoryasii virtually all specimens in the coalified compression flora from the howe-stephens quarry were previously recognized as the associated plant organs of a wholeplant araucaria (gee and tidwell, 2010). these organs consisted of the mature and immature seed and pollen cones, detached seed scales, isolated seeds, as well as branches and twigs with brachyphyllum-type scale leaves. whereas hundreds of individual compression specimens were excavated from the howe-stephens quarry, the biodiversity of the compression flora is extremely low, because nearly all of these specimens represent just a single species, araucaria delevoryasii. in 2010, most of the fossil plant material from the howe-stephens quarry that was not considered as belonging to this whole-plant species were the many pieces of silicified wood and the coalified tree trunks because they had not yet been studied. however, now that our current investigation has identified the silicified wood as pertaining to the araucariaceae and that the morphology and taper of the two coalified trunks in the quarry are consistent with living araucaria trunks, the likelihood of the fossil reproductive material, foliage, wood, and tree trunks representing the different parts of the same upper jurassic plant species is high. given the intimate association of the abundance of silicified wood and huge numbers of seed cones, seed cone scales, seeds, pollen cones, and twigs with leaves bearing cuticle, and the two giant tree trunks, as well as the extremely low paleobotanical diversity known from the howe-stephens quarry, it is extremely likely that the compression fossils and silicified wood all represent various parts of the whole plant consisting of araucaria delevoryasii and agathoxylon hoodii, which should be known hereafter as the araucaria delevoryasii tree. habitat of the araucaria delevoryasii tree because the fossiliferous sandstone lens at the howe-stephens quarry was interpreted as channel-fill deposits of a point bar sequence (ayer, 2000), the abundance of conifer compression and wood fossils in this horizon suggests that araucaria delevoryasii trees grew alongside this meandering river. that they were rooted directly on the riverbanks is suggested by the abundance of intermixed conifer cones and twigs all through the sandstone layer, which likely dropped directly into the river from overhanging branches, then were transfigure 9. occurrences of agathoxylon hoodii (stars) in the upper jurassic morrison formation. color key: yellow = howe-stephens quarry (hsq, this study), orange = rainbow draw (gee et al., 2019), blue = tal site (gee, unpublished data), and green = mt. ellen (tidwell and medlyn, 1993). map of morrison formation outcrops (black) courtesy of kenneth carpenter, museum of natural history, university of colorado. 310 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 ported by water. the occurrence of two large fossil tree trunks replete with their respective rootstocks in the howe-stephens quarry also offers more evidence that araucaria delevoryasii trees were likely rooted directly at the edge of the river, since these trees must have grown close enough to the river channel that they could slide into the river as entire trees once the riverbank substrate where they grew was eroded away. old-growth araucaria forests in the morrison formation the preserved diameters of 152 cm and 117 cm at dbh of the two tree trunks in the howe-stephens quarry and their minimum reconstructed heights of 74 to 78 m and 64 to 65 m, respectively, confirm the presence of old-growth forest trees in the morrison formation of what is today wyoming. based on their sizes, these two araucaria delevoryasii trees were likely some of the largest trees in the morrison forest. in the neighboring state of utah, the five silicified logs of a. hoodii with preserved diameters ranging from 71 to 127 cm (gee et al., 2019) were estimated to have reached minimum heights between 45 to 69 m (xie et al., 2024). in the present-day world, old-growth forest trees of araucaria have been found to possess a dbh ranging from 150 to 300 cm and to attain heights from 50 to 90 m (eckenwalder, 2009). these include the species a. hunsteinii, a. cunninghamii, and a. heterophylla in australasia and a. angustifolia and a. araucana in south america. in australia and papua new guinea, large trees of a. cunninghamii d. don range from 120 to 174 cm at dbh and reach heights up to 71 m, whereas those of a. hunsteinii k. schumann measured 120 to 136 cm at dbh and attained even greater heights up to 89 m (gray, 1975). of the living species of araucaria, the a. angustifolia trees in the brazilian atlantic forests have probably received the most attention, due to its critically endangered species status, the number of giant trees now being limited to 21 individuals (scipioni et al., 2019). here, the giant trees of a. angustifolia have very wide trunks with a dbh extending from 160 to 325 cm; many of these trees reached a total height of 40 m (scipioni et al., 2022), with an average of 38.4 m. it should be noted, however, that a. angustifolia trees tend to be relatively stout morphologically (table 4), compared to other species of araucaria. old-growth araucaria trees in living forests have specific structural characteristics associated with their trunks, such as basal cavities, regenerated branches, and new trunk growth (scipioni et al., 2022). basal cavities, for example, are usually found in giant trees of araucaria angustifolia that have a dbh exceeding 150 cm. these cavities can measure between 1 to 2 m wide and can extend over 4 m into the height of the inner tree trunk. trunk cavities in such large, old trees offer forest inhabitants shelter and are thus of high ecological value for wildlife. the decay of wood tissue is most commonly carried out by fungi (e.g., schwarze et al., 2000; zabel and morrell, 2020), although considerable damage can also be caused by wood-boring insects. all three genera of living araucariaceae trees are prey to a wide array of diseases and pathogens (balocchi et al., 2022). large trunk cavities were not observed in the howe-stephens quarry trees, nor in the fossil logs at rainbow draw, although silicified wood in the morrison formation in both utah and wyoming show evidence of ancient fungal degradation and insect activity. in utah, a fossil log of agathoxylon hoodii in rainbow draw, which likely attained heights of 68 to 72 m, shows evidence of wood-boring beetles and parasitic white-rot wood-decay fungus (gee et al., 2022). a fossil log of xenoxylon utahense in nearby miners draw, blue mountain, which has a diameter of 90 cm, contains the fossil hyphae of saprophytic white-rot fungi (xie et al., 2023). the more poorly preserved wood of a. hoodii from the howe-stephens quarry exhibits considerable cellular damage from what was likely ancient white-rot fungi (gee, unpublished data). the fossil trunks of agathoxylon hoodii at the howe-stephens quarry in wyoming and rainbow draw in utah clearly represent the remains of 150-million-year-old giant trees, but the araucarian forests of the morrison formation were certainly comprised of younger trees as well. the morrison forests likely con311 the whole plant of araucaria delevoryasii and agathoxylon hoodii—giant trees with silicified wood, gently tapering trunks, araucarian seed and pollen cones, and brachyphyllum-type leaves with cuticle from the upper jurassic morrison formation of the howe-stephens quarry, wyoming, usa gee, c.t., xie, a., and howell, m.m. geology of the intermountain west 2025 volume 12 sisted of a healthy, multi-generational population of trees that included several large and venerable trees, as it has been suggested for the escalante petrified forest state park in southern utah (gee et al., 2023; morgan et al., 2024). conclusions we describe here a new whole plant of agathoxylon hoodii (tidwell et medlyn) gee, sprinkel, bennis et gray and araucaria delevoryasii gee from the upper jurassic morrison formation of the howe-stephens quarry on howe ranch in north-central wyoming. the whole plant should be referred to as the araucaria delevoryasii tree. it is the first whole plant from the morrison and is known through anatomically preserved wood, coalified compressions of seed cones, detached seed scales and abscised seeds, pollen cones, branches with brachyphyllum-type leaves, and giant coalified tree trunks. the silicified wood of agathoxylon hoodii occurring in the howe-stephens quarry is identified and described in detail, which occurs intermixed with araucarian fossil compressions in a prolific dinosaur bonebed. the fossil plant assemblage also includes two enormous coalified tree trunks, which provide data on the gross morphology, size, and taper of the upper jurassic araucaria trees. according to height–diameter models, these two ancient trees reached heights between 64 to 78 m, comparable to those of living araucaria trees, and had a stem taper that is also similar to that of present-day araucarian species. the araucaria delevoryasii tree was likely rooted directly on the riverbanks of a meandering river. paleobiogeography of agathoxylon hoodii wood in what is today north-central wyoming and southern utah documents the widest extent of all wood species in the morrison formation. based on its size and paleobiogeographic range, the araucaria delevoryasii tree was likely the largest tree that flourished in widespread, old-growth conifer forests in the central morrison formation. acknowledgments we are grateful to hans-jakob (köbi) sieber and team (sauriermuseum aathal) for the many years of collection at the howe-stephens quarry, as well as for access to the collections at and loan of material from the sauriermuseum aathal. we also thank curator dr. cornelia löhne for access to the bonn university botanic garden and gardeners felix eisenhuth and jannick grund for assistance in measuring araucaria trees. thanks also go to olaf dülfer (university of bonn, germany) and nicki karyofylli for thin sectioning fossil wood specimens, but also to vincent cheng for his contribution, and to tania gross (university of bonn, germany) for initial cuticle preparation. we greatly appreciate the valuable comments of dr. xudong gou (kunming university, china) and a second, anonymous reviewer. financial support from the china scholarship council for the doctoral studies of aowei xie (csc no. 201804910527, 2018–2022) is gratefully acknowledged here. ctg and aw are co-corresponding authors. references andrews, h.n., and pannell, e., 1942, a fossil araucarian wood from western wyoming: annals of the missouri botanical garden, v. 29, p. 83–286. table 4. size comparison of fossil agathoxylon hoodii and living araucaria trees in regard to dbh and height. fossil agathoxylon hoodii or living araucaria spp. dbh or maximum preserved diameter (cm) reconstructed height of fossil trees or measured height of living trees (m) references hsq trees a, b 152, 117 up to 78, 65 this study rainbow draw, 5 logs 71–127 45–69 gee et al., 2019; xie 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(sauropoda: diplodocidae), with implications for neurocentral closure timing, and the cervico-dorsal transition in diplodocids: peerj, v. 5, e3179, https://doi.org/10.7717/peerj.3179. turner, c.e., and peterson, f., 1999, biostratigraphy of dinosaurs in the upper jurassic morrison formation of the western interior, u.s.a., in gillette, d.d., editor, vertebrate paleontology in utah: utah geological survey miscellaneous publication 99-1, p. 77–114. wiersma-weyand, k., canoville, a., siber, h., and sander, p.m., 2021, testing hypothesis of skeletal unity using bone histology—the case of the sauropod remains from the howe-stephens and howe scott quarries (morrison formation, wyoming, usa): palaeontologia electronica, article no. 24(1), a10, https://doi.org/10.26879/766. xie, a., 2022, gymnosperm woods of the upper jurassic morrison formation in the western interior of north america: bonn, germany, rheinische friedrich-wilhelms-universität bonn, ph.d. dissertation, 192 p., https://bonndoc.ulb.uni-bonn.de/xmlui/handle/20.500.11811/10279. xie, a., gee, c.t., bennis, m.b., gray, d., and sprinkel, d.a., 2021, a more southerly occurrence of in north america—x. utahense (xie et gee) sp. nov. from the upper jurassic morrison formation in utah, usa, and its paleobiogeographic and paleoclimatic significance: review of palaeobotany and palynology, v. 291, article no. 104451, 13 p., https://doi.org/10.1016/j.revpalbo.2021.104451. xie, a., gee, c.t., and griebele, e.m., 2024, modelling the height–diameter relationship of living araucaria (araucariaceae) trees to reconstruct ancient conifer tree height: palaeontology, e12693, 10.1111/pala.12693. xie, a., gee, c.t., and tian, n., 2023, ancient basidiomycota in an extinct conifer-like tree, xenoxylon utahense, and a brief survey of fungi in the upper jurassic morrison formation, usa: journal of paleontology, v. 97, p. 754–763, https://doi.org/10.1017/jpa.2023.12. zabel, r.a., and morrell, j.j., 2020, wood microbiology—decay and its prevention (second edition): san diego, academic press, 476 p. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 11 2024 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. piecing together a prehistoric puzzle: regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america kate morrison, natalya usachenko, jonathan erdman, shilah waters, and renee l. love geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover adolescent to young adult jeffersonian mammoth in soda springs, idaho. painted by university of idaho undergraduate student katie ebling and used by permission. inset photograph: dr. renee l. love reconstructing the prehistoric puzzle of the mammoth crania that was fragmented during excavation in 1966 from southeastern idaho. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 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dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 11 2024 21 abstract we evaluated the depositional age, taxonomy, diagenetic alteration, and osteology of mammoth skeletal remains from southeastern idaho. in this study, we identified the first record of m. jeffersonii present in idaho and only the second record of the species in western north america that lived 13,586 to 13,444 cal bp. the mammoth remains were preserved in an ancient hot spring deposit and have indicators of possible pre-mortem injuries. the diagenetic processes post-mortem suggest that it was not immediately buried and was gnawed on by small and large carnivores. our evaluation of the mammoth’s tusks, molars, and limb bones suggest that these remains belonged to a young adult male that had been around 29 years old at its time of death. this specimen lived at a time when mammoths were becoming endangered in western north america before their ultimate disappearance from the fossil record. piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america kate morrison1, natalya usachenko2, jonathan erdman3, shilah waters4, and renee l. love5 1department of earth and spatial sciences, university of idaho, moscow, id 83844-3022 usa; broo4823@vandals.uidaho.edu 2 department of geosciences, mississippi state university, mississippi state, ms, 39762 usa; nu52@msstate.edu 3department of earth and spatial sciences, university of idaho, moscow, id 83844-3022 usa; erdm4467@vandals.uidaho.edu 4johns hopkins bloomberg school of public health, baltimore, md 21205, usa; sloosle1@jh.edu 5department of earth and spatial sciences, university of idaho, moscow, id 83844-3022, usa; rlove@uidaho.edu citation for this article. morrison, k., usachenko n., erdman, j., waters, s., and love, r.l., 2024, piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america: geology of the intermountain west, v. 11, p. 21–44, supplemental material, https://doi.org/10.31711/giw.v11.pp21-44. introduction in the late pleistocene, 126 to 11.7 ka, mammuthus primigenius (woolly mammoths) and mammuthus columbi (columbian mammoths) had established populations in north america. near the end of that epoch, between 14,690 to 12,890 ka, earth was experiencing the bølling-allerød interstadial period, an abnormally warm period during the ice age that preceded the younger dryas (broecker et al., 1988). it marks the retreat of the laurentide and cordilleran ice sheets and is a period where climate change played a major role in altering the north american biome. as the ice sheets melted, cold, dry conditions transitioned into a wetter, more temperate environment typical of modern conditions (doerner and carrara, 2001). a north-south division of biomes allowed for multiple species of mammuthus to cohabitate through niche partitioning (yansa and adams, 2012; lister, 2017). for nearly 80 years, researchers (osborn, 1942; aguire, 1969; saunders et al., 2010; yansa and adams, 2012; enk et al., 2016; widga et al., 2017) debated the validity of a third species: mammuthus jeffersonii (jeffersonian mammoth). recent genetic studies have suggested that the m. jeffersonii could either be a m. primigenius, m. columbi hybrid (fisher, 2009; enk et al., 2011), a subspecies of m. columbi (aguire, 1969; maglio, 1973; graham, 1986; lister, 2017), or the product of introgression, which includes the hybridization and repeated backcrossing of genes between species through time (enk et 22 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 al., 2016). genes of the extant african elephant (loxodonta africana), close relative to both mammuthus and elephas, show introgressive behavior with recurrent backcrossing; this implies a genomic record response to ancient habitat changes (roca et al., 2005). palynological records (doernner and carrara, 2001) indicate a transition from a colder, sedge brush-dominated landscape to a higher concentration of spruce and pine, and more temperate conditions similar to those of the modern day during the bølling-allerød period. this is coincident with sedge-grasslands disappearing into more closed forests in the great lakes region and m. jeffersonii competing with mastodon food sources (yansa and adams, 2012). the long history of introgressive radiation within mammoth populations through major fluctuations of interglacial and glacial periods, shows that they were not only interbreeding but also competing for food resources to survive (yansa and adams, 2012; enk et al., 2016). mammoth populations were declining, eventually leading to the megafaunal extinction event on the north american continental mainland (bjorck et al., 1988; agenbroad, 2005; barnosky et al., 2015). megafauna, including mammoths, disappeared from the rock record, and a total of 35 mammalian genera went extinct or became extremely endangered, with 90% of all mammals over 45 kg (99 lbs) disappearing from the continent (gilmour et al., 2015). the primary driver of this extinction is still debated, although a combination of climate change and anthropogenic influences appears to be the most likely cause (fisher, 2018). a mammoth skeleton (specimen uissm-001-cola) was excavated from a hydrothermal spring deposit 11 km (7 mi) north of soda springs, idaho, in 1966 and is now located at the university of idaho (jones and bowers, 1968; figure 1). this deposit was postulated to be upper pleistocene in age (malde and powers, 1962; jones and bowers, 1968) based on nearby geologic mapping and seven species of freshwater gastropods that were discovered between 61 to 91 cm (2–3 ft) above the mammoth remains. original reconnaissance by r. jones in 1968 mapped a tufa rim of an ancient discontinuous ‘pleistocene spring’ that was about 1.6 km (1 mi) in length. nearly 100 springs have been mapped in the vicinity of soda springs and the aspen range to the east (lewicki et al., 2013) and many have been associated with active and non-active accumulations of travertine deposits (lewicki et al., 2013). the pleistocene spring is oriented against the east slope of a north-south-oriented fault block, along the trend with china hat (welhan et al., 2014; mccurry et al., 2015; welhan and breedlovestrout, 2016). the north-south-oriented fault block is part of the paris thrust fault system within the sevier fold and thrust belt in southeastern idaho (lewicki et al., 2013) and hydrothermal activity is associated with the quaternary blackfoot volcanic field (welhan et al., 2014). although more bones were searched for in the vicinity, the pleistocene spring was the only deposit to contain mammoth bones, which were discovered 2 m (6 ft) beneath the modern ground surface. here, we use several analytical techniques to evaluate taxonomy and paleontological history of uissm001-cola. specifically, the focus of this study was 5-fold: (1) precise radiometric dating of the molar, (2) preand post-mortem analysis of the health of the mammoth, (3) size, age, and gender determination, (4) diagenetic analyses, including recrystallization of bones and analysis of original material, and (5) taxonomic identification using the dimensions and morphology of the proboscidean’s molars and mitochondrial dna (mtdna) analysis. this study provides a snapshot into the life of one of the last mammoths recorded in the fossil record on mainland western north america during a time of great stress for ice age megabeasts, and provides unique insight into the impact of extinction drivers on pleistocene megafaunal specimen. this megafauna specimen also records the presence of mammuthus jeffersonii in the western united states, an area largely devoid of confirmed fossil evidence of the species. materials and methods radiometric dating using a sterilized drill, material from the center of the molar was extracted and placed in a sterile plastic container. samples were analyzed by beta analytic testing laboratory to obtain an accelerator mass spectrometry (ams) radiocarbon date. pretreatment methods included washing the sample in hot hydrochloric 23 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 acid (hcl) and alkali (naoh) to remove carbonates and organic acids. next the sample was bathed in sodium chlorite (naclo2) to eliminate wood cellulose that might be present. the techniques used to measure carbon-14 in the tooth utilized accelerator mass spectrometry. in calibrating the conventional radiocarbon date to calendar year equivalents, the high-probability density range method, intcal13, was used. the standard de? snake river plain 5100 4300 ? legend occurrence mammoth species dated age 1 ( ) colpen spring, wa m. jeffersonii 12,000 2 ( ) port of clarkston, wa m. columbi 12,000 3 ( ) tolo lake, id m. columbi (possible) m. primigenius 5100 4300? 4 ( ) grove mammoth site, id m. columbi 14,700 5 ( ) ra�lesnake cave, id mammuthus sp. 10,450 +/120 6 ( ) owl cave, id mammuthus sp. 12,850 +/150 12,250 +/200 10,920 +/150 7 ( ) soda springs, id m. jeffersonii ~13,500 8 ( ) preston, id m. columbi 12,150 figure 1. mammoth distribution in north america. gray shaded area represents the inferred range of mammoths during terminal pleistocene (15 to 10 ka) based on agenbroad (2005) and mammuthus sp. in faunmap (graham and lundelius, 2010). white shaded areas show extent of glaciation at this time. mammoth discoveries attributed to m. jeffersonii are represented with a black square. other mammoth species discovery sites are indicated with a black circle. inset: mammoth discoveries in washington and idaho that have been radiocarbon dated within 15 to 10 ka. descriptions of localities are included. sites 1 through 3 sourced from sappington (2019) and sites 4 through 8 are sourced from agenbroad (2005). 24 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 viations are not reported less than ±30 bp to prevent from misrepresenting the accuracy of the results. preand post-mortem analysis external and internal features such as calluses, fractures, enlarged pores, distinct porosity, and ulcers identified on the mammoth skeleton can indicate a pre-mortem event or skeletal-related disease (krzeminska and wedzicha, 2015; krzeminska et al., 2015; leshchinskiy, 2017). a total of 271 bones and bone fragments were imaged at gritman medical center in moscow, idaho, using computed tomography (ct) technology (see supplemental material for inventory of bones). the scans provided 18 dicom files and full images of the limbs, axial skeleton, and manus bones of the mammoth. the images were analyzed using  the processing  software:  analyze 14.0 (analyzedirect, overland park, ks), microdicom viewer (microdicom ltd, sofia, bulgaria), and itk-snap (yushkevich et al., 2006), and viewed in 3d microsoft paint to measure any abnormalities found internally such as enlarged pores and fractures and externally such as calluses and ulcers. the scans provided the ability to create 3d modeling of each bone for further assessment of surface features. the bones of the mammoth were then organized into a categorized inventory and evaluated based on external features. to determine how much of the skeleton had been recovered, the specimen was divided into the following regions: limbs, vertebral column and ribcage, autopodial bones, crania, tusk, and pelvis (supplemental material). these features were recorded, along with a detailed description of preservation quality. destructive features were documented and measured, and preservation quality was assessed using this scale: (1) very poorly preserved or severely fragmented, (2) poorly preserved or fragmented, (3) mostly preserved or slightly fragmented, and (4) well preserved or not fragmented (table 1). the regions were then given a total percentage present value based on observational analysis and the preservation quality given. the total percentage of skeleton present was achieved from the average value of each region’s total percentage intact combined. size, age, and gender estimates the ratios of metacarpal (mtc) iii length vs. radius length and manus height vs. radius length of the skeleton were determined based on bone measurements and compared to those of different proboscidean species from larramendi (2015) to show a comparison in body proportions. manus height was calculated from larramendi (2015) in which the length of the third metacarpal is multiplied by two. this is under the assumption that the length of the third metacarpal represents approximately 25% of the radius length in most proboscideans (table 2). using the following equation: a = b x c where: a = length of the specimen’s frontal limb bone. b = established percentage that the length of the respective limb bone is of the animal’s total height. c = total height from manus to shoulder, the height was estimated. this height estimation was then compared to skeletal percentages for both m. primigenius and m. columbi (larramendi, 2015; table 3). to remain consistent with the calculations made for manus height in this study, the length of the radius was used to calculate the shoulder height of uissm-001-cola. to determine the molar set that the mammoth was on at the time of death, we assessed the quantities of plates that were fully erupted and in wear, plates that were actively erupting and in wear, and plates that were in the process of erupting. these were compared to the data sets in roth and shoshani (1988) and lee and others (2012), which estimated molar set number according to these parameters. some authors (lee et al., 2012; lister, 2017; widga et al., 2017) use the designation of m1-m3 for the premolars and m1-m3 for the adult molar sets. here, we use the designation of m1-m6, which does not provide a distinction between the pre-molars and molars but lists all molars in order of eruption (stansfield, 2015). 25 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 three methods were used to estimate uissm-001cola’s age at its time of death: (1) dentition – the approximate age of the mammoth was first estimated using dental analysis as outlined by roth and shoshani (1988). the length, width, height, and plate number of the specimen’s right maxillary molar were measured to infer the respective molar set value and associated age range. in addition, states of eruption and wear were recorded on the four exposed mandibular molars. this method utilized the comparison of these measurements to fossil and extant elephas maximus (asian elephant) molars of known age, which are the sister taxon to mammuthus primigenius (roca et al., 2015; enk et al., 2016), to provide an accurate analogy of elephantid maturation. these results were additionally compared to standards established in laws (1966), as well as the records presented in lee et al. (2012) and haynes (2017), which assessed the molar characteristics of loxodonta africana (african elephant). (2) post-cranial skeletal assessment – age parameters were further determined through the examination of the degree of epiphyseal fusion in the intact proximal and distal regions of uissm-001cola’s humerus, ulna, radius, tibia, and femur, which were categorized as fused, partially fused, or unfused (lister, 1999; haynes, 2017; table 4). postcranial bone growth increases in mammals until their epiphyses are fused to their diaphysis. african elephant equivalent years (aey; lister,1999) are used to report relative mammoth ages. these were cross-referenced with the skeletal growth rates of modern proboscideans (haynes, 2017), molar set number, and gender determination. (3) age reference line – the final method utilized reference points along the lower jaw to determine the age reference point (arp) and age reference line (arl) following the methods of stansfield (2015; figure 2). using observed tooth lamellae along the endpoint of the arl, an additional age estimation was made. a hypothesis of the mammoth’s gender was made predominantly using its tusk characteristics, which included girth and curvature (averianov, 1996; el adli et region total % present preservation notes limbs 75 3 left femur and ulna fragmented. right femur not recovered. vertebral column and rib cage 25 2 many ribs and vertebrate with identified gnaw marks. several missing components on the spinous process and rib cage. autopodial 95 4 some phalanges missing. skull 20 2 primarily fragments except for three, fully intact molars. skull currently being reconstructed. tusks 90 1 highly fragmented and fragile. supported by plaster jacket. pelvis 5 1 highly fragmented. currently being reconstructed. entire mammoth 51.70 2 calculations based on the average percentage of each region. table 1. total percentage of specimen uissm-001-cola intact based on preservation quality. 26 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 al., 2015), and the degree of epiphyseal fusion observed in the radius, ulna, humerus, tibia, and femur (lister, 1999; stanfield, 2015; haynes, 2017; figure 3 and table 4). although an assessment of the pelvis would be ideal for more accurate gender determination, uissm-001cola's pelvis was severely fragmented upon excavation and could not be analyzed. instead, since mammoths were sexually dimorphic in body size and differed in their rates of skeletal maturation, we were able to use the size, shape, and length of their tusks to determine gender (laws, 1966; averionov, 1996; haynes, 2017). the appearance of the mandibular condyles was also considered; in males, these structures are more circular, whereas in females they are more ovular (yacobi et table 2. ratios between metacarpal (mtc) iii length vs. radius length and manus height vs. radius length of different proboscidean species found in larraramendi (2015). radius length from the proximal to distal end. species individual mtc iii length (mm) radius length (mm) calculated manus height (mm) mtc iii length vs. radius length (%) manus height vs. radius length (%) determined in this study uissm-001-cola 210 889 420 23.6 47.2 mammuthus primigenius pfannerhall 208 825 416 25.2 50.4 mammuthus primigenius fraasi steinheim 245 955 490 25.7 51.3 mammuthus trogontherii zhalainuoer iii 255 985 500 25.9 51.3 mammuthus meridionalis scoppito 266 950 525 28 51.8 mammuthus meridionalis nogaisk 265 1040 530 25.5 55.3 mammuthus columbi msl-140 237 948 474 25 51 mammuthus columbi nsm1597-62-2 194 823 388 23.6 50 mammuthus columbi sdsm 124688 244 928 488 26.3 47.2 table 3. height estimation of specimen uissm-001-cola based on limb bone measurements compared to specimens of larramendi (2015). mammoth species larramendi (2015) percentages ui-ssm-001cola radius length (cm) total height of uissm-001 cola (cm) m. primigenius 26.67 88.9 333.33 m. columbi 27.10 88.9 328.04 27 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 al., 2004). the last indirect method used to determine gender was to assess the epiphyseal regions in the limb bones; in females, the epiphyses would typically finish fusing between ages 30 and 35, and in males, between 45 and 50 (lister, 1999; haynes, 2017). diagenetic analysis the fossilization of bone is characterized by the replacement of protein and other organic biomolecules with inorganic material and the recrystallization of inorganic remains, such as hydroxyapatite in bone, into table 4. specimen uissm-001-cola's limb bones with degree of epiphyseal fusion. findings are compared to lister (1999) and suggest an age range of around 29 aey. bone epiphyseal fusion dental age (aey) from lister (1999) haynes (2017) corrected age using stansfield (2015) distal humerus fused ≥6 ≤24 proximal tibia fused ≥26 27-30 distal tibia fused ≥26 ≤24 proximal ulna fused ≤34 ≤24 distal femur fused ≤34 29-33 proximal humerus unfused ≤41 40-47 proximal femur unfused ≤43 37-42 distal radius unfused ≤43 distal ulna unfused ≤43 ≥52 figure 2. age estimation using the arl (stansfield, 2015). (a) a straight line was drawn from point a (the base of the mandibular foramen) to point b (the most distal section of molar occlusal wear). a second line, c, was visualized along the ridge of the medial mandible, and intersects the first line at point d, which is known as the arp. from this point, a distance of 10 cm (3.94 in) was measured, passing centrally, through the distal molar. this is the arl. the yellow line e marks the endpoint of the 10-cm (3.94 in) measurement in this example from stansfield (2015). (b) age reference line calculation on specimen uissm-001-cola. 28 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 a more stable form (pfretzschner, 2004; buckley and wadsworth, 2014; keenan et al., 2015; kendall et al., 2018). environments most suitable to preservation are those that are unfavorable to microbial activity; remains most likely to avoid diagenesis are those consisting of or encased by hydrophobic, inorganic lattices that are impermeable to water and are, therefore, protectant against biotic and abiotic decay (hedges et al., 1995; trueman and martill, 2002; jans, 2008; keenan, 2016). therefore, some hard surface remains, such as bone and teeth that have inorganic casings, can protect biomolecules including nucleic acids, proteins, lipids, and carbohydrates from degradation. this can, in turn, enable certain chemical and molecular analyses, which could provide insights into genetic information and environmental conditions. to determine the diagenesis of the bones, and to assess whether original material was remaining in the bones for genetic analysis, the external surface structure of a tusk and tooth were imaged using scanning electron microscopy (sem). superficial samples were collected from the tusk and tooth for analysis. the samples were prepared with a carbon coating to gain high resolution and imaging under the sem. elemental composition of each specimen was determined utilizing sem with energy dispersive spectroscopy (sem/eds). this analysis was performed on both external surface samples and internal samples. internal samples were obtained by drilling into the tusk, tooth, and femur. two samples were collected from the interior tusk, three from the tooth (outer, middle, inside), and two from the femur (epiphysis and diaphysis). samples were then imaged without a carbon coat to obtain accurate elemental composition profiles from eds. the molecular composition of the tusk was acquired using x-ray diffraction (xrd) performed at 40 kv. a total of 1561 data points were generated over a spectrum of 0 to 80°. steps equaled 0.05° in measurements of two-theta. figure 3. curvature of tusks, length, and girth. green arrow showing curved length of 266 cm (105 in). yellow arrow showing a non-curved length of 115 cm (45 in). red arrow showing width of distal end at 18 cm (7.1 in). inset image showing the circularity of mandibular condyle. 29 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 taxonomic identification proteinaceous composition of uissm-001-cola was determined using methods of cappellini et al. (2018) to determine if original material was remaining in the specimen for radiocarbon dating and taxonomic analysis. a femoral sample was collected using a sterilized drill at the junction between the articular surface of the knee and the shaft, just proximal to the epicondyle, at a depth of approximately 1 cm (0.4 in). when drilling into the bone, the periosteum was discarded to minimize contamination. treatment buffer was prepared using 0.125 m tris-cl, 4% sds, 20% v/v glycerol, 0.2 m dtt, and 0.02% bromophenol blue with a ph of 6.8. a sample of 15 mg was boiled for 15 minutes and then the sample was loaded into an sds gel composed of a 10% resolving gel and a stacking gel. polyacrylamide gel electrophoresis (page) was run for approximately 30 minutes to allow separation of the proteins and other components of the femur. the gel was stained with coomassie brilliant blue r-250 solution. taxonomic identification of uissm-001-cola was determined in two ways: (1) by using measurements of molar characteristics adapted from maglio (1973) and lister (2017), and (2) by extracting mtdna from a tooth sample. measurements of uissm-001cola’s molar included length (l), width (w), height of crown (h), enamel plate count (p), lamellar frequency (lf), and hypsodonty index (hi). the lf was calculated on an average of six measurements taken from the upper, middle, and lower portion of the crown on both the lingual and buccal side. the hi was calculated as hi = h/w x 100, or height of the crown as an expression of width standardized to a length of 100 mm (3.9 in). these measurements were obtained using a digital caliper on the maxillary right molar (figure 4). no estimation of missing plates was required due to the presence of the anterior-most root. the molar parameters of the specimen were then compared between holotypes or neotypes of m. primigenius, m. columbi, and m. jeffersoni (roth and shoshani, 1988; lee et al., 2012; lister and sher, 2015; haynes, 2017; lister 2017; widga et al., 2017; table 5). elemental composition analysis provided guidance on where to sample for mtdna. the anterior talon of the upper molar was sent to the university of california, santa cruz paleogenomics lab, for analysis. extraction and processing were performed according to dabney et al. (2013). initial sample preservation and assessment was performed using a single-stranded library preparation and sequencing on an illumina nextseq 2x150 run targeting 1 million raw reads. the reads were trimmed and aligned to loxodonta africana nuclear genome and mammuthus primigenius mitochondrial genome. subsequently, the sample underwent mtdna preparation and analysis using methods according to kirillova et al. (2017), mybaits v4.01 protocol (biodiscovery, llc dba arbor biosciences, 2018), and vershinina et al. (2020). sequencing occurred on an illumina nextseq 2 x 150 run targeting 0.5 million raw reads. afterwards, the reads were trimmed, merged, and filtered using seqprep2 (https://github.com/jstjohn/seqprep), fastx_ toolkit (http://hannonlab.cshl.edu/fastx_toolkit/), and prinseq lite (schmieder and edwards, 2011). the final consensus sequence was generated using mia (https:// github.com/mpieva/mapping-iterative-assembler) and compared to clades described in enk et al. (2016) to assign uissm-001-cola to a haplogroup. results radiometric dating radiocarbon dating was consistent with the estimated upper pleistocene age derived from the gastropod identification and yielded a age of 13,586 to 13,444 cal bp with 95.4% probability (figure 5; beta analytic testing laboratory specimen number: 524280). a c:n ratio was also obtained to test potential diagenetic alteration or contamination at 3.2, with an isotope ratio mass spectrometer reading of δ13c at –18.7 ‰ and δ15n at +11.32 ‰. modern bone is in the range of 2.9 to 3.5, suggesting that little to no diagenetic alteration or contamination occurred (deniro, 1985; enk et al., 2016). preand post-mortem analysis a total of 271 bones and bone fragments were itemized (supplemental material). the pelvis and crania have significant damage and are currently in fragments. 30 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 ta xo no m ic id m ol ar po si tio n pl at e n um be r l en gt h h ei gh t w id th e na m el t hi ck ne ss l am el la r fr eq ue nc y h yp so do nt y in de x av er ag e r an ge av er ag e r an ge av er ag e r an ge av er ag e r an ge av er ag e r an ge av er ag e r an ge av er ag e r an ge m . c ol um bi m 3( m 6) r ig ht si de 18 .9 18 -2 1 26 8. 6 18 035 9 18 1. 1 16 121 6 10 1. 3 69 -1 06 3. 1 2. 03. 0 5. 6 5. 29 -7 .5 3 20 9. 1 17 6. 725 3. 25 m 3( m 6) l ef t si de 18 15 -1 9 26 8. 2 16 631 5 17 9. 2 11 222 0 91 .6 69 -1 08 2. 9 2. 03. 0 6 5. 71 -7 .1 2 20 7 16 2. 32 24 3. 68 m 3( m 6) s id e u ns pe ci fie d 19 .1 18 -2 4 27 6. 3 26 034 0 19 4. 5 15 229 0 10 3. 8 74 -1 28 2. 4 1. 63. 9 6. 1 5. 88 -7 .6 9 19 1. 4 15 8. 44 24 6 to ta l 18 .9 15 -2 4 27 2. 6 16 635 9 19 0. 1 11 229 0 10 2. 2 69 -1 28 2. 6 1. 63. 9 6 5. 29 -7 .6 9 19 6. 1 15 8. 44 25 3. 25 m 2( m 5) s id e u ns pe ci fie d 10 .2 4. 016 .0 11 9. 2 13 819 9 14 7 13 116 2 88 .1 68 -1 11 .4 2. 2 1. 52. 5 6. 4 48. 71 11 5 021 7. 65 m . p ri m ig en iu s m 3( m 6) r ig ht si de 24 .6 20 -2 8 27 2. 6 20 532 8 17 3. 4 10 2. 121 9 93 .5 72 -1 22 1. 8 1. 03 -2 .8 3 8. 5 6. 91 10 .9 4 18 9. 4 12 8. 27 23 0. 77 m 3( m 6) l ef t si de 24 .7 20 -2 8 26 7. 4 19 532 5 14 8. 8 10 2. 217 9 96 .5 80 .9 -1 16 1. 8 1. 32. 37 8. 3 7. 23 10 .1 6 15 8. 8 10 3. 44 18 7. 64 m 3( m 6) s id e u ns pe ci fie d 23 .8 21 -3 0 27 1. 8 26 035 5 17 2. 6 15 521 3 94 .9 75 -1 25 1. 5 12. 1 8. 3 6. 15 -1 0 15 7. 6 16 822 7. 6 to ta l 24 .2 20 -3 0 27 1 19 535 5 16 7. 4 10 2. 121 9 94 .9 72 -1 25 1. 6 12. 83 8. 4 6. 15 10 .9 4 16 7. 4 10 3. 44 23 0. 77 m 2( m 5) s id e u ns pe ci fie d 13 .4 9. 016 .0 16 6. 6 77 -2 14 13 1. 6 92 -1 62 .9 71 .2 50 -8 9 1. 6 1. 51. 82 5 8. 8 6. 54 11 .7 6 11 3. 8 020 1. 73 m . j eff er so ni i m 3( m 6) r ig ht si de 22 .4 19 -3 1 28 7. 4 21 438 0 17 8 13 4. 424 9 10 1. 9 88 -1 20 2. 2 1. 52. 9 7. 5 510 .1 9 17 3. 5 74 .2 623 5. 96 m 3( m 6) l ef t si de 23 .4 22 -2 7 28 2 25 030 5 15 3. 4 75 -2 10 94 .9 80 .7 10 8. 5 2. 5 1. 52. 1 6. 6 7. 28. 07 18 4. 7 13 3. 98 21 8. 56 m 3( m 6) s id e u ns pe ci fie d 27 27 29 5 29 5 20 6 20 221 0 11 0. 6 10 311 7 2 1. 32. 7 8. 8 8. 8 18 8. 3 17 2. 65 20 3. 88 to ta l 23 19 -3 1 28 5. 8 21 438 0 17 3. 4 75 -2 10 10 1. 6 80 .7 -1 20 2. 3 1. 32. 9 7. 3 510 .1 9 17 8 74 .2 623 5. 96 m 2( m 5) s id e u ns pe ci fie d 15 24 1 83 1. 8 6. 2 0 u is sm -0 01 c o la m 2( m 5) u pp er r ig ht 1 9 2 78 1 54 8 2. 8 2 .4 8 1 86 ta bl e 5. t ot al av er ag es a nd ra ng es o f d en ta l p ar am et er s f ro m w id ga e t a l. (2 01 7) a nd l ist er ( 20 17 ) w ith co m pa ris on to th os e of sp ec im en u is sm 00 1c o la . n ot e: sp ec im en u is sm -0 01 -c o la 's m ea su re m en ts o f t he u pp er ri gh t m 5 m ol ar b et te r c oi nc id es w ith m . c ol um bi fo r t he p la te n um be r an d en am el th ic kn es s, an d m . p rim ig en iu s f or th e l am el la r f re qu en cy an d w id th . th e l en gt h, h ei gh t, an d hy so do nt y in de x ar e s im ila r f or ea ch o f t he sp ec ie s. a ll m ea su re m en ts in m m . 31 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 the tusks have also experienced a large amount of fracturing. the limb bones have significant breaks that separate them into two to three fragments. the right humerus is missing except for the proximal epiphysis. the vertebral column only shows small amounts of fracturing, but the ribs have significant damage, and most are missing. an estimated 10% of the mammoth’s ribcage is present. due to the large amount of fragmentation of the ribs, a full reconstruction was not possible. the manus and pes bones are well-preserved and exhibit only small amounts of fragmentation. observational analysis of the preservation quality showed that uissm-001cola has an overall average quality number of 2 out of a scale of 4. the total percentage of uissm-001-cola’s intact skeleton was estimated to be 51.7% (table 1). whereas over half of the remains were present for analysis, larger portions of the vertebral column, ribcage, crania, and pelvis were unrecovered or in fragments. external and internal observations revealed unusual markings and features on the joints, limbs, and autopodial bones, and can be indicators of premortem health conditions and injuries. the ribs of the mammoth contain gnaw markings with sizes ranging from presumed small mammalians to large carnivores. the marks on the ribs are currently under more investigation and will not be discussed further in this paper. an internal fracture, approximately 5.05 cm (2 in) in length, occurs inside the right calcaneum bone and is identified by a thickened callus around the fracture. the left calcaneum bone of the mammoth showed enlarged pore sizes of up to 3 mm (0.12 in) in diameter; this is in contrast to normal ranges for pores that are typically less than 0.1 mm (leshchinskiy, 2012). premortem deformations by ulcers were identified by an area up to 6 cm2 (2.4 in2) with a linear dimension typically no larger than 7 cm (2.8 in). these features are common on figure 4. analysis of molars. (a through d) assessment of molar parameters. (b through d) characteristics of mammoth molars showing plate, lamellar frequency, and enamel thickness. modified from roth and shoshani (1988). (e through f) upper teeth. 32 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 the articular surface. this mammoth presents a feature that matches this description on the distal end of its humerus measuring 4 x 4.5 cm (1.6 x 1.8 in). these ulcers were compared to leshchinskiy (2017) to confirm the identification. the seventh thoracic vertebra presents an oval-shaped deformation measuring 2 x 1.5 cm (0.8 x 0.6 in) which may be a premortem ulcer or a result of peripheral erosion on the articular surface. specimen uissm-001-cola shows significant dilation in the haversian cavities of the axis. studies have found that non-osteoporotic indications within haversian bones of these large animals would measure at typically less than 0.1 mm (leshchinskiy, 2012). the vertebral column of mammoths can indicate external signs of osteological changes with distinct porosity represented as numerous small, piercing holes (krzeminska and wojtal, 2015; leshchinskiy, 2017). this feature is present in uissm-001-cola’s seventh thoracic vertebra. these features are shown in figures 6 and 7. size, age, and gender estimates specimen uissm-001-cola’s jaw had a base alveoli diameter of 18.9 cm (7.4 in) and was fairly circular, indicating the specimen may have been a male. female alveolar diameters typically range between 8 and 10 cm (3 and 3.9 in) (pilgrim and western, 1983; vereschchagin and tikhonov, 1986; averianov, 1996; moss 1996). the length and curvature of the specimen’s tusk (figure 3) suggest that uissm-001-cola was a sexually mature male. female tusks tend to be slenderer, straighter, and more cylindrical in shape (fisher, 2009), and whereas male tusks are generally more massive, more conical in shape, and turned medially at the adult stage (lister and bahn, 2007). based on the specimen’s tusk characteristics, alveoli diameter, and the degrees of epiphyseal fusion in the limb bones (figures 8 and 9; table 4), it can be concluded that uissm-001-cola was a male mammoth. a morphological comparison of uissm-001-cola’s molars to those presented in roth and shoshani (1988) determined that uissm-001-cola would have already aged out of its first three sets of deciduous molars. one of its adult molar sets was in wear at its time of death. based off the dental aging standards of living elephants, mammoths would wear through and then lose each set of molars at approximately age 1, 5, 10, 22, figure 5 . conventional radiocarbon age for specimen uissm-001-cola is 13,586 to 13,444 cal bp. date provided by beta analytics laboratory. 33 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 35, and 65 (m1, m2, m3, m4, m5, and m6, respectively; laws 1966; lee et al., 2012). a comparison of measurements between uissm-001-cola’s molars and the values listed in roth and shoshani (1988) and lister (2017) suggest that the specimen’s 4th set of molars (m4 molars) had fully erupted, were in wear, and were almost completely gone, and its 5th molar set (m5) was almost fully erupted and in wear, placing its approximate age between 22 and 35, respectively (table 5; figure 4). the age reference line endpoint fell between the 10th and 11th lamella of the mammoth's left mandibular mofigure 6. (a) premortem deformation by ulcer on the distal end of the humerus bone measuring 4 x 4.5 cm (1.6 x 1.8 in) outlined in white, dashed box. (a1) premortem deformations by ulcers indicated by red arrows from leshchinskiy (2012) for comparison. (b) premortem ulcer or a result of peripheral erosion on the articular surface outlined in white, dashed box. (b1) premortem deformations by ulcers indicated by white arrows from leshchinskiy (2017) for comparison. (c) dilation of cavities opening into the vertebra foramen indicated by dashed, white box. (c1) diliation of cavities opening into the vertebra foramen from leshchinskiy (2017) for comparison. (d) distinct porosity in the seventh thoracic vertebra indicated by white arrows. (d1) distinct porosity shown with white arrows from krzeminska et al. (2015) for comparison. figure 7. ct rendering of the mammoth’s right (a) and left (b) calcaneum bones. potential fracture indicated by red arrow. enlarged pores indicated by white circle. 34 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 lar (figure 2). since this molar is an m5, the estimated age would be 28 to 29 aey (using lee et al., 2012, age class; stansfield, 2015). analysis of the mammoth’s front and rear limb bones revealed that none of the later epiphyseal plates had yet fully fused at its time of death, which places the estimated age range between 29 and 33 aey (figure 8) according to the classifications of lister (1999) and haynes (2017). using the categories established by lee et al. (2012), the specimen would lie somewhere between 27 and 31.5 years old. stansfield’s (2015) age reference line corroborates these age ranges with an estimate of 28 to 29 years old (figure 9). therefore, the ontogenetic age of the specimen was postulated to be 29 aey, as this was the age in common between all these estimates. diagenetic analysis the sem images revealed that the tusk exhibits high levels of porosity and permeability. the tooth, conversely, appears striated but generally remains predominantly non-porous (figure 10). the eds spectra demonstrated that most of the tusk, tooth, and femur are composed of calcium, phosphorus, and oxygen (figure 11). carbon is also present, but to a much smaller extent. considering the quality of the remains as well as the length of time since excavation, the major compound composing these samples is apatite – ca10(po4)6(oh)2. the eds spectra further suggested some elemental replacement in the apatite, as illustrated by the presence of fluorine. these conjectures are confirmed according to the xrd performed on the tusk (figure 12). whereas the majority of the tusk, tooth, and femur samples contain only minimal amounts of carbon relative to other elements, a high proportion of carbon occurs in some fragments of the interior tooth sample. however, the amount of carbon in the interior tooth sample is not homogenous; generally, the smaller fragments have higher fractions of carbon (figure 11). the sem revealed additional crystalline structures on the surface of the tusk and potential surface contaminants. eds inspection of the crystalline structures demonstrates predominant components of calcium, phosphorus, carbon, and oxygen. the main suspected surface contaminants appear fibrous and, according to eds, have high levels of carbon. no protein occurred in the mammoth femur after processing and running page. taxonomic identification the ratios found between the metacarpal (mtc) iii length vs. radius length and manus height vs. radius length in uissm-001-cola were found to be smallfigure 8. assessment of the epiphyseal fusion in limb bone fragments with scale. (a) proximal tibia; fused. (b) proximal humerus; unfused. (c) distal tibia; fused. (d) proximal femur; unfused. (e) proximal ulna; fused. (f) distal radius; unfused. (g) distal femur; fused. (h) distal ulna; unfused. 35 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 figure 9. age estimation for specimen uissm-001-cola based on a correlation of the condition of its epiphyses (see table 4) with prior correlations between molar wear and epiphyseal fusion in male and female specimens of loxodonta africana. modified from haynes (2017). overlap of the age estimate with the 5th set (m5) and degree of the epiphyseal fusion discounts that we could have only the 4th molar. 36 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 er than those in the comparison to other proboscidean species, including mammuthus primigenius, mammuthus primigenius fraasi, mammuthus trogontherii, mammuthus meridionalis, and mammuthus columbi (table 2; larramendi, 2015). individuals of m. columbi exhibited ratios nearest in value to those of uissm001-cola. the ratios found between the metacarpal (mtc) iii length vs. radius length and manus height vs. radius length in uissm-001-cola were found to be smaller than those in the comparison to other proboscidean species, including mammuthus primigenius, mammuthus primigenius fraasi, mammuthus trogontherii, mammuthus meridionalis, and mammuthus columbi (table 3; larramendi, 2015). individuals of m. columbi exhibited ratios nearest in value to those of uissm-001cola. specimen uissm-001-cola’s right maxillary had high lamellar frequency and thick enamel; the specimen's tooth measurements match both those of m. jeffersonii and m. columbi specimens (table 5). although different molars were measured (m5 in the case of this study compared to m6 in the holotypes), consistent similarities between these two molars have been considered sufficient for taxonomic comparisons (lister, 2017; widga et al., 2017). after extracting and sequencing mtdna from the molar, the results confirmed that uissm-001-cola belonged to haplogroup f (enk et al., 2016), the lineage of north american mammoths that includes m. columbi and m. jeffersonii (figure 13). discussion preand post-mortem analysis analysis of the percentage present and preservation quality (table 1) of the bones indicate that some skeletal remains were fragmented and exposed to the surface. this is largely due to the absence of larger portions of the vertebral column and ribcage. there are rib bones missing and the ones that remain either have carnivorous gnaw marks or are in fragments. this leads us to conclude that the mammoth was exposed above the water before the remains were buried. interpretation of the enlarged pores in the autopodium bones suggest that they are evidence of premortem lesions or deformation caused by an underlying bone disease. the pathologies, specifically osteoporosis, surrounding manus and pes bones are found to be commonly associated with ulcers and weakening of figure 10. sem images of specimen uissm-001-cola. (a through c) tooth surface fragment. (d through f) tuck surface fragment with scale. 37 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 the compact layer (leshchinskiy, 2017). pore widening within the vertebral column can be indicators of osteoporosis or other skeletal-related diseases such as kashin-beck disease (krzeminska et al., 2015; leshchinskiy, 2017). defects within the spinous structure indicate the possibility of genetic defects or diseases (krzeminska figure 11. (a) sem images of specimen uissm-001-cola tooth surface. (b through c) interior tooth. (d) tusk surface. (e through f) interior bone with scale alongside respective energy dispersive x-ray spectroscopy (eds) spectra. red crosshairs represent the location of spot eds analysis; images without crosshairs are alongside eds spectra averaged across the full image. 38 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 et al., 2015). in addition, large marrow cavity openings into the vertebral foramen within the vertebrates of mammoths are also diagnostic of osteoporosis (leshchinskiy, 2017). the internal fracture in the calcaneum could be an indicator of lameness (leshchinskiy, 2015; leshchinskiy, 2017). there is also evidence that osteofibrosis-related conditions can cause increased bone fragility that may have led to this fracture (krezerminska et al., 2015). these observations provide insights into possible bone diseases within the mammoth, whether it died because of bone disease or lameness, and preto postmortem states of the specimen. it is possible that the osteolytic conditions observed in uissm-001-cola could be representative of the broader implication that genomic defects may be correlated with the rise in osteolytic deformations within mammoths seen during the late pleistocene (krezerminska et al., 2015; leshchinskiy, 2015; leshchinskiy, 2017; rogers and montgomery, 2017); however, further research on additional specimens would be required before this assertion can be made. the study also provides an insight into the life of the mammoth’s modern relative, the asian elephant (elephas maximus; roca et al., 2015; enk et al., 2016). recent studies have shown a large trend in degenerative joint diseases within the asian elephant populations (luikart and stover, 2005; regnault et al., 2017). studies into the endangered e. maximus also lead to the larger, ongoing question of a possible bottlenecking event among their ancient relatives. studies suggest a low dna diversity among both the modern asian elephant and some species of mammoths including the m. primigenius (vidya et al., 2005; poinar et al., 2006; vidya, 2016). both e. maximus and mammoths have also faced similar population stressors such as habitat loss and over-predation (saunders et al., 2010; yansa and adams, 2012; gilmour et al., 2015; vidya, 2016; fisher, 2018). size, age, and gender estimates podial to limb bone length ratios of uissm-001-cola (table 2) suggest that the individual was smaller in body mass compared to the others within the larrarafigure 12. x-ray diffractogram of specimen uissm-001-cola tusk fragment. analysis was performed at 40 kv. a total of 1561 data points were generated over a spectrum of 0 to 80°. steps equaled 0.05° in measurements of two-theta. 39 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 mendi (2015) study. this may be due to the hypothesized age of the specimen at its time of death, corroborating that it was still a growing young adult. specimen uissm001-cola's height estimate at approximately 3.28 m (10.76 ft) places it out of the range of adult m. primigenius heights, which did not typically exceed 3 m (9.8 ft) but lies within the height range of adult m. columbi, whose maximum heights reached about 4 m (11–13 ft) at full maturity (lister and bahn, 2007). m. jeffersonii is largely a morphological descriptor for a form that might be a hybrid from introgression or a subspecies of m. columbi. gender differences exist in epiphyseal fusion rates, and it was pertinent to determine gender, even without a pelvis. if the mammoth were female, we would have observed many of its epiphysis fused to the diaphysis, or partially so, at the same time (haynes, 2017). we observed many of the limb bones (proximal humerus, distal ulna and radius, and proximal femur) still unfused, which aligns with the fusing sequence of male mammoths, not females (haynes, 2017; figures 8 and 9). this epiphyseal fusion is consistent with the m5 designation (figure 9). the proximal ulna and distal femur figure 13. maximum likelihood tree of speciemn uissm-001-cola’s (erdmand_strict_idaho_m.sp_hapf) mtdna from 100 raxml bootstrap replicates. specimen uissm-001-cola’s mtdna aligns strongly with haplogroup f, which includes m. columbi, m. jeffersonii, and an unidentified mammoth. 40 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 were the key limb bones in intermediate stages of epiphyseal fusion to examine. specimen uissm-001-cola died when the proximal ulna was fully fused, and the distal femur was almost completely fused. diagenetic analysis sem/eds, xrd, and protein analysis suggest that most of the protein and other organic components have degraded in the superficial areas of the tooth and tusk. because the tusk has a more homogenous anatomy than the tooth and given that the tusk is, currently, highly and easily fragmented, little to no recoverable organic materials remain in the tusk. the degradation of proteins, lipids, and genetic materials in the bones likely mirrored that of the tusk. this is evidenced by the lack of protein found by preliminary protein analysis. furthermore, a femur fragment tested for isotope analysis indicated that little to no collagen existed in the sample. due to their molecular structures, proteins and lipids can generally be analyzed on longer temporal scales than genetic material (briggs and summons, 2014; buckley and wadsworth, 2014; cappellini et al., 2018). thus, because proteins are not detectable in the femur at the time of this writing, most, if not all of, the ancient organic biomolecules likely vanished from the bone. the tooth, on the other hand, demonstrated more promising results of biomolecular preservation with the presence of high proportions of carbon in sem/eds analysis. the heterogeneity of elemental composition of the tooth may be explained by the protective barrier of enamel disrupting fossilization and degradation of the interior tooth (trueman and martill, 2002; kendall et al., 2018). during the sem/eds analysis, it appeared that the smaller particles from the tooth tended to contain more carbon, perhaps due to differences in fragmentation of the denser enamel and the more porous, interior dentin. additionally, it should be noted that likely surface contaminants may occur on the exterior of the tooth, which contained high levels of carbon according to eds analysis. whereas some level of contamination is inevitable, and the presence of these surface contaminants should be considered, it is unlikely that this contamination is significantly contributing to the elemental and molecular composition results. the crystalline structures on the surface of the tusk may have arisen from one of two sources: first, these structures may be remnants of calcium carbonate from the depositional environment of uissm-001-cola or, second, they may represent a product of the process of efflorescence. efflorescence occurs when carbon dioxide reacts with water to form carbonic acid, which then combines with calcium carbonate to form calcium bicarbonate. the calcium bicarbonate, a more soluble compound than calcium carbonate, can distribute and permeate into many areas of tusk. if the water begins to evaporate, the calcium bicarbonate is deposited on the exterior surface of the tusk as calcium carbonate. the process of efflorescence is evidenced by the finding of the crystalline structures on the surface of the tusk, but not on the other remains. this likely occurred to a greater extent in the tusk because of its porosity. the hard enamel on the surface of the tooth likely protected the teeth from calcite deposition. this finding is important to note, as the presence and absence of calcium carbonate crystals on the tusk and tooth, respectively, suggests that less water was able to seep into or evaporate off the tooth. thus, the interior of the tooth is a good candidate for any future biomolecular analysis, as results further demonstrate that organic matter remains there. taxonomic identification molars display different characteristics that are dependent on the tooth’s state of wear and the age of the mammoth, which can cause challenges in species identification (roth and shoshani, 1988; lister and sher, 2015). with this said, the dimensions and characteristics of uissm-001-cola’s right maxillary were compared to type specimens of m. primigenius, m. columbi, and m. jeffersonii. although uissm-001-cola displays a high lamellar frequency (table 5) similar for those reported for the type specimen of m. jeffersonii and neotype of m. primigenius, the plate number is still characteristic of m. columbi. whereas these characteristics were used to make the taxonomic assignment, the amount of overlap between the measurements on uissm-001-cola and the values presented for each taxon causes uncertainty (lister, 2017; widga et al., 2017). haplogroup f is a clade of mammoths common to 41 piecing together a prehistoric puzzle—regional inferences of microand macroscopic analyses of possibly one of the last hybrid mammoths in mainland western north america morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. geology of the intermountain west 2024 volume 11 the great plains and great basin, whereas haplogroup c is more common to the yukon, great lakes, and east coast. with that said, the differences between the mitochondrial genomes in these regions are minor and suggest that they all share a common matriline (enk et al., 2016; widga et al., 2017). widga et al. (2017) suggest morphological overlap between populations of mammuthus regionally and attribute this to varying environments and population history. specimen uissm-001cola's taxonomic placement is most closely related to the great plains and great basin mammoth group (haplogroup f). it has also recently been proposed that mammoths occupying certain biogeographic ranges display variability between members of the same species (widga et al., 2017). while most mammoth occurrences in idaho have not been taxonomically described according to current morphometrics, widga et al. (2017) observed biogeographic variation between mammoth occurrences in the western and eastern united states. mammoths from the great plains, west coast, and southwest have generally lower plate counts and thicker enamel than those from the midwest and east coast (widga et al., 2017). a more detailed description of mammoth collections from idaho, and by extension the northwestern u.s.a., is required to construct a more robust comparison of this variation. conclusion here, we determined that uissm-001-cola specimen was most likely a male mammoth 3.28 m (10.76 ft) tall at shoulder height, young adult around 29 years old (aey), living 13,586 to 13,444 cal bp. specimen uissm-001-cola was among some of the last mammoths to live on mainland of western north america as mammoth populations became extremely endangered during the bølling-allerød climatic event. the mammoth died with potential lameness in one foot and potential bone disease and was preserved in an ancient terrestrial hot spring deposit. the cause of death is still undetermined. over time, its remains underwent early stages of diagenetic alteration, and pores in the bones were infilled with recrystallized apatite and calcium carbonate. the incompleteness of the skeleton, along with the gnaw marks suggests partial disarticulation before ultimate burial. still, many of the large bones were preserved in a low-energy environment. while the driving forces of mammoth hybridization patterns are still not completely understood, they might represent interactions between distinct mammoth populations in response to the changing climate of the time. whether this interbreeding was a direct result of climatic pressures remains unclear, but uissm-001-cola provides potential evidence of m. primigenius and m. columbi interaction. extensive gene flow occurred between haplogroups c and f (enk et al., 2016; widga et al., 2017), and uissm-001-cola is designated into haplogroup f, the m. jeffersonii line. specimen uissm-001-cola’s death and subsequent preservation provides paleontologists with information about a key component to the ecosystem of idaho. further studies documenting other m. jeffersonii occurrences in western north america will undoubtedly reveal more about the paleoecology and population dynamics of one of the cenozoic’s most eponymous taxa, as well as insights into underlying causes of their eventual extinction. acknowledgments this project was funded by the office of undergraduate research grant and the hill undergraduate research fellowship from dr. brian and gayle hill at the university of idaho. the authors would like to acknowledge the help of dr. tom williams at the university of idaho for sem/xrd expertise. thank you to dr. lee deobald at the university of idaho microchemistry mass spectrometry laboratory and gritman medical services in moscow, idaho, for donation of their ct scanner. thank you to shelby dunn at ucsc paleogenomics lab for performing the dna analysis on the mammoth 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and love, r.l. s-1 supplemental material inventory of the bones supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-2 spinose process: catalog # scan id (if applicable) bone id % intact measurements (length/width; cm) sms001 1-4 vertebrae (portion) 20 sms002 2-2 lumbar vertebrae 80 sms003 2-13 vertebrae (portion) 20 sms004 2-16 sacrum 50 sms005 1-5 atlas 100 sms006 2-12 vertebrae (portion) 10 sms007 1-16 vertebrae (portion) 40 sms008 2-17 vertebrae (portion) 50 sms009 1-2 lumbar vertebrae 60 sms010 1-8 vertebrae (portion) 20 sms011 1-18 vertebrae (portion) 60 sms012 1-11 vertebrae (portion) 40 sms013 1-10 vertebrae (portion) 5 sms014 2-1 vertebrae (portion) 15 sms015 1-20 vertebrae (portion) 10 sms016 1-19 thoracic vertebrae 70 sms017 2-3 vertebrae 55 sms018 1-14 thoracic vertebrae 50 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-3 catalog # scan id (if applicable) bone id % intact measurements (length/width; cm) sms019 1-12 vertebrae (portion) 25 sms020 1-15 vertebrae (portion) 10 sms021 1-7 vertebrae (portion) 5 sms022 2-6 vertebrae 90 ribs: catalog # scan id (if applicable) bone id % intact measurements (length/width; cm) r001 9-21 rib n/a (so far) 26 / 7 r002 rib n/a (so far) 27 / 6 r003 rib n/a (so far) 10 / 4.5 r004 3-22 rib n/a (so far) 16 / 7 r005 3-11 rib n/a (so far) 14 / 9 r006 rib n/a (so far) 13 / 8 r007 3-1 rib n/a (so far) 16.5 / 7.5 r008 rib n/a (so far) 11.5 / 7 r009 rib n/a (so far) 21.5 / 5 r010 rib n/a (so far) 12 / 5 r011 3-25 rib n/a (so far) 15 / 6.5 r012 3-7 rib n/a (so far) 14.5 / 7.5 r013 rib n/a (so far) 10.5 / 4 r014 3-2 rib n/a (so far) 25.5 / 7 r015 rib n/a (so far) 22.5 / 6 r016 9-18 rib n/a (so far) 11.5 / 9 r017 rib n/a (so far) 10 / 5-7 r018 rib n/a (so far) 7.5 / 7.5 r019 rib n/a (so far) 12 / 6 r020 rib n/a (so far) 9 / 3.5 r021 rib n/a (so far) 7 / 4.5 r022 rib n/a (so far) 17 / 4.5 r023 rib n/a (so far) 13 / 5 r024 rib n/a (so far) 17 / 6 r025 rib n/a (so far) 11 / 6 r026 rib n/a (so far) 33 / 4 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-4 catalog # scan id (if applicable) bone id % intact measurements (length/width; cm) r027 rib n/a (so far) 17 / 3.5 r028 9-12 rib n/a (so far) 27 / 3.5 r029 rib n/a (so far) 14 / 3.5 r030 9-6 rib n/a (so far) 33.5 / 4.5 r031 3-5 rib n/a (so far) 33 / 5 r032 9-16 rib n/a (so far) 31 / 5 r033 rib n/a (so far) 14.5 / 3.5 r034 rib n/a (so far) 11 / 3.5 r035 rib n/a (so far) 26 / 4.5 r036 rib n/a (so far) 36.5 / 5.5-4 r037 rib n/a (so far) 29.5 / 5 r038 rib n/a (so far) 27 / 5-4 r039 rib n/a (so far) 17.5 / 4 r040 rib n/a (so far) 9 / 4 r041 3-18 rib n/a (so far) 26 / 5-4.5 r042 3-16 rib n/a (so far) 28.5 / 5.5-4-3 r043 3-12 rib n/a (so far) 34 / 6-5 r044 9-14 rib n/a (so far) 13.5 / 5.5 r045 rib n/a (so far) 19 / 4.5 r046 rib n/a (so far) 9.5 / 5 r047 rib n/a (so far) 19.5 / 5.5-5 r048 rib n/a (so far) 10.5 / 4.5 r049 rib n/a (so far) 24.5 / 4.5-4 r050 rib n/a (so far) 14 / 5-4.5 r051 rib n/a (so far) 11 / 4.5 r052 rib n/a (so far) 11 / 5-4 r053 rib n/a (so far) 9 / 4.5 r054 rib n/a (so far) 46.5 / 3.5-3 r055 rib n/a (so far) 55.5 / 4-3.5 r056 rib n/a (so far) 16 / 7 r057 rib n/a (so far) 21.5 / 8 r058 rib n/a (so far) 23.5 / 4 r059 rib n/a (so far) 10 /3.5 r060 rib n/a (so far) 12 /3 r061 rib n/a (so far) 5 / 4.5 r062 rib n/a (so far) 9.5 / 3.5 r063 rib n/a (so far) 9 / 2.5 r064 rib n/a (so far) 6 / 2.5 r065 rib n/a (so far) 7 / 3 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-5 catalog # scan id (if applicable) bone id % intact measurements (length/width; cm) r066 rib n/a (so far) 6 / 5 r067 rib n/a (so far) 9.5 / 4 r068 rib n/a (so far) 7 / 5 r069 rib n/a (so far) 9 / 3 r070 rib n/a (so far) 5.5 / 3 r071 rib n/a (so far) 16 / 3.5 r072 rib n/a (so far) 13 / 5-4 r073 rib n/a (so far) 13.5 / 3.5 r074 rib n/a (so far) 8 / 4 r075 rib n/a (so far) 6 / 3.5 r076 rib n/a (so far) 6.5 / 3.5 r077 rib n/a (so far) 11 / 3.5 r078 rib n/a (so far) 8 / 3.5 r079 rib n/a (so far) 11 / 3-2.5 r080 rib n/a (so far) 13 / 3 r081 rib n/a (so far) 8 / 2.5 r082 rib n/a (so far) 8 / 3 r083 rib n/a (so far) 4 / 3 r084 rib n/a (so far) 10 / 3.5 r085 rib n/a (so far) 7 / 2.5 r086 rib n/a (so far) 6.5 / 2.5 r087 rib n/a (so far) 7 / 4 r088 rib n/a (so far) 9 / 3 r089 rib n/a (so far) 11.5 / 3.5 r090 rib n/a (so far) 12 / 2.5 r091 rib n/a (so far) 8 / 4 r092 rib n/a (so far) 6 / 2.5 r093 rib n/a (so far) 6 / 3 r094 rib n/a (so far) 7 / 3 r095 rib n/a (so far) 9 / 3.5 r096 rib n/a (so far) 6 / 1.5 r097 rib n/a (so far) 4 / 3 r098 rib n/a (so far) 6.5 / 4 r099 rib n/a (so far) 15.5 / 4.5 r100 rib n/a (so far) 14 / 3.5 r101 rib n/a (so far) 12 / 3.5 r102 rib n/a (so far) 22.5 / 4 r103 rib n/a (so far) 8 / 5 r104 rib n/a (so far) 12 / 4 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-6 catalog # scan id (if applicable) bone id % intact measurements (length/width; cm) r105 rib n/a (so far) 24 / 3.5 r106 rib n/a (so far) 14.5 / 3.5 r107 rib n/a (so far) 11 / 2 r108 rib n/a (so far) 9.5 / 3.5 r109 rib n/a (so far) 9.5 / 3 r110 rib n/a (so far) 8 / 2 r111 rib n/a (so far) 5.5 / 3 r112 rib n/a (so far) 6.5 / 4 r113 rib n/a (so far) 15.5 / 4 r114 rib n/a (so far) 7 / 4.5 r115 rib n/a (so far) 16.5 / 4.5 r116 rib n/a (so far) 10 / 4.5 r117 rib n/a (so far) 17 / 3.5 r118 rib n/a (so far) 9.5 / 4.5 r119 rib n/a (so far) 11 / 4 r120 rib n/a (so far) 10 / 3.5 r121 rib n/a (so far) 8 / 3 r122 rib n/a (so far) 9 / 4 r123 rib n/a (so far) 16.5 / 5.5 r124 rib n/a (so far) 6 / 3.5 r125 rib n/a (so far) 11.5 / 5 r126 rib n/a (so far) 6 / 3 r127 rib n/a (so far) 15.5 / 4 r128 rib n/a (so far) 7 / 2 r129 rib n/a (so far) 10.5 / 4 r130 rib n/a (so far) 5 / 3-2 r131 rib n/a (so far) 11 / 4 r132 rib n/a (so far) 6.5 / 2.5 r133 rib n/a (so far) 9 / 4.5 r134 rib n/a (so far) 4.5 / 3.5 r135 rib n/a (so far) 8 / 3.5 r136 rib n/a (so far) 6.5 / 3.5 r137 rib n/a (so far) 10 / 4 r138 rib n/a (so far) 10 / 3.5 r139 rib n/a (so far) 8.5 / 2.5 r140 rib n/a (so far) 12.5 / 3.5 r141 rib n/a (so far) 11.5 / 4 r142 rib n/a (so far) 13 / 3 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-7 cranium: catalog # scan id (if applicable) bone id % intact measurements (length/width; cm) smc001 11-36 cranium (portion) 15 smc002 11-45 cranium (portion) 15 smc003 11-46 cranium (portion) 15 smc004 11-4 cranium (portion) 15 smc005 11-30 cranium (portion) 95 smc006 11-24 cranium (portion) 95 smc007 11-15 cranium (portion) 15 smc008 11-16 cranium (portion) 5 smc009 11-17 cranium (portion) 5 smc010 11-18 cranium (portion) 2 smc011 11-19 cranium (portion) 20 smc012 11-21 cranium (portion) 10 smc013 11-27 cranium (portion) 15 smc014 11-41 cranium (portion) 5 smc015 11-43 cranium (portion) 10 smc016 11-44 cranium (portion) 10 smc017 11-38 cranium (portion) 10 smc018 11-40 cranium (portion) 10 smc019 11-8 cranium (portion) 2 smc020 11-6 cranium (portion) 10 smc021 11-42 cranium (portion) 10 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-8 catalog # scan id (if applicable) bone id % intact measurements (length/width; cm) smc022 11-35 cranium (portion) 25 smc023 11-12 cranium (portion) 10 smc024 15-1 lower jaw/mandible 80 76.2 / 50.8 smc026 15-2 right tusk 90 228.6 smc027 15-3 (possibly) left tusk 90 smc028 15-1 lower left molar (m1) 100 smc029 15-1 lower right molar (m1) 100 smc030 upper left molar 100 front legs: catalog # scan id (if applicable) bone id % intact measurements (length; cm) ssmfl 1 7_1 ulna 75 66.04 ssmfl 2 7_2 humerus 90 38.10 ssmfl 3 7_3 radius 85 63.50 ssmfl 4 7_4 ulna 30 45.72 ssmfl 5 7_5 ulna 30 59.63 ssmfl 6 7_6 ulna 80 58.42 ssmfl 7 8_1 humerus 90 90.17 ssmfl 8 8_2 humerus 70 46.99 ssmfl 9 8_3 radius 95 50.80 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-9 catalog # scan id (if applicable) bone id % intact measurements (length; cm) ssmfl 10 8_4 radius 45 19.05 ssmfl 11 8_5 radius 50 22.86 ssmfl 12 8_6 humerus 90 20.32 ssmfl 13 8_7 radius 95 21.59 ssmfl 14 8_8 radius 15 10.16 ssmfl 15 8_9 radius 20 20.32 rear legs: catalog # scan id (if applicable) bone id % intact measurements (length; cm) smrl001 4-1 femur(distal) 40 51 smrl002 femur(distal) 50 73 smrl003 4-5 femur 15 45 smrl004 4-6 femur 15 41 smrl005 4-7 femur 15 44.5 smrl006 5-1 tibia 40 30.5 smrl007 tibia 20 33.7 smrl008 5-2 tibia3 40 37 smrl009 5-6 tibia 4 30 34 smrl010 4-8 patella 1 100 15.4 smrl011 5-4 pelvis 1 10 35.6 smrl012 5-3 pelvis 2 15 33.8 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-10 catalog # scan id (if applicable) bone id % intact measurements (length; cm) smrl013 6-6 pelvis 3 10 29.6 smrl014 6-4 pelvis 4 10 28.7 smrl015 5-5 pelvis5 10 26.8 smrl016 6-11 pelvis 6 10 20.3 smrl017 6-12 pelvis 7 5 17.7 smrl018 6-5 pelvis 8 5 18 smrl019 4-2 pelvis 9 5 20.4 smrl020 6-9 pelvis 10 5 14.6 smrl021 5-7 pelvis 11 10 28.3 smrl022 6-13 pelvis 12 5 23 smrl023 6-1 pelvis 13 5 19.5 smrl024 6-10 pelvis 14 5 21 smrl025 6-7 pelvis 15 5 20.5 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-11 forefeet: catalog # scan id (if applicable) bone id % intact measurements length and width; cm) smf009 cuneiform 80 10.5 / 9 smf010 magnum 50 8 / 10.5 smf011 unciform 96 15.5 / 10.5 smf013 trapezium 96 9 / 5 smf014 scaphoid 96 16 / 4 smf016 14-8 cuneiform 98 19 / 7 smf017 14-7 lunar 90 13.5 / 8 smf018 14-11 trapezium 98 9 / 4.5 smf019 14-3 pisiform 98 15 / 7 smf020 14-4 magnum 98 10.5 / 7.5 smf021 14-6 trapezoid 98 11 / 6 hindfeet: catalog # scan id (if applicable) bone id % intact measurements (length and width; cm) smf001 calcaneum 98 24 / 19 smf002 calcaneum 97 24 / 18 smf003 astragalus 65 9 / 7 smf004 navicular 75 13 / 4.5 smf005 external cuneiform 98 10.5 / 6.5 smf006 external cuneiform 96 11 / 7 smf007 internal cuneiform 98 8 / 5 supplemental material: inventory of the bones morrison, k., usachenko n., erdman, j., waters, s., and love, r.l. s-12 catalog # scan id (if applicable) bone id % intact measurements (length and width; cm) smf008 internal cuneiform 96 7.5 / 5.5 smf012 astragalus 98 17.5 / 8 smf015 cuboid 98 14.5 / 5 smf022 navicular 50 11.5 / 5 toes: catalog # scan id bone id % intact measurements (length and width; cm) smf023 14-9 metacarpal 98 18.5 / 6.5 smf024 14-1 metacarpal 90 21 / 5.5 smf025 14-2 metacarpal 96 19 / 6 smf026 10 -44 metacarpal 90 20 / 6 smf027 metacarpal 96 19.5 / 7 assemblage-level structure in morrison formation dinosaurs, western interior, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 5 2018 © 2018 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. assemblage-level structure in morrison formation dinosaurs, western interior, usa john a. whitlock, kelli c. trujillo, and gina m. hanik �eme issue an ecosystem we �ought we knew— �e emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover outcrop of brushy basin member of the morrison formation in southeast utah. photograph by rebecca hunt-foster. i 2018 president paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2018 president-elect peter nielsen peternielsen@utah.gov 801.537.3359 2018 program chair emily mcdermott ekeller@utah.gov 801.537.3389 2018 treasurer zach anderson zanderson@utah.gov 801.538.4779 2018 secretary christopher kravits ckravitsgeo@gmail.com 2018 past president bill loughlin bill@loughlinwater.com 435.649.4005 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental a�airs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt a�olter g�247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual �eld conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. �e uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. a�liated with the american association of petroleum geologists. volume 5 2018 �is is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and �gures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com �omas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors kelli c. trujillo — university of wyoming john foster — museum of moab cary woodru� — university of toronto octavio mateus — universidade nova de lisboa editors geology of the intermountain west an open-access journal of the utah geological association volume 5 2018 9 abstract �e upper jurassic morrison formation is both geographically extensive and well-sampled, making it an ideal candidate for biogeographic analysis at both coarse and �ner scales. historically, however, this has not translated into a consensus on patterns of ecological structure and connectivity, particularly with regard to the characteristic dinosaur faunas. here, we use both traditional (genus richness, alpha and beta diversity) and bipartite network-based (biogeographic connectivity, local endemism, and average occurrence) measures to examine patterns of structure on a per-locality basis. given the broad geographic range of the formation, we subdivide the morrison formation into four discrete regions based roughly on latitude and lithology—north (montana, south dakota, and northern wyoming), west (utah and western colorado), east (central and eastern colorado and southern wyoming), and south (arizona, new mexico and oklahoma). further investigation revealed many coeval sites (ca. 152 ma) in the east and west regions. presence-absence data were also compared using network analysis to determine the presence and content of discrete subassemblages within the larger region-level assemblages. based on our results, we favor reconstructions of the morrison formation as a ‘mosaic’ type environment over most of its depositional history, with patches of open environments interspersed with more closed, forested regions. �is is suggested by relatively low rates of local endemism (patches are consistent in plant and animal structure) and connectivity across the majority of the formation, as well as the recovery of three non-overlapping assemblages dominated by di�erent guilds of herbivorous dinosaurs. assemblage-level structure in morrison formation dinosaurs, western interior, usa john a. whitlock1, kelli c. trujillo2, and gina m. hanik1 1department of science and mathematics, mount aloysius college, cresson, pa 16630; jwhitlock@mtaloy.edu; gmhst4@student.mtaloy.edu 2haub school of environmental and natural resources, �e university of wyoming, laramie, wy 82071; kellitrujillo@icloud.com citation for this article. whitlock, j.a., trujillo, k.c., and hanik, g.m., 2018, assemblage-level structure in morrison formation dinosaurs, western interior, usa: geology of the intermountain west, v. 5, p. 9–22. © 2018 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction �e late jurassic morrison formation (~157-149 ma) of north america represents one of the most extensive mesozoic terrestrial depositional basins yet discovered, covering approximately 1.5 million square miles of territory, although much of the formation remains unexposed (foster, 2003). as a result, the morrison formation has proven to be one of the most productive sources for dinosaur material, with dozens of named taxa inclusive of a wide range of bauplans, body sizes, and ecological habits. despite the paleontological riches, however, little agreement on the basic ecosystem has been reached, with authors variously claiming a dominant conifer forest habitat, xeric plains-type habitats, or a “jurassic savanna” habitat dominated by lush, low-growing vegetation and at least seasonally wet climates, or a mosaic of at least two distinct habitat types. www.utahgeology.org 10 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 here, we show contrasting patterns in distribution between the largest bodied herbivores and all other dinosaurian taxa, and interpret the low degrees of endemism and connectivity as evidence for a ‘mosaic’ type landscape throughout most of the depositional basin represented by the morrison formation. prior studies of broad-scale ecological reconstruction in the morrison formation have primarily been focused on the abundant macroand microfossil paleobotanical evidence. plant fossils representing a diverse �ora of cheirolepidiaceans, conifers, ferns, ginkophytes, horsetails, and podocarpaceans are known throughout the formation (tidwell, 1990; ash and tidwell, 1998; parrish and others, 2004). between the abundance of drought intolerant plants (e.g., ferns, horsetails) and the known abundance of large herbivores (with their attendant forage requirements), some of the original interpretations of the morrison formation paleoenvironment focused on it as a lush, wet �oodplain (tidwell, 1990; ash and tidwell, 1998). additionally, the apparent absence of arrested growth structures in woody remains and the presence of wood-rotting fungi have also been cited as evidence for a generally humid, mesic environment (tidwell and others, 1998). more recently, however, two separate interpretations have taken root. one camp suggests that the paleoenvironment recorded by the morrison formation was xeric or only seasonally wet, with a �ora comprised primarily of herbaceous and lowto mid-height woody podocarpaceaean shrubs; taller woody plants would have been restricted to riparian environments (engelmann and others, 2004; parrish and others, 2004; rees and others, 2004). �is view interprets the paleoenvironment as roughly equivalent to a modern tropical savanna grassland, with ferns and bryophytes occupying the ground-level browse layer currently dominated by grasses. more recently, some authors have presented evidence for the paleoenvironment of the morrison formation as a ‘mosaic,’ either with a matrix of conifer forest dominating interspersed open habitats (gee, 2010; hotton and baghai-riding, 2010), or as a primarily open environment with interspersed woodland environments (whitlock, 2011). in all cases, it seems unlikely that dry-adapted plants such as cheirolepidiaceans would be restricted to riparian lands with wet soils, and indeed the opposite interpretation is now typically accepted (hotton and baghai-riding, 2010). �ere has been some attempt to segregate the morrison formation into ecological regions, such that the northern exposures of the morrison (particularly in montana and south dakota) represent a substantially wetter paleoenvironment than the exposures to the south (parrish and others, 2004; noto and grossman, 2010). montana, in particular, houses some localities reconstructed as a unique depositional environment, dominated by mires, coal swamps, and peat bogs (parrish and others, 2004). palynological evidence also indicates the presence of a more humid environment in the northern extremes with a potentially higher water table as well (hotton and baghai-riding, 2010). �is is corroborated by the more frequent occurrence of semi-aquatic reptiles (e.g., crocodilians, turtles; foster and mcmullen, 2017) in the morrison formation of montana, south dakota, wyoming, and eastern colorado. furthermore, there has been a suggestion of a longitudinal gradient of drainage and precipitation as well (demko and others, 2004; turner and peterson, 2004), with drier margins and a ‘center’ with the majority of standing water in the forms of lakes and wetlands. from the earliest stages of ecological assessment in the morrison formation, a ‘core’ fauna of large diplodocids, stegosaurus, and allosaurus has been recognized, with other taxa appearing with less regularity (dodson and others, 1980a, 1980b), although there has been little consensus on how those faunas have been constructed. more recently, noto and grossman (2010) analyzed the paleoecology of dinosaurs in the morrison formation (and other formations), dividing the localities into six “assemblages” based on geographic proximity and using ecological structure analysis (esa) to identify any potential relationships between the behavior or ecology of the dinosaurs (e.g., body size, locomotor habit) and the regional environment. although they did not make explicit statements about generic constituencies of any inferred communities, they did identify what they termed a “semi-arid” set of assemblages from the latitudinal center of the formation, bounded by a more arid set of assemblages from the northern and southern extremes. �is distinction was largely recognized in the faunas as a function of body size (smaller overall body 11 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 size in the semi-arid environments) and locomotor habit (semi-arid environments were more dominated by bipedal organisms; noto and grossman, 2010). here, we attempt to build on this prior work by examining the morrison formation on a quarry level to try and pull out any signal that might indicate the presence of distinct communities at the generic level. using classical ecological inferences (alpha and beta diversity and shared taxonomic scope) in concert with newer bipartite statistical methods (following sidor and others, 2013), we characterize the dinosaur assemblages at both regional and individual locality scales, and interpret the results in the context of describing the overarching ecological conditions present at the time of morrison formation deposition. methods because the morrison formation incorporates both a large geographic and temporal range, the 291 localities sampled were divided into four regions: north (65 localities), inclusive of localities in montana, south dakota, and northern wyoming (above 43°n); west (72 localities), inclusive of localities in utah and colorado just east of the city of gunnison, colorado (cabin creek [see turner and petersen, 1999] and westward); east (128 localities), inclusive of colorado east of cabin creek and wyoming below 43°n and the lithologically similar snowmass locality (foster and wedel, 2014); and south (26 localities), inclusive of localities in arizona, new mexico and oklahoma (�gure 1). di�erences in recognized members across the formation as well as limitations on the quality of intraformational correlations hamper further subdivision into more de�nitive age units at this time (trujillo, 2006). new 40ar/39ar and u-pb isotope ages, however, identify 28 localities across the east and west regions that are roughly coeval (ca. 152 ma; trujillo and others, 2014, 2015; trujillo and kowallis, 2015). �ese localities are examined independent of the rest of the data set to provide further insight into potential regional di�erences independent of time dilation e�ects. because we are predominantly interested in examining regional patterns of taxonomic structure, we refrain from attempts to group localities into bins of equal number or attempts to �lter localities by alpha diversity and other indicators. taxonomic data was pooled from the paleobiology database (http://fossilworks.org; see supplemental information) and supplemented with additional information from foster (2003). one caveat with using data of this sort is that we are, at best, two steps removed from the original material (collector->compiler->present authors), each step having the potential to introduce errors ranging from incorrect taxonomic assignment to typographic issues. as it is reasonable to assume the general care of our colleagues with regard to data collation, the biggest concern is misidenti�cation of the fossils themselves. dinosaur workers in general and those familiar with the morrison formation speci�cally will no doubt already be aware of the di�culty in correctly assigning many fossil specimens, as well as the potential for “hidden” taxonomic diversity (e.g., galeamopus, “elaphrosaurus;” chure, 2001; carrano and sampson, 2008; tschopp and others, 2015; tschopp and mateus, 2017). while recognizing the potential confounding e�ects of these issues, there is fundamentally little that can be done to resolve them at this level, and thus we note their existence here and calibrate our interpretations accordingly. similarly, we note the potential for taphonomic bias towards larger bodied taxa, which we attempt to mitigate again by limiting our scope to presence-absence rather than abundance. taxonomically unresolved taxa—e.g., “elaphrosaurus”—or records without identi�cation to the genus level were omitted. �e recently proposed generic separation between apatosaurus and brontosaurus (tschopp and others, 2015) is not incorporated into this analysis for reasons of practicality; the records in question predate this proposal, and in lieu of attempting to examine all specimens of apatosaurus in question (some 75 total records composed of untold numbers of individual specimens), we elect to simply continue use of the genus apatosaurus. to examine large-scale trends in connectivity and diversity, alpha diversity (using genus richness), beta diversity (as measured by sørenson’s index, or si), and shared taxonomic scope were calculated using the pooled assemblage data from each major region. sørenson’s index was chosen as a measure of beta diversity vis-à-vis continuity (sensu kole� and others, 2003). importantly, si satis�es the requirement of be12 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 ing sensitive only to proportions of species, not to total number (janson and vegelius, 1981), the latter being a potential issue given the unequal areas and taxonomic compositions of the regions under consideration. to characterize locality-level connectivity, bipartite resampling methods (following sidor and others, 2013) were used to calculate three measures: average occurrences per taxon (interpreted as range size, following sidor and others, 2013), average endemic taxa per locality, and biogeographic connectivity (the number of taxon linkages as a proportion of the maximum possible). each analysis presents a distribution of scores obtained via 1000 bootstrap replicates (see supplemental information for discussion of replicate choice). a welch two-sample unequal variances t-test was used to determine statistical signi�cance. to look for potentially distinct assemblages within the taxonomic samples, co-occurrence and edge matrices were computed in r using the cooccur package (gri�th and others, 2016); resultant networks were analyzed for patterns of generic clustering using gephi (bastian and others, 2009). for the temporal groupings in the east and west regions, localities with good stratigraphic data were correlated with the nearest precise radiometric age by k.c. trujillo. results alpha diversity is consistently high in the north, west, and east regions (21-22 genera) and substantially lower in the south region (10 genera; table 1). sauropod alpha diversity appears to decrease with decreasing latitude, but this trend is not seen in either theropods or ornithischians. in theropods, there appears to be a ‘bulge’ in diversity in a central region (west and east regions combined). beta diversity is highest between the figure 1. map of localities by county, color coded by region. heavy black line indicates approximate geographic extent of the morrison formation (modi�ed from turner and peterson, 2004). see supplemental information for full details. 13 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 north and east regions (si = 83% similarity; table 2), but is also notable between the west and east regions (71%). similarity is lower between the north and west regions (65%), and is lowest between the south region and all others (56-58%), with the north and south being most di�erent. �is trend is generally conserved when the samples are restricted by taxonomic group, with the exception of sauropods, where similarity is highest between the south region and the west and east regions (83%), although again the north and south are least similar (63%). shared taxonomic scope is reasonably high in the morrison formation (�gure 2). �is is exempli�ed by the large-bodied sauropods, where 5 of 12 taxa occur in all four regions and 8 of 12 occur in at least two. �e regionally endemic taxa, dyslocosaurus, dystrophaeus, kaatedocus, and suuwassea, are also known from only a single locality each, which suggests that their rarity is either a function of their rarity in the fauna as a whole or the rate at which they are misidenti�ed by collectors, or both. �eropod shared taxonomic scope is less robust, with only two of the largest bodied taxa (allosaurus and ceratosaurus) occurring in all four regions, and two others (the very large torvosaurus and the small coelurus) occurring in three. nearly half (4/10) of theropod taxa are known from a single region only, and there is the possibility of a great many more singleton taxa that would increase this total (e.g., any potential taxa subdivided from the catch-all genus “elaphrosaurus,” koparion). �ese regionally endemic theropods are invariably small-bodied. ornithischian-shared taxonomic scope is somewhat intermediate between sauropods and theropods, in that regional endemism is high (4/10 taxa), as in theropods, but as many taxa occur in at least three regions (4/10), a distribution somewhat similar to that seen in sauropods. two taxa (camptosaurus and stegosaurus) are known from all four regions. for the 152 ma time bin, absolute taxonomic diversity is highest in the east region (18 taxa vs. 12 taxa in the west). beta diversity is generally high (0.66), but this is largely driven by the sauropods (1.0). �eropod (0.5) and ornithischian (0.5) assemblages are both relatively less similar. �e di�erence in taxonomic scope is largely due to the absence of many relatively small bodied taxa, particularly theropods (e.g., coelurus) in the west. bipartite analyses result in signi�cantly di�erent (p <0.0001; t and df reported in supplemental information) distributions of all three characteristics (average occurrence, average endemics, biogeographic connectivity) for all regions, excluding only biogeographic connectivity between north, east, and west regions (1 ≤ p ≤ 0.9994). despite this statistical signi�cance, certain characteristics of certain regions appear more similar to each other than others. as noted, biogeographic connectivity is statistically identical in the north, east, and west regions (�gure 3), and is signi�cantly lower total generic diversity sauropods only theropods only ornithischians only north 22 11 4 7 west 21 7 9 5 east 21 7 7 7 south 10 5 3 2 152ma east 18 6 5 7 152ma west 12 5 3 4 table 1. alpha diversity (generic richness) for each of the four study regions. north west east south al l t ax a north west 65% east 83% 71% south 56% 58% 58% north west east south sa ur op od s north west 67% east 78% 71% south 63% 83% 83% north west east south th er op od s north west 67% east 73% 80% south 57% 36% 40% north west east south or ni th is ch ia ns north west 62% east 86% 62% south 44% 50% 44% table 2. beta diversity (sørenson’s index) for each of the four study regions. 14 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 than in the south region, where connectivity is highest. despite the lower connectivity scores, locality-level endemism is essentially zero in the central and north regions, with an order of magnitude higher rates recorded in the south region. average occurrence (ao) scores do increase as the number of localities sampled increases, but none are directly limited by the number of localities (i.e., all ao scores are less than 1/4 of the number of sampled localities). time-restricted samples show the same general pattern as the broader samples, with the exception of an unusually high connectivity in the east 152 ma time bin (�gure 3). assemblage-level structure in the morrison formation is generally built around a consistent “core” of taxa (allosaurus, apatosaurus, camarasaurus, diplodocus, and stegosaurus) that are highly connected with the majority of other taxa, and might be considered the ‘typical’ morrison fauna (dodson and others, 1980a, 1980b). camptosaurus and ceratosaurus are also commonly found co-occurring with most other taxa. larger herbivores (i.e., sauropods, camptosaurus) and some large predators (i.e., allosaurus, ceratosaurus) display little preference with regard to co-occurring taxa, although smaller carnivores (coelurus, tanycolagreus) and many other large predators (fosterovenator, stokesosaurus, torvosaurus) do appear to show some segregation. �ese patterns are most distinct in the central region (�gure 4). �e most locality level segregation is found among the mediumto small-sized ornithischians in the central region, which appear to sort themselves into three general groups based upon non-overlapping exemplar taxa: (1) a ‘mymoorapelta’ group, which co-occurs with no other smaller herbivores, only large sauropods; (2) an ’othnielosaurus’ group, which co-occurs with camarasaurus, camptosaurus, drinker, nanosaurus, and stegosaurus; and (3) a ‘dryosaurus’ group, consisting of apatosaurus, camarasaurus, camptosaurus, diplodocus, gargoyleosaurus, and stegosaurus. in the north region, where connectivity is relatively high, dryosaurus and othnielosaurus do co-occur in a single locality (howe-stevens, see supplemental information); the remaining combined 10 occurrences (as measured figure 2. shared taxonomic scope between the four regions of interest with distribution broken down by individual genera. 15 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 by presence/absence) in the north region and all 15 occurrences in the central region are mutually exclusive. othnielosaurus is a relatively rare taxon, but it is substantially more common in the northern morrison (�ve localities vs. two each in the west and east). coelurus is found exclusively with the othnielosaurus assemblage, and tanycolagreus is found exclusively with the dryosaurus assemblage, although the two taxa do co-occur (in the absence of both dryosaurus and othnielosaurus) in the west region. within the 152 ma time bin, we observe this segregation in the east (�gures 4e and 4f), but not in the west figure 3. box and whisker plots representing the results of the bipartite statistical analyses for each sampled region as well as the 152 ma sample of east and west. average occurrence represents the average number of localities a randomly selected species would occur in. average endemics reports the average number of per-locality endemic taxa recovered. biogeographic connectivity measures the proportion of recovered connections (shared taxa) as a function of the total potential connections. numbers reported represent distributions over 1000 replicates. 16 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 figure 4. network diagrams illustrating co-occurrence between genera in the central morrison formation. (a) network diagram of the north region, with conjoined dryosaurus and othneilosaurus network highlighted. (b) network diagram of the west region, with mymoorapelta assemblage highlighted. (c) network diagram of the west region, with dryosaurus assemblage highlighted. (d) network diagram of the west region, with othnielosaurus assemblage highlighted. (e) network diagram of the east region, with dryosaurus assemblage highlighted. (f) network diagram of the east region, with othnielosaurus assemblage highlighted. abbreviations: al = allosaurus; ap = apatosaurus; ba = barosaurus; br = brachiosaurus; ca = camarsaurus; ce = ceratosaurus; co = coelurus; cp = camptosaurus; di = diplodocus; dr = drinker; ds = dyslocosaurus; dt = dystrophaeus; dy = dryosaurus; fo = fosterovenator; fr = fruitadens; ga = gargoyleosaurus; gp = galeamopus; ha = haplocanthosaurus; he = hesperosaurus; ka = kaatedocus; ma = marshosaurus; my = mymoorapelta; na = nanosaurus; or = ornitholestes; ot = othneilosaurus; sg = stegosaurus; st = stokesosaurus; su = suuwassea; ta = tanycolagreus; to = torvosaurus. 17 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 (�gure 4d). furthermore, dryosaurus does not co-occur with any other taxa in this sample and so provides no information relevant to its participation in discrete assemblages. aside from a slightly lower taxonomic diversity, the 152 ma time bin is representative of the regions as a whole with regard to taxonomic assemblages. discussion diversity metrics (genus richness, si) generally suggest similar diversity levels in localities in the northern and central parts of the morrison formation, with the greatest diversity occurring in the central region. regional interconnectivity appears to be tied to some combination of body size and ecological habit. large-bodied herbivores (such as sauropods, and certain ornithiscians like camptosaurus) tend to occur in more regions overall (lower rates of endemism), and have a wider individual distribution (weighted towards occurrence in four regions over occurrence in two). camptosaurus is itself potentially cosmopolitan not simply within the morrison formation, but also may appear in coeval basins in europe as well (foster, 2013). �is would be a substantial geographic range for a single taxon, although representatives of other morrison formation genera such as allosaurus, ceratosaurus, stegosaurus, and torvosaurus have been reported from iberia (mateus, 2006; mateus and others, 2006; escaso and others, 2007; hendrickx and mateus, 2014). whether this is a true distribution or simply a matter of taxonomic ‘lumping’ (e.g., ‘elaphrosaurus;’ carrano and sampson 2008) is unclear, however. �ere does not appear to be a clear size-distribution relationship for theropods, as in general largeand small-bodied individuals are recovered as both widely distributed (e.g., allosaurus, coelurus) and regionally endemic (e.g., saurophaganax, stokesosaurus). �is may be due to increased competitive pressures facing carnivores, access to appropriate prey, and/or reinforcing behaviors such as territorialism. we agree with foster (2000) in that we �nd little evidence to suggest drastic di�erences in environment with latitude, particularly with regard to the northern morrison formation as an environmental outlier, as has been previously suggested (parrish and others, 2004; hotton and baghai-riding, 2010; whitlock, 2011). sauropod diversity does decline with declining latitude, but the di�erences between the north and central regions are not substantial and are primarily driven by the presence of two north region endemics, kaatedocus and suuwassea. �ese two taxa are both very recently described (harris and dodson, 2004; tschopp and mateus, 2013) and are represented by a single specimen each; consequently, it is not implausible that additional specimens from other regions are either undiscovered or misidenti�ed in existing collections. bipartite statistics predict greater provincialism when biogeographic connectivity and range sizes are small and average endemism is high (sidor and others, 2013). in the south region, we �nd agreement between range size and endemism—both of which predict a high degree of provincialism—but disagreement with biogeographic connectivity, which would predict a very cosmopolitan distribution of taxa. similarly, range sizes and endemism predict a more cosmopolitan distribution in the north, east, and west regions, but the comparatively lower biogeographic connectivity in those regions predicts provincialism. some of these e�ects may be attributable to time dilation e�ects; i.e., substantial turnover in environmental structure may result in these statistics capturing discordant e�ects due to overlaying di�erent environmental structures on top of each other, both in physical space (as a function of deposition) and in ‘statistical space’ (as a function of data pooling). however, we postulate that these results may be still interpretable due to a highly fractured environments. extremely patchy ecosystems would result in smaller ranges and increased regional endemism. if substantial corridors connecting similar patches did not exist (or were outside the depositional area recorded), these patches would be isolated from each other in the fossil record, which is consistent with a low per-locality connectivity measurement, as observed. we do interpret some degree of connectivity, largely driven by the cosmopolitan sauropod fauna, as complete balkanization of depositional environments has been shown to correspond to even lower degrees of connectivity than observed here (sidor and others, 2013). in the case of the widely distributed taxa (sauropods, large theropods like allosaurus), it seems likely that their large size would 18 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 have made them largely immune to barriers, inclusive of larger patches of less suitable habitat. in modern ecosystems, large rivers present barriers to dispersal for many organisms, including such varied groups as african bu�alo (naidoo and others, 2012), elephants (robertson, 2013), lions and other african carnivores (cozzi and others, 2013), wolves (blanco and others, 2005), passerine birds (ayres and clutton-brock, 1992; hayes and sewlal, 2004; but see gascon and others, 2000), and primates (goodman and ganzhorn, 2004; harcourt and wood, 2012), although there is some evidence that larger bodied taxa are less a�ected, particularly when the river in question is small or seasonally low (cozzi and others, 2013; robertson, 2013). �e river itself does not need to be impassable to be a barrier; in many cases the ecosystem on either side of the river is signi�cantly di�erent as to be a barrier unto itself (oates, 1998; meijard and groves, 2006). a more continuous environment would result in a signal with low regional endemism and high connectivity, as there would be no barrier regions where a variety of ecomorphs would be less likely to occur or be preserved. when restricted to localities deposited at or near 152 ma, however, our results paint a more consistent picture. �e west region scores lower in range size and connectivity and higher in endemism than the east, all of which suggest that the west was more provincial at this time. �is fragmentation supports the idea that there was no ‘rain shadow’ e�ect caused by coeval and preceding upli� and erosion of ri� shoulders associated with a magmatic arc west of the morrison formation’s depositional area (turner and fishman, 1998; dickinson, 2006). such upli� could have potentially created a ‘rain shadow’ on the leeward basin, resulting in an arid region without signi�cant permanent riparian structure. due to the high rate of sediment deposition attributable to erosion from those highlands (turner and fishman, 1998), however, it seems unlikely that there was a signi�cant rain shadow e�ect on the west region at this time (turner and peterson, 2004). in addition, a rain shadow would likely have resulted in a relatively homogenous, ‘savanna’ type environment without major river systems to serve as dispersal barriers for smaller dinosaurs (ash and tidwell, 1998; parrish and others, 2004). instead, the apparently robust riparian structure in that region may well have provided signi�cant (if ephemeral on geologic time scales) barriers to dispersal in the form of major river systems and alkaline-saline wetlands (e.g., “lake” too’di’chi’ in southwest colorado and southeast utah; fishman and others, 1995; turner and peterson, 2004), which could potentially have limited the range sizes and regional distribution of smaller dinosaurs (e.g., smaller theropods, ornithischians). �e riparian structure would have been less restrictive to the extremely large sauropods and larger theropods like allosaurus, which do indeed have a more cosmopolitan distribution. range size is also strongly correlated with body size in extant mammals (mcnab, 1966; swihart and others, 1988), largely as a function of energetics, which would further explain the consistently cosmopolitan distribution of these larger organisms. �e larger range sizes and degree of connectivity overall in the east, however, suggest greater environmental homogeneity, consistent with reconstructions of this region dominated by a broad alluvial plain (turner and peterson, 2004). �erefore, we favor the nuanced interpretation many modern studies have put forward, such that the geographically large region recorded by the morrison formation likely included a diverse array of habitats and habitat structures inclusive of both drier, ‘savanna’-type environments and wetter, riparian-dominated environments, consistent with regional tectonic and eustatic changes at the time. however, the patchiness (or ‘mosaic’ distribution) of these environments as well as the e�ects of time dilation make direct comparisons to modern ecosystems (e.g., ‘savanna’) somewhat problematic, particularly as the geographic scale of the study increases. �e interpretation of our bipartite analysis results is consistent with the network analysis which recovered three distinct ornithischian assemblages in the central region—a ‘mymoorapelta’ assemblage, a ‘dryosaurus’ assemblage, and an ‘othnielosaurus’ assemblage—as well as with prior work (noto and grossman, 2010). �e mymoorapelta group appears to be more ‘open’ adapted, based upon the feeding preferences of the locally dominant diplodocid sauropods (stevens and parrish, 1999; upchurch and barrett, 2000; stevens and parrish, 2005; whitlock, 2011), although the mymoorapelta type locality does feature abundant evidence for conifers 19 assemblage-level structure in morrison formation dinosaurs, western interior, usa whitlock, j.a., trujillo, k.c., and hanik, g.m. geology of the intermountain west 2018 volume 5 (tidwell and others, 1999; hotton and baghai-riding, 2010). �e dryosaurus and othnielosaurus assemblages both contain more closed-adapted genera, including a wide variety of other medium-sized ornithischians, but they di�er regarding sauropod content. dryosaurus assemblages include both diplodocids and the midto high-browser camarasaurus (fiorillo, 1998; upchurch and barrett, 2000; whitlock, 2011); othnielosaurus assemblages are strongly associated with camarasaurus. �is suggests the preference of dryosaurus for edge environments (where open and closed adapted taxa would be expected to intermingle) and closed environments for othnielosaurus. as othnielosaurus is reconstructed as substantially smaller than dryosaurus (e.g., farlow and others, 2010), this is a reasonable assumption to make. �ere is some evidence for habitat preference in theropods as well, with many large-bodied taxa appearing to prefer open environments and mediumto small theropods choosing closed or edge environments. �is association is not as strong, however, suggesting that habitat choice is more labile. �is is consistent with observations of modern animals, which o�en display variance in habitat preference largely dependent on nonbiotic environmental factors such as local temperature (may and others, 2010; van beest and others, 2012). conclusions a picture of the morrison formation paleoecosystem emerges as a mosaic of diverse communities and environmental structures in a massive, long-lived depositional basin, regionally dominated by distinct populations of relatively small-bodied ornithischian herbivores and theropod carnivores, with widespread and potentially migratory populations of large-bodied sauropods and certain other exemplar taxa such as allosaurus and camptosaurus. where temporal restriction is possible, distinct regional di�erences emerge between the western and eastern regions of the basin, consistent with coeval tectonic events, such that upli� and extensive riparian development to the west created greater habitat fractionation and provincialization in dinosaurian assemblages. direct comparisons to modern ecosystems (e.g., use of analogs such as ‘savanna’) are likely of limited application, at least at this geographic scale. �e apparent patchiness of much of the morrison basin suggests a ‘mosaic’ type environment, and as such we must look to di�erent approaches, such as this one, to gain a better understanding of the community-level dynamics in the megafauna. acknowledgments we thank c.v. beightol (university of washington), c.a. sidor (university of washington), and d. a. vilhena (cedar ai) for discussion and technical assistance with bipartite methods. j.r. foster (museum of moab), c.r. noto (university of wisconsin-parkside), and m. j. wedel (western university of health sciences) provided helpful commentary that greatly improved a previous dra�. j.r. foster, o. mateus (universidade nova de lisboa), and d.c. woodru� (university of toronto) co-sponsored (with k.c.trujillo) the morrison formation symposium that provided the impetus for this project. references ash, s.r., and tidwell, w.d., 1998, plant megafossils from the brushy basin member of the morrison formation near montezuma creek trading post, southeastern utah: modern geology, v. 22, p. 321–339. ayres, j.m., and 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microwear analyses: plos one, v. 6, no. 4, p. e18304. descriptive statistics mean, variance and standard deviation. average occurrence average endemics biogeographic connectivity m var sd m var sd m var sd north 10.43 0.12 0.35 0.0046 7.12e-05 0.00844 0.15 3.12e-05 0.00559 west 11.48 0.144 0.38 0.0014 1.78e-05 0.00422 0.15 2.78e-05 0.00527 east 18.44 0.25 0.50 1.60e-05 1.28e-07 0.00036 0.14 1.59e-05 0.00399 south 5.43 0.11 0.33 0.047 0.0013 0.03606 0.18 0.00019 0.01378 152ma east 3.85 0.033 0.18166 0.26 0.0092 0.09592 0.19 0.00015 0.01225 152ma west 2.327 0.0311 0.18 0.377 0.0136 0.11682 0.147 0.000383 0.01958 p, t-statistic and df for for welch's unequal variances t-test. average occurrence p t df north-west <0.0001 64.27 1984 north-east <0.0001 415.02 1788 north-south <0.0001 346.44 1991 west-east <0.0001 350.46 1864 west-south <0.0001 380.13 1959 east-south <0.0001 686.74 1730 152ma east-west <0.0001 205.161 1996 average endemics p t df north-west <0.0001 10.72 1469 north-east <0.0001 17.16 1002 north-south <0.0001 32.75 1123 west-east <0.0001 10.33 1013 west-south <0.0001 37.78 1026 east-south <0.0001 41.27 999 152ma east-west <0.0001 31.149 1850 biogeographic connectivity p t df north-west 1 0 999 north-east 0.9995 0.0006 999 north-south <0.0001 67.08 1998 west-east 0.9994 0 999 west-south <0.0001 64.3 1285 east-south <0.0001 88.17 1165 152ma east-west <0.0001 68.9153 1658 diversity alpha diversity & sts sorenson's similarity index n w e s 152e 152w apatosaurus 1 1 1 1 1 1 shared barosaurus 1 1 1 1 1 1 all spods orniths tpods diplodocus 1 1 1 1 1 1 nw 14 6 4 4 galeamopus 1 1 1 ne 17 7 6 4 camarasaurus 1 1 1 1 1 1 ns 9 5 2 2 haplocanthosaurus 1 1 ew 15 5 4 6 supersaurus 1 1 es 9 5 2 2 brachiosaurus 1 1 1 1 1 1 ws 9 5 2 2 dyslocosaurus 1 suuwassea 1 si kaatedocus 1 n w e s dystrophaeus 1 n stegosaurus 1 1 1 1 1 1 all w 65.1162790698 camptosaurus 1 1 1 1 1 1 e 82.9268292683 71.4285714286 drinker 1 1 1 s 56.25 58.064516129 58.064516129 dryosaurus 1 1 1 1 1 nanosaurus 1 1 1 othnielosaurus 1 1 1 1 w 66.6666666667 gargoyleosaurus 1 1 spods e 77.7777777778 71.4285714286 hesperosaurus 1 s 62.5 83.3333333333 83.3333333333 fruitadens 1 1 mymoorapelta 1 1 w 61.5384615385 allosaurus 1 1 1 1 1 1 ornith e 85.7142857143 61.5384615385 ceratosaurus 1 1 1 1 1 1 s 44.4444444444 50 44.4444444444 coelurus 1 1 1 1 saurophaganax 1 w 66.6666666667 fosterovenator 1 tpods e 72.7272727273 80 ornitholestes 1 1 s 57.1428571429 36.3636363636 40 stokesosaurus 1 tanycolagreus 1 1 1 marshosaurus 1 torvosaurus 1 1 1 1 all 22 21 21 10 18 12 sauropods 11 7 7 5 6 5 orniths 7 6 7 2 7 5 theropods 4 8 7 3 5 2 all north 65 localities south 26 localities east 126 localities west 74 localities north 65 localities pdbd # t&p 99 # locality name age state county member apatosaurus barosaurus diplodocus galeamopus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus paleodb 50714 horse coulee, amhn 03-30 mt big horn -0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38866 rattlesnake ridge mt carbon -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 paleodb 49624 mt-2 upper strickland creek mt park -0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 69890 mt-1 mother's day mt carbon -0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 t&j quarry mt gallatin -1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 wittecombe's ranch mt wheatland -0 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49625 sd-1 bear butte sd meade -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49630 sd-2 fuller's 351, st. onge sd lawrence -1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49633 parker's mystery sd fall river -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57905 sd-3 piedmont butte, hatch ranch, barosaurus type, sdsm v9140 sd meade -0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 132242 ahmn quarries, sturgis area sd meade -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 132243 usnm quarry, sturgis area sd meade -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49631 sd-4 wonderland, piedmont sd meade -0 1 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57904 sd-5 wonderland north sd meade -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 46468 wy-61 big al site wy big horn -0 0 1 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 big butte wy big horn 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 smithsonian quarry 1 wy big horn 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 dyer ranch 1 and 2 wy big horn 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 freezeout hills general wy big horn 0 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 57893 freezeout hills quarry 4 wy big horn 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57894 freezeout hills quarry 6 wy big horn 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57895 freezeout hills quarry l wy big horn 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 freezeout hills quarry n wy big horn 1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 paleodb 57896 freezeout hills quarry o wy big horn 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 46460 wy-62 howe quarry wy big horn -1 1 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 46462 howe quarry 2, sauriermuseum wy big horn -0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 paleodb 46465 howe-stephens quarry wy big horn -1 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 1 0 0 0 0 lake's quarry wy big horn 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 paleodb 46469 spring hill, howe ranch wy big horn -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55333 fox mesa wy big horn -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 matt quarry wy big horn 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 ninemile hill wy big horn 0 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55323 ?reopened by c. weege 1992? ninemile quarry (amnh), nine mile crossing, nine mile quarry wy big horn -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 reed's quarry 1.5 wy big horn 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 reed's quarry 5 wy big horn 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 reed's quarry 7 wy big horn 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 reed's quarry 12 wy big horn 0 0 1 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 62561 red canyon ranch, hope college reu wy big horn -0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 13214 freeze out mtns ks expedition wy converse -0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 74664 jimbo quarry 2a wy converse -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 paleodb 74665 jimbo quarry 2b wy converse -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58511 blacktail creek wy crook -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 lightning rod butte wy crook 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 paleodb 49634 inyan kara creek sdsm v9137 wy crook -0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56167 little houston, mammal quarry sdsm v941 wy crook -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49636 wy-11 little houston, main quarry sdsm v9138 wy crook -1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 warm springs ranch i wy crook 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56165 mile 175, sdsm v931 wy crook -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 paleodb 49637 sdsm v9139 wy crook -0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22650 bs quarry + s quarry, warm springs ranch wy hot springs -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22678 rb quarry, warm springs ranch wy hot springs -0 1 1 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 68100 fs quarry, foot site, warm springs ranch wy hot springs -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55320 si unit 1, warm springs ranch wy hot springs -1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 142334 brown's ranch (elk mountain) wy johnson -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55349 buffalo quarry, smith ranch wy johnson -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 176983 wy-72 poison creek quarry 1 wy johnson -1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 176984 wy-73 poison creek quarry 2 wy johnson -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 176985 wy-74 poison creek quarry 3 wy johnson -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58510 wy-71 poison creek wy johnson -1 0 1 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 paleodb 48565 red fork powder river quarry a wy johnson -0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58509 red fork powder river quarry b wy johnson -1 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 sheridan college allosaurus wy johnson 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 sheridan college 1 wy johnson 1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 sheridan college 2 wy johnson 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 106532 lance creek area, dyslocosaurus type wy niobrara -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 paleodb 58508 paint creek wy park -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 126540 dana wy washakie -1 1 1 0 1 0 1 1 1 1 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 0 paleodb 58507 ku camarasaurus wy weston -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 south 26 localities pdbd # t&p 99 # locality name age state county member apatosaurus barosaurus diplodocus galeamopus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus paleodb 70024 pinon az not reported 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49338 ok-1 stovall's pit 1, omnh quarry 1, kenton (omnh v92) ok cimarron brushy basin 1 1 1 1 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 49598 ok-4 stovall's pit 8, kenton ok cimarron brushy basin 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49596 ok-2 stovall's pit 5, kenton (omnh) ok cimarron not reported 1 0 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49597 ok-3 stovall's pit 6, kenton ok cimarron not reported 1 0 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56421 stovall's pit 3a, kenton ok cimarron not reported 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56422 stovall's pit 9, kenton ok cimarron not reported 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 51990 hagan basin, nmmnh locality l-210 nm sandoval brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38872 lee acres, nmmnh l-369 nm sandoval brushy basin 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 119021 mcconnell i nm sandoval brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22717 peterson quarry, nmmnh l-3282, ete locality 1593 nm bernalillo brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 68099 nm-3 san ysidro camarasaurus, nmmnh l-555, ridby's camarasaurus nm sandoval brushy basin 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 san ysidro 2 nm sandoval 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38871 nmmnh l-3285 nm sandoval brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38867 nmmnh l-3281 nm union brushy basin 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 51992 nm-4 seismosaurus quarry, nmmnh locality l-344 nm sandoval jackpile sandstone 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57910 nm-1 acoma site nm cibola not reported 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 36265 suwanee peak nm cibola not reported 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 boney canyon nm cibola 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 concho springs nm cibola 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 bull canyon nm guadalupe 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 exeter nm union not reported 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 51991 hagan basin, nmmnh locality l-211 nm sandoval recapture 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 quay county nm quay 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 blue peak nm mckinley 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 84308 section 19 mine nm mckinley salt wash 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 east 126 localities age pdbd # t&p # locality name state county member apatosaurus barosaurus diplodocus galeamopus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus garden of the gods co el paso -0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cleveland quarry co fremont -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 paleodb 48127 cope quarry 1, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48128 cope quarry ii, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48129 cope quarry iii, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48130 cope quarry iv, cope's nipple, saurian hill co fremont -0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48146 cope quarry v, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48147 cope quarry vi, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48148 cope quarry vii, cope's nipple, saurian hill co fremont -0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48149 co-1 cope quarry viii, the fort, cam quarry no. 2 co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48153 cope quarry xiv co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48158 co-76 cope quarry xv co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48154 co-71 copequarry xii co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48155 co-5 delfs co fremont -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 paleodb 48163 co-6 deweese slightly younger than 152.29 ± 0.27 ma co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48156 co-72 egg gulch co fremont -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 eric's tooth co fremont 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39377 co-4 felch quarry 2 co fremont -0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48164 greg's bone garden park slightly younger than 152.29 ± 0.27 ma co fremont -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48170 co-75 kenny's stegosaurus, garden park co fremont -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48160 co-7 kessler's slightly older than 152.29 ± 0.27 ma co fremont -0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48162 co-8 lindsey quarry, garden park slightly younger than 152.29 ± 0.27 ma co fremont -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48168 lucas's site, garden park co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 28366 co-3 marshfelch quarry, garden park co fremont -1 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 paleodb 48172 co-73 meyer site 1, garden park co fremont -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48171 co-73 meyer site 2, garden park co fremont -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48169 co-74 meyer site 3, garden park co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 meyer's pump house co fremont 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 sauropod quarry co fremont 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 paleodb 48161 co-11 small quarry, garden park slightly older than 152.29 ± 0.27 ma co fremont -1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48166 co-09 valley of death, garden park co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 70026 wilson creek co fremont -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 66909 alameda parkway morrison dinosaur site co jefferson -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39376 dinosaur ridge, lake's quarry 8 co jefferson -1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 lakes quarry 1 co jefferson 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 13341 lakes quarry 10 co jefferson -1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 28382 lakes quary 5, beckwith quarry co jefferson -0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 horsetooth co larimer 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 70029 masonville co larimer -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 purgatoire river co las animas 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 70030 villegreen co las animas -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 webster park co park -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 164787 gordon-bramson-brothers snowmass co pitkin -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 los ochos mine co saguache 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 heeney site co summit 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 amnh 550 wy albany 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55486 wy-42 bernice wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55487 wy-44 bertha between 157 and 152.51 ± 0.47 ma, closer to 157 wy albany -1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22648 wy-78 bone cabin slightly older than 152.51 ± 0.47 ma wy albany -1 0 1 1 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 49577 wy-79 bone cabin quarry west slightly older than 152.51 ± 0.47 ma wy albany -1 1 1 0 1 1 1 1 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 boris quarry wy albany 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 177492 breakfast bench wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 brown quarry a wy albany 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39372 brown quarry b wy albany 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39373 brown quarry c wy albany -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39374 brown quarry d wy albany -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 brown quarry g wy albany 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cam bench wy albany 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57902 carnegie quarry 4, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 142337 carnegie quarry 5, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 142335 carnegie quarry a, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 142336 carnegie quarry b, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 52815 carnegie quarry c, sheep creek wy albany -1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 13352 wy-91 carnegie quarry d wy albany -1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57897 carnegie quarry d(3), sheep creek wy albany -0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 52816 carnegie quarry e, sheep creek wy albany -1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57898 carnegie quarry f, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57899 carnegie quarry g, sheep creek wy albany -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57900 carnegie quarry j, sheep creek wy albany -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57901 carnegie quarry k, sheep creek wy albany -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48837 carnegie quarry n, sheep creek wy albany -1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 cassiopeia quarry wy albany 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 74000 como bluff (amnh 222) bone cabin? slightly older than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 168056 como bluff (amnh 223) bone cabin? slightly older than 152.51 ± 0.47 ma wy albany -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cope's como 1 wy albany 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cope's como 3 wy albany 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cope's como 4 wy albany 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cope's como 5 wy albany 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 convention site wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 drinker quarry wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 47065 wy-86 east camarasaurus 1993 (bcq) slightly older than 152.51 ± 0.47 ma wy albany -0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 ep thompson wy albany 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 haystack quarry wy albany 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 jeff p wy albany 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49628 wy-22 louise wy albany -1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 mummy wy albany 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49627 wy-39 nail quarry older than 152.51 ± 0.47 ma wy albany -1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56654 wy-82 ninemile hill very close to 152.51 ± 0.47 ma wy albany -0 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 okie wy albany 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49629 op-kat wy albany -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 pat m wy albany 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39368 wy-17 reed's quarry 10 slightly younger than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39369 wy-18 reed's quarry 11 wy albany -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39253 wy-46 reed's quarry 13 between 157 and 152.51 ± 0.47 ma, closer to 157 wy albany -0 0 1 0 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 39371 wy-16 reed's quarry 14 wy albany -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39339 wy-23 reed's quarry 2 slightly older than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39340 wy-20 reed's quarry 3 wy albany -0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39347 wy-19 reed's quarry 8 wy albany -0 0 1 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39431 quarry 9 1968-1970 152.51 ± 0.47 ma wy albany -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57903 reed's quarry r wy albany -1 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55330 red mountain wy albany -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 13212 wy-21 reed's quarry 1 wy albany -1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39342 wy-40 reed's quarry 4 wy albany -0 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39346 wy-28 reed's quarry 7, three trees wy albany -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 12816 wy-15 reed's quarry 9 152.51 ± 0.47 ma wy albany -0 0 0 0 1 1 1 1 0 1 0 0 0 0 1 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 regina quarry wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55483 stego 99 very close to 152.51 ± 0.47 ma wy albany -0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 two thigh wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 weege boys wy albany 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 75453 wy-92 zane quarry, sheep creek wy albany -1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 73998 aurora quarry 3 como bluff wy carbon -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58512 dyer ranch quarry 1 wy carbon -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58513 dyer ranch quarry 2 wy carbon -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57893 freezeout hills quarry 4 wy carbon -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57894 freezeout hills quarry 6 wy carbon -1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57895 freezeout hills quarry l wy carbon -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57896 freezeout hills quarry o wy carbon -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55484 graff ranch (matt quarry) between 157 and 152.51 ± 0.47 ma, closer to 157 wy carbon -0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39337 wy-27 lakes' 1a, big canyon wy carbon -0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38884 wy-83 meilyn quarry between 157 and 152.51 ± 0.47 ma, closer to 157 wy carbon -0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39338 wy-30 quarry 1.5 wy carbon -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39344 wy-26 quarry 5 wy carbon -0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39370 wy-29 robber's roost (reed's q 12) wy carbon -0 0 1 0 1 1 0 1 0 1 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 74663 alcova lake dave's othnielia (cottonwood creek 1) wy natrona -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 allen's alto wy natrona 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cottonwood creek quarry 2 wy natrona 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cottonwood creek quarry 3 wy natrona 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48557 stegosaurus longispinus type locality, alcova wy natrona -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 west 74 localities pdbd # t&p # locality name age state county member apatosaurus barosaurus diplodocus galeamopus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus paleodb 52872 middle park co grand -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 70027 radium co grand -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 blue mesa co gunnison brushy basin 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38883 co-49 dino cove 151.43 ± 0.36 ma co gunnison brushy basin 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 154925 dinosaur beach 151.43 ± 0.36 ma co gunnison brushy basin 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 154924 northern dinosaur beach 151.43 ± 0.36 ma co gunnison brushy basin 1 0 1 0 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49621 co-48 cabin creek co gunnison salt wash 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56586 co-27 bollan stegosaur site rabbit valley co mesa -0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 70032 co-55 cactus park (byu 681) co mesa -1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 35293 co-56 dominguez/jones co mesa brushy basin 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49652 co-33 eriksen ceratosaur fpa 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22708 fpa quarry 4 co mesa brushy basin 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 71476 fpa general site co mesa brushy basin 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 92360 fpa george's "coelurosaur" site, lacm loc. 5576 co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 fpa stego knoll co mesa brushy basin 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56684 riggs hill (holt quarry) co mesa brushy basin 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 48124 co-57 hups cactus park co mesa brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 paleodb 55329 kings view fruitamwc l-2002-11 co mesa brushy basin 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 53040 co-33 main callison quarry, fpa 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 11611 co-21 mygatt-moore 152.18 ± 0.29 ma co mesa brushy basin 1 1 1 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 paleodb 56599 co-26 rabbit valley east slightly older than 152.18 ± 0.29 ma co mesa brushy basin 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56596 co-22 rabbit valley camarasaurus slightly younger than 152.18 ± 0.29 ma co mesa brushy basin 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56590 co-23 rabbit valley iguanodon older than 152.18 ± 0.29 ma co mesa brushy basin 0 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 11924 riggs quarry 12, redlands co mesa brushy basin 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 36576 co-36 riggs quarry 15 co mesa brushy basin 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56683 co-35 riggs quarry 13 co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 split rock 1 co mesa 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 split rock 2 co mesa 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 wolny co mesa 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 70031 cactus park 3a co mesa not reported 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 68097 sinbad valley co mesa not reported 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 53022 co-34 kirkland site slightly older than 152.0 ± 0.3 ma co mesa salt wash 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 11925 riggs quarry 14 co mesa salt wash 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 homestead co moffat 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 lily park co moffat 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 mf amphitheater co moffat 0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 witherell co moffat 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 wolf creek co moffat 0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 25141 calico gulch lily park co moffat not reported 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 164830 mcelmo canyon co montezuma brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 yellowjacket canyon co montezuma 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 45975 co-58 dry mesa co montrose brushy basin 1 1 1 0 1 1 1 1 1 1 0 0 0 0 1 1 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 paleodb 49622 co-59 jones hole quarry, dry mesa 2 co montrose brushy basin 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49623 co-60 potter creek co montrose brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 53041 co-66 sheetz quarry 1, uravan co montrose brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 agate basin ut emery 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 46439 ut-7 cleveland-lloyd dinosaur ut emery brushy basin 1 0 1 0 1 1 1 1 1 1 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 duke site ut emery 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58551 emery county sauropod site ut emery brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ferron ut emery 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49626 ut-9 green river dinosaur ut emery brushy basin 0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 mussentuchit quarry ut emery 0 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 san rafael ut emery 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 64053 ut-8 sand bench ut emery brushy basin 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 66 quarry ut emery 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 47196 willow springs, byu esm-163r ut emery brushy basin 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 peterson site ut emery 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49614 hinkle site ut grand brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58516 mill canyon ut grand brushy basin 1 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58518 cisco sauropod site ut grand not reported 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58517 floy junction ut grand not reported 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 104715 la sal mountains ut san juan brushy basin 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 28360 ut-4 east canyon ~157 ma ut san juan tidwell 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 49595 brush creek (marsh allo) ut uintah brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 chevron's morrison north ut uintah 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 chevron's morrison south ut uintah 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22711 ut-25 rainbow park (dnm 94) younger than 151 ma ut uintah brushy basin 0 0 1 0 0 1 1 1 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 52110 ut-19 dinosaur national monument (dnm 315) 10 m above quarry ss) younger than 151 ma ut uintah brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 96826 ut-12 jensen/jensen ut uintah brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 55350 nielson gulch, dmn, marshosaurus ut uintah brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57913 ut-26 rainbow park microsite younger than 151 ma ut uintah brushy basin 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 21852 ut-18 dinosaur national monument carnegie quarry 150.91 ± 0.43 ma ut uintah brushy basin 1 1 1 0 1 1 1 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58515 ut-13 utah field house ut uintah not reported 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58514 hanksville-burpee ut wayne brushy basin 1 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 north north 65 localities pdbd # t&p 99 # locality name state county member apatosaurus barosaurus diplodocus galeamopus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus paleodb 50714 horse coulee, amhn 03-30 mt big horn -0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 38866 rattlesnake ridge mt carbon -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 paleodb 69890 mt-1 mother's day mt carbon -0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 t&j quarry mt gallatin -1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 49624 mt-2 upper strickland creek mt park -0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 wittecombe's ranch mt wheatland -0 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 49633 parker's mystery sd fall river -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 49630 sd-2 fuller's 351, st. onge sd lawrence -1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 49625 sd-1 bear butte sd meade -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57905 sd-3 piedmont butte, hatch ranch, barosaurus type, sdsm v9140 sd meade -0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 132242 ahmn quarries, sturgis area sd meade -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 132243 usnm quarry, sturgis area sd meade -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 49631 sd-4 wonderland, piedmont sd meade -0 1 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 57904 sd-5 wonderland north sd meade -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 46468 wy-61 big al site wy big horn -0 0 1 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 big butte wy big horn 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 smithsonian quarry 1 wy big horn 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 dyer ranch 1 and 2 wy big horn 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 freezeout hills general wy big horn 0 0 1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 5 paleodb 57893 freezeout hills quarry 4 wy big horn 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57894 freezeout hills quarry 6 wy big horn 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 57895 freezeout hills quarry l wy big horn 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 freezeout hills quarry n wy big horn 1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 5 paleodb 57896 freezeout hills quarry o wy big horn 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 46460 wy-62 howe quarry wy big horn -1 1 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 paleodb 46462 howe quarry 2, sauriermuseum wy big horn -0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 3 paleodb 46465 howe-stephens quarry wy big horn -1 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 1 0 0 0 1 0 0 0 10 lake's quarry wy big horn 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 4 paleodb 46469 spring hill, howe ranch wy big horn -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 55333 fox mesa wy big horn -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 matt quarry wy big horn 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 ninemile hill wy big horn 0 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 55323 ?reopened by c. weege 1992? ninemile quarry (amnh), nine mile crossing, nine mile quarry wy big horn -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 reed's quarry 1.5 wy big horn 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 reed's quarry 5 wy big horn 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 4 reed's quarry 7 wy big horn 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 reed's quarry 12 wy big horn 0 0 1 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 paleodb 62561 red canyon ranch, hope college reu wy big horn -0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 13214 freeze out mtns ks expedition wy converse -0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 74664 jimbo quarry 2a wy converse -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 paleodb 74665 jimbo quarry 2b wy converse -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 58511 blacktail creek wy crook -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 lightning rod butte wy crook 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 paleodb 49634 inyan kara creek sdsm v9137 wy crook -0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 56167 little houston, mammal quarry sdsm v941 wy crook -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 49636 wy-11 little houston, main quarry sdsm v9138 wy crook -1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 6 warm springs ranch i wy crook 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 56165 mile 175, sdsm v931 wy crook -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 paleodb 49637 sdsm v9139 wy crook -0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 22650 bs quarry + s quarry, warm springs ranch wy hot springs -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 22678 rb quarry, warm springs ranch wy hot springs -0 1 1 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 paleodb 68100 fs quarry, foot site, warm springs ranch wy hot springs -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 55320 si unit 1, warm springs ranch wy hot springs -1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 142334 brown's ranch (elk mountain) wy johnson -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 55349 buffalo quarry, smith ranch wy johnson -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 176983 wy-72 poison creek quarry 1 wy johnson -1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 176984 wy-73 poison creek quarry 2 wy johnson -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 176985 wy-74 poison creek quarry 3 wy johnson -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 58510 wy-71 poison creek wy johnson -1 0 1 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 7 paleodb 48565 red fork powder river quarry a wy johnson -0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 58509 red fork powder river quarry b wy johnson -1 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 sheridan college allosaurus wy johnson 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 sheridan college 1 wy johnson 1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 sheridan college 2 wy johnson 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 106532 lance creek area, dyslocosaurus type wy niobrara -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 paleodb 58508 paint creek wy park -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 126540 dana wy washakie -1 1 1 0 1 0 1 1 1 1 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 0 0 0 12 paleodb 58507 ku camarasaurus wy weston -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 3 west west 72 localities pdbd # t&p # locality name age state county member apatosaurus barosaurus diplodocus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus blue mesa co gunnison brushy basin 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 38883 co-49 dino cove 151.43 ± 0.36 ma co gunnison brushy basin 1 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 154925 dinosaur beach 151.43 ± 0.36 ma co gunnison brushy basin 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 154924 northern dinosaur beach 151.43 ± 0.36 ma co gunnison brushy basin 1 0 1 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 paleodb 49621 co-48 cabin creek co gunnison salt wash 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 56586 co-27 bollan stegosaur site rabbit valley co mesa -0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 70032 co-55 cactus park (byu 681) co mesa -1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 35293 co-56 dominguez/jones co mesa brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 49652 co-33 eriksen ceratosaur fpa 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 22708 fpa quarry 4 co mesa brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 71476 fpa general site co mesa brushy basin 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 5 paleodb 92360 fpa george's "coelurosaur" site, lacm loc. 5576 co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 fpa stego knoll co mesa brushy basin 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 56684 riggs hill (holt quarry) co mesa brushy basin 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 3 paleodb 48124 co-57 hups cactus park co mesa brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 2 paleodb 55329 kings view fruitamwc l-2002-11 co mesa brushy basin 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 53040 co-33 main callison quarry, fpa 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 11611 co-21 mygatt-moore 152.18 ± 0.29 ma co mesa brushy basin 1 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 7 paleodb 56599 co-26 rabbit valley east slightly older than 152.18 ± 0.29 ma co mesa brushy basin 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 56596 co-22 rabbit valley camarasaurus slightly younger than 152.18 ± 0.29 ma co mesa brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 56590 co-23 rabbit valley iguanodon older than 152.18 ± 0.29 ma co mesa brushy basin 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 11924 riggs quarry 12, redlands co mesa brushy basin 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 36576 co-36 riggs quarry 15 co mesa brushy basin 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 56683 co-35 riggs quarry 13 co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 split rock 1 co mesa 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 2 split rock 2 co mesa 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 wolny co mesa 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 70031 cactus park 3a co mesa not reported 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 68097 sinbad valley co mesa not reported 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 53022 co-34 kirkland site slightly older than 152.0 ± 0.3 ma co mesa salt wash 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 11925 riggs quarry 14 co mesa salt wash 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 homestead co moffat 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 2 lily park co moffat 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 2 mf amphitheater co moffat 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 witherell co moffat 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 2 wolf creek co moffat 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 25141 calico gulch lily park co moffat not reported 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 164830 mcelmo canyon co montezuma brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 yellowjacket canyon co montezuma 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 45975 co-58 dry mesa co montrose brushy basin 1 1 1 1 1 1 1 1 1 0 0 0 0 1 1 0 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 14 paleodb 49622 co-59 jones hole quarry, dry mesa 2 co montrose brushy basin 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 49623 co-60 potter creek co montrose brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 paleodb 53041 co-66 sheetz quarry 1, uravan co montrose brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 agate basin ut emery 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 46439 ut-7 cleveland-lloyd dinosaur ut emery brushy basin 1 0 1 1 1 1 1 1 1 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 11 duke site ut emery 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 58551 emery county sauropod site ut emery brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 ferron ut emery 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 49626 ut-9 green river dinosaur ut emery brushy basin 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 mussentuchit quarry ut emery 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 san rafael ut emery 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 64053 ut-8 sand bench ut emery brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 66 quarry ut emery 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 47196 willow springs, byu esm-163r ut emery brushy basin 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 4 peterson site ut emery 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 49614 hinkle site ut grand brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 58516 mill canyon ut grand brushy basin 1 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 paleodb 58518 cisco sauropod site ut grand not reported 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 58517 floy junction ut grand not reported 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 104715 la sal mountains ut san juan brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 28360 ut-4 east canyon ~157 ma ut san juan tidwell 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 paleodb 49595 brush creek (marsh allo) ut uintah brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 chevron's morrison north ut uintah 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 chevron's morrison south ut uintah 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 22711 ut-25 rainbow park (dnm 94) younger than 151 ma ut uintah brushy basin 0 0 1 0 1 1 1 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 6 paleodb 52110 ut-19 dinosaur national monument (dnm 315) 10 m above quarry ss) younger than 151 ma ut uintah brushy basin 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 96826 ut-12 jensen/jensen ut uintah brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 paleodb 55350 nielson gulch, dmn, marshosaurus ut uintah brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57913 ut-26 rainbow park microsite younger than 151 ma ut uintah brushy basin 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 5 paleodb 21852 ut-18 dinosaur national monument carnegie quarry 150.91 ± 0.43 ma ut uintah brushy basin 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 paleodb 58515 ut-13 utah field house ut uintah not reported 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 58514 hanksville-burpee ut wayne brushy basin 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 7 16 east east 128 localities age pdbd # t&p # locality name state county member apatosaurus barosaurus diplodocus galeamopus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus garden of the gods co el paso -0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 52872 middle park co grand -0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 70027 radium co grand -0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 cleveland quarry co fremont -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 paleodb 48127 cope quarry 1, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 48128 cope quarry ii, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 48129 cope quarry iii, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 48130 cope quarry iv, cope's nipple, saurian hill co fremont -0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48146 cope quarry v, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48147 cope quarry vi, cope's nipple, saurian hill co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48148 cope quarry vii, cope's nipple, saurian hill co fremont -0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 48149 co-1 cope quarry viii, the fort, cam quarry no. 2 co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48153 cope quarry xiv co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48158 co-76 cope quarry xv co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48154 co-71 copequarry xii co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48155 co-5 delfs co fremont -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 paleodb 48163 co-6 deweese slightly younger than 152.29 ± 0.27 ma co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48156 co-72 egg gulch co fremont -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 eric's tooth co fremont 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39377 co-4 felch quarry 2 co fremont -0 0 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 48164 greg's bone garden park slightly younger than 152.29 ± 0.27 ma co fremont -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48170 co-75 kenny's stegosaurus, garden park co fremont -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48160 co-7 kessler's slightly older than 152.29 ± 0.27 ma co fremont -0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 48162 co-8 lindsey quarry, garden park slightly younger than 152.29 ± 0.27 ma co fremont -0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 48168 lucas's site, garden park co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 28366 co-3 marshfelch quarry, garden park co fremont -1 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 12 paleodb 48172 co-73 meyer site 1, garden park co fremont -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48171 co-73 meyer site 2, garden park co fremont -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48169 co-74 meyer site 3, garden park co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 meyer's pump house co fremont 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 sauropod quarry co fremont 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 paleodb 48161 co-11 small quarry, garden park slightly older than 152.29 ± 0.27 ma co fremont -1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 48166 co-09 valley of death, garden park co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 70026 wilson creek co fremont -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 66909 alameda parkway morrison dinosaur site co jefferson -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39376 dinosaur ridge, lake's quarry 8 co jefferson -1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 lakes quarry 1 co jefferson 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 13341 lakes quarry 10 co jefferson -1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 28382 lakes quary 5, beckwith quarry co jefferson -0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 horsetooth co larimer 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 70029 masonville co larimer -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 purgatoire river co las animas 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 70030 villegreen co las animas -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 webster park co park -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 164787 gordon-bramson-brothers snowmass co pitkin -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 1 los ochos mine co saguache 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 heeney site co summit 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 amnh 550 wy albany 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 55486 wy-42 bernice wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 55487 wy-44 bertha between 157 and 152.51 ± 0.47 ma, closer to 157 wy albany -1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 22648 wy-78 bone cabin slightly older than 152.51 ± 0.47 ma wy albany -1 0 1 1 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 10 paleodb 49577 wy-79 bone cabin quarry west slightly older than 152.51 ± 0.47 ma wy albany -1 1 1 0 1 1 1 1 1 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 11 boris quarry wy albany 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 177492 breakfast bench wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 brown quarry a wy albany 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39372 brown quarry b wy albany 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39373 brown quarry c wy albany -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39374 brown quarry d wy albany -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 brown quarry g wy albany 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 cam bench wy albany 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 57902 carnegie quarry 4, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 142337 carnegie quarry 5, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 142335 carnegie quarry a, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 142336 carnegie quarry b, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 52815 carnegie quarry c, sheep creek wy albany -1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 13352 wy-91 carnegie quarry d wy albany -1 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 57897 carnegie quarry d(3), sheep creek wy albany -0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 52816 carnegie quarry e, sheep creek wy albany -1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 57898 carnegie quarry f, sheep creek wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57899 carnegie quarry g, sheep creek wy albany -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57900 carnegie quarry j, sheep creek wy albany -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 57901 carnegie quarry k, sheep creek wy albany -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48837 carnegie quarry n, sheep creek wy albany -1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 5 cassiopeia quarry wy albany 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 74000 como bluff (amnh 222) bone cabin? slightly older than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 168056 como bluff (amnh 223) bone cabin? slightly older than 152.51 ± 0.47 ma wy albany -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 cope's como 1 wy albany 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 cope's como 3 wy albany 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 cope's como 4 wy albany 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 cope's como 5 wy albany 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 convention site wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 drinker quarry wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 47065 wy-86 east camarasaurus 1993 (bcq) slightly older than 152.51 ± 0.47 ma wy albany -0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 3 ep thompson wy albany 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 haystack quarry wy albany 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 jeff p wy albany 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 49628 wy-22 louise wy albany -1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 mummy wy albany 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 49627 wy-39 nail quarry older than 152.51 ± 0.47 ma wy albany -1 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 paleodb 56654 wy-82 ninemile hill very close to 152.51 ± 0.47 ma wy albany -0 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 5 okie wy albany 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 49629 op-kat wy albany -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 pat m wy albany 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39368 wy-17 reed's quarry 10 slightly younger than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39369 wy-18 reed's quarry 11 wy albany -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 39253 wy-46 reed's quarry 13 between 157 and 152.51 ± 0.47 ma, closer to 157 wy albany -0 0 1 0 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 8 paleodb 39371 wy-16 reed's quarry 14 wy albany -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39339 wy-23 reed's quarry 2 slightly older than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39340 wy-20 reed's quarry 3 wy albany -0 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 39347 wy-19 reed's quarry 8 wy albany -0 0 1 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 paleodb 39431 quarry 9 1968-1970 152.51 ± 0.47 ma wy albany -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57903 reed's quarry r wy albany -1 0 1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 55330 red mountain wy albany -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 13212 wy-21 reed's quarry 1 wy albany -1 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 39342 wy-40 reed's quarry 4 wy albany -0 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 paleodb 39346 wy-28 reed's quarry 7, three trees wy albany -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 12816 wy-15 reed's quarry 9 152.51 ± 0.47 ma wy albany -0 0 0 0 1 1 1 1 0 1 0 0 0 0 1 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 9 regina quarry wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 55483 stego 99 very close to 152.51 ± 0.47 ma wy albany -0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 two thigh wy albany 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 weege boys wy albany 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 75453 wy-92 zane quarry, sheep creek wy albany -1 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 73998 aurora quarry 3 como bluff wy carbon -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 58512 dyer ranch quarry 1 wy carbon -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 58513 dyer ranch quarry 2 wy carbon -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57893 freezeout hills quarry 4 wy carbon -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57894 freezeout hills quarry 6 wy carbon -1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 paleodb 57895 freezeout hills quarry l wy carbon -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57896 freezeout hills quarry o wy carbon -1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 55484 graff ranch (matt quarry) between 157 and 152.51 ± 0.47 ma, closer to 157 wy carbon -0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39337 wy-27 lakes' 1a, big canyon wy carbon -0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 38884 wy-83 meilyn quarry between 157 and 152.51 ± 0.47 ma, closer to 157 wy carbon -0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 39338 wy-30 quarry 1.5 wy carbon -0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 39344 wy-26 quarry 5 wy carbon -0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 4 paleodb 39370 wy-29 robber's roost (reed's q 12) wy carbon -0 0 1 0 1 1 0 1 0 1 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 paleodb 74663 alcova lake dave's othnielia (cottonwood creek 1) wy natrona -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 allen's alto wy natrona 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 cottonwood creek quarry 2 wy natrona 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 cottonwood creek quarry 3 wy natrona 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 48557 stegosaurus longispinus type locality, alcova wy natrona -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 36 south south 26 localities pdbd # t&p 99 # locality name age state county member apatosaurus barosaurus diplodocus galeamopus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus paleodb 70024 pinon az not reported 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49338 ok-1 stovall's pit 1, omnh quarry 1, kenton (omnh v92) ok cimarron brushy basin 1 1 1 1 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 49598 ok-4 stovall's pit 8, kenton ok cimarron brushy basin 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49596 ok-2 stovall's pit 5, kenton (omnh) ok cimarron not reported 1 0 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49597 ok-3 stovall's pit 6, kenton ok cimarron not reported 1 0 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56421 stovall's pit 3a, kenton ok cimarron not reported 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56422 stovall's pit 9, kenton ok cimarron not reported 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 51990 hagan basin, nmmnh locality l-210 nm sandoval brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38872 lee acres, nmmnh l-369 nm sandoval brushy basin 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 119021 mcconnell i nm sandoval brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22717 peterson quarry, nmmnh l-3282, ete locality 1593 nm bernalillo brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 68099 nm-3 san ysidro camarasaurus, nmmnh l-555, ridby's camarasaurus nm sandoval brushy basin 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 san ysidro 2 nm sandoval 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38871 nmmnh l-3285 nm sandoval brushy basin 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38867 nmmnh l-3281 nm union brushy basin 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 51992 nm-4 seismosaurus quarry, nmmnh locality l-344 nm sandoval jackpile sandstone 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57910 nm-1 acoma site nm cibola not reported 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 36265 suwanee peak nm cibola not reported 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 boney canyon nm cibola 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 concho springs nm cibola 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 bull canyon nm guadalupe 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 exeter nm union not reported 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 51991 hagan basin, nmmnh locality l-211 nm sandoval recapture 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 quay county nm quay 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 blue peak nm mckinley 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 84308 section 19 mine nm mckinley salt wash 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 with ages only west pdbd # t&p # locality name age state county member apatosaurus barosaurus diplodocus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax elaphrosaurus fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus paleodb 38883 co-49 dino cove 151.43 ± 0.36 ma co gunnison brushy basin 1 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 154925 dinosaur beach 151.43 ± 0.36 ma co gunnison brushy basin 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 154924 northern dinosaur beach 151.43 ± 0.36 ma co gunnison brushy basin 1 0 1 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 paleodb 56586 co-27 bollan stegosaur site rabbit valley slightly older than 152.18 ± 0.29 ma co mesa -0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 paleodb 49652 co-33 eriksen certosaurus fpa 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 22708 co-33 fpa quarry 4 main quarry 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 71476 fpa general site fruitadens, mammals 152.0 ± 0.3 ma co mesa brushy basin 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 5 paleodb 92360 fpa george's "coelurosaur" site, lacm loc. 5576 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 53040 co-33 main callison quarry, fpa 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 11611 co-21 mygatt-moore 152.18 ± 0.29 ma co mesa brushy basin 1 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 7 paleodb 56599 co-26 rabbit valley east slightly older than 152.18 ± 0.29 ma co mesa brushy basin 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 56596 co-22 rabbit valley camarasaurus slightly younger than 152.18 ± 0.29 ma co mesa brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 56590 co-23 rabbit valley iguanodon older than 152.18 ± 0.29 ma co mesa brushy basin 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3 paleodb 53022 co-34 kirkland site slightly older than 152.0 ± 0.3 ma co mesa salt wash 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 46440 ut-25 rainbow park (dnm 94) younger than 151 ma ut uintah brushy basin 0 0 1 0 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 6 paleodb 52110 ut-19 dinosaur national monument (dnm 315) 10 m above quarry ss) younger than 151 ma ut uintah brushy basin 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 paleodb 57913 ut-26 rainbow park microsite younger than 151 ma ut uintah brushy basin 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 5 paleodb 21852 ut-18 dinosaur national monument carnegie quarry 150.91 ± 0.43 ma ut uintah brushy basin 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 paleodb 28360 ut-4 east canyon ~157 ma ut san juan tidwell 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 east pdbd # t&p # locality name age state county member apatosaurus barosaurus diplodocus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax elaphrosaurus fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus galeamopus paleodb 48163 co-6 deweese slightly younger than 152.29 ± 0.27 ma co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48164 greg's bone garden park slightly younger than 152.29 ± 0.27 ma co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48162 co-8 lindsey quarry, garden park slightly younger than 152.29 ± 0.27 ma co fremont -0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48161 co-11 small quarry, garden park slightly older than 152.29 ± 0.27 ma co fremont -1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48160 co-7 kessler's slightly older than 152.29 ± 0.27 ma co fremont -0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 12816 wy-15 reed's quarry 9 152.51 ± 0.47 ma wy albany -0 0 0 1 1 1 1 0 1 0 0 0 0 0 1 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22648 wy-78 bone cabin slightly older than 152.51 ± 0.47 ma wy albany -1 0 1 1 1 1 1 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 1 paleodb 47065 wy-86 east camarasaurus 1993 (bcq) slightly older than 152.51 ± 0.47 ma wy albany -0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49627 wy-39 nail quarry older than 152.51 ± 0.47 ma wy albany -1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56654 wy-82 ninemile hill very close to 152.51 ± 0.47 ma wy albany -0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39368 wy-17 quarry 10 slightly younger than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39253 wy-46 quarry 13 between 157 and 152.51 ± 0.47 ma, closer to 157 wy albany -0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 paleodb 39339 wy-23 quarry 2 slightly older than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39431 quarry 9 1968-1970 152.51 ± 0.47 ma wy albany -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39342 wy-40 reed's quarry 4 between 157 and 152.51 ± 0.47 ma wy albany -0 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55487 wy-44 bertha between 157 and 152.51 ± 0.47 ma, closer to 157 wy albany -1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 74000 como bluff (amnh 222) bone cabin? slightly older than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 168056 como bluff (amnh 223) bone cabin? slightly older than 152.51 ± 0.47 ma wy albany -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55483 stego 99 very close to 152.51 ± 0.47 ma wy albany -0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49577 wy-79 bone cabin quarry west slightly older than 152.51 ± 0.47 ma wy albany -1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 paleodb 55484 graff ranch (matt quarry) between 157 and 152.51 ± 0.47 ma, closer to 157 wy carbon -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38884 wy-83 meilyn quarry between 157 and 152.51 ± 0.47 ma, closer to 157 wy carbon -0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 age clusters west age cluster pdbd # t&p # locality name age state county member apatosaurus barosaurus diplodocus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax elaphrosaurus fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus younger than 151 paleodb 46440 ut-25 rainbow park (dnm 94) younger than 151 ma ut uintah brushy basin 0 0 1 0 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 52110 ut-19 dinosaur national monument (dnm 315) 10 m above quarry ss) younger than 151 ma ut uintah brushy basin 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 57913 ut-26 rainbow park microsite younger than 151 ma ut uintah brushy basin 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 ~151 ma paleodb 38883 co-49 dino cove 151.43 ± 0.36 ma co gunnison brushy basin 1 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 154925 dinosaur beach 151.43 ± 0.36 ma co gunnison brushy basin 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 154924 northern dinosaur beach 151.43 ± 0.36 ma co gunnison brushy basin 1 0 1 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 21852 ut-18 dinosaur national monument carnegie quarry 150.91 ± 0.43 ma ut uintah brushy basin 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ~ 152 ma paleodb 49652 co-33 eriksen certosaurus fpa 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22708 co-33 fpa quarry 4 main quarry 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 71476 fpa general site fruitadens, mammals 152.0 ± 0.3 ma co mesa brushy basin 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 92360 fpa george's "coelurosaur" site, lacm loc. 5576 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 53040 co-33 main callison quarry, fpa 152.0 ± 0.3 ma co mesa brushy basin 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 11611 co-21 mygatt-moore 152.18 ± 0.29 ma co mesa brushy basin 1 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 paleodb 56599 co-26 rabbit valley east slightly older than 152.18 ± 0.29 ma co mesa brushy basin 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56596 co-22 rabbit valley camarasaurus slightly younger than 152.18 ± 0.29 ma co mesa brushy basin 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 53022 co-34 kirkland site slightly older than 152.0 ± 0.3 ma co mesa salt wash 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56586 co-27 bollan stegosaur site rabbit valley slightly older than 152.18 ± 0.29 ma co mesa -0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56590 co-23 rabbit valley iguanodon slightly older than 152.18 ± 0.29 ma co mesa brushy basin 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 28360 ut-4 east canyon ~157 ma ut san juan tidwell 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 east age cluster pdbd # t&p # locality name age state county member apatosaurus barosaurus diplodocus camarasaurus stegosaurus camptosaurus allosaurus ceratosaurus coelurus saurophaganax elaphrosaurus fosterovenator fruitadens koparion ornitholestes stokesosaurus tanycolagreus marshosaurus torvosaurus drinker dryosaurus nanosaurus othnielosaurus uteodon gargoyleosaurus hesperosaurus mymoorapelta haplocanthosaurus supersaurus brachiosaurus dyslocosaurus suuwassea kaatedocus dystrophaeus galeamopus ~ 152 ma paleodb 48163 co-6 deweese slightly younger than 152.29 ± 0.27 ma co fremont -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48164 greg's bone garden park slightly younger than 152.29 ± 0.27 ma co fremont -0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48162 co-8 lindsey quarry, garden park slightly younger than 152.29 ± 0.27 ma co fremont -0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48161 co-11 small quarry, garden park slightly older than 152.29 ± 0.27 ma co fremont -1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 48160 co-7 kessler's slightly older than 152.29 ± 0.27 ma co fremont -0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 12816 wy-15 reed's quarry 9 152.51 ± 0.47 ma wy albany -0 0 0 1 1 1 1 0 1 0 0 0 0 0 1 0 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 22648 wy-78 bone cabin slightly older than 152.51 ± 0.47 ma wy albany -1 0 1 1 1 1 1 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 1 paleodb 47065 wy-86 east camarasaurus 1993 (bcq) slightly older than 152.51 ± 0.47 ma wy albany -0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49627 wy-39 nail quarry older than 152.51 ± 0.47 ma wy albany -1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 56654 wy-82 ninemile hill very close to 152.51 ± 0.47 ma wy albany -0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39368 wy-17 quarry 10 slightly younger than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39339 wy-23 quarry 2 slightly older than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39431 quarry 9 1968-1970 152.51 ± 0.47 ma wy albany -0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 74000 como bluff (amnh 222) bone cabin? slightly older than 152.51 ± 0.47 ma wy albany -1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 168056 como bluff (amnh 223) bone cabin? slightly older than 152.51 ± 0.47 ma wy albany -0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55483 stego 99 very close to 152.51 ± 0.47 ma wy albany -0 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 49577 wy-79 bone cabin quarry west slightly older than 152.51 ± 0.47 ma wy albany -1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 older than 152 ma paleodb 39342 wy-40 reed's quarry 4 between 157 and 152.51 ± 0.47 ma wy albany -0 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 39253 wy-46 quarry 13 between 157 and 152.51 ± 0.47 ma, closer to 157 wy albany -0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 paleodb 55484 graff ranch (matt quarry) between 157 and 152.51 ± 0.47 ma, closer to 157 wy carbon -0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 55487 wy-44 bertha between 157 and 152.51 ± 0.47 ma, closer to 157 wy albany -1 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 paleodb 38884 wy-83 meilyn quarry between 157 and 152.51 ± 0.47 ma, closer to 157 wy carbon -0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 7 2020 © 2020 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species wayne m. itano and kenneth carpenter geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover top: drawings of (1) the labial (outer) and (2) the lingual (inner) faces of the currently missing holotype of petalodus ohioensis safford 1853. from the original description. middle: (a) labial and (b) lingual views of a cast of the holotype of p. ohioensis from the collections of the yale peabody museum of natural history. scale bar = 1 cm. bottom: three casts of the holotype of p. ohioensis. left to right: cast of labial side, three-dimensional cast, cast of lingual side. from the collections of the field museum of natural history. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 197 abstract the validity of the chondrichthyan species petalodus ohioensis safford 1853, has long been in doubt due to the poor quality of the published figures and the unknown whereabouts of the holotype. that situation changed with the discovery of casts of the holotype in the collections of the yale peabody museum of natural history. the quality of the casts is poor, but sufficient to establish p. ohioensis as a valid species and as a senior synonym of p. alleghaniensis leidy 1856. recently, casts of the holotype of much better quality were found in the collections of the field museum of natural history, accompanied by documentation indicating that they were likely obtained directly from safford by o.p. hay in 1896. the field museum casts clearly show the bands of ridges at the base of the crown on the labial and lingual sides, which are not visible on the yale peabody museum casts. high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species wayne m. itano and kenneth carpenter museum of natural history, university of colorado, boulder, co 80309, usa wayne.itano@aya.yale.edu kenneth.carpenter-1@colorado.edu citation for this article. itano, w.m., and carpenter, k., 2020, high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species: geology of the intermountain west, v. 7, p. 197–203, https://doi.org/10.31711/giw.v7.pp197-203. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the holotype of petalodus ohioensis safford 1853, is a tooth from the cambridge limestone member of the glenshaw formation of the conemaugh group, guernsey county, ohio. petalodus is an extinct genus of cartilaginous fishes related to sharks and the cambridge limestone is upper pennsylvanian (missourian) in age (martino, 2004). safford (1853) published rough drawings of the holotype (figure 1) and a brief description in a short note. that note seems to have been unnoticed by other researchers for decades. during that period of neglect, p. alleghaniensis leidy 1856 and p. destructor newberry and worthen 1866 were described, based on teeth very similar to the holotype of p. ohioensis. in the description of yet another species of petalodus, p. securiger, hay (1895) noted safford’s description of p. ohioensis and raised the possibility that some or all of the later-described species, p. alleghaniensis, p. destructor, and p. securiger, might be junior synonyms of p. ohioensis. however, hay (1895) hesitated to formally synonymize these species with p. ohioensis, in part because hay questioned the accuracy of safford’s figures. hay (1895, p. 563) remarked that “it would be interesting to know whether or not the type of professor safford’s specimen is yet in existence.” hay later reconsidered the status of p. ohioensis, since p. alleghaniensis, p. destructor, and p. securiger (as p. securis) are all listed as 198 high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species itano, w.m., and carpenter, k. geology of the intermountain west 2020 volume 7 junior synonyms of p. ohioensis in the bibliography of fossil vertebrates of north america (hay, 1902). whereas some researchers (hansen, 1985, 1996; dalla vecchia, 1988; ramovš, 1997a, 1997b; lucas and estep, 2000; robb, 2003; elliott and others, 2004; hamm and cicimurri, 2005; brusatte, 2007; ginter and others, 2010; carpenter and ottinger, 2018) have followed hay in regarding p. ohioensis as the senior synonym, others (miller, 1957; miller and mann, 1958; mcnulty, 1963; zidek, 1976; goto and okura, 2004; monson, 2010) have followed eastman (1896) in giving priority to the name p. alleghaniensis, apparently regarding p. ohioensis to be a nomen dubium, due to the inadequacy of safford’s description. the status of petalodus ohioensis is difficult to resolve without having access to its holotype or even to an accurate illustration of it. institutional abbreviations fmnh = field museum of natural history, chicago, illinois; ypm = yale peabody museum of natural history, yale university, new haven, connecticut. casts at the yale peabody museum of natural history recently, the present authors located two casts at the yale peabody museum, accompanied by a label stating that they were copies of the holotype of petalodus ohioensis and that they were received from the museum of comparative zoology, harvard university (carpenter and itano, 2019). figure 2 shows labial (a) and lingual (b) views of one of the casts. there seems to be no reason to doubt the authenticity of the casts, which correspond closely to the drawings of safford (1853) (figure 1), even to the slight asymmetries of the crown margins. the casts were catalogued at the yale peabody museum on september 18, 1930, but might have been received at an earlier date (d. brinkman, yale peabody museum, email communication, june 15, 2018). currently, neither the holotype of p. ohioensis nor casts of it, nor any record of them, can be located at the museum of comparative zoology (j. cundiff, museum of comparative zoology, email communication, june 15, 2018). despite their low quality, the casts at the yale peabody museum are sufficiently detailed to establish the validity of p. ohioensis. they confirm that p. alleghaniensis is a junior synonym of petalodus ohioensis (carpenter and itano, 2019). it seems possible, even likely, that safford would have sent a cast of the holotype to l. agassiz, then at the museum of comparative zoology, whom safford (1853) credits with identifying the genus of the tooth. the poor quality of the yale peabody museum casts might be a result of their being copies of a cast, once figure 1. petalodus ohioensis from safford (1853, p. 142) in (1) labial and (2) lingual views. 199 high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species itano, w.m., and carpenter, k. geology of the intermountain west 2020 volume 7 held by the museum of comparative zoology, rather than being copies of the original specimen. casts at the field museum of natural history recently, one of the authors (itano) noticed the following entry in a catalogue of type specimens in the field museum of natural history (bruner, 1992): petalodus ohioensis (safford, 1851) = originally described as getalodus ohioensis safford 1851 pf 673 casts of holotype. casts of 3 teeth. pennsylvanian. ohio: guernsey county: near cambridge. collector: j. m. safford. safford, j. m. 1853. tooth of getalodus ohioensis. american journal of science, 2nd ser., 16: 142. desc. (p. 142) & fig. figs. 1, 2. the description leaves no doubt that the tooth referred to is the holotype of p. ohioensis. the date 1851 should be corrected to 1853, the date of safford’s publication. one of the authors (itano) requested information from the field museum as to the status of the casts and received a photograph (figure 3) and registration information (figure 4) (w. simpson, field museum of natural history, email communication, january 21, 2020). simpson also clarified that, although the entry in bruner (1992) refers to “casts of 3 teeth,” there are actually three casts of the same tooth: one of the entire tooth and one each of only the labial or lingual side. the field museum casts are of better quality than those of the yale peabody museum and reinforce the conclusions of carpenter and itano (2019) as to the validity and priority of petalodus ohioensis. that the field museum and yale peabody museum casts are of the same tooth is clear by observation. the close correspondence of the asymmetric lingual faces (rightmost cast of figure 3 versus figure 2b) is particularly striking. the field museum casts are important because they clearly show the bands of ridges at the base of the crown on the labial and lingual sides. the yale peabody museum casts are too rough to show the ridges, which are a feature of all petalodus teeth (hansen, 1985). bands of ridges on both labial and lingual sides distinguish petalodus from similar genera, for example, polyrhizodus, which has ridges only on the lingual side (hansen, 1985). the handwritten note in figure 3, with the words, “casts of petalodus ohioensis, j. m. safford, nashville, tenn., presented by o. p. hay,” together with the information from the registration record (figure 4) that the casts were received in 1896 from o.p. hay, allows one to reconstruct a plausible series of events. james merrill safford was a professor at cumberland university, figure 2. cast of the holotype of petalodus ohioensis in (a) labial and (b) lingual views. specimen number ypm pv 2861 from the collections of the yale peabody museum of natural history. scale bar = 1 cm. 200 high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species itano, w.m., and carpenter, k. geology of the intermountain west 2020 volume 7 lebanon, tennessee, from 1848 to 1873. from 1873 to 1900, safford was a professor at the university of nashville and at vanderbilt university, both in nashville, tennessee (stearns, 2018). one can speculate that, after writing the 1895 article, hay wrote to safford, who was then in nashville, enquiring as to the status of the holotype of p. ohioensis, received the casts shown in figure 3, and, in 1896, donated them to the field museum of natural history, which was then called the field columbian museum. based on the evidence of the casts, hay might then have concluded that p. ohioensis was the senior synonym of p. alleghaniensis, p. destructor, and p. securiger, as is reflected in hay (1902). attempts by the present authors to locate the original holotype have so far been unsuccessful. conclusions the casts of the holotype of petalodus ohioensis safford 1853, fmnh pf 673, in the collections of the field museum of natural history, show details not present on figure 3. three casts of the holotype of petalodus ohioensis. specimen number fmnh pf 673. from left to right: cast of labial side, three-dimensional cast, cast of lingual side. photograph by w. simpson (field museum of natural history). used with permission. 201 high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species itano, w.m., and carpenter, k. geology of the intermountain west 2020 volume 7 the casts in the collections of the yale peabody museum of natural history, ypm pv 2861. this reinforces the conclusions of the present authors (carpenter and itano, 2019) that p. ohioensis is a valid species and a senior synonym of p. alleghaniensis. acknowledgments we thank william simpson (field museum of natural history) for the photograph of the casts (figure 3) and the registration information (figure 4). we thank dan brinkman (yale peabody museum of natural history, new haven, connecticut) for access to collections and for information on the casts registered as ypm pv 2861. we thank jessica cundiff (museum of comparative zoology, harvard university, cambridge, massachusetts) for attempting to locate the holotype of p. ohioensis, or casts of it, in the museum collections. we thank james kirkland (utah geological survey) and spencer lucas (new mexico museum of natural history and science) for their constructive reviews. figure 4. registration information for fmnh pf 673. courtesy of w. simpson (field museum of natural history). used with permission. 202 high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species itano, w.m., and carpenter, k. geology of the intermountain west 2020 volume 7 references bruner, j.c., 1992, a catalogue of type specimens of fossil fishes in the field museum of natural history: fieldiana geology, v. 23, p. 1–54. brusatte, s.l., 2007, pennsylvanian (late carboniferous) chondrichthyans from the lasalle limestone member (bond formation) of illinois, usa: neues jahrbuch für geologie und paläontologie, abhandlungen, v. 244, no. 1, p. 1–8. carpenter, k., and itano, w.m., 2019, taxonomic validity of petalodus ohioensis (chondrichthyes, petalodontidae) based on a cast of the lost holotype: geology of the intermountain west, v. 6, p. 55–60, https://doi.org/10.31711/ giw.v6.pp55-60. carpenter, k., and ottinger, l., 2018, permo-pennsylvanian sharks from the lower cutler beds near moab, utah: geology of the intermountain west, v. 5, p. 105–116, https://doi.org/10.31711/giw.v5.pp105-116. dalla vecchia, f.m., 1988, first record of a petalodont (petalodus ohioensis safford, 1853) from the alps: gortania-atti del museo friulano di storia naturale, v. 9, p. 47–56. eastman, c.r., 1896, remarks on petalodus alleghaniensis leidy: journal of geology, v. 4, no. 2, p. 174–176, https:// www.biodiversitylibrary.org/item/96016#page/188/ mode/1up. elliott, d.k., irmis, r.b., hansen, m.c., and olson, t.j., 2004, chondrichthyans from the pennsylvanian (desmoinesian) naco formation of central arizona: journal of vertebrate paleontology, v. 24, no. 2, p. 268–280, https://doi. org/10.1671/1978. ginter, m., hampe, o., and duffin, c.j., 2010, chondrichthyes paleozoic elasmobranchii teeth, in schultze, h-p., editor, handbook of paleoichthyology, volume 3d: munich, verlag dr. friedrich pfeil, p. 1–168. goto, m., and okura, m., 2004, the chondrichthyan tooth remains from the carboniferous and permian of fukuji, gifu prefecture, central japan: earth science (chikyu kagaku), v. 58, p. 215–228. hamm, s.a., and cicimurri, d.j., 2005, middle pennsylvanian (desmoinesian) chondrichthyans from the lake neosho shale member of the altamont limestone in montgomery county, kansas: paludicola, v. 5, no. 2, p. 62–76. hansen, m.c., 1985, systematic relationships of petalodontiform chondrichthyans, in dutro, j.t., jr., and pfefferkorn, h.w., editors, neuvième congrès international de stratigraphie et de géologie du carbonifère, compte rendu, vol. 5: carbondale and edwardsville, southern illinois university press, p. 523–541. hansen, m.c., 1996, phylum chordata—vertebrate fossils, in feldmann, r.m., and hackathorn, m., editors, fossils of ohio: ohio division of geological survey bulletin 70, p. 288–369. hay, o.p., 1895, description of a new species of petalodus (p. securiger) from the carboniferous of illinois: journal of geology, v. 3, no. 5, p. 561–564, https://www.jstor.org/ stable/30055026. hay, o.p., 1902, bibliography and catalogue of the fossil vertebrata of north america: u.s. geological survey bulletin 179, 868 p., https://www.biodiversitylibrary.org/ item/59973#page/9/mode/1up. leidy, j., 1856, descriptions of some remains of fishes from the carboniferous and devonian formations of the united states: journal of the academy of natural sciences of philadelphia, v. 3, p. 159–165, https://www.biodiversitylibrary.org/item/113477. lucas, s.g., and estep, j.w., 2000, pennsylvanian selachians from the cerros de amado, central new mexico, in lucas, s.g., editor, new mexico’s fossil record 2: new mexico museum of natural history and science bulletin 16, p. 21–27. martino, r.l., 2004, sequence stratigraphy of the glenshaw formation (middle-late pennsylvanian) in the central appalachian basin, in pashin, j.c., and gastaldo, r.a., editors, sequence stratigraphy, paleoclimate, and tectonics of coal-bearing strata: american association of petroleum geologists studies in geology 51, p. 1–28. mcnulty, c.l., jr., 1963, teeth of petalodus alleghaniensis leidy from the pennsylvanian of north texas: texas journal of science, v. 15, no. 3, p. 351–353, https://www.biodiversitylibrary.org/item/249272#page/897/mode/1up. miller, h.w., jr., 1957, petalodus jewetti, a new species of fossil bradyodont fish from kansas: transactions of the kansas academy of science, v. 60, no. 1, p. 82–85. miller, h.w., jr., and mann, r.j., 1958, petalodus (bradyodont) from the permian of kansas and oklahoma: transactions of the kansas academy of science, v. 51, no. 1, p. 97–103. 203 high-quality casts of the missing holotype of petalodus ohioensis safford 1853 (chondrichthyes, petalodontidae) at the field museum of natural history and their bearing on the validity and priority of the species itano, w.m., and carpenter, k. geology of the intermountain west 2020 volume 7 monson, c.c., 2010, paleontology and paleoecology of the pennsylvanian in south-central iowa, in marshall, t., and fields, c., editors, the pennsylvanian geology of south-central iowa: geological survey of iowa guidebook 86, p. 27–35, https://s-iihr34.iihr.uiowa.edu/publications/uploads/gsi-086.pdf#page=33. newberry, j.s., and worthen, a.h., 1866, descriptions of new species of vertebrates, mainly from the sub-carboniferous limestone and coal measures of illinois: geological survey of illinois, v. 2, p. 9–134. ramovš, a., 1997a, petalodus ohioensis (chondrichthyes, upper carboniferous) from the karavanke mountains, slovenia: neues jahrbuch für geologie und paläontologie monatshefte, v. 1997, p. 109–113. ramovš, a., 1997b, two new petalodont teeth (chondrichthyes, upper carboniferous) from the karavanke mountains, slovenia: geologiya, v. 40, p. 109–112, https://doi. org/10.5474/geologija.1997.004. robb, a.j., iii, 2003, notes on the occurrence of some petalodont shark fossils from the upper pennsylvanian rocks of northeastern kansas: transactions of the kansas academy of science, v. 106, no. 1/2, p. 71–80. safford, j.m., 1853, tooth of getalodus [sic] ohioensis: american journal of science and arts, v. 16, no. 46, p. 142, https:// www.biodiversitylibrary.org/item/90339#page/149/ mode/1up. stearns, r.g., 2018, james merrill safford: tennessee historical society tennessee encyclopedia, online access 6 january 2020, https://tennesseeencyclopedia.net/entries/ james-merrill-safford. zidek, j., 1976, oklahoma paleoichthyology part 5—chondrichthyes: oklahoma geology notes, v. 36, no. 5, p. 175–192. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 10 2023 © 2023 utah geological association. all rights reserved. this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah william j. chandonia and john p. hogan geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view from the kanarra falls trail looking north upon overturned, thrusted permo-triassic carbonates and siliciclastics. the timpoweap member of the triassic moenkopi formation forms the higher, eastern ridge. duplication of the lower red member on either side of the timpoweap member reveals a major fold accommodation fault along the east limb of the kanarra fold-thrust structure—the kanarra creek thrust. inset: view south near the entrance to spring creek canyon of a break-thrust fold in the fossil mountain member of the permian kaibab formation, which is a smaller, partial mimic of the larger kanarra fold-thrust structure (see figure 12, p. 23 for a complete description). i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 10 2023 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2022–2023 uga board president rick ford rford@weber.edu 801.915.3188 president-elect eugene syzmanski eugenes@utah.gov 801.537.3364 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 treasurer aubrey dereuil aubrey@zanskar.us 850.572.2543 secretary tom chidsey tomchidsey@gmail.com 801.824.0738 past president john south johnvsouth@gmail.com 801.367.9292 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 10 2023 1 abstract the multiple origins proposed for the kanarra anticline in southwestern utah as a drag-fold along the hurricane fault, a laramide monocline, a sevier fault-propagation fold, or a combination of these processes, serve to muddy its tectonic significance. this in part reflects the structural complexity of the exposed eastern half of the fold. the fold evolved from open and up-right to overturned and tight, is cross-cut by multiple faults, and was subsequently dismembered by the hurricane fault. the western half of the fold is obscured because of burial, along with the hanging wall of the hurricane fault, beneath neogene and younger sediments and volcanics. we present the results of detailed bedrock geologic mapping, and geologic cross sections restored to late cretaceous time (prior to basin and range extension), to demonstrate the kanarra anticline is a compound anticline-syncline pair inextricably linked with concomitant thrust faulting that formed during the sevier orogeny. we propose the name kanarra fold-thrust structure to unambiguously identify the close spatial and temporal association of folding and thrusting in formation of this prominent geologic feature. we identify a previously unrecognized thrust, the red rock trail thrust, as a forelimb shear thrust that was in a favorable orientation and position to have been soft-linked, and locally hard-linked, with the thrust ramp of the basal detachment to form a break thrust. the east verging red rock trail thrust is recognized by a distinctive cataclasite in the lower jurassic navajo sandstone. the hanging wall of the red rock trail thrust is displaced eastward over the middle jurassic carmel formation and upper cretaceous formations and can be traced for at least 27 km and possibly farther. we contend the kanarra fold-thrust structure unambiguously defines the leading edge of the sevier fold-thrust belt in southwestern utah. stratigraphic relationships in the southern and northern part of the kanarra foldthrust structure constrain its development between the early and late campanian (about 84 to 71 ma) but possibly younger. in southwestern utah, initial movement along the iron springs thrust at about 100 ma (quick and others, 2020) and subsequent eastward advancement of the sevier deformation front to the red rock trail thrust at about 84 to 71 ma coincided with well-documented magmatic flare ups in the cordilleran arc in the hinterland of the sevier fold-thrust belt. this temporal relationship between magmatic flare ups and thrusting is consistent with a close correspondence between arc-related processes and episodic foreland deformation. the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah william j. chandonia1 and john p. hogan1,2 1department of geosciences and geological engineering and petroleum engineering, missouri university of science and technology, 129 mcnutt hall, 1400 north bishop, rolla, mo 64509 usa; williamjchandonia@gmail.com; 2 jhogan@mst.edu citation for this article. chandonia, w.j., and hogan, j.p., 2023, the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah: geology of the intermountain west, v. 10, p. 1–64, https://doi.org/10.31711/giw.v10.pp1-64. 2 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 introduction the sevier fold-thrust belt (armstrong, 1968; burchfield and davis, 1972) is an integral component of the more extensive cordilleran orogenic belt that affected western north america from the late jurassic (about 165 ma) to the eocene (about 50 ma) (yonkee and weil, 2015; herring and greene, 2016). magmatism, deformation, and accompanying sedimentation during this time was in response to subduction of the oceanic farallon plate along the western edge of the north america plate, and accretion of various outboard terranes (lageson and others, 2001; decelles, 2004; decelles and others, 2009; decelles and graham, 2015; ducea and others, 2015). across the cordilleran retro-arc several prominent east-directed thin-skinned thrusts folded and imbricated proterozoic to mesozoic miogeoclinal and terrestrial sediments resulting in at least 350 km of shortening at the latitude of central to northern utah (decelles, 2004; herring and greene, 2016). significant advancement in the understanding of the structural style, spatial progression, and effect on foreland sedimentation during collisional orogenesis have come from extensive investigation of the sevier fold-thrust belt in northern and central utah (constenius, 1996; constenius and others, 2003; decelles, 2004; decelles and coogan, 2006; chidsey and others, 2007; herring and greene, 2016; pujols and others, 2020) as well as in nevada (long, 2015; giallorenzo and others, 2018; di fiori and others, 2021). however, the temporal and spatial evolution of deformation associated with the sevier fold-thrust belt varies considerably along strike (e.g., see figure 1, p. 77, in quick and others, 2020). in central to northern utah, at the latitude of the salt lake salient (about 41° n.), the sevier foldthrust belt remained active longer (ca., 100 myr) over a wider deformation belt (about 500 km) and propagated farther inland (e.g., hogsback thrust, which continued moving east up to 56 ma). in contrast, in the southern part of the fold-thrust belt, at the latitude of the las vegas recess (about 36° n.), thin-skinned deformation was of shorter duration (ca., 50 myr) and formed a narrower deformation belt (about 100 km wide). quick and others (2020) attributed this along strike spatial and temporal variation in the advancement of the sevier deformation front to structural inheritance; the location of the buried western edge of precambrian continental crust least affected by extension (i.e., the “hingeline,” see kay, 1951; stokes, 1976; picha and gibson, 1985; picha, 1986 for a complete discussion) as well as the location of prominent extensional basement structures (e.g., transform faults). the sinuous trace defined by the multiple salients and recesses of the retro-arc sevier fold-thrust belt reflects the form of the rifted precambrian north american continental margin and the prominent role reactivated extensional structures in the basement had on the eastward advancement of the sevier deformation front (picha and gibson, 1985; paulsen and marshak, 1999; quick and others, 2020). the location and timing of arrival of the sevier deformation front in southwestern utah, the region linking the northern and southern parts of the fold-thrust belt (figure 1), remains a subject of debate (biek and others, 2009, p. 29, 31). this is due, in part, to the complexity of the bedrock and surficial geology of southwestern utah. here contractional structures associated with the sevier orogeny are variably dissected by cenozoic basin and range extensional faulting (e.g., the hurricane fault), obscured by intrusion of miocene laccoliths (e.g., the pine valley and/or three peaks laccolith), covered by neogene to holocene volcanic units, or buried by significant landslides (biek, 2003a, 2003b; hurlow and biek, 2003; biek and others, 2009; knudsen, 2014a, 2014b; biek and hayden, 2016; quick and others, 2020). biek and others (2009, p. 5) defined the leading edge of the sevier fold-thrust belt deformation in southwestern utah by the location of the square top mountain thrust (their easternmost significant thrust) and the virgin, pintura, and kanarra anticlines. the square top mountain thrust is linked with the keystone-muddy mountain-tule spring thrust system in southeastern nevada and its northern extension is linked with the blue mountain-iron springs-canyon range thrust system (see figure 5, p. 6, figure 40, p. 26, in biek and others, 2009). arrival of the leading edge of the sevier fold-thrust belt in southwestern utah is thus constrained by the emergence of the square top mountain thrust and the erosional beveling of the pintura anticline, which is unconformably overlain by the cretaceous canaan peak formation. the canaan 3 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 112°w113°w114°w115°w116°w 40 °n 39 °n 38 °n 37 °n 36 °n ! ! ! ! ! ! ! ! ! 0 100 scale 1:2,500,000 200 km n ce nt ra l n ev ad a th ru st b el t ea st er n ne va da fo ld b el t se vi er fo ld -th ru st b el t w es te rn u ta h th ru st b el t colorado plateau chl basin and range transition zone lv stg k p tl cccedar valley d slc pf ku gt kf ist stmt bmt wwt dt pvtfa sc crt paragonah lineament cove fort lineament scipio l. leamington l. tvt va hf rrtt rrtt markagunt plateau kolob plateau stf dlt gpt kt wpt lvvsz mmt hu rr ica ne cliff s trhnh pg tp nevada utah arizonase vie r f old -th ru st belt figure 1. regional overview map showing the sevier frontal fold-thrust belt in relation to cordilleran hinterland deformation belts and the craton. included are proterozoic rift-related lineaments, the cordilleran hinge line (chl), and basin and range structures. geographic abbreviations: slc–salt lake city; d–delta; cc–cedar city; k–kanarra; p–pintura; t– toquerville; l–leeds; stg–st. george; lv–las vegas; trh–the red hill; nh–north hills; pg–parowan gap; tp–three peaks. fold abbreviations: va–virgin anticline; kf–kanarra fold. fa–fillmore arch; sc–sevier culmination; ku–kaibab uplift (laramide). thrust abbreviations: kt–keystone thrust; dlt–dry lake thrust; mmt–muddy mountains thrust; gt–glendale thrust; bmt–blue mountain thrust; wpt–wheeler pass thrust; gpt–gass peak thrust; dt–delamar thrust; wwt–wah wah thrust; stmt–square top mountain thrust; ist–iron springs thrust; rrtt–red rock trail thrust; pvt– pahvant thrust (formerly spelled pavant thrust); crt–canyon range thrust; tvt–tintic valley thrust. basin and range structures: lvvsz–las vegas valley shear zone; hf–hurricane fault; stf–sevier-toroweap fault; pf–paunsaugunt fault. after quick and others (2020); compiled from stokes and others (1963), picha and gibson (1985), wernicke and others (1988), willis (1999), page and others (2005), long (2012, 2015), biek and others (2015), yonkee and weil (2015), herring and green (2016), giallorenzo and others (2018). dem visualization from the usgs national map 3d elevation program (3dep). 4 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 peak is broadly thought to be early to late campanian, about 84 to 71 ma, although these dates are poorly constrained and the timing of continued sevier deformation in this area may be younger (biek and others, 2009 p. 30–31). quick and others (2020) suggested an earlier arrival for the deformation front associated with the sevier fold-thrust belt in southwestern utah is constrained by emergence of the iron springs thrust at the three peaks. they used a 100.18 ± 0.04 crystallization age for zircons extracted from a previously unrecognized dacite lapilli ash-fall tuff associated with the marshall creek breccia to constrain movement of the iron springs thrust (also see fillmore, 1991) to latest albian–earliest cenomanian (about 100 ma); an age considerably earlier than previously proposed but similar in age to the about 99 ma keystone thrust of fleck and carr (1990). subsequently, biek and others (2015, p. 91) proposed the presence of an earlier period of cryptic thrusting for the paunsaugunt normal fault on the paunsaugunt plateau as the easternmost leading edge of the sevier fold-thrust belt. the discrepancy in the timing of arrival and location of the leading edge of the sevier fold-thrust belt in southwestern utah highlights the uncertainty associated with episodic sevier deformation in the region. we suggest this, in part, stems from long-lived uncertainty associated with the nature of the kanarra anticline (gregory and williams, 1947; averitt, 1962; threet, 1963a, 1963b; armstrong, 1968; biek, 2007a; biek and others, 2009; biek and hayden, 2016) and along strike correlation of structures (e.g., faults) and stratigraphic units. the kanarra anticline is coincident with the trace of the cordilleran hingeline in southwestern utah, extending from near toquerville to cedar city for about 53 km (figure 1). the development of the kanarra anticline has been contentious since it was first described by dutton (1880), who did not recognize the fold as a separate feature from the hurricane fault. over time, it has alternately been interpreted as forming during mesozoic reverse faulting along the hurricane fault (e.g., lovejoy, 1978), a laramide monocline (e.g., figure 1, p. 548 and figure 2, p. 549, in enriquez st. pierre and johnson, 2021), and as a sevier-age thin-skinned fault propagation fold (grant and others, 1994) modified by rotation of the footwall of the hurricane fault during basin and range extension (stewart and taylor, 1996). the ambiguity in the strain significance of the kanarra anticline reflects complications due to dismemberment of the anticline by the hurricane fault (i.e., the west-dipping limb may be buried beneath neogene and younger fill of cedar valley), offset of the axial trace of the fold (e.g., along the proterozoic paragonah lineament), and burial by prominent landslides (threet, 1963b; picha and gibson, 1985; biek and others, 2015). current consensus recognizes the kanarra anticline as a contractional fault propagation fold formed during the sevier orogeny (see biek and others, 2009) although alternative interpretations as a laramide age monocline persist (see figure 1, p. 548 and figure 2 p. 549, in enriquez st. pierre and johnson, 2021). the role of thrusting in the development of the kanarra anticline is poorly understood. grant and others (1994) and nowir and grant (1995) show the kanarra anticline near kanarraville, utah, to be an asymmetric, overturned anticline, with imbricate thrust splays merging into a high-level detachment fault that soles along the base of the permian kaibab formation (see figure 6, p. 201, in nowir and grant, 1995). older flank thrusts are shown on both limbs of the fold; the flank thrust on the overturned eastern limb corresponds to the taylor creek thrust system of kurie (1966) who interpreted it as a back thrust. the easternmost thrust fault is a “rollover-break-thrust,” a term assigned by nowir and grant (1995, p. 200), which displaced the overturned limb of the anticline to the east and is shown to have breached the surface. several of these thrusts, including the rollover-break thrust, were inferred and necessary to produce a balanced cross section through the kanarra anticline (nowir and grant, 1995). however, in their cross section the rollover-break thrust is shown to have simultaneously both normal and reverse separation along its length (see figure 6, p. 201, in nowir and grant, 1995). previous geologic maps (e.g., averitt, 1967) and subsequent geologic maps (e.g., biek and hayden, 2016) of the kanarra anticline include the west-directed taylor creek thrust system but do not show the presence of a leading edge east-directed thrust. as a result, many publications show the keystone-muddy mountain-square top mountain-iron springs-canyon range thrusts as the leading edge of 5 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 the sevier orogeny in southwestern utah (e.g., see figure 66, p. 61, in hintze, 2005). establishing the location of the leading edge of the sevier fold-thrust belt in southwestern utah is critical to linking the spatial and temporal advancement of the sevier deformation front along its strike length and interpretation of its effect on foreland sedimentation. we report the results of new detailed geologic mapping and structural cross sections of the kanarra anticline, near kanarraville, utah. our work demonstrates that thrust faults and folding are inextricably linked in all stages of formation of the kanarra anticline. our geologic mapping identifies the previously speculated (i.e., nowir and grant, 1995 rollover-break thrust), but unsubstantiated leading edge thrust of the sevier fold-thrust belt along the eastern overturned limb of this part of the kanarra anticline—our red rock trail thrust. following butler and others (2020), we propose the name kanarra foldthrust structure to unambiguously identify the close spatial and temporal association of folding and thrusting in formation of this prominent geologic feature. we characterize the complete profile of this fold-thrust structure, demonstrate regional continuity in tectonic style along its strike (e.g., the red hill), and identify the kanarra fold-thrust structure as the leading edge of the sevier fold-thrust belt in southwestern utah during the late cretaceous. structural setting in southwestern utah, the colorado plateau province consists of a set of high plateaus that are dissected by three large north-trending normal fault systems. these faults systems are 100s of kilometers long of which some continue southward into arizona and the grand canyon region. they form a series of structural blocks that step down to the west towards the basin and range province defining the basin and range-colorado plateau transition zone (figure 1). from east to west, these transition zone normal faults are the paunsaugant, sevier-toroweap, and hurricane fault systems (biek and others, 2015). the markagunt plateau is the westernmost of the high plateaus. the hurricane cliffs and hurricane fault lie just east of the cordilleran hingeline and mark the western edge of the markagunt plateau and the basin and range transition zone (figure 1). cropping out along the hurricane cliffs, between st. george and cedar city, are upper paleozoic to upper cretaceous sediments that have been uplifted, dissected, and are now well exposed in the rugged topography of the footwall of the hurricane fault. stratigraphic separation on the hurricane fault is estimated to be up to 2500 m just north of st. george near toquerville (stewart and taylor, 1996). north of st. george, from the town of toquerville to cedar city, these strata were deformed into the kanarra fold-thrust structure (i.e., the kanarra fold of gregory and williams, 1947) during the sevier orogeny (plate 1; figure 1). here the eastern limb of the kanarra fold-thrust structure trends northnortheast for over 50 km and is well exposed along its length in several across-strike canyons incised into the footwall of the hurricane fault (gregory and williams, 1947; averitt, 1962; biek, 2007a). part of the anticline of the fold-thrust structure has been displaced downward along with the hanging wall of the hurricane fault and is buried beneath neogene to holocene sediments and volcanics in the cedar valley graben (plate 1). beginning at shurtz creek, the anticline of the kanarra fold-thrust structure (i.e., the shurtz creek anticline of averitt, 1962) plunges northwards and a part of a fold closure is preserved near cedar city in the vicinity of the red hill (i.e., the squaw creek anticline of hintze, 2005, p. 175). the fold is likely a doubly plunging anticline (i.e., a pericline); however, the presumed southern closure of the fold has been sheared away along the hurricane fault near toquerville (plate 1). plates 1, 2a, 2b, and 3, and the supplemental files can be found at https:// scholarsmine.mst.edu/geosci_geo_peteng_facwork/2025/. near kanarraville, the approximate center of the fold-thrust structure, exposed strata preserve significant structural complexity in terms of folding and faulting (e.g., see nowir and grant, 1995; biek and hayden, 2016). here, bedding abruptly overturns along a 10-km section of the fold-thrust structure and is displaced and repeated along multiple faults. understanding the spatial and temporal evolution of this part of the kanarra fold-thrust structure through detailed geologic mapping is critical to resolving its tectonic significance to the evolution of the sevier orogeny in southwestern utah. our detailed 1:110,000-scale structural map of 6 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 the kanarra fold-thrust structure and our 1:15,000 geologic map of the central part of the kanarra fold-thrust structure are presented on plates 1 and 2a, respectively, and the stratigraphic column on plate 2b. stratigraphic setting deposition of paleozoic miogeoclinal sediments along the passive margin of the western coast of laurentia was strongly controlled by subsidence from post-rift lithospheric cooling and structural lineaments formed during rifting. during this time, cyclical deposition generated a zone of westward-thickening marine-marginal marine strata beginning at the craton edge, known as the cordilleran hingeline (kay, 1951; stokes, 1976; picha and gibson, 1985; wernicke and others, 1988). thick packages of competent strata—locally including the middle and upper cambrian bonanza king formation, upper cambrian nopah dolomite, mississippian redwall limestone, and permian queantoweap sandstone—were deposited on top of the lower cambrian tapeats sandstone and lower and middle cambrian bright angel shale during this period (hintze, 1986, 2005; hurlow and biek, 2003). whereas these competent units are unexposed in the map area, their presence in the subsurface and contribution to the mechanical response of the stratigraphic package are important to the development of the kanarra fold-thrust structure. the response of paleoproterozoic rocks in this area during sevier contraction appears to be limited to reactivation of basement structures or “structural inheritance” leading to formation of local promontories and reentrants along the kanarra fold-thrust structure as discussed in later sections. the ages, names, rock type, thicknesses, and patterns of formations cropping out in the map area, or included in the cross sections, are shown on plate 2b and are available in the supplementary data repository. towards the end of the permian, basin conditions began to change significantly (hintze, 1986, 2005; biek and others, 2009). a dwindling pattern of shorter and shorter cycles, marked by thinner strata, followed deposition of the queantoweap sandstone. during the beginning of the triassic, base level fell, and an unconformity (i.e., the tr-1 unconformity) surface developed on exposed, previously deposited marine sediments (pipiringos and o’sullivan, 1978). the absence of the incompetent harrisburg member of the permian kaibab formation marks the presence of this major unconformity (hintze, 1986). in the field area, the rock canyon conglomerate or the timpoweap members of the lower triassic moenkopi formation rests unconformably on either the harrisburg or fossil mountain members of the kaibab formation as discussed in later sections. following the rock canyon conglomerate, the final cycles of the passive margin sequence deposition are recorded in the moenkopi formation. higher frequency, relatively short-lived cycles led to deposition of relatively thin (e.g., meters), competent limestones and sandstones interbedded with thicker (e.g., tens of meters), incompetent mudstones and siltstones (see figures 3a and 3b, p. 152, in hofmann and others, 2013). the thicker incompetent packages of rock are also known as the triassic red beds: lower red member, middle red member, shnabkaib member, and upper red member of the moenkopi formation. the major competent layers within this package are found in the timpoweap and virgin limestone members, though both primarily consist of incompetent siltstone and shale as discussed in later sections. a switch to terrestrial (i.e., fluvial and lacustrine) conditions beginning in the late triassic and into the early jurassic, led to deposition of thin, competent layers of sandstone and conglomerate interbedded within relatively thicker layers of mudstone and siltstone (biek and others, 2009). significant thin (meters to tens of meters), competent strata within this package include the shinarump conglomerate member of the upper triassic chinle formation, the dinosaur canyon member of the upper triassic-lower jurassic moenave formation, the springdale sandstone member of the lower jurassic kayenta formation, and the shurtz tongue of the lower jurassic navajo sandstone (plate 2b). this package is capped by the last thick (hundreds of meters), competent layer deposited in the stratigraphic section, the navajo sandstone. unconformably overlying the navajo sandstone are the middle jurassic temple cap and carmel formations, which consist of interbedded competent layers of limestone and/or sandstone and incompetent layers 7 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 of mudstone and gypsum (sprinkel and others, 2011; knudsen, 2014a; biek and hayden, 2016). the upper part of the carmel formation was partially removed by erosion during the cretaceous, and is unconformably overlain by the thin, dispersed orogenic cedar mountain formation (biek and others, 2009; biek and hayden, 2016). the sub-cretaceous unconformity is capped everywhere on the plateau by the cretaceous naturita and straight cliffs formations. in the map area, the jurassic carmel formation and cretaceous strata crop out as gentle, vegetated slope formers and sub-horizontal ledges at the top of the hurricane cliffs. the incompetent pink member of the claron formation unconformably overlies the navajo sandstone in the north hills indicating considerable erosional beveling of mesozoic strata before or during the paleogene (plate 2b; biek and hayden, 2016). this unconformity has temporal significance as it constrains the timing of deformation associated with development of the kanarra fold-thrust structure during the sevier orogeny as discussed in a later section. methods geologic maps boots-on-the-ground geologic mapping using traditional techniques that included topographic base maps, aerial imagery, geologic compasses, gps units, and field notebooks was conducted during the summers of 2016 to 2019. approximately 2000 in-person field observations were collected—including structural orientation measurements—and used to construct the geologic maps (plates 2a and 3). the orientation of all planar features (e.g., bedding, faults, etc.) is reported using the following format – the three digits for the azimuth of the strike is reported first followed by the two digits for the angle of the dip. the orientation of all linear features (e.g., slicken line, mineral lineation, etc.) is reported using the following format—the two digits for the angle of the plunge is reported first followed by the three digits for the azimuth of the trend. for example, a fault plane (040, 65) contains slicken lines (63, 038) and mineral accretion steps (e.g., chatter marks) indicating normal-slip. field data were backed up in real time with fieldmove (from 2017 to 2018; muir, 2015) and strabospot (walker and others, 2019). across-strike and along-strike traverses at camp creek, spring creek, kanarra creek, short creek, murie creek, and along kanarra mountain road (plate 2a) were completed to efficiently cover ground. the location of all contacts mapped in person (particularly difficult and concealed contacts) were refined using a combination of geologic map data extractor (gmde) (allmendinger, 2020), google earth, and lidar data collected in 2020 by the utah geospatial resource center and the utah division of emergency management. in addition, we also used 107 strike and dip measurements extracted from previous geologic maps (averitt, 1962, 1967; biek and hayden, 2016). using our geologic map, aerial imagery, digital elevation models (dem), and gmde (allmendinger, 2020) we constrained unit thickness, three-dimensional projections of geologic contacts (e.g., faults), and axial traces at a regional scale (as opposed to outcrop scale) for the 1:15,000-scale geologic map and 1:10,000-scale structural map (plates 2a and 3, respectively). this allowed us to test structural interpretations in three-dimensions, thus removing ambiguity inherent in two-dimensional interpretations based upon separation (e.g., davis and others, 2011, p. 275). the 1:110,000-scale map of the kanarra fold-thrust structure (plate 1) was compiled from our field mapping, previous 7.5-minute quadrangles (averitt, 1962, 1967; averitt and threet, 1973; hurlow and biek, 2003; biek 2007a, 2007b; knudsen, 2014a, 2014b; biek and hayden, 2016), and three 30' x 60' quadrangles (rowley and others, 2006; biek and others, 2009, 2015). solely for the purpose of emphasizing structural relationships pertinent to the kanarra fold-thrust structure, we choose to show on the map the lower red member, middle red member, and upper red member using the same color scheme, as well as including the temple cap formation in with the carmel formation and displaying the upper cretaceous formations with one color (plates 2a, 2b, and 3). we do not attach, nor imply, any stratigraphic significance to these groupings; they are strictly for illustrative purposes such that the structures in the map area are readily visible in the figures. each map plate was compiled in arcmap 10.8.1 and finalized using adobe illustrator. the information used to construct the geologic maps presented in plates 2a and 3, are available in data repository files. 8 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 geologic cross sections the geologic cross sections are constructed using our geologic map (plate 2a), published unit thicknesses, and unit thicknesses based upon our current mapping, and using gmde (allmendinger, 2020) and the move™ software by petroleum experts (see suplemental data tables a1 and a2). we invoke “pumpelly’s rule,” which states that small-scale structures mimic the style and orientation of larger structures of the same episode of deformation in the same area (pumpelly and others, 1894). thus, establishing the geometrical forms of the folded rocks is an essential step in constructing the cross section. the kanarra fold-thrust structure includes inextricably related buckle folds, forced folds, a regional detachment fault, and earlyand late-forming fold accommodation faults (e.g., mitra, 2002a). these geometrical fold styles are well exposed and well developed within the timpoweap member of the moenkopi formation and the fossil mountain member of the kaibab formation (plates 2a and 3; figure 2) and are also observed in several other units as well. the fold shapes and position of fold accommodation faults (e.g., cloos, 1961, 1964; mitra, 2002a) within the layering suggest a component of buckling before faulting. each fold is comprised of smooth-hinged “kinks” formed by kink panels of varying size and number (figure 2; faill, 1973; also see p. 138–150 and figure 61, p. 143, in faill and wells, 1974). map-scale views of folded layers (plates 1, 2a, and 3) show smooth-hinged kinks in the field (figure 2). the southern cliff face at the mouth of spring creek hosts a large, outcrop-scale composite fold-thrust structure and buckle fold train immediately above the west-verging thrust within the fossil mountain member (figure 2a). at the western end of this fold train is a break-thrust fold (figure 2a; also see plate 33, p. 228, in willis, 1893; fischer and others, 1992). this family of folds and faults (cf., dahlstrom, 1969) mimics the structural style of the kanarra fold-thrust structure (see pumpelly and others, 1894). thus, we employed the kinked, parallel fold breakthrust model in construction of all our cross sections to reflect the geometrical style of folding and faulting observed in the field. the cross sections are based upon our geologic mapping (this study and unpublished geologic mapping) and where noted utilize data from the geologic maps of averitt and threet (1973) and knudsen (2014a). shear fracture measurements shear fracture sets occur within competent strata along the kanarra fold-thrust structure. they are found along the mapped traces of major fold accommodation faults. elsewhere, these shear fractures are commonly mesoscale or outcrop-scale faults. for clarity, we restrict the term fault to hundreds of meter-scale structures and shear fracture to meter-scale structures. for each shear fracture, the strike, dip, and rake of slickenlines are measured and recorded. rakes are measured down from right-hand rule strike directions along the fracture plane, and slip sense is interpreted separately. slip sense is interpreted from r-type and p-type fracture steps (common in sandstones) or mineral fibers (common in carbonates) on the fracture surface (petit, 1987; allmendinger and others, 1989). the slip sense is also constrained, where possible, by offset of marker beds, drag folds, and oblique exposures of shear fracture sets. these shear fractures are analyzed using faultkin and stereonet (marrett and allmendinger, 1990; allmendinger and others, 2013; cardozo and allmendinger, 2013) to produce a fault plane solution, which can be used to estimate the aggregate, map-scale orientation and slip sense of the fault plane at several locations on the fold limb. using the average bedding orientation at each shear fracture set location, we rotate the fault plane solutions model so that local bedding fits the average orientation of bedding at camp creek where the fold is upright and open. this allows for direct comparison of fault plane solutions along the length of the fold. we undertake these analyses primarily to document the presence and deformation history of early formed thrusts as the fold evolves from a gentle, open fold in the southern part of the map area to a steep, tight, overturned fold in the northern part of the map area. this serves as an approximate temporal progression of structural development and strain accumulation during folding. results the results of our field investigations are presented 9 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 as (1) a 1:110,000 bedrock geologic map of the kanarra fold-thrust structure (plate 1), (2) a 1:15,000 geologic map emphasizing the bedrock geology and structure of the central part of the kanarra fold-thrust structure (plate 2a), (3) a geologic cross section through the central part of the 1:15,000 geologic map of the kanarra fold-thrust structure, and (4) a 1:10,000 geologic map emphasizing faults, fold axes, field photo locations, and fault plane solutions along the central part of the kanarra fold-thrust structure (plate 3). in the following sections we expand upon significant details of the results of our geologic mapping as applied to specific topics related to the stratigraphy and structures present in this region as they relate to defining the kanarra fold-thrust structure. distinguishing the timpoweap member from the virgin limestone member of the moenkopi formation stratigraphic nomenclatural changes have been suggested for several mesozoic and cenozoic units in the map area within the past two decades (e.g., lucas and tanner, 2006; lucas and others, 2007; hautmann and others, 2013; hofmann and others, 2013, 2014; carpenter, 2014). some have been accepted, but not all trmt kct trmv pkf trmt pkh trmt pkf pkf b a c figure 2. (a) view south on a composite fold-thrust structure within the fossil mountain member of the kaibab formation in the core of the leading anticline. inset: close-up of the “leading” fold, a fractal model of the kanarra fold. (b) view south above the entrance to camp creek. folds within the lower ledge-forming unit of the timpoweap member of the moenkopi formation, cut by later, antithetic thrusts in the hanging wall of the kanarra creek thrust. (c) view north onto the leading anticline of the kanarra fold-thrust structure from the spring creek canyon trail. here, the lower ledge-forming unit in the timpoweap is duplicated along an early formed thrust–this may be a piece of the discontinuous kanarra creek thrust exposed to the north and south. structure initializations: kanarra creek thrust–kct. see plate 2b (stratigraphic column) for explanation of map unit symbols. 10 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 suggested changes are reflected in current maps. for this reason, we adopted the convention of using member and formation names based upon recent local mapping (e.g., knudsen, 2014a, 2014b; biek and hayden, 2016). nevertheless, the detailed characteristics of certain units—particularly the timpoweap and virgin limestone members of the moenkopi formation—are critical to unravelling the complex structural relationships along the eastern limb of the kanarra fold-thrust structure, especially the relative timing of earlyversus late-forming thrust faults in the development of the kanarra fold-thrust structure. in southwestern utah, the timpoweap and virgin limestone members of the moenkopi formation represent a series of intertonguing lithofacies (e.g., lucas and others, 2007; hofmann and others, 2013; figure 2 this paper). they record a cyclic stratigraphic pattern reflecting sequential transgressions and regressions along the cordilleran hingeline during the lower triassic. the shallow-marine and sabkha units generally represent transgressive packages, which correlate to units elsewhere as part of the thaynes formation (or thaynes group) of northern utah, whereas the red beds represent regressive packages (lucas and others, 2007). the shallow-marine lithosomes, particularly the timpoweap and the virgin limestone members, have similar lithologies and fossil distributions. this can make them difficult to distinguish in the field, especially in complexly faulted areas where they are juxtaposed and overturned. for accurate discernment between the timpoweap and virgin limestone members, careful consideration must be given to their topographic expression (i.e., “fingerprint”), distribution of lithologies, and characteristic local fossil assemblages. timpoweap member the topographic signature of the timpoweap member is distinct from that of the virgin limestone member (plates 2a and 3). the unit can be divided approximately in half. the lower half forms a thick (over 20 m) ledge, whereas the upper half forms a slope. the ledge is a thick-bedded, gray to pale yellow-orange to yellow-gray limestone (10yr 8/6 and 5y 8/4, see munsell color, 2009), whereas the slope former is an incompetent, yellow micritic shale (plates 2a and 3; figure 3). where the rock canyon conglomerate member is present, the conglomeratic facies grades upward into the ledge-forming timpoweap, so that the lowermost limestone beds may contain isolated, thin, pebble conglomerate lenses. some limestone beds in the ledge forming timpoweap are sand rich; others appear sandy on their weathered faces, particularly the light to medium gray (n6 to n7) to pale yellow-orange to yellow-gray beds, yet most of these are a crystalline limestone (see dunham, 1962) as revealed by fresh surfaces. this contrasts markedly with thick, yellowish-orange, yellowish-brown, and moderate yellow-gray (10yr 6/6, 10yr 5/4, and 5y 7/6) quartz arenite beds in the virgin limestone. the upper slope-forming part of the timpoweap includes thin, discontinuous, dark-brown, sand-bearing limestone. locally, the top of the yellow micritic shale unit can abruptly darken to a deep purple-gray before the contact with the overlying lower red member (figure 4). this purple-gray (5p 6/2 to 5p 4/2) layer is distinctly part of the timpoweap member (cf., lucas and others, 2007, p. 111), but it is not always present in the timpoweap, particularly at thrust contacts. however, where present, it can lead to a misidentification between the timpoweap and virgin limestone members because it resembles the purple mudstone beds within the virgin. fossils in the timpoweap member are scarce, particularly in comparison to the abundant fossiliferous virgin limestone member. the fossil assemblages of the timpoweap and the virgin limestone contain genera that are common to both members. however, there are key fossils intrinsic to the timpoweap that distinguish it from the virgin limestone assemblage (lucas and others, 2007; figure 5 this paper). a characteristic timpoweap fossil includes the ammonite wasatchites (figures 5a and 5c), which is exclusive to the timpoweap member; however, it is also rare and typically poorly preserved. the discovery of wasatchites (figure 5c) on the ridge north of kanarra creek confirms this unit as the timpoweap member (see plate 3 for location). virgin limestone member the most distinct mapto outcrop-scale characteristic of the virgin limestone is its topographic signa11 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 ture (figure 4). within the field area, the virgin limestone is dominantly composed of sandstone, siltstone or mudstone, and minor limestone, with the incompetent strata comprising over two-thirds of the total thickness. where depositional contacts are preserved, the top of the virgin limestone is marked by a sharp transition into a double layer of gypsum at the base of the middle red member. the virgin limestone consists of several thin, competent, resistant fins set within a much thicker (tens of meters) interval of incompetent mudstone and siltstone. the fins are gray (n7 to n5), medium to very thick bedded packstone and wackestone or tan (10yr 6/6 to 10yr 5/4 on weathered faces, and 5y 7/6 on fresh faces) fine-grained quartz arenite. locally, a fin can contain both lithologies separated by a sharp contact between sandstone and limestone. the fins are typically 1 to 4 m thick, although fins up to 8 m thick are reported (see knudsen, 2014a). where the fins are steeply dipping, they stand high above the intervening incompetent strata (figure 4b). the incompetent intervals contain mudstone and siltstone, typically varying in color from gray (n7 to n5) to brown (5yr 4/4) and locally purple (5p 6/2 to 5p 4/2). the virgin limestone member is also distinguished from the timpoweap member by the abundance of fossils and the presence of the following key marker trace fossils and fossils: (1) the trace fossil thalassinoides and two major body fossil types, (2) the brachiopod rhynchonella, and (3) the crinoid holocrinus (smithi?) (figure 6). the trace fossil thalassinoides was found only within the virgin limestone, along the bottom of a very thick bedded, tan quartz arenite ledge, which commonly trmv trcs trcs jks jks jn rrtt sct hf jtrm jtrm trmt sct cedar valley n 0 150 300 m trmt (lower) trmt (upper) trml trmv a b figure 3. (a) google earth 3d terrain view of the overturned stratigraphy along the kanarra fold limb, looking southwest into short creek. the spring creek and red rock trail thrusts are included to orient the reader to the map. here, the timpoweap member forms the first of several ridges rising above cedar valley. the ledge-forming gray to yellow lower limestone unit holds up the ridge, with the yellow calcareous shale upper unit outcropping beneath. (b) field photograph of the same view, looking farther westward onto the ridge of timpoweap member of the moenkopi formation. the dashed white line marks the transition into the upper yellow shale unit. near the contact with the lower red member, the shale grades vertically into a deep purple-gray color. structure initializations: hf–hurricane fault; sct–spring creek thrust; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 12 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 outcrops near the top of the unit (figure 6a). the trace fossil is preserved as interweaving casts of tunnels with triple junctions and is interpreted as thalassinoides (cf., see figure 16a, p. 166, in hofmann and others, 2013); this trace fossil was found at kanarra creek where the virgin limestone member is overturned. in addition, the brachiopod rhynchonella is common only to the virgin limestone (figure 6c), where it is restricted to the limestone layers. the brachiopod is most like rhynchonella from the thaynes formation of southeastern idaho (see plate 1, p. 311–312, in perry and chatterton, 1979); however, its size and plications also resemble piarorhynchella (cf., figure 9c1, p. 161, in hofmann and others, 2013) and lissorhynchia (wang and others, 2017). the brachiopods commonly form thin shell beds, and complete, individual shell fossils can be found near outcrops where they weather out of the limestone fins (figure 6c). they are small, with their long axes typically less than 2 cm long, and contain rounded, relatively wide, plications, which greatly increase in amplitude at the shell midpoint (figure 6c, inset). the crinoid holocrinus (smithi?) was found exclusively in the limestone or sandstone layers of the virgin limestone member as scattered stem plates (figure 6; cf., figure 3c, p. 101, in schubert and others, 1992). we observed two forms of crinoid stem plates. one has more rounded corners, straighter sides, and more closely resembles a pentagon (figure 6b), whereas the other sct trmt cedar valley trml trmv trms trmu n 0 100 200 m a trmv fins sct b figure 4. (a) field photograph view of the lower units in the exposed stratigraphic section–primarily moenkopi formation– looking north across spring creek. the leading anticline hinge of the kanarra fold forms the hill to the west. the western hilltop is capped by the timpoweap member of the moenkopi formation–yellow shale underlain by the gray-yellow ledge forming lower unit. the yellow shale grades into the deep purple-gray mudstone near the contact with the lower red member of the moenkopi. looking east across a saddle of lower red member, vertical to overturned gray limestone and tan sandstone fins interbedded with gray-purple mudstone form a ridge of the virgin limestone member of the moenkopi. the virgin limestone ridge is displaced by the spring creek thrust, truncating the middle red member of the moenkopi. inset (b) emphasizes the alternating competent fins and mudstone in the virgin limestone. structure initializations: sct–spring creek thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 13 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 resembles a five-sided star (figure 6d). the crinoid holocrinus is entirely unique to the virgin limestone and, along with the brachiopods, were used as marker fossils. description of the kanarra fold-thrust structure the complexity of structural elements, folds, and faults of the kanarra fold-thrust structure reflects the protracted, multi-phase geologic history of an area that straddles several major long-lived lithospheric boundaries: (1) the cordilleran hingeline, (2) the leading edge of the sevier fold-thrust belt, and (3) the boundary between the basin and range province and the colorado plateau province (figure 1). resolving the tectonic significance of the kanarra fold-thrust structure in the context of this extended geologic history requires understanding the inextricable temporal and spatial rea c b d figure 5. fossils used in the field to distinguish the timpoweap member of the moenkopi formation. ammonites of differing levels of preservation—this fossil type was scarce and poorly preserved in the field area. (a) the ammonite specimen appears to be anasibirites and is entirely replaced by calcite. (b) the ammonite specimen appears to be wasatchites identified from the shell decorations and size (cf., figure 5, p. 115, in lucas and others, 2007), although the level of preservation makes interpretation difficult. this specimen was found in a sandstone bed along the ridge capped by the timpoweap member north of kanarra creek. (c and d) specimens of eumorphotis (cf., figure 6, p. 161, in hautmann and others, 2013; figure 11, p. 562, in hofmann and others, 2014), a bivalve genus dominantly found in the timpoweap member in the field area. ammonites are known to occur in the virgin limestone member (hofmann and others, 2011), but none were found in the kanarraville area. five-sided crinoids a b c d figure 6. trace fossil and fossils used in the field to distinguish (identify) the virgin limestone member of the moenkopi formation. (a) interweaving bioturbations reminiscent of trace fossil thalassinoides found as casts on the bottom of an overturned, thick-bedded sandstone ledge capping the southern ridge near the entrance to kanarra creek. (b) holocrinus in gray limestone of the virgin limestone just north of spring creek. (c) brachiopod shell bed and well-preserved specimen (inset) found at kanarra creek. these are similar to lissorhynchia or the rhychonella species found elsewhere in the thaynes formation but were not found outside the virgin limestone in the kanarraville area. (d) holocrinus within tan, fine-grained sandstone in the virgin limestone. 14 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 lationship of contractional faults (i.e., thrusts) to the development of the kanarra fold-thrust structure. due to the abundance of faults associated with the kanarra fold-thrust structure, we have assigned names to the major faults and their splays, or closely associated faults, for clarity (tables 1 and 2). the relationship of folding and faulting is well preserved in the central part of the kanarra fold-thrust structure (plate 1) and is best understood using the detailed geologic map of this area (plates 2a and 3) and a structural cross section through the kanarra fold-thrust structure prior to its dismemberment by the hurricane fault during basin and range extension (figure 7). this cross section shows the full profile of the restored kanarra fold-thrust structure at the time of the sevier orogeny—prior to the western trailing limb of the kanarra anticline being severed and buried, along with the hanging wall of the hurricane fault in cedar valley, beneath a thick mantle of alluvium shed off the hurricane cliffs (plates 1 and 2a). the compound nature of the kanarra anticline is readily discernible in the cross section (figure 7). the central part of the compound kanarra anticline is defined by a broad sub-horizontal hinge zone that connects two anticlines. we refer to the anticline on the eastern half as the leading anticline, and the anticline on the western half as the trailing anticline. these terms reflect the spatial position of these folds within the kanarra anticline and are introduced for clarity in the discussion section (figure 7). the kanarra anticline the kanarra anticline is an asymmetric, east verging, overturned anticline with a compound geometric form (figure 7). the fold form has many of the characteristics of idealized fault propagation folds that develop in the hanging wall of blind thrust faults (e.g., mitra, 2002b; davis and others, 2011, p. 414–428). the anticline is defined by a long, shallow west-dipping trailing limb, a relatively flat hinge zone, and a shorter leading limb that is steeply dipping west and overturned. the overturned leading anticlinal limb verges eastward and transitions into a tight, east-verging syncline. field exposure of sparse, isolated remnants of the hinge zone along the strike of the leading anticline of the kanarra anticline (see figures 2a inset and 2c) exhibit a kink style geometry of folding. in cross section, the kanarra anticline-syncline pair can be represented with a series of kink panels (figure 7); collectively these kink panels contribute to defining the overall form of the anticline and the syncline. however, the leading anticline hinge zone also has an overall rounded form, which is characteristic of buckle folds. buckling (willis, 1893; fischer and others, 1992) may have contributed to the initial stages of folding of these strata. the trailing limb of the kanarra anticline includes an early fold accommodation fault, which has merged with the later, exposed spring creek thrust (figure 7; see later section for more detail). displacement along the spring creek thrust forms a trailing or distal faultbend fold (e.g., davis and others, 2011, p. 409–413) in the hanging wall of the trailing limb of the kanarra anticline. this fault-bend fold modifies the overall geometric form of the kanarra anticline into a composite fold with a trailing anticline and a leading anticline (figure 7). the trailing and central part of the kanarra anticline, along with the hanging wall of the hurricane fault are buried beneath younger geologic units in cedar valley and their relationship to the pintura anticline is presented in the discussion section. the axial trace of a fold, the line formed by the intersection of the axial surface of the fold with any other surface, occurs within the hinge zone of the fold (davis and others, 2011). the hinge zone of the leading anticline, where shallow west-dipping strata rotate into the eastern leading limb of the anticline, is sparsely exposed (plate 1). the remnants of the hinge zone are used to define the discontinuous axial trace of the leading anticline axial surface along the length of the kanarra fold-thrust structure (plate 1). previously, the hinge zone of the leading anticline was interpreted as the hinge zone of the kanarra anticline, and because of the discontinuous, dissected, nature of the leading anticline hinge zone along strike, was locally assigned other names (e.g., hintze, 2005, squaw creek anticline, p. 175). in the central part of the kanarra fold-thrust structure, there are three locations where the leading anticline hinge zone is well exposed: (1) camp creek, (2) spring creek, and (3) just south of kanarra creek (plates 2a and 3). 15 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 hinge zone at camp creek at camp creek, the leading anticline is upright and open. the axial trace is exposed in lower moenkopi units and the fossil mountain member of the kaibab formation, which crop out in the canyon at the mouth of camp creek. fault splays of the hurricane fault cut the hinge zone near the creek mouth (figure 8a) and the axial trace is lost south of the creek where it has been sheared away (plates 2a and 3). within the canyon, a steep axial surface separates consistently westward dipping (about 10 to 15° w.) from east dipping (about 15° e.) bedding in limestone of the fossil mountain member of the kaibab formation. here, in the core of the hinge zone, multiple meter-scale kink panels in the limestone impart an open, gentle flexure best seen at the bottom of the canyon (figure 8b). the geometry of the leading anticline is reflected in the shape of the hinge table 1. locations of faults on the kanarra fold-thrust structure that outcrop in the kanarraville area. fault name fault type timing initials vrg.* locality utm (e) utm (n) kanarra creek thrust limb wedge thrust early kct w kanarra creek 308241 4157135 taylor creek thrust limb wedge thrust early tct w camp creek 307079 4152057 hicks creek thrust limb wedge thrust early hct w kanarra creek 308528 4156697 spring creek thrust forelimb shear thrust late sct splay e kanarra creek 308180 4157130 primary splay spring creek thrust limb wedge thrust early–late** sct e spring creek 307538 4154717 main trace murie creek thrust1 forelimb shear thrust late mct1 e spring creek 307900 4154058 murie creek thrust2 forelimb shear thrust late mct2 e murie creek 309957 4157749 red rock trail thrust forelimb shear thrust late rrtt e red rock trail 308756 4155360 murie creek fault oblique-slip (rl) early–late*** mcf rl murie creek 312353 4159903 * vergence or displacement direction (cardinal) ** initially an east-verging limb wedge thrust; late movement observed in the field cuts across leading anticline hinge and limb *** initial movement uncertain, but we suggest it is likely syn-folding table 2. locations of faults on the kanarra fold-thrust structure that outcrop at the red hill. fault name fault type timing initials vrg.* locality utm (e) utm (n) spring creek thrust limb wedge thrust early–late sct e stephens canyon 319059 4172923 stephens canyon thrust (w) hinge wedge thrust early–late** stct(w) w stephens canyon 319288 4172058 stephens canyon thrust (e) limb wedge thrust early*** stct(e) w stephens canyon 319288 4172058 hicks creek thrust limb wedge thrust early hct w hicks creek 319592 4172798 coal creek thrusts hinge wedge thrust late ccts nw coal creek 319470 4172283 red rock trail thrust forelimb shear thrust late rrtt e lone tree mtn. (w slope) 320413 4170036 thunderbird gardens trail fault oblique-slip late tgtf ll thunderbird gardens trail 319835 4173373 * vergence or displacement direction (cardinal) ** late movement observed by truncation of trmm and indicated in cross section parallels strike of beds—likely began early and related to stct(e) *** duplicates shnabkaib member roughly parallel to strike 16 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 zone, which is horizontal and open, with the enclosing strata forming an interlimb angle of about 150° (gentle). hinge zone at spring creek the axial trace within the hinge zone of the leading anticline is well exposed within a 60-m-high canyon wall at the mouth of spring creek. the cliff face exposes the fossil mountain member of the kaibab formation capped by the timpoweap member of the moenkopi formation. the hinge zone, appearing rounded, tightens considerably between camp creek and spring creek. at spring creek, the interlimb angle is about 65° (close) and much tighter than the interlimb angle of 150° (gentle) at camp creek. here, the steep (about 80°), west-dipping axial surface roughly parallels the trace of the hurricane fault. farther east along spring creek, the transition from steeply dipping to overturned strata is readily shown by rotation of the primary bedding in the kaibab formation. in addition, steep, vertical, and overturned dips are recorded by the resistant “fins” in the virgin limestone member of the moenkopi formation (figures 4 and 9; plates 2a and 3). hinge zone near kanarra creek just north of spring creek, about 500 m from the transition to overturned bedding in the timpoweap member, the hinge zone of the leading anticline is truncated by the hurricane fault (plate 2a). east of this jn jtc kcn ks jks trcs trmv trms ct cbk cnd mr pql pqu pkf trmt jtc jn kcn ks jks trcs trmv trms pql ct cbk mr pqu pkf trmt xu west a meters 0 4000 2000 1000 3000 -1000 -2000 -3000 east a’ meters 4000 2000 1000 3000 -1000 -2000 -3000 sct kct rrtt hct tct tct trailing anticline hinge leading anticline hinge kink panel leading syncline kanarra anticline kanarra fold-thrust structure figure 7. cross section a–a' of the kanarra fold-thrust structure at kanarra creek showing the restored sevier structure circa 80 ma, based on field mapping along kanarra creek. kink axes and components of the hinge zone are annotated for reference. eroded geology is faded out. the pre-extension trailing limb and fold crest are constrained by the tilted, sub-horizontal layering along the hurricane cliffs and the shape of the closely related pintura anticline (hurlow and biek, 2003). no strata below the fossil mountain member of the kaibab formation (pkf) are exposed at the location of the cross section; unexposed layer thickness and presence are constrained by local data sources (hintze, 1986; van kooten, 1988; hurlow and biek, 2003; biek and others, 2009). unexposed, thick, competent layers (cbk-cnd, mr, pq) are colored according to age; exposed ridge-former colors correspond to the map. present-day topography is included to emphasize the ridge-formers. structure west of the hurricane cliffs, within the present-day cedar valley graben, does not represent present-day bedrock geology. structure initializations: sct–spring creek thrust; kct–kanarra creek thrust; hct–hicks creek thrust; tct–taylor creek thrust; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of all map unit symbols. line of section shown on plates 1 and 2. 17 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 truncation, several thrust faults of the spring creek thrust system cut through the hinge zone (see the later discussion on faults). the largest splay of the spring creek thrust system displaces overturned timpoweap member onto shallow, west-dipping (about 8° w.), and presumably upright virgin limestone member. a low topographic ridge underlain by the virgin limestone member east of the thrust truncation hosts a closed (about 35° interlimb angle), gently inclined, overturned fold. on the east side of this topographic ridge, between spring creek and kanarra creek, part of the reclined fold nose is preserved (figure 9b), and the middle red member double-gypsum layer is disharmonically folded into an “s-fold” on the eastern limb (307700 m e.; 4155810 m n.). bedding taken west of the fold nose indicate a shallow-dipping (15 to 35° w.), upright western limb, whereas bedding on its steeper (60 to 75° w.) eastern limb is overturned. the axial trace of this fold can be mapped northwards for nearly the entire length of the low virgin limestone member ridge (about 1000 m) until it dies out at kanarra creek, likely cut by the spring creek thrust. a small, later thrust (also about 1000 m long), cuts through the western limb of this fold (plates 2a and 3, also see avern 0 100 200 m kct kct fold camp creek kanarra creek spring creek cedar valley wayne canyon tct hf splays hf hfhf splay trmt trmr pkf pkf trmr trmt c trmv trmt trmt kct trmr trmr b a pkf black-banded chert chert bands and blebs trcs trcs trms trms trmv trmv trmt trmt trmt jks jtrm figure 8. (a) google earth 3d terrain view with landsat/copernicus imagery of the hurricane fault zone along the length of the exposed kanarra fold-thrust structure in the study area. splays of the hurricane fault zone in the area are exposed here at camp creek. (b) low-displacement normal faults within the eastward-diminishing hurricane fault zone at the mouth of camp creek. (c) larger-displacement normal faults; westernmost fault displaces the timpoweap member of the moenkopi formation next to the kaibab formation. field assistant dylan webb is 1.72 m tall. also shown is the permian unconformity, here seen as rock canyon conglomerate member of the moenkopi formation over black-banded, chert-rich kaibab formation. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; tct–taylor creek thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 18 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 itt, 1967). this thrust likely formed to accommodate strain within the overtightened fold hinge. the entire structure is transported eastward along the main trace of the spring creek thrust just to the east of the ridge. we interpret the tightly folded virgin limestone here to be the northernmost remnant of the leading anticline hinge zone in the study area, cut and modified by transport along the spring creek thrust. contraction faults the kanarra anticline-syncline pair is faulted along its length (plate 2a). the greatest density of faults crops out in the central section where the eastern limb is overturned (plate 3). typically, these faults (i.e., fault planes) are poorly exposed and inaccessible to direct observation. they are mappable through observations of truncation, folding, or attenuation of incompetent strata along competent ridge formers. where possible, striated, stepped shear fracture sets within competent units were measured in the field to determine the aggregate sense of slip of the larger thrust surfaces (e.g., petit, 1987; marrett and allmendinger, 1990). most of these faults are contraction faults associated with the sevier orogeny and the formation of the kanarra fold-thrust structure. jks jks jtrm jtrm jtrm trcs trmv trmv trmt camp creek cedar valley spring creek spring creek trmv trcs trmt trmt kct tct tct rrtt sct tct sct mct* hf jks n sct splay jks trcs tct kct a 0 100 200 m leading anticline hinge leading anticline hinge trmm trmv view looking north hf sct splay leading anticline hinge trmt view looking south b c figure 9. (a) google earth 3d terrain view with landsat/copernicus imagery looking south into spring creek where the kanarra fold-thrust structure overturns. selected faults and sedimentary contacts are shown for reference to the map. part of the leading anticline hinge here is defined by the shape of folded timpoweap and virgin limestone members of the moenkopi formation and kaibab formation strata. (b) view to the north onto a tight, gently reclined closure on the leading anticline hinge within the virgin limestone member just to the north of (a) and east of (c). (c) field photograph looking south of upright (middle and background) and overturned (middle ground) timpoweap, outlined by the white harrisburg member–timpoweap member contact. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; sct–spring canyon thrust; tct–taylor creek thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 19 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 early contraction faults contraction faults associated with the kanarra foldthrust structure can be subdivided into early and late contraction faults relative to the evolution of the anticline-syncline pair from open and upright to tight, overturned, and asymmetric (tables 1 and 2). early contraction faults include the kanarra creek, taylor creek, and hicks creek thrust faults. these early contraction faults all have the following attributes consistent with their inception as thrust faults at the earliest stages of folding: (1) the strike of these faults is typically sub-parallel to parallel to bedding (plates 2a and 3); (2) the map-scale patterns of the fault traces through the topography constrain the dips on these faults to be typically 10 to 25° steeper than dip of the bedding in their footwalls, consistent with early thrusts that are now folded (cloos, 1961, p. 106); (3) ridge-forming units are commonly duplicated by these thrusts, doubling, or tripling the original thickness of these units; (4) statistical solutions of measurements of rake, displacement direction, and orientation of striated, stepped shear fracture populations along these duplications indicate thrust sense of slip (plate 3; table 3); and (5) asymmetric folds, while not always present, indicate displacement consistent with thrusting (e.g., figures 2 and 9). in the central section of the kanarra anticline, several early formed contraction faults were folded and are overturned along with the eastern limb of the leading anticline—these faults can exhibit an apparent normal sense of displacement in the field (figure 7; plates 2a and 3). these early thrusts occur at all scales, with the largest, the taylor creek thrust (kurie, 1966; biek, 2007a) being tens of kilometers long (plate 2a). due to dismemberment of the kanarra anticline by the hurricane fault, these thrusts crop out only within the hinge zone of the leading anticline and the eastern limb of the kanarra anticline. however, similar early contraction thrusts are present on the western limb of the closely associated virgin anticline (e.g., at leeds, utah, to the southwest) and along its crest (biek, 2003a, 2003b). because these faults tend to form on the limbs (flanks) of folds, we refer to these early formed thrusts as flank thrusts (e.g., grant, 1987), though they are known by other names (a type of fold accommodation fault or wedge faults (cf., cloos, 1961; faill and wells, 1974; mitra, 2002a). we infer that flank thrusts were also present on the trailing limb of the kanarra anticline (i.e., the spring creek thrust) and their presence is supported by our mapping and structural cross section of the kanarra fold-thrust structure (figure 7; plates 2a and 3). the significant flank thrusts within the central parts of the kanarra fold-thrust structure are discussed in the following sections. kanarra creek thrust: the kanarra creek thrust is the westernmost exposed thrust in the map area (plate 2a). it is commonly associated with repetition of stratigraphic units lower in the section, typically the timpoweap and lower red members of the moenkopi formation and crops out close to the hinge zone of the leading anticline of the kanarra anticline. we infer its trace is discontinuous along the length of the kanarra anticline due to the structural level of exposure and to its removal from view because of displacement of the hanging wall of the hurricane fault. the southernmost occurrence of the kanarra creek thrust in the map area is at camp creek (plate 2a). here the leading anticline is upright and open. the kanarra creek thrust crops out along the hinge of the fold where it duplicates the ledge-forming limestone layer in the timpoweap member (figure 10). the thrust has been affected by folding and dips shallowly eastward at about 20° (about 10° greater than the strata in its footwall) and displaces strata in the hanging wall to the west. in the hanging wall of the thrust is an asymmetric (tops-tothe-west) fold within the lower red member (figure 8a) (306380 m e.; 4153120 m n.). based on structural level and repetition of stratigraphic units, the kanarra creek thrust continues southwards along strike into wayne canyon (see plates 2a and 3); farther south it may correlate to the thrust along the black ridge in the pintura 7.5-minute quadrangle (e.g., hurlow and biek, 2003). in spring creek, the kanarra creek thrust crops out along the hinge zone of the leading anticline (figure 9; plates 2a and 3). north of spring creek, parts of the fault and the hinge zone of the fold have been removed by the hurricane fault. continuing northward, remnants of the hinge zone of the leading anticline are complexly faulted by both early and late thrust faults. the inten20 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 location, fault name local bedding unrotated rotated* fault plane (s,d,r**) ** “r” is the rake, shown in aki-richards format (e.g., allmendinger, 2012) * rotated to the inclination at camp creek (38°) strike (s), dip (d) in degrees *** may be related to the folded kanarra creek thrust **** late (current) orientation favorable for reactivation, see text for explanation table 3. fault plane solutions for selected thrusts in the kanarra fold-thrust structure. na (022, 25, 122)(041, 38) camp creek taylor creek thrust n=17 na (208, 64, 95)(211, 57) kanarra creek spring creek thrust n=32 (353, 57, 105)(185, 60) spring creek taylor creek thrust n=13 n=13 82° short creek taylor creek thrust (235, 67) n=26 n=26 75° n=26 early**** (036, 60, 91) late (225, 56, 83) (064, 39, 71) murie creek taylor creek thrust (236, 65) n=54 77° n=54 (003, 39, 82)(206, 42) kanarra creek taylor creek thrust n=23 n=23 100° (202, 53, 85)(213, 81) kanarra creek murie creek thrust fold-thrust structure n=32 n=32 138° (032, 67, 100) kanarra creek kanarra creek thrust movement*** (211, 57) n=10 83° n=10 21 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 sity of deformation requires accurate identification of stratigraphic units and their spatial relationships to determine the location of the kanarra creek thrust. near the mouth of kanarra creek is a low hill with a water storage tank that is underlain by the kaibab and moenkopi formations up to the timpoweap member (figure 11). looking to the north (figure 11b) these same strata have been thrust eastward in the hanging wall of a splay of the spring creek thrust (discussed below). just east of this hill is a resistant ridge of overturned timpoweap member comprised of yellow limestone, stratigraphically overlain by yellow micritic shale, and capped by purple mudstone. the timpoweap is followed eastward (up section) by the lower red member and then the virgin limestone member. the succession of strata, confirmed by outcrop appearance, lithology, and fossils (cf., figures 3 to 6), shows an uninterrupted, overturned, stratigraphic section up to the main trace of the spring creek thrust (figure 11). the lower red member of the moenkopi formation also crops out on the western side of the ridge formed by the overturned limestone of the timpoweap member (figure 11; plates 2a and 3). this n jks jks jks jtrm jtrm trcu trmu jtrm trcs trcs trms trms trcu trmv trmv trmt trmt trmt kct tct hf cedar valley kct trmv trmt trmt trmr a b early thrust late thrust normal fault oblique-slip fault sedimentary contact early thrust (ot) figure 10. (a) google earth 3d terrain view into camp creek, looking south. the kanarra creek thrust is seen here as an upright, west-directed thrust duplicating the timpoweap member. this thrust continues southward along strike into wayne canyon (background). bottom right inset: legend for this and subsequent google earth 3d terrain views. (b) field photograph of the kanarra creek thrust looking southeast. ledge-forming timpoweap member of the moenkopi formation in the middle ground is thrust over the timpoweap and rock canyon conglomerate of the moenkopi outcropping on the kanarra fold crest in the foreground (southern side of camp creek). we place the laterally variable, gradational contact from where the rock canyon conglomerate weathers into hoodoos closer to the mouth of the creek (foreground). structure initializations: hf–hurricane fault; kct–kanarra creek thrust; tct–taylor creek thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 22 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 repetition within overturned strata marks the presence of an early thrust, the kanarra creek thrust, that was folded and overturned during formation of the leading anticline (figures 7 and 12; plate 2a). the kanarra creek thrust can be followed farther to the north as it continues along the resistant ridge defined by the limestone ledge of the timpoweap member. the trace of the thrust veers obliquely eastward across the ridge as it ramps up section (plates 2a and 3). displacement along the kanarra creek thrust ramp is revealed on the north side of the ridge, where the timpoweap member is juxtaposed directly adjacent the virgin limestone member (figure 13) (308635 m e.; 4157735 m n.). farther north along strike, the kanarra creek thrust soles into red beds of the moenkopi formation, placing the lower red member onto a sliver of the middle red member (figures 13b and 13c). a complex set of thrust splays followed by a synform in the timpoweap member marks the northern exposure of this part of the kanarra creek thrust before its main trace veers back to the west and is truncated by the hurricane fault (plates 2a and 3). jks jtc jn jks jtrm trcs trcs trmt trmt water storage tanks pkf mct2 rrtt hct kcthf kct n tct kanarra creek trmv trmv sct splay mct1 trmt 0 100 200 m hct a sct sct splay kct trmv continuous section trmt trmt pkf pkh trmr b cedar valley figure 11. (a) google earth 3d terrain view into kanarra creek looking northeast. selected faults and sedimentary contacts are included for reference to the map. (b) along-strike view upon ridges of the timpoweap and virgin limestone members of the moenkopi formation to the east. the lower red member of the moenkopi formation is also present west of the timpoweap, marking the kanarra creek thrust. farther west, the kaibab formation and part of the timpoweap member are thrust over this older thrust system on the spring creek thrust primary splay. the permian-triassic unconformity is marked by rock canyon conglomerate overlying the harrisburg member near the bottom of the kaibab formation-timpoweap member ridge (white contact) and absence of these units to the north. structure initializations: hf–hurricane fault; kct– kanarra creek thrust; sct–spring creek thrust; hct–hicks creek thrust; tct–taylor creek thrust; mct1, 2–murie creek thrust system; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 23 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 the northernmost appearance of the kanarra creek thrust in the map area is at the mouth of short creek (plates 2a and 3). here the thrust duplicates the timpoweap member (figure 14). the ledge-forming lower part of the timpoweap member defines the hanging wall, which is thrust over the lower red member, the upper yellow shale beds of the timpoweap, and the lower ledge-forming timpoweap in the footwall (figure 14a). the section here remains overturned, and the thrust is contained within these overturned units. along strike, to the north and to the south of short creek, the thrust soles into the timpoweap member, approximately doubling its thickness, before the thrust trace tips are truncated by the hurricane fault (plates 2a and 3). taylor creek thrust: the taylor creek thrust is a significant, west-directed, flank thrust, which can be traced over several kilometers along the eastern limb of the leading anticline (plates 2a and 3), from its type area in taylor creek (kurie, 1966; biek, 2007a) to the northernmost extent of the field area at murie creek (plates 2a and 3). in its type area at kolob canyon, the thrust is east panel b outcrop trmr pkh pkf cedar valley trmtkct sct splay trml trml panel c outcrop a quartzite clastsc chert clasts c chert gray crystalline limestone b brachiopod bryozoan stems fenestella? bryozoan stem brachiopods figure 12. (a) view looking northwest across kanarra creek onto faulted permian and triassic strata. the kanarra creek thrust (red) places the timpoweap member over the lower red member; the spring creek thrust primary splay truncates the older kanarra creek thrust. (b) overturned, fossiliferous and cherty limestone of the fossil mountain member of the kaibab formation. hammer handle points to stratigraphic top. inset: brachiopod and bryozoan fossils exposed along the top of the limestone bed pictured in (b), which reflect the greater diversity of kaibab fossils in comparison to adjacent younger strata. bryozoan shape reminiscent of fenestella. (c) rounded chert and quartzite clasts in the rock canyon conglomerate member of the moenkopi formation. structure initializations: sct–spring creek thrust; kct–kanarra creek thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 24 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 dipping and duplicates thin, competent ridge formers within the dinosaur canyon member of the moenave formation and the springdale sandstone member of the kayenta formation, and it soles into detachment layers within the petrified forest member of the chinle formation (lower) and the main body of the kayenta (upper). at taylor creek, several splays duplicating these units form a system of thrusts, which likely share the same detachments. several other west-directed flank thrusts crop out along the leading anticline, (e.g., the kanarra creek thrust fault, plates 2a and 3), for clarity we restrict the term taylor creek thrust to the west-directed thrusts duplicating lower jurassic units, primarily the springdale sandstone member, as seen in the type area. the taylor creek thrust is well exposed at camp creek (figure 15). here, a single splay of the thrust duplicates nearly the entire dinosaur canyon member and the springdale sandstone member. erosion through the duplicated section produced a broad hill underlain by two ridge-forming ledges of the springdale sandstone. south of this ridge top, shallow, east-dipping ledges of the springdale sandstone define a broad, gentle fold nose in the hanging wall of the taylor creek thrust, indicating west-directed transport (figure 15b) jks jtc jn jks jtrm trcs trcs trmt trmt water storage tanks pkf mct2 tct mct2 rrtt hct kcthf kct tct n kanarra creek trmv trmv tct sct splay mct1 trmt 0 100 200 m hct sct splay kct kct trmv trmv trmv trmt trmt trml trml trml trmm cedar valley b sct splay kct trmv trmvtrmv trmt cedar valley trmt c a figure 13. (a) google earth 3d terrain view looking northeast into kanarra creek. (b) field photograph of both the kanarra creek thrust and the spring creek thrust splay, farther to the north along strike. the obliquity of the view distorts the thrust traces to imply gentle apparent dips (see c). juxtaposition of virgin limestone member against timpoweap member of the moenkopi formation along the fault here is confirmed by fossils, lithology, and topographic signature. part of the purple-gray mudstone at the top of the timpoweap member can be seen in the left midground, juxtaposed against the virgin limestone member. (c) along-strike view of the faults in (b), taken standing on the timpoweap looking north. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; sct–spring creek thrust; hct–hicks creek thrust; tct–taylor creek thrust; mct1–murie creek thrust1; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 25 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 (307320 m e.; 4152110 m n.). this fold in the hanging wall mimics the broad fold in the springdale sandstone in the hanging wall of the easternmost thrust fault of the taylor creek thrust system (plate 2a; cf., figure 4 on plate 3, in biek, 2007a). analysis of shear fracture data in the camp creek area yield a fault plane solution of (022, 55) with a rake of 122°, indicating a thrust fault with a minor left-lateral component of displacement. this result is indicated in table 3 by the bolded great circle and slip vector. it is consistent with the attitude of the fault (033, 54), determined from the orientation of its map trace (plates 2a and 3). bedding in the footwall near the creek bed dips about 38° (plates 2a and 3). thus, at camp creek the taylor creek thrust is best characterized as a shallow thrust ramp, forming an angle about 16° from bedding and thickening the springdale sandstone member. the taylor creek thrust is less well exposed in spring creek. here, the steeply dipping overturned springdale sandstone member is double to nearly triple its stratigraphic thickness because of multiple duplications (plate 2a). the tectonically imbricated and overthickened sandstone ledges form a prominent topographic ridge that has been eroded by the creek jks jtrm trcs trmt trmt trmv trmv tct mct2 rrtt hct kct kct sct hf n short creek kct trmt cedar valley trmtb a figure 14. (a) google earth 3d terrain view southwest into short creek. selected faults and sedimentary contacts are included for reference to the map. these contacts show the overturned fold limb, overturned thrusts (taylor creek, hicks creek, and kanarra creek thrusts) and the spring creek thrust. here, the kanarra creek thrust duplicates the full section of timpoweap member. (b) south-facing, along-strike view of duplicated timpoweap member along the kanarra creek thrust. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; sct–spring creek thrust; hct–hicks creek thrust; tct–taylor creek thrust; mct2–murie creek thrust2; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 26 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 (figure 16). along the southern ridge isolated, slickensided outcrops of springdale sandstone on the hillside mark the presence of the thrust. a minor kink fold defined by shallow-dipping springdale sandstone ledges (dashed white line, figure 16b) indicates the thrust splay cropping out along the ridge is a ramp, which folded the overturned strata to very shallow inclinations (30 to 40° w.). this kink fold continues up the ridge. at the top of the ridge (top right), a late thrust exploited the shallow-dipping strata and displaced sandstone of the dinosaur canyon member over itself to form a conspicuous truncation (figure 16; plates 2a and 3; 307900 m e.; 4154060 m n.). along the topographic ridge on the north side of spring creek, the primary indication of the taylor creek thrust system is that the springdale sandstone is nearly double its normal stratigraphic thickness, suggesting at least one thrust flat is confined within the unit (figure 17; plates 2a and 3). in spring creek, shear fractures are best preserved on the southern ridge of springdale sandstone, where the thrust begins to ramp up section (figure 18). the unrotated fault plane solution is presented in plate 3 and table 3. to compare to camp creek, the data were rotated 82° clockwise along a bearing of 185° so that the n jks jks jks jtrm jtrm trcu trmu jtrm trcs trcs trms trms trcu trmv trmv trmt trmt trmt kct tct hf cedar valley a kcttrmv jtrm jks tct jtrm jks jks jn trcs b 0 200 400 m figure 15. (a) google earth 3d terrain view south into camp creek showing the taylor creek thrust duplicating the springdale sandstone member of the kayenta formation and the dinosaur canyon member of the moenave formation over the springdale sandstone in its footwall. here, the stratigraphic section and the taylor creek thrust are upright, and the fault verges westward. (b) edge-on field photograph of the taylor creek thrust duplication. the apparent fold nose formed by the springdale is not simply an effect of the view angle; the springdale at the top of the hill dips about 20° less than the springdale in the creek, which conforms to the thrust. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; tct–taylor creek thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 27 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 bedding inclination in the footwall (185, 60) coincides with the footwall at camp creek (38°). upon this rotation, the fault plane solution (table 3) yields a pre-overturning fault orientation of (353, 57)—a close match with the fault exposure in camp creek both in dip and angle to bedding. at kanarra creek, outcrop patterns and slickensides indicate the taylor creek thrust continues within the springdale sandstone member. slickensided outcrops are exposed along the thrust trace. creep of the rock may introduce more scatter in measurements along this steep ridge, but data collected along the thrust trace produce thrust-sense fault plane solutions (plate 3; table 3). when data are rotated so that local bedding matches the taylor creek thrust footwall at camp creek, the fault plane solution indicates a likely thrust at (003, 39)—i.e., a flat compared to camp creek (plate 3; table 3). this solution also matches the present-day map pattern of an overturned thrust flat within the springdale sandstone member. north of kanarra creek, the outcrop pattern of the springdale sandstone member changes. discordantly dipping sets of sandstone ledges in the springdale, near the head of the canyon north of kanarra creek (310036 jks jks jtrm jtrm jtrm trcs trcs trmv trmv trmt camp creek spring creek spring creek trmv trcs trmt trmt kct tct tct rrtt sct sct mct¹ hf jks n sct splay jks trcs tct a 0 100 200 m jks mct1 tct jtrm trcsjksjn b figure 16. (a) google earth 3d terrain view south into spring creek. structures outcropping in camp creek are in the background. here, duplication of the springdale sandstone on the taylor creek thrust is readily apparent on the southern ridge formed by the springdale sandstone of kayenta formation in spring creek (midground). (b) close-up of the southern springdale sandstone ridge and the taylor creek thrust duplications. the dinosaur canyon member-springdale sandstone contact is outlined in white. at the bottom of the ridge, above the second duplication, strata are gently overturned, whereas adjacent (footwall) strata are steeply overturned, consistent with an early formed, overturned thrust ramp. the murie creek thrust1 (mct1) appears to sole into the shallow, overturned strata in the taylor creek thrust hanging wall. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; sct–spring creek thrust; tct–taylor creek thrust; mct1–murie creek thrust1. see plate 2b (stratigraphic column) for explanation of map unit symbols. 28 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 m e.; 415799 m n.), indicate minimal, tops-to-the-east reactivation of the taylor creek thrust (plates 2a and 3). additional evidence for reactivation can be seen in the slickenside data collected near short creek (plate 3; table 3). the rotated fault plane solution produces a thrust at (036, 60), and outcropping riedel shear zones (e.g., figure 18) show shear sense matching an overturned thrust. yet, the fault plane solution for unrotated (present-day) data includes a potential fault, which closely matches the local orientation of the thrust trace at (225, 56). based on the outcrop pattern farther south, this cannot be discounted. we show the potential for reactivation along this part of the thrust trace with a slightly different style of the thrust fault barbs (figure 17). in addition, the barb style and side of the thrust are switched to indicate the location where the thrust appears to have begun limited, east-directed, movement (plates 2a and 3). at murie creek, isolated slickensided outcrops indicate the taylor creek thrust trace is exposed near the top of the southern and middle ridges of springdale sandstone (311667 m e., 4159286 m n.; plate 3). atjks trcs trmvtrmt jc (gently dipping e) jn rrtt rrtt splaymct² tct sct mcf hf jks ot jc jks jks jns mcf jtrm jns jtrm damage zone trcs mct tct jns 0 150 300 m n a b figure 17. (a) google earth 3d terrain view of the overturned kanarra fold limb, looking northwest into short and murie creeks. selected faults and sedimentary contacts are shown for reference to the map. potential reactivation of the taylor creek thrust is reflected in the position and style of the thrust barbs. (b) the taylor creek thrust as seen looking north along strike from the short creek saddle into murie creek. a double sandstone ledge with minor siltstone interbeds marks the duplication. here, a damage zone of altered rock (white arrow) outcrops near the creek bed. adjacent to the eastern springdale sandstone ledge of the kayenta formation, the main body of the kayenta is cut through by the late-formed murie creek thrust, nearly displacing the springdale sandstone onto the shurtz tongue of the navajo sandstone. the white arrow points to the location of (b). structure initializations: sct–spring creek thrust; tct–taylor creek thrust; mct2–murie creek thrust2; mcf–murie creek fault; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 29 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 tenuation of intervening siltstones between duplicated springdale sandstone ledges, and a zone of well-indurated, altered siltstone between the springdale ledges, mark the trace of the thrust (figure 17b). rotation of the shear fracture data (for comparison) produces a thrust fault plane solution (062, 39), closely resembling the result at kanarra creek. the unrotated (present-day) data does not produce a viable thrust for either potential fault plane. this result indicates that if the taylor creek thrust was reactivated, only an approximately 1.8 km segment between kanarra and short creeks underwent renewed, eastward movement. we trace the tayinset panel b ba c d top top top top p t figure 18. (a) view to the north looking upon riedel shears along overturned springdale sandstone beds (dipping about 65° w.) defined by deformation bands. here, shear surfaces that form low angles to bedding intersect r' shear surfaces at high angles to bedding. the sense of motion prior to overturning is tops to the west, synthetic with the taylor creek thrust. (b) view to west of shear fracture surface north of (a) within the taylor creek thrust damage zone. r shears along the fracture surface indicate the missing block moved upwards (tops-to-the-west). right hand rule strike, dip, and slip direction rake: 054, 77, and 69. inset: close-up of r shears on the fracture surface in (b) with arrow pointing in the direction of motion. lower right: diagram of r shears along a fracture surface, arrow pointing in the direction of motion of the missing block. (c) view to south of dylan webb measuring local bedding and shear fractures. outcrop with the shear fractures in (b) is just beyond webb along bedding strike. inset: close-up of p-t type shears with tops-to-the-east motion prior to overturning, antithetic to the main thrust. right hand rule strike, dip, and slip direction rake: 235, 73, and 87. lower right: diagram of p-t shears along a fracture surface, arrow pointing in the direction of motion of the missing block. (d) view to west of an outcrop-scale overturned thrust with tops-to-the-east motion prior to overturning. right hand rule strike, dip, and slip direction rake: 240, 78, and 86. inset: close-up of r shear steps along thrust surface with black arrow indicating motion of the missing block. all panels from springdale sandstone member of the kayenta formation outcrops within the taylor creek thrust damage zone (see plate 3 for locations). for all panels, arrow with "top" points to stratigraphic top. diagrams in (b) and (c) panels from petit (1987) and allmendinger and others (1989). 30 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 lor creek thrust past the northern fork of murie creek, where it is truncated by the murie creek fault (figure 17). hicks creek thrust: the thin, competent shinarump conglomerate member of the triassic chinle formation locally hosts the hicks creek thrust, a flank thrust with the same style and vergence as the two previously described faults (cf., averitt, 1962, the hicks creek fault). here, in comparison to where it crops out in the shurtz creek amphitheater and at the red hill, the hicks creek thrust is less significant and its trace semi-continuous (plates 2a and 3). averitt (1962) mapped this thrust as a normal fault at hicks creek, but its observed style in adjacent quadrangles to the north and south (averitt, 1967; biek, 2007b; knudsen, 2014a; biek and hayden, 2016; this paper) negates this interpretation. similar, west-directed flank thrusts cut through the upper red member and chinle formation at kolob canyon (biek, 2007a) and at the red hill (knudsen, 2014a). the hicks creek thrust is well exposed at kanarra creek (figure 19). here, it forms a conspicuous duplication of the shinarump conglomerate member. the overturned hicks creek flank thrust, previously interpreted as an upright, east-directed reverse fault (averitt, 1967), hosts an about 500-m-long duplication of the shinarump conglomerate and crosses the creek near utm 308496 m e.; 4156677 m n. the lower detachment of the thrust is within the lower unit of the chinle formation, and the upper detachment is in the petrified forest member. the trace of the hicks creek thrust is shown by averitt (1962) to die out near the murie creek fault. a near-identical duplication is exposed in the canyon north of kanarra creek, and we trace the hicks creek thrust from here into short creek where it truncates against a small cross fault. it is likely that the thrust soles into a higher detachment layer in the petrified forest member; this was not mappable in the field, so we query the trace of the thrust between these two shinarump conglomerate duplications. the hicks creek thrust becomes a major fault north of murie creek and at the red hill. along its northern trace, the thrust cuts deeper down section, soling into a lower detachment in the shnabkaib member. late contraction faults late contraction thrust faults (tables 1 and 2) associated with formation of the kanarra fold-thrust structure are east-verging and cut across bedding. these faults include the spring creek thrust, murie creek thrust, and red rock trail thrust faults. many of these faults are kilometer-scale features (plates 2a and 3). a lack of piercing points precludes determining their slip, but minimal displacement can be estimated in cross section by measuring the fault trace orientation and the magnitude of displacement consistent with the map pattern. these displacements can be tens to hundreds of meters; at kanarra creek, smaller thrusts displace strata up to 80 m along their length, whereas larger thrusts have minimum displacements of up to 300 m. the late thrusts commonly tectonically thin, fold, and/or truncate less competent stratigraphic units (e.g., red beds of the moenkopi formation). tectonic thinning of stratigraphic layers reflects ductile flow and/or truncation along the hanging wall. the trace of late thrust faults tends to parallel the strike of bedding. thrust fault inclinations are discordant to bedding and can achieve steep orientations, particularly when cutting through mechanically stiff layers to form ramps (e.g., the navajo sandstone). where these faults are well exposed and cut through competent strata, they are associated with cataclastic breccia zones several meters to tens of meters wide with varying degrees of induration. these late contraction thrusts and their connecting splays are best observed within the creek valleys that erode across the strike of the limb of the leading anticline (plate 3). spring creek thrust: the primary splay of the spring creek thrust and the kanarra creek thrust are closely associated spatially in the field (plates 2a and 3). however, as previously discussed, the kanarra creek thrust is overturned by folding and crosscut by the upright primary splay of the spring creek thrust (figures 7 and 20; plate 3). this demonstrates that the spring creek thrust and its splays are younger and distinct from the kanarra creek thrust. the trace of the spring creek thrust is well exposed along the northern side of spring creek, east of the leading anticline hinge zone, along its overturned 31 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 limb. the fault trace begins just south of spring creek and continues northwards for several kilometers (figure 20; plates 2a and 3). its tortuous map pattern consists of several thrust splays, which branch and curve through moenkopi strata. like the taylor creek thrust, the spring creek thrust is a thrust system, and this adds significant structural complexity to the overturned section along the kanarra fold (figure 7; plates 2a and 3). we identify the main trace of the spring creek thrust system as the easternmost continuous thrust within the system of splays. at the surface, the main trace commonly cuts across the eastern fold limb of the leading anticline, from the virgin limestone member into the shnabkaib member (figure 7; plates 2a and 3). the primary splay of the spring creek thrust system is exposed just east of the mouth of spring creek, where the timpoweap member and part of the lower red member are thrust eastward (figure 20; plates 2a and 3). to the north, and to the south, the lower red member is truncated by this same thrust (plates 2a and 3). the primary splay continues to the north where the timpoweap member is overturned, and here subsidiary splays of the spring creek thrust system displace the virgin limestone member. these splays form a jks jtc jn jks jtrm trcs trcs trmt trmt water storage tanks pkf mct2 rrtt hct kcthf kct n tct kanarra creek trmv trmv sct splay mct1 trmt 0 100 200 m hct sct a trcs trcs trcu trcl trcl trmu b figure 19. (a) google earth 3d terrain view looking northeast into kanarra creek. the hicks creek thrust vs gently west into the creek in the foreground and displaces the shinarump conglomerate member and lower members of the chinle formation and part of the upper red member of the moenkopi formation. another duplication is visible in the background. other early and late structures shown for reference to the map. (b) along-strike view of the hicks creek thrust duplication, from the perspective of the hanging wall on the southern side of kanarra creek. gently dipping shinarump conglomerate in the hanging wall conforms to the thrust, which truncates shinarump strata in the background. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; sct–spring creek thrust; tct–taylor creek thrust; hct–hicks creek thrust; mct1, 2–murie creek thrust1, 2. see plate 2b (stratigraphic column) for explanation of map unit symbols. 32 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 complex zone of faulting that has been dissected by the hurricane fault, leaving discontinuous remnants of the spring creek thrust system along the hinge of the leading anticline (figure 9; plates 2a and 3). the primary splay of the spring creek thrust system reemerges at kanarra creek and displaces the fossil mountain member and part of the timpoweap member over a ridge of lower red member and timpoweap in the hanging wall of the kanarra creek thrust (figure 21, also see figures 11a and 11b, lower left). on the south side of kanarra creek, a connecting splay branches from the main trace of the spring creek thrust system (figure 11a, lower left), accommodating displacement of the virgin limestone member over the lower red member that had been previously duplicated by the kanarra creek thrust. this connecting splay merges with the primary splay of the spring creek thrust on the north side of kanarra creek (plates 2a and 3). a smaller thrust splay displaces the timpoweap member onto the virgin limestone member ridge on the south side of kanarra creek. here, along the trail from the parking area (307994 m e.; 4156823 m n.) leading to the creek mouth, yellow limestone, shale, and tan, sandrich limestone crops out discordantly against the virgin 0 100 200 m jns jks jks jks jtrm trcs trmt trmv trcs spring creek jns jn jn jtc sct tct hf mct1 mct1 mct1 rrtt sct splay sct sct kct hct trcs trmv kct cedar valley a sct sct splay trmu trmt trmv folded trms folded trms b n figure 20. (a) google earth 3d terrain view looking northeast into spring creek. to the west, the spring creek thrust primary splay cuts the timpoweap member and displaces it over the lower red member and virgin limestone member of the moenkopi formation. to the east, the spring creek thrust main trace breaks across the more competent virgin limestone and displaces it over the middle red member and part of the shnabkaib member of the moenkopi. selected fault and sedimentary contacts are included for reference to the map. (b) close-up of the spring creek thrust deformation zone. here, it is clear the virgin limestone is displaced over a large part of the moenkopi section, cutting out the middle red member and much of the shnabkaib member. the displacement is accompanied by folding, as seen in the trace of a folded shnabkaib gypsum layer (black dashed line). structure initializations: hf–hurricane fault; kct–kanarra creek thrust; sct–spring creek thrust; mct1–murie creek thrust1. see plate 2b (stratigraphic column) for explanation of map unit symbols. 33 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 limestone. yellow timpoweap shale beds on the side of the path are contorted into meter-scale, complex folds. steep eastward dips on the timpoweap member above the trail indicate folding along an east-directed thrust (plates 2a and 3). near the timpoweap-virgin juxtaposition, mass wasting of the virgin limestone member obscures the exact location of the thrust splay and presumably the lower red member along the western side of the ridge. along this ridge, a minor normal fault associated with the hurricane fault zone cuts obliquely across strike and truncates the spring creek thrust splays (plates 2a and 3). the primary splay of the spring creek thrust system continues northward from kanarra creek along the west side of the topographic ridge held up by the duplicated timpoweap member (figures 13 and 21; plates 2a and 3). near the end of the ridge, the primary splay ramps down section, exposing more of the timpoweap in the hanging wall than seen at kanarra creek. the primary splay also truncates part of the overturned kanarra creek thrust and cuts out most of the lower red member (figure 13c; plates 2a and 3). from this location, the primary splay continues along strike to the north where it is truncated by the hurricane fault (309191 m e.; 4158719 m n.). the main trace of the spring creek thrust system jks jtc jn jks jtrm trcs trcs trmt trmt water storage tanks pkf mct2 tct mct2 rrtt hct kcthf kct n tct kanarra creek trmv trmv sct splay mct1 trmt 0 100 200 m hct sct n sct sct splay trmu trmt trmv trmt trml trmr pkh pkf trms b cedar valley a n figure 21. (a) google earth 3d terrain view looking northeast into kanarra creek. to the west, the spring creek thrust primary splay displaces the fossil mountain member of the kaibab formation and the timpoweap member over the lower red member of the moenkopi formation. to the east, the main trace of the spring creek thrust continues roughly parallel to the strike of bedding, displacing the virgin limestone member over the shnabkaib member of the moenkopi formation. (b) along-strike view to the north of the spring creek thrust main trace truncating the middle red member and spring creek thrust primary splay. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; sct–spring creek thrust; tct–taylor creek thrust; hct–hicks creek thrust; mct1, 2–murie creek thrust1, 2; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 34 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 first appears south of spring creek to the east of the primary splay (figures 9 and 20; plate 2a). it cuts through the hinge zone of the leading anticline on the eastern side of a gently folded ridge of virgin limestone member, at the upright-to-overturned transition on the eastern limb of the fold (307342 m e.; 4154074 m n.). the thrust thins the middle red member and truncates the lower double-layer of gypsum. a few tens of meters north of the truncation, the fault is marked by a calcite-encrusted, well-indurated fault megabreccia (cataclasite), which hosts cobbleto boulder-sized clasts of slickensided and folded virgin limestone member limestone (figure 22). the trace of the main spring creek thrust fault can be followed along strike to the north, where west-dipping, overturned middle red gypsum layers crop out and the trace of the thrust is within the middle red member. on the north side of spring creek, a prominent wall of vertical virgin limestone member fins crops out in the hanging wall of this thrust—these fins were transported east and over the middle red member (figure 20; plates 2a and 3). from spring creek, the main trace of the spring creek thrust system continues northward towards kanarra creek, juxtaposing steep overturned beds of the virgin limestone member onto the shnabkaib member. here, the hanging wall of the main spring creek thrust includes a 1-km-long, nearly-recumbent, overturned fold in the virgin limestone (figure 9). this fold is part of the hinge zone of the leading anticline that was displaced east on the thrust. the folded virgin limestone forms a low ridge, with shallow west-dipping strata (about 10 to 25° w.) on its western side and steeper, overturned (about 45 to 55° w.) strata on its eastern side. on the eastern side of the ridge, the trace of the main spring creek thrust system displaces overturned virgin limestone beds and the middle red double gypsum layer over the middle red member (307924 m e.; 4156400 m n.). at kanarra creek, the main trace cuts out much of the middle red member in the same structural style seen at spring creek. here, the thrust cuts shallow dipping (about 45 to 50°), duplicated virgin limestone member in the kanarra creek thrust hanging wall (figure 21). near the creek bed, slickenside measurements on the virgin limestone indicate two populations of shear fractures—a set of normal-sense slickensides, which mostly form low angles to bedding, and a set of thrustsense slickensides, also at low angles to bedding (figures 23b and 23d; plates 2a and 3; table 3). both populations include strike-slip shear fractures with minor normal-sense and thrust-sense displacement, indicated by their slickenline rakes (figures 23b inset and 23c). rotation of the normal sense shear fracture data to where bedding dips 38° e. (analogous to an earlier stage of folding at camp creek) yields a fault plane solution with a west-directed thrust at 27° to bedding. once restored, the normal-sense shear fractures are consistent with movement along the early kanarra creek thrust, which was later folded and overprinted (table 3). fault plane solutions from the thrust-sense shear fracture population indicate a steep, east-directed thrust, which matches the local orientation (208, 64) of the main trace of the spring creek thrust (plates 2a and 3; table 3). the spring creek thrust shallows to the north to (209, 45), where it exploits the shallow bedding on the duplicated virgin limestone. north of kanarra creek, the main trace of the spring creek thrust ramps up section and places the virgin limestone member over the shnabkaib member (figure 24). this juxtaposition of the virgin limestone against the shnabkaib continues another 3.5 km from kanarra creek into short creek. only the main thrust trace is present within short creek, again placing the virgin limestone member against the shnabkaib member (plates 2a and 3). the thrust trace veers westwards as it ramps down section from the shnabkaib member to the lower red member. as the thrust truncates the virgin limestone, it veers northward into sub-parallelism with the strike of bedding (310690 m e., 4159590 m n.). within murie creek, displacement along the main trace completely cuts out the lower red member, placing the timpoweap member against the virgin limestone member. just to the north of the creek mouth, the thrust is truncated by the hurricane fault (311370 m e., 4159990 m n.). murie creek thrust: east of spring creek, several late, east-directed thrusts are exposed in the jurassic section near the syncline axis of the kanarra fold-thrust structure. we group the first two of these thrusts together 35 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 as the murie creek thrust system. from west to east, the first murie creek thrust (mct1 in plates 2a and 3; figure 16) is a shorter, discontinuous thrust in the dinosaur canyon member of the moenave formation. we show it as an independent thrust rather than a splay of the longer murie creek thrust (e.g., mct2 in figure 17; plates 2a and 3). the second murie creek thrust is a longer, continuous thrust that crops out near kanarra creek (308910 m e.; 4156517 m n.) within the kayenta formation and can be traced for 5 km to the north. displacement along this thrust is revealed by folding and truncation of kayenta strata at the upper contact of the springdale sandstone member in kanarra creek. the first murie creek thrust crops out south of spring creek where it displaces the dinosaur canyon member over the springdale sandstone (307900 m e., 4154070 m n.). the thrust is well exposed where spring creek erodes through the topographic ridge underlain by sandstones of the springdale sandstone member. looking south along this ridge, a thick, persistent sandstone ledge in the dinosaur canyon member forms a prominent “t” discordance where it is folded and displaced over itself along the thrust plane (figure 16; plates 2a and 3). bedding above the thrust is overturned and shallow dipping (about 30°), whereas bedding beneath the thrust is steeply overturned (about 65 to 70°). looking north of spring creek along the continuation of this topographic ridge, the structural pattern is repeated but partially obscured by mass wasting and vegetation (figure 25). high on the topographic ridge, the thrust displaces the lower springdale sandstone member contact before it dies out. farther north towards kanarra creek, the first murie creek thrust recurs for a short distance where it again thrusts the dinosaur canyon member a b c d figure 22. (a) kink fold (layering traced by dashed white lines) on outcrop of brecciated limestone in the virgin limestone member of the moenkopi formation along the spring creek thrust. view sub-parallel to local strike (about 30°) and kink axial trace. hammer beneath dylan webb is placed parallel to the fold axis. (b) view nearly parallel to strike southeast along same structure as (a). flaggy breccia clasts (examples outlined in white), variably slickensided and oriented. (c) cobble-sized, slickensided clasts (white arrow) within a recrystallized calcite matrix. (d) calcite-encrusted outcrop containing several boulder-sized, angular clasts. well-developed calcite steps are exposed on the clast marked by the white arrow just above william chandonia. 36 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 over the springdale sandstone member (figure 25; plates 2a and 3). truncation of the petrified forest member of the chinle formation indicates the thrust may initiate farther down section, but the contact is complicated by mass wasting and by a late, across-strike normal fault (308220 m e.; 4155780 m n.). north of kanarra creek, fractured dinosaur canyon member and discordance with springdale sandstone bedding at the contact indicate the presence of the first murie creek thrust, but displacement is visibly diminished, and the thrust dies out (308940 m e., 4156670 m n.). the trace of the second murie creek thrust initiates just south of kanarra creek where the main body of the kayenta formation is dramatically thinned by the fault (plates 2a and 3; 308730 m e., 4156050 m n.). the thrust crops out along the kanarra creek falls trail, where the creek has eroded through the topographic ridge formed by the dinosaur canyon and spring creek sandstone members. the thrust is marked where overturned sandstones of the springdale sandstone define an east-verging fold in the hanging wall of the thrust (figure 26). the fold is a composite fold-thrust strucfigure 23. (a) overturned, slickensided outcrop of the virgin limestone member. examples of slickensided shear fractures marked by white arrows, slip direction by black arrow. view northeast, daniel quick for scale (1.84 m). lower right: diagram of mineral fiber steps characteristic of fault-related shear fractures in carbonates. slip direction is down the mineral fiber steps, and arrow points in the direction of motion of the missing block (from allmendinger and others, 1989). (b) view to northeast of another overturned, slickensided limestone outcrop nearby. white arrow points to a thrust-sense shear fracture (hanging wall moved up and east) exposed near the rock hammer; right hand rule strike, dip, and slip direction rake: 210, 84, and 83. inset: close-up of the same shear fracture showing the mineral fiber steps, with black arrow showing the slip direction of the missing block. (c) slickensided outcrop near the spring creek thrust contact, north of kanarra creek, view to west. white arrows show shear surfaces that are out of the plane of view, whereas black arrows show slip direction on the visible shear surfaces. the shear fracture set contains strikeand thrust-slip conjugate shear surfaces. closest fracture to viewer (long sub-horizontal slip direction arrow) is dextral strike-slip; right hand rule strike, dip, and slip direction rake: 187, 87, and 5. (d) view west onto a slickensided outcrop northeast of (a). stereonet shows the spatial relationship here between bedding (black) and the shear fracture (red), produced with the stereonet 11 software (allmendinger and others, 2013; cardozo and allmendinger, 2013). ba c d 212 22 5 37 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 ture. we interpret faults in the nose and on the front limb of this fold as small, older, east-directed thrusts, which were subsequently folded. these faults are well exposed along the trail on the north side of the creek where slickensides show normal separation, but rotation of the steep west-dipping (about 81° w.) bedding back to the local average orientation along the ridge (about 45° w.) shows a pre-folding thrust sense of motion with an average dip about 10° greater than bedding (see table 3). to the north, the kayenta formation thins dramatically as the second murie creek thrust continues along the springdale sandstone member-kayenta formation contact north towards short creek (plates 2a and 3). thinning of this unit, based on our measurement using gmde (allmendinger, 2020) and published thicknesses for the area (plate 2b), indicate a 63% reduction from 120 to 46 m along the main body of the kayenta formation. we interpret the reduced thickness is a result of movement along the second murie creek thrust, and east-directed thrusting of the springdale sandstone member over the kayenta formation. the trace of the second murie creek thrust can be followed n a jks jtc jn jks jtrm trcs trcs trmt trmt water storage tanks pkf mct² hct kcthf kct tct kanarra creek trmv trmv sct splay mct¹ trmt hct 0 100 200 m sct trmu trmv trms trmm sct ba n figure 24. (a) google earth 3d terrain view looking northeast into kanarra creek. (b) the spring creek thrust main trace seen looking north within an unnamed stream cut just north of kanarra creek. as in the other two creeks, the structural pattern of the virgin limestone member of the moenkopi formation being displaced over and truncating the shnabkaib member of the moenkopi is continued here. a sliver of the middle red member of the moenkopi containing a thick, double layer of gypsum persists all along the spring creek thrust hanging wall. the gypsum layers outcrop below the contact of the virgin limestone member with the middle red member and are indicated here by the dashed white and black line. structure initializations: hf–hurricane fault; kct–kanarra creek thrust; sct–spring creek thrust; tct–taylor creek thrust; hct– hicks creek thrust; mct1, 2–murie creek thrust1, 2. see plate 2b (stratigraphic column) for explanation of map unit symbols. 38 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 north to murie creek where the thrust is truncated by the murie creek fault, along with the rest of the fold limb (plates 2a and 3). the red rock trail thrust: the red rock trail thrust is the largest and easternmost thrust in the map area (plates 2a and 3). minor thrusts and buckle folds, which we associate with the kanarra fold-thrust structure, do crop out farther to the east of the red rock trail thrust (plates 2a and 3). the red rock trail thrust can be traced from spring creek to where it abuts the murie creek fault. in the cedar mountain quadrangle (averitt, 1962; doelling, 1972), the trace of the fault is less obvious but can be inferred by the presence of the cataclasite in the navajo sandstone (t.r. knudsen, utah geological survey, written communication, 2022). the red rock trail thrust outcrops in the cedar city 7.5-minute quadrangle (plate 2a) and we suggest it crops out in parowan gap as well (see discussion below). it begins within the kayenta formation near the springdale sandstone member contact in spring creek and cuts up section through the navajo sandstone, forming a persistent, poorly consolidated cataclasite zone at the kayenta–navajo contact (plates 2a and 3; figures 25 and 27). here, a resistant lens of the shurtz tongue of the navajo crops out from the creek bed, 0 100 200 m jns jks jks jks jtrm trcs trmt trmv trcs spring creek jns jn jn jtc sct tct hf mct1 mct1 rrtt sct splay sct sct kct hct trcs trmv kct jks jks mct¹ tct rrttjtrmtrcs jns jns b a n 0 100 200 m figure 25. (a) google earth 3d terrain view looking north into spring creek. the red rock trail thrust cuts the shurtz tongue of the navajo sandstone as it makes its way up section. the spring creek thrust, taylor creek thrust, and cross faults shown for reference to the map. (b) along-strike view northward of the red rock trail thrust cataclasite zone, seen here as thinned kayenta formation and offset shurtz tongue—through outcrop observations in the field, we connect this displacement to the red rock trail cataclasite along a steep, late-formed, east-verging thrust, the red rock trail thrust. also shown is the overturned taylor creek thrust and the murie creek thrust1. structure initializations: kct–kanarra creek thrust; sct–spring creek thrust; tct–taylor creek thrust; hct–hicks creek thrust; mct1–murie creek thrust1; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 39 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 striking obliquely to adjacent strata. this lens is truncated and offset 150 m to the north along the southernmost expression of the red rock trail thrust as it ramps up section. the cliffs near the contact are mantled with talus of pervasively slickensided clasts derived from the fault damage zone. the cataclasite zone is well exposed and readily accessible on the red rock trail (308700 m e.; 4155320 m n.). the fault damage zone associated with the red rock trail thrust is mapped as a cataclasite derived from the navajo sandstone (i.e., jnc, see plates 2a and 3). as with other thrusts along the kanarra fold, the red rock trail thrust is more likely a thrust fault system, but individual thrusts within the cataclasite are difficult to trace. within the central section of the kanarra fold-thrust structure, the red rock trail thrust forms the contact between the kayenta formation and p t tct mct² jkm jks jks ba c d figure 26. (a) view to south upon a fold-thrust structure in the springdale sandstone member and part of the main body of the kayenta formation on the murie creek thrust2 hanging wall. vergence demonstrates tops-to-the-east motion. daniel quick (outlined in white, bottom foreground) takes in the view to the south closer to the outcrop. earlier thrusts with tops-to-the-east motion, which are now folded within the hanging wall are in solid red. (b) outcrop of the fold limb where it is exposed looking northwest on the trail at the north side of kanarra creek, containing bedding-discordant, slickensided shear surfaces; right hand rule strike, dip, and slip direction rake of marked white slickenside: 218, 88, and 82. slip direction of the missing block (black arrow) is consistent with earlier, tops-to-the-east folded thrusts. (c) p-t shear fractures along the fold limb outcrop in (b) with black arrow showing slip direction of the missing block; right hand rule strike, dip, and slip direction rake: 42, 83, and 68. upper right: diagram of p-t shears along a fracture surface, arrow pointing in the direction of motion of the missing block. (d) slickensided shear fracture surface with well-developed, lunate r shear, black arrow points to direction of motion of missing block; right hand rule strike, dip, and slip direction rake: 210, 87, and 84. lower right: diagram of r shears along a fracture surface, arrow pointing in the direction of motion of the missing block. diagrams in (c) and (d) from petit (1987) and allmendinger and others (1989). structure initializations: tct–taylor creek thrust; mct2–murie creek thrust2. see plate 2b (stratigraphic column) for explanation of map unit symbols. 40 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 the cataclasite developed in the navajo sandstone. north of spring creek, talus aprons of cataclasite appear on the kayenta-navajo cliff face, indicating the presence of the red rock trail thrust damage zone. direct accessibility is poor due to the steepness of the cliff. the red rock trail thrust crops out along the red rock trail, and it is here that a damage zone consisting of a moderately indurated fault megabreccia—outcrop-sized clasts of faulted navajo surrounded by a matrix of smaller clasts (e.g., see “c” and “m” on figure 27c)—is well exposed at the fault contact with the kayenta formation and navajo sandstone and the planar-bedded, steeply overturned navajo sandstone is pervasively slickensided and host sets of deformation bands. farther east into the damage zone, remnant steep, upright bedding indicates fault-related discordance with overturned navajo in the hanging wall of the thrust. approximately 100 m east along the red rock trail and farther into the navajo, the megabreccia gives way to intact rock. at kanarra creek, near the entrance to the kanarra falls slot canyon, the trace of the red rock trail thrust is marked by strong discordance in bedding dips between channel sands in the kayenta formation and planar-bedded sandstone of the navajo sandstone (figure 0 100 200 m 0 100 200 m jns jks jks jks jtrm trcs trmt trmv trcs spring creek jns jn jn jtc sct tct hf mct1 mct1 rrtt sct splay sct sct kct hct trcs trmv kct jnc c c c c m m jks rrtt trcs trmt ur (steep) otrrtt c b a n figure 27. (a) google earth 3d terrain view looking north into spring creek. selected faults and sedimentary contacts shown for reference to the map. (b) view looking north on the red rock trail above the kayenta formation-navajo sandstone contact. foreground: flaggy, slickensided clasts of navajo cataclasite eroding off an outcrop above that is out of the view of the photograph. (c) view of the red rock trail thrust, looking northeast while standing on the red rock trail after crossing the thrust contact. cobble-sized and smaller slickensided clasts (m, matrix) surround larger boulder to outcrop sized clasts (c, clast). overturned (ot), west-dipping navajo sandstone beds are thrust over steep, upright (ur), east-dipping beds. prominent, overturned ridge formers on the exposed front limb of the kanarra fold-thrust structure are marked for reference. photograph by john p. hogan. structure initializations: kct–kanarra creek thrust; sct–spring creek thrust; tct–taylor creek thrust; hct–hicks creek thrust; mct1–murie creek thrust1; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 41 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 28; plates 2a and 3). this discordance reflects folding of the kayenta formation along the thrust (figure 28b). in the foreground of figure 28b, beds of navajo sandstone have been rotated to vertical and in the canyon to the east they return to upright, gentle eastward dips. to the north of the slot canyon, steeply overturned, folded planar beds of the navajo sandstone, seen in the background of figure 28b, are in fault contact with significantly thinned, shallow-dipping, overturned strata of the kayenta formation. though the red rock trail thrust appears to dip steeply to the east (i.e., verge west) at kanarra creek, the dominant vergence along the thrust is to the east. here the thrust contact may be complicated by the presence of an older, east-dipping thrust (see averitt, 1967). however, we associate this earlier interpretation with sinistral, out-of-the-syncline flexural slip and disharmonic folding of thin kayenta sandstone lenses adjacent to a thick, competent control unit, the navajo sandstone—see the discussion section for further details. at the saddle by the next canyon to the north (plate 2a; figure 3; 310000 m e., 4157700 m n.) the cedar city tongue of the kayenta formation is attenuated with a minimum 62% reduction, measured using gmde jks jtc jn jks trcs trcs trmt trmt water storage tanks pkf mct2 tct mct2 rrtt hct kcthf kct n tct kanarra creek trmv trmv sct splay mct1 trmt 0 100 200 m hct sct splay rrttjks jns folded jkc bedding folded jn bedding jn b a figure 28. (a) google earth 3d terrain view of the red rock trail thrust, looking northeast into kanarra creek. lateformed thrusts (spring creek thrust, murie creek thrust) shown for reference to the map. (b) view looking northeast onto jurassic units exposed near kanarra creek. folded kayenta formation (beds outlined in dashed white lines) abuts steep, overturned navajo sandstone along the red rock trail thrust. part of this contact may be complicated by the presence of an older, east-dipping thrust (e.g., averitt, 1967). structure initializations: kct–kanarra creek thrust; sct–spring creek thrust; tct–taylor creek thrust; hct–hicks creek thrust; mct1, 2–murie creek thrust1, 2; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 42 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 (allmendinger, 2020), in thickness along the red rock trail thrust (figure 29). the thrust contact dips moderately westward (about 50°), and overturned beds of the kayenta formation are displaced over steeply dipping, overturned navajo sandstone. east of the fault contact, the damage zone persists for 200 to 300 m into the navajo sandstone. talus of slickensided cataclasite mantle the top of the cliff (figure 29b). in this view, the damage zone can be traced from the foreground, through the vegetation, into the background to include steeply dipping, isolated outcrops of navajo sandstone. the red rock trail thrust and damage zone continue northward along the cliffs in the navajo sandstone. in the northeast part of the map area between short and murie creeks, dips on the carmel formation as high as 39° are observed (plates 2a and 3); the carmel is steeply overturned (about 85° w.) at murie creek. at the flatiron near the head of murie creek (311970 m e.; 4159330 m n.) both the kayenta formation and the navajo sandstone are overturned and dipping about 45 to jks jks trcs trcs trmv trmt jn jtc rrtt sct sct splay mct2 tct hf kanarra creek jnc jks attenuated jkmjns jn ot beds mct2 rrtt n 0 200 400 m b a figure 29. (a) google earth 3d terrain view looking south towards kanarra creek. selected faults and sedimentary contacts are shown for reference to the map. (b) view to the southwest of the red rock trail thrust contact at the head of the stream cut north of kanarra creek. here the navajo sandstone is overturned (ot). the contact is partially occluded where it vs westward, down the cliff. beginning here at the contact, isolated outcrops of pervasively fractured navajo mantled by slickensided talus define a megabreccia shear zone tens of meters wide. the main body and cedar city tongue of the kayenta formation are thinned near the contact. structure initializations: hf–hurricane fault; sct–spring creek thrust; tct–taylor creek thrust; mct2–murie creek thrust2; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 43 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 55° to the west along the east verging thrust (figure 30). sharp deflection of carmel strata into steep, overturned orientations (figure 30a, right, dashed white line in the carmel) suggests the thrust cuts up section. the highstrain zone is characterized by a great density of fractures, imparting a shattered appearance (i.e., cataclasite) to the navajo sandstone within the fault damage zone (figure 30b). movement within the fault megabreccia cataclasite zone appears to have rotated isolated outcrops of clasts of navajo sandstone with relict bedding to shallow, westward dips (figure 30b, right midground). a splay of the red rock trail thrusts crops out to the east of the main trace and displaces navajo sandstone eastward on top of the upper co-op creek limestone member of the carmel formation (t.r. knudsen, utah geological survey, written communication, 2022). the red rock trail thrust, splay, and damage zone continue northwards and abut against the murie creek fault (figure 30; plate 2a; 313000 m e.; 4159750 m n.). jks trcs trmvtrmt jc (gently dipping e) jn rrtt rrtt splaymct2 tct sct mcf hf jks ot jc jnc jns rrtt relict beds (ot) shattered rock b 0 150 300 m n a figure 30. (a) google earth 3d terrain view looking north into short and murie creeks. traces of the spring creek, taylor creek, and murie creek2 thrusts are shown for reference. to the east, a splay of the red rock trail thrust truncates the navajo-carmel contact, denoted by the solid white line (t.r. knudsen, utah geological survey, written communication, 2022). gently east-dipping carmel steepens and overturns east of the fault zone. the outcrop pattern of a white layer in the upper co-op creek limestone member of the carmel formation (bottom of white layer shown by white dashed line) and associated west-dipping flatiron emphasizes the overturning of the unit (ot) near the thrust. (b) view of the red rock trail thrust contact on the southern fork of murie creek. relict bedding along isolated outcrop-sized clasts within the navajo sandstone cataclasite (jnc) shear zone is overturned beyond 40° in some places, and the thrust appears to exploit the shallow-dipping navajo bedding planes and weak kayenta siltstone beds. structure initializations: hf–hurricane fault; sct–spring creek thrust; tct–taylor creek thrust; mcf–murie creek fault; mct2–murie creek thrust2; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. 44 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 cross faults other faults with ambiguous temporal relationships between sevier folding and basin and range tectonism are cross faults. where exposed along the kanarra foldthrust structure, cross faults vary in size from tens of meters to kilometers in length (e.g., the murie creek fault), tend to cut across bedding, nearly orthogonal to strike, and appear to be exclusive to the overturned limb of the leading anticline (see plates 2a and 3). estimates of displacement along many of these cross faults indicate a greater horizontal (i.e., strike slip) component than vertical (i.e., dip slip) component (e.g., the murie creek fault, also see averitt, 1962). cropping out at the red hill is a cross fault, similar in size to the murie creek fault but with opposite polarity that we refer to as the thunderbird gardens trail fault (plate 1, also see knudsen, 2014a). these two prominent cross faults displace much of the “salient” northern section of the kanarra fold-thrust structure upward and to the east (plate 1). the murie creek and thunderbird gardens trail faults indicate many of the cross faults associated with the kanarra fold-thrust structure are likely tear faults or lateral ramps that developed during folding. other cross faults include the approximately 800-m-long cross fault along the spring creek saddle. this cross fault affected units from the shnabkaib member to the springdale sandstone member (figures 16 and 27; plates 2a and 3; also see biek and hayden, 2016). notable cutoffs of the shinarump crop out north of the saddle (308150 m e.; 4155290 m n.) and along the springdale sandstone (308390 m e.; 4155290 m n.). this cross fault exhibits right-lateral separation and limited downto-the-south vertical displacement. the extent of this fault is unclear, as its western trace is concealed beneath a landslide deposit along part of the red rock trail. spatial relationships between the shnabkaib member north and south of the spring creek saddle (plates 2a and 3) indicate the fault may either disturb or truncate against the spring creek thrust fault. another, smaller cross fault, antithetic to the spring creek saddle cross fault, is revealed by offset across the shnabkaib member (plates 2a and 3) farther to the north (308150 m e.; 4155654 m n.). along the rest of the fold limb other, smaller cross faults are endemic to competent units in the jurassic section, and particularly affect the dinosaur canyon member, springdale sandstone, and shurtz tongue of the navajo sandstone. extension faults—hurricane fault zone the kanarra fold-thrust structure is crosscut by later extension faults. these notably include the hurricane fault, as well as other faults also associated with the basin and range transition zone (figure 1; plate 1). faults of the transition zone are largely restricted to the high plateaus immediately adjacent the kanarra fold-thrust structure. prominent examples of transition zone faults are the cougar mountain, bear trap canyon, and lone tree mountain faults (gregory and williams, 1947; averitt, 1962; biek and others, 2009; knudsen, 2014a; biek and hayden, 2016). displacement along the transition zone faults rotates the regional dip adjacent to the kanarra fold-thrust structure syncline axis, which approaches 6° east in the field area and 3 to 5° west near cedar city. the hurricane fault crosscuts the kanarra foldthrust structure, displacing the trailing western limb of the anticline in the hanging wall down to the west (plates 2a and 3). the main trace of the hurricane fault is largely concealed beneath colluvium and alluvial-fan deposits from the hurricane cliffs. however, subsidiary normal faults associated with basin and range extension can produce complex horse configurations (biek, 2003b, 2007a; hurlow and biek, 2003; biek and others, 2009). several large splays of the hurricane fault, south of the study area, displace moenkopi strata down onto permian units or completely cut out the paleozoic section (plate 1; biek 2007a; biek and others, 2009). within the central part of the kanarra fold-thrust structure, far fewer splays of the hurricane fault are present and crop out near (less than 150 m) the main trace of the hurricane fault. we recognize one notable splay just south of kanarra creek along the kanarra creek trail; the other splays are largely restricted to camp creek. the best exposed hurricane fault splays in the central area of the fold crop out en échelon at the mouth of camp creek, where they complicate the leading anticline hinge zone (figure 3; 305800 m e.; 4153000 m n.). here, short (less than 250 m long), low-displacement 45 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 normal faults form gently curved fault traces sub-parallel to the local strike of bedding. in figure 11, two of the three mappable splays can be seen; the largest (westernmost) is a synthetic fault splay, and the eastern, middle splay is antithetic to the hurricane fault. slickenside measurements and map patterns indicate down-to-thewest movement on the western and eastern splays, with little lateral motion (most slickenline rakes are between 87 to 93°). the middle, antithetic splay forms a miniature horst of rock canyon conglomerate member of the moenkopi formation (figure 8; plate 3). the largest and westernmost splay at camp creek forms a prominent, steeply west-dipping (65 to 70°) fault scarp along the rock canyon conglomerate member of the moenkopi formation. a trail leading into camp creek directly follows the scarp strike for about 50 m as it climbs in elevation, allowing good access to slickensides. near the start of the trail, black banded, chert-rich fossil mountain member is exposed in the footwall of the splay, with rock canyon conglomerate unconformably mantling it (figure 8c, inset). the splay displaces an outcrop of ledge-forming lower timpoweap member down to the west, where it rests beside the upper contact of the fossil mountain member. thus, based on the observed dip slip movement, minimal stratigraphic separation along this splay (i.e., throw) is in the tens of meters. farther east into camp creek, steep, west-dipping fractures with minimal detectable displacement outcrop on the canyon walls (figure 8b). these observations indicate more deformation and may represent a damage zone associated with the fault. this suggests a short zone (tens of meters) of decreasing displacement east from the main hurricane fault zone. discussion the kanarra fold-thrust structure in southwestern utah, deformation associated with the leading edge of the sevier fold-thrust belt resulted in formation of multiple thrusts, such as the square top mountain, iron springs, and red rock trail thrusts. deformation was also manifested as prominent folds, such as the virgin, pintura, and the kanarra anticlines (see figure 1; plate 1). these contractional structures are the result of regional layer-parallel compression associated with plate convergence along the cordilleran orogen (yonkee and weil, 2015). the hanging wall cover rocks were translated along a detachment several hundred meters above the crystalline basement within the cambrian bright angel shale and, potentially, the lower incompetent layers of the cambrain bonanza king formation (hintze, 2005; see cross sections a–a' and b–b' in biek and others, 2009). folding and thrusting are closely associated, and these fold-thrust structures (e.g., butler and others, 2020) are thought to have localized blind thrust ramps during folding (e.g., the virgin dome; see biek, 2003a, 2003b). early fold accommodation faults the initial stages of folding likely involved multilayer buckling (break-thrust folds of willis 1893; currie and others, 1962; fischer and others, 1992), followed by thrusting (eisenstadt and de paor, 1987; fault propagation folding of williams and chapman, 1983; see figure 15, p. 18, in cawood and bond, 2020). during buckling, many of these folds developed fold accommodation faults known as limb wedge thrusts or flank thrusts (e.g., cloos, 1961, 1964; faill and wells, 1974, eisenstadt and de paor, 1987; mitra, 2002a). these flank thrusts likely formed due to significant differences in thickness and competence between the currently exposed, relatively thin paleozoic-mesozoic ridge formers—namely the timpoweap and shinarump conglomerate members of the moenkopi formation and springdale sandstone member of the kayenta formation—and much thicker, incompetent units—the triassic red beds of the moenkopi formation, petrified forest member of the chinle formation, and kayenta formation. long-wavelength buckling of thick, competent control units—the cambrian bonanza king–nopah dolomite, mississippian redwall limestone, permian queantoweap sandstone, and jurassic navajo sandstone—may have determined the development of flank thrusts by inducing more intense buckling of thinner adjacent competent layers (e.g., currie and others, 1962; fischer and others, 1992; davis and others, 2011, p. 384–390). initial buckling within thin, competent layers transitions to accommodation of folding via thrusting once the layer can no longer fold, as seen on the west flank of the virgin an46 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 ticline where an east-directed flank thrust (i.e., a proxy for the hicks creek thrust) crops out near leeds, utah (see cross section a–a' and b–b' in biek 2003a, and cross section d–d' in biek, 2003b). the virgin, pintura, and kanarra anticlines all exhibit similar structural styles, as they share a stratigraphy with similar mechanical strength properties related to early development of flank thrusts within competent units on the limbs of gentle to open folds (e.g., the thrusts at leeds, utah, on the virgin anticline; see biek, 2003a; biek, 2003b). the presence of flank thrusts in the nascent stages of folding greatly affects the structural evolution of the fold as the amount of shortening increases; for example, along the strike of the axis of the leading anticline of the kanarra fold-thrust structure. along most of its length, the kanarra fold is upright, excepting local displacement by fold accommodation faults, such as that seen in the hanging wall of hurlow and biek’s (2003) taylor creek fault. the deepest structural levels of the fold crop out near its southern terminus between pintura and toquerville. at camp creek, early formed flank thrusts (e.g., the kanarra creek and taylor creek thrusts) along the east-dipping, upright limb of the open leading anticline are upright west-verging thrusts (plates 2a and 3). along strike to the north, the amount of shortening increases and leads to development of a fold style with many attributes of a fault propagation fold, including a gently dipping trailing fold limb and a steeply dipping, overturned leading fold limb (figure 7; cf., davis and others, 2011, p. 414–428). early formed flank thrusts along the eastern limb (e.g., taylor creek thrusts, plate 3, figures 7 and 15) were rotated, along with the stratigraphy, into steeply dipping to overturned orientations as the fold tightened. the resulting geometry of stratigraphic units juxtaposed along overturned early formed flank thrusts (e.g., hicks creek thrust, see figure 19) previously led to a two-dimensional, separation-based interpretation of these faults as normal faults. this is a misrepresentation of these folded thrusts and obscures their true structural significance in the development of the kanarra fold-thrust structure. slip will cease along an early formed flank thrust if the fault plane is rotated into an unfavorable orientation for failure with respect to the regional stress field (e.g., kanarra creek thrust, figure 11). in contrast, early formed flank thrusts on the trailing limb of the fold, such as the spring creek thrust, remain in favorable orientations for slip along the fault plane and continued to do so as the fold tightened. this is demonstrated by displacement of the folded kanarra creek thrust by the spring creek thrust (figures 7, 11, and 13). earlier movement along the spring creek thrusts at depth resulted in the development of a faultbend fold in the trailing limb of the anticline, imparting a broad crest profile, similar to a box fold, for the kanarra anticline (figures 7 and 31). late fold accommodation faults higher degrees of shortening in the central section of the kanarra fold-thrust structure resulted in lockup of the leading anticline, syncline, and early formed flank thrusts on the leading overturned limb. in addition to continued slip on faults in a favorable orientation for failure, new, late fold accommodation thrust faults (e.g., murie creek and red rock trail thrusts) formed in response to fold lockup within a continued layer-parallel compressive stress field (e.g., see figure 12, p. 122, in jadamec and wallace, 2014; see figure 15, p. 686, in mitra, 2002a; see figure 4, p. 1679, in mitra, 2002b). these late fold accommodation thrust faults are spatially associated with the locked hinge zones of the leading anticline and syncline, and thus are examples of forelimb shear thrusts (see mitra, 2002a). we link the red rock trail thrust with the well-exposed thrust at the red hill (plate 1). this inferred linkage is consistent with the position and structural style of the red rock trail thrust and the proposed correlative thrust at the red hill as seen in both cross sections (figures 7 and 32). we note that averitt (1962) does not map the red rock trail thrust in the cedar mountain quadrangle. the presence of cataclastic navajo sandstone in the cedar mountain quadrangle is consistent with such a fault, although a fault contact has yet to be identified (t.r. knudsen, utah geological survey, written communication, 2022). the possibility exists that the red rock trail thrust is segmented or in a nascent stage of development in the cedar mountain quadrangle. whereas the murie creek thrusts are relatively short and of low displacement, the red rock 47 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 trail thrust is in a favorable location and orientation to eventually link with the blind thrust deeper in the core of this fold-thrust structure (see dashed fault, figure 7). it is our contention that these two faults are locally hard linked in the subsurface in the vicinity of short creek, to form a break thrust (see eisenstadt and de paor, 1987; fischer and others, 1992). thus, the red rock trail thrust would represent a developing frontal ramp along the leading edge of the sevier fold-thrust belt in southwestern utah. the pintura anticline conundrum dissection of the kanarra fold-thrust structure by the hurricane fault yielded spectacular exposures of the leading anticline-syncline pair and associated thrust faults of the kanarra fold-thrust structure in its footwall block, the hurricane cliffs. the burial of the hanging wall block of the hurricane fault, and with it the trailing limb of the kanarra anticline, beneath neogene to quaternary sediments and volcanics of cedar valley, obfuscates the full tectonic significance of the kanarra fold-thrust structure to the sevier fold-thrust belt. this is borne out in a long-lived debate regarding the relationship between the virgin, pintura, and the kanarra anticlines (see hurlow and biek, 2003, for a complete summary) and the timing of sevier deformation in southwestern utah (biek and others, 2009). the pintura anticline, from early on, has been depicted as a broad gentle anticline separated from the smaller, tighter kanarra anticline by an intervening syncline (e.g., figure 2a, p. 249, in gardner, 1941). the folds were beveled by erosion and the angular unconformity capped by early to late campanian clastics (biek and others, 2010). the younger hurricane fault is pictured cutting the western limb of the kanarra anticline near the axis of the intervening syncline, isolating the partially eroded pintura anticline within the rotated hangeastwest sct splay sct kct kct rrtt jn jks jks trcs trms trms trcs trmv trmv pql* pqu* pkf trmt hct tct tct 0 500 1000 m no ve ? figure 36. large-scale blowup of the cross section of the kanarra fold-thrust system at kanarra creek. early-formed thrusts (fold accommodation faults) which were overturned at later stages of kanarra fold development are colored in red. here, the late-forming thrusts have formed a dextral shear zone across the fold limb, dissecting earlier flank thrusts. folding along the taylor creek thrust was inferred by extra area in the leading syncline. displacement along the red rock trail thrust is estimated here to be approximately 250 meters. sinistral flexural slip within the syncline core which may be responsible for the structural relationships at kanarra creek (figure 32b) is represented by the dashed , queried detachment beneath the navajo. all abbreviations on figure 9. figure 31. enlargement of the cross section a–a' of the kanarra fold-thrust structure at kanarra creek. early formed thrusts (fold accommodation faults), which were overturned at later stages of kanarra fold development, are colored in red. here, the late-forming thrusts have formed a dextral shear zone across the fold limb, dissecting earlier flank thrusts. folding along the taylor creek thrust was inferred by extra area in the leading syncline. displacement along the red rock trail thrust is estimated here to be approximately 250 m. sinistral flexural slip within the syncline core, which may be responsible for the structural relationships at kanarra creek is represented by the dashed, queried detachment beneath the navajo sandstone. structure initializations: sct–spring creek thrust; tct–taylor creek thrust; kct–kanarra creek thrust; rrtt–red rock trail thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. line of section shown on plates 1 and 2. 48 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 ing wall of the hurricane fault (e.g., see figure 2f, p. 249, in gardner, 1941). gardner (1941) notes “down-turning” of the hanging wall strata, as the contact with the hurricane fault is approached, enhances the intervening syncline, a process gardner attributes to gravitational “sag.” more recent mapping of the pintura 7.5-minute quadrangle (hurlow and biek, 2003) substantiate these findings and their cross section shows a similar broad pintura anticline, a faulted intervening syncline, and a tighter faulted kanarra anticline. we note that in our map area deformation associated with the hurricane fault is commonly represented by sparse normal faults that are sub-parallel to the trace of the hurricane fault (plates 2a and 3). whereas drag folds may be locally present, we interpret the several locations along the kanarra fold-thrust structure that preserve westward dips to be associated with the discontinuous remnants of the hinge zone of the leading anticline of the kanarra fold-thrust structure and these locations record sevier compression rather than drag along the hurricane fault (plates 2a and 3). cook (1957) called into question the existence of tgtf n 0 100 200 m rrtt rrtt ccts hct hct hct sct hf tgtf jtrm jtrm jks jks jns jn jn kcn jtc jnsjks trcs trcs coal creek trcs trcs trcs trmt trmv trmv trmv jtc ccts stct(e) stct(w) stct(w) hcttrcs a c trms trmv trmu trmm trcs trcs trcs b jks trcs trcs trcu trms trcl hct trmutrcl figure 32. (a) google earth 3d terrain view with landsat/copernicus imagery looking northeast onto the east limb of the kanarra fold-thrust structure at the red hill adjacent cedar city. stephens canyon forms the low area within the middle red member of the moenkopi formation, just east of the virgin limestone member of the moenkopi (also see plate 1). (b) view looking north upon a ridge of the shinarump member of the chinle formation, which forms the footwall of the hicks creek thrust, east of stephens canyon. (c) view northwest showing the curvature of the shnabkaib member of moenkopi as the beds rotate into the fold nose. structure initializations: ccts–coal creek thrust system; hct–hicks creek thrust; rrtt–red rock trail thrust; stct(e)–stephens canyon thrust (east); sct–spring creek thrust; stct(w)–stephens canyon thrust (west); tgtf–thunderbird gardens trail fault. see plate 2b (stratigraphic column) for explanation of map unit symbols. 49 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 the pintura anticline. cook (1957) noted that when bedding in the carmel formation is rotated to horizontal, the contact between the underlying navajo sandstone and carmel formation everywhere dips more steeply to the northwest; the east-dipping limb of the pintura anticline is missing or poorly exposed. hurlow and biek (2003) confirmed cook’s (1957) result and described two plausible interpretations of the data: (1) the pintura anticline is a west-dipping homocline (i.e., cook’s model) and (2) the pintura anticline is a broad anticline that shares an east-dipping limb with the intervening syncline that was modified by reverse drag along the hurricane fault (i.e., the model preferred by hurlow and biek, 2003). the results of our work have bearing on resolving the pintura anticline conundrum. the geologic cross section (figure 7) depicts a complete profile through the kanarra fold-thrust structure restored to the late cretaceous (i.e., prior to dissection by the hurricane fault). in our structural interpretation, the shape of the kanarra anticline is a compound fold, with a broad, sub-horizontal hinge zone flanked by a leading anticline on the east and by a trailing anticline on the west. the trace of the hurricane fault closely parallels the trace of the hinge zone of the leading anticline (plates 2a and 3). as previously suggested, during basin and range extension, the hurricane fault exploits the hinge zone of the leading anticline, and likely the underlying thrust as well, of the kanarra fold-thrust structure (threet, 1963b; grant and others, 1994; biek and others, 2009). downward displacement of the trailing limb of the composite kanarra anticline (figure 7) in the hanging wall of the hurricane fault would result in an apparent west-dipping homocline. the presence of the intervening syncline (i.e., between the pintura and kanarra anticlines) can be attributed to the development of a roll-over anticline and antithetic normal faults as the contact with the hurricane fault is approached (see figure 8.3.1, p. 433, in davis and others, 2011). however, downward displacement and clockwise rotation of the hanging wall along a listric normal hurricane fault could create the appearance that the western trailing anticline of the kanarra fold-thrust structure is a separate anticline—the pintura anticline. clockwise rotation of the broad sub-horizontal hinge zone of the kanarra fold associated with the kanarra fold-thrust structure (see figure 7) during normal faulting would then appear to be the east-dipping limb of the pintura anticline that is shared with the proposed intervening syncline. the dismembered kanarra anticline of the kanarra fold-thrust structure would now have the leading anticline (i.e., the kanarra anticline of biek and others, 2009) isolated and cropping out in the footwall of the hurricane fault. hanging wall strata adjacent to the hurricane fault would still be subjected to modification by development of a rollover anticline and antithetic faults. in either scenario, the pintura anticline is an “accidental anticline” that was cleaved from the compound kanarra anticline of the sevier age kanarra fold-thrust structure during basin and range extension rather than a unique fold. the relative stratigraphic ages used previously to constrain the timing of the formation of the pintura anticline to be between early and late campanian time (about 84 to 71 ma; see biek and others, 2009), and possibly younger, constrain the timing of formation of the kanarra foldthrust structure. the kanarra fold-thrust structure at the red hill we interpret the kanarra fold-thrust structure to be well exposed at the red hill near cedar city. the red hill is one of utah’s iconic geologic exposures (hintze, 2005). again, the fold has been dissected by the hurricane fault along the axial trace of the leading anticline (plate 1). the western trailing limb of the anticline has been displaced along with the hanging wall beneath the sediment fill in cedar valley, with the eastern limb of the anticline and leading syncline well exposed in the footwall. at this structural level, closure of the northerly plunging nose of the fold is well shown by the change in the strike and dip of upper triassic and lower jurassic strata from northeast to northwest dips (figure 32). the amount of shortening at the red hill is greater than along camp creek but less than along kanarra creek. the lower degree of shortening is reflected in the upright, gentle to steeply dipping stratigraphic section along the leading eastern limb of the anticline with moderate, additional structural complexity from faulting along the limb. 50 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 we utilize the structural style of folding and faulting for the kanarra fold-thrust structure near kanarraville (this paper) to provide new interpretations for the role of faulting at the red hill. for example, some of the faults at the red hill (e.g., the hicks creek thrust) were also previously classified based upon observed separation as normal faults (e.g., averitt, 1962; hintze, 2005), obscuring the true relationship of these faults to folding and to the sevier fold-thrust belt. based upon our unpublished in-person and remote geologic mapping as well as published geologic maps (averitt and threet, 1973; knudsen, 2014a; knudsen, 2014b) and with consideration for the structural style of the kanarra foldthrust structure (figure 7), we present a geologic cross section for the red hill at late cretaceous time and discuss the style of faulting at the red hill and why it is part of the kanarra fold-thrust structure (figures 33, 34b, and 35b). the profile through the kanarra fold-thrust structure at the red hill shares several features with the central part of the structure at kanarraville (figure 7). the anticline at the red hill is also an asymmetric, composite fold-thrust structure modified by late fold accommodation thrust faults. the structure also likely developed above a basal detachment in the cambrian bright angel shale and above a blind break-thrust ramp (figure 33). slip along the early formed spring creek flank thrust forms a fault-bend fold within the trailing limb of the anticline to produce a compound fold profile. the influence of kink axes on the fold profile gradually diminishes upwards such that the fold has a rounded profile more typical of buckle folds. the early formed hicks creek flank thrust, on the eastern limb of the fold, has been steepened by rotation during folding but remains upright (figures 32 and 33). duplication of the stratigraphic section along this west-verging flank thrust thickens the east-dipping limb and broadens out the hinge zone of the leading anticline of the fold (figures 33, 34b, and 35b). the stephens canyon thrusts are smaller early formed flank thrusts that crop out west of the hicks creek thrust (figures 33, 34b, and 35b; table 2). during folding, one of these thrusts duplicates the shnabkaib member. we also interpret several faults, the coal creek thrust system, as late fold accommodation faults as several of these thrusts truncate the earlier hicks creek thrust (figures 33, 34b, and 35b). displacement of formation contacts by these faults show right-lateral separation on the geologic maps (see figures 33, 34b, and 35b). the two-dimensional separation of formation contacts is compatible with normal-slip, strike-slip, and reverse-slip fault movement and several of these faults have been mapped as normal faults (averitt and threet, 1973; knudsen, 2014a). we use our mapping and gmde (allmendinger, 2020) to constrain the dip on these fault contacts to be consistently dipping southeast with dip magnitudes of about 45o and in the range of a low of 36o and a high of 50o. considering the dip on these faults does not exceed 60o, and that the dips are likely to have been increased as a result of eastward rotation of the fold limb during deformation, the lower dip values for the fault contacts is more typical of thrust faults than normal faults or strike-slip faults (davis and others, 2011, p. 291). tops-to-the-northwest movement of the hanging wall on southeast-dipping thrust faults will also produce right-lateral separation of formation contacts on a geologic map of the red hill. thus, we interpret the coal creek faults (figures 34 and 35) as a type of late, west-verging, fold accommodation fault known as hinge wedge thrusts (e.g., see figures 12 through 14, p. 113–115, in cloos, 1961, and figure 8, p. 680, in mitra, 2002a) and they are represented as such in our cross section through the red hill (see figures 33, 34b, and 35b). these thrusts likely formed in response to hinge zone tightening during the development of the kanarra fold-thrust structure. accepting that these are thrust faults, in the cross section they duplicate upper moenkopi and chinle units in the footwall of the hicks creek thrust and displace the hicks creek thrust several tens of meters west within the subsurface along the fold limb, though aggregate slip on each splay is higher (hundreds of meters). at the red hill, a late forelimb shear thrust fault is observed (figures 34 and 35). this fault has a highly similar structural style and location within the cross section (figure 33) as the red rock trail thrust at kanarraville (cf., figure 7). here, the forelimb shear thrust fault has ramped higher up section compared to kanarra creek (figure 35). like the red rock trail thrust, the forelimb shear thrust fault displaces the navajo sandstone over 51 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 the carmel formation (figure 34). we correlate this fault with the red rock trail thrust. we note that the carmel formation in the leading syncline is intensely deformed by a buckle fold train and associated minor thrust faults and duplexes well exposed in road cuts along cedar canyon. these buckle folds developed as a result of the carmel formation having a shorter dominant wavelength in comparison to the underlying navajo sandstone (fischer and others, 1992). the buckle fold train likely developed above a detachment in the temple cap formation (plate 2, also see threet, 1963a, p. 113). the proposed detachment along the temple cap formation may also play a role in the development of structures at parowan gap (see discussion below). at the red hill, the red rock trail thrust is also in a favorable location and orientation to have had the opportunity to merge with the blind thrust ramp deeper within the fold if horizontal shortening had progressed further. however, construction of the cross section for the amount of shortening required at the red hill indicates these two faults are not hard-linked and the frontal ramp was captured in the nascent stages of development (figure 33). salient and recess development along the kanarra fold-thrust structure the kanarra fold-thrust structure is defined by xu jn jks jcp jtm kcn ks trcs trmv ct cbk cn mr pql pqu pkf trmt trms sct ccts rrtt hct hct jn jtm jks jcp kcn ks trcs trmv ct cbk cn mr pql pqu pkf trmt trms west b meters 4000 3000 2000 1000 0 -1000 -2000 -3000 -4000 east b’ meters 4000 3000 2000 1000 0 -1000 -2000 -3000 -4000 figure 33. cross section b–b' of the kanarra fold-thrust structure showing the restored sevier structure circa 80 ma, based on unpublished mapping along coal creek and mapping by knudsen (2014a). eroded geology is faded out. the pre-extension trailing limb and fold crest are constrained by the tilted, sub-horizontal, west-dipping layering defined by the enveloping surface of the carmel buckle fold train (the pre-folding jn-jtm contact, dotted line) and the shape of the closely related pintura anticline (hurlow and biek, 2003). unexposed layer thickness and presence are constrained by local data sources (see table 1; hintze, 1986; van kooten, 1988; hurlow and biek, 2003; biek and others, 2009). unexposed, thick, competent layers (cbk-cnd, mr, pq) are colored according to age; exposed ridge-former colors correspond to the maps in the study area (figures 3 and 4). present-day topography is included to emphasize the ridge formers. structure west of the hurricane cliffs, within the present-day cedar valley graben, does not represent present-day bedrock geology. unexposed structure constrained by surface control, fold style, and assumption of buckle folding before break thrust faulting. ccts–coal creek thrust system; hct–hicks creek thrust; rrtt–red rock trail thrust; sct–spring creek thrust. see plate 2b (stratigraphic column) for explanation of map unit symbols. line of section shown on plate 1. 52 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 broad open curves along its strike (plate 1). near cedar city the curve is concave towards the hinterland and forms a salient. just south of kanarraville, the structure curves to be concave towards the foreland and forms a recess. the presence of salients and recesses is a common feature of many orogens, including the sevier foldthrust belt (quick and others, 2020). the presence of salients and recesses may reflect variation in stratigraphy (e.g., chapman and decelles, 2015), sediment thickness (paulsen and marshak, 1999), and variation in the shape of the rifted continental margin, which is controlled by the embayments and promontories that define the hingeline (thomas, 2006). the presence of strike-slip transform faults separating different rift basins in the precambrian basement contributes to development of an irregular hingeline to the extended continental crust. along strike variation in the temporal and spatial advancement of the leading edge of the sevier fold-thrust a n 0 100 200 m hct hct stct(e) hct rrtt rrtt ccts sct ccts jns jks jks jks jtrm jtrm jns trcs trcs trcs trcs trcs trmv folded strata trmt jns jnjtc jn jc tgtf trmv coal creek stct(w) trcs hctccts trcs jks 0 30 60 m nb trmv mr west sct ccts stct(w) stct(e) rrtt hct hct east 0 500 1000 m no ve jn jks trcs jcp jtm trms trmv jks jn jtm trms trcs pql pql pqu pkf c figure 34. (a) google earth 3d terrain view southeast onto the east limb of the kanarra fold-thrust structure at the red hill adjacent cedar city. early fold accommodation faults, which were later folded and cut along the ccts, are colored in red. nearby, the spring creek thrust emerges, bringing up timpoweap strata. the thunderbird gardens trail cross fault cuts across the fold in the foreground. contacts from unpublished field and gmde mapping by the authors, and knudsen (2014a). (b) the later set of thrusts in the coal creek thrust system cuts obliquely across the early set. (c) partial enlargement of b–b' (see figure 33, section is reversed), reflected vertically to match the southeast view of (a) and with early faults in red. structure initializations: ccts–coal creek thrust system; hct–hicks creek thrust; rrtt–red rock trail thrust; stct(e)– stephens canyon thrust (east); sct–spring creek thrust; stct(w)–stephens canyon thrust (west); tgtf–thunderbird gardens trail fault. see plate 2b (stratigraphic column) for explanation of map unit symbols. 53 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 belt front was largely inherited from the structure of the rifted precambrian crystalline basement of western north america (picha and gibson, 1985; picha, 1986; quick and others, 2020). we suggest that the close spatial association of the kanarra fold-thrust structure with the cordilleran hingeline (figure 1) indicates that structural inheritance is a contributing factor to the formation of salients and recesses that characterize this foldthrust structure (plate 1). we interpret the cross faults (e.g., murie creek fault) to reflect reactivation of proterozoic transfer zone faults (i.e., present-day basement lineaments) along the cordilleran hingeline in sevier time (picha and gibson, 1985; paulsen and marshak, 1999; thomas, 2006; quick and others, 2020). for example, the murie creek fault just north of kanarraville and the thunderbird gardens trail fault just north of cedar city, are both sub-parallel to the paragonah lineament (figure 1), suggesting they were localized as a result of reactivation of transform faults in the basement and aided along strike displacement of the n 0 100 200 m rrtt rrtt ccts stct(e) stct(w) stct(w) ccts hcthct hct hct sct hf tgtf jtrm jtrm jks jks jns jn jn kcn jtc jnsjks trcs trcs trcs trcs trcs trmt trmv trmv trmv jtc coal creek a west jn jks trcs jks jn jtm jcp jtm trmv trms trmv trms trcs mr pql pql pqu pkf sct ccts rrtt hct hct east 0 500 1000 m no ve stct(w) stct(e) b figure 35. (a) google earth 3d terrain view with landsat/copernicus imagery looking northeast onto the east limb of the kanarra fold-thrust structure at the red hill adjacent cedar city. selected faults and sedimentary contacts are shown for clarity. early fold accommodation faults, which were later folded and displaced are colored in red. this view is approximately along-strike to the late, northwest-vergent set of coal creek thrusts, showing their gentle to moderate dips (e.g., right midground). contacts from unpublished field and gmde mapping by the authors and knudsen (2014a). (b) partial enlargement of b–b' (see figure 33) with early faults in red. structure initializations: hf–hurricane fault; ccts–coal creek thrust system; hct–hicks creek thrust; rrtt–red rock trail thrust; stct(e)–stephens canyon thrust (east); sct–spring creek thrust; stct(w)–stephens canyon thrust (west); tgtf–thunderbird gardens trail fault. see plate 2b (stratigraphic column) for explanation of map unit symbols. 54 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 fold-thrust structure (plate 1). in addition, early formation of the murie creek fault during folding could present a structural discontinuity that hindered the along strike propagation of the red rock trail thrust. the red rock trail thrust abuts the murie creek fault (plates 2a and 3) and its trace farther to the north in the cedar mountain quadrangle (averitt, 1962; doelling, 1972) is inferred from the presence of a catacalsite zone in the navajo sandstone, before it is recognized again in the cedar city quadrangle. the leading edge of the sevier fold-thrust belt in southwestern utah several structures have been previously proposed to represent the leading edge of the sevier fold-thrust belt in southwestern utah. biek and others (2015) proposed that the bryce canyon anticline in the hanging wall the paunsaugunt normal fault initially formed due to thrusting and defines the easternmost extent of sevier deformation (biek and others, 2015 p. 91). their evidence for the presence of an older episode of thrusting along the paunsaugunt normal fault is based upon the subtle angular discordance between pre-claron strata and the paleocene-eocene claron formation on the paunsaugunt plateau. we note that the broad bryce canyon anticline in the hanging wall of the paunsaugunt normal fault is similar in style to the folds in the hanging wall of other normal faults on the plateau (e.g., the sevier fault; see cross section b–b' of biek and others, 2015) and likely formed as a roll-over anticline (see figure 6.136b, p. 333, in davis and others, 2011) during younger basin and range extension, thus eliminating the need for an earlier episode of cryptic thrusting along the paunsaugunt normal fault. alternatively, we suggest that the kanarra fold-thrust structure, which includes spatially associated minor folds and thrusts in the late cretaceous strata, for example at the red hill (knudsen, 2014a) and in parowan gap (threet, 1963a, 1963b) unambiguously defines the leading edge of the sevier fold-thrust belt in southwestern utah (figure 1). the red rock trail thrust is not hard linked along its entire length, for example at kanarra creek (figure 7) and the red hill (see figure 33). this is consistent with a sevier deformation front that was in the process of developing a frontal ramp along the red rock trail thrust before deformation abated. locally, where a frontal ramp may have developed, the navajo sandstone in the hanging wall was transported east and onto the carmel formation, for example near the mouth of short creek (plates 2a and 3), and we suggest also in parowan gap. in the central part of the kanarra fold-thrust structure, the red rock trail thrust is in a favorable orientation to have formed a hard linkage with the basal decollement in the bright angel shale to create a break thrust (figure 7). the thrust displaces navajo sandstone along with its distinctive cataclasite zone over the carmel formation. this same spatial relationship of fault-related units is well exposed along the prominent topographic ridge of navajo sandstone at the west entrance to parowan gap (threet, 1963a; maldonado and williams 1993; anderson and dinter, 2010). the thrust relationships are complicated by basin and range deformation. a steep normal fault along the eastern side of the navajo sandstone topographic ridge, down-dropped to the east the navajo cataclasite, the thrust fault, and the carmel formation in its hanging wall (figure 36). cropping out in the low hills in the hanging wall of the normal fault is an east-verging thrust that places cataclasite navajo sandstone over folded and fractured, laminated, micritic limestone of the carmel formation. we propose the following: (1) this thrust fault contact has a similar structural style and position as the red rock trail thrust and is part of a similar, but unique, foldthrust structure. this fold-thrust structure at parowan would be related to the kanarra fold-thrust structure in a similar fashion that the virgin anticline is related to the kanarra fold-thrust structure (see biek and others, 2015, p. 64) and (2) the westernmost thrust fault in parowan gap is correlative with the red rock trail thrust and the fold-thrust structure at parowan gap is part of the kanarra fold-thrust structure as originally proposed by threet (1963a, 1963b). if the fold-thrust structure at parowan gap is related to the kanarra foldthrust structure, it is exposed at a higher structural level as it preserves deformation in upper cretaceous strata. to the east of the westernmost thrust fault in parowan gap (the red rock trail thrust?), two other east-verging thrusts are well exposed in parowan gap (threet, 1963b, maldonado and williams, 1993; anderson and dinter, 2010; biek and others, 2015). these thrusts were 55 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 named “the thrust faults at parowan gap” by maldonado and williams (1993). they were correlated with the iron springs thrust by goldstrand (1992) and again by anderson and dinter (2010) and biek and others (2015). the original correlation of the thrusts at parowan gap to the iron springs thrust by goldstrand (1991, p. 58, and 113) is based upon these thrusts being on trend, exhibiting similar structural style, and stratigraphically correlating upper cretaceous rocks at parowan gap with the iron springs formation. we note that the along trend correlation of these thrust faults crosses about 30 km of younger sedimentary fill in the cedar valley graben and discounts disparate horizontal basin and range extension. cursory inspection suggests restoration of the red hills horst, and thus parowan gap to its pre-basin and range extension location, would place it closer to the markagunt plateau and on trend with the kanara fold-thrust structure. this supports the correlation of sevier structures in parowan gap as part of the kanarra fold-thrust structure as previously suggested by threet (1963b). in contrast, restoration of basin and range extension would still preserve the irons springs thrust in the three peaks horst cropping out well west of the kanarra fold-thrust structure. the thrusts at parowan gap placed carmel formation over the lower iron springs formation as well as the lower iron springs over upper iron springs, suggesting low displacement (threet, 1963b). the thrusts jnca jnc rrtt jc jnc jnb jnc c figure 36. (a) north-facing view of navajo sandstone cataclasite (jnc) at the west entrance to parowan gap. john p. hogan for scale, 1.86 m. inset: close-up of the navajo cataclasite a few meters to the east along the same outcrop. gravelto cobble-sized sandstone clasts are suspended within a network of fractures and finer cataclastic grains. (b) view to the north of the red rock trail thrust (rrtt) at the west entrance to parowan gap tens of meters north of (a). photograph by john p. hogan. (c) cataclastic navajo near (a), view to the northeast. photographs in (a) and (c) by michael wizevich, central connecticut state university. 56 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 are beveled off along an angular unconformity that is capped by the upper cretaceous grand castle formation. slight displacement of the unconformable contact by the thrusting constrains the waning stages of deformation to the early paleocene (anderson and dinter, 2010; biek and others, 2015). uncertainty and disagreement in the identification of the upper cretaceous units in parowan gap, particularly the presence or absence of the straight cliffs (e.g., the about 90 to 80 ma john henry member) and naturita formations, will affect the interpretation of the displacement and timing of movement on these thrusts (anderson and dinter, 2010; biek and others, 2015; enriquez st. pierre and johnson, 2021). the debate regarding the stratigraphic assignment of upper cretaceous units in parowan gap with upper cretaceous formations that are younger than the iron springs formation at three peaks further undermines the validity of correlating the thrusts in parowan gap with the iron springs thrust at the three peaks. considering recent findings reported here, and by quick and others (2020), correlation of the iron springs thrust, where it crops out in its type locality in the three peaks area, with the thrusts exposed in parowan gap is tenuous. the iron springs thrust at the three peaks crops out to the west of the kanara fold-thrust structure and the red rock trail thrust (figure 1). in parowan gap, the two eastern thrusts (i.e., those proposed to be the iron springs thrust) would reverse this spatial relationship if the westernmost thrust correlates with the red rock trail thrust or a similar style thrust. in contrast, in the context of the structural style of the kanarra fold-thrust structure, the two eastern thrusts at parowan gap would more likely have formed as out of the syncline thrusts east of the overturned limb of the leading anticline (cf., figures 7, 33, 34, and 35). these late fold accommodation faults, which are typically of lower displacement, would then potentially sole into the middle jurassic temple cap formation detachment, the same detachment underlying the buckle fold train at the red hill (e.g., averitt and threet, 1973; knudsen, 2014a) rather than into the regional basal detachment in southwestern utah (e.g., van kooten, 1988; biek and others, 2009). timing of sevier thrusting in southwestern utah advancement of the sevier deformation front in southwestern utah is episodic. quick and others (2020) connected movement along the iron springs thrust at 100 ma with the late albian to early cenomanian magmatic flare up in the cordilleran arc. they suggested that accelerated subduction, associated with a period of global plate reorganization, contributed to a magmatic flare up in the cordilleran arc. this event, along with steepening of the orogenic wedge, triggered widespread thrusting across the retroarc sevier deformation belts. the timing of deformation of the kanarra fold-thrust structure in southwestern utah (about 80 to 70 ma) also corresponds with a period of widespread thrusting in central utah (e.g., paxton, gunnison, and charleston-nebo thrusts) and in northern utah and southwestern wyoming (e.g., crawford and absaroka thrusts) as well as overlapping with major magmatic flare ups in the cordilleran arc (see figure 9, p. 85, in quick and others, 2020). this close temporal relationship between magmatic activity in the arc and widespread deformation in the sevier fold-thrust belt (see lageson and others, 2001; decelles and others, 2009; decelles and graham, 2015; yonkee and others, 2019; quick and others, 2020) requires further investigation. correlation of the iron springs thrust at the three peaks with the thrusts exposed in parowan gap is also unlikely due to disparity in the temporal relationships of these thrusts. quick and others (2020) constrained initial deposition of the iron springs formation and the initial movement on the iron springs thrust in the type location of the three peaks to 100 ma. stratigraphic relationships at the three peaks also constrain the latest movement on the iron springs thrust to be as late as early paleocene (knudsen and biek, 2014). this history of movement on the iron springs thrust is consistent with episodic pulses of deformation and syntectonic sedimentation during the sevier orogeny (quick and others, 2020). the initial movement on the iron springs thrust is tens of millions of years earlier than the motion on the easternmost thrusts in parowan gap if they cut the john henry member of the straight cliffs formation. this episode of deformation may be more in agreement with 57 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 the timing constraints on the movement of the kanarra fold-thrust structure in the south of about 84 to 71 ma (i.e., the former pintura anticline of hurlow and biek, 2003). the latest motion on the thrust in parowan gap is constrained to be late cretaceous to paleocene (anderson and dinter, 2010; biek and others, 2015). if the iron springs formation at three peaks is distinct from the upper cretaceous strata at parowan gap correlation of the iron springs thrust with the thrusts at parowan gap is considerably weakened considering that initial movement on the iron springs thrust is constrained to 100 ma (quick and others, 2020), potentially millions to tens of millions of years before the rocks at parowan gap were being deposited. we suggest that recognition of the westernmost thrust cropping out in parowan gap as the red rock trail thrust and the two easternmost thrust faults as late fold accommodation faults, rather than as the iron springs thrust, alleviates the apparent discrepancy in the timing of thrusting in southwestern utah. sediment dispersal in the sevier foreland the temporal and spatial advancement of topographic highs and lows associated with the progression of the sevier deformation front across southwestern utah significantly influences the redistribution of sediment in the sevier foreland basin. the emergence of the iron springs thrust in the late albanian to earliest cenomanian correlates with movement on the keystone-muddy mountain thrust, the pahvant thrust (formerly spelled pavant), the charleston nebo thrust, and the willard thrust system (see figure 9, p. 85, in quick and others, 2020). the deformation front advances eastward in southwestern utah with the development of the kanarra fold-thrust structure in the campanian. during this time, the kanarra fold-thrust structure likely formed a substantial, linear, topographic high with associated strike valleys that extended over a hundred kilometers from toquerville to north of parowan gap along the edge of the markagunt plateau (figure 1). investigation of cretaceous stratigraphy in southwestern utah documented the foredeep of the sevier orogeny was broken up into several discrete sub-basins presumably due to reactivation of northeast-trending structures in the basement as normal faults (see figure 10, p. 561, in enriquez st. pierre and johnson, 2021). creation of northeast-trending topographic highs and lows associated with horsts and grabens is suggested to have controlled the fluvial drainage patterns of the main axial river systems in what is now the plateau province. in this model, the sevier fold-thrust belt and wedge top was thought to be well west of the edge of what is now the markagunt plateau. this interpretation may have merit for the eastern plateaus adjacent to the cretaceous western interior seaway, however, it mischaracterized the kanarra fold-thrust structure as a laramide age monocline rather than the leading edge of the sevier fold-thrust belt during the late cretaceous (see figure 1, p. 548 and figure 2, p. 549, in enriquez st. pierre and johnson, 2021). we agree the distribution of cretaceous depocenters and fluvial drainage patterns are sub-parallel to the sevier deformation on the markagunt plateau, and to the immediate west, reflect the development of significant topographic features, as well documented by enriquez st. pierre and johnson (2021), but in response to the episodic advancement of the leading edge of the sevier fold-thrust belt in southwestern utah rather than due to extensional faulting. conclusions detailed geologic mapping and structural analysis of the central part of the kanarra anticline (gregory and williams, 1947; averitt, 1962; threet, 1963a, 1963b) demonstrate folding and thrusting are inextricably linked in all stages of deformation such that we identify this structure as the kanarra fold-thrust structure. the kanarra anticline of the kanarra fold-thrust structure has an overall compound form in that its hinge zone includes an open, upright, trailing anticline as well as the leading anticline now exposed at the surface. secondary structures associated with contractional deformation within the hinge of the leading anticline, as well as a blind thrust beneath the leading anticline, were in a favorable orientation to be reactivated during younger basin and range extension resulting in strain localization and formation of the hurricane fault. the trace of the hurricane fault variably dissected the hinge zone of the leading anticline such that scattered remnants of 58 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 the hinge zone and axial trace crop out discontinuously along the strike of the entire structure. the hinge zone of the composite fold, as well as the trailing anticline, were down dropped in the hanging wall of the hurricane fault and are obscured by younger neogene and quaternary clastics and volcanics in the grabens created along the strike of the fault. the consequences of basin and range deformation resulted in recognition of an accidental anticline, the pintura anticline, and an apparent intervening syncline, separate from the kanarra anticline. we demonstrate the pintura anticline is part of the trailing anticline on the broad crest of the composite kanarra anticline that is part of the kanarra fold-thrust structure. stratigraphic relationships associated with the pintura anticline apply to the kanarra fold-thrust structure and constrain the timing of deformation to be early to late campanian but possibly younger (hurlow and biek, 2003). mapped thrust faults associated with the kanarra fold-thrust structure can be divided into early (e.g., flank thrusts) and late (out-of-the-syncline) fold accommodation faults. early formed flank thrusts are common to many folds in this area (e.g., the virgin anticline). the taylor creek thrust system on the eastern limb of the leading anticline of the kanarra foldthrust structure is the best-known example of one of these faults (e.g., see biek, 2007a). early formed flank thrusts on this eastern limb (e.g., taylor creek thrust) were folded and overturned along with the stratigraphic section in the central part of the kanarra fold-thrust structure. this additional structural complexity resulted in several faults previously being misidentified as normal faults rather than as folded thrusts. rotation of these thrusts into an unfavorable orientation for continued slip resulted in fault lockup. however, early formed flank thrusts on the trailing western limb remained in a favorable orientation for slip. these thrusts affected both the early development and shape of the kanarra anticline, as well crosscutting and displacing folded thrusts on the overturned eastern limb (e.g., the spring creek thrust). upon hinge lockup, late-forming forelimb shear thrusts within the overturned eastern limb developed a kilometer-scale, east-directed shear zone (e.g., mitra 2002a; jadamec and wallace, 2014) shared by the leading anticline and syncline. of these faults, the red rock trail thrust was in a favorable position and orientation to grow and locally may have merged with the blind thrust beneath the leading anticline to form a break thrust (eisenstadt and de paor, 1987; fischer and others, 1992). the cross section through the kanarra fold-thrust structure indicates the red rock trail thrust transports the stratigraphic section in the kanarra anticline to the east and on top of the jurassic to upper cretaceous strata of the now markagunt plateau. the red rock trail thrust and its distinctive navajo sandstone cataclasite can be traced from its inception north of spring creek along the contact between the kayenta formation and navajo sandstone well to the north. at the red hill, the red rock trail thrust has climbed section and places navajo sandstone over folded carmel formation. in parowan gap, the distinctive pairing of the navajo sandstone cataclasite on top of tightly folded and overturned carmel we interpret as a remnant of the red rock trail thrust at the western end of the gap. the overturned carmel and iron springs formation(?) in parowan gap represent the eastern limb of the leading anticline of the kanarra fold-thrust structure—a structure, which can be traced for a minimum distance of about 90 km from the southern terminus near toquerville to north of parowan gap (also see threet, 1963a). we associate the thrusts east of the red rock trail thrust in parowan gap as late fold accommodation faults (i.e., out-of-the-syncline thrusts) with the kanarra fold-thrust structure rather than correlate them with the iron springs thrust at the three peaks. this reconciles the apparent conflict in the timing of initial movement of the iron springs thrust at three peaks at about 100 ma (quick and others, 2020) with the movement on the kanarra fold-thrust structure constrained to being between early to late campanian. the kanarra fold-thrust structure represents the leading edge of the sevier fold-thrust belt in southwestern utah during the late cretaceous. the sevier fold-thrust deformation front appears to have advanced episodically from the iron springs thrust at 100 ma (quick and others, 2020) to the red rock trail thrust in the early to late campanian. this is suggestive that movement on sevier thrusts may be temporally tied to episodes of magmatic flare ups in the cordilleran arc (see lageson and others, 2001; decelles and others, 2009; decelles and graham, 59 the kanarra fold-thrust structure—the leading edge of the sevier fold-thrust belt, southwestern utah chandonia, w.j., and hogan, j.p. geology of the intermountain west 2023 volume 10 2015; yonkee and others, 2019; quick and others, 2020). during the late cretaceous, and potentially persisting into the eocene, the keystone-muddy mountain-tule spring-square top mountain-blue mountain-iron springs-canyon range thrust system and the kanarra fold-thrust structure in the campanian would present substantial north-south, linear topographic highs flanked by linear valleys that stretched over a 100 km in southwestern utah. these imposing topographic features would have “sevier” consequences for sediment provenance and dispersal in the associated cordilleran foreland basin. acknowledgments john p. hogan extends his thanks to robert “bob” laudon (missouri university of science and technology) for welcoming him to be a part of the field camp many years ago and sharing his thoughts, as well as his recollections of past conversations with sheldon “kerry” grant (missouri university of science and technology, deceased), on the geology of the area. additional hearty thanks to michael wizevich (central connecticut state university), jonathan obrist-farner (missouri university of science and technology), and jason kaiser (southern utah university), for their insights and discussions regarding the geologic significance of many field exposures to the geology of southwest utah as well as their friendship and comradery while teaching the missouri s&t field camp. william chandonia would also like to thank jason kaiser for his help with logistics in utah and sharing methods for measuring shear fractures. tyler r. knudsen (utah geological survey) gave his time to meet in the field and shared his knowledge of the stratigraphy, which assisted with interpretations in the chinle formation. william also acknowledges brennan brunsvick (southern utah university), trey anglim (missouri university of science and technology), dylan webb (missouri university of science and technology), and daniel quick (missouri university of science and technology) for their valuable assistance helping him in the field. the donation of petroleum experts’ move software was invaluable to the study workflow and creating cross sections. this work was also enhanced by richard allmendinger’s (cornell university) programs gmde, faultkin, and stereonet. paul inkenbrandt’s (utah geological survey) csl code facilitated the compiling and styling of our references. the study was funded by two grants from the american association of petroleum geologists foundation grants-in-aid program, one grant from the geological society of america graduate student research grant program, and the chancellor’s fellowship and radcliffe scholarship from missouri university of science and technology. we acknowledge the substantial effort of tyler knudsen and doug sprinkel (azteca geosolutions) for their thorough reviews of our manuscript and appreciate their comments as well as the reviews of grant shimer (southern utah university) and bob biek (utah geological survey). references allmendinger, r.w., 2020, gmde—extracting quantitative information 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orogenic system: earth-science reviews, v. 150, p. 531–593, doi: https://doi.org/10.1016/j.earscirev.2015.08.001. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah kenneth carpenter and louis h. taylor geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover an outcrop of the quarry sandstone in the brushy basin member of the upper jurassic morrison formation located east of the quarry exhibit hall, dinosaur national monument, utah. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 12 2025 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2024–2025 uga board president keilee higgs keileeann@utah.gov 801.678.3683 president-elect rob buehring robbuehring@yahoo.com 713.412.9269 program chair mike arnoff marnoff@utah.gov 385.303.0431 treasurer will hurlbut wdhurlbut@gmail.com 860.733.3190 secretary trae boman tboman@teanues.com 801.648.5206 past president eugene syzmanski eugenes@utah.gov 801.537.3364 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greggavin@gmail.com 513.509.1509 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.580.1331 aapg house of delegates 2023–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor william lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 25 abstract this study investigates the depositional environment, sedimentological dynamics, and tectonic influences that shaped the quarry sandstone within the brushy basin member of the upper jurassic morrison formation in dinosaur national monument, utah. characterized by laterally extensive, multistory sandstone bodies, the origin of the quarry sandstone has been a subject of ongoing debate. by synthesizing new field data and revisiting existing interpretations, this research challenges prevailing hypotheses and offers new perspectives on the geological history of the morrison formation at the monument. whereas the morrison formation, deposited in a foreland basin setting on the colorado plateau, is generally well understood, the quarry sandstone's unique width-to-thickness ratio sets it apart from other sandstone units in the brushy basin member. this distinct feature suggests a depositional history that cannot be fully explained by traditional foreland basin models. to address this anomaly, the study places the sandstone within its stratigraphic framework, emphasizing the critical role of accommodation space in shaping its deposition. a key finding of this research is the proposed influence of a proto-split mountain anticline on the sedimentation patterns of the quarry sandstone. this minor structural feature, likely generated by oblique compressional forces associated with regional tectonics on the colorado plateau, appears to have played a pivotal role in reducing accommodation space during the deposition of the sandstone. evidence for this reduction includes localized thinning of stratigraphic units and increased lateral connectivity of braided channel sandstones. the structural uplift caused by the proto-split mountain anticline likely created an asymmetrical depositional setting. this uplift restricted accommodation, triggering a transition in fluvial systems from single-threaded sinuous channels to multithreaded braided rivers with frequent avulsions. the interconnected nature of these braided channels over time reshaped sediment distribution patterns, producing the distinctive characteristics of the quarry sandstone. a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah kenneth carpenter1 and louis h. taylor2 1museum of natural history, university of colorado, boulder, co 80309 usa; kenneth.carpenter-1@colorado.edu 2littleton, co 80128 usa; loutaylor44@aol.com citation for this article. carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. introduction the morrison formation, an extensive upper jurassic sedimentary succession in the western united states, is renowned for its rich paleontological record and diverse depositional environments set within a foreland basin. stretching from southern alberta and saskatchewan, canada to new mexico, united states, and encompassing over 1.8 million km2, this formation offers a unique opportunity to study a variety of 26 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 sedimentological processes and depositional settings. morrison formation stratigraphy features an array of lithologies, including fluvial sandstones, lacustrine mudstones, limestones, and overbank deposits, which collectively record the interplay of terrestrial and aquatic environments during the late jurassic period. historically, research on the morrison formation has focused primarily on its extraordinary dinosaur fossils since their earliest discoveries in 1877 (cope, 1877; marsh, 1877). however, recent advancements in sedimentology have expanded the emphasis toward understanding the depositional environments and sedimentary processes that contributed to the formation's geological complexity. these environments are interpreted to include meandering and braided river systems (e.g., kjemperud et al., 2008; hayden and lamb, 2020), distributive fluvial systems (e.g., weissmann et al., 2013; owen et al., 2015), floodplains (e.g., demko et al., 2004), lakes (e.g., dunagan and turner, 2004), and rare aeolian dunes (e.g., peterson, 1994; demko et al., 2004), each imparting distinct sedimentary structures and lithofacies. detailed sedimentological analysis of these deposits reveals critical insights into the paleoclimatic conditions, paleohydrology, and tectonic influences that shaped the morrison landscape (see papers in carpenter et al., 1998; turner and peterson, 1998; turner et al., 2004; foster and lucas, 2006). a comprehensive sedimentological study involves the examination of grain size distributions, sedimentary structures, facies associations, and stratigraphic relations. these analyses help reconstruct paleoenvironments and elucidate the dynamic processes responsible for sediment deposition. with this in mind, we investigated the unusual ridge of sandstone in which the world-famous dinosaur quarry is developed at dinosaur national monument, utah. the quarry originally occupied about 130 m of the 1500-m-long discontinuous sandstone ridge, which lies near the middle of the mudstone-dominated brushy basin member of the morrison formation. this study investigated the relations among the stratigraphic architecture, sedimentary processes, accommodation, and depositional environment of the sandstone ridge in the context of the brushy basin. examining how these factors interact provides a deeper understanding of the geological history and the conditions that led to the formation of the sandstone ridge and the preservation of dinosaur fossils within it. geological setting the study area is on the southern side of split mountain, on the southeastern flank of the east-west trending uinta mountains in northeastern utah (figure 1). these mountains, also known as the uinta arch or uinta anticline, mark the northern boundary of the colorado plateau. split mountain is an anticline associated with the uinta mountains and is crossed by the green river (figure 2a), providing extensive exposures of paleozoic and mesozoic strata (rowley et al., 1979; sprinkel, 2019; gregson et al., 2024). the morrison formation, well exposed around the nose of the split mountain anticline, extends into the yampa plateau and blue mountain areas within dinosaur national monument, across the utah-colorado border (figure 2b). the study area is specifically near the historic carnegie dinosaur quarry, now housed within the quarry exhibit hall (qeh), between douglass draw to the west and swelter shelter draw to the east (figure 2c). the famous dinosaur quarry is at the western end of the discontinuous sandstone ridge, which extends approximately 1.5 km through the brushy basin member (figure 3b). referred to as the quarry sandstone here, this sandstone is the “quarry interval” of turner and peterson (1992a, 1992b) and “quarry sandstone” of carpenter (2013) and brezinski and kollar (2018). unusual for its lateral extent within the brushy basin member, this sandstone and adjacent mudstone, are the focus of this study. study methods we measured sections by tape and brunton compass on both the east and west side of the qeh and through the thickest part of the remaining sandstone within the qeh (figure 4). we integrated these sections with measured sections made by fred (“pete”) peterson (formerly of the u.s. geological survey) and shared with us (figures 5 and 6). peterson made his sections in 1991 using benchmark 4992.8 on the east side of the qeh for horizontal and vertical control. peterson's sections averaged 30 m apart and connected laterally with 27 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 key beds and scour surfaces (turner and peterson, 1992a, 1993). peterson made another stratigraphic section 550 m west of the qeh in douglass draw, which was designated as the primary or master stratigraphic reference section for the morrison formation by turner and peterson (1999) for their biostratigraphy of dinosaur localities (see stratigraphic setting). we used photographs taken at different times during the 1930s by various national park service employees, especially geologist albert boyle overseeing work crews of the federal emergency relief administration (fera) and later the work progress administration (wpa) (carpenter, 2018), to reconstruct the now missing interval of strata that overlaid the fossil-bearing sandstone beds. this interval of strata was considered overburden and was removed from 1934–1938 by fera and wpa crews as part of the national park service's early development of what was to become the dinosaur quarry exhibit. these photographs and cited reports containing strata descriptions are housed in the archives of dinosaur national monument. other photographs, mostly by boyle, are housed in the uintah county regional history center, vernal, utah. correspondence of earl douglass is in the archives of the carnegie museum of natural history, pittsburgh, pennsylvania. diane iverson, granddaughter of earl douglass provided photographs of earl douglass through sue ann bilbey and evan hall (both uinta paleontological associates, inc., vernal, utah). we collected oriented hand samples in the trenches made for the measured sections on the west and east sides of the qeh, the samples are plotted on the measured sections in figure 4. rock color is based on the munsell (2009) hue, value, and chroma rock color figure 1. map showing the uinta mountains of northeastern utah and the location of split mountain and dinosaur national monument. 28 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 scheme. wagner petrographic (lindon, utah) made the thin sections of these samples. these and other thin sections are referenced below by their catalog numbers prefaced by dino. the thin sections are curated in the dinosaur national monument collections stored at the utah field house of natural history state park musefigure 2. (a) split mountain anticline. (b) outcrop map of the morrison formation in and around dinosaur national monument of utah and colorado. (c) distribution of the quarry sandstone in relation to the quarry exhibit hall (qeh) and named drainages referenced in the text. 29 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 um in vernal, utah. samples of the quarry sandstone were obtained from matrix still adhering to dinosaur bones collected by the carnegie museum crews between 1909–1922. these thin sections are listed by the bone catalog number prefaced by cm and are housed at the carnegie museum of natural history, pittsburgh. carpenter (2013) previously described some of these thin sections. the exact stratigraphic levels of these samples are unknown, but they are assumed to be in the lower two sandstone beds from which most dinosaur bones were excavated. in addition, we collected hand samples from the morrison formation along the north and west sides of split mountain anticline during our search for the upstream part of the fluvial system that deposited the quarry sandstone. no thin sections of these latter samples were made. we polished most of the cut surfaces of the samples to reveal internal texture. mudstone samples were hand-polished dry using progressively finer grit sandpaper. the polished faces and whole mounts of thin secfigure 3. (a) strata and distribution of sandstone beds in the study area. abbreviations: jmb – brushy basin member; jms + jmt – salt wash and tidwell members; jw + js – windy hill and stump formations; kcm + km – cedar mountain and muddy formations; qeh – quarry exhibit hall; qss – quarry sandstone. satellite view from google earth. (b) 180° panorama of the quarry sandstone from neilson draw to swelter shelter draw. (c) quarry sandstone (indicated by arrows) from douglass draw, viewed eastward. (d) quarry sandstone (indicated by arrows) from the quarry exhibit hall parking lot, viewed eastward (neilson draw). (e) abrupt contact between the lowest quarry sandstone and underlying muddy sandstone beds. photograph by earl douglass (carnegie museum) on the east-end of the quarry viewed west. date of photograph unknown. 30 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 figure 4. stratigraphic sections in and near the qeh, showing the location of the thin sections. dino 45156 and 45157 are 1.2 m below the bottom of the west side column. detailed descriptions of the thin sections are included in appendices 1 and 2. the term dino is not shown on the stratigraphic section because of space constraints. 31 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 tions are illustrated to show macroscopic features (figure 7). usually, these are subtle in color differences and were enhanced by darkening the image and increasing contrast. micrographs of thin sections were not enhanced. the thin sections and a portion of the associated hand samples were subjected to hydrochloric acid (hcl) and alizarin red-s stain to identify and enhance the presence of calcite. potassium ferricyanide stain was used on some sandstone thin sections to reveal ferroan dolomite cement. we conducted a petrographic examination using a zeiss photoscope iii petrographic microscope. thin section examinations provided overall lithology, mineralogy (including clay content), grain size, grain roundness, and sorting data. examination of the carbonate samples provided overall lithology, crystal or allochem size, and fossil content. petrographic examinations also included identification of diagenetic features. this information is shown in table format in the appendices, as are figures of all of the thin sections. mudstone with modifiers refers to a spectrum of fine-grained sedimentary rock in which 50% or more of its grains are mud (calcite, clay and silt) size (potter et al., 2005; lazar et al., 2022). clay particles are 4 μm or less in diameter, whereas silt particles range from 4 to 62.5 μm in diameter. whole rock mudstone terminology is based on macquaker and adams (2003) and lazar et al. (2022). grain size identification follows the udden-wentworth scale as included in ehlers and blatt (1982) and blair and mcpherson (1999), among others. a th-corrected 206pb/238u ca-id-tims zircon date reported below on a tuff we collected in the west trench was analyzed by kevin chamberlain, department of geology, university of wyoming. chronostratigraphic age names are those of the international chronostratigraphic chart v2023/09 (www.stratigraphy.org). stratigraphic setting the morrison formation, prominently displayed on the colorado plateau, consists of the thinly bedded siltstone and mudstone beds of the tidwell member, which is overlain by the sandstone-dominated salt wash member, and capped by the gray or variegated mudstone-dominated brushy basin member (figure 8a). figure 5. stratigraphic section of the morrison formation and adjacent strata along douglass draw. redrawn from a section provided by fred peterson (u.s. geological survey). clay data from bilbey (1992). 32 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 these three members are present in dinosaur national monument (turner and peterson, 1991, 1992b, 1999); however, the distinction between members can be challenging due to the scarcity of resistant sandstone beds within the salt wash member as initiatlly observed by stokes (1944) (figures 8b and 8c), and the tidwell member was not recognized by bilbey et al. (1974) in the monument. in the study area, the morrison formation is most extensively exposed in douglass draw, oriented perfigure 6. stratigraphic profile of the quarry sandstone from the qeh to near swelter shelter draw. the profile shows that the quarry sandstone consists of stacked and coalesced fluvial sandstone beds. courtesy of fred peterson, u.s. geological survey 33 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 pendicular to the formation's strike, and designated as a primary reference section by turner and peterson (1999). here, the tidwell member measures approximately 10 m in thickness, the salt wash member approximately 74.8 m, and the brushy basin member approximately 100 m thick (figure 5). tidwell member the tidwell member is poorly exposed in the study area (figures 8a and 8b). where visible, it comprises interbedded moderate reddish-brown (10r 4/6 of the munsell color scheme) and pale greenish-yellow (10y 8/2) mudstone, along with white (n9) fine-grained sandstone and siltstone. near the base, many areas feature a zone of red botryoidal authigenic chert, which peterson (1988) identified as a widespread marker unit on the colorado plateau. carpenter (2022), however, found its distribution to be inconsistent. marine dinoflagellates reported from the tidwell member near the quarry (turner and peterson, 1999) are actually from the redwater member of the stump formation (turner and peterson, 1992b, p. 88; litwin et al., 1998, p. 302). currently, compelling evidence for a marine influence on the tidwell member is lacking. the tidwell member serves as the base of the morrison formation across the colorado plateau (o'sullivan, 1984; peterson, 1988; carpenter, 2022). in the rainbow draw area north of split mountain (figure 2a), a volcanic ash layer within the tidwell has a recalibrated 40ar/39ar age of 156.84 ± 0.59 ma (middle oxfordian) (trujillo and kowallis, 2015), closely matching the 156.77 ± 0.55 ma age abtained 2.4 m above the base of the tidwell near notom, utah, 290 km farther south on the plateau (trujillo and kowallis, 2015). the windy hill formation (originally the windy hill member of the sundance formation, pipiringos, 1968), which underlies the tidwell member, has at times been considered a basal member of the morrison formation (peterson, 1994; sprinkel et al., 2019). however, we regard it as a separate formation, following the reasoning put forth by danise and holland (2018) and holland and wright (2020) (see wroblewski and morris, 2022, for a dissenting position). our field work in the formation has yielded a section of sauropod rib in the orchard draw drainage, 1250 m west of the qeh. it is the first reported dinosaur bone from this formation in the monument; pterosaur and sauropod tracks have been reported from wyoming (e.g., meters et al., 2009; meyers and breithaupt, 2014). salt wash member the coarse-grained sandstone beds of the salt wash member exhibit greater prominence in douglass draw (figure 8b) compared to east of the qeh, where rapid weathering due to higher clay content is evident (figure 8c). these sandstone beds, ranging from white to very light gray (n9–n8), are interbedded with non-swelling, moderate orange-pink to moderate red (10r 7/4–5r 4/6) mudstone. in douglass draw, the lower boundary of the salt figure 7. comparison of unenhanced (a) and enhanced (b) miscrohotographic images, illustrating subtle macro-features as a function of color in the whole slide sample. 34 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 wash member is marked by a white to very light gray (n9–n8) muddy sandstone at the base, juxtaposed against a very pale orange (10yr 8/2) muddy sandstone of the underlying tidwell member (figure 8b). the upper boundary of the salt wash member is identified by a similar white to very light gray (n9–n8) muddy sandstone or a moderate red (5r 4/6) mudstone just below a moderate orange-pink to moderate reddish-orange (10r 7/4–10r 6/6) mudstone of the brushy basin member (figure 8b). archival photographs show that the boundary between the salt wash and brushy basin members lies in the axis of the valley currently underlying the road from the lower parking lot to the upper parking lot at the qeh. around dinosaur national monument, the salt wash member is at the edge of its recognizable extent on the colorado plateau. sprinkel et al. (2019) identified the northernmost recognizable occurrence of the salt wash member in the rainbow draw area north of the split mountain anticline (figure 2b). beyond this region, sandstone beds no longer distinctly delineate the salt wash member, leading to its mapping as “undifferentiated” within the morrison formation (mullens and freeman, 1957). within dinosaur national monument, the salt wash member is interpreted as part of the “claystone and lenticular sandstone facies” of a distal part of an alluvial megafan (craig et al., 1955, 1977) or more recently as a distributive fluvial system (weissmann et al., 2013; owen et al., 2015, 2017). however, carpenter (2022) raised significant concerns regarding these interpretations based on paleocurrent data across the entire colorado plateau. brushy basin member the brushy basin member on the colorado plateau constitutes a thick slope-forming unit rich in clay and notably lacking in sandstone, contrasting sharply with the underlying salt wash member (e.g., figure 8a). the majority of the brushy basin member mudstone beds are composed of montmorillonite clay formed through the alteration of volcanic ash (keller, 1962). robinson and mccabe (1998) attributed the abrupt lithofacies shift from the sandstone-dominated salt wash member to the mudstoneor claystone-dominated brushy basin member to changes in watershed hydrology driven by climate or tectonism, with currie (1997) suggesting concomitant changes in fluvial dynamics. however, heller et al. (2015) found little difference in paleochannel architecture between the salt wash and brushy basin members in southeastern utah, proposing that reduced channel-belt stacking in the brushy basin resulted from decreased avulsion frequency, potentially figure 8. (a) typical morrison formation on the north-central colorado plateau, featuring erosion-resistant, ledge-forming sandstone beds in the salt wash member, positioned between the underlying siltstone of the tidwell member and the overlying mudstone of the brushy basin member (38.7982°n., -109.9867°w.; type location of the salt wash member). (b) morrison formation in douglass draw, characterized by a few ridges of erosion-resistant sandstone beds in the salt wash member (40.4419°n., -109.3084°w.). (c) salt wash member east of the qeh, showing the absence of resistant sandstone (40.4404°n., -109.2934°w.). abbreviations: jmb – brushy basin member, morrison formation; jms – salt wash member, morrison formation; jmt – tidwell member, morrison formation. 35 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 linked to increased volcanic ash input as airfall or washload in rivers. dawson (1970) also linked the abrupt decrease in clastics to volcanism, specifically the burial of clastic sources by volcanic deposits. despite differing causal interpretations, the transition between the salt wash and brushy basin members is diachronous (kjemperud et al., 2008) relative to a mid-morrison unconformity often represented by a paleosol at the top of the salt wash member (demko et al., 2004). this paleosol or unconformity, however, is not universally present (kjemperud et al., 2008; heller et al., 2015; maidment and muxworthy, 2019), and evidence for large-scale incisions or paleovalleys (demko et al., 2004) was not noted by currie (1997), nor have we seen such structures in the study area. within dinosaur national monument, the brushy basin member may be informally subdivided into a discontinuous lower unit exhibiting red and white weathering and an upper unit exhibiting gray weathering (figure 9; turner and peterson, 1999). the lower unit, approximately 12 m thick, predominantly exhibits hues ranging from grayish-pink (5r 8/2) to light-red (5r 6/6) and lacks the popcorn or frothy texture of weathered smectitic clay. this unit is overlain by an upper unit, 83 m thick, weathering from light-gray (n8) to medium-gray (n5) mudstone characterized by the popcorn texture of weathered smectite, the predominant clay in the brushy basin member (keller, 1962; bilbey et al., 1974; owen et al., 1989; heller et al., 2015). in its unweathered state, this silty clay-rich mudstone appears grayish-black (n2). the sandstone housing the dinosaur quarry is about 43 m above the salt wash member. the color and texture distinctions in the lower brushy basin member observed by turner and peterson (1992a, 1999) seem to correlate with their hypothesized morrison clay change marker representing a shift from non-swelling illitic clays to swelling smectitic clays. however, such a clay change was not confirmed by x-ray diffraction analysis of clays near the qeh by bilbey (1992), which revealed a mix of montmorillonite-illite (smectite-illite) clays in this interval (figure 5). trujillo (2006) suggested that the differing weathering patterns observed by turner and peterson are a reflection of the proportion of silt and sand grains, with amounts greater in the “illitic”-looking weather profile. this seems to be the case in the study area, where the lower unit is associated with multiple thin gravelly crevasse splays or levee deposits traceable laterally into channel sandstone beds along the road to the qeh (figure 9b). the upper contact (k-1 unconformity) of the brushy basin member across much of the western part of the northern colorado plateau is marked by the base of the chert-rich, cobbleto boulder-containing buckhorn conglomerate member of the lower cretaceous cedar mountain formation (kirkland et al., 2016). in areas where the conglomerate is absent, this boundary is identified at the top of a mottled yellow-orange mudstone paleosol bearing chert pebbles below the lowermost calcrete bed, separating smectitic, generally red or gray mudstone of the brushy basin member, from the non-smectitic, pastel-colored mudstone of the cedar mountain formation (figure 10a; sprinkel et al., 2012; kirkland et al., 2016). near the qeh, where the conglomerate is absent, the contact is found at the top of yellow-orange to moderate red mudstone, typically situated 1 to 3 m below a sporadically occurring calcrete paleosol (figure 10b; kirkland and madsen, 2007; chure et al., 2010; sprinkel et al., 2012, 2019). currie (1997) identified the top of this calcrete as the k-1 contact, indicating that a cretaceous paleosol developed within the top of the brushy basin member during a hiatus in sediment deposition. in contrast, brezinski and kollar (2018) placed the k-1 boundary at the base of the calcrete, positioning the paleosol and its host sediments entirely within the cedar mountain formation, implying a second hiatus with calcrete formation in earliest cretaceous sediments. this calcrete, discontinuous and thinning out approximately 600 m east and 320 m west of the qeh, is insufficient evidence alone to determine the boundary placement, as the lower cedar mountain formation contains several discontinuous calcrete beds (kirkland et al., 2016). at least three such beds are present in the lower cedar mountain formation along douglass draw (figure 10c). locating the yellow-orange to moderate red mudstone k-1 contact at dinosaur national monument can be challenging due to soil creep on steep slopes, though visible where erosion maintains clean exposures. 36 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 lithofacies description sandstone facies the distribution of sandstone lenses in the brushy basin member within the study area is depicted in figure 3a. although there are a few isolated lenticular sandstone bodies, most sandstone occurs in a narrow interval 3 to 9 m thick, forming a discontinuous ridge created by the quarry sandstone extending eastward from the qeh (figures 3b, 3d, and 6). this sandstone bed can be traced westward to douglass draw, although erosion has not yet made it a prominent ridge (figure 3c). the bases of the sandstone bodies are typically scoured into the underlying strata, resulting in abrupt contacts (figure 3e). these underlying strata generally consist of sandy mudstone or muddy sandstone, which is generally white and easily recognizable from a distance. the quarry sandstone bed dips to the south, with reported values varying as follows: 50° (hansen et al., 1983), greater than 55° (brezinski and kollar, 2018), 60° (e. douglass correspondence to assistant director douglas stewart, carnegie museum, september 24, 1909), 60 to 70° (turner and peterson, 1992a), 62° (carpenter, 2013), 65° (boyle, 1938a), and 67° (untermann and untermann, 1954; bilbey, 1992; lawton, 1977). these differences can be partly explained by the locations where the dips were measured in and around the qeh and in neilson draw. carpenter (2013) measured the dip on the flat sandstone surface on the east side of the qeh, and boyle (1938a) on the rock face formerly figure 9. (a) brushy basin on the north side of the qeh, showing the lower red and white unit overlain by the gray unit. (b) another view showing the red and white unit grading into channel sandstone. the red line connects the same sandstone bed (40.4411°n., -109.3014°w.). 37 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 present on the west side of the qeh (“dinosaur peak”). other measurements in the vicinity include 48° near the crest of the divide east of the qeh (hansen et al., 1983); 50° on the east side of camp gulch (rowley et al., 1979) and 62 to 68° east of the qeh along the quarry sandstone (lawton, 1976). isolated sandstone bodies although the emphasis of this study is on the quarry sandstone bed, for thoroughness and context, we briefly describe the few isolated lenticular sandstone bodies in the study area that occur below or above the quarry sandstone bed. such isolated bodies are more common in the brushy basin member than in the stacked sandstone bodies that dominate the salt wash member (currie, 1997; galli, 2014; heller et al., 2015). the isolated sandstone bodies are represented in the study area by two types of lithologies. an example of type 1 is approximately 27 m above the salt wash member (figures 11a and 11b). it is light-brown (5yr 5/6) to pale-yellowish-orange (10yr 8/6), coarse-grained to conglomeratic litharenite with quartz predominating as the coarse-grain fraction. the larger granule-to-pebblesize clasts are gray chert and some potassium feldspar. the brown tint is most likely due to iron hydroxide. an example of type 2 occurs about 10 m below the cedar mountain formation (figure 11c). it is a litharenite of quartz sand and polychromatic chert conglomerate, much like the quarry sandstone, with silica and calcium carbonate cements. these isolated coarse-grained bodies are narrow, and have a width/thickness (w/t) ratio (less than 4:1). stacked sandstone bodies (quarry sandstone) the quarry sandstone, about 43.9 m above the salt wash member, is composed of discontinuous multistory sandstone bodies that are predominantly stacked conglomeratic or coarseto fine-grained sandstone, and are white (n9) to very light gray (n8). these bodies weather to pale yellowish-orange (10yr 8/6) to pale reddish-brown (10r 5/4) due to the weathering of iron disseminated in pore spaces (hubert et al., 1996) in conjunction with desert varnish (figure 12a; see also cover photograph). the geometries of the stacked sandstone bodies are best seen in the qeh, where three major sets are exposed; at least one additional poorly cemented sandstone bed was mostly removed to expose the fossil bones in the lower sandstone for public viewing; this sandstone is mostly described from reports before it was removed beginning in the early 1950s. the three remaining sandstone beds in the qeh are generally similar except as noted in the following. the lowest sandstone is conglomeratic near the base, fining upwards, and varies in thickness from 0.6 to 1.8 m (walker, 1943). fossil bones occur but are mostly widely dispersed. the second and third sandstone beds, treated as a single sandstone by walker (1943), are conglomeratic or coarse-grained at the base and fine upwards; combined, they vary in thickness from 2.4 to 3 figure 10. (a) jurassic-cretaceous boundary on the colorado plateau at horse bench (38.8534°n., -110.2201°w.). (b) jurassic-cretaceous boundary near the qeh (40.4402°n., -109.3012°w.). (c) three carbonate beds (calcretes) near the base of the cedar mountain formation at douglass draw (40.4408°n., -109.3081°w.). abbreviations: jmb – brushy basin member; kcm – cedar mountain formation. 38 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 m. however, as walker noted, there are two bone levels within this sandstone, implying two depositional cycles, thus it is actually two stacked sandstone beds. on the quarry face today, these sandstone beds are separated by a clay drape, which was not noted by walker (1943). the grains of the three sandstone beds are predominantly subrounded to well-rounded, mediumto verycoarse-grained monocrystalline quartz and black chert (approximately 25+%), giving the sandstone a salt-andpepper appearance (figure 12b), hence the gray tint from a distance. this litharenite, referred to as a chert arenite by bilbey et al. (1974), has matrix-supported larger particles that are commonly coarse-sand to pebble-size, angular to subrounded grayish-black (n2) or light-gray (n7) to very light gray (n8) chert (figure 12c), or subrounded to rounded clasts of carbonate siltstone or mudstone that are occasionally up to cobble size (figure 12d). these fine-grained clasts (siltstone or mudstone, referred to as devitrified tuff fragments by bilbey et al., 1974) are less resistant to erosion, creating a pock-marked weathered surface (figure 12e). pockets of fineto medium-grained white (n9) sandstone also occur within the conglomeratic sandstone bodies (figure 12f). the pockets are often lobate and superficially resemble ball-and-pillow structures but are not connected to underlying mudstone. these do not appear to be transported fine sediment clasts but rather scour infill in the low-pressure, low-velocity recirculation zone on the downstream side of the scour crest during the waning phase of river flow (figure 12g). magnetite is rare, indicating a non-igneous, non-metamorphic source for the sand. chalcedony and calcite are the predominant cements (bilbey et al., 1974; lawton, 1977; hubert et al., 1996), although potassium ferricyanide staining reveals some ferroan dolomite cement in some sandstone adhering to bones collected by the carnegie museum (carpenter, 2013). chalcedony is a common sandstone cement where glassy volcanic ash is present because the thermodynamically unstable hydrous silica of the glass shards dissolves and reprecipitates in this more stable form (worden and morad, 2000). the abundance of volcanic ash characterizes the mudstone in the brushy basin member and sets it apart from the other members of the morrison formation (keller, 1962; heller et al., 2015). at dinosaur national monument, at least 42 predominantly rhyolitic volcanic ash beds spanning 2.2 million years are present in the brushy basin member both above and below the quarry sandstone (christiansen et al., 2015), thus providing a ready source of soluble silica. additionally, the chalcedony-cemented sandstones tend to have little interstitial clay because clay inhibits quartz cementation (worden and morad, 2000). large masses of chalcedony occur in sandstone at various places along the quarry sandstone. bedforms were revealed through erosion and quarrying along bed partings. these include wedge-shaped channel bars having a gently sloped stoss side and steep lee side (figure 13a); these can be seen in photographs taken during the excavations (figure 13b). these bedforms are rarely larger than 10 to 30 cm thick. the largest is preserved in the thickest remnant of the quarry sandstone today in the west half of the qeh (figure figure 11. lenticular sandstone facies. (a) type 1 brown coarse-grained and conglomeratic litharenite (40.4408°n., -109.2990°w.). (b) close-up showing quartz sand matrix and pebbles of chert and potassium feldspar. scale in cm. (c) type 2 quartz and chert conglomeratic litharenite with silica and carbonate cements. 39 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 13c). on the west side of the bar, a juvenile sauropod pelvis is preserved standing vertically through the deposit, indicating that sediment deposition was rapid (figure 13d; carpenter, 2020a). this mega-bedform is unusual for its height, being about 152 cm, and may have formed as a bank-attached bedform deposited in the thalweg. the predominant sedimentary structure of the quarry sandstone is trough cross-stratification. the tops of these structures can be seen on the top surfaces of the steeply dipping quarry sandstone, where the softer mudstone beds have eroded away (figure 13e). this surface typically preserves troughs in three dimensions, which indicate rapidly waning flows rather than the reworking of bedforms and previously deposited sediments. the same sedimentary structures are seen figure 12. stacked channel sandstone facies: (a) weathered quarry sandstone at neilsen gulch (40.4402°n., -109.2997°w.). (b) thin section cm70384 is fineto medium-grained “salt and pepper” sandstone composed of quartz and black chert. scale in mm. (c) thin section cm70384 is mediumto coarse-grained quartz and chert sandstone matrix supporting angular to subrounded multicolored chert granules and pebbles. scale in cm. (d) carbonate clasts on the east side of the qeh. scale in cm. (e) eroded fine-grained clasts creating a pockmarked surface on the east side of the qeh. scale in cm. (f) finer-grained sandstone lenses (indicated by arrows) infilling troughs in coarser-grained sandstone at neilsen gulch (40.4402°n., -109.2997°w.). (g) diagram illustrating finer sand deposition in the lee of a dune due to flow separation, recirculation, and velocity drop. 40 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 figure 13 caption is on the following page. 41 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 in archival photographs of the quarry sandstone before their removal during excavation (figure 13b). high-angled inclined strata (a.k.a. planar stratification) are also present and are best seen on the quarry face where strings of vertebrae are draped over the slip face (figure 13f); these inclined strata generally range from 10 to 30 cm thick. finer-grained sandstone atop the bedforms sometimes are horizontally laminated, indicative of high-energy deposition during supercritical flow over the top of bedforms during the waning stage of flow. also visible on the quarry face are infilled scours. many of these are adjacent to dinosaur bones as contrasting sediment grains (figure 13g). flume studies have shown that scours form as a result of three-dimensional flow separation (turbulence), creating areas of acceleration and deceleration. the highest values of turbulence occur in regions of highest pressure on the bed in front of and immediately adjacent to an obstacle (carpenter, 2020a) and indicate regions of flow turbulence (kirkil and constantinescu, 2010; euler and herget, 2012; maity and mazumder, 2014). helical flow results due to downwards hydrostatic pressure, creating a horseshoe vortex. this vortex plucks or lifts sand grains upwards into the flow, thereby causing bed erosion or scour. deposition of the transported sand occurs in the flow shadow, a region of flow deceleration and low pressure. if erosion exceeds the depth and width of the obstruction, underscour may result. upstream scouring may cause bones to dip upstream, thus contributing to their own burial (figure 13h; carpenter, 2022). smaller bones and shells are often found in what was the downstream flow shadow of larger bones (figure 13i). the sandstone bodies are separated in places by thin pale yellowish-orange (10yr 8/6), grayish-orange (10yr 7/4), and moderate red (5r 5/4) mottled sideritic mud drapes (figure 13j) across gently undulatory erosional surfaces that are similar to those within compound bars as revealed by ground-penetrating radar (sambrook smith et al., 2006). these drapes were noted by lawton (1977), dodson et al. (1980), and turner and peterson (1992a). the uppermost sandstone bed (fourth sandstone bed) is treated separately because little of it remains for study. it was removed because preservation of the fossil bones was generally poor (museum geologist theodore white, memorandum to superintendent jess lombard, october 1, 1963). archival color photographs and traces remaining in the qeh show that on the west side of the quarry, this sandstone is separated from sandstone 3 by a wedge of purple-tinted muddy sandstone or sandy mudstone (figure 14a), but it is in contact with sandstone 3 on the east side of the quarry (figures 14b and 14c). traces of sandstone 4 east of the qeh are white (n9) to very light gray (n8) and poorly cemented (figure 14c). walker (1943, p. 7) reports that this bed was 2.4 to 3 m thick, “composed of a fine to coarse sandstone with considerable clay as a binder [i.e., muddy sandstone]. it also has concretionary masses [recognized as indurated clay balls by boyle, 1938b] scattered throughout… the matrix composing this … layer is very unstable and weathers rapidly.” the sandstone on the east side of the qeh is clayey, medium sand to granule size, poorly sorted, subrounded to rounded, with mudstone figure 13 on the previous page. (a) linguoid dune in profile at camp gulch (40.4409°n., -109.3052°w.). (b) mega-bedform in the quarry was exposed several years earlier by a rockfall noted in a letter by earl douglass (november 4, 1916). photograph taken sometime between 1924–1929 and the bedforms have since been removed in the late 1930s by works progress administration workers. (c) mega-bedform, 1.52 m tall, on the quarry face. arrows designate slip faces on the lee side. the box indicates the location of a dinosaur pelvis laying facedown. (d) sketch showing how the pelvis in (c) was buried standing face down. scale in dm. (e) scours and troughs on the top surface of quarry sandstone (40.4401°n., -109.2987°w.). (f) planar face of a straight-crested bedform delineated by strings of dinosaur vertebrae as seen in the qeh. vertebrae on or near the same slip face (sf) become horizontal on the bed bottom (b). one string of vertebrae is nearly horizontal at the top (t) of the planar dune. note other scattered horizontal bones on the bed bottom. (g) infilled scour (indicated by arrows) downstream of the bone. clam (c) valves are in a stable position in the flow shadow. (h) upstream inclination (arrow) of large bones due to under scour. note that the bones cut across the bedding surface. (i) small bone in the flow shadow of a larger bone (sauropod ischium). scales in cm. (j) sideritic stained mud drape at qeh. 42 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 or siltstone clasts that are mostly the same color as the sandstone except for an occasional surface stain of pale yellowish-orange (10yr 8/6) or dark yellow-orange (10yr 6/6). less common clasts are of medium light -gray (n6) with flecks of black organic material. the clasts are 2 to 20 mm in diameter, rarely larger. sheet (tabular) sandstone beds thin sheet or tabular sandstone beds are present below and above the quarry sandstone. those below are often wedge-shaped and feathering at the edges, and are present on the east side of the qeh below the stacked sandstone beds (figures 15a and 15b). these thin hetfigure 14. (a) archival photograph of steeply dipping beds with view of bed tops. the purple mudstone (upper part of photograph) underlies the muddy white sandstone 4 towards the west end of the quarry. (b) archival photograph showing sandstones 3 and 4 in contact on the east end. the kneeling person in the red circle is pointing to fossil bones. the arrow indicates the general location of (c) today. (c) remnant of sandstone 4 on the east side of the qeh. (a) and (b) courtesy of the national park service, taken in the early 1950s. 43 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 erolithic sandstone wedges have abrupt and sometimes erosional bases, and internally they may exhibit one or more fining and coarsening cycles resulting from fluctuating flows (figure 15c). these sandstone beds feature increasingly larger clasts from the lowest to the highest bed, with scattered matrix-supported pebbles of subrounded grayish-black (n2) or light-gray (n7) to very light gray (n8) cherts. the upper surfaces may also contain mudstone clasts or pits from clasts that have eroded out (figure 15d). the lowest sandstone, numbered 1, is underlain by coarsening-upward muddy sandstone beds. the sandstone bodies are separated by white (n9) to very light gray (n8) muddy sandstone lenses that fine upwards (figure 15e). sandstones 1 and 2 (figures 15a and 15b) are wedge shaped, become thinner in the up-dip direction, as does sandstone 4. sandstone 3 thins in the down-dip direction on the east side, where it grades into a gravelly or figure 15. (a) edge view of tabular sandstone beds (labeled 1 through 5) exposed on the east side of the qeh. sandstone 3 wedges out downdip, and sandstone 4 wedges out updip. (b) oblique view of thin-bedded sandstone of (a). the arrow indicates the location of the view in (e). (c) sectioned sandstone 1, dino 48398, showing fining upwards, then coarsening upwards within a narrow zone. the arrow indicates upward direction. scale in mm. (d) carbonate (orange) and clay (white) pebble conglomerate at the top of sandstone 4. note pits from eroded clay nodules. (e) fining upwards from sandstone 3 (labeled 3) to the base of sandstone 5 (labeled 5). sandstone 4 wedges out and does not extend this far (see b). carbonate nodules (cn) formed in the muddy sandstone beneath the sandy mudstone below sandstone 5. scales in cm. 44 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 pebbly white (n2) to light-gray (n7) muddy sandstone. the gravel and pebbles are predominantly grayish-black and light-gray chert. sandstone 3 can be traced west to a muddy sandstone (see figure a1 in the appendix 1) on the west side of the qeh and is used as the datum for correlation. this datum indicates that the base of the quarry sandstone is about 1 to 1.5 m lower on the east side of the qeh than on the west (figures 4 and 10a). sandstone 5 forms the lowermost bone-bearing sandstone within the qeh, thus showing that these sandstone sheets are intimately linked to the quarry sandstone. the five thin sandstone beds are more resistant to erosion, being cemented with silica or calcium carbonate. whereas the muddy sandstone beds between them erode more easily, leaving the harder sandstone beds projecting where they crop out. similar thin sandstone beds are present beneath the quarry sandstone east of the qeh (figure 6). archival photographs show the now-missing tabular sandstone beds overlying the quarry sandstone (figure 16). this area is now occupied by part of the qeh and a service road. the sandstone beds considered overburden to the underlying bone-bearing sandstone beds were described by geologist albert boyle (1938a, p. 13), in charge of their removal, as “fine-grained friable greenish sandstone…” of variable thickness. the abundance of clay in these beds can be inferred by boyle's observation that “the sandstone sloughs down readily when slightly moistened.” the ease of slaking in water was confirmed with a small sample collected on the southwest corner of the qeh. as a result of its ease of weathering and erosion, these sandstone beds originally formed the saddle on the divide between camp draw on the west and neilson draw on the east and between the silicified quarry sandstone and calcrete of the cedar mountain formation (figure 17). on the west side of the qeh, the boundaries of many of the stacked sandstone sets are poorly defined in contrast to the sharp base of the overall unit. here, channel sandstone beds grade laterally with a rapid increase in silt and clay content over a span measured in meters (figure 18a). in the cross section of the strata visible in the qeh foundation trench, the sandstone is conglomeratic, consisting of rounded mudstone clasts (figure 18b) or irregular mudstone clasts in a sandstone matrix that also contains floating dark chert pebbles (figure 18c). these muddy sandstone bodies can be traced outside the qeh as a series of three sheet sandstone beds separated by mudstone (figure 18d). dinosaur bones are preserved in these sandstone beds. the most complete bone found recently is a femur (leg bone) oriented parallel to the local shallow flow in a direction away from the sandstone of the quarry (figure 18e). the sandstone beds coarsen upwards (figure 19a) or have an erosional base associated with the distributary channel part of the sheet sandstone beds (figure 19b). from the quarry wall in the qeh westward, there is a shift from chalcedonic to calcitic cementation of the sandstone as the clay content increases and the clay inhibits chalcedony formation (figure 18a), resulting in a reduction in resistance to weathering and erosion as seen in figure 18d. elsewhere along the ridge, areas of higher clay content are apparent in satellite imagery as light-colored soils and on the ground as gravelly or sandy, very light gray (n8) soils that are commonly vegetated and require trenching to expose the less weathered muddy sandstone. mudstone facies the mudstone facies are best accessed adjacent to the qeh because construction activity has removed vegetation and soil. much of the mudstone analysis was conducted there and is representative of the mudstone bracketing the quarry sandstone except as noted below. retallack (1997) proposed names for the paleosols mudstone facies at dinosaur national monument, but these have not been widely adopted (e.g., demko et al., 2004). on the west side of the qeh is a remnant of “dinosaur peak,” a topographic high point named by earl douglass. the east face is cut perpendicular to the strike, exposing the mudstone beds immediately below the quarry sandstone. at 4 m below the quarry sandstone, there is an abrupt color and textural change from a silty mudstone to a sandy mudstone unit (figure 20a). archival photographs of a less weathered surface show that the lower mudstone had a thin, light-colored ash bed or thin strings of light-colored sandstone (figure 20b). the lower mudstone (figures 20c and 21a) 45 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 is predominantly medium dark-gray (n4). in polished cross section, however, the mudstone is polychromatic in color, including pale greenish-yellow (10y 8/2), pale yellowish-green (10gy 7/2), very light gray (n8) to medium gray (n5), and even a little moderate pink (5r 7/4). these colors accentuate extensive bioturbation, including possible rhizoliths (figure 21b). the upper sandy and silty mudstone is light gray (n7) (figure 20d). this sandy mudstone facies correlates with the zone of muddy sandstone and tabular sandstone on the east side of the qeh (figures 4 and 14). the upper mudstone shows immature pedogenesis with mottles of grayish-purple (5p 4/3) mudstone that may be mottled up to 50% by diffused light greenish-gray (5g 8/1) redoximorphic iron depletion (figure 22a). these mottle sizes are in the coarse range (5 to 20 figure 16. archival photographs showing the now-missing strata over the quarry sandstone. (a) view west with workers in the circle. (b) view east showing part of the bedding in the protective overburden (1938). photographs by albert boyd, courtesy of uintah county library regional history center. 46 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 mm) of schoeneberger et al. (2012). other pedogenesis includes white (n9) redoximorphic iron depletion delineating root traces (figure 22b). pedogenesis on the east side of the qeh includes weathered bands of pale-purple (5rp 7/2) below the crevasse splays. unweathered mudstone, as exposed in trenches, is dusky purple (5rp 4/2) to grayish-purple (5p 4/2) with streaks of dusky-yellow (5y 6/4) to very light gray (n8) redoximorphic iron depletions (figure 22c). pedogenic alteration is also seen on the southwestern part of the quarry wall in the qeh (figures 22d and 22e). these diverse examples show that early protosol development is widespread in the mudstone facies. paleosol carbonates are present and are discussed under carbonates. one mineral identified in many of the thin sections (e.g., appendix 1, figure a2g) is the green mineral glauconite, or glaucony, as defined by odin and létolle (1978) and odin and matter (1981), where the proportion of smectitic and micaceous layers is undefined. it is present in both the mudstone and carbonate facies as green and brown grains, some of which are peloidal, suggesting a biogenic origin. non-biogenic glaucony is most likely from pore-water chemistry altering existing smectite clay (meunier, 2005), which is abundant in the brushy basin member, rather than from a marine incursion with which it is often associated (velde, 2014). furquim et al. (2010) report that glauconite in the pantanal wetland soils of brazil is often interstratified with smectite, forming a mixed-layered mineral structure. its formation is favored by alkaline, saline conditions with high potassium concentrations and reducing environments that stabilize fe3+. glauconite crystallizes through neoformation from amorphous silica-rich materials, or via transformation of smectite layers, with its formation varying based on seasonal microenvironmental changes. the mineral was previously reported from the brushy basin member by craig et al. (1955) and keller (1958, 1962), who referred to glaucony as “glauconitic mica.” a more detailed analysis of various mudstone beds is presented in appendices 1 and 2. tuff facies thin volcanic ash beds are present throughout the brushy basin member, and christiansen et al. (2015) reported 42 beds in douglass draw. these ashes are commonly shades of light gray or white (figure 23a) and sometimes have a faint pinkish, purplish, or greenish tint, as noted by turner and peterson (1991). internally, the ashes may be structureless, especially if diagenetically altered (figure 23b), laminated, or composed of accretionary ash pellets (figure 23c). another example of ash pellets consists of matrix-supported, 1 to 10 mm ellipsoid-to-spherical pellets distributed randomly throughout the tuff (figure 23d). these pellets are composed of the same ash that encases them and they lack internal organization. they resemble the ap2 accretionary pellets of brown et al. (2012), although they lack internal structure, and some are significantly larger. the loss of internal structure might be diagenetic, but retention of the external shape suggests a primary structureless interior. these ap2 pellets occur in an ash bed immediately underlying sheet-like sandstone 1 adjacent to the quarry sandstone on the west side of the qeh (figure 23e). this tuff is about 70 cm thick and slightly calcareous. unlike many of the ashes in the study area, there is no siliciclastic detritus, and this clean ash must represent a primary deposit of a large volcanic eruption of an ash-rich plume into a standing body of water. the predominant grain size of the tuff is 9 to 23 µm (fineto medium-silt size), but a small percentage is 30 to 60 µm (mediumto coarse-silt size). dispersed throughout figure 17. the saddle eroded into muddy tabular sandstones seen in figure 16. abbreviations: c – calcrete; jmb – brushy basin member of the morrison formation; kcm – cedar mountain formation; ms – mudstone facies; qss – quarry sandstone; tss – tabular muddy sandstone region; ms – mudstone. photograph by earl douglass (carnegie museum). 47 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 the ash are black minerals, primarily biotite. zircons are abundant and well preserved (figure 23f) and gave a weighted mean th-corrected 206pb/238u ca-id-tims zircon age of 150.77 ± 0.39 ma (k. chamberlain, university of wyoming, personal communication, october 5, 2021). this ash provides the best age yet for the deposition of the quarry sandstone, and hence of its preserved dinosaur fauna. carbonate facies carbonates faicies includes carbonate beds or nodules in the sandy mudstone facies and as reworked clasts up to 15+ cm in maximum diameter in sandstone beds (figure 24a). special attention was given to nodules in mudstone because dodson et al. (1980), fiorillo (1994), and retallack (1997) stated that some of those at dinosaur national monument were pedogenic in origin figure 18. (a) sandstone (ss) grading rapidly to muddy sandstone (mss) to sandy mudstone (smdst) at qeh. (b) rounded mud clast conglomerate exposed in the foundation trench that was excavated for the qeh. scale in cm. (c) irregular mud clast conglomerate exposed in the foundation trench. scale in cm. (d) muddy sheet sandstones (labeled 1, 2, 3) on the west side of the qeh. (e) long bone (stegosaurus femur) in a splay deposit on the west side of the qeh. 48 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 and indicative of well-drained or seasonally dry soils. in addition, retallack (1997) used the depth to the calcic horizon in the predominately dusky red (10r 3/3), clayey, calcareous paleosols overlying the quarry sandstone to estimated rainfall as approximately 600 to 900 mm/yr. nodules in mudstone are most commonly 0.75 to 2 cm in diameter and often have abrupt rather than diffuse boundaries with the encasing matrix (figure 24b). some of the oriented samples showing original structures indicate an in-situ formation (e.g., appendix 1, figure a7a). carbonate nodules typically erode from the mudstone (figure 24c) and accumulate as a lag of fragments and whole nodules at the base of slopes. in contrast, limestone beds are thin (about 10 cm) and are best seen on the west side of the qeh (figure 24d). this limestone tends to erode as large fragments (figure 24e) and may be the source for the larger carbonate clasts in the sandstone beds. both carbonate types are predominantly white (n8) or light greenish-gray (5g 8/1) to medium light-gray (n6) or even grayish-purple (5p 4/2). most carbonates have a weathered surface of pale yellow-orange (10yr 8/6) to grayish-orange (10yr 7/4) caused by the oxidation of iron within the carbonate. dodson et al. (1980) noted the carbonate horizons that they identified as calcretes in “red” or “purple” paleosols as well as in “gray-green” mudstone. only nodules from the mudstone beds weathered “gray-green” on the east side of the qeh were examined by thin section. some of these contained diplostracan branchiopods, ostracods, and rare charophytes. the fact that many of the diplostracan and ostracods are fragments or single valves, and some valves are at an angle relative to the bedding plane of oriented rock samples, suggests that these are mostly allochthonous fossil assemblages (e.g., appendix 1, figure a4). diagenetic events observed in cross-sections and thin sections of the carbonates include septarian cracks infilled with calcite or quartz (appendix 1, figure a4a) and pedogenetic fracturing (appendix 1, figure a5a). thin section analysis (appendix 1) indicates that the allochems in the carbonate facies are dominated by ostracod fossil fragments and complete or nearly complete shells (e.g., appendix 1, figure a4c). this and the abundance of calcareous mudstone suggest that the limestones were deposited in relatively quiet water. grains observed in the carbonate facies are predominantly quartz, with rare grains of other minerals that suggest their igneous origin. grains are mostly silt-sized or smaller and in such great abundance as to qualify the limestones as being silty. in contrast, lawton (1976, p. 5) noted that many of the lenticular limestone beds in her samples were “clean,” presumably meaning free of siliciclastics. lawton (1976) did note, however, that one limestone body contained “calcite-coated micro-mudballs and irregular blocky clasts of silt and clay in calcite and chalcedony cement.” we also noted the presence of mud clasts in some of our samples. see appendix 1 and appendix 2 for additional photographs and descriptions. interpretation of lithofacies isolated lenticular conglomeratic sandstone bodies are encased in sandy mudstone and we interpret them as fill of single-threaded channels. the sandy mudstone figure 19. (a) rapid coarsening upwards of sandstone 2. scale in mm. (b) lenticular bodies (distributary channels) associated with the sheet sandstones of figure 13d. scale in dm. 49 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 are interpreted as proximal overbank deposits. however, the poor exposure due to the steep dip and in-situ weathering makes it difficult to determine whether lateral accretions are present or if the proximal overbank deposits are levee or crevasse splay deposits. the lowest thin tabular and wedge-shaped sandstone in the context of the muddy sandstone are interpreted as a succession of crevasse splay deposits preceding an avulsion and redirection of the river that deposited the quarry sandstone. the different directions of wedging are expected as the loci of the crevasse splay deposition shift with each event (burns et al., 2019). of the upper, now missing, bedded tabular sandstone bodies (figure 16), little can be said because those beds cannot now be examined. a proposal has been submitted to trench through the access road around to the west side of the qeh to provide this important information. several lines of evidence taken together, rather than any single feature, indicate that the quarry sandstone consists of stacked braided (multichannel) fluvial deposits: (1) the sandstone bodies are sheetlike, having high width-to-thickness ratios characteristic of multithread rivers (labourdette, 2011); (2) vertical accretion of sandstone sheets separated by gently undulating erosional surfaces represents stacked compound bars similar to those of the south saskatchewan river (sambrook figure 20. (a) abrupt facies change from a lower clay-rich mudstone to an upper sandy and silty mudstone at dinosaur peak, west side of the qeh. also present are three limestone beds (labeled 1, 2, 3). abbreviation: s3 correlates with sandstone 3 on the east side (see figure 15). scale in decimeters. (b) historic photograph (around 1958) showing lenses of sandstone and carbonate in the unweathered gray mudstone. compare with (a). photograph courtesy of national park service. (c) pedogenic mottling (protosol) with colors saturated to bring out differences. (d) detail of blocky sandy and silty mudstone. scales in b through d in cm. 50 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 smith et al., 2006); (3) the coarse sand to cobble grainsize fraction ranges up to 1 cm in diameter (rarely greater than 10 cm), excluding the transported greater than 160-cm dinosaur limb bones, but the sand grains typically range from 0.5 to 1 mm in diameter with d50 1 mm (carpenter, 2013); (4) the generally clean sands indicate turbulent flow or bed reworking that winnowed out clay particles; (5) the presence of pockets of finegrain slack-water deposits in otherwise coarse-grained sandstone, which are mostly associated with troughs (lynds and hajek, 2006); (6) the abrupt transition from coarse-grain sandstone to fine-grain sandstone and thin clay drapes over undulating erosional surfaces indicates a rapid drop in transport energy associated with flashy discharge; (7) the presence of three-dimensional bars (mega-bedforms); and (8) the lack of lateral accretion deposits, which are more typical of sinuous single-threaded rivers. trough cross-stratification and planar stratification are not included as evidence because both also are present in single-channel sinuous river deposits and crevasse splays (brierley, 1996; bridge, 2003). these multiple lines of evidence align with modern alalogues of the complex subsurface architecture and history of sandy braided river deposits revealed by ground-penetrating radar of the saskatschewan river, deposits in canada (sambrook smith et al., 2006). the correlation between grain size/channel depth (grain size d50 = 1 mm; depth = approximately 1 m for the quarry sandstone) and slope (paola and mohring, 1996; friend and dade, 2005) suggests that the river depositing the quarry sandstone had a paleoslope of 10-3 to 10-4 with bedload dominating. this projected paleoslope is close to the 1.1 x 10-3 estimated for the morrison depositional environment by trampush et al. (2013), whereas lawton (1976) concluded the channel gradient at the quarry as 3.8 x 10-4. the paleoslope methods of lynds et al. (2014) were not used because these were developed for sandy suspended-load rivers with maximum grain size of less than 0.5 mm and d50 is significantly less; these values are significantly less than the 1 mm d50 of the quarry sandstone. peak discharge most likely occurred during seasonal rains, resulting in overbank flooding and floodplain inundation. paleocurrent data for the quarry sandstone figure 21. (a) detail of smectitic lower mudstone (dino 48397). (b) polished surface of (a) showing extensive bioturbation and possible rhizoliths (labeled r). scale in mm. 51 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 from sedimentary structures (figure 25a), unionid clam long-axes (figure 25b), and dinosaur limb bones (figure 25c) indicate the overall flow was toward the southeast. the greater vector spread of the limb bones is because some bones tend to roll perpendicular to the current, and some bones are trapped against the upstream side of bone piles or jams (carpenter, 2013). perhaps the best paleocurrent indicators are the long whip-like tails of diplodocid sauropods (figures 25d and 25e). these rope-like structures offered little resistance to water flow, as has been demonstrated experimentally in a water flume (carpenter, 2020b). few of the channel sandstone bodies in the quarry sandstone have distinctive lateral margins or show an abrupt change in lithology or grain size that could represent the incised channel margin or bank. most of the sandstone bodies show diffuse margins marked by a rapid increase in clay content, coincidental with a change from sandstone to muddy sandstone (figure 18a) to sandy mudstone in which grains up to 2 mm may be suspended. this lack of well-defined or absent margins implies a fluvial system of frequent spillage sedimentation building the confining banks (lewin and ashworth, 2014; lewin et al., 2017). such systems are typical for non-montane braided or multithreaded river systems with their complex of active and inactive channels on the braid plain. these inactive channels may convey water at high river stage, resulting in pockets of finer sand sediments in otherwise coarse-grained deposits. on outcrop, the transition from well-cemented, erosion-resistant channel sandstone to more easily eroded muddier sandstone typically takes place over a span of a few meters. this transition zone is not uniform, as local variation in clay content and cementation is reflected in the differential erodibility of the sandstone, such as seen on the west side of the qeh both within the building and adjacent to it (figure 18b). these transitional sandstone bodies typically are fine-grained distally and are interpreted to be the proximal overbank facies, predominantly spillage sedimentation of levees and crevasse splay deposits (e.g., cazanacli and smith, 1998; figure 22. diverse examples of pedogenesis in mudstone beds of the study area. (a) light-colored mottles in reddish mudstone (color enhanced). (b) rhizoliths in gray calcareous mudstone. (c) rhizoliths and light-colored mottles in gray to brown mudstone (color enhanced). (d) light-colored mottles in purple mudstone on the west end of the qeh (color enhanced). (e) light gray and dark gray mottles in mudstone on the west end of the qeh. scales in cm. 52 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 hudson, 2005; alexander and fielding, 2006; lewin et al., 2017). the coarseness of these proximal overbank deposits is most commonly associated with fluvial systems having highly variable discharge (alexander and fielding, 2006). levee and crevasse splay deposits share similar criteria (e.g., sharp bases, distal thinning, and fining), and distinguishing them is made more difficult by the limited exposure of the quarry sandstone on the steeply dipping cross sections. the radiating paleocurrent pattern of crevasse splays, which is not known to occur in levees, has been identified on the west side of the qeh where two sandstone beds merge in a small area corresponding to a breakout point in a levee (figure 18d). the main distributary channels of these splays are seen in cross section (figure 19b) and prograding into the flood basin, evident by the coarsening upwards (figure 19a). although levees tend to be well-drained because of their elevation above the bottomland, the absence of mature paleosols in any of the proximal sediments implies high rates of vertical accretion. dinosaur bones occur in the transitional sandstone beds, but their sizes decrease away from the channel, corresponding to a decrease in flow velocity. the burial of these bones was probably due to downstream progradation of the levees during floods (johnston et al., 2019). the finer-grained mudstone and bedded limestone are interpreted to be floodplain and lacustrine deposits distal to the levee and crevasse splay deposits, hence representing the distal overbank facies. the floodplain deposits are drab gray (n6 to n3) calcic gleysols with some carbonate nodules and some lacustrine limestone, as indicated by their microfossils. many of the diplostracans in the limestone consist of only one valve of the bivalved carapace, which furthermore may be broken, indicating turbulent fluvial transport across the floodplain prior to deposition in topographic lows (i.e., areas of negative relief). retallack (1997) referred to these gray mudstone beds as periodically waterlogged paleosols. figure 23. (a) thin bed of volcanic ash in douglass draw. (b) structureless diagenetically altered silicified ash from the right side of (a), dino 48399. (c) oriented compressed pellets of accretionary ash from the left side of (a), dino 48400. (d) matrix-supported type ap2 accretionary pellets from (e). (e) ash immediately below sandstone 1 of figure 18d. (f) example of pristine zircons from (e). courtesy of k. chamberlain, university of wyoming. 53 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 in contrast, the absence of clay or siliciclastic grains in the quarry ash indicates airfall sedimentation into a floodplain pond rather than fluvial transport of the ash into a topographic low. brown et al. (2012) noted that historic eruptions reaching the tropopause typically have a distal region of increased fallout composed of aggregates of ash. they identified several, mostly hydrometeor mechanisms for accretionary formation. the size of the largest pellets in the qvc tuff suggests a late-stage formation most likely involving water droplets. the distal mass deposition maxima of modern eruptions reaching the tropopause may be hundreds of kilometers from the volcano. for example, the centroid for the distal deposition maxima for the 1980 mount saint helens eruption was 500 km downwind (brown et al., 2012). for the ash at dinosaur national monument, the source is believed to have been the mohave volcanic center about 680 km to the southwest (hart et al., 2005; christiansen et al., 2015). deposition environment of the quarry sandstone accommodation the unusually wide quarry sandstone within the brushy basin member has been previously noted by several researchers (bilbey et al., 1974; lawton, 1977; turner and peterson, 1992a; carpenter, 2013; brezinski and kollar, 2018). the average paleocurrent trend is roughly perpendicular to the 1.5-km-wide exposure of these stacked and amalgamated sandstone beds suggesting the sandstone represents a broad fluvial system with multiple channels. recent studies of similar wide stacked and amalgamated sandstone beds emphasize the critical roles of both accommodation and sediment supply (e.g., labourdette, 2011; sharma et al., 2023). accommodation, closely tied to sediment accumulation, refers to the “thickness” of sediment deposited over time (muto and steel, 2000). sediment supply refers to figure 24. carbonates. (a) large reworked carbonate in quarry sandstone near the qeh. scale in cm. (b) nodule in situ at the tip of a pen, with an abrupt boundary with mudstone on the east side of the qeh. scale in cm. (c) nodules eroding in situ from mudstone, showing their relative density. hammer for scale. (d) edge view of multiple limestone beds. the upper right bed correlates with (e). jacob staff with alidade holder (1.25 m) for scale. these beds are also seen in figure 20a. (e) eroding surface of limestone bed at dinosaur peak, west side of the qeh. aluminum clipboard for scale. 54 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 the “volume” of sediment deposited within a given period. accommodation is primarily controlled by tectonic processes such as basin uplift or subsidence, along with changes in eustatic or local base level. sediment supply is influenced by erosion rates associated with uplift and climate in the catchment area (allen, 2017; caracciolo et al., 2020). sediment transfer through a sediment routing system from its origin to its final deposition site is governed by both allogenic and autogenic processes. these influences are evident in the variations observed in sedimentary successions, including changes in channel distribution, channel density, and the width of river channels and channel belt deposits. the resulting deposition continuum can range from low-density narrow shoe-string channels encased in finer overbank deposits, reflecting high accommodation-to-sediment supply ratios (a/s), to high-density interconnected tabular channels indicative of low a/s ratios (bridge and leeder, 1979; huerta et al., 2011). these a/s ratios remain consistent even when accounting for variables such as compaction (bridge and mackey, 1993). several studies illustrate the role of basin subsidence as a major factor influencing the a/s ratio. for example, labourdette (2011) in an in-depth study of the eocene olson member of the escanilla formation in the ainsa basin of northern spain, reported that variations in basin subsidence during the eocene were the primary drivers of accommodation space for sediment deposition. during periods of slow subsidence, low accommodation caused braided channels to laterally stack, forming wide multichannel belts. conversely, during periods of faster subsidence, high accommodation resulted in narrower and thicker single-threaded channels. in the morrison formation of the colorado plateau, variations in accommodation space have been linked to shifts in fluvial system dynamics and sedimentary facies distributions. heller et al. (2015) noted an inverse relationship between channel-belt stacking and floodplain aggradation in the upper jurassic morrison formation of utah, usa, linking this to basin subsidence and accommodation. they associated the density of channel stacking with avulsion frequency, which is coupled with the sedimentation rate in the channel belt (heller and paola, 1996; heller et al., 2015). whereas subsidence fluctuations in a basin are a major method of altering accommodation space, changes can also occur during the inversion of an intracratonic rift. this possibility has not been previously considered for the morrison formation, but we explore it here to account for the unusual quarry sandstone, given its proximity to the inverted uinta rift, which now forms the core of the uinta mountains (dehler and sprinkel, 2005). the uinta mountains, a product figure 25. quarry sandstone paleocurrent based on (a) sedimentary structures; (b) long axis of unionid bivalves; (c) dinosaur limb bones. arrow at margins indicates the axis of the mean. quarry excavation maps showing the effects of flowing water on long whip-tailed sauropods recovered from the quarry sandstone; (d) apatosaurus from gilmore (1936); (e) diplodocus, unpublished from earl douglass (carnegie museum). data for (a) and (b) provided by fred peterson, u.s. geological survey. 55 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 of the late cretaceous laramide orogeny, have a core composed of the neoproterozoic-aged uinta mountain group, which was deposited in mixed marine, deltaic, and braided river environments within a failed rift (dehler and sprinkel, 2005). this intracratonic rift represents an early phase in the breakup of the rodinia supercontinent along the western margin of laurentia. the rift was bounded by inward-dipping normal faults produced by crustal extension on the north and south. modeling suggests that during later contraction these faults were reactivated as reverse faults, and additional faults were created, including low-angle thrust faults (pinto et al., 2010). the uinta mountain rift basin experienced several contractional events between the late neoproterozoic and late cretaceous (hansen, 1986a, 1986b; stone, 1993; sprinkel, 2014), as evidenced by angular unconformities in formations around the uinta mountains (williams, 1953; sprinkel, 2014). contraction during the cenozoic led to the formation of numerous synclines and anticlines flanking the eastern uinta mountains (hansen, 1986a, 1986b). one of these, the split mountain anticline, formed between the asphalt ridge thrust fault to the south and the island park normal fault to the north, represents a reactivation of an older anticline developed during the late jurassic, as discussed below. the compressional forces acting against the uinta rift were oblique, directed toward the northeast (johnston and yin, 2001; ashby et al., 2005). these oblique forces likely resulted from the movement of the colorado plateau driven by the farallon subduction (sassi et al., 2012). paleomagnetic data indicate that the colorado plateau has moved 160 km ± 36 km since the triassic (erskine, 2001), accompanied by a clockwise rotation of approximately 9° during the jurassic relative to a euler pole on the north american continent (steiner, 2003). this movement was probably episodic, as suggested by the different paleopole positions of the lower and upper morrison formation (steiner, 2003) and the episodic growth of the mexico-alaska megashear zone (anderson, 2015). modeling suggests that oblique compression of one block relative to another can produce transpressional uplift or an anticline (dewey et al., 1998). bally (1984) previously predicted an asymmetrical “petit inversion” anticline adjacent to the bounding fault of an inverted rift (figure 26a). additionally, in bally’s (1984) model, syn-sedimentation would prevent the anticline from breaching the surface. although not explicitly stated, bally’s figure shows a reduction in accommodation space above the anticline, which would influence sediment deposition by any fluvial system flowing over it. similar situations were reported by peterson (1980, 1984) from the henry mountains basin, utah (see discussion). we propose that an example of “petit inversion” of bally (1984) as a proto-split mountain anticline likely influenced the deposition of the quarry sandstone, figure 26. (a) small anticline due to a “petit inversion” of a rift margin as predicted by bailey (1984, figure 4). (b) transpressive rift inversion caused by the colorado plateau during the latter part of the late jurassic. the effects on local sedimentation by the proto-split mountain anticline are visible in the accommodation space. t-1 represents pre-uplift with no change in accommodation space; unit thickness is uniform. uplift begins between t-1 and t-2, starting to reduce accommodation space over the anticline; peak reduction by t-2. 56 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 based on the thinning of the brushy basin member (figure 26a) along a north-south transect (figure 27b). in contrast, a thickening in the underlying middle jurassic curtis formation suggests that the “petit inversion” had not yet occurred at that time (figure 27c). the thickness of the morrison formation members indicates that the compression event and resulting transpressional uplift began after the deposition of the tidwell member sediments, making the event younger than the 156.84 ± 0.59 ma 40ar/39ar date from the tidwell member at rainbow draw (locality 2 on figure 27b; trujillo and kowallis, 2015). it is likely that the transpressional uplift began during the deposition of the brushy basin member, resulting in the morrison formation being 40 to 45 m thinner near the uplift than it is to the north or south. the location of the proto-split mountain anticline near the southern boundary fault of the uinta rift aligns with bally’s (1984) prediction, as the peak compression force on the inversion block dissipates from peak pressure near the boundary fault. additionally, this asymmetrical compression loading results in an asymmetrical anticline, with the steeper side facing the compression loading. the proto-split mountain anticline contributed to the shifting of multiple active and semi-active channels. the rapid reduction in accommodation is evidenced by the abrupt transition from isolated lenticular sandstone bodies to laterally interconnected braided river channel belt deposits of the quarry sandstone (figure 6). this connection results from channel avulsions, spillage, overlapping of channel deposits, and spillage cannibalism due to the lateral mobility of the channels (labourdette, 2011; colombera and mountney, 2021). the frequent avulsions were likely the result of aggradation of the channels, the availability of steeper alternative flow paths in the adjacent floodplains, and in some cases to the presence of large dinosaur bone accumulations. bone and carcasses probably had the same effect as wood in fluvial systems by increasing channel roughness, altering flow hydraulics, and decreasing sediment transport (cadol and wohl, 2011; spreitzer et al., 2012). the accumulation of bones and carcasses forming large jams (figure 28) in the channels may have also contributed to avulsions by obstructing the channels, directing flow toward the unstable margins much the same way as log jams can trigger avulsions (phillips, 2012). brummer and montgomery (2006) noted that the presence of boulders covering 20% of the riverbed was enough to cause channel widening during floods. log jams can initiate multi-channel patterns by diverting flow to a secondary path (sear et al., 2010; cadol and wohl, 2011), and carcasses (see figure 1 in carpenter, 2020a) and bone jams have been shown to have that effect (carpenter, 2020b). channel obstacles also act as sediment traps by increasing frictional flow resistance and causing turbulent eddies that reduce flow velocity and sediment transport competence (carpenter, 2020a). thus, bones behave much like boulders on the riverbed by constituting a major roughness element imparting form drag on flow (ferguson, 2007). the result is the deposition of sediment in the channel (spreitzer et al., 2021; chen et al., in press). this deposition is greater during floods, where the added suspended mass and increased viscosity enhance the logjam's ability to slow down the flow (chen et al., in press); bone jams would have the same effect. the sudden change in fluvial styles near the qeh began around 150.77 ± 0.39 ma, as indicated by volcanic ash immediately below the quarry sandstone and represented by the t2 timeline in figure 26b. the duration of the anticline’s subsurface uplift and the time until accommodation space was restored to pre-uplift conditions remain unknown, but it likely took thousands of years based on the local thickness of the brushy basin member and its depositional duration of less than 2 million years (christiansen et al., 2015). the quarry sandstone shows little confined flow due to avulsions and overlapping proximal overbank flow (levees and splays) across the floodplain until channels were re-established elsewhere. mud pebble clasts from bank or levee collapse, matrix-supported coarse grains, and weakly developed paleosol mottling are common. it lacks the lateral accretion or other features characteristic of meandering rivers, such as those identified below. a similar situation of lateral mobility leading to the formation of a new braid plain can be observed in the gravelly braided blaeberry river, british coloumbia, canada (figure 29). in this case, a crevasse splay preceded the avulsion event, indicating bank instability, but 57 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 the avulsion occurred farther upstream, creating a new braid plain parallel to the old one. whether an erosive breach becomes a crevasse splay or leads to an avulsion is determined by the balance between erosion and deposition processes, influenced by factors such as floodplain erodibility, vegetation, and water surface slope (nienhuis et al., 2018). a wide zone of interconnectivity is visible in the vicinity of the avulsion, highlighting the importance of spillage, especially crevasse splays, in connectivity between channels (columbera and mountney, 2021). figure 27. rift inversion impact on accommodation space is observed by (a) thinning of the morrison formation over the proto-split mountain anticline. redwater member, stump formation (jsr); tidwell member, morrison formation (jmt); salt wash member, morrison formation (jms); brushy basin member, morrison formation (jmbb); quarry sandstone (qss). (b) map of northern utah showing the boundaries of the uinta rift, location of measured sections, and the axis of the split mountain anticline today. (c) pre-rift inversion influence on the deposition of the underlying curtis member, stump formation (jsc); entrada sandstone (je). 58 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 fi gu re 2 8. b on e cl us te rs o r “b on e ja m s,” a na lo go us to lo g ja m s, un do ub te dl y im pa ct ed w at er fl ow a nd c au se d se di m en t d ep os iti on . ( a ) b on e ja m s su rr ou nd ed b y ba rr en o r n ea rly b ar re n ro ck . ( b) e xa m pl e of a sm al l b on e ja m . ( c ) d ow ns tr ea m v ie w o f a b on e ja m . 59 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 to test the hypothesis that the quarry sandstone resulted from a loss of accommodation space due to the activity of a proto-split mountain anticline, we examined sandstone beds along the western periphery of split mountain, which provides a nearly continuous exposure of the morrison formation from the qeh (figure 30a). our objective was to identify a sandstone body located upstream of the proto-split mountain anticline. the search criteria included stratigraphic placement near the middle of the brushy basin member, a similar conglomeratic salt-and-pepper lithology, and the presence of dinosaur bones with comparable preservation. although several sandstone bodies were identified, only two met all these criteria. one such sandstone body is 6.9 km west of the qeh (figures 30b and 30c), whereas the other is 8.6 km northwest of the qeh (figures 30d and 30e). the western sandstone represents an infilled thalweg on the cut bank side of a single-threaded river, with a paleocurrent direction of 182° as determined from the axis of the thalweg. this sandstone body measures approximately 70 m wide perpendicular to its axis. the northwestern sandstone, on the other hand, is a cross section of a single-threaded river deposit featuring accretionary deposits on the eastern side and the thickest sandstone on the west. the paleocurrent direction for this sandstone body is around 145°. the entire sandstone body, including the accretionary deposits, is 232 m wide, with the main body forming a resistant ridge measuring about 157 m in width. the northwestern sandstone body exhibits paleocurrents that suggest it served as the upstream segment for both the western sandstone and the quarry sandstone. it may have been the source of sediment for both at different times. as the upstream segment to the quarry sandstone, a sinuous single-threaded river likely transitioned into a multithreaded system as it crossed the proto-split mountain anticline and then possibly figure 29. relocation of a braided river channel over time as a model for the quarry sandstone, blaeberry river, british columbia (51.4264°n., -117.0709°w.). (a) pre-avulsion with crevasse splay sediment (arrow). image date: 2004. (b) pre-avulsion with recolonization of the crevasse splay surface by vegetation (arrow and similar brown patterns). image date: june 25, 2015. (c) post-avulsion in spring 2019, showing the abandonment of the previous braid plain. note the extensive reworking by shallow flow of the previous braid plain from the spring flood prior to complete abandonment. image date: september 4, 2019. (d) fully established new braid plain. a wide region of interconnectivity between the two braid plains is marked by a red box. image date: august 2022. images: (a) through (c) google earth; (d) bing maps. 60 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 figure 30. (a) distribution of the morrison formation around the western end of split mountain. two sandstone bodies match the lithology of the quarry sandstone. (b) outcrop of the western sandstone with (c) a sauropod vertebra (scale in cm). (d) outcrop of the northwestern sandstone with (e) a sauropod limb fragment (hammer head length approximately 17 cm). abbreviation: qeh – quarry exhibit hall. base map from topozone. 61 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 reverted to a single-threaded river afterward. such tripartite transitions are observed in modern rivers (e.g., figure 31). depositional model a hypothetical paleoenvironmental cross section from channel to floodplain is presented in figure 32 (see also carpenter, 2023). the vegetation is mostly based on palynomorphs recovered by f. peterson (u.s. geological survey) west of the qeh along camp draw (turner and peterson, 1991) and reported by litwin et al. (1998). megafloral specimens include the ginkgophyte, czekanowskia, from a fine-grained, horizontally laminated sandstone interbedded in the ridge sandstone, and a cycadeoid log fragment eroded from the ridge sandstone. these taxa plus other non-vertebrate fossils are given in table 1. we interpret the quarry sandstone channel facies as a braided river whose deposits are not well differentiated laterally from the proximal overbank facies, reflecting the rapid deceleration of overbank flow and deposition of coarse-grained sediment. flume work suggests that wide braided rivers that are not laterally constrained—i.e., have minimal bank cohesion, produce a stable channel when width is about 24 times depth (warburton, 1996). this is apparently controlled by grain size (paola and mohrig, 1996) and the development of natural levees thus lead to self-containment (cazanacli and smith, 1998). we propose a similar figure 31. example of a sinuous, single-threaded river transitioning to a multithreaded river and back to a sinuous, single-threaded river. flow is toward the left. blaeberry river, british columbia (51.4265°n., -117.0507°w.). imagery date: october 11, 2021, google earth. kingdom plantae division charophyta family characeae aclistochara bransoni aclistochara latisulcata alistochara madleri aclistochara miniscula? aclistochara obovata latochara /atitruncata latochara sp. peckisphaera verticillata porochara arguta porochara kimmeridgensis family clavatoraceae echinochara sp. division polypodiophyta family equisetaceae equisetum sp. division pteriodophyta family umkomasiaceae pteruchipollenites microsaccus* family osmundaceae todisporites minor * division unknown bennettitales (family and genus unknown) division pinophyta family araucariaceae callialasporites trilobatus * callialasporites. cf c. rugularus * family podocarpaceae microcachrydites antarcticus * parvisaccites sp. * rugubivesiculites sp. * division ginkgophyta family czekanowskiaceae czekanowskia sp. kingdom animalae class bivalvia family unionidae vetulonaia sp. genus unidentified class ostracoda family cyprididae candona sp. family limnocytheridae bisulcocypris pahasapensis helmdachia petersoni family incertae sedis cetacella sp. class branchiopoda family cyzicidae lioestheria sp. table 1. non-vertebrate fossils from the study area (see gregson et al., 2024, table 1 for vertebrates). the plants were used to reconstruct the habitat shown in figure 32. palynoflora marked with * from ash (1994); litwin et al. (1998). invertebrates from schudack et al. (1998), schudack unpublished (taxa updated by benjamin sames, personal communications, april 11, 2022), good (2004), lucas and kirkland (1998). 62 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 mechanism was in operation with the quarry sandstone fluvial system. the absence of interbedded paleosols in the proximal overbank suggests that flood disturbances and sediment deposition were frequent enough to maintain a continuously disturbed habitat colonized by polypodiopsid pteridophytes (ferns and tree ferns), known as pioneer species today (walker and sharpe, 2010). slower-growing tree seedlings attempting to establish themselves were likely smothered by sediment, along with older established trees, as the crevasse splays prograded, as indicated by the presence of dead trees. the coarseness and white color of the sediments suggest well-drained, oxidizing soil with limited organic carbon buildup. overbank facies sediments become finer-grained distally, with immature paleosols and rhizoliths in the b-horizon indicating sedimentation hiatuses in the range of decades rather than hundreds of years (kraus, 1987; burns et al., 2019). the absence of large rhizoliths of tree roots in the morrison formation has long been a mystery. trees are known to have been present in the vicinity of the quarry sandstone, as evidenced by a log on the quarry face (figure 33a). the absence of large tree tap-roots in paleosols of this study may be explained by conifers generally having shallow, horizontal roots (figure 33b), as a result of which trees commonly topple, exposing their shallow roots (figure 33c). decomposition of the roots by insects, especially termites known from the morrison (hasiotis, 2004), and saprophagic activity could have removed the evidence of large, horizontal roots over time (see gee, 2023). the vegetation in this area consisted of a mixed riverine conifer-dominated forest of two species of araucariacean, three species of podocarpacean, and the ginkgophyte czekanowskia, with an understory of shade-tolerant ferns. today, such trees inhabit moist, well-drained soils in humid climates. cycadeoids were also present, as evidenced by a section of log from the channel facies. in the flood basin, there were small water bodies that primarily received water sporadically from overland flow (crevasse splay drainage, floods, rain). longer-lasting water bodies probably also received groundwater seepage flowing through the coarser sediments of crevasse splays. fragmentary or single microcrustacean valves, some angled relative to the bedding plane of oriented rock samples, suggest the presence of some allochthonous assemblages. additionally, branchiopod diversity is very low in bulk samples of matrix collected by f. peterson (turner and peterson, 1991) along a transect west of the qeh having only one or two species, suggesting a similarity to modern stressed ecosystems. the brecciation of some lacustrine carbonates indicates pedogenetic episodes in the flood basin. discussion our analysis of the quarry sandstone and its surrounding strata provides a foundation for reassessing figure 32. reconstructed cross section from channel to floodplain, with inferred distribution of vegetation. no scale implied. 63 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 prior studies of the sedimentology of the morrison formation at dinosaur national monument. consistent with earlier research, we interpret the quarry sandstone as the product of braided river systems accompanied by finer-grained overbank deposits (e.g., lawton, 1977; turner and peterson, 1992a; carpenter, 2013). traditional interpretations of braided rivers often regarded associated overbank or vertical accretion deposits as volumetrically insignificant (e.g., miall, 1977; cant and walker, 1978; walker and cant, 1984). this perspective emerged primarily from studies of valley-confined or incised braided rivers, in which frequent channel shifts reworked overbank deposits, leaving behind only erosional remnants (cant and walker, 1978; bridge, 2003, p. 157). however, such interpretations are inconsistent with the stratigraphic record, which often reveals extensive overbank deposits associated with braided river systems. examples include the atcotas formation of spain (arche and lopez-gomez, 1999), the cutler formation of new mexico (eberth and miall, 1991), the escanilla formation of spain (bentham et al., 1993), and the salt wash member of the morrison formation on the colorado plateau (robinson and mccabe, 1998). the volume of finer-grained floodplain deposits in braided river systems correlates strongly with rates of basin aggradation (e.g., bentham et al., 1993; robinson and mccabe, 1998; labourdette, 2011). consequently, the relative thickness of vertical accretion deposits is no longer considered a primary criterion for distinguishing between meandering and braided river deposits (e.g., miall, 2014). additionally, proximity to orogenic mountains fronts does not necessarily dictate the development of braided river systems, as demonstrated by the 1899 topographical map of the platte river near columbus, nebraska (u.s. geological survey, 1899). this map illustrates that, prior to channelization and dam construction, the platte river was braided nearly 700 km downstream from the hartville uplift in eastern wyoming. this was also demonstrated by holbrook and allen (2020), who noted that the lower reaches of the missouri river were braided prior to damming and channelization. finally, bridge at al. (1998) described the braided part of the calamus river, which originates in the sand hills of western and central nebraska, not from any orogenic front. these and other studies support the prevalence of braided rivers, which are now recognized as being as common as meandering rivers globally (miall, 2014, p. 39). in a significant departure from the consensus that the quarry sandstone represents channel deposits, brezinski and kollar (2018) interpreted the quarry sandstone as a crevasse splay complex, which consists of multiple genetically related splay and crevasse-channel fill elements formed in an interfluve wetland or lake. they based their analogy on a distributary channel of the clay and silt mississippi river delta (figure 34a), as described and illustrated by coleman and prior (1982). brezinski and kollar (2018) identified the quarry sandstone as being composed of numerous laterally continuous and upward-coarsening sandstone bodies, which they interpreted as distributary mouth bars within crefigure 33. (a) fossil log on the quarry face in the qeh (approximately 3 m in length). (b) conifer showing laterally directed roots that provide a broad base for support. (c) root mass of a toppled conifer showing the absence of major taproots. 64 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 vasse splays. these bars were cut by trough cross-bedded and upward-fining sandstone lenses, which they identified as distributary channels. they proposed that the 130-m-wide quarry bed was formed within one of these channels. there is a moderate to strong correlation between crevasse splay width and parent channel width (millard et al., 2017; columbera and mountney, 2021; rahman et al., 2022). typically, channel widths are found to be about two to four times the width of associated splays. using this information, a rough estimation of the quarry sandstone's parent river width, based on a 130-m-wide splay, would suggest a river width of approximately 260 to 520 m. this range accounts for the variability in correlations observed across different fluvial systems, including sediment supply, floodplain gradient, and river morphology. however, no suitable body of sandstone is present to the west or north of the quarry sandstone, making the crevasse splay or complex of multiple splays interpretation for the quarry sandstone questionable. during the formation of a crevasse or breach in the levee, spillage into the floodplain results in a divergence of currents from the crevasse, which is recorded in the preserved sediments even for lobate splays (columbera and mountney, 2021). this divergence is crucial for developing wide and lobate splays (figures 34b and 34c; millard et al., 2017). however, no segment of the quarry sandstone preserves paleocurrents that can be backtraced to a crevasse splay. furthermore, coarser sediments in modern crevasse splays are deposited closer to the breakout point as the transport capacity of the unconfined flow rapidly decreases, while finer materials are carried farther away (millard et al., 2017; burns et al., 2019). the deceleration of crevasse water is even more rapid in standing water, such as swamps and lakes, which would restrict the dispersal of coarse grains and large bones to the most proximal part of the splay. the quarry sandstone shows no major reduction in the size or abundance of the coarse fraction at its western and eastern extremities when compared with the dinosaur quarry (figure 35). the rapid drop in transport competence as the crevasse water spills onto the floodplain often causes the healing of the breach (hajek and wolinsky, 2012). this breach healing also occurs when log or debris jams develop at the mouth of the breach, acting as barriers that reduce water flow and sediment transport, thereby allowing sediment deposition to fill the crevasse. this phenomenon contributes to the difficulty of explaining how large bones could get into the distributary channel of a crevasse splay without the bone jams healing the crevasse. our work updates the previous work of peterson (1980, 1984), who had identified paleo-anticlines based on localized thinning of the salt wash member of the morrison formation in southern utah. in discussing the effects of these subsurface paleo-anticlines on syn-deposition, peterson considered the paleo-anticlines as slight barriers to braided river flow, resultfigure 34. (a) distribution channels (center below arrow) on the lower mississippi river delta, serving as a model for the quarry sandstone as cited by brezinski and kollar (2018). the arrow indicates the direction of flow of the mississippi river. (b and c) crevasse splay development, columbia river, british columbia (50.9358°n., -116.4079°w.). (a) early phase (yandex maps, undated). (b) 2004 (google earth). note that most sediment is deposited proximally, with an increase in sediment divergence as the splay grows. 65 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 ing in coarser sediments being preferentially trapped in the paleo-synclines because the streams lacked the transport energy to move the sediments over the paleo-anticlines. winnowed fine-grained sediments were deposited on and beyond the paleo-anticlines. however, unresolved issues remain, including: (1) how did paleo-synclines downstream received coarse-grained sediments if they were trapped at the most upstream paleo-syncline-paleo-anticline pairs; (2) how did sedimentation rates maintain a delicate balance to trap coarse grains in the paleo-synclines without forming lakes; and (3) why did the restricted flow over the anticlines not actually increase in transportation capacity due to increased velocity? peterson (1980, 1984) postulated that the paleo-anticlines were located near the position of modern anticlines and suggested that the modern anticlines were a laramide reactivation of the paleo-anticlines. our research on the quarry sandstone and accommodation space associated with the proto-split mountain anticline suggests that the loss of accommodation space due to the paleo-anticlines can be shown by localized thinning of strata and the lateral aggregation and lateral interconnectedness of braided channel sandstone bodies. this interpretation suggests that switching the placement of the paleo-anticlines and paleo-synclines as determined by peterson (1980, 1984) would resolve many of the problems with his model, and the matter becomes one of accommodation space, a concept that was not well-developed during peterson’s time. conclusion this comprehensive study of the quarry sandstone within the morrison formation provides critical insights into the depositional environment, sedimentological processes, and the geological influences that shaped this unique sedimentary deposit. by synthesizing new data and reassessing previous interpretations, this study reinforces the view that the quarry sandstone represents braided river deposits, characterized by multithreaded channels and dynamic fluvial processes and the high width-to-thickness ratios of the sandstone bodies. our research challenges the alternative interpretation proposed by brezinski and kollar (2018), which suggested that the quarry sandstone formed as a crevasse splay complex. by critically evaluating the correlation between crevasse splay width and parent channel width, and by examining the distribution of coarse sediments and paleocurrents, this study refutes the crevasse splay hypothesis, instead favoring a model of stacked braided river deposits influenced by tectonic activity. this study also highlights the role of tectonic features, particularly paleo-anticlines, in influencing sediment deposition within the morrison formation. the proposed proto-split mountain anticline likely played a significant role in shaping the quarry sandstone by reducing accommodation space, leading to the lateral aggregation of braided channel sandstone bodies and frequent avulsions. this tectonic influence aligns with the earlier work of peterson (1980, 1984), who suggested that paleo-anticlines influenced local sediment transport. figure 35. comparison of the quarry sandstone at (a) the western end in douglass draw, (b) on the quarry face in the qeh, and (c) the eastern end near swelter shelter draw, showing the absence of distal fining expected of a crevasse splay. scales in cm. 66 a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah carpenter, k., and taylor, l.h. geology of the intermountain west 2025 volume 12 furthermore, this study provides a nuanced understanding of the complex interactions between accommodation space, sediment supply, and tectonic processes, illustrating how these factors collectively influenced the depositional patterns within the morrison formation. by revisiting and refining previous models, this research not only resolves longstanding questions about the formation of the quarry sandstone but also contributes to a broader understanding of fluvial dynamics in ancient, tectonically active regions. acknowledgments our study builds upon the foundational work at dinosaur national monument (1990–1993) by christine turner, u.s. geological survey, and the late fred “pete” peterson (1933–2019), u.s. geological survey. we are grateful to pete for his discussions on the morrison formation and for sharing his stratigraphic sections from dinosaur national monument, which were used in figures 5 and 6. we also thank kevin chamberlain, department of geology and geophysics, university of wyoming, for providing the calculated radiometric age. thin sections were prepared by wagner petrographic, lindon, utah. we extend our thanks to manja hethke, institute of geological sciences, freie universität berlin, and benjamin sames, department of geodynamics and sedimentology, university of vienna, for providing information on the late michael schudack’s, institut für paläontologie, freie universität berlin, ostracod and charophyte collection from dinosaur national monument. thanks to diane iverson, sue ann bilbey, and evan hall (uinta paleontological associates, inc.) for sharing the earl douglass photographs. fieldwork was conducted under national park service scientific research and collecting permits dino-2019-sci-0028, dino-2020-sci-0010, and dino-2021-sci-0008; we thank rebecca hunt-foster of dinosaur national monument for her assistance in expediting the permitting process. we thank isaac allred, brigham young university-idaho; tom chidsey, utah geological survey; john foster, utah field house of natural history state park museum; rebecca hunt-foster, dinosaur national monument; william lund, utah geological survey; theresa schwartz, u.s. geological survey; douglas sprinkel, azteca geosolutions; and jianqiao wang, colorado school of mines, for their constructive reviews. this is the ninth installment in a series by the senior author on dinosaur national monument. references alexander, j., and fielding, c.r., 2006, coarse-grained floodplain deposits in the seasonal tropics—towards a better facies model: journal of sedimentary research, v. 76, p. 539–556. allen, p.a., 2017, sediment routing systems—the fate of sediment from source to sink: new york, cambridge university press, 407 p. anderson, t.h., 2015, jurassic (170–150 ma) basins—the tracks of a continental-scale fault, the mexico-alaska megashear, from the gulf of mexico to alaska, in anderson, t.h., didenko, a.n., johnson c.l., khanchuk, a.i., and macdonald, j.h., jr. editors, late jurassic margin of laurasia—a record of faulting accommodating plate rotation: geological society of 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series, v. 1, p. 71–89. warburton, j., 1996, active braidplain width, bed load transport and channel morphology in a model braided river: journal of hydrology (new zealand), v. 35, p. 259–285. weissmann, g.s., hartley, a.j., scuderi, l.a., nichols, g.j., davidson, s.k., owen, a., atchley, s.c., bhattacharyya, p., chakraborty, t., ghosh, p., nordt, l.c., michel, l., and tabor, n.j., 2013, prograding distributive fluvial systems— geomorphic models and ancient examples, in dreise, s.g., nordt, l.c., and mccarthy, p.j., editors, new frontiers in paleopedology and terrestrial paleoclimatology: society for sedimentary geology (sepm) special publication 104, p. 131–147. williams, n.c., 1953, late pre-cambrian and early paleozoic geology of western uinta mountains, utah: american association of petroleum geologists bulletin, v. 37, p. 2734–2742. worden, r.h., and morad, s., 2000, quartz cementation in oil field sandstones—a review of the key controversies, in worden, r.h., and morad, s., editors, quartz cementation in sandstones: international association of sedimentologists special publication, v. 29, p. 1–20. wroblewski, a.f.j., and morris, e.a., 2022, unconformity generation and the shift from storm‐dominated to tide‐dominated processes in a jurassic retroarc foreland basin—insights from ichnology: the depositional record, v. 9, p. 253–299. appendix 1 appendix 1 is attached to the pdf. it includes photographs and photomicrographs showing details of the various lithologies applicable to this study. grain and fossil content are included. details included in the appendix 1 figure captions are presented in chart form in appendix 2. appendix 2 appendix is attached to the pdf amd is a spreadsheet summarizing details of appendix 1 figure captions. carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 1 appendix 1 appendix 1 includes photographs and photomicrographs showing details of the various lithologies applicable to this study. grain and fossil content are included. details included in the appendix 1 figure captions are presented in chart form in appendix 2. figure a1. sandy mudstone (dino 45151). poorly sorted, silty, sandy mudstone containing some grains from an igneous source. grains include quartz, chert, microcline feldspar, and rock fragments. coarse fraction ranges from medium to very coarse, angular to subrounded grains (0.4 to 1.6 mm). silt component 16 µm to 300 µm, with angular to subangular grains predominately of quartz and minor amounts of chert, chalcedony, microcline feldspar, glaucony, rock fragments, hornblende(?), pyrite, and biotite. calcite crystals about 6 µm. quartz overgrowths, calcite replacement, and evidence of dissolution are present. some quartz grains exhibit undulose extinction, a sign of stress. this suggests probable igneous source, as other signs of stress are absent. (a) oriented hand sample of distal crevasse splay sandy mudstone, with matrix supported, unsorted angular chert and quartz grains. purple pedogenic mottling. one unit on the scale is 1.0 mm. (b) partial thin section showing unsorted angular to subrounded siliciclastic grains. one unit on the scale is 1.0 mm. (c) plane-polarized light of siltand sand-bearing, calcareous mudstone. one unit on the scale is 30.0 µm. (d) crossed nicols of a rock fragment containing silt grains (white). the rock fragment has a partial rim of organic material (arrows). one unit on the scale is 0.1 mm. (e) quartz grain showing dissolution (arrow). one unit on the scale is 0.3 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 2 figure a2. mudstone (dino 45150). slightly silty and sandy calcareous mudstone (calcite crystals 2 to 5µm) with 2% to 3% grain content. most grains are quartz, with chert (much less than 1%) and mica (much less than 1%) less common. stressed quartz grains, probably from a volcanic source, are relatively common. some quartz grains are fractured. one compacted fine sand grain (0.4 x 0.25 mm) consists of both chalcedony and chert. rare large grains of angular chert up to 0.4 x 0.3 mm are present. a few grains consist of glaucony. one large (1.86 x 1.41 mm) angular fragment consisting of peloids, a portion of which are glaucony. pyrite is present but rare. there is a small amount of organic matter present. dark organic pellets are common. grains exhibit calcite or organic material coating. minor dissolution of quartz and calcite replacement are present. there is also evidence of possible preand post-depositional fracturing and later silica cementation and calcite cementation, and possible recrystallization. the post-depositional diagenesis may be related to tectonism. fossils present include burrows and rhizoliths. (a) hand sample polished parallel to bedding. one unit on the scale is 1.0 mm. (b) partial thin section, contrast enhanced to reveal details. abbreviations: b – burrow; r – rhizoliths. upper right white streak is a crack made during polishing. one unit on the scale is 1.0 mm. (c) plane-polarized light view of calcareous mudstone with minor quartz grains (white). one unit on the scale is 30 µm. (d) crossed nicols view of grains in calcareous mudstone matrix. quartz grain with calcite cement rim (left) and stressed quartz with filled fracture (arrow). one unit on the scale is 8.0 µm. (e) plane-polarized light view of a subrounded quartz grain with fracture (white arrow). portion of the grain appears to be partially dissolved and replaced by microcrystalline calcite (red https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 3 arrow). also, a rim of organic material (yellow arrow). one unit on the scale is 0.3 µm. (f) grain (0.4 x 0.25 mm) consisting of compressed calcedony and chert (arrow) in plane polarized light (left) and crossed nicols (right) views. (g) plane-polarized light view showing green glaucony grains (arrows). one unit on the scale is 8.0 µm. figure a3. laminated, silt-rich, sand-bearing, calcite-cemented mudstone with mud clasts (dino 45153). contains dark, organic-rich component and a lighter component, both with about 50% silt grains (8 to 25 µm) and far fewer (3% to 10%) sand grains (90 to 160 µm). the angular to subangular grains are predominantly quartz, with minor amounts of chert, biotite, and hornblende. rare quartz grains exhibit undulose extinction, a sign of stress. this suggests probable igneous source, as other signs of stress are absent. some darker clay clasts are present and contain silt-filled fractures, suggesting fracturing during deposition. (a) polished hand sample in cross section. one unit on the scale is 1.0 mm. (b) thin section oriented perpendicular to bedding, as deposited with up at the top, showing poorly laminated structure and scattered light and dark mud clasts. contrast enhanced. irregular fractures are also present in original hand sample. one unit on the scale is 1.0 mm. (c) plane-polarized light view showing the light component of thin section. the arrow points to organic material. one unit on the scale is 30 µm. (d) plane-polarized light view showing the darker, organic-rich components of thin section. note the horizontal arrangement of grains in both. one unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 4 figure a4. fossil-bearing calcareous mudstone concretion (dino 45145). carbonate grains range from 1 to 12 µm. quartz grains range from 25 µm (medium silt) to 128 µm (fine sand). calcite-filled septarian cracks are present. fossils that compose 5% to 10% of the mudstone are ostracod and diplostracan carapaces. geopetal structures exhibited by some ostracod carapaces indicate their orientation prior to deposition as individual grains. single carapaces and fragmentary carapaces indicate turbulent transportation. (a) oriented with up at the top, a nodule thin section showing septarian cracks filled with calcite, and a zone of ostracod and diplostracan carapaces above dark, organic-rich zone. contrast enhanced to show detail. one unit on the scale is 1.0 mm. (b) plane-polarized light view showing abundant, randomly oriented ostracod carapace fragments and single carapaces in silty mudstone matrix. small white grains are quartz. one unit on the scale is 30 µm. (c) plane-polarized light view showing closed ostracod carapaces exhibiting geopetal structures. note scattered small dark organic pellets in the matrix. one unit on the scale is 12.5 µm. (d) calcite-filled fracture under plane-polarized light. one unit on the scale is 30 µm. (e) same calcite-filled fracture under crossed nicols. one unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 5 figure a5. fine-grained, fossil-rich, calciteand clay-cemented nodule (dino 45154). mottled nodule contains two components. the darker, organic-rich component includes clasts up to 1.75 mm in greatest dimension. the clasts contain spherical peloids about 8 to 10 µm in diameter. medium to coarse silt grains (25 to 40 µm) are present in both components, but represent less than 1% of the lithology. most silt grains are quartz, with rare chert, glaucony, olivine, and chalcedony present. the light component contains about 3% to 5% ostracod and diplostracan carapaces and some paired ostracod carapaces that reach 0.35 mm in length. some closed ostracod carapaces have geopetal filling indicating their original orientation. single and fragmentary carapaces indicate turbulent transportation. calcite crystals (2 to 6 µm) fills voids created by dissolution of fossils. fractures within both components are also filled with calcite cement. the calcite crystals in the fractures reach 0.74 mm in greatest dimension. nodule is interpreted as pedogenetic modification of a distal splay pond deposit. (a) cut surface of nodule showing internal pedogenetic fracturing, incorporated clasts during nodule growth, and rhizoliths. slight contrast enhancement. one unit on the scale is 1.0 mm. (b) reversely oriented relative to figure a5a, this is a view of an unstained partial thin section with a pedogenetically fractured dark clast with calcite infilling (right) and calcite-filled rhizoliths (left). contrast enhanced. one unit on the scale is 1.0 mm. (c) crossed nicols view showing an olivine crystal (blue and red) surrounded by calcite. one unit on the scale is 0.3 µm. (d) plane-polarized light view of the dark component showing clasts that contain quartz silt grains. the interclastic area is filled with calcite cement. one unit on the scale is 30 µm. (e) oriented plane-polarized light view showing the contact between the light and dark components. note contrast in grain sizes, and probable fungal mycelium https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 6 trace in center of image. one unit on the scale is 30 µm. (f) plane-polarized light view of the light component showing calcite-filled ostracod and diplostracan carapaces. one unit on the scale is 30 µm. figure a6. fossil-bearing, silt-rich, pellet-rich, calcareous mudstone nodule (dino 45146). this mottled calcareous nodule consists of smalland larger-grained matrices. the finer matrix material consists of 1 to 2 µm grains or crystals, and the coarser matrix consists of about 8 µm grains or crystals. quartz grains dominate and range from 40 µm (coarse silt) to 112 µm (very fine sand), often with a calcite cement coating. less abundant grains include much less than 1% chert, glaucony, microcline feldspar, and possible hornblende. stressed quartz from a high temperature, probably volcanic, origin, and compacted grains are also present. one coarse sand-sized chert grain (0.1 mm) is present. fossils and ichnofossils include numerous burrows, ostracod carapaces, much less than 1% of possible charophyte fragments, ostracod calcite steinkerns[?], disarticulated carapaces, and organic pellets about 15 µm in size. (a) entire thin section with numerous burrows (some indicated by arrows). contrast increased to bring out burrows. one unit is 1.0 mm. (b) plane-polarized light view of silt-rich calcareous mudstone. silt and sand grains are white. the curved white feature is an ostracod carapace. one unit is 30 µm. (c) crossed nicols view of a quartz grain with a calcite cement rim. one unit on the scale is 8.0 µm. (d) crossed nicols view of a rock fragment with a calcite cement rim. one unit on the scale is 8.0 µm. (e) crossed nicols view of a compacted grain composed of quartz (gray) grain on the right and chert (black) on the left. one unit on the scale is 0.3 µm. (f) plane-polarized light view of a curved calcite-filled charophyte fragment. note the presence of silt grains (white) to the left the charophyte. one unit on the scale is 8.0 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 7 figure a7. siltand sand-bearing, calcareous mudstone nodule (dino 45149). the nodule is mottled. the dark component is fine calcareous mudstone (calcite crystals 2 to 4 µm) encasing dark peloids containing fine to fine silt (5 to 30 µm) grains. the mostly angular grains are predominantly quartz, with minor (much less than 1%) chert and biotite grains and glaucony present. the light component is coarse calcareous mudstone (80 µm calcite crystals) containing angular to subrounded, medium silt to fine sand quartz and less common chert grains (27 to 170 µm). this component contains much less than 1% biotite and glaucony grains. rare pyrite grains are present. some stressed quartz grains are present, indicating a high temperature source, probably volcanic. the edges of some quartz grains are partially dissolved and contain calcite on the edges, perhaps the result of partial replacement. some quartz grains are compacted due to pressure on the original source of the quartz. there are rare voids filled with calcite cement. rounded organic fragments reach 45 µm in greatest dimension. fossils include rare ostracod carapaces that were dissolved and the voids filled with sparry calcite cement. (a) oriented entire thin section showing micro-rhizolith (arrow) and load cast (center). contrast enhanced. one unit on scale is 1.0 mm. (b) detail of micro-rhizolith, entire scale is 5.0 mm. (c) plane-polarized light view of silt-and sand-bearing calcareous mudstone. one unit on the scale is 80 µm. (d) plane-polarized light view of a curved ostracod fragment in a calcareous mudstone matrix containing angular quartz (white) and non-quartz grains (dark). one unit on the sale is 30 µm. (e) crossed nicols view showing two larger grains. right grain (black and gray) is a compacted quartz grain. left grain is quartz partially replaced by calcite. the dark brown areas are organic pelletal material. the lighter areas are calcareous mudstone. one unit on the scale is 8.0 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 8 figure a8. siltand sand-bearing, calcareous mudstone nodule (dino 45152). calcareous, mottled mudstone (calcite crystals 2 to 6 µm) with 10% to 15% grains floating in the matrix. the angular to subrounded medium to coarse silt (26 to 52 µm) and fine to coarse sand grains (169 to 580 µm) are predominantly quartz, with minor amounts of chert, chalcedony, microcline feldspar, and biotite. some quartz is stressed, suggesting a high temperature source, probably volcanic. calcite cement to 65 µm thick is visible on the edges of the grains. (a) polished hand sample oriented perpendicular to bedding, showing matrix-supported grains and mud clasts (arrow). one unit on the scale is 1.0 mm. (b) unstained, oriented thin section with up at the top showing matrix supported unsorted, angular to subrounded siliciclastic grains and dark organic-enriched matrix. contrast enhanced. one unit on the scale is 1.0 mm. (c) plane-polarized light view of stained silt-bearing calcareous mudstone. one unit on the scale is 30 µm. letters refer to images (d) and (e). (d) crossed nicols view of a stressed quartz grain with a calcite cement coating. one unit on the scale is 8.0 µm. (e) crossed nicols view of a chert grain with a calcite cement coating. one unit on the scale is 8.0 µm. figure a9. silt-bearing calcareous nodule (dino 45158). nodule containing about 10% fine silt to very fine sand grains (14 to 80 µm). organic clasts are present, represented by areas about 180 µm in greatest dimension. sparry calcite coats many of the grains and organic clasts. (a) whole thin section of nodule. note color zonation. contrast enhanced. one unit on the scale is 1 mm. (b) plane-polarized light view of light-colored part of the nodule. one unit on the scale is 30 µm. (c) plane-polarized light view of the dark part of the nodule. one unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 9 figure a10. silt-bearing calcareous mudstone nodule (dino 45159). this calcareous mudstone nodule (calcite crystals 3 to 4 µm) contains about 3% grains. the angular and subrounded grains are predominantly quartz and chert. they have a bimodal distribution of coarse silt to very fine grained sand (40 to 120 µm) and fine-grained sand (170 to 220 µm). medium sand is present, but very rare. one round grain is 450 µm in diameter. many of the grains are coated with microcrystalline calcite. (a) partial thin section showing clay matrix-supported silt grains. contrast enhanced. one unit on the scale is 1.0 mm. (b) crossed nicols view showing quartz grains with calcite cement coatings. one unit on the scale is 0.3 µm. (c) crossed nicols view showing silt grains (white) and larger quartz sand grains (dark) with calcite cement coating. one unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 10 figure a11. silt-rich, calcareous-cemented, calcareous mudstone nodule (dino 45161). this mottled siltrich mudstone nodule consists of about 40% grains. the coarse silt grains (about 40 µm) and rare medium sand (to 275 µm) are predominantly quartz. additional grains (greater than 1%) consist of chert, stressed quartz, biotite, olivine, and hornblende. the stressed grains suggest a high temperature source, probably volcanic. mudstone clasts reach 360 µm in greatest dimension. fossils are rare, often visible as recrystallized calcite shadows. intergranular and coating calcite cements are sparry and microcrystalline calcite. silica cement fills fractures, but is less common than calcite cement. (a) polished hand sample oriented perpendicular to bedding, showing pedogenic fracturing and brecciation. dark lenticular object is a mudstone clast. one unit on the scale is 1.0 mm. (b) oriented with up at the top, thin section view showing light silty zone bracketed by darker, organic-rich silty zones. pedogenic brecciation in upper zone. few scattered burrows. contrast enhanced. one unit on the scale is 1 mm. (c) plane-polarized light view of siltrich calcareous mudstone with round clay clasts (dark) and angular to rounded silt grains. many of the grains and casts exhibit calcite cement coatings. one unit on the scale is 30 µm. (d) plane-polarized light view of silty, sandy calcareous mudstone. one unit on the scale is 30 µm. (e) crossed nicols view of a quartz grain which exhibits a microcrystalline calcite cement rim (arrow). microcrystalline calcite also fills the void above the quartz grain. one unit on the scale is 8.0 µm. (f) crossed nicols view of brecciation zone, with angular mudstone clasts cemented by intergranular sparry calcite cement (arrow). quartz grains (white and gray) can be seen within the clasts and surrounded by the calcite cement. one unit on the scale is 12.5 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 11 figure a12. fossil-rich, calciteand clay-cemented nodule (dino 45162). silty and clay-rich calcareous mudstone with 10% to 15% whole and fragmentary ostracod valves. whole ostracods filled with sparry calcite. (a) entire thin section showing concretionary banding. one unit on the scale is 1 mm. (b) planepolarized light view showing ostracod debris in calcareous mudstone. one unit on the scale is 30 µm. (c) calcite-filled ostracod within calcareous mudstone. left view under plane-polarized light, right view under crossed nicols. one unit on the scale is 0.3 µm. (d) crossed nicols view showing two quartz grains coated with calcite in a calcareous mudstone matrix. on unit on the scale is 0.3 µm. (e) crossed nicols view of quartz grain coated with silica and a secondary coating of calcite (arrow). multicolored grain to the right is calcite. one unit on the scale is 0.3 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 12 figure a13. silty limestone (dino 45156). silty, clay-rich (about 2 µm crystals) calcareous mudstone with minor (about 1%) ostracod valve fragments. organic peloids (about 15 µm) and clasts (about 0.5 mm) present. rare (less than 1%) grains (13 µm to 117 µm) are quartz with fewer chert, chalcedony, biotite, and glauconite grains. grains coated with calcite cement; some quartz grains partially replaced by microcrystalline calcite. calcite-filled porosity abundant (0.45 to 1.2 mm). few ostracod valve fragments. (a) thin section showing scattered organic-rich areas (e.g., arrow). one unit on the scale is 1 mm. (b) plane-polarized light view of ostracod valve porosity and other voids filled with calcite. dark material is organic matter (arrow). note the presence of clear white grains. one unit on the scale is 30 µm. (c) crossed nicols view of a quartz grain with sparry calcite rim (arrow) and small replacement calcite crystals within the grain. one unit on the scale is 0.3 µm. (d) plane-polarized light view of interclastic porosity filled with calcite cement. one unit on the scale is 30 µm. (e) plane-polarized light view showing chert grains (dark) with sparry calcite with calcite rim and fossil porosity filled with sparry calcite (white). note the dark claystone matrix, other grains, and calcite-filled porosity. one unit on the scale is 12.5 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 13 figure a14. silica and clay clasts with in situ brecciation suspended in calcareous mudstone (dino 45163). mottled calcareous mudstone and organic-rich silica and clay clasts surrounded by sparry calcite (crystals to 60 µm), and with calcite coating. clasts 0.25 to 0.1 mm, angular to subrounded, some with internal fractures and organic pellets within them. some clasts may be from rock fragments. shadows of very fine grained calcareous mudstone (crystals to 20 µm) present. a single mollusk shell fragment is present; rare ostracod valves are present in the matrix and within some clasts. (a) entire thin section slide showing upward coarsening of clasts and in situ brecciation within a matrix of calcareous mudstone (see also figure a15d another example). f refers to large clast shown in image f. one unit on the scale is 1 mm. (b) planepolarized light view of dark organic pellets within a micritic clast. one unit on the scale is 0.3 µm. (c) plane-polarized light view of clasts within sparry calcite matrix. one unit on the scale is 30 µm. (d) planepolarized light view of in situ brecciation of clasts. arrow shows incipient fracture. each mark on the scale is 30 µm. (e) plane-polarized light view of organic clast with sparry calcite coating (arrow). other smaller clasts within the calcareous mudstone matrix. one unit on the scale is 12.5 µm. (f) plane-polarized light view of a large clast with a seam of sparry calcite cement (arrow). clast is identified as f in image a. one unit on the scale is 30 µm. (g) plane-polarized light view showing curved mollusk shell fragment (arrow) within calcareous mudstone matrix. organic clasts are brown and dark brown. one unit on the scale is 12.5 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 14 figure a15. organic-rich limestone (dino 45164). tan organic-rich, with about 3% to 5% grain component. grains size bimodal size: about 10 µm (fine silt) most common and fewer (about 115 µm) very fine sand grains. grains predominantly quartz with rare (less than 1%) chert, glauconite, and stressed quartz indicating a volcanic source. some grains compressed, the result of high pressure. (a) partial thin section slide showing rhizoliths with iron halos in cross-section (arrows). one unit on the scale is 1.0 µm. (b) plane-polarized light view of brown calcareous mudstone with silt and sand grains (white). one unit on the scale is 30 µm. (c) plane-polarized light view of a polycrystalline quartz grain. each unit on the scale is 0.3 µm. (d) cross nicols view of quartz grain in image c. one unit on the scale is 0.3 µm. (e). rhizoliths with halos under plane-polarized light (left) and cross nicols (right) views. one unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 15 figure a16. fineto medium-crystalline, clay-rich limestone (dino 45144). the fine to medium-grained calcite matrix (crystals 0.1 to 12 µm) contains a very rare coarse silt component with grains reaching about 48 µm. pyrite is present, but rare. clay clasts from 0.24 to 0.46 mm are present. some clasts are broken with calcite cement visible between separated fragments. organic pellets are present. fossils present include ostracods and diplostracan branchiopods. many were dissolved, resulting in calcite-filled voids. (a) thin section oriented as deposited. contrast enhanced to bring out subtle details. area outlined in white is enlarged in figure a16c. one unit on scale is 1.0 mm. (b) plane-polarized light view of calcite-cemented fine mudstone with calcite-filled voids, many of which were formed by ostracod shells dissolution. image slightly enhanced to better show ostracod carapace fragments. one unit on the scale is 30 µm. (c) enlargement from image a showing part of a fossil soil fungal mycelium, a mass of hyphae that absorbs nutrients. color contrast enhanced. one unit on scale is 100 µm. (d) crossed nicols view showing in situ pedogenetically fractured clay clasts. note how the fragments fit together and are cemented by calcite. see also figure a13. one unit on the scale is 12.5 µm. (e) crossed nicols view of calcite filled ostracod. one unit on the scale is 12.5 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 16 figure a17. finely crystalline, organic-rich muddy limestone (dino 45155). one of the few, purple-tinted limestones, this finely crystalline (calcite crystals about 6 µm), mottled muddy limestone is organic rich, and contains about 3% grains. thin laminations or lenses of organic-rich clay are present. very fine to medium silt grains (5 to 25 µm) consist of quartz with rare chert and biotite grains present. one organicrich clast (about 0.5 mm) is partially coated with a about 30-µm-thick quartz cement. quartz-filled fractures are up to about 30 µm wide. organic material and quartz cement fill rare pores that reach 1.2 mm in size. (a) view of a polished hand sample showing weak laminations and mottling. one unit on the scale is 1.0 mm. (b) thin section oriented perpendicular to bedding, with up at the top, showing two cycles of fining upwards silt. slightly burrowed. contrast is enhanced. one unit on the scale is 1.0 mm. (c) plane-polarized light view showing the contact between lamina across the middle of the thin section. one unit on the scale is 30 µm. (d) crossed nicols view of a silica-filled fracture. one unit on the scale is 0.3 µm. (e) crossed nicols showing an organic-rich clast exhibiting a partial quartz cement coating. black organic material can be seen on the right side of the grain (arrow). one unit on the scale is 0.3 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 17 figure a18. slightly silty and sandy limestone (dino 45157). calcareous mudstone with very minor (less than 1%) silt and sand component. matrix with grains or crystals about 6 µm. quartz grains predominant, with minor biotite, glauconite, and possible olivine grains present. grain size about 30 µm (medium silt) with rare grains to 90 µm (very fine grained sand). secondary calcite coating on grains and organic clasts. organic clasts to 0.5 mm, with silt grains incorporated. (a) polished hand sample with manganese dendrites along edges. one unit on scale is 1.0 mm. (b) thin section, oriented perpendicular to bedding and with up at the top, showing burrows (arrows). one unit on the scale is 1 mm. (c) plane-polarized light view of calcareous mudstone with silt and sand grains (white) and dark organic clast with a calcite rim. one unit on the scale is 30 µm. (d) crossed nicols view of organic clasts (botryoccus?) with a calcite rim. one unit on the scale is 0.3 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 18 figure a19. bioturbated, clay-rich, siltand sand-bearing limestone (dino 45160). this mottled, clay-rich, siltand sand-bearing calcareous mudstone consists of dark and light components. the dark component consists of fine to medium-grained silt (4 to 10 µm) and with rare coarse silt (to 60 µm) grains. the light component consists of clay (1.5 to 2 µm) containing very rare fine silt grains. quartz is the dominant grain mineral, with fewer grains of biotite, glaucony, and hornblende. the dark coarse component includes clasts of the finer light component, most likely the result of bioturbation. fossils are rare, consisting of calcitefilled dissolved ostracod and/or diplostracan carapaces. (a) hand sample oriented perpendicular to bedding showing pedogenic mottling, extensive burrowing, and a few thin rhizoliths. one unit on the scale is 1.0 mm. (b) thin section, oriented perpendicular to bedding and with up at the top, showing mottling, burrows, and dark, organic-rich, clay-supported silt grains. one unit on the scale is 1.0 mm. (c) plane-polarized light view of calcareous mudstone with silt and sand grains (white). one unit on the scale is 30 µm. (d) planepolarized light view showing a contact between the relatively grain-free light clay area and darker area of clay-supported silt grains. note burrow at far left. one unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 19 figure a20. fossiliferous, clay-rich limestone (dino 45710). mottled in part, with abundant clays. ostracods, charophyte, and conchostracan fossils represent about 10% to 15% of sample. most are fragments. the dark features of the mottled texture are clay clasts or the result of bioturbation. the dark features are about 3 mm in greatest dimension. angular to subrounded silt grains (5 to 45 µm) represent less than 1% of the sample. most are quartz, some of which is stressed quartz, indicating a volcanic source. microcline feldspar and glauconite are present, but extremely rare. some quartz grains are partially dissolved, with finely crystalline calcite around and within them, perhaps the result of partial replacement. other quartz grains are coated with clays or, less commonly, calcite. rare angular fragments (to 385 µm in longest dimension) consisting of calcite and quartz appear to represent material from an external origin. they contain fossil fragments and appear to represent partial silicification of calcite crystals. the presence of erosional fragments supports a depositional environment of origin. original pores are uncommon, and appear to have resulted from fossil dissolution. they are lined with fine-grained calcite crystals (about 40 µm) and filled with larger calcite crystals (about 210 µm), representing two separate calcite cementation events. a single calcite-filled fracture (35 µm wide; 0.3 mm long) is present. (a) thin section showing calcite-filled voids. one unit on the scale is 1.0 mm. (b) plain-light view showing abundant clay (white) https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 20 and calcite (red). calcite is stained with alizarin red-s. entire scale is 0.5 mm. (c) plane-polarized light view of compressed quartz (gray) and chert (black and gray) grains surrounded by calcareous mudstone matrix. one unit on the scale is 0.3 µm. (d) plane-polarized light view showing abundant fossil fragments and a calcite-filled diplostracan at the top (arrow). one unit on the scale is 30 µm. (e) plane polarized light view of probable clast of eroded fossiliferous, siliceous limestone. one unit on the scale is 8.0 µm. (f) plane-polarized light view showing clay clast consisting of brown and gray components and containing a single quartz grain (arrow). one unit on the scale is 0.3 µm. (g) crossed nicols view showing quartz grain with clay coating. one unit on the scale is 0.3 µm. (h) plane-polarized light view of calcite-filled charophytes in cross section. one unit on the scale is 30 µm. (i) plane-polarized light view of amorphous organic material. one unit on the scale is 30 µm. (j). plane-polarized light view of a calcite-filled former void. two stages of calcite precipitation are visible: microcrystalline calcite lining the pore is followed by larger sparry calcite crystals filling the remaining void space. one unit on the scale is 0.3 µm. figure a21. clay-rich limestone (dino 45711). mottled with abundant clays. ostracods and charophyte (green algae) specimens are present but rare. the dark portions of the mottled texture are calcareous clay clasts. they contain fewer grains (less than 1%) than the lighter portion of the specimen. angular to subrounded silt and very fine sand grains represent 7% to 10% of the sample. most grains are quartz, some of which is stressed quartz, indicating either a high-temperature source or metamorphic alteration. biotite mica is present, but extremely rare. edges of some quartz grains are partially dissolved and with finely crystalline calcite around and within them, perhaps the result of partial replacement. other quartz grains are coated with clays or, less commonly, calcite. original pores, uncommon, and most likely resulting from https://doi.org/10.31711/giw.v12.pp25-73 carpenter, k., and taylor, l.h., 2025, a river runs through it—the quarry sandstone and adjacent strata, dinosaur national monument, utah: geology of the intermountain west, v. 12, p. 25–74, https://doi.org/10.31711/giw.v12.pp25-74. 21 fossil dissolution, are lined with fine-grained calcite crystals (about 40 µm) and filled with larger calcite crystals (about 210 µm), representing two separate calcite cementation events. some original pores contain large crystals of both calcite and quartz. (a) thin section showing faint mottling. one unit in the scale is 1.0 mm. (b) plain-polarized light view showing abundance of clay (light tan). darker areas are calcite. entire scale is 1.0 mm. (c) plane-polarized light view showing mottled texture with dark clasts containing fewer silt grains than the lighter areas. note the presence of an ostracod valve in the lower center. one unit on the scale is 30 µm. (d) plane-polarized light view of a once open void, most likely resulting from dissolution of a fossil, filled with calcite (pink) and quartz (white and gray). calcite is stained with alizarin red-s. one unit on the scale is 0.3 µm. (e) plane-polarized light view of an angular quartz grain partially replaced with microcrystalline calcite (pink). calcite is stained with alizarin red-s. one unit on the scale is 8.0 µm. (f) same grain as shown in figure a21e, under crossed nicols. one unit on the scale is 8.0 µm. (g) plane-polarized light view of an ostracod valve fragment within a calcite filled ostracod. one unit on the scale is 12.5 µm. (h) plane-polarized light view of a calcite-filled charophyte. one unit on the scale is 30 µm. https://doi.org/10.31711/giw.v12.pp25-73 sheet1 appendix figure catalog number location lithology occurence mottled lamination silt sand ostracod diplostracan charophyte peloids dissolution recrystalline replaced spar microcrystalline cement quartz cement clay cement clay coat compact % grains grain size (mm, except as labeled) grain shape fractures organics clay quartz stressed quartz fractured quartz polycrystalline quartz feldspar chert chalcedony glauconite biotite pyroxene hornblende olivine rock fragment calcite silt sandstone subangular subround calcite fill quartz fill a1 dino 45151 west side qeh muddy sandstone bed x x ~40 ~6 0.4 0.5 mm angularround x x x x x x x x ? x a2 dino 45150 west side qeh mudstone bed x x in clast x x x x x 2-3 0.4-1.6 mm angular subround x x x x x x x x a3 dino 45153 west side qeh mudstone bed x 50 8 12 to 90 160 silt fill x clasts x x x x x a4 dino 45145 east side qeh mudstone concretion x x x x ~2 1 12 25 128 x x x a5 dino 45154 west side qeh carbonate nodule x x x x x x x 1-3 25 40 x x x a6 dino 45146 east side qeh carbonate mudstone nodule x x x x ? x x 3-5 1-2 ~8 40 112 angular subround x x x x x x ? a7 dino 45149 west side qeh carbonate mudstone nodule x x x rare x x x x x x 12-15 2-4 80 5 30 to 170 angular round x x x x x x x a8 dino 45152 west side qeh carbonate mudstone nodule x x x x 10-15 26 52 169 247 angular subround x x x x x a9 dino 45158 east side qeh carbonate mudstone nodule x x x ? x x x 2-3 14 -80 x x x x x a10 dino 45159 east side qeh carbonate mudstone nodule x x x ~3 3 4 40 62 60 220 450 angular subround x x a11 dino 45161 east side qeh carbonate mudstone nodule x x x x x ~40 to 360 ~40 to 275 x x x x x x x a12 dino 45162 camp draw carbonate mudstone nodule x x x x x x 1-3 135 a13 dino 45156 west side qeh limestone bed x x x x x ~1 13 180 x x x x x x a14 dino 45163 camp draw limestone bed x x x x x 0 15 40 x x clasts a15 dino 45164 east side qeh limestone bed x x 3-5 10 115 x x x x x x a16 dino 45144 east side qeh limestone bed x x x x x x <1 x clasts x a17 dino 45155 west side qeh limestone bed x x x ~3 ~6 5 25 x x a18 dino 45157 west side qeh limestone bed x x x ? x x x <1 30 90 x x x x x ? a19 dino 45160 east side qeh limestone bed x x ? x 0-30 1.52 4 10 60 x x x x x a20 dino 45710 east side qeh limestone bed x x x x x x x x x <1 5 45 angular subround x clasts x x x x a21 dino 45711 east side qeh limestone bed x x x x x x x 7-10 25 90 angular subround clasts x x geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 9 2022 © 2022 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah—pulsed sedimentary response to rollback of the subducted farallon slab casey a. webb, michael s. jensen, bart j. kowallis, eric h christiansen, douglas a. sprinkel, and sam hudson geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover the contact between the starr flat member of the duchesne river formation (tds) and the overlying bishop conglomerate (tb). the contact is shown by the yellow dashed line. the contact is easily identified from the abrupt change from reddish-orange to yellow-gray. photograph was taken to the northeast at 40.4974° n., 109.7311° w. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 9 2022 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2021–2022 uga board president john south john.south@dominionenergy.com 385.266.2113 president-elect rick ford rford@weber.edu 801.915.3188 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 co-program chair ben gilder dgilder@gmail.com 337.962.8383 treasurer kellen gunderson kellen@zanskar.us 801.634.9737 secretary eugene syzmanski eugenes@utah.gov 801.537.3364 past president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 9 2022 153 abstract the uinta mountains are an east-west-trending, reverse fault-bounded, basement-cored laramide uplift. the eocene duchesne river formation and oligocene bishop conglomerate represent late stage, intermontane basin fill of the uinta basin in northeastern utah. detailed mapping (1:24,000 scale), clast counts in conglomerate beds, description of lithology and stratigraphic contacts, and radiometric dating of pyroclastic fall beds of the duchesne river formation and bishop conglomerate in the vernal nw quadrangle in northeastern utah reveal stratal geometries of middle cenozoic depositional units, the uplift and unroofing history of the eastern uinta mountains, and give evidence for the pulsed termination of laramide uplift related to rollback of the farallon slab and lithospheric delamination. these relationships show the continuation of laramide uplift in this region until after 37.9 ma and before 34 ma, an age younger than the previously reported 45 to 40 ma. the duchesne river formation consists of four members: the brennan basin, dry gulch creek, lapoint, and the starr flat. a normal unroofing signal is found within the formation with a downward increase in paleozoic clasts and an upward increase in proterozoic clasts. the oldest member, the brennan basin member contains 80% to 90% paleozoic clasts and less than 20% proterozoic clasts. conglomerate beds in the progressively younger dry gulch creek, lapoint, and starr flat members of the duchesne river formation show significant increases in proterozoic clasts (34% to 73%) and a decrease in paleozoic clasts (27% to 66%). the bishop conglomerate overlies the duchesne river formation, but shows no clear change in clast composition. in the duchesne river formation, the proportion of beds containing fine gravel to boulder-sized clasts decreases significantly with distance from the uinta uplift, from almost 100% near the source (<0.5 km) to 50% to 20% to the south (10 km). the lower part of the duchesne river formation exhibits a fining upward sequence that may represent a lull in tectonic uplift. the fine-grained lithofacies of the dry gulch stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah—pulsed sedimentary response to rollback of the subducted farallon slab casey a. webb1, michael s. jensen2, 3, bart j. kowallis2, 4, eric h christiansen2, 5, douglas a. sprinkel6, and sam hudson2, 7 1southern utah university, department of geosciences, cedar city, ut 84721; caseywebb@suu.edu 2brigham young university, department of geological sciences, provo, ut 84604; 3wasabae@gmail.com; 4bkowallis@gmail.com; 5e.h.christiansen@gmail.com; 7sam.hudson@byu.edu 6aztecta geosolutions, pleasant view, ut 84414; sprinkel@aztecageo.com citation for this article. webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s., 2022, stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah—pulsed sedimentary response to rollback of the subducted farallon slab: geology of the intermountain west, v. 9, p. 153–179, https://doi.org/10.31711/giw.v9.pp153-179. © 2022 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 154 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 introduction the uinta mountains, in northeastern utah and northwestern colorado, are a basement-cored uplift formed during the laramide orogeny that began in the late cretaceous and continued until the late paleogene (hansen, 1986b; blakey, 2008; sprinkel, 2014; hintze and kowallis, 2021). minor contraction from moderate angle reverse faults in the lower crust resulted in flexural basins to the north and south of the mountain range (decelles, 2004). the vernal nw quadrangle is near the south flank of the uinta mountains (figure 1) in the transition between the uplifted region and basin. here sediments were deposited onto folded cretaceous strata in the later stages of uplift. these sedimentary units are the eocene duchesne river formation with its four members (brennan basin, dry gulch creek, lapoint, and starr flat from oldest to youngest) and the oligocene bishop conglomerate (figure 2). the vernal nw quadrangle is an excellent location to explore the geometry of these late-stage basin-fill deposits that are proximal to uplifted regions and to examine the erosional and sedimentary response to tectonic processes. historically, the bishop conglomerate has been mapped separately from the starr flat member (untermann and untermann, 1964; sprinkel, 2007, 2018) except for rowley and others (1985) who mapped both units as bishop conglomerate, possibly due to the larger map scale. several researchers have also noted the similarities between the two units and have questioned whether there is a sufficient difference in lithology and age to warrant a division (hansen, 1986a, p. 18; bryant, 1989, p. j9). to further complicate the issue, the older brennan basin member, particularly proximal to the mountain front, also contains massive conglomerate beds similar to those found in the starr flat member and the bishop conglomerate (figure 2). differences in bedding dip between these units have been used to determine contact locations (sprinkel, 2007, 2018). however, in locations where outcrops are poorly exposed or dips are similar, the conglomeratic units are difficult to distinguish. finally, the duchesne river formation and bishop conglomerate formed during an important tectonic reorganization involving rollback of the subducting farallon plate (e.g., fan and carrapa, 2014; smith and others, 2014). therefore, this study addresses four main questions: 1. how can the conglomerates of the duchesne river formation and bishop conglomerate be creek and lapoint members of the duchesne river formation pinch out within about 1 to 2 km from the uinta uplift. in this proximal region conglomerates equivalent in age to the lapoint member cannot be separated from the younger conglomerates of the starr flat member and are mapped together as one unit. where the fine-grained lithologies appear farther from the uplift, the starr flat member conglomerates deposited above lapoint member siltstones represent a southward progradation of alluvial fans away from the uplifting mountain front. the starr flat member is overlain by the bishop conglomerate. these units are similar in sedimentary structure and clast composition and are distinguished by an angular unconformity that developed after 37.9 ma. stratigraphic and structural relationships between the duchesne river formation and bishop conglomerate reveal evidence of at least three episodes of laramide-age uplift of the uinta mountains during the deposition of these formations: (1) deposition of fining upward sequences beginning with a basal coarse-grained unit within the brennan basin, dry gulch creek, and lapoint members; (2) progradation of alluvial fans to the south form the younger starr flat member resulted from an increase in sediment supply likely associated with renewed uplift; and (3) tilting and truncation of duchesne river formation to form the gilbert peak erosional surface, and prograding alluvial fans of the bishop conglomerate. these episodes of pulsed uplift are possibly the result of dripping lithosphere that occurred during farallon slab rollback. new 40ar/39ar ages of 39.4 ma from ash beds in the dry gulch creek and lapoint members emplaced from farallon rollback volcanism help to constrain the timing of deposition and uplift. these new ages and other existing radiometric and faunal ages suggest a significant unconformity of as much as 4 m.y. between the duchesne river formation and the overlying bishop conglomerate, which ranges from 34 to 30 ma in age and show that laramide uplift continued after 40 ma in this region. 155 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 identified and distinguished from one another? 2. what are the chronostratigraphic relationships within the duchesne river formation and bishop conglomerate? 3. what do these formations, their associated conglomerates, and intervening erosion surfaces tell us about periods of uplift and quiescence of the uinta mountains during the late eocene and early oligocene? 4. what is the relationship of the stratigraphy to the contemporaneous rollback of the subducting farallon slab? to answer these questions, we combined traditional geologic mapping with lithologic observations including compositions of conglomerate clasts and new 40ar/39ar ages. we identified stratigraphic changes in the parts of the duchesne river formation and bishop conglomerate proximal to the uinta uplift. these changes and other evidence lead us to interpret uplift proximal stratigraphic contacts, locate chronostratigraphic boundaries, and find evidence of episodic tectonic uplift, erosion, and deposition. geologic history the uinta mountains stand as the highest mountain range in utah with peaks reaching 4000 m in elevation. near the start of the neoproterozoic breakup of the supercontinent rodinia, an episode of intracratonic rifting resulted in basin formation in the current location of the uinta mountains and formed the western margin of the laurentian craton (condie and others, 2001; dehler and others, 2010; yonkee and others, 2014). the accumulation of sediments from the surrounding wyoming, mojave, and yavapai provinces into this rift basin created the neoproterozoic uinta mountain group (figure 3), which is now extensively exposed throughout the uinta mountains (ball and farmer, 1998; mueller and others, 2007; dehler and others, 2010; hintze and kowallis, 2021). continued rifting along the western margin of laurentia produced a passive margin where an elongate belt of thick sediment accumulated throughout present day utah and eastern nevada (stewart and poole, 1974; condie and others, 2001; dickinson, 2004). near the end of the neoproterozoic, the region underutah lake great salt lake strawberry river duchesne river rock creek lake fork river w hiterocks r . ashley c reek green river beaver creekw illo w c re ek r ed c re ek sheep creek provo r. jo rd an r iv er u ta h co lo r a d o ? us 40 us 40 us 40 i-15 us 189 wyoming 109˚110˚111˚112˚ 112˚ 111˚ 110˚ 40˚ 41˚ 108˚ 109˚ 108˚ 40˚ 41˚ miles0 4 8 12 16 20 kilometers0 4 8 12 16 20 ? ?salt lake city provo heber city duchesne tabiona roosevelt little mountain rangely vernal uinta-sparks fault henrys fork fault uinta basin fault zone uinta basin fault zone south flank fault north flank fault n utah quaternary deposits cenozoic igneous rocks cenozoic sedimentary rocks mesozoic rocks paleozoic rocks precambrian scalebasal cambrian rocks map explanation normal faults thrust-reverse faults anticline inferred faults? concealed faults? vernal nw quad duchesne fault zone diamond mountain plateau figure 1. geologic map modified from sprinkel (2014) showing the location of the vernal nw quadrangle relative to geologic formations and structures. the quadrangle is located on the south flank of the uinta mountains and contains quaternary, cenozoic, and mesozoic sedimentary rock. source rocks for cenozoic formations are derived from precambrian and paleozoic formations to the north. 156 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 explanation conglomerate sandstone siltstone shale cross-bedded sandstone limestone oolitic limestone coal gypsum age formation symbol thickness meters not to scale lithology notes bishop conglomerate starr flat member lapoint member dry gulch creek member brennan basin member mesaverde group mancos shale frontier formation mowry shale dakota formation cedar mountain formation morrison formation stump formation entrada formation carmel formation tb tds tdl tdd tdb kmv kms kf kmo kd kc km js je jc 315 102–243 0–111 0–150 437–564 545 1004–1502 44 47 80–93 64 158–198 67–82 49–66 45–107 pa le og en e c re ta ce ou s ju ra ss ic unconsolidated deposits q less than 50quaternary d uc he sn e r iv er f or m at io n angular unconformity unconformity unconformity unconformity unconformity angular unconformity unconformity gilbert peak erosion surface massive conglomerate interbedded conglomerate/ sand/ silt prominent ash beds throughout tdl distinct sandstone tongues of tds fan conglomerates grade southwestward to sandstone tar sands oysters fish scales gypsum gypsum coal these units are covered by quaternary deposits and are not exposed within the vernal nw quadrangle 40ar/39ar age plagioclase 39.47 ± 0.16 ma k/ar age 34.03 ± 0.16 ma 40ar/39ar age sanadine 39.36 ± 0.15 ma k/ar age 35.54 ± 0.22 ma ma figure 2. stratigraphic column of formations exposed within the vernal nw quadrangle. thicknesses were measured in the field or calculated from the map using elevation, dip, and surface extent. sprinkel (in review) and sprinkel and kirkland (in preparation) have proposed that the term dakota formation be replaced with muddy formation in the uinta mountains and uinta basin. 157 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 went basin inversion along reactivated faults to form the uinta-cortez arch (sprinkel, 2014, 2018). during basin inversion the neoproterozoic strata were tilted and eroded. a cambrian-age transgression then deposited shallow marine sediments of the tintic quartzite (western uinta mountains) and lodore formation (eastern uinta mountains) on the erosional surface. the middle paleozoic into the mesozoic was a period of accretion and contraction as subduction occurred along the active margin of laurentia (figure 3). this subduction and accretion lead to a long period of orogenic activity that produced the north american cordillera (saleeby, 1983; lawton, 1994; dickinson, 2004). uplift of the antler highlands to the west contributed to a shallow marine setting that allowed for deposition of formations on a carbonate platform, such as the mississippian madison limestone (lawton, 1994; smith and others, 2004; katz and others, 2007; hintze and kowallis, 2021). during the middle jurassic, northeastern utah was situated along the eastern side of the sundance sea (figure 4), until the early cretaceous when the eastward-advancing sevier orogeny resulted in the thinskinned fold and thrust belt of the sevier highlands in western utah (decelles, 2004; decelles and coogan, 2006). throughout the sevier orogeny, oceanic lithosphere subducted at a relatively steep angle producing a typical volcano-plutonic arc extending through present day arizona, california, nevada, and idaho (cross, 1986; livaccari and perry, 1993; lawton, 1994; kowallis and others, 2001; christiansen and others, 2015). the foreland basin in utah was flooded by the western interior seaway in the late cretaceous, which ultimately divided laurentia into two halves, with the cordillera to the west and continental lowlands to the east (lawton, 1994; hintze and kowallis, 2021). sediment was shed from the uplifted sevier highlands and was deposited in the foreland basin, creating the jurassic morrison and cretaceous cedar mountain formations in a continental basin, and the mancos shale and mesaverde group in a marine basin (hettinger and kirshbaum, 2002; hintze and kowallis, 2021) (figures 2 and 4). the end of the cretaceous was marked by a break in magmatism likely caused by a change from steep siltstone cherty limestone dolomitic limestone shalesandstone conglomeratic sandstone cross-bedded sandstone explanation system formation lithologysymbol thickness meters not to scale park city and phosphoria formations weber sandstone morgan formation round valley limestone doughnut shale humbug formation madison limestone lodore sandstone red pine shale u in ta m ou nt ai n g ro up formation of hades pass p*w *m *rv mdh mm _l zur zuh pp p e rm ia n m is si ss ip p ia n p e n n sy lv a n ia n c a m b ri a n n e o p ro te ro zo ic 20–75 200–400 190–290 65–120 25–40 30–90 150–300 0–180 0–600 as much as 4500 buinta mountains little mountain uinta basin n figure 3. (a) oblique google earth image showing the location of the conglomerates studied within the vernal nw quadrangle and the likely conglomerate clast source location in the uinta mountains. image is taken from the south to give a sense of relief in the region. (b) stratigraphic column of proterozoic and paleozoic and rocks within the uinta mountains (from sprinkel, 2006), which are the source of clasts in conglomerate beds of the duchesne river formation and bishop conglomerate. 158 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 to shallow angle subduction (cross and pilger, 1982; cross, 1986; livaccari and perry, 1993). this change, perhaps caused by subduction of an aseismic ridge (cross and pilger, 1978; cross, 1986) or oceanic plateau (dickinson and others, 1988), resulted in an eastward migration of the cordilleran deformation front and eventually the laramide orogeny that started in some regions as early as 100 ma (kaempfer and others, 2021). most laramide-related tectonism occurred during the late cretaceous and early cenozoic (cross, 1986; copeland and other, 2017; rosenblume and others, 2021). the laramide orogeny, with its characteristic basement-cored uplifts, induced the rise of the uinta mountains. in the uinta mountains shortening occurred on moderate angle thrust faults, including the uinta basin fault zone located in the subsurface of the vernal nw quadrangle (figure 1) (hansen, 1986b; stone, 1993; haddox, 2005; sprinkel, 2007). another distinguishing characteristic of the laramide orogeny is the abundant intermountain basins and lakes that record the rise and erosion of adjacent uplifts (lawton, 2008; hintze and kowallis, 2021). lake uinta formed at the start of the eocene (ca. 55 ma) in the subsiding uinta and piceance basins, south of the uinta mountains, and persisted until late eocene at about 42 ma (figure 4) (kelly and others, 2012; hintze and kowallis, 2021). the deposits of the green river and uinta formations mark its extent and evolution. eventually the lake filled, and the uinta formation was buried by dominantly fluvial sediment of the eocene duchesne river formation (anderson 0 0 100 100 200 300 km 200 mi a b c d sundance sea western interior seaway sevier highlands western interior seaway sevier highlands uinta mountains lake gosuite lake uinta n n n n figure 4. paleogeography maps of the colorado plateau (blakey and raney, 2008). (a) middle jurassic tectonic subsidence led to the incursion of the shallow sundance seaway. this seaway and proximal environments lead to the deposition of the twin creek limestone in northern utah (north of the uinta mountains), the arapien formation in central utah, and carmel formation in eastern and southern utah. (b) in the early to middle cretaceous the sevier highlands rose in nevada and western utah, developing an eastward-migrating foreland basin to the east, which was ultimately flooded by the cretaceous western interior seaway. the fluvial, floodplain, deltaic, and nearshore deposits are responsible for the stratigraphy of this time. (c) the cretaceous western interior seaway reached its maximum transgression in the late cretaceous, depositing the marine mancos shale and deltaic to nearshore marine mesaverde group. (d) the laramide orogeny began in the early paleocene and created several uplifts in utah, including the uinta mountains. this uplift led to intermountain lakes which eventually became mostly infilled by the late eocene prior to the deposition of the duchesne river formation. 159 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 and picard, 1972; bryant and others, 1989) (figure 2). the termination of laramide tectonism is poorly constrained due to few features showing clear relationships with laramide faults but is estimated to have ceased between 40 and 45 ma (coney, 1972; cross, 1986; hintze and kowallis, 2021). this termination was caused by the subducting farallon slab rolling back to a steeper angle triggering volcanism far from the continental margin, known as the ignimbrite flare-up, which swept southward from present day montana about 54 ma and ended in the southern great basin about 20 ma (lipman and others, 1972; humphreys, 1995; best and others, 2013). slab rollback has also been associated with continued basement-cored uplift, exhumation, and basin subsidence in wyoming and utah (fan and carrapa, 2014; smith and others, 2014) and extensional deformation, sedimentation, and extension-related volcanism in nevada (canada and others, 2019). methods within the vernal nw quadrangle, the criteria and characteristics developed by anderson and picard (1972) were used to identify the members of the duchesne river formation. these units were mapped at a 1:24,000 scale using aerial photos.  in addition to field mapping, cardinal systems vrtwo three-dimensional (3d) software (https://www.cardinalsystems1.net/vrtwo) was used to map all stratigraphic contacts, faults, and folds onto a 3d surface. this was accomplished using field maps, key marker beds, and topographic expression of the units in vrtwo. bedding attitudes were measured in the field or as three-point solutions within vrtwo. all contacts, faults, and folds were then exported to esri’s arcmap software where unit polygons, faults, structures, and cross section lines were created. in areas where previously described contacts did not correlate with field observation (color, grain size, bedding inclination, or clast composition), new contacts and unit descriptions were developed. one stratigraphic section was measured at the starr flat member/bishop conglomerate contact to identify lithologic changes through the section (figures 5 and 6). in conglomerate-rich areas, counts of clast lithology were taken (figure 6) to determine the source material and unroofing signals of conglomerates in the different units. at conglomeratic outcrops, an area of about 1 m2 was outlined in a chalk circle (figure 7). within that area, each clast over 2 cm in diameter (coarse gravel) was tallied and classified based on source rocks from the uinta mountains described in table 1. the 2-cm diameter criexplanation conglomerate sandstone siltstone silty sandstone st ar r f la t m em be r o f t he d uc he sn e r iv er f or m at io n uinta mountain group figure 5. measured stratigraphic section of upper starr flat member and lower bishop conglomerate with clast count data. the contact is the unconformable surface above interbedded conglomerate, sandstone, and reddish-colored siltstone. there are no clear patterns in clast counts to suggest a formation change. the measured section is located in the northwest corner of the vernal nw quadrangle (40.4924° n., 109.7406° w.). 160 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 terion was used because clasts smaller than this lacked distinctive characteristics and were difficult to classify. the large clast size allowed us to count each clast over 2 cm within the 1-m2 area, therefore a counting grid as described in ross and white (2006) was not used. tallied clasts were then used to estimate the percentage of clasts from different source strata at each outcrop. this percentage was derived from the number of clasts present and not their volumetric proportions. samples of bentonitic volcanic ash from the lapoint member (sample drf-a) and dry gulch creek member (sample drf-h) were collected. plagioclase (drf-a) and sanidine (drf-h) grains were separated from these samples and dated at the university of wisconsin wiscar lab using a single crystal 40ar/39ar laser fusion methodology (http://geochronology.geoscience. figure 6. simplified geologic map of the vernal nw quadrangle with the locations of clast counts, ash samples, and measured section. the dry gulch creek and lapoint members pinch out in the northeastern region of the quadrangle near the bishop conglomerate label. modified from jensen and others (2020). 161 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 wisc.edu/analytical-approaches/). the samples and ages have been previously discussed and published by jensen (2017) and jensen and others (2020). these radiometric ages (damon, 1970; winkler, 1970; mcdowell and others, 1973; bryant and others, 1989; kowallis and others, 2005; sprinkel, 2018; sprinkel, in review; and b.j. kowallis, brigham young university, verbal communication, 2016) along with faunal ages (kelly and others, 2012) were used to determine the chronostratigraphy of the duchesne river formation and bishop conglomerate in the vernal nw quadrangle. previous stratigraphic studies anderson and picard (1972, 1974) describe the variety of fluvial strata in the duchesne river formation and divided it into four members: brennan basin, dry gulch creek, lapoint, and starr flat, from oldest to youngest. they related the deposition of the duchesne river formation to final movement of the laramide uplift near the end of the eocene. sato and chan (2015a, 2015b) identified various facies of the duchesne river formation and divided these into six different facies associations: (1) amalgamated and braided fluvial channels, (2) extensive floodplain and stacked broad fluvial channels, (3) extensive floodplain and isolated small streams, (4) alluvial-fan complexes, (5) dry and wet floodplains and fluvial channels, and (6) lacustrine deposits. these facies interpretations were made from 35 measured sections, including 5 in the vernal nw quadrangle. sato and chan (2015a) note the existence of a fining upward sequence starting in the brennan basin member with grain size decreasing through the dry gulch creek and lapoint members. at the contact with the starr flat member there is a significant increase in grain size. they interpret the onset of sequences to be caused by uinta mountain uplift, from which the gravels of the brennan basin member and the starr flat member were sourced. overlying the duchesne river formation is the bishop conglomerate that was first described by powell (1876) and is found on both the north and south flanks of the uinta mountains. the duchesne river formation is separated from the bishop conglomerate by the gilbert peak erosional surface (hansen, 1986a), which appears to have formed during a period of tectonic quiescence following uplift. this erosional surface is also found on both flanks of the uinta mountains. hansen (1986a) described the bishop conglomerate as rather “loosely cemented bouldery, cobbly conglomerate and coarse, poorly sorted, pebbly, friable sandstone.” maximum clast size ranges from 5 cm to 7.6 m and deposits extend 3 to 85 km from their source in the uinfigure 7. photograph of clast count circle (red dashed outline) within the brennan basin member of the duchesne river formation. all clasts larger than 2 cm in diameter within the circle were counted and classified based on table 1. clasts smaller than 2 cm were not counted because the source material was much more difficult to determine. water bottle used for the scale is 10 cm wide. name criteria park city formation light colored, dolomitic, contains glauconite weber sandstone well sorted, cross-bedded, mediumto fine-grained sandstone round valley limestone contains red chert madison limestone gray, fossil-rich limestone uinta mountain group purple or yellow quartz arenite unidentified limestone limestone, does not fit any other criteria unidentified chert non-red chert table 1. clast classification in conglomerates. 162 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 ta mountains. hansen (1986a) interpreted the bishop conglomerate as originating from debris flows, due to matrix-supported clasts, forming a bajada complex abutting the paleo-uinta mountain front and built on the gilbert peak erosion surface. hansen (1986a, p. 18), bryant (1989, p. j9), and haddox (2005, p. 38–39) suggested that the starr flat member of the duchesne river formation may be the basinward equivalent of the bishop conglomerate. however, sprinkel (2018) recognized an angular unconformity between the two units and has suggested that at certain bishop conglomerate localities, the unit has been incorrectly mapped as the starr flat member. results clast counts in conglomerates clast counting was conducted on cobble/boulder conglomerates within alluvial-fan facies in the brennan basin and starr flat members, and bishop conglomerate to detect potential changes in sediment provenance associated with uinta mountain unroofing (figure 8, table 2). the brennan basin member contains 70% to 90% paleozoic clasts with a majority (40% to 90%) derived from the madison limestone, which is distinguished as a gray, fossil-rich limestone. upward trends throughout the brennan basin member reveal a slight increase in precambrian uinta mountain group clasts (figure 8) made of purplish-gray and yellowish-gray quartz arenite. the basinward part of the brennan basin member has a composition like its uplift-proximal counterpart dominated by paleozoic clasts. the typically fine-grained dry gulch creek and lapoint members include rare conglomerates in coarse-grained braided river facies. in these locations, they show a sharp increase in uinta mountain group clasts (50% to 59%) when compared to the brennan basin member (0% to 17%). the cobble/boulder conglomerates of the starr flat member also exhibit a large percentage of uinta mountain group clasts (34% to 73%). overall, the clast counts in the dry gulch creek and lapoint members are similar to the starr flat member with the exception of more chert in the dry gulch creek member. red chert is characteristic of only the pennsylvanian round valley limestone whereas the origin of black chert, observed in the mississippian madison and deseret limestones and permian park city formation, is undetermined at this time. black chert is listed in table 2 as unidentified chert whereas red chert is grouped with round valley limestone. overall, chert abundance increases basinward (figure 8), likely due to its durability over long transport distances. the starr flat member differs slightly from the bishop conglomerate in clast composition (figure 5, table 2). the starr flat member typically contains greater than 50% uinta mountain group clasts (averaging 57%), whereas the bishop conglomerate consistently contains less than 50% uinta mountain group clasts (averaging 44%). the permian park city formation clasts in the starr flat member range from 2% to 9% (averaging 4.4%), whereas they range from 3% to 14% (averaging 8.3%) in the bishop conglomerate. unidentified limestone clasts account for 0% to 6% of clasts in the starr flat member (averaging 1.7%), whereas making up 4% to 11% (averaging 7.0%) of the bishop conglomerate. lithology and contacts identifying changes in lithology is an important part of locating stratigraphic contacts and interpreting uplift history. a summary of our stratigraphic contact descriptions can be found in table 3. we identified the contacts described by anderson and picard (1972) throughout much of the basinward (southern) part of the quadrangle and recognized the distinct facies with upward fining sequences described by sato and chan (2015a). the first sequence begins above the unconformity separating the uinta formation from the overlying brennan basin member. the deposits of the brennan basin member consist of braided river and some alluvial fan facies; the sequence fines upward through the dry gulch creek and lapoint members, which are dominated by floodplain/lacustrine facies. the contact between the dry gulch creek and lapoint members is placed below a very prominent, 39.4-ma ash layer that can be traced into the mountain front (figure 9). we observed an interfingering relationship between the fine-grained beds of the lapoint member and the course-grained al163 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 luvial fan facies of the lower part of the starr flat member. the upper starr flat is represented by progradation of the alluvial fan facies over the top of the youngest beds of the lapoint member. the starr flat member exhibits an overall coarsening upward sequence with the coarsest beds near the starr flat member/bishop conglomerate contact. within the vernal nw quadrangle, we observed increased dips and a distinct shift in facies closer to the uplift. the north-northeastern part of the quadrangle contains bedding of duchesne river formation that dips up to 30° to the south, whereas the regional dip is typically less than 10°. also, the average grain size in each of the duchesne river formation members is greater than in rocks of the same age found in more distal settings (table 3). additionally, in the north-northeast, the predominantly fine-grained and ash-rich lapoint member contains many resistant, coarse sandstone and pebble conglomerate beds like those found in the starr flat member. these coarse beds thin and disappear basinward (figure 8). since volcanic ash beds were found stratigraphically above many of these coarse-grained beds, the lapoint/starr flat contact was picked above the highest ash bed that marked an abrupt increase in coarse-grained rocks (figure 10). in one location, the dry gulch creek member pinches out completely placing the brennan basin member in contact with the overlying lapoint/starr flat members. this contact juxtaposes two conglomeratic units. here a marked increase in proterozoic uinta mountain group clasts was used to place the basal contact of the starr flat member (figure 8, table 2). overall, the starr flat member also contains more interbedded fine-grained rocks and has a smaller average clast size at its base than the underlying brennan basin member. previous researchers have suggested that the starr flat member is possibly a basinward equivalent of the bishop conglomerate (hansen, 1986a; bryant, 1989; haddox, 2005). however, sprinkel (2018) recognized an angular unconformity between the two units and has suggested that at certain bishop conglomerate lithologies contacts/markers explanation sw ne tdb1 tdb2 tdb3 tdb4 tdb5 tdb6 tdb7 tdb8 tdb9 tds5 tdl/s1 tdl1 tdd1 tdd2 tdd3 tdb12 tdb11 tdb10 tds2 tb1 uinta mountain group madison limestone park city formation weber sandstone unidenti�ed limestone unidenti�ed chert round valley limestone clast composition pa le oz oi c proterozoic conglomerate sandstone fine-grained rocks (silt/mud) 100 m 5 km brennan basin member dry gulch creek member lapoint member upper starr flat member volcanic ash stratigraphic contact bishop conglomerate cretaceous units uinta formation gilbert peak erosion surface unidenti�ed contact lower starr flat member figure 8. schematic cross section of the duchesne river formation and bishop conglomerate in the vernal nw quadrangle, with conglomerate point count data shown in pie charts. overall, the formation coarsens to the northeast, where all members are conglomeratic. clast counts show an upward increase in uinta mountain group and decrease in madison limestone. the duchesne river formation unconformably overlies cretaceous units. the bishop conglomerate unconformably overlies the duchesne river formation and cretaceous units. diagram was modified from anderson and picard (1974). 164 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 formation/ member locality no. uinta mountain group madison limestone round valley limestone weber sandstone park city formation unidentified limestone unidentified chert bishop cgl. tb3 25 0.44 0.4 0 0.04 0.08 0.04 0 bishop cgl. tb2 31 0.45 0.45 0 0 0.03 0.06 0 bishop cgl. tb1 37 0.43 0.3 0 0.03 0.14 0.11 0 starr flat mbr. tds7 33 0.39 0.45 0 0.03 0.09 0.03 0 starr flat mbr. tds6 40 0.68 0.28 0 0 0.03 0.03 0 starr flat mbr. tds5 33 0.55 0.33 0 0.03 0.03 0.06 0 starr flat mbr. tds4 43 0.65 0.33 0 0 0.02 0 0 starr flat mbr. tds3 32 0.34 0.63 0 0 0.03 0 0 starr flat mbr. tds2 27 0.67 0.26 0 0 0.07 0 0 starr flat mbr. tds1 26 0.73 0.23 0 0 0.04 0 0 lapoint mbr. tdl1 46 0.5 0 0 0 0 0.5 0 dry gulch creek mbr, tdd2 84 0.55 0.31 0 0.05 0 0 0.1 dry gulch creek mbr. tdd1 45 0.51 0.27 0.11 0 0 0 0.11 dry gulch creek mbr. tdd3 51 0.59 0.08 0 0 0 0.06 0.27 brennan basin mbr. tdb12 59 0.12 0.58 0.1 0 0 0.1 0.1 brennan basin mbr. tdb11 49 0.04 0.47 0.1 0 0 0.16 0.22 brennan basin mbr. tdb10 70 0.11 0.4 0.03 0 0 0.03 0.43 brennan basin mbr. tdb9 96 0.07 0.85 0.01 0.04 0.02 0 0 brennan basin mbr. tdb8 76 0.17 0.82 0 0.01 0 0 0 brennan basin mbr. tdb7 93 0.09 0.82 0.01 0.09 0 0 0 brennan basin mbr. tdb6 37 0.11 0.84 0.03 0.03 0 0 0 brennan basin mbr. tdb5 80 0.09 0.76 0.05 0.08 0.01 0 0.01 brennan basin mbr. tdb4 61 0 0.9 0 0.03 0.03 0 0.03 brennan basin mbr. tdb3 75 0 0.91 0 0.05 0.03 0 0.01 brennan basin mbr. tdb2 45 0.07 0.89 0 0 0 0 0.04 brennan basin mbr. tdb1 67 0.04 0.72 0 0.03 0 0.1 0.1 table 2. point count data showing percentage of each clast type collected at different localities within each member. 165 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 stratigraphic contact anderson and picard (1972) this study – basinward this study – uplift proximal starr flat member/ bishop conglomerate erosional unconformity that can be identified by an abrupt upward decrease of consolidation. the starr flat member is darker than overlying beds. no contact present angular unconformity marked by a color change from reddish-brown to gray. decrease in fine-grained rocks. lapoint member/ starr flat member base of the lowest reddish-brown sandstone or conglomerate overlying the highest bentonitic claystone of the lapoint member. same as anderson and picard (1972). same as anderson and picard (1972). due to the interfingering nature of the lapoint and starr flat members, marker beds are not laterally continuous. the contact is also marked by an abrupt upward increase in coarse-grained rocks. dry gulch creek member/lapoint member base of the lowest extensive, continuous, bentonitic bed of the lapoint member. same as anderson and picard (1972). not present. brennan basin member/ starr flat member not observed. not present. the lapoint member pinches out placing the starr flat member in contact with the brennan basin member. the contact is an upward change in clast composition. the brennan basin member contains primarily paleozoic limestone clasts, whereas the starr flat contains a majority precambrian quartzite clasts. increase in fine-grained rocks and color change from gray to reddish-brown. brennan basin member/lapoint member not observed. not present. the dry gulch creek member pinches out placing the lapoint member in contact with the brennan basin member. the contact is the base of the lowest extensive, continuous, bentonitic bed of the lapoint member above the gray, conglomeratic beds of the brennan basin member. brennan basin member/dry gulch creek member top of the highest resistant sandstone of the brennan basin member. increase in fine-grained rocks and reddish-brown color. top of the highest light-colored resistant sandstone. change from lightto darker-colored rock. increase in fine-grained rocks. this contact is covered by surficial deposits and was not observed. table 3. stratigraphic contact descriptions. 166 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 localities, the unit has been incorrectly mapped as starr flat member. our observations support those of sprinkel (2018) as we were able to note key differences between the starr flat member and the overlying bishop conglomerate. mapping of this contact is primarily based on a distinct color change from reddish-brown (below) to gray (above) (figures 11 and 12). the reddishbrown color is derived from abundant interbedded silt in the starr flat member, and less silt in the overlying bishop conglomerate resulting in an overall grayish color within the vernal nw quadrangle. this contact also marks an angular unconformity, which was described by sprinkel (2018). the starr flat member dips 6 to 21° to the southwest, whereas the overlying bishop conglomerate is close to horizontal, dipping less than 5°. radiometric ages laterally extensive, exposed ash beds were targeted and sampled to identify chronostratigraphic markers in the duchesne river formation (figure 6; drf-a through drf-k). due to sample quality, only samples drf-a and drf-h were selected for 40ar/39ar laser fusion methods at the university of wisconsin-madison wiscar geochronology lab. drf-a returned an age of 39.47 ± 0.16 ma (table 4). drf-a was collected from a thin tuffaceous sandstone a few meters above the brennan basin/lapoint contact near little mountain where the dry gulch creek member has pinched out. drf-h returned an age of 39.36 ± 0.15 ma. drf-h was collected near utah state route 121 a few meters below the prominent volcanic ash bed that marks the dry gulch creek/lapoint contact. thus, drf-h is stratigraphically lower and older than drf-a. the radiometric ages are inverted stratigraphically, but they are not statistically different, overlapping within the stated uncertainties. these two samples were collected 10 km from each other, which makes the relative stratigraphic position difficult to estimate. however, drf-a is located a few meters above the stratigraphic contact between the two members and drf-h is located a few meters below that contact, making it reasonable that the samples are separated by very little time. these ages are within the range of ages published in previous studies (mcdowell and others, 1973; hansen and others, 1981; bryant and others, 1989; sprinkel, 2018; sprinkel, unpublished data; kowallis, unpublished data). two ash beds in the bishop conglomerate east of the vernal nw quadrangle were collected and dated by kowallis and others (2005). the sample from the lower part of the bishop conglomerate on diamond mountain plateau has an age of 34.03 ± 0.04 ma. the sample from the upper part of the bishop conglomerate on yampa plateau has an age of 30.54 ± 0.22 ma (table 4). discussion significance of clast counts and lithology the duchesne river formation becomes increasingly rich in gravel to boulder-sized clasts closer to the mountain front. within the vernal nw quadrangle, all paleogene deposits near little mountain contain abundant conglomerate beds as the fine-grained facies of the dry gulch creek and lapoint members pinch out south of this point (figure 6). although the lithologies are similar, key differences in the conglomeratic facies of each unit warrant unit divisions. in the configure 9. lapoint (tdl)/dry gulch creek (tdd) contact. the base of the lowest prominent volcanic ash bed is used for the contact. offset of the volcanic ash bed shows down drop on the small fault to the south. photograph location is just west of halfway hollow near highway 121. view is to the west. 167 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 glomeratic facies of the brennan basin member there is an observable up-section increase in the proportion of precambrian uinta mountain group clasts (figure 8). this indicates that unroofing of the uinta mountain group actively occurred during the deposition of this unit, yet paleozoic rocks were still the primary source material. an abrupt increase in uinta mountain group clast abundance occurs across the brennan basin/starr flat contact in the northeast part of the quadrangle, from 0% to 12% in the brennan basin member to 34% to 73% in the starr flat member. paleozoic clasts are still present, so this increase cannot be due to a complete stripping of paleozoic rocks in the source region. it is possible that this variation is due to changes in upstream drainage patterns such as stream capture or a rapid unroofing of the uinta mountain group over a broader area. an alternative explanation is that the contact is unconformable and associated with a temporary figure 10. lapoint (tdl)/starr flat (tds) contact on the southern slope of little mountain. the upper lapoint member contact is marked by the highest laterally extensive ash fall tuff bed. the dashed yellow line shows the location of the contact where the ash bed terminates against a resistant conglomeratic bed that is characteristic of the starr flat member. the contact continues below this coarse bed where it is in contact with a lower ash bed. this interfingering relationship is typical of the contact near the upwarped part of the duchesne river formation. photograph taken to the northwest from 40.4617° n., 109.6943° w. 168 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 cessation of deposition followed by renewed uplift and unroofing. haddox (2005) mentions the possibility of an intraformational angular unconformity separating the lower and upper duchesne river formation nearby in the north adjacent dry fork quadrangle. although no angular unconformity was observed in the vernal nw quadrangle, the possibility of an unconformity cannot be eliminated. the observed increase in neoproterozoic clasts across the contact, the increase in silt, and the decrease in cobble to boulder clast size at the brennan basin/starr flat contact indicate a change not only in the source of the clasts, but a decrease in gradient or energy during the deposition of the starr flat member. a much greater abundance of madison limestone clasts in both the proximal and distal parts of the brennan basin member than in younger strata indicates that it was deposited throughout the quadrangle at a different time and earlier stage of unroofing than the younger members. the basinward increase in red chert from the round valley limestone and unidentified black chert (likely from the madison limestone) reflects the greater durability of the chert; it survived the approximate 5 km of fluvial transport while the limestone breaks down over this distance. figure 11. close-up photograph of the starr flat (tds)/bishop conglomerate (tb) contact. the contact is identified by the undulating, unconformable surface above interbedded conglomerate, sandstone, and reddish-colored siltstone. photograph was taken to the north from 40.4974° n., 109.7311° w. 169 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 proportions of clasts from the uinta mountain group are similar in the dry gulch creek (55% to 59%), lapoint (50%), and starr flat (34% to 73%) members. the main difference between these members is that no black chert was observed in the starr flat and lapoint members whereas 10% to 27% black chert was found in the dry gulch creek member. this pattern shows that the relatively fine-grained dry gulch creek and lapoint members were deposited at the same stage of uinta unroofing (figure 8) as the starr flat member. in the case of the lapoint member, we observed an interfingering relationship with the lower part of the starr flat member, which gives further evidence of the coeval nature of these two members proximal to the mountain front. the coarse-grained, gravel-rich beds identified as the starr flat member can be traced basinward where they pinch out completely amongst the fine-grained, mudand silt-rich beds of the lapoint member. the upper starr flat member is represented by progradation of the alluvial fan facies over the fine-grained lapoint member. the dry gulch creek member does not interfinger with the starr flat member and is stratigraphically older than the lapoint member as the contact can be traced by a prominent ash bed at the base of the lapoint (red dashed line; figures 9 and 10). near the conglomeratic facies of the brennan basin member, the contact with the overlying unit is covered by quaternary deposits, obscuring the dry gulch creek member. closer to the mountain front, the brennan basin member is in direct contact with the starr flat member as indicated by the increase in neoproterozoic clasts. it is unclear why the dry gulch creek member pinches out. however, clast counts, which show a much higher percentage of uinta mountain group, indicate that the dry gulch creek member was deposited at a later unroofing stage than the brennan basin member. these patterns have figure 12. starr flat (tds)/bishop conglomerate (tb) contact is shown by the red dashed line. the contact is easily identified from the abrupt change from reddish-orange to yellow-gray. photograph was taken to the northeast from 40.4974° n., 109.7311° w. 170 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 table 4. age data compilation for duchesne river formation and bishop conglomerate. study source age (ma) formation method quadrangle this study (drf-a) 39.47 ± 0.16 lapoint member 40ar/39ar, plagioclase vernal nw this study (drf-k) 39.36 ± 0.15 dry gulch creek member 40ar/39ar, sanidine vernal nw hansen and others (1981) 29.58 ± 0.86 bishop conglomerate k-ar, hornblende blair basin hansen and others (1981) 29.50 ± 1.08 bishop conglomerate k-ar, biotite blair basin winkler (1970), damon (1970) 26.2 ± 0.7 bishop conglomerate k-ar, biotite blair basin winkler (1970), damon (1970) 41.3 ± 1.1 bishop conglomerate k-ar, biotite stuntz reservoir kowallis and others (2005) 30.54 ± 0.22 bishop conglomerate 40ar/39ar, sanidine jensen ridge kowallis and others (2005) 34.03 ± 0.04 bishop conglomerate 40ar/39ar, sanidine stuntz reservoir mcdowell and others (1973) 39.3 ± 0.8 lapoint member k-ar, biotite lapoint sprinkel (unpublished) 39.24 ± 1.79 lapoint member u-pb, zircon vernal nw kowallis (unpublished) 41.52 ± 0.13 lapoint member 40ar/39ar, biotite lapoint kowallis (unpublished) 41.53 ± 0.61 lapoint member 40ar/39ar, biotite lapoint kowallis (unpublished) 41.10 ± 0.32 brennan basin 40ar/39ar, biotite lake mountain sprinkel (2018) 40.66 ± 1.9 brennan basin u-pb, zircon hancock cove kelly and others (2012) 40.26 ± .08 lapoint member 40ar/39ar, biotite vernal nw or lapoint kelly and others (2012) 37.92 ±? starr flat member duchesnean fauna ? bryant and others (1989) 30.4 ± 3.0 duchesne river formation (undivided) fission-track, zircon strawberry reservoir nw bryant and others (1989) 30.6 ± 1.5 duchesne river formation (undivided) fission-track, zircon blacktail mountain bryant and others (1989) 33.6 ± 3.1 duchesne river formation (undivided) fission-track, zircon dry mountain bryant and others (1989) 37.2 ± 1.7 duchesne river formation (undivided) fission-track, zircon farm creek peak bryant and others (1989) 38.2 ± 1.8 duchesne river formation (undivided) fission-track, zircon farm creek peak bryant and others (1989) 30.0 ± 1.5 starr flat member fission-track, zircon kidney lake bryant and others (1989) 34.0 ± 1.7 starr flat member fission-track, zircon kidney lake bryant and others (1989) 30.5 ± 1.4 starr flat member fission-track, zircon ice cave peak bryant and others (1989) 30.9 ± 3.1 starr flat member fission-track, zircon pole creek cave bryant and others (1989) 32.2 ± 2.8 starr flat member fission-track, zircon neola bryant and others (1989) 36.7 ± 3.9 starr flat member fission-track, zircon neola bryant and others (1989) 28.7 ± 2.0 lapoint member fission-track, zircon neola nw bryant and others (1989) 33.7 ± 5.6 lapoint member fission-track, zircon neola nw bryant and others (1989) 32.9 ± 4.5 lapoint member fission-track, zircon neola nw bryant and others (1989) 35.2 ± 1.6 lapoint member fission-track, zircon lapoint bryant and others (1989) 36.9 ± 1.8 lapoint member fission-track, zircon vernal nw bryant and others (1989) 33.0 ± 3.4 dry gulch creek member fission-track, zircon bluebell bryant and others (1989) 34.5 ± 4.4 dry gulch creek member fission-track, zircon bluebell 171 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 not previously been documented and likely indicate uplift and exhumation of older units within the uinta mountains. the widespread nature of this pattern is unknown and a shift in provenance for the dry gulch creek member is possible. near the starr flat/bishop conglomerate contact, beds in the starr flat member dip southwest as much as 21°, whereas beds in the overlying bishop conglomerate dip less than 5°. this angular unconformity suggests that there was significant uplift and erosion associated with displacement along the uinta basin fault zone after the deposition of the starr flat member but before deposition of the bishop conglomerate. however, this uplift episode is not reflected in clast assemblages of these formations. clast proportions in the starr flat member are very similar to those of the bishop conglomerate (figure 5). in a locality we observed near weasel point in the lake mountain quadrangle to the west-northwest of the vernal nw quadrangle, the bishop conglomerate has mostly paleozoic limestone clasts near its basal contact and shows an upward increase in proterozoic clasts suggesting unroofing during deposition of the bishop. this pattern was not observed in the vernal nw quadrangle. a plausible explanation for this is the drainage supplying sediment to the starr flat member and bishop conglomerate in the vernal nw quadrangle was more mature and had incised more deeply than the drainages feeding sediment to the deposits at weasel point. it is also important to note that the bishop conglomerate in the vernal nw quadrangle is much more conglomeratic than outcrops of the same formation in other areas, possibly also due to a more mature trunk stream sourcing the sediment in the quadrangle. timing of uplift and deposition the duchesne river formation represents a latestage basin fill that formed after the uinta basin was mature and had already been filled by thousands of meters of sediment of the eocene wasatch, green river, and uinta formations, which were deposited north and south of the uinta mountains in lake gosiute (north) and lake uinta (south) between 55 to 42 ma (sprinkel, 2007; kelly and others, 2012; hintze and kowallis, 2021) (figure 4). volcanic ash layers in the green river formation in wyoming exhibit similarities in composition and age to volcanic rocks in montana and idaho (smith and others, 2003; chandler, 2006). the eruptive source of the ash beds in the green river formation in utah has not been documented, but they are likely from the same sources identified in wyoming. the abundance of ash indicates that farallon slab rollback was underway to the north while the uinta mountains were still rising (christiansen and lipman, 1972; fan and carrapa, 2014; best and others, 2016). late-stage basin fill of the uinta basin is marked by the onset of deposition of the duchesne river formation onto deformed strata along the uinta mountain front (sato and chan, 2015a, 2015b). this onlap is expressed in the vernal nw quadrangle by the deposition of brennan basin member on an angular unconformity cutting both the cretaceous mesaverde group and mancos shale. these cretaceous formations were deposited prior to uinta mountain uplift near the western shoreline of the cretaceous interior seaway (hettinger and kirschbaum, 2002). in the northwest part of the vernal nw quadrangle, the upper cretaceous mesaverde group dips 44 to 54° southwest, whereas the eocene brennan basin member dips 24 to 30° southwest. this relationship indicates the mesaverde group was uplifted and tilted prior to the deposition of the brennan basin member. a two-stage uplift history for the uinta mountains has been proposed by untermann and untermann (1969). bradley (1995) attributed the first phase, from cretaceous to early paleogene, to displacement on the north flank and uinta thrusts. whereas the second phase, from early to middle eocene, resulted primarily from displacement on the uinta basin fault zone (formerly called the uinta basin-mountain boundary fault zone). fan and carrapa (2014) suggested that the first phase occurred during flat-slab subduction and initiated laramide uplift. the second phase occurred during slab rollback with uplift and associated basin subsidence occurring at an accelerated rate during the eocene (fan and carrapa, 2014; smith and others, 2014). based on its age, deposition of the duchesne river formation would have occurred during the second slab rollback phase, while uplift and tilting of cretaceous units oc172 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 curred during the first phase. within the duchesne river formation and overlying bishop conglomerate, we find evidence that, during this second phase, uplift was not constant but consisted of at least three periods of activity followed by quiescence. additional evidence of intermittent uplift and quiescence can be found in progressive unconformities between late cretaceous and paleocene units and early eocene to oligocene units near the town of tabiona, duchesne county, utah (sprinkel, 2018). if these features are related to slab rollback, uinta mountain uplift must have been discontinuous and punctuated. smith and others (2017) have attributed farallon slab removal to pulsed uplift in nevada. they propose that isostatic rebound in the eocene was caused by dense eclogite dripping off the base of the previously thickened lithosphere. garzione and others (2008) described similar, punctuated uplift in the subduction-related altiplano, in west-central south america, with a stage of rapid uplift of about 1.5 to 2.5 km related to dripping and delamination of eclogitic lower crust (and the underlying mantle lithosphere) that was preceded by a stage of crustal thickening. the thickness of the crust below the uinta mountains might then be evidence for this process. thick crust would be expected from the contractional history, but if the crust is anonymously thin, it could provide independent evidence for lithospheric delamination as the mechanism for periodic uplift in this region. however, the crustal thickness of the uinta mountains is not well constrained and seismic data-based crustal thickness range from less than 30 km thick (gilbert and sheehan, 2004), like that in the basin and range province to the west, to about 48 km thick (gilbert, 2012). it would be insightful to see if other late-stage laramide structures have thin or thick crust and exhibit the same pattern of pulsed uplift to get an overall sense of the tectonic setting that existed as uplift terminated in the laramide orogeny. the duchesne river formation and bishop conglomerate document the final episodes of uplift in the uinta mountains. the first period of uplift recorded in these units is evidenced by the coarser nature of brennan basin member of the duchesne river formation compared to the finer-grained underlying uinta formation. this pulse of coarse material suggests that it was deposited as a response to erosion following uplift. bryant and others (1989) obtained low-resolution fission track ages (table 4) for the tuffs in the brennan basin member but these data fail to constrain the age of the lower contact of this member at a resolution that can be achieved from other methods. the best constraint for age here is from the duchesnean land mammal fossils that occur in the lower brennan basin member (emry, 1981; rasmussen and others, 1999; kelly and others, 2012). global polarity time scale correlations for duchesnean fauna in california places the uintan-duchesnean faunal boundary at an age of about 41.4 ma, which constrains the age of the lower part of the duchesne river formation (kelly and others, 2012). this faunal age correlates well with an 40.66 ± 1.88 ma age from an altered tuff from the middle of the brennan basin member (utah geological survey and apatite to zircon inc., 2014; sprinkel, 2018). the change observed in clast composition above the brennan basin member likely indicates shifting drainage patterns or unroofing by incision rather than renewed uplift, since the general trend into deposition of the dry gulch creek and lapoint members is one of continuing upward fining. this upward fining sequence shows no change in dip up section and suggests a period of tectonic quiescence. this tectonic lull allowed sediment to fill the restricted basin and the gradient to decrease over time leading to the fining upward sequence. the best age constraints for the contact between the dry gulch creek and lapoint members come from radiometric dates on altered volcanic ash beds directly above and below this contact. this contact is identified by a prominent and laterally extensive ash bed, which has been sampled and dated by other researchers (mcdowell and others, 1974; bryant and others, 1989; kelly and others, 2012; sprinkel, unpublished data; kowallis, unpublished data). this ash bed is the most laterally extensive ash bed found in the duchesne river formation and forms a chronostratigraphic marker. however, our attempts to sample and date this ash bed failed due to an absence of usable feldspar grains. we were able to sample and date other ash beds located just above and below the marker bed used for the lower lapoint member contact. the ages of our samples drf-a (39.47 ± 173 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 0.16 ma) above and drf-h (39.36 ± 0.15 ma) below constrain the contact to about 39.4 ma (figure 13). the compositions and ages of these ash layers are similar to volcanic fields in northeastern nevada (jensen, 2017; jensen and others, 2020) confirming that by 39.4 ma the ignimbrite flare-up had migrated southward to nearly the same latitude where the uinta mountains were still actively rising (compare with christiansen and lipman, 1972; best and others, 2016). like the late tectonic activity in the uinta mountains, the flare-up is related to the rollback of the subducting farallon slab. the upper starr flat member represents the next pulse of uplift. this is indicated by its progradation over underlying members with deposits of primarily alluvial-fan facies (figure 8). haddox (2005) observed an angular unconformity between the starr flat member and the underlying members in the dry fork quadrangle but this relationship was not observed in the vernal nw quadrangle. unfortunately, volcanic ash beds are poorly preserved in the high-energy environment and there are no high-resolution ages from the starr flat member so constraints on the timing of this period of uplift are difficult to determine. the best age constraint for the starr flat member comes from kelly and others (2012) via duchesnean land mammal fauna, which gives an upper constraint of the starr flat member of about 37.9 ma for the last appearance of duchesnean fauna. 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 tdb tdd tdl tds tb ma sw ne 39.36 ± 0.15 sanidine 40ar/39ar (jensen and others, 2020) 39.3 ± 0.8 biotite k/ar (mcdowell and others, 1973) 39.47 ± 0.16 plagioclase 40ar/39ar (jensen and others, 2020) 30.54 ± 0.22 sanidine 40ar/39ar (kowallis and others, 2005) 34.03 ± 0.04 sanidine 40ar/39ar (kowallis and others, 2005) unconformity – gilbert peak erosion surface eocene o ligocene tu 2 km ? ? ? ? ? unconformity ? c 19r c 18r c 19n 41.25 ma 41.51 ma magnetostratigraphy (kelly and others, 2012) figure 13. chronostratigraphic diagram for the duchesne river formation and bishop conglomerate in the vernal nw quadrangle. ages from previous studies and from our own samples collected within the quadrangle are shown. dashed lines are inferred due to weak constraints on contact age. solid lines indicate a strong age approximation. tu – uinta formation, tdb – brennan basin member, tdd – dry gulch creek member, tdl – lapoint member, tds – starr flat member, tb – bishop conglomerate. 174 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 the approximately 4 m.y. hiatus (37.9 to 34.0 ma) between the end of the duchesnean fauna and an age from a tuff near the base of the bishop conglomerate (kowallis and others, 2005) indicates a significant unconformity between the two formations (figure 13). this implication is strengthened by the angular nature of the unconformity (up to 21˚ difference in dip) and the presence of the gilbert peak erosional surface (hansen, 1986a). uplift must have occurred along the uinta basin fault zone, which resulted in warping of the starr flat member and increasing the gradient of the uinta mountain flanks so that the gilbert peak erosion surface could form and truncate the already deformed duchesne river formation. in the vernal nw quadrangle, all the evidence refutes the notion that the starr flat member and the bishop conglomerate are coeval and should be grouped as a single unit. rather, they should continue to be mapped and described as separate units. we found no significant evidence of tectonic deformation in the bishop conglomerate that would suggest otherwise. the widespread gilbert peak erosion surface overlain by bishop conglomerate and the deformation of the starr flat member provides evidence that uinta mountain uplift continued along the uinta basin fault zone after 37.9 ma, which approximates the end of deposition of the starr flat member. these relationships show the continuation of laramide uplift in this region until an age younger than the previously reported 45 to 40 ma (coney, 1972; cross, 1986, hintze and kowallis, 2021). the formation of the gilbert peak erosion surface and subsequent deposition of the bishop conglomerate represents a final pulse of paleogene uplift that continued in this region until as late as 30 ma. uplift is documented by the widespread erosion forming the gilbert peak surface followed by renewed unroofing of the uinta mountains producing the alluvial fan deposits of the bishop conglomerate. subsequent downcutting by the colorado river drainage and post-10 ma uplift (aslan and others, 2010, 2017; karlstrom and others, 2012) has dissected the bishop conglomerate deposits and lowered the local base level so that these deposits are now found only as remnants of the former bajada that likely surrounded the uinta mountains 30 ma. conclusions throughout much of the vernal nw quadrangle on the southern flank of the uinta mountains, stratigraphic contacts in the duchesne river formation closely match the descriptions given by anderson and picard (1972). exceptions to this include the lapoint/starr flat contact and all contacts proximal to the mountains. we observed an interfingering relationship between the lapoint and starr flat members where the fine-grained lapoint eventually pinches out completely near little mountain. the dry gulch creek member also pinches out near little mountain. all paleogene formations near little mountain consist primarily of alluvial-fan facies with abundant conglomerates. in this northern part of the quadrangle two different conglomeratic units of the duchesne river formation (brennan basin and starr flat members) are in contact with each other. the brennan basin member can be identified by a high percentage of paleozoic limestone clasts (72% to 91%) whereas the starr flat member contains a much higher percentage of neoproterozoic clasts (34% to 73%). the contact separating these two conglomeratic units is possibly unconformable. the contact between the starr flat member and bishop conglomerate is also an angular unconformity despite the similar clast compositions between the two formations. clast compositions in uplift-proximal outcrops and their downstream counterparts are also similar. the member contacts in the duchesne river formation as described by anderson and picard (1972) appear to be conformable and represent chronostratigraphic boundaries in the deposits that are distal from the mountain front. however, the duchesne river formation member contacts near little mountain may not represent chronostratigraphic boundaries but can still be distinguished from lithological differences and clast composition. this pattern may also hold true to other uplift proximal deposits and can be mapped similarly. we found clear evidence for three distinct uplift events not previously documented in the duchesne river formation and bishop conglomerate, each occurring during a period of slab rollback as described by fan and carrapa (2014) and resulting in the final stages of uplift in the uinta mountains. ash layers found in the 175 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 dry gulch creek member and abundant in the lapoint member add additional evidence that uplift of uinta mountains during the eocene occurred as the farallon slab rolled back and the ignimbrite flare-up swept southward into northeastern nevada. the first of these uplift events is recorded at the contact between cretaceous units and the brennan basin member and is evidenced by an angular unconformity (54 to 24⁰) and deposition atop the unconformity of coarse conglomerates that fine upward. the age of the brennan basin member is estimated to be around 40.7 ma (sprinkel, 2018). the second episode of uplift is recorded by the progradation of the alluvial fan facies of the starr flat member across the finer-grained deposits of the lapoint member and the angular discordance between the lapoint and starr flat members seen in the north adjacent to the dry fork quadrangle (haddox, 2005). this period of uplift occurred between 39.4 and 37.9 ma. a third episode is recorded at the starr flat/ bishop contact and occurred between 37.9 and 34 ma. this is evidenced by another significant angular unconformity (7 to 21⁰ to less than 5⁰) followed by deposition of the coarse alluvial fan deposits of the bishop conglomerate. distinct pulses of uplift may be related to delamination and dripping of lithospheric mantle. neogene uplift, not associated with the duchesne river/ bishop conglomerate deposits later affected the region. acknowledgments we  thank kent brown (utah geological survey [ugs]) and the countless hours he spent assisting with gis questions, brian jicha (university of wisconsin) for providing high-resolution ages from samples we collected, the department of geological sciences at brigham young university for financial support, and sheralee webb for her constant support of her husband during the fieldwork, research, and writing. finally, we thank eugene szymanski (ugs) and paul anderson (consulting geologist) for their careful reviews of the manuscript. references anderson, d.w., and picard, m.d., 1972, stratigraphy of the duchesne river formation (eocene-oligocene?), northern uinta basin, northeastern utah: utah geological and mineral survey bulletin 97, 29 p. anderson, d.w., and picard, m.d., 1974, evolution of synorogenic clastic deposits in the intermontane uinta basin of utah, in dickinson, w.r., editor, tectonics and sedimentation: society for sedimentary geology 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quadrangle, duchesne and wasatch counties, utah: utah geological survey open-file report 689, 38 p., 2 plates, scale 1:62,500. sprinkel, d.a., in review, geologic map of the duchesne 30' x 60' quadrangle, duchesne and wasatch counties, utah: utah geological survey map xxxdm, xx p., gis data, 2 plates, scale 1:62,500, 1:62,500. sprinkel, d.a., and kirkland, j.i, in preparation, proposed lower cretaceous nomenclature for the uinta moun179 stratigraphic relationships of the eocene duchesne river formation and oligocene bishop conglomerate, northeastern utah— pulsed sedimentary response to rollback of the subducted farallon slab webb, c.a., jensen, m.s., kowallis, b.j., christiansen, e.h, sprinkel, d.a., and hudson, s. geology of the intermountain west 2022 volume 9 tains and uinta basin, utah—a recommendation to adopt the term muddy formation: utah geological survey. stewart, j.h., and poole, f.g., 1974, lower paleozoic and uppermost precambrian cordilleran miogeocline, great basin, western united states, in dickinson, w.r., editor, tectonics and sedimentation: society for sedimentary geology (sepm) special publication 22, p. 28–57. stone, d.s., 1993, tectonic evolution of the uinta mountains—palinspastic restoration of a structural cross section along longitude 109°15', utah: utah geological survey miscellaneous publication 93-8, 19 p., 2 plates. untermann, g.e., and untermann, b.r., 1964, geology of uintah county: utah geological and mineral survey 72, 112 p., p. 2 plates, scale 1:125,000. untermann, g. e., and untermann, b. r., 1969, geology of the uinta mountain area, utah and colorado, in lindsay, j.b., editor, geologic guidebook of the uinta mountains—utah’s maverick range: intermountain association of geologists and utah geological society sixteenth annual field conference, p. 79–86. utah geological survey, and apatite to zircon inc., 2014, u-pb detrital zircon geochronology result for the brennan basin member of the duchesne river formation, duchesne 30' x 60' quadrangle, duchesne and wasatch counties, utah: utah geological survey open-file report 635, 56 p. winkler, g.r., 1970, sedimentology and geomorphic significance of the bishop conglomerate and browns park formation, eastern uinta mountains, utah, colorado, and wyoming: salt lake city, university of utah, m.s. thesis, 115 p. yonkee, w.a., dehler, c.d., link, p.k., balgord, e.a., keeley, j.a., hayes, d.s., wells, m.l., fannign, c.m., and johnston, s.m., 2014, tectono-stratigraphic framework of neoproterozoic to cambrian strata, west-central u.s.— protracted rifting, glaciation, and evolution of the north american cordilleran margin: earth-science reviews, v. 136, p. 59–95. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 8 2021 © 2021 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin dean r. richmond, john pigott, richard lupia, michael behm, and david hein geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover photomicrograph of carbonate spherulites formed by a jurassic variant of the betaproteobacteria ralstonia eutropha h16. the spherulites are commonly found in the upper surfaces of mound spring deposits of the upper jurassic morrison formation of central montana. the black specks are interpreted to be fossil betaproteobacteria remnants preserved in the spherulite. image shown in crossed nicols. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new 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delegates 2020–2023 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 8 2021 1 abstract recent investigations of the upper jurassic morrison formation in central montana resulted in the discovery of 105 small (< 3 m diameter) carbonate buildups in close geographic and stratigraphic proximity. the buildups are divided into two groups by dominant mineralogic composition: siderite versus calcium carbonate. the buildups are found in five distinct spatial clusters and are distributed in association with, and in alignment to, regional jurassic-aged structural lineaments. the buildups are distributed stratigraphically between 40 to 52 m above the base of the morrison formation. interpretation of electrical resistivity tomography surveys indicates that additional buildups are present in the subsurface. carbonate-rich groundwater migrated up fractures to the capillary fringe or the surface. the siderite buildups formed in the near subsurface capillary fringe, whereas the carbonate mounds are subartesian mound spring tufa deposits. the bulk rock negative δ18o and δ13c values demonstrate the buildups were produced by meteoric waters in a continental setting with the groundwater having a short residence time in the subsurface. the presence of the subsurface buildups and mound spring tufa deposits scattered throughout a 12-m portion of the morrison section indicates that the region experienced extended periods of increased precipitation. carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin dean r. richmond1, john pigott1, richard lupia2, michael behm1, and david hein3 1school of geosciences, university of oklahoma, sarkeys energy center suite 710, norman, ok 73019, usa; drichmaond.ou.edu; jpigott@ou.edu; michael.behm@geodata.com 2sam noble museum, university of oklahoma, 2401 chautauqua avenue, norman, ok 73072, usa; rlupia@ou.edu 31021 toole circle, billings, mt 59105, usa citation for this article. richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d., 2021, carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin: geology of the intermountain west, v. 8, p. 1–26, https://doi.org/10.31711/ giw.v8.pp1-26. © 2021 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction the upper jurassic morrison formation, an expansive sequence of terrestrial sediments deposited in foreland basins formed by the north america cordilleran orogenic system, covers approximately 1.5 million km2 of the intermountain west (dodson and others, 1980). the formation has been intensely studied for uranium (turner-peterson and fishman, 1986), coal (harris, 1966; silverman and harris, 1966), oil and gas (johnson, 2005), and dinosaurs (foster 2007). jurassic dinosaurs have been discovered in every u.s. state where the morrison formation is exposed (turner and peterson, 1999). age equivalent rocks are found in south-central canada but have only yielded plant fossils; vertebrate fossils have yet to be discovered (brown, 1946; rouse, 1959; jansa, 1972). the recent discovery of dinosaurs in the northernmost portion of the morrison foreland basin prompted a geological investigation of the study area that led to the discovery of numerous strange hemisphereshaped terrestrial carbonate mounds (richmond and 2 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 others, 2020). these are the first terrestrial carbonate mounds for the morrison formation. the purpose of this paper is to document the surface and nearsubsurface spatial configuration of the buildups, place them into a stratigraphic framework, compare them to other terrestrial carbonates and draw conclusions as to the environmental conditions that led to their development, and understand their paleoclimatic significance. geologic setting the study area is in southeastern fergus county, montana, where the morrison formation is exposed along the flanks of the spindletop dome (figure 1). based on field stratigraphic measurements and well log data, the morrison formation in the study area is 72 m in thickness. the formation is bounded by the underlying upper jurassic swift formation and the overlying lower cretaceous kootenai formation. in central montana, the morrison formation is conformable with the underlying marine sandstone beds of the swift formation. the j-5 unconformity (pipiringos and o’sullivan, 1978), present at the base of the morrison formation in more southern states, is absent in central montana (this study; imlay, 1954; uhlir and others, 1988; khalid, 1990; meyers and schwartz, 1994; fuentes and others, 2011). the morrison formation is undifferentiated in central montana and consists of a mudstone-dominated section with fine-grained anastomosing fluvial channels and thin crevasse splay sandstone beds (richmond and murphy, 2020). the formation contains fossil invertebrates (richmond and others, 2017), dinosaurs (saitta, 2015; richmond and murphy, 2017), and fossil wood (richmond and others, 2019a, 2019b, 2019c). the overlying lower cretaceous (aptian) kootenai formation rests on the k-1 unconformity and is an alluvial and fluvial sequence comprised of deposits of coarseto medium-grained fluvial sandstone beds, overbank deposits of mudstone, and calcrete paleosols, with the formation capped by interstratified lacustrine limestone and dolomite units (dupree, 2009). there is a hypothetical relationship between the structural components of central montana and the development of the morrison carbonate buildups, therefore a summary of the structural features of the region is presented. the present-day structure of the figure 1. geographic distribution for carbonate (blue circles) and siderite (orange squares) buildups in southeastern fergus county, montana. the buildups are separated into five different clusters. only a sample of the 105 buildups is represented in the stratigraphic section. some of the carbonate mounds have associated fossil wood, as indicated. height in the stratigraphic section is reported in meters above the conformable swift/ morrison formational contact. 3 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 central montana region is complex (porter and others, 2002) as verified by fracture swarms and compressional and extensional faulting. the structure of central montana, and the majority of the state, is related to precambrian laterally extensive basement faults that trend at approximately 50o azimuth from southwestern to northeastern montana (sims and others, 2004). reactivation of these precambrian zones of crustal weakness during the laramide orogenic event of the late cretaceous and early paleogene likely formed many of the present-day structures of central montana, including the anticlinal structures of the big and little snowy mountains, spindletop dome, flat willow, and the cat creek anticlines and many other local anticlinal features (gardner, 1950). there are two major orthogonal lineaments present in the montana rocky mountains and the adjacent plains (maughan, 1993). the northeast-southwest lineaments (great falls, greenhorn, snake river-yellowstone, and greybull) strike between 45o to 50o azimuth and correlate to the precambrian basement faults. the major northwestsoutheast lineaments (bridger, chadron, and cedar creek) strike between 320o to 325o azimuth, (maughan, 1993; figure 2). in central montana, this broad zone of northeast-southwest-trending structures controlled depositional patterns for some paleozoic and mesozoic sedimentary rocks (o’neill and lopez, 1993). steeply dipping basement faults that strike northeast-southwest and southeast-northwest in fergus, petroleum, and garfield counties have been mapped in central montana and are thought to have been reactivated through geologic time (nelson, 1995). during the late jurassic, sevier orogenic thrusting formed large north-trending folds in southwestern montana (hutsinpiller and parry, 1985). a paleogeographic/paleotectonic high called “belt island” in north-central montana (porter, 2011) was likely the result of jurassic reactivation of precambrian basement faults in the plate interior. however, there are no known plutonic emplacements in central montana related to these jurassic regional paleostresses. the earliest granitic plutonism occurred during the late cretaceous between 74 and 69 ma in west-central montana in the big and little belt mountains (snee and others, 2002). methods geological data collection stratigraphic measurements were made using accepted geological methods and surveyed using a nikon dtm-322 total station. samples retrieved were thin sectioned by wagner petrographic (lindon, utah) and subsequently were examined under a zeiss petrographic microscope. the spatial position of each buildup was determined by a handheld garmin gps. the buildups appear to have a linear component to figure 2. regional stress lineaments for the central rocky mountains have a prolonged geologic history. the latest reactivation occurred during the laramide orogenic event. the major northwest-southeast lineaments (bridger, chadron, and cedar creek) strike between 320o to 325o azimuth, whereas the northeast-southwest lineaments (great falls, greenhorn, snake river-yellowstone, and greybull) strike between 45o to 50o azimuth. the lineaments are an important component of the development of the morrison formation carbonate mounds. the small black rectangle in southeastern fergus county indicates the study area. modified from maughan (1993). 4 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 them, therefore best fit lines were drawn for the spatial latitude and longitude data. geochemical analysis carbonate samples were prepared for x-ray diffraction (xrd) with accepted methods (moore and reynolds, 1997). powder xrd analyses were performed at the university of oklahoma school of geosciences using a rigaku ultima iv diffractometer. cu-k-alpha radiation (40 kv, 44 ma) was used with a scintillation detector. data analysis was completed using jade 2010 software with the international centre for diffraction data pdf4+ database. a thermo scientific niton xl3t ultra analyzer x-ray fluorescence (xrf) gun was used to measure the elemental abundance of the carbonates. the device measured each sample for 210 seconds. forty-one elements were measured using the xrf tool; 28 of these elements provide useful insight into the rock’s mineralogic composition. only the highest percentages of elements are shown for this study. isotopic data collection two siderite and fourteen carbonate mounds and the modern cascade tufa from sitting bull falls, (last chance canyon, new mexico), were sampled for standard isotopic data. a single sample was analyzed from each mound and the sitting bull falls tufa. the 17 samples were analyzed by beta lab services in houston texas. three duplicate samples (cm 13, cm 35, and cm 52) were also analyzed at the stable isotope geoscience facilities at texas a&m university. all isotope values are reported in delta notation relative to the vienna pee dee belemnite (vpdb‰) isotopic standard. geophysical data collection electrical resistivity tomography (ert) data were acquired using an ares-ii system with stainless steel electrodes at a 1-m and 2-m spacing. all four profiles were measured using a dipole electrode configuration, sensitive to both lateral and vertical changes in resistivity. the ert data were processed and inverted using agi earthimagertm 2d resistivity inversion and modeling software. overall, a relatively moderate to low data misfit (< 6%) was achieved after removing data outliers with a small number of iterations. challenges do arise in interpreting ert measurements when pronounced heterogeneity resulting from varying fracture density, karstification, or thin layering occurs below the resolution threshold (e.g., everett, 2013; loke and others, 2013). furthermore, electrical resistivity is largely governed by water content within the soil profile and greatly depends on the primary and secondary porosity of the rocks and soil. morrison formation buildups the morrison formation buildups can be separated into five geographic distinct areas designated by local coulee dams or other surface features (figure 3). the names of the clusters moving west to east: kootenai ridge cluster (46°51'10.45"n., 108°48'33.03"w.), homestead cluster (46°50'36.50"n., 108°48'21.86"w.), east blue dam cluster (46°50'37.61"n., 108°48'12.21"w.), west ralph dam cluster (46°50'31.10"n., 108°47'50.94"w.), and prairie dog dam cluster (46°50'23.67"n., 108°46'46.52"w.). the prairie dog dam cluster has the highest number of siderite and carbonate buildups (figure 3). the buildups are stratigraphically between 40 to 52 m above the base of the morrison formation. the majority of the buildups are small hemisphere-shaped features a meter in height above the ground surface elevation and up to 3 m in diameter. the buildups are divided into two classes: siderite (feco3) and carbonate (caco3) buildups. to distinguish between the two types of buildups, they will be referred to as siderite buildups (sb) and carbonate mounds (cm). at present, 34 siderite buildups and 71 carbonate mounds have been discovered. the buildups and mounds occur in 5 clusters and 10 carbonate mounds have fossil wood associated with them. all buildups and mounds are encased in variegated illitic or organic-rich mudstones with no associated fluvial or lacustrine facies. some of the designated carbonate mounds have siderite present beneath and on the flanks of the mound. the contact between the siderite and carbonate is always sharp and distinct where these siderite-carbonate mounds occur. 5 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 description of siderite buildups the morrison formation siderite buildups are typically found in clusters (e.g., prairie dog dam cluster) but solitary siderite buildups are present (figure 3). the homogenous siderite buildups can be several meters in length but are less than half a meter in height (figure 4a). there are no sandstone beds, horizontal carbonate strata, or fossil fauna or flora associated with them. the buildups are more elongate than circular, and the uppermost surfaces are irregular from the protrusion of conein-cone apices (figures 4b and 4c). cone-in-cone structures are common in the siderite buildups (figures 5a and 5b). in thin section, the siderite is homogenous displaying ghost traces of the cone-in-cone crystalline growth (figure 5c). some carbonate mounds have siderite on the flanks and/or beneath an overlying mound (e.g., cm 40 and cm 52; figure 3). a large broad carbonate mound (cm 40) a meter in height with a 7-meter diameter overlays a siderite base (figure 6a). the carbonate-peripheral siderites also display small cone-in-cone structures (figure 5d). xrd results on three siderite samples (sb 20, cm 40, 52) indicate the buildups are composed of 48.7% calcium carbonate (caco3), 16.7% quartz (sio2), 16.0% siderite/ ankerite (cafe(co3)/camgfe(co3)2), 10.5% illite, 7.3% kaolinite, and 0.9% pyrite (fes2). xrf was performed on five different siderite buildups (sb 12, 18, 19, 32, 33; appendix) and two carbonate-peripheral siderites (sb 40.1, 40.2; figures 6a and 7). the three major elements for each siderite buildup are calcium (ca), iron (fe), and silica (si). the analysis demonstrates a percentage variation in these three main elements as well as the trace elements (potassium [k], magnesium [mg], titanium [ti], manganese [mn], alluminum [al], phosphorus [p], sulfur [s], chlorine [cl], and strontium [sr]) (figure 7). standard isotope analysis was completed on two siderite buildups (sb 20, 40; table 1). the δ18o siderite figure 3. spatial map of the carbonate and siderite buildups. the buildups are divided into clusters that are named based on local surface features. the prairie dog dam cluster is subdivided into arrays (insert). the dashed lines a‒a', b‒b', c‒c', and d‒d' represent the electrical resistivity tomography (ert) profiles herein described. the four carbonate mounds highlighted by the red circles are specifically referred to herein. 6 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 data have close values of ‒5.08‰ and ‒5.49‰ with a mean of ‒5.29‰. the δ13c data ranges from ‒15.41‰ to ‒18.48‰ with a mean of ‒16.95‰. description of carbonate mounds in contrast to the siderite buildups, the majority of the carbonate mounds are not found close to one another, but small clusters of carbonate mounds are present (figure 3). the homogenous carbonate mounds vary in length and height. the mounds are generally hemisphere-shaped, are typically a meter in diameter and less than a meter in height (figures 6b and 6c) although larger mounds are present. there are no sandstone beds or other terrestrial carbonate beds associated with the carbonate mounds. the mounds do not have macroscale cone-in-cone structures. the majority of the carbonate mounds are composed of orthochemical micrite. clastic detrital grains common in many terrestrial carbonates (e.g., travertines, tufas, calcretes, etc.) are absent. in general, allochems are rare. few macrofossils are present with the carbonate mounds. ten carbonate mounds have fossil wood in proximity to the mound but only three have fossil logs incorporated into the mound (cm 13, 31, 52). typical macrophyte debris (leaves or twigs), hydrophytes, or charophytes are generally absent. only two microscopic woody macrophyte fossil fragments were discovered. the first is unidentifiable woody debris (figure 8a); the second is a partial tangential fragment figure 4. field images of the siderite buildups. (a) siderite buildups can be a few meters long but are less than 50 cm high. they can be isolated or found in clusters. (b and c) closeup views of the siderite buildup’s upper surfaces disrupted by cone-in-cone apices. meter stick and hammer used for scale. sample δ18o (0/00 vpdb) δ13c (0/00 vpdb) mt mrsn cm01 -12.03 -10.57 mt mrsn cm13 -16.72 -3.88 mt mrsn cm13* -15.49 -4.32 mt mrsn cm14 -9.27 -4.88 mt mrsn cm17 -16.05 -6.78 mt mrsn cm27 -10.83 -5.04 mt mrsn cm31 -16.96 -5.83 mt mrsn cm35 -16.11 -4.53 mt mrsn cm35* -16.00 -5.04 mt mrsn cm36 -12.85 -8.90 mt mrsn cm39 -15.48 -5.90 mt mrsn cm40 -15.48 -6.31 mt mrsn cm44 -11.83 -9.43 mt mrsn cm52 -15.59 -5.35 mt mrsn cm52* -16.88 -6.50 mt mrsn cm62 -15.39 -6.25 mt mrsn cm66 -14.30 -5.46 mt mrsn sb20 -18.48 -5.49 mt mrsn sb40 -15.41 -5.08 nm tufa sb1 -8.13 -6.40 cm — carbonate mound; sb — siderite buildup *different lab analyses table 1. oxygen and carbon isotope data from carbonate buildups. 7 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 of a homoxylous wood (figure 8b). in addition to the woody fragments, partial bryophyte leaves (liverworts; m. philippe, university lyon, written communication, 2020) are preserved in several mounds (cm 13, 17, 35; figure 8c). an organic fabric was discovered in mound cm 13 and might be tufa-associated green algae oocardium stratum nägeli (figure 8d). fossil freshwater invertebrates such as ostracods or gastropods are not observed. biogenic macrolaminae from cyanobacteria, typical of many terrestrial carbonates, are not observed. no trace fossils have been found. petrographic features of the carbonates include long dogtooth calcite crystals. some dogtooth crystals appear to be coated with microbial films (figure 9a). spherulites are observed in some carbonate mounds and have a very distinctive texture (figures 9b and 9c). spherulites have a radiating array of crystalline fibers that developed from a nucleus (beck and andreassen, figure 5. images of cone-in-cone features of the siderite buildups. (a) siderite cone-in-cone feature in place. (b) the same cone-in-cone feature is shown in a. this has been removed from the buildup to display the large size of the cone-in-cone feature. the 9-cm-long acid bottle is for scale. (c) photomicrograph of a cone-in-cone feature from a siderite buildup. the cone-in-cone feature (red lines) is difficult to differentiate in the micritic matrix. (d) along the flanks or underlying some carbonate mounds (e.g., cm 52) are pale yellowish-orange to dark yellowish-orange siderites. these are referred to as peripheral siderites and exhibit small cone-in-cone ridges. the sample shown is from beneath carbonate mound cm 52. the mound in shown in figure 6c. figure 6. field images of carbonate mounds. (a) carbonate mound cm 40. the hemispherical shape of the carbonate mound is visible. the carbonate mound (blue arrows) also displays peripheral and underlying siderites (orange line and arrows). meter scale. (b) carbonate mound cm 13. the buildup had a partially encased fossil log of circoporoxylon kräusel. unfortunately, the log was stolen. the red arrow shows where the log was present. in the background is the encasing illitic mudstone. 50 cm scale. (c) carbonate mound cm 52. a fossil log of xenoxylon gothan is encased atop the mound (not visible). some displaced fossil wood fragments are visible (red arrow). peripheral siderites are visible at the base and sides of the carbonate mound (orange arrows). hammer for scale. 8 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 figure 7. xrf comparison of several siderite buildups and two peripheral siderites (cm 40.1 and cm 40.2). the geochemical variability exhibited in the different buildups is thought to be the result of the interaction of the groundwater with different local soil chemistries during the development of the siderite buildup. figure 8. photomicrographic images of fossil organic material found in some carbonate mounds. (a) unknown fossil woody debris in thin section. (b) the tangential view of a fossil homoxylous woody plant. (c) a partial fossil bryophyte (liverwort) leaf. the circular chambers (red-outlined arrows) are filled with fossil cyanobacteria and bounded by the spongy mesophyll (blue-outlined arrows). collenchymatous cells (cluster of brown cells) present in the midline of the leaf (green-outlined arrows) are common in extant liverworts. (d) the fossil circular pores resemble the features of oocardium stratum, a green alga that is commonly associated with modern tufa deposits. the mean pore diameter is ≈ 30 μm. the large pore (pink outlined arrow) may represent the stem of a fossil hydrophyte. 9 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 2010). interestingly, the spherical crystal growth appears to have pushed organic material to the rim. organic material is concentrated in the interstitial space between adjacent spherules. occasionally organic material is encompassed by the spherule’s mineral growth. the organic material is likely residual microphytes (algae) or bacteria (chafetz and folk, 1984). many terrestrial carbonates have primary porosity. primary porosity in the carbonate mounds is limited to intergranular spaces between the spherulites and the porous structures of macrophytes. in addition to the primary orthochemical micrite and radial-fibrous spherulites, many carbonate mounds have late diagenetic fractures annealed with sparry calcite. xrd analysis was run on several carbonate mounds (cm 13, 38, 52, and 64). the data indicate that the carbonate mounds are composed of 98% calcium carbonate and 2% carbon. xrf was executed on eight different carbonate mounds. the three major elements are ca, fe in minor amounts, and si. variation in the three main elements and the trace elements (k, mg, ti, mn, al, p, s, cl, and sr) (figure 10) indicates that the geochemistry was distinct for each buildup. two carbonate mounds (cm 13 and 52) were analyzed with xrf on a cm-scale cross section from the bottom of a large cut slab of the buildup moving upward (figures 11 and 12). carbonate mounds 13 and 52 are stratigraphically separated by 5 m (figure 1). both mounds incorporate fossil wood, circoporoxylon kräusel and xenoxylon gothan, respectively. the most noticeable variation for carbonate mound 13 is the percentage of mg (figure 11; letters c, g, s, t). carbonate mound 52 data displays more consistent chemistry with only minor differences (figure 12). the fossil wood (xenoxylon; letters l-wd and m-wd) has distinct chemistry from the mound and implies wood preservation may involve nonmetals (si, p, s, and cl; figure 12). fourteen morrison formation carbonate mounds and a sample from the modern cascade tufa at sitting bull falls, sitting bull canyon, southwest of carlsbad, new mexico, were analyzed for standard isotope data (table 1). the δ18o morrison data displays variability ranging from ‒3.88‰ to ‒10.57‰ with a mean of ‒6.37‰. the δ13c also shows variability ranging from ‒9.27‰ to ‒16.96‰ with a mean of ‒14.21‰. the mean δ13c values are slightly lower than the preindustrial revolution atmospheric value of meteoric water precipitated calcite (‒6.5‰; noaa data; sharp, 2007). electrical resistivity tomography four localized electrical resistivity tomography (ert) surveys were conducted to understand the figure 9. (a) photomicrograph of dogtooth calcite crystals with cyanobacterial rinds (blue arrows) suggesting that crystals grew uninterrupted into a subaerial, carbonaterich pool and the cyano-bacteria had access to sunlight. (b and c) photomicrographs of spherulites. the spherulites are interpreted to be bacteria-derived. refer to text for information on the bacteria. primary porosity is evident (red arrow; dark blue epoxy). the dark spots scattered throughout the spherulites are fossil remnants of the bacteria. images b and c are crossed nicols. 10 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 figure 10. xrf comparison of several morrison formation carbonate mounds. the changes in mineralogical composition are likely a result of groundwater interaction with local strata and soils. the carbonate mound data represent different stratigraphic positions in the formation. no xrf measurements were made on fractures. the bar at the far right is data from the modern cascade tufa from sitting bull falls, sitting bull canyon, southwest of carlsbad, new mexico. figure 11. xrf data of cm 13 sampled at 1 cm increments. a large slab of the buildup was cut with measurement a at the bottom and moving upward. the most notable variation during the development of cm 13 is the increase in the percentage of magnesium (mg). no xrf measurements were made on fractures. 11 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 structure and potential subsurface continuation of the surface mounds, as was previously applied to delineate the subsurface continuation of a fossil tufa outcrop in northeast spain (huerta and others, 2016). on average, the obtained resistivities range from 20 to 200 ω-m. based on the correlation with outcrops and surface geology, two lithologies are interpreted to be present in the subsurface. lithology 1 (carbonate) resistivities range from 150 to 200 ω-m with thicknesses that range from 0.5 to at least 1.5 m. lithology 2 (mudstone) resistivities range 10 to 70 ω-m. the lowest resistivities associated with lithology 2 are attributed to the increased moisture content of some surface areas (dark blue) (figure 13). ert profile a‒a' (figure 13a) was run parallel to the prairie dog dam (pdd) eastern array (figure 3). although we attempted to pass over several carbonate mounds, the ert profile only shows high resistivity (> 150 ω-m) at the distal ends of the profile. the northeastern buildup is about 6 m across. the profile does not show any additional high-resistivity carbonates (cm) in the subsurface. ert profile b‒b' (figure 13b) was oriented perpendicular to profile a‒a' trending northwest (figure 3) and crossing the western, central, and eastern pdd arrays. the surface high resistivity (> 150 ω-m) at profile marker 58 m crosses over a small surface carbonate mound (figure 3). the ert profile crosses many of the siderite buildups of the pdd central array between 86 to 100 m. this profile section displays low resistivities (< 25 ω-m). although the profile crosses over several surface siderite buildups, the buildups are not discernible in the profile. there are several potential reasons why the buildups are not seen in the profile. the topographic low where the siderite buildups reside may have had a higher water saturation (ephemeral creek bed). the buildups are highly fractured, and those fractures can hold conductive water. it is also possible that the siderite buildups are thin surface features that would make them indiscernible in the ert since electrical current prefers conductive pathways. in figure 12. xrf data of cm 52 sampled at 1 cm increments. a large slab of the buildup was cut with measurement a at the bottom and moving upward. sample cm 52 shows less variability in mineral percentages. measurements l and m include fossil wood encased at the top of the carbonate mound. the unique chemical signature of the fossil wood implies preservation may involve si, p, s, and cl. 12 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 contrast, the profile does discern a small carbonate mound from the pdd western array at 116 to 118 m. in the subsurface between 36 to 60 m is a high resistivity (110 to 200 ω-m) zone interpreted to be a large mound or possibly two mounds separated stratigraphically. ert profile c‒c' (figure 13c) was run parallel to the east blue dam cluster over the largest observed surface carbonate mound (cm 40; figure 3). the hemispherical mound (cm 40) is 7 m long and 1 m thick and is underlain by a thin siderite bed. underlying the entire structure is a low resistivity zone (28 to 15 ω-m) interpreted to be a ≈ 2-m-thick mudstone bed. beneath this mudstone bed is a high resistivity zone (150 to 300 ω-m) interpreted to be a significantly sized carbonate mound in the subsurface. the lateral extent of this mound may range from 15 to 41 m. the suggested minimum thickness is around 1.5 m figure 13. electrical resistivity tomography (ert) profiles (a to d). refer to figure 3 for profile lines. (a) ert profile a‒a' was run parallel to prairie dog dam (pdd) eastern array. the ert profile shows high resistivities (> 150 ω-m) at the distal ends of the profile. the northeastern mound is about 6 m across. the profile does not show any additional high resistivity carbonates in the subsurface. (b) ert profile b‒b' at prairie dog dam was oriented perpendicular to profile a‒a' trending northwest across the western, central, and eastern arrays. the ert profile crosses several siderite buildups of the pdd central array between 86 to 100 m. this profile section displays low resistivities (< 25 ω-m) and the siderite buildups are not discernible in the profile. in contrast, the profile does differentiate a small carbonate mound from the pdd western array at 116 to 118 m. in the subsurface, between 36 to 60 m, is a high resistivity (110 to 200 ω-m) zone, interpreted to be a large mound or possibly two mounds stratigraphically separated. (c) ert profile c‒c' was run parallel to the east blue dam cluster over the largest observed surface carbonate mound (cm 40). this mound is underlain by a thin siderite bed. the hemispherical mound is 7 m long and 1 m thick. underlying the mound is a low resistivity zone (28 to 15 ω-m) interpreted to be a ≈ 2-m-thick mudstone bed. beneath this mudstone bed is a high resistivity zone (150 to 300 ω-m) interpreted to be a significantly sized carbonate mound in the subsurface. the lateral extent of this mound may be as long as 15 to 41 m. the estimated minimum thickness is 1.5 m. near the end of the profile, the high resistivities appear disjointed and stratigraphically higher and may represent another mound. (d) ert profile d‒d' was oriented perpendicular to profile c‒c'. high resistivities (150 to 200 ω-m) at profile marker 18.2 m represent a small surface buildup. underlying the high resistivity zone is a lower resistivity zone (30 to 20 ω-m). similar to profile c‒c', beneath the lower resistivity zone is a high resistivity zone (150 to 200 ω-m). this zone is interpreted to represent a significantly sized buildup. the lateral extent of this mound is at least 24 m and may extend beyond the profile. the estimated thickness is 1 to 1.5 m. it should be noted that the large d‒d' profile subsurface mound(s) has a different subsurface elevation than the large c‒c' profile subsurface mound. therefore, they are not stratigraphically equivalent. 13 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 because ert images tend to blur vertically with depth. near the end of the profile, the carbonate subsurface layers appear disjointed and stratigraphically higher. this may be interpreted as representing a different smaller carbonate mound. given the inherent low resolution of ert imaging, however, this interpretation is speculative. ert profile d‒d' (figure 13d) was oriented perpendicular to profile c‒c' (figure 3). the high resistivities (150 to 200 ω-m) at profile marker 18.2 m represent a small surface buildup. underlying the high resistivity zone (cm) is a lower resistivity zone (30 to 20 ω-m). similar to profile c‒c', below the lower resistivity zone is a subsurface high resistivity zone (150 to 200 ω-m). this zone is interpreted to represent a significantly sized mound, or possibly two coeval mounds. the lateral extent of this mound is at least 24 m and may extend beyond the profile. the estimated thickness is 1 to 1.5 m. it should be noted the large d‒d' profile subsurface mound(s) has a different subsurface elevation than the large c‒c' profile subsurface mound. they are therefore not stratigraphically equivalent. the four ert surveys help to define the lateral extent of the surface mounds and the relative stratigraphy of several previously unknown carbonate mounds in the subsurface. the surface mounds and subsurface carbonates are decoupled by a thin low-resistivity zone that represents the encasing illitic mudstone. the ert data indicate the presence of additional large stratigraphically isolated carbonate mounds in the subsurface. groundwater-fed carbonate deposits groundwater-fed carbonate deposits include travertine, tufas, sinters, and speleothems (chafetz and folk, 1984; steinen, and others, 1987; pedley, 1990; golubic and others, 1993; koban and schweigert, 1993; ford and pedley, 1996; pentecost and coletta, 2007; capezzuoli and others, 2014; della porta, 2015; mohammadi and others, 2019). the classification of groundwater-fed carbonate deposits has a diverse history (see jones and renaut, 2010). modern freshwater springs are categorized by the mean water temperature at the vent, where temperatures range from cold to boiling (jones and renaut, 2010). pedley (1990) and ford and pedley (1996) use water temperature to delineate between travertine and tufa deposits. herein we follow the general classification of pedley (1990), but further define tufas as being precipitated under cooler water temperatures (< 20oc) whereas travertines as being precipitated under thermal conditions (> 20oc; barilaro and others, 2012). sinters can be siliceous or carbonaceous. they are commonly associated with hot springs or geysers in active volcanic terrains where mineral-charged geothermal fluids are discharged at the surface (campbell and others, 2015; munoz-saez and others, 2016). at the other end of the temperature spectrum, speleothem deposits form in caves by evaporation of cool mineral-enriched waters. travertines are usually considered abiotic due to the hydrothermal water conditions that prohibit the existence of higher organisms (chafetz and folk, 1984; koban and schweigert, 1993; ford and pedley, 1996; evans, 1999). different invertebrates, plants, mosses, protozoa, algae, fungi, and bacteria have different tolerances of high-water temperature (renaut and jones, 2000). as discharged thermal waters flow away from the vent and cool, biota with differing temperature tolerances begin to inhabit these varying temperature zones. travertine is enriched in 13c and often contains high levels of sulfur (pedley, 2009). travertines tend to show less macrofacies diversity than tufa systems on account of their relatively limited lateral extent and biota (ford and pedley, 1996). cool water tufa carbonate precipitation occurs at ambient temperatures (< 20oc) and is usually associated with proximal paludal or lacustrine depositional facies (pedley, 1990; ford and pedley, 1996). these tufas are characterized by the presence of heterotrophic bacteria, cyanobacteria, microphytes (algae), hydrophytes, macrophytes, and freshwater invertebrates (kerney, 1959; pedley, 1990; ford and pedley, 1996, koban and schweigert, 1993; evans, 1999; capezzuoli and others, 2014). vertebrate fossils can also be associated with tufa deposits (kerney, 1959; springer and others, 2017). inorganic precipitation (e.g., degassing co2) and organic microbial activity are important factors for carbonate precipitation in tufa environments. tufa deposits have been further divided into allochthonous and autochthonous deposits (pedley, 1990). allochthonous tufas consist of either cemented 14 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 phytoclasts, intraclasts of siltand sand-sized clasts sourced from tufas, micritic tufa material, or peloids and are usually associated with fluvial depositional systems (pedley, 1990). autochthonous tufas consist of stromatolitic horizontal laminations related to seasonal growth patterns of cyanobacteria (janssen and others, 1999). morrison formation siderite buildups and carbonate mound springs interpretation of near-surface siderite buildups the morrison siderite buildups are interpreted to be near-surface buildups and not surface tufa deposits. siderite is the product of the interaction of numerous dynamic inorganic and organic systems. groundwater chemistry is the summation of meteoric and subsurface water interactions with the local geology, aquifer lithologies, and soils. the availability and solubility of iron in soils are partly a byproduct of the decomposition of organic matter. ferrous carbonate (siderite/ankerite) and ferric hydroxide (goethite and polymorphs) precipitate at a circumneutral ph (hedrich and others, 2011). acidic groundwater (ph < 4) causes iron and carbonate (caco3) to remain in the solution. alkaline groundwater (ph > 9) causes bicarbonate (hco3) to precipitate and release co2. to form siderite, the complexing agent caco3 binds with the ferrous/ferric iron at a circumneutral ph (blöthe and roden, 2009). soils in wet climates are typically acidic, whereas in dry climates the soils are alkaline (slessarev and others, 2016). the interaction of acidic surface soil waters with alkaline groundwater likely developed the circumneutral ph required for proteobacteria to precipitate siderite. in modern neutral ph freshwater environments iron-oxidizing phylum proteobacteria govern iron redox reactions (blöthe and roden, 2009; hedrich, and others, 2011; roden and others, 2012). iron redox states are interconnected to inorganic compounds in soils and sediments. micro-organisms play a fundamental function in iron redox reactions (blöthe and roden, 2009). betaproteobacteria are the most common microbes in modern circumneutral ph freshwater environments including soil horizons (roden and others, 2012). these lithotrophic iron-oxidizing bacteria often colonize in the soil transition zone between the anaerobic and aerobic subsurface environments (roden and others, 2004). the position of the anaerobic/aerobic transition zone (i.e., the capillary fringe) can vary by precipitation, the upward migration of groundwater, or the deoxygenation of groundwater by microorganisms. the morrison formation siderite buildups formed from precipitation-fed groundwater at the capillary fringe or by moving up small fractures as subsurface seeps into the vadose zone. the groundwater then interacted with the organicand iron-rich forest soils and aided by iron-oxidizing betaproteobacteria resulting in siderite precipitation. the chemical variabilities of the siderite buildups as shown by the xrf data (figure 7) likely resulted from homogenous groundwater interacting with localized variable soil chemistries. cone-in-cone structures are common world-wide, known from every geologic age, and usually form in calcite, gypsum, or quartz (cobbold and others, 2013). they commonly form in low-permeability saturated sediments such as shale or mudstone. cobbold and others (2013) advocate that cone-in-cone structures develop from fractures that form coeval with mineral growth. the fractures are formed either by the force of crystallization, or fluid over-pressurization. sellesmartinez (1994) agrees that crystalline fibers grow in saturated over-pressured regimes where fractures are induced by a decrease in pore pressure of the overlying sediments. in short, the difference between the saturated over-pressured zone (phreatic) and the hydrostatic zone (vadose) at the capillary fringe creates the boundary conditions that allow cone-in-cone structures to form. although the paleoelevation of the capillary fringe is unknown, it is interpreted to have resided at a shallow burial depth based on the presence of peripheral-siderite buildups and owning to the similar elevation of proximal carbonate mounds. terrestrial siderites form in humid continental environments where precipitation exceeds evaporation. siderites typically accumulate in poorly drained/anoxic wetland soils (sheldon and tabor, 2009; ludvigson and others, 2013; fernandez and others, 2014). the presence of the morrison siderite buildups indicates a humid climate 15 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 with a near-surface groundwater capillary fringe. the siderite buildup cluster in the prairie dog dam central array (figure 3) may be related to an anoxic wetland. interpretation of carbonate mound springs the carbonate mounds lack the many characteristics that are recognized to define modern groundwaterfed terrestrial deposits such as travertine and tufas. the morrison carbonate mounds are composed of orthochemical micrite, show low primary porosity, display no cyanobacterial laminae, and fossil allochems are scarce. the general characteristics suggest the carbonate mounds may represent travertine deposits. however, as stated previously, there are no known jurassic-aged hydrothermal sources to have created groundwater-fed carbonate mounds with water temperatures above 20o c. carbon dioxide degassing is an important component of travertine deposition with the bubbles being preserved in the carbonate. these primary porosity structures are not observed in the field, nor in the thin sections for any of the studied morrison carbonate mounds. this suggests co2 degassing was not violently occurring at the surface during precipitation and therefore the buildup was likely not hydrothermally sourced. fossil evidence and standard isotopic data indicate the carbonate mounds are tufa deposits. the incorporation of the microscopic woody macrophyte fossil fragments, homoxylous wood, bryophyte leaves (liverworts; figure 8), and the proximity of logs of cupressinoxylon, circoporoxylon, and xenoxylon indicate that plants were growing near the mounds. although different plants can have varying water temperature tolerances, the proximity to such a small diameter mound suggests an ambient water temperature. the fossilized microphyte fabric that may be the eukaryotic microalgae (zygnematophyceae) oocardium stratum nägeli (pfiester, 1976) also indicates water temperature. the calcifying desmid o. stratum is a colonial freshwater green alga commonly associated with modern tufas (pentecost, 1991, 2005; linhart and schagerl, 2011). the pore diameter of the morrison fossil microphyte is ≈ 30μ, whereas the pore diameter of the calcite tubes of modern o. stratum is between 17 to 20μ (ibarra and sanon, 2019). the alga o. stratum is known from waters with a temperature range from 7o to 13o c but can exist in cooler (4o c; tran and others, 2019) or warmer water temperatures with an optimum water temperature of 13oc (pentecost, 1991; sanders and rott, 2009; linhart and schagerl, 2011; rott and others, 2012; ibarra and others, 2014). additional observed niche conditions for modern o. stratum include carbonate supersaturation, gradual co2 degassing, and circumneutral ph 7 to 8 in spring waters (rott and others, 2012). associated with the o. stratum are two 142μ diameter pores that may represent the stems of hydrophytes growing in association with the algae. if the fossil is o. stratum, its presence preserved in the carbonates indicates phneutral water with ambient temperatures (i.e., < 20o c). radial-fibrous spherulites are found in outcrop at the upper surfaces of the carbonate mounds. spherulites are a common feature of fossil and modern tufa deposits (guo and chafetz, 2012) and are present in the modern sitting bull falls tufa. bacterially precipitated vaterite and calcite in marine and terrestrial environments are well documented (boquet and others, 1973; chafetz and folk, 1984; merz, 1992; castanier and others, 2000; braissant and others, 2003; párraga and others, 2004; ronholm and others, 2014; baumann and others, 2016). chafetz and folk (1984) suggest bacterial carbonate precipitation may account for 90% of a tufa’s framework grains. the spherulites are likely formed by the secretion of biofilms (i.e., glycocalyx) from betaproteobacteria such as ralstonia eutropha h16 (braissant and others, 2003), or a jurassic variant. r. eutropha h16 is a chemolithoautotrophic bacterium able to grow within organic substrates under aerobic conditions (müller and others, 2013). the modern bacterium r. eutropha h16 has an identical xrd diffractogram as calcium carbonate (braissant and others, 2003). the bacterial formation of spherulites also indicates an ambient temperature. the standard isotopic data of the carbonate mounds indicate that they are tufas. the δ18o values are the product of meteoric water isotopic fractionation from latitude, elevation, precipitation and evaporation, seasonal temperature variation, and the precipitation of calcite (dansgaard, 1964; sharp, 2007). the mean δ18o value derived from marine shell carbonates during the late jurassic (150 ma) is ‒1‰ vpdb (veizer and others, 1999). 16 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 in general, freshwater carbonates have negative δ13c values, but these values can become even lighter if there are significant contributions of organic carbon (sharp 2007). paleo δ13c values require a correction due to secular variation of the δ13c throughout geologic time (mackenzie and pigott, 1981). the total dissolved carbon in the oceans has changed through geologic time. variations in oceanic dissolved inorganic carbon are related to tectonism, erosion, productivity, and carbonate deposition (sharp, 2007). during the late jurassic (150 ma), the secular variation was near +2‰ vpdb (veizer and others, 1999). for terrestrial environments, the δ13c of the freshwater carbonate is controlled by the dissolved inorganic carbon in the groundwater and its interaction with the soil. carbonates precipitated at lower altitudes where vegetation productivity is generally higher (the morrison planation surface of central montana), should have lighter δ13c values due to a greater contribution of 12c from c3 plants. at higher elevations, where plant productivity is poor, δ13c will have isotopically heavier values. isotopic data of the morrison tufa deposits (table 1) shows the δ18o values are similar to the present weight annual δ18o global distribution for comparable latitudes, suggesting minimal diagenetic alteration (darling and others, 2006). based on isotopic analysis of pedogenic carbonates and fossils, δ18o values for paleometeoric waters of the morrison formation were highly depleted (ekart and cerling, 1996). the δ18o values derived from fossil crocodile teeth and turtle scutes from four locations in the morrison formation show comparable values. from south to north the fossil localities are kenton, ok; fruita, co; nine mile hill, wy; and upton, wy with the respective δ18o values ‒16.14‰, ‒20.30‰, ‒16.31‰, and ‒16.94‰ (brundridge, 2013). the central montana δ18o values (table 1) are slightly heavier than the more southern morrison formation δ18o values signifying minor input from the retreating sundance sea, perhaps due to changes in atmospheric circulation during the winter months. the central montana morrison δ13c data (table 1) indicate the dissolved inorganic carbon was derived from atmospheric co2 and the groundwater had a short residence time with minor interactions with organic matter in the soil (darling and others, 2006; sharp, 2007). woody plants (c3) are enriched in 12c with values of δ13c ≈ ‒25‰ (park and epstein, 1961; sharp, 2007; bacon and others, 2011) and the soils they produce have similar values (diochon and kellman, 2008). pedogenic carbonates δ13c values are dominated by the isotopic signal of plant communities (sharp, 2007). the δ13c values indicate these are not pedogenic carbonates. the morrison siderite buildup, carbonate mound, and the sitting bull falls tufa standard isotopic data were plotted on a cartesian graph with δ18o on the x-axis and δ13c on the y-axis (figure 14). fluvial and lacustrine tufas have negative δ18o values. in contrast, lacustrine tufas have positive δ13c values, whereas fluvial tufas have negative δ13c values. in contrast, thermogenic waters exhibit low to very low negative δ18o values coupled with positive δ13c values. the negative δ18o values indicate a meteoric source (gandin and capezzuoli, 2008; della porta, 2015), whereas the positive δ13c values signify an increase in dissolved inorganic carbon as a result of deep subsurface circulation and longer residence times in limestone aquifers (andrews, 2006). the sitting bull falls tufa plots as expected in the region for fluvial tufas. the morrison siderite buildup and carbonate mound data consist of both negative δ18o and δ13c values. the morrison isotopic data plots in the range of the oldest north american tufas, those associated with the lower jurassic navajo sandstone (parrish and others, 2019). the negative isotopic values for the morrison formation siderite buildup and carbonate mound reveal that they were produced by meteoric waters in a continental setting (andrews, 2006; sharp, 2007). the isotopic data also provides insights into the variation of water chemistry during the mound formation. the main cluster of δ18o values (mean ‒15.53‰) correspond to the expected values for the paleolatitude of ≈ 50o north (terzer, and others, 2013; richmond and others, 2019a). in drier climates, the groundwater’s residence time is increased owing to decreased recharge, resulting in isotopically heavier δ13c values (tanner, 2010). the negative δ13c for the main cluster (mean ‒5.78‰) indicates the groundwater had a short residence time in the subsurface indicating regular and/or high precipitation. several isotopic data points diverge from the main 17 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 data cluster, but these present insights into the climatic variance recorded by the tufas. the less negative δ18o values (figure 14, group a; mean ‒10.05‰) implies a marine isotopic component. changes in atmospheric circulation may have brought northern-sourced precipitation from the sundance sea to central montana. the more negative δ13c values (figure 14, group b; mean ‒8.31‰) indicate short drier periods resulted in a longer subsurface residence time allowing groundwater to interact with plant carbon in the subsurface. the difference between the positive late jurassic oceanic δ13c values (+2‰) and the negative values (mean ‒6.13‰) of the morrison formation of central montana suggest the region had a low elevation with high plant productivity and a wet climate. the observed and inferred characteristics of the morrison carbonate tufa mounds are analogous with the artesian mound springs of the great artesian basin (gab) in the lake eyre south region of southern australia (keppel and others, 2011, 2012). the gab mound springs acquired their name for their hemispherical shape that forms by the accretion of sediment around the spring figure 14. a plot of published standard isotopic data of tufas and travertines and the isotopic data from the central montana morrison formation siderite buildups and mound springs. plotted data indicates that the mound springs are freshwater tufa deposits. the dark blue circles represent carbonate mounds (cm), the red squares are siderite mounds (sb), the light blue circles are carbonate mounds run at another lab for comparison. the green triangle represents the modern cascade tufa at sitting bull falls, sitting bull canyon, southwest of carlsbad, new mexico. the isotopic data shows that the buildups are ambient water-temperature tufa mounds. these are the first tufa mounds recorded for the morrison formation and are the second oldest tufa deposits in north america. the isotopic data also provides some insights into the variation in water chemistry. the δ18o matches the expected paleolatitude of the region. a few data points show variance in the geochemistry recorded by the tufas. the δ13c for the central cluster indicates the groundwater had a low residence time in the subsurface indicating regular and/or high precipitation. the more negative δ18o values in group a suggest there may have been precipitation input from northern storms from the retreating sundance sea. the more negative δ13c values of group b suggest drier periods resulting in a longer subsurface residence time allowing groundwater to interact with plant carbon in the subsurface. 18 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 outlet. the outlet gradually rises in elevation forming a domeor shield-shaped cone and are typically between 2 to 5 m in height (williams and holmes, 1978; keppel and others, 2011). many gab mound springs do not consist of the characteristic calcareous mound but either emerges at ground level or consist of soft, silty mounds. the gab mound springs form under a semiarid to arid climate (harris, 1981). the gab-associated paludal environments are limited in size due to the high rates of evaporation (> 10 mm/day; holmes and others, 1981). gab mound spring formation is related directly to a low flow rate (ponder, 1986). springs with higher flow rates have associated channels (i.e., spring tails) that distribute the discharged fluids away from the spring vent, whereas decreased flow rates allow for the precipitation at the vent, resulting in the building up of the mound. the gab mound springs are composed of eolian sand, plant debris, and mud and sand carried up through fractures by the spring discharge (ponder, 1986). according to stokes law, a discharge rate of greater than 4 cm/s is required to lift fine sand within a fracture (williams and holmes, 1978). the morrison carbonate mound springs are similar in shape to the gab mound springs but have a subartesian component. no detrital sand or clay has been found in the morrison mound springs suggesting discharge rates were < 4 cm/s. low flow rates facilitated the building of the mound. the lack of associated fluvial, paludal, or lacustrine facies supports the interpreted low surface discharge rate. the spatial distribution of the siderite buildups and carbonate mounds in proximity to late jurassic faults or fractures corresponds to the azimuth orientation of the present-day major montana lineaments (figure 15). the morrison floral productivity in central montana is a manifestation of low elevation and precipitation rates. the floral productivity resulted in abundant decomposing organic carbon on the forest floor and into the shallow subsurface. the precipitation and groundwater geochemically interacted with the organic carbon to produce more negative δ13c values. the high productivity of the region (rees and others, 2000, 2004), and the low negative δ13c values suggest that the groundwater had a relatively short residence time in the subsurface otherwise the δ13c values would have been substantially isotopically lighter (≈ ‒25‰). in contrast, a relatively longer subsurface residence time is suggested by the isotopic values for group b in figure 14. paleoclimatic significance morrison formation sediments are interpreted to have been deposited under a strongly seasonal arid to semi-arid climate (dodson and others, 1980; parrish and others, 1982, 2004; hotton, 1986; parrish and peterson, 1988; turner and fishman, 1991; valdes and sellwood, 1992; demko and parrish, 1998; demko and others, 2004). the aridity was likely generated by several factors including the latitudinal position in the subtropical dry belt, the sevier orogenic belt acting as a rain shadow (demko and parrish, 1998), and oceanic upwelling driven by coastal wind patterns (parrish and peterson, 1988). peterson and turner-peterson (1987) suggested the presence of narrow but extensive riparian environments that supported abundant plant life to sustain the large herbivorous dinosaurs that roamed the morrison basin. similar to modern continentality, the proximity of the northward-retreating sundance sea during the late jurassic likely created cool and wet coastal climates in central montana in contrast to the more southern inland continental regions. palynological research over the morrison basin shows the paleoclimate transitioned from arid in the southern latitudes to a more humid climate in the northern clines (hotton and baghairiding, 2010; baghai-riding and others, 2015). the discovery of the boreal wood xenoxylon in the morrison formation of central montana corroborates a wet climate in the northern basin latitudes (richmond and others, 2019a). the newly discovered partial bryophyte leaves with their chambers occupied by cyanobacteria also provide some insights into the paleoclimate. bryophytes live in a wide variety of habitats; however, they prefer moist environments (schuster, 1966; shaw and renzaglia, 2004). their preservation in mound springs indicates proximity to the outlet. if the microphyte fabric is o. stratum or a close relative, then its presence in association with the morrison carbonate mound springs provides additional insights into the paleoclimate of the morrison formation of central montana. modern 19 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 o. stratum is present in warmand cool-temperate climates (pentecost, 1990, 2005) but is more prevalent in regions where summer temperatures exceed 25oc (pentecost, 1991). semi-arid conditions are incapable of sustaining the perennial highwater table necessary for continuous discharge to form tufa deposits (pedley, 1990). consequently, regions with higher rainfall and temperatures promote tufa formation (ford and pedley, 1996). an average annual temperature between 5o to 15o c is suggested to be the most favorable to tufa formation and growth (pentecost, 1991; ibarra and others, 2014). stable isotope data from the mound springs have a negative δ18o. this verifies that during the late jurassic central montana’s paleolatitude was between 40o to 50o (richmond and others, 2019a) and that the area experienced increased rainfall. tufas generally occur in regions characterized by an annual rainfall over 500 mm/year (pentecost, 1991; ibarra and others, 2014). tufas with oocardium commonly have rainfall that exceeds 1000 mm/year (ibarra and others, 2014). using the elemental analyses to calculate the calcium and magnesium weathering index (calmag) of paleosol b horizons in the morrison formation of south-central montana, myers and others (2014) estimated a mean annual rainfall for the region ≈ > 1200 mm/year. the occurrence of the tufas and a varied paleoflora and the calmag data of myers and others (2014) indicate that during the late jurassic central montana experienced a warm temperate (rees and others, 2004) to cool temperate climate with dry warm summers and with increased precipitation during the cool winter months. the ert data displays the presence of larger mounds in the subsurface, with mudstone strata between the figure 15. spatial map of the carbonate and siderite buildups. the buildups are divided into clusters. the insert shows the prairie dog dam cluster arrays. lines of best fit for the respective arrays and clusters are shown. the azimuth bearing of each line is similar to the strike of the regional lineaments of montana, suggesting a correlation between the buildups and the structural lineaments. refer to figure 2 for the locations of the structural lineaments. 20 carbonate mound springs of the upper jurassic morrison formation of central montana and their paleoclimatic significance for the northern foreland basin richmond, d.r., pigott, j., lupia, r., behm, m., and hein, d. geology of the intermountain west 2021 volume 8 surface and the subsurface mounds. these subsurface data provide two inferences about the mounds. first, the larger mounds record a prolonged period of increased precipitation. second, the environmental conditions required for the mounds were not continuous. the separation of the subsurface and surface by mudstone deposition suggests that there were dry periods with insufficient precipitation to create mounds. the numerous carbonate mound springs, and their variable stratigraphic positions within the formation (40 to 52 m), suggest wet cycles during the late jurassic of central montana, interspersed with drier periods of undetermined duration. conclusions the discovery of numerous mound springs represents the first observed occurrence of tufa deposits in the morrison formation and some of the oldest tufa deposits documented for north america (dorney and others, 2017; parrish and others, 2017, 2019). the spatial data demonstrate a linear relationship to the buildups and mounds that were likely sourced by carbonate-rich water from fractures along jurassic-aged lineaments. the siderite buildups, with their cone-in-cone structures, formed in the subsurface near the capillary fringe. in the subsurface, the groundwater interacted with the iron-rich soils of the forest floor. xrf data of the various siderite buildups suggest a variable chemistry caused by the groundwater interacting with local soils. betaproteobacteria advanced the precipitation of the iron carbonates in the subsurface. the carbonate mound springs formed from groundwater surface seeps leaking up fractures. spring flow rates are interpreted to have been subartesian, as there are no connecting fluvial or lacustrine facies. the precipitation of the carbonate mounds was inorganic and organic. the presence of spherulites shows that betaproteobacteria played a part in the carbonate precipitation. the mound spring waters discharged at the surface are interpreted to have been cool (< 20oc) based on the isotopic data, the lack of evidence for co2 degassing at the vent, low sulfur percentages, and the associated algal material (e.g., oocardium). the presence of the algal material in the spherulites, algal films on the dogtooth calcite crystals, the incorporation of oocardium, bryophyte leaves, and homoxylous wood of gymnosperm logs into the mounds also indicate the mounds formed at the surface with plants living near the springs. the isotopic δ13c data indicate that the groundwater was meteoric in origin, occurring in a low elevation continental setting that experienced high rainfall. the stratigraphic sections and the ert subsurface data of the mound springs imply repeated periods of increased precipitation separated by drier periods. this wet climate for the morrison formation of central montana is in contrast to the climate models and interpretations of the more southern regions. acknowledgments we especially thank the hein family for access to their ranch and their wonderful support during this research project. the senior author is grateful to nate murphy of judith river dinosaur institute, billings montana, for his continuous field support and use of field equipment. the senior author also wishes to express appreciation to dr. judith totman parrish (university of idaho, emerita) and dr. giovanna della porta (university of milan) for insights and discussions. references andrews, j.e., 2006, palaeoclimatic records from stable isotopes in riverine tufas—synthesis and review: earthscience reviews, v. 75, p. 85–104. bacon, k.l., belcher, c.m., hesselbo, s.p., and mcelwain, j.c., 2011, the triassic‒jurassic boundary carbon isotope excursions expressed in taxonomically identified leaf cuticles: palaios, v. 26, p. 461–469. baghai-riding, n., hotton, c.l., davis, k., and davidson, t., 2015, palynological evidence for a latitudinal moisture gradient in the late jurassic morrison formation [abs.]: geological society of america abstracts with programs, v. 47, no. 7, p. 143. barilaro, f., della porta, g., and capezzuoli, e., 2012, depositional geometry and fabric types of hydrothermal travertine deposits 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0.00 329.16 1097.50 1331.31 35802.16 1522.89 18405.64 2656.32 2068.02 1041.84 110597.36 38.67 32.37 16.64 3.23 0.00 0.99 1.20 1.38 2.40 1.87 0.94 0.30 100.00 4 mt mrsn 5e sm 33 3853.65 108347.52 11322.44 336.68 1323.54 823.06 41170.79 2628.18 14476.71 1889.63 2011.68 872.01 189055.89 57.31 21.78 7.66 2.04 5.99 0.70 0.44 1.39 1.00 1.06 0.46 0.18 100.00 5 mt mrsn 5e sm 40.1 (rtm) 6920.68 227556.95 9538.82 171.53 2240.90 1111.31 53465.97 47274.84 136991.89 0.00 889.17 0.00 486162.06 46.81 11.00 28.18 1.42 1.96 0.46 0.23 9.72 0.00 0.18 0.00 0.04 100.00 6 mt mrsn 5e sm 40.2 (rtm) 5245.61 307804.75 12134.64 222.29 1661.44 1585.15 51842.40 27104.46 88913.66 0.00 1129.22 151.20 497794.82 61.83 10.41 17.86 1.05 2.44 0.33 0.32 5.44 0.00 0.23 0.03 0.04 100.00 7 mt mrsn 5e cm 40 (rtm) 0.00 461396.53 0.00 531.89 0.00 2043.22 4191.58 0.00 8879.2 0.00 1430.72 0.00 478473.14 96.43 0.88 1.86 0.00 0.00 0.00 0.43 0.00 0.00 0.30 0.00 0.11 100.00 8 mt mrsn 5e cm 13 (tf1) 0.00 366751.13 4313.82 385.17 729.78 3371.20 932.58 0.00 4468.97 0.00 806.93 560.62 382320.21 95.93 0.24 1.17 0.00 1.13 0.19 0.88 0.00 0.00 0.21 0.15 0.10 100.00 9 mt mrsn 5e cm 14 (tf2) 855.99 442650.75 0.00 553.64 788.41 3335.80 2798.71 7202.68 20035.29 824.64 7478.83 69.49 486594.23 90.97 0.58 4.12 0.18 0.00 0.16 0.69 1.48 0.17 1.54 0.01 0.11 100.00 10 mt mrsn 5e cm 31 0.00 482371.59 0.00 512.65 312.63 1971.81 889.29 2791.17 5546.98 0.00 1190.16 141.59 495727.87 97.31 0.18 1.12 0.00 0.00 0.06 0.40 0.56 0.00 0.24 0.03 0.10 100.00 11 mt mrsn 5e cm 31 fracture 0.00 438273.25 0.00 295.66 1022.15 2478.04 7409.45 9438.82 26429.73 0.00 1735.04 313.41 487395.55 89.92 1.52 5.42 0.00 0.00 0.21 0.51 1.94 0.00 0.36 0.06 0.06 100.00 12 mt mrsn 5e cm 35 0.00 473172.34 0.00 375.90 0.00 716.75 1539.01 0.00 3414.16 0.00 772.19 0.00 479990.35 98.58 0.32 0.71 0.00 0.00 0.00 0.15 0.00 0.00 0.16 0.00 0.08 100.00 13 mt mrsn 5e cm 52 (wtf) 0.00 373501.91 0.00 400.89 731.08 1852.91 1463.46 0.00 4361.09 0.00 1291.29 672.71 384275.34 97.20 0.38 1.13 0.00 0.00 0.19 0.48 0.00 0.00 0.34 0.18 0.10 100.00 14 mt mrsn 5e cm 52 pw1 0.00 25522.96 0.00 28.06 46.52 120.35 380.47 0.00 42517.47 1632.49 1276.36 617.77 72142.45 35.38 0.53 58.94 0.00 0.00 0.06 0.17 0.00 2.26 1.77 0.86 0.04 100.00 15 mt mrsn 5e cm 52 pw2 0.00 46060.44 0.00 46.48 55.81 248.88 306.75 0.00 41739.52 1505.88 1286.07 795.64 92045.47 50.04 0.33 45.35 0.00 0.00 0.06 0.27 0.00 1.64 1.40 0.86 0.05 100.00 16 mt mrsn 5e cm 62 0.00 472265.28 14118.54 450.99 258.67 4288.00 3661.13 3183.74 10151.90 0.00 1951.41 0.00 510329.66 92.54 0.72 1.99 0.00 2.77 0.05 0.84 0.62 0.00 0.38 0.00 0.09 100.00 17 mt mrsn 5e cm 64 0.00 464517.72 0.00 524.01 498.62 2183.68 3149.12 0.00 5178.43 0.00 366.01 176.92 476594.51 97.47 0.66 1.09 0.00 0.00 0.10 0.46 0.00 0.00 0.08 0.04 0.11 100.00 18 mt mrsn 5e spring 1 0.00 450894.25 0.00 582.51 746.74 2431.35 2950.03 6019.50 16748.51 0.00 3103.56 63.74 483540.19 93.25 0.61 3.46 0.00 0.00 0.15 0.50 1.24 0.00 0.64 0.01 0.12 100.00 19 mt mrsn 5e spring 2 0.00 1135.67 9515.13 115.71 2530.29 135.59 892.31 13490.54 464707.34 1253.83 1129.61 0.00 494906.02 0.23 0.18 93.90 0.00 1.92 0.51 0.03 2.73 0.25 0.23 0.00 0.02 100.00 20 mt mrsn 5e sm lime 0.00 2256.36 7441.88 26.75 4731.57 0.00 2726.36 40057.17 395972.38 1503.80 805.60 0.00 455521.87 0.50 0.60 86.93 0.00 1.63 1.04 0.00 8.79 0.33 0.18 0.00 0.01 100.00 21 mt mrsn 5e paleosol 1 0.00 69271.71 11306.36 114.51 3772.76 269.16 23357.60 8939.69 312282.59 931.69 1596.20 265.34 432107.61 16.03 5.41 72.27 0.00 2.62 0.87 0.06 2.07 0.22 0.37 0.06 0.03 100.00 22 mt mrsn 5e paleosol2 0.00 4330.17 6967.00 66.35 5207.51 150.26 14377.39 6635.15 302754.63 1544.18 1367.18 78.98 343478.80 1.26 4.19 88.14 0.00 2.03 1.52 0.04 1.93 0.45 0.40 0.02 0.02 100.00 23 nm sit bull tufa 0.00 441389.34 15766.72 250.37 941.36 77.18 847.50 4699.54 16960.11 0.00 1668.01 119.45 482719.58 91.44 0.18 3.51 0.00 3.27 0.20 0.02 0.97 0.00 0.35 0.02 0.05 100.00 cm 13 (tufa 1) index sample k ca mg sr ti mn fe al si p s cl total ppm ca% si% mn% fe% s% ti% cl% sr% mg% al% p% 1.00 cm 13 t1 a 0.00 370368.28 0.00 396.79 224.56 3124.52 1224.04 1391.14 3980.99 0.00 2681.77 604.70 383996.79 96.45 1.04 0.81 0.32 0.70 0.06 0.16 0.10 0.00 0.36 0.00 100.00 2.00 cm 13 t1 b 0.00 364566.13 0.00 392.55 0.00 2789.28 3021.21 0.00 3934.17 0.00 2078.91 534.39 377316.64 96.62 1.04 0.74 0.80 0.55 0.00 0.14 0.10 0.00 0.00 0.00 100.00 3.00 cm 13 t1 c 0.00 374920.19 10370.35 383.74 257.94 1913.42 1459.74 0.00 3884.57 0.00 1342.35 550.14 395082.44 94.90 0.98 0.48 0.37 0.34 0.07 0.14 0.10 2.62 0.00 0.00 100.00 4.00 cm 13 t1 d 0.00 369914.47 0.00 391.53 333.31 1831.99 2401.01 0.00 3685.58 0.00 1256.41 627.81 380442.11 97.23 0.97 0.48 0.63 0.33 0.09 0.17 0.10 0.00 0.00 0.00 100.00 5.00 cm 13 t1 e 0.00 360265.50 0.00 386.59 428.45 1898.12 3502.09 0.00 3966.92 0.00 1188.92 693.95 372330.54 96.76 1.07 0.51 0.94 0.32 0.12 0.19 0.10 0.00 0.00 0.00 100.00 6.00 cm 13 t1 f 0.00 360922.09 0.00 350.31 490.64 1981.44 2075.44 0.00 4351.30 0.00 1229.82 614.35 372015.39 97.02 1.17 0.53 0.56 0.33 0.13 0.17 0.09 0.00 0.00 0.00 100.00 7.00 cm 13 t1 g 0.00 373122.53 23929.49 383.38 565.73 2180.98 715.37 0.00 4440.27 0.00 905.85 591.45 406835.05 91.71 1.09 0.54 0.18 0.22 0.14 0.15 0.09 5.88 0.00 0.00 100.00 8.00 cm 13 t1 h 0.00 377277.31 0.00 364.85 595.21 1902.61 1296.46 0.00 4707.07 0.00 1171.94 590.95 387906.40 97.26 1.21 0.49 0.33 0.30 0.15 0.15 0.09 0.00 0.00 0.00 100.00 9.00 cm 13 t1 i 0.00 378719.69 0.00 420.50 648.83 1894.45 1608.29 0.00 4631.01 0.00 951.76 664.55 389539.08 97.22 1.19 0.49 0.41 0.24 0.17 0.17 0.11 0.00 0.00 0.00 100.00 10.00 cm 13 t1 j 0.00 379652.97 0.00 433.80 664.51 1863.99 2619.07 0.00 4581.89 0.00 626.70 546.23 390989.16 97.10 1.17 0.48 0.67 0.16 0.17 0.14 0.11 0.00 0.00 0.00 100.00 11.00 cm 13 t1 k 0.00 387689.09 0.00 1060.70 713.29 2088.26 1540.34 0.00 4398.08 0.00 651.20 605.24 398746.20 97.23 1.10 0.52 0.39 0.16 0.18 0.15 0.27 0.00 0.00 0.00 100.00 12.00 cm 13 t1 l 0.00 377078.81 0.00 420.46 728.14 2047.69 1513.93 1333.34 4093.75 0.00 820.21 507.13 388543.46 97.05 1.05 0.53 0.39 0.21 0.19 0.13 0.11 0.00 0.34 0.00 100.00 13.00 cm 13 t1 m 0.00 383102.31 0.00 443.02 745.98 2145.64 818.92 0.00 5046.44 0.00 980.01 463.62 393745.94 97.30 1.28 0.54 0.21 0.25 0.19 0.12 0.11 0.00 0.00 0.00 100.00 14.00 cm 13 t1 n 0.00 386069.91 0.00 426.15 792.52 1933.16 1071.15 0.00 4169.70 0.00 694.96 547.56 395705.11 97.57 1.05 0.49 0.27 0.18 0.20 0.14 0.11 0.00 0.00 0.00 100.00 15.00 cm 13 t1 o 0.00 378143.66 0.00 438.33 807.13 1825.42 1104.27 0.00 4876.85 0.00 831.33 532.40 388559.39 97.32 1.26 0.47 0.28 0.21 0.21 0.14 0.11 0.00 0.00 0.00 100.00 16.00 cm 13 t1 p 0.00 361110.88 0.00 381.54 806.60 1515.15 2465.85 0.00 4667.98 0.00 1362.02 588.92 372898.94 96.84 1.25 0.41 0.66 0.37 0.22 0.16 0.10 0.00 0.00 0.00 100.00 17.00 cm 13 t1 q 0.00 373837.81 0.00 418.60 853.52 1679.53 1586.49 0.00 5182.90 0.00 980.96 594.73 385134.54 97.07 1.35 0.44 0.41 0.25 0.22 0.15 0.11 0.00 0.00 0.00 100.00 18.00 cm 13 t1 r 0.00 368078.00 0.00 416.97 819.08 1579.81 1219.43 0.00 5054.91 0.00 909.77 592.73 378670.70 97.20 1.33 0.42 0.32 0.24 0.22 0.16 0.11 0.00 0.00 0.00 100.00 19.00 cm 13 t1 s 0.00 371777.38 17172.13 388.57 882.27 1755.04 1697.21 0.00 4977.64 0.00 1037.06 626.80 400314.10 92.87 1.24 0.44 0.42 0.26 0.22 0.16 0.10 4.29 0.00 0.00 100.00 20.00 cm 13 t1 t 0.00 377012.59 10889.51 420.83 848.94 1930.34 964.47 0.00 5076.95 0.00 1077.17 649.30 398870.10 94.52 1.27 0.48 0.24 0.27 0.21 0.16 0.11 2.73 0.00 0.00 100.00 21.00 cm 13 t1 u 0.00 364071.00 0.00 408.56 703.90 1782.86 1853.13 0.00 5154.03 252.09 1077.87 634.32 375937.76 96.84 1.37 0.47 0.49 0.29 0.19 0.17 0.11 0.00 0.00 0.07 100.00 cm 52 (wtufa) index sample ba sn ag nb zr sr bi pb w cu co fe mn cr ti ca al p si cl s mg total ca% si% mn% fe% s% ti% cl% sr% ba% w% 1.00 cm 52a 207.58 0.00 0.00 4.50 34.07 385.41 13.05 0.00 134.47 91.53 63.59 1001.84 2982.96 0.00 501.71 366003.69 0.00 0.00 3904.69 529.01 820.15 0.00 376678.25 97.17 1.04 0.79 0.27 0.22 0.13 0.14 0.10 0.06 0.04 2.00 cm 52b 190.41 0.00 5.44 2.32 30.85 389.37 8.89 0.00 209.87 119.53 37.64 1114.55 2222.11 40.87 555.15 337175.22 0.00 0.00 4853.09 649.52 1005.34 0.00 348610.17 96.72 1.39 0.64 0.32 0.29 0.16 0.19 0.11 0.05 0.06 3.00 cm 52c 210.14 25.42 0.00 3.00 41.86 394.08 4.94 0.00 130.20 87.55 48.39 1293.03 2521.04 66.49 682.23 372918.78 0.00 0.00 4016.09 633.50 959.95 0.00 384036.69 97.10 1.05 0.66 0.34 0.25 0.18 0.16 0.10 0.05 0.03 4.00 cm 52d 236.10 17.90 0.00 3.36 44.69 381.85 7.03 0.00 117.28 83.65 61.10 1011.38 2604.37 0.00 646.74 365351.34 0.00 0.00 3838.44 441.74 914.95 0.00 375761.92 97.23 1.02 0.69 0.27 0.24 0.17 0.12 0.10 0.06 0.03 5.00 cm 52e 225.82 22.81 0.00 1.86 29.07 411.46 6.95 6.58 135.54 95.34 58.08 674.66 2624.24 0.00 676.07 376557.69 0.00 0.00 4591.11 397.09 699.27 0.00 387213.64 97.25 1.19 0.68 0.17 0.18 0.17 0.10 0.11 0.06 0.04 6.00 cm 52f 186.89 0.00 0.00 4.02 30.58 381.23 9.10 7.10 195.72 108.01 40.21 834.65 2828.43 0.00 762.17 343277.44 0.00 0.00 4990.37 619.81 827.78 0.00 355103.51 96.67 1.41 0.80 0.24 0.23 0.21 0.17 0.11 0.05 0.06 7.00 cm 52g 204.03 16.72 0.00 3.90 27.90 379.48 8.87 5.33 160.68 97.46 51.14 800.60 3108.79 0.00 730.61 363350.22 0.00 0.00 4629.61 600.32 800.30 13468.61 388444.57 93.54 1.19 0.80 0.21 0.21 0.19 0.15 0.10 0.05 0.04 8.00 cm 52h 231.37 21.25 5.05 2.96 25.35 384.57 5.58 5.84 134.70 98.99 39.77 1062.01 4619.75 0.00 874.71 376216.13 0.00 0.00 5133.17 658.38 787.57 12766.41 403073.56 93.34 1.27 1.15 0.26 0.20 0.22 0.16 0.10 0.06 0.03 9.00 cm 52i 252.42 23.56 6.03 3.26 25.41 388.77 5.16 0.00 145.02 94.40 55.26 777.10 4742.91 56.41 874.20 379984.66 0.00 0.00 4582.75 544.48 641.00 0.00 393202.80 96.64 1.17 1.21 0.20 0.16 0.22 0.14 0.10 0.06 0.04 10.00 cm 52j 223.93 16.07 0.00 2.34 33.74 371.51 5.58 4.93 140.56 93.28 50.70 720.99 3871.05 0.00 869.23 382692.31 0.00 0.00 4215.58 546.57 705.66 0.00 394564.03 96.99 1.07 0.98 0.18 0.18 0.22 0.14 0.09 0.06 0.04 11.00 cm 52k 216.89 15.01 4.58 3.82 25.30 369.12 10.32 5.28 144.93 94.78 59.29 967.58 4957.59 48.60 854.81 370734.97 1801.16 0.00 4403.77 546.42 714.21 21216.99 407195.42 91.05 1.08 1.22 0.24 0.18 0.21 0.13 0.09 0.05 0.04 12.00 tx tufa 500.06 19.10 4.36 2.45 11.71 250.37 12.40 5.88 124.27 104.39 48.36 847.50 77.18 48.64 941.36 441389.00 4699.54 0.00 16960.10 11.45 1668.01 15766.70 483492.83 91.29 3.51 0.02 0.18 0.34 0.19 0.00 0.05 0.10 0.03 geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter bryan hockett, ted goebel, and kelly graf geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover top photograph is a view of the siblings west shelter (left) and siblings east shelter (right), eastern nevada; note the person at the entrance of the siblings east shelter. see figure 3 for more information. the lower photograph shows ted goebel, kelly graf, and bryan hockett at the end of the bonneville estates rockshelter site stabilization project, western bonneville basin, nevada. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 12 2025 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2024–2025 uga board president keilee higgs keileeann@utah.gov 801.678.3683 president-elect rob buehring robbuehring@yahoo.com 713.412.9269 program chair mike arnoff marnoff@utah.gov 385.303.0431 treasurer will hurlbut 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www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 169 abstract we analyzed faunal remains from two rockshelters in the far western bonneville basin of eastern nevada: bonneville estates rockshelter and siblings east shelter. the analysis focused on paleobiogeographic changes between 17,500 and 5500 cal yr bp. bonneville estates rockshelter contains faunal remains dating to the heinrich 1 stadial (18,000 to 14,700 cal yr bp), whereas both shelters contain faunal remains dating to the bølling-allerød interstadial (14,700 to 12,900 cal yr bp), younger dryas stadial (12,900 to 11,700 cal yr bp), early holocene (11,700 to 9300 cal yr bp), and middle holocene (9300 to 5500 cal yr bp). identified faunal remains from these records indicate cool and either moist or dry climate compared to today between 17,500 and 10,200 cal yr bp, and increasingly warm temperatures impacting animal biogeographies beginning in the latter stages of the younger dryas and first one-half of the early holocene, culminating in xeric-adapted species like today by 9300 cal yr bp. bonneville estates rockshelter also contains specimens of either gray wolf (canis lupus) or the extinct dire wolf (aenocyon dirus) and one felid phalanx of either puma/ cougar (puma concolor) or the extinct north american “cheetah” (miracinonyx trumani), whereas siblings east shelter contains a rib of an extinct large horse of the genus equus. radiocarbon dated faunal remains were found directly atop lake bonneville beach gravels deposited inside siblings east shelter on the provo terrace of lake bonneville, suggesting the lake dropped from this elevation prior to 14,300 cal yr bp. faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter bryan hockett1, ted goebel2, and kelly graf3 1department of anthropology, university of nevada, reno, reno, nv 89557 usa; paleohawk@gmail.com 2department of anthropology, university of kansas, lawrence, ks 66045 usa; goebel@ku.edu 3department of anthropology, university of kansas, lawrence, ks 66045 usa; graf@ku.edu citation for this article. hockett, b., goebel, t., and graf, k., 2025, faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter: geology of the intermountain west, v. 12, p. 169–200, https://doi. org/10.31711/giw.v12.pp169-200. introduction the eastern great basin encompasses the lake bonneville basin and surrounding higher terrain that drains water into that basin (figure 1). it is the largest of the closed basins in the basin and range physiographic province (hubbs and miller, 1948; o’connor, 1993) and encompasses much of the western one-half of utah as well as smaller sections of eastern nevada, southeastern idaho, and southwestern wyoming. climatic shifts in the bonneville basin during the late pleistocene and holocene over the past 18,000 years (cal yr bp) are indicated by a variety of proxies including lake-level fluctuations (antevs, 1948; mifflin and wheat, 1979; mcgee et al., 2012; oviatt, 2015, 2024; thompson et al., 2016; oviatt et al., 2021; oviatt and pedone, 2024), macrobotanical remains (thompson, 1990; rhode and madsen, 1995; rhode, 2000; madsen et al., 2001), faunal remains 170 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 (grayson, 1998, 2000, 2016; broughton et al., 2000; hockett, 2007, 2015; schmitt and lupo, 2012, 2016, 2018; milligan and mcdonald, 2017), and pollen (madsen and currey, 1979; spencer et al., 1984; louderback and rhode, 2009; thompson et al., 2016). these proxies result in a robust picture of inferred changes in temperature and precipitation and their impacts on biogeography and the transgressions and regressions of lake bonneville during the heinrich 1 stadial 18,000 to 14,700 cal yr bp (naughton et al., 2023a), bølling-allerød interstadial 14,700 to 12,900 cal yr bp (naughton et al., 2023b), younger dryas stadial 12,900 to 11,700 cal yr bp (naughton et al., 2023c), early holocene 11,700 to 9300 cal yr bp, and subsequent middle holocene and later climatic episodes post-9300 cal yr bp (rhode and madsen, 1995; grayson, 1998, 2000; hockett, 2007; louderback and rhode, 2009; schmitt and lupo, 2012, 2016; oviatt, 2015; oviatt and pedone, 2024). figure 1. general location of bonneville estates rockshelter, siblings east shelter, and other sites mentioned in the text in relation to the bonneville basin and the high stand of pleistocene lake bonneville. 171 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 the bonneville basin experienced shifting cooling and warming events during the latest pleistocene between 18,000 and 11,700 cal yr bp (rhode and madsen, 1995; grayson, 1998; louderback and rhode, 2009; schmitt and lupo, 2012; oviatt, 2015). from a regional perspective, conifers such as limber pine (pinus flexilis), prostrate juniper (juniperus communis), and spruce (picea) inhabited areas 300 to 600 m (1000–2000 ft) below their modern distributions, with rocky mountain juniper (juniperus scopulorum) occupying some areas now exclusively inhabited by utah juniper (juniperus osteosperma) (rhode and madsen, 1995; rhode, 2000; madsen et al., 2001). on the west side of the snake range in far east-central nevada, macrobotanical remains from indurated woodrat (neotoma sp.) middens demonstrate that bristlecone pine (pinus longaeva) similarly occupied much lower elevations than its current range (mead et al., 1982). sagebrush (artemisia spp.) dominated the understory now occupied by warm-adapted shrubs such as greasewood (sarcobatus spp.) and shadscale (atriplex spp.) (thompson, 1990; rhode and madsen, 1995; louderback and rhode, 2009; madsen, 2000; madsen et al., 2001). although lake bonneville submerged the modern blue lake marshes along the western shore of the lake during this time, pollen grains from marsh plants such as sedges (cyperaceae) and cattail (typha spp.) in relatively low frequencies indicate that shallow-water marsh habitat was present in the western bonneville basin (louderback and rhode, 2009, p. 318). cooland mesic-adapted extant animals also occupied much lower elevations and greater ranges than they do today. yellow-bellied marmot (marmota flaviventris), pika (ochotona princeps), pygmy rabbit (brachylagus idahoensis), sage vole (lemmiscus curtatus), and sage-grouse (centrocercus urophasianus) are among the key species that display greater geographic ranges during the late pleistocene (grayson, 2000, 2006; hockett, 2007, 2015; schmitt and lupo, 2012). additionally, the western longwing katydid (capnobotes occidentalis) is present in the younger dryas sediments of bonneville estates rockshelter (ber) (hockett, 2007, 2015) but is not present near the shelter today. longwing katydids prefer woodlands and sagebrush habitats (tinkham, 1944) commensurate with the presence of pygmy rabbits, sage voles, and sage-grouse. bison (bison sp.) is also present in the younger dryas deposits of ber (hockett, 2015). shifts in patterns of abundance of extant small animals are also seen, including the dominance of bushytailed woodrats (neotoma cinerea) in comparison to desert woodrats (neotoma deserti) at lower elevations. this pattern is evident during the bølling-allerød at ber, dated between 14,575 and 13,255 cal yr bp, where schmitt and lupo (2012, p. 99) found bushy-tailed woodrats dominated in comparison to desert woodrats 94 to 6%, respectively. a similar pattern is seen during the younger dryas stadial at both ber and homestead cave (grayson, 2000; schmitt and lupo, 2012). several extant eastern great basin reptiles and amphibians are present in heinrich 1 and bølling-allerød dated woodrat middens from the snake range including the great basin spadefoot (spea intermontana), which belongs to the family of amphibians scaphiopodidae and also known as spadefoots, pygmy shorthorned lizard (phrynosoma douglasii), and desert night snake (hypsiglena torquata) (mead et al., 1982; holman, 1995). these species still occupy the area from which the woodrat middens were collected. other animals that have been dated to the late pleistocene and likely maintained their general ranges throughout the holocene prior to euroamerican contact include several artiodactyls (deer [odocoileus], mountain sheep [ovis canadensis], and pronghorn [antilocapra americana]), carnivores including wolf (canis lupus) and red fox (vulpes vulpes), a wide variety of aquatic birds such as grebes (podicipedidae) and ducks (anatidae), and raptorial birds including owls (strigidae), falcons (falconidae), and hawks (accipitridae) (livingston, 2000; hockett, 2015; milligan and mcdonald, 2017; duke et al., 2022). several extinct animals were present in the bonneville basin or nearby during the latest pleistocene. heinrich 1-, bølling-allerød-, or younger dryas-dated specimens include camel (camelops), short-faced bear (arctodus simus), mammoth (mammuthus spp.), mastodon (mammut), jefferson’s ground sloth (megalonyx jeffersonii), and flat-headed peccary (platygonus com172 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 pressus) (reviewed in schmitt and lupo, 2016; milligan and mcdonald, 2017; mead et al., 2023). undated extinct animals include horse (equus/harringtonhippus) and helmeted ox (bootherium bombifrons). as noted, one bison bone is present in the younger dryas sediments at ber (hockett, 2007, 2015), but it is not known whether it is bison antiquus or bison bison. these pleistocene-aged plants and animals lived primarily around the margins of the dominant aquatic feature at this time—lake bonneville. the timing of lake bonneville’s transgressions and regressions over the past 18,000 years is generally known although several questions remain (oviatt, 2014, 2015, 2020, 2024; oviatt and pedone, 2024). lake bonneville reached its high-stand bonneville shoreline no later than 18,000 cal yr bp (oviatt, 2020, p. 309). approximately 17,500 cal yr bp the lake began its overflow stage into the snake river drainage system, dubbed the ‘bonneville flood’ (oviatt, 2020, p. 310). the lake may have dropped and began carving the provo shoreline only several years after the beginning of the overflow, and then subsequently regressed below the provo level approximately 14,500 cal yr bp (oviatt and pedone, 2024, p. 34). the precise timing of the regression of the lake from the provo terrace is still in question and is addressed again below with new data recovered from siblings east shelter (ses) (figure 1). the lake then may have dropped as low as the level of great salt lake before transgressing again briefly during the younger dryas to the “gilbert” level, now called the “currey cycle,” before regressing once again (oviatt, 2014, 2015; oviatt et al., 2024). the sites that have set the standard for understanding long-term changes in animal biogeography over the past 18,000 years in the bonneville basin are homestead cave (broughton, 2000; grayson, 2000; madsen, 2000) and ber (hockett, 2007, 2015; schmitt and lupo, 2012). ber contains well-preserved faunal remains dating more than 14,500 cal yr bp, and homestead cave displays similar preservation dating to 13,000 cal yr bp. both sites display comparable patterns of changing animal presence and abundance in response to climatic shifts throughout the latest pleistocene and holocene. the primary differences between these two sites are in the mode of deposition of their respective faunal remains and their microenvironmental settings within the bonneville basin. the homestead cave fauna was deposited primarily by raptors, most notably owls, beginning near the onset of the younger dryas 12,900 cal yr bp (madsen, 2000). most of the ber rodent fauna was also deposited by raptors or carnivores (schmitt and lupo, 2012), but deposition of terrestrial sediments inside the shelter began before the onset of the bølling-allerød 14,700 cal yr bp (goebel et al., 2021; this paper). additionally, most of the younger dryas and early holocene non-rodent fauna from ber was deposited by human foragers (hockett, 2007, 2015). ber is at 1590 m asl (5250 ft) along the high-stand bonneville terrace. homestead cave, in contrast, is at 1406 m asl (4640 ft) between the provo terrace (about 1470 m [4850 ft]) and the younger dryas-aged currey cycle lake level (about 1295 m [4275 ft]). thus, ber is approximately 175 m (574 ft) higher in elevation than homestead cave and was open to terrestrial sediment and biotic deposition as soon as the lake catastrophically dropped from the bonneville terrace about 17,500 cal yr bp. nevertheless, both sites display nearly identical biogeographic patterning in their mammalian faunal remains during the younger dryas and first one-half of the early holocene with mesic-adapted species dominating the identification lists (grayson, 2000; hockett, 2007, 2015; schmitt and lupo, 2012). in addition, both sites, as well as camels back cave (figure 1), indicate that shifts to xeric-adapted animals closely matching today’s faunal communities near these sites, including the extirpation of marmots, pika, sage voles, sage-grouse, and pygmy rabbits, as well as the increased dominance of desert woodrats over bushy-tailed woodrats, occurred by 9300 cal yr bp (8300 14c yr bp) (grayson, 2000; hockett, 2007; schmitt and lupo, 2012; oxcal, v4.4; reimer et al., 2020), marking the beginning of the middle holocene in this region. however, this marked shift from mesicto xeric-adapted fauna, as well as the near abandonment of ber by human foragers, began during the early holocene (grayson, 2000; schmitt and lupo, 2012; goebel et al., 2021). as schmitt and lupo (2012, p. 98) stated when comparing the homestead cave and camels back cave rodent faunas: “although this combined rodent-only data represents a modifica173 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 tion of previously reported analyses and comparisons… the results are the same; there is a sharp decline in the abundance of ma [mesic-adapted] species by approximately 9000 14c yr bp (10,200 cal yr bp)…” here we report on another remarkable record from ses that contains well-dated evidence of late pleistocene and early holocene biogeography in the western bonneville basin, as well as the heinrich 1and bøllingallerød-aged fauna from ber not reported previously. ses (bureau of land management nevada site designator crnv-11-7736) is one of a group of four rockshelters dubbed “the four siblings” that contains a similar record of nonculturally deposited fauna to that reported from homestead cave (grayson, 2000) and ber (schmitt and lupo, 2012). like homestead cave, owls deposited most of the bones inside ses (hockett, 1995). however, ses is at an elevation of 1485 m (4872 ft) along a provo-aged terrace of pleistocene lake bonneville in between the elevational settings of homestead cave and ber. further, faunal remains began accumulating in ses shortly after lake bonneville dropped from the provo terrace and thus provides a record that potentially reaches 1300 years earlier than homestead cave. also, ses provides new evidence for a minimum date for the occurrence of the drop in lake bonneville from the provo terrace. setting bonneville estates rockshelter and siblings east shelter rest upon relic bonneville-era and provo-era shorelines, respectively, of pleistocene lake bonneville in the far western bonneville basin of eastern nevada (figure 1). today the floor of ber is at an elevation of about 1590 m (5250 ft) whereas ses is at about 1485 m (4900 ft). ses is approximately 4.5 km (3 mi) east of ber (goebel et al., 2021), 4 km (2.5 mi) southwest of the blue lake marsh (louderback and rhode, 2009), 100 km (62 mi) southwest of homestead cave (madsen, 2000), and 30 km (19 mi) south of danger cave (jennings, 1957) (figure 1). both ber and ses face southeastward (figures 2 and 3). ber is on the foothill slopes between the bonneville salt flats to the east and the goshute mountains to the west. the mouth of ses overlooks the bonneville salt flats and the blue lake marsh (figure 4) in the distance. ber is the largest known rockshelter in the area, measuring 25 m (82 ft) wide and 15 m (49 ft) deep at its center with a 10-m-high (33 ft) ceiling (graf, 2007). ses is much smaller, measuring 9 m (30 ft) wide and 7 m (23 ft) deep with a ceiling reaching about 2.5 m high (8.2 ft). because of their relatively low elevations, local vegetation today is sparse and desertic. however, the lower-elevation ses is characterized by shadscale, greasewood, and some cacti (e.g., opuntia sp.); whereas surrounding ber, these same xerophytic plants are present with the addition of sparse sagebrush, rabbitbrush (chrysothamnus sp.), ephedra (ephedra sp.), and several kinds of grass including great basin wild rye (leymus cinereus), indian ricegrass (oryzopsis hymenoides), and needle-and-thread grass (hesperostipa comata) requiring somewhat cooler temperatures and more moisture. small fauna in the area is characteristic of xeric-adapted species inhabiting the great basin desert including desert woodrat, various species of kangaroo rats (dipodomys spp.), black-tailed jackrabbit (lepus californicus), and cottontail (sylvilagus). the only artiodactyl spotted near the shelters today is pronghorn. the nearest water source is the freshwater springs that create the perennial marshes along the edge of the bonneville playa at blue lake about 4 km (2.5 mi) northeast of ses and 7 km (5.5 mi) east of ber. these marshes harbor a variety of waterfowl, particularly ducks. the bonneville and provo shorelines are prominent features in this part of eastern nevada, and the lake carved several east-facing caves and rockshelters in the region. the bonneville terrace formed some 18,000 cal yr bp due to increasing moisture and decreasing evaporation. the provo terrace formed between approximately 17,500 and 14,500 cal yr bp when the level of lake bonneville catastrophically fell from its high stand and then stabilized at this level for about 3000 years (oviatt, 2015). ber has been dry and open to terrestrial sediment deposition for the past 18,000 to 17,000 years, while ses has been dry and open for at least the past 14,000 years. we found faunal remains deposited by owls sitting directly atop provo beach gravels at ses. stratum 20 (heinrich 1) and stratum 19 (bølling-al174 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 lerød) at ber produced paleontological faunal remains although the lowest of these sediments near the bonneville high-stand beach gravels (stratum 21) were devoid of organics in the units excavated due to poor preservation conditions (figure 5). materials and methods in this paper, we report the findings of the paleontological remains recovered from ber during annual field schools held between 2000 and 2009 and from test excavations at ses in 2006. at ber the two lowest terrestrial strata above the lake bonneville gravels, designated 20 and 19 (figure 5), are paleontological. a description of the excavation strategy, plan view map of the area excavated within the shelter, and a representative stratigraphic profile can be found in graf (2007) and goebel et al. (2021). schmitt and lupo (2012, 2016) reported on the small rodent bones recovered from strata 20 and 19. hockett (2007, 2015) previously reported on the number of identified specimens (nisp) and minimum number of individuals (mni) of artiodactyls, carnivores, leporids (hare and cottontail), sage-grouse, and katydids throughout the younger dryas and holocene-aged strata (18-1). below we provide a final update to the values reported in hockett (2007, 2015), with an emphasis on the non-rodent heinrich 1 and bølling-allerød strata 20 and 19 fauna. as the ten-year field study of ber was in full swing, the elko field office of the u.s. department of interior, bureau of land management discovered that ses had been looted. the goals of the ses project were twofold: first, to determine the extent of damage done by earlier looting; and second, to evaluate the site’s significance for addressing important questions related to the early biogeographic history of the region. it was known to figure 2. bonneville estates rockshelter and surrounding terrain and vegetation, looking westward. 175 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 us that sites like ses might contain a wealth of biogeographic information. in the early 1990s a large collection of great horned owl (bubo virginianus) pellets from the surface of dondero shelter, near ber and ses (figure 1), served as an important set of proxy data to assist in distinguishing leporid bones modified and deposited on the landscape by owls versus humans (hockett, 1995). similarly, the surface of ses contained abundant raptor pellets, small bones exposed by degraded pellets, carnivore scats (visual inspection pointed to coyote [canis latrans]), and larger bones likely carried to the site by woodrats. we excavated two contiguous 1-m2 (3ft2) units in 5-cm (2-in) levels and screened all materials through 1/8” mesh. the units were designated n1w1 and n2w1 (figure 3). we excavated n1w1 to a depth of 160 cm (63 in) below datum (bd) where we encountered a large chunk of rockfall that prevented further excavation (figure 6). n2w1 was largely unencumbered by rockfall, and we were able to excavate it to a depth of 255 cm (100 in) bd where we encountered provo-aged lake bonneville beach gravels (stratum 9) devoid of organic remains (figure 6). the fauna reported here are from the paleontological levels of n2w1 between 138 and 255 cm (54–100 in) bd. we noted stratigraphic breaks during excavations at ses, and levels were ceased between identified strata. it was evidently clear during excavations that most bones were deposited via raptor pellets and carnivore scats. depending on the level excavated, most 5-cm (2-in) levels were dominated by small rodent, leporid, waterfowl, and fish bones that were stained and polished by gastric fluids, with raptor or carnivore puncture marks evident on some bones (andrews, 1990; schmitt and juell, 1994; hockett, 1995). the faunal analysis from both shelters focuses on those animals most sensitive to climatic change during the late pleistocene and early holocene. ironically, waterfowl bones were abundantly present at almost every level excavated in ses, so they were not good climatic indicators. most of the waterfowl bones were small ducks, particularly teal-sized ducks. great horned owls occasionally hunt these ducks and other larger waterfowl (voous, 1988, p. 85), and they are the likely depositor of their bones in pellets inside ses just as they were at homestead cave (broughton, 2000). we tallied waterfowl bones and they are reported below but are not discussed in detail. other species that we identified in low numbers that provided limited biogeographic information include the northern and southern pocket gophers (thomomys talpoides and thomomys bottae), pocket mice of the genus perognathus, several small carnivores including long-tailed weasel (mustela frenata) and badger (taxidea taxus), and the pallid bat (antrozous pallidus). these, along with notations of the presence of snake and raptor bones, are reported in footnotes and discussed as appropriate in the summary and discussion section below. we identified bones using known specimens housed at the natural history museum of the university of nefigure 3. (a) siblings west shelter (left) and siblings east shelter (right, white arrow and person present at the entrance), eastern nevada; (b) plan view map and location of test units excavated inside siblings east shelter. 176 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 vada, reno (unr), nevada state museum, carson city (nsm), the san bernardino county museum (sbcm), denver museum of nature and science (dmns), museum of the north, fairbanks, alaska (mon), university of kansas natural history museum (kunhm), and the author’s personal comparative collection (pcc). quantification per taxon was by nisp and mni for ber and nisp for ses. primary methods of species identifications were as follows: the equus sp. rib from ses was identified by direct comparison to a complete pleistocene equus specimen housed at nsm; sage-grouse bones were identified at the sbcm; sage vole mandibles were identified by the location of the mandibular foramen as described by grayson (1983) and by direct comparison to specimens housed at unr; kangaroo rat (dipodomys spp.) mandibles with teeth were identified by direct comparison to specimens housed at unr; the alveolar lengths of bushy-tailed woodrat (greater than 9.3 mm) and desert woodrat (less than 8.7 mm) mandibles were used to distinguish between these two species (grayson, 1985, p. 150; grayson, 1988, p. 21); the large canid bones from ber were measured and compared to gray wolf (canis lupus) and dire wolf (aenocyon dirus; perri et al., 2021) housed at the dmns, mon, and kunhm; we identified the artiodactyls and pygmy rabbit using the author’s pcc; spadefoot was identified using the author’s pcc and by consulting pugener (2010), jorgensen (2011), broughton and miller (2016), and gomez and turazzini (2016); we identified katydids via personal communication with nsm staff. finally, fish vertebrae were common in the lower levels of ses, but they were not identified beyond the general category “osteichthyes.” it is presumed that the fish were scavenged from the shoreline of the post-provo regressive phase of lake bonneville as owls such as bubo virginianus are not known to hunt fish directly from lake waters, so the presence of fish vertebrae in ses indicates fish die-offs east of the shelter along the receding shoreline. their disappearance in the shelter likely indicates the time at which lake levels could no longer support figure 4. the lush blue lake marshes along the western edge of the bonneville salt flats, looking northward. the leppy hills are in the background. the marsh was submerged by pleistocene lake bonneville until sometime after ca. 12,500 cal yr bp. 177 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 fish that inhabited deeper, colder, and less saline lake bonneville waters (broughton, 2000, p. 121; broughton et al., 2000). stratigraphy and dating we mapped 21 stratigraphic units at ber (graf, 2007; goebel et al., 2021). table 1 presents the beginning and ending dates of each stratigraphic unit based on the bayesian analysis in goebel et al. (2021). stratum 19 is most pronounced in the western part of the shelter and contains abundant sticks and other macrobotanical remains along with some bones (graf, 2007). it lies directly below the initial human occupation of ber designated as stratum 18. stratum 20, below stratum 19, primarily consists of silt, sand, and gravel with few organic remains save bones (figure 5). strata 19 and 20 are strictly paleontological. stratum 19 dates to the bølling-allerød interstadial, between 14,575 and 13,255 cal yr bp. the age of the stratum 20 sediments is bracketed by the timing of lake bonneville dropping below its high-stand and stratum 19. thus, stratum 20 was deposited between 17,500 and 14,575 cal yr bp. stratum 18 at ber represents repeated short-term occupations by human foragers and was deposited during the younger dryas stadial between 12,950 and 11,600 cal yr bp (table 1; figure 7). stratum 17b’ above stratum 18 is similar in character and dates to the first half of the early holocene between 11,600 and 10,500 cal yr bp. stratum 17 primarily consists of sterile silt and gravel and dates to the second half of the early holocene between 10,200 and 8475 cal yr bp. during this period of increasing warming in the western united states (palmer et al., 2023), ber was largely abandoned by human foragers. in contrast, the old river bed delta (figure 1) southeast of ber appears to have been intensively occupied between about 12,300 and 9500 cal yr bp due to favorable groundwater conditions that created productive marshland habitat (madsen et al., 2015; bradbury et al., 2020; palacios-fest et al., 2021; duke et al., 2022, 2024) following the transgression of the currey cycle between 12,700 and 12,400 cal yr bp (oviatt et al., 2024). nearby danger cave was also occupied during the early holocene abandonment period at ber, probably due to a reliable springhead in front of the site (rhode et al., 2006). strata 16-13 date between 8300 and 4900 cal yr bp and are a combination of natural sediment accumulations interspersed with shortterm human occupations during the generally warm and dry middle holocene. human occupation of ber intensified after about 5300 cal yr bp and saw repeated occupations until euroamerican contact. strata 12 and 11 represent a transitional period between the warm and dry middle holocene and the cooler and wetter late holocene, dating between 4900 and 4150 cal yr bp. stratum 10 was deposited during the early late holocene (palmer et al., 2023) between 4150 and 4025 cal yr bp. the neoglacial (millar and thomas, 2024) is represented by stratum 9, figure 5. lower sediment profile in the east block excavation area of bonneville estates rockshelter. the bonneville high-stand beach gravel and sand (stratum 21) are visible at the base of the profile. the two reddish-orange features near the top of the photograph are late pleistocene-aged hearths (stratum 18b). between stratum 21 and stratum 18b lie strata 20 and 19, the strictly paleontological sediments inside the shelter. 178 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 dating between 4025 and 2950 cal yr bp. the late holocene dry period (mensing et al., 2013, 2023) is represented by strata 8 through 5, dating between 2950 and 1830 cal yr bp. strata 4 and 3 were laid down during the medieval climate anomaly (mca) or medieval warm period (cook et al., 2004; mann et al., 2009) between 1830 and 840 cal yr bp. the mca witnessed drought conditions in the western great basin (stine, 1994) but generally warm and wet conditions in the eastern great basin (currey and james, 1982). finally, strata 2 and 1 represent the little ice age/modern climate (mann et al., 2009), dating between 535 and 25 cal yr bp. though the ses deposits represent a consistent deposition of owl pellets and carnivore scats, we mapped nine stratigraphic units during the excavations (figure 6; table 2). table 3 provides details of the stratigraphic profile from ses, including descriptive information from both n1w1 and n1w2. the upper sequence of strata in the profile, designated strata 6, 5, 4, 3b, 3a, 2, and 1, are predominantly archaeological in nature and will be described elsewhere. the paleontological strata detailed here above the lake bonneville beach gravels (stratum 9), from bottom to top, are designated as strata 8b, 8a, 7b, and 7a (basal two levels). owls and carnivores repeatedly occupied ses between about 14,300 and 9300 cal yr bp (table 2). we submitted organic samples to beta analytic and the university of georgia for sample preparation. regarding the bones, only samples from terrestrial animals (e.g., hares, marmots, artiodactyls) were used for radiocarbon dating, rather than mixing terrestrial-based and water-based (e.g., waterfowl, fish) bones for consistency. fauna appears to have been deposited shortly after lake bonneville’s regression from the provo shoreline standstill, generally dated between 15,000 and 14,000 cal yr bp (oviatt, 2015). ses radiocarbon dates suggest figure 6. log of the stratigraphic profile (north wall of 1 x 2-m [3 x 6 ft] excavation) and radiocarbon dates (cal yr bp) from siblings east shelter. 179 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 lake bonneville dropped below the provo terrace by about 14,300 cal yr bp. three radiocarbon dates indicate the lowest 25 cm (9.8 in) within stratum 8b (255 to 230 cm [100–90 in] bd), excavated in four levels, date to the bølling-allerød interstadial between 14,300 and 13,250 cal yr bp. the top of stratum 8b/base of stratum 7b (230 to 225 cm [91–100 in] bd) returned a radiocarbon date of about 12,700 cal yr bp near the beginning of the younger dryas. the transition from bølling-allerød to younger dryas is represented in the upper three levels of stratum 8b where dates indicate five to six centuries of very slow sedimentation and owl pellet/woodrat midstratum age range (cal bp) sage grouse pronghorn bison mnt. sheep deer hare cottontail pygmy rabbit katydid carnivora n 1 130 – 25 0 6(1) 1(1) 2(1) 0 0 0 0 0 0 9(3) 2 535 – 130 0 7(1) 2(1) 0 0 4(1) 0 0 0 2(1) 15(4) 3a 1400 – 840 0 33(1) 13(1) 9(1) 0 9(1) 0 0 0 0 64(4) 3b/4 1830 – 1,450 0 4(1) 0 1(1) 0 54(5) 0 0 0 0 58(7) 5 1850 – 1830 0 148(3) 0 1(1) 1(1) 40(4) 0 0 0 0 190(9) 6 2000 – 1850 0 1(1) 0 1(1) 0 0 0 0 0 0 2(2) 7 2250 – 2000 0 220(4) 2(1) 6(1) 1(1) 55(5) 1(1) 0 0 0 285(13) 8 2950 – 2250 0 10(1) 0 1(1) 0 3(1) 0 0 0 0 14(3) 9 4025 – 2950 0 20(1) 5(1) 2(1) 0 2(1) 0 0 0 1(1) 30(5) 10 4150 – 4025 0 0 0 0 0 4(1) 0 0 0 0 4(1) 11 4730 – 4150 3(1) 6(1) 2(1) 1(1) 1(1) 9(1) 5(1) 0 0 0 27(7) 12 4900 – 4800 0 3(1) 0 0 0 1(1) 0 0 0 0 4(2) 13 6400 – 4900 5(1) 8(1) 0 0 0 21(2) 6(1) 0 0 0 40(5) 14 7600 – 6400 21(2) 24(1) 0 8(2) 0 117(9) 53(4) 0 0 12(1) 235(19) 15 7700 – 7600 0 1(1) 0 0 0 1(1) 0 0 0 0 2(2) 16 8300 – 7700 2(1) 0 1(1) 0 1(1) 16(2) 2(1) 0 0 0 22(6) 17a,b 10,200 – 8475 0 0 0 0 0 0 0 0 0 0 0(0) 17b’ 11,600 – 10,500 90(5) 0 0 0 0 55(4) 284(19) 26(3) 0 2(1) 457(32) 18 12,950 – 11,600 516(13) 7(1) 1(1) 3(1) 1(1) 163(11) 338(24) 124(9) 21(21) 3(2) 1177(84) 19 14,575 – 13,255 17(2) 0 0 1(1) 0 33(2) 104(8) 16(2) 0 5(3) 176(18) 20 17,500 – 14,575 3(1) 1(1) 0 1(1) 0 51(4) 27(3) 4(1) 0 3(3) 90(14) n 657(26) 499(21) 27(8) 37(14) 5(5) 638(56) 820(62) 170(15) 21(21) 28(12) 2902(240) 1while most of the faunal remains suggest cultural modification and deposition, the small rodent assemblage (schmitt and lupo 2012) indicates that raptors occasionally deposited pellets inside the shelter. in this regard, one specimen of western screech owl (megascops kennicottii), one of great-horned owl (bubo virginianus), and four specimens of long-eared/short-eared owl (asio sp.) were recovered from stratum 18. 2raptors were likely also responsible for the deposition of the limited number of fish (pisces), teal/pintail-sized duck (anatidae), and long-tailed weasel (mustela frenata) bones. of the five fish bones recovered, one each was found in strata 20, 19, and 18, and two were found in stratum 14. of the 11 duck bones, four were found in stratum 18 and seven in stratum 17b’. of the five weasel bones, three were found in stratum 18, one in stratum 17b’, and one in stratum 16. 3eleven marmot (marmota flaviventris) bones were identified from the shelter. of these, five were found in the paleontological strata: two in stratum 20 and three in stratum 19. of the remaining six marmot bones, five were found in stratum 18 and one in stratum 14. there is no positive evidence that any of the marmot bones represent human food waste and may have been deposited in the shelter by one of the three mammalian carnivore species noted in footnote 4. 4in addition to the lepus, sylvilagus, and brachylagus bones identified, a total of 707 bones were identified as leporidae. these bones were primarily metapodials, phalanges, and skull fragments. most of these bones (552/707, or 78%) were recovered from strata 18 and 17b’. 5six species of mammalian carnivores were identified from the shelter. collectively they only account for a total of 28 bones. of these 24 specimens, 19 are bobcat (lynx rufus), two are badger (taxidea taxus), two are coyote (canis latrans), two are gray wolf/dire wolf (canis lupus/aenocyon dirus), two are dire wolf, and one is cougar/north american cheetah (puma concolor/miracinonyx trumani). of the 19 bobcat bones, one was found in stratum 20, two each in strata 19, 18, and 17b’, and 12 in stratum 14. some of the 16 bobcat bones recovered from strata 18, 17b’, and 14 could be the result of human trapping although none of these bones were burned, and none displayed cutmarks. one badger bone was recovered from stratum 19 and is therefore paleontological, and one was in stratum 9. both coyote bones were recovered from stratum 2. table 1. number of identified specimens (nisp) and minimum number of individuals (mni; parentheses) per stratum of the faunal remains and insects identified from bonneville estates rockshelter1-5. 180 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 den accumulation. a total of 55 cm (22 in) of sediment (230 to 175 cm [91–69 in] bd) was deposited during the younger dryas. we excavated these upper stratum 7b sediments in 11 levels and they are chronologically informed by four radiocarbon dates ranging between approximately 12,700 and 11,600 cal yr bp. the end of the younger dryas and the beginning of the early holocene appears to begin in the 175 to 173 cm (69–68 in) bd level. early holocene deposits are 27 cm (11 in) thick and were excavated in five levels, all within stratum 7b (175 to 148 cm [91–58 in] bd). we obtained four radiocarbon ages within these levels that match near the accepted ranges of the beginning and end of the early holocene between 11,600 and 9300 cal yr bp. the 148 cm (58 in) bd level near the base of stratum 7a corresponds with a 4000-year hiatus in owl pellet deposition between approximately 9300 and 5400 cal yr bp. given there was no stratigraphic change or erosional surface observed, depositional rates appear to have exceedingly slowed resulting from prolonged drought conditions. stratum 7a sediments are strictly paleontological between 148 to 138 cm (58–54 in) bd, and we excavated this 10 cm (4 in) block in two levels. between 6000 and 5000 cal yr bp marks a transitional climatic phase between the warmer and drier middle holocene that prevailed prior to this time and the overall cooler and wetter climate that prevailed after this time, with ber witnessing a resurgence in occupation by human foragers and ses witnessing initial occupation by humans coupled with a resurgence of visiting owls. humans began occupying ses periodically after the 138 cm (54 in) bd level within the upper part of stratum 7a, and their presence is recorded by cultural remains from stratum 6 to stratum 1 (figure 6). results table 1 lists the nisp and mni values for ber, and table 4 lists the nisp values for ses. extant species at ber there is a clear difference in biodiversity between strata 20 and 17b’ (pre-14,575 to 10,500 cal yr bp) and strata 17 through 13 (10,200 to 4900 cal yr bp). the heinrich 1, bølling-allerød, younger dryas, and first half of the early holocene (strata 20 through 17b’) are figure 7. profile of an unprepared pleistocene hearth from stratum 18, east block, bonneville estates rockshelter. the reddish-orange layer below the charcoal layer has been stained and hardened by heat. note two sage-grouse bones protruding from the charcoal layer to the left of the scale bar. charcoal from the hearth returned a date of 12,635 to 12,492 cal yr bp; 10,600 ± 40 14c bp. 181 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 stratum elevation (below datum) lab number conventional radiocarbon age (14c yr bp) calibrated age range (2 σ; cal yr bp) calibrated age (2 σ mean and error; cal yr bp) material dated notes 3a 57 beta-221279 190 ± 40 307-present 169 ± 89 hearth charcoal date first reported in coe (2020) 3b 65-70 beta-221280 2160 ± 40 2002-2310 2169 ± 87 cordage fragment date first reported in coe (2020) 3b 65-70 ugams-26684 4376 ± 25 4860-5037 4933 ± 47 woven mat date first reported in coe (2020) 5 100-105 beta-297413 4350 ± 40 4842-5041 4927 ± 59 point with binding date first reported in smith et al. (2013) 7a 115-120 ugams-26683 4499 ± 25 5047-5295 5164 ± 76 basket fragment date first reported in coe (2020) 7a 132 beta-221281 5260 ± 40 5929-6182 6049 ± 76 artiodactyl dung date first reported in coe (2020) 7a 138-143 beta-686311 4700 ± 30 5321-5572 5410 ± 66 lepus bone 7a 143-148 beta-689414 4400 ± 30 4862-5214 4971 ± 80 lepus bone end of middle holocene, beginning of transitional period; significant period of non-owl deposition of bones between about 10,500 and 5500 cal yr bp – essentially the entire middle holocene 7b 148-153 beta-686312 9190 ± 40 10,245-10,491 10,352 ± 69 artiodactyl bone 7b 153-163 beta-221282 8300 ± 90 9027-9481 9278 ± 122 artiodactyl dung last appearance of marmot; date first reported in coe (2020) 7b 163-168 beta-689413 10,020 ± 40 11,318-11,738 11,518 ± 113 lepus bone first appearance of southern (desert) pocket gopher 7b 168-173 beta-686313 9970 ± 30 11,264-11,613 11,412 ± 102 lepus bone first appearance of desert woodrat; bushytail and desert woodrats are sympatric 7b 173-175 first appearance of chisel-toothed kangaroo rat 7b 175-180 beta-686314 10,070 ± 40 11,398-11,813 11,601 ± 119 lepus bone end of younger dryas, beginning of early holocene; end of amphibians and pygmy rabbit 7b 180-185 7b 185-190 beta-660161 10,270 ± 30 11,824-12,429 11,991 ± 112 lepus bone last appearance of sage-grouse 7b 190-195 7b 195-200 last appearance of sage vole 7b 200-205 beta-689412 10,600 ± 30 12,496-12,707 12,630 ± 58 lepus bone few fish after this level 7b 205-210 7b 210-215 first appearance of ord’s kangaroo rat 7b 215-220 8a 220-225 beta-660159 11,930 ± 40 13,608-14,016 13,819 ± 106 equus bone equus rib* 8b 225-230 beta-221283 10,690 ± 50 12,620-12,746 12,693 ± 41 lepus bone beginning of younger dryas; date first reported in coe (2020) 8b 230-235 beta-660160 11,370 ± 30 13,175-13,309 13,244 ± 40 lepus bone end of bølling-allerød 8b 235-240 first appearance of bats 8b 240-245 beta-221284 11,560 ± 50 13,316-13,571 13,420 ± 56 artiodactyl dung first appearance of the sage vole and pygmy rabbit; date first reported in coe (2020) 8b/9 contact 245-255 beta-660162 12,310 ± 40 14,091-14,808 14,330 ± 204 marmota bone beginning of bølling-allerød; first appearance of bushy-tailed woodrat, marmot, deer/ canyon mouse, little pocket mouse, amphibians, fish, sage-grouse, and waterfowl 9 > 255 lake bonneville gravel; provo shoreline *this date is out of sequence and suggests that the final presence of extinct equus stratigraphically occurred more than a millennium earlier, during the time of lower stratum 8b. likely the bone was in a secondary context. table 2. radiocarbon dates and notable paleoecological events, siblings east shelter. 182 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 characterized by cool and mesic adapted animals indicating woodland habitat with an understory of mature sagebrush. these animals include sage-grouse, pygmy rabbit, and longwing katydid. while not overly abundant (mni = 7), pronghorn and mountain sheep were present near the shelter during the bølling-allerød and younger dryas, and bison and deer were present during the younger dryas as well. no artiodactyl specimens stratum 1: loose, poorly sorted, surface sediment of pale-brown (10yr 6/3) silt with abundant (40-80%) rounded, medium (<1-3 cm) gravels and common (5-15%) subangular cobbles and small boulders (10-30 cm). twigs and ungulate-sized dung are present. unit 1 measures 5-12 cm in thickness and forms a clear, smooth boundary at its base. archaeological materials are found in this stratum mixed with looters’ overburden. stratum 2: hardened light brownish-gray (10yr 6/2) silt with abundant (60-80%) dung. stone clasts are few to common (2-10%) with both subangular (4-20 cm) and rounded (≤3 cm) gravels and cobbles. unit 2 measures 10-22 cm in thickness and forms a clear, wavy lower boundary. archaeological materials are found in this stratum. stratum 3: unit 3a is a burn feature covering much of the northern half of the combined n1w1 and n1w2 excavation and consisting of charred, dark grayish-brown (10yr 4/2) silt in the lower <1-15 cm and light gray (10yr 7/1) ashy silt in the upper 2-10 cm. in total, 3a measures 2-20 cm in thickness and forms an abrupt, smooth boundary at its base. unit 3b is a very loose yellowish brown (10yr 5/4) silt and rubble zone measuring 5-40 cm in thickness. stone clasts are poorly sorted, common (5-15%) in number, mostly subangular with few (<5%) rounded gravels with most ranging from <1-5 cm. three bands, rich in vegetation and bone organics with thicknesses of 5-7 cm, 15 cm, and 1-5 cm, respectively, are present in the easternmost 75 cm of n1w1. boundaries between sublayers of 3b are clear and smooth. this sublayer contains several rodent burrows in the silt and rubble zone. the lower boundary of 3b is gradual and wavy. archaeological materials are found in this stratum. stratum 4: organic-rich (plant and bone debris) unit with poorly sorted brown (10yr 5/3) silt and rubble zone. stone clasts are common (5-15%), mostly subangular, but some are rounded. all clasts are <10 cm gravels. unit 4 measures 5-17 cm in thickness and has a gradual, wavy boundary with the underlying stratigraphic unit. archaeological materials are found in this stratum. stratum 5: unit 5 is a light yellowish-brown (10yr 6/4) silt. subangular to rounded stone clasts are common (5-15%) and medium-coarse (<1-6 cm in diameter) gravel-sized. this unit contains very little vegetation. it ranges from 3-13 cm in thickness, and its basal boundary is mostly abrupt and smooth except in the eastern corner which had a gradual boundary due to bioturbation. archaeological materials are found in this stratum. stratum 6: loose, grayish-brown (10yr 5/2) silt with few (2-5%) organics of plant and bone debris with many (~40-50%) subangular cobbles and small boulders (5-30 cm). rounded medium gravels (<2 cm) are very few (<2%) in the matrix. unit 6 ranges from 7-20 cm in thickness and has a clear, wavy boundary except for in the eastern corner of the excavation where the boundary is gradual due to heavy bioturbation. archaeological materials are found in this stratum. stratum 7: unit 7a is a gray-brown (10yr 5/2) silt with heavy, packed organic lenses containing mostly twigs and rodent-sized dung, but also present were small animal (e.g., bird, rabbit) bones, raptor-pellet fragments, shredded bark, and a few archaeological materials. subangular and rounded gravels are common (5-15%) and few (~2-5%) cobbles and small boulders (5-30 cm) are present. toward the east, organics disappear with only silt and rubble present. unit 7a measures 20-40 cm in thickness and generally forms a clear, smooth lower boundary. the eastern corner is bioturbated, blurring the boundary. unit 7b is a compact, brownish-yellow (10yr 6/6) silt, rubble, and organic zone. stone clasts size and quantity are same as 7a. organics consist of rodent dung, twigs, few small animal bones, and several concentrations of indurated sediment and organics, especially rodent dung. this sublayer is 85 cm thick with a clear, smooth lower boundary. stratum 8: this unit is subdivided into 8a and 8b. unit 8a is a dark yellowish-brown (10yr 4/6) silt, rubble and organic zone with common (5-15%) medium-coarse (<6 cm) subangular and rounded gravels. organics were twigs, rodent dung, and occasional indurated concentrations. it measures 7-10 cm in thickness and has a diffuse boundary with underlying 8b. unit 8b has the same characteristics of overlying unit 8a, but it is more compact, measuring 25-30 cm in thickness, and with a clear, smooth lower boundary. stratum 8/9 contact zone: brown (10yr 5/3) silt, rubble, and light organic (including rodent dung and twigs) zone to the base of the excavation. stone clasts are mixed subangular and rounded gravels. thickness is 5-8 cm. stratum 9: presence of well-rounded beach gravel with little fine sediment encountered below ~255 cm bd. table 3. descriptions of the siblings east shelter stratigraphic profile. 183 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 elevation (cm bd) calibrated age (2σ mean and error; cal yr bp) horse marmot sage vole chisel toothed k-rat ord’s k-rat pygmy rabbit bushy tailed woodrat desert woodrat sage grouse ducks/ geese fish spadefoot 138-143 5410 ± 66 1 3 20 143-149 4971 ± 80 1 1 27 148-153 10,352 ± 69 1 7 153-163 9278 ± 122 1 2 28 163-168 11,518 ± 113 2 7 168-173 11,412 ± 102 2 1 42 173-175 1 1 18 175-180 11,601 ± 119 1 31 1 180-185 4 25 185-190 11,991 ± 112 1 1 13 1 1 190-195 1 1 34 195-200 1 2 2 1 31 1 3 200-205 12,630 ± 58 1 1 1 53 3 8 205-210 1 3 1 63 15 12 210-215 1 2 1 79 13 7 215-220 1 42 28 9 220-225 1 7 2 1 66 31 225-230 12,693 ± 41 1 2 6 1 61 28 16 230-235 13,244 ± 40 1 7 6 1 58 38 13 235-240 1 7 2 1 73 28 9 240-245 13,420 ± 56 3 2 2 3 1 49 31 9 245-255 14,330 ± 204 3 1 1 43 39 17 > 255 provo gravels total nisp 1 9 5 1 3 29 41 7 12 870 256 105 1one specimen of long-tailed weasel (mustela frenata) was recovered from the 153-163 level. specimen identified from the author’s comparative collection. 2one specimen of pallid bat (antrozous pallidus) was recovered from the 143-149 level. specimen identified utilizing hermanson and o’shea (1983). 3one specimen of northern pocket gopher (thomomys talpoides) was recovered from the 153-163 level, and three specimens of southern pocket gopher (thomomys bottae) were recovered from the 153-173 levels, suggesting that both the warm-adapted t. bottae and cool-adapted t. talpoides were present in the vicinity of the shelter during the early holocene. specimens identified utilizing thaeler (1980). 4fifteen mid-trunk vertebrae representing the snake family colubridae are present between levels 230-235 and 148-153. all 15 vertebrae display hemal keels, or hypapophyses, and thus constrictors such as the rubber boa (charina bottae) within the family boidae that lack these structures (holman, 2000, p. 34; hollenshead 2002, p. 86) are not represented. additionally, one mid-trunk vertebra specimen of a rattlesnake (crotalus sp.) only appears in the 115-120 level dated to ca. 5100 cal yr bp. 5within the artiodactyls, two specimens of mountain or bighorn sheep (ovis canadensis) were identified in the 90-95 level dated to ca. 4300 cal yr bp, and one specimen of pronghorn (antilocapra americana) was identified in the 110-115 level dated to ca. 5000 cal yr bp. these three specimens were found within the human occupation levels of the shelter and thus may be cultural rather than paleontological. 6four specimens of little pocket mouse (perognathus longimembris) were recovered between the 245-255 level (ca. 14,500 cal yr bp) and the 210-215 level (ca. 12,500 cal yr bp). four specimens of peromyscus maniculates/crinitus (deer mouse/canyon mouse) are present between the 245-255 level (ca. 14,500 cal yr bp) and the 205210 level (ca. 12,500 cal yr bp). two specimens of microtus sp. (vole) were recovered between 153-173 levels, dating approximately 11,400 cal yr bp. 7two species of raptors were identified in the deposits. two specimens representing the prairie falcon (falco mexicanus) were identified in the 240-255 levels, thus dating to the bølling-allerød climatic phase. in addition, one specimen of a long-eared owl (asio cf. otus) was identified in the cultural zone in the 115-120 level dated to ca. 5100 cal yr bp. table 4. number of identified specimens (nisp) of the faunal remains recovered from the paleontological levels at siblings east shelter, nevada1-7. 184 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 were morphometrically identified from the earliest early holocene sediments (stratum 17b’), but based on the "artiodactyl-size" of unidentifiable large mammal bone fragments indicate that they were present at this time. most of the carnivore remains (mni = 9/12 or 75%) are from these early strata. additionally, the cottontail:jackrabbit ratio indicates cooler habitats than today surrounding the shelter. cottontails are generally indicative of cooler and more mesic habitats than jackrabbits in the great basin. of the 75 mni representing the genera sylvilagus and lepus, 72% (54/75) are cottontails in the strata dating pre-14,575 to 10,500 cal yr bp. in contrast, only four sage-grouse individuals and one carnivore are present in the sediments dating to the second half of the early holocene and the middle holocene (strata 17 through 13). the drop in sagegrouse numbers may indicate an expansion of more xeric-adapted vegetation at the expense of sagebrush habitat. also, pygmy rabbits and longwing katydids disappear and never return in the deposits, suggesting a lack of mature stands of sagebrush and a reduction in conifers. the cottontail:jackrabbit mni ratio drops to just 30% (6/20), again indicating a warmer climate in the region. artiodactyls are present in low numbers, but they are as abundant as they were in the earlier sediments representing cooler climate (mni = 6). overall, artiodactyls do not become relatively abundant compared to earlier climatic phases until the onset of the neoglacial, and this pattern continues through the late holocene dry period and the medieval climate anomaly. this 3500-year period (strata 12 through 3a) includes a minimum of 29 individual pronghorn, bison, mountain sheep, and deer deposited in these strata, perhaps due to increased human hunting targeting these species. turning to the faunal record from ses, as noted above, anseriformes (waterfowl) are present at all levels excavated. this may indicate that the lake dropped below the level of blue lake along the western edge of the bonneville flats within several centuries of its regression from the provo high-stand terrace. it could also indicate that ponds were available for waterfowl use in low-lying bowls or water catchments away from the shoreline. the bølling-allerød period at ses (14,300 to 13,250 cal yr bp) contains a wealth of mesic-adapted species. marmot, sage vole, pygmy rabbit, sage-grouse, fish, and spadefoot (figures 8 and 9) are all relatively common. in addition, all the woodrat mandibles are from bushytailed woodrats, and none are from desert woodrats (table 4). sage vole, pygmy rabbit, and sage-grouse all indicate mature stands of sagebrush grew in the vicinity of ses at this time. marmot and bushy-tailed woodrat indicate mesic boreal-type climate. spadefoot are present throughout much of nevada and the great basin today, but they, too, prefer sagebrush and woodland habitats, being found in higher elevations among spruce (picea spp.) and fir (abies spp.) forests (stebbins, 1962). they are also known to inhabit caves and rockshelters, as one of us (hockett) observed in july 2024, at the connley caves in south-central oregon (figure 9). the younger dryas period at ses (12,700 to 11,600 cal yr bp) contains all the mesic-adapted species found at the bølling-allerød levels except marmot. bushytailed woodrats are also the only woodrat species found in the younger dryas levels. however, there are indications that shifts in plant and animal biogeographies began during the later younger dryas. sage vole, pygmy rabbit, sage-grouse, fish, and spadefoot are either rare or disappear by the 190 to 185 cm (77–73 in) bd level, radiocarbon dated to about 12,000 cal yr bp. in addition, dipodomys ordii (ord’s kangaroo rat) enters the early younger dryas record by about 12,600 cal yr bp, while dipodomys microps (chisel-toothed kangaroo rat) first enters during the waning centuries of the younger dryas. grayson (2000) noted that chisel-toothed kangaroo rats generally become more abundant at homestead cave in relation to ord’s kangaroo rat post-pleistocene as climate warmed. d. ordii prefers sagebrush habitat while d. microps prefers more xeric shadscale habitat. major changes in biogeography occur after 175 cm (69 in) bd during the early holocene at ses. one marmot bone occurred in the early holocene levels (175 to 148 cm [69–58 in] bd), but sage vole, pygmy rabbit, sage-grouse, fish, and spadefoot all disappear from the record during the early stages of the early holocene between 11,600 and 11,400 cal yr bp. the absence of fish likely means the fish die-off in the remaining remnants 185 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 of pleistocene lake bonneville was complete along its former western shores. the disappearance of sage vole, pygmy rabbit, ord’s kangaroo rat, and sage-grouse signals the replacement of mature stands of sagebrush with warm, xeric-adapted plants. the disappearance of spadefoot probably indicates the disappearance of former woodlands in this low elevation area. finally, while bushy-tailed woodrats remain in lower numbers, desert woodrats appear for the first time approximately 11,400 cal yr bp. extinct species dire wolf (aenocyon dirus) (perri et al., 2021) and the north american cheetah-like cat miracinonyx trumani (orr, 1969) may be present at ber, and a large extinct horse comparable in size to equus occidentalis (leidy, 1865; azzaroli, 1998; heintzman et al., 2017) is present at ses. our excavations at ber recovered four large canid bones, one in stratum 20, two in stratum 19, and one in stratum 18. three of these bones are from the lower foot, specifically a phalanx, calcaneus, and astragalus. the fourth bone is a patella (figures 10 through 14). the phalanx recovered from stratum 18 may belong to the same individual as the calcaneus and astragalus recovered in stratum 19. the phalanx was burned (figure 10) and hockett (2007) previously identified it as a black bear (ursus americanus). the act of burning modified the size and morphology of the bone. further comparison to both bear and canid bones identified the bone as more likely belonging to a canid. the stratum 19/stratum 18 contact consisted of a concentration of figure 8. spadefoot (spea intermontana). (a) ilium, humerus, fused sacrum and urostyle, fused astragalus and calcaneus, radio-ulna, and tibio-fibula, stratum 8b, sisters east shelter, 245 to 255 cm (96–100 in) bd, 14,300 cal yr bp. (b) pelvis (ilium, ischium, pubis), humerus, fused sacrum and urostyle, fused astragalus and calcaneus, radio-ulna, and tibio-fibula, modern, eastern nevada. 186 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 burned sticks and twigs that we interpreted as inadvertently burned by a basal stratum 18 hearth that was built directly above the natural accumulation of sticks in stratum 19. the burned canid phalanx likely became charred during this process and was later retrieved in the basal stratum 18 sediments, although, as noted, it likely was originally deposited in the stratum 19 inadvertently burned wood feature. the canid calcaneus and astragalus from stratum 19 are unburned. lacking dna analysis, we re-identify the phalanx as cf. gray wolf/dire wolf (cf. canis lupus/aenocyon dirus). the remaining three canid bones are all too large to be coyote (canis latrans), and thus they are either gray wolf or dire wolf. although coyotes tended to be larger during the late pleistocene compared to their holocene descendants, they did not reach the size of gray wolves or dire wolves (merriam, 1912; meachen and samuels, 2012; tomiya and meachen, 2018). for example, measurements on the greatest length of a dire wolf femur from la brea reported in merriam (1912, p. 240) is 260 mm, whereas the mean greatest length of gray wolf femora from la brea is approximately 225 mm (tomiya and meachen, 2018). in contrast, meachen and samuels (2012) report that the mean greatest length of coyote femora at la brea is approximately 185 mm. similarly, the mean greatest breadth of the distal femur where the patella is located for pleistocene-aged gray wolves and coyotes at la brea are approximately 42 mm and 30 mm, respectively (meachen and samuels, 2012; tomiya and meachen, 2018). the large canid patella is worn and would have been larger during the life of the animal (figure 11). even in its worn condition, it is significantly larger than the modern gray wolf patellae we examined, so it is very unlikely to be from a coyote. nevertheless, dire wolves are known to vary in size between eastern and western north american specimens, and there is size overlap between dire wolves and some modern gray wolves from northern habitats (anyonge and roman, 2006). like the canid phalanx, we conservatively identify the patella as gray wolf/dire wolf (canis lupus/aenocyon dirus). the calcaneus and astragalus are exceptionally well preserved and offer greater confidence in a morphological identification. the calcaneus and astragalus are similar in size to specimens of modern gray wolf curated at the dmns (figures 12 and 13), and the stratum 19 specimen is considerably less robust than a complete calcaneus of aenocyon dirus from carrol cave, missouri (kunhm-72521) (figure 14). the ber calcaneus measures 62 mm in length and 25 mm in maximum breadth, whereas the carrol cave dire wolf calcaneus measures 69.6 mm in length and 27.7 mm in maximum breadth. nevertheless, two morphological features noted on the carrol cave aenocyon dirus calcaneus are not shared by the modern gray wolf calcanei examined, and these same features are shared by the ber specimen. first, the posterior facet is round in the ber and carrol cave aenocyon dirus calcanei but noticeably oval in the modern canis lupus calcanei. second, the distal ends of the ber and carrol cave dire wolf calcanei are convex whereas the modern gray wolf specimens display straight distal ends (figures 12 and 14). no distinct features were noted between the ber and modern gray wolf astragali. the ber calcaneus and astragalus were found lying next to one another and undoubtedly befigure 9. the great basin spadefoot (spea intermontana) recently photographed in the connley hills, oregon. among other microhabitats, spadefoots inhabit and burrow inside caves and rockshelters. 187 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 long to the same individual. we conclude that the large canid calcaneus and astragalus from stratum 19 at ber probably belong to a dire wolf rather than to a gray wolf and tentatively identify them as cf. aenocyon dirus. future dna analysis may produce a final resolution. if the identification of aenocyon dirus is correct, this places the dire wolf along the western margin of the bonneville basin in nevada between 14,575 and 13,255 cal yr bp. dire wolves went extinct approximately 13,000 cal yr bp (peri et al., 2021). the felid central phalanx from stratum 20 at ber is too large to be either bobcat (lynx rufus) or lynx (lynx canadensis). it is either from the extinct north american “cheetah” (miracinonyx trumani) or the cougar/ mountain lion (puma concolor). miracinonyx and the african cheetah (acinonyx jubatas) are not closely related although some of their bones are similar due to convergent evolution (morgan and seymour, 1997; hockett and dillingham, 2004). the extinct north american “cheetah” is instead more closely related to the north american cougar/mountain lion (barnett et al., 2005). comparing the ber felid phalanx to several modern cougar and african cheetah specimens (the latter for illustrative purposes only) curated at dmns (figure figure 10. canid phalanges. (a) aenocyon dirus, carrol cave, missouri (kunhm-72521). (b) stratum 18/19, bonneville estates rockshelter. (c) aenocyon dirus, carrol cave, missouri (kunhm-72521). 188 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 15) as well as a direct comparison to specimens of miracinonyx trumani from natural trap cave, wyoming (figure 16), indicates that the worn specimen from ber could identify with either puma or miracinonyx. if the ber specimen is miracinonyx, then this places a date on the phalanx of a north american “cheetah” between 17,500 and 14,575 cal yr bp. in 2024 the ber felid phalanx was sent to the max planck institute in germany to attempt a direct ams date and to determine if zooms (zooarchaeology by mass spectrometry) (buckley et al., 2009; antonosyan et al., 2024) could provide a definitive identification. the results of this analysis are not yet complete and will be reported at a later date. the only extinct fauna present at ses is a horse rib from stratum 8a (figure 17). the rib matches in size and morphology to a large pleistocene-aged horse rib curated at the nsm, and thus we infer that it belongs to equus rather than to the smaller ‘stilt-legged’ horse harringtonhippus (formerly equus conversidens) (heintzman et al., 2017). the rib was directly dated to the bølling-allerød at approximately 13,800 cal yr bp. summary and discussion heinrich 1 stadial 18,000 to 14,700 cal yr bp bones began accumulating in ber prior to 14,575 cal yr bp (goebel et al., 2021); however, no bones have been dated yet from the corresponding older stratum 20 sediments. we assume stratum 20 began accumulating shortly after lake bonneville dropped below its high-stand terrace during the bonneville flood episode estimated at 17,500 cal yr bp (oviatt, 2020, p. 309), so bones recovered from stratum 20 date between the onset of the bonneville flood and the earliest date from overlying stratum 19, or between 17,500 and 14,575 cal yr bp. thus, with the accepted beginning of the bølling-allerød at 14,700 cal yr bp (naughton et al., 2023b), most bones from stratum 20 at ber date to the heinrich 1 stadial (18,000 to 14,700 cal yr bp; naughton et al., 2023a), the beginning of which roughly correlates with the timing of the bonneville flood. the presence of sage-grouse and pygmy rabbit from stratum 20 suggests an understory of mature stands of sagebrush grew near ber during heinrich 1. pronghorn and mountain sheep foraged in the hills surrounding the shelter. interestingly, jackrabbits slightly outnumber cottontails. likely the primary hare species at this time was the white-tailed jackrabbit (lepus townsendii) rather than the black-tailed jackrabbit (lepus californicus). while both species can be found in open grassy or sagebrush covered habitat, white-tailed jackrabbits are known to also inhabit more montane settings including coniferous forests, subalpine meadows, and even figure 11. canid patellae. (a) stratum 20 (#15377), bonneville estates rockshelter. (b) modern adult female canis lupus (dmns #10939). (c) modern adult male canis lupus (dmns #8141). (d) modern adult female canis lupus (dmns #7731). 189 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 the alpine zone above tree line (lim, 1987). montane, mesic, or sagebrush-adapted small mammals also include marmot, sage vole, bushy-tailed woodrat, and northern pocket gopher (thomomys talpoides) (schmitt and lupo, 2012, p. 99). one fish vertebra from stratum 20 suggests scavenging of fish carcasses along the lake shore by raptors or carnivores. carnivores hunting in the area included bobcat as well as a large canid (either aenocyon dirus or canis lupus), and a large felid (either miracinonyx trumani or puma concolor). rhode and madsen (1995) reported on the macrobotanical contents of two heinrich 1-aged woodrat middens in an alcove next to ber. the “be 1a” and “be 4b” middens date to approximately 16,550 cal yr bp (13,820 ± 90 14c bp; beta-70607) and 15,630 cal yr bp (12,810 ± 70 14c bp; beta-76179), respectively (rhode and madsen, 1995, p. 248). the vegetation surrounding the shelter at this time conforms to the faunal species present. montane shrub vegetation dominated the midden sample. big sagebrush (artemisia tridentata), snowberry (symphoricarpos sp.), prostrate juniper (juniperus communis), cinquefoil (potentilla sp.), currant (ribes sp.), and the thistle cirsium cf. eatonii all indicate open montane shrubby vegetation dominated the hills surrounding ber, although minor amounts of limber pine needles indicate some woodland habitat. within this montane environment, however, two plants typically found in xeric-adapted settings today are present, rabbitbrush (chrysothamnus viscidiflorus) and horsebrush (tetradymia sp.). figure 12. canid calcanei. (a) stratum 19 (#21096), bonneville estates rockshelter. (b) modern adult female canis lupus (dmns #10939). (c) modern adult male canis lupus (dmns #8141). (d) modern adult female canis lupus (dmns #7731). 190 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 bølling-allerød interstadial 14,700 to 12,900 cal yr bp stratum 19 at ber dates between 14,575 and 13,255 cal yr bp (goebel et al., 2021). for ses, a radiocarbon date is available for the initial 10 cm (4 in) of terrestrial deposit lying directly above the provo terrace beach gravels. this date, 12,310 ± 40 14c bp, has a calibrated age of 14,330 ± 204 cal yr bp (reimer et al., 2020; oxcal, 2024). if lake bonneville fell from the provo terrace approximately 14,500 cal yr bp (oviatt and pedone, 2024, p. 34), then owls began occupying ses within just a few centuries of it being dry. in any case, the estimated 14,300 cal yr bp date demonstrates the regression of lake bonneville from the provo terrace in the western bonneville basin had occurred by that time. fauna present in the bølling-allerød sediments at ber and ses are like the preceding heinrich 1 period with montane and mesic-adapted animals dominating the samples. sage-grouse, pygmy rabbit, sage vole, marmot, bushy-tailed woodrat, and northern pocket gopher are all present. mountain sheep is the only artiodactyl recovered from either shelter. in contrast to the heinrich 1 fauna, cottontails outnumber jackrabbits 4:1 at ber. owls hunted waterfowl near ses, perhaps along the lake bonneville shoreline and from inland small ponds or lakes near the shelters. owls or perhaps the prairie falcon (falco mexicanus) captured spadefoot amphibians, as a prairie falcon bone was identified at ses. owls also scavenged fish carcasses along the shoreline of the lake. carnivores present include bobcat, badfigure 13. canid astragali. (a) stratum 19 (#20703), bonneville estates rockshelter. (b) modern adult female canis lupus (dmns #10939). (c) modern adult male canis lupus (dmns #8141). (d) modern adult female canis lupus (dmns #7731). 191 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 ger, and cf. aenocyon dirus. an extinct large horse of the genus equus roamed the hills near the shelters. vegetation growing in the area is informed by a woodrat midden collected from a shelter between ber and ses. the “ps 1” midden dates between 13,650 and 13,580 cal yr bp (11,830 ± 70 14c bp; beta-68146) (rhode and madsen, 1995, p. 249). there is a shift apparent from heinrich 1 times, with rhode and madsen (1995, p. 250) describing the vegetation in the region as a “limber pine woodlands and woodland/steppe mosaic.” limber pine trees are more apparent compared to the heinrich 1 middens, while sagebrush, prostrate juniper, and snowberry continue to be present along with rabbitbrush and horsebrush. not present in the bølling-allerød sample are cinquefoil, currant, and the thistle cirsium cf. eatonii. newcomers to the landscape include the prickly pear cactus opuntia, indian ricegrass (oryzopsis hymenoides), and knotweed (polygonum sp.). overall, the fauna and flora suggest a rather cold and dry climate. younger dryas stadial 12,900 to 11,700 cal yr bp both shelters continued to accumulate bones throughout the younger dryas stadial. sagebrush continues to be a major shrub component in the area as sage-grouse, sage vole, and pygmy rabbit, as well as ord’s kangaroo rat are all present. bushy-tailed woodrats and marmots continue their presence, and cottontails outnumber jackrabbits by a 2:1 margin at ber, suggesting mesic, montane conditions. new species hitherto absent from the shelters include the longwing katydid capnobotes occidentalis and homo sapiens at ber. the presence of human foragers explains the katydids inside ber and probably explains the expanded presence of artiodactyls including pronghorn, mountain sheep, bison, and deer at ber. it is possible that the population sizes of these smaller artiodactyls increased following the extinction of megafauna and large carnivores in the bølling-allerød or early younger dryas. carnivores include the long-tailed weasel (mustela frenata) and bobcat. three types of owls are present at ber: the western screech owl (megascops kennicottii), great horned owl (bubo virginianus), and long-eared/short-eared owl (asio sp). these raptors continued to hunt waterfowl and scavenge fish in the area, also depositing their bones inside ses. extinct animals are absent in the younger dryas-aged sediments from both shelters. the presence of waterfowl in the ses record and their near absence in the ber record may reflect the relative proximity of ses to the marshes at blue lake. the absence of humans at ses during the younger dryas may reflect the small size and rather secluded nature of that rockshelter compared to ber. rhode and madsen (1995, p. 249, table 1) examined one fossil woodrat midden labeled “be 3a” from the younger dryas and dated to approximately 12,900 cal yr bp (11,020 ± 60 14c bp; beta-76178). the midden was in an alcove next to ber. rhode and madsen (1995, p. 251) describe the vegetation patterning in this midden as “sagebrush-shadscale scrub,” suggesting a cooler figure 14. (a) aenocyon dirus calcaneus, carrol cave, missouri (kunhm-72521). (b) stratum 19, bonneville estates rockshelter. 192 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 and more mesic environment than today but one that is becoming increasingly xeric. sagebrush is present but limber pine and prostrate juniper needles are rarer than in the bølling-allerød-aged midden. overall, the midden is dominated by sagebrush, shadscale (atriplex confertifolia), horsebrush, rabbitbrush, and snakeweed (guiterrezia sp.). early holocene 11,700 to 9300 cal yr bp both shelters witnessed bone deposition during the early holocene between 11,700 and 9300 cal yr bp, but this was not an even process across the entire period. at ber, the first one-half of the early holocene was geologically discernible through the deposition of stratum 17b’ radiocarbon dated between 11,700 and 10,500 cal yr bp. human foragers deposited most of this faunal debris inside the shelter. sage-grouse and pygmy rabbit are present suggesting the continued existence of sagebrush in the area, but their bone numbers dwindle compared to the number deposited during the younger dryas, and both species disappear between 10,200 and 8475 cal yr bp, during the deposition of stratum 7 at ses. no sage voles are present. cottontails far outnumber jackrabbits (5:1) prior to 10,500 cal yr bp then disappear entirely between 10,200 and 8475 cal yr bp at ber. cottontails similarly disappear from the camels back cave record approximately 9000 cal yr bp (schmitt et al., 2002, p. 89). no identifiable artiodactyls or katydids are found at ber between 11,600 and 8475 cal yr bp. humans, too, are for the most part absent from ber by 10,500 cal yr bp (goebel et al., 2021). instead, the entire early holocene sediments at ber become dominated by desert woodrats (schmitt and lupo, 2012), and the desert woodrat enters the ses record for the first time about 11,400 cal yr bp, not surprising given ses’s lower elevafigure 15. felid central phalanges. (a) stratum 20 (#15355), bonneville estates rockshelter. (b) modern adult male puma concolor (dmns #11070). (c) modern adult male puma concolor (dmns #11070). (d) modern african cheetah acinonyx jubatas (dmns #1689). 193 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 tion. bobcat and long-tailed weasel were present prior to 10,500 cal yr bp at ber. owls continued to deposit bones inside ses during the early holocene; however, it is a depauperate fauna including single bones of marmot and the xeric-adapted kangaroo rat dipodomys microps. there is, therefore, a clear indication of a deteriorating and exceedingly xeric environment in the region during the early holocene. at ber, a combination of mesicand xeric-adapted fauna persisted between 11,600 and 10,500 cal yr bp, although it was diminished compared to the heinrich 1, bølling-allerød, and younger dryas faunas. between 10,500 and 8475 cal yr bp humans and nonhuman animals alike largely abandoned the shelter. this pattern is starkly evident at ses where the sediments display a nearly 4000-year gap in time and very slow deposition between about 9300 and 5000 cal yr bp. the shelter appears to have been abandoned by raptors and other animals and sedimentation rates support hot and dry conditions limiting the deposition of sediment and bones during this period. conclusion and implications for early human settlement in the bonneville basin among the earliest evidence for human settlement in the bonneville basin is found at ber during the boundary of the bølling-allerød interstadial and the younger dryas stadial (goebel et al., 2021). humans entering the basin during the early heinrich 1 stadial (18,000 cal yr bp) would have encountered a nearly 300-m-deep (900-ft) lake bonneville that stretched west-to-east from the foothills of the goshute mountains in nevada to the wasatch range in utah. along the western fringes of the lake, near ber and ses, a diverse suite of cool-adapted, now-extirpated or extinct plants and animals, along with many extant species, were available to these as-yet-to-be-identified human foragers. this lake would have been relatively shortlived, as humans living in the basin 17,500 years ago likely would have witnessed the catastrophic drop in lake bonneville to the provo terrace. nevertheless, a figure 16. felid central phalanges. (a) stratum 20, bonneville estates rockshelter. (b) miracinonyx trumani from natural trap cave, wyoming (kunhm unnumbered). 194 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 still-formidable 200-m-deep (700-ft) lake stabilized for 3000 years, continuing to span from the foothills of the goshute mountains to the wasatch range. human foragers in the western bonneville basin during the early bølling-allerød interstadial (14,700 cal yr bp) would have witnessed even greater changes to the lake and its surrounding environs. lake bonneville’s regression from the provo terrace began by 14,300 cal yr bp and perhaps as early as 14,500 cal yr bp, with the lake dropping in elevation to near-modern great salt lake levels relatively quickly thereafter (oviatt, 2015). only minor shifts in plant biogeography are documented in the western bonneville basin compared to heinrich 1 (rhode and madsen, 1995), and the animals inhabiting the landscape near ber and ses also did not undergo major changes in kind or distribution indicating relatively cool conditions prevailed despite the drop in lake levels. the earliest well-dated context for human occupation of the western bonneville basin is at ber beginning at the transition to the younger dryas (12,900 cal yr bp) (goebel, 2007; graf, 2007; hockett, 2007, 2015; goebel et al. 2011, 2021), and soon thereafter humans appear at nearby danger cave and the old river bed delta (rhode et al., 2005; duke et al., 2022, 2024). humans likely witnessed the resurgence of a relatively shallow 15-m-deep (50-ft) lake that once again spanned from the nevada-utah border to present-day salt lake city (oviatt et al., 2024). during this early younger dryas-aged transgression, the blue lake marshes near ses and ber, as well as the old river bed delta to the southeast became submerged underwater and devoid of marshes and the diverse plants and animals that they harbor (louderback and rhode, 2019; palacios-fest et al., 2021; oviatt et al., 2024). ber and ses, in contrast, remained high and dry and open for habitation. ironically, however, human foragers chose to repeatedly occupy ber throughout the younger dryas while no such occupation is similarly documented at ses. this is probably due to ber being a much bigger shelter situated along a major wash draining a large area of the goshute mountains and foothills, in contrast to ses, which is in a locally draining, lower-elevation wash. human foragers hunted a diverse suite of large and small mammals, terrestrial birds (sage-grouse), and insects around ber in the foothill slopes above the currey cycle lake (hockett, 2007, 2015). around 12,300 cal yr bp, when the lake dropped in elevation again, reaching below the old river bed delta and blue lake, re-establishing their marshes, human foragers probably made forays between ber and the delta allowing them to add a diverse suite of waterfowl (duke et al., 2022) to their already diverse diet of terrestrial animal resources being consumed at ber for the previous six centuries. ironically, ses is between ber and the old river bed delta, not to mention about half the distance to the blue lake marsh, yet humans eschewed using the site as a domestic camp. we found no evidence for humans processing waterfowl carcasses inside ses or ber. if they figure 17. equus rib from siblings east shelter. the bone was directly dated to 13,819 ± 106 cal yr bp. 195 faunal extirpations, range shifts, and extinctions in the western bonneville basin, 17,500 to 5500 cal yr bp—paleobiogeography of bonneville estates rockshelter and siblings east shelter hockett, b., goebel, t., and graf, k. geology of the intermountain west 2025 volume 12 were hunting these birds at blue lake, such processing sites are more likely buried there in open-air contexts and remain undiscovered. the younger dryas pattern of hunting terrestrial and aquatic animal resources continued during the first half of the early holocene between 11,700 and 10,500 cal yr bp. due to deteriorating conditions caused by increasingly warmer, and perhaps drier climate, humans largely abandoned ber by 10,500 cal yr bp, and their 2500-year history of consuming a diverse suite of terrestrial resources in the foothills of the goshute mountains came to a halt. nonetheless, human foragers were able to continue to exploit marsh resources at the old river bed delta for the next millennium, until approximately 9500 cal yr bp (madsen, et al., 2015; duke et al., 2022). the overall warm and dry middle holocene that commenced by 9300 cal yr bp in the eastern great basin saw human foragers largely abandon both ber and the old river bed delta in favor of places on the landscape that still provided reliable sources of water such as danger cave to the north and hogup cave to the northeast. ses does not contain a viable biogeographic record during most of the middle holocene, specifically between 9300 and about 5000 cal yr bp. the ses stratigraphic record documents a 4000-year hiatus of owl pellet and sediment deposition with no clear evidence of an erosional event. during this time, however, ber was periodically occupied by human foragers (hockett, 2007, 2015; goebel et al., 2021), including a brief occupation that corresponds to the 8200 cal yr bp (8.2 ka) global cooling event in the north atlantic (alley and agústsdóttir, 2005; schmidt and legrande, 2005) and another longer-term series of occupations between 6400 and 4900 cal yr bp (goebel et al., 2021), the latter being associated with a late middle holocene transitional period of increased moisture (hockett, 2007). ses, too, began seeing humans visiting the shelter for the first time at about 5500 cal yr bp. humans repeatedly occupied both ber and ses thereafter until euroamerican contact with relatively brief periods of non-occupation, such as the 550-year span of non-occupation at ber associated with the late holocene dry period (goebel et al., 2021). acknowledgments funding for the excavations in bonneville estates rockshelter and siblings east shelter was provided by the bureau of land management, nevada; university of nevada, reno; and the first americans professorship at the center for the study of the first americans, texas a&m university. for access to museum and other specimens that assisted in the identification of faunal remains we thank chris feldman and ally coconis (university of nevada, reno, natural history museum), mike cox, christy klinger, jeff petersen, and chris crookshanks (nevada department of wildlife), anthony miller (miller bison, llc), scott shirar and joshua reuther (museum of the north, fairbanks, alaska), eric scott (former curator of paleontology, san bernardino county museum), john demboski (denver museum of nature and science), and chris beard and megan sims (university of kansas, natural history museum). although bryan hockett took the photographs of the bones, figures 8 through 17 were created by beth potter (university of kansas). besides the authors, lisbeth louderback, tim murphy, and sergey vasil’ev (russian academy of sciences, st. petersburg) participated in the fieldwork at the four siblings shelters in 2006. many thanks for their hard work. we thank greg mcdonald (bureau of land management), emily lindsey (la brea tar pits museum), david madsen (university of nevada, reno), and david rhode (desert research institute) for their reviews and comments which improved the manuscript. thank you also to rachel delovio (nevada state museum) and rolfe mandel (odyssey program, kansas university) for their support. references alley, r., and agústsdóttir, a., 2005, the 8k event—cause and consequences of a major holocene abrupt climate change: quaternary science reviews, v. 24, p. 1123–1149. andrews, p., 1990, owls, caves and fossils: chicago, university of chicago 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journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover tidwell member of the morrison formation (gray bed) between the underlying summerville formation and sandstone beds of the salt wash member of the morrison formation. woodside anticline, emery county, utah. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 9 2022 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2021–2022 uga board president john south john.south@dominionenergy.com 385.266.2113 president-elect rick ford rford@weber.edu 801.915.3188 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 co-program chair ben gilder dgilder@gmail.com 337.962.8383 treasurer kellen gunderson kellen@zanskar.us 801.634.9737 secretary eugene syzmanski eugenes@utah.gov 801.537.3364 past president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 uga committees environmental affairs craig eaton eaton@ihi-env.com 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giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 9 2022 49 abstract the tidwell member, a lithostratigraphic unit on the colorado plateau, has variously been referred to the upper jurassic morrison formation or the upper jurassic summerville formation. its authorship has been ascribed to u.s. geological survey geologists robert b. o'sullivan or fred peterson. because peterson and o'sullivan have different type sections, a resolution to authorship is needed. both authors meet the minimum requirements for a new stratigraphic unit as given by the 1983 north american stratigraphic code under which peterson and o'sullivan operated. however, both authors also operated under the more restrictive stratigraphic nomenclature in reports of the u.s. geological survey, which makes it clear that o'sullivan used tidwell member informally, whereas peterson made a formal proposal. thus, peterson is the rightful author and the type section is at shadscale mesa, emery county, utah. to resolve the issue of which formation the tidwell member belongs, its strata were examined across the northern colorado plateau in context with both the underlying marine summerville formation and the overlying terrestrial salt wash member of the morrison formation. meters-thick gypsum beds, one criterion for including the tidwell member in the summerville, was found to be mostly restricted to the west side of the colorado plateau. numerous low-angled anticlines at the top of the summerville formation are truncated beneath this gypsum, thus the gypsum beds cannot be part of the summerville formation. the unconformity marks the j-5 unconformity. detailed analysis of the gypsum beds shows a complex origin indicative of smaller playa lakes rather than broad coastal sabkhas. the gypsum beds show an interfingering relationship with the overlying and lateral interbedded thin sandstone-siltstone-mudstone-limestone facies assemblage of the tidwell member. this relationship is interpreted as localized gypsum playa lakes that formed at the terminus of prograding fluvial fans from the elko highlands to the west, with possible lesser contribution from the growing fluvial fan exiting from the grand canyon bight near the present-day arizona-nevada border. an isopachous map of the tidwell member supports this interpretation, and also indicates additional, less significant source areas to the southeast and east of the northern colorado plateau. a widespread tabular sandstone at the base of the tidwell member lateral to the gypsum facies known as bed a, is interpreted to have originated mostly as a sand sheet analogous to the selima sand sheet of the eastern sahara or the sand sheet of the gran dieserto in sonora, mexico. the source of the sand is from the fluvial fans to the west. similarities between the lithofacies of the contemporaneous tidwell and ralston creek members of the morrison formation indicates deposition under similar environmental conditions. this supports the inclusion of the ralston creek member in the morrison formation as previously suggested, rather than as a separate formation. the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? kenneth carpenter museum of natural history, university of colorado, boulder, co 80302; kenneth.carpenter-1@colorado.edu citation for this article. carpenter, k., 2022, the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when?: geology of the intermountain west, v. 9, p. 49–114, https://doi.org/10.31711/giw.v9.pp49-114. © 2022 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 50 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 introduction the upper jurassic morrison formation is widely distributed on the colorado plateau and has been divided into several members that are listed in the national geologic map database (lexicon; https://ngmdb. usgs.gov/geolex/search; * accepted names by the u.s. geological survey [usgs]): *bluff sandstone, *brushy basin, casamero, *chavez, *fiftymile, *jackpile sandstone, *prewitt sandstone, *recapture, *salt wash, *tidwell, and *westwater canyon. off the plateau, six other members are known: boise, cimarron, kenton, ralston creek, *windy hill, and *unkpapa sandstone (figure 1); those in oklahoma were recently named by richmond and others (2020) (figure 1), and their acceptance by the geological community as required by the north american stratigraphic code (north american commission on stratigraphic nomenclature [nacsn], 2021, article 5, remark (a)) is not yet known. nor is acceptance yet known for the ralston creek member, which was formerly a formation below the morrison formation in eastern colorado (carpenter and lindsey, 2019). however, not all of the members are universally accepted as lithostratigraphic units of the morrison formation. the bluff sandstone is considered as a formation in the san rafael group by some authors (e.g., anderson and lucas, 1992, 1995; lucas, 2014), along with the recapture and salt wash members (anderson and lucas, 1994, p. 312; this position was reversed in anderson and lucas, 1995), but these positions were not accepted by others (e.g., turner and peterson, 2004; see further discussion on this issue by kirkland and others, 2020). the windy hill is considered as a member of the morrison formation by some (e.g., sprinkel and others, 2019), as a member of the sundance formation (e.g., trujillo and kowallis, 2015), or as a distinct lithostratigraphic unit (holland and wright, 2020). the most controversial member of the morrison formation is the tidwell because of two contradictory issues: (1) who first named the tidwell member and (2) to which formation does it belong. these two controversies about the tidwell member are examined below in attempted resolutions. methods as part of the investigation into the naming of the tidwell member of the morrison formation, unpublished reports and maps created between 1951 and 1970 were among the documents examined. these particular documents are part of the 2700+ “gray literature” on the geology and occurrences of radioactive ores prepared between 1945 and 1981 by the grand junction office of the u.s. atomic energy commission (aec), the u.s. department of energy (doe), and bendix field engineering corporation on behalf of the aec or doe (johnson, 1981; doelling, 1983; u.s. geological survey open-files service section, 1984). many of these documents are available online: mountain scholar open access repository: https://mountainscholar.org/; national geologic map database: https://ngmdb.usgs.gov/ ngmdb/ngmdb_home.html; university of north texas digital library: https://digital.library.unt.edu/; u.s. department of energy office of scientific and technical information: https://www.osti.gov/pages/; u.s. geological survey publications warehouse: https://pubs.er.usgs. gov/. some of the gray literature was subsequently published either in part or in whole. for example, craig and others (1955) is the declassified craig and others (1951), and mullens and freeman (1957) is mullen and freeman (1954), which is based on their contribution in the craig and others (1951) report, but with some differences (e.g., details of the isopachous maps). the accompanying cover letter with mullens and freeman (1954) report requested approval for publication in the bulletin of the geological society of america, but security clearance delayed publication until 1957. field work for this project was conducted across the northern part of the colorado plateau in utah and colorado. outcrops of the summerville formation and its lateral equivalent wanakah formation, and the tidwell member of the morrison formation were examined, photographed, measured, and sampled. hand samples were cut and surfaces polished to reveal lithology and texture. select samples of gypsum were dissolved with hot hydrochloric acid or a solution of sodium citrate for recovery of detrital minerals (mostly silicate grains). to gain a better understanding of a natural gypsum depositional environment, the salt flat, which straddles the eastern new mexico and west texas border was examined and several pits excavated to see the subsurface deposits. salt flat covers approximately 9495 km2 and 51 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 is a playa complex containing approximately 40 gypsum-producing playas that have been the subject of several studies (e.g., boyd, 1982; chapman, 1984; hussain, 1986; boyd and kreitler, 1987; hussain and warren, 1985, 1988, 1989, 1991; chapman and kreitler, 1990; mahan and kay, 2012). abbreviations for fossils: fhpr – field house park record, utah field house of natural history state park museum, vernal, utah; usnm pal – united states national museum, paleobiology (now the national museum of natural history, smithsonian institution), washington dc. history of nomenclature and the authorship controversy geologists have long noted that there was a stratifigure 1. distribution of the morrison formation in the western united states and location of type localities for the formation (bold text) and members. “tidwello” is the location of the type tidwell of o'sullivan (1984a); “tidwellp” is the location of the type tidwell of peterson (1988a). delineation of the colorado plateau based on bayer (1983). thickness isopach (100-foot contours) from mckee and others (1956); see peterson (1972) for another interpretation. 52 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 graphic interval of slope-forming, thinly bedded, lenticular siltstone, sandstone, limestone, and mudstone beds between the lowest, whiteto gray-colored, thick bedded, typical coarse-grained sandstones of the salt wash member of the morrison formation, and the characteristic thin, evenly bedded siltstone beds of the summerville formation (figure 2) (e.g., dake, 1918; emery, 1918; gilluly and reeside, 1928; gilluly, 1929; stokes, 1944, 1952; coleman and others, 1945; baker and others, 1952; stokes and holmes, 1954; craig and dickey, 1956; young and others, 1957, 1960; holmes, 1960; craig and shawe, 1975; imlay, 1980). these slope-forming strata have been included in the summerville formation (e.g., baker, 1946), the salt wash member (e.g., gilluly, 1929), partially in both (e.g., craig and others, 1955), or as a separate stratigraphic unit variously called the “lower member,” “lower unit,” and “tidwell unit.” the “peeples member” was proposed by holmes (1960) in his dissertation for this same unit, but the name was never formally published (stokes, 1980), and the north american stratigraphic code (nacsn, 2021) does not recognize a dissertation as a valid publication (article 4, remarks (a) inadequate publication). thompson and stokes (1970) named the unit the white point sandstone member of the summerville formation, with the type section near white point south of escalante, utah. they also noted that the member was probably equivalent to part of the morrison formation. despite having priority as acknowledged by peterson (1988a, p. 42), the white point sandstone member has not been widely used and is hereby formally abandoned under article 7(c) of the nacsn, 2021, which states, “priority in publication is to be respected, but priority alone does not justify displacing a well-established name by one neither well-known nor commonly used; nor should an inadequately established name be preserved merely on the basis of priority…” (see also nacsn, 2021, article 20). these beds today are called the tidwell member of the morrison formation (o'sullivan, 1984a) or the tidwell member of the summerville formation (lucas and anderson, 1997; anderson and lucas, 1994, 1995, 1996, 1998; anderson and others, 1997; previously, anderson and lucas, 1992, did not recognize the tidwell as a valid lithostratigraphic unit). the earliest use of the term “tidwell member” is claimed by robert young (1987, p. 17), who referred to an earlier report (young and others, 1957). this earlier report on the uranium geology of the green river minfigure 2. slope-forming tidwell member of the morrison formation bracketed by the underlying summerville formation and overlying salt wash member of the morrison formation. (a) tidwell bottoms on the west side of the tidwell mineral belt. (b) close-up of exposures outlined in a. butte is at 38.9414°, -110.3938°. 53 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 ing district was written while young was employed by the grand junction office of the aec (1955–1963, the daily sentinel, 2011). young (1987, p. 17) stated that the earlier usage was an informal designation. the name as used by young (1987) presumably derived from either tidwell bottoms or tidwell draw, both of which occur in a small area on the west side of the green river mining district (figures 2a and 3a). young (1978) does not list the tidwell member among the four members of the morrison formation in his discussion of the uranium deposits of the colorado plateau. a problem arises, however, in crediting young and others (1957) with the term “tidwell member,” because that the term does not occur in the 1957 report, nor in their revised report (young and others, 1960). instead, they identify the salt wash member of the morrison formation as in unconformable contact with the underlying summerville formation. my search of around 150 relevant documents written between 1951 and 1970 for the aec failed to produce any mention of the “tidwell member.” both young (1987, p. 17) and peterson (1988a, p. 35) do refer to a discussion between them in 1986 in which “tidwell member” was discussed and it is possible that young conflated “tidwell member” and “tidwell mineral belt,” because the latter appears for the first time in young and others (1957); compare technical staff (1951), clark and million (1956), and johnson (1956, 1957) with young and others (1960), trimble (1976), mickle and others (1977), trimble and doelling (1978), and bluhm and rundle (1980). the tidwell mineral belt, also known as tidwell district, is an area immediately east of tidwell bottoms in emery counfigure 3. (a) overview of main study area: 1 – area where young and others (1957) allegedly introduced the informal term “tidwell member.” 2 – location of duma point. 3 – location shadscale mesa. yellow b is the location of the old highway bridge across the san rafael river. (b) duma point area: 4 – location of the stratigraphic section of o'sullivan (1984a); 5 – stratotype of the salt wash member by lupton (1914) also shown for reference. (c) shadscale mesa area: 6 – location of the stratigraphic section of peterson (1988a). other sites include: 7 – butte with tidwell channel incised into the summerville, see figure 15c (38.8794°, -110.4436°). 8 – “the notch,” well exposed gypsum, see figure 16 (38.8844°, -110.4456°). 9 – cliff face showing angular unconformity at the top of the summerville, see figures 7a and 7b (38.8859°, -110.4438°). satellite imagery and location coordinates here and throughout from google earth. 54 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 ty, utah (figures 2 and 3a), which produced uranium and vanadium during the 1950s and 1960s (young and others, 1960; trimble, 1976; mickle and others, 1977; trimble and doelling, 1978). the term tidwell mineral belt is still used today (e.g., gloyn and others, 2003). the earliest verifiable use of the “tidwell” name for strata was by peterson (1980a) for rocks he previously referred to as the “lower member” of the morrison formation in the henry basin (peterson, 1974, 1977, 1978). in introducing the term “tidwell,” he referred to the lower member as the “tidwell unit of the morrison,” but stated that the term was informal (peterson, 1980a, p. 70). his justification for using “tidwell” was because “several uranium companies have resurrected the name ‘tidwell member’ for this unit because that name appeared on unpublished and unauthored maps thought to have been compiled by r.g. young in the 1950’s [sic] that are in the files of the u.s. department of energy (formerly the u.s. atomic energy commission) and are available to the public” (peterson, 1980a, p. 70). it is unfortunate that peterson did not reference specific maps because my search failed to find the name on any unpublished geological maps or other documents in the aec archives (christine turner, u.s. geological survey, retired, was unable to provide any insights to these files either; written communication, january 19, 2022). these unpublished maps and documents do reference the salt wash and brushy basin members, but not the tidwell member. furthermore, these documents state that the salt wash member overlays the summerville formation. o'sullivan (1980a, 1980b, 1981a, 1981b, 1981c), noted that a reddish, slope-forming stratigraphic interval at the base of the morrison formation is exposed through much of the colorado plateau and initially called it the “lower beds” of the salt wash member in a series of stratigraphic correlation charts. later, the beds were referred to as the “tidwell unit” and acknowledgment was given to peterson (1980a) for introducing this informal term (o'sullivan and pierce, 1983; o'sullivan and pipiringos, 1983). tham and others (1981) used the name “tidwell unit” for the stratigraphic unit below the salt wash and credited peterson for the name. however, he [peterson] did not use that name in the three references they cited. the name tidwell unit was also credited to peterson (1980a) by toth and others (1983) in their unpublished report on the geology of the dominguez canyon wilderness study area in western colorado. later, toth and others (1987) referred to the tidwell member in their published, much abbreviated geology of the dominguez canyon wilderness study area, but no credit for the unit name is given. tyler (1981) and tyler and ethridge (1983a, p. 69) refer to the tidwell member as “the earliest fluvial deposit of the morrison formation” in the slick rock uranium district. in addition, they show it on a stratigraphic section (also in tyler and ethridge, 1983b). they do not state the origin of the name and present it as if it was widely known. after 1983, the history of the tidwell member nomenclature becomes complicated. o'sullivan (1984a) presented a detailed discussion about the base of the morrison formation in east-central utah, and included a lithological definition of the tidwell member at duma point, grand county, utah (figures 3b and 4). duma point is 2.18 km south of lupton’s (1914, p. 126) measured section for the type salt wash member at an unnamed side canyon on white wash (figure 5; note: cadigan, 1967, p. 9, erroneously referred to the type locality for the salt wash member as at duma point). o'sullivan considered the angular unconformity between the underlying summerville formation and overlying tidwell member near the san rafael swell as the definitive boundary between the two lithostratigraphic units. o’sullivan traced this boundary eastwards across the colorado plateau as a disconformity that he considered as the j-5 unconformity of pipiringos and o'sullivan (1978). the following year, usgs geologist brenda steele (1985) credited o'sullivan (1984a) for the name tidwell member, which has an important ramification regarding authorship as is discussed in the next section. that same year, usgs geologist cornelius molenaar (1985) cited “peterson (in press)” for the name tidwell member, but there was no mention of o'sullivan, 1984a. this citation suggests that a manuscript by peterson proposing the name was circulating in the usgs offices in denver, colorado, at least three years before its publication. o'sullivan (1986) used the name tidwell member in stratigraphic sections between uravan and telluride, colorado, and cited peterson (1980a, as the “tidwell 55 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 unit”); however, neither his own work nor peterson's unpublished manuscript are cited as the source for the name. doelling (1985) describes the tidwell member in and adjacent to arches national park citing o'sullivan (1980a) as the source for the name. peterson and tyler (1985) referred to the tidwell member, but gave no reference for the name; they did cite peterson (in press) for the fiftymile member in the same article. peterson (1986) referred to the tidwell member without a reference in his discussion of the jurassic paleotectonics of the central colorado plateau implying an accepted name. finally, in peterson and turner-peterson (1987, p. 4), both o'sullivan (1984a) and peterson (in press) are cited for the “newly recognized tidwell member…” here, peterson and turner-peterson seemingly acknowledged o'sullivan as author, while also acknowledging that the peterson version was not yet published. goldhaber and others (1987) refer to the tidwell member in the henry basin of south-central utah and noted that the local geology had been described by peterson (1980b). they replicated his stratigraphic section and changed “tidwell unit” to “tidwell member,” but do not give a reason for the change. baars and doelling (1987) cite doelling (1985) for the tidwell member, whereas kowallis and heaton (1987) cite a personal communication from peterson for the name. in 1988, peterson's manuscript proposing the name tidwell member was finally published. the delay between the circulation of peterson's draft manuscript and its publication was due to his mandatory involvement in the monumental usgs multidisciplinary analysis of the morrison formation in the grants uranium district in northwestern new mexico (christine turner, usgs, retired, written communication, september 18, 2020). the volume (turner-peterson and others, 1986) was a crucial summary of uranium ore genesis in context of the evolution of a sedimentary basin by the usgs under pressure of the ronald reagan administration (1981–1989). the delay forced peterson's manuscript to go through the internal usgs review process a second time (christine turner, usgs, retired, written communication, september 18, 2020). the published version is mostly a repeat of what peterson had previously published, although he cites very few of these earlier publications. one important addition was a descriptive stratigraphic section at shadscale mesa, which he calls figure 4. duma point location where o'sullivan (1984a) made his measured section (a). (b) close-up of the supplemental reference section of the tidwell member (38.7818°, -109.9783°); box shown in a. 56 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 the type section for the tidwell member (figures 3 and 6). in the years since peterson (1988a), various researchers have credited peterson for naming and describing the tidwell member (e.g., lucas, 2018), but others credit o'sullivan (1984a) (e.g., kirkland and others, 2020). because o'sullivan and peterson give different localities that could be construed as the type section of the tidwell member (duma point vs shadscale mesa, figure 3), it is important to determine who is the rightful or first author to formally proposed the name tidwell member. the north american stratigraphic code (nasc) presents standardized procedures for stratigraphic nomenclature as agreed upon by the geological community (jordan, 2009). for this reason, the nasc is incorporated into the guidelines for usgs technical reports (cohee, 1974). both o'sullivan (1984a) and peterson (1988a) operated under the 1983 version of the nasc (nacsn, 1983), which gives the minimum requirements for naming a new geologic unit in article 3 and which are elaborated upon in articles 4 through 15. both o'sullivan (1984a) and peterson (1988a) fulfilled the basic requirements for naming the tidwell member as summarized in table 1. however, the nasc states that the naming of a new geologic unit is actually a proposal that lacks status until used by others showing that the name served a purpose. in other words, that there was a recognized need by others for the name (nasc, article 5, remark(a)). for o'sullivan, this recognition was fulfilled when usgs geologist steele (1985) credfigure 5. (a) location of lupton's (1914) measured section of the salt wash member of the morrison formation along an unnamed side canyon of white wash (38.7982°, -109.9867°). the geographical feature salt wash is 3.6 km north in the next drainage. (b) close-up of the type section; box shown in a. lupton (1914) included the tidwell strata with the underlying part of the “mcelmo formation” as it was called. 57 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 ited o'sullivan (1984a) for the tidwell member. for peterson (1988a), this recognition came from northrop and others (1990a). despite these recognitions, there is a complication in recognizing o'sullivan as the author for the tidwell member. the internal usgs guidelines, stratigraphic nomenclature in reports of the u.s. geological survey, requires that the naming of a new stratigraphic name by usgs personnel must include a “1. statement of intent to introduce a name: this unit is here named ....” (cohee, 1974, p. 5). o'sullivan (1984a) makes no such statement and usage of the name as far as the usgs is concerned is assumed to be informal. it is rather unfortunate that the survey did not enforce the 1983 nasc article 30, remark (h) on informal units: “when geographic names are applied to such informal units as … informal members …, the unit term should not be capitalized.” using “tidwell member” rather than “tidwell member” would have been less ambiguous as to o'sullivan's intent. in contrast, peterson (1988a, p. 35) wrote, “the tidwell member is here named for grayish green mudstone strata at the base of the morrison formation…” making an unambiguous statement of his intention for naming a new stratigraphic unit. i conclude that, although o'sullivan (1984a) fulfilled the requirements for naming a new stratigraphic unit according to the 1983 nasc, his intent as far as the usgs was concerned, was of an informal usage. therefore, peterson (1988a) should be credited with formally naming the tidwell member of the morrison formation and consequently the type section is at shadscale mesa, emery county, utah (figure 6). o'sullivan (1992a) designated a reference section (nasc, article 8, remark (e), reference sections) for the tidwell member along a minor drainage of the gunnison river in montrose county, colorado (38.6113°, -107.8449°). in his reference section, he notes a thickness of 50 m, of which gypsiferous beds comprise the lower 24 m. o'sullivan's (1984a) section at duma point (figure 4) may be considered a supplementary reference section (nasc, article 8, remark (e)) because it lacks the basal gypsum seen at the type and principal reference sections and is more representative of most of the tidwell east of the san rafael swell and henry basin. the descriptions of the tidwell member by peterson (1988a) and by o'sullivan (1984a) share similarifigure 6. south side of shadscale mesa, type section of peterson (1988a). (a) distant view, (b) closeup. (38.8821°, -110.4341°); box shown in a. 58 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 ties but also important differences as well, because peterson’s work concentrated on the western side of the colorado plateau and o'sullivan on the central and eastern sides. where o'sullivan (1984a) noted that the dominant lithology was red siltstone, peterson (1988a) noted that it was gray mudstone. both, however, noted that the tidwell member also included interbedded sandstones and limestones, a basal sandstone referred to as bed a, cherts as small botryoidal masses (welded chert) or larger nodules, and thick basal gypsum beds near the san rafael swell. there are also differences in the reported thicknesses of the tidwell member. o'sullivan (1984a) reported that the thickness at duma point as 10.8 m, and noted that it ranges from 4.8 to 28.6 m elsewhere in east-central utah, with an average of 17.2 m. in contrast, peterson (1988a) reported the thickness of the tidwell member at shadscale mesa as 29.3 m, of which the basal 5.2 m was gypsiferous. elsewhere, the tidwell member ranges up to 30 m in the san rafael swell and from 8 to 21 m in the henry basin where the basal gypsiferous beds in the northern end of the basin are up to 14 m thick. o'sullivan (1984a, p. 15) also noted that towards blanding, utah, the tidwell member is replaced laterally by the bluff sandstone member of the morrison formation and near glenwood springs, colorado, it merges with the undivided morrison. peterson (1988a) does not discuss lateral correlation but does show graphically (his figure b18) that the tidwell member correlates with the lower parts of both the bluff sandstone and recapture members. tidwell—a member of the morrison formation or of the summerville formation? having established that peterson (1988a) as the geologist who formally named the tidwell member and established the type locality at shadscale mesa, there remains the question of whether the tidwell member is a member at the top of the summerville formation or a member at the base of the morrison formation. two issues to resolving this problem is the identification of the j-5 unconformity and the placement of the thick, basal gypsum beds in the san rafael swell and henry table 1. north american stratigraphic code (1983) requirements for the naming of a lithostratigraphic unit as fulfilled by o'sullivan (1984a) and peterson (1988a). applicable north american stratigraphic code o'sullivan, 1984a peterson, 1988a article 4–publication permanent, widely available usgs bulletin 1561 usgs bulletin 1633 article 5–intent and utility p. 7–11 p. 35–36 article 6–category and rank p. 5 as “tidwell member” p. 35 as “tidwell member” article 7–compound name for a geographic feature p. 5 “tidwell member,” but does not give the geographic feature for the name. p. 35 “tidwell member” after tidwell bottoms article 8–stratotype p. 13 (duma point) p. 53 (shadscale mesa) article 9–unit description p. 12, photographic section; p. 13 descriptive section. p. 38, graphic section; p. 52–53 descriptive section. article 10–boundaries p. 6, j-5 unconformity to the salt wash member. p. 38, j-5 unconformity to the salt wash member. article 11–historical background p. 3–5, 7–11 p. 36 article 12–dimensions and regional relations p. 5, 13, 15 p. 38, 52 article 13–age p. 1 with p. 5, late jurassic figure b2, upper jurassic; p. 20, late jurassic article 14–correlation p. 15 figure b18 article 15–genesis p. 5, terrestrial, but locally marine or quasi-marine. p. 42, lacustrine, evaporative, mudflat, minor eolian, fluvial. 59 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 basin. these two issues were examined in context of the tidwell and summerville across the northern half of the colorado plateau (figures 7 and 8). in addition, the laterally equivalent wanakah formation as defined by o’sullivan (1992a), was examined as well because there is disagreement as to whether the strata are distinct from the summerville (see below). in the following sections, first the basic lithologies of the summerville formation and tidwell member are described, then detailed descriptions of the gypsum in the summerville and the controversial, thick gypsum beds at the contact between the summerville and tidwell in the san rafael swell and henry basin, followed by evidence for placement of the j-5 unconformity, and finally comparisons are made with the gypsum of the ralston creek member which provides indirect support for the placement of the thick gypsum beds. summerville formation the summerville formation conformably overlies the curtis formation in central and east-central utah, and the curtis and summerville are correlative with the stump formation to the north. the summerville formation is considered the regressive phase of a single transgressive-regressive (t-r) sequence represented by with the curtis-summerville-stump formations (wilcox and currie, 2008). dinoflagellates and ammonites in the basal curtis and stump formations date this t-r sequence to the early oxfordian (wilcox and currie, figure 7. locations of summerville and tidwell strata shown in figure 8. letters of localities (a, b, c, etc.) correspond to figures 8a, 8b, 8c, etc. 60 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 figure 8a–l. documenting facies variation of the tidwell member (morrison formation) and underlying summerville formation across the colorado plateau. (a) butte along bullfrog creek, utah (37.6072°, -110.7689°). (b) escalante petrified forest state park, utah (37.7876° -111.6294°). (c) divide canyon, capitol reef national park, utah (38.0312°, -111.0637°). (d) lone cedar flat, utah (38.1081°, -110.6324°; cf., hunt and others, 1953, figure 17). (e) notom junction, utah (38.2858°, -111.1277°). (f) fremont river, utah (38.3727°, -110.7571°). (g) i-70, mulligan wash, utah (38.8318°, -111.1370°). (h) horn silver gulch, utah (39.0403°, -110.9706°). (i) lucky flats, utah (39.3026°, -110.6377°), arrow indicates a lenticular sandstone in the summerville formation. (j) woodside anticline, utah (39.1830°, -110.4139°), arrow indicates a lenticular sandstone in the summerville formation. (k) tidwell bottoms, utah (38.9244°, -109.4479°). (l) horse bench (38.8007°, -110.2181°). abbreviations: je – entrada formation; jem – entrada formation, moab tongue; jmb – morrison formation, brushy basin member; jms – morrison formation, salt wash member; jmt – morrison formation, tidwell member; js – summerville formation; jw – wanakah formation. image c from google earth street view. 61 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 2008; about 163.5 + 1.0 – 160 ma, international commission on stratigraphy, 2021). the summerville formation was named by gilluly and reeside (1928) for summerville point in the northeastern san rafael swell where is it exposed in its entirety (figures 9a and 9b). however, internal bedding is better seen 4.5 km to the east in the woodside anticline on the east flank of the san rafael swell, emery county (figure 9c). a better exposure is in a roadcut along interstate 70 (i-70) on the west side of the san rafael swell (figure 9d). this outcrop has been featured in several studies (e.g., stanton, 1976; steiner, 1978; caputo, 1988; caputo and pryor, 1991; bazard and butler, 1992; wilcox, 2007; wilcox and currie, 2008). hunt and others (1953) gave a regional overview of the summerville in the vicinity of the henry mountains, and caputo (1988) in the vicinity of the san rafael swell and eastward. the summerville formation lithology is not uniform across the colorado plateau. in the western part of the plateau, the formation consists of thinly bedded, figure 8m–u. documenting facies variation of the tidwell member (morrison formation) and underlying summerville formation across the colorado plateau, continued. (m) unnamed side canyon, white wash, utah (38.7982°, -109.9867°). (n) mine draw, yellow cat mining district, utah (38.8242°, -109.5468°). (o) near dewey springs, utah (38.8203°, -109.2845°). (p) us 191 roadcut, kane springs canyon, utah (38.4061°, -109.4472°). (q) mcintyre canyon, colorado (38.0938°, -108.9401°). (r) san miguel river, colorado (38.3474°, -108.7056°). (s) escalante canyon, colorado (38.7116°, -108.2774°). (t) near artist point, colorado national monument, colorado (39.0713°, -108.7268°). (u) rainbow draw, utah (40.5489°, -109.1825°). abbreviations: je – entrada formation; jem – entrada formation, moab tongue; jmb – morrison formation, brushy basin member; jms – morrison formation, salt wash member; jmt – morrison formation, tidwell member; js – summerville formation; jw – wanakah formation. image p from google earth street view. 62 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 medium-grained, subarkosic and sublitharenitic sandstones or siltstones, alternating with softer, thinly bedded wacke or sandy shale. mcknight (1940) noted muscovite in some sandstone beds east of the green river. anhydrite or gypsum occurs as nodules or thin beds, and thin, gray limestones also occur. white, pink, orange-red, and blue-gray authigenic cherts occur sporadically throughout the formation, either associated with limestone (mcknight, 1940), as small botryoidal masses of welded cherts (e.g., shadscale mesa area), or as lenses figure 9. summerville formation in utah. (a) type locality at summerville point (39.1800°, -110.4635°). red arrow points to a sandstone lens. (b) the only place the type locality where the internal bedding is visible shows thinly bedded siltstone to fine-grained sandstone with little gypsum present. (c) thinly bedded siltstone, fineto medium-grained sandstone, and light-colored gypsum, woodside anticline (39.1826°, -110.4100°). (d) mostly thinly bedded siltstone, fine-to medium-grained sandstone with little gypsum present, i-70 roadcut, mulligan wash (38.8321°, -111.1324°). (e) characteristic alternating fine-grained sandstone or siltstone and mudstone or shale, roadcut state highway 24 near hanksville (38.3710°, -110.7509°). (f) coarsening and thickening upwards sequence of sandstone beds (lower half to upper half), horse bench (38.8032°, -110.2190°). (g) channel sandstone (note cross-bedding in insert); i-70 roadcut (38.8302°, -111.1385°). (h) siltstone flakes in fine-grain sandstone, lucky flats. (i) rippled sandstone, lucky flats. (j) climbing ripples, horn silver gulch. (k) more abundant and thicker sandstone beds (up to about 1 m thick) near white wash, utah (38.7978°, -109.9876°), about 20 km east of f. 63 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 up to a meter thick (stokes and mobley, 1954). the clay matrix is mostly illite, although kaolinite co-occurs at the woodside anticline (weeks, 1953). the upper contact is abrupt (e.g., figure 9e). where the summerville is exposed in cliffs or roadcuts, the resistant sandstone and siltstone beds are more resistant to erosion and protrude (e.g., figures 9d and 9f). colors range from various darker hues of red and orange, with some interbedded lighter sandstone or siltstone beds (figures 8 and 9). the thin-bedded sandstones may be locally lenticular (figures 8j and 9g). thin, irregular siltstone flakes in fine-grained sandstone (figure 9h) are ripup clasts or clasts from bank collapse of tidal channels (stanton, 1976). the thin-bedded sandstone may show fining or coarsening upward successions, ripples (figure 9i), climbing ripples (figure 9j), load casts, cross-laminations, and desiccation cracks (stanton, 1976; caputo and pryor 1991). the summerville formation becomes progressively sandier and thicker bedded eastwards at the expense of siltstones and shales, with some of the sandstone becoming over a meter thick (compare eastward progressing figures 9d, 9f, and 9k). gilluly and reeside (1928) also noted this lithological change and proposed that the summerville in the eastern part was deposited on a broad, flat continental plain that sloped westward into a restricted, shallow-marine environment. they suggested that the lenticular sandstones in the south and east indicated continental deposition, and the ripple marks, mud cracks, and gypsum in the west indicated marine deposition. their eastern-most summerville includes strata that is now the wanakah formation (burbank, 1930), a formation that is a source of controversy (anderson and lucas, 1992; lucas,1993; anderson and lucas, 1994; lucas and others, 2006; vs condon, 1993). the summerville formation thins south and east (figure 10) from a maximum of 129 m in the western san rafael swell. east of the green river, the summerville is very thin (about 4 m) near dewey bridge (figure 8o). west of the san rafael swell, well data indicates that the summerville grades laterally into the upper part of the twist gulch formation near salina canyon, sevier figure 10. relative thickness and relationship of the tidwell member of the morrison formation, and summerville and wanakah formations across the colorado plateau. (a) restored stratigraphic diagram. the boundary between the lithologies of the summerville and wanakah is gradational, and the two formations are separated artificially by the utah-colorado border. (b) index map of the stratigraphic diagram (base map from topozone). locations for reference: 1, buckhorn flat, san rafael swell; 2 – dellenbaugh butte; 3 – salt wash valley; 4 – dewey bridge; 5 – west water; 6 – fruita; 7 – bridgeport; 8 – escalante canyon; 9 – dry creek basin; 10 – north ouray. data from o'sullivan (1980a, 1981b, 2004), o'sullivan and pierce (1983), and o'sullivan and pipiringos (1983). 64 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 county, utah (perkes, 2010). strata of the summerville-wanakah formations can be traced almost continuously from the stratotype of the summerville formation at summerville point around the north and east sides of the uncompahgre plateau to the stratotype of the wanakah formation near ouray, colorado (figure 10; holmes, 1960; o'sullivan and pipiringos, 1983). criteria for separating the two units are vague because holmes (1960) considering the wanakah formation as the more calcareous and gypsiferous mudstone facies of the summerville. o'sullivan (1980b) noted that the summerville formation bevels out in the vicinity of moab and the la sal mountains in eastern utah, and recommended that the name wanakah formation be used instead of summerville formation in southwestern colorado and southeastern-most utah. the absence of the summerville formation can be seen, for example, south of moab near kane springs where the tidwell member sits atop the middle jurassic entrada sandstone (figure 8p; o'sullivan, 1981a). however, as noted above, the summerville formation can be traced around the north end of the uncompahgre plateau (lohman, 1965; gualtieri, 1988; willis, 1994; willis and others, 1996). o'sullivan and piperingos (1983) placed a pair of red and green mudstone beds (figure 11a) along the north side of the uncompahgre plateau in the lower part of the tidwell member based partly on the assumption that an underlying sandstone was bed a, which marks the base of the tidwell. this assumption was challenged by willis and others (1996), who considered the red and green mudstone beds and the underlying sandstone to be the summerville formation based on previous work by doelling (1993). later, based on correlations on the east side of the uncompahgre plateau, o'sullivan (2004) agreed with willis and others (1996), and moved the base of the tidwell member to a higher sandstone (formerly called bed b) and identified the underlying red and green mudstones as belonging to the wanakah formation, which he considered to be predominately nonmarine. elsewhere on the northeastern colorado plateau, the wanakah formation is dominated by red mudstone and sandstone beds (figures 11b and 11c; see o'sullivan, 1992a, for other lithologies and extensive discussion) and resembles the summerville formation farther west. these summerville-like strata are variously known informally as the “marl member” or “beds at sawpit” (o'sullivan 1992a; burbank and luedke, 2008). figure 11. wanakah formation, colorado. (a) green and red beds at angle point, colorado national monument; now mostly obscured by talus since this photo was taken in 2007 (39.0727°, -108.7242°). (b) escalante canyon (38.7116°, -108.2774°). (c) roadcut, state highway 141 south of uravan (38.3504°. -108.7096°). base of wanakah in (b) and (c) at the bushes at the bottom. image (a) by james st. john from wikimedia commons, creative commons 2.0. 65 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 currently, the predominately marine summerville formation has a state-line boundary separating it in utah from the predominately nonmarine(?) wanakah formation in colorado (however, see o’sullivan and others, 2006, for marine fossils). a more thorough analysis of the wanakah and summerville formations is needed because some of the arguments for assigning former summerville strata to the wanakah are based on correlation, rather than lithology (e.g., condon and huffman, 1986). such an analysis is beyond the scope of this paper. tidwell member the tidwell member shows considerable lateral variation as noted by the description of the type section at shadscale mesa (peterson, 1988a) and the supplemental reference section at duma point (o'sullivan, 1984a). there is no doubt that the two sections demonstrate a lateral variation of the same stratigraphic unit because the tidwell member can be traced along a near continuous cliff between the two sections (figure 3a; see also o'sullivan, 1980a). thickness of the tidwell member is variable and ranges up to 35+ m thick in its southern occurrences (robinson, 1994). much of this variability is due to differences in the interfingering of the tidwell member with the overlying salt wash member and with the base of the salt wash sandstone channels scoured into the tidwell member (figure 8). as described by peterson (1988a), the tidwell member has two distinct parts: a lower gypsum facies and an upper thin, interbedded sandstone-mudstone-limestone facies assemblage. because the gypsum facies has been a source of controversy it is described in a separate section. where the gypsum facies is missing, the base of the base of the tidwell member is often a tabular sandstone called bed a (o'sullivan, 1980a, 1984a). bed a over much of the eastern part of the colorado plateau where the basal gypsum is absent in the tidwell member, o'sullivan (e.g., 1980a, 1984a) noted a widespread tabular sandstone at or slightly above the contact with the summerville formation, which he referred to as bed a (figures 8 and 12). this sandstone was previously noted by holmes (1960) as a persistent datum plane that he used to mark the top of the summerville formation. the sandstone ranges from 0.1 m near white sand dunes recreational area, grand county, utah, to 10 m in western colorado (o'sullivan, 1992b). it frequently overhangs the softer summerville (e.g., figure 12c). the sandstone is various hues of brown, red, white to gray, and generally fineto medium-grained. bluhm and randle (1980) described a 0.9 m-thick bed a on the west side of the san rafael swell. it was composed of a very calcareous quartz arenite with about 40% micritic and sparitic carbonate, 45% to 50% fine to medium-grained, subangular to subrounded, single-crystal and polycrystalline quartz (some of volcanic origin); 5% to 8% fineto medium-sized, subangular to subrounded, microcrystalline chert; 1% to 2% fineto coarse-grained, angular to subrounded chalcedony; 1% very fine to fine-sized, subangular to subrounded feldspar (microcline and plagioclase); 1% to 3% very fine to medium-grained, subrounded sedimentary rock fragments (micritic carbonate clasts and mudstone fragments); and trace amounts of detrital gypsum, zircon, garnet, tourmaline, muscovite, biotite, and opaques. bed a is conglomeratic in places, which include red and green mudstone clasts, or rounded black and gray chert pebbles. kirkland (utah geological survey, written communication, september 21, 2021) reports a sheetlike conglomerate bed at the base of the tidwell extending from notom junction northward across the northern region of capitol reef national park to at least the south rim of cathedral valley in the park. this conglomerate bed is probably the same as that described by ali-adeeb (2007) as matrix supported and interpreted as debris flows. bed a is often thickly bedded or massive, showing no structure, but occasionally showing wavy lamination in possible eolian deposits (figure 12e), as well as cross-bedding, ripple marks, or planar bedding, which occurs in fine-grained sandstone (figures 12f and 12g). bed a may not be the same bed everywhere or maybe composed of several closely associated sandstones beds (e.g., figure 12a) that thin and wedge out (e.g., notom junction, location e, figure 7). peterson (1988a) suggested that bed a correlated with the windy hill sandstone in the northern utah and wyoming because 66 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 both were underlain by the j-5 unconformity of piperingos and o'sullivan (1978). in contrast, holland and wright (2020) concluded that the base of the windy hill is not an unconformity and is a tide-dominated deltaic system that prograded north over the redwater shale in wyoming. furthermore, the windy hill is conformably overlain by the tidwell in the northern uinta basin, eastern utah (sprinkel and others, 2019; figure 7, location u, figure 8u). as an important side note, o'sullivan (2004) corrected previous misidentifications of bed a, which he had referred to as bed b located in the middle of the tidwell, thus moving the contact higher; the stratigraphic significance of this has not always been recognized (e.g., bernier and chan, 2006). interbedded thin sandstone-siltstone-mudstonelimestone-dolomite facies assemblage the tidwell member above the thick gypsum or bed a is what typically characterizes the member: thickly laminated to thinly bedded, mostly white, very pale-orange, or pale-greenish yellow, fineto medium-grained sheet sandstone alternating with various shades of lighter reds, and yellowish-gray siltstone, mudstone, and very light to medium-gray limestone and dolomite (figures 13a and 13b). these lithologies are grouped as an interbedded facies assemblage, hereafter abbreviated the ssmld facies assemblage, which peterson (1980b, 1982a, 1982b, 1982c) originally described as the informal “tidwell unit” in the henry basin. weathering and erosion of this facies assemblage is what typically creates the slope-forming interval between the sandstones of the salt wash member and summerville formation. seen from afar, ignoring color, the thin beds of the ssmld facies assemblage can superficially resemble the summerville and wanakah formations (e.g., figures 6b, 8a, 8e, 8f, 8k, 8r, and 8s), a point raised by anderson and lucas (1998) as reason for including the tidwell member in the summerfigure 12. variations in bed a. (a) thin-bedded base below thicker bedded upper part, notom junction, utah. (b) above thin-bedded summerville, duma point, utah. (c) thicker bed a above the wanakah, escalante canyon, colorado. (d) very thin and discontinuous bed a, northwestern rim of the white sand dunes recreational area, utah (38.8171°, -110.0347°); here the tidwell and summerville may be in conformable contact. structures in bed a. (e) wavy lamination in possible fluvially reworked zibar deposit, duma point, utah. (f) planar laminated, upper flow regime, lone cedar flat, utah. (g) ripples with trace fossils, escalante canyon, utah. 67 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 ville formation. however, the ssmld facies assemblage is not unique to the tidwell member, occurring locally between channel sandstones of the salt wash member (figure 13c). in places this facies assemblage in the salt wash member can be traced laterally and become continuous with the ssmld facies assemblage of the tidwell member (see further discussion below in contact with the salt wash member of the morrison formation section). these facies assemblages in the salt wash member have been described numerous times, such as by craig and others (1955), peterson (1980a), tyler and etheridge (1983a, 1983b), robinson and mccabe (1998) among others. details of the interbedded facies assemblage of the tidwell member is only visible in fresh exposures or cliff faces (figures 4b, 6b, 8e, 8f, 8p, 8r, 8s, and 8u) because weathering typically creates the characteristic slope that lies between salt wash member and the cliff-forming summerville formation (figures 8c, 8i, 8j, 8l, 8n, 8o, and 8q). in the henry basin, the relative proportion of finer-grained strata decrease and thin-bedded sandstones predominate (figures 8a, 8d, and 8e). this presumably reflects a southern source area (peterson, 1984). the sheet sandstone component of the ssmld facies assemblage are tabular beds, have a thickness measured in decimeters (typically less than 5 dm), and generally composed of fineto medium-grained sandstones. it is difficult to trace individual beds due to talus, but what can be visually followed along the cliff faces suggests the beds may extend for hundreds of meters and some possibly a kilometer or more. fisher and others (2007) used a two-dimensional computational fluid dynamics model to show that an unconfined sheet flood can transport sand up to a kilometer across a shallow gradient. sheet flow is generally not uniform across the surface due to microtopography and vegetation (abraham and others, 1994), but tends to concentrate as lobes making a bird’s foot or bifurcating pattern (emmett, 1970). a cross section of the lobes would show discontinuous sheet sands on the same surface. such a morphology is seen in some of the discontinuous thin sandstone beds of the ssmld facies assemblage (figure 14a). some of these sheet sandstones can also be traced into small lenticular bodies of sandstone. sand sheets on opposite sides of a sandstone body were called “wings” by hirst (1991; fielding and others 2011; miall, 2014) and “steer-head channels” by kjemperud and others (2008). fielding and others (2011) noted that these wings are distally thinning extensions of the channel margin and figure 13. thin, interbedded sandstone, siltstone, mudstone, limestone, and dolomite facies assemblage of the tidwell member: (a) above the gypsum unit at the type section of the tidwell member. (b) at the supplemental reference section of the tidwell member at duma point. although these alternating thin bed facies are considered typical of the tidwell member, they in fact also occur within the salt wash member, e.g. (c) where they are bracketed between two sandstone beds in the salt wash member, mine draw, yellow cat mining district (38.8289°, -109.5449°). jacob staff with alidade holder in b is 125 cm. 68 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 are characteristic of channel lithosomes of strongly seasonal discharge rivers in dryland environments where the rivers commonly inundate the floodplain with fast flowing water transporting coarse-grained sediments during high-stage flow. dryland is a collective term for hyper-arid, arid, semiarid, and dry-subhumid environments (tooth, 2004) and used here because the sedimentary rock record is not always clear as to the climate during sediment deposition. some of the sandstone bodies with wings appear inverted, with the channel figure 14. interbedded sandstone, siltstone, mudstone, limestone, and dolomite facies assemblages. (a) lenticular sandstone bodies with wings of thin sheet sandstones at their bases (yellow arrows). also, example of two sandstone bodies (red arrows) connected by the same sandstone sheet at their base. type locality for the tidwell member, shadscale mesa (colors enhanced to bring out lithological differences by color, compare with figure 6b). sequence of roadcuts showing the same coarse-grain overbank deposit (crevasse splay) along rimrock drive, colorado national monument, colorado: (b) distal, (c) middle, and (d) proximal (source channel at far right). sequence is about 160 m long between 39.0700°, -108.7295° and 39.0705°, -108.7282°. (c) and (d) are in adjacent roadcuts, (d) is angled about 30o relative to (c) and (d) because the road curves. (e) sandstone bed showing sharp upper and lower contacts; sand grains fine distally away from viewer. (f) predominately white chert pebbles in a coarse-grain sandstone. the sandstone was over 1 m thick and is just to the left off picture of e. (g) thin beds of limestone interbedded in gray mudstone between orange-weathering sandstone beds. 69 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 sandstones convex-upwards and wings extending from their planar bases (figure 14a, yellow arrows). these wings, or sheet sandstone beds may connect multiple convex-upwards channel sandstone bodies (figure 14a, red arrows). friend (1978) interpreted similar convex-upwards lobes of sand in terminal fan deposits as formed from the loss of flow strength at the margins as the water infiltrated into the adjacent sediment. other thin sandstone sheets are crevasse splays. for example, at colorado national monument sandstone stacks can be traced laterally into distally thinning and fining sheet sandstones in overbank deposits (figures 14b through 14d). this example is similar to the model of burns and others (2019) of splays having different breakout times from the same breakout point. these crevasse splays tend to be irregularly spaced in overbank sediments (compare figure 14b with 14a). other sandstone beds in the ssmld facies assemblage include lenticular channel sandstone up to 1.3 m thick. these tend to show sharp bottom and top contacts with mudstone (figures 14e and 14g; see bernier and chan, 2006, figure 9, for another photographic view). the coarser parts of these beds are composed of angular, coarse-grain quartz matrix, supporting rounded pebbles of mostly light-colored cherts, with some dark cherts and gray limestone, and light-colored carbonate (figure 14f). interbedded thin carbonate and non-pedogenetic nodular carbonate beds occur most commonly among gray mudstone and shale intervals (e.g., figures 14g, 15a, and 15b). some of the limestone beds are wackestones with rounded extraclasts of micrite in a black matrix, a few broken fragments of diplostracan shells, and smell of petroleum when broken (figure 15a). a light etching of the polished surface with dilute hydrochloric acid produced siliciclastic silt-sized grains. bluhm and randle (1980) described a sandy limestone from east of ferron, emery county, utah, as composed of 84% sparitic and micritic calcite; 13% very fine to fine-sized, subangular to subrounded, single-grain quartz; 1% or less of chert, opaques, and feldspar (microcline, plagioclase, and perthite); and trace amounts of muscovite, biotite, tourmaline, and zircon. about 4 km farther southeast, three other limestone beds were 51% to 97% sparitic and micritic carbonate, and have up to 20% fineto granule-sized, subangular to subrounded, microcrystalline chert, with macro-quartz, remnant carbonate, chalcedony, and opaques; less than 1% to 30% chalcedony as secondary replacement of carbonate or as vug fillings; 2% to 15% siltto coarse-sized, subangular to subrounded, single and polycrystalline quartz; up to 10% mediumto granule-sized, subrounded carbonate and mudstone clasts; and less than 1% altered potassium feldspar, opaques, and tourmaline. micrites often show microtubules presumably of roots and may either be hollow (figure 15b) or filled with calcite. some of the bedded carbonates that do not react well with hydrochloric acid are presumed to be dolomitic. these beds may be primary in origin because the mineral is an early precipitate in the evaporative mineral precipitate sequence (warren 2016). domed microbialites associated with lacustrine limestones have been reported by kjemperud and others (2008). they have also been reported from grand county between the blue hills and duma point by kirkland and others (2020), and from the northern capitol reef national park and the fruita paleontological research natural area by kirkland (utah geological survey, written communication, september 23, 2021). unfortunately, none of these specimens have been described in the detail comparable to that of neuhauser and others (1987) for specimens from the morrison formation of northeastern new mexico. thus, it is not known if these are stromatolites or thrombolites (layered or clotted) microbialites (kennard and james, 1986). lacustrine shales also occur in the ssmld facies assemblage (figure 15d), although these are less abundant than laminated siltstone and fine-grained sandstone beds (figures 15e and 15f). the shale at the kane springs roadcut (figure 7, locality p) is composed of dark gray silt-clay couplets, which presumably reflect silt input by individual sheetwash into ponded water followed by mud drapes as the water calmed between events. the yellow mineral stain is probably jarosite, which is indicative of stagnant water after iron depletion is completed (vepraskas and vaughan, 2016). good (2004) reported the unionid bivalve vetulonaia sp. from lacustrine mudstone in the tidwell member. he inferred optimum conditions for growth, including abundant plankton, a constant supply of clean, well-ox70 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 ygenated, warm, carbonate-rich water having a ph greater than 7, and less than 7 m deep. the absence of growth banding implied continuous growth in a stable, non-seasonal environment, a point cited by owen and others (2017) as indicating a uniform and stable climate during deposition of the tidwell sediments. these unionid clams also include those previously reported by yen (1952; emmett evanoff, university of northern colorado, written communication, february 6, 2021) as the holotype of unio stewardi utahensis from his locality figure 15. caption is on the following page. 71 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 23, southeast of green river city (figures 16a through 16m). the site was originally discovered in 1943 by harold ernest vokes, who, at the time was the senior geologist for the usgs prospecting for uranium in the green river desert (vokes, 1998). the site was relocated by me using information provided by yen (1952, p. 31) and was discovered to be in a crevasse splay deposit underlying the basal most salt wash sandstone (figure 16p). the sediments fine distally (eastwards) and vertically. most likely this splay deposit preceded a later avulsion of the channel represented by the overlying sandstone, thus technically the splay deposit belongs with the salt wash member rather than the tidwell member. the fossiliferous part of the splay deposit extends 28.5 m (figure 16p, between the yellow arrows) and has been altered by pedogenesis, especially distally where it is mottled red and gray (figures 16q through 16s). many fossil clams are in horizontal position, but others are at various angles, including vertical on its lateral edge (figure 16r, #1), hinge-side up (figure 16r, #2), and oblique through the sediments (figure 16s, #1). shells include single valves and paired closed valves, many of which are collapsed from compaction of the encasing sediments. single valves are both in current stable and current unstable positions. although good (2004) reported the absence of annual banding in vetulonaia as indicative of continuous growth in a well-oxygenated, warm, stable pond, other specimens (e.g., figure 16n) show annual banding of various widths (figure 16o) indicative of an unstable environment as would be expected in a fluvial system in a seasonal environment (demko and others, 2004). except for a wide growth band indicating a spurt of rapid growth, most bands are narrow to very narrow indicating growth in suboptimal environmental conditions (mutvei and westermark, 2001). i did not analyze these shells for seasonal variation of manganese as is known to occur in modern unionids subjected to oxygen depletion and eutrophication (mutvei and westermark, 2001). such an analysis would resolve the issue of water quality for early morrison time. although these fossil unionid clams occur at the base of the salt wash member, their presence in east-central utah is significant for the tidwell because they support the sedimentological evidence for seasonality in a dryland environment during early morrison time. furthermore, assuming unionids of the morrison formation had already evolved a parasitic larval phase (glochidium) on a fish host as is known to occur today (wächtler and others, 2001; watters, 2001), then we may assume that freshwater fish were present in the salt wash fluvial system as well, despite the absence of fossils. however, a parasitic larval stage at this early time of unionid evolution is far from certain (watters, 2001). paleosols are very prominent in the interbedded mudstone intervals of the ssmld facies assemblage. originally many of these strata were referred to as lacustrine deposits (e.g., peterson, 1978, 1980a), but some were later identified as paleosols by demko (1998; demko and others, 2004). ali-adeeb (2007) reports calcisols and silicified calcisols at the top of the tidwell east of the town of moore south to cathedral valley, which contain questionable “mammals burrows,” carbonate nodules, and rhizoconcretions. ejembi (2018) figure 15 (figure is on the previous page). tidwell carbonates. (a) extraclasts in a black micritic matrix from lowest limestone in figure 14g, near the type section. (b) lightly mottled micrite with microtubules from fremont river, utah (figure 8f). (c) carbonate mudstone nodule from paleosol in g; gray specks are small, abraded carbonate grains, and orange tint is part of the diffused iron mass seen in g. lacustrine or paludal rocks: (d) shale of silt and clay couplets, with sulfide stain (probably jarosite), us 191 roadcut, kane springs canyon, utah (figure 8p). (e) laminated siltstone, san miguel river, colorado (figure 8r). (f) detail of laminated siltstone from (e); scale in mm. paleosols: (g) gleysol with carbonate cemented nodules and diffuse iron, type tidwell; arrow is the specimen in a. (h) stage ii carbonate nodules in a calcisol, upper tidwell, escalante canyon, colorado (38.7375°, -108.2679°). (i) calicisols with stage ii and iii carbonate nodules in siltstone beds near duma point, utah (figure 4). (j) protosol underlying a channel sandstone. the upper part is a high-chroma, silty, eluviated horizon containing gypsum seams, diffuse iron mass, and irregular carbonate nodules; it is in sharp contact with the mottled red, purple and gray bk horizon with diffuse and irregular silty carbonates nodules, and pale iron depletion along root channels at the type section of the tidwell member. (k) rhizoconcretions in a protosol bk horizon with an upper bleached zone underlying a channel sandstone, i-70 roadcut, mulligan wash, utah. (l) gypsisol with multiple horizons of gypsum formed in the vadose zone of a playa margin, west of white sand dunes recreational area, utah (38.8173°, -110.0605°). 72 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 figure 16. bivalves supposedly from the tidwell member southwest of green river, utah. the specimens show a high degree of plasticity in shell morphology that is typical for the unionid clams. vetulonaia sp.: (a–c) usnm pal 106989 (holotype of unio stewardi utahensis yen, 1952, probable female shell morphology); (d–e; j–m) usnm pal 107031 (paratypes of unio stewardi utahensis yen, 1952), (h–i) usnm pal 106990 (paratype of unio stewardi utahensis yen, 1952, probable male shell morphology). (n) longitudinal cut showing annual banding (fhpr 17808). (o) close-up of box in (n) showing wide and narrow annual banding. (p) distant view of the bivalve locality (38.8689°, -110.3685°). specimens occur beneath the sandstone between the yellow arrows; none occur in deposits at the far left. (q) view of the crevasse splay beneath the channel sandstone. (r) pedogenically modified distal crevasse splay. red dots are bivalves: 1, specimen standing on lateral edge, and 2, specimen hinge up. (s) pedogenically modified more proximal crevasse splay. red dots are bivalves: 1, specimen extending oblique through sediments. a–m courtesy of national museum of natural history, smithsonian institution. 73 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 reports vertisols, gleysols, oxisols, and protosols in the paradox basin on the east side of the colorado plateau. the paleosols indicate periods of landscape stability between episodes of major sheetfloods. gleysols (wetland soils) are preserved in many of the mudstone intervals at the type section and typically are very light gray to dark gray, subangular, blocky, coarse granular paleopeds, and contain mudstone carbonate nodules (figures 15c and 15g). the orange iron mass of a redox concentration (figure 15g) is the result of anaerobic soil becoming aerobic again (vasilas and others, 2010). gleysols also occur near hanksville, utah (figure 8f). more commonly, the paleosols tend towards a higher chroma (figures 15h and 15i) indicative of well-drained soil profiles. these are usually calcisols (figures 15h and 15i) developed in siltstone intervals. carbonate nodules are common, although not all react with hydrochloric acid in the field and are assumed to be dolomitic. the reaction of other nodules ranges from weakly calcareous to strongly calcareous as defined by retallack (2001). both stage ii and stage iii nodule development (mack and others, 1993; tabor and others, 2017) may be present indicating moderately to strongly developed paleosols. early stage ii nodules have diffuse edges and some may be rhizoliths (figure 15j). rhizoconcretions can be extensively developed, especially in underlying channel sandstone beds (figure 15k). these rhizoconcretions, as stacked coalesced nodules (blodgett, 1988) in the i-70 roadcut near mulligan wash, utah, suggests the presence of extensive vegetation at least in the vicinity of channels prior to their avulsion over the site. such vegetation explains the presence of large vertebrate herbivores (bernier and chan, 2006) in an otherwise inhospitable environment. excluding the massive gypsum bed to be discussed separately, gypsisols are especially common in marginal playa strata lateral (distal) to large gypsum beds (discussed separately below). vertically aligned lenticular crystals grew displacively in the siliciclastic muds near the top of the water saturation zone of the groundwater table where evaporation is highest (rosen, 1991). these may be seen, for example, in the band above the scale in figure 15l. gypsum growth can also take place between lamina deposited by sheetwash (hardie and others, 1978), also shown in figure 15l. gypsum can also be deposited in the vadose zone through evaporative pumping (capillary wicking) pulling subsurface brines towards the surface. these gypsums include small spheres or nodules, which may merge into botryoidal layers (figure 15l, lower left). geochemical analysis of mudstone beds shows a magnesium spike at the base of the tidwell member in the southern henry basin (northrop and others, 1990b). in addition, the mudstones contain sulfur as pyrite, gypsum, and barite (northrop, 1982; northrop and others, 1990a); pyrite was also identified in mud clasts that occur as lenses in cross-bedded sandstones in the tidwell member. most of these mud clasts are derived from bank collapse or bank erosion (karcz, 1969, 1972; li and others, 2017) despite being commonly called “rip-up clasts,” and their greenish color indicate the floodplain source within a reducing environment. contact with the salt wash member of the morrison formation throughout the colorado plateau, the salt wash member of the morrison formation overlies the ssmld facies assemblage of the tidwell member. o’sullivan (1984a) placed the contact between the two units at the base of the lowest channel sandstone that is a part of a continuous zone of channel sandstones. peterson (1988a) states that the tidwell and salt wash members interfinger, but the evidence presented is based on interpretated relationships between measured sections (peterson, 1988a, figures b10, bl1, b13, and b21). anderson and lucas (1998) argue that the evidence for interfingering is non-existent and that the basal sandstones of the salt wash member are in an irregular unconformable contact with the underlying tidwell strata. this indeed is true for the most part (figures 4b, 6b, 8b, 8c, 8e, 8f, 8j, 8k, 8m, 8o, 8p, 8r, 8s, 8u) and in places the salt wash member is incised deeply into the tidwell member. in contrast, maidment and muxworthy (2019) separate the tidwell and lower salt wash members by a sequence boundary. such a boundary is not supported here as evidenced by the interfingering between the tidwell and salt wash members, such as seen in a roadcut southwest of green river, utah, where thin crevasse splay sandstones can be traced from a salt wash sandstone body 74 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 into the ssmld facies assemblage of the tidwell member (figure 17a and 17b) or where the uppermost thin-bedded sandstone bed of the tidwell member can be traced into the salt wash sandstone (figure 17c). robinson and mccabe (1998) also noted interfingering over a 2-meter interval in the lost springs wash and bullfrog creek located in the southern henry basin. gradational contact is inferred for thickening upwards of thin bedded sandstones immediate below salt wash sandstone (figure 17d). these examples of interfingering and gradational contact imply a depositional relationship between the tidwell and the salt wash members (peterson, 1988a: kjemperud and others, 2008; owen and others, 2015b, 2017; hagen-kristiansen, 2017). figure 17. interfingering between the tidwell member and salt wash member east of shadescale mesa. (a) showing the outcrop context of the summerville formation, tidwell member, and salt wash member. (b) the interfingering, as thin crevasse splay sandstones, is seen in the roadcut along state highway 24 (38.8636°, -110.3685°). for orientation, a red line connects the same prominent salt wash sandstone bed in (a). red boxes show location of close-ups of the strata. (c) another example of interfingering on the north side of shadescale mesa (38.9196°, -110.4019°). the thin sandstone beds of the tidwell member originated as crevasse splays from the salt wash member. (d) gradual contact between the tidwell and salt wash members is seen as thickening upwards thin sandstone beds of the tidwell member (south of uravan, colorado, 38.3595°, -108.7146°). abbreviations: jms – salt wash member, jmt – tidwell member, js – summerville formation. 75 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 controversial gypsum facies the gypsum beds of the summerville formation and the thick gypsum beds between the summerville and the ssmld facies assemblage of the tidwell member have not been given the attention they deserve, despite gypsum being a key point for the placement of the boundary between the summerville and morrison formations (lupton, 1914; mullens and freeman, 1957; trimble, 1976; trimble and doelling, 1978; bluhm and rundle, 1980; anderson and lucas, 1992, 1994, 1998; lucas and others, 2006; lucas, 2014). this lack of study seems to be due to the mistaken impression that the gypsum beds are homogenous units deposited in hypersaline environments, which have been interpreted as restrictive marine, sabkhas, or evaporative basins (imlay, 1980; peterson, 1986, 1994; peterson and turner-peterson, 1987; o'sullivan, 1992a; kirkland and others, 2020). or, in the case of the gypsum of the tidwell member (in the sense of peterson, 1988a), as a gypsol created from mobilization of gypsum from the underlying summerville formation (demko and others, 2004). although gypsum can be altered through dissolution and reprecipitation (e.g., hussein and warren, 1989; warren, 2016), unless deeply buried at some point in their history, the original texture may be retained (magee 1988; rosen, 1989, 1991; schreiber and others, 2007), as well as preserve primary structures (e.g., vertebrate tracks, bennett and others, 2021). these attributes are important for allowing the interpretation of the gypsum beds and gypsiferous strata of the summerville formation and the thick gypsum beds at the summerville formation-tidwell member boundary on the west side of the colorado plateau. these gypsums are described in detail below and show that they formed in different environments. gypsum of the summerville formation gypsum is present locally in the summerville formation as beds, seams, and nodules, but it is not ubiquitous and was not used to define the summerville formation by gilluly and reeside (1927, p. 80: “the even-bedded red and white sandstones and maroon shales of the summerville formation, so named…”). see also scott and others (2001). gypsum in the summerville is more common on the west side of the colorado plateau where the late middle to early late jurassic elko foredeep developed east of the elko uplift (peterson, 1994; thorman and peterson, 2003; thorman, 2011; thorman and others, 2020). elsewhere on the colorado plateau, gypsum is less common in the summerville formation, but it is locally present in the wanakah formation in the eastern part of the colorado plateau and adjacent areas (o'sullivan 1992a; burbank and luedke, 2008). these gypsum beds were interpreted as marginal marine based on sulfur isotopes (o’sullivan, 1992a). this interpretation is supported by the limited fossil evidence indicating a marine incursion (o’sullivan and others, 2006). gypsum nodules may occur along bedding planes and exhibit varying textures. the nodules may be roughly spherical, but are commonly botryoidal (figure 18a). some of the nodules show displacive growth where clay and silt are crowded towards the margins as gypsum crystals grew diagenetically within the substrate producing what is called “chicken wire” texture (figure 18b). other nodules are of pure gypsum and have a granular texture of equant, anhedral crystals (figure 18c). such texture may be the result of rapid precipitation in solutions supersaturated with gypsum under the influence of mutual interference (jafarzadeh and burnham, 1992). the anhedral crystals are probably not tertiary evaporite textures created by partial bed dissolution in the near surface weathering zone (warren, 2016) with the recent uplift of the san rafael swell because the texture extends to the core of even the largest nodules. some gypsum beds also are composed of vertically elongated, tightly packed pelloids that show displacive growth in the substrate (figure 18d), whereas other beds are composed of siltto fine-sand sized clear gypsum grains (grainstones; figure 18e). very thin, vertical to diagonal tertiary satin spar gypsum seams are locally common in the near surface weathered zone (figure 18f) and may occur in the absence of other forms of gypsum. the gypsum of the summerville formation is most similar to gypsum of the marine middle jurassic piper formation in the bighorn basin, wyoming (imlay, 1980). the similarities include being laterally extensive, and having granular texture (figure 18g) and “chicken wire” 76 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 texture of displacive growth (figures 18h and 18i). these similarities with the gypsum of the piper formation, but in contrast with gypsum of the tidwell member described below, suggests that the gypsum of the summerville formation had a similar origin as the gypsum in the piper formation, i.e., a broad coastal intertidal and supratidal sabkha. in such a depositional setting, renewal of groundwater tidally as well as by seawater infiltration is irregular allowing the underground water to reach the saturation point for gypsum through evaporative pumping at the surface in a warm or hot dryland environment (al-youssef, 2014; warren, 2016). gypsum may also precipitate beneath algal mats in the intertidal zone within the sabkha (al-youssef, 2014). figure 18. similarities between the gypsum of the summerville formation (a–f) and the gypsum from the marine piper formation, bighorn basin, wyoming (g–i). (a) bed of nodular gypsum, woodside anticline (39.1831°, -110.4137°). (b) nodular gypsum showing weakly developed “chicken-wire” texture of displacive growth (sample wetted with water); sample location as a. (c) nodular gypsum with granular texture, woodside anticline (39.1927°, -110.3958°). (d) pelloidal gypsum with displacive growth, middle summerville, shadscale mesa (38.8855°, -110.4464°). (e) bed of granular gypsum, approximately 24 m above the base, shadscale mesa (38.8887°, -110.4437°). (f) gypsum seams parallel and cross-cutting to bedding, shadscale mesa (38.8890°, -110.4435°). (g) bed of granular gypsum, piper formation (45.0199°, -108.4586°). (h) gypsum showing “chicken-wire” texture of displacive growth, upper piper formation (45.0113°, -108.4470°). (i) cut and polished gypsum showing “chicken-wire” texture of displacive growth (nh.101.11, draper museum of natural history, cody, wyoming); bright flares are reflections of display lights. scales in cm, except e in mm. 77 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 gypsum beds at the summerville formation– tidwell member boundary thick beds of gypsum occur above the red, thinly bedded summerville formation and below the ssmld facies assemblage of the tidwell member. these gypsum beds are up to 14 m thick and are restricted to the western part of the colorado plateau, from the san rafael swell to the henry basin. unlike the laterally extensive gypsum beds and gypsiferous facies of the summerville formation, these gypsum beds may be laterally discontinuous, show rapid facies change, and have a heterogenous structure, which can be illustrated by three examples. the first example is gypsum exposed at the southwestern corner of shadscale mesa where rock fall created a right-angled notch. this notch is located 1 km west of the type section for the tidwell member (location h on figure 3c and figure 19a). this feature, here called “the notch,” formed between 15 august, 1994 and 19 august, 1998 based on dates of aerial photos (see acknowledgments). unlike most gypsum exposures, which are weathered so that only gross features are visible due to gypsite formation (figures 19b and 19c), the gypsum exposed in the notch is more pristine. slight weathering has, however, etched the gypsum bringing out relief and detail showing that the gypsum formation here had a complex depositional history. in contrast, weathering of a roadcut in a similar thick gypsum along i-70 has obliterated much of the internal structure (figure 19c). this roadcut was made between 1964 and 1966 based on aerial photographs (see acknowledgments) and provides an indication of the rate of gypsum weathering. the base of the gypsum facies at the notch is in sharp contact with the underlying fineto medium-grained, moderate-red sandstone of the summerville formation. the contact is irregular, with several centimeters of relief (figures 19d and 19e). a thin pale-green bleached zone (about 1 cm thick) is present at the top of the summerville and similar zones occur throughout that formation. the summerville formation is eroded beneath the gypsum, exposing the undersurface of the gypsum facies. this surface preserves traces of a boxwork of thin gypsum that formerly extended down into vertical cracks in the summerville. in a few places, the undersurface of the gypsum where it is undercut is nodose or lumpy, with nodes a few centimeters in diameter. the lower part of the gypsum facies consists of stratified gypsarenite, which is best seen on the southeast wall of the notch (figure 19e). bedding is well developed and includes laminations (figures 19f and 19k), cross laminations (figure 19i) and crossbedding of aquatic dune migrations (figure 19k). these beds are bracketed by bounding surfaces (e.g., figure 19k arrows). also sitting on bounding surfaces are oblate gypsum spheres with flattened bottoms (figures 19e and 19h). these gypsum spheres have an aphanitic internal fabric of leiolites (structureless microbialites) and the flattened bottoms indicate that these microbialite domes grew in situ in a shallow (less than 1.5 m) perennial saline lake. there is no evidence that the domes were exposed subaerially for extended periods (de deckker, 1988; bąbel, 2004; riding, 2011; farías and others, 2014; rasuk and others, 2014; warren, 2016; herrero, 2019). the aphanitic fabric is probably not due to secondary diagenesis because the surrounding gypsarenite shows no loss of texture. instead, the fabric indicates continuous accretion (braga and others, 1995; see contrasting interpretation by riding, 2000). the elongate shapes suggest that the domes grew parallel to the dominate water flow direction as indicated by cross-bedding of the gypsarenite (bąbel and others, 2011). gypsarenite supported small, irregular gypsum blocks and spheres (figure 19e), which are probably reworked fragments and possibly small, displaced leiolites (figure 19j). stratification of the gypsarenite is distorted in places (e.g., figure 19f), especially around leiolites (figures 19e and 19h). the upper part of the gypsum facies on the wall of the notch shows a gradual change in the saline lake. there is an abrupt absence of cross-bedding accompanying a change from reddish-colored gypsarenite to gray (figure 19e) that appears to indicate an increase in detrital clay, although this was not confirmed by thin section. at the top of the gray horizon are what appear to be small (about 6 to 10 cm tall), tightly packed, flattopped columnar thrombolites (figure 19l). the contact between the two layers is irregular and the bases of the thrombolites fade into gray layers at staggered intervals 78 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 indicating that the start of their growth was not simultaneous. these possible microbialites were buried by an influx of fine-grain clastic sediment within which vertically aligned gypsum later grew. this type of gypsum shows the characteristic displacive crystallization fabric of tightly packed competitive gypsum formation from playa groundwater (rosen and warren, 1990a, 1990b; warren, 2016). alternating light and dark bands of very thinly bedded or thickly laminated gypsum (figure 19f) is reminiscent of similar bands in modern playa environments, such as salt flat playa in west texas (figures 20a and 20b). the influx of fine-grain clastic sedfigure 19. caption is on the following page. 79 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 iments is seen in several thin beds (figure 19g) and on the weathered face where they separate thicker gypsum beds (figure 19a). the lower clastic influx has a thin layer of dolomite, which becomes thicker on the north wall, indicating a period of standing water. the uppermost part of the east wall is difficult to discern due to weathering, brecciation and possible mobilization and redeposition of gypsum. dissolution of a small fragment of gypsarenite (using the sodium citrate solution method) from the lower part of the east wall produced a residue of very well sorted, sub-angular to rounded quartz of sand that was windblown into the playa (figure 19m). the changes in in the lake may be related to inflow volume and change in water chemistry. warren (2016) associated such changes to a change in climate, fluvial supply, and/or tectonics. the second example is the peripheral playa facies 0.5 km north and across a box canyon (figure 21a). the deposits, nicknamed “the road,” occurs adjacent to a uranium prospecting road built between 13 september, 1952 and 9 october, 1955 (based on dates of aerial photographs) during the peak of uranium prospecting on the colorado plateau. the thick gypsum unit can be physically traced around the canyon to the notch (figure 21b). the peripheral playa facies occur in the lower part of the gypsum cliff (figure 21c) and are overlain by thick gypsum beds that are weathered. the peripheral playa unit consists of lithofacies, which are, in ascending stratigraphic order, (1) a basal muddy interval, (2) thinly bedded interval, (3) a thicker gypsum interval, (4) cross-bedded sandstone interval, and (5) a massive, weathered gypsum interval. the basal muddy, gypsiferous claystone and sandy mudstone interval is in scoured into the underlying summerville formation (figure 21d). the basal bed also contains several lags of small gypsum pebbles (figure 21e) that are similar in size to those produced in a modern playa (figure 20c) and indicate the pebble lag originated from reworking of playa sediments. several dolomitic boulders occur higher in the interval, including a large one that is about 32 cm in diameter, with the overlying gypsum layer deformed over it from compaction (figure 21f). to move this boulder, water velocity is roughly estimated as 0.7 m/s using the gauckler-manning equation (williams, 1984): v = r0.67•s0.50/n, where r is hydraulic radius or mean depth (in m), which here is the boulder height; s is channel slope, which for the tidwell is assumed to be 0.0011 (based on trampush, 2013; trampush and others 2013), and n is the roughness coefficient (manning’s n), which for medium-grained sand is 0.022 (arcement and schneider, 1989). the resultant water flow velocity is only meant to be an approximation because there are many unknowns, including the dimensions of the channel, actual bed roughness, obstacles, such as vegetation, etc., that all affect velocity. regardless, the approximated velocity is reasonable for the size of the boulder in a sand channel. the boulders occur at the same stratigraphic level as the lower cross bedded gypsarenites at the notch (figure 19a), thus indicating that flowing water rather than blowing wind was the cause for the cross-bedding at the notch. overlying the basal muddy interval is an interval of mostly alternating thinto thinly bedded, greenish-gray and reddish-gray mudstones and gypsum, dolomites, gypsiferous sandstones, and sandstones that is about 1.33 m thick (figures 21c, 21g, and 21h). this interval is figure 19 (figure is on the previous page). “the notch” on shadescale mesa, emery county, utah (38.8843°, -110.4456°). (a) the notch, d is the face shown in (d), e is the face shown in (e). (b) south side showing the deeply weathered face of the gypsum. (c) deeply weathered thick gypsum in a roadcut along i-70; the cut shows the extend of weathering in just over 55 years (vertical white streaks are remnants of drill holes). (d) north face of the notch, which is more weathered than the east face suggesting that this face formed part of a fissure allowing weathering for many years before the rockfall. (e) east face showing the more pristine gypsum face. (f) bedded gypsarenite distorted around a leiolite in the lower right corner. (g) close-up of shale layer on north face (see l). (h) close-up of an in situ leiolite. (i) close-up and color-enhanced gypsarenite with dark clay and chert detritus. arrow indicates cross-bedding. blue bar = 3 cm. (j) grain-supported larger fragments of gypsum (including a small leiolite?). (k) cross-bedding in gypsarenite and bounding surfaces (arrows). (l) possible thrombolites (t?) at the top of a gray gypsarenite (clay enriched?) and below red and gray mudstones with a thin dolomite layer (d) and gypsum seams. note patch of vertically aligned gypsum showing displacive growth on far-left side below dolomite. (m) eolian sand from layer 2; scale in 0.01 mm increments. 80 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 overlain by a 1.3-m-thick bed of gypsum, the upper and lower parts of which are formed by coalesced gypsum nodules. this gypsum bed is overlain by a 1.1-m-thick sequence of red and gray siltstone with gypsum seams (figure 21i), dolomite with rhizoliths (figure 21j), a red and gray mudstone with a meshwork of gypsum (figure 21k). the presence of root-traces in sediments of the playa complex indicates that gypsophylic plants had evolved by the late jurassic. laterally to the gypsum meshwork the gypsum grades into clusters of gypsum blades (i.e., poorly developed desert roses; figure 21l). this red and gray siltstone and mudstone interval is overlain by cross-bedded, medium-grain, gypsiferous sandstone that is 0.9 m thick (figure 21m). the sandstone is overlain by a massive, 5+ m thick, deeply weathered gypsum, which caps the exposure. where broken, the massive gypsum shows seams of displaced red and gray mudstone (figure 21n) and localized authigenic, red chert (figure 21o). massive gypsum deposits in nonmarine environments can originate as eolian deposits on the margins of playas, such as seen at salt flat playa in west texas (figure 20d). gypsum dunes tend not to have trough or festoon cross-bedding that characterizes sand dunes (warren, 2016). the varying lithofacies of these two examples, the notch and the road, can be correlated for 0.5 km and records the changes across the playa lake (figure 22a). the siliciclastic layers probably represent floodouts (figure 22b) from the fluvial fan extending from the eastern-most part of the elko highlands, with sediment input into the playa from heavy precipitation events in the catchment or on the fan (goudie, 2013). these episodes of freshwater and sediment input at the road may correlate with some of the bounding surfaces seen at the notch. the dimensions of the playa lake are unknown due to truncation of the gypsum on the south figure 20. modern gypsum playa and its deposits. (a) salt flat playa, hudspeth county, texas (31.7563°, -104.9860°). view north, with the northern end of the guadalupe mountains to the right. white bands on the horizons are gypsum dunes. dark surface due to high water content and extensive microbialite cover (see d). (b) alternating light (gypsum) and dark sediment (dolomite and organic carbon-rich) bands in the upper part of the playa. (c) in situ gypsum nodules. (d) cross section of a gypsum dune on the east side of the playa; wind from the left. (e) wrinkled sediment encrusted microbialite on playa surface. scales in cm. 81 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 figure 21. (a) peripheral playa deposits at the road locality, emery county, utah (38.8890°, -110.4431°). (b) peripheral playa deposits (red box) can be traced continuously to the gypsum deposits at the notch (cliff, right side). (c) close-up showing the peripheral playa deposits and alternating layers of mudstone, and of limestone and gypsum. (d) basal sandy, gypsiferous mudstone (gray) in erosional contact with the red summerville. (e) lags of gypsum pebbles. (f) reworked dolomite boulder. (g) example of a red and gray mottled mudstone, (h) detail of coalesced gypsum nodules. incipient nodules seen in the red mudstone, grading upwards into coalesced nodules. (i) pale-red and green siltstone beds bisected by a tan, fine-grain sandstone. (j) rhizoliths in a dolomite. (k) mesh of gypsum blades. (l) clusters of gypsum blades (desert roses). (m) cross-bedded medium grain sandstone. (n) massive gypsum with seams of displaced clay. (o) authigenic red chert in gypsum. 82 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 and west sides of shadscale mesa, but the gypsum bed can be continuously traced 7.53 km eastwards along the southern face of the mesa to where it grades rapidly into gypsiferous siltstone beds within a few hundred meters. this rapid lateral change is common in the thick gypsum beds (figure 23a). gypsum thickness data on the east side of the san rafael swell from trimble (1976) shows that the saline lake at shadscale mesa was the southern-most of three centers of thickest gypsum deposition (figures 23b and 23c). these lakes are infigure 22. (a) correlation of the peripheral deposits at the road with the gypsum deposit at the notch. (b) reconstructed sequence interpretation for sediment deposition of the periphery playa lake deposits (left side) and main playa lake (right). not to scale. 83 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 formally named the shadscale mesa, tidwell bottoms, and cottonwood wash playa lakes. the absence or near absence of gypsum at locations 4 and 5 of figures 23b and 23c suggests that little or no gypsum was deposited there and represent interplaya mudflats (this absence was not independently verified owing to inaccessibility on the now heavy eroded old uranium prospecting access road). the third example of a thick gypsum bed is exposed in the cut bank of horn silver gulch (location h on figure 7) and shows that gypsum beds also occur as infilling of paleochannels. gypsum along horn silver gulch was briefly described by gilluly (1929, p. 114) and by lupton (1913), who noted a sample was 97.3% pure gypsum, the rest being “impurities” including nodules of variegated chert. a sample that i dissolved produced eolian quartz grains and red clay among the residue. the gypsum bed at horn silver gulch is deposited into a broad channel cut 4.3 m into the underlying summerville formation (figure 24a, red arrows). this channel was infilled by over 4.8 m of gypsum beds separated by thin mudstone layers. the texture and fabric of these gypsum layers share some similarities with those on shadescale mesa, but with some important differences as well. the fabric of the gypsum at horn silver gulch includes closely packed vertical pelloidal gypsum surrounded by displacive clay matrix (figure 24b), and vertical lenticular blades that are also surrounded by displacive matrix (figure 24c). the displaced sediments show that these two fabrics formed within the sediments of playas rather than on the sediments of a playa bottom or be transported into the channel by wind or water. the absence of microbialite domes (stromatolites, dendrolites, thrombolites, leiolites [warren, 2016]), suggests that standing water was too irregular for microbialites to grow. this does not exclude the possibility that biolaminates (cyanobacterial mats) may have been present because these are common on modern playa surfaces (e.g., figure 20e; also, dupraz and others, 2011). gypsarenite is absent but because the exposed surfaces are more weathered than at the notch (example 1), i cannot rule out that this absence is due to weathering figure 23. (a) rapid lateral change in the basal gypsum from a maximum of approximately 3 m to a thinner gypsiferous siltstone. red arrows denote the gypsiferous bed, east of san rafael river, utah (38.8548°, -110.3672°). (b) gypsum thickness at the base of the tidwell member relative to the j-5 unconformity along a section of the eastside of the san rafael swell. three major depositional centers as peaks are indicated. (c) map showing the location of the ten measured sections given by trimble (1978) used to infer the basal gypsum thickness. image from google earth. 84 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 and a surface coating of gypsite. examination of a core through the deposit might resolve this. the individual gypsum beds range in thickness from a few centimeters to almost 0.75 m, and many are separated by thin red or gray claystone or mudstone seams. not all of the seams are continuous across the outcrop and adjacent gypsum beds may merge. superimposed on the gypsum beds is a u-shaped fluvial channel, a paleo-gully (figure 24a, yellow arrows; figure 24d) that is approximately 11.5 m wide and 3 m deep. the channel does not extend into the underlying summerville formation. below the lowest part of the channel, the gypsum is extensively brecciated. on the north (left) side, gypsum blocks show a chaotic arrangement of a paleo-gully bank collapse (figure 24d, red box). above the channel bed, is an interval of thinly bedded red and gray mudstone and this in turn, is overlain by two gypsum beds separated by a thin mudstone. three explanations may account for the channel and infilling. one is incision of a channel between two smaller playa lakes due to a drop in water level of a larger playa lake leaving the smaller lakes isolated, such as seen at the south end of lake kurdyma, a large playa lake among many playas in the steppes of southeastern aktobe oblast, kazakhstan (48.0192°, 63.0278°). the second explanation is the incision of a gully into peripheral playa deposits due to intense, heavy rains as is common in dryland environments (blair and mcpherson, 2009; goudie, 2013). possibly there had been a drop in the base level of the playa lake from a period of little rain fall. after the channel was cut, downward seepage into the channel bed by fluvial water, which was undersaturated with respect to gypsum, dissolved the underlying gypsum causing it to collapse and brecciate. siliciclastic sediment, represented by the red and gray mudstone, brought by the fluvial water, is found intermingled with the breccia and eventually sealed the bed thereby halting further dissolution. a rise in the playa lake or localized ponding of gypsiferous water and subsequent evaporation created the overlying gypsum beds. the figure 24. (a) thick gypsum bed at horn silver gulch, emery county, utah (39.0402°, -110.9722°). red darts indicate the unconformable contact with the summerville formation; yellow darts indicate a channel cut into the gypsum and filled with gypsum. two major gypsum morphs: (b) closely packed vertically oriented pelloids; note clay layer separating beds. near the base of the gypsum. (c) tightly packed lenticular gypsum blades higher than the pelloid gypsum layer. (d) close-up of the fluvial channel cut and collapsed bank gypsum debris (red box). 85 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 third explanation is that the channel is a karst feature and the mudstone layers are siliciclastic grains liberated from the dissolution of a gypsum bed. this hypothesis seems less likely because of the uniform cross section of the channel, and its smooth edges appear water worn. in addition, a single sinkhole would be unusual because no others were seen in the area. the significance of the example from horn silver gulch is that the channel that was cut into the gypsum about midway during the history of gypsum deposition. such a deep cut in a marine or coastal sabkha seems unlikely given the widespread uniformity of the depositional environment. rather, the very localized erosion and infilling by siliciclastic sediments is more in keeping with fluvial erosion and deposition. excluding interbedded mudstones, the thick gypsum deposits around the san rafael swell contain a small percentage of windblown detrital grains. bluhm and randle (1980) report that detrital grains comprised less than 10% by volume of the gypsum. the grains are subangular to subrounded, very fine to fine-sand sized grains consisting of ferric oxide-stained clay, single crystal detrital quartz, sparitic carbonate cement, little altered to fresh plagioclase and microcline feldspars, disseminated detrital opaques, detrital chert, and detrital chalcedony. weeks (1953) reported the presence of the water-soluble anhydrous sodium sulfate mineral thenardite. the specimen was reported to be from the summerville formation, but is more likely to have come from the tidwell member because this mineral forms in playas and is among the last minerals to precipitate out (warren, 2016). contact between the gypsum facies and the overlying interbedded thin sandstone, mudstone, and limestone facies assemblage is very poorly exposed because of talus or weathering. seen from a distance, there appears to be an abrupt change in lithology, which trimble and doelling (1978) and anderson and lucas (1998) construed as an unconformity. peterson (1988a), however, interpreted the change as due to local dissolution of the gypsum. the contact is well exposed opposite the type section and this shows, at least here, that the transition is gradational, with interfingering with the base of the ssmld facies assemblage (figure 25). placement of the j-5 unconformity the contact between the summerville formation and the base of the morrison formation was originally considered to be an erosional unconformity by emery (1918), dake (1919), and gilluly and reeside (1927). in contrast, mullens and freeman (1954, 1957) considered the morrison-summerville formations to be in conformable contact over most of the colorado plateau and that the change in lithologies was due to a change from marine to terrestrial depositional environments as a result of withdrawal of the sundance sea figure 25. interfingering between the top of the thick gypsum and the ssmld facies assemblage opposite peterson’s stratotype at shadscale mesa. abbreviations: jms – salt wash member, morrison formation; jmtg – tidwell member, morrison formation, gypsum bed; jmtssmld – tidwell member, morrison formation, thin bedded sandstone, siltstone, mudstone, limestone and dolomite facies assemblage; js – summerville formation. 86 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 from this region. this position was supported by mobley and santos (1956), who considered the summerville formation to interfinger with the basal sandstone beds of the salt wash member of the morrison formation. craig and shawe (1975) were equivocal, noting that the morrison formation appeared to be conformable with the summerville formation, but they did not rule out that the contact might be a disconformity because of the temporal gap between what was then considered the callovian aged summerville and kimmeridgian aged morrison. peterson (1980b), however, concluded that the conformable interpretations of the contact were in error because tidwell strata were placed in the top of the summerville. the prominent, thick gypsum beds in the green river mining district were placed at the base of the salt wash member of the morrison formation by some authors (e.g., gilluly and reeside, 1927; gilluly, 1929; mcknight, 1940; young and others, 1957, 1960). whereas other authors place the beds in the summerville formation (e.g., lupton, 1914; clark and million, 1956; mullens and freeman, 1957; trimble, 1976; bluhm and rundle, 1980; anderson and lucas, 1994, 1998; lucas and others, 2006; lucas, 2014), and some have done so despite acknowledging an angular unconformity below the gypsum (e.g., trimble, 1976; trimble and doelling, 1978). given that this part of the colorado plateau is not underlain by pennsylvanian salt deposits (hallgarth, 1962; peterson, 1983), halokinesis cannot be the cause for the angular unconformity. peterson (1984, 1988a) linked the cause of the angular unconformity to the emery uplift without elaboration. the angular unconformity between the summerville sandstones and siltstones and the thick gypsum beds is one of many unconformities that truncate low-amplitude anticlinal folds at the top of the summerville formation (figures 26a through 26e) around shadscale mesa (trimble, 1976; trimble and doelling, 1978) and in the henry basin (figures 26f through 26h). the anticlines occur as far east as the green river. the amplitude of the anticlines based on the amount of truncation is between 30.5 and 61 m (trimble, 1976; trimble and doelling, 1978). the distance from crest to trough varies considerable from 200 to 800+ m (trimble, 1976; trimble and doelling, 1978). despite their wide distribution, the anticlines have largely gone unnoticed or unremarked (e.g., hunt, 1953; witkind, 2004; bernier and chan, 2006). it is also probable that the gilbert-style delta reported by kirkland and others (2020, their figures 4b through 4d) at the top of the summerville is the southern limb of an anticline, with the northern limb hidden by talus from the overlying morrison formation. otherwise, the delta is prograding south in opposition to the northeastward regression of the sundance sea. because most anticlines in the summerville are visible as cross sections in cliffs, the azimuth for most of the fold axes can seldom be determined and the orientation of the anticlines relative to the sundance sea or elko highlands are unknown. however, it is possible to extrapolate the fold axis azimuth for one anticline at the southwest corner of shadscale mesa. the summerville formation here forms an angular unconformity with the overlying thick gypsum. a thin, distinctive gypsum bed near the top of the summerville formation is truncated by the angular unconformity on both sides of a ridge or spur (figures 26a and 26b). a plane parallel to the gypsum bed intercepts the unconformity on both sides of the ridge (figure 26c, line connecting points a and b, which correspond to figures 26a and 26b) with an azimuth of n. 21° e. and a dip direction of 290o w. indicating that the summerville formation here is the west limb of an anticline (dip angle was not calculated). the east limb of the anticline is visible in cross section along the south face of shadscale mesa (figure 26d, corresponds to point d in figure 26c), and the fold axis is seen in a shallow box canyon (figure 13c, green line). the axis is n. 21° e., parallel to the plane intercept of the west limb with the angular unconformity. the azimuth confirms the observation by trimble (1976) that the almost two dozen paleo-folds, as he called them, trend north to northeast (he does not explain how these were determined). these orientations are roughly parallel to the elko uplift and may reflect movement of the elko forebulge. peterson (1980b) mentioned the presence of anticlines in the summerville formation in the henry basin, but nothing is said about their orientation. he does note that paleo-anticlines in the lower part of the morrison formation in the henry basin trend mostly 87 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 northwest-southeast, which would be perpendicular to the southern part of the elko highland front as shown by thorman (2011). these paleo-anticlines were inferred from variations in bed thickness and recurring facies over the inferred anticlines and synclines (peterson, 1980a, 1984, 1986). re-examination of these anticlines is needed to determine if they were formed post-summerville deposition. the significance of the truncated summerville anticlines is that they demonstrate a passage of time between the withdrawal of the sundance sea and deposition of the thick gypsum beds (figure 27). the summerville is therefore a diachronous surface from south to north as the sea regressed northwards. the truncating of the anticlines may have also coincided with the erosion of the top of the summerville east between the green and colorado rivers reported by o’sullivan (1980a). the amount of time represented by the erosional surface is unknown, but was long enough for the anticlines to develop and be truncated. anticline uplift rates of 2.1+ mm/yr have been reported (li and others, 2020; kleber and others, 2021) and based on the estimated amplitudes of 30.5 to 61 m (trimble, 1976; trimble and doelling, 1978), those in the summerville may have formed in as little as 14,500 to 29,000 years. considering how rapidly the summerville formation erodes today (howard, 2009), assuming the erosion rate equaled uplift rate, the anticlines formed and were eroded in as little as 29,000 to 58,000 years. however, given that rates of erosion may have been significantly less in the jurassic arid environment, a reduction of erosion to 25% of uplift rate, the anticlines could have formed and been eroded in 58,000 to 232,000 years. the actual time would very much depend on the rate of anticline formation, and even if halved, the results suggest that the j-5 unconformity was less than a half-million years as also estimated by peterson (1994). this weathered and eroded surface across the top of the summerville formation has been identified as the j-5 unconformity (pipiringos and o'sullivan, 1978; o'sullivan, 1984a; peterson, 1988a). as a result, this places the thick gypsum beds in the san rafael swell and henry basin at the base of the tidwell member of the morrison formation as originally stated by peterson (1988a). o'sullivan (1984a) and peterson (1980a) believed that the j-5 unconformity can be traced almost continuously over most of the colorado plateau as a disconformity, an idea previously suggested by mcknight (1940, p. 108). the disconformity can be difficult to determine if exposures are weathered and the most commonly used criterion introduced by o’sullivan (1980a) has been the presence of the bed a sandstone (figures 8 and 12a through 12d). a similar criterion is used to separate the thinly bedded windy hill member of the morrison in northeastern utah from the overlying tidwell member (sprinkel and others, 2019). however, in places the lower tidwell can be thin bedded (figure 12a) giving the impression that the contact is gradational. placing the boundary in the vicinity of white sand dunes recreational area west of duma point, is problematic because the sandstone that could be construed as bed a is thin and discontinuous (figure 14d). here, at least, i cannot rule out that the tidwell is conformable with the summerville. mcknight (1940) made a similar observation in the area and used the color change from red or reddish-brown of the summerville and lavender of the morrison as the contact. potter-mcintyre and others (2016) and ejembi and others (2021) concluded that the wanakah and tidwell in western colorado were conformable based on similar cambrian detrital zircon dates sourced from recycled older deposits. at most, the similar zircon dates indicate continued erosion of the same source and do not by themselves rule out a disconformity. channel cuts into the top of the summerville formation occur (figure 28), some containing black cherts (figures 28a and 28b; peterson, 1988a, figure b23) and others containing paleozoic fossils derived from the elko highlands (peterson, 1987; 1994). significantly, no lithic fragments of the summerville have been found in the base of the tidwell member suggesting that the sediments had not undergone significant lithification prior to erosion. hunt and others (1953) report channels up to 15 m deep cut into the summerville formation. the incision of these channels may be due to the fall of regional base level that marked the withdrawal of the curtis-summerville sea and the development of the j-5 unconformity (caputo and pryor, 1991; peterson, 1994). 88 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 figure 26. caption is on the following page. 89 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 comparisons of the tidwell and the ralston creek, two basal members of the morrison formation in eastern colorado, the gypsiferous ralston creek member of the morrison formation is in part a contemporaneous playa lake complex to the tidwell member of the morrison formation (carpenter and lindsey, 2019). peterson (1994) noted several similarities between the two members, including that both (1) lay immediately above the j-5 unconformity, (2) interfinger with other the morrison strata above, (3) have a basal sandstone, (4) locally have strata composed of interbedded thin mudstones and sandstones (figures 29a and 29b), marlstone beds, thin limestone, gypsum beds (figures 29c and 29d), and (5) have a zone of red and yellow cherts nodules. the gypsum in both the ralston creek and tidwell members include the vertically aligned, lenticular crystals (figures 29e to 29g). this type of crystals typically forms displacively in marginal playa sediments (cody and cody, 1988; rosen and warren, 1990a, 1990b; carpenter and lindsey, 2019). in addition, the geochemical signature of the gypsum in both members is nonmarine. these similarities provide indirect support for placing the thick beds of gypsum at the summerville formation-tidwell member boundary in the tidwell member. on lithostratigraphic grounds, the case could be made that the two members should have the same lithostratigraphic name. the name ralston creek (leroy, 1946) is older than tidwell (peterson, 1988a) and would have priority. however, the two members were deposited in separate basins separated by remnants of the ancestral rocky mountains and are slightly different in age. hager (2015) reported a date of 152.99 ± 0.10 ma for the ralston creek member and trujillo and kowallis (2015) gave a date of 156.77 ± 0.55 ma for the tidwell member. for these reasons the two lithostratigraphic units are considered distinct, with their lithologies due to deposition under similar environmental conditions. the ralston creek playa lake complex was named the ralston creek boinka as discussed by carpenter and lindsey (2019) because it was a through-flow groundwater system with surface discharge as playas and playa lakes (rosen, 1994). however, because macumber (1980) inferred a specific meaning for “boinka” as a large groundwater discharge basin (typically saline), which cannot be demonstrated for the ralston creek, i refer to it now as the “ralston creek playa complex.” the gypsum facies of the tidwell member on the western colorado plateau may have been a similar playa complex where groundwater flowed down the potentiometric gradient from mountains on the west; it is here named the “tidwell playa complex.” source of the tidwell member sediments the tidwell member is considered intimately linked to the overlying salt wash member as the distal facies of the salt wash alluvial fan (peterson, 1977, 1980a, 1984, 1994; condon and peterson, 1986) or as the distal facies of the salt wash distributive fluvial system (weissmann and others, 2013; owen and others, 2015b, 2017). the distributive fluvial system is an inclusive term encompassing a continuum from alluvial fans to megafans (hartley and others, 2010); it is not a term recognized by geomorphologists (e.g., goudie, 2004a, 2013; north figure 26 (figure is on the previous page). angular unconformities at the top of the summerville formation. angular unconformity (arrows) at shadscale mesa (38.8844°, -110.4455°): (a) west side of spur and (b) east side of spur. (c) strike of the angular conformity is determined from the intercepts (a, b) with the overlying bed; limb dips west-northwest. the anticline axis (green) is determined from the corresponding east dipping limb shown in (d) and ground observation of the crest (38.8822°, -110.4383°). (e) possible reactivated low-angled anticline on the west side of shadscale mesa (38.9037°, -110.4360°). anticline in the entrada (je) is truncated and overlain by the curtis (jc), which is not thinned over the anticline. north limb of an anticline in the summerville (js) denoted by arrows. south limb is to the right of photograph. anticlines in the henry basin: (f) west limb exposed in lone cedar flat, utah. (g) north and south limbs (between arrows) exposed on unnamed mesa, cottonwood wash (38.0305°, -110.6282°); usgs photo hcb00707. (h) interpretative sketch of (g): green and red are the two uppermost strata in the summerville formation showing the north and south limbs of the anticline and its truncation by the tidwell member (yellow). 90 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 and warwick, 2007; shroder, 2013; bowman, 2019) and rejected by some sedimentologists (e.g., fielding and others, 2012). the concept of the salt wash alluvial fan, was first discussed by craig and others (1951, 1955) based on lithofacies and isopachous maps of the salt wash member. they concluded that there was a single source apex in south-central utah near the present-day confluence of the colorado and san juan rivers. although a map of paleocurrent azimuths also was given, these were not used to identify the location of the fan apex, but rather were cited as supporting evidence for the location of the fan apex. emphasis on paleocurrent data to locate the salt wash fan apex was done by owen and others (2017) using statistical analysis to place the apex about 150 km farther west and south in the vicinity of the kaibab plateau north of the grand canyon, arizona. this plateau, superimposed on the colorado plateau, formed by laramide reactivation of basement faults (davis and bump, 2009), but otherwise this region of the colorado plateau lacks evidence for a jurassic orogeny as the owen and others (2015a, p. 150) model requires. this lack of evidence for an orogeny also holds true for the location of the fan apex of craig and others (1951, 1955) and mullens and freeman (1954, 1957). the mogollon highlands, the northern rift shoulder to the bisbee basin, were over 150 km farther south from the fan apex of owen and others (2015a, 2017) based on evidence presented by bilodeau (1986), dickinson and lawton (2001), and turner and peterson (2004). in contrast to the problematic single source model, others have concluded that the strata of the tidwell and salt wash members had multiple sources mostly from the south and west of the colorado plateau (cadigan, 1967; peterson, 1980, 1986, 1987, 1988b, 1994; peterson and turner-peterson, 1987; robinson and mccabe, 1998; turner and peterson, 2004; dickinson and gehrels, 2008, 2010; maidment and muxworthy, 2019), and also from the southeast (potter-mcintyre and others, 2016; ejembi, 2018). peterson and turner-peterson (1987) and peterson (1988b) argued that the localized thickness of the salt wash presented by craig and others (1951, 1955) was due to basin subsidence during deposition, rather than proximity to source. in addition, the presence of 1-m-diameter boulders in the henry basin and san rafael swell indicated a western source. different source areas for sandstone are supported by detrital zircons. dickson and gehrels (2008, 2010) determined that sandstone from near notom, utah (near location e, figure 7), in the west-central part of the colorado plateau originated from recycling of older jurassic eolianites from the elko and mogollon highlands, and particularly from a drainage system figure 27. summary illustration for the formation of the basal gypsum of the tidwell member. approximately west to east: (a) regression of the sundance sea with gypsum formation in the sabkha environments of the coastal, tidal and supratidal zones; (b) syncline and anticline phase; (c) erosional truncation of the anticlines and development of playa complex; (d) progradation of the megafan over the former playa complex. these sediments are of the ssmld assemblage facies. 91 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 emerging from their syntaxis in what is now the grand canyon area (stokes and heylmun, 1963, named this syntaxis the “grand canyon bight”). peterson (1987, 1994) used pennsylvanian and early permian invertebrates in pebbles to identify two narrow source zones in the eastern elko highlands, and an additional source of red and green cherts from ordovician and silurian strata in the western elko highlands in central nevada. yingling (1987) and yingling and heller (1992) located three possible sources for paleozoic cherts in the eastern basin and range, of which the southern two coincide with those identified by peterson (1994). potter-mcintyre and others (2016) concluded that detrital zircons in the northeastern part of the colorado plateau indicate a source from the wet mountains in the southern ancestral rocky mountains of south-central colorado, as did ejembi (2018) and ejembi and others (2021), who also suggested additional sources in in the amarillo-wichita mountains of southwestern oklahoma. the multiple sources may reflect the time of transition from streams originating from pangaean terranes and the north american craton of the early and middle jurassic to the cordilleran terranes of the late jurassic and cretaceous (blakey, 2019). precambrian quartzites in triassic and jurassic conglomerates along the arizona and new mexico border suggests that the eastern mogollon highland was an active sediment source during the mesozoic (dodge, 1973). an eastern mogollon locality for some paleozoic cherts was also noted by yingling (1987). an isopachous map of the tidwell member supports multiple source areas to the west, southwest, south, and east (figure 30), whereas paleocurrent data for sandstones in the ssmld facies assemblage presented by bernier and chan (2006) suggests primarily a west-southwest source (figure 31a). assuming that the sediments of the tidwell member are the distal facies of salt wash fluvial fans (peterson, 1977, 1980a, 1984, 1994; condon and peterson, 1986), then the paleocurrent data for the salt wash member should also reflect the paleocurrents of the tidwell member. these paleocurrents for the salt wash are presented in figure 31b. based on a larger data pool than those originally given by craig and others (1951, 1955), these paleocurrents suggest multiple sources to the west and southwest (figures 31c and 31d). the southwestern source does coincide with the grand canyon bight, and is approximately 150 km farther west than the location of the fan apex for the salt wash distributive fluvial system given by owen and others (2015a). the source lies in the direction of the “las vegas cluster” of intersecting back figure 28. channels and fills cut into the summerville formation. (a) conglomeratic channel fill near summerville point (39.1691°, -110.4574°); red box shown in b. (b) close-up of fill showing abundant black cherts. scale in cm. (c) deep channel cut filled with gypsum, near shadscale mesa (38.8794°, -110.4436°). (d) gypsum filled 15 m channel cut 1 km northeast of muddy river, west side of little wild horse mesa (38.5408°, -110.9187°), usgs photo hcb00360. 92 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 traces of paleocurrents given by owen (2014), which lies near lake mead along the nevada-arizona border. the average paleocurrents should reflect the ground slope in the direction of the retreating sundance sea, hence the surface upon which the tidwell was deposited. webber (1946) had previously suggested that the flat topography left by the regression of the sundance sea in a dryland environment greatly influenced the deposition of the salt wash member, and by extension the underlying tidwell member. the paleogradient for the flat landscape was estimated to be 1.1 x 10-3 (i.e., 1.1 m/km, or 0.06o) and was consistent throughout the deposition of the morrison formation (trampush, 2013; trampush and others, 2013). however, these paleocurrents show a strong eastward azimuth (figure 31) and less of a northeastward component, which is surprising given that the sundance sea is thought to have regressed towards the utah-colorado-wyoming borders (peterson, 1994; holland and wright, 2020). a possible explanation is an eastward deflection of the fluvial system from the grand canyon bight by fluvial fans from the elko highlands to the west. these results do not support the distributive fluvial system model for the salt wash advocated by weissmann and others (2013), owen (2014), and owen and others (2015b, 2017). as for the gypsum facies of the tidwell member in the san rafael swell and henry basin, brine evolution models (e.g., hardie and others, 1978; warren, 2016) predict the evaporite sequence based on available ions. the predominance of gypsum in the lower tidwell on the westside of the colorado plateau indicates a continuous renewal of both calcium and sulfur from a source area, which was most likely itself a gypsum. it is probably no coincidence that the tidwell playa complex, containing an estimated 24 km3 of gypsum (assuming an average thickness for the gypsum of 3 m), is east of the elko highland, where evaporites of the summit springs member of the pequop formation were exposed by the figure 29. similarities of the tidwell and ralston creek members. alternating thin bedded sandstones and siltstones or mudstones: (a) upper tidwell on the north side of shadscale mesa (38.9196°, -110.3978°), (b) ralston creek along nine mile creek (38.5375°, -105.2216°); thick bed of gypsum (c) tidwell at shadscale mesa (38.8887°, -110.4426°), (d) ralston creek at eight mile park (38.4959°, -105.0806°); characteristic marginal playa lenticular gypsum in the tidwell at (e) shadscale mesa (38.8885°, 38.8885°) and (f) tidwell on the woodside anticline (39.1828°, 39.1828°); (g) tidwell in ralston creek (38.5446°, -104.9582°). 93 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 late middle to early late jurassic (thorman, 2011; thorman and others, 2020). such recycling of older gypsum is known to be a major source for later gypsum deposits (warren, 2016). an analogous situation occurs with the gypsum playa complex of salt flat, new mexico and texas, in which the gypsum is sourced from erosion of the permian evaporites and carbonates of the nearby guadalupe mountains (chapman, 1984; hussain, 1986; chapman and kreitler 1990; hussain and warren, 1991). despite the great thickness of some of the gypsum beds, the time involved may not have been great. schreiber and hsű (1980) report that the depositional rate for gypsum is 1 to 2 m/kyr, whereas allen and others (2009) reported an accumulation rate of 0.5 m/kyr based on c14 dates of organic material in the pleistocene lake otero basin in new mexico. these rates can be applied to the basal gypsum of the tidwell member to estimate possible duration of gypsum accumulation. the retention of texture and minimal bed distortion indicates that the gypsum did not undergo deep burial and significant compaction (warren 2016). therefore, the thickest gypsum bed (14 m) reported by peterson (1988a) required only between 7000 to 28,000 years to precipitate. discussion summerville depositional environment mcknight (1940) interpreted the summerville formation on the western colorado plateau as a delta that emptied into a lagoon that underwent cyclic evaporation causing the precipitation of gypsum. mcknight (1940) interpreted the summerville formation in the eastern colorado plateau as continental deposition because of the sequence of lenticular sandstone beds. baker (1946) also considered the thin, regularly bedded sandstone and siltstone and the bedded gypsum as infigure 30. isopach of tidwell thickness, contours in m. several depositional sites are present around the peripheries, the most important of which are towards the west and southwest. data from peterson (1978, 1980a, 1980b, 1982c, 1988a), o’sullivan (1980a, 1980b, 1981a, 1981b, 1984a, 1984b, 1986, 1989, 1991, 1992b, 1995a, 1995b, 1996, 1998, 2000, 2004), o’sullivan and pipiringos (1983), kowallis and heaton (1987), robinson (1994), kjemperud and others (2008), doelling and kuehne (2013), swan (2018), kirkland and others (2020). 94 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 figure 31. paleocurrent summaries. (a) rose diagram summary for the ripple sandstone facies of the tidwell member. (b) compilation of paleocurrent arrows plotted on map of the salt wash member (green area). (c) rose diagram of paleocurrent arrows shown in b excluding outliers (e.g., around vernal, utah). average azimuth is 83° and the median is 68°, close to the average azimuth for a. (d) rose diagram of the southwestern most paleocurrents which suggest multiple sources. (a) modified from bernier and chan (2006), figure 6. (b) base map modified from craig and others (1955). data for paleocurrents from stokes (1954), stokes and mobley (1954), craig and others (1955), dawson (1970), derr (1974), mickle and others (1977), tyler (1981), peterson and royce (1982), peterson (1984), yingling (1987), owen (2014), and chesley and leier (2018). 95 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 dicative of deposition in large shallow lagoons. webber (1946) suggested that the summerville was deposited in a large playa because of the gypsum. in the first detailed study of the summerville formation, stanton (1976) interpreted the depositional environment of the summerville formation as a broad tidal flat crisscrossed with tidal channels. the tidal range was assumed to be up to a meter in height based on channel sandstone thickness. subsequent depositional environment interpretations have been variations of this tidal-flat model, including as a supratidal flat (e.g., kocurek and dott, 1983; wilcox and currie, 2008; zuchuat and others, 2018, 2019). caputo (1988) and caputo and pryor (1991) interpret the summerville deposition as a supratidal sabkha because of the gypsum. they suggested inundation by spring tides, storm surges, and wadi flooding in a restricted evaporative basin with hypersaline conditions. given that the summerville formation extends almost the entire north-south length of utah (about 390 km), only a narrow band shoreward of the northeastward regressing sundance sea could have been an active tidal flat (= intertidal zone between normal low and high tide). the narrowness of the tidal flat is due to the limitations imposed by slope and tidal ranges. assuming that the paleoslope 5.09 x 10-4 to 1.53 x 10-3 estimated for the morrison formation is inherited from the curtis-summerville depositional sequence (trampush, 2013; trampush and others, 2013), and the tidal range is estimated to be 2.6 m (mesotidal range) for the curtis seaway (zuchuat and others, 2020), then the active zone of the tidal flat would be 1.7 to 4.4 km wide, which is reasonable based on modern tidal flats (gao, 2019, table 10.1). the implication for the overlying tidwell member is that much of the summerville sediments were exposed to weathering prior to the deposition of the tidwell sediments and therefore the surface of the summerville was a diachronous surface from south to north as the sundance sea regressed. tidwell depositional environment possibly coincidental with the withdrawal of the sundance sea was the formation of the low-amplitude anticlines and synclines, and the subsequent erosional truncation of the anticlines (figure 27). the absence of coarse lag erosion remnants at the top of the summerville formation may be due to the limited size range (silt and fine sand grains) composing the summerville sediments. the folds in the summerville formation suggest renewed tectonic activity of the elko orogeny before deposition of the thick gypsum beds in the tidwell member. although it might seem logical that the synclines would provide the low-relief areas in which individual playas developed, that does not appear to be the case. gypsum over the synclines do not appear to be thicker, nor does gypsum over the anticlines appear to be thinner. in many places, such as along the south face of shadescale mesa and in the henry basin, the gypsum appears to occupy very broad, very shallow topographic lows that were eroded into the top the summerville formation across both anticlines and synclines (summarized in figure 27). although water erosion is usually assumed to be the mechanism in such cases, deflation by wind may have also played a role and might be the source for the eolianites of the bluff sandstone member located downwind. aeolation (wind erosion) is a major cause of erosion of landforms in some dryland environments (shao, 2008; goudie, 2004b, 2013). the geographic area covered by the thick gypsum deposits extends from north of the woodside anticline to approximately 25 km south of hanksville (north of butler wash), and from the west side of the san rafael swell to within about 1.5 km of the white sand dunes recreation area (see figures 7 and 8 for location information). this large area of approximately 6800 km2 indicates the existence of a huge playa complex composed of playa lakes as indicated by the local thicker gypsum bodies (e.g., figures 23b and 23c). the sulfur isotope of this gypsum and carbon isotope of associated limestone indicates a nonmarine source of brines in a closed basin (northrop, 1982). thus, these saline bodies of water are not coastal sabkhas. what is not certain is whether all of these gypsum-depositing playa lakes were active at the same time, or whether they record a sporadic shift eastward with the prograding elko highland fluvial fans. the presence of a non-pedogenic limestone bed at the base of the gypsum near the yen (1952) clam site suggests a localized lacustrine setting prior to salinization and gypsum deposition. as noted previously, the gyp96 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 sum probably originated from weathering and erosion of the evaporites of the lower permian summit springs member of the pequop formation in the elko highlands (steele, 1960; kellogg, 1963). the north-south arrangement of the thick gypsum beds along the west side of the colorado plateau supports this interpretation. the gypsum playas probably formed at the distal end or terminus of fluvial fans as they do in modern situations (shaw and bryant, 2011; goudie, 2013). where the basal gypsum is absent, bed a is present at the base of the tidwell member. however, this stratigraphic unit is rather problematical in that it is a relatively thin, tabular sandstone that is wide spread across the central and eastern side of the northern colorado plateau. bernier and chan (2006) considered the origin of bed a in terms of traditional fluvial deposition as overbank sheetflood in part because of ripple structures (e.g., figure 12g). not resolved, however, is the originating channels for the overbank flows. demko and others (2005) suggested instead that bed a in the henry mountains was deposited in part as zibars, but unfortunately gave no reason for this conclusion. zibars are a low-relief (less than 10 m) eolian bedform composed of coarse sands or granules (0.3 to 0.65 mm) and lacking well-developed slip faces (biswas and others, 2014). zibars are typically spaced 50 to 100 m and are preserved as sand sheets that are usually structureless, but may retain low-angled, flat-rippled laminae, and interbedded coarser-grained sand interzibar deposits (biswas, 2005). zibars occur on the upwind margin of dune fields as the winnowed residues because the grains are too heavy for wind mobilization into dunes (nielson and kocurek, 1986; lancaster, 2009). zibar deposits would be expected on the paleo-upwind side adjacent the sand dune deposits represented by the bluff sandstone member of the morrison formation. a possible fluvially reworked zibar deposit (based on the uniform coarse grain size) in the tidwell member is present at duma point (figure 12e). sand sheets like bed a also can form in dryland environments where conditions limit mobility of sand into dunes. these limiting conditions include a high water table (capillary water tension), periodic or seasonal flooding (wetting of the surface), microbial surface binding (by cyanophytes and fungi) or cementation (duricrusts and rain-splash crust), coarse-grained sand (including surface armoring), and the stabilizing effect of vegetation (kocurek and nielson, 1986). these same features also promote sand accumulation as sheets where otherwise sand transport without deposition would occur. perhaps the best analogous modern sand sheet to part or most of bed a is the selima sand sheet on the border between sudan and egypt (centered at 22o n., 28o e.). occupying 120,000 km2 (maxwell and haynes, 2001), the enormous size is due to the absence of topographic barriers allowing long distance wind transport (breed and others, 1987). sand sheet microstrata are composed of bimodal combination of fine to medium sand laminae separated by granules or coarse sand. these laminae are nearly horizontal because the stoss and lee slopes are < 5o. the recent sand sheet rests disconformably on an older, more consolidated, massive sand sheet that lacks the distinctive coarse-fine laminae (breed and others, 1987). the source for the sand is the underlying cretaceous nubia formation. the sand is moved across the selima sand sheet in giant ripples up to 10 m thick. because the ripples are low profiled and very wide, they give the ground a gently undulating surface making them difficult to discern on the ground; they are best seen on satellite images (breed and others, 1987). the ripples have no slip faces and lack grainflow stratification, so are not classified as dunes (breed and others, 1987). bed a is estimated to have originally covered over 32,000 km2, but much of this was lost with erosion of the monument uplift. nevertheless, the area is a quarter of the selima sand sheet, so bed a as a large sand sheet is well within the realm of possibility. the main sources for the sand may be deflation of the summerville surface and unchannelized flow or floodouts at the distal end of fluvial fans or distributive fluvial systems. floodouts occur in a variety of environments today, but are especially common in dryland settings (tooth, 1999, 2004, 2013; north and davidson, 2012), such as shown in figure 32. the sand sheet and floodout origin for bed a calls into question the stratigraphic occurrence of unionid bivalve escape structures reported by hasiotis (2004) from the base of bed a at hatt ranch located just east of the type section of the tidwell member. bed a by defi97 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 nition occurs at the base of the tidwell member (o’sullivan, 1984a), but at hatt ranch, the base of the tidwell is represented by the thick gypsum facies. it seems more likely that the fossils came from a sandstone higher in the tidwell member or more likely, a sandstone in the salt wash member. the continued progradation of the fluvial fans across the colorado plateau resulted in the interfingering of the gypsum facies and the overlying ssmld facies assemblage (figure 25), which kjemperud and others (2008) considered as indicative of an increasing accommodation/sediment supply (a/s) regime. this interfingering of gypsum and ssmld shows that cessation of gypsum deposition was not abrupt, but rather clastic influx was discontinuous as would be expected in a dryland environment (blair and mcpherson, 2009; goudie, 2013). wide spread of overbank sheet sand from channelized streams are common in the ssmld assemblage facies as seen by the “wings” extending from channel sandstones (e.g., figures 14a through 14e), which are common in dryland floodplains (fielding and others, 2011). other sheet sandstones may represent floodout deposits. north and davidson (2012) note that the rate of flow deceleration would be low for an unconfined flow across the planar surface of the playa, thus allowing for wider dispersal of floodout deposits. peterson (1978, 1980a) and demko and others (2005) note that lacustrine facies dominate the ssmld facies assemblage. however, it is difficult to account for the large volume of water that is implied in a dryland environment with ephemeral fluvial sources (demko and others, 2004, 2005). rainfall was probably both strongly seasonal and erratic from year to year (parrish and others, 2004), as it is in modern drylands (goudie, 2013). a further complication is the absence of prograding deltaic sandstone facies associated with the supposed lacustrine facies. in addition, there is an apparent absence of seasonal salinization of the lakes as would be expected under such climatic conditions (eugster and hardie 1978; warren 2016). nevertheless, figure 32. example of a floodout at the distal end of a fluvial fan near darya-ye namak (“sea of salt”), northern iran. (a) the fluvial fan from space (digitally enhanced to show channels). (b) close-up of red box in (a) showing floodouts distal to two channels (1, 2) (34.6412°, 51.6609°). note the smaller distributive channels extending from channels 1 and 2, which are themselves distributive channels of a larger network. (c) concave-up cross section of the proximal fan at line 1–2 of (a). dart shows location of the active channel, which is on the right flank of the fan. (d) concave-up longitudinal profile of the fluvial fan; dart is location of cross section of (c). length is approximately 68 km between points 3 and 4 of a. point 3 is approximately 47 m higher than point 4. gradient at the floodout example is 0.29°. images from google earth; profiles redrawn from google earth. 98 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 the presence of the lacustrine algae, botryococcus, and charophytes in some of the dark mudstones do indicate the presence of ponds or lakes (peterson, 1984). these may have formed from occasional overbank flow and ponding on the floodplain. however, not all of the dark mudstones are lacustrine. some are paleosols with a high organic content as discussed previously. given the importance of organic material, especially plant debris, in promoting redoximorphic conditions (vepraskas, 2015; vepraska and vaughan, 2016), the presence of redox reduction features in some of the dark mudstone is an indirect indication for the presence of vegetation. this explains how large herbivorous sauropod dinosaurs could exist in the tidwell environment (gillette, 1996; bernier and chan, 2006). the tidwell member in northeastern utah has been interpreted as marginal marine, tidal flat or lagoon complex because of symmetrical ripples in sandstone interpreted as due to oscillatory waves (currie, 1998). such oscillation ripples can also form in lacustrine environments, so that alone is insufficient for conclude a marine setting. turner and peterson (2004) also considered the tidwell member in northeastern utah as having brief marine transgressive beds based on the presence of glauconitic sandstone (peterson, 1994). however, glauconite can also form in nonmarine alkaline environments (furquim and others, 2010; roelofse, 2010). finally, a previous report of marine dinoflagellates in the tidwell member near dinosaur national monument (turner and peterson, 1999), is now known to be in error. the specimens came from the redwater member of the stump formation (litwin and others, 1998, p. 302). currently, there is no compelling evidence for a marine influence in the tidwell member in northeastern utah. a visual summary of depositional environment for the tidwell member is presented in figure 33. placement of the elko orogeny is based on thorman (2011) and the three ranges that were sources for the morrison formation are based on yingling (1987). the windy hill formation as a coastal depositional environment is based on holland and wright (2020). the laurentian fluvial system is based on the conclusions of ejembi and others (2021). the mogollon uplift as the northern rift shoulder with associated slope is based on bilodeau (1986). two interesting discoveries in the compellation of the image was the position of the playa complex and two of the sources of yingling (figure 33, number 5 with numbers 4a and 4b), and the relative position of the southernmost source for the fluvial fan that may have deflected eastward the salt wash fluvial fan (figure 33, number 4c with number 8). these discoveries are preliminary and need confirmation. conclusions the tidwell member belongs as a member of the morrison formation, not the underlying summerville formation. the member is here considered to have been formally named by peterson (1988a). although o'sullivan (1984a) earlier met all the requirements of nasc, he did not meet the requirements of the usgs. the tidwell member is restricted to the colorado plateau where it crops out between the underlying summerville or wanaka formations and the overlying salt wash member of the morrison formation. in the northwestern part of the colorado plateau (san rafael swell-henry basin), the tidwell is composed of a lower gypsum facies and an overlying interbedded thin sandstone-siltstone-mudstone-limestone-dolomite (ssmld) facies assemblage. elsewhere across the plateau, the tidwell member consists only of the ssmld facies assemblage overlying a basal sandstone, bed a. this assemblage in the southern part of utah differs from the type and supplemental reference sections in being dominated by sandstones, and in the northern part of the plateau (uinta basin) in having proportionally more mudstone. identifying these outliers as the tidwell member is based more on stratigraphic correlation with the type and reference sections than lithology. the lower gypsum facies is separated from the summerville formation by the less than 500,000 year gap of the j-5 unconformity, which in places are angular conformities from truncated low amplitude anticlines. these anticlines and associated synclines may be the last gasp of the elko foreland basin, which was more active as a depositional center during the middle jurassic (thorman, 2011). gypsum deposition preceded the arrival of the distal clastic sediments of the fluvial fans of the salt wash member. the arrival of these clastic sediments ef99 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 figure 33. reconstruction of the region of the colorado plateau during tidwell deposition. (1) regressing sundance seaway. (2) coastal deposition of the windy hill formation. (3) exposed surface of the summerville formation. (4) remnants of the elko orogeny, with a volcanic region in the north; placement of ranges 4a, 4b, and 4c based on yingling (1987; see also peterson, 1994). (5) playa complex with playa lakes. (6) relict fluvial system from laurentia. (7) eolian dunes of the bluff sandstone member with zibars along the west side. (8) early phase of what will become the salt wash fluvial system. (9) region of the grand canyon bight. (10) mogollon highlands. (11) mongollon slope. although the landscape may look barren, it was probably covered with xeric and gypsophilic plants except in active playa lakes and dune field. composed from google earth images. 100 the lithostratigraphic tidwell member of the morrison or summerville formations (upper jurassic)—who, what, where, when? carpenter, k. geology of the intermountain west 2022 volume 9 fectively smothered the playa complex, and spread over the exposed summerville surface on the eastern part of the colorado plateau. acknowledgments historic aerial photographs to determine the date for the formation of the notch (ar4u94c0423a013, ar4u98b01013002) and the i-70 roadcut (ar1vbn000201) were obtained from the usgs's earthexplorer (https://earthexplorer.usgs.gov/); historical outcrop photographs are from the usgs denver library photographic collection (https://library.usgs. gov/photo/). i was greatly aided in the search for a copy of young and others (1957) by rachel ahrens, librarian for the doe/legacy management in grand junction, colorado; amber j. d'ambrosio, special collections & archives librarian, colorado mesa university, grand junction; and susie foust and catherine pepmiller, doe office of scientific and technical information. thanks to yvonne wilson for help in the field. review comments by tom chidsey (utah geological survey, retired), james kirkland (utah geological survey), bart kowallis (brigham young university, retired), dean richmond (university of oklahoma), and douglas sprinkel (utah geological survey, retired) are appreciated. references abraham, a.d., parsons, a.j., and wainwright, j., 1994, resistance to overland flow on semiarid grassland and shrubland hillslopes, walnut gulch, southern arizona: journal of hydrology, v. 156, p. 431–446. allen, b.d., love, d.w., and myers, r.g., 2009, evidence for late pleistocene hydrologic and climatic change from lake otero, tularosa basin, south-central new mexico: new mexico geology, v. 31, p. 9–25. ali-adeeb, 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tidal forcing, and bed shear stress: sedimentology, https://eartharxiv.org/ repository/object/1928/download/4049/. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 8 2021 © 2021 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona charlotte l. priddy, amy v. regis, stuart m. clarke, a. graham leslie, and thomas j. h. dodd geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover example of proximal contorted heterolithic facies observed at sevenmile canyon, utah, displaying internally contorted, locally derived clasts with mud draping along the folded foresets and antiformal stacking towards the base of the unit. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 8 2021 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2020–2021 uga board president john south john.south@dominionenergy.com 385.266.2113 president-elect rick ford rford@weber.edu 801.915.3188 co-program chair megan crocker meganlynncrocker@gmail.com 801.538.5290 co-program chair ben gilder dgilder@gmail.com 337.962.8383 treasurer kellen gunderson kellen@zanskar.us 801.634.9737 secretary eugene syzmanski eugenes@utah.gov 801.537.3364 past president riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach 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geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 eutretauranosuchus@ gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 8 2021 27 abstract this study presents a detailed synopsis of the sedimentological and structural features displayed within an underdescribed enigmatic facies observed in the basal lower jurassic kayenta formation of the colorado plateau. the facies comprises pebble to cobble-sized clasts of fine to medium-grained crossbedded sandstone with mud-draped and deformed foresets, as well as clasts of parallel-laminated but highly contorted siltstone and mudstone, supported in a silty to sandy matrix. the deposits are internally deformed and show both ductile and brittle structures in close spatial proximity, with a consistent and pervasive westdirected sense of shear. the facies occurs consistently within the same approximate stratigraphic interval, at or near the base of the kayenta formation. it is, however, observed only at four localities, distributed in a crudely linear arrangement parallel to the utah-idaho trough, despite extensive studies of outcrops of the same stratigraphic interval widely distributed across both utah and arizona. this study interprets the depositional processes as that of a partially subaerial debris flow with depositional events perhaps taking place during the waning period after ephemeral stream activity. the clast morphology and composition suggests a local source for the sediment entrained within the flow, and a limited transport distance. all of these observations are difficult to reconcile with the consistency of the stratigraphic interval in which the facies occur, or with the regional distribution of preserved examples. consequently, this study discusses the potential for a common and time-equivalent triggering mechanism across all examples, which may have regional significance in the jurassic evolution of the region. localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona charlotte l. priddy1, amy v. regis1, stuart m. clarke1, 2, a. graham leslie2, 1, and thomas j. h. dodd 2,1 1basin dynamics research group, school of geography, geology and the environment, keele university, keele, st5 5bg, uk; c.priddy@keele.ac.uk; a.v.regis@keele.ac.uk; s.m.clarke@keele.ac.uk; agle@bgs.ac.uk; tdodd@bgs.ac.uk 2british geological survey, the lyell centre, research avenue south, edinburgh, eh14 4ap, uk citation for this article. priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h., 2021, localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona: geology of the intermountain west, v. 8, p. 27–44, https://doi. org/10.31711/giw.v8.pp27-44. © 2021 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction during the early to middle jurassic period, compressional tectonic activity to the west of the colorado plateau resulted in asymmetrical subsidence along the wasatch line that formed the utah-idaho trough (figure 1). associated subsidence in the foreland of the cordilleran magmatic arc formed the zuni sag (figure 1) (bjerrum and dorsey, 1995; blakey, 2008; blakey and ranney, 2018; hassan and others, 2018). evidence for both paleotopographic lows is provided by abrupt westward thickening of the jurassic-aged strata across the colorado plateau (figure 2) (blakey, 1994; kirkland and others, 2014). sediments of the late sinemurian to early toarcian kayenta formation were funnelled through the south28 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 east–northwest-trending zuni sag and into the southwest–northeast-trending utah-idaho trough (olsen, 1989; blakey, 1994; kirkland and milner, 2006). these deposits are of dominantly ephemeral braided fluvial origin (bromley, 1991; north and taylor, 1996; martin, 2000; priddy and clarke, 2020), deposited onto a broad arid alluvial plain. sediment transport was by both southwestward to westward-flowing rivers that sourced sediment from the uncompahgre uplift of the ancestral rocky mountains (north and taylor, 1996), and northwestward-flowing rivers that sourced sediment from the mogollon highlands of the cordilleran magmatic arc. the initial deposits of the formation overlay a marked unconformity termed the ‘j-sub-k’ unconformity (marzolf, 1994; blakey, 1994; lucas and tanner, 2006, 2014). by contrast, the upper boundary with the succeeding eolian deposits of the navajo sandstone is gradational and interfingering. extensive fieldwork that examined regional patterns in the sedimentology of the kayenta formation has revealed a distinctive contorted heterolithic facies, observed within proximal sediments of the uncompahgre-sourced fluvial system (priddy and clarke, 2020). the facies comprises contorted intraformational mudstone and sandstone clasts, with internal mud-draped and deformed foresets, as well as contorted and buckled beds and laminations. these deposits were previously interpreted as the deposits of localized debris flows that formed as a result of bank collapse of active river channels into highly sediment-laden flows (priddy and clarke, 2020). however, subsequent fieldwork, discussed herein, has revealed further examples that display brittle structures related to sediment transport and deposition, as well as distal examples with a siltier composition. all identified examples occur near the base of the kayenta formation, within approximately the same stratigraphic interval, and form a constrained “belt” oriented approximately parallel to the trend of the utah-idaho trough. this study examines the contorted heterolithic facies with the specific objectives of: (1) describing their sedimentology in detail, (2) identifying the possible depositional processes and mechanisms, and (3) discussing possible hypotheses for their formation. are they (a) localized occurrences controlled by isolated process-scale events that are somewhat “typical” of the fluvial system, or (b) may they relate to a regionally significant event linked to the j-sub-k unconformity, and to the utah-idaho trough? geological setting the colorado plateau is a large high-standing block that spans approximately 360,000 km2 across southeastfigure 1. outline of the colorado plateau (brown line), southwestern usa, and within it the exposure of upper triassic to lower jurassic deposits (yellow), and structural features active during deposition of these sediments, including the zuni sag and utah-idaho trough (modified from dickinson, 2018). locations from regional studies of the kayenta formation (priddy and clarke, 2020, 2021) are highlighted in gray, with the four locations discussed within this study (sevenmile canyon, lions park, capitol reef national park, and potter canyon) highlighted in pink. 29 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 ern utah, northeastern arizona, southwestern colorado, and northwestern new mexico (figure 1) (gilfillan and others, 2008). from the early jurassic to early cretaceous, the plateau was influenced profoundly by several orogenic events. the 160to 150-ma elko orogeny (thorman and others 1990; thorman and peterson, 2004; thorman, 2011) resulted in raised uplands to the west of the colorado plateau (lawton, 1994), and asymmetrical subsidence along the wasatch line that formed the northeast–southwest-trending utah-idaho trough (figure 1) (bjerrum and dorsey, 1995; blakey, 2008; blakey and ranney, 2018). associated subsidence, caused by loading and contraction of the cordilleran magmatic arc and mogollon highlands, resulted in the formation of a northwest to southeast retro-arc foreland basin, referred to as the zuni sag (figure 1) (blakey, 2008; hassan and others, 2018). subsidence of both depocenters began during the lower jurassic, accelerated rapidly throughout the middle jurassic, and ceased during the upper jurassic (bjerrum and dorsey, 1995). the zuni sag formed a southeast–northwest-trending paleotopographic low on the western edge of the north american craton that extended through presentday central arizona, and into southwestern utah (figure 1) (tanner and lucas, 2009; antonietto and others, 2018). it is somewhat poorly-constrained geographically, but its northeastern limit follows a northwest–southeast-trending line between page and tuba city, arizona (figure 1) (blakey, 1994). by contrast, the utah-idaho trough is a northeast–southwest-trending feature that extends from north-central utah to the state’s southwestern corner and on into southeastern nevada (figure 1) (peterson, 1988). the trough was bound to the north by a submerged barrier coinciding with the western continuation of the unita mountains (sprinkel, 1994), but its western edge is poorly constrained due to erosion of lower to middle jurassic strata; it probably lies close to the present-day nevada-utah border (peterson, 1988). stratigraphy the presence of the zuni sag and utah-idaho trough resulted in westward thickening of sedimentary successions into these paleotopographic lows, and a system of sedimentary reworking between coeval depositional regimes (blakey, 1994; kirkland and others, 2014). the deposited successions belong to the upper triassic to lower jurassic glen canyon group (figure 2) (lewis and others, 1961; lucas and others, 2005, 2006; sprinkel and others, 2011b; martz and others, 2014, 2017; irmis figure 2. schematic cross section through the lower and middle jurassic stratigraphy, highlighting the unconformities that bound the glen canyon group (moenave formation/wingate sandstone, kayenta formation, and navajo sandstone). the orientation of the schematic cross section is shown by the red line of the inset map (modified from blakey, 1994). 30 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 and others, 2015). the group is exposed across southern utah, northern arizona, northwest new mexico, and western colorado, and comprises four stratigraphic units: the wingate sandstone and coeval moenave formation, the kayenta formation, and navajo sandstone (figure 2). the sediments were deposited in eolian, fluvial, and lacustrine settings, and facies from each environment interfinger numerous times to suggest relatively continuous deposition under shifting climatic conditions (middleton and blakey, 1983). the strata of the glen canyon group are truncated by several unconformities, the stratigraphic locations of which have long been contentious. the j-0 regional unconformity, at the base of the glen canyon group was thought to be the basal bounding surface of the jurassic strata (pipiringos and o’sullivan, 1978; blakey, 1994; kirkland and milner, 2006). however, recent work suggests the triassic-jurassic boundary may sit within the wingate sandstone or coeval moenave formation and, as such, the j-0 regional unconformity may be conflated with the tr-5 unconformity (lockley and others, 2004; lucas and others, 2005, 2006; sprinkel and others, 2011b; martz and others, 2014, 2017; irmis and others, 2015). the glen canyon group is capped by either the j-1 unconformity which truncates the top of the navajo sandstone in the west, towards nevada, or by the j-2 unconformity that truncates the top of the middle jurassic temple cap formation (as well as the navajo sandstone and kayenta formation) in the east, towards colorado and new mexico (figure 2) (dickinson, 2018). however, and similarly to the j-0 unconformity, there is debate over the veracity of the j-2 regional unconformity (sprinkel and others, 2011a; doelling and others, 2013). a disconformity—termed the ‘j-sub-k disconformity’ (riggs and blakey, 1993; lucas and tanner, 2006)—is located between the j-0 and j-1 unconformity and marks the base of the springdale sandstone member of the kayenta formation. the j-sub-k disconformity is an erosional surface with between 1 and 15 m of relief that is identified by clasts of lacustrine sediment derived from the whitmore point member of the moenave formation below (kirkland and milner, 2006). the feature marks a two-million-year-long depositional hiatus in parts of the plateau (marzolf, 1994; blakey, 1994; lucas and tanner, 2006, 2014). these varying unconformities have been linked to the initiation of the cordilleran magmatic arc and associated thrusting along the western continental margin (reynolds and others, 1989; marzolf, 1991). the laterally equivalent moenave formation and wingate sandstone overly the j-0 unconformity and together comprise the oldest deposits of the glen canyon group. the moenave formation, of rhaetian to hettangian age (208 to 199 ma), consists of a succession of terrestrial red-bed sediments, including units of fine-grained sandstone, siltstone, and mudstone, which were deposited by fluvial, lacustrine, and eolian processes (tanner and lucas, 2007). sediments were derived from the mogollon highlands and transported by fluvial systems northwestward along the zuni sag into west-central utah (figure 1) (blakey, 1994). they were then transported back to the east by prevailing westerly winds, into the eolian erg system of the wingate sandstone that covered 110,000 km2 across present-day northeastern arizona and central utah (harshbarger and others, 1957; clemmensen and others, 1989; tanner and lucas, 2009). because of contemporaneous sedimentation, the moenave formation and the wingate sandstone interfinger frequently across a 150-km wide northwest-trending section near tuba city, arizona (tanner and lucas, 2007; blakey, 2008). the wingate sandstone consists of very fine to fine-grained, well-sorted, sub to well-rounded, quartz-rich sandstone. the sediments are typically preserved in stratigraphic sections of cross-bedded sets and cosets that form sheer, vertical cliffs (harshbarger and others, 1957) and represent deposition by migrating eolian dune forms. the upper sinemurian to lower toarcian continental red-bed assemblage of the kayenta formation overlies the moenave formation and the wingate sandstone. the formation comprises units of fine-grained sandstone, siltstone, and occasional intraformational conglomerates (harshbarger and others, 1957; peterson and pipiringos, 1979; luttrell, 1993), which were deposited on a broad alluvial plain by southwestwardto westward-flowing rivers from the uncompahgre uplift of the ancestral rocky mountains (north and taylor, 1996), and by northwestward-flowing rivers from 31 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 the mogollon highlands in the cordilleran magmatic arc (luttrell, 1993). in southwest and south-central utah and northern arizona, the kayenta formation includes the springdale sandstone member and the overlying main body of the kayenta (figure 2). however, in south-central and parts of southwestern utah, the lamb point tongue of the navajo sandstone is present and separates the main body of the kayenta (below) from the tenney canyon tongue of kayenta (above) (doelling, 2008; biek, 2010). the lowermost springdale sandstone member was originally described as part of the moenave formation due to lithological similarities with the dinosaur canyon member of that formation around tuba city, arizona (wilson, 1967; wilson and stewart, 1967; pipiringos and o’sullivan, 1978), but has since been re-assigned on the basis of the identification of the j-sub-k disconformity and the member’s relationship to that surface (marzolf, 1994; lucas and heckert, 2001; lucas and others, 2005). the member is mostly pale yellow-brown and comprises approximately 30 m of medium to coarse-grained, planar and trough-cross-stratified units of sandstone, with discontinuous lenses of conglomerate and subsidiary lenses of mudstone (lucas and tanner, 2007). the basal part of the springdale sandstone is often conglomeratic, with pebbles of chert and limestone, as well as angular clasts of siltstone and mudstone derived from the underlying whitmore point member (kirkland and others, 2014). the main body of the kayenta formation conformably and gradationally overlies the springdale sandstone member and comprises 28 to 460  m of red-brown, fineto coarse-grained sandstone, siltstone, and subordinate claystone (luttrell, 1993). limestone beds and nodules, as well as conglomeratic beds, are also present locally within the main body of the formation (north and taylor, 1996; fillmore, 2011). towards the top of the kayenta formation, the tenney canyon tongue comprises up to 98 m of pale reddish-brown, lenticular fine-grained sandstone, siltstone, and mudstone, with subordinate limestone and claystone, all deposited in a distal river and playa system (luttrell, 1993). methods this study draws upon extensive regional fieldwork that examined the sedimentology of the moenave and kayenta formations during four field campaigns between 2016 and 2019. throughout these studies, a total of 30 detailed vertical sections (cm-scale resolution) were logged at 25 separate locations (figure 1), with a cumulative measured length of over 2000  m. each of the 30 sedimentary logs includes the upper strata of the wingate sandstone or the moenave formation and extend through the full thickness of the kayenta formation to include the lowermost strata of the overlying navajo sandstone. from the 25 locations, the distinctive contorted heterolithic facies was observed in four of the measured sections, the locations of which form a northeast to southwest transect (figure 3). traditional sedimentological methods of facies analysis, augmented by photographic interpretations, were applied to field data in order to interpret depositional processes and sub-environments (sensu walker, 1992). the four localities (figure 3) have been separated into proximal and distal settings in this study, with respect to the dominant sediment source for the kayenta formation (priddy and clarke 2020, 2021). proximal localities include exposures at sevenmile canyon and lions park, to the northwest, and at capitol reef national park, approximately 150 km to the southwest of moab, utah (figure 1). the distal locality occurs within a series of cliffs and valleys at potter canyon, near colorado city, arizona, approximately 33 km west of kanab, utah. the deposits in each of the four locations where contorted heterolithic units are present, examples occur at approximately the same stratigraphic interval of the kayenta formation. in the proximal localities of sevenmile canyon, lions park, and capitol reef, the boundary between the kayenta formation and the underlying wingate sandstone is challenging to identify because of the gradational nature of the contact. however, the contorted heterolithic facies occurs within the first fluvial incursion, which is 1 to 2 m above the underlying eolian sediments of the wingate sandstone. in the distally located potter canyon locality, the contorted heterolithic facies marks the boundary between the underlying moenave formation 32 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 and the kayenta formation. all examples occur along the western limit of exposure of jurassic strata, in a northeast to southwest-trending belt. proximal examples (sevenmile canyon, lions park, and capitol reef) comprise moderately to poorly sorted, subrounded clasts that are up to 30 cm in diameter, and comprise plastically deformed and contorted cross-stratified sandstone with mud-draped foresets. the clasts are supported within a purple to brown, siltstone to fine-grained sandstone matrix (figures 4 and 5). smaller, bladed to prolate clasts display depositional imbrication, with the long axis parallel to the dip of the clasts (figures 4d and 4f). the facies form sedimentary units, 1 to 3 m thick, with a flat to slightly concave upwards base and an erosive upper bounding surface (figure 4). the units overlay 0.7 to 1.2 m of purple to dark-brown parallel-laminated siltstone to very fine grained sandstone, which are then overlain by 0.8to 2.1-m-thick, pale-orange to brown, medium-grained, structureless to crudely cross-bedded sandstone, each with erosive bases and basal rip-up clasts that are distributed along the foresets of crude cross-bedding (figures 4, 5, and 6). the distal example (potter canyon) is composed of a purple-brown, siltstone to very fine grained sandstone matrix that supports subrounded, poorly to moderately sorted clasts of highly contorted parallel-laminated siltstone, with interlaminae of mudstone (figure 7). graygreen diagenetic features in the form of either mottling or haloes surround some clasts. clasts are less than 10 cm in diameter and lack consistent orientation, but are distributed to give the units a bipartite structure in which an upper clast-rich interval overlays a lower clastpoor interval dominated by contorted laminations. the units are 3 m thick in total, and occur as localized, lensshaped scours, with erosional lower and upper bounding surfaces. they overlay 1 m of brown-purple, parallel-laminated siltstone and mudstone of the underlying whitmore point member, or a 50-cm-thick, channelized, pale-orange to brown medium-grained structureless sandstone with muddy laminations, that pinches out beneath the contorted heterolithic facies, and is replaced by the brown-purple siltstone. the contorted heterolithic facies is capped by 0.5to 2-m-thick units of pale-orange to brown, medium-grained structureless to planar-bedded sandstone, each with erosive bases, and containing rip-up clasts of mudstone, and 5to 30-cm-thick interbeds of red-brown mudstone between ‘u-shaped’ sandstone bodies. in both proximal and distal examples, internally figure 3. schematic vertical sedimentary sections of the study localities (pink stars on the insert map) that expose examples of the contorted heterolithic facies, highlighted in gray. insert map modified from harshbarger and others (1957); middleton and blakey (1983); blakey (1994). pc = potter canyon, cr = capitol reef, sc = sevenmile canyon, lp = lions park, sdst = sandstone, slst = siltstone. 33 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 layered clasts are observed to have been folded; the fold style is distinctive such that fold hinges are thickened and the fold limbs are thinned and attenuated. structural imbrication and antiformal stacking of packages of clasts (figures 4b and 4f), and the enclosing matrix sediment, is also consistently developed (figures 4b and 5f), typically towards the base of individual units. the fold hinges in some examples are markedly curvilinear and individual sheath fold geometries are evident locally (figures 4a and 4b); the orientations of these fold axes are highly variable but are, in general terms, broadly perpendicular to the stacking direction indicated in the spatially associated imbricate structures. in all examples, the observed sense of shear is consistently orientfigure 4. examples of the proximal contorted heterolithic facies observed at sevenmile canyon, utah (unannotated on left, annotated on right). (a–b) overview of the geometry, bounding surfaces, and internal structure of the contorted heterolithic facies, highlighting the basal detachment zone and erosional upper bounding surface. (c–d) close-up of the internally contorted, locally derived clasts with mud draping along the folded foresets, and depositional imbrication of clasts near the basal boundary. (e–f) western edge of the contorted heterolithic facies where clasts display antiformal stacking at the base of the unit. 34 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 figure 5. examples of the proximal contorted heterolithic facies observed at lions park, utah (unannotated on left, annotated on right). (a–b) overview of the geometry, bounding surfaces, and internal structure of the contorted heterolithic facies. (c–d) close-up of the upper bounding surface to the unit of contorted heterolithic facies, with soft-sediment deformation and mud rip-up clasts within the deformed sandstone layer. (e–f) deformed sandstone clasts with mud draping along folded foresets and imbrication of clasts. 35 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 ed between top-to-the-west, and top-to-the-southwest. where individual fold axes are more curvilinear in aspect, they appear to have been attenuated in a direction approximately parallel to the structural transport that created the observed imbricate stacking. extensional structures (e.g., figure 6) indicate that extensional collapse occurred in the same general direction as shown by the other sense of shear criteria described above. in some examples, depositionally imbricated deformed clasts appear caught up within the packages defining structurally imbricated stacks (e.g., figure 4f). process of formation the presence of units of parallel-laminated siltstone and mudstone that preserve mud-draped sandy foresets within clasts, suggests original subaqueous deposition. within the distal region of the kayenta depositional system, the sediments were deposited dominantly through suspension settling, whereas in the proximal region, deposition occurred within migrating bedforms and bar forms during highly sediment-laden, episodic, and irregular flow (owen, 1996; rana and others, 2016; van den berg and others, 2017; carling and leclair, 2019). in the proximal setting, the fine fraction may be deposited at times of near-stagnant water, or after the flow reaches its maximum carrying capacity (olsen, 1987; nwajide, 1988; priddy and clarke, 2020). distortion and folding of individual clasts, and structural imbrication of packages of clasts, suggest remobilization of the sediments within a sufficiently short time after initial deposition, such that the sediments were not fully lithified and therefore able to deform (scholz and others, 2011) in a ductile or brittle-ductile manner. the muddy matrix-supported nature of the resultant deposit, coupled with the style of depositional imbrication of the prolate clasts, suggests a non-newtonian plastic or pseudo plastic nature to the remobilizing flow. this is perhaps a consequence of a high sediment concentrations, which prevented disaggregation of the sandy clasts through attrition, and allowed them to deform (shanmugam, 1996; wozniak and pisarska-jamrozy, 2018). the distinctive fold style observed, with thickened fold hinges and thinned attenuated fold limbs, gives a clear indication of non-coaxial plastic deformation under translational shear within the flow (parrish and others, 1976; mies, 1993). the consistent overall top-to-the-west or top-to-the-southwest sense of shear indicated by these deformational features is aligned with the local paleoslope. the markedly curvilinear sheath-fold axes were probably formed as a result of intense non-coaxial deformation with the fold hinges progressively rotated figure 6. examples of the proximal contorted heterolithic facies observed at capitol reef, utah, with folded foresets and evidence of collapsed deformation packages in the direction of shear (unannotated on left, annotated on right). 36 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 figure 7. examples of the distal contorted heterolithic facies observed at potter canyon, arizona. (a) panel photograph highlighting the contorted heterolithic facies relative to the surrounding sediments. (b) overview of the geometry and bounding surfaces of the distal contorted heterolithic facies. white box highlights approximate location of image c. (c) overview of the structure of the contorted heterolithic facies including the clast-poor lower interval, and clast-rich upper interval. white boxes highlight approximate locations of images d and e. (d) detailed view of image c. (e) contorted mud-clasts and silt lenses within the upper interval of the contorted heterolithic facies. (f) deformed bedding planes and soft-sediment deformation within the lower interval of the contorted heterolithic facies. (g) gray-green diagenetic reduction mottling observed towards the base of the contorted heterolithic facies. 37 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 into the transport direction (sensu alsop and carreras, 2007). the variable orientations of the fold axes suggest that folds may actually have initiated in a range of orientations prior to more pervasive internal shearing and rotation within the flow. non-coaxial flow would have been the principal influence constraining the overall fold shape (sensu adamuszek and dabrowski, 2017), with the development of curvilinear fold hinge lines as a result of individual fold hinges being dragged out in the overall shear (flow) direction (alsop and carreras, 2007). despite evidence for plastic flow, the structural imbrication and antiformal stacking of sheared packages of clasts and their enclosing matrix suggest sufficient cohesion at times, and in places, to promote brittle deformation. deformation was dominantly compressional to build-up structurally thickened packages that overall suggest a sense of shear comparable, at least locally, to the paleocurrent indicated by depositional imbrication. sporadically, brittle structures that are clearly superimposed upon the more ductile and/or brittle-ductile deformation features, indicate collapse and extension in the same (forward) direction and overall sense of shear (figure 6b). deformation was progressive, becoming more brittle in style where cohesion in the deforming package increased, for example by thickening and stacking, or perhaps by localized de-watering. the local juxtaposition of brittle-ductile and ductile deformation suggests a depositional process for these sediments that is capable of supporting both styles, either contemporaneously or consecutively within the time frame of the event. some evidence for depositionally imbricated clasts caught up in structural imbricated packages suggests a temporal link whereby a plastically deforming flow evolves to become more cohesive through time (enos, 1977). the general sedimentology suggests a debris flow in which deformation is predominantly by laminar shear; the composition and orientation of the contorted heterolithic clasts suggest that they were derived locally (from the substrate), and then deformed within the flow. non-coaxial deformation suggests many contorted heterolithic clasts may have contained pre-existing folds that were subsequently modified by the debris flow, or the sediments may have been deformed under localized stress fields during clast development, to form structures that were later modified by the overriding shear of the flow. through time, the flow becomes more cohesive, particularly along its basal surface. discussion examples of the contorted heterolithic facies were first identified within the basal units of the kayenta formation to the northwest of moab, utah (priddy and clarke, 2020). those examples were in locations proximal to the dominant sediment source for the kayenta formation, namely the uncompahgre uplift. from their locations, internal sedimentology, and localized associations, the facies was interpreted as ‘debris-flow deposits’ formed by the collapse of river banks into the flow (priddy and clarke, 2020). that interpretation is supported by previously published descriptions and interpretations of the fluvial sedimentology and depositional processes of the kayenta formation, which indicate sporadic, high-discharge events (stephens, 1994; north and taylor, 1996; priddy and clarke, 2020). the observations and interpretations of this study (which includes additional localities to those of priddy and clarke, 2020) are consistent with the interpretation of a debris flow as the depositional mechanism for their emplacement (sensu priddy and clarke, 2020). the facies and depositional imbrication, along with the ductile structures developed within the contorted clasts, are consistent with a high sediment to fluid ratio, and they indicate a plastic flow in which deformation is predominantly by laminar shear rather than fluid turbulence. the close spatial association of ductile and brittle-ductile structures within the deposits, and the temporal relationships implied by the depositionally imbricated clasts that are subsequently caught up in structurally imbricated packages, suggest flows became more cohesive through time (enos, 1977). plausible situations under which this scenario could occur are loss of water from flow through time, a sharp reduction in basal slope angle over which the flows travel, and/or a reduction in flow velocity. the scenario favors subaerial deposition as the loss of water from more coherent flow types into ambient waters of subaqueous environments 38 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 is more difficult (talling, 2013). additionally, gradually reducing flow velocity over progressive transport distances is known to be more typical for subaerial debris flows than compared with their subaqueous counterparts (see breien and others, 2007). a loss of water from the flows, as well as reduced flow velocities over prolonged transport distances, possibly enhanced by a change in gradient (decrease in slope angle), would easily explain the increase in cohesion and progression from ductile, through ductile-brittle, to brittle deformation as observed in these examples. based on our observations and previous studies, we interpret the contorted heterolithic facies as the products of debris flows that took place subaerially. as the kayenta formation represented a high-energy ephemeral fluvial system (priddy and clarke, 2020), and there are fluvial channel deposits formed above these deposits (e.g., figure 4), it is likely that these contorted heterolithic facies initiated by collapse of material into empty channels, or into channels with low flow conditions. once initiated, the debris flows lose water to become cohesive and deform in a brittle fashion in the later stages of the flow. the formation of debris flows requires destabilization of deposited sediment, usually following some form of triggering mechanism or event (i.e., seismicity, oversteepening, or changes in base level). in a fluvial setting the most probable triggers are sudden input of water to the system (rainfall) (bookhagen and others, 2005; aguilar and others, 2020), over-steepening of a sediment pile (keaton and others, 1991), or changes in base level (scherler and others, 2016). the channel cut surface at the base of the contorted heterolithic deposits suggest a sudden input of water or rise in the water table as the dominant triggers, as does the nature of the flow itself, but oversteepening cannot be discounted as a contributing factor. indeed, it may provide some explanation for the curvilinear fold axes/folds developed within clasts, as localized slumping may deform clasts to generate folding as they enter the flow. equally, the cross-bedded and mud-draped sedimentary architecture of many sandstone clasts within the proximal examples, coupled with evidence of pre-existing ductile deformation, may suggest clasts were derived from recently deposited bar forms of the ephemeral system. in-situ plastic deformation of foresets within bar form sediments (so called recumbent cross-bedding or rip-back curls) have been observed elsewhere within the kayenta formation (priddy and clarke, 2020). these deformational features have a sandstone composition, and contorted foresets that define similar sheath fold geometries with curvilinear fold axes, and in some cases have been observed up to meter-scale in size. consequently, a scenario can be envisaged in which localized ephemeral stream activity may cut channels through recently deposited bar forms. following the flood event, the saturated and potentially over-steepened channel banks fail, resulting in debris flows. both partially ductile failure in the failing sediments, as well as any pre-existing folded fabrics, may contribute to the preserved folding of the sediments within clasts. the folds are later reworked by laminar shear within the flow. as the debris flows develop, they lose water rapidly to the sandy substrate, which promotes brittle deformation within the lower parts of the flow under the shear of the overriding, and still plastic, upper parts. the subaerial debris flows were most probably localized, with progressively reducing flow velocities, leading to relatively short transport paths (up to tens of meters), which may go some way to explaining the intraformational nature of the clasts, the localized and sporadic occurrences of the facies, and the differences in sedimentary texture between proximal and distal examples. despite the fit of the observations across all sites examined with this interpretation, it is difficult to explain the regional distribution of the contorted heterolithic facies by that process of formation alone. interestingly, units of the contorted heterolithic facies occur within the same narrow stratigraphic interval just above the boundary of the kayenta formation with the underlying moenave and wingate formations. thus, it is tempting to hypothesize that their occurrences may be linked, and this could suggest that examples of the facies were deposited coevally as a result of a regional event, possibly linked also to formation of the j-sub-k unconformity. furthermore, examples of the contorted heterolith39 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 ic facies occur in a northeast to southwest transect, near the northwesterly limit of exposure for triassic–jurassic strata. notwithstanding the constraints of exposure, this facies has not been found elsewhere despite an extensive, regular, and grid-based logging strategy (where outcrop exposure allowed) to support regional studies of the moenave and kayenta formations (priddy and clarke 2020, 2021). the alignment of the localities discovered and reported here is parallel to the consistent paleoflow indicated by internal deformation and shearing within the flow, and parallel to the axis of the utah-idaho trough (peterson, 1988; bjerrum and dorsey, 1995). therefore, this facies may be constrained to a narrow belt, possibly reflecting funnelling of mass-transport debris-flow deposits towards the zuni sag (figure 1). despite regional and temporal distributions of the contorted heterolithic facies that could imply a physical link between all four examples, such an interpretation is inconsistent with sedimentological observations. it is difficult to conceive of a single mass flow event capable of sustaining the physical characteristics indicated by the sedimentology of these deposits over distances indicated by the spread of localities. the most likely explanation for the spatial distribution of the localities, is one in which the mass flows are separate occurrences, with sediment derived locally. their consistent paleocurrent direction simply indicates the general trend of the depositional system in which they reside. however, it is inescapable from the studies presented herein that mass flows with the same style are occurring regionally (although sourced locally) within a somewhat similar stratigraphic position. this suggests potential for a shared and significant triggering mechanism. it is conceivable that this could be a climatic trigger that promoted a period of widespread but episodic flash flooding, or a rise in the water table, but further studies are required to draw full conclusions. it is also possible that the region was influenced by tectonic instability linked to the initiation of the cordilleran magmatic arc and any associated thrusting (reynolds and others, 1989; marzolf, 1991). therefore, the significance of these enigmatic contorted heterolithic deposits to the evolution of the region during the jurassic period requires and deserves further detailed investigation. conclusions the contorted heterolithic facies of the lower jurassic kayenta formation described within this study were first identified in the proximal localities of sevenmile canyon and lions park, northwest of moab, and at capitol reef national park, utah. detailed analysis of the sedimentology and the brittle structures developed within these deposits suggests transport and deposition via debris flows that became more cohesive through time. this interpretation is inconsistent with subaqueous deposition in a highly energetic ephemeral flow. consequently, we suggest a model in which collapse and debris flow takes place at least in part sub-aerially to transport locally derived sediment over short distances. such a situation could be conceived during and following episodic flash flooding. this model explains the sedimentological observations and the spatial distribution of the outcrops, but it does not explain their occurrence within approximately the same stratigraphic level within the strata, near the basal boundary of the kayenta formation. despite being locally sourced, their stratigraphic coincidence may suggest initiation was triggered by some regional-scale autogenic event, perhaps of a climatic nature, and potentially related to the j-sub-k unconformity and evolution of the environment. however, in this context, the interpretation presented may be considered very much of a preliminary nature, and extensive additional work is required to better understand the depositional processes behind these examples of the contorted heterolithic facies, and to constrain their significance in a regional context. acknowledgments this research was conducted during a study undertaken as part of the natural environment research council (nerc) centre for doctoral training (cdt) in oil & gas under its extending the life of mature basins theme (grant number: nem00578x/1). it is sponsored by keele university nerc and the british geological survey (uk research and innovation) via the british university funding initiative (bufi) whose support is gratefully acknowledged. this paper is published by 40 localized bank collapse or regional event?—a study of distinct contorted heterolithic facies observed in the lower jurassic kayenta formation, utah and arizona priddy, c.l., regis, a.v., clarke, s.m., leslie, a.g., and dodd, t.j.h. geology of the intermountain west 2021 volume 8 permission of the executive director, british geological survey (ukri). we are also grateful to the united states national park service for permitting this research and granting scientific research permits for arches and capitol reef national parks. we are very grateful to ranie lynds (wyoming state geological survey) and doug sprinkel (azteca geosolutions) for their constructive and useful comments that have greatly improved this work. the authors declare that they have no conflicts of interest and the data that support the findings of this study are available from the corresponding author upon reasonable request. references adamuszek, m., and dabrowski, m., 2017, sheath fold development in monoclinic shear zones: terra nova, v. 29, p. 356–362. aguilar, g. cabré, a., fredes, v., and villela, b., 2020, erosion after an extreme storm event in an arid fluvial system of the southern atacama desert—an assessment of the magnitude, return time, and 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and triassic (?) formations between southwestern utah and southern nevada: u.s. geological survey bulletin 1244-d, 20 p. wozniak, p.p., and pisarska-jamrozy, m., 2018, debris flows with soft-sediment clasts in a pleistocene glaciolacustrine fan (gdansk bay, poland): catena, v. 165, p. 178–191. yonkee, w.a., and weil, a.b., 2015, tectonic evolution of the sevier and laramide belts within the north american cordilleran orogenic system: earth-science reviews, v. 150, no. 11, p. 531–593. upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 © 2017 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah jeffrey w. martz, james i. kirkland, andrew r.c. milner, william g. parker, and vincent l. santucci a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover the chinle formation section above the shinarump member near the circle cliffs overlook. the wingate sandstone forms the jagged cliffs that cap the chinle. i 2017 president bill loughlin bill@loughlinwater.com 435.649.4005 2017 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2017 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2017 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2017 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2017 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 4 2017 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 4 2017 99 abstract the chinle formation and the lower part of the overlying wingate sandstone and moenave formation were deposited in fluvial, lacustrine, paludal, and eolian environments during the norian and rhaetian stages of the late triassic (~230 to 201.3 ma), during which time the climate shifted from subtropical to increasingly arid. in southern utah, the shinarump member was largely confined to pre-chinle paleovalleys and usually overprinted by mottled strata. from southeastern to southwestern utah, the lower members of the chinle formation (cameron member and correlative monitor butte member) thicken dramatically whereas the upper members of the chinle formation (the moss back, petrified forest, owl rock, and church rock members) become erosionally truncated; south of moab, the kane springs beds are laterally correlative with the owl rock member and uppermost petrified forest member. prior to the erosional truncation of the upper members, the chinle formation was probably thickest in a southeast to northwest trend between petrified forest national park and the zion national park, and thinned to the northeast due to the lower chinle formation lensing out against the flanks of the ancestral rocky mountains, where the thickness of the chinle is largely controlled by syndepositional salt tectonism. the gartra and stanaker members of the ankareh formation are poorly understood chinle formation correlatives north of the san rafael swell. osteichthyan fish, metoposaurid temnospondyls, phytosaurids, and crocodylomorphs are known throughout the chinle formation, although most remains are fragmentary. in the cameron and monitor butte members, metoposaurids are abundant and non-pseudopalatine phytosaurs are known, as is excellent material of the paracrocodylomorph poposaurus; fragmentary specimens of the aetosaurs calyptosuchus, desmatosuchus, and indeterminate paratypothoracisins were probably also recovered from these beds. osteichthyans, pseudopalatine phytosaurs, and the aetosaur typothorax are especially abundant in the kane springs beds and church rock member of lisbon valley, and typothorax is also known from the petrified forest member in capitol reef national park. procolophonids, doswelliids, and dinosaurs are known but extremely rare in the chinle formation of utah. body fossils and tracks of osteichthyans, therapsids, crocodylomorphs, and theropods are well known from the lowermost wingate sandstone and moenave formation, especially from the st. george dinosaur discovery site at johnson farm. upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah jeffrey w. martz1, james i. kirkland2, andrew r.c. milner3, william g. parker4, and vincent l. santucci5 1department of natural sciences, university of houston-downtown, 1 main st., office n808, houston, tx 77002; typothorax@gmail.com 2utah geological survey, p.o. box 146100, salt lake city, ut 84116; jameskirkland@utah.gov 3st. george dinosaur discovery site at johnson farm, 2180 east riverside drive, st. george, ut 84790; arcmilner@gmail.com 4petrified forest national park, box 2217, petrified forest, az 86028; william_parker@nps.gov 3national park service, geologic resource division, washington dc 20240; vincent_santucci@nps.gov citation for this article. martz, j.w., kirkland, j.i, milner, a.r.c., parker, w.g., and santucci, v.l., 2017, upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah: geology of the intermountain west, v. 4, p. 99–180. © 2017 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org www.utahgeology.org 100 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 introduction the triassic period was one of the most critical intervals in the history of tetrapod evolution—a time when terrestrial ecosystems recovered from the permian extinction with a spectacular adaptive radiation that included early dinosaurs, crocodylian-like archosaurs, and mammals (e.g., sues and fraser, 2010; nesbitt, 2011). at the end of the triassic, a globally variable array of terrestrial ecosystems in which different amniote groups enjoyed varying degrees of success (ezcurra, 2010; sues and fraser, 2010) gave way to uniformly dinosaur-dominated ecosystems as a result of complex environmental changes that are only beginning to be understood (e.g., rowe and others, 2010; irmis, 2011; irmis and others, 2011; olsen and others, 2011; parker and martz, 2011). understanding the nature and timing of these changes requires detailed analysis of lithostratigraphy, depositional systems, and biostratigraphy (e.g., parker and martz, 2011, 2017; martz and parker, 2017). the upper triassic chinle formation, which is exposed across the four corners states and southern nevada (figure 1), provides a remarkable record of environmental and biotic change during the last 25 million years of the triassic period, from roughly 230 ma to sometime before 201.3 ma (irmis and others, 2011; ramezani and others, 2011, 2014; atchley and others, 2013; martz and others, 2014). under current calibrations of the late triassic time scale (furin and others, 2006; muttoni and others, 2010; schoene and others, 2010; hüsing and others 2011), this places the beginning of chinle deposition very close to the beginning of the norian, and the end of chinle deposition during the rhaetian (e.g., olsen and others, 2011; atchley and others, 2013). the sandstone and mudstone beds of the chinle formation were deposited primarily by braided and meandering fluvial systems, associated lacustrine and paludal environments, and in the upper part of the section, rare eolian dunes (e.g., blakey and gubitosa, 1983, 1984; dubiel, 1987a, 1987b, 1989; demko and others, 1998, 2005; dubiel and hasiotis, 2011). throughout the norian and rhaetian, several fluvial aggradational cycles (facs) were deposited within the chinle formation in response to tectonically driven uplift of the early mesozoic cordilleran arc to the southwest (figure 1), and associated basin subsidence (trendell and others, 2012; atchley and others, 2013; howell and blakey, 2013), and/or to variations in discharge and sediment transport related to climate change (dubiel and hasiotis, 2011). the chinle formation was deposited in a subtropical climate with distinct seasonality (e.g., dubiel and others, 1991; dubiel and hasiotis, 2011). paleosols and depositional systems indicate that lakes and swamps were common in western north america early in the norian, but that the climate became increasingly hot and arid after 215 ma during the middle-late norian and rhaetian. this climate shift may have been due to western north america moving from the tropics into the more arid mid-latitudes, or to the development of a rain shadow resulting from the growing cordilleran arc accompanied by an associated increase in atmospheric co2 (blakey and gubitosa, 1983, 1984; dubiel and others, 1991; cleveland and others, 2008; dubiel and hasiotis, 2011; atchley and others, 2013; nordt and others, 2015). the overlying dune and interdune deposits of the wingate sandstone and fluvial deposits of the stratigraphically equivalent moenave formation were probably initially deposited during the rhaetian (donohoo-hurley and others, 2010; kirkland and others, 2014a; suarez and others, 2017). the triassic-jurassic boundary, which is well constrained radioisotopically at 201.3 ma (schoene and others, 2010; blackburn and others, 2013), has long been accepted to lie within the moenave formation (molina-garza and others, 2003; cornet and waanders, 2006; donohoo-hurley and others, 2006; kirkland and milner, 2006; tanner and lucas, 2007; downs, 2009; kirkland and others, 2014a). recent radioisotopic dating places it within the dinosaur canyon member of the moenave formation (suarez and others, 2017). this controversial topic has been discussed in detail in milner and others (2012), in kirkland and others (2014a), and in suarez and others (2017). the bulk of work on the lithostratigraphy and depositional systems of the chinle formation has been done in southern utah and northern arizona. the lithostra101 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 tigraphy of the chinle formation in southern utah was described in detail by several studies published between the late 1950s and early 1970s (stewart, 1956, 1957; harshbarger and others, 1957; stewart and others, 1959; poole and stewart, 1964; wilson and stewart, 1967; repenning and others, 1969; o’sullivan, 1970; stewart and others, 1972a; o’sullivan and maclachlan, 1975; o’sullivan and green, 1977). these studies established much of the stratigraphic nomenclature that is still in use for the members within the chinle formation, and correlated these members across the region. the most notable of these studies is the magisterial work of stewart figure 1. late triassic tectonic and geographic controls on chinle formation deposition. extent of chinle formation sediment cover, shinarump paleovalleys, and isopach lines representing thickness (in meters) after blakey (2008, figures 18 and 21) and blakey and gubitosa, 1983, figure 8); extent of dockum group sediment cover and isopach lines after lehman (1994); extent of vampire and waterman formations sediment cover, distribution of cordilleran volcanic arc, and locations of late triassic magmatism after riggs and others (2013, figure 1; 2016, figure 1); other geographic features after dickinson and gehrels (2009, figure 7). dashed isopach lines indicate region where upper part of chinle formation erosionally truncated, indicating that original thickness was probably greater (see figure 2a). width of modern basin and range province compacted to approximate pre-extensional width. arrow on zuni sag trend line shows predominant direction of sediment transport. 102 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 and others (1972a), which synthesized previous studies and proposed detailed correlations within the chinle formation across the western united states. during the 1980s, ronald blakey, russell dubiel, and their colleagues published a handful of extremely influential publications presenting lithostratigraphic correlations across southern utah that largely corroborated previous studies, and gave detailed interpretations of the depositional systems represented by different members (blakey and gubitosa 1983, 1984; blakey and middleton, 1986; dubiel, 1987a, 1987b, 1989, 1994). lucas (1993; lucas and others, 1997a) formally raised the chinle formation to group rank, presented somewhat different interpretations of correlations within the chinle formation across the colorado plateau, and also extended the names of several members to areas where they had not previously been used (e.g., the extension of the name rock point member from northern arizona into southern utah to replace the name church rock member). lucas (1993) also proposed several new lithostratigraphic units within the chinle group, notably the cameron formation and the blue mesa and painted desert members of the petrified forest formation. following most subsequent workers, we differ from lucas (1993; lucas and others, 1997a) by using more traditional nomenclature and rank, referring to the chinle as a formation and its subunits as members (e.g., dubiel, 1994; woody, 2006; blakey, 2008, p. 268; martz and parker, 2010; see zeigler and others, 2008, for revisons in new mexico). since 2000, several studies have developed increasingly detailed lithostratigraphic models for the chinle formation that have been used as frameworks for increasingly detailed biostratigraphic studies, permitting, in turn, ever more detailed models relating late triassic environmental change to biotic change (e.g., martz and parker, 2010; parker and martz, 2011; atchley and others, 2013). these models have become increasingly well-calibrated to the geochronologic time scale by providing a detailed and accurate stratigraphic framework on which to hang the steadily growing body of data on radioisotopic dates and magnetostratigraphy (e.g., olsen and others, 2011; irmis and others, 2011; ramezani and others, 2011, 2014; atchley and others, 2013; zeigler and others, 2017). although the most detailed of these studies have been conducted in petrified forest national park in northern arizona (e.g., heckert and lucas, 2003a; woody, 2006; martz and parker, 2010; parker and martz, 2011; ramezani and others, 2011; martz and others, 2012; trendell and others, 2012; atchley and others, 2013; howell and blakey, 2013), there have also been detailed stratigraphic studies of the chinle formation in southern utah (e.g., beer, 2005; kirkland and others, 2014b; martz and others, 2014, 2015). moreover, our understanding of chinle depositional and paleoclimatic changes has become enhanced through recent depositional system and paleosol studies (e.g., therrien and fastovsky, 2000; tanner, 2003; prochnow and others, 2006; cleveland and others, 2007, 2008; driese and others, 2010; dubiel and hasiotis, 2011; loughney and others, 2011; trendell and others, 2012, 2013; atchley and others, 2013; howell and blakey, 2013). whereas large vertebrate collections exist from the chinle formation of arizona and new mexico (e.g., long and murry, 1995; fiorillo and others, 2000; heckert, 2004; irmis, 2005; irmis and others, 2007; nesbitt and stocker, 2008; parker and martz, 2011), relatively little has been published on the upper triassic vertebrate fauna of utah and collection has been sporadic. lisbon valley in southeastern utah has historically been the most prolific area for collecting vertebrate fossils within the chinle formation in utah (cope, 1877; schaeffer, 1967; morales and ash, 1993; lucas and others, 1997a, p. 92, 1997b; milner, 2006; milner and others, 2006a, 2008, 2011, 2012; gibson, 2013a, 2013b; martz and others, 2014; hunt-foster and others, 2016). comparatively little has been published on upper triassic vertebrates from elsewhere in the state and most publications are post 1990 (heckert and others, 1999; parrish, 1999; fraser and others, 2005; parker and others, 2006; gauthier and others, 2011; schachner and others, 2011; kirkland and others, 2014b; martz and others, 2015). the quality of much of this material is, however, spectacular (e.g., schachner and others, 2011; gibson, 2013a, 2013b). moreover, paleontological inventories of national parks conducted by the utah geological survey and the national park service (santucci and koch, 2003; deblieux and others, 2006; kirkland and others, 2010; santucci and kirkland, 2010; madsen and others, 2012; tweet and others, 2012; kirkland and 103 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 others, 2014b; martz and others, 2015) suggest that the enormous paleontological potential of the chinle formation of utah has barely been tapped. this paper presents a brief synthesis of what is known of the depositional history, lithostratigraphy, and vertebrate paleontology of the chinle formation in southern utah, with particular regions of interest described in more detail. abbreviations amnh: american museum of natural history, new york; cany: canyonlands national park; care: capitol reef national park; glca: glen canyon national recreation area; gsenm: grand staircase-escalante national monument; mna: museum of northern arizona, flagstaff; pefo: petrified forest national park; sgds: st. george dinosaur discovery site at johnson farm, st. george; ucm: university of colorado museum, boulder; umnh: natural history museum of utah, salt lake city; usnm: national museum of natural history (smithsonian), washington d.c.; ypm: yale peabody museum of natural history, new haven; zion: zion national park. geographic and tectonic controls on chinle sedimentation deposition of the chinle formation across what is now the colorado plateau was controlled by a combination of early mesozoic tectonic activity and inactive remnants of late paleozoic tectonism (figure 1), many of which followed a striking southeast to northwest trend that parallels or overlies much older proterozoic basement lineaments with the same orientation (baars, 1993). the cordilleran volcanic arc along the western margin of north american continent was well-established by the triassic (dickinson, 2004) and was active in southwestern arizona and eastern california during the late triassic (e.g., barth and wooden, 2006; riggs and others, 2013). the arc and the northeasterly sloping region of southwestern arizona flanking it (the “mogollon slope” sensu bilodeau, 1986) provided important sources of chinle detrital sediments from plutonic, volcanic, and paleozoic sedimentary sources, and also formed the southwestern boundary of the chinle depositional basin (stewart and others, 1972a; dickinson and gehrels, 2008, 2009; riggs and others, 2012, 2013, 2016). the chinle basin was also bounded by largely inactive remnant late paleozoic highlands produced by the accretion of pangea (figure 1). in central colorado, the ancestral uncomphagre highlands (also called uncomphagria or the ute highlands; e.g., nesse, 2008; blakey, 2008) bounded the chinle basin to the northeast. the ouachita-marathon orogenic belt and amarillo-wichita uplift in texas, as well as mesoamerican upland sources, lay to the southeast of the colorado plateau chinle formation depocenter. all of these uplifts were additional sources of chinle detritus (stewart and others, 1972a; riggs and others, 1996; dickinson and gehrels, 2008; dickinson and others, 2010). the chinle depositional basin itself was an actively subsiding back-arc basin oriented southeast to northwest across the four corners states, roughly parallel to the cordilleran arc itself (lawton, 1994; dickinson and gehrels, 2008), and was deepest to the southwest, proximal to the arc (see below). a smaller depocenter, the eagle basin (dubiel, 1992), lay between the ancestral uncomphagre highlands and the more easterly located ancestral front range (also called frontrangia or the arapahoe highlands; e.g., blakey, 2008; nesse, 2008). the chinle formation overlies a major disconformity wherever it occurs throughout the colorado plateau, the tr-3 unconformity (pipiringos and o’sullivan, 1978), usually manifested in the form of southeast to northwest-trending paleovalleys of various depths carved into pre-chinle strata (e.g., painted desert and vermilion cliffs paleovalleys in figures 1 and 2a) (blakey and gubitosa, 1983, 1984; blakey, 2008). most commonly, the chinle formation overlies the early and earliest middle triassic moenkopi formation (figures 2 and 3) (stewart and others 1972b; blakey and others, 1993), but locally it overlies permian strata such as the cutler and dechelly formations, or even older precambrian crystalline rocks (e.g., blakey and gubitosa, 1983, 1984; blakey, 2008). as the youngest members of the moenkopi formation are early anisian (early middle triassic; blakey and others, 1993) and chinle deposition began around the earliest norian (ramezani and others, 2011, 2014; atchley and others, 2013), the tr-3 104 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 2 caption on following page. 105 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 unconformity eliminates most of the anisian, the entire ladinian (late middle triassic), and probably the entire carnian (early late triassic)—a time span of nearly 20 million years (ogg, 2012). paleocurrents indicate that the chinle fluvial systems flowed predominantly from southeast to northwest, roughly parallel to the long axis of the basin (stewart and others, 1972a; blakey and gubitosa, 1983; beer, 2005), although tributaries flowed eastwards in the southern part of the state and northwards in northern arizona (stewart and others, 1972a; johns, 1988; riggs and others, 2013). the shinarump member, the basal unit of the chinle formation across much of the colorado plateau, is thickest in a southeastto northwest-oriented zone just southwest of the four corners region (figure 1) including canyon de chelly in arizona and capitol reef national park (care) and the circle cliffs area of gsenm, indicating that this zone contained the deepest pre-norian paleovalleys, the painted desert paleovalley (blakey and gubitosa, 1983, figure 8, 1984; blakey, 2008). the shinarump river system confined to the painted desert paleovalley was fed by tributaries in smaller paleovalleys. a separate shinarump fluvial system was confined to the northerly oriented vermilion cliffs paleovalley extending north from northeastern arizona to southwestern utah (figure 1) (blakey and gubitosa, 1983, figure 8, 1984; blakey, 2008). several workers (blakey and gubitosa, 1983; demko and others, 1998; dubiel and hasiotis, 2011) have suggested that units overlying the shinarump member, such as the monitor butte and blue mesa members, were also deposited within these paleovalleys. however, the recent recognition that the mesa redondo member is a shinarump member correlative (irmis and others, 2011, supplemental data; riggs and others, 2016) suggests that, at least in northern arizona, only the earliest stages of shinarump deposition were confined to paleovalleys, and that during the norian these valleys were mostly filled to permit a more laterally continuous depositional system. this is supported by the recognition that the monitor butte, bluewater creek, cameron, and lower blue mesa members are probably correlative units overlying the shinarump/mesa redondo fluvial deposits (figures 2 and 3) (lucas, 1993; lucas and others, 1997a; irmis and others, 2011, supplemental data; kirkland and others, 2014b; martz and others, 2015). moreover, blue mesa member deposition in northern arizona may have been controlled by expansion of a large fluvial fan extending northeasterly from the cordilleran volcanic arc (trendell and others, 2013), which would have extended across the areas occupied by the vermilion cliffs and painted desert paleovalleys (blakey and gubitosa, 1983; blakey, 2008), further supporting the notion that these valleys had filled by the late early norian so that laterally continuous deposition occurred across the region. the thickness of the chinle formation is greatest in northern arizona and western new mexico (stewart and others, 1972a, plate 1; blakey and gubitosa, 1983, figure 3c; blakey, 2008, figures 16 and 18), indicating that the basin was deepest closest to the cordilleran arc and shallower to the northeast along the flanks of the ancestral uncomphagre highlands. for example, the stratigraphic thickness of the chinle formation in pefo is about 400 m despite the rock point member being locally absent there (parker and martz, 2011, figure 6), and in excess of 500 m in the southern parts of the navajo nation and in westernmost new mexico where the rock point member occurs (stewart and others, 1972a). blakey (2008, figure 18) shows the chinle formation thinning between northeastern and northwestern arizona and southwestern utah (figure 1). however, it is likely that this is a result of the top of the chinle formation becoming increasingly truncated by erosion (figure 2a) in the western part of the colorado plateau region (this region of truncation is indicated by dashed isopach lines in figure 1 (e.g., stewart and others, 1972a, plate 2). for example, in zion national park (zion) only the lower part of the chinle formation is preserved (figure 2) (martz and others, 2015), but this figure 2 (figure on previous page). chinle formation correlations in southern utah. (a) simplified and idealized stratigraphic cross section of upper triassic and lower jurassic strata from southwestern utah near st. george and zion to the salt anticline region near moab. (b) simplified stratigraphic sections for areas discussed in detail in the text. in the map beneath, chinle formation exposures in dark red, national parks and monuments in gray (see figure 4 for more detail). 106 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 fi gu re 3 . v er te br at e b io st ra tig ra ph y of th e c hi nl e f or m at io n in so ut he rn u ta h. c om po sit e s tr at ig ra ph ic co lu m n sh ow s c or re la tio ns o f a ll m aj or li th ost ra tig ra ph ic u ni ts in s ou th er n pa rt o f s ta te . n um er ic al a ge s an d pl ac em en t o f b io zo ne b ou nd ar ie s ar e ex ce ed in gl y te nt at iv e an d ex pl ai ne d in te xt . ve rt eb ra te ta xa k no w n fr om v ar io us m em be rs sh ow n on th e le ft; th e m oe na ve f or m at io n ta xa a re la rg el y kn ow n fr om tr ac ks . 107 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 preserved thickness is greater than the nearly complete section at care. this suggests that the zone of greatest thickness of the chinle formation originally extended along a more southeast to northwest-trending zone that cuts across the divide between the older vermilion cliffs and painted desert paleovalleys that controlled early shinarump deposition (figure 1) (blakey and gubitosa, 1983). interestingly, this southeastto northwest-trending zone of greatest chinle thickness closely approximates the zuni sag (figure 1), a structural depression considered to have developed in the early jurassic due to a regional tectonic event that slightly changed the orientation of the depositional basin (blakey, 1994). the observation that chinle deposition occurs across the same regional trend suggests that the zuni sag, which overlies the southeast to northwest-trending walker-texas lineament (baars, 1993), may have actually developed during norian time (if not before) due to existing weaknesses in the precambrian basement. general lithostratigraphy of the chinle formation in southern utah the depositional record of the chinle formation in utah (figures 2 and 4) is most complete in the southeastern part of the state, southwest of the salt anticline region of the paradox basin (stewart and others, 1972a, figures 2 and 10). this area includes chinle formation exposures in care, gsenm (figure 2a), red canyon, and the northern part of the navajo nation (e.g., blakey and gubitosa, 1983, 1984; beer, 2005; kirkland and others, 2014b). most members of the chinle formation in northern arizona (where the formation is thickest) have correlatives in this region of southern utah. the section in care, the circle cliffs region of gsenm, and lake powell in glen canyon national recreation area (glca) near the junction of the colorado and san juan rivers varies from approximately 125 m to at least 170 m in thickness, generally thickening to the south (e.g., kirkland and others, 2014b; martz and others, 2015; j.w. martz, unpublished data). at zion, the preserved section is about 180 m thick (martz and others, 2015). as discussed above, these thicknesses were probably considerably greater prior to partial erosional truncation of the chinle formation across the region (figure 2a). to the north and northwest, where the basin thins on the flanks of the ancestral uncomphagre highlands, the lower strata pinch out so that chinle formation exposures within the san rafael swell and salt anticline region are missing lower members such as the shinarump and monitor butte members (figure 2a) (e.g., stewart, 1957; stewart and others, 1972a; blakey and gubitosa, 1983, 1984). however, as the upper part of the chinle formation in the salt anticline region is generally not strongly erosionally truncated as in care, gsenm, and zion, the preserved section in the salt anticline region is not generally thinner than in sections to the west (figure 2). in lisbon valley and the region around arches national park, the chinle formation comprises mostly the church rock member and locally the kane springs beds, and the total formation is generally 110 to 200 m thick (e.g., martz and others, 2014; j.w. martz, unpublished data). the region just to the southwest of the ancestral uncomphagre highlands overlies the pennsylvanian evaporite deposits of the paradox basin and was subject to active salt tectonism during the triassic that formed southeastto northwest-trending salt anticlines (e.g., hazel, 1994), as it still does today. the upper triassic in southern utah includes the chinle formation, lower part of the wingate sandstone, and lower part of the moenave formation (figure 3). the chinle consists of several correlative members (figure 2). shinarump member of the chinle formation above the tr-3 unconformity, the base of the chinle formation in utah and arizona is usually a unit of sandstone and conglomerate called the shinarump member (gilbert, 1875), which is composed almost exclusively of extrabasinal quartz, quartzite, chert, and volcanic clasts characterized by diagenetic quartz overgrowths (stewart, 1957; stewart and others, 1972a; blakey and gubitosa, 1983, 1984; dubiel, 1987a, 1987b). in some parts of northern arizona, there is a reddish mudstone-dominated unit with interbedded siliceous sandstone and conglomerate, the mesa redondo member (cooley, 1958), which is probably correlative to the shi108 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 narump member (irmis and others, 2011, supplemental data). the mesa redondo member has been radioisotopically dated at 228 to 225 ma, or earliest norian (early lacian) (ramezani and others, 2014), which is therefore presumably the age of the correlative shinarump member. the shinarump member was deposited by figure 4. field trip route and major stops. chinle formation outcrops shown in red, national parks and monuments shaded in gray. 109 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 northwest-flowing braided rivers that filled pre-norian paleovalleys incised into the moenkopi formation and pre-triassic units (blakey and gubitosa, 1983, 1984; blakey, 2008). mottled strata of the chinle formation in most places, both the shinarump and mesa redondo members are overprinted by a distinctive mottled paleosol that sometimes extends into the uppermost moenkopi formation, and is variously referred to as the mottled member, mottled strata, purple mottled unit, temple mountain member, or zuni mountain formation (robeck, 1956; poole and stewart, 1964; stewart and others, 1972a; dubiel, 1987a, 1987b, 1992, 1994; heckert and lucas, 2003b; dubiel and hasiotis, 2011). this mottling marks a gleyed paleosol formed by fluctuating water tables, and is comprised of patches of multi-colored iron oxide interspersed with iron-depleted patches, and often densely packed with crayfish burrows (tanner and lucas, 2006; dubiel and hasiotis, 2011). a slightly different pattern occurs in care and the circle cliffs area of gsenm, where the top of the shinarump member is eroded and sometimes entirely excised (stewart and others, 1972a; dubiel, 1987a, 1987b; demko, 2003; beer, 2005; kirkland and others, 2014b), and the mottled strata seem to be restricted to below the base of the shinarump member (kirkland and others, 2014b; j.w. martz, unpublished data). in regions where the mottled strata overprint the shinarump member (dubiel, 1987a, 1987b; dubiel and hasiotis, 2011; irmis and others, 2011, supplemental data; atchley and others, 2013; martz and others, 2014), formation of this paleosol likely occurred during a depositional hiatus that followed shinarump deposition. as the uppermost mesa redondo member has been dated radioisotopically at 225.185 ma or early norian (lacian) (ramezani and others, 2011), the mottled strata overprinting both the shinarump and mesa redondo members may have formed about 225 million years ago. the mottled strata should not be considered a distinct formation or member (e.g., zuni mountains formation) because they represent an episode of paleosol formation overprinting pre-existing stratigraphic units, not distinct stratigraphic units in their own right. monitor butte and cameron members of the chinle formation in southeastern utah, the shinarump member/ mottled strata are overlain by a drab-colored, mudstone-dominated unit with interbedded sandstone and conglomerate—the monitor butte member (kiersch, 1956). the bluewater creek member (lucas and hayden, 1989), blue mesa member, and cameron member (lucas, 1993) in southwestern utah, northern arizona, and western new mexico may be correlative to the monitor butte member (lucas, 1993; lucas and others, 1997a; kirkland and others, 2014b). the blue mesa member type section (lucas, 1993) has been radioisotopically dated between about 225 to 220 ma (ramezani and others, 2011, 2014; atchley and others, 2013); these dates are a reasonable estimate for the correlative cameron and monitor butte members. the lower part of the monitor butte member in care contains distinctly contorted strata (dubiel, 1987a, 1991; kirkland and others, 2014b), similar to contorted strata that occur in the lower bluewater creek member in parts of northeastern arizona and the zuni mountains in western new mexico (green, 1956; repenning and others, 1969; stewart and others, 1972a, p. 25–26; ash, 1978; blakey and gubitosa, 1983, p. 66–68; dubiel and others, 1993; kirkland and others, 2014b). these contorted strata seem to have been deposited along a southeast to northwest depositional trend paralleling the zuni sag. the monitor butte member was deposited by meandering rivers and associated overbank lacustrine and paludal environments (blakey and gubitosa, 1983, 1984; dubiel, 1987a, 1987b; beer, 2005) indicating relatively high-precipitation subtropic climatic conditions in western north america during the lacian (dubiel and hasiotis, 2011; atchley and others, 2013; trendell and others, 2013). the contorted strata in the lower part of the monitor butte member are the result of syndepositional slumping of overloaded lacustrine or paludal deltas (e.g., blakey and gubitosa, 1983, 1984; dubiel and others, 1993). at zion in southwestern utah, the cameron member rather than the monitor butte member makes up the lower part of the chinle formation that overlies the 110 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 shinarump member. the cameron member (including the sandstone and mudstone member of phoenix, 1963) is considerably thicker than the monitor butte member to the northeast (figure 2) (e.g., kirkland and others, 2014b; martz and others, 2015) and consists of drab-colored mudstone with abundant interbedded pale-colored sandstone, which laterally pinch out to form striking reddish paleosols. as with the contorted strata of the monitor butte member, deposition of the cameron member seems to fall within the southeast to northwest trend paralleling the zuni sag; this trend includes zion, lees ferry in glca, the southwestern part of the navajo nation near cameron, and pefo. the lower part of the blue mesa member type section in pefo (lucas, 1993) is nearly identical to the zion section (lucas, 1993; martz and others, 2015) and should probably be referred to the cameron member. moss back member of the chinle formation the moss back member is a multi-storied, conglomeratic sandstone unit deposited by northwest-flowing braided and meandering rivers that overlies the monitor butte member east of care (stewart and others,1972a; blakey and gubitosa, 1983; blakey, 2008). the moss back, like most of the conglomerates in the chinle formation above the shinarump member, is at least locally dominated by intrabasinal clasts of reworked pedogenic carbonate and clastic sedimentary rock (stewart and others, 1972a). however, a massive ledge-forming conglomeratic sandstone that is composed almost entirely of extrabasinal siliceous clasts occurs low in the chinle formation in the san rafael swell area, and was identified as the moss back member by stewart and others (1972a). a sandstone unit potentially correlative with the moss back member is present at the same stratigraphic position in care, the circle cliffs, and the surrounding region (dubiel, 1991; kirkland and others, 2014b; j.w. martz, unpublished data). it is likely that the moss back member is at least partially correlative to the sonsela member of northern arizona (lucas, 1993; howell and blakey, 2013), which was deposited between the early and middle norian (latest lacian and alaunian) from 220 to 213 ma (ramezani and others, 2011, 2014; atchley and others, 2013). the sonsela member however is a much thicker and more complex sandstoneand conglomerate-dominated unit compared to the moss back member (e.g., martz and parker, 2010), and it is not clear which part of the sonsela member that the moss back member correlates with. petrified forest member of the chinle formation the nomenclature of the upper reddish and pastel-colored beds of the chinle formation is broadly shared between arizona and utah, with some regional variations (e.g., stewart and others, 1972a; blakey and gubitosa, 1983, 1984; lucas, 1993). above the moss back member is a reddish unit of interbedded mudstone, sandstone, and conglomerate containing abundant pedogenic carbonate nodules, the petrified forest member (gregory, 1950 sensu woody, 2006; parker, 2006; martz and parker, 2010; = painted desert member of the petrified forest formation sensu lucas, 1993; see martz and others, 2015, for a discussion of the complex nomenclatural history of this unit). following the same thickness trends observed with the chinle formation as a whole, the petrified forest member is 230 m thick at monument valley (stewart and others, 1972a) and 130 m thick at pefo (martz and others, 2012), but less than 60 m thick at circle cliffs in gsenm and care in southeastern utah (kirkland and others, 2014b; j.w. martz, unpublished data). the petrified forest member was deposited by meandering rivers that underwent frequent avulsions due to large input of volcanic detritus (blakey and gubitosa, 1983; johns, 1988) as western north america was beginning to undergo an interval of aridification (tanner, 2003; dubiel and hasiotis, 2011; atchley and others, 2013). the petrified forest member was deposited between about 213 to 209 ma during the middle to late norian (latest alaunian to sevatian), and possibly earliest rhaetian (e.g., atchley and others, 2013). the owl rock member and kane springs beds of the chinle formation the owl rock member (kiersch, 1956) is a pastel-colored unit dominated by non-bentonitic mud111 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 stone and sandstone, with ledge-forming carbonate beds that have a generally gradational lower contact with the petrified forest member (stewart and others, 1972a; blakey and gubistosa, 1983, 1984; dubiel, 1993; martz and others, 2012). the owl rock member was deposited by lakes, swamps, and associated river systems during a phase of relatively low volcanic input compared to underlying chinle deposits (blakey and gubitosa, 1983; dubiel, 1987a, 1987b; dubiel and hasiotis, 2011) during the rhaetian, about 209 to 205 ma (atchley and others, 2013). in the salt anticline region of the paradox basin (notably lisbon valley, indian creek, canyonlands national park, and dead horse point state park), where the lower units of the chinle formation are absent, the base of the formation consists of drab-colored sandstone and conglomerate with interbedded mudstone beds. these beds are called the kane springs beds (blakey and gubitosa, 1983, 1984), and are probably correlative with the owl rock member and possibly part of the petrified forest member (figure 2a) (blakey and gubitosa, 1983, 1984; hazel, 1994; martz and others, 2014). the kane springs beds were deposited by meandering and braided rivers originating off uncompahgria and flowing through poorly drained floodplains confined within contemporaneous, northwesterly oriented salt anticlines (hazel, 1994). to the west and southwest, these rivers probably joined with the petrified forest and/or owl rock member depositional systems (blakey, 1978; huber, 1980, 1981; blakey and gubitosa, 1983, 1984; dubiel and brown, 1993; hazel, 1994). church rock member of the chinle formation the uppermost unit of the chinle formation consists of reddish-brown siltstone, sandstone, and conglomerate referred to as the church rock member (stewart, 1957) in utah, the rock point member (harshbarger and others, 1957) in northern arizona, the dolores formation in southwestern colorado (cross and howe, 1905) and the siltstone member in northern new mexico (stewart and others, 1972a). although lucas (1993) assigned all of these strata to the rock point member, facies variations within these uppermost beds are complex enough that regional variations in nomenclature may be justified (j.w. martz and w.g. parker, unpublished data), and it is moreover possible that these strata are not all precisely correlative. o’sullivan (1970) claimed that the type section of the church rock member in northern arizona (witkind and thaden, 1963) was only correlative with the hite bed at the very top of the strata assigned to the church rock member in southern utah. he referred to the younger southern utah strata as the “reddish-orange siltstone member.” as o’sullivan’s (1970) hypothesis has never been investigated in detail by subsequent authors, we retain the traditional nomenclature, referring to all of the uppermost chinle formation strata in southern utah as the church rock member. in southern utah, the church rock member contains prominent ledge-forming conglomeratic sandstone. the black ledge beds (sensu martz and others, 2014; = black ledge sensu stewart and others, 1959) occur at the base of the member, whereas the hite bed (stewart and others, 1972a) and red ledge beds (martz and others, 2014) both occur higher in the member. the lower owl rock member has been dated radioisotopically at about 207 ma (atchley and others, 2013), indicating that the overlying church rock was probably deposited during the rhaetian (e.g., martz and others, 2014). the church rock member was deposited by northwest-flowing, coarse-grained braided streams outcropping in a belt extending from southwestern colorado to the san rafael swell (stewart and wilson, 1960). rare eolian sandstone beds also occur within the church rock member (stewart and others, 1972a; dubiel, 1989; hazel, 1994). lower wingate sandstone and moenave formation the j-0 (tr-5) unconformity, which erosionally caps the chinle formation across most of the colorado plateau, separates the chinle formation from the lowermost formations of the glen canyon group: the wingate sandstone and moenave formation (pipiringos and o’sullivan, 1978; blakey, 1994; kirkland and others, 2014a). the wingate sandstone is an extremely well-sorted, siliceous, cliff-forming sandstone that occurs northeast 112 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 of a line extending through tuba city, arizona, and paria, utah, including the san rafael swell, state road (sr) 128, sr 313, dead horse point state park, and care. locally, discontinuous lenses of sandstone and conglomerate sometimes referred to informally as the big indian rock beds occur at the base of the wingate sandstone (martz and others, 2014; irmis and others, 2015). the dinosaur canyon member of the moenave formation, which is laterally equivalent to the wingate sandstone (figures 2 and 3), occurs southwest of the line running through tuba city and paria, including at zion and st. george dinosaur discovery site at johnson farm (sgds). the dinosaur canyon member is a reddish-brown unit of interbedded sandstone and mudstone (clemmensen and others, 1989). the overlying whitmore point member consists of a series of thin-bedded shale, limestone, and sandstone that separates the dinosaur canyon member from the overlying springdale sandstone member of the kayenta formation along the arizona strip and in southwestern utah west of kanab (wilson, 1967). the contact between the dinosaur canyon and the overlying whitmore point members is usually taken as a limestone bed partially replaced by red chert (wilson, 1967; kirkland and others, 2014a). the big indian rock beds represent localized channels that flowed within paleovalleys incised into the uppermost church rock member that were subsequently buried by the wingate erg before the end of the rhaetian (lucas and others, 1997a, 1997b; martz and others, 2014). the lower part of the wingate sandstone is probably rhaetian, as at least part of the dinosaur canyon member of the moenave formation, and possibly part of the whitmore point member (donohoo-hurley and others, 2010; kozur and weems, 2010; lucas and others, 2011; kirkland and others, 2014a). the triassic-jurassic boundary, which probably lies high in the fluvially deposited dinosaur canyon member or fluvial-lacustrine lower whitmore point member, is well constrained radioisotopically at 201.3 ma (schoene and others, 2010; blackburn and others, 2013). stratigraphic notes on upper triassic units in northern utah chinle formation exposures in north-central and northeastern utah (figure 4) have generally received much less study than the chinle formation south of interstate highway 70 (i-70). the stratigraphic relationships between the chinle formation in northeastern utah to the rest of the colorado plateau are poorly understood. patchy exposures of upper triassic strata across much of north-central utah have been assigned to the gartra and stanaker members of the ankareh formation (thomas and krueger, 1946; kummel, 1954; rigby, 1968; brandley, 1988, 1990) and/or bell springs formation (lucas, 1993; may, 2015), but little work has been done correlating these with the southern utah members. informally named units of the chinle formation in the dinosaur national monument area of northeastern utah (e.g., dubiel, 1992; jensen and kowallis, 2005; irmis and others, 2015) also have poorly understood stratigraphic relationships with the chinle formation members of the colorado plateau with the exception of the gartra member, which is generally considered to be correlative with the shinarump member (kinney, 1955; stewart and others, 1972a; brandley, 1990; lucas, 1993). lucas (1993) correlated the bell springs “formation,” the uppermost putative upper triassic unit below the navajo sandstone, with the rock point member. vertebrate paleontology of the chinle formation in southern utah during the late triassic, the vertebrate fauna of western north america consisted of a combination of surviving permian faunal elements and relatively new vertebrate groups that radiated during the triassic (e.g., sues and fraser, 2010; nesbitt, 2011). the most successful tetrapod clade in western north america were the archosauromorphs, particularly phytosaurs, pseudosuchians (crocodylian-line archosaurs), and dinosauromorphs (e.g., long and murry, 1995; nesbitt and others, 2007; nesbitt, 2011; stocker and butler, 2013; desojo and others, 2013; irmis and others, 2013; langer and others, 2013; nesbitt and others, 2013). addition113 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 ally, metoposaurid temnospondyls, dicynodonts, and other non-mammalian synapsids represent surviving permian lineages that continued to enjoy a measure of success during the late triassic in north america (e.g., fröbisch, 2009; sues and fraser, 2010; brusatte and others, 2015). freshwater sharks, coelacanths, lungfishes, and a wide variety of “ray-finned fish” were important components of the freshwater vertebrate fauna (e.g., schaeffer, 1967; murry, 1989; gibson, 2013b). many of these faunal elements are known from southern utah (figures 3 and 5). osteichthyes elasmobranchs are well known from the chinle formation and dockum group (e.g., murry, 1989) but have not been described from the chinle formation in utah. bony fishes (osteichthyes) are, however, represented, including both cranial material and teeth of lobe-finned fishes (sarcopterygii) and a variety of spectacular ray-finned fishes (actinopterygii) (figure 5). the church rock member of lisbon valley has produced many complete coelacanth skeletons, including the holotype specimen of chinlea sorenseni schaeffer 1967 (figure 5a) (amnh 5652) and other referred specimens (amnh 5656, amnh 5660, amnh 5704; schaeffer, 1967), including specimens collected for the natural history museum of utah (milner and others, 2006a). lungfish tooth plates have been recovered from the stanaker member of the ankareh formation near spanish fork (brandley, 1990), two tooth plates of arganodus have been collected from the lower church rock member of the chinle formation in lisbon valley (a.r.c. milner, unpublished data), and two specimens are known from the monitor butte member at the circle cliffs in gsenm (figure 5b) (ypm 57071) and an un-numbered specimen collected in 2016 (w.g. parker and j.w. martz, unpublished data). another lungfish tooth plate has been collected from the owl rock member of care (figure 5c) (un-numbered specimen from locality wn0183; kirkland and others, 2014b). parrish and good (1987) reported lungfish tooth plates from the petrified forest member at the four acres mine in white canyon. the church rock member of southern utah, especially lisbon valley has yielded by far the richest and most diverse collection of freshwater ray-finned fishes from the chinle formation (schaeffer, 1967; milner and others, 2006a; gibson, 2013a, 2013b, 2015), rivaled only by specimens from the correlative dolores formation in nearby southwestern colorado (schaeffer, 1967; dubiel and others, 1989). schaeffer (1967) described most of these specimens following intensive collecting in 1953 by the atomic energy commission, utah geological survey, and the museum of comparative anatomy at harvard university. although schaeffer (1967, p. 292–293) gave locality information only detailed enough to locate the quarries approximately, more recent excavations by andrew milner (milner and others, 2006a; martz and others, 2014) have produced numerous new specimens from walt’s fish quarry, occurring in fluvial deposits in the upper part of the church rock member. specimens recovered from lisbon valley include the non-teleostean ganoid hemicalypterus weiri schaeffer, 1967 (figure 5d), the redfieldiiforms cionichthys dunklei (figure 5e) (e.g., amnh 5615), lasalichthys hillsi (e.g., amnh 5636), and synorichtys stewarti (e.g., amnh 5646), the palaeonisciform turseodus sp., and the semionotiforms lophionotus sanjuanensis gibson, 2013a (figure 5f) (e.g., amnh 5680) and lophionotus chinleana (e.g., umnh vp 19417) (schaeffer, 1967; milner and others, 2006a; gibson, 2013a, 2013b, 2015). the type specimens of most species above occur at lisbon valley (schaeffer, 1967; gibson, 2013a, 2013b). these fish range in length from about 4.5 to 35 cm (schaeffer, 1967; gibson, 2013b). whereas most were probably carnivorous, the teeth of hemicalypterus are multidenticulate, and it may be the earliest known herbivorous fish (gibson, 2015). metoposaurids metoposaurids were temnospondyl amphibians that were common large aquatic carnivores in north america, europe, morocco, and india (e.g., hunt, 1993; sulej, 2002; brusatte and others, 2015). in western north america, upper triassic metoposaurid amphibians are usually assigned to three genera (colbert and imbrie, 1956; hunt, 1993; sulej, 2002). large specimens with prominent parietal flanges are usually 114 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 5. fish fossils from the chinle formation of utah. (a) coelocanth chinlea sorenseni amnh 5652 (schaeffer, 1967, pl. 26) from the church rock member of lisbon valley. (b) un-numbered lungfish tooth from the monitor butte member of gsenm. (c) un-numbered lungfish tooth form the owl rock member of care (kirkland and others, 2014a, figure 22). actinopterygiian fish from the church rock member of lisbon valley: (d) hemicalypteris weiri usnm 23425 (gibson, 2015, figure 1a). (e) cionichthys dunklei amnh 5615 (schaeffer, 1967, pl. 11). (f) semionotus sp. amnh 5680 (schaeffer, 1967, pl. 22). scale bars = 1 cm. 115 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 placed in the species metoposaurus or koskinonodon (= buettneria; see mueller, 2007) bakeri or koskinonodon perfectus, whereas small specimens with reduced parietal flanges are placed in the genus apachesaurus (e.g., hunt, 1993; long and murry, 1995; sulej, 2002). in recent treatments metoposaurus and koskinonodon are distinguished almost exclusively based on whether the lacrimal contacts the orbit and the size of the area on the interclavicle covered with rounded and hexagonal pits (hunt, 1993; long and murry, 1995; sulej, 2002), although more detailed descriptions of metoposaurid variation are currently underway (brusatte and others, 2015). temnospondyl specimens tentatively identifiable as metoposaurid are known in the chinle formation of utah (figures 6a to 6e), including both large and rounded centra with notochordal depressions (figure 6e) and fragments of heavily sculptured cranial and pectoral bones (figures 6a and 6b). almost none of this material however, can be assigned with certainty to an alpha taxon, and indeed its tentative referral to metoposauridae is based only on the absence of any other known large temnospondyl taxa from the chinle formation. a partial metoposaurid interclavicle was reported from the shinarump member in monument valley (lewis and trimble, 1960), a unit in which tetrapod remains are generally rare; we do not know where this specimen is reposited. large metoposaurid fragments occur in the monitor butte member of care and the circle cliffs (figures 6a and 6b) (e.g., ypm 57154, 57126; kirkland and others, 2014b; w.g. parker and j.w. martz, unpublished data) and the vermilion cliffs (parker and others, 2006), as well as in the cameron member of zion (figure 6e) (martz and others, 2015). six additional sites are known outside of zion in the lower cameron and shinarump members. additionally, large metoposaurid fragments, including a mandible fragment, have been recovered from the capitol reef bed in the upper petrified forest member at care (figures 6c and 6d); these are unusually high occurrences stratigraphically (kirkland and others, 2014b). finally, there are two metoposaur sites in the lower chinle formation in the las vegas, nevada area (joshua bonde, university of nevada, las vegas, verbal communication, 2015). the large size of the specimens, and the fact that the vertebral centra are shorter than wide (figure 6e) indicate only that they are probably referable to metoposaurus or koskinonodon (= buettneria) rather than apachesaurus (hunt, 1993). smaller metoposaurid vertebrae that may be referable to apachesaurus (ypm 57075, ypm 57106) because of having elongate vertebral centra (hunt, 1993) are known from the circle cliffs (w.g. parker, unpublished data), although their precise stratigraphic position has not been determined. fragmentary metoposaurid material is also known from the church rock member of lisbon valley (milner and others, 2011; martz and others, 2014; a.r.c. milner, unpublished data), indicating that metoposaurids persisted at least until the final stages of chinle deposition. procolophonids procolophonid parareptiles are not commonly encountered in the chinle formation. chinleogomphius jacobsi (murry, 1987) from the blue mesa member of arizona has been identified as procolophonid (sues and olsen, 1993), and several undescribed specimens similar to hypsognathus from the owl rock member of arizona await description (sues and others, 2000, p. 283). the only known specimen from utah is a mostly complete skull (figure 6f) (mna v9953) recovered from the owl rock member in the manti-la sal national forest southwest of lisbon valley (fraser and others, 2005). this specimen is probably a leptopleurine procolophonid closely related to hypsognathus, though distinct from the specimens from the owl rock member of arizona (fraser and others, 2005). doswellids doswellids were armored basal archosauriforms that may have had a semi-aquatic predatory lifestyle as in proterosuchids, proterochampsids, and phytosaurs (sues and others, 2013). parrish and good (1987) and parrish (1999) noted that fragmentary osteoderms from the blue lizard mine locality in red canyon, occurring very low in the monitor butte member, have similarities to the north american doswellid taxon doswellia (figure 6g). specifically, these osteoderms possess fine sub-circular pits and rugose articular 116 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 6 caption on following page. 117 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 edges (parrish and good, 1987), which also occur in doswellia (weems, 1980; sues and others, 2013). phytosaurs phytosaurs were large predatory archosauriforms that superficially resembled modern crocodylians in form and probably in lifestyle (e.g., hunt, 1989; stocker and butler, 2013), and are among the most commonly encountered vertebrates in the chinle formation. throughout the stratigraphic thickness of the chinle formation and the correlative dockum group of new mexico and texas, the massive, long-snouted skulls of phytosaurs show phylogenetic changes in the posterior region of the skull that correspond well to their stratigraphic position (e.g., lucas and hunt, 1993; martz and parker, 2017); specifically, the external nares become posteriorly displaced above the antorbital fenestra, the supratemporal fenestra tend to become increasingly reduced and depressed below the skull roof, and the postorbitosquamosal bars become increasingly broadened (ballew, 1989; stocker, 2010, 2012). as a result, the utility of phytosaurs as biostratigraphic index fossils has been recognized for decades (e.g., colbert and gregory, 1957; gregory, 1972; lucas and hunt, 1993; lucas, 1998; parker and martz, 2011; martz and parker, 2017). the oldest appearances of phytosaur taxa are used to define and bound four late triassic land vertebrate “faunachrons” or biozones in western north america; from lowest to highest, these are the otischalkian, adamanian, revueltian, and apachean (e.g., lucas, 1998; parker and martz, 2011; desojo and others, 2013). the phytosaur taxa used to define all four biozones are known from the dockum group in texas (e.g., lucas, 1998; martz, 2008). in the chinle formation, however, the fossil record of phytosaurs is less complete; this is particularly true of utah. fragmentary phytosaur material, including teeth, partial skulls and mandibles, and postcranial elements are frequently encountered throughout the chinle formation of utah (e.g., stewart and others, 1972a; parrish and good, 1987; deblieux and others, 2005, 2006; kirkland and others, 2014b; martz and others, 2014, 2015). indeed, a phytosaur mandible from clay hill in southern utah identified as heterodontosuchus (lucas, 1898) is one of the oldest triassic vertebrate fossils known from the state, although the taxon is a nomen dubium (stocker and butler, 2013). phytosaurs are, however, referred to alpha taxa almost exclusively using cranial characters, especially from the posterior region of the skull (ballew, 1989; stocker, 2010, 2012, 2013; hungerbühler and others, 2013), and specimens preserving this region are extremely rare in utah, with the notable exception of lisbon valley (martz and others, 2014). as a result, biostratigraphic subdivision of the chinle formation in southern utah is generally problematic, with the exception of the apachean biozone (see below). basal phytosaurs (e.g., parasuchus and wannia; stocker, 2013; kammerer and others, 2015), which define the otischalkian biozone (lucas, 1998; martz and parker, 2017), are unknown from the chinle formation. basal members of the clade leptosuchomorpha (e.g., smilosuchus and leptosuchus sensu stocker, 2010), which define the base of the adamanian biozone (lucas, 1998; parker and martz, 2011), are abundant in arizona (stocker, 2010), but only two possible specimens are known from utah. one is a nearly complete phytosaur skull (figure 7a) (umnh vp.21917) from the lower cameron member near zion (martz and others, 2015, figure 15e; see below), which has a deep squamosal and partially depressed supratemporal fenestra, charfigure 6 (figure on previous page). non-archosauriform tetrapods from the chinle formation of southern utah. (a and b) metoposaurid fragments. un-numbered cranial or pectoral fragments from the monitor butte member of care (kirkland and others, 2014a, figures 16b and 16c). (c) un-numbered right dentary fragment from the petrified forest member of care (kirkland and others, 2014a, figure 20f-h) in (top to bottom) medial and lateral view. (d) interpretive drawing showing placement of same specimen (modified from sulej, 2002, figure 3). (e) metoposaurid centrum (zion 15679) from the cameron member of zion in (left to right) anterior, lateral, and ventral views. (f) procolophonid skull (mna v9953) in (left to right) dorsal and ventral views (fraser and others, 2005, figure 3.1-2). (g) doswellia osteoderms (ucm 76194) from the blue lizard mine in the lowest monitor butte member of red canyon (parrish, 1999, figure 4). scale bars = 1 cm for 6a to 6c and 6e to 6f; scale bar = 5 cm for 6d. 118 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 acteristics of basal leptosuchomorphs (stocker, 2010), although martz and others (2015) suggested it might be a more basal taxon. another undescribed, nearly complete skull collected from the monitor butte member of fry canyon by phil bircheff is a non-pseudopalatine leptosuchomorph (w.g. parker, unpublished data) that figure 7. phytosaur skulls from the chinle formation of southern utah. (a) leptosuchomorph or non-leptosuchomorph phytosaurid umnh.vp.21917 in left lateral view (martz and others, 2015, figure 15e). (b) machaeroprosopus sp. umnh vp 24304 in dorsal view. (c) same specimen in left lateral view (martz and others, 2014, figures 14b and 14c). (d) latex peel of the “last phytosaur” steinkern, “redondasaurus” (machaeroprosopus) sp. (mna v3498/umnh vp 22354) in dorsal view (martz and others, 2014, figure 14a). scale bars = 10 cm. 119 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 may be referable to the pseudopalatine sister-taxon pravusuchus hortus stocker 2010 (mccormack and parker, 2017). all specimens suggest the base of the adamanian biozone occurs somewhere in the monitor butte and cameron members. three partial phytosaur skulls collected from fry canyon by the atomic energy commission in 1953 were assigned to rutiodon tenuis (= machaeroprosopus pristinus; parker and irmis, 2006) by parrish and good (1987); however, these specimens are probably non-pseudopalatine leptosuchomorphs (j.w. martz, unpublished data), as they possess deep plate-like squamosals rather than the shallower and knob-like squamosals found in the pseudopalatine machaeroprosopus pristinus (e.g., long and murry, 1995; parker and irmis, 2006; stocker, 2010). parrish and good (1987) stated that these specimens were recovered from the petrified forest member; we have not, however, had the opportunity to confirm this by revisiting the locality. pseudopalatinae (sensu parker and irmis, 2006, = mystriosuchini sensu kammerer and others, 2015) is a derived phytosaur clade within leptosuchomorpha very well represented in western north america by the genus machaeroprosopus (sensu parker and others, 2013; hungerbühler and others, 2013; = pseudopalatus), the first appearance of which defines the revueltian biozone (lucas, 1998; parker and martz, 2011). machaeroprosopus can be distinguished from non-pseudopalatine phytosaurs in having broadened postorbitosquamosal bars and greatly reduced and depressed supratemporal fenestrae (e.g., stocker, 2010; hungerbühler and others, 2013). these characters are further exaggerated in specimens of machaeroprosopus that are traditionally assigned to the genus “redondasaurus” in which the supratemporal fenestrae are virtually eliminated and the postorbitosquamosal bar is greatly broadened (e.g., hunt and lucas, 1993; spielmann and lucas, 2012; hungerbühler and others, 2013; martz and others, 2014). whereas the basal species of machaeroprosopus (e.g., m. pristinus and m. buceros) that define the base of the revueltian biozone are well known from the chinle formation in arizona and new mexico (e.g., long and murry, 1995), they have not been reported in utah. more derived specimens however, at least some of which can be assigned to the “redondasaurus” morphotype, are known from the church rock member of lisbon valley (figures 7b to 7d) (martz and others, 2014). two of these specimens (umnh vp 24304 and umnh vp 24236) are represented by nearly complete skulls (figures 7b and 7c) (martz and others, 2014). the stratigraphically highest known specimen of machaeroprosopus from anywhere in the western united states is from the big indian rock beds (martz and others, 2014) at the base of the wingate sandstone; this specimen (figure 7d) (umnh vp 22354) is a steinkern of a skull roof referred to informally as the “last phytosaur” (morales and ash, 1993; lucas and others, 1997b; spielmann and lucas, 2012; martz and others, 2014). aetosaurs aetosaurs are a clade of armored pseudosuchian archosaurs that were common worldwide during the late triassic, with the most diverse fossil record known from the dockum group of texas and new mexico and the chinle formation of new mexico and arizona (e.g., desojo and others, 2012, 2013; parker, 2016a). clades and alpha taxa are diagnosed primarily using the osteoderm characters, specifically the shape and ornamentation patterns on the paramedian osteoderms covering the back and the lateral osteoderms covering the sides (e.g., long and ballew, 1985; long and murry, 1995; heckert and lucas, 2000; parker, 2007; desojo and others, 2012, 2013). two major clades have been consistently identified in recent phylogenetic analyses (e.g., desojo and others, 2012, 2013; heckert and others, 2015; parker, 2016a): typothoracinae, which generally have extremely mediolaterally broad paramedian osteoderms and lateral osteoderms with tapering dorsal flanges, and desmatosuchinae, which generally have narrower and thicker paramedian osteoderms and spikey lateral osteoderms with more subrectangular dorsal flanges. other taxa basal to these clades have paramedian osteoderms with radiating surface ornamentation and subrectangular lateral osteoderms without spikes, but these taxa probably do not form a monophylum (desojo and others, 2013; parker 2016a). like phytosaurs, aetosaur taxa have biostratigraphic utility (e.g., long and ballew, 1985; lucas, 1998; heckert and lucas, 2000; parker and martz, 2011; martz and others, 120 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 2013), and their occurrences may therefore help delineate the late triassic land vertebrate biozones in utah. heckert and others (1999) described a badly worn aetosaur paramedian osteoderm (nmmnh p-26938) with an associated tooth and undescribed postcranial material from canyonlands national park, which was recovered about 11.5 m above the base of what they identified as the blue mesa member. examination of their measured section (heckert and others, 1999, figure 1) suggests that this is actually the middle mudstone-dominated unit of the kane springs beds. based on its narrow width, transverse arching, presence of an anterior bar, and radiating ornamentation pattern, heckert and others (1999) assigned the osteoderm to stagonolepis. however, north american material often referred to this taxon (e.g., heckert and lucas, 2000) is distinct enough from the type material of stagonolepis from scotland to warrant assigning it to two distinct genera: calyptosuchus and scutarx (long and ballew, 1985; parker, 2016b). we have not had the opportunity to examine the canyonlands specimen, and cannot comment on its identification. however, the presence of either calyptosuchus or scutarx in the kane springs beds would be anomalously high, as these are adamanian taxa (heckert and lucas, 2000; martz and others, 2013; parker, 2016b) and the kane springs beds probably fall within the revueltian and apachean biozones. in care and the circle cliffs area of gsenm, more diagnostic material has come to light. a partial paramedian osteoderm with the distinctive pitted ornamentation and pronounced ventral strut of typothorax (e.g., heckert and lucas, 2000; martz, 2002) is known from the petrified forest member of care (figure 8a) (un-numbered specimen from locality wn0147), although the exact stratigraphic level is unclear (kirkland and others, 2014b). parrish and good (1987) reported a fragment of a typothorax osteoderm from the petrified forest member at the four acres mine in white canyon, although the specimen is a fragment and we have not had the opportunity to examine it. typothorax occurs as a rare occurrence in the adamanian biozone (e.g., parker and martz, 2011; martz and others, 2013) but is far more abundant in the revueltian and apachean biozones (e.g., heckert and lucas, 2000; parker and martz, 2011; desojo and others, 2013; martz and others, 2014), which is consistent with the stratigraphic occurrence of the specimen in the petrified forest member at care (see below). several osteoderms from the circle cliffs area collected by yale university are referable to the aetosaur clade paratypothoracini (ypm 57096, ypm 57118, ypm 57124, ypm 57113; w.g. parker and j.w. martz, unpublished data), which lies within typothoracinae. one specimen from the same area can be assigned to desmatosuchus (ypm 57132; w.g. parker, unpublished data), and at least one specimen can be assigned to the genus calyptosuchus (ypm 57152; w.g. parker, unpublished data; parker and others [2006] had previously assigned this specimen to stagonolepis). although paratypothoracins are known from both the adamanian and revueltian biozones in western north america (e.g., parker and martz, 2011; desojo and others, 2013), calyptosuchus is restricted to the lower adamanian biozone (parker, 2016b) and desmatosuchus to the adamanian and lower revueltian (parker and martz, 2011; martz and others, 2013). the stratigraphic level at which these specimens occur is therefore significant, and is currently being investigated using field data collected by yale university. several osteoderms referable to typothorax are known from the kane springs beds (figure 8b) (e.g., umnh vp 24247) and church rock member (figures 8c and 8d) (e.g., umnh vp 21880; umnh vp 24232) in lisbon valley, making at least some of them apachean biozone occurrences (martz and others, 2014). these include both fragmentary paramedian osteoderms with pitted ornamentation and lateral osteoderms with triangular dorsal flanges; both characters diagnose the genus typothorax (e.g., martz, 2002). a fragmentary osteoderm with pitted ornamentation that may be referable to typothorax is also known from the lower church rock member of arch (j.w. martz and j.i. kirkland, unpublished data). paracrocodylomorphs paracrocodylomorpha is the clade that includes mostly carnivorous pseudosuchians traditionally referred to as “rauisuchians,” as well as crocodylomorphs (nesbitt, 2011; irmis and others, 2013; nesbitt and oth121 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 8. pseudosuchian archosaurs from the chinle formation of southern utah. (a) un-numbered partial paramedian osteoderm of the aetosaur typothorax coccinarum from the petrified forest member of care in (left) dorsal and (right) ventral views (kirkland and others, 2014a; figures 20j to 20k). (b) partial typothorax paramedian umnh vp 22971 from the kane springs beds of lisbon valley. (c) partial typothorax paramedian umnh vp 24641 from the church rock member of lisbon valley (martz and others, 2014, figures 15f and 15j). (d) partial typothorax lateral osteoderm umnh vp 24232 from the church rock member of lisbon valley (martz and others, 2014, figures 16a and 16d). scale bar for a to d = 2 cm. (e) nearly complete skeleton of poposaurus gracilis ypm vp 057100 from the monitor butte member of gsenm (gauthier and others, 2011, figure 1a), scale bar = 10 cm. (f) possible crocodylomorph osteoderms from the blue lizard mine in the lowermost monitor butte member of red canyon (parrish, 1999, figure 1), scale bar = 10 cm. 122 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 ers, 2013), although a closer relationship between aetosaurs and crocodylomorphs has been proposed that places the latter clade outside of paracrocodylomorpha (brusatte and others, 2010; butler and others, 2011). within paracrocodylomorpha, the clades poposauroidea and crocodylomorpha are represented in the chinle formation of utah; rauisuchidae, a possibly paraphyletic group that consists entirely of large-bodied carnivores such as postosuchus (weinbaum, 2011, 2013; nesbitt and others, 2013) and vivaron (lessner and others, 2016) has not yet been documented in southern utah. poposauroidea is a clade within paracrocodylomorpha that includes taxa with a wide array of locomotor and dietary adaptations (nesbitt and others, 2013). in north america, poposauroids are represented by poposaurus, a bipedal carnivore with remarkable convergent resemblance to theropods (weinbaum and hungerbühler, 2007; gauthier and others, 2011; schachner and others, 2011), and the shuvosaurids (= chatterjeeids), a clade of generally smaller bipedal poposauroids with edentulous beaks that were probably herbivorous (e.g., nesbitt and others, 2013). one of the most spectacular tetrapod specimens from the chinle formation of utah is a nearly complete and fully articulated skeleton lacking only the skull (figure 8e) (ypm 57100) referable to poposaurus gracilis (gauthier and others, 2011; schachner and others, 2011). an isolated ischium (ypm 57129), probably from the monitor butte member, may also belong to poposaurus (w.g. parker, unpublished data). shuvosaurid material has not yet been identified from southern utah. several basal crocodylomorph specimens have been recovered in southern utah. parrish and good (1987) and parrish (1999) described fragmentary material from the blue lizard mine locality in red canyon (figure 8f) (e.g., ucm 76195). by far the best crocodylomorph specimen from the chinle formation is a complete articulated skeleton found in association with the poposaurus skeleton from circle cliffs, nicknamed the “popo-buddy.” parrish and good (1987) tentatively identified a distal tibia from the moss back member at red canyon as a crocodylomorph, although we have not examined this specimen and are uncertain where it is reposited. the church rock member in lisbon valley has produced an articulated hind limb and partial tail of a crocodylomorph (milner and others, 2011). all of these are modest-sized specimens (probably no more than 1 to 2 m long), but larger crocodylomorph material, including a partial skull, have been recovered from the church rock member in lisbon valley (a.r.c. milner, unpublished data). large crocodylomorph specimens have also been recovered from the apachean biozone in new mexico (nesbitt, 2011, p. 235–236; nesbitt and others, 2005; axel hungerbühler, mesalands comminity college, and jonathan weinbaum, southern connecticut university, verbal communication, 2015), suggesting that crocodylomorphs may have been important large predators during the apachean (irmis and others, 2013). ornithodira the ornithodiran record from the chinle formation of southern utah is poor. the proximal end of a tibia referable only to ornithodira (ypm 57231) is known from the chinle formation in circle cliffs, but its stratigraphic position has not yet been relocated. tracks of grallator have been recovered from the big indian rock beds immediately below the wingate sandstone (milner and others, 2006a; hunt-foster and others, 2016; a.r.c. milner, unpublished data), confirming the presence of theropods in the apachean biozone. parrish (1999) identified unguals (ucm 76197) from the blue lizard mine locality from red canyon as theropod, although the assignment was not justified, and a caudal vertebra (ucm 76198) was also assigned from the same locality as theropod due to having a “distinctive, subhexagonal cross section;” it is not at all clear if this character has any phylogenetic significance (nesbitt, 2011). local exposures of the chinle formation in southern utah chinle formation exposures are readily accessible throughout southern utah (figure 4), particularly in its many beautiful national parks and monuments. several key exposures of the chinle formation in southern utah are discussed below, presented as one might visit them in a loop starting at salt lake city, moving 123 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 through southeastern utah to southwestern utah and back north again (figure 4). note, in keeping with odometers used in the united states distances in miles are in parentheses. stop 1 u.s. highway 6 road cut southeast of spanish fork the first triassic outcrops traversed on this trip occur just southeast of spanish fork. after taking i-15 from salt lake city south through provo to spanish fork, take u.s. highway 6 southeast. red bed outcrops occur about 20 km (12 mi) southeast of the junction of i-15 and u.s. highway 6, with the best exposures being about 1.2 km (0.8 mi) past the turnoff for diamond fork road (forest road 029), in a road cut just northeast of the ghost town of thistle (figures 4 and 9a) (rigby, 1968; brandley, 1988, p. 90–176, 1990; may 2015, p. 26–31). stratigraphy and sedimentology these red beds have been assigned by various authors (rigby, 1968; brandley, 1988, p. 90–176, 1990; may 2015, p. 26–31) to the ankareh formation (figures 9b to 9d), a name originally applied to exposures in park city about 70 km (44 mi) to the north (boutwell, 1907). the ankareh formation consists mostly of lower and upper triassic fluvial deposits and has been divided into three members: the mahogany, gartra, and stanaker (figure 9b) (thomas and krueger, 1946; kummel, 1954; brandley, 1990). unlike the authors cited above, lucas (1993) followed stewart and others (1972a) in restricting the term “ankareh formation” to lower triassic rocks correlative with the moenkopi formation, and extended upper triassic stratigraphic nomenclature of southern wyoming into the region by assigning the strata overlying the garta member in northern utah to the popo agie and bell springs formations. although lucas (1993) did not specifically discuss the spanish fork road cut, his application of the names popo agie and bell springs likely refer to the lower and upper parts of what brandley (1988, 1990) called the stanaker member of the ankareh formation. the lowermost 120 m of the mahogany member, including the contact with the underlying thaynes limestone, is not exposed in the u.s. highway 6 road cut, but the mahogany member (figure 9b) nonetheless makes up the majority of the roughly 300 m of triassic exposures in the road cut (brandley, 1988, 1990). the mahogany member consists of primarily dark reddish-brown interbedded siltstone and sandstone with common ripple cross-laminations and rare mud cracks and raindrop marks, as well as some conglomerate composed of re-worked mudstone clasts (rigby, 1968; brandley, 1990). the mahogany member is spathian (late early triassic) in age and partially syndepositional with the more extensive moenkopi formation of southern utah and northern arizona (blakey and others, 1993). both the mahogany member and correlative members of the moenkopi formation were deposited by northwesterly flowing meandering rivers and associated tidal and sabkha environments bordering the marine environments covering much of utah (brandley, 1990; blakey and others, 1993). above the mahogany member lie the much thinner gartra and stanaker members (sensu brandley, 1990), which are probably upper triassic in age and correlative with the chinle formation (stewart and others, 1972a; brandley, 1990). these upper triassic members are confined to the southeastern part of the u.s. highway 6 road cut. the gartra member, which was deposited by braided rivers flowing across northern utah and colorado and is considered to be correlative with the shinarump member (stewart and others, 1972a; brandley, 1990), was identified as unit 192 in brandley’s (1988, 1990) measured section. this member is a 10-m-thick unit lithologically distinct from both the underlying and overlying strata in consisting of pinkish, resistant, and extremely quartzose sandstone and conglomerate with abundant trough cross-bedding, deposited as multiple lenticular channel fills. about 40 m below the unit identified by brandley (1990) as the gartra member is an intensely mottled paleosol (figures 9b and 9c) that resembles the mottled strata that typically occur at the base of the upper triassic section throughout the western united states. the mottled strata form a resistant ledge (brandley, 1990, 124 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 units 166–170) composed of well-cemented quartz sandstone with “four color” mottling of iron oxide, as is often seen in the mottled strata at the base of the chinle formation. it is possible that this ledge is a better candidate for the gartra member than the sandstone identified as that unit by brandley (1990). if the mottled strata do indeed represent the base of the upper triassic section, then the stanaker memfigure 9. ankareh formation exposures near spanish fork. (a) map of outcrop location. (b) road cut exposures, view southeast along u.s. highway 6; the mahogany and stanaker members comprise all reddish exposures to the left and right of the mottled strata, respectively. (c) ledge of well-lithified mottled paleosol that may represent base of chinle formation. (d) fish scales in ledge-forming unit of stanaker member (location shown in figure 9e). (e) stratigraphically highest exposures in road cut of stanaker member. the yellow and pinkish ledge-forming unit was interpreted by brandley (1988, 1990) as meandering channel and levee deposits. the deep red mudstone beneath were interpreted as floodplain deposits. 125 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 ber in the u.s. highway 6 road cut comprises units 176–211 in brandley’s (1988, 1990) section, and is about 76 m thick, rather than 10 m thick as it would be if the stanaker formation only comprises brandley’s (1990) units 203–211. like the mahogany member, the stanaker member consists of dark reddish-brown mudstone and sandstone deposited primarily by meandering rivers (brandley, 1990). the lowermost 10 m of the stanaker member consists predominantly reddish-brown mudstone (figure 9d), with abundant root traces (including rhizoconcretions) and siltstone lenses with erosional bases (brandley, 1988, p. 90–98), which have been interpreted as floodplain deposits and channel fills deposited by meandering streams. the uppermost beds of the stanaker member in the highway 6 road cut consist mostly of ledge-forming sandstone, conglomerate, and some interbedded mudstone (figure 9d). the lower part of this sequence is a conglomeratic channel lag with a distinctly scoured base, with the overlying sandstone and interbedded mudstone having been interpreted as splay deposits by brandley (1990). the uppermost stanaker member, which may be equivalent to the strata that lucas (1993) assigned to the bell springs formation in northern utah, is not exposed in the road cut. these beds contain evaporites and reddish-brown and grayish-orange quartz sandstone that have been interpreted as eolian deposits, recording a climatic shift to arid conditions that culminate with the early jurassic eolian deposition of the nugget sandstone (brandley, 1990). the nugget sandstone forms prominent cuestas just to the southeast of the road cut (figure 9b), and may be correlative with the wingate sandstone or navajo sandstone farther south (kinney, 1955; poole and stewart, 1964; peterson, 1988). paleontology brandley (1990) reported small pieces of silicified and carbonized permineralized wood up to 10 cm in diameter, as well as a lungfish tooth plate, from the conglomeratic channel unit (unit 202). the overlying sandstone identified as splay deposits by brandley (1990; brandley’s unit 203) contain in situ fish (figure 9d). none of these plant or fish fossils have been assigned to an alpha taxon. stop 2 big bend along sr 128 along the colorado river, northeast of moab from the spanish fork road cut, continue to follow u.s. highway 6 southeast for 185 km (115 mi) until it joins i-70 just west of green river, then proceed east along i-70 for 45 km (28 mi) to the junction with u.s. highway 191. proceed south on u.s. highway 191 south for 47 km (29 mi), turning northeast onto sr 128 just north of moab, and follow it along the colorado river for about 19 km (12 mi) to the parking area on the north side of the road near big bend, just west of where the canyon opens into castle valley (figure 10a). stratigraphy and sedimentology sr 128 is one of the most spectacular scenic drives in southern utah. here, thick exposures of the moenkopi formation are capped by the chinle formation, which is in turn capped by the tremendous vertical cliffs of upper triassic-lower jurassic wingate sandstone (figure 10b). in castle valley and richardson amphitheater to the north, the moenkopi is well exposed; farther southwest, heading towards moab the entire section dips so that the moenkopi enters the subsurface and the chinle formation is exposed closer to the road, particularly between westernmost castle valley and the big bend along the colorado river. approaching moab along sr 128, the chinle formation also disappears into the subsurface and the wingate lines the road. at the pull-out stop, the chinle formation is fully exposed. sr 128 occurs near the edge of the chinle basin, in the salt anticline region. this geographic placement has two major impacts on the lithostratigraphy of the chinle formation: 1. only the uppermost chinle formation is preserved, and the bulk of the section is usually assigned to the church rock member (e.g., stewart and others, 1972a, section u-18; martz and others, 2014). indeed, one problematic aspect of studying the chinle formation along sr 128 is that the contact between the moenkopi formation and the church rock member of the chinle for126 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 10. big bend along sr 128 near moab. (a) map of big bend showing approximate pulloff location. (b) outcrops on the northern side of the colorado river, easily visible from the road. (c) same outcrops, showing incision of the sub-horizontal “shinarump member” into the tilted strata of the moenkopi formation; both units are intensely mottled. (d) mottled strata with vertical streaks probably representing crayfish burrows in the tilted moenkopi (?) formation. (e) one of the lower ledge-forming conglomeratic sandstone beds in the church rock member. (f) upper tan-colored sandstone in the church rock member with little discernible bedding. (g) small burrows in the upper tan sandstone. (h) phytosaur or crocodylomorph osteoderm in the lower conglomeratic beds of the church rock member. 127 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 mation is locally difficult to discern (baker, 1933), as here both formations are predominantly reddish-brown units of interbedded sandstone and mudstone. 2. the thickness of the chinle formation is highly variable, as it was controlled largely by syndepositional salt diapirism that generated salt anticlines during late triassic time. along sr 128, the thickness of the chinle formation is about 140 m (stewart and others, 1972a; j.w. martz and others, unpublished data), notably thicker than the sections in nearby arch (j.w. martz, unpublished notes), and was probably deposited in an area of subsidence that prochnow and others (2006) and prochnow (2007) called the big bend minibasin, resulting from subsurface salt evacuation. despite variations in thickness, however, the chinle formation sections along sr 128 and arch are essentially identical (j.w. martz, unpublished data). along sr 128, there are striking variations in the nature of the chinle-moenkopi contact and the ease with which it is identified. in richardson amphitheater and castle valley, the contact can be very difficult to discern. there is, however, a thin layer of light-colored siliceous sandstone at the contact that can be faintly discerned in this area that stewart and others (1972a, section u-18) referred to as the “basal sandstone unit.” within castle valley and at the big bend, where there is a pronounced angular unconformity at the base of the chinle formation (figures 10b and 10c), this siliceous unit is a thick, ledge-forming conglomeratic sandstone composed almost exclusively of extrabasinal quartz. the unit is intensely mottled with shades of red, purple, yellow, and gray taking the form of vertical streaks probably representing crayfish burrows; both mottling and burrowing extend into the tilted strata below the contact (figures 10c and 10d), which the siliceous unit incises to varying depths (figure 10c). from a distance the unit is distinctly paler than the overlying and underlying units, making its identification easy. this unit corresponds to fac set 3 of prochnow and others (2006). although baker (1933) identified this siliceous mottled unit as the shinarump member, stewart and others (1972a, figure 10) assigned it to moss back member, and ronald blakey (northern arizona university, written communication, 2016) also favors this latter correlation. however, we have not observed the development of a four-color gleyed paleosol on top of the moss back member elsewhere (including the san rafael swell, see below), whereas this mottling occurs above the shinarump member in the majority of the areas of southern utah where that unit is deposited. for this reason, identifying this basal sandstone as either the shinarump member or a correlative is our favored interpretation. if the siliceous sandstone and mottled strata at the base of the chinle formation along sr 128 are correlative with the shinarump member, the unconformity between these beds and the church rock member is at least 12 myr, and probably greater (martz and others, 2014). above the mottled siliceous sandstone, the remainder of the chinle formation can be assigned to the church rock member (figures 10b, 10e, and 10f) corresponding to fac sets 4-6 of prochnow and others (2006). along the big bend, the siliceous mottled sandstone is less than 10 m thick and the overlying 125 m of the chinle formation are assigned to the church rock member and shows a broadly fining-upward sequence (figure 10b); reddish ledge-forming sandstone and conglomerate, composed mostly of reworked intrabasinal clasts, occur low in the sequence (figure 10e), and generally become less conglomeratic and dominated by climbing ripple cross-stratification higher in the section. the uppermost church rock member consists of dull tan sandstone that often lack any discernable bedding (figure 10f), and resemble eolian sandstone of the wingate sandstone. the hite bed of the church rock member, which occurs in this part of utah (stewart and others, 1972a), may be reworked eolian sandstone (hazel, 1994), and possibly, these uppermost beds may represent similar depositional conditions. the angular unconformity developed along sr 128 at the base of the mottled siliceous sandstone between the big bend and castle valley to the east is easily seen by looking across the colorado river to the northwestern side of the canyon (figure 10b). interpretations of 128 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 this unconformity have varied. popular opinion is that the tilted strata below the unconformity are part of the chinle formation, with the angular unconformity representing deformation due to salt tectonism that occurred during late triassic time (e.g., prochnow and others, 2006; martz and others, 2014). however, based on recent investigations, it seems likely that the beds below the unconformity are pre-chinle strata, and probably part of the moenkopi formation; this conclusion follows the interpretations of dane (1935) and o’sullivan and maclachlan (1975, p. 135) in richardson amphitheater. the overall sequence of strata is far more consistent with chinle formation sections throughout the salt anticline region if strata below the angular unconformity are excluded. in arch, where no angular unconformity occurs, the chinle formation section is identical to the sr 128 sequence aside from being slightly thinner. in arch, an intensely mottled, siliceous, conglomeratic sandstone is overlain by reddish-brown conglomerate with gravel-sized clasts mostly composed of reworked intrabasinal sediments that generally fine upwards into sandstone with abundant ripple cross-laminations, and then tan sandstone with little discernible bedding. elsewhere in the salt anticline region, such as dead horse point and along sr 131 (see below), the kane springs beds underlie the church rock member, but are virtually identical to the church rock lithologically other than being drab-colored (martz and others, 2014). moreover, along sr 313, mottled siliceous sandstone beds locally occur immediately below the kane springs beds (see below), forming the base of the chinle formation as they do along sr 128. if our interpretation is incorrect and the beds below the mottled siliceous sandstone and angular unconformity along sr 128 are actually part of the chinle formation (e.g., prochnow and others, 2006; martz and others, 2014), they represent a unit present nowhere else in the entire salt anticline region. moreover, including the tilted strata below the mottled siliceous sandstone would add considerably to the thickness of the chinle formation along sr 128. the thickness of the chinle formation throughout the salt anticline region varies from less than 100 to more than 200 m (stewart and others, 1972a; blakey and gubitosa, 1983; prochnow and others, 2006; martz and others, 2014; j.w. martz, unpublished data); the section along sr 128 above the angular unconformity is ~140 m thick (stewart and others, 1972a; martz and others, unpublished data). whereas we have not measured the section below the angular unconformity, it is easily in excess of 60 m, indicating that the total thickness of the chinle formation would be greater than we have observed anywhere else in the salt anticline region. it is far more parsimonious to conclude that the strata below the angular unconformity do not belong to the chinle formation. paleontology burrowing is common throughout the chinle formation along sr 128. the probable crayfish burrows in the mottled strata are generally 20 to 30 cm wide and vertically oriented, but smaller burrows less than 1 cm wide and in more variable orientations are often seen in the finer grained sandstone beds higher in the section (figure 10g). fragmentary vertebrate bones and teeth have been observed in the conglomeratic sandstone in the lower part of the church rock member at the big bend, including a probable phytosaur or crocodylomorph osteoderm (figure 10h). within arch, vertebrate bone is also common in the lower conglomeratic sandstone of the church rock member, although little of it is identifiable. aetosaur osteoderm fragments that may be referable to typothorax have been recovered from this interval within arch, as have natural molds of the enigmatic broad leaf plant sanmiguelia (j.i. kirkland and j.w. martz, unpublished data), which occurs at several stratigraphic levels in the chinle formation (ash, 1976; ash and hasiotis, 2013). stop 3 sr 313 near junction with u.s. highway191 from the big bend road cut, take sr 128 back west about 19 km (12 mi) to the junction with u.s. highway 191, then proceed north 13.6 km (8.5 mi) to the junction with sr 313. proceed west about 2.1 km (1.3 mi) and pull off to examine the outcrops north of the road (figures 11a to 11c). 129 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 sedimentology and stratigraphy as with arch and along sr 128, the area that includes canyonlands national park and dead horse point state park, lisbon valley, and indian creek were situated near the edge of the chinle depositional basin in the salt anticline region (blakey and gubitosa, 1983, 1984; hazel, 1994; martz and others, 2014); however, unlike arch and sr 128, in this region the kane springs beds underlie the church rock member (figures 2 and 3). the chinle formation section at both canyonlands and dead horse point cannot be easily examined close up by the casual visitor, requiring a lengthy drive or hike from the top of the wingate sandstone and overlying figure 11. sr 313 and dead horse point state park. (a) map of sr 313 showing stops for exposures. (b) exposures along sr 313 near the junction with highway 191. (c) mottled strata in same area. (d) exposures visible from dead horse point state park visitor center overlook on the northern side of the canyon. (e) exposures visible from dead horse point state park visitor center overlook on the southern side of the canyon. 130 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 units capping the cliffs to the valley floor. however, the section is more accessible along sr 313 near the junction with u.s. highway 191, just north of moab (figure 11a). the section is similar to that exposed elsewhere in the region in being composed primarily of two units: the lower greenish-gray kane springs beds and the upper reddish-brown church rock member (figure 11b) (e.g., blakey and gubitosa, 1983, 1984; hazel, 1994; martz and others, 2014). as noted by previous workers (stewart, 1956, 1957; stewart and others, 1959, 1972a; martz and others, 2014), the petrified forest and owl rock members are virtually absent in this region of southeastern utah except for locally occurring tongues of the owl rock member (blakey and gubitosa, 1983, figure 10; martz and others, 2014, p. 426–427). along sr 313, a siliceous mottled sandstone that may be equivalent to the one seen at arch and along sr 128 occurs at the base of the section below the kane springs strata (figures 11b and 11c) (martz and others, 2014). it is only a few meters thick here, and is locally completely truncated farther south (including canyonlands, lisbon valley, and indian creek) wherever the base of the kane springs beds is a thick ledge-forming sandstone (martz and others, 2014). russ dubiel (u.s. geological survey, verbal communication, 2016) has also observed remnants of the siliceous mottled strata below the kane springs beds near six shooter peaks and west of lisbon valley. the kane springs beds have a bimodal grain size composition of predominantly siltstone to fine-grained sandstone, often with horizontal planar bedding and climbing ripple cross-lamination, and conglomerate composed of reworked intrabasinal sedimentary clasts with some extrabasinal siliceous clasts (hazel, 1994; martz and others, 2014). although the kane springs beds in lisbon valley and some other outcrops such as bridger jack mesa in indian creek valley to the west of sr 211 are divisible into lower and upper ledge-forming conglomeratic sandstone separated by a finer grained middle unit (huber, 1980, 1981; blakey and gubitosa, 1983, 1984; hazel, 1994; martz and others, 2014; a.r.c. milner, unpublished data), there is considerable variation throughout the surrounding region. in the outcrop north of sr 313 (figure 11b), these upper and lower ledge-forming sandstone beds are absent, and the overall unit resembles the middle kane springs beds in lisbon valley in being predominantly slope-forming mudstone with interbedded sandstone which rest unconformably on the siliceous sandstone and mottled strata (martz and others, 2014). contrary to many workers (e.g., stewart, 1956, 1957; stewart and others, 1959; huber, 1980, 1981; lucas, 1993; lucas and others, 1997a; baars, 2010), the kane springs beds are not correlative to the moss back member (blakey, 1978; blakey and gubitosa, 1983, 1984; martz and others, 2014). in lisbon valley, the kane springs beds have a clear sedimentological similarity to the overlying church rock member, and there is a gradational contact between the two units (blakey, 1978; martz and others, 2014). moreover, the kane springs beds are at least partially correlative with the owl rock member and possibly the petrified forest member (stewart and others, 1972a; blakey and gubitosa, 1983, 1984; martz and others, 2014), which occur stratigraphically much higher in the section than the moss back member. the church rock member in this part of utah is dominated by siltstone and very fine to fine-grained sandstone with abundant climbing ripple cross-lamination and horizontal planar bedding, and some interbedded conglomerate dominated by intrabasinal clasts of reworked siltstone, sandstone, and pedogenic carbonate (e.g., martz and others, 2014). along sr 313, a massive ledge-forming sandstone at the base of the church rock member caps the kane springs beds unconformably (figure 11b), as it does in lisbon valley (martz and others, 2014), although along sr 313 this ledge makes up most of the member. martz and others (2014) assigned this ledge to the black ledge beds, although all the ledge-forming units assigned this name may not form a continuous outcrop belt. paleontology although fossils have not been reported along sr 313 or in dead horse point state park, the section is similar to that exposed in canyonlands national park and especially lisbon valley, where fossils are abundant (e.g., schaeffer, 1967; hasiotis, 1993; 1995; heckert and others, 1999; milner, 2006; milner and others, 2006a, 131 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 2011; santucci and kirkland, 2010; gibson, 2013a, 2013b, 2015; martz and others, 2014). stop 4 dead horse point state park visitors center from the sr 313 stop, proceed west along sr 313 for about 34 km (21 mi) to the visitor center in dead horse point state park (figure 11a). a short path leads from the parking lot and visitor center to the overlook into the canyon below, where the chinle formation section can be observed (figures 11d and 11e). although we have not had the opportunity to examine the chinle formation in dead horse point state park close-up, it seems to have the same members seen in canyonlands national park and lisbon valley (martz and others, 2014). these units are easily visible from the dead horse point state park visitor center overlook, about 2 km (1.2 mi) north of dead horse point (figures 11d and 11e). the chinle formation section visible from dead horse point is estimated to be about 200 m thick, with the lower 60 m comprising the kane springs beds and the remaining 140 m comprising the church rock member. here the chinle formation is considerably thicker than the ~130-m-thick section exposed along sr 128 near moab, and not quite twice as thick as the chinle formation sections in arch and lisbon valley. at the visitor center overlook, lithologic variation in the kane springs beds can be observed. on the northern, south-facing exposures (the left-hand exposures seen from the overlook; figure 11d), the lower part of the kane springs beds seems to be predominantly fine grained and slope-forming as along sr 313 and in the middle unit at lisbon valley, but with an upper ledge-forming sandstone immediately below the black ledge beds of the church rock member, similar to the upper unit of the kane springs beds in lisbon valley. however, on the southern, north-facing exposures (the right-hand exposures seen from the overlook; figure 11e), there seems to be a lower ledge-forming sandstone at the base of the kane spring beds, but no upper ledge, as is also the case in parts of canyonlands national park (martz and others, 2014). ron blakey (northern arizona university, written communication, 2016) believes that the black ledge beds may have locally truncated the upper ledge of the kane springs beds. blakey and gubitosa (1983, figure 10) indicated that the kane springs beds at dead horse point contain a tongue of the owl rock member, but this is difficult to evaluate without examining the outcrop up close. it is also currently unknown if the siliceous mottled unit occurring at the base of the kane springs beds along sr 313 also occurs at dead horse point state park. on both sides of the valley (figures 11d and 11e), a thick ledge where the section changes from greenish-gray to reddish-brown, is interpreted as the transition between the kane springs beds and the black ledge beds at the base of the church rock member. other ledge-forming units occur higher in the section; one occurs approximately in the lower third of the church rock member and two superimposed ledges are visible near the top of the church rock member on the south-facing exposures (figure 11d); on the north-facing exposures these ledges seem to be less prominent (figure 11e). whether these ledges correlate to the red ledge beds in lisbon valley (martz and others, 2014) or the hite bed (stewart and others, 1972a) is unclear. stop 5 lisbon valley from the dead horse point state park visitors center, proceed back north along sr 313 for 36 km (22.4 mi) to u.s. highway 191. turn right and head south on u.s. highway 191 for 73 km (45.6 mi), passing through moab, until reaching the junction with big indian road (figure 12a). proceed about 12 km (7.5 mi) east along big indian road, through the west-dipping cuestas (dipping mesas) capped by the upper triassic-lower jurassic glen canyon group, until reaching the big indian rock, on the south side of the road. park to examine the reddish outcrops of chinle formation north of the road (figures 12c and 12d). sedimentology and stratigraphy the valley before you, bounded on the west by the cliff-forming sandstone of the wingate sandstone and other overlying units of the glen canyon group, is lisbon valley. lisbon valley represents the exposed por132 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 12 caption on following page. 133 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 tion of the doubly plunging and faulted lisbon valley anticline, one of several northwestto southeast-trending salt anticlines within the salt anticline region of the paradox basin of southeastern utah and southwestern colorado (e.g., stewart, 1956; stewart and wilson, 1960; hazel, 1994). the salt is produced in the paradox formation of the pennsylvanian hermosa group, which occurs at a depth of about 500 m in lisbon valley (byerly and joesting, 1959; stewart and wilson, 1960). southwest-dipping exposures (figures 12c and 12d) of the middle pennsylvanian hermosa group, upper pennsylvanian-lower permian cutler group, upper triassic chinle formation, and the upper triassic-lower jurassic wingate, kayenta, and navajo formations occur on the southwestern side of the fault in lisbon valley (e.g., doelling, 2004). unlike most of southeastern utah, the lower to middle triassic moenkopi formation is locally absent, pinching out near the southwestern flank of big indian wash (stewart, 1957), so that the chinle rests on the cutler formation (figure 12b). the hogbacks on the west side of lisbon valley are bisected by drainages into a series of cuestas (figure 12c) exposing the wingate sandstone, chinle formation, and cutler group. skull ridge (figure 12d) is the cuesta lying immediately northwest of big indian road. the chinle formation in southern lisbon valley varies from about 112.1 to 123.4 m in thickness (martz and others, 2014), and the stratigraphy is broadly similar to that seen along sr 313 and in dead horse point state park (figure 12c). the kane springs beds are approximately 30 to 45 m in total thickness, whereas the church rock member in the study area varies in thickness from 59.6 to 112.1 m, with the top of the member being truncated to varying degrees below the wingate sandstone (figure 12e) (martz and others, 2014). siliceous mottled strata are not seen below the kane springs beds here, possibly because they have been erosionally truncated by the lower kane springs sandstone (martz and others, 2014). overall, the kane springs beds and church rock member in lisbon valley seem to be fairly similar lithologically, with no major unconformities and only slight erosional contacts at the bases of coarser grained subunits that tend to fine upwards. the kane springs beds and church rock member both have strongly bimodal grain-size distributions, which are most pronounced in the church rock member, whereas the kane springs beds are slightly coarser and compositionally immature (e.g., huber, 1980; blakey and gubitosa, 1983; chenoweth, 1990; martz and others, 2014). both the kane springs beds and church rock member consist predominantly of very fine to fine-grained sandstone and siltstone (figures 12f and 12g). however, both the kane springs beds and church rock member also contain interbedded conglomerates with granule to cobble-sized clasts predominantly composed of reworked intrabasinal micrite, sandstone, and siltstone, and a matrix of mediumto coarse-grained sandstone (figures 12h and 12i) (blakey, 1978; dubiel and brown, 1993). extrabasinal clasts composed of chert, quartz, and quartzite occur locally in conglomerates of both the kane springs beds (huber, 1980; matrz and others, 2014) and the lower part of the church rock member, although these do not exceed a few centimeters in diameter (pebble-size) and are never in greater abundance than the reworked sedimentary clasts. conglomeratic beds and figure 12 (figure on previous page). lisbon valley. (a) map of route between u.s. highway 191 and lisbon valley along big indian road. (b) contact between permian cutler formation and upper triassic kane spring beds at base of chinle formation. (c) panoramic view across lisbon valley from the south of big indian road to the north showing the dipping cuestas; the gray kane springs are distinctly visible. (d) skull ridge, with different units of the chinle formation labeled. (e) the chinle-wingate contact, showing the big indian rock beds lensing in at the contact. (f) climbing ripple cross-stratification in the middle unit of the kane springs beds. (g) horizontal planar bedding and gently dipping cross-bedding in the upper unit of the kane springs beds. (h) lower kane springs beds sandstone with distinct conglomeratic beds. (i) close-up of intrabasinal conglomerate in the lower kane springs beds; the orange clasts are mostly reworked siltstone. (j) fine-grained fissile sandstone and mudstone of the middle kane springs beds; the dipping block on the left appears to represent syndepositional slumping similar to that seen elsewhere in the contorted beds of the monitor butte member. (k) reddish-brown siltstone of the church rock member with some greenish-gray mottling, but no clear signs of paleosol formation. 134 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 many sandstone beds are well-cemented and resistant ledge-forming units. sedimentary structures in sandstone beds of both the kane springs beds and church rock member are dominated by horizontal planar bedding (figure 12g) (blakey, 1978; martz and others, 2014), although festoon stratification and climbing ripple cross-stratification are also extremely common (figure 12f). scour surfaces, trough cross-bedding, planar cross-bedding, and mud cracks occur more rarely. lateral accretion beds occur locally (blakey, 1978; martz and others, 2014). in lisbon valley, the kane springs beds consist of lower and upper ledge-forming multistoried conglomeratic sandstone separated by a more mudstone-dominated middle unit as is seen elsewhere (blakey and gubitosa, 1984; hazel, 1994; martz and others, 2014). the lower ledge-former occupies scours incised into the cutler formation, whereas the upper unit is more laterally continuous. the more mudstone-dominated middle kane springs beds locally contain fissile mudstone possibly representing lacustrine or paludal deposition (figure 12j) (martz and others, 2014), similar to that seen in the monitor butte member (dubiel and hasiotis, 2011). unoxidized uranium, vanadium, and sulfide minerals are locally concentrated in sandstone in the kane springs beds, both in grain interstices and as clast replacements; this mineralization is especially pronounced in the lowest ledge-forming sandstone, particularly north and southeast of the study area (e.g., chenoweth, 1990). blakey (1978) reported limestone beds from the kane springs beds, although we have not observed these. the upper contact between the kane springs beds and church rock member is gradational south of big indian rock, but near big indian rock road a prominent dark reddish-brown conglomeratic sandstone is lithologically similar to the ledge-forming upper and lower kane springs beds. martz and others (2014) assigned this unit to the black ledge beds (figure 12d), a modification of the term black ledge applied to the dark conglomeratic sandstone locally occurring at this level in the salt anticline region (stewart and others, 1972a; blakey and gubitosa, 1983; hazel, 1994). above the black ledge beds, the bulk of the lower church rock member is reddish-brown, locally massive, ripple cross-laminated (and sometimes horizontal planar bedded) siltstone and very fine grained sandstone with some greenish-gray mottling. these strata are interpreted here as overbank deposits. however, slightly more complex and coarse-grained ledge-forming units, generally less than 15 m thick, commonly occur 20 to 25 m below the red ledge beds, including at skull ridge (figure 12d). these sandstone beds tend to be very fine to fine-grained, interbedded with minor amounts of conglomerate, dominated by horizontal planar-bedded and climbing ripple cross-lamination with some planar cross-bedding and scour surfaces, and usually have a somewhat lighter orange hue than the red ledge beds. these are interpreted as being deposited by channel systems prior to deposition of the red ledge beds (martz and others, 2014). the red ledge beds (figure 12d) are the most prominent ledge-forming sandstone beds in the church rock member in lisbon valley other than the black ledge beds (martz and others, 2014). the red ledge beds are generally single-storied and about 8 to 12 m thick. although huber (1980) suggested that the red ledge beds represent point bar deposits, martz and others (2014) did not observe any lateral accretion sets, and the red ledge beds are generally similar to the kane springs beds in architecture and sedimentary structures. martz and others (2014) therefore interpreted the red ledge beds as bedload-dominated braided channel deposits. bimodal grain-size distribution, mud cracks, and vertebrate tracks (e.g., milner and others, 2006a, figure 1), suggest highly variable (and even ephemeral) flow and occasional subaerial exposure (martz and others, 2014). the thickness between the top of the red ledge beds and the base of the wingate sandstone is about 30 m at skull ridge (figure 12d). the upper part of the church rock member contains abundant ripple cross-laminated sandstone, often directly overlying the red ledge beds that are probably proximal overbank deposits. the upper part of the church rock member also contains slightly more gravel than the lower part of the church rock member, and these conglomerates are interpreted as small bedload-dominated channel systems. at skull ridge, a distinctive sandstone unit about 1.5 m thick locally occurs about 3 m below the wingate sandstone, below the variegated sandstone. this bed 135 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 is tabular, almost structureless, well sorted, very fine grained, and weathers with conchoidal fracture. similar sandstone in the owl rock member have been interpreted as loessites by dubiel and hasiotis (2011, p. 403), and may indicate more arid conditions than observed lower in the church rock member. paleosols are only occasionally encountered in the church rock member in lisbon valley but occur locally in finer grained sediments (usually siltstone and very fine grained sandstone) interpreted as overbank deposits. the lisbon valley paleosols are generally poorly developed or weakly calcified (figure 12k) (martz and others, 2014), consistent with paleosols observed elsewhere in the non-bentonitic mudstone beds of the dolores formation, and rock point and church rock members of the chinle formation (blodgett, 1988; prochnow and others, 2006; tanner and lucas, 2006; cleveland and others, 2008; dubiel and hasiotis, 2011). greenish-gray mottling in reddish-brown overbank siltstone and very fine grained sandstone are extremely common. in some cases, these mottles are nearly spherical haloes varying from a few millimeters to centimeters in diameter, suggesting that they nucleated around tiny particles of organic matter that generated local reducing conditions. more irregular and often elongate greenish-gray mottles most likely formed around burrows and roots that generated localized reducing conditions (e.g., cleveland and others, 2008). however, clear evidence of distinct a or b horizons (including well-calcified bk horizons) within the church rock member is extremely rare. as a result, martz and others (2014) considered most of the overbank deposits to be entisols, inceptisols, or protosols (figure 12k) (sensu mack and others, 1993). some intervals can be recognized in which overbank deposits weather into spheroidal shapes suggesting nucleated calcification, sometimes associated with greenish-gray mottling, desiccation cracks, rhizoliths, and/or burrows. these were tentatively classified by martz and others (2014) as aridisols or calcisols (e.g., dubiel and hasiotis, 2011). at least locally in the uppermost church rock member, immediately below the wingate sandstone, blocky peds and arcuate slickensides are developed into overbank siltstone beds, and were interpreted by martz and others (2014) as vertisols. vertisols are generally rare in the uppermost part of the chinle formation compared to lower bentonitic units such as the petrified forest member (e.g., therrien and fastovsky, 2000; dubiel and hasiotis, 2011). a light greenish-gray band, possibly indicating reducing conditions, frequently occurs at the base of the wingate sandstone, and mud cracks also occur locally at the contact, leading martz and others (2014) to conclude that the wingate erg was initially deposited on a ground surface that was at least locally saturated. in lisbon valley, the sharp erosive contact is most discernible at the base of discontinuous multistoried lenses of interbedded sandstone and conglomerate, referred to by martz and others (2014) as the “big indian rock sandstones” (figure 12e), which occur locally at the chinle-wingate contact (lucas and others, 1997a, 1997b). these sandstone beds are similar in color and superficial appearance to the eolian deposits of the wingate sandstone, but distinct from them in containing conglomeratic layers and more variable bedding. at skull ridge, the big indian rock beds are mostly very fine to fine-grained and horizontally planar bedded, although climbing ripple cross-stratification and highly convoluted bedding produced by syndepositional slumping also occurs. the big indian rock beds at this locality comprise several superimposed sandstone sequences separated by basal scours; at the base of each sequence is an intrabasinal conglomerate that contains clasts of reworked sandstone and siltstone up to 10 cm in diameter. these conglomerates locally contain isolated vertebrate bones. martz and others (2014) agree with the interpretation of lucas and others (1997a, 1997b) that the big indian rock beds are probably fluvial deposits given the lenticular nature of the unit and the combined characteristics of conglomerates, trough cross-bedding, and climbing ripple cross-lamination. the thinness of individual tiers, combined with the conglomeratic bases and absence of distinct lateral accretion beds, suggests that they were deposited by small bedload-dominated channels that preceded deposition of the wingate erg system. these lenses were probably deposited in localized scours incised into the top of the church rock member. the presence of conglomeratic layers and lack of trough cross-stratification differentiates them from 136 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 ephemeral stream deposits found within the wingate sandstone (clemmensen and others, 1989), although they are similar to these other wingate fluvial deposits in being dominated by very fine to fine-grained sand and possessing abundant climbing ripples. the big indian rock beds (figure12e) generally have a conformable relationship with the overlying wingate sandstone (martz and others, 2014). although lucas and others (1997a, 1997b) claimed that the contact between these lenticular sandstone beds and the wingate sandstone is gradational, there is usually a discernible sharp contact between them. however, the contact appears to be conformable (i.e., there is not a clear erosional scour incised into the big indian rock beds), and probably does not represent a great deal of missing time. paleontology at lisbon valley, abundant petrified logs occur in the lower kane springs beds (martz and others, 2014), and flattened permineralized wood occurs near the top of the church rock member, as do foliage compressions of the giant horsetail neocalamites, the fern cynepteris, the bennetitalean zamites, and the enigmatic seed plants pelourdea and sanmiguelia (ash, 1987; milner, 2006). invertebrates include ostracods, conchostrachans, and rare gastropods from the kane springs beds; invertebrate trace fossils are also present (a.r.c. milner, unpublished data; martz and others, 2014). coelacanth material, much of it referable to chinlea, is known from the kane spring beds (figure 5a) (schaeffer, 1967; milner and others, 2006a). lisbon valley is well known for its spectacular collection of ray-finned fishes (figures 5a and 5d to 5f) (redfieldiid palaeonisciforms, perleidiforms, and semionotiforms) including several holotypes from ledge-forming sandstone beds in the church rock member (figures 5a and 5d to 5f) (schaeffer, 1967; milner and others, 2006a; gibson, 2013a, 2013b, 2015). excellent ray-finned fish fossils, including the lobe-finned chinlea, are also known from the correlative dolores formation in southwestern colorado (schaeffer, 1967; elliott, 1987). fragmentary metoposaurid material has been recovered from the kane springs beds and church rock member in lisbon valley (martz and others, 2014; a.r.c. milner, unpublished data). phytosaur postcranial material has been recovered from the kane springs beds in lisbon valley, although it cannot be referred to an alpha taxon (milner and others, 2006a; martz and others, 2014). several specimens of the derived phytosaur machaeroprosopus, including some specimens referable to “redondasaurus,” occur in the church rock member and overlying big indian rock beds at the base of the wingate sandstone (figures 7b to 7d) (morales and ash, 1993; lucas and others, 1997a, 1997b; martz and others, 2014). the so-called “last phytosaur” (figure 7d) from the big indian rock beds at the base of the wingate sandstone in lisbon valley is the stratigraphically highest known phytosaur in the western united states (morales and ash, 1993; lucas and others, 1997a, 1997b; martz and others, 2014). putative phytosaur tracks and swim traces have also been recovered from the church rock member at lisbon valley (milner and others, 2006a milner and lockley, 2016; hunt-foster and others, 2016; a.r.c. milner, unpublished data). multiple specimens referable to the aetosaur typothorax were recovered from the upper kane springs beds in lisbon valley (figure 8b) (martz and others, 2014), and the poorly preserved aetosaur osteoderm from canyonlands national park described by heckert and others (1999) was probably recovered from the middle kane springs beds (see above). specimens of typothorax, including at least one referable to t. coccinarum, also occur within the kane springs beds and church rock member at lisbon valley (figures 8c and 8d) (martz and others, 2014). an excellent brachycheirotherium trackway has been recovered from the upper church rock member (milner and others, 2006a); this ichnotaxon may have been made by typothorax (heckert and others, 2010). undescribed crocodylomorph material has also been recovered from the church rock member at lisbon valley (a.r.c. milner, unpublished data), as have grallator tracks indicating the presence of theropod dinosaurs (milner and others, 2006a). stop 6 the san rafael swell, black dragon overlook from lisbon valley, return west along big indian road to u.s. highway 191, and proceed north through 137 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 moab to i-70. take i-70 west. approximately 65 km (40 mi) after joining i-70, the highway approaches the steeply rising slopes of the san rafael swell, a large double-plugging anticline with a 70 km (44 mi) long axis oriented approximately southwest to northeast (figure 4). the cliff-forming middle jurassic entrada sandstone caps the reddish-brown carmel formation on the lower east-tilting flanks of the swell, whereas the pale-colored sandstone of the early jurassic navajo sandstone form most of the sloping surface (figure 13a). after passing west through the road cut lined by sheer cliffs of navajo sandstone on either side, the cliffs above are now capped by the early jurassic kayenta formation and cliff-forming wingate sandstone, with the chinle formation occurring immediately below, and the reddish and orangish rocks of the lower triassic moenkopi formation forming the slope below (figure 13b). exit at the black dragon canyon overlook, about 82 km (51 mi) after exiting u.s. highway 191 to join i-70. the east-facing exposures along the west side of the san rafael swell (figure 13b) represent the spotted wolf canyon section of beer (2005); the buckhorn wash (u-3) section of stewart and others (1972a) is about 26 km (16 mi) to the north. about 19 km (12 mi) farther west of the black canyon overlook on i-70, exit north on county road (cr) 332 (buckhorn draw road). this exit affords a view of a mesa capped by the chinle formation just north of the i-70 (figures 13c to 13f) just south of the small hill called the wickiup, and just west of stewart and others’ (1972a) cane wash (u-4) section. although we have not had an opportunity to closely examine the chinle formation on the eastern flank of the san rafael swell, we were able to briefly examine the section south of the wickiup. sedimentology and stratigraphy the chinle formation in this part of the san rafael swell is about 106 m thick (stewart and others, 1972a; sections u-3 and u-4). the formation is dominated by a massive cliff-forming sandstone that could easily be mistaken at a distance for part of the wingate sandstone (the “moss back member” in figures 13b and 13d), locally with well-developed paleosols at the base (figures 13d and 13e), and overlain by a sequence of interbedded conglomeratic sandstone and mudstone. the stratigraphic identity of these units is open to debate. the paleosol at the base of the chinle formation is the temple mountain member (robeck, 1956), a sequence of mottled strata that can locally be as much as 30 m thick but is usually 6 to 9 m thick (robeck, 1956; stewart and others, 1972a). as indicated by beer (2005), there are two distinct paleosol zones within the temple mountain member (figure 13e). the lower paleosol is a quartz sandstone with “four-color” mottling that was identified by beer (2005) as a gleyed oxisol, with vertical streaks interpreted as crayfish burrows that seem to be identical to those often occurring in the mottled strata above, within, or below the shinarump member in other parts of southern utah and northern arizona (e.g., figure 10d). above the lower mottled paleosol is a mudstone-dominated drab-colored paleosol identified by beer (2005) as a gleyed vertisol. the overlying massive ledge-forming sandstone varies in thickness in the san rafael swell from about 18 to 51 m (stewart and others, 1972a), although beer (2005) indicates the unit can be up to 100 m thick. this ledge locally truncates the temple mountain member, and is overwhelmingly dominated by pale-yellow siliceous sandstone with interbedded mudstone and conglomerates composed mostly of quartz and quartzite with some chert and reworked sedimentary clasts (stewart and others, 1972a; sections u-3 to u-6). dominated by siliceous sand and conglomerate, the unit is lithologically similar to the shinarump member. this, combined with the position of the unit at the base of the section, would suggest the unit belongs to the shinarump member as indicated by lucas (1991). however, this unit was identified as an unusually siliceous representation of the moss back member by stewart and others (1972a), blakey and gubitosa (1983), and beer (2005), who explain its basal position within the chinle formation in the san rafael swell as due to the thinning of the formation along the flanks of the ancestral uncompahgre highlands, where the lower units of the chinle formation have mostly pinched out (figure 2a). ultimately, the question cannot be answered without more careful tracing of the unit southwards to where unquestioned outcrops of both the shinarump and moss back mem138 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 13. the northern san rafael swell. (a) map showing location of black dragon canyon overlook at the eastern edge of the san rafael swell. (b) cliffs to the north of i-70 visible from black dragon canyon overlook. (c) map showing location of the wickiup and the mesa to the south near the western side of the san rafael swell. (d) mesa visible from pulloff by i-70 south of the wickiup. (e) the temple mountain member at same mesa, showing upper and lower paleosols. (f) the upper chinle exposures on top of the mesa probably represent the petrified forest or owl rock member. the well-developed calcareous paleosol below the ledge-forming conglomeratic sandstone is very similar to the paleosol developed underneath the capitol reef bed in care. 139 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 bers occur. the presence of a siliceous mottled unit below the massive ledge-former supports the identification of this unit as the moss back member, although it is worth noting that “four color” mottled strata occur below the shinarump member in the circle cliffs region to the southwest (j.w. martz, unpublished data). the relatively thin section of interbedded sandstone and mudstone overlying the cliff-forming sandstone (figures 13b and 13e) has been assigned to the church rock member by stewart and others (1972a), but lucas (1991, 1993) correlated these beds to the cameron, moss back and rock point members. although we have difficulty assigning any of these upper strata in the san rafael swell to any particular member, we at least agree with lucas (1991) that these strata probably do not all belong in the church rock (or correlative rock point) member. the church rock member tends to be somewhat unimodal and dominated by reddish-brown siltstone to fine-grained sandstone, or bimodal with those fine-grain sizes interbedded with pebble-cobble conglomerate (martz and others, 2014). whereas, the sequence above the massive ledge-forming sandstone in the san rafael swell consists largely of purplishand greenish-gray mudstone with well-developed carbonate nodule horizons interbedded with ledge-forming conglomeratic sandstone dominated by intrabasinal clasts of reworked siltstone and carbonate (stewart and others, 1972a). these beds are more reminiscent of the petrified forest member or even owl rock member than of the church rock member. paleontology little information exists on the paleontology of the chinle formation in the san rafael swell. in addition to crayfish burrows in the temple mountain member (beer, 2005), carbonized permineralized wood occurs in the massive ledge-forming “moss back member” (stewart and others, 1972a). in the beds above the “moss back member,” the intrabasinal conglomerates contain vertebrate bone fragments, including one tiny jaw with exposed alveoli that was observed on the mesa south of the wickiup (j.i. kirkland and j.w. martz, unpublished data). stop 7 chimney rock trail, capitol reef national park return east along i-70, leaving the san rafael swell, and drive for about 11.4 km (7.1 mi) east of the black dragon canyon overlook until reaching sr 24. proceed south on sr 24 about 70.8 km (44 mi) to hanksville, and from there continue west about 64 km (40 mi). this route passes through the waterpocket fold, a monoclinal fold that extends for approximately 160 km (100 mi) southeast from the edge of the san rafael swell to lake powell in glca. passing through the waterpocket fold, sr 24 follows the fremont river through a canyon lined by the sheer, east-dipping cliffs formed by the navajo sandstone to eventually enter the wider valley in the western part of the waterpocket fold at the town of fruita. here, as in the other localities visited on this tour, the cliffs are capped by the wingate sandstone, which lies stratigraphically beneath the kayenta formation and navajo sandstone. the slope below is formed by the moenkopi and chinle formations (figures 14b and 14c). the chimney rock trailhead is encountered about 5.3 km (3.3 mi) west of the care visitor center on the north (right-hand side driving east) side of the road (figure 14a). a dramatic fault is visible from the chimney rock trail parking lot. to the right of the fault (including the chimney rock pinnacle), reddish-brown moenkopi formation is capped by the shinarump member of the chinle formation, whereas to the left of the fault section the shinarump member is exposed close to the level of the parking lot, and is overlain by the stratigraphically higher grayish-colored monitor butte member. the trail leads up through the entire chinle formation section, passing through the shinarump member and up the steep slope formed by the drab-colored monitor butte member. on top of the mesa, the trail continues past exposures on the northern (left) side of the reddish-colored petrified forest member capped by the capitol reef bed. leaving the trail and climbing on top of the capitol reef bed allows access to the owl rock member and the base of the wingate sandstone. sedimentology and stratigraphy care (figures 14 and 15) and the adjacent circle cliffs region of gsenm contains one of the most 140 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 14 caption on following page. 141 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 complete chinle formation sections in southern utah, and is located far enough from the flanks of the ancestral uncomphagre highlands that the lower part of the section is well preserved (figure 2a). to the west (including in zion; see below), the upper part of the section becomes increasingly erosionally truncated at the base of the glen canyon group (figure 2a), but in care only the church rock member is absent. the shinarump, monitor butte, petrified forest, and owl rock members are all well exposed in care (figures 14b and 14c), and a conglomeratic sandstone occurs at the base of the petrified forest member that may be correlative with the moss back member (kirkland and others, 2014b). in care, the shinarump member overlies the tr-3 unconformity truncating the moenkopi formation. the shinarump member in care is a well-cemented white and yellow conglomeratic sandstone with abundant clasts of quartz, quartzite, and chert (kirkland and others, 2014b). the shinarump member forms a distinct ledge-forming unit (figure 14d) that varies from 0 to 25 m in thickness (dubiel, 1987a). at care the contact with the overlying monitor butte member is disconformable (stewart and others, 1972a), and the thickness of the shinarump member is more controlled by the degree to which it is incised below the monitor butte than the degree to which it incises the underlying moenkopi formation (beer, 2005; kirkland and others, 2014b). in places, the shinarump member is almost completely eroded away, that resulting in deep scours on the surface of the unit into which the overlying monitor butte member was deposited. unlike most areas in southern utah and northern arizona, in care and at the circle cliffs, the “four-color” mottled strata that are usually developed on top of (and sometimes within) the shinarump member occurs below it (figure 14e) or not at all. mottled strata have been observed beneath un-mottled shinarump member, and at the moenkopi-chinle contact in places where the shinarump is absent (kirkland and others, 2014b). as with the mottled strata in zion and elsewhere (martz and others, 2015), reddish-colored silicified layers locally occur in the mottled strata at care (kirkland and others, 2014b). at care, the monitor butte member is a complex unit in which generally drab grayish and greenish-colored mudstone and muddy sandstone beds (figure 14b) are interbedded with sandstone and conglomerate that are often resistant and reddish-brown. in some places, including in the vicinity of the chimney rock trail, the lower part of the monitor butte member is strikingly contorted, with some sandstone and conglomerate beds dipping at up to about 90° (figures 14f and 14g). these folds are clearly syndepositional, because they are not only capped by undeformed strata, but overlie undeformed, horizontally oriented strata (stewart and others, 1972a; dubiel, 1991; kirkland and others, 2014b). in contrast to the upper, more uniformly drab-colored part of the monitor butte member, the contorted strata low in the member are strongly variegated. in these variegated beds, dark gray and greenish-gray mudstone beds are interbedded with yellowish-, orangish-, and reddish-colored beds (usually sandstone or conglomerate) (figure 14f). there are abundant anhydrite, calcium carbonate, and limonite concretions, the latter often with botryoidal habit. gypsum often occurs as slickenside fillings. sandstone beds in the lower contorted strata are often very fine to fine-grained and dominated by figure 14 (figure on previous page). care. (a) map showing location of chimney rock trailhead. (b) cliffs just to the west of the chimney rock trailhead showing the complete chinle formation section. (c) exposures of the chinle formation along the scenic drive south of the visitor center; the color difference between the reddish-colored petrified forest member and pastel-colored owl rock member is especially striking; note the difference in appearance between the fresh outcrop of owl rock member immediately below the wingate sandstone and the eroded slope of the same unit below. (d) the shinarump member near the western boundary of the park along sr 24, showing the variability in thickness of the unit due to erosion. (e) mottled strata exposed below the shinarump member west of chimney rock trail. (f) contorted strata in the lower monitor butte member; the strongly variegated beds dip to the right at almost 90°, although beds below and above are roughly horizontal. (g) ripple cross-laminated sandstone bed with a dip of 90° in the contorted beds. (h) the carbonate nodule-rich paleosol at the top of the monitor butte member, truncated by the “moss back member.” 142 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 15 caption on following page. 143 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 climbing ripple cross-lamination (kirkland and others, 2014b). above the contorted strata, two horizontal conglomeratic sandstone beds occur in the upper, drab-colored part of the monitor butte member (kirkland and others, 2014b). the uppermost few meters of the monitor butte member is a zone of redand purple-mottled mudstone containing abundant carbonate nodules, sometimes concentrated into horizons (figures 14c and 14h). fresh exposures of the upper red paleosol contain vertisols that can be identified by the presence of distinct slickensides, and sometimes contain vertical crayfish burrows (kirkland and others, 2014b). a mediumto coarse-grained sandstone with some interbedded conglomerate and mudstone dominated by horizontal planar bedding and planar cross-bedding frequently occurs at the base of the petrified forest member at care and the circle cliffs, capping the upper red paleosol (figures 14c and 14h). usually the unit is a ledge-former several meters thick, although locally it is friable enough to be a slope-former. the unit varies considerably in color. at care, the unit is frequently pinkishor reddish-colored so that it is difficult to discern from the reddish-colored strata above and below it. we informally refer to this unit as the “moss back member” due to its stratigraphic position at the base of the petrified forest (stewart, 1957; stewart and others, 1972a), although the true moss back member occurs mainly in southern utah to the east of care (stewart and others, 1972a; blakey and gubitosa, 1983; dubiel, 1987b). the reddish-colored mudstone, sandstone, and minor conglomerate overlying the “moss back member” in southern utah are usually referred to the petrified forest member (e.g., stewart and others, 1972a; kirkland and others, 2014b), although they are correlative to what is often called the upper petrified forest member or painted desert member in northern arizona (e.g., stewart and others, 1972a; lucas, 1993; see martz and others, 2015 for a discussion of the nomenclatural history of the petrified forest member). at care and the circle cliffs (figures 14c to 14h, 15a, and 15b), the lower part of the petrified forest member is dominated by mudstone with some thinner sandstone and conglomerate beds containing intrabasinal sedimentary clasts. mudstone beds are commonly vertisols with slickensides, carbonate nodules, and greenish-gray mottling (dubiel and hasiotis, 2011). the capitol reef bed (figures 14c and 15a to 15d) (stewart and others, 1972a) is a prominent fineto coarse-grained ledge-forming sandstone with minor interbedded conglomerate that occurs high in the petrified forest member in care and the circle cliffs. the unit is almost continuous across this region, although it varies considerably in thickness. the capitol reef bed is usually a multistoried channel sandstone dominated by horizontal planar bedding and planar cross-bedding (figure 15d), although locally it contains abundant climbing ripple cross-stratification and has rare trough cross-beds (j.w. martz, unpublished data). a well-developed, highly resistant calcareous paleosol with abundant crayfish burrows occurs locally below the capitol reef bed in parts of care (figures 15b and 15c) (kirkland and others, 2014b). the contact between the petrified forest member and the owl rock member is placed at a subtle color change (figures 15b and 15c) from deeper reddish-brown bentonitic mudstone with popcorn weathering to paler pastel colors with harder mudstone generally lacking popcorn weathering (kirkland and others, 2014b); elsewhere across the colorado plateau, stewart and others (1972a), dubiel (1993), and martz and others (2012) also place the contact between the petrified forest and owl rock members according to these criteria. the owl rock member at care and circle cliffs is dominated by slope-forming mudstone, figure 15 (figure on previous page). care. (a) the lower petrified forest member above the “moss back member” along the chimney rock trail. (b) nearly the entire petrified forest member near chimney rock in care; the purple beds immediately below the capitol reef bed are the calcareous paleosol in figure 15c; the outcrop in figure 14c. (c) the calcareous paleosol below the capitol reef bed. (d) well-expressed bedding in the capitol reef bed, mostly consisting of gently dipping planar cross-beds, although trough cross-bedding is visible just below and to the left of the rock hammer. (e) owl rock member exposures near chimney rock trail, just above the exposures in a. (f) fresh exposures of the owl rock member (as in figure 14c) showing well-developed calcretes. 144 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 with drab-mottling and large slickensides and desiccation cracks that are often filled with gypsum. a few resistant ledges always occur in the owl rock member, most of which are calcareous paleosols developed into the mudstone units; however, some ledges (especially high in the member) are conglomeratic sandstone. the calcareous paleosol ledges often have a brecciated texture, greenish-gray mottling, and patches that have been replaced by silica (kirkland and others, 2014b). paleontology care and the adjacent circle cliffs area of gsenm have produced one of the most important collections of vertebrate fossils in southern utah. fossils are known from all stratigraphic levels within the chinle formation, giving the care-gsenm region the greatest potential within southern utah for developing a detailed biostratigraphic framework. permineralized wood is common throughout the chinle formation section, although the nature of preservation varies. the wood is white and well silicified in the shinarump member, whereas poorly preserved stumps in both prone and upright growth position occur in the monitor butte member. ash (1975) described horsetail, fern, conifer, and bennettitalean compressions from mudstone lenses in the shinarump member at care. plant remains are also all exceptionally common in the monitor butte member; permineralized logs occur as poorly preserved upright trunks often surrounded by orangishand yellowish-colored oxides (probably limonite and carnotite), and better preserved yellowish-colored perminerlized logs that occur in the sandstone and conglomerate beds. giant horsetail fossils occur locally in upright growth position not far the chimney rock trail, and even more impressive specimens referable to equisetites have been documented along south draw, south of capitol gorge (dubiel, 1987a, 1987b, figure 8; kirkland and others, 2014b). within the contorted beds, carbonized plant compressions are preserved, including excellent bennettitalean specimens (kirkland and others, 2014b). permineralized logs also occur in the “moss back member” at the base of the petrified forest member, and from the capitol reef bed near the top of the petrified forest in both care (kirkland and others, 2014b) and the circle cliffs. ash (1982) described compressions of the shrubby seed plant sanmiguelia from the owl rock member at care. the drab-colored mudstone beds in the monitor butte member that produce plant compressions have also produced conchostracans in care (kirkland and others, 2014b), just as similar organic-rich mudstone in the kane springs beds have produced both plant compressions and small invertebrates (milner, 2006; martz and others, 2014). unionid bivalves occur locally in the capitol reef bed, and occur densely in at least one bed in the upper owl rock member in care (kirkland and others, 2014b). probable crayfish burrows that may belong to the ichnogenus camboygma (hasiotis and mitchell, 1993) occur in the paleosol at the base of the capitol reef bed near chimney rock trail, and other invertebrate traces have been observed in the upper petrified forest member at care (kirkland and others, 2014b). a lungfish tooth plate has been recovered from the owl rock member at care (kirkland and others, 2014b). fragmentary metoposaur and phytosaur remains are fairly common in the monitor butte member at care. teeth and fragmentary bones are often found in conglomerates, and one locality in the upper part of the monitor butte member has produced well-preserved phytosaur postcranial elements after only preliminary prospecting (kirkland and others, 2014b); dull-gray gypsiferous mudstone beds and bone preservation is reminiscent of the placerias quarry in northern arizona. so far none of this material can be referred to an alpha taxon. a mandible fragment from a large metoposaurid is known from the top of the capitol reef bed near chimney rock trail, and other indeterminate vertebrate material has been recovered from that level. at least one paramedian osteoderm referable to typothorax is known from the petrified forest member at care (figure 8a), although the exact stratigraphic level is unclear (kirkland and others, 2014b). 145 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 stop 8 circle cliffs, grand staircase-escalante national monument from the chimney rock trail, there are two possible routes to the circle cliffs, both using burr trail, which extends from boulder through circle cliffs in gsenm and the waterpocket fold in care. one can take sr 24 west out of care, and then turn south onto sr 12 to boulder, turning east onto burr trail road and drive from there to circle cliffs. however, if driving a passenger vehicle without a trailer, we recommended taking the more scenic route from the west (figure 16a). from the chimney rock trailhead, drive east 17 km (10.6 mi) along sr 24 to the junction with notom-bullfrog road, and proceed south. after roughly 30 km (20 mi), this road meets the dipping mesozoic strata of the waterpocket fold, and affords an excellent view of the mesozoic section. the gray cliffs to the left (east) are upper cretaceous mancos shale overlain by coastal and floodplain strata of the muley canyon sandstone, masuk formation, and tarantula mesa sandstone (kirkland and others, 2014b; lawton and others 2014; titus and others, 2016) and underlain by thin exposures of the naturita formation (formerly dakota formation; carpenter, 2014) at the base of the cliffs, with spectacular variegated exposures of the upper jurassic morrison formation occurring along to the road. on the right (west) side, one sees the upper surfaces of the predominantly reddish-colored middle jurassic strata. in decending: the summerville, curtis, entrada, carmel, and page formations; beyond which lie the massive white cliffs of the lower jurassic navajo sandstone. roughly 50 km (30 mi) after turning onto notom-bullfrog road, the road curves right (west), passing through the navajo sandstone and up the burr trail switchback (figure 16a). the switchback ascends more or less along the contact between the navajo sandstone and the reddish-brown kayenta formation. upon reaching the top, the burr trail continues east, passing through the west-facing exposures of the wingate sandstone and chinle formation (kirkland and others, 2014b). from here, the burr trail passes through exposures of the moenkopi formation flooring the central basin of the circle cliffs uplift for about another 24 km (15 mi) before reaching the west side. the circle cliffs are a topographic result of a domal anticlinal structure for which the waterpocket fold in care represents the eastern, west-dipping side. the circle cliffs expose the upper triassic section around their entire circumference. on crossing the central basin of the circle cliffs, the burr trail climbs upwards through the shinarump member (figure 16b), then through most of the chinle formation section before reaching the spectacular east-facing overlook (stop 8) at about the petrified forest-owl rock member contact, below cliffs of wingate sandstone (figure 16c). the overlook affords an excellent view of the chinle formation section. proceeding back east a short distance along burr trail, one can turn south onto the wolverine road, and proceed south about 10 km (6 mi) to the wolverine petrified forest trailhead. a short hike along the trail passes through the monitor butte member, including impressive exposures of lower monitor butte ripple cross-laminated sandstone beds, before reaching an area covered with black permineralized logs weathering out of the “moss back member.” sedimentology and stratigraphy the stratigraphy of the chinle formation in the circle cliffs of gsenm is broadly similar to that in care, which is not surprising given its close proximity. as in care the stratigraphic sequence consists of the shinarump (figure 16b), monitor butte, “moss back,” petrified forest, and owl rock members (figure 16c), and the overall lithology of these units matches fairly well what is seen in care. the entire section is visible from the burr trail circle cliffs overlook; the monitor butte, “moss back,” petrified forest, and owl rock members form a continuous slope capped by the wingate sandstone, whereas the shinarump member caps a lower tier of mesas overlying the moenkopi formation. as in care, the shinarump member varies enormously in thickness throughout the circle cliffs, and locally pinches out to nothing (figure 16d), although the unit is overall a more continuous resistant ledge former than in care (figure 16b). also as in care, the upper contact of the shinarump member seems to be fairly sharp and at least locally disconformable, and 146 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 mottling seems to occur locally below the shinarump rather than above it. interestingly, as in the san rafael swell there seem to be two distinct paleosol horizons below the shinarump member (e.g., beer, 2005)—a lower paleosol with distinct “four-color” mottling, and an upper less mottled zone that in the circle cliffs is usually greenish gray (figure 16d) (j.w. martz, unpublished data). the monitor butte member is also broadly similar to the unit in care, and also shows a degree of lateral variability within the circle cliffs. locally, ripple cross-laminated sandstone beds are abundant in the lower monitor butte member, most notably at a striking outcrop encountered on the wolverine petrified forest trail (figure 16e). these reddish-colored ripple cross-laminated sandstone beds (figure 16f) are somefigure 16 caption on following page. 147 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 times interbedded with interbasinal conglomerate and show a striking degree of variable dip across small areas, although they are not as dramatically contorted as in care. however, the senior author has had the opportunity to examine the chinle formation section not far from circle cliffs along lake powell in glca with graduate students susie wisehart of the university of washington and susie hertfelder of the university of nevada, las vegas. here, there are beds in the lower monitor butte member that are as strikingly contorted as in care; the lake powell contorted strata are unusual for the chinle formation in containing limestone beds. as in care, the bulk of the monitor butte member is grayish-colored mudstone and interbedded sandstone. locally, reddish-colored zones occur within the monitor butte in the circle cliffs that are somewhat reminiscent of the reddish-colored zones seen in the cameron member at zion. also as in care, poorly preserved perminerlized logs (figure 16g) are often found in both upright and horizontal positions within the monitor butte member at circle cliffs, and vertebrate fossils occur locally. as elsewhere in southeastern utah, a well-developed reddish-colored paleosol with abundant large orangish-colored carbonate nodules dominates the uppermost several meters of the unit (figure 16h). the upper contact of the monitor butte member is strongly unconformable at circle cliffs, and has locally been observed to cut down deeply into the monitor butte member, even locally entirely excising the reddish-colored paleosol. in most places, a somewhat resistant ledge-forming conglomeratic sandstone occurs at this contact that is interpreted as being the same “moss back member” seen at care. locally, this unit is a more-or-less uniform dark reddish-brown, but in other places it consists of a lower ledge-forming grayish-colored conglomeratic unit and an upper friable slope-forming orangish-colored unit as is seen in the wolverine petrified forest and the surrounding area, where abundant permineralized logs (figure 16i) and less common vertebrate material occur close to the contact between the two units. the petrified forest and owl rock members are broadly similar to the units in care, and the capitol reef bed, or at least a similar ledge-forming sandstone at roughly the same stratigraphic level as in care, also occurs in the upper petrified forest member at circle cliffs. the lower petrified forest member in circle cliffs generally contains a striking zone of bright-orange mudstone not usually observed in care, although a similar orangish-colored zone occurs at lees ferry in northern arizona (j.w. martz, unpublished data). occasionally, dramatic fluvial cut-and-fill structures can be seen in the petrified forest (figure 16j) there is evidence of unusual syndepositional slumping in the petrified forest at circle cliffs that has not been observed elsewhere (figure 16k); the capitol reef bed and strata immediately above are locally deformed by downward slumping that does not seem to impact strata either lower or higher in the section. paleontology the preservation of plant material in the circle cliffs is overall very similar to what is observed at care. upright-growing giant horsetail pith casts have been documented in the lower monitor butte member at the circle figure 16 (figure on previous page). the circle cliffs in gsenm. (a) map of the waterpocket fold and circle cliffs, showing the location of burr trail and the circle cliffs overlook. (b) the shinarump member at the base of the chinle formation, which is often a ledge-forming sandstone capping the moenkopi formation. (c) the chinle formation section above the shinarump member near the circle cliffs overlook. (d) outcrop where the shinarump member locally pinches out (it is not clear if this is due here to erosional truncation or thinning over an interfluve). (e) outcrop of ripple cross-laminated sandstone in the lowermost monitor butte member along the wolverine petrified forest trail. (f) ripple cross-laminated sandstone also showing ripples on the bedding plane. (g) poorly preserved petrified tree stump in the monitor butte member. (h) carbonate nodules in the reddish-colored paleosol at the top of the monitor butte member. (i) permineralized log in the “moss back member” at the circle cliffs. (j) cross section through a channel-fill deposit in the lower petrified forest member, showing a probable cut bank and point bar sequence. (k) slumping at the level of the capitol reef bed in the upper petrified forest member. 148 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 cliffs (j.w. martz, unpublished data). as in care, poorly preserved permineralized logs, many in growth position, occur within the monitor butte member (j.w. martz, unpublished data), and permineralized logs are also common in the “moss back member.” at the wolverine petrified forest (ash, 2003), an unusually dense concentration of permineralized logs in the circle cliffs area, most logs occur in the “moss back member,” although well-preserved examples are also fairly common in the capitol reef bed. these logs have a preferred southeast to northwest orientation, although many have an orientation that is roughly perpendicular to this (j.w. martz, unpublished data). the circle cliffs area is slowly yielding one of the most impressive collections of upper triassic vertebrate faunas in southern utah outside of lisbon valley, most of it collected by yale university. currently, efforts are underway by the senior author to precisely constrain the yale localities stratigraphically. yale has collected abundant vertebrate material from the monitor butte member at the circle cliffs, including a lungfish tooth plate, metopsaur material, and phytosaur material, although none of the latter can be assigned to an alpha taxon; recently students working with the senior author recovered another lungfish tooth plate from the monitor butte member (figure 5b) (w.g. parker and j.w. martz, unpublished data). within southern utah, the circle cliffs has produced the largest number of vertebrate specimens referable to an alpha taxon outside of lisbon valley (w.g. parker and j.w. martz, unpublished data). an astonishing nearly complete and fully articulated specimen of poposaurus gracilis (figure 8e), and an associated crocodylomorph skeleton were recovered by yale university (parker and others, 2006; gauthier and others, 2011; schachner and others, 2011) from the lower monitor butte member (j.w. martz, unpublished data), and material referable to the aetosaurs genera calyptosuchus and desmatosuchus, as well as paratypothoracins, have also been recovered, probably from the monitor butte member (w.g. parker and j.w. martz, unpublished data). stop 9 black’s canyon, zion national park from the circle cliffs overlook, drive west on burr trail for 28 km (17.5 mi) to the junction with sr 12 in boulder. from here, proceed south on sr 12 for 141 km (87 mi) through escalante, across the northern kaiparowits plateau, through cannonville, and past bryce canyon on the paunsaugunt plateau to the junction with u.s. highway 89. titus and others (2016) described the geology and vertebrate paleontology along this route. proceed south on u.s. highway 89 for 70 km (43.2 mi) to the junction with sr 9. proceed west on sr 9 for 40 km (25.1 mi) through the spectacular exposures of the navajo sandstone in the southeastern part of zion and proceed into the town of springdale. turn right (northwest) onto lion boulevard and proceed approximately 1.2 km (0.75 mi) to the gate for the o.c. tanner amphitheater (figure 17a). park by the striking purplish-colored beds of the upper chinle formation capped by the reddish-brown moenave formation (figure 17b). in zion, the chinle formation section is about 180 m thick, but only the uppermost 25 m or so is exposed at black’s canyon (figure 17b). the lowermost exposures here are a gray, friable, slope-forming sandstone that may be correlative with the “friable sandstone” in the mt. kinesava section (see below). the predominantly purple and gray mudstone and interbedded sandstone beds of the uppermost chinle formation in black’s canyon belong to what martz and others (2015) refer to as the “purple pedogenic beds” (figure 17b). these beds may be equivalent to the upper monitor butte member or blue mesa member or even the basal petrified forest member, although this is not clear (see below). the “purple pedogenic beds” are purple-weathering mudstone that are a variety of grayish-red, reddish-brown, and yellowish-gray shades in fresh outcrop. these beds are rich in nodules of calcium carbonate and anhydrite as well as non-horizontal veins of evaporite (figure 17c), all of which are absent lower in the section (martz and others, 2015). anhydrite nodules also occur in the uppermost chinle formation at st. george (kirkland and others, 2014a). the nodules are both scattered throughout the unit and concentrated into horizons, often with striking greenish-gray mottling, but there are also zones several meters thick where nodules are totally absent. the evaporite veins occur only in the uppermost 10 m or so of the purple pedogenic beds (figure 17c) and may 149 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 be composed of anhydrite or selenite. the fact that the veins are generally not perfectly horizontal in orientation suggest they formed as postdepositional diagenetic features when hypersaline groundwater seeped into the subsurface while the dinosaur canyon member was being deposited (see below) and left gypsum in slickensides and desiccation cracks in the purple pedogenic beds. very thin horizontal beds of gypsum also occur in the purple pedogenic beds, but these may be syndepositional (martz and others, 2015). the purple pedogenic figure 17. black’s canyon in zion. (a) map showing location of chinle formation exposures. (b) overview of the uppermost chinle formation and moenave formation exposures near o.c. tanner ampitheater. (c) anhydrite or selenite beds in the uppermost chinle formation, just below the base of the dinosaur canyon member. (d) the anhydrite-clast conglomerate marking the base of the dinosaur canyon member. (e) ledge-forming sandstone in the dinosaur canyon member. (f) laminated mudstone of the whitmore point member under the overhanging springdale sandstone member. 150 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 beds may be equivalent to the red and purple carbonate nodule-rich paleosol at the top of the monitor butte member in care; if so, the unconformity between the chinle and moenave formations may span about 18 million years of middle to late norian and rhaetian time. above the purple pedogenic beds of the chinle formation, the section is dominated by reddish-colored subhorizontal sandstone and mudstone of the moenave formation. the basal dinosaur canyon member and overlying whitmore point member of the moenave are exposed here (figure 17b), and are in turn overlain by the springdale sandstone member of the kayenta formation (gregory, 1950; biek and others, 2010; milner and others, 2012; martz and others, 2015). the section is essentially identical to that exposed at st. george (kirkland and milner, 2006; kirkland and others, 2014a). the base of the dinosaur canyon member is distinctly unconformable, with a conglomerate composed of clasts of reworked white anhydrite and chert pebbles (figure 17d) as it is in other parts of southern utah (kirkland and milner, 2006; kirkland and others, 2014a). immediately above is a fluvial sandstone bed also containing conglomerate with clasts of reworked anhydrite. in the lowermost few meters of the dinosaur canyon member, reddish-colored mudstone contain horizontal anhydrite beds probably representing original deposition; as already discussed, the hypersaline conditions that produced these layers are likely also responsible for filling what were then subsurface slickensides in the uppermost chinle formation with evaporites. above these lower mudstone and anhydrate beds, the dinosaur canyon member is about 57 m thick and consists of complexly interbedded, predominantly reddish-brown mudstone and ledge-forming sandstone (figures 17b to 17e); as with the church rock member along sr 128, the upper part of the unit becomes increasingly dominated by climbing ripple cross-lamination. the base of the whitmore point member is a ledge of calcareous sandstone with nodules of reddish-colored chert (martz and others, 2015) as elsewhere in southwestern utah (wilson, 1967; kirkland and others, 2014a). the whitmore point member is a thin unit only a few meters thick, that is composed of laminated mudstone (figure 17f), and capped by the thick ledge-forming springdale sandstone member of the kayenta formation (figure 17b). stop 10 southern side of mt. kinesava, zion national park return down lion boulevard to sr 9 and turn right, proceeding south for 4.8 km (3 mi). immediately after coming around a right curve, take a hard right onto anazazi way (figures 18a and 18b) which proceeds steeply upwards. parking for the chinle trail is just to the east at the start of anazazi way near the base of the hill. it is also possible to drop people off farther up the hill. proceed for approximately 1.8 km (1.1 mi) as anasazi way passes north and northwest through a housing complex. just before the road curves back south, stop at the pull-out by the concrete bridge (figure 18b). in the distance to the north are the chinle formation exposures at the base of mt. kinesava (figures 18c and 19a). there is a trail that leads into the park from here, but proceeding instead towards the exposures along the bottom of the the wash affords the opportunity to examine outcrops of the shinarump member. stratigraphy and sedimentology along the southern face of mt. kinesava near springdale at the southern end of zion, the entire chinle section is preserved between the upper red member of the moenkopi formation and the dinosaur canyon member of the moenave formation, and the moenave is capped in turn by the kayenta formation and massive cliffs of the navajo sandstone (figure 18c). only the lower part of the chinle formation is probably preserved here, and the upper part is truncated by erosion (figure 2a), and is capped unconformably by the dinosaur canyon member (martz and others, 2015). nonetheless, the total thickness of the chinle formation preserved here is about 180 m (martz and others, 2015), thicker than the entire chinle formation section in care (kirkland and others, 2014a). the basal unit of the chinle formation at zion is the shinarump member (figures 18c and 18d), which is a thick ledge-forming siliceous conglomeratic sand151 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 18. mt. kinesava in zion and the surrounding region. (a) overview of the area south of mt. kinesava, indicating the turnoff for anasazi way and the location of exposures of interest; the lightened box shows the area expanded in figure 18b. (b) close-up of anasazi way showing the location of the parking area. (c) overview of the lower mesozoic section at mt. kinesava, photographed from across the valley to the south. (d) the shinarump member exposed in huber wash on the west side of mt. kinesava. (e) “lower sandstones” above the shinarump member exposed near huber wash showing the unusual orange mottling and abundant permineralized wood. (f) permineralized log weathering out of the “lower sandstones” along huber wash on the mt. kinesava trail. 152 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 stone as seen elsewhere in southern utah (e.g., blakey and gubitosa, 1983, 1984). in zion, the shinarump member varies in thickness from 18 to 41 m (biek and others, 2010), but is about 22.6 m thick where measured by martz and others (2015) near mt. kinesava. the shinarump is well exposed in drainages south of mt. kinesava, near the chinle trailhead just south of zion, and even better exposed in huber wash on the western side of mt. kinesava (figures 18a to 18d). the sandstone and conglomerate beds in the shinarump member at zion are generally poorly sorted, and dominated by siliceous extrabasinal clasts, especially multi-colored quartzite, although there are rare intrabasinal sedimentary clasts. bedding within the shinarump member consists mostly of horizontal planar bedding, planar cross-bedding, and trough cross-bedding (martz and others, 2015). the uppermost meter of the moenkopi formation below the shinarump member at zion is a yellowish-colored zone of alteration that also occurs in care. fossil logs are very common in the shinarump member at zion (deblieux and others, 2005; martz and others, 2015) as they are in the member elsewhere across the colorado plateau (e.g., ash, 1975), and vertebrate remains are present but rare and unidentified (deblieux and others, 2005; martz and others, 2015). unlike at care, the shinarump member does not have an erosionally truncated upper surface, but instead has a gradational contact with the overlying beds as in most areas of the colorado plateau. as in zion, these overlying beds are generally slope-forming sandstone about 14 m thick (martz and others, 2015) that gregory (1950) referred to as the “lower sandstones” (figure 18e). these “lower sandstones” are predominantly siliceous as in the shinarump member, but differ in containing abundant dark-colored accessory minerals and in being rich in mudstone, organic material, gypsum, anhydrite, carnotite, iron oxide, and concretions (martz and others, 2015); in these regards, the “lower sandstones” are somewhat similar to parts of the monitor butte member, and have been considered correlative to it (stewart and others, 1959; doelling and davis, 1989). gregory (1950) noted the striking similarity between the bulk of the chinle formation strata in zion (figures 19a and 19b) and at petrified forest national park (pefo) in arizona, naming the petrified forest member for exposures at both parks, although a type section was not designated. indeed, the chinle formation sediments gregory (1950) assigned to the petrified forest member also have striking similarities to the lower chinle formation seen farther southeast at lees ferry in the southern part of glca, and in the navajo nation between lees ferry and cameron (lucas, 1993; martz and others, 2015). at lees ferry, phoenix (1963) referred to these beds as the “sandstone and mudstone member,” and lucas (1993) later proposed the name cameron member for the same sediments at cameron on the navajo nation in northern arizona. lucas (1993) and martz and others (2015) also applied the name cameron member to the beds in zion that gregory (1950) referred to as the petrified forest member, and the overall appearance and lithology of the beds at zion are indeed strikingly similar to the cameron member in northern arizona. in these areas, drab-colored mudstone (especially light olive-gray) dominate the sequence that are punctuated by reddish-brown zones that locally contain sandstone beds that grade laterally into mudstone (figures 19a and 19b). these beds are also quite similar, and occupy roughly the same stratigraphic position, as the lower blue mesa member of pefo; it is very likely that this is what prompted gregory (1950) to name the beds at zion the petrified forest member. in pefo, the newspaper rock bed is a prominent ledge-forming fluvial channel sandstone that grades laterally into reddish-colored, finer grained facies representing a floodplain paleosol (demko, 1995; parker, 2006; trendell and others, 2010), and it is likely that the same is true of these reddish-colored bands seen at mt. kinesava. this southeast to northwest-trending zone of cameron member/lower petrified forest member from pefo to zion is much thicker than and lithologically distinct from the monitor butte member. the cameron member is strikingly different from the monitor butte member in having fewer organic-rich facies with abundant evaporites, oxides, and gypsum (although these do occur, especially low in the cameron member). the contorted strata often seen in the lower part of the monitor butte and bluewater creek members have not yet been observed in the cameron member. we concur with lucas (1993; lucas and others, 1997a) and irmis 153 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 19. mt. kinesava in zion and the surrounding region (continued). (a) overview of the chinle formation on the south side of mt. kinesava. (b) close-up of the exposures showing the thick reddish-colored zones and unusual yellowish colored mottled horizons. (c) close-up of yellowish-colored mottling. (d) barite concretion at the base of one of the reddishcolored zones. (e) the “four-color” mottled zone, here a well-cemented ledge. (f) the “four-color” mottled zone with thin reddish-colored silicificed beds probably filling slickensides. 154 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 and others (2011, supplemental data) that the cameron, bluewater creek, and monitor butte members should be considered distinct from each other. the cameron member at mt. kinesava is about 110 m thick (martz and others, 2015), and seems to have a gradational lower contact with the “lower sandstones.” the unit consists predominantly of mudstone with interbedded very fine grained sandstone, and less-abundant claystone, coarser sandstone, and conglomerate; the latter two grain sizes mostly occur in ledge-forming channel sandstone beds. slope-forming mudstone tend to be bluish-gray and greenish-gray, whereas coarser grained beds are often reddish-brown or yellowish-colored (figures 19b and 19c) (martz and others, 2015). mudstone beds in both reddishand drab-colored zones are usually mottled with a variety of shades of yellowish-, reddish-, and greenish-gray, varying from large patches several centimeters across to thin stringers a few millimeters wide. these probably mostly represent root traces and possibly animal bioturbation as well. although mottling is common in the chinle formation, abundant yellowish-colored mottling (figures 19b and 19c) is unusual. slickensides are common in fresh exposures of mottled mudstone at zion, indicating that these are probably vertisols. concretions apparently composed of barite and iron oxides occur at the bases of some of the reddish-colored zones (figure 19d). five particularly thick reddish-colored zones are present in the cameron member at mt. kinesava (figures 19a and 19b); the upper part of the zone is often friable sandstone and the lower part is siltstone. the red bands likely represent paleosols that formed on interfluve sediments, as with the newspaper rock paleosol in pefo (trendell and others, 2013). several thick ledge-forming sandstone beds with minor interbedded conglomerate are present that are referred to informally as the “middle sandstones” (figure 19a). these sandstone beds tend to be slightly coarser grained than most slope-forming sands in the cameron member. the "middle sandstones" are characterized by mostly horizontal planar bedding and planar cross-bedding, and have small burrows and some greenish copper mineralization. on the southern side of mt. kinesava, the lowermost part of the cameron member consists of reddish-colored, largely ripple cross-laminated, very fine to fine-grained micaceous sandstone similar to those seen locally in the lower part of the monitor butte member to the northeast at care and the circle cliffs, although the sandstone beds at mt. kinesava are not contorted into high-angle folds. these sandstone beds often contain burrows consisting of vertical holes and horizontal grooves less than 1 cm in diameter (martz and others, 2015). in the lower part of the mudstone-dominant sequence, about 30 m above these lower reddish-colored sandstone beds and just above the second thick reddish-colored zone, is a horizon of “four-color” mottled strata of gray, red, purple, and yellowish-orange colors (figures 19e and 19f). the horizon is usually well lithified, and often contains sheets of reddish-colored chert (figure 19f). in all of these characteristics, the mottled strata are strikingly similar to the mottled paleosols usually developed on top of the shinarump member in northern arizona and parts of utah (e.g., dubiel and hasiotis, 2011; irmis and others, 2011, supplemental data). however, as this mottling occurs well above the top of the shinarump member, it likely does not represent the same episode of paleosol formation, unless the rate of sedimentation following shinarump deposition was much greater here prior to formation of the paleosol. given how thick the cameron member is here compared to lower chinle strata in other parts of southern utah, this possibility cannot be discounted. above the cameron member are mudstone-dominated strata (figure 17a) that have similarities to both the upper part of the blue mesa member at pefo (e.g., martz and parker, 2010) and the uppermost portion of the monitor butte member elsewhere in southern utah. the beds immediately above the cameron member consist mostly of gray mudstone with one thick red sandstone bed (the “friable sandstone” of martz and others, 2015). the uppermost 25 m of the chinle formation consists of the “purple pedogenic beds”— a purple mudstone with abundant carbonate and sulfate nodules and sulfate veins, as is seen in black’s canyon and throughout much of the region (kirkland and milner, 2006; milner and others, 2012; kirkland and others, 2014a). as discussed above, these beds are somewhat similar to the uppermost part of the monitor butte 155 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 member at care and the circle cliffs. the moenave formation section has not been examined in detail by several of the authors, but thick horizontal beds of gypsum occur in the lower part of the dinosaur canyon member as seen in blacks canyon. paleontology as with the shinarump member, the “lower sandstones” contain abundant permineralized wood (figure 18f) and rare vertebrate material, at least some of which has been identified as phytosaurian (deblieux and others, 2005; martz and others, 2015). preservation of permineralized wood is similar to that seen in the monitor butte member in that trees are poorly preserved, and often associated with carnotite and iron oxides. although permineralized wood is common in the shinarump member and in the overlying “lower sandstones,” it is surprisingly rare in the cameron member given that wood is common at the cameron member type section in arizona (j.w. martz and w.g. parker, unpublished data). this may be due to the relatively fine-grained nature of the unit at zion; in the chinle formation well-preserved permineralized logs tend to occur in mediumto coarse-grained conglomeratic channel units, which are a relatively minor component of the cameron member at mt. kinesava. however, poorly preserved permineralized wood with associated orange and yellow oxides (probably carnotite and limonite) has been observed in a drab-colored zone low in the cameron member at zion. this lower zone is unusually rich in organic material with preservation similar to what is seen in the “lower sandstones” at zion and the monitor butte member elsewhere. unidentified plant compression fossils have also been recovered from the cameron member. ash and others (2014) reported a well-preserved specimen of sanmiguelia lewisii from the upper part of the whitmore point member of the moenave formation in zion. this is the youngest record of sanmiguelia, and its first documented occurrence in the early jurassic. small burrow traces including both horizontally and vertically oriented grooves and punctures occur in the fine-grained, ripple cross-laminated sandstone low in the cameron member (martz and others, 2015) as they do in similar sandstone beds in the monitor butte member at care. these burrows may be referable to scoyenia, cylindricum, or the “type 5” burrows that hasiotis and dubiel (1993) identified at pefo. phytosaur and metoposaur material is fairly common in the cameron member, although it is usually too fragmentary to identify an alpha taxon. the metoposaurid material includes vertebral centra that are shorter aneteroposteriorly than wide (figure 6e) (martz and others, 2015), indicating that they are probably referable to koskinonodon or metoposaurus rather than apachesaurus (hunt, 1993). the phytosaur material from zion includes abundant teeth and some postcranial material, none of which can be assigned to an alpha taxon. a large, nearly complete phytosaur skull with mandibles has been recovered (deblieux and others, 2011a, 2011b) from low in the cameron member in the eagle crags area south of zion (figure 6a) (umnh vp 21917). the skull has fairly deep and plate-like squamosals and partially depressed supratemporal fenestrae (martz and others, 2015), indicating that it may be a basal leptosuchomorph (parker and irmis, 2006; stocker, 2010) although martz and others (2015) suggested that it might be a more basal phytosaurid. a possible partial phytosaur humerus has also been recovered from the friable sandstone above the cameron member at mt. kinesava (martz and others, 2015). stop 11 st. george dinosaur discovery site at johnson farm although this paper is an overview of the upper triassic of southern utah, it is also a field trip guide. thus, a stop at the important st. george dinosaur discovery site at johnson farm to view the faunas in the overlying moenave formation was a logical end to the field trip. return down anasazi way to sr 9. proceed 60 km (37 mi) west through rockville, la verkin, and hurricane until reaching the junction with i-15. proceed south about 8.7 km (5.4 mi) on i-15 towards st. george, exit onto sr 212 and turn left to proceed south. this becomes n 3050 e and then curves southwest to be156 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 come riverside drive. the sgds is on the left side of the road about 4 km (2.5 mi) after exiting i-15 (figure 20a). stratigraphy and sedimentology only the uppermost chinle formation (purplish mudstone beds possibly correlating to the purple-colored pedogenic beds at zion) is exposed around st. george. however, the moenave formation (rhaetian to hettangian or latest triassic to earliest jurassic in age) in the area of the sgds is 73.97 m thick, and is divided into the dinosaur canyon member (56.41 m thick) and the overlying whitmore point member (17.56 m thick) (kirkland and milner, 2006; milner and others, 2012; kirkland and others, 2014a). the dinosaur canyon member was deposited by predominantly northwesterly flowing rivers bordering the southwestern edge of the massive erg that deposited the wingate sandstone (clemmenson and others, 1989; blakey, 1994). at the sgds, the predominantly fluvial facies of the dinosaur canyon member is divided into three intervals: (1) a basal conglomerate about 80 cm thick, immediately above the unconformity at the top of the chinle formation, (2) a lower mudstone interval about 34.8 m thick, and (3) an upper sandstone interval about 20.46 m thick (kirkland and milner, 2006; kirkland and others, 2014a). based on a variety of fossil, magnetostratigraphic, and c-isotope chemostratigraphic evidence, the triassic-jurassic boundary lies in the dinosaur canyon member (see milner and others, 2012; kirkland and others, 2014a; suarez and others, 2017). in 1967, wilson described the whitmore point member as a series of thin-bedded shale, limestone, and sandstone that separated the dinosaur canyon member from the overlying springdale sandstone member along the arizona strip and in southwestern utah west of kanab. wilson (1967) also defined the contact between the dinosaur canyon and whitmore point members in the leeds area, utah, as a limestone bed partially replaced by red chert. this bed defines the contact between these members over much of southwestern utah (martz and others, 2015), including at sgds (kirkland and others, 2014a). the whitmore point member at the sgds was deposited by lake dixie, an extensive body of water that formed across a huge area of southwestern utah and northwestern arizona during the latest triassic(?) to earliest jurassic (kirkland and milner, 2006; kirkland and others, 2014a). the whitmore point member at sgds has a lower, complex interval (4.48 m thick) composed of shoreline deposits laid down in subaerial and subaqueous environments that display lake-level transgressions and regressions along the western margin of lake dixie. this lower interval largely represents deepening and then shallowing of lake dixie (kirkland and milner, 2006; kirkland and others, 2014a). above this are a middle sandstone (7.64 m thick) interval and an upper, shale-dominated (6.55 m thick) interval that represents an upper lake cycle that is best developed in the st. george region, thus two major deepening and shallowing cycles are represented (kirkland and milner, 2006; kirkland and others, 2014a). the upper, shale-dominated interval is unconformably overlain by the springdale sandstone member of the kayenta formation (kirkland and milner, 2006; kirkland and others, 2014a). one of the most striking features of the sgds is the relationship of trackways, topography, and the local paleogeography. it is not possible to map the paleogeography at every track level because surfaces are exposed only sporadically and the cost of additional excavation would be prohibitive. however, it is possible to map the “top surface layer,” on which most of the trackways were made by animals walking on an undulating surface. in contrast to this onshore location, an extensive track-bearing continuation of the “main track layer” surface discovered to the northwest on washington county school district and darcy stewart properties preserves abundant dinosaur swim tracks (characichnos; see below) representing an offshore facies equivalent to the onshore surface marked by well-preserved eubrontes tracks (milner and others, 2006c; milner and lockley, 2016). this same marginal lacustrine onshore-offshore relationship can be seen in the sedimentary structures. offshore or nearshore, submerged sedimentary structures include a variety of current and symmetrical ripples (figures 21b and 21c), tool marks (figure 21d), flute casts, and scratch circles (figure 21e). 157 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 20. sgds. (a) map showing location of sgds at st. george. (b) stratigraphic section of the moenave formation in st. george. the acronyms refer to paleontology localities discussed in the text. 158 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 21. common sedimentary structures from the sgds and vicinity. (a) mud-crack natural casts (sgds 10). (b) eubrontes and grallator trackways with current ripples and joints (sgds 18.t1). (c) symmetrical wave-formed ripples (sgds 620). (d) tool mark marks (sgds 262) and sedimentary structures formed by objects such as mud clasts, rock, plant fragments, etc., bouncing and scraping along a submerged substrate. (e) scratch circles (specimen number pending). (f) structures believed to be triclinic sulfate salt-crystal casts, but some researchers suggest they may be the trace fossil lockeia (sgds 40). (g) raindrop impressions around a pagiophyllum conifer branch (sgds 491) (from milner and others, 2012). 159 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 likewise, onshore, subaerial sedimentary structures include mud cracks (figure 21a), possible evaporative salt-crystal casts (figure 21f), and raindrop impressions (figure 21g). many fish remains have been recovered from areas to the north and northwest of the sgds museum site on former darcy stewart, washington county school district, and lds properties, especially from higher stratigraphic levels of the whitmore point member (figure 20b) (milner and others, 2006a, 2006b). this indicates that at the time the “top surface layers” of the johnson farm sandstone bed were deposited, the lake shoreline ran somewhere between the sgds and darcy stewart sites, probably with a north-northeast– south-southwest trend. fish scales have been found in mudstone beds that were deposited directly on the “top surface” tracksites, suggesting a lacustrine transgression soon after track formation (milner and lockley, 2006). further support for this interpretation of shoreline trend comes from trackway orientations, symmetrical wave-form and current ripple marks, and other sedimentary structures (figure 21). on the “top surface” are a series of large ridges and swales with a west-northwest– east-southeast trend, and between the ridges, are abundant, unidirectional current ripples that suggest a somewhat consistent flow pattern toward the west-northwest. other sedimentary structures that support this flow direction include chevron marks, flute casts, and rill marks, all of which formed during high runoff in the direction of the lake (kirkland and milner, 2006; milner and lockley, 2006; milner and others, 2012; kirkland and others, 2014a). locally, this topography has been eroded and reworked by small-scale water action; however, on a much larger scale, the ridges and swales are erosional megaripples that formed during a deeper lacustrine phase by large wave action moving from the northeast toward the southwest across a partially exposed beach shoal or spit (kirkland and milner, 2006; milner and others, 2012; kirkland and others, 2014a). furthermore, symmetrical wave-form ripples (figure 21c), with a n. 30° e. ripple crest orientation, suggest small-scale waves lapping parallel to the paleoshoreline and perpendicular to the ridge-and-swale topography (kirkland and milner, 2006; milner and lockley, 2006; milner and others, 2012). paleontology the sgds has received enormous attention (kirkland and milner, 2006; lucas and others, 2006; milner and kirkland, 2006; milner and lockley, 2006; milner and others, 2006b, 2006c, 2006d, 2012; milner and spears, 2007; kirkland and others, 2014a; harris and milner, 2015; milner and lockley, 2016) as one of the most important jurassic dinosaur tracksites in the world. tracks have been identified on 25 stratigraphic levels in the immediate vicinity of the sgds (figure 20), and many of these layers have been mapped in situ. hunt and lucas (2006) classified the sgds as a konzentrat-ichnolagerstätte, although it could also be considered a konzentrat-lagerstätte because of the abundance of associated plants, conchostracans, ostracods, a variety of fishes, and tetrapod material (milner and spears, 2007). collectively, the sgds provides a window into an early jurassic ecosystem associated with the shores of lake dixie (e.g., milner and spears, 2007; milner and others, 2012; harris and milner, 2015). this is the only tracksite in the western united states that rivals the preservation quality and abundance of the famous lower jurassic sites in eastern north america. dinosaur tracks and other tetrapod footprints considered to be early jurassic in age are well known in the southwestern united states (lockley and hunt, 1995). however, until the sgds discovery, only a small number of tracksites (e.g., the warner valley tracksite; miller and others, 1989) had been scientifically documented in southwestern utah, none of which are in the moenave formation. the sgds site, therefore, fills an important stratigraphic gap in the trackway fossils record in the southwestern united states. four track-producing layers have been recognized in the uppermost part of the dinosaur canyon member at the sgds (figure 20b). two very important localities, walt’s quarry 1 and walt’s quarry 2, named in honor of walter jessop who discovered both sites, were mapped in situ during careful excavation on former darcy stewart property in 2004–2005. part of the walt’s quarry 1 site was recovered as a single, 23.59 metric ton block now displayed in the sgds museum (figure 20a). it was originally mapped and described as having 47 grallator tracks in 11 trackways (milner and others, 160 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 2006d), but remapping in 2011 revealed 58 grallator in 13 trackways, and is one of the most visually spectacular specimens in the sgds collection. part of walt’s quarry 2 was incorporated into a 13.11-m-long by 4.57-m-high wall (sgds 567) during the first phase of the sgds museum construction and development; it now occupies much of the rear (west) wall of the museum building and restoration was completed in 2014. about 200 dinosaur tracks (mostly grallator), fish swim traces, and crocodylomorph tracks are on the blocks comprising this wall. the first tracks discovered at the sgds are from a horizon called the “main track layer” (figure 20b), situated at the base of the johnson farm sandstone bed (kirkland and milner, 2006; milner and others, 2012; kirkland and others, 2014a), a unit that is quite extensive and mapable in the st. george area. tracks from the “main track layer” (figures 22b and 22c) are preserved as robust, natural sandstone casts (positive hyporelief) and associated with mud cracks, possible sulfate salt-crystal casts, flute casts, and many other sedimentary structures. internally the bed displays several 15 to 25-cm-thick sets of climbing ripple bedding as in underlying sandstone in the upper dinosaur canyon member. the johnson farm sandstone bed generally varies in thickness between 30 and 70 cm, although it has been eroded away and infilled by overlying units in some areas at the site. it is well-sorted, fine-grained sandstone about 53 m above the base of the moenave formation (figure 20b). the track casts (figures 22b and 22c) have up to 20 cm of relief and can be seen only after blocks of the johnson farm sandstone bed had been turned over. flipping the massive blocks required heavy equipment and necessitated removing blocks from their original in situ positions to their current locations in the sgds building and elsewhere. several other track layers also occur above the “main track layer,” most notably the stewart-walker tracksite, which occurs approximately 1–1.5 m above the johnson farm sandstone bed upper surface (kirkland and milner, 2006; milner and lockley, 2006; milner and others, 2006d; kirkland and others, 2014a). together, the mapped areas document approximately 3000 tracks (not including some 3000 theropod swim track claw marks) in their in situ orientations and stratigraphic contexts. many of the dinosaur trackways at the sgds parallel the paleoshoreline, although some are perpendicular to shoreline trends. this same kind of trend for trackways is noted at many other tracksites elsewhere in the world (lockley and hunt, 1995). the shore-perpendicular trackways tend to follow the orientations of the ridges and swales on the sgds top surface. although many quadruped trackways also tend to parallel the top surface paleoshoreline, a concentration of batrachopus tracks along ridge tops (i.e., shore-perpendicular) indicate track makers preferentially walked across higher terrain (milner and lockley, 2006; milner and others, 2006d, 2012). tetrapod tracks from the sgds have been assigned to the theropod dinosaur (e.g., olsen and others, 1998) ichnotaxa grallator, eubrontes (figures 22a to 22c), and kayentapus, the ornithischian dinosaur ichnotaxon anomoepus (figure 22d), the crocodylomorph ichnotaxon batrachopus (figure 22e) (e.g., olsen and padian, 1986; olsen and others, 1998; lockley and others, 2004), and the possibly sphenodontian ichnotaxon exocampe (milner and others, 2012; harris and milner, 2015). this ichnoassemblage is remarkably similar to those described by hitchcock (1858) and lull (1953) from the early jurassic of new england and strata of similar age from elsewhere around the world (olsen and others, 2002), including elsewhere in the western united states (lockley and hunt, 1995). theropod tracks from the sgds (figures 22a to 22c) have a remarkable size range. the smallest are only about 1.8 to 3 cm long, but several of these tracks have exceptionally long steps between footprints. in fact, one of the smallest track makers, with a footprint length of 2 cm, has step lengths of 23 to 36 cm, suggesting locomotory speeds of 3.2 to 6.4 m/s presuming animals with hip heights equal to five times track length. another track maker, with a footprint length of 5.2 cm, has a step of 57 cm (milner and lockley, 2006; milner and others, 2006d). other small tracks (footprint lengths 8 cm, including heel traces) have short steps and exhibit metatarsal and hallux impressions (milner and lockley, 2006; milner and others, 2006d). grallator footprints (figures 22a and 22b) are the most common ichnites at the sgds. grallator tracks at the site range in size from 10 to 25 cm long and 8 to 11 161 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 22. tracks from sgds. (a) 23.59 ton-block of sandstone preserving 58 grallator tracks in 13 trackways (sgds 568) (from milner and others, 2012). (b) grallator tracks (sgds 197a). (c) eubrontes natural cast track (sgds 9). (d) anomoepus tracks in situ from the “unit 19 road cut site” (site no. 2 on figure 20) a = anomoepus, g = grallator, k = kayentapus. e. manus and pes set of batrachopus (sgds 170). f. possible synapsid pes track (sgds 190). 162 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 cm wide, whereas eubrontes tracks (figure 22c) tend to have foot lengths >32 cm. very few intermediate track sizes (foot lengths between 25 to 32 cm) are known from the sgds, and few grallator footprints actually exceed 20 cm in length (milner and lockley, 2006; milner and others, 2006d). with no intermediate footprint sizes, this strongly suggests the likelihood that grallator and eubrontes track makers were different theropod species (figure 3, top), and may not represent an ontogenetic series of tracks produced by the same species as suggested by olsen and others (1998). many small, non-dinosaurian tracks have been found at the sgds; most resemble the well-known, early jurassic ichnogenus batrachopus (figure 22e) (olsen and padian, 1986). these tracks typically range from 1 to 5 cm in length, though maximum lengths of about 8 cm are known, although very rare. pes prints, which are more commonly preserved, are always larger than the manus. in fact, the pes sometimes overprints the manus, occasionally leading to misinterpretations of the trackways and the potential track makers. a classic example is selenichnus, described by lull (1953), which was produced by animals passing through a soft substrate. lull (1953) interpreted these tracks as produced by bipedal dinosaurs, but discoveries at the sgds suggest that selenichnus was produced by a quadrupedal crocodylomorph whose pedes overprinted its manus tracks (lockley and others, 2004; milner and others, 2006d). batrachopus trackways are often hard to follow in detail, although several trackways have been recorded at the sgds, including one trackway that can be traced for 5.8 m paralleling the crest of an erosional megaripple on the “top surface layer.” various other quadruped tracks suggest the possibly that there are sphenodontian ichnotaxon exocampe, although the true ichnotaxonomic status of exocampe needs to be resolved. brasilichnium-like footprints (figure 22f) that may have been produced by mammalian relatives (probably cynodont synapsids) are also present at sgds (milner and others, 2012; harris and milner, 2015). “protomammal” tracks are known from other triassic-jurassic boundary sequences in the western united states, though they are most common in eolian deposits, unlike those represented in the whitmore point member of the moenave formation. both batrachopus and the possible “protomammal” tracks are quite common transitioning from walking tracks to swim tracks and vice-versa (milner and others, 2006c; milner and others, 2012). two very important dinosaur track associations are preserved at the sgds. these are abundant swim or floundering tracks and a trackway of a large theropod that stops and sits on the substrate. first, sgds preserves the largest and best preserved collection of dinosaur swim tracks in the world (e.g., milner and lockley, 2006, 2016; milner and others, 2006c, 2012; milner and spears, 2007; harris and milner, 2015), which resolved a long-standing controversy among paleontologists as to what these kinds of structures truly represent. tridactyl swim tracks of dinosaurs are usually arranged in sets of three parallel scrape marks that taper at each end, corresponding to the three functional digits of the theropod dinosaur pes. the longer digit iii left a more elongate and deeper scrape mark compared to shorter digits ii and iv. dinosaur swim tracks from the middle jurassic of england were described and given the name characichnos by whyte and romano (2001). a varying arrangement of theropod swim track morphotypes are represented in the sgds collection showing: (1) animals swimming against a current, (2) animals swimming with the current that produced claw and digit impressions vertically or clear grallator-type footprints with claw scrape marks directed caudally from the footprints, and (3) animals that were swimming cross-current (milner and others, 2006c, 2012; milner and lockley, 2016). many of these swim tracks preserve spectacular details such as skin impressions, scale scratch lines, and details on claw cuticles. the second important association at the sgds is a 22.3-m-long (73.2-ft-long) eubrontes trackway (sgds 18.t1) preserved in situ on the top surface within the sgds museum. this trackway displays very rare tail drag marks along much of its length. near the beginning of this same trackway are crouching traces produced when the track maker sat down on the substrate (on one of the large ridges mentioned previously), then shuffled forward and sat down a second time, creating two overlapping but distinct crouching impressions consisting of pes prints with hallux impressions, ischial callosi163 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 ties, tail traces, and even scale scratch lines (milner and others, 2009). in addition, this unique trace fossil has clear, associated manus impressions (milner and lockley, 2006; milner and others, 2006d, 2009, 2012; harris and milner, 2015). both tail drag and crouching traces produced by theropod dinosaurs are extremely rare, and the manus impressions are unique among known theropod traces (weems [2006] reported possible manus traces associated with kayentapus tracks from the early jurassic of virginia, but the manus impressions lack detail). the track maker proceeded through sediments of differing consistencies and gradients, providing an opportunity to better understand the interplay between sediment consistency, substrate morphology, animal behavior, and track morphology (milner and lockley, 2006; milner and others, 2006d, 2009). the sgds also has a large number of fish swim trails and coprolites. fish swimming traces include fine examples of undichna, formed by the caudal fin (and sometimes other fins) of a fish scraping on a submerged lacustrine substrate (seilacher, 2007), and parundichna, probably made by pectoral and pelvic fins of a coelacanth scraping along a muddy substrate (simon and others, 2003; seilacher, 2007). parundichna traces are known elsewhere from the middle triassic (ladinian) lower keuper of rot am see, baden-württemberg, germany (simon and others, 2003). a moderately diverse compressional flora is preserved in sandstone beds in the upper part of the dinosaur canyon member a few meters below the “main track-bearing surface” (kirkland and milner, 2006; tidwell and ash, 2006). the flora is conifer dominated and includes the holotypes of araucarites stockeyi (sgds.515.a & b), saintgeorgeia jensenii (sgds.627a & b), and milnerites planus (sdds.513a). a low-diversity, invertebrate ichnofauna occurs in close association with tetrapod traces, sedimentary structures, and some body fossils at and around the sgds (e.g., lucas and others, 2006; milner and others, 2012; harris and milner, 2015). an unusual feature of the sgds is the co-occurrence of invertebrate ichnofossils with body fossils in the whitmore point member. most of the associated body fossils are invertebrates, including the ostracods darwinula sp. and cypridoidea indet. (schudack, 2006), and two species of conchostracan euestheria brodieana and bulbilimnadia killianorum (lucas and milner, 2006; kozur and weems, 2010; lucas and others, 2011). extensive collections of early jurassic fishes from the sgds and surrounding area are currently being prepared and studied (milner and kirkland, 2006; milner and lockley, 2006; milner and others, 2006b, 2012; milner and spears, 2007; harris and milner, 2015). fishes that have already received some study include two new species described by milner and kirkland (2006): the hybodontoid shark lissodus johnsonorum (figures 23a and 23b) and the lungfish ceratodus stewarti (figure 23c). other fishes, include one palaeoniscoid (figure 23e), abundant semionotids likely belonging to the genus lophionotus (figures 23f and 23g), and a new, large species of chinlea-like coelacanth (figure 23d) represented by many isolated elements including disarticulated and associated skulls and an articulated caudal fin. although far rarer than the fishes, tetrapod skeletal remains from the sgds have also been recovered, all of which pertain to theropod dinosaurs thus far (kirkland and others, 2005; milner and lockley, 2006; milner and kirkland, 2007; milner and others, 2012; harris and milner, 2015). at least two types of theropod teeth and a single, well-preserved dorsal vertebra (figures 24a to 24c) have been found. the larger teeth, which are conical and sometimes preserve serrations under the right circumstances (figure 24f), have an overall shape similar to those of spinosaurids from the early cretaceous of north africa and elsewhere (figures 24e and 24f), although they are not spinosaurids. teeth like these have not been reported in any early jurassic theropod and thus likely pertain to a new taxon. smaller, serrated, blade-like teeth (figure 24g) may belong to megapnosaurus/syntarsus, fragmentary remains of which have been reported from the dinosaur canyon member of the moenave formation (lucas and heckert, 2001), or to an unknown coelophysoid theropod. it is likely that theropod dinosaurs were entering the waters of lake dixie to catch fish (kirkland and others, 2005; milner and kirkland, 2007). upper triassic vertebrate biostratigraphy in southern utah as previously discussed, the late triassic otischalkian, adamanian, revueltian, and apachean land ver164 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 figure 23 caption on following page. 165 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 tebrate “faunachrons” or biozones of western north america are defined and bounded using phytosaur taxa (e.g., lucas, 1998; parker and martz, 2011; desojo and others, 2013). the biozones have also long been recognized as containing distinctive faunal associations consisting of various alpha taxa of phytosaurs, aetosaurs, metoposaurids, and other late triassic vertebrates (colbert and gregory, 1957; gregory, 1972; lucas and hunt, 1993; lucas, 1998; parker and martz, 2011). although the biozones were recognized in arizona and texas, where the upper triassic vertebrate fossil record of western north america is known best (colbert and gregory, 1957; gregory, 1972; lucas and hunt, 1993; lucas, 1998; parker and martz, 2011; martz and others, 2013), our knowledge of the vertebrate record from the chinle formation of southern utah is rapidly improving. although the biostratigraphic significance of many taxa from southern utah is unclear, a few taxa offer an opportunity for a preliminary assessment of the biozones. the shinarump member of the chinle formation in southern utah and the santa rosa formation of new mexico and texas are probably correlative units (lucas, 1993; riggs and others, 1996). as the santa rosa formation and overlying beds contain basal phytosaurs that diagnose the otischalkian biozone (hunt and lucas, 1991; martz and others, 2013), it is likely that the shinarump member and beds immediately above, including those containing the blue lizard mine in red canyon on the east side of glca (parrish and good, 1987; parrish, 1999) are also otischalkian. doswellia, which occurs in the blue lizard mine (figure 6g), is known from the otischalkian of texas (e.g., long and murry, 1995; lucas, 1998) and from the adamanian biozone in the blue mesa member in pefo (parker and others, 2016), but has not been reported from the revueltian or apachean biozones. the presence of putative basal leptosuchomorph phytosaurs from the monitor butte and lower cameron members (figure 7a) suggests that these units fall within the adamanian biozone (figure 3), consistent with the lithostratigraphic correlation of these units with each other and with the blue mesa member in arizona (lucas and others, 1997a; irmis and others, 2011, supplemental data). however, neither the monitor butte member phytosaur specimens nor the cameron member specimen have been described in detail, and the precise biostratigraphic position of the monitor butte specimens requires further assessment, although the stratigraphic position of the cameron formation skull is well constrained as occurring near the base of the unit (martz and others, 2015). stratigraphic reconnaissance of the circle cliffs indicates that specimens of the aetosaurs calyptosuchus and desmatosuchus recovered there (figure 3) (w.g. parker, unpublished data) probably also occur within the monitor butte member (j.w. martz, unpublished data), although as with the phytosaur specimens the precise stratigraphic horizon of these specimens has not yet been determined. this is also consistent with the near restriction of both aetosaur taxa to the adamanian biozone of texas and arizona (e.g., lucas, 1998; parker and martz, 2011; martz and others, 2013). the spectacular specimen of the paracrocodylomorph poposaurus from the monitor butte member of circle cliffs (figure 8e) (gauthier and others, 2011; schachner and others, 2011) is consistent with this, as the poposaurus is probably restricted to the otischalkian and adamanian biozones (e.g., lucas, 1998; parker and martz, 2011). fragmentary metoposaurid remains seem to be more abundant in the cameron and monitor butte members than in overlying members, again consistent with the relative abundance of metoposaurids in the otischalkian and adamanian biozones in arizona and texas (e.g., hunt and lucas, 1993; lucas, 1998; parker and irmis, 2011). figure 23 (figure on previous page). examples of fishes from the sgds and surrounding areas. (a) holotype specimen of lissodus johnsonorum milner and kirkland (2006) lower left jaw with complete tooth sets (sgds 857). scale bar = 1 cm. (b) lissodus johnsonorum dorsal fin spine in left lateral view (sgds 828). scale bar = 2 cm. (c) holotype ceratodus stewarti milner and kirkland (2006) lungfish tooth plate (umnh-vp 16027). (d) large left angular from a new species of chinlea-like coelacanth (sgds 892). scale bar = 5 cm. (e) nearly complete, unidentified palaeoniscoid fish (sgds 1241). scale bar = 2 cm. (f) nearly complete semionotid fish (sgds 1193). scale bar = 5 cm. g. lower jaw of a semionotid fish (sgds 814). scale bar = 1 cm (from milner and others, 2012). 166 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 the boundary between the adamanian and revueltian biozones has been very well constrained in arizona and texas (e.g., parker and martz, 2011; martz and others, 2013), but is less clear in southern utah because this boundary is defined by the lowest stratigraphic occurrence of the phytosaur machaeroprosopus. species of machaeroprosopus (e.g., m. pristinus and m. buceros) that occur at the base of the revueltian in northern arizona and western texas (e.g., parker and martz, 2011; martz and others, 2013) are unknown in utah. this is figure 24. theropod dinosaur remains from the sgds. (a to d). theropod cranial thoracic (anterior dorsal) vertebra (sgds 768). (a) left lateral view. (b) anterior view. (c) right lateral view. (d) posterior view. scale bar = 3 cm. (e) large theropod tooth (sgds 852). scale bar = 2 cm. (f) large theropod tooth that was broken while still articulated in the jaw. it preserves serrations and wear facets (sgds 1335). (g) small serrated tooth, possibly from a coelophysoid theropod (sgds 851). 167 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 unfortunate as the adamanian-revueltian boundary may indicate a faunal turnover resulting from climatic change or a major bolide impact (olsen and others, 2011; parker and martz, 2011). although it is tempting to correlate the moss back member with the sonsela sandstone bed of the petrified forest member and trujillo formation in arizona and texas (e.g., lucas, 1993) where the adamanian-revueltian transition occurs (parker and martz, 2011; martz and others, 2013), this is conjectural until a precise lithostratigraphic correlation between the moss back member and sonsela sandstone bed can be explored in more detail. the aetosaur typothorax is known from the petrified forest member of care (figure 3) (kirkland and others, 2014b) and from the kane springs beds and church rock member of lisbon valley (martz and others, 2014). this taxon is most abundant in the revueltian and apachean biozones (e.g., lucas, 1993; heckert and others, 2010; martz and others, 2014), although rare occurrences are known in the adamanian biozone in arizona and texas (parker and martz, 2011; martz and others, 2013). the utah occurrences support the placement of the petrified forest member in southern utah into the revueltian biozone, although as previously noted, the exact position of the lower boundary of the biozone is unclear. in southern utah, the base of the apachean biozone, which is defined by the appearance of derived species of machaeroprosopus traditionally referred to as “redondasaurus” (figures 7b and 7c) (e.g., lucas, 1998; martz and others, 2014) is also difficult to precisely place. parker and others (2011) identified a phytosaur skull from the owl rock member in arizona as “redondasaurus,” but in southern utah the stratigraphically lowest occurrences are in the church rock member (martz and others, 2014), which overlies the owl rock member and correlative kane springs beds (e.g., blakey and gubitosa, 1983, 1984). it is unclear if this is because the lowest occurrence of “redondasaurus” or the beginning of owl rock deposition is diachronous between arizona and utah, or if the utah fossil record is merely incomplete (martz and others, 2014). the top of the apachean biozone is difficult to precisely place in southern utah because it is defined by the lowest occurrence of the basal crocodylomorph protosuchus (lucas, 1998), which has not been reported from utah. in arizona, the lowest occurrence of protosuchus is in the dinosaur canyon member of the moenave formation (e.g., clark and fastovsky, 1986; sues and others, 1994; lucas and others, 2005), which overlies the chinle formation. the moenave formation is lithostratigraphically correlative with the wingate sandstone (e.g., blakey, 1994), indicating that the top of the apachean biozone probably occurs within the latter formation as well. the precise placement of the top of the apachean biozone relative to the triassic-jurassic boundary has been difficult, and has relied on various interpretations of fossil and magnetostratigraphic data. however, the triassic-jurassic boundary and the end-triassic mass extinction probably occur slightly after the end of the apachean biozone (milner and others, 2012; kirkland and others, 2014a; suarez and others, 2017). acknowledgments all paleontological field research was undertaken under permits from the national park service, u.s. bureau of land management, and the state of utah. funding for our research in the national parks of utah was provided by the national park service and the utah geological survey. funding for research in the lisbon valley region was provided by the canyonlands natural history association, national geographic, and utah friends of paleontology. alan titus (gsenm) provided permitting for research and collection in the circle cliffs area, and marilyn fox of yale university provided critical collections data that are currently being used to relocate vertebrate material there. susie wisehart of the university of washington and susie hertfelder of the university of nevada, las vegas, were able to arrange access to chinle formation exposures on lake powell, and julia murchie of glca provided transportation. university of houston-downtown students sage muttel, william reyes, heather savage, and jonathan torres provided invaluable assistance during 2016 fieldwork. scientific reviews by russell dubiel, ron blakey, and don deblieux are appreciated. technical reviews were provided by mike lowe, kimm harty, and mike hylland sharpening the prose. 168 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and 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triassic-jurassic boundary in the four corners area, southwestern u.s.a: palaeogeography, palaeoclimatology, palaeoecology, v. 244, p. 111–125. therrien, f., and fastovsky, d.e., 2000, paleoenvironments of early theropods, chinle formation (late triassic), petrified forest national park, arizona: palaios, v. 15, p. 194–211. thomas, h.d., and kruger, m.l., 1946, late paleozoic and early mesozoic stratigraphy of uinta mountains, utah: american association of petroleum geologists bulletin, v. 30, no. 8, p. 1255–1293. tidwell, w.d., and ash, s.r., 2006, preliminary report on the early jurassic flora from the st. george dinosaur discovery site, utah, in harris, j.d., lucas, s.g., spielmann, j.a., lockley, m.g., milner, a.r.c., and kirkland, j.i., editors, the triassic-jurassic terrestrial transition: new mexico museum of natural history and science bulletin 37, p. 414–420. titus, a., eaton, j.g., and sertich, j., 2016, late cretaceous stratigraphy and vertebrate faunas of the markagunt, paunsaugunt, 180 upper triassic lithostratigraphy, depositional systems, and vertebrate paleontology across southern utah martz, j.w., kirkland, j.i., milner, a.r.c., parker, w.g., and santucci, v.l. geology of the intermountain west 2017 volume 4 and kaiparowits plateaus, southern utah: geology of the intermountain west, v. 3, p. 229–291. trendell, a.m., parker, w.g., atchley, s.c., and nordt, l.c., 2010, stop three; lacustrine deposits of the upper blue mesa member—biota, paleosols, and paleoclimatic significance, in trendell, a.m., editor, paleosols and soil surface system analogs: sepm-nsf research conference and workshop, p. 83–88. trendell, a.m., atchley, s.c., and nordt, l.c., 2012, depositional and diagenetic controls on reservoir attributes within a fluvial outcrop analog—upper triassic sonsela member of the chinle formation, petrified forest national park, arizona: american association of petroleum geologists bulletin, v. 96, no. 4, p. 679–707. trendell, a.m., atchley, s.c., and nordt, l.c., 2013, facies analysis of a probable large-fluvial-fan depositional system—the upper triassic chinle formation at petrified forest national park, arizona, u.s.a: journal of sedimentary research, v. 83, p. 873–895. tweet, j.s., santucci, v.l., connors, t., and kenworthy, j.p., 2012, paleontological resource inventory and monitoring—northern colorado plateau network: national park service natural resource technical report nps/nrpc/nrtr-2012/585, 525 p. weems, r.e., 1980, an unusual newly discovered archosaur from the upper triassic of virginia, usa: transactions of the american philosophical society, v. 70, p. 1–53. weems, r.e., 2006. the manus print of kayentapus minor; its bearing on the biomechanics and ichnotaxonomy of early mesozoic saurischian dinosaurs, in harris, j.d., lucas, s.g., spielmann, j.a., lockley, m.g., milner, a.r.c., and kirkland, j.i., editors, the triassic-jurassic terrestrial transition: new mexico museum of natural history and science bulletin 37, p. 369–378. weinbaum, j.c., 2011, the skull of postosuchus kirkpatricki (archosauria: paracrocodyliformes) from the upper triassic of the united states: paleobios, v. 30, no. 1, p. 18–44. weinbaum, j.c., 2013, postcranial skeleton of postosuchus kirkpatricki (archosauria: paracrocodylomorpha), from the upper triassic of the united states, in nesbitt, s.j., desojo, j.b., and irmis, r.b., editors: anatomy, phylogeny, and paleobiology of early archosaurs and their kin: geological society, london, special publications 379, p. 525–553. weinbaum, j.c., and hungerbühler, a., 2007, a revision of poposaurus gracilis (archosauria, suchia) based on two new specimens from the late triassic of the southwestern u.s.a: paläontologische zeitschrift, v. 81, no. 2, p. 131–145. whyte, m.a., and romano, m., 2001, a dinosaur ichnocoenosis from the middle jurassic of yorkshire, uk: ichnos, v. 8, p. 233–234. wilson, r.f., 1967, whitmore point, a new member of the moenave formation in utah and arizona: plateau, v. 40, p. 29–40. wilson, r.f., and stewart, j.h., 1967, correlation of upper triassic and triassic(?) formations between southwestern utah and southern nevada: u.s. geological survey bulletin 1244-d, p. d1–d20. witkind, i.j., and thaden, r.e., 1963, geology and uranium-vanadium deposits of the monument valley area, apache and navajo counties, arizona, with sections on serpentine at garnet ridge and mineralogy and paragenesis of the ore deposit at the monument no. 2 and cato sells mines: u.s. geological survey bulletin 1103, p. 1–171. woody, d.t., 2006. revised stratigraphy of the lower chinle formation (upper triassic) of petrified forest national park, arizona, in parker, w.g., ash, s.r., and irmis, r.b., editors, a century of research at petrified forest national park: museum of northern arizona bulletin 62, p. 17–45. zeigler, k.e., kelley, s., and geissman, j.w., 2008, revisions to stratigraphic nomenclature of the upper triassic chinle group in new mexico—new insights from geologic mapping, sedimentology, and magnetostatigraphic/paleomagnetic data: rocky mountain geology, v. 43, no. 2, p. 121–141. zeigler, k.e., parker, w.g., and martz, j.w., 2017, the lower chinle formation (upper triassic) at petrified forest national park, southwestern u.s.a.—a case study in magnetostratigraphic correlations, in zeigler, k., and parker, w.g., editors, terrestrial depositional systems—deciphering complexities through multiple stratigraphic methods: amsterdam, netherlands, elsevier, p. 237–277. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 10 2023 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana dean r. richmond geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover fossil dinosaur bones were first discovered in the upper jurassic morrison formation near the town of grass range, montana, in 1987. the first excavation commenced in 2003 by the judith river dinosaur institute. the discovery of numerous fossil dinosaur bones and ongoing excavations prompted geologic research in the area. the photograph is of the 2017 judith river dinosaur institute quarry 3 excavation. the quarry is stratigraphically 28 m above the underlying swift formation. large, disarticulated sauropod bones can be seen exhumed from a gray mudstone bed. scales are 1 m and 0.5 m. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 10 2023 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 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state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov editors geology of the intermountain west an open-access journal of the utah geological association volume 10 2023 223 abstract since the discovery of dinosaurs in the late 19th century, the upper jurassic morrison formation has received considerable scholarly attention. however, the formation in central montana needed to be sufficiently investigated. recent dinosaur excavations from exposed morrison strata on the southern flank of spindletop dome near the town of grass range, montana, prompted a review of the formation’s geology, paleobotany, and paleoclimate. a review of historical stratigraphic measurements of the formation in montana reveals a considerable variance in measured thicknesses. stratigraphic measurements and regional log data indicate that the formation averages 71 m thick across central montana. a new regional isopach map of the formation from well-log data illustrates a broad distributive fluvial system that migrated from the southwest toward the northeast. the formation is divided into two informal facies in the study area: lower and upper depositional facies. the lower depositional beds represent the mud-rich distal-most distributive fluvial facies that overlies the stranded muddy tidal flat of the swift formation. an increased sandstone:mudstone ratio and small isolated fluvial channel and crevasse splay beds indicate that the upper depositional beds represent the slow progression of the distributive fluvial system. however, a review of the regional field stratigraphy and well-log data did not provide a regional correlatable facies change to warrant subdividing the formation into members. the stratigraphic positions and climatic interpretations for lithologic, faunal, and floral paleoclimatic proxies are specified. the compilation of climate proxy data from central montana demonstrates that the climate in this region was wetter than in southern parts of the morrison foreland basin. the climatic proxies signify that the environmental conditions were variable during the late jurassic in central montana, displaying changing temperatures with mesic and xeric intervals of unknown duration. stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana dean r. richmond sam noble museum, university of oklahoma, norman, ok 73072 usa; drrichmond@ou.edu. citation for this article. richmond, d.r., 2023, stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana: geology of the intermountain west, v. 10, p. 223–276, https://doi.org/10.31711/giw.v10.pp223-276. introduction the upper jurassic morrison formation, an expansive sequence of terrestrial sediments deposited in foreland basins formed by the north america cordilleran orogenic system, covers approximately 1.5 million km2 of the north american intermountain west (dodson and others, 1980). the formation has been intensely studied for uranium (turner-peterson and fishman, 1986), coal (harris, 1966; silverman and harris, 1966), oil and gas (norwood, 1965; johnson, 2005), and dinosaurs (foster, 2007). since the dinosaur bone wars of othniel charles marsh and edward drinker cope during the 1870s in the newly-opened american west, dinosaurs have been the focus of research and imagina224 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 tion. dinosaurs have been discovered in every u.s. state where the morrison formation is exposed (turner and peterson, 1999). the morrison formation is widespread in montana, but formation surface exposures are limited (woodruff and foster, 2017). as a result, the morrison and the dinosaurs of this northern part of the jurassic foreland basin still need to be better understood. early studies of the morrison formation in montana mentioned dinosaur bones, bone fragments, gastroliths, freshwater bivalves, fossil plants, and seeds (calvert, 1909; fisher, 1909; gardner and others, 1945; brown, 1946; vine, 1956; knechtel, 1959). moreover, in the rocky mountains of southwestern montana, exposures of the morrison strata have been investigated (malone and suttner, 1991; cooley, 1993; smith and others, 2006). however, the stratigraphy and sedimentology of the formation in central montana have received inadequate attention. for example, recently newly discovered carbonate mound springs (i.e., tufa deposits) were described from the formation in central montana (richmond and others, 2021b); however, the stratigraphy and sedimentology of the region were only superficially discussed. montana is well known for its cretaceous-age dinosaurs (sahni, 1972; giffen and others, 1988; horner, 1988; maxwell, 1993; white and others, 1998; schott and others, 2009; jackson and varricchio, 2010, wosik and others, 2017; prieto-marquez and guenther, 2018); limited studies, however, have focused on the jurassic morrison formation and the dinosaurs of the northern part of the foreland basin (turner and peterson, 1999). a new diplodocoid dinosaur, suuwassea emilieae, was discovered in the morrison in south-central montana and described (harris and dodson, 2004; harris, 2006a, 2006b, 2007). several papers describe and discuss the recently discovered hesperosaurus mjosi (previously stegosaurus) from quarry 2 of the judith river dinosaur institute (saitta, 2015 [reported as the jdri 5es quarry therein]; maidment and others, 2016, 2018; woodruff and others, 2019). woodruff and foster (2017) described a remarkably well-preserved camarasaurus dinosaur discovered, excavated, and prepared by judith river dinosaur institute from quarry 1. storrs and others (2012), in their taphonomic assessment of the mother’s day quarry south of billings, montana, discuss an assemblage of 13 disarticulated subadult diplodocus dinosaurs. various invertebrates have been discovered from different localities and described (calvert, 1909; fisher, 1909; yen, 1952; evanoff and others, 1998; good, 2004; richmond and others, 2017). additionally, several fossil wood genera have recently been described from central montana (richmond and others, 2019b, 2019c, 2019d, 2021a, 2022). geologic setting the field study area is located in the southeastern part of fergus county, montana (red box on figure 1a), whereas the subsurface interpretation extends into parts of the surrounding five counties (dashed box on figure 1a). spindletop dome is a small anticline on the eastern flank of the big snowy mountain uplift at the convergence of the rocky mountains and great plains provinces (figure 1b). the morrison formation is exposed along the southwestern hinge zone limb of spindletop dome and in limited outcrops in the surrounding region (figure 1c). the morrison formation is stratigraphically underlain by the middle to upper jurassic ellis group, comprising carbonate and clastic marine deposits of the piper (sawtooth), rierdon, and swift formations. these marine formations were deposited during the inundation and withdrawal of the late jurassic sundance sea. the mid-late oxfordian swift formation consists of shallow-marine shelf sandstone deposits that accumulated during the final transgressive-regressive marine sequence (imlay, 1954; khalid, 1990; fuentes and others, 2011). the swift formation can be divided into four parasequences based on well-log data (n = 212). the first three (offshore, lower, and upper shoreface) are open marine parasequences and coarsen upward (figure 2). the fourth uppermost parasequence is a fining-upward, tidal flat facies (richmond, 2022) (figure 3a). the tidal sequence sandstones are glauconitic, calcite-cemented, angular (0.91), well sorted (0.46), fine-grained (2.76 φ) quartz arenites (n = 8; figures 4a and 4b). the northward retreat of the seaway established a flat planation surface on which the northern morrison sediments were deposited (richmond and others, 2019d). the j-5 unconformity (pip225 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 iringos and o’sullivan, 1978), present at the base of the morrison formation in most southern states, is absent in central montana (dekalb, 1922; imlay, 1954; uhlir and others, 1988; khalid, 1990; meyers and schwartz, 1994; fuentes and others, 2011; this study). the morrison formation in central montana is undifferentiated and consists of non-marine variegated illitic mudstones, thin carbonaceous shale, siltstone, sandstone, freshwater limestone, and coal beds. rapid lateral transitions of terrestrial facies impede the corcat creek oil field sweetgrass arch cinnabar mt. xenoxylon circoporoxylon cupressinoxylon protocedroxylon piceoxylon plant site figure 1. (a) montana regional index map with the main field study area of the morrison formation is highlighted by the red box near the small town of grass range in southeastern fergus county. the map includes locations referenced in the paper as well as index cities. the dashed black box represents the area reviewed with subsurface well-log data. well-log cross sections a‒a' and b‒b' are constructed across central montana (figures 8 and 9). (b) index map of the local research area including some of the physiographic structures referred to in the text. the main focus area is the southern and western limbs of a laramide-age anticline known as spindletop dome. the red box along forest grove road designates a field stratigraphic measurement of the formation. the blue triangle represents the location of the partial stratigraphic measured section i (see figure 10). (c) spindletop dome index map showing the stratigraphic measured sections a through h. section i was measured near button butte (figure 1b). the trees represent the locations of the different fossil wood genera and the plant icon represents the location of the fossil plant site. 226 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 relation of strata over an extensive distance (moritz, 1951). unlike the well-exposed strata of the morrison formation of the colorado plateau, the morrison strata of central montana are usually covered by great plains mixed prairie grasses, dominated by western wheatgrass (pascopyrum smithii) and ponderosa pine (pinus ponderosa). on the spindletop dome, six recently discovered dinosaur quarries are in various stages of excavation. (1) quarry 1 (36 m above the swift formation), where an exceptionally preserved camarasaurus (woodruff and foster, 2017) and disarticulated hesperosaurus limb material (woodruff and others, 2019) was discovered in 2003. (2) quarry 2 (47 m above the swift formation), where a single disarticulated macronarian sauropod and numerous disarticulated hesperosaurus mjosi (saitta, 2015) were excavated. saitta (2015) interpreted the sauropod in quarry 2 to be deposited after the stegosaurs. (3) quarry 3 (28 m above the swift formation), where a disarticulated sauropod was found. preliminary observations suggest the sauropod is similar to haplocanthosaurus. (4) quarry 4 vertebrate fossil material is from an unknown sauropod (approximately 28 m above the swift). (5) quarry 5, 18.5 m stratigraphically above the swift formation, has produced disarticulated material suggestive of camptosaurus. (6) quarry 6 is about 36 m above the swift yielding miscellaneous unidentified vertebrate fossil material. currently, quarries 4‒6 are in the preliminary stages of excavation. all dinosaur excavations have been conducted, and fossil material has swft fm swft tidal flat parasequence swft upper shoreface parasequence swft offshore parasequence rrdn fm 1500 0.2 2000 gr mirror gr (api) rt (ω) den/neu 0.10.3 schye 1 api 25045210180000 lat: 46.13666n, long: 108.80629w swft lower shoreface parasequence northeastern judith basin county 2000 2100 2200 2300 figure 2. the schye 1 well log (api 25045210180000) from the northeastern judith basin county displays the four marine parasequences of the oxfordian swift formation that are present throughout central montana. subsea depths are measured in feet. formation abbreviations are as follows: rierdon (rrdn) and swift (swft). a b figure 3. (a) photograph of the uppermost tidal parasequence of the jurassic swift formation. the uppermost interlaminated siltstone/mudstone beds of the swift tidal mudflat are conformable with the overlying jurassic morrison formation. 1.5 m jacob’s staff for scale. (b) photograph of the k-1 unconformity and the sediments that underly the lower cretaceous kootenai formation’s basal sandstone bed. the fluvial sandstone bed is usually flat-bottomed. meter scale. 227 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 been prepared by the judith river dinosaur institute of billings, montana (see saitta, 2015). the k-1 unconformity (pipiringos and o’sullivan, 1978) separates the upper jurassic (kimmeridgian/ tithonian) morrison formation from the lower cretaceous (aptian) kootenai formation. the amount of time represented by the unconformity is debated. near cut bank, montana (figure 1a), the pre-kootenai erosion has removed the morrison and swift formations (cobban, 1945). near great falls, montana, the k-1 unconformity is angular (harris, 1968). in the study area, thinly laminated, friable sediments are present beneath the basal kootenai sandstone bed, which may represent sedimentation during some stage of the k-1 unconformity (figure 3b). the friable sandstone is a subangular (1.43), moderately sorted (0.70), medium-grained (1.64 φ) quartz arenite with mudstone clasts (figure 4c). geochronological data indicates that the missing time from the geologic record represents 20 ma (fuentes and others, 2011). however, high-resolution biostratigraphic data from terrestrial ostracodes suggests that the unconformity represents less than 10 ma (sames and others, 2008, 2010). the kootenai formation is a terrestrial sequence comprised of mudstone deposits, coarseto medium-grained sandstone beds, and calcrete paleosols and is usually capped by interstratified limestone and dolomite units (dupree, 2009). in north-central montana, the kootenai formation’s lower unit is the cutbank figure 4. (a) photomicrograph of a swift tidal channel sandstone. the sandstone is a calcite-cemented, fine-grained quartz arenite. glauconite is present in varying amounts (green arrows). crossed nichols. (b) photomicrograph of a swift muddy tidal flat sandstone. the sandstone is a calcite-cemented, very fine grained quartz arenite. the intergranular porosity is filled with clay. crossed nichols. (c) photomicrograph of the friable sediments beneath the kootenai basal sandstone (see figure 3b). the sandstone is a medium-grained quartz arenite with mudstone clasts. crossed nichols. (d) photomicrograph of kootenai sandstone which is calcite-cemented, coarse-grained quartz arenite. (e) and (f) photomicrographs of morrison upper depositional facies sandstones. the sandstones are fine-grained quartz arenites. sutured grain contacts are common, suggesting a metasedimentary source. (g) photomicrograph of a morrison lower distal floodplain facies sandstone, which is a coarsegrained, quartz-rich siltstone. (h) photomicrograph of the uppermost quarry 2 sandstone bed showing very thin laminae (< 1 cm) of banded microbialite (cyanobacteria, i.e., stromatolitic) that formed atop the sandstone bed. the sandstone is a fine-grained quartz arenite. 200 µm a 500 µm e 500 µm d 200 µm f 500 µm g 500 µm h c 500 µm b 100 µm 228 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 sandstone member, which consists of cross-bedded, coarse-to medium-grained, quartz arenite sandstone that contains abundant black and gray chert grains (porter and others, 1996). on the sweetgrass arch in northern montana (figure 1a), the oil-producing basal sandstone is called the sunburst sand (collier, 1929). the cat creek anticline oil targets are the kootenai sandstone beds. the cat creek anticline is 64 km northeast of the study area (figure 1a). the sandstone bed targets are locally called the 1st and 2nd cat creek zones (ames, 1993). the nonproductive 3rd cat creek sandstone is stratigraphically equivalent to the basal sandstone and is an artesian water zone (ames, 1993). historically this sandstone bed has received various names; however, herein, it is referred to as the basal kootenai sandstone bed. in the study area, the basal sandstone bed has a variable thickness but can be 30 m thick. there is a marked increase in polycrystalline and microcrystalline quartz grains in the sandstones with a visible distinct “salt and pepper” appearance in a hand sample. the basal kootenai sandstone is a subrounded (2.27), well sorted (0.37), coarse(0.96 φ) to medium-grained (1.27 φ) quartz arenite (n = 2; figure 4d). methods stratigraphic measurements were made using a jacob’s staff and surveyed using a nikon dtm-322 total station. following the conventional practice, the morrison formation includes the terrestrial mudstone, limestone, and sandstone strata between the underlying swift formation and k-1 unconformity (cobban, 1945). in the field, the contact between the swift and the morrison formations is further defined as the top surface of the uppermost glauconitic sandstone bed of the swift formation. in well logs, the top of the swift is marked at the top of the uppermost sandstone bed, identified by a clean gamma-ray profile. since the k-1 unconformity is rarely exposed in the field, it is defined as the bottom surface of the basal sandstone bed of the kootenai formation. in well logs, the top of the morrison formation is selected at the base of a thick, clean gamma-ray profile interpreted to represent the kootenai formation basal sandstone bed. the type well log for central montana is the gorman 11-19 well (api 25027211260000), 7 km southeast of the judith river dinosaur institute (jrdi) quarry 1. the type well log (figure 5) displays the interpreted divisions of the swift and morrison formations and the kootenai formation basal sandstone bed. the transition between the swift and the morrison is often difficult to select in vintage well logs with indistinct curves (e.g., sp, ild). therefore, the swift formational contact was placed at the top of the swift sandstone/morrison mudstone demarcation resulting in a maximum thickness for the morrison formation. a gamma-ray (gr) > 75° api was used in the well logs to classify the log units as sandstone. the percentage of sandstone for the formation was derived from the formational well-log thickness divided by the total footage where the gr log > 75° api and multiplied by 100. in the field, 68 sandstone beds were measured for thickness. twenty-two additional sandstone beds had their width and thickness measured to determine the width:thickness ratio. sandstones used for thin section analysis were obtained from the measured stratigraphic sections. thin sections were prepared by wagner petrographic (lindon, utah) and were examined under a zeiss petrographic microscope. grain-size measurements for the well-cemented sandstones were produced using jmicrovision v1.27 from scaled digital thin-section images. a 300-framework grain point count was performed on each sandstone to determine mineralogy and sandstone classification, according to dott (1964). in thin sections, monocrystalline quartz grains are defined as those consisting of a single crystal. polycrystalline quartz grains have distinguishable crystal aggregates, whereas microcrystalline quartz (chert) grains have no distinguishable aggregate boundaries. three hundred framework grains were measured to determine a grain-size distribution. standard petrology equations (folk and ward, 1957) were used to determine grain-size distribution and sorting. a random 100-grain count determined sandstone grain rounding from digital thin-section images. grains were allocated to a rounding class: 0 – very angular, 1 – angular, 2 – subangular, 3 – subrounded, and 4 – rounded. the average grain roundness was calculated. carbonates are designated using folk’s classification scheme (folk, 1959). 229 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 x-ray fluorescence (xrf) and x-ray diffraction (xrd) of morrison formation sandstones and mudstones were completed by the bureau of economic geology, the university of texas at austin. a thermo scientific niton xl3t ultra analyzer xrf gun was used to measure the elemental abundance of the silcrete, a newly discovered rhyolitic ash, and two rhyolite rocks samples from the yellowstone basin. the device measured each sample for 210 seconds. forty-one elements were measured using the xrf tool. however, only the top nine element percentages are shown and account for greater than 99% of the elements. one hundred meso and macropore diameters of the rhyolitic ash were measured using a digital caliper from hand samples. additionally, 300 micropore diameters were measured using jmicrovision v1.27 from scaled digital thin-section images of the ash. all pore sizes are grouped according to the classification of loucks and others (2012). kate huntington ran the oxygen isotope analyses at the university of washington, seattle. seven carbonate samples were analyzed, but only one produced viable temperature results. palynology samples were processed by vera korasidis at the university of melbourne, australia, and were reviewed by carol hotton from the national museum of natural history. morrison formation stratigraphy stratigraphic measurements of the morrison formation have been defined previously for the more southern states. a historical review of the stratigraphic measurements in montana is presented herein, followed by stratigraphic field measurements and regional well-log data from central montana. historical stratigraphic measurements the morrison formation, named initially by g.h. eldridge (emmons and others, 1896), was correlated to montana by fisher (1909). a historical review of the formation’s measurements is provided herein to show the inconsistencies in the stratigraphic thicknesses of the morrison formation across the state (figure 6). many 20th-century researchers reported a formation thickness for their particular study area/region but provided no location details of their stratigraphic measurements (freeman, 1919; dekalb, 1922; harris, 1966, 1968; silverman and harris, 1966, 1967; suttner, 1969; walker, 1974; lindsey, 1980). in addition, in some references, the morrison formation has been combined with other formations for regional isopach maps (francis, 1956, 1957; peterson, 1966, 1981). the review is presented chronologically, reexamining the stratigraphy of central and southwestern montana and the williston basin. the morrison formation coal beds of central mon70 m ktna basal sand mrsn fm swft fm 1500 0.2 2000 gr mirror gr (api) rt (ω) dt (us/f) 40140 gorman 11-19 api 25027211260000 lat: 46.79102n, long: 108.7544w rrdn fm 30 m 62 m figure 5. the gorman 11-19 well log (api 25027211260000) from southeastern fergus county. the well is 7 km southeast of the judith river dinosaur institute quarry 1 locality. the well log displays the formation thicknesses and log characteristics of the swift and morrison formations and the basal sandstone bed of the kootenai formation. this type well log was the template for the well-derived morrison formational thicknesses utilized for the central montana isopach map (figure 7). formation abbreviations are as follows: rierdon (rrdn), swift (swft), morrison (mrsn), and kootenai (ktna). 230 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 tana prompted the first stratigraphic measurements in the state. fisher (1909; a on figure 6) reported thicknesses from 24 to 36 m bordering the little and big belt mountains. calvert (1909; b on figure 6) measured the morrison formation west of garneill, montana, and specified a thickness of 44 m. lupton and lee (1921) stated the formation is about 45 m thick east of lewistown. however, they did not provide a location. oil finds on the cat creek anticline (lupton and lee, 1921) and in the devils’ basin in central montana prompted reeves (1927) to measure the formation in the region, reporting thicknesses between 60 and 90 m. gardner and others (1945, 1946; c on figure 6) measured numerous stratigraphic sections across south-central and west-central montana. additional morrison stratigraphic measurements can be examined in gardner and others (1946), but only the data from their 1945 measurements are presented herein. gardner (1950, 1959; d on figure 6) measured the formation along forest grove road west of grass range, montana. the 40 236 70 26 d 68 73 f 67 88 c 77 84 c 130 22* 48* 45* 91 95 p 88 58* 49 23 a e helena butte billings miles city montana n 0 200 km 49on49on 47on47on 45on45on 109ow 107ow 105ow 111ow113ow 115ow 109ow115ow 113ow 111ow 107ow 105ow 126 30 49 54 20 20 12 0 e e e 44 b 114hi j j a 86 cc 38 cc c 52 c 64 87 110 109 29 73 c great falls 129 c r k k l n o s 61 s 67 s 61 s 49 e d a 37 c c c c c c 123 k 3527 70 m95 110 c 86c q g g g g 100 22 47 c grass range key: a-fisher, 1909; b-calvert, 1909; c-gardner and others, 1945, 1946; d-gardner, 1950, 1959; e-hadley and milner, 1953; f-miller, 1954; g-scholten and others, 1955; h-hadley, 1956; i-vine, 1956; j-knechtel, 1959; k-moritz, 1951, 1960; l-christie, 1961; m-fraser and others, 1969; n-hobbs, 1967; o-malone and suttner, 1991; p-cooley, 1993; q-smith, 2001; r-maidment and muxworthy, 2019; s-francis, 1957. figure 6. historical stratigraphic measurements of the morrison formation in montana. each letter refers to the author(s) who published the stratigraphic measurement. see the letter key. the letter(s) placement on the map is where the stratigraphic measurement were made by the author. the majority of the measurements were made along structural features where the formation is uplifted and exposed. values with an asterisk (*) indicate interpreted thicknesses. see the text for information pertaining to corrections. the italicized values represent probable erroneous measurements where a corrected estimate could not be determined. red squares represent field measurements, whereas blue squares are data derived from well-log curves. thicknesses are in meters. 231 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 thicknesses are 73 and 68 m, respectively. hadley and milner (1953; e on figure 6) used well-log data (sp and resistivity curves) to determine the formational thickness from central montana to south-central saskatchewan, canada. they noted that the formation was interbedded with glauconitic sandstones. their data suggests they included the uppermost swift formation sandstone beds in their measurements. miller (1954; f on figure 6) measured a detailed stratigraphic section northwest of lewistown, montana in the south moccasin mountains. scholten and others (1955; g on figure 6) measured the morrison in the mountains around lima, montana. hadley (1956; h on figure 6) estimated the morrison to be 114 m from subsurface well logs from the cat creek anticline in central petroleum county. this thicker measurement likely includes strata from the uppermost swift formation. the tidal flat parasequence is challenging to delineate in well logs using only vintage sp and resistivity curves. vine (1956; i on figure 6) measured the formation to be 49 m in central judith basin county. knechtel (1959; j on figure 6) measured the formation thicknesses as 20 and 23 m south of the little rocky mountains, which are east of hays, montana. however, knechtel mentioned glauconitic sandstones were present in the morrison formation. this implies that knechtel, too, may have included the uppermost swift strata in the measurements.   in southwestern montana, moritz (1951, 1960; k on figure 6) measured three sections of the morrison formation with variable results: 22, 82, and 119 m. the two thickest sections each have a “salt and pepper” sandstone bed, one of thickness 11 m and one of thickness 23 m. the kootenai basal sandstone bed is identified in the field by its characteristic “salt and pepper” appearance (fraser and others, 1969; walker, 1974; this study). omitting the “salt and pepper” kootenai sandstone beds from moritz’s stratigraphic measurements yields formational thicknesses between 22 and 58 m. christie (1961; l on figure 6) divided the formation into three informal lithologic units. the basal unit consists of 45 m of “thin-bedded shales, mudstone, limestones, siltstones, and a few sandstones.” the middle unit comprises 45 m of sandstone, and the upper unit includes 61 m of red sandy mudstone. the three units equate to a 151-m morrison section. the lithologic description of the lower unit is analogous to the morrison strata. however, the middle and upper units convincingly describe the basal sandstone bed and red (maroon-colored) mudstone beds of the kootenai formation. therefore, christie’s (1961) morrison formation measurement likely equates to 45 m. fraser and others (1969; m on figure 6) measured 95 m of formation thickness at cinnabar mountain in park county. hobbs (1967; n on figure 6) divided the formation into three informal members northwest of dillon, montana, for a total of 236 m. from this description, it is difficult to discern which member should be correctly identified as the morrison formation. hobbs defines the contact between the morrison and kootenai formations as a gradational contact at the base of a gastropod-bearing biomicrite bed. a freshwater gastropod limestone bed has been described in the upper part of the kootenai formation (cobban and others, 1976). hobbs (1967) likely included most of the kootenai formation in the morrison measurements. malone and suttner (1991; o on figure 6) made several morrison stratigraphic measurements across the willow creek fault zone that was active during the late jurassic. their measurements show the formation varies between 120 and 130 m thick in relation to the willow creek fault zone. cooley (1993; p on figure 6) measured the formation south of livingston, montana. these measurements specify formation thicknesses between 75 and 95 m. smith (2001; q on figure 6) made five stratigraphic measurements of the formation north-northwest of dillon, montana, where the formation averaged 26 m in thickness. maidment and muxworthy (2019; r on figure 6) published a thickness of approximately 20 m for central and southwest montana. francis (1957) generated a morrison formation isopach map for montana and north dakota and saskatchewan and manitoba, canada. the isopach was generated using well-log data and focused on the williston basin. francis’ north-south jurassic strata log cross section shows four well logs along the western flank of the williston basin in eastern montana. the four well logs displayed in the cross section were reviewed for the formation thicknesses (rhodes f-11-6, now the j. heier f-11-6p, api 25019050140000; east poplar unit, 25085050580000; casterline 1, api 25021051650000; macioroski 1, api 25079050380000; s on figure 6). 232 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 francis’ (1957) isopach map shows the thickest strata in southwestern montana, which thins eastward with a zero-edge in central north dakota, southern saskatchewan, and manitoba. according to this isopach map, the formation is estimated to be 61 m thick in the current study area. the review of the historical measurements of the formation shows a wide variation in thickness around the state. the disparity in thicknesses observed on figure 6 is likely related to several factors. first is the possible variation in the paleotopographic surface at the top of the swift formation. second, in some sections, the uppermost swift parasequence consists solely of mudstone, making it challenging to ascertain the formation top. third, the possible erosion and downcutting of the morrison formation during the k-1 unconformity and the subsequent erosion by the kootenai basal conglomerate and sandstone beds. fourth, the basal kootenai sandstone bed is only sometimes in the section. fifth, the structural complexities that include compressional and extensional tectonics (i.e., folding, thrust faults, and normal faulting) are common across the state and can contract or expand sections of the formation. and finally, the complicated geology resulting from the previous factors can result in unintentional erroneous measurements. regional stratigraphic thickness from well logs two complete stratigraphic measurements of the morrison formation were completed in southeastern fergus county. due to the structural complexity of spindletop dome, the first stratigraphic measurement required a composite of several surveyed partial sections made on the southern and western limbs of the anticline. the second section was measured west of grass range along the forest grove road (46°59'52.36" n., 109°4'32.92" w.) from the uppermost swift formation sandstone bed to the basal kootenai sandstone bed. both field measurements determined the formation is 72 m thick in the study area (red triangle on figure 7, richmond and others, 2021b). three hundred and ninety-three well logs from six counties in central montana were reviewed to verify the field measurements (figure 7). the formation thickness, as derived from well-log data, in contrast to the historical field data (figure 6), shows that the formational thickness is relatively consistent across central montana. the median formational thickness across the six-county area is 71 m. both log cross section a‒a' (figures 1 and 8), which trends northwest-southeast across southern fergus and northern musselshell counties, and log cross section b‒b' (figures 1 and 9) that trends southwest-northeast across wheatland, fergus, and petroleum counties, display a relatively consistent thickness in the formation. no discernible faults in the formation were observed in the well logs. undivided morrison formation the morrison formation in montana has yet to be divided into formal members; however, the morrison formation has been divided into a total of eleven members in arizona, colorado, new mexico, south dakota, utah, and wyoming. the most recognized members of the colorado plateau in stratigraphic order are the tidwell, salt wash, and brushy basin members. the tidwell member, named and described by peterson (1988) and recently described by carpenter (2022), does not extend northward into wyoming or montana. the salt wash member was named for sandstone beds of the mcelmo formation (now morrison formation) southeast of the town of green river, grand county, utah (lupton, 1914) and is restricted to the colorado plateau (mullens and freeman, 1957; owen and others, 2015). gregory (1938) named the brushy basin member for the variegated shales in san juan county in southeastern utah. a comprehensive regional investigation of the brushy basin member still needs to be completed, but it likely does not extend north into montana. walker (1974) informally subdivided the morrison formation into lower and upper “members” in the area of great falls, montana. the “lower” morrison consists of mudstone and limestone beds, and the “upper” part of the formation consists of mudstone and sandstone beds. walker proposed that the “lower” morrison deposition was lacustrine, whereas fluvial deposition dominated the “upper” part. malone and suttner (1991) proposed a tripartite division of the formation for the 233 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 northern tobacco root mountains in southwestern montana. they locally divided the formation based on the architectural geometry of lithologic units and siltstone:mudstone ratios on a low-energy terminal fan. the formation was investigated in the grass range region with eight composite stratigraphic sections measured along the southwestern limb of spindletop dome, where the formation is exposed (figure 10). the upper 20 m of the formation dip southward and are often covered by large, displaced blocks of the kootenai basal sandstone. in places, the kootenai basal sandstone blocks form a deflation surface and should not be interpreted as in situ. normal faulting in and around the anticline makes obtaining accurate stratigraphic measurements difficult. the stratigraphic field sections shown on figure 10 provide a general overview of the formation. 0 50 km figure 7. morrison formation isopach map for central montana. formation thickness was derived from 393 well logs from six counties. the median formation thickness in central montana is 71 m. each black dot represents a well location, and the yellow value is the formation thickness in meters. where well locations cluster too close to post values, an average thickness was calculated and posted in the center of the well cluster (blue values). n equals the number of wells in the cluster. the red triangle is the location of the spindletop dome field area. the thin gray dashed line is the outline of the snowy mountains. the isopach contours are thickest in the southwest and thin in the northeast. the data indicate a broad fluvial system prograded northeastward across central montana. 234 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 based on the field observations and measurements, no definable formation division is recommended. the regional well-log data were also reviewed to provide a broader scope to determine if the formation could be divided into members. the regional well-log data shows a coarsening upward sequence in the type well log. a potential subdivision (dashed line on figure 5) may be extrapolated on the log curves locally; however, the marker does not extend across central montana (figures 8 and 9). with no discernible lithologic changes in the formation and the lack of field or correlative log markers, the formation cannot be divided into members. morrison formation sedimentology and geochemistry mudstone sedimentology and geochemistry in the grass range area of montana, the morrison formation is a mudstone-dominated section with thin td = 5848 td = 2800 td = 1810 td = 1420 td = 1650 td = 1550 td = 3870 m r sn sw ft k t n a schye 1 25045210180000 king colony ranch 1-19 25027211730000 mcmillian a1 25027211670000 holland 1-21 25027211620000 n bar ranch 1 25027050070000 gorman 11-19 25027211260000 erin k1 25065216870000 a (nw) a' (se)132 km figure 8. a seven-well log cross section (a‒a'; see figure 1 for the line of section) that extends from central judith basin county across fergus county to the southeast. the cross section passes just south of the field study area and into northcentral musselshell county. the cross section is flattened on the top of the morrison formation. the implied lithologies are derived from the mirrored gamma-ray (gr) curve scaled 0 to 150° api. the thickness of the morrison formation is consistent across fergus county (132 km). the displayed gr curves illustrate that the formation has a low sandstone:mudstone ratio. log total depths (td) are measured in feet. formation abbreviations are as follows: swift (swft), morrison (mrsn), and kootenai (ktna). 235 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 sandstone and limestone beds. the sandstone:mudstone ratio from stratigraphic field measurements is 9%. the regional well-log data (n = 205) specifies a higher average sandstone:mudstone ratio of 25%. the base of the morrison formation in the lewistown area is defined by a mudstone bed (calvert, 1909; freeman, 1919) that extends from the top of the swift formation to the first sandstone or limestone bed of the morrison formation. along the southern flank of spindletop dome and elsewhere in the research area, a reddish illitic mudstone bed is also present. the reddish illitic mudstone bed extends into the morrison formation from the top of the swift formation to 15 m. this formation section generally lacks sandstone beds, with only a few narrow, thin-bedded siltstone beds observed. at the top of the reddish mudstone bed is a sharp, distinct color change to variegated mudstone beds of green, gray, and yellow hues interbedded with thin limestone and sandstone beds (figure 11). additional reddish mudstone beds occur in the variegated td = 8000 td = 7555 td = 2005 td = 1650 td = 2630 td = 2410 m r sn sw ft k t n a bn 1 25027210100000 wegner 3-7 25027210300000 taylor smr 41-24 25027210190000 n bar ranch 1 25027050070000 teigen 1 25027211380000 delaney 3akd 2506520540000 b (sw) b'(ne)116 km figure 9. a six-well log cross section (b‒b'; see figure 1 for the line of section) that traverses southeastern fergus county. it extends from western petroleum county through the field study area in southeastern fergus county into northwestern musselshell, northern golden valley, and northeastern wheatland counties. the cross section is flattened on the top of the morrison formation. the implied lithologies are derived from the mirrored gamma-ray curve scaled 0 to 150° api. the thickness of the morrison formation is consistent along the five-county transect of 116 km. the displayed gr curves demonstrate that the formation has a low sandstone:mudstone ratio. log total depths (td) are measured in feet. formation abbreviations are as follows: swift (swft), morrison (mrsn), and kootenai (ktna). 236 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 units, but these beds are usually localized and less than a few meters thick. a noticeable color and clay mineralogy change from reddish illitic mudstones to variegated smectitic mudstones was one of three marker beds first described by peterson and turner (1993) in the morrison formation of the western interior. the “clay change” usually occurs in the lower part of the brushy basin member of the morrison formation. this change in clay mineralogy has been used as a local and regional marker to place dinosaur quarries in a stratigraphic order within the formation (peterson and turner, 1993; turner and peterson, 1999; richmond and stadtman, 1996; litwin and others, 1998; richmond and morris, 1998; schudack and others, 1998; turner and peterson, 1999) and correlation of depositional facies (demko and others, 2004). however, trujillo (2006) recommends that the morrison formation “clay change” should not be used as a regional correlative tool because clay mineralogy varies laterally and vertically. x-ray diffraction and x-ray fluorescence analyses were completed on mudstone samples for clay identification, mineral, elemental, and rare earth elements (ree). the normalized average clay composition of the formation mudstones (n = 7) is illite (38%), goethite (28%), kaolinite (26%), and smectite (8%). the xrf data indicated no mineralogical change from illite to smectite at the color change. the morrison formation 5e ranch buck creek section a ne 1/4, nw 1/4, se 1/4, sec 35 t13n, r23e, tyler, mt 46°50'32.23"n, 108°46'2.78"w 1:100/100% klakken ranch section sw 1/4, ne 1/4, ne 1/4, sec 24 t13n, r22e, becket ne, mt 46°52'42.89"n, 108°52'14.87"w 5e ranch nw section sw 1/4, se 1/4, nw 1/4, sec 27 t13n, r23e, tyler, mt 46°51'38.43"n, 108°47'58.13"w 5e ranch sw section nw 1/4, se 1/4, sw 1/4, sec 34 t13n, r23e, tyler, mt 46°50'20.14"n, 108°47'41.27"w 5e ranch q2 section e1/2, nw 1/4, sec 34 t13n, r23e, tyler, mt 46°50'46.65"n, 108°47'35.76"w 5e ranch buck creek section b ne 1/4, ne 1/4, sw 1/4, sec 35 t13n, r23e, tyler, mt 46°50'32.68"n, 108°46'14.81"w 5e ranch buck creek section d sw1/4, se1/4, nw1/4, sec 35 t13n, r23e, tyler, mt 46°50'38.02"n, 108°46'5.46"w quarry 4 0 10 20 30 (m ) li th ol og y mud sand cl ay si lt fin e co ar se 15 25 5 quarry 3 0 10 20 30 15 25 5 35 (m ) li th ol og y mud sand cl ay si lt fin e co ar se xenoxylon 0 10 20 30 15 25 5 35 40 45 50 (m ) li th ol og y mud sand cl ay si lt fin e co ar se quarry 1 quarry 2 0 10 20 30 15 25 5 35 40 45 50 (m ) li th ol og y mud sand cl ay si lt fin e co ar se (m ) li th ol og y mud sand cl ay si lt fin e co ar se 20 30 15 25 5 35 40 (m ) li th ol og y mud sand cl ay si lt fin e co ar se 20 30 15 25 5 35 40 20 30 15 25 5 35 40 45 50 (m ) li th ol og y mud sand cl ay si lt fin e co ar se (m ) li th ol og y mud sand cl ay si lt fin e co ar se 5e ranch buck creek section c ne 1/4, ne 1/4, sw1/4, sec 35 t13n, r23e, tyler, mt 46°50'37.39"n, 108°46'23.43"w swift formation morrison formation 10 10 10 15 0 00 0 10 20 30 25 35 40 5 a b c d e f g h xenoxylon piceoxylon 0 10 20 (m ) li th ol og y mud sand cl ay si lt fin e co ar se 15 5 i degner ranch upr. mrsn section se 1/4, se 1/4, nw 1/4, sec 30 t14n, r24e, milk springs, mt 46°56'50.05"n, 108°43'38.51"w mudstone mud-clast conglomeratelimestone silcrete rhyolite ashsandstone 45 50 55 dinosaur bones fossil wood fossil bivalvesrippleslaminar beds figure 10. seven partial stratigraphic sections (a through g) were measured along the southern limb of the spindletop dome (see figure 1c) where the majority of the morrison formation is exposed. the upper 20 m of the formation are often covered by large allochthonous blocks of overlying kootenai formation. partial stratigraphic sections h and i were measured at additional locations. the stratigraphic sections provide a general overview of the sedimentation in central montana. most mudstone and sandstone samples for xrd and xrf were acquired from these sections. 237 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 “clay change” of the colorado plateau does not extend into central montana (turner and peterson, 1999; this study). the major minerals in the formation of mudstones are quartz, illite, goethite, kaolinite, and smectite, with minor percentages of orthoclase, calcite, dolomite, and pyrite (figure 12a). the mudstone’s primary elements are silica, calcium, iron, aluminum, and potassium, with minor percentages of sodium, titanium, sulfur, manganese, and phosphorus (figure 12b). the alkaline earth and transitional metals are barium, strontium, chromium, zirconium, nickel, rubidium, zinc, and vanadium, with minor ppm of cobalt, copper, molybdenum, gallium, niobium, lead, thorium, arsenic, and uranium. yttrium is the only rare earth element present (figure 12c).   sandstone sedimentology and geochemistry the sandstone beds are characteristically thin-bedded, flat-bottomed, isolated single-bodied units. sandstone bed vertical aggradation is uncommon. the average thickness of 68 sandstone beds is 94 cm, with a median thickness of 50 cm. bedforms are usually absent, but some beds display planar or ripple laminations. trough cross-bedding and lateral accretion from point bar migration were observed in only a few sandstone beds. twenty-four sandstone bodies were measured to determine width:thickness ratios. the average sandstone body width:thickness ratio is 13.0. morrison formation sandstones are angular to subangular (0.87‒1.98), moderately well to very well sorted (0.50‒0.25), very fine to fine-grained (3.48‒2.03 φ) quartz arenites (n = 22). grains are cemented with sparry calcite and have low matrix percentages (< 10) (figures 4e and 4f). the grain composition of the morrison sandstones is mainly monocrystalline quartz with low percentages of polycrystalline and microcrystalline quartz. sutured composite quartz grains are common in the sandstones suggesting a sedimentary quartzite source. the quartz-rich sandstone mineralogy indicates a recycled orogen provenance for the morrison sandstones (see dickinson and suczek, 1979). to differentiate morrison sandstones from the underlying swift and overlying kootenai sandstones, percentages of monocrystalline, polycrystalline, and microcrystalline quartz grains can be used (figure 13). x-ray fluorescence analysis was completed on sandstones from the swift (n = 3), morrison (n = 11), and kootenai (n =1) formations for elemental composition. the sandstone samples are in stratigraphic order. all the sandstones are composed of varying percentages of silicon, calcium, iron, and aluminum with minor proportions of potassium, sodium, titanium sulfur, manganese, and phosphorus (figure 14a). the morrison sandstones generally have higher percentages of iron and magnesium than the other formational sandstones. the sandstone’s alkaline earth and transitional metals are barium, strontium, chromium, zirconium, vanadium, and copper, with minor ppm of rubidium, zinc, cobalt, molybdenum, gallium, niobium, lead, thorium, arsenic, and the rare earth element yttrium (figure 14b). uranium, if present, is undetectable. the xrf confirms that the sandstones are quartz arenites. limestone sedimentology thin (< 20 cm) micrite beds are scattered throughout the morrison section, and most of the beds appear to be laterally limited (figure 10). in the lower part of figure 11. the mudstone color change that is prevalent in the study area between the “lower” and “upper” morrison depositional facies. there is no “clay change” (i.e., illite/smectite) as has been observed in the morrison formation on the colorado plateau. this color change can be observed along highway 87 south of grass range, montana, and represents a change in the depositional facies and climate. meter scale. 238 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 the formation, 14.5 m above the swift formation, is a 1.5-m-thick micrite bed with thinly interbedded mudstones (20 cm). the micrite bed may have an area larger than approximately 5 km2, but exposures are limited (stratigraphic section h on figure 10). the micrite beds contain unpaired fossil ostracods and charophyte gyrogonites (johnson-carroll, 2014). the disarticulated bone material tentatively assigned to the diplodocid suuwassea was encased in the top of the uppermost micrite bed. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 5e sc-u2 5e sd-u2 fb sh-u7 5e se-ba 5e se-bb 5e se-bc 5e se fe 5e sf-8 mt mrsm xrf primary elements %si %ca %fe %al %k %na %ti %s %mn %p 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 5e sc-u2 5e sd-u2 fb sh-u7 5e se-ba 5e se-bb 5e se-bc 5e se fe 5e sf-8 mt mrsn xrd mudstone mineral comparison quartz illite goethite kaolinite smectite calcite orthoclase dolomite pyrite 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 5e sc-u2 5e sd-u2 fb sh-u7 5e se-ba 5e se-bb 5e se-bc 5e se fe 5e sf-8 mt mrsn xrf alkaline earth and transitional metals ba sr cr zr ni rb zn v co cu mo y ga nb pb th as u a b c figure 12. graphs of x-ray diffraction (xrd) and x-ray fluorescence (xrf) analyses of mudstone samples for mineral composition, primary elements, and alkaline and transitional metals. two mudstone samples (5e section c and section d are from the lower distal floodplain facies (less than 15 m) above the swift formation. sample fb lm is stratigraphically about 20 m above the swift formation. samples 5e section e-a, b, c, and fe are from quarry 2 stratigraphically at 47 m above the swift formation. sample 5e se-fe is a goethite concretion found in the quarry. sample section 5e f-8 is stratigraphically 55 m above the swift formation. (a) xrd analyses of several mudstones from the study area indicate that the mudstones are composed of illite, goethite, and kaolinite, with minor percentages of smectite. the illite and goethite indicate intense weathering and high organic content. (b) xrf shows the percentages of the primary elements for the formation. (c) xrf graph that displays the distribution of alkaline earth and transitional metals for the formation. element abbreviations are as follows: silica (si), calcium (ca), iron (fe), aluminum (al), and potassium (k), with minor percentages of sodium (na), titanium (ti), sulfur (s), manganese (mn), and phosphorous (p). the alkaline earth and transitional metals are barium (ba), strontium (sr), chromium (cr), zirconium (zr), nickel (ni), rubidium (rb), zinc (zn), vanadium (v), with minor ppm of cobalt (co), copper (cu), molybdenum (mo), gallium (ga), niobium (nb), lead (pb), thorium (th), arsenic (as), uranium (u), and yttrium (y). 239 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 one hundred and seven small (< 3 m diameter) carbonate buildups were discovered in the morrison formation of central montana (richmond and others, 2021b). the buildups are distributed stratigraphically between 40 and 52 m above the swift formation. the mound springs were produced by subartesian groundwater moving up fractures to the surface. bulk rock negative δ18o and δ13c values demonstrate the buildups were produced by meteoric waters in a continental setting, with the groundwater having a short residence time in the subsurface, indicating that the region experienced extended periods of increased precipitation (richmond and others, 2021b; figure 15).   button butte is a prominent laramide uplift 10 km southeast of grass range, montana. southwest of button butte (1.4 km) there are several thin (20 to 50 cm) micrite beds in the uppermost morrison section. the beds are stratigraphically located 56.6 m above the swift formation. the lateral extent is unknown as the outcrop exposure is limited in stratigraphic section i on figure 10. rhyolitic ash bed stratigraphically 38 m above the swift formation is a 20-cm-thick, laterally extensive, coarse-grained, tuffaceous, rhyolitic ash bed (figure 16a). this is the first discovery of an in situ upper jurassic-aged ash in central montana. the majority of magmatism in montana occurred during the late cretaceous and the paleogene epochs. intrusive complexes dominated the late cretaceous followed by volcanism during the paleogene (scarberry and others, 2020). the weathered ash bed surface exhibits dissolution pores with the primary pores ranging from macroto micropore sizes (figure 16b). one hundred mesoand macropore diameters were measured from hand samples. the mean meso/macropore diameter is 4.5 mm with the largest macropore diameter observed measuring 26 mm. three hundred micropore diameters were measured from a thin section indicating the micropores are very fine grained (3.89 φ). in the fine ash, quartz grains are uncommon. in unweathered rock, the pores are filled with gray-green clay. the ash matrix and the pore material were analyzed with xrf to determine the geochemistry. the xrf indicates that the ash is very silica-rich and therefore is classified as rhyolitic ash. xrf was also performed on two yellowstone rhyolitic ashes for comparison. although there is variability in the morrison ash, its chemical makeup resembles the ashes from the yellowstone caldera (figure 17). the pore material was altered to a mixture consisting of silica and aluminum-rich clay. in the thin section, the pore material is coarser grained than the matrix with abundant quartz grains; therefore, the pore material is interpreted to have been lapilli, as opposed to an ash aggregate (figure 16c). morrison formation depositional facies historical review the early researchers of the morrison formation in montana (calvert, 1909; fisher, 1909, freeman, 1919; lupton and lee, 1921; dekalb, 1922; reeves, 1927; gardner and others, 1945, 1946; gardner, 1950, 1959; towse, 1954; francis, 1956, 1957; hadley, 1956; vine, qm qp qmcr mrsn swft ktna figure 13. tertiary diagram displaying the three typical petrographic quartz grain morphologies. the percentages of monocrystalline (qm), polycrystalline (qp), and microcrystalline quartz (qmcr) grains can be used to differentiate the morrison formation (mrsn) from the underlying swift (swft) and overlying kootenai (ktna) sandstones. this change in quartz grain morphology also suggests a change in provenance for each formation. 240 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% swft upr swft upr swft upr mrsn11 mrsn12 mrsn13 mrsn16 mrsn18 mrsn20 mrsn29 mrsn32 mrsn39 mrsn47 mrsn50 ktna lwr mt swft/mrsn/ktna xrf primary elemental comparison %si %ca %fe %al %k %na %ti %s %mg %p 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% swft upr swft upr swft upr mrsn11 mrsn12 mrsn13 mrsn16 mrsn18 mrsn20 mrsn29 mrsn32 mrsn39 mrsn47 mrsn50 ktna lwr mt swft/mrsn/ktna alkaline earth and transitional metals comparison mn ba sr cr zr ni rb zn v co cu mo y ga nb pb th as a b figure 14. x-ray fluorescence (xrf) comparison of the swift (swft), morrison (mrsn), and kootenai (ktna) sandstones. the percentages of the primary elements were derived from the xrf (a), whereas the percentages for the alkaline and transitional metals (b) were normalized from ppm to show the relative abundance of the elements present in the sandstones. the swift sandstones are from the upper part of the formation. the morrison sandstones are labeled by their stratigraphic position above the swift formation (example: mrsn11‒11 m above the swift). the primary elements, alkaline, and transitional metals, are likely related to the availability and solubilities of elements from the soil and groundwater from the decomposition of organic matter that subsequently became incorporated into the sandstone bodies. the elements suggest that the climate was humid and warm with high plant productivity. element abbreviations are as follows: silica (si), calcium (ca), iron (fe), aluminum (al), and potassium (k), with minor percentages of sodium (na), titanium (ti), sulfur (s), manganese (mn), and phosphorous (p). the alkaline earth and transitional metals are barium (ba), strontium (sr), chromium (cr), zirconium (zr), nickel (ni), rubidium (rb), zinc (zn), vanadium (v), with minor ppm of cobalt (co), copper (cu), molybdenum (mo), gallium (ga), niobium (nb), lead (pb), thorium (th), arsenic (as), uranium (u), and yttrium (y). 241 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 1956; knechtel, 1959; moritz, 1960; christie, 1961; mcmannis, 1965; norwood, 1965; ballard, 1966; harris, 1966; silverman and harris, 1967; fraser and others, 1969) provided stratigraphic measurements and lithologic characteristics; however, they did not postulate on the depositional facies but only stated that the formation was a nonmarine or freshwater deposit. moritz (1951) was the first to propose that after the retreat of the sundance sea, southwest montana consisted of a low-gradient plain with fluvial deposits and ephemeral lakes. hadley and milner (1953) proposed that the formation was “lagoonal in character.” peterson (1966) proposed that during morrison's time, a large lake occupied the montana trough during a “moist” climate. silverman and harris (1966) agreed with peterson’s (1966) lake hypothesis but stated that the upper morrison consisted of lacustrine, floodplain, and fluvial channel deposition. harris (1968) stated the formation is comprised of mudstone beds interbedded with freshwater lacustrine limestone and fluvial sandstone beds. walker (1974) reviewed the formation in the great falls area and proposed a lacustrine and fluvial depositional model. a study of the sedimentology of the differing lithofacies and sandstone body architecture in the northern beartooth and gallatin ranges determined the formation was deposited on an anastomosing floodplain (cooley, 1993; cooley and schmitt, 1998). a review of the differing lithofacies of the formation north-northwest of dillon, montana, smith and others (2006) concluded that the depositional facies were the product of a mud-dominated fluvial system of a low-gradient floodplain.  lower distal floodplain facies there does not appear to be a regional stratigraphic marker to subdivide the formation into members; however, locally, there is a distinct and abrupt change in the depositional facies. locally, a thick, laterally extensive reddish illitic mudstone bed (figure 11) rests conformably on the sandstone beds of the upper swift tidal parasequence. isolated small siltstone beds are uncommon. the siltstone/sandstone beds are generally less than 20 cm thick with a minimal limited lateral extent (< 1 m). the siltstones are angular (0.58), moderately sorted (0.61), coarse-grained (4.59 φ), matrix-supported siltstones (n = 2; figure 4g). the sandstones are angular (0.52), well sorted (0.50), fine-grained (2.95 φ), quartz arenites (n = 1). no fossils have been found in the lower unit. the facies association with the swift uppermost tidal flat facies (richmond, 2022) designates that the lower reddish mudstone bed represents a well-drained distal floodplain with its associated very small distributive fluvial channels. no micrite beds were observed associated with the facies. upper fluvial depositional facies the upper depositional facies is also a mudstone-dominated section (≥ 75%) with small sandstone bodies that have an average width:thickness ratio of 13 (n = 24) and thin, flat-bottomed sandstone beds (n = 68). the beds are composed of subangular, well sorted, very fine to fine-grained sandstones. the small sandstone beds that display channel geomorphology have a low width:thickness ratio and sometimes display latfigure 15. a typical carbonate mound spring buildup. this particular mound spring encased a partial fossil log of circoporoxylon. for further information about the mound springs refer to richmond and others (2021b). 50 cm scale. 242 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 eral accretion (figure 18). the beds have abrupt lithofacies transitions and are composed of finer-grained sediments interpreted to represent anastomosing fluvial channels (smith and putman, 1980; smith and smith, 1980; rust, 1981; morris and richmond, 1992; richmond and others, 2020). anastomosing (distributive) sandstone channels have width:thickness ratios of less than 40 (gibling, 2006) and are relatively narrow and deep, with fine-grained sand carried along as bedload in the channel thalweg. channel fills consist of finer-grained sediments (i.e., silt or mud). trough cross-bedding is uncommon. the flat-bottomed, singleand multistory sandstone beds are interpreted to be crevasse splays. herein, flood and crevasse splays are differentiated. during normal flood stages, water tops the channel’s levees, depositing siltand clay-sized particles onto the floodplain (fisher and others, 2008; burns and others, 2019). this repeated flooding results in floodplain aggradation (shen and others, 2015). in contrast, a crevasse splay occurs when the levee wall is breached, cutting down to the channel bottom to release sand-sized sediment onto the floodplain. morrison formation crevasse splay sandstone deposits are flat-bottomed, thin (0.9 m average), usually structureless sandstone beds (richmond and others, 2020). with a few exceptions, the thin, laterally limited micrite beds scattered throughout the section represent interfluve lakes or ponds (flood ponds). lacustrine and palustrine deposition is commonly recorded by mudstone deposition (richmond and others, 2017; hunt and richmond, 2018; richmond and murphy, 2020). the depositional model of anastomosing fluvial channels with associated flood and crevasse splay and interfluve lacustrine micrite and mudstone deposits in central montana agrees with previous depositional interpretations for the formation of western montana (cooley, 1993; cooley and schmitt, 1998; smith and others, 2006). additionally, the fluvial channel geomorphology, sedimentology, and floodplain facies are similar to those of the brushy basin member of the morrison formation on the colorado plateau (kantor, 1995; richmond and morris, 1996) and the kenton member of the morrison formation of oklahoma (richmond and others, 2020). the distributive fluvial system model has been used a b c 100 µm figure 16. (a) field outcrop of a 20-cm-thick, laterally extensive, coarse-grained, tuffaceous, rhyolitic ash bed stratigraphically 38 m above the swift formation. (b) a hand sample of the rhyolite ash. the meso and micropores from the weathered lapilli are clearly discernible. 5-cm scale. (c) photomicrograph of a lapilli clast surrounded by a fine ash groundmass. crossed nichols. 243 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 to characterize the deposition of the salt wash and brushy basin members of the colorado plateau and the kenton member of oklahoma (owen, 2014; owen and others, 2015; richmond and others, 2020). the northeastward thinning of the morrison formation (figure 7) and the interpreted depositional model support the northeastward progradation of a broad fluvial system across central montana. furthermore, the uniform formation thickness across central montana implies that numerous fluvial channels migrated across the broad, flat floodplain providing fine-grained sediment across the region.  discussion: morrison paleoclimate proxies morrison basin paleoclimatic overview based on climate models and lithologic proxies, many researchers have proposed the morrison foreland basin experienced a semiarid to arid zonal climate (parrish and others, 1982, 2004; parrish and peterson, 1988; demko and parrish, 1998; turner and fishman, 1991; valdes and sellwood, 1992). to support the giant herbivorous dinosaurs which roamed the morrison basin, some researchers have proposed that there were riparian environments that supported abundant plant life (peterson and turner, 1987). by the late jurassic, north america’s northward movement fragmented the triassic monsoonal climate pattern resulting in a low-pressure cell over the continent (parrish and peterson, 1988). modeled temperatures for western north america during the late jurassic ranged from 5oc (winter) to greater than 36oc (summer) and were about 5oc warmer than at present (demko and parrish, 1998). temperature independently does not account for the aridity of western north america during the late jurassic. the aridity was likely generated by several factors, 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% mtx a mtx b mtx c mtx d pore a pore b pore c pore d pore e ysr-1 ysr-2 mt mrsn rhyolite ash xrf data si% al% k% ti% ca% mg% fe% s% ba% figure 17. x-ray fluorescence analyses of the morrison ash bed. the high silica percentages of the ash matrix (mtx a through d) indicate that the ash is rhyolitic. the xrf of the lapilli (pore a through e) indicates it altered to a high silica and aluminum clay. two rhyolites from the yellowstone basin (ysr-1 and ysr-2) as shown for comparison. the nine mineral percentages represent 99% of the rock. element abbreviations are as follows: silica (si), aluminum (al), potassium (k), titanium (ti), calcium (ca), magnesium (mg), iron (fe), sulfur (s), and barium (ba). 244 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 including the latitudinal position in the subtropical dry belt, the sevier orogenic belt acting as a rain shadow (demko and parrish, 1998), and oceanic upwelling driven by coastal wind patterns, which would have increased the aridity of western north america (parrish and peterson, 1988). using eolian lithologic units from the tidwell, salt wash, bluff sandstone, junction creek, and recapture members of the morrison formation, a westerly wind direction was ascertained for the late jurassic of north america (parrish and peterson, 1988; peterson, 1988). these eolian units of the morrison are stratigraphically in the lower part of the formation (demko and parrish, 1998). a zonal climate model by parrish and others (1982) predicted low rainfall patterns for much of the morrison basin during the volgian regional stage (tithonian). they also mapped evaporates and coals for the same stage, and the spatial representation for these proxies corresponds to a tithonian zonal climate. further geologic evidence for a dry climate is the large saline lake, lake t’oo’dichi, demarcated by diagenetic zeolites and feldspars, indicating the lake underwent repeated wetting and drying under arid conditions punctuated by episodic rainfall (turner and fishman, 1991). richmond and morris (1998) reported similar findings at the dry mesa dinosaur quarry. the quarry is located on the northeastern margin of lake t’oo’dichi and records an extreme drought (phase 3; shipman, 1975) in which 30 genera of vertebrates, including dinosaurs, pterosaurs, crocodiles, lungfish, and mammals, died at a local waterhole. following decomposition and disarticulation, their bones were transported for a short distance by a catastrophic flash flood and were buried. additional evidence for drier climatic intervals is the presence of evaporite-associated chert beds (magadi-type cherts). evaporite-associated chert beds have been reported from the morrison formation in wyoming (surdam and others, 1972), colorado (dunagan and others, 1997), and oklahoma (richmond and others, 2019a, 2020). these evaporite-associated cherts form in a shallow acidic (ph > 9) phreatic zone as a result of the silicification of sulfate evaporites (anhydrite). the antecedent lacustrine evaporites designate prolonged periods of increased evaporation due to increased temperature or decreased precipitation. gypsum mineralization signifies a mean annual precipitation of less than 350 mm/year (gu and others, 2015). in contrast, other lithologic evidence supports the presence of perennial fluvial, pluvial, and lacustrine facies in the morrison basin (lockley and others, 1984, 1986; dunagan, 1999; dunagan and turner, 2004; gorman, 2007; gorman and others, 2008; richmond and others, 2020). several paleolakes have lacustrine ooid facies (lockley and others, 1984; 1986). ooids can take over a thousand years to form (neese and pigott, 1987), suggesting a long-term presence for these paleolakes. the first tufa deposits for the morrison formation have been identified in central montana and are indicative of a high groundwater table (richmond and others, 2021b). there is also an indication of ephemeral deposition, particularly from fluvial and pluvial deposits signifying seasonal or episodic precipitation was sufficient for fluvial deposition and the wetting of ponds (richmond and morris, 1996; richmond and others, 2020). dodson and others (1980) suggested a strongly seasonal climate based on dinosaurian fauna and taphonomy. however, some dinosaurs are assumed to have been migratory (bronzo and others, 2017). therefore, their presence or absence from a region should not be used as lateral accretion figure 18. an example of an anastomosing fluvial channel bed in the morrison formation. the lateral accretion direction is to the north. typically, the small fluvial channel beds are isolated in a mudstone-dominated section. the sandstone bed is stratigraphically 34 m above the swift formation. the outcrop is exposed along the tyler cut road, southwest of grass range, montana. meter scale. 245 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 evidence to infer paleoclimate. the presence of aquatic vertebrates, e.g., crocodiles (dunagan, 1999; connely, 2002; hunt and richmond, 2018), turtles (gaffney, 1979; hunt and richmond, 2018), lungfish (kirkland, 1987), boney fish (small and others, 2007, gorman and others, 2008), and amphibians (hecht and ester, 1960) are generally associated with their aquatic environment and indicate perennial lakes and rivers were present in the morrison basin (gorman and others, 2008; richmond and others, 2020). aquatic invertebrates have specific environments in which they live (evanoff and others, 1998; schudack and others, 1998; good, 2004; richmond and others, 2017) and usually require clean perennial lakes and rivers to survive. aquatic invertebrates are present throughout the morrison basin (evanoff and others, 1998). horsetails, ferns, cycads, and various large gymnosperms indicate sufficient precipitation for growth. according to tidwell (1990), the abundance of plant fossils in the formation indicates a humid, tropical climate. a newly described fossil wood, agathoxylon hoodi, from the salt wash member of the morrison formation in eastern utah infers a warm equable climate for the eastern basin lowlands (gee and others, 2019; sprinkel and others, 2019). three fossil wood genera were newly discovered in close proximity to one another in the boise member of the morrison formation in western oklahoma. the occurrence of three fossil wood genera, xenoxylon meisteri, cupressinoxylon, and agathoxylon, in the same stratigraphic horizon, indicates a period of increased precipitation at the southern basin periphery during deposition of the boise member (richmond and others, 2018, 2020). different regions of the morrison formation have been explored for palynology (newman, 1972; tschudy and others, 1980, 1988; hotton, 1986; litwin and others, 1998; baghai-riding and hotton, 2009, 2011; hotton and baghai-riding, 2010, 2016; baghai-riding and others, 2013, 2014, 2015, 2018) the majority of the data indicates arid climatic conditions for the formation with wetter conditions in the more northern part of the foreland basin. demko and parrish (1998) suggested plants only represent a small spatial and stratigraphic part of the formation and are inconsequential to the overall climatic interpretation. climatic proxies require a stratigraphic and areal position, and although there were intervals and regions where the formation was wetter, overall, the morrison of the southern states and colorado plateau is considered semiarid to arid (column a on figure 19). in the following sections, climate proxies will be addressed in order of lithologic proxies, faunal and floral proxies, and will be, where applicable, presented in stratigraphic order. each proxy will be first described and then followed by its climatic interpretation. lithologic climatic proxies sandstone geochemistry sandstone geochemistry is a compilation of sandstone mineralogy, groundwater chemistry, and diagenetic fluids. the sandstones are quartz arenites with low percentages of the interparticle matrix, and there is no evidence of diagenetic overprinting on the sandstones. the primary elemental percentages are derived from the sandstone’s composition (see figure 14a). the alkaline earth metal barium and the transitional metal manganese together typically make up more than 50% of the alkaline earth and transitional metal elements (see figure 14b). the high percentages of these two elements may be related to the availability and solubilities of these elements from the soil and groundwater as byproducts of the decomposition of organic matter. therefore, the mobilization pathways of these elements are evaluated. the accumulation of organic materials is chiefly a function of the annual litterfall minus decomposition. the most sizable proportion of allochthonous organic matter is from foliage, seeds, branches, and bark. the main litterfall contribution is from the overstory, with understory plants supplying about 10% (binkley and fisher, 2019). storms can accelerate litterfall volumes, whereas elevated temperatures and soil moisture can hasten decomposition rates. conversely, ground fires can consume organic materials. annual litter production can be related to latitude. during the late jurassic, central montana was at a paleolatitude of 50o north (richmond and others, 2019d). most modern conifer forests have an annual litterfall of 1975 to 5900 kg/hectare/year (binkley and fisher, 2019); however, a temper246 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 ate forest at 50o north latitude generates 3700 kg/hectare/year (bray and gorham, 1964). the rate of organic decay depends on the interaction of physical factors, water chemistry, and biological agents. decomposition can be rapid, with turnover rates varying between 1 to 3 years for cool temperate climates (binkley and fisher, 2019). litterfall on the forest floor is fragmented by arthropod and annelid decomposers, then consumed by rotifers and pervasive microbes. the top organic soil layer comprises undecomposed litter that overlies the fermentation layer, where decomposition occurs. this layer overlies the humus layer, where decay is nearly complete. in boreal forests nutrient turnover is slow. potassium and sodium are quickly leached from the soil. nitrogen, phosphorus, sulfur, and magnesium are released into the soil after a long period. iron, zinc, and copper are left in the accumulated litter material (staaf, 1980). barium and manganese are related to vegetative cycling. barium concentrations are controlled by soil acidity but also by the concentration of sulfates (guyette and cutter, 1994; jennings and others, 2015). according to jennings and others (2015), barite formation occurs in exposed wetland, lacustrine, and coastal plain environments. wetlands contain sulfate-reducing microorganisms resulting in a high sulfate reduction rate (pester and others, 2012). sulfate-reducing microorganisms may limit the sulfate concentration in groundwater and lower the soil’s barium concentration. manganese is an essential plant nutrient in the bole wood and foliage (guyette and cutter, 1994). the subsurface geology controls soil manganese concentrations and increases vegetation cycling (richardson, 2017). the soil ph controls its solubility and concentrations, with more acidic soils greatly influencing potencies (guyette and cutter, 1994). soils in wet climates are typically acidic, whereas in dry climates, the soils are alkaline (richmond and others, 2021b; slessarev and others, 2016). the high mobilization of manganese and barium demonstrates the presence of acid soils, which are indicative of a wetter climate. interestingly, a lower morrison splay sandstone bed stratigraphically 18 m (sample mrsn18 on figure 14b) above the swift formation and 1.5 m above a lacustrine limestone bed has a high percentage of copper. copper climate proxies 0 10 20 30 40 50 60 70 h ei gh t a bo ve s w ift f or m at io n (m ) a ib c d e f g h j k l m n o p q r s t u arid/semiarid (bwh/bsh) dry subtropical (csa) humid subtropical (cfa) temperate (csc) “wet” figure 19. summary of the central montana morrison climate proxies displayed in stratigraphic position with their interpreted ranges. the colors and climate categories follow the köppen-geiger climate classification system (beck and others, 2018). the climate codes are bwh/bsh: b (arid), w (desert), h (hot); b (arid), s (steppe), h (hot); cfa: c (temperate), f (fully humid), a (hot summer); csa: c (temperate), s (dry summer), a (hot summer); csc: c (temperate), s (dry summer), a (cold summer). whereas “wet” signifies that there was sufficient precipitation for the formation of local lakes and flooding of rivers. to associate the climate codes to modern locations, the bwh/bsh climate is analogous to the deserts of the southwestern u.s. and northwestern mexico; the cfa climate is comparable to the climate of houston, texas, and the coastal states; and the csc climate is similar to the climate of the mediterranean where summers are cool and the majority of precipitation is received during the winter months. the overall climatic interpretation for the morrison formation of the colorado plateau is provided in column a. sandstone and mudstone geochemistry proxies are combined in column b. 247 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 is an essential element for plant growth, and soils naturally contain copper ranging from 2 to 100 ppm and averaging about 30 ppm. this sandstone has greater than 900 ppm copper (figure 14b). acidic soils are more likely to be deficient in copper, but a higher ph with humid and wet climatic conditions supports copper concentrations in soils (ballabio and others, 2018). the more alkaline ph may be due to its stratigraphic proximity to the lacustrine limestone and not a drier climate. the sandstone alkaline earth and transition metals concentrations suggest a wet environment with associated high plant productivity. vegetation decomposition leeched minerals into the soil and groundwater and subsequently into the fluvial channels to become incorporated into the sandstone bodies. the sandstone geochemistry suggests a humid subtropical climate was pervasive during the deposition of the upper fluvial depositional facies (column b on figure 19). mudstone geochemistry the distinct clay mineral type and abundance in any deposit depend upon three major factors: provenance, transformation, and neoformation. clay minerals can be a reliable indicator of provenance and depositional environments (chaudhri and singh, 2012). illite is the allogenic product of weathering feldspathic and micaceous crystalline rocks under cool/temperate and dry conditions (chaudhri and singh, 2012; raigemborn and others, 2014). kaolinite is the byproduct of in situ weathering of feldspars, micas, smectite, and other volcanic material under warm and mesic conditions (singer, 1980, 1984; raigemborn and others, 2014). in addition to the three principal clays of the morrison formation, mudstones of the formation in central montana also have significant percentages of goethite (figure 12a). the two most common pedogenic fe-oxides in soils are hematite and goethite. hematite formation is facilitated by alternating wet (less than 350 mm/year; wu and others, 2018) and dry environmental conditions under warm to hot temperatures (zhao and others, 2017). the presence of hematite contributes a predominantly reddish hue to soils. in contrast, goethite is formed under continuously wet conditions under a wide range of temperatures and gives a yellowish reflectance to the soil (zhao and others, 2017; wu and others, 2018). the mudstone strata of the well-drained distal floodplain depositional facies (< 15 m) are locally a deep reddish color (figure 11). in contrast, the upper fluvial depositional facies are variegated with hues of green, gray, yellow, and red (figure 11). stratigraphically percentages of goethite tend to increase higher in the upper fluvial section (figure 12a). the mudstone color change from red to variegated hues may signify a climatic change from alternating wet and dry to continuously wet conditions. soils with a high organic content tend to favor goethite formation over hematite. analysis of channel geomorphology and channel fill can determine the climatic regime under which the anastomosing fluvial systems were deposited; however, the associated floodplain facies give the strongest signal. in mesic regions, interfluve sediments consist of lacustrine and palustrine deposits; coals are often present (smith and smith, 1980; north and others, 2007). in arid environments, there is a general absence of levees. as a result, crevasse avulsions, lacustrine, palustrine, and organic deposits are primarily absent from the floodplain (rust, 1981; nanson and others, 1986; north and others, 2007). in central montana, morrison interfluve sediments comprise crevasse and flood splay deposits, lacustrine, palustrine, and organic-rich deposits. x-ray fluorescence data of the mudstones (b paleosol horizons) can be used to calculate the chemical index of alteration minus potassium (cia‒k) and the calcium and magnesium weathering index (calmag). these values have been used to estimate mean annual precipitation (map) for the morrison formation in north america (myers, 2009; myers and others, 2012b, 2014) and the lourinhã formation in portugal (myers, 2009; myers and others, 2012a). the estimated mean annual rainfall for northern wyoming and southern montana was greater than 1200 mm/year (myers and others, 2012b, 2014). the central montana cia‒k values range from 57 to 86, averaging 73. the calculations provide a cia‒k map estimate between 759 to 1270 mm/year with an average of 999 mm/year. the calmag values range from 53 to 91, averaging 74. the calmag calculations yield map estimates between 775 to 1625 mm/year with an average of 1234 mm/year (table 1). 248 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 a review of the stratigraphic position of the samples in table 1 shows that the mean annual precipitation was not constant throughout the section. however, the average cia‒k map (999 mm/year ) and calmag map (1234 mm/year) correlate with the estimates for the region derived by myers and others (2014). mudstone geochemistry, interfluve sedimentation, and calmag data show a predominantly humid subtropical climate for the formation (column b on figure 19). micrite and mudstone beds west of spindletop dome along the tyler cut road, stratigraphically at 14.5 m, is a 6-m-thick section of interbedded micrite and mudstone beds (johnson-carroll, 2014). some micrite beds are fossiliferous, containing small bivalves, ostracods, and charophyte gyrogonites, whereas others appear unfossiliferous (johnson-carroll, 2014). the lateral extent of the micritic section is unknown due to the lack of outcrop exposures but is estimated to be at least 10 km2. the micrite and mudstone section represents shallow lacustrine and subsequent palustrine depositional facies. also associated with these beds are the vertebrate fossils (?suuwassea, and an identified ornithopod dinosaur) and the fossil wood, xenoxylon meisteri. above the lacustrine/palustrine facies at 19 m is a greenish illitic mudstone bed. the mudstone bed contains abundant invertebrate fossils. the mudstone bed, with its numerous invertebrate fossils, is interpreted to be a flood splay deposit that transported the fossils (richmond and others, 2017). the invertebrate fossils and their paleoclimatic interpretation will be discussed below. the lacustrine/palustrine depositional facies recorded the transition from shallow ponds to wetlands and a fluvial floodplain documenting a flooding event. the facies transition may be due to sediment infilling of the lake or as a response to a drier paleoclimatic trend. the presence of a small lake, associated wetlands, and splay events indicate high precipitation during the deposition of these strata (column c on figure 19). mud-clast conglomerate bed southwest of quarry 2 is a meter-thick, mud-clast conglomerate bedset stratigraphically 21 m above the swift formation (see stratigraphic columns e and f on figure 10). the bedset is divided into numerous beds sample strat. (m) al2o3 (wt%) cao (wt%) mgo (wt%) na2o (wt%) cia-k cia-k map (mm yr-1) calmag calmag map (mm yr-1) mrsn mm36 < 15* 16 0.78 1.45 0.36 91.69 1270.39 86.3 1522.26 mrsn mm38 < 15* 11.94 8.97 1.46 0.26 56.39 766.72 53.36 774.88 mrsn 5e sec c 13.5 7.61 1.78 -0.02 1.24 71.54 982.87 81.15 1405.49 mrsn 5e sec d 16 11.76 8.25 0.14 1.05 55.87 759.33 58.39 889 mrsn klkn bv 19 14.5 4.99 1.65 0.34 73.13 1005.52 68.6 1120.69 mrsn 5e sec b 28 15.85 1.42 1.63 0.28 90.32 1250.77 83.87 1467.24 mrsn 5e sec e 47 9.85 6.5 -0.04 1.05 56.6 769.78 60.39 934.48 mrsn 5e sec e 47.5 14.9 4.68 0.22 1 72.4 995.14 75.25 1271.56 mrsn 5e sec e 48.5 14.45 4.29 -0.16 1.04 73.07 1004.68 77.77 1328.86 mrsn 5e sec f 55 14.86 1.45 0.51 1.02 85.77 1185.86 90.84 1625.32 average 72.68 999.11 73.59 1233.98 table 1. ten mudstone samples were used for cia-k mean annual precipitation and calmag mean annual precipitation. the samples mrsn mm 36 and 38 are from highway 87 and mile markers 36 and 38, respectively. these samples are interpreted to be from the morrison lower distal floodplain facies. sample mrsn klkn bv is from the bivalve location off tyler cut road. the other samples are from the measured stratigraphic sections shown on figure 10. each measurement is provided stratigraphically in meters above the swift formation. data from the formation displays a high average precipitation for the region. 249 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 of rip-up conglomerate, fine-grained sandstone, and mudstone (figure 20). the bedset represents a proximal crevasse splay deposit produced from multiple flooding events. no correlative fluvial channel has been recognized. the repeated flooding indicates high, possibly seasonal, precipitation (column d on figure 19). silcrete bed a reddish illitic mudstone bed is capped by a 20-cm thick, laterally extensive, silcrete bed. the silcrete bed is stratigraphically 23 m above the swift formation. the parent rock is a subangular (1.34), moderately well sorted (0.60), very fine grained (3.95 φ) quartz arenite. in a hand sample cross section, the silcrete exhibits angular and subangular blocky microstructures resulting in ped blocks and nodules that range in size up to 20 mm (figures 21a and 21b). in the thin section, the microstructure matrix is light and dark (figures 21c and 21d). figure 21c shows an annealed fracture, whereas figures 21d and 21e display fractures filled with organic-rich sediments. additional interesting features observed in the thin section are concentric rings (figure 21f) interpreted to be the initial stages of concentric nodule formation. the silcrete ped block (figure 21a, site 1) and the microstructure matrix (figure 21a, site 2) were analyzed by xrf. both the ped block and microstructure matrix have high percentages of silica. however, the moderate reddish-orange matrix (figure 21a, site 2) has higher percentages of aluminum, titanium, calcium, and iron (figure 22). silcretes form in the phreatic zone associated with soil formation and require stable geological conditions for an extended time (milnes and thiry, 1992). silcrete customarily forms in arid or semi-arid climates according to numerous cenozoic studies of silcretes in southern africa, australia, and elsewhere (summerfield, 1983; trewin and fayers, 2005). however, silcretes also form where there is an abundance of water and organic acids. the water, which may be seasonal, is required to migrate organic acids and mobilize silica. the organic acids, formed by copious plant life, enhance quartz dissolution but not its solubility (taylor and eggleton, 2017). in topographically low areas, near fluvial systems or lakes with slow-flowing or stagnant water and abundant plants, organic-rich water produces the acidic reducing conditions for silica dissolution. silica-saturated alkaline groundwater (ph ≥ 9) precipitates silica, especially when mixing with a lower ph surface water. these added ions will facilitate the silica precipitation if aluminum, iron, magnesium, or sodium chloride ions are also present (trewin and fayers, 2005; taylor and eggleton, 2017). metallic oxides, such as aluminum, titanium, and iron, are most common where the climate is warm and wet but unusual at higher elevations and cool temperate zones (ségalen, 1971). titanium comprises about 0.57% of the earth’s crust. therefore, a concentrated titanium weight percent in silcretes is typical. australian silcretes have an average weight percentage of 1% (taylor and eggleton, 2017). the montana morrison silcrete samples have high concentrations of titanium at 1.4% and 5.5%. titanium is mobile in weathering environments with a ph less than 4, but between a ph of 4.7 and 6.7 (figure 22), titanium hydroxyls tend to be absorbed in silica because silica and titanium have opposite charges over this ph range. a highly acidic environment in which titanium is soluble and incorporated into silcrete suggests abundant vegetation and a mesic to subtropical climate (summerfield, 1983). figure 20. the outcrop of a crevasse splay mud-clast conglomerate bed. the meter-thick bed is stratigraphically 21.5 m above the swift formation (stratigraphic column f on figure 10). the collated layers show numerous repeated splay flooding on the proximal facies. 40 cm ruler for scale. 250 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 blocky microstructures often form by contraction from sediment desiccation (stoops and others, 2010). vertisols repeatedly crack and swell in response to desiccation and precipitation with successive wet and dry cycles, gradually and progressively reducing the size of the peds from blocky to platy (kovoda and mermut, 2010). the width of the microstructures implies long dry periods. however, the large size of the ped blocks indicates that dry/wet cycles were few. the light and dark microstructures (figures 21c, 21d, and 21e) suggest multiple dry cycles followed by cementation. the light microstructure (figure 21c) is likely from the remobilization of quartz from the sandstone. in contrast, the dark microstructure is a subsequent dry/cementation cycle infilled with a high percentage of organic matter (kovoda and mermut, 2010). concentric nodules are common in vertisols and suggest a moist climatic regime with seasonal wet/dry cycles (kovoda and mermut, 2010), but the conditions were insufficiently long for the concretion to form fully. the central montana morrison silcrete indicates a minimum of several prolonged dry periods followed by wet intervals. the thinned bedded, fine-grained quartz arenite is interpreted to be a crevasse splay bed. incor1 2 a b e f 500 µm500 µm c 500 µm d 500 µm figure 21. two different silcrete hand samples (a and b) from a 20-cm thick silcrete layer that is exposed 0.85 km west of quarry 2. the layer is stratigraphically 23 m above the swift formation (figure 10 column e). samples (a) and (b) show the angular and subangular blocky microstructures, resulting in ped blocks and nodules ranging up to 20 mm. sample a shows the two sites (red circles labeled 1 and 2) where xrf analyses were performed. (c) a microstructure that has been annealed with light-grained sediments (border outlined by yellow arrows, sample a). (d) a microstructure that has been filled with dark organic sediments (sample a). (e) an additional microstructure filled with dark organic sediments (crossed nichols; sample a). in the examples, the edges of the ped blocks can clearly be observed. (f) the swirl pattern (red arrow) is interpreted to be the initial stages of a concentric nodule (crossed nichols; sample b). these concentric nodules were observed in both thin sections. the microstructures with the blocky peds and the concentric nodules of the silcrete indicate several prolonged dry periods followed by wet intervals. 251 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 porated into the upper phreatic zone, it and any overlying soil cracked from a prolonged dry period. some microstructures were cemented during a subsequent wet interval with the white quartz. a subsequent dry period again produced sand cracks that were infilled with a dark organic, mineral-rich matrix. the matrix chemistry indicates an abundance of vegetation that grew in a typically warm, mesic climate. the formation of the silcrete exhibits a complicated climate record marked by an overall dry period (column e on figure 19). quarry 2 mudstone and sandstone bed sequence the stratigraphic sequence at quarry 2 records a depositional facies transition from a humic pond to a fluvial floodplain capped by distal crevasse splay beds (figure 23). the lowest exposed bed of the sequence is an indurated yellowish-brown illitic mudstone bed (figure 23, bed a). the subsequent stratum is a 15-cmthick, reddish illitic mudstone bed (figure 23, bed b). the bonebed is located at the base of a 70-cm-thick, gray illitic mudstone bed stratigraphically 47 m above the swift formation (figure 23, bed c). a 140-cm-thick, greenish illitic mudstone bed is overlying the bone bed (figure 23, bed d) and is capped by a 20-cm-thick sandstone bed. this sandstone is a subangular, well sorted (0.35), fine-grained (2.83 φ), quartz arenite (figure 23, bed e). the sandstone bed is overlain by a 20-cm-thick mudstone bed and is capped by numerous stacked, thin-bedded (< 5 cm) sandstone beds totaling 70 cm thick. the sandstones are subangular, moderately sorted (0.50), fine-grained (2.98 φ) quartz arenites. the xrf analysis of the lowest mudstone bed recorded a high concentration of molybdenum (144 ppm) (figures 12c, column 5e se-ba). the average background molybdenum concentration for morrison mudstone beds is 8 ppm. in terrestrial environments, molybdenum is typically enriched in humic or dystrophic lake or pond environments filled with decaying organic material. the overlying reddish mudstone bed likely represents well-drained sediments of the desiccated or infilled underlying humic pond. the overlying gray dinosaur-yielding mudstone bed is interpreted to represent the reoccurrence of the pond. no microvertebrate or invertebrate fauna were found in the bed. only a few charophyte gyrogonites (aclistochara), freshwater diatoms, and algae (unidentified calcispheres) were recovered (styles, 2014). clumped oxygen isotope analysis of the quarry mudstone yielded a paleotemperature of 44o c. the greenish mudstone records the transition to a floodplain depositional facies. the 20-cm-thick sandstone bed represents an isolated distal crevasse splay. numerous thin (< 5 cm) distal crevasse splay sandstone beds cover the intercalated mudstone bed. often preserved atop the sandstone beds are very thin laminae (< 1 cm) of banded microbialites formed by cyanobacteria (figure 4h). the sedimentary succession indicates a variable paleoclimate with an overall trend of high precipitation exceeding evaporation with elevated temperatures (richmond and murphy, 2020; column f on figure 19). 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% silcrete a site 1 silcrete a site 2 mt mrsn silcrete xrf data si% al% k% ti% ca% mg% p% fe% s% ba% figure 22. x-ray fluorescence (xrf) analyses of the silcrete. site 1 (figure 21a) xrf analysis of a ped block, whereas site 2 (figure 21a) was of the moderate reddish-orange microstructure matrix. both sites display high percentages of silica, aluminum, and titanium. metal oxides, aluminum, and titanium are common where the climate is warm and wet. element abbreviations are as follows: silica (si), aluminum (al), potassium (k), titanium (ti), calcium (ca), magnesium (mg), iron (fe), sulfur (s), and barium (ba). 252 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 carbonate mound springs one hundred and seven small carbonate buildups were discovered in the morrison formation of central montana. they are interpreted to be subartesian freshwater mound springs and occur stratigraphically between 40 and 52 m above the swift formation (richmond and others, 2021b). these are the first tufa mounds recorded for the morrison formation and are north america's second oldest tufa deposits (richmond and others, 2021b). the mound springs indicate long durations of groundwater discharge at the surface. the mound springs' oxygen and carbon isotopic data indicate they are ambient water-temperature tufa mounds. the δ18o data matches the expected paleolatitude of the region. the δ13c data indicates a short residence time for the groundwater in the subsurface. interestingly, variation in the data sets provides 47.0 47.5 48.0 48.5 49.0 49.5 50.0 cl ay si lt v. fi ne fin e m ed . m et er s a b c d e f figure 23. the stratigraphic sequence at quarry 2 records a depositional facies transition from a humic pond to a fluvial floodplain capped by distal crevasse splay beds. mudstone bed a represents a humic pond with high concentrations of molybdenum (144 ppm). mudstone bed b is a 15-cmthick bed. the bed records the transition from the humic pond to well-drained floodplain sediments. mudstone bed c is the bone bed. dinosaur bones were excavated from the base of the 70-cm-thick bed. the gray mudstone bed is interpreted to represent the reoccurrence of the pond. clumped oxygen isotope analysis of the quarry mudstone yielded a paleotemperature of 44°c. overlying the bone bed is a 140-cm-thick, greenish illitic mudstone bed (mudstone bed d) capped by a 20-cm-thick sandstone bed (sandstone bed e). the sandstone is a subangular, well sorted (0.35), fine-grained (2.83 φ) quartz arenite. between sandstone beds e and f, there is a 20-cm-thick mudstone bed. the capping sandstone unit is comprised of numerous stacked thin sandstone beds. the sandstones are subangular, moderately sorted (0.50), fine-grained (2.98 φ) quartz arenites. the thin beds are interpreted to be a sequence of distal splay beds indicating repeated crevasse splay flood events. the sedimentary succession specifies a variable paleoclimate with an overall trend of high precipitation exceeding evaporation with elevated temperatures. 253 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 additional insights into the paleoclimate. a few more negative δ18o values infer there may have been precipitation input from northern storms from the retreating sundance sea. a cluster of more negative δ13c values also implies drier periods. this resulted in a longer subsurface residence time allowing groundwater to interact with plant carbon. the average annual temperatures most favorable to tufa formation and growth are between 5o and 15o c (pentecost, 1991; ibarra and others, 2014). therefore, the mound springs' occurrences in central montana indicate a regular high precipitation rate with cool paleotemperatures (richmond and others, 2021b; column g on figure 19). micrite and mudstone beds (upper section) southwest of button butte is a laterally limited outcrop of the uppermost morrison formation stratigraphic section. the exposed outcrop begins at 55 m above the swift formation and extends to the basal kootenai sandstone bed (72 m). the uppermost section is dominated by mudstone; however, four micrite beds are in the section's lower part. the lowest micrite bed is stratigraphically at 56.6 m, and the uppermost bed is at 60.7 m. the 20to 50-cm-thick micritic beds are separated by 1.5 m of mudstone beds. the micrite beds indicate the presence of shallow ponds or lakes of unknown size. the intercalated mudstone and micrite beds suggest dry intervals followed by periods of increased precipitation (column h on figure 19). morrison formation coal strata high volatile bituminous coal beds are known from the uppermost stratigraphic section of the morrison formation of central montana (daniel and others, 1992). overlying the coal strata is the k-1 unconformity and basal kootenai sandstone bed (harris, 1966; daniel and others, 1992). however, in the early days of exploration, researchers interpreted the coal beds to be part of the “kootanie” series, a name proposed by dr. george m. dawson in 1885 for the indian tribe that had previously hunted the region (fisher, 1908; knowlton, 1908). geologists of the transcontinental survey and the yellowstone and missouri river exploration party in 1860 first reported on the coal beds of central montana (hayden, 1869). fisher (1909) lists a comprehensive literature review of the pre-1909 publications. newberry (1888) briefly mentioned “kootanie” age (lower cretaceous) coals at the falls of the missouri river (i.e., great falls, montana). newberry (1891) later reviewed the fossil flora from the coal beds of sand coulee and belt creek, montana, saying that coal miners had reported fern impressions in the coal. based on the coal plant fossils and their comparison to other formations, newberry maintained that the coal was of lower cretaceous age. fontaine (1893) reviewed a small collection of plants preserved from the coals and said that the sample consisted of fossil plants from the families of polypodiaceae, equisetaceae, cycadaceae, and coniferae. knowlton (1908) completed a more in-depth fossil plant review from the coals and added the family ginkgoaceae to the then-known fossil plant varieties. the first geological evaluation of the great falls coal was performed by weed (1892), who measured the coal beds as more than 3 m thick and intercalated with thin shale beds. the coal beds are overlain by a prominent sandstone ledge that measures up to 15 m thick (i.e., kootenai basal sandstone bed). fisher (1907) erroneously placed the coal-bearing strata in the overlying kootenai formation and reported that the coal beds were 18 m above the base of the formation. the following year, fisher (1908) suggested that the central montana coal strata correlated to other coal beds to cretaceous-aged coal strata around montana and the cloverly formation of the bighorn basin. fisher (1909) described the general geology of the great falls area, including the coal beds, whereas calvert (1909) explained similar parameters for the lewistown area and its coal field. since then, several papers have further discussed the geology and economic importance of the coal (harris, 1966, 1968; silverman and harris, 1966, 1967). although the coal's fossil plants, stratigraphy, and economic aspects have been evaluated, the depositional facies that produced the coal still needs to be sufficiently explored. daniel and others (1992) propose that the morrison coals formed in situ in flooded swamps composed of ginkgophytes and other plant materials. based on the abundant layers of fusain, daniel and others (1992) also suggested that the marshes occasionally burned and were later followed by clay-rich sediment 254 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 deposition. although a large-scale depositional model has yet been proposed for the morrison coal strata, the freshwater coal swamps likely formed on the prograding fluvial plain. interestingly, the upper jurassic-lower cretaceous coal strata of the kootenay formation of the southern canadian rocky mountains were formed by deltaic accretion of coastal marshes that developed on a prograding coastal plain (jansa, 1972). coals require abundant plant growth from high precipitation, poor drainage on low gradient topography, or changes in the eustatic sea level (parrish and others, 1982). based on the previously described lithologic proxies, the morrison coal beds were likely formed in an environment with high precipitation and/ or poor drainage. the presence of abundant plants to generate greater than meter-thick coal beds indicate climatic conditions were suitable for copious plant growth for long durations. however, the presence of fusain and clay-rich interbeds suggest that unfavorable climatic conditions were sufficiently long to dry the swamps and enable fires to burn them (i.e., droughts; column i on figure 19). biologic climatic proxies modern terrestrial fauna and flora are assembled by climatic zones in which they reside. the preferred climatic zone and their biological characteristics have been used repeatedly to develop paleoclimatic interpretations. vertebrate proxies currently, the dinosaurs discovered in the research area include hesperosaurus (saitta, 2015; maidment and others, 2016, 2018), camarasaurus (woodruff and foster, 2017), ?haplocanthosaurus, ?camptosaurus, allosaurus (identified from shed teeth in quarry 2), and ?suuwassea. dinosaurs are suggested to have elevated metabolic rates more akin to living endotherms. therefore, their fossil record and bone growth are not as reliable proxies for climatic changes as those of other organisms. semiaquatic vertebrates, including crocodiles and turtles, have bone tissue that does show environmental sensitivity. connely’s (2006) unpublished report stated that fossil turtle, crocodile, and possibly amphibian material was recovered from the bivalve splay mudstone bed, but this material has not been located. no additional environmentally sensitive fossil vertebrates have been reported. invertebrate proxies bivalvia a gray-green fossiliferous mudstone bed stratigraphically 19 m above the swift formation (column h on figure 10), is interpreted to be a flood splay deposit because of the diversity and concentration of fossil material (richmond and others, 2017). the bed contains seven genera of bivalves, including unio felchi, u. mammillaris, u. nucalis, u. stewardi, u. toxonotus, vetulonaia whitei, and v. mayoworthensis (figure 24a). thickand thin-shelled ecophenotypes are represented, indicating lotic and lentic environments. gastropods (viviparus and tropidina), ostracods (alicenula, candona, ?cetacella, and theriosynoecum), and charophytes (aclistochara, mesochara, and porochara) are also represented. fish bones and piscivorous teeth were also recovered (richmond and others, 2017). the unio and vetulonaia specimens are the largest recorded sizes for the morrison formation (> 13 cm). this indicates a long-lived salubrious perennial clear freshwater environment. ten shells were thin-sectioned to observe the growth bands. thin closure lines demarcate the various growth bands. interestingly, the observed bandwidths correlate among the specimens. this infers the community response is likely linked to environmental disruptions. shell closure recorded by the thin bands represents short periods of adverse conditions due to turbidity from seasonal storms or eutrophication. the paleoclimate, as recorded by the bivalves, showed negligible seasonal variation but was punctuated by occasional storms (column j on figure 19). a single thick-shelled bivalve, v. mayoworthensis, was found in a green-gray mudstone bed at 65.7 m. the genus is interpreted to inhabit lentic environments and was likely deposited onto the floodplain by a flood splay. the bivalve indicates the presence of a lentic freshwater body nearby (stratigraphic column i on figure 10 and column j on figure 19). 255 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 gastropoda the fossiliferous flood splay bed at 19 m also contained the prosobranch gastropod genera viviparus and tropidina (richmond and others, 2017). prosobranchs of the morrison formation are interpreted to have lived in perennial well-oxygenated lentic environments (evanoff and others, 1998). neither gastropod genera have any biostratigraphic significance for the morrison (evanoff and others, 1998). the depositional environment inferred from the gastropods correlates with that designated by the bivalve genera (column k on figure 19). ostracoda ostracods are abundant in the calcareous shales and limestones of the morrison formation in central montana (peck, 1956, 1957, 1959). unidentified ostracods are present in the lacustrine/palustrine micrite beds (johnson-carroll, 2014) of the paleolake at 13 m. the gray-green illitic fossiliferous bed at 19 m contains the ostracod genera alicenula, candona, ?cetacella, and theriosynoecum (richmond and others, 2017). near button butte there is a 5-m exposure of four interbedded micrite and mudstone beds (column i on figure 10). the micrite beds vary from 20 to 50 cm in thickness. a limited outcrop exposure constrains an assessment of the lateral extent. the micrite and mudstone beds represent a shallow paleolake. the uppermost and thickest bed (60.5 m above the swift formation) is an ostracodal biomicrite with numerous separated ostracod valves and unidentified charophyte gyrogonites. fortuitously, there are also some exceptionally preserved ostracods. a magnificently preserved ostracod specimen is identified as a female theriosynoecum individual showing preserved anterior and posterior duplicatures (figure 24b). theriosynoecum is a representative upper jurassic‒lower cretaceous genus (horne, 2002). the ostracod taxa indicate perennial freshwater bodies with no seasonal drying indicating precipitation exceeded evaporation (b. sames, university of vienna, written communication, 2021) (column l on figure 19). palaeobotanical proxies fossil wood in contrast to brown (1946), who stated the morrison formation in montana is “practically barren of plant u ni o fe lc hi unio nucalis b 100 µm theriosynoecum a figure 24. (a) a green illitic mudstone flood splay bed at 19 m consisting of seven genera of jurassic freshwater bivalves, including unio felchi, u. mammillaris, u. nucalis, u. stewardi, u. toxonotus, vetulonaia whitei, v. mayoworthensis. unio felchi and u. nucalis displayed in situ. additionally, the bed contained gastropods (viviparus, tropidina), ostracods (alicenula, candona, ?cetacella, theriosynoecum), and charophytes (aclistochara, mesochara, porochara). fish bones and piscivorous fish teeth were also recovered. the presence of the numerous invertebrate genera indicates a long-lived salubrious perennial clear freshwater environment. (b) a magnificently preserved female theriosynoecum showing the anterior and posterior duplicatures from a micritic bed stratigraphically 60.5 m above the swift formation. the presence of the ostracod taxa indicates perennial freshwater bodies with no seasonal drying. 256 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 fossils throughout most of its sequence;” in the formation research area, fossil wood is abundant throughout the section. the majority of the fossil tracheidoxyls are found between 40 and 60 m above the swift formation. fossil wood preservation varies from extremely well (richmond and others, 2019d) to poor. to date, five fossil wood genera have been described, including xenoxylon (richmond and others, 2019d), piceoxylon (richmond and others, 2019b), circoporoxylon (richmond and others, 2019c), cupressinoxylon (richmond and others, 2021a), and protocedroxylon (richmond and others, 2022). two wood genera (xenoxylon and circoporoxylon) are associated with or are encased in mound spring deposits (richmond and others, 2021b). ten xenoxylon fossil sites have been identified (in stratigraphic order: fb pw1, rr pw1, 5e pw20, 5e pw17, 5e pw18, 5e pw21, 5e pw6, 5e sqrt, 5e pw5, and 5e wtfa; table 2) showing a current stratigraphic range for the genus that extends from approximately 17 to 51 m (column m on figure 19). the numerous discoveries indicate that xenoxylon was an integral part of the jurassic paleoforest and that the climate in central montana was suitable for its proliferation. five circoporoxylon fossil sites have been identified (5e pw16, 5e pw14, 5e tufa1, 5e tufa2, and 5e pw13; table 2). the current stratigraphic range of the known circoporoxylon sites is 35 to 46 m (column n on figure 19). three cupressinoxylon fossil sites have been identified (5e tufa4, 5e pw33, and 5e cspw; table 2). the current stratigraphic range of the known cupressinoxylon sites is 46 to 53 m (column o on figure 19). one piceoxylon fossil site has been identified (5e tree1; table 2) at 25 m (column p on figure 19). one protocedroxylon fossil site has been identified (5e pw4; table 2) at 46 m (column q on figure 19). the same boreal wood genera have been reported together in the high-latitude boreal forests of the cretaceous period of north america (harland and others, 2007). the upper jurassic fossil wood assemblage and in particular xenoxylon, are suggestive of a cool/wet climate (philippe and thévenard, 1996; marynowski and others, 2008; philippe and others, 2009, 2017; tian and others, 2016). the occurrence of these five boreal fossil wood genera designates that for the stratigraphic interval from 17 to 53 m, the climate was cool and/or wet (richmond, 2023). macro and microfossil flora additional coniferales from the morrison formation of central montana include podozamites lanceolatus (podocarpaceae), pityophyllum lindstromi (gnetophyta), pityocladus sp. (cycadophyta), and pagiophyllnm sp. (brown, 1972). based on palynology, the families pinaceae and podocarpaceae were also present (hotton and baghai-riding, 2010). subdominant understory woody plants included cycadales (zamites arcticus), ginkgoales (ginkgoites marginatus, ginkgoites pluripartita), and bennettitales (cycadolepis sp., nilssonia compta, and weltrichia sp.) (brown, 1972). the groundcover in the late jurassic of central montana was comprised sample assigned fossil wood genus stratigraphic position (m) mrsn fb pw1 xenoxylon 17.5* mrsn rr pw1 xenoxylon 17.9* mrsn 5e pw20 xenoxylon 42.5 mrsn 5e pw17 xenoxylon 43.2 mrsn 5e pw18 xenoxylon 43.4 mrsn 5e pw21 xenoxylon 43.4 mrsn 5e pw6 xenoxylon 44.1 mrsn 5e sqrt xenoxylon 45.4 mrsn 5e pw5 xenoxylon 45.9 mrsn 5e wtfa xenoxylon 51.1 mrsn 5e pw 16 circoporoxylon 35.0 mrsn 5e pw14 circoporoxylon 44.4 mrsn 5e tufa1 circoporoxylon 45.9 mrsn 5e tufa2 circoporoxylon 45.9 mrsn 5e pw13 circoporoxylon 51.6 mrsn 5e tufa4 cupressinoxylon 45.9 mrsn 5e pw 33 cupressinoxylon 48.0 mrsn 5e cspw cupressinoxylon 53.1 mrsn 5e tree1 piceoxylon 25.0 mrsn 5e pw4 protocedroxylon 45.8 table 2. list of currently identified fossil wood genera from the study area with each sample’s stratigraphic position within the formation measured in meters above the swift formation. the samples with the associated asterisks show approximate stratigraphic positions. 257 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 of fungi, the sphenophyte equisetum lateralis, the pteridophytes hausmannia fisheri, coniopteris hymenophylloides, adiantites montanensis, cladophlebis alberta, cladophlebis heterophylla, and cladophlebis virginiensis, and the pteridosperm sagenopteris elliptica (brown, 1972). brown (1972) reexamined previous late 19th-century fossil plant assemblages and collected additional fossil plants from several locations in central montana. brown’s fossil specimens were from carbonaceous shales of the formation’s upper strata. as mentioned, brown (1972) identified a pteridophyte of the dicksoniaceae tree fern family. specimens from the belt and lewiston areas of montana were described as the fern coniopteris hymenophylloides. dicksoniaceae (coniopteris) first appeared in the early jurassic (seward, 1900; vakhrameyev, 1964; wang, 2002) and is found northern hemisphere in the middle jurassic (vakhrameyev, 1964; vaez-javada, 2018; xin and others, 2018; yuan and others, 2018; zhang and others, 2019), late jurassic (vakhrameyev, 1964; brown, 1972; miller, 1987; ash and tidwell, 1998), and lower cretaceous strata (lapasha, 1982; lapasha and miller, 1985; miller, 1987). c. hymenophylloides is the only member of the dicksoniaceae family recognized from the morrison formation (ash and tidwell, 1998) and has only a few occurrences. in addition to the locations in central montana (brown, 1972; miller, 1987), it is also known from the montezuma creek locality in southeastern utah (ash and tidwell, 1998), the temple park area near cañon city, colorado (gorman and others, 2008), the turtle island plant site north of vernal, utah (foster and others, 2003), and the jurassic sald bar site in southeastern utah (foster and others, 2022, 2023). additionally, c. hymenophylloides has also been described from the lower cretaceous kootenai formation of central montana (lapasha, 1982; lapasha and miller, 1985; miller, 1987). the sterile and fertile pinna of c. hymenophylloides (figure 25a) (e. kustatscher, museum of nature south tyrol, written communication, 2021) were recently discovered in a thin carbonaceous shale bed stratigraphically at 38 m in the study area. foster and others (2023) differentiate between the fertile and sterile pinna, classifying the fertile pinna as coniopteris and the sterile pinna as sphenopteris. coniopteris is interpreted to be a small to large rhizomatous fern that grew in mesic environments (deng, 2002). numerous researchers propose that the paleoecology of the coniopteris signifies a warm and mesic paleoenvironment (wang, 2002; vaez-javada, 2018; xin and others, 2018; zhang and others, 2019) (column r on figure 19). an unidentified pteridophyte was discovered in the same shale bed (figure 25b). most fern diversity is encountered in mesic and warm environments. an unidentified ginkgophyte was also discovered in the same shale bed (figure 25c). extant ginkgophytes prefer mesic environments but can tolerate a wide range of soil moistures and temperatures. palynology the majority of palynological data for the morrison formation comes from utah, colorado, arizona, and new mexico (tschudy and others, 1980, 1988; hotton, 1986; litwin and others, 1998; baghai-riding and hotton, 2009, 2011; baghai-riding and others, 2013, 2014, 2015, 2018; hotton and baghai-riding, 2010, 2016). in addition, limited sampling has been done in the more northern parts of the morrison basin in wyoming and montana (newman, 1972; litwin and others, 1998; baghai-riding and hotton, 2009, 2011; hotton and baghai-riding 2010; baghai-riding and others, 2015). for an overview of the palynology of the morrison formation, refer to litwin and others (1998) and hotton and baghai-riding (2010). palynological studies of the canadian upper jurassic kootenay formation are interpreted as the northern equivalent of the morrison formation in south-central canada. the formation has numerous coal seams, and these were investigated for pollen in the 20th century by berry (1929), bell (1956), and rouse (1959). newman (1972) was the first to review the palynology of the morrison formation in montana and only sampled one morrison site. the majority of newman’s paper discussed cretaceous and paleogene palynology. four palynology samples are from a carbonaceous shale bed, 3 m stratigraphically below the kootenai basal sandstone bed, 0.5 km south of belt, montana (stop 6 of the 1966 billings geological society 17th annual field conference, 258 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 p. 36; newman, 1972). newman only mentioned four palynological genera: callialasporites dampieri, eucommiidites, classopollis, and inapertisporites pseudoreticulatis. newman specified that eucommiidites were prevalent and that classopollis were infrequent (table 3). litwin and others (1998) sampled the formation west of the yellowstone river south of livingston, montana (samples r4684a, b) and along the eastern flank of shell mountain along the west boulder road southeast of livingston (samples r4690a, c, e). only data from samples r4690a, c, and e were published; however, no stratigraphic information was provided (table 3). hotton and baghai-riding (2010) processed a sample collected near belt, montana; however, they did not publish the data. in the study area, a limited palynological sample was procured from a carbonaceous shale bed stratigraphically 38 m above the swift formation (table 3). the mudstone sediments yielded several fossil pollen and spores (table 3). several carbonaceous shales were also sampled but did not yield viable material, but each contained an abundance of fusain. the morrison coals from the five fingers coal mine near sand coulee, montana were also sampled. palynomorph recovery was poor due to maceral debris and the degradation of the pollen. some pollen were tentatively identified to the family and genus level including ?araucariaceae, a cb figure 25. a carbonaceous shale stratigraphically at 38 m above the swift formation has compressed plant fossils. a preliminary investigation has yielded the pteridophyte coniopteris hymenophylloides. (a) photograph of shale fragments that displays both the sterile and fertile pinna (red box) of c. hymenophylloides. (b) photograph displaying an unidentified pteridophyte. (c) photograph displaying an unidentified ginkgophyte. the pteridophytes and the ginkgophyte suggest a mesic and warm environment. scale bars are each 3 cm. 259 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 r ef er en ce c la ss o rd er fa m ily g en us sp ec ie s po si tio n m oi st ur e te m pe ra tu re n ew m an , 1 97 2 pi no ps id a a ra uc ar ia le s a ra uc ar ia ce ae ca lli al as po rit es da m pi er i 69 m w et to m es ic m eg at he rm ic pi no ps id a c he iro le pi di al es c he iro le pi di ac ea e cl as so po lli s sp . “ dr y m eg at he rm ic g ne to ps id a e rd tm an ith eca le s er dt m an ith ec ac ea e eu co m m iid ite s sp . “ w et to m es ic eu ry th er m ic un kn ow n u nk no w n un kn ow n in ap er tis po rit es ps eu do re tic ul at is “ u nk no w n un kn ow n li tw in pi no ps id a pi na le s po do ca rp ac ea e pr ist in us po lle ni te s m icr os ac cu s u nk no w n m es ic m eg at he rm ic an d ot he rs , pi no ps id a pi na le s po do ca rp ac ea e pa rv isa cc ite s sp . “ w et to m es ic m eg at he rm ic 19 98 pi no ps id a pi na le s pi na ce ae pi ty os po rit es sp . “ w et to m es ic m es ot he rm ic pi no ps id a pi na le s ?p in ac ea e ru gu bi ve sic ul ite s sp . “ un kn ow n un kn ow n g in kg oo ps id a c ay to ni al es c ay to ni ac ea e vi tre isp or ite s pa lli du s “ w et to m es ic m eg at he rm ic po ly po di op sid a c ya th ea le s c ya th ea ce a cy at hi di te s co nc av us “ w et (l oc al ly ) eu ry th er m ic po ly po di op sid a sc hi za ea le s sc hi ze ac ea e co nc av iss im isp or ite s m on tu os us “ w et (l oc al ly ) m eg at he rm ic po ly po di op sid a sc hi za ea le s sc hi ze ac ea e co nc av iss im isp or ite s irr or at us “ w et (l oc al ly ) m eg at he rm ic po ly po di op sid a sc hi za ea le s a ne m ia ce ae ci ca tr ico sis po rit es sp . “ w et (l oc al ly ) m eg at he rm ic po ly po di op sid a o sm un da le s o sm un da ce ae to di sp or ite s m in or “ w et (l oc al ly ) m es ot he rm ic po ly po di op sid a un kn ow n un kn ow n g ra nu la tis po rit es da ily i “ un kn ow n un kn ow n po ly po di op sid a un kn ow n un kn ow n isc hy os po rit es di sju nc tu s “ w et (l oc al ly ) un kn ow n ly co ps id a un kn ow n se la gi ne lla ce ae n eo ra ist ric ki a sp . “ w et (l oc al ly ) eu ry th er m ic s ph ag no ps id a sp ha gn al es sp ha gn ac ea e st er ei sp or ite s sp . “ w et (l oc al ly ) eu ry th er m ic ?m ar ch an tio ps id a un kn ow n un kn ow n ?h ym en oz on ot ril et es m es oz oi cu s “ un kn ow n un kn ow n pr es en t s tu dy pi no ps id a pi na le s pi na ce ae al isp or ite s bi la te ra lis 38 m m es ic eu ry th er m ic pi no ps id a c he iro le pi di al es c he iro le pi di ac ea e cl as so po lli s sp . “ dr y m eg at he rm ic g ne to ps id a er dt m an ith eca le s er dt m an ith ec ac ea e eu co m m iid ite s tro ed ss on ii “ w et to m es ic eu ry th er m ic po ly po di op sid a g le ic he ni al es d ip te rid ac ea e d ic ty op hy lli di te s sp . “ w et to su ba rid m eg at he rm ic un kn ow n un kn ow n cy ca do pi te s fra gi lis " w id e ra ng e eu ry th er m ic ta bl e 3. s um m ar y of th e pa ly no lo gi ca l s am pl es fr om th e m or ris on f or m at io n of m on ta na . th e ta bl e pr ov id es th e ta xo no m ic al id en tifi ca tio n, th e st ra tig ra ph ic p os iti on a bo ve th e sw ift f or m at io n, a nd th e po lle n’s p re fe rr ed m oi st ur e an d te m pe ra tu re . 260 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 ?osmundaceae, ?dictyophyllidites, ?gleicheniidites, ?ischyosporites, and cycadopites (hotton, national museum of natural history, written communication, 2022). gymnospermae: callialasporites dampieri (pinopsida/ araucariales/araucariaceae). callialasporites dampieri is a conifer pollen with affinities to either araucariaceae or podocarpaceae. however, a review of the ultrastructure of the exine designates the pollen genus as araucariaceae (batten and dutta, 1997; schrank, 2010). callialasporites are present in the salt wash and brushy basin members of the morrison formation in utah (tschudy and others, 1980, 1988; hotton, 1986). the ecological range of modern araucaria extends from rainforests to cool temperate forests. extent araucaria are generally hygrophytes and megathermic trees (schrank, 2010; zhang, 2022). pristinuspollenites microsaccus (pinopsida/pinales/ podocarpaceae). the genus is often found with alisporites and other mesic pollens. extant podocarpaceae are common to the southern hemisphere in tropical-subtropical climates and mountains, and are generally hygrophytes and megathermic trees (zhang, 2022). parvisaccites sp. (pinopsida/pinales/podocarpaceae). extant podocarpaceae are common to the southern hemisphere in tropical-subtropical climates and mountains, and are generally hygrophytes and megathermic trees (zhang, 2022). alisporites bilateralis (pinopsida/pinales/pinaceae; figure 26a). the genus is also present in the kootenay formation of british columbia, canada (rouse, 1959). extant pinaceae are generally mesophytes and microthermal plants that grow in acidic, wet, or rocky habitats in northern temperate zones (zhang, 2022). pityosporites sp. (pinopsida/pinales/pinaceae). the genus is considered a bisaccate gymnosperm pollen with no known affinities (ludvigson and others, 2010; zhang, 2022). however, hotton (national museum of natural history, written communication, 2022) believes that the genus is synonymous with alisporites. rugubivesiculites sp. (pinopsida/?pinales/?podocarpaceae). rugubivesiculites is a bisaccate gymnosperm pollen with uncertain affinities (falcon-lang and others, 2003). extant podocarpaceae are common to the southern hemisphere in tropical-subtropical climates and mountains, and are generally hygrophytes and megathermic trees (zhang, 2022). classopollis sp. (pinopsida/cheirolepidiales/cheirolepidiaceae; figure 26c). classopollis is a dominant group of conifers during the mesozoic (kürschner and others, 2013). the genus was not found in the salt wash or brushy basin members of the morrison formation in utah (tschudy and others, 1980, 1988); however, the morrison formation of arizona and new mexico is dominated by classopollis (hotton, 1986). cheirolepidiaceae are drought-resistant xerophytes (vakhrameyev, 1982; zhang, 2022). eucommiidites troedssonii (gnetopsida/erdtmanithecales/erdtmanithecaceae; figure 26b). this pollen mimics angiosperm pollen, although a recent review of the exine ultrastructure assigned this pollen to the family erdtmanithecaceae in the order erdtmanithecales (tekleva and others, 2006). eucommiidites are present in the salt wash and brushy basin members of the morrison formation in utah (tschudy and others, 1980, 1988).  erdtmanithecaceae are considered xerophytes and eurythermic plants (zhang, 2022). vitreisporites pallidus (ginkgoopsida/caytoniales/ caytoniaceae). caytoniaceae is an extinct cosmopolitan seed fern family of small trees. caytoniaceae fossils are found in deltaic and floodplain environments in subtropical regions suggesting they were hygrophytes and megathermic trees (zhang, 2022). cycadophyta: cycadopites fragilis (bennettitales, ginkgoales, or cycadales; figure 26d). extant cycads are generally in tropical and subtropical zones occurring in the rainforest and open woodland habitats. they are mesophytic, megathermic plants (zhang, 2022). pteridophyta: cicatricosisporites sp. (polypodiopsida/ schizaeales/anemiaceae). the genus is found elsewhere in the morrison formation (chure and others, 2006) and the lourinhã formation of portugal (mateus, 2006). extent anemiaceae mostly live in subtropical to tropical regions and are considered mesophytes and megathermic plants (zhang, 2022). concavissimisporites montuosus and c. irroratus (polypodiopsida/schizaeales/ lygodiaceae). the genus is also present in both the salt wash and brushy basin members of the morrison formation in utah (tschudy and others, 1980, 1988), the upper jurassic lourinhã 261 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 formation of portugal (mateus, 2006), and the lower cretaceous yellow cat member of the cedar mountain formation in utah (joeckel and others, 2019). extent lygodiaceae are hygrophytes and megathermic plants (zhang, 2022). cyathidites concavus (polypodiopsida/cyatheales/ cyatheaceae). the genus is present in both the salt wash and brushy basin members of the morrison formation in utah (tschudy and others, 1980, 1988). extant cyatheaceae are tropical tree ferns that generally grow in the undergrowth of moist forests and are considered hygrophytes and megathermic ferns. dictyophyllidites sp. (polypodiopsida/gleicheniales/ dipteridaceae; figure 26e). dipteridaceae are commonly known as umbrella ferns. extant species are found in tropical and warm-temperate regions from asia to australia, implying they are hygrophytes and megathermic plants. todisporites minor (polypodiopsida/osmundales/ osmundaceae). the genus is also present in the salt wash and brushy basin members of the morrison formation in utah (tschudy and others, 1980, 1988). extent osmundaceae are mesophytic plants generally found in tropical climatic zones (tryon and tryon, 1982), implying they are hygrophytes and megathermic plants. granulatisporites dailyi (polypodiopsida/uncertain pteridophyte, ludvigson and others, 2010; zhang, 2022). inapertisporites pseudoreticulatus (polypodiopsida/ uncertain pteridophyte, chure and others, 2006; ludf cycadopites fragilis c classopollis sp. aa alisporites bilateralis b eucommiidites troedssonii d e dictyophyllidites sp. fungal material figure 26. photomicrographs of the pollen and spores were recovered from a mudstone bed (section f) at 38 m above the swift formation. (a) alisporites bilateralis (pinaceae). extant pinaceae prefer moist and cool environments. (b) eucommiidites troedssonii (erdtmanithecaceae). the family is considered to favor drier environments with a wide range of temperatures. (c) classopollis (cheirolepidiaceae). cheirolepidiaceae also favor drier environments and are drought-resistant xerophytes. (d) cycadopites fragilis has uncertain cycad affinities. extant cycads prefer mesic and warm environments. (e) dictyophyllidites sp. (dipteridaceae.) extant dipteridaceae prefers mesic and warm environments. (f) unidentified fungal body (yellow arrow – 19 m above the swift formation) and spores (red arrow – 55 m above the swift formation). fungal spores require moisture to grow and prefer warm environments. red bars are 20 μm for all samples. 262 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 vigson and others, 2010). the genus is also known from the kootenay formation of southeastern british columbia, canada (rouse, 1959) and the lourinhã formation of portugal (mateus, 2006). hotton (national museum of natural history, written communication, 2022) believes that the genus may be a “wastebasket” category for fungal, algal, or bryophytic taxa. ?gleicheniidites (polypodiopsida/gleicheniales/ gleicheniaceae). ?ischyosporites (uncertain pteridophyta). neoraistrickia sp. (lycopsida/selaginellales/selaginellaceae). neoraistrickia, a lycopsid, is an herbaceous vascular plant related to the club mosses. extant selaginellaceae are considered euryphytes and eurythermic plants (zhang, 2022). bryophyta: stereisporites sp. (sphagnopsida/sphagnales/ sphagnaceae). extent sphagnum mosses are cosmopolitan and are commonly found in wetlands. they are considered hydrophytes and eurythermic plants (zhang, 2022). the morrison formation palynology has thus far yielded several samples, but in those samples is recorded a diverse flora including seven gymnosperm families, one cycad, five pteridophyte families, and a single bryophyte family. the paleoenvironmental interpretation derived for the more mobile gymnosperm pollen shows a xeric preference, whereas the locally disseminated pteridophyte spores exhibit wet conditions (column s on figure 19). most of the pteridophytes were identified in litwin and others’ (1998) samples, but no stratigraphic position was provided. their sample implies the morrison formation in central montana was, at one time, wet and warm. the upper stratigraphic samples (newman, 1972; present study) signify that the climate of the upper section may have been more temperate. fungi: unidentified fungal bodies and spores were found in the mudstones from 14 and 55 m stratigraphically above the swift formation (figure 10, columns h and f, respectively). fungal spores require moisture to grow and prefer warm environments. uncertain affinity: ?hymenozonotriletes mesozoicus (?marchantiopsida). no information can be provided for this litwin and others (1998) specimen since no known affinities exist. charophyta modern charophytes live in clear lentic oligotrophic freshwater environments. charophytes in morrison formation limestone beds indicate standing water (turner and fishman, 1991). charophytes are abundant in the calcareous shales and limestones of the central montana morrison (peck, 1956, 1957, 1959). the most common and distinctive gyrogonites of the morrison are latochara latitruncata and aclistochara bransoni (peck, 1956). the morrison biozones of l. latitruncata are 1 through 5, whereas the biozones a. bransoni are 1 through 4 (schudack and others, 1998). charophyte gyrogonites of aclistochara latisulcata are present in the micritic limestone beds (14.5 to 16.5 m). the micrite beds are interpreted to represent a small paleolake and wetland. in flood-splay mudstone beds (19 m), the charophyte genera aclistochara, mesochara, and porochara have been reported (richmond and others, 2017). the charophyte gyrogonites p. minima assign the bed to biozone 3. based on the bivalve genera, the source of the splay bed was both lotic and lentic aquatic environments (richmond and others, 2017). the quarry 2 mudstone bone bed (47 m) yielded charophyte gyrogonites of the genus aclistochara complanata, aclistochara latisulcata (biozones 3 through 4), and mesochara voluta (biozones 1 through 4) (styles, 2014). charophyte gyrogonites support the sedimentological and geochemical interpretation of a waterhole at the quarry (richmond and murphy, 2020). charophyte gyrogonites of aclistochara latisulcata are also present in the micritic limestone beds (60.5 m). the micrite beds are interpreted to represent a small paleolake, but the lateral extent of the beds is still being determined due to the lack of additional exposures. the presence of charophytes in these strata indicates a perennial water source and therefore an interval where precipitation is greater than evaporation (column t on figure 19). algal and cyanobacterial buildups an organic fabric was discovered in mound spring cm 13 (45 m above the swift formation) that may be the tufa-associated green algae oocardium stratum nägeli (see richmond and others, 2021b, figure 7d). tufas generally occur in regions with an annual rainfall 263 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 of over 500 mm/year (pentecost, 1991; ibarra and others, 2014). tufas with associated oocardium commonly have rainfall that exceeds 1000 mm/year (ibarra and others, 2014; richmond and others, 2021b). the presence of fossil oocardium specifies a high rainfall during the deposition of this mound spring. additionally, banded cyanobacterial microbialite buildups were fortuitously discovered in thin section on the upper surfaces of the thin (5 cm) sandstone splay beds (50 m) capping the quarry 2 pluvial/fluvial sequence (see figure 23, bed f). the banded buildups atop the sandstone beds indicate both a high-water table and the repeated reflooding of the distal crevasse splay beds (figure 4h). cyanobacterial buildups are also found on dogtooth calcite crystals growing on the spring mounds (see richmond and others, 2021b, figure 9a). carbonate spherulites, present in some of the spring mounds (48 to 50 m), were formed by a jurassic variant of the betaproteobacteria ralstonia eutropha h16 (see richmond and others, 2021b, figures 9b and 9c). cyanobacteria and ralstonia eutropha h16 can grow over a wide temperature range. however, optimal growth occurs at warm temperatures (29 to 30o c; lürling and others, 2013; nowroth and others, 2016) (column u on figure 19). conclusions the upper jurassic morrison formation in central montana had yet to be sufficiently studied. the historical stratigraphic measurements of the formation vary greatly. recent field measurements in central montana indicate the formation is 72 m thick. a review of well-log data over central montana shows that formation does display variation, but the average thickness over the region is 71 m. the thickest part of the formation is in northeastern wheatland county, suggesting a distributive fluvial system migrating from the southwest. there is no discernable well-log marker across the region nor consistent change in lithology to warrant a division of the formation into members. although there is no distinguishable break in the formation to separate it into members, the lower mudstone interval is interpreted as the distal floodplain facies. the upper depositional facies marks a transition to a mudstone-dominated, anastomosing fluvial depositional facies. the fluvial facies consist of small, isolated, fine-grained anastomosing channel beds, and thin crevasse and flood splay beds. based on climate models and lithologic proxies, many researchers have proposed the morrison foreland basin experienced a semiarid to arid zonal climate. climate proxies provide an interpretation over a short climate window; however, a comprehensive proxy assemblage compiled over a stratigraphic range and confined to a specific region delivers a full view of the climatic past. the retreat of the sundance seaway and its proximity to the northern part of the morrison foreland 50o n 40o n extent of the morrison formation and related strata mt hw cb dn cl dm sv figure 27. a modified paleogeography map of the upper jurassic of western north america. the dots represent wellknown dinosaur quarries (mt–montana quarries; hw– howe quarries; cb–como bluff quarries; dn–dinosaur national monument quarry; cl–cleveland-lloyd quarry; dm–dry mesa quarry; and sv–stovall quarries). overlain on the morrison foreland basin is an interpreted climatic map with the warm coloration representing a warmer and drier region and the cool coloration designating cooler and wetter areas. gom–gulf of mexico. source map © 2016 colorado plateau geosystems inc. 264 stratigraphy, sedimentology, and paleoclimatic proxies of the upper jurassic morrison formation of central montana richmond, d.r. geology of the intermountain west 2023 volume 10 basin had a dramatic effect on the paleoclimate of the region. the compilation of lithologic, faunal, and floral proxies from the northern part of the basin recorded in sediments in central montana demonstrates the climate in this region was wetter than in more southern parts of the morrison foreland basin (figure 27). based on the numerous climatic proxies, environmental conditions were not static but indicate that the late jurassic of central montana experienced an overall subtropical humid/dry climate with intervals of temperate oceanic climate. acknowledgments i am grateful to the hein, klakken, and finkbinder families, who provided access to their ranches for a field review of the geology. with their permission and support, this research was accomplished. i especially thank david hein of billings, montana, for his passion for this research and his assistance in many aspects of the research. i am grateful to nate murphy, who started me on this project and assisted in providing support and discussion. i appreciate bethany schatzke’s (rocky mountain college, billings, montana) tireless efforts in finding research papers. for this project, tgs-nopec geophysical company donated access to the digital and raster well logs for fergus county, montana, and surrounding areas. a special acknowledgment is due to harry rowe, who completed the geochemical analysis of the mudstones and sandstones at the bureau of economic geology at the university of texas, austin. i appreciate katherine huntington and keith hudson (university of washington, seattle) for performing the clumped isotope analysis. richard lupia (university of oklahoma) and carol hotton (national museum of natural history) freely assisted with the paleobotany. benjamin sames (university of vienna, austria) aided with the identification of invertebrates. quintin carlson assisted with the gis data in mapping the morrison formation. jim shaffer, mitch lukens, serena celestino, linda freeman, deana and michael richmond assisted with the surveying and the stratigraphic measurements. and finally, i am grateful for all the field collectors who took their time to dig and study dinosaurs in montana. as is often the case with a large project with such a broad scope, many unmentioned contributed their time and talents in helping to accomplish this work. kenneth carpenter, university of colorado museum, boulder, colorado, and thomas chidsey, utah geological survey emeritus, and john foster, utah field house of natural history state park museum, carefully reviewed and significantly improved the manuscript. i am very grateful for doug sprinkel, utah geological survey emeritus, for his editing efforts and the time devoted to its publication. references ames, v., 1993, cat creek oil field, in hunter, l.d.v., editor, energy and mineral resources of central montana: montana geological society 1993 field conference guidebook—old timers’ rendezvous edition, p. 129–142. ash, s.r., and tidwell, w.d., 1998, plant megafossils from the brushy basin member of the morrison formation near montezuma creek trading post, southeastern utah: modern geology, v. 22, p. 321–339. baghai-riding, n.l., and hotton, c., 2009, palynological evidence for conifer dominance and arid climate in the late jurassic morrison formation, u.s.a. 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applied geosciences of the technischen universität darmstadt, ph.d. dissertation, 113 p. zhang, y., lui, b., and liang, f., 2019, a new species of coniopteris moguqiensis sp. nov. from the middle jurassic wanbao formation in eastern inner mongolia, china: acta geologica sinica, v. 93, p. 1317‒1324. zhao, l., hong, h., fand, q, yin, k., wang, c., li, z., torrent, j., cheng, f., and algeo, t.j., 2017, monsoonal climate evolution in southern china since 1.2 ma—new constraints from fe-oxide records in red earth sediments from the shenglia section, chengdu basin: palaeogeography, palaeoclimatology, palaeoecology, v. 473, p. 1‒15. about:blank about:blank geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section james i. kirkland, m. ryan king, and kevin g. bylund geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover view to southeast toward the henry mountains from the old notom road, 3190 s. (blm 0086) across morrison and cedar mountain formations to characteristic double escarpment formed of the mancos group on the northern end of the henry mountains basin. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 12 2025 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2024–2025 uga board president keilee higgs keileeann@utah.gov 801.678.3683 president-elect rob buehring robbuehring@yahoo.com 713.412.9269 program chair mike arnoff marnoff@utah.gov 385.303.0431 treasurer will hurlbut wdhurlbut@gmail.com 860.733.3190 secretary trae boman tboman@teanues.com 801.648.5206 past president eugene syzmanski eugenes@utah.gov 801.537.3364 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greggavin@gmail.com 513.509.1509 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.580.1331 aapg house of delegates 2023–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor william lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 75 abstract the mancos group is an upper cenomanian-middle campanian lithostratigraphic unit that records large-scale changes in sedimentation patterns associated with the incursion of the western interior seaway across western colorado into central utah. understanding the stratigraphic relationships in this unit is of critical scientific importance to understanding marine stratigraphic sequences across the globe. this field trip focuses on synonymizing units into consistent lithostratigraphic packages in the framework of biostratigraphy and currently available geochronology. field trip stops emphasize the hierarchical division of each mancos unit, the information present/absent for correlation, and fossil occurrences and how they relate to paleoenvironment and index fauna, as well as disparate sedimentological characteristics (grainsize, bioclastic content, glauconite abundance, cementation). revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section james i. kirkland1, m. ryan king2, and kevin g. bylund3 1utah geological survey, salt lake city, ut 84114 usa; jameskirkland@utah.gov 2western colorado university, gunnison, co 81231 usa; mrking@western.edu 3independent researcher, spanish fork, ut 84660 usa; kgbylund@gmail.com citation for this article. kirkland, j.i., king, m.r., and bylund, k.g., 2025, revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section: geology of the intermountain west, v. 12, p. 75–154, https://doi.org/10.31711/giw.v12.pp75-154. introduction this field trip is part of the 75th annual meeting of the rocky section, geological society of america, and focuses on the proposed lithostratigraphic framework and molluscan biostratigraphy of the cretaceous mancos group in east-central utah. the field trip will examine surficial exposures from the northern henry mountains basin across the southeastern uinta basin, northern paradox basin, and southwestern piceance basin along the book cliffs to approximately loma, colorado, and along the western book cliffs to the northern end of the san rafael swell north of helper, utah, into the mouth of price canyon (figures 1 and 2). the mancos group has important implications for subsurface fluid flow (hydrocarbons, groundwater, and carbon sequestration) as the shale and mudrock units provide a thick seal and are an important aquitard (lines et al., 1983; goodknight and smith, 1996), whereas permeable sandstone units serve as conduits and reservoirs relative to fluid flow. numerous studies have been conducted on the clay-rich shale to understand the quality of the seal in terms of interand intra-granular permeability (goral et al., 2020), fracture and rock mechanics (petrie et al. 2014; chandler et al., 2016; choens et al., 2019), and fluid-rock interactions (espinoza et al., 2018; sheng et al., 2021). studies of the coarser lithologic bodies (e.g., ferron sandstone, emery formation, and prairie canyon) within the mancos group have focused on understanding reservoir characteristics as well 76 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 figure 1. utah’s cretaceous outcrop belt relative to the sevier thrust belt. black text indicates important depositional areas: bb = blanding basin, c = coalville area, cr = capitol reef national park, d = dinosaur national monument, hb = henry mountains basin, kp = kaiparowits plateau, mp = markagunt plateau, pp = paunsaugunt plateau, pv = pine valley mountains, blue g = western extent of greenhorn formation into the blanding basin. red letters indicate location of type sections: bx = bar x shale, bg = blue gate shale, cs = coon spring sandstone member, e = emery formation, f = ferron formation, h = helper formation, jt = jessies twist member, m = mancos group, pc = prairie canyon formation, t = tununk shale, tr = tropic shale. from kirkland et al. (2024). 77 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 as sequence stratigraphic relationships of these units (gardner, 1993, 1995; cole et al., 1997; hampson et al., 1999; anderson et al., 2004; barton et al., 2004; forster et al., 2004; gardner et al., 2004; garrison and van den bergh, 2004; ryer, 2004; stevens, 2004; edwards et al., 2005a, 2005b). the less permeable lithologies have been targeted as shale gas reservoirs and investigated as organic-rich source rocks (schamel, 2008; chidsey and vanden berg, 2015; hawkins et al., 2016). additionally, the surficial/shallow subsurface meteoric processes in the mancos have implications for groundwater and surface water (morrison et al., 2012; mast et al., 2014; tuttle et al., 2014), as well as it being loci for landslide hazards (varnes, 1949; godfrey, 1997). the mancos group is a thick, widespread upper cretaceous marine and marginal marine sequence prefigure 2. late jurassic through late cretaceous tectonic framework for the southwestern united states. depositional basins: bm = black mesa basin, g = axis of the grand canyon bight, hb = henry mountains basin, kb = kaiparowits basin, pb = paleozoic, paradox basin, sjb = san juan basin, ub = uinta basin, zb = zuni basin. red star = mesa verde national park, type area for mancos group. white star = approximate location of classic upper cretaceous sequence west of pueblo, colorado, colorado front range. modified after kirkland et al. (2024). 78 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 served within many basins across the colorado plateau region (figure 2). a highly refined invertebrate biostratigraphy permits detailed correlations of these upper cretaceous strata to be made across the western interior and internationally (figure 3) and has been most recently summarized by cobban et al. (2004) and singer et al. (2023). the mancos shale was initially named by cross (cross and purington, 1899) for “typical exposures” that occur in the mancos river valley between the laplata mountains and mesa verde near mancos, colorado. in this area the unit consists predominantly of marine shale and mudstone with subordinate lithologies including thin beds of limestone (four corners region only), calcarenite, bentonite, concretions, and sandstone. in its type section, in the northern part of the san juan basin, the mancos shale records nearly continuous marine deposition from late cenomanian to earliest campanian time (leckie et al., 1997). kirkland et al. (2024) formally proposed to raise the mancos shale to mancos group (from that of a formation across the region) as its traditional members in utah are already mapped as separate formations. this work extended the original members defined for the mancos shale in central utah eastward as formations separating the members recognized in the mancos shale reference section (figure 4) at mesa verde, colorado, by leckie et al. (1997). at the mesa verde reference section, the only discrepancies with the central utah section included raising of the juana lopez member to formational status separating the tununk interval and blue gate shale, and dividing the tununk interval into two formations, a lower greenhorn formation and an upper carlile shale where the limestone-shale couplets of the bridge creek member are recognized. jameson (1911) originally applied the term “mancos group” to 6698 feet (2042 m) of marine shale and sandstone between the dakota and mesa verde formations in western wyoming. this section included what we now identify as the lower cretaceous, albian-age skull creek shale up into the campanian-age pierre shale. “mancos group” was also applied to the marine upper cretaceous section in northwestern new mexico by zakis (1952), as well as a 1957 study of microfossils in the book cliffs (sarmiento, 1957). in describing the mancos in the henry mountains basin region, peterson and ryder (1975, 1980), noted that the five mappable members were present and should be raised to formation status. molenaar and wilson (1990) more formally raised the mancos shale to group rank on the north figure 3. upper cretaceous time scale used herein vs. current ammonite zonation. data compiled following cobban et al. (2004) and singer et al. (2023). 79 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 sides of the uinta and piceance basins because the frontier and mowry formations were widespread mappable units (formation status): “the mancos is raised to group rank in the report area where it is divided into, in ascending order, the mowry shale, an unnamed shale unit, the frontier formation, and the main body.” on the north side of the uinta mountains, the term mancos is not used. despite the aforementioned exceptions, group rank has not been widely applied to the mancos shale across the core of its outcrop area. at best, it can be said that group usage has been tentative across the uinta and piceance basins (kirschbaum, 2003; u.s. geological survey uinta-piceance assessment team, 2003). figure 4. mancos group reference section at mesa verde national park. correlation of gamma-ray profile of the mancos group principal reference section with geophysical log profiles from the northern part of the san juan basin. modified after leckie et al. (1997) with stratigraphic nomenclature proposed by kirkland et al. (2024). 80 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 the mancos group records several global tectono-eustatic sea level rise and fall sequences or cyclothems. whereas it was initially described more simply in the central western interior of the united states as consisting of symmetrical packages of sediments recording transgression of deepening marine strata over coastal terrestrial strata followed by shallowing marine environments with regression of the sea from the region (kauffman, 1969, 1977; kauffman and caldwell, 1993), it was soon determined that these cyclothems were highly asymmetric, as the shallow marine environments were typically sediment starved. the clastic sediment supply was trapped in the coastal estuarine environments having rising depositional baselevel, with disconformities representing more minor sea level rise events. (ryer, 1976, 1977, 1984; molenaar, 1983; molenaar et al., 2002). three major third-order cyclothems are recorded by the mancos: (1) the cenomanian into middle turonian greenhorn cyclothem recorded by the naturita formation, tununk shale, and lower ferron formation, (2) the middle turonian through lower campanian niobrara cyclothem recorded by the upper ferron formation, juana lopez formation, blue gate shale, emery formation, helper formation, and prairie canyon formation, capped by the regressive marine star point sandstone and lower half of the blackhawk formation (see below), and (3) the upper lower through middle campanian claggett cyclothem recorded by the upper regressive blackhawk formation, bar x shale, lower castlegate sandstone, buck shale and interfingering sego sandstone, and anchor mine shale. the unconformity bound sage breaks hemicyclothem of the upper carlile shale is generally included at the transgressive phase of the niobrara cyclothem as these unconformities are largely amalgamated across the central western interior seaway (hattin, 1975; glenister and kauffman, 1985; mereweather et al., 2007). the upper middle turonian through turonian sage breaks hemicyclothem is recorded by the upper ferron formation, juana lopez formation, and montezuma valley member of the blue gate shale. kauffman et al. (1977) proposed the juana lopez formation and the overlying montezuma valley member represented a t7a-r7a transgressive-regressive cycle of within the overall niobrara cyclothem (kauffman, 1969; kauffman et al., 1977; barlow and kauffman, 1985; leckie et al., 1997; nelson and sonnenberg, 2021). mancos group the lower contact of the mancos group is bound by the transgressive naturita (formerly dakota) formation (carpenter, 2014) and the upper contacts marked by regressive deposits of the mesaverde group that, from south to north, includes the moreno hill formation, toreva formation, gallup sandstone, crevasse canyon formation, straight cliffs formation, muley canyon sandstone, emery formation, star point sandstone, blackhawk sandstone, castlegate sandstone, sego sandstone, and point lookout sandstone (peterson and kirk, 1977; fouch et al., 1983; eaton et al., 1987; eaton, 1990, 1991; franczyk et al., 1992; dyman et al., 1993; elder and kirkland, 1993a, 1993b; cole et al., 1997; leckie et al., 1997). the proposed mancos group lithostratigraphic units are subsequently described in roughly stratigraphic order below as tununk shale (jessies twist member, coon spring sandstone member, blue hill shale member), ferron formation, juana lopez formation, blue gate shale (montezuma valley member, smoky hill member), emery formation, helper formation, prairie canyon formation, and bar x shale. tununk shale the cenomanian-turonian tununk shale (day 1, stop 2, 4, 6, 7; day 2, stop 5) is named for its occurrence in the henry mountains region (figures 1 and 5) by gilbert (1877). the tununk shale is well-exposed across the henry mountains basin (hunt, 1941; hunt et al., 1953), as well as along much of the san rafael swell below the coal and book cliffs. on the east side of the swell, molenaar and cobban (1991) noted the tununk thinned to the southeast, at 400 feet (120 m) thick near farnham dome to about 300 feet (90 m) thick near thompson springs. farther east, merewether et al. (2006) measured a total thickness of 236 feet (72 m) near mack, colorado. the tununk may also form the base of the mancos group across much of the 81 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 blanding basin in southeastern utah. the tropic shale across southern utah (elder et al., 1994; leithold, 1994; eaton et al., 2001; tibert et al., 2003; lauren and sageman, 2007; titus et al., 2016; jones et al., 2019) and the mancos shale at black mesa in northeastern arizona (kirkland, 1991; leckie, et al., 1991) are fully correlative with the tununk shale (peterson and kirk, 1977; eaton et al., 1987; titus et al., 2016) and should be considered as part of the mancos group (kirkland et al., 2024) as the tropic shale of the mancos group. the tununk shale unconformably overlies either the cedar mountain formation/burro canyon formation or the naturita formation (eaton et al., 1990; molenaar and cobban, 1991) across a transgressive unconformity that is often marked by a reworked shell lag of pycnodonte newberryi newberryi and/or p. newberryi umbonatus, oyster taxa specifically indicative of the late cenomanian or early turonian, respectively, and offshore water depths up to 100 feet (30 m) (kirkland, 1996). to the south and east, coquinas of p. newberryi newberryi cap the naturita formation. across the western outcrops, the basal tununk unconformity is characterized by an abundance of pycnodonte with chert and quartzite pebbles up to several centimeters across that are interpreted to have been derived from the basal conglomeratic beds of the naturita formation as they were reworked off the crest of the san rafael swell during the late cenomanian. on the western side of the san rafael swell, the pycnodonts are represented by subspecies p. newberryi umbonata, a variety with a figure 5. type areas of the tununk and blue gate shales. (a) type area of the tununk shale on the flank of gilmore’s (1880, plate 1) tununk plateau on the southwest side of the henry mountains on the south side of the henry mountains basin. oblique view from the south-southwest. (b) type area of the blue gate shale around the blue gate (fremont river water gap) between the north and south caineville mesas. oblique view from the northwest. image source google earth ©2023. 82 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 smooth umbonal (beak) area characteristic of the basal turonian (eaton et al., 1990; kirkland, 1991, 1996; molenaar and cobban, 1991; kirkland and madsen, 2007; santucci and kirkland, 2010; kirkland et al., 2016). the upper contact of the tununk shale is a gradational transition into the lower ferron formation to the west and is unconformable with the juana lopez formation along the book cliffs to the southeast (molenaar and cobban, 1991). from the east side of the swell to colorado the tununk shale can be divided into three lithostratigraphic units: the fine-grained “jessies twist” member and blue hill shale, separated by an intervening sandy interval, termed the coon spring sandstone. jessies twist member in the book cliffs region of eastern utah and western colorado, we propose calling the stratigraphic interval between the basal tununk unconformity and the overlying coon spring member, the jessies twist member (figure 6) with a type section to the southwest of green river, utah (day 1, stops 6 and 7; day 2, stop 5). with only a 1.5° northeastward dip (marshall, 1955), it is estimated that the thickness of the jessies twist member in its type area is roughly 120 feet (37 m). nearby, katich (1951) measured a section across the airport road 1 mile (1.6 km) south of green river reporting 125 feet (38 m) of what we interpret to represent the jessies twist member. this unit is often poorly exposed in the region, but the base is marked by a small (1to 2-inch thick [2–5 cm]) basal chert-pebble conglomerate, which is overlain by a dark-gray slightly calcareous shale (20 to 30 feet thick [6–9 m]) with a prominent bentonite (2 feet [50 cm] thick) grading upwards into 100 to 120 feet (30–36 m) of mediumto dark-gray bioturbated siltstone (molenaar and cobban, 1991). the upper contact of the jessies twist member is gradational with the overlying coon spring member having increasing sand content. the 2-foot-thick (0.6 m) bentonite noted in the middle unit is almost certainly bentonite “c” of elder (1988). we believe that the oyster pycnodonte associated with the basal conglomerate in the green river area may also represent p. newberryi umbonata indicating an earliest turonian age (as in capitol reef national park; kirkland, 1996; kirkland et al., 2016) in this region as well. the base of the tununk is younger in eastern utah and western colorado where pycnodonte newberryi newberryi occurs, indicating a late cenomanian age for the base of the tununk shale in this area (merewether et al., 2006). to the north, the inoceramid mytiloides cf. m. mytiloides is found 15 feet (4 m) above the base of the tununk shale at farnham dome, also indicating an early turonian age for the basal part of the tununk. the upper age is bound by the occurrence of collignoniceras woollgari regulare in the overlying coon spring member, which is middle turonian. coon spring sandstone member the type section of the coon spring sandstone member is northwest of woodside, utah (figure 1). this unit was described by molenaar and cobban (1991) at the 45-foot-thick (14 m) type section as a gradationally based, very fine grained, poorly bedded, bioturbated sandy mudstone grading upward into fine-grained, muddy sandstone capped by 2 feet (60 cm) of resistant, cross-bedded, calcareous sandstone. this upper bed in the coon spring is best recognized by the break in slope formed by a zone of large, often fossiliferous sandstone concretions 5 feet (1.5 m) thick. the name coon spring sandstone (day 1, stops 6 and 7; day 2, stop 5; day 3, stop 2) replaced terms used for the unit in the subsurface (part of the “dakota silt;” munger, 1965) and on the surface (“woodside sandstone;” cotter, 1975, 1976). molenaar and cobban (1991) give no reason for abandoning the name “woodside” from cotter (1975). however, it might be due to the use of woodside (a priori) to describe triassic rocks along the wasatch front in utah as woodside shale (type area woodside gulch, park city area of boutwell [1907]; also used by johnson [1959] and black [1965]) or woodside formation (eardley, 1933; reeside et al., 1957; witkind 1995) and woodside sandstone (witkind, 1994 [used both formation and sandstone]), and in eastern idaho/western montana the woodside sandstone (witkind, 1972; peterson and witkind, 1975; mitchell and bennett, 1979). kummel (1954) used woodside formation across southeastern idaho, western wyoming, and northeastern utah. use of the term “woodside” was further com83 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 plicated by swift (1987) who applied the term woodside sandstone to beds that were santonian in age for a unit near the town of woodside, utah. we discuss this issue and its resolution in the prairie canyon formation section. the coon spring sandstone member is best developed in the area northwest of green river extending north to farnham dome beyond which, and along the west side of the san rafael swell, it is no longer possible to readily separate the tununk shale into members. to the south it appears to be represented by a finer unit near hanksville and caineville (m.a. kirschbaum, u.s. geological survey, communication in molenaar and cobban, 1991; li and schrieber, 2018). merewether et al.’s (2006) blue hills shale member in their mack, colfigure 6. summary of stratigraphic nomenclature for the lower mancos group in the southern uinta basin region. modified after kirkland et al. (2024). l = lower, m = middle, u = upper. correlations based on ammonite zones in figure 3. 84 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 orado, section probably represents the eastern surficial expression of the coon spring sandstone with the upper 85 feet (26 m) representing the blue hill shale member proper. the dominant fossil in the coon spring sandstone member is the large epifaunal oyster rhychostreon suborbiculata, along with common pinna kauffmani, infaunal bivalves, and gastropods indicating a shallow open-marine sand flat environment (kauffman, 1967, 1969; kauffman et al., 1977; kirkland, 1991, 1996). the lower middle turonian ammonite collignoniceras woollgari has been found throughout the coon spring sandstone member with fossils identifiable to the subspecies collignoniceras woollgari regulare in sandstone concretions at westwater, utah, refining the age to the upper subzone of c. woollgari (cobban et al., 2006). the presence of collignoniceras woollgari regulare in the hopi sandy member of the mancos shale at black mesa in northeastern arizona (kirkland 1991, 1996) and small collignoniceras woollgari in the fairport shale member up to the disconformity below the blue hill shale member supports a correlation of hopi sandy member to the coon spring sandstone member associated with the fairport-blue hills disconformity (leckie et al., 1991; leithold, 1994). additionally, molenaar and cobban (1991) noted, “a relatively resistant unit consisting of interbedded, very fine-grained sandstone and siltstone that occurs in the middle of the tununk member in the hanksville and caineville areas, 55 to 65 miles (88–105 km) southwest of green river, is probably equivalent to the coon spring sandstone bed (m.a. kirschbaum, u.s. geological survey, verbal communication, 1989).” the coon spring apparently was deposited as an apron on the south side of the vernal high (merewether and cobban, 1986a, 1986b; ryer and lovekin, 1986; li and schrieber, 2018), and sediments of the coon spring may have been derived from there as well (southern paleocurrents of cotter [1975] and molenaar and cobban [1991]). whereas the correlative hopi sandy member of black mesa, arizona, was derived from the mogollon highlands to the south (kirkland, 1991). blue hill shale member the distinct “blue” shale beds overlying the ostrea shale (fairport chalky shale) were named by logan (1897) for the outcrop in western kansas where it underlies the codell sandstone (hattin, 1962; glenister and kauffman, 1985). with the type section of the blue hill shale member this far east, it is the most widely distributed member in the tununk shale. it is noncalcareous and largely unfossiliferous mudstone that ranges from 80 to 140 feet (24–43 m) thick near green river (katich, 1951; molenaar and cobban, 1991). however, throughout the book cliffs region it is considerably siltier and includes more intercalated thin sandstone layers than are present in the member farther east. the lower contact with the underlying coon spring sandstone member is gradational with the basal blue hill (day 1, stops 6 and 7; day 2, stop 5; day 3, stop 2) consisting of very fine, soft, argillaceous sandstone fining over tens of feet into mudstone and shale. its upper contact with the juana lopez formation is a sharp and disconformable boundary, whereas its upper contact with the overlying ferron formation to the north and west is gradational and intertonguing. in the farnham dome area this interval averages about 130 feet (40 m) thick and forms a slope beneath the resistant ferron. it is expressed as the slope beneath the cuesta-forming juana lopez formation to the south and east. near the woodside anticline, a thick ash bed is present above a resistant, blue-gray, sandy mudstone marker bed, 1 foot (25 cm) or less thick, about 30 feet (9 m) above the top of the coon spring sandstone member or equivalents, as well as a geophysical log gamma spike at this level farther south (molenaar and cobban, 1991). whereas this interval is rather low in the member in eastern utah, it may correlate to a thick ash much higher in the blue hill member at mesa verde, colorado (leckie et al., 1991). the upper part of the blue hill shale member is considered to have been deposited during the prionocyclus hyatti zone as is the equivalent lower ferron formation overlying it to the north of the woodside anticline and along the west side of the san rafael swell. this may account for the relative difference in the position of the thick blue hill bentonite unit. in the northern uinta basin, the thin tununk shale sequence consists only of the blue hill shale member. in the north, kirkland has observed prionocyclus hyatti in these beds in a road cut on the east side of the of the green river near jensen, utah, in 1985. 85 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 ferron formation the ferron sandstone was initially a member named by lupton (1914) for the sandstone, shale, and coal beds in castle valley near and to the south of the town of ferron, utah. kirkland et al. (2024) proposed that the ferron be raised to formation status with elevation of the mancos to a group following the initial suggestion of ryer (2004) for the ferron. whereas no type section was described, lupton (1916) included a section from the ivie creek area south of the town of emery, utah. back then a type section was not required, although ryer (2004) thought this area would have been chosen, where the unit is 476 feet (145 m) thick, because it is representative of the ferron strata (figure 7). davis (1954) subdivided the ferron into upper (day 1, stops 2 and 5) and lower (day 3, stop 5), with the lower ferron up to 70 feet (21 m) thick of fine-grained, carbonaceous, calcareous marine sandstone and siltstone containing two very persistent calcareous concretion zones that thicken to the northwest of emery. the upper unit includes coal-bearing marine and fluvial sandstone (as in the ivie creek area) thickening to the west-southwest (katich, 1953). a petrographic difference further substantiated the upper and lower provenance sources with the increasing presence of garnets in the upper ferron toward the south (see knight, 1953 for details). the lower ferron was subdivided into four units by cotter (1975): the farnham, woodside, washboard, and clawson. the woodside unit should be removed from nomenclature given that molenaar and cobban (1991) identified it as the coon spring sandstone. kirkland et al. (2024) tentatively proposed the washboard and clawson should become elevated to members within the informal lower division of the ferron formation, and the farnham unit, which is of limited lateral extent and is enclosed within the washboard (cotter 1975, 1976), should remain as a unit within the washboard member. subsequent to cotter (1975), only becker et al. (2010) have subdivided the lower ferron formation to the area around farnham dome at the north end of the san rafael anticline (riemersma, 1989; molenaar and cobban, 1991; riemersma and chan, 1991; edwards, 2003, 2005a). to better constrain these relationships, we suggest that additional stratigraphic work is needed across the farnham dome area. in the uppermost tununk shale, immediately below the lower ferron formation, becker et al. (2010) identified a possible collignoniceras woollgari. conversely, given the high density of secondary flank ribs and the lack of long, clavate tubercles on the venter, we think this ammonite represents a juvenile specimen of prionocyclus hyatti (cf. kennedy et al., 2001). medial middle turonian index fossils of the prionocyclus hyatti zone occur throughout strata of the lower ferron. above the lower ferron, the younger prionocyclus macombi, cameleolopha (formerly lopha) lugubris are present in the overlying juana lopez formation (riemersma, 1989; molenaar and cobban, 1991; riemersma and chan, 1991). the two members of the lower ferron formation interfinger with the tununk shale south of emery, as two discrete sandstone beds before pinching out south of interstate 70 (i-70) (chidsey and anderson, 2019). the upper ferron is reported to range from the upper part of prionocyclus hyatti to upper scaphites preventricosus zones in castle valley region (upper ferron suggested type location) indicating a middle turonian to early coniacian age, which is equivalent with the juana lopez formation to the east. whereas the upper ferron in the henry mountains basin is entirely turonian in age (from p. hyatti to p. macombi zones) (gardner and cross, 1994, and references therein). the base of the upper ferron in castle valley is a gradational contact with the tununk (cotter, 1975; peterson and ryder, 1975; ryer, 1981), whereas the top is a sharp flooding surface with local indication of erosion during transgression (garrison and van den bergh, 2004). the top of the upper ferron is represented by a significant unconformity across much of southern utah, with up to 130 feet (40 m) of relief in the henry mountains basin (peterson and ryder, 1975; gardner, 1994). clawson member of the lower ferron formation cotter (1975) named the clawson member, east of the town of clawson, utah, for the poorly sorted, heavily bioturbated sandy siltstone to sandstone with large, brown, carbonate concretions. the clawson is typically 18 to 27 feet (6–9 m) thick (thickest 45 feet [13.7 m] near ferron, utah), stretching from at least northeast 86 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 of huntington to where it grades into the tununk shale southeast of emery, utah (cotter, 1975). cotter suggested both boundaries were gradational with the muddy interval between the clawson and the overlying washboard. the clawson member contains prionocyclus hyatti (biozone namesake), inoceramus howelli, inoceramus flaccidus, and placenticeras pseudoplacenta (molenaar and cobban, 1991). washboard member of the lower ferron formation the washboard member sits gradationally above the clawson member, separated by an intervening muddier interval, as a less than 30-foot-thick [10 m] unit, dominantly composed of thin laminated sandstone and bioturbated silty sandstone named for washboard wash (cotter, 1975). cotter (1975) proposed that the washboard is more laterally extensive than the clawson stretching from farnham dome as thin laminated sandstone interbeds and local hummocky bedded sandstone (farham unit) to the south of the old railroad stops of mounds and cedar as a bioturbated silty sandstone with large concretions. with the exception of becker (2010) subsequent researchers have not extended either the clawson or washboard members into the farnham dome area (day 3, stop 5) (riemersma, 1989; riemersma and chan, 1992; edwards, 2003, 2005). on the north and east side of the san rafael swell the upper contact with the juana lopez formation is sharp, often marked with a sand unit or pebble lag having common and diverse shark teeth (becker et al., 2010), that fines to the east along the south side of the book cliffs where this thin bed overlies the tununk shale (riemermsa, 1989; molenaar and cobban, 1991; riemersma and chan, 1992; edwards, 2003; figure 7. type area of ferron formation. (a) oblique view from east of type area of the ferron formation between emery and ferron, utah. white bar indicates the extent of the mancos group. town sites on utah state route 10, both labeled in yellow. (b) oblique view from east of the ferron creek area across which significant nomenclatural changes have been proposed (e.g., witkind et al., 1987; witkind, 1988). image from google earth ©2023. 87 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 edwards et al., 2005; becker et al., 2010). the washboard member locally contains the middle turonian cameleolopha (formerly lopha) bellaplicata that is associated with the p. hyatti-macombi zones (molenaar and cobban, 1991; hook and cobban, 2012). juana lopez formation the juana lopez formation (day 2, stop 6; day 3, stops 2 and 4) is 107 feet (32.6 m) thick in its type area in north-central new mexico. here it includes the lower middle turonian prionocyclus macombi zone up into the basal upper turonian prionocyclus novimexicanus zone (dane et al., 1966; hook and cobban, 1980, 2013; cobban et al., 2006). the juana lopez is characterized as an alternating sequence of interbedded dark olive-gray noncalcareous shale and calcarenite composed largely of calcite prisms from inoceramid shells and oyster shell fragments. along the southside of the book cliffs the juana lopez is 80 to 100 feet (24– 30 m) thick (molenaar and cobban, 1993). fossiliferous concretions are common particularly in the upper parts of this formation. katich (1951) first recognized these strata (his “castlegate shale”) as a distinctive sequence of interbedded thin sandstone and dark shale preserving a prionocyclus wyomingensis fauna above his “woodside sandstone” (equivalent to lower ferron formation) around the north end of the san rafael swell to the south in ferron creek, where the beds interfingered with the ferron sandstone (equivalent to upper ferron formation). across most of the book cliffs region from south of farnham dome and to the east as far as the canyonlands field airport north of moab, the juana lopez includes a sharp basal mediumto coarsegrained sandstone with grain-supported chert pebbles and shark teeth interpreted to represent a transgressive unconformity that cut out the more distal facies of the lower ferron formation (molenaar et al., 1993; becker et al., 2010, 2012). farther to the east and southeast, a basal calcarenite bed marks the base of the juana lopez and includes the prionocyclus macombi zone (leckie et al., 1997; merewether et al., 2006, 2007). the unconformity below the juana lopez shows no evidence of subaerial exposure or incision by channels (riemersma and chan, 1992). the upper contact of the juana lopez formation is generally difficult to discern at outcrop where it occurs at the top of the long dip slope formed above the ridge of resistant sandstone and calcarenite in the prionocyclus wyomingensis zone. the top of the juana lopez should be placed lithostratigraphically at the top of the highest calcarenite or fine sandstone layer, above which, the shale beds are lighter in color and calcareous, marking the base of the blue gate shale. the underlying dip slope is typically shingled by thin plates of sandstone and calcarenite. fossils of scaphites ferronensis and scaphites whitfieldi indicate the age of the formation ranges into the basal upper turonian prionocyclus novimexicanus zone. from the south side of the farnham dome along the entire mancos group outcrop belt, the juana lopez is characterized by differential weathering of a low hogback formed by a resistant series of calcarenite beds deposited during the latest middle turonian prionocyclus wyomingensis zone. these beds are characterized by distinctive assemblage of fossils including scaphites warreni (zone name bearer), inoceramus dimidius, and cameleolopha (formerly known as lopha) lugubris (cobban, 1951; walaszczyk, and cobban, 2000; kennedy et al, 2001; cobban et al., 2006; hook and cobban, 2012). below these beds is a slope-forming interval of varied thickness characterized by concretions that commonly preserve the mollusks prionocyclus macombi and inoceramus dimidius. along the ruby ranch road (day 2, stop 6), the base of the prionocyclus wyomingensis zone overlies the basal juana lopez disconformity. farther east along the colorado-utah state line, nearly the entire juana lopez may have been deposited in the underlying prionocyclus macombi zone (merewether and cobban, 2006). molenaar and cobban (1993) proposed that the juana lopez did not extend west of farnham dome and instead grades laterally into the ferron formation. marking a rare instance where the authors disagree with them, we noted on the west side of farnham dome that rippled fine-grained sandstone and shale and sandy calcarenite preserving prionocyclus wyomingensis and scaphites ferronensis are present above the top of the lower ferron formation dip slope. these beds are in turn capped by a thick sequence of dark olive-gray, noncalcareous shale capped in turn by pleistocene ter88 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 race gravels. these shale beds are characteristic of the juana lopez formation. furthermore, kevin bylund (unpublished guidebook, 2002) has shown kirkland fossiliferous outcrops characteristic of the juana lopez overlying the lower ferron formation from north of ferron creek to well north of the cleveland, utah, area. as opposed to many publications (i.e., dereuil and birgenheier, 2018), the juana lopez formation is interpreted to correlate with the upper ferron formation to the southwest as had previously been noted by katich (1951) in his unpublished ph.d. dissertation, with the lower ferron underlying it. the upper prionocyclus wyomingensis-scaphites ferronensis-bearing and younger juana lopez strata extend west across the northern san rafael swell and continue south until these beds merge into the northern extent of the upper ferron “last chance delta” at ferron creek. blue gate shale the type area of the blue gate shale is exposed around the “blue gate” between the south and north caineville mesas in western wayne county, utah (figure 5b). this unit is largely correlative with the montezuma valley member, smoky hill member, and lower 535 feet (163 m) of the cortez member as defined in the mancos group type area at mesa verde national park (gilbert, 1877; leckie et al., 1997, molenaar et al., 2002). to the north along the southern coal cliffs, the blue gate (day 1, stops 1, 5, and 8; day 2, stop 6) is restricted to the interval between the top of the upper ferron formation or juana lopez formation to the base of the emery or prairie canyon formations (figure 6). the blue gate on the western side of the san rafael swell is lower coniacian to upper santonian and about 3500 feet (1070 m) thick. around the north end of the san rafael swell to just east of price, utah, the blue gate ranges from late turonian to latest santonian in age. from the northern part of the san rafael swell along the entire book cliffs eastward into colorado, the blue gate can be divided into two members—the lower upper turonian montezuma valley member and an unconformably overlying and much thicker smoky hill member. the montezuma valley member has not been recognized along the western side of the san rafael swell or in the henry mountains region where it is currently impossible to divide the blue gate shale into members. to the east the blue gate member is largely replaced by the niobrara formation with the northward and western limits of the fort hays limestone angling to the west between pagosa springs south and north of fruita in the grand valley, colorado. the fort hays limestone and the niobrara formation do not seem to cross the douglas creek arch into the uinta basin (cole and hood, 2014; nelson and sonnenberg, 2021). montezuma valley member the montezuma valley member was first described at mesa verde national park where it consists of 53 feet (16.2 m) of slightly silty to slightly sandy calcareous shale that contains numerous septarian concretion horizons (leckie et al., 1997). in western colorado near mack, it is represented by an interval that merewether et al. (2006) recognized as 115 feet (35 m) of medium to dark-gray, slightly calcareous shale with fossiliferous concretions preserving scaphites whitfieldi sharply overlying (conformably or disconformably) the juana lopez formation. the lower blue gate is generally poorly exposed across the study area, and the presence of concretions, calcareous shale, and an upper turonian fauna are the best indicators of the montezuma valley member. this interval between the top of the juana lopez and the glauconitic sandy unit f-1 of anderson and harris (2006) and ressetar et al. (2014) represents the montezuma valley member with the thickness ranging between 160 and 260 feet (50–80 m) across the uinta basin. the upper contact of the montezuma valley member is unconformable with the overlying smoky hill member, which is recognizable at a distance as a yellowish-band in a low bluff on the northeast side of the loma exit off i-70 in western colorado (day 2, stop 1). the montezuma valley is upper turonian in age based on the presence of prionocyclus novimexicanus (biozone namesake) and mytiloides incertus along ruby ranch road southeast of green river (kirkland et al., 2024). it also includes the prionocyclus novimexicanus and scaphites whitfieldi fauna (stephen et al., 2012) a few feet above the top of the juana lopez formation in the canyonlands field airport (courthouse syncline) area, north of moab, and 89 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 near the grassy railroad siding north of woodside on the east flank of the san rafael swell (forster et al., 2020). smoky hill member as also documented at mesa verde national park (leckie et al., 1991), the lower calcareous shale of smoky hill member along the book cliffs unconformably overly the montezuma valley member (day 2, stops 1 and 7; day 3, stop 1). conversely, the upper smoky hill member is a noncalcareous shale over hundreds of feet thick below its sharp contact with the overlying prairie canyon formation. the smoky hill is thickest in the west, ranging from about 2900 feet (885 m) to around 1900 feet (580 m) in the central and eastern uinta basin (ressetar et al., 2014). the base of the unit is denoted by a glauconite-bearing sandy mudstone zone (figure 6) that is widespread across outcrops of western colorado from mesa verde northward to mesa county (leckie et al., 1997; merewether et al., 2006; ball, 2015; nelson and sonnenberg, 2021). in the subsurface this is referred to as the f-1 glauconite zone of anderson and harris (2006) and ressetar et al. (2014). this unconformity at the top of the underlying montezuma valley member/base of smoky hill member apparently extends across nearly the entirety of the cretaceous western interior seaway marking the base of the main niobrara sequence (merewether et al., 2007). the oldest fossils recognized in the lower smoky hill member in the book cliffs area are of middle coniacian age. along the ruby ranch road to the southeast of green river these include inoceramus undabundus (walaszczyk and cobban, 2006) previously identified as inoceramus (platyceramus) stantoni in the revision of the mancos shale (leckie et al., 1997). up section, thick inoceramid shell fragments interpreted to represent volviceramus involutus are found through the coniacian above the base of the smoky hill with species of magadiceramus ranging through the entirety of the upper coniacian (kirkland et al., 2024). the basal glauconitic unit may also be present along the ruby ranch road, where a less distinctive yellowish-band is associated with fragments of volviceramus shells (kirkland et al., 2024). the shell fragments are identified by their thick shells (about 1 cm thick), smooth external surface lacking evidence of rugae as in the thinner-shelled, lower coniacian species of cremnoceramus or basal middle santonian volviceramus koeneni. the curved shell fragments suggest enrolled shells, unlike the large santonian species platyceramus, which occurs in abundance up section (walaszczyk and cobban, 2000; cobban et al., 2006). these examples of platyceramus cycloides are so abundant northeast of green river that this area has been nick-named the “platyceramus hills” (day 1, stop 8). farther west, in the sevier foredeep basin on the west side of the san rafael swell from castle dale south to about i-70, lower coniacian inoceramid cremnoceramus deformis and ammonites forresteria alluaudi and scaphites preventricosus occur (kennedy and cobban, 1991; gardner and cross, 1994; bylund and stephen, in press). these same fossil indicators of the lower coniacian are present even farther west in sanpete valley and to the north near manti, and record the farthest evidence of the westernmost extent of marine strata of the niobrara cyclothem and the mancos sea in general. a distinct bluff held up by a series of thin sandstone beds in the lower smoky hill member can be traced from green river north to woodside. kennedy and cobban (1991) report scaphites ventricosus in a low ridge-forming sandy unit 19 miles (31 km) north of green river. this bed potentially overlaps scaphites depressus (as asserted by landman et al., 2017) in the basal upper coniacian. however, concretionary sandstone beds outcrop below the main sandstone unit at the first stop on day 3 and may well be the source of the scaphites ventricosus. to the south along ruby ranch road another more distinctive sandstone-capped bluff extends across floy wash and is associated with upper coniacian fauna, which includes mytiloides crenulatus. based on our cursorial examination of these outcrops (kirkland et al., 2024), it is possible that the smoky hill member includes a series of silty and sandy horizons. however, the zone preserving the scaphites depressus fauna is certainly the most prominent and we suggest naming this sandy interval the “floy wash sandstone bed” (figure 6) (day 2, stop 7). to the east, this bed was potentially recognized by willis (1994) and mapped as the m-2 unit across the agate quadrangle. in the subsurface of the uinta basin, this unit has potentially been recognized by ressetar et al. (2014) as the “blue gate silt.” 90 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 emery formation the emery sandstone (referred to now as the emery formation) was first described by spieker and reeside (1926) as a member of the mancos shale for a series of interbedded sandstone, siltstone, and silty shale below the wasatch plateau southwest of emery, utah (day 1, stop 1). these strata were traced along the coal cliffs, where, at the northern end of the outcrop near price, utah, the lower bench-forming interval of the emery (day 3, stop 7) was formally described as the garley canyon sandstone (fouch et al., 1983). the emery formation is only mapped eastward to just north of price (witkind, 1995), where the sandstone beds interfinger into the upper blue gate shale. in outcrop, the emery can only be traced south of i-70 until the beds are covered by colluvium near the last chance monocline west of cathedral valley. it has been noted that they extend west into the subsurface for a few miles before merging with the mesaverde group along with the subsurface interfingering pinch-out of the overlying helper formation (ryer, 1984; franczyk et al., 1992; edwards et al., 2005). a 204-foot-thick (62.1 m; third informal unit) sandy interval in the middle of the cortez member at mesa verde national park is correlative with the emery formation (leckie et al., 1997). smith (1983) replaced the improper use of the emery sandstone in the henry mountains basin (hunt, 1946) with campanian-age muley canyon sandstone member of the mancos shale, which eaton (1990) later raised to formational rank. ryer (1984) noted that the emery is 820 feet (250 m) thick on the southern end of the wasatch plateau and caroll (1987) plotted approximately 1150 feet (350 m) on the north end of the coal cliffs west of price canyon. edwards et al. (2005) recorded a range of 740 to 1640 feet (225–500 m) although his measured sections only ranged from 740 to 984 feet (225–300 m) and indicate that the emery formation thickens rapidly westward in the subsurface. edwards et al. (2005) documented 17 coarsening upward parasequences within the emery that he correlated along the wasatch plateau with coal-bearing fluvial sequences capping some of these sequences in the subsurface to the west. they noted that the bulk of the emery consisted of partially amalgamated, bioturbated or hummocky cross-stratified, well-sorted, fineto very fine grained sandstone arranged in upward-coarsening and -thickening beds interspersed with silty shale. across the mouth of price canyon, caroll (1987) and russon (1987) noted a dozen sandstone beds in the emery formation above the garley canyon sandstone, for which caroll (1987) named the upper three as new members of the upper mancos shale. these were from bottom to the top of sequence: (1) the 21-foot-thick (6.7 m) dempseyville sandstone member overlain by 121 feet (27 m) of mostly covered shale, below (2) the 47.9-footthick (14.6 m) bull point sandstone overlain by 66 feet (20 m) of silty shale, below the locally capping (3) the 23 feet (7 m) of wildcat canyon sandstone. these stratigraphic units are west of kirkland et al. (2024) study area as mapped and deserve further investigation. the top of the wild cat sandstone was picked as the base of the newly defined helper formation discussed below. kirkland et al. (2024) questioned if any of these sandstone members, which they noted as largely lenticular, warrant member status. one of us, k.g. bylund, has collected many examples of clioscaphites vermiformis from the basal emery formation northward into the garley canyon sandstone member, as first noted by cobban (1976). cobban (1976) also noted the collection of a partial desmoscaphites bassleri and cataceramus balticus at the top of the emery just east of u.s. highway 6/191 between spring glen and helper north of price. this locality is east of where the upper emery is mapped (weiss et al., 2004) but is still clearly near the top of the emery formation proper and may be correlated below the lenticular wildcat sandstone bed of caroll (1987). these index fossils would bracket emery deposition as ranging from within the middle santonian to latest santonian in the area around price (cobban et al., 2006; singer et al., 2023). this correlation indicates that the helper formation correlates with the upper smoky hill member in the eastern book cliffs (figures 6 and 8). the sandstone-filled scours at the base of match mesa's prairies canyon sequence (stevens 2004; chaiwongsaen, 2007), and our beckwith sandstone bed (described nomenclatural change below) at the base of the western book cliffs, may correlate to the transgressive surface at the top of the helper formation. 91 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 8. cross section of the cretaceous along the book cliffs. (a) original cross section from cole (1987) working with robert young. (b) cole (1987) modified to reflect proposed nomenclature. note scale does not permit plotting of the members of the tununk shale on cross section. members of the tununk shale can only be differentiated by medial coon spring sandstone member extending from north of sunnyside southwest into westernmost colorado. 92 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 the lowest sandstone interval of the emery formation (day 3, stop 6) forms a double-tiered sandstone bench at the northern end of the san rafael swell northwest of price, utah. this unit has been formally described as the garley canyon sandstone member (fouch et al., 1983). this unit records two major coarsening upward sequences (fouch et al., 1983; edwards, 2005). this member ranges from its lateral pinch-out east of helper, utah, to 209 to 233 feet (64–71 m) thick to the west on the standardville quadrangle (carol, 1987) before merging to the south into the lower emery formation west of price. it is mapped from the southern border of carbon county on the west side of the san rafael swell northward to the east side of u.s. highway 6/191 north of price (witkind, 1988, 1995). the garley canyon member is middle santonian (figures 3 and 5), dated to the clioscaphites vermiformis zone (cobban, 1976; edwards et al., 2005; cobban et al., 2006; singer et al., 2023). helper formation the proposed “helper formation” (day 1, stop 1; day 3, stop 7), and the underling emery formation that bounds it, only occurs in the western part of the san rafael swell, extending from helper down to i-70. the helper is denoted as a formation rather than a shale interval, because it is dominantly poorly bedded or structureless silty-sandy mudstone with sandier zones increasing into the overlying star point sandstone (kirkland et al., 2024). the helper formation is 540 to 650 feet (164–201 m) thick in this region. the basal contact of the helper formation is sharp with the top of caroll’s (1987) 23-foot-thick (7 m) “wildcat canyon sandstone” bed which caps the emery formation in this area. the upper contact is a rapid gradational transition, which can be defined as the transition from a dominance of silty to sandy mudstone with subsidiary sandstone beds to more than 50% sandstone with the basal 79 feet (24 m) of the helper generally fining upwards from a sandy mudstone with minor occasional sandstone beds. the santonian-campanian boundary probably lies within the lower part of helper formation based on the occurrence of baculites aquilaensis 300 feet (91 m) below the base of the star point sandstone about 1 mile (1.6 km) east of kenilworth, utah. this baculite is characteristic of the range of lower campanian forms of scaphites hippocrepis (reeside, 1927; cobban, 1976) suggesting that the helper formation correlates to the lower parts of the prairie canyon formation to the east. the helper merges into the prairie canyon just east of kenilworth, utah, with the pinch-out of the overlying star point and the projected eastern limit of the top of the underlying emery. near the top of the helper is a 16.5-foot-thick (5 m) unit named the trail canyon sandstone member within the upper mancos group (caroll, 1987; hansen, 1996). this unit is 95 to 118 feet (29–36 m) below the star point west of price canyon. the trail canyon was apparently never officially defined in a publication nor can it be used because the name trail canyon is already defined for a unit in the oquirrh group of idaho (cramer, 1971). prairie canyon formation originally known widely as the “mancos b” (e.g., cole, 1987; cole and young, 1991), the prairie canyon formation (day 2, stops 2 and 3) is 1000 feet (300 m) thick near the utah-colorado border. across the outcrop belt the unit can range from 384 to 1220 feet (117– 372 m) in thickness (cole et al., 1997). the prairie canyon formation crops out along a lengthy swath at the base of the book cliffs from north of woodside, utah, to east of grand junction, colorado (hampson et al., 1999). the prairie canyon formation is correlative to the upper 755 feet (230 m) (upper three informal units) of the cortez member of the mancos group at mesa verde national park (leckie et al., 1991). the lower contact of the prairie canyon formation is a sharp change from fissile, silty claystone to interlaminated sandstone and shale around 2300 feet (700 m) above the base of the blue gate shale. the lower prairie canyon is often covered in outcrop, although the more resistant nature of the cleaner, better-cemented, sandstone layers often result in a change of the topographic profile (cole et al., 1997). conversely, a shift to finer lithologies 295 to 425 feet (90–130 m) below the lower castlegate (cole et al., 1997; gall et al., 2020) marks the 93 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 top of the unit. this shift is more subtle in outcrop and is best mapped at the color change between olive-gray silty and sandy prairie canyon strata and dark olive-gray, organic-rich shale of the overlying bar x shale. the gradational upper contact is more easily recognized in the subsurface with geophysical logs. the lower interval of the prairie canyon formation is composed of 358 feet (109 m) of thinly interbedded, very fine grained sandstone (discontinuous in nature) and shale, with scattered sandy dolomite concretions overlying a scoured coarse-grained surface preserving desmoscaphites bassleri (cole et al., 1997). the correlation of the basal beds of the prairie canyon is controversial. fouch et al. (1983) illustrated the lower part of the prairie canyon as a sandy zone with discontinuous beds that stretched from the distal parts of the emery formation near sunnyside, utah, extending to the utah-colorado border. franczyk et al. (1992) suggested that these discontinuous sand bodies of the uppermost santonian (desmoscaphites bassleri zone; at the base of the prairie canyon member) go from near hanksville, utah, northward into wyoming. this lower interval of the prairie canyon has been mapped as an extension of the emery formation (clark, 1928; cullins, 1968; russon, 1987) or “mancos b” within the subsurface (kellogg, 1977; cole, 1987). additionally, there seems to have been some nomenclature confusion as to whether this unit relates to the woodside sandstone. hampson (1999) notes that cotter (1975), in defining it, made it a lower sandstone unit of the ferron formation southwest of woodside, utah. hampson also noted that swift et al. (1987) and chan et al. (1991) correlated it to the emery formation. this confusion began with swift et al. (1987) in noting that the occurrence of desmoscaphites bassleri in a sandstone unit below the book cliffs east of woodside as reported by reeside (1927) and cobban (1987) was from the same “woodside sandstone” described by cotter (1975) that is now accepted as the coon spring sandstone member (molenaar and cobban, 1991). given the current referral of this sandstone interval to nomenclature already used in the triassic (see above explanation in the coon spring section), we propose to rename the woodside sandstone of swift et al. (1987) and the emery marker of cole (1987) to the beckwith sandstone bed (figures 6 and 8)—an unconformable marker bed at the base of the prairie canyon formation. the beckwith sandstone bed is best expressed around the base of the beckwith plateau. the term, beckwith formation, was used by veatch (1907) for early cretaceous beds in southwestern wyoming, but was formally abandoned only nine years later by mansfield and roundy (1916). although we define the beckwith sandstone bed as an informal unit here, we plan to formalize its nomenclature in the near future. cole et al. (1997) considered the lower prairie canyon formation to extend from the upper d. bassleri to s. hippocrepis i zones, with the middle prairie canyon to be dominantly within the s. hippocrepis ii zone. cole also considered the upper prairie canyon to be from the s. hippocrepis iii-baculites sp. (smooth) zones indicating latest santonian through early campanian age for the entirety of the formation. farther west from the type area near green river, utah, the main sand interval of hatch mesa sandstone (day 2, stop 8) and the middle mountain-gunnison butte lenticular body have been mapped as equivalent to the kenilworth member in age (kp2 of pattison, 2005). however, the lowermost isolated dolomitic sand bodies of the hatch mesa area are desmoscaphites bassleri zone equivalent to the top of the emery formation in the uppermost santonian (stevens, 2004; chaiwongsaen, 2007), and the intervening coarse channelized sandstone and oolite contain scaphites hippocrepis (cobban ids in stevens’ [2004] stratigraphic framework). stevens (2004) has suggested that in the hatch mesa area that the lower prairie canyon member includes a basal interval of channelized coarser sediment and dolomitic sandstone with dolomicrite within dominantly mudstone beds. fossils of the d. bassleri-s. hippocrepis zones support a correlation westward to the beckwith sandstone bed and uppermost emery formation. given the somewhat contradictory biostratigraphic determinations and the lack of figured specimens and, for the most part, the complete absence of curated proxy specimens, we follow the consistent reports of desmoscaphites bassleri occurring at the scoured base of the type section of the prairie canyon formation. the desmoscaphites bassleri is below the basal dolomitic sandstone beds in the hatch mesa area, and in the beckwith sandstone bed (day 3, stop 3), which is along the base 94 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 of the eastern book cliffs from green river to the north of sunnyside, utah, and at the top of the emery formation north of price, utah (reeside, 1927; cobban, 1987; cole et al., 1997; stevens 2004; chaiwongsaen, 2007; casaleggio, 2009). this surface is tentatively identified as representing a transgressive disconformity marking sea-level rising and expanding shoreward over the emery formation. thus, this scoured surface marks an appropriate mappable lower contact for the base of the prairie canyon (cobban et al., 2006; singer et al., 2023). the middle prairie canyon formation is 413 feet (126 m) thick in the type area (day 2, stop 3). cole et al. (1997) described four coarsening upwards sequences (sequence a through d) that are prominent in outcrop due to their sandy nature. these intervals commonly include poorly to moderately sorted, bioturbated siltstone-sandstone with prominent dolomite marker beds similar to those in the cortez member (figure 4) of the blue gate shale at mesa verde (leckie et al., 1997). persistent dolomite-cemented markers are present to the west (salt wash to strychnine wash areas, utah) and have been named in descending stratigraphic order as w, x, y, z (hampson et al., 1999). these intervals/ markers are not correlated into the a through d intervals of the type area but are correlated through subsurface data to the middle interval of the prairie canyon (hampson, 2016). the rarity of biostratigraphically significant fossils and the absence of proxy specimens in curated collections has hindered the correlation of beds within the prairie canyon formation across the region (kirkland et al., 2024). the hatch mesa sandstone, which forms a bench dominated by interbedded ripple-laminated sandstone and mudstone topped by three bentonite beds, may correlate with the middle prairie canyon formation (stevens, 2004). conversely, due to lack of biomarkers, hampson (2010) agreed more with pattison (2005) in correlating the hatch mesa sandstone (middle interval of prairie canyon member of stevens, 2004) to the second sand body in the kenilworth member, suggesting middle prairie canyon based off well log correlation (middle prairie canyon of stevens, 2004— the type area roughly equivalent to much of the kenilworth). kirkland et al. (2024) suggest that tracing the beds laterally in outcrop indicates that the kenilworth member of the blackhawk formation broadly correlates to the upper part of the middle and upper interval of the prairie canyon (figures 6 and 8), but biostratigraphic testing is critical. the upper interval of the prairie canyon formation is dominantly shale with variable silt-sand content with abundant sandy dolomite concretions. it is 413 feet (126 m) thick at the type locality (cole et al., 1997). welllog correlation of chaiwongsaen (2007) and hampson (2010) suggests the upper prairie canyon correlates to the interval of the upper part of the kenilworth member to near the top of the grassy member in the west. however, by tracing the relationships of the overlying bar x shale to the west into the blackhawk formation, it is apparent that the top of the prairie canyon essentially correlates to the top of the kenilworth member of the blackhawk. thus, to the west, the prairie canyon interfingers into the lower blackhawk and star point sandstone with the name for its lower part being replaced by helper formation north of price, where that sequence is sandwiched between the top of the underlying emery formation and overlying base of the star point sandstone. instead, howell and flint (2002) suggest that the prairie canyon correlates with the upper blackhawk. to the east the prairie canyon formation is traceable across the piceance basin (hampson, 2016), beyond which it would grade into the upper smoky hill member of the niobrara formation and the basal pierre shale. gill and hail (1975) show baculites sp. (weak flank ribs) around 26 feet (8 m) below the top of the prairie canyon at the type locality. kirkland identified baculites sp. (weak flank ribs) in the shale beds close to the basal contact of the overlying bar x shale at prairie canyon, western colorado, suggesting the total prairie canyon formation spans the upper santonian d. bassleri zone to the lower campanian baculites sp. (smooth form)-baculites sp. (weak flank ribs) zone (cobban et al., 2006; singer et al., 2023). bar x shale kirkland et al. (2024) proposed naming the shale interval between the top of the prairie canyon formation up to the base of the mesaverde group the bar x 95 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 shale (day 1, stop 8; day 2, stops 2 and 3) for the bar x ranch area in easternmost utah along the west side of prairie canyon (figures 1 and 8). the type section is 337.5 feet (102.9 m) thick. the formation consists of dark olive-gray shale and silty shale with light yellowish-brown sideritic siltstone beds and large fossiliferous dolomitic concretions. the upper 70 feet (22 m) includes many more interbeds of fine sandstone and grades through more than 10 feet (~3 m) of interbedded thin sandstone and silty shale into the overlying castlegate sandstone. these upper beds grade into the desert and sunnyside members of the blackhawk formation farther west in eastern utah. its lower contact with the underlying prairie canyon formation is placed where sandy and silty shale is rapidly replaced by darker more carbon-rich shale. farther west, its lower contact is placed similarly, with the correlative top of the kenilworth member of the blackhawk formation. the bar x shale is richly fossiliferous in its type area. the unit preserves a diversity of ammonites, inoceramid bivalves, and even fossil crabs and conifer fragments. ammonites indicate it ranges from the upper lower campanian baculites sp. (smooth 1) or baculites sp. (weak flank ribs) zones up through the lower middle campanian baculites maclearni zones correlating to the lower pierre shale of eastern colorado and wyoming (gill and cobban, 1966; cobban et al., 2006, singer et al., 2023). the bar x contains noteworthy vertebrate fossils where it crosses prairie canyon, including plesiosaurs, mosasaurs, and a juvenile hadrosaur identified as being a species of gryposaurus (carter et al., 1987; lucas et al., 2006). its extensive middle campanian marine vertebrate fauna is reminiscent of that preserved in the correlative sharon springs member of the pierre shale (gill and cobban, 1966; carpenter, 1996a, 1996b; bertog, 2010), although its more diverse benthic fauna suggests a better oxygenated seafloor. several distinct bentonites occur in the lower part of the bar x, including 0.5 feet (16 cm) ash at 64.3 feet (19.6 m), may be correlative to the ardmore bentonite marker bed in the lower sharon springs member of the pierre shale of wyoming (gill and cobban, 1966). in the piceance basin, farther to the southeast, beyond the pinch-out of the overlying castlegate, this stratigraphic interval between the underlying prairie canyon formation and the overlying informal lujane point sandy shale bed, correlates to the lower pierre shale from the sharon springs member down to its base (noe et al., 2007; noe 2010; cole and hood, 2014). this bar x shale has also been described as the “castlegate condensed zone” in the subsurface within the piceance basin of colorado where it is an important petroleum source rock (schwendeman, 2011; rogers, 2012). buck shale fisher (erdmann, 1934; fisher, 1936) named the buck tongue from buck canyon to the north of cisco, utah, where it is 269 feet (82 m) thick. it thickens eastward to the utah-colorado border where it is 351 feet (107 m) thick before the castlegate sandstone pinches out beneath it to the east (fisher 1936). the basal contact of the buck shale of the mancos group with the lower castlegate below is often sharp, marked in a more proximal (northwest) position by a potential paleosol horizon of nodular hematitic mudstone and chert that stretches almost to green river (hettinger and kirschbaum, 2002). the buck shale (day 2, stop 2) has baculites perplexus in the lower half of the member (gill and hail, 1975) that are older than the mollusks of the basal baculites scotti zone in the sego sandstone above (zapp and cobban, 1960). kirkland (herein) identified baculites (smooth 2) and cataceramus at the base of the buck shale in easternmost utah near the state line. this indicates a middle campanian age spanning three to four ammonite zones, baculites sp. (smooth 2) through baculites reduncus (cobban et al., 2006; singer et al., 2023). the buck shale pinches out into the lower mudstone of the price river formation at the beckwith plateau northwest of green river, utah (day 2, stop 9). witkind (1988) used the green river in desolation canyon, utah, as the cut off point for the stratigraphic nomenclature of the eastern and western book cliffs. to the east in colorado, beyond the castlegate pinch-out, the buck shale is recognized between the lujane point beds and overlying sego sandstone in the southern piceance basin until it merges eastward(?) with the anchor shale (noe, 2010; cole and hood, 2014). kirkland et al. (2024) suggested that from this point east, it may be best to revert to pierre shale terminology for the uppermost mancos group. within 96 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 the northern and central piceance basin, the loyd sandstone sequence is completely within the buck shale dividing it into a lower and upper sequence (gill and hail, 1975; rogers. 2011; schwendeman, 2011). anchor mine shale the anchor mine shale (day 2, stop 2) was originally named the anchor mine tongue of the mancos group for the finer deposits splitting the sandstone beds of the sego sandstone (erdman, 1934). at the utah-colorado state line the anchor mine shale is around 100 feet (30 m) thick. the unit extends eastward until the lower parts of the sego pinch-out north of fruita, colorado (young, 1955, 1957). farther to the east the unit merges with the underling buck shale. at this longitude the unit is 233 feet (71 m) thick (hettinger and kirschbaum, 2002). the basal contact of the anchor mine is sharp with an abrupt fining of grain-size (willis and gabel, 2003). the anchor mine contains pinching and swelling sand bodies with the upper contact of the unit often shown to be sharp. locally the upper contact is gradational (gill and hail, 1975; van wagoner, 1991; willis and gabel, 2003). the anchor mine spans the middle campanian based on baculites gregoryensis to low baculites scotti zones (young, 1983), didymoceras binodosum (lower b. scotti zone) in the lower parts of this unit (kennedy and cobban, 1991), as well as b. scotti within the middle and upper parts of this unit (gill and hail, 1975). road log the road log consists of three days across central utah (figure 9). the first day starts in salina and ends in green river, utah. the second day starts and ends in green river. the third day starts in green river and ends in spanish fork, utah. day 1 road log starts in salina, utah inc. cum. mileage mileage milepost description 0 0 mp-56.5 enter i-70 eastbound at exit 56 from salina. extensive exposures of middle jurassic arapien formation in this area are contorted by diapiric movement of salt and gypsum layers. 2.5 2.5 mp-59 dirt frontage road ends on north side of i-70. 0.4 2.9 mp-59.4 road cut to north side of i-70 (left) exposing cedar mountain formation at base of utah’s cretaceous section. (figure 10). unfortunately, given the long drive to the first day’s stops, these important outcrops can only be pointed out as the trip passes by (n. 38° 56.023, w. 111° 48.060; 12s e. 430574 n. 4309726). the westernmost exposures of cedar mountain formation in central utah are in the san pitch mountains southeast of nephi, and near the mouth of salina canyon (figure 10). farther to the west, it correlates to the lower part of the canyon range conglomerate (sprinkel et al., 1999). in salina canyon, the cedar mountain is dominantly pale variegated mudstone and sandstone and is 617 feet (188 m) thick (sprinkel et al., 1999) representing the skull creek-thermopolis cyclothem. the cedar mountain is separated from a few tens of feet of strata tentatively assigned to the upper jurassic morrison formation at its western pinchout by a poorly exposed conglomerate 97 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 that is assumed to be the buckhorn conglomerate member of the cedar mountain formation (d.a. sprinkel, utah geological survey, personal communication, 2004). there is no established morrison foredeep basin, it pinches out and the thickened pale variegated mudstone sequences to the west are representative of the aptian-albian ruby ranch member of the cedar mountain formation (kirkland et al., 2016). the absence of upper jurassic strata to the west is a possible figure 9. cretaceous outcrops (in green) of east-central utah with field trip route and stops. l indicates lunch stop. 98 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 result of isostatic rebound following the middle jurassic elko orogeny prior to the aptian-albian onset of the sevier orogeny (thormon and peterson, 2003; thormon, 2011). in the san pitch mountains, the cedar mountain formation unconformably overlies the reddish-orange sandstone beds of the middle jurassic twist gulch formation or underlying arapien formation. figure 10 caption is on the next page. 99 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 the recognition of middle to late albian palynomorphs in the basal indianola group facilitated the recognition of a lower cretaceous san pitch formation at the base of these strata. the san pitch formation consists of interbedded reddish-brown conglomerate, sandstone, and mudstone, and has a type section near christianburg, at the south end of the san pitch mountains, where it measures 646 feet (197 m) thick and is divided into three informal members (sprinkel et al., 1999). it is over 3000 feet (1000 m) thick to the north along the west flank of the san pitch mountains. only the uppermost member is present in salina canyon, where it is 277 feet (84.4) m thick (figure 10) and has been dated palynologically as late albian (sprinkel et al., 1999). conglomerate beds at the base of the san pitch formation unconformably overlie the variegated mudstone of the cedar mountain formation and are readily recognized as the first cliff above the slopes of the cedar mountain. regionally, a light-colored quartzite boulder conglomerate marks the unconformity at the base of the cenomanian sanpete formation overlying the san pitch formation (sprinkel et al., 1999). a detailed description of this exceptionally exposed angular unconformity separating mesozoic strata from the overlying paleogene strata is provided by judge et al. (2023). 4.3 7.2 mp-63.7 cretaceous exposures over the next 10 miles (16 km) are cut by many northsouth-trending faults marking the eastern extent of the sevier orogenic belt. 9.3 16.5 mp-73 outcrops of the uppermost cretaceous to lower paleocene north horn formation begin here and extend for the next 3 miles (4.8 km). note, that there is an abundance of pedogenic carbonate nodules on these light-colored exposures. this valley formed by these less-resistant beds marking the western boundary of the colorado plateau. 0.7 17.2 mp-73.7 exit 73 provides good access to extensive exposures of north horn formation. 2.7 19.9 mp-76.4 exposures of carbonaceous mesaverde group unconformably underlie the north horn formation. the campanian mesaverde group extends northward from the figure 10 is on the previous page. western outcrops of the lower cretaceous strata. (a) distribution of lower cretaceous strata in central utah. the cedar mountain formation is exposed in nearly continuous outcrops at the base of the cretaceous section around the san rafael swell, the north end of the henry mountains basin, and south of the book cliffs eastward to the colorado river (figure 9). west of the san rafael swell, the cedar mountain and san pitch formations are exposed in discontinuous outcrops from the san pitch mountains southward to salina canyon. farther west, the equivalent canyon range conglomerate is exposed as discontinuous outcrops from the canyon mountains south to the pahvant range. the location of the san pitch formation type section at christianburg, utah, southwest of the west end of salina canyon. from sprinkel et al. (1999), courtesy of doug sprinkel. (b) measured section of cedar mountain formation and san pitch formation from north side of i-70 in salina canyon. from sprinkel et al. (1999), courtesy of doug sprinkel. (c through f) salina canyon section from i-70 looking north. (c) detail of base of section with buckhorn conglomerate indicated. (d) lower part of salina canyon section with area of c indicated by red arrows. (e) roadcut of cedar mountain formation. (f) upper part of salina canyon section with position of san pitch formation indicated (n. 38° 56.023, w. 111° 48.060; 12s e. 430574 n. 4309726). blue arrow indicates position of basal conglomerate of sanpete formation. rc indicates east end of roadcut in e. red line = angular unconformity at base of flagstaff formation. 100 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 eastern escarpment of the wasatch plateau to price. the mesaverde is divided into the upper price river formation and lower coal-rich blackhawk formation separated by the castlegate sandstone, with the basal star point sandstone below the blackhawk reflecting the coastline following the final eastward regression of the late cretaceous western interior seaway in this area. progressively younger mesaverde sediments are exposed along the highway over next 9 miles (15 km). 8.6 28.5 mp-85 entering the west side of castle valley. exposures of star point sandstone are visible capping slopes of the “helper formation” (formally the upper unnamed shale member of mancos shale of peterson and ryder (1975) and ryer (1984) on the east side of wasatch plateau. 2.5 31.0 mp-87.5 exposures of the upper santonian emery formation of mancos group rise and fall near i-70 due to north-south-trending faults and folds in the joes valley-paradise valley graben (easternmost basin and range style faulting). 1.2 32.2 mp-88.7 extensive cliffs formed by resistant sandstone beds in the emery formation overlie a thick section of blue gate shale of the mancos group, which become visible north and south of i-70. the blue gate shale, the intermediate emery formation, and the overlying “helper formation” are largely correlative to the smoky hill member of niobrara formation (niobrara cyclothem) of central united states. older lower coniacian age fossils correlative to the underlying fort hays limestone member are only recorded from this area in a narrow belt of basal blue gate shale extending from i-70 up to emery, utah, and in cretaceous strata farther to the northeast near manti, utah (kennedy and cobban, 1990; bylund and stephen, in press). 2.6 34.8 mp-91.3 exit 91, junction of utah state route 10, exit. turn right (south) at stop sign onto the last chance road. 5.6 40.4 drive south uphill turning east after less than 1 mile (1.6 km). in 2.8 miles (4.5 km) take u-turn at intersection returning 1 to 2 miles (1.6–3.2 km) to park along road to discuss the upper mancos group exposed below the mesaverde group to the northwest. stop 1 (n. 38° 45.844, w. 111° 20.088; 12s e 470913 n 4290648): emery formation in type area (figure 11). the emery formation was described as a series of interbedded sandstone, siltstone and silty shale near base of the eastern escarpment of the wasatch plateau southwest of emery, utah, as a member of the mancos shale by spieker and reeside (1926). the most comprehensive study of these strata was by edwards et al. (2005) documenting 17 coarsening upward parasequences that they correlated along the coal cliffs with a coal-bearing fluvial sequences capping some to the west in the subsurface. we propose assigning these strata to the emery formation because of these sedimentological complexities. the overlying slope-forming unit was initially improperly referred to the masuk shale of the mancos group (younger campanian age masuk formation), before being correctly identified as a younger unit by peterson and ryder (1975) and ryder (1985). these studies determined that the “emery sandstone” is not present in the henry mountains basin and 101 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 the slope-forming unit above the emery formation was subsequently referred to as the “unnamed shale member” or as “upper blue gate shale.” the “helper” is denoted as a formation rather than a shale, as it is dominantly a structureless mudstone with sandier zones and there are few strata that are at all well-bedded in the type area. these strata are in turn capped by the star point sandstone of the mesaverde group. continue back onto i-70 eastbound. 4.4 44.8 mp-95.7 the freeway cuts down through top of the upper ferron formation of the mancos group. the ferron represents a middle to upper turonian riverto wave-dominated delta system that formed along the west side of the san rafael swell and henry mountains basin. the capping middle turonian lower ferron formation interfingers with the underlying tununk shale, representing the greenhorn cyclothem. the upper ferron formation largely correlates to the juana lopez formation and overlying upper turonian montezuma valley member of the blue gate shale, which represent the minor sage breaks cyclothem separating the more extensive greenhorn and overlying niobrara cyclothems. the ferron formation is highly important economically for its coal and natural gas and has been the subject of numerous scientific studies as a fluvial-deltaic reservoir analog (lupton, 1916; ryer, 1981; garrison et al., 1997; montgomery et al., 2001; gloyn et al., 2003; garrison and ven den bergh, 2004; biber et al., 2017; li and zhu, 2012; ahmend et al., 2014; li et al., 2018; chidsey and anderson, 2019). 0.9 45.7 mp-96.6 the base of the ferron formation overlying the tununk shale of the mancos figure 11. upper mancos group underlying the mesaverde group to north of day 1, stop 1. (a) outcrop north of i-70. emery formation (formally emery sandstone) interval indicated by thin blue bars. helper formation (formally unnamed upper shale member) indicated by yellow bar. white dotted line designates the approximate eastern boundary of the colorado plateau. image from google earth ©2018. (b) outcrop of emery formation about 17 miles (27 km) north of emery west of clawson. 102 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 group is exposed on both sides of i-70. 0.8 46.5 mp-97.4 a classic example of river-dominated delta clinoforms are preserved in the ferron formation in the ivie creek area on the north side of i-70. a more detailed explanation of this outcrop is provided by anderson et al. (2004) and chidsey and anderson (2019). 2.5 48.3 mp-99.1 continue east on i-70 for 2.5 miles (3.3 km) turning south at exit 99 to stop 2 (n. 38° 48.320, w. 111° 12.374; 12s e 482093 n 4295194): lower mancos – tununk shale and ferron formation. across most of this region the base of the mancos group is characterized by a transgressive unconformity characterized by a mixed chert-pebble conglomerate—pycnodonte newberryi coquina—variably overlying either the naturita or cedar mountain formations (eaton et al., 1990; molenaar and cobban, 1991). at this stop, the top of the naturita preserves the late cenomanian index fossils inoceramus pictus and i. flavus and within a short distance up section there is a prominent basal turonian bentonite bed identified as bentonite c from which several radiometric ages are used to refine the age for the base of the turonian stage (obradovich, 1993; sageman et al., 2006; ogg et al., 2012; gale et al., 2020; singer et al., 2023) (figures 12a and 12b). additional study of this contact has been made 11.2 miles (18 km) to the northeast at the moore cutoff road, where bentonite c is sandwiched between the basal turonian inoceramid mytiloides kossmati below and the ammonite pseudaspidoceras flexuosum above (kennedy et al, 2000; cobban et al., 2006). below the inoceramid-bearing sandstone capping the naturita formation, there are a pair of ashes, each on the order of 8 inches (20 cm) thick, that are tentatively identified as representing bentonite a (figures 12c through 12e). uranium-lead dating of the zircons from these two bentonite beds is still pending. the chert pebble conglomerate is interpreted to be a result of reworking of the basal conglomerate off the crest of the san rafael swell during sea-level rise in the latest cenomanian with the presence of pycnodonte newberryi indicating that these gravels were being reworked across the region until water depths exceeded storm wave-base (eaton et al., 1990; kirkland et al., 2007; santucci and kirkland, 2010). if the identification of bentonite a is correct, the entire process of uplift, and reworking of these pebbles across the region would have occurred within the span of approximately 100,000 years. the upper ferron formation directly overlies the undivided tununk shale in this area, and the clawson and washboard members of the lower ferron formation are reported to pinch out into the tununk just to the north at ivie creek (chidsey and anderson, 2019). as noted in kirkland et al. (2024), the nomenclature question arises, should the lower and upper ferron be split into separate formations, as they are parts of separate marine sequences and are already mapped separately. in such a scenario, the southwestern-sourced upper ferron would be retained as the ferron formation and more northern-sourced lower ferron (katich, 1951, 1953; cotter, 1975), including the clawson and overlying washboard members, would be designated as a separate formation. 3.9 52.2 mp-100.5 exposures of the cenomanian naturita formation at base of the mancos group 103 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 12. (a) well-exposed tununk shale exposures south of i-70 at day 1, stop 2. arrow points to bentonite “c” of elder (1985, 1988). (b) examples of inoceramus flavus from the upper cenomanian burroceras clydense zone at the top of the naturita formation in this area. the basal gravel in this area represents the uppermost cenomanian. (c) simplified cross section of the basal tununk shale, its basal conglomerate, and its unconformable relationship with underling strata. modified from eaton et al., (1990). red arrow indicates the position of the moore cutoff road 11.2 miles (18 km) to the northeast. (d) pseudaspidoceras flexusum from a few feet above bentonite c. (e) examples of mytiloides kossmatti from immediately below bentonite c. ceum indicates that the specimen is located at the utah state university eastern, prehistoric museum. 104 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 and overlying the cedar mountain formation. 0.9 53.1 mp-101.4 excellent exposures of both the pale-gray, smectitic mussentuchit and the underlying pale-mauve, pedogenic, carbonate-rich ruby ranch members of the cedar mountain formation are on north side of i-70. 0.2 54.3 mp-101.6 the western margin of the buckhorn conglomerate interfingering with the yellow cat member facies with the characteristic ferruginous paleosols at the base of cedar mountain formation and caps the morrison formation on both sides of i-70 (kirkland et al., 2016). 2.8 57.1 mp-103.4 the off ramp for the salt wash rest area is built on light-colored transgressive marine sandstone of the curtis formation. the curtis is overlain by brownish-red shallow-marine strata of summerville formation, which in turn is overlain by morrison formation. this middle jurassic marine sequence lies above the regional j-3 unconformity developed on top of the entrada sandstone as indicated by localized lenses of small chert pebbles on this surface (pipiringos and o’sullivan, 1978). 4.6 61.7 mp-108 a thick section of reddish-colored entrada sandstone and windsor member of the carmel formation are exposed in mesas and canyons throughout area. 4.0 65.7 mp-112 begin climbing long dip slope on west side of san rafael swell through exposures of lower middle jurassic marine carmel formation. gypsum is mined in several areas in the carmel on this side of the san rafael swell (bowden et al., 2016). the road continues to cut down section until crest of san rafael swell. 8.4 74.1 mp-115.3 looking across canyons from the view area are exposures of the lower jurassic glen canyon group. 0.5 74.6 mp-115.8 travel eastbound on i-70 and take off ramp for exit 116—the moore cutoff road. 1.8 76.4 mp-116.6 excellent exposures of the upper triassic-lower jurassic glen canyon group downward through the lower triassic moenkopi formation are present along the road across the crest of the san rafael swell for the next 25 miles (40 km). the san rafael swell is one of the most dramatic geological features in utah. it is a doubly plunging anticline that forms a huge north-south-trending elongate “bulls-eye” that is more than 200 miles (320 km) in circumference (figure 13). it serves as a model for the study of petroleum reservoirs such as the navajo sandstone, which preserves dead oil around the entire structure, and is considered to be a breached “mega”-reservoir. the san rafael swell exposes older rocks from the deep subsurface. these outcrops are used to model possible reservoir trends. additionally, the san rafael swell was studied as a reservoir for the sequestration of carbon dioxide. 16.4 92.8 mp-133 for the next 2 miles (3.2 km) the crest of the san rafael swell is formed of the permian black box dolomite (kaibab limestone of many reports). 7.0 99.8 mp-140 rest area. spectacular views of the east side of the san rafael swell as the strata dip down the steep side of swell forming the san rafael reef. the marine sinbad 105 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 13. san rafael swell. (a) generalized geological map. line a–a' shows location of cross section. (b) west-to-east cross section of san rafael swell approximately 50 miles ((80 km) across. vertical scale about 80 times horizontal scale. from doelling and hylland (2002). red stars = day 1, stop 2 and day 1, stop 3, lunch stop. 106 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 limestone member of the early triassic age moenkopi formation is exposed on the west side of rest area. permian white rim sandstone (coconino sandstone of many reports) is cut into by the deepest canyons. stop 3 (n. 38° 55.964, w. 110° 28.314; 12s e 545772 n 4309444) for lunch (30 minutes). 4.0 103.8 mp-144 the rest area is on middle jurassic entrada sandstone with a strike valley of middle jurassic carmel formation. to the west and below the carmel, a dip-face of huge flatirons of the lower jurassic navajo sandstone and local outcrops of the middle jurassic temple cap formation forms the san rafael reef (sprinkel et al., 2011). to the southeast, resistant sandstone of the salt wash member of the morrison formation hold up cliffs formed from exposures of reddish-brown summerville formation overlying, light-colored curtis formation. 5.2 109.2 mp-149.4 exit 149. exit for utah state route 24 (sr-24) southbound to hanksville, utah. upper part of salt wash member is exposed here. merge right to hanksville and begin sr-24 mileposts. 0.8 110.0 mp-160 driving on top of the salt wash member of the morrison formation. the buckhorn conglomerate caps slopes of brushy basin member of the morrison formation on left for about next 3 miles (4.8 km). to the right, navajo sandstone flatirons form the san rafael reef. 3.1 113.1 mp-156.9 we will take the “old” sr-24 to green river on our return. road cuts down through the tidwell member of the morrison formation. note white patches along right side of road; these reflect gypsum deposits in the tidwell. the summerville formation forms cliffs below tidwell member. 0.3 113.4 mp-156.6 crossing san rafael river. 3.6 117.0 mp-152 between here and hanksville, the bedrock is discontinuously covered by a combination of active dunes and dunes stabilized by vegetation. this probably reflects an environment similar to that of the lower campanian djadokhta formation in mongolia’s gobi desert. there are an abundance of small vertebrates (lizards, birds, and mammals) living in the high desert on the colorado plateau as there were in the late cretaceous of the gobi desert. coyote and bobcat are analogous to the cretaceous carnivores like velociraptor and oviraptor, whereas the pronghorn would comparable to the herbivores such as protoceratops and pinacosaurus. 1.7 118.7 mp-150.3 exposures of the middle jurassic entrada sandstone. 5.6 114.3 mp-144.7 exposures of the underlying carmel formation are visible in the valley on the right. 8.5 122.8 mp-136.3 turnoff to goblin valley state park on right. 4.3 127.1 mp-132 the road goes down grade into the valley of the muddy, fremont, and dirty devil rivers. the scattered buttes along the route to hanksville are made of entrada sandstone. 4.0 131.1 mp-128 henry mountains are seen to the south. to the west (right), light-colored sand107 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 stone of curtis formation overlies red beds of entrada sandstone and in turn is overlain by brownish-red beds of summerville formation. 1.7 132.8 mp-126.3 leaving emery county and entering wayne county. 5.9 138.7 mp-120.4 hanksville airport is on right. 0.7 139.4 mp-119.1 crossing the dirty devil river. muddy creek joins the fremont river from northwest to form dirty devil river just west of this bridge. 2.4 141.8 mp-116.7 at the intersection of sr-24 with sr-95 in hanksville, utah, turn west (right) to continue on sr-24 toward capitol reef national park. 0.4 142.2 mp-116.2 steel “dinosaur” graveyard on right. 0.2 142.4 mp-116.0 rock shop on right. 0.6 143 mp-115.4 crossing the fremont river on west side of hanksville. outcrops of the light-colored curtis formation below the brownish-red summerville formation north of road. 1.4 144.7 mp-114.0 passing outcrops of the summerville formation on right side of road with fremont river on left side. 0.7 145.4 mp-113 passing through exposures of the salt wash member of the morrison formation. note the relative thinness of this section compared to that in the green river area as will be seen on day 2. 2.2 147.6 mp-110.5 exposures of naturita formation overlying brushy basin member of the morrison formation on the right. 0.6 148.3 mp-109.9 passing onto the basal tununk shale. turn right on dirt track up and over tununk before turning east to park. stop 4 (n. 38° 22.168, w. 110° 49.167; 12s e 515771 n 4246824): basal unconformable tununk shale contact with the naturita formation. in the hanksville area, the naturita formation may be split into three units (antia and fielding, 2011): (1) a basal conglomeratic fluvial sandstone rich in quartzite, (2) a medial carbonaceous paludal sequence, and (3) an upper fossiliferous transgressive marine sandstone (figure 14). the top of the naturita and the base of the tununk are characterized by thick accumulations of pycnodonte newberryi, which were so thick here that it was mined to provide the roadbed for sr-24 across the mancos group to capitol reef national park. 3.1 151.4 mp-106.8 abandoned giles townsite is on the left (south) side of road along the fremont river. the ferron formation forms cliff above tununk shale. 0.7 152.1 mp-106.1 passing up through the basal ferron formation. on the left side of road, a fallen block of sandstone was found to preserve shark teeth, turtle shell sections, and the sacrum of a small ornithopod dinosaur, which are now in the collections of the burpee museum, rockford, illinois. 0.4 152.5 mp-105.7 passing up through the top of ferron formation. extensive paludal facies at the 108 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 figure 14. the upper cretaceous transgressive sequence in the hanksville area. (a) generalized upper cenomanian-lower turonian transgressive sequence largely based on the stratigraphic section preserved west of hanksville, utah, (stop 4) showing the distribution of various oyster taxa relative to the facies in which they are preserved. oyster figures from stanton (1893) with ecological interpretations from kirkland (1996). figure updated from santucci and kirkland (2010). (b) the naturita and basal tununk section just east of stop 4 with the distribution of oyster species documenting the ecologic progression from freshwater environments, brackish water, beach, shallow shelf sands reworked periodically by storm processes to quiet shelf settings below storm wave base. molluscan data following kirkland (1990, 1991, 1996; santucci and kirkland, 2010). (c) the same section about 0.6 miles (1.0 km) to the east showing approximate position of morrison laser ablation sr-pb zircon age from kowallis et al. (2007). abbreviations: us = upper sandstone member, mc = middle carbonaceous member, lc = lower conglomerate member. 109 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 top of the ferron are well exposed across this bench. 0.5 153.0 mp-105.6 turn off for factory butte on right. 5.1 158.1 mp-100.5 continue west through blue-gray blue gate shale badlands between north and south caineville mesas. 2.8 160.9 mp-97.6 continue west through caineville, utah, and pass through the water gap formed by the caineville reef, where road turns south along this monoclinal structure. 5.3 162.2 mp-92.0 continue south along the west side of the caineville reef to the notom road. the caineville reef is held up by sandstone of the ferron formation with the tununk shale forming the valley floor. the more resistant beds in the lower cretaceous cedar mountain formation forms a low ridge on the western side of the road immediately below the tununk (figures 15a and 15b). this unconformable contact has been discussed here by kirkland et al. (2016) and as elsewhere is represented by a lag of pycnodonte newberryi shells with scattered chert pebbles. turn left (south) onto the notom road and turn around to proceed back north on sr-24. 2.5 167.7 mp-94.5 passing by the entrance to sleepy hollow campground on right, just south of where sr-24 crosses the fremont river (figure 15b). note: the sandy resistant beds in the tununk shale slope below the caineville reef. these beds appear to correlate with the coon spring sandstone member of the tununk shale (molnaar and cobban, 1991), but are they continuous with the coon spring and are they also sourced from the north? there have been no stratigraphic studies on the tununk in this area. 9.1 176.8 mp-105,6 drive north on factory butte road for 13 miles (21 km) where we will turn around and park for stop 5 (n. 38° 28.060, w. 110° 54.130; 12s e 508534 n 4257710): factory butte. factory butte consists of a thick section of blue gate shale of the mancos group capped by the muley canyon sandstone (figure 15c). superficially, the muley canyon sandstone would appear to be correlative with the emery formation of the mancos group, except that it is early campanian in age and underlies the terrestrially deposited middle campanian masuk formation. additionally, the emery formation is late santonian in age and underlies the helper formation of the mancos group (eaton, 1990; titus et al., 2016; kirkland et al., 2024). along the sides of the road, we can examine the disconformity between the top of the ferron formation and the base of the blue gate shale, where we can collect pycnodonte aucella and fragments of volviceramus involutus (figure 15d) indicating that the basal blue gate is no younger than upper middle coniacian in this area. return to sr-24. 26.0 202.8 mp-105 turn east on sr-24 for 10.8 miles (17.4 km) to hanksville. bear left to continue north for 52.1 miles (83.9 km) across the san rafael river, then turn right on the old abandoned sr-24. the bench is formed by the salt wash member of the morrison formation 62.9 265.7 mp-156.9 cattleguard. we will take the “old” sr-24 (bureau of land management [blm] road 9102) toward green river, utah. 110 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 1.1 266.8 there are no mile posts along the abandoned sr-24 route. cross the clay-change from illitic to smectitic mudstone beds marking the transition from salt wash to the brushy basin member of the morrison formation. 0.7 267.5 entering jessies twist; an important accessible exposure of the upper morrison formation and the yellow cat and poison strip members of the cedar mountain formation. 0.3 267.8 note the iron-stained ferruginous paleosols marking the basal beds of the yellow cat member, documenting an exceedingly wetter climatic interval at the beginning of the cretaceous before a return to dryer conditions in the middle of the yellow cat (kirkland et al., 2016; kirkland and deblieux, 2024). also useful to note that the mudstone beds in the lower cretaceous of the paradox basin are figure 15. mancos group around north end of henry mountains basin. (a) basal contact of tununk shale with cedar mountain formation at the south end of caineville reef (38°16'27.56"n., 111° 3'58.48"w.). (b) oblique view from west of tununk shale along caineville reef south of fremont river. google earth ©2024. (c) exposures to the northeast of factory butte just to the east of the type area for the blue gate shale at stop 5. (d) examples of the common fragments of the inoceramid volviceramus and the oyster pycnodonte aucella from the base of the blue gate shale. 111 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 nonsmectitic, such that the change in the weathering profile is a useful way to map the contact between the convexly weathering morrison formation and the flat to concave weathering profile of the yellow cat member of the cedar mountain formation. the yellow cat member has been dated as ranging from the berriasian through valanginian using a combination of biostratigraphy of microfossils (palynology, charophytes, and ostracodes), and chemostratigraphy calibrated with detrital u/pb ages from paleosols (joeckel et al., 2019, 2023). 0.3 268.1 cross onto bench formed by sandstone within the poison strip member of the cedar mountain formation. within 30 feet (10 m) of this bed—1.5 miles (2.4 km) to the northwest—warren and carpenter (2004) collected a large nodosaurid curated at the denver museum of nature and science that is similar to sauropelta and represents the lowest record of an aptian-age dinosaur in the paradox basin (kirkland et al., 2016). 0.7 268.8 the largely vegetated bench is composed of poorly exposed ruby ranch member of the cedar mountain formation. turn left (northwest) onto blm road 9130. 0.5 269.3 follow the dirt track past borrow pits exposing pale-green mudstone of the upper ruby ranch member of the cedar mountain formation. after s-curve in track turn around and park. stop 6 (n. 38° 54.624, w. 110° 19.486; 12s e 558543 n 4307050): basal tununk unconformity. mixed chert pebble conglomerate and coquina of pycnodonte newberryi subundata (figure 16) indicating the unconformable base of the tununk in this area is basal turonian in age. this is the type area of the proposed jessies twist member of the tununk shale. the jesse twist extends from the basal conglomeratic lag up to the base of the coon spring sandstone member. a type section has been measured approximately 2 miles (3.2 km) farther northwest. this stratigraphic interval is composed of dark olive-gray, calcareous, silty to sandy shale with numerous, thin fine-grained sandstone layers less than 0.2 inches (0.5 cm) thick individually. this unit is remarkably unfossiliferous, without a single inoceramid bivalve or ammonite encountered until the basal sandstone layers beneath the main coon spring sandstone concretion level, which preserved the ammonite collignoniceras woollgari. 0.4 269.7 return to “old” sr-24 and take the left fork onto blm road 9137. 0.8 270.5 stop alongside of road. stop 7 (n. 38° 55.092, w. 110° 18.609; 12s e 559804 n 4307925): coon spring sandstone concretion level. these sandstone beds are interpreted to have been sourced from the north across the uinta basin region (cotter,1975; riemersma, 1989; molenaar and cobban, 1993), where only the uppermost middle turonian tununk shale is exposed beneath the sandstone beds of the frontier formation (ryer and lovekin, 1986; molenaar and wilson, 1990). these sandstone concretions preserve a shallow water molluscan fauna (figure 17). we have proposed designating the shale interval between the coon spring sandstone and juana lopez formation as the blue hill shale member of the tununk shale. in this area, these unfossiliferous, dark, noncalcareous beds include many thin sandstone beds. 112 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 figure 16. jessie twist member in green river area. (a) pycnodonte newberryi at day 1, stop 7. (b) contact of ruby ranch member of cedar mountain formation, with conglomeratic coquina at the base of the jessies twist member at its proposed type section. (c) carbonate-cemented conglomeratic coquina at the base of the jessies twist member north of blm road 1043, 2.1 miles (3.4 km) east of “old” sr-24. (d) lower mancos group in the green river area. jt = jessies twist, k = tununk shale section of katich (1951), mc = tununk shale section south of fault of molenaar and cobban (1991), p = “platyceramus hills,” an area preserving abundant large specimens of platyceramus cycloides. red square = type area for the jessies twist member of the tununk shale south of i-70. dashed red lines = approximate positions of formational boundaries in the lower mancos group. white numbers refer to stops 6, 7, and 8 on day 1. dotted white line indicates occurrence of sandy bluff preserving scaphites depressus fauna (“floy wash sandstone” marker bed). note the repetition of this marker bed across the arcuate little grand wash fault zone (blue dashed line) south of green river. image from google earth ©2023. (e) tununk shale section 2 miles (3 km) east of “old” sr-24. (f through h) type section of jessies twist member of tununk shale 2.5 miles (4 km) northwest of “old” sr-24 parallel to i-70; (f) lower part, (g) middle part, and (h) upper part. yellow bar marks position of bentonite c. 113 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 0.3 270.8 passing up through the juana lopez formation. the base of the formation is marked by a 8to 12-inch-thick (20–30 cm) sandstone with common scattered chert pebbles and shark teeth marking a transgressive unconformity. the crest of the ridge is marked by numerous fossiliferous, thin sandstone and calcarenite beds preserving a latest middle turonian prionocyclus wyomingensis fauna including scaphites ferronensis, inoceramus perplexus, and cameleolopha lugubris (cobban et al., 2006; hook and cobban, 2012). 0.5 271.3 for approximately the next 0.5 miles (0.8 km), the road gradually descends the figure 17. upper tununk shale and lower juana lopez formation east along “old” sr-24. (a) overview of section at day 1, stop 7. (b through d) most common bivalves in coon spring sandstone member near green river, utah. (e) typical cretaceous bivalve paleoecosystem in a healthy shallow marine shelf sandstone. modified from lazo (2007). 114 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 back slope of the juana lopez formation preserving a basal upper turonian ammonite fauna including prionocyclus novimexicanus and scaphites whitfieldi. from this point, the lower blue gate shale is poorly exposed and, whereas the upper turonian montezuma valley member is recognized to the north and east, it has not yet been differentiated from the lower smoky hill member of the blue gate shale in this area. 3.8 275.1 continue across large culvert to the northeast on “old” sr-24 for nearly 4 miles (6 km) before turning a sharp right (east) off the abandoned sr-24 onto blm road 9100. 1.1 276.2 continue east for a little more than 1 mile (1.6 km) and pull over to the side of the road. stop 8 (n. 38° 57.925, w. 110° 14.235; 12s e 566080 n 4313215): blue gate shale and the book cliffs. we will stroll over to the edge of the ravine for an overview of the blue gate shale and the book cliffs above green river, utah (figure 18). given enough time, participants can wander down the slope a bit to examine examples of the lower santonian index fossil platyceramus cycloides. 1.4 277.6 continue southeast along southside of the green river airport and bear left (north) at fork south of the end of the runway. 0.9 278.5 continue north and bear right onto the paved airport road. 3.2 281.7 continue north along the bluff formed by the juana lopez formation on left, beneath i-70 overpass and across railroad tracks to the stop sign on green river road, and turn left. 0.1 281.8 turn right on long street. 0.3 282.1 drive past pearl baker park on left to the market street (i-70 business loop). turn right (east) onto market street. 1.6 283.7 drive east across the green river, past the john wesley powell river history museum on the left and up the hill. the super 8 hotel is on the right. check in! day 2 road log starts in green river, utah inc. cum. mileage mileage milepost description 0 0 leave the super 8 hotel on i-70 business loop. 1.3 1.3 mp-164.4 drive southeast on i-70 business loop to i-70, exit 164, interchange crossing highway and turning left (east) onto i-70. 78.0 79.3 mp-11 travel east on i-70 to exit 11 at mack, colorado. 115 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 0.1 79.4 turn right and then left onto the south frontage road. 4.3 83.7 follow frontage road to the east, notice that the low ridge to south is held up by the juana lopez formation. merewether et al. (2006) measured their section of the lower mancos up through the montezuma valley member by the conical hill about 2 miles (3.2 km) along this road. (figure 19a). continue past the colorado entrance station and cross i-70 at exit 15. note the yellow band on the bluff on northeast side of the exit 15 interchange (figure 19). stop 1 (n. 39° 10.783, w. 108° 48.774; 12s e 688914 n 4338998): disconformity between the montezuma valley and the smoky hill members of the blue gate shale. figure 18. upper mancos and lower mesaverde near green river. (a) mancos group at day 1, stop 8, large examples of platyceramus cycloides weathering out on slope in foreground. (b) red arrows point to examples of p. cycloides weathering out in the “platyceramus hills” northwest of green river (p in figure 16d). (c) platyceramus cycloides from the “platyceramus hills” on exhibit in the utah state university eastern, prehistoric museum in price. photograph courtesy of hannah pettijohn. (d) upper mancos and lower mesaverde northwest of green river. (e) upper mancos and lower mesaverde north of green river. 116 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 1.3 85.0 continue north and turn left onto the “old” u.s. highway 6 and 50 (us-6 & 50). 5.8 90.8 continue northwest on old us-6 & 50 about 2 miles (3.2 km) past mack, colorado, and turn right onto 8 road heading north. 3.5 94.3 turn left (west) on s road. 3.0 97.3 bear right (north) onto 4 road. 6.2 103.8 take west fork northward on the prairie canyon road (u-1 5/10 road) for 4.7 miles (7.6 km) to the top of the mancos group. turn around. stop 2 (n. 39° 22.052, w. 109° 2.5930; 12s e 668568 n 4359389): top of the mancos group. to figure 19. lower mancos group in the western grand valley area, colorado. (a) mack and loma, colorado, area. c = contact between the montezuma valley and smoky hill members of the blue gate shale. m = approximate location of merewether et al.’s (2006) mack village section of tununk shale and juana lopez formation. s.d. = location of carbonate unit preserving scaphites depressus, baculites codyensis, and wood fragments. (b) oblique google earth view from west of i-70, loma, exit 11. image from google earth ©2009. (c) exposure from the west illustrating the amount of revegetation on this road cut (day 2, stop 1). white arrow points to glauconitic sandy unit contact between the montezuma valley and smoky hill members of the blue gate shale. dotted white line indicates basal contact of the smoky hill member with the underlying montezuma valley member of the blue gate shale. 117 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 the northeast, the upper cliff face represents the sego sandstone, which is split into upper and lower units by the less resistant anchor mine shale in this area (s 20a through 20c). below the sego sandstone lies the mudstone beds of the buck shale and a sandy bench of the “lower” castlegate sandstone, which is within the baculites asperiformis zone in the middle campanian (cobban et al., 2006; singer et al., 2023). to the west, the organic-rich, volcanic ash-bearing shale below is the bar x shale (figures 20d and 20e; kirkland et al., 2024), containing upper lower campanian baculites sp. (smooth 1) or baculites sp. (weak flank ribs) zones to lower middle campanian baculites maclearni zones at the top correlating to the lower pierre shale of eastern colorado and wyoming (gill and cobban, 1966; figure 20. uppermost manco group in prairie canyon area. (a) view of mancos-mesaverde group transition north of day 2, stop 2 on east side of prairie canyon. (b) west salt creek facing west. (c) view to east of day 2, stop 2 of uppermost mancos group based on young (1955) and willis and gabel (2003). (d) oblique view across west side of prairie canyon at type section of bar x shale. image from google earth ©2023. (d) west side of prairie canyon section at day 2, stop 2, upper type section of bar x shale. red arrowhead indicates hadrosaur site reported in lucas et al. (2006). 118 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 cobban et al., 2006, singer et al., 2023). 1.1 104.9 backtrack to base of the bar x shale. the base of the bar x and top of the prairie canyon formation is marked by a slight fining of the sediment associated with a gradational color change (figure 21a), some large nodule horizons below the boundary, and may be more easily distinguished with geophysical tools such as gamma ray (cole et al., 1997; kirkland et al., 2024). 1.6 106.5 continue backtracking to the south. after about 1.6 miles (2.6 km) note the exposures of the prairie canyon formation, especially on the left (east) side of the road (figure 21b). stop 3 (n. 39° 19.269, w. 108° 59.223; 12s e 673521 n 4354348): exposures of the middle prairie canyon in the type area close to the road. the upper prairie canyon is composed of silty shale, whereas the middle member is a series of sandy coarsening upward cycles, with the contact between the middle and upper representing a major flooding surface (cole et al., 1997). 1.7 108.2 farther south, channelized deposits occur in the lower prairie canyon formation (figure 21c). the lower prairie canyon here likely correlates to the beckwith sandstone bed (proposed herein) near woodside, which are latest santonian, figure 21. prairie canyon formation at prairie canyon. (a) upper contact of the prairie canyon formation with the overlying bar x shale at color change from olive-gray to dark olive-gray. photograph taken after a rain when the color contrast is more apparent. (b) upper prairie canyon overlying middle prairie canyon on the east side of prairie canyon (day 2, stop 3). (c) lower prairie canyon formation facing east at the southern mouth of prairie canyon. 119 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 based on desmoscaphites bassleri locations (fouch et al., 1983; chan et al., 1991), and potentially linked to marine flooding at the top of the emery formation main body (cole et al., 1997). 0.3 108.5 return to 4 road, take right toward the south. 10.3 118.8 return to old us-6 & 50, turn left. 2.0 120.8 mp-11 in mack, turn right on “old” us-50 and proceed to westbound ramp of i-70. proceed on i-70 to exit 2. 9.0 129.8 mp-2 take exit 2, rabbit valley. lunch and stop 4 (n. 39° 11.716, w. 109° 1.2360; 12s e 670934 n 4340312): the mygatt-moore dinosaur quarry and the beginning of the trail though time. these sites are in the brushy basin member of the morrison formation. the bluff to the west is held up by the naturita formation overlying a short section of the cedar mountain formation. this morrison dinosaur site is one of the most significant ongoing excavations in western colorado (figure 22) for recent descriptions of this site see foster et al. (2016, 2018). note: one of your trip leaders (kirkland) discovered the first and most complete ankylosaur, mymoorapelta maysi, ever found in the jurassic of north america (kirkland and carpenter, 1994; kirkland et al., 1998) at this site. 6.5 126.3 mp 227.3 continue west on i-70 into utah at 3.8 miles (6.1 km), mp-229.8, cross up and over the juana lopez formation. turn left (south) under i-70 at exit 227, at westwater. 0.2 126.5 turn south on blm 192, down to harley dome. 5.2 131.7 proceed southwest turning more to south at about 1.5 miles (2.4 km) with exposures of the naturita formation on the right. turn right (northwest) onto blm road 191. 1.0 132.7 follow the road as it loops around the south end of bluff held up by the naturita formation. as the road runs north, it parallels an important reference section (figure 23) of the tununk shale and overlying juana lopez formation described by anderson and harris (2006). stop 5 (n. 39° 6.6390, w. 109° 9.5300; 12s e 659187 n 4330669): lower mancos group at westwater. important to note at this section is that large fossiliferous sandstone concretions of the medial coon spring sandstone member of the tununk shale are well-developed in this area. a tonstein in the underlying naturita formation preserves a diverse, well-preserved flora that has been dated using u-pb from zircons extracted from multiple volcanic ash layers as middle cenomanian (97.5 to 98.0 ma) by barclay et al. (2015). 1.5 134.2 continue to follow blm road 191 north along tununk and juana lopez section turning left (northwest) at about 0.8 miles (about 1.3 km) toward i-70. as road approaches i-70, it turns southwest and then northwest going beneath i-70. the road circles back to the north to join frontage road. note: on the geological map (figure 23f) of the agate quadrangle, willis et al. (1996) mapped in the lower blue gate shale two marker beds that have subsequently been recognized throughout 120 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 figure 22. mygatt-moore quarry area (day 2, stop 4). (a) brushy basin member of morrison formation in rabbit valley with the position of the mygatt-moore quarry indicated. after foster et al. (2018). (b) detailed section through mygattmoore quarry. from chin and kirkland (1998). (c) oblique air photograph of mygatt-moore quarry. red bar = site of detailed stratigraphic section in b. (d) overview of northwest side of rabbit valley showing relation of mygatt-moore quarry with colorado exit 2, i70. image from google earth ©2023. (e) mygatt-moore quarry bone map. from foster et al. (2018). m&m = mygatt-moore quarry. 121 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 the southern uinta basin (ressetar et al., 2014; kirkland et al., 2024). m1 (f1 of anderson and harris, 2006) marks the disconformable contact between the upper turonian montezuma valley member and the middle coniacian through santonian smoky hill member of the blue hill shale throughout the southern uinta basin. 1.2 135.4 mp-222.1 follow the frontage road one mile before turning left to i-70, exit 222, dutch flat. south of exit 222 is the new grand junction terminal that serves as a hub for supplying gasoline and diesel fuel to gas stations in the region. 34.5 169.9 mp -187.6 drive west on i-70. over the next 44 miles (71 km) the highway follows the broad figure 23. lower mancos group in westwater area. (a) line of anderson and harris’ (2006) stratigraphic section with prominent marker beds. modified from anderson and harris’ figure 4a. (b) outcrop of tununk shale from west (day 2, stop 5). from anderson and harris’ (2006) figure 4b. (c) same area from more to west (day 2, stop 6). (d) an example of collignoniceras woollgari regulare (ceum 86875) from the coon spring sandstone concretion level in this immediate area. (e) oblique view of anderson and harris’s (2006) research area from the east. image from google earth ©2009. (f) northeastern portion of the geological map agate, utah 7.5' quadrangle (willis et al., 1996) emphasizing the distribution of laterally traceable marker beds. m1 = glauconitic sandstone marking the disconformable base of the smoky hill member of the blue gate shale (leckie et al., 1997; nelsen and sonnenberg, 2001; ressetar et al., 2014; kirkland et al., 2024), f1 glauconitic marker bed of anderson and harris (2006). m2 = blue gate silt (fisher, 2007; ressetar et al., 2014) and is being designated the “floy wash sandstone beds” by kirkland et al. (2024). 122 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 bench formed by erosion of the thick blue gate shale. to the south, the juana lopez formation forms a low escarpment that dips a few degrees to the north forming the southern margin of the uinta basin. typically, the upper juana lopez formation and the overlying montezuma valley member are poorly exposed on this dip slope. this region is largely covered by a high desert scrubland, which replaced the high desert grasslands due to continued grazing pressure during the near continent-wide drought of the 1930s dust bowl interval. as shown by ressetar et al. (2014), the marker beds in the lower blue gate member are not well exposed on the juana lopez formation dip slope, but easily identified in the subsurface across the southern uinta basin (figure 24). exposures of the upper mancos group occur in the lower slopes of the book cliffs below the mesaverde group. a great deal of research has been ongoing on this regressive cretaceous coastline largely figure 24. subsurface correlation of lower mancos group west to east across southern uinta basin. nomenclature proposed herein on west side and original subsurface nomenclature on the east side of cross section. modified from ressetar et al. (2014). 123 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 within the canyons cutting through the book cliffs as the strata help to interpret subsurface data farther to the north in the uinta basin. these strata also serve as an important model in understanding the depositional environments along the coasts of stable continental shelves. passing the thompson, exit 187; the hopeful future north entrance to arches national park. 11.8 181.7 mp-175.8 over the next 12 miles (19 km) to the south and southeast, the salt valley anticline that forms the core of arches national park is visible. this structure was formed by a salt-wall rising in the paradox basin during the late paleozoic and mesozoic from the thick beds of salts that accumulated in this foreland basin formed on the west side of the ancestral rockies during the pennsylvanian (doelling, 2024). passing crescent junction, exit 182; the turnoff for arches and canyonlands national parks, moab, and points south. continue west to the floy wash, exit 175, and turn left (south). 4.5 186.2 drive south on ruby ranch road down section through the blue gate shale and juana lopez formation and turn around for stop 6 (n. 38° 51.838, w. 109° 57.666; 12s e 590133 n 4302194): lower mancos group on ruby ranch road. note that the tununk shale is poorly exposed in this area. however, 0.5 miles (0.8 km) farther south on the ruby ranch road, there is an open dirt track on the right (west) that crosses a pipeline and leads to extensive well-exposed tununk outcrops over an interval of 2 to 5 miles (3.2–8.1 km) for which a high clearance vehicle is required (figure 25). scramble up the slope to examine the conglomeratic sandstone at the base of the juana lopez formation. the trip leaders have not traced this bed east of the salt valley anticline; however, this bed is well expressed on the southeastern side of the axis of the san rafael swell along farnham dome at mounds. this bed is derived by the erosion of the eastern margin of the lower ferron formation and its reworking across the southern uinta basin during an upper turonian sea level rise. the extra-basinal pebbles are derived from reworking of units in the upper part of the washboard member of the lower ferron formation (kirkland et al., 2024). shark teeth (figure 25f) are also abundant in this bed (becker et al., 2010, 2012). 1.5 187.7 drive north on ruby ranch road. at 0.4 miles (0.6 km), cross the top of the juana lopez formation on the back slope of ridge formed by more resistant beds in the basal upper turonian prionocyclus wyomingensis zone with scaphites ferronensis, inoceramus perplexus, and cameleolopha lugubris. as we drive through the medium olive-gray shale beds of the montezuma valley member of the blue gate shale look for concretions characteristic of these strata. the prionocyclus novimexicanus zone spans the contact with the underlying juana lopez and the prionocyclus quadratus zone is at the top of these strata. a superficial examination of these rocks west of the road yield ammonites only identifiable as prionocyclus sp. and mytiloides incertus (figures 25g and 25h). about 0.3 to 0.4 miles (0.5–0.6 km) farther the basal disconformable contact is marked by a pale olive-yellow band on the tops of low hills along the east side of road and broken fragments of volviceramus involutus probably marking the upper part of the middle coniacian scaphites 124 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 ventricosus zone. after crossing a deep dry wash turn left (west) into parking area. stop 7 (n. 38° 53.125, w. 109° 57.321; 12s e 590605 n 4304580): floy wash sandstone bed. to the southwest is an excellent exposure of the floy wash sandstone bed (figure 25e) in its type area just east of floy wash. this prominent maker bed angles to the southeast such that the medium olive-gray calcareous shale exposed here has yielded good specimens of the upper coniacian inoceramid magadiceramus crenulatus (figure 25j). the floy wash area would be an excellent area to figure 25. blue gate shale along the ruby ranch road. (a) google earth view of exposures of the blue gate shale and bounding strata in the area of the ruby ranch road. image from google earth ©2023. (b) oblique view of the juana lopez formation and the lower blue gate shale along the ruby ranch road. image from google earth ©2023. white stars designate day 2, stops 6 and 7. (c) montezuma valley member. (d) upper montezuma valley member and basal smoky hill member, view to north. external mold of venter of prionocyclus sp. from locality p. in a and b. (e) “floy wash sandstone” type area. west of ruby ranch road looking south (day 2, stop 7). fws in b. (f) basal conglomeratic sandstone of juana lopez formation. note extra-basinal and ferron pebble-sized clasts with a diversity of shark teeth in this transgressive marker bed. (g) prionocyclus sp. (h) inoceramus incertus also from locality p. in a and b. (i) inoceramus undabundus from middle coniacian locality i.u. in a and b. (j) magadiceramus crenulatus from upper coniacian locality m.c. in a and b. solid black lines indicate approximate stratigraphic boundaries. dashed black line indicates occurrence of sandy bluff preserving lowest fragments of volviceramus. v.i. = locality yielding fragments of volviceramus involutus. dotted white line indicates low sandstone bluff associated with an upper coniacian scaphites depressus-magadiceramus crenulatus fauna (floy wash sandstone marker bed). fws = type area for flow wash sandstone bed. 125 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 establish a refined reference section of the entire mancos group such as that of leckie et al. (1997) for the type section of the mancos group. from this point the section would need to veer to the northeast away from the ruby ranch road (figure 25a). some effort would also need to be made to trace a marker bed across i-70 into the basal prairie canyon formation below hatch mesa. 3.2 190.9 drive back north across the floy wash, exit 175, bearing left (west) on the northern frontage road, the old elgin highway. 0.3 193.2 turn right north onto blm road 225. 2.0 195.2 drive north across railroad tracks. in about 2 miles (3.2 km), we will turn around and return south for about 1 mile (1.6 km) and stop along the road for stop 8 (n. 38° 55.906, w. 109° 55.845; 12s e 592678 n 4309748): prairie canyon formation. the prairie canyon formation below hatch mesa (figure 26) has been the focus of many research projects over the years (riemersma et al., 1992; chaiwongsaen, 2007; casaleggio, 2009). however, stevens (2004) conducted the most focused study of this important stratigraphic section (figures 26b and 26c). stevens split the section into three distinctive sedimentological packages. (1) a lower unit consisting of isolated scour-filled units of sandstone, oolitic ironstone, and dolomicrite reported to preserve ammonites marking the santonian-campanian boundary. (2) the medial “hatch mesa sandstones” further divided into eight sandstone-mudstone sequences interpreted to be deposited sediment gravity flows. (3) the uppermost beds, which are the offshore facies of the kenilworth, sunnyside, and grassy members of the blackhawk formation. we (kirkland et al., 2024) interpret the sunnyside member as pinching out into the “bar x shale” here and that the kenilworth member forms the top of the prairie canyon formation where the “bar x shale” can be recognized (figure 26a). an important nomenclatural question that needs to be more rigorously examined, is if the beckwith sandstone bed, examined day 3, stop 3, correlates to stevens (2004) hatch mesa sandstones? 2.0 197.2 mp -175.8 return to i-70 turning right to head westbound toward green river. 10.8 208.0 mp-165.0 exit right at exit 164 onto green river business loop. 1.5 209.5 turn right (north) onto hastings road. 18.0 227.5 at 7 miles (11 km) driving on the east bank of the green river. note the exposures to the northeast and southwest of the transition between the prairie canyon formation and the members of the blackhawk formation. the bar x shale continues to thin and is sandwiched here between the kenilworth and sunnyside members of the blackhawk (figures 27b and 27c). at 9 miles (15 km), the road enters desolation canyon. at 9.5 miles (15.3 km), pass the popular swasey’s beach. at 18 miles 29 km), turn in at nefertiti. stop 9 (n. 39° 11.720; w. 110° 4.629; 12s e 579692 n 4338858): examine the pinch out of the buck shale in the cliffs above (figure 27a). 18.0 245.5 return to the green river business loop and turn left to hotel. 126 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 figure 26. geology of the hatch mesa area. (a) view of southeastern hatch mesa from day 2, stop 8. (b) facies map of upper mancos group at hatch mesa with location of sections. note: our stratigraphic interpretations are highlighted in red. we would propose that the kenilworth correlates with the upper prairie canyon formation. (c) detailed stratigraphic cross section of lower prairie canyon strata (lower dolomitic sandstone beds up through hatch mesa sandstones) exposed at base of slope south of hatch mesa. note occurrence of the ammonite desmoscaphites bassleri in scours at base of sequence. figures b and c modified from stevens (2004). 127 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 27. the mancos group to mesaverde group transition north of green river, utah. (a) view to southeast from near end of hastings road on the green river near nefertiti rock at the pinchout of the buck shale; day 2, stop 9. (b) blackhawk formation east of the green river. note that between here and hatch mesa the sunnyside member of the blackhawk formation grades into the bar x shale (figure 26a). (c) blackhawk formation and overlying lower castlegate sandstone west of the green river. 128 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 day 3 road log starts in green river, utah inc. cum. mileage mileage milepost description 0 0 leave the super 8 hotel on i-70 business loop. 3.2 3.2 160.5 drive west across the green river, past the john wesley powell river history museum on the left and up the hill. turn right onto i-70 west bound at exit 160. 2.0 5.2 158.5 take exit 157 off i-70 and bear right (north) onto us 6/191 toward price, utah. 5.0 10.2 297.2. off to right of road on the other side of the railroad tracks the low hills have been informally been nick-named the platyceramus hills for the large numbers of the large lower santonian inoceramid platyceramus cycloides weathering out of the smoky hill member of the blue gate shale (figures 16d, 18b, and 18c). 10.0 20.2 287.2 continuing north, us 6/191 crosses over union pacific railroad tracks near the former grassy siding. turn to right in 0.3 miles (0.5 km) for stop 1 (n. 39° 8.416, w. 110° 20.126; 12s e 557432 n 4332552): overview of the floy wash sandstone beds. in this area, the upper coniacian ammonite scaphites depressus has been recovered in the main sandstone marker bed and with the middle coniacian ammonite scaphites ventricosus recovered in discontinuous concretionary sandstone about 30 feet (10 m) lower (figure 28). fragmentary volviceramus involutus are present on the surface throughout this area indicating that the smoky hill member exposed in this area is upper middle into upper coniacian. west of the us 191, forster et al. (2020) described the upper turonian biostratigraphy and as a result documented the presence of the montezuma valley member at the base of blue gate shale in this area (figures 28a and 28e). 0.1 20.3 287.3 return to us 6/191 and turn right continuing north. 13.8 33.4 283.5 turn left across us 6/191 onto the green river cutoff road. 3.1 36. 6 the first few miles of the green river cutoff road (blm road 409) zigzags on the way to the steeply dipping strata on the east side of the woodside anticline. driving northwest in 1 mile (1.6 km), turn left to southwest, in 0.5 miles (0.8 km) after crossing under railroad overpass turn left. in another 1.0 miles (1.6 km) the road turns west through the hogback formed by the juana lopez formation and turns west, in 0.4 miles (0.6 km) the road turns south along valley floor formed by poorly exposed jessie twist member of tununk shale east of the dip slope formed by the naturita formation in this area. after 0.7 miles (1.1 km) stop 2 is on a side road to left where we will turn around for the return to us 6/191. stop 2 (n. 39° 12.490, w. 110° 22.178; 12s e 554424 n 4340066): examine the sandstone bench formed by the coon spring sandstone member of the tununk shale in its type area (figure 29). the type section of the coon spring is 8.2 miles (13.2 129 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 28. mancos group on southwest side of uinta basin. (a) oblique view to east of mancos group across us-191 with stratigraphic interpretation. image from google earth ©2009. (b) view to northwest along floy wash sandstone at day 3, stop 1 in lower smoky hill member of blue gate shale. from kennedy and cobban’s (1991) u.s. geological survey mesozoic locality d12987. fragments of volviceramus involutus are common on lower slope at base of upper coniacian scaphites depressus zone. (c) view down back slope of sandy bluff toward book cliffs. open rectangle = prairie canyon formation; solid rectangle = bar x shale. (d) scaphites depressus from top of floy wash sandstone bed at day 3, stop 1. photograph courtesy of kevin bylund. (e) oblique view of cretaceous exposures from the west across us-191 north of i-70. dotted white lines indicate approximate formational and member boundaries. dashed white line indicates occurrence of sandy bluff (floy wash sandstone marker bed) preserving scaphites depressus fauna. thin white bar indicates glauconitic sandstone bed at base of smoky hill member of the blue gate shale. image from google earth ©2009. 130 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 km) north of the stop (figures 29e and 29f) just across the price river (molenaar and cobban, 1991), whereas this is the type area of the woodside sandstone of cotter (1975). cotter linked this bed to the ferron formation to north, correctly indicating it was sourced from the north. however, molenaar and cobban (1991) abandoned the name “woodside” and named these sandstone beds, together with the sandstone concretion zone along the southern book cliffs, the coon spring sandstone bed. 3.2 39.8 283.4 return to us 6/191 and turn left (north). 5.1 44.9 278.3 continue north crossing the price river in 4.8 miles (7.7 km). in another 0.3 miles (0.5 km), turn right (east) across from woodside, utah, on to the price river campground road (blm road 129). 3.6 48.5 follow the road southeast to price river campground, where we will turn around before proceeding down section. note the well exposed upper mancos group transition with mesaverde group in this area (figure 30b). 1.6 50.1 outcrop of beckwith sandstone bed is on northeast side of road (figure 30e). stop 3 (n. 39° 15.356, w. 110° 18.826; 12s e 559207 n 4345402): discussion of the beckwith sandstone bed. biostratigraphically, the reported occurrence of desmoscaphites bassleri (spieker and reeside, 1926; katich, 1951; cobban 1976) with cataceramus balticus (figures 30c and 30d) is in this extensively outcropping marker bed along the west site of the book cliffs, which suggests it correlates to the base of the prairie canyon formation. but is it contiguous? 2.0 52.1 278.3 continue northwest along road, look toward the northeast over the next mile to get a sense of the lateral continuity of the proposed beckwith sandstone bed (figure 30a). on returning to us 6/191 turn right (north). 9.8 61.9 268.5 drive north through rolling hills in the smoky hill member of the blue gate shale. at 7.4 miles (12 km) north of woodside, turnoff to the right to the lila canyon coal mine providing a paved access through the upper mancos group into the basal mesaverde group as an alternative to stop 3 in case of rain. start up a 0.5mile (0.8 km) grade up through a prominent pleistocene terrace. 0.8 62.7 267.3 rest area and road to horse canyon, the canyon through the book cliffs that is the source of this boulder terrace. 10.5 71.3 253.2. turn left across us 6/191 onto the mounds road. 2.8 74.1 following mounds road south along bench, turn onto track right to edge of bench formed by the shallow marine sandstone of the lower ferron formation overlooking the lower cretaceous cedar mountain formation at the center of farnham dome (figure 31c). stop 4 (n. 39° 29.122, w. 110° 37.483; 12s e 532273 n 4370708): lunch in this area. cotter (1977) emphasized the separation of his upper and lower ferron sandstone. however, we could not distinguish separate clawson and washboard members at farnham dome (figures 31a and 31b). 131 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 29. tununk shale and juana lopez formation east side of us-191. (a) overview of section east of green river cutoff road (day 3, stop 2); east side of woodside anticline. (b) looking south along valley formed by jessies twist member. demonstrating the poor quality of exposures of the lower mancos group along much of the book cliffs. (c) vertical exposure of the coon spring sandstone member (scale bar = ~ 2 m). the well-cemented, capping sandstone in this area was named the woodside sandstone bed by cotter (1976). the sequence is very similar to the type section of the coon spring sandstone member north of price (molenaar and cobban, 1991). (d) a view of the blue hill shale member. (e) overview of location of coon spring type section with the west turn from us-191 onto east silvagani ranch road. w = woodside, utah. (f) oblique view from west of the coon spring type area. cs = bench formed on carbonate-cemented sandstone at top of the coon spring. jl = bench formed of main concentration of calcarenitic sandstone layers within the juana lopez formation. white dot indicates approximate location of type section (molenaar and cobban, 1991). both images google earth ©2023. 132 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 figure 30. exposures of upper mancos group along northeast side of the woodside road, blm road 129. (a) overview of section looking northeast. (b) view across woodside road sandstone beds to southeast. (c) cataceramus balticus from underling concretionary horizon. (d) example of a cataceramus from woodside road sandstone. (e) exposure of the beckwith sandstone bed close to the woodside road, day 3, stop 3. note, the internal scoured surfaces. black dotted line represents line of main beckwith sandstone bed; white dotted line represents line of underlying concretion horizon. 133 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 31 caption is on the following page. 134 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 5.4 79.5 continue south along the mounds road, which at 2 miles (3 km) we will turn east following the escarpment through these popular fossil collecting areas in the basal juana lopez formation. along this entire area a course sandstone lag with chert pebbles and shark teeth forms the base of the juana lopez formation (figure 31e) as described by becker et al. (2010, 2012). carbonate concretions in the lower juana lopez formation are known to preserve large specimens of prionocyclus macombi (figure 31d) marking the top of the middle turonian (cobban et al., 2006). at 4.5 miles (7.3 km) the road winds south through the lower ferron formation dropping to the south. after crossing over the railroad tracks turn right (west) onto the farnham road to the west. 3.8 83.3 continue northwest along the south side of rail line. note, the lower sandstone bluff formed by the coon spring sandstone member of the tununk shale below the escarpment formed by the lower ferron formation over the next 3 miles (5 km) (figures 31f through 31h) before the road crosses the axis of the san rafael swell. the lower cedar mountain formation is exposed in the center of farnham dome up slope north of rail line. 2.2 85.5 in 0.4 miles (0.6 km), farnham road turns north crossing the railroad track and continues northwest along rail line. in another 1.8 miles (2.9 km) to the southwest, miller creek enters soldier wash from the west. katich (1951, figure 13) documented the presence of a distinct lithofacies and upper turonian fossils as the sage breaks fauna in the basal blue gate shale reflecting the presence of the montezuma valley member in this area above the juana lopez formation west of the axis of the san rafael swell. 0.7 86.2 continuing northwest as the farnham road curves to the north, where we take a sharp right onto a short road leading into a sandstone quarry in the lower ferron formation. stop 5 (n. 39° 30.967, w. 110° 40.963; 12s e 527273 n 4374101): marine sandstone beds of the lower ferron formation. at this site, the marine sandstone beds of the lower ferron formation are overlain by the shallow marine heterolithics beds of edwards’ (2005a) 3rd transgressive systems track (tst3) (figfigure 31 is on the previous page. farnham dome area. (a) index map of section sites from cotter (1975, figure 1). (b) simplified section modified from cotter (1977, figure 2) emphasizing the separation of his upper and lower ferron sandstone. note, we cannot distinguish separate clawson and washboard members at farnham dome. (c) oblique overview of farnham dome area from the southwest indicating locations of stops 4 and 5. image from google earth ©2023. p.w. = location of molluscan fauna from the basal upper turonian prionocyclus wyomingensis zone north of us-191. white bar labeled a = edwards’ (2005) section a on the northwest side of us 6/191. k = approximate site of katich’s (1951) figure 13 image of the fossiliferous basal blue gate on the south side of miller creek. white rectangles indicate approximate areas of f through h. (d) large example of the latest middle turonian index fossil prionocyclus macombi protruding from a concretion from the lower juana lopez formation at mounds. (e) contact between lower ferron formation and overlying juana lopez formation. (f) view from west mounds road to northwest along escarpment formed by lower ferron formation. (g) view of the eastern end of escarpment below mounds from farnham road. (h) view of the western end of escarpment below mounds from farnham road. white arrowhead indicates position of pebbly, shark tooth lag marking sequence boundary at base of juana lopez formation and top of upper coarsening upward sandstone sequence of lower ferron formation. black arrowhead marks top of lower coarsening upward sandstone sequence of lower ferron formation. black arrow marks the coon spring sandstone member of the tununk shale. 135 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 ure 32). within tst3, dispersed chert pebbles are present (figure 33f) and almost certainly represent the source of the pebbles in the conglomeratic shark tooth lag at the base of the overlying juana lopez formation at mounds (becker, 2010), as well as farther to the south and east (figure 25f). there needs to be a closer examination of the transition of facies across the axis of the san rafael swell in outcrop at farnham dome and in the subsurface. 1.7 87.9 continue north on the farnham road. turn right on ridge road at wellington, utah. 0.3 88.2 249.3 turn left (west) onto us 6/191 on the east side of wellington, utah. 11.8 100.0 237.5 drive northwest on us 6/191 that curves around the west side of price, utah, home of utah state university eastern and its prehistoric museum. pull off to right into the northbound utah port of entry at mile marker 238 and proceed to the north end. stop 6 (n. 39° 37.564, w. 110° 51.550; 12s e 512086 n 4386265): discuss the basal garley canyon member of the emery formation of the mancos group. the basal garley canyon member forms a distinct double sandstone bench along both sides of us 191 starting here (figure 33). 1.9 101.9 235.6 continue north on us-6/191 before turning left onto consumers road heading east. 6.8 108.7 drive west to stop 7 (n. 39° 39.249, w. 110° 58.826; 12s e 501678 n 4389372): overview the type section of the helper formation (figure 34). formally referred to as the unnamed shale tongue of the blue gate shale, this slope-forming interval separates the emery formation from the overlying star point sandstone at the base of the mesaverde group and extends along the entire west site of the san rafael swell south of i-70. this section consists almost exclusively of mudstone and sandy mudstone with numerous muddy sandstone beds, lacking any finely bedded units. for this reason, it is considered more appropriate to refer to these strata as a formation rather than a shale (kirkland et al., 2024). 6.8 115.5 235.6 return to us 6/191 and turn left (north) toward price canyon. 5.9 121.4 229.7 at mp 233 drive through helper, utah. the escarpment directly ahead to north of road consists of the helper formation overlain by the panther tongue member of the star point sandstone, which pinches out into the helper formation within 10 miles (16 km) to the east. the road winds through the blackhawk formation and at mp 230.1 continue straight north on us 6 as us 191 splits off to northeast. cuts on either side of road provide excellent exposures of coal-bearing strata in the lower blackhawk formation. pull into north end of long pullout on right by block preserving dinosaur track at stop 8 (n. 39° 43.933, w. 110° 52.253; 12s e 511093 n 4397994): overview of blackhawk formation and castlegate sandstone (figures 35 and 36). note that all of these strata interfinger into the upper mancos group in western colorado. 7.0 128.4 222.7 continue up price canyon. on the west side of the last long sweeping curve near the top of the canyon, note the color change in the north horn formation from 136 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 figure 32. stratigraphic correlation panel of the lower ferron sandstone. edwards’ (2005a) captions this figure as follows; “the lower ferron contains 2 constituent higher-order sequences within a lower-order sequence. the lower-order sequence is dominated by a falling stage systems tract that contains three higher-order component sequences, characterized in sequences 2 and 3 by sharp-based shoreface successions bound by regressive surfaces of marine erosion (rsme), capped by transgressive surfaces (ts) and deposited during higher-order falls in relative sea-level (fsst2 and fsst3). the lowermost shoreface units appear to consist of 'normal' parasequences deposited during a highstand systems tract (hst1). the oldest sharp-based shoreface package is bound at its base by a regressive surface of erosion and is capped by an abrupt transgressive surface. relative sea-level rise at this time was too rapid to preserve lowstand systems tract deposits. falling sea level during the deposition of sequence 3 (fsst3) is recorded by sharp-based shoreface deposits bounded by a regressive surface of erosion at section a that correlates basinwards to slumped sandstones. the lowstand systems tract of this sequence (lst3), and indeed of the lower-order sequence too, is represented by turbidite deposition basinward of the preceding sharp-based shoreface package at section a and corresponds chronostratigraphically with a gravely bypass lag surface at section c. there is no evidence for subaerial exposure during this time of reduced accommodation. the transgressive surface that separates lst3 from the overlying transgressive systems tract (tst3) is denoted by an abrupt increase in water depth and intensely bioturbated crests of the fsst3 deposits at sections a and b and corresponds to a cessation of lowstand deposition. a thin, distal shoreface succession above the fsst3 at section a represents transgressive systems tract deposition, the top of which marks maximum flooding at both low and higher-order levels.” we interpret his lst3 sequence as a transgressive unconformity at the base of the juana lopez formation and not as turbidites and that the juana lopez strata preserving the prionocyclus wyomingensis fauna extents west across top of the tst3 systems track on the west side of farnham dome. 137 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 33. northwest side of farnham dome and lower ferron and juana lopez formations. (a) oblique view of strata on west side of farnham dome. white bar = edwards’ (2005) section a on the northwest side of us-6/192. p.w. = juana lopez exposures preserving a prionocyclus wyomingensis fauna in f through h. image from google earth ©2023. (b) lower ferron formation on farnham road just south of turn into day 3, stop 5. (c) lower ferron formation exposure of the contact between sandstone-dominated falling sea-level system’s track 3 (fsst3) and overlying carbonaceous transgressive system’s track 3 (trt3) as expressed at day 3, stop 5. (d) detail of the carbonaceous tst3 strata at day 3, stop 5. (e) tst3 at top of lower ferron formation overlain by juana lopez formation north of turn into day 3, stop 5. (f) dispersed pebbles in mudstone beds of tst3 at day 3, stop 5. (g) interbedded rippled sandstone and mudstone in the lower juana lopez formation. (h) typical fossils from lower juana lopez formation at this site, a, prionocyclus wyomingensis, b, scaphites ferronensis, and c, inoceramus dimidius. (i) upper juana lopez is dominated by dark organic-rich shale with prionocyclid ammonites and inoceramid bivalves. systems tracks after edwards (2005) (see figure 32). 138 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 drab medium-gray to pinkish-gray marking the cretaceous-paleogene contact. in the canyon this contact is thought to be represented by a slight disconformity. the limestone beds up slope capping the rim of the canyon are the paleocene flagstaff formation. 11.7 126.9 211.0 at the top of the price canyon, us 6 turns west. along the north and east side of road extensive outcrops of the pale-red flood plain deposits of the lower eocene colton formation overlain by the thick lacustrine beds of the middle eocene green river formation over the next 12 miles (19 km) to the crest of soldier summit. figure 34. garley canyon member of emery formation. (a) exposures of garley canyon to the northeast of day 3, stop 6. (b) transition between the blue gate shale and base of the garley canyon member to the northwest of day 3, stop 6. 139 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 figure 35. helper formation and the transition between the mancos group and the mesaverde group. (a) overview of transition between upper mancos group and mesaverde group across mouth of price canyon. dashed white box = area in b. white box = area in e. (b) oblique view of bull point. line of type section of helper formation in black from day 3, stop 7. (c) detailed route of helper formation type section (in black) up southwest end of bull point. (d) bull point from the southeast. (e) helper formation northeast of us-191 at helper, utah. dashed white lines indicate formation boundaries. images from google earth ©2023. 140 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 18.0 144.9 193.0 driving down the western slope of soldier summit, exposures of the eocene lacustrine green river formation are present over the next 17 miles (27 km). a structurally complex interval between mile markers 194 and 193 marks the boundary between the colorado plateau and the basin and range province with the cretaceous rede narrows conglomerate superimposed on the eocene green river formation. 4.0 148.9 189.0 tabular boulder conglomerate and mudstone of the red narrows conglomerate (young, 1976) are the result of the alluvial fans formed proximal to the sevier orofigure 36. price canyon. (a) correlation of blackhawk formation with upper mancos group. modified after cole et al. (1997), stevens (2004), and chaiwongsaen (2007). ages taken from singer et al. (2023). (b) coal-bearing blackhawk formation exposed in roadcut on west side of us-6 at mp 229.9. (c) blackhawk and castlegate formations to northeast of pull out at day 3, stop 8. note: natural casts of ceratopsian tracks in fallen sandstone block from blackhawk formation. 141 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g.. geology of the intermountain west 2025 volume 12 genic belt (figure 37). strikingly, the correlative coastal strata in price canyon includes barely any pebbles within its fluvial sequences across the narrow floodplain 30 miles (48 km) to the southeast. this reflects the rapid subsidence of the narrow cretaceous foredeep basin of northern utah. 3.5 152.4 185.5 traversing west for the next 3 miles (5 km), lower cretaceous strata of the kelvin formation (granger, 1953) that outcrops along the north side of the road appears gradational with the overlying red narrows conglomerate due to its isolated sheet conglomerate in its upper part documenting the early phases of the sevier orogeny. a short northward curve in the road is bounded by marine middle jurassic arapien formation (sprinkel et al., 2024). as the road starts down slope to the north, the extensive scar of the 1980s thistle landside is visible to the west across the deep valley. 6.6 158.0 179.0 the road continues to drop down through the mesozoic section for the next 1.5 miles (2.4 km) through the early triassic thaynes formation as the road turns west again just past the diamond fork turnoff on the right. the road continues to cut down section through the upper paleozoic to the small windfarm at the mouth of the canyon on the east side of spanish fork, utah. 5.5 163.5 173.5 continue on us-6 northwest across spanish fork and merge onto i-15 northbound to provo. road log ends in spanish fork, utah figure 37. red narrows conglomerate. tabular-bedded boulder conglomerate of the red narrows conglomerate represent alluvial fans adjacent the upper cretaceous sevier orogenic belt (n. 39° 59.603, w. 111° 23.927; 12s e 465956 n 4427099). 142 revisiting the cretaceous mancos group in utah—problems, previous methods, and new perspectives on a world-class cretaceous marine section kirkland, j.i., king, m.r., and bylund, k.g. geology of the intermountain west 2025 volume 12 acknowlegments we would like to thank josh lively, utah state university eastern prehistoric museum for his contributions to our stratigraphic descriptions and in refining the logistics of this field trip. kirkland would like to acknowledge mike gardener (retired, u.s. geological survey) for renewing his interest in the mancos group and sharing the research of his former students at the colorado school of mines. stefan kirby (utah geological survey [ugs]) is also credited for promoting a statemap project to update the stratigraphic nomenclature for the mancos in eastern utah. fred zelt (retired, exxonmobil) is thanked for sharing an unpublished powerpoint presentation on the tropic shale. discussions of cretaceous matters with mark leckie (university of massachusetts) are appreciated. robert ressetar (ugs), donna anderson (colorado school of mines), and kim stevens (hog resources inc.) are thanked for permitting the modification of figures from their important research to express hypotheses developed during the course of this research. reviews by don deblieux, stefan kirby, stephanie carney, and darlene batatian (all of the ugs), paul anderson (consulting geologist), and mark leckie improved the manuscript. we thank doug sprinkel, tom chidsey, and bill lund (giw editors) for improving this paper through their editing. references ahmed, s., bhattacharya, j.p., garza, d.e., and li, y., 2014, facies architecture and stratigraphic evolution of a river-dominated delta front, turonian ferron sandstone, utah, u.s.a.: journal of sedimentary research, v. 84, no. 2, p. 97–121. anderson, d.s., and harris, n.b. 2006, integrated sequence stratigraphic and geochemical resource characterization of the lower mancos shale, uinta basin, utah: u.s. geological survey open-file report 483, 68 p. anderson, p.b., and ryer, t.a., 2004, regional stratigraphy of the ferron sandstone, in chidsey, t.c., jr., adams, r.d., and morris, t.h., editors, regional to wellbore analog for fluvial-deltaic reservoir modeling—the ferron sandstone of utah: american association of petroleum geologists studies in geology 50, p. 211–224, https://doi.org/10.1306/ st50983. antia, j., and fielding, c.r., 2011, sequence stratigraphy of a condensed low-accommodation succession—lower upper cretaceous dakota sandstone, henry mountains, southeastern utah: american association of petroleum geologists bulletin 95, p. 413–447. barton, m.d., tyler, n., and angle, e.s., 2004, stratigraphic architecture of fluvial-deltaic sandstones from the ferron sandstone outcrop, east-central utah, in chidsey, t.c., jr., adams, r.d., and morris, t.h., editors., regional to wellbore analog for 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professional paper 400-b, p. b246–b249, https://pubs.usgs.gov/pp/0550b/report.pdf. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 10 2023 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah andrew r.c. milner, vincent l. santucci, john r. wood, tylor a. birthisel, erica clites, and martin g. lockley geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover two hypothetical, eubrontes-producing theropods walking across a sandy, water-saturated, microbial-matrich interdunal playa during an early phase of the navajo erg in the early jurassic. this restoration was created based on the spectacular undertracks preserved on the john wesley powell fossil track block. the ornithopodlike undertracks now visible on the track block were registered in horizons situated below stromatolitic or endoevaporitic layers (represented in green). these undertracks display different morphologies than the true tracks, which would have resembled eubrontes. artwork by brian engh (dontmesswithdinosaurs.com). i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 10 2023 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2023–2024 uga board president eugene szymanski eugenes@utah.gov 801.537.3364 president-elect keilee higgs keileeann@utah.gov 801.678.3683 program chair chris stallard cstallard@utah.gov 801.386.0976 treasurer aubry dereuil aubry@zanskar.us 850.572.2543 secretary trae boman tbowman@teamues.com 801.648.5206 past president rick ford rford@weber.edu 801.915.3188 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2024–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.824.0738 tomchidsey@gmail.com john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov editors geology of the intermountain west an open-access journal of the utah geological association volume 10 2023 185 abstract a large fallen block of early jurassic navajo sandstone located at lake powell, within glen canyon national recreation area, south-central utah, displays natural casts of vertebrate tracks. the footprints occur on at least three track-bearing horizons preserved on and between stromatolitic sandstone beds. two large, parallel trackways, plus a third, divergent trackway, on the main track layer (mtl) superficially resemble ornithopod footprints; however, they were produced by large-sized theropod dinosaurs, rather than ornithischians, and we identify these as eubrontes. small coelophysoid theropod tracks (grallator) are the most common vertebrate ichnofossils on all track-bearing horizons, with approximately 50 footprints preserved on the mtl, six on the highest surface, and three on thinner float slabs stratigraphically lower in section. an additional 12 tracks in three trackways of anchisauripus size occur on the mtl, but they superficially resemble kayentapus in having wider divarication angles than typical anchisauripus. the mtl also preserves at least five closely associated tetradactyl footprints that we identify as cf. brasilichnium. a nearby, smaller fallen block preserves distinct batrachopus tracks, which are rare in eolian environments. the microbial (possibly endoevaporitic) mats and stromatolitic horizons on which the animals had walked produced a distinct ichnomorphologic variation because of substrate consistency and the elastic properties of the mats, resulting in differential compaction of the bedding surfaces. lithic compaction of the finer-grained sediments between denser, more resistant sandstone beds preand/or post-lithification resulted in additional deformation of the tracks, followed by natural erosion. we interpret these natural cast footprints on the mtl as possible transmitted tracks. the track-bearing, microbial-mat surfaces represent interdunal pooling of water, probably during periods of increased precipitation and/or rising water tables during wet seasons. the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona andrew r.c. milner1, vincent l. santucci2, john r. wood3, tylor a. birthisel4, erica clites5, and martin g. lockley6 1st. george dinosaur discovery site at johnson farm, st. george, ut 84790 usa; arcmilner@gmail.com 2national park service, geologic resources division, washington, dc 20005 usa; vincent_santucci@nps.gov 3national park service, geologic resources division, natural resources stewardship and science directorate, lakewood, co usa 80225; jack_wood@nps.gov 4natural history museum of utah, salt lake city, ut 84108-1214 usa; tbirthisel@nhmu.utah.edu 5michigan state university extension, detroit, mi 48238 usa; eclites@gmail.com 6dinosaur trackers research group, university of colorado denver, denver, co 80217-3364 usa; martin.lockley@ucdenver.edu citation for this article. milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g., 2023, the john wesley powell fossil track block— theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona: geology of the intermountain west, v. 10, p. 185–222, https://doi.org/10.31711/giw.v10.pp185-222. 186 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 introduction glen canyon national recreation area (glca) preserves an incredible abundance of tetrapod trace fossils, especially those of dinosaurs, because of extensive exposures of late triassic–early jurassic chinle formation and glen canyon group strata (lockley and others, 1998, 2014). these strata were deposited in paleoenvironmental conditions conducive to track preservation, such as fluvial, lacustrine, and eolian environments. many important tracksites submerged by and around lake powell have been recorded by two of us (vls and mgl), the national park service (nps), and others (lockley and hunt, 1995; lockley and others, 1998, 2014; santucci and others, 2009; santucci and kirkland, 2010; kirkland and others, 2010; delgalvis, 2015; tweet and santucci, 2018; bennett and others, 2023). one such example, which is the focus of this paper, is a large, approximately 7-m-tall fallen block (nps locality # glca 10) of early jurassic navajo sandstone we have designated as the john wesley powell fossil track block (pftb), honoring major john wesley powell, who perilously explored the colorado river along its length on two occasions in 1869 and 1871-1872, including the glen canyon area in which man-made lake powell reservoir now lies. the pftb was discovered in 2009 by jessalyn imdieke and reported to the office of the state paleontologist at the utah geological survey (ugs) by stuart havenstrite. the locality was then reported by dr. james kirkland (ugs) to the nps. it was subsequently investigated in a joint effort between the nps and ugs in 2009. the block was reported and illustrated for the first time in an internally distributed nps document (kirkland and others, 2010, figure 32), and later figured and partially described on other occasions (lockley and others, 2014, figure 26; lockley and xing, 2015, figure 4; tweet and santucci, 2018, figure 3e). the site is located along the eastern shore of lake powell, near the san juan confluence within glca (figure 1). because of high levels of tourism in the lake powell area and the need to protect this valuable fossil resource from potential damage, specific locality information about the site is withheld here, but will be made available to qualified researchers upon request. the pftb preserves a spectacular assemblage of tracks (figure 2), primarily produced by bipedal theropod dinosaurs, although two of the trackways superficially resemble ornithopod tracks. approximately 85 footprints are preserved on three identified track-bearing horizons exposed on the vertically oriented block and nearby associated float slabs. the most prominent tracks lie on a horizon referred to as the main track layer (mtl); other tracks present at the site occur on, or on float slabs originating from, both a higher and a lower stratigraphic horizon. during the original inspection of the pftb, the ornithopod-like tracks were recognized as morphologically unusual, prompting the question of whether some unknown large ornithopod dinosaurs may have produced them. however, this hypothesis seems unlikely because the pftb tracks are significantly older than the oldest-known body fossils of even small ornithopods, such as the dryosaurid callovosaurus from the middle jurassic of the united kingdom (ruiz-omeñaca and others, 2007; díaz-martinez and others, 2015), and kulindadromeus from the middle–late jurassic of russia (godefroit and others, 2014), which was recovered as utah arizona n 37º37º 111º 111º figure 1. approximate location (red circle) of the john wesley powell fossil track block site (glca #10). 187 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 figure 2. the john wesley powell fossil track block (ptfb) at locality glca #10. (a) photograph of track block looking to the west. (b) an inverted map of the middle and upper track-bearing surfaces. tracks have been assigned unique track and trackway numbers. arrows indicate directions of travel of individual trackmakers; the inset rose diagram shows the prevalence of travel directions relative to the estimated north orientation of the pftb. tracks have been colored: dark orange = eubrontes; brown = grallator; light orange = medium-size theropod tracks (anchisauripus-sized tracks); red = cf. grallator; in box marked qt = brasilichnium; light purple = unidentified tracks. scale = 1 m. 188 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 an ornithopod by dieudonné and others (2022). moreover, the oldest recorded tracks assigned to ornithopod dinosaurs (which, from an ichnological perspective, has been used as something of a wastebasket) are middle jurassic (milàn and others, 2020) and late jurassic in age, including the ichnotaxa camptosauropus vialovi from tajikistan (gabunia and kurbatov, 1988), wealdenichnites iguanodontoides (kuhn, 1958) from germany, sinoichnites youngi (kuhn, 1958) from china, and ostensible ornithopod tracks from the morrison formation in the western united states (foster and lockley, 2006). note that sinoichnites was identified as late jurassic, but because its source locality is unknown, the proposed age is suspect (díaz-martinez and others, 2015). additionally, li and others (2012) found evidence that sinoichnites might be a thyreophoran track with some resemblance to moyenisauropus. all of these ichnotaxa were considered nomina dubia by díaz-martinez and others (2015). moreno and others (2012) defined ornithopod tracks as, “tridactyl, mesaxonic, with lengths of digits ii, iii, and iv only slightly different; wide digits with rounded ends; digits converge proximally into a broad metatarsophalangeal impression (‘heel pad’). ornithopod ichnites are similar in anteroposterior and mediolateral dimensions, and their general shapes resemble a clover.” following closer examination of the pftb tracks, we agree with lockley and xing (2015) in inferring a saurischian (specifically theropod), rather than ornithischian, origin for these footprints. lockley and xing (2015, p. 87–88, figure 4) assigned these tracks to eubrontes and interpreted the “fleshy” appearance of the footprints as a result of compaction and deformation of the track casts due to extensive loading on finer-grained and softer beds between thick, dense, eolian sand layers. while we agree this is, in part, correct, we expand on this hypothesis below. following martin (2014, p. 71), additional points should be considered in attributing tracks to specific clades of trackmakers, especially with tridactyl dinosaur tracks, include: (1) the overall shapes of digit impressions (thin, medium, robust) relative to entire track length; (2) the distal ends of digits—are they blunt and rounded or do they possess discreet claw marks?; (3) the shape of the proximal portion of track (i.e., “heel”); (4) the kind(s) of substrate on which the tracks are preserved and how this may have affected overall track morphology; (5) track morphology subject to behavioral differences (e.g., stopping, turning, speed, etc.); (6) sediment collapse into the tracks after foot extraction, changing overall track morphology; (7) the substrate drying after the track was formed, which can alter overall track morphology; and (8) whether or not the visible track actually is an “undertrack,” or more precisely a transmitted track and how far below the surface the undertrack was transmitted (thulborn, 1990). in this study, we consider all these points along with the shapes of the anterior triangles of the tracks (how far the digit iii trace extends distally beyond the ends of the digit ii and iv traces—i.e., the degree of mesaxony or the “toe extension” measurement of some authors) (olsen, 1980; lockley and hunt, 1995; lockley, 2009; farlow and others, 2018) and the dimensions of the proximal proportions of the tracks, following farlow and others (2018). materials and methods logistics, tracksite mapping, and site excavation our initial detailed documentation of the pftb in 2010 was complicated by the vertical orientation and large size of the block, making accessing much of the mtl difficult. the initial investigation employed a 6-ft (1.8-m) ladder to access higher areas of the block, but we were still limited on how much of the track surface we could physically access and examine in detail. unstable float slabs (rock debris broken off from the pftb and its adjacent source cliff) at the base of the block made positioning the ladder difficult, and maintaining balance safely was an issue (figures 3a and 3b). many of the float slabs in front of the pftb also contain dinosaur tracks from layers underlying the mtl, and these tracks could easily be damaged when walked or climbed on. initially we were unable to map the lowermost part of the pftb because the float slabs partially obscured the lower tracks and trackways. these slabs were systematically recorded (positionally and stratigraphically), excavated, and removed with the assistance of nps 189 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 a b c d figure 3. methods used in john wesley powell fossil track block (ptfb) tracksite documentation. gridding pftb for mapping. (a) dan whalen working on a ladder to place pink string datum line in place above eubrontes trackway 1. (b) tylor birthisel chalking upper part of the pftb while standing on precarious rock. (c) nps crew excavating the covered part of the track block in which tracks were found in situ on lower horizons. (d) september 2014 photogrammetry of track block; left to right: john “jack” wood and sarah doyle. 190 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 staff (figure 3c) in june 2015. this led to the confirmation of a slightly older track horizon several centimeters below the mtl. photogrammetry and data processing methods we generated high-quality, three-dimensional models of the track-bearing surface of the pftb to enhance mapping and morphological assessments. to accomplish this, structure-from-motion (sfm) photogrammetry was employed following matthews (2008) and mallison and wings (2011). additional details on photogrammetry methods for the pftb location were presented by wood and others (2021, figure 1b). the imagery for the photogrammetry was collected with two different digital cameras at two different times. the initial effort, in september 2014, targeted the upper section of the block because the lower part had not yet been revealed (supplementary file: https://irma.nps.gov/ datastore/reference/profile/2299562). this initial phase captured 92 images using a nikon d800 35 mm digital, single reflex lens camera with a 28 mm f/2.4 prime lens (figure 3d). horizontally and vertically spaced images were taken in a gridded pattern with the aid of a 7-m telescopic camera mast and a camranger remote triggering system. the mast was a “home-made” rig, comprised of an aluminum tree-saw pole with a swivel/tilt camera tripod head attached. the construction of the mast allowed the camera positions to change between landscape and portrait positions (rotated to 90° and 270°). the lower portion of the pftb was photographed in june 2015 by the first author after removal of the debris at the base of the block (supplementary file: https:// irma.nps.gov/datastore/reference/profile/2299562). this second phase captured 131 images using a nikon coolpix l110 with a fixed nikkor 15x wide optical zoom vr (5.0–75.0 mm) lens. the lens zoom settings were set to emulate a 35 mm camera set for a 28 mm focal length to match the first-phase photographs. handheld photography was completed with the camera rotated between landscape and portrait orientations. finally, photogrammetric images of the small cf. brasilichnium tracks on the mtl were taken in march 2023 by conner bennett using a nikon d800 35 mm digital single reflex lens camera with a 28 mm f/2.4 prime lens. a total of 58 images were taken. several 28 cm control sticks were used, calibrated to ± 0.23 mm (supplementary file: https://irma.nps.gov/datastore/ reference/profile/2299562). images were processed with the photogrammetry package photoscan (now known as metashape) v. 1.2.6 build 2834 by agisoft, llc. raw nikon (.nef) images for the upper part were pre-processed for color, exposure, vignetting, and spherical aberration in adobe bridge as a batch process. lens distortion was corrected as part of the photograph alignment and sparse-cloud processing with photoscan. once the two sections of the pftb were processed to dense cloud models, the two portions were merged within the software to create a uniform surface for the full 7-m-high, track-bearing surfaces (supplementary file: https://irma.nps.gov/ datastore/reference/profile/2299562). the model is internally scaled using control sticks of 30 and 50 cm lengths, calibrated to ± 0.1 mm. calibration for these scales was completed by comparing the distances between the printed targets with an astm certified ruler. the estimated error reported from the processing of the model is ± 0.4 mm, which instills high confidence in the fidelity of model feature measurements. both high-definition digital cinematography and high-resolution digital photography are essential elements to the future of monitoring paleontological sites. digital documentation provides data for historical sideby-side and overlay comparisons of high-quality images and real-time footage (wood and others, 2021). the collected images and footage can be used to monitor natural or man-made changes to sites, including vandalism, theft, and erosion, for new and existing paleontological sites. implementing digital technology is a vital and essential component for raising public awareness, minimizing impact, and preserving paleontological resources. measurements of tracks and trackways individual track measurements were recorded (after https://irma.nps.gov/datastore/reference/profile/2299562 https://irma.nps.gov/datastore/reference/profile/2299562 https://irma.nps.gov/datastore/reference/profile/2299562 https://irma.nps.gov/datastore/reference/profile/2299562 https://irma.nps.gov/datastore/reference/profile/2299562 https://irma.nps.gov/datastore/reference/profile/2299562 https://irma.nps.gov/datastore/reference/profile/2299562 https://irma.nps.gov/datastore/reference/profile/2299562 191 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 olsen and others, 1998; farlow and others, 2018; figure 4a) including total track length, maximum track width, estimated track depth, estimated lengths of digits ii, iii, and iv, divarication angles between digits ii to iv, ii to iii, and iii to iv, anterior track length (atl), anterior track width (atw), and indication of symmetry (i.e., were tracks produced by left or right feet?). some of the aforementioned measurements could only be estimated because most footprints at the site are not exceptionally well preserved: following the 0-1-23 preservation scale established by belvedere and farlow (2016) and later modified by marchetti and others (2019), tracks on the pftb mostly score “1.” most tracks on the pftb do not show digit pads; nearly all have been impacted by modern-day weathering (e.g., exfoliation) and have some form of lithic deformation, which is discussed in more detail below. some grallator tracks can be scored “2” because track outlines are sharp, and some toe pads can be discerned. finally, two overlapping batrachopus pedal tracks found at the site on a smaller float block we consider elite tracks, or “3” on the preservation scale. consequently, most measurements taken for digit lengths, divarication angles, anterior triangle lengths, and anterior triangle widths are necessarily estimates. in addition to individual track measurements, the following measurements were recorded for bipedal trackways (after lockley, 1991; farlow and others, 2018; figure 4b): pace, stride, pace angulation, trackway width, footprint rotation, and direction of travel. generally, trackway orientations are recorded using a compass when preserved in situ; however, on the pftb, this could not be accomplished because the track surfaces are ex situ. nevertheless, we were able to orient the estimated position of the block with the adjacent, in situ cliff, and we were able to estimate directions of travel. specific ichnological terminologies and definitions are used based on standards summarized by marty and others (2016). institutional abbreviations acm-ich, “appleton cabinet,” beneski museum of natural history (formerly pratt museum of amherst college), amherst, massachusetts; glca, glen canyon national recreation area, page, arizona; sgds, st. george dinosaur discovery site at johnson farm, st. george, utah; ucm, university of colorado at boulder, boulder, colorado; ucmp, university of california, museum of paleontology, berkeley, california. geology stratigraphy the glen canyon group within glca is composed, in stratigraphic order from oldest to youngest, of the wingate sandstone, kayenta formation, and navajo sandstone. the wingate sandstone (about 75 m thick), which holds the triassic–jurassic boundary (in part, laterally equivalent to the moenave formation to the west and southwest), overlies the upper triassic church rock member (or rock point member of some authors) of the chinle formation (or chinle group of some authors). the kayenta formation overlies the wingate, but it is thin (about 95 m thick) and sandy in glca compared to its siltier lithology in north-central arizona and southwestern utah, where it measures approximately 144 m and 305 to 320 m thick, respectively. above the kayenta formation, the navajo sandstone ranges from 350 to 400 m thick; it is unconformably overlain by the middle jurassic carmel formation of the san rafael group within most of glca, and the middle jurassic temple cap formation (formerly page sandstone) in the southern and western parts of the park (doelling and others, 2013). as in drainage basins during the late triassic through early jurassic, represented by the chinle, wingate sandstone, moenave, and kayenta formations, most river systems flowed from the southeast toward the northwest through the navajo erg depositional basin (figure 5). the braided fluvial systems of the kayenta formation brought in massive accumulations of sand with increased aridity, leading to the formation of the navajo erg (blakey, 1994, 1996; peterson, 1994; bryant and miall, 2010), the largest sand sea known in earth history (kocurek and dott, 1983). the upper part of the kayenta and lower navajo sandstone are both grada192 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 tional and intertongue substantially with one another over large areas, and we observe this same interfingering between fluvial and eolian systems on a smaller scale within the vicinity of, and immediately below the pftb. we follow other authors and refer to this sequence as the kayenta–navajo transition (harshbarger and otha b tl tw paº st rid e pa ce atl aw ii-ivº iii-ivº ii-iiiº iv l ii l iii l tww figure 4. track and trackway measurements taken. (a) individual eubrontes footprint showing measurements used in this paper. (b) bipedal dinosaur trackway showing pace or step, stride, trackway width, and pace angulation. modified from lockley (1991). ii, iii, iv = digits; ii–iii° = divarication angle between digits ii and iii; ii–iv° = divarication angle between digits ii and iv; iii–iv° = divarication angle between digits iii and iv; ii l = digit ii length; iii l = digit iii length; iv l = digit iv length; atl = anterior track length; aw = anterior track width; pa° = pace angulation; tl = total track length; tw = total track width; tww = trackway width.. 193 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 ers, 1957; middleton and blakey, 1983; sansom, 1992; herries, 1993, blakey, 1996; lockley and others, 2014). the navajo sandstone was deposited in a low-latitude erg that was situated on the western margin of pangaea during the early jurassic (pliensbachian–toarcian; approximately 180 to 190 million years ago; loope and others, 2001). although uncommon, interdunal carbonate beds in the navajo sandstone, especially in south-central and southeastern utah, are more prominent in the lower half of the formation (marzolf, 1983), but these beds rarely measure greater than 1 m in thickness. these carbonate beds can span areas of over 1 km (doelling and other, 1989; stokes, 1991; bryant and others, 2016), and many are made up of dolostone and cherty limestone deposited between dune sets along interdunal surfaces. vertebrate tracks and invertebrate traces can be locally abundant on and within these interdunal carbonates. additionally, stromatolites and california colorado utahnevada idaho wyoming south dakota montana ? navajo erg un ce rta in st ra tig ra ph y lo w er in la nd lim it m ar in e th ru st be lt proto-pacific ocean subduction nugget erg zone arizona texas mexico nebraska kansas oklahoma oregon tr-j magmatic arc jurassic lower-middle new mexico n 0 100 200 300 km ju ras sic erosional margin ?? california figure 5. depositional and structural features during the early jurassic and onset of the navajo erg. tadpole symbols indicate location (dot) and average foreset dip directions (tails). dark gray represents eroded basement rocks during the early jurassic. red arrows indicate estimated wind directions based on sand dune data. blue arrow represents predominant fluvial flow directions during late triassic–early jurassic (figure modified from bryant and miall, 2010, and bryant and others, 2016; data after blakey, 1994; parrish and peterson, 1988; peterson, 1994; dickinson and gehrels, 2003). 194 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 microbial mat surface are quite common in some areas, including many localities within glca. sedimentology the track-bearing horizons at the pftb are in the lower part of the navajo sandstone, approximately 15.8 m above the conformable contact between the “sandy facies” of the kayenta formation and navajo sandstone (figure 6a). due to rough terrain, vegetation, and poor exposures, a “clean” stratigraphic section had to be measured several hundred meters to the south of the pftb locality where the kayenta–navajo transition could be observed up to a traceable, laterally extensive interdunal/paleoerosional parting (“crack”) extending between both sites (figure 6a). three additional sections were measured at the pftb locality: (1) the in situ cliff face adjacent to the pftb (figures 6b and 6c); (2) the south side of the pftb (figure 6d); and (3) the north side of the pftb (figure 6e). all three of these short sections have nearly identical stratigraphic features that can easily be correlated with one another. the wavy-laminated beds preserving the tracks within the cliff (figures 6b and 6c) compare well with measurements taken from both sides of the pftb (figures 6d and 6e): in the cliff, the thickness from the base of a dark brown, oxidized unit to the bottom of the track-bearing unit measures 1.86 m. another oxidized, brown bed below the wavy-laminated track-bearing unit is about 30 cm thick and is composed of poorly sorted, fine-grained sandstone nearly identical to the cross-bedded layers below it that are dune sequences. the section measured on the south side of the pftb comprises lower wavy-laminated beds; middle massive beds; and upper thick, planar-laminated beds (figure 6d). the thinner track-bearing beds pinch out toward the top of the block, and similar sets of sandstones were observed in situ within the cliff next to the pftb (figures 6b and 6c). whereas wavy-laminated beds, as well as localized chert and carbonate beds, are present in a laterally traceable layer continuing for several hundred meters to the north (figures 7b through 7d) and south of the pftb in the cliff, the thickest parts of these beds are found in situ near the pftb. the stratigraphic section measured on the north side of the pftb is 5.25 m thick (figure 6e). the main track-bearing surface lies at the base of the section, starting with approximately 0.5 m of wavy, fineto very fine, well-cemented sandstone. we recognize three track horizons located on some of these carbonate-rich, wavy-laminated surfaces, which are stromatolitic (figures 6f, 6g, and 7b). microbial mats certainly were present when animals walked across the surfaces judging from the pitted texture of the mtl, as well as some other horizons. above the mtl is approximately 25 cm of massive to poorly laminated, coarse-grained sandstone that shows evidence of soft-sediment deformation. an additional 25 cm of finely laminated, medium-grained sandstone that is oxidized to a dark brown are followed by about 4 m of planar-laminated, fine to very fine sandstone making up the lower part of a dune sequence. float blocks between the exposed track surfaces of the pftb and the cliff face mostly pertain to additional beds that were present below the mtl. the wavy-laminated beds bearing the tracks formed during a time of wet conditions in which substantial water, either a rise in the water table during a wet season and/or during a monsoon season (loope and others, 2001), would have been able to accumulate and pool on flats between dunes (i.e., interdunal playas). the resulting carbonate-rich beds commonly preserve microbial laminates and even large stromatolites at some localities (eisenberg, 2003; parrish and falcon-lang, 2007; dorney, 2009; dorney and parrish, 2009; chure and others, 2014; parrish and others, 2017). although some parts of the pftb surfaces are heavily weathered, the majority is well-preserved, exhibiting sedimentary structures such as small mudcracks (figure 8a), and the aforementioned pitted, rugose texture likely formed by microbial mats. branching horizontal structures that may represent poorly preserved invertebrate grazing trails, and unidentified larger, mudcrack-like structures were also observed and mapped (figure 8b), but we have not been able to definitively identify any of these sedimentary structures with confidence. additionally, several float blocks contain invertebrate burrows, but their exact stratigraphic positions 195 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 a b d 4.0 m 0.5 m 0.25 m 0.25 m 1.86 m 0.3 m 1 meter c unit 1 unit 2 unit 3 unit 4 unit 5 unit 6 kayenta formation navajo sandstone e l1l2 l3 0.2 ml2 l1 l3 f 1 meter unit 5 unit 6 unit 3 unit 4 g g f figure 6. stratigraphy and lithology of the john wesley powell fossil track block (ptfb). (a) view of pftb location (red circle) from the lake looking east. red line indicates where stratigraphic section was measured to determine distance above the kayenta–navajo contact; yellow arrows point to interdunal surface that traces to the top of the main track-bearing, stromatolitic beds; the white arrow points to northern exposure of track beds north of the pftb. (b) in situ cliff adjacent to pftb. (c) corresponding stratigraphic section of in situ cliff (b), and comparison with the pftb (in d and e). track-bearing layers are designated l1–l3. (d) stratigraphy of the south side of the pftb. (e) stratigraphy on the north side of the pftb. (f) close-up of distinct units on north side of pftb. dashed box indicates area shown in g. (g) close-up of track-bearing, stromatolitic, wavy laminated carbonate-rich sandstone beds. white arrow points to possible track in cross section. 196 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 below the track-bearing surfaces are uncertain. these back-filled burrows resemble taenidium barretti (figure 8c; see keighley and pickerill, 1994; matt stimson, new brunswick museum, personal communication, 2022). structural fractures, which are aligned approximately 90° to larger scale joint orientations, can be recognized on the track block surface. using the orientations of joint and fracture trends in the approximate location of the rockfall, and because the orientation of joints and varying stratigraphy from one side of the block to the other, we can safely estimate the in situ position of the pftb, thereby allowing us to also estimate travel orientations of track producers (figure 2b, inset). paleontological description of the powell fossil track block a total of 104 footprints were observed on the main track block itself, preserved on at least three track horizons (figures 2 and 6c). tracks indicate a moderately a d cb k figure 7. (a) medium-grained, stromatolitic sandstones bearing grallator tracks in track layer 1 (see figure 6 for the position of this layer), the oldest tracks identified at the john wesley powell fossil track block (ptfb). (b) in situ track-bearing stromatolitic beds with cherty layers immediately below, located north of the pftb. (c) another track surface in situ north of the pftb. white arrow points to tracksite surface under overhang. (d) close-up of overhang in c; white arrows point to in situ natural cast tracks; red arrows point to unidentified sedimentary structures. 197 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 diverse ichnofauna including three to four theropod dinosaur size groups, crocodylomorphs, and possible cynodont synapsids. grallator and grallator-like tracks (figures 9 and 10, tables 1 to 3) we identify small tracks and trackways of bipedal theropods from the pftb as grallator (hitchcock, 1858) or grallator-like because of their size, general outline, and trackway configuration. grallator is the most abundant track type at the pftb, with a total of 49 individual tracks, 22 of which are within three distinct trackways. these small theropod footprints range from 4.5 to 22 cm in length and 4.0 to 12.5 cm in width, and average 13.3 cm long and 9.2 cm wide (table 1). grallator trackway t5 (figures 2b, 9a, and 9b, tables 1 and 2) comprises 10 footprints, starts near the middle of the pftb, and ends in the upper right corner. the trackway shows a very slight left turn where the animal changed its pace and stride: the first three footprints following the turn (t5-4 to t5-6) have shorter stride and wider pace angulation values (i.e., minimum of 62.5 cm and average of 122.3º) followed by longer stride and narrower pace angulation values (averaging 75.1 cm and 166.3º) nearly identical to those displayed prior to the direction change. this individual was travelling toward the northeast. the best preserved footprint in this trackway is t5-10, which is a left print (figure 10a). grallator trackway t7 was traveling toward the north, opposite to the direction of eubrontes trackway t1 (figures 2b, 9c, and 9d) and at a later time than eubrontes t1 because t7-3 overprints t1-3, and t7-4 overprints the displacement rim of t1-2. t7 is one of the smallest theropod trackways preserved on the pftb, having an average footprint length of 12 cm and width of 7.4 cm. the best-preserved print in this trackway is t7-4, a right track with some indication of a 2-34 toe pad arrangement, as is typical for grallator, visible in the photogrammetric images (figure 10b). trackway t7 has an average stride of 140 cm, an average trackway width of 13.4 cm, and an average pace angulation of 172º (table 2). grallator-like trackway t36 consists of only two poorly preserved tracks that average 21.8 cm long and 9.7 cm wide (figure 2b; table 1). the lengths of these tracks may have been exaggerated by metatarsal traces, but this cannot be confirmed due to poor preservation. grallator tracks on the mtl of the pftb, including those of trackway t7, are “inflated” or “expanded” in a similar way to those of the larger theropod tracks, though not as exaggerated. examples of this “inflation” include the distal end of the trace of digit ii in track t7-4 (figure 10b), isolated left track t12 (figure 10e), and left track t7-1 (figure 10c); the latter has an identifiable grallator shape, but the distal end of the trace of digit ii is missing, and the intersection between the 1 cm a b 1 cm 1 cm c figure 8. sedimentary structures on the main track surface of the john wesley powell fossil track block (ptfb). (a) small mudcracks and possible horizontal, branching burrows. (b) large, rope-like structures that could be mudcracks. (c) back-filled invertebrate burrows (cf. taenidium barretti) found in float between the pftb and cliff where the block originated. 198 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 track # sym. tl tw atl atw digit ii l digit iii l digit iv l ii-ivº ii-iiiº iii-ivº td t 5-1 right 13.0 9.8 5.5 7.8 5.9 12.0 8.3 40 26 14 n/a t 5-2 left 11.5 10.5 4.4 8.7 6.0 10.5 9.5 50 22 28 n/a t 5-3 right 10.5 8.6 4.6 8.4 —  —  — 83 41 43 n/a t 5-4 left 9.2 7.7 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 5-5 right 13.2 8.3 n/a 7.1 n/a n/a n/a 44 20 25 n/a t 5-6 left 13.5 10.7 6.2 8.1 7.5 12.5 9.6 n/a n/a n/a n/a t 5-7 right 13.0 11.0 6.4 9.5 7.5 12.3 9.5 n/a 23 n/a n/a t 5-8 left 13.4 11.0 n/a 8.6 n/a n/a n/a 46 28 18 n/a t 5-9 right 16.0 11.5 6.4 8.6 7.9 15.0 10.0 69 34 37 n/a t 5-10 left 13.6 10.7 6.1 9.1 6.4 12.5 8.6 45 18 27 n/a avg.   12.7 10.0 5.7 8.4 6.9 12.5 9.3 54 27 27 n/a t 7-1 left 12.8 7.6 5.9 6.7 5.7 11.5 8.0 50 25 25 1.0 t 7-2 right 12.2 7.6 n/a 5.9 n/a n/a n/a 46 26 20 2.5 t 7-3 left 12.1 6.5 n/a n/a n/a n/a n/a n/a n/a n/a 2.0 t 7-4 right 11.7 7.6 4.2 6.0 7.1 10.1 8.6 47 26 21 0.5 t 7-5 left 11.0 7.8 n/a n/a n/a n/a n/a 41 29 15 n/a avg.   12.0 7.4 5.1 6.2 6.4 10.8 8.3 46 27 20 1.5 t 38-1 n/a 23.5 9.6 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 38-2 n/a 20.1 9.7 n/a n/a n/a n/a n/a n/a n/a n/a n/a avg.   21.8 9.7 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 9 right 16.0 10.9 6.5 8.7 8.0 14.0 9.5 59 31 28 ~0.5 t 10 right 15.3 10.4 6.8 8.9 6.5 12.5 9.3 52 26 28 n/a t 12 left 15.0 9.5 7.0 8.8 7.5 12.5 9.3 50 26 24 1.0 t 13 right 14.1 8.4 5.2 6.9 8.8 12.8 9.0 47 24 23 n/a t 14 right 12.4 7.9 4.5 6.7 6.5 10.3 10.7 33 19 14 n/a t 15 left? 12.0 11.0 5.8 8.5 n/a n/a n/a 64 28 34 1.0 t 16 left? 14.0 12.6 6.3 10.1 n/a n/a n/a 58 29 33 1.0 t 17 right 9.7 6.0 3.5 6.0 3.9 9.2 6.3 48 28 24 n/a t 18 n/a 12.4 11.5 4.7 7.9 n/a n/a n/a n/a n/a n/a n/a t 19 n/a 12.0 11.5 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 20 left 8.9 5.3 3.5 4.7 3.8 7.1 5.0 33 20 14 n/a t 21 right? 12.4 7.3 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 22 n/a 8.5 6.6 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 23 n/a 8.7 7.3 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 24 right 14.3 10.5 5.5 7.7 6.2 11.4 11.5 63 24 40 n/a t 25 n/a 9.5 7.9 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 26 left 11.5 7.8 4.6 4.9 5.4 10.0 7.4 30 12 18 n/a t 27 right 16.0 10.0 6.3 7.8 7.4 13.3 9.5 35 13 21 n/a t 28 na 4.5 4.0 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 29 left 17.4 12.5 5.5 11.8 10.3 14.0 12.5 49 29 23 n/a t30 n/a 22.0 12.5 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 31 right? 12.0 8.9 4.8 8.6 6.2 10.2 7.8 63 35 38 n/a t 32 left 16.0 12.5 7.0 11.0 8.3 15.5 12.5 47 19 28 n/a t 35 left 16.5 10.5 8.3 7.0 8.5 15.0 10.5 n/a n/a n/a n/a t 36 n/a 9.9 6.5 n/a n/a n/a n/a n/a n/a n/a n/a n/a t 37 right 11.6 9.5 6.5 7.0 n/a n/a n/a 57 36 21 n/a t 40 right? 16.5 10.9 7.6 10.6 n/a n/a n/a n/a n/a n/a n/a table 1 caption is on the next page. 199 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 table 1 is on the previous page. measurements (cm) of 44 individual grallator tracks on the main track layer of the john wesley powell fossil track block. atl = anterior triangle length; atw = anterior triangle width; avg. = average; digit ii, iii, and iv l = digit ii, iii, and iv lengths; ii–iv, ii–iii, and iii–iv = divarication angles between digits ii–iv, ii–iii, and iii–iv; n/a = no data; sym. = symmetry (i.e., left or right tracks); td = track depth; tl = track length; tw = track width. c t7-1 t7-2 t7-3 t7-4 t7-5 dct5-10 t5-9 t5-8 t5-7 t5-6 t5-5 t5-4 t5-3 t5-2 t32 t5-1 1 m et er ba 1 m et er figure 9. grallator trackways on the john wesley powell fossil track block (pftb). (a–b) inverted trackway t5, which shows a change in pace/stride of the trackmaker due to very slight change in travel direction: (a) photogrammetry, (b) interpretive map of trackway. (c–d) natural cast trackway 7: (c) photogrammetry, (d) interpretive map of trackway. 200 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 traces of digits ii and iii is not visible. this print was underlain by a thicker layer of sand, and its “inflated” morphology possibly is a result of the transfer of sticky, sandy sediment from one foot strike to the next. better preserved grallator tracks on surfaces directly below the mtl (track layer 1; figure 10d) exhibit more typical overall shapes for grallator than many of those on the mtl. only a few theropod tracks were identified during the excavation of float slabs in front of the pftb, all of which pertain to grallator. several grallator tracks on the youngest track surface preserved on the right side of the pftb have a lower quality of preservation due to dinoturbation and significant erosion of the exposed parts of the tracksite. for these reasons, many of the tracks on this surface cannot be properly identified. a total of ten tracks have been identified as grallator and have length and width ranges between 10.2 to 19.7 cm and 5.9 to 17.6 cm, respectively (table 3). grallator tracks from the navajo sandstone would have been produced by contemporaneous, small, coelophysid-like theropods, such as segisaurus halli, which is known only from the navajo sandstone of northern arizona (camp, 1936; carrano and others, 2005). medium-sized tridactyl cf. kayentapus tracks (figure 11; tables 4 and 5) medium-sized theropod tracks on the mtl comprise two trackways (t4 and t6) and a single isolated track (t8) (figure 2b). t4 consists of six footprints with average pace and strides of 85.9 and 173.3 cm (table 5). the maximum trackway width is 27.4 cm and pace angulation of approximately 164°. individual tracks in t4 have an average length and width of 24.8 and 18.5 cm, respectively (table 4). trackway t6 (figures 2b and 11) is made up of eight footprints, but t6-6 is nearly unrecognizable, represented only by an elongate mound. tracks in this trackway have an average length and width of 21.9 cm and 16.7 track # sym. pl sl paº tw fr t 5-1 right n/a n/a n/a n/a n/a t 5-2 left 44.0 80.1 154 20.2 n/a t 5-3 right 38.5 72.0 112 29.8 n/a t 5-4 left 48.0 79.0 135 21.5 n/a t 5-5 right 38.0 62.5 120 27.7 n/a t 5-6 left 34.5 73.5 143 26.2 n/a t 5-7 right 37.0 73.0 167 18.3 n/a t 5-8 left 37.0 76.5 169 17.4 n/a t 5-9 right 42.0 77.5 163 16.9 n/a t 5-10 left 36.7 n/a n/a n/a n/a average 39.5 74.3 145 22.3 n/a t 7-1 left n/a n/a n/a n/a n/a t 7-2 right 62.8 145.0 174 14.8 9 t 7-3 left 62.9 140.0 167 12.6 5 t 7-4 right 58.1 135.0 175 12.8 4 t 7-5 left 59.5 n/a n/a n/a n/a average 60.8 140.0 172 13.4 6 table 2. two grallator trackway measurements (cm) on the main track layer of the john wesley powell fossil track block. fr = footprint rotation; n/a = no data; pa = pace angle; pl = pace length; sl = stride length; sym. = symmetry; tw = trackway width. 201 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 cm, respectively. the average divarication angles between the traces of digits ii–iv in t4 and t6 are 51° and 40°, respectively. like the holotype tracks of kayentapus hopii (ucmp 83668; figure 15c), the pftb tracks are strongly mesaxonic, with an estimated anterior triangle length compared to entire track length of 40% in the holotype, whereas for pftb tracks in trackway t4 is 40% and t6 is 38%. finally, the pace angulation of the holotype trackway is narrow at approximately 174 to 175° (welles, 1971), which is close to those of pftb trackways t4 and t6 that average 164° and 170°. the pftb cf. kayentapus tracks bear some morphological similarities to those in the holotype trackway of kayentapus from the kayenta formation near tuba city, navajo nation, arizona (welles, 1971; lockley and others, 2011); our tentativeness in firmly assigning the pftb tracks to kayentapus stems from the lower quality of preservation of tracks at the ptfb (i.e., lacking toe pads) and deformation/inflation (expansion) of the digit traces. additionally, the divarication angles between traces of digits ii–iv across the tracks in t6 are consistently lower by about 10° than those in the holotype trackway. the holotype tracks were identified as “slight” undertracks by lockley and others (2011, p. 333), as is our interpretation of the pftb tracks. several authors have suggested that kayentapus is a junior synonym of eubrontes and that its apparent morphological distinction is due to the poor preservation of the holotype tracks (rainforth, 2005; lucas and others, 2006). paul olsen (columbia university, personal communication, 2017) suggested that kayentapus tracks are partially penetrative eubrontes tracks, and that the partial penetration splayed the digits, resulting in wider divarication angles, and gave the digits a narrower appearance. this may be partially true, but the holotype tracks of kayentapus are shallow and not penetrative, and many examples of clear eubrontes exist that are also partial or fully penetrative in a variety of substrates. despite these concerns, many still consider kayentapus valid (lockley and hunt, 1995; gierliński, 1996; piubelli and others, 2005; weems, 2006 and many citations therein; lockley, 2009; xing and others, 2020; lockley and others, 2011; farlow and others, 2018). medium-sized theropod tracks on the mtl superficially resemble kayentapus, so we refer to them here as cf. kayentapus. however, aside from these tracks having larger sizes than the above-mentioned grallator and grallator-like tracks, the anterior track length/track length ratios and divarications angles between digits ii-iv do not differ significantly between all these footprint categories. therefore, the cf. kayentapus could be considered large cf. grallator tracks as well. a thorough b1 b2a c1 c2 d e1 e2 figure 10. natural cast grallator tracks on the john wesley powell fossil track block (pftb). (a) close-up photogrammetry of left natural cast track t5-10. (b1) photograph of t7-4 and (b2) photogrammetry of t7-4. (c1) photograph of t7-1 and (c2) photogrammetry of t7-1. (d) grallator natural cast track from oldest pftb track surface. (e1) photograph of isolated grallator track t12 and (e2) photogrammetry of t12. all scale bars = 10 cm. 202 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 differentiation between kayentapus and grallator (and anchisauripus) is beyond the scope of this report. no potential trackmakers of the size required to make the cf. kayentapus tracks are known currently from body fossils from the navajo sandstone; however, dilophosaurus was found near the kayentapus type locality, so juveniles or subadults of this larger taxon could have been the trackmaker (welles, 1954, 1970, 1984; marsh and rowe, 2020). eubrontes (a.k.a., “ornithopod-like tracks”) (figures 12 and 14; tables 6 and 7) by far the most prominent and eye-catching footprints on the pftb are the two parallel, “ornithopod-like” natural cast trackways arranged horizontally across the mtl (t1 and t2; figures 2, 12, and 13). a third trackway (t3) only preserves two footprints (figures 2b and 14a through 14g). these three trackways, produced by large bipedal dinosaurs, have average track lengths of 34.3, 34.5, and 35.8 cm, respectively. the average widths are 35.2, 32.1, and 37.5 cm (table 6), respectively. after close examination of these tracks, and through the use of photogrammetry, we agree with lockley and xing (2015) that these tracks pertain to eubrontes. although the overall track morphologies, which display “inflated” digit traces and exaggerated track widths, are “ornithopod-like,” we propose that these footprints may not be distorted solely by sediment load compaction and deformation following lithification. the deformation of muddy, and potentially spongy microbial mats and/or endoevaporitic substrates by the feet will often produce steep-walled mud rims around the footprints, as seen in trackways t1 and t2 (figures 12 and 13). additionally, the transfer of wet, sticky substrate from one track to the next into successive tracks may also be a contributing factor to the “bulkiness” of the digit impressions. also, overgrowth of microbial mats into and over tracks following their formation could have occurred, further distorting the footprints and distorting overall track morphology (marty and others, 2009). studies of modern bird tracks (emus and domestic chickens) through controlled experimentation also show incredible variations in track preservation from poor to exceptional based on sediment type and quantities (i.e., percentages of different sediment types such as clay and sand), as well as water content or lack thereof (milàn, 2006; falk and others, 2017; farlow and others, 2018). farlow and others (2018, p. 166) even suggest how a theropod foot table 3. ten grallator-like individual track measurements (cm) from uppermost track horizon on the john wesley powell fossil track block. atl = anterior triangle length; atw = anterior triangle width; avg. = average; digit ii, iii, and iv l = digit ii, iii, and iv lengths; ii–iv, ii–iii, and iii–iv = divarication angles between digits ii–iv, ii–iii, and iii–iv; n/a = no data; sym. = symmetry (i.e., left or right tracks); td = track depth; tl = track length; tw = track width. track # sym. tl tw atl atw digit ii l digit iii l digit iv l ii-ivº ii-iiiº iii-ivº l1 right 10.2 5.9 4.6 4.6 3.5 6.6 6.2 50.0 25.0 25.0 l2 n/a 16.5 (18) 11.3 n/a n/a n/a n/a n/a n/a n/a n/a l3 right 17.6 13.8 5.5 9.5 11.5 11.7 12.6 48.0 30.0 18.0 l4 left 23.7 15.8 9.8 11.0 10.0 18.3 16.6 59.0 42.0 18.0 l5 left? 11.3 8.5 5.0 5.9 n/a n/a n/a n/a n/a n/a l6 right? 19.7 17.6 6.8 13.4 n/a n/a n/a n/a n/a n/a l7 right? 17.7 10.5 8.8 8.6 n/a n/a n/a n/a n/a n/a l8 n/a 16.0 n/a n/a n/a n/a n/a n/a n/a n/a n/a l9 n/a 17.0 7.7 n/a n/a n/a n/a n/a n/a n/a n/a l10 n/a 17.5 n/a n/a n/a n/a n/a n/a n/a n/a n/a 203 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 interacting with the right substrate conditions could produce a footprint that is ornithopod-like, especially if the main sediment was a sand with lower water content resulting in sediment collapse into the track. so, rather than ornithopod-like dinosaurs being the track producers at the pftb, more likely the producers were medium-sized theropods similar in size to dilophosaurus, which is known from the underlying kayenta formation of north-central arizona and possibly utah (welles, 1954, 1970, 1984; madsen and others, 2012; marsh and rowe, 2020). in t1, the trackway width is approximately 42 cm wide from footprints t1-1 to t1-3, and about 43 cm wide from t1-5 to t1-7. however, at t1-4, the trackway width expands to 53 cm. also, at t1-4, the foot rotation increased, and the animal toed out with the left foot as the pace angulation decreases by a couple of degrees toward the right between footprints t1-4 and t1-5. we speculate that this slight alteration was due to slippage and/or a reaction to sediment consistency. deformation on the outside edge of t1-4 track wall is marked by an unidentified, subrectangular, poorly preserved track (cf. grallator; figure 12). trackway t1 preserves seven footprints with average pace and strides of 87.1 and 170.0 cm, respectively (table 7). the maximum trackway width is 47.6 cm, and the average pace angulation is approximately 167°. in trackway t2 (figures 2 and 13), track t2-5 displays an elongated and tapered digit iii trace, and traces of digits ii and iv are not as rounded and do not divaricate as widely like those in the preceding footprints in this trackway. tracks t2-1 to t2-4 look more like those in t1 (figures 2 and 13), whereas t2-4 preserves a sharp claw mark on the trace of digit iii that is only visible through the use of photogrammetry. an elongated digit iii trace and the presence of sharp claws would be extable 4. measurements (cm) of 15 kayentapus-like individual theropod tracks on the john wesley powell fossil track block. atl = anterior triangle length; atw = anterior triangle width; avg. = average; digit ii, iii, and iv l = digit ii, iii, and iv lengths; ii–iv, ii–iii, and iii–iv = divarication angles between digits ii–iv, ii–iii, and iii–iv; n/a = no data; sym. = symmetry (i.e., left or right tracks); tl = track length; tw = track width. track # sym. tl tw atl atw digit ii l digit iii l digit iv l ii-ivº ii-iiiº iii-ivº t 4-1 left n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a t 4-2 right 25.0 17.5 n/a n/a n/a n/a n/a 53 27 26 t 4-3 left 22.5 18.5 8.8 13.4 12.0 21.2 16.5 60 28 32 t 4-4 right 28.0 20.0 10.6 15.0 13.5 22.5 19.0 n/a n/a n/a t 4-5 left 26.0 17.5 11.3 15.6 12.5 24.5 16.5 45 22 23 t 4-6 right 22.5 19.0 8.7 15.9 14.5 17.5 14.2 44 24 20 avg. – 24.8 18.5 9.9 15.0 13.1 21.4 16.6 51 25 25 t 6-1 right 20.0 16.2 9.0 15.0 12.5 17.5 11.7 32 18 16 t 6-2 left 22.5 17.2 7.5 14.3 17.0 20.0 12.5 38 18 20 t 6-3 right 22.5 17.0 9.0 16.1 11.5 18.5 14.5 44 21 23 t 6-4 left 22.0 15.5 n/a n/a n/a n/a n/a 49 22 27 t 6-5 right 21.0 16.2 7.9 14.5 12.5 20.5 14.2 39 24 15 t 6-6 left 18.5 16 n/a n/a n/a n/a n/a n/a n/a n/a t 6-7 right 21.8 17.0 7.3 15.0 12.9 19.4 17.0 67 34 33 t 6-8 left 23.5 16.5 8.3 14.5 15.0 20.5 16.5 57 38 19 avg. – 21.9 16.7 8.2 14.9 13.6 19.4 14.4 47 25 22 t 8 right 22.5 18.0 8.0 15.2 13.8 18.7 15.8 40 21 19 204 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 pected of theropod tracks. trackway t2 consists of five tracks with average pace and strides of 88.4 and 173.3 cm (table 7). the maximum trackway width is 57.1 cm, and the average pace angulation is approximately 159°. the first footprint in t3 (t3-1) is a left track, although it is not well preserved (figure 14). t3-1 and t3-2 have track lengths of 35.5 and 33.0 cm, and widths of 26.5 and 27.0 cm, respectively (table 6). like those of t1 and t2, both tracks in t3 appear ornithopod-like, although t3-1 has a clear, sharp claw impression preserved on digit ii, and track t3-2 has a sharp claw mark on digit iii. both of these tracks are also narrower than all of the footprints of t1 and t2, with the exception of t2-5. like tracks t2-4 and t2-5, the presence of sharp claws in narrower tracks strongly suggests that they were made by theropod dinosaurs, and the unusual, inflated morphology is likely the result of sediment compaction (lockley and xing, 2015), weathering, and/or sediment consistency as mentioned above, and discussed in more detail below. the step between these two tracks is 100 cm (table 7). the common orientation and lack of overlap of the two longer trackways, t1 and t2, suggests possible gregarious behavior by the trackmakers (hamblin and others, 2006; lockley and others, 2006; getty and others, 2015). such social behavior is well-established for later ornithischian dinosaurs from both body fossil and track records, but not for early jurassic ornithischians based on tracks such as anomoepus (but see olsen and rainforth [2003] for a contrary perspective). gregarious behavior has been well documented in early jurassic theropods, however (ostrom, 1972; raath, 1977; colbert, 1989; currie, 1993; lockley and matsukawa, 1999; hamblin and others, 2006; lockley and others, 2006; milner and others, 2006; currie and eberth, 2010). in fact, theropod dinosaurs in general, throughout their existence from the late triassic to the late cretaceous, show strong evidence of at least occasional gregarious behaviors (hitchcock, 1836; hamblin and others, 2006; lockley and others, 2006), although some tracksites table 5. kayentapus-like trackway t4 and t6 measurements (cm) on the main track layer of the john wesley powell fossil track block. avg. = average; fr = footprint rotation; n/a = no data; pa = pace angle; pl = pace length; sl = stride length; sym. = symmetry; tw = trackway width. track # sym. pl sl paº tw fr t 4-1 left n/a n/a n/a n/a n/a t 4-2 right 96.0 183.0 160 n/a 11 t 4-3 left 93.0 172.0 165 23.8 11 t 4-4 right 81.0 160.0 162 28.4 n/a t 4-5 left 78.0 158.0 170 30.1 n/a t 4-6 right 81.5 n/a n/a n/a n/a avg. 85.9 173.3 164 27.4 11 t 6-1 right n/a n/a n/a n/a n/a t 6-2 left 78.0 149.0 172 20.8 0 t 6-3 right 70.8 139.0 161 26.2 12 t 6-4 left 68.8 136.0 172 20.7 0 t 6-5 right 67.7 126.0 172 n/a 0 t 6-6 left 57.8 137.0 175 n/a n/a t 6-7 right 83.3 125.0 n/a n/a 0 t 6-8 left 62.5 n/a n/a n/a n/a avg. 69.8 135.3 170 22.6 2 205 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 from the newark supergroup of eastern north america do not support this claim (getty and others, 2015). early jurassic ornithischian trackways, such as those of anomoepus and moyenisauropus, show the trace of pedal digit iii toeing inward; occasionally, these trackways also include manus impressions (lockley and gierliński, 2006; wilson and others, 2009; milner and others, 2012, figure 58). the tracks in t1 have digit iii traces either parallel with the trackway axis or toeing outward slightly, a characteristic more indicative of a saurischian than an ornithischian trackmaker (day and others, 2002; lockley, 2003), although examples do exist of theropods toeing inward (day and others, 2002). additional support for the interpretation of a eubrontes affinity for trackways t1, t2, and t3 is based upon mesaxony, which by two-dimensional ichnological definition (lockley, 2009; romano and others, 2018) measures the general proportionality of the greater distal projection of digit iii anterior to the distal tips of digits ii and iv (a.k.a., toe extension), as measured by the shape of the anterior triangle (olsen, 1980). mesaxony has been used by many authors in morphometric analysis of theropod tracks (e.g., weems, 1992; lockley and others, 2014, p. 174; farlow and others, 2018; abrahams and others, 2022). anterior triangles that are strongly mesaxonic, meaning that they have digit iii impressions that project well beyond the distal ends of the traces of digits ii and iv (lockley, 2009), show that the shape difference of the anterior triangle has a consistent relationship to overall track shape (length/width ratio), and is not simply the result of variation in digit divarication angles, which is often extramorphologically controlled by substrate consistencies (lockley and others, 2014). the natural cast holotype eubrontes giganteus (acm-ich-15/3; figure 15a) from the early jurassic portland formation of holyoke, massachusetts, has a a1 a2 b1 c1 d1 d2c2b2 figure 11. medium-sized theropod tracks (cf. kayentapus) from trackway six (t6) on the john wesley powell fossil track block (pftb) shown as photographs (above) and color contour photogrammetry images (below): (a1-2) t6-1, (b1-2) t6-2, (c1-2) t6-3, (d1-2) t6-7. scale = 10 cm for all pictures. contour color relief to left of box. 206 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 1-2 1-3 1-4 1-5 1-6 1-7 1-1 10 cm 10 cm 10 cm 10 cm 10 cm a b c figure 12. eubrontes natural cast trackway t1 on the john wesley powell fossil track block. (a) photograph of complete trackway. (b) photogrammetry of trackway shown in color relief with 1 mm contours. (c) close-ups of individual tracks. from left to right: photographs; drawings; and photogrammetric image with color relief and 1 mm contour lines. tracks t1-1 to t1-7 are incomplete. 207 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 2-1 2-2 2-3 2-4 2-5 a b figure 13. eubrontes natural cast trackway t2 on the john wesley powell fossil track block. (a) photogrammetry of trackway shown in color relief with 1 mm contours. (b) close-up photographs (left), interpretive sketches (center), and photogrammetric images (right) of individual tracks; drawings with 10 cm scale bars; and photogrammetric images with color relief and 1 mm contour lines. 208 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 total track length of 35.7 cm, digit tip width of 24.4 cm, digit ii–iv divarication of 45º, and the anterior triangle length (i.e., toe extension) is 11.1 cm (farlow and others, 2018, p. 559–560; jim farlow, purdue university, personal communication, 2023). specimen sgds 9 (figure 15b) from the early jurassic (hettangian) whitmore point member of the moenave formation of st. george, utah, has similar proportions to the eubrontes holotype with a total track length of 37.5 cm, total track width of 28.5 cm, anterior track length of 13.0 cm, and digit ii–iv divarication of 35º. as mentioned above, kayentapus hopii has an average track length of 33.5 cm, track width of 29 cm, anterior triangle length range of 12.0 to 13.5 cm, and digit ii–iv divarication of 52º. dilophosauripus williamsi type (ucmp 79690-4; figure 15d; welles, 1971), which has been synonymized with eubrontes, is a natural cast with a length of 32.5 cm and width of 28.0 cm, with sharp claw traces, and a digit table 6. measurements (cm) of 17 large, “ornithopod-like” theropod individual tracks (i.e., eubrontes) on the main track layer of the john wesley powell fossil track block (glca #10). atl = anterior triangle length; atw = anterior triangle width; avg. = average; digit ii, iii, and iv l = digit ii, iii, and iv lengths; ii–iv, ii–iii, and iii–iv = divarication angles between digits ii–iv, ii–iii, and iii–iv; n/a = no data; sym. = symmetry (i.e., left or right tracks); td = track depth; tl = track length; tw = track width. track # sym. tl tw atl atw digit ii l digit iii l digit iv l ii-ivº ii-iiiº iiiivº td t 1-1 right 25.7 (28) 36.5 17.5 28.5 n/a n/a n/a 58 31 27 3.5 t 1-2 left 35.5 35.9 13.5 27.2 20.5 32.0 23.0 48 23 25 3.0 t 1-3 right 36.2 37.2 11.8 30.1 25.7 33.0 26.3 59 27 32 2.5 t 1-4 left 36.8 34.5 11.1 26.8 26.5 31.5 22.5 45 18 27 3.5 t 1-5 right 34.5 36.5 11.7 29.1 20.0 31.3 24.5 50 21 29 3.0 t 1-6 left 36.0 35.0 12.5 29.9 20.5 33.0 27.0 49 23 26 3.5 t 1-7 right 29 (34) 30.5 5 (9) 26.9 20.0 28 (24) 23.5 54 22 32 4.0 avg. 35.8 35.2 12.1 28.4 22.2 28.2 24.5 52 24 28 3.3 t 2-1 left 34.5 32.6 19.7 25.9 24.0 32.0 25.0 48 24 24 1.0 t 2-2 right 33.5 31.7 12.7 24.8 17.5 32.5 19.7 50 24 26 n/a t 2-3 left 35.0 34.7 11.2 26.3 22.5 31.7 27.0 45 18 27 3.5 t 2-4 right 33.0 32.0 n/a n/a n/a n/a n/a 42 20 22 n/a t 2-5 left 37.0 29.5 18.8 26.8 19.0 32.0 24.5 44 22 22 3.0 avg. 34.6 32.1 15.0 26.0 20.8 31.9 25.8 46 22 24 2.5 t 3-1 left 35.5 26.5 11.3 24.6 20.5 29.0 27.0 56 33 23 3.5 t 3-2 right 33.0 27.0 11.0 24.4 18.0 27.0 24.5 47 25 22 2.5 avg. 34.3 26.8 11.2 24.5 19.3 28.0 25.8 52 29 23 3.0 t 33-1 left 45.0 34.5 14.5 26.6 26.1 40.4 35.0 53 30 24 n/a t 33-2 right 48.0 40.4 n/a n/a n/a n/a n/a n/a n/a n/a n/a avg. 46.5 37.5 14.5 26.6 26.1 40.4 35.0 53 30 24 n/a t 11 left? 29.5 29.5 n/a n/a n/a n/a n/a 50 22 28 n/a 209 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 ii–iv divarication of 54º (welles, 1971). james farlow (purdue university, personal communication, 2023) measured this same type footprint with somewhat similar results – length as 34.5 cm, track width of 28.2 cm, anterior track length of 9.6 cm, and digit ii-iv divarication of 60º. the overall shape of dilophosauripus is very similar to the ornithopod-like eubrontes tracks on the pftb (figures 13e through 13g). additionally, weems (2003, 2019) suggested eubrontes tracks were produced by a basal sauropodomorph (a.k.a., “prosauropod”) as well as attributing otozoum (figure 15l) to a sauropodomorph: we agree with the latter, but not the former interpretation. these two ichnotaxa are clearly morphologically distinct from one another, even in overall shape (figure 15). the lengths of the traces of digits i to iv and arrangements of eubrontes tracks do not match those of otozoum, or any other ostensible sauropodomorph footprints (e.g., navahopus from the navajo sandstone; baird, 1980; milàn and others, 2008; farlow and others, 2022; lockley and others, 2023). therefore, sauropodomorphs from the navajo sandstone can be ruled out as producers of the ornithopod-like tracks from the pftb. comparisons with the pftb ornithopod-like tracks and known ornithischian footprints from the early jurassic must be considered. both moyenisauropus (figure 15j) and anomoepus (figure 15k) are known from the navajo sandstone, but once again, overall track morphology does not compare well with the pftb eubrontes footprints. finally, comparisons with the younger ichnogenus caririchnium (figure 15l), for example, c. lotus from the lower cretaceous jiaguan formation (barremian–albian) of china (xing and others, 2015), has similar rounded digits, but does not display sharp claws like those seen on the pftb. additionally, the worldwide geologic range of large “ornithopod” tracks table 7. three eubrontes trackway measurements (cm) on the main track layer of the john wesley powell fossil track block. fr = footprint rotation; n/a = no data; pa = pace angle; pl = pace length; sl = stride length; sym. = symmetry; tw = trackway width. track # sym. pl sl paº tw fr t 1-1 right n/a n/a n/a n/a n/a t 1-2 left 84.5 174.0 172 42.0 3 t 1-3 right 90.5 173.0 166 50.0 2 t 1-4 left 84.0 167.0 161 53.0 3 t 1-5 right 86.5 167.0 167 50.0 4 t 1-6 left 83.5 175.0 171 43.0 3 t 1-7 right 93.5 n/a n/a n/a n/a average 87.1 171.0 167 47.6 3 t 2-1 left n/a n/a n/a n/a n/a t 2-2 right 87.0 171.0 162 48.7 4 t 2-3 left 83.0 174.0 153 62.2 15 t 2-4 right 94.5 175.0 161 60.4 3 t 2-5 left 89.0 n/a n/a n/a n/a average 88.4 173.3 159 57.1 7 t 3-1 left n/a n/a n/a n/a n/a t 3-2 right 100.0 n/a n/a n/a n/a average 100.0 n/a n/a n/a n/a 210 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 a b c d e f g h i figure 14. other large theropod natural cast tracks on the john wesley powell fossil track block. (a) photogrammetry of eubrontes trackway 3. (b) close-up photograph of t3-2. (c) sketch of t3-2. (d) photogrammetric image of t3-2. (e) closeup photograph of t3-1. (f) sketch of t3-1. (g) photogrammetric image of t3-1. (h) photograph of large cf. eubrontes track t33-1. (i) photogrammetry of t33-1. color relief and 1 mm contour lines in a, d, g, and i. scale bars in b, e, and h equal 10 cm. 211 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 a b c d e f g h i lj k figure 15 caption is on the next page. 212 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 is much younger than those preserved in the navajo sandstone. no potential trackmakers of the size required to make the eubrontes tracks are known currently from body fossils in the navajo sandstone. the trackmaker was presumably a medium-sized neotheropod similar to dilophosaurus. we speculate that most, if not all the tracks preserved on the pftb could be transmitted tracks (leonardi, 1987; gatesy, 2003), and the transfer of substrate from one footprint to the next may have resulted in a lower quality of track preservation. also, the collapse of sediment back into footprints as suggested by martin (2014, p. 71), or the regrowth of microbial mats within and over tracks could also result in the loss of footprint details (marty and others, 2009; dai and others, 2015). growth of microbial mats over footprints is a good possibility based on our examination of the photogrammetry of t2-4 (figure 13) that shows the same pustulate, pitted texture often produced by microbial mats (simpson and others, 2022). microbial mats aid in the preservation of tracks (thulborn, 1990; cohen and others, 1991; kvale and others, 2001; marty, 2008; marty and others, 2009; wilson and others, 2009; de souza carvalho and others, 2013; dai and others, 2015; simpson and others, 2022). the elasticity of cyanobacterial laminites (avanzini, 1998) and the compaction of tracks following burial due to loading (lockley and xing, 2015) are likely both responsible for the deformation of tracks on all three track horizons recorded at pftb. suitable wet environments for the formation of microbial mats that assist in track-making conditions have been documented previously in the navajo sandstone (gilland, 1979; peterson and pipiringos, 1979; middleton and blakey, 1983; herries, 1992; sansom, 1992; de souza carvalho and others, 2013; simpson and others, 2022). finally, three very large, but poorly preserved, tracks (figures 14h and 14i) probably also made by large theropods occur on the pftb. the best of these tracks is t33-1, a left footprint measuring approximately 45 cm long and 34.5 cm wide (table 6). surprisingly, this track is very shallow considering the size and weight of the theropod that must have produced it. it is possible that this track was produced at a later point in time after wet sediment had dried, making the track-maker less able to register a deeper track. quadruped tracks cf. brasilichnium (figures 16a through 16d; supplementary file: https://irma.nps.gov/ datastore/reference/profile/2299562) five or six small tracks (figures 2b and 16a through 16d) are preserved on the pftb mtl surface. although very difficult to see in natural lighting, photogrammetry has greatly assisted in interpretation of these footprints (figure 16a). the better-preserved example of these tracks, a left footprint (qt1), measures 3.5 cm long by 3 cm in width. it displays four digits, with digit iv being figure 15 is on the previous page. comparison of ornithopod-like eubrontes tracks with other known early jurassic dinosaur tracks, including eubrontes, kayentapus, dilophosauripus, otozoum, moyenisauropus, and anomoepus, and early cretaceous caririchnium. (a) acm-ich-15/3, holotype eubrontes giganteus from the portland formation of holyoke, massachusetts (photograph courtesy of james o. farlow). (b) sgds 9, eubrontes from the “main track layer,” lower whitmore point member, moenave formation, st. george dinosaur discovery site, southwest utah. (c) plaster replica of a right track from kayentapus hopii holotype trackway (ucmp 83668), lower kayenta formation, tuba city area, arizona. (d) plaster replica of holotype dilophosauripus williamsi left track from the kayenta formation near tuba city, arizona (ucmp 79690-4). (e) photogrammetry of eubrontes t1-6 from pftb. (f) eubrontes t2-3 from pftb. (g) photogrammetry of eubrontes t3-2 from pftb. (h) photogrammetry of eubrontes t3-1 from pftb. (i) otozoum moodii sauropodomorph track from navajo sandstone, glca loc. 359, utah (photograph courtesy of jim l. williams). (j) sgds 1321, replica of moyenisauropus natator ornithischian tracks from the lower jurassic zagaje formation, poland. (k) sgds 1296, replica of anomoepus isp. ornithischian track from kayenta-navajo transition, red hills desert garden, st. george, utah. (l) caririchnium from qijiang tracksite, jiaguan formation, china (photograph courtesy of jerry d. harris). scale equals 10 cm in all figures except k which equals 5 cm. https://irma.nps.gov/datastore/reference/profile/2299562 https://irma.nps.gov/datastore/reference/profile/2299562 213 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 slightly longer than digit iii, and digits ii and v of similar length (figures 16a and 16b). these small tracks, possibly of the ichnotaxon brasilichnium, were likely produced by quadrupedal tritylodont synapsids whose footprints are commonly preserved on eolian dune surfaces in the navajo sandstone, including within glca (lockley and others, 1996, 2014; lockley, 2011a, 2011b) and at localities near the pftb. winkler and others (1991) recorded a partial tritylodont skeleton from the navajo sandstone in northern arizona, but the vast majority of early jurassic tritylodont body fossils within the glen canyon group come from the underlying kayenta formation (kermack, 1982; lewis, 1986; sues, 1986a, 1986b; sues and others, 1994; irmis, 2005; sues and jenkins, 2006), from which there is a much greater yield of body fossils associated with the silty facies. however, in march 2023, one of us (arcm) discovered a tritylodont bone bed with interdunal facies of the kayenta–navajo transition in relatively close proximity and stratigraphic distance to the pftb. nearby, and stratigraphically lateral to this bone bed, within interbedded, thin carbonate sandstones, siltstones, and mudstones, abundant tracks were found including cf. brasilichnium, eubrontes, and grallator. these cf. brasilichnium tracks provide stronger support for tritylodonts being the presumptive trackmakers. batrachopus (figures 16e through 16g) an associated float slab (locality glca #209) from an uncertain stratigraphic horizon, located immediately south of the pftb, has 11 poorly preserved natural cast tracks, including two trackways (figures 16e and 16f) that we refer to the crocodylomorph ichnotaxon batrachopus. two of these tracks are well preserved and show overlapping pes tracks (figure 16g). this is the only record of batrachopus from the beds at the pftb locality. possible producers of batrachopus are basal protosuchian crocodyliforms resembling protosuchus (colbert and mook, 1951). fragmentary protosuchian skeletons were recovered from the navajo sandstone to the southwest of the pftb locality in northern arizona (rinehart and others, 2001), documenting the existence of such a potential trackmaker. very few batrachopus are known from eolian environments, although they are not that uncommon in wet, interdunal environments as reported for the lake powell area by lockley and others (2014) based on ucm collections especially from the kayenta-navajo transition. an example of batrachopus tracks in an eolian environment occurs at the north moccasin mountain tracksite in the navajo sandstone close to coral pink sand dunes state park near the town of kanab, kane county, utah (milner and others, 2012). qt1qt2qt3 qt4 qt5 a b c d e f g bt1 bt2 bt3 bt4 figure 16. quadruped natural cast footprints from localities glca #10 and glca #209. (a–d) unidentified quadruped footprints (cf. brasilichnium) from the john wesley powell fossil track block (glca #10). photogrammetry (a), photograph (b), interpretive sketch (c), and close-up of track qt1 (d). (e-g) well-preserved batrachopus natural cast trackway (glca #209). photograph of trackway (e) and interpretive sketch (f), and close-up of two overlapping pes tracks bt1 and bt2 (g). d, g scale bar =1 cm; c, e scale bar = 10 cm. 214 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 paleontological resource management, protection, and potential site development for public interpretation the size and weight of the pftb, as well as its remote location, make field collection or removal of this massive block for preservation, conservation, or protection impossible. in situ management and study of the block would benefit from long-term monitoring of the stability and condition of its ichnological resources. both natural processes and, potentially, human activities may contribute to the loss or deterioration of the track block over time. through the development of a cyclic monitoring strategy, any changes or impacts to the track block can be documented and help to inform park management regarding future preservation and protection of the pftb. the first assessment and documentation of the pftb by the national park service and the utah geological survey occurred in 2009 during an initial attempt to develop a strategy for monitoring in situ paleontological resources at glca (kirkland and others, 2010, 2011). this project represented a prototype effort for the national park service to implement recommendations and guidance developed for monitoring in situ paleontological resources (santucci and koch 2003; santucci and others, 2009). to monitor any changes in the track-bearing layers of the pftb, two crack sensors were placed on the south of the pftb face in 2009. since their placement, no movement was detected when checked in 2017. as evidenced by the hollow sound of the rock surface and wider cracks on the south side of the block, this part of the pftb will eventually fall off within years. a visit to the site in march 2023 revealed that both crack monitors were broken, and this crack may have widened slightly, or weathering caused the monitors to break. because of its uniqueness, replication of the large ornithopod-like theropod trackway is recommended. replication can be accomplished through the use of photogrammetry data and rapid prototyping technologies. with this recently detected deterioration, we also highly recommend some sort of artificial stabilization to ensure longevity of this unique track site. additionally, the collection of isolated track slabs at the base of the pftb from the older track surface could be useful for further study, exhibits, and preservation of specimens in a proper museum as a partial record of the locality. given public knowledge of the pftb, the park may want to consider the installation of a remote camera to monitor visitor activity at the fossil locality. theft, vandalism, and other paleontological resource crimes have been documented at fossil localities within glca, and the scientific and educational values of the pftb warrant some ability to monitor this important fossil vertebrate tracksite. public interpretation of the pftb has been discussed by nps staff. careful planning for any interpretation, such as installation of an interpretive wayside exhibit, should consider resource protection of the fossil locality. any interpretation of a paleontological locality should incorporate a resource protection message about non-renewable resources and that the collection or disturbance of fossils, including replication, is prohibited unless undertaken through a scientific research and collecting permit. conclusions the john wesley powell fossil track block preserves approximately 104 tracks on three different track horizons, all preserved on stromatolitic surfaces. this ichnoassemblage includes abundant grallator, possible kayentapus, large ornithopod-like tracks attributed to eubrontes, three large cf. eubrontes, possible brasilichnium, and rare batrachopus. the most noticeable footprints are those of two large, parallel trackways that superficially resemble ornithopod footprints. closer examination of these two trackways, and a third consisting of only two footprints, show that they were produced by medium-sized theropod dinosaurs, rather than ornithischians. the presence of sharp claw marks, and narrower digits on some of the tracks made more visible through the use of photogrammetry, clearly show these footprints pertain to eubrontes (figure 17). 215 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 additionally, abundant, small coelophysoid theropod tracks we identify as grallator and grallator-like are the most common forms on all track-bearing horizons. medium-sized theropod tracks that superficially resemble kayentapus by having wider divarication angles than typical other theropod tracks recorded at the site are the least common ichnomorphotype. at least five small, closely associated tetradactyl footprints that we identify as brasilichnium-like occur on the mtl of the pftb. on a nearby fallen block, also made up of microbial laminites, distinct trackways of batrachopus occur. batrachopus tracks are rare in eolian environments. the presence of microbial (possibly endoevaporitic) mats and stromatolitic horizons the animals had walked upon produced a distinct ichnomorphologic variation likely due to substrate consistency and the elastic properties of the mats, resulting in differential compaction of the beds. the possible transfer of sediment from one footprint to the next, and overgrowth of the tracks by microbial mats could also have been a contributing factor to the poor preservation of track details and distortion of overall track shapes. microbial mats formed on interdunal surface where water pooled to produce lakes and ponds, likely during periods of increased precipitation and/or rising water tables during wet seasons. figure 17. two hypothetical, eubrontes-producing theropods walking across a sandy, water-saturated, microbial-mat-rich interdunal playa during an early phase of the navajo erg in the early jurassic. this restoration was created based on the spectacular undertracks preserved on the john wesley powell track block. the ornithopod-like undertracks now visible on the track block were registered in horizons situated below stromatolitic or endoevaporitic layers (represented in green). these undertracks display different morphologies than the true tracks, which would have resembled eubrontes. artwork by brian engh (dontmesswithdinosaurs.com). 216 the john wesley powell fossil track block—theropod tracks with ornithopod-like morphology from the early jurassic navajo sandstone, glen canyon national recreation area, utah-arizona milner, a.r.c., santucci, v.l., wood, j.r., birthisel, t.a. clites, e., and lockley, m.g. geology of the intermountain west 2023 volume 10 acknowledgments the pftb is within the ancestral homelands of the nuwuvi (southern paiute) and dine' (navajo) peoples. we would like to thank the nps and sgds dinosaurah!torium foundation for funding fieldwork and research efforts. thank you to nps/glca staff, including john spence, taryn preston, matthew miller, mark anderson, ann miller, maria rodriguez, and many others for transporting us to the site, assisting with logistics and excavation, and for their great hospitality. special thanks to sarah doyle (glca paleontology intern) who assisted us in the field with stratigraphy, collection of locality data, photogrammetry, and her boating skills. thank you to james i. kirkland (utah geological survey) for lengthy discussions about this locality and jerry d. harris (utah tech university) for reviewing an earlier version of this manuscript. thank you to jim farlow (purdue university fort wayne), tom chidsey (utah geological survey), and justin tweet (national park service) for their helpful reviews that greatly improved this manuscript. a special thanks to brian engh (dontmesswithdinosaurs.com) for providing his beautiful artwork. thank you to conner bennett (former sgds intern) for photographing and creating the photogrammetry of the small cf. brasilichnium tracks on pftb. thanks to don deblieux and scott madsen from the utah geological survey for their early assessment of the pftb. thank you to neffra matthews (blm, denver) and mike santella (former sgds volunteer) for helping with preliminary photogrammetry. we thank matt stimson (new brunswick museum, saint john, new brunswick, canada) for assistance with invertebrate trace identifications. thanks to dan w. whalen (sgds volunteer) for documenting all our 2010 fieldwork through photography and videography, and to sgds volunteer david l. slauf for assistance in the field. thank you to jaleesa buchwitz (sgds deputy curator) for her assistance with the graphics in figure 5. appreciation to jim farlow (purdue university fort wayne) for providing the photo in figure 15a, jim williams (sgds volunteer) for providing the photograph for figure 15i, and jerry d. harris for figure 15l. finally, thank you to editor, doug sprinkel (utah geological survey), for his patience and help in editing this paper. references abrahams, m., bordy, e.m., knoll, f., and farlow, j.o., 2022, theropod tridactyl tracks across the triassic–jurassic boundary in southern africa—implications for pedal morphology evolution: frontiers in ecology and evolution, v. 10, p. 1–18. avanzini, m., 1998, anatomy of a footprint—bioturbation as a 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c., rainforth, e.c., and schultz, r.j., 1998, a survey of fossil footprint sites at glen canyon national recreation area (western usa)—a case study in documentation of trace fossil resources at a national preserve: ichnos, v. 5, p. 177–211. lockley, m.g., kukihara, r., pionek, l., and delgalvis, a., 2014, a survey of new fossil footprint sites from glen canyon national recreation area (western usa), with special reference to the kayenta–navajo transition zone (glen canyon group, lower jurassic): new mexico museum of natural history and science bulletin, v. 62, p. 157–179. lockley, m.g., lallensack, j.n., sciscio, l., and bordy, e.m., 2023, the early mesozoic saurischian trackways evazoum and otozoum—implications for ‘prosauropod’ (basal sauropodomorph) gaits: historical biology, doi: 10.1080/08912963.2022.2163170. lockley, m.g., and matsukawa, m., 1999, some observations on trackway evidence for gregarious behavior among small bipedal dinosaurs: palaeogeography, palaeoclimatology, 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congleton, j.d., and downs, w.r., 1991, life in a sand sea—biota from jurassic interdunes: geology, v. 19, p. 889–892. wood, j.r., bozek, m.a., milner, a.r.c., mims, a.l., frost, f., and santucci, v.l., 2021, structure from motion photogrammetry enhances paleontological resources documentation, research, preservation and education efforts for national park service areas: new mexico museum of natural history and science bulletin, v. 82, p. 513–523. xing, l., dai, h., wei, g., lockley, m.g., klein, h., persons, w.s., wang, m., jing, s., and hu, h., 2020, the early jurassic kayentapus dominated tracks from chongqing, china: historical biology, v. 33, no. 10, p. 2067–2073. xing, l., lockley, m.g., mart, d., zhang, j., wang, y., klein, h., mccrea, r.t., buckley, l.g., belvedere, m., mateus, o., gierliński, g.d., piñuela, l., persons, w.s., iv, wang, f., ran, h., dai, h., and xie, x., 2015, an ornithopod-dominated tracksite from the lower cretaceous jiaguan formation (barremian–albian) of qijiang, south-central china—new discoveries, ichnotaxonomy, preservation and palaeoecology: plos one, v. 10, no. 10, e0141059. the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 © 2016 utah geological association. all rights reserved. for permission to copy and distribute, see the following page or visit the uga website at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata james i. kirkland, marina suarez, celina suarez, and rebecca hunt-foster a field guide prepared for society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa pre-meeting field trip october 23–25, 2016 geology of the intermountain west an open-access journal of the utah geological association production cover design and desktop publishing douglas a. sprinkel cover cedar mountain formation at the stikes quarry on utahraptor ridge. the stike quarry (just below sandstone cliff) is in the upper yellow cat member. the underlying morrison formation is the reddish slope at the bottom of photograph and the naturita formation caps the ridge. i 2016 president bill loughlin bill@loughlinwater.com 435.649.4005 2016 president-elect paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2016 program chair andrew rupke andrewrupke@utah.gov 801.537.3366 2016 treasurer robert ressetar rrgeology@gmail.com 801.949.3312 2016 secretary tom nicolaysen tnicolaysen@utah.gov 801.538.5360 2016 past-president jason blake blake-j@comcast.net 435.658.3423 uga board uga committees education/scholarship loren morton lmorton@utah.gov 801.536.4262 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign terry massoth twmassoth@hotmail.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications roger bon rogerbon@xmission.com 801.942.0533 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2016-2018 term craig morgan craigmorgan@utah.gov 801.422.3761 state mapping advisory committe uga representative jason blake blake-j@comcast.net 435.658.3423 uga newsletter newsletter editor bob biek bobbiek@utah.gov 801.537.3356 uga website www.utahgeology.org webmasters paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 lance weaver lanceweaver@utah.gov 801.403.1636 become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 3 2016 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. earthquake safety committe chair grant willis gwillis@utah.gov 801.537.3355 douglas a. sprinkel utah geological survey 801.391.1977 giw@utahgeology.org bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net society of vertebrate paleontology editors james i. kirkland (editor-in-chief) — utah geological survey rebecca hunt-foster — bureau of land management greg mcdonald — bureau of land management martha hayden — utah geological survey editors geology of the intermountain west an open-access journal of the utah geological association volume 3 2016 101 abstract although only recognized as a discrete stratigraphic unit since 1944, the cedar mountain formation represents tens of millions of years of geological and biological history on the central colorado plateau. this field guide represents an attempt to pull together the results of recent research on the lithostratigraphy, chronostratigraphy, sequence stratigraphy, chemostratigraphy, and biostratigraphy of these medial mesozoic strata that document the dynamic and complex geological history of this region. additionally, these data provide a framework by which to examine the history of terrestrial faunas during the final breakup of pangaea. in fact, the medial mesozoic faunal record of eastern utah should be considered a keystone in understanding the history of life across the northern hemisphere. following a period of erosion and sediment bypass spanning the jurassic–cretaceous boundary, sedimentation across the quiescent colorado plateau began during the early cretaceous. thickening of these basal cretaceous strata across the northern paradox basin indicate that salt tectonics may have been the predominant control on deposition in this region leading to the local preservation of fossiliferous strata, while sediment bypass continued elsewhere. thickening of overlying aptian strata west across the san rafael swell provides direct evidence of the earliest development of a foreland basin with sevier thrusting that postdates geochemical evidence for the initial development of a rain shadow. the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata james i. kirkland1, marina suarez2, celina suarez3, and rebecca hunt-foster4 1utah geological survey, p.o. box 146100, salt lake city, utah, 84114; jameskirkland@utah.gov 2department of geological sciences, the university of texas at san antonio, one utsa circle, san antonio, texas, 78249; marina.suarez@utsa.edu 3department of geosciences, university of arkansas, 226 gearhart hall, fayetteville, arkansas, 72701; casuarez@uark.edu 4canyon country district, bureau of land management, 82 east dogwood, moab, utah, 84532; rhuntfoster@blm.gov citation for this article. kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r., 2016, the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata: geology of the intermountain west, v. 3, p. 101–228. © 2016 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. introduction this field trip begins in salt lake city and proceeds southeast across utah. during the morning of day 1 south of interstate 70 (i-70) along yellow cat ranch road on lands managed by the bureau of land management (blm), northeast of arches national park. these stops focus on the eastern exposures of the cedar mountain formation including the definition of its members, their contacts, and how they document active salt tectonics in the northern paradox basin during the early cretaceous (figure 1). the afternoon of day 1 will be spent examining the exposures of the cedar mountain formation on lands managed by the state of utah www.utahgeology.org 102 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 1. map of utah with location of field trip stops and outcrops of cedar mountain formation. 103 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 west of arches national park where outcrops show contrasting the effects of salt tectonics on either side of the salt valley anticline during the early cretaceous. additionally, we will examine the blm’s mill canyon tracksite that has been newly developed as an interpretive site. the first and second nights will be spent in green river, utah. the morning of day 2 will be spent examining the cedar mountain south of green river. the afternoon will be spent examining outcrops of the cedar mountain formation between hanksville and capitol reef national park where outcrops display lateral changes in the upper and lower contacts of the cedar mountain relative to the interface between the paradox basin and the forebulge as expressed by the san rafael swell. before returning to salt lake city on day 3, we will proceed west on i-70 to the western side of the san rafael swell to examine the effects and relative timing of early cretaceous deposition in the sevier foredeep. conventions: locations of stratigraphic sections and other important sites are given in latitude and longitude in degrees, minutes, and seconds derived from google earth™. locations of fossil sites from lands managed by the blm are not given, per the 2009 paleontological resource protection act, but are referred to by their repository location numbers, where the fossils are or will be curated. these data are available to permitted researchers. important cedar mountain repositories referred to herein are as follows where # indicates specimen number: • brigham young university, paleontological museum, provo, utah; byu # • denver museum of nature and science; dmnh# • dinosaur national monument; dnm# • oklahoma museum of natural history, norman, oklahoma; omnh# • utah natural history museum, salt lake city, utah; umnh# • utah state university eastern, prehistoric museum, price, utah: uses locality numbers from utah paleontological locality database (upld); utah (county abbreviation)# • utah geological survey (ugs): uses numbers from upld unless already curated into a recognized utah repository; utah (county abbreviation) # localities plotted on stratigraphic sections are correlated into the line of section and are located in the same region. all research discussed herein is based on work done under blm or utah state permits. other research groups referred to herein with collections from these strata include: burpee museum, rockford, illinois; the field museum, chicago, illinois; and the north carolina museum of natural history, raleigh, north carolina. in discussing driving distances, we only refer to miles in keeping with the distances logged onto odometers in the united states. overview: cedar mountain formation in east-central utah utah is justifiably famous for its dinosaurs and preserves what may be the most complete and well-dated figure 2. kuang hang-wei of the chinese geological survey admires the type area for the cedar mountain formation at buckhorn reservoir (39°14'32.15"n, 39°14'32.15"n). 104 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 terrestrial mesozoic record in the world (kirkland and farlow, 2012). with historically renowned sites such as the carnegie quarry at dinosaur national monument and the cleveland-lloyd quarry, utah’s upper jurassic morrison formation is particularly well known for its dinosaurs. however, lower cretaceous strata that overlie the morrison formation preserve an even greater number of dinosaur species spanning a much longer time interval. only over the past two decades have new discoveries revealed the importance of dinosaurs preserved in utah’s lower cretaceous cedar mountain formation. university of utah’s william lee stokes can be credited for setting the stage for future research on the lower cretaceous of utah. in 1948, stokes and phoenix (1948) described the burro canyon formation as a mappable lower cretaceous unit of pebbly channel sandstones and green floodplain mudstones near slick rock in west-central colorado. the following year, stokes (1944, 1952) applied the name cedar mountain shale to the drab, slope-forming rocks lying between the buckhorn conglomerate and naturita formation (= dakota formation), based on a type section defined on the southwest flank of cedar mountain at the north end of the san rafael swell by buckhorn reservoir (figure 2) in emery county, utah. stokes (1952) renamed the shale the cedar mountain formation and included the buckhorn conglomerate member as its basal member. where the cliff-forming buckhorn was not present, the rules of thumb for distinguishing the cedar mountain formation from the underlying morrison formation included: (1) a more drably variegated color, (2) more abundant carbonate nodules commonly with a thick carbonate paleosol (ancient soil) at the base, (3) the presence of common, polished chert pebbles identified as gastroliths (stokes, 1944, 1952), and (4) the absence of dinosaur bones (kirkland, 2005a). the cedar mountain and contiguous burro canyon formations were distinguished based on thickness, pebble size, and paleocurrent directions (craig, 1981). according to stokes (1952) and craig (1981), both units were deposited atop the upper jurassic morrison formation and formed a broad alluvial plain—rivers flowing from highlands to the south deposited the sediments of the burro canyon formation, and those flowing from the west deposited the material of the cedar mountain formation (lawton and others, 1997, 2007). the southwest-flowing (modern) colorado river (figure 1) has served as the arbitrary boundary between the cedar mountain (northwest) and burro canyon (southeast) formations (stokes, 1952; craig, 1981; tschudy and others, 1984; milán and others, 2015). in the southwestern portion of utah beyond the contiguous outcrop belt of the cedar mountain formation, the dating of outcrops of pale-green, fine-grained strata below the naturita formation (= dakota formation) as early cretaceous, has led to the recognition of the cedar mountain on a number of geological maps in this region (biek and others, 2009, 2010, 2015; hylland, 2010). these sites are considered local in extent and radiometric dates indicate that only the late albian portion of the cedar mountain formation is representfigure 2. kuang hang-wei of the chinese geological survey admires the type area for the cedar mountain formation at buckhorn reservoir (39°14'32.15"n, 39°14'32.15"n). 105 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 ed (figure 2). along the sevier thrust belt in northern utah, the cedar mountain formation is replaced by the much thicker kelvin formation (mathews, 1931; granger, 1963; decelles and currie, 1996). few fossils have been reported from this thick sequence of strata, but it includes microvertebrate remains and dinosaur eggshells (jensen, 1970; prothero, 1983; zelenitsky and others, 2000). the reported absence of dinosaur bones in the cedar mountain formation limited the interest of paleontologists in these rocks for many years. because geologists lacked any accepted means of subdividing these rocks, they were long considered a rather monotonous sequence of lower cretaceous strata that generally thicken to the west. young’s (1960) report, “dakota group of colorado plateau,” although strongly rebutted (craig and others, 1961) and largely ignored at the time, has been reinstated as a major contribution to our understanding of these rocks (kirkland and madsen, 2007; sprinkel and others, 2012; carpenter, 2014). young’s proposal that the correlative burro canyon formation be included as simply an extension of the cedar mountain formation has not been followed, but these correlations have held up well with the recognition of marker sandstones, basically preceding the application of sequence stratigraphic principles (kirkland and madsen, 2007; sprinkel and others, 2012). currie (1998, 2002), currie and others (2008, 2012), and mcpherson and others (2006), working mainly along the east-west trend of the uinta mountains, developed a model for the deposition of the cedar mountain formation within a foreland basin system, but the complexities of preexisting structures and salt tectonics hamper the use of a simplistic foreland basin model. the recognition of significant vertebrate fossils has provided age control on these rocks, supporting young’s (1960) principal conclusions regarding the cedar mountain formation (kirkland and others, 1997, 1999; kirkland and madsen, 2007; sprinkel and others, 2012). young identified regionally extensive sandstone marker beds on which the correlations are based by applying sequence stratigraphic principles to these rocks before the methodology had actually been developed (figure 3). given young's limited biostratigraphic and chronostratigraphic tools, the overall accuracy of the correlations is remarkable. the principle disputes between young (1960) and craig and others (1961), largely came down to a difference in their conceptual paradigms being applied to the nomenclature. up to this time, the upper cretaceous strata overlying the cedar mountain formation had often been referred to as “?dakota” or “so-called” dakota on the colorado plateau. young (1960, 1965) proposed to reassign these overlying strata to the naturita formation but that was met with resistance (craig and others, 1961). as these strata are upper cretaceous and not lower cretaceous, and are not contiguous with the dakota sandstone in its type area of eastern nebraska, they are now being more properly referred to the naturita formation (carpenter and others, 2008; carpenter, 2014; milán and others, 2015; cifelli and others, 2016), as they are herein. new dinosaur species reported in the mid-1990s led to a rush of researchers from many institutions prospecting for dinosaurs in the cedar mountain formation. brigham young university, utah state university eastern (formally college of eastern utah) prehistoric museum, denver museum of nature and science, dinosaur national monument, oklahoma museum of natural history, north carolina museum of natural history, the field museum (chicago), and the utah geological survey are just some of the many research groups presently looking for fossils in these rocks. a wealth of new fossil sites (figure 4), along with radiometric ages, have established that this relatively thin layer (normally less than 100 m) of lower cretaceous cedar mountain formation, which separates thousands of meters of jurassic rocks from thousands of meters of upper cretaceous rocks, is more complex than previously thought. additionally, it preserves nearly 30 million years of what may be the most intriguing episode of dinosaur history, apart from their origin and extinction. these studies have in turn spawned additional directions of research in taphonomy, sedimentology, tectonics, geochemistry, radiometric dating, and paleomagnetics. in addition to dinosaur bones, fossil dinosaur eggshells (jensen, 1970; bray, 1998; zelenitsky and others, 2000) and tracks (decourten, 1991; lockley and others, 1999, 2004, 2014a, 2014b, 2015; wright and others, 2006) have been identified at several stratigraphic levels 106 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 fi gu re 3 . c ro ss s ec tio n of th e c ed ar m ou nt ai n an d n at ur ita f or m at io n fr om c as tle d al e, u ta h (s ou th o f c ed ar m ou nt ai n fo rm at io n ty pe a re a) to c ol on a, c ol or ad o. s ee y ou ng (1 96 0, fi gu re 6 ) f or lo ca lit y da ta . f ro m y ou ng (1 96 0) . 107 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 throughout the cedar mountain formation. while not directly expanding the known diversity of dinosaurs from these rocks, these discoveries are adding considerable ecological and behavioral information concerning cedar mountain dinosaurs. kirkland and others (1997, 1999) used the distribution of specific dinosaur faunas (groups of dinosaurs living together) and their relationship to distinct rock types to define four additional members of the cedar mountain formation. in ascending order, these are the yellow cat member, poison strip sandstone, ruby ranch member, and mussentuchit member. together with the buckhorn conglomerate member, these rock units and the fossils they contain are shedding light on the previously obscure early cretaceous history of utah (figures 4 and 5). please note that the poison strip sandstone of kirkland and others (1997) is herein renamed poison strip member (see the poison strip member section below for details). six dinosaur faunas are now recognized within the figure 4. outcrop map of cedar mountain formation in the central colorado plateau area with approximate locations of many of the major fossil sites referred to in the text indicated. arrows indicate type sections: black – cedar mountain formation and buckhorn conglomerate; yellow – yellow cat member; orange – poison strip sandstone; purple – ruby ranch member; gray – mussentuchit member; and blue – short canyon member. 108 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 cedar mountain formation on the basis of changes at the genus and species level. more substantial faunal breaks at higher taxonomic levels provide a natural three-fold division that appears to have greater paleogeographic and evolutionary significance (kirkland and others, 1997, 1999). the lower (“polacanthid”) faunal division is grouped together based on presence of polacanthid ankylosaurs, spatulate toothed sauropods, basal styracostern “iguanodonts,” and large dromaeosaurine dromaeosaurids, and is recovered from throughout the yellow cat and poison strip members. the medial (“tennontosaurid”) faunal division is characterized by nodosaurid ankylosaurs, slender-toothed titanotosauriform sauropods, and basal iguanodonian tennontosaurids, and is restricted to the ruby ranch member. the upper (“eolambia”) fauna division is restricted to the mussentuchit member and is dominated by the hadrosauroid iguanodontian eolambia, having a mix of faunal holdovers from the medial “tennontosaurid” fauna and new faunal elements derived from asia (kirkland and others, 1997, 1998, 1999; kirkland and madsen, 2007). as described in subsequent sections, the lower fauna appears to be divisible into three sequential faunas and the medial fauna into two sequential faunas. these three distinct dinosaur faunal divisions match three “chronofacies” based on detrital zircon age distributions from 100 randomly dated zircon grains extracted from sandstones in these intervals (figure 6). figure 5. simplified cross section of cedar mountain formation across eastern utah showing the relationship of its various members, select dinosaur sites, and adjacent stratigraphic units. updated after kirkland and others (1997). 109 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 fi gu re 6 . c or re la tio n of l ow er c re ta ce ou s c hr on of ac ie s r ou gh ly fr om w es t ( se vi er th ru st b el t) to ea st (p ar ad ox b as in ). d ar k gr ay = b as al l ow er c re ta ce ou s c hr on of ac ie s; m ed iu m g ra y = up pe r l ow er c re ta ce ou s c hr on of ac ie s; lig ht es t g ra y = ba sa l u pp er c re ta ce ou s c hr on of ac ie s. d ak ot a fo rm at io n = n at ur ita f or m at io n. f ro m h un t a nd o th er s ( 20 11 ). 110 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 following methodologies developed by dickenson and gehrels (2008), chronofacies is a proxy for grouping strata based on similar aged source rocks (lawton and others, 2010; hunt and others, 2011). these three dinosaur faunas have a somewhat restricted distribution geographically. the lower polacanthid fauna is only documented in the yellow cat and the poison strip members in grand county, utah. of the 496 cedar mountain localities recorded for utah in the upld, 302 are in grand county. the middle “tenontosaurid” fauna is present wherever the ruby ranch member of the cedar mountain formation has been documented, but is only known from a few scattered localities largely due to the difficulty of prospecting for bone fragments amongst the carbonate debris covering many exposures of this member. the upper eolambia fauna is only known from the mussentuchit member on the western side of the san rafael swell in emery county and at very limited exposures in sevier county (three localities). emery county includes 167 of the known cedar mountain fossil localities making grand and emery counties clearly the focal point for lower cretaceous paleontological research in utah. buckhorn conglomerate member the basal buckhorn conglomerate member has a type section in the area of buckhorn reservoir on the northwest side of the san rafael swell. in its type area, the buckhorn consists largely of a chert-pebble to cobble conglomerate up to 25 meters thick that defines a complex northeast-flowing paleo-river system along the west flank of the san rafael swell from the north end of capitol reef national park (yingling, 1987; currie, 1998; figure 7). well-developed buckhorn conglomerate extends north of i-70 across the northeast side of the san rafael swell and in northeastern utah at dinosaur national monument, colorado and utah, and the surrounding area (currie, 1998; greenhalgh and britt, 2007; currie and others, 2012; sprinkel and others, 2012). the chert pebbles and cobbles preserve late paleozoic marine fossils reworked from ancient mountains in northwest arizona and nevada. in recent years, controversy has arisen over the age of the buckhorn conglomerate in its type area, as a thick carbonate paleosol locally overlies the buckhorn and a carbonate paleosol has been used to define the base of the cretaceous elsewhere (aubrey, 1996, 1998). because of the maturity of this paleosol, it has been proposed that it represents an unconformity between the jurassic and cretaceous (aubrey, 1998; roca, 2002; ayers, 2004; roca and nadon, 2007). however, well-developed paleosols may occur at a number of stratigraphic positions within the cedar mountain formation and it is possible the carbonate paleosol could well post-date the deposition of the buckhorn conglomerate (kirkland and others, 1997; carpenter and others, 2001; al-suwaidi, 2007; kirkland and madsen, 2007; ludvigson and others, 2010a). recognition of the buckhorn conglomerate is also complicated in that it may be poorly or completely uncemented locally and be nearly unrecognizable except by trenching out the section. this is notable just north of the type area above the cleveland-lloyd quarry and on cedar mountain on the north end of the san rafael swell. the recent discovery of a possible ankylosaur (armored dinosaur) skeleton within the buckhorn conglomerate in this area (figure 7d) suggests a cretaceous age, as these dinosaurs are rare in the jurassic and are abundant in the lower cretaceous (carpenter and kirkland, 1998; kirkland, 2005a; kirkland and madsen, 2007). elsewhere, the sole body fossils identified in the buckhorn conglomerate consist of isolated sauropod bones, which unfortunately do not provide any biostratigraphic information. at the eastern margin of the buckhorn conglomerate exposure on the east side of the san rafael swell near green river, utah, the buckhorn conglomerate and poison strip members appear to merge; the buckhorn conglomerate member is used nomenclaturally, where there is no underlying fine-grained yellow cat (kirkland and madsen, 2007). good, continuous buckhorn conglomerate forms a bench at the base of the cedar mountain formation along the entire northeastern side of the san rafael swell, starting approximately 16 km (10 mi) directly north of i-70. where the green river cutoff road (blm 401) crosses the cedar mountain outcrop belt, shapiro and others (2009) noted that dinosaur bone-bearing oncolites at the contact between the buckhorn conglomerate and the overlying ruby ranch member may best be referred to as a poison strip 111 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 facies that is incorporated into the top of the buckhorn conglomerate (r.s. shapiro, california state university chico, personal communication, 2008). conglomeratic fluvial facies of the buckhorn have been shown to interfinger with interfluvial facies characteristic of the (at least in part) laterally equivalent yellow cat member of the cedar mountain formation (greenhalgh, 2006; greenhalgh and others, 2006; greenhalgh and britt, 2007) on the south end of the san rafael swell east of capitol reef national park. however, these strata are much sandier than is typical of the yellow cat member in its outcrop belt to the north. in the san rafael swell area, demko and others (2004) interpreted areas of fine-grained strata with iron enriched paleosols to represent wet climatic conditions at the end of morrison formation deposition that were preserved only on drainage divides within the buckhorn drainage system. we follow greenhalgh and britt’s (2007) interpretation that these strata interfinger with the buckhorn conglomerate member and argue below (see the section on the lower yellow cat) that the wet climatic conditions are represented by iron-stained beds of the lower yellow cat member. an excellent example of buckhorn conglomerate interfingering with buckhorn interfluvial facies is exposed along of i-70 on the west side of the san rafael swell west of the rest area milepost 103.5. looking west from the rest area, a well-developed ledge of buckhorn conglomerate caps the variegated slope formed by the brushy basin member of the morrison formation on the skyline (figure 8a). farther west (5.6 km) and around a bend in the highway at the top of the grade, i-70 cuts through the base of the cedar mountain formation along a well-exposed roadcut where the basal buckhorn conglomerate is absent (figure 8d). over this short distance the buckhorn is observed interfingering with an interfluvial facies. this interfluvial facies is very similar to lithologies in the lower yellow figure 7. buckhorn conglomerate. (a) boulder of buckhorn conglomerate next to road southeast of buckhorn reservoir (39°14'23.54"n, 110°48'35.20"w. (b) outcrop of buckhorn conglomerate near buckhorn draw. (c) buckhorn conglomerate unconformably overlying the morrison formation just east of capitol reef national park in the bentonite hills (38°21'30.00"n, 111°7'44.53"w). (d) marina suarez examining ankylosaur partial skeleton lying on back in middle part of buckhorn conglomerate under overhang near buckhorn draw road. 112 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 8. caption on following page. 113 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 cat member of the cedar mountain formation in the paradox basin as discussed in that section. these finegrained strata preserve common small lenses and floating pebbles of chert and quartzite. iron-stained nodules and layers of chert are also present. these strata are capped by cherty, calcareous, fine-grained sandstone that can be traced laterally onto the top of the buckhorn conglomerate member. this bed is in turn overlain by the ruby ranch member of the cedar mountain formation. the buckhorn conglomerate represents a large anastomosing river system and these interfingering finer grained strata are herein referred to as the yellow cat facies of the buckhorn conglomerate. in this way, they are separated nomenclaturally from the carbonate nodule-bearing ruby ranch member, which overlies them. for mapping purposes, it seems logical to map these interfluvial strata within the outcrop belt of the buckhorn conglomerate as a yellow cat facies of the buckhorn conglomerate. additionally, it has been documented that gravel floating in fine-grained matrix in the basal cedar mountain formation define the lower yellow cat member across the paradox basin east of the buckhorn outcrop area as discussed in that section. large chert and quartzite cobbles, associated with sauropod and ankylosaur bones in the lower yellow cat on the western margin of the paradox basin south of green river, utah (greenhalgh and britt, 2007; kirkland and madsen, 2007; mcdonald and others, 2010), are much larger than the pebbles typical of the lower yellow cat elsewhere and are thought to represent direct evidence that the lower yellow cat is laterally equivalent with the buckhorn conglomerate. the facies changes in the basal cedar mountain formation between the paradox basin and the san rafael swell has the potential to reveal interesting data concerning the onset of cretaceous deposition following an interval of nondeposition and erosion across the jurassic-cretaceous temporal boundary at the interface between two differing tectonic regimes (see peterson, 1984). in the southern paradox basin of southeastern utah and to the east of the paradox basin in western colorado, young (1960) noted a lower cedar mountain (conglomeratic) sandstone that may have been equivalent to the buckhorn conglomerate, but was not assign these beds to the buckhorn due to the lack of continuity in deposition. as these exposures are in the burro canyon outcrop area, we are in complete agreement with young’s nomenclature. interestingly, along an extensive road cut along u.s. highway 191 (us 191) south of blanding, the entire stratigraphic interval between the underlying morrison formation and the overlying naturita formation (= dakota formation) consists of stacked ferugeneous, pebbly paleosols similar to those present in the buckhorn interfluvial facies, documenting the presence of the yellow cat interfluvial facies in the burro canyon formation in southern utah (figure 8i to k). finally, it is worth noting that stokes (1950) reported that both the shinarump member of the upper triassic chinle formation and the buckhorn conglomerate were broadly similar in being very widespread and relatively thin conglomeratic fluvial units formed on regional unconformities and composed mainly of mafigure 8 (figure on previous page). exposures of the basal cedar mountain formation between i-70 milepost 104 and 108. (a) middle mesozoic strata on north side of i-70 at rest stop on west side of san rafael swell (38°49'56.80"n, 111° 6'46.07"w). note that the smectitic mudstones of the brushy basin member make up most of the morrison formation capped by buckhorn conglomerate on the skyline. (b) buckhorn conglomerate member with interfingering yellow cat interfluvial facies west of outcrop in a. (c) overview of b showing that the cherty, calcareous sandstone (ccs) capping the road cut in d to f overrides the buckhorn conglomerate. red line shows separation between ccs and underlying tongues of buckhorn conglomerate. (d) overview of road cut exposing yellow cat interfluvial facies (38°49'4.22"n, 111°10'16.00"w). (e) close-up view of cherty, calcareous sandstone (labeled ccs on c, d, and f) capping the road cut. (f) detail of road cut exposing yellow cat interfluvial facies showing position of close up pictures g and h. (g) lenses of pebble conglomerate. (h) iron-stained nodules in basal cedar mountain formation. (i) largely fine-grained facies of the burro canyon formation exposed on west side of us 191 south of blanding, utah (37°25'59.62"n, 109°28'13.83"w), viewed from south. (j) same exposure on south end as viewed from southwest. (k) contact between burro canyon formation and overlying naturita formation on eastern side of us 191 road cut. 114 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 terials derived from the underling strata. in this, stokes (1950) referred to the pediment concept, although the term regolith is as applicable. although our research on the chinle formation in utah is still in its preliminary stages (martz and others, in review), it is worth noting that shinarump, interfluvial deposits near the head of red canyon in san juan county in southern utah, are remarkably similar to those we have noted at the base of the cedar mountain formation on the san rafael swell, which suggests that investigating these sequences in comparison to each other may yield interesting results. yellow cat member the yellow cat member consists of drab, variegated, illitic mudstone, limestone, and paleosols, with some sandstone lenses. the type section (figures 4 and 9) is west of where the yellow cat road crosses the bench held up by the overlying poison strip member of the cedar mountain formation at the gaston quarry (kirkland and others, 1997). the yellow cat is recognized in the area south of i-70 between the green and colorado rivers, where it is thought to reflect the last effects of salt diapirism in the northern paradox basin around arches national park (doelling, 1988; doelling and kuehne, 2013a). the burro canyon formation in the central paradox basin south of moab has never been studied paleontologically; however, in the lisbon valley area, approximately 40 m of conglomerate and sandstone beds host economically important copper deposits. the copper-bearing beds are overlain by 20 to 40 m of mudstone beds with nodules suggesting that the yellow cat member is not present in this area (young, 1960; hahn and thorson, 2006). a stratigraphic cross section along the outcrop belt (figures 10 and 11) lends considerable support to the hypothesis that the yellow cat member, as used herein, is restricted to the northern paradox basin in grand county, utah. the yellow cat member was originally defined as being underlain by a massive carbonate paleosol, reflecting an approximately 25-million-year hiatus in sediment accumulation between the late jurassic and middle early cretaceous (aubrey, 1996, 1998; kirkland and others, 1997, 1999; skipp, 1997; demko and others, 2004; kirkland, 2005a). early cretaceous fossils have now been found below the base of this carbonate interval, thus necessitating a redefinition of the lower boundary of the cedar mountain formation at the first occurrence of abundant chert pebbles above typical morrison swelling clays (kirkland, 2005b; kirkland and madsen, 2007). the yellow cat member is overlain by the poison strip member and pinches out to the east and west (figure 5). it is worth noting that the yellow cat is well defined in young’s (1960) cross section below the “middle sandstone unit” between sections 30 and 38 (figure 3). figure 9. the cedar mountain formation on the west side of gastonia point (east of yellow cat flat), northeast of arches national park, with distribution of members labeled. this is the type section of the yellow cat member and gaston quarry (utah gr 184v) type locality for gastonia and utahraptor (kirkland and others, 1997). 115 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 jurassic-cretaceous boundary and the k-1 unconformity over the past 60 years, the jurassic-cretaceous boundary has progressively been pushed stratigraphically lower in the northern paradox basin as additional cretaceous fauna have been discovered. the boundary appears to have stabilized just above the highest smectitic mudstone beds of the brushy basin member of the morrison formation (figure 12). with the recognition of cretaceous strata below the marker calcrete of aubrey (1996, 1998), a new set of criteria is needed to define the base of the cedar mountain formation in a consistent manner. these criteria also may be applied to those areas in the buckhorn conglomerate outcrop belt, where fine-grained interfluvial strata (“yellow cat facies”) form the base of the cedar mountain formation. given the presence of cretaceous dinosaurs below the marker calcrete, the old rule of thumb that the cedar mountain formation can be distinguished from the underlying morrison formation based on its drabber, variegated mudstones (stokes, 1952; young, 1960) is problematic, as the basal yellow cat member often includes brightly colored red beds. it is important to note that, whereas the upper jurassic brushy basin member of the morrison formation is highly smectitic on the colorado plateau (peterson, 1994; turner and peterson, figure 10. stratigraphic key for stratigraphic sections presented herein. 116 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 fi gu re 1 1. c ro ss s ec tio n of c ed ar m ou nt ai n fo rm at io n ac ro ss th e no rt h en d of th e pa ra do x ba sin , g ra nd c ou nt y, u ta h. e ac h se ct io n ex am in ed in gr ea te r d et ai l e lse w he re h er ei n. b s= bu ck m as te r d ra w, d r= d on 's ri dg e, rr = ru by r an ch r oa d, k b= k lo nd ik e bl uff s r oa d, u r= u ta hr ap to r r id ge , lm =l ak e m ad se n se ct io n, y c =y el lo w c at r oa d, p s= po iso n st rip se ct io n, h m =h ot el m es a, r v =r ab bi t v al le y, d b= d oe lli ng 's bo w l, pr =p ric e r iv er se ct io n, m w =m us se nt uc hi t w as h, b f= bl ue f la ts , m c =m ud dy c re ek ( ri ve r) , a nd m r= m oo re r oa d. k ey to s tr at ig ra ph ic s ym bo ls as in fi gu re 1 0. ve rt ic al sc al e in m . 117 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 12. falling jurassic-cretaceous boundary in paradox basin plotted against yellow cat road section. byu 7210 = approximate position of dalton wells quarry (britt and others, 2009); dmnh 2182 = tony’s bonebed, type locality for planocoxa and veneosaurus (dicroce and carpenter, 2001; tidwell and others, 2001); dmnh 2183 = lorrie’s site, type locality for gastonia lorriemcwhinneyae (kineer and others, 2016); omnh v857 = hotel mesa site, type locality for brontomirus; umnh 1207 = andrew’s site, type locality for hippodraco; umnh 1208 = doelling’s bowl bonebed, type locality for yurgovuchia; utah gr 184v = gaston quarry, type locality for gastonia and utahraptor; and utah gr190v = nedcolbertia site, type locality for nedcolbertia. 118 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 1999; trujillo and kowallis, 2015), the overlying yellow cat member of the cedar mountain formation is not (kirkland and others, 1997, 1999; kirkland and madsen, 2007). additionally, the lower yellow cat member is characterized by chert beds and laminae (silcretes?), iron oxide cemented nodules, stacked root-mottled paleosols, and scattered chert pebbles (dick, 2006; dick and others, 2006; kirkland and madsen, 2007; toth, 2010). the most consistent sedimentological characteristic found at the base of the cedar mountain formation is the presence of a chert pebble lag or first occurence of chert pebbles “floating” in a mudstone matrix. workers have suggested that the materials that compose the basal cedar mountain formation are materials winnowed from the underlying morrison formation (eberth and others, 2006; hunt and others, 2011; sprinkel and others, 2012). the methodology now employed in our research to pick the base of the cedar mountain formation in the field is to find the highest smectitic mudstones in the underlying brushy basin member of the morrison formation and then trench up through the overlying mudstones into cedar mountain strata that clearly preserves matrix-supported or “floating” chert pebbles in root-mottled paleosols with or without chert layers, ferruginous nodules, and iron oxide staining. then, the strata are carefully examined to find the first occurrence of small chert pebbles, which is then used to mark the base of the cedar mountain. defined by this field proceedure, we have recognized that the uppermost morrison formation is typically not smectitic and may exhibit minor root-mottling and iron staining, indicating weathering of the erosion surface prior to initial deposition of the cedar mountain formation. these pebbles may form a distinct horizon that can be readily distinguished, or the contact may only be represented as scattered, very coarse, brightly colored, chert grains within a mudstone matrix. from a distance and in aerial photography the boundary can be picked based on differences in the weathering profile of the slope. mudstone beds in the brushy basin member of the morrison formation are highly smectitic and generally have a convex profile to their exposed slopes. mudstone beds in the yellow cat member of the cedar mountain formation are never smectitic and the slope profile is flat to concave. color is not a good criterion as bright red strata are commonly present in the lower yellow cat, although these strata tend to be drabber than those of the underlying morrison formation. combined with field inspection, these have proven to be useful criteria for mapping purposes (doelling and kuehne, 2013a). the contact between the morrison and cedar mountain formations defined in this way is still identified as representing the k-1 unconformity. the length of time represented by this hiatus is impossible to determine accurately at this time. the youngest ages for morrison strata in this area are (1) 148.96 +2.54 to -2.21 ma based on u-pb ages determined by laser ablation of zircons extracted from a volcanic ash bed about 9 m below the base of the naturita formation (= dakota formation), which rests directly on the morrison formation in these outcrops west of hanksville, wayne county, utah (kirkland and madsen, 2007; kowallis and others, 2007; hunt and others, 2011) and (2) 150.00 ± 0.52 ma from near the top of the brushy basin member, near little cedar mesa, emery county, utah, based on a recalibrated 40ar/39ar age (trujillo and kowallis, 2015). thus, the top of the morrison formation dates to the lower third of the tithonian stage near but not to the end of the jurassic (cohen and others, 2013). dates from the yellow cat member of the cedar mountain formation are limited to u-pb analysis determined by laser ablation of detrital zircons. the most widely cited age of 124.2 ± 2.6 ma (greenhalgh, 2006; greenlalgh and britt, 2007; britt and others, 2009; ludvigson and others, 2010a) is from the 20 youngest of 62 zircon grains sampled from a sandy green mudstone stratigraphically a few meters higher and two kilometers west of byu’s dalton wells quarry (byu 7510). a detrital zircon u-pb age of 146.6 +4.1 to -3.9 ma from the dalton wells quarry supported the hypothesis that the quarry sediment was derived completely from material reworked from the underlying morrison formation (eberth and others, 2006). the dalton wells quarry preserves a dinosaur fauna consistent with that of the upper part of the yellow cat member (kirkland and madsen, 2007; britt and others, 2009; kirkland and others, 2012). mori (2009) reported a number of additional u-pb ages from detrital zircons at several other 119 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 sites, but stratigraphic misinterpretations relative to the stratigraphic framework presented herein and limited sample sizes raise some questions as to the accuracy of those results. of some interest, mori (2009) reported a maximum age of 121.8 ± 2.2 ma for a sandy unit just above the crystal geyser bonebed in the lower yellow cat, and a maximum age of 122.6 ± 0.7 ma just above the capping sandstone above the suarez site and below the martharaptor site at the base of the upper yellow cat member as interpreted in that area (kirkland and others, 2005a, 2005b; kirkland and madsen, 2007; senter and others, 2010, 2012b). older ages for the lower cedar mountain formation have recently been proposed based on ostracods and charophytes extracted from the upper yellow cat member. these ages are based largely on the comparison of these microfossils with those known from the berriassian purbeck formation of southern england (sames and others, 2010; sames, 2011; martin-closas and others, 2013). furthermore, u-pb ages from detrital zircons collected from paleosols in which a minimum of 300 zircon grains were dated have suggested dates ranging from 137 to 139 ma from throughout a section of the yellow cat member at utahraptor ridge north of arches national park (hendrix and others, 2015). a 139.7 ± 2.2 ma age (based on the two youngest zircon grains of 300 dated) occurs in the lowest paleosol in the section and is stratigraphically the lowest non-jurassic maximum age extracted from the basal cedar mountain formation. of the 3000 zircons dated in total, not a single aptian radiometric age has been recovered from this locality (greg ludvigson, kansas geological survey, verbal communications, 2016), a surprising result considering many have considered the basal yellow cat member to span the aptian. another detrital zircon age from the doelling's bowl bonebed in the lower yellow cat yielded a maximum age of ~132 ma (g. hunt, former utah geological survey intern, verbal communication, 2012). the disparities of ages for the yellow cat member requires further investigation, but suggest the time missing across the k-1 unconformity in the paradox basin ranges from a maximum of 26 million years to as little as 10 million years. with such a significant unconformity, it may not be surprising to observe a wide range of radiometric ages. numerous periods of pedogenisis are likely to have accumulated a range of zircon populations and “pedoturbation” may have caused mixing of these zircons. preliminary unpublished paleomagnetic data indicate that deposition of the yellow cat at least, in part, preceded the onset of the middle cretaceous long-normal at the base of the aptian (ziegler and others, 2007; ziegler, 2008). in addition, somewhat ambiguous chemostratigraphic profiles also suggest barremian to aptian age (see section of chemostratigraphy). lower yellow cat member the lower yellow cat member is defined as extending from the first “gravelly” beds at the base of the cedar mountain formation to the top of aubrey’s (1996, 1998) marker calcrete bed, which also includes numerous centimeter-scale pebbles scattered within it (figure 13). essentially, the lower yellow cat consists of a stacked sequence of root-mottled paleosols, reflecting the apparent low sediment accumulation rate following the hiatus represented by the k-1 unconformity. the basal contact locally preserves concentrations of manganese, which were exploited as ore during the early 20th century in the little grand mining district south of green river, utah (baker and others, 1952). originally noted as being in the upper morrison formation, the manganese locally permeates the basal yellow cat immediately above the k-1 unconformity, may permineralize bone at don's ridge, and forms a patina on some of the best preserved bones at the crystal geyser quarry (figure 13d). the lower part of the member is often characterized by paleosols with iron oxide nodules that impart a red and yellow appearance. additionally, the lower part of the yellow cat member includes red bed intervals, which are similar to portions of the underlying morrison formation but differentiated based on clay mineralogy and presence of chert as described above. the abundance of iron and the absence of carbonate nodules in the lower part of the lower yellow cat indicates wetter paleoclimatic conditions than indicated by paleosols in the underlying morrison formation and higher in the cedar mountain formation, from the calcrete marker bed and higher stratigraphically (see section on geo120 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 13. caption on following page. 121 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 chemistry). these conclusions were reached relative to this stratigraphic interval by demko and others (2004) analysis of morrison paleosols and their paleoclimatic implications. however, in their study, aubrey’s (1998) marker calcrete was identified as the uppermost stratum of the upper jurassic morrison formation and to quote: “…very distinctive, reddish and yellowish color-mottled unit. the coloration is due to extensive redistribution of iron minerals within the paleosol. these features (ferruginous nodules, iron and clay depleted and enriched zones) suggest alternating saturated and well-drained (hydroximorphic and redoximorphic) conditions during soil formation (e.g., vepraskas, 1994). there is no pedogenic carbonate associated with these paleosols.” ….. “the well-developed paleosol complex (redoximorphic gleysol) at the top the morrison was formed under wetter conditions than any of the paleosols in the lower portions of the formation. the paleosol complex formed under dominantly saturated soil moisture conditions (with periodic drying out) and low sedimentation rates.” (demko and others, 2004). these are the only “wetland” paleosols (figure 13c, f, and g) described on the colorado plateau anywhere in the interval between and middle jurassic and the base of the upper cretaceous. given that, we are redefining the k-1 such that these wet climatic conditions are formed during the early cretaceous and not the late jurassic, is significant in interpreting the climatic history of the entire region. however, it is important to note that ferruginous nodules may occur at the very top of the morrison formation, where they are interpreted to have formed just prior to cretaceous deposition (figure 13i to k). demko and others (2004) interpreted the stacking of these paleosols as representing a reduction of sedimentation rates toward the end of the late jurassic prior to the development of the k-1 unconformity, whereas we interpret them as representing the gradual increase in accommodation following the erosion surface represented by the k-1 unconformity. further research on these interesting paleosols is warranted. another characteristic feature of the lower yellow cat is the presence of chert layers that are often associated with silicified roots. initially, on discovering that there were cretaceous dinosaur remains between these prominent cherts and aubrey’s marker calcrete bed, it was assumed that the chert layers represented a silcrete marker bed at the jurassic-cretaceous contact (dick, 2006; dick and others, 2006). however, with the redefinition of the base of the of the cedar mountain formation using the presence of chert pebbles to separate the cedar mountain from the underlying morrison appearing within the illitic floodplain strata bounding the k-1 unconformity, it has been noted that the chert beds have never been observed at the base of the cedar mountain formation and may in fact appear only above the iron-rich paleosols. although generally present as thin (1 cm) discontinuous sheets of silica, through less than a meter interval of strata, they may occur in thicker laminated beds that may extend for tens of meters laterally. in the area of the doelling's bowl bonebed, figure 13 (figure on previous page). features at base of the lower yellow cat member. (a) newly recognized thick sequence of lower yellow cat below type section of the ruby ranch member (figure 11, rr) on the north side of the ruby ranch road (38°51'15.12"n, 109°59'16.24"w). ac = aubrey’s (1998) massive calcrete bed at top of lower yellow cat, al = algal, cherty limestone in upper yellow cat member, bc = basal level of carbonate nodules, fn = ferruginous nodule zone in c. (b) coarse pebble lenses and pebbles floating in fine-grained mottled strata indicated in a. (c) ferruginous nodule zone indicated in a. (d) small manganese mine south of green river, utah (109°59'15.35"w, 110° 5'48.54"w). (e) stacked, pebbly, mottled paleosols in lower yellow cat east ps section (figure 11) (38°52'40.51"n, 109°25'3.83"w). (f) carbonate concretion from base of crystal geyser quarry bonebed form directly upon contact with underlying morrison formation, on correct orientation to show pavement of limb bones and floating chert pebbles (umnh loc. # 157). (g) ferruginous nodule zone near base section at utahraptor ridge (figure 11, ur). (h) detail from g.(i) ferruginous nodule zone in fine-grained sandstone at top of morrison formation east of section at utahraptor ridge (38°50'53.37"n, 109°39'19.73"w). (j) enlargement of ferruginous nodule from i. (k) enlargement of another ferruginous nodule from i with cross-cutting burrows and roots. 122 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 chert beds may form mounds as thick as 1 m or occur as amalgamated sheets of horizontal roots (figure 14). these roots only sporadically preserve cell structure. brigham young university’s famed paleobotanist, the late william tidwell identified one specimen as the fern tempskya, which builds a pseudo-trunk out of coalesced roots (tidwell, 1998). however, tempskya are only known from the mussentuchit member of cedar mountain and naturita formations (= dakota formation) and thus are exclusively from the basal upper cretaceous. when i (kirkland) reported that the thin section was from a horizontal meandering root, tidwell said, “that this was impossible.” as these roots are 25 to 35 ma older than tempskya, perhaps they represent an ancestral condition. with the passing of tidwell, additional samples were examined by brian axsmith (university of south alabama, personal communication, 2014), who only committed to the fern root identification. silicification in this interval occurred near or at the surface as silicified root fragments of the same morphology occur in the doelling's bowl bonebed immediately overlying the chert. a similar occurrence of chert layers and silicified roots is present near the top of the sonsela member figure 14. lower yellow cat chert interval as developed at doelling’s bowl: (a) chert mound. (b) laterally extensive chert layer approximately 25 cm thick. (c) surface expression of laterally extensive chert layer. (d) fern root mat preserved in top of chert layer. (e) basal chert interval with pebbles, thin chert layers and silicified roots. (f) silicified fern roots exposed on surface. (g) cross section of chert layer. (h) cross section of rotted root section from doelling’s bowl bonebed. (i) weathered iguanodont femur in doelling’s bowl bonebed immediately above chert zone. 123 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 (persistent red silcrete zone) of the chinle formation at the petrified forest national park (martz and parker, 2010), where it is associated with faunal and floral turnover at the late triassic (norian) adamanian–revueltian faunal and floral transition (parker and martz, 2011). this silcrete zone is interpreted to represent the silica replacement of peat (histosols) and pedogenetic carbonate in an interval recording a pronounced shift from humid to overall drier climates as indicated by abundant pedogenetic carbonate nodules up section (driese and others, 2010). stacked paleosols continue up section in the lower yellow cat member and the mottling fades in appearance. the overlying calcrete described by aubrey (1996, 1998) as marking the jurassic-cretaceous contact is recognizable in nearly all sections from 5 or more km west of the poison strip (ps) section to about 5 km west of the ruby ranch road (rr) section (figure 11). in this area, as noted by aubrey (1998), this carbonate zone is a honeycomb of nodular and pedotubule calcrete with interstitial matrix and floating pebbles having various amounts of secondary silica. these calcareous units grade upward from the base and may consist of one or several superimposed calcrete sequences with or without interspersed pedogeneic carbonate nodules or sheets. this marker interval typically is from less than 1 m to 10 m or more thick, where it is composed of multiple sequences. it locally forms a massive cliff along the ruby ranch road, where aubrey (1998, figure 9) refers to it as a hardpan calcrete. where this cliff of carbonate is well developed, it is always overlain a few meters up section in the upper yellow cat member by an approximately 1-m-thick, dark-brown, algal limestone (figure 15f) that is partially replaced by chert laminae (mistakenly referred to as the marker calcrete in ludvigson and others [2010a, figure 5c]). we believe that at this particular site, the marker calcrete was enhanced diagenetically, relative to an overlying lacustrine environment. aubrey (1996, 1998) initially placed the base of the cedar mountain formation at its gradational lower contact, based on the presence of pebbles within it, whereas others placed the contact at the top of this unit with the understanding that it would have been developed on the k-1 unconformity (kirkland and others, 1997, 1999; demko and others, 2004). herein, the top of the “lower” yellow cat is placed at the top this calcrete bed as matrix-supported or “floating” pebbles are not characteristic of the yellow cat member higher in the section. calcrete of the open morphology described by aubrey (1998) and illustrated here (figure 15) are not present along the west side the salt valley anticline (west side of arches national park). along most of this portion of the outcrop belt the contact between the lower and upper yellow cat is placed at a dense carbonate (limestone) bed separating facies typical of the lower yellow cat from those typical of the upper yellow cat. at the south end of these outcrops at dalton wells, there is no carbonate unit in the unusually thin yellow cat member, and the upper yellow cat is separated from the underlying morrison formation by a “single” mudstone conglomerate bed (eberth and others, 2006; kirkland and madsen, 2007; britt and others, 2009). a ridge-forming limestone bed has been recognized in the collapsed salt anticline near the fiery furnace in arches national park but vanishes to the south along this outcrop belt within the park (figure 15l), as the yellow cat thins (stikes, 2006). there does not appear to be a lower yellow cat exposed anywhere within arches national park. interestingly, a specimen of apatosaurus at the top of the morrison formation (foster, 2005) south of the pinchout of this limestone bed has a bit of carbonate on the bone and well-indurated bones appears to be have held up a ~5to 10-m-high paleo-hill at the unconformity just below the overlying poison strip member. similarly, there is no carbonate bed as described by aubrey (1998) in the yellow cat outcrops on the west side of the paradox basin south of green river, utah. there, pebbly facies typical of the lower yellow cat are separated from facies of the upper yellow cat by a thin, laterally persistent, calcareous, gravelly sandstone bed locally capped by stromatolites that is referred to as the caprock (kirkland and others, 2005b; kirkland and madsen, 2007; suarez and others, 2007a, 2007b; senter and others, 2012b). there is a similar unit capping aubrey’s (1998) enhanced calcrete at the ruby ranch road section (figure 15c to e) that adds weight to this potential correlation. as noted by demko and others (2004), these carbonate units mark a return to semiarid conditions 124 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 with a net evaporative flux. research on stable isotopes from pedogenetic and paludal carbonates and vertebrate material in the upper yellow cat and in the ruby ranch members has shown that this area was in a rain shadow downslope from the sevier orogenic belt (ludvigson and others, 2010a, 2015; suarez and others, 2014). we interpret the formation of these laterally extensive calcretes at the top of the lower yellow cat member as marking the initiation of this rain shadow, reinforcing the need for developing an accurate chronology of these strata. figure 15. caption on following page. 125 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 vertebrate taxa from the lower yellow cat member the discovery of a distinct fauna below a medial yellow cat ‘caprock’ near green river, utah, characterized by the basal therizinosaur falcarius (kirkland and others, 2005b; zanno, 2006, 2010), cf. falcarius n. sp. (zanno and others, 2014), a primitive troodont geminiraptor suarezarum (senter and others, 2010), a large basal steracosternid iguanodont iguanocolossus fortis (mcdonald and others, 2010), and a giant (nearly double the size of gastonia) polacanthid ankylosaurid (kirkland and others, 2012) suggests the presence of dinosaur fauna that may be older than that of the upper yellow cat fauna. the correlation of this ‘caprock’ with the calcrete cannot be proven, but appears likely. forty-nine km (30 mi) east of green river, a multitaxic early cretaceous dinosaur fauna is preserved below the marker calcrete and immediately above the chert interval in the doelling's bowl bonebed (figure 16). the occurrence of these new dinosaur taxa raised the possibility of testing the hypothesis that the calcrete, although not representing the k-1 unconformity, at a minimum represents evolutionary time as dinosaur genera turned over fairly rapidly, on the order of every 1 to 10 million years (dodson, 1990; wang and dodson, 2006; brusatte, 2012; bensen and others, 2014; starrfelt and liow, 2016). this hypothesis may be tested by examining related species in different dinosaur clades occurring above and below the calcrete (kirkland and others, 2012). at doelling's bowl, the dromaeosaur yurgovuchia has proven close to utahraptor (senter and others, 2012a). still under study, the iguanodont material includes many dentaries lacking the distinct shelf of hippodraco and many humerae lacking the well-developed deltopectoral crest present in hippodraco (mcdonald and others, 2010) (figure 16). the doelling's bowl iguanodont may be assigned to iguanocollossus based on the distinct upturned preacetabular process of the pubis. additionally, osteohistological analyses indicate the taxon could theoretically reach the large size of iguanacolossus (sartin and others, 2015). a second iguanodont may be present based on the presence of a more complex ilium, whereas the other ilia are of a simpler morphology, more in keeping with iguanacolossus. the polacathine ankylosaurs at doelling's bowl represent a new taxon based on comparisons with the braincases of the jurassic gargoyleosaurus and mymoorapelta and the 10 known braincases of gastonia (figure 17). most promising has been the discovery of a juvenile sauropod skeleton, which had been mired in doelling's bowl bonebed and is associated with parts of a larger adult animal. much of the skeleton is preserved, including skull material, pelvic elements, limb bones, an articulated pes and lower leg, and most of the vertebral column including the semi-articulated terminal 10 procoelus vertebrae of the tail. brigham young university is researching extensive material from more figure 15 (figure on previous page). aubrey’s (1998) marker calcrete in the northern paradox basin. (a) aubrey’s enhanced calcrete below the type section of the ruby ranch member (109°59'16.24"w, 109°59'10.02"w) of the cedar mountain formation at ruby ranch road section (see below) as viewed from the east. (b) typical expression of aubrey’s (1998) marker calcrete ruby ranch road section on west side of canyon in c, where yellow cat member was measured (figure 13a). (c) typical expression of aubrey’s (1998) marker calcrete ruby ranch road section at head of canyon with capping gravelly unit overlying it (109°59'10.02"w, 109°59'15.35"w). (d) scott madsen examining gravelly, calcareous sandstone capping aubrey’s (1998) enhanced calcrete on east wall of canyon in c. (e) detail of same bed in d. (f) cherty algal limestone in upper part of yellow cat member on west side of canyon in c. (g) multi-tiered calcrete marker bed at utahraptor ridge below stikes quarry (figure 11). (h) calcrete marker bed on the west side of the west end of the yellow cat loop road (38°51'14.86"n, 109°32'56.74"w). (i) thin calcrete marker bed on the east side of the east end of the yellow cat loop road (109°32'56.74"w, 109°32'56.74"w); note subtle expression in outcrop. (j) limestone marker bed on northwest side of salt valley anticline (38°49'0.69"n, 109°45'35.54"w). (k) the same limestone marker bed at one of mori’s (2009) sections, for which the author has a very different stratigraphic interpretation, in that there the mussentuchit member is below the naturita formation (smectitic “lake carpenter” facies at top of ruby ranch member) and that the morrison formation is below the poison strip member. (l) cedar mountain formation west of the fiery furnace in arches national park as viewed from the north showing the presence of a “basal carbonate marker bed” here. 126 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 16. caption on following page. 127 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 than a dozen individuals of a closely related sauropod found with gastonia and utahraptor at the dalton wells quarry north of moab, utah (britt and others, 2009). differences in character states between these sauropods provide an additional test of our hypothesis. probably the most noticible of these is that the medial cervical ribs deepen in the doelling's bowl taxon and are divided in the dalton wells taxon. our most recent analysis suggests that it is closest to the turiasaurid sauropods of southern europe (royo-torres and others, 2016). in addition to these four taxa, the doelling's bowl bonebed preserves large shed teeth of an allosauroid theropod. crocodillian skull fragments and teeth that may pertain to aguatic goniopholid crocodilians occur, as do distinctive shell fragments of the turtle naomichelys. just to the east of utahraptor ridge (ur; figure 11) scattered dinosaur bones occur even lower in the yellow cat in the ferruginous nodular zone below the chert level. these bones include a well-preserved humerus of a polacanthid ankylosaur (figure 17p). lower yellow cat fauna chelonia: cf. naomichelys (finely beaded shell surface) crocodilia: aquatic goniopholid crocs. dinosauria theropoda large allosauroid falcarius utahensis kirkland and others (2005b) yugovuchia doellingi senter and others (2012a) geminiraptor suarezarum senter and others (2010) sauropoda brachiosaurid indet. new turiasaurid (royo-torres and others, 2016) thyreophora new polacanthid ankylosaur (kirkland and others, 2012) new giant polacanthid ankylosaur (kirkland and others, 2012) ornithopoda iguanacolossus fortis (mcdonald and others, 2010) unstudied second iguanodont taxon (complex ilia) the upper yellow cat member the yellow cat member was originally defined as extending from the top of aubrey’s (1998) marker calcrete to the base of the poison strip member of the cedar mountain formation (kirkland and others, 1997). new dinosaur taxa (kirkland and others, 1993, 1998a, 1998b, 1999; kirkland, 1998a) from these rocks have been critical in stimulating many additional researchers to investigate the cedar mountain formation. it was considered problematic to define another member of the cedar mountain formation below the yellow cat member, as the yellow cat was just starting to be mapped as a discrete stratigraphic unit on 7.5-minute geological maps (1:24,000). given the steep slopes below the capping poison strip member, it was considered simplier to lower the basal contact of the cedar mountain formation at this stage of geologic mapping (doelling and kuehne, 2013a). however, using a subdivided yellow cat gained traction, especially as it became clear that different dinosaur faunas characterized figure 16 (figure on previous page). important vertebrate localities in the lower yellow cat member. (a) crystal geyser dinosaur quarry. (b) bones of falcarius utahensis in crystal geyser dinosaur quarry. (c) stratigraphic section at the crystal geyser quarry with positions of important data points in area. (d) suarez site. (e) bones as exposed in and just below the caprock. (f) correlation between the lower yellow cat member on the east side of the yellow cat road (yc in figure 11) and at doelling’s bowl. (g) stratigraphic sequence at doelling’s bowl and the distribution of dinosaurs. (h) isolated teeth and ossicles characteristic of the doelling’s bowl bonebed. a) polacanthid ankylosaur tooth. b) polacanthid ankylosaur ossicles. c) iguanodont teeth. d) sauropod teeth. e) crocodilian teeth. f) allosauroid teeth. section key as in figure 10. 128 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 17. caption on following page. 129 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 strata on either side of the marker calcrete, the boundary used to subdivide the lower and upper yellow cat. thus, biostratigraphic evidence supports defining a lower and upper yellow cat member in the northern paradox basin and has expanded our understanding of utah’s geological history during the early cretaceous. the lower yellow cat member includes interfluvial facies that is similar to lithofacies of the buckhorn conglomerate (figure 8, see above) and locally at the base of the burro canyon formation.the upper yellow cat member, however, appears to be completely restricted to the northern paradox basin (figure 11). west of the salt valley anticline on the west side of arches national park and running westward to the pinchout of the yellow cat member below the poison strip member south of green river, utah (figure 11), the upper yellow cat is characterized by fine-grained floodplain facies having common to abundant pedagenic carbonate nodules and isolated ribbon sandstones representing the thalwags of low-sinuosity rivers as discussed below (figure 16a). the yellow cat outcrop belt that runs east–west between the salt valley anticline at arches national park and the colorado river (figure 4) includes lacustrine strata east of the poison strip section (kirkland and others, 2016). these strata are an important part of the upper yellow cat member and are informally referred to as lake madsen, as scott madsen discovered the deepest water-laid facies known near the top of the member (scott madsen, formerly with dinosaur national monument and utah geological survey, personal communication, 2005). this site consists of organic-rich shale that preserves freshwater hybodont sharks, conchostracans, ostracodes (sames and others, 2010; sames, 2011), and the only palynomorph-bearing strata known in the yellow cat member (figure 18). northeast of arches nation park, it appears that there may be two lacustrine sequences; a lower and an upper sequence separated by an interval of paleosols with dewatering features (kirkland and others, 2016) (figure 19). it is not clear if these lacustrine sequences are part of one contiguous lake system or if the upper yellow cat member represents an extensive wetlands system resulting from subsidence in the northern paradox basin. the lower lacustrine system immediately overlies the marker calcrete where it is often associated with dispersed vertebrate remains (kirkland and others, 1998a, 2016). the nedcolbertia justinhoffmani sites at the base of the upper yellow cat member preserve mostly pedal and caudal elements suggesting that these specimens were preserved by miring as lacustrine environments first spread out over the marker calcrete (kirkland and others, 1998a). the medial hiatus or restriction of lacustrine environments preserves dinosaur tracks locally and at the stikes quarry on utahraptor ridge (figure 19), the complex bonebed consists of a series of interconnected sandstone masses (“blobs”) that encased unfossiliferous floodplain-derived mudstone beds with carbonate nodules. the main upper “blobs” consist of numerous skeletons of utahraptor that, with only mifigure 17 (figure on previous page). dinosaurs from the lower yellow cat member. (a) falcarius utahensis. (b) maxilla of gemniraptor suarezarum from suarez site in ventral, oblique-medial, and lateral views; top to bottom. (c) large osteoderms from suarez site. photo courtesy of ken carpenter, prehistoric museum (utah state university eastern). (d) type material of iguanocolossus fortis from mcdonald (2010). (e) partial pubis from cf. iguanocolossus from doelling’s bowl bonebed (unmh 1208). (f) comparison of type hippodraco humerus from upper yellow cat (andrew’s site, umnh 1207) vs. three smaller humerae from cf. iguanocolossus from umnh 1208. (g) dromaeosaur (yugovuchia?) pelvis found under ankylosaur pelvis in k from umnh 1208. (h) type braincase of mymoorapelta maysi from mygatt-moore quarry, upper jurassic morrison formation, rabbit valley (rv), western colorado. (i) basicranium of new polacanthid ankylosaur from umnh 1208. (j) basicranium of type of gastonia burgei from the upper yellow cat, gaston quarry, utah gr184. (k) pelvis of new polacanthid ankylosaur from umnh 1208. (l) mired leg of new sauropod in situ at umnh 1208. (m) same mired lower leg in ventral view. (n) large vs. small dentary of new sauropod from umnh 1208. (o) first mount of new sauropod from upper yellow cat, dalton wells quarry (byu 7510) at eccles dinosaur park, ogden, utah, with undivided cervical ribs as in doelling’s bowl sauropod. (p) corrected mount of dalton wells sauropod with divided cervical ribs. (q) polacanthid ankylosaur humerus from ferruginous paleosol interval east of utahraptor ridge (ur, figure 11). 130 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 18. lake madsen section. (a) lake madsen (lm) section measured from 38°50'50.18"n, 109°33'41.95"w up through 38°51'32.50"n, 109°33'46.52"w with stable isotope geochemistry data from hatzell (2015). bs = ben sames (sames and others, 2010; sames 2011) ostracod site. gq = level of gaston quarry relative to upper and lower lake madsen sequences. ls = laurie’s site, initially described as in basal ruby ranch member (carpenter, 2006). ts = tony’s bonebed. section symbols as in figure 10. (b) outcrop expression of yellow cat member at discovery site of lake madsen facies. (c) mid-mesozoic outcrops on the north side of the yellow cat flat with lower lake madsen section indicated. note the entire bench exposed to the north is composed of the poison strip member of the cedar mountain formation (doelling and kuehne, 2013a). 131 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 19. cedar mountain section at utahraptor ridge (ur) measured from 38°50'51.49"n, 109°39'24.99"w (base) to 38°50'55.46"n (top), 109°39'25.80"w showing the position of the stike’s quarry (kirkland and others, 2011, 2016) and bird track locality (lockley and others, 2015). detrital zircon u-pb dates from hendrix and others (2015). stratigraphic symbols as in figure 10. 132 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 nor preparation of the main plaster jackets to date, include a minimum of three “yearlings” (skull length of ~ 12 cm), five juveniles (skull lengths of ~ 25 cm), and one adult (skull length of about 50 cm), and a juvenile and adult iguanodont (poole, 2008). this unusual dinosaur locality is interpreted to represent a large collapsed dewatering feature formed on the margin of lake madsen and thus is the first dinosaur site ever to be attributed to trapping by “quicksand” (kirkland and others, 2011, 2016). another important site in the medial upper yellow cat member is the gaston quarry from which the type specimens of the polacanthid ankylosaur gastonia burgei (kirkland, 1998a) and utahraptor ostromaysorum (kirkland and others, 1993) were collected. this site is interpreted to rest on deposits from the shore of lake madsen with the bones subjected to a greater degree of subaerial weathering than those preserved in some other major yellow cat dinosaur sites (howard, 2014). the flattened bones at this site (figure 9) rest directly upon a rippled, sandy carbonate preserving dinosaur tracks (kirkland and others, 2005a; kirkland and madsen, 2007) in a pale-green mudstone lense overlain by another sandy carbonate preserving uncrushed bones (). as many as six gastonia are represented at the site by hundreds of skeletal and armor elements with four skulls including the type (kinneer and others, 2016), one adult utahraptor represented by scattered elements (kirkland and others, 1993), and a few bones and teeth representing iquanodonts. the dalton wells site is very extensive and located on utah state land managed by the utah division of forestry, fire & state lands along the west side of arches national park and at the south end of the cedar mountain formation outcrop belt. brigham young university has excavated several thousand dinosaur bones representing a diversity of dinosaur species. the bones at dalton wells have been interpreted to represent an accumulation of bones emplaced in a series of four superimposed debris flows (eberth and others, 2006; britt and others, 2009). this site preserves the thinnest sequence of the yellow cat member in the central paradox basin, and the bonebed rests directly on a pebble lag directly overlying the morrison formation as discussed below. other than, perhaps, this pebble lag, the entire section is interpreted to represent the upper yellow cat member as it preserves many taxa known from only from the upper yellow cat from other sites and none of the dalton wells dinosaurs are recognized as conspecific with taxa from the lower yellow cat member. the top of the upper yellow cat member is generally a coarsening upward, regressive lacustrine sequence. the contact with the base of the overlying poison strip member is a sharp break between fine-grained lacustrine strata and overlying cliff-forming, coarse-grained fluvial sandstones. this basal contact is easily picked as seen in the outcrops bounding the yellow cat flat and along the south rim of the poison strip escarpment (figures 18, 20, and 21). in areas, where only interfluvial facies are present, the poison strip member does not hold up an escarpment and, almost universally, this is where roads cross the outcrop belt. in these areas, the contact may be difficult to pick without carefully tracking facies from the adjoining fluvial facies capping the escarpment on either side of the road. such outcrops are limited, however. a more widespread problem is picking the contact where sandstone units formed by coastal lacustrine processes are preserved in the top of the yellow cat member. a good example of this is the laterally extensive bird track bed (lockley and others, 2015) at the top of yellow cat at utahraptor ridge (figure 19). as it is in the base of the cliff formed by the fluvial units of the poison strip member, it is unavoidably mapped as part of the poison strip member (doelling and kuehne, 2013a). stikes (2006) picked this contact correctly in this area (long valley section). a similar difficulty is encountered in the lower jurassic of southwestern utah in picking the contact between the lacustine sequence in the basal jurassic whitmore point member of the moenave formation and the unconformably overlying fluvial springdale sandstone member of the kayenta formation (kirkland and others, 2014). more research needs to be directed at the contact between these members to determine if it represents a regional unconformity. as discussed below, the upper yellow cat fauna and the poison strip fauna appear to be completely nonoverlaping, but is this a case of a temporal gap, the effects of different taxa residing in different adjoining environments, or a factor of taphonomic bias? 133 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 fauna from the upper yellow cat member invertebrate fossils from the upper yellow cat member include freshwater ostracods with charophytes (sames and others, 2010; sames, 2011; martin-closa and others, 2013), conchostracans, and viviparid snails. fish include ganoid scales and teeth from semionotid fish, high crowned amiid teeth, hybodont shark teeth and spine fragments, with short spiral coprolites containing abundant ganoid scales (figure 22a), and lungfish tooth plates (figure 22b). a new species of mammal is represented by a 7-cm-long cranium (huttenlocker and others, 2016; figure 22d). although potential microvertebrate sites are known, it has so far proven impossible to break down the matrix (scott madsen, formally with dinosaur national monument and utah geological survey, verbal communication, 2005). bainid turtles are common on the east end of the yellow cat loop road, and one site has yielded a number of skulls assigned to a new species of trinitichelys (brinkman and others, 2015). a large eilenodontid sphenodont, similar to toxolophosaurus, is represented by isolated jaws, and a partial skeleton. given the abundance of this taxon, it probably was an important small terrestrial herbivore during the deposition of the upper yellow cat member. a small proximal femur from the dalton wells quarry has been identified as a primitive neochoristodere (britt and others, 2006). a variety of aquatic crocodilians are represented by teeth. a small, possibly terrestrial, basal mesoeusuchian crocodilian, represented by a complete skull and articulated osteoderms, is currently under study. britt and others (2009) have recovered an isolated pterosaur bone from dalton wells. dinosaurs identified in the upper yellow cat member include numerous skeletons of the polacanthine ankylosaur, gastonia burgei (kirkland, 1998a), from several sites making it the best-characterized polacanthid known (blows, 2015). basal steracosternid iguanodonts (bipedal plant eaters with thumb spikes) are diverse represented by a minimum of three taxa (a. scheetz, brigham young university, paleontology museum, verbal communication, 2015). “iguanodon” ottingeri (galton and jensen, 1979) is represented by an undiagnostic maxilla fragment with two teeth. hippodraco scutidens is represented by a significant portion of a juvenile skeleton with a skull (figure 22o and p), which was found at andrew’s site (umnh 1207; figure 12) with a large adult iguanodon that lacks diagnostic overlapping skeletal elements (mcdonald and others, 2010). hippodraco scutidens is closest to theiophytalia kerri from the lytle member of the purgatory formation of the colorado front range (brill and carpenter, 2007; mcdonald, 2011). scheetz and others (2010b) have described a partial skeleton of a large iguanodont with elongate neural spines, quite unlike the short, squared-off, proximal caudal, neural spines on the large specimen from andrew’s site (figure 22q). iguanodontian tracks are relatively abundant in the upper yellow cat member (figure 22k), but it is noteworthy that none have yet approached the size of the large iguanodontian tracks known from the wealden of england (sarjeant and others, 1998; martill and naish, 2001b). hypsilophodont grade ornithopods are represented by a foot and a scapula (figure 22n). there are several sauropod families present, represented by the brachiosaurid cedarosaurus weiskopfae (tidwell and others, 1999; sanders and others, 2001) and a possible camarasaurid (eberth and others, 2006; britt and others, 2009) (figures 17p and 22m). one unusual sauropod is present in large numbers at the dalton wells quarry and is represented by a minimum of 17 individuals based on braincases (brooks britt, brigham young university, personal communication, 2007). this sauropod is convergent on titanosaurs in many characters and was thought to represent a primitive new titanosaurid for many years (britt and others, 1997; britt and stadtman, 1997). primitive vertebral development has suggested that it represented a primitive macranarian (britt and others, 2009). however, recent comparisons with taxa from the upper jurassic of spain suggest that like the new sauropod from the doelling's bowl site (figure 17o), it represents a turiasaurid sauropod; a basal eusauropod group not identified previously in north america (royo-torres and others, 2016). theropod dinosaurs include the small coelurosaur, nedcolbertia justinhoffmani (kirkland and others, 1998a), which is represented by several partial juvenile specimens, may be a primitive ornithomimid, and would have left tracks like those in figure 22j. a larger ornithomimid partial skeleton with skull material was reported by scheetz and others (2010a). the 134 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 20. gaston quarry. (a) overview of gaston quarry from south. b) overview of gaston quarry from southwest. (c) detail of portion of the bonebed approximately matching red box in figure g. (d) rob gaston (white shirt on right) and don burge (behind holding quarry map) overseeing work on sauropod tracks exposed at base of bonebed in foreground indicated by yellow arrows. (e) quarry profile with red arrow indicating base of bonebed impressed into surface of limestone. (f) schematic profile of gaston quarry highwall. (g) quarry map of gaston quarry excavation. (h) second pedal ungula (sickle-claw) of utahraptor holotype in situ. 135 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 giant dromaeosauriid or “raptor,” utahraptor ostrommaysorum (kirkland and others, 1993), is now known from four major sites and bone scraps from other sites. it was the sixth and still most massive dromaeosaurid ever discovered and although initially described from a scattering of bone, new discoveries (kirkland and others, 2011; kirkland and others, 2016) indicate that eventually it may become one of the best-known dromaeosaurids. while utahraptor is a dromaeosaurine, a small velociraptorine (senter and others, 2012a) also appears to be represented in these strata (figure 22g). martharaptor greenriverensis was initially identified as a therizinosaurid and its poorly represented skeletal remains were collected a short distance above the caprock figure 21. uppermost yellow cat member and its contact with poison strip member. (a) south escarpment below utahraptor ridge (figures 11 and 19). note trackhoe near center of image; broad yellow arrow designates base of poison strip member. (b) upper yellow cat contact on west side of us 191 in railroad cut (38°43'15.16"n, 109°42'51.37"w) with approximate position of detrital zircon date (greenhalgh, 2006; greehaulgh and others, 2007; britt and others, 2009); matt joeckel (nebraska state geologist) for scale. (c) uppermost yellow cat on the southwest side of doelling’s bowl with matt joeckel (right of red and white bar) examining underside of a sauropod trampolite surface, which rests on the dark-colored beds as indicated by red arrow; broad yellow arrow designates base of poison strip member; redand white-banded bar equals 10 m. (d) steep exposure of yellow cat member exposed on west side of small canyon on the southwest corner of gaston’s bowl (38°51'54.67"n, 109°29'3.99"w) with paleoenvironmental interpretation; redand white-banded bar equals 10 m. (e) matt joeckel and greg ludvigson looking at coastal vertisol on west side of gaston’s bowl near top of yellow cat member (38°52'30.72"n,109°28'30.78"w). (f) thin interval of yellow cat member exposed on west side of hotel mesa on east side of colorado river (38°49'58.79"n, 109°16'32.28"w). 136 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 22. caption on following page. 137 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 south of green river, utah (senter and others, 2012b). other undescribed theropod species have been identified from dalton wells quarry west of arches national park (britt and stadtman, 1997; eberth and others, 2006). there have been no teeth or bones indicating the presence of a large allosauroid in the upper yellow cat fauna, although they are represented in faunas above and below. upper yellow cat fauna chondrichthyes polyacrodontidae ?polyacrodus sp. teeth and fine spines, coprolites? osteichthyes semionitidae n. gen. n. sp. scales and ridge scales amiidae high-crowned tooth crowns dipnoi neoceratodontidae ceratodus sp. chelonia baenidae trinitichelys n. sp. (fine reticulate shell) (brinkman and others, 2015) rhynchocephalia cf. toxolophosaurus, large eilenodontid choristodera small neochoristodere indet. (britt and others, 2006) crocodilia new medium-sized (20 cm skull) basal mesosuchian terrestrial crocodilian aquatic goniopholid crocs. pterosauria ?pterosaur (britt and others, 2009) dinosauria theropoda small slender teeth similar to richardestesia ? nedcolbertia justinhoffmani (kirkland and others, 1998a) ornithomimid n. sp. ? (scheetz and others, 2010a) martharaptor greenriverensis senter and others (2012b) poorly resolved oviraptorisaur or therizinosaur utahraptor ostrommayorum kirkland and others (1993) figure 22 (figure on previous page). characteristic faunal elements from the upper yellow cat member of cedar mountain formation. (a) spiral coprolite embedded with small ganoid scales from nedcolbertia site utah gr190v (figure 12). (b) lower ceratodus tooth plate from nedcolbertia site utah gr190v (figure 12). (c) basal mesoeusuchia crocodilian skull from andrew’s site umnh 1207 (figure 12) in a) dorsal, b) ventral, and c) ventral view in uv light. (d) skull of new mammal from andrew’s site umnh 1207 (figure 12) in a) ventral, b) dorsal, ventral in uv light, and d) dorsal view in uv light. (e) mount of utahraptor as exhibited at utah state university eastern’s prehistoric museum in price. (f) lower leg of holotype of nedcolbertia as exhibited at utah state university eastern’s prehistoric museum in price. (g) tail of veloceraptorine dromaeosaur from andrew’s site umnh 1207 (figure 12) in uv light. (h) premaxilla of “baby” utahraptor from stikes quarry at utahraptor ridge. (i) bird tracks (aquatilavipes) from utahraptor ridge (figure 19) (lockley and others, 2015). (j) theropod tracks from same site as i. (k) randy nydam with iguanodont tracks from just below andrew’s site (figure 12) (lockley and others, 1998). (l) skeletal reconstruction of gastonia based on material from gaston quarry. scale bar for holotype skull, given perspective. photo of gaston design reconstruction courtesy of francois gohier. (m) holotype skeleton of brachiosaurid sauropod cedarosaurus laid out on floor of the denver museum of nature and science. note arrow pointing to gastroliths found within rib cage (sanders and others, 2001). photo courtesy of ken carpenter, prehistoric musem (utah state university eastern). (n) hypsilophadont scapula from andrew’s site umnh 1207 (figure 12) (mcdonald and others, 2010). (o) postcranial skeletal reconstruction of holotype of hippodraco from andrew’s site umnh 1207 (figure 12) (mcdonald and others, 2010). (p) skull of holotype of hippodraco from andrew’s site umnh 1207 (figure 12) (mcdonald and others, 2010). (q) proximal tail of large iguanodont from andrew’s site umnh 1207 (figure 12) (mcdonald and others, 2010); note very short neural spines. 138 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 veloceraptorine dromaeosaurid indet. (senter and others, 2012a) assorted theropod tracks (lockley and others, 2015) bird tracks (lockley and others, 2015) sauropoda cedarosaurus weiskopfae tidwell and others (1999) new turiasaurid (royo-torres and others, 2016, by reference to kirkland and others, 2012) camarasaurimorph (britt and others, 2009) thyreophora gastonia burgei kirkland (1998a), polacanthid ankylosaur ornithopoda hypsilophodont grade ornithischian (mcdonald and others, 2010) hippodraco scutodens mcdonald and others (2010) sail-backed iguanodont (scheetz and others, 2010b) third styracosternid iguanodont n. gen. n. sp. (a. scheetz, byu, personal communication, 2014) mammalia n. gen. n. sp. large 7 cm long skull (huttenlocker and others, 2016) the dinosaurs, together with pollen and charophytes (green algae), and various isotopic dating methodologies suggest that the yellow cat member rocks are anywhere from 137 to 120 million years old (kirkland and others, 1997, 1998b, 1999; eberth and others, 2006; britt and others 2009; ludvigson and others, 2010a; hendrix and others, 2015). in europe, similar types of dinosaurs are also known from rocks of this age (martill and naish, 2001a), a time when the northernmost atlantic ocean had not yet opened, thereby permitting the exchange of animals between these two regions prior to the formation of an alaskan land bridge (cifelli and others, 1997; kirkland and others, 1997, 1998b, 1999, 2013a, 2015; kirkland and madsen, 2007; brikiatis, 2016). however, britt and others (2006) dispute this interpretation based on a small proximal femur identified as a primitive neochoristodere (an extinct semiaquatic lizard-like group) from the dalton wells quarry west of arches national park. it is related to taxa known only from asia in the early cretaceous. britt and others’ (2006) interpretation does not take into account that this group may be tied to asia through europe as suggested for falcarius (kirkland and others, 2005b) given that no land connection to asia existed at this time (plafker and berg, 1994; brikiatis, 2016). brikiatis (2016) suggests that the last direct land connection between north america and europe was early in the barremian around 131 ma after which north america would have been an isolated island continent. poison strip member the poison strip member is a complex of well-cemented sandstone beds that indicate deposition in amalgamated low-sinuosity anastomosing and meandering river systems, and coeval interfluvial deposits (kirkland and others, 1997, 1999; kirkland, 2005a; kirkland and madsen, 2007; stikes, 2003, 2006). the type section (figure 23a) is up section to the north of the ringtail mine on the west end of the poison strip, and is 5.4-m-thick, trough cross-bedded, mediumto coarse-grained sandstone with chert-pebble lenses in the lower part, fining upward to medium-grained sandstone with mudstone partings at the top (kirkland and others, 1997). unfortunately, the type section did not have a clear contact with the overlying ruby ranch member given that the upper contact is picked at a dramatic change to floodplain deposition with abundant pedogenetic carbonates. although initially described as the poison strip sandstone (kirkland and others, 1997), the variety of strata other than sandstone, necessitates renaming it to the poison strip member to avoid misinterpretation. in the arches national park area, stikes (2006) found the poison strip member to represent an amalgam of river channels as much as 15 m thick due to decreased subsidence rates dominated by lowto moderate-sinuosity channels with lateral bars and distal braided channels (miall, 1996). as kirkland and others (1997) noted, as many as three sandstone beds may define the poison strip member, although one prominent ledge is the norm and locally may have no sandstone beds. 139 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 23. poison strip member of the cedar mountain formation. (a) type section on the west end of poison strip escarpment above ringtail mine of yellow cat mining district (38°51'11.56"n, 109°31'36.02"w). (b) northeastern rim of doelling’s bowl, where there are no major cliff forming sandstone benches in the member and it is mostly an interfluvial floodplain sequence. (c) exposures toward eastern end of the poison strip escarpment (38°51'16.30"n, 109°28'33.78"w). (d) one of many small quartzite sites on top of the poison strip escarpment utilized for lithic material by native people. (e) chert hammerstone with arrow pointing to it in d. (f) panel diagram poison strip channel sandstone above vertisol in figure 21e to show large scale lateral accretion bedding. arrow indicates direction of lateral migration of channel. (g) poison strip member resting on morrison formation south of green river, utah (38°56'57.58"n, 110° 5'41.84"w), whereby ugs convention, it would be mapped as buckhorn conglomerate. (h) overview of same locality as in g as viewed from east. 140 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the cisco gas field northeast of arches national park is hosted within sandstones of this member. stikes (2006) reported that these sandstones are more porous than the sandstones in the underlying morrison formation. young (1960) referred to these resistant sandstones as the middle cedar mountain sandstone and noted that they form the most continuous marker bed in the cedar mountain formation. these resistant sandstone beds hold up an extensive cliff of lower cedar mountain and upper morrison formation extending across much of east-central utah from the eastern san rafael swell to western colorado. the term poison strip member is only used in the northern paradox basin in grand county, utah, where the yellow cat member separates these strata from the underling morrison formation (figure 11). even in the dewey bridge area (figures 21f and 24a) on the western boundary of the paradox basin, a thin interval of yellow cat member is present below the poison strip member, and farther east in rabbit valley, colorado, the ruby ranch member rests directly on the morrison formation (figure 24b and d). elsewhere in western colorado and southwestern utah, young (1960) recognized the middle sandstone of the cedar mountain formation. our own research has not extended into this region and the extention of the poison strip member in the burro canyon formation remains a decision for future researchers. to the west the poison strip member rests directly upon the morrison formation and, following utah geological survey (ugs) convention, these strata should be referred to as the buckhorn conglomerate member, which we hypothesize are the youngest buckhorn conglomerate strata. shapiro and others (2009; personal communication, 2007) have suggested that the lacustrine units preserving the dinosaur bone shard, bearing oncoids that they described from immediately above the buckhorn conglomerate along the green river cutoff road on the northeastern side of the san rafael swell around the woodside anticline area (39°12'4.43"n,110°22'36.31"w) may be correlative with the poison strip member. stikes (2006) reported that the generally northeasterly trending poison strip channel sandstones contained bedforms characterizing both vertical and lateral accretion (figure 23f) and noted that paradox basin salt tectonics do not appear to have played a role in poison strip depositional patterns, instead, it records an interval of reduced accommodation reflecting low net sedimentation. the lack of accommodation space allowed for fluvial systems to migrate laterally across one level, and stikes (2006) concluded that the poison strip member represented a degradational systems tract controlled more by sevier tectonics from distal areas to the foreland basin. hunt and others (2011) and hunt (2016) have noted that an analysis of detrital zircons indicate that there is an increasing proportion of material derived from the morrison formation in the poison strip member from west to east across the paradox basin. in the few areas in the northern paradox basin where well-indurated sandstone beds are absent, the poison strip member does not cap a steep escarpment and roads cross the outcrop belt at these “paleo-water-gaps” making these the most accessible outcrops of the poison strip and yellow cat members of the cedar mountain formation (kirkland and madsen, 2007). the only way to calibrate the thickness of the poison strip is to trace the crevasse splays and lacustrine limestone beds from areas in the fluvial systems holding up the escarpments on either side of these roads into the outcrops along the roads. a good example of this is in the access point to doelling's bowl on its northeast side (figure 23b). a prominent sandstone channel system forms the south rim of the bowl that can be traced into the base of the interfluvial poison strip member. to the northeast, the poison strip fluvial system can be traced into the top of this interval of interbedded crevasse splays, mudstone, and lacustrine limestones. the interrelationships between large channel systems and their interfluvial deposits occur en echelon over distances of kilometers and are not easily documented. although they are recognized in the field, they are difficult to photographically record at a scale appropriate to this volume. this broadly en echelon pattern of fluvial deposition led several workers to interpret lorrie’s site as having a “yellow cat fauna” extending upward into the ruby ranch member (shaw, 2003; kirkland and others, 2005a; carpenter, 2006; lee, 2014; kinneer and others, 2016). given our earlier interpretations of poison strip deposition, this is a logical conclusion as site dmnh 141 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 24. cedar mountain sections on the east side of the paradox basin. (a) hotel mesa (hm) section measure from 38°49'51.36"n, 109°16'29.82"w up to 38°49'57.95"n, 109°16'28.54"w. omnh v857 is the type locality of brontomerus mcintoshi (taylor and others, 2011); currently the youngest and most eastern described dinosaur in the paradox basin. (b) rabbit valley, colorado, section (rv)measured at 39°11'56.04"n, 109°1'29.16"w about 0.5 km northwest of the trail through time. (c) index map. (d) cedar mountain exposure and approximate line of rabbit valley section. symbols for sections in figure 10. 142 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 2183 occurs on the surface of a poison strip channel sandstone and forms a bench more than 1 km across that vanishes under a road to the west of the site. however, if one stands on the sandstone bench and looks to the west, the poison strip sandstone bed holding up the escarpment there can be traced east and to the north back across the road to a point where it pinches out upslope of site dmnh 2183. thus, this site is mapped as being in the poison strip member (figure 18) on the geological map of the area (doelling and kuehne, 2013a). the poison strip member has little evidence regarding its age beyond biostratigraphy (see flora and fauna section below) and chemostratigraphy. at the ruby ranch road section (figure 11), a u-pb laser ablation age of detrital zircons yields a maximum age of 146 ± 0.49 to 0.47 ma (75% confidence), which is upper jurassic. the two youngest zircons yielded a nearly identical age of 131 ma and a u-pb age from diageneticly enriched uranium in an algal limestone lense a few meters lower (near the base of the poison strip) yielded a maximum age of 119.4 ± 2.6 ma (ludvigson and others, 2010a). chemostratigraphic studies of stable carbon isotopes from pedigenic carbonate nodules suggest the base of the ruby ranch member is approximately 118 ma (ludvigson and others, 2010a, 2015). overall, an early to middle aptian age assignment seems most likely for these strata (see also section on geochemistry). flora and fauna of the poison strip member trace fossils are so abundant and diverse in the poison strip member that they may be considered a defining character of the member. petrified logs and cycads are common in these beds (dayvault and hatch, 2005). unfortunately, most wood specimens do not preserve adequately defined cell structure for specific identification (w.d. tidwell, brigham young university, personal communication, 1997). dinosaurs are less commonly preserved and, unfortunately, these strata have not received the paleontological attention that they deserve. the first dinosaur described from the cedar mountain formation was a large polacanthid ankylosaur from the poison strip member on blm lands on the western side of arches national park. it was originally referred to as cf. hoplitosaurus (bodily, 1969) and subsequently, mistakenly assigned to sauropelta (carpenter and others, 1999). the specimen is characterized by massively constructed and very dense armor (figure 25e to g). the ugs has found another site preserving this same type of armor in the poison strip member well to the east, south of cisco, utah, but excavation of the site has not been undertaken. carpenter’s team (carpenter, 2006; kinneer and others, 2016) has completed the description of gastonia lorriemcwhinneyae from the poison strip member (see above), represented by an extraordinary amount of material, including many partial skulls (kinneer and others, 2016). this material includes numerous examples (figure 25h) of a distinct armor type described as splates (blows, 2001), not known to be so well-developed in any other polacathid ankylosaurs except those in europe and hoplitosaurus marshi from the lakota formation of south dakota. hoplitosaurus preserved a splate so similar to the english, barremian-age polacanthus foxi that pereda-suberbiola (1994) renamed it polacanthus marshi and proposed that polacanthus represented a transatlantic early cretaceous genus. although we do not agree with this synonoymy, perhaps gastonia lorriemcwhinneyae is more closely related to hoplitosaurus than to gastonia burgei and provides a biostratigraphic link to the lakota formation. iguanodontids are relatively common in the poison strip member. dicroce and carpenter (2001) described a partial skeleton of a small iguanodont with a distinctive ilium and no skull as planicoxa venenica. a few years later, gilpen and others (2006) described a larger, even more incomplete iguanodont, cedroestes crichtoni, from nearly the same stratigraphic level about 1 km to the northwest. the genus was based largely on a prominent “antitrochanter” dorsal to the ischial peduncle. this same feature is present, although not so well developed, in the juvenile holotype of planicoxa, and examination of the illia in both specimens indicates than any differences between the specimens can be explained by ontogeny and distortion (figure 25i). thus, cedroestes would be a junior synonym of planicoxa (kirkland and madsen, 2007). a different view has been put forth by mcdonald and others (2010) who proposed that planacoxa was too distorted to represent a valid taxon and 143 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 that of the two, cedrorectes was the valid taxon. the reassignment of camptosaurus depessus from the lakota formation in western south dakota to planicoxa depressus (carpenter and wilson, 2008; carpenter and ishida, 2010) provides another possible biostratigraphic link between the poison strip member and the lakota formation, although this assignment has also been questioned (mcdonald, 2011) in that p. depessus is also too distorted to be taxonomically valid. the titanosauromorph sauropod venenosaurus dicrocei was recovered in tony’s bonebed (figure 25d) with the type of planacoxa (tidwell and others, 2001). this sauropod has been found to be part of the same clade as the spanish brachiosaurid tastavinsaurus and cedarosaurus from the upper yellow cat member (royo-torres and others, 2012, 2014), suggesting a further transatlantic connection. dinosaurs from poison strip member theropoda cf. utahraptor sp. (joe sertich, denver museum nature and science, personal communication, 2016) sauropoda venenosaurus dicrocei tidwell and others (2001) thyreophora gastonia lorriemcwhinneyae kinneer and others (2016) ornithopoda planicoxa venenica dicroce and carpenter (2001) ?cedroestes crichtoni gilpen and others (2006) large steracosternid iguanodontid n. gen. n. sp. (a. scheetz, brigham young university, personal communication, 2014) ruby ranch member the ruby ranch member is present everywhere the cedar mountain formation is recognized and thickens to the west and northwest, probably indicating the earliest development of a foreland basin caused by sevier figure 25. flora and fauna from poison strip member. (a) “conifer” log in the poison strip member on top of the poison strip escarpment with the late brigham young university paleobotanist william d. tidwell for scale. (b) “conifer” log in the vertical cliff of poison strip member on western margin of yellow cat flats with tom mellenthin for scale. (c) bennetalian cycadeoidea weathered out of the top of the poison strip member in the moab area. (d) venenosaurus bones in tony’s bonebed (dmns 2182). photo courtesy of ken carpenter, prehistoric museum (utah state university eastern). (e) massive dorsal osteoderms from bodily’s “hoplitosaurus” site, byu 1072. (f) tail vertebrae from bodily’s “hoplitosaurus” site. (g) caudal plates from bodily’s “hoplitosaurus” site. (g) caudal plates from bodily’s “hoplitosaurus” site. (h) splates from gastonia lorriemcwhinneyae. from lorrie’s site (dmnh 2183) (figure 18). (i) comparison of ilia from a) cedrorectis and b) planocoxa. 144 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 thrust belt in central utah (kirkland and others, 1997, 1998b; currie, 1998; kirkland, 2005a, 2005b; kirkland and madsen, 2007; ludvigson and others, 2010a, 2015) (figures 3, 5, and 6). the type section is just north of the ruby ranch road (figures 11, 15a, and 26), above the massive “calcrete” reported by aubrey (1998; kirkland and others, 1997). the ruby ranch member is lithologically similar to the yellow cat member east of the salt valley anticline, except that carbonate nodules are much more common and cover the ground to such an extent making it difficult to find fossil bone fragments. the carbonate nodules developed in paleosols and ephemeral ponds formed under semiarid conditions. ribbon sandstones representing low-sinuosity rivers are prevalent in this member (kirkland and others, 1997, 1999; kirkland and madsen, 2007). they are very well expressed southwest of green river, utah, between the green river and sr 24 to the west. these ribbon sandstone units form classic geomorphic examples of inverse topography, weathering in relief to cap branching and sinuous ridges that can be traced for kilometers (figure 26e) and are now being employed as an analogue for interpreting similar features on mars (harris, 1980; lorenz and others, 2006; williams and others, 2007, 2011). across most of the northern paradox basin, the ruby ranch member is of rather uniform thickness ranging from 15 to 30 m. a dramatic exception is immediately west of the salt valley anticline, where a thick lacustrine sequence (montgomery, 2014) overlies a major northeast-trending coarse-grained, trough cross-bedded sandstone interpreted to represent a braided, low-sinuosity river channel overlying an otherwise typical sequence of ruby ranch member for this region (figure 11). this large ribbon sandstone has been nicknamed the “klondike river” and it was originally mapped as the basal unit of the “dakota formation” (doelling, 1985). the thick lacustrine section has been nicknamed “lake carpenter” as carpenter (prehitoric museum, utah state university eastern, verbal communication, 2008) reported on the presence of a thick lacustrine sequence in the “dakota formation” on the east side of arches national park. upon examination of the section, we determined it was overlain by a quartzite pebble conglomerate typical of the basal naturita formation (= dakota formation). the recent geological map for the klondike bluffs 7.5-minute quadrangle incorporates this change (doelling and kuehne, 2013a). this distinctive sequence will be examined in detail on the afternoon of day 1. across the the northern part of the paradox basin, these strata are a rather monotonous sequence of purplish-gray mudstone with abundant carbonate nodules. studies have revealed an impressive amount of diagenetic complexity to these carbonates reflecting their formation in a variety of floodplain environments (ludvigson and others, 2010a, 2015). where the naturita formation (= dakota formation) directly overlies the ruby ranch member east of the san rafael swell, several meters at the top of the member may be bleached to a pale green color, such that it may appear superficially to represent the mussentuchit member. the abundance of carbonate nodules in this interval provides evidence that this is not the case. the ruby ranch member thickens across the san rafael swell, as well as from south to north along its western side (kirshbaum and schenk, 2011). the thickest section measured by kirkland was on the the north end of the san rafael swell to the east of where the price river crosses the cedar mountain outcrop belt (figure 27). the ruby ranch member at the price river section rests upon approximately 18 m of buckhorn conglomerate member and ranges from approximately 100 to 160 m thick, depending on how much of an overlying mussentuchit member is recognized below the naturita formation (= dakota formation). at approximately 94 m above the buckhorn, there is a major complex of multitiered calcrete 6 to 8 m thick. that had been previously interpreted as aubrey’s (1998) marker calcrete in a number of publications (kirkland and others, 1997; burton and others, 2006). this calcrete caps a distinctive red bed interval that could represent a north american aridification event that may have peaked about 114 to 113 ma (al-suwaidi, 2007; ludvigson and others, 2015; also see the geochemistry section below). stratigraphically above this interval, the mudstone becomes significantly more smectitic and was initially thought to represent the mussentuchit member of the cedar mountain formation (carpenter and others, 2001, 2008; kirkland and madsen, 2007; ludvigson and others, 2010a). how145 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 ever, this interval preserves abundant small carbonate nodules that characterize the top of the ruby ranch member in its thicker section along the western side of the san rafael swell. we think it represents a transition zone below the sequence boundary separating the mussentuchit member from the ruby ranch member as discussed more fully below. it is worth noting that this has not been the first misinterpretation of these strata. the pr1 sandstone bed in or near the top of the ruby ranch member yielded a partial cf. tenontosaurus from the price river i quarry (utah em271v). that bed was mistakenly identified as the poison strip member (kirkland and others, 1997), largely due to the red mudstone interval underlying the calcrete interval in this area identified as marking the top of the morrison formation (figure 27). burton and others (2006) published four maximum u-pb ages from detrital zircons in the upper part of the price river section (figure 27) by the price river ii quarry (utah em372), carbon county, utah. they logged these dated samples relative to their placement above the morrison formation, which were picked at the top of the price river calcrete. these maximum detrital zircon ages are 114 ma at 1.6 m, 116 ma at 14 m, 113 ma at 15 m, and 109 ma at 40 m. the maximum age of the lowest sample may fit the chemostratigraphy (see geochemistry section below) of the interval just below the calcrete. the overlying two zircon samples would represent the “younger” upper ruby ranch transitionary facies. the maximum age of the highest sample may be correlative with the transitionary facies or even the mussentuchit member; however, the dates seem to be too old for these strata given that these are maximum ages and is inconsistent with reported ages elsewhere. overall, based on zircon ages and chemostratigraphic studies, the ruby ranch member ranges in age from approximately middle aptian to middle albian (about 118 to 105 ma) for the western paradox basin and northern san rafael swell. other radiometric ages indicate the presence of upper albian strata as well (chure and others, 2010; ludvigson and others, 2010a, 2015; sprinkel and others, 2012). note that some workers had assumed the base of the cedar mountain formation should always be marked by a calcrete (see aubrey, 1998; burton and others, 2006; roca and nadon, 2007). it was also assumed by kirkland and others (1997, 1999) and (kirkland and madsen, 2007) that the first prominent conglomerate encountered going down section through the ruby ranch member around the san rafael swell must be the buckhorn conglomerate. however, a prominent discontinuous conglomerate is present at many places in the middle of the ruby ranch member unrelated to the buckhorn conglomerate. this was the case in the mussentuchit wash area as well (doelling and others, 2009; h. doelling, utah geological survey [retired] verbal communication 2010). because of this revelation, the ruby ranch member was found to be as much as twice as thick as previously assumed, although this had no effect on our definition of the type section of the mussentuchit member. an additional case is kirkland and others (1997, 1999, figure 20) analysis of the section at the carol site (type locality for eolambia) east of castle dale, utah, where a laterally extensive conglomeratic channel sandstone in the medial ruby ranch member was mistaken for the buckhorn conglomerate member. it has recently become apparent that utilizing the simple presence of smectitic mudstones overlying ilitic mudstones is not sufficient to identify the contact between the ruby ranch and mussentuchit members of the cedar mountain formation because the two members are separated by a sequence boundary (kirkland and others, 1999; kirkland and madsen, 2007; sprinkel and others, 2012). the mussentuchit member is often lignitic with plant debris and does not preserve carbonate nodules. we have noted that there seems to be less than a meter of smectitic, carbonate nodule-bearing strata below the base of the mussentuchit member in its type area around mussentuchit wash on the southwestern margin of the san rafael swell. this interval thickens to the north as the ruby ranch correspondingly thickens. where radiometrically dated, these strata are albian in age and may reflect an interval of wetter climatic conditions as the skull creek-thermopolis seaway expanded toward northeastern utah and into central colorado. this transgression occured during the late albian based on three high-precision u-pb ages of 103.8, 103.9, and 104.6 ma ± 0.04 ma, respectively, from volcanic ash beds in the plainview formation at fossil ridge along 146 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 26. caption on following page. 147 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the front range escarpment west of denver. sam bartlett (friends of dinosaur ridge), kirk johnson (smithsonian institution [formerly the denver museum of nature and science]), and sam bowring (massachusetts institute of technology [mit]) collected the ash beds. the age analysis was done at mit by robert buchwaldt and sam bowring as part of the earthtime initiative. unfortunately, these dates have only been published in a short article in the friends of dinosaur ridge newsletter (annonymous, 2009). these “transitional facies” also cap the cedar mountain formation to the southeast of capitol reef national park and in northeastern utah where they were also referred to as mussentuchit member (kirkland and madsen, 2007; chure and others, 2010; ludvigson and others, 2015). unfortunately, these transitional facies were mapped as mussentuchit member on the fruita 7.5-minute quadrangle (mclelland and others, 2007). the abundant carbonate nodules in the ruby ranch member have been the subject of a number of diagenetic studies and are providing a source of primary pedogenic carbonate that is being utilized for stable carbon and oxygen isotope studies. these are, in turn, being applied to early cretaceous paleoclimatologic and paleohydrographic studies, and the chronology is discussed in geochemistry studies. what is most pertinent here is the developing utility of stable isotope geochemistry in forming a basis for chronostratigraphic correlations within the aptian-albian time interval (smith and others, 2001; sorenson and others, 2002; ludvigson and others, 2002, 2003a, 2003b, 2004, 2006; kirkland and others, 2003; ludvigson and others, 2010a, 2015). the correlation of stable carbon isotope curves with those of marine reference sections (figure 28) suggests the ruby ranch ranges in age from approximately middle aptian to middle albian (about 118 to 105 ma) for the western paradox basin and northern san rafael swell; however, the radiometric ages from the ruby ranch member in northeastern utah indicate the presence of upper albian strata as well (chure and others, 2010; sprinkel and others 2012; ludvigson and others, 2015). ruby ranch fauna(s) given the extent of ruby ranch exposures across east-central utah, it would seem logical that these strata would have yielded the bulk of fossils from the cedar mountain formation; however, this is not the case. the vast abundance of fragmented carbonate nodules and sandstone covering the slopes makes prospecting for bone fragments and microvertebrates difficult. additionally, even where fossils are found to be plentiful, carbonate encrustation may make excavation and preparation difficult as with the long walk quarry (umnh 0002) (decourten, 1991; kirkland and others, 1997). regardless, numerous localities are being found throughout the ruby ranch outcrop belt with new excavations, and preparations are ongoing. the following discussion is divided into a section of the lower (aptian) ruby ranch fauna and a section on the upper (albian) ruby ranch fauna, although potentially more faunal levels are present or a continuity between the currently recognized aptian-albian faunas may be distinguished in the future. dinosaurs from the ruby ranch member are distinct from those identified in the underlying members of the cedar mountain formation. there are no polacanthid ankylosaurs, steracosternid iguanodontids, and sauropods with thick spatulate teeth; instead nodosaurid ankylosaurs, basal iguanodontian tenontosaurs (opportunists?), and slender toothed titanosauriform saufigure 26 (figure on previous page). ruby ranch member. (a) ruby ranch road section (rr) includes type ruby ranch member measured from 38°51'15.12"n, 109°59'16.24"w, 38°51'18.49"n, 109°59'8.85"w via three segments in b. radiometric dates from ludvigson and others (2010a). (b) overview of ruby ranch section from ridge to southwest; al = cherty algal limestone near top of the yellow cat member. (c) easily accessible ruby ranch section exposed on west end of green river cutoff road on northeastern side of san rafael swell about half way between green river, utah, and the price river sites. oncolitic carbonate described by shapiro and others (2009); (39°12'4.43"n, 110°22'36.31"w). (d) typical exposure of ruby ranch member with abundant pedogenetic carbonates in situ and covering slope at top. lower portion of section in c. (e) exhumed ruby ranch sinuous paleo-channel (ribbon sandstone) southwest of green river, utah. photo courtesy of rebecca m.e. williams of the planetary science institute. 148 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 27. caption on following page. 149 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 28. temporal correlation of price river and ruby ranch sections based on the correlation of high-resolution aptian-albian chronostratigraphy and c-isotope stratigraphy from the vocontian basin of southeast france (herrle and others, 2004) with the c-isotope chemostratigraphy of the cedar mountain formation at the price river (pr, figure 27) and ruby ranch road (rr, figure 26) sections, with the radiometric dates that constrain the chronostratigraphy of the cedar mountain formation at ruby ranch road and price river. the curve of herrle and others (2004) is a ten-point moving average. absolute ages in the left panel are from leckie and others (2002). modified from ludvigson and others (2010a). figure 27 (figure on previous page). cedar mountain formation on the north end of the san rafael swell in the price river area. (a) price river section (pr) as updated from carpenter and others (2001) and ludvigson and others (2010a, 2015); section measure in several steps between 39°25'25.45"n, 110°37'14.11"w and 39°26'21.44"n, 110°37'7.54"w"; abbreviations: mss = middle ruby ranch sandstone that is a useful marker bed in area, pr1 = laterally extensive sandstone bench hosting the pr-1 cf. tennontosaurus locality (utah em 352) high or perhaps at the top of the ruby ranch member. prc = price river calcrete marker bed high in the ruby ranch member (ali-suwadi, 2007). (b) pr-2 quarry (utah em372). (c) overview of pr-2 quarry to show track-bearing sandstone lense overlying price river marker calcrete below locality. (d) price river marker calcrete beds. (e) view to north toward ceu vertebrate localities along approximate line of measured section. (f) buckhorn conglomerate at base of section. 150 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 ropods replace them (kirkland and others, 1997, 1998b, 1999; kirkland and madsen, 2007). instead of this faunal change occurring at the end of the barremian, as previously thought, it apparently occurred sometime during the aptian and may reflect biological processes occurring across the northern hemisphere during the aptian (kirkland and others, 2013, 2015). the university of utah’s long walk quarry near the base of the ruby ranch member on the west side of the san rafael swell was the first ruby ranch locality to be extensively excavated, but given the difficulty in excavating the carbonate hosted bones, excavation ended in the early 1990s even though the site was donated to the natural history museum of utah (decourten, 1991; kirkland and others, 1997). numerous specimens were collected and bone preservation is excellent with an abundance of sauropod elements and a large allosaurid noted among the material (figure 29). the denver museum of nature and science has taken the lead on the difficult preparation and research on this important collection. mori (2009) averaged three different, somewhat discordant, u-pb ages from three detrital zircon sites and calculated an overall maximum age of 115 ma for the lower 35 m of the cedar mountain section at the long walk quarry. kirkland was alerted to an illegal dinosaur excavation on the east side of the colorado river at hotel mesa (figure 24a) in the mid-1990s. preliminary investigation revealed that the site was low in the ruby ranch member and that there was a significant amount of sauropod material with a fair amount of small bone (theropod claws and crocodilian teeth). the site was turned over to the oklahoma museum of natural history, who are investigating microvertebrate fossils in the cedar mountain formation. the site was visited over a three-day weekend to collect the exposed bones and the matrix for screenwashing, and to backfill the site. given that the sandstone matrix would not break down, figure 29. aptian dinosaurs from lower ruby ranch member. (a) iguanodont jaw fragment from east of arches national park. (b) allosauroid tooth from long walk quarry (umnh 0002). (c) slender titanosauriform sauropod teeth from long walk quarry. (d) holotype juvenile brontomirus ilium (omnh 66430) from hotel mesa site (omnh v857). (e) adult sauropod scapula assigned to brontomirus. (f) cervical spines from cf. sauropelta. 151 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the site was not reopened; however, the bones that were collected were from a mix of juvenile and adult sauropods that includes unique diagnostic characters, which became the basis for the sauropod brontomirus mcintoshi (taylor and others, 2011) (figure 29). the site also preserved hybodontid sharks, lungfish tooth plates, unidentified bits of boney fishes, a variety of aguatic crocodilian teeth, and small theropod material. it is hoped that this interesting site will be reopened and researched further someday. the denver museum of nature and science has found a number of sites in the ruby ranch member in the northern paradox basin that yielded parts of basal iguanodontians best referred to cf. tenontosaurus until further research is carried out. one site, south of green river, utah (dmnh 2840), yielded an incomplete large nodosaurid (warren and carpenter, 2004) that was within 10 m of the underlying poison strip member and appears to be similar to sauropelta (ostrom, 1970; carpenter and kirkland, 1998) from the cloverly formation (figure 29). finally, carpenter (prehistoric museum, verbal communication, 2001) randomly picked up a carbonate nodule north of the ugs’s doelling’s bowl site and recognized that it encased a complete eilinodontid sphenodontian skull, further emphasizing the potential for important discoveries in these aptian strata. fauna from the lower ruby ranch member chondrichthyes indet. hybodontid (taylor and others, 2011) ?polyacrodus sp. (taylor and others, 2011) osteichthyes indet. (taylor and others, 2011) indet. gar (taylor and others, 2011) dipnoi ceratodus sp. (taylor and others, 2011) chelonia unidentified rhynchocephalia eilenodontid, cf. toxolophosaurus sp. crocodylia gen. et sp. indet. (taylor and others, 2011) bernissartia sp. (taylor and others, 2011) indet. goniopholid (taylor and others, 2011) indet. atopoaurid (taylor and others, 2011) dinosauria theropoda indet. small theropod (taylor and others, 2011) large allosauroid sauropoda brontomerus mcintoshi taylor and others (2011) thyreophora cf. sauropelta sp. (warren and carpenter, 2004) ornithopoda cf. tenontosaurus sp. the fauna from the albian strata at the top of the ruby ranch is best documented at the price river quarries (figures 27 and 30) which have been excavated since the 1990s (kirkland and others, 1997, 1999; carpenter and others, 2001, 2008). the only dinosaurs described to date are ankylosaurs, including a gigantic nodosaurine nodosaurid peloroplites cedrimontanus (figure 30f) that is perhaps related to sauropelta (carpenter and others, 2008). a more surprising discovery is the long-skulled basal ankylosaur cedarpelta bilbyhallorum (carpenter and others, 2001, 2008). the first specimens of this taxon were identified by two large, juvenile disarticulated skulls with associated postcranial skeletal elements from the kem site across the valley from the larger pr-2 quarry. it most obviously groups with shamasaurine grade ankylosaurids because it has short distal limb elements, straight ischia, skull texture, and because it closes off the lower temporal opening in lateral view (figure 30d and e). in phylogenetic analyses, cedarpelta variably forms a clade with nodosaurids (vickyarous and others, 2004) or ankylosaurids (thompson and others, 2011; arbour and currie, 2015) reflecting its potential significance in phylogenerics and paleobiogeography. much larger diagnostic post-cranial elements of cedarpelta from the pr-2 quarry indicates that cedarpelta reach the same large size as peloroplites 152 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 30. dinosaur fossils from the ruby ranch member. (a) proximal caudal vertebrae and chevrons from cf. tennontosaurus pr-1 (utah em352v). (b) teeth from cf. tennontosaurus pr-1 (utah em352v). c) teeth from cf. tennontosaurus from upper ruby ranch transitional facies just east of capitol reef national park (utah wn). (d) type partial juvenile skull of cedarpelta in dorsal view from the kem site (utah em419v) in the upper ruby ranch member at same horizon but across the valley from main price river quarries (figure 27). (e) same partial holotype skull of cedarpelta in lateral view. (f) peloroplites mounted skeleton in the utah state university eastern’s prehistoric museum in price, utah. (g) prehistoric museum’s exhibit of cedar mountain ankylosaur skulls; a) peloroplites, b) cedarpelta, and c) gastonia. (h) holotype skull of abydosaurus from upper ruby ranch transitional facies at dinosaur national monument (dnm 16). (i) articulated of mired brachiosaurid sauropods from pr-2 (utah em272); a) forefoot, b) hind foot. (j) brachiosaurid sauropod femurs from pr-2 (utah em272). (k) additional brachiosaurid sauropod femurs from pr-2 (utah em272) including from back to front: dorsal vertebrae, cervical vertebrae, and metatarsals. 153 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 (kirkland and madsen, 2007; carpenter and others, 2008). with multiple individuals of both taxa preserved at these correlative sites, it raises the question as to how these two gigantic ankylosaurs were nitch partitioning the same habitat? sauropods (figure 30i to k) are the dominant taxa at pr-2 and are represented by at least two taxa (r. barrick, former director of prehistoric museum, personal communication, 2000; k. carpenter, prehistoric museum, personal communication, 2016; and m. taylor, university college london, personal communication, 2016). the site has also produced some ornithopod material and an indeterminant pterosaur phalanx. a limited amount of large allosauroid theropod material has been collected in these sites as well. a large tooth from pr-3 (utah em273) has extremely fine serrations for a tooth that size and seems to be closest to the older genus acrocanthosaurus (currie and carpenter, 2000). in northeastern utah, a sauropod bonebed in the cedar mountain formation near the carnegie quarry at dinosaur national monument (dnm 16) has been dated to a maximum of 104 ma (chure and others, 2010). this site has yielded four sauropod skulls of abydosaurus mcintoshi (chure and others, 2010), and part of a dromaeosaurid skeleton (chure and others, 2007). to the north across dnm, the ugs collected a scrappy ornithopod skeleton (utah un153v) that is best referred to cf. tenontosaurus. another partial skeleton referable to cf. tenontosaurus (figure 30a and b) was collected from the pr-1 site (utah em352v) up section from the price river sites discussed above. additional ornithopod partial skeletons tentatively assigned to cf. tenontosaurus have been collected by ugs and oklahoma museum of natural history (omnh) crews from ruby ranch transitional facies in the area east of capitol reef national park. ludvigson and others (2015) published a u-pb zircon age of 103.7 ± 2.6 ma obtained from a volcanic ash (preserved within dinosaur tracks) underlying a particularly interesting lacustrine facies near muddy creek that preserves snail opercula, fragments of bony fish, and turtles. the site has also yielded a partial titanosauriform sauropod femur and parts of an allosauroid theropod skeleton that had mostly eroded away (judd and others, 2013). it is important to note that all of the isolated sauropod teeth found in the ruby ranch are slender, spatulate-teeth and may represent several species, often referred to as astrodon or pleurocoelus (kirkland and others, 1998b; chure 2000; coulson and others, 2004; bird, 2005; chure and others, 2006, 2010). fauna from the upper ruby ranch member osteichthyes indet. bones and teeth chelonia unidentified crocodilia aquatic goniopholid crocodilians pterosauria pterosaur indet. (reese barrick, prehistoric museum, personal communication, 2000) dinosauria theropoda cf. deinonychus (chure and others, 2007) large allosauroid cf. acrocanthosaurus based on minute tooth serrations large allosauroid with short neural spines (judd and others, 2013) sauropoda abydosaurus mcintoshi chure and others (2010) at least one maybe two additional taxa (carpenter and others, personal communication, 2016) thyreophora cedarpelta bilbyhallorum carpenter and others (2001) peloroplites cedrimontanus carpenter and others (2008) ornithopoda cf. tenontosaurus sp. similar dinosaur faunas are known across much of north america, suggesting these rocks formed 115 to 101 ma when flowering plants first radiated and came to dominate the world’s floras (kirkland and others, 154 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 1998b). the ruby ranch dinosaur assemblage includes several taxa known only from north america at this time (slender toothed brachiosaurs, tenontosaurus, and large nodosaurid ankylosaurs). this suggests isolation of north america from the rest of the world as the result of rising sea levels flooding europe prior to the development of the alaskan land bridge connecting north america and asia and as sea levels flood the dawson straights in western canada in the late albian (plafker and berg, 1994; cifelli and muzion, 1997; kirkland and others, 2015; brikiatis, 2016). the apparent low diversity of dinosaurs across all of north america during this time interval lends further support to the concept of north america as an island continent during the late early cretaceous following a middle aptian extinction event that resulted in the loss of spatulate-toothed sauropods, polacanthid ankylosaurs, and steracosternid iguanodontids (kirkland and others, 1997, 1998b, 1999, 2013, 2015; kirkland and madsen, 2007). short canyon member separating the ruby ranch member from the overlying mussentuchit member north of i-70 on the western side san rafael swell is a discontinuous series of pebble to cobble conglomerates. these conglomerates were referred to as the “moore road conglomerate” by kirkland and madsen (2007), but has recently been named the short canyon member as an informal member of the cedar mountain formation (doelling and kuehne, 2013b). they designated a type section north of short canyon at about 38°58'50.68"n, 111°2'13.70"w. doelling and kuehne (2013b) found that the short canyon member consisted of up to three conglomerate beds separated by slope-forming sandstone and locally gray to black carbonaceous (and possibly coaly) shale and was best developed near short canyon on the northern end of the short canyon 7.5-minute quadrangle. thickness ranges from 12 to 32 m, thickening at the expense of both the ruby ranch and mussentuchit members. this bed is as distinctive as the underlying buckhorn conglomerate with which it is often confused (kirkland and others 1997; kirkland and madsen, 2007). the buckhorn conglomerate is also discontinuous in this area and, where present, lacks the distinctive quartzite clasts. the presence of these quartzite-bearing conglomerate beds have been used as a marker for the base of the naturita formation (= dakota formation) (lawton and others, 1997, 2007, 2010) and they are a characteristic of the coarse-grained units of the third detrital zircon chronofacies (figure 6) of hunt and others (2011). in fact, the presence of white, “sugary-looking” quartzite pebbles and cobbles are characteristic of the conglomerates (figure 31). the clasts are derived from the initial unroofing of ordovician eureka quartzite in the sevier thrust belt and separates the basal upper cretaceous from the underlying uppermost lower cretaceaus strata of the ruby ranch member (lawton and others, 1997, 2007, 2010; hunt and others, 2011). a quartzite-rich conglomerate of this same type overlies the lower cretaceous (albian) san pitch formation in the sevier thrust belt foredeep in central utah marking the base of the upper cretaceous (sprinkel and others, 1999). at present no fossils of any kind have been recognized from the short canyon member other than paleozoic invertebrates preserved within chert cobbles. mussentuchit member the mussentuchit member forms the top of the cedar mountain formation and is only present along the west side of the san rafael swell (figures 4, 5, and 6). in its type area (figure 32) on the southwest side of the san rafael swell in the mussentuchit wash area, it is separated from the underlying ruby ranch member by a black chert-pebble lag (kirkland and others, 1999; kirkland and madsen, 2007). in the area of the moore cutoff road in the central portion of the western san rafael swell, it is separated by a cobble conglomerate as much as 5 m thick and characterized by abundant quartzite clasts, and informally designated the short canyon member of the cedar mountain formation (doelling and kuehne, 2013b). the upper contact of the mussentuchit member, and the ruby ranch member to the east, is overlain by the naturita formation (= dakota formation). where the naturita has been removed by late cretaceous erosion, the base of the tununk member of the mancos shale includes a darkly stained chert and quartzite pebble lag mixed with shallow, open-marine oysters (pycnodonte newberryi subundata) characteristic of the basal turo155 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 nian (kirkland, 1996; leckie and others, 1997; kirkland and madsen, 2007). these marine conglomeratic units also cap the naturita formation (= dakota formation) in this area, indicating that as sea level rose in the latest cenomanian, uplift along the general trend of the san rafael swell exceeded sea level rise with subsequent coastal erosion through to the basal naturita conglomerate, which continued to be reworked across the area by storm waves even after the sea had submerged the area (eaton and others, 1990; kirkland and madsen, 2007). the mussentuchit member is characteristically distinguished by the abundance of smectitic clays (altered volcanic ash) in its mudstone beds, a near absence of carbonate nodules, and the local presence of lignite (lowgrade coal) beds (kirkland and others, 1997, 1999). locally, the smectite is so pure that these swelling clays are mined for this industrial material. a radiometric age of 98.37 ± 0.07 ma was obtained by the omnh from volcanic ash within the mussentuchit member (cifelli and others, 1997, 1999). additional ages by garrison and others (2007) ranging from 96.7 ± 0.5 to 98.2 ±0.6 ma indicate that the mussentuchit member was deposited over an interval of 1.5 ma during the early cenomanian and supports a correlation with the siliceous marine mowry shale to the north, which is well-constrained from 40ar/39ar sanidine ages obtained from bentonite beds that bracket the mowry in wyoming; the basal arrow creek bentonite is 98.5 ± 0.5 ma and the capping clay spur bentonite is 97.2 ± 0.7 ma (obradovich, 1993; ogg and hinnov, 2012; sprinkel and others, 2012) near the base of the upper cretaceous. where radiometrically dated, isolated outcrops of smectitic strata mapped by ugs geologists as cedar mountain formation in southwestern utah (figure 1) are all of latest albian to earliest cenomanian age (biek and others, 2009, 2010, 2015; hylland, 2010). therefore, these strata correlate to the mussentuchit member, which they most closely resemble lithologically. in addition to being a basal mudstone unit restricted to the foreland basin, the mussentuchit member represents the terrestrial strata equivalent to the basal cenomanian muddy-mowry marine cycle (ludvigson and others, 2010b) and is equivalent to the wayans formation in the foredeep of eastern idaho (krumenacker, 2010; krumenacker and others, 2016). this member is also equivalent to fossiliferous strata occurring in piggyback basins within the sevier thrust belt. the willow tank formation at valley of fire state park in southern nevada preserves a dinosaur fauna that may include eolambia (bonde and others, 2008, 2012). recently acquired high-precision u-pb zircon ages obtained from the middle carbonaceous interval of the naturita formation (= dakota formation) at the pafigure 31. quartzite-rich conglomerate beds forming the base of the upper cedar mountain chronofacies 3 of hunt and others (2011); the muddy-mowry sequence of ludvigson and others (2010b). (a) the basal naturita conglomerate on the poison strip bench east of doelling’s bowl. note the “snowy” white eureka quartize pebble near center of picture. (b) the short canyon member on the south side of the moore cutoff road with an abundance of eureka quartzite pebbles. 156 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 32. caption on following page. 157 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 leobotanical sites near westwater in eastern utah range from 97.95 +0.037 -0.12 ma to 97.601 +0.049 -0.13 ma and overlap with those from the mussentuchit. whereas, ages obtained from the middle carbonaceous interval of the naturita formation (= dakota formation) from the eastern kaiparowits basin in southern utah are younger than the mussentuchit ages (barclay and others, 2015). this once again validates young’s (1960) theories regarding the west to east transition from more inland to more coastal facies along time lines (marker sandstones) or as currently viewed within sequence stratigraphic architecture. it is difficult for some geologists to reason why the mussentuchit member in its type area was separated from the underlying ruby ranch member. were it not for the pebble lag at the base of the mussentuchit, indicating the position of a sequence boundary, many of our colleagues would not have accepted it as being worthy of separation. north of i-70 along the moore cutoff road, the short canyon member makes the break obvious (doelling and kuehne, 2013b). this unit pinches out to the north, reappears, and pinches out again. it is not until the outcrop reaches the latitude of castle dale and the cleveland lloyd quarry that the conglomerate becomes continuous and part of the naturita formation proper (= dakota formation). there is still a proper smectitic mudstone interval that is characteristic of the mussentuchit member up section from the basal naturita conglomerate in this area (kirshbaum and schenk, 2011; sorenson, 2011). clearly, the musentuchit interfingers into the naturita (= dakota) to the north. this pattern has led geologists working on the naturita formation (= dakota formation) to look at these strata from the top down, while the geologists working on the cedar mountain formation look at these strata from the bottom up. the solution to this is to consider the mussentuchit as a member of the cedar mountain formation in the south and to be a member of the naturita formation (= dakota formation) in the north, in much the same way that the smoky hill is a member of the niobrara chalk on the great plains, but is considered to be a member of the mancos shale in western colorado (hattin, 1982; leckie and others, 1997). flora and fauna of the mussentuchit member the mussentuchit member has yielded significant paleobotanical materials. these materials include a diversity of unique fossil wood taxa including what had been interpreted as some of the oldest known angiosperm wood (thayne and others, 1983, 1985; thayne and tidwell, 1984; tidwell and thayne, 1985; tidwell, 1996). the only palynomorph assemblages described from the cedar mountain formation are from these rocks and were considered to indicate an albian age (tschudy and others, 1984; garrison and others, 2007) prior to the lower placement of the albian-cenomanian boundary based on ammonite correlations with the type cenomanian in europe (cobban and kennedy, 1989; nichols and sweet, 1993; ogg and hinnov, 2012). however, one recent paper (arens and harris, 2015) on an angiosperm-dominated flora from the northeastern side of the san rafael swell almost certainly pertains to the overlying naturita formation (= dakota formation) and not the cedar mountain formation (mike leschin, blm geologist, personal communication, 2015). the omnh have been using wet screen-washing techniques (cifelli, 1996; cifelli and others, 1997, 1999) to recover tiny fossil mammal remains from microvertebrate sites in the mussentuchit member (figure 33). most of these sites are in the type area of the mussentuchit member on the southwest side of the san rafael swell. other researchers have conducted less ambitious figure 32 (figure on previous page). mussentuchit member of the cedar mountain formation in the mussentuchit wash area. (a) revised type section (mw) reflecting the thicker ruby ranch member measured from 38°39'46.47"n, 111°15'31.31"w to 38°39'47.66"n, 111°15'39.66"w. (b) type section of the mussentuchit member on the south side of mussentuchit wash viewed from the south. (c) well exposed section of the cedar mountain formation along the last chance monocline viewed from the west (38°39'32.73"n, 111°17'52.72"w). (d) well-exposed section of the mussentuchit member in mussentuchit wash. (e) looking south across mussentuchit wash with yellow dashes indicating the ruby ranch-mussentuchit contact and the red dashes indicating the position of the naturita formation which pinches out locally in this area. (f) index map showing the location of the mussentuchit wash area. 158 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 screen washing programs to the north in the mussentuchit east of ferron and castle dale (nelson and crooks, 1987; eaton, 1987; fiorillo, 1999). by sorting the bone residues generated in this way, more than 90 species have been recognized (cifelli and others, 1997, 1999;) including a diversity of fish (kirkland and others, 1997, 2013b; fiorillo, 1999; garrison and others, 2007), frogs (cifelli and others, 1997; gardner and demar, 2013), albanerpetonids (gardner, 1999), salamanders (gardner and demar, 2013), turtles (cifelli and others, 1997; fiorillo, 1999; herzog and others, 2015), lizards (cifelli and nydam, 1995; nydam, 1999, 2000, 2002, 2013), some of the oldest north american snakes (gardner and cifelli, 1999), crocodilians (cifelli and others, 1997; fiorillo, 1999; garrison and others, 2007), bird teeth (cifelli and others, 1997), and mammals (eaton and nelson, 1991; cifelli and muizon, 1997; cifelli and madsen, 1998, 1999; eaton and cifelli, 2001; cifelli and others, 2016), including the world’s oldest and most primitive marsupials (cifelli, 1993, 2004; cifelli and muizon, 1997). this is one of the most diverse terrestrial faunas in the mesozoic of north america (eaton and kirkland, 2003) with 22 species of mammals alone (cifelli and others, 2016). additionally, no other fauna of this age has ever been found anywhere else in the world. a wealth of dinosaur teeth have also been recovered with ornithischia represented by ankylosaurid and nodosaurid ankylosaurs, several ornithopod taxa (a new small species, tenontosaurus, and eolambia), dome-headed pachycephalosaurs, and primitive horned dinosaurs (cifelli and others, 1997, 1999; kirkland and others, 1997; chinnery and others, 1998; kirkland and others, 1998b). tiny, slender brachiosaurid sauropod teeth (figure 33g) represent the last known sauropods in north america until the titanosaurid alamosaurus appeared more than 30 million years later in the north horn formation as an immigrant back into north america (maxwell and cifelli, 2000; kirkland and madsen, 2007). meat-eating dinosaur teeth are diverse and abundant, including primitive coelurosaurs, troodontids, dromaeosaurine and velociraptorine dromaeosaurids, and north america’s earliest known tyrannosaufigure 33. oklahoma museum of natural history’s microvertebrate project. (a) omnh’s screen-washing station. (b) teeth of the freshwater pavement toothed guitarfish cristomylus nelson. (c) tyrannosaurioid teeth, smallest tooth is a diagnostic premaxillary tooth. (d) jaw of early marsupial kokopellia juddi courtesy of rich cifelli (omnh). (e) neoceratopsian tooth. (f) nodosaurid tooth, perhaps animantarx. (g) small slender-toothed brachiosaurid sauropod tooth. tick marks are in mm. 159 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 rids (figure 33c). suarez and others (2012) obtained abundant stable isotope data from these microvertebrate sites (see geochemistry section below). only two dinosaur species from the mussentuchit member are so far represented by relatively complete skeletons (holotypes now housed in the collections of the utah state university eastern’s prehistoric museum in price, utah) (figure 34). they are named for a husband/wife team of amateur paleontologists from castle dale, utah. the advanced iguanodont ornithopod eolambia caroljonesa (kirkland, 1998b; head, 2001; mcdonald and others, 2012a) was named for carol jones, figure 34. dinosaurs from mussentuchit member of the cedar mountain formation. (a) jaws of holotype eolambia caroljonesa from carol site, northwestern san rafael swell in ceu collection, a) left maxilla, b) right dentary. (b) juvenile eolambia from mussentuchit area, southwestern san rafael swell in omnh collection, a) left squamosal, b) right premaxilla, c) left dentary. (c) adult eolambia manual unguals from cifelli i site (= eolambia 1 site), mussentuchit area in ceu collection, a) “thumb-spike,” b) typical manual ungual. (d) holotype dorsal vertebra of the large neoventorid allosauroid siats meekerorum in collection of the chicago field museum of natural history. photo courtesy of lindsay zanno (north carolina museum of natural history). (e–i) holotype of animantarx ramaljonesi from carol site, northwestern san rafael swell in ceu collection. (e) postcranial skeleton (f) dorsal view of partial skull. (g) lower jaw. (h) ventral view of partial skull. (i) reconstructed skeleton on exhibit at utah state university eastern’s prehistoric museum constructed by gastondesign. 160 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 who discovered the carol site east of castle dale. the late university of utah radiological technician ramal jones discovered the skeleton of the primitive nodosaurid ankylosaur, animantarx ramaljonesi (carpenter and others, 1999), as part of a highly refined radiological survey made of the carol site (jones and burge, 1998). this is the only dinosaur ever discovered by technology alone. fragments of a large neovenatorid allosauroid, siats meekerorum (figure 34d), have recently been described by zanno and makovicky (2013). dinosaur eggshell is fairly common in the mussentuchit member and includes some of the first fossil eggshell material recognized in north america (jensen, 1970; bray, 1998). botetuoolithus carlyensis was reassigned to the oogenus macroelongolithus (zelenitsky and others, 2000), which has subsequently been shown to represent the eggshell of the huge (10 m) asian caenegnathid oviraptoroid gigantoraptor (paul, 2010, p. 153). recently, makovicky and others (2014) have recovered skeletal remains verifing the presence of a giant caenegnathid oviraptoroid nearly as large as gigantoraptor in the mussentuchit member as indicated by the fossil eggshell. the mussentuchit fauna is particularly interesting in that it is the oldest dinosaur fauna with representatives of each family characteristic of the remainder of the late cretaceous in north america (cifelli and others, 1997), in addition to preserving a few last examples of early cretaceous dinosaurs (basal titanosaurimorph sauropods and cf. tenontosaurus). the direct ancestors of the tyrannosaurids, the derived hadrosauroid iguanodont eolambia, and the marsupials have asian affinities. therefore, their presence in the basal cenomanian of utah suggests that these rocks document the first immigration of animals across the alaskan land bridge. this event may have led to an immigration-induced extinction of many of north america’s “homegrown” (endemic) dinosaur groups (cifelli and others, 1997; kirkland, and others, 1997, 1998b, 1999, 2015; kirkland, 2005a, b; kirkland and madsen, 2007). the alaskan land bridge has remained an important migration corridor for life on land in the northern hemisphere periodically to the present day. as the mussentuchit member appears to preserve a mixture of early and late cretaceous dinosaurs, it has been said that utah’s dinosaurs are dating the origin of alaska, having caught the immigration-induced extinction in the act. the thick cedar mountain formation sections exposed along the western margin of the san rafael swell preserve dinosaurs at several stratigraphic levels and have the potential to document this immigration-induced faunal turnover in considerable detail. vertebrate fauna from the mussentuchit member chondrichthyes hybodontidae? hybodus? sp. (fiorillo, 1999) polyacrodidae lonchidion n. sp.? (kirkland and others, 2013) orectolobidae cretorectolobus sp. (fiorillo, 1999) rhinobatidae rhinobatis? sp. (cifelli and others, 1997, 1999) cristomylus nelsoni kirkland and others (2013) scelerorhynchiidae texatrygon n. sp. (cifelli and others, 1999, in sense of kirkland and others [2013]) osteichthyes neopterygii gen. and sp. indet. semionotidae n. gen. n. sp. (double spined dorsal ridge scales) lepisosteiformes ?lepisosteidae gen. and sp. indet. (garrison and others, 2007) ?pycnodontidae gen. and sp. indet. (garrison and others, 2007) amiiformes gen. and sp. indet. (garrison and others, 2007) dipnoi neoceratodontidae ceratodus sp. cf. c. frasieri (kirkland, 1987) lissamphibia albanerpetontidae 161 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 albanerpeton sp. cf. a. nexuosum (gardner and demar, 2013) gen. and sp. indet. (gardner and demar, 2013) urodela scapherpetontidae 2 n. gen. and spp. (cifelli and others, 1997; gardner and demar, 2013) anura family incertae sedis gen. et sp. indet. (multiple taxa) sauropsida chelonia baenidae gen. et sp. indet. (cifelli and others, 1997) solemydidae cf. naomichelyssp. glyptopsidae glyptops sp. (cifelli and others, 1997) trionychidae gen. and sp. indet. (fiorillo, 1999) squamata teiidae bicuspidon numerosus nydam and cifelli (2002) dicothodon moorensis nydam (1999) harmodontosaurus emeryensis nydam (2002) dicothodon sp. (nydam, 1999) ?paramacellodidae cf. pseudosaurillus sp. (nydam, 2002) scincoidea dimekodontosaurus madseni nydam (2002) bothriagenys mysterion nydam (2002) gen. and sp. indet. (nydam, 2002) anguidae (2) indet. spp. monstersauria primaderma nessovi nydam (2000) serpentes aniliidae coniophis sp. (gardner and cifelli, 1999) gen. et sp. indet. crocodilia bernissartidae bernissartia (2) sp. (garrison and others, 2007) goniopholidae cf. dakotasuchus sp. (cifelli and others, 1997) polydectes sp. atoposauridae gen. and sp. indet. (garrison and others, 2007) teleosauridae machimosaurus sp. (cifelli and others, 1997) gen. and sp. indet. (cifelli and others, 1997) pholidosauridae gen. and sp. indet. (garrison and others, 2007) dinosauria theropoda neoventordae siats meekerorum zanno and makovicky (2013) tyrannosauroidea gen. and sp. indet. (zanno and makovicky, 2013) caenagnathoidea giant n. sp. (makovicky and others, 2014) dromaeosauridae gen. and sp. indet. dromaeosaurine gen. and sp. indet. veloceraptorine troodontidae ? gen. and sp. indet. (cifelli and others, 1997) family indet. richardoestesia sp. cf. r. isosceles (garrison and others, 2007) family indet. cf. paranychodon sp. (garrison and others, 2007) avialae hesperornithiformes gen and sp. indet. (cifelli and others, 1997) 162 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 order indet. gen. and sp. indet. (cifelli and others, 1997) sauropoda titanosaurimorpha cf. astrodon sp. (maxwell and cifelli, 2000) ornithopoda basal ornithopoda gen. and sp. new (makovicky and zanno, in press) orodrominae gen. and sp. new (makovicky and others, 2014) iguanodontia (basal) cf. tenontosaurus sp. (kirkland and others, 1997, 1999; kirkland and madsen, 2007) hadrosauridiformes eolambia caroljonesa kirkland (1998b) ankylosauria nodosauridae animantarx ramaljonesi carpenter and others (1999) pachycephalosauria family indet. gen. and sp. indet. (cifelli and others, 1997) ceratopsia neoceratopsia gen. and sp. indet. (chinnery and others, 1998; carpenter and cifelli, 2016) mammalia gen. and sp. indet. eutriconodonta triconodontidae astroconodon delicatus cifelli and madsen (1998) corviconodon utahensis cifelli and madsen (1998) jugulator amplissimus cifelli and madsen (1998) multituberculata ?plagiaulacidae gen. et sp. indet. neoplagiaulacidae ?mesodma sp. (eaton and cifelli, 2001) family incertae sedis janumys erebos eaton and cifelli (2001) cf. paracimexomys perplexus eaton and cifelli (2001) dakotamys robisoni (eaton and nelson, 1991) bryceomys intermedius eaton and cifelli (2001) cedaromys bestia (eaton and nelson, 1991) cedaromys parvus eaton and cifelli (2001) ameribaatar zofiae eaton and cifelli (2001) trechnotheria spalacotheriidae spalacolestes cretulablatta cifelli and madsen (1999) spalacolestes inconcinnus cifelli and madsen (1999) spalacotheridium noblei cifelli and madsen (1999) ?spalacotheriidae gen. et sp. indet. tribosphenida family incertae sedis dakotadens pertritus cifelli and others (2016) culicolestes kielanae cifelli and others (2016) metatheria ?stagodontidae pariadens mckennai cifelli (2004) family incertae sedis adelodelphys muizoni cifelli (2004) kokopellia juddi cifelli (1993) sinbadelphys schmidti cifelli (2004) geochemical studies of the cedar mountain formation in east-central utah geochemical data pertaining to the cedar mountain formation are mostly centered in east-central utah and can be grouped into two types of data. one group 163 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 includes data relating to chemostratigraphy for which the goal is correlation between sections within the cedar mountain formation and to better dated marine sequences. the principle behind c-isotope chemostratigraphy is related to the fact that the carbon cycle during the cretaceous experienced a number of perturbations (likely a result of phases of volcanic eruptions and oceanic crust production as well as abundant carbon burial) that led to changes to the δ13c of ocean-atmosphere system (scholle and arthur, 1980). these changes are reflected in all of the interacting reservoirs of the carbon cycle including sedimentary organic carbon and carbonate carbon. a good overview of c-isotope chemostratigraphy, especially as it pertains to use in continental strata, can be viewed in ludvigson and others (2010a, 2015) and references therein. the second group is primarily stable isotope data of various materials including carbonate beds and nodules (lacustrine, palustrine, and pedogenic), and vertebrate tooth enamel, ganoine scales, scutes, and bone. these data pertain to elucidating paleoenvironmental and paleoclimatic conditions of the cedar mountain formation. table 1 provides a summary of the data detailed in the sections below. lower yellow cat member chemostratigraphy carbon isotope profiles of bulk sedimentary organic carbon have been constructed from a number of localities in eastern utah (suarez and others, in press) for both the lower and upper yellow cat member. these localities include doelling's bowl, a section near andrew’s site (yc), the locality termed “lake madsen” (figure 18), and a site off the yellow cat road. the results of these carbon isotope profiles, however, were ambiguous, and correlation was initially based off the appearance of the regional calcrete. from overall trends in the carbon isotope record, the lower yellow cat member is tentatively correlated to the barremian. the c-isotope record of the barremian is relatively constant indicating no major c-cycle perterbations; however, at the beginning and end of the barremian, the faroni and taxy events respectively occur. globally, these two events are thought to correspond to warm humid episodes. overall, however, the barremian globally is thought to have been cool and arid. paleoclimate geochemical paleoclimate proxies for the lower yellow cat member are somewhat limited owing to the fact that the recognition of the “lower” yellow cat member is relatively recent. in addition, typical climate archives used for interpretations such as soil carbonates are not present in the lower yellow cat member. suarez and others (2014) used the oxygen isotopic composition of phosphate from a variety of taxa to suggest that the oxygen isotopic composition of meteoric water was relatively enriched during the deposition of the lower yellow cat member (-4.2‰ vs. vienna standard mean ocean water [vsmow] based on semi-aquatic taxa, specifically crocodilia). herbivorous dinosaurs such as sauropods consumed rather isotopically enriched water (-3.4‰), likely due to physiological effects, and iquanodontids consumed isotopically light waters (-9.3‰), likely due to consumption of isotopically depleted river water drained from the mogollan highlands. some turtle material from umnh 1208 (figure 16f) have been recovered and await analyses for δ18o of phosphate. recent data from hatzell (2015) pairs the δ13c of tooth enamel with δ13c of bulk sedimentary organic matter to calculate mean annual temperature from equations derived from kohn (2010) and diefendorf and others (2010). hatzell (2015) suggests the mean annual precipitation (map) for the cedar mountain formation was 850 mm/yr. if correct, such rainfall amounts could have supported forests. demko and others (2004) have described the paleosol at the top of the morrison formation, but as mentioned above, we suggest the strata making up these paleosols are creteceous. the presence of redoximorphic characteristics, iron accumulations, and lack of carbonates suggest wetland or at least seasonally saturated conditions. while this seems slightly wetter than the estimates of hatzell (2015), it is still consistent with the carbon isotope-derived map estimate. depending on the age of pedogenesis, the wetland soils may be consistent with globally warm and humid episodes associated with either the taxy or faroni events (föllmi, 2012). 164 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 member chemostratigraphy temperature hydrology pco2 lower yellow cat data: bulk organic c from db, nas, lm, ycr interpretation: inconclusive, though tentatively correlated to barremian to lower aptian data: no geochemical data currently exists data: 18opo4; 13c of bioapatite; and δ13c bulk sedimentary organic carbon. interpretation:δ18omw range from -2.9‰ (allosauroid) to -9.3‰ (iguanodontid) vs vsmow; δ13c derived map = 850 mm/year data: no geochemical data currently exists upper yellow cat data: bulk organic c from db, nas, lm, ycr; carbonate c from ycr interpretation: inconclusive, though tentatively correlated to barremian to lower aptian data:δ18oco3undifferentiated by member; ∆47 (clumped isotope) data from carbonate nodule from nas interpretation: temperature of carbonate formation averages 27.5°c for undifferentiated nodules; 47 derived temperature = 34°c data: 18opo4 ; 13c of bioapatite; 13c of bulk sedimentary organic carbon; ∆47 derived data from nas interpetation:δ18omw range from -8.1‰ (turtle scute) to -5.4‰ (utahraptor) vs vsmow;δ18omw = -4‰ vs vsmow from ∆47 derived temperature; δ13c data used to estimate map of 455 mm/yr. data: 13cco3 interpretaton: 1900 to 3500 ppmv poison strip member data: carbonate c from rrr interpretation: aptian data: 18oco3 data from rrr interpretation: no temperature have been estimated from these data data: 18o of carbonate data from rrr; 18o derived data from lacustrine oncoids from woodside anticline interpretation: 18omw = -7 to -9‰ vs vsmow from lacustrine oncoids data: 13cco3 interpretation: 1179 ppmv ruby ranch data: carbonate c from rrr, pr2; bulk organic c and carbonate c from lc interpretation: upper aptian to lower albian. more specifically, carbon isotope segments include the c10 cie data: 18oco3 from rrr, pr2, lc interpretation: no temperatures have been estimated from these data data: 18oco3; 18opo4; 13c of bioapatite; 13c of bulk sedimentary organic carbon interpretation: meteoric calcite lines and independent latitudinal temperature gradients used to estimate 18omw = -6‰ vs. vsmow; positive linear covariant trends suggest significant precipitation deficits especially in c10 cie interval at pr2. 18omw range from -15.5‰ (ornithischians) to -2‰ vs vsmow (allosauroid). 13c data used to estimate map = 643 mm/year data: 13cco3 interpretation: range from 746 to 1335 ppmv, with peak at the c10 cie. mussentuchit data: no c-isotope stratigraphy currently available data: no geochemical data currently available, though leaf physiognomy data exists interpretation: 16°c to 26°c. data: 18opo4 ; 13c of bioapatite and bulk sedimentary organic c. leaf physiognomy data interpretation: 18omw averages about -6‰ but is as light as -9.3‰ vs vsmow. map estimated from δ13c proxies = 1278 mm/year; map based on leaf physiognomic proxies = 810 mm/year data: no geochemical data currently available table 1. summary of data types and key interpretations for each of the members of the cedar mountain formation. see text for details and references. abbreviations used: db = doelling’s bowl; pr2 = price river 2 locality; rrr = ruby ranch road; ycr = yellow cat road; nas = near andrew’s site (umnh 1207); lm = lake madsen; lc =lake carpenter; cie = carbon isotope excursion; vsmow = vienna standard mean ocean water; ppmv = parts per million by volume; mw = meteoric water. 165 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 upper yellow cat member chemostratigraphy the carbon isotope profiles described above also extend into the upper yellow cat member (suarez and others, in press). the tentative correlation of the upper yellow cat member is barremian to lower aptian. the prominent negative isotope excursion (c3 isotope segment of menegatti and others, 1998) in the lower aptian has yet to be confirmed in the existing chemostratigraphic profiles; however, the excursion has been tentatively identified in the yellow cat road section in the uppermost yellow cat and lower poison strip member. this dramatic carbon isotope excursion globally is thought to represent a significant disturbance to the carbon cycle, an increase in atmospheric co2 due to volcanism, and a warm humid phase (föllmi, 2012). paleoclimate one of the distinguishing characteristics of the upper yellow cat member is the abundant carbonate nodules interpreted as pedogenic carbonates. one carbonate nodule from the nas section has been analyzed in duplicate for δ47, a measure of the abundance of 13c-18o bonds in the carbonate. the abundance of these bonds (multiply substituted isotopologues or “clumped isotopes”) is a relatively new and exciting opportunity to determine temperature using stable isotopes without having to assume the oxygen isotopic composition of precipitating fluid (ghosh and others, 2006; schauble and others, 2006; eiler, 2011; eagle and others, 2013). preliminary clumped isotope analysis of this carbonate nodule from the nas provides a temperature of 34°c (suarez and passey, 2014). clumped isotope temperatures are known to generally be warm season biased (passey and others, 2010) so mean annual air temperatures would likely have been lower. skipp (1997) also utilized stable isotopes of carbonate nodules to estimate temperature (using assumptions about δ18o of water). while skipp (1997) does not use the member nomenclature used here, the stratigraphic descriptions suggest that most of the nodules come from the upper yellow cat member. temperature estimates of skipp (1997) average 27.5°c, much cooler than the clumped isotope derived estimate. this may not be a very large discrepancy considering the various assumptions necessary for the estimates of skipp (1997) and the warm season bias of the clumped isotope paleothermometer. recently, suarez and passey (2014) investigated the possibility of utilizing bone carbonate clumped isotopes as a substitute for soil carbonates. however, it would appear that bone carbonate is much more susceptible to burial diagenetic conditions and the clumped isotope temperature derived from a sauropod bone fragment from the dalton wells quarry resulted in a temperature of about 51°c. an additional advantage to the clumped isotope paleothermometer is the fact that the δ47 derived temperature and the δ18o of carbonate (determined during the analysis of δ47) can be used to determine the δ18o of the precipitating fluid (meteoric water). based on the preliminary analysis of carbonate nodules, this is -4‰ vs. vsmow, which is more enriched than estimates based on lacustrine oncoids from the woodside anticline by shapiro and others (2009), that range from as low as -9‰ to -7‰ vs. vsmow. phosphate δ18o of suarez and others (2014) has somewhat similar values. these estimates range from 8.1‰ vs. vsmow for turtle (likely aquatic to semi-aquiatic) to -5.4‰ vs. vsmow for utahraptor. the more enriched value for the soil carbonate estimate via clumped isotope analysis is likely due to soil carbonate growth typically occurring during warm seasons when evaporation is greater. soil carbonate formation generally occurs when there is a precipitation deficit, and a reduction in precipitation from the lower yellow cat member is consistent with a lower map estimate from hatzell (2015) of 455 mm/ year. the increasing aridity is thought to be a result of a rain shadow effect due to the uplift of the sevier highlands. finally, skipp (1997) used carbonate nodule δ13c and the diffusion model of cerling (1991) to estimate pco2 values. these values range from 1900 to 3500 ppmv. poison strip member chemostratigraphy locations where c-isotope profiles span the poison 166 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 strip member include ruby ranch road (ludvigson and others, 2010a, 2015) and the yellow cat road sections (suarez and others, in press). ludvigson and others (2010a) correlate the δ13c trend across the poison strip member to the aptian, particularly to the positive and negative isotope excursions (c5 to c7). paleoclimate overall, few paleoclimate proxies have been widely sampled from the poison strip member. the lowermost sample ludvigson and others (2015) used for determining pco2 from carbonate nodules occurs in the poison strip member. this sample provides a value of 1179 ppmv. while this value is lower than the pco2 values that were estimated by skipp (1997), it is likely that the two estimates cannot be compared due to various sources of error and various assumptions about variables involved in the calculation of pco2. sources of error include the concentration of soil co2 used, the δ13c value of atmosphere, and the δ13c value of soil co2. for example, the estimate of soil co2 used by skipp (1997) comes from an estimate of organic matter from the morrison formation. ruby ranch member chemostratigraphy a number of c-isotope profiles have been constructed for the ruby ranch member. these profiles are from carbonate nodules collected at the price river section and ruby ranch road type section (ludvigson and others, 2010a) and organic matter from lacustrine strata (lake carpenter) near klondike bluffs road (montgomery, 2014). these profiles (figure 28) suggest that the ruby ranch member spans the aptian-albian boundary and encompass carbon isotope segments c8 through 13c of herrle and others (2004). paleoclimate ludvigson and others (2010a) extensively sampled carbonate nodules through the ruby ranch member to estimate pco2 concentrations. the most significant finding by this study is that pco2 values peak during the 10c carbon isotope excursion. in addition, ludvigson and others (2015) use trends in δ18o vs. δ13c space to determine that evaporation peaked during the carbon isotope segment. overall, ludvigson and others (2015) suggest that meteoric water values determined from average δ18o were approximately -6‰ vs. vsmow. suarez and others (2014) used carbonate nodules to estimate δ18o of meteoric water as -5.6‰ vs. vsmow, which is consistent with water values determined from crocodile bioapatite (-5.3‰ vs. vsmow). meanwhile, the isotopic composition of most dinosaurs are much lower (as low as -15.5‰ for ornithischian dinosaurs). we interpret this as representing the incorporation of isotopically depleted water from the sevier highlands into the catchment basin. this water may have been additionally depleted by snowmelt since the sevier highlands would locally have been reaching high elevation. hatzell (2014) calculated a slight increase in map at 643 mm/year, and considering the large error, the map likely is not changed significantly from the upper yellow cat member. mussentuchit member chemostratigraphy no chemostratigraphic profiles are published for the mussentuchit member. this is partially because 40ar/39ar ages determined by cifelli and others (1997) and garrison and others (2007) reflect a cenomanian age. therefore greater efforts were shifted toward the less well-constrained portion of the cedar mountain formation. there is certainly a need to obtain high-resolution chemostratigraphic profiles for the mussentuchit member. paleoclimate one of the characteristics of the mussentuchit member is the lack of carbonate nodules. a significant amount of data, however, has been derived from bioapatites as the mussentuchit contains numerous fossil sites, especially microvertebrate sites. this large dataset of phosphate samples suggest that the area became significantly more humid during the deposition of the mussentuchit member (suarez and others, 2012, 2014). dinosaur-ingested water as well as precipitation water 167 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 isotope proxies suggest a rather stable isotopic composition around -6‰ with values as light as -9.3‰, which likely represented water drained from highlands. a likely controlling factor of this return to humidity was the advancement of the western interior seaway. tooth enamel carbonate isotopes support this interpretation with a large increase in map calculated at 1278 mm/ yr. no temperature estimates from geochemical data have been determined from the mussentuchit member. recently, however, leaf fossils purportedly from the mussentuchit member (see flora and fauna from the mussentuchit member section) have been used to determine both temperature and precipitation via leaf physiognomic methods (arens and harris, 2015). depending on the method used, temperature ranged from a low of 16°c to a high of 26°c. map is estimated at 810 mm/yr and mean growing season precipitation is estimated at 1380 to 1870 mm/yr. a brief overview of the cedar mountain formation in northeastern utah lithostratigraphy and correlation significant exposures of the cedar mountain formation are also present in northeastern utah (figure 1) along the northern margin of the uinta basin (extending into colorado). these outcrops are geographically isolated from the east-central utah exposures by the central uinta basin; however, the cedar mountain formation is present in the subsurface of the basin (mcpherson and others, 2006; sprinkel, 2006, 2007; currie and others, 2008). though this field trip will not visit these northern exposures, a brief look at the geology and paleontology of this corner of utah is included here for general information purposes. the presence of lower cretaceous terrestrial rocks has long been recognized in northeastern utah. while exposures are fairly limited due to folding and faulting in the area, exposures are generally along hogbacks in the vicinity of dnm (figure 35), sr 40 (extending east into colorado), and us 191 and sr 44 (north of vernal, utah, and near the wyoming border). stokes (1952), young (1960), hansen (1965), and others conducted some of the more detailed early work in the area. the early cretaceous age (aptian-albian) was confirmed based on charophyte and ostracod evidence found near flaming gorge and correlations with other strata. though disputes and resolution of nomenclature, exact ages, and relationships of sandstone bodies continues, these and other workers recognized several of the basic features that characterize the cedar mountain, cloverly, and burro canyon formations. these include (generally from the bottom up): (1) limonite staining in the uppermost few meters of the brushy basin member of the morrison, (2) the presence of a basal conglomeratic sandstone, (3) calcareous sandstone lenses common in the lower part of the section, (4) an upper mudstone unit that becomes more carbonaceous upward and is commonly drabber in color and more fissile than in the morrison, (5) abundant calcareous nodules in mudstone units, and (6) locally abundant, highly polished pebbles (“gastroliths”). though many of these features are discontinuous or not present at all locations, together they form a relatively easy way to recognize the formation. in addition, these features typically appear in roughly the same stratigraphic succession as they do along i-70 and the san rafael swell, although the ages and paleoenvironments may be somewhat different (figure 35). little additional research was done since the 1960s until interest in the cedar mountain formation was revitalized in the early 1990s. at this time the “morrison ecosystem project” (see turner and others, 2004; turner and peterson, 2004) focused some attention on the long-standing boundary issues, addressing the criteria used to distinguish the contact between the morrison and cedar mountain formations and attempting to place some age constraints on the rocks (e.g., currie, 1998; mcpherson and others, 2006; currie and others, 2008, 2012). their lower boundary was defined at the base of the lowest calcrete if the buckhorn conglomerate member was not present. our own research used the first occurrence of significant gravel within the mudstones as an identifier of interfluvial facies lateral to the channels represented by the buckhorn conglomerate member, which were identified in northwestern colorado as pediment gravels by dolson and muller (1994). in this way, the limonite-stained intervals (figure 35) were shifted from the top of the morrison formation to 168 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 35. cedar mountain formation in northeastern utah. (a) the middle mesozoic section looking west from the carnegie quarry at dinosaur national monument to the dnm 16 section; line of section along ridge crest. (b) reef pipeline section with line of section indicated in yellow measured from 40°29'53.72"n, 109°22'3.74"w to 40°29'58.71"n, 109°22'1.46"w. (c) gary hunt examining a pebbly red mudstone in the yellow cat facies near base of the cedar mountain formation at the reef pipeline section. (d) the yellow cat and ruby ranch facies of the cedar mountain formation at the reef pipeline section. (e) basal contact of cedar mountain formation at six mile draw north of dnm (40°33'51.74"n, 109°12'53.30"w). (f) cedar mountain section east of sr 191 by north end of steinaker reservoir north of vernal, utah (40°31'59.22"n, 109°31'11.07"w). red lines mark base of cedar mountain formation. 169 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the base of the cedar mountain formation (ludvigson and others, 2003a, 2003b; sprinkel and others, 2012). constraining the age of the cedar mountain formation in northeastern utah has so far proved difficult and has been the subject of much recent work (sprinkel and others, 2012). until recently in this area, the relative lack of diagnostic vertebrate fossils, invertebrates and microfossils (either flora or fauna), and the apparent scarcity of rocks within the cedar mountain formation datable by radiometric means has meant that most work focused on bracketing the age by dating the morrison (early tithonian) (trujillo and kowallis, 2015) and dakota formations (albian-cenomanian) (sprinkel and others, 2012). elsewhere in utah, paleontological and geological evidence suggests an age range of albian-barremian is represented in the cedar mountain formation (as discussed elsewhere herein); however, lacking published well-log data, direct correlations with the nearest dated outcrops to the south (some 165 km) has been problematic. currie (1998) has identified the buckhorn conglomerate at the base of the cedar mountain formation in the colorado portion of dnm to the east. the buckhorn conglomerate has also been mapped near the western side of steinaker reservoir (haddox, 2005; haddox and others, 2010) to the east. recent research on terrestrial carbon isotope stratigraphy from pedogenic carbonate nodules at dnm (smith and others, 2001; sorenson and others, 2002; ludvigson and others, 2002, 2003a, 2003b, 2015; kirkland and others, 2003) has established the correlation between the outcrops of the fine-grained upper cedar mountain formation at dnm with the ruby ranch member of the cedar mountain formation near price, utah, indicating the lower part of the section is at least as old as aptian. studies of palynomorphs and microfaunas near the top of the section supports an albian age for the top of the cedar mountain formation and at least the lower part of the dakota formation, as well as a marine influence (currie and others, 2006; sprinkel and others, 2012). however, the correlation between the mussentuchit member of the san rafael swell area and the mowry shale at dnm indicates that the entire dakota formation at dnm can be correlated with part of the cedar mountain formation (upper ruby ranch member up through the short canyon member) in central utah, supporting the prior correlations of young (1960) and molenaar and cobban (1991). directly datable materials from the cedar mountain formation at dnm are still lacking. some of the member names have been applied to the cedar mountain formation in the vernal area by chure and others (2010), although kirkland and madsen (2007) have restrained from extending this terminology across the uinta basin to the vernal area. however, for the purpose of this discussion, the cedar mountain formation will be discussed as being divided into three superimposed facies (figure 36): (1) a basal “yellow cat” facies, (2) a middle “ruby ranch” facies, and (3) an upper “transitional” facies. basal “yellow cat” facies the basal “yellow cat” facies can be considered as the interfluvial facies of the buckhorn conglomerate fluvial system in this area. as such, if the buckhorn conglomerate in this region represents the “down river” equivalents to the buckhorn in the san rafael swell area, these strata would be essentially equivalent to the lower yellow cat in the paradox basin and the “yellow cat” facies of the buckhorn conglomerate in the san rafael swell region. indeed these sediments share almost all the characteritics of the lower yellow cat south of the uinta basin, including chert and limestone gravels mixed into the basal mudstone and sandstones, ferruginous paleosols, and even locally thin chert laminae. likewise, these basal strata are composed largely of recycled material from the underlying morrison formation. an attempt to date a basal light-gray, siliceous siltstone bed (porcelainite) at the base of the the section at the reef pipeline section (figure 36) yielded a detrital zircon u-pb maximum age of late jurassic, 153.05 ± 3.69 ma (sprinkel and others, 2012). we now tentatively interpret this bed as a loessite derived from the underlying morrison formation. middle “ruby ranch” facies the middle “ruby ranch” facies in northeastern utah, as with the ruby ranch to the south, is characterized by illitic mudstones with abundant pedogenetic carbonate nodules. in many areas, a prominent cherty 170 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 36. correlation of the reef pipeline section with the dnm 16 section at west end of dinosaur national monument across the split mountain anticline with radiometric dates and important dinosaur sites indicated. key to stratigraphic symbols as in figure 10. modified from sprinkel and others (2012). 171 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 calcrete marks the base that makes a prominent break in the slope such as at the dnm 16 section (figures 35a and 36). elsewhere, the contact is noted at the sudden appearance of abundant carbonate nodules such as at the reef pipeline section (figures 35b, 35c, and 36). a prominent sandstone occurs near the middle of this unit, which has been referred to the poison strip member. a late albian age is indicated for the sandstone by a maximum u-pb age of 104.46 ± 0.95 ma from detrital zircons collected from this sandstone at dnm16 (chure and others, 2010). this precludes a correlation with the poison strip to the south because the poison strip member is well constrained as aptian in age (ludvigson and others, 2010a, 2015). the top of the “ruby ranch” facies is gradational with the overlying “transitional” facies. upper “transitional” facies the upper “transitional” facies is characterized by a reduction of carbonate nodule abundance and an increasing amount of swelling clay in the mudstone beds such that the upper part of the facies, below the base of the overlying naturita formation (= dakota formation), are drab and very smectitic. although these strata are similar to the mussentuchit member on the west side of the san rafael swell, they are never lignitic. the late albian age for the “transitional” facies at the top of cedar mountain formation is constrained by middle to late albian palynomorphs obtained from the base of the overlying basal naturita formation (= dakota formation) (sprinkel and others, 2012). of particular importance in dating the top of the cedar mountain is that dinoflagellates are present in the floral assemblage at the base of the naturita formation (= dakota formation) at the strike valley section (40°33'57.06"n, 109°29'47.97"w) of sprinkel and others (2012), indicating the incursion of at least brackish water into the area during peak sea level rise of the albian skull creek seaway. marine strata of this age (thermopolis shale), overlie the cloverly formation in the bighorn basin (ostrom, 1970). the kiowa-skull creek cycle is dated by 40ar/39ar analysis of sanidine grains from bentonites in the thermopolis shale in wyoming at about 104.4 to 100.9 ma (obradovich and others, 1996; scott and others, 2009). the top of the cedar mountain formation is further constrained by a u-pb zircon age of 101.4 ± 0.4 ma from a volcanic ash near the center of the naturita formation (= dakota formation) (sprinkel and others, 2012) the age of these strata also supports their correlation with the “transitional” facies at the top of the ruby ranch member in the western san rafael swell. the middle cretaceous within the western interior basin includes the kiowa-skull creek marine depositional cycle (aptian-albian) and greenhorn marine depositional cycle (cenomanian) (brenner and others, 2000). recently, ludvigson and others (2010b) proposed a new muddy-mowry depositional cycle that separates the kiowa-skull creek and greenhorn cycles. the cedar mountain formation in northeastern utah is the landward time-equivalent of the kiowa-skull creek cycle (figure 37). the basal dinoflagellate-bearing mudstone and shale unit of the naturita formation (= dakota formation) represents peak sea level during the kiowa-skull creek cycle and the initial marine incursion into northeastern utah. the overlying non-marine part of the dakota formation and marine mowry shale represents the newly recognized muddy-mowry cycle (figure 37). marine environments did not transgress into central utah until the late cenomanian (elder and kirkland, 1993,1994; cobban and others, 1994). since the muddy formation is the proper term for the sandstone dominated coastal sequence between upper albian marine strata (skull creek and other units) and basal cenomanian marine strata (mowry shale) (weimer, 1984; ludvigson and others, 2010b), perhaps the naturita formation (= dakota formation) on the northern side of the uinta basin would most properly be referred to as the muddy formation. cedar mountain vertebrate remains in northeastern utah the many fossil discoveries in the cedar mountain formation in central utah inspired staff at dnm to focus more attention on fossil inventories and excavations in the cedar mountain in dnm and vicinity; work has yielded some spectacular results. diagnostic vertebrate fossils from the cedar mountain formation of northeastern utah have proven to be uncommon; 172 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 37. caption on following page. 173 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 even scrap bone is uncommon. a notable exception is a quarry at dnm located just across the road, west of the carnegie quarry. this quarry, dnm16 was first identified by researchers working in the area on a model for the dinosaur sites present in the morrison formation (dodson and others, 1980). this quarry in the middle of the cedar mountain formation has produced several complete and incomplete titanosauriomorph sauropod skulls (figures 30h and 36) as well as postcranial material described as abydosaurus mcintoshi (chure, 2000; chure and others, 2010). in addition, this site (dnm 16) produced a partial skeleton of a dromaosaurid (cf. deinonychus sp.) (chure and others, 2007, 2010) and provided the maximum u-pb age from detrital zircons of 104.46 ± 0.95 ma. a site just outside dnm boundaries has recently produced iguanodontid remains assigned to cf. tenontosaurus (figure 30c) and a single mammalian tooth. these and other sites may eventually provide enough diagnostic material that comparisons and correlations can be made with cedar mountain formation faunas known elsewhere. we hope that these fossils, together with the renewed geological interest in the area, will soon produce a more detailed picture of the tectonics, depositional setting, and environment of the cedar mountain formation in northeastern utah. conclusion geologically, research on the cedar mountain formation has confirmed that young (1960) was largely correct regarding the use of marker beds to correlate lower cretaceous strata across utah. research has also confirmed that within these rock packages, the mudstone intervals with carbonate nodules (drier) in the west gave way to more organic-rich (wetter) strata toward the east. deposition and preservation of the yellow cat member in the northern paradox basin is the result of early cretaceous salt tectonics as proposed by doelling (1988). additionally, ferruginous paleosols at the jurassic-cretaceous contact indicate a period of wet climatic conditions in the middle mesozoic (demko and others, 2004). the occurrence of the marker calcrete at the top of the lower yellow cat member and stable isotope geochemistry refects a strong drying of the climate caused by the onset and long-term effect of a rain shadow that formed east of the sevier orogenic belt (ludvigson and others, 2010a, 2015; suarez and others, 2014). however, the development of the foreland basin is delayed by several million years as indicated by the first thickening of stratigraphic packages to the west beginning with the aptian-albian ruby ranch member. farther to the west, this thickening is well documented in the synorogenic deposits of the san pitch formation in the central utah thrust belt (sprinkel and others, 1999; hunt, 2016). these synorogenic conglomerate beds intertongue and grade into the dominantly finegrained beds to the east (sprinkel and others, 1999). thickening of the section continues up through the mussentuchit member, which is only developed in the distal foreland basin (figure 38). utah’s cedar mountain dinosaurs are contributing critical information about an important period in the history of terrestrial life in the northern hemisphere. globally, this was a time of changing climatic conditions and exceptionally high atmospheric carbon dioxide levels causing “super-greenhousing” (a world with no polar ice caps and a sluggish, poorly oxygenated ocean), major restructuring of biogeographic migration corridors, and a complete restructuring of plant communities, i.e., the origin and rapid rise to dominance of flowering plants. researchers from a host of different institutions continue to discover and integrate new data from the cedar mountain formation into an increasingly robust history of utah during the early cretaceous. this research over the past 25 years, first on microvertebrate assemblages, then on skeletal materials, figure 37 (figure on previous page). (a) correlation chart of cretaceous formations from the san rafael swell in central utah to southwest wyoming and associated marine depositional cycles. modified after sprinkel and others (2012). (b) the paleogeographic map shows the western interior seaway in late albian time at peak sea level at the end of the kiowa–skull creek marine cycle. the approximate position of the stratigraphic columns a–d is shown on the map, which is modified from cobban and others (1994) and dickinson (2006). 174 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 38. simplified history of the middle mesozoic of central utah plotted against the yellow cat road section. 175 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 has established that a robust, well-dated record of lower cretaceous terrestrial faunas is preserved in central utah (see kirkland and others, 1997, 1999, 2012; cifelli and others, 1997, 1999; eaton and kirkland, 2003; kirkland and madsen, 2007; kirkland and farlow, 2012). coupled with new research in the jurassic and upper cretaceous sequences in southern utah, these new dinosaur discoveries only serve to show that utah has the most complete middle mesozoic dinosaur record in the world (figure 39), and that there is still a great deal to learn from this extraordinary record. these discoveries have been made in lockstep with a series of extraordinary discoveries in china (zhou and others, 2003; pan and others, 2015; zhou, 2015). the european lower cretaceous faunas of southern britain have been well documented for more than 150 years (martill and naish, 2001a; batton, 2011; lomax and tamura, 2014). new faunas being recovered from hungary (e.g., osi and others, 2012) and spain (e.g., pereda-suberbiola and others, 2012; alcala and others, 2012; mcdonald and others, 2012b; kirkland and others, 2013a) are filling out the middle cretaceous story for europe. while the temporal resolution of these strata in utah is good, precise correlation of these strata between continents is still far from resolved. correlation of lower cretaceous strata in utah is even difficult with strata in the northern usa. the earliest cretaceous strata in the cedar mountain formation of east-central utah (yellow cat through poison strip members) preserve a series of terrestrial faunas dominated by polacanthid ankylosaurians, styracosternan iguanodontians, and basal macronarian and brachiosaurid sauropods from the barremian to middle aptian (125 to 115 ma). the oldest of these faunas could possibly extend back to more than 135 ma (kirkland and others, 2012; hendrix and others, 2015). these faunas in utah broadly correlate to the european wealden fauna and asian hekou and jehol faunas, indicating european paleogeographic connections and not asian at this time (kirkland and others, 1998b, 2015; brikiatis, 2016). the most characteristic taxa in these asian faunas are species of psittacosaurus not known in europe or north america. a marked faunal change (extinction?) within the aptian may be tied to the isolation of north america with the opening of the atlantic basin and the flooding of much of europe (kirkland and others, 2013a, 2015) and/or global changes during oceanic anoxic event oae 1a or oea 1b. an interval of marked short-term intense volcanic activity and global cooling spanning the end of the aptian has also been identified at this time (leckie and others, 2002; herrle and others, 2015). the middle cedar mountain faunas of the late aptian through albian preserved in the ruby ranch member overlap the better known aptian-albian faunas of the cloverly formation (ostrom, 1970; oreska and others, 2013). they are characterized by nodosaurid ankylosaurians, basal iguanodontians (tenontosaurids), and exclusively slender-toothed, basal somphospondylan titanosauroids, suggesting isolation from eurasia. a number of taxa are known from the cloverly fauna that are considered asian taxa and are thought to indicate immigration events from asia in late aptian to earliest albian. these immigrants include caenegnathid oviraptors, tyrannosaurids (zanno and makovicky, 2011), neoceratopsians (farke and others, 2014), and the triconodontid mammaliform gobiconidon (jenkins and schaff, 1988). as current research reveals new data, these taxa may have entered from europe, but key european fossils may not yet been discovered. the mammal gobiconodon is pan-laurasian and was present in the barremian of both china (yuan and others, 2009) and europe (cuenca−bescósand and canudo, 2003). in asia, basal neoceratopsians along with possible polacanthids and basal ankylosaurid ankylosaurians, more derived hadrosauroid iguanodontians, and titanosaurid sauropods typify the mazongshan fauna; psittacosaurus is notably absent (tang and others, 2001). in europe, struthiosaurine nodosaurids replace polacanthids whereas styracosternid iguanodonts continue to dominate along with titanosaurids (ariño fauna) (alcala and others, 2012; kirkland and others, 2013a). a significant faunal change occurs in the mussentuchit member at the top of the cedar mountain formation at the base of the cenomanian of utah at about 100 to 98 ma. hadrosauroids replace tenontosaurids among iguanodontians during a shift from early to late cretaceous style faunas associated with an asian immigration event (cifelli and others, 1997; kirkland and others, 1997, 1999) and/or the oae 1d. the over176 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 fi gu re 3 9. d ist rib ut io n of d in os au r f au na s d ur in g th e m id dl e m es oz oi c in u ta h pl ot te d ag ai ns t s ta bl e ca rb on is ot op e cu rv e (o gg a nd h in no v, 20 12 ), lin ea r t im e, an d th e g en er al iz ed st ra tig ra ph ic se qu en ce o f s ou th er n u ta h, w ith h yp ot he tic al co rr el at io ns o f c re ta ce ou s d in os au r f au na s i n th e n or th er n w es te rn in te rio r. d ist rib ut io n of d in os au r fa un as h ig hl y m od ifi ed fr om k irk la nd a nd f ar lo w (2 01 2) , a nd a pt ia na lb ia n co ld s na p aft er l ec ki e an d ot he rs (2 00 2) . 177 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 lap of sauropod and tennontosaurid teeth together with the presence of a large allosauroid theropod (zanno and others, 2014) suggest that this mussentuchit fauna may actually preserve the transition between faunas of lower cretaceous aspect with those of upper cretaceous aspect in the mussentuchit member of the cedar mountain formation over an interval of 1.5 to 2 myr. in utah, extensive microvertebrate faunas in the middle to late cenomanian (95 to 93 ma) naturita formation (= dakota formation of others; young, 1960, 1965; carpenter, 2014) preserve a jurassic-grade aquatic fauna dominated by lungfish, semionotids, and “glyptopsid” turtles (eaton and others, 1997; eaton and kirkland, 2003). no major changes in terrestrial faunas are noted at the beginning of the turonian, but the aquatic fauna changes to one dominated by gars and amioids are significant, coinciding with the cenomanian-turonian extinctions in the marine realm (oae 2) (elder, 1989, 1991; ogg and hinnov, 2012). from middle turonian through late santonian, the straight cliffs formation of utah documents the continued dominance of nodosaurid ankylosaurians and hadrosauroid iguanodonts and the introduction of more derived neoceratopsians (eaton and others, 1997: eaton and kirkland, 2003). a similar pattern is documented by the bissekty, bayn shire, and iren dabasu faunas in asia with titanosaurs, ankylosaurids, hadrosauroids, and protoceratopsians (averianov and sues, 2012). the more restricted santonian record (iharkút fauna) of central europe is characterized by neoceratopsians, basal rhabdodontid iguanodonts, and struthiosaurine nodosaurids, suggesting a more endemic fauna (osi and others, 2012). approximately 10 discrete terrestrial faunas are documented in utah in the lower cretaceous through the santonian. similarities in the dinosaur faunas suggest that four to five more broadly based dinosaur assemblages can be recognized roughly correlated to similarly broadly based assemblages in asia and europe. such correlations are, at most, only generally correlative, and any definitive causation of these patterns at a global and even in most cases a local scale are highly speculative. however, it would seem that for the first time, there is real potential to look at these patterns at a large scale, begin intelligent discussions, and develop protocols to improve the basis for these discussions. the future for such research appears bright. the field trip day 1 (am) – cedar mountain formation in the region north of arches national park from salt lake city we will travel south on i-15 to spanish fork, and proceed on us 6 across soldier summit through price to green river between the san rafael swell to the west and the book cliffs. after refueling in green river, we will drive east on i-70 continuing along the south side of the book cliffs, one of the longest continuous exposures of the regressing late cretaceous coastline anywhere in north america (van wagoner and others, 1991). we will make a short stop at the rest area immediately prior to crescent junction for a brief overview of the salt valley anticline to the south to discuss the importance of the paradox basin and salt tectonics on mesozoic depositional patterns in this area (figures 1 and 40). note that all road distances are given in miles to match odometers. all aerial distances will continue to be given in metric. crescent junction rest area this stop provides an excellent view of the geology south of the book cliffs and north of arches national park. the rest area is built on a carbonate-cemented gravel pediment of pleistocene age formed on the marine upper cretaceous mancos shale. keep this exposure in mind when we examine the basal cedar mountain formation over the next couple of days. in this area, a nearly complete section of the mesozoic is exposed. the book cliffs form the escarpment north of i-70. this magnificent exposure of upper cretaceous rocks extends east-west from green river, utah, to grand junction, colorado. west of here at green river, the escarpment extends north past price, before bending west and then south around the north end of the san rafael swell, where it is called the coal cliffs/wasatch plateau on the west side of the swell. the marine mancos shale is overlain by the marginal-marine and coastal-floodplain-deposited strata of the mesaverde group. this 165-km cross section of the eastward-regressing 178 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 campanian facies track of the late cretaceous western interior seaway has become a research and educational model for petroleum geologists for stable continental shelf environments (see van wagoner and others, 1991). the mountains on the skyline to the south were formed by the unroofing of 29-million-year-old laccoliths (doelling, 2001) following the uplift of the colorado plateau—the henry mountains to the southwest and the la sal mountains to the southeast. to the west, the san rafael reef is visible, and far off to the east, the uncompahagre plateau, which approximates the position of the uncompahagre mountains of the pennsylvanian-aged ancestral rocky mountains, is visible along the colorado border. on the east side of us 191, the salt valley anticline can be seen trending directly north-northwest toward the rest area. this is a collapsed salt anticline and forms most of arches national park. along the axis of this structure, intact sections of the cedar mountain formation are preserved overlying strata as old as late paleozoic (doelling, 1985, 1988; lockley and others, 2004; stikes, 2006; doelling and kuehne, 2013a). the cedar mountain sections we will examine today are on the northeast and southeast flanks of this structure. exposures of the fossiliferous middle mesozoic section on land managed by the blm and the state of utah in the area around arches national park are a world-class paleontological resource (figure 40). the rest area is built upon alluvium deposited on a broad pediment surface cut into the mancos shale. the alluvium is cemented with pedogenic carbonate that forms a resistant caprock that protects the mancos from erosion. the pediment has subsequently been dissected forming alluvial-capped mesas. a hypothesis to be presented on this trip will be that the basal yellow cat sediments represent a distal pediment developed on the unconformity above the morrison formation under wetter climatic conditions. perhaps the basal yellow cat member strata are better compared to holocene sediments deposited on the surface of the great plains of central north america rather than pediment deposits laid down near their source area (e.g., book cliffs). from here, we will proceed east to the cisco exit on i-70 and take the frontage road on the south side of the highway to the yellow cat loop road. beware of a series of drainage dips over this stretch of road. the yellow cat loop road cuts through the cedar mountain escarpment, running along the escarpment to the yellow cat uranium mining district before to turning back north to i-70. this region includes many important fossil sites (figure 4) that have been developed since rob gaston of fruita, colorado, first showed kirkland the gaston quarry site (figure 20) in 1990, which yielded the type specimens of utahraptor (kirkland and others, 1993) and gastonia (kirkland, 1998a). the ugs, prehistoric museum (utah state university eastern), byu paleontology museum, and dmns have and are actively excavating paleontological sites in this area. as with all public lands, no collection of fossil vertebrates or their traces can be made without valid permits from the appropriate land management agency (in the case of this area, the blm or the state of utah). east end of the poison strip the lower yellow cat member is not well exposed along the road, but farther to the east and west where poison strip escarpment rises, it is well developed as described below with distinct ferruginous nodules. aubrey’s (1998) marker calcrete is thin here, but it makes a low and distinctive break in the slope (figures 17i). the east end of the poison strip has an easily accessed section of the cedar mountain formation. a stratigraphic section east of the road contains many sedimentary facies of interest including some features not documented elsewhere (figure 41). the upper yellow cat member has yielded many interesting fossils in this area, including common fish, turtles, and eileenodontid sphenodont remains, as well as eggshell fragments. most dinosaur fossils in this area have been recovered in the upper yellow cat member and include the polacanthid ankylosaur gastonia, a partial skeleton of an iguanodontid, and claws of a dromaeosaur. the type specimen of the brachiosaurid sauropod cedarosaurus was excavated by the denver museum of nature and science about 2 km to the east (tidwell and others, 1999). a number of other important dinosaur excavations are being actively worked by byu and the ugs, including sites in the overlying 179 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 poison strip member. those excavations have yielded well-preserved turtles (brinkman and others, 2015), additional iguanodont skeletal material, a basal ornithomimid (scheetz and others, 2010a), more utahraptor material, and at least parts of the same massive polacanthid ankylosaur described from west of arches national park by bodily (1969). one of the two localities that yielded ostracods was low in the upper yellow cat section exposed in a gully about 300 m west of the road (sames and others 2010; sames, 2011). this is also one site where the matrix does not break down as well as it does at lake madsen (scott madsen, formerly ugs, personal communication, 2007). the charophytes reported by kirkland and others (1997) came from a site on the east side of the road and were found with microvertebrates (fish and dinosaur teeth); howerver, the matrix would not break down at this site either. the top of the yellow cat member is interpreted to represent a lacustrine shoreline. an extensive sandstone lens representing the coastal bar facies forms a resistant ledge to the east of the road that has been mistaken for the poison strip member, which is stratigraphically a few meters higher in the section (figure 41). the “beach facies” overlies thin, rippled sandstones with bivalve escape structures, and a variety of other invertebrate figure 40. google earth view of the northern paradox basin and san rafael swell region to show field trip stops in the context of the spectacularly exposed mesozoic stratigraphy in the region. compare with figure 1. 180 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 42. cedar mountain exposures at poison strip section (ps) on the east end of the poison strip (figure 41). (a) cedar mountain formation on the east side of the yellow cat loop road. line of section was just behind ridge in foreground. (b) yellow cat member at base of poison strip section. (c) upper yellow cat member below lenticular bar sandstone complex. (d) possible sauropod track surface in lenticular bar sandstone complex. (e) clam escape structures in base of lenticular bar sandstone complex above a series of thin ripple-bedded sandstone. (f) aeolian cross-bedding in fine-grained sandstone exhibiting inverse graded laminae at top of lenticular bar sandstone complex. (g) upper cedar mountain section from top lenticular bar sandstone complex to base of naturita formation. (h) stromatolitic layer overlying sandstone in lower poison strip member. (i) capping poison strip sandstone with stromatolitic layer at the top of the poison strip member. (j) coastal vertisol complex on west side of the yellow cat loop road below fluvial poison strip member approximately 1.5 km to the southwest. 181 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 trace fossils. there are wind-drift cross-beds exhibiting inverse grading at the top indicating subaerial exposure of the bar (figure 42d and e). mudstone with weakly developed paleosols overlie this sandstone lens. matt joeckel (nebraska soil and conservation survey) has been working with the ugs in researching well-exposed vertisols exposed below the poison strip member on the west side of the valley and figure 41. comparison of the yellow cat road section (yc) measured from 38°51'19.12"n, 109°32'37.38"w with the poison strip section (ps) measured from 38°52'25.39"n, 38°52'25.39"n to 38°52'37.36"n,109°26'18.50"w. for explanation see figure 10. 182 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 farther to the east (figures 21d, 21e, 23f, and 42j). marginal lacustrine sandstone facies are recognized in a number of areas near the contact between the yellow cat member and the fluvial poison strip member. even when closely associated with the cliff formed by the poison strip member, their genetic relationship with the underlying fine-grained lacustrine facies of the upper yellow cat member has resulted in the inclusion of these sandstone beds in the yellow cat member (stikes, 2006). unusual for this region is the abundance of stromatolite lenses and beds associated with sandstone beds at the top of the yellow cat and throughout the poison strip member (figures 41, 42h, and 42i). as noted above, as the cedar mountain formation is traced to the eastern margin of the paradox basin, first the yellow cat thins and pinches out followed by the poison strip member (young, 1960; stikes, 2006, herein; figures 11 and 24). the overlying ruby ranch member is exposed in this region but has not been the subject of any specific research. the poison strip escarpment proceeding south, the trip will cross the morrison formation by driving up through an escarpment held up by sandstone beds of the salt wash member exposed on the east end of the yellow cat mining district. bear right at the fork and head west along the salt wash bench with the poison strip escarpment on the right (north) side of the road for approximately about 6 km. the brushy basin member of the morrison through the cedar mountain formation is exposed. the fluvial sandstone architecture of the poison strip member is excellently expressed (stikes, 2006). where the naturita formation (= dakota formation) is preserved on the cedar mountain formation in this area, it provides stark evidence that the ruby ranch member is relatively thin compared to the yellow cat member. this drive also provides an opportunity to practice placing the contact between the morrison and the cedar mountain formations; it is at the break in slope with the convex profile associated with the change from smectitic clays of the morrison formation to the non-smectitic clays in the yellow cat member. this convex slope profile is in stark contrast to a flat to slightly concave slope profile that characterizes the overlying yellow cat member, coupled with iron-stained (ferruginous) paleosols of the basal yellow cat and the overall drabber variegated color of the yellow cat member (figure 23c). toward the west end of the escarpment, we will pass the ringtail mine workings below the type section of the poison strip member (figure 23a). as discussed in kirkland and madsen (2007), this was not a good choice for the type section as it is relatively inaccessible and there is no clear upper contact with the overlying ruby ranch member. take the right fork at the west end of the poison strip escarpment turning north between the poison strip escarpment on the east and gastonia point to the west. after driving up through the escarpment capped by the poorly expressed poison strip member, turn right and park on the oil-well pad, where we will have lunch and examine the yellow cat member in its type area. west end of the poison strip – the yellow cat area the type section of the yellow cat member was initially defined by a stratigraphic section described on the west side of gastonia point (kirkland and others, 1997) (figure 9). this research conducted in the early 1990s used the calcrete of aubrey (1998) as the top of the morrison formation (figure 12). during the summer of 2005, while excavating the nearby andrew’s site, kirkland recognized that both the calcrete and a chert or silcrete layer several meters lower down in the section could be correlated to another fossil-producing area known as doelling's bowl to the west (figure 16f to h). the chert layer is 5 to 30 cm thick, displays fine wavy bedding, and is associated with silicified root traces. the chert layers at doelling's bowl had been identified as being near the base of the cedar mountain formation as early cretaceous fossils are preserved just above this interval. initially, when first discovered in 1990, kirkland had assumed that the chert beds correlated to the basal calcrete. the correct correlation of the chert and calcrete bed resulted in recognizing cedar mountain formation beds below the calcrete and redefining the jurassic/cretaceous boundary downward in this area (dick and others, 2006). the presence of a poorly sorted, chert-pebble lag a short distance below 183 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the chert bed was utilized to redefine the base of the cedar mountain formation in this area. this lower yellow cat member represents a stack of ferruginous paleosols, separated by scours filled with chert pebbles (figure 43b). only the upper one or two of these paleosols at the top of the lower yellow cat member is characterized by pedogenic carbonate nodules (kirkland and madsen, 2007). figure 43. cedar mountain exposures at yellow cat road section (yc) on the west end of the poison strip (figure 41). (a) yellow cat member on the west side of the yellow cat road from the northeast. modified from kirkland and madsen (2007). (b) lower yellow cat member paleosols on the west side of the yellow cat road. (c) same outcrop as in figure a from the east. yc = yellow cat member. (d) upper yellow cat and poison strip members long the east side of the yellow cat road. note the difficulty in distinguishing the poison strip member along the road. (e) upper yellow cat as exposed just to the east of the yellow cat road. (f) series of limestone beds within the poison strip member a bit farther east than shown in figure d. laterally the limestone includes a carbonate bed that is basically a limestone conglomerate filled with broken dinosaur bone shards. (g) poorly exposed ruby ranch member at the top of the section. 184 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the upper yellow cat overlying aubrey’s (1998) calcrete is largely lacustrine with fossils concentrated in the lower and upper parts (lake margins?). several nedcolbertia have been recovered from the base of the sequence and it has been hypothesized that they became trapped in the mud at the the edge of a lacustrine system, accounting for the bias toward preserving the legs and tails of these small dinosaurs (kirkland and others, 1998a). a laterally extensive dinosaur track site is preserved at the base of a bioturbated crevasse splay near the top of the yellow cat member (lockley and others, 1999) where the tracks are mostly preserved as natural casts (figures 22k, 42, and 43). as with similar sites, fluvial sandstone beds are not well developed in the overlying poison strip member. where the road crosses the outcrop belt is an excellent place in which to observe how the fluvial sandstone of the poison strip hold up the cliffs and interfingers with the interfluvial facies from the southeast and southwest (figure 43). given the numerous dinosaur localities in the area and the excellent access afforded by the yellow cat loop road, a stratigraphic section was measured and described along the east side of the road to serve as a reference section for both the yellow cat and poison strip members (figure 41). excavations of many significant fossils have been made within 5 km of this point by the prehistoric museum in price, dmns, and the ugs. several type species are included in this list, including the first dinosaur described from the cedar mountain formation, the giant dromaeosurine utahraptor ostromaysorum (kirkland and others, 1993), gastonia burgei (kirkland, 1998a), nedcolbertia justinhoffmani (kirkland and others, 1998a), hippodraco scutidens (mcdonald and others, 2010), yurgovuchia doellingi (senter and others, 2012a) all from the yellow cat member, and from the overlying poison strip member, venenosaurus dicrocei (tidwell and others, 2001), planicoxa venenica (dicroce and carpenter, 2001), and cedroestes crichtoni (gilpen and others, 2006). several additional new species are under study by researchers at all three institutions. eventually this small outcrop area will be the source of more than 10 genoholotype dinosaur specimens, making it one of the very most important paleontological research areas in the country. in addition, this area yielded a rich assemblage of associated fossil vertebrates that includes lungfish tooth plates, a hybodont shark spine fragments and teeth, and spiral coprolites preserving abundant ganoid scales, turtle shell fragments, crocodilian teeth, and rare eileenodontid sphenodontian jaw fragments. day 1 (pm) – cedar mountain formation on the west side of arches national park region following lunch, we will drive north to i-70 then west to crescent junction (with a brief stop at the utah welcome center at the west-bound rest area). at crescent junction, we will drive south on us 191 toward moab. as we travel south, the ruby ranch member of the cedar mountain formation is visible on the left side of road toward the west-dipping slope formed by the salt valley anticline in arches national park. after travelling about 13.2 miles, we will pass the moab airport on the right. we will turn left onto the klondike bluffs road, a dirt road 1.5 miles south of the airport. traveling southeast on this winding road, we will pass through the cedar mountain section for a few miles. take a left as we drop into the little salt valley and drive about 1.5 miles to the next stop where we will examine the yellow cat member of the cedar mountain formation before proceeding back up through the klondike road section (figure 44). klondike bluffs section – yellow cat through lower ruby ranch members a poorly indurated pebble conglomerate marks the base of the yellow cat member at this section. paleosols are only moderately well developed in the red mudstone beds of the lower yellow cat member, but there are a number of unusually preserved casts of small in situ tree stumps (figure 44g). a bluish-gray, cherty limestone has been picked as the top of the lower yellow cat, but the contact may be higher in the section. a second ledge-forming septarized limestone bed occurs higher in the section with carbonate nodules occurring below the bed. therefore, picking the contact between the lower and upper yellow cat is not as clear as in sections farther north. dinosaur fossils are preserved in the upper yellow cat in this area with one site best described 185 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 as a fragmentary dinosaur bone conglomerate with many small pieces of complexly pneumatic sauropod vertebra. intact material consists of sauropod toe bones, spatulate sauropod teeth, and theropod teeth. this site has never been investigated properly. the base of the poison strip member is a sharp contact and placed at the base of a thick fluvial sandstone that is exposed along the entire western side of arches national park (figures 15k, 21b, 44a, and 44f). the top of the poison strip member consists of an amalgam of sandstone channels and interfluvial units (figure 15k). at the klondike bluffs section, isolated ribbon sandstone beds in the lower ruby ranch member may cut down into the top of the poison strip member, making the pick of the upper contact difficult (figure 45a). however, tracing these sandstone beds laterally demonstrates that they interfinger with a continuous sequence of mudstone beds with abundant pedogenic carbonate nodules. the lower ruby ranch member is typical of exposures across the northern paradox basin. it is composed mostly of pale-purplish-red to pale-green mudstone slopes covered with carbonate nodules and includes isolated southwestto northeast-trending ribbon sandstone beds. one dinosaur site is recorded south of the section that included an iguanodont jaw fragment in the float. the site is unusual as the bone is permineralized in red chert like many bone sites in the morrison formation. carbonate nodules are pervasive in the site and may partially to completely encase many of the bones. as difficult as this site may be to excavate, it certainly deserves a more careful exploration in the future. we will drive slowly back up the road to observe these characteristics of the poison strip and lower ruby ranch members. after crossing the top of the lower ruby ranch member, turn right on a small track heading directly west and park on the broad bench formed by the klondike river facies of the ruby ranch member. klondike bluffs section – klondike river and lake carpenter facies in about 2010, kirkland was contacted by ken carpenter regarding a thick lacustrine sequence in the naturita formation (= dakota formation) east of the moab airport. on inspecting the site, we found that the lacustrine sequence was capped by the quartzite-rich pebble conglomerate of the basal naturita (= dakota). these strata had been mapped as part of the naturita formation (= dakota formation) since they were organic rich in their lower part and rested upon a thick, laterally extensive conglomeratic fluvial sandstone (e.g., doelling, 1985). this conglomerate consists mostly of gravel-sized chert pebbles with some larger carbonate clasts derived from the underlying ruby ranch member (figure 45b). additionally, from the top of the main bluff capping our section, we observed that this fluvial sequence was simply a very large ribbon sandstone, 0.4 km across and extending north along the west side of arches national park, that we refer to as the klondike river. the base of the lacustrine sequence includes organic-rich strata initially described as coaly. these strata preserve the only identifiable plant material in the ruby ranch member and include fragments of the horsetail equisetem and ferns. these strata (figure 45c) are in a greenish weathering zone that preserves a siliceous dolostone at its base. we correlate that basal siliceous dolostone to the siliceous dolostone preserving the mill canyon dinosaur tracksite 4.7 km south-southwest of here (lockley and others, 2014a, 2014b) (figure 45e). these dolostones were at first thought to represent altered volcanic ash; they are not. however, they were sampled for zircons and the second one up section (figure 45c) yielded a maximum age of 113 to 112 ma (montgomery, 2014). this age, however, may soon be irrelevant as samples collected from several volcanic ashes in the lower part of the sequence are pending and could potentially provide more accurate u-pb ages. it is useful, at least locally, to note that the main body of the lacustrine sequence may be divided into three subequal intervals based on the overall color of the weathered strata. these are: (1) lower third of the sequence weathers drab green and is characterized by dark organic shales with plant debris, light-gray siliceous dolostone and sandstone. tiny (1–2 mm) reddish-brown vesicular beads of calcite are a unique character186 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 44. caption on following page. 187 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 istic of this interval. (2) middle interval weathers silvery gray and is characterized by fresh dark olive-black, well-laminated, calcareous shale, dolostone, and high-magnesium carbonate with fish debris. this interval appears to represent the deepest water and has the greatest lateral extent. (3) upper interval weathers yellowish and consists of pale-yellowish-gray limestone and dolostone preserving freshwater mollusks and fish debris capped by a resistant dark-brownishstained dolostone marker bed. we recognize the same three intervals to the south along the axis of the lake at the mill canyon dinosaur tracksite. the same lithostratigraphy of the limestone sequence at both sites supports our correlation between these areas. the recognition of fish fossils raised hopes that complete fish might be located within these beds. therefore, the universty of texas at san antonio funded a trench to be excavated through these beds to collect fresh material for lithological and geochemical analysis, and perhaps uncover more complete vertebrate remains. although no significant vertebrate remains were found, a significant amount of data resulted. the section excavated and described is approximately 30-m thick and starts at the top of a prominent conglomerate (“klondike river facies”). samples were collected every 25 cm to develop a c-isotope chemostratigraphic profile (figure 46) in an attempt to correlate this section with existing chemostratigraphic sections in the ruby ranch member, and with global c-isotope chemostratigraphic profiles. the δ13corg profile correlated well with the existing profiles of ludvigson and others (2010) suggesting the lake carpenter facies also span the aptian-albian boundary. this includes c-isotope segments c9-c11 of bralower and others (1999). lithologically, the lake sequence shows an overall shallowing environment. many of the carbonate beds are dolomitic, and stable isotope analyses of the bulk carbonate reveals positive covariance in the δ18o and δ13c plots, both of which suggest a closed-basin lacustrine environment (figure 46). interestingly, the δ18oco3 values have a distinct shift toward lighter values upsection which may indicate an increase in high altitude run off similar to the interpretation of δ18opo4 by suarez and others (2014). the trench was reclaimed, but we hope to secure a full research core through this entire sequence, especially considering the amount of data already recovered from this simple trench. no other sequence like this has been identified elsewhere in the ruby ranch member. the ruby ranch member underlying the klondike river facies compares well in thickness with sections of the complete ruby ranch section to the east and to the west (figure 11). additionally, this upper ruby ranch lacustrine sequence seems to extend nearly the entire length of the western side of the salt valley anticline from the north end of the structure south to near the end of this outcrop belt near dalton wells. given this pattern we hypothesize that this lacustrine system was a result of early cretaceous salt tectonic activity with subsidence along the west side of the salt valley anticline resulting from figure 44 (figure on previous page). klondike bluffs road section (kb) and the lower cedar mountain formation. (a) klondike bluff road section (kb, figure 11) measured in four parts: 1) the lower section of the yellow cat member was measured from 38°46'4.68"n, 109°42'34.45"w to 38°46'4.53"n, 109°42'38.81"w, 2) the middle section of the poison strip member through the klondike river facies of the ruby ranch member from 38°46'16.89"n, 38°46'16.89"n to 38°46'6.62"n, 109°43'31.51"w, 3) the lake carpenter section was trenched by a track-hoe from 38°45'54.00"n, 109°43'36.83"w to 38°45'59.52"n, 109°43'39.68"w, and the last short interval from the dense brown dolomite marker bed to the basal naturita conglomerate from 38°45'55.20"n, 109°43'51.68"w to 38°45'54.84"n, 109°43'52.73"w. explanation of symbols in figure 10. (b) index map for section. (c) portion of poison strip member. (d) trough cross-bedding in course-grained sandstone to pebble conglomerate trending to the northeast. (e) contact between the yellow cat and poison strip members at the base of the middle section. (f) yellow cat member of cedar mountain (lower section). red line represents basal contact with morrison formation. (g) sandstone filled stump in lower yellow cat member with arrow indicating position in section in figure f. 188 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 salt shifting into the axis of the anticline from the west. doelling (1985, 1988; doelling and kuehne, 2013a) had speculated that salt tectonics continued in the northern paradox basin into the early cretaceous; these data support their hypothesis. beyond our research on the section at the klondike bluffs road area and research by montgomery (2014) and research on the mill canyon dinosaur tracksite by lockley and others (2014a, 2014b), there has been little research on the lacustrine strata in the lake carpenter facies. we and others have noticed that this sequence is nearly completely composed of highly smectitic clays in the northern end of figure 45. caption on following page. 189 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the lake (kirkland and others, 1997, 1999; mori, 2009) and considered this to be a lens of the mussentuchit member preserved east of the san rafael swell. this is not compatable with our current understanding of these strata, as the first quartzite-rich conglomerate of the 3rd cedar mountain chronofacies (hunt and others, 2011; hunt, 2016) marking the base of the muddy-mowry sequence occur above the lake carpenter facies (figures 37, 45i). perhaps, wind directions across the surface of the lake were predominately to the north, such that floating vesicular glass shards from volcanic ash falls tended to drift north, enriching this area in ash that altered to smectite. future research on this system would prove or disprove this hypothesis. following our examination of the klondike river and lake carpenter facies of the ruby ranch member, we will return to us 191 and head south (left turn) for 2.5 miles where we will turn left onto the dirt road at dalton wells. we will drive a few hundred meters and park below the cottonwood trees to discuss the geological and paleontological history here. dalton wells quarry the use of the plural term dalton wells, as opposed to the singular dalton well, has been researched by brooks britt, who found that use of the plural is consistent with use by the dalton family and the local community. the use of the singular on the merrimac butte 7.5-minute quadrangle is an error on the part of the u.s. geological survey (eberth and others, 2006). however, the use of the plural is being challenged by others (kinneer and others, 2016). during the 1930s, a civilian conservation corps (ccc) camp was established here, known as cg-32, dalton wells camp. the site was also used briefly during world war ii as a japanese internment camp, of which the concrete slabs and cottonwood trees are the last remnants. southwest of us 191, the moab fault cuts through the cedar mountain outcrop belt juxtaposing the triassic-jurassic wingate sandstone (lucas and others, 2006; lucas and tanner, 2007; kirkland and others, 2014) and the underlying upper triassic chinle formation on the west side of the fault against the cedar mountain formation. this fault has been a conduit for fluids that have altered the adjoining strata (chan and others, 2000; garden and others, 2001), giving both the morrison formation and the yellow cat member of the cedar mountain formation their distinctive green color (eberth and others, 2006). the dalton wells quarry is visible on the point at the west end of the escarpment, which is held up by the poison strip member capping the less resistant beds of the yellow cat member of the cedar mountain formation above the much thicker brushy basin member of the morrison formation to the northeast across courthouse wash (figure 47). the dalton wells quarry is very significant in the history of paleontological research on figure 45 (figure on previous page). upper cedar mountain formation at the klondike bluff section (kb, figures 44 and 11). (a) upper part of middle section with dark-brown ribbon sandstone at base of ruby ranch member cutting down into top of the lighter, more laterally extensive sandstone of the poison strip member; klondike river sandstone facies capping bluff above typical section of the ruby ranch member. (b) coarse-grained, trough cross-bedded klondike river facies conglomerate with many large multi-centimeter, angular carbonate interclasts derived from underlying ruby ranch member. (c) basal organic-rich (coaly) lake carpenter facies with siliceous dolostone that correlates with or nearly with the mill canyon dinosaur tracksite. position of siliceous dolostone sample for u-pb dating that yields a proximately 113 to 112 ma maximum age. (d) well-exposed lake carpenter facies west of moab airport viewed from east with three-fold division of well developed lacustrine lake carpenter facies: 1) low drab green organic shale, gray siliceous dolostone, sandstone, and plant debris; 2) middle interval weathering silvery gray (fresh dark olive black), well-laminated, calcareous shale, dolostone, and high-magnesium carbonates with fish debris; and 3) upper yellowish limestone and dolostone interval with scattered freshwater mollusks and fish debris capped by dark brownish marked dolostone. (e) view toward south-southwest along thalwag of klondike river to mill canyon dinosaur tracksite designated by red star. (f) view of exposures of lake carpenter facies as viewed from the northwest. (g) sampling track-hoed trench through lake carpenter for geochemistry and microfossils. (h) upper trench below naturita formation. (i) upper contact of cedar mountain formation with basal conglomerate of naturita formation. (j) reclaimed track-hoed trench; mb = dense, dark-brown dolostone marker bed. 190 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 46. detailed lithological profile of the upper ruby ranch portion of the klondike bluffs section (kb) with carbon isotope profile of bulk sedimentary organic carbon from montgomery (2014). also shown are the δ18o versus δ13c cross plots of bulk carbonate samples (both calcite and dolomite) showing positive covariance in their values. 191 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 47. dalton wells quarry. (a) location of dalton wells quarry near us 191. (b) view of the site from southwest. (c) view of site from northwest. (d) brigham young university excavation team in the 1990s pictured from right to left is dee hall, brooks britt, and ken stadtman. (e) dinosaur vertebral centrum in situ. (f) utah fire, forestry, and state land’s sign explaining state law forbidding the pillaging of fossil sites on state lands. (g) quarry map from britt and others (2009). ms = medial dinosaur track-bearing sandstone. 192 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the cedar mountain formation (britt and stadtman, 1997; eberth and others, 2006; britt and others, 2009) because: (1) it may be the first paleontological site discovered in the cedar mountain formation and is certainly the first site discovered in the yellow cat member, (2) it is one of the largest known single paleontological sites in the lower cretaceous of north america and is certainly the largest known in the yellow cat member, and (3) with nine dinosaur taxa recognized, it preserves the most diverse single dinosaur fauna yet known from any single paleontological site in the lower cretaceous of north america. the quarry has been worked since the 1970s by byu, and to date, more than 4200 dinosaur bones have been recovered and many thousands more await excavation. an area of only 215 m2 has been excavated and it is estimated that the entire bonebed extends over 4000 m2 (eberth and others, 2006; britt and others, 2009). the most abundant dinosaur is a yet to be named sauropod nick-named “moabosaurus” with a minimum of 17 individuals (figures 17o and 17p). the locality is managed by the utah division of forestry, fire, and state lands. the yellow cat section is extremely thin at this site (figure 47) and, as on the entire west side of arches national park, there is no massive pedogenic carbonate in the yellow cat member or for that matter, no carbonate beds at all. the base of the yellow cat is placed at the first concentration of chert pebbles, which is at the base of the bonebeds. eberth and others (2006) interpreted the site to represent a 2-m-thick succession of four stacked bonebeds deposited in a back-bulge setting by subaerial debris flows (cohesive mudflows) triggered by intense rainfall or seismic events, which transported the bones over a relatively short distance. they interpreted the carbonate cementation of the poorly sorted host matrix to represent a calcrete formed through diagenesis and not paleosol development. we concur that there is no genetic relationship between the calcretes north of arches national park and the bonebeds at dalton wells. we consider that as opposed to a backbulge model for depositional pattern at dalton wells, perhaps salt tectonics and the proximity to the moab fault is in part responsible for this unusual sequence. the presence of utahraptor, nedcolbertia, cedarosaurus, and gastonia at the dalton wells dinosaur quarry supports its inclusion in the upper yellow cat member as described above. kirkland and madsen (2007) erroneously assumed that there was no evidence of the lower yellow cat interval along the west side of arches national park, but beyond the basal pebble bed, there is no lower yellow cat member at dalton wells. britt and others (2009) noted that there are mostly juvenile animals preserved at dalton wells. additionally, they noted that there was an exceptional amount of bioerosion of the bones due to the activity of invertebrates. from here we will return to us 191 and go north (turn right) for 2.3 km (1.4 miles), and, as we exit the narrows formed by the poison strip member, turn left (carefully) onto the dirt mill canyon road. we will follow this road for approximately 3 km (~2 miles), taking the left fork as we drive out of the dry wash onto the flats and continuing south until a right turn takes us into large parking area lined with bright red sandstone boulders. from here we will walk down the short trail to the mill canyon tracksite. mill canyon dinosaur tracksite the mill canyon dinosaur tracksite (mcdt) was discovered by a local resident riding down the abandoned access road below the powerlines. the mcdt is in the ruby ranch member of the cedar mountain formation, located on blm land near moab, and is the largest and most diverse of the eight known cedar mountain tracksites. although well known for its lower cretaceous vertebrate fauna, the cedar mountain formation is lesser known for its dinosaur tracksites because few of its many tracksites have been described (lockley and others, 1998, herein). among the best known tracksites are the arches national park sites (lockley and others, 2004; martin and others, 2014) and another unnamed tracksite on utahraptor ridge (figures 19, 22i, and 22j) which has a large assemblage of what may be north america’s oldest bird tracks (lockley and others, 2015). both are important locations and within a 20-km radius of the mcdt. preliminary findings from the mcdt site (lockley and others, 2014a, 2014b) indicate the presence of at least eight named ichnotaxa including three distinct 193 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 theropod track morphotypes, identified as irenesauripus, a dromaeosauripus-like form, and an unnamed ichnite. poorly preserved bird tracks have also been identified. sauropod tracks include brontopodus and another morphotype of probable titanosaurid affinity, and manus-only sauropod undertracks. the ornithopod tracks at the site resemble caririchnium. the tracks are in the upper part of the ruby ranch member. however, the trackbed is complex lithologically and best described as a light-gray, microcrystalline impure cherty dolostone, having a hardness of 5.5. the hardness of the track-bearing layer has contributed to its preservation. in fact, in addition to the main tracksite area (figure 48), which has at least 175 well-defined tracks and undertracks comprosing more than 20 trackways, there are two nearby areas, one to the north that has about 35 tracks in at least eight trackways (lockley and others, 2014a, 2014b) and another one to the east that has about 30 tracks. both of these areas are within about 100 m of the main site and are on the same surfigure 48. mill canyon dinosaur tracksite. (a) soon after discovery, a sauropod-theropod dance floor. (b) more large theropod and small sauropod tracks. (c) a small theropod trackway; perhaps an ornithomimid (track length about 25 cm). (d) dromaeosaurid trackway. (e) another view of dromaeosaurid trackway. (f) crocodilian resting trace. (g) theropod heading for boardwalk. (h) site is all cleaned and ready for visitors. (i) fully interpreted site was dedicated in 2016. artwork in i by brian engh. 194 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 face, which is intermittently exposed over a large area between and around these sites. the mcdt is one of six tracksites in different geological formations on federal land near moab that have recently been developed for public visitation and interpretation. partly with such developments in mind, the mcdt has been subject to special study using innovative strategies. first the site was considerably enlarged from the size of the original natural exposure, using mechanical excavation techniques, which are not often used at tetrapod tracksites. unusually, for research in this region, this phase of work was funded through university of colorado (denver) by the korean national research institute of cultural heritage. second, the site was subject to a thorough photogrammetric survey which provided images for publications (e.g., lockley and others, 2014b) and interpretative signs. third, a boardwalk up to 80 m long and 2 m wide was installed over the site so that visitors can “walk with the dinosaurs” without stepping on or damaging the tracks (figure 48g to i). a shade ramada was also installed. utah friends of paleontology and moab giants were community partners in these efforts during most phases of the project. the mcdt has revealed a number of enigmatic traces that can broadly be described as slip and scratch marks. some resemble swim tracks but cannot definitively be placed in this category. likewise, the largest of these traces, a pair of elongate grooves, are only tentatively inferred to be of possible crocodilian origin (lockley and others, 2014a). an herbivore coprolite was also found in the middle of the main site (lockley and others, 2014b). the site has considerable potential for further excavation and future study. from here we will return to us 191, drive north to i-70, and return to green river, utah, where we will spend the night. day 2 (am) – cedar mountain formation south of green river, utah white sands missile launch complex we leave green river at the east end of town, crossing south over i-70 and turning left (east) on the frontage road. abandoned steel buildings to the right were part of the (now decommissioned) green river missile launch complex, a part of the white sands missile range. the site played an important part in the development of the athena and pershing cruise missiles as they were launched from here and crashed into white sands, new mexico. the army has turned this area over to the blm, which keeps careful track of the area due to its heavy atv usage and its scientific importance. note, that the cuesta to the left (north) is held up by the calcarenites (transgressive carbonate sandstones) of the upper turonian juana lopez member of the mancos shale. after driving 5 km (3 miles) on the frontage road, turn right and proceed south on the crystal geyser road. field crews of the denver museum of science and nature used the steel building on the right as their base of operations in the late 1990s. they recovered several isolated dinosaur bones on the dip slope formed by the basal conglomerate of the naturita formation (= dakota formation). upper paludal and coastal sediments preserve a few resistant sandstone beds in this area and form part of the valley shaped by erosion of the basal tununk member of the mancos shale. through much of eastern utah and western colorado, a lag of the small oyster pycnodonte newberryi (often referred to as “devils toenails” and sometimes still incorrectly referred to the jurassic genus gryphaea) marks the base of the tununk, and where the transgressive marine sandstone of the naturita formation (= dakota formation) are well preserved, the top of the naturita (young, 1960; kirkland, 1996; santucci and kirkland, 2010). pycnodonte, like gryphaea, with which it is convergent, lived in shallow marine environments of normal salinity, low turbidity, and low sedimentation rates as it spent most of its life floating on its left valve on the substrate and had no ability to move on its own. thus, it is characteristic of transgressive marine sequences (kirkland, 1996). the crystal geyser road winds down section through the cedar mountain (figure 23g and h) and morrison formations for 2.7 km (1.7 miles), where the road turns west at an east-west-trending fault, where the salt wash member of the morrison on the north is against the juana lopez member of the mancos shale on the south. the cold-water (co2) crystal geyser on 195 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the green river and older pleistocene spring and geyser carbonate deposits are associated with this fault (kirkland and madsen, 2007). immediately past the bluff of mancos shale on the left, turn left onto the crystal geyser safari route. this road has been improved recently to facilitate the installation of a power line. after crossing the mancos shale for 1.3 km (0.8 miles), the road winds down and across little grand wash up onto a bench formed by channel sandstones in the poison strip and ruby ranch members. after about 0.5 km (0.25 miles), take the right fork and continue on the crystal geyser safari route. continue to wind south and back around to the north to skirt a large ribbon sandstone in the ruby ranch member. we will follow this exhumed channel sandstone on the right side (east) for the 0.8 km (0.5 miles) as we head south-southeast before dropping back down section to the level of the brushy basin member. continue south-southwest up a canyon rimmed by fluvial sandstone of the poison strip member for about 0.62 km (1 mi). pull over on a faint track and park here. the lower part of the don's ridge section was measured on don's ridge to the southwest and the upper part of the section was measured on the east side of the road (figure 49). in this area, the yellow cat member of the cedar mountain formation can be divided into lower and upper sequences by a laterally continuous, calcareous, dark-brown sandstone (caprock) that may be encrusted locally by stromatolitic-looking mounds of carbonate (figures 16a-e and 49a). as with the lower yellow cat interval northeast of arches national park, the lower yellow cat in this area is characterized by common chert pebbles floating in fine-grained matrix and in lenses. however, paleosols are not nearly as well-developed here and the chert pebbles tend to be significantly larger. the possible correlation of the caprock in the area of the green river missle launch complex with the gravelly, calcareous sandstone at the top of the calcrete at the ruby ranch road section (figure 15c to e) needs to be tested. the excavation of vertebrate remains at sites in both areas will provide a biostratigraphic test of this correlation, as will paleomagnetic studies and acquiring more radiometric ages. there are several important fossil sites within 1 to 2 km (mile) to the east that have been excavated and researched by the ugs in this area at the base of the cedar mountain formation (figure 16a to e). the suarez site was turned over to the utah state university eastern’s prehistoric museum for excavation as discussed above. the crystal geyser site is currently being excavated by the north carolina museum of natural history on the far side of the bench on which the ugs originally worked. here, they have uncovered parts of a sauropod in addition to numerous bones of falcarius utahensis (l.e. zanno, north carolina museum of natural history, personal communication, 2016). don’s ridge dinosaur sites in 2005, while prospecting for fossil sites, ugs paleontologist don deblieux found a relatively small area of less than 1 km2 that preserves about a dozen bone-bearing sites at multiple stratigraphic horizons below the caprock identified at the crystal geyser quarry. at least two bone-bearing intervals can be traced for several hundreds of meters and incorporate several individual sites (figure 50). the lowest interval is near the base of the lower yellow cat and consists mostly of broken sauropod bones in association with lenses of chert cobbles and carbonate mounds, which might represent spring deposits (suarez and others, 2007b). another zone of bonebeds is near the middle of the lower yellow cat and is also associated with lenses of chert cobbles and broken bones, but in contrast to the lower interval, preserves skeletal associations of iguanodonts, sauropods, and ankylosaurs. this area has become known as don's ridge. the lower yellow cat is 9.3 m thick at don's ridge, which is more than four times thicker than in the area around the crystal geyser quarry, and preserves much larger chert clasts than it does in the crystal geyser area to the east (figure 50c). the thickness of this interval makes it a prime candidate for paleomagnetic studies, which are being conducted by kate ziegler and linda donohoo-hurley at the university of new mexico. ziegler (2008) and ziegler and others (2007) recovered preliminary evidence that indicates the yellow cat was deposited, at least in part, before the magnetic long normal began at the base of the aptian (ogg and hinnov, 2012). 196 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 49. don's ridge section. (a) cedar mountain section at don's ridge (dr) measured roughly from 38°53'40.68"n, 110° 5'40.38"w to 38°54'22.20"n, 110° 5'29.51"w. stratigraphic symbols after figure 10. (b) index map for stratigraphic section. (c) ruby ranch member of cedar mountain formation at top of the section. (d) unusual example of significant erosional relief on the surface of the morrison formation prior to cedar mountain deposition. (e) cedar mountain formation north of don's ridge. 197 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 it is interesting that the lower yellow cat, as well as the entire yellow cat member, pinches out a few kilometers to the west (figure 23g and h). preliminarily, it is thought that the lower yellow cat interval at don's ridge represents a mixed-load river system developed on the unconformity at the base of the cedar mountain formation (figure 49c). additionally, the larger size of the chert clasts (having a maximum diameter of greater than 30 cm) suggests that perhaps the lower yellow cat at don's ridge has a genetic relationship with the buckhorn conglomerate in its type area, implying that the buckhorn conglomerate is older than the poison strip member. research at the don's ridge area is still ongoing and promises to be very productive geologically and paleontologically. from here we will return to i-70 at green river and drive west for 26 km (16.2 miles) before exiting at the hanksville exit (exit 149). as we drive west on i-70, we will drop down section from the juana lopez member of the mancos shale through the ruby ranch member figure 50. don’s ridge dinosaur sites. (a) aerial view of don's ridge from northeast. (b) lower yellow cat section at don's ridge south; cm/mor = cedar mountain-morrison formations. (c) upper dinosaur site at don's ridge south with cobble to pebble lag below bone layer resting on zone of thin chert layers (cb). (d) cedar mountain section as viewed from don's ridge north, iguanocolossus type locality (umnh 1206) above bonebed of mostly broken sauropod bones with chert cobbles. (e) yellow cat section viewed from iguanocolussus type locality as don deblieux poses with rare intact, jacketed sauropod humerus. 198 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 of the cedar mountain formation. it is important to note that the naturita (= dakota) is absent here as in many areas in the vicinity of the san rafael swell (eaton and others, 1990; kirkland and madsen, 2007). at this exit we will turn right on the dirt road along the base of the buckhornmorrison escarpment and drive west for approximately 1.6 km (1 mile) to have lunch and discuss the nature of the cedar mountain formation in the buckmaster draw area. buckmaster draw section looking up the long slope formed by the brushy basin member of the morriosn formation, the capping buckhorn conglomerate member of the cedar mountain formation is clearly visible. the large boulders along the road are also buckhorn that have rolled down the slope. a stratigraphic section was measured to document the rapid thinning of the cedar mountain below the unconformity at the base of the mancos shale and to accurately locate and describe the upper contact. this was done a few kilometers north in the buckmaster mining district. at this section, the buckhorn conglomerate is absent and the yellow cat facies of the buckhorn conglomerate forms the base of the section below the ruby ranch member (figure 51). the basal cedar mountain contact is placed at the base of a thin conglomeratic mudstone that unconformably overlies a yellowish-orange-stained upper contact of the morrison formation. there is only 5.5 m of yellow cat facies with a well-developed zone of chert beds in the middle of the member below the carbonate-nodule-rich mudstone of the ruby ranch member. looking south, a thick cliff formed by beds of the correlative buckhorn conglomerate is visible above our lunch spot (figure 51e). to the north the buckhorn conglomerate forms the base of the section again 17 km north of i-70 and continues without a break to the north end of the san rafael swell. the ruby ranch member includes several ribbon sandstone beds in the area and is unconformably truncated by a pebble bed mixed with shells of pycnodonte newberryi at the base of the tununk member of the mancos shale (figure 51a). day 2 (pm) – cedar mountain formation west of hanksville following lunch, we will proceed back south across i-70 and continue on sr 24 for 66 km (41 mi) to hanksville. to the right, the flatirons of the lower jurassic navajo sandstone form the san rafael reef for most of the drive to hanksville. the first 6.5 km (4 mi) we will drive on top of the salt wash member of the morrison formation. buckhorn conglomerate caps slopes of the brushy basin member of the morrison formation on the left (east). as we drop down section through the basal tidwell member of the morrison formation into the upper summerville formation of the san rafael group to the san rafael river, we cross an approximately 40-km-wide saddle of middle jurassic san rafael group strata geographically separating upper jurassic and lower cretaceous strata on the eastern side of the paradox basin from correlative strata on the north end of the henry mountains basin. an extensive dune field discontinuously covers these jurassic strata across this saddle. there is a combination of active dunes and dunes stabilized by vegetation. this probably reflects an environment similar to that of the lower campanian djadokhta formation in mongolia’s gobi desert. there is an abundance of small vertebrates (lizards, birds, and mammals) living in the high desert on the colorado plateau as there were in the late cretaceous of the gobi desert. coyote and bobcat would reflect the cretaceous carnivores like velociraptor and oviraptor, while the pronghorn would be analogous with herbivores such as protoceratops and pinacosaurus. in hanksville, we will turn right (west) on sr 95 toward capitol reef national park. following the fremont river for the next 6 miles, we will slowly rise up section through the upper san rafael group to the brushy basin member of the morrison formation. here we will pull over well to the right side of the road to discuss the absence of the cedar mountain formation on the east side of the henry mountains basin. hanksville section identification of the formations at the hanksville section was the subject of considerable debate (kirkland and madsen, 2007). at this section, the naturita forma199 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 tion (= dakota formation) includes a lower conglomerate unit, a middle carbonaceous unit, and an upper condensed transgressive sandstone unit, a succession that is typical across much of the colorado plateau (young, 1960; kirkland, 1990, 1991). however, underlying the naturita (= dakota), kirkland (in kirkland and madsen, 2007) argued that the light-colored interval below the naturita formation (= dakota formation) (figure 52) represented the cedar mountain formation as it does in sections on the west side of the henry mountains basin; whereas madsen considered this interval the upper morrison formation, arguing that cedar mountain formation was not preseved at this section. during april 2005, the ugs geologic mapping program organized a trip to define mapping units in the cedar mountain formation for future mapping of geological maps at the 7.5-minute quadrangle scale. an ash was identified at this section a short distance below the contact with the naturita formation (= dakota formation) and bart kowallis of brigham young university offered to date it. kowallis and others (2007) reported the age of the ash as late jurassic, confirming that the morrison formation directly underlies the conglomerate at the base of the naturita formation (= dakota formation) and validating madsen’s hypothesis (figure 52). kowallis and others (2007) also proposed that the conglomerate at the base of the naturita formation (= dakota formation) might represent the buckhorn conglomerate, but the abundance of eureka quartzite clasts in the conglomerate identifies it as the naturita formation (= dakota formation) (hunt and others, 2011). along this outcrop to the northwest, for about 10 km to approximately the latitude of the morrison hanksville-burpee quarry near muddy creek, the naturita formation (= dakota formation) appears to pinch out. thirteen km to the northwest at the north end of the henry mountains basin where the ford across muddy creek on the southwest side of the san rafael swell, a well-developed cedar mountain section is directly and unconformably overlain by the tununk member. a study of these stratigraphic relationships is very much a practical undertaking across this entire interval as there is a continuous, well-exposed outcrop belt. at the next stop, the cedar mountain section is much like that at muddy creek. the southeastern pinch out of the cedar mountain formation in that area on the western side of the henry mountains basin is south of notom near the southern wayne county line (figures 1 and 4). from here we will drive west. for about the next 23 km we will cross upper cretaceous outcrops in the northern henry mountains basin. for the most part, we will be driving on the ferron sandstone member of the mancos shale capping the tununk member. this middle to upper turonian delta complex is correlative to the shelf deposits represented by the juana lopez member to the east. extending the length of the henry mountains basin and western san rafael swell, the ferron is probably the best exposed large delta sequence in the world and a source of considerable organic fuel resources. it is a natural laboratory for researchers the world over. to the north is factory butte, which is formed by the blue gate shale member capped by the muley canyon sandstone; both are members of the mancos shale (eaton, 1990). our muddy creek section is north of factory butte at the north end of the henry mountains basin (figure 53). passing between the north and south cainville mesas, we will drive south along the cainville reef, which bounds the northwest side of the henry mountains basin and the southeast side of the san rafael swell. for 10 km (6 mi), the ferron sandstone and tununk member are exposed on the left (east) and the cedar mountain formation is exposed on the right. note the absence of the naturita formation (= dakota formation) in this area. following the westward curve in the road around the south end of the caineville reef, turn right into the west entrance to the fremont river ford. caineville reef exposures of the cedar mountain formation in this area are of particular interest because of rapid facies changes relative to the basal buckhorn conglomerate and the upper contact at the unconformity at the base of the tununk member. looking north across the fremont river, a well-developed cliff of buckhorn conglomerate separates the underlying morrison formation from the ruby ranch member of the cedar mountain formation (figure 54a). approximately 2.6 km (mi) to the northwest and 200 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 51. caption on following page. 201 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 west of the east hartnet road, we excavated a partial skeleton of an ornithopod from near the top of the cedar mountain formation, which is still under study. although we only described the top of the section to put the skeleton into stratigraphic context, it was clear that a thick ruby ranch member overlies a well-developed buckhorn conglomerate. like elsewhere in the region, the tununk member unconformably overlies the smectitic transitional facies of the ruby ranch member. mcllelland and others (2007) mapped the southern pinch out of the naturita formation (= dakota formation) just north of our excavation site. the ruby ranch member is several times thicker than measured at the muddy creek section 32 km to the north-northwest toward the eastern pinch out of the cedar mountain formation. a u-pb age (zircon) for the base of the ruby ranch member of 103.7 ± 2.6 ma (ludvigson and others, 2015) suggests that the upper ruby ranch was onlapping an unconformable surface on the buckhorn conglomerate (figure 53). along caineville reef, well-developed basal cedar mountain conglomerate beds come and go as discontinuous buckhorn conglomerate (mcllelland and others, 2007). however, as can be seen in these outcrops, a conglomerate caprock often occurs at the top of the sandy buckhorn conglomerate member well above the unconformable contact at the base of the cretaceous (figure 53d and f). although kirkland and madsen (2007) have not studied the cedar mountain in this area to the same degree that they had in other areas, they proposed that the lower steep, light-colored interval consisting of stacked fine-grained sandstone and conglomeratic lenses (figure 54) represents the buckhorn conglomerate member. this interval is similar to what is exposed just to the northeast of the fremont river, and these beds represent a lateral facies of the main buckhorn river channel. another hypothesis we have considered is that, in this area, the coarse-grained strata correlative to the poison strip member directly overlie strata correlative to the buckhorn conglomerate. greenhalgh (2006) and greenhalgh and britt (2007) proposed that these fine-grained sandstone beds represent the yellow cat member of the cedar mountain formation interfingering with the buckhorn conglomerate. we concur that these strata are in fact correlative with at least the lower yellow cat, but we fail to recognize the characteristics we have noted elsewhere in the interfluvial yellow cat facies of the buckhorn conglomerate member. for mapping purposes, splitting these units would be impractical. the overlying pale-colored variegated mudstone preserves common pedogenic carbonate nodules and compares well lithologically with the ruby ranch member of the cedar mountain formation elsewhere. this section also compares well with the cedar mountain section north of muddy creek, which we have studied in more detail. the ruby ranch member of the cedar mountain formation underlies the unconformity at the base of the tununk member in this area (figure 54). the naturita formation (= dakota formation) is completely removed by mid-cretaceous erosion. similar exposures are present in less accessible sections near muddy creek on the southwest side of the san rafael swell, and at the north end of capitol reef national park on the west side of the blue flats. eaton and others (1990) first documented this unusual contact at the top of the cedar mountain formation on the west side of the san rafael swell near ferron, utah. the basal tununk member at all of these sites is figure 51 (figure on previous page). cedar mountain section along the eastern margin of the san rafael swell at buckmaster draw. (a) stratigraphic section at near buckmaster draw (bd) measured from 38°58'17.19"n, 110°21'47.48"w to 38°58'18.33"n, 110°21'35.63"w. see figure 10 for explanation. (b) index map for section. stratigraphic symbols after figure 10. (c) upper ruby ranch member unconformably overlain by tununk member of the mancos shale. (d) lower half of section with yellow cat facies of buckhorn conglomerate member overlain by ruby ranch member. (e) view to south from base of section showing well developed cliff-forming buckhorn conglomerate member. (f) yellow cat facies of buckhorn conglomerate member with basal pebbly mudstone resting on iron oxide stained upper contact of morrison and well-developed chert beds near center of unit. 202 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 distinctive. it consists of a chert pebble conglomerate in a matrix of marine shale with shells of the marine oyster pycnodonte newberryi, and at several sites, shark teeth. this conglomeratic bed is in turn overlain by a few centimeters, or tens of centimeters, of mudstone followed by a dense shell bed of pycnodonte newberryi umbonata, a subspecies of pycnodonte with a relatively smooth beak area that only occurs in the basal turonian (kirkland, 1996; leckie and others, 1997). within a meter of this pycnodonte bed is the first thick (20 to 50 cm) volcanic ash (altered to bentonite) in the lower turonian. the 40ar/39ar (sanidine) age of the volcanic ash is 93.25 ± 0.55 ma (obradovitch, 1993) and 93.46 ± 0.6 ma (kowallis and others, 1995). this important volcanic ash marker bed may be readily traced across the western interior in all marine sections (elder and kirkland, 1985; elder, 1988, 1989, 1991; kirkland, 1991; kennedy and others, 2000). eaton and others (1990) proposed that the chert pebble layer at the base of the tununk was sourced from chert pebbles originally deposited in the buckhorn conglomerate. on examing the lower naturita formation (= dakota formation) at hanksville, we now propose that the source of the pebbles was more likely the basal conglomerate of the naturita (= dakota). the important thing to note at these sections is that there is convincing evidence that during one of the most rapid global eustatic sea-level-rise events in the phanerozoic, proximal to the actively subsiding cretaceous foreland basin, there was uplift along the san rafael swell in central utah that exceeded both sea-level rise and regional subsidence (eaton and others, 1990). the distribution of facies at the base of the tununk member needs to be mapped in detail across the san rafael region to determine if this was simply a broadly developed forebulge or the reactivation of known precambrian basement structures. from here, we turn left (east) on sr 95 toward hanksville and in just under 1.6 km (1 mile) , turn left again onto a dirt track on the south end of the caineville reef to get a different perspective on the relationships of the buckhorn conglomerate and its lateral facies changes (figure 54b and c). from here we will make our way back to our hotel in green river, utah, with additional stops if time permits (figure 54d and 54e). day 3 (am) – cedar mountain formation southwestern san rafael swell leave green river, utah, and drive west on i-70 west for 92.5 km (57.5 miles), crossing the san rafael swell to the rest area by milepost 103.5, where we will exit the interstate. we will make a few short stops while crossing the san rafael swell to appreciate the magnificent triassic through jurassic section exposed here. rest stop – i-70 section overview the rest area is built on light-colored transgressive marine sandstone beds of the upper jurassic curtis formation overlain by brownish-red shallow-marine strata of the summerville formation. the summerville is overlain by the morrison formation. the marine curtis lies on the regional j-3 unconformity developed on the top of the middle jurassic entrada sandstone as indicated by localized lenses of small chert pebbles on this surface. to the northwest, the buckhorn conglomerate, at the base of the cedar mountain formation, caps the morrison formation (figure 8a). in this area, the brushy basin member is similar in thickness to the sections on the west side of the san rafael swell, but the underlying salt wash member is considerably thinner. when we leave the rest area we will continue to the west on i-70; however, as we round the bend on the interstate in about 5 km (3 miles) at about milepost 98 we will slow down so that you may observe the intertonguing between the buckhorn conglomerate and the yellow cat facies of the buckhorn described below and shown in figure 8. unfortunately, it is illegal for a caravan of vehicles to stop and get out on an interstate highway so pay close attention to the cedar mountain formation exposed in the cuts lateral to the buckhorn conglomerate on the right (north) side of i-70. the ruby ranch member can be distinguished as a pale-purplish-pink mudstone with abundant carbonate nodules weathered out on the surface with a concave weathering profile in the lower slope. the overlying mussentuchit member exposed below the naturita formation (= dakota formation) has a convex weathering profile due to its high content of swelling clays. there is also a sharp but subtle color change to a pale olive gray. 203 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 52. hanksville section. middle mesozoic section west of hanksville. (a) contact between underlying morrison formation with naturita formation showing approximate position of radiometric date confirming that these smectitic strata are the upper jurassic morrison formation and not a smectitic facies of the cedar mountain formation (kowallis and others, 2007). (b) another view of section with the distribution of oyster species documenting the ecologic progression from freshwater, brackish water, beach, and shallow-shelf sand, reworked periodically by storm processes, to quiet shelf settings below storm wave base. molluscan data from kirkland (1990, 1991, 1996) and santucci and kirkland (2010). abbreviations: us = upper sandstone member, mc = middle carbonaceous member, lc = lower conglomerate member. stratigraphic symbols after figure 10. 204 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 53. caption on following page. 205 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 continue west for 10 miles, rising through the upper cretaceous section onto a bench formed by the ferron sandstone. take exit 91 and turn right (north) at the bottom of the exit onto sr 10 to emery. we will drive north to emery on sr 10, but the mussentuchit badlands are south of i-70 and worth seeing on a future trip. the badlands along mussentuchit wash are reached by turning south at this exit, driving up the hill, and following the road east above i-70 before taking the right fork south. after about 5.6 km (3.5 miles) on the ferron bench, the road drops down through the cliff and turns back to the east across the tununk member. drive about 3.7 km (2.3 miles) and take the next right fork that is just after crossing willow wash. drive south on the upper last chance road—the mussentuchit badlands (figure 32) are to the east below the naturita (= dakota formation) escarpment for the next 4 km (2.5 miles). the mussentuchit badlands are an important area for paleontological research initiated by the oklahoma museum of natural history in the 1990s and carried on by the utah state university eastern’s prehistoric museum, the chicago field museum of natural history, and the north carolina museum of natural history. the blm keeps a close watch on this area as well, and all paleontological research here must be done under blm or utah state paleontological permits. however, we are going to drive north on sr 91 from exit 10 for 25.7 km (16 miles) through the town of emery before taking a right turn angling east toward moore. after driving on this road for 4 km (2.5 miles), we will turn right once again on the moore cutoff road to the east toward i-70. head east for 4 km (2.5 miles) before the road drops down through the cliff formed by the ferron sandstone and continue on across the bench at the base of the tununk member and down through the naturita and cedar mountain formations. we will find a spot to turn around so that we may park along the westbound side of the road near the base of the cedar mountain section where we will be visible to any traffic. we will spend the rest of the morning exploring this important and accessible section. cedar mountain formation along moore cutoff road the cedar mountain section along the moore cutoff road is of particular importance because it is accessible by a paved route across the west flank of the san rafael swell crossing an unbroken section spanning the middle jurassic through middle cretaceous. with the spectacular mesozoic section exposed along the road, it is studied by geology classes from across the nation. a prominent cobble conglomerate near the top of the section has been pointed out to geology student after geology student as representing the buckhorn conglomerate. this suggested that the outcrop was noteworthy in being the only known area along the entire western san rafael swell where little or no ruby ranch member was recognized between the buckhorn conglomerate and mussentuchit members of the cedar mountain formation (kirkland and others, 1997, 1999). the ruby ranch is thick to the north and south, and such a dramatic thinning in this area is at odds with the tectonic grain of the developing cretaceous foredeep basin (see currie, 2002). while nearly every geologist and paleontologist working on the cedar mountain formation has commented to us on what a strange section of cedar mountain formation this was, no one seriously doubted that this conglomerate was the buckfigure 53 (figure on previous page). cedar mountain sections east of capitol reef national park. (a) upper portion of cedar mountain section measured on the southwest side of the blue flats (bf) west of the hartnet road measured from 38°17'38.15"n, 111°6'3.38"w to 38°17'32.63"n, 111°6'10.94"w. a much thicker ruby ranch member is exposed here overlying a well-developed buckhorn conglomerate member. (b) index map for study areas. (c) exposure of measured stratigraphic interval. (d) cedar mountain section measured to the north of the muddy river ford (mc) north and west of wild horse road from 38°32'14.82"n, 110°54'4.45"w to 38°32'11.29"n, 110°53'57.41"w. (e) ruby ranch unconformably overlain by tununk member of the mancos shale. a thick volcanic ash marker bed (bentonite c of elder (1988) overlies a mudstone-supported pebble bed at the contact. (f) soft, fine-grained sandstone described as yellow cat interfingering with buckhorn conglomerate member by greenhalgh and britt (2007) beneath a local dark-brown, calcareous pebbly sandstone marker bed. stratigraphic symbols after figure 10. 206 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 horn conglomerate. for its importance as a geological reference section, the ugs picked the short canyon 7.5-minute quadrangle for a detailed geological map. during the fall of 2006, ugs geologists hellmut doelling and paul kuehne spent a day walking kirkland back and forth across the quadrangle to show him what their mapping of cedar mountain units across this area had revealed to them. by the end of the day, they convinced kirkland that there is a thick section of ruby ranch present every-figure 55. caption to the right. figure 54. cedar mountain formation along the caineville reef. (a) buckhorn conglomerate member separating brushy basin member of the morrison formation below from ruby ranch member of the cedar mountain formation above as exposed north of turnoff from sr 24 to ford across fremont river east of capitol reef national park (38°16'30.41"n, 111°5'22.02"w). (b) exposure of basal cedar mountain formation at the south end of caineville reef (38°16'27.56"n, 111°3'58.48"w) looking west. (c) exposure of upper cedar mountain formation at the south end of caineville reef looking north. (d) exposure of basal cedar mountain formation near middle of caineville reef (38°18'3.97"n, 111°2'38.97"w). (e) exposure of cedar mountain formation near middle of caineville reef. red arrows indicate top of buckhorn member interval. red bracket indicates interval representing buckhorn conglomerate member. black arrows indicate contact between ruby ranch member of the cedar mountain formation and tununk member of the mancos shale. note the absence of naturita formation in this area. 207 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 where under this major conglomerate bed, which can be traced from the north to south end of the map area. as is typical everywhere else, the ruby ranch member here is largely non-smectitic and contains a great abundance of pedogenic carbonate nodules. additionally, hiking down through the section several kilometers to the north along short canyon, a lower major conglomerate bed at the base of the ruby ranch member was identified that almost certainly represents the buckhorn conglomerate. on the south side of the moore cutoff road, we identified a cherty carbonate close to this same stratigraphic position (figure 55). at the time it was thought this might represent a spring deposit or calcrete developed on the unconformity at the base of the cedar mountain formation. the prominent conglomerate developed between the ruby ranch and mussentuchit members in this area reflects a river channel developed on the erosion surface (sequence boundary) indicated by the chert lag identified at this contact along the entire southwestern side of the san rafael swell. this conglomerate was mapped across the entire short canyon quadrangle and designated as the short canyon member of the cedar mountain formation (doelling and kuehne, 2013b). in april 2016, kirkland examined a dinosaur track site previously noted as being in the morrison formation and realized that the track-bearing sandstone included a fair amount of very coarse grained sandstone. kirkland hypothesized that bed may represent the base of the cedar mountain formation. additional evidence figure 55 (on right). cedar mountain section along the south side of the moore cutoff road (sr 803) (mr) measured from 38°56'19.66"n, 38°56'19.66"n to 38°56'4.99"n, 111°5'3.58"w. stratigraphic key, figure 10 and index map, figure 57a. abbreviations of marker beds in figure 57: bct = possible tongue or lense of buckhorn conglomerate 1.02 m thick, cb = 98 cm interval of thin chert beds in pebbly mudstone 153 cm below marked color change to thick (~16 m) overall reddish brown mudstone with abundant carbonate nodules, eb = interval of bioturbated, interbedded, en echelon grayish-orange, fine to medium-grained sandstone and reddish mudstone, rmb = lateral extensively thick 50 to 100 cm sandstone, 262 cm below top of the reddish-brown interval, tb = basal gravelly, bioturbated sandstone with dinosaur track casts. stratigraphic symbols after figure 10. figure 55. caption on left. 208 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 that supported placing the base of the cedar mountain formation here is that the track-bearing bed is above the highest smectitic mudstone typical of the brushy basin member of the morrison formation, there is significant iron straining associated with this horizon, and the overlying mudstone beds are mottled. arguments against placing the contact here are that the bed appears to be gradational with the underlying strata, a 1-m-thick pebble conglomerate occurs 14 m above the contact, and a cherty zone that is another 4 m above that. furthermore, some of the tracks may represent stegosaurids, which are not known above the jurassic in north america although there appears to be a number of iguanodont tracks, which are more abundant in the cretaceous (figure 56). the section discussed herein was described along the south side of the moore cutoff road. the track bed may represent reworking of morrison strata at the unconformity and, if these are indeed stegosaurid tracks, there is nothing against them representing a late surviving species. but it is possible that the pebble conglomerate represents more than a tongue or lens of the buckhorn conglomerate and actually represents the base of the cedar mountain formation. only further study of this interval across the area will fully determine this (figure 57). if the track bed marks the base of the cedar mountain formation, there is a total of 22.83 m of yellow cat facies of the buckhorn conglomerate below the base of the ruby ranch member. the basal 14.66 m of the ruby ranch is dominated by red mudstone with abundant pedogenetic carbonate nodules that consolidate into calcrete zones at 3 and 6 m above the base of the ruby ranch. a laterally extensive sandstone marker bed occurs at 2.5 m from the top of the red bed interval. across the road, well to the north, an extensive conglomeratic ribbon sandstone occurs at the top of the red mudstone sequence that in lateral view (from the road) resembled the buckhorn conglomerate, but is clearly too high in the section (figure 58). overlying the red mudstone is about 20 m of greenish mudstone interval capped by nearly a meter of consolidated septarian carbonate nodules. overlying that is 3 m of pale-purplish-pink mudstone with figure 56. dinosaur track casts at the base of the moore road section. (a-c) pairs of pes (larger) and manus tracks pertaining to either a small sauropod or a stegosaur. (d) iguanodont track. (e) matched pair of iguanodont tracks defining a pace. (f) theropod track. 209 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 abundant nodules capped by a very light-colored claystone marker bed that is 15 m thick and bounded by very fine grained sandstone splays. the splays averaged 0.4 to 0.7 m thick. the next overlying 13.5 m interval is once again dominated by greenish to olive-gray mudstone with pedogenetic carbonate. two well-developed ribbon sandstone beds occur in the next 10 m as the mudstone beds begin to become slightly smectitic. the uppermost 5.6 m of the ruby ranch is dark olive-gray smectitic mudstone with common carbonate nodules representing the transitional facies of the ruby ranch and is sharply overlain by the short canyon member (figure 57i). total thickness of the ruby ranch member is 61.8 m. the short canyon member consists of 3.7 m of quartzite-rich, trough cross-bedded pebble to cobble conglomerate capped by 1.4 m of very coarse grained, trough cross-bedded sandstone. the capping unit forms a broad bench below the smectitic mudstones of the mussentuchit member and a high escarpment holding up the thick section of the ruby ranch member. the overlying fine-grained portion of the mussentuchit member is 28.9 m thick and consists of highly smectitic mudstone that is often lignitic with a few beds of volcanic ash. the top 11 m contains a number of lenticular sandstone beds, some that appear to have an en echelon relationship with each other. the base of the overlying fluvial sandstone of the naturita formation (= dakota formation) is sharp. these sandstone beds preserve abundant flattened casts and molds of tree trunks and branches. a mudstone pebble bed with pycnodonte newberryi shells forms the base of the overlying tununk member of the mancos shale. geologically and paleontologically, the cedar mountain section along the moore cutoff road needs to be further studied and sampled for chemostratigraphy. the hypotheses presented here need to be tested. however, it is likely that the new stratigraphic interpretation presented here is largely correct, as it certainly simplifies the facies relationships for the cedar mountain formation on the western side of the san rafael swell. from here we will drive back toward moore, stopping for lunch at a site with native american rock art and turonian dinosaur tracks (jones, 2001), which are preserved on fallen blocks of the ferron sandstone at an interpreted site along the side of the road. following lunch, we will return to sr 10 and turn right (north) to drive 34 km (21 miles) north through the town of castle dale where we will turn right (east) on the green river cutoff road. drive about 24 km (15 miles) down section through the upper and lower cretaceous (note that the type locality of eolambia was less than 1 km (0.6 miles) south of this road, and to a flat plain formed in the valley on the middle jurassic. turn left (north) on the buckhorn draw road and proceed approximately 8 km (5 miles) to the type area of the cedar mountain formation and buckhorn conglomerate. type area of the cedar mountain formation and buckhorn conglomerate we will first briefly examine the buckhorn conglomerate, where large house-sized blocks have rolled down near the road. then we will proceed about 0.5 miles to the dam at buckhorn reservoir, where the type section of the cedar mountain shale was established by stokes (1944, 1952). unfortunately, a broad valley is formed between the basal conglomerate of the naturita formation (= dakota formation) and the buckhorn conglomerate such that much of the ruby ranch member is covered. we will continue along the road for another 2.4 km (1.5 mi) as it turns back to the west and climbs through the low ridge formed by the basal conglomerate of the naturita formation (short canyon member equivalent). this is the area where sorenson (2011) conducted research on exhumed channel sandstones and the lateral relationships between the mussentuchit and naturita (= dakota). climbing up through the naturita (= dakota) in this area, it is pretty clear that above what is mapped as naturita (= dakota) is an interval of smectitic mudstone characteristic of the mussentuchit member. the mussentuchit member is difficult to separate from the underlying ruby ranch member to the south and, if we had not found the pebble lag indicating the presence of a sequence boundary, many sedimentologists would have continued to consider the separation of the ruby ranch and mussentuchit members unjustified. however, in the northern part of its outcrop belt 210 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 figure 57. caption on following page. 211 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 the mussentuchit is part of the naturita formation (= dakota formation) overlying a contiguous basal naturita conglomerate (short canyon member equivalent). to most fully satisfy all the geologists working in the region, the most satisfactory solution is to consider the mussentuchit member a member of the cedar mountain south of the type area and as a member of the naturita formation (= dakota formation) north of the type area, where the basal conglomerate is continuous and contiguous with the naturita formation (= dakota formation) in total. this transition would seem to happen in this area (figure 59). geological mapping in this area would pin it down more accurately. farther to the north and east the mussentuchit is not recognized within the beds of the naturita formation (= dakota formation) and would truly appear to be purely a product of foreland basin development on the west side of the san rafael swell. from here, we will continue back to sr 10 for our return to salt lake city. if time permits, we can visit the utah state university eastern’s prehistoric museum in price, utah, to examine some of the fossils from the cedar mountain formation. acknowledgments all field paleontological research described herein was conducted under permits from the bureau of land management (blm), national park service (nps), and state of utah. kirkland thanks discovery communications quest grants, blm, nps, utah friends of paleontology, and ugs for funding. this publication reflects the research of a great many scientists referenced herein and the authors appreciate the countless discussions we have had with colleagues and students on these topics over the years in the field, on the phone, and at meetings. while no one else is held responsible for the ideas presented herein, none of this work was done in a vacuum and everyone’s contributions are appreciated. we thank sooz kirkland, martha hayden, ed simpson, doug sprinkel, mike lowe, tom chidsey, mike hylland, and stephanie carney for reviewing the manuscript. references alcalá, l., espílez, e., mampel, l., kirkland, j.i., ortega, m., rublo, d., gonzález, a., ayala, d., cobos, a., royo-torres, gascó, f., and pesquero, m.d., 2012, a new lower cretaceous vertebrate bonebed near ariño (teruel, aragón, spain)—found and managed in a joint collaboration between a mining company and a palaeontological park: geoheritage, v. 4, p. 275–286. al-suwaidi, a.h., 2007, a ped’s story—weathering out climatic change during the mid-cretaceous: lawrence, kansas, university of kansas, m.s. thesis, 134 p. anonymous, 2009, new ash-bed dates at dinosaur ridge: dinosaur ridge newsletter, v. 21, p. 14. arbour, v.m., and currie, p.j., 2015, systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs: journal of systematic palaeontology, 60 p. http://dx.doi.org/10.1080/147 72019.2015.1059985http://dx.doi.org/10.1080/14772019.201 5.1059985http://dx.doi.org/10.1080/14772019.2015.1059985 arens, n.c., and harris, e.b., 2015, paleoclimatic reconstruction for the albian-cenomanian transition based on a dominantly angiosperm flora from the cedar mountain formation, utah, usa: cretaceous research, v. 53, p. 140–152. aubrey, w.m., 1996, stratigraphic architecture and deformational history of early cretaceous foreland basin, eastern utah and southwest colorado, in huffman, a.c., lund, w.r., and godwin, l.h., editors, geology and resources of the paradox bafigure 57 (figure on previous page). cedar mountain strata long the moore cutoff road. (a) index map for moore road area. (b) basal, perhaps gradational contact, at base of the cedar mountain formation. (c) detail of contact with dinosaur track casts preserved under upper sandstone layer. (d) yellow cat facies of buckhorn conglomerate member with thin buckhorn tongue or lense (bct) and overlying zone of thin chert beds (cb). (e) base of approximately 16 m interval of reddish mudstone with numerous pedogenetic carbonate nodules and amalgamated carbonate nodule beds. (f) overview of red interval to south of section. (g) upper part of red bed interval in line of section. (h) sandstone marker bed near top of red bed interval (rbm) with upper ruby ranch member in distance. (i) drab, smectitic upper ruby ranch mudstone with carbonate nodules below short canyon member. (j) short canyon member. (k) view west across bench formed by the short canyon member to the exposures of the mussentuchit member capped by fluvial sandstones of the naturita formation. (l) sharp contact of basal fluvial sandstones of the naturita formation with underlying mussentuchit member. the sandstone beds preserve abundant log and branch impressions. abbreviations as plotted against stratigraphic section in figure 55. 212 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 sin: utah geological association publication 25, p. 211–220. aubrey, w.m., 1998, a newly discovered, widespread fluvial facies and unconformity marking the upper jurassic/lower cretaceous boundary, colorado plateau, in carpenter, k., chure, d., and kirkland, j.i., editors, the upper jurassic morrison formation—an interdisciplinary study, part i: modern geology, v. 22, p. 209–233. averianov, a., and sues, h-d., 2012, correlation of late cretaceous continental vertebrate assemblages in middle and central asia: journal of stratigraphy, v. 36, p. 463–485. ayers, j.d., 2004, lithological evidence of the jurassic/cretaceous boundary within the nonmarine cedar mountain formation, san rafael swell, utah: athens, ohio university, m.s. thesis, 189 p. baker, a.a., duncan, d.c., and hunt, c.b., 1952, manganese deposits of southeastern utah—a report on manganese resources in the little grand district and areas to the east, west, and south: u.s. geological survey bulletin, v. 979-b, p. 63–157. barclay, r.s., rioux, m., meyer, l.b., bowring, s.a., johnson, k.r., and miller, i.m., 2015, high precision u-pb zircon geochrofigure 58. panoramas of cedar mountain formation along moore cutoff road. (a) panorama of mussentuchit member exposures south of road. (b) panorama of cedar mountain formation north of road from the southeast. (c) panorama of cedar mountain formation north of road from the short canyon escarpment in south. abbreviations: fs = ferron sandstone member of the mancos shale, nf = naturita formation, rmbc = large lenticular channel conglomerate at about position of red bed marker sandstone (rbm in figures 55 and 57) at top of red bed interval. scc = short canyon member, tb = basal dinosaur track marker bed at top of smectitic morrison formation, ts = tununk member of the mancos shale. 213 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 fi gu re 5 9. p an el d ia gr am o f n at ur ita f or m at io n an d bo un di ng st ra ta al on g t he w es t s id e o f t he s an r af ae l s w el l w he re w e p ro po se th at th e m us se nt uc hi t m em be r b e c on sid er ed a pa rt o f t he c ed ar m ou nt ai n fo rm at io n so ut h of it s t yp e a re a a nd p ar t o f t he n at ur ita f or m at io n no rt h of th e c ed ar m ou nt ai n ty pe a re a. l et te rs a bo ve se ct io ns k ey ed to lo ca lit y m ap . n ot e t ha t t he m es a bu tte se ct io n, c , i s j us t s ou th o f o ur m oo re r oa d se ct io n fo r w hi ch w e h av e ca lc ul at ed a co ns id er ab ly g re at er th ic kn es s f or th e ru by r an ch m em be r ( fig ur e 55 ). fi gu re m od ifi ed a fte r k irs ch ba um a nd s ch en k (2 01 1) . 214 the lower cretaceous in east-central utah—the cedar mountain formation and its bounding strata kirkland, j.i., suarez, m., suarez, c., and hunt-foster, r. geology of the intermountain west 2016 volume 3 nology for cenomanian dakota formation floras in utah: cretaceous research, v. 52, p. 213–237. batton, d.j. 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at www.utahgeology.org for information. email inquiries to giw@utahgeology.org. the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. theme issue an ecosystem we thought we knew— the emerging complexities of the morrison formation society of vertebrate paleontology annual meeting, october 26 – 29, 2016 grand america hotel salt lake city, utah, usa ee bbrruusshhyy bbaassiinn mmbbrr.. bbuurrrroo ccaannyyoonn ffmm..nnoo--mmaannss iissllaanndd bbeeddss bblluuffff ssaannddssttoonnee mmbbrr.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. rreeccaappttuurree mmbbrr.. bbaassaall rreeccaappttuurree bbeenncchh uuppppeerr rreeccaappttuurree geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover unannotated (top) and annotated (bottom) photograph of the nearly complete section of upper jurassic morrison formation exposed on west side of mccracken point east of the mouth of recapture creek, navajo nation, utah. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $20 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 7 2020 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. editors society of vertebrate paleontology editors kelli c. trujillo — university of wyoming cary woodruff — university of toronto octavio mateus — universidade nova de lisboa douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com bart j. kowallis brigham young university 801.422.2467 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583-1146 geox-slc@comcast.net thomas c. chidsey, jr. utah geological survey 801.537.3364 tomchidsey@utah.gov john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov uga board 2020 president leslie heppler lheppler@utah.gov 801.538.5257 2020 president-elect riley brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 program chair paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 treasurer greg gavin greg@loughlinwater.com 801.538.4779 2020 secretary elliot jagniecki ejagniecki@utah.gov 801.537.3370 2020 past president peter nielsen peternielsen@utah.gov 801.537.3359 uga committees education/scholarship zack anderson zanderson@utah.gov 801.538.4779 environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greg@loughlinwater.com 801.541.6258 historian paul anderson paul@pbageo.com 801.364.6613 membership rick ford rford@weber.edu 801.626.6942 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education paul jewell pwjewell@mines.utah.edu 801.581.6636 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.942.0533 aapg house of delegates 2017–2020 term tom chidsey tomchidsey@utah.gov 801.537.3364 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 earthquake safety committee chair grant willis gwillis@utah.gov 801.537.3355 uga newsletter newsletter editor bill lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 geology of the intermountain west an open-access journal of the utah geological association volume 7 2020 137 abstract in 2016 and 2017, the utah geological survey partnered with the u.s. bureau of land management to conduct a paleontological inventory of the morrison formation south and west of blanding, utah, along the eastern margin of the bears ears national monument. the morrison in this region is critical to understanding upper jurassic stratigraphy across the colorado plateau because it is the type area for the bluff sandstone, recapture, westwater canyon, and brushy basin members of the morrison formation, which are the basis for nomenclature in new mexico and arizona as well. researchers have disagreed about nomenclature and correlation of these units, which transition northward in the study area into the tidwell, salt wash, and brushy basin members. numerous vertebrate localities make inclusion of the bluff sandstone and recapture members in the middle jurassic san rafael group, as suggested by some previous workers, unlikely. the salt wash member does not separate the bluff sandstone and recapture members at recapture wash, but sandstone lenses of salt wash facies occur higher in northern recapture exposures. northward, along the outcrop belt east of comb ridge, the bluff-recapture interval thins, interlenses, and pinches out into the tidwell and lower salt wash, with the main lower sandstone interval of the westwater canyon merging northward into the upper salt wash member. the partly covered, 1938 type section of the brushy basin member is identified along elk mountain road at the southern end of brushy basin. we describe a detailed, accessible morrison formation reference section about 11.2 km (7 mi) to the south along butler wash. there, 81.68 m (268 ft) of brushy basin member is well exposed along a road between the top of the westwater canyon member and the base of the lower cretaceous burro canyon formation. we informally call the upper sandstone bed(s) of the westwater canyon member that cap mesas and benches in the region “no-mans island beds.” smectitic mudstones between the no-mans island beds and the main sandstone body of the westwater canyon suggest that the salt wash-brushy basin contact to the north may be somewhat older than the base of the brushy basin member as originally defined in its type area. determining whether the no-mans island beds pinch out to the north or are removed by erosion below the regional basal brushy basin paleosol requires further research. several significant fossil vertebrate and plant sites have been documented in the brushy basin type area. newly identified volcanic ashes provided zircons for u-pb ages of 150.67 ± 0.32 ma from near the top of the brushy basin member and of 153.7 ± 2.1 ma and 153.8 ± 2.2 ma for two zircons in lower part of recapture member. at the top of the brushy basin member, ferruginous paleosols commonly overlying conglomeratic sandstone are speculated to be of early cretaceous age (detrital zircon age pending) and are assigned herein to the yellow cat member of the burro canyon formation. these iron-rich paleosols suggest wetter climatic conditions during the jurassic-cretaceous transition in the blanding basin. the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah james i. kirkland1, donald d. deblieux1, rebecca k. hunt-foster2, john r. foster3, kelli c. trujillo4, and emily finzel5 1utah geological survey, p.o. box 146100, salt lake city, ut 84114-6100; jameskirkland@utah.gov; dondeblieux@utah.gov 2national park service, dinosaur national monument, p.o. box 128, jensen, ut 84035; rebecca_hunt-foster@nps.gov 3utah field house of natural history state park museum, 496 east main street, vernal, ut 84078-2605; johnfoster@utah.gov 4albany co. campus, laramie county community college, laramie, wy 82070; ktrujillo@lccc.wy.edu 5earth and environmental science dept., university of iowa, 115 trowbridge hall, iowa city, ia 52242; emily-finzel@uiowa.edu citation for this article. kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e., 2020, the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah: geology of the intermountain west, v. 7, p. 137–195, 3 appendices, https://doi.org/10.31711/ giw.v7.pp137–195. © 2020 utah geological association. all rights reserved. for permission to use, copy, or distribute see the preceeding page or the uga website, www.utahgeology.org, for information. email inquiries to giw@utahgeology.org. 138 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 introduction in 2016, the u.s. bureau of land management (blm) requested that the utah geological survey (ugs) paleontology team conduct a preliminary inventory of paleontological resources within the upper jurassic (mostly morrison formation) outcrop belt on the west side of u.s. highway 191 on the west side of the blanding basin, utah, along the eastern margin of bears ears national monument (figures 1 and 2). this area was chosen for survey because the utah paleontological locality database, managed by the ugs, indicated that few sites had been recorded in the area. geologic maps showed that fossiliferous rocks of upper jurassic morrison formation and lower cretaceous burro canyon formation (equivalent to the cedar mountain formation to northwest of the colorado river) crop out in this region. the morrison formation in this region is critical for understanding upper jurassic stratigraphy across the southern colorado plateau because it is the type area for several important stratigraphic units including the bluff sandstone, recapture, westwater canyon, and brushy basin members of the morrison formation. additionally, for decades there has been disagreement about stratigraphic nomenclature and correlation of these units (as discussed below). utah geological surevy personnel recorded more than 50 new fossil localities in the study area. some sites yielding dinosaur bones were found in the recapture member indicating the potential for significant sites in this unit. the brushy basin member is well known for preserving abundant vertebrate fossils and many localities were discovered during this project. numerous sites contained isolated sauropod bones and a few sites had many bones eroding out over a small area, warranting additional exploration. several sites have the potential to produce vertebrate microfossils through wet screen washing (cifelli and others, 1996). one important new site is a multi-meter-thick plant debris bed, likely representing a marsh setting, that preserves numerous compressional plant fossils and petrified wood in addition to bones and bone fragments. this site is quite unusual for the morrison formation and resembles deposits better known in the upper cretaceous of the western u.s. and canada. one laterally extensive organic mudstone near the top of the morrison formation preserves a 10-cmthick (4-in) thick volcanic ash that was sampled for palynology and radiometric dating. we spent only limited time prospecting the burro canyon formation and no vertebrate localities were found. the illegal collection of vertebrate fossils has been an ongoing problem in the morrison formation outcrops in utah for many years (e.g., bertog, 2014; foster and others, 2016b). although one site in the morrison formation, salvaged by the blm, had been vandalized by unauthorized excavation, the morrison formation in this area appears considerably less vandalized than morrison fm. outcrop utah az nm co wy study area type tidwell mbr. o’sullivan (1984) bh cr d f j t bm type tidwell mbr. peterson (1988) type salt wash mbr. area type burro canyon formation 100 miles 100 km 6 41 2 a a' 3 5 figure 1. the morrison formation outcrop belt in utah and the four corners region with the location of the blanding basin study area indicated. line of cross section a–a' for figures 5b amd 5c. bh = blue hills area; bm = black mesa; cr = northern capitol reef area; d = dinosaur national monument; f = fruita paleontological area; j = jurassic national monument (formally the cleveland-lloyd quarry). 139 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 morrison exposures in other areas of the state (kirkland and deblieux, 2017; kirkland and others, 2017). methods during the summer of 2016, kirkland and deblieux spent 10 days prospecting morrison outcrops for unreported paleontological resources along the west side of the blanding basin between the south side of black mesa and decker cove northward to the elk mountain road (figure 2). we followed the standard practice of laterally traversing benches with the least vegetated exposures looking for fossil fragments. when fossil material was located, closer examination was made and additional fossil fragments were traced upslope to determine the source of the fossils. upon locating the site, photographs were taken, and its location was determined using topographic maps and global positioning system device. additionally, utilizing ugs locality forms as a template, geological data about the site were documented. in general, we followed best practices for mitigation developed by the ugs and the society of vertebrate paleontology (kirkland and others, 2006; u.s. bureau of land management, 2008; kirkland and foster, 2009; society of vertebrate paleontology, 2010; murphey and others, 2014, 2019). furthermore, we used taphofacies analysis to identify unusual local environments where rare small vertebrates or plant remains may be found (e.g., kirkland, 2006). the rarity of taxonomically useful plant and palynomorph sites in the morrison makes their identification every bit as important, scientifically, as a significant vertebrate locality. during these 10 days we recorded 35 fossil localities. an additional 10 days of prospecting was completed in the fall of 2017 during which we documented an additional 21 fossil localities. using these methods, most of the more extensive exposures were inventoried for significant fossil sites. we note that even within the areas examined it is not possible to locate every potential site, because a fossil locality may be very subtle, and, in some cases, significant fossils may crumble to dust before becoming exposed on the surface. all locality data have been incorporated into the utah paleontological locality database maintained by the office of state paleontologist at the ugs and are available to permitted paleontologists conducting research in the area or by written consent from the u.s. bureau of land management’s regional paleontologist. in preparing for conducting fieldwork in this area, a review of the published literature revealed that there is some dispute as to the appropriate stratigraphic nomenclature to be used on these rocks. this inventory project provided an opportunity to evaluate the various stratigraphic nomenclatures for this area as summarized below. additionally, we noted that the type section of the most paleontologically significant member of the 191 bc mp r e c a p tu re c re e k m on te zu m a va lle y 10 mi 10 km 163 262 bbllaannddiinngg study area northern limit bluff sandstone mbr. northern limit recapture mbr. northern limit westwater mbr. explanation black steer mesa sec. type area no-mans island beds type sec. bluff ss. type sec. recapture member type sec. westwater member type sec. brushy basin member gregory (1938) brushy basin mbr. type section new morrison reference section dinosaur tracksite original eastern boundary bears ears bs bb w b r ni 95 191 163 bb w r ni b black mesa elk mt. rd. bw bblluuffff wwhhiittee mmeessaa d th c o m b r id g e d e c k e r c o v e n 95 b ru sh y b as in b ru s h y b a s in r im bs figure 2. google earth© image of study area on the west side of the blanding basin with locations of type sections of members of the morrison formation noted. the butler wash (bw) tracksite (lockley and mickelson, 1997), the deltapodus (d) site (milán and chiappe, 2009), and a unionid bivalve site in the salt wash member in black steer mesa section (bs) (cadigan, 1955; o’sullivan, 1980) are the only paleontological localities published on within the study area. utah’s only vertebrate tracksite in the overlying lower cretaceous burro canyon formation (bc) is indicated (milán and others, 2015). northern limits of lower members of morrison formation after o’sullivan (1998, 2000). mp = mccracken point, th = the horn. 140 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 morrison formation, the brushy basin member, had been inadequately defined by gregory (1938). careful reading between the lines resulted in the identification of the largely covered type section along the elk mountain road on the south end of brushy basin. in 2017, we described a detailed section of the morrison formation 11.2 km (7 mi) to the south of gregory’s type section at a site where the brushy basin member is completely exposed and readily accessible to serve as a primary reference section for this important stratigraphic unit (figures 2 and 3; appendix a). additionally, we conducted a parallel paleontological inventory of the morrison and cedar mountain formations in the blue hills region north of moab, examining the type areas for the tidwell and salt wash members of the morrison (figure 1) as summarized by lupton (1914), o’sullivan (1984), and kirkland and deblieux (2017). kirkland has had several opportunities to examine the tidwell member of peterson (1988) in the historic type area at tidwell bottoms. finally, current research on these strata in the northern half of capitol reef national park (figure 1) has resulted in a broader understanding of these rocks. these observations have been important in our developing a general gestalt for these stratigraphic units. paleo-solutions inc. (murphey and zubin-stathopolos, 2018) conducted inventory work in the lower half of the morrison formation (salt wash member in their report) north of utah state route (sr) 95 and south of the elk mountain road (figure 2). their 12 new morrison fossil localities are incorporated into the utah paleontological locality database and merged into the stratigraphic framework presented here. on a two-day field review on october 27 and 28, 2018, kirkland and deblieux with grant willis, program manager for the ugs geologic mapping and paleontology program, and christine turner, u.s. geological survey, retired, reached a general consensus regarding the basal contact of the recapture member with the underlying bluff sandstone. additionally, it was decided that the “yellow cat facies” at the top of the brushy basin member should be reassigned as the yellow cat member of the burro canyon formation. the yellow cat unit was sampled for dating utilizing detrital zircons and for palynology that should validate basal bench r ec ap tu re m em be r burro canyon formation yellow cat member smectitic mudstone ju r a ss ic c r et . m or ris on f or m at io n su m m er vi lle f m . w an ak ah f m . b lu ff sa nd st on e bwb bsk sa n r af ae l g r. w es tw at er c an yo n m br . b ru sh y b as in m em be r ti dw el l f ac ie s sa lt w as h fa ci es n om an s is la nd sdeb m ai n ss . b od y explanation gravelly, x-bedded sandstone x-bedded conglomerate x-bedded sandstone sandstone muddy sandstone calcareous sandstone sandy mudstone root-mottled mudstone sandy, smectitic mudstone ripple x-bedded sandstone mudstone smectitic mudstone smectitic claystone claystone rooting dinosaur tracks volcanic ash burrows chert pebbles dinosaur bones carbonate nodules septarian nodules ferrugenous nodules x x xx xx x xx xx x xx xx x x xx xx xx xx x 100 110 120 130 170 180 190 200 210 220 230 240 250 260 270 280 290 300 140 150 160 srete m 0 10 20 30 40 50 60 70 80 90 figure 3. morrison formation at measured section on northwest side of black mesa (see figure 2 and appendix a). 141 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 or refute the reassignment. these decisions were made to facilitate future geological mapping of the morrison formation in the region. kirkland returned to recapture creek in early april 2019 to examine the type area for the recapture member of the morrison formation considering the new observations south of black mesa presented herein. kirkland observed that the stratigraphic relations of the recapture member were consistent throughout the southwestern blanding basin. morrison formation the morrison formation is probably the most famous jurassic-age dinosaur-bearing unit in the world, subject of more than 150 years of dedicated paleontological research (dodson and others, 1980; morales, 1996; carpenter and others, 1998; turner and peterson, 1999, 2004; foster, 2003, 2007; foster and lucas, 2006). the morrison was initially named for dinosaur-bearing strata along the colorado front range by cross (1894). pipiringos and o’sullivan (1978) noted that across the colorado plateau the morrison unconformably overlies the san rafael group on the j-5 unconformity and is in turn unconformably (k-1 unconformity) overlain by the lower cretaceous burro canyon formation in the blanding basin and the cedar mountain formation farther to the north in central utah, west of the colorado river (stokes, 1952). additionally, o’sullivan (1980) noted an angular discordance beneath the j-5 unconformity (bed a) in the type area for the tidwell and salt wash members (figure 1). however, this feature (figure 4a) may well represent a gilbert “style” delta formed in the shallow coastal waters of the summerville sea as sea level rose and fell, much as is exposed in the summerville west of sr 276 near ticaboo, utah (figures 1 and 4b to 4d). note, that demko and others (2005) interpreted these specific beds as within the tidwell member of the morrison formation. although noting the presence of extensive unconformities above and below the tidwell on the southwestern margin of the outcrop belt (figures 4e to 4i), we interpret their effect to diminish farther to the north and do not recognize a regional unconformity at the base of the morrison formation across the northern colorado plateau, but instead interpret the coarser-grained bed a, used by o’sullivan to define the j-5 unconformity, as representing the transition from shallow subtidal (summerville formation) to supratidal in an arid clastic sabkha environment. although this coastline was apparently low energy, the reported erosional indicator (unconformity) is interpreted to be the result of the winnowing away of finer sediment during storms. in this interpretation, bed a would be regionally diachronous. however, the summerville formation is missing on the west side of the blanding basin, with the strata overlying the entrada formation referred to by the u.s. geological survey as the wanakah formation. truncation of these coastal strata is evidence for an unconformity in the area toward comb ridge at the base of the eolian bluff sandstone member of the morrison formation (turner and peterson, 2010a). the morrison formation on the west side of the blanding basin includes a critical series of exposures for understanding upper jurassic stratigraphy across the southern colorado plateau. gregory (1938) divided the morrison formation into four members in this area. the lower three members—bluff, recapture, and westwater canyon members—all either pinch-out or are replaced laterally by other rock units within a few kilometers north of their type sections (figure 2), and these members are important stratigraphic units to the south in northwestern new mexico and northeastern arizona. the overlying brushy basin member type section is near the center of its lateral distribution and these brightly variegated strata are readily identified at the top of the morrison formation throughout most of the colorado plateau region. the stratigraphic nomenclature in the southern part of the study area is significantly different than that in the northern part of the study area, where the formation consists of the tidwell, salt wash, and brushy basin members. the definitions of these stratigraphic units and their relationship across the area have been a hotly debated issue between two groups of researchers: (1) the u.s. geological survey, largely centered around the research of fred (pete) peterson and christine turner (peterson, 1988, 1994; turner and fishman, 1991; turner and peterson, 2004, 2010a), and (2) a new mexico group, largely centered around the research of orin anderson, new mexico bureau of mines and 142 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 aa cc dd notom rd. byu sec a 4.1 km 2.5 mi 16.6 mi 26.7 km 5.7 west o 38.3 west o m o rr is o n f m . summerville fm. j-5 j-6? 157.2 ± 1.9 ma s a lt w a s h m b r. t id w e ll m b r. m e te rs 0 10 20 30 sr-24 hartnet rd. ash m e te rs 0 10 20 30 40 m e te rs 0 10 20 30 40 ttiiddwweellll mmbbrr.. ssaalltt wwaasshh mmbbrr.. ssuummmmeerrvviillllee ffmm.. ttiiddwweellll mmbbrr.. ssaalltt wwaasshh mmbbrr.. 1 2 3 ssuummmmeerrvviillllee ffmm.. ssuummmmeerrvviillllee ffmm.. ttiiddwweellll mmbbrr.. ssaalltt wwaasshh mmbbrr.. jj--66?? jj--66?? j-5 4 5 7 8 9 10 11 12 6 115577..22 ±± 11..99 mmaa bb ssww ss ee ee ff gg hh ii ssuummmmeerrvviillllee ffmm.. ttiiddwweellll mmbbrr.. ssaalltt wwaasshh mmbbrr.. jj--55 jj--55 j-5 jj--66?? j-6? figure 4. caption is on the following page. 143 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 mineral resources and spencer lucas, new mexico museum of natural history and science (anderson and lucas, 1996, 1997, 1998; lucas and anderson, 1997; lucas, 2014, dickinson, 2018). largely, these arguments/ questions are (1) should the bluff sandstone be separated from the morrison formation and included in the san rafael group and (2) does (as the u.s. geological survey team proposed) the salt wash member directly overlie the bluff sandstone member in its type area and in turn, is it overlain by the recapture and westwater canyon members as initially described by stokes (1944) and craig and others (1955)? the new mexico group has argued that the bluff sandstone should be included in the san rafael group and that it interfingers with the overlying recapture member. as such they have proposed that both the bluff sandstone and much of gregory’s recapture member should be included in the san rafael group and that the j-5 unconformity should be placed at the base of the lowest laterally extensive fluvial unit that they assigned to the base of the salt wash member. additionally, they considered the westwater canyon member to be the upper part of the salt wash member (figure 5). as discussed below, we consider parts of both stratigraphic interpretations to be correct. we interpret that the upper recapture and the lower part of the westwater canyon members correlate to the salt wash member in east-central utah and have identified several vertebrate fossil sites in the lower recapture member that support including the basal recapture in the morrison formation. furthermore, as discussed below, we agree with the u.s. geological survey team that recognized coarse sands and gravels at the base of the bluff sandstone with considerable erosional relief as representing the j-5 unconformity locally (o’sullivan, 1980, 2000; turner and peterson, 2010a) (figure 6). the bluff sandstone member interfingers with the tidwell member to the north (turner and peterson, 2010a) and is overlain by approximately 5 m (16 ft) of similar red mudstone of similar character. we therefore retain the bluff sandstone member as the basal member of the morrison formation. we disagree with turner and peterson’s (2010a) acceptance of craig and others’ (1955) interpretation that the salt wash underlies the recapture member (figure 5b), which resulted in their correlating the recapture into the basal brushy basin member in the central and northern colorado plateau area (turner and peterson, 2004, 2010a). in 2016, we thought we had observed apparent interfingering and interlensing of eolian bluff sandstone facies with the lower part of the recapture member. on march 4, 2017, kirkland met with christine turner to discuss the stratigraphy in this area. turner noted that recent observations by o’sullivan (2010a, 2010b) of the u.s. geological survey at the type recapture section (figures 2 and 4) support the interpretation that in this immediate area the basal tidwell member is laterally equivalent to the bluff sandstone and that the salt figure 4 (figure is on the previous page). gilbert delta versus angular unconformity in summerville formation and tidwell member of morrison formation at capitol reef national park. (a) contact between the summerville formation and the tidwell member of the morrison formation (figure 1) northeast of dellenbaugh butte (see figure 6 of o’sullivan, 2010a). vertical arrow points to position of j-5 unconformity at the base of o’sullivan’s marker bed named bed a. arrow in lower right corner points to shadow of photographer for approximate scale. (b) gilbert delta in the summerville formation west of sr 276 near ticaboo, utah (12 s, 522135.64 m e, 4165396.99 m n). (c) detail of gilbert delta from near center of figure b. (d) another view of gilbert delta in summerville formation laterally along outcrop (12 s, 526116.00 m e, 4178260.75 m n). (e) stratigraphic sections of the tidwell member of the morrison on the east side of water pocket fold, northern capitol reef national park (figure 1). (f) notom road byu section a (units 1–12 of peterson and roylance, 1982; 12 s. 490055.00 m e, 4232678.00 m n). red arrow position of “tidwell” age sample (kowallis and others, 1998) below j-5 unconformity. (g) tidwell section in canyon southwest of sr 24 (12 s, 489440.00 m e, 4236646.00 m n). (h) tidwell section on north side of the canyon along the western hartnet road (12s, 473110.86 m e, 4257708.98 m n). (i) panorama of northwest canyon wall southwest of sr 24. red arrow is position of new bentonitic clay sampled in upper tidwell (12 s, 489656.00 m e, 4236731.00 m n). a = bed a at base of tidwell member, e = entrada sandstone, s = summerville formation, sw = salt wash member of morrison formation, t = tidwell member of morrison formation. pale blue arrow labeled j-5 = position of unconformity j-5. orange arrow labeled ?j-6 = position of possible regional unconformity j-6. 144 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 a anderson and lucas, 1998 diagram of stratigraphic sequence exposed at mouth of recapture creek, 10 km east of bluff, utah gregory, 1938 ydob nia m er ut pace r r eb me m er ut pace r r b m el ahs . enot sdnas ff ul b r eb me m w tl as hsa r eb me m ni sa b yhsur b r eb me m yhsur b ni sa b r b m el ahs . w -t se r et a w r b m . na c . ) puor g l eaf a r nas( enot sdnas ff ul b noit a mr of nosirr o m noit a mr of nosirr o m suoecat er c skcor suoecat er c skcor cross-bedded unit correlates with acoma tongue of bluff salt wash/summerville contact of gilluly and reeside (1928), not recognized by gregory (1938) j k? j-5 = ?j-6 tidwell member of summerville formation summerville formation (main body) summerville formation bluff sandstone bluff sandstone member salt wash membersalt wash member recapture member recapture member jmru 6 6 5 5 3 3 4 4 2 2 1 1 ? ? a a’ j-5 j-5 = ?j-6 jza jza correlative with acoma tongue of zuni ss.jbr (jmru =) brushy basin member westwater canyon member jackpile jackpile ss. ss. brushy basin member morrison formation bluff ss. morrison formation cretaceous (not to scale) cretaceous middle jurassic rocks fiftymile member kaiparowits basin henry basin four corners bluff san juan basin blanding basin fiftymile member tidwell member tidwell member salt wash member b c figure 5. comparison of stratigraphic interpretations of gregory (1938), anderson and lucas (1996, 1997, 1998) and peterson and turner-peterson (1987) for the morrison formation. (a) gregory (1938) versus anderson and lucas (1997, 1998) interpretation of the upper jurassic along recapture creek. (b) peterson and turner-peterson’s (1987) stratigraphic hypothesis across the colorado plateau. interpretation: jmru = upper part of recapture member, (jmru=) = equivalent to upper part of recapture member. line of correlation as in figure 1. note correlation developed prior to recognition of clay change in basal brushy basin member. (c) anderson’s revised interpretation of peterson and turner-peterson’s (1987) stratigraphic hypothesis. jza = acoma tongue of the zuni sandstone, jbr = recapture member of bluff sandstone, j-5 = basal morrison unconformity. j-5 = ?j-6 indicates our interpretation that anderson and lucas (1996, 1997, 1998) recognized a younger regional unconformity at the base of the salt wash member and near the base of gregory’s (1938) recapture member. modified from anderson and lucas (1997). generalized figures are not to scale. 145 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 wash member does not onlap the bluff sandstone as proposed by stokes (1944), craig and others (1955), and turner and peterson (2004). instead, turner noted that the recapture member directly overlies the bluff sandstone in its type area (turner and peterson, 2010a, 2010b; verbal communication, 2017) and continued to propose that the salt wash is stratigraphically below the recapture and, with the underlying tidwell member, is laterally equivalent with the bluff sandstone and as such both are not identifiable in outcrop across the southwestern blanding basin. however, o’sullivan (1980, 1998, 2000, 2010b) proposed that sandstone lenses typical of the salt wash appear in the recapture well above its base north of the recapture type section in montezuma canyon (figure 2), more closely following anderson and lucas’ (1998) interpretation of gilluly and m o rr is o n f m . m o rr is o n f m . m o rr is o n f m . m o rr is o n f m . m o rr is o n f m . m o rr is o n f m . s a n r a fa e l g ro u p s a n r a fa e l g ro u p s a n r a fa e l g ro u p s a n r a fa e l g ro u p s a n r a fa e l g ro u p s a n r a fa e l g ro u p b lu ff s a n d st o n e bluff sandstone mbr. bluff sandstone. bluff sandstone main body bluff ss. mbr. bluff ss. mbr. entrada ss. entrada ss. entrada ss. entrada ss. entrada ss. summerville (?) formation summerville formation summerville formation wanakah formation wanakah formation dakota (?) formation dakota (?) formation burro canyon formation burro canyon formation burro canyon formation not discussed in text peterson (1988) anderson and lucas (1998) o’sullivan (2000)gregory (1938) stokes (1944) craig and others (1955) recapture shale mbr. recapture shale mbr. recapture shale mbr. recapture member recapture member recapture member westwater canyon sandstone mbr. westwater canyon sandstone mbr. westwater canyon sandstone mbr. westwater canyon mbr. westwater canyon member salt wash sandstone mbr. salt wash sandstone mbr. salt wash member salt wash sandstone mbr. salt wash mbr. tidwell mbr. tidwell member brushy basin shale mbr. brushy basin shale mbr. brushy basin shale mbr. brushy basin member brushy basin member j-5 j-5 j-5 m o rr is o n f m . s a n r a fa e l g ro u p m o rr is o n f m . m o rr is o n f m . m o rr is o n f m . m o rr is o n f m . s a n r a fa e l g ro u p s a n r a fa e l g ro u p s a n r a fa e l g ro u p s a n r a fa e l g ro u pb lu ff s s. t id w e ll m b r. bluff sandstone bluff sandstone member basal bench ? ? ? ? junction creek mbr. bluff ss. mbr. bluff ss. mbr. entrada ss. entrada ss. entrada ss. entrada ss. entrada ss. summerville formation wanakah formation summerville formation wanakah formation wanakah formation lower lower upper upper burro canyon formation burro canyon formation burro canyon formation burro canyon formation burro canyon formation turner & peterson (2004) turner & peterson (2010,a, b) lucas (2014) dickinson (2018) this report recapture shale mbr. recapture shale mbr. recapture shale mbr. recapture shale mbr. recapture shale mbr. westwater canyon member westwater canyon member westwater canyon member westwater canyon member nmi beds yellow cat member salt wash member salt wash member salt wash member salt wash member salt wash member tidwell member tidwell member tidwell mbr. brushy basin member brushy basin member brushy basin member brushy basin member brushy basin member j-5 ?j-6 ?j-7 j-5 j-5 j-5 cc cc cc figure 6. history of nomenclature for the morrison formation and bounding strata along east side of comb ridge. cc = position of “clay change,” j-5 = basal morrison unconformity, ?j-6 = possible regional unconformity below salt wash member, ?j-7 possible unconformity at the “clay change.” 146 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 reeside (1928) (figures 2 and 4). using cadigan’s (1952) black steer knoll section on the southwest side of the abajo mountains north of the elk mountain road, o’sullivan (1980, 2000) noted that the tidwell member is overlain by the salt wash member, forming the base of the morrison formation (figures 2 and 6). utilizing these data points, together with subsurface data, o'sullivan proposed that the bluff sandstone pinches out to the north, where it and the thinning recapture member are replaced by the basal reddish mudstones of the tidwell member and overlying fluvial-dominated salt wash member (o’sullivan, 1980, 1998, 2000; turner and peterson, 2010a). both o’sullivan (1980) and lucas (2014) documented that the bluff sandstone interfingers with the tidwell member over a 3 to 5 km (2–3 mi) interval extending north from around whiskey draw, with o’sullivan (1998, 2000) noting that the bluff sandstone is not recognizable at the elk mountain road (figure 2). however, turner and peterson (2010a, plate 6) illustrated the interfingering of the bluff sandstone with the tidwell member on the north side of cottonwood wash (625381.23 m e, 4168492.67 m n) just south of where the elk mountain road crosses the wash (turner, verbal communication, october 27, 2018). taken there by christine turner, we were not able to visit the specific site as the ute tribe posted numerous no trespassing signs in the area. however, kirkland noted that approximately an additional 5 to 10 m (16–32 ft) of red mudstone and sandstone overlie this intertonguing interval that can reasonably be interpreted as tidwell or a northern tongue of the recapture member, below what appears to be a series of sandstone ledges typical of the salt wash member. while we think the strongest evidence supports the hypothesis that the bluff interfingers with and should be included as a member of the morrison formation, we recognize that there is evidence that could result in a somewhat different interpretation. we noted that conglomerate beds separate the bluff sandstone from the overlying recapture member of the morrison formation on the west and south sides of black mesa. in fact, even gregory (1938, section 23, unit 3) noted an unconformity near the base of the overlying recapture at its type section on recapture creek. if this is evidence of a regional unconformity in the basal recapture, perhaps the bluff sandstone is best removed from both the san rafael group and the morrison formation and elevated to formation status. however, this upper conglomeratic layer has not been documented as extending across the entire outcrop of the bluff farther to the east and we suspect that it may be reflecting local mesozoic uplift along comb ridge as has been proposed for the san rafael reef to the north (eaton and others, 1990; kirkland and madsen, 2007; kirkland and others, 2016). in conclusion, there is evidence both for and against including the bluff in the morrison, but the strongest evidence supports its inclusion. the general physiographic pattern formed by the morrison formation and its bounding strata across the south side of the blanding basin is a series of three extensive benches. these benches are readily observed where crossed by u.s. highway 191 between bluff and white mesa, utah (figure 7). 1. the first (southernmost) bench extends along east-west just north of the san juan river and consists of a dark brownish-red escarpment of the san rafael group capped by light brownish-gray eolian bluff sandstone member. 2. the second bench starts with a short step (basal recapture bench) formed by light brownish-gray fluvial and less commonly eolian sandstone beds at the base of the recapture member of the morrison formation, and extends up through the steeper cliff formed by fluvial sandstones (no-mans island beds) capping the westwater canyon member. the hovenweep road (sr 262) extends east from u.s. highway 191 along the top of this bench. 3. the third bench is made up of the slope-forming brushy basin member of the morrison formation capped by resistant cretaceous fluvial sandstones of the burro canyon and naturita formations, and forms the “jump off” south of white mesa. these benches can also be recognized along the southwest side of black mesa as the morrison outcrop belt narrows and turns north along comb ridge (figure 7). unfortunately, northward facies changes in the 147 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 morrison formation are hidden as they extend beneath cretaceous strata forming the center of the blanding basin. these relationships at the base of the morrison formation have been documented in the subsurface by o’sullivan (1998, 2000). however, the north-south band of jurassic outcrops along the west side of the blanding basin on the east side of comb ridge exhibits the transition from the southern stratigraphic nomenclature proposed by gregory (1938) to the terminology used across east-central utah by turner and peterson (2004). the steeper eastward dip imparted to the strata by comb ridge has resulted in a complete sequence of the upper jurassic extending from the south end of black mesa northward until the outcrop becomes largely obscured by vegetation and landslide deposits on the southwest side of the abajo mountains (figure 8). the critical transitions in this terminology apparently occur in the outcrops north of where sr 95 crosses this outcrop belt (miller, 1955a; o’sullivan, 1998, 2000). miller (1955a, 1956), on the photogeologic map of the black mesa butte 7.5-minute quadrangle (figure 2), found that north of sr 95 the recapture member is no longer recognizable and the recapture and westwater canyon members were replaced with “lower” morrison on millers map; whereas, o’sullivan (1998, 2000) continued to recognize the westwater canyon member a few kilometers farther north (figure 2), replacing it with salt wash member at the elk mountain road. our detailed stratigraphic section of the morrison formation just south of sr 95 on the northwest side of black mesa (appendix 2 miles bbllaacckk mmeessaa nnoo--mmaannss iissllaanndd rr ee ccaa pp ttuu rree cc rree ee kk cc oo ttttoo nn ww oo oo dd ww aa ss hh jjuummpp--ooffff bblluuffff rr bb tthh mmpp 3333 33 33c o m b r id g e 22 22 11 11 aa 191 191 262 262 0.5 miles 2 miles bbllaacckk mmeessaa cc rrss 11 11 22 22 33 33 ccoommbb rriiddggee ssttee pphh eenn ss cc aann yyoo nn 0.2 miles bb figure 7. southwestern blanding basin (google earth©). (a) oblique view to north into western blanding basin from near san juan river. red arrow on both photos indicates site where dated volcanic ash was collected near top of the morrison formation. b = type section of the bluff sandstone, r = type section of recapture member, mp = mccracken point, th = the horn. (b) oblique view of jurassic outcrop between comb ridge and black mesa from the south. rs = site of morrison reference section (appendix a). c = site where chert gravel conglomerate was observed at base of recapture on southwest side of black mesa. 1, 2, 3 on tops of benches referred to in text. 148 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 a) follows along this line of nomenclatural transition critical to interpreting the morrison formation on the southern colorado plateau relative to its stratigraphic nomenclature across east-central utah (figure 8). basal contact of the morrison formation we follow the u.s. geological survey in recognizing an unconformity below the bluff sandstone member that they interpret as the j-5 unconformity of pipiringos and o’sullivan (1978), o’sullivan (1998, 2000, 2010a, 2010b), and turner and peterson (2004, 2010a, 2010b). we suggest that the topographic relief documented at this unconformity, the intrabasinal source of the larger clasts in the conglomeratic beds, and the lateral variability of the units at the top of the san rafael group, combined with the local derivation of these clasts (peterson and turner, 2010a), supports syndepositional tectonics along the comb ridge uplift during the formation of this unconformity, as has been proposed for the san rafael swell during the middle mesozoic (eaton and others, 1990; kirkland and madsen, 2007; kirkland and others, 2016) and elsewhere on the colorado plateau (peterson, 1969, 1984, 1986; kirkland 1990, 1991). although not the focus of this study, we would have preferred to abstain from committing to a specific terminology for the strata immediately underlying the bluff sandstone (figures 3, 6, and 8). gregory (1938) san rafael group 1 2 ? ? 3burro canyon formation recapture member tidwell member bluff sandstone member recapture bench recapture benchrecapture bench sw facies sw facies sw facies sw facies sw facies sw facies no-mans island beds westwater canyon member “main sandstone interval” westwater canyon member “smectitic mudstone” w es tw at er ca ny on m br .br us hy ba si n m br . ty pe bb m br . noit a mr of nosi rr o m noit a mr of nosi rr o m brushy basin member yellow cat mbr. of burro canyon fm. salt wash member rew. bluff e.f. blanding no-mans island mesa white black mesa brushy basin rim abajo mts. 3 mi 5 kmn comb ridge bluff type sections brushy basin bluff recapture westwater canyon type section reference section a b ? figure 8. generalized upper jurassic stratigraphic relationships along comb ridge. (a) viewed from the west across comb ridge and the blanding basin (google earth©). (b) simplified diagram of relationships of morrison formation units, along with bounding strata, for east side of comb ridge. no vertical scale intended. 1, 2, 3 indicate tops of regional benches referred to in text. sw facies = channel sandstone facies of salt wash character; rew. bluff e.f. = reworked bluff eolian facies. 149 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 questioned use of the term summerville formation for the strata underlying the bluff, because the strata are unlike that of the type summerville formation. the u.s. geological survey recognized the wanakah formation below their j-5 unconformity in this area (o’sullivan 1998, 2000, 2010a, 2010b; turner and peterson, 2010a, 2010b), named for the wanakah mine near ouray, colorado, by burbank (1930). o’sullivan (1984, 1992) and o’sullivan and others (2006) noted that it correlates to the lower curtis and uppermost entrada formations, which implies that the j-3 unconformity marking the entrada-curtis boundary lies within the wanakah formation, possibly at the base of the butler wash beds in the southern blanding basin (o’sullivan 1998, 2000, 2010b). complicating the use of the term wanakah formation in this area, grabeau (1917) informally proposed a devonian wanakah shale member of the ludlowville formation in upstate new york, which was formally defined by cooper (1930). thus, there has been debate as to whether the wanakah formation is a valid term for these strata or if another name should be applied (armstrong, 1995, p. 5). burbank (1930) was aware of the duplication of names and felt there would be no confusion, given the vastly different age of the strata in different regions of the country. the north american stratigraphic code (nasc) allows the duplication of nomenclature if there is no chance of confusion. o’sullivan (2010a, p. 99) noted that the nasc’s discouraging the duplication of names was published after wanakah was applied to these strata in both areas and that “the continued use of the name wanakah formation is highly preferable to the use of summerville formation, which is absent in the four corners area” (o’sullivan, 1980, 1984, 1992, 1998, 2000, 2010a; condon and hoffman, 1988). summerville formation has been applied incorrectly to these more complex strata most recently by lucas (2014) and dickinson (2018). resolving this ongoing debate is beyond the scope of this paper and wanakah formation is used without implying a preference over summerville. several subdivisions of the wanakah formation have been proposed and have variably been applied to these rocks in the blanding basin (o’sullivan, 1980, 1984, 1992, 1998, 2000, 2010a; condon and hoffman, 1988; lucas, 2014). we found that it is difficult to recognize some of these units in outcrop and that different authors have applied different terms to the same beds over the years. for example, near the top of the wanakah a prominent pair of sandstone ledges were referred to as the bed at black steer knoll (o’sullivan, 1980). subsequently, o’sullivan (1997, 1998, 2000) discontinued using this nomenclature in favor of the horse mesa beds (erected for sandstone beds near the top of the wanakah in northern arizona by condon and hoffman [1988]). however, in describing these strata as summerville formation, lucas (2014) used the black steer knoll bed for this same pair of sandstone beds. in describing the wanakah formation at the base of the morrison reference section, we found it nearly impossible to be certain which of the previously described subdivisions within the wanakah preserved the butler wash dinosaur tracksite (figure 3), although the tracksite is well below the base of the bluff sandstone (lockley and mickelson, 1997). west of bluff, utah, turner and peterson (2010a, figure 1.25, p. 16) noted angular red chert fragments in the basal contact of the bluff sandstone member that were derived from dark red chert lenses in the uppermost part of the wanakah formation that are cut out by an unconformity which has tens of meters of relief locally (figure 9a). similarly, to the north of sr 95, where the bluff sandstone member interfingers with the tidwell member, o’sullivan (1980, 2000) and turner and peterson (2010a, plate 7, p. 79) recognized coarse sandstone bed a representing the j-5 unconformity. this contact was also followed in carr-crabaugh and kocurek’s (1998) examination of the san rafael group as a complex, wet eolian system in this area. in addition to the j-5 unconformity at the base of the bluff sandstone member, we note that there is another unconformity at the top of the bluff below a finegrained, fluvial and eolian bench-forming facies. we interpret these beds to represent eolian sands reworked across this unconformity from the underlying bluff sandstone member into the basal recapture member of the morrison formation. thus, we do not interpret these sandstones as representing intertonguing between the bluff and recapture members or as fluvial sandstones pertaining to the salt wash member. 150 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 bluff sandstone member following the usage of baker and others (1936), gregory (1938) described the bluff sandstone member as the basal member of the morrison formation from outcrops at the top of the middle jurassic “summerville formation” of the san rafael group on either side of the san juan river near bluff, utah. we interpret the type section to be in an alcove to the northeast of bluff, utah, (figure 2) based on the photograph of the team surveying the bluff sandstone member (gregory, 1938, plate 3c). gregory described the bluff as follows: “the bluff sandstone member is white, brownstained, commonly cross-bedded, and made up of medium to coarse quartz grains. typically it is one massive bed 200 to 350 feet thick that here and there includes aggregates of large quartz grains, clay balls, and short thin lenses of red mudstone. in some places it is arranged as long overlapping sandstone wedges bordered by a little red shale, and in other places as poorly defined beds 20 to 40 feet thick. traced eastward, the bluff sandstone that forms the top of tank mesa is less persistently massive. near the mouth of montezuma canyon 10 to 20 feet of bedded white sandstone are incorporated in red sandy shale that thins, thickens, bunches up, or flattens out along the strike. traced northward along butler wash and cottonwood canyon the bluff sandstone is represented in places by three or more beds.” lower contact workers have had varied interpretations of how the bluff relates to other units and the nature of the basal contact. stokes (1944) considered the bluff a formation and correlated the bluff sandstone with the entrada sandstone, resulting in an apparent unconformity between the bluff sandstone and morrison formation. craig and others (1955) noted that it interfingers with cc rreeccaappttuurree ffaacciieess bbaassaall rreeccaappttuurree bbeenncchh ttoopp bblluuffff ssss.. bblluuffff ssaannddssttoonnee bblluuffff ssaannddssttoonnee uu bbwwll ee eerroossiioonnaall rreelliieeff aa bb figure 9. upper san rafael group and bluff sandstone and basal recapture members of the morrison formation in the western blanding basin in the bluff and southern black mesa areas. (a) upper san rafael group capped by bluff sandstone viewed to west from bluff, utah, toward comb ridge. bracket denotes clearly expressed erosional base of bluff sandstone discussed by turner and peterson (2010a, figure 1.25). (b) upper san rafael group and bluff sandstone bench at bluff, utah, as described by o’sullivan (2010a). bw = bed at butler wash of the wanakah formation, e = entrada sandstone, l = lower member of wanakah formation, u = upper member of wanakah formation. (c) basal fluvial bench of recapture member of morrison formation sitting above regional bench 1 formed by top of the bluff sandstone southwest of no-mans island looking south. 151 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 both the underlying summerville formation and the overlying salt wash member of the morrison formation, and thus is transitional between the two stratigraphic units. likewise, dickinson (2018) recently reported intertonguing between the underlying summerville and the bluff sandstone, reflecting the complexities in the transition in the upper san rafael group in this area. o’sullivan and maberry (1975) identified trace fossils (interpreted as having marine origins) in the bluff sandstone member near the arizona border and indicated that this supported a genetic link with the underlying san rafael group. these observations preclude the presence of a j-5 unconformity either above or below the bluff sandstone. anderson and lucas (1996, 1998) removed the bluff sandstone from the morrison formation and elevated it to a formation in the underlying san rafael group. they correlated the bluff sandstone to similar eolian units (zuni and cow springs sandstones) to the south in new mexico and arizona that occur at the top of the middle jurassic san rafael group. the basal unit a of the bluff sandstone preserving “marine” burrows south of the san juan river (o’sullivan and maberry, 1975) was referred to as the horse mesa member of the wanakah formation by some workers (condon and hoffman, 1988; o’sullivan, 2010b). peterson (1994) interpreted the bluff sandstone to represent a coastal eolian unit. in contrast, turner and peterson (2004, 2010a) reported that the bluff sandstone unconformably overlies the san rafael group, where they document a basal gravel and several tens of meters of relief on the regional scoured contact west of bluff, utah. where the upper san rafael group is thinly bedded, this basal contact of the bluff sandstone member is easily recognized (figures 9a and 9b). o’sullivan (1980) reported that the black steer knoll bed, a distinctive marker bed near the top of the wanakah formation north of sr 95, is truncated by an angular unconformity at the base of the bluff sandstone to the south. researching these same sections, lucas (2014) interpreted the bluff sandstone as interfingering northward of sr 95 into the tidwell member, which put in the summerville formation, but did not speculate on the loss of the underlying black steer knoll bed to the south. dickinson (2018) noted that the provenance as indicated by the suite of ages determined for detrital zircons in the bluff sandstone is comparable to that of the underlying eolian entrada sandstone and laterally underlying the marine curtis formation and as such, the bluff should be considered part of the san rafael group. surprisingly, entrada eolian sands were transported by middle jurassic paleowinds from the north and north-northeast and those in the bluff sandstone member from late jurassic paleowinds from the southwest as reported by dickinson (2018). given the erosional relief at the base of the bluff sandstone member (turner and peterson, 2010a), reworking sand grains (including zircons) from the underlying formations of the san rafael group could well account for the similarity in provenance data as determined by detrital zircons. upper contact the top of the bluff sandstone member forms a broad bench across the south side of the blanding basin north of the san juan river (figure 8). on the south and west sides of black mesa, a distinct second bench 5 to 15 m (16–50 ft) thick is formed by flat-bedded, reddish-brown mudstone and sandstone beds, or simply softer sandstone capped by fine, light brownish-gray fluvial and eolian sandstone beds apparently derived from reworking of the upper bluff sandstone member. this lower bench is at the base of a steep slope-forming interval that extends through the overlying recapture member and steeper westwater canyon member (figures 9c and 10). our documentation of coarse chert clasts up to 10 cm in diameter at the base of these fluvial sandstones precludes these beds from being part of the bluff sandstone member as mapped by miller (1955b) and supports the observation that the bluff is bounded above and below by unconformities at least locally in the southwestern blanding basin. given that gregory (1938, section 23, unit 3) noted an unconformity near the base of the overlying recapture member at its type section on recapture creek east of the study area (figure 2), it was critical to reexamine this section. we found that gregory’s unit 3 was a channel sandstone lens cutting down into the lower recapture strata and that unit 3 was the same sandstone interpreted by anderson and lucas (1996, 1997, 1998) 152 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 aa bb cc dd bblluuffff ssss.. bblluuffff ssss.. bblluuffff ssss.. nnoo--mmaannss iissllaanndd bbeeddss ssmmeeccttiittiicc mmuuddssttoonnee mmaaiinn bbooddyy rreeccaappttuurree mmbbrr.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. hh iigg 95 ff ee bblluuffff ssss.. bbaassaall rreeccaappttuurree bbeenncchh bbaassaall rreeccaappttuurree bbeenncchh ccoonngglloommeerraattee bbaassaall rreeccaappttuurree bbeenncchh bbaassaall rreeccaappttuurree bbeenncchh bbaassaall rreeccaappttuurree bbeenncchh bbaassaall rreeccaappttuurree bbeenncchh wweessttwwaatteerr ccaannyyoonn mmbbrr.. bblluuffff ssss.. bblluuffff ssss.. bblluuffff ssss.. 2 cm figure 10. lower morrison formation (bluff sandstone, recapture, and westwater members) west of black mesa. (a) northern margin of alcove at base of morrison formation just northwest of ash site (figures 2 and 5) on the southwest side of black mesa. (b) recapture and westwater canyon members on northwest escarpment of alcove on southwest side of black mesa. (c) view up exposure in b from conglomerate unit between bluff sandstone and reworked lenses of bluff sandstone facies in basal recapture member. (d) basal conglomerate unit above bluff sandstone (c in figure 5). (e) exposure on west side of black mesa from butler wash road (at about 621854.36 m e, 4153612.63 m n) with thick fluvial sequence at the base of the recapture member overlying eolian bluff sandstone. (f) transition between bluff sandstone and basal recapture member of morrison formation at reference section for brushy basin member. (g) upper bluff sandstone west of butler wash tracksite at 12 s 0622447 e, 4154912 n. (h) contact between bluff sandstone and base of recapture member at 12s 0622624 e 4155098 n. (i) intraformational conglomerate at contact between bluff sandstone and morrison formation in same area. 153 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 as representing the base of their salt wash member capping their recapture member of the bluff sandstone. this area is described in more detail below in the recapture member section. o’sullivan (1998) and turner and peterson (2010a) documented that the bluff sandstone member pinches out into the tidwell member of the morrison north of sr 95 above the marker bed formed by the underlying horse mesa member of the wanakah formation (figure 2). inexplicably, dickinson (2018) included the horse mesa member (black steer knoll bed) of the wanakah formation as the basal unit in the bluff sandstone. turner and peterson (2004, 2010a) noted that the bluff sandstone member interfingers with and is overlain by the tidwell member in some areas and is overlain by the salt wash member in others. this interpretation follows stokes’ (1944) and craig and others’ (1955) view that the recapture member overlies rather than underlies the salt wash member. subsequently, turner and peterson (2010a, 2010b; verbal communication, 2017) revised this interpretation following o’sullivan (1998, 2010a, 2010b) in recognizing that the recapture member directly overlies and intertongues with the bluff sandstone member in the area around recapture creek and the south side of black mesa. this suggests that both the tidwell and salt wash members are laterally equivalent to the bluff. we observed that the isolated eolian lenses (dunes) were much less common than similarly appearing fine-grained fluvial units in the lower part of the overlying recapture member on the south side of black mesa, which supports the observation that the bluff sandstone member of the morrison formation appears to be genetically associated with the basal recapture member (anderson and lucas, 1996, 1998; turner and peterson 2010a, 2010b). we noted that along the west side of black mesa conglomerate is at least locally present at the base of the lower morrison slope at the top of the bluff sandstone. on the southwest side, we noted a gravel conglomerate overlying the bluff sandstone member about 30 cm (1 ft) thick with white and gray chert grains with diameters up to 2 cm (1 in) (figures 10c and 10d). to the north, south of sr 95 in our new morrison reference section (appendix a), we observed a largely intraformational clast conglomerate with clasts up to 50 cm (1.5 ft) across above the bluff sandstone member (figures 10h and 10 i). at both sites light-colored, fine-grained fluvial and minor eolian sandstones less than 10 m (30 ft) thick are also present at the base of the recapture member. the presence of these conglomerates a few meters above the contact between the bluff sandstone member and the recapture member indicates that a more careful reconnaissance of the contact throughout the area is called for to establish if these conglomerates extend farther across the blanding basin. the present evidence supports the hypothesis that the bluff sandstone member does not interfinger with the recapture member of the morrison formation, at least on the southwest side of the blanding basin, but that the basal sandstone units of the recapture are composed mainly of fine sands reworked from the underlying bluff sandstone member across this unconformity. we expect that at most sites, where this fine sandstone interval is fluvial in nature and directly overlies the basal conglomeratic bed, an interpretation that these sandstones represent the salt wash member of the morrison formation (stokes, 1944; craig and others, 1955) is completely understandable. given that the bluff sandstone member, as we interpret it, is bounded by unconformities just above the top, and at its base, and given the distinctiveness of its much lighter color relative to the underlying strata of the san rafael group, it is tempting to consider it as a distinct formation lying between the underlying san rafael group and overlying morrison formation. we agree with turner and peterson (2004, 2010a) and o’sullivan (1980, 2010a, 2010b; lucas, 2014) that the bluff sandstone member interfingers into the lower part of the tidwell member of the morrison formation to the north of whiskey draw (12 s, 620605.59 m e, 4162400.38 m n) and extending to the elk mountain road. however, the conglomerates at the top of the bluff sandstone have only been identified on the southwest side of the blanding basin and until the lateral extent of these coarse units can be determined, we retain the bluff sandstone as the basal member of the morrison formation at this time (figures 3, 6, and 8). paleontology no fossils were observed in the bluff sandstone 154 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 member during this study, although these strata likely preserve invertebrate trace fossils and perhaps even dinosaur tracks elsewhere. the butler wash dinosaur tracksite (figure 2) on the northwest side of black mesa was described as being immediately below the bluff sandstone (lockley and mickelson, 1997). however, we find no genetic association of the tracksite with the bluff at the base of our new morrison formation reference section (appendix a). we identify the tracksite as near the middle of the wanakah formation (o’sullivan, 1980, 1992, 1998, 2000, 2010a, 2010b), but cannot tie this site to a specific bed in any previously measured sections in the area (o’sullivan, 1980; lucas, 2014). tidwell member history and lithology the term “tidwell member” has had a complicated history of usage. the tidwell member was named for tidwell bottoms along the san rafael river in emery county, utah, and was first used on a number of unpublished geological maps produced by robert young over several decades for the atomic energy commission and subsequently the u.s. department of energy (peterson, 1988). the first formal description was published by o’sullivan (1984), who defined the tidwell member of the morrison formation as the relatively thin (about 10 m [32 ft]) interval of light-gray-colored sandstone and sandy shale beds spanning the slope from the j-5 unconformity up through the base of the first laterally extensive fluvial sandstone (figures 1, 4a, and 11) of the overlying salt wash member, with a section on the west side of dumas point in grand county, utah (ne1/4ne1/4sw1/4 and se1/4se1/4nw1/4, section 30, t. 23 s., r. 18 e, salt lake base line and meridian). o’sullivan (1984) described the lithology of the tidwell member as: “…. somewhat varied. siltstone is the dominant rock type. chert beds as much as 1.5 m thick, rounded limestone nodules, and gray limestone beds are conspicuous lithologic features of the tidwell member. gypsum is also present in some abundance from the san rafael swell to just east of the green river. gray ledge-forming sandstones as much as 2 m thick, in which bedding is absent or not apparent, crop out at many localities; light-gray crossbedded channel sandstone beds typical of the overlying salt wash member are absent at most places, but where present form a minor lithology in the slope-forming tidwell member. at places, the tidwell contains persistent thin ledge-forming sandstone beds, generally less than 1 m thick, which are blocky, ripple marked, and commonly carry coarse grains of chert. a widespread sandstone, termed for convenience bed a, marks the base of the tidwell member at most places. throughout large areas of east-central utah, bed a is generally less than 0.5 m thick but locally is as much as 2.5 m thick. here and there the bed contains coarse grains, is ripple marked, and tends to form a resistant ledge that overhangs the j-5 unconformity and underlying rocks.” complicating the story, peterson (1988) defined the tidwell member using a section to the west in emery county located 5 to 8 km (3–6 mi) south of tidwell bottoms and 24 km (15 mi) southwest of green river, utah. in this area, gypsum beds with authigenic chert characterize the lower few meters of the section, instead of bed a, which o’sullivan (1984) used to mark the j-5 unconformity across much of eastern utah. stratigraphically, o’sullivan’s (1984) and peterson’s (1988) type sections are essentially correlative and so do not confuse the use of the term tidwell in this area. interestingly, peterson (1988) did not reference o’sullivan (1984) regarding the tidwell member, but acknowledged o’sullivan’s paper in the discussion of the type section of the overlying salt wash member. we observed stromatolites (figure 11c) preserved in dark-gray limestone beds that are associated with the surface of the basal sandstone bed (bed a) of the tidwell member in a broad area between the blue hills westward to duma point (kirkland and deblieux, 2017). similar algal limestone beds appear to cap some of the thin, red sandstone beds in the upper part of the underlying summerville formation as well. given the presence of extensive gypsum beds along the summerville-tidwell contact to the west, such as at tidwell bottoms (peterson, 1988) southwestward to the east side of capitol reef national park, we interpret this transition 155 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 between the san rafael group and the morrison formation to represent the “higher” energy shoreline of a clastic “sabkha” (thompson and meadows, 1997; saleh and others, 1999; kirkland, 2006) and not necessarily the presence of a regional j-5 unconformity (o’sullivan, 1984; turner and peterson, 2004). sedimentary features such as stromatolites and evaporites are all consistent with a clastic sabkha interpretation of the transition between the summerville formation and the overlying tidwell member of the morrison formation. we interpret o’sullivan’s (1984) bed a as representing the normally quiet-water sabkha’s waterline, occasionally agitated by storms such that coarser grains are winnowed out of the sediment forming a diachronous bed a. wind deflation may have also served to concentrate these coarser grains given a depositional hiatus in these flat-ripple bedded, coastal sediments. anderson and lucas (1996,1998) reported that the salt wash member unconformably overlaid the tidwell member marking the position of the j-5 unconformity and the base of the morrison formation in this area. we identified large tidwell or summerville stromatolite clasts in the basal salt wash member here, further supporting the presence of a significant unconformity at the base of the salt wash member. at capitol reef (figures 1 and 4e to 4i) we recognized a 2 to 3 m (6–10 ft) pebble conglomerate extending over more than 50 km (30 mi) across the north end of the park along the basal contact of the tidwell member marking the j-5 unconformity (figures 4e to 4i). o’sullivan (1984) noted that the upper contact of the tidwell member may be difficult to place because of intertonguing between the salt wash and tidwell members. we observed that less laterally extensive sandstone channels of salt wash aspect occur in the upper half of the tidwell member in nearly all sections examined in utah. the conglomeratic salt wash member likewise marked a major regional unconformity across this reaa ssaann rraaffaaeell ggrroouupp ssuummmmeerrvviillllee ffmm.. ssaann rraaffaaeell ggrroouupp ssaalltt wwaasshh mmbbrr.. ssaalltt wwaasshh mmbbrr..ssaalltt wwaasshh mmbbrr.. ttiiddwweellll mmbbrr.. ttiiddwweellll mmbbrr.. bb cc ee ff dd figure 11. tidwell member and its fossils. (a to c) tidwell member in o’sullivan’s (1984) type area (figure 1). (a) photo of a bluff along the ten-mile wash road on the west side of the blue hills showing the contact of the morrison formation with the san rafael group. (b) the tidwell-salt wash member contact along ten-mile wash road. (c) stromatolite in the basal tidwell member. (d to f) dinosaur tracksite (sa1445) where bluff sandstone interfingers with, and is overlain by, tidwell member (o’sullivan, 1980) north of sr 95 discovered by john foster during paleo solutions paleo-inventory (murphey and zubin-stathopoulos, 2018). (d) overview of site with natural casts of sauropod tracks, (e) detail of sauropod track displaying scratch marks from scales, (f) detail of natural cast of three-toed dinosaur track. 156 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 gion as well, with meters of relief at its lower contact (figures 4e to 4i). perhaps in the future we should consider the tidwell-salt wash contact to represent a j-6 unconformity. thus we have concluded that across most of central and southern utah, an unconformity marks the top and bottom of the tidwell. maidment and muxworthy (2019) proposed that the tidwell member be excluded from the morrison formation as a separate sequence bounded by unconformities. these unconformities were not identified in the basal morrison formation in the area around dinosaur national monument (figure 1, sprinkel and others, 2019; d.a. sprinkel, ugs, verbal communication, 2019). thus, we suggest that these unconformities are subsumed within complexities of the marginal marine to terrestrial facies shift marking the base of the morrison formation as the sundance sea continued to retreat to the north. demko and others (2004) suggested that the regional paleosol at the base of the brushy basin member reflected a regional unconformity. kirkland (2006) agreed with their conclusion and furthermore noted that such an unconformity would explain the dramatic change from illitic to smectitic clays noted at this level across the colorado plateau (peterson and turner-peterson, 1987; turner and peterson, 2004, 2010a). therefore, as the three members of the morrison formation spanning the central and northern colorado plateau preserve large dinosaur remains and are bounded by unconformities there is no reason to separate the tidwell member from the rest of the morrison formation. paleontology though not examined extensively, no fossils were found in the tidwell member at the base of the morrison formation in the northern part of the study area. however, farther to the north, the tidwell is known to preserve the oldest morrison vertebrate fossil sites, including the oldest associated sauropod dinosaur body fossil in north america, dystrophaeus (gillette, 1996a, 1996b; turner and peterson, 1999; foster, 2007; trujillo and kowallis, 2015; foster and others, 2016a; kirkland and deblieux, 2017). this important dinosaur site is approximately 57 km (35 mi) north-northeast of gregory’s (1938) brushy basin type section on the elk mountain road and is in the middle of an 8-m (26-ft) tidwell member section. any identifiable fossils from the tidwell member are of considerable significance. paleo-solutions inc., as part of their inventory of paleontological sites within the mapped lower morrison formation (salt wash member of miller [1955b]) between sr 95 and the elk mountain road (murphey and zubin-stathopoulos, 2018), discovered a dinosaur tracksite. the tracksite consists of natural casts of sauropod tracks and one track of a three-toed dinosaur from a couple of meters above the bluff sandstone member (figures 11d to 11f). this site is in the interval north of sr 95 where the bluff begins to interfinger with the tidwell member and may be the oldest known morrison dinosaur tracksite. recapture member history and lithology the type section of the recapture member is on recapture creek northeast of bluff, utah (figures 2, 7a, and 12). these strata are well exposed across the southern portion of the study area (figures 12 to 14). gregory (1938) initially referred these rocks to the recapture shale member summarized as follows: “the interval between the bluff sandstone member and the lowermost bed characteristic of the westwater canyon sandstone member is occupied by a series of strongly colored shales and sandstones 100 to 300 feet thick. they appear in many places as sloping platforms at the base of cliffs and are particularly well displayed near the mouth of recapture creek, from which the name is derived. the shales are prevailingly dark red, but some are variegated pink, ash, brown, and gray. many of them include firm, strongly calcareous beds that break into slabs and friable, imbricated gypsiferous beds that weather as tiny cliffs. the sandstones are white beds of glistening quartz cemented by lime, few of them more than a foot thick or continuous for more than 1,000 feet….the shales and sandstones combine to form slopes, low mesas, and platforms, and the edges of sandstone beds appear as shelves and small benches. the outcrops are attractively color-band157 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 ed, but as the shale and sandstone feather out and replace each other along the strike the arrangement of sections 1,000 feet apart is quite different.” gregory (1938) recorded that the recapture member averages about 60 m (200 ft) thick throughout the region. at its type section along recapture creek, gregory (1938, section 23) measured 67 to 88 m (220–290 ft) of rreeccaappttuurree mmbbrr.. rreeccaappttuurree mmbbrr.. rreeccaappttuurree mmbbrr.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. nnoo--mmaannss iissllaanndd bbeeddss nnoo--mmaannss iissllaanndd bbeeddss nnoo--mmaannss iissllaanndd bbeeddss bbrruusshhyy bbaassiinn mmbbrr.. bbuurrrroo ccaannyyoonn ffmm.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. ee aa dd bb ff wweessttwwaatteerr ccaannyyoonn mmbbrr.. rreeccaappttuurree mmbbrr.. bblluuffff ssss.. nnoo--mmaannss iissllaanndd bbeeddss bbaassaall rreeccaappttuurree bbeenncchh bbaassaall rreeccaappttuurree bbeenncchh bbaassaall rreeccaappttuurree bbeenncchh bbaassaall rreeccaappttuurree bbeenncchh cc figure 12. basal recapture bench on south side of black mesa. (a) lower units in morrison formation on southwest side of no-mans island viewed to east. note continuation of basal recapture bench from figure 9c. (b) morrison formation through burro canyon formation strata viewed toward north on east side of decker cove along west side of no-mans island and northward to south end of black mesa. (c) geologists (yellow arrows) climbing through fluvial sandstone forming basal recapture bench south of no-mans island. (d) dark layers (red arrows) formed by heavy mineral concentrations typical of recapture member in fluvial sandstone forming basal recapture bench. (e) lower morrison formation strata at the south end of black mesa. view toward west. (f) lower morrison formation strata at the southwest end of black mesa farther to the west than in e. 158 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 bblluuffff mmbbrr.. sshhaacckk 10 m gg--33 aa&&ll--1122 bb 0.5 miles bblluuffff ssss.. rr eecc aapp ttuu rree mm bb rr.. rr ee cc aa pp ttuu rree cc rree ee kk sshhaacckk sshhaacckk ff cc dd ee bblluuffff mmbbrr.. bblluuffff mmbbrr.. bblluuffff mmbbrr.. aa bblluuffff mmbbrr.. gg hh ii jj kk figure 13. caption is on the following page. 159 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 recapture in five lithologic units. unfortunately, while noting that the morrison section along recapture creek was based on correlating six sections, gregory did not record on which stratigraphic units these correlations were made (gregory, 1938). in reevaluating gregory’s type section, anderson and lucas (1996, 1998) marked the top of the recapture at the base of gregory’s (1938, section 23) unit 3, 34.14 to 77.42 m (112–254 ft) below the top of the section of the recapture member (see figure 11e and 11f of lucas and anderson, 1997). gregory (1938) identified an unconformity at the base of unit 3 represented by voids, where weathered, and jumbled fragments of green and red clay (rip-up clasts) 5 to 15 cm (2–6 in) across at the base of the sandstone (figure 13f) that was used to define the base of salt wash member by anderson and lucas (1996, 1998). kirkland examined the section on recapture creek and discerned that the sandstone is a lenticular, low sinuosity channel sandstone extending across recapture creek from the southwest cutting down into the basal recapture bench (figures 13a to 13e). gregory (1938) noted that the recapture member resembles beds 13 km (8 mi) south of woodside, utah, which were placed at the base of the salt wash member by gilluly and reeside (1928), apparently noting a similarity to the tidwell member as it is currently used. gregory compared these basal morrison strata near woodside as like the recapture shale member for the dominance of red mudstone characterizing the rocks (figures 12 and 13), although subsequent authors have used recapture member. stokes (1944) noted that laterally the recapture interfingers with, and is underlain by, the salt wash member. craig and others (1955) recognized that the recapture member thickens to the south and, based on the local presence of granite pebbles, appears to have been sourced from the south, as is the overlying and genetically related westwater canyon member. an apparent salt wash tongue was thought to split the recapture into upper (recapture member) and lower (tidwell member) members in the southern part of the study area (peterson and turner-peterson, 1987; turner and peterson, 2004), based on a laterally extensive channel sandstone near the middle of the member. thus, in the area of the southwestern blanding basin, turner and peterson (2004) divided the morrison formation into: (1) bluff sandstone member, (2) tidwell member, (3) salt wash member, (4) recapture member, (5) westwater canyon member, and (6) brushy basin member (figure 6). as noted above, a low (about 10 m [30 ft]) bench largely capped by light-brown to gray to nearly white fluvial sandstone is present along the west and across the south side of black mesa makes up the base of the recapture member, which miller (1955a) mapped as the top of the bluff sandstone (figures 8, 9c, 10, and 12). these sandstone beds do not seem to pertain to the salt wash member because they include heavy mineral concentrations along bedding planes (figure 12d) that figure 13 (figure is on the previous page). lower recapture member along recapture creek. (a) oblique view from south of the type section of the recapture member following gregory (1938) and anderson and lucas (1997, 1998) (google earth©). (b) lower recapture section on recapture creek described by anderson and lucas (1998) as recapture member of the bluff formation from southeast; compare with lucas and anderson (1997, figure 11e). g-3 = gregory’s (1938, section 23) unit 3 and a&l-12 = anderson and lucas’ (1998) “type section of bluff formation,” unit 12 as base of salt wash member (red arrow indicates this channel sandstone). orange line indicates approximate position of upper contact of bluff sandstone member. height of door frame in shack is 1.8 m (6 ft) with total height of shack 2 m (6.5 ft). (c) same area in b from southwest across recapture creek. light blue arrow indicates level of h and i. (d) same area in b from the west across recapture creek. red arrow indicates position of channel sandstone (gregory’s [1938], section 23, unit 3; anderson and lucas’ [1998], unit 12). (e) correlative section as viewed to southwest across recapture creek. red arrow indicates position of correlative channel sandstone (gregory’s [1938], section 23, unit 3; anderson and lucas’ [1998], unit 12). dark blue arrow indicates position of coarse-grained strata in j and k. (f) basal surface of channel cutting down into lower bench of recapture member. rock hammer head about 18 cm (7 in). (g) escarpment formed by basal bench of recapture member to northwest across recapture creek. orange arrow indicates top of bench. (h) overview of coarse-grained sandstone as indicated in c. (i) detail of carbonate-cemented sandstone and mudstone grains in h. (j) top view of coarse-grained sandstone as indicated in e. (k) oblique view of coarse-grained sandstone as indicated in e. 160 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 0.5 miles bblluuffff ssss.. ddeecckkeerr ccoovvee wweessttwwaatteerr ccaann.. mmbbrr.. rreeccaappttuurree mmbbrr.. bbrruusshhyy bbaassiinn mmbbrr.. ccoottttoonnwwoooodd wwaasshh bbllaacckk mmeessaa nnoo--mmaannss iissllaanndd 22 33 11 bb dd e rreeccaappttuurree mmbbrr.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. nnoo--mmaannss iissllaanndd bbeeddss ff gg cc aa rreeccaappttuurree mmbbrr.. bbaassaall rreeccaappttuurree bbeenncchh bbaassaall rreeccaappttuurree bbeenncchh westwater canyon mbr. bblluuffff ssaannddssttoonnee mmbbrr.. figure 14. caption is on the following page. 161 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 are only characteristic of the fluvial sandstones in the recapture member (christine turner, verbal communication, october 27, 2018). thus, identifying that this bench is made up of the basal-most beds of the recapture member is an important contribution of this project. the basal recapture bench extends east of black mesa to the type section of the recapture member on recapture creek (figure 13) where it thickens and includes more than one coarse-grained, ledge-forming unit. in this area, each of these ledge-forming units are commonly conglomeratic, composed largely of small (0.5 to 2 cm [0.2–1.0 in]) carbonate-cemented intraclasts of mudstone and fine sandstone (figures 13h to 13k). anderson and lucas (1996, 1998) restricted the recapture member to the lower bench-forming interval, assigned it as a member of the bluff sandstone of the san rafael group, and included the upper more fluvial interval in an expanded salt wash member (figure 5). in their description of the recapture type section anderson and lucas (1996, 1998) described only the lower 17.9 m (55 ft) as recapture member, stopping at a “reddish” sandstone bench that they interpreted as the base of their salt wash member. we found that this sandstone is lenticular and cuts down into the top of the lower recapture bench (figures 13b to 13e). even if we identified this bed as a salt wash-style channel sandstone, we would follow gregory (1938) in extending the recapture member in the southern blanding basin for another 35 to 70 m (115–230 ft) up the red slope to the base of drab, yellowish-gray sandstones and sandy mudstones characteristic of the basal westwater canyon member (figure 14). this is in keeping with gregory’s (1938, section 23, p. 76) type section of 67 to 88 m (220–290 ft) thickness in which it was noted that shale constituted more than 85% of this upper recapture interval. however, we want to point out that both turner and peterson (e.g., 2010a) and anderson and lucas (1996, 1998) identified important breaks in depositional history in this area. we tentatively suggest that unconformity below the bluff sandstone member represents the j-5 and the unconformity associated with the lower recapture bench tentatively represents our j-6 unconformity at the base of the salt wash member (figure 6). the distinctive feldspathic, red-bed sequence in the type area of the recapture, does not support assigning these strata to the salt wash as in so doing would obscure the depositional history of these important stratigraphic units. in anderson and lucas’ (1997, 1998) system, the morrison formation is restricted to a lower fluvial-sandstone-dominated salt wash member and an upper variegated-mudstone-dominated brushy basin member. to some degree this followed the way craig and others (1955) split the morrison for their analysis of the distribution of facies and sedimentological properties, although they never proposed combining these rock units or changing names. in their 2004 overview of morrison paleoenvironments, turner and peterson (2004) indicated that above the bluff sandstone member at recapture creek, both the tidwell and the salt wash members underlie the recapture member, apparently following anderson and lucas (1996, 1998) in identifying the fluvial sandstone bench in the lower part of gregory’s (1938) type recapture section as pertaining to the salt wash member. in 2010, turner and peterson (2010a, plate 6b, verbal discussion, 2017) revised their interpretation and followed figure 14 (figure is on previous page). recapture member of the morrison. (a) exposure of total recapture member and its bounding strata at the horn on the west side of recapture creek (figure 2). note the long slope of red recapture mudstones and thin sandstones overlying the lower recapture bench. (b) oblique view from south of upper jurassic outcrops south of black mesa (google earth©). blue bar stratigraphic extent of westwater canyon member. red bar stratigraphic extent of recapture member. red star is the brushy basin dated ash site. number 1 is the lower bench, number 2 is the middle bench, and number 3 is the upper bench. (c) recapture member on the west side of no-mans island viewed toward north. blue arrow denotes basal contact of the westwater canyon member. (d) typical exposures of the recapture member northwest of no-mans island. (e) lower morrison formation strata on south side of no-mans island looking north. (f) overview of recapture exposures described for morrison reference section on the northeast side of black mesa (appendix a). (g) salt wash-style channel sandstone in recapture member, morrison reference section on the northeast side of black mesa (appendix a). 162 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 o’sullivan (1998, 2000, 2010a, 2010b) in recognizing that the recapture member along the southwest side of the blanding basin rests directly on, and intertongues with, the bluff sandstone member of the morrison formation (figures 6 and 8). however, they also noted that both the salt wash and tidwell members correlate laterally with the lower bluff sandstone member. this is in keeping with their correlation of the recapture with the basal brushy basin member above the salt wash member to the north (turner and peterson, 2004). in this scenario, the entire westwater canyon member pinches out between the recapture member and the overlying brushy basin member to the north. miller (1955a) mapped the northern limit of the recapture member on the northwest side of black mesa south of sr 95 at about the latitude of the butler wash tracksite (figure 2). this is approximately along the line of our morrison reference section (figure 3; appendix a). additionally, on the east side of black mesa, miller (1955a) mapped its northern limit in cottonwood wash only about 1 km (0.6 mi) north of the type section of the overlying westwater canyon member of the morrison formation. gregory (1938) and anderson and lucas (1996, 1998) noted that no recognizable recapture is below the lowest described beds of the westwater canyon member at its type section. to the north beyond our morrison reference section (figure 3), miller (1955a, 1956) mapped the combined recapture and westwater canyon members as the lower morrison formation. o’sullivan (1998, 2000) replaced the recapture member with the salt wash member at approximately this same position but extended the westwater canyon member several kilometers farther north. to the east of the study area, o’sullivan (2000, 2010a) recognized several prominent sandstone channels within the recapture member at montezuma creek east of black mesa considered to be of salt wash morphology. likewise, we recognize that the red mudstone in the upper two-thirds of the recapture member is replaced over a relatively short distance by ledge-forming sandstones typical of the salt wash member on the north end of black mesa. thus, we follow o’sullivan (1980, 1998, 2000, 2010b) in recognizing the interfingering of the upper part of the recapture with the salt wash member and the correlation of the lower part of the recapture with the upper tidwell member, with the northward pinch-out of the last tongues of bluff sandstone member into the tidwell and regional thinning of the basal recapture beds overlying the northernmost expression of the bluff (figure 8). given its southern source area, we recognize the recapture member as thinning to the north. we expect that the more westerly derived salt wash member represents a distributive fluvial system (owen and others, 2015, 2017) that onlaps the southerly derived recapture such that salt wash fluvial sandstones would progressively interlense diachronously with the wedge of mostly finer-grained recapture sediments as both members thicken and expand their distribution to the north and east. to the north is a fining of southern-sourced materials in the recapture, with a loss of both the granitic materials and the eolian beds noted as characteristic of the member in northern arizona (dickinson, 2018). with the northern pinch-out of the bluff sandstone member, the lower part of the recapture member merges with the tidwell member and fluvial sandstones of the eastward-prograding salt wash member (figure 8). we conclude that the recapture in its type area on the southwest side of the blanding basin does not overlie the salt wash member as stated by turner and peterson (2004, 2010a). we propose that the salt wash distributary megafan expanded to the east over the coastal tidwell deposits, where it onlapped and interfingered with the coarsening upward, southerly sourced, distributary megafan formed by both the recapture and overlying westwater canyon members. herein, we use the term distributary megafan in the sense of miall (1966) rather than distributive fluvial system (owen, 2015, 2017), noting that they essentially mean the same thing. our model largely supports the conclusions reached by dickinson (2018), supplemented by additional observations of the interactions of these two important sedimentary packages (hurd and others, 2006). additionally, our model suggests that strata referred to the salt wash member, below the recapture member in the region of the four corners and in northern new mexico (tyler and ethridge, 1983; peterson, 1994, turner and peterson, 2004; lucas, 2018), represent fluvial systems associated with a distributary megafan farther east than the salt wash member in its type area of central utah. 163 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 while examining strata lateral to vertebrate locality sa1115v in the lower recapture member above the lower recapture bench south of black mesa, thin smectitic clay layers a few mm thick were identified interspersed with thin layers of mudstone and sandy shale. this interval was sampled for detrital zircons resulting in a mixing of these thin clastic layers. the resulting zircons included some fine, clear, and elongate crystals that might well have be derived from a near contemporaneous ash (appendix b). the youngest single grain in the dataset is 145.9 ± 1.6 ma, which is younger than any ash date known for the morrison formation (trujillo and kowallis, 2015). the next youngest single grain for which discordance is <20% is 150.2 ± 2.1 ma, which is close to our new age for the top of the brushy basin member in this area (appendix c). the next two youngest grains that pass the discordance filter are 153.7 ± 2.1 ma and 153.8 ± 2.2 ma, which are approximately 1.5 million years older than ages for the base of the brushy basin member. even these ages seem a bit young for the lower recapture and would suggest as much as 130 m (about 430 ft) (figure 3; appendix a) would have had to be deposited in 1.5 million years. maidment and muxworthy (2019) have suggested the lower morrison formation was deposited as rapidly as the brushy basin member with a larger, previously unidentified unconformity spanning 2 to 3 million years separating the tidwell member from the overlying salt wash member. our initial laser ablation data for the lower recapture lends credence to their hypothesis, but further analysis of the zircons from this site is needed. paleontology one fossil site was recognized in the basal recapture bench, sa0918t. it is identified as a trace fossil produced by social insects, in this case, termites (e.g., bown, 1982; hasiotis and bown, 1992; thorne and others, 2000; hasiotis, 2004, 2008; bromley and others, 2007) (figures 15a and 15b). we identified several dinosaur sites in the recapture member above the basal recapture bench (figures 15c and 15d) adding credence to its inclusion within the morrison formation, as no dinosaur remains are known from the san rafael group. it is noteworthy that the lower “recapture” portion of the morrison formation preserves most of the known dinosaur and invertebrate remains to the southwest at black mesa in northern arizona, where the brushy basin member has been stripped off the westwater canyon member below the regional angular unconformity on the rift shoulder of the mogollon uplift at the base of the cretaceous unconformity (harshberger and others, 1957; kirkland 1990, 1991). this pattern seems to be like that in the southwestern blanding basin, where we identified several vertebrate sites in the recapture member and few sites in the overlying westwater canyon member. the abundance of dinosaur bones a short distance above the bluff sandstone member adds to the evidence leading us to reject the anderson and lucas (1996, 1998) hypothesis that the recapture member should be included within the san rafael group. most fossil sites in the lower recapture member to the south and west of no-mans island consist of scattered small bone chips associated with thin (<0.6 m [<2 ft]), light-gray-colored, sandy intervals about 10 to 20 m (32–65 ft) above the top of the bluff sandstone (e.g., sa1131v, sa1132v, figures 13h and 13i). one locality (sa1115v; figures 14c, 15c, and 15d) preserved several bones along a single bedding plane and appears to be deserving of additional scientific examination. previously, the only morrison locality that has been published from the study area is a natural cast of a stegosaur track referred to the ichnogenus deltapodus by milán and chiappe (2009). their study was the first report of this track type in the jurassic of north america. this locality, sa448t (figure 15e), is in an area that we did not investigate in the extreme southeastern part of the study area (figure 1). however, we were able to determine that the locality is in the recapture member. salt wash member history and lithology lupton (1914) first described the salt wash member from the west side of salt wash, grand county, utah (nw1/4, section 19, t. 23 n., r. 18 e., salt lake base line and meridian). gregory (1938) provided an excellent summary: “in reports on the geology of the region north of 164 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 moab and other places in east-central utah lupton (1914) described a coarse-grained ‘gray conglomeratic sandstone’, in places lenticular and cross-bedded, that forms cliffs about 350 feet from the top of the morrison strata sufficiently uniform and persistent to serve as a datum plane for mapping. for this sandstone he proposed the name ‘salt wash member of the mcelmo formation.’ as classified by gilluly and reeside (1928) the salt wash sandstone member lies at the base of the morrison and includes not only gray conglomeratic sandstones but also clay, limestone, and gypsum. baker (1933) defines this member as ‘white conglomeratic sandstones interbedded with red sandy mudstones and red shale’ that occupy the lower half of the morrison south of moab.” craig and others (1955) followed stokes (1944) in extending the salt wash member into the recapture ddcc ee aa bb figure 15. fossils in the recapture member. (a) possible termite traces in lower recapture bench west of recapture creek sa0918t. yellow arrow points to close-up view shown in b. (b) detail of sa0918t showing individual galleries in larger scale structure. (c, d) close-ups of dinosaur bone (red arrows) in situ at sa1115v. (e) natural cast of deltapodus (“stegosaur” track) from the recapture member below the southeast margin of white mesa at sa448t (milán and chiappe, 2009). 165 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 member as defined by gregory (1938) across the four corners region of the colorado plateau as summarized below: “gregory (1938) did not recognize the salt wash member in the southeastern corner of utah, but subsequently stokes (1944) recognized the member in the lower part of gregory’s recapture member in this area as well as in the carrizo mountains area of northeastern arizona. the extension of the salt wash member as a recognizable unit through southeastern utah and into northeastern arizona and northwestern new mexico constitutes a restriction of gregory’s original definition of the recapture member.” o’sullivan’s (1984) plot (figures 1, 14a and 14b) of the type section of the salt wash member is in the same location noted by lupton (1914). however, the proposed site of the type section by anderson and lucas (1998) is about 3 km (2 mi) farther north. kirkland and deblieux (2017) documented large, isolated, cobble-sized, stromatolitic limestone clasts in the basal sandstone of the salt wash member in its type area (figures 16c to 16f). these large clasts appear to have been sourced from the base of the tidwell member and similar beds toward the top of the summerville formation (figures 11b and 11c). this supports the view that the j-5 unconformity is at the base of the lowest salt wash channel sandstone (anderson and lucas, 1996, 1998). however, isolated channel sandstones in the upper tidwell member are present at other sites, below the more obvious break formed by the first set of continuous, ledge-forming channel sandstones that are generally picked as the base of the salt wash member. thus, in many areas, the tidwell appears to be gradational with the overlying salt wash with a decrease in coastal fine-grained facies and an increase in fluvial channel sandstones. we propose that these large stromatolite clasts are reworked from the underlying tidwell member, maybe a result of local late jurassic salt tectonics within the paradox basin such as has been documented in the lower cretaceous, or a phase of uplift along the san rafael reef during the late jurassic (kirkland and madsen, 2007; kirkland and others, 2016; kirkland and deblieux, 2017). given the recognition of a significant unconformity above and below the tidwell in the capitol reef area (figures 4e to 4i), we suggest that once again anderson and lucas (1996, 1998) have recognized a possible j-6 unconformity (figure 6). as another example of evidence of this uplift during the late jurassic, demko and others (2004) documented the pinch-out of both the tidwell and the salt wash members between the summerville formation and the brushy basin member on the southwest side of the san rafael swell along the last chance monocline. in discussing the salt wash member, it is important to note that peterson (1988) and turner and peterson (2004) interpreted the salt wash member of the morrison formation in the western blanding basin as separating the tidwell and the overlying recapture (figure 6). turner and peterson (2010a, 2010b; verbal communication, 2017) now interpret the salt wash to onlap the bluff sandstone member from the north, such that around the southern end of black mesa, the recapture member directly overlies the bluff sandstone member and that both the salt wash and underlying tidwell members are lateral equivalents to the bluff sandstone unlike what we propose here for the salt wash (figures 3, 6, and 8). o’sullivan (1998) plotted the salt wash member as overlying the tidwell member in the black steer mesa section at the north end of the study area (figure 2). o’sullivan (2000) noted that isolated sandstone lenses of salt wash character within the recapture member just to the east of the study area in the montezuma valley provide evidence that the salt wash indeed interfingers with the recapture member, as noted by stokes (1944) and craig and others (1955). miller (1955a, 1956) noted on the photogeological maps that the recapture and overlying westwater canyon members could not be separated below the brushy basin rim within the brushy basin (figure 2), and from about the current position of sr 95 northward mapped these beds as lower morrison formation. a nearly continuous line of outcrops extends from this line northward to the black steer mesa section (cadigan, 1955; o’sullivan, 1980, 1998), and provides an opportunity to rigorously document the interfingering of the salt wash and recapture members in this area (figure 2). we follow o’sullivan (1998, 2000) in recognizing that the lower morrison formation in this area consists of the tidwell member overlain by the salt wash member. we also find 166 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 it noteworthy that reddish mudstone beds interspersed between sandstone benches of the salt wash member in east-central utah are nearly identical to similar mudstones that form the bulk of the recapture member in the southwestern blanding basin (figures 13 and 14). paleontology the salt wash member was not examined for fossils during this study. however, within its type area, kirkland and deblieux (2017) found it to be fossiliferous with numerous sites preserving natural casts of dinosaur tracks and several sites with bone fragments on the surface. a single invertebrate fossil locality has been noted at the black steer mesa section in the salt wash member from an exposure in the wash to the northeast of that section (cadigan, 1952). this locality (sa0083i) as listed in the utah paleontological locality database is based on a passing reference to bivalve shells “in the eastern wall of cottonwood wash east of the indian school.” it is the most northern morrison fossil site recorded along comb ridge. from october 16 to 20, 2017, paleo solutions inc. conducted an inventory of paleontological sites largely within the salt wash member (mapped as lower morrison formation by miller, 1955b, 1956) between sr 95 and the elk mountain road (murphey and zubin-stathopoulos, 2018). during this study, two fossil plant sites, one sauropod dinosaur tracksite, and seven dinosaur bone localities were documented (figures 16g to 16n). the surficial skeletal materials observed at the surface were fragmentary. westwater canyon member history and lithology recognizing that the westwater canyon member may be partially or even wholly correlative to the salt wash member to the north in grand county, utah, gregory (1938) established the westwater canyon sandstone member for the sandstone cliffs in the lower to middle part of the morrison because he was uncertain as to the exact correlation of these rocks. he noted that the westwater canyon member caps the mesas in the southern part of the study area across the southern part of black mesa and around decker cove as later documented on the photogeological map of this area (miller, 1955b) (figures 2, 6, and 9). gregory (1938) summarized the properties of the westwater canyon member as follows: “this member is essentially a series of white sandstones composed of rounded medium to coarse grains of quartz, cemented by calcium carbonate and arranged in lenticular, irregular beds 1 to 30 feet thick. they include conglomeratic bands and stringers composed of quartz aggregates, colored chert, concretionary masses of compact green-white clay, and rare fragments of petrified wood and dinosaur bones. interbedded with the sandstones are red earthy soft fine-grained sandy shales perhaps better called ‘mudstones’ that thin, thicken, or disappear in short distances. with them are associated a few thin short lenses of gray limestone conglomerate. these mudstones, which make up 8 to 20 percent of measured sections, are extremely irregular. …unconformable contacts at the base of the westwater canyon member were observed at several places. features that indicate exposure of the top beds before the brushy basin shale was laid down were noted in mcelmo canyon, but generally the sandstone grades upward through a series of gray sandy shales and merges into the variegated shales at different horizons….the thickness of eight measured sections of the westwater canyon sandstone member ranges from 222 to 295 feet.” as with the recapture member, the term westwater canyon member was applied to correlative strata across the four corners area, northeastern arizona, and northern new mexico. whereas, the u.s. geological survey has maintained gregory’s (1988) usage, anderson and lucas (1997, 1998) proposed that the westwater canyon member be dropped in favor of the salt wash member. they identified gregory’s (1938) type section where westwater canyon joins cottonwood canyon (figures 17a and 17b) and provided a redescription (anderson and lucas, 1997, 1998), noting, as have we, that the basal contact with the underlying 167 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 ssaann rraaffaaeell ggrroouupp ssaalltt wwaasshh mmbbrr.. ssaalltt wwaasshh mmbbrr.. ttiiddwweellll mmbbrr.. salt wash mbr. ssaalltt wwaasshh mmbbrr.. brushy basin mbr. bbrruusshhyy bbaassiinn mmbbrr.. bbrruusshhyy bbaassiinn mmbbrr.. ssuummmmeerrvviillllee ffmm.. ttiiddwweellll mmbbrr.. ttiiddwweellll mmbbrr.. ssaann rraaffaaeell ggrroouupp gg jj mm ii ll hh kk nn ff bb dd aa cc ee figure 16. salt wash member. (a to f) salt wash member in its type area (figure 1). (a) type section of salt wash member on the south end of duma point as modified from o’sullivan (1984). stratigraphic units are written out. (b) type area of the salt wash member around duma point as viewed from the west with stratigraphic units labeled. (c) salt wash member northwest of duma point. (d) stromatolite fragments on slope of tidwell reworked from overlying salt wash member. (e) stromatolite clast in basal sandstone of the salt wash reworked from top of summerville or base of tidwell as indicated by double-headed arrow. (f) detail of stromatolite clast in basal sandstone of the salt wash member as indicated by double-headed arrow. (g to n) typical fossils in the salt wash member north of sr 95 (lower morrison of miller [1955a] from paleo-inventory of paleo solutions [murphey and zubin-stathopoulos, 2018]). (g) petrified log from sa1450. (h to i) fossil plant impressions from sa1466. (j) overview of sa1447. double-headed red arrow indicates position of sauropod vertebra in k. (k) sauropod vertebra external impression of centrum below scale with cross section of highly pneumatic bone above scale. (l) overview of bone scatter at sa1441. double-headed red arrow indicates position of bone scatter on slope. (m) detail of bone scatter. (n) dinosaur bone fragments at sa1444 as indicated by red arrow. 168 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 recapture member is not exposed in the floor of the canyon. in craig and others’ (1955) discussion of the morrison formation, the westwater canyon member was shown to be a wedge of coarse strata, both thickening and coarsening directly south of the study area. the presence of granitic fragments and detrital zircons indicates it was derived directly from the south where protorozoic granites were becoming exposed along the central arizona rift shoulder of the mogollon highlands on the north side of the bisbee basin (e.g., kirkland, 1990, 1991; dickinson and gehrels, 2008, 2010). genetically, these rocks can be considered a distributary megafan similar to the coarse, westerly sourced sandstone wedge (fifty mile member) that is interpreted to replace the brushy basin member to the southwest in the southern kaiparowits basin (peterson, 1988). however, the genetic similarity does not presuppose equivalence as has been proposed by others (turner and peterson, 2004; dickinson, 2018). we suggest that the westwater canyon is somewhat older and is only correlative with the lower part of the brushy basin member to the north. in fact, we have observed (2019, research in progress with grant willis, ugs) that the lower cretaceous buckhorn conglomerate member of the cedar mountain formation cuts the entirety of the brushy basin member such that the buckhorn rests directly on the similar appearing salt wash member in the northern part of capitol reef national park (figures 1, 5b, and 5c) south of cathedral valley (12s., 472691.00 m e , 4258154.00 m n). it is now thought that the fifty mile member of the morrsion formation may represent the buckhorn conglomerate on the south end of the straight cliffs, where it has cut out the brushy basin member in this area. there are no outcrops where the lateral relationships of the fifty mile member with other strata may be observed. provenance studies will be needed to test the identity of these sedimentary packages. in our limited explorations in the southern part of the study area around decker cove (figure 2), we note that the lower half of the member forms a main cliff formed by stacked sandstones of the westwater canyon member that is separated from a smaller upper cliff that caps the mesas (following miller, 1955b) by an appreciable slope of pale-greenish mudstone that we initially identified, at a distance, as the overlying brushy basin member (figure 17c). turner and peterson (2004, figure 3) correlated the upper half of the westwater above the main cliff with the lower part of the brushy basin member in its type area in brushy basin, ignoring gregory’s (1938) description of the type section, but in keeping with our correlation with the brushy basin farther to the north (figure 8). a sharp break between mudstones without smectitic clays to highly smectitic mudstones has been used as a marker horizon to separate a basal “lower brushy basin” from the bulk of the brushy basin member across the colorado plateau region and is referred to as the “clay change” (peterson and turner-peterson, 1987; turner and peterson, 2004, 2010a). turner and peterson (2004) correlated the “clay change” to the base of the mudstone slope dividing the westwater canyon member (figure 6). the main cliff (“main body”) of the westwater canyon member appears as a series of closely spaced sandstone ledges in naturally weathered outcrop. this lower half of the westwater canyon member is nearly all sandstone in composition with the weathered ledges appearance related mainly to induration and percent clay content. overall, even the most mudstone-appearing partings are, at best, muddy sandstone intervals. gravel-sized chert and limestone grains make up conglomerate lenses mostly in the upper third of this unit. this interval is well-expressed along a steep dugway on the west side of stephens canyon (figure 7b) on the west side of black mesa (12 s, 623450.00 m e, 4148459.00 m n). the pale mudstones overlying these sandstones are moderately smectitic (figure 8). the presence of these mudstones is similar to those in the brushy basin member because smectitic clays are completely absent in the salt wash member to the north in east-central utah (keller, 1962). we agree with turner and peterson (2004) that this interval must correlate with the lower portion of the smectitic upper brushy basin farther to the north (figure 8). one or two well-cemented conglomeratic sandstones overlie this smectitic mudstone interval and cap a series of mesas and cuestas along the south side of black mesa, and form the top of the second bench described below (figures 5, 6, and 8), which can be traced east across the southern blanding basin nearly to colorado (e.g., figure 17c and 17e). miller 169 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 (1955a, 1955b) used this surface to define the top of the westwater canyon member in the photogeological maps and as the top of the lower morrison formation along the elk mountain road (miller, 1956). we informally refer to these beds as the no-mans island beds as they are well developed capping no-mans island (figaa nnoo--mmaannss iissllaanndd bbeeddss nnoo--mmaannss iissllaanndd bbeeddssnnoo--mmaannss iissllaanndd bbeeddss nnoo--mmaannss iissllaanndd bbeeddss bbuurrrroo ccaann.. ffmm.. bbuurrrroo ccaann.. ffmm.. rreeccaappttuurree mmbbrr.. ssmmeeccttiittiicc mmuuddssttoonnee ssmmeeccttiittiicc mmuuddssttoonnee mmaaiinn bbooddyy mmaaiinn bbooddyy bbrruusshhyy bbaassiinn mmbbrr.. bbrruusshhyy bbaassiinn mmbbrr.. cc dd bb ee bbrruusshhyy bbaassiinn mmbbrr.. bbuurrrroo ccaannyyoonn ffmm.. bblluuffff ssaannddssttoonnee mmbbrr.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. rreeccaappttuurree mmbbrr.. bbaassaall rreeccaappttuurree bbeenncchh uuppppeerr rreeccaappttuurree figure 17. westwater canyon member of the morrison formation. (a) overview of type area of westwater canyon member, where westwater canyon joins cottonwood wash. pink arrow indicates westwater canyon as viewed from south. blue arrow indicates cottonwood wash. yellow bracket shows extent of type section. (b) detail of exposure of type section of westwater canyon member near mouth of westwater canyon. red arrow shows position of b in a. (c) extensive exposure of westwater canyon member on southwest side of white mesa (figure 2). (d) exposures of westwater canyon member along route of morrison reference section (appendix a), below southwest side of black mesa. (e) nearly complete section of morrison formation exposed on west side of mccracken point southeast of basal recapture type section (figure 2). red arrows indicate position of the no-mans island beds at top of the westwater canyon member. 170 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 ures 2, 7, 8, 12b, 12f, and 14e). miller (1955a, 1956) only mapped the westwater canyon member south of the northern limit of the recapture member. thus, on miller’s (1955a) photogeological map the usage of westwater canyon member only extends north of its type section for approximately 0.8 km (0.5 mi), with the morrison formation from this point northward divided into a “lower morrison formation” and an upper brushy basin member. however, o’sullivan (2000) recognized the westwater as extending several kilometers farther north. prospecting for fossils below the brushy basin rim north of sr 95, we noted that the lower brushy basin member is very sandy and largely devoid of significant vertebrate fossils, and we initially concluded that turner and peterson’s (2004) correlation of the upper interval of the westwater canyon with the lower brushy basin member was probably correct. however, we have subsequently examined the upper contact of the westwater canyon member farther north along the elk mountain road and noted that in gregory’s (1938) type section, the no-mans island beds are present at the top of the westwater canyon member and below the base of the type section of the brushy basin member (gregory, 1938, section 25, p. 77). thus, we now recognize that this unfossiliferous interval is actually the upper smectitic mudstone near the top of the westwater canyon member. the complexities in correlating the southern and northern portions of the study area are daunting, but we believe correlating this interval from south to north along the west side of the blanding basin by using the resistant no-mans island beds as a marker bed is key; these beds can indeed be traced north from the south end of black mesa to the southwest side of the abajo mountains using aerial imagery (figure 8). paleontology during our paleontological inventory no significant fossils were noted in the westwater canyon member. gregory (1938) reported that the member preserves dinosaur bone and petrified wood. we found the remains of a shattered dinosaur limb bone on the west side of decker cove (sa1135v) near the base of the westwater canyon (figures 18c to 18e) and dinosaur bone fragments in the upper westwater canyon member north of sr-262 (hovenweep road) in recapture canyon. additionally, we identified a sandstone bed preserving abundant carbonaceous plant detritus (figures 18a and 18b) in the upper westwater canyon in a rather densely vegetated area west of the north end of black mesa (sa1126p). none of the plant remains appeared identifiable. similar fossils were noted by paleo solutions inc. (figures 16g to 16n) where they examined the correlative salt wash strata mapped by miller (1955a) as “lower” morrison formation below the brushy basin rim (murphey and zubin-stathopoulos, 2018). brushy basin member in establishing the brushy basin shale member for the variegated mudstone interval that forms the upper part of the morrison formation across the colorado plateau region, gregory (1938) did not state the specific location for the type section. gregory (1938) however, titled section 25 solely as “morrison formation in brushy basin.” in utah place names, van cott (1990, p. 52), reported: “brushy basin (san juan [county]) is on the southern slopes of the abajo mountains six miles south of mount linnaeus. it drains south into the brushy basin wash and is named for its heavy growth of upland desert shrubs. s7, 18, t35s, r22e, slm; ca. 7500' (2,286m).” although not describing the lateral extent of brushy basin, on the geological map, gregory (1938, plate 1) indicated that the brushy basin physiographic feature extends from the southwest side of the abajo mountains along brushy basin wash to its confluence with cottonwood wash west of brushy basin rim and north of sr 95. in the 1930s, a dirt road extended westward from blanding, across the southern part of brushy basin, and through the bears ears to natural bridges national monument (gregory, 1938, plate 1). this road is now referred to as the elk mountain road (blm 092). we assume that gregory measured the section along this road. less than 1 km (0.6 mi) south of the road are excellent, deeply dissected exposures of the brushy basin member (figures 19a and 19d); however, gregory 171 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 (1938) noted in the description of a 68-m-thick (224-ft) unit 18 that the unit is partially concealed by landslides, which indicates that the section would have been closer to the road. we noted a wooden culvert under the road at the top of the no-mans island beds that could date to the 1930s. on thoroughly investigating the transition between the westwater canyon member and the bushy basin member, we interpret gregory’s (1938)unit 13 at the top of the underlying westwater canyon member as also representing the top of the no-mans island beds (figures 6, 8, and 19). further support for this interpretation came from driving up the elk mountain road following a rain storm and finding it impossible to continue up the slope formed by gregory’s (1938) unit 12 because of the swelling clays, which first appear beneath the no-mans island beds (figure 3). a complete section of the brushy basin can be pieced together utilizing the exposures south of the elk mountain road (figure 19a). however, this section would be difficult to access in the more deeply dissected and vegetated terrain of this area. the brushy basin type section of gregory (1938) is as follows: 25. section of morrison formation in brushy basin dakota (?) sandstone. unconformity. morrison formation: brushy basin shale member: 28–24. shale, red and white, sandy, and white lenticular coarse grained porous sandstone, in alternating beds; forms stepped slope ..................................................................61 ft 23. sandstone, white and greenish yellow, ssaa11112266pp ssaa11113355vv bb dd aa cc ee figure 18. fossils from westwater canyon member. (a) overview of plant debris bed in the upper westwater canyon member below northwestern black mesa (sa1126p). (b) detail of fine sandstone fragments preserving carbonaceous plant debris at sa1126p. (c) overview of shattered dinosaur limb bone site near base of the westwater canyon member on northwest side of dexter cove (sa1135v). view from south. (d and e) limb bone fragments at sa1135v. 172 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 coarse, very lenticular, in part cross-bedded; lenses of conglomerate consist chiefly of red and black chert, fragments of green sandstone, and clay balls; includes round white aggregates of quartz and elongated brown concretions of iron and sand; forms cliff .......................................27 ft 22–20. shale, red, ash gray, yellow, and green, sandy, and lenses of white sandstone; forms color-banded slope ..............................59 ft 19. sandstone, dark green, hard, very fine grained, persistent ledge .................................. 2 ft 18. shale, red, yellow, green, purple, and white; color distributed in regular bands and in blotches to form variegated slope; beds include lenses of pink, purple, and white limestone, white and brown sandstone, and limestone conglomerate conaa ccbb wwcc oocc eemmrr nncc nnoo--mmaannss iissllaanndd bbeeddss bbrruusshhyy bbaassiinn mmbbrr.. bbuurrrroo ccaann.. ffmm.. ssaalltt wwaasshh mmbbrr.. bbuurrrroo ccaann.. ffmm.. yyeellllooww ccaatt mmbbrr.. bbrruusshhyy bbaassiinn mmbbrr.. bbrruusshhyy bbaassiinn mmbbrr.. mmoorrrriissoonn ffmm.. dd ee ff figure 19. gregory’s (1938) type section of the brushy basin member of the morrison formation. (a) central portion of brushy basin viewed to the east toward the brushy basin rim. red arrows indicate elk mountain road (blm 0620. red star indicates where the elk mountain road crosses onto the brushy basin rim. yellow star indicates site of culverts in b and c. (b) three generations of culverts. nc = new culvert, oc = old abandoned culvert, wc = wooden culvert. (c) detail of the contact between the no-mans island beds at the top of the westwater canyon member and the overlying brushy basin member as indicated by double-headed yellow arrow (12 s, 625171.42 m e, 4166584.89 m n). emr = elk mountain road. double-headed red arrow position of the culverts detailed in b. (d) view toward west from elk mountain road on brushy basin rim across brushy basin toward bears ears on horizon. (e and f) view east across small canyon from elk mountain road on brushy basin rim at exposure at the top of gregory’s (1938) type section of the brushy basin member. note that the yellow cat member of burro canyon formation was initially within the top of gregory’s (1938) type section of the brushy basin member. 173 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 sisting of concretionary balls, chert, and bone fragments; weathers to form loose, fluffy, marl-like material, partly concealed by landslides ......................................224 ft 17. sandstone, dark green, resistant, like no. 6 ... 1 ft 16. sandstone, brown; appears as massive ledge but weathers readily to shale-like beds ...12 ft 15. shale, dark red, unevenly bedded; thin band of white powder-fine sandstone at top and base .....................................................15 ft 14. shale, red and slate-colored ...........................29 ft total brushy basin member .....................................450 ft westwater canyon sandstone member: 13. sandstone, white and greenish yellow, with lenticular partings of greenish shale; top surface hardened and uneven ......24 ft 12. shale, banded red and greenish white, flaky, and thin white sandstone, in overlapping lenticular beds ...................................30 ft 11. sandstone, white, thin-bedded, and red shale, irregularly interfoliated; forms broad platform ................................................16 ft 10. sandstone like no. 1 but coarser-grained; forms strong ledge ..........................................20 ft 9. shale, red, streaked greenish white ................ 3 ft 8. sandstone like no. l .........................................22 ft 7. shale, red; forms bench .................................... 8 ft 6. sandstone like no. 1; base firmly cemented mass of fragments of sandstone, red shale, and white mud shale; rests in hollows and about ridges at top of no. 5 ............25 ft 5. sandstone, greenish-white, and lumpy mudshale; contains lime concretions and fragments of carbonaceous material ....... 5 ft 4. shale, red; forms platform ............................... 3 ft 3. sandstone like no. 1 ........................................23 ft 2. shale, red, unevenly bedded, imbricated; weathers to leaf-like chips .............................30 ft 1. sandstone, white; weathers yellowish white, most of it cross-bedded and lenticular; lenses of conglomerate made up chiefly of lozenges and scales of greenish-white clay, chert, and fragments of shale; a few very thin short lenses of red shale; weakly cemented with lime; round holes and slots give weathered cliff face a spongy appearance .........................................46 ft total westwater canyon member exposed ...........255 ft gregory (1938) summarized the characteristics of the brushy basin shale member as follows: “the upper part of the morrison of the san juan country consists of the well-known variegated shales (morrison shales, mcelmo shales) that generally in utah and western colorado lie immediately below the dakota (?) sandstone. in fact, they owe their preservation to the resistant dakota cover. directly beneath cliffs of dakota (?) sandstone they stand in almost vertical walls; where the sandstone has been stripped back, they form slopes that continue outward into mounds and ridges spread over a platform of westwater canyon sandstone. their appearance is everywhere the same brightly variegated masses that are exceeded in beauty of coloring only by the chinle “marls.” the dominant beds are white, gray, green, purple, and red sandy shales and sandstones. …subordinate beds are gray, pink, blue, and gray limestones; conglomerates of red, green, and white cherts; and buff hard sandstones. the buff sandstone is more abundant near the base and seems to increase in amount eastward toward the colorado line.” the brushy basin member is well exposed across the southern blanding basin (figure 17e) and in the southward-draining canyons cutting through the third bench formed by the burro canyon formation (figures 7 and 8). some of the most continuous, non-vegetated sections are along the west side of black mesa above stephens canyon (figure 20a) and on the south side of black mesa where black mesa road cuts down through the brushy basin section (figures 20b to 20h) at the escarpment formed south of the third bench (12 s, 624213.94 m e, 4144247.69 m n). about 200 m (700 ft) northeast of the black mesa road, we identified an organic-rich mudstone layer that extends across this entire portion of the outcrop (figures 20b to 20h) that we 174 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 100 meters blm 233 bbuurrrroo ccaannyyoonn ffmm.. eedd bbuurrrroo ccaannyyoonn ffmm.. nnoo--mmaannss iissllaanndd bbeeddss ttoopp wweessttwwaatteerr ccaannyyoonn mmbbrr.. - nnoo--mmaannss iissllaanndd bbeeddss bbrruusshhyy bbaassiinn mmbbrr.. bbrruusshhyy bbaassiinn mmbbrr.. bbuurrrroo ccaannyyoonn ffmm.. aa bb bbuurrrroo ccaannyyoonn ffmm.. cc bbuurrrroo ccaannyyoonn ffmm.. 1111..1122 mm hhgg burro canyon fm. j u r a s s ic c r e t . m o rr is o n f o rm a ti o n b ru s h y b a s in m b r. -20 -10 150.62 ma 0 x x xx xx x xx xx x xx xx x x xx xx xx xx x xx xx xxxx xxxx xx xxxx xxxx xx xxxx xxxx xx xx xxxx xxxx xxxx xxxx xx xx xx xxxx xxxx xx xxxx xxxx xx xxxx xxxx xx xx xxxx xxxx xxxx xxxx xx x x xx xx x xx xx x xx xx x x xx xx xx xx x m e te rs xx xx xxxx xxxx xx xxxx xxxx xx xxxx xxxx xx xx xxxx xxxx xxxx xxxx xx ff figure 20. brushy basin member of the morrison formation on west and south sides of black mesa. (a) overview of brushy basin exposures on west side of black mesa as viewed east across stephens canyon. (b to e) brushy basin member on the south side of black mesa (figure 7b). (b) brushy basin exposures west of black mesa road (blm 233) as viewed from south. yellow arrow indicates sa1133vp, where productive palynomorph sample was taken. (c) brushy basin exposures near black mesa road (blm 233) as viewed obliquely from south (google earth©). red arrow = position of dated volcanic ash. yellow line indicates basal contact of burro canyon formation. (d) overview of pollen-ash site sa1114. red double headed arrow indicates position of ash sample (appendix b). (e) close-up view of volcanic ash layer at sa1114p. rock hammer head about 18 cm (7 in). (f) section across morrison-burro canyon transition 110 m (360 ft) n 104° e from sa1114 with dated ash indicated. (g) morrison-burro canyon transition. double-headed red arrow indicates stratigraphic position of dated ash 11.12 m (36.48 ft) below base of burro canyon formation. (h) organic interval preserving volcanic ashes near top of the brushy basin member. green arrow indicates lower undated ash. red arrow indicates position of dated ash. 175 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 sampled for palynomorphs (sa1133p). it was processed under the direction of carol hotton at the smithsonian institution, who initially found it to be barren of palynomorphs. this fine-grained, organic-rich bed extends for hundreds of meters west (figure 20b; locality sa1114vp) from where a colleague, nina baghai-riding, extracted a palynoflora dominated by exisipollenites, with lesser amounts of conifer and ginkophyte pollen, and with many fewer spores of mosses, horsetails, and ferns (baghai-riding and others, 2018). within the organic layer we identified a 20-cmthick (5-in) volcanic ash (figures 20d to 20e) that was processed by one of us (kct), with kevin chamberlain, at the university of wyoming, who reported that it preserves pristine needles of zircon (appendix b) that yielded a highly-resolved uranium-lead age following chemical abrasion to remove the altered rind on the crystals. chamberlain reported an age that incorporates both the 206pb/238u and 207pb/235u data, of 150.67 ± 0.32 ma (95% confidence limits) from this sample (appendix b). this is one of the most highly resolved ages for the top of the brushy basin member of the morrison formation (kowallis and others, 2007; trujillo and kowallis, 2015; chamberlain and trujillo (verbal communication, 2017). this ash is situated only 11.12 m (36.5 ft) below the erosional contact with the overlying burro canyon formation (figures 20f to 20h). more recently, an age of 149.45 ± <0.10 ma was determined from a volcanic ash a couple of meters below the top of the morrison formation in western colorado south of fruita (galli and others, 2018). our new morrison age appears to weakly support galli and others (2018) and maidment and muxworthy (2019) hypotheses that the top of the morrison is older to the west as a result of tectonic beveling. forested cover is extensive over the brushy basin outcrop belt north of sr 95. however, gregory (1938, plate 13d) illustrated typical exposures of the brushy basin on the northwest corner of black mesa, where some of the most extensive exposures of the morrison formation in the area are located (figure 21). the dirt road (blm 233) from sr 95 to the top of black mesa now traverses the entire section of the brushy basin member, making it one of the most accessible brushy basin exposures in the region. this exposure is only 11.2 km (7 mi) due south of gregory’s original 1938 type section. given the paleontological significance of the brushy basin member of the morrison formation, we decided that this is a good site to designate as an accessible reference section for the brushy basin member (figures 3 and 18; appendix a). the brushy basin member is noticeably thicker in the brushy basin area than in other areas on the colorado plateau. gregory’s (1938) measured section along the elk mountain road, gave a thickness of 137.25 m (450 ft). he found 108 to 132 m (360–440 ft) on recapture creek (gregory, 1938, section 23). however, we measured only 77.50 m (254.2 ft) at our reference section along the black mesa road. we also recognize that there are few conglomeratic channel sandstones in the brushy basin member along comb ridge. such “ribbon” sandstones are present in most other areas of brushy basin exposure, reflecting deposition on a floodplain dominated by low-sinuosity anastomosing rivers (e.g., kirkland, 2006). in fact, there is not a single channel sandstone in the brushy basin reference section we measured on the northwest side of black mesa (figures 3, 21, and 22). a large proportion of sand-sized material is characteristic of approximately the lower 18 m (59 ft), with beds of sandstone, muddy sandstone, and smectitic sandy mudstone. gregory (1938) also noted that sandstone beds are most apparent in the lower brushy basin member. dark-green, ledge-forming sandstones (units 58, 61, and top of 63) may be colored by vanadium oxide, and units 61 and 63 form local marker beds (figures 22 and 23a to 23d). up section, the mudstones are much richer in smectitic clays. these swelling clays give the slope the typical convex natural weathering profile characteristic of the brushy basin member (figures 19 and 20d to 20g). on the surface these clays display characteristic “popcorn” weathering typical of smectitic mudstone beds (keller, 1962). these smectitic clays formed from the natural decomposition of volcanic glass (ash) initially mixed throughout the fine sediments of the brushy basin floodplain. these volcanic ashes erupted from large caldera-forming eruptions in the magmatic arc to the west (christiansen and others, 2015). within the mudstone intervals of units 66, 76, and 82 are intervals colored a distinctive orange-pink (figures 22 and 23d to 20g) 176 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 that look like clinoptilolite diagenetic mineral zones described by c. turner (turner and fishman, 1991, 1998; dunagan and turner, 2004; turner and peterson, 2010a, plate 5) for alkaline-saline wetland deposits of ancient “lake” t’oo’dichi’. in the montezuma creek area, turner (2010) noted tawny brown beds that contain authigenic albite characteristic of a more central “lake” t’oo’dichi’ setting. such beds in the reference section may include units 74, 80, 95, and 97, but a detailed analysis of the minerals in these beds would be needed to identify the presence of these alteration products. additionally, it is noteworthy that the zeolites in the morrison formation have also been interpreted as to be purely a diagenetic phenomenon (tanner and others, 2014). well-developed paleosols are not typical of the brushy basin member (demko and others, 2004). carbonate nodules with associated root traces, which may reflect pedogenic or paludal processes, are present in the upper portion of the lower sandy interval in units 62 and 64. kirkland (2006) proposed that the basal brushy basin paleosol documented by demko and others (2004) farther north represents an unconformity that explains the dramatic clay change across the central and northern colorado plateau (turner and peterson, 2004). could this also explain the apparent loss of at least the upper westwater canyon member beneath the brushy basin to the north? tracing this contact along the west side of the abajo mountains would be an important test of this hypothesis versus a simple pinch-out of the no-mans island beds to the north (figure 8). additional incipient paleosols may also be recognizable near the middle of the brushy basin member. unit 69 is a bed of coalesced septarized carbonate nodules 23 cm (9 in) thick. the highest stratigraphic unit associated with abundant carbonate nodules is unit 71. fragments of sandstone from the interspersed sandstone beds together with carbonate fragments armor the mudstone outcrop for several meters downslope. small carbonate nodules are present toward the top of unit 74. only a more detailed analysis by a specialist in paleosols would distinguish if these carbonate-bearing intervals represent paleosols. unit 77 is 65 cm (25 in) of pale grayish-yellow mudstone with burrows and root traces overlain by 22 cm (8.5 in) of very well indurated, blackish-red, perhaps siderite-cemented, muddy sandstone with additional root traces. perhaps this distinct horizon represents a wetter incipient paleosol (tabor and others, 2017). much of the upper brushy basin member exposed bbrruusshhyy bbaassiinn mmbbrr.. bbrruusshhyy bbaassiinn mmbbrr.. wweessttwwaatteerr ccaannyyoonn mmbbrr.. bbuurrrroo ccaannyyoonn ffmm.. bbuurrrroo ccaannyyoonn ffmm..bb cc aa bbuurrrroo ccaannyyoonn ffmm.. bbuurrrroo ccaannyyoonn ffmm.. bbllaacckk mmeessaa wweessttwwaatteerr ccaannyyoonn mmbbrr.. bbrruusshhyy bbaassiinn mmbbrr.. dd 95 figure 21. brushy basin member of the morrison formation at its newly proposed reference section. (a) gregory’s (1938, plate 13d) photograph of typical exposures of the brushy basin member on “west” side of black mesa. (b) northwest corner of black mesa viewed from north. (c) northwest corner of black mesa viewed from west with blm 233 angling up across the brushy basin exposure to the top of black mesa. (d) northwest corner of black mesa viewed from above and west (google earth©) with blm 233 angling up across the brushy basin exposure to the top of black mesa. red line is approximate contact between brushy basin and westwater canyon members. red arrows indicate the black mesa road, (blm 233). 177 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 aa cc cc cc b u rr o c a n y o n f m . smectitic mudstones j u r a s s ic c r e t. m o rr is o n f o rm a ti o n w c m b ru s h y b a s in m e m b e r yellow cat member n o -m a n s is la n d b e d s 190 200 210 220 230 240 250 260 270 280 290 300 m e te rs 7733 7711 7744 6633 6611 5555 6666 8811 8822 8888 9900 9966 9988 110022 110055 cc cc bb bbuurrrroo ccaannyyoonn ffmm.. nnoo--mmaannss iissllaanndd bbeeddss wweessttwwaatteerr ccaannyyoonn mmbbrr.. 7733 6633 6666 8811 5555 8822 7744 7711 figure 22. brushy basin member reference section on northwestern black mesa. (a) brushy basin reference section on and below black mesa road (blm 233) on northwest side of black mesa. wcm = upper part of westwater canyon member. (b) brushy basin reference section below black mesa road (blm 233 as noted by red arrow) and extending up to burro canyon formation on northwest side of black mesa as viewed from sandstone-capped ridge to west. yellow arrow indicates the basal contact of the brushy basin member. pink cs indicate zones of clinoptilolite after turner and fishman (1991) and turner and peterson (2010a). black numbers indicate stratigraphic units in appendix a and noted in figures 19 to 21. see figure 3 for explanation of symbols shown on a. 178 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 along the black mesa road above unit 82 is less brightly variegated, although it includes several thin, dark-red mudstone units that tend to be obscured by debris from the surrounding drably colored mudstones. however, units 95 to 97 form a dark reddish-brown band (figure 20k) more than 7 m (23 ft) thick near the top of the brushy basin member that is apparently widespread across the study area. bb ff gg jj kk hh ii aa cc bbuurrrroo ccaannyyoonn ffmm.. cc cc cc eedd 9988 9988 9966 9966 8811 8822 6666 6611 6633 6633 7711 7711 6611 6611 8811--8822 7744 7733 7711 7744 7744 5555 6633 6666 6666 8888 9900 figure 23. exposures of brushy basin member along morrison reference section. (a) deeply weathered uppermost sandstone of the no-mans island beds at top of the westwater canyon member. (b to f) lower half of the brushy basin member downslope below black mesa road (blm 233 as noted by red arrows in c, f, and g). (g to k) upper brushy basin member along black mesa road (blm 233 as noted by red arrow). pink cs indicate zones of clinoptilolite after turner and fishman (1991) and turner and peterson (2010a). black numbers indicate stratigraphic units in appendix a. 179 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 overlying this smectitic red-bed interval at the top of the brushy basin member is a marked change in deposition that we initially referred to as the “yellow cat facies” (kirkland and others, 2018), but is herein recognized as the yellow cat member of the burro canyon formation and lithologically preserves ironrich paleosols and mudstone-supported conglomeratic lenses typical of the “lower” yellow cat member of the cedar moutain formation northwest of the colorado river (kirkland and others, 2016). the upper contact of the brushy basin member is generally marked by a conglomeratic sandstone or mudstone with dispersed pebbles that is overlain by nonsmectitic mudstones, which may include zones of ferruginous nodules. the absence of smectitic clays gives the yellow cat member a straight to concave slope profile as opposed to the convex weathering profile characteristic of the brushy basin interval. where present, the overlying yellow cat member is generally no thicker than 10 to 15 m (30–45 ft). elsewhere, coarse, cliff-forming conglomeratic sandstones of the main body of the burro canyon formation directly overlie the brushy basin member that exhibits basal cretaceous aquifer bleaching of the uppermost jurassic mudstones to a pale green. such a jurassic–cretaceous contact is present at the south end of black mesa on either side of the black mesa road (figures 20b to 20h) and at the los angeles county museum’s dinosaur tracksite in the central blanding basin (milán and others, 2015; figure 2). paleontology at present more than 65 fossil localities have been documented in the morrison formation within the study area; approximately 50 of these are in the brushy basin member. we found that the brushy basin fossil sites in the western blanding basin are mostly in the middle and upper portions of the member. to the north, in the blue hills area, fossil sites appear to be more evenly distributed within the brushy basin but may be most abundant in the lower part as documented for the member in general by turner and peterson (1999). the brushy basin member is generally the most fossiliferous member of the morrison formation and preserves more significant dinosaur fossil remains than nearly any other rock unit in north america (carpenter and others, 1998; turner and peterson, 1999; foster and lucas, 2006; foster, 2007). the most common fossils recognized in the brushy basin member are fragmentary dinosaur bones eroded out onto the surfaces of the mudstone intervals and as bone chip lags at the toes of steeper slopes. this is the setting that produced the few identified tooth fragments. the smectitic mudstones of the brushy basin are notorious as swelling clays. rainwater will quickly destroy the dinosaur bones that are partially uncovered by wetting and expanding the surrounding mudstone, which then shrinks again on drying. repeating this process quickly shatters even relatively well-preserved dinosaur bones. experience shows that to preserve any bones left in situ requires that they be protected by waterproof tarps. but even with the use of a tarp, the condensation of moisture under the tarp may still damage the bone. therefore, uncovering bones in the brushy basin member should not be done unless the intent is to immediately document the position of the bones and collect them. most bones encountered during the course of the project appear to represent isolated bones or, at most, a few associated bones (figures 24e to 24h). only limited test excavations were conducted at a few bone sites, so it is conceivable that in a few cases more extensive accumulations of bone may have been obscured by debris weathered down slope. a few laterally extensive bone accumulations were encountered (figures 24i to 24n) that may represent bone bed accumulations (e.g., rogers and others, 2007) or large associated skeletal elements like the diplodocus caudal vertebrae identified by our team (jrf, ddd, rkh-f) at sa1232v (figures 24l to 24n). a number of these sites warrant additional research that is beyond the scope of this project. fragments of petrified wood, logs, and stumps are also relatively common (figures 24c and 24d), but not as common as dinosaur bone. trace fossils and rooting are present, but are not as ubiquitous as one might suppose, and are generally restricted to specific horizons and zones (figures 24a and 24b). susannah maidment reported to the blm the only dinosaur site (sa1155v) in the entire study area that we are aware of that has clearly been uncovered by unper180 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 ssaa11115555vv oo pp ddaa ccbb hhee ll gg nn ff mm ii jj kk figure 24. examples of fossils in the brushy basin member. (a) trace fossils preserved on underside of crevasse splay block below sa1127t. (b) possible termite nest(?) associated with vertebrate remains at sa1122v. (c) tree stump preserved in situ at sa1130p. (d) section of petrified log (red arrow) at sa1108p. (e) broken up sauropod vertebra at sa1129v. (f) broken up dinosaur bone at sa1128v 100 m to east. (g) nearly complete dinosaur bone in situ at sa1110v. (h) bone fragments at sa1112v. (i) extensive scatter of dinosaur bones within the red outline at sa1113v. (j) caudal vertebral centrum at sa1113v. (k) laterally extensive bone site at sa1229v. red arrows point to bones. (l and m) possible diplodocus skeleton at sa1232v. (l) broken caudal vertebra. (m) john foster examines another caudal vertebra (red arrow). (n) a naturally weathered limb bone. (o) overview of vandalized dinosaur bone locality sa1155v. view looking north. (p) telephoto view of sa1155v from the same location shown in o. rock hammer in d, e, and f is 30 cm (12 in) long. hoe pick head in g, h, k, and n is about 40 cm (16 in). 181 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 mitted excavation (figures 24o and 24p). we assumed that it had been worked by individuals with experience excavating bones in the brushy basin member as it had been covered by a blue tarp and reburied. salvaged by the blm, the site consisted only of a couple of large bone fragments. farther to the north, in the blue hills area northwest of moab, utah, vandalism of fossil sites is much more widespread with nearly all evidence of isolated bones, petrified logs, and even agate removed in some areas (kirkland and deblieux, 2017; kirkland and others, 2017, 2018). less than 15 total sites in the morrison formation of utah are on file in the utah paleontological locality database with any identifiable leafy plant fossils. many of the strata in the morrison formation are highly alkaline such that leafy vegetation and palynomorphs are rare, with less than 10% of the identified pollen and spore types represented by macroscopic plant remains (parrish and others, 2004; kirkland 2006). therefore, we search for these sites as carefully as we would for those preserving vertebrate remains. toward the south end of the study area an organic layer approximately 15 m (50 ft) below the burro canyon formation and below the “yellow cat facies” preserves a significant palynomorph assemblage (baghai-riding and others, 2018) associated with a dated volcanic ash as described above (figure 20c to 20h). toward the northern end of the study area near the middle of the brushy basin member about 50 m (165 ft) below the burro canyon formation (figure 2), we identified a thick organic plant debris bed (sa1134vp). several meters thick, this site appears to cross the valley floor for approximately 100 m (330 ft). the site preserves copious amounts of carbonaceous plant material with petrified driftwood and isolated bones through its lower 2 m (6 ft) (figure 25). this bed is very different than other plant-bearing beds in the morrison formation on the colorado plateau, which are generally dark-gray mudstones with more disseminated plant material (parrish and others, 2004; kirkland, 2006). the main bed resembles the plant debris beds in the lower cretaceous wessex formation of england, which are famous for the abundance and diversity of the flora and fauna they preserve (martill, 2001; sweetman and insole, 2010). the ugs obtained a permit to conduct a test excavation in may 2017 to evaluate the paleontological potential of this locality. this resulted in the recognition of a paleobotanical site preserving abundant czekanowskia, ginkgoes, ferns (dominated by coniopteris), conifer shoots, coprolites, less common conchostracans, a giant water bug (lara and others, 2020), and impressions of possible salamander bones, in a finely laminated shale at the top of the exposure overlying a 10-cm-thick (4-in) volcanic ash (sampled). tentatively identified were possible impressions of small bones and insects. additionally, this is a rare example of a compressional plant site that also preserves pollen (baghai-riding and others, 2018). this compressional plant horizon is considered to be highly significant and was given its own locality number sa1212p (figure 25). we have come to consider this complex site to have so much paleontological potential that we classify it as a small “paleontological site complex” (kirkland and foster, 2009). paleontological site complexes (pscs) are areas having microvertebrate sites, bonebeds, and areas with dense concentrations of individual sites that require comprehensive and longterm management—potentially in perpetuity. as such, we have been putting together a team of paleontologists to excavate and research this “marsh/pond deposit.” the results of this research will be presented elsewhere. burro canyon formation yellow cat member history and lithology the uppermost brushy basin member at its reference section (figures 22 and 26), as originally defined, includes ferruginous paleosol(s) (units 100 to 103 appendix a) indicating a wetter climate than has been previously interpreted for the morrison formation (demko and others, 2004; kirkland and others, 2016). these ferruginous paleosols were first recognized at the top of the brushy basin slope by turner and peterson (2010a), who suggested that they may represent an interval of cretaceous-age strata. because these paleosols are underlain by a distinctive conglomeratic sandstone (unit 98), we also interpret the paleosols to be within basal cretaceous strata resting on the jurassic-cretaceous unconformity (k-1 unconformity). when com182 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 ssaa11221122pp ssaa11221122pp aasshh ssaa11113344vvpp dd ccaa ee ff gg hh bb interbedded sandstone and shale finely laminated shale petrified wood compressional plants (leaves) smectitic mudstone soft muddy sandstone claystone sandstone gravely sandstone isolated chert pebbles plant fragments bone fragments clay clasts volcanic ash bentonite conchostracans x x xx xx x xx xx x xx xx x x xx xx xx xx x explanation x x xx xx x xx xx x xx xx x x xx xx xx xx x x x xx xx x xx xx x xx xx x x xx xx xx xx x x x xx xx x xx xx x xx xx x x xx xx xx xx x x x xx xx x xx xx x xx xx x x xx xx xx xx x x x xx xx x xx xx x xx xx x x xx xx xx xx x x x xx xx x xx xx x xx xx x x xx xx xx xx x m e te rs 1 2 3 4 5 6 ssaa11221122pp ssaa11113344vvpp ii figure 25. caption is on the following page. 183 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 pared to correlative strata farther to the north, this sequence compares well with the interfluvial yellow cat facies that laterally interfingers with the buckhorn conglomerate of the cedar mountain formation (lower cretaceous) on the western san rafael swell and with the lower yellow cat member of the cedar mountain formation in the northern paradox basin (kirkland and others, 2016). as with the yellow cat member of the cedar mountain to the north, the mudstones of this interval do not appear to be smectitic and form a flat to concave slope as opposed to the convex slope formed by the underlying smectitic mudstones of the brushy basin member (kirkland and others, 2016). however, at this time, no radiometric or biostratigraphic ages exist for these strata so a latest jurassic age cannot be completely ruled out; sediment samples have been collected that will hopefully remedy this situation. given that these beds were included within gregory’s (1938) type section of the brushy basin member (figures 19e and 19f), and that this thin sequence of rock is rarely exposed below the sandstone rubble from the overlying burro canyon formation, we initially chose not to separate these possible cretaceous strata from the brushy basin member. however, we now agree with the u.s. geological survey and separate the yellow cat interval from the underlying morrison formation (aubrey, 1998) as the basal interval of the cedar mountain formation as a member of the burro canyon formation in the blanding basin. in addition to also being recognized at the top of the type section of the brushy basin member along the elk mountain road (figures 19e and 19f), yellow cat strata are recognized in road cuts along paved roads in the region, where further study may be readily undertaken. kirkland and others (2016) recognized these facies at gregory’s (1938) “jump-off ” on u.s. 191 south of white mesa (figures 7a, 27a, and 27b) for which, given our new observations, we provide an updated interpretation. the “jump off ” exposures differ in that the upper dark-red mudstone interval is strongly mottled, suggesting the beginning of soil modification prior to the deposition of the yellow cat member. additionally, the upper part of the yellow cat member appears to be so organic-rich that it was initially interpreted as being part of the naturita formation (kirkland and others, 2016). these beds have been sampled for palynology. it would be informative to test if they preserve a pre-angiosperm palynomorph flora. an exceptional exposure (figures 27c to 27g) of the yellow cat member is on the north side of sr 95 near mile post 120 on the eastern margin of the study area. at this site, the conglomeratic basal unit contains larger chert pebbles that are more varied than those observed in unit 98 in the brushy basin reference section. in addition, the ferruginous paleosol is well developed at this site. finally, dark-green claystones preserving plant fragments are present near the top of the sequence and have also been sampled for palynomorphs. none of these samples yielded palynomorphs or enough zircons to substantiate a maximum age. the upper contact of the yellow cat member is sharp with the scoured base of the fluvial sandstones at the base of the main body of the burro canyon formation (figures 16e, 16f, 21g to 21j, and 22). this is like the unconformity between the yellow cat member and overlying fluvial sandstones at the base of the poison strip member of the cedar mountain formation in the northern paradox basin (kirkland and others, 2016). the yellow cat member and the main body of the burro canyon member do not appear to intertongue, such as has been observed in the western san rafael swell between the interfluvial yellow cat facies and the buckhorn conglomerate member of the cedar mountain formation (kirkland and others, 2016). the yellow cat member is notably absent at several sites in the blanding basin. it is not present at the los angeles county museum’s burro canyon dinosaur tracksite (milán and others, 2015), which has several meters of relief documented where the basal conglomfigure 25 (figure on the previous page). fossiliferous marsh/ pond deposit. (a) overview of plant debris bed at locality sa1134v and overlying compressional fossil plant locality sa1212p. (b) close-up of bone fragments initially found at sa1134v. (c) petrified wood exposed at sa1134v. (d and e) bone and plant fragments near base of sa1134v. (f) closeup of volcanic ash underlying sa1212p. (g and h) typical compressional plant fossils preserved in sa1212p. (i) stratigraphic section of paleontological site complex geometrically estimated at about 50 m (164 ft) below top of brushy basin member. 184 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 eratic sandstone unit is incised directly into the brushy basin member of the morrison formation. likewise, on the south end of black mesa, where the black mesa road cuts down through the brushy basin member, a fluvial sandstone characteristic of the burro canyon formation directly overlies the brushy basin member (figures 17b to 17h). in both areas the upper brushy basin member apparently has been bleached to a pale green below the unconformity. we were tempted to retain the “yellow cat facies” in the brushy basin member for the following reasons: 1. the “yellow cat facies” was included by gregory (1938) as part of the type section of the brushy basin member (figures 19e and 19f). dd gg ffee 2255 ccmm aa ccbb iihh jj bbuurrrroo ccaann.. ffmm.. bbuurrrroo ccaann.. ffmm.. yyeellllooww ccaatt mmeemmbbeerr 9988 9966 9988 9988 110022 110055 110077 figure 26. morrison reference section, yellow cat member of burro canyon formation at top of the brushy basin member. black numbers indicate stratigraphic units in appendix a. (a and b) contact of red mudstone unit 97 with conglomeratic sandstone at base of burro canyon formation, unit 98. double-headed red arrow indicates position of 30-cm-long rock hammer. (c) close-up of unit 98 showing light-colored pebbles of chert and quartzite. (d) overview of yellow cat member of burro canyon formation viewed to south along blm 233. (e) lower part of yellow cat member of burro canyon formation. orange double-headed arrow indicates greatest concentration of ferruginous nodules in paleosol. (f) ferruginous nodules in unit 102. (g) transition from top of yellow cat member with fluvial facies of burro canyon formation. yellow double-headed arrow indicates location of burrows in h. (h) burrows in unit 105. (i) basal fluvial sandstone ledge of burro canyon formation. (j) burrows in unit 107 at base of fluvial burro canyon formation. 185 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 bbaa cc yyeellllooww ccaatt mmeemmbbeerr yyeellllooww ccaatt mmbbrr.. bbuurrrroo ccaannyyoonn ffmm.. bbuurrrroo ccaann.. ffmm.. bbuurrrroo ccaann.. ffmm.. ee ff gg dd yyeellllooww ccaatt mmeemmbbeerr bbuurrrroo ccaann.. ffmm.. figure 27. yellow cat member of burro canyon formation along paved roads in the western blanding basin. (a and b) upper brushy basin, yellow cat member and main body of burro canyon formation at the ‘jump off ’ on west side of u.s. highway 191 at mile marker 37, between bluff and blanding, utah (12s, 635214.22 m e, 4160060.00 m n). (a) exposure from the south, and (b) exposure at north end of cut from the northeast. (c to g) top of the brushy basin member of morrison formation and lower burro canyon formation on north side of sr 95 at mile marker 120 (12 s, 631151.75 m e, 4160060.65 m n). (c and d) exposure from the south of eastern part of roadcut. (e to g) exposure toward west end of outcrop. (e) detail of basal conglomerate at base of yellow cat member. (f) overview of yellow cat member. double-headed red arrow indicates position of conglomerate in e. double-headed blue arrow indicates position of ferruginous nodules in g. (g) ferruginous nodules above conglomeratic sandstone at base of yellow cat member of the burro canyon formation. 186 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 2. doing so would preserve the long-established break between the mudstone-dominated brushy basin member and the overlying sandstone-dominated burro canyon formation that is clearly recognized throughout the burro canyon outcrop belt. in contrast, to the north, the cedar mountain formation contains a large percentage of mudstone. even the overlying poison strip member (initially the poison strip sandstone) may not include any sandstone units locally (kirkland and others, 1997, 2016). 3. in places, the resistant sandstone ledge at the base of the main body of the burro canyon formation completely overhangs the “yellow cat facies,” such that the yellow cat is not visible in map view. 4. the “yellow cat facies” and the unconformity are commonly obscured by sandstone rubble armoring the upper slopes, which masks the difficult-to-map contact. in the end, a consensus developed to recognize these strata as part of the overlying burro canyon formation for the following reasons: 1. it is preferable to restrict the morrison to upper jurassic strata below the k-1 unconformity. 2. the same criteria used to define the k-1 unconformity in the northern paradox basin in the type area of the yellow cat member of the cedar mountain formation can be used here (kirkland and others, 2016). 3. it is preferable for future geological mapping in the region to maintain the use of the map symbol jm for the morrison formation and jmb for the brushy basin member of the morrison formation, instead of jkm and jkmb, respectively. 4. coarse fluvial sandstones at the base of the main body of the burro canyon formation apparently cut out the yellow cat member in some areas of the blanding basin, such that the main basal ledge of the burro canyon formation immediately overlies the brushy basin member. 5. the ferruginous paleosols in the lower yellow cat member indicate that wetter climatic conditions (demko and others, 2004) appear to be characteristic of the transition between the underlying morrison formation and basal conglomeratic sandstone beds at the base of the cliff-forming burro canyon formation in this area (figures 13a to 13d). similar beds in this position to the north in the basal cedar mountain formation were found to be cretaceous based on dinosaur remains (kirkland and others, 2016). paleontology sandstone unit 105 near the top of the yellow cat member at the brushy basin reference section is notable in preserving distinctive traces attributed to insects (figure 26h), as does the basal sandstone of the burro canyon formation (figure 26j). abundant invertebrate traces are characteristic in the overlying fluvial facies within the poison strip member of the cedar mountain formation in the northern paradox basin (kirkland and others, 2016; kirkland, 2017). main body of the burro canyon formation history and lithology the burro canyon formation was not a major focus of this study because it is not known to contain many vertebrate fossils, but this was also true of the correlative (and highly fossiliferous) cedar mountain formation until the last 25 years (e.g., kirkland and others, 2016). in 1948, stokes and phoenix (1948) described the burro canyon formation in burro canyon, san miguel county, west-central colorado (figures 1; utm 12s., 685639.00 m e, 4213275.00 m n) as a mappable relatively thin (45 to 80 m [148–262 ft]) lower cretaceous unit of: “alternating conglomerate, sandstone, shale, limestone and chert ranging from 150-260 feet in thickness. the sandstone and conglomerates are gray, yellow, and brown, and the shales are faintly varicolored mainly purple and green. …the lower contact 187 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 is at the base of the lowest resistant, light-colored, conglomeratic sandstone above the varicolored brushy basin shale member of the morrison; the upper boundary is placed above the highest varicolored beds so as to exclude any carbonaceous shales or sandstones in which plant materials are abundant. this contact has no topographic expression but is remarkably persistent and useable over a wide area in and adjoining gypsum valley. the burro canyon shows a slight thinning in passing over the crests of the dolores anticline and the gypsum valley anticline; this may indicate a slight upgrowth of these structures during the early cretaceous.” the sandstone making up the bulk of the main body of the burro canyon formation is distinguished based on thickness, pebble size, and paleocurrent directions (craig, 1981). according to stokes (1952), the burro canyon formation accumulated atop the upper jurassic morrison formation and formed a broad alluvial plain deposited by rivers flowing from highlands to the south. young’s (1960) proposal that the correlative burro canyon formation be considered as simply a southern and eastern extension of the cedar mountain formation has not been adopted. the colorado river has been used as the defining line in lower cretaceous rocks between the burro canyon formation and the cedar mountain formation to the northwest. paleontology no vertebrate body fossil sites are known or were found in the burro canyon formation in utah during this study, although two of us (jrf, rkh-f) have noted a large sauropod dinosaur humerus fragment in these beds on recapture creek. recently, a diverse dinosaur tracksite (milán and others, 2015) was revealed by road construction in these beds east of the study area (figure 2). the tracks were salvaged and are now housed at the natural history museum of los angeles county. these natural track molds document a minimum of six to seven dinosaur taxa divided among three theropods, one to two sauropods, one to two ornithopods, and one thyreophoran that is possibly a stegosaur (first cretaceous example in north america). a sample of the track-bearing sandstone was collected to extract detrital zircons to provide an estimate of the site’s maximum age (dickinson and gehrels, 2008, 2010). the sample was processed by apatite to zircon, inc. in viola, idaho. the two youngest zircon u-pb dates were 130.17 ma and 131.03 ma; five additional young zircons, ranging in age from 139.57 to 137.68 ma, suggest a maximum age of 131 ma (milán and others, 2015). within the study area a low hill on the northern end of black mesa overlying the morrison reference section exposes very well-indurated quartzite preserving the terrestrial scoyenia ichnofacies (sa1124t) enhanced by desert varnish (figure 28). conclusions exposures of the morrison formation and its bounding strata on the southwest side of the blanding basin south of black mesa and along comb ridge are significant in understanding upper jurassic stratigraphic relationships across the colorado plateau. gregory’s (1938) bluff sandstone, recapture, westwater canyon, and brushy basin members were defined in this region and have been applied across the southernmost outcrops of the morrison formation in arizona and new mexico. the outcrops extending north along comb ridge from the town of bluff to the west side of the abajo mountains expose the transition from the stratigraphic nomenclature of gregory (1938) to the tidwell, salt wash, and brushy basin member terminology applied to these strata on the central and northern colorado plateau (figure 8). the j-5 unconformity at the base of the bluff sandstone member and the interfingering relationship of the bluff sandstone into the tidwell member at its northern terminus, supports retaining the bluff as the basal member of the morrison formation in its type area. coarse conglomeratic fluvial beds within the basal bench of the recapture member of the morrison formation on the west and south sides of black mesa are not representative of the salt wash member. this surface may represent a j-6 unconformity at the base of the salt wash member to the west of the study area at capitol reef and the blue hills area. it is possible that these near basal recapture conglomerates are a result of local uplift along comb ridge. given either interpretation, the reports of interfingering between the bluff sandstone and recapture members are incorrect, and that 188 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 sediment derived from the bluff sandstone has been reworked across this surface into the basal recapture. we note that the recapture preserves potentially significant vertebrate paleontological sites. we follow o’sullivan (1999, 2000) in recognizing that the recapture interfingers into both the upper tidwell and lower salt wash members as it thins to the north. likewise, the “main body” of the westwater canyon member grades into the upper salt wash member as it thins to the north. the presence of a smectitic mudstone sequence below the resistant bench-forming no-mans island beds complicates the current use of the salt wash member for these uppermost westwater canyon beds on the west side of the abajo mountains. whereas a single salt wash distributary megafan expanding across the region has been widely accepted (e.g., owen and others, 2015, 2017), the feldspathic composition of the recapture and westwater canyon members indicate that a more northward-directed distributary megafan was progressively buried by a more lithic-dominated, northeasterly directed salt wash distributary megafan, prior to deposition of the brushy basin member. gregory’s (1938) type section of the brushy basin member along the elk mountain road clearly extends from the top of the no-mans island beds up section to the coarse fluvial sandstones at the base of the main body of the burro canyon formation. it is yet to be determined whether the upper beds of the westwater canyon member pinch-out into a temporally more expansive brushy basin member to the north or are truncated by an unconformity cutting down to the nonsmectitic mudstones beneath the brushy basin member proper, forming a j-7 unconformity at the “clay change”. on the southwest side of the blanding basin, including within gregory’s (1938) brushy basin type section, a capping ferruginous interval, herein referred to as the yellow cat member of the burro canyon formation, almost certainly correlates to the lower yellow cat member of the cretaceous cedar mountain formation of central utah. aa dd ffee ccbb figure 28. burro canyon trace fossils. (a) overview of low hill armored by desert varnished quartzite preserving scoyenia ichnofacies at top of the burro canyon formation on northwest side of black mesa (sa1124t). (b to f) examples of scoyenia ichnofacies preserved in hard quartzite at sa1124t. 189 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 a reference section of the brushy basin member of the morrison formation established below the northwest rim of black mesa lends support to these stratigraphic hypotheses. further stratigraphic research of the morrison along comb ridge and farther north along the west side of the abajo mountains is needed to more fully substantiate the observations reported here. we recorded a number of significant paleontological sites in these rocks along the western margin of the blanding basin. most of the vertebrate sites represent isolated bones in the recapture and brushy basin members, although a few sites that may represent bonebeds were also identified, which deserve to be tested for future excavation. petrified logs and stumps were encountered at a number of sites within the brushy basin and salt wash members, as were a few interesting plant debris sites. the overlying burro canyon formation was barely examined and as such its paleontological potential in the region currently cannot be defined. acknowledgments this work was carried out under blm permit ut07-003s-sw. we thank blm personnel in moab and monticello for their help in facilitating our work. funding was provided by the blm and the ugs. addition funding for our examination of the blue hills area by the blm and for our research in the northern capitol reef area by vince santucci and the national park service, has been essential in constraining the conclusions developed in this manuscript. we were helped in the field by scott madsen (precision fossilworks inc.), kevin madalena (blm volunteer, jemez pueblo), kate zeigler (zeigler geologic consulting, llc), christine turner (retired, usgs), grant willis (ugs), ron long (volunteer), and amy cairn (volunteer). edmund “gus” gustason (enerplus resources) provided kirkland the location data for the gilbert deltas illustrated in figure 4. we thank sid ash (retired weber state university) for researching the compressional plant fossils. martha hayden (ugs) helped with the locality database. paul murphey (paleo-solutions inc.) provided additional data relative to the 2017 paleo-solutions inc. inventory of the northern portion of the study area. as with anything to do with morrison stratigraphy, discussions with christine turner and the late fred “pete” peterson (retired usgs) were extremely helpful, although they do not agree with everything presented herein. likewise, comments on an earlier version of the manuscript benefitted by comment by tim demko (exxonmobil). carol hotton’s smithsonian institution) interest in the palynomorph flora from these beds is appreciated. we thank ugs reviewers kimm harty, mike hylland, grant willis, and bill keach (all ugs) for their critical reviews of this and an earlier version of this manuscript. technical reviews of the manuscript by ken carpenter (prehistoric museum, price, utah) and susannah maidment (natural history museum, london) led to the clarification of several interpretations. references anderson, o.j., and lucas, s.g., 1996, the base of the morrison formation (upper jurassic) of northwestern new mexico and adjacent areas, in morales, m., editor, the continental jurassic: museum of northern arizona bulletin 60, p. 443–456. anderson, o.j., and lucas, s.g., 1997, the upper jurassic morrison formation in the four corners region, in anderson, o.j., kues, b.s., and lucas, s.g., editors, mesozoic geology and paleontology of the four corners region: new mexico geological society guidebook, 48th field conference, p. 139–156. anderson, o.j., and lucas, s.g., 1998, redefinition of morrison formation (upper jurassic) and related san rafael group strata, 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utah place names: salt lake city, the university of utah press, 453 p. young, r.g., 1960, dakota group of colorado plateau: american association of petroleum geologists bulletin, v. 44, p. 158–194. a-1 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 appendix a morrison formation and bounding strata along butler wash up to the top of northwest side of black mesa section measured by james i. kirkland, sept. 13–17, 2017. section measured in segments along prominent unnamed drainage extending from near the north end of black mesa at approximately s. 30° w. to join butler wash (figure a1). base of measured section (12s 0622143 e 44154963 n) on top of nearly white caprock at the top of eolian sandstone flooring the wash to the southwest that is interpreted as representing the top of the entrada sandstone. measured lower part of section along wall of wash to butler wash dinosaur tracksite (unit 17), where butler wash road (blm 262) crosses butler wash (12 s 0622294 e 4155019 n). dip n. 7° e., 2–3° southeast. from east side of blm 262 section was measured up to the top of thick, largely eolian sequence nearly due east (top unit 21). this surface was followed back to the north to butler wash (12 s 0622790 e 4155201 n), where the transition between the san rafael group and the overlying morrison formation was described from observations on both the north and south sides of butler wash. it is noteworthy that the bluff sandstone is well-expressed on the north side of the wash, but not on the south side. lower 33 m (108 ft) of the recapture member measured on south side of butler wash up through ridge (12 s 0622711 e 4154456 n) capped by laterally extensive channel complex (salt wash facies?) that was traced back to butler wash to the north (12 s 623180 e 4155315 n), from which the section continued to be measured from bluff to bluff along the north side of butler wash up to the top the lower of the two sandstones forming the no-mans island beds (12 s 0623807 e 4155992 n). these beds were traced north to a ridge just west of the north end of black mesa, where the section was described through the top of the thicker capping sandstone of the westwater canyon member at 12 s 0623873 e 4156394 n. the top of this marker sandstone was traced east into gully (12 s 0624083 e 4156432 n), at base of the steep slope formed by the brushy basin member on the northwest side of black mesa. from here the brushy basin member was measured eastward up the side of black mesa to where it crosses blm 233. from here (12s 0624189 e 4156563 n), the upper half of the brushy basin member was measured in a series of segments linked by local marker beds traced to the south along the upslope side of black mesa along blm 233 through the burro canyon formation. the top of section within the burro canyon formation was at east side of cattle guard (12 s 0624497 e 4155947 n), where blm 233 crosses south onto the top of black mesa. dip n. 12° e., 1–2° southeast. color identification using the geological society of america rock color chart. 0.5 miles 884 meters b sr b black mesa brushy basin rim b rt rt rsw rsw wc blm 233 blm 233 bb bc 95 bw figure a1. northeast side of black mesa with approximate line of morrison reference section indicated. red bars = line of section. yellow bars indicate stratigraphic divisions. bottom to top: sr = san rafael group, b = bluff sandstone, rt = recapture member, tidwell facies, rsw = recapture member, salt wash facies, wc = westwater canyon member, bb= brushy basin member, bc = burro canyon formation. bw = butler wash dinosaur tracksite. a-2 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 unit description thickness (m) interval total burro canyon formation 108. sandstone, grayish-orange 10yr7/4, medium to very-coarse-grained with conglomeratic lenses, pebbles to 3 cm, large scale trough cross-bedded organized into beds 2 to 3 m thick, very well indurated cliff-former, overlying undescribed sandstone beds are set back from edge of cliff into a series of benches, but laterally, may in part be incorporated into this resistant cliff, defining the margins of black mesa, described along road to just above cattle guard (12 s 0624497 e 4155947 n), where road crosses onto top of black mesa ......................................................... 8.20 305.79 107. sandstone, grayish-orange 10yr7/4, medium to coarse grained, divided by sandy partings into two sub-equal beds, rooted and burrowed. sharp lower contact less than 50 cm of relief visible in roadcut. ................................................................................................................................................ 0.87 297.59 total incompletely measured main body of burro canyon formation .......................................................9.07 unconformity sharp with less than 50 cm in relief. yellow cat member 106. mudstone, grayish red-purple 5rp4/2, top 40 cm bleached light green 10g8/1, below unconformity at base of burro canyon formation .................................................................................................... 1.66 296.78 105. sandstone yellowish-gray 5y8/1, fine grained, poorly bedded, divided into two beds with wavy parting at about 30 cm, rooted with insect burrows ............................................................................. 0.72 295.12 104. mudstone, grayish red-purple 5rp4/2 .............................................................................................................. 0.96 294.40 103. mudstone, moderate green 5g5/6, some ferruginous patches ..................................................................... 2.45 293.44 102. mottled sandy mudstone and muddy very fine to fine-grained sandstone, complexly inter-mottled gray yellow-green 5gy7/2, moderate yellow-brown 10yr5/4, and grayish-red 10r4/2, sideritic nodules, ferruginous paleosol .............................................................................................. 1.11 291.99 101. interbedded fineto medium-grained sandstone in beds about 15 cm thick, grayish yellow-green 5gy7/2, some mottling, rooted with ferruginous nodules ......................................................... 1.01 289.87 100. mottled sandy mudstone and muddy sandstone, mottled olive gray 5y4/2 and yellow green 5gy7/2 ferruginous nodules, rooted ................................................................................................................ 0.83 288.86 99. mudstone, light blue 10b8/1, cherty ................................................................................................................. 0.09 287.97 98. conglomeratic sandstone, yellow gray 5y8/1 to nearly white 5y8.5/1, fine-grained sandstone matrix, light-colored chert pebbles 0.5 to 1.0 cm, trough cross-bedded, marker bed at base of possible “yellow cat facies” (kirkland and others, 2016)” at top of morrison formation on western side of blanding basin. marker horizon along road cut. basal unconformable contact sharp and irregular with less than 50 cm of relief along outcrop. ................................................................. 1.64 287.88 total yellow cat member ............................................................................................................................14.14 total incompletely measured burro canyon formation ...........................................................................23.21 a-3 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 unconformity sharp and irregular between underlying mudstone and overlying conglomerate. brushy basin member, morrison formation 97. mudstone, dark reddish-brown 10r3/4, upper 5 cm bleached light green 10g8/1 ................................... 1.14 286.24 96. interbedded sandy mudstone, moderate reddish-brown 10r6/4, and patchy sandstone, yellowish-gray 5y7/1 and medium red-orange 10yr5/6, rounded sandstone sets about 20 to 30 cm, mudstone and thinner ~5 cm sandstone sets form medial about 50 cm .............................................. 1.24 285.08 95. mudstone, dark reddish-brown 10r3/4, moderately smectitic ..................................................................... 4.76 283.84 94. mudstone, pale green 5g7/1, platy, moderately indurated with well indurated 10 cm caprock............... 1.41 279.08 93. mudstone, pale olive 10y6/2, moderately smectitic ....................................................................................... 0.75 278.33 92. mudstone, dark dusky-red 5r3/2, marker bed locally, feathering out vanishing into base of unit 93 to south along road ................................................................................................................................ 0.72 276.92 91. mudstone, light greenish-gray 5g8/1, moderately smectitic ......................................................................... 1.56 276.20 90. nodular, sandy mudstone, dark dusky-red 5r3/2, calcareous, well indurated ........................................... 0.18 274.64 89. smectitic mudstone, light greenish-gray 5g8/1, fine-grained, calcareous, olive-gray 564/2, sandstone layers about 10 cm thick at about 0.4 m and about 1.0 m above base ........................................ 1.34 274.46 88. mudstone, moderate red 5r4/6, rooted ............................................................................................................ 0.30 273.12 87. smectitic mudstone, yellowish-gray 5yr8/1, popcorn weathering on surface of convex slope ............... 1.69 272.81 86. sandstone, greenish-gray 5gy6/1, fine-to medium-grained sandstone, platy in set about 5 to 10 cm thick with thin, discontinuous, mudstone partings, moderately well indurated............................. 0.32 271.12 85 smectitic mudstone, pinkish-gray 5yr8/1, popcorn weathering on surface of convex slope .................. 2.62 270.80 84 sandstone, greenish-gray 5gy6/1, fine-to medium-grained sandstone, cross-bedded in set about 20 to 30 cm thick with thin, discontinuous, mudstone partings, moderately well indurated, laterally extensive ledge ............................................................................................................................ 1.02 268.18 83. smectitic mudstone, light olive-gray 5y6/1, popcorn weathering on surface continuing convex slope of unit 82 .............................................................................................................................................. 1.23 267.16 82. smectitic mudstone, pale red 10r6/2, for basal 3.5 m of unit grading to moderate orange-pink 10r6/6 for approximately next 2 m before gradationally retuning to pale red 10r6/2 at top, slightly sandy in part, popcorn weathering on surface forming convex slope, central orange-pink interval rooted, upper contact gradational over about 10 cm ..................................................... 7.58 265.93 81. sandstone, light yellow-gray 5gr7/1, in sets about 50 to 70 cm banded pale red-brown 10r5/4 by 20–30 cm interbeds of sandy mudstone ...................................................................................................... 2.87 258.35 80. smectitic mudstone, moderate reddish-brown 10r4/4, popcorn weathering surface forming a-4 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 darker convex slope, distinctly darker than unit 79 ........................................................................................ 4.44 255.48 79. smectitic mudstone, pale reddish-brown 10r5/4, popcorn weathering surface forming darker convex slope, small bone fragments weathered down slope to toe of slope, 5 to 7 cm finegrained, better indurated sandstone bed at 105 cm above base. ................................................................... 1.83 251.04 78. muddy sandstone, blackish-red 5r2/2, fine grained, very well indurated, brittle, ferruginous-sideritic cement, rooted ........................................................................................................................... 0.22 249.21 77. mudstone, grayish-yellow 5y8/4, rooting and insect traces .......................................................................... 0.65 248.99 76. smectitic mudstone, central meter moderate orange-pink 10r6/6 representing a clinoptilolite zone, pale red 10r6/2 for basal and upper about 0.5 m of unit, slightly sandy in part, popcorn weathering on surface forming darker convex slope ...................................................................................... 2.04 248.34 75. sandstone, light bluish-gray 10b7/1, very fine grained, well indurated local marker bed, crossed blm 233 to east on this bed (12s 0624189 e 4156563 n) ............................................................... 0.17 246.30 74. smectitic mudstone, grayish-red 10r4/2, very smectitic, popcorn weathering surface forming darker convex slope, some thin fine sandstone beds and small calcareous concretions in upper 1 to 2 m ..... 5.51 246.13 73. interbedded sandstone and slightly smectitic sandy mudstone, fine-grained sandstone, orange-pink 10r8/2, poorly indurated, mudstone pale-brown 10r6/4, forms about 30 to 60 cm bands on straight steep slope below 12 cm hard, rooted calcareous sandstone caprock. .......................... 3.33 240.62 72. finely interbedded slightly smectitic mudstone and sandy mudstone, pale purple-pink 5rp 6/2, forms straight slope, bone fragments noted ............................................................................................. 1.24 237.29 71. interbedded sandy mudstone and sandstone, overall pale-brown 5yr5/2, 30 to 50 cm thick mudstone intervals, moderately smectitic with numerous lenticular carbonate concretions, sandstone beds 5 to 20 cm thick, forms steep straight slope ......................................................................... 3.60 236.05 70. muddy sandstone, yellow-gray 5y7/2, fine to medium grained, poorly indurated forming concave slope, armored in sandstone and concretion fragments from unit 71 .......................................... 2.44 232.45 69. concretionary limestone bed, medium yellowish-brown 10yr5/4, septarized ........................................ 0.23 230.01 68. smectitic claystone to mudstone, moderate orange-pink 5yr8/4, popcorn weathering forming convex slope, scattered small (2 to 3 cm) carbonate nodules. ................................................................. 0.98 229.78 67. muddy sandstone to sandstone, yellowish-gray 5y7/2, fine grained, nearly structureless, poorly indurated, weathers into a concave slope ............................................................................................. 1.15 228.80 66. claystone to mudstone, very smectitic, moderate orange-pink 5yr8/4, popcorn weathering forming convex slope, represents a clinoptilolite zone, small 3 to 5 cm, irregular carbonate nodules .... 4.24 227.65 65. sandstone, very light-yellow 5y8/1, fine grained, moderately indurated, divided into two sub-equal beds ... 0.36 223.41 64. smectitic sandy mudstone, pale pink 5rp8/2, more orange in places, interbedded with very fine sandstones and muddy sandstone intervals, about 10 cm moderately indurated, calcareous, rooted muddy sandstones, pale yellow-green 10gy7/2, overlying 10 to 15 cm carbonate nodule horizons at about 1 and 3 m up, additional 10 cm carbonate nodules toward top of unit ........... 3.96 223.05 a-5 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 63. sandstone, pale yellow-gray 5y7/2, poorly bedded, moderately indurated with dark greenish-gray 5g4/1 well-indurated caprock about 10 cm thick ............................................................................ 1.27 219.09 62. smectitic sandy mudstone, fresh light olive-gray 5y6/1, weathered surface pale pinkish-purple 5rp7/2, slightly lighter at top, popcorn weathering with distinctly convex slope profile, small carbonate nodules about 2 to 7 cm across first appear at about 1 m up, larger carbonate nodules 10 to 15 cm across in horizon at about 2 m up, about 30 to 40 cm in diameter spar coated carbonate nodule horizon about 80 cm below top ............................................................................ 4.22 217.92 61. sandstone, dark green-gray 5g4/1, very fine grained with few coarse grains, well indurated, fine root traces, erosional base with 10 cm of relief ........................................................................................ 0.18 213.70 60. smectitic sandy mudstone, fresh dusky yellow-brown 10yr2/2, weathered surface pale pinkish-purple 5rp7/2, popcorn weathering surface with distinctly convex slope profile ............................... 2.22 213.52 59. sandy mudstone to muddy sandstone, pinkish-gray 5yr8/1, poorly laminated, poorly indurated, friable, concave slope................................................................................................................................ 1.24 211.30 58. sandstone, gray-green 10gy5/2, very coarse grained, well indurated, includes moderately to well-rounded lithic (mudstone) fragments up to 1 cm across, bed pinches out laterally over about 50 m ..... 0.28 210.06 57. sandy mudstone, pale yellow-brown 10yr6/2, smectitic, poorly laminated, poorly indurated, first distinct zone with surface characterized by popcorn weathering ......................................................... 0.99 209.78 56. sandstone, very pale yellow 5y7/2 to grayish-yellow-green 5gy7/2, fine to medium grained, poorly indurated, darker dusky yellow-green 5gy5/2 zones slightly better indurated forming rounded breaks in slope ...................................................................................................................................... 2.95 208.89 total brushy basin member ......................................................................................................................775.00 westwater canyon member of morrison formation 55. sandstone, dark yellowish-orange 10yr6/6, medium to coarse grained, planar and trough cross-bedded in sets about 40 cm thick, moderately well indurated at base becoming increasingly well indurated up section to very resistant caprock (12 s 0623873 e 4156394 n), forms top of no-mans island beds set back from bench formed by unit 53, traced this surface down slope to east to gully at base of black mesa, 12 s 0624083 e 4156432 n ...................................................... 3.10 205.14 54. claystone to mudstone, grayish yellow-green 5gy 7/2, slightly smectitic .................................................. 1.48 202.84 53. sandstone, moderate yellow-brown 10yr5/4, fine to coarse grained with conglomeratic lenses, trough cross-bedded, in thick 1.5 to 2 m sets, well indurated caps bench (12 s 0623807 e 4155992 n), traced north to point nearly due west of north end of black mesa, lower of two prominent sandstones referred to as no-mans island beds........................................................................... 4.49 201.36 52. sandy mudstone, somewhat smectitic, more so toward top, medium olive-gray 10y6/2 grading upward to greenish-gray 5g6/1, a few sandstone layers in lower half, few scattered dark orange concretions in upper few meters........................................................................................................... 9.56 195.89 51. sandstone, light-brown 5yr6/4, medium to coarse grained, trough cross-bedded in tabular a-6 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 sets about 40 cm thick, very well indurated forms laterally extensive marker bed, top of main body of westwater canyon member (12 s 0623598 e 4156052 n) trace to south east to base of slope below ridge capped by unit 53. ............................................................................................................ 1.52 186.33 50. muddy sandstone grading upward into sandy mudstone, drab olive gray 10y5/2, poorly indurated slope former ................................................................................................................................................ 4.46 184.71 49. sandstone, light yellow-gray 5gr7/1, trough cross-bedded in sets of about 50 to 150 cm thick, some pale reddish-brown 10r6/4 mudstone interbeds, but overall nearly pure fine sandstone, mostly only moderately indurated forming slope with harder ledges, some conglomeratic lenses with chert pebbles about 0.5 to 2 cm, basal unit of the main body of the westwater canyon member ................................................................................................................................................ 24.07 180.25 48. mudstone, moderate 10r6/6, with scattered thin sandstone beds 5 to 20 cm thick, comparable to typical recapture floodplain facies, some lenticular sandstone beds up to 50 cm thick, much higher proportion of sand to the north ................................................................................................. 4.33 156.18 47. sandstone, light yellow-gray 5gr7/1, medium grained, highly convoluted bedding ................................ 0.38 151.85 46. sandstone, light yellow-gray 5gr7/1, trough cross-bedded in sets of about 40 cm thick, in places moderately well indurated, in places a slope former ........................................................................... 2.95 151.47 45. sandstone, orange-gray 10yr7/4, medium to course grained, cross-bedded in sets 30 to 60 cm thick capped with 25 cm of hard slabby sandstone, well indurated marker bed .................................. 2.14 148.52 44. mudstone, moderate reddish-brown 10r6/4, with scattered thin sandstone beds 5 to 20 cm thick, comparable to typical recapture floodplain facies ............................................................................... 5.09 146.38 43. sandstone, light yellow-gray 5y8/1, fine-grained, cross-bedded, in sets 30 to 50 cm thick, separated by medium olive-gray 10y4/2 mudstone beds 10 to 30 cm thick, thin “chips” of sandstone cover slope .......................................................................................................................................... 2.88 141.39 42. hard calcareous sandstones, light yellow-gray 5y8/1, fine grained, root traces and abundant vertical burrows, 18-cm-thick bed that caps unit 41, and a nearly identical bed 12 cm thick is separated from it by an intervening 33-cm-thick medium olive-gray 10 yr5/1, mudstone .................... 0.63 138.44 41. sandstone, light yellow-gray 5y8/1, lower 2 m more gray-orange 10yr7/4, fine grained, trough cross-bedded, sets 40 to 80 cm thick with some mudstone interbeds, moderately to poorly indurated, overall slope former, sandstones feather out to southwest over 100s of meters .......... 5.82 137.81 total westwater canyon member ...............................................................................................................74.15 recapture member of morrison formation 40. mudstone, interbedded with platy, flat-bedded, fine-grained sandstone beds, 2 to 3 cm thick overall, pale-red 10r6/6 on surface with fresh rock dusky-red 5r3/4, units 40 and 38 merge together to south with pinching out of unit 39 ................................................................................................ 4.01 130.99 39. sandstone, light yellow-gray 5y8/1, fine to medium grained, trough cross-bedded in sets of a-7 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 30 to 50 cm thickening to about 1 m to north, unit interfingers with mudstone on unit 38 to south and pinches out over 100s of meters, upper meter ripple cross-bedded with burrows and shaly interbeds in 20-cm-thick sets ........................................................................................................... 2.22 126.98 38. mudstone, interbedded with platy, flat-bedded, fine-grained sandstone beds, 2 to 3 cm thick overall pale-red 10r6/6 on surface with fresh rock dusky-red 5r3/4 .......................................................... 2.93 124.76 37. interbedded sandstone, light yellow-gray 5y8/1, planar cross-bedded, with about 50% mudstone, moderate red-brown 10r4/6, in sets about 50 cm thick, increasing thickness of sandstone such that about 2 m up sandstone dominates with lenses of mudstone every 50 cm, induration increases up section as well, capped by 10 cm of softer structureless sandstone .................... 5.48 121.83 36. sandstone, light yellow-gray 5y8/1, fine to medium grained, planar cross-bedded in sets of about 30 cm ....... 0.99 116.35 35. mudstone, interbedded with platy, flat-bedded, fine-grained sandstone beds, 2 to 3 cm thick overall pale-red 10r6/6 on surface with fresh rock dusky-red 5r3/4, at about 1.5 m up is sandstone lens (channel) 50 cm thick by 50 m across, light yellow-gray 5y8/1, fine to medium grained, flat bedded .....................................................................................................................................................3.23 115.36 34. sandstone, light yellow-gray 5y8/1, fine to medium grained, trough cross-bedded in sets of 30 to 50 cm ....... 1.23 112.13 33. mudstone, interbedded with platy, flat to ripple cross-bedded, fine-grained sandstone beds, 2 to 5 cm thick overall pale-red 10r6/6 on surface with fresh rock dusky red 5r3/4, a higher proportion of mudstone to sandstone than in unit 31.................................................................................... 3.60 110.90 32. sandstone, light yellow-gray 5y8/1, fine to medium grained, flat bedded, thickens to 3.5 m and becomes trough cross-bedded to south in butler wash ......................................................................... 0.40 107.30 31. mudstone, interbedded with platy, flat to ripple cross-bedded, fine-grained sandstone beds, 2 to 5 cm thick overall, pale-red 10r6/6 on surface with fresh rock dusky-red 5r3/4, at about 2.0 and 2.5 cm, 30-cm-thick sandstone beds, light yellow-gray 5y 8/1, cross-bedded splays laterally extended in to channel sandstone lenses ........................................................................................... 4.40 106.90 30. sandstones, pale-red 10r 6/6 in beds about 50 cm thick separated by darker red 10r4/6 mudstones beds 5 to 15 cm thick that completely amalgamate into unit 29 to south ........................................ 3.10 102.50 29. sandstone, yellowish-gray 58/1, fine to medium grained, wavy and trough cross-bedded in set 30 to 50 cm thick at ridge (12 s 0622711 e 4154456 n) the top of this sand traced northeast to butler wash (12 s 623180 e 4155315 n), where the unit is completely trough cross-bedded in sets averaging about 50 cm thick ....................................................................................................................... 1.57 99.40 total recapture salt wash facies.................................................................................................................33.16 recapture tidwell facies 28. mudstone, overall moderate red-orange 10r6/6 on surface with fresh rock dusky-red 5r3/4, with thin friable muddy sandstone layers, thin fine-medium-grained sandstone layers 5 to 10 cm thick, light green-gray 5gy8/1 every 1.0 to 1.5 m forming breaks in slope, much like unit 24, burrows present in sandstones, 50 cm thick sandstone splay 90 cm below top of unit a-8 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 appears to correlate to multimeter trough cross-bedded sandstone lens to north at butler wash .......... 8.62 97.83 27. sandstone, yellowish-gray 5y8/1, fine to medium grained, trough cross-bedded, well indurated, upper about 30 cm, reddish, flat to ripple cross-bedded in sets 10 cm thick, pinches out over 200 m laterally ............................................................................................................................................. 1.24 89.21 26. mudstone interbedded with platy, flat to ripple cross-bedded, fine-grained sandstones, overall moderate red-orange 10r6/6, light-green to yellow-gray 5gy8/2, fineto medium-grained sandstone lenses about 50 cm thick and 50 to 100 m across every 1 to 2 m, much like unit 24 but with much more sandstone (50%) ............................................................................................................ 11.13 87.97 25. sandstone, yellow-gray 5y8/1, medium grained, lower two-thirds trough cross-bedded in sets 30 to 40 cm thick, upper third with shaly interbeds of set 10 to 20 cm thick, pinches out over 100 m laterally 1.54 76.84 24. mudstone, overall moderate red-orange 10r6/6 on surface with fresh rock dusky-red 5r3/44, with thin friable muddy sandstone layers, thin, fineto medium-grained sandstone layers 5 to 10 cm thick, light green-gray 5gy8/1 every 1.0 to 1.5 m forming breaks in slope, thicker about 50 cm thick sandstone lens at about 8.5 m above base ........................................................................ 9.04 75.30 23b. sandstone, yellow-gray 5y8/1, fine grained although scattered very coarse grains at base, large scale trough cross-beds sets 1 to 2 m thick, to south along outcrop this unit pinches out at 12s 0622624 e 4155098 n and continues to thicken to north, toward south capped by coarser sandstone as in unit 23a. this unit is interpreted to represent reworked sandstone from the underlying bluff sandstone ................................................................................................................................ 4.27 66.26 23a. sandstone, pale red-brown 10r5/4 to yellow-gray 5y8/1, medium to course grained, trough cross-bedded, sets 30 to 40 cm thick, well indurated, burrowed in places. this unit thickens to about 4 m thick south of butler wash and appears to directly underlie reddish mudstones typical of the recapture member, south of butler wash this unit underlies eolian sandstone of the bluff sandstone facies (unit 23b), the north-south transition across butler wash is complex. south of the wash the lowest set is softer and recessed, preserving intraformational clasts up to 50+ cm in diameter within a finer grained matrix, suggesting that this interval records the j-5 unconformity and that there may have been uplift along comb ridge at the end of san rafael group deposition. a discontinuous interval of moderate red-brown 10r6/4 mudstone up to a meter thick may separate units 23a and 23b locally .......................................................................... 1.39 61.99 total recapture tidwell facies ...................................................................................................................37.23 total recapture member .............................................................................................................................70.39 unconformity broadly undulatory over many meters, recognized by large rip-up clasts deposited on the surface. bluff sandstone 22. sandstone, moderate red-brown 10r4/6, faintly, medium scale cross-bedded, nearly structureless, forming more vertical cliff than unit 21, includes mudstone lenses, red-brown 10 r6/6, 0.4 to 1.0 m thick by 10s of m wide, scoured surface representing the j-5 unconformity locally, this surface with overlying unit 23 was traced north to where bed crossed butler wash ............ 4.33 60.60 21. sandstone, moderate pink 5r7/4 grading upward to moderate orange-pink 10r 7/4, fine a-9 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 grained, well indurated, large scale trough cross-bedded with sets about 1.5 to 4.0 m thick, sets broadly rounded in surface expression, at 4.4 m shaly parting seeping water, at 5.8 m above base hard silica cemented wavy layer, 1 cm thick, forms local marker bed. main body of the beds of bluff sandstone (o’sullivan, 1980) .............................................................................................. 22.50 56.27 total bluff sandstone ..................................................................................................................................32.49 total morrison formation ........................................................................................................254.53 unconformity present not recognizable beyond sharp basal contact. san rafael group summerville -wanakah formation 20. interbedded fine-grained sandstone and sandy mudstone, grading from moderate red-brown 10r5/6 to pale red-brown 10yr4/4 up section, laterally variable, overall interbedded at 20 to 30 cm in lower 1 to 1.5 m, sandstone beds thicken to 0.8 to 1.5 m up section with about 40 cm sandy mudstone lenses 10s of m across separating sandstone sets with no internal bedding observed, but many burrows and root traces, disconformity at top of san rafael group? ....................... 4.34 33.77 19. sandstone, light brown 5yr5/6, fine grained, sweeping trough cross-beds in sets 20 to 50 cm thick in lower and upper meter, medial sets 1 to 1.5 m .................................................................................. 8.39 29.43 18. mudstone, moderate red-brown 10yr6/6, includes a few fineto medium-grained sandstone layers less than 0.5 cm thick. .............................................................................................................................. 0.38 20.94 17. sandstone, light-brown 5yr5/6, fine grained, bedded in sets of 5 to 10 cm thick, internal bedding obscure weakly ripple bedded in part, dinosaur tracks at top of basal set about 10 cm above base, about 140 cm above base, and at top of well indurated 11-cm-thick caprock, main butler wash dinosaur tracksite level, cross blm 262 to east on this surface; units 17 to 19 interpreted as representing the black steer knoll beds as used by o’sullivan (1980) and lucas (2014) ... 2.85 20.56 16. sandstone, light-brown 5yr5/6, fine grained, bedding obscure in sets 20 to 40 cm thick, weakly expressed cross-bedding and some ripple bedding, some dinosaur tracks at top ......................... 2.38 17.71 15. sandstone, moderate red-brown 10r6/6, fine grained, massive, cross-bedded, weakly expressed convolute bedding toward top ............................................................................................................. 2.24 15.33 14. sandstone, moderate light-brown to salmon 5yr5/6, fine to medium grained, coarsening upward with increasing induration, wavy bedded, sets in lower 22 cm about 1 to 3 cm, overlying beds thicken to 20 to 30 cm ............................................................................................................................... 0.88 13.09 13. mudstone, moderate red-brown 10r3/6 .......................................................................................................... 0.57 12.21 12. sandstone light-brown to salmon 5yr5/6, fine to medium grained, flat bedded in sets 25 to 40 cm thick, with unit 11 forms straight cliff in sides of wash, top 10 cm thick set forms more resistant caprock. ................................................................................................................................................. 0.95 11.64 a-10 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 11. sandstone light-brown with salmon streaks along bedding 5yr5/6, medium-grained, large scale tough cross-bedding, more indurate sandstone columnar structures in lower 30 cm, small sandstone nodules 0.2 to 30 cm in upper 20 cm, units 12 to 11 interpreted as representing the butler wash beds as used by o’sullivan (1980, 2010a) and lucas (2014) ...................................... 0.89 10.69 10. sandstone, yellow-gray 5y8/1 at base darkening to light-brown 10r6/6, very fine grained, flat bedded, like unit 9 except better indurated and for yellow-gray clay parting in lower portion ............... 0.25 9.40 9. sandstone, red-brown 10r6/6, very fine grained, flat bedded to low angle cross-bedded, vague ripple cross-bedded ............................................................................................................................................. 0.45 9.15 8. mudstone, moderate red-brown 10r6/6, about 10-cm-thick sandy mudstone marker bed with light yellow-gray 10 yr 8/2 sandstone nodules 3 to 5 cm thick by 10 cm wide at 8.4 m .................. 0.68 8.70 7. interbedded muddy sandstone and mudstone, pale red-brown 10r4/4, coarsening upward in 10 to 20 cm sets, moderately indurated, poorly bedded, light yellow-gray sandstone nodules toward top 5 cm thick by 10 to 20 cm wide, in about upper 15 cm .............................................................. 0.86 8.02 6. sandstone, medium red-orange 10r6/6, lighter mottles, fine grained, in two sets about 10 cm thick, separated by sandy mudstone with sandstone lenses ........................................................................... 0.32 7.16 5. mudstone, red-brown 10r4/6 ............................................................................................................................ 0.16 6.84 4. sandstone, yellow gray 5y8/1, fine to medium grained, slabby, little clear bedding, sets 5 to 10 cm ...... 0.42 6.68 3. shaly mudstone, partially covered, pale red-brown, 10r4/4, with scattered mm thick sand layers, like unit 1 .................................................................................................................................................. 3.87 6.26 2. sandstone, moderate pink 5r7/4, fine-medium grained, platy, planar cross-bedded grading upward into ripple cross-bedded, in set 3 to 10 cm thick with shaly partings, ripple crests n. 70° w. to n. 30° w. .............................................................................................................................................. 0.60 2.39 1. shaly mudstone, pale red-brown, 10r4/4, with scattered mm thick sand layers, one about 10 cm fine, slabby, sandstone starting at about 1.2 m .......................................................................................... 1.79 1.79 total summerville-wanakah formation ...................................................................................................33.77 entrada sandstone(?) sandstone, light gray n2, fine to medium grained, only upper surface exposed and examined, appears to have been heavily tracked by dinosaurs to the point of obscuring individual tracks (dinoturbated), may represent the top of the entrada sandstone .................................................not measured total san rafael group ................................................................................not measured b-1 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 appendix b processing, analysis, and maximum depositional age for sa1115v by emily finzel earth and environmental science deparment, university of iowa while examining a vertebrate locality sa1115v in the lower recapture member above the lower recapture bench south of black mesa, thin smectitic clay layers a few mm thick were identified interspersed with thin layers of mudstone and sandy shale. this interval was sampled for detrital zircons resulting in a mixing of these thin clastic layers. detrital zircons were separated from the sa1115v sample at the university of iowa (figure b1). samples were crushed using a jaw crusher and disc mill, followed by processing through an ultrasonic clay separator (e.g., hoke and others, 2014), sieving to <350 µm, and cycling through free fall and barrier frantz magnetic separators to eliminate grains with high magnetic susceptibilities. the final nonmagnetic fraction was separated using methylene iodide (ρ = 3.32 g/cm3) where lighter minerals float and heavier minerals (including zircon) sink. all zircon grains were hand picked from the heavy liquid sinks, mounted with standards in a 1-in puck with epoxy, and polished down to a depth of about 20 µm to expose grain interiors prior to analysis. detrital zircons were analyzed by laser ablation inductively coupled plasma mass spectrometry (laicpms) at the university of arizona’s laserchron center using a thermo element2 single-collector icpms (gehrels and others, 2008). standards used include duluth gabbro (fc) zircon (~1099 ma), sri lanka (sl) zircon (~563.5 ma), and r33 (~420 ma). fractionation corrections were made using 207pb/206pb and 206pb/238u ratios as well as a correction for 204pb (stacey and kramers, 1975) using the e2agecalc excel spreadsheet at the arizona laserchron center. best ages were determined using the filter of 206pb/238u ages for grains younger than 900 ma and 206pb/207pb ages for grains older than 900 ma. analyses with discordance greater than 20% for ages >700 ma or uncertainty greater than 10% for all ages are not reported. calculating discordance using the difference between the 206pb/238u and 206pb/207pb ages for young grains is difficult using a la-icpms approach because the 206pb/207pb system relatively insensitive for young systems and measuring small 207pb signals in young zircon grains is challenging. in order to interpret the maximum depositional age (mda) of this sample, and for the type of dataset presented here (n = about 100 with a small-moderate number of near-depositional age grains), using the youngest single grain (ysg) to approximate the true depositional age of the sample has been shown to be the most successful method in most cases, although pb-loss and reproducibility are potential issues (coutts and others, 2019; dickinson & gehrels, 2009). the youngest single grain in the dataset is 145.9 ± 1.6 ma, but the youngest single grain for which discordance is <20% is 150.2 ± 2.1 ma. the next two youngest grains that pass the discordance filter are 153.7 ± 2.1 ma and 153.8 ± 2.2 ma (see attached table b1). another technique that has been demonstrated to approximate the true depositional age in this type of dataset is the youngest detrital zircon (ydz) method (dickinson and gehrels, 2009; coutts and others, 2019). figure b1. representative transmitted light microscope image of zircon crystals from sample sa1115v. b-2 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 this method applies an algorithm in isoplot (ludwig, 2012) that uses ~10,000 iterations in a monte carlo approach to perturb each date randomly by its assigned error, selects the youngest ages from each iteration, and then calculates the mode using all the youngest dates as the best estimate of the youngest age, with the upper and lower limits defining the uncertainties at 95% confidence. the mda based on this technique is 144.38 +2.7 -4.7 ma. a third technique that has been used to assess mda is the weighted average of the group of youngest grains whose ages overlap within their 1σ error. the mda calculated from this approach is 151.4 ± 1.8 ma with n = 18 and an mswd of 2.9. both of these techniques use all of the young grains in the dataset, even those who do not pass the discordance filter. references coutts, d.s., matthews, w.a., and hubbard, s.m., 2019, assessment of widely used methods to derive depositional ages from detrital zircon populations: geoscience frontiers, v. 10, no. 4, p. 1421–1435, doi:10.1016/j.gsf.2018.11.002. dickinson, w.r., and gehrels, g.e., 2009, use of u-pb ages of detrital zircons to infer maximum depositional ages of strata—a test against a colorado plateau mesozoic database: earth and planetary science letters, v. 288, no. 1–2, p. 115125, doi:10.1016/j.epsl.2009.09.013. gehrels, g.e., valencia, v.a., and ruiz, j., 2008, enhanced precision, accuracy, efficiency, and spatial resolution of u-pb ages by laser ablation-multicollector-inductively coupled plasma-mass spectrometry: geochemistry, geophysics, geosystems, v. 9, no. 3, p. 1–13, doi:10.1029/2007gc001805. hoke, g.d., schmitz, m.d., and bowring, s.a., 2014, an ultrasonic method for isolating nonclay components from clay rich material: geochemistry, geophysics, geosystems, v. 15, p. 492–498, doi:10.1002/2013gc005125. ludwig, k.r., 2012, user’s manual for isoplot 3.75—a geochronological toolkit for microsoft excel: berkeley, california, geochronology center special publication no. 5, 75 p. stacey, j.s., and kramers, j.d., 1975, approximation of terrestrial lead isotope evolution by a 2-stage model, earth and planetary science letters, v. 26, no. 2, p. 207–221, doi:10.1016/0012-821x(75)90088-6. c-1 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 appendix c final report on u-pb dating of morrison ash sample sa1114vp, southern black mesa, utah by kevin chamberlain, research professor, university of wyoming, april 24, 2017 introduction zircons were isolated from the ash sample using a multistage ultrasonic separation technique to deflocculate clays and release all crystalline grains. heavy liquid density and magnetic separations purified the zircons further. the sample contained abundant elongate zircons with longitudinal bubble tracks and cavities that are characteristic of ash-fall volcanic origins (figure c1). sub-populations of these ‘ash-fall’ zircons along with euhedral grains were selected for single grain u-pb dating. a minor population of rounded, detrital zircons also exists but was not dated. selected zircons were annealed at 850°c for 50 hours, then dissolved in two steps in a chemical abrasion, thermal ionization mass spectrometric u-pb dating method (catims) modified from mattinson (2005). the first dissolution step was in hydrofluoric acid (hf) and nitric acid (hno3) at 180°c for 12 hours. this removed the most metamict zircon domains in the annealed crystals (figure c2). individual grains were then spiked with a mixed 205pb-233u-235u tracer (et535), completely dissolved in hf and hno3 at 240°c for 30 hours, and then converted to chlorides. the dissolutions were loaded onto rhenium filaments with phosphoric acid and silica gel without any further chemical processing. pb and uo2 isotopic compositions were determined in single daly photomultiplier mode on a micromass sector 54 mass spectrometer. data were reduced, and ages calculated using pbmacdat and isoplot/ex after ludwig (1988, 1991, 1998). measured procedural blanks and total common pb varied from 2.0 to 0.3 picograms, except for one analysis (see attached table c1). all common pb was assigned to blank. results five single grain analyses from jk16-10 produced concordant data that overlap within error (figure c3; see attached table c1). the concordia age (ludwig, 1998) from these data, which incorporates both the 206pb/238u and 207pb/235u data, is 150.67 ± 0.32 ma (95% confidence figure c1. examples of recovered elongate (left) and euhedral, short to equant (right) zircons from morrison ash jk16-10. a minor population of rounded, detrital zircons also exists, but was not imaged. longitudinal bubble tracks and transverse channels displayed in the elongate zircons are characteristic of ash-fall zircons. single grains of both morphologies were dated and yielded similar results. figure c2. close-up image of elongate, ash-type zircons from jk16-10, upper morrison ash, after the first partial dissolution step of chemical abrasion (ca). gray domains have been partially dissolved. individual grains were selected for subsequent, complete dissolution and isotope dilution thermal ionization mass spectrometric dating (idtims). c-2 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 limits, mswd 0.11; figure 3) including uncertainties in the two u decay constants, and with correction for 230th disequilbrium (after schärer, 1984) assuming a magma th/u of 2.2. the weighted mean 206pb/238u date from these same five analyses is 150.68 ± 0.29 ma (figure c4; 95% confidence, mswd 3.7), th-corrected. weighted mean 206pb/238u date from the youngest three analyses is 150.48 ± 0.44 ma (figure 4; 95% confidence, mswd 1.6). the 230th correction increased the dates by about 80 ka. the concordia age of 150.67 ± 0.32 ma is interpreted as the best estimate of the eruption age for this sample. this date includes all external sources of u-pb errors and can be directly compared to 40ar/39ar dates as long as the 40ar/39ar dates have similarly included all external errors and have been recalculated to reflect the new age for the fish canyon 40ar/39ar standard (e.g., kuiper and others, 2008; smith and others, 2010). references krogh, t.e., 1973, a low-contamination method for hydrothermal decomposition of zircon and extraction of u and pb for isotopic age determinations: geochimica et cosmochimica acta, v. 37, p. 485–494. kuiper, k.f., deino, a., hilgen, f.j., krijgsman, w., renne, p.r., and wijbrans, j.r., 2008, synchronizing rock clocks of earth history: science, v. 320, p. 500–504, doi:10.1126/ science.1154339. ludwig, k.r., 1988, pbdat for ms-dos, a computer program for ibm-pc compatibles for processing raw pb-u-th isotope data, version 1.24: u.s. geological survey open-file report 88-542, 32 p. ludwig, k.r., 1991, isoplot for ms-dos, a plotting and regression program for radiogenic-isotope data, for ibm-pc compatible computers, version 2.75: u.s. geological survey, open-file report 91-445, 45 p. ludwig, k.r. 1998, on the treatment of concordant uranium-lead ages: geochimica et cosmochimica acta, v. 62, no. 4, p. 665–676. mattinson, j.m, 2005, zircon u-pb chemical abrasion (“catims”) method—combined annealing and multi-step partial dissolution analysis for improved precision and accuracy of zircon ages: chemical geology, v. 220, p. 47–66. figure c3. concordia plot of eight single zircon catims analyses from volcanic ash sample jk16-10, upper morrison. data from the five youngest zircons (green ellipses) overlap each other and concordia and are interpreted to reflect the eruptive age. the concordia age (aqua ellipse; ludwig, 1998) includes both 206pb/238u and 207pb/235u data and propagates the decay constant errors in this case. it can be directly compared to dates from other methods as long as those dates include all external sources of error. the older zircons (gray ellipses) are interpreted as pre-eruptive, antecrystic zircons from the magma chamber, or slightly older, volcanic zircons entrained during ash-fall deposition. their data were excluded from the concordia age calculation. concordia is plotted as a swath reflecting the errors in decay constants. figure c4. plot of thorium-disequilibrium corrected 206pb/238u dates of the eight zircon analyses from jk16-10, and weighted mean calculations of the five (green box) and three (yellow box) single grain, youngest analyses (green bars). weighted mean dates overlap the concordia age calculation from these same zircons. c-3 the morrison formation and its bounding strata on the western side of the blanding basin, san juan county, utah kirkland, j.i., deblieux, d.d., hunt-foster, r.k., foster, j.r., trujillo, k.c., and finzel, e. geology of the intermountain west 2020 volume 7 parrish, r.r., roddick, j.c., loveridge, w.d., and sullivan, r.d., 1987, uranium-lead analytical techniques at the geochronology laboratory, geological survey of canada, in radiogenic age and isotopic studies, report 1: geological survey of canada paper 87-2, p. 3–7. schärer, u., 1984, the effect of initial 230th equilibrium on young u-pb ages—the makula case, himalaya: earth and planetary science letters, v. 67, p. 191–204. smith, m.e., chamberlain, k.r., singer, b.s., and carroll, a.r., 2010, eocene clocks agree—coeval 40ar/39ar, u-pb, and astronomical ages from the green river formation: geology, v. 38, no. 6, p. 527–530, doi: 10.1130/g30630.1. stacey, j.s., and kramers, j.d., 1975, approximation of terrestrial lead isotope evolution by a two-stage model: earth and planetary science letters, v. 26, p. 207–221. steiger, r.h., and jäger, e., 1977, subcommission on geochronology—convention on the use of decay constants in geo and cosmochronology: earth and planetary science letters, v. 36, p. 359–362. sheet1 appendix b data table. laser ablation inductively coupled plasma mass spectrometry (la-icpms) data of detrital zircon grains from sample sa1115v from the upper morrison formation. isotope ratios apparent ages (ma) analysis u (ppm) 206pb/204pb u/th 206pb*/207pb* ± (%) 207pb*/235u* ± (%) 206pb*/238u ± (%) error correction 206pb*/238u* ± (ma) 207pb*/235u ± (ma) 206pb*/207pb* ± (ma) best age ± (ma) conccordance (%) uncertainty (%) sa1115v-spot 198 228 1096 1.2 27.8370 2.3 0.1134 2.5 0.0229 1.1 0.43 145.9 1.6 109.0 2.6 na na 145.9 1.6 na 1.1% sa1115v-spot 215 1607 3330 0.9 16.2807 3.9 0.1939 4.4 0.0229 1.9 0.43 146.0 2.7 180.0 7.2 653.1 84.3 146.0 2.7 22.4 1.9% sa1115v-spot 160 220 1538 1.3 24.8478 1.9 0.1277 2.5 0.0230 1.7 0.66 146.7 2.4 122.0 2.9 na na 146.7 2.4 na 1.6% sa1115v-spot 197 357 2157 1.0 23.0082 1.9 0.1382 2.3 0.0231 1.3 0.58 147.0 1.9 131.4 2.8 na na 147.0 1.9 na 1.3% sa1115v-spot 261 1223 688 0.5 8.2686 6.6 0.3883 6.8 0.0233 1.5 0.23 148.5 2.3 333.1 19.4 1969.3 118.6 148.5 2.3 7.5 1.5% sa1115v-spot 165 410 7373 1.5 20.0688 1.3 0.1619 1.9 0.0236 1.4 0.75 150.2 2.1 152.4 2.7 186.0 29.1 150.2 2.1 80.8 1.4% sa1115v-spot 138 270 1849 0.9 24.1824 2.3 0.1346 2.7 0.0236 1.4 0.52 150.5 2.1 128.3 3.2 na na 150.5 2.1 na 1.4% sa1115v-spot 144 478 6969 1.2 21.1249 1.5 0.1552 2.1 0.0238 1.4 0.69 151.6 2.1 146.5 2.8 65.2 35.7 151.6 2.1 232.4 1.4% sa1115v-spot 244 587 5101 1.3 21.0436 1.5 0.1559 2.1 0.0238 1.4 0.67 151.6 2.1 147.1 2.8 74.4 36.5 151.6 2.1 203.8 1.4% sa1115v-spot 178 650 12513 1.4 20.9354 1.5 0.1579 2.0 0.0240 1.4 0.68 152.8 2.1 148.9 2.8 86.7 35.4 152.8 2.1 176.3 1.4% sa1115v-spot 180 561 35162 0.9 20.5169 1.1 0.1613 1.7 0.0240 1.3 0.76 153.0 2.0 151.9 2.4 134.3 26.1 153.0 2.0 113.9 1.3% sa1115v-spot 133 1116 56557 1.0 19.9716 1.0 0.1662 1.5 0.0241 1.2 0.77 153.4 1.8 156.1 2.2 197.3 22.1 153.4 1.8 77.7 1.2% sa1115v-spot 170 1103 15702 1.0 20.1830 1.1 0.1648 1.7 0.0241 1.4 0.78 153.7 2.1 154.9 2.5 172.7 25.4 153.7 2.1 89.0 1.3% sa1115v-spot 176 996 54767 1.1 20.1373 1.3 0.1652 1.9 0.0241 1.4 0.75 153.8 2.2 155.2 2.8 178.0 29.5 153.8 2.2 86.4 1.4% sa1115v-spot 260 629 12578 1.9 20.7314 1.0 0.1622 1.9 0.0244 1.6 0.83 155.4 2.4 152.6 2.6 109.8 24.4 155.4 2.4 141.5 1.5% sa1115v-spot 209 426 4036 1.9 21.2102 1.7 0.1586 2.1 0.0244 1.2 0.60 155.4 1.9 149.4 2.9 55.6 39.9 155.4 1.9 279.3 1.2% sa1115v-spot 163 915 19985 1.5 20.2771 1.1 0.1673 1.8 0.0246 1.4 0.78 156.7 2.2 157.0 2.6 161.9 26.4 156.7 2.2 96.8 1.4% sa1115v-spot 235 611 4267 1.0 21.5414 1.3 0.1575 2.2 0.0246 1.8 0.81 156.8 2.8 148.6 3.0 18.6 31.0 156.8 2.8 843.9 1.8% sa1115v-spot 257 271 4755 0.8 19.2869 4.0 0.1848 4.3 0.0259 1.5 0.36 164.6 2.5 172.2 6.8 277.8 91.9 164.6 2.5 59.3 1.5% sa1115v-spot 182 898 16829 1.4 19.8110 1.6 0.1855 2.1 0.0267 1.4 0.66 169.7 2.3 172.8 3.3 216.0 36.1 169.7 2.3 78.5 1.3% sa1115v-spot 130 1790 39233 1.2 20.0972 1.1 0.1834 1.6 0.0267 1.2 0.76 170.2 2.1 171.0 2.6 182.7 24.6 170.2 2.1 93.2 1.2% sa1115v-spot 169 688 18439 0.7 20.1492 1.4 0.1847 2.0 0.0270 1.5 0.73 171.8 2.5 172.1 3.2 176.6 32.6 171.8 2.5 97.2 1.5% sa1115v-spot 140 6717 33404 1.9 19.3919 0.6 0.1964 1.5 0.0276 1.4 0.91 175.7 2.4 182.1 2.5 265.3 14.8 175.7 2.4 66.2 1.4% sa1115v-spot 167 883 53529 1.9 20.0231 1.0 0.2033 1.9 0.0295 1.6 0.83 187.6 2.9 187.9 3.2 191.3 24.0 187.6 2.9 98.1 1.5% sa1115v-spot 246 271 8570 1.0 19.8873 1.5 0.2061 1.9 0.0297 1.2 0.63 189.0 2.3 190.3 3.4 207.1 35.0 189.0 2.3 91.2 1.2% sa1115v-spot 164 732 17758 4.0 19.5564 1.4 0.2152 2.0 0.0305 1.4 0.72 193.9 2.7 197.9 3.5 245.9 31.3 193.9 2.7 78.9 1.4% sa1115v-spot 220 3693 42586 14.2 18.6664 1.2 0.2682 2.3 0.0363 2.0 0.85 230.0 4.4 241.2 5.0 352.1 27.8 230.0 4.4 65.3 1.9% sa1115v-spot 207 1044 33085 5.4 19.1352 1.1 0.2819 2.0 0.0391 1.7 0.83 247.5 4.0 252.1 4.5 295.8 26.0 247.5 4.0 83.7 1.6% sa1115v-spot 139 345 12005 1.6 18.6905 1.3 0.2913 1.8 0.0395 1.3 0.72 249.8 3.2 259.6 4.2 349.2 28.7 249.8 3.2 71.5 1.3% sa1115v-spot 240 1351 8240 3.7 17.6070 2.8 0.3101 3.3 0.0396 1.7 0.51 250.5 4.1 274.3 7.9 482.7 62.5 250.5 4.1 51.9 1.7% sa1115v-spot 151 320 5866 1.4 19.7419 1.4 0.2813 1.8 0.0403 1.2 0.65 254.6 3.0 251.7 4.1 224.1 32.2 254.6 3.0 113.6 1.2% sa1115v-spot 200 1872 58888 1.5 18.8751 0.9 0.2962 1.6 0.0406 1.3 0.84 256.3 3.3 263.4 3.7 326.9 19.4 256.3 3.3 78.4 1.3% sa1115v-spot 199 1222 34440 2.3 18.4485 1.1 0.3032 2.2 0.0406 1.8 0.86 256.5 4.6 268.9 5.1 378.6 25.1 256.5 4.6 67.7 1.8% sa1115v-spot 121 1154 12770 4.0 19.8481 0.9 0.2947 1.8 0.0424 1.5 0.86 268.0 4.0 262.3 4.1 211.7 21.1 268.0 4.0 126.6 1.5% sa1115v-spot 230 194 2032 1.3 21.7882 1.6 0.2710 1.9 0.0428 0.9 0.49 270.4 2.5 243.5 4.1 na na 270.4 2.5 na 0.9% sa1115v-spot 223 1046 81554 3.0 18.9079 1.1 0.3132 1.9 0.0430 1.5 0.79 271.2 3.9 276.6 4.5 323.0 26.1 271.2 3.9 84.0 1.4% sa1115v-spot 131 960 16137 6.4 19.6534 0.9 0.3034 1.6 0.0433 1.3 0.83 273.0 3.5 269.0 3.8 234.5 20.9 273.0 3.5 116.4 1.3% sa1115v-spot 142 1467 41887 6.1 19.1331 0.8 0.3139 1.7 0.0436 1.5 0.88 275.0 4.0 277.2 4.1 296.1 18.2 275.0 4.0 92.9 1.5% sa1115v-spot 177 158 4936 2.2 19.7516 2.6 0.3057 3.0 0.0438 1.4 0.47 276.4 3.8 270.9 7.1 223.0 60.5 276.4 3.8 124.0 1.4% sa1115v-spot 213 248 6026 1.6 19.7337 2.7 0.3078 3.2 0.0441 1.6 0.50 278.0 4.3 272.4 7.5 225.0 63.3 278.0 4.3 123.5 1.5% sa1115v-spot 224 1256 26045 3.3 18.7262 1.1 0.3298 1.8 0.0448 1.4 0.79 282.6 3.8 289.4 4.4 344.9 24.4 282.6 3.8 81.9 1.4% sa1115v-spot 249 147 6909 2.2 19.4610 1.6 0.3184 2.6 0.0450 2.0 0.77 283.5 5.5 280.6 6.3 257.1 37.6 283.5 5.5 110.2 1.9% sa1115v-spot 132 890 52875 4.3 18.9300 0.8 0.3364 1.5 0.0462 1.3 0.84 291.2 3.6 294.4 3.9 320.4 18.9 291.2 3.6 90.9 1.2% sa1115v-spot 122 868 35584 1.0 19.1222 1.0 0.3336 1.7 0.0463 1.4 0.81 291.7 3.9 292.3 4.3 297.3 22.7 291.7 3.9 98.1 1.3% sa1115v-spot 134 2387 93282 3.7 18.9896 0.9 0.3410 1.7 0.0470 1.4 0.84 296.0 4.1 297.9 4.3 313.2 20.5 296.0 4.1 94.5 1.4% sa1115v-spot 125 745 16671 2.5 19.2330 1.1 0.3423 1.7 0.0478 1.3 0.75 300.8 3.8 298.9 4.5 284.2 26.2 300.8 3.8 105.9 1.3% sa1115v-spot 254 1880 40574 2.9 19.1241 0.9 0.3552 1.6 0.0493 1.3 0.81 310.2 4.0 308.6 4.3 297.1 21.3 310.2 4.0 104.4 1.3% sa1115v-spot 229 1271 39732 6.3 19.0690 1.1 0.3641 1.7 0.0504 1.4 0.78 316.8 4.2 315.3 4.7 303.7 24.6 316.8 4.2 104.3 1.3% sa1115v-spot 166 255 7789 2.2 18.0895 1.1 0.4432 1.9 0.0582 1.5 0.80 364.5 5.4 372.5 5.9 422.6 25.1 364.5 5.4 86.3 1.5% sa1115v-spot 168 420 178637 0.7 18.3127 1.2 0.4597 1.8 0.0611 1.3 0.73 382.2 4.8 384.1 5.7 395.2 26.9 382.2 4.8 96.7 1.3% sa1115v-spot 237 615 132549 0.9 18.0248 1.0 0.4916 1.9 0.0643 1.6 0.86 401.7 6.3 406.0 6.3 430.6 21.7 401.7 6.3 93.3 1.6% sa1115v-spot 212 472 33789 2.3 18.2383 0.9 0.4969 1.4 0.0658 1.1 0.80 410.5 4.5 409.6 4.8 404.3 19.3 410.5 4.5 101.5 1.1% sa1115v-spot 145 535 33039 2.2 18.0465 1.2 0.5144 1.7 0.0674 1.2 0.71 420.2 5.0 421.4 6.0 427.9 27.2 420.2 5.0 98.2 1.2% sa1115v-spot 173 533 36142 3.8 18.1784 0.8 0.5115 1.6 0.0675 1.3 0.84 420.9 5.4 419.5 5.4 411.7 19.0 420.9 5.4 102.2 1.3% sa1115v-spot 196 755 104780 4.3 17.7549 1.1 0.5248 1.8 0.0676 1.4 0.80 421.7 5.8 428.4 6.2 464.2 23.4 421.7 5.8 90.9 1.4% sa1115v-spot 152 75 7085 7.5 17.9869 1.5 0.5423 1.9 0.0708 1.2 0.65 440.8 5.2 439.9 6.8 435.3 32.4 440.8 5.2 101.3 1.2% sa1115v-spot 222 1195 45322 8.2 17.4746 1.0 0.5640 1.8 0.0715 1.6 0.85 445.3 6.7 454.2 6.7 499.3 21.0 445.3 6.7 89.2 1.5% sa1115v-spot 206 495 16560 5.7 17.9207 1.2 0.5510 2.6 0.0717 2.3 0.90 446.1 10.0 445.7 9.4 443.5 25.7 446.1 10.0 100.6 2.2% sa1115v-spot 126 276 19698 1.9 17.9944 1.1 0.5529 1.7 0.0722 1.3 0.77 449.3 5.7 446.9 6.1 434.4 24.0 449.3 5.7 103.5 1.3% sa1115v-spot 242 1788 175596 6.1 17.1198 0.8 0.5822 1.5 0.0723 1.3 0.83 450.1 5.5 465.9 5.6 544.3 18.3 450.1 5.5 82.7 1.2% sa1115v-spot 208 459 13429 3.0 17.7477 1.3 0.5630 1.9 0.0725 1.4 0.73 451.2 6.1 453.5 7.0 465.0 28.8 451.2 6.1 97.0 1.4% sa1115v-spot 190 1600 89385 3.4 17.5247 0.9 0.5745 1.6 0.0730 1.3 0.84 454.5 5.9 460.9 5.9 493.0 19.1 454.5 5.9 92.2 1.3% sa1115v-spot 153 1731 19176 2.0 17.4834 0.9 0.5789 1.5 0.0734 1.2 0.78 456.8 5.1 463.7 5.5 498.2 20.6 456.8 5.1 91.7 1.1% sa1115v-spot 253 4275 511143 2.5 16.6233 1.0 0.6121 2.1 0.0738 1.8 0.87 459.2 8.2 484.9 8.2 608.2 22.6 459.2 8.2 75.5 1.8% sa1115v-spot 157 160 5037 1.3 18.3682 1.5 0.5587 2.0 0.0745 1.2 0.64 463.0 5.6 450.7 7.1 388.4 33.9 463.0 5.6 119.2 1.2% sa1115v-spot 181 448 1287577 1.4 17.2714 1.1 0.6017 1.4 0.0754 0.8 0.61 468.6 3.8 478.3 5.2 525.0 23.7 468.6 3.8 89.3 0.8% sa1115v-spot 203 688 31624 0.8 17.8539 1.0 0.5833 1.9 0.0756 1.6 0.84 469.6 7.4 466.6 7.2 451.8 23.3 469.6 7.4 103.9 1.6% sa1115v-spot 252 377 28923 1.4 17.9049 0.8 0.6006 1.7 0.0780 1.5 0.88 484.3 7.1 477.6 6.6 445.5 18.2 484.3 7.1 108.7 1.5% sa1115v-spot 264 357 16720 3.9 15.9323 1.1 0.7303 1.7 0.0844 1.3 0.76 522.4 6.6 556.7 7.4 699.3 24.1 522.4 6.6 74.7 1.3% sa1115v-spot 149 351 9312 1.7 17.6070 0.8 0.6739 1.7 0.0861 1.5 0.89 532.4 7.7 523.1 6.9 482.7 17.1 532.4 7.7 110.3 1.4% sa1115v-spot 156 319 16864 0.9 16.8724 1.1 0.7101 2.0 0.0869 1.6 0.83 537.4 8.3 544.8 8.2 576.0 23.9 537.4 8.3 93.3 1.5% sa1115v-spot 194 836 15956 1.8 16.2727 1.2 0.7655 2.0 0.0904 1.6 0.80 557.8 8.4 577.2 8.6 654.2 25.1 557.8 8.4 85.3 1.5% sa1115v-spot 135 1574 77811 0.7 16.9735 0.9 0.7644 1.4 0.0941 1.1 0.77 580.0 6.1 576.6 6.2 563.0 19.6 580.0 6.1 103.0 1.0% sa1115v-spot 201 345 175552 2.5 16.6939 1.2 0.7859 1.8 0.0952 1.3 0.76 586.2 7.5 588.8 7.9 599.1 25.0 586.2 7.5 97.8 1.3% sa1115v-spot 128 515 45611 2.2 16.7973 0.9 0.7817 1.5 0.0953 1.3 0.82 586.7 7.1 586.5 6.9 585.7 18.9 586.7 7.1 100.2 1.2% sa1115v-spot 265 191 4769 1.5 17.1164 2.7 0.7761 3.0 0.0964 1.3 0.43 593.2 7.4 583.3 13.4 544.7 59.5 593.2 7.4 108.9 1.2% sa1115v-spot 129 460 49162 1.2 16.5614 0.8 0.8043 1.5 0.0967 1.3 0.86 594.8 7.2 599.3 6.7 616.3 16.6 594.8 7.2 96.5 1.2% sa1115v-spot 171 382 14396 0.4 16.8036 1.0 0.7939 1.8 0.0968 1.5 0.82 595.6 8.4 593.4 8.1 584.9 22.3 595.6 8.4 101.8 1.4% sa1115v-spot 193 123 4580 1.5 17.9295 1.5 0.7479 2.0 0.0973 1.2 0.63 598.5 7.1 567.0 8.5 442.4 33.6 598.5 7.1 135.3 1.2% sa1115v-spot 259 114 4227 2.5 17.4932 1.3 0.7709 2.1 0.0979 1.6 0.77 601.8 9.3 580.3 9.2 497.0 29.1 601.8 9.3 121.1 1.5% sa1115v-spot 141 964 74957 2.4 16.4026 0.8 0.8260 1.6 0.0983 1.4 0.86 604.5 8.1 611.4 7.5 637.1 17.6 604.5 8.1 94.9 1.3% sa1115v-spot 127 1199 60209 23.9 15.4260 1.1 0.9051 1.8 0.1013 1.5 0.79 622.1 8.6 654.4 8.9 767.7 23.9 622.1 8.6 81.0 1.4% sa1115v-spot 225 314 30289 2.8 14.8728 1.1 0.9444 1.9 0.1019 1.5 0.79 625.6 8.8 675.2 9.2 844.2 23.5 625.6 8.8 74.1 1.4% sa1115v-spot 245 446 37750 1.0 16.4345 1.0 0.8657 1.7 0.1032 1.4 0.82 633.3 8.4 633.3 8.0 632.9 21.2 633.3 8.4 100.1 1.3% sa1115v-spot 216 398 28362 4.0 16.3609 1.1 0.8828 2.1 0.1048 1.8 0.86 642.5 11.1 642.5 10.0 642.6 22.9 642.5 11.1 100.0 1.7% sa1115v-spot 186 240 4613 1.3 16.6940 2.9 0.8839 3.3 0.1071 1.5 0.45 655.7 9.3 643.1 15.7 599.1 63.5 655.7 9.3 109.4 1.4% sa1115v-spot 179 25 1438 1.5 17.9264 2.8 0.8255 3.3 0.1074 1.8 0.54 657.5 11.3 611.1 15.3 442.8 62.5 657.5 11.3 148.5 1.7% sa1115v-spot 124 82 17181 2.7 15.5844 1.4 1.0319 1.7 0.1167 1.0 0.58 711.4 6.6 719.9 8.8 746.2 29.6 711.4 6.6 95.3 0.9% sa1115v-spot 255 197 62984 2.8 14.9916 1.0 1.1885 1.8 0.1293 1.5 0.83 783.8 11.0 795.3 9.9 827.6 21.2 783.8 11.0 94.7 1.4% sa1115v-spot 188 296 30579 1.7 14.8822 1.1 1.2280 2.0 0.1326 1.7 0.83 802.7 12.8 813.4 11.5 842.9 23.7 802.7 12.8 95.2 1.6% sa1115v-spot 228 257 39398 2.3 14.2170 1.3 1.5060 1.9 0.1554 1.4 0.74 930.9 12.3 932.8 11.6 937.3 26.2 937.3 26.2 99.3 2.8% sa1115v-spot 210 146 34587 1.6 13.7930 0.9 1.7645 1.8 0.1766 1.5 0.85 1048.3 14.5 1032.5 11.4 999.1 18.8 999.1 18.8 104.9 1.9% sa1115v-spot 258 128 20216 1.4 13.6473 1.1 1.7392 1.9 0.1722 1.6 0.82 1024.3 14.8 1023.2 12.3 1020.7 22.3 1020.7 22.3 100.4 2.2% sa1115v-spot 185 475 198357 3.3 13.6044 0.9 1.6949 1.4 0.1673 1.1 0.79 997.3 10.4 1006.6 9.1 1027.0 17.5 1027.0 17.5 97.1 1.7% sa1115v-spot 250 529 37358 2.0 13.5462 1.0 1.7902 1.8 0.1760 1.5 0.84 1044.9 14.8 1041.9 11.9 1035.7 20.1 1035.7 20.1 100.9 1.9% sa1115v-spot 161 397 62401 2.0 13.5270 1.1 1.7472 1.7 0.1715 1.3 0.76 1020.3 11.9 1026.1 10.7 1038.6 21.8 1038.6 21.8 98.2 2.1% sa1115v-spot 256 399 23581 2.4 13.4185 1.0 1.8198 1.8 0.1772 1.4 0.82 1051.6 14.0 1052.6 11.6 1054.8 20.7 1054.8 20.7 99.7 2.0% sa1115v-spot 226 1102 41545 49.5 13.1966 0.9 1.8864 1.8 0.1806 1.6 0.87 1070.4 15.7 1076.3 12.2 1088.3 18.4 1088.3 18.4 98.4 1.7% sa1115v-spot 241 156 31742 3.0 13.1920 1.1 1.8817 1.8 0.1801 1.4 0.77 1067.6 13.5 1074.7 11.8 1089.0 22.7 1089.0 22.7 98.0 2.1% sa1115v-spot 233 774 106741 3.6 12.9457 0.7 2.0521 1.7 0.1928 1.5 0.91 1136.3 15.6 1133.0 11.3 1126.7 14.0 1126.7 14.0 100.9 1.2% sa1115v-spot 205 148 59406 139.7 12.9144 0.9 1.9332 1.6 0.1812 1.3 0.81 1073.3 12.4 1092.7 10.4 1131.5 18.2 1131.5 18.2 94.9 1.6% sa1115v-spot 158 630 85174 3.1 12.8136 0.8 2.1278 1.7 0.1978 1.5 0.87 1163.6 16.2 1157.9 12.0 1147.1 16.7 1147.1 16.7 101.4 1.5% sa1115v-spot 243 512 31198 2.4 12.7558 0.8 2.1042 1.5 0.1948 1.3 0.86 1147.1 13.6 1150.2 10.4 1156.0 15.5 1156.0 15.5 99.2 1.3% sa1115v-spot 263 191 11466 3.0 12.4893 1.0 2.2851 1.9 0.2071 1.6 0.85 1213.2 17.5 1207.7 13.2 1197.8 19.7 1197.8 19.7 101.3 1.6% sa1115v-spot 155 463 78592 5.5 12.4626 1.1 2.3379 2.1 0.2114 1.7 0.84 1236.3 19.4 1223.9 14.6 1202.0 22.1 1202.0 22.1 102.9 1.8% sa1115v-spot 219 433 112107 1.0 12.3656 1.2 2.2452 1.8 0.2014 1.3 0.74 1183.1 14.5 1195.3 12.8 1217.4 24.2 1217.4 24.2 97.2 2.0% sa1115v-spot 238 422 32071 2.6 12.2774 1.1 2.2529 1.6 0.2007 1.2 0.72 1179.0 12.8 1197.7 11.6 1231.5 22.2 1231.5 22.2 95.7 1.8% sa1115v-spot 251 67 7690 2.4 11.5897 1.2 2.8234 1.8 0.2374 1.4 0.77 1373.3 17.5 1361.8 13.7 1343.7 22.4 1343.7 22.4 102.2 1.7% sa1115v-spot 137 560 96963 3.7 11.1435 0.7 3.0891 1.7 0.2498 1.6 0.90 1437.3 20.1 1430.0 13.2 1419.1 14.2 1419.1 14.2 101.3 1.0% sa1115v-spot 136 559 192917 3.8 11.1391 0.8 3.1037 1.6 0.2509 1.3 0.84 1442.9 16.9 1433.6 12.0 1419.9 16.2 1419.9 16.2 101.6 1.1% sa1115v-spot 231 205 15158 3.5 10.8777 1.0 3.2014 1.8 0.2527 1.6 0.85 1452.3 20.3 1457.5 14.2 1465.1 18.4 1465.1 18.4 99.1 1.3% sa1115v-spot 147 764 242057 2.2 10.8286 0.8 3.3974 1.8 0.2669 1.6 0.90 1525.2 22.0 1503.8 14.1 1473.7 14.8 1473.7 14.8 103.5 1.0% sa1115v-spot 221 385 128120 2.7 10.6595 0.8 3.3675 1.5 0.2605 1.3 0.83 1492.2 17.0 1496.9 12.0 1503.5 15.9 1503.5 15.9 99.2 1.1% sa1115v-spot 189 122 41731 1.8 10.0635 0.9 4.0059 1.7 0.2925 1.5 0.86 1654.0 21.7 1635.4 14.1 1611.5 16.6 1611.5 16.6 102.6 1.0% sa1115v-spot 214 258 38839 1.9 9.8177 0.8 4.0975 1.4 0.2919 1.1 0.79 1651.0 16.0 1653.8 11.3 1657.4 15.6 1657.4 15.6 99.6 0.9% sa1115v-spot 217 251 6476556 1.6 9.7528 0.9 4.0816 1.7 0.2888 1.4 0.83 1635.7 20.4 1650.6 13.9 1669.7 17.5 1669.7 17.5 98.0 1.1% sa1115v-spot 175 197 20193 1.4 9.6865 0.9 4.1861 1.7 0.2942 1.4 0.84 1662.5 20.3 1671.3 13.5 1682.3 16.6 1682.3 16.6 98.8 1.0% sa1115v-spot 204 141 23556 4.3 9.5610 0.8 4.2941 1.8 0.2979 1.6 0.89 1680.9 23.0 1692.2 14.4 1706.3 14.9 1706.3 14.9 98.5 0.9% sa1115v-spot 234 201 514842 1.1 9.5119 1.0 4.3287 1.9 0.2988 1.5 0.83 1685.1 22.9 1698.8 15.3 1715.8 18.9 1715.8 18.9 98.2 1.1% sa1115v-spot 232 75 5832 1.1 9.2146 1.1 3.7793 1.7 0.2527 1.2 0.74 1452.3 15.9 1588.4 13.4 1774.0 20.5 1774.0 20.5 81.9 1.2% sa1115v-spot 174 94 48050 1.0 9.1675 0.9 4.5282 1.7 0.3012 1.5 0.85 1697.3 22.0 1736.2 14.4 1783.3 16.6 1783.3 16.6 95.2 0.9% sa1115v-spot 202 496 19618 1.6 8.8783 1.0 5.1617 1.7 0.3325 1.3 0.80 1850.5 21.7 1846.3 14.2 1841.5 18.0 1841.5 18.0 100.5 1.0% sa1115v-spot 192 607 77235 3.2 8.1802 1.0 6.0165 1.8 0.3571 1.5 0.84 1968.4 25.3 1978.2 15.4 1988.5 17.1 1988.5 17.1 99.0 0.9% sa1115v-spot 247 200 12360 2.5 8.0214 1.1 6.2632 1.8 0.3645 1.4 0.78 2003.6 23.6 2013.3 15.4 2023.3 19.7 2023.3 19.7 99.0 1.0% sa1115v-spot 187 472 66566 4.5 7.8488 1.1 6.2835 1.9 0.3578 1.5 0.81 1971.9 26.2 2016.2 16.6 2061.7 19.5 2061.7 19.5 95.6 0.9% sa1115v-spot 148 93 16681 0.8 5.5176 0.8 12.4170 1.4 0.4971 1.2 0.81 2601.4 25.2 2636.5 13.6 2663.5 13.9 2663.5 13.9 97.7 0.5% sa1115v-spot 159 141 35039 1.5 5.2525 0.8 13.7688 1.5 0.5247 1.2 0.83 2719.3 27.3 2733.9 14.0 2744.8 13.5 2744.8 13.5 99.1 0.5% *denotes a common-pb-corrected radiogenic value. page &p sheet1 appendix c data table. catims u-pb zircon data of sample jk16-10. sample was collected froma tuff a few meters below burro canyon formation in the upper morrison formation, bears ears national monument, utah. sample location is 37°26'19.03"n ; 109°35'53.96"w. 150.67 ± 0.32 ma concordia age of 5 youngest grains (mswd = 0.11), plus antecrystic and detrital grains. corrected atomic ratios sample weight (µg) u (ppm) pb (ppm) pb (pg) cpb (pg) pb*/pbc th/u 206pb/204pb 208pb/206pb (rad.) 206pb/238uth % error (rad.) 207pb/235u % error (rad.) 207pb/206pbth % error 206/238th age (ma) error 207/235 age (ma) rho elong sd 0.6 634 40.3 24.5 17.0 0.6 0.54 52 0.17 0.02354 (0.4) 0.1577 (5.6) 0.0567 (5.3) 150.01 ±0.65 148.7 0.63 elong si 1.6 165 4.1 6.6 0.3 19.9 0.52 1220 0.16 0.02361 (0.1) 0.1602 (0.9) 0.0574 (0.8) 150.45 ±0.20 150.9 0.38 elong se 2.0 149 3.6 7.2 0.9 7.6 0.48 481 0.15 0.02364 (0.2) 0.1591 (2.2) 0.0575 (2.1) 150.64 ±0.32 149.9 0.46 elong sa 0.5 377 9.4 4.8 0.6 7.6 0.53 473 0.17 0.02367 (0.2) 0.1604 (2.2) 0.0608 (2.1) 150.79 ±0.24 151.1 0.57 euh sc 1.9 399 9.9 19.2 0.6 29.7 0.52 1814 0.17 0.02368 (0.1) 0.1598 (0.6) 0.0571 (0.5) 150.88 ±0.19 150.5 0.36 elong sg 3.4 75 1.9 6.3 1.7 3.8 0.52 249 0.17 0.02374 (0.2) 0.1633 (4.3) 0.0569 (4.1) 151.27 ±0.35 153.6 0.72 elong sb 1.4 196 4.9 6.9 1.1 6.4 0.52 402 0.17 0.02375 (0.2) 0.1611 (2.6) 0.0572 (2.5) 151.30 ±0.26 151.6 0.61 elong sh 0.7 432 10.9 7.8 0.9 8.5 0.55 526 0.18 0.02398 (0.2) 0.1640 (2.0) 0.0574 (2.0) 152.75 ±0.29 154.2 0.48 notes: sample: euh = euhedral, equant; elong = elongate euhedral; s_= single grain. weight: represents estimated weight after first step of catims zircon dissolution and is only approximate. u and pb concentrations are based on this weight and are useful for internal comparisons only. picograms (pg) sample and common pb from the second dissolution step are measured directly however, and are accurate. sample pb: sample pb (radiogenic + initial) corrected for laboratory blank. cpb: total common pb. all was assigned to laboratory blank. pb*/pbc: radiogenic pb to total common pb (blank + initial). corrected atomic ratios: 206pb/204pb corrected for mass discrimination and tracer, all others corrected for blank, mass discrimination, tracer and initial pb, values in parentheses are 2 sigma errors in percent. __th = 206pb/238u and 207pb/206pb ratios and dates corrected for th disequilibrium assuming th/u magma of 2.2. rho: 206pb/238u vs 207pb/235u error correlation coefficient. zircon dissolution and chemistry were adapted from methods developed by krogh (1973), parrish and others (1987) and mattinson (2005). all zircons were chemically abraded (catims). final dissolutions were spiked with a mixed 205pb/233u/235u tracer with silica gel without any ion exchange cleanup; isotopic compositions were measured in single daly-photomultiplier mode on a micromass sector 54 thermal ionization (et535). pb and uo2 from zircons were loaded onto single rhenium filaments mass spectrometer at the university of wyoming. mass discrimination for pb was 0.245 ± 0.10 %/amu for daly analyses based on replicate analyses of nist srm 981. u fractionation was determined internally during each run. measured procedural blanks ranged from 2 to 0.38 pg pb during the course of the study. u blanks were consistently less than 0.1 pg. isotopic composition of the pb blank was measured as 18.649 ± 0.403, 15.540 ± 0.48, and 37.804 ± 1.69 for 206/204, 207/204 and 208/204, respectively. concordia coordinates, intercepts, uncertainties and cooncrdia ages were calculated using pbmacdat and isoplot programs (based on ludwig 1988, 1991, 1998); 206pb/238u and 207pb/206pb ratios and dates corrected for th disequilibrium assuming th/u magma of 2.2 following schärer (1984). the decay constants used by pbmacdat are those recommended by the i.u.g.s. subcommission on geochronology (steiger and jäger, 1977): 0.155125 x 10-9/yr for 238u, 0.98485 x 10-9/yr for 235u and present-day 238u/235u = 137.88. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america gregory s. paul geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover the color rendering of utetitan zellaguymondeweyae in its habitat. same scale comparison of mature (scaled to usnm 15560) and juvenile (scaled to tmm 43621) skeletal restorations of generalized composite north american maastrichtian titanosaurids. scale bar equals 2 m. illustrattions by gregory s. paul. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 12 2025 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2024–2025 uga board president keilee higgs keileeann@utah.gov 801.678.3683 president-elect rob buehring robbuehring@yahoo.com 713.412.9269 program chair mike arnoff marnoff@utah.gov 385.303.0431 treasurer will hurlbut wdhurlbut@gmail.com 860.733.3190 secretary trae boman tboman@teanues.com 801.648.5206 past president eugene syzmanski eugenes@utah.gov 801.537.3364 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greggavin@gmail.com 513.509.1509 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.580.1331 aapg house of delegates 2023–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor william lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 201 abstract after the return of giant sauropod dinosaurs in the form of titanosaurids to north america in the campanian of the late cretaceous, alamosaurus sanjuanensis is generally considered to have been the sole taxon on the continent over a few million years. the possibility of one species existing that long is very low because sauropods often exhibit taxonomic diversity in the same habitat. the fossils from the southwestern states and northern mexico are all incomplete, overlapping elements are often scarce, and sometimes differ in ontogenetic development. the fragmentary new mexican a. sanjuanensis material from the early maastrichtian lower ojo alamo formation shows significant distinctions from the much later partial skeletons from the late maastrichtian lower north horn formation of utah. the latter is therefore made the holotype of utetitan zellaguymondeweyae. some late maastrichtian texas fossils can be assigned to u. zellaguymondeweyae, others cannot. fossils from the middle campanian cannot be assigned to either genus. southwestern north america supported a diversity of titanosaurids, which may have formed a utetitan miniclade as they evolved in semi-isolation from the global titanosaurid fauna. past calculations that these titanosaurids were among the most massive in the group are not borne out by scaling of skeletal restorations. stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america gregory s. paul baltimore, md 21218 usa; gsp1954@aol.com citation for this article. paul, g.s., 2025, stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america: geology of the intermountain west, v. 12, p. 201–220, https://doi.org/10.31711/giw.v12.pp201-220. introduction after an absence from the fossil record of north america over most of the late cretaceous, sauropod dinosaurs returned to the southwestern part of the continent in the campanian in the form of the only sauropod clade extant by then, titanosaurids (d’emic, 2010, see below). it has long been widely presumed to varying degrees of confidence that all fossil juvenile to adult titanosaurid specimens (figure 1) from new mexico, utah, texas, and chihuahua (figures 2 and 3), none of which preserved the majority of the individual, represent one species, alamosaurus sanjuanensis (gilmore, 1922, 1946; lawson, 1972; mateer 1976; wolberg et al., 1986; lucas and hunt, 1989; lehman and coulson, 2002; woodward, 2005; lehman et al., 2006; rivera-sylva et al., 2006; d’emic et al., 2010, 2011; fowler and sullivan, 2011; jasinski et al., 2011; wick and lehman, 2014; carrano and d’emic, 2015; curtice, 2016; tykoski and fiorillo, 2017)—or at least the one genus, the exact taxonomic intent is not always clear in these papers. the holotype of the taxon is an incomplete scapula, supported by a paratype pubis that probably does not belong to the same individual. a number of other fossil remains ranging from fragmentary to a major minority of a skeleton have been assigned to the other species. a rare expression of skepticism of the single taxon hypothesis has been lucas and sullivan (2000) whose analysis 202 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 figure 1. same scale comparison of postcranial elements of maastrichtian north american titanosaurids, entire bar equals 1 m (this figure is more accurate to a common scale than figure 5 in d’emic et al., 2011), appendicular elements are from the left side (reversed when necessary), dotted lines indicate missing bone, arrows point to taxonomic characters discussed in text and listed in diagnoses as numbered; traced from published images as indicated. (a) scapulae in lateral view: left, early maastrichtian alamosaurus sanjuanensis holotype usnm 10846 (plate 1 in gilmore, 1922, plate 10 in gilmore, 1946; figure 5c in d’emic et al., 2011, bone is not as complete); middle, latest maastrichtian utetitan zellaguymondeweyae referred bibe 45958 juvenile (figure 12a in tykoski and fiorillo, 2017); right, late maastrichtian u. zellaguymondeweyae holotype usnm 15560 (figure 5d in d’emic et al., 2011, contrast to figure 6 in gilmore, 1946). (b) ischia in anterior view: top, a. sanjuanensis paratype usnm 10847 (plate 2 in gilmore 1922); middle left, late maastrichtian titanosaurid incertae sedis tmm 41541-1 (figure 11b in tykoski and fiorillo, 2017); middle right, late maastrichtian titanosaurid incertae sedis tmm 43621-1 juvenile (figure 9 in lehman and coulson, 2002); bottom, usnm 15560 (figure 11 in gilmore, 1946). (c) mid cervicals in left lateral view left, a. sanjuanensis provisionally referred smp vp-1850 (figure 1a in fowler and sullivan, 2011); right, bibe 45854 (figure 3a in tykoski and fiorillo, 2017). (d) anterior caudals in posterior view; left, a. sanjuanensis provisionally referred smp vp-2104 (figure 2b in fowler and sullivan, 2011); middle, tmm 41541-1 (figure 10c in tykoski and fiorillo, 2017); right, usnm 15560 (plate 8 in gilmore, 1946). 203 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 indicated that alamosaurus sanjuanensis had become a wastebasket taxon for the late cretaceous titanosaurids from the region. fronimos and lehman (2014) and lehman et al. (2018) declined to refer some texas titanosaurid elements to a. sanjuanensis while doing so with others. lozinsky et al. (1984) noted the common tendency to refer late cretaceous north american sauropods to alamosaurus without justification, while doing it themselves. because of the taxonomically deficient nature of the fragmentary a. sanjuanensis holotype usnm 10486, and the lack of sufficient anatomical overlap between the limited titanosaurid fossils from the early maastrichtian lower ojo alamo formation in northwestern new mexico, the species has largely been defined by the utah specimen usnm 15560 partial skeleton, it being the best single specimen available. diagnosing a species based on fossils from a different geographic and stratigraphic location is inherently problematic and must be considered provisional until the systematic unification is verified, or perhaps more probably refuted, on morphological and stratigraphic grounds. while preparing a new edition of a field guide (paul, 2024), it became apparent that a solid verification has not been established regarding alamosaurus, in part because the deep time evolutionary issues have not been adequately addressed in the literature. this brief study is largely limited to assessing whether the pertinent fossils can be confidently assigned to one species, or if they more probably belong to at least two taxa at the species and perhaps genus level. this is not a major examination of larger issues of titanosaurid systematics, phylogeny, or biogeography, the investigation being only that necessary to achieve the basic aims. also examined is the issue of the maximum masses indicated by the larger fossils of these titanosaurids. abbreviations amnh – american museum of natural history, new york city, new york. byu – brigham young university – provo, utah. bibe – big bend national park, texas. nmmnh – new mexico museum of natural history and science, albuquerque, new mexico. pmns – perot museum of nature and science, dallas, texas. figure 2. map of the southwestern states and bordering mexico showing the locations of formations containing late cretaceous titanosaurid fossils, and town of huntington, utah; entire scale bar equals 500 km; ut = utah, nm = new mexico, tx = texas, and ch = chihauhau state (mexico). 204 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 pmu – paleontological museum, uppsala university, uppsala, sweden. smm – science museum of minnesota, saint paul, minnesota. smp – state museum of pennsylvania, harrisburg, pennsylvania. tmm – texas memorial museum, austin, texas. ttu – museum of texas tech university, lubbock, texas. usnm – united states national museum of natural history, washington, d.c. utep – centennial museum at the university of texas at el paso, texas. previous work the titanosaurid fossils from the new mexico, utah, texas and the chihuahua provinces, mexico, have been extensively described and illustrated including with figure 3. stratigraphic chart for north american late cretaceous titanosaurids. ages indicated by vertical dashed lines with placement of selected specimens also indicated—among the latter, those that are oriented vertically are less well dated than those that are oriented horizontally based on references listed in the main text. all formation boundaries (horizontal dotted lines) and levels of most specimens are approximate to varying degrees, sometimes very much so, such as the chh specimen that is from either the upper aguja or lower javelina formations, which apparently have substantial missing sediments between them. the most precisely located fossils are tmm 43621, which is close to cretaceous/paleogene (k/pg) boundary. a javelina formation, from which an uncollected femur (t.m. lehman, texas tech university, written communication, 2025) has an isotopic (u/pb) age of 69 ± ma (lehman et al., 2006). in some locations the top of the javelina is close to the k/pg boundary. in the lower ojo alamo, hall lake, javelina, and north horn formations, the vertical dashed lines incorporate multiple specimens of uncertain exact level. dalman et al. (2024) has obtain an isotopic age of 73 ma (late campanian) from the hall lake formation. 205 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 photographs (gilmore, 1922, 1946; lawson, 1972; mateer, 1976; lucas and hunt, 1989; lucas and sullivan, 2000; lehman and coulson, 2002; rivera-sylva et al., 2006; williamson and weil, 2008; d’emic et al., 2011; fowler and sullivan, 2011; jasinski et al., 2011; fronimos and lehman, 2014; wick and lehman, 2014; tykoski and fiorillo, 2017). the author has seen and examined much of the north american titanosaur material over the decades. element illustrations (figure 1) are traced at large scale directly from published photographs. note that the illustrations of the usnm 15560 scapula in gilmore (1946, figure 6) differs from the actual fossil (figure 5d in d’emic et al., 2011). two photographs of the scapulae are available, but i chose not to include them here because they are medial views of the bones showing their very poorly preserved inner surfaces that no one uses because they are very badly preserved on that side, and therefore useless. there is no point publishing these since high-quality photographs of the lateral surfaces are already in the literature, and there are no good resolution photographs in the files of the smithsonian institution’s museum of natural history in washington, d.c. recent photographs of the usnm 10486 and usnm 15560 scapulae (figures 5c and5d in d’emic et al., 2011) show the bones have been somewhat degraded over the decades (compared to plate 1 in gilmore, 1922, and figure 6 in gilmore, 1946). the new illustrations are the most accurate images of the fossils yet produced. evidence has grown that herbivorous dinosaur species were prone to turning over rapidly, with species typically not lasting more than a few hundreds of thousands of years (ryan and evans, 2005; paul, 2006, 2016, 2024, in press; gates, 2012; scannella et al., 2014; tschopp et al., 2015; mallon, 2017, 2019). the same studies also often found that a given herbivorous dinosaur family can exhibit diversity at the same level in a particular formation, including sauropods. even taking possible over splitting of taxa into account, differing stratigraphic levels each feature an array of diplodocid, camarasaurid, and brachiosaurids, and the same is true of titanosaurids in the adamantina, lower allen, lower and upper anacleto, lower bajo barreal, huincul, portezuelo and rio neuguen formations of south america (weishampel et al., 2004; tschopp et al., 2015; paul, 2016, 2024, in press). the possibility that just one titanosaur taxon inhabited the entirety of the north american southwest during most of the maastrichtian is correspondingly quite low and nonparsimonious. a factor in the fast and diverse evolution of dinosaur taxa may have a genetic basis due to high chromosome numbers that remain operative in the many thousands of species of modern birds (o’connor et al., 2018). the rapid, r-strategy reproduction of giant dinosaurs depositing large numbers of their small eggs may have also favored swift evolution and diversification compared to calf dropping k-strategy breeding big mammals. it is therefore presumed that if fossils are separated by more than a few hundred thousand years that they probably are different species, unless strong evidence indicates otherwise. the latter includes near identical morphology of overlapping elements as further discussed below. nor can it be presumed that incomplete specimens found at the same stratigraphic level of a formation from a given family represent one species—unless found in very close association—rather than being from more than one taxon. any conclusion one way or another on north american titanosaur diversity needs to be based on the preponderance of the data. consisting of multiple species, genera can last over long stratigraphic periods. yet gradistic anatomical differences may favor generic separation, even if the taxa are closely related to one another relative to other known fossil members of the taxonomic family. there is a good probability that gaps in the fossil record make two dinosaur species appear to be sibling taxa on a phylogenetic chart when they actually are separated by a number of intra subfamily species that created considerable gradistic space not readily accommodated in one genus. in order to provide more clarity regarding these issues and tighten up the taxonomic specifics, diagnoses based on a substantial number of specimens of the pertinent taxa are used to determine the species on a gradistic basis. this comparative anatomy approach is similar to work by chure and loewen (2022), danison et al. (2024), and paul (2025), who do not include statistical or phylogenetic analysis among fossils that are obviously closely related, but different enough to be divided at the genus and/or species levels. 206 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 an in-depth phylogenetic analysis of titanosaurids is far beyond the scope of this modest study. nor would such likely to be productive because the differences between the late cretaceous north american specimens is of the modest degree expected within a subfamily that had been evolving with some degree of isolation from other titanosaurs in south america and/or asia, probably forming a mini-clade. the north american specimens are too few and incomplete to produce phylogenetic results reliable enough to improve the taxonomy on the existing limited data base (as per the fossils examined in danison et al., 2024). all specimens this researcher is aware of are listed and characterized in systematics, with primary data and illustration sources noted. overcoming evidence for taxonomic distinction at the species level between members of a subfamily, despite a large separation in time, requires that the fossils be very similar in form in all details of the crania and postcrania, as is a norm within species at a given ontogenetic stage (paul, 2025). an exception is strong sexual dimorphism, but that has not been observed among dinosaurs (mallon, 2017). determining this norm for sauropod scapulae is aided by a sample of a number of such elements, all little distorted, for adult camarasaurus supremus, all found from the same quarry (osborn and mook, 1921; figure 4); a badly distorted subadult scapula (figure 76 in osborn and mook, 1921) is excluded. aside from some possinle slight alterations due to minor distortion, none of the scapulae are markedly divergent in configuration. they share the same basic distinctive profile. this includes the prominence and shape of the large acromion process. and a prominent triangular glenoid process. if divergence in the north american titanosaur scapulae is greater than in c. supremus, especially from specimens from differing stratigraphic levels, then that is evidence they do not represent a united taxon. paul (1997, 2016, 2024, in press), larramendi (2016), and brassey (2017) detail the methods for restoring skeletons and body masses via volumetric models, with paul (2019) focusing on the broad bellied titanosaurids, including specimens assigned to alamosaurus. larramendi et al. (2021) modified the results with higher specific gravity values of 0.96, except for the sauropod pneumatic neck at 0.85. because the fossil remains are so incomplete, an approximate composite restoration of the collective maastrichtian north american titanosaurids is all that can be prepared (figure 5), which is then scaled to the most widely shared size class of large specimens, as well as a juvenile, with some modifications in each to represent their different growth stages based in part on age specific data from lehman and coulson (2002) and tykoski and fiorillo (2017). that the restorations are composites based on incomplete fossils renders the resulting mass estimates more approximate than those based on more completely known taxa. their composite natures also mean that there is not mass to dimensions allometric scaling between growth stages that may have existed, other than the head of the juvenile is rendered a little larger in relation to the rest of the animal. late cretaceous north american titanosaurid stratigraphy although substantial uncertainties exist in some cases, there is broad consensus regarding the general ages of the beds containing late cretaceous north american titanosaurid fossils (table 1, figures 2 and 3). a fossil from the upper aguja formation or the lower javenila formation in the northeastern chihuahua province, mexico, is late campanian or early maastrichtian (woodward and lehman, 2005; rivera-sylva et al., 2006; rivera-sylva and carpenter, 2014; h.e. rivera-sylva, national autonomous university of mexico, written communication, 2024). their boundaries apparently being a major nonconformity (fowler, 2017), there appears to be a significant time gap between the top of aguja and the base of the javelina formations. if the specimen is from the javelina formation, it may be the earliest known of the north american titanosaurs, dating from near the end of the campanian. if so, its southerly location may reflect the migration of titanosaurs from the south. probably deposited over a short period of time, the thin naashoibito section of the lower ojo alamo formation in northwestern new mexico preserved the a. sanjuanensis types and numerous other specimens. the absence of lambeosaurine hadrosaur 207 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 fossils precludes a late maastrichtian age as explained by jasinski et al. (2011). fowler (2017) provisionally places the sediments at 70 ma based on a disputed radiometric result that is discussed. assertions that a 69-million-year age for texas titanosaurid fossils assigned to a. sanjuanensis (as per lehman et al., 2006) show that the ojo alamo types are about that age (as per jasinski et al., 2011) but cannot be verified because the very fragmentary easterly material is not taxonomically determinate. for example, lehman et al. (2006) assign nondiagnostic texas titanosaurid material to a. sanjuanensis covering a taxonomically improbably long time span of 3 million years. also not temporally informative is a large tyrannosaurid scapula-coracoid (jasinki et al. 2011) because gigantic members of the group do not belong to the latest maastrichtian species of tyrannosaurus (paul, 2025), which are known from the late campanian (stein and triebold, 2013; dalman et al., 2024). the apparently middle maastrichtian middle section of the hall lake formation of southern new mexico (amato et al., 2017; dalman et al., 2022, 2024) contains fragmentary fossil remains (lozinsky et al. 1984; wolberg et al. 1986; also see the systematic paleontology section in this article). the lower north horn formation of the wasatch plateau of central utah produced usnm 15560 and a few other titanosaur elements. this part of the formation being shallower relative to the cretaceous/paleogene (k/pg) boundary than it is elsewhere, the fossils are later late maastrichtian, with the titanosaurid specimens not yet known from particularly close to the cretaceous-paleogene boundary (figure 3 in lawton et al., 1993; cifelli et al., 1999; difley and ekdale, 1999; sampson and loewen, 2005; difley, 2007; d’emic et al., 2010; jasinski et al., 2011; curtice, 2016). the presence of a giant tyrannosaurid in the north horn formation in the same location at usnm 15560 is suggestive of such an age, but not entirely definitive as noted above. also, the specimen of concern (sampson and loewen, 2005) consists of only two temporal cranial elements that are not sufficiently diagnostic at the genus level to be of stratigraphic value regarding taxonomic identification (paul, 2025). missing from the specimen is the taxonomically critical lacrimal. that bone does not bear a hornlet that is found only in tyrannosaurus among american tyrannosaurids. thus, lacking that element, the fossil cannot be shown to be a tyrannosaurus. being from significantly different levels of the maastrichtian, specimens usnm 10846 and usnm 15560 are therefore separated by a few million years. the southwestern texas big bend and nearby chihuahua region javelina and lower black peaks formations feature fairly abundant titanosaurids that range figure 4. same scale comparison of undistorted adult camarasaurus supremus amnh scapulae from the upper morrison formation (late jurassic) cope quarry at garden park, colorado; bar equals 1 m. shown as lefts (reversed when necessary). based on figures 74, 75, 77, 79, and 80 in osborn and mook (1921) and personal observation. (a) 5760/3, (b) 5761/4, (c) 5761/5, (d) 5761/1, and (e) 5761/4. 208 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 from perhaps the later early to late maastrichtian, with some in the black peaks very close to the k/pg boundary (lehman and coulson, 2002; woodward, 2005; lehman et al., 2006; rivera-sylva and carpenter, 2014; fowler, 2017). part of the top of the javelina is also very late maastrichtian, although it does not necessarily reach the k/pg boundary (caitlin et al., 2018; lehman et al., 2022). late cretaceous titanosaurids were present in north america for 5 to perhaps 6 million years (figure 3). that is abundant time for taxa to experience substantial evolution, especially at the species level. the possibility that one species lasted even half that long is hardly tenable—a million years for a species would be a bioevolutionary stretch. a genus being present for 5 million years is plausible but not necessarily probable. because the upper javelina and lower black peaks formations that contain titanosaurids are late maastrichtian (lehman and coulson, 2002; tykoski and fiorillo, 2017), they are good potential candidates for being the same taxon as specimen usnm 15560, but that still requires comparative osteological confirmation. imprecise dating of the ojo alamo fossils especially and also of the north horn formation in utah and some texas and mexican material (as per wick and lehman, 2013), leaves most of the information on the stratigraphic chart (figure 3) approximate. however, exacting stratigraphic placement is not necessary regarding the issues at hand because the only two named taxa are based on type materials with 3 to 4 million years between them. results and discussion that the new mexican a. sanjuanensis holotype and paratypes usnm 10846 and usnm 10847 were found about 300 m from one another (gilmore, 1922) disfavors figure 5. same scale comparison of mature (scaled to usnm 15560) and juvenile (scaled to tmm 43621) skeletal restorations of generalized composite north american maastrichtian titanosaurids; scale bar equals 2 m. 209 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 their being from the same individual. that the paratype ischium appears to be too small to belong to the same animal as the large scapula (figures 1a and 1b) increases the probability that the two specimens, usnm 10846 and usnm 10847, are from two individuals. because the scapula is missing some parts from the holotype (figure 1a), the species is dangerously close to being a nomen dubium (doubtful name) (lucas and sullivan, 2000). the standard titanosaurid form paratype ischium (figure 1b), that may or may not be the same species, does little to improve the taxonomic understanding of lower ojo alamo formation’s titanosaurids. the same applies to additional fragmentary and usually badly damaged titanosaurid fossil remains from the same level of the ojo alamo formation—the aft end of a cervical (figure 1c), an anterior caudal (figure 1d), a distal femur, a fairly complete pes, and numerous other elements (d’emic et al., 2011; fowler and sullivan, 2011; jasinski et al., 2011). it therefore is not known how many taxa are represented by these nonoverlapping fossils, contrary to jasinski et al. (2011) who insist on a presumption of one taxon while not noting that multiple titanosaurid and formation location age specimen lower black peaks west texas latest maastrichtian bibe 45854, 45958; tmm 43621-1 lower north horn central utah late maastrichtian usnm 15560 (utetitan holotype), byu 9087, 11392, 11393 upper javelina west texas middle to late maastrichtian amnh 21531; tmm 41541-1 middle javelina west texas middle to late maastrichtian tmm 46052-1 lower javelina west texas, northeastern chihuahua province middle to late maastrichtian tmm 40699, 41060, 41061, 41398-12, 41450-1-2; ttu 542, 546; utep p-25, uncataloged chihuahua fossil remains javelina (stratigraphic position was not available) west texas middle to late maastrichtian tmm 40597-5, 41063, 41396-1, 41541, 42495-7, 43090-2, 43598-1-6, 43599-1-3, 45601-1, 45602-1, 458541-8, 45855-1-4, 45856-1, 45857-1, 45859-1, 45861-1, 45862-1, 45863-1, 45864-1, 45865-1, 45888-1, 458901&2, 45891-1-17, 45864-1 middle hall lake southern new mexico middle maastrichtian tkm 007, 009 lower ojo alamo northwestern chihuahua early maastrichtian usnm 10846 (alamosaurus holotype), 10847, 15658; nmmnh 22544, 25072, 25077, 25077, 27291, 28741, 29031, 29722, 29723, 29724, 29725, 29726, 29727, 29728, 49967; pmu 24305, 24893; smp vp 1097, 1136, 1138, 1139, 1271, 1494, 1539, 1541, 1581, 1625, 1626, 1641, 1715, 1718, 1850, 1864, 1866, 1876, 2043, 2065, 2097, 2104, 2175, 2230, 2233, 2507, 2696, 3323, ssm 5428 upper aguja or lower javelina northeastern chihuahua late campanian or early maastrichtian uncataloged tibia table 1. north american titanosaur-bearing formations and their usually approximate stage ages and fossil contents; see systematics for additional information. 210 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 other sauropod taxa often inhabit the same habitats. found on the eastern rim of joe’s valley in utah’s wasatch plateau, usnm 15560 is the most complete north american latest cretaceous titanosaurid specimen (gilmore, 1946). because its scapula is a little smaller than that of specimen usnm 10846 (figure 1a), usnm 15560 was probably somewhat lesser sized in life. specimen usnm 15560 ischium is about the same size as that of specimen usnm 10847, which indicates that those two dinosaurs were similar in overall dimensions (figure 1b). thus, it is not clear whether the utah dinosaur was somewhat smaller in life than the new mexico dinosaur or about the same size. importantly, the usnm 15560 scapula is well preserved. its acromion process point is markedly more prominent than that of a. sanjuanensis usnm 10846 (figure 1a). d’emic et al. (2011) seem to attribute the differences of the two specimens to distortion of usnm 15560, but the exact basis of this assertion is not documented. i have examined the specimens and did not observe any distortion after directly comparing the two bones. the latter has a markedly deeper indentation in the profile of the posterior edge immediately dorsal to the glenoid (gilmore, 1946), resulting in a prominent triangular glenoid process similar to that of some c. supremus (figure 2). these divergences on their own are not in good accord with taxonomic synonymy. the paired tubercles just above the posterior indentation cited as evidence for conspecifity by d’emic et al. (2011) are widely separated and quite prominent on the utah scapula despite its not being a larger animal. their presence on usnm 10846 is at most marginal if they are true morphological features. they are not widely spaced, and such structures are present on some other titanosaurids from other regions and geologic ages (d’emic et al., 2011). these structures are consequently not necessarily species specific diagnostic characters, contrary to d’emic et al. (2011) and tykoski and fiorillo (2017). instead, they are different enough to help define at least two species, if not genera. the same comments apply to the both similar but also different dorsal flaring of the scapula blades cited as taxonomically significant by d’emic et al. (2011) and tykoski and fiorillo (2017), that of specimen usnm 15560 being greater than that of specimen usnm 10846. the cumulative differences between the two usnm scapulae are readily seen to markedly exceed that observed between the five camarasaur scapulae from one quarry (compare figures 1a and 1b to figures 4a through 4e). so much so that usnm 15560 looks somewhat like a camarasaur scapula; usnm 10846 is not close to having such a shape. far from sharing the sufficient anatomical uniformity to surmount the stratigraphic differential, the morphological divergences are sufficient to indicate two different taxa even if the bones were found at the same level of the same formation. a badly damaged immature ojo alamo scapula (jasinski et al., 2011) does not have a prominent acromion process, paired tubercles, or ventroposterior indentation in accordance with the a. sanjuanensis holotype. of great interest is the juvenile ventral scapula bibe 45958, which is a near perfect match in the relative strong prominence and form of the acromion process, the strong indentation just above the glenoid resulting in a substantial triangular glenoid process, and very similar development and placement of the two tubercles compared to the much larger usnm 15560. the two elements are so alike that specimen bibe 45958 looks like the juvenile of the same specimen as usnm 15560 despite the geographic distance between them. both are markedly different from specimen usnm 10846 found in new mexico. such a close similarity between these two late maastrichtian specimens reinforces the probability that shared characteristics are genetically determined, and therefore of taxonomic significance. thus, specimen bibe 45958 can be confidently assigned to the same taxon as contemporary specimen usnm 15560, but not to the geologically earlier specimen usnm 10846. the claims by d’emic et al. (2011) and tykoski and fiorillo (2017) that four ischia are similar in form are not correct, they are all divergent from one another (figure 1b). specimens usnm 10847 and tmm 41541-1 have distinctly longer lateral processes relative to midline length than does specimen usnm 15560, and the first two have far deeper and more subcircular concave arcs to their postero-lateral edge profiles. specimen tmm 41541-1 is more curved than specimen usnm 15560. there is, therefore, no reason to conclude these pelvic 211 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 bones are indicative of just one or even just two taxa. the same applies to the north american titanosaur ilia and pubes. the elements of a large individual from the late maastrichtian black peaks formation are very different from those of a similar sized, much earlier fossil from the lower javelina formation (figure 7 in fronimos and lehman, 2014). the younger example has a pubic peduncle about half the length of, yet more massive than, that of the other, and the shapes of the anterior and aft ilial plates are quite distinctive. the latter maastrichtian pubis has a longer and more gracile ventral process than its older counterpart. these two specimens could easily represent different genera, with the earlier possibly being alamosaurus, although not necessarily a. sanjuanensis. complicating matters is another black peaks formation ilium (figure 8 in lehman and coulson, 2002), which is different in all respects from the other two titanosaurids. its anterior plate is shallower and the posterior plate deeper. meanwhile the pubic peduncle is very long like the earlier potential alamosaurus, and very divergent from the short process of the contemporary ilium. that means two terminal maastrichtian regional titanosaurid taxa is possible. that the three ilia appear to share an indentation on the dorsal rim may indicate an alliance within a common titanosaurid subclade. the relative proportions and shape of the texas juvenile tmm 43621-1 ischium is more similar to that of the a. sanjuanensis paratype and specimen tmm 41541-1 than to specimen usnm 15560, but the juvenile status of the first obscures the systematic significance of this observation (figure 1b). the anterior caudals of specimen usnm 15560 from utah are not in close accord with those of either earlier new mexico specimen smp vp-2104, or similar texas specimen tmm 41541-1. the latter two having a broader centrum relative to their own heights (figure 1e). it is possible that the differences are due to ontogenetic changes, smp vp-204 and tmm 41541-1 being larger than usnm 15560, but that is speculative. proximal ends of a humerus and femur from the north horn formation are close to usnm 15560, but do not belong to that specimen (curtice, 2016). a titanosaurid femur and humerus are present in the correlative mcrae formation of southern new mexico (lozinsky et al., 1985; wolberg et al., 1986), and a number of humeri and femora, many complete or close to it, from juvenile to adult are known from texas (lehman and coulson, 2002; fronimos and lehman, 2014; wick and lehman, 2014). as those researchers have noted, these fossil elements are sufficiently similar enough to represent a single taxon, but they were not definitive at addressing whether the fossils are or not. that may be due to the fossil assemblage greatly differing in the sizes of the specimens due to ontogeny and, in some cases, the bones being incomplete and/or distorted. early maastrichtian ojo alamo formation femora are too incomplete (lucas and sullivan, 2000; fowler and sullivan, 2011) to compare to the late maastrichtian utah and texas specimens, and a humerus from the first locale is not yet known. wick and lehman (2014) observe that two femora from the upper javelina formation are more robust, even though immature, than the three specimens found lower in the formation. that may be of taxonomic significance, although sexual and individual variation cannot be ruled out. the similar size of the ojo alamo and north horn specimens cited by d’emic et al. (2011) as suggestive of one species is not an important taxonomic item in many species being similar in size, which is all the more so because some of the ojo alamo material is markedly larger than anything from the north horn to date (figure 1d; fowler and sullivan, 2011). sexual and individual variations may or may not justify taxonomic synonymy if the specimens were from the same stratigraphic level of the same formation, but in view of their being separated by millions of years the possibility of a monospecies is small. there is not sufficient reason to maintain the ojo alamo and north horn formations’ titanosaurid fossils in the same species, or even genus, with the stratigraphic and morphological data at hand. therefore, taxonomic division is strongly favored. because they lived at the same time or close to it (figure 3), the late maastrichtian utah and texas titanosaurid fossils are candidates for being the same taxon at least at the genus level, but such should not be automatically presumed to avoid the risk of oversimplifying the systematic situation at the end of the cretaceous 212 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 based on the very limited fossil data set. whereas the similarities between the two black peaks ilia favor that they the same taxon perhaps at the species level, their differences with the north horn formation ilium indicate the former and the latter are not the same taxon, probably at the genus level. in contrast, the utah and bibe 45958 scapulae are so extremely alike that they are entirely compatible with the latter being a juvenile of the same species as usnm 15560. that the last two are so alike while being so different from earlier usnm 10846 reinforces the systematic separation of early from end maastrichtian titanosaurids. concerning ontogeny, the small juvenile status of tmm 43621-1 (lehman and coulson, 2002) severely limits its taxonomic utility as a potential type specimen. meanwhile, the great differences in cervical morphology between large (tykoski and fiorillo, 2017) and small (lehman and coulson 2002) may represent differential ontogeny, or systematics, or both. the dorsals of a large specimen (fronimos and lehman, 2018) and a juvenile (lehman and coulson 2002) appear fairly similar, but the size differences, and the disarticulation of the juvenile’s neural spines from the centra, hinder needed anatomical comparisons. the lack of sufficient overlap between the large cervicals described by tykoski and fiorillo (2017) with other latest cretaceous regional titanosaurids means their taxonomic value is currently nil. tmm 43621-1 and bibe 45854 are therefore indeterminate specimens. because the tmm 41541-1 ischium and caudal are so distinct from specimen usnm 15560, they are not readily referable to the same taxon and may be a distinct form. perhaps closer to a. sanjuanensis than usnm 15560, specimen tmm 41541-1 should be considered indeterminate titanosaurid fossils until more information becomes available. two late maastrichtian osteoderms found with utah usnm 15560 (carrano and d’emic, 2015) and from texas (fronimos, 2021) are compatible with their being one taxon, but they do not establish such. nor do they offer comparison to earlier alamosaurus for which no armor is yet known. the suggestions by fronimos and lehman (2018) and lehman et al. (2018) that latest maastrichtian lower blacks peak formation and earlier javelina formation titanosaurids are distinct taxa is sound, but their assignment of the former to the much older a. sanjuanensis is not well founded. even if future information indicates that some of the texas titanosaurids constitute a distinct taxon, none of the known specimens is of holotype quality. the few vertebral, pectoral, and pelvic characters shared by the collective end cretaceous specimens, their geographic isolation from non-north american titanosaurids, and considering genetic drift, suggest north american titanosaurids formed a small clade distinct from other titanosaurids that are diagnosed as a subfamily—a higher level titanosaur taxonomy is currently too unsettled to assign this little group to a larger family. but there is no strong evidence which are considered a subfamily . but there is no strong evidence that they all belong to one species in one genus, such would be probable only if all the southwestern titanosaurids were structurally very similar and came from one narrow stratigraphic level. however, that is far from the actual situation because there is too much time stratigraphic separation (figure 3) and morphological variation (figure 2) between the north american titanosaurids to place them in one species that lasted for millions of years during the maastrichtian or even earlier up to the k/pg crisis in natural selection stasis. therefore, the dinosaurs that dwelled together experienced rapid and extensive darwinian evolution, including the apparent loss of whole clades of north american albertosaurines, lambeosaurines, centrosaurines, and classic chasmosaurines in favor of over-sized tyrannosaurines, edmontosaurines and triceratopsines (paul, 2016, 2024, 2025, in press). no other dinosaur species is currently projected to have lasted so long based on extensive fossil remains. my interpretation is the utah material can be readily differentiated from the new mexico fossils, and at least two taxa need to be recognized, with the understanding that more, perhaps many more, taxa may have been present over that time on the continent. diagnosing the relatively complete usnm 15560 as a holotype is more readily done than for any other north american titanosaurid. the failure to identify usnm 15560 as the basis of a taxon, and using it to help identify the far less adequately characterized a. sanjuanensis, is not 213 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 well advised. the more difficult question is whether the taxonomic separation is just specific or is also generic. continuing to place the north horn formation specimen in alamosaurus is problematic because the genus is founded on such poor material. the differences are substantial, and—very importantly—ongoing congeneric status, risks encouraging the continued use of the ojo alamo and north horn material to define one dubious genus and tossing assorted specimens in a probable genus level taxonomic wastebasket (as per d’emic et al., 2011; tykoski and fiorillo, 2017). so usnm 15560 is designated the holotype of a new genus and species. the generic name recognizes the original peoples of the region, and the specific title honors a centurion resident of the wasatch plateau area in which it was found. a few other incomplete titanosaurid fossil remains from the lower north horn are referred on a tentative basis, but the characters they exhibit should not be used to diagnose the taxon until further comparisons are made. despite living at a similar time, most of the texas specimens are not placed in the new taxon because, in part, they are not sufficiently identifiable at the genus and/or species level, and avoids potentially contaminating the taxon and its identification with dinosaurs from a different horizontal location. this also precludes future taxonomic inertia from leading researchers to presume synonymy as has been the past tendency, rather than more aggressively investigating the taxonomic situation. the new genus is not intended to be another wastebasket taxon for incomplete specimens across the late maastrichtian of the north american southwest. because it is quite possible that more than one titanosaurid lived in the same place at the same time, alamosaurus sanjuanensis is authoritatively identified on the one element that definitely belongs to the taxon, usnm 10846. the characteristics of the paratype ischium are highly tentative, the reference of the specimen to the species being suspect. the other lower ojo alamo formation specimens are referred to a. sanjuanensis on a very provisional basis and need to be considered as potentially distinct taxa as they do not exhibit the diagnostic features and the age is inconclusive. the tibia from chihuahua is a taxonomic floater. the differential identifications are intended to distinguish the north american titanosaur taxa from one another, not from foreign examples. systematic paleontology dinosauria owen 1842 sauropoda marsh 1878 titanosauria bonaparte and coria 1993 utetitaninae n. sf. provisional diagnosis: circumferential depression limited to ventral half of the anterior condyle of biconvex first caudal centrum, multiple large foramina pierce lateral surface of first caudal, paired tubercles dorsal to scapula glenoid, base of blade cross section asymmetrically concave with thinner anterior and thicker posterior margin, antero-dorsal blade edge nearly straight whereas postero-dorsal edge flares posteriorly. small indentation on dorsal rim of ilium. alamosaurus gilmore 1922 type species a. sanjuanensis diagnosis: as for type species alamosaurus sanjuanensis gilmore 1922 holotype: usnm 10846 (nearly complete left scapulacoracoid, gilmore, 1922; figure 1a). paratype: usnm 10847 (nearly complete right ischium, gilmore, 1922; figure 1b). provisional referred specimens: nmmnh p-22544 (proximal and distal right tibia), 25072 (nearly complete left scapula), 25077 (fragmentary right femur) (mateer, 1976), nmmnh 25077 (fragmentary right femur), 27291 (anterior caudal, nmmnh 28741 (partial mid caudal), 29031 (partial caudal), 29722 (partial mid caudal), nmmnh 29723 (partial anterior caudal), nmmnh 29724 (seven tooth fragments), nmmnh 29725 (tooth fragment), nmmnh 29726 (four tooth fragments), nmmnh 29727 (tooth fragment), nmmnh 29728 (tooth fragment), nmmnh 49967 (nearly complete right pes), (lucas and sullivan, 2000; d’jasinski et al., 2011); pmu 24305 (fragmentary right ilium), pmu 24893 (last sacral and first caudal); smp vp 1097 (partial tooth), smp vp 1136 (posterior left ilium), smp vp 1138 (partial left femur), smp vp 1139 214 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 (partial right? pubis), smp vp 1271 (tooth root), smp vp 1494 (2 partial left caudals), smp vp 1539 (partial scapula), smp vp 1541 (skull fragments), smp vp 1581 (distal caudal), smp vp 1625 (distal left femur), smp vp 1626 (nearly complete right fibula), smp vp 1641 (fragmentary dorsal), smp vp 1715 (coracoid and possible associated fragments), smp vp 1718 (fragmentary femur), smp vp 1850 (posterior cervical, figure 1c), smp vp 1864 (partial dorsal), smp vp 1866 (partial dorsal), smp vp 1876 (nearly complete dorsal), smp vp 2043 (proximal tibia), smp vp 2065 (partial tibia), 2097 (partial left ischium, right femur), smp vp 2104 (partial anterior caudal, fragments, figure 1d), smp vp 2175 (distal right radius), smp vp 2230 (nearly complete caudal), smp vp 2232 (partial ribs), smp vp 2233 (anterior right ilium), smp vp 2507 (tooth), smp vp 2696 (chevron, fragments), smp vp 3323 (partial left pubis) (lucas and sullivan, 2000; fowler and sullivan, 2011; jasinski et al. 2011); ssm 5428; usnm 15658 (distal caudal, kues et al., 1980), tkm 007 (nearly complete right humerus), 009 (femur), (lozinsky et al., 1984). location, horizon, age: northwestern new mexico, lower (naashoibito member) ojo alamo formation; southern new mexico? lower hall lake? early maastrichtian. diagnosis: acromion process not strongly prominent (1), posterior profile of scapula gently sinuous so a triangular glenoid process is absent (2), paired tubercles dorsal to glenoid very subtle and closely spaced (3), flare of postero-dorsal edge of blade subtle (4), lateral process of ischium long? (5), postero-lateral profile of ischium has a strong concave subcircular arc? (6). utetitan n.g etymology: after the original ute peoples of central utah upon whose ancient lands the fossil was found. type species u. zellaguymondeweyae n.s. diagnosis: as for type species. utetitan zellaguymondeweyae n.s. etymology: after the author’s maternal grandmother zella guymon dewey (1901–2002), born and raised in huntington, utah, 30 km northeast of the usnm 15560 quarry, who called the wasatch plateau “the hills of home.” shortly after the specimen was excavated her family moved from salt lake valley to the wartime washington, d.c. suburbs a few kilometers from the fossil’s new smithsonian location where i visited with her on occasion. she is buried in arlington national cemetery with her husband william e. dewey (1899–1962). gilmore, 1922 alamosaurus sanjuanensis holotype: usnm 15560 (partial dorsal ribs, caudals 1-30, 25 chevrons, both sternals, right scapula coracoid, humerus, radius, ulna, metacarpus, both ischia, osteoderm, gilmore, 1946). referred specimens: bibe 45958 (partial left scapula (tykoski and fiorillo, 2017); very probably byu 9087 (proximal left humerus and femur, curtice, 2016), byu 11392 (anterior caudal), byu 11393 (anterior caudal), (d’emic et al., 2011). location, horizon, age: central utah, lower north horn formation; west texas, upper javelina? and lower black peaks formations; late maastrichtian. diagnosis: acromion process strongly prominent (1), posterior profile of scapula strongly sinuous so a prominent triangular glenoid process is present (2), paired tubercles dorsal to glenoid fairly prominent and widely separated (3), flare of postero-dorsal edge of blade more prominent (4), lateral process of ischium modest in size (5), postero-lateral profile of ischium moderately concave arced (6), femur robust? middle/late maastrichtian utetitan or titanosaurid incertae sedis: amnh 21531 (right femur, wick and lehman, 2014); bibe 45854 (cervicals 6-14; tykoski and fiorillo 2017), tmm 40597-5 (pubis), tmm 40699 (mid caudal), 41060 (right ilium), tmm 41061 (right rib), tmm 41063 (left pubis), tmm 41396-1, tmm 41398-1-2 (cervical centrum, proximal left humerus), tmm 41450-1 and tmm 41450-2 (1st caudal, right ulna), tmm 41541 (partial posterior cervical, right ischium), tmm 41541-1 (anterior dorsal ribs, 1st caudal), tmm 42495-7 (pubis), tmm 43090-2 (partial femur), tmm 43598-1-6 (partial cervical, nearly complete anterior dorsal, partial dorsal centrum, partial anterior caudals, partial left femur, right metatarsal ii), tmm 43599-1-3 (partial rib, anterior caudal), tmm 215 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 43600-2 (right humerus), tmm 43621-1 (7-8 partial cervicals, 6-7 partial dorsals, partial sacral and sacral rib, left coracoid, left humerus, left ulna, left ilium, left fibula, distal right tibia), tmm 45601-1 (right fibula), tmm 45602-1 (right tibia), tmm 45854-1-8 (rib material), tmm 45855-1-4 (left dorsal rib/s, proximal left scapula, proximal right metacarpal ii?), tmm 45856-1 (left ulna), tmm 45857-1 (partial left humerus), tmm 45859-1 (right femur), tmm 45861-1 (nearly complete left fibula), tmm 45862—1 (partial left ischium), tmm 45863-1 (right humerus), tmm 45864-1 (partial mid caudal), tmm 45865-1 (distal caudal), tmm 458881 (osteoderm, fronimos, 2021), tmm 45890-1 and tmm 45890-2 (nearly complete right tibia, nearly complete right ungual), tmm 45891-1-17 (5 complete and partial dorsals, sacral fragments, partial anterior caudal, transverse process, left and right nearly complete humeri, nearly complete left ilium, fragment of right ilium, nearly complete left pubis, nearly complete left ischium,), tmm 45864-1 (anterior mid-caudal), tmm 46052-1 (nearly complete left femur) (lawson, 1972; woodward and lehman, 2009; fronimos and lehman, 2014; wick and lehman, 2014); ttu 542 (nearly complete right femur, wick and lehman, 2014), ttu 546 (proximal caudal, lehman and coulson, 2002), utep p-25 (nearly complete left femur, wick and lehman, 2014). late campanian and/or early maastrichtian alamosaurus or titanosaurid incertae sedis: uncatalogued chihuahua fossils (right tibia, minority of skeleton, rivera-sylva, 2006; rivera-sylva and carpenter, 2014). skeletal restorations and body mass the large (scaled to usnm 15560, close to usnm 10846, usnm 10847, and tmm 41541) and juvenile (scaled to tmm 43621-1) skeletals (figure 5) are broadly similar to those produced by lehman and coulson (2002), with an improvement that the mature version is able to incorporate the adult cervicals subsequently described by tykoski and fiorillo (2017), and a juvenile partial scapula from the same reference. reliably estimating the relative size of the neck in adults is currently not possible, the large cervical series not being accompanied by more posterior postcranial elements (tykoski and fiorillo, 2017) necessary for cross scaling. the length of the cervical series in the large skeletal is scaled to the same ratio relative to the dorso-sacrals of the juvenile, and that results in a large mature neck. but the quite large bibe 45854 cervicals may favor the neck being a fifth or more longer relative to the body, or they may have been attached to a larger bodied individual. the volume greater than mass results for juvenile tmm 43621-1 is approximately 1.3 mt, the somewhat larger bibe 45958 is approximately 3 mt. the similar sized tmm 46052-1 (femur 1510 mm), usnm 10487, and usnm 15560 are approximately 16 to 17 mt. the larger usnm 10846 is in the range of 20 mt, and still heftier utep p-25 (femur 1675 mm) and tmm 41541 (femur 1730 mm) is 22 to 24 mt. the tmm 41541 mass value is about three quarters the estimate for the specimen based on bone strength factors (lehman and coulson, 2002), which is in fair agreement; although long bone circumferences have a much greater mass estimate error range than do scientifically proportioned volumetric models (paul, 1997, 2019; larramendi, 2016; brassey, 2017; larramendi et al., 2021). a middle cervical, anterior caudal, and femur from the ojo alamo formation have been offered as evidence of much larger putative alamosaurus individuals (fowler and sullivan, 2011). the incomplete nature of all these bones prevents rigorous quantitative comparisons. the cervical is quite large, but the true dimensions of the very fragmentary vertebra (figure 1d) are correspondingly very unclear—the short distance from the posterior rim of the centrum to the postero-lateral end of the wing of the parapophysis suggests the total length was much less than that of the mid cervicals of puertasaurus (figure 1a2 versus 1b2 in fowler and sullivan [2011] sans speculative outlines), which reached 60 to 70 mt as do some other south american titanosaurids (paul, 2019; larramendi et al., 2021; paul and larramendi, 2023). the cervical appears to be similar in size to the more ordinary sized black peaks formation cervical series (figure 1d) in which that big individual may have been in the range of 30 or somewhat more tonnes. the caudal centrum is markedly larger than those of usnm 15560 (figure 1e) 216 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 and is similar in size to that of futalognkosaurus (figures 2b and 2c in fowler and sullivan, 2011), which was approximately 30 mt (paul 2019; larramendi et al., 2021). the large femur also suggests a 30-mt individual, as does the large pes described by d’emic et al. (2011), and the tibia from chihuahua (rivera-sylva et al., 2006). the largest known ojo alamo titanosaurids were 30 mt or little more, which is in general agreement with paul (2019) and larramendi et al. (2021), although higher estimates cannot be ruled out on the limited data on hand. at this time, it appears that neither alamosaurus nor utetitan matched the enormous bulk of south american or indian super titanosaurids and other sauropods of 50 to possibly well over 100 mt (paul, 2019; larramendi et al., 2021; paul and larramendi, 2023). nor can these end mesozoic sauropods said to be the largest known north american sauropods, those being nontitanosaurids known from the late jurassic and early cretaceous (paul, 2019, 2024, in press). but the small north american fossil titanosaurid sample allows for much larger examples having existed. with all the elements used to produce the pmns composite display mount originating from the late maastrichtian the fossil is not alamosaurus. because part of fossil is modeled after usnm 15560 it can be tagged utetitan, although there is a possibility the fossil is at least a species and perhaps generic chimera. it is possible that utetitan did not have as wide a hindlimb gauge as most titanosaurids (wick and lehman, 2014). conclusion the possibility that all the titanosaurids of the late campanian and maastrichtian stages of the north american southwest over the 5 or more million years of the return of sauropods to the continent were just one taxon, especially species—the universal alamosaurus sanjuanensis thesis—is not a systematically viable hypothesis. a closer look at the specimens from the region shows sufficient anatomical diversity to demonstrate that more than one taxon, probably including two known genera, were present over the stratigraphic stage as is to be expected among dinosaurs that are prone to exhibit rapid evolution and diversification starting in the campanian. sauropods in the latter stage were probably one or more distinct indeterminate taxa whose detailed characteristics are not yet known. alamosaurus sanjuanensis was very probably restricted to the early maastrichtian lower ojo alamo formation of new mexico and any lateral regional formations. even then, multiple taxa may have been extant at that time and preserved among the known fossils. additional fossil remains discovered over time may resolve this question. later stage sauropods probably went extinct later in the maastrichtian, possibly after having spawned related taxa via cladogenesis and/or anagenesis. the late maastrichtian lower north horn formation in utah was home to the distinct utetitan zellaguymondeweyae that probably went extinct at the end of the mesozoic. titanosaurids from contemporary lateral formations such as the black peaks formation in texas may be the same species, but more than one titanosaurid taxon was present in the north horn and/or black peaks habitats at that time is at least plausible, if not probable. again, there is a need for additional fossil remains. i suggest that incomplete north american titanosaurid elements not be assigned to a specific taxon unless there are strong anatomical and stratigraphic reasons to do so, if not they should be tagged as enigmatic taxa. with the titanosaurid fossils in alamosaurus spanning millions of years, their biostratigraphic utility is limited to showing that the sediments containing them were latter campanian and maastrichtian. under the new scheme fossil remains that can be assigned to a. sanjuanensis are indicative of early maastrichtian age, those to u. zellaguyondemeya to late in the stage. neither alamosaurus nor utetitan or any close relatives appear to have been much over 20 to 30 mt, which is far short of observed titanosaurid maximums, although higher masses cannot be eliminated. being classic titanosaurids, alamosaurus and utetitan could not have directly descended from much earlier north american sauropods (d’emic et al., 2010). this analysis does not provide any compelling evidence regarding the asian versus south american origin of north american maastrichtian titanosaurids; howev217 stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the late cretaceous (campanian-maastrichtian) of southwestern north america paul, g.s. geology of the intermountain west 2025 volume 12 er, lucas and sullivan (2000) and tykoski and fiorillo (2017) suggest that an improved understanding of the low level taxonomy of the beasts may eventually be productive. the absence of fossil sauropod fossils in alaskan dinosaur-bearing beds (chiarenza et al. 2022)—although there are substantial stratigraphic gaps in the bering land bridge dinosaur fossil record—may be due to the severe climate restricting the food base for the land giants (paul, 2024). additionally, the very large, attenuated necks and tails of sauropods could have precluded the heat retention needed in polar winters. if so, then a south american origin is favored. that once back in north america titanosaurids were just one static taxon for millions of years is not evolutionarily logical. the combination of shared vertebral and pectoral characters of a. sanjuanensis, u. zellaguymondeweyae, and other maastrichtian north american titanosaurids on one hand, along with significant differences between them on the other, indicate that utetitans formed their own small local clade, presumably because of their restricted geographic isolation and experienced darwinian selection that caused them to become anatomically distinct from their foreign ancestors. individuals investigating titanosaurid phylogeny should use the north american fossils with caution, the collective partial fossils represent multiple genera and species that risk complicating cladistic results if they are assumed to represent just one taxon. alamosaurus sanjuanensis was not the last known north american titanosaurid, that was utetitan zellaguymondeweyae, and possibly another taxon or more. acknowledgments thanks go to richard gilreath and matthew carrano (smithsonian institute), and thomas lehman (texas tech university) for providing information on 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stratigraphic distribution of sauropods in the upper cretaceous of the san juan basin, new mexico, with comments on north america’s cretaceous ‘sauropod hiatus’: journal of vertebrate paleontology, v. 28, p. 1218–1223. wolberg, d.l., lozinsky, r.p., and hunt, a.p., 1986, late cretaceous vertebrate paleontology of the mcrae formation, elephant butte area, sierra county, new mexico, in clemons, r.e., king, w.e., mack, g.h., and zidek, j., editors, truth or consequences region: new mexico geological society 37th field conference guidebook, p. 227–234. woodward, h.n., and lehman, t.m., 2005, bone histology of the sauropod dinosaur alamosaurus sanjuanensis from the javelina formation, big bend national park, texas: microscopy and microanalysis, v. 13, p. 508–509. geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah david malone, grace stevens, sarah r. lesmann, tiffany rivera, robert biek, michael braunagel, w. ashley griffith, david hacker, and peter rowley geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover volcaniclastic sandstone and mudstone of the eocene brian head formation at the south end of the sevier plateau. dixie national forest, garfield county, utah. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 12 2025 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2024–2025 uga board president keilee higgs keileeann@utah.gov 801.678.3683 president-elect rob buehring robbuehring@yahoo.com 713.412.9269 program chair mike arnoff marnoff@utah.gov 385.303.0431 treasurer will hurlbut wdhurlbut@gmail.com 860.733.3190 secretary trae boman tboman@teanues.com 801.648.5206 past president eugene syzmanski eugenes@utah.gov 801.537.3364 uga committees environmental affairs craig eaton eaton@ihi-env.com 801.633.9396 geologic road sign greg gavin greggavin@gmail.com 513.509.1509 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.580.1331 aapg house of delegates 2023–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor william lund uga.newsletter@gmail.com 435.590.1338 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair grant willis gwillisgeol@gmail.com 801.537.3355 douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 155 abstract the eocene-oligocene brian head formation is the basal volcanic unit throughout much of the southern marysvale volcanic field but rests atop sevier-laramide synorogenic strata of the claron foreland basin in southern utah. the brian head formation reaches 300 m in thickness and consists of light-colored volcaniclastic sandstone, siltstone, mudstone, and minor conglomerate and airfall tuff; in northern exposures, the upper part locally contains a volcanic section of lava flows, ash-flow tuff, and volcanic mudflow breccia. these rocks were deposited in a slowly aggrading fluvial to lacustrine depositional environment distal to the indian peak caldera complex to the west. we sampled three volcaniclastic sandstone units near the top of the formation, specifically near haycock mountain and along the southern and western flanks of the sevier plateau near casto butte and blind spring mountain. the sandstone beds are compositionally and texturally immature and classify as lithic and arkosic wacke. u-pb geochronological data for samples from the three sites were obtained on zircon by inductively coupled plasma mass spectrometry (icp-ms) at the university of arizona laserchron center. a total of 370 zircon crystals were analyzed. most zircons were pale, translucent, and euhedral. the detrital zircon age spectra of the three sites are statistically indistinguishable. each sample contained greater than 80% paleogene zircons and had prominent age peaks of about 34.5 ma. we interpret that the maximum depositional age is about 33.4 ma. older zircons range from mesozoic to archean in age. we suggest that the brian head formation was sourced from the indian peak caldera and its environs, which are greater than 150 km to the west. thus, brian head deposition in the claron basin represents the transition from a sevier-laramide foreland basin characterized by the synorogenic claron formation to a system dominated by more distally derived sediments from the indian peak caldera complex, which is probably the most prominent eruptive center on the nevadaplano uplift. claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah david malone1, grace stevens1,6, sarah r. lesmann1,6, tiffany rivera2, robert biek3, michael braunagel4, w. ashley griffith5, david hacker6, and peter rowley7 1illinois state university, notmal, il 61790 usa; dhmalon@ilstu.edu 2university of missouri, columbia, mo 65211 usa; trivera@missouri.edu 3utah geological survey, retired, salt lake city, ut 84116 usa; bob@biek.org 4university of minnesota-duluth, duluth, mn 55812 usa; braun578@d.umn.edu 5the ohio state university, columbus, oh 43210 usa; griffith.223@osu.edu 6kent state university, kent, oh 44242 usa; gsteve15@kent.edu 7geologic mapping inc., new harmony, ut 84757 usa; pdrowley@rushisp.com citation for this article. malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p., 2025, claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah: geology of the intermountain west, v. 12, p. 155–168, https://doi.org/10.31711/giw.v12.pp155-168. 156 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 introduction the tectonic regime of the north american cordillera transitioned from mesozoic-paleogene sevier-laramide crustal shortening to paleogene-neogene crustal extension accompanied by the “great ignimbrite flareup.” the conventional view is that mesozoic crustal thickening in the sevier-laramide belt produced the nevadaplano uplift, a high plateau in the region that is now the great basin (decelles, 2004; lund snee and miller, 2022). however, there is disagreement regarding the timing of the nevadaplano uplift, the nature of its topography, its maximum elevation, and its time and duration of collapse (parsons et al., 1994; best et al., 2009; mix et al., 2011; cassel et al., 2012; chamberlain et al., 2012; lee et al., 2017; bahadori et al., 2018). based on the configuration of regional cenozoic ash-flow deposits filling broad paleovalleys (best et al., 2013; henry and john, 2013; biek et al., 2019), a north-trending eocene drainage divide passed through central nevada in the sevier-laramide hinterland, east of the mesozoic arc and west of the foreland fold and thrust belt (lund snee et al., 2016, 2022). the claron basin is a sevier-laramide foreland basin that subsided during eocene time, accumulating more than 400 m of synorogenic strata of the paleocene-eocene claron formation (eaton, 1995). the marysvale volcanic field consists of calc-alkaline and bimodal volcanic rocks and their intrusive equivalents resulting in thick successions of volcaniclastic strata (cunningham and steven, 1979; rowley et al., 1979, 1994, 2005, 2019, 2020; cunningham et al., 1998, 2007; figure 1). the field covers parts of the colorado plateau and basin and range physiographic provinces. the main activity occurred during the oligocene and early miocene, from about 32 to 14 ma (cunningham et al., 1998), which is partly coeval with basin and range extension that began here at about 20 ma. the eocene-oligocene brian head formation is the oldest volcanogenic stratigraphic unit in the southern marysvale volcanic field and the youngest unit in the laramide claron basin (davis et al., 2009). the marysvale volcanic field includes a complex array of locally derived volcanic and volcaniclastic rocks that intertongue with volcanic rocks sourced from calderas in the basin and range physiographic province. isotopic dating is one of the best tools for understanding the resulting complex stratigraphic succession (best et al., 2013). here we present detrital zircon u-pb data from three sandstone units in the uppermost brian head formation (oligocene). our goal is to determine the age and provenance of these rocks to further understand the development of the marysvale volcanic field and the coeval transition from terrestrial sedimentation in a laramide foreland basin to volcaniclastic sedimentation. this transition corresponds to the collapse of the sevier fold and thrust belt, as claron basin sedimentation shifted from recycling of paleozoic-precambrian strata to new source areas dominated in a new volcanic highland that developed in nevada more than 150 km to the west (dickinson and gehrels, 2003, dickinson and gehrels, 2009; best et al., 2013; biek et al., 2019; foreman et al., 2022; malone et al., 2022). background the paleogene claron formation, which comprises the lower stratigraphic succession of the claron basin, is notable for its vivid pink, orange, and white mudstone, limestone, sandstone, and conglomerate seen in bryce canyon national park and cedar breaks national monument (biek et al., 2019, 2024). these strata were deposited in fluvial and lacustrine environments and were shed from the sevier-laramide fold and thrust belt to the west and south. the claron formation is mostly flat lying, and unconformably overlies deformed cretaceous strata. a poorly understood conglomerate at boat mesa in bryce canyon national park (as much as 30 m thick) rests in slight unconformity above the claron formation (biek et al., 2019; cull et al., 2024). the brian head formation rests unconformably above the conglomerate at boat mesa, which is notably devoid of volcanic clasts. thus, the brian head reflects the first volcanic influx into the claron basin during latest eocene-oligocene time. it also reflects the first volcanic-sourced strata in the marysvale volcanic field. gregory (1944) first named the brian head formation for the light-colored tuffaceous and volcanic rocks that 157 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 occur at the base of the marysvale volcanic field. the brian head name was later abandoned because of erroneous correlations, inconsistent boundary definitions, and the designation of new units such as the bear valley formation (anderson, 1971; anderson and rowley, 1975). however, the name was later reinstated to indicate rocks between the claron formation and needles range group (anderson, 1993; sable and maldonado, 1997; biek, et al., in press). the type section is a poorly exposed, 150-m-thick section near the north view overlook at cedar breaks national monument (brian head is a prominent peak about 3 km to the north), where a thin, 35.77 ± 0.28 ma ash bed in the lower brian head formation overlies the conglomerate at boat mesa (biek et al., 2019, in press). this is similar to other isotopic ages for ash beds in the brian head formation, which are late eocene to early oligocene in age, ranging from about 37 to 33 ma (biek et al., 2019). the brian head formation consists of light-colored, poorly exposed volcaniclastic mudstone, siltstone, silty sandstone, sandstone, volcanic ash, micritic limestone, and minor conglomerate. quartzite clasts are abundant figure 1. map of the marysvale volcanic field showing the location of the three gravity slides. hachures enclose the various mountain ranges in the regions. red lines = tertiary normal faults, bgs = black mountains gravity slide, mgs = markagunt gravity slide, sgs = sevier gravity slide. large black dots show central part of calderas (cb = casto butte, tc = three creeks). bc = bryce canyon, bm = boat mesa, c = cedar city, m = milford, p = panguitch, pa = parowan. modified from rowley et al. (1994) and biek et al. (2019). sample locations are indicated by the red dots: 1 = haycock mountain, 2 = blind spring mountain, 3 = casto butte. we collected the casto butte and blind spring mountain samples in the autochthonous lower plate of the sevier gravity slide. we collected the haycock mountain sample from the allocthonous upper plate of the markagunt gravity slide. 158 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 in many conglomerate layers. these facies were deposited in low-relief fluvial, floodplain, and lacustrine environments rich in volcanic ash (sable and maldonado, 1997). at the southern end of the sevier plateau, the brian head is well exposed and is about 150 m thick. here it rests disconformably over the conglomerate at boat mesa, and is overlain in turn by allochthonous volcanic rocks of the sevier gravity slide (sgs), described below. the lower brian head consists of evenly stratified variegated mudstone, siltstone, and sandstone. the upper brian head is coarser grained, and consists of lithic wacke and arenite, conglomerate, and some limestone. the southern part of the marysvale volcanic field experienced three sequential mega-scale collapse events referred to collectively as the marysvale gravity slide complex (mgsc) (figure 1). the mgsc comprises, from east to west, the about 25 ma sevier (sgs), about 23 ma markagunt (mgs), and about 21 ma black mountains (bgs) gravity slides. each is differentiated by geological mapping and isotopic dating of deformed and undeformed volcanic rocks, which indicate gravitational collapse occurred during the growth of the marysvale volcanic field from the late oligocene to early miocene (hacker et al., 2014; biek et al., 2019, 2022; mayback et al., 2022; braunagel et al., 2023, 2025; holliday et al., 2022; rivera et al., 2025; figures 2 through 4). the uppermost brian head formation was deformed by the emplacement of the sgs, some of it being incorporated into the slide basal layer (biek, et al., 2019; braunagel et al., 2025). methodology we collected three samples of brian head formation sandstone from different localities across the mgsc. we collected one sample north of haycock mountain (37.743205° -112.589376°) in the upper (i.e., allochthonous) plate of the mgs. we collected two samples of autochthonous (uppermost lower plate) brian head sandstone in the lower plate of the sgs. we collected one of these two samples east of blind spring mountain (37.853823° -112.317677°) and the other from east of casto butte (37.806674°-112.202501°). for the sgs lower plate casto and blind spring samples, the uppermost brian head sandstone was collected. for the mgs upper plate haycock sample, the collection horizon is less certain, but probably near the top of the formation. u-pb geochronologic analyses were conducted by laser ablation inductively coupled plasma mass spectrometry (la-icpms) at the arizona laserchron center. please refer to the appendix (element2) methodology at www.laserchron.org for the details of our analytical techniques. these u-pb geochronology methods also have been described by gehrels et al. (2008), gehrels and pecha (2014), and sundell et al. (2021). the details of the zircon u-pb data and analytical methodology are also provided in the supplementary files. the ages are presented as a probability density plot using isoplot (ludwig, 2008). ranked age diagrams display the weighted mean (weighted according to the square of the internal uncertainties), its internal uncertainty, external systematic uncertainty, final age uncertainty, and mean squared weighted deviation (mswd). figure 5 shows the maximum depositional ages (mdas) for the three brian head formation samples, probability density plots for the tertiary zircon fractions, and a combined plot for precambrian zircon ages (n = 82). the maximum depositional age (mda) was calculated by taking the weighted mean average of the youngest zircon populations (e.g., malone et al., 2016a). results a total of 370 zircons were analyzed among the blind springs mountain, castro butte, and haycock mountain samples. most zircons were pale, translucent, and euhedral. for the blind spring mountain sample 122 zircons were analyzed, ranging in age from 32880 to 3.8 ma. all but 25 are paleogene in age. the principal age peak for paleogene zircons in this sample is 34.81 ma, and the maximum depositional age is 34.28 ± 0.16 ma. for the casto butte sample, 125 zircons were analyzed, ranging in age from 1840 to 30.8 ma. all but 15 are paleogene in age, and the principal paleogene age peak is 34.20 ma. the maximum depositional age is 33.40 ± 0.19 ma. for the haycock mountain sample, 123 zircons were analyzed, ranging from 2996 to 32.6 ma. all but 17 were paleogene in age. the principal age 159 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 peak for paleogene zircons is 34.28 ma. the maximum depositional age is 33.49 ± 0.12 ma. we combined the precambrian-paleozoic (pre-volcanic and pre-sevier laramide) zircons from the three samples (n = 50). the most prominent age peaks are 2874 and 1104 ma, with the spectrum ranging from 2996 to 376 ma. discussion radio-isotopic dating using multiple systems constrains the age of the brian head formation from about 38 to 33 ma (maldonado and moore, 1995; davis et al., 2009; biek et al., 2019). our mda of about 33.4 ma fits well in this framework, with brian head sedimentation concluding after this time. the paleogene zircons were likely derived from the indian peak caldera complex, which was active from 36 to 29 ma (best et al., 1989). unfortunately, the available geochronology for units associated with the indian peak caldera is insufficient to reveal a single eruptive event at this time. as more than 80% of these detrital zircon ages are early oligocene, and the indian peak caldera complex is the nearest to the claron basin, we interpret that brian head sediment derived from there was transferred east greater than 150 km to the claron basin through a variety of fluvial, eolian, and eruptive processes (figure 6). the paleozoic-precambrian zircons were likely defigure 2. stratigraphic column of principal rocks associated with the markagunt and sevier gravity slides modified from biek et al. (2019). the claron formation rests beneath the oligocene and miocene volcanic rocks. the brian head formation is principally in the lower plate of the sevier gravity slide at the top of the former land surface. it is in both the upper and lower plates of the markagunt gravity slide. 160 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 figure 3. stratigraphic column of the brian head formation at the base of casto butte. here the brian head is well exposed and approximately 125 m thick. the brian head formation here rests disconformably over the claron formation, and it is overlain by allochthonous volcanic rocks of the sevier gravity slide (sgs). the lower brian head consists of evenly stratified variegated mudstone, siltstone, and sandstone. the upper brian head is coarser grained, and consists of lithic wacke and arenite, conglomerate, and some limestone. the uppermost brian head was deformed by the emplacement of the sgs, some of it being incorporated into the slide basal layer (mayback et al., 2022; braunagel et al., 2025). we collected samples for the lower plate casto and blind springs, and the uppermost brian head sandstone. for the upper plate haycock sample, the collection horizon is uncertain. 161 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 figure 4. (a) scanning electron microscope image of brian head zircons. (b) field photograph of interbedded upper brian head sandstone and conglomerate. (c) polymict cobble-boulder conglomerate. (d) haycock mountain sampling locality. (e) barrel fold (craddock et al., 2015) in allochthonous brian head sandstone near haycock mountain. (f) east looking view of the sevier gravity slide upper and lower plates from blind spring mountain (g) blind spring mountain sampling locality. (h) sevier gravity slide exposure east of casto butte. (i) casto butte sampling locality. 162 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 figure 5. weighted mean ages (left) and probability density plots/histograms (right) of tertiary zircons of each of the samples. the aggregate of paleozoic-precambrian zircons for each of the three samples is the lowest figure on the right. 163 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 rived from recycling of phanerozoic strata in the sevier-laramide foreland fold and thrust belt (malone et al., 2022). preliminary data indicates that thrust belt sourcing dominated deposition of the underlying claron formation (cull et al., 2024). because of the preponderance of archean (greater than 2.5 ga), grenville (1.3 to 1.0 ga), and taconic-acadian (450 to 350 ma) zircons in the brian head formation, it is likely that erosional denudation had not as yet reached the ubiquitous neoproterozoic quartzites that rest beneath, or the distal thrust sheets that are armored by these rocks were not as yet part of the brian head drainage basin (yonkee et al., 2014; malone et al., 2016b, 2022). these older detrital zircon age groups are evident in carboniferous-cretaceous strata across laurentia reflecting the development and denudation of the appalachian highlands during the assembly of pangea and forming one of the greatest clastic wedges in earth’s history (dickinson and gehrels, 2003; dickinson et al., 2009; thomas et al., 2020; foreman et al., 2022). this is in contrast to the 26 to 24 ma bear valley formation, where the precambrian subset of zircons has a unimodal age peak of about figure 6. oligocene reconstruction of the sevier foreland and hinterland (modified from davis et al., 2009; best et al., 2013; lund snee and miller, 2022). the bulk (paleogene age) brian head zircons were derived from the indian peak caldera complex 100 to 200 km to the west prior to the 29 ma eruption of the massive wah wah springs ignimbrite (not shown). older zircons were recycled from the underling sevier-laramide foreland fold and thrust belt and transported eastward to the vestiges of the eocene claron basin. red circles indicate sample localities. 164 claron basin provenance shift from sevier-laramide compression to basin and range extension—detrital zircon geochronology from the eocene-oligocene brian head formation, utah malone, d., stevens, g., lesmann, s.r., rivera, t., biek, r., braunagel, m., griffith, w.a., hacker, d., and rowley, p. geology of the intermountain west 2025 volume 12 1700 ma, which indicates recycling from neoproterozoic brigham group strata (yonkee et al., 2014, malone et al., 2016b), which are in the thrust belt and have prominent coeval age peaks. abundant quartzite clasts in the brian head formation support this interpretation. the near absence of mesozoic grains indicates that the volcanic arc in the sevier hinterland did not contribute sediment to the claron basin during brian head deposition indicating that the arc was west of the presumed late eocene-early oligocene drainage divide of the nevadaplano uplift (lund snee and miller, 2022). the oligocene-miocene volcanism in the marysvale volcanic field is part of a complex array of magmatic activity that migrated from north to south over time (best et al., 2013). the ignimbrite flare-up province of nevada and western utah records more than 200 massive eruptions from several dozen caldera complexes and involved more than 70,000 km3 of material (best et al., 2013). deposition of the brian head formation ceased following the eruption of the wah wah springs ashflow tuff at about 30.5 ma, which also originated from the indian peak caldera and is one of the most extensive about 22,000 km2) and voluminous (3000 km3) eruptive rocks ever described (best et al., 1989). the brian head formation represents the distal toe of the volcanic and sedimentary apron derived from the indian peak caldera complex as the volcanic highlands became prominent following the erosional denudation of the sevier-laramide fold and thrust belt that occurred between this new locus of volcanic activity and the claron basin. this indicates that the inception of volcanic activity in the marysvale volcanic field proper had not yet begun. following eruption of the wah wah springs formation at about 30.5 ma, volcanic activity in the marysvale volcanic field proper commenced in earnest, with local eruptive centers dominating sourcing (holliday et al., 2022; rivera et al., 2025). the calderas to the west remained active during marysvale volcanism, as the 27.9 ma lund formation, the about 26 ma isom formation, and the about 24 to 22 ma quichapa group ash-flow tuffs are interlayered with the locally derived marysvale volcanic succession, providing much needed age and stratigraphic control. zircons derived from the indian peak caldera complex also occur more than 1500 km to the northeast in the white river formation of the central rocky mountains and great plains, further demonstrating the significance of this caldera complex in particular and the ash-flow tuffs of the nevadaplano uplift as the most prominent late paleogene sediment source for many areas to the east (moll et al., 2024). conclusions our conclusions for this research are: 1. the detrital zircon age spectra for three brian head formation samples in the claron basin in southern utah show prominent unimodal zircon age peaks of 35 to 34 ma. 2. these age peaks represent sediment sourcing from the indian peak caldera complex 150 km to the west, and reflect a provenance shift from the sevier fold and thrust belt and hinterland that dominated the deposition of the underlying claron formation. 3. this provenance reflects the rise of the nevadaplano uplift as the principle sediment source area for this region during the eocene-oligocene transition and the collapse of the sevier fold and thrust belt. acknowledgments funding for this research was provided by the national science foundation grants ear2113158 and ear2412838, and the illinois state university foundation. ear2050246 supported the arizona laser-chron center operations. samples for this work were obtained from the homelands of the ute, southern paiute, and goshute people. grant willis (retired, utah geological survey) and kelli trujillo (university of wyoming) provided valuable feedback on our initial submission. references anderson j.j., 1971, geology of the 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keeley, j.a., hayes, d.s., wells, m.l., fanning, c.m. and johnston, s.m., 2014, tectono-stratigraphic framework of neoproterozoic to cambrian strata, west-central us— protracted rifting, glaciation, and evolution of the north american cordilleran margin: earth-science reviews, v. 136, p. 59–95. summary sample name year lat (dec deg) long (dec deg) formation name geologic period # of good analyses mda peak bh blind spring 2022 37.853823 -112.317677 brian head oligocene 122 34.28±0.16 34.81 bh casto 2018 37.806674° -112.202501° brian head oligocene 125 33.40±0.19 34.25 bh haycock mtn 2018 37.743205° -112.589376° brian head oligocene 123 33.49±0.12 34.28 370 plotdat11 source sheet blind spring 30 0 33.5 0 30 0 plot name probdens5 30.014 0 34.2 0 57.986 0 plot type 16 30.028 0 34.2 11 1st free col 9 30.042 0 33.5 11 sigma level 1 30.056 0 33.5 0 absolute errs true 30.07 0 errbox errbox symbol type 1 30.084 0 34.2 0 inverse plot false 30.098 0 34.9 0 color plot true 30.112 0 34.9 37 3d plot false 30.126 0 34.2 37 linear false 30.14 0 34.2 0 data range x2:y98 30.154 0 errbox errbox filled symbols true 30.168 0 34.9 0 concage false 30.182 0 35.6 0 concswap false 30.196 0 35.6 32 1st symbol-row 1 30.21 0 34.9 32 30.224 0 34.9 0 30.238 0 errbox errbox 30.252 0 35.6 0 30.266 0 36.3 0 30.28 0 36.3 9 30.294 0 35.6 9 30.308 0 35.6 0 30.322 0 errbox errbox 30.336 0 36.3 0 30.35 0 37 0 30.364 0 37 4 30.378 0 36.3 4 30.392 0 36.3 0 30.406 0 errbox errbox 30.42 0 37 0 30.434 0 37.7 0 30.448 0 37.7 2 30.462 0 37 2 30.476 0 37 0 30.49 0 errbox errbox 30.504 0 37.7 0 30.518 0 38.4 0 30.532 0 38.4 1 30.546 0 37.7 1 30.56 0 37.7 0 30.574 0 errbox errbox 30.588 0 55.2 0 30.602 0 55.9 0 30.616 0 55.9 1 30.63 0.0000000105 55.2 1 30.644 0.0000000118 55.2 0 30.658 0.0000000133 errbox errbox 30.672 0.0000000149 30.686 0.0000000166 30.7 0.0000000186 30.714 0.0000000208 30.728 0.0000000233 30.742 0.0000000261 30.756 0.0000000291 30.77 0.0000000325 30.784 0.0000000363 30.798 0.0000000405 30.812 0.0000000452 30.826 0.0000000503 30.84 0.0000000561 30.854 0.0000000625 30.868 0.0000000695 30.882 0.0000000773 30.896 0.000000086 30.91 0.0000000955 30.924 0.0000001061 30.938 0.0000001178 30.952 0.0000001307 30.966 0.000000145 30.98 0.0000001607 30.994 0.0000001897 31.008 0.0000002105 31.022 0.0000002334 31.036 0.0000002588 31.05 0.0000002867 31.064 0.0000003176 31.078 0.0000003516 31.092 0.000000389 31.106 0.0000004303 31.12 0.0000004757 31.134 0.0000005257 31.148 0.0000005807 31.162 0.0000006411 31.176 0.0000007076 31.19 0.0000007805 31.204 0.0000008607 31.218 0.0000009486 31.232 0.000001045 31.246 0.0000011507 31.26 0.0000012665 31.274 0.0000013934 31.288 0.0000015324 31.302 0.0000016844 31.316 0.0000018507 31.33 0.0000020548 31.344 0.0000022566 31.358 0.0000025 31.372 0.000002744 31.386 0.0000030105 31.4 0.0000033015 31.414 0.00000363 31.428 0.000003978 31.442 0.0000043576 31.456 0.0000047824 31.47 0.000005235 31.484 0.0000057283 31.498 0.0000062655 31.512 0.0000068504 31.526 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false 10 34.1957386829 0.3729593555 1.85 34.3450257358 linear false 11 34.1960978949 0.3860667127 1.85 33.2595013634 data range x2:y29 12 34.214106142 0.5312201419 errbox errbox filled symbols true 13 34.2321595892 0.3572320935 2.85 33.2446390562 concage false 14 34.2333778681 0.4664694407 3.15 33.2446390562 concswap false 15 34.2971621165 0.4562263985 3.15 34.5000562238 1st symbol-row 1 16 34.3311853561 0.3950308852 2.85 34.5000562238 17 34.3528882337 0.5444247401 2.85 33.2446390562 18 34.4452691332 0.5036017317 errbox errbox 19 34.451222057 0.4422991828 3.85 33.5360505951 20 34.4898199597 0.4685866181 4.15 33.5360505951 21 34.5065577681 0.4378853233 4.15 34.4132992404 22 34.508268535 0.3710061926 3.85 34.4132992404 23 34.5281894123 0.5229007491 3.85 33.5360505951 24 34.5307481532 0.3196681431 errbox errbox 25 34.5489681824 0.4474493565 4.85 33.6077302014 26 34.5495720992 0.5058498306 5.15 33.6077302014 27 34.5647217702 0.5244454335 5.15 34.3973631071 28 34.5747785089 0.3814802552 4.85 34.3973631071 isoline isoline isoline 4.85 33.6077302014 errbox errbox 5.85 33.7047591268 6.15 33.7047591268 6.15 34.4667421068 5.85 34.4667421068 5.85 33.7047591268 errbox errbox 6.85 33.7135255189 7.15 33.7135255189 7.15 34.4631296532 6.85 34.4631296532 6.85 33.7135255189 errbox errbox 7.85 33.5664643745 8.15 33.5664643745 8.15 34.6226469116 7.85 34.6226469116 7.85 33.5664643745 errbox errbox 8.85 33.648039602 9.15 33.648039602 9.15 34.6412648718 8.85 34.6412648718 8.85 33.648039602 errbox errbox 9.85 33.8227793274 10.15 33.8227793274 10.15 34.5686980383 9.85 34.5686980383 9.85 33.8227793274 errbox errbox 10.85 33.8100311822 11.15 33.8100311822 11.15 34.5821646076 10.85 34.5821646076 10.85 33.8100311822 errbox errbox 11.85 33.6828860001 12.15 33.6828860001 12.15 34.7453262839 11.85 34.7453262839 11.85 33.6828860001 errbox errbox 12.85 33.8749274957 13.15 33.8749274957 13.15 34.5893916827 12.85 34.5893916827 12.85 33.8749274957 errbox errbox 13.85 33.7669084273 14.15 33.7669084273 14.15 34.6998473088 13.85 34.6998473088 13.85 33.7669084273 errbox errbox 14.85 33.840935718 15.15 33.840935718 15.15 34.753388515 14.85 34.753388515 14.85 33.840935718 errbox errbox 15.85 33.9361544709 16.15 33.9361544709 16.15 34.7262162412 15.85 34.7262162412 15.85 33.9361544709 errbox errbox 16.85 33.8084634936 17.15 33.8084634936 17.15 34.8973129737 16.85 34.8973129737 16.85 33.8084634936 errbox errbox 17.85 33.9416674015 18.15 33.9416674015 18.15 34.9488708648 17.85 34.9488708648 17.85 33.9416674015 errbox errbox 18.85 34.0089228742 19.15 34.0089228742 19.15 34.8935212398 18.85 34.8935212398 18.85 34.0089228742 errbox errbox 19.85 34.0212333416 20.15 34.0212333416 20.15 34.9584065778 19.85 34.9584065778 19.85 34.0212333416 errbox errbox 20.85 34.0686724449 21.15 34.0686724449 21.15 34.9444430914 20.85 34.9444430914 20.85 34.0686724449 errbox errbox 21.85 34.1372623424 22.15 34.1372623424 22.15 34.8792747275 21.85 34.8792747275 21.85 34.1372623424 errbox errbox 22.85 34.0052886632 23.15 34.0052886632 23.15 35.0510901614 22.85 35.0510901614 22.85 34.0052886632 errbox errbox 23.85 34.2110800101 24.15 34.2110800101 24.15 34.8504162964 23.85 34.8504162964 23.85 34.2110800101 errbox errbox 24.85 34.1015188259 25.15 34.1015188259 25.15 34.996417539 24.85 34.996417539 24.85 34.1015188259 errbox errbox 25.85 34.0437222686 26.15 34.0437222686 26.15 35.0554219299 25.85 35.0554219299 25.85 34.0437222686 errbox errbox 26.85 34.0402763367 27.15 34.0402763367 27.15 35.0891672037 26.85 35.0891672037 26.85 34.0402763367 errbox errbox 27.85 34.1932982537 28.15 34.1932982537 28.15 34.9562587641 27.85 34.9562587641 27.85 34.1932982537 errbox errbox blind spring sample u (ppm) th(ppm) 6/4c 8/4 ratio u/th 6/7 ratio ±(%) 8/2 ratio ±(%) 7/5 ratio ±(%) 6/8 ratio ±(%) errcorr 6/8 age ±(ma) 7/5 age ±(ma) 6/7 age ±(ma) 8/2 age ±(ma) best age ±(ma) spot 69 584.6577465478 178.9135880761 7506.6768908311 100 3.2678219292 21.5674593534 2.1502985728 0.0018604912 11.7016823351 0.0335884014 2.568385395 0.0052562508 1.4045709613 0.546869237 33.7952290718 0.4734359001 33.5448367232 0.8474847868 15.6655369804 na 37.5507602453 4.3899895093 33.7952290718 0.4734359001 spot 42 90.5265711707 95.7663783977 19919.926761126 429.7553258234 0.9452855238 17.7441393399 6.0551966075 0.0019206849 10.7436814334 0.0408341961 6.2655582444 0.0052573477 1.6099112272 0.2569461753 33.8022635496 0.5427621862 40.6381715635 2.4959335265 465.4593081699 134.2457213443 38.7645002777 4.1607412972 33.8022635496 0.5427621862 spot 115 166.3037664177 196.6947319772 1883.1461515991 100 0.8454917157 26.1119233046 3.4611857085 0.001620195 10.7580975368 0.0278062207 3.9283699553 0.0052682767 1.8580322917 0.4729779305 33.87234764 0.6277085838 27.8485535604 1.0791285393 na na 32.7047259144 3.515559939 33.87234764 0.6277085838 spot 6 455.2303726456 216.5734330565 14309.113024745 125.2634623945 2.1019677539 21.1136675396 2.4967338862 0.0017144342 13.8923297098 0.0344929715 2.8123389637 0.005284234 1.2944382365 0.4602710602 33.9746749178 0.4386243227 34.4330853241 0.952139905 66.5083729961 59.4407230615 34.6053788491 4.8033782307 33.9746749178 0.4386243227 spot 113 178.5542832638 157.5174196806 8740.7146540225 137.2608934188 1.1335526168 21.0824396954 4.081838785 0.0016605858 10.4083896361 0.034572477 4.2446173212 0.0052885805 1.164202876 0.2742774644 34.0025466543 0.3948164529 34.5111191539 1.4402514463 70.0371490072 na 33.5193651329 3.4859334162 34.0025466543 0.3948164529 spot 117 91.9330051201 48.4378494411 1974.365995594 100 1.8979580262 22.1141871667 5.4585865352 0.0016164307 16.439856088 0.0330403474 5.5724446673 0.0053015558 1.1207018372 0.2011149332 34.0857506168 0.38099149 33.0062931539 1.8096869553 na na 32.6288017798 5.3597986423 34.0857506168 0.38099149 spot 100 338.6125886308 248.9106933565 6348.2201775021 100 1.3603778289 23.2941452803 3.3491423744 0.0017152464 18.428651862 0.0313690759 3.5259137069 0.0053019577 1.1024122752 0.3126600271 34.0883275861 0.3748020671 31.36225776 1.0889034557 na na 34.6217588854 6.374859521 34.0883275861 0.3748020671 spot 85 135.2975702231 100.9400435279 11978.2825488891 172.2058458391 1.3403755883 24.7009353704 3.8351736364 0.0017346727 11.6244765378 0.029587935 4.1376770013 0.005302929 1.5530016569 0.3753317759 34.094555643 0.5280912685 29.6072082617 1.2073631361 na na 35.0135323525 4.0666148233 34.094555643 0.5280912685 spot 78 207.4521924437 211.7640363267 7567.6854558893 156.3795952599 0.9796384506 21.4666598375 4.0663214078 0.0018127973 12.7693606432 0.0340959604 4.319905972 0.0053107414 1.4582927741 0.3375751194 34.1446522369 0.4966126349 34.0433333504 1.4462607009 26.8795345473 na 36.5890129799 4.667954633 34.1446522369 0.4966126349 spot 111 339.0264533538 151.2057275008 8541.3615930627 100 2.2421535147 22.4558559416 2.1684443708 0.0018134948 19.9248019912 0.0326429055 2.4285829095 0.0053187083 1.0935556497 0.4502854918 34.1957386829 0.3729593555 32.6155694072 0.7795097874 na na 36.6030798556 7.2864884858 34.1957386829 0.3729593555 spot 110 186.5471687196 103.6519640239 3870.6304278275 100 1.7997456245 23.121117771 3.4960784523 0.0016824139 14.439070061 0.031704008 3.6747699304 0.0053187644 1.1319759258 0.3080399446 34.1960978949 0.3860667127 31.691944975 1.1466194414 na na 33.9596011516 4.8993316563 34.1960978949 0.3860667127 spot 18 165.8138501382 101.2393569272 1297.4406764074 100 1.6378398201 27.3303070477 4.2791903852 0.0018777864 9.8881644132 0.0268353793 4.553566544 0.0053215727 1.5567587859 0.341876806 34.214106142 0.5312201419 26.8889935656 1.2083387913 na na 37.8995068375 3.7440525235 34.214106142 0.5312201419 spot 103 678.5108096486 180.3865581274 19536.3931253428 100 3.7614266644 20.8021197514 1.8122317039 0.0016682356 18.8878896772 0.0352755964 2.0926038036 0.0053243882 1.0463302205 0.5000135327 34.2321595892 0.3572320935 35.2009626046 0.7239946939 101.7628525876 42.8337127298 33.6736488597 6.35494403 34.2321595892 0.3572320935 spot 112 674.8417223094 648.6024277878 8346.3245070884 146.7679192034 1.0404551284 19.5506752045 2.4629960136 0.0016757131 12.6810908727 0.0375349372 2.816549884 0.0053245782 1.3662371266 0.485074713 34.2333778681 0.4664694407 37.4144762808 1.0346190541 246.5763855554 56.704244508 33.8244586738 4.28572159 34.2333778681 0.4664694407 spot 33 322.2152106075 108.4516134726 4007.1639578948 100 2.9710504094 23.8875844627 3.2269375186 0.0017394423 13.7228122682 0.0307776745 3.4917096003 0.0053345255 1.333757918 0.3819784778 34.2971621165 0.4562263985 30.7798559128 1.0586172906 na na 35.1097213119 4.813856947 34.2971621165 0.4562263985 spot 36 669.0389031595 1355.809031363 12661.0559800963 456.1034416873 0.4934610168 21.3068367983 2.2767916996 0.0016568445 3.8585354036 0.0345398794 2.552417789 0.0053398315 1.1537140574 0.4520083124 34.3311853561 0.3950308852 34.4791256987 0.8652773978 44.7967546525 na 33.4439080084 1.289377473 34.3311853561 0.3950308852 spot 94 168.24572283 31.091121464 8796.644743678 100 5.4113751743 19.1276948117 3.5398351793 0.001801667 26.4571584478 0.0384992574 3.8801339764 0.0053432161 1.5890269282 0.4095288817 34.3528882337 0.5444247401 38.3577694518 1.4605724143 296.7144584142 80.7931068177 36.364565147 9.6123773898 34.3528882337 0.5444247401 spot 22 137.1674753533 84.3866131511 2399.3522689116 100 1.6254648721 23.9310530552 3.7652121079 0.0015115885 13.1294388916 0.0308547916 4.0405215318 0.0053576234 1.4659440752 0.3628106084 34.4452691332 0.5036017317 30.8558184625 1.2279838955 na na 30.5140843552 4.0033039605 34.4452691332 0.5036017317 spot 12 198.37008889 137.7084379026 9520.8089719715 114.6160842311 1.4405078724 23.0501326374 3.886676019 0.0016157808 17.0543160515 0.0320395382 4.0943043948 0.0053585518 1.2872754176 0.3144063786 34.451222057 0.4422991828 32.0221135861 1.2906253307 na na 32.6156938852 5.5578959035 34.451222057 0.4422991828 spot 32 155.9918736214 110.8536941977 1846.0989947775 100 1.4071869661 22.6372668019 9.8482826969 0.0017539926 19.1690199017 0.0326605342 9.9420534228 0.0053645714 1.3622606887 0.1370200532 34.4898199597 0.4685866181 32.6329033545 3.1928104722 na na 35.4031535774 6.7804948149 34.4898199597 0.4685866181 spot 108 267.008797389 777.3214915366 6386.2935912558 325.4168809699 0.3434985399 19.5237232512 4.9820100869 0.0016734436 5.8949206268 0.0378874962 5.1419260331 0.0053671818 1.2723909869 0.2474541599 34.5065577681 0.4378853233 37.759449372 1.9059077315 249.7067405664 114.7153191556 33.7786864801 1.9895629803 34.5065577681 0.4378853233 spot 106 473.0126208425 54.9504666885 44781.4580741145 100 8.6079818671 20.9954118097 2.0403787363 0.0015975935 26.4570879487 0.0352334962 2.3076471523 0.0053674486 1.0780027791 0.4671436784 34.508268535 0.3710061926 35.1596704648 0.7974745436 79.8471423481 48.4593099916 32.2488619847 8.5253039229 34.508268535 0.3710061926 spot 34 124.1676635102 83.4287374884 1810.5942021287 100 1.4883080728 27.3931557795 5.0430755181 0.0014566545 20.8838665303 0.027020251 5.2667239315 0.0053705554 1.5184763049 0.2883151509 34.5281894123 0.5229007491 27.0717868768 1.4069579381 na na 29.4059509738 6.1366324343 34.5281894123 0.5229007491 spot 13 480.1923542212 498.1453149196 4629.1864191852 100 0.9639603944 22.4205887108 3.1069431087 0.0016467989 18.2090746577 0.0330154106 3.2426390594 0.0053709544 0.928230892 0.286257852 34.5307481532 0.3196681431 32.9817822976 1.0522975954 na na 33.2413013651 6.047956411 34.5307481532 0.3196681431 spot 92 598.8718775646 296.9122746161 173435.330629171 2103.2903647447 2.0169993926 21.0366182249 2.1638595661 0.0018114219 6.7609015666 0.0352060658 2.5236133434 0.005373796 1.2985900374 0.5145756741 34.5489681824 0.4474493565 35.1327657294 0.8714521007 75.1889408604 51.4354670996 36.5612775756 2.4696365732 34.5489681824 0.4474493565 spot 95 120.9749652569 139.4089898638 9250.5601321857 210.5959806456 0.8677701874 22.1568964005 4.6617000535 0.0018194249 13.4948050471 0.0334265925 4.8873951937 0.0053738902 1.4680546278 0.3003756745 34.5495720992 0.5058498306 33.3858654147 1.6051669313 na na 36.7226610906 4.9511502277 34.5495720992 0.5058498306 spot 81 93.6765901165 60.4743681032 2069.1744016529 100 1.5490296642 24.7486291429 5.3205324208 0.0014567533 18.2080997079 0.0299392412 5.5337682689 0.0053762529 1.5213566359 0.2749223607 34.5647217702 0.5244454335 29.9536085606 1.6333544427 na na 29.4079445692 5.3507325369 34.5647217702 0.5244454335 spot 126 319.2714437276 291.1737042194 6791.7300011289 109.5738438645 1.096498204 21.19672217 2.4035960155 0.0016219222 16.948618515 0.0349663186 2.6459771984 0.0053778214 1.1063098701 0.4181101299 34.5747785089 0.3814802552 34.8975821145 0.9076947369 57.1400366807 57.2989763066 32.739561071 5.5444095772 34.5747785089 0.3814802552 spot 74 927.8564251564 937.3692659033 47290.1052637419 861.4627416281 0.9898515547 21.721001228 2.0697752431 0.0017240284 5.2416478845 0.0341253585 2.3465539192 0.0053782974 1.1055974579 0.4711579175 34.5778311024 0.3812681685 34.0721989939 0.7862570812 na na 34.7988689205 1.8224640936 34.5778311024 0.3812681685 spot 82 397.8405006107 120.9573189315 5335.874465596 100 3.2890982053 22.2931441442 3.448416439 0.0015464976 15.2916294061 0.0332624269 3.6270302748 0.0053803808 1.124176444 0.3099440476 34.5911892606 0.3878245461 33.2245533537 1.1855628582 na na 31.2182433308 4.7700915982 34.5911892606 0.3878245461 spot 80 270.9417691027 78.3573140385 13330.7090150907 100 3.457772544 22.5449895261 2.9942830816 0.0016523014 16.1314180626 0.0329211502 3.1658468006 0.0053853359 1.0280344313 0.3247265253 34.6229607305 0.3549818209 32.8891266425 1.0245373219 na na 33.352279347 5.3757570006 34.6229607305 0.3549818209 spot 50 112.2805658701 74.7363309865 33715.7570967946 400.2939242587 1.5023558742 18.8354310475 5.6612312817 0.0017325628 15.3332428903 0.0394224156 5.942998983 0.005387739 1.8082304297 0.3042622815 34.6383694888 0.624661796 39.2599779168 2.2886925492 331.7321093395 128.4925442523 34.9709822941 5.3575473165 34.6383694888 0.624661796 spot 118 435.9174342993 243.8385808995 8969.1455760148 100 1.787729541 21.4887573351 3.392326219 0.0017361012 18.9033549609 0.0345755074 3.5819065783 0.0053909787 1.1498598001 0.3210189252 34.6591421326 0.3974621081 34.5140933637 1.215488188 24.4478419395 na 35.0423408265 6.6184364942 34.6591421326 0.3974621081 spot 124 232.7746682574 315.0103419086 5190.4774041387 125.3119519583 0.7389429402 20.3748659839 3.156477203 0.0016911932 14.2923297487 0.0364728757 3.3505218917 0.0053920328 1.1236763831 0.3353735386 34.6659003731 0.3884870459 36.3745579935 1.1971667257 150.6606191944 74.0075396207 34.1366621974 4.8748046246 34.6659003731 0.3884870459 spot 35 490.3235780618 340.9990607109 61379.7302079373 831.5098957876 1.4379030166 22.6550446606 2.2739557658 0.0018434097 5.6126533501 0.0328561897 2.4631595305 0.0054009465 0.9467206809 0.384352158 34.7230535053 0.3278465776 32.8252670414 0.7956093541 na na 37.2063163154 2.0863397576 34.7230535053 0.3278465776 spot 48 78.5825137225 109.5501069812 3210.214109313 100 0.7173202828 19.1513854394 7.4119091777 0.0016027394 20.9535667245 0.0388796675 7.5698915907 0.0054026955 1.5384606061 0.2032341663 34.7342680031 0.5329359715 38.7296438128 2.8765904088 293.8685556366 169.4236918735 32.3526538751 6.7736099029 34.7342680031 0.5329359715 spot 107 153.94388615 96.8960877502 3037.0932592781 100 1.58875234 23.8715633694 3.6883068128 0.0016214352 11.7129408173 0.0312005418 4.0137802199 0.0054041918 1.5832954583 0.3944649113 34.7438616508 0.548618229 31.1963223774 1.233112546 na na 32.7297389278 3.8305112105 34.7438616508 0.548618229 spot 109 74.0578657216 103.6415822427 7949.5725399697 205.4244149623 0.7145574597 22.0485374039 5.6277943475 0.0017218168 14.0712375186 0.0337834183 5.9450258021 0.0054046943 1.9160539058 0.3222953053 34.7470833395 0.6639817645 33.7364005377 1.9726872129 na na 34.7542666391 4.8861513854 34.7470833395 0.6639817645 spot 31 282.2257037275 147.3835608811 9907.3311549334 111.0955343157 1.9149062625 21.7955600134 3.8443397388 0.0019632666 16.967652958 0.0341899721 4.007865292 0.0054069771 1.1331531986 0.2827323565 34.7617206017 0.3928434107 34.1356395553 1.3453698927 na na 39.6230693685 6.7165163038 34.7617206017 0.3928434107 spot 15 133.2503052552 83.0612087884 3022.281309492 100 1.6042423076 18.9081862858 5.572303393 0.0019163159 18.659266422 0.0394122346 5.6673921475 0.0054071533 1.0338126762 0.1824141773 34.7628504548 0.358415493 39.250032365 2.1820117173 322.9708103159 126.6391811256 38.6764066268 7.2098303136 34.7628504548 0.358415493 spot 125 1542.9674871529 1031.466402982 305710.568252102 4931.035666681 1.4958969897 20.6873506205 1.4484725806 0.0017725151 2.981508512 0.0360447456 1.7325410533 0.005410465 0.950592281 0.548669412 34.784084116 0.3297643342 35.955052721 0.6120359746 114.8296041999 34.1888893865 35.7766876839 1.0657410261 34.784084116 0.3297643342 spot 1 220.2350394674 143.2080481424 4380.2234433279 100 1.5378677548 22.3474021112 4.6111579836 0.0016420412 22.0536757202 0.0333713912 4.8461078224 0.0054111442 1.4906317708 0.3075936041 34.7884389046 0.5171707981 33.3316264372 1.5890633656 na na 33.1453436041 7.3037736442 34.7884389046 0.5171707981 spot 104 1113.0326965222 884.9364846222 25257.5139382463 365.4486620949 1.2577543314 21.1026702466 1.5236080116 0.0016399242 6.2861314256 0.0353488922 1.656171528 0.0054125382 0.6492478396 0.3920172691 34.7973766925 0.2253125572 35.2728474441 0.5741486603 67.7808464578 36.2376135902 33.102646514 2.0791719615 34.7973766925 0.2253125572 spot 86 136.5201934117 153.445288699 2306.4231120839 100 0.889699479 23.5119612926 3.816110114 0.0015054493 15.3245357678 0.031750627 3.9909990934 0.0054166268 1.168493629 0.2927822336 34.8235918439 0.4058143592 31.7378253749 1.2470656655 na na 30.390248001 4.6536633365 34.8235918439 0.4058143592 spot 77 221.2729401819 61.3795414079 16057.5890032709 100 3.604995005 19.8290493869 3.4809724112 0.0018023237 22.7224848688 0.0376500692 3.7158692675 0.0054169575 1.3001982487 0.3499041961 34.8257118271 0.4515823972 37.5271439009 1.36900634 213.9234067698 80.6686810814 36.3778064243 8.2585042391 34.8257118271 0.4515823972 spot 40 912.536131335 2537.434252401 115270.115744122 5607.8752478936 0.3596294684 22.2698812167 2.0174205226 0.0016735691 3.2645330035 0.0335238845 2.2416989065 0.0054170144 0.9773578782 0.4359898091 34.8260767904 0.3394576377 33.4814542399 0.7383139697 na na 33.7812161171 1.1018774302 34.8260767904 0.3394576377 spot 19 97.0246855788 67.0907352745 3405.8376662078 100 1.4461711469 19.781961053 6.0690058956 0.0016275539 22.530332047 0.0377774856 6.2814008916 0.0054223824 1.6196186586 0.2578435426 34.8604948243 0.5630832057 37.6518184138 2.3217528306 219.4288071458 140.5521254557 32.8531486533 7.3959084529 34.8604948243 0.5630832057 spot 130 121.5200129687 96.9071771428 3083.0949037361 100 1.2539836218 23.250468407 4.9030048498 0.0017746408 20.7753919937 0.0321771817 5.0997280356 0.0054283453 1.40277207 0.2750680154 34.898726305 0.4882268456 32.1575265505 1.6142509173 na na 35.8195553175 7.4350599823 34.898726305 0.4882268456 spot 26 55.1471319845 70.3295076701 560.049523772 100 0.7841250964 62.3672268229 30.9354983398 0.0017619036 19.8497643604 0.0120005836 30.9993815097 0.0054305843 1.9891195159 0.0641664259 34.9130816841 0.6925857464 12.1126542893 3.7325574497 na na 35.5626924599 7.05290132 34.9130816841 0.6925857464 spot 97 226.061955597 217.2177797733 10178.2658589147 182.1713626047 1.0407157086 21.1752995169 3.3496330504 0.0017930221 11.1357855327 0.0353631261 3.5469828958 0.0054333536 1.1666388004 0.328910185 34.9308373609 0.4064145996 35.2868068188 1.230119134 59.5968135463 na 36.1902341176 4.0264592987 34.9308373609 0.4064145996 spot 121 259.7931566979 384.6115488839 2526.7294841352 100 0.6754689438 21.2628176674 3.7605215721 0.0017526279 18.1098346672 0.0352256987 4.1124112202 0.0054346075 1.6644529281 0.4047389327 34.9388772502 0.5799680648 35.1520224903 1.4208600437 49.7581367406 na 35.3756328483 6.4008629443 34.9388772502 0.5799680648 spot 39 437.2162911792 240.9746506023 4020.9477902098 100 1.8143663248 21.5868125823 4.5254077256 0.0016196199 19.1241596817 0.0347423938 4.7179132329 0.0054417178 1.3339378512 0.2827389537 34.9844649089 0.4654070042 34.6778705695 1.6084505708 13.4759829608 na 32.6931252117 6.2472293304 34.9844649089 0.4654070042 spot 96 417.2787917473 165.9556445484 13446.171124776 100 2.5143995125 20.1171212867 2.8160115412 0.0017034487 16.0565128725 0.0373007883 3.0039916536 0.0054446705 1.0459659911 0.348192043 35.0033961276 0.3651314087 37.1853007372 1.0968370291 180.3671580327 65.640591986 34.3838285045 5.5161484145 35.0033961276 0.3651314087 spot 73 349.4463552656 178.4400811946 7234.9341557894 100 1.9583400373 22.322695123 2.6328443819 0.0015812107 16.2617396704 0.0336425671 2.8654701259 0.0054490841 1.1309507078 0.3946824284 35.0316940703 0.3951166307 33.5980469733 0.946988409 na na 31.9184220589 5.1863925859 35.0316940703 0.3951166307 spot 17 238.2433755924 116.3483981581 16138.2263473051 146.2842676135 2.0476721585 20.9509009644 3.2040802774 0.0017832959 9.8353824125 0.0358538159 3.3941100412 0.0054503682 1.119755575 0.329911394 35.039927177 0.3912971139 35.767913449 1.1928695244 84.9300872284 76.0206355468 35.9940948576 3.5370050211 35.039927177 0.3912971139 spot 47 458.4040017767 734.723015532 17689.0167432253 501.4400875686 0.6239140357 20.7509174296 2.3876439212 0.0016984783 4.6939878891 0.0362035942 2.6510799296 0.0054510071 1.152120349 0.4345852934 35.0440232313 0.4026538773 36.1107215014 0.9405014106 107.6329993975 56.3838478886 34.2835853138 1.6079026246 35.0440232313 0.4026538773 spot 41 680.0499877921 824.5933441933 8974.1730790229 206.9486454976 0.8247095281 21.2846647556 1.7955256669 0.0017863252 7.2166046665 0.0353026008 2.0266422814 0.0054520681 0.9398757984 0.4637600858 35.0508258602 0.328540241 35.2274477544 0.7016919202 47.2972756321 42.8926738252 36.0551846344 2.5996396316 35.0508258602 0.328540241 spot 129 634.3527973003 1029.6529453566 14500.5802937136 420.9577306511 0.6160840895 21.3480839738 2.0652006063 0.0017257354 5.1021467801 0.0352187389 2.3391543636 0.0054553228 1.0984487207 0.4695922329 35.0716935929 0.3841985071 35.1451959943 0.8080357214 40.1932819962 na 34.8332933379 1.775714433 35.0716935929 0.3841985071 spot 25 461.007265856 306.7508881288 5293.6986262632 100 1.5028718211 23.8986759392 2.2876132328 0.0016157011 14.0380276716 0.031512723 2.5666730935 0.0054644635 1.163888511 0.4534619208 35.1302978168 0.4077654149 31.5036684642 0.7961811664 na na 32.6140856395 4.5746807756 35.1302978168 0.4077654149 spot 11 182.9723988768 94.6466891876 4400.2960311794 100 1.9332149962 22.4713400253 4.8876117757 0.0020815829 19.5096586707 0.0335145777 5.0257403687 0.0054645006 1.1701783558 0.2328370091 35.1305358808 0.4099718169 33.4723107395 1.654807533 na na 42.0084738801 8.187195059 35.1305358808 0.4099718169 spot 61 165.5169698375 117.7693352753 1769.9486725369 100 1.4054335065 25.5202365407 4.6467303878 0.0017532353 12.9354058024 0.029534241 4.9684107487 0.0054688784 1.7586932851 0.3539750182 35.158603443 0.6166488764 29.5542537596 1.4472138741 na na 35.3878833432 4.5735594715 35.158603443 0.6166488764 spot 105 484.997923183 837.2353071381 23262.1073412787 717.2786653204 0.5792850816 21.270722106 2.3005238139 0.0017594312 6.6276592715 0.0354485376 2.7119790388 0.0054710201 1.436112979 0.5295442769 35.1723349253 0.503738991 35.3705666288 0.9427274848 48.8231278198 na 35.5128332877 2.3516020697 35.1723349253 0.503738991 spot 87 371.8180226292 192.2445746461 4001.207772541 100 1.9340885084 21.4791484551 2.556644619 0.002109197 21.34397655 0.0351095153 2.8768418503 0.0054717929 1.3190099787 0.4584923494 35.177289167 0.4627282813 35.0380596003 0.9907967411 25.5197914453 na 42.5651676538 9.0755356892 35.177289167 0.4627282813 spot 66 96.7668993176 85.3843484175 1566.399199326 100 1.1333095715 27.3078413157 4.7795665471 0.0017904298 13.5117647397 0.0276271802 5.0056882675 0.0054740869 1.487500808 0.2971620941 35.1919968707 0.522054952 27.6716617545 1.3664537942 na na 36.1379573774 4.8785111657 35.1919968707 0.522054952 spot 2 99.5815955923 83.2656079405 1314.7149707865 100 1.1959511022 30.5656010861 4.7330912065 0.0017271973 11.2093061651 0.0247107241 4.9826399636 0.0054803231 1.55709622 0.3125042611 35.2319793962 0.5470994111 24.7858580843 1.2200392891 na na 34.862776391 3.904505406 35.2319793962 0.5470994111 spot 102 207.2479967658 92.8139418485 2487.8357318425 100 2.2329403604 23.0001739721 4.1503499842 0.0017907197 11.0190720061 0.0328506674 4.3798127681 0.0054823035 1.3990549995 0.3194326045 35.2446758929 0.4917469048 32.8198381599 1.4144656312 na na 36.1438036675 3.9791511559 35.2446758929 0.4917469048 spot 30 144.6158512887 97.3200357262 2773.8724598036 100 1.4859823079 18.6941550673 4.9444613543 0.0018707643 17.8447558512 0.0404343769 5.1596637794 0.0054845923 1.4745956162 0.2857929662 35.2593502204 0.5185135086 40.2480540941 2.0360477421 348.788685103 111.8717761226 37.7579107599 6.7315146232 35.2593502204 0.5185135086 spot 83 356.068280164 173.7606838974 8180.9352044673 100 2.049187838 17.8699402283 4.7663700727 0.0017482259 19.5628506018 0.0423229458 4.8645815322 0.0054876543 0.9725583852 0.199926423 35.2789811953 0.3421715433 42.0894797285 2.005624158 449.7896343502 105.9461570143 35.286860026 6.897090651 35.2789811953 0.3421715433 spot 59 621.1419919033 773.9543127421 52824.9749095027 1281.6032526658 0.8025564063 16.7303149389 4.6922545847 0.001875857 4.4068219612 0.0452342323 4.9234970678 0.0054910967 1.4911640721 0.3028668549 35.301051595 0.5249579331 44.9215677891 2.1635047388 594.3581811511 101.7454647282 37.8606023281 1.6668868977 35.301051595 0.5249579331 spot 23 237.2014151505 375.9919915408 49741.1746405229 1446.4553264129 0.6308682645 22.1552228945 3.2718575817 0.0018650871 6.0792565778 0.0341604668 3.6799534125 0.0054914581 1.6843411422 0.4577071918 35.3033684397 0.5930039051 34.1066704654 1.2342647062 na na 37.6434334972 2.2863101573 35.3033684397 0.5930039051 spot 101 199.7893214708 41.6559677975 2934.711020287 100 4.7961752429 25.2429669615 4.9317245869 0.0017373391 17.390146158 0.0300085836 5.121119578 0.0054963408 1.3798399657 0.2694410753 35.3346720177 0.4862281308 30.0219685753 1.5149552427 na na 35.0673056857 6.0929661857 35.3346720177 0.4862281308 spot 20 490.3157282412 159.5279471906 69364.2895389022 439.7408519009 3.0735412627 20.4909568194 2.3318581355 0.0018973707 8.5156952658 0.0369963079 2.5158950354 0.0055005786 0.9445451102 0.3754310482 35.3618417352 0.3330941172 36.8872100914 0.9113888695 137.302827118 54.8088343797 38.294403777 3.2579459451 35.3618417352 0.3330941172 spot 88 567.3168055887 159.5307293304 16305.8576206779 100 3.556160045 22.3585496035 2.0551524277 0.0017436259 14.0063926697 0.0339770808 2.3161784805 0.0055121045 1.0681906442 0.4611866716 35.435735573 0.3774827566 33.9265982485 0.7728178914 na na 35.1940919564 4.9251315136 35.435735573 0.3774827566 spot 8 346.2064537015 566.5761613579 3387.3163602536 100 0.6110501594 23.4966720974 3.109629478 0.0015545784 5.5078227267 0.03234635 3.3357392293 0.0055146683 1.2072119597 0.3619023781 35.4521717455 0.4268081626 32.3239286979 1.0612605378 na na 31.3812378726 1.7270812092 35.4521717455 0.4268081626 spot 57 1837.969317052 1906.5693131985 100124.160394818 1726.647254781 0.9640191439 21.2036626322 1.306321339 0.0016374891 2.7219061898 0.0358672007 1.5729281715 0.0055181833 0.876143591 0.5570143677 35.4747069005 0.3099557436 35.7810336038 0.5530090584 56.3965803026 31.1651131041 33.0535320937 0.8989505272 35.4747069005 0.3099557436 spot 46 206.7726411414 155.0723665799 14771.5882036313 203.5070152927 1.3333945028 21.0363759521 3.4886850751 0.0018018226 10.6060156174 0.0361644444 3.8491105426 0.0055200178 1.6262620995 0.4225033502 35.4864676758 0.5755174572 36.0723575444 1.3640920167 75.2163144644 na 36.3677031501 3.8536945688 35.4864676758 0.5755174572 spot 21 119.323027604 89.943302299 2070.8472080237 100 1.3266471717 24.0163448336 6.7900645644 0.0018439554 23.6359793008 0.03168412 7.052312028 0.0055212361 1.9052895191 0.2701652326 35.4942781618 0.6744103917 31.6723714006 2.1991609404 na na 37.2173207501 8.7885808841 35.4942781618 0.6744103917 spot 62 1055.836687305 761.7810509825 19831.0186037732 255.5980816787 1.3860106995 21.0261387004 1.9414677721 0.0016659075 7.5215803059 0.0362045928 2.0980884236 0.0055234566 0.7954105375 0.3791120186 35.508514155 0.2816620178 36.1116999721 0.7443409805 76.3731940919 46.1131330585 33.6266948856 2.5271550379 35.508514155 0.2816620178 spot 65 259.1581034394 294.0001311151 3238.8515689194 100 0.8814897546 20.9737377445 3.9994069995 0.0017522933 11.9962576845 0.0363345462 4.1840520141 0.0055294677 1.229241599 0.2937921409 35.5470514401 0.4357566076 36.2390341564 1.4895224813 82.2986783048 na 35.3688862366 4.239230775 35.5470514401 0.4357566076 spot 89 140.5130936612 68.053846543 7822.9336538089 100 2.0647340422 24.4427190459 3.4720068501 0.0016482913 18.1812221304 0.0312143979 3.9268933908 0.0055359509 1.8345735568 0.4671819105 35.5886149095 0.6511004071 31.2099658523 1.2069387224 na na 33.2714003996 6.0441688523 35.5886149095 0.6511004071 spot 64 313.1266403855 196.9993769409 7377.6034447426 100 1.589480359 22.3323294608 2.6306882773 0.0015821517 17.93890854 0.0341789499 2.8398995861 0.0055383513 1.0698172023 0.3767095173 35.6040031282 0.3798478218 34.1248178078 0.9530068998 na na 31.9374022157 5.7246952452 35.6040031282 0.3798478218 spot 75 313.5811098667 210.9115226231 15748.8962024604 187.0311174062 1.4867898442 23.0190190692 3.2423693191 0.001699211 12.024442542 0.0332267074 3.4228229737 0.0055496025 1.096703382 0.320409028 35.6761331115 0.3901806823 33.1894512684 1.1176509909 na na 34.2983636345 4.1206881072 35.6761331115 0.3901806823 spot 63 230.6299082588 140.3378616209 5110.2638403896 100 1.6433904977 23.2513987396 3.5564779382 0.0017093739 15.625908199 0.0329980889 3.7280254246 0.0055670565 1.1178721937 0.2998563761 35.7880270138 0.398955953 32.9647561845 1.2092003168 na na 34.5033250499 5.3868565708 35.7880270138 0.398955953 spot 52 2262.784395911 629.1750426856 82660.9356977386 411.0139809485 3.5964306312 21.0619579171 1.0957062517 0.0017839872 6.3538150132 0.0365239154 1.5038446108 0.0055816657 1.030037098 0.6849358575 35.8816821413 0.3685679348 36.424557889 0.5380602589 72.3428154281 26.0441061905 36.0080356483 2.285846236 35.8816821413 0.3685679348 spot 58 104.4190580719 53.805552831 888.9324605063 100 1.9406743836 31.1795867624 5.0662800174 0.0015186233 19.813637047 0.024684312 5.3862056143 0.0055844337 1.8286655532 0.3395090504 35.8994263931 0.6546558985 24.7596860792 1.317479973 na na 30.6559879482 6.0694600872 35.8994263931 0.6546558985 spot 53 720.220433632 202.144411228 21490.1801128983 114.1409592805 3.5629005485 19.4444619936 2.3683048131 0.001728771 16.6177942719 0.0396921809 2.6177593445 0.005600008 1.115256158 0.4260346393 35.9992667526 0.4003651027 39.523470029 1.0147520989 259.0620210806 54.4211583906 34.8945139288 5.7936935944 35.9992667526 0.4003651027 spot 98 114.6344819204 93.1607288541 3343.1911455544 100 1.2305022012 21.8547744465 4.5230323359 0.0020133352 16.0160169738 0.0353672339 4.7279024603 0.0056083509 1.376677218 0.2911813917 36.0527487276 0.4949446549 35.2908353109 1.6398550984 na na 40.6325480329 6.5011758791 36.0527487276 0.4949446549 spot 4 199.9892558533 139.0810315868 5822.4876960545 100 1.4379333657 13.5662330222 5.4446293481 0.0019757849 19.6419308993 0.0572802924 5.5638309752 0.0056383529 1.145524501 0.2058877249 36.2450724575 0.4140311467 56.5566827324 3.0606963314 1032.7064583884 110.1204925926 39.8754670404 7.8245873085 36.2450724575 0.4140311467 spot 38 209.2641060853 100.9579923117 7243.8307714189 100 2.07278395 23.0803921773 4.2747543543 0.001696167 19.5486224464 0.0337125377 4.4254611474 0.0056457596 1.1450683723 0.2587455486 36.2925515571 0.4144069044 33.6667792032 1.4654817224 na na 34.236972748 6.6871886934 36.2925515571 0.4144069044 spot 91 234.8200283982 198.1351257953 5984.6472399547 100 1.185150929 23.1201876652 3.313889919 0.001505381 18.7201601982 0.0337688997 3.4712264875 0.0056649492 1.0332216279 0.2976531873 36.4155597681 0.3751927171 33.7221402385 1.151347693 na na 30.388870542 5.6845688224 36.4155597681 0.3751927171 spot 70 441.0600220381 333.3768543608 6526.5407247885 100 1.3230073302 18.7022829807 4.0239572543 0.0018928281 18.1232411676 0.0420102432 4.7003498523 0.0057008232 2.4292090789 0.5168145256 36.6455118774 0.8876706748 41.7848135781 1.9241716992 347.7624910661 91.015641937 38.2028082293 6.9170450764 36.6455118774 0.8876706748 spot 5 98.2165360208 67.8661953896 10900.0755091113 140.7068526753 1.4472085175 21.1886700255 4.6908839915 0.0017823504 20.115694658 0.0372012147 4.8870292906 0.005719375 1.3706431577 0.2804655091 36.7644253334 0.5024748918 37.0878264258 1.7797926218 58.0458124331 na 35.9750283452 7.2301876248 36.7644253334 0.5024748918 spot 49 286.949439119 179.592025449 19529.7543122833 251.0908962465 1.5977849707 19.8288331022 2.5125286577 0.0020286779 11.5534070711 0.0399162044 2.7229489992 0.0057429383 1.0495956346 0.3854628327 36.9154584351 0.3863557498 39.7422320574 1.0612567573 213.9491216854 58.1988486212 40.9418777563 4.7253919748 36.9154584351 0.3863557498 spot 90 140.2777713575 57.2530614357 90034.8145342666 1236.2016954462 2.4501357279 10.3862659455 9.2004488364 0.0034713709 12.2775243091 0.0764066324 9.3207551634 0.0057580874 1.4927216841 0.1601502945 37.0125574088 0.5509114092 74.7609295737 6.7180315865 1552.4271291091 173.1162369375 70.0072643446 8.5802839437 37.0125574088 0.5509114092 spot 127 104.3897598221 83.8820000924 1349.9405147654 100 1.2444834375 23.534339003 5.6300700956 0.0016820206 13.4354348533 0.0342781993 5.8507922119 0.005853394 1.5918794633 0.2720793024 37.6233969815 0.5971747822 34.2222586499 1.9689095179 na na 33.9516688625 4.5577234839 37.6233969815 0.5971747822 spot 29 219.2952121004 165.7141414949 10513.0313496994 223.3898222585 1.3233343282 9.4950419872 9.9403305966 0.0030191403 10.6447253715 0.0858241705 10.0052270966 0.0059128146 1.1377156435 0.1137121259 38.0042061211 0.4311077733 83.6059326902 8.0300088702 1719.0587194041 183.1404387575 60.9008451733 6.4729663616 38.0042061211 0.4311077733 spot 14 812.2342308576 166.783561577 29894.486667005 101.6891792894 4.8699897231 21.6543850686 1.2986082633 0.0023416089 16.1226473496 0.0554256609 1.7143357824 0.0087085227 1.1191799469 0.652835902 55.8957117091 0.6228693016 54.7739814575 0.9141325001 5.9564872791 na 47.2499305807 7.6090382904 55.8957117091 0.6228693016 spot 116 75.3244362848 52.2784714004 523.0295344973 100 1.4408308863 2.3249409631 7.2578169741 0.0156867871 6.7557124023 0.6428296721 7.4463133343 0.0108441521 1.6648348394 0.2235784024 69.5295786716 1.1513324931 504.0566227026 29.5935823123 4017.2161105498 108.5559294645 314.4448723911 21.078529516 69.5295786716 1.1513324931 spot 24 601.411955034 97.092878122 35435.8419344391 184.234625028 6.194192269 13.1863867511 2.3198251931 0.0084094045 8.5379957729 0.1752136169 3.4481913504 0.0167641454 2.5511633939 0.7398555169 107.1727836285 2.7115505252 163.933525622 5.2200676928 1089.8469290549 46.4650223889 169.1766144374 14.3839830898 107.1727836285 2.7115505252 spot 122 188.6955472999 250.1365164358 10758.0530574895 255.9290033034 0.7543702534 20.4925173094 1.560386059 0.0076319259 4.2915891735 0.1646570791 1.7290871469 0.0244829346 0.744941413 0.4308293045 155.9260676536 1.1476225469 154.7714789138 2.4821612689 137.1522320922 36.6503852367 153.5949517667 6.5666698893 155.9260676536 1.1476225469 spot 99 490.0267919632 286.7446616455 250891.458789318 4464.0309044869 1.7089308277 11.4902108005 0.7721116688 0.0276007298 2.3643259502 0.7881990626 1.5653262876 0.065713056 1.3616497191 0.8698823561 410.2763017163 5.412464824 590.1497721781 7.0058644817 1360.3146983668 14.8790364487 550.0342708947 12.829164364 410.2763017163 5.412464824 spot 10 211.1908659085 83.0109292159 38885.891380595 451.6771438701 2.5441332594 11.9460517546 0.7843633565 0.039516088 4.0695924158 0.8678943661 1.2467909891 0.0752279133 0.9691552484 0.7773197407 467.5755133545 4.37109363 634.4233020515 5.8822432618 1284.949165503 15.2752943247 782.9354517313 31.2527898425 467.5755133545 4.37109363 spot 27 142.9627045485 51.903467413 31175.9338861941 100 2.7543960293 13.3776906207 0.9493358623 0.0131479579 17.6623502051 0.9001734093 1.2107705318 0.0873765881 0.7514830013 0.6206650902 540.0031932577 3.8927142393 651.8202265048 5.8241085325 1060.964640301 19.1182760349 263.8843185293 46.3051702998 540.0031932577 3.8927142393 spot 71 163.2688909206 91.0276021292 56790.9084658117 564.091574891 1.7936195956 14.6857635295 0.6205096918 0.0443681328 3.3983130577 1.3184686878 1.0524535177 0.1404928122 0.8500741905 0.8077071112 847.4485760206 6.7505125318 853.8426353273 6.0772430538 870.484320916 12.863716037 877.0110080468 29.1659433095 847.4485760206 6.7505125318 spot 72 50.112761527 30.3337305702 28494.1369689901 290.3380821394 1.6520474266 13.2481692722 1.3994976048 0.0547625054 4.5412933866 1.9487084394 1.6051779062 0.1873227345 0.7861313914 0.489747204 1106.8555652723 7.9953093538 1098.0019874309 10.7717039539 1080.5073388138 28.0606797685 1077.0833978882 47.6325455646 1080.5073388138 28.0606797685 spot 3 184.8664046559 99.5264814966 117359.608853592 1060.8976880367 1.8574594608 13.022934856 0.7795903491 0.0561010207 3.3712450133 1.9517860745 1.1805528352 0.1844288413 0.886534762 0.750948823 1091.1243699437 8.8988546728 1099.0612135172 7.9263180773 1114.8293226232 15.5601230519 1102.7039234291 36.1785271588 1114.8293226232 15.5601230519 spot 60 397.6546922354 147.9991866716 619633.295812813 4833.328766449 2.6868707942 12.9659812694 0.698526899 0.0509697838 2.2843014186 1.8689533696 1.2512714032 0.175829447 1.0381427146 0.8296702953 1044.1502716428 10.0074376466 1070.1602108846 8.2768679279 1123.5528014877 13.9306848223 1004.3099299944 22.3805600342 1123.5528014877 13.9306848223 spot 76 322.8953814956 106.8768453037 428982.079643642 2760.0198253255 3.0211911717 12.7396661547 0.6443609238 0.0464482211 4.3485338943 1.9115308084 1.5312232816 0.1766961569 1.3890441814 0.9071467226 1048.9002061426 13.4461410798 1085.1185397249 10.2080544446 1158.5481319353 12.7910321386 917.2077486042 38.9932596838 1158.5481319353 12.7910321386 spot 128 139.8773570288 62.1387470245 129410.535061929 922.2001182078 2.2510488822 12.6176241802 0.7137020266 0.0569288342 3.2109809178 2.1043111338 1.0689504187 0.1926527866 0.7957916905 0.7444608063 1135.7296275801 8.2866522235 1150.2176308017 7.3576611692 1177.6488089443 14.1334928502 1118.5328590928 34.9397266518 1177.6488089443 14.1334928502 spot 79 115.9253374446 42.3976424082 153400.546195356 940.4345237053 2.7342401808 11.7716327539 0.6126451601 0.0666176055 3.5286121688 2.6225658184 0.9635732636 0.2240014634 0.7437333811 0.7718493333 1302.9839141687 8.7741421612 1306.9833623162 7.0832375685 1313.5340276298 11.8834515049 1302.8792974875 44.5225163593 1313.5340276298 11.8834515049 spot 51 128.6276990649 99.6049623841 165172.356763038 2080.7433862163 1.2913784212 11.4595299085 0.6850473128 0.0664930866 2.6809094474 2.7543718033 0.9437544144 0.2290219566 0.6491398723 0.687827111 1329.3711255318 7.7978375256 1343.2715389892 7.0304177403 1365.4676613871 13.192113848 1300.5207399703 33.7672582832 1365.4676613871 13.192113848 spot 43 200.8408440602 73.8798053094 31217.8233971393 192.7582220512 2.71848096 11.1832458281 1.4038132279 0.059452271 8.2467297338 2.4805913077 1.6181196512 0.2012847366 0.804748176 0.4973353951 1182.2181975548 8.6924730778 1266.387973143 11.7101371853 1412.3092703293 26.8595474315 1166.7080627132 93.4903349543 1412.3092703293 26.8595474315 spot 7 181.8477633677 111.8808181823 76961.8157385693 787.1372330767 1.6253703389 9.8568649821 0.6701605919 0.0832515822 2.5707825562 3.9212627145 1.1710731799 0.2804481 0.9603630426 0.8200709052 1593.618660812 13.5595353251 1618.0790443799 9.4749284857 1650.0308961752 12.4252825552 1615.4998436825 39.9138733241 1650.0308961752 12.4252825552 spot 67 174.2329167529 46.9256970433 95368.7626944078 408.3902406338 3.7129531948 9.4630463994 0.6443853801 0.0872627405 2.5687281033 4.4773846984 1.0600797708 0.3074277982 0.8417461626 0.7940403976 1728.0367070297 12.759255611 1726.7885893614 8.7989428108 1725.2599391098 11.8340080464 1690.1674848649 41.6493181578 1725.2599391098 11.8340080464 spot 9 162.5092523291 102.8051804056 306001.636026249 4015.8903174929 1.580749644 7.8709114923 0.5165831609 0.1083965187 2.4734829168 6.7646376027 0.9672698457 0.3863290077 0.8177730689 0.8454446012 2105.7808343286 14.6907094537 2081.1085798813 8.5567961325 2056.7678483342 9.1179421246 2079.0786506293 48.8680202247 2056.7678483342 9.1179421246 spot 16 70.3221545621 56.3032841369 130794.281290025 1588.4810287277 1.2489885029 5.5022741756 0.592577149 0.1425051142 2.7120239021 12.6992468722 0.8994059793 0.5069999863 0.6765969539 0.7522709093 2643.8092542633 14.6738370849 2657.6035523084 8.4659757189 2668.1074040007 9.8148348441 2691.3802042578 68.3380005824 2668.1074040007 9.8148348441 spot 56 119.2087688534 163.9056879418 584243.778495725 16491.29886178 0.7273009885 4.887019209 0.5940469034 0.1581711776 1.9171170787 15.9852730922 0.8882444785 0.5668287379 0.6603684806 0.743453516 2894.7859109992 15.4005311673 2875.9168197365 8.4882872916 2862.7170192413 9.6652611523 2966.5088882093 52.8931004196 2862.7170192413 9.6652611523 spot 28 636.7812377381 563.3062423686 593775.649910125 10860.6473150346 1.1304352586 4.8693506138 0.4721959092 0.1505128698 2.1832867446 15.4732899353 1.0337992942 0.5466904212 0.9196586345 0.8895910838 2811.3936242527 20.9548451764 2844.8395973471 9.860118037 2868.6084008418 7.6786073889 2832.481146087 57.701740797 2868.6084008418 7.6786073889 spot 114 146.225139124 174.8450490054 212742.12104864 5169.7079740618 0.8363127235 4.8635279785 0.4407019345 0.1543897598 2.2354609878 15.8288338643 0.9071292357 0.5585834884 0.7928841373 0.8740586304 2860.7728508042 18.3183826467 2866.5215176849 8.6637220671 2870.5538851421 7.1652062937 2900.4415735598 60.3989260109 2870.5538851421 7.1652062937 spot 120 116.6896501908 164.2962384899 271302.196182043 7745.9535045944 0.7102393291 4.8498744993 0.4529013124 0.1509066041 2.3018892562 15.6491023607 0.9139206172 0.5506906289 0.7938080975 0.8685744501 2828.0444720623 18.1726141063 2855.6189294824 8.7226345288 2875.1236540474 7.360526334 2839.3935995855 60.9745648711 2875.1236540474 7.360526334 spot 37 320.0480757539 342.3125048751 2147081.15830581 46255.4566004289 0.9349587619 4.8498601965 0.4638508746 0.1553846845 1.6837135148 15.9909912902 0.9728636038 0.5627200128 0.8551642869 0.8790176584 2877.8591516332 19.8509054519 2876.2585972413 9.2971678751 2875.1284468671 7.5384769087 2917.8454289068 45.7451804728 2875.1284468671 7.5384769087 spot 45 234.8887131817 166.2540424266 503022.562148405 7206.4611819759 1.4128300867 4.8338071211 0.4762689074 0.1533788253 2.4139130695 15.9258879624 1.0210708503 0.5585740142 0.9031907933 0.8845525196 2860.7336650319 20.8666398786 2872.3605442096 9.755540718 2880.5154381372 7.7329666667 2882.7422927689 64.850204822 2880.5154381372 7.7329666667 1.            analyses with >10% uncertainty (1-sigma) in 206pb/238u age are not included. 2.            analyses with >10% uncertainty (1-sigma) in 206pb/207pb age are not included, unless 206pb/238u age is <400 ma. 3.            best age is determined from 206pb/238u age for analyses with 206pb/238u age <900 ma and from 206pb/207pb age for analyses with 206pb/238uage >900 ma. 4.            concordance is based on 206pb/238u age / 206pb/207pb age.  value is not reported for 206pb/238u ages <400 ma because of large uncertainty in 206pb/207pb age. 5.            analyses with 206pb/238u age >400 ma and with >20% discordance (<80% concordance) are not included. 6.            analyses with 206pb/238u age >400 ma and with >5% reverse discordance (<105% concordance) are not included. 7.            all uncertainties are reported at the 2-sigma level, and include only measurement errors. 8.            systematic errors are as follows (at 2-sigma level): [sample 1: xxx% (206pb/238u) & xxx% (206pb/207pb)] these values are reported on cells w1 and y1 of e2agecalc. 9.            analyses conducted by la-icpms, as described by gehrels et al. (2008) and gehrels and pecha (2014). 10.         u concentration and u/th are calibrated relative to fc-1 zircon standard and are accurate to ~20%. 11.         common pb composition assigned uncertainties of 1.5 for 206pb/204pb, 0.3 for 207pb/204pb, and 2.0 for 208pb/204pb. 12.         u/pb and 206pb/207pb fractionation is calibrated relative to fragments of large sri lanka zircons and individual crystals of fc-1, and r33.    plotdat10 source sheet all pc 0 0 320 0 0 0 plot name probdens4 1.6 0 480 0 3198.4 0 plot type 16 3.2 0 480 4 1st free col 9 4.8 0 320 4 sigma level 1 6.4 0 320 0 absolute errs true 8 0 errbox errbox symbol type 1 9.6 0 480 0 inverse plot false 11.2 0 640 0 color plot true 12.8 0 640 2 3d plot false 14.4 0 480 2 linear false 16 0 480 0 data range a1:b49 17.6 0 errbox errbox filled symbols true 19.2 0 800 0 concage false 20.8 0 960 0 concswap false 22.4 0 960 1 1st symbol-row 1 24 0 800 1 25.6 0 800 0 27.2 0 errbox errbox 28.8 0 960 0 30.4 0 1120 0 32 0 1120 8 33.6 0 960 8 35.2 0 960 0 36.8 0 errbox errbox 38.4 0 1120 0 40 0 1280 0 41.6 0 1280 7 43.2 0 1120 7 44.8 0 1120 0 46.4 0 errbox errbox 48 0 1280 0 49.6 0 1440 0 51.2 0 1440 5 52.8 0 1280 5 54.4 0 1280 0 56 0 errbox errbox 57.6 0 1440 0 59.2 0 1600 0 60.8 0 1600 1 62.4 0 1440 1 64 0 1440 0 65.6 0 errbox errbox 67.2 0 1600 0 68.8 0 1760 0 70.4 0 1760 3 72 0 1600 3 73.6 0 1600 0 75.2 0 errbox errbox 76.8 0 1760 0 78.4 0 1920 0 80 0 1920 2 81.6 0 1760 2 83.2 0 1760 0 84.8 0 errbox errbox 86.4 0 1920 0 88 0 2080 0 89.6 0 2080 1 91.2 0 1920 1 92.8 0 1920 0 94.4 0 errbox errbox 96 0 2560 0 97.6 0 2720 0 99.2 0 2720 3 100.8 0 2560 3 102.4 0 2560 0 104 0 errbox errbox 105.6 0 2720 0 107.2 0 2880 0 108.8 0 2880 5 110.4 0 2720 5 112 0 2720 0 113.6 0 errbox errbox 115.2 0 2880 0 116.8 0 3040 0 118.4 0 3040 7 120 0 2880 7 121.6 0 2880 0 123.2 0 errbox errbox 124.8 0 126.4 0 128 0 129.6 0 131.2 0 132.8 0 134.4 0 136 0 137.6 0 139.2 0 140.8 0 142.4 0 144 0 145.6 0 147.2 0 148.8 0 150.4 0 152 0 153.6 0 155.2 0 156.8 0 158.4 0 160 0 161.6 0 163.2 0 164.8 0 166.4 0 168 0 169.6 0 171.2 0 172.8 0 174.4 0 176 0 177.6 0 179.2 0 180.8 0 182.4 0 184 0 185.6 0 187.2 0 188.8 0 190.4 0 192 0 193.6 0 195.2 0 196.8 0 198.4 0 200 0 201.6 0 203.2 0 204.8 0 206.4 0 208 0 209.6 0 211.2 0 212.8 0 214.4 0 216 0 217.6 0 219.2 0 220.8 0 222.4 0 224 0 225.6 0 227.2 0 228.8 0 230.4 0 232 0 233.6 0 235.2 0 236.8 0 238.4 0 240 0 241.6 0 243.2 0 244.8 0 246.4 0 248 0 249.6 0 251.2 0 252.8 0 254.4 0 256 0 257.6 0 259.2 0 260.8 0 262.4 0 264 0 265.6 0 267.2 0 268.8 0 270.4 0 272 0 273.6 0 275.2 0 276.8 0 278.4 0 280 0 281.6 0 283.2 0 284.8 0 286.4 0 288 0 289.6 0 291.2 0 292.8 0 294.4 0 296 0 297.6 0 299.2 0 300.8 0 302.4 0 304 0 305.6 0 307.2 0 308.8 0 310.4 0 312 0 313.6 0 315.2 0 316.8 0 318.4 0 320 0 321.6 0 323.2 0 324.8 0 326.4 0 328 0 329.6 0 331.2 0 332.8 0 334.4 0 336 0 337.6 0 339.2 0 340.8 0 342.4 0 344 0 345.6 0 347.2 0 348.8 0 350.4 0 352 0 353.6 0 355.2 0 356.8 0 358.4 0 360 0 361.6 0.0000001602 363.2 0.0000012459 364.8 0.000007587 366.4 0.0000361831 368 0.0001351427 369.6 0.0003953062 371.2 0.0009055824 372.8 0.0016247098 374.4 0.0022828484 376 0.0025120703 377.6 0.0021649106 379.2 0.0014611729 380.8 0.0007723545 382.4 0.0003197313 384 0.000103659 385.6 0.0000263659 387.2 0.0000054036 388.8 0.0000013885 390.4 0.0000018731 392 0.0000050278 393.6 0.0000130591 395.2 0.0000310813 396.8 0.0000677849 398.4 0.0001354611 400 0.0002481071 401.6 0.0004165728 403.2 0.0006418772 404.8 0.0009103392 406.4 0.0011969101 408 0.0014805244 409.6 0.0017639758 411.2 0.0020749332 412.8 0.002426526 414.4 0.0027570482 416 0.0029190451 417.6 0.0027667672 419.2 0.0022820059 420.8 0.0016101173 422.4 0.0009628818 424 0.0004859592 425.6 0.0002068144 427.2 0.0000743936 428.8 0.0000227628 430.4 0.0000059991 432 0.0000013921 433.6 0.0000002943 435.2 0.0000000592 436.8 0 438.4 0 440 0 441.6 0 443.2 0 444.8 0 446.4 0 448 0.0000000822 449.6 0.0000003961 451.2 0.0000016691 452.8 0.0000061509 454.4 0.0000198247 456 0.0000558836 457.6 0.0001377757 459.2 0.0002970786 460.8 0.0005602484 462.4 0.0009240605 464 0.0013330019 465.6 0.0016817899 467.2 0.0018557662 468.8 0.0017909579 470.4 0.0015116737 472 0.0011159412 473.6 0.0007205019 475.2 0.0004068549 476.8 0.0002009345 478.4 0.0000867921 480 0.0000327881 481.6 0.0000108334 483.2 0.0000031305 484.8 0.0000007912 486.4 0.0000001749 488 0.0000000338 489.6 0 491.2 0 492.8 0 494.4 0 496 0 497.6 0 499.2 0 500.8 0 502.4 0 504 0 505.6 0 507.2 0 508.8 0 510.4 0 512 0 513.6 0 515.2 0 516.8 0 518.4 0 520 0 521.6 0.0000000293 523.2 0.0000001881 524.8 0.0000010192 526.4 0.0000046636 528 0.0000180231 529.6 0.0000588469 531.2 0.0001622514 532.8 0.0003778958 534.4 0.0007436533 536 0.0012371055 537.6 0.0017418676 539.2 0.0020822563 540.8 0.0021302386 542.4 0.0019043063 544 0.0015656706 545.6 0.0013097675 547.2 0.0012470487 548.8 0.0013598071 550.4 0.0015409748 552 0.0016656241 553.6 0.0016496185 555.2 0.0014759612 556.8 0.0011878881 558.4 0.0008589376 560 0.0005578202 561.6 0.0003253486 563.2 0.0001704162 564.8 0.0000801641 566.4 0.0000338654 568 0.0000128481 569.6 0.0000043775 571.2 0.0000013395 572.8 0.0000003681 574.4 0.0000000908 576 0 577.6 0 579.2 0 580.8 0 582.4 0 584 0 585.6 0 587.2 0 588.8 0 590.4 0 592 0 593.6 0 595.2 0 596.8 0 598.4 0 600 0 601.6 0 603.2 0 604.8 0 606.4 0 608 0 609.6 0 611.2 0 612.8 0 614.4 0 616 0 617.6 0 619.2 0 620.8 0 622.4 0 624 0 625.6 0 627.2 0 628.8 0 630.4 0 632 0 633.6 0 635.2 0 636.8 0 638.4 0 640 0 641.6 0 643.2 0 644.8 0 646.4 0 648 0 649.6 0 651.2 0 652.8 0 654.4 0 656 0 657.6 0 659.2 0 660.8 0 662.4 0 664 0 665.6 0 667.2 0 668.8 0 670.4 0 672 0 673.6 0 675.2 0 676.8 0 678.4 0 680 0 681.6 0 683.2 0 684.8 0 686.4 0 688 0 689.6 0 691.2 0 692.8 0 694.4 0 696 0 697.6 0 699.2 0 700.8 0 702.4 0 704 0 705.6 0 707.2 0 708.8 0 710.4 0 712 0 713.6 0 715.2 0 716.8 0 718.4 0 720 0 721.6 0 723.2 0 724.8 0 726.4 0 728 0 729.6 0 731.2 0 732.8 0 734.4 0 736 0 737.6 0 739.2 0 740.8 0 742.4 0 744 0 745.6 0 747.2 0 748.8 0 750.4 0 752 0 753.6 0 755.2 0 756.8 0 758.4 0 760 0 761.6 0 763.2 0 764.8 0 766.4 0 768 0 769.6 0 771.2 0 772.8 0 774.4 0 776 0 777.6 0 779.2 0 780.8 0 782.4 0 784 0 785.6 0 787.2 0 788.8 0 790.4 0 792 0 793.6 0 795.2 0 796.8 0 798.4 0 800 0 801.6 0 803.2 0 804.8 0 806.4 0 808 0 809.6 0 811.2 0 812.8 0 814.4 0 816 0.0000000234 817.6 0.0000000685 819.2 0.00000019 820.8 0.0000004982 822.4 0.0000012347 824 0.0000028927 825.6 0.0000064071 827.2 0.0000134161 828.8 0.0000265577 830.4 0.0000497 832 0.0000879275 833.6 0.0001470602 835.2 0.0002325242 836.8 0.0003475708 838.4 0.0004911572 840 0.0006561453 841.6 0.0008286701 843.2 0.0009893855 844.8 0.0011167387 846.4 0.0011916256 848 0.0012020714 849.6 0.001146365 851.2 0.0010335173 852.8 0.000880876 854.4 0.000709764 856 0.000540649 857.6 0.000389331 859.2 0.0002650482 860.8 0.0001705818 862.4 0.000103787 864 0.0000596974 865.6 0.0000324616 867.2 0.0000166873 868.8 0.0000081097 870.4 0.0000037259 872 0.0000016183 873.6 0.0000006645 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0.0000217711 76.775 0.0000213817 76.8 0.0000209984 76.825 0.000020621 76.85 0.0000202495 76.875 0.0000198839 76.9 0.000019524 76.925 0.0000191699 76.95 0.0000188213 76.975 0.0000184783 77 0.0000181407 77.025 0.0000178086 77.05 0.0000174818 77.075 0.0000171602 77.1 0.0000168438 77.125 0.0000165326 77.15 0.0000162264 77.175 0.0000159252 77.2 0.0000156289 77.225 0.0000153375 77.25 0.0000150508 77.275 0.0000147689 77.3 0.0000144916 77.325 0.000014219 77.35 0.0000139508 77.375 0.0000136871 77.4 0.0000134279 77.425 0.0000131729 77.45 0.0000129223 77.475 0.0000126759 77.5 0.0000124336 77.525 0.0000121955 77.55 0.0000119614 77.575 0.0000117313 77.6 0.0000115051 77.625 0.0000112828 77.65 0.0000110643 77.675 0.0000108496 77.7 0.0000106386 77.725 0.0000104312 77.75 0.0000102274 77.775 0.0000100272 77.8 0.0000098305 77.825 0.0000096373 77.85 0.0000094474 77.875 0.0000092609 77.9 0.0000090776 77.925 0.0000088976 77.95 0.0000087208 77.975 0.0000085472 78 0.0000083766 78.025 0.0000082091 78.05 0.0000080446 78.075 0.000007883 78.1 0.0000077244 78.125 0.0000075686 78.15 0.0000074157 78.175 0.0000072655 78.2 0.0000071181 78.225 0.0000069734 78.25 0.0000068313 78.275 0.0000066918 78.3 0.0000065549 78.325 0.0000064205 78.35 0.0000062886 78.375 0.0000061591 78.4 0.000006032 78.425 0.0000059073 78.45 0.000005785 78.475 0.0000056649 78.5 0.0000055471 78.525 0.0000054315 78.55 0.0000053181 78.575 0.0000052068 78.6 0.0000050976 78.625 0.0000049905 78.65 0.0000048855 78.675 0.0000047824 78.7 0.0000046814 78.725 0.0000045822 78.75 0.000004485 78.775 0.0000043896 78.8 0.0000042961 78.825 0.0000042044 78.85 0.0000041145 78.875 0.0000040263 78.9 0.0000039399 78.925 0.0000038551 78.95 0.000003772 78.975 0.0000036906 79 0.0000036107 79.025 0.0000035324 79.05 0.0000034557 79.075 0.0000033804 79.1 0.0000033067 79.125 0.0000032345 79.15 0.0000031637 79.175 0.0000030943 79.2 0.0000030263 79.225 0.0000029596 79.25 0.0000028943 79.275 0.0000028304 79.3 0.0000027677 79.325 0.0000027063 79.35 0.0000026461 79.375 0.0000025872 79.4 0.0000025295 79.425 0.0000024729 79.45 0.0000024175 79.475 0.0000023633 79.5 0.0000023102 79.525 0.0000022581 79.55 0.0000022072 79.575 0.0000021573 79.6 0.0000021084 79.625 0.0000020606 79.65 0.0000020137 79.675 0.0000019679 79.7 0.000001923 79.725 0.000001879 79.75 0.000001836 79.775 0.0000017938 79.8 0.0000017526 79.825 0.0000017123 79.85 0.0000016728 79.875 0.0000016341 79.9 0.0000015963 79.925 0.0000015592 79.95 0.000001523 79.975 0.0000014875 isoline isoline casto analysis u 206pb u/th 206pb* ± 207pb* ± 206pb* ± error 206pb* ± 207pb* ± 206pb* ± best age ± conc (ppm) 204pb 207pb* (%) 235u* (%) 238u (%) corr. 238u* (ma) 235u (ma) 207pb* (ma) (ma) (ma) (%) base of markagunt landslide-spot 115 68.6017221178 732.6316127872 0.7081656692 38.7781759448 5.5222976291 0.0182315753 5.7343441027 0.0051297869 1.5449696385 0.2694239499 32.9842023545 0.5082944155 18.3453042417 1.0425369304 na na 32.9842023545 0.5082944155 na base of markagunt landslide-spot 44 158.7513200224 1292.4220318755 1.5549908648 26.54083024 8.177146828 0.0267708886 8.2531166602 0.0051554318 1.1172306658 0.1353707589 33.1486740186 0.3693965845 26.8252201408 2.1849313968 na na 33.1486740186 0.3693965845 na base of markagunt landslide-spot 55 261.1685231606 9398.7413523873 2.2221800844 22.0182323921 2.266809702 0.0322884752 2.5862914467 0.0051584324 1.245181602 0.4814544794 33.1679177497 0.4119401497 32.2670033046 0.8213985392 na na 33.1679177497 0.4119401497 na base of markagunt landslide-spot 127 134.5722158521 4467.1066787243 0.6532926385 23.9407715537 3.1963127108 0.0297250212 3.4237856542 0.0051635462 1.2271484266 0.35841859 33.2007145313 0.4063746805 29.7423941554 1.0035465615 na na 33.2007145313 0.4063746805 na base of markagunt landslide-spot 83 86.2284784031 7992.7327767651 0.7919335565 20.3230331974 3.4712621316 0.0351301378 3.8787397259 0.0051803146 1.7305955839 0.446174713 33.3082541125 0.5749445443 35.0582888911 1.3366130587 156.6164932432 81.2767451798 33.3082541125 0.5749445443 na base of markagunt landslide-spot 56 904.4690290409 45513.126872985 1.1939947496 21.1678179778 1.7742065758 0.0337326389 1.9515428917 0.0051810068 0.8128411187 0.416512044 33.3126935108 0.2700808306 33.6865237371 0.6466215265 60.4396898261 42.2757016336 33.3126935108 0.2700808306 na base of markagunt landslide-spot 38 314.264990861 5191.9232290652 3.5480964084 22.4992990467 1.6246023022 0.031776683 1.9537559147 0.0051875859 1.0852785512 0.5554831814 33.3548865222 0.3610585337 31.7634677784 0.6109745525 na na 33.3548865222 0.3610585337 na base of markagunt landslide-spot 110 128.7004919882 1849.1651324876 1.3018078603 23.1401927817 4.242472452 0.03091324 4.4123686119 0.0051903812 1.212610515 0.2748207645 33.3728126725 0.4036365301 30.9133879733 1.3434588187 na na 33.3728126725 0.4036365301 na base of markagunt landslide-spot 68 423.2142327032 24793.8314355648 1.5156594295 21.6732964442 1.4349374558 0.0330560014 1.7386569302 0.0051983204 0.9817751367 0.5646744448 33.4237278314 0.3272966238 33.0216795329 0.5648983486 3.8549719951 34.540642909 33.4237278314 0.3272966238 na base of markagunt landslide-spot 65 671.9688849524 10672.5230195806 0.4605623397 19.8525087604 1.4122311908 0.0360926907 1.7494716888 0.005199031 1.0325958811 0.5902329759 33.4282851725 0.3442856672 36.0020405049 0.6188102986 211.1406157225 32.7482396029 33.4282851725 0.3442856672 na base of markagunt landslide-spot 126 90.5995787905 5563.1301795239 1.4386383309 22.3191228678 3.4950133546 0.0321529415 3.7399304023 0.0052069761 1.3311502791 0.355929158 33.4792374931 0.4445037073 32.1336804604 1.1829606085 na na 33.4792374931 0.4445037073 na base of markagunt landslide-spot 106 199.4981054009 6624.2547722868 1.2616229751 22.1778528546 2.7432150021 0.0323684042 2.9703424008 0.0052086904 1.1391687455 0.3835142862 33.490230812 0.3805209509 32.3456203209 0.9456341232 na na 33.490230812 0.3805209509 na base of markagunt landslide-spot 75 208.120149894 1726.9943551539 1.9543605932 24.3649694553 4.1417935237 0.0294740491 4.3074312719 0.0052106683 1.1830091164 0.2746437591 33.5029153327 0.3953144013 29.4948873793 1.252197655 na na 33.5029153327 0.3953144013 na base of markagunt landslide-spot 103 226.1154937511 6948.5879005492 0.6361446134 19.8189841719 2.1430397773 0.0362457094 2.447310544 0.0052122561 1.1818246112 0.4829074978 33.513098124 0.3950383057 36.1519895812 0.8691864689 215.0550454026 49.6490540104 33.513098124 0.3950383057 na base of markagunt landslide-spot 8 262.0099629445 14478.5672414809 1.360161154 18.7816220732 2.594754513 0.0383454552 2.8553221955 0.005225583 1.1916853014 0.4173558078 33.5985625267 0.3993475325 38.2073796628 1.0706739208 338.1812094174 58.7616947521 33.5985625267 0.3993475325 na base of markagunt landslide-spot 122 214.8772582346 3052.141037693 1.7483684789 23.451676013 6.2614310409 0.0307745081 6.4556483015 0.0052366405 1.5715840139 0.2434432516 33.6694728961 0.5277646038 30.7767368851 1.9570312555 na na 33.6694728961 0.5277646038 na base of markagunt landslide-spot 37 195.9248592169 2428.3274565225 1.0869240737 23.6536426962 6.4032139158 0.0305438463 6.4860516689 0.0052421508 1.0333043117 0.1593117608 33.7048095939 0.3473643697 30.5494938653 1.9519473595 na na 33.7048095939 0.3473643697 na base of markagunt landslide-spot 92 246.4787285165 87946.4501312177 0.8077410176 19.9975302831 1.633256149 0.0361973992 1.9911396937 0.0052522028 1.1389080873 0.5719880383 33.7692703592 0.3835953503 36.1046509111 0.7062632042 194.290649303 37.9608067929 33.7692703592 0.3835953503 na base of markagunt landslide-spot 50 97.1243149375 1953.8895049727 2.3843595406 25.4459664299 4.0127272484 0.0284664766 4.3541013634 0.0052558192 1.6900351218 0.3881478589 33.7924617434 0.5696102049 28.5006195011 1.2236923138 na na 33.7924617434 0.5696102049 na base of markagunt landslide-spot 25 109.828534103 12327.7198874827 0.770615622 19.9828596423 2.4428808129 0.0363015245 2.6819481689 0.005263447 1.1068781842 0.412714234 33.841376307 0.3736013171 36.2066794853 0.9539357955 195.996336121 56.7564962868 33.841376307 0.3736013171 na base of markagunt landslide-spot 10 207.0563797574 9727.4775503979 1.7442186431 21.6564934139 2.0631987086 0.0335287868 2.3516505316 0.0052685818 1.1284818614 0.4798680103 33.8743041183 0.3812627802 33.486270435 0.7746366491 5.7337529418 49.6672865618 33.8743041183 0.3812627802 na base of markagunt landslide-spot 76 106.1658556809 66025.5995617255 2.1540285853 20.1815222136 3.6302684168 0.0359816391 3.8299428665 0.0052689323 1.2204972685 0.3186724479 33.8765513898 0.4123778924 35.8932028115 1.3506765099 172.9133496243 84.7363217991 33.8765513898 0.4123778924 na base of markagunt landslide-spot 86 170.2246621747 14511.6553938045 1.8278412401 19.9295351803 2.4408427694 0.036454892 2.7035680652 0.0052715792 1.1625690768 0.4300128751 33.8935252965 0.3930015905 36.3569400071 0.9655455336 202.158455261 56.6442148626 33.8935252965 0.3930015905 na base of markagunt landslide-spot 19 458.8678754574 2887.9715639255 0.6633744726 23.0380565745 1.074159063 0.0315512494 1.5653863279 0.0052741218 1.1386907671 0.7274183675 33.9098298353 0.3851143128 31.5415918009 0.4861577721 na na 33.9098298353 0.3851143128 na base of markagunt landslide-spot 80 403.4873477669 13480.1802840855 1.6628824871 20.7646656228 2.5447337941 0.0350342112 3.6227531497 0.0052784333 2.5785015612 0.7117519341 33.9374776958 0.8727789869 34.9641879315 1.2451065283 106.0232167861 60.1135228846 33.9374776958 0.8727789869 na base of markagunt landslide-spot 27 256.3930757374 4056.2686185619 1.8715448991 22.714739349 1.9402887797 0.0320433631 2.3587542122 0.005281212 1.3412683867 0.5686342306 33.9552961832 0.4542343062 32.02587668 0.7436230145 na na 33.9552961832 0.4542343062 na base of markagunt landslide-spot 45 127.5423950473 1085.2541323841 1.0878251736 30.4733359051 3.1798925802 0.0238879735 3.4154190873 0.0052818621 1.2463429383 0.3649165466 33.95946517 0.4221385156 23.9702693392 0.8090975213 na na 33.95946517 0.4221385156 na base of markagunt landslide-spot 119 172.5433565413 2841.3945768267 4.6716075007 23.1566573709 3.1216660716 0.0314521603 3.5369976628 0.0052846242 1.6629953108 0.4701714475 33.9771766303 0.5635523904 31.4440510894 1.0951314294 na na 33.9771766303 0.5635523904 na base of markagunt landslide-spot 33 319.4279070465 10504.9849928658 1.2466187191 21.3868992062 2.0851827687 0.0340564617 2.3245481549 0.0052848797 1.0273932769 0.4419754759 33.9788150403 0.3481776397 34.004548628 0.7773629091 35.7984091689 49.9267199596 33.9788150403 0.3481776397 na base of markagunt landslide-spot 36 261.0208401472 2850.9954894253 0.58949555 22.4764885723 6.1888970654 0.0324133008 6.334294524 0.0052861499 1.3493851308 0.2130284794 33.9869607949 0.4574081567 32.389777275 2.0192886513 na na 33.9869607949 0.4574081567 na base of markagunt landslide-spot 109 79.4781798938 17626.1600877405 0.9364211308 19.2150854117 4.51341808 0.037948553 4.7640203218 0.0052908481 1.5247776433 0.3200611123 34.0170878128 0.5173188305 37.8191804835 1.7685744548 286.2820836326 103.2337321712 34.0170878128 0.5173188305 na base of markagunt landslide-spot 13 407.1701364722 10334.6715138605 4.1568562291 22.6459558928 2.0002359907 0.0322064008 2.3255899352 0.0052920094 1.1863492439 0.5101283016 34.0245344072 0.4025864357 32.1862698298 0.7367816004 na na 34.0245344072 0.4025864357 na base of markagunt landslide-spot 39 186.1702014487 16120.0800888651 1.5737234929 21.8205143957 2.5069737085 0.0334401032 2.8435707027 0.0052944439 1.3420049056 0.4719435688 34.0401454864 0.4556164282 33.3991401283 0.9342785171 na na 34.0401454864 0.4556164282 na base of markagunt landslide-spot 52 145.3285040459 1745.375894573 0.8176454929 24.3044737418 3.1417060361 0.0300595299 3.5021080803 0.0053009799 1.5473991692 0.4418479195 34.082057654 0.5259937938 30.0721902311 1.0377182777 na na 34.082057654 0.5259937938 na base of markagunt landslide-spot 105 79.6497025205 2346.5833579364 1.4299659715 24.0585969704 4.44649148 0.0303944272 4.7697109936 0.0053058139 1.7259364072 0.361853456 34.1130551035 0.5872145616 30.4022622067 1.4286068362 na na 34.1130551035 0.5872145616 na base of markagunt landslide-spot 4 345.8415569891 212176.151068825 1.4648000626 20.6307030677 1.4567828975 0.035460954 1.8095028318 0.0053082601 1.0733518007 0.593174977 34.1287412527 0.3653534748 35.3827422971 0.629224931 121.3199052303 34.304293544 34.1287412527 0.3653534748 na base of markagunt landslide-spot 34 288.7681577271 7617.850132522 2.0714185058 20.0225420088 2.7831736808 0.0365448153 2.9651863231 0.0053092447 1.0228754532 0.3449616118 34.1350543715 0.3482362883 36.4450313085 1.0614993794 191.3839707849 64.736958565 34.1350543715 0.3482362883 na base of markagunt landslide-spot 9 161.8875665614 5127.216382508 1.05562636 18.4298698152 5.6465387672 0.0397081001 5.7342284762 0.0053099341 0.9989875711 0.1742148181 34.1394752143 0.340147628 39.539016892 2.223685063 380.8462465821 127.0164712467 34.1394752143 0.340147628 na base of markagunt landslide-spot 51 142.1944520814 25381.6754348654 2.6941508584 20.0624823597 2.8539426512 0.0364830604 3.0448725477 0.0053108457 1.0612540581 0.3485380887 34.1453208349 0.3614105999 36.3845353466 1.0882489296 186.702231641 66.4401574339 34.1453208349 0.3614105999 na base of markagunt landslide-spot 63 44.5519914424 1140.4102465087 1.00995908 23.262420876 8.3700883078 0.0314735099 8.4895951732 0.0053123642 1.4194533891 0.1671991844 34.1550579686 0.4835330453 31.4650678376 2.6302980465 na na 34.1550579686 0.4835330453 na base of markagunt landslide-spot 114 150.3147902313 2001.0152916561 1.9675392146 24.8064329687 2.7348093898 0.0295159464 2.9308786744 0.0053126204 1.0539769474 0.3596112513 34.1567008751 0.3590516854 29.5362103667 0.8532012603 na na 34.1567008751 0.3590516854 na base of markagunt landslide-spot 47 219.8847187393 5217.7770885877 1.8770640032 22.037576655 2.7404071202 0.033237359 3.2436017184 0.005314692 1.7352581719 0.5349788052 34.1699844369 0.5913687541 33.1999189189 1.0594586175 na na 34.1699844369 0.5913687541 na base of markagunt landslide-spot 40 347.0691188255 3535.7873261443 1.4414437292 22.1827534349 2.1913711501 0.0330253609 2.5122404537 0.0053155815 1.2285131581 0.4890109767 34.175688222 0.4187418657 32.9915627655 0.8155071963 na na 34.175688222 0.4187418657 na base of markagunt landslide-spot 66 253.3724899274 4595.0752748865 1.2894325542 23.6313605697 2.1979006261 0.0310047222 2.4429594419 0.0053162369 1.0664350297 0.4365340707 34.1798909909 0.363541702 31.0034880372 0.7459563841 na na 34.1798909909 0.363541702 na base of markagunt landslide-spot 43 179.46996584 2016.9086381296 2.8552348327 24.4047067345 2.9914886932 0.0300340307 3.1539192958 0.0053183262 0.9991007571 0.3167806984 34.1932880394 0.3407209693 30.0470540864 0.9337758903 na na 34.1932880394 0.3407209693 na base of markagunt landslide-spot 62 285.1363629541 3806.7870287697 1.3146410847 23.1180960611 2.6841248447 0.0317076973 2.8745857882 0.0053186881 1.0289398775 0.3579437016 34.195608788 0.3509206868 31.6955758348 0.8970431419 na na 34.195608788 0.3509206868 na base of markagunt landslide-spot 79 390.8279777249 26053.6165289206 0.7007061824 21.780753539 1.7326025277 0.033672471 2.1778168771 0.0053215193 1.3194600529 0.6058636366 34.2137634605 0.4502410783 33.6274221246 0.7203496998 na na 34.2137634605 0.4502410783 na base of markagunt landslide-spot 42 188.5901920564 2636.0210868583 1.506376597 23.4911286975 2.6806432186 0.0312225186 2.9725305569 0.0053218125 1.28455823 0.4321429857 34.2156436505 0.4383555079 31.2179617779 0.9138436541 na na 34.2156436505 0.4383555079 na base of markagunt landslide-spot 24 167.5386093288 2361.6783499929 3.958365821 23.9274172842 2.7268222003 0.0306748811 3.0210425915 0.0053255745 1.3004380138 0.4304600066 34.2397666247 0.4440865274 30.678592743 0.912952269 na na 34.2397666247 0.4440865274 na base of markagunt landslide-spot 100 207.4703430199 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63 0.0051572987 63.02 0.0051735633 63.04 0.0051859185 63.06 0.005194336 63.08 0.0051987965 63.1 0.00519929 63.12 0.0051958151 63.14 0.00518838 63.16 0.0051770015 63.18 0.0051617058 63.2 0.0051425276 63.22 0.0051195107 63.24 0.0050927072 63.26 0.0050621777 63.28 0.0050279912 63.3 0.0049902243 63.32 0.0049489612 63.34 0.0049042937 63.36 0.0048563203 63.38 0.0048051463 63.4 0.004750883 63.42 0.0046936477 63.44 0.004633563 63.46 0.0045707566 63.48 0.0045053605 63.5 0.004437511 63.52 0.0043673476 63.54 0.0042950133 63.56 0.0042206535 63.58 0.0041444159 63.6 0.0040664495 63.62 0.0039869049 63.64 0.003905933 63.66 0.0038236854 63.68 0.0037403129 63.7 0.0036559661 63.72 0.0035707942 63.74 0.0034849449 63.76 0.0033985639 63.78 0.0033117946 63.8 0.0032247777 63.82 0.0031376508 63.84 0.003050548 63.86 0.0029635998 63.88 0.0028769326 63.9 0.0027906684 63.92 0.002704925 63.94 0.0026198152 63.96 0.0025354469 63.98 0.0024519229 64 0.0023693408 64.02 0.0022877928 64.04 0.0022073657 64.06 0.0021281406 64.08 0.0020501931 64.1 0.0019735933 64.12 0.0018984056 64.14 0.0018246886 64.16 0.0017524957 64.18 0.0016818745 64.2 0.0016128673 64.22 0.0015455111 64.24 0.0014798376 64.26 0.0014158734 64.28 0.0013536401 64.3 0.0012931546 64.32 0.001234429 64.34 0.001177471 64.36 0.0011222839 64.38 0.0010688671 64.4 0.0010172158 64.42 0.0009673217 64.44 0.0009191728 64.46 0.0008727541 64.48 0.000828047 64.5 0.0007850306 64.52 0.0007436808 64.54 0.0007039714 64.56 0.0006658737 64.58 0.0006293571 64.6 0.0005943892 64.62 0.0005609357 64.64 0.000528961 64.66 0.0004984283 64.68 0.0004692996 64.7 0.0004415359 64.72 0.0004150978 64.74 0.0003899448 64.76 0.0003660365 64.78 0.0003433318 64.8 0.0003217896 64.82 0.000301369 64.84 0.0002820288 64.86 0.0002637284 64.88 0.0002464272 64.9 0.0002300853 64.92 0.0002146632 64.94 0.0002001219 64.96 0.0001864233 64.98 0.0001735298 65 0.0001614048 65.02 0.0001500125 65.04 0.0001393178 65.06 0.0001292869 65.08 0.0001198866 65.1 0.0001110849 65.12 0.0001028509 65.14 0.0000951545 65.16 0.0000879669 65.18 0.0000812602 65.2 0.0000750075 65.22 0.000069183 65.24 0.0000637622 65.26 0.0000587212 65.28 0.0000540376 65.3 0.0000496895 65.32 0.0000456564 65.34 0.0000419187 65.36 0.0000384576 65.38 0.0000352553 65.4 0.000032295 65.42 0.0000295607 65.44 0.0000270373 65.46 0.0000247104 65.48 0.0000225665 65.5 0.0000205929 65.52 0.0000187776 65.54 0.0000171092 65.56 0.0000155771 65.58 0.0000141715 65.6 0.0000128828 65.62 0.0000117024 65.64 0.000010622 65.66 0.000009634 65.68 0.0000087312 65.7 0.000007907 65.72 0.0000071552 65.74 0.0000064698 65.76 0.0000058457 65.78 0.0000052777 65.8 0.0000047613 65.82 0.0000042922 65.84 0.0000038663 65.86 0.00000348 65.88 0.0000031299 65.9 0.0000028129 65.92 0.0000025261 65.94 0.0000022667 65.96 0.0000020325 65.98 0.0000018211 66 0.0000016304 66.02 0.0000014586 66.04 0.0000013038 66.06 0.0000011646 66.08 0.0000010395 66.1 0.0000009271 66.12 0.0000008262 66.14 0.0000007358 66.16 0.0000006547 66.18 0.0000005822 66.2 0.0000005172 66.22 0.0000004592 66.24 0.0000004074 66.26 0.0000003611 66.28 0.0000003199 66.3 0.0000002831 66.32 0.0000002504 66.34 0.0000002213 66.36 0.0000001954 66.38 0.0000001724 66.4 0.000000152 66.42 0.000000134 66.44 0.0000001179 66.46 0.0000001037 66.48 0.0000000912 66.5 0.0000000801 66.52 0.0000000703 66.54 0.0000000617 66.56 0.000000054 66.58 0.0000000473 66.6 0.0000000414 66.62 0.0000000362 66.64 0.0000000316 66.66 0.0000000276 66.68 0.0000000241 66.7 0.000000021 66.72 0.0000000183 66.74 0.0000000159 66.76 0.0000000138 66.78 0.000000012 66.8 0.0000000104 66.82 0 66.84 0 66.86 0 66.88 0 66.9 0 66.92 0 66.94 0 66.96 0 66.98 0 67 0 67.02 0 67.04 0 67.06 0 67.08 0 67.1 0 67.12 0 67.14 0 67.16 0 67.18 0 67.2 0 67.22 0 67.24 0 67.26 0 67.28 0 67.3 0 67.32 0 67.34 0 67.36 0 67.38 0 67.4 0 67.42 0 67.44 0 67.46 0 67.48 0 67.5 0 67.52 0 67.54 0 67.56 0 67.58 0 67.6 0 67.62 0 67.64 0 67.66 0 67.68 0 67.7 0 67.72 0 67.74 0 67.76 0 67.78 0 67.8 0 67.82 0 67.84 0 67.86 0 67.88 0 67.9 0 67.92 0 67.94 0 67.96 0 67.98 0 68 0 68.02 0 68.04 0 68.06 0 68.08 0 68.1 0 68.12 0 68.14 0 68.16 0 68.18 0 68.2 0 68.22 0 68.24 0 68.26 0 68.28 0 68.3 0 68.32 0 68.34 0 68.36 0 68.38 0 68.4 0 68.42 0 68.44 0 68.46 0 68.48 0 68.5 0 68.52 0 68.54 0 68.56 0 68.58 0 68.6 0 68.62 0 68.64 0 68.66 0 68.68 0 68.7 0 68.72 0 68.74 0 68.76 0 68.78 0 68.8 0 68.82 0 68.84 0 68.86 0 68.88 0 68.9 0 68.92 0 68.94 0 68.96 0 68.98 0 69 0 69.02 0 69.04 0 69.06 0 69.08 0 69.1 0 69.12 0 69.14 0 69.16 0 69.18 0 69.2 0 69.22 0 69.24 0 69.26 0 69.28 0 69.3 0 69.32 0 69.34 0 69.36 0 69.38 0 69.4 0 69.42 0 69.44 0 69.46 0 69.48 0 69.5 0 69.52 0 69.54 0 69.56 0 69.58 0 69.6 0 69.62 0 69.64 0 69.66 0 69.68 0 69.7 0 69.72 0 69.74 0 69.76 0 69.78 0 69.8 0 69.82 0 69.84 0 69.86 0 69.88 0 69.9 0 69.92 0 69.94 0 69.96 0 69.98 0 isoline isoline plotdat19 source sheet haycock 0.2 33.0502620997 1 32.6034162685 0.3770061812 0.85 32.2264100874 plot name average14 12.8 33.0502620997 2 32.6907730712 0.5354746576 1.15 32.2264100874 plot type 15 3 32.8341038655 0.411767643 1.15 32.9804224497 1st free col 8 4 32.8489777283 0.3256411561 0.85 32.9804224497 sigma level 1 5 32.9020240883 0.4166964214 0.85 32.2264100874 absolute errs true 6 32.9989734715 0.382961434 errbox errbox symbol type 1 7 33.0584304133 0.3247164703 1.85 32.1552984136 inverse plot false 8 33.1802124617 0.305920206 2.15 32.1552984136 color plot true 9 33.2426131375 0.46354794 2.15 33.2262477288 3d plot false 10 33.2614958985 0.2980553337 1.85 33.2262477288 linear false 11 33.2816199632 0.3134843775 1.85 32.1552984136 data range r8:s19 12 33.3576597197 0.4276475245 errbox errbox filled symbols true isoline isoline isoline 2.85 32.4223362225 concage false 3.15 32.4223362225 concswap false 3.15 33.2458715085 1st symbol-row 1 2.85 33.2458715085 2.85 32.4223362225 errbox errbox 3.85 32.5233365722 4.15 32.5233365722 4.15 33.1746188844 3.85 33.1746188844 3.85 32.5233365722 errbox errbox 4.85 32.4853276668 5.15 32.4853276668 5.15 33.3187205097 4.85 33.3187205097 4.85 32.4853276668 errbox errbox 5.85 32.6160120376 6.15 32.6160120376 6.15 33.3819349055 5.85 33.3819349055 5.85 32.6160120376 errbox errbox 6.85 32.733713943 7.15 32.733713943 7.15 33.3831468836 6.85 33.3831468836 6.85 32.733713943 errbox errbox 7.85 32.8742922557 8.15 32.8742922557 8.15 33.4861326677 7.85 33.4861326677 7.85 32.8742922557 errbox errbox 8.85 32.7790651976 9.15 32.7790651976 9.15 33.7061610775 8.85 33.7061610775 8.85 32.7790651976 errbox errbox 9.85 32.9634405648 10.15 32.9634405648 10.15 33.5595512323 9.85 33.5595512323 9.85 32.9634405648 errbox errbox 10.85 32.9681355857 11.15 32.9681355857 11.15 33.5951043408 10.85 33.5951043408 10.85 32.9681355857 errbox errbox 11.85 32.9300121952 12.15 32.9300121952 12.15 33.7853072443 11.85 33.7853072443 11.85 32.9300121952 errbox errbox haycock analysis u 206pb u/th 206pb* ± 207pb* ± 206pb* ± error 206pb* ± 207pb* ± 206pb* ± best age ± conc (ppm) 204pb 207pb* (%) 235u* (%) 238u (%) corr. 238u* (ma) 235u (ma) 207pb* (ma) (ma) (ma) (%) 9-17-9-spot 109 160.8664302514 978.5043622519 1.8149478379 30.0935728921 19.2632386751 0.0232210634 19.2980895995 0.0050704162 1.1592661193 0.0600715482 32.6034162685 0.3770061812 23.3086834206 4.4469232928 na na 32.6034162685 0.3770061812 na 9-17-9-spot 7 381.2905472221 4356.0040728862 0.9960198186 22.1853714533 2.3311614897 0.0315830581 2.8514892118 0.0050840362 1.642156154 0.5758942195 32.6907730712 0.5354746576 31.572901418 0.8864448725 na na 32.6907730712 0.5354746576 na 9-17-9-spot 104 171.5165758956 1332.4456698852 2.0104825041 26.7761235324 4.5955094146 0.0262831849 4.7643954551 0.0051063837 1.2572817001 0.2638911299 32.8341038655 0.411767643 26.342810901 1.238935521 na na 32.8341038655 0.411767643 na 9-17-9-spot 51 449.8712155196 16053.9939088398 2.2430394397 21.4485713563 1.5658373456 0.0328264951 1.8546148912 0.0051087028 0.9938560267 0.5358826953 32.8489777283 0.3256411561 32.7960744028 0.5985230061 28.9243439791 37.5325398393 32.8489777283 0.3256411561 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0.0009262304 1736 0.0010357304 1737.6 0.0011833852 1739.2 0.0013148941 1740.8 0.0013756618 1742.4 0.0013322364 1744 0.0011848758 1745.6 0.0009655594 1747.2 0.0007235272 1748.8 0.0005070875 1750.4 0.0003508562 1752 0.000272365 1753.6 0.0002755539 1755.2 0.0003556306 1756.8 0.0005008368 1758.4 0.0006911696 1760 0.0008967949 1761.6 0.0010801454 1763.2 0.0012033025 1764.8 0.0012386156 1766.4 0.0011777279 1768 0.0010343864 1769.6 0.0008391317 1771.2 0.0006287631 1772.8 0.0004351645 1774.4 0.0002781822 1776 0.0001642536 1777.6 0.0000895798 1779.2 0.0000451247 1780.8 0.0000209956 1782.4 0.000009023 1784 0.0000035817 1785.6 0.0000013132 1787.2 0.0000004447 1788.8 0.0000001391 1790.4 0.0000000402 1792 0 1793.6 0 1795.2 0 1796.8 0 1798.4 0 1800 0 1801.6 0 1803.2 0 1804.8 0 1806.4 0 1808 0 1809.6 0 1811.2 0.0000000374 1812.8 0.0000001137 1814.4 0.0000003248 1816 0.0000008705 1817.6 0.0000021889 1819.2 0.0000051648 1820.8 0.0000114353 1822.4 0.000023758 1824 0.0000463164 1825.6 0.0000847278 1827.2 0.0001454396 1828.8 0.0002342638 1830.4 0.0003540735 1832 0.0005021659 1833.6 0.0006682926 1835.2 0.0008345489 1836.8 0.0009779183 1838.4 0.0010752735 1840 0.0011094329 1841.6 0.0010741099 1843.2 0.0009758029 1844.8 0.0008318425 1846.4 0.0006654046 1848 0.0004994547 1849.6 0.0003517807 1851.2 0.000232495 1852.8 0.0001441853 1854.4 0.0000839062 1856 0.0000458176 1857.6 0.0000234767 1859.2 0.0000112877 1860.8 0.0000050926 1862.4 0.000002156 1864 0.0000008565 1865.6 0.0000003193 1867.2 0.0000001117 1868.8 0.0000000367 1870.4 0 1872 0 1873.6 0 1875.2 0 1876.8 0 1878.4 0 1880 0 1881.6 0 1883.2 0 1884.8 0 1886.4 0 1888 0 1889.6 0 1891.2 0 1892.8 0 1894.4 0 1896 0 1897.6 0 1899.2 0 1900.8 0 1902.4 0 1904 0 1905.6 0 1907.2 0 1908.8 0 1910.4 0 1912 0 1913.6 0 1915.2 0 1916.8 0 1918.4 0 1920 0 1921.6 0 1923.2 0 1924.8 0 1926.4 0 1928 0 1929.6 0 1931.2 0 1932.8 0 1934.4 0 1936 0 1937.6 0 1939.2 0 1940.8 0 1942.4 0 1944 0 1945.6 0 1947.2 0 1948.8 0 1950.4 0 1952 0 1953.6 0 1955.2 0 1956.8 0 1958.4 0 1960 0 1961.6 0 1963.2 0 1964.8 0 1966.4 0 1968 0 1969.6 0 1971.2 0 1972.8 0 1974.4 0 1976 0 1977.6 0 1979.2 0 1980.8 0 1982.4 0 1984 0 1985.6 0 1987.2 0 1988.8 0 1990.4 0 1992 0 1993.6 0 1995.2 0 1996.8 0 1998.4 0 2000 0 2001.6 0 2003.2 0 2004.8 0 2006.4 0 2008 0 2009.6 0 2011.2 0 2012.8 0 2014.4 0 2016 0 2017.6 0 2019.2 0 2020.8 0 2022.4 0 2024 0 2025.6 0 2027.2 0 2028.8 0 2030.4 0 2032 0 2033.6 0 2035.2 0.0000000213 2036.8 0.0000001054 2038.4 0.000000461 2040 0.0000017825 2041.6 0.0000060938 2043.2 0.000018418 2044.8 0.0000492159 2046.4 0.0001162722 2048 0.000242859 2049.6 0.0004484771 2051.2 0.0007322077 2052.8 0.0010569052 2054.4 0.0013487937 2056 0.0015218184 2057.6 0.0015180565 2059.2 0.0013388157 2060.8 0.0010439061 2062.4 0.000719631 2064 0.0004385974 2065.6 0.0002363361 2067.2 0.0001125905 2068.8 0.0000474222 2070.4 0.0000176591 2072 0.0000058139 2073.6 0.0000016923 2075.2 0.0000004355 2076.8 0.0000000991 2078.4 0.0000000199 2080 0 2081.6 0 2083.2 0 2084.8 0 2086.4 0 2088 0 2089.6 0 2091.2 0 2092.8 0 2094.4 0 2096 0 2097.6 0 2099.2 0 2100.8 0 2102.4 0 2104 0 2105.6 0 2107.2 0 2108.8 0 2110.4 0 2112 0 2113.6 0 2115.2 0 2116.8 0 2118.4 0 2120 0 2121.6 0 2123.2 0 2124.8 0 2126.4 0 2128 0 2129.6 0 2131.2 0 2132.8 0 2134.4 0 2136 0 2137.6 0 2139.2 0 2140.8 0 2142.4 0 2144 0 2145.6 0 2147.2 0 2148.8 0 2150.4 0 2152 0 2153.6 0 2155.2 0 2156.8 0 2158.4 0 2160 0 2161.6 0 2163.2 0 2164.8 0 2166.4 0 2168 0 2169.6 0 2171.2 0 2172.8 0 2174.4 0 2176 0 2177.6 0 2179.2 0 2180.8 0 2182.4 0 2184 0 2185.6 0 2187.2 0 2188.8 0 2190.4 0 2192 0 2193.6 0 2195.2 0 2196.8 0 2198.4 0 2200 0 2201.6 0 2203.2 0 2204.8 0 2206.4 0 2208 0 2209.6 0 2211.2 0 2212.8 0 2214.4 0 2216 0 2217.6 0 2219.2 0 2220.8 0 2222.4 0 2224 0 2225.6 0 2227.2 0 2228.8 0 2230.4 0 2232 0 2233.6 0 2235.2 0 2236.8 0 2238.4 0 2240 0 2241.6 0 2243.2 0 2244.8 0 2246.4 0 2248 0 2249.6 0 2251.2 0 2252.8 0 2254.4 0 2256 0 2257.6 0 2259.2 0 2260.8 0 2262.4 0 2264 0 2265.6 0 2267.2 0 2268.8 0 2270.4 0 2272 0 2273.6 0 2275.2 0 2276.8 0 2278.4 0 2280 0 2281.6 0 2283.2 0 2284.8 0 2286.4 0 2288 0 2289.6 0 2291.2 0 2292.8 0 2294.4 0 2296 0 2297.6 0 2299.2 0 2300.8 0 2302.4 0 2304 0 2305.6 0 2307.2 0 2308.8 0 2310.4 0 2312 0 2313.6 0 2315.2 0 2316.8 0 2318.4 0 2320 0 2321.6 0 2323.2 0 2324.8 0 2326.4 0 2328 0 2329.6 0 2331.2 0 2332.8 0 2334.4 0 2336 0 2337.6 0 2339.2 0 2340.8 0 2342.4 0 2344 0 2345.6 0 2347.2 0 2348.8 0 2350.4 0 2352 0 2353.6 0 2355.2 0 2356.8 0 2358.4 0 2360 0 2361.6 0 2363.2 0 2364.8 0 2366.4 0 2368 0 2369.6 0 2371.2 0 2372.8 0 2374.4 0 2376 0 2377.6 0 2379.2 0 2380.8 0 2382.4 0 2384 0 2385.6 0 2387.2 0 2388.8 0 2390.4 0 2392 0 2393.6 0 2395.2 0 2396.8 0 2398.4 0 2400 0 2401.6 0 2403.2 0 2404.8 0 2406.4 0 2408 0 2409.6 0 2411.2 0 2412.8 0 2414.4 0 2416 0 2417.6 0 2419.2 0 2420.8 0 2422.4 0 2424 0 2425.6 0 2427.2 0 2428.8 0 2430.4 0 2432 0 2433.6 0 2435.2 0 2436.8 0 2438.4 0 2440 0 2441.6 0 2443.2 0 2444.8 0 2446.4 0 2448 0 2449.6 0 2451.2 0 2452.8 0 2454.4 0 2456 0 2457.6 0 2459.2 0 2460.8 0 2462.4 0 2464 0 2465.6 0 2467.2 0 2468.8 0 2470.4 0 2472 0 2473.6 0 2475.2 0 2476.8 0 2478.4 0 2480 0 2481.6 0 2483.2 0 2484.8 0 2486.4 0 2488 0 2489.6 0 2491.2 0 2492.8 0 2494.4 0 2496 0 2497.6 0 2499.2 0 2500.8 0 2502.4 0 2504 0 2505.6 0 2507.2 0 2508.8 0 2510.4 0 2512 0 2513.6 0 2515.2 0 2516.8 0 2518.4 0 2520 0 2521.6 0 2523.2 0 2524.8 0 2526.4 0 2528 0 2529.6 0 2531.2 0 2532.8 0 2534.4 0 2536 0 2537.6 0 2539.2 0 2540.8 0 2542.4 0 2544 0 2545.6 0 2547.2 0 2548.8 0 2550.4 0 2552 0 2553.6 0 2555.2 0 2556.8 0 2558.4 0 2560 0 2561.6 0 2563.2 0 2564.8 0 2566.4 0 2568 0 2569.6 0 2571.2 0 2572.8 0 2574.4 0 2576 0 2577.6 0 2579.2 0 2580.8 0 2582.4 0 2584 0 2585.6 0 2587.2 0 2588.8 0 2590.4 0 2592 0 2593.6 0 2595.2 0 2596.8 0 2598.4 0 2600 0 2601.6 0 2603.2 0 2604.8 0 2606.4 0 2608 0 2609.6 0 2611.2 0 2612.8 0 2614.4 0 2616 0 2617.6 0 2619.2 0 2620.8 0 2622.4 0 2624 0 2625.6 0 2627.2 0 2628.8 0 2630.4 0 2632 0 2633.6 0 2635.2 0 2636.8 0 2638.4 0 2640 0 2641.6 0 2643.2 0 2644.8 0.0000000181 2646.4 0.0000000809 2648 0.0000003243 2649.6 0.0000011698 2651.2 0.0000037933 2652.8 0.0000110604 2654.4 0.0000289974 2656 0.000068357 2657.6 0.000144891 2659.2 0.0002761428 2660.8 0.0004732173 2662.4 0.0007291585 2664 0.0010102239 2665.6 0.0012584843 2667.2 0.0014096534 2668.8 0.0014197482 2670.4 0.001285715 2672 0.0010469177 2673.6 0.0007665047 2675.2 0.0005046049 2676.8 0.0002986913 2678.4 0.0001589747 2680 0.0000760796 2681.6 0.0000327373 2683.2 0.0000126663 2684.8 0.0000044065 2686.4 0.0000014366 2688 0.0000006368 2689.6 0.0000010511 2691.2 0.0000032807 2692.8 0.0000099901 2694.4 0.0000273029 2696 0.000066714 2697.6 0.0001457905 2699.2 0.0002850766 2700.8 0.000499206 2702.4 0.0007839867 2704 0.00110695 2705.6 0.0014112725 2707.2 0.0016367264 2708.8 0.0017481344 2710.4 0.0017525513 2712 0.0016917043 2713.6 0.0016140496 2715.2 0.001546097 2716.8 0.0014820158 2718.4 0.0013955116 2720 0.0012623372 2721.6 0.001077392 2723.2 0.0008575955 2724.8 0.0006324687 2726.4 0.0004306748 2728 0.00027032 2729.6 0.0001562712 2731.2 0.0000831658 2732.8 0.0000407511 2734.4 0.0000183794 2736 0.00000763 2737.6 0.0000029155 2739.2 0.0000010254 2740.8 0.000000332 2742.4 0.0000000989 2744 0.0000000271 2745.6 0 2747.2 0 2748.8 0 2750.4 0 2752 0 2753.6 0 2755.2 0 2756.8 0 2758.4 0 2760 0 2761.6 0 2763.2 0 2764.8 0 2766.4 0 2768 0 2769.6 0 2771.2 0 2772.8 0 2774.4 0 2776 0 2777.6 0 2779.2 0 2780.8 0 2782.4 0 2784 0 2785.6 0 2787.2 0 2788.8 0 2790.4 0 2792 0 2793.6 0 2795.2 0 2796.8 0 2798.4 0 2800 0 2801.6 0 2803.2 0 2804.8 0 2806.4 0 2808 0 2809.6 0 2811.2 0 2812.8 0 2814.4 0 2816 0 2817.6 0 2819.2 0 2820.8 0 2822.4 0 2824 0 2825.6 0 2827.2 0 2828.8 0 2830.4 0 2832 0 2833.6 0 2835.2 0 2836.8 0 2838.4 0 2840 0.0000000232 2841.6 0.000000104 2843.2 0.0000004183 2844.8 0.0000015079 2846.4 0.0000048716 2848 0.0000141045 2849.6 0.0000365962 2851.2 0.0000851591 2852.8 0.00017771 2854.4 0.0003331838 2856 0.0005630937 2857.6 0.000864244 2859.2 0.0012217455 2860.8 0.0016282822 2862.4 0.0021073084 2864 0.0027100352 2865.6 0.0034669735 2867.2 0.0043254423 2868.8 0.0051438608 2870.4 0.0057661345 2872 0.0060991326 2873.6 0.0061132327 2875.2 0.0058045627 2876.8 0.0052015174 2878.4 0.0043914635 2880 0.0034942558 2881.6 0.0026075002 2883.2 0.0017961894 2884.8 0.0011157217 2886.4 0.0006105923 2888 0.0002891882 2889.6 0.0001171752 2891.2 0.0000403312 2892.8 0.0000117471 2894.4 0.0000028833 2896 0.0000005989 2897.6 0.0000001048 2899.2 0 2900.8 0 2902.4 0 2904 0 2905.6 0 2907.2 0 2908.8 0 2910.4 0 2912 0 2913.6 0 2915.2 0 2916.8 0 2918.4 0 2920 0.0000000796 2921.6 0.0000003837 2923.2 0.0000016633 2924.8 0.0000061797 2926.4 0.0000201209 2928 0.0000574845 2929.6 0.0001443285 2931.2 0.0003190706 2932.8 0.0006225173 2934.4 0.0010746838 2936 0.00164622 2937.6 0.0022436881 2939.2 0.0027273362 2940.8 0.0029616716 2942.4 0.0028752762 2944 0.0024951543 2945.6 0.0019349192 2947.2 0.0013442764 2948.8 0.000851012 2950.4 0.0005276023 2952 0.000393727 2953.6 0.000440929 2955.2 0.0006565042 2956.8 0.0010326697 2958.4 0.0015611998 2960 0.0022192708 2961.6 0.0029494266 2963.2 0.0036392952 2964.8 0.0041224458 2966.4 0.004228734 2968 0.0038767759 2969.6 0.0031432268 2971.2 0.0022382857 2972.8 0.0013953911 2974.4 0.000761906 2976 0.0003658471 2977.6 0.0001559844 2979.2 0.0000611126 2980.8 0.0000269382 2982.4 0.0000253892 2984 0.0000502556 2985.6 0.0001104816 2987.2 0.0002233508 2988.8 0.0004048892 2990.4 0.0006561961 2992 0.000950449 2993.6 0.0012302693 2995.2 0.0014231404 2996.8 0.0014711993 2998.4 0.0013591629 3000 0.0011221416 3001.6 0.0008279423 3003.2 0.0005459195 3004.8 0.0003216869 3006.4 0.0001694004 3008 0.0000797208 3009.6 0.0000335278 3011.2 0.0000126013 3012.8 0.0000042325 3014.4 0.0000012705 3016 0.0000003408 3017.6 0.0000000817 3019.2 0 3020.8 0 3022.4 0 3024 0 3025.6 0 3027.2 0 3028.8 0 3030.4 0 3032 0 3033.6 0 3035.2 0 3036.8 0 3038.4 0 3040 0 3041.6 0 3043.2 0 3044.8 0 3046.4 0 3048 0 3049.6 0 3051.2 0 3052.8 0 3054.4 0 3056 0 3057.6 0 3059.2 0 3060.8 0 3062.4 0 3064 0 3065.6 0 3067.2 0 3068.8 0 3070.4 0 3072 0 3073.6 0 3075.2 0 3076.8 0 3078.4 0 3080 0 3081.6 0 3083.2 0 3084.8 0 3086.4 0 3088 0 3089.6 0 3091.2 0 3092.8 0 3094.4 0 3096 0 3097.6 0 3099.2 0 3100.8 0 3102.4 0 3104 0 3105.6 0 3107.2 0 3108.8 0 3110.4 0 3112 0 3113.6 0 3115.2 0 3116.8 0 3118.4 0 3120 0 3121.6 0 3123.2 0 3124.8 0 3126.4 0 3128 0 3129.6 0 3131.2 0 3132.8 0 3134.4 0 3136 0 3137.6 0 3139.2 0 3140.8 0 3142.4 0 3144 0 3145.6 0 3147.2 0 3148.8 0 3150.4 0 3152 0 3153.6 0 3155.2 0 3156.8 0 3158.4 0 3160 0 3161.6 0 3163.2 0 3164.8 0 3166.4 0 3168 0 3169.6 0 3171.2 0 3172.8 0 3174.4 0 3176 0 3177.6 0 3179.2 0 3180.8 0 3182.4 0 3184 0 3185.6 0 3187.2 0 3188.8 0 3190.4 0 3192 0 3193.6 0 3195.2 0 3196.8 0 3198.4 0 isoline isoline geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover an extant american bison strides atop an underlying sequence of phanerozoic strata and fossils. these are arranged by geologic period (cambrian, permian, early triassic, late triassic, jurassic, cretaceous, paleogene, and quaternary) and from left (west) to right (east) in approximate accordance with their occurrence across the national park service areas of utah. iconic rock formations representing the “mighty five” national parks (zion, bryce canyon, capitol reef, canyonlands, and arches national parks) form the nearest skyline, and other landmarks (powell point to the west and the henry mountains to the east) form the horizon. artwork by benji paysnoe, camben creatives llc, used with permission. i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 12 2025 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2025–2026 uga board president rob buehring robbuehring@yahoo.com 713.412.9269 president-elect trae boman traebgeologist@gmail.com 801.648.5206 program chair mike arnoff marnoff@utah.gov 385.303.0431 treasurer will hurlbut wdhurlbut@gmail.com 860.733.3190 secretary kylie arcaris kaarcaris@gmail.com 801.628.6731 past president keilee higgs keileeann@utah.gov 801.678.3683 uga committees environmental affairs seeking a volunteer geologic road sign greg gavin greggavin@gmail.com 513.509.1509 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.580.1331 aapg house of delegates 2023–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor mike barber uga.newsletter@gmail.com 435.640.1382 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair seeking a volunteer douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 221 abstract the national park service (nps) stewards 13 park units across the state of utah, which is world-renowned for its stunning landscapes, complex geologic history, and globally significant fossil assemblages. although most nps areas in utah are best known for their scenic landscapes, they all preserve geologic records with significant paleontological resources. the nps paleontology program, through sustained partnership with such organizations as the utah geological survey and the utah geological association, has conducted years of field inventory and outreach to promote the stewardship, study, and education on paleontological resources within the nps administered lands. the most comprehensive and publicly available literature reviews on fossils across utah’s nps areas were completed more than a decade ago, and numerous field inventories and publications have since been completed. this document serves as a thorough update to those previous works by providing detailed and easily comprehensible biostratigraphic diagrams with accompanying descriptions for each nps unit in utah. by providing this resource, this document aims to support park managers, educators, and external partners in protecting, preserving, and educating the public on the diverse and scientifically significant paleontological resources across the nps areas of utah. a visual paleontological inventory of utah’s national park service areas tut tran1, andrew r.c. milner2, justin s. tweet3*, donald d. deblieux4*, rebecca hunt-foster5, austin b. shaffer6, james i. kirkland4**, ethan warner-cowgill4***, and vincent l. santucci3** 1idaho museum of natural history, pocatello, id 83201 usa; derektran@isu.edu 2st. george dinosaur discovery site at johnson farm, st. george, ut 84790 usa; arcmilner@gmail.com 3national park service paleontology program, washington, d.c. 20240 usa; 3*justin_tweet@nps.gov, 3**npspaleo12@gmail.com 4utah geological survey, salt lake city, ut 84112 usa; 4*dondeblieux@utah.gov, 4**jameskirkland@utah.gov, 4***ecowgill@utah.gov 5dinosaur national monument, ut usa; rebecca_hunt-foster@nps.gov 6school of earth, environment, and sustainability, university of iowa, iowa city, ia usa 52242 usa; austin-shaffer@uiowa.edu citation for this article. tran, t., milner, a.r.c., tweet, j.s., deblieux, d.d., hunt-foster, r., shaffer, a.b., kirkland, j.i., warner-cowgill, e., and santucci, v.l., 2025, a visual paleontological inventory of utah’s national park service areas: geology of the intermountain west, v. 12, p. 221–292, https://doi.org/10.31711/giw. v12.pp221-292. national park service (nps) abbreviations arch, arches national park; brca, bryce canyon national park; cany, canyonlands national park; care, capitol reef national park; cebr, cedar breaks national monument; dino, dinosaur national monument; glca, glen canyon national recreation area; gosp, golden spike national historical park; hove, hovenweep national monument; nabr, natural bridges national monument; rabr, rainbow bridge national monument; tica, timpanogos cave national monument; zion, zion national park. 222 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 background the state of utah is home to 13 nps areas: one national historical park (gosp), one national recreation area (glca), six national monuments (cebr, dino, hove, nabr, rabr, tica), and five national parks (arch, brca, cany, care, zion). these were collectively dubbed the “mighty five” national parks in a campaign by the utah office of tourism industry in the early 2010s) (figure 1). the nps also co-administers the old spanish national historic trail (nht) alongside the bureau of land management (blm), which connects los angeles, california, with santa fe, new mexico, and crosses through south-central utah (90th congress, 1968; 107th congress, 2002). several fossils were reported by the macomb expedition of 1859 in california, new mexico, colorado, and utah, including the holotype of the sauropod dystrophaeus viaemalae from the tidwell member of the upper jurassic morrison formation close to the trail near moab, utah (newberry et al., 1876; cope, 1877). despite the occurrence of these important fossils, the fact the old spanish nht spans across several states means that it falls beyond the scope of what is covered in this document. utah’s nps areas are renowned for their visually striking landscapes and unique geologic features, such as the eponymous rock arches of arch and the enigmatic hoodoos of brca, as well as their rich natural and cultural history. historically, these areas were inhabited by diverse indigenous peoples who were displaced over the course of the 16th through 19th centuries with the arrival of spanish explorers and mormon pioneers. it was these collective communities who first experienced the wonder that these landscapes inspire in current and future generations. the settlement of euro-american communities across utah in the 19th century paved the way for developments in the early 20th century, especially the establishment of these areas as federally protected national parks and monuments. starting with president theodore roosevelt’s designation of nabr in 1908 (roosevelt, 1908), several presidents in the early 20th century invoked the antiquities act of 1906 (59th congress, 1906) to protect these lands as national monuments (zion, taft, 1909; wilson, 1918; rabr, taft, 1910; dino, wilson, 1915; tica, harding, 1922; hove, harding, 1923a; brca, harding, 1923b; arch, hoover, 1929; care, roosevelt, 1937). following the formal creation of the national park service through the organic act of 1916 (64th congress, 1916), some of the previously established national monuments were re-designated as national parks through acts of congress (arch, 92nd congress, 1971; brca, 68th congress, 1924; 70th congress, 1928; and zion, 66th congress, 1919). in the latter half of the 20th century, park units were established almost exclusively through acts of congress (cany, 88th congress, 1964; gosp, 89th congress, 1965; glca, 92nd congress, 1972). by designating these lands under the stewardship of the nps, the natural and cultural resources contained within fell under federal protection. little known to legislators and the general public at the time of their establishment (with the notable exception of dino), the paleontological resources contained within each and, as it turned out, every park unit in utah fell within this purview. since the late 2010s, the “mighty five” national parks have hosted approximately 13.5 million visitors annually, and that number is expected to grow as time progresses (nps, 2025a; table 1). this naturally places strain on the management of people and visitors at these and other parks as growing visitation increases the likelihood of human-caused disturbance to paleontological and other natural resources (e.g., trampling, deliberate vandalization, and/or theft). the recognition of the significance of paleontological resources in parks is a relatively recent development, and thus few parks have robust internal programs for managing and monitoring them. therefore, management, research, and educating the public about park fossils is often done in collaboration with outside entities and through internships and short-term positions. most nps areas with paleontological resources request support from the nps paleontology program, which provides agency-wide support to at least 288 parks with fossil-related needs. ideally, parks should develop programs outlined in the paleontological resources preservation act of 2009 (prpa; 111th congress, 2009) and nps management policies (2006, 223 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 section 4.8.2.1). utah’s national parks and monuments display a strong and complex geological and paleontological history, mostly in the mesozoic era or “age of reptiles” (figure 2), thanks to the state’s geographic and physical features (e.g., the grand staircase geologic feature, which includes brca, cebr, zion, and glca), making them excellent places for research and outreach as resources permit. despite the overall lack of sustained paleontological programs across utah’s national parks, short-term field inventories have been coordinated by the nps paleontology program through partnerships with professional figure 1. a map of utah showing its 13 national parks and monuments managed by the nps. the “mighty five” national parks are noted by an asterisk after their name (*). scale bar equals 60 miles (about 96.5 km). park unit boundaries adopted from data produced by the nps land resources division (https://www.arcgis.com/home/item.html?id=6f2f40e0b1c74b8ea886261fe8e0431f). see page 221 for nps unit abbreviations. 224 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 paleontologists, collaboration with outside researchers, and recruitment of paleontology interns to help them protect, monitor, and study their fossils (arch, swanson et al., 2005, madsen et al., 2012; brca, tran et al., 2024; cany, deblieux et al., 2021, 2023, 2024; care, kirkland et al., 2014a, 2020; glca, kirkland et al., 2010; milner et al., 2024; zion, deblieux et al., 2005, 2006; clites and santucci, 2012). literature reviews have also been published (koch and santucci, 2002; tweet et al., 2009, 2012b through 2012l). however, these reports often contain sensitive locality information, which prohibits public dissemination in order to protect the vulnerable and nonrenewable fossils discussed within. despite this limitation, the nps paleontology program has, over the last 23 years, published both sensitive and public versions of park-specific paleontological resource inventory reports and management plans to increase information accessibility and outreach impact (e.g., varela et al., 2019; kottkamp et al., 2020; salcido et al., 2022). public versions of these documents are easily searchable and are distributed openly to park staff and partner organizations. however, most of the nps-produced field inventories in utah predated this practice, as utah and colorado parks served as pilot programs for nps paleontology program in the late 1990s through the early 2000s. just two public paleontological resource inventory reports are currently available for nps units in utah (arch, swanson et al., 2005; brca, tran et al., 2024). other avenues used by the nps paleontology program for promoting the integration of and education on paleontological resource management include the park paleontology newsletter (e.g., hunt-foster, 2021; deblieux et al., 2022; henderek, 2023; tran, 2023a), the parks stewardship forum (e.g., santucci et al., 2024; hunt-foster, 2024), and the annual national fossil day (nfd) event hosted at several parks across the agency. a few utah parks have been showcased through fossil logo artwork related to nfd, commissioned by the nps paleontology program (brca, dino, glca, zion; figure 3). many nps units in utah are highlighted in, or are directly involved with these educational efforts, as they provide opportunities to showcase ongoing research and management projects (arch, brca, care, cany, dino, glca, zion). even so, these publications are often focused on current work, and full overviews of each park’s paleontology and geology are beyond the scope of these materials. these factors discussed above have prevented the public, park staff, and often potential researchers from receiving complete and accurate information on the complete scope of the fossils documented in each of utah’s national parks and monuments. materials created by non-nps agencies, especially the utah geological survey (ugs), utah friends of paleontology, and university of utah press have provided invaluable educational overviews of dinosaur fossils found across the state (figure 4) (gillette, 1999; decourten, 2013; kirkland et al., 2024). by comparison, the most comprehensive overviews of paleontological resources with particular focus on nps areas in utah were included in previous editions of geology of utah’s parks and monuments, produced by the utah geological association park unit visitation in 2024 highest annual visitation (year) arch* 1,482,045 1,806,865 (2021) brca* 2,498,075 2,679,478 (2018) cany* 818,492 911,594 (2021) care* 1,422,490 1,422,490 (2024) cebr 722,834 909,199 (2017) dino 326,529 534,274 (1993) glca 4,725,610 5,206,934 (2023) gosp 53,015 169,600 (1969) hove 35,231 47,593 (1999) nabr 83,760 151,504 (1993) rabr 17,488 346,151 (1995) tica 114,034 226,600 (1974) zion* 4,946,592 5,039,835 (2021) total (2024) 17,256,195 table 1. recent and record visitation numbers at utah’s nps units. the “mighty five” national parks are noted by an asterisk after their name (*). data available at https://irma.nps.gov/ stats/ssrsreports/park%20specific%20reports/annual%20 park%20recreation%20visitation%20(1904%20-%20last%20 calendar%20year)?park=tica (accessed april 21, 2025). 225 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 66.0 mass ex�nc�on mass ex�nc�on mass ex�nc�on mass ex�nc�on mass ex�nc�on early shelled organisms trilobite maximum early fishes first land plants first amphibians first rep�les coal-forming swamps first dinosaurs, mammals, pterosaurs diverse dinosaurs early flowering plants ice ages in north america present day 33.9 56.0 23.03 ce n o zo ic m es o zo ic ju ra ss ic m id m id m id m . la te la te la te l. l. l. la te pa l. eo ce ne o lig . m io ce ne ea rl y ea rl y ea rl y e. e. e. m id . m id . ep o ch 2 m ia o li n gi an fu ro n gi an te rr en eu vi an m id . l. e. ea rl y tr ia ss ic pe rm ia n de vo n ia n o rd o vi ci an si lu ri an ca m br ia n neoproterozoic pe n n . pa le o ge n e n eo ge n e ca rb o n if er o u s te rt ia ry m is s. cr et ac eo u s pa le o zo ic 5.332.58 0 mya 100.5 ~113 ~125 358.9 419.2 382.7 393.3 485.4 ~497 ~509 ~521 443.8 458.4 470.0 541.0 323.2 330.9 346.7 315.2 298.9 307.0 251.9 259.5 273.01 247.2 ~237 201.3 174.1 163.5 ~145 ca re * quaternary pliocene salt lake city dino gosp tica cany nabr hove rabr brca*cebr ogden st. george logan provo arizona nm wyoming utah co lo ra do n ev ad a 0 30 60 miles n i-15 i-70 i-15 zion* arch*care* cany* glca hadrosaur bones and footprints (brca) diverse dinosaur tracks (arch) diverse plesiosaurs (glca) mammoth jaw (arch) bison vertebra (zion) apatosaurus louisae and many other dinosaurs (dino) phytosaur bones and teeth (cany and other parks) diverse plants (care) vertebrate trackways (glca) geologic time in utah’s national parks and monuments geologic �me scale modified from walker et al. (2022). age ranges es�mated from tweet et al. (2009, 2012b through 2012l). the “mighty five” na�onal parks are noted by an asterisk a�er their name (*). horn corals (tica and other parks) crinoids (arch, glca) tritylodont bonebeds (glca) grallator tracks (zion and other parks) trilobites (dino) freshwater snails (brca) meekocera�d ammonites (zion) legend preserved sedimentary rock / geologic �me missing sedimentary rock / geologic �me br ca * ce br zi o n * south west north east northwest utah generalized paleontology gl ca ar ch * ca n y* ra br n ab r go sp ti ca ho ve di n o figure 2. utah national parks and monuments mapped against the geologic time scale. time scale modified from walker et al. (2022). age estimates from tweet et al. (2009, 2012b through 2012l). 226 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 (uga; santucci, 2000, later expanded and updated into santucci and kirkland, 2010). however, more than a decade has passed since these materials were first published. in that time, several inventories, publications, conference abstracts, and outreach materials on fossils in utah’s nps areas have been produced (e.g., lockley et al., 2004; deblieux et al., 2006; eaton, 2013; martz et al., 2017; bennett et al., 2023; milner et al., 2023a, 2023b, 2024; santucci et al., 2024; tran et al., 2024). these advancements render the uga reviews outdated. this document aims to serve as a comprehensive update to santucci (2000) and santucci and kirkland (2010) by providing diagrams that compile all of the most recent and accurate data available on the paleontology and geology of each national park and monument in utah. methods this work began after the tut tran created a biostratigraphic diagram for brca, first for the society of vertebrate paleontology 83rd annual meeting (tran, 2023b), and subsequently for the full brca paleontological resource inventory (tran et al., 2024). vince santucci requested that tran make similar diagrams for all nps units in utah, as the parks and monuments throughout the state are known to produce many significant fossils (e.g., dino, glca, arch, etc.). the impetus for this work was, in part, to serve as an update on previous reviews on paleontological resources in nps areas in utah, especially santucci (2000) and santucci and kirkland (2010). more importantly, this document fills in a gap created by the exclusion of an updated chapter from the most recent edition of geology of utah’s parks and monuments (sprinkel et al., 2024), a volume which is widely distributed by the uga and serves as an important source for geological education and outreach, due to constraints. this document allows uga and nps to provide an easily accessible avenue on park paleontological resources that, importantly, have been greatly expanded to include detailed and easily comprehensible biostratigraphic diagrams for each park. the organisms represented in each park diagram are derived from nps-produced inventories and field reports produced by partner researchers, especially the ugs. the inventory reports of tweet et al. (2009, 2012b through 2012l) served as good overviews of nps paleontological resources. more recent reports were added to this baseline. figure 3. national fossil day park logos (from left to right) for bryce canyon national park (drafted for use in 2028), dinosaur national monument (drafted for use c. 2013), glen canyon national recreation area (2024), and zion national park (drafted for use in 2029), depicting fossil taxa and paleoenvironments documented at each park unit. artwork by studio105. 227 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 figure 4. dinosaurs of utah mapped against the state’s geologic formations and a geologic time scale. adopted from anatomical record (2023). 228 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 the stratigraphic columns included in this document were modified from several uga and ugs publications, especially existing stratigraphic columns and geologic maps (doelling and kuehne, 2007, 2013; anderson et al., 2010; biek et al., 2010, 2015; constenius et al., 2011; titus et al., 2016). the ugs maps cited have minor variations in their color designations for various geologic units. however, many of the utah parks and monuments contain the same rock formations and/or units of roughly equivalent ages and depositional environments. for the sake of simplicity, and to promote understanding of the geologic time, formations, and fossils that many parks share in common, most colors have been made uniform across the park diagrams and paleogeographic maps. nomenclature for certain stratigraphic units, such as the members of the chinle formation (arch, cany, care, dino, glca, nabr, zion), the wahweap formation (brca), and the mancos group (arch, care, dino) has been recently updated (martz et al., 2017; beveridge et al., 2022; kirkland et al., 2025). these recent names have been applied to biostratigraphic diagrams where feasible. appropriate citations are listed within each diagram and its accompanying text. colors for the geologic time scale were adopted from the geologic time scale v. 6.0 (walker et al., 2022). fossil organisms recovered in nps units are shown in their general stratigraphic context based on available data. taxa that have been identified to the genus and/ or species level are explicitly shown with those diagnoses; other identifications (e.g., phytosauria indet.) are represented with a generalized individual of that taxon. species that were described using type specimens originating from nps lands are starred. body fossils are mostly represented by organisms drawn in the left-lateral view. trace fossils (for which no representative body fossils have been documented) are displayed with a speculative reconstruction of a “possible track maker.” the track maker is always walking toward the upper right-hand corner of each diagram. for example, the eubrontes ichnogenus is common throughout nps units containing the kayenta and navajo sandstone formations. these footprints are represented with a walking dilophosaurus as their “possible track maker.” these reconstructions are included to help audiences visualize and understand the scope of biodiversity that trace fossils provide. except in the case of arch, all taxa/ichnotaxa shown in these diagrams have been confirmed through available literature and archives to have been observed and/or collected at their respective parks. a comprehensive taxonomic list with citations, organized by park and geologic unit, is provided in the appendix of this document. all biostratigraphic diagrams and paleogeographic maps throughout this paper were generated in adobe illustrator 2023. we provide a generalized geologic history of the utah nps units below to broadly synthesize the geologic time and environments preserved across these parks and monuments. individual park units are presented in alphabetical order. generalized geologic history this section elaborates upon the geologic time scale shown in figure 2. whereas there is great variation in the geologic and taxonomic nomenclature for formations and fossils across the state of utah, nps units share depositional environments, ecosystems, and fossils sufficiently to discuss geologic time on a grand scale. here, we provide a review to help readers understand general patterns in geology and paleontology across all of utah’s national parks and monuments. figure 5 shows a generalized stratigraphic column for utah’s nps areas, arranged from west to east. this figure provides a visual summary of all geology across the state’s nps units (excluding igneous and metamorphic rocks) and is modeled after the “dinosaurs of utah” diagram from the ugs (figure 4). however, figure 5 is more comprehensive in its temporal range as it also includes paleozoic and cenozoic strata. formations (distinctive and mappable geologic units) are scaled loosely in this figure against geologic time, not actual thickness. subdivided members of formations are excluded except in the case of the late triassic chinle formation and the early cretaceous cedar mountain formation because both formations represent comparatively large stretches of geologic time (about 25 million years for the chinle formation, about 40 million years for the cedar mountain formation). 229 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 ce n o zo ic m es o zo ic ju ra ss ic m id m id m id m . la te la te la te l. l. l. la te pa l. eo ce ne o lig . m io ce ne ea rl y ea rl y ea rl y e. e. e. m id . m id . ep o ch 2 m ia o li n gi an fu ro n gi an te rr en eu vi an m id . l. e. ea rl y tr ia ss ic pe rm ia n de vo n ia n o rd o vi ci an si lu ri an ca m br ia n neoproterozoic pe n n . pa le o ge n e n eo ge n e ca rb o n if er o u s te rt ia ry m is si ss ip pi an cr et ac eo u s claron fm bishop congl br o w n s pa rk boat mesa congl brian head fm morrison formation navajo sandstone kayenta formation moenkopi formation cedar mesa ss lower cutler organ rock fm white rim ss honaker trail fm paradox fm n u g -g et naturita tropic shale mow front muddy straight cliffs mancos group temp cap page ss moenave fm wingate ss cu tl er g rp bu rr o c yn (h o ve ) gl en c yn sa n ra fa el carmel shinarump conglomerate moss back mbr petrified forest mbr cameron mbr owl rock mbr monitor bu�e kane springs beds church rock mbr entrada summerville curtis stump mesaverde groupwahweap unnamed k (cebr) pa le o zo ic quaternary pliocene kaibab limestone quaternary sediments park city fm o q u ir rh (g o sp o nl y) morg. rv lshe rm o sa gr o u p gr ea t bl u e ls des ls fi tc hv il le do lo m it e maxfield tin qtz mutual fm ophir gard ls do u gh n u t humbug formation madison pa rt in g fm weber lodore uintah mt group di n o di n o di n o di n o ti ca ti ca di n o sw utah sizes of forma�ons and members are approximated from ages, not from thickness. column excludes igneous and metamorphic forma�ons. west east mass ex�nc�on mass ex�nc�on mass ex�nc�on mass ex�nc�on mass ex�nc�on early shelled organisms trilobite maximum early fishes first land plants first amphibians first rep�les coal-forming swamps first dinosaurs, mammals, pterosaurs diverse dinosaurs supercon�nent pangea intact pangea breakup begins immense sand dunes (ergs) swamps and floodplains sundance seaway encroaches into southern utah ancestral rocky mountain upli� western interior seaway evolu�on “lake carpenter” prominent in eastern utah “lake too’di’chi” prominent in four corners region sevier orogeny laramide orogeny freshwater lake systems across utah basin and range extension colorado plateau upli� early flowering plants ice ages in north america present day global geologic and biologic events (c) geologic context(b) generalized paleontology(a) geologic units generalized geology of utah’s nps areas utah geologic events and paleoenvironments hadrosaur bones and footprints (wahweap fm at brca) diverse dinosaur tracks (cedar mountain fm at arch) diverse plesiosaurs (tropic shale at glca) mammoth jaw (q seds at arch) bison vertebra (q seds at zion) apatosaurus louisae (morrison fm at dino) phytosaur bones and teeth (chinle fm at cany and other parks) diverse plants (chinle fm at care) vertebrate trackways (cedar mesa sandstone at glca) horn corals (deseret limestone at tica) crinoids (paradox fm in arch, glca) tritylodont bonebeds (navajo sandstone at glca) (possible track maker) segisaurus grallator tracks (navajo sandstone at zion and other parks) trilobites (lodore fm at dino) freshwater snails (claron fm at brca) (possible track macker) gastonia sp. meekocera�d ammonites (moenkopi fm at zion) cedar mountain formation (undivided) ch in le f m ch in le f m ruby ranch mbr poison strip mbr yellow cat mbr buckhorn congl muss. mbr figure 5. generalized geology in utah’s nps areas. (a) geologic formations mapped against geologic time, (b) generalized paleontology, and (c) major global and regional geologic and biologic events. ages for members of the chinle and cedar mountain formations were approximated from martz et al. (2017), joeckel et al. (2020), and suarez et al. (2023). 230 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 the neoproterozoic era the oldest strata recorded in any nps area within utah are of neoproterozoic age. such strata are only found in the uinta mountain group at dino (evanoff, 1988) and the more recent mutual formation at tica (constenius et al., 2011). neither have yet yielded fossils in the nps areas, although the uinta mountain group has yielded microfossils elsewhere in utah (nagy and porter, 2005). the paleozoic era dino and tica are also the only nps units in utah to contain cambrian-aged rocks. these are the lodore formation at dino, and from oldest to youngest, the tintic quartzite, ophir formation, and maxfield limestone at tica. strata from the cambrian period record times during which most of western utah was submerged in shallow seas (blakey and middleton, 2012; figure 6a). the advance and retreat of oceanic boundaries and seaways surrounding and even submerging utah is a constant theme across paleozoic and mesozoic eras in utah. ordovician and silurian formations are not exposed (or absent) in nps units in utah; however, outcrops preserving these systems are prevalent along the western margin of the state, especially the ordovician (harris and sheehan, 1997; clark et al., 2023a). notably, dino records igneous dikes of cambrian–early ordovician age (nps geologic resources division, 2006). the only park units to record devonian time are dino and tica. at dino, the devonian is preserved within the newly reported parting formation between the underlying lodore formation (cambrian) and overlying madison limestone (mississippian) (myrow et al., 2023a, 2023b; figure 6b). the fitchville formation or dolomite is the only devonian unit at tica; this unit spans the late devonian–early mississippian (sandberg and gutschick, 1979). several formations across utah’s nps areas record the carboniferous (mississippian and pennsylvanian) period (figure 7), as shallow seas persisted across what is now utah, and this paleoenvironment is preserved as limestone in a few parks and monuments in the state. as with cambrian and devonian strata, sequences of mississippian limestone are found at tica (mayo et al., 2024) and dino (evanoff, 1988). the paradox basin in southeastern utah (arch, cany, care, glca, nabr) contains strata representing pennsylvanian and permian times. this is a key interval in the evolution of utah paleoenvironments, as the complete formation of the supercontinent pangea by the early permian (and subsequent dispersal from the triassic into the cretaceous) influenced regional basin deposition, tectonics, and climate (figure 8). the oldest of these strata fall within the pennsylvanian hermosa group, which typically consists of the paradox formation and the overlying honaker trail formation. notably, the evaporite salts that were originally deposited in the marine paradox formation in the arch area were squeezed into the underlying domes and diapirs that directly influenced the erosion and formation of the iconic geology of that park. within nps areas, these units have been known to produce diverse invertebrates (doelling, 2024). the early permian cutler group overlies the hermosa group in the paradox basin. the oldest units in this group pertains to the elephant canyon-halgaito formations. the elephant canyon formation is a carbonate laterally equivalent to the more clastic halgaito formation. the remaining units in the cutler group include, from oldest to youngest, the cedar mesa sandstone, the organ rock formation, and the white rim sandstone. these represent a sequence of nearshore marine, coastal sand dunes, and floodplains, influenced by the presence of a mountain range to the northeast (the uncompahgre highlands or ancestral rocky mountains) and an ocean immediately to the west (panthalassa), as eastern utah sat along the west coast of pangea (condon, 1997; huntoon et al., 2002; dimichele et al., 2014; figure 8). as the central and western parts of the state were completely submerged in open ocean, early to middle permian outcrops in these areas often pertain to the marine kaibab limestone (care, zion) (huntoon et al., 2002). in northeastern utah, the permian period is represented by the upper part of the eolian weber sandstone and the shallow marine park city formation at dino (gregson et al., 2024). 231 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 figure 6. utah’s “mighty five” national parks mapped against a generalized reconstruction of the (a) cambrian and (b) devonian periods. modified from blakey and middleton (2012). colors from walker et al. (2022). see page 221 for nps unit abbreviations. figure 7. utah’s “mighty five” national parks mapped against a generalized reconstruction of the (a) mississippian and (b) pennsylvanian periods. modified from lawton et al. (2021). colors from walker et al. (2022). 232 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 many of the best and most recently discovered vertebrate body fossils and traces from the cutler group have been recovered from the blm-administered bears ears national monument, close to a few nps units with similar outcrops (arch, cany, glca, nabr) (huttenlocker et al., 2018; gay et al., 2020). the paleontology of the cutler group provides important insights into faunas and ecosystems leading up to the permian–triassic mass extinction (about 252 ma), which wiped out an estimated 95% of life on earth at the time. recent and ongoing fieldwork by the ugs at cany and glca has underscored the paleontological potential for the cutler group in utah’s nps areas (deblieux et al., 2023; see the cany section of this document). the mesozoic era the triassic period (c. 252 to 201 ma) seven out of 13 national park units in utah preserve some part of the triassic period. this period is recorded by the early–early middle triassic moenkopi formation and the late triassic chinle formation. both formations are usually divisible into multiple members that tend to be limited to small areas (e.g., stewart et al., 1972a, 1972b). therefore, the member-level stratigraphy varies widely across utah and neighboring states. despite this complexity, the nps exposures are important outcrops for study because they record the recovery and rapid diversification of vertebrates (including the first dinosaurs and mammals) and other organisms after the permian–triassic mass extinction. the moenkopi formation and its members are interpreted mostly as coastal plains as the paleoshoreline remained relatively close to its position during the permian (blakey and ranney, 2008; riggs et al., 2020; figure 9a). occasional fluctuations of sea level resulted in carbonate and/or evaporite beds interspersed with more terrestrial fluvial sediments. its paleontology is consistent with this interpretation, as various members preserve assemblages of marine invertebrates (meekoceratid ammonites, crinoids, and bivalves in the timpoweap/sinbad/virgin limestone members) and swim tracks of vertebrates at care (the torrey member) (peabody, 1956; mickelson et al., 2006a). lockley et al. (1998) also reported multiple ichnotaxa within the moenkopi formation of glca. ongoing fieldwork by the ugs has revealed that the torrey member at cany is of particularly high importance because of the abundance of vertebrate and invertebrate traces documented in that unit there (deblieux et al., 2023). the chinle formation, which lies unconformably above the moenkopi formation, records several paleoenvironments. these range from braided and meandering rivers to swamps and floodplains. the deposition of the sediments comprising the chinle was dominated by southeast–northwest-trending river systems in western north america (riggs et al., 1996, 2020; figure 9b). historically, this formation has been much better studied in arizona and new mexico than in utah, and the figure 8. utah’s “mighty five” national parks mapped against a generalized reconstruction of the permian cutler group (paradox basin). modified from condon (1997) and huntoon et al. (2002). see page 221 for nps unit abbreviations. 233 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 nomenclature of its members varies across (and within) all three study areas. in southern utah, the chinle contains the following members, from oldest to youngest: the shinarump member/mottled strata, the monitor butte member (= cameron member at zion), moss back member, petrified forest member, owl rock member (= kane springs beds at arch and cany), and the church rock member at the top (martz et al., 2017). these members vary greatly in thickness and extent of exposure across southern utah’s nps areas, though the sequence at care is considered the most complete among them (martz et al., 2017). the chinle is also exposed at dino in the northeast corner of the state. the chinle formation is overlain by the moenave formation in the west (zion) and the wingate sandstone in the central and east parts of the state (arch, cany, care, dino, glca, nabr, and zion). the fluvial, floodplain, and swamp environments preserved in the chinle formation are reflected in the diverse fossil animal and plant assemblages, which have been consistently found in national parks and monuments where the formation is observed. among the most famous areas containing the chinle are petrified forest national park in arizona and ghost ranch in new mexico. both areas are renowned for yielding benchmark specimens of diverse fossils for the late triassic record in north america. by comparison, chinle exposures in utah have not been as well-sampled as in arizona and new mexico with preliminary fieldwork undertaken in arch, care, glca, and zion (lockley et al., 1998, 2014; deblieux et al., 2005, 2006; swanson et al., 2005; santucci and kirkland, 2010; madsen et al., 2012; kirkland et al., 2014a; martz et al., 2015, 2017; deblieux et al., 2021, 2023; milner et al., 2024). therefore, the chinle in utah’s nps and other public lands provide a frontier for understanding how life recovered figure 9. utah’s “mighty five” national parks mapped against the (a) the early triassic moenkopi formation and (b) the late triassic chinle formation. modified from riggs et al. (2020); figures 7a and 7c from riggs et al. (1996). see page 221 for nps unit abbreviations. 234 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 after the permian–triassic extinction event, especially with regard to the evolution and diversification of the earliest dinosaurs and mammals. the jurassic period (c. 201 to 145 ma) the jurassic period is recorded in several nps units across utah; furthermore, some of the best late triassic–early jurassic continental strata are well preserved in these areas. many of the sandstone units that were originally deposited during the jurassic have since weathered into the iconic red rocks, arches, and canyons for which most of utah’s national parks and monuments are famous today. the late triassic–early jurassic transition is recorded in a series of sandstone formations belonging to the glen canyon group across most of utah. the oldest of these formations are the moenave formation (zion) and the approximately age-equivalent wingate sandstone (southeastern utah parks and glca). these formations preserve the boundary between the triassic and jurassic periods, which is exemplified by the transition of vertebrate tracks within each formation. throughout central and eastern utah, the lower wingate sandstone preserves typical late triassic tracks, whereas the middle to upper parts of the formation preserve typical early jurassic tracks (milner et al., 2024). in southwestern utah, the triassic–jurassic boundary has been identified within the dinosaur canyon member of the moenave formation (suarez et al., 2017, 2023). in st. george, southwest of zion, the moenave formation is famous for producing the spectacular st. george dinosaur discovery site at johnson farm (sgds), which is replete with dinosaur tracks and other vertebrate traces, invertebrate traces, and the body fossils of plants, invertebrates, fishes, and dinosaurs that lived in and around the so-called lake whitmore (milner and kirkland, 2006; kirkland et al., 2014b). by contrast, the wingate sandstone represents an extensive sand sea (erg). the emergence and disappearance of vast sand dune fields is a common theme throughout the jurassic sequence in utah, and the wingate is the oldest. the moenave formation and wingate sandstone are overlain by the early jurassic kayenta formation, deposited by rivers and floodplains. dinosaur and other vertebrate trace fossils become even more common in the kayenta, especially those of functionally tridactyl theropod dinosaurs. the kayenta formation has also yielded body fossils of various vertebrates, but these are mostly found in fine-grained rocks in northern arizona; in utah the kayenta formation is coarser-grained, and kayenta fossils in utah parks and monuments are comprised almost entirely of footprints with some rare exceptions. the upper part of the glen canyon group is another erg interval known as the navajo sandstone, as seen at glca and all of the “mighty five” except for brca (figure 10a). in the north, for example at dino, there is the partially equivalent nugget sandstone. the navajo–nugget erg system is the largest known from north america, but despite this seemingly inhospitable environment, vertebrate trace fossils and even stromatolites are well-documented in the national parks of utah (see bennett et al., 2023; milner et al., 2023b, 2024). significant fossils are known from oasis settings (lockley et al., 1998, 2004; santucci and kirkland, 2010; milner et al., 2023a, 2023b, 2024) and interdunes (loope et al., 2004; bennett et al., 2023; milner et al., 2024), where moisture was sheltered. the sedimentary sequence overlying the navajo sandstone (= nugget sandstone at dino) is classified as the middle jurassic san rafael group, named for the san rafael swell geologic feature in central utah (gilluly and reeside, 1928). these formations are tied to the transgression and regression of the sundance seaway, which during the middle jurassic epoch covered much of central canada and reached as far south as wyoming and south-central utah (hintze and kowallis, 2021; figure 10b). the expansions and retractions of the sundance seaway in this region produced the sequence of alternating terrestrial sandstone and marine limestone that comprises the san rafael group (peterson, 1994; wilcox and currie, 2008). these include the temple cap formation, the carmel formation and its alternating terrestrial and intertidal members, the eolian entrada formation, and the marine curtis formation (gilluly and reeside, 1928). the curtis formation is named for the curtis sea, which refers to the south235 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 ernmost extent of the sundance seaway in the middle jurassic in south-central utah. more northerly deposits (e.g., dino) of the sundance seaway near the end of the middle jurassic are known as the stump formation. the northward retreat of the seaway following the deposition of the curtis and stump formations led to the deposition of the summerville formation, the uppermost unit in the san rafael group (peterson, 1994; wilcox and currie, 2008). the youngest jurassic formation documented in utah is the morrison formation. following the retreat of the sundance seaway, utah became increasingly humid, hosting a suite of fluvial floodplain, swamp, and lacustrine environments. a major lake in the morrison depositional system was the alkaline-saline “lake t’oo’dichi’” in the four corners region (turner and fishman, 1991; figure 11a). the brushy basin member of the morrison formation is particularly famous for producing a high diversity of dinosaurs and other fossils from the latest jurassic of utah and other western states. dino is especially renowned for the abundance and preservation quality of fossils at a single locality in this formation. the cretaceous period (c. 145 to 66 ma) the cretaceous period is separated into two epochs: the early cretaceous (about 145 to 100.5 ma) and the late cretaceous (about 100.5 to 66 ma). in utah, the early cretaceous is recorded almost entirely by the cedar mountain formation (figure 11b). from oldest to youngest, its members include the buckhorn conglomerate, yellow cat, poison strip, ruby ranch, and mussentuchit members. these units preserve highly diverse dinosaur faunas that are of major global significance. this significance is due in part to the fact that the cedar mountain provides a primary dataset for paleontologists to understand life in the early cretaceous epoch, a period of global climate change and major biotic infigure 10. utah’s “mighty five” national parks mapped against (a) the early jurassic navajo and nugget ergs and (b) part of the middle–late jurassic san rafael group. paleogeography for (a) modified from bryant and miall (2010) and bryant et al. (2016); (b) modified from ejembi et al. (2021). see page 221 for nps unit abbreviations. 236 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 terchanges between what is now asia, north america, and europe (kirkland et al., 1999, 2024). this formation is best exposed in east-central utah (arch, care, dino). along the border with colorado, strata roughly equivalent in age are known as the burro canyon formation (hove) (kirkland et al., 2020b). in the uinta mountains and uinta basin, the muddy formation unconformably overlies the cedar mountain formation (sprinkel et al., 2012; sprinkel, 2024). the late cretaceous of southern utah is dominated by varying amounts of marine influence from the western interior seaway (figure 12). the western margin of this epicontinental sea fluctuated during this time. as a result, environments across utah ranged from open ocean to swamps to floodplain or river environments, depending on proximity to the shoreline. the oldest unit in the late cretaceous sequence in utah is the coastal naturita formation (formerly the dakota formation or group, changed after carpenter [2014]). the deposition of this unit preceded the westward encroachment of the seaway (figure 12a). the naturita formation has been identified across many of utah’s nps units; however, outcrops at dino previously referred to as the dakota have been reassigned to the early cretaceous muddy formation based on radiometric dating (sprinkel et al., 2012) and regional stratigraphic work (sprinkel, 2024). marine invertebrates, especially oysters, are common wherever these formations outcrop in nps areas (santucci and kirkland, 2010). the subsequent expansion of the seaway deposited what are known as the tropic shale in the southwest (brca, glca), and the mancos group in the east (arch, care, dino; figure 12b; kirkland et al., 2025). the mowry shale represents the earliest part of this marine deposition at dino and is partially equivalent to the tropic shale and tununk shale of the manfigure 11. utah’s “mighty five” national parks mapped against the (a) late jurassic morrison formation and (b) early cretaceous cedar mountain formation. paleogeography for (a) modified from turner and peterson (2004, figure 9); (b) modified from elder and kirkland (1993, figure 5c). see page 221 for nps unit abbreviations. 237 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 figure 12. utah’s “mighty five” national parks mapped against the shoreline of the late cretaceous western interior seaway, during deposition of (a) the cenomanian naturita formation; (b) the turonian tropic and tununk shales of the mancos group; (c) the santonian straight cliffs formation and the ferron formation and blue gate shale of the mancos group; and (d) the campanian wahweap and mesaverde formations. western interior seaway shoreline for (a), (c), and (d) modified from roberts and kirschbaum (1995); (b) modified from elder and kirkland (1993). formation colors adopted from biek et al. (2015). see page 221 for nps unit abbreviations. 238 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 cos group to the southwest (elder and kirkland, 1993; slattery et al., 2016; kirkland et al., 2025; figure 12b). ammonites, bivalves, fishes, and sharks are common within these units. after about 94 ma, the shoreline of the western interior seaway began to retreat eastward, exposing more land in which dinosaurs and other terrestrial organisms could flourish. among utah’s nps units, terrestrial late cretaceous environments are best recorded in the straight cliffs and wahweap formations (brca, cebr; figures 12c and 12d). terrestrial strata of approximately equivalent age in central utah fall within the mesaverde group (care). eastern utah remained submerged in the western interior seaway for most of the remaining late cretaceous epoch. as a result, the blue gate shale of the mancos group is the predominant youngest cretaceous unit in that region (arch, dino; kirkland et al., 2025). however, some terrestrial late cretaceous units are found within this sequence, namely in the ferron formation and juana lopez formation of the mancos group (arch, care; kirkland et al., 2025) and the frontier formation (dino). these strata are partially equivalent in age to the straight cliffs formation at brca and cebr (seymour and fielding, 2013). multiple younger late cretaceous units are exposed throughout the state (e.g., kaiparowits, canaan peak, price river, neslen, north horn formations; hintze and kowallis, 2021). however, these units are not recorded within the nps areas of utah, and their fossil biota are excluded from this document as a result. the cenozoic era the paleogene and neogene periods (c. 66 to 2.6 ma) although paleogene and neogene strata are not well-documented in most of utah’s nps areas, these periods contain key, large-scale tectonic and volcanic events that directly pertain to utah’s modern landscape. these events include the mountain building of the laramide orogeny (about 80 to 50 ma, i.e., the formation of the rocky mountains, tindall et al., 2010), miocene volcanism (e.g., the marysvale volcanic field north of brca, davis and pollock, 2024), and basin and range extension (about 15 to 5 ma, davis and pollock, 2024). laramide tectonism contributed to the uplift of the colorado plateau throughout the first part of the cenozoic era, exposing the paleozoic and mesozoic strata for which many of the nps areas in utah are world-renowned. despite an eventful tectonic history, relatively few sedimentary rocks are recorded from paleogene or neogene within the nps units of utah. major exceptions are the stunning rocks of the claron formation, which comprises the iconic hoodoos and rock fins at brca and cebr. these sediments were deposited in what is now known as lake claron from about 60 to 40 ma (figure 13). however, the depositional interpretation of this formation remains in flux. although the upper white member is a limestone, indicative of lacustrine conditions, the lower more iconic pink member is a blend of conglomerate and calcareous sandstone, suggesting a more fluvial influence (eaton et al., 2018). notably, the pink member of the claron formation has produced diverse ichnofossils pertaining to insect burrows and pupae (bown et al., 1995). the brca and cebr region also preserves the late eocene boat mesa conglomerate, the oligocene brian head formation, and basaltic lava flows from the miocene epoch (tweet et al., 2012c, 2012f; biek et al., 2015). relatively complete fossil remains are exceedingly rare within these units at brca and cebr, although significant discoveries have been made in the claron and brian head formations surrounding these parks. dixie national forest north of brca has produced informative charophytes, ostracods, and the only vertebrates yet recorded from the claron formation (eaton et al., 2018; sanjuan et al., 2020; antonietto et al., 2022). the rarity of fossils and virtually total absence of macrovertebrates is in spite of the partial age equivalence between the claron formation and the green river formation in the uinta basin near dino, which is known to produce impressively complete plants, molluscs, fishes, reptiles, birds, mammals, insects, other arthropods (spiders, scorpions), and stromatolites from lacustrine deposits (figure 13). tracks of birds and mammals have also been recorded in some parts of the green river formation, especially in central utah. dino is the only other nps unit in the state to contain neogene formations, namely the bishop con239 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 glomerate and the browns park formation. no fossils have been reported from either the bishop or browns park within dino; however, vertebrate body fossils and trackways have been documented in these units elsewhere (honey and izett, 1988; lockley and milner, 2014). the quaternary period (c. 2.6 ma to present) quaternary-aged sediments deposited during and after the last ice ages in the pleistocene epoch are present across all nps units. the sediments vary in characteristics as a result of differences in regional geology, underlying strata, and depositional processes. this period is recorded in packrat middens, which have been reported in almost every nps unit in utah. desert packrats (neotoma sp.) gathers twigs, conifer needles, and other loose plant detritus, and even animal bones when constructing their middens. the packrats also urinate on these structures throughout their construction and residence. the urine is often so depleted in water that it rapidly crystallizes, preserving the middens (tweet et al., 2012a). as a result, middens record key insights into taxonomic diversity and climatic conditions at the time they were constructed, and quaternary-focused paleontologists can sample them to understand past plant and animal diversity and obtain radiocarbon dates. packrat middens from several nps units in utah have provided data in such studies (agenbroad and mead, 1989; tweet et al., 2012a). biostratigraphic diagrams arches national park (arch) similar to most of the other large nps units in southern utah, arch’s stratigraphic record preserves a large span of geologic time stretching back into the latter paleozoic era (pennsylvanian) (figure 14). one of the most striking aspects of the fossil record at arch is the abundance and quality of dinosaur footprints in the ruby ranch member of the cedar mountain formation (early cretaceous). these represents theropods (including dromaeosaurs, and other small [cf. carmelopodus sp.] and large [cf. irenesauripus sp.] unidentified morphotypes), sauropods, ornithopods, ankylosaurs, and even some enigmatic feeding traces (lockley et al., 2004; swanson et al., 2005; madsen et al., 2012; martin et al., 2014). footprint localities at arch are comparable in age and ichnotaxa to the nearby mill canyon tracksite, which is managed by the blm (see lockley et al., 2014a). other than dino, arch may preserve the best record of life in the cedar mountain out of any nps unit in utah. just three sources provide the bulk of the knowledge of fossils at arch (figure 15): (1) an initial paleontologfigure 13. utah’s “mighty five” national parks mapped against the shallow lakes of the paleogene period. paleogeography modified from dickinson et al. (1988) and davis et al. (2009). see page 221 for nps unit abbreviations. 240 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 a. a rc h st ra ti g ra ph y st ra �g ra ph ic c ol um n dr aw in g, c ol or s, an d un it th ic kn es se s a do pt ed fr om d oe lli ng a nd k ue hn e (2 01 3) . b. a rc h fo ss il d iv er si ty ve r� ca l a rr an ge m en t o f t ax a is no t c or re la te d on eto -o ne w ith p re ci se st ra �g ra ph ic o cc ur re nc e. u nc ite d ta xa w er e re co rd ed d ur in g fie ld su rv ey a nd /o r c on fir m ed p re se nt in a rc h’ s p al eo nt ol og ic al c ol le c� on s d at ab as e (ic m s) . w ips um cretaceous jurassic triassic permian pennsylvanian mancos group morrison chinleentrada navajo sandstone wingate sandstone moenkopikayenta cutler honaker trail paradox carmel curtiscmfn at sv albiancenom. plensbachiantoarcian bath. tununk brushy basin church rock kane springs bedsmoabblue gate shale jl salt wash tidwell dewey bridge slick rock sandstone turoniancon. sant. lae ycpsrr ph yt os au ria in de t. m ad se n et a l. (2 01 2) ph yt os au ria in de t. ch iro th er iu m m ad se n et a l. (2 01 2) pe tr ifi ed w oo d pe tr ifi ed w oo d un io ni d cl am s pe tr ifi ed w oo d sa nm ig ue lia sp . m et op os au rid ae in de t. cf . t yp ot ho ra x sp . (o st eo de rm ) m ar tz a nd k irk la nd , un pu bl ish ed fi el d no te s (p os sib le g ra lla to r tr ac k m ak er ) co el op hy sis gr al la to r (p os sib le g ra lla to r tr ac km ak er ) se gi sa ur us gr al la to r iso la te d di no sa ur b on e fra gm en t (p os sib le bu rr ow er ) ka ye nt at he riu m (p os sib le tr ac k m ak er ) te no nt os au ru s (p os sib le tr ac k m ak er ) br on to m er us pl at yc er am us cy cl oi de s ps eu do pe rn a co ng es ta py cn od on te n ew be rr yi um bo na ta m ad se n et a l. (2 01 2) (p os sib le tr ac k m ak er ) dr om ae os au rid ae in de t. ap at os au ru s s p. a nd ot he r s au ro po ds sw an so n et a l. (2 00 5) ; m ad se n et a l. (2 01 2) th er op od a in de t. m ar sh e t a l. (2 02 4) (p os sib le tr ac k m ak er ) ga st on ia sp . (p os sib le tr ac k m ak er ) pt er os au r ( or b ird )? sa ur op od a in de t. m ad se n et a l. (2 01 2) th er op od a nd o th er d in os au r b on es (p os sib le tr ac k m ak er ) n ed co lb er tia tr id ac ty l t ra ck s cf . m eg al ob ro nt es sy na ps id (m am m al -li ke re p� le ) bu rr ow s st ro m at ol ite s m ad se n et a l. (2 01 2) ro ot ca st s te rm ite g al le rie s po ss ib le a nk yl os au r sw an so n et a l. (2 00 5) po ss ib le a nk yl os au r m an us tr ac k en ig m a� c fe ed in g tr ac es o rn ith op od tr ac k al l fr o m lo ck le y et a l. (2 00 4) sa ur op od tr ac ks cf . b ro nt op od us gr ac ile th re e -to ed tr ac k tw oto ed dr om ae os au r t ra ck pr od uc �d b ra ch io po ds br yo zo an s sw an so n et a l. (2 00 5) ru go se co ra ls tr ilo bi te s q . s ed s. cr in oi ds th er op od tr ac ks br ac hi op od s fo ss ils fo un d ju st o ut si de a rc h (m el to n 19 72 ; o � ng er , w ri� en co m m un ica �o n, 1 99 5) br yo zo an s co ra ls tr ilo bi te s fu su lin id fo ra m in ife ra sn ai ls pe ly co po d bi va lv es sh ar k te et h cr in oi ds sn ai ls (p os sib le tr ac k m ak er ) ph yt os au ria in de t. bi so n bi so n m ea d et a l. (1 99 1) o vi s c an ad en sis m am m ut hu s c ol um bi sa nt uc ci e t a l. (2 00 1) pa ck ra t m id de ns bi rd b on es re p� le b on es o st ei ch th ye s i nd et . ho rs et ai ls br i� (1 99 6) late earlymiddle late early fi gu re 1 4. b io st ra tig ra ph ic d ia gr am fo r a rc he s n at io na l p ar k (a rc h ). (a ) s tr at ig ra ph y of a rc h , m od ifi ed fr om d oe lli ng an d ku eh ne (2 01 3) ; ( b) fo ss il di ve rs ity o f a rc h . a bb re vi at io ns : ( ge ol og ic ti m e) c en om ., c en om an ia n; c on ., c on ia ci an ; s an t., s an to ni an ; ( st ra tig ra ph y) s v, s um m er vi lle fo rm at io n; c m f, c ed ar m ou nt ai n fo rm at io n; y c , y el lo w c at m em be r; ps , p oi so n st rip m em be r; rr , r ub y ra nc h m em be r; n at , n at ur ita f or m at io n; jl , j ua na l op ez f or m at io n (f ro m k irk la nd e t a l., 2 02 5) ; q . s ed s. q ua te rn ar y se di m en ts . 241 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 figure 15 caption is on the next page. 242 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 ical survey in 2000 by brooke swanson and colleagues (swanson et al., 2005); (2) a detailed paleontological survey of the mesozoic fossils at arch conducted by the ugs and nps in 2011 (madsen et al., 2012); and (3) a literature summary as part of the northern colorado plateau network in 2012 (tweet et al., 2012b). these sources include some information on fieldwork conducted in arch by brooks britt (c.1996), george engelmann (c. 1990), and jim kirkland (c. 2000). aside from the significant trace fossils discovered in the cedar mountain formation (lockley et al., 2004), important finds at arch include vertebrate fossils in the chinle formation and wingate sandstone, as well as the first dinosaur fossils recorded in the kayenta formation within utah (madsen et al., 2012; marsh et al., 2024). this fragmentary material has been diagnosed as indeterminate theropod remains (marsh et al., 2024). additional specimens and further study will be necessary to expand our knowledge of important dinosaur body fossils within this unit. fossils from the pennsylvanian paradox formation were encountered during the 2005 swanson survey, but were not recorded as an official locality, despite being the only known record of specimens from that formation at arch (swanson et al., 2005). similarly, several invertebrates and cladodont and brachydont sharks have been recorded in the pennsylvanian honaker trail formation immediately outside arch (figure 14; melton, 1972; l. ottinger [deceased], written communication, 1995). although no localities within this unit have yet been documented inside the park itself, exposures of the honaker trail at arch, along with the proximity of the localities of melton (1972) and ottinger (written communication, 1995) to said exposures, were sufficient cause to include these taxa in figure 14. bryce canyon national park (brca) in contrast to the rest of utah’s “mighty five'' national parks, brca’s fossil record is unique in being entirely younger than about 100 ma. instead, brca preserves a mostly uninterrupted record of marine and terrestrial environments during the late cretaceous epoch (about 100.5 to 77 ma), and the lake system environment of the claron formation (about 60 to 40 ma), which forms the park’s iconic hoodoo landscapes. whereas some other utah parks do preserve late cretaceous rocks, most do not record terrestrial ecosystems. care, cebr, and glca are exceptions, but their terrestrial cretaceous rocks have not been as well-documented as those at brca. therefore, brca likely possesses the best late cretaceous terrestrial record of any nps unit in utah. the park’s stratigraphy and fossil diversity are most comparable to the late cretaceous record in the neighboring grand staircase-escalante national monument (gsenm), which is famous for producing numerous new species of dinosaurs and other organisms (figure 16). the fossils found at brca were mostly inventoried by jeffrey eaton, professor emeritus of geosciences at weber state university, from 1988 until 2013. during that time, eaton and many colleagues and students discovered diverse vertebrates (fishes, sharks, frogs, salamanders, lizards, turtles, neosuchians, mammals, and dinosaurs) in the late cretaceous straight cliffs and wahweap formations, including some holotypes (figure 17, starred; eaton, 2013; kirkland et al., 2013; nydam, 2013). eaton also ventured into the claron formation to find invertebrate traces, gastropods, and plants within the final years of that inventory. several of the specimens that eaton collected have been described figure 15 is on the previous page. fossils from arch. (a) chirotherium natural cast manus/pes set from the moenkopi formation (locality arch66t). (b) leaves of sanmiguelia cf. s. lewisii from the chinle formation (locality arch41p). (c) pair of theropod tracks from the ruby ranch member, cedar mountain formation (locality arch7t; pen for scale). (d) dromaeosaurid track from locality arch7t. (e) replica (ucm 199.78) of undescribed vertebrate feeding traces from arch7t. scale = 1 cm. (f) unidentified, branching invertebrate burrows from the chinle formation. pen for scale. (g) unidentified arthropod trackway from the chinle formation that was originally identified as octopodichnus by swanson et al. (2005, figure 6h). (h) mammuthus columbi from a cave deposit within arch. scale = 10 cm. a through c modified from madsen et al. (2012). 243 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 in the scientific literature (eaton, 2002, 2013; brinkman et al., 2013; gardner and demar, 2013; gardner et al., 2013; gates et al., 2013; irmis et al., 2013; kirkland et al., 2013; nydam, 2013; roček et al., 2013). fossils that brca staff found since 2022 have been consistent with what eaton found but include many that were previously unknown, such as the first recorded instance of dinosaur footprints in the park’s 100-year history (figure 18). data compiled in the 2022–2023 field season, along with legacy data collected by eaton and other scientists, were used to complete a comprehensive paleontological resource inventory for brca (tran et al., 2024). park staff continued fieldwork into 2024. new discoveries include the first localities documented in the naturita formation at brca, the first identifiable vertebrate fossil in the park’s tropic shale (an isolated fragmentary protostegid coastal), and a possible tyrannosauroid in the straight cliffs formation based on an isolated metatarsal fragment (figure 19). park staff have also collected newly documented fossils in the claron formation in the park, including gastropods, invertebrate ichnofossils, and leaf impressions (figure 20). these new data will expand the park’s knowledge to draft a paleontological resources management plan, which will help the park preserve its fossils and their scientific and educational value for generations to come. the geology and fossil diversity at brca as displayed on figure 17 highlights the research and educational potential of the park’s fossils. for example, although eaton and colleagues fleshed out the diversity figure 16. generalized map of cretaceous outcrops in southern utah. modified from titus et al. (2016, figure 2). see page 221 for nps unit abbreviations. 244 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 u ro de la g en . e t s p. n ov . ga rd ne r e t a l. (2 01 3) le pi so st eu s s p. an d ot he r fi sh es le pi so st eu s s p. an d ot he r fi sh es le pi so st eu s s p. u m n h pb l oc . 6 1 di ve rs e am m on oi ds co bb an (1 99 6) sn ai ls sn ai ls di ve rs e in se ct tr ac e fo ss ils in de te rm in at e tr ac e fo ss ils re w or ke d pa le oz oi c fo ss ils (s an tu cc i a nd k irk la nd , 2 01 0) pa ck ra t m id de ns (a ge nb ro ad e t a l., 1 99 2) tu rt le s in oc er am us p ic tu s an d ot he r b iv al ve s co bb an (1 99 6) ce ra to ps id ae in de t. (te et h) ea to n et a l. (1 99 8) te xa tr yg on b ry ce ns is ki rk la nd e t a l. (2 01 3) co lu m bu sia d eb lie ux i ki rk la nd e t a l. (2 01 3) da ko ta m ys sh ak es pe ar i ea to n (2 01 3) m on oc ne m od on sy ph ak os n yd am (2 01 3) a. b rc a st ra ti g ra ph y co lo rs , u ni t t hi ck ne ss es , a nd a ge c or re la �o ns a do pt ed fr om b ie k et a l. (2 01 5) . co lu m n dr aw in g m od ifi ed fr om f ig . 1 4 in t itu s e t a l. (2 01 6) . ce no zo ic u ni ts n ot to sc al e w ith th ic kn es s. n at ur al fo ot pr in t c as ts ha dr os au rid ae in de t. th er op od a in de t. (te et h) di ve rs e m am m al s ea to n et a l. (1 99 8) ; ea to n (2 01 3) dr om ae os au rid ae in de t. (te et h an d un gu al ) ha dr os au ro m or ph a in de t. ha dr os au ro m or ph a in de t. co lli gn on ic er as w oo lg ar i th er op od a in de t. (u ng ua l) le pi so st eu s s p. + ot he r fi sh es ha dr os au ro m or ph a in de t.b. b rc a fo ss il d iv er si ty ve r� ca l a rr an ge m en t o f t ax a is no t c or re la te d on eto -o ne w ith p re ci se st ra �g ra ph ic o cc ur re nc e. u nc ite d ta xa w er e re po rt ed in th e br ca p al eo nt ol og ic al r es ou rc e in ve nt or y (t ra n et a l., 2 02 4) a nd /o r r ec or de d in b rc a’ s p al eo nt ol og ic al c ol le c� on s d at ab as e (ic m s) . an ky lo sa ur ia in de t. (te et h) ea to n et a l. (1 99 8) an ky lo sa ur ia in de t. (te et h) tu rt le s cr oc od yl om or ph a in de t. cr oc od yl om or ph a in de t. irm is et a l. (2 01 3) po ss ib le ty ra nn os au ro id (d ist al m et at ar sa l f ra gm en t) o rn ith om im os au rid ae in de t. (m an ua l u ng ua ls) cf . a st he no po di cn hi um (m ay fly n ym ph b ur ro w s) an d ot he r t ra ce fo ss ils cf . a st he no po di cn hi um an d ot he r t ra ce fo ss ils cf . a st he no po di cn hi um an d ot he r t ra ce fo ss ils cr oc od yl om or ph a in de t. tu rt le s di ve rs e m am m al s ea to n (2 01 3) tu rt le s u ro de la g en . e t s p. n ov . ga rd ne r e t a l. (2 01 3) an ur a in de t. ro ce k et a l. (2 01 0) an ur a in de t. ro ce k et a l. (2 01 0) cr ab c la w = ty pe sp ec ie s o rig in al ly d es cr ib ed fr om b rc a sp ec im en s sc ip on oc er as g ra ci le co bb an (1 99 6) tu rr ite lla w hi te i an d ot he r s na ils co bb an (1 99 6) m am m ite s n od os oi de s co bb an (1 99 6) le av es cf . s ab al ite s s p. le av es le av es sn ai ls w ill ia m s a nd lo he ng re l ( 20 07 ) le av es bi va lv es bi va lv es cf . a dm et op sis sp p. ho ffm an (2 00 5) bi va lv es cf . e xo gr yr a sp . pr ot os te gi da e in de t. pe tr ifi ed w oo d pe tr ifi ed w oo d pe tr ifi ed w oo d pe tr ifi ed w oo d eocone paleogene pink w . bm c claron upper tcsh john henry dtpc lower members undivided turonian c en . c on .santoniancampanian cretaceous n at u r it a tropic shalestraight cliffswahweap sh tc lower q ua te rn ar y se di m en ts fi gu re 1 7. b io st ra tig ra ph ic d ia gr am fo r b ry ce c an yo n n at io na l p ar k (b rc a ). (a ) s tr at ig ra ph y of b rc a , a do pt ed fr om b ie k et a l. (2 01 5) an d ti tu s et a l. (2 01 6) (b ) f os sil d iv er sit y of b rc a . a bb re vi at io ns : ( ge ol og ic ti m e) c on ., c on ia ci an ; p a l. , p al eo ge ne ; p al ., pa le oc en e; (s tr at ig ra ph y) n at ., n at ur ita f or m at io n; t c , t ib be t c an yo n m em be r, st ra ig ht c liff s f or m at io n; s h , s m ok y h ol lo w m em be r, st ra ig ht c liff s f or m at io n; d t, d rip t an k m em be r, st ra ig ht c liff s f or m at io n; p c , p ar tn er c an yo n m em be r, w ah w ea p fo rm at io n (e at on , 1 99 1; b ev er id ge e t a l., 2 02 2) ; w , w hi te m em be r, c la ro n fo rm at io n; b m c , b oa t m es a c on gl om er at e. 245 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 of microfossils in the straight cliffs formation, paleontologists still have not yet formally described plant or dinosaur fossils from that unit. although ceratopsomorph and tyrannosauroid teeth have recently been confirmed from the straight cliffs formation outside of brca (mccuen and zanno, 2023), diagnostic postcranial material pertaining to these taxa have yet to be formally described. similarly, the wahweap formation in gsenm is well-known for producing multiple named dinosaur and other vertebrate taxa (eaton et al., 1999; kirkland and deblieux, 2010; gates et al., 2011; loewen et al., 2013; gates et al., 2014; lund et al., 2016). several of the type localities for these taxa have been tightly chronostratigraphically constrained (beveridge et al., 2022). likewise, outcrops of the claron formation at sweetwater creek north of brca have recently produced ostracods (antonietto et al., 2022), charophytes (sanjuan and eaton, 2016; sanjuan et al., 2020), and the only vertebrate fossils yet documented in this unit (eaton et al., 2018). furthermore, the sweetwater section has been measured and divided into distinct depositional units (antonietto et al., 2022). given this regional context, brca is likely the nps area with the best potential to contribute to understanding of utah’s late cretaceous and paleogene terrestrial ecosystems. canyonlands national park (cany) cany, like the other “mighty five” national parks, is not broadly known for its paleontological resources, despite possessing a mostly uninterrupted geologic record of pennsylvanian–middle jurassic strata (szymanksi et al., 2024). although a number of paleontological studies have documented fossils in and around cany throughout its history (mcknight, 1940; hasifigure 18. the first dinosaur footprints recorded at brca, occurring in the wahweap formation. don deblieux photogrammetry scanning two cf. caririchnium hadrosaur footprints (left); a close-up photograph of a third footprint (right). scale bar = 10 cm. figure modified from tran (2023b) and tran et al. (2024). 246 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 otis and mitchell, 1989; hasiotis, 1993; sumida et al., 1999a), no paleontological resource preservation program was established in light of these works. a new period of paleontological inventory and research began in 2020, when the ugs obtained funding for the first phase of field paleontological resource inventory. since that project began, the ugs has recovered several significant fossils across the permian–jurassic strata of cany (figure 21). these include vertebrate body fossils in the permian cedar mesa sandstone, abundant track sites in the early–middle triassic moenkopi formation (figure 22), vertebrates (chondrichthyans, phytosaurs, aetosaurs, and metoposaurs) in the late triassic chinle formation (figure 23), and dinosaur tracks in the late–early jurassic wingate sandstone, and early–middle jurassic kayenta formation, and navajo sandstone (deblieux et al., 2021, 2023, 2024). abundant and newly discovered traces pertaining to chirotheriid-type swim tracks in the torrey member of the moenkopi formation are of particular scientific interest (deblieux et al., 2021, 2023; figure 22). these discoveries, along with ongoing work in the same formations at glca (deblieux et al., 2023; milner et al., 2023a, 2023b, 2024), expand our understanding of the permian–jurassic ecosystems of the paradox basin of southeastern utah. capitol reef national park (care) at first glance, the fossil record at care appears rather sparse compared to utah’s other “mighty five” national parks (figure 24). like those parks (except brca), care’s geologic record stretches from the permian period into the lower part of the late cretafigure 19. close-up photographs of (a) an indeterminate protostegid turtle from the tropic shale and (b) an isolated distal metatarsal fragment, possibly referable to a tyrannosauroid, from the straight cliffs formation of brca, with a drawing of metatarsal ii of moros intrepidus (zanno et al., 2019, figure 1j) for comparison. scale bar in (a) in mm, scale bars in (b) = 5 cm. 247 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 ceous epoch, including some marine and terrestrial formations. within this large span of time (more than 200 million years), an important paleontological record from the triassic moenkopi and chinle formations is documented at care. notably, care possesses the most complete sequence of chinle members when compared to any other nps unit in utah, and overall, within the state (kirkland et al., 2014a; martz et al., 2017). triassic paleontology has been a notable feature at care for much of its history. significant vertebrate and invertebrate traces in the moenkopi formation at care were known as early as the 1940s (peabody, 1956), and a single horsetail specimen identified as equisetum was recovered from the park (mickelson et al., 2006a). similarly, plants in the chinle formation were also known and reported for many decades (berry, 1927; ash, 1975a, 1982, 1987, 1993, 2001, 2004; dubiel, 1987; kirkland et al., 2014a; figure 25). the diversity of these fossils is displayed in the attached diagram (figure 24). vertebrate body fossils have been underrepresented in care’s fossil record until relatively recently. park staff had known of some bone fragments throughout the park for decades; however, concerted research effort would not begin until the ugs became involved in the 2010s. to date, the ugs and colleagues have conducted two surveys at care (kirkland et al., 2014a, 2020). the first focused on the geology and paleontology of the chinle formation (kirkland et al., 2014a), whereas the second examined exposures of the morrison and cedar mountain formations (kirkland et al., 2020a). through figure 20. fossils from the hoodoo-forming pink member of the claron formation at brca. (a) gastropods, cf. viviparus; (b) ichnofossils cf. eatonichnus and parowanichnus isp.; (c through d) leaf impressions with primary and secondary venation and leaf edges traced over. scale bars = 5 cm. photographs courtesy of alexandra bonham. 248 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 moenkopichinleh ite b ed s m ot tle d st ra ta h os ki nni ni si nb ad bl ac k le dg e be ds late earlyearlymiddle triassicjurassic permian early late middle cedar mesa sandstone honaker trail paradoxkayenta lower cutler group organ rock wingate ss navajo ss w h it e ri m sa n d st o n e carent slick rock torrey dewey bridge church rock moody canyon black dragon kane springs beds pennsylvanian a. c an y st ra ti g ra ph y st ra �g ra ph ic c ol um n dr aw in g m od ifi ed fr om d oe lli ng (2 00 4) . ch in le a nd m oe nk op i f or m a� on m em be rs a dd ed fr om de bl ie ux e t a l. (2 02 3) f ig . 5 . c ol or s f ro m d oe lli ng (2 00 4) , do el lin g an d ku eh ne (2 00 7, 2 01 3) a nd b ie k et a l. (2 01 0, 2 01 5) . b. c an y fo ss il d iv er si ty ve r� ca l a rr an ge m en t n ot c or re la te d on eto -o ne w ith p re ci se st ra �g ra ph ic p os i� on . q . s ed s. ph yt os au ria in de t. ph yt os au ria in de t. de bl ie ux e t a l. (2 02 3) ca m bo ry gm a (c ra yfi sh b ur ro w s) po ss ib le st em a m ni ot e te tr ap od tr ac ks ite cr in oi ds cr in oi ds st ee le -m al lo ry (1 98 2, 1 98 7) m ck ni gh t ( 19 40 ) la ng fo rd e t a l. (2 00 7) de bl ie ux e t a l. (2 02 3) vi vi pa ro id sn ai ls br ac hi op od s cf . i ch ni ot he riu m sc ol ic ia fe ed in g tr ac es rh izo lit hs rh izo lit hs de bl ie ux e t al . ( 20 23 ) en ig m a� c fe ed in g tr ac es ch iro th er iid -ty pe sw im tr ac ks de bl ie ux e t a l. (2 02 3) de bl ie ux e t al . ( 20 24 ) ro to da ct yl us sy na pti ch ni um pr oc ol op ho ni ch ni um ga st ro po d st ei nk er ns lu ca s e t a l. (1 99 5) m ee ko ce ra s? li ng ul a m on oti s s p. ct en ac an th ifo rm sh ar k sp in e ha pl isti on sp ha er ic um ri gb y an d st ok es (1 97 1) gr iffi th id es a nd o th er tr ilo bi te s m ck ni gh t ( 19 40 ) gr al la to rgr al la to r lu ca s e t a l. (1 99 5) eu br on te s gr al la to r cf . t yp ot ho ra x sp . cf . t yp ot ho ra x sp . de bl ie ux e t a l. (2 02 3) un io ni d cl am s de bl ie ux e t a l. (2 02 3) un io ni d cl am s lu ng fis h to ot h pe tr ifi ed w oo d (e le ph an t c an yo n fm ?) w eb b et a l. (2 00 4) cf . s ta go nol ep is sp . he ck er t et a l. (1 99 9) pe tr ifi ed w oo d w ilk en s ( 20 08 ) (p os sib le tr ac k m ac ke r) co el op hy sis o st ei ch th ye s in de t. re tic ul od us de bl ie ux e t a l. (2 02 1) o st ei ch th ye s i nd et . cr in oi ds (” ri co ” fm ) ba ke r ( 19 33 ) sc ap ho po ds (” ri co ” fm ) br yo zo an s (” ri co ” fm ) br ac hi op od s ba ke r ( 19 33 ), cr in oi ds la ng fo rd e t a l. (2 00 7) st ro m at ol ite s w ai ss (2 00 5) (p os sib le b ur ro w er ) ka ye nt at he riu m co m pl ex v er te br at e bu rr ow s ha sio �s e t a l. (2 00 7) fu su lin id fo ra m in ife ra (e le ph an t c an yo n fm ?) bi lli ng sle y et a l. (2 00 2) , s zy m an sk i e t a l. (2 02 4) pa la eo ni sc id fi sh (e le ph an t c an yo n fm ?) su m id a et a l. (1 99 9a ) fu su lin id fo ra m in ife ra br yo zo an s br yo zo an s m am m ot h bi va lv es in se ct s sn ai ls pl an ts am ph ib ia ns li za rd s ro de nt s ho rs es ho e cr ab tr ac es (d eb lie ux e t a l. 20 21 ) (p os sib le tr ac k m ak er ) cy no do nt a in de t. (p os sib le tr ac k m ak er ) di no sa ur om or ph a in de t. (p os sib le tr ac k m ak er ) ar ch os au rifo rm es in de t. (p os sib le tr ac k m ak er ) m et op os au rid ae in de t. br ac hi op od s (p os sib le tr ac k m ak er ) di lo ph os au ru s (p os sib le tr ac k m ak er ) th er op od a in de t. (p os sib le tr ac k m ak er ) se ita ad (p os sib le tr ac k m ak er ) m eg ap nos au ru s ka ye nt ap us o to zo um m et op os au rid ae in de t. co ra ls bi va lv es ga st ro po ds de bl ie ux e t a l. (2 02 3) ca n y co lle c� on s de bl ie ux e t a l. (2 02 3) sz ym an ks i e t a l. (2 02 4) m ck ni gh t ( 19 40 ) fi gu re 2 1. b io st ra tig ra ph ic d ia gr am fo r c an yo nl an ds n at io na l p ar k (c a n y) . ( a ) s tr at ig ra ph y of c a n y, m od ifi ed fr om d oe lli ng (2 00 4) ; ( b) f os sil di ve rs ity o f c a n y. a bb re vi at io ns : ( ge ol og ic ti m e) m ., m id dl e t ria ss ic ; ( st ra tig ra ph y) s s, sa nd st on e; c a r, c ar m el f or m at io n; e n t, e nt ra da s an dst on e; q . s ed s. , q ua te rn ar y se di m en ts . 249 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 those studies, the ugs determined that the chinle is by far the most fossiliferous and paleontologically important unit in the park. cedar breaks national monument (cebr) cebr, which sits along the western edge of the markagunt plateau, is much like brca of the paunsaugunt plateau in that it is best known for its exposures of the brilliant pink hoodoo-forming claron formation. however, they differ greatly in the extent of paleontological research conducted in each park unit. whereas brca has hosted decades of intensive study in its late cretaceous and paleogene strata, cebr has few fossil resources reported within its boundaries. this is in spite of the fact that cebr also contains some of the same cretaceous units as brca, namely the straight cliffs and wahweap formations (figure 26). there are just two reports of paleontological resources likely originating from cebr. the first is provided by gregory (1950). gregory defers to reeside in listing the gastropods bulinus, helix spatiosa, and planorbis utahensis, the trace fossil celliforma spirifer, and some possible leaf impressions from the top of the wasatch formation in jericho canyon (gregory, 1950). it is important to note that (1) jericho canyon does lie within cebr, and (2) “wasatch” in this literature refers to what is now recognized as the pink member of the claron formation. however, no locality information figure 22. (a) overview and (b through d) close-up photographs of locality sa2273, the “sistine trample,” a chirotheriid-type swim track locality in the torrey member of the moenkopi formation at cany. from deblieux et al., 2023). 250 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 figure 23. fossils from the triassic chinle formation at cany. (a) reticulodus chondrichthyan tooth. (b) metoposaur tooth. (c) “crayfish” burrows (cf. camborygma) in the owl rock member of the chinle formation at cany (photograph courtesy of david slauf). scale bars = 1 cm. 251 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 cr et ac eo u s ju ra ss ic la te la te m id d le ea rl y la te ea rl y ea rl y pe rm ia n e. m an co s g ro u p en tr ad a sa n d st o n e w in g at e ss ch in le n av a jo s an d st o n e m o en ko pi ca rm el m o rr . bl u e g at e sh al e fe rr o n tu n u n k m ai n bo dy w in so r to rr ey sl lt bd m c yn o r m b sr pf pr temple cap nat cmf curt. kay. ka ib ab ls cu tl er g ro u p td sw bb a. care stratigraphy stra�graphic column drawing and unit thicknesses from doelling and kuehne (2007). colors from doelling and kuehne (2007, 2013) and biek et al. (2010, 2015). b. care fossil diversity ver�cal arrangement of taxa is not correlated one-to-one with precise stra�graphic occurrence. uncited taxa were recorded during field survey and/or confirmed present in care’s paleontological collec�ons database (icms). sv q. seds lungfish (tooth plates) equisetites equisetites rotodactylusdiplichniteskouphichnium characichnos palaeophycusarenicolitesundichna fuersichnus chirotherium laurozamites phlebopteris cynepteris cladophlebis pagiophyllum araucarioxylon zamites powelli berry (1927); ash (1975b) metoposauridae indet. cobban (pers. comm, 2000) cobban (pers. comm, 2000) metoposauridae indet. cf. typothorax sp. camborygma (crayfish burrows) hasio�s and mitchell (1993) possible aetosaur osteoderm? kirkland et al. (2014a)sanmiguelia sp. ash (1982) phytosauria indet. phytosauria indet.unionid clams petrified wood kirkland et al. (2014a) ash (1975a) petrified wood (kirkland et al., 2014a) stromatolites kirkland et al. (2020a) kirkland et al (2020a) scrappy dinosaur bones scrappy dinosaur bones dinosaur vertebrae scrappy dinosaur bones exogyra (santucci and kirkland, 2010) giant stromatolites santucci and kirkland (2010) shark teeth shark teeth ammonites ammonites rhynchosauroides (possible track maker) lepidosauromorpha indet. (possible track maker) theropod indet. (possible track maker) pseudosuchia indet. horsetails isocrinus bivalvessnails bivalvessnails packrat middens phytoliths (possible track maker) dromomeron (possible track maker) millipede (possible track maker) horseshoe crab mickelson et al. (2006a) figure 24. biostratigraphic diagram for capitol reef national park (care). (a) stratigraphy of care. modified from doelling and kuehne (2007). (b) fossil diversity of care. abbreviations: (stratigraphy, ascending) ls, limestone; bd, black dragon member; sl, sinbad limestone member; m cyn, moody canyon member; sr, shinarump conglomerate; mb, monitor butte member; pf, petrified forest member; or, owl rock member; ss, sandstone; kay., kayenta formation; lt, lower tongue of the navajo sandstone; pr, paria river member; curt., curtis formation; sv, summerville formation; td, tidwell member; sw, salt wash member; bb, brushy basin member; cmf, cedar mountain formation; nat, naturita formation; q. seds, quaternary sediments. 252 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 is provided, nor are there sufficient specimens in the cebr collections to corroborate this description. mentions of fish fossils from the claron at cebr citing personal communication with jeffrey eaton (santucci and kirkland, 2010; tweet et al., 2012f) were made in error. to date, eaton has never conducted any paleontological survey in the monument (weber state university, verbal communication, 2024). the second report of fossil resources in cebr is on the pollen and macrofossil plant samples of alpine pond (anderson et al., 1999), from about the past 3000 years. despite an overall paucity of fossils, cebr does preserve strata that are not present in brca’s geologic record. these include, namely, the late eocene–early oligocene brian head formation, which is known for producing diverse vertebrates including mammals, turtles, and other reptiles, as well as charophytes (eaton et al., 1999b; cook et al., 2014; sanjuan et al., 2017). importantly, an ash bed at the base of the formation at cebr was radiometrically dated to 35.77 ± 0.28 ma (biek et al., 2015). the other major unit at cebr that is not seen at brca is what has been referred to as the “cretaceous beds on the markagunt'' by biek et al. (2015, map unit “km”). past literature and maps listed the strata between the wahweap and claron formations at cebr as the grand castle formation (tweet et al., 2012f; hatfield et al., 2024). however, the identification and definition of the grand castle and cretaceous strata along the markagunt plateau more generally have been in flux. the grand castle was originally described with three informal members by goldstrand and mullett (1997). however, subsequent examination found that the lower figure 25. fossil plants from the monitor butte member of the chinle formation at care. (a) jack wood (nps geologic resources division) collecting photogrammetric data on in situ equisetites locality wn0151 (kirkland et al., 2014a). (b) close-up photograph of an equisetites stem, locality wn0151. laurozamites powelli specimens from (c and d) locality wn0160, and (e) locality ga1463 (kirkland et al., 2014a). scale bar in (e) in cm. photographs courtesy of jim kirkland and vince santucci. 253 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 and middle members were in fact the drip tank member of the straight cliffs formation and the capping sandstone member (now the pardner canyon member, beveridge et al., 2022) of the wahweap formation, respectively (biek et al., 2015). as a result, biek et al. (2015) redefined the grand castle, restricting it to just the uppermost conglomeratic member as described by goldstrand and mullett (1997). the beds overlying the pardner canyon member (beveridge et al., 2022) of the wahweap formation and underlying the pink member of the claron formation at cebr do not match the grand castle formation of biek et al. (2015), which is conglomeratic. by contrast, these beds consist of fine sandstone, resembling the base of the claron. palynomorphs recovered from this unit in the region range from campanian to maastrichtian in age; these beds may be referable to part of the kaiparowits formation (biek et al., 2015). these factors led biek et al. (2015) to map these strata as an informal unit, “cretaceous beds on the markagunt,” at cebr. we adhere to this nomenclature in figure 26. although few fossils have been confirmed to originate from inside cebr, the paleontology of the southwestern utah region highlights the monument’s potential for study and education. multiple productive microfossil localities were recovered by jeffrey eaton in the straight cliffs and wahweap formations along the markagunt and western paunsaugunt plateaus (see titus et al., 2016). vertebrate fossils that were at first thought to originate from the pink member of the claron formation were in fact float fossils from the overlying brian head formation (eaton et al., 2011, 2018). these discoveries, along with the numerous fossils known from equivalent strata in the brca and gsenm regions to the east, underscore the potential for cebr’s strata to yield fossils that can enhance understanding of late cretaceous and paleogene ecosystems in southern utah. dinosaur national monument (dino) dino is most famous for its world-renowned quarry wall (the carnegie quarry; figures 27 and 28a cl ar o n br ia n h ea d w ah w ea p k beds on the markagunt st ra ig ht c li ff s cr et ac eo us pa le o ge n e eo ce ne o lig oc en e pa le oc en e ca m pa ni an sa nt on ia n pi nk m em be r lo w er m id up pe r sm ok y ho llo w jo hn he nr y (u nd iv id ed ) dr ip ta nk ca pp in g ss t w hi te m em be r m aa . bulinus celliforma spirifer leaf impressions diverse plant spores, seeds, wood anderson et al. (1999) biomphalaria utahensis (formerly planorbis utahensis) glyptostoma spatiosum (formerly helix spatiosa) all from gregory (1950) quaternary sediments cebr biostratigraphy stra�graphic column drawing modified from biek et al. (2015). figure 26. biostratigraphic diagram for cedar breaks national monument (cebr). stratigraphic column modified from biek et al. (2015). abbreviations: (geologic time) maa., masstrichtian; (stratigraphy) sst, sandstone. 254 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 through 28g), originally discovered by earl douglass in 1909. excavation over several decades by multiple research groups (carnegie museum of natural history, smithsonian museum of natural history, and university of utah) would ultimately reveal numerous fossils of dinosaurs and other organisms in the brushy basin member of the late jurassic morrison formation. the significance of the carnegie quarry led dino to be designated by president woodrow wilson as a protected monument in 1915 (wilson, 1915), predating the establishment of the nps in 1916. fossils from the carnegie quarry and elsewhere in the morrison at dino paint a fully fleshed ecosystem occupied by diverse plants, invertebrates, fishes, amphibians, turtles, crocodylomorphs, mammals, and especially dinosaurs near the end of the jurassic period, about 150 ma. several holotypes are included in this group of fossils, such as that for the iconic sauropod apatosaurus louisiae. figure 27 shows at least one representative from each major taxonomic group of organisms recovered from the brushy basin member at dino; however, the faunal list for this unit in the monument is extensive and goes beyond what is shown here (foster, 2003). a full list of taxa is provided in the appendix of this document. at least 10 dinosaur taxa have been recorded within the carnegie quarry alone (foster, 2003; carpenter, 2013). these are the sauropods apatosaurus, barosaurus, camarasaurus (figure 28b), diplodocus, and the newly described dicraeosaurid athenar (whitlock et al., 2025), the ornithischians stegosaurus (figure 28f), camptosaurus, and dryosaurus, and the theropods allosaurus, ceratosaurus, and torvosaurus. foster (2003) reported a possible haplocanthosaurus; however, carpenter (2013) proposes that this may instead be a juvenile diplodocus. we defer to the latter source as more recent (figure 27). the animals range in age from juveniles to adults, providing a wealth of information on the life histories of these late jurassic dinosaurs. although we have visually segregated organisms based on their presence in the carnegie quarry, viewers should note that dinosaurs and other animals shown in the quarry have in fact been found elsewhere at dino, but not vice-versa. for example, the theropod marshosaurus has been found within dino but not in the carnegie quarry. apatosaurus, on the other hand, has been recovered from multiple localities across the monument (foster, 2003). dino’s significant fossils extend beyond the iconic morrison formation. in fact, dino preserves the greatest extent of geologic time of any utah national park or monument, as its rock record stretches as far back as the neoproterozoic era and includes cenozoic rocks of oligocene and miocene age, younger than the paleocene– eocene claron formation of brca and cebr. like the morrison, some of these units have produced holotype specimens from dino (starred), including the titanosauriform sauropod abydosaurus mcintoshi (chure et al., 2010; figure 28g), which was originally reported from the cedar mountain formation at dino. holmes (2017) posited that this type locality occurs at the base of the naturita formation; however, more recent chronostratigraphic and geochemical study confirms that this locality is indeed within the cedar mountain formation (lee et al., 2021). holotypes have also been described from dino’s paleozoic rocks (e.g., amplexus zaphrentiformis white 1876; figure 29). most of the knowledge on dino’s paleozoic fossils comes from surveys in the mid-20th century (untermann and untermann, 1949a, 1949b, 1954). however, ongoing study in the monument’s cambrian lodore formation and other paleozoic rocks (davis, 2010), including the newly identified devonian parting formation (myrow et al., 2023a, 2023b) seeks to understand life in utah before the age of dinosaurs. it is important to note that dino is currently the only nps unit in utah with a permanently employed park paleontologist or equivalent staff member for much of its history. this staffing, along with the fact that paleontological resources are inherent to the spirit and identity of dino, makes it much easier than at other parks for personnel of all disciplines to keep fossils at the forefront of management decisions and interpretive strategies. glen canyon national recreation area (glca) glca contains an immense fossil record represented by more than 700 localities and 40,000 museum spec255 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 sh ar pe (1 99 1) pa ck ra t m id de ns an gi os pe rm an d co ni fe r f os sil s nugget ss browns park q . s ed s. weber sandstone madison ls uinta mt group ch in -l emorrison late jurassiccretaceousneog. pa l. triassic pennsylvanian mississippian camb. de v. neoprot.lateol. mi. latem earlye. early st e c pc p d rv ls h b m u d m s m a n co s bc fr cm t brushy basin salt wash moenkopi morgan lodore pa rt in g (p os sib le tr ac k m ak er ) le pi do sa ur om or ph a in de t. (p os sib le tr ac k m ak er ) sa ur op od om or ph a in de t. ap at os au ru s lo ui sa e ho lla nd (1 91 6) al lo sa ur us cf . f ra gi lis m ar sh osa ur us fo st er (2 00 3) to rv os au ru s cf . t an ne ri st eg os au ru s cf . s te no ps di pl od oc us sp . ba ro sa ur us le nt us ca m ar as au ru s cf . l en tu s ce ra to sa ur us sp . ca m pt os au ru s ap ha no ec te s ca rp en te r a nd w ils on (2 00 8) al lo sa ur us ji m m ad se ni ch ur e an d lo ew en (2 02 0) at he na r b er m an i w hi tlo ck e t a l. (2 02 5) ho pl os uc hu s k ay i gi lm or e (1 92 6) ko pa rio n do ug la ss i ch ur e (1 99 4) n ew u nn am ed de in on yc ho sa ur br i� e t al . ( 20 21 ) di no ch el ys w hi te i ga ffn ey (1 97 9) gl yp to ps u ta he ns is gi lm or e (1 91 6) ab yd os au ru s m ci nt os hi ch ur e et al . ( 20 10 ) gl iro do n gr an di s en ge lm an n an d ca lli so n (1 99 9) rh ad in os te us pa rv us he nr ic i ( 19 98 ) iri do tr ito n he ch ti ev an s e t al . ( 20 05 ) tr ico no le st es cu rv ic us pi s en ge lm an n an d ca lli so n (1 99 8) eo sc in cu s o rn at us br ow ns te in et a l. (2 02 2) he lio sc op os di ck er so na e m ey er s e t a l. (2 02 3) ha im irc hi a am on en sis pl es io sa ur s sn ai ls (k os m id is et a l. 20 02 ) sh ar k te et h sn ai ls cr oc od yl om or ph a ha ns en e t a l. (1 98 3) gr eg so n et a l. (2 02 4) st ew ar t e t a l. (1 99 4) sc hi lle ro sa ur us ut ah en sis n yd am e t a l. (2 01 3) go ni op ho lis ce ra to du s s p. fo st er (2 00 3) ve tu lo na ia sp .o pi st hi as fo st er (2 00 3) dr yo sa ur us el de ra e ca rp en te r a nd ga lto n (2 01 8) bi va lv es am m on ite s un te rm an n an d un te rm an n (1 95 4) pe tr ifi ed w oo d o st ei ch th ye s ph yt os au ria in de t. st ew ar t e t a l. (1 97 2a ) bi va lv es (s pr in ke l p er s. co m m . 2 01 2) sp he no ph yt a in de t. go od (2 01 3) re p� le tr ac ks (s pr in ke l p er s. co m m . 2 01 2) o ct op od ic hn us pa le oh el cu ra ta en id iu m lo ck le y (2 01 1) gr al la to r lo ck le y et a l. (1 99 2) rh yn ch os au ro id es ps eu do te tr as au ro pu s gw yn ne di ch ni um cf . b ra ch yc hi ro th er iu m o to zo um (p os sib le tr ac k m ak er ) se ita ad (p os sib le tr ac k m ak er ) se gi sa ur us (p os sib le tr ac k m ak er ) sp id er (p os sib le tr ac k m ak er ) sc or pi on (p os sib le tr ac k m ak er ) ta ny st ro ph ei da e in de t. (p os sib le tr ac k m ak er ) ar ch os au rif or m es in de t. (p os sib le ?v ar an op us tr ac k m ak er ) ca pt or hi ni da e in de t. (p os sib le ?d ip lic hn ite s tr ac k m ak er ) m ill ip ed e fu su lin id fo ra m in ife ra sp on ge s sn ai ls sn ai l c f. eu om ph al us bi va lv es rh izo lit hs cr in oi ds a nd e ch in oi ds cr in oi ds cr in oi ds cr in oi ds an d ec hi no id s br ac hi op od s cr in oi d fra gm en ts di ve rs e br ac hi op od s di ve rs e br ac hi op od s di ve rs e br ac hi op od s un te rm an n an d un te rm an n (1 95 4) br ac hi op od s hy ol ith s el ra th ie lla sp p. di ce llo m us ? w es to ni a sp . pa la eo ph yc us a nd n um er ou s in ve rt eb ra te ic hn ot ax a sn ai ls un te rm an n an d un te rm an n (1 95 4) fu su lin id fo ra m in ife ra to ly pa m m in a (fo ra m in ife ra ) m ill er el la ci rc ul i th om ps on (1 94 5) ca la m ite s le pi do de nd ro n le pi do de nd ro n bi va lv es br yo zo an s br yo zo an s co ra ls tr ilo bi te s am pl ex us za ph re nti fo rm is w hi te (1 87 6) co ra ls br yo zo an fr ag m en ts br yo zo an s n au �l oi ds a nd a m m on ite s sc he ll an d yo ch el so n (1 96 6) go od a nd e kd al e (2 01 4) ch ur e et a l. (2 01 4) fe ne st el la (m ay er 1 96 4) b. d in o f o ss il d iv er si ty ta xa sh ow n in th e fa m ou s c ar ne gi e q ua rr y ar e ci te d in f os te r ( 20 03 ), gr eg so n et a l. (2 02 4) , ca rp en te r ( 20 14 ), an d hu nt -f os te r ( 20 24 ), w ith th e la �e r t w o pr ov id in g th e m os t s pe ci fic id en �fi ca �o ns . ve r� ca l a rr an ge m en t n ot c or re la te d on eto -o ne w ith p re ci se st ra �g ra ph ic p os i� on . a. d in o s tr at ig ra ph y st ra �g ra ph ic c ol um n dr aw in g m od ifi ed fr om e va no ff (1 98 8) . th e de vo ni an p ar �n g fo rm a� on h as b ee n ad de d in li gh t o f m yr ow e t a l. (2 02 3) . c ol or s f ro m b ie k et a l. (2 01 0, 2 01 5) , do el lin g an d ku eh ne (2 00 7, 2 01 3) , a nd s pr in ke l ( 20 07 ). ca rn eg ie q ua rr y di n o sa u r n at io n al m o n u m en t ca rn eg ie q ua rr y = ty pe sp ec ie s o rig in al ly d es cr ib ed fr om d in o sp ec im en s se rp en te s i nd et . fo st er (2 00 3) cz ek an ow sk ia sp . as h (1 99 4) br as ili ch ni um en ge lm an n et a l. (2 01 0) cf . p ro to ch iro th er iu m sy na pti ch ni um ?v ar an op us ?d ip lic hn ite s (p os sib le tr ac k m ak er ) ka ye nt at he riu m le av es pe tr ifi ed w oo d be nn e� ta le s in de t. (p os sib le tr ac k m ak er ) ps eu do su ch ia in de t. cr ay fis h bu rr ow s di ve rs e ch ar op hy te s an d os tr ac od s sc hu da k et al . ( 19 98 ) pa ly no m or ph s li tw in e t al . ( 19 98 ) eq ui se tu m sp . th om so n et a l. (2 01 4) da vi s ( 20 10 ) un te rm an n an d un te rm an n (1 95 4) m yr ow e t a l. (2 02 3) un te rm an n an d un te rm an n (1 95 4) un te rm an n an d un te rm an n (1 95 4) ch ur e et a l. (2 01 4) hu nt e t a l. (1 99 3) fi gu re 2 7. b io st ra tig ra ph ic d ia gr am fo r d in os au r n at io na l m on um en t ( d in o ). (a ) s tr at ig ra ph y of d in o , m od ifi ed fr om e va no ff (1 98 8) . ( b) f os sil d iv er sit y of d in o . a bb re vi at io ns : ( ge ol og ic ti m e) n eo pr o t. , n eo pr ot er oz oi c; p, p er m ia n; m id ., m id dl e ju ra ss ic ; e ., ea rly c re ta ce ou s; pa l. , pa le og en e; o l. , o lig oc en e, m i., m io ce ne ; ( st ra tig ra ph y) u in ta m t, u in ta m ou nt ai n g ro up ; l s, m ad iso n li m es to ne ; h b, h um bu g fo rm at io n; d , d ou gh nu t f or m at io n; r v l s, r ou nd v al le y li m es to ne ; p c , p ar k c ity f or m at io n; s s, n ug ge t s an ds to ne ; c , c ar m el f or m at io n; e , e nt ra da s an dst on e; st , s tu m p fo rm at io n; c m t, c ed ar m ou nt ai n fo rm at io n; m u d , m ud dy f or m at io n; m s, m ow ry sh al e; f r, fr on tie r f or m at io n, m a n , m an co s g ro up (o f k irk la nd e t a l., 2 02 5) ; b c , b ish op c on gl om er at e; q . s ed s. , q ua te rn ar y se di m en ts . 256 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 figure 28. overview of key vertebrate fossils and the carnegie quarry at dino. (a) overview of the quarry exhibit hall. (b) skull of camarasaurus cf. lentus in the carnegie quarry. (c) overview of the carnegie quarry wall. (d) dino 16488, the holotype of abydosaurus mcintoshi (chure et al., 2010) (e) dino 11541, the holotype of allosaurus jimmadseni (chure et al., 2020). (a) and (b) courtesy of tt; (c) courtesy of ken carpenter; (d) and (e) courtesy of rebecca hunt-foster. 257 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 imens. the fact that it continues to produce fossils of high scientific importance, especially those that illuminate vertebrate ecosystems and behavior in the first half of the mesozoic era, underscores glca’s importance as a paleontological park. it rivals even dino in its breadth and abundance of significant material (figure 30). for these reasons, glca was selected as the prototype paleontological resource monitoring park in 2009. the pilot project to establish this monitoring program was undertaken as a partnership between the nps paleontology program and the ugs (kirkland et al., 2010). glca is a real “walking with dinosaurs” experience in that it possesses a wealth of well-studied and protected vertebrate tracksites stretching as far back as the permian period. the glca is best known to science for producing many footprints of dinosaurs and other animals from the late triassic and early jurassic epochs, especially in the chinle formation, wingate sandstone (figure 31), kayenta formation, and navajo sandstone. hundreds of localities have revealed footprints and associated traces of several types of dinosaurs (theropods, sauropodomorphs, ornithischians), pseudosuchians, and synapsids (lockley et al., 1998, 2014b; milner et al., 2023b, 2024; figure 32). a notable figure 29. holotype specimen of the horn coral amplexus zaphrentiformis (white, 1876), originally collected from the morgan formation in lodore canyon at dino by john wesley powell (photograph courtesy of vince santucci). 258 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 m iln er e t a l. (2 02 4) m ea d et a l. (1 99 3) m ea d et a l. (1 99 2) a. g lc a st ra ti g ra ph y st ra �g ra ph ic c ol um n dr aw in g an d un it th ic kn es se s ad op te d fr om a nd er so n et a l. (2 02 4) , f ig . 4 . co lo rs a do pt ed fr om b ie k et a l. (2 01 0, 2 01 5) , do el lin g (2 00 4) , a nd d oe lli ng a nd k ue hn e (2 00 7, 2 01 3) . navajo ss moen. paradoxcedar mesa ss htcut.or w rkayenta wingate ca r. triassicjurassic permian early late middle pennsylvanian n at . tropic shale straight cliffs smoky + tib.dt + jh early early glen canyon groupsan rafael group middlelate late late tc cretaceousq . s ed s. mor. ti dw el l sa lt w as h br us hy ba si n sv chinle cutler group hermosa group b. g lc a fo ss il d iv er si ty ve r� ca l a rr an ge m en t o f t ax a is no t c or re la te d on eto -o ne w ith p re ci se st ra �g ra ph ic o cc ur re nc e. u nc ite d ta xa w er e re co rd ed d ur in g fie ld su rv ey a nd /o r c on fir m ed p re se nt in g lc a’ s pa le on to lo gi ca l c ol le c� on s d at ab as e (ic m s) . en t ss sh in aru m p m on ito r bu tt e h os ki nni ni m os s ba ckowl rock / petri�ed forest upper ch ur ch ro ck eo po ly co ty lu s r an ki ni al br ig ht e t a l. (2 00 7b ) br ac ha uc he ni us lu ca si al br ig ht e t a l. (2 00 7a ) tr in ac on er um ? be nt on ia nu m al br ig ht e t a l. (2 00 7b ) sa ra bo sa ur us d ah li po lc yn e t a l. (2 02 3) d es m at oc he ly s lo w i an d ot he r t ur tle s sc al am ag nu s t ro pi ce ns is (c la rk e t a l. 20 23 b) (fo rm er ly d ol ic ho rh yn ch op s t ro pi ce ns is sc hm ei ss er m ck ea n 20 12 ) o to zo um ev az ou m ga te w ay en sis sw im tr ac ks d eb lie ux e t a l. (2 02 3) an om ol op us cf . k ou ph ic hn iu m st en ic hn us lo ck le y et a l. (1 99 8) lo ck le y et a l. (1 99 8) cf . p sa m m ic hn ite s m iln er e t a l. (2 02 4) sa ur op od h an d tr ac ks sa ur op od fo ot pr in t w ith sk in im pr es sio n lo ng -n ec ke d pl es io sa ur v er te br ae sc hm ei ss er m ck ea n (2 01 3) un na m ed p le sio sa ur c f. pa ha sa pa sa ur us sc hm ei ss er m ck ea n an d gi lle �e (2 02 1) cf . k ay en ta th er iu m m iln er e t a l. (2 02 3a , 2 02 4) pa la eo ph yc us sk ol ith osve rt eb ra te b ur ro w s ta en id iu m c f. ba rr etti m iln er e t a l. (2 02 3b ) bi va lv e m ol d co qu in a lo ck le y et a l. (2 01 4b ) st ro m at ol ite s ( lo ck le y et a l., 1 99 8) st ro m at ol ite s cf . g w yn ne di ch ni um rh yn ch os au ro id es br ac hy ch iro th er iu m (p se ud osu ch ia n tr ac ks ) (p os sib le e ub ro nt es tr ac k m ak er ) di lo ph os au ru s (p os sib le k ay en ta pu s tr ac k m ak er ) th er op od a in de t. (p os sib le a no m ol op us tr ac k m ac ke r) sp he na co do n (p os sib le st en ic hn us tr ac k m ac ke r) (p os sib le o to zo um tr ac k m ak er ) se ita ad (p os sib le a no m oe pu s tr ac k m ak er ) sc ut el lo sa ur us (p os sib le m oy en isa ur op us tr ac k m ak er ) sc el id os au ru s (p os sib le ba tr ac ho pu s tr ac k m ak er ) pr ot os uc hu s un di ch na eu br on te s w oo d et a l. (2 02 1) cf . k ay en ta pu s w oo d et a l. (2 02 1) (p os sib le gr al la to r tr ac k m ak er ) se gi sa ur us (p os sib le tr ac k m ak er s) m eg ap no sa ur us an om oe pu s ki rk la nd et a l. (2 01 0) an om oe pu s m oy en isa ur op us m oy en isa ur op us m iln er e t al . ( 20 24 ) na va ho pu s (ra re g ra ci le sa ur op od om or ph tr ac ks ) m iln er e t a l. (2 02 4) br as ili ch ni um ki rk la nd e t a l. (2 01 0) cf . b ra sil ic hn iu m sy na ps id tr ac ks ba tr ac ho pu s m iln er e t a l. (2 02 3b ) ba tr ac ho pu s am m on ite s sa nt uc ci a nd k irk la nd (2 01 0) in oc er am id cl am s ic th yo de c� d fis he s sq ua lic or ax a nd ot he r s ha rk s tu rr itt el la w hi te i an d ot he r g as tr op od s ph yt os au ria in de t. ph yt os au ria in de t. de bl ie ux e t a l. (2 02 3) pe tr ifi ed w oo d pe tr ifi ed w oo d pe tr ifi ed w oo d (re w or ke d) fr og ri �e r e t a l. (2 00 2) pl at yh ys tr ix su m id a et a l. (1 99 9) pa ro to su ch us w el le s ( 19 67 ); m or al es (1 98 3, 2 00 5) gr al la to r ka ye nt ap us m iln er e t a l. (2 02 3b ) cf . k ay en tap us cf . a m eg hi ni ch nu s gr al la to r cr ou ch in g tr ac es gi er lin sk i ( 20 09 ); m iln er e t a l. (2 02 4) eu br on te s cr ou ch in g tr ac e m iln er e t a l. (2 02 4) ch ar ac ic hn os tr id ac ty lu s (s w im m in g tr ac es ) di ve rs e m am m al d un g sh as ta g ro un d slo th bi gh or n sh ee p ca m el op s m ea d et a l. (1 98 4) po ss ib le co el ac an th fi ne ll et a l. (1 96 3) lo ph io no tu s s pp . cl am s la sa lic ht hy s s pp . an d ot he r r ed fie ld iid fi sh o ra va ic hn iu m is p. sc oy en ia cf . z am ite s cf . n eo ca la m ite s m aw so ni id ae pa lm fr on ds cl am s cl am s el de r ( 19 87 ) tu rt le s br ac hi op od s br yo zo an s co ra ls tr ilo bi te s fu su lin id fo ra m in ife ra sn ai ls bi va lv es cr in oi ds cr in oi ds br ac hi op od s sn ai ls fu su lin id fo ra m in ife ra br ac hi op od s br yo zo an s m ou nt ai n go at ho rs e sh ru b ox m am m ot h = ty pe sp ec ie s o rig in al ly d es cr ib ed fr om g lc a sp ec im en s m ar m ot ra bb it sn ak e pa ck ra t (b on es + m id de ns ) (p os si bl e tr ac k m ak er ) pr ot o -s uc hi da e rh yn ch osa ur oi de s (p os sib le gw yn ne di ch ni um tr ac k m ak er ) ta ny st ro ph ei da e (p os sib le o ra va ic hn iu m tr ac k m ak er ) w ed ge -fo ot b iv al ve (p os sib le s co ye ni a tr ac km ak er ) be et le la rv ae rh yn ch os au ro id es at re ip us lo ck le y et a l. (1 99 8) pe tr ifi ed w oo d ki rk la nd e t a l. (2 01 0) m et op os au rid ae in de t. ki rk la nd e t a l. (2 01 0) cf . t yp ot ho ra x sp . de bl ie ux e t a l. (2 02 3) st ro m at ol ite s pa la eo ph yc us cf . o ct op od ic hn us ?p al eo he lc ur a (p os sib le o ct op od ic hn us tr ac k m ak er ) ar ac hn id (p os sib le ?p al eo he lc ur a tr ac k m ak er ) be et le m iln er e t a l. (2 02 4) sk ol ith os m iln er e t a l. (2 02 4) m iln er e t a l. (2 02 4) m iln er e t a l. (2 02 4) m iln er e t a l. (2 02 4) m iln er e t a l. (2 02 4) lo ck le y an d hu nt (1 99 5) al br ig ht e t a l. (2 01 3) fi gu re 3 0. b io st ra tig ra ph ic d ia gr am fo r g le n c an yo n n at io na l r ec re at io n a re a (g lc a ). (a ) s tr at ig ra ph y of g lc a , a do pt ed fr om a nd er so n et al . ( 20 24 ); (b ) f os sil d iv er sit y of g lc a . a bb re vi at io ns : ( ge ol og ic ti m e) (s tr at ig ra ph y) h t, h on ak er t ra il fo rm at io n; c u t. , c ut le r f or m at io n; s s, sa nd st on e; o r, o rg an r oc k fo rm at io n; w r, w hi te r im s an ds to ne ; m o en ., m oe nk op i f or m at io n; t c , t em pl e c ap f or m at io n; c a r, c ar m el fo rm at io n; e n t ss , e nt ra da s an ds to ne ; s v, s um m er vi lle f or m at io n; m o r. , m or ris on f or m at io n; n at ., n at ur ita f or m at io n; s m ok y + ti b. , sm ok y h ol lo w a nd t ib be t c an yo n m em be rs , u nd iv id ed ; d t + jh ; d rip t an k an d jo hn h en ry m em be rs , u nd iv id ed . 259 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 figure 31. triassic fossils from glca. (a) horseshoe crab resting trace with associated kouphichnium traces (glca 23838, ucm 140-5) from moenkopi formation. scale = 2 cm. (b) bennettitales (cf. zamites) from shinarump member, chinle formation. (c) redfieldiidae fish in right lateral view from church rock member, chinle formation. (d) cf. gwyneddichnium (glca 25204, ucm 98261) from the shinarump member, chinle formation. scale = 1 cm. (e) batrachopus tracks from church rock member, chinle formation. (f) grallator natural cast from lower wingate sandstone. scale for b, c, e, and f in cm. photographs b, c, and e courtesy andre delgalvis. 260 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 permian trackway has been cleverly dubbed “permian murder” because it possibly shows a predator snatching up a smaller vertebrate mid-stride (lockley et al., 1998). although already well-known, vertebrate trace localities at glca continue to provide new insights into paleoenvironments and species diversity in the early–middle jurassic of southern utah (milner et al., 2023a, 2023b, 2024). a new group of important localities at the kayenta– navajo transition were discovered in early 2023 thanks to the low water level of lake powell at the time. these localities bore multiple vertebrate-bearing horizons, namely tritylodontid synapsids (milner et al., 2023a, 2024; figure 32c). this is an important discovery because vertebrate body fossils in the kayenta formation of utah and the navajo sandstone overall are exceedingly rare. only one set of body fossils has been identified from the kayenta in utah (a fragmentary theropod from arch; marsh et al., 2024). similarly, just two vertebrate taxa have been named from the navajo sandstone: the sauropodomorph seitaad in utah (sertich and loewen, 2010) and the small theropod segisaurus in arizona (camp, 1936; carrano et al., 2005). because of this context, the recently discovered bonebeds are a new priority for fieldwork and protection at glca. glca also has the best record of late cretaceous marine vertebrates of any nps unit in utah, and likely the entire nps. paleontologists, the late david gillette and janet gillette, led several expeditions into the tropic shale in the park during their tenure at the museum of northern arizona in flagstaff, arizona. their efforts revealed several significant specimens of short-necked plesiosaurs, including a well-preserved skull of the pliosaur brachauchenius lucasi (albright et al., 2007a; figure 33) and the holotypes of the polycotylids eopolycotylus rankini (albright et al., 2007b) and scalamagnus tropicensis (clark et al., 2023b, originally dolichorhynchops tropicensis schmeisser mckean, 2012) (figure 30). glca also produced the oldest known mosasaur in north america, sarabosaurus dahli (starred; polcyn et al., 2023). other fossils in the tropic shale at glca include sea turtles, fishes, sharks, ammonites, gastropods, and bivalves (albright et al., 2013). glca is also notable for its quaternary (pleistocene–holocene) fossil resources. whereas most nps units in utah have some record of this period in the form of packrat middens, which frequently capture scrappy plant and animal remains, glca stands out because its cave resources have preserved the most abundant and diverse mammal dung specimens yet found in any park unit in utah. much of this dung was recovered from the aptly named bechan cave, as “bechan'' translates to "big feces” in the navajo language (davis et al., 1984; mead et al., 1984; tweet et al., 2009; hunt et al., 2012; figure 34). most animals identified from pleistocene-age dung at glca are also represented by some skeletal remains (mead et al., 1993) and hair (davis et al., 1984). however, a few, namely bighorn sheep, bison, north american camel (camelops), and shasta ground sloth (nothrotheriops shastensis) have been identified exclusively by their droppings (mead et al., 1984). they are depicted in the “possible trace maker” pose as a result. the late martin lockley, professor emeritus at university of colorado, denver, served as one of the primary stewards of paleontological research at glca, generating decades’ worth of fieldwork and knowledge on the numerous vertebrate trace fossils in the park. his friends and colleagues, especially paleontologists at the sgds and the ugs, carry on his legacy of study and resource stewardship at glca. golden spike national historical park (gosp) gosp was established in 1957 to commemorate the location of the joining of the westward central pacific railroad and the eastward union pacific railroad in 1869, signified with an eponymous golden rail spike. this union formed the first transcontinental railroad in the united states. this historical significance greatly overshadows the park’s paleontological resources. whereas they are limited in geologic scope and taxonomic breadth, they do represent a diverse paleozoic ecosystem. although gosp contains fewer than 3000 acres, the park does contain small outcrops of the lower limestone member of the pennsylvanian oquirrh group. the only confirmed record of fossils from this unit in the park was provided by arvid aase (park paleontologist, fos261 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 figure 32. jurassic fossils from glca. (a) little cave cove tracksite main block from mid-part of the wingate sandstone. note, man's head at the top of the block. (b) kayentapus (glca 23976, ucm 183.63) natural cast from the kayenta formation. (c) tritylodontid mandible from the uppermost kayenta formation. (d) batrachopus manus-pes set (glca 23891, ucm 180.33) from the kayenta formation. scale = 2 cm. (e) grallator and (f) otozoum footprints at the crossing of the fathers tracksite, navajo sandstone. (g) photogrammetric model of a eubrontes crouching trace with possible manus impressions from the lower navajo sandstone (modified from milner et al., 2024, figure 17e). scale = 10 cm. scale for c, e, and f in cm. 262 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 sil butte national monument, wyoming) c. 2007–2008. aase’s survey returned diverse fossils, including sponges, corals, bryozoans, brachiopods, crinoids, trilobites, and phosphatic fish and shark fossils (figure 35). none of the fossils that aase reported were collected (tweet et al., 2012h). no paleontological inventory has since been conducted at gosp, likely due in part to aase’s assessment that fossils in the park are too obscure from the public eye to be threatened by many visitors. hovenweep national monument (hove) hove, a set of six small park units in southeastern utah and southwestern colorado, was established in 1923 primarily to preserve the significant cultural resources there. a paleontological resource inventory and field assessment was completed at hove in april 2024 (shaffer et al., 2024). this work found that only two mesozoic geologic units are preserved in the monument: the early cretaceous burro canyon formation and late cretaceous naturita formation (figure 36). previously, hove was considered to contain strata pertaining to the brushy basin member of the morrison formation (nps, 2004). the april 2024 field assessment reclassified these strata as the younger yellow cat member of the burro canyon formation, a unit generally lacking substantial fossil resources in southeastern utah. furthermore, much of the rest of hove is covered by quafigure 33. skull of the pliosaur, brachauchenius lucasi (specimen mna v9433), from the tropic shale of glca (photograph courtesy of vince santucci). 263 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 ternary sediments considered unlikely to produce significant paleontological resources. scant paleontological resources were observed by austin shaffer and vince santucci in sandstone beds of the naturita formation at hove. these include invertebrate trace fossils, possible root traces, and fossil plant fragments; however, these fossils are poorly preserved and of infrequent occurrence (figure 37). natural bridges national monument (nabr) nabr is a small park unit east of glca and south of cany. very few fossils have been documented in figure 34. bechan cave at glca. (a) pleistocene mammoth dung and (b) glen canyon nra paleontological resource scoping field trip in november 2000 at bechan cave. personnel in (b) (front row): alan titus, ron blakey, norm henderson, vincent santucci, jim kirkland; (back row): the late larry agenbroad, the late dave gillette, steve hasiotis, greg mcdonald, kris thompson, pat monaco, debra mickelson, and ken cole. photographs courtesy of vince santucci. pe n n . o hq u ir rh br id al v ei l li m es to ne a. gosp stratigraphy stra�graphic column drawing modified from constenius et al. (2011). colors from constenius et al. (2011). exclusion of all other units within the oquirrh group based on tweet et al. (2012h). b. gosp fossil diversity ver�cal arrangement not correlated one-to-one with precise stra�graphic posi�on. all taxa included based on aase (undated) and tweet et al. (2012h). quaternary sediments bryozoans brachiopods trilobites crinoid corals phospha�c shark teeth nau�loids sponges phospha�c fish bones figure 35. biostratigraphic diagram for golden spike national historical park (gosp). (a) stratigraphy of gosp, modified from constenius et al. (2011). (b) fossil diversity of gosp. 264 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 nabr to date (figure 38). whereas the vast majority of the monument overlies the permian cedar mesa sandstone, which forms the eponymous natural bridges, some outcrops of overlying early–early middle triassic moenkopi formation and late triassic chinle formation do occur. however, very few fossil resources have been recorded in these units. to date, a handful of root casts and other trace fossils have been noted from the cedar mesa sandstone, reworked fragments of petrified wood from the chinle formation, and packrat middens and bones of the rare but significant harrington’s mountain goat (mead et al., 1987) represent the quaternary at nabr. given that the cedar mesa has proven to be highly fossiliferous in other park units (cany, glca) and in bears ears national monument to the southeast, one should expect that this unit at nabr may produce similarly significant fossils of vertebrates, invertebrates, and trackways that point to life before the largest known mass extinction event in the fossil record at the end of the permian period. rainbow bridge national monument (rabr) rabr is a tiny park unit that sits along one of the southeast edges of the much larger and more famous glca. neighboring glca is well-known for having numerous vertebrate trace fossil localities in permian, triassic, and jurassic formations (see the glca section of this document). in contrast, rabr has just one recorded fossil occurrence: a theropod tracksite in the early jurassic kayenta formation (lockley et al., 1998; figures 39 and 40). future work will be necessary to determine whether the better exposed navajo sandstone, which comprises the eponymous rainbow bridge, includes paleontological resources inside rabr. timpanogos cave national monument (tica) tica was originally established to protect 5600 feet of caves in the mississippian deseret limestone (figure 41). whereas a handful of invertebrate fossils have been collected from this unit (r. horrocks, nps, personal communication, 2001; santucci et al., 2001; figures 42a and 42b), the best study of paleontological resources at tica was provided by george (1999). in that study, george sampled packrat middens from several localities within the monument in order to identify mammal remains. this survey returned diverse fossilized mammals (figures 42c and 42d) and even snake and bird remains, all of extant species. small mammals (rodents, hares, mustelids) represented the majority of the collected material, and bighorn sheep comprised the largest proportion of macromammal specimens. the still-extant status of the taxa observed led george to conclude that the middens were likely of holocene age, and that the diversity recorded within is consistent with the modern ecosystem in the american fork region (george, 1999). to date, this study remains the only systematic survey for paleontological resources at tica. because george (1999) focused on the mammal taxa in the study, he did not assign the snake and bird fossils to alpha taxa. these materials are fragmentary and include a single snake mandible and a few bird bones of “relatively large size” (george, 1999). we represent hove biostratigraphy stra�graphic column drawing and colors adopted from doelling and kuehne (2013). all fossils cited from shaffer et al. (2024) bu rr o c an yo n naturita ea rl y cr et ac eo us la te ye llo w c at invertebrate burrows possible root casts plant fragments quaternary sediments figure 36. biostratigraphic diagram for hovenweep national monument (hove). stratigraphic column and colors modified from doelling and kuehne (2013); all taxa from shaffer et al. (2024). 265 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 these as a gopher snake and a golden eagle, respectively, because these taxa are well-known to inhabit utah for at least part of the year. santucci and kirkland (2010) reported a bison skeleton collected at tica based on a report from monument cave resource specialist rod horrocks (nps, written communication, 1999). zion national park (zion) the geology and paleontology of zion is consistent with those of the other large nps units in utah (arch, cany, care, glca). the best overall information on zion fossils was obtained during an inventory conducted by the ugs (deblieux et al., 2005). much of what they found is consistent with many southern utah nps units (e.g., arch, cany, glca), especially in the fossils of the chinle formation and the overlying early and middle jurassic formations at zion (figure 43). as in other parks, these units at zion have produced abundant petrified logs and scrappy vertebrate remains (usually metoposaurs, aetosaurs, and phytosaurs) in the chinle formation and footprints across the moenave (equivalent to the wingate sandstone at arch, cany, and glca) and kayenta formations and the overlying navajo sandstone. vertebrate traces at zion and other utah parks include the theropod footprint taxa eubrontes and grallator as well as four-toed footprints that may have been made by small non-mammalian synapsids (smith and santucci, 2001; deblieux et al., 2006; mickelson et al., 2006b; figure 44). the late triassic chinle formation at zion has proven to be fossiliferous, as revealed through the ugs field inventory in 2005. an important discovery during the 2005 ugs survey was a tooth of a herbivorous reptile named revueltosaurus (heckert et al., 2006). similarities between the teeth of revueltosaurus and those of ornithischian dinosaurs led paleontologists to classify this animal into that larger group (hunt and lucas, 1994). however, with the discovery of more complete specimens in arizona, revueltosaurus was later found to be a pseudosuchian archosaur closer to crocodylians than to birds and dinosaurs (parker et al., 2005, 2021; irmis et al., 2007). paleontological work is ongoing at zion thanks to the efforts of physical scientist, robyn henderek. in 2023, henderek hired scientists-in-the-parks intern conner bennett to help manage collections and configure 37. paleontological resources from the late cretaceous naturita formation at hove. (a) possible root casts and (b) invertebrate burrows. photographs courtesy of austin shaffer (shaffer et al., 2024). 266 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 m o en ko pitr ia ss ic pe rm ia n u pp er ho sk ini ni shina. quaternary sediments m on ito r bu �e m os s ba ck o rg an ro ck ce da r m es a sa n ds to n e ch in le nabr biostratigraphy stra�graphic column drawing modified from lewis et al. (2011). colors from doelling (2007), biek et al. (2010), and lewis et al. (2011). ver�cal arrangement of taxa not correlated one-to-one with precise stra�graphic posi�on. mountain goat bones and dung mead et al. (1987) reworked petrified wood nps (undated) root casts ver�cal and horizontal burrows figure 38. biostratigraphic diagram for natural bridges national monument (nabr). abbreviations: shina., shinarump member, chinle formation. 267 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 duct fieldwork. during his internship, bennett discovered the first recorded coelacanth specimen from zion (a disarticulated partial skull) in the whitmore point member of the moenave formation. coelacanths from this geological unit have been recorded elsewhere, especially at sgds (milner and kirkland, 2006; harris and milner, 2015). paleontological outreach efforts are also being conducted at zion. bennett and henderek organized the first national fossil day event in the park, and henderek commissioned paleoartist brian engh to decorate the newly installed electric buses at zion with reconstructions of vertebrates from the navajo figure 40. close-up photograph of a single eubrontes track at rabr, the only fossil thus far documented in the monument (from chidsey et al., 2010, figure 5). n av a jo s an d st o n e ka ye n ta ju ra ss ic ea rl y g le n ca ny on g ro up quaternary sediments eubrontes (possible eubrontes track maker) dilophosaurus rabr biostratigraphy stra�graphic column drawing modified from chidsey et al. (2024). occurrence of eubrontes based on hall (1934) and lockley et al. (1998). figure 39. biostratigraphic diagram for rainbow bridge national monument (rabr). stratigraphic column for rabr modified from chidsey et al. (2024). 268 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 sandstone (henderek, 2023; figure 45). recent collaborative field survey between zion and the sgds documented a large scorpion tracksite (cf. paleohelcura) in the navajo in the park (milner, sgds, personal observations). in the summer of 2025, zion opened a new temporary exhibit on the flora, fauna, and paleoenvironment of the triassic-jurassic transition within the park, driven by the research of celina suarez (university of arkansas) and collaboration with sdgs and ugs (nps, 2025b). a. tica stratigraphy stra�graphic column drawing modified from constenius et al. (2011). colors from sprinkel (2007) and constenius et al. (2011). b. tica fossil diversity ver�cal arrangement not correlated one-to-one with precise stra�graphic posi�on. ca m br ia n n eo pr o te ro zo ic m is si ss ip pi a n dev. ophir humbug quaternary sediments m u tu a l ti n ti c q u a rt zi te g re at b lu e li m es to n e u pp er li m es to ne sh al e llst d es er et li m es to n e maxfield limestone fitchville dolomite gardison limestone colonial corals santucci et al. (2001) horn corals snails snake bird all from george (1999) except where noted ground squirrel mink and pine marten marmot raccoondeer mice harepackrats (bones + middens) vole black bearbighorn sheep bison santucci and kirkland (2010) crinoids figure 41. biostratigraphic diagram for timpanogos cave national monument (tica). (a) stratigraphy of tica, modified from constenius et al. (2011). (b) fossil diversity of tica. abbreviations: llst, lower limestone member, great blue limestone. 269 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 conclusions and future work the biostratigraphic diagrams for the 13 nps units in utah showcase the full extent of the complex geologic history, diverse paleoenvironments, and fossil taxa and ichnotaxa that are preserved in these parks and monuments. together, these parks and monuments record most of utah’s geologic history, especially in the paleozoic and mesozoic eras. we hope that, by showing all data and work conducted in each park through 2024, these diagrams can serve as a launch board for future research and interpretation. studies through partnerships like that between the nps paleontology program and the ugs should investigate the gaps in knowledge for utah’s geological record. the nps areas of utah provide opportunities for this work because most preserve fossiliferous strata with high potential to reveal insights into key intervals of deep time. examples of these types of studies are already underway, with the recent discovery of new fossil localities in the chinle formation, wingate sandstone, kayenta formation, and navajo sandstone at glca (milner et al., 2024), the moenkopi and chinle formations at cany (deblieux et al., 2021, 2023, 2024), and in the late cretaceous and paleogene strata at brca (tran et al., 2024). these projects are sigfigure 42. overview of fossils recovered from tica. fossils include (a) coral and (b) gastropod, likely from the deseret limestone, and (c) miscellaneous bones and (d) a rodent skull from quaternary cave deposits at tica. photographs courtesy of camille mckinney, tica (tweet et al., 2012k, figures 4 through 7). 270 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 moenkopi kaibab triassic chinlekayenta navajo sandstone jurassic cr et . moenave tenney canyon la m b po in t (n av s st ) cameron sp rin gd al e ss t shnabkaib middle red lower red upper red permian temple capcarmel n at u ri ta + ce d ar m t. vi rg in l st ti m po w ee p ro ck c an yo n cg l. w hi te th ro ne si na w av a co-op creek limestone crystal creek pa ria ri ve rwinsor di no sa ur ca ny on w hi tm or e pt main body sh in ar um p co ng lo m er at e pu rp le p edo ge ni c be ds fossil mt. harrisburg earlymiddle ea rl y earlylate early q . h ol o. + pl ei st . su r� ci al d ep os its m ya lin a sp . de bl ie ux e t a l. (2 00 5) bi va lv ia sp p. de bl ie ux et a l. (2 00 5) m ol lu sc a in de t. sa nt uc ci (2 00 0) as te ro id ea in de t. ga st ro po da sp p. de bl ie ux e t a l. (2 00 5) bi so n sp . sa nt uc ci (2 00 0) ar �o da ct yl tr ac k sa nt uc ci (2 00 0) bi rd tr ac k sa nt uc ci (2 00 0) iso cr in us n ico le tti de bl ie ux et a l. (2 00 5) am m on ite s sa nt uc ci (2 00 0) m ee ko ce ra �d am m on ite s m iln er , p er so na l ob se rv a� on s m et op os au rid ae in de t. de bl ie ux e t a l. (2 00 6) eu br on te s ka ye nt ap us m iln er et a l. (2 01 2) ch ar ac ic hn os (s w im m in g tr ac es ) (p os sib le e ub ro nt es tr ac k m ak er ) di lo ph os au ru s (p os sib le g ra lla to r an d ch ar ac ic hn os tr ac k m ak er s) m eg ap no sa ur us sa nm ig ue lia le w isi ae to sa ur ia in de t. de bl ie ux e t a l. (2 00 5) ph yt os au ria in de t. de bl ie ux a nd e t a l. (2 00 6) cr oc od yl om or ph a m iln er , p er so na l o bs er va �o ns lo ph io no tu s s p. lo ph io no tu s s p. fo ur -to ed tr ac k de bl ie ux et a l. (2 00 5) (p os sib le tr ac k m ak er ) ka ye nt at he riu m as te ro so m a (b ri� le st ar re s� ng tr ac e) de bl ie ux et a l. (2 00 5) ch iro th er iu m rh yn ch os au ro id es m ic ke lso n et a l. (2 00 6b ) ?a no m oe pu s de bl ie ux e t a l. (2 00 6) di ve rs e tr ac k bl oc k de bl ie ux e t a l. (2 00 6) (p os sib le tr ac k m ak er ) ps eu do su ch ia in de t. (p os sib le tr ac k m ak er ) le pi do sa ur om or ph a in de t. gr al la to r re vu el to sa ur us a ff. r . c al le nd er i he ck er t e t a l. (2 00 6) (p os sib le k ay en ta pu s tr ac k m ak er ) th er op od a in de t. o st ei ch th ye s i nd et . pe tr ifi ed w oo d pe tr ifi ed w oo d pe tr ifi ed w oo d pl an ta e sp p. zi o n 6 35 n ew co el ac an th (2 02 3) gr al la to r m iln er e t a l. (2 01 2) pl an ta e sp p. ar au ca rit es sp . sa in tg eo rg ia sp . (p os sib le g ra lla to r tr ac k m ak er ) se gi sa ur us a. z io n s tr at ig ra ph y st ra �g ra ph ic c ol um n dr aw in g an d un it th ic kn es se s ad op te d fr om c lit es a nd s an tu cc i ( 20 12 ), fi g. 1 . co lo rs a do pt ed fr om b ie k et a l. (2 01 0) . b. z io n f o ss il d iv er si ty ve r� ca l a rr an ge m en t o f t ax a is no t c or re la te d on eto -o ne w ith p re ci se st ra �g ra ph ic o cc ur re nc e. u nc ite d ta xa w er e re co rd ed d ur in g fie ld su rv ey a nd /o r c on fir m ed p re se nt in z io n s p al eo nt ol og ic al c ol le c� on s d at ab as e (ic m s) . q ua dr up ed al tr ac ks de bl ie ux e t a l. (2 00 5, 2 00 6) gr al la to r de bl ie ux e t a l. (2 00 5, 2 00 6) (p os sib le tr ac k m ak er ) ka ye nt at he riu m cf . p al eo he lc ur a m iln er , p er so na l ob se rv a� on s (p os sib le p al eo he lc ur a tr ac k m ak er ) sc or pi on fi gu re 4 3. b io st ra tig ra ph ic d ia gr am fo r z io n n at io na l p ar k (z io n ). (a ) s tr at ig ra ph y of z io n , m od ifi ed fr om b ie k et a l. (2 00 3, 2 01 0) . ( b) f os sil di ve rs ity o f z io n . a bb re vi at io ns : ( ge ol og ic ti m e) c re t. , c re ta ce ou s; h ol o. , h ol oc en e; p le ist ., pl ei st oc en e; q ., q ua te rn ar y se di m en ts ; ( ge ol og y) c gl ., co ng lo m er at e; l st , l im es to ne ; s st , s an ds to ne ; n av s st , n av aj o sa nd st on e; m t., m ou nt ai n; p t., p oi nt . 271 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 nificant because they both aid in identifying and managing the resource and they contribute to the overall knowledge of the paleoenvironments and biodiversity recorded in regionally significant geologic formations. the results of these and future research projects may be made more accessible through expanded interpretation and outreach programming. it is important to reiterate that it is the duty of the nps and the department of interior to preserve, research, and conduct outreach on its paleontological resources for the enjoyment and education of future generations of the public. this is mandated through multiple laws, regulations, and policies, especially the organic act of 1916 (64th congress, 1916), the paleontological resources preservation act of 2009 (prpa; 111th congress, 2009), and nps management policies (2006, section 4.8.2.1). ongoing collaboration between the nps (the nps paleontology program and staff at individual parks) and outside organizations (the ugs, the sdgs, and other researchers) has been vital to fulfilling this responsibility, as exemplified through the inventories, research, and outreach discussed throughout this document. this cooperation ensures that the public continues to benefit scientifically and educationally from the paleontological resources already discussed and yet to be discovered within these iconic and scenic landscapes. this document is not the intended final iteration of this project. we encourage individual parks, nps regional offices, and cooperating partner organizations to incorporate the included visuals into easily accessible and engaging interpretive materials such as interactive figure 44. key fossils from the triassic–jurassic of zion national park (zion). (a) a swim track block from the moenkopi formation in the kolob canyon area; (b) specimen of sanmiguelia lewisi from the uppermost whitmore point member, moenave formation (modified from ash et al., 2014); (c) tridactyl theropod track (deblieux et al., 2006); and (d) eubrontes at the subway tracksite in the kayenta formation (deblieux et al., 2006). photographs a through c courtesy of andrew milner; photograph d courtesy of don deblieux). 272 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 and comparative website map applications. such products would serve as an educational and scientific tool to help the public, nps staff, and researchers quickly and easily understand the temporal and taxonomic diversity of paleontological resources thus far documented in the national parks and monuments of utah. acknowledgments we extend our gratitude to douglas a. sprinkel, azteca geosolutions, who was very enthusiastic about publishing this work in the geology of the intermountain west. his encouragement and coordination between us and the journal were pivotal to formalizing and disseminating the material within this manuscript. many reviewers offered insight and feedback on earlier versions of the text and diagrams. these include robert gay (idaho museum of natural history), joshua lively (prehistoric museum, utah state university eastern), and jeffrey martz (museum of texas tech university). jerry harris (st. george dinosaur discovery site at johnson farm) also provided helpful suggestions for constructing and formatting the attached appendix. their contributions have been invaluable to ensuring the accuracy and accessibility of this material. thank you to the following people for providing photographs: alexandra bonham (stephen w. carothers & associates), ken carpenter (museum of natural history, university of colorado), andre delgalvis (delgalvisart studio 2138), camille mckinney (timpanogos cave national monument), and david slauf (st. george dinosaur discovery site at johnson farm). we also thank several curators and collections managers for access to specimens and allowing us to photograph them in museum exhibits and collections: joshua lively, matt mers, and katy corneli (utah state university eastern prehistoric museum), carolyn levitt-bussian and randy b. irmis (natural history museum of utah), figure 45. zion’s fleet of electric buses adorned with reconstructions of the navajo sandstone and its faunas by paleoartist brian engh. modified from henderek (2023). 273 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 and karen chin and jacob van veldhulzen (university of colorado at boulder). we would like to thank paleoartist benji paysnoe of camben creatives llc for illustrating the cover art for this document. thank you for bringing our concept to life, combining the parks’ temporal and taxonomic diversity with their iconic modern features. finally, we extend our appreciation to the countless current and former interns, staff, volunteers, researchers, and partners who have contributed to the preservation of and education on paleontological resources in utah’s nps areas. this work would not have been possible without the foundation of data, stewardship, and outreach produced by these dedicated individuals. references 59th congress, 1906, public law 59-209—an act for the preservation of american antiquities. 64th congress, 1916, public law 64-235—an act to establish a national park service, and for other purposes. 66th congress, 1919, public law 66-83—an act to establish the arches national park in the state of utah. 68th congress, 1924, public law 68-227—an act to establish the utah national park in the state of utah. 70th congress, 1928, public law 70-74—an act to change the name of the utah national park, the establishment of which is provided for by the act of congress approved june 7, 1924 (forty-third statues, page 593), to the “bryce canyon national park,” and for other purposes. 88th congress, 1964, public law 88-590—an act to provide for the establishment of the canyonlands national park in the state of utah, and for other purposes. 89th congress, 1965, public law 89-102—an act to authorize the secretary of the interior to acquire lands for, and to develop, operate, and maintain, the golden spike national historic site. 90th congress, 1968, public law 90-543—an act to establish a national trails system, and for other purposes. 92nd congress, 1971, public law 92-155—an act to establish the arches national park in the 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of the intermountain west 2025 volume 12 appendix taxonomic list of fossils in the national park service areas in utah background although the diagrams are comprehensive in biostratigraphic extent, they do not completely capture the full taxonomic diversity that has been recorded within the nps areas in utah. for example, eaton (2013) figured and described numerous multituberculates and other mammals to the genus level within the straight cliffs and wahweap formations at brca. however, these genera are summarized visually as a singular mammal individual (except dakotamys shakespeari, eaton, 2013) in figure 17. this approach of depicting multiple taxa with a single representative individual was used across all diagrams to mitigate visual noise and promote the ease of comprehension. in order to ensure completeness of data, we include this appendix of all known fossil taxa and associated references from the nps areas in utah, listed by park and geologic formation. this appendix is modeled after the taxonomic list of titus et al. (2016). type species originally described from fossils first documented in these parks are indicated with asterisks (*). because these are based on the literature, some taxonomy and identifications are inevitably outdated. arches national park (arch) paradox formation, pennsylvanian (arch) anthozoa rugosa gen. et sp. indet. (in swanson et al., 2005) bryozoa gen. et sp. indet. (in swanson et al., 2005) brachiopoda productida gen. et sp. indet. (in swanson et al., 2005) echinodermata crinoidea gen. et sp. indet. (in swanson et al., 2005) arthropoda trilobita gen. et sp. indet. (in swanson et al., 2005) moenkopi formation, early triassic (arch) pseudosuchia chirotherium isp. (in madsen et al., 2012) church rock member, chinle formation, late triassic (arch) plantae sanmiguelia sp. (in madsen et al., 2012) gen. et sp. indet. (in madsen et al., 2012) amphibia a-2 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 metoposauridae gen. et sp. indet. (in madsen et al., 2012) pseudosuchia aetosauria cf. typothorax sp. (in martz and kirkland, unpublished field notes) phytosauria gen. et sp. indet. (in madsen et al., 2012) wingate sandstone, late triassic–early jurassic (arch) pseudosuchia phytosauria gen. et sp. indet. (in madsen et al., 2012) dinosauria grallator isp. (in madsen et al., 2012) gen. et sp. indet. (in madsen et al., 2012) kayenta formation, early jurassic (arch) dinosauria theropoda gen. et sp. indet. (in marsh et al., 2024) theropod tracks (in madsen et al., 2012) navajo sandstone, early jurassic (arch) theropoda grallator isp. (in madsen et al., 2012) curtis formation, late jurassic (arch) theropoda cf. megalobrontes isp. (in britt, 1996) salt wash member, morrison formation, late jurassic (arch) plantae gen. et sp. indet. (in britt, 1996) mollusca bivalvia unionidae gen. et sp. indet. (in britt, 1996) dinosauria theropoda gen. et sp. indet. (in britt, 1996) brushy basin member, morrison formation, late jurassic (arch) plantae gen. et sp. indet. (in swanson et al., 2005) dinosauria ornithischia ankylosauria gen. et sp. indet. (in swanson et al., 2005) a-3 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 saurischia sauropoda apatosaurus sp. (in swanson et al., 2005; madsen et al., 2012) yellow cat member, cedar mountain formation, early cretaceous (arch) plantae gen. et sp. indet. (in madsen et al., 2012) dinosauria saurischia sauropoda gen. et sp. indet. (in madsen et al., 2012) poison strip member, cedar mountain formation, early cretaceous (arch) plantae gen. et sp. indet. (in madsen et al., 2012) ruby ranch member, cedar mountain formation, early cretaceous (arch) dinosauria saurischia sauropoda cf. brontopodus isp. (in madsen et al., 2012) theropoda ornithomimosauria gen. et sp. indet. (in madsen et al., 2012) deinonychosauria gen. et sp. indet. (in madsen et al., 2012) ornithischia ornithopoda gen. et sp. indet. (in madsen et al., 2012) ankylosauria gen. et sp. indet. (in madsen et al., 2012) tununk shale, mancos group, late cretaceous (arch) mollusca bivalvia pycnodonte newberryi umbonata (in madsen et al., 2012) blue gate shale, mancos group, late cretaceous (arch) mollusca bivalvia platyceramus cycloides (in madsen et al., 2012) pseudoperna congesta (in madsen et al., 2012) eocene (reworked) (arch) mollusca bivalvia plesielliptio sp. (in oviatt, 1988) gen. et sp. indet. (in oviatt, 1988) a-4 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gastropoda biomphalaria sp. (in oviatt, 1988) cf. biomphalaria sp. (in oviatt, 1988) drepanotrema? sp. (in oviatt, 1988) goniobasis tenera (in oviatt, 1988) goniobasis cf. g. tenera (in oviatt, 1988) physa sp. (in oviatt, 1988) planorbidae gen. et sp. indet. (in oviatt, 1988) quaternary sediments (arch) plantae rhizoliths (in oviatt, 1988) polypodiophyta equisetales equisetum sp. (in nittmann, 1993) gymnospermae cupressaceae juniperus osteosperma (in sharpe, 1991; smith and betancourt, 1998) juniperus sp. (in nittmann, 1993) pinaceae picea pungens (in smith and betancourt, 1998) pinus edulis (in smith and betancourt, 1998) pinus flexilis (in sharpe, 1991) cf. pinus sp. (in sharpe, 1991) pseudotsuga menziesii (in sharpe, 1991; smith and betancourt, 1998) angiospermae nyctaginaceae abronia sp. (in sharpe, 1991) rosaceae amelanchier utahensis (in sharpe, 1991) cercocarpus cf. c. montanus (in sharpe, 1991) coleogyne ramosissima (in sharpe, 1991) cf. rosa sp. (in sharpe, 1991) boraginaceae amsinckia sp./cryptantha sp. (in sharpe, 1991) cryptantha cf. c. cinerea (in sharpe, 1991) cf. cryptantha sp. (in sharpe, 1991) lithospermum cf. l. incisum (in sharpe, 1991) tiquilia sp. (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) papaveraceae argemone sp. (in sharpe, 1991) asteraceae artemisia sp. (in sharpe, 1991) artemisia sp./chrysothamnus sp. (in sharpe, 1991) cf. chrysopsis sp. (in sharpe, 1991) chrysothamnus sp. (in sharpe, 1991) cf. chrysothamnus sp. (in sharpe, 1991) a-5 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 cirsium sp. (in sharpe, 1991) cf. cirsium sp. (in sharpe, 1991) gutierrezia cf. g. microcephala (in sharpe, 1991) gutierrezia cf. g. sarothrae (in sharpe, 1991) gutierrezia sp. (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) fabaceae astragalus sp. (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) amaranthaceae atriplex sp. (in sharpe, 1991) chenopodium sp. (in sharpe, 1991) krashcheninnikovia lanata/ceratoides lanata (in sharpe, 1991) cheno-am pollen (in nittmann, 1993) chenopodiaceae gen. et sp. indet. (in sharpe, 1991) poaceae bouteloua sp. (in sharpe, 1991) heteropogon sp. (in sharpe, 1991) stipa hymenoides (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) cyperaceae carex sp. (in nittmann, 1993) santalaceae comandra umbellata (in sharpe, 1991) cornaceae cornus sericea (in sharpe, 1991) brassicaceae dithyrea wislizenii (in sharpe, 1991) dyssodia acerosa (in sharpe, 1991) lepidium sp. (in sharpe, 1991) oleaceae cf. fraxinus anomala (in sharpe, 1991) loasaceae mentzelia sp. (in sharpe, 1991) cactaceae opuntia polyacantha (in sharpe, 1991) opuntia sp. (in sharpe, 1991; nittmann, 1993) gen. et sp. indet. (in sharpe, 1991) apiaceae osmorhiza depauperata (in sharpe, 1991) salicaceae populus sp. (in sharpe, 1991) anacardiaceae rhus aromatica (in sharpe, 1991) rhus trilobata (in smith and betancourt, 1998) grossulariaceae ribes montigenum (in sharpe, 1991) malvaceae a-6 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 sphaeralcea sp. (in sharpe, 1991) asparagaceae yucca cf. y. angustissima (in sharpe, 1991) yucca sp. (in sharpe, 1991) polemoniaceae gen. et sp. indet. (in sharpe, 1991) mollusca bivalvia pisidium cf. p. variable (in nittmann, 1993) pisidium cf. p. walkeri (in nittmann, 1993) pisidium sp. (in nittmann, 1993) gastropoda deroceras laeve (in nittmann, 1993) discus whitneyi (formerly d. cronkhitei) (in nittmann, 1993) euconulus fulvus (in nittmann, 1993) galba bulimoides (formerly fossaria (bakerilymnaea) bulimoides) (in nittmann, 1993) galba dalli (formerly fossaria (bakerilymnaea) dalli (in nittmann, 1993) galba cf. g. obrussa (formerly fossaria obrussa) (in nittmann, 1993) galba sp. (formerly fossaria sp.) (in nittmann, 1993) gastrocopta pellucida (in nittmann, 1993) gastrocopta sp. (in nittmann, 1993) hawaiia miniscula (in nittmann, 1993) nesovitrea hammonis electrina (in nittmann, 1993) oxyloma sp. (in nittmann, 1993) physella sp. (in nittmann, 1993) pupilla blandi (in nittmann, 1993) pupilla muscorum (in nittmann, 1993) pupilla sp. (in nittmann, 1993) pupoides hordaceous (in nittmann, 1993) vallonia cf. v. gracilicosta (in nittmann, 1993) vallonia cyclophorella (in nittmann, 1993) vallonia sp. (in nittmann, 1993) cf. zonitoides arboreus (in nittmann, 1993) succineidae gen. et sp. indet. (in nittmann, 1993) gen. et sp. indet. (in madsen et al., 2012) arthropoda ostracoda gen. et sp. indet. (in oviatt, 1988; nittmann, 1993) reptilia gen. et sp. indet. (in sharpe, 1991; nittmann, 1993) aves gen. et sp. indet. (in nittmann, 1993) mammalia gen. et sp. indet. (in nittmann, 1993) rodentia neotoma sp. middens (in tweet et al., 2012a) proboscidea mammuthus columbi (in santucci et al., 2001; swanson et al., 2005) a-7 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 artiodactyla bison bison (in mead et al., 1991) ovis canadensis (in mead et al., 1991) diatomista gen. et sp. indet. (in oviatt, 1988) bryce canyon national park (brca) naturita formation (dakota formation in older references), late cretaceous (brca) mollusca bivalvia cf. exogyra sp. (in this paper) tropic shale, late cretaceous (brca) mollusca cephalopoda ammonoidea allocrioceras annulatum (in cobban, 1996) baculites gracilis (in reeside, 1937) baculites yokoyamai (in cobban, 1996) baculites sp. (in tran et al., 2024) burroceras irregulare (in cobban, 1996) collignoniceras woollgari (in tran et al., 2024) euomphaloceras septemseriatum (in cobban, 1996) mammites nodosoides (in cobban, 1996) metoicoceras geslisianum (in cobban, 1996) prionocyclus hyatti (in cobban, 1996) sciponoceras gracile (in cobban, 1996) bivalvia anomia sp. (in reeside, 1939) corbicula (cyrena) securis (in reeside, 1939) corbicula (cyrena) sequilateralis (in reeside, 1939) exogyra columbella (in reeside, 1939) inoceramus pictus (in cobban, 1996) inoceramus sp. (in cobban, 1996) ostrea prudentia (in reeside, 1937) ostrea soleniscus (in reeside, 1939) parvilucina juvensis (formerly nymphalucina juvensis) (in cobban, 1996) phelopteria sp. (in tran et al., 2024) psilomya meeki (in cobban, 1996) pycnodonte newberryi (in cobban. 1996) volsella sp. (in reeside, 1939) gastropoda euspira sp. (in cobban, 1996) neritina bellulata (in reeside, 1937) neritina incompta (in cobban, 1996) perissoptera prolabiata (in cobban, 1996) a-8 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 turritella whitei (in cobban, 1996) viviparus sp. (in cobban, 1996) testudines protostegidae gen. et sp. indet. (this paper) smoky hollow member, straight cliffs formation, late cretaceous (brca) plantae angiospermae gen. et sp. indet. (in tran et al., 2024) mollusca bivalvia gen. et sp. indet. (in tran et al., 2024) gastropoda admetopsis spp. (in hoffman, 2005) actinopterygii lepisosteiformes lepisosteus sp. (in tran et al., 2024) crocodylomorpha gen. et sp. indet. (in tran et al., 2024) dinosauria hadrosauromorpha gen. et sp. indet. (in santucci and kirkland, 2010; tran et al., 2024) theropoda gen. et sp. indet. (in tran et al., 2024) testudines gen. et sp. indet. (in tran et al., 2024) john henry member, straight cliffs formation, late cretaceous (brca) plantae angiospermae cf. cercidiphyllum sp. (in tran et al., 2024) cf. saliciphyllum sp. (in tran et al., 2024) menispermaceae indet. (in tran et al., 2024) mollusca bivalvia corbula sp. (in tran et al., 2024) gastropoda gen. et sp. indet. (in tran et al., 2024) elasmobranchii brachyrhizodus sp. (in williamson et al., 2011) actinopterygii teleostei gen. et sp. indet. type o (in brinkman et al., 2013) acanthomorpha gen. et sp. indet. (in brinkman et al., 2013) a-9 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 hiodontidae gen. et sp. indet. (in brinkman et al., 2013) lepisosteiformes lepisosteus sp. (in brinkman et al., 2013) ostariophysi otophysi gen. et sp. indet. (in brinkman et al., 2013) pycnodontiformes micropycnodon sp. (in brinkman et al., 2013) paralbula sp. (in brinkman et al., 2013) amphibia allocaudata albanerpedontidae gen. et sp. indet. (in gardner and demar, 2013) cf. albanerpeton nexuosum (in gardner and demar, 2013) anura scotiophryne pustulosa (in roček et al., 2010, 2013; gardner and demar, 2013) urodela batrachosauroididae opisthotriton sp. (in gardner et al., 2013) family incertae sedis gen. et sp. nov. (in gardner et al., 2013) scapherpedontidae scapherpeton sp. (in gardner et al., 2013) sirenidae habrosaurus sp. (in gardner et al., 2013) gen. et sp. indet. (in roček et al., 2010; gardner and demar, 2013) crocodylomorpha gen. et sp. indet. (in tran et al., 2024) eusuchia gen. et sp. indet. (in irmis et al., 2013) mesoeucrocodylia gen. et sp. indet. (in irmis et al., 2013) neosuchia gen. et sp. indet. (in irmis et al., 2013) unnamed clade of atoposauridae + eusuchia gen. et sp. indet. (in irmis et al., 2013) dinosauria hadrosauromorpha gen. et sp. indet. (in santucci and kirkland, 2010; gates et al., 2013; tran et al., 2024) theropoda dromaeosauridae gen. et sp. indet. (in tran et al., 2024) ornithomimosauria gen. et sp. indet. (in this paper) tyrannosauroidea gen. et sp. indet. (in this paper) testudines a-10 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 adocus sp. (in tran et al., 2024) aspideretoides sp. (in tran et al., 2024) baenidae neurankylus sp. (in tran et al., 2024) naomichelys sp. (in eaton, 1999) gen. et sp. indet. (in tran et al., 2024) trionychidae gen. et sp. indet. (in tran et al., 2024) squamata autarchoglossa morphotype d (in nydam, 2013) ophidia coniophis sp. (in nydam, 2013) platynota cf. colpodontosaurus sp. (in nydam, 2013) morphotype b (in nydam, 2013) morphotype c (in nydam, 2013) scincomorpha monocnemodon syphakos* (in nydam, 2013) gen. et sp. indet. (in nydam, 2013) mammalia multituberculata cimolodontidae cedaromys sp. cf. c. hutchisoni (in eaton, 2013) cimolodon similis (in eaton, 2013) cimolodon sp. cf. c. foxi (in eaton, 2013) cimolodon sp. cf. c. similis (in eaton, 2013) cimolomyidae cimolomys sp. b (in eaton, 2002, 2013) ?cimolomys sp. a (in eaton, 2013) neoplagiaulacidae mesodma sp. (in eaton, 2013) mesodma sp. cf. m. minor (in eaton, 2013) marsupalia “didelphomorpha” apistodon sp. cf. a. exiguus (in eaton, 2013) gen. et sp. indet. (in eaton, 2013) “alphadontidae” ?varalphadon sp. (in eaton, 2013) didelphidae gen. et sp. indet. (in eaton, 2013) stagodontidae eodelphis sp. (in eaton, 2013) pediomydiae ?leptalestes sp. (in eaton, 2013) gen. et sp. indet. (in eaton, 2013) triconodonta cf. alticonodon sp. (in eaton, 2013) a-11 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. (in eaton, 2013) trechnotheria ?spalacotheridium sp. (in eaton, 2013) symmetrodontoides sp. (in eaton, 2013) drip tank member, straight cliffs formation, late cretaceous (brca) crocodylomorpha gen. et sp. indet. (in tran et al., 2024) dinosauria hadrosauromorpha gen. et sp. indet. (in gates et al., 2013; tran et al., 2024) wahweap formation, late cretaceous (brca) plantae angiospermae cf. sabalites (in tran et al., 2024) arthropoda crustacea ostracoda gen. et sp. indet. (in meyers and knauss, 2021) xanthidae gen. et sp. indet. (in milner, written communications) paguiroidea gen. et sp. indet. (in milner, written communications) mollusca bivalvia gen et sp. indet. (in tran et al., 2024) gastropoda physa sp. (in tran et al., 2024) reesidella sp. (in tran et al., 2024) viviparus sp. (in tran et al., 2024) elasmobranchii chiloscyllium missouriense (in kirkland et al., 2013) columbusia deblieuxi* (in kirkland et al., 2013) cristomylus cifellii (in kirkland et al., 2013) lonchidion sp. (in kirkland et al., 2013) texatrygon brycensis* (in kirkland et al., 2013) actinopterygii amiidae amia sp. (in tran et al., 2013) lepisosteiformes lepidotes sp. (in brinkman et al., 2013) lepisosteus sp. (in brinkman et al., 2013) otophysi gen. et sp. indet. (in brinkman et al., 2013) pycnodontiformes micropycnodon sp. (in brinkman et al., 2013) paralbula sp. (in brinkman et al., 2013) a-12 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 teleostei acanthomorpha gen. et sp. indet. (in brinkman et al., 2013) amphibia allocaudata albanerpedontidae gen. et sp. indet. (in gardner and demar, 2013) anura scotiophryne pustulosa (in roček et al., 2010, 2013; gardner and demar, 2013) morphotype 1 (in roček et al., 2013; gardner et al., 2016) family incertae sedis nezpercius dodsoni (in gardner and demar, 2013) urodela scapherpedontidae scapherpeton tectum (in gardner and demar, 2013) scapherpeton sp. (in gardner and demar, 2013) crocodylomorpha gen. et sp. indet. (in tran et al., 2024) dinosauria ankylosauridae gen et sp. indet. (in eaton et al., 1998) hadrosauridae gen. et sp. indet. (in tran et al., 2024) hadrosaurid pes tracks (in tran et al., 2024) theropoda gen. et sp. indet (in eaton et al., 1998) ceratopsidae gen. et sp. indet. (in eaton et al., 1998; tran et al., 2024) testudines adocidae adocus sp. (in meyers and knauss, 2021) baenidae gen. et sp. indet. (in tran et al., 2024) neurankylus sp. (in tran et al., 2024) chelydridae gen. et sp. indet. (in tran et al., 2024) compsemys sp. (in eaton et al., 1998) bothremys sp. (in tran et al., 2024) naomichelys sp. (in tran et al., 2024) trionychidae gen. et sp. indet. (in tran et al., 2024) aspideretoides sp. (in tran et al., 2024) squamata chamops segnis (in eaton et al., 1998) contogenys sp. (in eaton et al., 1998) mammalia multituberculata cimolodonta a-13 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 family incertae sedis ?paracimexomys sp. (in eaton, 2013) cimolodontidae cedaromys sp. cf. c. hutchisoni (in eaton, 2013) cimolomyidae cimolomys sp. (in eaton, 2013) family incertae sedis dakotamys shakespeari* (in eaton, 2013; originally referred to the john henry member, straight cliffs formation) neoplagiaulacidae mesodma sp. cf. m. formosa (in eaton, 2013) mesodma sp. cf. m. minor (in eaton, 2013) marsupalia pediomydiae gen. et sp. indet. (in eaton, 2013) varalphadon sp. cf. v. creber (in eaton, 2013) pink member, claron formation, paleogene (brca) arthropoda insecta hymenoptera celliforma isp. (in davis et al., 2015; tran et al., 2024) coleoptera eatonichnus claronensis (in davis et al., 2015; tran et al., 2024) eatonichnus utahensis (in davis et al., 2015; tran et al., 2024) parowanichnus isp. (in davis et al., 2015; tran et al., 2024) angiospermae celtis sp. (in tran et al., 2024) gen. et sp. indet. (in tran et al., 2024) mollusca bivalvia unionidae indet. gastropoda (in tran et al., 2024) physa pleromatis (in tran et al., 2024) cf. physa sp. (in tran et al., 2024) cf. viviparus sp. (in tran et al., 2024) actinopterygii lepisosteiformes lepisosteus sp. (in tran et al., 2024) white member, claron formation, paleogene (brca) indeterminate trace fossils (in this paper) boat mesa conglomerate, paleogene (brca) paleozoic invertebrates (reworked) (in santucci and kirkland, 2010) quaternary sediments (brca) plantae a-14 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gymnospermae pinopsida gen. et sp. indet. (in agenbroad et al., 1992) cupressaceae juniperus osteosperma (in agenbroad et al., 1992) juniperus scopulorum (in agenbroad et al., 1992) juniperus sp. (in agenbroad et al., 1992) pinaceae pinus edulis (in agenbroad et al., 1992) pinus ponderosa (in agenbroad et al., 1992) angiospermae eudicotidae caryophyllales cactaceae echinocereus sp. (in agenbroad et al., 1992) fagales fagaceae quercus gambelli (in agenbroad et al., 1992) quercus sp. (in agenbroad et al., 1992) ranunculales berberidaceae berberis repens (in agenbroad et al., 1992) sapindales anacardiaceae rhus trilobata (in agenbroad et al., 1992) monocotidae poales poaceae oryzopsis hymenoides (in agenbroad et al., 1992) insecta coleoptera buprestidae gen. et sp. indet. (in agenbroad et al., 1992) carabidae rhadine sp. (in agenbroad et al., 1992) chrysomelidae altica sp. (in agenbroad et al., 1992) cleridae cymatodera latifasciata (in agenbroad et al., 1992) curculionidae sapotes sp. (in agenbroad et al., 1992) ophryastes sp. (in agenbroad et al., 1992) elateridae esthesopus parcus (in agenbroad et al., 1992) melanotus sp. (in agenbroad et al., 1992) latridiidae gen. et sp. indet. (in agenbroad et al., 1992) a-15 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 mycetophaginae litargus sp. (in agenbroad et al., 1992) ptinidae niptus cf. ventriculus (in agenbroad et al., 1992) niptus spp. (in agenbroad et al., 1992) ptinus sp. (in agenbroad et al., 1992) scarabaeidae aphodius sp. (in agenbroad et al., 1992) gen. et sp. indet. (in agenbroad et al., 1992) staphylinidae pselaptrichus sp. (in agenbroad et al., 1992) quedius sp. (in agenbroad et al., 1992) tenebrionidae gen et sp. indet. (in agenbroad et al., 1992) coniontis sp. (in agenbroad et al., 1992) eleodes spp. (in agenbroad et al., 1992) entrodes sp. (in agenbroad et al., 1992) cf. metaponium sp. (in agenbroad et al., 1992) diptera gen. et sp. indet. (in agenbroad et al., 1992) hemiptera lygaeidae gen. et sp. indet. (in agenbroad et al., 1992) hymenoptera apoidea gen. et sp. indet. (in agenbroad et al., 1992) formicidae camponotus sp. (in agenbroad et al., 1992) formica sp. (in agenbroad et al., 1992) pheidole sp. (in agenbroad et al., 1992) pogonomyrmex sp. (in agenbroad et al., 1992) orthoptera acrididae gen. et sp. indet. (in agenbroad et al., 1992) mammalia rodentia neotoma sp. (in agenbroad et al., 1992) canyonlands national park (cany) honaker trail formation, late pennsylvanian (cany) porifera haplistion sphaericum (in rigby and stokes, 1971) anthozoa rugosa gen. et sp. indet. (in szymanski et al., 2024) arthropoda trilobita a-16 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 proetida griffithides sp. (in mcknight 1940; szymanski et al., 2024) brachiopoda gen. et sp. indet. (in szymanski et al., 2024) bryozoa gen. et sp. indet. (in szymanski et al., 2024) foraminifera fusulinida gen. et sp. indet. (in szymanski et al., 2024) echinodermata crinoidea gen. et sp. indet. (in langford et al., 2007) mollusca bivalvia gen. et sp. indet. (in szymanski et al., 2024) gastropoda gen. et sp. indet. (in szymanski et al., 2024) lower cutler group, late pennsylvanian–early permian (cany) brachiopoda gen. et sp. indet. (in baker, 1933; mcknight, 1940) bryozoa gen. et sp. indet. (in mcknight, 1940) echinodermata crinoidea gen. et sp. indet. (in baker, 1933; mcknight, 1940) foraminifera fusulinida gen. et sp. indet. (in billingsley et al., 2002; szymanski et al., 2024) mollusca scaphopoda gen. et sp. indet. (in mcknight, 1940) actinopterygii palaeonisciformes palaeoniscidae gen. et sp. indet. (in sumida et al., 1999a) plantae gen. et sp. indet. (in webb et al., 2004) cedar mesa sandstone, early permian (cany) brachiopoda gen. et sp. indet. (in langford et al., 2007) bryozoa gen. et sp. indet. (in langford et al., 2007) echinodermata? scolicia isp. (in deblieux et al., 2023) crinoidea gen. et sp. indet. (in langford et al., 2007) a-17 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 chondrichthyes ctenacanthiformes gen. et sp. indet. (in deblieux et al., 2023) osteichthyes gen. et sp. indet. (in deblieux et al., 2023) tetrapoda gen. et sp. indet. (in deblieux et al., 2023; huttenlocker, university of southern california, written communication) cf. ichniotherium isp. (in deblieux et al., 2023) organ rock formation, early permian (cany) plantae rhizoliths (in deblieux et al., 2023) white rim sandstone, early permian (cany) echinodermata crinoidea gen. et sp. indet. (in steele-mallory, 1982; steele, 1987) sinbad member, moenkopi formation, early triassic (cany) brachiopoda lingula sp. (in mcknight, 1940) mollusca cephalopoda ammonoidea ?meekoceras sp. (in mcknight, 1940) bivalvia monotis sp. (in mcknight, 1940) gastropoda viviparoidea gen. et sp. indet. (in mcknight, 1940) family incertae sedis gen. et sp. indet. (in lucas et al., 1993) torrey member, moenkopi formation, early triassic (cany) arthropoda xiphosura cf. kouphichnium isp. (in deblieux et al., 2023) actinopteriygii undichna isp. (in deblieux et al., 2023) tetrapoda temnospondyli “chirotheriid-type” swim tracks (in deblieux et al., 2023) reptilia procolophonichnium isp. (in deblieux et al., 2023) archosauromorpha synaptichnium isp. (in deblieux et al., 2023) rotodactylus isp. (in deblieux et al., 2023) a-18 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 kane springs beds, chinle formation, late triassic (cany) arthropoda camborygma isp. (in deblieux et al., 2023) bivalvia unionidae gen. et sp. indet. (in deblieux et al., 2023) plantae gen. et sp. indet. (in deblieux et al., 2023) chondrichthyes hyobodontiformes reticulodus sp. (in deblieux et al., 2021) actinopterygii gen. et sp. indet. (in deblieux et al., 2023) amphibia metoposauridae gen. et sp. indet. (in deblieux et al., 2023) pseudosuchia aetosauria cf. stagonolepis sp. (in heckert et al., 1999) cf. typothorax sp. (in deblieux et al., 2023) phytosauria gen. et sp. indet. (in deblieux et al., 2023) dinosauria theropoda grallator isp. (in deblieux et al., 2023) church rock member, chinle formation, late triassic (cany) bivalvia unionidae gen. et sp. indet. (in deblieux et al., 2023) sarcopterygii dipnoi gen. et sp. indet. (in deblieux et al., 2023) pseudosuchia aetosauria cf. typothorax sp. (in deblieux et al., 2023) phytosauria gen. et sp. indet. (in deblieux et al., 2023) dinosauria theropoda grallator isp. (in lucas et al., 1993) wingate sandstone, late triassic–early jurassic (cany) dinosauria theropoda grallator isp. (in deblieux et al., 2024) a-19 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 kayenta formation, early jurassic (cany) dinosauria theropoda eubrontes isp. (in deblieux et al., 2024) grallator isp. (in deblieux et al., 2024) navajo sandstone, early jurassic (cany) stromatolites gen. et sp. indet. (in waiss, 2005) plantae gen. et sp. indet. (in wilkens, 2008) chordata gen. et sp. indet. (in hasiotis et al., 2007) dinosauria theropoda eubrontes isp. (in deblieux et al., 2024) kayentapus isp. (in deblieux et al., 2024) sauropodomorpha otozoum isp. (in deblieux et al., 2024) quaternary sediments (cany) plantae gymnospermae cupressaceae juniperus communis (in coats et al., 2008) juniperus osteosperma (in coats et al., 2008) juniperus scopulorum (in coats et al., 2008) juniperus sp. (in reheis et al., 2005) pinopsida picea pungens (in coats et al., 2008) picea sp. (in reheis et al., 2005) pinus edulis (in coats et al., 2008) pinus edulis var. fallax (in coats et al., 2008) pinus flexilis (in coats et al., 2008) pinus sp. (in reheis et al., 2005) pseudotsuga menziesii (in coats et al., 2008) ephedraceae ephedra torreyana (in coats et al., 2008) ephedra sp. (in reheisa et al., 2005; coats et al., 2008) angiospermae asteraceae ambrosia acanthicarpa (in coats et al., 2008) artemisia sp. (in reheis et al., 2005) chrysothamnus sp. (in coats et al., 2008) cirsium vulgare (in coats et al., 2008) gutierrezia sarothrae (in coats et al., 2008) hilaria jamesii (in coats et al., 2008) a-20 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 low-spine asteraceae pollen (in reheis et al., 2005) fabaceae astragalus sp. (in coats et al., 2008) berberidaceae berberis fremontii (in coats et al., 2008) cannabaceae celtis reticulata (in coats et al., 2008) rosaceae cercocarpus intricatus (in coats et al., 2008) coleogyne ramosissima (in coats et al., 2008) rosa sp. (in coats et al., 2008) amaranthaceae corispermum villosum (in coats et al., 2008) krascheninnikovia lanata/ceratoides lanata (in coats et al., 2008) cheno-am pollen (in reheis et al., 2005) boraginaceae cryptantha flava (in coats et al., 2008) lithospermum incisum (in coats et al., 2008) euphorbiaceae euphorbia sp. (in coats et al., 2008) oleaceae fraxinus anomala (in coats et al., 2008) brassicaceae lepidium montanum (in coats et al., 2008) gen. et sp. indet. (in reheis et al., 2005) cactaceae opuntia sp. (in reheis et al., 2005; coats et al., 2008) poaceae oryzopsis hymenoides (in coats et al., 2008) stipa comata (in coats et al., 2008) gen. et sp. indet. (in reheis et al., 2005) plantaginaceae penstemon sp. (in coats et al., 2008) fagaceae quercus gambelii (in coats et al., 2008) rhamnaceae frangula betulifolia (formerly rhamnus betulifolia) (in coats et al., 2008) anacardiaceae rhus trilobata (in coats et al., 2008) sarcobataceae sarcobatus sp. (in reheis et al., 2005) elaeagnaceae shepherdia rotundifolia (in coats et al., 2008) malvaceae sphaeralcea sp. (in reheis et al., 2005) capriofoliaceae symphoricarpos sp. (in coats et al., 2008) asparagaceae a-21 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 yucca angustissima (in coats et al., 2008) tubuliflorae gen. et sp. indet. (in reheis et al., 2005) mollusca bivalvia pisidium casertanum (in nittmann, 1993) pisidium nitidum (in nittmann, 1993) pisidium walkeri (in nittmann, 1993) gastropoda discus cronkhitei (in nittmann, 1993) euconulus fulvus (in nittmann, 1993) galba dalli (formerly fossaria (bakerilymnaea) dalli) (in nittmann, 1993) galba sp. (formerly fossaria) (in nittmann, 1993) gyraulus circumstriatus (in nittmann, 1993) hawaiia miniscula (in nittmann, 1993) oreohelix sp. (in nittmann, 1993) oxyloma sp. (in nittmann, 1993) pupilla muscorum (in nittmann, 1993) vallonia cyclophorella (in nittmann, 1993) vallonia gracilicosta (in nittmann, 1993) vertigo sp.? (in nittmann, 1993) zonitoides arboreus (in nittmann, 1993) succineidae gen. et sp. indet. (in nittmann, 1993) arthropoda insecta coleoptera amara sp. (in elias et al., 1992) eleodes spp. (in elias et al., 1992) niptus sp. (in elias et al., 1992) pachybrachis sp. (in elias et al., 1992) chrysomelidae gen. et sp. indet. (in elias et al., 1992) dermestidae gen. et sp. indet. (in elias et al., 1992) elateridae gen. et sp. indet. (in elias et al., 1992) scarabaeidae gen. et sp. indet. (in elias et al., 1992) tenebrionidae gen. et sp. indet. (in elias et al., 1992) gen. et sp. indet. (in elias et al., 1992) hymenoptera formica sp. (in elias et al., 1992) lepidoptera gen. et sp. indet. (in elias et al., 1992) amphibia anura spea hammondii (formerly scaphiopus hammondii) (in cany museum records) squamata iguania cf. sceloporus sp. (in cany museum records) phrynosomatidae gen. et sp. indet. (in cany museum records) aves a-22 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. (in cany museum records) mammalia rodentia dipodomys sp. (in cany museum records) neotoma cinerea (in cany museum records) neotoma sp. (in cany museum records) neotoma sp. middens (in tweet et al., 2012a) peromyscus sp. (in cany museum records) microtinae gen. et sp. indet. (in cany museum records) muridae gen. et sp. indet. (in cany museum records) gen. et sp. indet. (in tweet et al., 2012d) proboscidea mammuthus sp. (in tweet et al., 2012d; cany museum records) capitol reef national park (care) torrey member, moenkopi formation, early triassic (care) plantae equisetales gen. et sp. indet. (in mickelson et al., 2006a) annelida arenicolites isp. (in mickelson et al., 2006a) arthropoda diplichnites isp. (in mickelson et al., 2006a) fuersichnus isp. (in mickelson et al., 2006a) koupichnium isp. (in mickelson et al., 2006a) palaeophycus isp. (in mickelson et al., 2006a) actinopterygii undichna isp. (in mickelson et al., 2006a) tetrapoda characichnos isp. (in mickelson et al., 2006a) reptilia lepidosauromorpha rhynchosauroides isp. (in mickelson et al., 2006a) archosauromorpha rotodactylus isp. (in mickelson et al., 2006a) pseudosuchia chirotherium isp. (in mickelson et al., 2006a) shinarump member, chinle formation, late triassic (care) plantae tracheophyta bennettitales zamites powellii (in berry, 1927; ash, 1975b) pinopsida a-23 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 araucarioxylon sp. (in ash, 1975a) pagiophyllum sp. (in ash, 1975a) polypodiopsida cladophlebis sp. (in ash, 1975a) cynepteris sp. (in ash, 1975a) equisetites sp. (in kirkland et al., 2014a) phlebopteris sp. (in ash, 1975a) arthropoda camborygma isp. (in hasiotis and mitchell, 1993) monitor butte member, chinle formation, late triassic (care) plantae gen. et sp. indet. (in kirkland et al., 2014a) bennettitales laurozamites sp. (in kirkland et al., 2014a) polypodiopsida equisetites sp. (in kirkland et al., 2014a) temnospondyli metoposauridae gen. et sp. indet. (in kirkland et al., 2014a) pseudosuchia phytosauria gen. et sp. indet. (in kirkland et al., 2014a) petrified forest member, chinle formation, late triassic (care) plantae gen. et sp. indet. (in kirkland et al., 2014a) bivalvia unionidae gen. et sp. indet. (in kirkland et al., 2014a) temnospondyli metoposauridae gen. et sp. indet. (in kirkland et al., 2014a) pseudosuchia aetosauria cf. typothorax sp. (in kirkland et al., 2014a) phytosauria gen. et sp. indet. (in kirkland et al., 2014a) owl rock member, chinle formation, late triassic (care) plantae gen. et sp. indet. (in kirkland et al., 2014a) sanmiguelia sp. (in ash, 1982) sarcopterygii dipnoi gen. et sp. indet. (in kirkland et al., 2014a) pseudosuchia aetosauria a-24 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. (in kirkland et al., 2014a) navajo sandstone, early jurassic (care) stromatolites (in eisenberg, 2003; santucci and kirkland, 2010) winsor member, carmel formation, middle jurassic (care) echinodermata crinoidea isocrinus sp. (in tweet et al., 2012e) tidwell member, morrison formation, late jurassic (care) stromatolites (in kirkland et al., 2020a) reptilia dinosauria gen. et sp. indet. (in kirkland et al., 2020a) salt wash member, morrison formation, late jurassic (care) plantae gen. et sp. indet. (in kirkland et al., 2014a) dinosauria gen. et sp. indet. (in kirkland et al., 2020a) brushy basin member, morrison formation, late jurassic (care) dinosauria gen. et sp. indet. (in kirkland et al., 2020a) cedar mountain formation, early cretaceous (care) dinosauria gen. et sp. indet. (in kirkland et al., 2020a) naturita formation (dakota formation in older references), late cretaceous (care) mollusca bivalvia cf. exogyra sp. (in santucci and kirkland, 2010a) tununk shale, mancos group, late cretaceous (care) mollusca bivalvia gen. et sp. indet. (in cobban, u.s. geological survey, written communication) cephalopoda ammonoidea gen. et sp. indet. (in cobban, u.s. geological survey, written communication) mollusca gastropoda gen. et sp. indet. (in cobban, u.s. geological survey, written communication) chondrichthyes a-25 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. (in cobban, u.s. geological survey, written communication) blue gate shale, mancos group, late cretaceous (care) mollusca bivalvia gen. et sp. indet. (in cobban, u.s. geological survey, written communication) cephalopoda ammonoidea gen. et sp. indet. (in cobban, u.s. geological survey, written communication) gastropoda gen. et sp. indet. (in cobban, u.s. geological survey, written communication) chondrichthyes gen. et sp. indet. (in cobban, u.s. geological survey, written communication) quaternary sediments (care) plantae rhizoliths (in oviatt, 1988) polypodiophyta equisetales equisetum sp. (in nittmann, 1993) gymnospermae cupressaceae juniperus osteosperma (in cole et al., 1997; cole and murray, 1999) juniperus scopulorum (in cole and murray, 1999) juniperus sp. (in cole et al., 1997; cole and murray, 1999) pinaceae abies sp. (in cole and murray, 1999) picea sp. (in cole and murray, 1999) pinus edulis (in cole et al., 1997) pinus flexilis (in cole and murray, 1999) pinus sp. (in cole and murray, 1999) pinus spp. (in cole et al., 1997) pseudotsuga menziesii (in cole and murray, 1999) pseudotsuga sp. (in cole and murray, 1999) ephedraceae ephedra sp. (in cole and murray, 1999) ephedra spp. (in cole et al., 1997) angiospermae amaranthaceae amaranthus sp. (in cole et al., 1997) cf. amaranthus sp. (in cole et al., 1997) atriplex spp. (in cole et al., 1997) krascheninnikovia lanata/ceratoides lanata (in cole et al., 1997) cheno-am (in cole and murray, 1999) “chenopodiaceae” gen. et sp. indet. (in cole et al., 1997) asteraceae ambrosia sp. (in cole et al., 1997; cole and murray, 1999) a-26 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 artemisia sect. tridentatae (in cole et al., 1997) artemisia sp. (in cole et al., 1997; cole and murray, 1999) heterotheca sp. (in cole et al., 1997) fabaceae cf. amorpha sp. (in cole and murray, 1999) rhamnaceae ceanothus sp./rhamnus sp. (in cole and murray, 1999) rosaceae cercocarpus intricatus (in cole and murray, 1999) cercocarpus sp. (in cole et al., 1997; cole and murray, 1999) cowania mexicana (in cole et al., 1997) gen. et sp. indet. (in cole et al., 1997) cleomaceae cf. cleome sp. (in cole and murray, 1999) boraginaceae cryptantha spp. (in cole et al., 1997) phacelia sp. (in cole et al., 1997) euphorbiaceae euphorbia sp. (in cole et al., 1997) oleaceae fraxinus sp. (in cole and murray, 1999) cf. fraxinus anomala (in cole and murray, 1999) poaceae hilaria sp. (in cole et al., 1997) oryzopsis sp. (in cole and murray, 1999) sporobolus spp. (in cole et al., 1997) stipa hymenoides (in cole et al., 1997) stipa sp. (in cole et al., 1997) juglandaceae juglans sp. (in cole and murray, 1999) brassicaceae lepidium densiflorum (in cole et al., 1997) cactaceae opuntia polyacantha (in cole et al., 1997) opuntia sp. (in cole et al., 1997; cole and murray 1999) pediocactus sp./echinocereus sp. (in cole et al., 1997) betulaceae ostrya knowltoni (in cole and murray, 1999) gen. et sp. indet. (in cole and murray, 1999) salicaceae populus sp. (in cole and murray, 1999) salix sp. (in cole and murray, 1999) fagaceae quercus sp. (in cole and murray, 1999) adoxaceae sambucus sp. (in cole and murray, 1999) sarcobataceae sarcobatus sp. (in cole et al., 1997) a-27 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 elaeagnaceae shepherdia rotundifolia (in cole et al., 1997) malvaceae sphaeralcea coccinea (in cole et al., 1997) sphaeralcea sp. (in cole et al., 1997) asparagaceae yucca angustissima (in cole et al., 1997) yucca cf. y. angustissima (in cole and murray, 1999) compositae gen. et sp. indet. (in cole et al., 1997; cole and murray, 1999) cruciferae gen. et sp. indet. (in cole and murray, 1999) gramineae gen. et sp. indet. (in cole et al., 1997; cole and murray, 1999) labiatae gen. et sp. indet. (in cole and murray, 1999) leguminosae gen. et sp. indet. (in cole and murray, 1999) onagraceae gen. et sp. indet. (in cole et al., 1997) polygonaceae gen. et sp. indet. (in cole and murray, 1999) mammalia rodentia neotoma sp. middens (in tweet et al., 2012a) other undetermined fungal spores (in cole et al., 1997; cole and murray 1999) cedar breaks national monument (cebr) pink member, claron formation, paleogene (cebr) plantae angiospermae gen. et sp. indet. (in gregory, 1950) insecta hymenoptera celliforma spirifer (in gregory, 1950) mollusca gastropoda bulinus sp. (in gregory, 1950) glyptostoma spatiosum (formerly helix spatiosa) (in gregory, 1950) biomphalaria utahensis (formerly planorbis utahensis) (in gregory, 1950) quaternary sediments (cebr) chlorophyta pediastrum sp. (in anderson et al., 1999) plantae a-28 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gymnospermae ephedraceae ephedra sp. (in anderson et al., 1999) pinaceae abies lasiocarpa (in anderson et al., 1999) abies sp. (in anderson et al., 1999) picea engelmannii (in anderson et al., 1999) picea sp. (in anderson et al., 1999) pinus sp. (in anderson et al., 1999) pinus (strobus) sp. (in anderson et al., 1999) pinus (pinus) sp. (in anderson et al., 1999) cupressaceae gen. et sp. indet. (in anderson et al., 1999) angiospermae fagaceae quercus sp. (in anderson et al., 1999) asteraceae artemisia sp. (in anderson et al., 1999) ambrosia sp. (in anderson et al., 1999) gen. et sp. indet. (in anderson et al., 1999) poaceae gen. et sp. indet. (in anderson et al., 1999) cyperaceae gen. et sp. indet. (in anderson et al., 1999) mollusca gen. et sp. indet. (in sharpe, 1993) dinosaur national monument (dino) lodore formation, middle cambrian (dino) invertebrate traces bergaueria isp. (in myrow et al., 2023a) diplocraterion isp. (in myrow et al., 2023a) monocraterion isp. (in myrow et al., 2023a) rusophycus isp. (in myrow et al., 2023a) cruziana isp. (in myrow et al., 2023a) arenicolites isp. (in myrow et al., 2023a) cf. palaeophycus isp. (in untermann and untermann, 1954) skolithos isp. (in myrow et al., 2023a) teichichnus isp. (in myrow et al., 2023a) brachiopoda billingsellida billingsella-like shells (in untermann and untermann, 1954) obolidae dicellomus sp.? (in myrow et al., 2023a) westonia sp. (in myrow et al., 2023a) cf. westonia ella (in myrow et al., 2023a) a-29 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. aff. lingulepis (in myrow et al., 2023a) arthropoda trilobita elrathiella decora? (in myrow et al., 2023a) elrathiella cf. e. domensa (in myrow et al., 2023a) elrathiella cf. e. rectangularia (in myrow et al., 2023a) elrathiella sp. nov. 1 (in myrow et al., 2023a) elrathiella sp. nov. 2 (in myrow et al., 2023a) hyolitha hyolithes sp. (in untermann and untermann, 1954) gen. et sp. indet. (in myrow et al., 2023a) incertae sedis hyolithes-like form “having heavy concentric rings resembles tentaculites” (in untermann and untermann, 1954) parting formation, late devonian (dino) “bioturbation” (in myrow et al., 2023a) madison limestone, early–middle mississippian (dino) anthozoa rugosa cf. lithostrotion sp. (in untermann and untermann, 1954) cf. neozaphrentis sp. (in untermann and untermann, 1954) tabulata cf. favosites sp. (in untermann and untermann, 1954) syringopora surcularia (in mayer, 1964) cf. syringopora sp. (in untermann and untermann, 1954) brachiopoda cf. schuchertella sp. (in untermann and untermann, 1954) bryozoa fenestella cf. f. rudis (in mayer, 1964) fenestella cf. f. serratula (in mayer, 1964) mollusca gastropoda cf. euomphalus sp. (in untermann and untermann, 1954) arthropoda trilobita gen. et sp. indet. (in untermann and untermann, 1949a) echinodermata crinoidea gen. et sp. indet. (in untermann and untermann, 1954 [as deseret limestone]) humbug formation, middle mississippian (dino) anthozoa rugosa gen. et sp. indet. (in untermann and untermann, 1954) echinodermata crinoidea a-30 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. (in untermann and untermann, 1954) doughnut formation, middle–late mississippian (dino) plantae polypodiopsida calamites sp. (in untermann and untermann, 1954) lepidodendron sp. (in untermann and untermann, 1954) arthropoda ostracoda gen. et sp. indet. (in untermann and untermann, 1954) foraminifera tolypammina sp. (in untermann and untermann, 1954) round valley limestone, early pennsylvanian (dino) (belden formation of thompson, 1945; morrow or lower member of the morgan limestone of untermann and untermann, 1949b, 1954 [beds 69 to 104 in 1949b, per thickness in 1954]) algae gen. et sp. indet. (in davis, 2010) asphaltina sp. (in davis, 2010) stacheoides sp. (in davis, 2010) anthozoa rugosa “‘zaphrentoid’ cup corals of the ratiphyllum type” (typo for unknown genus) (in untermann and unter mann, 1949b, 1954) gen. et sp. indet. (in davis, 2010) bryozoa rhomboporoid forms (in untermann and untermann, 1949b) stenoporoid forms (in untermann and untermann, 1949b) gen. et sp. indet. (in untermann and untermann, 1949b; davis, 2010) brachiopoda composita subtilita (in untermann and untermann, 1954) composita cf. c. subtilita (in untermann and untermann, 1949b) dictyoclostus sp. (in untermann and untermann, 1949b) echinoconchus sp. (in untermann and untermann, 1949b) marginifera haydenensis? (in untermann and untermann, 1954) neospirifer cf. n. cameratus (in untermann and untermann, 1954) neospirifer sp. (in untermann and untermann, 1949b) spirifer occidentalis (in untermann and untermann, 1954) spirifer rockymontanus (in untermann and untermann, 1949b) spirifer cf. s. rockymontanus (in untermann and untermann, 1954) spirifer sp. (in untermann and untermann, 1949b) gen. et sp. indet. (in untermann and untermann, 1949b; davis, 2010) productida undetermined (in untermann and untermann, 1949b) mollusca bivalvia gen. et sp. indet. (in davis, 2010) a-31 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gastropoda gen. et sp. indet. (in untermann and untermann, 1949b; davis, 2010) arthropoda ostracoda gen. et sp. indet. (in davis, 2010) trilobita gen. et sp. indet. (in davis, 2010) echinodermata undetermined ossicles (in untermann and untermann, 1949b) echinoidea gen. et sp. indet. (in untermann and untermann, 1949b; davis, 2010) crinoidea gen. et sp. indet. (in davis, 2010) foraminifera climacammina sp.? (in untermann and untermann, 1949b) endothyra sp. (in untermann and untermann, 1949b, 1954; davis, 2010) endothyra sp.? (in untermann and untermann, 1949b) eostaffella sp. (in davis, 2010) millerella circuli* (in thompson, 1945) millerella cf. m. marblensis (in thompson, 1945) millerella sp. (in untermann and untermann, 1949b, 1954) millerella sp. (evolute) (in untermann and untermann, 1949b, 1954) millerella sp. indet. (in thompson, 1945) paleonubecularia sp. (in davis, 2010) planoendothyra sp. (in davis, 2010) pseudoglomospira sp. (in davis, 2010) trepeilopsis sp. (in untermann and untermann, 1949b, 1954) trepeilopsis sp.? (in untermann and untermann, 1949b) “calcitornellids” (in untermann and untermann, 1949b) “tolypamminids” (in untermann and untermann, 1949b) morgan formation, middle pennsylvanian (dino) taxa from white, 1876 (“lower aubrey group”) are placed here based on sando (1965) attributing the type material of amplexus zaphrentiformis to the morgan formation, but it is possible that some pertain to the round valley limestone. tubular burrows (in fryberger, 1979) algae “peculiar form” (in untermann and untermann, 1949b) gen. et sp. indet.? (in untermann and untermann, 1949b) porifera chaetetes milleporaceus (in white, 1876) chaetetes milleporaceus? (in untermann and untermann, 1949b) chaetetes cf. c. milleporaceus (in untermann and untermann, 1954) gen. et sp. indet. (spicules) (in untermann and untermann, 1949b, 1954) anthozoa rugosa amplexus zaphrentiformis* (in white, 1876; barytichisma zaphrentiforme of sando, 1965) tabulata a-32 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 acervularia sp.? (in white, 1876) bryozoa archimedes sp.? (in white, 1876) fenestella sp.? (in white, 1876) prismopora sp. (in untermann and untermann, 1954) rhombopora-like form (in untermann and untermann, 1949b) stenopora-like form (in untermann and untermann, 1949b) gen. et sp. indet. (in untermann and untermann, 1949b) brachiopoda chonetes platynota (in white, 1876) composita subtilita (in white, 1876, as spirigera; untermann and untermann, 1954) composita subtilita? (in untermann and untermann, 1949b) composita cf. c. elongata (in untermann and untermann, 1954) composita cf. c. ovata (in untermann and untermann, 1954) composita cf. c. subtilita (in untermann and untermann, 1949b, 1954) dictyoclostus coloradoensis (in untermann and untermann, 1954) dictyoclostus cf. d. coloradoensis (in untermann and untermann, 1954) dictyoclostus sp. (in untermann and untermann, 1949b) dictyoclostus sp. (small) (in untermann and untermann, 1949b, 1954) dielasma boyoidens? (in untermann and untermann, 1954) echinoconchus semipunctatus (in untermann and untermann, 1954) echinoconchus sp. (in untermann and untermann, 1949b) hemipronites crinistria (in white, 1876) hystriculina aff. h. wabashensis (in sando, 1965) inflatia sp.? (in sando, 1965) juresania sp. (in untermann and untermann, 1954) linoproductus sp. (in untermann and untermann, 1954) linoproductus sp.? (in untermann and untermann, 1949b) neospirifer dunbari (in untermann and untermann, 1954) neospirifer cf. n. cameratus (in untermann and untermann, 1954) neospirifer cf. n. dunbari (in untermann and untermann, 1949b, 1954) productus costatus? (in white, 1876) productus costatus var. (in white, 1876) productus longispinus? (in white, 1876) productus muricatus? (in white, 1876) spirifer rockymontanus (in white, 1876; untermann and untermann, 1949b) spirifer rockymontanus? (in untermann and untermann, 1954) spirifer cf. s. occidentalis (in untermann and untermann, 1954) spirifer cf. s. rockymontanus (in untermann and untermann, 1954) gen. et sp. indet. (in untermann and untermann, 1949b) arthropoda ostracoda gen. et sp. indet. (in untermann and untermann, 1949b) trilobita ?phillipsia sp. (in white, 1876) echinodermata gen. et sp. indet. (in untermann and untermann, 1949b, 1954) crinoidea a-33 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. (in untermann and untermann, 1949b, 1954) echinoidea gen. et sp. indet. (in untermann and untermann, 1949b) conodonta adetognathus sp. (in broadhead and driese, 1994) hindeodus sp. (in broadhead and driese, 1994) idiognathus sp. (in broadhead and driese, 1994) ?idiognathus sp. (in broadhead and driese, 1994) ?idioprionodus sp. (in broadhead and driese, 1994) foraminifera ammodiscus sp. or cornuspira sp. (in untermann and untermann, 1954) bradyina sp. (in untermann and untermann, 1949b, 1954) calcitornella-like form (in untermann and untermann, 1949b) climacammina spp. (in untermann and untermann, 1949b, 1954) deckerella goessi? (in untermann and untermann, 1949b, 1954) endothyra sp. (in untermann and untermann, 1949b, 1954) endothyra sp.? (in untermann and untermann, 1954) eoschubertella sp. (in untermann and untermann, 1949b, 1954) eoschubertella or fusulinella (in untermann and untermann, 1949b) fusulina curta? (in untermann and untermann, 1949b, 1954) fusulina pristina? (in untermann and untermann, 1954) fusulina aff. f. leeri (in untermann and untermann, 1949b, 1954) fusulina aff. f. rockymontana (in untermann and untermann, 1949b, 1954) fusulina sp. (in untermann and untermann, 1949b, 1954) fusulinella gephyraea (in untermann and untermann, 1949b) fusulinella cf. f. haywardi (in untermann and untermann, 1949b, 1954) fusulinella sp. (in untermann and untermann, 1954) fusulinella sp.? (in untermann and untermann, 1949b) millerella sp. (in untermann and untermann, 1954) ozawainella sp. (in untermann and untermann, 1949b, 1954) pseudostaffella sp. (in untermann and untermann, 1949b, 1954) pseudostaffella sp.? (in untermann and untermann, 1949b, 1954) spiroplectammina sp. (in untermann and untermann, 1949b, 1954) tetrataxis sp. (in untermann and untermann, 1949b, 1954) wedekindellina euthysepta (in untermann and untermann, 1949b) wedekindellina matura (in untermann and untermann, 1954) wedekindellina perforata (in untermann and untermann, 1949b, 1954) wedekindellina aff. w. magna (in untermann and untermann, 1949b, 1954) wedekindellina sp. (in untermann and untermann, 1949b, 1954) wedekindellina? sp. (in untermann and untermann, 1949b) wedekindellina sp. or possibly fusulina sp., minute (in untermann and untermann, 1949b) “calcitornellids” (in untermann and untermann, 1949b) fusulinida (minute form) (in untermann and untermann, 1949b) textulariidae gen. et sp. indet. (in untermann and untermann, 1949b) weber sandstone, middle pennsylvanian–early permian (dino) root traces or invertebrate burrows (in driese, 1985) tubular burrows (in bissell, 1964) a-34 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 algae ?gen. et sp. indet. (in bissell, 1964) bryozoa gen. et sp. indet. (in bissell, 1964; chure et al., 2014) arthropoda ?diplichnites isp. (in chure et al., 2014) echinodermata crinoidea gen. et sp. indet. (in bissell, 1964; chure et al., 2014) reptilia captorhinomorpha? ?varanopus isp. (in chure et al., 2014) foraminifera fusulinida schwagerina sp. (in bissell, 1964) gen. et sp. indet. (in chure et al., 2014) park city formation, permian (dino) spindle-shaped borings in shells (in schell and yochelson, 1966) bryozoa fenestrate bryozoans (in schell and yochelson, 1966) small ramose bryozoans (in schell and yochelson, 1966) brachiopoda beecheria cf. b. bovidens (in schell and yochelson, 1966) composita sp. (in schell and yochelson, 1966) spiriferina cf. s. pulchra (in schell and yochelson, 1966) mollusca bivalvia aviculopecten sp. indet. (in schell and yochelson, 1966) myalina (myalinella) cf. m. (m.) meeki (in schell and yochelson, 1966) nuculana (leda) cf. n. bellistriata (in untermann and untermann, 1954) ?permophorus sp. indet. (in schell and yochelson, 1966) polidevcia sp. (in schell and yochelson, 1966) schizodus sp. (in schell and yochelson, 1966) yoldia cf. y. mcchespeyana (in untermann and untermann, 1954) ?parallelodont bivalve, indet. (in schell and yochelson, 1966) cephalopoda ammonoidea cf. pseudogastrioceras sp. (in schell and yochelson, 1966) gen. et sp. indet. (in schell and yochelson, 1966) nautiloidea gen. et sp. indet. (in schell and yochelson, 1966) gastropoda naticopsis (naticopsis) sp. indet. (in schell and yochelson, 1966) bellerophontoidea indet. (in schell and yochelson, 1966) bellerophontid similar to bucanopsis sp. (in untermann and untermann, 1954) murchisoniidae indet. (in schell and yochelson, 1966) ?pleurotomariacea indet. (in schell and yochelson, 1966) a-35 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 scaphopoda plagioglypta canna (in untermann and untermann, 1954) moenkopi formation, early triassic (dino) archosauria synaptichnium isp. (in thomson et al., 2014) archosauriformes cf. protochirotherium isp. (in thomson et al., 2014) chinle formation, late triassic (dino) plantae petrified wood (in untermann and untermann, 1949a, 1954; erickson, 2007) root traces (in erickson, 2007) invertebrata invertebrate burrows (in erickson, 2007) arthropoda (traces) acripes isp. (in hartung et al., 2021) isopodichnus isp. (in lockley et al., 1992a; hartung et al., 2021) kouphichnium isp. (in lockley et al., 1992a) scoyenia gracilis (in lockley et al., 1992a) crayfish burrows (in erickson, 2007) lepidosauromorpha rhynchosauroides isp. (in lockley et al., 1992a) tanystropheidae gwynnedichnium isp. (in lockley et al., 1992a) dinosauria theropoda “agialopus isp.” (in lockley et al., 1992a) sauropodomorpha pseudotetrasauropus isp. (in lockley et al., 1992a) pseudosuchia ?chirotherium isp. (in lockley et al., 1992a) brachychirotherium isp. (in lockley et al., 1992a) phytosauria ?apatopus isp. (in lockley et al., 1992a) nugget sandstone, late triassic–early jurassic (dino) plantae sphenophyta gen. et sp. indet. (in good, 2013) arthropoda (traces) octopodichnus isp. (in good and ekdale, 2014) paleohelcura isp. (in good and ekdale, 2014) taenidium isp. (in good and ekdale, 2014) osteichthyes gen. et sp. indet. (in hunt et al., 1993) mammaliamorpha a-36 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 brasilichnium isp. (in engelmann et al., 2010; good and ekdale, 2014) dinosauria sauropodomorpha otozoum isp. (in lockley, 2011) theropoda grallator isp. (in lockley, 2011) pseudosuchia phytosauria gen. et sp. indet. (in stewart et al., 1972a; hunt et al., 1993) carmel formation, middle jurassic (dino) bivalvia gen. et sp. indet. (d.a. sprinkel, utah geological survey [retired], written communication, 2012) reptilia gen. et sp. indet. (d.a. sprinkel, utah geological survey [retired], written communication, 2012) salt wash member, morrison formation, late jurassic (dino) plantae gen. et sp. indet. dinosauria theropoda allosaurus jimmadseni* (in chure and loewen, 2020) brushy basin member, morrison formation, late jurassic (dino) algae charophyta characeae aclistochara bransoni (in schudak et al., 1998) aclistochara latisulcata (in schudak et al., 1998) alistochara madleri (in schudak et al., 1998) aclistochara miniscula? (in schudak et al., 1998) aclistochara obovata (in schudak et al., 1998) latochara latitruncata (in schudak et al., 1998) latochara sp. (in schudak et al., 1998) peckisphaera verticillata (in schudak et al., 1998) porochara arguta (in schudak et al., 1998) porochara kimmeridgensis (in schudak et al., 1998) clavatoraceae echinochara sp. (in schudak et al., 1998) plantae polypodiophyta equisetales equisetum sp. (in schudak et al., 1998) pteridophyta umkomasiaceae pteruchipollenites microsaccus (in ash, 1994; litwin et al., 1998) osmundaceae todisporites minor (in ash, 1994; litwin et al., 1998) a-37 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 bennettitales family incertae sedis gen. et sp. indet. (in ash, 1994) pinophyta araucariaceae callialasporites trilobatus (in ash, 1994; litwin et al., 1998) callialasporites cf. c. rugularus (in ash, 1994; litwin et al., 1998) podocarpaceae microcachrydites antarcticus (in ash, 1994; litwin et al., 1998) parvisaccites sp. (in ash, 1994; litwin et al., 1998) rugubivesiculites sp. (in ash, 1994; litwin et al., 1998) ginkgophyta czekanowskiaceae czekanowskia sp. (in ash, 1994) mollusca bivalvia unionidae vetulonaia sp. (in carpenter, 2013) gen. et sp. indet. (in good, 2004) arthropoda ostracoda cyprididae candona sp. (in schudak et al., 1998) limnocytheridae bisulcocypris pahasapensis (in schudak et al., 1998) helmdachia petersoni (in schudak et al., 1998) family incertae sedis cetacella sp. (in schudak et al., 1998) spinicaudata cyzicidae lioestheria sp. (in lucas and kirkland, 1998) actinopterygii amiiformes gen. et sp. indet. (in foster, 2003) sarcopterygii dipnoi ceratodus sp. (in foster, 2003) amphibia anura alytidae enneabatrachus sp. (in foster, 2003) gen. et sp. indet. (in foster, 2003) family incertae sedis rhadinosteus parvus* (in henrici, 1998) caudata iridotriton hechti* (in evans et al., 2005) gen. et sp. indet. (in foster, 2003) reptilia a-38 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 choristodera cteniogenys sp. (in foster, 2003) rhynchocephalia opisthodontia opisthias sp. (in foster, 2003) theretairus sp. (in foster, 2003) crocodylomorpha goniopholidae goniopholis sp. (in foster, 2003) eutretauranosuchus sp. (in foster, 2003) protosuchidae hoplosuchus kayi* (in gilmore, 1926) dinosauria saurischia theropoda allosaurus cf. fragilis (in foster, 2003; carpenter, 2013) ceratosaurus sp. (in foster, 2003; carpenter, 2013) koparion douglassi* (in chure, 1994) marshosaurus (in foster, 2003) torvosaurus cf. tanneri (in foster, 2003; carpenter, 2013) sauropoda apatosaurus louisae* (in holland, 1916) athenar bermani* (in whitlock et al., 2025) barosaurus lentus (in foster, 2003; carpenter, 2013) camarasaurus lentus (in foster, 2003; carpenter, 2013) diplodocus sp. (in foster, 2003; carpenter, 2013) ornithischia camptosaurus aphanoectes* (in carpenter and wilson, 2008) dryosaurus elderae* (in carpenter and galton, 2018) stegosaurus sp. (in carpenter, 2013 squamata eoscincus ornatus* (in brownstein et al., 2022) helioscopus dickersonae* (in meyer et al., 2023) schillerosaurus utahensis* (in nydam et al., 2013; formerly schillera utahensis, in evans and chure, 1999) serpentes gen. et sp. indet. (in foster, 2003) testudines dinochelys whitei* (in gaffney, 1979) glyptops utahensis* (in gilmore, 1916) mammaliaformes docodon sp. (in foster, 2003) mammalia dryolestida dryolestes sp. (in foster, 2003) euthlastus sp. (in foster, 2003) eutriconodonta priacodon sp. (in foster, 2003) triconolestes sp. (in foster, 2003) a-39 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 multituberculata glirodon grandis* (in engelmann and callison, 1999) family incertae sedis gen. et sp. indet. (in foster, 2003) cedar mountain formation, early cretaceous (dino) arthropoda ostracoda gen. et sp. indet. (in kosmidis et al., 2002) mollusca gastropoda gen. et sp. indet. (in kosmidis et al., 2002) dinosauria theropoda deinonychosauria gen. et sp. nov. (in britt et al., 2021) sauropoda abydosaurus mcintoshi* (in chure et al., 2010) mowry shale, late cretaceous (dino) plantae angiospermae gen. et sp. indet. (in stewart et al., 1994) mollusca cephalopoda ammonoidea gen. et sp. indet. (in untermann and untermann, 1954) chondrichthyes haimirchia amonensis (in hansen et al., 1983) actinopterygii aulopiformes enchodontidae enchodus sp. (in stewart et al., 1994) alepisauroidei gen. et sp. indet. (in stewart et al., 1994) ichthyodectiformes gen. et sp. indet. (in stewart et al., 1994) sphenocephaliformes sphenocephalidae gen. et sp. indet. (in stewart et al., 1994) reptilia plesiosauria gen. et sp. indet. (in stewart et al., 1994) crocodylomorpha gen. et sp. indet. (in hansen et al., 1983; stewart et al., 1994) frontier formation, late cretaceous (dino) plantae a-40 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 unidentified leaves (in untermann and untermann, 1954) petrified wood (in gregson et al., 2024) gymnospermae pinopsida brachyphyllum sp. (in untermann and untermann, 1954) invertebrata invertebrate burrows (in gregson et al., 1954) mollusca ammonoidea prionotropis sp. (in untermann and untermann, 1954) scaphites sp. (in untermann and untermann, 1954) gen. et sp. indet. (in gregson et al., 2024) bivalvia inoceramus sp. (in untermann and untermann, 1954) gen. et sp. indet. (in gregson et al., 2024) gastropoda viviparus sp. (in untermann and untermann, 1954) gen. et sp. indet. (in gregson et al., 2024) chondrichthyes gen. et sp. indet. (in untermann and untermann, 1954; gregson et al., 2024) quaternary sediments (dino) plantae gymnospermae cupressaceae juniperus communis (in sharpe, 1991) juniperus osteosperma (in sharpe, 1991) juniperus scopulorum (in sharpe, 1991) juniperus cf. j. scopulorum (in sharpe, 1991) juniperus sp. (in sharpe, 1991) pinaceae picea pungens (in sharpe, 1991) pinus flexilis (in sharpe, 1991) pseudotsuga menziesii (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) angiospermae asteraceae artemisia ludoviciana (in sharpe, 1991) artemisia tridentata (in sharpe, 1991) cf. aster sp. (in sharpe, 1991) cirsium sp. (in sharpe, 1991) gutierrezia sp. (in sharpe, 1991) helianthus sp. (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) amaranthaceae atriplex confertifolia (in sharpe, 1991) chenopodium sp. (in sharpe, 1991) rhamnaceae a-41 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 ceanothus sp. (in sharpe, 1991) rhamnus sp. (in sharpe, 1991) rosaceae cercocarpus intricatus (in sharpe, 1991) rosa sp. (in sharpe, 1991) cactaceae cf. echinocereus sp. (in sharpe, 1991) mammillaria sp. (in sharpe, 1991) opuntia polyacantha (in sharpe, 1991) opuntia sp. (in sharpe, 1991) cf. pediocactus sp. (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) brassicaceae lepidium sp. (in sharpe, 1991) boraginaceae amsinckia sp./cryptantha sp. (in sharpe, 1991) lithospermum sp. (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) anacardiaceae rhus sp. (in sharpe, 1991) poaceae stipa hymenoides (in sharpe, 1991) gen. et sp. indet. (in sharpe, 1991) caprifoliaceae symphoricarpos sp. (in sharpe, 1991) fabaceae gen. et sp. indet. (in sharpe, 1991) mammalia rodentia neotoma sp. middens (in tweet et al., 2012a) neotoma sp. (in sharpe, 1991) glen canyon national recreation area (glca) paradox formation, middle pennsylvanian (glca) brachiopoda derbyia cf. d. crassa (in lewis and campbell, 1965) mesolobus mesolobus (in lewis and campbell, 1965) chonetina flemingi (in lewis and campbell, 1965) hustedia mormoni (in lewis and campbell, 1965) neospirifer cf. cameratus (in lewis and campbell, 1965) neospirifer cf. n. kansasensis (in lewis and campbell, 1965) enteletes sp. (in lewis and campbell, 1965) nubeculara sp. (in lewis and campbell, 1965) antiguatonia hermosanus (in lewis and campbell, 1965) composita subtilita (in lewis and campbell, 1965) bryozoa a-42 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 fenestella sp. (in lewis and campbell, 1965) rhombotrypella sp. (formerly rhomboporella) (in lewis and campbell, 1965) echinodermata crinoidea chlorophyta dasycladales diploporaceae diplopora sp. (in lewis and campbell, 1965) cyanobacteria cyanophyceae oscillatoriales girvanella sp. (in lewis and campbell, 1965) foraminifera fusulinida gen. et sp. indet. (in nail, 1996) ozawainellidae ozawaniella sp.? (in lewis and campbell, 1965) schubertellidae schubertella sp. (in lewis and campbell, 1965) triticitidae triticites sp. (in lewis and campbell, 1965) triticites sp. aff. t. confertus (in lewis and campbell, 1965) triticites kellyensis? (in lewis and campbell, 1965) endothyrida bradyinidae bradyina sp. (in lewis and campbell, 1965) endothyridae endothyra or endothyranella (in lewis and campbell, 1965) globivalvulinidae globivalvulina sp. (in lewis and campbell, 1965) palaeotextulariidae climacammina sp. (in lewis and campbell, 1965) osagia sp. (in lewis and campbell, 1965) miliolida gen. et sp. indet. (in lewis and campbell, 1965) calcivertellidae treipeilopsis sp. (in lewis and campbell, 1965) treipeilopsis sp.? (in lewis and campbell, 1965) glomospiroididae plummerinella sp. (in lewis and campbell, 1965) rhizoliths (in williams, 2009) honaker trail formation, late pennsylvanian (glca) anthozoa gen. et sp. indet. (in ritter et al., 2002) brachiopoda gen. et sp. indet. (in doelling, 1975; ritter et al., 2002) “compositids” (in doelling, 1975) a-43 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 “productids” (in doelling, 1975) “rhynchonellids” (in doelling, 1975) “spirifers” (in doelling, 1975) bryozoa gen. et sp. indet. (in ritter et al., 2002) echinodermata crinoidea gen. et sp. indet. (in doelling, 1975; ritter et al., 2002) echinoidea gen. et sp. indet. (in doelling, 1975) foraminifera fusulinida gen. et sp. indet. (in doelling, 1975; ritter et al., 2002) mollusca gastropoda gen. et sp. indet. (in ritter et al., 2002) stromatolites gen. et sp. indet. (in ritter et al., 2002) lower cutler group, late pennsylvanian–early permian (glca) brachiopoda gen. et sp. indet. (in o’sullivan, 1965) mollusca gastropoda cf. psammichnites isp. (in milner et al., 2024) amphibia temnospondyli platyhystrix sp. (in sumida et al., 1999b) cedar mesa sandstone, early permian (glca) synapsida “cf. anomalopus isp.” (in lockley and madsen, 1993; lockley et al., 1998) stenichnus isp. (in lockley et al., 1998) upper moenkopi formation, early triassic (glca) arthropoda xiphosura cf. kouphichnium isp. (in lockley et al., 1998) sarcopterygii coelacanthiformes gen. et sp. indet. (in finell et al., 1963) amphibia temnospondyli parotosuchus sp. (in welles, 1967; morales 1983, 2005) reptilia chirotheriid-type swim tracks (in deblieux et al., 2023) lepidosauromorpha rhynchosauroides isp. (in lockley et al., 1998) a-44 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 shinarump member, chinle formation, late triassic (glca) plantae gen. et sp. indet. (in kirkland et al., 2010) bennettitales cf. zamites (in milner et al., 2024) equisetales cf. neocalamites sp. (in milner et al., 2024) arthropoda (trace) scoyenia isp. (in milner et al., 2024) mollusca (trace) oravaichnium isp. (in milner et al., 2024) reptilia tanystropheidae cf. gwynnedichnium isp. (in milner et al., 2024) owl rock/petrified forest member, chinle formation, late triassic (glca) phytosauria gen. et sp. indet. (in milner et al., 2024) church rock member, chinle formation, late triassic (glca) actinopterygii redfieldiformes redfieldiidae lasalichthys stewarti (in milner et al., 2024) lasalichthys sp. (in milner et al., 2024) gen. et sp. indet. (in milner et al., 2024) semionotiformes semionotidae lophionotus sanjuanensis (in milner et al., 2024) lophionotus sp. (in milner et al., 2024) semionotidae indet. (in milner et al., 2024) sarcopterygii coelacanthiformes mawsoniidae gen. et sp. indet. (in milner et al., 2024) amphibia temnospondyli metoposauridae gen. et sp. indet. (in kirkland et al., 2010) archosauromorpha dinosauromorpha atreipus isp. (in lockley et al., 1998) dinosauria saurischia theropoda grallator isp. (in lockley et al., 1998) pseudosuchia a-45 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 aetosauria cf. typothorax sp. (in deblieux et al., 2023) brachychirotherium isp. (in milner et al., 2024) phytosauria gen. et sp. indet. (in milner et al., 2024) crocodylomorpha batrachopus isp. (in lockley et al., 1998, 2014b; milner et al., 2024) lepidosauromorpha rhynchosauroides isp. (in milner et al., 2024) wingate sandstone, late triassic–early jurassic (glca) cyanobacteria stromatolites (in lockley et al., 1998) archosauromorpha dinosauria saurischia sauropodomorpha evazoum gatewayensis (in milner et al., 2024) theropoda eubrontes isp. (in wood et al., 2021; milner et al., 2024) grallator isp. (in lockley et al., 1998) kayentapus isp. (in wood et al., 2021; milner et al., 2024) crocodylomorpha batrachopus isp. (in milner et al., 2024) aetosauria brachychirotherium isp. (in milner et al., 2024) kayenta formation, early jurassic (glca) invertebrate traces palaeophycus isp. (in milner et al., 2024) skolithos isp. (in milner et al., 2024) actinopterygii undichna isp. (in milner et al., 2024) synapsida mammaliamorpha cf. kayentatherium sp. (in milner et al., 2023a, 2024) cf. ameghinichnus isp. (in milner et al., 2024) cf. brasilichnium isp. (in lockley et al., 1998, 2014b; milner et al., 2024) indet. tracks (in milner et al., 2024) archosauromorpha dinosauria saurischia sauropodomorpha cf. otozoum isp. (in kirkland et al., 2010; lockley et al., 2014b) theropoda characichnos tridactylus (in lockley et al., 2014b; milner et al., 2024) characichnos isp. (in lockley et al., 2014b; milner et al., 2024) eubrontes isp. (in lockley et al., 1998, 2014b; milner et al., 2024) a-46 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 grallator isp. (in lockley et al., 1998, 2014b; milner et al., 2024) cf. kayentapus isp. (in milner et al., 2024) ornithischia anomoepus isp. (in lockley et al., 1998, 2014b; milner et al., 2024) moyenisauropus isp. (in lockley et al., 1998, 2014b; milner et al., 2024) crocodylomorpha batrachopus isp. (in lockley et al., 1998, 2014b; milner et al., 2024) lepidosauromorpha cf. rhynchosauroides isp. (in milner et al., 2024) navajo sandstone, early jurassic (glca) arthropoda (traces) cf. octopodichnus isp. (in milner et al., 2024) palaeophycus isp. (in milner et al., 2024) ?paleohelcura isp. (in milner et al., 2024) taenidium cf. barretti (in milner et al., 2023b, 2024) mollusca bivalvia unionidae gen. et sp. indet. (in lockley et al., 2014b) archosauromorpha dinosauria saurischia sauropodomorpha otozoum isp. (in kirkland et al., 2010; lockley et al., 2014b; milner et al., 2024) navahopus isp. (in milner et al., 2024) theropoda eubrontes isp. (in lockley et al., 1998, 2014b; milner et al., 2024) grallator isp. (in lockley et al., 1998, 2014b; milner et al., 2023b, 2024) kayentapus isp. (in milner et al., 2023b, 2024) ornithischia anomoepus isp. (in lockley et al., 1998, 2014b; milner et al., 2024) moyenisauropus isp. (in lockley et al., 1998, 2014b; milner et al., 2024) crocodylomorpha batrachopus isp. (in milner et al., 2023b, 2024) synapsida mammaliamorpha cf. kayentatherium sp. (in milner et al., 2023a, 2024) brasilichnium isp. (in lockley et al., 1998, 2014b; milner et al., 2024) indet. tracks (in milner et al., 2024) temple cap sandstone, middle jurassic (glca) plantae petrified wood (in national park service, 1999 [= page sandstone of reference]) entrada sandstone, middle jurassic (glca) archosauromorpha dinosauria a-47 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 saurischia theropoda unidentified theropod tracks previously attributed to the navajo sandstone (in lockley et al., 2005) morrison formation, late jurassic (glca) arthropoda (traces) termite nests (in engelmann, 1999) archosauromorpha dinosauria dinosauria indet. (in anderson et al., 2000) saurischia sauropoda unidentified sauropod track with skin impressions (in lockley and hunt, 1995) naturita formation (dakota formation in older references), late cretaceous (glca) plantae undetermined material (wood tissue, resin blebs) (in peterson, 1969) chlorophyta botryococcus sp. (in peterson, 1969) polypodiopsida anemia sp. (in peterson, 1969) appendicisporites sp. (in peterson, 1969) cicatricosisporites sp. (in peterson, 1969) gleichenia sp. (in peterson, 1969) gleicheniidites sp. (in peterson, 1969) other fern spores (in peterson, 1969) gymnospermae pinopsida conifer pollen (in peterson, 1969) angiospermae monosulcites sp. (in peterson, 1969) retitricolpites sp. (in peterson, 1969) tricolpopollenites sp. (in peterson, 1969) other monosulcate and tricolpate pollen (in peterson, 1969) mollusca cephalopoda ammonoidea metoicoceras defordi (in peterson, 1969) metoicoceras cf. m. whitei (in peterson, 1969) bivalvia brachiodontes multilinigera (in peterson, 1969) brachiodontes sp. (in peterson, 1969) callistina sp.? (in peterson, 1969) cardium sp. (in peterson, 1969) corbicula sp.? (in peterson, 1969) corbula sp. (in peterson, 1969) exogyra levis (in peterson, 1969) a-48 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 exogyra olisiponensis (in peterson, 1969) ostrea sp. (in peterson, 1969) phelopteria sp. (in peterson, 1969) pinna petrina (in peterson, 1969) plicatula sp. (in peterson, 1969) gastropoda gyrodes sp.? (in peterson, 1969) testudines gen. et sp. indet. (in peterson, 1969) tropic shale, late cretaceous (glca) anthozoa platycyathus sp. (in elder, 1987) trochocyathus sp.? (in peterson, 1969) brachiopoda discinisca sp. (in elder, 1987) mollusca ammonoidea allocrioceras annulatum (in peterson, 1969) baculites sp. (in peterson, 1969) baculites sp.? (in peterson, 1969) collignoniceras woollgari (in peterson, 1969) kanabiceras septemseriatum (in peterson, 1969) kanabiceras sp.? (in peterson, 1969) mammites sp. (in peterson, 1969) metoicoceras whitei (in peterson, 1969) metoicoceras sp. (in peterson, 1969) neocardioceras sp.? (in peterson, 1969) sciponoceras gracile (in peterson, 1969) watinoceras sp.? (in peterson, 1969) belemnoidea actinocamax sp. (in peterson, 1969) bivalvia anomia sp. (in peterson, 1969; elder, 1987) astarte sp.? (in elder, 1987) aucinella sp. (in elder, 1987) botula sp.? (in peterson, 1969) camptonectes platessa (in peterson, 1969) camptonectes sp. (in peterson, 1969) cardium cf. c. pauperculum (in peterson, 1969) cardium sp. (in peterson, 1969) corbicula sp.? (in peterson, 1969) corbula kanabensis (in peterson, 1969) corbula sp. (in peterson, 1969; elder, 1987) corbula sp.? (in peterson, 1969) cymbophora sp. (in elder, 1987) exogyra acroumbonata (in elder, 1987) exogyra levis (in peterson, 1969; elder, 1987) a-49 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 exogyra olisiponensis (in peterson, 1969) exogyra sp. (in peterson, 1969) gervillia sp. (in elder, 1987) gryphaea newberryi (in peterson, 1969) gryphaeostrea sp. (in elder, 1987) inoceramus flavus flavus (in elder, 1987) inoceramus flavus pictoides (in elder, 1987) inoceramus labiatus (in peterson, 1969) inoceramus pictus gracilistriatus (in elder, 1987) inoceramus pictus pictus (in elder, 1987) inoceramus tenuistriatus (in elder, 1987) inoceramus sp. (in peterson, 1969; elder, 1987) lima utahensis (in peterson, 1969) lima sp. (in elder, 1987) liopistha concentrica (in elder, 1987) liopistha elongatula (in elder, 1987) liopistha meeki (in elder, 1987) lucina subundata (in peterson, 1969) lucina sp. (in peterson, 1969; elder, 1987) mytiloides aff. m. duplicostatus (in elder, 1987) mytiloides aff. m. submytiloides (in elder, 1987) mytiloides n. sp. a (in elder, 1987) mytiloides opalensis (in elder, 1987) nemodon sp. (in elder, 1987) ostrea sp. (in peterson, 1969) phelopteria cf. p. gastrodes (in peterson, 1969) phelopteria sp. (in peterson, 1969) phelopteria sp. indet. (in elder, 1987) pholadomya sp. (in elder, 1987) plesiopinna sp. (in elder, 1987) plicatula sp. (in elder, 1987) protocardia sp. (in elder, 1987) pseudoptera sp. (in elder, 1987) psilomya concentrica (in peterson, 1969) psilomya meeki (in peterson, 1969) pycnodonte newberryi (in elder, 1987) solemya obscura (in peterson, 1969; elder, 1987) syncyclonema sp. (in elder, 1987) veniella mortoni (in peterson, 1969) yoldia? sp. (in peterson, 1969) arcidae indet. (in elder, 1987) inoceramidae indet. (in elder, 1987) indet. oysters (including oyster spat) (in elder, 1987) infaunal bivalve indet. (in elder, 1987) “ligumen” [typo?] (in elder, 1987) gastropoda anchura sp. (in elder, 1987) anisomyon sp. (in elder, 1987) a-50 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 arrhoges prolabiata (in peterson, 1969) cerithiopsis sp. (in elder, 1987) cerithium sp. (in peterson, 1969) cerithium sp.? (in peterson, 1969) cylichna sp. (in elder, 1987) drepanochilus ruida (in peterson, 1969; elder, 1987) eunaticina textilis (in elder, 1987) euspira concinna (in elder, 1987) euspira sp. (in peterson, 1969) “mesostoma” sp. (in elder, 1987) perissoptera sp. (in elder, 1987) rostellites sp.? (in peterson, 1969) sigaretus (eunaticina?) textilis (in peterson, 1969) turritella whitei (in peterson, 1969; elder, 1987) turritella sp. (in elder, 1987) gen. et sp. indet. (in elder, 1987) scaphopoda gen. et sp. indet. (in elder, 1987) annelida hamulus sp. (in elder, 1987) serpula intrica (in peterson, 1969; elder, 1987) serpula sp. (in elder, 1987) chondrichthyes cretolamna appendiculata (in albright et al., 2013) oxyrhina cf. o. angustidens (in peterson, 1969) ptychodus whipplei (in peterson, 1969) ptychodus cf. p. polygyrus (in peterson, 1969) ptychodus sp. (in peterson, 1969) scapanorhynchus raphiodon (in albright et al., 2013) scapanorhynchus subulatus (in peterson, 1969) squalicorax curvatus (in albright et al., 2013) gen. et sp. indet. (in peterson, 1969) actinopterygii undetermined scales (in peterson, 1969) ichthyodectidae gillicus arcuatus (in albright et al., 2013) xiphactinus audax (in peterson, 1969) pycnodontoidea pycnodontoid tooth (in peterson, 1969) mosasauridae sarabosaurus dahli* (in polcyn et al., 2023) plesiosauria pliosauridae brachauchenius lucasi (in albright et al., 2007a) polycotylidae eopolycotylus rankini* (in albright et al., 2007b) scalamagnus tropicensis* (in clark et al., 2023b; formerly dolichorhynchops tropicensis, in schmeisser mckean, 2012) a-51 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 trinacromerum ?bentonianum (in albright et al., 2007b) gen. et sp. nov., cf. palmulasaurus (in schmeisser mckean and gillette, 2021) testudines desmatochelys lowi (in albright et al., 2013) foraminifera bulimina sp. (in peterson, 1969) dentalina sp.? (in peterson, 1969) frondicularia sp. (in peterson, 1969) haplofragmoides sp.? (in peterson, 1969) hedbergella cf. h. delrioensis (in peterson, 1969) heterohelix moremani (in peterson, 1969) marginulinopsis sp.? (in peterson, 1969) planulina dakotensis (in peterson, 1969) proteonina difflugiformis (in peterson, 1969) ?ticinella aprica (in peterson, 1969) undetermined planktonic foraminifera (in peterson, 1969) straight cliffs formation, late cretaceous (glca) plantae angiospermae geonomites? sp. (in peterson, 1969) mollusca cephalopoda ammonoidea placenticeras sp. (in peterson, 1969) protexanites shoshonensis (in peterson, 1969) bivalvia cardium cf. c. pauperculum (in peterson, 1969) inoceramus howelli (in peterson, 1969) inoceramus (volviceramus) involutus (in peterson and barnum, 1973) inoceramus cf. i. stantoni (in peterson, 1969) inoceramus sp. (in peterson, 1969) ostrea sp. (in peterson, 1969) gastropoda bellifusus sp.? (in peterson and barnum, 1973) gyrodes cf. g. conradi (in peterson, 1969) gyrodes cf. g. depressus (in peterson, 1969) gyrodes sp. (in peterson and barnum, 1973) helicaulax sp.? (in peterson and barnum, 1973) rostellites sp.? (in peterson, 1969) annelida serpula sp. (in peterson, 1969) arthropoda (traces) ophiomorpha isp. (in peterson, 1969) chondrichthyes ptychodus sp. (in peterson, 1969) quaternary sediments (glca) a-52 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 plantae gymnospermae cupressaceae juniperus sp. (in davis et al., 1984) juniperus communis (in davis et al., 1984) pinaceae picea pungens (in davis et al., 1984) angiospermae asteraceae artemisia cf. tridentata (in davis et al., 1984) cirsium sp. (in davis et al., 1984) cf. heleanthus (in davis et al., 1984) betulaceae betula occidentalis (in davis et al., 1984) cactaceae opuntia sp. (in davis et al., 1984) opuntia polyacantha (in davis et al., 1984) sclerocactus sp. (in davis et al., 1984) caprifoliaceae sambucus sp. (in davis et al., 1984) symphoricarpos sp. (in davis et al., 1984) chenopodiaceae atriplex sp. (in davis et al., 1984) atriplex cf. canescens (in davis et al., 1984) atriplex cf. confertifolia (in davis et al., 1984) chenopodium sp. (in davis et al., 1984) corispermum sp. (in davis et al., 1984) cleomaceae cleome sp. (in davis et al., 1984) cornaceae cornus stolonifera (in davis et al., 1984) cyperaceae carex cf. lenticularis (in davis et al., 1984) carex cf. interior (in davis et al., 1984) carex lasiocarpa (in davis et al., 1984) scirpus sp. (in davis et al., 1984) fagaceae quercus sp. (in davis et al., 1984) gramineae cf. agropyron (in davis et al., 1984) poaceae oryzopsis hymenoides (in davis et al., 1984) panicum sp. (in davis et al., 1984) spartina gracilis (in davis et al., 1984) sporobolus sp. (in davis et al., 1984) labiatae cf. marrubium sp. (in davis et al., 1984) a-53 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 leguminosae cf. dalea sp. (in davis et al., 1984) liliaceae cf. smilacina sp. (in davis et al., 1984) malvaceae sphaeralcea sp. (in davis et al., 1984) potamogetonaceae potamogeton diversifolium (in davis et al., 1984) rosaceae amelanchier sp. (in davis et al., 1984) purshia sp. (in davis et al., 1984) rosa sp. (in davis et al., 1984) rubus sp. (in davis et al., 1984) saxifragaceae ribes sp. (in davis et al., 1984) mollusca bivalvia pisidium casertanum (in kaufman et al., 2002) pisidium nitidum (in kaufman et al., 2002) pisidium subtruncatum (in kaufman et al., 2002) pisidium walkeri (in kaufman et al., 2002) pisidium sp. (in kaufman et al., 2002) gastropoda catinella sp. (in kaufman et al., 2002) fossaria dalli (in kaufman et al., 2002) gyraulus parvus (in kaufman et al., 2002) vertigo ovata (in kaufman et al., 2002) arthropoda ostracoda cypridopsis okeechobei (in kaufman et al., 2002) cypridopsis vidua (in kaufman et al., 2002) darwinula stevensoni (in kaufman et al., 2002) heterocypris incongruins (in kaufman et al., 2002) hyocypris bradyi (in kaufman et al., 2002) strandesia meadensis (in kaufman et al., 2002) amphibia anura scaphiopus intermontanus (in mead et al., 1993) scaphiopus cf. bombifrons (in mead et al., 1993) reptilia ophidia crotalus cf. viridis (in mead et al., 1993) pitulophis melanoleucus (in mead et al., 1993) mammalia afrotheria mammuthus columbi (in mead et al., 1984) artiodactyla bison sp. (in mead and agenbroad, 1992) a-54 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 euceratherium collinum (in mead et al., 1993) camelops sp. (in mead and agenbroad, 1992) odocoileus sp. (in mead et al., 1984) oreamnos harringtoni (in mead et al., 1993) ovis canadensis (in mead and agenbroad, 1992) perissodactyla equus sp. (in davis et al., 1984) lagomorpha brachylagus idahoensis (in mead et al., 1993) sylvilagus sp. (in mead and agenbroad, 1992) rodentia lagurus curtatus (in mead et al., 1993) marmota flaviventris (in mead et al., 1993) microtus sp. (in mead et al., 1993) neotoma cinerea (in mead et al., 1993) spermophilus sp. (in mead et al., 1993) thomomys sp. (in mead et al., 1993) xenarthra nothrotheriops shastensis (in mead et al., 1984; mead and agenbroad, 1992) golden spike national historical park (gosp) bridal veil limestone, oquirrh group, pennsylvanian (gosp) porifera gen. et sp. indet. (in aase, undated; tweet et al., 2012h) anthozoa rugosa gen. et sp. indet. (in aase, undated; tweet et al., 2012h) arthropoda trilobita gen. et sp. indet. (in aase, undated; tweet et al., 2012h) brachiopoda gen. et sp. indet. (in aase, undated; tweet et al., 2012h) bryozoa gen. et sp. indet. (in aase, undated; tweet et al., 2012h) echinodermata crinoidea gen. et sp. indet. (in aase, undated; tweet et al., 2012h) mollusca nautiloidea gen. et sp. indet. (in aase, undated; tweet et al., 2012h) elasmobranchii gen. et sp. indet. (in aase, undated; tweet et al., 2012h) actinopterygii teleostei gen. et sp. indet. (in aase, undated; tweet et al., 2012h) a-55 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 quaternary sediments (gosp) plantae gymnospermae pinopsida juniperus osteosperma (in rhode, 2000) angiospermae amaranthaceae amaranthus sp. (in rhode, 2000) chenopodium sp. (in rhode, 2000) papaveraceae argemone sp. (in rhode, 2000) asteraceae artemisia sect. tridentatae (in rhode, 2000) brickellia sp. (in rhode, 2000) chrysothamnus sp. (in rhode, 2000) gutierrezia cf. g. sarothrae (in rhode, 2000) haplopappus sp. (in rhode, 2000) tetradymia sp. (in rhode, 2000) gen. et sp. indet. (in rhode, 2000) fabaceae astragalus sp. (in rhode, 2000) poaceae festuca sp. (in rhode, 2000) gen. et sp. indet. (in rhode, 2000) rubiaceae gallium sp. (in rhode, 2000) boraginaceae lappula redowskii (in rhode, 2000) cyperaceae scirpus sp. (in rhode, 2000) fabaceae gen. et sp. indet. (in rhode, 2000) mammalia rodentia neotoma sp. middens (in tweet et al., 2012a) hovenweep national monument (hove) naturita formation (dakota formation in older references), late cretaceous (hove) plantae gen. et sp. indet. (in shaffer et al., 2024) natural bridges national monument (nabr) chinle formation, late triassic (nabr) plantae a-56 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. (in santucci and kirkland, 2010) quaternary sediments (nanra) plantae gen. et sp. indet. (in mead et al., 1987) polypodiophyta equisetales equisetum sp. (in mead et al., 1987) gymnospermae pinopsida juniperus sp. (in mead et al., 1987) picea sp./abies sp./pseudotsuga sp. (in mead et al., 1987) pinus flexilis-type pollen (in mead et al., 1987) pinus sp. (in mead et al., 1987) pseudotsuga sp. (in mead et al., 1987) ephedraceae ephedra sp. (in mead et al., 1987) angiospermae sapindaceae acer sp.? (in mead et al., 1987) betulaceae alnus sp. (in mead et al., 1987) betula sp. (in mead et al., 1987; mead and agenbroad, 1992) asteraceae antennaria sp./cirsium sp. (in mead et al., 1987) artemisia sp. (in mead et al., 1987) high-spine asteraceae pollen (in mead et al., 1987) low-spine asteraceae pollen (in mead et al., 1987) nyctaginaceae boerhavia sp. (in mead et al., 1987) poaceae bromus sp. (in mead et al., 1987) poa sp. (in mead et al., 1987) gen. et sp. indet. (in mead et al., 1987) cyperaceae carex sp. (in mead et al., 1987) gen. et sp. indet. (in mead et al., 1987) rhamnaceae ceanothus sp./cercocarpus sp. (in mead et al., 1987) rhamnus sp. (in mead et al., 1987) cannabaceae celtis sp. (in mead et al., 1987) oleaceae fraxinus sp. (in mead et al., 1987) juglandaceae juglans sp. (in mead et al., 1987) cactaceae opuntia sp. (in mead et al., 1987) a-57 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 plantaginaceae plantago sp. (in mead et al., 1987) salicaceae populus sp. (in mead et al., 1987) fagaceae quercus sp. (in mead et al., 1987) polygonaceae rumex sp. (in mead et al., 1987) sarcobataceae sarcobatus sp. (in mead et al., 1987) malvaceae sphaeralcea sp. (in mead et al., 1987) amaranthaceae cheno-am pollen (in mead et al., 1987) liguliflorae gen. et sp. indet. (in mead et al., 1987) rosaceae gen. et sp. indet. (in mead et al., 1987) mammalia rodentia neotoma sp. middens (in tweet et al., 2012a) artiodactyla oreamnos harringtoni (in mead et al., 1987) rainbow bridge national monument (rabr) kayenta formation, early jurassic (rabr) eubrontes isp. (in hall, 1934; lockley et al., 1998) timpanogos cave national monument (tica) deseret limestone, mississippian (tica) anthozoa gen. et sp. indet. (in santucci et al., 2001) rugosa gen. et sp. indet. (in santucci et al., 2001) echinodermata crinoidea gen. et sp. indet. (in santucci et al., 2001) mollusca gastropoda gen. et sp. indet. (in santucci et al., 2001) quaternary sediments (tica) reptilia squamata a-58 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 ophidia gen. et sp. indet. (in george, 1999) aves gen. et sp. indet. (in george, 1999) mammalia rodentia sciuridae marmota flaviventris (in george, 1999) spermophilus sp. (in george, 1999) muridae microtus sp. (in george, 1999) neotoma cf. cinerea (in george, 1999) neotoma sp. middens (in tweet et al., 2012a) peromyscus cf. maniculatus (in george, 1999) lagomorpha lepus americanus (in george, 1999) carnivora martes americana (in george, 1999) mustela vison (in george, 1999) procyon lotor (in george, 1999) ursus americanus (in george, 1999) artiodactyla bison bison (in santucci et al., 2001; santucci and kirkland, 2010) ovis canadensis (in george, 1999) zion national park (zion) kaibab limestone, early permian (zion) mollusca bivalvia myalina sp. (in deblieux et al., 2005) lower red member, moenkopi formation, early triassic (zion) lepidosauromorpha rhynchosauroides isp. (in mickelson et al., 2006b) pseudosuchia chirotherium isp. (in mickelson et al., 2006b) virgin limestone member, moenkopi formation, early triassic (zion) mollusca gen. et sp. indet. (in santucci, 2000) ammonoidea meekoceratidae gen. et sp. indet. (in santucci, 2000) echinodermata asterozoa asteroidea a-59 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gen. et sp. indet. (in santucci, 2000) ophiuroidea asterosoma sp. (in deblieux et al., 2005) middle red member, moenkopi formation, early triassic (zion) plantae gen. et sp. indet. (in deblieux et al., 2005) cameron member, chinle formation, late triassic (zion) plantae gen. et sp. indet. (in deblieux et al., 2005) actinopterygii gen. et sp. indet. (in deblieux et al., 2005) amphibia metoposauridae gen. et sp. indet. (in deblieux et al., 2005) reptilia pseudosuchia crocodylomorpha revueltosaurus cf. r. callendari (in heckert et al., 2006) gen. et sp. indet. (milner, written observations) aetosauria gen. et sp. indet. (in deblieux et al., 2005) phytosauria gen. et sp. indet. (in deblieux et al., 2005) dinosaur canyon member, moenave formation, late triassic–early jurassic (zion) plantae gen. et sp. indet. (in deblieux et al., 2006) pinopsida araucarites sp. saintgeorgia sp. whitmore point member, moenave formation, early jurassic (zion) plantae sanmiguelia lewisii (in ash et al., 2014) actinopterygii semionotiformes semionotidae (in hesse, 1935; milner et al., 2012) lophionotus sp. (in milner et al., 2012) sarcopterygii coelacanthiformes gen. et sp. indet. (in c.j. bennett, [former] national park service, zion national park, unpublished field notes, 2023) dinosauria theropoda eubrontes isp. (in deblieux et al., 2006) a-60 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 grallator isp. (in milner et al., 2012) “?grallator isp. or ?anomoepus isp.” (in deblieux et al., 2006) kayenta formation, early jurassic (zion) dinosauria theropoda characichnos isp. eubrontes isp. (in deblieux et al., 2005, 2006) grallator isp. (in deblieux et al., 2005, 2006) kayentapus isp. (in milner et al., 2012) synapsida mammaliamorpha brasilichnium isp. (in deblieux et al., 2005, 2006) navajo sandstone, early–middle jurassic (zion) arthropoda arachnida (trace) cf. paleohelcura isp. dinosauria theropoda grallator isp. (in deblieux et al., 2005, 2006) synapsida mammaliamorpha gen. et sp. indet. (in deblieux et al., 2005, 2006) co-op creek limestone member, carmel formation, middle jurassic (zion) mollusca bivalvia gen. et sp. indet. (in deblieux et al., 2005) gastropoda gen. et sp. indet. (in deblieux et al., 2005) echinodermata crinoidea isocrinus nicoletti (in deblieux et al., 2005) cedar mountain formation–naturita formation undivided (late early–early late cretaceous) (zion) plantae leaf impressions (in deblieux et al., 2005) mollusca bivalvia gen. et sp. indet. (in deblieux et al., 2005) straight cliffs formation (reworked) (late cretaceous) (zion) mollusca bivalvia crassostrea soleniscus (in deblieux et al., 2005) quaternary sediments (zion) a-61 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland, ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 plantae gen. et sp. indet. (in hamilton, 1979; hevly, 1979) pteridophyte spores (in hevly, 1979) bryophyta gen. et sp. indet. (in hevly, 1979) gymnospermae pinaceae abies sp. (in hevly, 1979) picea sp. (in hevly, 1979) pinus sp. (in hamilton, 1979; hevly, 1979) pseudotsuga sp. (in hevly, 1979) white pine pollen (in hevly, 1979) yellow pine pollen (in hevly, 1979) cupressaceae juniperus sp. (in hevly, 1979) angiospermae riparian tree pollen (in hevly, 1979) salvinaceae azolla sp. (in hamilton, 1979) potamogetonaceae potamogeton sp. (in hamilton, 1979; hevly, 1979) fagaceae quercus sp. (in hevly, 1979) typhaceae typha sp. (in hevly, 1979) araceae lemna sp. (in hevly, 1979) haloragaceae myriophyllum sp. (in hevly, 1979) amaranthaceae cheno-am pollen (in hevly, 1979) compositae gen. et sp. indet. (in hevly, 1979) cruciferae gen. et sp. indet. (in hevly, 1979) cyperaceae gen. et sp. indet. (in hevly, 1979) gramineae gen. et sp. indet. (in hevly, 1979) umbelliferae gen. et sp. indet. (in hevly, 1979) mollusca gen. et sp. indet. (in hamilton, 1979) mollusk burrows (in hamilton, 1979) bivalvia musculium partumeium (in hamilton, 1979) pisidium sp. (in hamilton, 1979) mussel impression (in hevly, 1979) a-62 a visual paleontological inventory of utah’s national park service areas tut tran, andrew r.c. milner, justin s. tweet, donald d. deblieux, rebecca hunt-foster, austin b. shaffer, james i. kirkland ethan warner-cowgill, and vincent l. santucci geology of the intermountain west 2025 volume 12 gastropoda cochlicopa (cionella) lubrica (in hamilton, 1979) discus whitneyi (formerly d. cronkhitei) (in vanatta, 1921) discus shimekii (in hamilton, 1979; hevly 1979) euconulus fulvus alaskensis (in hamilton, 1979) gyraulus parvus (in hamilton, 1979) heliosoma sp. (in hamilton, 1979) lymnaea (stagnicola) bulimoides (in hevly, 1979) microphysula ingersollii (in hamilton, 1979) oreohelix haydeni var. oquirrensis (in vanatta, 1921) oreohelix strigosa (in hamilton, 1979) oreohelix strigosa var. depressa (in vanatta, 1921) physa sp. (in hamilton, 1979) physa virgata (in hamilton, 1979) planorbella tenuis (in hamilton, 1979) polita indentata (in vanatta, 1921) stagnicola sp. (in hamilton, 1979) succinea avara (in vanatta, 1921; hamilton, 1979) vallonia perspectiva (in hamilton, 1979) nematomorpha horsehair worm trail (in hamilton, 1979) arthropoda insecta ant tracks (in hamilton, 1979) beetle tracks (in hamilton, 1979) aquatic insect larva trails (in hamilton, 1979) actinopterygii gen. et sp. indet. (in hamilton, 1979) aves gen. et sp. indet. (in hevly, 1979) large bird track (in hamilton, 1979) mammalia rodentia thomomys sp. (in hevly, 1979) artiodactyla bison sp. (in hamilton, 1979) camel? track (in hamilton, 1979) ovis canadensis (in hamilton, 1979) microfossils diatomista fragilaria vaucheriae (in hevly, 1979) navicula sp. (in hevly, 1979) geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 volume 12 2025 this is an open-access article in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. email inquiries to giw@utahgeology.org. differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west an open-access journal of the utah geological association issn 2380-7601 production cover design and desktop publishing douglas a. sprinkel cover hypothetical reconstruction of the distribution of osteoderm elements of mymoorapelta maysi with reconstructed pelvis in ventral view as compared to that of gargoyleosaurus parkpinorum’s pelvis and lateral osteoderm elements. scale of fossil elements by reference to figures in manuscript. comparison of gargoyleosaurus third cervical rings modified after carpenter et al. (2013). i become a member of the uga to help support the work of the association and receive notices for monthly meetings, annual field conferences, and new publications. annual membership is $30 and annual student membership is only $5. visit the uga website at www.utahgeology.org for information and membership application. the uga board is elected annually by a voting process through uga members. however, the uga is a volunteer-driven organization, and we welcome your voluntary service. if you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. utah geological association formed in 1970 from a merger of the utah geological society, founded in 1946, and the intermountain association of geologists, founded in 1949. affiliated with the american association of petroleum geologists. volume 12 2025 geology of the intermountain west (giw) is an open-access journal in which the utah geological association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. 2025–2026 uga board president rob buehring robbuehring@yahoo.com 713.412.9269 president-elect trae boman traebgeologist@gmail.com 801.648.5206 program chair mike arnoff marnoff@utah.gov 385.303.0431 treasurer will hurlbut wdhurlbut@gmail.com 860.733.3190 secretary kylie arcaris kaarcaris@gmail.com 801.628.6731 past president keilee higgs keileeann@utah.gov 801.678.3683 uga committees environmental affairs seeking a volunteer geologic road sign greg gavin greggavin@gmail.com 513.509.1509 historian paul anderson paul@pbageo.com 801.364.6613 outreach greg nielsen gnielsen@weber.edu 801.626.6394 public education zach anderson zanderson@utah.gov 801.537.3300 matt affolter gfl247@yahoo.com publications paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 publicity paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 social/recreation roger bon rogerbon@xmission.com 801.580.1331 aapg house of delegates 2023–2026 term david a. wavrek dwavrek@petroleumsystems.com 801.322.2915 state mapping advisory committee uga representative bill loughlin bill@loughlinwater.com 435.649.4005 uga newsletter newsletter editor mike barber uga.newsletter@gmail.com 435.640.1382 uga website — www.utahgeology.org webmaster paul inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 scholarship golf tournament co-chair rick ford rford@weber.edu 801.915.3188 co-chair john south jsouth@utah.gov 385.266.2113 earthquake safety committee chair seeking a volunteer douglas a. sprinkel azteca geosolutions 801.391.1977 giw@utahgeology.org dsprinkel@gmail.com thomas c. chidsey, jr. utah geological survey, emeritus 801.824.0738 tomchidsey@gmail.com bart j. kowallis brigham young university 801.380.2736 bkowallis@gmail.com steven schamel geox consulting, inc. 801.583.1146 geox-slc@comcast.net john r. foster utah field house of natural history state park museum 435.789.3799 johnfoster@utah.gov william r. lund utah geological survey, emeritus 435.590.1338 williamlundugs@gmail.com editors geology of the intermountain west an open-access journal of the utah geological association volume 12 2025 315 abstract since the first jurassic ankylosaur from north america, mymoorapelta maysi, was described in 1994, considerably more material has been recovered from the type locality in western colorado. this taxon is the most complete ankylosaur from the morrison formation and is completely distinct from gargoyleosaurus. the new material from this and 11 other known morrison ankylosaur localities justify a new description of the available fossils to better characterize these two morrison dinosaur genera and better resolve their distribution through the extent of the morrison formation. mymoorapelta is restricted to the upper morrison formation in utah, colorado, and southern wyoming, whereas gargoyleosaurus is found near the base of the morrison and up section into the upper morrison. gargoyleosaurus may well be represented by more than one species through its stratigraphic range. differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland1, rebecca k. hunt-foster2, kirsty morgan3, julia b. mchugh4, and john r. foster5 1utah geological survey, salt lake city, ut 84114-6100 usa; jameskirkland@utah.gov 2dinosaur national monument, jensen, ut 84035 usa; rebecca.k.hunt@gmail.com 3department of geosciences, university of arkansas fayetteville, ar 72701 usa; kirstymorgan08@gmail.com 4museum of western colorado, grand junction, co 81502 usa; jmchugh@mowc.co 5utah field house of natural history state park museum, vernal, ut 84078 usa; johnfoster@utah.gov citation for this article. kirkland, j.i., hunt-foster, r., morgan, k., mchugh, j.b., and foster, j.r., 2025, differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality: geology of the intermountain west, v. 12, p. 315–393, https://doi.org/10.31711/giw.v12.pp315-393. introduction with its description in the 1990s (kirkland and carpenter, 1994; kirkland et al., 1998), mymoorapelta became the first well-documented ankylosaur from the upper jurassic morrison formation. this was soon followed by the description of gargoyleosaurus (carpenter et al., 1998). although both are from the morrison and mymoorapelta is better preserved, the nearly complete skull of gargoyleosaurus made it favored with taxonomists. however, continued excavations at the type location, at the mygatt-moore quarry (foster et al., 2018; drumheller et al., 2020; mchugh et al., 2020, 2023) in westernmost colorado, have resulted in the recovery of nearly every skeletal element of mymoorapelta, including much of the skull, making it the most completely represented morrison ankylosaur. skull elements include jugal, postorbital, quadrate, braincase, and teeth that compare well with gargoyleosaurus, whose jugals, quadrates, and braincase were damaged during extraction. however, differences in the proportions in the braincase, pelvis, caudal vertebrae, caudal osteoderms, and in the stratigraphic positions of specimens of mymoorapelta and gargoyleosaurus confirms the retention of the latter as a distinct genus. of the major postcranial skeleton, only the pubis and femur are not represented in the material for mymoorapelta present in the mygatt-moore quarry but are the only skeletal elements known from the hindquarters of the holotype 316 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 of gargoyleosaurus. all osteoderms of the external carapace are well represented including significant portions of cervical rings. clearly, mymoorapelta and gargoyleosaurus are similar in nearly every morphological feature of the shared, preserved skeletal elements. mymoorapelta preserves a mosaic of characters relative to more derived ankylosaurs that may provide important information as to what are the primitive character states in ankylosauria. for instance, the ischium is bent as in polacanthids, nodosaurids, and most stegosaurs indicating that the straight ischium of ankylosaurids is actually a derived character state. the scapular spine forms a vertical ridge opposite the glenoid in mymoorapelta as in ankylosaurids and the only other morrison ankylosaur scapula from the dry mesa quarry in western colorado (kirkland et al., 1998). mymoorapelta has short limbs with even shorter distal limb elements as in ankylosaurids and polacanthids. this new analysis indicates that mymoorapelta and gargoyleosaurus share unique characters with polacanthus, hylaeosaurus, gastonia, and hoplitosaurus (blows, 2015). ankylosaur remains from the morrison formation ankylosaur remains are now documented in the upper jurassic morrison formation of colorado, utah, wyoming, and new mexico (figure 1). the first morrison ankylosaur fossils were recognized in 1990 in western colorado (kirkland and carpenter, 1994) at the mygatt-moore quarry and are all curated into the collections of the museum of western colorado (mwc) and by 1998, ankylosaur fossils had been recognized from six localities (kirkland et al., 1998). there are currently 12 localities recognized across four states. these localities span nearly the entire morrison outcrop belt (figure 1). colorado localities mygatt-moore quarry the mygatt-moore quarry in western colorado is near the middle of the brushy basin member of the morrison formation (figures 2a through 2d). the site is the type locality for mymoorapelta (kirkland and carpenter, 1994; kirkland et al., 1998) and is the only site in the morrison that has yielded the remains of more than one individual ankylosaur. the taphonomy of the quarry has recently been described in detail by foster et al. (2018). this site is discussed in more detail below. cactus park ankylosaur in the early 1990s, denver high school teacher kent hups discovered an ankylosaur skeleton weathering out of a calcite-cemented sandstone ledge in the brushy basin member on the east side of cactus park southeast of grand junction, colorado (figure 2e). the fossil (specimen mwc 2610) is an articulated skeleton lying ventral side down. it was assigned to mymoorapelta based on the morphology of its caudal plates (kirkland et al., 1998). the curated fossil material consists of broken sandstone blocks collected from the slope below the ledge that revealed much of the posterior portion of the skeleton. this material consists largely of external molds of the bones and unprepared bones within the sandstone blocks. much of the anterior portion of the skeleton remains uncollected in the field where it appears to be preserved in a multi-ton block of sandstone that remains in continuity with the sandstone ledge. requests to bring in heavy equipment to collect this large specimen have been turned down by the bureau of land management, as the site is within the dominguez-escalante national conservation area. however, during a visit to the site, its discoverer kent hups found the skull in the highly cemented sandstone and brought it to the denver museum of nature and science (dmnh) for preparation. the skull, which initially had been complete, became fragmented during the course of preparation. the highly fragmented skull is in sections coated by sandstone and is undergoing consolidation and preparation in the paleontology lab at dinosaur journey, mwc, which is expected to take several years. hopefully this entire specimen will be collected and studied in the future. garden park tibia in 1992, the dmnh collected a partial ankylosaur 317 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 tibia (specimen dmnh 15162) beneath a stegosaurus skeleton they had been excavating at the locally wellknown small quarry within the garden park area, south-central colorado. initially identified as indeterminate (kirkland et al., 1998), it compares well with the partial tibia from the mygatt-moore quarry and cactus park. given its stratigraphic position in the upper morrison formation just above the “clay change,” a regional marker horizon where the surface weathering of morrison mudstone indicates a significant increase in smectitic (swelling) clay and thus input of volcanic ash (peterson and turner, 1998; turner and peterson 1999, 2004; demko et al., 2004; kirkland, 2006; christiansen et al., 2015; kirkland et al., 2020), it is now considered to represent a possible occurrence of mymoorapelta. dry mesa quarry field crews from brigham young university’s museum of paleontology (byu) have collected an abundance of diverse dinosaur remains from the dry mesa quarry in the medial morrison formation of western colorado over many years (miller et al., 1991); among these are several ankylosaur elements. a well-preserved scapulocoracoid (specimen byu 725-12963) was collected in 1990 from the dry mesa quarry in the lower brushy basin member by rod scheetz (kirkland et al., 1998); subsequently, a grooved shoulder spine and several caudal plates have been prepared from the site. the co-occurrence of allosaurus jimmadseni suggests that it is temporally equivalent stratigraphically from the type locality in the salt wash member of the morrison formation at dinosaur national monument and in the lower morrison of wyoming (chure and loewen, 2020). stratigraphically, turner and peterson (1999) place the dry mesa quarry at a clay composition change (sudden appearance of smectitic clays near base of brushy basin) that has been noted by them and others (e.g., demko et al., 2004; kirkland, 2006) as forming a distinct surface across the colorado plateau associated with a major calcrete horizon. extending that marker bed into wyoming and farther north has not been considered possible as smectitic clay in the morrison vanishes northward across wyoming (trujillo, 2006). figure 1. locality map of the rocky mountain region indicating where ankylosaurs have been found in the morrison formation. abbreviations: b = los angeles county museum’s blanding mymoorapelta sacrum locality; cp = cactus park, hups quarry’s mymoorapelta skeleton; dm = dry mesa quarry (scattered mymoorapelta elements); g = type locality of gargoleosaurus at bone cabin west quarry; gp = denver museum of science and nature’s garden park stegosaurus site (ankylosaur tibia); hb = associated skeleton at hanksville-burpee quarry; m&m = mygatt-moore quarry, type locality of mymoorapelta; mq = mailyn quarry (ankylosaur caudal vertebrae and caudal plates); mv = movie valley ankylosaur; p = peterson quarry (ankylosaur osteoderm); s = simon quarry has yielded gargoyleosaurus pelvis and tibia; sc = sheep creek; b = boris quarry cf. mymoorapelta braincase and perhaps zane quarry ankylosaur caudal vertebra. 318 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 2. mymoorapelta localities in the morrison formation of western colorado. (a) brushy basin member of morrison formation in rabbit valley with the position of the mygatt-moore quarry indicated after foster et al. (2018). (b) detailed section through mygatt-moore quarry from chin and kirkland (1998), scale is in meters. (c) oblique aerial photograph of the mygatt-moore quarry area. red bar indicates position of detailed stratigraphic section in b (google earth image). (d) j.d. moore and pete mygatt, discoverers of the mygatt-moore quarry. (e) overview of the cactus park mymoorapelta site. red arrowhead indicates ankylosaur site. red bar indicates base of the lower cretaceous burro canyon formation. note that much of the brushy basin member of the morrison formation has been truncated at the basal cretaceous unconformity. (f) kent hups during the initial excavations of the cactus park in the mid-1990s. figures e and f courtesy of harley armstrong, retired, bureau of land management. 319 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 wyoming localities bone cabin quarry dinosaur excavations have been undertaken at bone cabin quarry since the american museum of natural history (amnh) first opened the quarry in 1898 northwest of laramie (colbert, 1968). however, it was not until the mid-1990s that excavations to the west of the main amnh site by western paleontology labs of orem, utah, yielded the remains of a partial ankylosaur skeleton with a well-preserved skull in a subsite referred to as bone cabin west. following their donation of the specimen to the dmnh, it was described as gargoyleosaurus parkpinorum (carpenter et al., 1998; kilbourne and carpenter, 2005). bone cabin quarry is the stratigraphically highest site (figure 3) from which diagnostic gargoyleosaurus material has been collected (schmude and weege, 1996) and it is the only site where it co-occurs with allosaurus fragilis (turner and peterson, 1999; foster, 2003). this occurrence supports overlap in the temporal ranges of mymoorapelta and gargoyleosaurus. boris quarry a water-worn ankylosaur braincase at the university of wyoming, specimen uw 21869 was recovered during the excavation of an apatosaurus femur at the “boris” locality, specimen uw v-93101, near sheep creek in south-central wyoming by robert t. bakker and volunteers on a dinamation international society dig in july of 1993. bakker’s field notes indicate that stratigraphically, the locality is situated about 19 m below the base of the dakota formation (muddy formation) in smectitic mudstone well above the regional calcrete marking the “clay change” in the upper morrison formation of this region. this site was referred to as the mummy quarry in kirkland et al. (1998). the specimen includes the braincase and skull roof overlying it. abrasion on the margins of the fossil suggests wear during transport prior to burial in the bone lag accumulation represented by the “boris” locality at sheep creek as interpreted by bakker (field interpretation on file at the university of wyoming geological museum). the proportions of the basicranium and its stratigraphic position suggest this specimen represents an example of mymoorapelta from wyoming. meilyn quarry excavations in the 1990s at the meilyn quarry northwest of medicine bow in southern wyoming (figures 1 and 3) undertaken by western paleontology labs has yielded two caudal vertebrae and three caudal plates. the meilyn quarry is situated 7 m above the base of the morrison formation (schmude and weege, 1996) even farther to the southwest than the boris quarry along the west flank of the medicine bow anticline. these interesting specimens were sold to private collectors with the caudal plates going to one unknown collector and a medial caudal vertebra going to another unknown collector (jason cooper, dinosaurs of america llc., verbal communication, 2000). one proximal caudal vertebra has been curated into the collections of the elizabeth dee shaw stewart museum of paleontology at the george s. eccles dinosaur park, ogden, utah. although we have been able to view photographs of the specimens in private hands, access to future researchers is not likely. perhaps future excavations at the meilyn quarry will yield additional material. zane quarry kirkland et al. (1998) reported on a partial mid-caudal vertebra collected by robert t. bakker from the zane quarry near the base of the morrison formation near sheep creek in south-central wyoming and reported as curated at the tate museum, casper college, casper, wyoming. turner and peterson (1999) record several sites at the zane quarries as wy-92, but no known records exist as to their specific location, but they may be near the boris quarry. the low stratigraphic occurrence of this locality suggests that it may be nearly correlative with the meilyn quarry. following up with the tate museum, it was revealed that no specimen had ever been curated into their collections from the zane quarry. simon quarry the most recently discovered ankylosaur material 320 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 3. relative stratigraphic position of gargoyleosaurus localities in southern wyoming. red star is holotype gargoyleosaurus parkpinorum locality at bone cabin quarry. blue star is the oldest morrison ankylosaur in meilyn quarry. modified after schmude and weege (1996). 321 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 in wyoming is from the bob simon’s red ranch quarries about 20 to 30 m above the base of the morrison formation on the northeast side of the big horn basin (maidment et al., 2015). specimen dmnh 58831 consists of a complete sacrum with right ilium and the right second cervical half ring. carpenter et al. (2013) assigned this specimen to gargoyleosaurus parkpinorum based on its similar cervical half ring, the differences in the stratigraphic level of the simon and bone cabin quarries could bring the specific identification of the simon quarry specimen as gargoyleosaurus parkpinorum into question. however, as discussed below, given the great disparity in the characters of the sacrum and ilium of this specimen and mymoorapelta, we agree that it is most parsimonious to assign this specimen to the genus gargoyleosaurus based on the similarities of the cervical ring. utah localities movie valley ankylosaur during the 1970s, jim jensen of byu excavated several associated dorsal vertebrae and rib fragments from a site in the southern part of little valley near the cat ballou movie set west of arches national park. although the original site has not been relocated, it is assumed the fossils are from the brushy basin member, as much of the valley is formed by erosion of these strata and the preservation of the bone suggests that the fossils were collected from the morrison formation. these fossils compare well with those of mymoorapelta, but as they are not in themselves diagnostic and the stratigraphic position of the site has been in question, they can only be questionably referred to as mymoorapelta. recently, matt wedel (western university of health sciences) found a bone and wood scatter in the medial part of the brushy basin, which includes a diagnostic ankylosaur rib section near the south end of this valley that may pertain to the specimen. subsequent exploration resulted in more ankylosaur fragments and the specific identification of wedel’s site. because we are unable to prove that this is the original movie valley ankylosaur site, the specimen has been assigned its own locality number within the state of utah’s paleontological locality database (matt’s ankylosaur in the woods gr1381v [see gr335v: movie valley ankylosaur]). los angeles county museum sacrum while conducting excavations at a dinosaur site (lacm locality 7683) in the medial brushy basin member near blanding in southwestern utah, the los angeles county museum (lacm) uncovered an ankylosaur sacrum. it has been identified as mymoorapelta based primarily on the presence of a groove along the ventral surface of the sacral centra as in the material assigned to the holotype individual. additionally, this specimen lacks a fused series of dorsal vertebrae to form a synsacrum. hanksville-burpee ankylosaur in june of 2014, kirkland was asked to examine ankylosaur material being uncovered by the burpee museum in a huge dinosaur site in the brushy basin member northeast of hanksville, utah. numerous dorsal osteoderms and several ribs were collected from what may be an associated ankylosaur specimen. additional material is still being recovered from the locality and under study at the burpee museum. initially the fossils were attributed to mymoorapelta (tremaine et al., 2015). subsequently, large (2023) proposed that these fossils pertain to gargoyleosaurus on the basis of sharing a lateral depression on the lateral side of the dorsal osteoderms. new mexico locality a single keeled ankylosaur osteoderm has been curated into the collections of the new mexico museum of natural history and science (nmmnh). specimen nmmnh p-58749 was collected from the peterson quarry in west-central new mexico, 26 m below the top of brushy basin member (heckert et al., 2003; burns and lucas, 2015). it was hypothesized as being closer to mymoorapelta as the base of the osteoderm was only shallowly excavated. however, its external surface is smooth without the fine vascular pits and grooves characteristic of mymoorapelta, although morphologi322 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 cally, it appears to be more similar to gargoyleosaurus in superficial appearance. given such limited material, we agree that ankylosauria indeterminant is a suitable taxonomic identification. materials and methods all of the ankylosaur materials discussed within were examined first hand by the senior author with the assistance of several of the coauthors. all of the ankylosaur fossils from the mygatt-moore quarry up through the end of the 2025 field season were photographed and described first hand by the senior author with measurements made using calipers. all other photographs were also made by the senior author during his research except those of ankylosaur sacrum from southeastern utah, which were provided by luis chiappe at the dinosaur institute at the lacm. no attempt was made to undertake a phylogenetic analysis as the senior author thinks the construction of a completely new character matrix would be essential in properly establishing an up-to-date phylogeny of the ankylosauria and is beyond the scope of this review. thus, only a differential diagnosis was performed in the description the jurassic ankylosaurid fossils presented herein. terminology we employed the monophyletic clade polacanthidae of carpenter (2001) to facilitate comparison with and discussion of a number of similar taxa (gargoyleosaurus, mymoorapelta, hylaeosaurus, polacanthus, horshamosaurus, hoplitosaurus, and gastonia). the analysis of polacanthids as a monophylogenetic subfamily of nodosaurids was by yang et al. (2013), who similarly defined them as the most inclusive clade containing polacanthus foxii but not ankylosaurus magniventrisor and panoplosaurus mirus. while in the phylogenetic analysis of the thyreophoria, raven (2021) and raven et al. (2023) recovered a clade identified as polacanthidae. however, they never formally described it, excluded gargoyleosaurus, and included several taxa, that we would not include within the polacanthidae; as such, their definition will not be considered further here. osteoderm is used in reference to nearly all dermal elements of the fossils described herein, along with the term ossicle for simple ovoid dermal bones of approximately 1 cm or less in diameter following burns (2015). cervical half rings may be fused or unfused and for jurassic polacanthids consist of one to two dorsal osteoderms and laterally a solid spine. dorsal armor is ventrally flat to moderately concave with larger crested, subrectangularto teardrop-shaped elements interpreted to be situated anteriorly; smaller, more posterior dorsal osteoderms are more circular with a low crest or low apical prominence. the larger osteoderms in the sacral region are also round with low apical prominences surrounded by fused ossicles. simple elongate crested osteoderms are considered to be situated on the legs or along the tail and/or on the lateral margins of the body posterior to the posteriorly grooved shoulder spines and anterior to the sacral-caudal plates. the bases of the grooved shoulder spines and sacral-caudal plates are deeply excavated with medial vascular openings a few mm in diameter (kirkland et al., 1998). the caudal plates appear to be of taxonomic utility (kirkland et al., 2016; morgan et al., 2016) and readily distinguish mymoorapelta and gargoyleosaurus (figure 4). we use the term caudal rib instead of the misused term caudal transverse process. institutional abbreviations we employ the following institutional abbreviations: amnh, american museum of natural history, new york, new york; byu/ byu vp, museum of paleontology, brigham young university, provo, utah; ceum, prehistoric museum, utah state university eastern, price, utah; dmnh, denver museum of nature and science, denver, colorado; edp-sm, elizabeth dee shaw stewart museum of paleontology at the eccles dinosaur park, ogden, utah; fcptd/ map, fundación conjunto paleontológico de teruel-dinópolis/museo aragonés de paleontología, teruel, spain; ivpp, institute of vertebrate paleontology and paleoanthropology, beijing, china; kuvp, kansas museum of natural history, lawrence, kansas; lacm, natural history museum of los angeles county, los 323 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 angeles, california; mpc, mongolian paleontological center, ulaan baatar, mongolia; mwc, dinosaur journey, museums of western colorado, fruita, colorado; nhmuk, formally bmnh, natural history museum, london, england; nmc, national museum of canada, ottawa, canada; nmw, national museum of wales, cardiff, wales; nova-fct, nova school of sciences and technology, lisbon portugal; qm, queensland museum, queensland, australia; rom, royal ontario museum, toronto, canada; sdnhm, san diego natural history museum, san diego, california; sgds, saint george dinosaur discovery site at johnson farm, st. george, utah; smp, state museum of pennsylvania, harrisburg, pennsylvania; smu, schuler museum, southern methodist university, dallas, texas; usnm, national museum of natural history, smithsonian institution, washington, d.c. systematic paleontology dinosauria owen, 1842 ornithischia seeley, 1887 thyreophora nopcsa, 1915 ankylosauria osborn, 1923 (undefined, p. 3) polacanthidae haekel, 1910 diagnosis: the most inclusive clade containing polacanthus foxii but not ankylosaurus magniventris or panoplosaurus mirus (yang et al., 2013). gargoyleosaurus carpenter et al., 1998 diagnosis: as for species. gargoyleosaurus parkpinorum carpenter et al., 1998 (modified carpenter, 2001) figure 4. comparison of north american and european polacanthid ankylosaur proximal caudal plates. from kirkland et al. (2016) and morgan et al. (2016). 324 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 diagnosis: differs from all other polacanthid ankylosaurs except mymoorapelta in the possession of premaxillary teeth. differs from mymoorapelta in having a relatively narrower basicranium with smaller basitubera, in possessing a ventrally keeled sacrum, more elongate vertebral centra, possessing more fully excavated dorsal osteoderms, and in having more expansive, less reclined caudal osteoderms. type locality: bone cabin quarry west; 33 m west of original amnh bone cabin quarry. this locality was mistakenly described as being in the lower part of the morrison formation in strata equivalent to the salt wash member on the colorado plateau by turner and peterson (1999). they report the site as being east of the main bone cabin quarry, when it is actually to the west. this important locality is stratigraphically high (figures 1 and 3) in the morrison (schmude and weege, 1996; kelly trujillo, univeristy of wyoming, written communication, 2018) in strata equivalent to the brushy basin member on the colorado plateau. type material: specimen dmnh 27726, a partial, articulated skeleton preserving a nearly complete skull (minus articular ends of both quadrates, left jugal, left quadratojugal and most of right, posterior portion of left maxilla, and posterior palate), right mandible, proatlas, first three cervical vertebrae, six caudal vertebrae, fragmentary cervical, and dorsal ribs, fragments of several ossified tendons, partial right scapula and coracoid, partial right humerus, partial pubis, right femur, and an abundance of dermal armor including left and right first cervical half rings, left second cervical half ring, two grooved lateral shoulder spines, caudal plates, and fused sacral shield fragments. referred specimen: specimen dmnh 58831, a partial pelvis and cervical ring were described from the simon quarry in the lower morrison formation of the northwestern bighorn basin in northern wyoming (carpenter et al., 2013). the similarities of the cervical ring with that from the holotype specimen were used for the specific identification. the somewhat larger cervical ring from the simon quarry had small ossicles fused to the surface between the larger osteoderms. this was interpreted as being an ontogenetic feature of no taxonomic importance. however, arbour and currie (2013b) have noted that intermediate fused osteoderms in late cretaceous of western north america are of taxonomic significance in the ankylosauridae. therefore, it is probably safer to regard this specimen as gargoyleosaurus sp. cf. g. parkpinorum, given that the fusion of additional ossicles to the cervical half ring may be a specifically significant character, as opposed to being a purely ontogenetic character. gargoyleosaurus sp. a well-preserved, fused scapulocoracoid (byu 72512963) from byu’s dry mesa quarry (figure 1) was described by kirkland et al. (1998) as genus indeterminate. subsequent examination of the caudal plates from the dry mesa quarry reveals that they are most readily comparable in overall morphology to those from the holotype of gargoyleosaurus parkpinorum (figure 4). additional material from this locality includes a reclined, posteriorly grooved shoulder spine. the co-occurrence of allosaurus jimmadseni suggests that it is temporally equivalent to stratigraphic occurrences of allosaurus jimmadseni from the type locality in the salt wash member at dinosaur national monument and in the lower morrison formation of wyoming (chure, 2000; chure and loewen, 2020). excavations at the meilyn quarry northwest of medicine bow in southern wyoming (figures 1 and 3) have yielded two caudal vertebrae and three caudal plates, that were situated about 15 m above the base of the morrison formation (schmude and weege, 1996). these fossils were part of a traveling exhibit put together by western paleontology labs in orem, utah. subsequently, these fossils were sold off piecemeal. the proximal caudal vertebra was curated into the collections of the edp-sm (edpsm 2017.01.096). fortunately, although most of these fossils have been lost to science, photographs of these fossils exist (figure 5). discussion: initially, the senior author assumed that gargoyleosaurus was the same taxon as mymoorapelta. the discovery of additional fossil material (carpenter et al., 325 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 2013; kirkland et al., 2016), made it clear that these genera were distinctly different in a number of important diagnostic characters. specimens assigned to gargoyleosaurus from other localities are all represented by limited fossil material and their assignment to gargoyleosaurus has been based primarily on the comparison of their osteoderms. the presence of more than one species of gargoyleosaurus cannot be disproved with the fossil material at hand. it is therefore possible that gargoyleosaurus parkpinorum is a species from the upper morrison associated with the co-occurrence of allosaurus fragilis and a second species with lower caudal plates and cervical rings ornamented by larger osteoderm elements separated by numerous ossicles occurs in the lower morrison, where it is associated with allosaurus jimmadseni. until additional discoveries are made, it is impossible to test this speculation. mymoorapelta kirkland and carpenter, 1994 diagnosis: as for species. mymoorapelta maysi kirkland and carpenter, 1994 type locality: mwc loc. 2; mygatt-moore quarry. the quarry is about 48.5% up section into the brushy basin member (figure 2) as measured by foster (see trujillo et al., 2014; foster et al., 2018). turner and peterson (1999) place the site at around 42% up section in the brush basin member. one of the most refined radiometric dates from the morrison formation has been published by trujillo et al. (2014) from volcanic ash in the mygatt-moore quarry. it is a urafigure 5. polacanthine ankylosaurs remains from the basal morrison meilyn quarry in southern wyoming. (a) proximal caudal vertebra edp-sm 2017.01.096 in posterior view. (b) posterior view of caudal vertebra in private hands. (c through e) caudal plates reside in private hands. 326 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 nium-lead date of 152.18 ± 0.29 ma from zircons. the main bone level at the mygatt-moore quarry preserves portions of two ankylosaurs (figure 6). a partial abraded sacrum from the basal “pebble” bed represents a third individual since an erosive surface (figure 2a) separates this interval from the overlying bonebed (chin and kirkland, 1998; kirkland et al., 2005; foster et al., 2018). the east pit preserves an associated partial skeleton of the holotype ilium, mwc 1815; individual elements from this skeleton are among the most pristinely preserved skeletal elements in the mygatt-moore quarry. type material: the expanded hypodigm includes a number of skull elements: jugal, specimen mwc 5435; quadrate, mwc 4035; postorbital, mwc 6744; and braincase, mwc 5435; one possible premaxillary tooth, mwc 6740; two cheek teeth, mwc 6741 and 6742; the axis, mwc 1933; one cervical vertebra, mwc 6738; nine dorsal vertebrae, mwc 1800, 1801, 1802, 1803, 3613, 4032, 5940, 6737, and 6739; one sacral centrum, mwc 5104; one caudosacral vertebra, mwc6736; nine isolated caudal vertebra, mwc 1804,1805, 1806, 1807, 1808, 1839a, 1839b, 1907, 1913, 5019, 5104, and 5820; one isolated caudal vertebra with a fused chevron, mwc 1907; two pairs of fused distal caudal vertebrae with fused chevrons, mwc 1818 and 1819; one proximal chevron, mwc 1912; 19 partial ribs, mwc 1810, 1811, 1812, 1840, 1905, 1915, 3568, 3620, 3652, 3747, 3763, 4329, 5013, 5094, 5720, 6729 (three sections), and 6923; one partial scapula, mwc 6743; one humerus, mwc 6745; both ulnae, mwc 1814 and 5638; one radius, mwc 5438; three metacarpals, mwc 10638, 1908, and 1816; one manual phalanx, mwc 3616; one possible manual ungula, mwc 939; one left ilium (original holotype element), mwc 1815; one ischium, figure 6. google earth images of the mygatt-moore quarry area. (a and b) the mygatt-moore quarry at the beginning of the “trail through time” with mygatt-moore quarry map (foster et al., 2018) superimposed. area of the excavation where the holotype was recovered indicated by red oval and that of the larger paratype animals indicated by a yellow oval. (c) overview of northwest side of rabbit valley showing relation of mygatt-moore quarry with colorado exit 2, interstate 70. m&m = mygatt-moore quarry. 327 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 mwc 4027; one partial tibia, mwc 6746; one metatarsal, mwc 4028; two pedal phalanxes, mwc 1932 and 3615; three pedal unguals, mwc 3714, 3752, and 6728; four dorsal cervical ring elements, mwc 1834, 3744, 5320, and 6977; two cervical spines, mwc 1825 and 6752; one shoulder spine, mwc 1818; ten dorsal caudal spines, mwc 1819, 1820, 1821, 1822, 1823, 2678, 2867, 2868, 5148, and 5642; five lateral caudal spines, mwc 1824, 2677, 6747, 4226, and 5479; seven large dorsal scutes, mwc 1835, 1836, 1837, 4018, 4030, 4223, and 6761; two sacral shield fragments, mwc 1838 and 6751; dorsal scutes, mwc 7064 (cut for histological study [burns, 2010], under field # mwc 211), 1023, 1813, 1826, 1827, 1828, 1829, 1830, 1831, 1833, 1834, 1841, 1842, 1843, 1844, 1845, 1852, 1909, 1910, 1911, 1914, 1937, 2737, 3629, 3860, 4022, 4029, 4196, 4228, 4229, 4344, 5016, 5099, 5320, 5479, 5838, 5894, 5920, 5928, 6749, 6752, 6754, 6755, 6756, 6757, 6758, 6759, 6760, 6761, 6762, 6763, 6764, 6765, 6766, 6767, 6768, 6769, 6785, 6786, 6787, 6788, 6789, 6790, 6791, 6793, 6794, 6795, 6796, 6797, 10486, and 10487. referred elements not assigned to the hypodigm: the north pit preserves elements from a skeleton that is significantly larger (about 133%) and more poorly preserved. the referred specimens include four dorsal vertebrae, mwc 5705, 6733, 6734, and 6735; an isolated sacral centrum, mwc 3613; a partial sacrum, mwc 6932; four isolated caudal vertebra, mwc 5705, 6733, 6734, and 6735; and one rib, mwc 5061. an isolated spine may be from a third individual largely because it is a considerable distance from the other skeletal associations. a partial synsacrum, mwc 10347 from the underlying “pebble” bed, represents a separate individual. referred specimens from other sites cactus park ankylosaur, mwc loc. 197: in the early 1990s, denver high school teacher kent hups discovered an ankylosaur skeleton weathering out of a calcite-cemented sandstone ledge in the brushy basin member on the east side of cactus park southwest of grand junction, colorado. the fossil (mwc 2610) is an articulated skeleton lying ventral side down assigned to mymoorapelta (kirkland et al., 1998). the curated fossil material consists of broken sandstone blocks collected from the slope below the ledge and preserve much of the posterior portion of the skeleton. this material consists largely of external molds of the bones and unprepared bones within the sandstone blocks. these described materials include unfused posterior dorsal vertebra with associated ossified tendons, the articulated pelvis with sacrum, portions of the hind limbs including four articulated metatarsals, a mold of a nearly complete sacral shield, and caudal and dorsal armor. the articulated proximal ischium and pubis demonstrates the presence of a long post-public rod extending along the ischium (gaston et al., 2001), and that the spacing of the caudal plates appears to be only about 2 cm apart (kirkland et al., 1998). los angeles county museum sacrum: while conducting excavations at lacm locality 7683 in the medial brushy basin member near blanding in southeastern utah, the lacm uncovered an ankylosaur sacrum. it has been identified as that of mymoorapelta based primarily on a ventral groove like that in the expanded hypodigm material and because it lacks a fused series of dorsal vertebrae. additionally, it is from a nearly correlative stratigraphic position. university of wyoming braincase: a water-worn ankylosaur braincase, uw 21869, was recovered during the excavation of an apatosaurus femur at the “boris” locality uw v-93101 near sheep creek in south-central wyoming by robert t. bakker and volunteers on a dinamation international society dig in july of 1993. stratigraphically, the locality is situated about 19 m below the base of the dakota formation (currently muddy sandstone) in smectitic mudstone, well above the regional calcrete marking the “clay change” in the upper morrison formation of this region. this site was referred to as the mummy quarry in kirkland et al. (1998). the specimen includes the braincase and skull roof overlying it. abrasion on the margins of the fossil suggest wear during transport prior to burial in the bone lag accumulation represented as discussed above. the proportions of the basicranium (table 1) and its strati328 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 graphic position suggest this specimen represents an example of mymoorapelta from wyoming. diagnosis mymoorapelta’s skull differs from that of gargoyleosaurus in having a narrow, rounded head on the quadrate having no indication of fusion with the squamosal or paraoccipital process. mymoorapelta is wider across its more robustly developed basitubera and the robust keel on the ventral side of the basiocciput does not extend as far posteriorly as it does in gargoyleosaurus. buccal teeth are lower crowned than those in gargoyleosaurus. the cervical rings are anterioposteriorly narrow and more massive with the medial pair of osteoderms having keels only extending anteriorly from the apex of osteoderm. sacral vertebrae are wide with a ventral depression, absent in gargoyleosaurus. neural spines of posterior dorsal vertebrae are lined by flattened, spindle-shaped ossified tendons. the preacetabular processes of the ilia flex ventrolaterally to form a vertical, lateral surface that gives the ilia a rectangular appearance in dorsal view. proximal caudal osteoderms (plates) are relatively narrow and reclined posteriorly such that the apex of the plate would overlap the anterior margin of following caudal plate. the dorsal surfaces of the lateral plates are ornamented by faint parallel ridges absent in gargoyleosaurus. description of skull material for comparative descriptive purposes the isolated skull elements in figure 7 are oriented like the skull of its sister taxon gargoyleosaurus (carpenter et al., 1998). postorbital (figures 7d through 7h) the wedge-shaped, right postorbital (mwc 6744) has a vertical break anteriorly behind the orbit along a straight medial to lateral line approximately 3 cm forward of the posterior margin of the postorbital horn. as table 1. measurements of landmarks on north american polacanthid ankylosaur basicrania. mymoorapelta cranial measurements in mm mymoorapelta maysi gargoyleosaurus parkpinorum gastonia burgei gastonia lorriemcwhinnyae cactus park ankylosaur boris braincase dmnh 27726 ceum 1307 dmnh 53000 mwc loc. 197 uw 21869 postorbital cornice mwc 6744 cornice width 55.1 56.8 82.3 cornice length from base to apex 38.7 48.7 40.8 jugal cornice mwc 2843 anterioposterior length below orbit 40.1 39.1 46.6 cornice length orbit to apex 42.3 45.3 43.3 quadrate mwc 4035 length 106.1 width of mandibular condyles 28.3 22.8 30.8 width of squamosal condyle 19.6 braincase mwc 5435 width occipital condyle 46.8 53.5 55.3 45.4 52.5 90.9 height occipital condyle below foramen magnum 27.4 24.2 22.1 21.4 26.3 73.3 width foramen magnum 25.3 26.5 28.7 24.7 24.8 71 height foramen magnum 27.0 22.2 26.0 23.2 68.1 width across basitubera 57.7 46.6 60.1 52.65 48.2 97.3 midline length of ventral braincase 72.7 81.2 83.1 83 79.4 114.8 total length with basipterygoids 78.3 86.1 109.2 97.1 86.7 329 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 preserved, the shape of the well-vascularized, postorbital horn is nearly identical in size and shape with that of gargoyleosaurus (carpenter et al., 1998; kilbourne and carpenter, 2005) and compares well with that of gastonia (kirkland, 1998) in that it is pyramidal in shape. kilbourne and carpenter (2005) report that the postorbital horn extends onto the squamosal, but on the isolated postorbital of mymoorapelta, this is not the case and indicates that the squamosal is more posterior and medial in both skulls, in keeping with the position of the nearly horizontally directed proximal end of the quadrates anteriorly to the paroccipital processes in gargoyleosaurus (figure 8). the horizontal dorsal surface forms one face with the posterior face inclined figure 7. skull material from revised hypodigm of mymoorapelta. partial braincase specimen mwc 5435 in (a) caudal, (b) ventral, and (c) right lateral views. right postorbital mwc 6744 in (d) dorsal, (e) rostral, (f) lateral, (g) medial, and (h) caudal views. left quadrate mwc 4035 in (i) lateral, (j) rostral, (k) caudal, and (l) medial views. left jugal mwc 2843 in (m) rostral, (n) caudal, (o) dorsal, (p) medial, and (q) ventral views. sketch of gargoyleosaurus skull with skull elements known from holotype of mymoorapelta in pink in (r) caudal, (s) ventral, and (t) dorsal views. abbreviations: bo = basioccipital, bpp = basipterygoid process, bt = basitubera, mc = mandibular condyle, o = position of orbit, oc = occipital condyle, p = paraoccipital process, po posterior surface of the orbit, qs = qudratojugal suture, sc = squamosal condyle, v = fifth cranial nerves. 330 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 anteriorly and the lateral face inclined medially. the bone extends medially between the squamosal and perhaps the parietal. below this and extending laterally is a rostrally convex sheet of bone separating the posterior surface of the orbit from the lower temporal opening posteriorly. unfortunately, the total ventral extent of this postocular septum cannot be determined as the thin ventral margin is broken away, but it extends ventrally as much as 8 mm as preserved. a sutural contact with the jugal is visible on the postorbital below the horn on the lateral side indicating the postorbital makes up entire posterior margin of the orbit. posterior-medially to the horn, a shallow fossa is visible about 2 cm across with a laterally directed vascular opening. a second ventrally directed vascular opening enters the bone just lateral to the fossa and medial to the postorbital horn. a figure 8. skulls gargoyleosaurus and gastonia. gargoyleosaurus parkpinorum holotype skull dmnh 27726 in (a) ventral, (b) right lateral, (c) posterior, and (d) dorsal views. gastonia burgei ceum 1307 in (e) ventral, (f) left lateral, (g) posterior, and (h) dorsal views. abbreviations: bo = basioccipital, bpp = basipterygoid process, bs = basisphenoid, bt = basitubera, fm = foramen magnum, ipf = interpterygoid fossa, j = jugal, m = maxilla, n = narial opening, nc = nuchal caputegulae, oc = occipital condyle, p = paraoccipital process, pm = premaxilla, pmt = premaxillary tooth, po = postorbital, pso = parietal “spider” ornament, pt = pterygoid, q = quadrate, so = supraocccipital, v = vomer. 331 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 third dorsally directed vascular opening enters the bone about 1 cm ventrally at the medial margin of the horn. jugal (figures 7m through 7q) the left jugal (mwc 2843) is well preserved. it makes up the ventral margin of the orbit, and unlike most ankylosaurs (vickaryous, 2001; vickaryous et al., 2001, 2004) the triangular suborbital horn is formed exclusively by the jugal as in gargoyleosaurus (carpenter et al., 1998) and gastonia (kirkland, 1998). kilbourne and carpenter (2005) describe the only preserved jugal in gargoyleosaurus as pathologic (figure 8b), but this right jugal is a mirror image of the left jugal of mymoorapelta, suggesting that the gargoyleosaurus jugal is not pathologic. as with gargoyleosaurus, the well-vascularized jugal horn extends ventrally and recurves to an apex ventrolaterally. unlike most other ankylosaurs, except gargoyleosaurus (carpenter et al., 1998; kilbourne and carpenter, 2005) and gastonia (kirkland, 1998), there is no sign that the buccal emargination of the maxilla extended up onto the lateral margin of the jugal. medial to and below the broken inner margin of the orbit, there is a large depression into much of the base of the jugal horn as in gargoyleosaurus. posterior to the ventral surface of the orbit, there is an irregular sutural surface for the postorbital in the same position as in gargoyleosaurus (kilbourne and carpenter, 2005). the sutural surface for the quadratojugal extends ventrally along the posterior margin of the medial depression. the quadratojugals in gastonia, gargoyleosaurus, and mymoorapelta would appear to be small mediolaterally directed bones between the jugals and quadrates based on this interpretation, whereas these are situated posterior to the jugal primitively as in scelidosaurus (norman, 2020a) and in most other ankylosaurs (vickaryous et al., 2004). the quadratojugals do not support any of the suborbital horn as in other ankylosaurs (vickaryous et al., 2004). superficially it appears that the suborbital horn resides solely on the jugal in the basal nodosaurid pawpawsaurus (lee, 1996), but in that taxon, the suborbital horn is also supported by the quadratojugal ventrally. close examination of the jugal and quadrate of mymoorapelta reveals that, in contrast to most other ankylosaur skulls (vickaryous et al., 2004), the quadratojugal is situated medially to the jugal as in gargoyleosaurus and gastonia (kirkland, 1998; kilbourne and carpenter, 2005). this is also the case in the nodosaurid texasites (=pawpawsaurus) (lee, 1996). quadrate (figures 7i through 7l) the isolated left quadrate (mwc 4035) is well preserved. it is anteriorly arched as in many ankylosaurs and as in both gargoyleosaurus and gastonia (figure 9a), the slender dorsal ramus would have been directed nearly horizontally. the articular surface for expanded mandibular condyles is well developed and proportionally more massive than in gastonia. it is ovoid in shape and is deeper medially, reflecting the anterioposterorly elongate medial mandibular condyle, which is separated from the low lateral mandibular condyle by a broad but shallow intercondylar groove. a deeply recessed suture for the quadratojugal extends dorsally up the lateral side from the mandibular condyles for 3 cm, much like gastonia and is unknown in gargoyleosaurus. a thin and triangular pterygoid process extends medially from the quadrate shaft at this point as opposed to the more dorsally situated subrectangular pterygoid process in cedarpelta (carpenter, 2001). immediately posterior to the quadratojugal suture, a distinct groove is present as reported in gargoyleosaurus and many other dinosaurs (kilbourne and carpenter, 2005). the distinct, rounded head forming the dorsal end of the ramus would articulate with the articular surface of the squamosal and the distal end of the paroccipital process as in cedarpelta (carpenter et al., 2001) and unlike the apparently expanded sutural contact in gargoyleosaurus (kilbourne and carpenter, 2005). in lateral view, the ramus is thicker anteroposteriorly than in either gargoyleosaurus or gastonia. braincase (figures 7a through 7c, 9, and 10) an undistorted braincase (mwc 5435) was recovered from a spoils bucket by the sharp eyes of rodney scheetz (byu), who recovered additional fragments. it consists of the lower portion and right side of the braincase with the paroccipital process broken off at its neck. the absence of 332 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 the left side permitted the inside of the braincase to be prepared such that the entrance and exit points of the cranial nerve are readily observable. the endocranial impression extends forward to the position of the pituitary fossa at the posterior margin of the parasphenoid. the sutures between individual elements of the braincase are almost completely fused and their relative position and extent are best determined by comparison of the strikingly similar braincases of gargoyleosaurus (carpenter et al., 1998; kilbourne and carpenter, 2005) (figures 8a through 8d) and gastonia (kirkland, 1998) (figures 8e through 8g). the supraocciptal is broken vertically just to the left of the midline. its suture with the exocciptal is completely obscured by fusion so the extent to which it makes up figure 10. additional stereo views of the braincase mwc 5435 of mymoorapelta in (a) caudal, (b) rostral, (c) ventral, and (d) dorsal views. abbreviations: bo = basioccipital, bpp = basipterygoid process, bs = basisphenoid, bt = basitubera, j = jugular, oc = occipital condyle, p = paraoccipital process, po = post ocular shelf, r = ridge on basicranium, so = suproccipital, vc = vesicular canal, and iii, v, ix, x, xi, xii = cranial nerves. figure 9. stereo views of the braincase mwc 5435 of mymoorapelta in (a) lateral, (b) medial, and (c) dorso-medial views. abbreviations: ar = auditory recess, bo = basioccipital, bpp = basipterygoid process, bs = basisphenoid, bt = basitubera, j = jugular, oc = occipital condyle, po = paraoccipital process, and iii, iv, v, vi, vii, vii, ix, x, xi, xii = cranial nerves. 333 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 the dorsal margin of the foramen magnum is unknown. dorsally, it is broken off just below the nuchal shelf of the parietal. below this break, a shallow, horizontally oriented depression extends across the midline into a deep pit unlike the shallow depressions on either side of the nuchal crest, as observed in many other ankylosaurs such as the nodosaurids pawpawsaurus (lee, 1996), animantarx (carpenter and kirkland, 1998), and sauropelta. about 1.5 cm laterally above the base of the paroccipital process, a small post-temporal foramen (lee, 1996) enters the bone and angles medially before exiting on the upper surface of the braincase above the area of the opisthotic. a horizontal flexure below the nuchal shelf due to crushing may be obscuring this area in gargoyleosaurus. the post-temporal foramen is also well expressed in gastonia (kirkland, 1998) and pawpawsaurus (lee, 1996). unlike many ankylosaurs (vickaryous et al., 2004), no nuchal or medial crest is developed above the foramen magnum. the supraoccipital is dorsoventrally expanded and divided at the midline above the foramen magnum in gargoyleosaurus (carpenter et al., 1998; kilbourne and carpenter, 2005) reflecting the fusion of the proatlas to the supraoccipital as in animantarx, whereas it is smooth across this area as in gastonia (kirkland, 1998). although the supraoccipital is nearly vertical below the nuchal shelf in gastonia, it slopes caudoventrally in mymoorapelta and gargoyleosaurus. the foramen magnum is circular and angled caudoventrally (figures 9 and 10). the occipital condyle is wide transversely and extends ventrally below the foramen magnum in the form of a broad lip as described for the braincase of polacanthus (norman and faiers, 1996). it is posteriorly more flattened than that of gargoyleosaurus (figure 8d) and not as medially depressed on its ventral surface to suggest two low condyles as in gastonia (figure 8e). its strong ventral inclination suggests that mymoorapelta’s cranium was angled down from the horizontal. the right exoccipital is broken such that only the proximal portion of the paroccipital process is preserved and the left paroccipital process is broken off through cranial nerve openings ix-xii. the exoccipital makes up the lateral margin of the foramen magnum and a portion of the lateral margin of the occipital condyle as it does in gargoyleosaurus (carpenter et al., 1998; kilbourne and carpenter, 2005), gastonia (kirkland, 1998), and many ankylosaurids (vickaryous et al., 2004). ventrally at the base of the paroccipital process (figure 11c), the foramen for cranial nerves xii-ix forms a nearly equilateral triangle, whereas they are linearly arranged in the braincase tentatively assigned to polacanthus by norman and faiers (1996) and are intermediate in configuration in gastonia (kirkland, 1998). unfortunately, the braincase in gargoyleosaurus was crushed and sheared such that the cranial nerve openings have all been obscured (k. carpenter, museum of natural history, university of colorado, personal communication, 2025). anteriorly, the foramen for the combined passage of cranial nerves xi-ix and the jugular vein is separated from the auditory recess by a narrower strut of bone than it is in polacanthus (norman and faires, 1996). additionally, in lateral view, a line drawn through this cranial nerve opening extending anteriorly through the cranial nerve openings for vii and v angles upward at about 40˚ relative to the plane formed by the occipital condyle and the basitubera as in silvisaurus (eaton, 1960), whereas this line is nearly parallel with the base of the braincase in gastonia (kinneer et al., 2016), polacanthus (norman and faires, 1996), pawpawsaurus (lee, 1996), sauropelta (parson and parson, 2009), bessektipelta (parish and barrett, 2004), saichania (maryańska, 1977), and euoplocephalus (coombs, 1978a; vickaryous, 2001). the ventral surface of the braincase between the occipital condyle and the basitubera is constricted with a weak keel originating in its middle and strengthening anteriorly to a rugose crest between the basitubera. this keel is better developed and extends posteriorly to the base of the occipital condyle in gargoyleosaurus and is absent in gastonia and polacanthus, which are depressed between the basitubera. the basitubera are more widely spaced than in gargoyleosaurus (figure 8) and are large as in gastonia (figure 9) but are more rugose with a well-developed rugose depression in their anteriolateral margins unlike other ankylosaurs. the pterygoid processes are well developed (figures 7b and 10) diverging anteriolaterally and end in expanded pads 334 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 indicating they could freely articulate with the pterygoids as in gastonia and gobisaurus (vickaryous et al., 2001). as preserved, there is no indication that elongate pterogoid processes were present in gargoyleosaurus (figure 8a). the pterygoid processes of mymoorapelta are much shorter than those in gastonia (figure 9) and are proportionally more divergent, suggesting that mymoorapelta had a wide and anterioposteriorly shorter interpterygoid fossa. there is no visible parasphenoid rostrum unlike the condition in sauropelta, peloroplites, and cedarpelta (carpenter et al., 2008). in general proportions, the holotype braincase is similar to the boris quarry braincase (figure 11), although it represents a larger individual (table 1) comparable to the larger mymoorapelta vertebral material described below. uw 21869 is a water-worn skull composed of a braincase and posterior skull roof. it was buried with the anterior broken surface down such that the figure 11. boris quarry at sheep creek ankylosaur braincase uw 21869 in (a) caudal, (b) rostral, (c) right lateral, (d) ventral, (e) dorsal, and (f) left lateral views. abbreviations: ar = auditory recess, bo = basioccipital, bs = basisphenoid, bt = basitubera, fm = foramen magnum, j = jugular, ltf = lower temporal fossa, oc = occipital condyle, p = paraoccipital process, po = post ocular shelf, r = ridge on basicranium, vid = vidian canal, and i, ii, iii, iv, v, vi, vii, ix, x, xi, xii = cranial nerves. 335 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 “high” points of the skull, such as the posterior surface of the occipital condyle, the supraoccipital and the posteriorly projecting lateral margins of the nuchal shelf were worn flat. the left paraoccipital process is completely broken away and the ventrolaterally directed right paraoccipital process is broken at the medial constriction as in the holotype braincase (figures 11a, 11b, and 11d). the skull roof is truncated near the posterior margin of the left orbit extending medially to midline before angling posteriorly to the right posterior corner of skull. both postorbital horns are mostly broken away. in anterior view, only the left postocular shelf is largely undamaged, the front of braincase is open at the constriction between the brain and the olfactory bulb, and the basicranium is broken at the basipterygoid processes. the basicranium was broken away perhaps in preparation along a line formed by the cranial nerve openings and then subsequently repaired. uw 21869 compares well with the holotype braincase of mymoorapelta (mwc 5435). as in the type specimen, in lateral view, a line drawn through the openings for cranial nerve xii extending anteriorly through the cranial nerve openings for vii and v angles upward at about 40˚ relative to the plane formed by the occipital condyle and the basitubera. it differs from gargoyleosaurus and is more like mymoorapelta in its proportionally wider basicranium with larger and more rugose basitubera and a ventral midline ridge does not extend as far posteriorly. not known in the type material of mymoorapelta, the ornamentation of the posterior skull roof is similar to that of gargoyleosaurus except it is not so sharply defined. as in both gargoyleosaurus and gastonia, the parietal ornamentation is centered on a small, raised area near the center of the parietal about the size of the occipital condyle with transverse ridges less than 1 cm wide leading away from it, in a pattern reminiscent of a crab or spider. although damaged, the nuchal shelf appears to be considerably dorsoventrally thicker with a squamosal that extends laterally farther beyond it than in gargoyleosaurus. because uw 21869 lacks quadrates to obscure the ventral side of the skull roof on either side of the braincase, the postocular shelf clearly divides the vaulted chamber formed by the closure of the supratemporal opening to form the large supratemporal fossa above the recessed lower temporal opening (figures 11b and 11d). as initially recovered, the braincase of the fragmented cactus park mymoorapelta skull (mwc 2610), although still coated in matrix, was largely intact (figure 12a). the overall skull beneath the matrix revealed that it compared well with other polacanthines such as gastonia (figures 12a through 12d). the skull roof is less vaulted than in gastonia and appears to be similar to gargoyleosaurus in lateral profile (figure 12d). preliminary preparation has revealed the basic proportion of the cactus park braincase (figures 12g through 12i, table 1) are similar to those of mymoorapelta. however, the basicrania appears to be narrower and although of similar length the anterior ends of the pterygoid processes are not expanded (figure 12h). the parocciptal process is not preserved on any other braincases assigned to mymoorapelta and appears to be more laterally expanded than in either gargoyleosaurus or gastonia (figure 8). the mandibular condyles of the left quadrate are exposed (figure 12i) and are notable wider (table 1) than in the quadrate preserved at the mygatt-moore quarry (mwc 4035). future preparation and analysis of ct data will hopefully reveal more of this important specimen. description of teeth three isolated teeth are assigned to the holotype of mymoorapelta (figures 13a through 13i). all three have anterioposteriorly expanded crowns with a cylindrical, somewhat barrel-shaped root constricted below the crown. additionally, no secondary ridges extend down the faces of the crown from the denticles as in many stegosaurs, nodosaurids, and ankylosaurids (blows and honeysett, 2014a). two teeth are from the buccal region of either the dentary or maxilla based on their low crown height. the best preserved of these teeth (mwc 6741) has a somewhat damaged crown (figures 13e through 13h). the total tooth height preserved with root is 18.0 mm. following the orientation of the teeth of gargoyleosaurus (kilbourne and carpenter, 2005), the lingual margin of the tooth is swollen but does not quite form a cingulum. its crown is 6.7 mm 336 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 long, 4.0 mm wide, and a minimum of 4.8 mm tall as the apex of the crown is damaged. eight denticles are preserved on what is interpreted as the anterior carina with space for as many as ten. a transversely oriented, sloping wear facet has removed all the preserved denticles on the posterior carina of the tooth except for the two at the base of the crown. the second example of this tooth form (mwc 6742) is significantly smaller with a minimum root height of 14.0 mm (figures 13e through 13h). its crown is more damaged and no denticles are figure 12. cactus park skull mwc 2610. (a) kent hups comparing cactus park skull within sandstone block with gastonia cast skull. (b through e) cactus park skull at denver museum of nature and science preparation lab in (b) dorsal, (c) posterior, (d) lateral, and (e) left dentary views. (f) cactus park skull fragments being ct scanned following return to museum of western colorado. (g through i) braincase following initial preparation in (g) posterior view, (h) basicranium in ventral view, and (i) ventral view. abbreviations: bo = basioccipital, bp = basipterygoid process, bs = basisphenoid, bt = basitubera, fm = foramen magnum, oc = occipital condyle, p = paraoccipital process, q = quadrate, r = ridge on basicranium, so = superaoccipital. figures 12a through 12e courtesy of harley armstrong, retired, bureau of land management. 337 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 preserved; it is a minimum of 4.5 mm long. one well-preserved tooth (mwc 6740) kept little of the root (figures 13a through 13d). by comparison to gargoyleosaurus (kilbourne and carpenter, 2005), this larger, taller, and more asymmetric crown suggests that it represents a premaxillary tooth. the crown is 5.3 mm long, 4.0 mm wide, and 7.8 mm tall. no cingulum is present, although the lateral side of tooth is thicker, as in gargoyleosaurus. there are seven denticles preserved on the anterior carina below the apex with six slightly worn denticles preserved on the posterior carina below apex. the denticles decrease in size apically. the medial side of the tooth is finely wrinkled with an apically directed groove toward the anterior and posterior margins of the crown setting off the carina from the central portion of the tooth. the teeth of stegosaurs, nodosaurids, and ankylosaurids possess fewer denticles and welldeveloped cingulae (coombs, 1990; galton and upchurch, 2004; blows and honeysett, 2014a). the teeth of the jurassic ankylosaurs scelidosaurus, sarcolestes, and priodontognathus are higher crowned with well-developed cingulae (galton, 1983a, 1983b; blows and honeysett, 2014a; norman, 2020a). teeth from the valanginian and barremian (early cretaceous) of southern england tentatively assigned to hylaeosaurus and polacanthus, respectively, are higher crowned with fewer denticles (blows and honeysett, 2014a). the teeth appear to be proportionally lower crowned and have one to two more denticles than those of gargoyleosaurus (kilbourne and carpenter, 2005) (figures 13j and 13k). overall, the buccal teeth compare best with those of gastonia (figure 8l) in the lateral profile of the crown and the number of denticles (kirkland, 1998; blows and honeysett, 2014a). description of axial skeleton there are numerous vertebrae from throughout the skeleton assigned to the expanded hypodigm of mymoorapelta and several larger and more poorly preserved vertebrae from a larger referred specimen (table 2). the vertebral column of ankylosaurs has not been described as a complete unit by previous authors except for a few papers on ankylosaurids (carpenter, 2004; carpenter et al., 2011). particular attention has been made relative to the function of the tail club of the ankylosauridae (arbour 2009; arbour and currie, 2013a). descriptions for other less derived taxa are generally restricted to discussing isolated vertebra and/or select representative vertebra from various points along the vertebral column. cervical vertebrae it has been observed that all vertebrae in mymoorapelta from at least the anterior cervical vertebrae to the figure 13. teeth from revised hypodigm of mymoorapelta. premaxillary tooth mwc 6740 in (a) rostral, (b) medial, (c) caudal, and (d) lateral views. maxillary tooth mwc 6741 in (e) rostral, (f) medial, (g) caudal, and (h) lateral views. mwc 6742 in (i) lateral view. typical tooth from gargoyleosaurus parkpinorum holotype skull dmnh 27726 in (j) medial and (k) lateral views. tooth ceum 5145 from within gastonia burgei holotype skull in (l) lateral view. 338 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 table 2. vertebral measurements of mymoorapelta material from the mygatt-moore quarry (measurements in mm). anterior centrum poserior centrum centrum neural canal total width height width height length width height height (from neural canal) length from neural spine cervical vertebrae mwc 1933 axis 48.1 22.2 55.2 25.7 21.2 mwc 6738 anterior cervical 48.3 36.8 47.52 37.8 35.1 22.6 21.5 89.7 33.3 32.2 mwc 6737 posterior cervical 52.6 38.9 48.9 41.3 37 21.1 16.2 96.1 39.4 61.5 dorsal vertebrae mwc 1800 1st dorsal 48.5 49 37.7 43.5 16.8 19.4 69.4 mwc 5705 anterior dorsal 56.3 51.9 47.4 52.7 14.8 24.2 mwc 1802 medial dorsal 45.4 47.5 42.5 49.1 52.6 14.5 19.1 mwc 1801 medial dorsal 38 46.2 42.3 44.7 52.6 15.4 18.2 mwc 1803 posterior dorsal 46.4 38.1 45.4 57.9 14 26.7 mwc 6734 large dorsal referred specimen 51.9 46.9 47.1 53.2 60.9 17.9 25.4 mwc 6733 large dorsal referred specimen 60.1 57.2 68.9 16.6 17.3 mwc 6735 large dorsal referred specimen 54.2 52.5 72.9 16 17.6 large dorsal referred specimen mwc 5940 large dorsal referred specimen sacral centra mwc 6932 large 56.5 29 mwc 3616 large sacrocaudal 51.8 59.4 67.3 mwc 6736 ? caudosacral 52.4 14 14.5 mwc 5104 small sacrocaudal caudal vertebrae mwc 5070 large proximal caudal referred specimen 67.1 68.1 69.7 70.8 60 18.9 18.7 mwc 1804 first caudal 56.5 56.4 54 53.7 13.9 12.8 mwc 1806 second caudal 58.8 44.9 57.6 50.7 42.4 10.9 13.2 122.7 60.9 115.1 mwc 1805 third caudal 58.9 44.8 60.1 49.2 43.3 12.6 13.8 122.1 58.4 118.5 mwc 4036 large medial caudal referred specimen 64.3 63.7 67.3 61.1 54.3 15.7 16.2 mwc 3651 large medial caudal referred specimen 57 55.2 57.4 58.1 57.3 12.1 15.6 large medial caudal referred specimen mwc 6732 large medial caudal referred specimen 58.3 50.7 59.7 55.2 51.3 9.2 12.1 mwc 1807 medial caudal 45.5 39.7 46.1 39.9 44.4 7.2 9.3 94.6 42.5 63.1 mwc 6739 medial caudal 40.5 43.9 mwc 1913 posterior medial caudal 42 36.8 38.2 34.4 49.7 7.2 6.7 67.9 24 42.1 mwc 1907 posterior medial caudal 39.4 33.1 42.6 47 8.4 posterior medial caudal mwc 5830 large distal caudal referred specimen 33.3 61.4 5 mwc 1808 distal caudal 51.8 mwc 5819a fused extremely distal caudal 34.2 29.3 32.3 29 47.9 4 mwc 5819b fused extremely distal caudal 32.6 27.2 33.3 26.7 44.5 mwc 5820a fused extremely distal caudal 27.6 4 fused extremely distal caudal mwc 5820b fused extremely distal caudal 38 339 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 medial caudal vertebrae possess a deep anterioposteriorly elongate fossa extending into the centrum from the central midline of the ventral surface of the neural canal. this fossa extends approximately one-third the length of the centrum. it has only recently been described in ankylosaurs perhaps because the fossa is obscured by the neural canal (barrett and maidment, 2011; blows and honeysett, 2014b; blows, 2015). it has been figured without comment by previous authors; carpenter (2004, figure 11a*) figures this feature in a cervical vertebra of ankylosaurus and it is figured for stegopelta (carpenter and kirkland, 1998, figure 22c). written communications (2015) by larry witmer (witmer lab, ohio university) and matt wedel (western university health sciences) note that this feature is widespread in the archosauria for the vascularization of the centrum from the basivertebral vein and suggest calling it the basivertebral venous fossa. this fossa is paired in crocodilia (l. witmer, witmer lab, ohio university, personal communication, 2015). the mymoorapelta atlas intercentrum is represented by mwc 1933 (figures 14a through 14e). it is wedge shaped in cross section and 55.2 mm across laterally. the gargoyleosaurus holotype atlas intercentrum (figure 15a) is considerably larger at 72.1 mm wide (kilbourne and carpenter, 2005). the mymoorapelta ventral surface of the atlas is flattened, and the dorsal margin is notched to receive the odontoid of the atlas. its neural arch is not attached but has not been broken off; either indicating lack of fusion due to ontogeny or a different character state. mwc 6738 is a complete medial cervical vertebra (figures 14f through 14k). the vertebra is platycoelan with the faces of the centrum shallowly excavated. the anterior and posterior centrum faces are parallel, but the posterior face is lower than anterior face as they are in many nodosaurids (gilmore, 1930; carpenter and kirkland, 1998) and ankylosaurids (maleev, 1954, 1956; maryanska, 1977; carpenter, 2004) but not saichania (=pinacosaurus; carpenter et al., 2011, although debated in kinneer et al., 2016). the centrum is broadly depressed in cross section with the ventral surface of the centrum mostly rounded transversely, with a pair of facets similar in appearance to the chevron facets on the caudal vertebrae present on the ventral margin of the posterior face of centrum. the third cervical centrum of gargoyleosaurus (figure 15b) has more evenly positioned faces of the centrum and is proportionally more elongate (kilbourne and carpenter, 2005). two vascular foramina enter the centrum of mymoorapelta approximately 1 cm from each side of the midline on ventrolateral surface of the centrum, the right foramen is better developed than the left. the neural canal is expansive and wider (2.6 mm) than tall (21.5 mm). the basivertebral venous fossa is well developed below the neural canal extending for approximately half the length of the centrum. a keel extends up the anterior and posterior sides of the low, posteriorly inclined neural spine. the ventral surfaces of the transverse processes are rounded. the prezygapophysial facets are angled medially 105˚ toward each other. the postzygapophysial facets are slightly cupped to overlap adjoining zygapophyses and angled at 115˚ away from each other. a tapering ridge extends down the posterior neural spine pinching out between zygapophyses. the transverse processes are rounded in cross section extending from below the level of zygapophyses bowing ventrally with these lightly expanded diapophyses oriented anterioventrally at 15˚ and facing ventrolaterally. the parapophyses are located near the anterior margin of the centrum close to the dorsal margin. mwc 6737 is a posterior cervical vertebra (figures 14l through 14o). it is platycoelous with the anterior face of the centrum more deeply excavated than the posterior face. the posterior face of the centrum is parallel and even with the anterior face of the centrum. the ventral margin of the centrum is more narrowly rounded, giving it a more heart-shaped cross section. the neural canal is smaller than in mwc 6738 (table 2), but still wider (21.1 mm) than tall (16.2 mm) and subrectangular in anterior view. the basivertebral venous fossa is well developed below neural canal and two asymmetrical nutritive foramina enter the lower ventrolateral surface of the centrum. the parapophyses are in the same position as mwc 6738. the centrum is about as long as tall, but the neural arch is significantly taller than mwc 6738, although the neural spine is still short. a weak keel extends up the anterior and posterior sides of the 340 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 low, posteriorly inclined neural spine. posteriorly, there is a fossa in the neural arch below the neural spine. on the anterior sides of the centrum, the parapophyses distinctly raised pads to articulate with the head of the cervical ribs. the transverse processes are subtriangular in cross section and angle upward to the diapophyses, which in turn are angled somewhat dorsally at approximately 20˚ and face posteriorly for the tuberculum of the cervical rib. the prezygapophyses angle 96˚ toward each other, whereas the postzygapophyses are angled at 136˚ away from each other. a wide depression is below each prezygapophysis to receive the preceding postzygapophysis. a ventrally bowed lamina connects the postzygapophyses. mwc 6737 does not possess a tapering ridge between postzygapophyses as seen in mwc 6738. a dorsoventrally ovate posterior fossa in neural arch is below the neural spine, and anteriorly below the neural spine there is a shallow depression that is wider than tall between prezygapophyses. mwc 1913 is a poorly preserved medial cervical centrum similar to that of mwc 6737. neither of mymoorapelta’s cervical vertebrae exhibit the paired fossae dominating the ventral surface of the centra exhibited by the lower cretaceous nodosaurids texasites, animantarx, and europelta (carpenter and kirkland, 1998; carpenter et al., 1999; kirkland et al., 2013). figure 14. cervical vertebrae from the revised hypodigm of mymoorapelta. atlas mwc 1933 in (a) cranial, (b) caudal, (c) dorsal, (d) ventral, and (e) right lateral views. mid-cervical vertebra mwc 6738 in (f) cranial, (g) caudal, (h) dorsal, (i) ventral, (j) right lateral, and (k) left lateral views. posterior cervical mwc 6737 in (l) cranial, (m) caudal, (n) dorsal, (o) ventral, and (p) right lateral views. abbreviations: d = diapophysis, p = parapophysis, po = post zygopophysis, pr = prezygopophysis. 341 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 dorsal vertebrae four dorsal vertebrae can be assigned to the expanded hypodigm of mymoorapelta (figures 16a through 16s). of these, only the most anterior dorsal vertebra (mwc 1800) still retains the transverse processes and neural spines. this pervasive damage may be a result of predation or scavenging as suggested by the numerous tooth marks on the dorsal surface of the ilium. therefore, it is impossible to determine their morphology. all dorsal centra exhibit a well-developed basivertebral venous fossa in the centrum below the neural canal. the centra are amphiplatyan with a tendency for the anterior margin to be more cupped than the posterior margin. the sides of the centra are smooth and depressed laterally and ventrally. dorsal vertebrae are considered to be anterior if the centrum is relatively short and the diapophysis is not exclusively on the neural spine. medial dorsal vertebrae are interpreted to possess a dorsoventrally ovate neural canal with a relatively taller neural arch, whereas the most posterior dorsal vertebrae have more elongate centra and possess a circular neural canal with a relatively shorter neural arch by comparison with ankylosaurus (carpenter, 2004). the pedicel of the neural arch arises from the anterior part of the centrum and there are depressions below the postzygapophyses (best seen in lateral view) extending forward to the transverse processes. thus, the neural arch appears to be angled anteriorly. however, the neural spine is posteriorly placed figure 15. vertebrae from holotype of gargoyleosaurus parkpinorum dmnh 27726. atlas (a) in posterior view. third cervical vertebra in (b) lateral view. anterior medial caudal vertebrae in (c) lateral, (d) posterior, (e) anterior, and (f) dorsal views. posterior medial dorsal vertebra in: (g) posterior, (h) lateral and (i) anterior views. more distal vertebra in (j) posterior, (k) lateral, (l) anterior, and (m) dorsal views. abbreviations: c = caudal ribs, d = diapophysis, p = parapophysis, po = post zygopophysis, pr = prezygopophysis. 342 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 16. dorsal vertebrae of mymoorapelta from mygatt-moore quarry. first dorsal assigned to the revised hypodigm mwc 1800 in (a) cranial, (b) caudal, (c) dorsal (d) ventral, and (e) right lateral views. medial dorsal vertebra assigned to the revised hypodigm mwc 1803 in (f) cranial, (g) right lateral, and (h) left lateral views. second medial dorsal vertebra assigned to the revised mwc 1802 in (i) cranial, (j) caudal, (k) ventral, (l) right lateral, and (m) left lateral views. referred dorsal vertebra mwc 1801 in (n) cranial, (o) caudal, (p) dorsal, (q) ventral, (r) right lateral, and (s) left lateral views. referred anterior dorsal vertebra mwc 5705 in (t) caudal, (u) dorsal, and (v) left lateral views. referred dorsal vertebra mwc 6737 in (w) cranial, (x) ventral, and (y) right lateral views. paratype dorsal vertebra mwc 6733 in (z) right lateral view. dorsal vertebra mwc 6735 in (aa) cranial, (bb) caudal, (cc) dorsal, (dd) ventral, (ee) right lateral, and (ff) left lateral views. abbreviations: d = diapophysis, p = parapophysis, po = post zygopophysis, pr = prezygopophysis. 343 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 on all the vertebrae. its anterior margin arises at the front of the parapophyses with the base extending back to above or just posterior to the posterior margin of the centrum between the postzygapophyses. although breakage makes the neural spine appear to be reclined, it was probably fully erect. there is only a narrow gap between the prezygapophyses, and the postzygapophyses are adjoined with a lamina extending at their base to the top of the neural canal. thus, the medial and dorsal vertebrae have nearly the same tongue and groove articulation, which limits the mobility of the dorsal vertebrae as in ankylosaurids (brown, 1908; maleev, 1954; carpenter, 2004). the parapophyses form raised circular to ovate pads on pedicels adjoining the base of the transverse processes. they have depressed centers and flaring rims to encompass the capitulum of the rib. there is no evidence of fusion of the ribs with any vertebrae. mwc 1800 is identified as the first dorsal vertebrae (figures 16a through 16e). the centrum is nearly circular in cross section as is the overlying the circular neural canal. the neural arch is relatively tall and arises from the anterior two-thirds of the centrum. the neural spine is erect and blade-like with the top of neural spine broken off such that it is impossible to determine if the neural spine is expanded dorsally as in many other ankylosaurs (ostrom, 1970; arbour and currie, 2013a; park, 2022). there is a subtriangular fossa 0.5 mm deep and 7 mm wide below the neural arch anteriorly, and slightly above to either side there are elongate shallow fossae approximately 18 mm wide, which would have received adjoining postzygapophyses allowing for increased lateral maneuverability. a vascular canal 2.6 mm in diameter is present on the medial side of both fossae. a ventrally bowed lamina connects the postzygapophyses below the medial triangular fossa. posteriorly the postzygapophyses are separated below the neural spine. the prezygapophyses face inwards at an angle of 147˚, postzygapophyses are 148˚, indicating the potential for a great deal of lateral flexure. the postzygapophyses are slightly cupped to overlap prezygapophyses. the transverse process is t-shaped in cross section as is characteristic of ankylosaur transverse processes. the parapophyses face ventrolaterally from lateral ends of transverse processes and the diapophyses are at the base of the neural spine on the suture between the neural spine and centrum. carpenter (2004; carpenter et al., 2011) noted that in ankylosaurids the parapophysis shifts upward such that it lies completely on the lateral surface of the neural arch by the third dorsal vertebra. mwc 1803 is a medial dorsal vertebra distinguished by its tall neural canal (figures 16f through 16h). the faces of centrum are shallowly excavated. the neural arch is inclined anteriorly. it is not well preserved but the most striking feature is how anteriorly inclined the neural arch appears relative to the centrum. mwc 1802 is a more posterior dorsal vertebra (figures 16i through 16m). although too damaged to measure, the angles between faces of the zygapophyses form a more acute angle than in mwc 1803. the centrum is more elongated in length than in width (table 2). the neural spine is broken off near base, less teardrop-shaped in cross section, and the base is approximately 50 mm long with a max width of 8 mm. parapophyses are below the transverse processes and well above suture between the neural spine and centrum. mwc 1801 is a posterior dorsal vertebra (figures 16n through 16s). faces of the centrum are shallowly excavated. the centrum is longer than wide and the neural spine flat and blade like (table 2). the parapophysis is situated under the transverse process. even though poorly preserved, the faces of the prezygapophyses appear to form a more acute angle. the neural spine, although not complete, is more complete than the other dorsal vertebrae, with a length of approximately 50 mm and width of 5 mm. zygapophyses on this specimen are the best preserved of those of any of the posterior dorsal vertebrae, the prezygapophysial facets angle toward each other at of 97˚, and the post-zygapophysial facets angle away from each other at 108˚. there are also four larger, poorly preserved, dorsal vertebrae from the referred individual (figures 16t through 16ff) that are approximately 25% larger (table 2), although they are not described in detail. mwc 5705 is a large anterior dorsal vertebra, suspected to be from the larger animal (figures 16t through 16v). the parapophysis is positioned on the suture between the neural spine and centrum. faces of amphiplatyan centra are shallowly excavated and the 344 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 centrum is slightly medially constricted with a well-developed basivertebral venous fossa. the lateral margins are damaged around both anterior and posterior faces of the centrum, so it is difficult to determine the original shape. although damaged, the prezygapophyses appear to form a relatively obtuse angle of 137˚ as in mwc 1800. a rugose depression extends down the posterior side of the neural arch between postzygapophyses to the top of the neural canal and there is a large pit on the side of the neural arch anterior to the transverse process. the neural spine is broken off just above the zygapophyses, and in cross section it widens from 5 mm anterior to 13 mm near the posterior margin and is somewhat teardrop shaped in cross section. at the base of the neural spine, anteriorly, is an elongate slot-shaped fossa, which extends at angles 45˚ posteroventral above the neural canal. mwc 6734 is a large, poorly preserved dorsal vertebra (figures 16w through 16y) with well-developed basivertebral venous fossa. there is no excavation below the neural spine anteriorly. a ridge extends down the posterior side of the neural arch from below the prezygapophyses extending back to top of the neural canal. parapophysis is well-developed immediately below the transverse process and the ventral margin of the centrum is rounded. faces of the centra are shallowly excavated. the neural arch appears to incline anteriorly. mwc 6733 is a large, more poorly preserved dorsal vertebra (figure 16z) that appears to have been damaged and weathered prior to burial. the pedicel appears shorter than that of mwc 6734 and this vertebra is considered to be more posterior. it also displays no fossa below the neural spine anteriorly. a ridge also extends down the posterior side of the neural arch from below the postzygapophyses to the top of the neural canal. mwc 6735 is a large posterior dorsal vertebra from the referred material and, although not well preserved, it is the best-preserved dorsal vertebra represented by the referred material (figures 16aa through 16ff). this vertebra exhibits the shortest pedicel for any known vertebrae assigned to mymoorapelta and is interpreted to represent an extremely posterior dorsal vertebra, perhaps positioned in the range of the dorsosacrals of gargoyleosaurus (carpenter et al., 2013) and gastonia (kirkland, 1998). there is no fossa below the neural spine. a keel extends anteriorly down the posterior side of the neural arch below the prezygapophyses to the top of the neural canal. the diapophysis are well developed immediately below the transverse process, and the ventral margin of the centrum is rounded. the length of neural spine is about 70 mm and the width is 6 mm. no dorsal vertebrae are recognized in the holotype of gargoyleosaurus (kilbourne and carpenter, 2005). three dorsal vertebrae (figure 17) were collected with the movie valley ankylosaur byu 773-9430. they cannot be assigned with any certainty to either mymoorapelta or gargoyleosaurus. the most complete example (figures 17f through 17i) preserves a complete neural spine with transverse processes that angle upward at about 30˚ to near the top of the neural spine, which is unexpanded unlike nodosaurids (e.g., ostrom, 1970; kirkland et al., 2013) and ankylosaurids (e.g., vickaryous et al., 2004; park, 2022). ribs have not been observed to be fused to the free dorsal vertebrae in any jurassic ankylosaurs. sacral vertebrae mymoorapelta sacra from the mygatt-moore quarry are fragmentary and represent portions of the sacra from at least three individuals (figure 18). mwc 3613 is interpreted to be a sacral centrum from the revised hypodigm of mymoorapelta (figure 18a). it is approximately 20% to 25% smaller than those assigned to the referred specimens. as with the dorsal and cervical vertebrae, a well-developed basivertebral venous fossa extends down into the centrum from the center of the neural canal. the centrum was too damaged and abraded to yield meaningful measurements but was wider than tall. it appears not to have been fused to with adjoining centra and may represent a caudal sacral or perhaps a dorsosacral. there are two quite deep, circular pits or excavations on the posterior half of the centrum, below and on either side of the neural arch. these pits characterized the better-preserved sacral vertebra of the referred specimen described below. mwc 6736 may be a caudosacral from the revised hypodigm of mymoorapelta (figure 18b). it is not very well preserved. the anterior face of the centrum is com345 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 pletely broken away and the neural arch is broken off above the neural canal. a well-developed basivertebral venous fossa extends down into the centrum from the center of the neural canal. the posterior face of the centrum is depressed and displaced ventrally about half the height of the centrum. the caudal ribs extend directly laterally as preserved and appear to be more massive than those on mwc 1804 or the other anterior caudal vertebrae from the revised hypodigm. portions of a larger sacrum have been recovered that are interpreted to pertain to the larger referred individual. the central portion is represented by two large fused figure 17. dorsal vertebrae from movie valley ankylosaur byu 773-9430. dorsal vertebra in (a) cranial, (b) caudal, (c) dorsal, (d) right lateral, and (e) left lateral views. posteriororsal vertebra in (f) cranial, (g) caudal, (h) dorsal, and (i) right lateral views and (j) cranial, (k) caudal, (l) right lateral, and (m) left lateral views. abbreviations: d = diapophysis, p = parapophysis, po = post zygopophysis, pr = prezygopophysis. 346 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 sacral vertebrae (mwc 6932) with what is interpreted to be just the poster margin of a third vertebra fused on anteriorly (figures 18c through 18f). most notably there is a ventral depression, whereas there is a keel on the underside of the sacrum from the simon quarry assigned to gargoyleosaurus (figure 19) by carpenter et al. (2013). traces of sutures between centra indicate the length of each centra is 56.5 mm, and medially at the narrowest point the posterior centum is 55.8 mm wide and the more anterior centrum is 58.7 mm wide. each centrum includes a well-developed basivertebral venous fossa extending down into the centrum from the neural canal. the neural spines are broken off at the neural canal, which has considerable abrasion along the break. figure 18. sacral vertebrae from revised hypodigm and referred specimens of mymoorapelta. holotype abraded sacral centra mwc 5104 in (a) dorsal view. holotype partial caudosacral vertebra mwc 6736 in (b) caudal view. paratype partial sacrum preserving two plus centra mwc 6932 in (c) left lateral, (d) left lateral (e) ventral, (f) dorsal, and views. paratype caudosacral centra mwc 3613 in (g) ventral, (h) anterior, (i) dorsal, (j) posterior, (k) right lateral, and (l) left lateral views. paratype partial sacrum mwc 10347 in (m) ventral, n, anterior, (o) left lateral, (p) dorsal, and (q) posterior views. 347 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 the sacral ribs were broken off and abraded nearly flush with the sides of the centra posteriorly. the neural canal at the widest visible point measures about 29 mm. there is a third sacral vertebra of comparable size (mwc 3613). the centrum is clearly wider than tall, and there is considerable abrasion around margins of faces of centrum and where the neural spine has broken away from centrum (figures 18g through 18l). it appears that the centrum was not fused to the sacrum. the depressed ventral margin of the centrum is gently convex with no ventral depression. this centrum may represent a caudal sacral. two pits/excavations are on the posterior half of the centrum, below and on either side of the neural arch. although damaged it appears the anterior face of centrum was wider than the posterior face. this position as a sacral caudal is determined by comparison with mwc1804, which appears to be a damaged first caudal vertebrae from the revised hypodigm that shows similar but more shallow pits in this position. a partial, fully fused anterior sacrum (mwc 10347) was recovered from the basal “pebble” bed (chin and kirkland, 1998) in 2022 indicating the presence of a minimum of three individuals of mymoorapelta at the mygatt-moore quarry. although broken prior to burial, the specimen is the most complete portion of a sacrum recovered from the site (figures 18m through 18q). as preserved, the fossil has a maximum length of 209.75 mm and a maximum height toward the posterior end of 96.4 mm. it consists of four fused vertebrae broken where the ribs meet the transverse processes on the left side and through the base of the transverse processes on the right side. the neural spines are broken off above the neural arch, which fully obscures the neural canal. the anterior-most vertebra is damaged, but largely the anterior break appears to coincide with the anterior face of this vertebra (figure 18n). this face is somewhat heart-shaped, narrowing ventrally, with a round neural canal estimated at 19.8 mm wide and 17.1 mm tall. the vertebrae increase in size posteriorly. the posterior-most preserved vertebra is highly damaged posteriorly and ventrally such that it cannot be determined figure 19. gargoyleosaurus sacrum from simon quarry, northern wyoming. dmnh 58831 in (a) ventral, (b) lateral, and (c) dorsal views. 348 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 if it had a ventral depression. the centrum appears to be wider than tall, with a neural canal estimated to be 27.4 mm wide and 17.4 mm tall comparing well to that of the sacral neural canal in mwc 3613 (figure 18p). we propose that mwc 10357 consists of two sacral vertebra and two dorsal vertebra forming part of the anterior synsacrum. the bases of the transverse processes of the anterior-most sacral and posterior-most dorsal synsacral vertebrae extend for approximately the length of the vertebrae and only extend laterally to the ribs at the anterior end. the lacm sacrum (lacm.154873) has been identified as that of mymoorapelta based on the distinct groove along the ventral surface of the sacral centra as in the holotype material (figure 20b). it consists of three sacral vertebrae and one caudosacral vertebra. the sacral ribs are fused together distally to form a yoke to attach to the ilia. the specimen lacks any fused dorsosacral vertebra to form a synsacrum. the initial discovery of the cactus park mymoorapelta (mwc 2610) included several large sandstone blocks preserving external molds of portions of the sacrum. one block (figure 21c) preserves the three sacral ribs (kirkland, 1998; carpenter et al., 2013). an external mold of the ventral portion of the anterior synsacrum with the associated ribs is joined to the preacetabular portion of the ilium (figure 21a). vertebrae associated with this block (not figured) are represented by slightly constricted cylindrical centra that were not fused together. an overlying sandstone block preserves ossified tendons that would have been placed along each side of these neural spines (figure 21b). it is estimated that a fully developed sacrum of mymoorapelta would consist of one caudosacral vertebra, three sacral vertebrae, and four dorsosacral vertebrae fused into the synsacrum. in addition to lacking a ventral groove on the sacrum (carpenter et al., 2013), gargoyleosaurus differs in possessing four sacral vertebra (figure 19). the ventral groove of the sacrum is present on most other sacra assigned to polacanthines (blows, 2015; kinneer et al., 2016; raven et al., 2020) and nodosaurids (carpenter et al., 1995; burns, 2015; lull, 1921). it is noteworthy that the sacrum of the new specimen of the late jurassic ankylosaur dracopelta (nova-fctdct-5556) from portugal has the same sacral formula as the simon quarry specimen of gargoyleosaurus and also lacks the ventral groove (russo, 2024). the presence of a ventral sacral groove in mymoorapelta, polacanthines, and in north america’s nodosaurids appears to be a derived character as it is not present in scelidosaurus (norman, 2020b). it is also absent in the middle jurassic chinese ankylosaur tianchisaurus (dong, 1993), ankylosaurids (penkalski and blows, 2013; park et al., 2021), and europe’s struthiosaurids (garcia and pereda–suberbiola, 2003; kirkland et al., 2013; ősi et al., 2019). caudal vertebrae numerous caudal vertebrae are preserved with revised hypodigm and referred specimens of mymoorapelta at the mygatt-moore quarry (figures 22 and 23). mwc 1804 had been interpreted as a caudosacral centrum (kirkland and carpenter, 1994; kirkland et al., 1998), but it may instead represent the first caudal (figures 22b through 22e). it is tentatively interpreted as belonging to the holotype individual because of its size but was reportedly collected as a float specimen by pete mygatt soon after the locality was discovered (p. mygatt, museum of western colorado volunteer, verbal communication,1982). it is somewhat wedge-shaped in lateral view such that the ventral length of the centrum may have been slightly shorter than the dorsal length. it also appears to have a narrower, flattened ventral margin of the centrum than the other anterior caudal vertebrae. the caudal ribs and the neural spine are broken off. the base of the neural spine is subtriangular in cross section at the neural canal and is widest anteriorly, narrowing posteriorly (figure 22d). mwc 1806 and 1805 (figures 22f through 22o) are adjoining proximal caudal vertebrae that were described previously (kirkland and carpenter, 1994; kirkland et al., 1998). both neural spines expand upwards towards the dorsal terminus. mwc 1806 expands more than mwc 1805 and thus is interpreted to be the more anterior of the two. the neural spine in mwc 1806 is more erect than mwc 1805, which is angled slightly more posteriorly. the sutural contacts of the neural spines with the centra narrow anteriorly as in pola349 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 canthus. the ventral sides of both centra are narrowly rounded and both possess a faint keel. a well-developed basivertebral venous fossa extends down into the centra from the center of the neural canals. the notochordal prominence is present on the posterior face of both caudal centra. faces of centra have a more ovate or kidney bean shape in anterior view whereas they become more strongly heart shaped with a more pronounced chevron facet on the posterior face. posterior chevron facets narrow anteriorly. the development of the chevron facet occurs at about the third caudal vertebra (pereda-suberbiola, 1994). viewed dorsally, the prezygapophyses are widely separated and angle away from each other at about 60˚; however, they form a very obtuse angle of approximately 150˚ in a vertical plane. this feature is not preserved in mwc 1806, which was reconstructed to match mwc 1805. postzygapophyses angle away from each other at approximately 105˚ vertically. disparity between angles suggests fair amount of cartilage between zygopophyses, which may not be to the same degree in the dorsal vertebrae, allowing for increased maneuverability in the tail. the caudal ribs of both vertebrae extend horizontally flexing ventrally to about an angle of about 45˚ as in the compton bay polacanthid nhmuk r9293 (blows, 1987, 2015), whereas they tend to angle more abruptly downward from the centrum on gastonia (kirkland, 1998; kinneer et al., 2016) and the correlative bexhill polacanthid (blows and honeysett, 2014b, figures 5a and 5b; blows, 2015). they are ovate in cross section, being about twice as long as tall and taper distally with no terminal expiation as in some ankylosaurids (ostrom, 1970). in dorsal view the left caudal rib of mwc 1805 appears to turn slightly posteriorly and the right appears to turn slightly anteriorly. in mwc 1806 both are turned slightly anteriorly, suggesting the posterior turn on the left of mwc 1805 is either distortion or an ontogenetic abnormality. the neural spines are inclined posteriorly from 10˚ to 15˚ and have an expanded dorsal terminus as in gastonia, polacanthus, and sauropelta (ostrom, 1970; kirkland figure 20. complete mymoorapelta sacrum from southeastern utah. lacm.154873 in (a) dorsal and (b) ventral views. 350 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 1998; blows, 2015; kinneer et al., 2016). in posterior view, the neural spine of mwc 1805 expands from 13 mm to at least 25 mm at dorsal terminus. however, the lateral margins of the terminus are worn. the neural spine maintains a consistent anterior to posterior length of 22 mm from the prezygapophyses to its dorsal termination. the proximal caudal vertebra tentatively assigned to gargoyleosaurus sp. (figure 5a) from the maelyn quarry at the eccles dinosaur park in ogden, utah (edp-sm 2017.01.096). although this specimen is poorly preserved and more lightly constructed it appears to compare well with those of mymoorapelta. a partial proximal haemal arch or chevron (mwc 1912) from about this position on the tail of the holotype individual has been identified (figures 22p through 22r). the left side bounding the haemal canal is broken and the distal end is incomplete. however, it appears to have been approximately as long as the neural proximal neural spines and caudal ribs of those of the proximal caudal vertebrae (mwc 1805, 1805). the flattened right articular surface is oval, and although it is flaring, it appears to have been separate from the left articular surface. its anterior posterior length is consistent from the articular surface to its distal end, and it is lensoidal in cross section. in lateral view, it curves uniformly posteriorly. those preserved in the cactus park mymoorapelta (figure 21d) are similar in morphology, but appear to be proportionally longer, perhaps reprefigure 21. axial skeletal molds from pelvic area of the cactus park mymoorapelta, mwc 2610. (a) ventral mold of the synsacral area with dorsal ribs. (b) ossified tendons from along synsacral vertebral neural spines. (c) ventral mold of a portion of the right side of sacrum. (d) right lateral mold of proximal caudal vertebrae. abbreviations: cr = impression of base of caudal ribs, ch = impressions of chevrons. 351 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 senting a more anterior position below the tail. unlike the haemal arches in proximal polacanthid and nodosaurid tails, the haemel arches in ankylosaurds are typically fused to the centra (arbour et al., 2009; thompson et al., 2011; arbour and currie, 2016). mwc 1807 is a well-preserved, small medial caudal vertebra from the revised hypodigm (figures 23n through 23r) that may represent about the same position in the tail as mwc 3651 from the paratype individual. the top of the neural spine is slightly but distinctly expanded. it has an anterior notochordal bump just above the middle of centrum on the anterior face. the centrum is about as long as it is wide (table 2). the ventral sides of the centra are flattened with a central depression. both anterior and posterior chevron facets are developed, but the poster facets are much more strongly expressed. in dorsal view, the right caudal rib is inclined posteriorly, and the left is inclined anteriorly. in lateral view the caudal ribs extend nearly horizontally; an apparent downward flexion consists mainly of thinning of the rib laterally from the dorsal side. the notochordal prominence is well developed on the central face anteriorly and is recognizable on the centrum face posteriorly. ventral chevron facets are developed figure 22. proximal caudal vertebrae from revised hypodigm and referred specimens of mymoorapelta. partial proximal caudal vertebra from paratype mwc 5878 in (a) cranial view. partial first caudal vertebra from revised hypodigm mwc 1804 in (b) cranial, (c) posterior, (d) dorsal, and (e) left lateral views. second caudal vertebra from revised hypodigm mwc 1805 in (f) cranial, (g) posterior, (h) dorsal, (i) ventral, and (j) right lateral views. third caudal vertebra from revised hypodigm mwc 1806 in (k) cranial, (l) posterior, (m) dorsal, (n) ventral, and (o) right lateral views. proximal chevron from revised hypodigm mwc 1912 in (p) cranial, (q) right lateral, and (r) posterior views. abbreviations: c = caudal ribs, po = post zygopophysis, pr = prezygopophysis. 352 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 23. medial to distal caudal vertebrae from revised hypodigm and referred specimen of mymoorapelta. medial caudal vertebra from referred specimen mwc 4036 in (a) cranial, (b) posterior, (c) dorsal, (d) ventral, and (e) right lateral views. medial caudal vertebra from paratype mwc 3651 in (f) cranial, (g) posterior, (h) dorsal, (i) ventral, and (j) left lateral views. partial medial caudal vertebra from referred specimen mwc 6732 in (k) cranial, (l) posterior, and (m) right lateral views. medial caudal vertebra from revised hypodigm mwc 1807 in (n) cranial, (o) posterior, (p) dorsal, (q) ventral, and (r) right lateral views. medial caudal vertebral centra from revised hypodigm mwc 1913 in (s) dorsal view. medial caudal vertebra with fused chevron from revised hypodigm mwc 1907 in (t) posterior and (u) right lateral views. partial medial caudal vertebra from revised hypodigm mwc 5012 in (v) cranial, (w) ventral, and (x) left lateral views. medial caudal vertebra from revised hypodigm mwc 6739 in (y) cranial and (z) ventral views. partial distal caudal vertebra from revised hypodigm mwc 1808 in (aa) right lateral view. distal caudal vertebral centra from revised hypodigm mwc 5830 in (bb) ventral and (cc) right lateral views. pair of fused distal vertebra with fused chevrons from revised hypodigm mwc 1839 in (dd) cranial, (ee) posterior, (ff) dorsal, (gg) ventral, and (hh) right lateral views. partial pair of fused distal vertebra with fused chevron from revised hypodigm mwc 5820 in (ii) left lateral and (jj) right lateral views. pair of fused distal vertebral centra from revised hypodigm mwc 5818 in (kk) left lateral view. abbreviations: c = caudal ribs, ch = chevron, po = post zygopophysis, pr = prezygopophysis. 353 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 anteriorly and posteriorly but are more prominent posteriorly. the underside of the centrum is flattened and appears to be depressed due to the prominence of the facets for the chevrons. the prezygapophyses rise from above the neural canal almost horizontal to each other and flex upward laterally producing a curved articular surface angling from 180˚ to 100˚ as they flex along their length. the postzygapophyses are deflected away from each other forming an angle of 80˚ and face laterally. the neural spine is slightly expanded dorsally from the zygapophyses giving a posterior width of 8 mm expanding to 12 mm at the dorsal termination. in lateral view the neural spine tapers very little and is approximately 14 mm long. it is angled 30˚ posteriorly. the holotype of gargoyleosaurus preserves three medial caudal vertebrae. kilbourne and carpenter (2005) describe the most anterior of these (figures 15c through 15f), as a proximal caudal vertebra and propose that its differences from the proximal caudal vertebrae of mymoorapelta as representing diagnostic differences between these two taxa. we note that this vertebra compares well with mwc 1807 as a medial caudal vertebra and given the scarcity of caudal vertebral remains from gargoyleosaurus in general, it is impossible to distinguish these taxa based on caudal vertebra. mwc 6739 is a small, poorly preserved mid-caudal centra 43.9 mm long with a distinct ventral groove that appears to have been slightly longer than wide and is 34.4 mm at its tallest point (figure 23s). medial caudal vertebra in in mymoorapelta and perhaps polacanthines in general have centra whose width, length, and height are subequal with more distal centra becoming more elongate. mwc 1907 is a bit more posterior caudal vertebra in which the zygapophyses were largely obliterated in preparation and bases smoothed over and filled to the extent which no sign of them remains (figures 23t and 23u). the neural spine is fairly short and angles posteriorly beyond centrum at 56˚ and is slightly expanded distally. the transverse processes are short and straight and extend 18 mm downward at about 45˚. its straight chevron is about the length of the neural spine, inclined posteriorly past centrum at about 25˚, and is fully fused to the posterior end of the centrum. it is slightly anteroposterior expanded just below the haemal arch. the ventral margin is rounded. mwc 5019 may be a more anterior element than mwc 1907 (figures 23v through 23x). fragments of the neural spine are present but cannot be attached to the centrum. the caudal ribs appear to have been longer and less ventrally inclined. the anterior face of the centrum appears to be only slightly depressed relative to the posterior face. mwc 6739 is another poorly preserved medial caudal vertebra about as long as wide with a rounded ventral surface (figures 23y and 23z). mwc 1808 is a poorly preserved distal caudal centra that is 51.8 mm long with a distinct caudal rib preserved as a round bump about 5 mm high on the flank of the centrum (figure 23aa). mwc 5830 is a large distal caudal centra with the characteristic lateral ridge along the side of centrum that reflect the caudal ribs on all of the most distal centra. the ventral margin of the centra is sharply rounded. the six most distal caudal vertebrae (figures 23dd through 23kk) of mymoorapelta are fused together as are those of the struthiosaurine nodosaurid europelta (kirkland et al., 2013). this may also be the case with the “incipient” tail club in the holotype of polacanthus foxi nhmuk r175 noted by blows (1987) and reinterpreted by carpenter and kirkland (1998; blows, 2015). whether this is a natural character or rather the result of a pathology is unknown; however, we propose it is a result of relying on swinging the tail in defense (arbour and snively, 2009; arbour and zanno, 2018, 2020). mwc 1839 is a well-preserved pair of distal caudal attached to each other by their mutual fusion with the intervening chevron (figures 23dd through 23hh). the faces of the centra are flat. the neural arches are low without neural spines. the prezygapophyses are fused together and extend back over the tiny pair of postzygapophyses much as in the handle of a derived ankylosaurid (arbour and snively, 2009; arbour et al., 2009). the caudal ribs form a slight expansion of a distinctive ridge that extends down the side of the centra. the ventral side of the centra has a distinct keel that extends between the fused centra. the chevrons are skid-shaped, extending farther anteriorly than posteriorly, but do not touch. their ventral margins are flattened. the haemael 354 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 canal is round in cross section and is about 5 mm in diameter. mwc 5820 (figures 23ii and 23jj) is a more distal pair of fully fused vertebrae. their preserved neural arch is fully fused such that it is difficult to interpret. the neural canal can barely be discerned but appears to be only a few mm across. laterally, the centra are swollen broadly. the preserved chevron is skid-shaped but damaged anteriorly and posteriorly. its ventral margin is flattened. the haemael canal is round in cross section and is about 4 mm in diameter. both the anterior and posterior ends are broken off suggesting that they had adjoining vertebrae fused to these in life. mwc 5818 (figure 23kk) is an even more distal pair of fused vertebral centra from the expanded hypodigm that are difficult describe morphologically as there are no distinct neural spines or chevrons. these may represent the distal end of the tail. four caudal vertebrae are interpreted to represent the larger referred individual from the southwest pit. all possess a well-developed basivertebral venous fossa that extends down into the centra from the center of the neural canals. mwc 5070 is a large proximal caudal (figure 22a) from the referred individual. although it looks like it may have been weathered prior to burial, considerable damage appears to have been caused during collection. it might represent the same position as mwc 1805 or a bit more posterior as there is a slight depression on the ventral side of the centrum. mwc 4036, 6732, and 3651 are large, proximal to medial caudal vertebrae (figures 23a through 23m). all appear to have been weathered prior to burial. the ventral sides of the centra are flattened with a central depression. both anterior and posterior chevron facets are developed, but the posterior facets are much more strongly expressed. they are superficially like mwc 1807 except for their larger size (table 2). ribs several ribs and partial ribs have been recovered (figure 24). in general, they are typical for ankylosaurs, except for the more medial ribs being more triangular in cross section versus more t-shaped as is typical in more derived ankylosaurs (vickaryous et al., 2004). mwc 3747 (figures 24a through 24c) is the proximal end of anterior dorsal rib. as with other anterior dorsal ribs it is l-shaped in cross section just distal to the tuberculum, where it measures 19.3 mm across and 24.1 mm deep. mwc 5061 is a large anterior dorsal rib from the southwestern part of the quarry, as with other anterior dorsal ribs it is l-shaped in cross section just distal to the tuberculum where it measures 31.3 mm across and 38.2 mm deep just distal to the tuberculum. mwc 5094 is a small anterior dorsal rib as with other anterior dorsal ribs it is l-shaped in cross section just distal to the tuberculum where it measures 16.0 mm across and 28.9 mm deep. mwc 1810 (figures 24d through 24f) is a long t-shaped rib 23.7 mm wide and 19.0 mm deep just distal to the tuberculum. this rib expresses how wide mymoorapelta would be in life. mwc 3763 (figures 24g through 24i) is a large more t-shaped rib section 29.6 mm wide and 25.5 mm deep just distal to the tuberculum. mwc 4329 (figures 24j through 24l) is a damaged t-shaped rib more than 26 mm wide and 29.5 mm deep just distal to the tuberculum. mwc 1811 (figures 24m through 24o) is a posterior t-shaped rib 21.7 mm wide and 18.4 mm deep to the tuberculum, mwc 1840 (figures 24p and 24q) is a dorsal-sacral rib only moderately swollen medially and is 28.0 mm wide and 15.8 deep just distal to the tuberculum. it would have extended from the anterior synsacrum to join with the preacetabular process of the ilium. it compares well with those preserved with the cactus park mymoorapelta (figure 21a). pectoral girdle a worn distal end of a right scapula mwc 6743 has been recovered from the mygatt-moore quarry (figures 25a through 25c). the distal end of scapula is broken off across the acromion process extending to its lower margin where it would be in contact with the coracoid. by comparison, the coracoid is fused to the scapula (figures 25h through 25j) on the larger dry mesa scapula-coracoid (byu 725-12963). the acromion process rises from the entire lateral margin of mwc 6743, as preserved, tapering along the posterior margin towards its distal, broken end. the depth of this scapula, including the acromion process is 49.7 mm (mediolat355 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 eral thickness at the acromion). at this point it is 61.7 mm wide, anteroposterior. between the acromion process the glenoid is smoothly concave. the area of the glenoid is thickened and smoothly concave. it faces laterally at an angle of about 45˚. the width of the scapula at the glenoid (anteroposterior) is 96.1 mm. the glenoid itself on the scapula is 45.0 mm (mediolaterally). the glenoid is more laterally oriented in the mwc specimen than it is in the isolated fused scapula from the dry mesa quarry. the dry mesa scapula-coracoid is well preserved and undistorted although there is some damage to the posterior margin of the coracoid (figures 25h through 25j). it was originally described as ankylosauria indeterminant (kirkland et al., 1998) but is herein considered to represent a fused scapulocoracoid of gargoyleosaurus, if not gargoyleosaurus parkpinorum, as determined by the morphology of the co-occurring caudal plates (figure 4). it does not appear as robust as mwc 6743. it is strongly bowed through an arc of approximately 135°, indicating that it came from an animal with a body rounded in cross section. the maximum length of the scapulocoracoid is 414 mm (453 mm along the lateral surface); nearly one-third of the length is made up of the coracoid as observed in sauropelta (ostrom, 1970; coombs, 1978a). both the extreme ends are pitted and rugose indicating both a cartilaginous scapular extension distally and a cartilaginous contact with the sternals proximally. the scapula is proportionally more slender than that of any known ankylosaur. it has a maximum width of 97.8 mm proximally and a minimum width of the blade of 67.9 mm. it thins from 43.5 mm at the base of the acromion process to 15.1 mm distally. the scapula seems to lack any synapomorphic features of the nodosauridae. it has figure 24. dorsal ribs from revised hypodigm of mymoorapelta. left anterior dorsal rib head mwc 3747 in (a) medial, (b) posterior, and (c) anterior views. left anterior medial dorsal rib mwc 1810 in (d) medial, (e) posterior, and (f) anterior views. right medial dorsal rib mwc 3763 in (g) anterior, (h) medial, and (i) posterior views. right medial dorsal rib head mwc 4329 in (j) anterior, (k) medial, and (l) posterior views. left posterior dorsal rib mwc 1811 in (m) posterior, (n) medial, and (o) anterior views. left posterior dorsal rib mwc 1840 in (p) posterior, (q) medial, and (r) anterior views. 356 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 a low acromian process, 43.3 cm high along the anterior margin of the scapula opposite the glenoid reminiscent of the primitive condition observed in mymoorapelta (figure 25a) and the ankylosauridae (coombs, 1978a; coombs, and maryańska, 1990; vickaryous et al., 2004; parish, 2005). the glenoid measures 60.0 mm wide across its inner surface. the coracoid is 154.6 mm long by 119.6 mm wide at the distal margin of the glenoid. the coracoid foramina extends laterally from about 1 cm behind the glenoid just below the suture with the scapula on the medial surface of the coracoid. it is interesting that the more elongate coracoid appears more similar to that of nodosauridae and the scapula compares best with an ankylosaurid (coombs, 1978a; sereno, 1986). however, the coracoids are proportionally much more elongate in nodosaurids texasites (=pawpawsaurus) and animantarx (coombs, 1995; carpenter and kirkland, 1998; carpenter et al., 1999). a cranioventral process is well developed and is separated from glenoid by a broad subglenoid notch. although rarely noted, this character is present in gastonia (kirkland, 1998) and many ankylosaurids, but is largely abfigure 25. scapula-coracoids. partial right distal scapula from revised hypodigm of mymoorapelta mwc 6743 in (a) lateral, (b) cranial, and (c) medial views. proximal right scapula blade of holotype of gargoyleosaurus dmnh 27726 in (d) lateral and (e) medial views. proximal right scapula blade of holotype of gargoyleosaurus dmnh 27726 in (f) lateral and (g) medial views. fused right scapula-coracoid from gargoyleosaurus, dry mesa quarry byu 725-12963 in (h) lateral, (i) medial, and (j) cranial views. partial distal scapula from holotype of mymoorapelta mwc 6743 in (d) lateral, (e) cranial, and (f) medial views. abbreviations: ap = acromium process, cf = corocoid foramen, cvp = cranioventral process, g = glenoid, scs = scapula-corocoid suture. 357 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 sent in nodosaurids (coombs, 1978a; coombs and maryańska, 1990; vickaryous et al., 2004; parrish, 2005). the holotype of gargoyleosaurus preserves the proximal and distal portions of the fused scapulocoracoid (figures 25d through 25g). the proximal end of the scapula is more expanded than that of the dry mesa scapula and was measured at 157 mm wide by kilbourne and carpenter (2005). they also measured the coracoid as 154.6 mm long. the cranioventral process is not well developed if the shallow subglenoid notch is restricted to just ventral to the glenoid. overall, this portion of the coracoid appears to be more like that of the nodosaurid sauropelta (coombs, 1978a). when viewed together, these differences add support to our idea that the dry mesa ankylosaur elements may represent a different species than gargoyleosaurus parkpinorum. forelimb humerus: the revised hypodigm includes a well-preserved, undistorted right humerus (mwc 6745) that measures 263.5 mm in total length (figures 26a through 26f). there is some bone missing on the articular surfaces. the humeral head is missing less than 5 mm of bone as can be determined by the unabraded medial portion, which is deeply pitted for the cartilaginous cap. therefore, the total length of the humerus would be closer to 270 mm if perfectly preserved. even less bone is missing on the margins of the articular surfaces on the distal end. coombs (1978b) provides the most comprehensive description of ankylosaur forelimb morphology. many of the muscle origin and insertion scars are well expressed forming major landmarks in describing the morphology of the bone. there are tooth marks on the bone best exemplified by a series of seven on echelon cuts, 6 to 8 mm long and 3 to 6 mm apart on the posterior surface of the bone below the neck of the shaft. the proximal margin of the deltopectoral crest is well below the level of the humeral head and is lower than the internal process as in other polacanthids for which the humerus is known; polacanthus nhmuk r1106 (pereda-suberbiola, 1994; blows, 2015) and gastonia byuvp 14549 (listed as byu vp136 in kirkland, 1998, figure 6f). thus, the mediolateral width of the proximal end (96. 8 mm) is measured from the lateral margin of the humeral head to the internal process. the head of the humerus measures 73.1 mm across (mediolaterally) and anterior-posteriorly 43.6 mm. the humeral head is in line with the long axis of the humerus as in ankylosaurids, whereas it is inclined more medially in nodosaurids like sauropelta (coombs, 1978b). it is almost exclusively on the posterior and proximal surface and is scarcely visible anteriorly unlike the well-preserved gastonia humerus from the dalton wells quarry (figures 27c through 27h). the internal process forms a triangular, medial expansion of the humerus that is separated from the humeral head by a shallow trough sloping down the posterior surface such that it is not visible as a distinct notch in anterior view. this is the opposite case with gastonia. the maximum mediolateral width of the proximal end of the humerus from the proximal end of the deltopectoral crest to the position of the internal process is 137.5 mm. however, the lateral margin of the deltopectoral crest expands away from the shaft of the humerus, unlike that of polacanthus (pereda-suberbiola, 1994; and blows, 2015) and gastonia (kirkland, 1998) where it is nearly parallel to the long axis of the humerus. the deltopectoral crest is flexed anteriorly at about 80˚ relative to the long axis of the humeral head as in other polacanthids and nodosaurids, unlike struthiosaurids, ankylosaurids, and stegosaurs (thompson et al., 2011; kirkland et al., 2013). the anterior surface on the proximal end of the deltopectoral crest has a deep circular pit about 8 mm across on the anterior margin of the expanded insertion scar for the scapular deltoid muscle. the insertion for the pectoralis muscle forms a thickened elevated scar on the anterior surface on the distal end of the deltopectoral crest about 18 mm across. nearly opposite and more medial to this on the posterior surface of the deltopectoral crest is an even greater roughed expansion of more than 20 mm across that marks the insertion for the scapulohumeralis anterior muscle. thus, the distal end of the deltopectoral crest is markedly thicker at as much as 40 mm. a roughen attachment area separates the lower half of the 358 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 deltopectoral crest from the shaft of the humerus on the posterior side of the humerus instead of the proximally tapering ridge marking this boundary in gastonia and polacanthus. the distal end of the deltopectoral crest extends distally approximately 50% the total length of the humerus. the shaft of the humerus is waisted between the base of the deltopectoral crest and the distal condyles. at its narrowest, the shaft is 32.9 mm wide (mediolaterally) and is 35.2 mm wide (anteroposteriorly), with a circumference of 111.4 mm. a distinct ridge extends obliquely across its anterior surface from the deltopectoral crest to the margin of the radial condyles as in gastonia, but unlike polacanthus (blows, 2015; kinneer et al., 2016). the distal end of the humerus is 112.1 mm (mediolaterally). the lateral (radial) condyle is slightly smaller than the medial condyle and is nearly even with it distally. although separated by broad depressions anteriorly and posteriorly, no distinct notch separates the distal condyles as in polacanthus, whereas a shallow notch is present in gastonia. additionally, the medial condyle in gastonia is proportionally much narrower than in mymoorapelta. lateral to the radial condyle there is an expansion on the lower surface of the humerus for the lateral epicondyle. it is abraded, but clearly less expanded than in gastonia or polacanthus. coombs (1978a) noted ankylosaurid humeri could be distinguished from those of nodosaurids in having figure 26. forelimb bones from revised hypodigm of mymoorapelta. right humerus mwc 6745 in (a) cranial, (b) lateral, (c) caudal, (d) medial, (e) proximal, and (f) distal views. right ulna mwc 1814 in (g) cranial, (h) lateral, (i) proximal, (j) medial, (k) caudal, and (l) distal views. left ulna mwc 1814 in (m) cranial, (n) lateral, (o) caudal, (p) medial, (q) proximal, and (r) distal views. left ulna mwc 5643 and left radius mwc 5643 in articulation in (s) cranial view. left radius mwc 5438 in (t) cranial, (u) lateral, (v) caudal, (w) medial, (x) proximal, and (y) distal views. abbreviations: dp = deltopectoral process, hh = humeral head, lc = lateral condyle, mc = medial condyle, o = olecranon, s = sigmoid notch. 359 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 deltopectoral crests extending for 50% of the total length of the humerus with a flattened ovate vs. spherical lateral (radial) condyle. in this, polacanthids, including mymoorapelta, are like ankylosaurids in having a long deltopectoral crest with a flattened radial condyle (figures 26f and 27g). the known complete polacanthid humeri are essentially identical except, as noted above, and the humeri for gastonia and polacanthus are more robust with more strongly developed muscle attachments suggesting more mature individuals. gastonia (byu vp 14549) has a minimum circumference of 149.6 mm with a length of 287.5 mm. it is worth noting that most bones in the gaston quarry, as exemplified by ceum 11205 (figure 27i), are extremely flattened due to compaction, but it is difficult to explain the extremely distal margin of its deltopectoral process purely by compaction. perhaps this very ankylosaurid trait reflects ontogeny, as this is the largest known gastonia humerus. the partial humerus from the type specimen of gargoyleosaurus (figures 27a and 27b) is missing much of its proximal end and the distal end is distorted and, as noted by kilbourne and carpenter (2005), perhaps pathological. it is considerably more massively constructed with a minimum circumference of the shaft of 175 mm. ulnae: both the right and the left ulnae are preserved with the expanded hypodigm from the mygate-moore quarry (figures 26g through 26s). the right ulna, mwc 1814 (figures 26g through 26l), has a total length of 198.0 mm. it has been figured in previous descriptions of mymoorapelta (kirkland and carpenter, 1994, figure 6; kirkland et al., 1998, figures 4a and 4b). it has a massive olecranon. the lateral marfigure 27. forelimb of gargoyleosaurus and gastonia. humerus of holotype of gargoyleosaurus dmnh 27726 in (a) lateral and (b) anterior views. subadult gastonia right humerus from dalton wells quarry at utahraptor state park, north of moab, utah, byu 7510-14549 in (c) proximal, (d) cranial, (e) lateral, (f) caudal, (g) distal, and (h) medial views. gastonia left humerus from gaston quarry ceum 11205 in (i) cranial view. gastonia left ulna ceum 3565 in (j) lateral view. abbreviations: dp = deltopectoral process, hh = humeral head, ip = internal process, lc = lateral condyle, mc = medial condyle. o = olecranon, sn = sigmoid notch. 360 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 gin of the olecranon is slightly damaged, proximally and distally. the height of the olecranon from the base of the articular surface with the humerus is 65.5 mm. the shaft of the ulna is laterally compressed with a width of 18.9 mm, mediolaterally, and is anterolaterally narrowest just above the distal condyles at 25.3 mm. the anterior-lateral width of the ulna at the base of the proximal articular surface is 76.8 mm. the left ulna, mwc 5438, is better preserved (figures 26m through 26s) and has a total length of 198.4 mm. the articular surface from the top of the olecranon to the base of the sigmoid notch is 81.7 mm. the maximum width of the anterolateral face of the olecranon is 78.2 mm. the anterior-lateral width of the ulna at the base of the proximal articular surface is 83.9 mm. the distal end of the left ulna flexes slightly towards the radius, and measures 44.6 mm wide (mediolateraly) and is 28.8 mm wide (anterior-posteriorly). the shaft is flattened anterolaterally and measures at its narrowest 19.7 mm wide anteriolaterally by 24.1 mm across posteriolaterally with a minimum circumference of 82.4 mm just above the expansion for the distal condyle. on both ulnae, the olecranon is highly rugose with a striated texture that strengthens proximally. on both, three well-developed foramina penetrate the bone in a line parallel and just medial to the distinct rim that separates the vertical articular surface with the humerus. the radial notch is open and angled somewhat laterally. a low, rounded ridge extends proximally up to the top of the olecranon lateral to the medial process separating the laterally facing articular surface for the articular condyles of the humerus above the position for the proximal articular surface of the radius. the medial and lateral processes form a broadly obtuse angle of approximately 130˚, with the margin for the radius a raised roughed ridge that would have anchored cartilage and connective tissue. about 20 mm below this boundary there is a raised roughened area possibly for connective tissue that would be opposed to a similar matching roughed area on the radius. below this, the distal 30 mm is raised and roughened possibly for connective tissue that would be opposed to a similar matching roughed area on the distal end of the radius. the gap formed between these connective tissues between the ulna and radius can only be speculated upon, but the close correlation between these features suggests that there was little mobility between the ulna and radius. about 35 mm above the distal end of the ulna below the lateral process, a strongly developed but small tubercle extends out from the shaft. the margins of the distal end of the ulna are roughed for connective tissue. the distal end is flexed medially. the surface of the distal end is flattened with pitting for the attachment of cartilage. the ulnae in gastonia (figure 27j) appear to be considerably more massive with a proportionally large olecranon (kirkland, 1998; kilbourne and carpenter, 2005) as in cedarpelta (carpenter et al., 2008) and many ankylosaurs (maryańska, 1977). the more elongate ulnae of mymoorapelta are more similar to those found in peloroplites (carpenter et al., 2008) and other nodosaurids (carpenter et al., 1999). radius: the well-preserved left radius, mwc 5438 (figures 26s through 26y), is 156 mm long. the proximal end is widest anteroposteriorly at 59 mm. in proximal view the flattened proximal end is grooved and pitted to hold the cartilaginous cap and forms an obtuse triangle, with the open angle fitting between the medial and lateral process of the ulna below the radial notch. the proximal end is 39 mm wide, and slopes downward laterally at about 70˚ relative to the shaft, forming a continuous, flat articular surface for the humerus with the top of the medial process of the ulna. about 20 to 25 mm below the obtuse angle formed by the proximal end articulation with the ulna, there is a slightly raised roughed area that may be for connective tissue with ulna, below which, near the distal end there is a second larger raised area for connective tissue matching that on the distal end of the ulna. about 30 mm above the distal end of the radius, below the contact with the end of the medial process of the ulna, there is a strongly developed but small tubercle extending out from the shaft. the shaft of the radius is slender, sub-cylindrical, and 22.5 mm in diameter with a minimum circumference of 67 mm. there is a distinct tuberosity on the lateral side of the radius about 25 mm above the distal condyle near the midpoint of the shaft. the distal end is nearly circular in cross section and 361 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 smoothly convex with weak pitting for the cartilaginous cap. it measures 45.4 mm anteriorly-posteriorly and 39.9 mm mediolaterally. the margins are both rugose for connective tissue. the distal end of the radius is angled medially at about 70˚ relative to the shaft, such that the entire radius appears to be skewed laterally. in articulation with the ulna (figure 26s) and the humerus, the elbow was angled from the vertical by at least 20˚. manual elements: three metacarpals have been identified from the mygatt-moore quarry, two large examples (mwc 10638 and mwc 1816) and one smaller example (mwc 1908). the largest mwc 10638 (figures 28a through 28g) is proximodistally 48.7 mm long and proximally anteroposteriorly longer (31.0 mm) than wide (25.6 mm). the distal end is twisted 103° relative to the long axis of the proximal end and is 27.4 mm mediolaterally across its articulation and 20.2 mm mediolaterally. the minimum width of the shaft is 13.4 mm. this metatarsal is interpreted to represent metacarpal iii by comparison with ankylosaur manus models of currie et al. (2011) and senter (2011). the slightly smaller mwc 1816 (figures 28h through 28l) is 48.2 mm long, and proximally mediolaterally wider (32.8) mm than deep (19.8 mm). the distal end is twisted much less at about 10° to 15° relative to the proximal end; it is wider than long at 26.9 mm in mediolateral width and 16.2 mm depth. it may represent metacarpal ii (currie et al., 2011; senter, 2011). the smaller mwc 1908 (figures 28m through 28r), appears to be a more lateral, metacarpal only 29.9 mm long. its proximal end is more symmetrical at 21.3 mm wide and 17.1 mm deep. the distal end is 17.8 mm wide and 12.3 mm deep. it may represent metacarpal v. (currie et al., 2011; senter, 2011). there are two manual phalanges, mwc 1817 (figures 28s through 28x) and 3613 (figures 28y through 28cc), identified. most significantly are their extremely short lengths, less than a cm each, and near symmetrical convex distal and concave proximal ends. there is one possible manual ungual, mwc 939 (figures 28tt through 28xx). superficially it is similar to the pedal unguals. however, it is acutely pointed at its distal end (as opposed to rounded as in the pedal unguals) and it is asymmetric mediolateral. it is 39.6 mm long and 19.6 mm deep at its articulation. pelvic girdle ilium: in the initial description of mymoorapelta maysi (kirkland and carpenter, 1994), the ilium, mwc 1815 (figures 29a through 29f), was designated the holotype specimen for the species. even with the expanded hypodigm for the species presented here, this ilium is the most unique individual bone in mymoorapelta with its near rectangular shape in dorsal view and its long ventrally enrolled preacetabular process. mwc 1815 has a total anteroposterior length of 530 mm and horizontal width of 127 mm, at the position of the acetabulum. given the downward flexure of the preacetabular process, the ilium’s width is nearly the same front and back. there is no evidence of any distortion in the preservation of this bone and the vertically enrolled preactetabular process appears to be unique among ankylosauria. ventrally (figure 29f), the length from the anterior margin of the pubic peduncle to the posterior margin of the ischial peduncle is 164 mm. the width of the acetabulum between these peduncles (as expressed on the ilium) is 115 mm. the length of the opening of the acetabulum is estimated at 59.5 mm. the mediolateral depth of the acetabulum is 53 mm. the post-pubic length of the ilium from the center of the acetabulum is 192.3 mm making the length of the post-acetabular about equal to that of the length of the acetabulum. the pre-acetabular length of the ilium from the center of the acetabulum is 347.5 mm. the post-acetabular portion of the ilium is decidedly thicker from the ischial peduncle to the posterior margin. it is about as long as the length of the acetabulum as in polacanthids and nodosaurids (lull, 1921). the depth of the ilium at the pubic peduncle (from the top if the ilium) is 125.4 mm. the depth of the ilium at the ischial peduncle (from the top of the ilium) is 69.8 mm. the acetabulum was open unlike that of other ankylosaurs (coombs, 1978a; coombs, and maryańska, 1990; vickaryous et al., 2004; parrish, 2005) the length of attachment with the sacral yoke extends from near the posterior margin of the prepubic process, posteriorly for 209.5 mm. it is estimated that there were three sacral rib attachments and one caudal rib attachment in this sacral yoke. looking anteriorly, there is no specific scar for the first dorsal-sacral rib. 362 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 28. manual and pedal elements from revised hypodigm and referred specimens of mymoorapelta. metacarpal mwc 10638 in (a) dorsolateral, (b) dorsal, (c) medial, (d) ventral, (e) lateral, (f) dorsal, and (g) ventral views. metacarpal mwc 1816 in (h) ventral, (i) lateral, (j) medial, (k) proximal, and (l) distal views. metacarpal mwc 1908 in (m) ventral, (n) lateral, (o) medial, (p) dorsal, (q) proximal, and (r) distal views. possible manual phalanx mwc 1817 in (s) dorsal, (t) lateral, (u) proximal, (v) ventral, (w) medial, and (x) distal views. possible manual phalanx mwc 3616 in (y) medial, (z) ventral, (aa) lateral, (bb) proximal, and (cc) distal views. metatarsal possibly from right pes mwc 4028 in (dd) ventral, (ee) medial, (ff) lateral, (gg) proximal, and (hh) distal views. pedal phalanx mwc 3615 in (ii) dorsal, (jj) ventral, (kk) lateral, (ll) medial, (mm) proximal, and (nn) distal views. pedal phalanx mwc 1932 in (oo) ventral, (pp) lateral, (qq) medial, (rr) proximal, and (ss) distal views. possible manual ungual mwc 939 in (tt) dorsal, (uu) proximal, (vv) ventral, (ww) lateral, and (xx) other lateral views. pedal ungual mwc 6728 in (yy) dorsal, (zz) proximal, (aaa) ventral, (bbb) lateral, and (ccc) other lateral views. pedal ungual mwc 3752 in (ddd) dorsal, (eee) proximal, (fff) ventral, (ggg) lateral, and (hhh) other lateral views. pedal ungual mwc 3714 in (iii) dorsal, (jjj) proximal, (kkk) ventral, (lll) lateral, and (mmm) other lateral views. pedal ungual mwc 8237 in (nnn) dorsal, (ooo) proximal, (ppp) ventral, (qqq) lateral, and (rrr) other lateral views. 363 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 however, anterior to this rib position, there is thickening of the ventral surface of the ilium and a scar for the attachment of each of the three more anterior ribs under this ventral side. the most anterior of these has the distal end of the rib still attached; these ribs are approximately 54 mm apart. given that spacing, the next rib in the series would have been along the anterior margin of the ilium (figures 29b and 29f). the dorsal surface of the ilium (figure 29a) is crossed by dozens of grooves interpreted as representing tooth marks of a predatory dinosaur, in keeping with the hypothesis that the neural spines of the dorsal vertebrae were bitten off (kirkland and carpenter, 1994; kirkland et al., 1998). similar grooves were noted on the dorsal surface of the bexhill “polacanthus,” but were interpreted as representing a natural feature of unknown purpose but perhaps in relation to the overlying sacral shield in polacanthids (blows and honeysett, 2014b; blows, 2015). further study of these grooves is warranted. although no ilia were preserved with the type specimen of gargoyleosaurus parkpinorum, a complete right ilium 559 mm long with attached synsacrum from figure 29. pelvic girdles. holotype mymoorapelta right ilium mwc 1815 in (a) dorsal, (b) medial, (c) caudal, (d) lateral, (e) cranial, and (f) ventral views. lateral side of articulated proximal ischium and pubis of cactus park mymoorapelta mwc 2610 in (g) eternal mold and (h) latex peal. referred right ischium mwc 4027 in (i) lateral, (j) proximal, (k) caudal, (l) medial, and (m) anterior views. right pubis of holotype of gargoyleosaurus dmnh 27726 in (n) lateral view. abbreviations: a = acetabulum, iilp = ilial peduncle of ischium, ilp = ilialpeduncle of pubis, ip = ischial peduncle, obn = obturator notch, pp = pubic peduncle, r = rib scars on preacetabular portion of ilium by overlapping distal dorsal ribs. 364 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 a larger individual (dmnh 58831) was assigned to gargoyleosaurus based on comparison of its cervical ring (carpenter et al., 2013). several significant differences deserve to be pointed out. the preacetabular process is not nearly as enrolled laterally and angles away from the main axis of the ilium at about 30° (figure 19). the post-acetabulum is proportionally shorter, such that the length of the post-acetabular is about one half the length of the acetabulum as in more derived ankylosaurids (coombs, 1978b; carpenter et al., 2013). ischium: a well-preserved left ischium, mwc 4027 (figures 29i through 29m), was recovered with the type material, but its large size may indicate that it may pertain to the larger referred individual. the ischium has a total length of 404.5 mm. the width across the proximal end is 159.3 mm; between the peduncles, the slightly damaged opening of acetabulum measured approximately 72 mm. the pubic peduncle is smaller than the iliac peduncle and is somewhat subtriangular in shape. the pubic peduncle is flattened overall, somewhat trapezoidal in shape tapering to the edge of the open acetabulum. the ischium has a distinct bend about two-thirds of its length down the shaft. the upper portion of the ischium above the bend narrows slightly to 67.7 mm, at the bend it has widened to 99.4 mm, and the bend is 250.7 mm below the proximal end along the posterior margin. the distal length of the posterior margin of the ischium below the bend is 176.2 mm, and the distal end of the ischium is slightly expanded and measures 37.1 mm anteroposteriorly and 24.3 mm mediolaterally. the lateral margin above the distal end of the ischium is thickened and rugose, with an attachment area that extends all the way up along the medial posterior boundary to the bend in the ischium, which is expanded and rugose for the rectus abdominis and the ischiocaudalis (coombs, 1979). the attachment scar for the ischio-trochantericus starts above the terminal expansion and runs proximally up the lateral side of the posterior margin, just to and just above the bend on the ischium. the scar for the adductor femoris is not as well marked but is found along the anterior margin extending from well above the bend in the ischium at approximately the narrowest part of the upper ischium and to within less than 100 mm of the pubic peduncle. the expanded width of the ischium at the bend makes the overall ischium look less bent than is typical in nodosaurids (coombs, 1978a). however, in nodosaurids, the ischium does not expand at the bend. this ischium is most similar to that of gastonia burgei (kirkland, 1998; kinneer et al., 2016); however, it is narrower at the bend in gastonia. additionally, in gastonia lorriemcwhinneyae the thinner ischium is smoothy curved as in nodosaurids (kinneer et al., 2016). the angular bed in the ischium of mymoorapelta and gastonia burgei is reminiscent of that of many stegosaurs (galton and upchurch, 2004; maidment et al., 2015) and may well be a shared character that documents this as the primitive character state in ankylosauria with the straight ischium of ankylosaurids the derived character state (kirkland, 1998; kirkland et al., 2013). there is a lateral mold of proximal portion of a right ischium in articulation with a right pubis preserved in a sandstone block (gaston et al., 2001) from the cactus park mymoorapelta, mwc 2610 (figures 29g and 29h). though adding little to the morphological description of the ischium, its articulation with its pubis lends considerable support to the documentation that mymoorapelta maintained an open acetabulum. pubis: although no pubis is preserved in the type material of mymoorapelta, the lateral mold of the cactus park mymoorapelta, mwc 2610 pubis (figures 29g and 29h) provides valuable information as to the morphology of the pubis in mymoorapelta. the right pubis is preserved with the holotype of gargoyleosaurus (figure 29i) and was described in detail by kilbourne and carpenter (2005). the pubis of mymoorapelta and gargoyleosaurus are morphologically similar to each other in that the main body is subrectangular and is smooth where it makes up a portion the acetabulum. the slender postpubic process extends from near the center of the main body in both, and both bear a small ventrally situated triangular flange. the post acetabulum is more complete in mymoorapelta and extends ventrally along the length of the preserved portion of the ischium (figures 29g and 29h). an elongate postpubic process is also recognized in kun365 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 barrasaurus from the lower cretaceous of australia, although it is highly reduced in most other ankylosaurs where known (molnar, 1996; vickaryous et al., 2004; parrish, 2005; raven, 2021; raven et al., 2023). hindlimb femur: the hind limb is poorly known in mymoorapelta and gargoyleosaurus. only the femur is known in the type material of gargoyleosaurus (kilbourne and carpenter, 2005). at 465 mm long and with a shaft 193 mm in circumference, it is robustly constructed and primitive in maintaining a well-separated femoral head and anterior trochanter. it is refigured herein (figures 30a through 30e) largely for completeness and to provide contrast to the smaller tibia and the type specimen of mymoorapelta, mwc 6746 (figures 30f through 30i). an unprepared femur is present with the cactus park mymoorapelta, mwc 2610. tibia: a partial left tibia is preserved at the mygatt moore quarry, mwc 6746 (figures 30f through 30i). overall, it compares well with the partial tibia dmnh 15162 (figures 30j through 30m) from garden park, colorado. it is 251.3 mm long and damaged both proximally and distally. the proximal end is damaged around the entire proximal margin and the proximal surface is flat (slightly convex) and slopes posterolateral. the distal end on the side medial to the contact with the astragalus is broken off. as with other ankylosaurs, the tibia is expanded on both ends, with the long axis of the distal articulation twisted about 70° laterally, relative to the proximal end. the shaft is narrow with a 36.2 mm mediolateral width, with the narrowest anterior-posterior width of 33.9 mm a bit lower on the shaft. a slight notch is on the lateral margin of the tibia distally for the articulation of the fibula. the astragalus is not fused to the tibia. in nearly all features this tibia compares well with an isolated tibia dmns 15162 (figures 30j through 30m) from garden park described in kirkland et al. (1998). pes: one metatarsal, mwc 4028 (figures 28dd through 28hh), was collected. it is tentatively identified as the third and is 90.1 mm long. its proximal end is subrectangular, deeper at 54.6 mm tall, and 25.4 wide indicating that proximally, the metatarsals were closely appressed on either side. the posterior articulation slopes posteriorly. the distal end is asymmetric. there are two proximal phalanges. mwc 3615 (figures 28ii through 28nn) is 31.8 mm in length and is asymmetric (anterior medially). mwc 1932 (figures 28oo through 28ss) is 26.3 mm in length. it has a larger proximal articulation than mwc 3615 and is less mediolateral asymmetric. there are four pedal unguals (figures 28yy through 28rrr). they are wedge shaped in lateral view with evenly rounded termination. the largest of these, mwc 3714 (figures 28iii through 28mmm), has a maximum dorsal length of 48.3 mm, a proximal height of the articulation of 26.9 mm, and is damaged on both lateral margins. the best-preserved pedal ungual (mwc 3752) is only slightly smaller at 45.1 mm long (figures 28ddd through 28hhh). the proximal articulation is 20.1 mm high and 24 mm wide. its surface is fairly rugose, and in dorsal view has a blunt ‘arrowhead’ shape with strong vascular grooves on either side of the attachment point of the claw. the unguals are similar to those of nodosaurids such as sauropelta (ostrom, 1970) and niobrarasaurus (carpenter et al., 1995), and are proportionally longer than those of ankylosaurids such as dyoplosaurus (arbour et al., 2009) and pinacosaurus (currie et al., 2011). the partial manus reported for the type specimen of dracopelta from the upper jurassic of portugal (pereda-suberbiola et al., 2004) has been reinterpreted as a pes based on its short blunt unguals, phalangeal formulas, and the presence of other right hindlimb elements, namely a partial femur, and tibia and fibula (russo and mateus, 2021; russo, 2024). there is a partial articulated pes from the cactus park mymoorapelta mwc 2610 (figure 31). it is interpreted to represent a right pes prepared in dorsal view on the sandstone block in which it is preserved. metatarsal one is considered to missing with the preserved metatarsal tentatively identified as representing two through five. a single tarsal is preserved and overlaps the proximal articular surfaces of metatarsals two and three. as with the preserved third metatarsal of the type specimen mwc 4028 the proximal end of metatarsal three is narrow. the numbers of pedal digits in ankylo366 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 saurids are only known for a few taxa and vary between and within species (currie et al., 2011) and as such is a difficult character to utilize in phylogenetics. dermal skeleton all thyreophorans are characterized by an extensive covering of large scales underlain by dermal bone (osteoderms) forming transverse bands that are commonly recovered in the fossil record (brown, 1908; coombs, 1971, 1978a; martill et al., 2000; arbour et al., 2014; arbour and evans, 2017; brown, 2017; brown et al., 2017; norman, 2020c). however, although we are confident that the overall pattern of scales is present figure 30. hindlimb bones. holotype femur of gargoyleosaurus dmnh 27726 in (a) proximal, (b) anterior, (c) lateral, (d) posterior, and (e) posterior views. mymoorapelta revised hypodigm partial left tibia mwc 6746 in (f) anterior, (g) lateral, (h) medial, and (i) posterior views. distal right tibia from garden park dmnh 15162 in (j) anterior, (k) lateral, and (l) posterior views, and mwc 6746 (m) distal view. abbreviations: 4th = fourth trochanter, a = depression for astragulas, at = anterior trochanter, cn = cnemial crest, h = femoral head, lc = lateral condylus, mc = medial condylus. 367 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 when the young thyreophoran first hatches from its egg (stanford et al., 2011), the overall ontogenetic history of thyreophoran osteoderms beyond the early ossification of the cervical rings in the ankylosaur pinacosaurus (hill et al., 2003; burns et al., 2011, burns, 2015) is unknown. in most ankylosaurs, there are no midline osteoderms, and the transverse bands (rows) are formed of flat or low keeled elements along each side of the midline, which become more spinose or plate-like laterally. large, erect, dorsal spines are an exception and are only known in a few taxa such as the derived polacanthinae polacanthus (ex. blows, 2015) and gastonia (kirkland, 1998; kinneer et al., 2016), and the european struthiosaurinae nodosauridae, struthiosaurus (nopcsa, 1929; ösi and pereda-suberbiola, 2017) and hungarosaurus (ösi and makádi, 2009; ösi and pereda-suberbiola, 2017). superficially basal thyreophoran osteoderms in scutellosaurus are smooth with fine pits and short irregular grooves on the order of a mm across (main et al., 2005). a similar appearance is characteristic of mymoorapelta osteoderms (kirkland and carpenter, 1994; kirkland et al., 1998). although it has been noted that the surface of polacanthid ankylosaurs is smooth, the fine pitting and grooving on the surface of mymoorapelta osteoderms has not been noted. however, in gargoyleosaurus (kilbourne and carpenter, 2005), gastonia (kirkland, 1998; blows, 2015; kinneer et al., 2016), and hoplitosaurus (bodily, 1969) the surface of the osteoderms is considerably smoother. blows (1987, 2015) considered polacanthus osteoderms to have an overall coarser surface texture than any of the other polacanthid. structurally, polacanthid osteoderms are closer to basal thyreophoran osteoderms like those of scutellosaurus and scelidosaururs in having a well-developed external and internal cortex with structural fibers surrounding a remodeled trabecular core that may be from 50% to 80% of the total thickness of the osteoderm (scheyer and sanders, 2004; burns, 2010; burns and currie, 2014). nodosaurids differ in having a very thin or no internal cortex, whereas ankylosaurids have proportionally thinned the entire osteoderm retaining both external and internal cortex with some including haversian bone in their cores (scheyer and sander, 2004; burns and currie, 2014). both gargoyleosaurus (hayashi et al., 2010) and mymoorapelta (burns and currie, 2014) fit this model well (figure 32). as with basal thyreophorans, both gargoyleosaurus and mymoorapelta have concave bases (scheyer and sanders, 2004; hayashi et al., 2010; burns and currie, 2014), however most ankylosaurs assigned to the polacanthinae have flatter, less concave bases (blows, 2015). a very large polacanthine from the poison strip member of the lower cretaceous cedar mountain formation of utah has thickened dorsal osteoderms with decidedly convex bases (bodily, 1969). similar massive dorsal osteoderms with convex bases are also present in hoplitosaurus marshi from the lower cretaceous lakota formation of south dakota (gilmore, 1914, figure 70). figure 31. cactus park mymoorapelta partial left pes mwc 2610 in dorsal view. abbriviations: mt2 = second metatarsal, mt3 = third metatarsal, mt4 = fourth metatarsal, mt5 = fifth metatarsal, t = tarsal. 368 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 osteoderm is used in reference to nearly all dermal elements of the fossils described herein, with the term ossicle for simple ovoid dermal bones of approximately 1 cm or less in diameter following (burns and currie, 2014). cervical half rings may be fused or unfused for jurassic polacanthids. dorsal armor is ventrally concave with larger crested subrectangularto teardrop-shaped elements interpreted to be situated anteriorly, with smaller, more posterior dorsal osteoderms more circular in outline with low crest or low apical prominence. the larger osteoderms in the sacral region are also round with low apical prominences surrounded by fused ossicles. simple elongate crested osteoderms are considered to be situated on the legs, along the tail, and/or on the lateral margins of the body posterior to the posteriorly grooved shoulder spines and anterior to the sacral-caudal plates. the bases of the grooved shoulder spines and sacral caudal plates are deeply excavated with medial vascular openings a few mm in diameter (kirkland et al., 1998). generally, the form and arrangement of osteoderm are assumed to be of taxonomic significance (e.g., coombs, 1978a; ford, 2000; burns, 2008), but they have rarely and only recently been applied to phylogenetics (vickaryous et al., 2004; arbour and currie, 2016; raven, 2021; raven et al., 2023; russo, 2024). cervical ring elements: several osteoderms from the cervical rings of mymoorapelta have been recovered from the mygatt-moore quarry (figure 33). to properly describe the cervical armor of mymoorapelta, it is important to consider the morphology of basal ankylosaur cervical armor in a phylogenetic sense. ankylosaurs cervical rings are made up of three pairs of cervical osteoderms fused to a band of underlying dermal bone in adult animals. ankylosaurids possess two full cervical rings and nodosaurids possess three cervical rings divided at the midline (penkalski, 2001; vickaryous et al., 2004). scelidosaurus primitively has five to six cervical rings consisting of three pairs of osteoderms with deeply interdigitating sutures based on examining the cast of david sole’s (amateur british collector) specimen exhibited in st. george, utah sgds 1311 described by norman (2020c). the fused cervical rings in derived ankylosaurs consist of cervical osteoderms fused to a band formed of subdermal connective tissue (arbour and currie, 2013a, 2016). osteoderms pertaining to the cervical rings of mymoorapelta are recognized by the presence of ossified connective tissues attached to the base of these osteoderms (figure 33) with that of the lateral spines origfigure 32. osteoderm histology. mymoorapelta dorsal osteoderm mwc 7064 (a and c) part and counterpart of cut osteoderm. (b) thin section. gargoyleosaurus dorsal osteoderm dmnh 27726 (d and e) part and counterpart of cut osteoderm. 369 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 inating from the base of spines (figures 33g through 33j) as in gastonia (figures 34i, 34k, and 34l). gargoyleosaurus was found with parts of two cervical rings (figures 34a through 34d) that are more completely preserved than those of mymoorapelta. the articulated skeleton of dracopelta from the upper jurassic of portugal has three cervical rings (russo, 2024). given the general incompleteness of the type specimen of gargoyleosaurus, it cannot be discounted that a third ring is missing in this specimen. kilbourne and carpenter’s (2005) interpretation that the first cervical ring of gargoyleosaurus included a single, medial figure 33. cervical osteoderms from revised hypodigm of mymoorapelta. possible first cervical half ring section mwc 6977 in (a) posterior, (b) anterior, (c) dorsal, (d) ventral, (e) lateral, and (f) medial views. possible second cervical spine mwc 1825 in dorsal (g) and (h) ventral views. possible third cervical spine mwc 6752 in (i) dorsal and (j) ventral views. anterior medial cervical half ring fragment mwc 3744 in (k) dorsal and (l) ventral views. cervical or perhaps anterior dorsal osteoderm mwc 1834 in (m) dorsal, (n) ventral, (o) lateral, (p) posterior, and (q) other lateral views. cervical ring fragment mwc 5320 in (r) dorsal, (s) ventral, and (t) lateral views. 370 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 osteoderm unlike any previously described ankylosaur has been substantiated by the identification of a similar midline osteoderm on the midline of the first cervical ring of dracopelta (russo, 2024). unfortunately, no lateral spines are preserved with the cervical rings of dracopelta. figure 34. comparison of cervical osteoderms. (a through d) gargoyleosaurus dmnh 27726. part and counterpart of cut first right quarter ring, (a and b) and right second quarter ring in (c) dorsal and (d) ventral views. second right quarter ring of gargoyleosaurus from simon quarry dmnh 58831 in (e) dorsal and (f) ventral views. mymoorapelta second lateral cervical spine mwc 6753 in (g) dorsal view. gastonia burgei first cervical ring ceum 1212 in (h) dorsal view. gastonia burgei second or possibly third lateral cervical spine ceum 1215 in (i) dorsal view. gastonia lorriemcwhinneyae large first cervical ring dmns 45665 in (j) dorsal view. gastonia lorriemcwhinneyae second lateral cervical spine dmns 49698 in (k) ventral view. gastonia lorriemcwhinneyae third lateral cervical spine, “splate” dmns 57635 in (l) ventral view. 371 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 based on this interpretation, gargoyleosaurus had a minimum of two cervical rings as in ankylosaurids but not joined at the midline as in a nodosaurids. each half ring was ventrally concave to conform to the neck and was thickest where each major osteoderm came together. the larger half ring (figure 34c) from the midline out was formed of the small scute with a central apex followed by a keeled scute two to three times larger, and a triangular plate sticking out laterally from the neck and, although forming a nearly equilateral triangle, was recurved anteriorly. small ossicles are fused to the dorsal surface of the ring on the margins and intermediate to these larger elements in the larger second ring from the simon quarry (figures 34e and 34f). note, that the cervical ring section figured for tianchisaurus nedegoapeferima from the middle jurassic of northwestern china is superficially like those of gargoyleosaurus (dong, 1993). in mymoorapelta, the cervical rings may represent a less mature stage of development as the major elements are not fused together. however, it is important to recognize that fully fused cervical rings are not known for any polacanthine taxon (e.g., gastonia [kirkland, 1998; blows, 2015; kinneer et al., 2016]). the extensive collection of gastonia lorriemcwhinneyae from the type locality at the dmnh includes multiple examples of each of three types of lateral cervical spines (kinneer et al., 2016). 1. a somewhat triangular spine attached to a curved basal ring of connective tissue that would have wrapped around the neck just posterior to the back of the skull (figure 34j). this spine is interpreted as lining up with the postorbital boss at the back of the skull. the spine would angle anteriodorsally, whereas the same spine in gastonia burgei (figure 34h) would angle out more horizontally. these are interpreted as representing lateral spines of the first cervical ring. 2. a broad spine (figure 34k) with a moderately elongate tip that appears to be longer than those identified as comparable in gastonia burgei (figure 34i). ossified connective tissue extends out of the base of these spines and are considered to be analogous to the lateral spines preserved in the half rings of gargoyleosaurus. these spines are interpreted as representing the lateral spines of the second cervical ring. 3. a narrow, elongated spine with a broad base (figure 34l) matches the morphology of the splates (spine-plates) in polacanthus and hoplitosaurus (gilmore, 1914, plate 28; blows, 1987, 2001, 2015; pereda-suberbiola, 1993, 1994; blows and honeysett, 2014b). this cervical spine morphology is not recognized in gastonia burgei. blows (2015) interpreted these as being from the shoulder region, but herein, we propose that these as representing the lateral spines of the third cervical ring. it is not possible to assign the dorsal osteoderms to specific cervical rings in mymoorapelta, but we can propose the placement of the lateral cervical elements to specific rings. kilbourne and carpenter (2005) mistakenly interpreted that the solid blade-like plates (spines) of mymoorapelta as not represented in gargoyleosaurus; however, we recognize them as representing the unfused lateral plates of mymoorapelta’s cervical rings (blows, 2015). these cervical spines are similar to those of the second ring in gastonia (kirkland, 1998, figures 7a through 7d) (figures 34i, 34k, and 34l). their dorsal surfaces and thus orientation are recognized by the presence of small ossicles fused to their bases on their dorsal side as in gargoyleosaurus. the first cervical ring in mymoorapelta may be represented by mwc 6977 (figures 33a through 33f) and the second cervical ring is 56.0 mm wide anterioposteriorly at the apex of the scute and about 47 mm thick. the line marking a separation between the keratin-covered external portion of the scute and the internal ring of bone is best developed along the posterior margin. the medial of element, where it would articulate with the next more lateral scute, has a deep and complexly fluted surface similar to that observed between adjoining cervical elements in the scelidosaurus, sgds 1311. the small biconvex cervical plate, mwc 1825 (figures 33g and 33h), is interpreted as possibly representing the lateral spine of a right cervical half ring. 372 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 the anterior edge is longer and more convexly arcuate. weak ridges about 0.5 cm apart extend from the base of the dorsal surface and toward the apex. one small ossicle fused to the posterior margin of the base appears as a small subsidiary spine. this cervical plate is 51.1 mm wide at its exposed base, 27.9 mm thick, and extended outward 59.4 mm. blows (2001) speculated that this plate may represent one of the spines (his “tricorn”) from immediately behind the skull in scelidosaurus (norman, 2020c). the larger cervical spine (mwc 6752) is interpreted to represent the lateral spine of the third cervical half ring. this cervical spine is 76.6 mm wide anteroposteriorly at its exposed base, 34.4 mm thick, and extended outward 76.0 mm and, thus, while thicker, it is similar in size (figure 34g) to the lateral spine on the smaller (figures 4a and 4b) versus the larger cervical ring (figures 34c and 34d) of the gargoyleosaurus type specimen (kilbourne and carpenter, 2005). the plate is nearly flat on the dorsal surface and convex on the ventral surface and is convexly arcuate anteriorly and slightly concave posteriorly. very weak ridges nearly 1 cm apart extend from the exposed base toward the apex of the plate on its dorsal surface. similar ridges are more strongly expressed in the lateral cervical spine of the largest cervical half ring of gargoyleosaurus from the simon quarry (figures 34e and 34f) and are not expressed at all in gastonia. blows (2015, figure 7.10) suggested that elongate ridged spines attached a basal plate of connective tissue from the compton bay polacanthus (nhmuk pv r9293) and represent upright cervical spines oriented at 90° to the interpreted orientation of the cervical spines discussed here. laterally oriented cervical spines such as described here for mymoorapelta, gargoyleosaurus, and gastonia, differ strongly from the cylindrical, upright cervical spines that occur in struthiosaurus (seeley, 1881) and hungarosaurus (ösi et al., 2019). it is assumed that the more medial dorsal cervical osteoderms are oriented, so the “medial” ridge or keel (burns, 2008) is more laterally positioned with its apex positioned posteriorly (figures 33m through 33t). the smaller of the cervical osteoderms (mwc 3744) is ventrally broken along its posterior and lateral side. however, the separation between the keratin-covered external portion of the scute and the internal ring of bone is apparent anteriorly. medially, small intermediate ossicles are present along the broken margin. it is 44.8 mm wide anteroposteriorly at the apex of the scute and 46.3 mm thick. we hypothesize that the initial origin of the cervical bands in ankylosaurids would have been from the ossification of the connective tissues originating from the base of the lateral cervical spines of primitive ankylosaurs like mymoorapelta. cervical rings with spinose lateral plates are not characteristic of ankylosaurids (coombs, 1978a; coombs and maryańska, 1990; vickaryous et al., 2004; parrish, 2005) and some nodosaurids such as stegopelta (carpenter and kirkland, 1998), silivaurus (eaton, 1960; carpenter and kirkland, 1998), and panoplosaurus (carpenter, 1990), whereas they characterize many nodosaurids such as sauropelta (carpenter, 1984; carpenter and kirkland, 1998), edmontonia (carpenter, 1990), and borealopelta (brown, 2017; brown et al., 2017) and struthiosaurids such as struthiosaurus (seeley, 1881; nopcsa, 1929; pereda-suberbiola and galton, 2001) and hungarosaurus (ösi, 2005; ösi et al., 2019). dorsal osteoderms: the first fossils of mymoorapelta recognized at the mygatt-moore quarry as an ankylosaur from the morrison formation were three dorsal osteoderms recovered in august of 1989 (figures 35n, 35o, and 35dd through 35gg). subsequently, many osteoderms attributed to the dorsal surface of mymoorapelta have been recovered from the site for which the 36 best-preserved examples are figured here to show the breadth of anatomy displayed by these osteoderms (figure 35). largely, dorsal osteoderms are identified as having a base length longer than the height of the osteoderm. whereas most of these osteoderms are attributed to the back of mymoorapelta overlying the ribs, some may have been from tail and the legs. some large subrectangular to ovate osteoderms are interpreted to be from the shoulder region (figures 35a through 35m) like those in many nodosaurids (lambe, 1919; russell, 1940; carpenter, 1990; brown, 2017; brown et al., 2017), struthiosaurids (ösi, 2005; kirk373 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 land et al., 2013; ösi et al., 2019) and at least some ankylosaurids (carpenter, 2004; arbour and currie, 2013b, arbour and mallon, 2017). large, subrectangular osteoderms are not present in the shoulder region of dracopelta (russo and mateus, 2021; russo, 2024). the hypothetical orientation on mymoorapelta’s dorsal shoulder osteoderms is based on the orientation of osteoderms on the backs of other ankylosaurs where they are preserved in situ such as edmontonia (matthews, 1922) and borealopelta (brown, 2017; brown et al., 2017). these osteoderms are somewhat longer anteroposteriorly than wide and narrow anteriorly with figure 35. caption is on the following page. 374 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 a laterally situated keel that comes to a low apex at the posterior margin of the osteoderm. the base of these osteoderms are deeply excavated under the posterior apex of this keel. many of the larger dorsal osteoderms of nodosaurids are distinctly different, having tear-drop or comma shapes with the posteroventral depression extending beyond the ventral margin of the osteoderm into the overhanging apex of the medial keel (lambe, 1919; burns, 2008). smaller oval to nearly circular osteoderms are typically about 50 mm or less in diameter and are more abundantly associated with the holotype of mymoorapelta (figures 35u through 35ee). in these, the crest with its posterior apex is more medially oriented. these are interpreted to form rows on the back of mymoorapelta anterior to the sacrum. it is possible that some of the more anteroposteriorly elongate forms were situated on the dorsal surface of the tail (figures 35mm through 35oo and 35tt through 35aaa). there is no evidence for the abundant interstitial ossicles characteristic of the polacanthine ankylosaurs from the cedar mountain formation (kirkland, 1998; kinneer, et al., 2016; kirkland et al., 2016). although there were fewer curated examples, a similar array of dorsal osteoderms (figure 36) are documented for the holotype of gargoyleosaurus. similar large osteoderms from the shoulder region (figures 36a through 36l) are present as are smaller osteoderms (figures 36q through 36aa) that would have formed rows farther back dorsally on the type specimen of gargoyleosaurus (kilbourne and carpenter, 2005). large (2023) identified the ankylosaur specimen from the hanksville-burpee quarry (figure 1) as gargoyleosaurus based on a distinct depression of the dorsal osteoderms lateral to the medial keel. this depression is apparent on the larger dorsal osteoderms, but not so much on the smaller, more posterior osteoderms (figure 36), so we consider this identification tentative, basically considering the limited diagnostic skeletal material associated with this specimen to date. however, we do agree that dorsal osteoderms, particularly when examined in a large population of elements, may well be of taxonomic importance. the many dorsal osteoderms from the compton bay polacanthus, nhmuk pv r9293 (blows, 1987, 2015), appear to be diagnostic in figure 35 is on the revious page. dorsal osteoderms from revised hypodigm of mymoorapelta. anterior dorsal osteoderm mwc 1835 in (a) dorsal, (b) caudal, and (c) ventral views. anterior dorsal osteoderm mwc 1836 in (d) dorsal, (e) caudal, and (f) ventral views. anterior dorsal osteoderm mwc 4018 in (g) dorsal, (h) caudal, and (i) ventral views. anterior dorsal osteoderm mwc 4223 in (j) dorsal and (k) ventral views. anterior dorsal osteoderm mwc 4030 in (l) dorsal view. smaller possible anterior dorsal osteoderm mwc 6761 in (m) dorsal view. smaller possible anterior dorsal osteoderm mwc 1832 in (n) dorsal and (o) ventral views. smaller possible anterior dorsal osteoderm mwc 6753 in (p) dorsal view. section of fused sacral shield mwc 1838 in (q) dorsal and (r) ventral views. section of fused sacral shield mwc 6751 in (s) dorsal and (t) ventral views. dorsal osteoderm mwc 6762 in (u) dorsal view. dorsal osteoderm mwc 6755 in (v) dorsal view. dorsal osteoderm mwc 4228 in (w) dorsal view. dorsal osteoderm mwc 6768 in (x) dorsal view. dorsal osteoderm mwc 6767 in (y) dorsal view. dorsal osteoderm mwc 6769 in (z) dorsal view. dorsal osteoderm mwc 6763 in (aa) dorsal view. dorsal osteoderm mwc 4029 in (bb) dorsal view. dorsal osteoderm mwc 5016 in (cc) dorsal view. dorsal osteoderm mwc 1826 in (dd) dorsal and (ee) ventral views. dorsal osteoderm mwc 1829 in (ff) dorsal and (gg) ventral views. dorsal osteoderm mwc 6766 in (hh) dorsal view. dorsal osteoderm mwc 1831 in (ii) dorsal and (jj) ventral views. dorsal osteoderm mwc 6759 in (kk) dorsal view. dorsal osteoderm mwc 6764 in (ll) dorsal view. elongate dorsal osteoderm mwc 6754 in (mm) dorsal view. elongate dorsal osteoderm mwc 4196 in (nn) dorsal view. elongate dorsal osteoderm mwc 6765 in (oo) dorsal view. dorsal osteoderm mwc 6760 in (pp) dorsal view. dorsal scute mwc 6757 in (qq) dorsal view. dorsal osteoderm mwc 1911 in (rr) dorsal view. dorsal osteoderm mwc 6756 in (ss) dorsal view. elongate “hollow” osteoderm mwc 10487 in (tt) dorsal, (uu) anterior, (vv) lateral, and (ww) ventral views. elongate “hollow” osteoderm mwc 10486 in (xx) dorsal, (yy) anterior, (zz) lateral, and (aaa) ventral views. dorsal osteoderm mwc 5838 in (bbb) dorsal view. dorsal osteoderm mwc 6758 in (ccc) dorsal view. dorsal osteoderm mwc 5200 in (ddd) dorsal view. small dorsal osteoderm mwc 3860 in (eee) dorsal view. 375 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 also having a depression lateral to the keel and having a distinct ridge around the margin of the osteoderm. these features are not present in the holotype of polacanthus foxi, nhmuk pv r175 (blows, 2015), supporting the separation of these specimens proposed by raven et al. (2020). likewise, the bases of the larger dorsal osteoderms (including dorsal spines) are surrounded by a circumference marked by radial ridges and grooves in gastonia burgei that are not present in gastonia lorriemcwhinneyae (kirkland, 1998; kinneer et al., 2016). there are no examples of massive dorsal spines in mymoorapelta, gargoyleosaurus (kilbourne and carpenter, 2005), and dracopelta (russo, 2024) as have been documented in derived polacanthids such as gastonia, hoplitosaurus, and polacanthus (gilmore 1914; blows, 1987, 2015; pereda-suberbiola, 1993, 1994; kirkland, 1998; kinneer et al., 2016) and possibly in nodosaurus (lull, 1921). figure 36. dorsal osteoderms from holotype of gargoyleosaurus parkpinorum. large dorsal osteoderms from shoulder region in dorsal views (a through c). large dorsal osteoderm from shoulder region in (d) dorsal and (e) posterior views. large dorsal osteoderm from shoulder region in (f) dorsal and (g) posterior views. large dorsal osteoderms in dorsal view (h and i). large dorsal osteoderm in (j) dorsal, (k) lateral, and (l) ventral views. elongate osteoderms (m through p). dorsal osteoderms in dorsal views (q, r, and u through aa). dorsal osteoderms in (s) dorsal and (t) lateral views. fragments of sacral shield in dorsal view (bb and cc). portion of sacral shield in (dd) dorsal and (ee) ventral views. 376 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 sacral shield: a sacral shield of fused osteoderms across the pelvic area was once thought to be a unique characteristic of polacanthine ankylosaurs (blows, 1987; pereda-suberbiola, 1994; kirkland, 1998; ösi and pereda-suberbiola, 2017; carpenter, 2001) but is now acknowledged to be widespread across various ankylosaur clades (arbour et al., 2011, 2014; raven, 2021; raven et al., 2023). arbour et al. (2011) defined a sacral or pelvic shield as a continuous carapace of osteoderms, not forming transverse bands, extending across the ilia and sacrum of an ankylosaur and noted that they were represented by three distinct morphologies: 1. unfused osteoderms in the form of rosettes but not coossified, 2. fused osteoderm rosettes, and 3. coossified polygonal osteoderms of fairly uniform size. rosettes are defined by larger osteoderms isolated from each other by bands of smaller ossicles. type 2 sacral shields appear to be restricted to polacanthid ankylosaurs, whereas the other sacral shield types are found in both ankylosaurid and nodosaurid clades (arbour et al., 2011). both the type specimen of mymoorapelta (figures 35q through 35t) and the type specimen of gargoyleosaurus (figures 36bb through 36ee) only preserve portions of what can best be described as partial rosettes of incompletely fused sacral shields (kirkland et al., 1998; kilbourne and carpenter, 2005). it would be a logical conclusion to assume that these taxa did not process fully formed sacral shields, particularly as no fully formed sacral shields have yet been recognized for either species of gastonia (kirkland, 1998; kinneer et al., 2016). however, a fully formed sacral shield is preserved in sandstone blocks associated with the pelvic region of the cactus park mymoorapelta specimen (figure 37). although, mostly represented by external molds, the fossils seem to indicate that the sacral shield was constructed of large osteoderms like the isolated presacral osteoderms from the holotype of mymoorapelta arranged in anteroposterior directed rows surrounded by small ossicles (kirkland, 1999; blows, 2015). larger osteoderms may have been arranged along the lateral margins (figure 37a). the specimens suggest that a fully fused sacral shield was developed in mature or even gerontic individuals of both mymoorapelta, gargoyleosaurus, and gastonia. it is worth noting that dracopelta also processed a fully developed sacral shield (russo, 2024). the sacral shield of polacanthus foxii had a more irregular arrangement of larger osteoderms across the center of the shield although clearly laterally large, slightly elongate osteoderms ran along its lateral and posterior margins (hulke, 1888; pereda-suberbiola, 1994; blows, 2015; raven et al., 2020). the larger osteoderms on the sacral shield sections of gastonia burgei are distinctive in that, like its larger dorsal osteoderms, they are surrounded by a circumference marked by radial ridges and grooves that are absent in gastonia lorriemcwhinneyae (kirkland, 1998; kinneer et al., 2016). shoulder spine: a single beautifully preserved left shoulder spine, mwc 1816 (figures 38a through 38d), is known from the type material of mymoorapelta; it was described and figured in kirkland and carpenter (1994) and kirkland et al. (1998). its anterior length is 284.6 mm, and its posterior length is 219.1 mm. as in gargoyleosaurus, gastonia, polacanthus, and hoplitosaurus, it has a wide posterior groove 10 to 15 mm deep that extends from the apex to the base of the spine, giving the spine a triangular cross section unlike any of the plates described below. the spine is 57.1 mm wide below the posterior groove. the excavated attachment area extends up the spine posteriorly such that the spine is interpreted to be reclined at an angle of about 45˚ relative to the base length (135.5 mm) of the attachment area. about the first 40 mm of the anterior edge is more vertically oriented before inclining posteriorly. as with the majority of the caudal plates there are weak ridges 12 to 14 mm apart on the dorsal face of the spine that extend from the base distally before fading away about halfway to the apex of the spine. the ridges do not converge on the apex of the spine but maintain their spacing such that they would intersect with the ante377 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 rior margin of the spine if they did not vanish on the surface first. the ridges are best developed posteriorly. two grooved shoulder spines (figures 38e through 38h) are present among the elements preserved with the type specimen of gargoyleosaurus (dmnh 27726) (kilbourne and carpenter, 2005). although both are more reclined with a narrower posterior groove and lack dorsal ridges, their general morphology is strikingly similar to that of the mymoorapelta shoulder spine. both were initially described as right shoulder spines as they appeared to be articulated (kilbourne and carpenter, 2005), but we interpret only the longer, more erect spine (figures 38e and 38f) as being from the right side, whereas the lower, even more reclined spine (figures 38g and 38h) as being from the left side of the animal. we are in agreement that there was a minimum of two pairs of posteriorly grooved shoulder spines in gargoyleosaurus. the question remains as to whether there was a more erect shoulder spine like that preserved in mymoorapelta situated more anteriorly and is missing in the type material of gargoyleosaurus. certainly, it is likely that there was more than one pair of shoulder spines of this morphology in mymoorapelta. the possible gargoyleosaurus material from the dry mesa quarry includes a posteriorly grooved shoulder spine, byu 725-17351 (figures 38i and 38j). although not so well preserved, this spine compares well with the longer, more erect of the two spines from the type specimen of gargoyleosaurus. grooved shoulder spines are not known from the type specimen of polacanthus foxii (hulke, 1882; pereda-suberbiola, 1993, 1994; raven et al., 2000; blows, 2015), the compton bay polacanthus (blows, 1987, 2015), or hylaeosaurus (blows, 2015; raven et al., 2020). however, two isolated grooved shoulder spines have been recovered from the lower cretaceous wessex formation on the isle of wight, england (delair, 1982; blows, 2015). the type material of hoplitosaurus marshi from the lakota formation includes a well-preserved right grooved shoulder spine 330 mm long (gilmore, 1914, plate 29). it is more erect like mwc 1816, has a broken off apex, and is more massive. grooved shoulder spines are well represented in gastonia with at least ten from gastonia lorriemcwhinneyae figure 37. cactus park mymoorapelta sacral shield sections mwc 2610. (a) lateral portion of sacral shield. (b and c) sandstone blocks preserving external molds of the dorsal sacral shield. 378 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 38. grooved shoulder spines. left lateral grooved shoulder spine from revised hypodigm of mymoorapelta maysi mwc 1818 in (a) caudal, (b) dorsal, (c) medial, and (d) ventral views. gargoyleosaurus parkpinorum holotype grooved shoulder spines dmnh 27726. right shoulder spine in (e) dorsal and (f) ventral views. left shoulder spine in (g) dorsal and (h) ventral views. dry mesa gargoyleosaurus right lateral grooved shoulder spine byu 725-17351 in (i) caudal, (j) ventral, and (k) dorsal views. 379 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 in the collections of the dmnh ranging from somewhat erect to recumbent (kirkland, 1998; kinneer et al., 2016), suggesting that a minimum of three pairs of this spine form in the shoulder region of at least north america’s polacanthids. caudosacral plates: there are at least 17 dorsoventrally thin, hollow-based, recurved, asymmetrical, triangular plates (figure 39, table 3). as with the large grooved shoulder spine, it is assumed that the point of the triangle recurved posteriorly. these plates are similar in appearance to those in polacanthus (hulke, 1882; blows, 1987, 2015; pereda-suberbiola, 1993, 1994; gasulla et al., 2011; raven et at., 2020). similar plates are present in gargoyleosaurus (kilbourne and carpenter, 2005) and gastonia (kirkland, 1998; kinneer et al., 2016), and are believed to be mostly lateral caudal plates. lateral caudal plates are widely distributed in the ankylosauria (seeley, 1881; ostrom, 1970; arbour et al., 2009, 2013; kirkland et al., 2013; arbour and currie, 2016; arbour and evans, 2017; norman, 2020c). all caudal plates are biconvex in cross section, although the dorsal side is more so than the ventral side. the biconvexity of the spines results in sharp anterior and posterior margins. there are nine complete “typical” inclined caudal plates (figures 39a through 39s). in addition, there are three specimens (mwc 6747, 6748, and 6750) that were not figured as they were only represented by the distal 100 to 120 mm apical portion of the plate. as with polacanthus, the larger plates are assumed to be positioned more proximally along the tail. in dorsal profile, the anterior edge of the plate is convex and is longer than the posterior concave edge. the result is that the apex of the plates overhangs the posterior margin of the base. the bases of the plates are hollow, and the rims are asymmetrical, similar to those of the neck spine. in all but one plate, the most proximal point of the basal rim of the fluted side is more posterior than that of the rim of the other side; this gives the plate its asymmetrical appearance. the base length of the caudal plates (table 3) would appear to overlap with approximately two caudal vertebrae. as in the cervical spine, the caudal plates also have several nutrient foramina 3 to 4 mm across along the mid line of the deeply hollow base (e.g., figure 39h). on the most convex (dorsal) side, there is faint, parallel fluting 1 to 1.5 cm apart with the ridge in the position of 4th to 6th from the posterior margin curving back to the apex of the plate. as the ridges are parallel with each other, anterior ridges would impinge on the anterior edge of the plate and more posterior ridges would impinge on the posterior edge. however, these ridges vanish before reaching the margin of the plate. three smaller plates (figures 39z through 39ee) with longer base lengths (table 3) are assumed to be caudal plates from the more distal tail. two plates, mwc 1824 and 2677 (figures 39v through 39y), appear to represent a matched pair of plates. they are in the same size range as the laterally inclined caudal plates (figures 39a through 39s) but have a proportionally longer base length relative to the height of the plate (table 3). otherwise, they are nearly morphologically identical to the inclined caudal plates of mymoorapelta (kirkland et al., 1998). it is hypothesized that this pair of plates was situated laterally along the posterior margin of the sacral shield area. similar plates have been identified in several ankylosaurids (arbour, 2009; arbour et al., 2009, 2013; carpenter et al., 2011; park et al., 2021) and possible in sauropelta (carpenter and kirkland, 1998). one plate fragment, mwc 2868 (figures 39t and 39u), has the base broken away and a relatively broad symmetrical apex. the dorsal surface appears fairly convex and the basal surface is flat. it is relatively smooth and unornamented. although assumed to be situated laterally on mymoorapelta, there is no evidence as to where such a plate would be situated. proximal caudal plates appear to have taxonomic potential (morgan et al., 2016); as in a population of specimens the plates have distinctively different shapes in dorsal view (figure 40). the external molds of the caudal plates from the cactus park ankylosaur (figure 40) compare well with those of mymoorapelta (figure 39). along these lines, the caudal plates from the type specimen of gargoyleosaurus (figures 41a through 41p) are clearly distinct from those of the type material of mymoorapelta (kilbourne and carpenter, 2005), in that, the apexes of the plates are only slightly posterior to the posterior margin of the plate or even anterior to it. 380 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 39. caudal plates from revised hypodigm of mymoorapelta. left upper caudal plate mwc 1819 in (a) dorsal and (b) ventral views. right upper caudal plate mwc 1820 in (c) dorsal and (d) ventral views. right upper caudal plate mwc 1821 in (e) dorsal and (f) ventral views. right upper caudal plate mwc 1822 in (g) dorsal, (h) basal, and (i) ventral views. left upper caudal plate mwc 1823 in (j) dorsal and (k) ventral views. right upper caudal plate mwc 2678 in (l) dorsal and (m) ventral views. right upper caudal plate mwc 2867 in (n) dorsal and (o) ventral views. left upper caudal plate mwc 5148 in (p) dorsal and (q) ventral views. right upper caudal plate mwc 5642 in (r) dorsal and (s) ventral views. possible sacral plate mwc 2868 in (t) dorsal and (u) ventral views. left sacro-caudal plate mwc 1824 in (v) dorsal and (w) ventral views. right sacro-caudal plate mwc 2677 in (x) dorsal and (y) ventral views. possible distal caudal plate mwc 6747 in (z) dorsal and (aa) ventral views. distal lower caudal plate mwc 4226 in (bb) dorsal and (cc) ventral views. distal right upper caudal plate mwc 5479 in (dd) dorsal and (ee) ventral views. 381 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 this results in the posterior side of the plate being nearly vertical or sloping anteriorly. thus, the caudal plates of mymoorapelta and gargoyleosaurus have a very different morphology in dorsal view. these differences are distinct enough, such that, although only three caudal plates (figures 41q through 41v) have been recovered from the dry mesa quarry in western colorado, it is apparent that ankylosaur represents gargoyleosaurus. the ankylosaur fossils from the meilyn quarry near the base of morrison formation in southern wyoming (figures 1 and 3) include several long, low caudal plates (figures 5c through 5e) of a morphology most similar to gargoyleosaurus but more recurved like mymoorapelta. taken together with their caudal vertebrae (figures 5a and 5b), they might have been diagnostic as a distinct new species of morrison ankylosaur. sadly, these unique fossils have been dispersed mostly into private collections, where the specimens are not available for study. perhaps future collections from this locality will provide material to more fully characterize this taxon. conclusions there are two well-documented ankylosaur genera within the morrison formation distinguished primarily on differences in their basicrania, pelvic regions, and osteoderms. both share characteristics that have been used to differentiate the polacanthidae from the rest of ankylosauria, including a triangular skull in dorsal view, similar forelimbs and pectoral girdles, and a similar pattern of osteoderms. superficially, mymoorapelta and gargoyleosaurus mounted skeletons appear very similar (figure 42) as the animals are similar in size and elements from both taxa have been used in the development of these mounted skeletons. future generations of mounted skeletons and carefully researched paleoart should be able to better differentiate these taxa. whereas the type specimen of gargoyleosaurus has a well-preserved skull and cervical rings, the material of mymoorapelta from the mygatt-moore quarry more completely reflects the genus. overlapping skeletal elmymoorapelta spines and plates anterior length anterior straight segment to flexture above base posterior length base length maximum thickness angle of apex in degrees dorsal ridges present? mwc 1818 shoulder spine 284.8 43.6 219.1 135.5 57.1 18 yes mwc 1819 caudal plate 228.2 14.7 158.3 151.9 34 43.5 yes mwc 1820 caudal plate 241.4 52.5 136.2 162.2 37.5 29 yes mwc 5148 caudal plate 253.7 16.6 123.8 188.2 31.6 24 yes mwc 5642 caudal plate 231.7 29.1 138.6 165.3 33.3 39 yes mwc 2678 caudal plate 253.7 45.4 122.8 171.9 35.6 26 yes mwc 2867 caudal plate 77.2 131.3 47.2 60 yes mwc 1823 caudal plate 195.7 34.9 136.2 118.7 36.7 40 weak mwc 1822 caudal plate 212.2 0 133.2 139.2 49.2 36.5 yes mwc 1821 caudal plate 42.9 36 yes mwc 1824 caudal plate 220.2 15.2 91.4 220.1 51.3 16 yes mwc 2677 caudal plate 225.3 16.6 104.9 193.1 44.3 17 yes mwc 6747 caudal plate 154.8 0 68 135.2 32.6 19 no mwc 4226 distal caudal plate 92 no mwc 5479 distal caudal plate 30.4 no table 3. measurements (in mm) of lateral shoulder spine and lateral caudal plates mymoorapelta material from the mygattmoore quarry. 382 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 ements from various sites that have yielded ankylosaur material from throughout the morrison formation have added considerably to our knowledge of each genus. mymoorapelta maysi is only known from the upper morrison, whereas gargoyleosaurus appears to occur throughout the morrison and may be represented by more than one species. neither genus is known from strata younger than kimmeridgian (turner and peterson, 1999; trujillo and kowallis, 2015). given that these dinosaurs represent an entire order unknown in the morrison formation prior to 1990 and now documented at 12 localities spanning 4 states, it is clear that additional paleontological field work in even the best studied formations may yield significant results. acknowledgments don deblieux (utah geological survey [ugs]) assisted in the photography of the braincase of mymoorapelta. all paleontological excavations on public lands done under permits issued by bureau of land management or the state of utah. ken carpenter (museum of natural history, university of colorado) is thanked for providing a cast of the holotype skull and cervical rings of gargoyleosaurus that were essential in carrying out this project, as were our many discussions about ankylosaur systematics. don burge former director of the utah state university eastern’s prehistoric museum provided casts of gastonia, animantarx, peleroplites, and cedarpelta. bill blows (retired department of applied biological sciences, city university, london) and jim madsen (deceased dinolab, salt lake city and first utah state paleontologist) provided us with casts of polacanthus material. rob gaston (gastondesign, inc.) is thanked for providing several casts of ankylosaur skulls that were critical to this research. photographs of the meilyn ankylosaur specimens were provided by jason cooper (dinosaurs of america llc.). discussions on vertebral anatomy with larry witmer (witmer lab, ohio university) and matt wedell (western university of health sciences) are appreciated. kelli trujillo (university of wyoming) is thanked for her help working out the stratigraphy of figure 40. cactus park mymoorapelta caudal plates mwc 2610. (a) external mold of dorsal surface caudal plate. (b) external molds of adjoining caudal plates. (c) external molds of a second pair of adjoining caudal plates with a possible tibia fragment. 383 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 41. caudal plates from gargoyleosaurus. caudal plates from holotype of gargoyleosaurus dmnh 27726. well-preserved proximal plates in (a) dorsal and (b) ventral views. left caudal plate in (c) dorsal and (d) ventral views. right caudal plate in (e) dorsal and (f) ventral views. right caudal plate in (g) dorsal and (h) ventral views. left caudal plate in (i) dorsal and (j) ventral views. smaller left caudal plate in (k) dorsal and (l) ventral views. right caudal plate in (m) dorsal and (n) ventral views. smaller right caudal plate in (o) dorsal and (p) ventral views. caudal plates of gargoyleosaurus from dry mesa quarry. left caudal plate byu 725-17643 in (q) dorsal and (r) ventral views. left caudal plate byu 725-17623 in (s) dorsal and (t) ventral views. partial left caudal plate byu 725-13891 in (u) ventral view. partial left caudal plate byu 725-13975 in (v) ventral view. 384 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 figure 42. skeletal mounts of ankylosaurs from the morrison formation. reconstructed skeleton of mymoorapelta by gastondesign.com (about 2010) in (a) anteriodorsal and (b) in lateral views. reconstructed skeleton of gargoyleosaurus at museum of ancient life at thanksgiving point, lehi, utah, in (c) dorsolateral view. 385 differentiating ankylosaur species in the upper jurassic morrison formation in light of newly recovered skeletal elements of mymoorapelta maysi from its type locality james i. kirkland, rebecca k. hunt-foster, kirsty morgan, julia b. mchugh, and john r. foster geology of the intermountain west 2025 volume 12 the morrison formation in central wyoming. joshua lively (utah state university eastern prehistoric museum) is thanked for photographing the dorsal osteoderms of gargoyleosaurus. carolyn staehle (independent paleoartist) is gratefully acknowledged for her drawings of the gargoyleosaurus skull. ethan cowgill is thanked for exposing the basicranium in the cactus park specimen. we also thank the many scientists and curators that made access to specimens in their collections possible, kevin seymour (royal ontario museum), kieran sheppard (deceased, canadian museum of nature), andrew newman (royal tyrrell museum of paleontology), phil currie (university of alberta), mark loewen (utah museum of natural history), malcolm mckenna (deceased, american museum of natural history), mark norrell (deceased, american museum of natural history), rinchen barsbold (mongolian institute of geology, ulaanbaatar), don burge (former director of the prehistoric museum), john bird (retired, utah state university eastern prehistoric museum), ken carpenter (museum of natural history, university of colorado), joshua lively (utah state university eastern prehistoric museum), rod scheetz (brigham young university [byu] museum of paleontology), joe sertich (smithsonian tropical research institute and the colorado state university), ken stadtman (retired, byu museum of paleontology), angela milner (deceased, natural history museum of london), dong zhiming (institute of vertebrate paleontology and paleoanthropology [ivpp], chinese academy of sciences), xu xing (ivpp), hailu you (ivpp), and luis alcalá (dinopolis foundation, tyrell, spain). technical reviews by don deblieux, stefan kirby, and stephanie carney (all ugs) are appreciated. 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